Patent GB-665363-A (GB)
Abstract: 665,363. Fluid-pressure servomotor-control systems. BAILEY METERS & CONTROLS, Ltd. Dec. 2, 1948 [Dec. 3, 1947], No. 31200/48. Class 135 [Also in Groups XII and XXXV] In a control system for a furnace, the supply of fuel and air is automatically regulated and the fuel supply is readjusted in dependence on an analysis of the gases leaving the furnace. The invention is shown applied to a vapour generator comprising a number of cyclone furnaces 2, Fig. 1, in parallel feeding into a secondary furnace 1, the cyclone furnaces being tangentially supplied with air from a forced draft blower 3 through' conduits 6 ....8. Coal is supplied by a feeder 18, driven by a variable speed motor 19, to a crusher 20 where it is mixed with air supplied through conduit 6. The various 'air conduits are provided with dampers 5, 15 ... 17, 22, and 23. The products of combustion are discharged by a fan 9, and the discharge conduit for these gases is also provided with dampers 10. As the cyclone furnaces are slightly inclined, the fused ash can run to one end and out of the burner. A sample of the combustion gases can be taken off at 27 for analysis. Specification 598,141, [Group XII], is referred to in connection with the furnace. As a measure of the load on the unit, the outlet steam pressure is taken and applied to a Bourdon tube 24, Fig. 2, which actuates a pilot valve 28 similar to that described in Specification 425,507, [Group XII]. The pilot valve controls a relay 30, as described in Specification 461,389, which applies a regulating pressure through a manual-automatic change-over valve 32 as described in Specification 657,631 to a. bellows 35. This regulating pressure is opposed by the forced draft duct pressure which is applied to a diaphragm 37 connected to bellows 35, and the resultant movement of the diaphragm and bellows actuates a pilot valve 38 controlling a further relay 40. The regulating pressure produced by relay 40 is passed through manual-automatic change-over valves 42 and used to control the speed or otherwise regulate the output of the forced draft blower 3. The maximum and minimum values of the regulating pressure passing through change-over valves 32 are limited by means of relays 33. The regulating pressure at the output of valve 32 is applied directly through further manual-automatic change-over valves 44 to control the dampers 15 ... 17, 22, and it is also used to control the fan 9, dampers 10, and the speed of the motor 19, by applying it to further relays 46, 67. Relay 46 constitutes an averaging relay as it is actuated by a second regulating pressure proportional to the furnace draft, and this second regulating pressure is obtained from a device 48 which controls a relay 50, and the output pressure from this latter relay is applied to relay 46 past a manually-actuated restriction 52. The output pressure from relay 46 is applied through manual-automatic change-over valves 53 to control dampers 10 and through changeover valves 54 and further relays 57, 60 to control the speed of fan 9. A further control of fan 9 by means of its own-speed is obtained by applying a loading pressure obtained from a tachometer 55 to the averaging relay 57. Indications of the rates of steam flow and of the flow of combustion products and excess air through the unit are given by meters 61, 62, respectively, and such indications are used to actuate a. pilot valve 63 which controls a relay 65 producing a regulating pressure applied to the averaging relay 67. The output pressure of the lastmentioned relay is applied to further relays 73 ... 75 controlling, through manual-automatic change-over valves 72, the fuel feeder motors 19. Relays 73 ... 75 incorporate in their final regulating pressures an adjustment in accordance with the amount of excess air in the flue gases leaving the associated cyclone furnaces. As only one analyser 76 is provided for the battery of furnaces, the ducts leading from the sampling points 27 in the furnaces are controlled by cut-off valves 77 operated in timed sequence by a timer 80. The latter is provided with two cams for each sampling duct, the first cam in each set operating a switch which actuates a solenoid opening the appropriate valve 77 a short time before the second cam closes a switch in the circuit of the appropriate motor 81. If the analyser indicates that a re-adjustment is required, it actuates a reversing switch controlling the motors 81, and the selected motor is set in operation to adjust the loading spring 84 of the relay 73 with which it is associated when a further switch in the motor circuits is closed by a motor controlled interrupter. The latter ensures that the impulse given to the adjusting means is of short duration to prevent over-correction.