Karady, G.G. Conventional Power Generation"" The Electrical Engineering Handbook Ed. Richard C. Dorf Boca raton crc Press llc. 2000
Karady, G.G. “Conventional Power Generation” The Electrical Engineering Handbook Ed. Richard C. Dorf Boca Raton: CRC Press LLC, 2000
59 Conventional power Generation 59.2 Fossil Power plants Fuel Handling. Boiler. Turbine. Generator. Electric System. Condenser.Stack and Ash Handling. Cooling and Feedwater System 59.3 Nuclear power plants Pressurized Water Reactor. Boiling-Water Reactor George G. Karady 59.4 Geothermal Power plants Arizona State University 59.5 Hydroelectric Power Plants 59.1 Introduction The electric energy demand of the world is continuously increasing, and most of the energy is generated by conventional power plants, which remain the only cost-effective method for generating large quantities of energy Power plants utilize energy stored in the earth and convert it to electrical energy that is distributed and used y customers. This process converts most of the energy into heat, which increases the entropy of the earth. In this sense, power plants deplete the earths energy supply. Efficient operation becomes increasingly important to conserve energy. Typical energy sources used by power plants include fossil fuel(gas, oil, and coal), nuclear fuel (uranium) geothermal energy(hot water, steam), and hydro energy(water falling through a head). Around the turn of the century, the first fossil power plants used steam engines as the prime mover. These plants were evolved to an 8-to 10-MW capacity, but increasing power demands resulted in the replacement by a more efficient steam boiler-turbine arrangement. The first commercial steam turbine was introduced by DeLaval in 1882. The boilers were developed from heating furnaces. Oil was the preferred and most widely used fuel in the beginning. The oil shortage promoted coal-fired plants, but the adverse environmental effects (sulfur dioxide generation, acid rain, dust pollution, etc. )curtailed their use in the late seventies. Presently the most acceptable fuel is natural gas, which minimizes pollution and is available in large quantities. During the next two decades, gas-fired power plants will dominate the electric industry. The hydro plants' ancestors are water wheels used for pumping stations, mill driving, etc. Water-driven turbines were developed in the last century and used for generation of electricity since the beginning of their commercial use. However, most of the sites that can be developed economically are currently being utilized. No significant new development is expected in the United States in the near future Nuclear power plants appeared after the Second World War. The major development occurred during the sixties; however, by the eighties environmental considerations stopped plant development in the United States and slowed it down all over the world. Presently, the future of nuclear power generation is unclear, but the abundance of nuclear fuel and the expected energy shortage in the early part of the next century may rejuvenate nuclear development if safety issues can be resolved c 2000 by CRC Press LLC
© 2000 by CRC Press LLC 59 Conventional Power Generation 59.1 Introduction 59.2 Fossil Power Plants Fuel Handling • Boiler • Turbine • Generator • Electric System • Condenser • Stack and Ash Handling • Cooling and Feedwater System 59.3 Nuclear Power Plants Pressurized Water Reactor • Boiling-Water Reactor 59.4 Geothermal Power Plants 59.5 Hydroelectric Power Plants 59.1 Introduction The electric energy demand of the world is continuously increasing, and most of the energy is generated by conventional power plants, which remain the only cost-effective method for generating large quantities of energy. Power plants utilize energy stored in the earth and convert it to electrical energy that is distributed and used by customers. This process converts most of the energy into heat, which increases the entropy of the earth. In this sense, power plants deplete the earth’s energy supply. Efficient operation becomes increasingly important to conserve energy. Typical energy sources used by power plants include fossil fuel (gas, oil, and coal), nuclear fuel (uranium), geothermal energy (hot water, steam), and hydro energy (water falling through a head). Around the turn of the century, the first fossil power plants used steam engines as the prime mover. These plants were evolved to an 8- to 10-MW capacity, but increasing power demands resulted in the replacement by a more efficient steam boiler–turbine arrangement. The first commercial steam turbine was introduced by DeLaval in 1882. The boilers were developed from heating furnaces. Oil was the preferred and most widely used fuel in the beginning. The oil shortage promoted coal-fired plants, but the adverse environmental effects (sulfur dioxide generation, acid rain, dust pollution, etc.) curtailed their use in the late seventies. Presently the most acceptable fuel is natural gas, which minimizes pollution and is available in large quantities. During the next two decades, gas-fired power plants will dominate the electric industry. The hydro plants’ ancestors are water wheels used for pumping stations, mill driving, etc. Water-driven turbines were developed in the last century and used for generation of electricity since the beginning of their commercial use. However, most of the sites that can be developed economically are currently being utilized. No significant new development is expected in the United States in the near future. Nuclear power plants appeared after the Second World War. The major development occurred during the sixties; however, by the eighties environmental considerations stopped plant development in the United States and slowed it down all over the world. Presently, the future of nuclear power generation is unclear, but the abundance of nuclear fuel and the expected energy shortage in the early part of the next century may rejuvenate nuclear development if safety issues can be resolved. George G. Karady Arizona State University
Geothermal power plants are the product of the clean energy cond ept, although the small-scale,local application of geothermal energy has a long history. Presently only a few plants are in operation. The potential for further development is limited because of the unavailability of geothermal energy sites that can be developed Typical technical data for different power plants is shown in Table 59.1 59.2 Fossil power plants The operational concept and major components of a fossil power plant are shown in Fig. 59.1 Fuel Handling The most frequently used fuels are oil, natural gas, and coal. Oil and gas are transported by rail, on ships, or through pipelines. In the former case the gas is liquefied Coal is transported by rail or ships if the plant is near a river or the sea. The power plant requires several days of fuel reserve. Oil and gas are stored in large metal tanks, and coal is kept in open yards. The temperature of the coal layer must be monitored to avoid self-ignition Dil is pumped and gas is fed to the burners of the boiler Coal is pulverized in large mills, and the powder is mixed with air and transported by air pressure, through pipes, to the burners. The coal transport from the yard to the mills requires automated transporter belts, hoppers, and sometimes manually operated bulldozers. boiler Two types of boilers are used in modern power plants: subcritical water-tube drum-type and supercritical once- through type. The former operates around 2500 psi, which is under the water critical pressure of 3208.2 (540C)because of turbine temperature limitations 0 psi. The superheated steam temperature is about 1000%F The latter operates above that pressure, at around 350 A typical subcritical water-tube drum-type boiler has an inverted-U shape On the bottom of the rising part is the furnace where the fuel is burned. The walls of the furnace are covered by water pipes. The drum and the superheater are at the top of the boiler. The falling part of the U houses the reheaters, economizer(water heater), and air preheater, which is supplied by the forced-draft fan. The induced-draft fan forces the flue gases out of the system and sends them up the stack, which is located behind the boiler. A flow diagram of the drum- type boiler is shown in Fig. 59. 2. The steam generator has three major systems: fuel, air-flue gas, and water-steam. Fuel System. Fuel is mixed with air and injected into the furnace through burners. The burners are equipped with nozzles, which are supplied by preheated air and carefully designed to assure the optimum air- fuel mix. The fuel mix is ignited by oil or gas torches. The furnace temperature is around 3000oF. Air-Flue Gas System. Ambient air is driven by the forced-draft fan through the air preheater, which is heated by the high-temperature(600@F)flue gases. The air is mixed with fuel in the burners and enters into the furnace, where it supports the fuel burning. The hot combustion flue gas generates steam and flows through the boiler Steam Energy Boiler generator Cooling Water eed water Cooling System Pond, River FIGURE 59.1 Major components of a fossil power pl e 2000 by CRC Press LLC
© 2000 by CRC Press LLC Geothermal power plants are the product of the clean energy concept, although the small-scale, local application of geothermal energy has a long history. Presently only a few plants are in operation. The potential for further development is limited because of the unavailability of geothermal energy sites that can be developed economically. Typical technical data for different power plants is shown in Table 59.1. 59.2 Fossil Power Plants The operational concept and major components of a fossil power plant are shown in Fig. 59.1. Fuel Handling The most frequently used fuels are oil, natural gas, and coal. Oil and gas are transported by rail, on ships, or through pipelines. In the former case the gas is liquefied. Coal is transported by rail or ships if the plant is near a river or the sea. The power plant requires several days of fuel reserve. Oil and gas are stored in large metal tanks, and coal is kept in open yards. The temperature of the coal layer must be monitored to avoid self-ignition. Oil is pumped and gas is fed to the burners of the boiler. Coal is pulverized in large mills, and the powder is mixed with air and transported by air pressure, through pipes, to the burners. The coal transport from the yard to the mills requires automated transporter belts, hoppers, and sometimes manually operated bulldozers. Boiler Two types of boilers are used in modern power plants: subcritical water-tube drum-type and supercritical oncethrough type. The former operates around 2500 psi, which is under the water critical pressure of 3208.2 psi. The latter operates above that pressure, at around 3500 psi. The superheated steam temperature is about 1000°F (540°C) because of turbine temperature limitations. A typical subcritical water-tube drum-type boiler has an inverted-U shape. On the bottom of the rising part is the furnace where the fuel is burned. The walls of the furnace are covered by water pipes. The drum and the superheater are at the top of the boiler. The falling part of the U houses the reheaters, economizer (water heater), and air preheater, which is supplied by the forced-draft fan. The induced-draft fan forces the flue gases out of the system and sends them up the stack, which is located behind the boiler. A flow diagram of the drumtype boiler is shown in Fig. 59.2. The steam generator has three major systems: fuel, air-flue gas, and water-steam. Fuel System. Fuel is mixed with air and injected into the furnace through burners. The burners are equipped with nozzles, which are supplied by preheated air and carefully designed to assure the optimum air-fuel mix. The fuel mix is ignited by oil or gas torches. The furnace temperature is around 3000°F. Air-Flue Gas System. Ambient air is driven by the forced-draft fan through the air preheater, which is heated by the high-temperature (600°F) flue gases. The air is mixed with fuel in the burners and enters into the furnace, where it supports the fuel burning. The hot combustion flue gas generates steam and flows through the boiler FIGURE 59.1 Major components of a fossil power plant
TABLE 59.1 Power Plant Technical Data lized Construction Equivalent Typical lant Cost, Lead Time, Heat Rate, Fuel Cost Scheduled O&M Fixed. variable MW Size Btu/kwh S/MBtu Fuel Type Outage Rate Outage Rate S/kw/year S/MWh 10,400 Pulverized coal fluidized bed Gas turbine Combined-cycl 300 06624666 14 11,200 4.00 Nat. gas 4.00 Nat. gas 9500 c 2000 b CRC Press LLC
© 2000 by CRC Press LLC TABLE 59.1 Power Plant Technical Data Capitalized Construction Equivalent Equivalent Cost Generation Typical Plant Cost, Lead Time, Heat Rate, Fuel Cost, Forced Scheduled O&M Fixed, Variable Type MW Size $/kW Years Btu/kWh $/MBtu Fuel Type Outage Rate Outage Rate $/kW/year $/MWh Nuclear 1200 2400 10 10,400 1.25 Uranium 20 15 25 8 Pulverized coal steam 500 1400 6 9,900 2.25 Coal 12 12 20 5 Atmospheric fluidized bed 400 1400 6 9,800 2.25 Coal 14 12 17 6 Gas turbine 100 350 2 11,200 4.00 Nat. gas 7 7 1 5 Combined-cycle 300 600 4 7,800 4.00 Nat. gas 8 8 9 3 Coal-gasification combined-cycle 300 1500 6 9,500 2.25 Coal 12 10 25 4 Pumped storage hydro 300 1200 6 — — 5 5 5 2 Conventional hydro 300 1700 6 — — 3 4 5 2
Flue Gas To Low-Pressure Turbine Saturated ste Pressure Turbine Air Preheater Reheater EConom Feedwater (Risers 口T Downcomer FIGURE 59.2 Flow diagram of a typical drum-type steam boiler to heat the superheater, reheaters, economizer, etc. Induced-draft fans, located between the boiler and the stack, increase the flow and send the 300oF flue gases to the atmosphere through the stack. Water-Steam System. Large pumps drive the feedwater through the high-pressure heaters and the economizer, which further increases the water temperature(400-500@F). The former is heated by steam removed from the turbine; the latter is heated by the flue gases. The preheated water is fed to the steam drum Insulated tubes, called downcomers, are located outside the furnace and lead the water to a header. The header distributes the hot water among the risers. These are water tubes that line the furnace walls. The water tubes are heated by the combustion gases through both convection and radiation. The steam generated in these tubes flows to the drum, where it is separated from the water. Circulation is maintained by the density difference between the water in the downcomer and the water tubes. Saturated steam, collected in the drum, flows through the superheater. The superheater increases the steam temperature to about 1000@E Dry superheated steam drives the high-pressure turbine. The exhaust from the high-pressure turbine goes to the reheater, which again Increases he steam temperature. The reheated steam drives the low-pressure turbine The typical supercritical once-through-type boiler concept is show Fig. 59. The feedwater enters through the economizer to the boiler, which consists of riser tubes that line the furnace wall. all the water is converted to steam and fed directly to the superheater. The latter increases the steam temperature above the critical temperature of the water and drives the turbine. The construction of these steam generators is more expensive Boiler than the drum-type units but has a higher operating efficiency. Turbine The turbine converts the heat energy of the steam into mechanical energ Econg Modern power plants usually use one high-pressure and one or two lower pressure turbines. A typical turbine arrangement is shown in Fig. 59.4 FIGURE 59.3 Concept of once- The figure shows that only one bearing is between each of the machines. The shafts are connected to form a tandem compound steam turbine unit. High-pressure steam enters the high-pressure turbine to flow through and drive the turbine. The exhaust is reheated in the boiler and returned to the lower-pressure units. Both the rotor and the stationary part of the turbine have blades. The length of the blades increases from the steam entrance to the exhaust e 2000 by CRC Press LLC
© 2000 by CRC Press LLC to heat the superheater, reheaters, economizer, etc. Induced-draft fans, located between the boiler and the stack, increase the flow and send the 300°F flue gases to the atmosphere through the stack. Water-Steam System. Large pumps drive the feedwater through the high-pressure heaters and the economizer, which further increases the water temperature (400–500°F). The former is heated by steam removed from the turbine; the latter is heated by the flue gases. The preheated water is fed to the steam drum. Insulated tubes, called downcomers, are located outside the furnace and lead the water to a header. The header distributes the hot water among the risers. These are water tubes that line the furnace walls. The water tubes are heated by the combustion gases through both convection and radiation. The steam generated in these tubes flows to the drum, where it is separated from the water. Circulation is maintained by the density difference between the water in the downcomer and the water tubes. Saturated steam, collected in the drum, flows through the superheater. The superheater increases the steam temperature to about 1000°F. Dry superheated steam drives the high-pressure turbine. The exhaust from the high-pressure turbine goes to the reheater, which again increases the steam temperature. The reheated steam drives the low-pressure turbine. The typical supercritical once-through-type boiler concept is shown in Fig. 59.3. The feedwater enters through the economizer to the boiler, which consists of riser tubes that line the furnace wall. All the water is converted to steam and fed directly to the superheater. The latter increases the steam temperature above the critical temperature of the water and drives the turbine. The construction of these steam generators is more expensive than the drum-type units but has a higher operating efficiency. Turbine The turbine converts the heat energy of the steam into mechanical energy. Modern power plants usually use one high-pressure and one or two lowerpressure turbines. A typical turbine arrangement is shown in Fig. 59.4. The figure shows that only one bearing is between each of the machines. The shafts are connected to form a tandem compound steam turbine unit. High-pressure steam enters the high-pressure turbine to flow through and drive the turbine. The exhaust is reheated in the boiler and returned to the lower-pressure units. Both the rotor and the stationary part of the turbine have blades. The length of the blades increases from the steam entrance to the exhaust. FIGURE 59.2 Flow diagram of a typical drum-type steam boiler. Header Air Water Tubes (Risers) Steam Drum Freewater Regulator Downcomer Reheater To High-Pressure Turbine Attemperators Superheater Saturated Steam Primary Secondary To Low-Pressure Turbine From HighPressure Turbine Forced Draft Fan Air Preheater Feedwater from High-Pressure Feedwater Heater Air InducedDraft Fan Flue Gas to Stack Water Air Economizer Fuel FIGURE 59.3 Concept of oncethrough-type steam generator