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 once￾through 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 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 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