Guidelines for Processing Plant KLM Technology #03-12 Block Aronia, Jalan Sri Perkasa 2 Taman Tampoi Utama 81200 Johor Bahru Malaysia, Standards and Software www.klmtechgroup.com Kolmetz Handbook of Process Equipment Design (ENGINEERING DESIGN GUIDELINE) Page : 1 of 70 Rev 01 Co Author Rev 01 Aprilia Jaya Editor / Author Karl Kolmetz KLM Technology has developed; 1) Process Engineering Equipment Design Guidelines, 2) Equipment Design Software, 3) Project Engineering Standards and Specifications, and 4) Unit Operations Manuals. Each has many hours of engineering development. KLM is providing the introduction to this guideline for free on the internet. Please go to our website to order the complete document. www.klmtechgroup.com TABLE OF CONTENT INTRODUCTION 4 Scope 4 General Design Consideration 5 DEFINITIONS 30 NOMENCLATURE 33 THEORY OF THE DESIGN 34
Page 2 of 70 Specific Volume 34 Enthalpy 34 Entropy 36 Steam 38 Rankine Cycle 43 Design Characteristics 47 Steam Turbine Calculation Sizing 48 Efficiency 55 Steam Consumption 58 APPLICATION Example 1: Steam Turbine Sizing 62 Example 2: Calculation of ASR and total steam for multi and single stage 65 REFEREENCES 68 CALCULATION SPREADSHEET 69 LIST OF TABLE Table 1: Steam Turbine Blading Failure Mechanisms 24 Table 2: Steam Characteristics 39 Table 3: Important features of different heating media. 42
LIST OF FIGURE Page 3 of 70 Figure 1: Steam turbine blades arrangement of reaction blades 8 Figure 2: Single Stage Impulse Steam Turbine Cutaway 9 Figure 3: Principle of impulse turbine 10 Figure 4: Section of reaction turbine blading 11 Figure5: Principle of reaction turbine 11 Figure 6: Diagram of simple impulse and reaction turbine stages. 12 Figure 7: Operating Range of Steam Turbines 13 Figure 8: Condensing steam turbine for approximately 65-MW output. 14 Figure 9: Backpressure steam turbine for approximately 28-MW output. 15 Figure 10: Extraction condensing steam turbine. 16 Figure 11: Non-Condensing Steam Turbine, Extraction Steam Turbine 17 Figure 12: Schematics of typical (a) high-, (b) intermediate-, and (c) low-pressure steam turbine sections. 20 Figure13: Turbine steam chest and valve assembly. 21 Figure14: Single Valve with Hand Valves 22 Figure 15: Multi-Valve Inlet 23 Figure 16: Double-flow low-pressure turbine showing variation in blade size. 26 Figure17: the effect of temperature to entropy 38 Figure 18: Steam Phase Diagram 40 Figure 19: Components of a Boiler/Steam Turbine System 43 Figure 20: A theoretical Rankine Cycle 44 Figure 21: Turbine base diameter selection and maximum blade height. 51 Figure 22: Basic Efficiency of Multi-Valve, Multi-Stage Condensing Turbines 52 Figure 23: Basic Efficiency of Multi-Valve, Multi-Stage Non-Condensing Turbines 53 Figure 24: Steam rate in single stage application 54 Figure 25: Stages Required per 100 Btu/lb of Available Energy as a Factor of Normal Turbine Speed 55
Page 4 of 70 Figure 26: Efficiency of Reaction Turbine 57 Figure 27: Mechanical Efficiency 58 Figure 28: Output power, speed and enthalpy range for several design of Curtis Turbine 60 Figure 29: Output power, speed and enthalpy range for several design of Rateau Turbine 61
INTRODUCTION Scope Page 5 of 70 Steam is used for large industrial process heating. One of pieces of equipment which uses steam is the steam turbine, as a heat engine. Steam turbines are used in industry for several critical purposes: 1) to generate electricity by driving an electric generator and 2) to drive equipment such as compressors, fans, and pumps. Steam turbines are available in a wide range of steam conditions, horsepower, and speeds. The design of Steam Turbine is influenced by factors, including process requirements, economics and safety. This engineering design guideline covers the basic elements of Steam Turbines in sufficient detail to allow an engineer to design a Steam Turbine with the suitable inlet and exhaust diameter, Steam rate, enthalpy change and number of stages. The theory section explains properties of steam, types of steam turbine and their characteristics, steam turbine efficiencies and how to calculate the sizing and selection of a steam turbine. General Design Consideration A heat engine is one that converts heat energy into mechanical energy. The steam turbine is classified as a heat engine. Other heat engines are the internal combustion engine and the gas turbine. Steam turbines are used in industry for several critical purposes: to generate electricity by driving an electric generator and to drive equipment such as compressors, fans, and pumps. Steam turbines are available for a wide range of steam conditions, horsepower, and speeds. Typical ranges for each design parameter are: Inlet Pressure, psig 30 2000 Inlet Temperature, F saturated 1000 Exhaust Pressure, psig saturated 700 Horsepower 5 100,000 Speed, rpm 1800 14,000 The steam turbine has a stationary set of blades (called nozzles) and a moving set of adjacent blades (called buckets or rotor blades) installed within a casing. The two sets of blades work together such that the steam turns the shaft of the turbine and the connected load. The stationary nozzles accelerate the steam to a high velocity by expanding it to lower pressure. A rotating bladed disc changes the direction of the
Page 6 of 70 steam flow, thereby creating a force on the blades that, because of the wheeled geometry, manifests itself as torque on the shaft on which the bladed wheel is mounted. The combination of torque and speed is the output power of the turbine. Steam turbines used as process drivers are usually required to operate over a range of speeds, in contrast to a turbine used to drive an electric generator which runs at nearly constant speed. The steam turbine permits the steam to expand and attain high velocity. It then converts this velocity energy into mechanical energy. Mechanical drive steam turbines are categorized as: Single-stage or multi-stage Condensing or non-condensing exhausts Extraction or admission Impulse or reaction Based on Stage 1. Single stage In a single-stage turbine, steam is accelerated through one cascade of stationary nozzles and guided into the rotating blades or buckets on the turbine wheel to produce power. A Rateau design has one row of buckets per stage. A Curtis design has two rows of buckets per stage and requires a set of turning vanes between the first and second row of buckets to redirect the steam flow. Single-stage turbines are usually limited to about 2500 horsepower and for larger units need special designs. Below 2500 horsepower the choice between a single and a multistage turbine is usually an economic one. A single-stage turbine will have a lower capital cost for a given shaft horsepower but will require more steam than a multi-stage turbine because of the lower efficiency of the single-stage turbine.
2. Multi Stage Page 7 of 70 A multi-stage turbine utilizes either a Curtis or Rateau first stage followed by one or more Rateau stages. The following criteria are used for selection steam turbine type 1. Curtis (Stand alone or Single Stage) a. Compact b. Power is relative small (up to 2000 kw). c. Speed is relative low (up to 6000 rpm, except for special design up to 12000 rpm). d. Enthalpy drop is high. 2. Rateau (Multi rows) a. Efficiency is higher than Curtis b. Power is high (up to 30,000 kw) c. Generally, speed is higher than Curtis (up to15000 rpm) d. Enthalpy drop for each row lower than Curtis but still high, higher than Reaction 3. Reaction (Multi row reaction + 1 row impulse for control stage) a. More efficient b. Power is high c. Speed is high (up to15000 rpm) d. Enthalpy drop each row is low e. For low steam pressure.
Page 8 of 70 Reteau Curtis Reaction Figure1: Steam turbine blades arrangement
Page 9 of 70 Based on Blade Geometry / Stage Design In a steam turbine, high-enthalpy (high pressure and temperature) steam is expanded in the nozzles (stationary blades) where the kinetic energy is increased at the expense of pressure energy (increase in velocity due to decrease in pressure). The kinetic energy (high velocity) is converted into mechanical energy (rotation of a shaft increase of torque or speed) by impulse and reaction principles. In the case of the fire hose, as the stream of water issued from the nozzle, its velocity was increased, and because of this impulse, it struck the window glass with considerable force. A turbine that makes use of the impulsive force of high-velocity steam is known as an impulse turbine. While the water issuing from the nozzle of the fire hose is increased in velocity, a reactionary force is exerted on the nozzle. This reactionary force is opposite in direction to the flow of the water. A turbine that makes use of the reaction force produced by the flow of steam through a nozzle is a reaction turbine. 1. Impulse Turbine The impulse principle consists of changing the momentum of the flow, which is directed to the moving blades by the stationary blades. The jet s impulse force pushes the moving blades forward. This energy is converted into mechanical energy by rotating the shaft in turbine nozzle. Kinetic energy to be converted to blade become mechanical energy and transferred through rotor, shaft and coupling to the load. Enthalpy drop is high for each moving blades. It has one velocity-compounded stage (the velocity is absorbed in stages) and four pressure-compounded stages. The velocity is reduced in two steps through the first two rows of moving blades. In the moving blades, velocity decreases while the pressure remains constant. Impulse blades are usually symmetrical and have an entrance and exit angle of approximately 20 o. They are generally installed in the higher pressure sections of the turbines where the specific volume of steam is low and requires much smaller flow areas than that at lower pressures. The impulse blades are short and have a constant cross section In a pure impulse turbine, when the steam passes through the stationary blades, it incurs a pressure drop. There is no pressure drop in the steam as it passes through the rotating blades. Therefore, in an impulse turbine, all the change of pressure energy into
Page 10 of 70 kinetic energy occurs in the stationary blades, while the change of kinetic energy into mechanical energy takes place in the moving blades of the turbine. Figure 2: Single Stage Impulse Steam Turbine Cutaway (1)
Page 11 of 70 2. Reaction Turbine Figure 3: Principle of impulse turbine The reaction principle consists of a reaction force on the moving blades due to the steam accelerating through the nozzles. The nozzles are actually created by the blades. In reaction turbine, there is no nozzle to convert steam energy to mechanical energy. Each stage of the turbine consists of a stationary set of blades and a row of rotating blades on a shaft. Moving blades work due to differential pressure of steam between front and at behind of moving blades. Since there is a continuous drop of pressure throughout each stage, steam is admitted around the entire circumference of the blades and, therefore, the stationary blades extend around the entire circumference. Steam passes through a set of stationary blades that direct the steam against the rotating blades. As the steam passes through these rotating blades, there is a pressure drop from the entrance side to the exit side that increases the velocity of the steam and produces rotation by the reaction of the steam on the blades. In general, reaction turbine is not stand alone, but works at behind impulse turbine whether constructed in one rotor or at separated rotor, but still connected by coupling.
Page 12 of 70 The purpose of impulse turbine is to control speed and reduce steam enthalpy to specified level. Reaction turbine is just receiving steam condition from impulse blades. The reaction stages are preceded by an initial velocity-compounded impulse stage where a large pressure drop occurs. This results in a shorter, less expensive turbine. Figure 4: Section of reaction turbine blading Figure5: Principle of reaction turbine
Page 13 of 70 Figure 6: Diagram of simple impulse and reaction turbine stages. (11)
Page 14 of 70 Operating range of steam turbines can be shown in Speed Power chart such as the following figure. Stand alone rateau stages Speed (rpm) Stand alone high speed curtis Rateau stages + Reaction stages Stand alone curtis Power (KW) Figure 7: Operating Range of Steam Turbines
Page 15 of 70 Based on Steam Supply When classifying steam turbines by their steam supply and exhaust conditions, they are categorized as condensing, non-condensing or backpressure, reheat-condensing, and extraction and induction. 1. Condensing turbine. This type of steam turbine is used primarily as a drive for an electric generator in a power plant. These units exhaust steam at less than atmospheric pressure to a condenser Figure 8: Condensing steam turbine for approximately 65-MW output. (12)
Page 16 of 70 2. Noncondensing or backpressure turbine. This type of turbine is used primarily in process plants, where the exhaust steam pressure is controlled by a regulating station that maintains the process steam at the required pressure. Figure 9 shows a typical arrangement of a backpressure turbine. Figure 9: Backpressure steam turbine for approximately 28-MW output. (12)
Page 17 of 70 3. Reheat-condensing turbine. This type of turbine is used primarily in electricity-producing power plants. In these units, the main steam exhausts from the high-pressure section of the turbine and is returned to the boiler, where it is reheated with the associated increase in steam temperature. The steam is now at a lower pressure but often at the same superheat temperature as the initial steam conditions, and it is returned to the intermediate- and/or low-pressure sections of the turbine for further expansion. 4. Extraction and induction turbine. This type of turbine is also found primarily in process plants. On extraction turbines, steam is taken from the turbine at various extraction points and is used as process steam. In induction turbines, low-pressure steam is introduced into the unit at an intermediate stage to produce additional power. Figure 10: Extraction condensing steam turbine. (12)
Page 18 of 70 High pressure steam High pressure steam Turbine Power out Turbine Power out Low pressure steam to process Medium/low pressure steam to Condenser Figure 11: Non-Condensing (Back-Pressure) Steam Turbine, Extraction Steam Turbine Casing or shaft arrangement. Steam turbines are also classified by their casing or shaft arrangement as being single, tandem-compound, or cross-compound and are described as follows: 1. Single casing. This is the basic arrangement for smaller units, where a single casing and shaft are used. 2. Tandem-compound casing. This arrangement has two or more casings on one shaft that drives a generator 3. Cross-compound casing. This arrangement has two or more shafts that are not in line, with each shaft driving a generator. These units are found in large electric utility power plants.
Page 19 of 70 Steam Turbine Components The turbine consists of a shaft, which has one or more disks to which are attached moving blades, and a casing in which the stationary blades and nozzles are mounted. The shaft is supported within the casing by means of bearings that carry the vertical and circumference loads and by axial thrust bearings that resist the axial movement caused by the flow of steam through the turbine. Seals are provided in the casing to prevent the steam from bypassing the stages of the turbine. The major portions of a turbine are shown in Figure 12. (a)
Page 20 of 70 (b)
Page 21 of 70 (c) Figure 12: Schematics of typical (a) high-, (b) intermediate-, and (c) low-pressure steam turbine sections. (11) Trip and Throttle Valve/Stop (Block) Valve A trip-and-throttle valve or stop valve, or both, may be positioned between the steam supply and the turbine inlet control valve(s). During normal operation this valve remains fully open and its primary function is to shut off the steam supply in response to a trip (shutdown) signal. In addition a trip-and-throttle valve can be used to modulate the steam flow during startup and can be either manually or hydraulically positioned from zero lift to 100% lift. The stop valve can only be positioned either in the closed or fully open positions. In order to minimize the pressure drop through the trip-and-throttle valve, maximum inlet velocities
Page 22 of 70 are usually limited to 150 ft/sec. Velocities above this level will usually result in high pressure drops which will reduce turbine efficiency. Important to any turbine is the ability to start and stop the machine under normal (controlled) and emergency conditions. For steam turbines, being able to shut off the steam supply quickly and reliably is required. This is normally accomplished by either main steam (MS) stop valves or trip and throttle (T&T) valves which are usually installed in the inlet piping to the steam turbine or on the turbine shell. The valves are designed to be leak tight otherwise any steam leakage may keep the turbine turning at low speed after shutdown or causing an overspeed because the valve did not close completely after a shutdown or trip. Figure13: Turbine steam chest and valve assembly (12)
Inlet Control Valves Page 23 of 70 The primary function of the inlet control valve(s) is regulation of the steam flow to provide the appropriate horsepower and speed. These valves may also close in response to a shutdown signal. Throttling which occurs across the control valve(s) reduces the thermal performance of the turbine. This efficiency loss is a function of the control valve design and overall turbine pressure ratio. For a given amount of throttling, turbines with large pressure ratios suffer smaller efficiency losses than turbines with smaller pressure ratios. Multi-stage turbines may have a single inlet control valve or several control valves to regulate the inlet steam. Typical multi-valve steam turbines will have from three to eight control valves. Multi-valve turbines have higher efficiencies at reduced loads because only the flow through one of the control valves is incurring a throttling loss. Turbines with a single control valve will often employ hand valves to improve efficiency at reduced loads. For the turbine shown in Figure 14 both hand valves would be open at or near full load. As the load on the unit is reduced one or both of these hand valves can be closed to reduce throttling loss. Figure14: Single Valve with Hand Valves (3)
Page 24 of 70 Figure 15: Multi-Valve Inlet (3) Nozzles/Blades (Buckets) Steam turbines produce power by converting the energy in steam provided from a boiler or heat recovery steam generator (HRSG) into rotational energy as the steam passes through a turbine stage. A turbine stage consists of a row of stationary blading and a row of rotating blading. Stationary blading is to direct the flow of the passing steam to the rotating blading at the proper angle and velocity for the highest efficiency and extraction of power while the rotating blading is to convert the directed mass flow and steam velocity into rotational speed and torque. The turbine efficiency depends on the design and construction of the blades. Stationary blading may be referred to as nozzles, vanes, stators, partitions, and stationary blading while rotating blades may be referred to as buckets, blades, and rotating blading. Steam turbine blading have different shapes which are referred to as either impulse blading or reaction blading.
Page 25 of 70 Reaction blading is characterized by high velocity fluids entering the turbine blade. Typical reaction blading has tear-drop shaped leading edges with a tapered thickness to the trailing edge. The blades may have twist to their shape which may range from low amounts of twist or reaction at the base of the blade to high twist or reaction at the tip of the blade. Impulse blading is characterized by high velocity fluids (higher than reaction blade) entering the turbine blade. Typical impulse blades are crescent or U-shaped and may not always be symmetrical. Impulse type blading is typically utilized in the high pressure or front sections of the steam turbine while reaction blading is utilized in the lower pressure or aft sections of the turbine. On constant speed turbines a design objective is to avoid all bucket resonances at the operating speed. On variable speed turbines, although the design objectives remain the same, it is seldom possible to avoid all blade resonance because of the wide operating speed range. In these cases it is important to identify all blade resonance and to verify that all stresses are well below the material strength. The blade tips may be covered with bands peened to their tips which connect several blades together in groups, or the blades may have integral shrouds which are part of the blades, or may have no tip cover bands or shrouds (free standing). The blade shrouds and cover bands are utilized to keep the passing steam from leaking over the tip of the blades which reduces efficiency and power output and to reduce or dampen the vibration characteristics of the blading. Both stationary and rotating blading can have shrouds or covers depending on the turbine design. Steam turbine blading can be subjected to several failure mechanisms in service. Table 1 Steam Turbine Blading Failure Mechanisms (Latcovich et al, 2005) Failure Mechanism Corrosion Creep Erosion Resultant Damage Extensive pitting of airfoils, shrouds, covers, blade root surfaces Airfoils, shrouds, covers permanently deformed Thinning of airfoils, shrouds, covers, Cause(s) of Failure Chemical attack from corrosive elements in the steam provided to the turbine Deformed parts subjected to steam temperatures in excess of design limits 1) Solid particle erosion from very fine debris and scale in the steam provided
Page 26 of 70 Failure Mechanism Fatigue Foreign/Domestic Object Damage (FOD/DOD) Stress Corrosion Cracking (SCC) Resultant Damage blade roots Cracks in airfoils, shrouds, covers, blade roots Impact damage (dents, dings, etc.) to any part of the blading Cracks in highly stressed areas of the blading Thermal Fatigue Cracks in airfoils, shrouds, covers, and blade roots Cause(s) of Failure in the turbine 2) Water droplet erosion from steam which is transitioning from vapor to liquid phase in the flowpath 1) Parts operated at a vibratory natural frequency 2) Loss of part dampening (cover, tie wire, etc.) 3) Exceeded part fatigue life design limit 4) Excited by water induction incident water flashes to steam in the flowpath Damage from large debris in steam supplied to the turbine (foreign) or damage from debris generated from an internal turbine failure (domestic) which causes downstream impact damage to components Specialized type of cracking caused by the combined presence of corrosive elements and high stresses in highly loaded locations Parts subjected to rapidly changing temperature gradients where thick sections are subjected to high alternating tensile and compressive stresses during heat-ups and cooldowns or when a water induction incident occurs where the inducted cool water quenches hot parts
Page 27 of 70 Figure 16: Double-flow low-pressure turbine showing variation in blade size. (11) Exhaust Casings Turbine exhaust casings are categorized by pressure service (condensing or noncondensing) and number of rows of the last stage buckets (single flow, double flow, triple flow). Non-condensing exhausts are usually cast steel with most of the applications between 50 and 700 psig exhaust pressure. Most condensing exhausts are steel fabrications although some utilize cast iron construction. Maximum exhaust flange velocities are typically 450 ft/sec. Velocities above this level will usually result in substantial increases in exhaust hood losses and will decrease turbine efficiency. Moisture Protection As steam expands through the turbine both the pressure and temperature are reduced. On most condensing and some non-condensing exhaust applications, the steam crosses the saturation line thereby introducing moisture into the steam path. The water droplets which are formed strike the buckets and can cause erosion of the blades. In
Page 28 of 70 addition, as the water is centrifuged from the blades, the water droplets strike the stationary components, also causing erosion. Where the moisture content is greater than 4%, moisture separators, which are internal to the turbine, can be used to remove a large percentage of the moisture, improving the turbine efficiency and reducing the impact erosion on the buckets. Stainless steel moisture shields can also be used to minimize the impact erosion of the stationary components. Control Systems Mechanical governors were the first generation control systems employed on mechanical drive turbines. Shaft speed is sensed by a fly-ball governor with hydraulic relays providing the input to the control valve. A second generation control system was developed and utilized analog control circuitry with the fly-ball governor replaced by speed pick-ups and the hydraulic relays with electronic circuit boards. A third generation control system was developed and replaced the electronic circuitry with digital logic. A microprocessor is used and the control logic is programmed into the governor. The major advantage of this system is the ability to utilize two governors simultaneously, each capable of governing the turbine alone. If the primary governor incurs a fault, the back-up governor assumes control of the turbine and provides diagnostic information to the operator. Discs, Rotors, Shafts, Blade Rings, Shells, and Diaphragms To transmit the torque produced in each stage of the turbine, the rotating blading is fastened to discs or wheels through a specially designed attachment shape at the blade base or root. The root shape may be fir-tree, T-slot, or semi-circular fir-tree shaped or may use multiple pins to hold the blades to the discs. The turbine discs may be shrunk fit onto a shaft with an anti-rotation key or the discs may have been forged with the shaft as an integral assembly. The output shaft from the shrunk fit or integral disc rotor is then connected to the driven equipment through a flange connection or flexible coupling. Similarly, stationary blading roots may be attached to slots in shells, casings, or blade rings or where the stationary blading is welded to support rings to create a stationary blading assembly referred to as a diaphragm. Depending on the pressure and temperature of the steam to the turbine, there may be dual sets of shells or casings; an inner shell which holds the stationary blading and an outer shell which acts as pressure boundary for the turbine as well as accommodating attachment of blade rings.
Page 29 of 70 Bearings and Lubrication Systems Bearings are utilized to support the turbine rotor inside housings installed in the turbine shells. Depending on the size and number of stages of the steam turbine, different types of bearings may be utilized. It is common for smaller steam turbines to utilize rolling element bearings while larger turbines will utilize journal and multi-pad thrust bearings. There needs to be a complete lubrication system that reliably provides clean, cool lube oil to the turbine bearings. For many large steam turbines, shaft lift oil systems are utilized to lift the shaft in their journal bearings during starting and to keep the shaft lubricated during coast down of the turbine rotor after steam to the turbine is shut off. For some turbines, lube oil (usually mineral oil) is utilized to power servomotors and actuators for stop and control valves. Steam and Oil Seals In order to keep the steam from going around the stationary and rotating blading, steam turbines utilize seals to keep the steam confined to the flowpath. Depending on the size and type of steam turbine, various types of steam seal designs (carbon rings, labyrinth, retractable labyrinth, brush) may be utilized. These systems are usually pressurized with steam to minimize the pressure differential across these seals so that leakage from the higher pressure parts of the turbine is less likely to occur. Similar type seals are utilized to keep bearing oil confined to the bearing housing. As such, seal systems may have filters, pressure regulators, coolers, and the like to maintain a seal pressure as required. Steam Line Connections and Drains Proper connections and support of the steam lines to the turbine are important as well as the steam drains. If the steam supply lines are putting a load on the turbine, it is likely to cause the turbine to vibrate and will cause mechanical distress to the attachment locations. Similarly, when steam turbines are started, there is a warm-up time to heat the turbine to the proper temperature level before admitting full starting steam. Removal of condensed steam from the stop valve and T&T valves, the turbine shells, and any sealing steam locations during this period of operation is important to prevent damage to the turbine. As such, low point drains, steam traps and drain valves, vents, and the like need to be functioning properly and piping runs orientated so that the water drains out
Page 30 of 70 General Advantages of Steam Turbines Compared with reciprocating engines 1. Require less floor space, lighter foundations, and less attendance; 2. Have a lower lubricating-oil consumption, with no internal lubrication, the exhaust steam being free from oil; 3. Have no reciprocating masses with their resulting vibrations; 4. Have uniform torque; 5. have no rubbing parts excepting the bearings; have great overload capacity, great reliability, low maintenance cost, and excellent regulation; 6. Capable of operating with higher steam temperature and of expanding to lower exhaust pressure than the reciprocating steam engine. 7. Their efficiencies may be as good as steam engines for small powers, and much better at large capacities. 8. Single units can be built of greater capacity than can any other type of prime mover. 9. Small turbines cost about the same as reciprocating engines; 10. Larger turbines cost much less than corresponding sizes of reciprocating engines, and they can be built in capacities never reached by reciprocating engines. 11. Combustion gas turbines possess many of the advantages of steam turbines but are not available in ratings much exceeding 175 and 225 MW for 60- and 50-Hz service, respectively.
DEFINITIONS Page 31 of 70 Blowdown - High pressure water at the steam saturation temperature released from a steam boiler to control sludge and total dissolved solids. Boiling Point - The temperature at which water boils to form steam. This temperature increases as the pressure is increased. Boiler - a closed vessel or arrangement of vessels and tubes, together with a furnace or other heat source, in which steam or other vapor is generated from water to drive turbines or engines, supply heat, process certain materials, etc. Backpressure - Pressure developed in opposition to the flow of liquid or gas in a pipe, duct, conduit, etc.; due to friction, gravity, or some other restriction to flow of the conveyed fluid. Backpressure turbine - the type of turbine used in turbo chargers it utilizes the back pressure from ones engine to created more horse power. The back pressure turbine discharges the steam into a pressurized piping system to be used for process heating elsewhere or as the supply to other turbines. For instance a turbine may receive steam at 600 psig and discharge into a 100 psig system. Check Valves - Non-return valves inserted into lines to prevent everse flow. Condensate - The liquid which is formed as steam condenses. Ideally pure water. Compounding of steam turbines - the method in which energy from the steam is extracted in a number of stages rather than a single stage in a turbine. A compounded steam turbine has multiple stages i.e. it has more than one set of nozzles and rotors, in series, keyed to the shaft or fixed to the casing, so that either the steam pressure or the jet velocity is absorbed by the turbine in number of stages. Control Valves - valves used to control conditions such as flow, pressure, temperature, and liquid level by fully or partially opening or closing in response to signals received from controllers that compare a "setpoint" to a "process variable" whose value is provided by sensors that monitor changes in such conditions. [1] Control Valve is also termed as the Final Control Element.
Page 32 of 70 Desuperheater - A device where water is added to return steam to saturated conditions. Enthalpy drop - the difference in steam enthalpy between turbine inlet conditions and turbine outlet conditions. This is applicable to individual turbine sections such as high pressure section or intermediate pressure section. Electric generator - a generator is a device that converts mechanical energy to electrical energy for use in an external circuit. Exhaust steam - to be emitted or to escape from an engine after being expanded Flash Steam - The steam produced when the pressure of hot condensate is reduced. Generator - a machine that converts one form of energy into another, especially mechanical energy into electrical energy, as a dynamo, or electrical energy into sound, as an acoustic generator. Heat rate Heat consumption per hour per unit output. The turbine is charged with the aggregate enthalpy of the steam supplied plus any chargeable aggregate enthalpy added by the reheaters. It is credited with the aggregated enthalpy of feed water returned from the cycle to the steam generator. Heat engine - a mechanical device designed to transform part of the heat entering it into work Impulse Turbine Type of steam turbine where there is no change in the pressure of the steam as it passes through the moving blades. There is change only in the velocity of the steam flow. Kinetic energy - the energy of a body or a system with respect to the motion of the body or of the particles in the system. Latent Heat - Heat that changes the state of a substance with no accompanying temperature rise. When water is changed into steam, the heat is also known as the Enthalpy of Evaporation. Mechanical energy - the sum of potential energy and kinetic energy. It is the energy associated with the motion and position of an object. The principle of conservation of
Page 33 of 70 mechanical energy states that in an isolated system that is only subject to conservative forces the mechanical energy is constant. Nozzles - A projecting part with an opening, as at the end of a hose, for regulating and directing a flow of fluid. a device designed to control the direction or characteristics of a fluid flow (especially to increase velocity) as it exits (or enters) an enclosed chamber or pipe. Power the useful energy per unit of time, delivered by the turbine or turbine-generator unit Reaction Turbine - Type of steam turbine where there is change in both pressure and velocity as the steam flows through the moving blades Steam rate Steam consumption per hour per unit output in which the turbine is charged with the steam quantity supplied Steam turbine - turbine in which steam strikes blades and makes them turn. Turbine is rotary engine in which the kinetic energy of a moving fluid is converted into mechanical energy by causing a bladed rotor to rotate Sensible Heat (Specific Enthalpy) - Heat that increases the temperature of the water or steam with no change of state. Superheated Steam - Steam to which sensible heat has been added to increase its temperature to above its boiling point. Thermal Fluids - Generally mineral oils with high heat capacities that can be used as alternatives to steam or hot water for process heating in the range 200-400 C. Throttle Valve - a valve designed to regulate the supply of a fluid (as steam or gas and air) to an engine and operated by a handwheel, a lever, or automatically by a governor; especially : the valve in an internal-combustion engine incorporated in or just outside the carburetor and controlling the volume of vaporized fuel charge delivered to the cylinders
NOMENCLATURES Page 34 of 70 An ASR Dex Din Eff hex hf hg hin Pin Pout Pwr RPM S sf sg sin Tin TSR vex vin W x y Nozzle area, in² Actual steam rate, lb/hp.hr Exhaust diameter, in Inlet diameter, in Efficiency,% Exhaust enthalpy, btu/lb Specific enthalpy of saturated water, btu/lb Specific enthalpy of saturated steam, btu/lb Specific enthalpy of superheated steam, btu/lb inlet pressure, psia exhaust pressure, psia Horsepower, HP Speed, rpm number of stages Specific entropy of saturated water, btu/lb.f Specific entropy of saturated steam, btu/lb.f Specific entropy of superheated steam, btu/lb. F inlet temperature, F Theoretical steam rate, lb/hp.hr velocity of exhaust, ft/s velocity of inlet steam, ft/s Mass flowrate, lb/hr liquid fraction in the exhaust vapor fraction in the exhaust Greek Leters Δh ρgex ρgin Enthalpy change, btu/lb Density steam in exhaust, lb/ft³ Density steam inlet, lb/ft³ Superscript ASR RPM TSR Actual steam rate, lb/hp.hr Speed, rpm Theoretical steam rate, lb/hp.hr