GB1099479A - Starting method and system for a power plant containing a prime mover and a vapour generator - Google Patents

Abstract

1,099,479. Raising steam. FOSTER WHEELER CORPORATION. April 9, 1965 No. 15259/65. Heading F4A. [Also in Division F1] The invention is concerned with avoiding high temperature damage and thermal shock during starting of a plant containing a oncethrough vapour generator and a prime mover. During cold start, a pump 16, Fig. 1, delivers about 30% of full load flow through high pressure heaters 18, 20, 22, vapour generating sections 24 to 32 and superheating sections 34, 35 to a main line 40 containing a shut-off valve 40a and extending to a high pressure turbine 38. The valve 40a is closed but a valve 58a is opened to permit the flow to pass through an optional attemperator 62 to a flash tank 36. The valve 58a reduces the flow pressure adiabatically from approximately 3500 psia (full load pressure) to less than 15% of this value. Drainage from the flash tank passes through a shut-off valve 70a to the heater 20 and through a pressure reducing valve 70b to a condenser hot well 52, The furnace is fired at about 15% full load rate and the flash tank pressure is set at about 15% (about 500 psia) of the full load pressure. Some of the flash tank steam is supplied to a turbine gland seal regulator 66b, a deaerator 12 and the heater 22. About 2 to 10 per cent of full load steam flow is supplied from the flash tank through a valve 72a to an intermediate reheater section 42a isolated from an adjacent section 42 by closed valves 80, 82, the reheater sections being heated in the vapour generator. Since the turbine requires only 2-3% of full load flow, the surplus delivered from the flash tank and through the reheater is bled through line 84 and valve 84a to the condenser, and later in the starting cycle the flow from the flash tank is reduced to about 2-3% of full load flow to produce an enthalpy build up in the turbine steam. The reheated steam passes through a check valve 74 and a shut-off valve 76 to the turbine inlet throttle valve (not shown) which reduces the steam pressure to about 50 psia (at a temperature of about 400‹ F.) for initial warming and driving of the turbine up to the rated speed. When the enthalpy of the steam leaving the superheater 35 rises to about 800 Btu per 1b. the flash tank pressure is set at 1000 psia. When the generator reaches equilibrium at the 15% firing rate, the enthalpy leaving the superheater 35 is about 78% (about 1090 Btu per 1b.) of the full load value. At this point some flash tank steam is dumped into the condenser through line 64, and all the drainage from the flash tank is dumped into the condenser hot well. When the turbine is up to temperature, a flow of about 15% full load flow is bled through a line 56 and a valve 56a, thereby increasing the enthalpy of the steam delivered by the superheaters. The flow to the turbine is thereafter increased with increasing turbine load by reducing the amount of bled fluid. Moreover, a constant enthalpy valve 78a is made operative to supply the turbine with steam which matches the conditions of that supplied from the reheater section 42a. The valve 72a is then closed and the valves 80, 82 opened. The valve 78a is adjusted in proportion to increases in turbine load up to 28% turbine load (i.e. just before full pressure at 30% turbine load), whereafter the valve 78a is cut out of service and the valve 40a is opened for direct flow to the turbine. The flue gases passing through the reheater may be controlled by dampers (104), Fig. 2 (not shown), to provide additional control of turbine steam temperature build-up. During hot start, flash tank steam at 1000 psia heated to a suitable enthalpy level in the reheater section 42a is supplied to the turbine, and gradual changeover to the main steam flow is accomplished by mixing an increasing flow through the valve 78a with decreasing flow from the flash tank. In an alternative hot start arrangement, Fig. 3 (not shown), the flash tank is by-passed.