Patent GB-815724-A (GB)
Title: Method and apparatus for generating heated gases
IPC: F22G5/04
Filed: 1956-02-08
Abstract: 815,724. Combustion apparatus ; recirculating combustion gases. COMBUSTION ENGINEERING Inc. Feb. 8, 1956 [Feb. 16, 1955], No. 3925/56. Class 51 (1). [Also in Group XIII] In a steam generating unit fuel from a source 6 is burnt in a water-tube lined chamber 4 in the presence of a mixture of oxygen and recirculated combustion gases fed into the chamber around the motor-driven tiltable burners 10 through a windbox 48. The resulting combustion gases traverse passes accommodating a superheater 26 and an economizer 17 before being discharged by a fan 30 to either a gas recirculating duct 36 or a chimney 34, the quantity of gas passing either way being controlled by a motor-driven damper 38. Oxygen is fed to the duet 36 from a source 42 through valve means 44. The steam temperature actuates a thermostat 80 in the steam outlet pipe 78 whilst the steam pressure is indicated by a device 60 in the steam-and-water drum 16. Variations in the gas flow over the economizer 17 are noted by measuring the gas flow pressure difference between points 70, 72, whilst variations in the recirculated gas and oxygen mixture flow are measured between points 47, 49, of a venturi-type device in the duct 36. Superheat control, in dependence upon the action of the thermostat 80, may be effected either by automatically tilting the burners or automatically operating the recirculated gas flow valve 38. These operations are effected by electric circuits controlling burner motors 84 and the motor 58 of a valve 38 through changeover switches 88, 56, 54. Devices 82, 50, 74, which translate thermostat action and gas pressure differentials, respectively, into electrical impulses, are provided in the circuits. When the " tilting burner " method is to be employed the switches 88, 56 are thrown into the positions shown so that variations in the thermostat 80 will directly control the movement of the burners 10 through the circuit 82, 86, 88, 92, 84, whilst the amount of combustion gas in the oxygen-combustion gas mixture is maintained constant through the circuits 74, 76, 54, 55, 56, 57, 58, or 50, 52, 54, 55, 56, 57, 58, depending on whether the switch 54 is " up " or " down." If the superheat control is to be by gas recirculation, switches 88 and 56 are thrown to their right-hand positions such that the control of the valve 38 is effected through circuit 82, 86, 88, 94, 57, 58. Control of the amounts of fuel and oxygen fed to the chamber 4 is effected from a device 60 which translates steam pressure changes into electrical impulses and controls the fuel valve 11 and oxygen valve 44 through respective actuators 62, 64. A duct 95 and fan 96 are provided for transferring, if desired, hot furnace gases from the chamber 4 to mix with the cooler gases entering the duct 36. Gases may also be withdrawn, if required, from behind the superheater through a duct 97. As the nitrogen content of combustion air is replaced by combustion gases the percentage of these gases in the fuel, oxygen, combustion gas mixture, which act as a dilutent, can be reduced to a value below the percentage of nitrogen in air. It is stated that by suitably controlling the amount of recirculated gas in the mixture, the steam temperature of the boiler may be held constant over a load range of from 25 per cent to 100 per cent. The control system may be pneumatically or hydraulically operated. Specification 642,671 is referred to.