GB1089056A - Improvements in or relating to apparatus for starting up vapour power plants - Google Patents

Abstract

1,089,056. Raising steam in forced flow once through boilers. BABCOCK & WILCOX CO. Aug. 3, 1965 [Aug. 4, 1964], No. 33160/65. Heading F4A. A vapour power plant comprises a oncethrough forced flow vapour generator 14, having an economizer 16, vapour generating section 17 and superheater 18 connected in series, a turbine 22, a condenser 31, condensate pump 33, low pressure feed water heater 36, de-aerator 37, feed pump 10, and high pressure feed water heater 12. On start up a quarter full load water flow is established through feed pump 10, heater 12, economizer 16, vapour generating section 17 and conduit 39 to flash tank 42, valves 21, 48, 50 and 60 being closed so that no steam can enter the superheating section 18, the valve 41 maintaining full load pressure at the outlet of vapour generating section 17. Water from flash tank 42 flows through conduit 49 to de-aerator 37 and so back to the feed pump 10. Firing is commenced and as the deaerator and flash tank pressures rise to 20 p.s.i.a. valve 51 starts to close, controlling the de-aerator pressure and valve 70 in line 65 begins to control the flash tank water level by passing the flash tank condensate to the shell of heater 12 and then to the condenser 31 through conduit 71. Consult 52 and valve 53 pass any excess flash tank water direct to the condenser 31. Steam flashing in tank 42 passes via line 59 to seal the turbine, then as the pressure increases also via conduits 54 and 57 to the deaerator 37 and high pressure heater 12. Flash steam is next passed at a pressure of 150 p.s.i.a. upwards' through conduit 45 and superheater 18 and round turbine by-pass line 43 to the Condenser 31, the flow being diverted through the turbine 22 for. rolling when suitable flash steam conditions are reached. This is facilitated by tempering the superheater outlet steam with saturated steam from flash tank 42 which bypasses superheater 18, through valved conduit , 65. Similarly the steam flow from reheater 76 to the low pressure part of turbine 22 may be tempered by saturated steam from flash tank 42 supplied through valved conduit 78. Turbine steam control at this stage is effected on valve 25 with valve 24 closed and valve 26 open. The turbine load is increased from 2 to 10% full load by closing the turbine by-pass valve 44, and then to 20% full load by increasing the firing rate, valves 50, 60 and 79 in conduits from the flash tank being closed as valve 48 in by-pass conduit 47 is opened. When valve 48 is full open, valve 41 closes and all steam from vapour generating section 17 flows directly to superheater 18 to pass to the turbine. As the by-pass system steam pressure decays turbine extraction flows take over the deaeration and feed water heating. As the load is brought up to its full value valve 21 is opened and valve 48 closed and turbine control is transferred from valve 25 to valve 26, valve 24 being fully open. During start up any excess flash steam is passed direct to the condenser 31 through conduit 62.