GB781861A - Improvements in tubulous vapour generating units - Google Patents

Abstract

781,861. Water-tube steam boilers; regulating steam temperature. BABCOCK & WILCOX, Ltd. Feb. 9, 1955 [Feb. 9, 1954], No. 3821/55. Classes 123(2) and 123(3) A water-tube boiler has a steam generating tube lined furnace of rectangular crosssection divided into two furnace chambers 10, 12 by a tubular partition 14, the chambers 10, 12 each being fired by a set of burners such as 16, 18, 20. Furnace gases leave the upper regions of chambers 10, 12 through respective lateral passes 34, 84, which are spaced sufficiently far apart to provide an access and maintenance space 82 therebetween so that lance soot blowers can be used from both sides of each pass. The pass 34 locates a pendent superheater 40 constituting stage two of the secondary superheater of the boiler and leads to a gas turning space 36 whence gases flow through a downpass 38 in which are disposed tube banks 42, 44, 45, 46 constituting stage one of the primary superheater. From the said tube banks the gases flow downwardly through an economizer bank 56, an outlet controlled by dampers 62 and an air heater 60 to the boiler stack. The pass 84 from the furnace chamber 12 locates banks of tubes 86, 92 constituting respectively stage one of the secondary superheater and stage two of the boiler reheater and leads to a gas turning space 106 and downpass 80 wherein are disposed tube banks 100 contube banks 108, 109, 110 forming stage two of the primary superheater, the gases flowing from the latter downwardly through an economizer bank, a dampercontrolled outlet and air heater as for the other downpass. From each downpass outlet a duct such as duct 160, Fig. 1, conveys cooled flue gas to fans 152, 164, Fig. 2, the outlets of which are connected to respective manifolds such as 166 from which a number of outlet ducts 172 carry the gas into inclined outlet throats 170 extending from the hopper bottoms of the respective chambers 10, 12, the inclination of the throats directing the gases towards the rear wall of the chambers whereon they form a moving screen or blanket of gas which serves to reduce the amount of heat radiated to the wall tubes and correspondingly to increase the heat content of the gases flowing from the furnaces. The generating tubes of the furnace chamber deliver into a steam and water drum 30 whence steam flows through tubes lining both downpasses into a header 50, Fig. 3 at the bottom of pass 38. From the header 50 the steam passes successively through stages one and two of the primary superheater, interstage attemperators (not shown) inserted in lines 178, 180 and stages one and two of the secondary superheater to a final outlet header 186, 188. Control of reheat and superheat temperatures is effected by regulating the amount of flue gas recycled to each furnace chamber and by proportioning gas flows through the two parallel gas passages by means of the outlet dampers, the dampers preferably being used to maintain a predetermined reheat temperature, control of recirculated gas flow being effected to maintain the desired superheat temperature. Attemperation is utilized when necessary, e.g. at high loads, to limit the temperature of superheat. The control of superheat and reheat is further augmented by differential firing of the furnace chambers and by varying the distance from the gas outlets of the operative burners, e.g. at low loads, burners 16 rather than burners 20 are used. Specifications 781,862 and 781,863 are referred to.