Patent GB-281705-A (GB)
Title: Improvements in and relating to combustion control
IPC: F23N1/02
Filed: 1927-12-02
Abstract: 281,705. British Thomson-Houston Co., Ltd., (Assignees of Bennett, F. S., and Biggs, L. R.). Dec. 3, 1926, [Convention date]. Regulating combustion.-In a steam generator plant comprising a battery of boilers such as 1 supplying steam through mains such as 3 to a common header 4, electrically operated means are provided whereby the fuel supply to each boiler is regulated in accordance with the flow of steam therefrom while the air supply to all the boilers is controlled in accordance with the pressure of steam in the header 4, further regulation of the fuel supply being effected in accordance with the ratio of steam flow to air flow and successive adjustments of the air supply being effected at intervals governed by the extent of the departure of the operating conditions of the boiler from the normal value. An electric flow meter M of the kind described in Specification 214,632, [Class 106 (ii), Dynamometers &c.], is arranged in the main 3 and is connected to the alternating current mains 20, 21 through the conductors 28, 29, solenoids 30, 32, rheostat lever 34, resistance 35 and conductors 36, 37, the flow of current in this circuit being a measure of the flow of steam. A flow meter N of the kind described in Specification 241,201, [Class 106 (ii), Dynamometers &c.], is connected by pipes 41, 42 to suitable points in the furnace to measure the drop of pressure or draught, the flow meter mechanism serving to operate an armature 46 in a field comprising a winding 48 connected to the mains 20, 21 and varying the current therein in accordance with the draught or air supply. The winding 48 is also in circuit with conductor 50, solenoid 51, conductor 52, rheostat arm 53, resistance 54 and conductors 55 and 37. The fuel-feeding means 6 is driven by a motor 7 connected to direct current mains 22, 23. The field winding 9 of the motor 7 is in circuit with the mains 22, 23 through the conductor 57 and rheostat arm 59, resistance 60 and conductor 61. The rheostat arm 59 is mounted on the same shaft as rheostat arm 65 co. operating with a resistance 66 connected to the mains 20, 21 and including in its circuit conductors 67, 68. solenoid 69, conductor 70, resistance 71, rheostat arm 72, conductor 73, rheostat arm 74, resistance 75, and conductor 37. The rheostat arms 59, 65 are operated simultaneously by a motor 78 having field windings 79, 80 either of which may be connected to mains 22, 23 to operate the motor 78 and vary the resistances 60, 66 the field 9 and solenoid 69. By varying the field 9 the speed of the fuel feed motor is varied while the variation of the current in the solenoid 69 provides a measure of the fuel being supplied. The field winding 79 is connected to the mains 22, 23 and is in circuit with conductors 57, 91, switch arm 90, conductor 89. contacts 85, 84 and conductors 94, 63, while field winding 80 is connected to the mains through conductors 57, 88, switch arm 87, conductor 86, contacts 83, 82 and conductors 94, 63, The contacts 82, 84 are mounted on a pivoted arm 81 connected to the plungers of the selenoids 30, 69. The plungers of the solenoids 32 and 51 are, connected to a pivoted arm 95 carrying the rheostat arm 72. A dashpot 96 damps the movement of the solenoid 32. In the event of a demand for steam the flow increases and solenoid 30 is operated to move contact 84 into engagement with contact 85 and close the circuit through the field winding 79. The resistance 60 is increased and the field strength in the winding 9 is reduced to effect an increase in the fuel supply. The resistance 66 is also reduced and the current through the solenoid 69 increased to again separate the contacts 84. 85 and stop the motor 78. The air control apparatus comprises a fan 10 driven by a motor 11 the speed of which is varied by a, resistance 12<1> adapted to be cut in and out of circuit by a motor 17 through gearing 14, 15. The motor is provided with two field windings 18, 19 .adapted to be energized to rotate the motor in either direction. The winding 18 is connected to the mains 22. 23 through conductors 174, 175, 176, switch 177. conductors 178, 179, contacts 173, and conductor 127. The field winding 19 is connected to the mains through conductors 174, 175, switch 183, conductor 184, contacts 181 and conductor 127. In the event of a drop of steam pressure in the main 4 the device 100 causes the shaft 102 to rotate in an anti-clockwise direction and turn the beam 106 mounted thereon. This beam is provided with contacts 107, 108 adapted to engage with contacts 110, 111 on a beam 109 freely mounted on the shaft 102 and provided with contact arms 112, 113 adapted to engage with contacts 114, 115 on an insulated member 116. The rotation of the beam 106 in the direction stated above causes the closing of the contacts 107, 108 and the contact arm 112 and contact 114. Current passes from the main 22 through the conductor 124. 123, contacts 122, 120, dosed by a solenoid plunger 156, conductor 118, beam 106, contacts 107, 110, contact arm 112, contact 114, solenoid winding 126 and conductor 127. The solenoid plunger of the winding 126 is raised and the contact 173 closed to permit a flow of current to the winding 18 of the motor 17 to effect decrease of the resistance 12<1> and an increase of speed of the motor 11 and of the supply of air to the furnace. Simultaneously current flows from the mains through the contacts 122, 120 closed by the solenoid plunger 156 to the solenoid winding 162 and effects closing of contacts 166 in the circuit of the solenoid winding 168, causing the solenoid plunger 156 to rise and break the contacts 122, 120. The circuit of the field winding 18 is thus broken and the motor 17 stopped. The plunger 156 in its upward movement rotates a shaft 142 coupled by a ball and ratchet coupling to a shaft 144 in such a manner that the shaft 144 is not rotated during the upward movement of the plunger. The shaft 144 carries a magnetic clutch 146 geared to a magnetic retarding device 153. In the event of a small change in the steam pressure the fall of the solenoid plunger 156 is retarded by energizing the magnetic clutch through contacts 133, 134 mounted on arms 132, 135 connected to the mains 22, 23, but in the event of a considerable change of steam pressure the roller 131 on the arm 132 is operated by the arm 130 on the shaft 102 to separate the contacts 133, 134 so that the magnetic clutch is put out of action and the solenoid plunger 156 is allowed to fall quickly and effect a further increase of air supply. The arm 135 is adapted to be operated by a cam 139 to break the contacts 133, 134 and so vary the speed with which the solenoid plunger 156 falls.