Patent GB-844349-A (GB)
Title: Control of superheat in a steam generating unit
Inventor: HAWLEY CHARLES FREEMAN
IPC: F22B21/34
Filed: 1958-07-03
Abstract: 844,349. Water-tube steam boilers; steam superheaters. RILEY STOKER CORPORATION. July 3, 1958, No. 21355/58. Classes 123(2) and 123(3) A steam generating unit 10 for maintaining the temperature of superheated and reheated steam at a selected level comprises a combustion chamber 11 which is divided by opposed inwardly directed abutments 19, 23 on its front and rear walls 14, 15 into upper and lower parts respectively. The combustion gases flow through a horizontal pass 42, defined by a nose 41 projecting forwardly from the rear wall 15, and into a back-pass 35 which is divided by a wall 36 into forward and rearward passes 37, 38 having outlet openings which are controlled respectively by dampers 51, 44. The back-pass 35 is connected through a fuel air heater 56 to a breaching 57 leading to a stack, not shown. Large downcomer tubes, not shown, convey water from a steam-andwater drum 31 to water wall tubes 20 which line the combustion chamber 17 and lead to the drum 31. Steam tubes 32 lead from the drum 31 to a primary superheater 33 which is located in the rear back-pass 38 and is connected to a secondary super heater 34 formed in part by pendant platens which are heated by radiation in the combustion chamber 17. The remainder of the superheater 34, located in the horizontal-pass 42, is heated by convection. A low-temperature reheater 39, accommodated in the forward backpass 37, is connected to a high-temperature reheater 43 housed in the horizontal-pass 42. The output ends of the superheater 34 and the reheater 43 are connected respectively to headers 59, 58 which lead; e.g. to a steam turbine, not shown, and are provided with temperature responsive devices, e.g. thermo-couples 76, 78. The latter are connected by lines 75, 77 to a main control 49 which, through lines 54, 55 and 47, 48, regulates hydraulic cylinders 53, 46 operatively connected to the dampers 51, 44 by rods 52, 45 respectively. Directional flame burners 26, 27 are supplied with fuel and air warmed in the heater 56, through openings arranged in the lower surface of the abutments 19, 23 corresponding gaps being provided in the wall tubes 20. Additional control of the superheat and reheat temperatures, particularly when at low loading and corresponding low fuel input the desired rise in temperature cannot be obtained by operation of the dampers 51, 44, is provided by reintroducing a controlled amount of combustion gas into the combustion chamber 17. This is carried out. by means of a fan 67 the input and output of which communicate respectively with the duct connecting the back-pass 35 with the heater 56 and a pipe 65 housing a regulating damper 66. The pipe 65 leads to branch pipes 62, 63 which open into the upper walls of the abutments 19, 23 so that the recirculated combustion gases blanket the front and side walls of the combustion chamber 17 before being mixed with the primary combustion gases as they pass the nose 41. The damper 66 is connected by rods 69, 71 to a hydraulic cylinder 72 communicating through lines 73, 74 with the main control 49. The latter, when sensing that further adjustment of the dampers 51, 44 is of no avail regulates the damper 66 to provide an increase of gases flowing through unit to raise the temperature of the steam to the desired level. Specification 765,298 is referred to.