GB719986A - An improved method of and unit for generating and superheating vapour - Google Patents

Abstract

719,986. Fluid-pressure servomotor-control systems. BABCOCK & WILCOX, Ltd. Oct. 8, 1952 [Oct. 8, 1951], No. 25217/52. Class 135. [Also in Group XIII] In a forced-flow steam boiler in which feedwater from a pump 80 flows, in succession, through an economizer 14, 16, located in a convection pass 100 extending from the outlet of the furnace 10, radiantly-heated tubes 98 lining the walls of the furnace 10, tube banks 60, 61, 62, 63 in the pass 100, an external attemperator 70, and a superheater S in said furnace outlet, the total available heat is divided between the furnace 10 and pass 100 by returning gases from the pass back to the furnace so as to maintain the water-stream transition zone within the convection-heated tube banks 60 ... 63. Recirculation of the gases is effected by a constant-speed fan 184 which discharges into the furnace hopper throat 170 and/or a plurality of furnace wall openings 172 through a junction box 188 and, respectively, a duct 190 with control damper 192 or a duct 194 with damper 196, these dampers 192, 196 being operated so that at low load there is a maximum flow of gases through the duct 190 and a minimum flow through the duct 194, the reverse conditions holding at high load. As shown, the damper 192 is regulated through an operator 222 by a controller T<SP>11</SP>, responsive to superheat temperature at a point T<SP>1</SP> in the tube banks 60 ... 63 beyond the transition zone, modified by a steam flow controller F, connected to opposite sides of an orifice 208 in the steam outlet pipe 200, and a recirculated gas flow controller 252, connected to opposite sides of an orifice 258 in the suction duct 182 of the fan 184, whereas the damper 196 is regulated through an operator 214 by a temperature responsive element K at the outlet of the furnace modified by said steam flow controller F. The feedwater pump 80 is regulated jointly by a pressure-responsive element P in the steam outlet pipe 200 and the steam flow controller F which is interconnected with a water flow controller W associated with an orifice 217 in the pump supply pipe, and the rate of firing by a steam temperature controller T3, associated with a temperature responsive element 241 in the steam outlet pipe 200, and the said controller F. Specifications 425,507, [Group XIII], and 461,389, and U.S.A. Specifications 1,064,748, 1,962,676, 2,155,986, 2,298,257, 2,526,843 and 2,536,184 are referred to.