Patent GB-761639-A (GB)
Title: Improvements in or relating to a control system for regulating the supply of fuel and air delivered for combustion to a boiler furnace
IPC: F23N1/02
Filed: 1954-11-17
Abstract: 761,639. Fluid-pressure servomotor control systems. COMBUSTION ENGINEERING, Inc. Nov. 17, 1954 [Dec. 1, 1953], No. 33269/54. Class 135. In a steam generator wherein fuel is supplied to the boiler furnace from a pulverizing mill by entraining the fuel in an air stream, the flow of air is controlled partly in response to steam pressure at the outlet of the boiler and partly in response to the difference between the pressures in the mill and in the furnace. In an embodiment, fuel is supplied by a feeder 18 to a pulverizing mill 3 and, from there, it is conveyed in an air stream to the burner 2 of the furnace of a steam generator 1. The air for entraining the fuel is supplied by a fan 6, past a heater 5 and a further forced draught fan 4, to the mill 3, and the amount of air supplied is controlled by a damper 15 in the pipe leading from the heater to fan 4. Cold air from fan 6 can be supplied through a pipe 11 to by-pass the heater, and the proportion of hot and cold air supplied is varied by means of a valve 14. The pressure of steam in the outlet header 23 is measured by means of a Bourdon tube 21 which adjusts a pilot valve 26. The output pressure from the pilot valve is supplied past a relay 32 to a bellows.44 which varies the rate of feed of fuel into the pulverizing mill 3. Relay 32 comprises four chambers A, B, C, D, chambers A and B being separated by a diaphragm 33 and chambers C and D being separated by a diaphragm 34. The diaphragms are connected to a spindle which moves.a lever 36 and the whole assembly is loaded by a tension spring 42. Lever 36 actuates inlet and exhaust valves 38, 39, respectively, to give an output pressure in chamber D, and this pressure is also fed to chamber C past a restriction 41. The output pressure from relay 32 is also supplied to the chamber A<SP>1</SP> of a further relay 54 which is similar to relay 32. Whereas chamber 3 of relay 32 is open to atmosphere, chamber B<SP>1</SP> of relay 54 is supplied with a pressure indicative of the rate of flow of air in the pipe 17 between the mill 3 and the burner 2. This pressure is obtained from a pilot valve 52 which is actuated by a manometer 46 subject to the differential pressures from the mill 3, via a line 48, and from the furnace 2, via a line 50. The output pressure from relay 54 is conveyed to a bellows 57 which actuates damper 15, or it actuates a resistance controlling the motor driving fan 4. In order to ensure that the air is hot enough to dry the fuel in the mill, the temperature of the issuing air is detected by means of a thermal element 58 which actuates a pilot valve 59. The output of the pilot valve is supplied to the chamber A<SP>11</SP> of a relay 61, which is similar to the relay 32, and the output pressure from this relay is fed to a bellows 63 which controls the valve or damper 14. In a modification, valve 14 at the junction of the pipe conveying the heated and cold air is replaced by a damper consisting of a weight loaded flap valve which controls a supply of cold air from the atmosphere.