Pumping of Liquids 221
Pump Selection H, = Head at no flow, or shutoff, ft
0
I-I"' = Head of viscous fluid, ft
Reciprocating pump selection follows the fundamen- H; = Water equivalent head, fl
tals of centrifugal pumps: hd = Discharge head on a pnmp, ft of fluid
h, = Suction head ( or suction lift) on a pump, ft of fluid
hsL, huL = Friction losses in pipe and fiuings., subscript SL for
1. Evaluation suction side head loss. suction line; and DL for discharge line, ft �f fluid
2. Evaluate discharge side head loss. h, = Velocity head, ft of fluid
3. Determine system static pressure. L = S = Static head, suction side, ft (Figure 3-38)
4. Determine total differential head across pump. I = Water depth in sump, ft (Figure 3-62)
N, = Specific speed, dimensionless
5. Determine the NPSHA available on suction of pump. NP = Number of pumps
6. From manufacturer's performance tables, select n = Ro �� ve speed, revolutions per minute = RP;\1 = rpm
pump nearest to GPM and head requirements. P = Positive external pressure on surface of liquid ( +)
7. Contact manufacturer for final recommendations , or partial vacuum on surface of liquid ( - )
give complete system requirements, and physical Pa = Atmospheric pressure or absolute pressure in ves-
sel, psia
properties of liquid. Figure 3-69 is convenient for Pso = Brake horsepower at shutoff or no flow
this purpose. P,d = Differential pressure between absolute pressures at
outlet and inlet to pump, psi
Nomenclature P,., = Vapor pressure of liquid at pumping temperature,
ps1a
a = Area of piston or plunger; sq in. p' = Absolute pressure, inches mercury abs
Bct = Bell diameter of vertical sump pump, ft p', = Atmospheric pressure or absolute pressure in ves-
BHP = Brake horsepower sel expressed as ft of fluid
(BHP)v,s = Brake horsepower when handling viscous material p'vp = Vapor pressure of liquid at pumping temperature
CE = Viscosity correction for efficiency to convert to expressed as ft of fluid
water performance Q = Flow rate, gal per minute
CH = Viscosity correction for head, to convert Lo water Q' = Capacity of rotary pump, fluid plus dissolved
performance gases/ entrained gases at operating conditions, GPM
CQ = Viscosity correction for capacity, Lo convert to Q�r = Minimum flow, GPM
water performance QN = Head at best efficiency point on pump curve, ft
cp = Specific heat of liquid, BTU/lb - °F Qm = Viscous liquid capacity, GPM
D = Height of liquid (static) above ( +) or below (-) Qw = Water capacity, GP'.\1
the centerline of the pump on discharge side, ft S = Suction static head, ft, or height of liquid (static)
D' = Incremental height of liquid (static) above normal above ( +) or below (-) the center line of the
D level, to establish "worst case" condition fr Fig- pump on suction side. fL, or,
i:re 3-38 ' ' ' S = Suction lift, negative suction head, ft
D" = Theoretical displacement volume displaced per S' L = Worst case suction side static lift, ft (Figure 3-39)
revo lutionrs) of driving rotors, cu in./rev S" = Slip, quantity of fluid that leaks through internal
d = Impeller diameter, in. clearances of rotary pump per unit time, GPM
dp = Diameter of piston or plunger, in. SpGr = Specific gravity of liquid at pumping temperature
referred Lo water = 1.0
d, = Diameter of piston rod, in. s = Stroke, in.
d' = Liquid displacement, cu ft/min
d" = Theoretical displacement, cu ft/min 1h = Temperature rise, °F
eHP = Electrical horsepower t.T, = Temperature rise, °F/min
t = Piston speed or travel, fl/min
E = Efficiency, percent V = Liquid velocity, ft/sec
En = Fraction entrained gas by volume al atmospheric v = Average velocity, ft/sec
pressure W = Width of channel with series pumo ft
E, = Volumetric efficiency, ratio of actual pump capaci- W1 = Weight of liquid in pump, lb r :
L;- to volume displaced per unit of time
Ew = Pump efficiency with water, percent whp = Water or liquid horsepower
Evis = Pump efficiency with viscous fluid, percent whp. = Power imparted by pump Lo fluid discharged (also
iiquid horsepower)
e = Pump efficiency, fraction
e., = Pump efficiency with water, fraction
evis = Pump efficiency with viscous fluid, fraction Subscripts
e, 01 = Volumetric efficiency, fraction
e\ 1 = Maximum safe flowing efficiency, overall pump, 1,2 = Refer to first and second condition respectively
fraction A = Available from pump system (NPSH)
g = Acceleration of gravity, 32 ft/sec/sec L = Liquid
H = Total head developed by a pump, fl of !1uid; or cl = Discharge side of pump
total head/stage, ft, 01� d, = Friction losses for pipe fittings and related items
H = Static head discharge ft (Figure 3-38, -39, -40) on discharge side of pump
222 Applied Process Design for Chemical and Petrochemical Plants
s 1 = Friction losses for pipe valves and other system 26. Karassik, I., "Are You Short on NPSH?," Combustion, July
losses, suction side of pump 1980, p. 37.
R = Required by pump (NPSH) 27. Taylor, I., B. Cameron, and B. Wong, "A Users Guide to
s = Suction side of pump Mechanical Seals," Chem. Eng., V. 95, No. 12, 1988, p. 81.
28. Yedidiah, S., "Multistage Centrifugal Pumps," Chem. Eng., V.
91, No. 24, 1984, p. 81.
Greek Symbols
29. Neerken, R. F., "How LO Select and Apply Positive Rotary
Pumps," Chem. Eng: V. 87, No. 7, 1980, p. 76.
p = Fluid mass gravity, lb/ cu ft 30. O'Keefe, 'vV., Special Report: "Metering Pumps for Power
Plants," Power, Aug., 1982, p. I.
References 31. Taylor, I., "Pump Bypass Now More Important," Chem. Eng.,
V. 94, No. 7, 1987, p. 53.
I. Bakewell, W. E., Bulletin T-3, Viking Pump Co., Cedar Falls, Iowa. 32. Kern, R., "How Discharge Piping Affects Pump Perfor-
2. Brkich, A., Vertical Pump Model Tests and Intake Design, pre- mance," Hydro. Proc., V. 51, No. 3, 1972, p. 89.
sented Boston Section A.S.M.E., Feb. 1953. 33. We lch, H.J., Ed., Transamerica DeLaval Engineering Handbook,
3. Brkich, A., Rid Vertical-Pump Intake Design of Guess With Model 4th Ed., McGraw-Hill Book Co., Inc., 1970 and 1983 by
Tests, Power, No. 2, 1953, p. 90. Transamerica DeLaval, Inc., Ii\·10 Industries Div.
4. Carter, R. and I. J. Karassik, Basic Factors in Centrifugal Pump
Application and Basic Factors in Preparing A Centrifugal Pump Bibliography
Inquiry, Reprint RP-477, Worthington Corp., Harrison, N.J.,
reprinted from Water and Sewage ,vorks magazine. Anonymous, "Metering Pump Survey," Instruments and Control
5. "Centrifugal Pump Fundamentals," Form 7287, Ingersoll-Rand Systems, April 1971, p. 103.
Co., Cameron Pump Division, P. 0. Box 636, Woodcliff Lake, Anonymous, "Single Stage Pump Challenges Multistage Units,"
NJ. 07657. Chem. Engineering, April 14, 1975, p. 56.
6. Church, A.H. and H. Cartrnann, Editors, "Delaval Handbook," Birk,J. R. andJ. H. Peacock, "Pump Requirements for the Chem-
2nd Ed., Delaval Steam Turbine Co., 1955, Trenton, NJ. ical Process Industries," Chem. Engineering, Feb. 18, 1974, p. 117.
7. Dean Brothers Pumps, Engineering Catalog Circular No. 190, Black, H. A., "Metering Pumps Feed Precisely, Save Money,"
Mar. 1958, Indianapolis, Ind. Powe,;June 1970, p. 70.
8. Dolman, R. E., Pumps, Chemical Engineering, March 1952. Caplan, E., "Finding Required Centrifugal Pump Flow," Plant
9. Jacks, R. L., Process Design and Specificoiion of Pumping Equip- Engineering, April 2, 1970, p. 44.
ment, Chem. Eng. Prog., 49, 1953, p. 134. Doolin,J. H., "Updating Standards for Chemical Pumps," Chem-
10. Karassik, I. J. and T. W. Edwards, Centrifugal Pumps on Cl.osed ical Engineering, June 11, 1973, p. 117.
Discharge, Industry and Power, No. 6, 1955, p. 54. Glickman, M., "Positive Displacement Pumps, Chem. Engineering,
11. Karassik, 1.J., W. C. Krutzsch, ,v. H. Fraser, and]. P. Messina, Oct. 11, 1971, p. 37.
Pump Handbook, McGraw-1-Iill Book Co., N.Y, 1976. Hancock, W. P., "How to Control Pump Vibration," Hydrocarbon
12. Mann, M. S., Horizontal vs. Vertical Pumps, Pet. Ref., 32, No. Processing, March 1974, p. 107.
12, 1953, p.111. Hauiangadi, U. S., "Diagram Speeds Up Pumps' Specifications
13. Mann, M., How lo Use System-Head Curoes, Chem. Engr. No. 2, Job," Chem. Engineering,July 13, 1970, p.114.
1953, p. 162. Hernandez, L. A. Jr., "Controlled-Volume Pumps," Chem. Engi-
14. Peerless Pump Co., Sales Information Bulletin, June 1952. neering, Oct. 21, 1968, p. 124.
15. Westaway, C.R. and A. W. Loomis, editors, Cameron Hydraulic Jackson, C., "How to Prevent Pump Cavitation," Hydrocarbon Pro-
Data, 16th Ed., Ingersoll-Rand Co., 1979, Woodcliff Lake, NJ. cessing, May 1973, p. 157.
16. Sniffen, T.J., Mechanical Seals from "A" to "Z': Power and Flu- Kern, Robert, "How to Design Piping for Pump Suction Condi-
ids, Winter, Worthington Corp., 1958, Harrison, NJ. tions," Chem. Engineering, April 28, 1975, p. 119.
17. Hydraulic Institute Standards for Cenl1ifugal, Rotary and Recipro- Knoll, H. and S. Tinney, "\Vhy Use Vertical Inline Pumps?,"
cating Pumps, 13th Ed., 1975, and Engineering Data Book, 1st HJdrocarbon Processing, May 1971, p. 131.
Ed., 1979, Hydraulic Institute. Also see 14th Ed., 1983 and Neerken, R. F., "Pump Selection for the Chemical Process Indus-
2nd Ed., 1991 respectively. tries, Chem. Engineering, Feb. 18, 1974, p. l04.
18. Ibid, Reciprocating Pump Section. Reynolds, J. A., "Pump Installation and Maintenance," Chem.
19. Union Engineering Handbook, 9th Ed. Union Steam Pump Co., Engineering; Oct. 11, 1971, p. 67.
Battle Creek, Mich., 1921. Rost, M. and E. T. Visich, "Pumps," Chem. Engineering, April 14,
20. Lahr, P. T., "Better Standards: Better Pumps," Chem. Eng. \!. 1969, p. 45.
96, No. 7, 1989, p. 96. Stindt, W. H., "Pump Selection," Chem. Engineering, Oct. 11,
21. Dufou1-,J. v«, "Revised API Pump Standard," Chem. Eng.,\!. 1971, p. 43.
96, No. 7, 1989, p. 101. Thurlow, C., "Centrifugal Pumps," Chem. Engineering; Oct. 11,
22. Reynolds,]. A., "New ANSI Pump Standards," Chem. Eng., V. 1971, p. 29.
96, No. 7, 1989, p. 98. Tinney, W. S., H. J. Knoll and C. H. Diehl, "Loop Extends
23. Adams, W. V., "Troubleshooting Mechanical Seals," Chem. Mechanical Seal Life," Hydrocarbon Processing,Jan. 1973, p. 123.
Eng., V. 90, No. 3, [983, p. 48. Trent, A. W., "Metering with Gear Pumps," Chem. Engineering.
24. Fischer, E. E., "Seals and Packings Selection Criteria," Chem. Jan. 20, 1975, p. 107.
Proc., Oct., 1983, p. 60. Poynton, J. P., Metering Pumps, Marcel Dekker Co., 1983.
25. Karassik, I. and R. Caner, Centrifugal Pumps, McGraw-Hill Rankin, D. R., "It's Easy to Determine NPSH," Petroleum Refiner;
Book Co., 1960. V. 32, No. 6, 1953.
Pumping of Liquids 223
Ullock, D. S., "Evaluating the Mechanical Design of End-Suction Bloch, H.P., "How to Select a Centrifugal Pump Vendor," Hydro.
Centrifugal Pumps," Chem. Eng. Prog., V. 51, No. 5, 1955. Proc., June 1978.
Tsai, M, J., "Accounting for Dissolved Gases in Pump Design," Simo, F., "Which Flow Control: Valve or Pump?", Hydro. Proc., V.
Chem. Eng., V. 89. No. J.5, 1982. 52, No. 7, 1973.
Olmstead, P. ]., "Selecting Centrifugal Pumps," Heating and Kern, R., "How to Get the Best Process-Plant Layouts for Pumps
Ventilating, Feb .. 1946. and Compressors," V. 84, No. 26, 1977.
Hallam,]. L., "Centrifugal Pumps: Which Suction Specific Speeds Bloch, H.P., "How to Buy a Better Pump," Hydro Proc -: , V. 61, No.
are Acceptable?", Hydrocarbon Processing; V. 61, No. 4, 1982. 1, 1982.
:\'eerken, R. F., "Pump Selection for the Chemical Process Indus- Wilkins, C., '"NPSH and Pump Selection: Two Practical Exam-
tries," Chem. Eng., Feb. 18, 1974. ples," Heating; Piping and Air Conditioning, October 1988.
:\leerken, R. F., "Progress in Pumps," Chem. Eng., V. 94, No. 12, l 987. Van Blarcorn, P. P., "By Pass Systems for Centrifugal Pumps,"
McKelvey,J. M., U. Naire, and F. Haupt, "How Gear Pumps and Chem. Eng., V. 91, No. 3, 1974.
Screw Pumps Perform in Polymer-Processing Applications," Van Blarcom, P. P., "Recirculation Systems for Cooling Centrifu-
Chem. Eng., V. 83, No, 20, 1976. gal Pumps," Chem. Eng., V. 87, No. 6, 1980.
Kern, R., "Size Pump Piping and Components," Hydrocarbon Pro- Yedidiah, S., "Diagnosing Problems of Centrifugal Pumps-Part
cessing, V. 52, � o. 3, 1973. II," Chem. Eng., V. 84, No. 25, 1977.
Fang, Ken-Shou, "How Accurate are Predictions of Required Ibid., Part III, Chem. Eng., V. 84, �o. 26, 1977.
NPSH When Based on Speed-Scale Effect?", Power, V. 123, No. Yedicliah, S., "Unusual Problems with Centrifugal Pumps," Chern.
2, 1979. Eng., V. 93, No, 23, 1986.
Taylor, I., "Pump By Pass Now More Important," Chem. Eng., V. Durand, A. A., "A Quick Estimate for Centrifugal Pump Effi-
94, No, 7, 1987. ciency," Chem Eng., V. 96, No. 7, 1989.
Poynton, ]. P., "Metering Pumps: Types and Applications," Karassik, I. J., "Installation of Centrifugal Pumps," Chemical Pro-
Hydrocarbon Processing, V. 60, No. 11, 1981. cessing, Mar, 1989.
Burdris, A. R., "Preventing Cavitation in Rotary Gear Pumps," McCaul, C., "Keep the Wear Out of Pump Wear Rings," Chem.
Chem. Eng .. V. 87, No. 9, 1980.
Eng., V. 96, No. 10, 1989.
Brauer, Rudiger, "Diaphragm Metering Pumps," Chem. Engr. McNally, L. "Increase Pump Seal Life," Hyd1v. Proc. V. 58, :'\lo. I, 1979.
Prog., V. 83, No. 4, 1987.
Doolin, J. H. and L. M. Teasdale, "Sealless Magnetic-Drive Lapp, S., "How to Avoid Problems with Cold Service Pumps,"
Hydro. Proc., V. 60, No. 1, 1981.
Pumps: Stronger than Ever," Chem. Eng., V. 97, No. 8, 1990.
Karassik, I., "Fact or Fiction: Some Misconceptions About Desir- Grohmann, M., "Extend Pump Application with Inducers,"
able Construction features of CenLrifugal Pumps," Chemical Hydro. Proc., V. 59, No. 12, 1979.
Processing, Mid-March 1989. Shull, W. W. and M. L. Church, "Improve Pump Efficiency,"
Makay, E., "HO\\' to Avoid Field Problems With Boiler Feed Hydro. Proc.,\!. 69, No. 7, 1990.
Pumps," Hydrocarbon Processing; V. 55, No. 12, 1976. Palmateer, L. and P. Grout, "Pump Suction Specific Speeds
Miller, J. E., "Bucking Up Reciprocating Pump Performance," above 20,000," Hydro. Proc., V. 63, No. 8, 1984, p. 66.
Chem. Eng., V. 96, :\lo. 9, 1989. Gulich,]. F. and A. Rosch, "Cavitation Erosion in Centrifugal
Watkins, D. L., "Consider the Flexible Impeller Pump," Chem. Pumps," Chem. Eng. Prog., V. 85, No. 11, 1989, p. 68.
Eng., V. 96, No. 1, 1989. "Keeping Pump Emissions Under Control," Equipment Focus
Nasr, A. M., "When to Select a Sealless Pump," Chem. Eng., May Section, Chem. Eug., V. 98, No. 2, 1991, p. 93.
26 .. 1986. Fegan, D. S., "Select the Right Zero-Emissions Pump," Chem.
Johnson,]. D., "Variable-Speed Drives Can Cut Pumping Costs," Eng. Prog., V. 86, J\:o. 9, 1990, p. 46.
Chem. Eng., Aug. 10, 1981. Margus, E., "Choosing Thermoplastic Pumps," Chem. Eng., V. 98,
Dalstad.]. I., "Slurry Pump Selection and Application," Chem. No. 7, 1991, p. 106.
Eng., V. 84, No. 9, 1977. "Magnetic-Drive Pumps," Plant Notebook, Chem. Eng., V. 98, No. 7,
Monroe, P. and M. Pawlik, "New Pump Handles Low Flowratc at 1991, p. 159.
Very High Pressure," V. 97, :\Jo. 1, l990. Shull, \•V. W. and M. L. Church, "Field Performance Test: Key to
Report-"Surging Interest in Leakproof Pumps," Chem. Eng., V. Pump Savings," Hydro. Proc., V. 70, No, I, 1991, p. 77.
96, No. 6, 1989. Adams, W. V., "Control Fugitive Emissions from Mechanical
Garbers, A. W. and A. K. Wasfi, "Preventing Cavitation in High Seals," Chem. Eng. Prog., V. 87, No. 8, 1991, P: 36.
Energy Centrifugal Pumps," Hydrocarbon Processing, V. 69, No. Chase, G. G., "Match Centrifugal Pumps to Piping Systems,"
7, 1990. Chemical Engineering, V. JOO, No. 5, May 1993, p. 151.
Lightle,J. and]. Hohman, "Keep Pumps Operating Efficiently," Karassik, I.J., "When to Maintain Centrifugal Pumps," Hydrocar-
Hydrocarbon Processing, V. 58, No. 9, 1979. bon Processing, V. 72. No. 4, April 1993, p. 101.
Yedidiah, S., "Unique Aspects of Pump Efficiency," Hydro. Proc., Nasr, A., "Extending the Life of Magnetic-Drive Pumps," Chemi-
V. 66, No. 10, 1987. cal Engineering, V. 98, �o. 10, October 1991, p. 159.
Chapter
4
Mechanical Separations
PracticaJly every process operation requires the separa- data the range and distribution of particle sizes, or be in
tion of entrained material or two immiscible phases in a a position to intelligently estimate the normal and
process. This may be either as a step in the purification of extreme expectancies. Figures 4-1 and 4-lA give a good
one stream, or a principal process operation [64]. These overall picture of dimensions as well as the descriptive ter-
separations may be: minology so important to a good understanding of the
magnitude of a given problem. The significant laws gov-
l. liquid particles from vapor or gas erning particle performance in each range is also shown.
2. liquid particles from immiscible liquid Particle sizes are measured in microns, µ. A micron is
3. dust or solid particles from vapor or gas
1/1000 millimeter or 1/25,400 inch. A millimicron, mu,
4. solid particles from liquid is 1/1000 ofa micron, or 1/1,000,000 millimeter. Usually
5. solid particles from other solids particle size is designated as the average diameter in
microns, although some literature reports particle radius.
These operations may sometimes be better known as Particle concentration is often expressed as grains/ cubic
mist entrainment, decantation, dust collection, filtration, feet of gas volume. One grain is 1/7000 of a pound.
centrifugation, sedimentation, screening, classification,
scrubbing, etc. They often involve handling relatively The mechanism of formation has a controlling influ-
large quantities of one phase in order to collect or sepa- ence over the uniformity of particle size and the magni-
rate the other. Therefore the size of the equipment may tude of the dimensions. Thus, sprays exhibit a wide parti-
become very large. For the sake of space and cost it is cle size distribution, whereas condensed particles such as
important that the equipment be specified and rated to fumes, mists and fogs are particularly uniform in size.
operate as efficiently as possible [9]. This subject will be Table 4-1 gives the approximate average particle sizes for
limited here to the removal or separation of liquid or dusts and mists which might be generated around process
solid particles from a vapor or gas carrier stream (1. and plants. Figure 4-2 indicates the size ranges for some
3. above) or separation of solid particles from a liquid aerosols, dusts and fumes. Table 4-2 gives typical analysis
(item 4). Reference [56] is a helpful review. of a few dusts, and Table 4-3 gives screen and particle size
Other important separation techniques such as pres- relationships. Table 4-4 gives approximate mean particle
sure-leaf filtration, centrifugation, rotary drum filtration size for water spray from a nozzle.
and others all require technology very specific to the
equipment and cannot be generalized in many instances.
Preliminary Separator Selection
Particle Size
The Sylvan Chart [2] of Figure 4-3 is useful in prelimi-
The particle sizes of liquid and solid dispersoids will nary equipment selection, although arranged primarily
vary markedly depending upon the source and nature of for dust separations, it is applicable in the appropriate
the operation generating the particular particles. For parts to liquid separations. Perry [23) presents a some-
design of equipment to reduce or eliminate particles what similar chart that is of different form but contains
from a fluid stream, it is important either to know from much of the same information as Figure 4-1 and 4-lA.
224
Mechanical Separations 225
Table 4-1 Table 4-3
Sizes of Common Dusts and Mists Dry Particle Screen Sizes
Average Particle Diameter, W. S. Tyler Screen
Dust or Mist Microns Scale Micron (approximate)
Human Hair (for comparison) .... 50-200 80 · · · · · · · · · · · - · · · · ·. · · - 174
Limit of visibility with naked eye .. 10-40 100 .................................. 146
Dusts 115 .................................. 123
Atmospheric dust . 0.5 150 .............................•.... 104
Aluminum . 2.2 170 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
Anthracite Coal Mining 200 . . . . . . . . . . . . . . . . . . . . . . . . . . . • . . . . . . 74
Breaker air . 1.0 250 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
Mine Air . 0.9 270 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
Coal Drilling . 1.0 325 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Coal loading . 0.8
Rock drilling . 1.0
Alkali fume . 1-5
Ammonium Chloride fume . 0.05-0.1-1 Table 44
Catalyst (reformer) . 0.5-50
Cement . 0.5-40-55 Approximate Particle Sizes From Liquid Full Cone
Coal . 5-10 Spray Nozzles*
Ferro-manganese, or silicon . 0.1-1
Foundry air . 1.2 Liquid: Water
Flour-mill . 15
Fly Ash (Boiler Flue gas) . 0.1-3
Iron (Gray Iron Cupola) . 0.1-10 Operating Pressure, Approx. Mean Particle
Iron oxide (steel open hearth) .. 0.5-2 Nozzle Size, In. Psig Size, Microns
Lime (Lime Kiln) . 1-50 ---y;----:-:-:-: . . . . . . . . . . . 15 . . . . . . . . . . . . . . . . 1200
Marble cutting . 1.5 60 . . . . . . . . . . . . . . . 750
Pigments . 0.2-2 % 10 1600
Sandblasting . 1.4 40 1000
Silica . 1-10 ............... 15 1750
Smelter . 0.1-100 40 1250
Taconite Iron ore lYz 15 2300
(Crushing & Screening) . 0.5-100 60 .........•...... 1800
Talc · ·. 10 3 . . . . . . . . . . . . . . . 10 5300
Talc Milling . l.5 30 .........•...... 4300
Tobacco smoke . 0.2
Zinc oxide fume . 0.05
Zinc (sprayed) . 15 *Private communication, Spraying Systems Co., Bellwood, Ill.
Zinc (condensed) . 2
Mists
Atmospheric fog . 2-15 Example 4-1: Basic Separator Type Selection [2, 17]
Sulfuric acid . 0.5-15
Compiled from References 1, 13, and 15. A suitable collector will be selected for a lime kiln Lo
illustrate the use of the Sylvan Chart (Figure 4-3). Refer-
ring to the chart, the concentration and mean particle
Table 4-2 size of the material leaving the kiln can vary between 3
Typical Dust Size Analysis-IC· and 10 grains/ cu ft with 5 to 10 microns range of mass
mean particle size. Assume an inlet concentration of 7.5
DUST grains/ cu ft and inlet mean particle size of 9 microns.
Cement ----- Projection of this point vertically downward Lo the collec-
Kiln Foundry
Rock Exhaust Sand Limestone tion efficiency portion of the chart will indicate that a low
-�--
Sp. Gravity 2.63 2.76 2.243 2.64 resistance cyclone will be less than 50% efficient; a high
Apbarent we, efficiency centrifugal will be between 60 and 80% effi-
1 s./cu.ft. . .... 61.3 52.0 45.9 72.0
Screen Analysis cient, and a wet collector, fabric arrester and electro-stat-
( Percent passed) ic precipitator will be 97%-plus efficient. The last three
100 Mesh 98.8 99.6 91.2 85.6
200 Mesh ..... 92.8 92.2 78.4 76.4 collectors are often preceded by a precleaner so a high
325 Mesh ..... 79.6 80.8 67.6 66.4 efficiency centrifugal will be selected. Using the average
400 Mesh ..... 70.8 73.2 64.4 63.2
Elutriation Analysis: line of this group, the efficiency will be 70%. Therefore,
Percent Under the effluent from this collector will have a concentration
Terminal Velocity of 7.5(1.00 - 0.70) = 2.25 grains/cu ft.
320 In./min. 75.8 78.0 64.2 70.5
80 In./min. .. 37.0 61.0 53.9 52.0
20 In./min . . . 17.5 40.8 42.0 33.0 Draw a line through the initial point with a slope par-
5 In./min . . . 8.9 23.0 32.0 18.0 allel to the lines marked "industrial dust." Where devia-
-�------ tion is not known, the average of this group of lines will
*Compiled from Bulletin No. 1128, American Blower Corp.,
Detroit, Michigan. normally be sufficiently accurate to predict the mean par-
Grovi ty Sett Ii ng Of Spheres in Slill Fluid
Cc mme rcrc l
Port icle General Common Mel hods Equipment for Spheres of Spheres of
Diameter Classification of Mea,uring Collection or Unit Densify Any Densily Crilical Par ti cit Diameter
Port icol Si,e Removal ot i n Air in An1 Fluid Lows of Sel lling Above Which Law Will Not
Microns Particles from Diomet er, Reynolds Apply
o Gos Microns Number
URe
100,000 ; 100,000 - 200,000 �, r
5 New Ion's Law t
glp(ps-pl,
Op,crit = Ker
C=0.44
-lin.- )gLOp{p,-p)
2
; u t : 1.74
: f
10,000 =I cm. . I -10,000-
-I Ker =2,360 for Newton's Law
= in.
5 4 I
I
"' �
.,
2 ..CJ
' . . : E ' I 500-
. .
0
u
1,000 .<= I 1,000- Intermediate Law Kc, : 43.5 far
"'
.,- "' -.,,- C = 18.5 Nri.°"6 Intermediate Law
-�-
,- ·-
,-
>-- :;::
5 ____ w_
- ., -2-
- "'- C> 0 - en -�- ·- 0.153gt71 Op l.14(fsf')0.7.
>-
-- - "' ---- - -
..
>-
u u, =
0
a.,
·;:.
�
0.
0
29
2 -'- o::- -.�----:.;- -- � p° f' 0.43
a.,-
f--->
(J) ·en e � (J)
·- <!) 2 >
> -
100 ' �-�:- 100-
-2.0- 0
I - ' � ���� "' Stokes ' Law Ker : 33 for Stokes ' Law
E
- >-
.... �
....
- 0 ' en � - �� �
5 - 0. ' I- 1
- '"'en "' I - ,_- 0. C = 2 4 N R;
0
0
E
C>
- "' .s I - � " rr r � 2
·- �
0
·-
0
- '
2 -;; 2 ' - �r "' gl Dp (fs-f)
"' .,
"' ut =
- "' '
0
}. w '-' I !: ' u »» = u,s
�
10 I I ' LL I 10- -
.,
§ '
"'O 0
-
,-- (/} "'c,: -
-
- ... ..... c,,
5-6 .... if ., :*� I �- 1-.L �:t: �
...
·-
I
CO I
-
I ·-
"'
0. ' ; .. I ., - T -
..c
_-o
.0
0 0 �� � �i 0.0001- u
...
u
2 >-- --- - -� �r - U o O c.. Stokes-Cunningham Law .The Cunningham Correction on Stokes•
Low Becomes lrnper tcnt for Particles
--U
0
u
"'
I�
:::;; ·- C.. I cn o> c.. = Km u ts of Diameters Under 3 Microns for
:::;;
Settling in Gases ond Under 0.01
I
1.0 I I .,;: . 1.0- ut Micron for Sellling in Liquids.
u
•
-
I
(I)
5 a., )( t� �,,_--.o - Km = I +Km, ( >. m I Op)
The Value Km, hos Experimentally been Shown to lie Between 1.3 and 2.3
Cl.,--,-�
r-"
I
� g- �1- :,=ff=:. for Different Goses I Particle Sizes I and Materials {Wasser I Physik.Z. 34 1
1
�
I
-
-Q.J-- Q)- r---1- o "= -r- E 11- I-· �
2 -=, �e- �I- � � -1- ] .i. ..... ., i � 257- 278 [1933 )). An Approximate Average Value Booed on lhe Doto of
E
""'
Millikan is Empiricolly Given by
0
�
u, en � Q) ...... '* a, I �
(..) ;:) I C: - I � Km, =1.644 +0.552e -(0.656 Op/>.m)
::::,
0.1 � I 7 t ·� ..... 0 0.1
u .
* .!:: a. - <,.) ·-
.....
�� j:Q) � g ... !: : Brownian Movement Brownian Movement is o Random
5 OW 01 <I - ., "' Motion Superimposed upon 1ne
"'O
w
=>
<,.)
� I-�-*·- -w " Grovitotionol Settling Velocity of
�
�
"'
u
the Particle it Becomes Appreciobe
.� ��-.2 "' t:i.x = 4gc RT Km t for Particles under 3 Microns
0
E Q) "u :;; Diameter end Becomes Entirely
2 � 1---U-c, I "' 3 .r 2 f N Op Predominant for Particles Under
::::!
- 0 ::::, = zs t I <!) 0 0.1 Micron.
::::,
0.01 IOOA >, 0.01- �
0
� 0:: I . ....!
• ,.,, I t . I I :::;;
>
5 ' x o.>
0
"'
o.>
-- Q) ' t -
�:5
2�,,_o t I ·-
u
o�
....! 0 ' I ' I
0
,:::1: Q_
t-- 0.001 ' 0.001
+ Furnishes Average particle Diameter, but no Size 01sfr1bufion Nomencloture: I Any Self-Consiste11t System of Units moy be Employedj English units are given by
x Size DistrJbut1on may be Obtained by Special Calibration way of E,ampte.)
c : Overall Oroq Coefficient, Dlmensionless NRc = Reynolrls Number ,Dimensionless =Dppl" E/P,
Op :: D:Ometer of Spherical Particle, ft. R = Gos Constant, 1,546 (ff.-lb. Force) lib. mole)( °F)
From Kinetic Theory of Gases: Dp crit =Critical Particle Diameter Abo¥e Which LOW I =Time, sec.
will Not Apply, ft. T = Absolute Gos Temperature °F abs.,or 0 R
1
)..,. = 3 fl p v gc = Conversion Foe tor 1 32.17 (lb.moss /lb. Forcei I •1 = Terminal Settling Velocity of Particle Under
It 1./sec.)
Action of Gravity, ft./sec.
gc DLocol Acceleration due to Gravity ,(ft.)/lsec.) 'ts = Terminal Settling verocity of Particle as
v =JBg, RT /irM ls"·.l Colculated from Stokes' Law I ft./uc.
Ker = Proportional i ly Factor I Dimensionless v = Mean Moleculor Speed, fl./sec.
Km = Stokes-Cunningham Correction Factor, Ax = Average Linear Amplitude or Oisplocement of
Dimensionless Particle in Time t I ff.
Kme = Proportionolify Factor, Dimensionless p = Fluid Density, lb. moss/cu. fr.
L N = Number ot Gos Molecules in o mole I •m = Mean Free Poth of Gos Molecules ,ft.
M = Molecular Weight, lb./mole
P, =True Density of Porticle,lb.mass/cu.ft.
µ = Fluid Viscosity, (lb. mos,)/ (ft.Ilse,)
2.76 x 102t' f'olecule; /lb. mole
Figure 4-1. Characteristics of dispersed particles. By permission, Perry, J. H., Ed., Chemical Engineers Handbook, 3rd. Ed., 1950, McGraw-
Hill Company, Inc.
Mechanical Separations 227
SIZE AND CHARACTERISTICS OF AIR-BORNE SOLIDS
DIMI. RATE OF
OF U.S. SCALE OF SETTLING
IN f P_M.
PAA- ST'D
FDA
TICU:S MESH SPHERES
••
MICRONS ATMOSPHERIC IMPURITIES SPEC. GRAV.1
AT 7Cf'F.
8000
w
6000 .; ,_ ,.. tl!iO
4000 I - .. .....
w
::I
en
0 z ... :
2000 s
-
.!..
0
10 16 z ;= .... u;
1000 ::: != � c 7!10
800 20 -- - -
-
600 - z - .... !i!i!i
....
400 64 ... � .. � � z
I
u
�
c
;;;;;
60 1" - - c ;":' ;
200 128 .. u -
z
100 IC :z: :,:: � cc IC
a.
Cl
100 150 >- u 0 !i!l 1
80 200 -· .. :.: -
-
60 250 w z � .., - :- ..... 14 A
40 32� >- � w >- ... Cl
�
0::
so;; ! - u - �
;:::
-·
20 c.::, u 0 .. ii: ;::.:;
;;;
a:
�
�
1000 CII w :I ..
:z:
10 :,: .!i92
8 = � - ..
6 - � ... ... "" � 14A
...
4 ;;;;; ... "5 = ·� a.
....
en ...
:z:
::I
0
v,
2 ... z 0:: v• ::E � en
::::;
...
"II
:E
u ci
....
w
0
-
I � 0... >- .... .... !:IC .007=
.6 - - - ... .... oo,=
11
PER HR .
. 8
-
.4 - -
m
i:
0 ... "' ... w \4"
::I
PER HR .
:E ::I z ""' �
::I
.2 c � - � "' I
..
I- Cl ::E o 00007=
.1
PER HR.
,..., - .... - - 4 0
...
....
...
w .... :. -
I w - � z � .... 1;;::; =-
t u w O .... � u � ... u -
;::: z: � � er
u
u
t.ll,y
en
; = c:z: ii: ... 5 a:i :;; �o -
.. ; � z ::. Q Cl) :E IC
.... �
Q.
0 -
.01 "' a: __, ::,,:: I- � - 0
- �
-
= -
� - - � - �- n
0 a: - �
w � " � c[ = - :-:
-- cc
- .... .... - :i ::;
:::i!i
v, ;:: � ... t:i ... :;:;:w u
a:
- :> c:;
.001 <( al IO
IT IS ASSUMED THAT THE PARTICLES ARE OF UNIFORM SPHERICAL SHAPE HAVING
SPECIFIC GRAVITY ONE AND THAT THE DUST CONCENTRATION IS 0.6 GRAINS PER
1000 CU. FT. OF AIR, THE AVERAGE OF METROPOLITAN DISTRICTS.
Figure 4-1A. Size and characteristics of air-borne solids. By permission, Hoffman Handy Engineering Data, Hoffman Air and Filtration Sys-
tems, Inc.
ticle size in the collector effluent. Where this line inter- A projection of this point of coliector effluent vertical-
sects the horizontal line marked 2.25 grains/cu ft, a verti- ly downward shows that a second high efficiency centrifu-
cal line through the point will indicate the effluent mean gal will be less than 50% efficient. A wet collector, fabric
particle size of 6.0 microns. arrester and electro-static precipitator will be not Jess than
228 Applied Process Design for Chemical and Petrochemical Plants
AIN .MIST � DSMOKE
GROUND LIMESTONE ROSIN SMOKE
=
c __ DIAMETERS OF
-------
GAS MOLECULES
ALKALI FUM
DUST
METALLURGICAL FUME
TYLER
VIRUS S PROTEIN
ACT ER IA
Figure 4-2. Particle-size ranges for aerosols, h � S H_3 5 ��� ...L...L;,!!,_ILL....l'---L � ,J;-.L....,__-L.... � '----.-);-.L...l.---'- � -L----;; � -'--c � - :- : � -=c, , � 1 ,.---- �� __j_
Ei
dusts, and fumes. Courtesy, H. P. Munger, Bat- 1000 � �
telle Memorial Institute. PARTICLE SIZE - MCRONS
93% efficient. Selection of a good wet collector will show The fundamentals of separation for a particle moving
an efficiency of 98%. The effluent leaving this collector with respect to a fluid are given by the drag coefficient of
will have a concentration of 2.25 (1.00 - 0.98) = .045 Figure 4-6.
grains/ cu ft. Using the line initially drawn, at the point The motion of particle and fluid are considered rela-
where it intersects the line of 0.045 grains/ cu ft will indi- tive, and the handling of the relations are affected only by
cate a mean particle size in the effluent of 1.6 microns. conditions of turbulence, eddy currents, etc.
Guide to Dust Separator Applications Terminal Velocity
Table 4-5 [10] summarizes dry dust particle separators When a particle falls under the influence of gravity it
as to general application in industry, and Table 4-6 and will accelerate until the frictional drag in the fluid bal-
Figures 44 and 4-5 [ 42] compare basic collector charac- ances the gravitational forces. At this point it will contin-
teristics. Figure 4-5 presents a typical summary of dust col- ue to fall at constant velocity. This is the terminal velocity
lection equipment efficiencies which have not changed or free-settling velocity. The general formulae for any
significantly for many years except for specialized equip- shape particle are [13]:
ment to specialized applications.
Guide to Liquid-Solid Particle Separators
(4-1)
Table 4-7 summarizes liquid particle separators as to
the general process-type application.
For spheres:
Gravity Settlers
(4- 2)
The use of these settlers is not usually practical for
most situations. The diameters or cross-section areas
become too large for the handling of anything but the
very smallest of flowing vapor streams. In general, gravity (a) Spherical particles between 1500 and 100,000
settlers of open box or tank design are not economical for microns; Newton's Law:
particles smaller than 325 mesh or 43µ [23].
They are much more practical for solids or dusts,
although even for these situations the flow quantities
must be small if the sizes are not to become excessive. (4- 3)
With unusually heavy and/or large particles the gravity
separator can be used to advantage. C = 0.445 average drag coefficient
Mechanical Separations 229
100 t I �
::;;
l.L.
u
en
(!) i=!- J
-l- l
�
� - ..... ·t---t--+"'-t--t-t-+-t- � --t"+- � +--t-+-+-+- � +- �� -4 � --1 � -+--+--+-4-1-Hl-- ���� � l--.J...--l--l-l-+-I
� o.o•:!>,.l.-'4-��.....4---�t;;i=!+1�=:if::-2�.g21s.11 r i"p_ . " � " -.2.J9B�'.;=-�0$45�:tt::::::::::1j::::::t::::1l::::tl:t::1�tj�::::::::::j::::::t:::t::i:;ttjjj
-' :Ii:
8 :::!:t-t+-t--t � -.,i;--t- � -t--t--lf-l-t-hH- �� --11-- � 1---+--1- � -+-1-+l-- �� -l- � -+ � +--I--I- ��
Cl)
::E ,__ O•t-t+-t-t�-.J..._-t-�-t--t--lf-l-t-t-H-��--ii--�1---+--l--+--+-H-+-��-l-�-J.�.J...--1--1-��
I-
Cl) � 0
::::> <[ 0
0 0.01 :x: a:
PNEUMATIC CONVEYIN(
jll::I
98
97 (I)
1.1.J
zs
96 z
95
UJ
u
i.:
90 u,
UJ
u,
a: 0
� i0.005 ..... 80 UJ
�1 ' 70 <[
-'
u
� 50
�1 - 60 (J)
<t I ooo 0
0.1 10 100 1000
MEAN Pi\RTICLE IN MICRONS
Figure 4-3. Range of particle sizes, concentration, and collector performance. Courtesy American Air Filter Co. Inc.
230 Applied Process Design for Chemical and Petrochemical Plants
99.99---.---...- ...... �.,..,.--.,.........,.--,-,....,-i��---,�...,......, ... O.Ql
(o,., 0.05
99.9 .. l!>;z. 0.1
99.8 "-,/�� 'JC), 0.2
C),C'/, 0.5
99.0 o,,& 1.0
95.0 5.0
90.0 10.0 '*'
ii'
20.0 c: .,
·.;
..
i:
50.0 c:
.2
t,
�
0
20.0 o
10.0 90.0
5.0 95.0
1.0 99.0
0.5
0.2
Figure 4-4. Comparison chart showing ranges of 0.1 99.8
99.9
periormance of several collection/control devices 0.05
in air streams. By permission, Vandegrift, et. al. O.Ql ..__ ..... _.._..._.._.....,.w.. __ _.._.._..._..._A,.., ..... ..._ ..._ _ _. 99.99
Chemical Engineering, Deskbook Issue, June 18, 0.01 0.1 1.0
1973, p. 1 09. Particle diameter, microns
(b) Spherical particles between 100 and 1500 microns (d) Spherical particles between 0.1 and 3 microns:
diameter [BJ: Stokes-Cunningham Law [12]:
u. = .K,,,urs (4-6)
o.J53g/·710/14 (p, - p)o.1
l1 l = (4-4)
p 0.29µ 0.43 (4-7)
-06
C = 18.5 NRc · , (See Figure 4-1) (4-8)
This represents a correction on Stokes Law and is sig-
(c) For spherical particles between 3 and 100 microns nificant for 3 micron and smaller particles in gases and
and Reynolds numbers between 0.0001 and 2.0, 0.01 micron and smaller particles in liquids. Table 4-8
Stokes Law: gives values of K,,,.
When two free settling particles of different climen-
CNRe = 24 sions, D' pl and D' P 2 and different densities, Ppl and Pp2,
fall through a fluid of density, Pr, they will attain equal
velocities when:
and:
(4-9)
(4-5) where n = 1 in eddy-resistance zone (more turbulent) and n =
0.5 in streamline fall.
Alternate Terminal Velocity Calculation
for particles smaller than 0.1µ the random Brownian
motion is greater than the motion due to gravitational set- In contrast to individual particles settling in a very
tling. Therefore the above relations based on Stokes Law dilute solution/fluid, is the case of sedimentation where
will not hold. particles must settle in more concentrated environment,
Mechanical Separations 231
Figure 4-5. Efficiency curves for various types of dust collection equipment as of 1969. Only marginal improvements have been made since
then. By permission, Sargent, G.D., Chemical Engineering, Jan. 27, 1969, p. 130.
and hence, particles influence adjacent particles. This is If, K < 3.3, then Stokes' law applies. If 3.3 � K � 43.6, the
often termed hindered settling [23,46]. Depending upon intermediate law applies, and if K > 43.6, Newton's law
the particles concentration, the hindered terminal set- applies. If K > 2,360, the equations should not be used.
tling velocity will generally be somewhat lower than for
the terminal settling velocity of a single desired particle in Values of a and b 1
the same medium.
From Reference [ 46]: =========-=====-:=--=== -- --
K is a dimensionless number that establishes the Law Range b1 a
regime of settling class, reference to the settling laws: Stokes' K< 3.3 24.0 1.0
Intermediate 3.3 � K� 43.6 18.5 0.6
Newton's K> 43.6 0.44 0
=-.cc=======��- - - �- - ---=- --
113
[
_ , p f (p p - p f ) ]
K - 34.8 DP (4-10)
µ 2 (text continued 011 page 234)
232 Applied Process Design for Chemical and Petrochemical Plants
Table 4-5
Applications of Dust Collectors in Industry
COLLECTOR TYPES USED IN INDUSTRY
Concen- Particle Cyclone High Eff. Wet Fabric Hi-Volt See
tration Sizes Centrif- Collector Arrester Electro- Remark
Operation ugal static No.
Ceramics
a. Raw product handling light fine rare seldom frequent frequent no 1
b. Fettling light fine to rare occasional frequent frequent no 2
medium
c. Refractory sizing heavy coarse seldom occasional frequent frequent no 3
d. Glaze & vitr. enamel spray moderate medium no no usual occasional no
Chemicals
a. Material handling light to fine to occasional frequent frequent frequent rare 4
moderate medium
b. Crushing grinding moderate fine to often frequent frequent frequent no 5
to heavy coarse
c. Pneumatic conveying very fine to usual occasional rare usual no 6
heavy coarse
d. Roasters, kilns, coolers heavy med-coarse occasional usual usual rare often 7
Coal Mlnlng and Power Plant
a. Material handling moderate medium rare occasional frequent frequent no 8
b. Bunker ventilation moderate fine occasional frequent occasional frequent no 9
c. Dedusting, air cleaning heavy med-coarse frequent frequent occasional often no 10
d. Drying moderate fine rare occasional frequent no no 11
Fly Ash
a. Coal burning-chain grate light fine no rare no no no 12
b. Coal burning-stoker fired moderate fine to rare usual no no rare
coarse
c. Coal burning-pulverized fuel heavy fine rare frequent no no frequent 13
d. Wood burning varies coarse occasional occasional no no no 14
Foundry
a. Shakeout light to fine rare rare usual rare no 15
moderate
b. Sand handling moderate fine to rare rare usual rare no 16
medium
c. Tumbling mills heavy med-coarse no no frequent frequent no 17
d. Abrasive cleaning moderate fine to no occasional frequent frequent no 18
to heavy medium
Grain Elevator, Flour and Feed Mills
a. Grain handling light medium usual occasional rare frequent no 19
b. Grain dryers light coarse no no no no no 20
c. Flour dust moderate medium usual often occasional frequent no 21
d. Feed mill moderate medium usual often occasional frequent no 22
Metal Melting
a. Steel blast furnace heavy varied frequent rare frequent no frequent 23
b. Steel open hearth moderate fine to no no doubtful possible probable 24
coarse
c. Steel electric furnace light fine no no considerable frequent rare 25
d. Ferrous cupola moderate varied rare rare frequent occasional occasional 26
e. Non-ferrous reverberatory varied fine no no rare ? ? 27
f. Non-ferrous crucible light fine no no rare occasional ? 28
Metal Mining and Rock Products
a. Material handling moderate fine to rare occasional usual considerable 29
medium
b. Dryers, kilns moderate med-coarse frequent frequent frequent rare occasional 30
c. Cement rock dryer moderate fine to rare frequent occasional no occasional 31
medium
d. Cement kiln heavy fine to rare frequent rare no considerable 32
medium
e. Cement grinding moderate fine rare rare no frequent rare 33
f. Cement clinker cooler moderate coarse occasional occasional ? ? ? 34
Metal Working
a. Production grinding, scratch
brushing, abrasive cut off light coarse frequent frequent considerable considerable no 35
b. Portable and swing frame light medium rare frequent frequent considerable no
c. Buffing light varied frequent rare frequent rare no 36
d. Tool room light fine frequent frequent frequent frequent no 37
e. Cast iron machining moderate varied rare frequent considerable considerable no 38
Mechanical Separations 233
Table 4-5
Application for Dust Collectors in Industry (cont.)
COLLECTOR TYPES USED IN INDUSTRY
Concen- Particle Cyclone High Eff. Wet Fabric Hi-Volt See
tration Sizes Centrlf- Collector Arrester Electro- Remark
Operation ugal static No.
Pharrnaceu tical and Food Products
"-• Mixers, grinders, weighing,
blending, bagging, packaging light medium rare frequent frequent frequent 39
b. Coating pans varied fine to rare rare frequent frequent no 40
medium
Plastics
b. Raw material processing (See comments under Chemicals) 41
a. Plastic finishing light to varied frequent frequent frequent frequent no 42
moderate
Rubber Products
o.. Mixers moderate fine no no frequent usual no 43
b. Batchout rolls light fine no no usual frequent no 44
c. Talc dusting and dedusting moderate medium no no frequent usual no 45
d. Grinding moderate coarse often often frequent often no 46
Woodworking
c . 'Woodworking rnachiues moderate varied usual occasional rare frequent no 47
b. Sanding moderate fine frequent occasional occasional frequent no 48
c. Waste conveying, hogs heavy varied usual rare occasional occasional no 49
By Permission John M. Kane, Plant Engineering, Nov. (1954).
REMARKS REFERRED TO IN TABLE 4-5
I. Dust released from bin filling, conveying, weighing, mixing, 20. Collection equipment expensive but public nuisance com-
pressing, forming. Refractory products, dry pan and screen- plaints becoming more frequent.
ing operations more severe. 21. In addition to grain handling, cleaning rolls, sifters, purifiers,
2. Operations found in vitreous enameling, wall and floor tile, conveyors, as well as storing, packaging operations are in-
pottery. volved.
3. Grinding wheel or abrasive cut off operation. Dust abrasive. 22. In addition to grain handling, bins, hammer mills, mixers,
feeders, conveyors, bagging operations need control.
4. Operations include conveying, elevating, mixing, screening, 23. Primary dry trap and wet scrubbing usual. Electrostatic is
weighing, packaging. Category covers so many different ma- added where maximum cleaning required.
terials that recommendation will vary widely. 24. Cleaning equipment seldom installed in past. Air pollution
5. Cyclone and high efficiency centrifugals often act as primary emphasis indicates collector use will be more frequent in
collectors followed by fabric or wet type. future.
6. Usual set up uses cyclone as product collector followed by 25. Where visible plume objectionable from air pollution stand-
fabric arrester for high over-all collection efficiency. ards, use of fabric arresters with greater frequency seems
7. Dust concentration determines need for dry centrifugal; plant probable.
location, product value determines need for final collectors. 26. Most cupolas still have no collectors but air pollution and
High temperatures are usual and corrosive gases not unusual. public nuisance emphasis is creating greater interest in con-
8. Conveying, screening, crushing, unloading. trol equipment.
9. Remote from other dust producing points. Separate collector 27. Zinc oxide loading heavy during zinc additions. Stack tem-
usually. peratures high.
10. Heavy loading suggests final high efficiency collector for all 28. Zinc oxide plume can be troublesome in certain plant loca-
except very remote locations. tions.
11. Difficult problem but collectors will be used more frequently 29. Crushing, screening, conveying, storing involved. Wet ores
often introduce water vapor in exhaust air stream.
with air pollution emphasis. 30. Dry centrifugals used as primary collectors, followed by
12. Public nuisance from boiler blow-down indicates collectors are final cleaner.
needed. 31. Collection equipment installed primarily to prevent public
13. Higher efficiency of electrostatic indicated for large installa- nuisance.
tions especially in residential locations. Often used in con- 32. Collectors usually permit salvage of material and also reduce
junction with dry centrifugal. nuisance from settled dust in plant area.
14. Public nuisance from settled wood char indicates collectors 33. Salvage value of collected material high. Same equipment
are needed. used on raw grinding before calcining.
15. Hot gases and steam usually involved. 34. Coarse abrasive particles readily removed in primary col-
lector types.
16. Steam from hot sand, adhesive clay bond involved. 35. Roof discoloration, deposition on autos can occur with
17. Concentration very heavy at start of cycle. cyclones and less frequently with dry centrifugal. Heavy
18. Heaviest load from airless blasting due to higher cleaning duty air filters sometimes used as final cleaners.
speed. Abrasive shattering greater with sand than with grit 36. Linty particles and sticky buffing compounds can cause
or shot. Amounts removed greater with sand castings, less trouble in high efficiency centrifugals and fabric arresters.
with forging scale removal, least when welding scale is Fire hazard is also often present.
removed. 37. Unit collectors extensively used, especially for isolated ma-
19. Operations such as car unloading, conveying, weighing, stor- chine tools.
ing. (Remarks cont. on next page)
234 Applied Process Design for Chemical and Petrochemical Plants
Remarks from Table 4-5 (Cont.) and other fine additions make collection and dust free dis-
posal difficult.
44. Often no collection equipment is used where dispersion from
38. Dust ranges from chips to fine floats including graphitic exhaust stack is good and stack location favorable.
carbon. 45. Salvage of collected material often dictates type of high
39. Materials involved vary widely. Collector selection may de- efficiency collector.
pend on salvage value, toxicity, sanitation yardsticks. 46. Fire hazard from some operations must be considered.
40. Controlled temperature and hwnidity of supply air to coat- 4 7. Bulky material. Storage for collected material is consider-
ing pans makes recirculation from coating pans desirable. able, bridging from splinters and chips can be a problem.
41. Manufacture of plastic compounds involve operations allied 48. Production sanding produces heavy concentration of par-
to many in chemical field and vary with the basic process ticles too fine to be effectively caught by cyclones or dry
employed. centrifugals.
42. Operations are similar to woodworking and collector selection 49. Primary collector invariably indicated with concentration and
involves similar considerations. See Item 13. partial size range involved, wet or fabric collectors when
43. Concentration is heavy during feed operation. Carbon black used are employed as final collectors.
Table 4-6
Comparison of Some Important Dust Collector Characteristics"
I
Higher
Efficiency
Range on
Particles Max.
Greater Pressure SENSIVITY TO Temp., F,
than Loss, Water, Gal. CFM CHANGE Standard
Mean Size Inches per 1,000 Humid Air Con-
Type in Microns Water CFM Space Pressure Efficiency Influence struction
Electro-Static 0.25 72 . . . . . . Large Negligible I Yes Improves 500
Efficiency
Fabric:
Conventional 0.4 3 -6 ...... Large As cfm Negligible May make 180
recondition-
ing difficult
Reverse Jet 0.25 3 -8 ...... Moderate As cfm Negligible 200
Wet:
Packed Tower 1 -5 1Yz-3Yz 5 -10 Large As cfm
Wet Centrifugal 1 -5 2Yz-6 3 -5 Moderate As (cfm) 2 i::
Wet Dynamic 1 -2 Note 1 Yz to 1 Small Note 1 No } None Unlimited
Orifice Types 1 -5 2:\1--6 10-40 Small As cfm Varies with
or less design
Higher Efficiency:
Nozzle 0.5-5 2 --4 5 -10 Moderate As (cfm) 2 Slightlv to } None Note 2
Venturi 0.5-2 12 -20 ...... Small Moderately Unlimited
Dry Centrifugal:
Low Pressure Cycle 20-40 %-lYz ...... Large As (cfm) 2 I May cause 750
Yes
High Eff. Centrif. 10-30 3 -6 ...... Moderate As (cfm) 2 Yes condensa- 750
Dry Dynamic 10-20 Note 1 ...... Small Note 1 No tion and 750
Louver 15-60 1 -3 ...... Small As (cfm) 2 Moderately plugging 750
I
Note 1: A function of the mechanical efficiency of these combined exhauster and dust collectors.
Note 2: Precooling of high temperature gases will be necessary to prevent rapid evaporation of fine droplets.
* By permission, John M. Kane, "Operation, Application and Effectiveness of Dust Collection Equipment," Heating and Ventilating.
Aug. 1952, Ref. (10)
(text continued from page 231) For hindered particle settling in a "more crowded"
The terminal settling velocity for single spheres can be environment, using spherical particles of uniform size:
determined using the contrasts for the flow regime.
( 4-12)
Referring the above to other than uniform spherical par-
v, (4-11) ticles does not create a significant loss in accuracy for
industrial applications. For higher concentration, the val-
ues ofVts are lower than V In large particles in small ves-
1•
Mechanical Separations 235
Table 4-7
General Applications of Liquid Particle Separators
COLLECTOR TYPES
Impinge- I
Operation Concentration Particle Sizes Gravity ment Cyclone Scrubbers Electrical
Pipeline entrained liquid light fine to coarse No Frequent Yes Occasional Few
Compressor discharge liquid light fine No Frequent Occasional Occasional Rare
Compressor oil haze very light very fine No Frequent Frequent Frequent Occasional
Flashing liquid light to mod. fine to medium No Frequent Frequent Occasional Rare
Boiling or bubbling light to heavy fine to coarse Occasional Frequent Frequent Occasional Rare
Spraying light to heavy fine to coarse No Frequent Frequent Rare Rare
Corrosive liquid particles light to heavy fine to coarse Occasional Frequent Occasional Frequent Rare
Liquid plus solid particles light to heavy medium Occasional Occasional Frequent Frequent I Occasional
100,000 '"
'�
I� Symbols and Legend
�� Ap= Area of Particle Projected on Plane Normal to
Direction of Flow or Motion, sq. fl.
"\ c =Overall Drag Coefficient, Dimensionless
10,000 ' "" " ... Op =Diameter of Particle, ft .
... ' Fd =Drag or Resistance lo Motion of Body in Fluid,
""" ��
ct <, ,, Poundals
i:-i
... ..... � NR,=Reynolds Number, Dimensionless
u, N ::, 1,000 " ,,
-� ' . � u =Relative Velocity Between Particle and Main Body
II I'' of Flu id , ft./sec.
- <, � p
u I� JJ, = Fluid Viscosity, (lb. mass) I ( ftXsecJ = Centipoises + 1488
c:
a,
:� 100 ,, =Fluid Density ,(lb.mass)/(cu. ft.)
::::: <, r� (Any Consistent System of Units may be Employed in
Place of the English Units Specified l
"'
0
u <, "' �
... 1, "I �
Cl
0
Q 10 -- Spheres
...... --- Disks
� ... - � -- Cylinders
:,.,..._ --
-ol:;. .. � ==:- -- .. - --
1.0 - _-:,. ' -
\ ..
\ �
0.1
0.0001 0.001 0.01 0.1 1.0 10 100 1,000 10,000 100,000 1,000,000
DpPU
Reynolds Number , NRe = T
Figure 4-6. Drag coefficients for spheres, disks, and cylinders in any fluid. By permission, Perry, J. H., Chemical Engineers Handbook, 3rd Ed.,
McGraw-H!ll Company, 1950.
sels, the wall effect can become significant (see Refer- Where D' P = diameter of particle, in. or mm
ence [231). a., = acceleration due to gravity, 32.2 ft/s or 9.8 m/s 2
2
Pp = density of particles, lb/ft 3 or kg/rn3
P1 = density of fluid, lb/ft3 01' kg/rn 3
For a single particle, DP can be taken as 2 (hydraulic µ = viscosity of fluid. cp
radius), and the Sauter mean diameter for hindered b , = constant given above
particles. n = constant given in text.
236 Applied Process Design for Chemical and Petrochemical Plants
Table 4-8 Solve for settling velocity, V 1:
Values of K 111 for Air at Atmospheric Pressure 12
2 0 6
0 6
Particle Diameter, v = [ 4(32.2) (0.01) (] + - ) (500 - 0.08)] l/( - ' )
Microns 70° F. 212° F. 500° F. l 3(18.5) (0.02) 0·6 (0.08) (l - 0 - 06 )
0.1 2.8 3.61 5.14
0.25 1.682 1.952 2.528 vi = 9.77 ft/sec
0.5 1.325 1.446 1.711
1.0 1.160 1.217 1.338
2.5 1.064 1.087 1.133 Reynolds number, N Re= DP V p, /µ
1
5.0 1.032 1.043 1.067 -([0.01] )
10.0 1.016 1.022 1.033 (9.77) (0.08)
(12) (0.02) (6.72 X ]0-4)
µ = (cp) (6.72 X 10- 1), lb/ft sec
m = exponent given by equations in Reynolds num-
ber table below NRc = 48.46
V, = settling velocity for single spherical particle, ft/s Then, m = 4.375(NR.,)- 0· 0875 = 4.375(48.46)- 0· 0865 = 3.1179
and m/s (terminal)
V,s = settling velocity for hindered uniform spherical For 0.1 volume fraction solids for hindered settling
particle, ft/s or m/s (terminal) velocity:
c = volume fraction solids
K = constant given by equation above
NRc = Reynolds number, DP V,pr/µ Vr.s = V, (1 - c)?"
= 9.77(1 - 0.1)3.1179
= 7.03 ft/sec
Values ofm
(e) Particles under 0.1 micron:
4.65 < 0.5
4.375 (NRc)-0.0875 0.5 � NRe � 1,300
2.33 NRe > 1,300 Brownian movement becomes appreciable for particles
================================� under 3 microns and predominates when the particle size
reaches 0.1 micron [13]. This motion usually has little effect
in the average industrial process settling system except for
NRc = DpVJ)r/µ, dimensionless (4-13)
the very fine fogs and dusts. However, this does not mean
that problems are not present in special applications.
Example 4-2: Hindered Settling Velocities Figure 4-1 gives the limiting or critical diameter above
which the particular settling law is not applicable. Figure
Using the example of Carpenter [ 46): 4- 7 gives terminal velocities for solid particles falling in
standard air (70°F and 14. 7 psia), and Figure 4-8 gives par-
Pr= fluid density = 0.08 lb/cu ft ticles falling through water. Ifa particle (liquid or solid) is
µ = viscosity = 0.02 cp falling under the influence of gra\<ity through a vapor
Pp = 500 lb/ cu fl stream, the particle will continue to fall until, or unless
D'P = particle diameter, in. = 0.01 the vapor flow rate is increased up to or beyond the ter-
c = volume fraction solids, 0.1. minal velocity value of the particle. If the vapor velocity
exceeds this, then the particle will be carried along with
Solving equation for K, for unhindered particle: the vapor (entrained).
_ [0.08 (500- 0.08)] 113 Pressure Drop
O 01)
K - 34.81 ( .
(0.02) 2
Pressure drop through gravity settlers is usually
K = 16.28 extremely low due to the very nature of the method of
handling the problem.
Then, for K = 16.28 (intermediate range), b 18.5; n Figure 4-9 is convenient for quick checks of terminal
= 0.6. settling velocities of solid particles in air and in water [23].
Mechanical Separations 237
tr 1
401---..--i--1-'--+-+-+�-L---t---+--+--+-l--+-t-t-t---!
30 tl---"- �·+----+--+---l---'---'-+-l--�-+---1---
r
I 201
51·--+----1-f-l-+-+--1----+-------1---l-----l--+
1
5 1ot- -----+--+-+--+--H---l---+--+---+-+--�r""l--+--i,..,::=---,,,.-f'-"'7"''!,,-<�>+-7"'-Y"':7!"'71"'?"'9rF+----+--t---j
t-
� el---+-1--+--1-+-+-+----+--+---1---+,.....-r-+7""�.4,,,L.-7""1�-"'l-:�_....::��7"b-""'i--l-+-+-t------�--+---1
'
< ,�-+--t--t-·-+-+-t-r--l---+--t-,,�-t---cJ.-""-t-71"'- ��J.-S--".::.4-7""��
� 6f---+-f--!--f---l--+-r---+-�·+--7"C-+--7-f--:*'C.,,.-"JJ-1'7ii'5!-
j 5f----+-+-+-+-1-++----+-r'Cf--,,Lj--,,-<q,..q....g."5!"'q,,.r.J,,s-""',,-�
v
� 41---+-l--+--l-+-l--h--.c._-l-c,.,,:::.+.,-��,.....:;..+S,-""+:;,-,4,,.-fS,¥';,f,-<f-:,,L.-_..LSi--+�·--+--'-----'--,-t-++-f---'----i--�;--j
� 31---+-t--:lr"l--t-:l,,-fC--7""'--l,,-"':;·�7"7"''-::J,,-�-:;,-'17"";!,-""'-,j,.-"t,-f-jH--�l---j --+---,--f-�-"---"'--'-�-�----'___J
TERMINAL VELOCITIES
FOR
2 F---J,�l-::,-f-::,f"":J,-"&l"r�-4.>..,...7"1"-...-<::...,,..'re>�-+-+-+-t-+-+----+----t---+--+--; SOLID SPHERIC AL PAR TIC LES
IN
STANDARD AIR
:.o t:.-LJ..L...=...i::_JL!_Le.L- _ _L_._.__ _ _,_ _ _,__,_--l.-1..->-1-l.--1-.--'---L---'--L-.L-L.l_L.L_ _ _L___.J
_!__.L_ _
.3 .4 .s .s .7 .e 1.0 1.s 2.0 3.o 4.o so 60 1.0 eo 10 15 20 30 40 so so 10 so ICO 150 200 300 400
TERMINAL VELOCITY - INCHES PER MINUTE
Air/ VISCOSITY= 0.0181 CENTI POISE AND DENSITY= 0.0749 LBS. /CU. FT. AT 70° F.
Figure 4-7. Terminal velocities for solid spherical particles in standard air. Courtesy of American Blower Div. American Radiator and Standard
Sanitary Corporation.
1,000
.,. " I
J
v � / / / �
/ .,. v .,. v
�v .,., ..... � / v
i ,, I, v .,. v"' � r.>
,,
/
True ·specific Gravity of Particle£ v ,,, .... / ,,, "'
/
,,,:.-
-
1.10 / v v .,.
.,. �
J �
/ .,. I, I.S� / .,.
.,.,,,
/ »: �-0 »< /
/
"',, / / J-r� v I I
v"
.,..
/
v ,,,i.- v v" v I I
,,,
� I/ I L,/ / ,, ,,. I
.,
/
CL. 10 .,. � / .,. I/ Fluid : Water at 70° F
.,.
,.,. Viscosity =0.981 Cenlipoise
� ,� ,, � Density = 62.3 lbs/cu. fl
/ .... j J .... Specific Gravity of Particlt
is Referred ta Water at
1
v v _,,/ 4 C (39.2°F) I
v.,.,, v
v
I
i ! i
0.0001 0.001 0.01 0.1 1.0
Terminal Settling Velocity, Feel/Second
Figure 4-8. Terminal settling velocity of particles in water. By permission, Lapple, C. E., Fluid and Particle Mechanics, 1st Ed., University of
Delaware, Newark, 195L.
238 Applied Process Design for Chemical and Petrochemical Plants
Equivalent standard
Tyler screen mesh
Theoretical screen mesh I() o o I() o o N N v w N en r-- 10 I() I()
-�_.;..._.;..._:..c.._""'-----"--- C\I I() r,.. - CX> ID V I"> C\I - - I"'> '
0 0 0 r()N-- N
0 0 0 000 � 1ol()a,l() Ovo1 wvl
�
�
�
Q 0. � I() I()
0 N. C\I O r-- 0 0 ID v I"> C\l'T T I
C\IN--
7 '? C\I - I.D � I
.... j
102 --
- . ., ...-
/�
/ ; v. v.,.
/
/,, ,, �.,
/_.��
10
, ,
,,
I ,1
i, // / J � ....
I,
V/' J / I,., � '!
v
I � "'/JV i,/ . .. "
I,,
j ...... I; 1
, .,
I , � I I
/ v
J I I I/ ; " / J
I /J IJ ' / / / / 1,i'
II VJ I ��1VJ l/ 11�11 "/ I/"
o"'- o'
o· 1111 II th Q 1-n II J �
I
- --/, �� �� �� (()
-1
" LI\
I I
cfo
-e
-
.._ Al I/ J
vs
���
01,
··,:
O',:
t::J:.
Q �
0
:=:::- ·S' � rv � o, ::J ,.,,. l'\t !() ....._ •
°' I
..___ -� � ..... rv
t o,
,.._� q, '" I
� q7 "!)j "> (,j II I II J J II
�II cl'/ J I
1:1
I ,VJ LI I' I/ I
//, I /J �
3 'i 1 I/
I '
I
I I I I I
JJ IJ I Notes
I i I J I J I. Numbers on curves represe nt
If J J J II I ! II true ( not bulk or apporent )
Ill, LI// j specific gravity of particles
4// i I' referred to water at 4 ° C.
2. Stokes-Cunningham corr-
I
I J I J I ection factor is included for
I I fine porticles settling in air.
l J J J y � I/ I
'/1 3. Physical properties used
5 }1 Temp. Viscosity Density
u / Fluid � centipoise lb./cu. ft.
I I II Air 70 0.0181 0.0749
II I Water
I J 70 0.981 62.3
VIV l l I I I II 11 I I I I II Ill I l 11 1111
6V1 J,/ I Ill I 1111 I 111 Ill
10 100 1000 10,000
Particle diameter, 1.1-,n
Figure 4-9. Terminal velocities of spherical particles of different densities settling in air and water at 70°F under the action of gravity. To con-
vert feet per second to meters per second, multiply by 0.3048. (From Lapple, et. al., Fluid and Particle Mechanics, University of Delaware,
1951, p. 292. By permission, Perry, J. H. Chemical Engineers Handbook, 6th Ed., McGraw-Hill Book Co., Inc. 1984, p. 5-67.
Mechanical Separations 239
API-Oil Field Separators
The American Petroleum Institute Manual on Disposal
of Refinery Wastes provides specific design and construc-
tion standards for APl-separators that are often used in
oilfield waste disposal [24].
Liquid/Liquid, Liquid/Solid Gravity Separations,
Decanters, and Sedimentation Equipment
Lamella Plate Clarifier; [see Figure 4-10]
This angle plate gravity separator removes suspensions
of solids from a dilute liquid. The unit is more compact
than a box-type settler due to the increased capacity
achieved by the multiple parallel plates. The concept is
fairly standard (U.S. Patent 1,458.805-year 1923) but
there are variations in some details. For effective opera-
tion, the unit must receive the mixture with definite par- Bo1h Sides
TyD!CaJ
QI
ticles having a settling velocity The units are not totally ..
Larnclta Prates
effective for flocculants or coagulated masses that may
have a tendency to be buoyant.
Flow through the plates must be laminar, and the criti- Wa.te•Conta111ng w.Hoc Particles Loauld Sludge
Cianhed Water
Bemcvat
F'oc Parnc'es
cal internal areas are [25,54,61]: Pcrroved
Figure 4-10. Lamella Clarifier. By permission, Graver Water Div. of
• Distribution of the inlet flow the Graver Co.
o Flow between each parallel plate surface
• Collection of clarified water clarifying, wastewater clarification and thickening. A good
summary discussion is given in Reference [27].
Because these units are essentially open, the "standard"
design does not fit into a closed process system without
adding some enclosures, and certainly is not suitable for a Horizontal Gravity Settlers or Decanters, Liquid/Liquid
pressurized condition. Many processes require the separation of immiscible
Although the main suspended flow is through a top liquid/liquid streams; that is, water/hydrocarbon. The
mixing chamber, the mixture flows around the angled settling unit must be of sufficient height (diameter) and
(avg. 55°) parallel plate enclosure and begins its settling length to prevent entrainment of the aqueous phase into
path from the bottom of the plates, flowing upward while the hydrocarbon and vice versa. Horizontal units are usu-
depositing solids that slide countercurrent into the bot- ally best for settling and possibly vented units for decanta-
tom outlet. The purified liquid flows overhead and out tion (but not always).
the top collecting trough.
Residence time of the mixture in the vessel is a func-
Manufacturers should be contacted for size/rating
information, because the efficiency of a design requires tion of the separation or settling rate of the heavier phase
proper physical property information as well as system droplets through the lighter phase. Most systems work sat-
capacity and corrosion characteristics. isfactorily with a 30 minute to 1 hour residence time, but
this can be calculated [26]. After calculation, give a rea-
sonable margin of extra capacity to allow for variations in
Thickeners and Settlers
process feedrate and in the mixture phase composition.
Generally, large volume units for dewatering, settling From Stokes' Law, the terminal settiing velocity:
of suspensions, and thickening of solids, and concentra-
tion of solids and clarification must be designed by the V, = gD/ (Pp - p)/18µ, ft sec (4-14)
specific manufacturer for the process conditions and
physical properties. Some typical processes involving this µ = viscosity of surrounding fluid, lb/ft sec
class of equipment are lime slurrying, ore slurrying, ore DP = diameter of particle, fl
240 Applied Process Design for Chemical and Petrochemical Plants
for assumed spherical particles in a surfactant-free system The minimum residence time as determined by
[26]. The minimum particle diameter for many fine dis- Stokes' Law terminal settling velocity is:
persions is 100 microns; however, Reference [28] has
reviewed a wide variety of liquid drop data and suggests
that a good choice is 150 micron or 0.15 cm or 0.0005 ft. tmin = b /v., min (4-17)
This is also the particle size used in the API Design Manu-
al [24]. Using too large an assumed particle diameter will he = height of segment of circle, in.
cause the settler unit to become unreasonably small.
vt = terminal settling velocity, in./min
Assuming a horizontal unit, as illustrated in Figure 4-
11, has a segment ofa circle equal to 25% to 75% [27,26]
of the circular area (the highest of this segment will be Average residence time related to minimum residence
about 30% to 70% of the diameter), then height of the time is:
interface will be [26]:
( 4-18)
H/D = 0.8A/(7iD 2 /4) + 0.1, ft (4-15)
f = factor relating average velocity to maximum velocity
or, he = 38.4A/ ( TID) + l.20, in (4-15A)
where H = height of segment of a circle, fl This relationship is related to the viscosities of the
hydrocarbon and aqueous phases at the interface. Based
he = height of segment of a circle, in.
on data from different systems:
D = diameter of vessel, ft
A = area of segment of circle, sq ft
f = 2.0 (use for design)
The average volumetric residence time in the settler is:
The active volume occupied by either phase is:
la,g = 7.48 (VseJF), min ( 4-16)
V = AL, cu ft ( 4-19)
Vw = active volume of settler occupied by one of the phases,
cu ft
L = length of vessel, ft, inlet to outlet
F = flow rate of one phase GPM
lavg = average residence time based on liquid flow rate and ves-
sel volume, min he = 7.48 ALvJ (ff) ( 4-20)
Water alternate makeup
------L------
.. HC inlet-HG outlet Washed hydrocarbon
Hydrocarbon Mixer <}--
to be washed (in-line) Safety
plus water
LC
-----,
I
I
I
i
I Alternate blowdown
*Velocity< 10"/min
Q
Aqueous circulation I
Blowdown to disposal
Figure 4-11. Settler vessel; runs full. Adapted by permission, Abernathy, M. W., Vol. 25, Encyclopedia of Chemical Processing and Design, J.
J. McKetta, Ed., Marcel Dekker, 1987, p. 77 and Hydrocarbon Processing, Sept.1977, p.199 [25] and private communication.
Mechanical Separations 241
For an aqueous-hydrocarbon or organic solvent mixture: Optimum vessel diameter:
Assume 20% cross-sectional area is occupied by an
The top layer will be hydrocarbon, with the aqueous layer emulsion and is recognized as a "dead volume." This is
droplets settling through the hydrocarbon. 111e terminal actually the height over which the interface level will vary
velocity is: during normal operations [26].
vhc = 12.86 (6SpGr)/µhc, in./min (4-21) (4-24)
vhc = terminal settling velocity of aqueous droplets in 0 = ± [a/2 ± (a 2 - 4b) 112 /2] 112, ft (4-25)
hydrocarbon phase in top of vessel, in./min
6SpGr = differences in specific gravity of the particle and sur- (4-26)
rounding fluid
(4-27)
µhe = viscosity of surrounding fluid, cp
The economical vessel ratio is L/D = r
Height of hydrocarbon layer to the interface:
Modified Method of Happel and Jordan [29]
(4-21A)
This method is a modification of the earlier method
h, = 38.4 A/ (rcO) + 1.20 (4-l5A) [30] by Reference [26], as follows, and can be less con-
servative [26] than the original method [30]. A basic
ht= height of continuous hydrocarbon phase in the top of assumption is that particles must rise/fall through one-
vessel, in. half of the drum vertical cross-sectional area [26].
(4-22) t = h/v
A 1 = cross-sectional area at top of vessel occupied by the con- t = (1/2) (7.48) [0.8 1t0 2 L/4]F, (4-28)
tinuous hydrocarbon phase, sq ft
Ab = cross-sectional area at bottom of vessel occupied by con- F, = flow rate of both phases
tinuous aqueous phase, sq ft v, = v = terminal settling velocity, in./min
This assumes 20% of the cross-sectional even as "dead vol-
For the bottom aqueous phase:
ume." The height from the interface can be determined
hydrocarbon droplets settle out of the continuous aque- by combining the above equations:
ous phase. The terminal velocity is for hydrocarbon
droplets: h = (0.748)TC0 2 Lv/F, ( 4-29)
The height for each interface is:
"•q = 12.86 (6SpGr)/µ.iq, in./min (4-23)
(4-30)
Vaq = terminal settling velocity of hydrocarbon droplets in
aqueous phase in bottom of vessel, in./min hb = (0.748) TC0 Lvaq/F, ( 4-31)
2
µaq = viscosity of aqueous phase, cp
A,= [(0.748) TC0 2 Lvhc/F, - 1.20] TCD/38.4 ( 4-32)
Height of aqueous layer to the interface:
Ab= [(0.748) TC0 2 Lvaq/F, - l.20] TCD/38.4 (4-33)
(4-21A) Example 4-3: Horizontal Gravity Settlers
(4-15A) Using the data from Sigales [31] and following the
design of [26]:
hb = height of continuous aqueous phase in bottom of vessel, Data for propane/caustic wash:
in. Fhc = 95 GP:tv1
Ab = cross-sectional area al bottom of vessel occupied by con- Faq = 39 GPM
tinuous aqueous phase, sq ft
Vaq = 5 in./rnin
Vhc = 120 in./min
Ab= l.20[(7.48)Lvaq(f,gF,g) - 38.4/(TC0)]- 1 (4-22) r = 3.4
242 Applied Process Design for Chemical and Petrochemical Plants
The terminal (highest calculated) settling velocity of the In summary:
aqueous droplet in/ through the hydrocarbon phase is:
Design Calculation Practical Design Use
�����--���
Vhc = (1.2) (5 in./min) (95/39 GPM) = 14.6 in./min
Diameter 3.34 ft ( 40.08 in.) 3.5 ft. ( 42 in.) or 3.83 ft ( 46 in.)
Length HC inlet/outlet: 11 ft 12 or 14 ft
Because this is more than the 10 in./min recommend-
ed earlier, then use:
Abernathy [26] has compared several design methods
as follows:
Vhc = 10 in./min
Assume for design: fhc = fag = 2 (from earlier discus- This Modified Rule-of-
sion). Si gales Method Happel Happel Thwnb
Diameter 2.67 ft 3.34 ft 3.36 ft 4.01 ft 4.1 ft
ht 10 in. 22 in. 22.6 in. 24 in. 32.5 in.
Then, a= (1.889((10)(2)(39) + (5)(2)(95)]/[(3.4)(10)(5)]
hb 8 in. 12 in. 11.3 in. 24 in. 16.7 in.
a = 19.22 Interface 14 in. 6 in. 6.4in. O in. O in.
b = (3.505)(2)(95)(2)(39)/[(3.4) 2 (]0)(5)] HC residence 1.1 min 4.4 min 4.6min. 6.8min. lOmin.
time
b = 89.87
Solving for D: Decanter [32]
In most general applications, a decanter is a continu-
D = [19.22/2 ± [(19.22)2 - 4(89.87))11 2 /2] l/2
ous gravity separation vessel that does not run full, as con-
trasted to a settler that usually runs full, with one stream
D = 3.34 ft or -2.83 ft (latter is an unreal negative number, exiting at or near the top of a horizontal vessel. For most
so use 3.34 ft) decanters, one phase of a two-plane mixture overflows out
of the vessel (see Figure 4-12). The concept of the
Area of segment at top of vessel = At, substituting into decanter involves the balancing of liquid heights due to
Equation 4-22: differences in density of the two phases, as well as settling
velocity of the heavier phase falling through the lighter,
A,= 1.2 D [(7.48) (3.4)D(l0)]/[(2)(95)]-38.4/(nD)]- 1 or the lighter rising through the heavier.
Settling Velocity: Terminal [32]
Using: L/D = 3.4:
For the bottom segment of the vessel, aqueous layer: • (pd - Pc)
v = gd· ft I sec (4-34)
d 18 µ c ,
Ab = l.2(3.34) [ (7.48) (3.34) (3.4) (5) ]/ [ (2) (39)] - (38) I
n(3.34)r 1 where vd = terminal settling velocity of a droplet, ft/sec
Ab = 2.2448 sq ft g = acceleration due to gravity, 32.17 ft/sec-sec
d = droplet diameter, ft(l ft= 304, 800µm, or Iurn =
O.OOlmm)
Then, using Equation 4-21A: Pd = density of fluid in the droplet, lb/cu ft
Pc= density of fluid continuous phase, lb/cu ft
h, = 7.48(4..942) (3.4) (10)/(2.0) (95) = 22.1 in. µc = viscosity of the continuous phase, lb/ (ft) (sec)
Note: 1 cp = 6.72 X 10- lb/(ft)(sec)
4
hb = 7.48(2.2448)[(3.34)(3.4)](5)/(2)(39)] = 12.2 in.
µm = millimicron
Then, h 1 /D = (22.1)/(12)(3.34) X 100 = 55%
For a decanter that operates under gravity flow with no
instrumentation flow control, the height of the heavy
hb/D = 12.2/ (] 2) (3.34) X 100 = 30% phase liquid leg above the interface is balanced against
the height of one light phase above the interface [23].
Since h. and h , are between 30% and 70% of the diam- Figures 4-12 and 4-13 illustrate the density relationships
eter, the solution is acceptable. and the key mechanical details of one style of decanter.
Mechanical Separations 243
Decanter -
Light phase overflow
I I
Light phase
Drain interface
/ ,
for emulsion __ ,
J
Heavy phase
Light phase out
Figure 4-12. Gravity decanter basic dimensions. Adapted by permission, Schweitzer, P.A., McGraw-Hill Book Co. (1979) [32].
Vessel heads bend or tangent
lines
15'+2
z
15'
Partial baffle at interface clear
Inlet top by 0.3D and be 1'-6"
t ,.r·O"in/llnj vertical height only 4-trial outlet nozzles, one at
estimated interface
Min. 0.340 to 0.450
I=' Interface
0
0.550 to (")
Dispersion Band= 10%0
0.660 = c
II
7.34 ft
2" drain hole flush with floor
Tee on feed inlet
Velocity= 0.5-1'sec
Baffle, solid except top 6 .. with
Perforated underflow baffle, 1 .. pert. holes on 1.5<t_ 11
holes area approx = outlet areas Water phase out. Perforated
with min. W' holes, tee Baffle height at estimated baffle, set min. 6" off bottom,
Interface = 2-4 .. from bottom, 2 to 3 times nozzle diameter
sealed at bottom
Figure 4-13. Decanter for Example 4-1.
244 Applied Process Design for Chemical and Petrochemical Plants
The same results can be achieved with internal flat plate h = distance from center to given chord of a vessel, ft
baffles and outlet nozzles. I = width of interface, ft
D = decanter diameter, ft
(4-35) L = decanter length, ft
r = vessel radius, ft
zh = heavy phase outlet dimension from bottom of horizontal
decanter Horizontal vessels as cylinders are generally more suit-
zi = interface measured from bottom able for diameters up to about 8 feet than other shapes,
z 1 = light phase outlet measured from bottom of decanter or vertical, due in part to the increased interfacial area
for interface formation. For a horizontal drum (See Fig-
Droplet diameter, when other data is not available: ure 4-12):
= 150µm (d = 0.0005 ft) J = 2(r 2 - h 2) 1 2 (4-37)
1
Reference [32] recognizes that this is generally on the �=� (4-�)
safe side, because droplets generated by agitation range
2
500 to 5000 urn, turbulent droplet range 200 to 10,000 AL= l/2 m 2 - h(r 2 - h 2)112 - r arc sin(h/r) (4-39)
µm. Due to limitations of design methods, decanters sized
for droplets larger than 300 µm often result in being too or use the methods from the Appendix to calculate
small to work properly [32]. area of a sector of a circle. The arc is in radians:
The continuous phase moves through the vessel on a Radians= (degrees) (n:/180)
uniform flow equal to the overflow rate. To identify which
is the continuous phase (from [65] by [32]):
DL = 4 AJ (J + P) (4-41)
( 4- 36)
Da = 4 A1-i/ (I + 2 nr - P) ( 4-42)
e Result where P = 2r arc cos (h/r)
< 0.3 light phase always dispersed
0.3-0.5 light phase probably dispersed Degree of turbulence [32]:
0.5-2.0 phase inversion probable, design for worst case
2.0-3.3 heavy phase probably dispersed
> 3.3 heavy phase always dispersed (4-43)
where QJ = dispersed volumetric flow rate, cu ft/sec c = continuous phase
Qi, = volumetric flow rate, cu ft/sec, light phase Dr-I = hydraulic diameter, ft = 4 (flow area for the phase in
Qi-1 = volumetric flow rate, cu ft/sec, heavy phase question/wetted perimeter of the flow channel)
PL = density oflight phase fluid, lb/cu ft vc = velocity down the flow channel
PH = densi Ly of heavy phase fluid, lb/ cu ft
µH = viscosity of heavy phase, lb/ (ft) (sec)
µL = viscosity of light phase, lb/(ft) (sec) Guidelines for successful decanters [32]:
To begin, there is a dispersion band through which the Results
phases must separate. Good practice [32] normally keeps < 5000 little problem
the vertical height of the dispersed phase, Hn < 10% of 5000-20,000 some hindrance
decanter height (normally a horizontal vessel), and: 20,000-50,000 major problem may exist
Above 50,000 expect poor separation
l/2H 0 A 1 /Qn > 2 to 5 rnin =============================
where Ar = area of interface assuming flat interface, sq ft Velocities of both phases should be about the same
Ai. = cross-sectional area allotted to light phase, sq ft through the unit. By adjusting mechanical internals, a
AH = cross-sectional area allotted co heavy phase, sq ft ratio of « 2:1 is suggested (internals do not need to be
H 0 = height of the dispersion band, ft equal) [32]. Velocities for entrance and exit at the vessel
Qn = volumetric flow, dispersed phase, cu ft/sec nozzle should be low, in the range of0.5 lo 1.5 ft/sec. The
Mechanical Separations 245
feed must not 'jet" into the vessel, and should be baffled and:
to prevent impingement in the main liquid body, keeping
turbulence to an absolute minimum to none. Baffles D � l/2(Q/vct) 112 � 1/2(0.187 /0.005) 11 2
can/ should be placed in the front half of the unit to pro- D = 3.057 ft
vide sloto flow of the fluids either across the unit or
up/ down paths followed by the larger stilling chamber, Length, L = 50 = 5(3.0) = 15 ft
before fluid exits. (See Figure 4-13)
Interface Level: Assume: Hold interface one foot below
Example 4-4: Decanter, using the method of top of vessel to prevent interface from reaching the top
Reference (32] oil outlet.
A plant process needs a decanter to separate oil from Then, h = 0.5 ft
water. The conditions are: r = 3.0/2 = 1.5 ft
I= 2(r 2 - h 2)112 = 2[(1.5) 2 -- (0.5) 2)112 = 2.828 ft
Aoil = (1/2) (rr) (1.5) 2 - 0.5[(1.5) 2 - (0.5) 2]'/2 - (1.5)2
Oil flow = 8500 lb/hr arc sin (0.5/1.5)
p = 56 lb/cu ft
= 3.534 - 0.707 - 0.765
µ = 9.5 centipoise = 2.062 sq ft
Water flow = 42,000 lb/hr
p = 62.3 lb/cu ft Note: In radians: Arc sin (0.5/1.5) (19.47 I l80)1T =
µ = 0.71 centipoise 0.3398
Units conversion: Awarer= Jt(l.5) 2 - l\,il = 7t(2.25) - 2.06 = 5.01
sq ft
Q,,i1 = (8500) (56) (3600) = 0.0421 cu ft/sec P = 2(!.5)[arc cos (0.5/1.5)] = 3.69 sq ft
.Uoil = (9.5) (6.72 X 10- 4) = 63.8 X 10-·l lb/ft-sec Area interface, A1 = (2.828) (15) = 42.42 sq fr
Q,a,cr = 42,000/ (62.3) (3600) = 0.187 cu ft/sec
µw = (0.71)(6.7;! X 10- 1) = 4.7'7 X 10- 4 lb /ft-sec Secondary settling: Continuous phase water droplets
to resist the oil overflow rate if it gets on wrong side of
interface.
Checking dispersed phase, Equation 4-36:
Vwatcr � Q,il/ A1 = 0.0421 I 42.42 = 0.0009924 ft/ sec
EJ- 0.042� [ (56)(4.77Xl0- 4) ]0.3
0.187 (62.3) (63.8 x 10- 4) Then, from settling-velocity equation:
= 0.010009
d = [(18)(6.38 x 10- )(0.0009924)/(32.17)(62.3 - 56)] /2
1
3
d = 0.0007498 ft, (216 um)
Therefore, light phase is always dispersed since 0 is less
than 0.3. Checking coalescence time:
Settling rate for droplets of oil through water: Assume Hj, = height of dispersion band= 10% ofD =
Assume droplet size is d = 0.0005 ft ( 150 µm), as earli- 0.3 ft
er discussed. Time available to cross the dispersed band
voil = (32.17)(0.0005) 2 (56 - 62.3)/((18)(4.77 X 10- 4)] = 1/2(1-1 0 A 1 /Qo) should be> 2 to 5 min
= -0.005 ft/sec = l/2[(0.3)(42.42)/(0.0421)]
= 150 sec, which is 2.5 min
The ( - ) sign means the oil rises instead of settles.
Overflow rate: Should be acceptable, but is somewhat low.
Assume I (Figure 4-12) is 80% diameter, D, of vessel
0
and that L/D = 5. Then D i1 = 4(2.062) I (2.828 + 3.69) = l .265 ft
V ;1 = 0.0421/ (2.062) = 0.0204 ft/sec
0
Then, C&:/ Ar< Vct
A1 = IL = (0.80) (SD) = 4D 2, then, N = (0.0204) (l.265) (56) = 226 5
_
2
Qj4D < Vct Re oil 6.38 x 10- 3
246 Applied Process Design for Chemical and Petrochemical Plants
D""'tcr = 4(5.01)/[2.828 + 27t (1.5) - 3.69) = 2.34ft There are basically three construction types for
impingement separators:
"water= 0.187/5.01 = 0.0373ft/sec
1. Wire mesh
N = (0.0373) (2.34) (62.3) = ll, 399
Re (water) 4.77 X 10-,j 2. Plates ( curved, flat or special shaped)
3. Packed Impingement Beds
d = droplet diameter, ft.
Knitted Wire Nlesh
The degree of turbulence would be classified as accept-
able, but the unit must not be increased in capacity for A stationary separator element of knitted small diame-
fear of creating more water phase turbulence. ter wire or plastic material is formed of wire 0.003 in. to
0.016 in. (or larger) diameter into a pad of 4 inches, 6
inches or 12 inches thick and serves as the impingement
B. Impingement Separators
surface for liquid particle separation. Solid particles can
be separated, but they must be flushed from the mesh to
As the descriptive name suggests, the impingement prevent plugging. Although several trade name units are
separator allows the particles to be removed to strike available they basically perform on the same principle,
some type of surface. This action is better accomplished and have very close physical characteristics. Carpenter [ 4]
in pressure systems where pressure drop can be taken as a presented basic performance data for mesh units. Figure
result of the turbulence which necessarily accompanies 4-15 shows a typical eliminator pad.
the removal action.
Figure 4-16 pictorially depicts the action of the wire
Particle removal in streamline flow is less efficient than mesh when placed in a vertical vessel.
for turbulent flow, and may not be effective if the path of Referring to Figure 4-16, the typical situation repre-
travel is not well baffled. sents a vapor disengaging from a liquid by bursting bub-
The "target" efficiency for impingement units express- bles and creating a spray of liquid particles of various
es the fraction of the particles in the entraining fluid, sizes. Many of these particles are entrained in the moving
moving past an object in the fluid, which impinge on the vapor stream. The largest and heaviest particles will settle
object. by gravity downward through the stream and back to the
bottom of the vessel or to the liquid surface. The smaller
The target efficiencies for cylinders, spheres, and rib--
bonlike particles are given for conditions of Stokes Law in particles move upward, and if not removed will carry
along in the process stream. With wire mesh in the mov-
an infinite fluid by Figure 4-14.
ing stream, the small particles will impinge on the wire
If the particles are close enough together in the fluid surfaces; coalesce into fluid films and then droplets, run
to affect the path of each other, then Figure 1-11 gives to a low point in their local system; and fall downward
conservative efficiencies. For particles differing consider- through the up-fl.owing gas stream when sufficiently large.
ably from those given in the curves, actual test data The gas leaving is essentially free from entrained liquid
should be obtained. unless the unit reaches a flooding condition.
1.0 Db = Min. dla. of particle completely
;;. .... i-- � ::;.--- collected, feet
,;..0.9 - ... VO = Average velocity of gas, feet/sec.
,....
- <> c: �y / -'.'.'. u, = Terminal settling velocity of
Q.
a> .!!1 0.8
I <>yy'
3: .2
o�
Cl) :t: Q;-1 �0· particle under action of gravity, feet/sec.
gL = 32.2 feet/sec.•
c: w 0.7
�m � <>
.£ � 0.6
� I- I �Q �0 b0 s; •
� c: 0.5
.. 0 I .1Vcf�
� j0.4
O t, I 1/V
.:
5 s 0.3
-- 0 Intercepts: j /
� � 0.2 Ribbon or Cylinder: 1/ �
u.. E Sphere: 1/241 / /
� 0.1 Figure 4-14. Target efficiencies for spheres,
> Ii 1kZ/
o.o cylinders, and ribbons. By permission, Perry, J.
0.01 0.1 1.0 10 100 H., Chemical Engineers Handbook, 3rd Ed.,
Separation Number, utV O /gLDb McGraw-Hill Company, 1950 [13].
Mechanical Separations 247
s r r r r r 1 r r r
4
3
2
When a gas is generated in, or passes through, a liquid (1), the
gas, on bursting from the liquid surface (2) carries with it a fine
spray of droplets-liquid entrainment-which are carried upward in
the rising gas stream (3). As the gas passes through the mist elimi-
nator, these droplets impinge on the extensive surface of the wire,
where they are retained until they coalesce into large drops. When
these liquid drops reach sufficient size, they break away from the
Figure 4-15. Details of wire mesh construction. Courtesy of Otto H. wire mesh (4) and fall back against the rising gas stream. In this
York Co. way, the entrained droplets are literally "wiped out" of the gas
which, freed from liquid entrainment, (5) passes on unhindered
through the mesh.
For special applications the design of a mist eliminator
unit may actually be an assembly in one casing of wire Figure 4-16. Diagram of action of wire mesh in liquid-vapor separa-
tion. Courtesy of Metal Textile Corp., Bulletin ME 9-58.
mesh and fiber packs/pads or in combination with
Chevron style mist elements (see Figure 4-l 7A and 17B
and -17C.) This can result in greater recovery efficien- ditions which will prevail and select a mesh to fit as close
cies for small particles and for higher flow rates through to the conditions as possible. The procedure is outlined
the combined unit. Refer to the manufacturers for appli- below:
cation of these designs.
Allowable vapor velocity (mesh in horizontal position)
Mesh Patterns
There are several t)'pes of mesh available, and these are
identified by mesh thickness, density, wire diameter and
weave pattern. Table 4-9 identifies most of the commer-
cial material now available. The knitted pads are available
in any material that can be formed into the necessary Va = maximum allowable superficial vapor velocity across inlet
weaves, this includes: stainless steels, monel, nickel, cop- face of mesh, fl/sec
per, aluminum, carbon steel, tantalum, Hastelloy, Saran, k = constant based on application, Table 4-10, average for
polyethylene, fluoropolymer, and glass multi-filament. free flowing system = 0.35 for 9-12 lb/cu ft mesh
Capacity Determination PL = liquid density, lb/ cu fl
p, = vapor density, lb/ cu ft
The usual practice in selecting a particular mesh for a
given service is to determine the maximum allowable
velocity and from this select a vessel diameter. In the case For other mesh densities, use k(52) of 0.4 for 5 lb/cu
of existing vessels where mesh is to be installed, the ft mesh (high capacity), and 0.3 for plastic mesh such as
reverse procedure is used, i.e., determine the velocity con- Teflon® and polypropylene.
248 Applied Process Design for Chemical and Petrochemical Plants
Table 4-9
Identification of Wire Mesh Types
I
Density, Surface Area Thickness, Min. Eff.
General Type Lbs./cu. ft.* Sq. ft./cu. ft. In.** Wt.% Application
High Efficiency 12 115 4+ 99.9+ Relatively clean, moderate velocity.
Standard Eff. ll 85 4+ 99.5+ General purpose
Optimum Eff. or VH Efficiency. and
Wound type 13-14 120 4+ 99.9+ For very high efficency
Herringbone, High through-put or For services containing- solids, or
Low Density 5--7 65± 4-6+ 99.0+ "dirty" materials
I
-
"If the mesh is made of nickel, monel or copper, multiply the density values by 1.13, referenced to stainless steel.
•• 4" is minimum recommended thickness; 6" is very popular thickness; IO" and 12" recommended for special applications such as fine
mists, oil vapor mist.
Compiled from references (3) and (21).
Reference [52] suggests "dry" mesh pressure drop of: where a = specific surface area, sq ft/ cu ft
( = friction factor, dimensionless
(4-45) gc = gra\'itational constant, 32.2 lb-ft/lb-sec-sec
1 = wire mesh thickness, ft
(4-46) Ll.pn = pressure drop, no entrainment, in. of water
Ll.p'L = pressure drop, due to liquid load, in. of water
For �PL see manufacturer's curves. Ll.f>r = pressure drop, total across wet pad, in. of water
A rough approximation of operating mesh pressure V, = superficial gas velocity, ft/sec
drop is 1 inch water or less. The calculated pressure drop E = void fraction of wire mesh, dimensionless
at the maximum allowable velocity is close to 1.5 inches of PL= liquid density, lb/cu ft
p, = vapor density, lb/ cu ft
water. Therefore: f = generally ranges 0.2 to 2 fur dry mesh
(4-47) Subscript:
How FLEXICHEVRON® Mist Eliminators Work Act = actual
Gases with entrained liquid droplets flow between the Max = maximum
zig-zag baffles. The gos can easily make the turns while the
liquid droplets impinge upon the walls of the baffles and
coalesce to a size such that they drop downward, The correlation factor, k, is a function of the liquid drop
being too heavy to be carried in the gas.
size, liquid viscosity, liquid load, disengaging space, type of
mesh weave, etc. k varies somewhat with system pressure; as
THE CHEVRON pressure increases the k value decreases. The manufactur-
IMPINGEMENT ers should be consulted for final design k valves for a sys-
PRINCIPLE DE-ENTRAINED GASES
MIST LADEN GASES-- .i e - LARGE FALLING
T e DROPLETS
FLOW 10 20 30 40
Droplet Size (microns)
Figure 4-17A. Separation/Impingement action of Chevron-style mist
eliminators. Flow is up the V-shaped plates assembly. Courtesy of Figure 4-178. Capture efficiency vs particle size for four standard
Bulletin KME - 12, Koch Engineering Co. York-Vane mist eliminators. By permission, Otto H. York Co. Inc.
r- Mechanical Separations 249
tern, because the wire style, size, and material also affect the
2. value. For pressures below 30 psig, k = 0.35 avg., then
above 30 psig, k value decreases with pressure with an
Certain values have been found satisfactory for estimating
I I I approximate value of 0.30 at 250 psig and 0.275 at 800 psig.
systems described in Table 4-10 and Table 4-11.
I For conditions of high liquid loading, use caution in
1. 0 design. Use the high velocities for very fine mist to
.4
.9 0 I remove the small particles, and use two mesh pads in
.8 0 , series with the second mesh operating at a lower velocity
.7 0 I a Lo remove the larger drops re-entrained from the first
.4
.60 mesh. Systems involving high viscosity fluids should be
/��t.3 checked with the various manufacturers for their case his-
.5 0 tory experience. Lower k values are used for systems with
� f �P�2 high vacuum, high viscosity liquids, low surface tension
.40 ,
I
! i Table 4-10
.30
6' "k" Values for Knitted Mesh
::z::"' /Ji.
E ! � Bottom of mesh at least 12 inches above liquid surface
; Service Conditions "k" General Type Mesh
.20
"'t" Clean fluids, moderate 0.35 to 0.36 Standard
� ' liquid load, fits 90% of 0.35 High Efficiency
� ' process situations 0.25 Very High Efficiency
ON High viscosity, dirty 0.40 Low density or
I suspended solids Herringbone, high
(/) ' through-put
Q.J
s: .4�- j Vacuum operations:
� .10 2" Hg. abs. 0.20 Standard or
I� 'II 16" Hg. abs. 0.27 High Efficiency
g; .09 II II Corrosive Chemical 0.21 Plastic coated wire,
� .08 or plastic strand
II II
� .D7 II II Compiled from various manufacturer's published data. Note: k values
� .06 II u for estimating pm·poses, not final design unless verified by manufactur-
(/)
w er. Unless stated, all values based on stainless steel wire.
a: ,
c, .05 II�
TYPEi 1i r Variation of k with Disengaging Height*
.04 Table 4-11
.03 Disengaging Height Above Mesh, Inches Allowable k Value
�� '//;' 4 0.15
3 .......•.................. 0.12
0.22
.02 TYPE' 5 0.19
6
I 7 ........••....•........... 0.25
I II
I ' I 8 0.29
9
0.32
10
11 0.35
0.38
!2 0.40
13 0.42
0.2 0.3 0.4 0.5 0.6 0.7 14 0.43
K-factor, V/[(pl - pv}lpv]"' ft/sec (x 0.3048 = m/sec)
*By permission, 0. H. York, Reference (21).
Note: Values based on 12 lb/cu ft wire mesh. Design practice normally
Figure 4-17C. Pressure drop vs K-factor for standard York-Vane mist does not exceed k of 0.4 even for higher disengaging height.
eliminators, air-water system. By permission, Otto H. York Co., Inc.
250 Applied Process Design for Chemical and Petrochemical Plants
liquids and systems with very bad fouling conditions.
Table 4-11 indicates the effect of disengaging height on
the allowable k value. Similar relations should hold for
other mesh densities.
Low Density or
Velocity Limitations �100 , High Through-Put Mesh,
c
� ��
Cl)
Very low velocities will allow particles to drift through - Standard Mesh- \
� 80
the mesh and be carried out with the leaving vapor. Also,
very high velocities will carry liquid to the top of the LL.I
c 60
mesh, establish a "flooding" condition, and then re- Cl>
(.)
entrain the liquid from the surface of the mesh. For most cf 40
situations very good performance can be expected for all - Data for Air-Water
System
velocities from 30% to 100% of the optimum allowable �20 Atmospheric Pressure -
Cl>
design velocity. The minimum allowable safe design veloc- 3: I I I I
ity is 10 percent of the value calculated by the equation. 2 4 6 8 10 12 14 16 18
The flooding velocity of the mesh is usually about 120 per- Superficia I Vapor Velocity, Feet/Second
cent to 140 percent of the maximum allowable velocity.
Generally the maximum allowable velocities are lower Figure 4-18. Typical wire mesh efficiency.
under conditions of pressure, and higher under condi-
tions of vacuum. The limits and ranges of each area being
determined by the relative operating densities of the 100
vapor and liquid, the nature of the entrainment, and the 90
degree of separation required. � BO
When the mesh is installed with the pad vertical or >,
o
c
inclined, the maximum allowable velocity is generally used at ·c:; 70 153 mm (6") thick except as noted
Q)
0.67 times the allowable value for the horizontal position. i: 60 -----+--Air/Water System
UJ
� Ambient Conditions
::,
1i 50 ..,...-..,1---+-- 2.4 meters per second (8 feet per second
"'
Design Velocity o K=.085 (.280")
To allow for surges, variations in liquid load and pecu- 2 3 4 5 6 7 8 9 10
liarities in liquid particle size and physical properties, use: Droplet Size (microns)
Figure 4-19. Capture efficiency vs particle size for four types of
V 0 = 0.75 V,, ( 4-48) DEMISTER® knitted mesh mist eliminators. By permission, Otto H.
York Co., Inc.
for the design of new separators. When checking existing
vessels to accept wire mesh, some variation may have to be recovery efficiencies [see Figure 4-19]. Particles smaller
accepted to accommodate the fixed diameter condition, than this usually require two mesh pads or the fiber pack
but this is no great problem since the range of good oper- style discussed later. Carpenter [ 4,5] shows the calculated
ation is so broad. effect of decreasing particle size on percent entrainment
removed at various linear velocities. For water particles in
Efficiency air at atmospheric pressure, the 8µ particles are 99 per-
cent removed at 3.5 ft/sec, the 7µ al 5 ft/sec, and the 6µ
For most applications the efficiency will be 98-99 per- at 6.8 ft/sec. Excellent performance may be obtained in
cent plus as long as the range of operating velocity is most systems for velocities of 30% to 110% of calculated
observed. The typical performance curves for this type of values [35].
material are given in Figures 4-l 7B, 4-18, and 4-19. For
hydrocarbon liquid-natural gas system, guarantees are
made that not more than 0.1 gallon of liquid will remain Pressure Drop
in the gas stream per million cubic feet of gas. Special
designs using a 3-foot thick pad reduce radioactive Pressure drop through wire mesh units is usually very
entrainment to one part per billion [21]. low, in the order of I-inch water gauge for a 4-inch or 6-
For the average liquid process entrainment the mesh inch thick pad. For most pressure applications this is neg-
will remove particles down to 4 to 6 microns al 95%+ ligible. If solids are present in the particle stream, then
Mechanical Separations 251
solids build-up can become appreciable, and is usually the special situations have been placed at an angle to the hor-
guide or indicator for cleaning of the mesh. A 12-inch pad izontal, but these usually accumulate liquid in the lower
may require a 3-inch water drop. Figures 4-20 and 4-21 portion of the mesh. Since the material is not self-sup-
present the range of expected pressure drops for a spread porting in sizes much over 12 inches in diameter, it
of 3 to 1600 lb/hr-ft for liquid rates. Although this is for requires support bars at the point of location in the vessel.
2
air-water system at atmospheric pressure it will not vary In most instances it is wise to also install hold-down bars
much unless the physical properties of the vapor and liq- across the top of the mesh in accordance with manufac-
uid deviate appreciably from this system, in which case the turers' instructions as the material will tend to blow
general Fanning equation can be used to approximate upward with a sudden surge or pulsation of vapor in the
the pressure drop under the new conditions. Approxi- system. Many early installations made without the bars on
mate values based upon air-water tests suggest these rela- top were soon found ineffective due to blowout holes, and
tions [3]: wire particles were found in pipe and equipment down-
For the standard weave, 4 inches thick: stream of the installation. Figures 4-22 and 4-23 show a
typical installation arrangement in a vertical vessel. The
t.p = 0.2 V 02 p,, in. water ( 4-49) mesh is wired to the bottom support bars and the hold-
down on top.
For the low density weave (high through-put), 6 inches A few typical arrangements of mesh in vessels of various
thick: configurations are shown in Figure 4-24.
Note that in some units of Figure 4-24 the mesh diam-
( 4-50) eter is smaller than the vessel. This is necessary for best
Installation
5.o...------------.------.---,--..---,
The knitted mesh separator unit may be placed in a
pipe in which case a round flat rolled unit is usually used, 4.0.--------+----+---�-+-----
or it may be placed in a conventional vessel. Although the 3.0 .A. 3 GPM/Sq.Ft. (.12m"lminlm 2) t--+--+--+-------i
.A.
• 2 GPM/Sq.Ft. (.08m !minlm
2)
2
vessel may be horizontal or vertical, the mesh must always 2 0 • 1 GPM/Sq.Ft. (.04m /min!m 2)
3
.
be in a horizontal plane for best drainage. Some units in A
I
(5'1.01---------+-----+;=---l-4j----,i----J
10 ��.Bt--------t--�---rf--_.'!'-J'lill,,-,H-4 ..... �
� .71---------+----rl---+---f-++,f--,...--¥1-----1
"
� .5i----------t---,f--t---r--;--;:ft--,lll-,F---;
Entroinmut Load
lb1./(h<li1q. ft. Crou·Stclion) � .41---------+�_,_--��-=;:=.l,L--#---l-l--�
Appro1imate 3 o�
� .31------::...._--+�---r-lr"---.11.£--hl--l-t---f
1600
;:;
<,
I
I c- '/ I .21----------A---l'-4�+--"-l--�---l--+---#-l
"'
Q)
s:
o
' /. � v £ �----1---+----I
a: 0.1 >--------++....,____,,__
I L "� 0
� .OBt---------...<t-F----,.._+illl--
il.O I I ...., .... -t---1--t----i
L ,..... r-; I UJ
§.06t---------+---#--#+-il-----l---+----f
io.1 '../ w.051---------+-_.,.,._.,_ ,,..__ __ ___,
+--
f I
t-, 'I Generally Applicobl, 10 4• u1d- �.041---------+---�-#+----#--+---+-----I
o.. 0.5 6 .. Mtsh. ,.......
I a:
I ....... ''l-/ Battd on Co111po1if1 of Data Cl. .031----------+-------,,_-+-- __ --+---+-----<
froni S1vtrol Sytrcm1 IH,;,.9 -
"[J
j, " r----,..... '7 Difhrtnl Typn of lllnh.
<,
v: <, ·01.__------ � a � , � 5 � -- � a � . 2,----=o � . 3---::0 � . 4,---'
0.2 � r-, 'r--... -I
<,
<,
0. I <, r-, ;v I i K-Factor, \//[(pl - pv)/,c,.,]'''ft/sec (x 0.3048 = m/sec)
re so 70 /00
Sc.lptrficial Vtlocir1 1 Fut I Second
Figure 4-21. Typical wire mesh mist eliminator pressure drop curves
Figure 4-20. Typical pressure drop range for most wire mesh sepa- for one style of mesh at three different liquid loadings. Others follow
rators. similar pressure drop patterns. By pennission, Otto H. York Co., Inc.
252 Applied Process Design for Chemical and Petrochemical Plants
keep velocities low and not to force or carry the liquid
through to the downstream side of the mesh.
Example 4-5: Wire Mesh Entrainment Separator
Design a flash drum to separate liquid ethylene
entrainment for the following conditions:
Volume of vapor= 465 CFM @-l l0°F and 35 psig
Density of vapor= 0.30 lb/cu ft
Density of liquid ethylene = 33 lb/ cu ft
Allowable velocity for wire mesh:
Va=k¥
I P v
Figure 4-22. Typical installation of mesh strips in vertical vessel. Use, k = 0.35 for clean service, moderate liquid loading
Courtesy of Otto H. York Co., Inc.
Va= 0.35 � (33 - 0.3)/0.3
= 3.66 ft/sec, allowable loading velocity
Use, Vo= 0.75 Va
Design velocity:
V0 = 0.75(3.66) = 2.74 ft/sec
1/4" Dia. Skewtr Pin Required vessel cross-section area:
Welded to Grid
r" X 1/8" Cross Bar A= 465/ (60) (2.74) = 2.83 sq ft
Figure 4-23. Typical installation of wound mesh pads in vertical ves- Vessel diameter:
sel. Courtesy of Metal Textile Corp., Bulletin ME 9-58.
� 2·8 � 4
operating efficiency under the system conditions, and D = ( ) = 1.898 = I' -11"
applies particularly when using an existing vessel.
When placing mesh in small diameter vessels it is Try: 2'-0" I.D. vessel
important to discount the area taken up by the support Deduct 4 inches from effective diameter for 2-inch sup-
ring before determining the operating velocity of the port ring inside.
unit. For small 6-, 8-, and 12-inch vessels (such as in-line,
pipe-with-mesh units) it is usual practice to use 6- or 8- 24" - 4" = 20"
inch thickness of mesh for peak performance.
Net area:
Provide at least 6- to 12-inch minimum (preferably 18-
inch min.) disengaging space ahead of the inlet face of 7t (20) 2
the mesh, i.e., above any inlet nozzle bringing the liquid- A= =2.18sqft
carrying vapors to the vessel, or above any liquid surface 4 (144)
held in the vessel. Leave 12-inch minimum of disengaging ( 2·83)
space above the mesh before the vapors enter the vessel Actual velocity at ring: 2. 74 2.18 = 3.56 ft I sec
vapor exit connection. The mesh may be installed in hor-
izontal, vertical or slanting positions in circular, rectangu- This is 97% of maximum allowable design, too high.
lar or spherical vessels. For locations where the liquid Second Try:
drains vertically through the mesh pad perpendicular or Increase diameter to next standard dimension, 2 ft, 6-
angular to its thickness dimension, care must be taken to in. Although intermediate diameters could have been
Mechanical Separations 253
EVAPORATO�S HORIZONTAL SEPARATORS HORIZONTAL SEPARATORS FRACTIONATIN6 rDWERS
H f Ir I I 11 111 I, ' , ,
'
...,,. r' r »;
f11th,
�--
OPEN SEPARATORS IN-LINE GAS SCRUBBERS Oil-GAS SEPARATORS OVER-SIZE VESSEL
Figure 4-24. Typical mesh installations in process equipment. Courtesy of Metal Textile Corp., Bulletin ME-7.
selected, the heads normally available for such vessels run Use stainless 304 mesh due to low temperature opera-
in 6-inch increments ( either O.D. or I.D.). tion. Carbon steel is too brittle in wire form at this tem-
Net inside diameter at support ring: perature.
The check or specification form of Figure 4-2fi is nec-
30" O.D. - 4" - 3/4" = 25 1/4" essary and helpful when inquiry.ing wire mesh entrain-
ment units, either as the mesh alone, or as a complete
Note that vessel wall assumed %-inch thick. turnkey unit including vessel.
Net area = 3.46 sq ft For services where solids are present or evaporation of
droplets on the mesh might leave a solid crust, it is usual
2 83 practice to install sprays above or below the mesh to cover
Actual velocity at ring: · (2. 74) = 2. 24 ft/ sec
3.46 the unit with water (or suitable solvent) on scheduled (or
necessary) operating times, as the plugging builds up.
Percent design velocity: 2.24(100)/3.66 = 61.3%. This This is checked by a manometer or other differential pres-
is acceptable operating point. sure meter placed with taps on the top and bottom side of
Note that if 28-inch O.D. X %-inch wall pipe is available the mesh installation.
this could be used with weld cap ends, or dished heads. A few case examples for guidance include:
The percent design velocity would be = 71.8%.
This is also an acceptable design.
Pressure drop is in the order of 0.1 inch to 0.5 inches • 2-3% caustic solution with 10% sodium carbonate.
water. This condition might plug the wire mesh. Sprays
would be recommended.
Notes: Since this vessel will operate as a flash drum with
a iiquid level at approximately Yi of its height up from • Raw river water. This presents no plugging problem
bottom, place the inlet at about center of vessel. See Fig- • Light hydrocarbon mist. This presents no plugging
ure 4-25. problem
254 Applied Process Design for Chemical and Petrochemical Plants
.. Wire �tro.in!';:i11nt !�esh S!lecif1cat1on9
Job No.--------
p ... , ... ,, A. A;,pl1Mtion Service
••••
u,.itPriu
e./MNo. _ 1. Source or :;:ntrain'Dent:
DRUII OR TANK SP!CIFICA TIOMS N•. U•lt1 J
.• _ ... _ o- .J 2. Oncratlnf' Conditions: Give (1) Jior-�al (2) lfaxirnum
Su'f'lo:•_p/�!._�o.,,_::- -,..,d ...f.,� .... -..a.;,a-
SIH 30" o. o. ,c 10'-o" ilen• L,;,e T)'P•----------------1 (3) I-'.inia,u,-,,, where possible
Te·.-.perature ---------
Pr0ssure
Vapor Ph,1,se
Flow R:lte --------
*Velocity
Density -------- at operating conditions
!�olecular ;ie1!rht
Co-npos1t1o!l or li'ature of Phase---------
Liquid Entr:,.in�ent Phtlse
DISIGN DATA
Op•rath11 Po, •• ,_ ;5 PSl..f...__ O,•Ntl11e r.... - //0 "P. ',uant1ty (if kno,m): -------------
D•1l1n Prn1we lop PSI L_ 0.1t1,. T--,, -139 "F. Density:
Cod• AJ ME s,... YfJ Letliel c.,11,. �""'�--- o-11ty el C...Mflot1 _..J.L..Lhlcv. tt r � ;f �� ;t;!.n-s � i-o-n- ,---------------
M111u;al11 Sh.II Law �•�«•OCt'i!CC r1t«t/ HM41 t.ew,-�, Jl«•J S...en1 C•r'•"" ,j;•/
Lhllnf; Metel No R11 ....... •rPle,tlc __ = ,.,.•-------------1
B,1c.k IV• Ce91-1_..:;M;,; • ---r-4 Composition or t:ature of Entrainment: ------
h11u11al e.,,.,..,1 ... All•-nce � ,! .,. S.11 s..,.,u,.,_,.y�,.s'---- '"'•lwtl•: Cifr •• D Nt, a .. , -11o•P
NOZZLl!I ......... Droplet Si?.es or distribution (if known):
s.,..1c• N.. R9<11'tl!. Slae ,.,, •• c1 ••• '•cl"' Solids Content (Compoaition Md Quantity): _
....
'"'"' ". I.SO ,a T,/ A Dissolved:
v ..... o .. ,
6-
'lTJ
I.So
Llquitl! Oi.t .e" ,.ro A!TJ "'
0,.1,, iluspended:
s.ter., v.1 .... I .... ,so RTJ " 3. Perfor:1iance
u.'
Ln11I C-nl
�7J
JI•
.... 2 In .... 0 c.c...-t;,. " Allo�a;1e Tot�l Se�arator Pressure Dro�:
,,. .. -r.,
£
I
,
Ge,• c1 ••• :I, ,i" JSO A!TJ ...
"'""""'• .. . .. ,s. A!TJ N Allo..,able ���esh Pressure Drop:
H•oh J,.c,.,c/ ,,Q/o.;-,,,,
Low Lc'll"c/ .&Jl11r- �· IS't> IPTJ r Al10C1able Entrain,nent:
IIIMAHS r1i:oah Thicnless Recolll!Dended:
lAl,·,�NJ�"''- ,',o be .S'/ondlordll'l•d.-• 1.•,1,111·cK·N>-,h.,-,.-../ r� ,.,...,., ·�;,/,1 ,L-.1. B, Construction and Installation
P,o�··d& .:,u--11r'J- o,.,J ,',o-h#fd .. do .,t;,. --•,I. ,.�
•, lc"i,,•4 11 ..... , .... *Di2,,oeter, I.DI
o ... I I I I I
P.O. T•:---------------------------- Construction i:·iaterial:
*Position (Horizontal, Vertical, Inclined):
Figure 4-25. Specification design sheet for separator using wire
mesh. *Shape (Circul�r, Square, etc.):
Type (Ev<1.por.�tor, Still, Drum, etc,):
Existing or Proposed:
• Heavy oil with suspended matter. This might plug. A 2. Entrain:nent J.!esh
light oil or solvent spray would be recommended for Construction !�ter1al
flushing the mesh.
Separator Y.esh ------��
&.lpport Grid
Installation ,!ethod (Di!nensions)
Fiber Beds/Pads Impingement Eliminators
Vessel Open End:
The use of fiber packing held between wire mesh con- �'.anhole (size):
taining screens is best applied in the very low micron c. Special Conditions:
range, generally 0.1 to > 3 microns with recoveries of *Assumes vessel size �ixed prior to mesh 1nau1ry
entrained liquid of up to 99.97% (by weight). Figures 4- Figure 4-26. Wire entrainment mesh specifications.
27A, B, and C illustrate the design concept and its corre-
sponding data table indicates expected performance. The
fibers used mean the bed packing can be fabricated from removed by direct interception, inertial impaction, and
fine glass, polypropylene fibers, or can be selected to be Brownian capture.
the most resistant to the liquid mist entering the unit The design rating for this equipment is best selected by
from corrosive plant operations such as sulfuric acid, the manufacturers for each application.
chlorine, nitric acid, ammonia scrubbing for sulfur oxides The concept of removal of entrained liquid particle is
control, and many others. The entrained particles are essentially the same as for wire mesh designs, except the
Mechanical Separations 255
clean gas
r,,
- - .,
part.cte-laoen gas
Materials of construction
Packing of York-Fiberbed high efficiency mist eliminators consists of
ceramic, glass, polypropylene, fluoropolymer fibers. Cages and
frames are fabricated from all stainless steels and other weldable Collection
alloys as well as FRP. KOCH Primary Efficiency Element
type Collection Particle SJZe Efficiency µre�re Bad
Mechanism (Microns) (%) Drop Velocity
Figure 4-27A. Details of a cylindrical York-Fiberbed® mist eliminator. (lnche.WG) (f't/Mln)
Courtesy of Otto H. York Co., Inc., Bullet in 558. BD Brownian :>3 Es,enttally 100 2-20 5-40
Up 1099.95
<3
Diffusion
>3 Essen holly 100
IC Impaction 7--9 250-
450
particle size removed may be much smaller. Just as for 1-3 05-99 1-
other types of mist eliminators, the performance is affect- >J Essontial ly 100
ed by the properties of the liquid particles, entraining gas, IP impaction 1·3 85--97 5-7 400
500
temperature, pressure, liquid viscosity, particle size distri- 05-1 50-85
bution of entrained material and the quantity of total IS Impaction '>3 EssenllOlly 100 ,_ 2 �00-
entrainment, and the desired process removal require- ,:J 15-30 500
ment. Some designs of these units provide excellent per- NOlE: inoe � lC, IP and IS operate prirnONtv ov lmpoci,on 1
formance removal efficiencies at a wide range of rates dbov&collEK)t,on elf101enc!e$ c!•oi:i off ct Qr.l'i II� below' Obovl 75 ot
collf:lci
deilgnrol19Sond d�nd on t"8specmc grovl"1 ol
liQukl
11 0
c,
Fleklf!be 1ype &D. Normoltf ,:ynl"l(fr\col In
and
(turndown), even at low gas rates. Wide vot1ety of mal'eflal ond ,lzt1� wilt po:::l<ad element 01& Mo:1o J
Pressure drop is usually low depending on many fac- sanes
tors, but can be expected in the range of 2 to 20 inches of AJIIO ovo11oble cs wound bedi [Marie II or 1111 tor lower inlti al cosr encl Mt
of repocldr,g. ond w,111 eQi.ll\lCllent cotlecflcn 91!/c ncv o! '°' or
water [33). lower pre1.1ure d1'oP cvallobl, Jr, o
F\e1111ber4' 1ype IC: NormoQy cyti1'dt1eol In :110p,;, o
vcrfefy or malerlcls and 11ZBs
F,exlflber" 11,-palPQlld IS: ormalfy rei;:fo1'1Q'Jklr In shape OJ'l<:I ovo1!0l)lg
Ba!Jle Type Impingement In vorlou, rneltll1.
There are many baffle type impingement separators. Figure 4-278. Fiber-pack® mist eliminator pack separators. By per-
The efficiency of operation for entrainment is entirely a mission, Koch Engineering Co., Inc. Note that other manufacturers
function of the contacting action inside the particular have basically the same concept; however, the identification of
types are peculiar to each.
unit. There are no general performance equations which
will predict performance for this type of unit; therefore
manufacturers' performance data and recommendations liquid droplets run down on the plate surfaces counter-
should be used. A few of the many available units are current to the up-flowing gas stream. See Reference [59]
shown in Figures 4-28 to 4-31. Many use the Chevron-style for performance study.
vertical plates as shown in Figures 4-17 A and 4-30. Spacing of the plates and their angles is a part of the
design using the manufacturers' data. Multiple pass designs
Baffles (Chevrons/Vanes) can result in higher recovery efficiencies. The units can be
designed/installed for vertical or horizontal flow.
One of the common impingement plate assemblies is Some of the same physical properties of the liquid and
of the Chevron "zig-zag" style of Figures 4-17 A and 4-30. gas phases as well as temperature and pressure and the
This style of impact separation device will tolerate higher amount of entrained liquids ( or solids if present) and the
gas velocities, high liquid loading, viscous liquids, reason- expected particle size and its distribution control the
able solids, relatively low pressure drops. The collected design and performance of these units also.
256 Applied Process Design for Chemical and Petrochemical Plants
Figure 4-27C. Typical fiberbed mist eliminators are available in both
candle and panel configurations. By permission, Otto H. York Co., Inc.
For preliminary selection: Figure 4-28. Wall-wiping centrifugal type separator. Courtesy of
Wright-Austin Co.
Vo= k[(P1 - p,)/Pvl112 ( 4-51)
p, = vapor density, lb/cu ft at actual conditions through a surface contact medium such as excelsior, hay,
PL = liquid density, lb/cu ft at actual conditions cotton or wool bats, or cartridges of fibers similar in
k = 0.40 for up-flow at 0.65 for horizontal flow, for estimating nature and weave to those of Table 4-12A and -12B. Figure
4-32 illustrates some of these types.
Required flow area estimate only,
Efficiency
A = (ACFS)/V0, sq ft
A= area sq ft The efficiency of this type of unit varies, and is a func-
ACFS = actual flow, cu ft/ sec tion of the effectiveness of the impingement baffling
V 0 = design velocity, ft/sec arrangement. About 70% of separator applications can
use the line-type unit; the other 30% require the vessel
Generally, this style of unit will remove particles of 12 construction. The preference of the designer and prob-
to 15 microns efficiently. The typical droplet separator is lems of the plant operator are important in the final selec-
shown for an air-water system in Figure 4-17 A. This will tion of a unit to fit a separation application.
vary for other systems with other physical properties. The The efficiency for removal of liquid and solid sus-
variations in capacity (turndown) handled by these units pended particles is 97-99%+ when handling 15-micron
is in the range of 3 to 6 times the low to maximum flow, particles and larger. For steam service, a typical case
based on k values (33]. would be 90% quality entering steam with 99.9 percent
A liquid-liquid separator used for removing small, usu- quality leaving.
ally 2% or less, quantities of one immiscible liquid from Some units will maintain a reasonable efficiency of sep-
another is termed a coalescer. These units are not gravity aration over a range of 60%-120% of normal perfor-
settlers, but agglomerate the smaller liquid by passing mance rating while other types will not. This flexibility is
Mechanical Separations 257
.lli-Pha.
.. ScrubbinQ Separation
Liquid
Liquid
Outlel
High Flow Four th Si•th
(Top Oulltl Mist Ellroctor Phase Phase
Optional)
Access E•ponsion Fifth
OpeninQ Spoce Phase
Low Flow Third Fourth
Mist Extractor Phase Phase
E•ponsion Third
Space Phase
Centrifugal Second
Separator ond
Drain from Liquid Scrubbina Phase
CenlrifuQol--�---4--lll
Separator Expansion Phase
..
First
Space
Oil SforoQe Contractor Tubes
for SurQes First
and HiQh Gos Liquid Scrubbing Phase
Flows Inlet Section
Figure 4-29. Multiphase gas cleaner. Courtesy of
Blaw-Knox Co.
Oil and Dusi
Resenoir
-
Blow Down-
Numerous Tube
Passages ill Second
/
Cylindrlcol Baffle
Stripping One of Several
Louvre Open inQS
Vanes in First Cytindrtcol
Baffle
Baffle Drains to
Return Separated
Oil to Oil Body
Inlet Flow
Diverter --"-'--JU-
Over Oil and
Gas Intel
Gos Releo,e
- Riser
Back Pressure
, Gos Control
Valve
""-condensate Oil Outlet
Outlet Valve -,
Drain
Figure 4-30. Impingement separator. Courtesy of Peerless Manufac-
turing Co. Figure 4-31. Combination separator. Courtesy of National Tank Co.
258 Applied Process Design for Chemical and Petrochemical Plants
EMULSION OF PRODUCT INLET OUTLET 3. Note that some units use pipe line size for the sepa-
WATER & SOLIDS COALESCING
MEDIA
rator size designation, others do not.
4. From the system operating pressure, establish the pres-
sure rating designation for the separator selection.
5. Note that most separators for pressure system opera-
REMOVABLE
HEAD tions are fabricated according to the ASME code.
6. Specify special features and materials of construc-
tion, such as alloy or nonferrous impingement parts,
WATER or entire vessel if affected by process vapor and liq-
ACCUMULATOR
SWING BOLTS DRAIN 5UMP uid. Specify special liquid reservoir at base of unit if
necessary for system operations. Line units normally
have dump traps or liquid outlet of separator, while
vessel type often use some type ofliquid level control.
7. Specification sheet: see Figure 4-33.
FLOW LEGEND
� CONTAMINATED PRODUCT
�'-:--.-;,i WATER
¢=:J CLEAN DRY PRODUCT
Figure 4-32. Typical coalescer unit. By permission, Facet Enterpris-
es, Inc., Industrial Div.
Bartle :r,pe Separator Spec1r1cationa
Separator .lppl1cat1on1 (Give Sarrtce) --------
very peculiar lo the internal design of the unit. Some Dea1gn Operating Conditions:
units are guaranteed to reduce mechanical entrainment Maln Stream l"lov Rate __ Sp. Gr. or Mol. Wt. __
loss to less than 0.1 gallon per million standard cubic feet Entrained Material rate(U Jmovn)Source or entra1111111ent __
of entraining gas. Min. Preaaure __ psi (g) or (a), Jlax. Temp, __ or.
Max. Pressure __ pe1 (g) or (a)
Entrained Particle a1ze (meah)(H1crona)
Pressure Drop
Veaael 3pectr1cat1ona:
Pressure drop in most units of this general design is Dea1gn Preaaure __ PSI __ Dea1gn Temp. __ or.
very low, being in the order of 0.1 to 3 psi. Coile: .lPI-.1.SME -- .lBIIE 1949 Ed. __ .I.SHE 1950 m. --
State Code __ ; Hon-Code __ , Cuatomei's Spec. __
X-Ra7 __ Stress Rel1et' __
How to Specify
Corrosion allovande ----
D1mena1ons: __ •o.D. x __ • long bend line to bend llne
Manufacturers' catalogs are usually available and com-
plete with capacity tables for the selection of a unit size. Baae SUpport ----
However, it is good practice lo have this selection checked H1at Ex.tractor: , Mat'l. ot Conatructlon _
by the manufacturer whenever conditions will allow. This Connect1ona
avoids misunderstandings and misinterpretations of the 1. Gae inlet and outlet:(S1ze, .I.SA. pressure rat1ne;, tuie
catalog, thereby assuring a better selection for the separa- rlanp;e)
tion operation, and at the same time the experience of 2. Uqu1d outiet ----
the manufacturer can be used to advantage. 3. Uquld Level aage ----
With a manufacturer's catalog available: 4. Uquid Level Control ----
5. Pressure Gsuge ----
6. Reller Valve ----
1. Establish the normal, maximum, and minimum gas
flow for the system where the unit will operate. This 7. Bursting Dlac ----
is usually in standard cubic feet per minute, per 8. High Level Alarm----
hour or per day. Note the catalog units carefully, and 9. Low Level Alarm ----
also that the reference standard temperature is usu- 10. Thermometer ----
ally 60°F for gas or vapor flow. 11. F.qual1zer ----
2. Use the rating selection charts or tables as per cata- 12. Drain ----
13. Others: ( apeei:l'Y)
log instructions. For specific gravity or molecular
weight different than the charts or tables, a correc- 6pec1a1 Features:
tion factor is usually designated and should be used. Figure 4-33. Baffle-type separator specifications.
Mechanical Separations 259
Note that these units should not be connected in lines Efficiency
larger than their pipe inlet, since inlet velocity conditions
are very important, the swaging down or reduction tends The efficiency of centrifugal units is:
to produce a jet effect by the gas upon the mist elimina-
tor unit. This may erode the unit and cause other erratic
performance _ Type Efficiency Range _
High Velocity 99% or higher, of entering liquid.
Stationary Vanes Residual entrainment 1 ppm or less
Dry-Packed Imf;ingement .Beds Cyclone 70-85% for LO micron, 99% for
40 micron and larger. For high
entrainment, efficiency increases
Although this type of unit is not used as frequently as with concentration.
98% for agglomerating particles
most of the others discussed, it does have some specific Rotary ===================:::::=:::====�=======
applications in sulfuric acid mist removal and similar very
difficult. applications. The unit con sis Ls of a bed of gran u-
lar particles or ceramic packing, sometimes graduated in Cyclone Separators
size, operating dry as far as external liquid application to
aid in the separation. The superficial velocities of 0.5 to 8 The cyclone »r= unit is well recognized and accept-
feet per seccnd through the unit are rather low for most ed in a wide variety of applications from steam con-
separators therefore the vessels become large. Due to the densate lo dusts from kilns. In this unit the carrier gas
packed heights of 2 feet (min.) and higher, the pressure and suspended particles enter tangentially or volutely
drop can be appreciable. Particle removal may be 0.5 Lo 5 into a cylindrical or conical body section of the unit,
microns al 99% efficiency for a good design. These units then spiral downward forcing the heavier suspended
will plug on dust service and must be back washed to matter against the walls. Solids tend to slide down the
regain operability at reasonable pressure drops. wall while liquid particles wet the wall, form a running
film and are removed at the bottom. Figure 4-41 gives a
good typical cyclone arrangement, but this is by no
Centrifugal Separators means the highest efficiency or best design. References
[ 43,45,51] provide good design and performance
analysis.
Centrifugal separators utilize centrifugal action for the Some commercial units are shown in Figures 4-42 to 4-45.
separation of materials of different densities and phases. The zone of most efficient separation is in the conical
They are built in (a) stationary and (b) rotary types. Vari- region designated by dimension Z; in Figure 4-41. The
ous modifications of stationary units are used more than larger particles have already been thrown against the wall
any other kind for separation problems. The cost is mod- before the outlet was reached. The finer particles are
erate; it is simple in construction, and is reasonably flexi- thrown out in the inner vortex as the direction of motion
ble in service, being useful for gas-liquid or gas-solid sys- is reversed. Here, the relative velocity difference between
tems. In addition Lo serving as finishing separators the particle and the carrier is the greatesL for any point in
centrifugal units are also used to take a "rough cut" into a the separator. Although the tangential velocity compo-
separation problem. They may be followed by some addi- nent predominates throughout the cyclone, the axial
tional unit of special cyclone action or filtration through velocity prevails in the turbulent center. Van Dongen and
woven cloth pads, etc., Lo completely remove last traces of ter Linden [20] measured pressure patterns in a typical
entrained particles.
cyclone and found the lowest total pressure at the
extreme bottom point of the cone, even lower than al the
gas exhaust. Their pressure profiles indicate considerable
Stationary Vane eddy or secondary gas movement in the unit near the ver-
tical axis.
The stationary vane type is quite popular and adapts to
many applications. It is used in vessels or pipe lines as Particle Size Separation
illustrated in Figures 4-34 to 4-40. They are usually of high
efficiency for both liquid and solid particles such as rust, The theoretical minimum diameter particle to be sep-
scale, dirt, etc. When the system is dry with dust a special arated in a cyclone of the basic type given by Figure 4-41
design is used. is given by the relation of Rosin [ 13].
260 Applied Process Design for Chemical and Petrochemical Plants
D = ( 4- 52)
p
(Min.)
N, has been found to be about 5 turns of the gas stream
in the unit, and is considered somewhat conservative.
When re-entrainment takes place, N 1 may drop to 1.0 or Figure 4-35. Scrubber
2.0. The API study presents an excellent survey of cyclone with spray ring as
dust collectors [7]. alternate arrangement
for Figure 4-34. Cour-
Solid Particle Cyclone Design tesy of Centrifix Corp.
Following the general dimensional relations of the typ-
ical cyclone as shown in Figure 4-41, the following gener- Cleon Air, Steam
al guides apply. This cyclone is better suited to solid par- or Gos---
ticles removal than liquid droplets. To avoid
re-entrainment it is important to keep the separated
material from entering the center vortex of the unit. Solid
particles generally slide down the walls with sufficient ver-
tical velocity to avoid re-entrainment.
a. Select outlet diameter to give gas velocity out not
exceeding 600 ft per min. Bear in mind that higher
velocities can be used in special designs.
Figure 4-36. Line-type centrifugal separator. Courtesy of V. D.
b. Due to the usual conditions of limiting pressure Anderson Co.
drop, entrance velocities range from 1000 to 4000 ft
per min. 3000 fpm is good average, although veloci-
ties to 6000 fpm are used in some applications.
Oomnllow Ur.if
Figure 4-37. Centrifugal separa-
tor applications. By permission,
Centrifix Corp.
Figure 4-38. Centrifugal separa-
tor applications. By permission,
Centrifix Corp.
Figure 4-39. Centrifugal separa-
Figure 4-34. Scrubber with internal liquid feed. Courtesy of Centrifix tor applications. By permission,
Corp. Centrifix Corp.
Mechanical Separations 261
c. Select cylindrical shell diameter, D with two consid- Efficiency
0
erations in mind:
Typical estimating efficiencies are given in Figures 4-46
• Large diameter reduces pressure drop and 4-47. Note the curves indicate how much dust of each
• Small diameter has higher collection efficiency for particle size will be collected. The efficiency increases as
the same entrance conditions and pressure drop. the pressure drop increases; that is, a smaller separator
might have a higher efficiency due to the higher gas
d. The length of the inverted cone section, Zc, is critical, velocities and increased resistance than a larger unit for
although there is no uniformity in actual practice. The the same gas flow. For example, there are several curves
dimensions suggested in Figure 4-41 are average. of the typical shape of Figure 4-46, with each curve for a
definite resistance to flow through the unit.
lnltl lnltl The pressure drop in a typical cyclone is usually
i rarely exceeds 10 inches water for single units. The API
\nit! between 0.5 and 8 inches of water. It can be larger, but
study [7] summarizes the various factors. Lapp le [ 13, 16]
gives calculation equations, but in general the most reli-
Oulltl able pressure drop information is obtained from the man-
ufacturer.
Figure 4-40. Centrifugal separator applications. By permission, Cen- Here is how the pressure drop may be estimated.
trlflx Corp.
For the typical cyclone of Figure 4-41 [13]
A A (a) Inlet velocity head based on inlet area:
L _ _j
hui = 0.003p v( 2 (4-53)
- I I
Gas
In
I
__ .J. __ ..L
Sc I
�-D,-..JT I I -.. aT-l'AH
W1= Dc/4 Le DUIT CHAHNll
D,• Dc/2 I
He= Dc/2 I I ---- IHIIT ro•
oun lADIN GASU
Lc•2 De ---De-- I
Sc• Dc/8 I I
Zc•2 De 1-------J-t
Jc• Arbitrary, I
Usually Dc/4 I
I
I
I
I
I
fc
I
I
I
I
I
Section A-A I I
--1..
Jc
Dust J Out
Figure 4-41. Cyclone separator proportions-dust systems. By per-
mission, Perry, J. H., Chemical Engineers Handbook, 3rd Ed., Figure 4-42. Van Tongeran dust shave-off design. Courtesy of Buell
McGraw-Hill Company, 1950. Engineering Co.
262 Applied Process Design for Chemical and Petrochemical Plants
(b) Internal cyclone friction loss:
(4-54)
( 4- 55)
Helical
Inlet K has been found to be constant at 3.2 for cyclones
Cone with an involute entrance
W/De = 1/8 to 3/8
He/De= 1.0
Figure 4-43. Helical entry
cyclone. Courtesy of The Ducon De/De= 1/4 to 3/4
Co., Inc.
For the typical cyclone of Figure 4-41 with tangential
inlet:
KWiHc
(4-56)
Oust D 2
c
K = 16.0
Fev = 8.0
-NOTE-
BY-PASS IS OPTIONAL., DUE TO
LOADING AND WHEN USED IS
PROPORTIONAL TO THE FlOW
THRU THE IJNIT.
Figure 4-44. Involute entry
cyclone. By permission, American
Blower Div. American Radiator
and Standard Sanitary Corp. Figure 4-45. Stationary vane centrifugal separator. Courtesy of Centrifix Corp.
Mechanical Separations 263
If inlet vane is formed with inlet connection: Areas: Gas Velocity Velocity Head*
-----
Inlet duct: 1.398 sq ft 47.7 ft/sec 0.50 in. water
K = 7.5
Cyclone inlet: 2.0 sq ft 33.33 ft/sec 0.25 in. water
Cyclone exit duct: 3.14 sq ft 21.2 ft/sec 0.10 in. water
Example 4-6: Cyclone System Pressure Drop
02
8 Vclocity head, inches water= V /(16) (10 6), Vr, = ft/min
A cyclone system is to be installed as a part of a bagging Friction Loss CD to ®
operation. The unit is shown in Figure 4-48. Determine
the head required for purchase of the fan. The conditions NRc = 398,000 f = 0.0038
are:
Air volume: 4000 cu ft per min of air at 70°F 4fL 4 (.0038) (18)
No. Vel. I-Id. 0.204vel. head
Air density: 0.075 lb/ cu ft D (16/12)
100
90
�� __ :_=�-t---=-�==-; _ _J_�
80
_L__ _ __ L _ __ J_ ; __ -� __ _ I
70 _ -C _
>- l
u I '
z '. J__ _L_ --- 1----+- -
w
u 60 ---j-- --
.:;:: I I : I I I : '
..... -- ----l------t---------------1--_;____
w 50 --- . -�----<
.... . ' _j_ I I :
z
�
�
w �o
� � ��
u -- --+�:-=�. -----_ - ---±- -TI-Cl----:-- ,.[J , .-l-V-. -C?,_ :-C ITY _:_------i-<
"' ... --+ -
w
30 ..
_-r_r---+---- ---- -
20 1
10 ------->----+--
PARTICLE SIZE-MICRONS
0
c 5 10 15 10 15 30 35 40
Figure 4-46. General efficiency curves, applies specifically to helical entry cyclone dust separators. Courtesy of The Ducon Co.
100 -
-
90
I
80 v """
f-
z 70 ./ -
ul »>
u
a: /
"'60 ---
IL I /
I l
>- /
li 50 /
"' u I / -\...--- --- I ---'----· I
;;:
"- 40 v . � �-
ul ' i
z / .. --
0 1� i
;:: / I i
td 30 v - ---- i COLLECTION EFFICIENCY
� / I I I - -- -�-- __ VS
TERMNAL VELOCiTY
U 2!> v --:------ -- -- - TT_T_
I I
20
.3 .4 .!I .e :1.s 1.0 1.5 2.0 3.0 4.0 50 6.0 W 8.0 10 15 20 30 40 50 60 70 80 IOO 150 «>0 300 400
TERMINAL VELOCITY - INCHES PER MINUTE
Figure 4-47. General efficiency curve applies specifically to involute entry cyclone dust separators. Courtesy of American Blower Div., Amer-
ican Radiator and Standard Sanitary Corp.
264 Applied Process Design for Chemical and Petrochemical Plants
18° Liquid Cyclone- Type Separator
I·
<D The unit shown in Figure 4-49 has been used in many
16" Duct
lnle1 ,--1-------'�==�--..,...--,--,-,---'�-!--,---,
->, process applications with a variety of modifications
�-i-----------...--1 [ 18, 19,20]. It is effective in liquid entrainment separation,
Fan Discharge
66.67 cu. ft./sec. but is not recommended for solid particles due to the
arrangement of the bottom and outlet. The flat bottom
plate serves as a protection to the developing liquid sur-
face below. This prevents re-entrainment. In place of the
plate a vortex breaker type using vertical cross plates of 4-
inch to 12-inch depth also is used, (Also see Reference
[58] .) The inlet gas connection is placed above the outlet
Nolt: This is Not Drawn dip pipe by maintaining dimension of only a few inches at
to Scale.
point 4. In this type unit some liquid will creep up the
walls as the inlet velocity increases.
Figure 4-48. Pressure drop for cyclone separator system. Adapted
by permission, Lapple, C. E., Fluid and Particle Dynamics, 1st Ed., In order to handle higher loads, the liquid baffle is
University of Delaware, 1954. placed at the top to collect liquid and cause it to drop
back down through the gas body. If the baffle is omitted,
the liquid will run down the outlet pipe and be swept into
Loss= (0.204) (.5) = 0.102 in. water
the outlet nozzle by the outgoing gas as shown in Figure
Friction Loss ® to ® : 4-50B. Figure 4--50 and 4-51 show several alternate
Assume as 1 vel. head (conservative) entrance and exit details. The unit with a tangential entry
is 30%-60% more efficient than one with only a turned-
down 90° elbow in the center.
Friction loss = (1) (.50) = 0.50 in. water
If the design of Figure 4-41 is used for liquid-vapor sep-
aration at moderately high liquid loads, the liquid sliding
Friction Loss ® to (D (thru cyclone):
down the walls in sheets and ripples has somewhat of a
tendency to be torn off from the rotating liquid and
KW.I-I 5 2 become re-entrained in the upward gas movement.
' c (1 ) (l) ( ) = 8.0 vel. heads
D 2 (2)2
e
Liquid Cyclone Design (Based on air-toater at atmospheric
pressure) Figure 4-49
Friction loss = 8.0(0.25) = 2.0 in. water
Friction Loss © to ® : For maximum liquid in outlet vapor of 4 weight per-
cent based on incoming liquid to separator: Figure 4-49.
NRc = 280,000, f = 0.004
a. Select inlet pipe size to give vapor velocity at inlet of
100 to 400 ft per second for tangential pipe inlet.
4fL (4) (.004) (4.5) b. Select separator diameter to give velocity of 0.02 to
No. ve I I . 1ea s = - = ------
d
0 2 0.2 (max.) times the inlet velocity. At 400 feet/sec-
= . 036 vel. head
ond pipe velocity the separator velocity should be
0.018 to 0.03 times the pipe velocity. At 130 feet/sec-
Loss = 0.036(.10) = 0.0036 in. water
ond pipe velocity the separator velocity should be
0.15 to 0.2 times the pipe velocity.
Since the unit exhausts to atmosphere with no addi-
tional restrictions, the total pressure drop is: c. Establish dimensions from typical unit of Figure 4-
49. Always evaluate the expected performance in
terms of the final design, adjusting vertical dimen-
ti.P (total) = sions to avoid gas whipping on liquid films or
Friction loss + downstream vel. head at®- upstream vel. head droplets. Do not direct inlet gas toward an outlet.
= (0.102 + 0.50 + 2.0 + 0.0036) + O* - 0.50
ti.P (total) = 2.6056 + 0 -- 0.50 = 2.10 in. water Place manway on same side of vessel as tangential
inlet.
*Note that point (5) is at atmospheric pressure and the velocity head is d. Pressure drop is essentially negligible for the average
zero; however, if there had been a back pressure or resistance at this conditions of use. Some estimate of entrance and
point before discharging it would have to be added in. exit losses can be made by fluid flow techniques, and
Mechanical Separations 265
c 1
�---;_-L- ,c;...._,.;,...;.._--=-_,_-_...,.,f
c
·e
-N Outlet Dip Pipe
� CD
a
s @) Tangential to
a shell wall
�
Inlet
•4-·-
(Also Dtsigned lo Wrap
"'t-"T"T.,-:r�-t
c
·e 90° lo 180° Araund Vt11tl
� 0
-N lo glH Tangential Inlet).
0
.., Figure 4-51. Separator inlets for liquid-vapor service .
a
:::,.
a � Clearance about 1112"
-I
s -- -- , ----- Depending on Liqaid Load
[i]
1 The Webre design as tested by Pollock and Work [14]
ffi About 6" AboH Liquid Ltwel showed (Figure 4-50C) that internal action in the separa-
Maintain Liquid Lent 4" to 12" tor was responsible for some of the entrainment, particu-
Liquid�Ou! Mini111u111 AboH Liquid Out Nozzle
larly liquid creep up the vessel walls.
IZI 2" Wide Ring Around l11id1 af The performance of this unit correlated for several dif-
V1111I , Alternate Dtsign to Baffle ferent types of particle distribution by [14]:
©
© @® Vapor Outlet hos Pronn ( 4-58)
Acceptable whn Stopped at
Thu Appro1i111ate Positions.
a = 2 for Webre unit
2
@ Liquid Surface Protection Plott, L,. = entrainment, lb liquid/min/ft of inlet
2
1101 b1 Perforated.If Cron-Plate V' = vapor vel. entering, lb/min/ft of inlet
Vortu Brtoktr Uud in Platt of L 1 = liquid entering, lb/min/ft of inlet
2
Flot Plall @, Place 10 Portion
i1 Both in ond out of Liquid Ln1I.
a, b, c, constants associated with the type and physical con-
Figure 4-49. Centrifugal liquid separator. ditions of the system. For the unit of Reference [14]:
b = 1.85 and c = 0.00643
""" '"'"' '"'LJ - Liquid-Solids Cyclone (Hydrocyclones) Separators
Nonie Flush
Inlet
(Tonqenliall
Li ��� t t Vapor Ou!
This type of solids removal device, Figures 4-52A, and
(Al IB) IC)
Poor Nol Much Betltr lhon IA) Webre T1pe B, is a relatively low cost approach to remove/separate
Unlen Ring Baffle Added, Effectivt • Particularf y solids from solid/liquid suspensions. The incoming feed
Fig.· 27. in Vacuum Service
to such a unit is injected along the inner wall where the
Figure 4-50. Separator outlets for liquid-vapor service. centrifugal force causes rotation at high angular velocity.
The kinetic energy of this feed is converted to centrifugal
force. The coarse/heavier particles will be concentrated
at the bottom as underflow. Most of the feed liquid and
an internal loss of0.25 to 2.0 psi assumed, depending part of the fine solids will discharge through the vortex
upon system pressure and general unit dimensions. and overflow.
e. For liquids and vapors other than air-water: This unit is good lo pre-thicken feed to centrifugal fil-
ters and similar applications. One cyclone may satisfy a
requirement, or the units can be arranged in parallel for
[ PL - P,. )0.25 large capacities or in series for removal of extreme fines.
V (separator) = 0.1885 V sn - ( 4- 57)
--p- " See Figure 4-53 for a counter-current wash system. Solids
as small as 10 microns can be separated.
where V,a is the selected separator velocity when using an These units are made of abrasion resistant metals, solid
air-water system, feet/sec. plastics, or with corrosion/wear resistant plastic liners,
266 Applied Process Design for Chemical and Petrochemical Plants
•
•
Figure 4-52A. Liquid-solids removal cyclones. Feed enters tangen-
tially along sidewall. By permission, Krebs Engineers.
such as molded rubber and elastomers; for example butyl,
Hycar®, Hypalon®, urethane, and metal alloys, silicon car-
bide, alumina ceramics. These units require little or no
maintenance. 1. Feed inlet and overflow connections are elastomer lined spool-
piece adapters.
The manufacturer requires complete solids and/or liq- 2. The top cover plate has all wetted surfaces lined, including the
uids data, feed size analysis, and requirements for separa- area mating with the overflow adapter.
tion. In some instances, it may be best to have a sample 3. The vortex finder is completely elastomer covered.
tested by the manufacturer in their laboratory. 4. The molded liners for the inlet head, cylinder section, and coni-
cal sections have integral molded gaskets for sealing at the
References [ 44,62] give good performance analysis of flanged joints. Molded liners and vulcanized linings are offered
these designs. in gum rubber, polyurethane, nitrile rubber, butyl, Neoprene®,
Viton®, Hypalon®, and other liner materials can be supplied.
Many of the molded elastomer liners are interchangeable with
Solid Particles in Gas/Vapor or Liquid Streams
ceramic liners of silicon carbide or high purity alumina.
5. All metal housings are of cast or fabricated mild steel. Standard
The removal of solid particles from gas/vapor or liq-
uid streams can be accomplished by several techniques, housings are for system pressures up to 25 psi, and special
designs are available for higher system pressures.
some handling the flow "dry," others wetting the
stream to settle/agglomerate the solids (or even dis- Figure 4-528. Liquid-solids cyclone fabricated to resist corrosion
solve) and remove the liquid phase from the system and abrasion. By permission, Krebs Engineers.
with the solid particles. Some techniques are more
adaptable to certain industries than others. Figure 4-54
illustrates typical ranges of particle size removal of var- Inertial Centrifugal Separators
ious types of common equipment or technique. All of
these will not be covered in this chapter. Attention will Specification Sheet, Figure 4-55, can be used as a guide
be directed to the usual equipment associated with the in summarizing and specifying conditions for this type of
chemical/ petrochemical industries. equipment.
Mechanical Separations 267
STRONG
SOLUTION
50Lt0S·Ll0U10
FEED
"--- ....
Figure 4-53. Cyclones used for countercurrent washing system. By permission, Krebs Engineers.
PHYSICAL
ATTRIBUTE
CONTROLLING
Color, appearance
Size and density
Magnetic permeability
0.001 n.oi O I 1()(\
Figure 4-54. Size ranges where particular solid-solid/solid-liquid separation techniques can be applied. By permission, Roberts, E. J. et. al.,
Chemical Engineering, June 29, 1970 [35].
268 Applied Process Design for Chemical and Petrochemical Plants
Specitication Sheet There are a few mechanical arrangements that use
G&s Phase Centritup:31 Entroin,:ient Separator external power to exert centrifugal force on the gas par-
(L1ouid or Solid Particles) ticle stream. The fan type blades direct the separating
1. Application: (Describe service application ot unit v�en particles to the collection outlet. Figures 4-56 and 4-57
show such a unit. These units are compact and have
poaaible)
been used in various dust applications. However, cau-
2. Fluid Stream: ---- Composition: (Vol. :Cl _
tion should be used to avoid installations involving
:,. Entrained Part1ole11 (L1quid or solid) -------
sticky or tacky materials which might adhere to the walls
Compo a1 t1on and blades of the unit. The efficiency of these is about
a. Size Mnee ---- microns (or l(eah) ----- 90%-99%, similar to a small, high pressure drop
b. Size percentage d1atribut1on :. cyclone. The air handling performance can be predict-
e , True Specitic Gr&Tit.7 ---- (or po.rt1cle), re- ed using the fan laws.
terred to water= 1,0
d, Bulk denait.7 ----- ot particle
e. Source or ent:rw.iment 1 ( Bo1lin_g liquid, kiln duat,
eta,)
4. Operating Condi t1onu Jl'.aldllNIII Minimum l'iol"Jl&l
a.a Flov rate
Ent:rw.1ned Flov Rate
Tnperature, 0 r.
heaaure, PSI
Moisture Content
Dev Point, 0 r.
5, Installation Altitude:
a, !lol'llal barometer ---- m:11 Hg,
6 ... ture or entrained material:
Solids: (a) Describe (dry, moist, stick7, at operating Figure 4-56. Inertial centrifugal dust separator. Courtesy of Ameri-
conditions) ------------- can Air Filter Co.
(b) H7groscop1o:
(o) Angle or repose------------
Uq'llid: (a) Describe: (Corroe1ve, 0117) ------- Feed Pipe
(b) Surtact111nsion at operatlns conditions:
(c) Viscos1t7 at operating conditions: ----
7. Insulation required: ---- F!e:uon ------- Circulating Fon
8; Construction Feat.urea:
Shutter Adjustment -
(a) Describe separator location in a7ste'11 ------ Cent rifugol Fon
(b) Indoors, outdoors, inside another vessel (ProTide
sketch it possible)--------------
(0) Storage required tor collected dust or liquid
-------- (hours)
(d) Prelimin&J"7 size inlet connection: ____ inches,
(dlllm., roct., aq.) --------------
(el T7pe or duet removal required----------
(t) Su!e;eated Materials or Constr-.iction
shell: ---- internals ----------
9. Special conditions:---------------
Tailings Discharge i
Fines Discharge
Agure 4-55. Specification Sheet, gas phase centrifugal entrainment Figure 4-57. Inertial centrifugal dust separator. Courtesy of Univer-
separator (liquid or solid particles). sal Road Machinery Co.
Mechanical Separations 269
Scrubbers Cleon
� -----' �
Scrubber separators use a liquid to form some type of
liquid surface (spray droplets, film, etc.) to assist the inter-
nal arrangements of the separator in the separating Cyclonic
action. Essentially the incoming dust or liquid particles Liquid in Separator
are wet by the action of the liquid (usually water or oil)
and are made larger and/ or heavier and thus can be sep-
arated from the moving stream. There are many types and
styles of units falling in this classification (see Figures 4-58
to 4-64. Reference [36] provides a good summary of man- Figure 4-59. Venturi scrubber. Courtesy of Chemical Construction
ufacturers and their products for wet scrubbing. Corp.
One or more of the following mechanisms are
employed in the separating action of the wet scrubbers.
I. Impingement-on internal pans.
2. Wetting-of particle to help agglomerate and pre-
vent re-entrainment.
3. Diffusion-dust particles deposited on the liquid
droplets. Predominant for the submicron and parti-
cles up to about 5µ.
Clean Gas
Care Buster Disc------
Tangential Gas Inlet
Swinging Inlet
Damper
Wafer Water
Outlet Inlet
Figure 4-58. Cyclonic scrubber. Courtesy of Chemical Construction Figure 4-60. Impingement scrubber. Courtesy of Peabody Engineer-
Corp. ing Corp.
270 Applied Process Design for Chemical and Petrochemical Plants
GAi INLET
CLEAN AIR OUTLET
t
1 1 I 1
SUPPLEMENTARY INSPECTION
WATER INLET�� --DOOR
INSPECTION
WASHING --oooR
LIQUID INLET
INSPECTION
--oooR
BOX
VANES
INSPECTION
DCOR -
Figure 4-62. Spray scrubber-fume scrubber arranged for vertical
SLUDGE OUTLET
downflow. Courtesy of Schutte & Koerting Co.
Figure 4-61. Spray scrubber. Courtesy of The Ducon Co., Inc.
4. Humidification-aids in flocculation and agglomer- the various types of equipment illustrated in Figures 4-58
ation of particles. to 4-64.
Figures 4-64 and -64A use a floating valve variable ori-
5. Condensation-will cause particle size to grow if gas fice opening as used in distillation contacting on the one
cooled below its dew-point.
or more trays included in the manufacturer's design. This
6. Dust Disposal-running film action of liquid washes provides for good contact to wet down the solid particles
dust and collected liquid out of scrubber. as well as scrub many water soluble gas/vapors in the
7. Gas Partition-segregates gas into small streams and incoming stream (such as chloride, sulfur, and nitrogen
segments when flowing through a liquid or foam. compounds). Heat and mass transfer can take place
under these conditions. The pressure drop through this
8. Electrostatic Precipitation-the electrical charging type unit typically ranges from 1 inch water to 2 inches of
of the liquid droplets may come about by the inter- water for a five-fold increase in gas flow rates. Particle
action of the gas and liquid streams. Not much removal can go as low as 0.5 micron to greater than 30
known of this action. microns. Usually a wire mesh entrainment pad is mount-
ed in the outgoing "clean" vapors to knock out liquid
The separating ability of most units is limited to 5- entrained particles, not solids.
micron particles. However, some will take out 1 to 5µ par-
ticles at a sacrifice in collection efficiency. Due to the Cloth or Fabric Bag Separators or Filters
peculiarities of each system as well as the equipment avail-
able to perform the separation, it is well to consult manu- Reference [55] provides additional details beyond the
facturers regarding expected performance. Quite often bag filter applications, and Reference [60] provides a
they will want to run test units, particularly on difficult technical and analytical review of flowing gas-solids sus-
separations. References [12,13] give good descriptions of pensions.
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