GB1152501A - Once Through Forced Flow Boilers - Google Patents

Abstract

1,152,501. Once through forced flow vapour generators. FOSTER WHEELER CORP. 21 Oct., 1966 [22 Oct., 1965], No. 47407/66. Heading F4A. A once through forced flow vapour generator comprises a Furnace chamber 12 fired by Burners 14; 16; the combustion gases exiting through a tube screen 24 to enter a convection section 30, including parallel front and rear passageways 32; 34. A feed water supply controlled by valve 58, passes through economizer 38 and downcomer 59 to furnace water wall tubes 60 which defines series of passes in the lower part of the furnace enclosure, and then through upper front and side wall tubes 62 to downcomer 64. This leads fluid to upper furnace rear wall 66, tube screens 24 and 28, and horizontal convection pass side walls 70 and floor 72. Downcomer 74 then feeds the fluid to convection pass front, rear, side and division walls 78, 80, 82 and 84 respectively, after which the fluid passes through roof tubes 86 and pressure reducing valves 88, 90 to radiant heated pendant superheater 22. During normal operation, the fluid then flows to finishing superheater 26 and a high pressure turbine (not shown). Intermediate and low pressure reheaters 42, 40 are located in the parallel convection passageways 34, 32 respectively. On start up a 25 to 30% full load fluid flow is established through the circuitry up to outlet header 94 of pendant superheater 22, and since valve 100 ih the line connecting superheaters 22 and 26 is closed, the fluid is passed through valve 102 to flash separator 98. Water from the separator passes through line 106 to a condenser and demineralizer (not shown) and/or to a heat recovery system (not shown), so bypassing finishing superheater 26. Firing at about 15 to 20% of the full load rate is commenced, the flue gases passing the finishing superheater 26 being kept below 1,200‹ F., flash steam from separator 98 being passed through line 92 to finishing superheater 26 to warm and roll the turbine. Firing continues, and the load is increased till 95% quality steam is produced by outlet header 94, when valve 100 is opened and valve 104 closed, for normal operation, thereby removing separator 98 from fluid circuit. In normal operation, superheat steam temperatures are controlled by varying the firing rate, or the feed water supply, one re-heat steam temperature is controlled by proportioning the gas flow through the parallel passes 32, 34 by means of dampers 52, 54, and the other reheat steam temperature is controlled by varying the gas recirculation rate back to the furnace chamber 12 from the convection pass outlet, through ducts 46 by means of the setting of dampers 50.