GB782252A - An improved method of regulating superheat and reheat temperatures and improvements in or relating to vapour generating, superheating and reheating units - Google Patents

Abstract

782,252. Regulating steam temperature in boilers. BABCOCK & WILCOX, Ltd. March 2, 1956 [March 3, 1955], No. 6567/56. Classes 123(2) and 123(3) [Also in Group XXIX] In a steam boiler comprising an upright furnace 10 lined with steam generating tubes extending between headers 24, 26 and a steam and water drum 20 and fired through the front wall 14 by burners 28...30 and wherein combustion gases leave the upper part of the furnace through a lateral pass 82 locating a secondary superheater 34, 36, a reheater 38 and a primary superheater 40, 42, 44, the provisions for controlling steam temperature include firstly a gas by-pass formed between a horizontal baffle 132 extending across the tops of the tube 42, 44J and the roof 66 of the pass 32, gas flow through the by-pass being controlled by a damper 136, secondly a spray attemperator 96, preferably of the form described in Specification 656,551 between the primary and secondary superheater stages and one (not shown) in the outlet line 120 from the reheater and thirdly, means for recirculating flue gas from a point beyond the primary superheater to the furnace, the gas being withdrawn through a duct 144 by a fan 140 which delivers it through ductwork 148 to a distributing chamber 150 whence it flows into the furnace through a series of ports. The amount of gas recirculated is controlled by a damper 156 in the duct 144 and by regulating the fan speed. In operation, see Fig. 9, as the load falls from a control point load of, say 100 per cent, when superheat and reheat temperatures are at the predetermined value without gas recirculation, attemperation or by-passing, to a low load of 53 per cent, the dampers 136, 156 are opened gradually as shown by curves CD, CE respectively to bring the reheat and superheat temperatures, which would otherwise follow the curves KF, KM, to the desired value KH. Below a load value of 53 per cent, superheat attemperation is employed as indicated by the line RP. At overloads, reheat attemperation is used as shown by the curve CS whilst superheater by-passing, line CT and then attemperation, line VW, is employed to correct the rising steam temperatures indicated by curves KG, KX. In modifications, the invention is applied to a downwardly fired boiler and also to one having parallel convection down-passes housing superheaters and a reheater. A servomotor-control system may be used to control the by-pass damper, attemperators, &c. automatically, (see Group XXIX). Specifications 425,507 [Group XII], 461,389 [Group XXIX], and 526,825 also are referred to.