GB807282A - Improvements in tubulous vapour generating and vapour heating units - Google Patents

Abstract

807,282. Water-tube steam boilers; regulating steam temperature. BABCOCK & WILCOX Ltd. May 7, 1957 [May 8, 1956], No. 14231/56. Classes 123(2) and 123(3) A high capacity steam generator comprises an upright chamber 1 with generating tube lined radiation chambers 2, 3 located at its lower end disposed side by side and separated by a tube wall 4, the chambers leading upwardly to respective tube lined parallel gas passes 5, 6. At opposite sides of the unit are disposed respective rows of cyclone furnaces 7, 8 suitably of the form described in Specification 552,747 [Group XII], and lined with wall tubes of arcuate form as described in Specification 779,857 [Group XII]. The furnaces 7, 8 discharge through throats 29, 30 suitably formed of tubes bent as described in Specification 598,142 [Group XII], into respective secondary furnace chambers 9, 10 whence the hot gases flow through slag screens 33, 34 into the chambers 2, 3. The tubes lining the furnaces, radiation chambers and associated passes and forming the wall 4 extend between a lower drum 15 supplied by downcomers 58, 59 and a steam and water drum 16 which is equipped with separators as described in Specification 526,825. The lower ends of the passes 5, 6 are spanned by secondary superheater tube banks 82...85. Above the superheater 82 the passes 5, 6 respectively contain primary superheater banks 66...69 and reheater banks 72...75, economizers 64, 65 being respectively located at the tops of the passes 5, 6. Steam flows from the drum 16 to a superheater inlet header 70 and thence serially through the banks 66...69, the bank 82, an interstage attemperator 87, suitably of the form described in Specification 656,551, and banks 85, 84, 83, to an outlet header 78. Steam to be reheated enters a header 76, flows through banks 72...75 and discharges from headers 80, 81. The superheater and reheater passes 5, 6 have respective lateral outlets 88, 90 controlled by proportioning dampers 89, 93 and leading into a common outlet duct 94. From the outlet duct cool flue gas is withdrawn by a fan which delivers it to ducts 103, 104 disposed horizontally above the rows of cyclone furnaces, whence a number of spaced, damper-controlled ducts 105, 106 deliver the gas through outlets 107, 108 in a downward direction into the lower regions 38, 39 of the radiation chambers 2, 3. The recirculated gas is also delivered through a damper-controlled duct into a space or chamber 37 formed in the wall 4 by spacing apart the tubes 97, 98 thereof, gas outlets 99, 100 from this chamber into the regions 38, 39 being formed by offsetting the tubes 97, 98. The gas recirculation ducting is protected from reverse flow of hot gas in the manner described in Specification 778,712. In operation, the dampers 89, 93 proportion the gas flow between the passes 5, 6 to control the reheat temperature, the superheat temperature being controlled by the attemperator 87. The total heat available for steam heating is controlled by varying the rate of gas recirculation, the gas flow from opposite sides of the lower regions 38, 39 of the chambers 2, 3 creating highly turbulent conditions resulting in thorough mixing of the fresh and recirculated gas. Inequality in temperature across the width of the chambers 2, 3 is rectified by adjusting the gas recirculation to different regions thereof.