GB750484A - Improvements relating to tubulous vapour generating units - Google Patents

Abstract

750,484. Pulverised-fuel fired furnaces. BABCOCK & WILCOX, Ltd. Sept. 29, 1954 [Sept. 30, 1953], No. 26849/53. Class 51(1). A tubulous vapour generating unit of the pulverised-fuel fired type operating with a regulable recirculation of gas through a portion of the unit including convection heat exchange surfaces whereby control of the flue gas temperature at the inlet to the surfaces may be effected is characterised in that part of the gases withdrawn for recirculation are used for fuel-drying and for this purpose are returned to the unit by way of a wind-swept type of pul. verising mill followed by a separator and feeding means are arranged to supply the separated particles to the furnace of the unit for combustion therein. In the unit shown, the construction of which is detailed in Specification 744,797 combustion gas is withdrawn from below the economiser 26 by a fan 50 and returned to the radiation chamber 12 of the unit in the vicinity of the slag screen 11 through two paths one direct-through a damper controlled pipe 51-and the other indirectly-through a damper controlled pipe 55 and pulverizer mill 58 with associated separator 61. The mill 58 is of the type disclosed in Specification 523,753, [Group II] classified fuel particles entrained in the gas passing to the centrifugal separator 61 through a pipe 60. Below the separator is a hopper 62 arranged to receive separated fuel particles and to supply them, via a feeder 63, to a mixing valve 64 in which they are entrained in a stream of hot air, supplied through a duct 65 from an air heater arranged in the gas flow path of the generating unit, and passed through a duct 3 to ports 4 of a cyclone furnace chamber 1 and to that of its companion (not shown). Gases from the separator which normally contain fine fuel particles are led wholly or partly to auxiliary burners 68 (one not shown) depending upon the damper setting 74 of a gas circulation path set up by a fan 72 for the recirculation of some of the gas from the mill and separator back therethrough. The two burners 68 are fed with preheated air from a pipe 70 which connects with the secondary air nozzles of the furnace chambers. Specification 706,504 also is referred to.