GB806561A - Forced flow, once through vapour generators - Google Patents

Abstract

806,561. Regulating forced-flow steam boilers. SULZER FRERES S. A. March 5, 1957 [March 6, 1966], No. 7325/57. Class 123(2) A once-through steam-generator which may operate at or above critical pressure has three parallel-connected groups of tubes A, B, C comprising respectively four tubes 1...4, 5...8, and 9...12. The outlet end of each tube is connected to a header 20 whilst the inlet ends of tubes 1...3, 5...7, and 9...11 originate in respective subheaders 28, 30, 32 which are connected to the main inlet header 34 by respective conduits 36, 38, 40 having valves 46, 48, 50. The inlets of the remaining tubes in each group, namely the tubes 4, 8, 12, are connected directly to the header 34 and are fitted with respective valves 52, 54, 56. Feedwater flows into the header 34 through a line 42 controlled by a valve 44 whilst steam with a small amount of entrained water which carries most of the impurities, flows from the header 20 through a separator 58, wherein the water is removed, to an outlet 62. To control the condition of the steam entering the separator, the tubes 4, 8, 12 have respective temperature sensitive signal transmitters 68, 70, 72 adjacent their outlets. The transmitter signals are passed respectively to three bellows 78, 79, 80 in a selector mechanism 74, each of the bellows being expanded to a height corresponding to the associated steam temperature. The bellows connected to the transmitter sensing the highest temperature contacts a cross bar 82 of a lever 83 connected by a link 85 to an oil valve 86 through which pressure is transmitted through a line 76 to an actuator 75 which adjusts the feed water regulator valve 44 or, in a modification, (Fig. 3, not shown), the fuel supply valve so as to maintain the temperature constant. In operation, the rate of supply of feedwater or fuel is first adjusted so that steam having about 10‹F. of superheat is generated in the tube groups A, B, C, the valves 46, 48, 50 and 52, 54, 56 then being adjusted to give the same steam temperature at the outlets of the tubes 1...12. The superheat in one of the control tubes 4, 8, 12, e.g. the tube 12, is raised to 100‹F. by partially closing the valve 56 and then lowered to 25‹F. by opening the feed valve 44, the latter adjustment reducing the steam temperature in the other tubes to just below saturation level. Thereafter the valve 44 is adjusted in response to changes in the steam temperature in the tube 12, which is the tube delivering the hottest steam, the adjustments automatically maintaining constant the quality of the steam leaving the other tubes. If the tube 12 becomes slagged, its steam temperature will fall and eventually one of the control tubes 4 or 8 will take over control of the feed or fuel supply valves.