GB975388A - Steam generating unit - Google Patents

Abstract

975,388. Water tube steam boilers; regulating steam temperature. RILEY STOKER CORPORATION. Jan. 14, 1963 [Jan. 16, 1962], No. 1553/63. Heading F4A. In a steam generator having an upright furnace fired by burners disposed below abutments projecting from opposed furnace walls, one of the walls having a nose on its upper portion below a lateral gas offtake whilst the other wall supports a radiant superheater, the superheat temperature is controlled by adjusting the burners or the air supply thereto in response to final steam temperature to position the flame within the furnace near to or remote from the radiant superheater, the effect being accentuated by blowing secondary air through openings formed above the abutments, the amounts of air entering from each side being varied so as to assist in directing the flame either towards or away from the radiant superheater. In the form shown, the generator has a vertical tube-lined furnace 19 divided by opposed abutments 21, 22 into a radiation chamber 24 and a lower high temperature cell 23 into which burners 25, 26 fire. Above the abutments are air openings 78, 81. A nose 27 is formed on the rear furnace wall 15 below a lateral offtake 28 which leads to two parallel downpasses 33, 34, the flows of gas through which are controlled by proportioning dampers 91, 95. Gases leave the boiler through an air heater 35 and stack 36. On the front wall 14 of the furnace is mounted a radiant superheater 47 which receives steam from a primary superheater disposed in the pass 34, the steam then flowing through a pendent superheater 49 and outlet header 51 to a turbine. Steam to be reheated flows through a primary reheater disposed in the pass 33 and a pendent reheater 53 to return to the turbine through an outlet header 54. The headers 51, 54 contain respective temperature pick-offs 72, 71, which transmit signals representative of superheat and reheat temperature to a controller 68. At high loads when the superheat temperature would otherwise tend to rise above the desired value, the controller increases the air flow to the burner 25 and that from the openings 78 whilst decreasing the flow from the openings 81. The unbalanced air injection to the burners serves to deflect the stream of hot gases away from the superheater 47, the effect being accentuated by the additional air injected at 78. This lowers the gas temperature as it enters the lateral pass by causing the stream to take a long path through the chamber 19. At low loads; the burner 26 and the openings 81 receive the major portion of air, thus deflecting the gases towards the superheater 47 and shortening their flow path in the chamber thus maintaining the correct superheat temperature. Instead of varying the proportions of the air passing to the burners to control flame placement in the furnace 24 the burners may have intertube vanes which are adjusted relative to one another to produce the same effect. Temperature correcting adjustments are simultaneously made to the dampers 91, 95 and to the rate of water injection to a interstage desuperheater 105. Depending on the load on the boiler the controller 68 also varies the proportion of air passing to the burners to that passing to the openings 78, 81 so that at low load the burner air proportion is increased whilst at high load the air flow to the openings is increased. The formation of nitrous oxide at high loads is thereby minimized whilst the air injection completely oxidizes any nitrous oxide formed.