Patent GB-846807-A (GB)
Title: Control of superheat in a steam generating unit
Inventor: GRIFFITH LOUIS EUGENE
IPC: F22B21/34
Filed: 1958-07-03
Abstract: 846,807. Regulating fuel supply to steam generators. RILEY STOKER CORPORATION. July 3,1958, No. 21354/58. Class 51 (1). [Also in Group XIII] A steam-generating unit adapted to maintain the temperature of the superheated steam at a constant preselected value comprises a structural framework 13 which supports a boiler 12 and a furnace 11 with front, rear and side walls 14, 15 and 16 respectively defining a combustion chamber 17 which is lined with water wall tubes 22 and has a lower hopper 23. The boiler 12 consists of a steam-and-water drum 18 having downcomers 19 connected to a lower header 21 for the wall tubes 22. Combustion gases flow successively through a secondary twostage superheater 25, having a first radiant section 27 and a second convection section 28 and a primary superheater 24 which is located in a back-pass and is supplied with steam from the drum 18. The secondary superheater 25 is connected to a header 51 which supplies steam to a turbine, not shown. Fuel, e.g. pulverized coal or gas, is delivered to a conduit 38 having an apportioning vane 39 pivoted at 41 at the junction of two branch conduits 33, 36. Series of burners 29, 31 mounted respectively in the furnace front and rear walls 14, 15 each have two burners, e.g. 63, 65, Fig..2, with downwardly projecting vanes 67, Fig. 3, and two burners, e.g. 64, 66, with upwardly projecting vanes 67, Fig. 4, the latter communicating through pipes 32, 34 with the pipe 33. The burners 63, 65 are connected by pipes 35, 37 to the pipe 36. A fuel regulating valve 52, located in the tube 38, is operable by an hydraulic cylinder 56 connected by lines 57, 58 to a controller 59 which responds to signals received over a line 61 from a pressure bulb 62 located in the drum 51. A controller 47 connected by a line 48 to a thermo-couple 49 located in the header 51 controls an hydraulic cylinder 44, the piston of which is connected to an operating arm 42 of the vane 39. When the turbine load drops, the corresponding rise of pressure in the header is felt by the bulb 62 which transmits an appropriate signal to the controller 59 which, through the actuator 56, rotates the valve 52 to reduce the amount of fuel delivered to the burners so that the steam pressure quickly drops to the desired value. The consequent reduction of combustion, however, correspondingly reduces the gas flow over the superheater elements so that the steam collected in the header 51 is at a lower temperature. The latter is sensed by the thermocouple 49 which sends a signal through the line 48 to the controller 47 which operates the actuator 44 so that the vane 39 is moved to a position to direct respectively more and less fuel through the branches 33, 32, 34 and 36, 35, 37 to the upwardly and downwardly orientated burners. The net effect is to increase the temperature of the gases passing over the superheater elements until the temperature of the superheated steam is restored, the vane 39 thereafter being regulated to maintain the correct apportioning of the fuel to maintain the temperature of the superheated steam in the header 51 constant.