Patent GB-805257-A (GB)
Title: Improvements in and relating to steam power plants
Inventor: ARTSAY NICHOLAS C
IPC: F22B21/34
Filed: 1957-02-19
Abstract: 805,257. Critical pressure boilers. FOSTER WHEELER, Ltd. Feb. 19, 1957, No. 5623/57. Addition to 761,617. Class 123(2) The steam power plant described in the parent Specification is modified so that it may operate efficiently at fractional loads by providing means for maintaining constant throughout the operating range the degree of wetness of the steam passed from the supercritical stage turbines to the steam and water drum. As shown in Fig. 1, in the subcritical stage of the plant steam passes from the boiler steam and water drum 12 by way of a separator 12A removing water droplets containing contaminants through a superheater 15, the high pressure turbine stage 21 of a turbine set 22, a feedwater heater 100, a steam compressor 64 driven by the supercritical stage turbine 60, a reheater 16, the intermediate and low pressure turbine stages 25, 27 of the turbine 22 and exhausts into a condenser 29. A pump 17 pumps condensate through four bled steam heaters 101...104 and the heater 100 to the drum 12. A pump 33 driven by the supercritical stage turbine 37 withdraws water 'from the drum and forces it at supercritical pressure through the evaporating section 14 of the boiler, the fluid from which is distributed between the turbine 37, 60 by valve ducts 70, 78. The wet steam exhausting from the turbines 37, 60 flows into the drum 12 Temperature and pressure controllers 52, 76 regulate the power and speed of the turbines 37, 60 respectively in response to the temperature and pressure of the fluid leaving the heating surface 14. The rate of firing of boiler burners 89 is controlled by a controller 133 responsive to the steam pressure at the outlet of the superheater 15 whilst a constant level is held in the drum 12 by a feed water regulator 105. When the turbine set 22 is to operate at reduced load the superheater outlet pressure increases and the controller 133 decreases the firing rate of the burners 89, thereby reducing the heat available to the surface 14. The controller 52 senses the drop in fluid temperature at the heating surface outlet and decreases the speed of turbine 37 and pump 33 to reduce the water flow to the surface and thereby restore the temperature to the preset value. The resulting reduction of pressure of the fluid leaving the surface 14 is sensed by the controller 76 which reduces the flow to the turbine 60 to restore the pressure so that both pressure and temperature conditions and consequently the condition of the steam leaving the turbines 37, 60 are then the same for the reduced load as for full load conditions. To start the plant, an independent motor and pump set 150, 151 is provided, Fig. 4, the pump receiving water from the drum 12 and delivering it to the heating surface 14. A starting valve 156 is arranged in a conduit 155 connected to the outlet of the surface 14. Parallelarranged, pressure-actuated valves 157 communicate with the valve 156 and are adjusted to open at a slightly supercritical pressure, each valve 157 being connected to a flash orifice and diffuser 158 connected through a header 160 to the drum 12. When the plant is started from cold, the stop valves of turbines 37, 60 are closed and water is pumped by the pump 151 through the starting valve, flash orifices and diffusers into the drum 12. The burners 89 are then lit and steam pressure built up in the drum to the level at which the turbine set 22 may be started and placed on load. The stop valves of turbines 37, 60 are then opened and the starting valve closed, the starting pump motor being stopped when the turbine 37 reaches the required speed to operate the plant normally.