P a g e 99 | 126 COMPANY PROFILE Cairo Petroleum Refining Company is a subsidiary of Suez Petroleum Manufacturing Company, which is considered to be the oldest and oldest refinery in the Arab Republic of Egypt to cover the needs of the domestic market of petroleum products. Which are marketed and distributed by the Egyptian General Petroleum Corporation. The company also manufactures some special products, which are marketed through the company, established in 1982. Its mission; oil refining and processing, basic and detailed engineering designs and study projects, local manufacturing of towers, switches, furnaces, pressure vessels and warehouses; according to international codes (ASME, API, ASIM, ANSI), carrying out all project implementation works from civil works until the project starts operation, installations for petroleum production units and industrial facilities for the company and petroleum and industrial companies, maintenance and technical services for petroleum and industrial companies, engineering inspection works, carrying out chemical analyzes of petroleum ores, products and water, marketing of petroleum products. The company includes two factories: Mostorod refinery with a capacity of 8 million tons per year and Tanta refinery with a capacity of 2 million tons per year. PRODUCTS The company meets the local market needs in the following products: Butane, Different gasoline, Kerosene, Jet fuel and the diesel. UNITS 1. Distillation unit 2. Hydrotreating unit 3. Reforming Unit 4. Isomerization Unit
P a g e 100 | 126 Distillation unit The target of this unit is physical separation. There are four manufactures in distillation unit; each manufacture contain heat exchanger, desalter, furnace, pumps, preflasher and distillation tower; the type used by the company is the bubble cap type. Improving the specs of middle distillates (kerosene and gas oil), by treating in presence of hydrogen and catalyst to remove impurities such as sulfur, nitrogen, oxygen, halides and metals. Firstly: Reaction section The feed is pumped from tanks by feed booster pump P-0, and then heated through 11E-8 with unit’s product across the tube side The feed enters 11D-1 at temperature 120-130 C and pressure 3 kg/cm, and then is pumped with feed pump 11p-1 to 11E-2 A&B shell side to be heated with reactor effluent. Feed is then further heated through the furnace 11H-1; convection section and radiation section, and exits with temperature 370-380 C.
P a g e 101 | 126 The feed is mixed with hydrogen before entering the reactor 11R-1. The mixture; feed and hydrogen, enter 11R-1 from top with temperature 325- 340°C, where reactions take place over the catalyst then the effluent leaves the reactor at temperature 338-347 C and pressure 36 kg/cm2 . The reactor effluent is cooled through 11E-1A&B tube side with hydrogen, then 11E-2A&B tube side with the feed then 11E-3 tube side with hydrogen, then E-4A&B tube side with 11C-1 feed, then across 11E-5 air cooler and water cooler 11E-6. The effluent enters the high pressure separator; H.P.S, 11D-3 with temperature 50 C and pressure 35 kg/ cm2 where hydrogen is separated from the top and sent to 11D-6, and the effluent is sent to the low pressure separator; LP.S , 11D-2 after it has passed through 11 LIC-1 to lower its pressure to 5.5 kg/cm2 . Secondly: Distillation section The bottom of L.P.S; 11D-2, is sent to 11E-4 B&A shell side to be heated across reactor effluent, then to 11E-7A&B tube side to be heated with the product. The product enters the fractionation column 11C-1@ trays number 11&15 with temperature 210-220 C and pressure 1.8 kg/cm where light hydrocarbons and reactions products such as H.S and NH, are separated from the top of the tower. The top of the tower is cooled through water cooler 11E-11, then enters the overhead drum 11D-4 with temperature 40°C, the liquid is pumped from the bottom of the drum by 11P-5 and sent as total reflux to 11C-1. The bottom of 11C-1 (the product) is divided into two steams, the first stream is pumped by 11P-3 and cooled through 11E-7 B&A shellside, then 11E-8 shellside and finally through water cooler 11E-10,then sent to storage tanks. The second stream is pumped by 11p-4 to reboiler heater 11H-2 where it is heated through convection and radiation sections to 250°C then returned back to the bottom of the tower to maintain the bottom temperature at 230°C. Third: Hydrogen cycle The hydrogen is separated from the reactor effluent at H.P.S then enters S compressor suction drum (1ID- 6), then enters the compressor 11K-1 with pressure 35 kg/e m and exit with pressure 40 kg/cm2 . The recycled hydrogen is then mixed with the makeup hydrogen which comes from 20K-1 A, B&C. The hydrogen isthen heated through 11E-3 shellside and 11E-1A&B shellside before it is mixed with the feed.
P a g e 102 | 126 Reforming Unit In catalytic reforming, the change in the boiling point of the stock passed through the unit is relatively small, as the hydrocarbon molecular structures are rearranged to form higher-octane aromatics with only a minor amount of cracking. Thus, catalytic reforming primarily increases the octane of motor gasoline rather than increasing its yield; in fact, there is a decrease in yield because of hydrocracking reactions that take place in the reforming operation. Hydrocarbons boiling above 400°F (204°C) are easily hydrocracked and cause an excessive coke laydown on the catalyst. The feedstocks to catalytic reformers are heavy straight-run; HSR, naphthas [180 to 375°F (82 to 190°C)] and heavy hydrocracker naphthas. These are composed of the four major hydrocarbon groups: paraffins, olefins, naphthenes, and aromatics (PONA). the paraffins and naphthenes undergo two types of reactions in being converted to higher octane components: cyclization and isomerization. The ease and probability of either of these occurring increases with the number of carbon atoms in the molecules, and this is one of the reasons that only the naphthas containing seven or more carbon atoms are used for reformer feed. The LSR naphtha [C5-180°F (C5-82°C)] is largely composed of pentanes and hexanes; the pentanes do not contain enough carbon atoms to make an aromatic ring, and the hexanes can be converted into benzene. Because the benzene content of gasolines is limited by the EPA, the hexane content of the reformer feed is minimized. As in any series of complex chemical reactions, reactions occur that produce undesirable products in addition to those desired. Reaction conditions have to be chosen that favor the desired reactions and inhibit the undesired ones. Desirable reactions in a catalytic reformer all lead to the formation of aromatics and isoparaffins, as follows: 1. Paraffins are isomerized and to some extent converted to naphthenes. The naphthenes are subsequently converted to aromatics. 2. Olefins are saturated to form paraffins, which then react as in (1). 3. Naphthenes are converted to aromatics. 4. Aromatics are left essentially unchanged. Reactions leading to the formation of undesirable products include: 1. Dealkylation of side chains on naphthenes and aromatics to form butane and lighter paraffins. 2. Cracking of paraffins and naphthenes to form butane and lighter paraffins. As the catalyst ages, it is necessary to change the process operating conditions to maintain the reaction severity and to suppress undesired reactions.
P a g e 103 | 126 1. Dehydrogenation of alkylcyclohexanes to aromatics: 2.Dehydroisomerization of alkylcyclopentanes to aromatics: 3. Dehydrocyclization of paraffins to aromatics:
P a g e 104 | 126 Aromatics have a higher liquid density than paraffins or naphthenes with the same number of carbon atoms, so 1 volume of paraffins produces only 0.77 volume of aromatics, and 1 volume of naphthenes about 0.87 volume. In addition, conversion to aromatics increases the gasoline end point, because the boiling points of aromatics are higher than the boiling points of paraffins and naphthenes with the corresponding number of carbons. The yield of aromatics is increased by: 1. High temperature (increases reaction rate but adversely affects chemical equilibrium) 2. Low pressure (shifts chemical equilibrium to the right) 3. Low space velocity (promotes approach to equilibrium) 4. Low hydrogen-to-hydrocarbon mole ratios (shifts chemical equilibrium to the right) Isomerization of paraffins and cyclopentanes usually results in a lower octane product than does conversion to aromatics. 1. Isomerization of normal paraffins to isoparaffins: 2. Isomerization of alkylcyclopentanes to cyclohexanes, plus subsequent conversion tobenzene: Isomerization yield is increased by: 1. High temperature (which increases reaction rate) 2. Low space velocity (which increases reaction time) 3. Low pressure There is no isomerization effect due to the hydrogen-to-hydrocarbon mole ratios, but high hydrogen-to- hydrocarbon ratios reduce the hydrocarbon partial pressure and thus, favor the formation of isomers. The hydrocracking reactions are exothermic and result in the production of lighter liquid and gas products. They are relatively slow reactions, and therefore most of the hydrocracking occurs in the last section of the reactor.
P a g e 105 | 126 The major hydrocracking reactions involve the cracking and saturation of paraffins. Hydrocracking yields are increased by: 1. High temperature 2. High pressure 3. Low space velocity In order to obtain high product quality and yields, it is necessary to carefully control the hydrocracking and aromatization reactions. Reactor temperatures are carefully monitored to observe the extent of each of these reactions. The active material in most catalytic reforming catalysts is platinum. Certain metals, hydrogen sulfide, ammonia, and organic nitrogen and sulfur compounds will deactivate the catalyst. Feed pretreating, in the form of hydrotreating, is usually employed to remove these materials. The hydrotreater employs a cobalt-molybdenum catalyst to convert organic sulfur and nitrogen compounds to hydrogen sulfide and ammonia, which then are removed from the system with the unreacted hydrogen. Any metals in the feed are retained by the hydrotreater catalyst. Hydrogen needed for the hydrotreater is obtained from the catalytic reformer. If the boiling range of the charge stock must be changed, the feed is redistilled before being charged to the catalytic reformer. Reforming processes are classified as continuous, cyclic, or semiregenerative, depending upon the frequency of catalyst regeneration. The equipment for the continuous process is designed to permit the removal and regeneration or replacement of catalyst during normal operation. As a result, the catalyst can be regenerated continuously and maintained at a high activity. As increased coke laydown and thermodynamic equilibrium yields of reformate are both favored by low- pressure operation, the ability to maintain high catalyst activities and selectivities by continuous catalyst regeneration (CCR) is the major advantage of the continuous type of unit. This advantage has to be evaluated with respect to the higher capital costs and possible lower operating costs due to lower hydrogen recycle rates and pressures needed to keep coke laydown at an acceptable level.
P a g e 106 | 126 The semiregenerative unit is at the other end of the spectrum and has the advantage of minimum capital costs; a CCR unit without the regeneration section does not cost much more than the semiregenerative unit and permits the replacement of catalyst while the unit is still onstream. Regeneration requires the unit to be taken off-stream. Depending upon the severity of operation, regeneration is required at intervals of 3 to 24 months. High hydrogen recycle rates and operating pressures are utilized to minimize coke laydown and consequent loss of catalyst activity. The cyclic process is a compromise between these extremes and is characterized by having a swing reactor, in addition to those on-stream, in which the catalyst can be regenerated without shutting the unit down. When the activity of the catalyst in one of the on-stream reactors drops below the desired level, this reactor isisolated from the system and replaced by the swing reactor containing freshly regenerated catalyst. The catalyst in the replaced reactor is then regenerated by admitting hot gas containing about 0.5% oxygen into the reactor to burn the carbon off the catalyst. After regeneration and reactivation of the catalyst, it is used to replace the next reactor needing regeneration. The reforming process can be obtained as a continuous or semiregenerative operation and other processes as either continuous, cyclic, or semiregenerative. The semiregenerative reforming process is typical of fixed- bed reactor reforming operations and will be described here. The semiregenerative process is shown in the simplified process flow diagram given in Figure 10.1. The pretreated feed and recycle hydrogen are heated to 925 to 975°F (498 to 524°C) before entering the first reactor. In the first reactor, the major reaction is the dehydrogenation of naphthenes to aromatics, and as this is strongly endothermic, a large drop in temperature occurs. To maintain the reaction rate, the gases are reheated before being passed over the catalyst in the second reactor. As the charge proceeds through the reactors, the reaction rates decrease and the reactors become larger, and the reheat needed becomes less. Usually three or four reactors are sufficient to provide the desired degree of reaction, and heaters are needed before each reactor to bring the mixture up to reaction temperature. In practice, either separate heaters can be used or one heater can contain several separate coils. The reaction mixture from the last reactor is cooled, and the liquid products condensed. The hydrogen- rich gases are separated from the liquid phase in a drum separator, and the liquid from the separator is sent to a fractionator to be debutanized. The hydrogen-rich gas stream is split into a hydrogen recycle stream and a net hydrogen by-product, which is used in hydrotreating or hydrocracking operations or as fuel. The reformer operating pressure and the hydrogen/feed ratio are compromises among obtaining maximum yields, long operating times between regeneration, and stable operation. It is usually necessary to operate at pressures from 50 to 350 psig(345 to 2415 kPa) and at hydrogen charge ratios of 3 to 8 mol H2/mol feed [2800 to 7600 scf/bbl (500–1350 Nm3/m3)]. Liquid hourly space velocities in the area of 1 to 3 are in general use. The original reforming process is classified as a semiregenerative type because catalyst regeneration is infrequent and runs of 6 to 24 months between regenerations are common. In the cyclic processes, regeneration is typically performed on a 24-or 48-hour cycle, and a spare reactor is provided so that regeneration can be accomplished while the unit is still on-stream. Because of these extra facilities, the cyclic processes are more expensive but offer the advantages of lower pressure operation and higher yields of reformate at the same severity.
P a g e 107 | 126 Reforming Catalyst All of the reforming catalyst in general use today contains platinum supported on an alumina base. In most cases, rhenium is combined with platinum to form a more stable catalyst that permits operation at lower pressures. Platinum is thought to serve as a catalytic site for hydrogenation and dehydrogenation reactions, and chlorinated alumina provides an acid site for isomerization, cyclization, and hydrocracking reactions. Reforming catalyst activity is a function of surface area, pore volume, and active platinum and chlorine content. Catalyst activity is reduced during operation by coke deposition and chloride loss. In a high-pressure process, up to 200 bbl of charge can be processed per pound of catalyst (64m3/kg) before regeneration is needed. The activity of the catalyst can be restored by high-temperature oxidation of the carbon followed by chlorination. This type of process is referred to assemiregenerative and is able to operate for 6- to 24-month periods between regenerations. The activity of the catalyst decreases during the on-stream period, and the reaction temperature is increased as the catalyst ages to maintain the desired operating severity. Normally, the catalyst can be regenerated in situ at least three times before it has to be replaced and returned to the manufacturer for reclamation. Catalyst for fixed-bed reactors is extruded into cylinders 1/32 to 1/16 in. (0.8 to 1.6 mm) diameter with lengths about 3/16 in. (5 mm). The catalyst for continuous units is spherical, with diameters approximately 1/32 to 1/16 in. (0.8 to 1.6 mm). The continuous catalyst regeneration unit moves the catalyst between the reactor and regenerator and permits the catalyst to be regenerated and returned to the reactor while the unit is operating. The catalyst flows by gravity through the reactor. It is then picked up in a nitrogen stream and carried to the top of the regeneration unit. As the catalyst flows through the regenerator, the coke is burned from the catalyst using a nitrogen stream containing a small amount of oxygen. The oxygen content is carefully regulated to prevent the catalyst from overheating and becoming permanentlydeactivated. After regeneration, it is carried in a hydrogen stream to the top of the reactor to begin its journey through the cycle again. From the time a catalyst particle enters the top of the reactor until it goes through the cycle and is returned to the top of the reactor, a period of 5 to 7 days isrequired.
P a g e 108 | 126 Reactor Design Fixed-bed reactors used for semiregenerative and cyclic catalytic reforming vary in size and mechanical details, but all have basic features as shown in Figure 10.3. Very similar reactors are used for hydrotreating, isomerization, and hydrocracking. The reactors have an internal refractory lining that is provided to insulate the shell from the high reaction temperatures and thus reduce the required metal thickness. Metal parts exposed to the high-temperature hydrogen atmosphere are constructed from steel containing at least 5% chromium and 0.5% molybdenum to resist hydrogen embrittlement. Proper distribution of the inlet vapor is necessary to make maximum use of the available catalyst volume. Some reactor designs provide for radial vapor flow rather than the simpler straight-through type shown here. The important feature of vapor distribution is to provide maximum contact time with minimum pressure drop. Temperature measurement at a minimum of three elevations in the catalyst bed is considered essential to determine catalyst activity and as an aid in coke burn-off operations. The catalyst pellets are generally supported on a bed of ceramic spheres about 12 to 16 in. (30 to 40 cm) deep. The spheres vary in size from about 1 in. (25 mm) on the bottom to about 0.35 in. (9 mm) on the top.
P a g e 109 | 126 INTRODUCTION Suez Oil Processing Company (SOPC) refined 1.2 million tons of crude oil in fiscal year (FY) 2017/18, 10% more than in the previous fiscal year, Egypt Oil & Gas reports. SOPC is currently establishing a production unitthat will process up to 60,000 tons of butane each year, and an asphalt production unit with a maximum annual capacity of 396,000 tons. The company is also refurbishing the coking unit to reach maximum capacity and produce diesel that meets global standards. Crude oil is sent to the atmospheric distillation unit after desalting and heating. The purpose of atmospheric distillation is primary separation of various ‘cuts’ of hydrocarbons namely, fuel gases, LPG, naphtha, kerosene, diesel and fuel oil. The heavy hydrocarbon residue left at the bottom of the atmospheric distillation column is sent to vacuum distillation column for further separation of hydrocarbons under reduced pressure. As the name suggests, the pressure profile in atmospheric distillation unit is close to the atmospheric pressure with highest pressure at the bottom stage which gradually drops down till the top stage of the column. The temperature is highest at the bottom of the column which is constantly fed with heat from bottoms reboiler. The reboiler vaporizes part of the bottom outlet from the column and this vapor is recycled back to the distillation column and travels to the top stage absorbing lighter hydrocarbons from the counter current crude oil flow. The temperature at the top of the column is the lowest as the heat at this stage of the column is absorbed by a condenser which condenses a fraction of the vapors from column overhead. The condensed hydrocarbon liquid is recycled back to the column. This condensed liquid flows down through the series of column trays, flowing counter current to the hot vapors coming from bottom and condensing some of those vapors along the way. Thus a reboiler at the bottom and a condenser at the top along with a number of trays in between help to create temperature and pressure gradients along the stages of the column. The gradual variation of temperature and pressure from one stage to another and considerable residence time for vapors and liquid at a tray help to create near equilibrium conditions at each tray.
P a g e 110 | 126 So ideally we can have a number of different vapor-liquid equilibria at different stages of this column with varying temperature and pressure conditions. This means that the hydrocarbon composition also varies for different trays with the variation in temperature and pressure. The heaviest hydrocarbons are taken out as liquid flow from the partial reboiler at bottom and the lightest hydrocarbons are taken out from the partial condenser at the column overhead. For the in between trays or stages, the hydrocarbons become lighter as one moves up along the height of the column. Various other cuts of hydrocarbons are taken out as side draws from different stages of the column. Starting from LPG at the top stages, naphtha, kerosene, diesel and gas oil cuts are taken out as we move down the stages of atmospheric column. The heaviest hydrocarbon residue taken out from partial reboiler is sent to the vacuum distillation column for further separation under reduced pressure. The different cuts of hydrocarbons taken out at this stage are the result of primary separation and undergo further processing before being transformed to end products.
P a g e 111 | 126 2-Delayed Coker Coking is a thermal cracking process in which a low value residual oil, such as an atmospheric or vacuum residue is converted into valuable distillate products, off-gases and petroleum coke. Continuous coking process where residuum is sprayed on to fluidized bed of hot coke particles. Here cracking takes place at much higher temperature than delayed coking (temperature up to 565 °C). Continuous coking processlike Fluid Coking which includes a gasification section of coke produced in Fluid Coking Operation. Is the most commonly used carbon rejection process that upgrades residues to a wide range of lighter hydrocarbon gases and distillates through thermal cracking. The byproduct of delayed coking process is petroleum coke. The goal for delayed Coker operation is to maximize the yield of clean distillates and minimize the yield of coke. Delayed coking technology is preferred for upgrading heavier residues due to its inherent flexibility to handle even the heaviest residues while producing clean liquid products. The main products of delayed coker operation are off-gas (from which LPG is recovered), naphtha, Light Gas Oil (LCGO) and Heavy Gas oil (HCGO). LCGO is sent to Hydrotreater for production of Gas Oil. HCGO to refinery FO Pool/ RFCC feedstock/ OHCU feedstock. Delayed coking is a semi-continuous process while the coking process is continuous where the coke removal, handling and disposal are carried out in a batch manner . The term “delayed” was attributed to the fact that the coking reaction is delayed until after the heated feed is transferred into the coke drum, where adequate residence time is provided for the coking reaction to reach completion. The yield slate for a Delayed Coker can be varied to meet a refiner’s objective through the selection of operating parameters. Three operating parameters govern the yield pattern and product quality of Delayed Coker Increasing coking temperature decreases coke production and increases liquid yield and gas oil endpoint , However temperature can be adjusted only a narrow range to control volatilities left in coke. Increasing pressure and/or Recycle Ratio (RR) increases gas and coke make and decreases liquid yield and gas oil endpoint. RR can be used in many percentages.
P a g e 112 | 126 3- Utilities: Water treatment Modern trend of Delayed Coking technology is to minimize the coking pressure and recycle ratio within the economic and technical constraints for designing a unit while producing clean Heavy CokerGasOil(HCGO) product within following quality: • Low contaminant level of carbon residue. • Low contaminant level of metal. • End point within acceptable level. Decompositions of large molecules into smaller molecules including free radicals free radicals are highly reactive and short lived spices react with other hydrocarbons , combine with other free radical resulting in termination , or decompose further to olefins and smaller radicals , and so on. Polymerization and condensation These reactions result in the formation of polycondensed aromatic compounds. When these planner compounds rearrange and become stacked in a fixed direction , the state is called the mesophase or (liquid crystal state) Refineries are among the major consumers of water due to cooling towers and process usage. During the treatment and refining of crude oil, large quantities of wastewater are generated, which require treatment.The quality of this wastewater depends on the grade of the crude oil and the process for treating the oil. As environmental regulations for wastewater disposal are getting stricter, and fresh water resources are becoming increasingly limited, the industry requires more efficientmanagement and reuseofthiswastewater. 1. Physical process units 2. Chemical process units 3. Biochemical process units In dissolved-air flotation (DAF) systems, air is dissolved in the wastewater under a pressure of several atmospheres, followed by release of the pressure to the atmospheric level. In small pressure systems, the entire flow may be pressurized by means of a pump to 275 to 350 kpa (40 to 50 lb/in2 gage) with compressed air added at the pump suction. The entire flow is held in a retention tank under pressure for several minutes to allow time for the air to dissolve. It is then admitted through a pressure-reducing valve to the flotation tank where the air comes out of solution in very fine bubbles. In the larger units, a portion of the DAF effluent (15 to 120 percent) is recycled, pressurized, and semi- saturated with air. The recycled flow is mixed with the un-pressurized main stream just before admission to the flotation tank, with the result that the air comes out of solution in contact with particulate matter at the entrance to the tank. Pressure types of units have been used mainly for the treatment of industrial wastes and for the concentration of solids.
P a g e 113 | 126 4- Reforming The purpose of reforming is to improve the anti-knock characteristics of straight- run gasoline or of a gasoline fraction by changing the molecular structure of the components. This can be achieved by subjecting the gasoline to thermal treatment similar to the cracking process, which is referred to as thermal reforming. Another way of achieving a similar object is by a catalytic process in the presence of hydrogen, which is the most common nowadays. The chemical reactions which take place in thermal reforming are similar to those in thermal cracking, i.e. long-chain paraffin hydrocarbons yield olefins and paraffins of lower boiling points. The ringtype hydrocarbons—the naphthenes and aromatics — also form unsaturated molecules, either by decomposition of the ring itself or by the splitting of the side chains. The products formed as a result of these complicated chemical re-arrangements have a much wider boiling range and a higher anti-knock value than the gasoline or gasoline fraction used as the feedstock. In addition to gasoline, gas and gas oil are obtained as products from thermal reforming. Since the smaller molecules of the hydrocarbons of all types present in the feedstock are thermally more stable than the larger molecules which compose straight-run gas oils and residues, reforming requires higher temperatures and longer reaction times than those used in the cracking of heavier products. If the reactions were allowed to proceed too far, excessive gas formation and a lower yield of gasoline would result. In order to prevent this, the hot products leaving the furnace are immediately cooled by the addition of relatively cold oil, referred to as quench oil. The extent of reforming, and consequently the nature of the products formed, are controlled by this means.
Heat transfer units There are two devices used together for heating crude oil in petroleum refinery as in figure, and these devices are: Furnaces are used throughout the industry to provide the heat, using the combustion of fuels. These fuels are solid, liquid or gaseous. Furnaces consist essentially of an insulated, refractory lined chamber containing tubes. Tubes carry the process fluid to be heated, and sizes are device for burning the fuel in air to generate hot gases. • Vertical cylinder process heater • Horizontal tube “cabin “heater P a g e 114 | 126
P a g e 115 | 126 Main parts of furnaces: 1. Radiant section 2. Convection section 3. Burner 4. Soot blower 5. Stack 6. Insulation The radiant section is where the tubes receive almost all its heat by radiation from the flame. In a vertical, cylindrical furnace, the tubes are vertical. Tubes can be vertical or horizontal, placed along the refractory wall, in the middle, etc., or arranged in cells. Studs are used to hold the insulation together and on the wall of the furnace. They are placed about 1 ft. (300 mm) apart in this picture of the inside of a furnace. The tubes, shown below, which are reddish brown from corrosion, are carbon steel tubes and run the height of the radiant section. The tubes are a distance away from the insulation so its radiation can be reflected to the back of the tubes to maintain a uniform tube wall temperature. Tube guides at the top, middle and bottom hold the tubes in place. The convection section is located above the radiant section where it is cooler to recover additional heat. Heat transfer takes place by convection here, and the tubes are finned to increase heat transfer. The first two tube rows in the bottom of the convection section and at the top of the radiant section is an area of bare tubes (without fins) and are known as the shield section, so named because they are still exposed to plenty of radiation from the firebox and they also act to shield the convection section tubes, which are normally of less resistant material from the high temperatures in the firebox. The area of the radiant section just before flue gas enters the shield section and into the convection section called the bridge zone. Crossover is the term used to describe the tube that connects from the convection section outlet to the radiant section inlet. The crossover piping is normally located outside so that the temperature can be monitored and the efficiency of the convection section can be calculated. The sight glass at the top allows personnel to see the flame shape and pattern from above and visually inspect if flame impingement is occurring. Flame impingement happens when the flame touches the tubes and causes small isolated spots of very high temperature. The burner in the vertical, cylindrical furnace as above, is located in the floor and fires upward. Some furnaces have side fired burners, e.g.: train locomotive. The burner tile is made of high temperature refractory and is where the flame is contained in. Air registers located below the burner and at the outlet of the air blower are devices with movable flaps or vanes that control the shape and pattern of the flame, whether it spreads out or even swirls around. Flames should not spread out too much, as this will cause flame impingement. Air registers can be classified as primary, secondary and if applicable, tertiary, depending on when their air is introduced. The primary air register supplies primary air, which is the first to be introduced in the burner. Secondary air is added to supplement primary air. Burners may include a pre-mixer to mix the air and fuel for better combustion before introducing into the burner.
P a g e 116 | 126 4- Soot blower Some burners even use steam as premix to preheat the air and create better mixing of the fuel and heated air. The floor of the furnace is mostly made of a different material from that of the wall, typically hard castable refractory to allow technicians to walk on its floor during maintenance. A furnace can be lit by a small pilot flame or in some older models, by hand. Most pilot flames nowadays are lit by an ignition transformer (much like a car’s spark plugs). The pilot flame in turn lights up the main flame. The pilot flame uses natural gas while the main flame can use both diesel and natural gas. When using liquid fuels, an atomizer is used, otherwise, the liquid fuel will simply pour onto the furnace floor and become a hazard. Using a pilot flame for lighting the furnace increasessafety and ease compared to using a manual ignition method (like a match). Soot blowers are found in the convection section. As this section is above the radiant section and air movement is slower because of the fins, soot tends to accumulate here. Soot blowing is normally done when the efficiency of the convection section is decreased. This can be calculated by lookingat the temperature change from the crossover piping and at the convection section exit. Soot blowers utilize flowing media such as water, air or steam to remove deposits from the tubes. This is typically done during maintenance with the air blower turned on. There are several different types of soot blowers used. Wall blowers of the rotary type are mounted on furnace walls protruding between the convection tubes. The lances are connected to a steam source with holes drilled into it at intervals along its length. When it is turned on, it rotates and blows the soot off the tubes and out through the stack. The flue gas stack is a cylindrical structure at the top of all the heat transfer chambers. The breeching directly below it collects the flue gas and brings it up high into the atmosphere where it will not endanger personnel. The stack damper contained within works like a butterfly valve and regulates draft (pressure difference between air intake and air exit) in the furnace, which is what pulls the flue gas through the convection section. The stack damper also regulates the heat lost through the stack. As the damper closes, the amount of heat escaping the furnace through the stack decreases, but the pressure or draft in the furnace increases which poses risks to those working around it if there are air leakages in the furnace, the flames can then escape out of the firebox or even explode if the pressure is too great. Insulation is an important part of the furnace because it prevents excessive heat loss. Refractory materials such as firebrick, castable refractories and ceramic fiber, are used for insulation. The floor of the furnace is normally castable type refractories while those on the walls are nailed or glued in place. Ceramic fiber is commonly used for the roof and wall of the furnace and is graded by its density and then its maximum temperature rating. For e.g. 2,300°F means 8 lb/ft density with a maximum temperature rating of 2,300°F.An example of a castable composition is kastolite. Fired heaters are an essential component of most process plants. They are primarily used to heat all types of hydrocarbons. They are also used to heat hot oils, steam, or air. Fired heaters are major consumers of energy and even the smallest improvements in efficiency can save thousands of dollars. In the refining industry, typical energy consumption is approximately 0.44 MM Btu/BBL of crude oil processed. This translates into 2667 MM Btu/hr. for a 200,000-barrel-per-day (BPD) refinery. Even a 1% improvement in thermal efficiency translates into energy savings of 600,000 $per year. Ethylene plants (22 MM Btu/ton of ethylene) and ammonia plants (28.5 MM Btu/ton of ammonia) are equally energy intensive.
P a g e 117 | 126 2-Heat Exchanger A heat exchanger can be simply referred to a piece of equipment built to efficiently transfer heat from one medium to another. Heat exchangers are used in a wide variety of applications such as home heating, refrigeration, air conditioning, petrochemical plants, refineries as well as in natural gas processing. In many industrial processes a heat exchanger helps in using the wasted heat from one process to be utilized in another process which saves a lot of money while being efficient at the same time. There are multiple types of heat exchangers available depending upon their applications in various parts of the industry: 1. Shell and Tube heat exchangers: To make it simple, this type of heat exchanger works with a series of tubes containing the fluid that must be either heated or cooled and these tubes run in a shell or a much larger tube containing another liquid that either heats up and warms the tubes or absorbs and cools the fluid running in the smaller tubes. Shell and Tube heat exchangers work better in high pressure and demanding environments. 2. Plate heat exchanger: These heat exchangers work with a line-up of multiple thin and closely placed plates which have a very large surface area and fluid flow passages for better heat dispersion. Plate heat exchangers are more practical compared to Shell and Tube ones in applications where there is a space restriction. 3. Adiabatic wheel heat exchanger: This type of a heat exchanger uses a separate material which can either be a solid or a liquid material to store the held heat which then moves to another side of the heat exchanger to be released. Plate fin heat exchanger: Plate fin heat exchangers are usually made of aluminum alloy with varieddesigns such as cross flow, counter flow, along with different types of fins which result in very effective heat transfer. They however offer a disadvantage at times in the procedure of servicing them correctly because of the extremely thin plates.
P a g e 118 | 126 About UGDC: United Gas Derivatives Company was established to receive the gas produced from North Port Said, Ras El Bar and Temsah concessions through the gas treatment plants of El Gmail and Happy in order to extract the NGL and produce propane, LPG and Condensates. Originally, the liquid propane is stored in the refrigerated tank at Damietta to be exported to the international market through marine vessels. While the LPG and the condensate are pumped to the relevant pipeline network owned by EGPC for local consumption. Currently, the liquid propane is transferred to the Egyptian Propylene & Polypropylene Company (EPPC) for petrochemical industry to maximize foreign currencies returns and added value. EPP is producing Propylene and the UGDC existing Damietta facilities are modified to be utilized to import Propane “The project is under commissioning” in addition to export the excess commercial propane to international market through marine vessels. Work Location: 1. Company Main Office is located in Maadi , Helwan. 2. Port Said NGL Plant is located on the Mediterranean Sea to the West of Port Said. 3. Propane shipping and exporting facilities are located within New Damietta Port. Port Said NGL Plant has been designed for deep extraction of NGL cut from a mixed feed gas; it is classified as one of the largest NGL plants in Egypt regarding the plant processing capacity reaching about 1350 million standard cubic foot per day (MMSCFD). The plant is designed to produce valuable liquids, namely propane, LPG or butane and condensate. In future, it is possible to retrofit the plant in order to produce also ethane. Basically, the feed gas comes from the Egyptian Gas National Grid via two
P a g e 119 | 126 pipelines from PHARONIA and PETROBEL plants and the residue gas is sent back to the Gas Grid. The NGL plant is consist of 4 main sections: 1. Pre-treatment section 2. NGL extraction section 3. Fractionation section 4. Storage & loadingsection The feed gas is received in the Pre-treatment section before any operation to be sure of eliminating the main impurities and contaminants in the gas such as solids, liquids and particulates to prepare the gas for processing. Solids are removed using a series of filters. Water vapor accompanied with feed gas is removed via a dehydration package, thus provides dry gas for processing in the cold section of the plant by lowering the dew point of the feed gas to the minimum limits. This process is important to avoid the formation of hydrates (complex solidified material) at very low cryogenic temperatures in the NGL extraction unit of the plant that could harmfully affect the performance of the plant and may lead to a shutdown. Then at last comes the removal of mercury particulates present in the feed by nature from the ground wells of the gas, this is carried out via a unit using catalytic effect of special materials to lower mercury presence to the minimum allowable limits to avoid its corrosive effect on aluminum materials used in the NGL extraction unit.
P a g e 120 | 126 The dehydration package consists of: • A coalescer (03-F-04) • Mol. sieve driers (03-R-01 A/B/C/D/E) • Driers gas filters (03-F-01 A/B) • Mercury removal unit Objective: To Separate NGL from Dry feed gas in order to perform further processing in Fractionation unit to get the final products
P a g e 121 | 126 Description: 1. De-mercurized gas stream will split & pre-cool versus warming residue gas stream in the G/G PFHE (Unit 10-E-01) and liquid bottom streams (expander feed separator & absorber) in the G/L PFHE (Unit 10-E02) respectively. 2. Pre-cooled gas willbeflashed into Expander Feed Separator (Unit 10-V-01), to separate any condensed liquids, These liquids in the source of the cooling duty for feed gas in G/L (10- E-02) “PASSB” 3. Gas will then expand through Turbo-Expanders(Unit 10 U-01A/B), with further cooling to -74 C, Two J.T. valves are provided in parallel to Expanders, to maintain plant in operation during Expanders trip and facilitate plant start-up.
P a g e 122 | 126 4. The Demethanizer (Unit 10-C-01) overhead vapor will cool versus warming residue gas stream in the G/G PFHE (Unit 10-E-03), and will be flashed to Absorber (Unit 10-C-02) top where accumulated condensed liquids are placed in chimney tray 5. Demethanizer Re-boiler (10-E-04) generate sufficient hot vapors to strip ethane and lighter components from the liquid flowing down the Demethanizer Column. to maintain C2/C3 Liq. Vol. % ratio of NGL liquids stream not to exceed 1.0%
P a g e 123 | 126 Fractionation Section Fractionation unit produces & controls the gas derivatives; propane, Liquefied Petroleum Gas (LPG) and Debutanized Natural Gasoline (DNG) according to specifications, through fractionation towers (De-propanizer & De-butanizer). These two towers produce propane, LPG and DNG from hydrocarbon liquids which have been separated in the NGL extraction unit
P a g e 124 | 126 De-propanizer: The depropanizer column pressure is set in order to condense the overhead with air, i.e. at about 50 deg.C. The resulting pressure is about 17 bar g. The condenser duty varies from 7.5 to about 16 MM kcal/h according to the operating mode. The column pressure is controlled with the usual ‘hot-by-pass’ while the temperature in a sensible top tray and therefore the composition is used to control the reflux flowrate. The analyzer in the overhead product is used to monitor the ethane and butane contents. The reflux pumps (30-P-01) are used also to send the C3 product to treatment, metering and storage. Hot oil is used as heating medium in the reboiler (30-E-01, 60/70 deg.C and 5 to 14 MM kcal/h) according to the operational mode: C4 or LPG production). The bottom product flows to the debutanizer in level control with no pumps required. The feedstock content in H2S and mercaptans indicates that no product treatment should be required. As a precaution, an absorbent type treatment to remove Sulphur components (Unit 30-X-01, nonregenerable absorbent bed) is included upstream the propane storage. The debutanizer column pressure is set in order to condense the overhead products with air, i.e. at above 50 degC. The resulting pressure is about 10 bar g. in the LPG production mode and possibly lower in the butane production. The condenser duty is about 6 to 8 MM kcal/h according to the operating mode. The column pressure is controlled with the usual ‘hot-by-pass’ while the temperature in a sensible bottom tray and therefore the composition is used to control the hot oil flowrate. The analyzer in the overhead product is used to monitor the propane and pentanes contents. The reflux pumps (30- P-02) are also used to send the C4 or LPG product to treatment, metering and storage. Hot oil is used as heating medium in the reboiler (about 110/140 degC and 4 to 7 MM kcal/h). The DNG bottom product flows to metering and storage under level control with no pumps required. Both overhead and bottom products are run-down cooled in order to guarantee storage temperature at not more than 50 degC. The feedstock content in H2S and mercaptans indicates that no LPG/butane treatment should be required. As a precaution, a non-regenerable adsorbent type treatment (Unit 30-X-02) is included upstream the propane storage. No treatment is required for DNG In future, a de-ethanizer system will be installed upstream of the de-propanizer to recover the ethane from the NGL. The NGL recovery section will be of course operated in ethane recovery mode. A pump will be installed as well (10-P-03) on the NGL product from NGL extraction section (de-methanizer) in order to guarantee maximum flexibility for the de-ethanizer pressure with respect to the de-methanizer. In particular, the possibility to lower the de-methanizer pressure if additional residue gas compressor power is available. The new pump will feed the NGL Surge Drum and from there the de-ethanizer. Possibly, the NGL surge Drum will be supplemented with a second parallel one in order to keep same residence time with the increased liquid flowrate. The de-ethanizer column pressure will be set in according to the data available when the design will be done. A figure of 25.8 bar g has been assumed so far.
P a g e 125 | 126 A condensing temperature of about –5 deg.C results from the simulations for a total condensing scheme. A dedicated propane refrigeration system (Unit 15) is included. The propane compressors (15-K-01) are gas turbine driven. The condensing duty is about 13 to 15 MM kcal/h. The column pressure is controlled with the usual ‘hot-by-pass’ while the temperature in a sensible top tray hence the composition is used to control the reflux flowrate. The analyser in the overhead product is used to monitor CO2, methane and propane contents. The analyser in the bottom product monitor ethane content to prevent propane off-spec. The reflux pumps (25- P-01) are used also to send the ethane product to metering and storage. Hot oil is used as heating medium in the re-boiler (about 90 deg.C and 15 to 19 MM kcal/h). The NGL bottom product flows to the de-propanizer in level control with no pumps required. The possible ethane treatment is outside the scope of this job. This will be determined by the requirement of petrochemical consumers. Considering that CO2 concentrates in the ethane product it is likely that a CO2 removal unit will be required for the ethane stream. The plant includes three spherical tanks to store the produced LPG, with the possibility of storing propane in one of these spheres. In addition a bullet is provided for gathering the produced propane before being pumped to the main storage and refrigeration facilities at Damietta. LPG is then loaded from NGL Plant in Port Said to the LPG bottling plants in Shata & Damietta through LPG pipeline, while DNG is stored in two bullets , then DNG is loaded to the refinery at Suez. For the propane product; it has two ways of loading, either to Damietta facilities to be stored and exported or loaded to the petrochemicals factory next to UGDC port-said plant.