Patent GB-299198-A (GB)
Title: Improvements in means for regulating combustion in boiler furnaces
IPC: F23N1/02
Filed: 1927-11-04
Abstract: 299,198. Sandison, A. G. S., and Etectroflo Meters Co., Ltd. Nov. 4, 1927. Regulating combustion; stoking.- In the automatic regulation of combustion in boiler furnaces a measuring current dependent on the steam flow and/or pressure determines by electrodynamic means the strength of a control current, the effect of which is balanced against a iorce dependent on the flow of air or gas in the furnace in such a way as to maintain a constant relation between steam flow and air or gas flow. In a battery of boilers each boiler is controlled by a branch, in parallel, of a control current produced as above and dependent on the total steam flow. The fuel supply may also be controlled. An electric flow-metering device 1, including in its circuit a winding 3, regulates the resistance in the circuit in inverse proportion to the steam flow in the main pipe 2. The winding 3 acts inductively on a rotatable metal disc 9 to produce a torque proportional to the current. The disc 9 through reduction gearing controls a resistance 11 in circuit with a winding 12 acting similarly to the winding 3, but in the opposite direction. Included in the control circuit is a solenoid 13, the core 14 of which is suspended on a balance 15 carrying a bell-float 16 exposed to a pressure difference taken between two points in the boiler flue and proportional to the square of the air or gas flow in the boiler fluc, The balance 15, through a pilot valve 19, operates the servo-motor 23 of the damper 24. In operation, a change in the steam flow changes the resistance in the measuring circuit and therefore the flow of current in the winding 3. The consequent rotation of the disc 9 continues until the control current in the winding 12 has changed in the corresponding ratio. In the meantime the changing control current, acting on the solenoid 13 in proportion to the square of the current, puts the arm 15 out of balance thus shifting the damper 24 until the resulting change of flow of air or gas in the furnace restores the balance by means of the bell-float 16. To provide for the maintenance of a constant pressure in the main 2 the measuring circuit includes part of the windings of an auto-transformer 4 having a series of tappings 6 engaged by a contact arm 7 movable by the pressure responsive device 8. An indicator 26 included in the control circuit and calibrated in terms of fuel supply serves as a guide for the operation of the stokers. The ratio of air or gas flow to steam flow is adjusted as required by adjustment of the balance 15 or by shunting the solenoid 13 with an adjustable resistance or by adjusting the ratio of influence of the windings 3 and 12 on the disc 9. The source of electric supply is a transformer 5. In the case of a battery of boilers there is a single control current, produced as above, in dependence on the total steam flow, but for each boiler there is a branch in parallel regulatable by a resistance 28 and switch 27, Fig. 2. each branch having the dampercontrolling means as before. There may in addition be parallel control circuits, preferably of relatively high resistance, for controlling a main fan, a stoker, or other auxiliaries.