GB781750A - Improvements in tubulous vapour generating, superheating and reheating units and a method of operating such units - Google Patents

Abstract

781,750. Water-tube steam boilers; regulating steam temperature. BABCOCK & WILCOX, Ltd. March 21, 1956 '[March 25, 1955], No. 8863/56. Classes 123(2) and 123(3) A water-tube boiler comprises an upright, steam generating tube lined setting which is divided into two parts by a partition formed of other generating tubes 22, the parts including radiation chambers 24, 26 of a reheater and superheater furnace respectively. Secondary furnaces 42, 70 fired by cyclone furnaces 46, 64, for example of the form described in Specification 598,141, are disposed below respective chambers 24, 26, the hot gases flowing into the chambers through slag screens 54, 72. From the upper part of the chamber 24 a lateral pass locating a convection reheater 82 and primary superheater 84 conveys gases to a main flue 124 in which is disposed an economizer 86. The floor 34 of the lateral pass forms the roof of the chamber 26 and of a short lateral pass conveying gases from that chamber into chamber 24, the short pass locating a secondary superheater 80. At maximum output, the furnaces 64, 70 and chamber 26 are designed to give excessive gas temperature at the entrance of the secondary superheater pass, whilst the design of the reheater furnaces 46, 42 and of the chamber 24 provides that optimum reheat temperature is obtained. The superheater and reheater absorbed heat and heat absorbed in steam generation are proportioned to maintain the correct steam temperatures over a wide range of loads by recirculating cool flue gas withdrawn by a fan 120 from the flue 124 to the secondary furnace 42 through a dampercontrolled duct 128 and to a region in chamber 26 adjacent the entrance to the secondary superheater pass through a dampercontrolled duct 132. The flow of recycled gases entering chamber 26 is controlled according to load conditions to bring the fresh gases therein to the temperature ensuring correct superheat whilst a constant reheat is maintained by oppositely varying the recycled gas flow to the furnace 42. In a modification, the superheater and reheater are disposed in parallel, damper-controlled gas passes extending upwardly from the secondary furnaces.