Patent GB-781995-A (GB)
Title: A method of and apparatus for automatically controlling the operation of combustion apparatus including a plurality of cyclone furnaces
IPC: F23C3/00
Filed: 1955-02-18
Abstract: 781,995. Cyclone furnaces. BABCOCK & WILCOX, Ltd. Feb. 18, 1955 [Feb. 18, 1954], No. 4999/55. Class 51 (1). A steam generator 1 is fired by cyclone furnaces 2, 3 and waste gases are discharged to atmosphere through air-heater 4 and fan 5. Fans 8, 9 draw combustion air through a duct 7-having a measuring orifice 6- and ducts 10, 11, and then force it through pipelines 12, 13, air-heater sections 14, 15 and pipelines 16, 17 to respective furnaces 2, 3. Air-heater sections 14, 15 are connected by equalizing ducts 18, 19. Fuel is fed to beater mills 26, 27 by rotary feeders 22, 23. Hot waste gas streams are supplied to the mills through pipelines 28, 29 and fans 30, 31. The dried and ground fuel is taken by the gas through pipelines 32, 33 to centrifugal separators 34, 35. The separated ground material is discharged through locks 36, 37 to bunkers 38, 39. The gas streams are partly returned through lines 40, 41, fans 42, 43 and lines 44, 45 to the lines 28, 29 and partly discharged to atmosphere through lines 40, 41, fans 42, 43, lines 46, 47 and an electrostatic precipitator 48. Separated dust passes to the bunkers 38, 39 through a lock 50. The quantity of fuel in the bunkers governs the speed of feeders 22, 23. The gas and vapour temperature in mill classifiers 52, 53 is maintained at a predetermined value through thermostats 54, 55, impulse lines 56, 57 and dampers 58, 59 in the lines 28, 29. The gas and vapour flow rate through lines 32, 33 is kept constant by dampers 60, 61 disposed in lines 40, 41 and controlled, as indicated by lines 64, 65, in dependence on flow rates determined by means including orifices 62, 63, provided in the lines 40, 41. Similarly, the gas and vapour return flow rate through lines 44, 45 are kept constant by means of dampers 66, 67 which are controlled, as indicated by lines 70, 71, by means including measuring orifices 68, 69 provided in the lines 44, 45. To keep the flow rates in lines 32, 33, 44, 45 constant while the rates past dampers 58, 59 are variable, lines 100, 101 lead waste gases from in front of heater 4 to the lines 28, 29 behind dampers 58, 59. The pulverized fuel is discharged from bunker 38 by rotary roller feeders 72, 74 to lines 76, 78, 80, 82 which lead to the corresponding fuel nozzles of furnace 2 and fuel is discharged from bunker 39 by feeders 73, 75 to lines 77, 79, 81, 83 which lead to the fuel nozzles of furnace 3. Hot air is conveyed into lines 76, 78, 80, 82 from the line 16 through line 84 and into the lines 77, 79, 81, 83 from the line 17 through line 85. The main quantity of hot air flows through lines 86, 87 to the secondary air nozzles of furnaces 2, 3. In operation, either the supply rates of fuel and air are both controlled directly by a boiler load index-e.g. rate of vapour flow or vapour pressure-or the fuel rate or air rate is controlled directly by the index and the other of said rates is controlled in relation to the rate governed directly by the said index. The speed of feeders 72-75 serves as an indication of fuel supply rate whilst air flow rate is indicated by pressure drop readings at orifice 6. A throttling device adjacent each of fans 8, 9 is arranged to respond to vapour flow rate or/and vapour pressure and to air flow rate in such manner as to adjust the total combustion air flow to suit the load. The device may be in the form of adjustable vanes arranged at the suction side of the fan but if desired the air flow rate may be controlled by blade adjustment within fans 8, 9. Means responsive to vapour pressure or/and vapour flow rate regulate the speed of feeders 72-75. In dependence on the aggregate speed of feeders 72, 74 or 73, 75, the positions of dampers of the secondary air nozzles are adjusted such that the velocity of air leaving the nozzles is kept constant. The air supply rate to each furnace 2, 3 is controlled by the ratio of the aggregate speeds of feeders 72, 74 or 73, 75 of that furnace to the aggregate speeds of feeders 73, 75 or 72, 74 of the other furnace. This ensures that stoppage of fuel supply to either furnace is accompanied by simultaneous reduction of air. Automatically operated dampers 88, 89 are fitted for this purpose. An indication of the ratio of air flow rates may be obtained by means including nozzles 90, 91. Alternatively to the above the secondary air nozzle dampers may be operated by means responsive to combustion air flow measuring means. Thus means responsive to pressure drops across orifices 90, 91 may effect actuation of the dampers of respective furnaces 2, 3. The percentage of excess air with which each furnace operates is kept constant. It is determined either by flue gas analysis or temperature measurement at the outlet of the furnace, or secondary combustion, chamber and is utilized to effect a correction of either fuel feed or secondary air flow rate. Damper 88 may be adjusted or feeders 72, 74 regulated in dependence on the excess air in the chamber of furnace 2 whilst damper 89 may be adjusted or feeders 73, 75 regulated in dependence upon such air in furnace 3, The primary air flow rate is kept constant by installing dampers 92, 93 in lines 84, 85 controlled by means including measuring orifices 94, 95, and impulse lines 96, 97. The furnaces may be started and stopped by hand operation of feeders 72, 74 or 73, 75 and dampers 98 or 99. For automatic operation means must be provided to start or stop the fuel and air supplies in dependence upon a load index. If only one furnace is in operation lines 18, 19 ensure that heated air from both airheater sections 14, 15 flows to that furnace. The pressure in each furnace chamber is kept constant by controlling the output of fan 5 in dependence on pressure variations in the chamber.