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 lower￾pressure 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 High￾Pressure Turbine Forced Draft Fan Air Preheater Feedwater from High-Pressure Feedwater Heater Air Induced￾Draft Fan Flue Gas to Stack Water Air Economizer Fuel FIGURE 59.3 Concept of once￾through-type steam generator