Power Plant Engineering Equipment 1 | CHAPTER 1: PUMP 1.0 Pump Definition: A pump is a device that is used for lifting the liquid from ground sources to the upper top surface or from one place to another place. Pumps are operated by the mechanism that is rotary, reciprocating and it consumes energy while performing mechanical work which is moving fluid from one place to another. This can be operated by many energy resources which include manual operation, electricity, engine, wind power and many more, day to day life to industrial applications. 1.1 Difference Between Pump and Compressor Sometimes the words "pump" and "compressor" are used interchangeably, but there is a difference: A pump is a machine that moves a fluid (either liquid or gas) from one place to another. A compressor is a machine that squeezes a gas into a smaller volume and (often) pumps it somewhere else at the same time. 1.2 Types of Pumps: A pump can broadly be classified into two categories, and those are: • Positive Displacement Pump • Dynamic Pump Also, there are two types of Positive Displacement Pump, and those are: • Rotary Pump o Single Rotor Pump (For example, Piston Pump, Vane Pump, Screw Pump) o Multiple Rotor Pump (For example, Gear pump, Lube pump) • Reciprocating Pump
Power Plant Engineering Equipment 2 | o Diaphragm Pump (For example, Fluid Operated Pump, Mechanically Operated Pump) o Piston Plunger Type Pump And again, Dynamic Pumps can be classified into two types: • Centrifugal Pump • Axial Pump 1.3 What is a Pump? A pump is a device used to transfer different types of liquids or gases from one place to another by applying mechanical action. These devices typically convert electrical energy into hydraulic energy. Generally, pumps are operated by a mechanism (reciprocating or rotary) and take energy to do mechanical work that moves the working fluid. This equipment is capable of lifting liquids from low to high levels and moving fluids from low to high-pressure areas. Pumps are powered by means of several power sources, requiring a manual operation, electricity, engine, wind power, and more. Typically, pumps work by a vacuum in which air pressure forces the liquid out. All pumps work by creating an area of low pressure. Pumps have been used for so long, so it’s no wonder that there are a wide variety of sizes and types available. 1.4 Types of Pumps Following are the main types of pumps: a) Positive displacement • Reciprocating pump o Piston pump o Plunger pump o Diaphragm pump.
Power Plant Engineering Equipment 3 | • Rotary pump o Screw pump. o Progressive cavity pump o Gear pump. b) Dynamic pump • Centrifugal pump o Axial flow o Mixed flow o Peripherial • Special effect pump o Jet pump o Electromagnetic pump Figure 1.1: Classification of Pump 4.4.1 Positive Displacement Pump
Power Plant Engineering Equipment 4 | A positive displacement pump uses the reciprocating, rotary, or pneumatic motion to move the liquid through the pump. Here, the discharge of the fluid occurs in the form of pulses instead of a smooth liquid flow. These types of pumps are operated by trapping a fixed amount of fluid into the pump chamber at an inlet valve and then it discharges through an outlet valve. These pumps are utilized based on their ability to work in high viscosity fluid at high pressure. a) Rotary Pump It is also a type of positive displacement pump in which a fixed volume of fluid is moving with each revolution. These pumps can provide continuously delivered capacity regardless of pressure. Rotary pumps use rotating gears to move the fluid. This revolving gear forms a liquid seal with the pump casing and makes suction at the pump inlet. The fluid now drawn into the pump is locked within the teeth of its rotating gears and transferred to the discharge. It certainly gives an advantage that it is a 100% oil-free operation. Figure 1.2: Rotary Pump i) Gear Pump The gear pump uses gear meshing to pump the fluid by displacement. They are known as the most common types of pumps that are utilized for hydraulic power applications. As this gear rotate, they separate on the intake side of the pump which creates a vacuum and suction area for the fluid. The fluid is moved by gears to the discharge side of the pump, where a meshing of gears replaces the fluid. This tighter clearance along with the speed of rotation of the gears effectively prevents
Power Plant Engineering Equipment 5 | fluid from leaking backward. The primary use of gear pumps is for pumping high viscosity fluids in chemical installations. Figure 1.3: Gear Pump ii) Screw Pump These types of pumps use one or several screws to move the liquid along the screw axis. A screw pump generates pressure by using additional axial acceleration in the fluid within its clearance area. The simplest form of screw pump is the Archimedes screw. Screw pumps operate using two rotating screw rotors, arranged in such a way that they rotate towards each other. This stores the gas in the space between the screws of their rotors. When the screw begins to rotate, this stored volume is reduced resulting in compressed gas that drives it toward the exhaust. Figure 1.4: Screw Pump iii) Progressive Cavity Pump
Power Plant Engineering Equipment 6 | These types of pumps are use rotor and stator assembly to transfer the fluid by means of the progress through the pump. This rotor is a helical-shaped worm part that rotates within the stator. The stator has a more ‘worm thread’ than the rotor and is made of a flexible material. This arrangement allows for rotation of the stator and the condition of a transfer space that creates the progressive cavity needed for the fluid. These pumps are typically used in the metering of liquids and the pumping of viscous or shear-sensitive materials. Figure 1.5: Progressive Cavity Pump b) Reciprocating Pump Reciprocating pumps use the amount of water that is collected in an enclosed volume and is sent to discharge by applying pressure. Reciprocating pumps are used with low volume flow at high pressure. This pump consists of a piston that moves back and forth in a fixed cylinder. The piston is fastened to the crankshaft via a connecting rod. This piston moves as the movement of the connecting rod are due to the movement of the crankshaft. This crankshaft connects to a motor which helps it to turn.
Power Plant Engineering Equipment 7 | Figure 1.6: Reciprocating Pump i) Piston Pump These are types of pumps where a high-pressure seal relates to a piston. Piston pumps are used to move liquids or gases and they operate over a wide range of pressures. In this, the pumps can also deal with viscous media and media containing solid particles. This pump works by means of a piston cup which provides the oscillating mechanism where the downstroke causes the pressure difference. This action fills the pump chambers, where the up stroke pumps the fluid out for the required application. It is usually used in systems that require high and consistent pressure. Figure 1.7: Piston Pump
Power Plant Engineering Equipment 8 | ii) Plunger Pump In this type of pump, the high-pressure seal is fixed and a cylindrical plunger slides through the seal. Plunger pumps use a plunger instead of the piston to move media through a cylindrical chamber. These are operated by either steam-powered, pneumatic, hydraulic, or electric drives. These are often used in higher pressures, to move municipal and industrial sewage. It uses a crank mechanism to create a reciprocating motion along an axle, which then creates pressure in the cylinder or working barrel to force the gas or fluid through the pump. These plunger pumps are used for drill cutting injection and chemical injection. Figure 1.8: Plunger Pump iii) Diaphragm Pump A diaphragm pump is a pump that uses a combination of reciprocating rubber, thermoplastic, or Teflon diaphragms. Diaphragm pump uses rubber membrane and works on air displacement principle. In this type, the diaphragm is filled with one side in the fluid to be pumped (air or hydraulic fluid). As the volume of the chamber increases (the diaphragm moves upward), the pressure decreases, and fluid enters the chamber. And when the pressure of the chamber is increased by the subsequently reduced volume (going down the diaphragm), the drawn fluid is drained out. Finally, the diaphragm moves again up, drawing fluid into the chamber, completing the cycle.
Power Plant Engineering Equipment 9 | Figure 1.9: Diaphragm Pump 1.4.2 Dynamic Pump A dynamic pump uses centrifugal force to create velocity in the liquid. This velocity is further converted into pressure energy by decreasing the kinetic energy. This difference in pressure moves the fluid through the system. It consists of a rotating impeller that creates a vacuum that moves the fluid. The impeller is held in the housing as it reduces the pressure at the inlet. This created motion drives the fluid outside the housing of the pump. At this stage, the pressure builds up to send it out for discharge. These are classified into two types. The hydraulic machine which converts the mechanical energy into hydraulic energy is called Pumps. The hydraulic energy is in the form of pressure energy if the mechanical energy is converted into pressure energy by means of a centrifugal force acting on the fluid, the hydraulic machine is called a Centrifugal Pump.
Power Plant Engineering Equipment 10 | Figure 1.10: Centrifugal Pump Main Parts of Centrifugal Pump: • Impeller • Casing • Suction pipe with a foot valve • strainer and • Delivery pipe o Impeller: • An impeller is a rotating component of a centrifugal pump which transfers energy from the motor that drives the pump to the fluid being pumped by accelerating the fluid outwards from the centre of rotation. o Casing: • The Casing that receives the fluid being pumped by the impeller, slowing down the fluid's rate of flow. • A volute is a curved funnel that increases in area as it approaches the discharge port.
Power Plant Engineering Equipment 11 | o Suction pipe with a foot valve and strainer: • A pipe whose one end is connected to the inlet of the pump and another end dips into the water in a pump is known as a suction pipe. • A foot valve is found at the end of a pipeline in a suction lift application. • They function as a check valve, but they also have a strainer affixed to their open end. o Delivery Pipe: • A pipe whose one end is connected to the outlet of the pump and other ends delivers the water at a required height is known as a Delivery pipe. Figure 1.11: Centrifugal Pump a) Centrifugal pump Centrifugal pumps are employed to move the fluid through the transfer of rotational energy from the rotor, this device is known as an impeller. The fluid enters the rotating impeller and is ejected by centrifugal force through the vane tip of the impeller. This action of the impeller causes the fluid velocity and pressure to increase and also directs it towards the outlet. The pump casing is specially designed to compress fluid from the pump inlet, direct it into the impeller and control the fluid before discharging.
Power Plant Engineering Equipment 12 | Pumps of this type are used for the water supply, fire protection systems, and beverage industries. These are also classified into three types, which are explained below. i) Axial Flow The Axial flow type of pump basically consists of an axial impeller in a pipe. The propeller can be pushed directly into the pipe with help of an arranged electric motor or by a petrol/diesel engine that is mounted on the outside the pipe. Axial flow pumps have an electronic rotor that handles the liquid along a path parallel to the axis of the pump. Thus, the fluid travels in a fairly straight path from the inlet pipe to the outlet pipe through the pump. These are used as compressors in turbo-jet engines. Figure 1.12: Axial Flow Pump ii) Mixed Flow Mixed flow pumps are a combined version of both radial flow pumps and axial flow pumps. This pump is built with an impeller that sits and twists within the pipe, but the turning mechanism is essentially diagonal. It uses centrifugal force to move the water along, accelerating it further with a push from the axial direction of the impeller. This action generates enough force to produce a high rate of flow. Pumps of this type are used for those requiring a high level of flow combined with a relatively low discharge pressure.
Power Plant Engineering Equipment 13 | Figure 1.13: Mixed Flow Pump iii) Peripheral Pump It is a closely coupled centrifugal pump consisting of an impeller with large number of radial vanes at the outer edges. These pumps require clean fluid because of the narrow clearance between the impeller vane and the pump casing, meaning any solids will clog the impeller. The centrifugal force inside the rotor generates a flow between the impeller and the casing channel. The speed of the fluid and the impeller are basically the same. Therefore, the fluid flows from the covered channel to the impeller in a rotational path, and this cycle is repeated. Figure 1.14: Peripheral Pump b) Special Effect Pump The kinetic pumps are also known as special effects pumps. This type of pump is one in which adding energy is still kinetic and velocity, but it employs other effects than centrifugal pumps. These pumps are further classified into two types.
Power Plant Engineering Equipment 14 | i) Jet Pump These types of pumps are used to flow the fluid by a driving nozzle that converts the fluid pressure into a high-speed jet. To run a typical jet pump, it must be completely filled with water. When the system is primed, a centrifugal pump is used to push the water out. Some of the water gets discharged while the rest is recirculated into the driveline. When water enters the nozzle, fluid is pushed through the venturi by generating a vacuum. Then, it draws the water up the well through a foot valve. As the water moves the venturi tube into the section line it comes with a greater pressure to force the water back into the pump impeller. Figure 1.15: Jet Pump ii) Electromagnetic Pump An electromagnetic pump is installed for moving mediums alike liquid metals, molten salts, brine, or other electrically conductive liquids by using electromagnetism energy. In this, a magnetic field is set at right angles to the direction in which the liquid moves and the current flows. This generates an electromagnetic force that moves the liquid forward. These are commonly used to pump liquid metal through the cooling system. In addition, they are also seen in many wave soldering machines that use electromagnetic pumps to circulate the molten solder.
Power Plant Engineering Equipment 15 | Figure 1.16: Electromagnetic Pump 1.5 Applications of Centrifugal Pumps: • Centrifugal pumps are used in buildings for pumping the general water supply, as a booster and for domestic water supplies. • The design of a centrifugal pump makes them useful for pumping sewage and slurries. • They are also used in fire protection systems and for heating and cooling applications. • Beverage industry: Used to transfer juice, bottled water, etc. • Dairy industry: Used to transfer dairy products such as milk, buttermilk, flavoured milk, etc. • Various industries (Manufacturing, Industrial, Chemicals, Pharmaceutical, Food Production, Aerospace, etc.) for the purposes of cryogenics and refrigerants. • Oil Energy: pumping crude oil, slurry, mud; used by refineries, power generation plants. 1.6 Advantages of Pump: These are some advantages of Pump: • As there is no drive seal so there is no leakage in the pump. • There are very less frictional losses. • The construction of the pump is Simple. • Almost no noise. • Minimum wear as compared to others.
Power Plant Engineering Equipment 16 | 1.7 Disadvantages of Pump These are some disadvantages of Pump: • Produce cavitation. • Corrosion. • Cannot be able to work at high speed. 1.8 Applications of Pump The main applications of the pump are: • As we already discussed Pumping Water from one place to another place. • Aquarium and pond filtering • This is also used for Water cooling and fuel injection in automobiles. • Pumping oil or gas and operating cooling towers in the energy industry. • Uses in waste-water recycling, pulp, and paper, chemical industry, etc. 1.9 Five Things to Select Perfect Pump a) Fluid This is the most important factor when selecting a pump to avoid corrosion and unnecessary wear and tear on your pump. What’s the chemical makeup of the fluid to be pumped? What’s the consistency? Is it a slurry (thick suspension of solids in liquids), or is it a clean fluid? b) Flow Rate You need to know the flow rate to select the proper pump. This is measured in gallons per minute (GPM), although in day-to-day speak, this translates into the pump diameter measurement. Remember: a higher flow rate means a larger pump size is needed. c) Viscosity In order to select the right pump, you need to know the viscosity of the fluid to be pumped. High viscosity fluids require more robust pumping equipment. Nine times out of 10, however, our customers are pumping fluid with a viscosity less than that of motor oil. d) Temperature
Power Plant Engineering Equipment 17 | How hot will the fluid you are pumping be? This will affect which pump materials are best suited for your application. e) Pressure Another factor you should consider when selecting your pump is what the pressure conditions on the inlet and outlet of your pump will be. This information will help you determine the right equipment. 1.10 Important Factors to Considerations for Extending Pump Life. a) Radial Force • Anybody who has been around the industry very long probably knows that the No. 1 best practice is to operate the pump at or near its best efficiency point (BEP). b) Oil Contamination • For ball bearings, more than 85 percent of bearing failures result from the ingress of contamination, either as dirt and foreign material or as water. Just 250 parts per million (ppm) of water will reduce bearing life by a factor of four. • Oil service life is critical. Operating a pump can be similar to operating a car continuously at 60 miles per hour. c) Suction Pressure • Other key factors for bearing life are suction pressure, driver alignment and, to some degree, pipe strain. • For a single-stage horizontal overhung process pump such as an ANSI B 73.1 model, the resultant axial force on the rotor is toward the suction, so a counteracting suction pressure—to some degree and with limits—will actually reduce the axial force, which decreases the thrust bearing loads, contributing to longer life. • For example, a standard S-frame ANSI pump with a suction pressure of 10 pounds per square inch gauge (psig) can typically expect a bearing life of six to seven years, but at a suction of 200 psig, the expected bearing life will improve to more than 50 years. d) Driver Alignment
Power Plant Engineering Equipment 18 | • Misalignment of the pump and the driver overloads the radial bearings. • Radial bearing life is an exponential factor when calculated with the amount of misalignment. • For example, with a small misalignment of just 0.060 inches, end users can expect some sort of bearing or coupling issues at three to five months of operation; at 0.001 inches of misalignment, however, the same pump will likely operate for more than 90 months. e) Pipe Strain • Pipe strain is caused by misalignment of the suction and/or discharge pipe to the pump flanges. • Even in robust pump designs, the resultant pipe strain can easily transmit these potentially high forces to the bearings and their respective housing fits. The force (strain) causes the bearing fit to be out of round and/or incongruent with the other bearings so that the centrelines are in different planes. f) Fluid Properties • Fluid properties (the fluid’s personality) such as pH, viscosity and specific gravity are key factors. If the fluid is acidic or caustic, the pump wetted parts such as the casing and impeller materials need to hold up in service. The number of solids present in the fluid and their size, shape and abrasive qualities will all be factors. g) Service • The severity of the service is another major factor: • How often will the pump be started during a given time? h) NPSHa/r Margin • The higher the margin of net positive suction head available (NPSHA ) is over net positive suction head required (NPSHR ), the less likely the pump will cavitation. • Cavitation will create damage to the pump impeller, and resultant vibrations will affect the seals and bearings. i) Pump Seed
Power Plant Engineering Equipment 19 | • The speed at which the pump operates is another key factor. • For instance, a 3550-rpm pump will wear out faster than a 1750-rpm pump by a factor of 4-to-8. j) Impeller Balance • An unbalanced impeller on an overhung pump or on some vertical designs can cause a condition known as shaft whip, which deflects the shaft just as a radial force does when the pump operates away from the BEP. • Radial deflection and whip can occur at the same time. • Impeller should be balanced at least to International Organization for Standardization (ISO) 1940 grade 6.3 standards. • If the impeller is trimmed for any reason, it must be rebalanced. k) Pipe Geometry • Another important consideration for extending pump life is the pipe geometry, or how the fluid is “loaded” into the pump. • For example, an elbow in the vertical plane at the pump’s suction side will induce fewer deleterious effects than one with a horizontal elbow. The impeller is hydraulically loaded more evenly, so the bearings are also loaded evenly. l) Pump Operating Temperature • Whether hot or cryogenic, the pump operating temperature—and especially the rate of temperature change—will have a large effect on pump life and reliability. • The temperature at which a pump operates is important, and the pump needs to be designed to operate there. • More important, however, is the rate of temperature change. m) Casing Penetration • While not often considered, the reason casing penetrations are an option rather than a standard on ANSI pumps is the number of pump casing penetrations will have some effect on pump life because these sites are prime for the setup of corrosion and stress risers.
Power Plant Engineering Equipment 20 | • Many end users want the casing drilled and tapped for drains, vents, gauge ports or instrumentation. • Every time you drill and tap a penetration in the casing, it sets up a stress riser in the material that becomes an origin source for stress cracks and presents a site for corrosion to initiate. 1.11 Types of Energy /Head Loses in Pipelines. Loses of energy in pipe are due to: • Shock Loss at Sudden Enlargement (hL) • Shock Loss at Sudden Contraction (hc) • Loss at Sharp Entrance (hi) • Loss at Sharp Exit (ho) • Frictional Resistance to Flow (hf) a) Shock loss at sudden enlargement • Fluid flows from small diameter pipe 1 to a larger diameter pipe 2. Figure 1.17: Sudden Enlargement in Pump • In a sudden enlargement, the loss of head when a pipe undergoes a sudden increase in diameter. • To calculate the loss, the following equation is given.
Power Plant Engineering Equipment 21 | • V= velocity in the pipe Figure 1.18: Loss of Head at Enlargement b) Shock loss at sudden contraction • Fluid flows from a larger diameter pipe 1 to a smaller diameter pipe 2. Figure 1.19: Shock loss at sudden contraction • In a sudden contraction, the loss of head when a pipe undergoes a sudden decrease in diameter. • To calculate the loss, the following equation is given. Cc= Coefficient of contraction Figure 1.20: Shock loss at sudden contraction c) Loss at sharp entrance
Power Plant Engineering Equipment 22 | • Fluid from reservoir or tank with a sharp entrance flow into pipe. Figure 1.21: Loss at sharp entrance • In the entrance of a pipeline from a reservoir is sharp (no rounded or bell mouthed) it is equivalent to a sudden contraction from a pipe of infinite size to that of the pipeline. • The loss of head at sharp entrance is v= velocity in the pipe Figure 1.21: Loss at sharp entrance equation d) Loss at sharp exit • Fluid from the pipe flows into the reservoir or tank. Figure 1.22: Loss at sharp exit
Power Plant Engineering Equipment 23 | • When a pipe discharges into a large reservoir through a sharp exit, conditions are equivalent to a sudden enlargement. Figure 1.23: Loss at sharp exit equation e) Frictional resistance to flow • Head loss due to friction occurring in the pipes. If there are two (2) pipes in a pipeline system so there are two (2) friction; hf1 and hf2. Figure 1.24: Frictional resistance to flow • When there is a loss of head due to friction in a pipeline in terms of the velocity head; we assume that the frictional resistance per unit area of the pipe wall is proportional to the square of the mean velocity of flow. f =Friction factor (Darcy formula; f = 0.01) d = Diameter of pipe L = Length of pipe Figure 1.19: Loss of Head due to friction
Power Plant Engineering Equipment 24 | TUTORIAL: PUMP Question 1 Calculate the pressure in the unit N/m2 to 25 cm of water column at 5C. Question 2 Pressure at the pump that pumps the water at 80C is 150 kN/m2 . Determine the pressure head in meters. Question 3 A pipe carrying 0.02 m3 /s of water. Calculate the head losses in pipe due to diameter changing below: (i) 30 cm to 45 Question 4 A pump is required to operate the water temperature of 70C on standard barometric pressure. Friction head is 2.5m, the velocity of the fluid in the suction pipe is 5 m / s and pumps maker said the pump must have a net positive suction head (NPSH) 3 meter to operate at its maximum capacity. Determine the suction lift (HS) for the pump. Question 5 An open tank of water at 90C. If the head friction and other losses on the suction side is five meters, determine the minimum water column theoretically required. Question 6 Determine the loss of head due to friction in a new cast –iron pipe 365m long and 150mm diameter which carries 43 dm3 /s. Use the Darcy Formula, taking =0.005.
Power Plant Engineering Equipment 25 | *For purposes of the calculation formula below can be used NPSH. NPSH = [(Pa -pv) / pg] - hf - hv - fitting + hs Pa = barometric pressure Pv = vapor pressure associated with supply water temperature Vf = volume of the water temperature hf = friction head hv = velocity head hs = head pressure - (- ve) If the source of supply under the pump - (+ve) if the supply is above the pump
Power Plant Engineering Equipment 26 | CHAPTER 2: COMPRESSOR 2.0 What Is a Compressor? • A compressor is a device that is typically powered by an electric motor. • This motor turns a shaft that, in turn, compresses air in one of three ways. Figure 2.1: Compressor 2.1 What is compressed air? Who uses it? • Compressed air is a utility used by over 70% of industry as a resource for operating key components in production and services. • It is stored energy in the form of compressed and stored gas (air). • It is used to perform various functions in industry, the most popular being the actuation of large valves and the operation of pneumatic tools, especially in the automotive industry.
Power Plant Engineering Equipment 27 | Figure 2.2: Various types of compressors • Automobile manufacturers commonly use both pneumatic and hydraulic robots for the assembly of cars and trucks. • The automotive repair industry also uses compressed air to fill tires and to power pneumatic tools. Figure 2.3: Application of compressed air in Automotive Industries
Power Plant Engineering Equipment 28 | 2.3 What Is a Compressed Air Dryer? There are two different types of compressed air dryers, both serving the purpose of removing moisture/humidity from the newly compressed air. Figure 2.4: Dryer Tower 2.4 Compressor Tanks While tanks are meant to provide an area in which the compressed air resides, they also allow the air to cool, which similarly releases moisture from the air, which is then later drained from the storage tank. Figure 2.5: Compressor tank
Power Plant Engineering Equipment 29 | 2.5 Significant Inefficiencies • Compressors: 5 to > 50,000 hp • 70 – 90% of compressed air is lost Figure 2.6: Loss in compressor 2.6 Main Components in Compressed Air Systems • Intake air filters • Inter-stage coolers • After coolers • Air dryers • Moisture drain traps • Receivers
Power Plant Engineering Equipment 30 | Figure 2.7: Compressor Air Plant Layout 2.7 Types of Compressors Figure 2.8: Type of Compressor a) Reciprocating Compressor • In industry, reciprocating compressors are the most widely used type for both air and refrigerant compression. • They work on the principles of a bicycle pump and are characterized by a flow output that remains nearly constant over a range of discharge pressures. Also, the compressor capacity is directly proportional to the speed. The output, however, is a pulsating one. • Reciprocating compressors are available in many configurations. Type of compressor Positive displacement Reciprocating Rotary Dynamic Centrifugal Axial
Power Plant Engineering Equipment 31 | ▪ The four most widely used are horizontal, vertical, horizontal balance-opposed and tandem. ▪ air-cooled or water-cooled. ▪ lubricated and non-lubricated ▪ may be packaged. ▪ provide a wide range of pressure and capacity selections. The reciprocating air compressor is considered single acting when the compressing is accomplished using only one side of the piston. A compressor using both sides of the piston is considered double acting. Figure 2.9: Reciprocating Compressor b) Rotary Compressor • Rotary compressors have rotors in place of pistons and give a continuous pulsation free discharge. They operate at high speed and generally provide higher throughput than reciprocating compressors. Their capital costs are low, they are compact in size, have low weight, and are easy to maintain. For this reason, they have gained popularity with industry. They are most commonly used in sizes from about 30 to 200 hp or 22 to 150 kW. • Types of rotary compressors include: Lobe compressor, Screw compressor, Rotary vane / sliding-vane. The picture shows a screw compressor • Rotary screw compressors may be air or water-cooled. Since the cooling takes place right inside the compressor, the working parts never experience extreme operating temperatures. The rotary compressor, therefore, is a continuous duty, air cooled or watercooled compressor package.
Power Plant Engineering Equipment 32 | Figure 2.10: Rotary Compressor c) Centrifugal Compressor • The centrifugal air compressor is a dynamic compressor, which depends on transfer of energy from a rotating impeller to the air. The rotor accomplishes this by changing the momentum and pressure of the air. This momentum is converted to useful pressure by slowing the air down in a stationary diffuser. • The centrifugal air compressor is an oil free compressor by design. The oil lubricated running gear is separated from the air by shaft seals and atmospheric vents. • The centrifugal is a continuous duty compressor, with few moving parts, that is particularly suited to high volume applications-especially where oil free air is required. • Centrifugal air compressors are water-cooled and may be packaged; typically, the package includes the after-cooler and all controls. • These compressors have appreciably different characteristics as compared to reciprocating machines. A small change in compression ratio produces a marked change in compressor output and efficiency. Centrifugal machines are better suited for applications requiring very high capacities, typically above 12,000 cfm (cubic feet per minute).
Power Plant Engineering Equipment 33 | Figure 2.11: Centrifugal Compressor 2.8 Comparison of Compressors These factors are important when selecting a compressor. • Noise level • Size • Vibration • Maintenance • Capacity • Pressure • Oil carry-over • Efficiency at full, partial and no load
Power Plant Engineering Equipment 34 | 2.9 Formula for Compressors Work input per cycle = ( ) 2 1 . 1 m R T T n n − − Indicated Power = N P P pV n n n n − − − 1 1 1 1 2 Indicated Power = − − − 1 1 1 1 2 1 . n n P P m R T n n Where, V = (Va –Vd) , N = Motor Speed, P = Input Pressure Compressor mechanical efficiency = Indicated Power Shaft Power Swept Volume = (Va-Vc)=Vs (m3 ) Where Vs = L d 4 2 and d = diamater and L = length of the stroke (m3 ) Clearance Volume = Vc (m3 ) Volume induced = (Va-Vd) where n P P Vd Vc 1 1 2 = (m3 /min) Delivery temperature T2 = n n P P T 1 1 2 1 −
Power Plant Engineering Equipment 35 | F.A.D = ( ) 1 2 2 1 P P T T Va −Vd where F.A.D stand for free air delivery Volumetric efficiency = 1 1 1 1 2 − − n P P Vs Vc Volumetric efficiency = a c a d V V V V − −
Power Plant Engineering Equipment 36 | TUTORIAL: COMPRESSOR Question 1 A single-stage reciprocating compressor takes 1 m3 of air per minute at 1.013 bar and 15C and delivers it at 7 bars. Assuming that the law of compression is pV1.35 = constant, and that clearance is negligible, Calculate: i) Mass delivered per min ii) Delivery temperature iii) Indicated power iv) The power of the motor required to drive the compressor if the mechanical efficiency of the compressor is 85% Question 2 A single stage reciprocating compressor running at 600 rev/min takes 7 liters of air per second at 0.1013 MN/m2 and delivers it at 1.4 MN/m2 . Assuming that the law of compression is pV1.3=constant, and that clearance is negligible. The mechanical efficiency of the compressor is 82%. Determine the shaft power required to drive the compressor. Question 3 A single stage, single acting air compressor takes 0.0233m3 of air per second at 1.013bar and 15C. The delivery pressure is 7 bar and the speed 300 rev/min. Take the clearance volume as 5% of the swept volume with a compression and re-expansion index of n = 1.3. Calculate: i) Swept volume of the cylinder ii) Delivery temperature iii) Indicated power Question 4 A single stage, single acting air compressor running at 500 rev/min, has a bore of 200 mm and stroke of 300 mm. The clearance volume is 5% of the swept volume. The inlet pressure and temperature are 97 kN/m2 and 20C. The delivery pressure is 550 kN/m2 . Assume the index of compression is 1.3. Calculate:
Power Plant Engineering Equipment 37 | i) Free air delivery ii) Volumetric efficiency iii) Delivery temperature iv) Indicated power Question 5 A single stage, single acting air compressor running at 8 rev/ per second, has a bore and stroke of 150 mm. The clearance volume is 6% of the swept volume. The inlet pressure is 100 kN/m2 and the delivery pressure is 550 kN/m2 . Assume the index of compression is 1.32 for the process. Calculate: i) Volumetric efficiency ii) Indicated power iii) Clearance Volume Question 6 A single-stage, single-acting air compressor running at 1000 rev/min delivers air at 25 bars. For this purpose, the induction and free air conditions can be taken as 1.013 bar and 15 °C, and the FAD as 0.25 m3 /min. The clearance volume is 3% of the swept volume and the stroke/bore ratio is 1.3/1. Calculate: i) the bore and stroke ii) the volumetric efficiency iii) the indicated power iv) the delivery temperature Take the index of compression and re-expansion as 1.3.
Power Plant Engineering Equipment 38 | CHAPTER 3: COMBUSTION 3.0 Classification of Fuel Fuel may be chemical or nuclear. A chemical fuel is a substance which release heat energy on combustion. The principal combustible elements of each fuel are carbon and hydrogen. • Fuel can be classified according to whether: o They occur in nature called primary fuels or are prepared called secondary fuels. o They are in solid, liquid, or gaseous state. o The detailed classification of fuels can be given in a summary form as follows: Table 3.1: Types of fuel TYPE OF FUEL NATURAL (Primary) PREPARED (Secondary) Solid Wood Lignite coal Peat Coke Briquettes Charcoal Liquid Petroleum Gasoline Kerosene Alcohol Gaseous Natural gas Petroleum gas 3.1 Basic Chemistry 3.2.1 Atoms • Chemical elements cannot be divided indefinitely and the smallest particle which can take part in a chemical change is called an atom. • If an atom is split as in a nuclear reaction, the divided atom does not retain the original chemical properties.
Power Plant Engineering Equipment 39 | 3.2.2 Molecules • Elements are seldom found to exist naturally as single atoms. • Some elements have atoms which exist in pairs, each pair forming a molecule (e.g oxygen), and the atoms of each molecule are held together by strong inter-atomic forces. Table 3.2: Relative atomic and molecular masses of some common substances Element Atomic Symbol Relative atomic mass Molecular grouping Relative molecular mass Carbon C 12 C 12 Hydrogen H 1 H2 2 Oxygen O 16 O2 32 Sulphur S 32 S 32 Nitrogen N 14 N2 28 Table 3.3: Compounds and their relative molecular masses. Compound FORMULA Relative molecular mass Water, steam H2O (2x1)+(1x16) = 18 Carbon monoxide CO (1x12)+(1x16)=28 Carbon dioxide CO2 (1x12)+(2x16)=44 Sulphur dioxide SO2 (1x32)+(2x16)=64 Methane CH4 (1x12)+(4x1)=16 Benzene C6H6 (6x12)+(6x1)=78 Propane C3H8 (3x12)+(8x1)=44 3.3 Combustion Equations for Complete and Incomplete Combustion a) The Complete Combustion of Carbon-to-Carbon Dioxide 1 kg C + 3 8 kg O2 → 3 11 kg CO2 b) The Incomplete Combustion of Carbon-to-Carbon Monoxide
Power Plant Engineering Equipment 40 | 1 kg C + kg 3 4 O2 + kg 24 105.3 N2 → kg 3 7 CO + kg 24 105.3 N2 c) Combustion Of Hydrogen to Steam 1 kg H2 + 8 kg O2 + 4 105.3 kg N2 → 9 kg H2O + kg 4 105.3 N2 d) Combustion Of Sulphur-to-Sulphur Dioxide 1 kg S + 1 kg O2 + kg 32 105.3 N2 → 2 kg SO2 + kg 32 105.3 N2 3.4 Stoichiometric Air-Fuel Ratio. • A stoichiometric (or chemically correct) mixture of air and fuel is one that contains just sufficient oxygen for the complete combustion of the fuel. • A weak mixture is one which has an excess of air. • A rich mixture is one which has a deficiency of air. • Percentage (%) excess air = Actual A/F ratio – Stoichiometric A/F ratio Stoichiometric A/F ratio (where A and F denote air and fuel respectively) The ratio is expressed as follows: o For gaseous fuels by volume o For solid and liquid fuels by mass o For boiler plant the mixture is usually greater than 20% weak o For gas turbines it can be as much 300% weak. o Petrol engines have to meet various conditions of load and speed and operate over a wide range of mixture strength. • Mixture strength = Stoichiometric A/F ratio
Power Plant Engineering Equipment 41 | Actual A/F ratio • The reciprocal of the air fuel ratio is called the fuel-air (F/A) ratio. Stoichiometric Air-Fuel Ratio: C + 8H + S − O 3 8 23.3 100 Actual A/F Ratio: + + + − + + − C H S O excessair C H S O 8 3 8 23.3 100 100 . 8 3 8 23.3 100 3.5 Exhaust and Flue Gas Analysis • The product of combustion is mainly gaseous. • When a sample is taken for analysis, it is usually cooled down to a temperature which is below the saturation temperature of the steam present. • The steam content is therefore not included in the analysis, which is then quoted as the analysis of the dry products. • Since the product are gaseous, it is usual to quote the analysis by volume. • An analysis which includes the steam in the exhaust is called a wet analysis.
Power Plant Engineering Equipment 42 | Example 1: A sample of dry anthracite has the following composition by mass. C 90%; H 3%; O 2.5%; N 1%; S 0.5%; ash 3% Calculate: (i) the stoichiometric A/F ratio (ii) actual A/F ratio (iii) analysis of the product of combustion by mass when 20% excess air is supplied. Solution: Stoichiometric A/F ratio: = C + 8H + S − O 3 8 23.3 100 = ( ) ( ) ( ) ( ) 0.9 + 8 0.03 + 0.005 − 0.025 3 8 23.3 100 = 2.62 23.3 100 O2 required per kilogram of coal = 11.245kg. For an air supply which is 20% in excess: = 11.245 100 20 = 2.249 kg Actual A/F ratio: = stoichiometric A/F ratio + excess air = 11.245 + 2.249 = 13.494 kg
Power Plant Engineering Equipment 43 | The mass analysis for this combustion can be calculated by this method. Combustion Result Mass (KG) % Mass (a) 0.9 3 11 3 11 CO2 = C = 3.300 22.82% (b) H2O = 9H = 90.03 0.270 1.87% (c) SO2 = 2S = 20.005 0.010 0.07% (c) O2 = (0.233 actual A/F ratio) - O2 required = (0.233 13.494) – 2.62 0.524 3.62% (d) N2 = 0.767 actual air + N2 supplied = (0.767 13.494) + 0.01 10.359 71.62% TOTAL 14.463 100% Example 2: C 88%, H 2.4%, O2.1%, N 0.6%, S 0.8%, ash 6.1%. Calculate the A/F ratio and the dry and wet analysis of the products of combustion by mass and by volume, when 25% excess air is supplied. Stoichiometric A/F ratio: = C + 8H + S − O 3 8 23.3 100 = ( ) ( ) ( ) ( ) 0.88 + 8 0.024 + 0.008 − 0.021 3 8 23.3 100 = 100 23.3 × [2.526] O2 required per kilogram of coal = 10.841 kg. For an air supply which is 25% in excess:
Power Plant Engineering Equipment 44 | = 25 100 × 10.841 = 2.710 kg Actual A/F ratio: = stoichiometric A/F ratio + excess air = 10.841 + 2.710 = 13.551 kg Example 3: Chemical Equilibrium Method The analysis of a supply of gas is as follow: 27% H2, 7% CO, 48% CH4, 13% C2H4, 3% CO2 and 2% N2 Calculate: (i) The stoichiometric A/F ratio using the chemical equilibrium method. (ii) The wet and dry analysis of the products of combustion if the mixture strength is 50% weak. Solution: Com. Results Mass/kg Fuel % Mass M Mass/kg fuel / M % wet analysis % dry analysis CO2 0.88 3.227 3 11 = 22.272 44 0.0733 15.377 15.774 H2O 90.024 = 0.216 1.491 18 0.0120 2.517 0.00 SO2 20.008 = 0.016 0.110 64 0.0003 0.063 0.065 O2 O2 = (0.233 actual A/F ratio) - O2 required. = (0.233 13.551) – 2.526 = 0.631 4.355 32 0.0197 4.133 4.239 N2 N2 = 0.767 actual air + N2 supplied. = (0.767 13.551) + 0.006 = 10.399 71.772 28 0.3714 77.910 79.922 TOTAL 14.489 100% WET 0.4767 100% 100% DRY 0.4647
Power Plant Engineering Equipment 45 | H2 = 27% = 0.27 CO = 7% = 0.07 CH4 = 48% = 0.48 C2H4 = 13% = 0.13 CO2 = 3% = 0.03 N2 = 2% = 0.02 Carbon Equilibrium: ( ) ( ) ( ) ( ) 0.84 0.07 0.48 0.26 0.03 1 0.07 1 0.48 2 0.13 1 0.03 = + + + = + + + = a a a Hydrogen Equilibrium: ( ) ( ) ( ) 1.49 2 2.98 2.98 2 0.54 1.92 0.52 2 2 0.27 4 0.48 4 0.13 2 = = = + + = + + = b b b b Oxygen Equilibrium: ( ) ( ) ( ) 1.52 0.07 0.06 2 1.68 1.49 0.07 0.06 2 2 0.84 1.49 1 0.07 2 0.03 2 2 = + + = + + + = + + + = + x x x x a b 100 21 × 1.52 = (7.238 × 28.96) = 209.612
Power Plant Engineering Equipment 46 | = (0.27 × 2) + (0.07 × 28) + (0.48 × 16) + (0.13 × 28) + (0.03 × 44) + (0.02 × 28) = (0.54 + 1.96 + 7.68 + 3.64 + 1.32 + 0.56) = 15.70 Stoichiometric A⁄F ratio = 209.61 15.70 = 13.351 kg air⁄kg fuel Actual A F ratio = 13.351 0.50 ⁄ = 26.702 (i) Wet and dry analysis of the products Excess oxygen: (0.21 × 26.702) − 1.52 = 4.087 Total amount of nitrogen in products: (0.79 × 26.702) + 0.02 = 21.115
Power Plant Engineering Equipment 47 | TUTORIAL: COMBUSTION Question 1 Calculate the stoichiometric A/F ratio for benzene ( ). C6H6 : Question 2 Calculate the stoichiometric A/F ratio for Propane ( ) C3H8 . Question 3 A sample of bituminous coal gave the following ultimate analysis by mass: C 81% ; H 4.5% ; O 6% ; N 2.3% ; S 2.5; ash 3.7% . Calculate : (i) the stoichiometric A/F ratio (ii) actual A/F ratio (iii) analysis of the products of combustion by mass when 20% excess air is supplied. Question 4 A sample of dry anthracite has the following composition by mass: C 88%; H 5%; O 2.5%; N 1%; S 0.5%; ash 3% Calculate: (i) the stoichiometric A/F ratio (ii) the A/F ratio and the dry and wet analysis of the products of combustion by mass and by volume, when 20% excess air is supplied. Question 5 A sample of dry anthracite has the following composition by mass: C 85%; H 6%; O 2.5%; N 1%; S 0.5%; ash 5%
Power Plant Engineering Equipment 48 | Calculate: (i) the stoichiometric A/F ratio (ii) mixture strength (iii) the A/F ratio and the dry and wet analysis of the products of combustion by mass and by volume, when 20% excess air is supplied. Question 6 Calculate the stoichiometric air-fuel ratio for the combustion of a sample of dry anthracite of the following by mass: Carbon (C) = 88 percent Hydrogen (H2) = 4 percent Oxygen (O2) = 3.5 percent Nitrogen (N2) = 1 percent Sulphur (S) = 0.5 percent Ash = 3 percent If 30 percent excess air is supplied determine: (i) Air-fuel ratio (ii) Actual A/F ratio (iii) Wet dry analysis of the product of combustion by volume Question 7 The analysis of a supply of gas is as follow: 81.3% CH4, 2.9% C2H6, 0.4% C3H8, 0.2% C4H10, 14.3% N2, and 0.9% CO2 Calculate: (iii) The stoichiometric A/F ratio using the chemical equilibrium method. (iv) The actual A/F ratio if the mixture strength is 25%
Power Plant Engineering Equipment 49 | Question 8 The analysis of a supply of gas is as follow: 59.4% H2, 5.6% CO, 22% CH4, 5% C4H8, 0.3% O2, 1.5% CO2, 6.2% N2 Calculate: (i) The stoichiometric A/F ratio using the chemical equilibrium method. (ii) The actual A/F ratio if the mixture strength is 20%
Power Plant Engineering Equipment 50 | CHAPTER 4: NOZZLE 4.1 Definition of Nozzle A nozzle is a duct of smoothly varying cross –sectional area in which a steadily flowing fluid can be made to accelerate by a pressure drop along the duct. Figure 4.1: Nozzle 4.2 Application of Nozzle There are many applications in practice which require a high-velocity stream of fluid and the nozzle is the best means of obtaining this: For example: • Nozzles are used in steam and gas turbines. • In jet engines • In rocket motors • In flow measurement • For pumping fed water into boilers • To maintain high vacuum in power plant condenser or steam jet refrigeration condenser.