Patent GB-264852-A (GB)
Title: Improvements in and relating to furnace regulation
IPC: F23N1/02
Filed: 1927-01-20
Abstract: 264,852. British Thomson-Houston Co., Ltd., (Assignees of Smith, A. R.). Jan. 20, 1926, [Convention date]. Regulating combustion. - In a plant for the generation of elastic fluids, such as steam, variation in the load on the plant or of the pressure in the steam main common to a group of generators produces a variation in the fuel or air supplied to each furnace of the plant, the fuel and air supplied to each furnace being maintained in a definite ratio through a balanced electric relay operated by electric currents which are measures of the fuel and air supplies. Fig. 1 shows a furnace 1 for generating steam in a boiler 2 discharging through a conduit 23 into a main 24 common to a group of boilers. The fuel feeder 3 is driven by an electric motor 4 and the draught is produced by a suction blower 14 arranged in connection with the waste gas conduit 13 and driven by an electric motor 15. In the event of a decrease in the demand for steam, the pressure in the main 24 increases and operates an electric pressure gauge 59 and causes a flow of current from the supply lines 5, 6 to the coil 67 of a master relay 68 common to all the furnaces. The movable contact 70 engages with the fixed contact 72 and completes the circuit of a coil 77 which operates a switch 80 and allows a current from the mains 5, 6 to pass through the field winding 81 of a motor 12. The latter is moved in a direction to decrease the amount of resistance 10 in the field 9 of the motor 4, the speed of which is reduced to reduce the fuel supply. A reduction of the flow of steam in the pipe 23 follows and operates an electric flow meter 40 of the type described in Specification 214,632, [Class 37, Electricity, Measuring &c.], or of other suitable type connected by pipes 41, 42 to opposite sides of a device 43 in the pipe 23 for creating a pressure difference. A current flows from the mains 5, 6 through the conductors 44, 46, 39 to the coil 47 of a balanced relay 38 and carries the movable contact 49 to engage the stationary contact 50 and close a circuit for energizing a coil 53 and operating a switch 82, thus allowing current to flow through the field winding 83 of the motor 21. The latter operates to reduce the resistance 19 in the field 18 of the motor 15, the speed of which is thereby decreased and the furnace draught reduced. The reduction in the draught operates an electric flow meter 27 of the type described in Specification 241,201, [Class 106 (ii), Dynamometers &c.], or other suitable type, connected to the discharge pipe 13, and the first pass in the furnace by pipes 31, 32 and produces in the conductors 34, 36, 39 and coil 37 of the balanced relay 38 a current proportional to the draught. As soon as the currents in the coils 47, 37 of the balanced relay 38 obtain the desired relation the contact 49 moves away from the contact 50. By adjusting resistances in the circuits of the coils 37, 47 the desired relation between the fuel and air for all loads mav be obtained. When there is an increase in the demand for steam and a consequent reduction in pressure in the main 24, the master relay makes contact at 71 and energizes the coil 75 so as to operate the switch 84 and close the circuit through the field winding 85 to increase the speed of the fan motor 15 and the draught. This is reflected in the flow meter 27 and the coil 37 of the balanced relay 38 which then makes contact at 51, closing the circuit through coil 56 and switch 78. The field winding 79 is then energized to operate the motor 12, reduce the resistance 10, and increase the speed of the fuel-feeding motor 4. The pressure in the furnace also operates through a pipe 89 a meter 88, relay 190, and motor 26 to vary the position of dampers 25. In a modification, the meters 27 and 40 are operated respectively by a differential pressure in the air supply conduit, and the pressure in a conduit proportional to the speed at which the stoker is driven by an electric motor.