GB939429A - Improvements in or relating to steam turbine power plant - Google Patents

Abstract

939,429. Power generating systems; steam turbine plant. BABCOCK & WILCOX Ltd. Dec. 22, 1959 [Dec. 26, 1958], No. 43446/59. Classes 110 (3) and 122 (3). [Also in Group XIII] A steam turbine power plant has a turbine 26 arranged to receive superheated steam and has provision for the condensation of bled steam in feed heating means, and at a point in a bleed line between the turbine and the feed heating means is located the heating surfaces of a boiler adapted for generating and superheating steam and has means provided for leading the steam from said boiler to a turbine stage. A natural circulation boiler unit 1 fired by the combustion of natural gas includes a water cooled furnace 4. The main flow circuit for the working fluid is from the steam space of a boiler drum 24, through a primary superheater 9, a spray type attemperator 32, a secondary superheater 7, high-pressure turbine stages in a casing 25, a primary reheater 11, a spray-type attemperator 33, a secondary reheater 8, low-pressure turbine stages in a casing 26, a condenser 27, an extraction pump 28, a feed water heating train 29, a heat exchanger 30, a feed pump 31, an economiser 13 and to the water space of the boiler drum 24. Dampers 14, 15 control the flow of combustion gases before a combustion air heater 5. The feed train 29 comprises heat exchanges 41-46 which receive heat from steam in bleed lines 61 to 66 respectively at successively higher temperatures and pressures. The steam is condensed in the heat exchangers and by virtue of the pressure difference between them the condensate flows through connections 46A to 41A to the condenser 27. The heat exchanger 41 has desuperheating surfaces 41C and condensing surfaces 41D. In the remaining heat exchangers 42-46 the surfaces are all adapted for steam condensation. Desuperheaters 72 to 76 are arranged between the bleed points and heat exchangers 41 to 46. A closed circuit 37 leads from a pump 36 through the desuperheaters 72, 73, 74 to the heat exchanger 30, in which heat is transferred to the feed water, and back to the pump 36. The desuperheater 74 contains heat exchanger surfaces 74B which form the economiser of a boiler 83. The steam generating surfaces of the boiler are formed by the desuperheater 75 which receives water from a drum 84 and supplies steam to the drum and the superheating surfaces of the boiler are formed by the desuperheater 76. The rate of heat absorption in the boiler 83 is varied by adjusting the pressure therein. In operation of the installation, therefore, not all the steam entering the high-pressure turbine undergoes full turbine expansion, but the latent heats of the bled steam are conserved for the thermodynamic efficiency of the system. Some of the steam produced in the boiler 83 may be used for soot-blowing in the boiler unit 1. The steam produced in the boiler 83 is expanded in the turbine via the connection 101. If the maximum water temperature in the circuit 37 is too low, the heat exchanger 30 may be positioned as at location 30<SP>1</SP>. Instead of utilising the heat exchanger 30 the circuit 37 may be connected to an air heater 100. More than one desuperheater may be placed in each bleed line and may form the elements of another boiler. In the modification shown in Fig. 2 a steam and water drum 111 of a further boiler 112 is supplied by a pump through the desuperheater 73. Steam from the drum 111 joins with steam from the drum 84 and passes to the heat exchanger 21 via the desuperheater 76 acting as a superheater. In a further modification the respective elements viz. economiser, vapour generator and superheater, of both boilers 83, 112 may be housed in separate desuperheaters in the respective bleed lines 64, 65, 66. Specifications 899,328 and 914,748 are referred to.