GB941311A - An improved method of generating power by means of a steam turbine and improvements in steam turbine power plant - Google Patents

Abstract

941,311. Heating feedwater; water tube steam boilers; superheaters. BABCOCK & WILCOX Ltd. Feb. 12, 1960 [Feb. 17, 1959], No. 5515/59. Heading F4A. [Also in Division F1] In a steam turbine power plant 2 having a turbine receiving superheated steam and having provision for the bleeding of steam from the turbine to heat-exchangers 51-58 of a feed train 42, desuperheaters 82-88 are connected in the bleed lines 62-68, to form a heatexchange system receiving water from the feed train, to vaporize and superheat a portion of the diverted water to discharge an unevaporated portion of the diverted water back to the feed train 42 and to discharge into the turbine at an intermediate pressure point, the steam generated in the desuperheating means. The main flow circuit of the working fluid is from the steam space of the boiler drum 30, through side walls of a gas passage 5 and side, front and rear walls of a downflow gas pass 7, through a primary superheater 12, a secondary superheater 24, a tertiary superheater 9, high pressure turbine stages in a cylinder 32, a primary reheater 14, a secondary reheater 10, intermediate and low pressure turbine stages in cylinders 33, 34, a condenser 35, extraction pump 41, the feed train 42, a feed pump 43, economizer 8 and to the water space of the boiler drum 30. The steam flows entering the bleed lines 61-68 are at successively higher pressures and in the lines 61-66 are at successively higher temperatures. The temperature of the reheated steam entering the low-pressure turbine is the same as that entering the high-pressure turbine and the temperature of the steam entering the bleed line 66 is higher than that entering the line 68. Heat-exchangers 51-53 and 55-58 are of the indirect contact type and heat-exchanger 54 is a de-aerator, into which flows the feed water from the heat-exchangers 51-53 and the bled steam from the line 64. Owing to the pressure difference existing between successive heatexchangers and the condenser 35, condensate from the bleed line flows as indicated in the lines 51A-53A, and 56A-58A. A pump 59 passes the condensate from a drain tank 60 into the deaerator 54. Desuperheaters 92, 93 serve as water heaters; a pump 101 withdraws water from the feed water line, and the water rejoins the feed water line at a point between heatexchangers 57, 58. The heat-exchange surfaces of the desuperheaters 84, 85 are connected in parallel and serve as heaters and vaporizers for water withdrawn from the feed water line in a line 103. The desuperheater 86 comprises casings 186, 286 connected in series as regards the bleed flow, the heat exchangers in the latter forming a heater and vaporizer for water in a line 107, which also supplies the heat exchange surfaces of the parallel connected desuperheaters 87, 88. The steam and water mixtures from the desuperheaters 84, 88 are led to a boiler pressure drum 104 provided with cyclone separators 105 and scrubbers 106. A second or lower drum 99 is connected to the drum 104 by a series of connectors 100. A discharge line 108 leads from the drum 99 to the feed water line, and the water component of the mixtures may augment the feed water under the control of a pump 119 and valve 133. The heatexchange surfaces in the casing 186 partially desuperheat the steam in the bleed line 66 and superheat the steam from the boiler drum 104. The superheated steam passes to a line 110 from which a branch 111 leads to the turbine cylinder 32 and a branch 112 conducts steam to a fuel gas heater 26, which desuperheats and condenses the steam, and subsequently cools the condensate. A pressure-reducing valve 116 between the condenser 115B and a coder 115A reduces the water pressure and the water is returned to the feed water line via a line 114 by a pump 113. The water level in the drum 104 is automatically regulated by known means (not shown) operating upon feed regulating valves 121, 122 and by further automatic means controlling the pump 119. Isolating valves 131, 132, 133 close automatically if there should be a complete loss of load on the electric generator 3. A steam line 134, with a normally closed valve 135, is provided so that should the valve 132 be closed steam is still available for fuel gas heating. The heat-exchanger 52 contains additional heatexchange surfaces 142 in a closed circuit 143 which includes a water circulating pump 144 and an auxiliary air heater 145 running continuously or when required to prevent corrosion in the main air heater 23. The heat-exchangers for the desuperheaters 82-88 may be of the type disclosed in Specification 914,748.