Patent GB-440419-A (GB)
Title: Improvements in or relating to automatic heating systems operating with pulverized fuel
IPC: F24H9/18
Filed: 1934-06-22
Abstract: 440,419. Pulverulent-fuel burning-apparatus. TUGWOOD, R. J., 77, Chancery Lane, London.-(Jeffrey Manufacturing Co. ; 1st Avenue, Columbus, Ohio, U.S.A.) June 22, 1934, No.18560. [Classes 75 (i) and 75 (iii)] In an automatic heating system, pulverized fuel is supplied to a preliminary combustion chamber arranged within the main combustion chamber of the furnace, as described in Specification 440,417, and is ignited by means which are automatically put out of action when the preliminary combustion chamber reaches a combustion supporting temperature. Fig. 1 shows a furnace 14 in which powdered fuel is fed from a bin 59 by an apparatus 66 such as described in Specification 440,418, [Group XXX], to a preliminary combustion chamber 15 which is adjustably mounted on standards 16 in a main combustion chamber 152. The combustion chamber 15 is of refractory material and comprises a dome 19 resting on a cylindrical casing 18 formed with rectangular openings 20. The fuel discharged from a pipe 24 into the combustion chamber 15 is ignited by an atmospheric gas burner 39, Fig. 4, fed by pipes 44, 47. The gas burner 39 is ignited by the secondary current from a transformer 27 jumping across two spark gaps arranged in series between terminals 37, 38, 40, the primary circuit of the transformer 27 being completed simultaneously with the circuit to an electromagnetically operated gas valve 46. The gap between the terminals 37, 38 is relatively short so as to produce a hot spark and the gap between the terminals 38, 40 is relatively long so as to produce a flaming arc. A constantly burning gas flame supplied by a pipe 53 ignites the burner 39 if the electric ignition fails. The gas valve 46 is closed and the primary circuit of the transformer 27 is broken when the preliminary combustion chamber is sufficiently heated by a stack switch device 118, Figs. 10 and 13, comprising a thermostatic element 120 arranged in the furnace flue 119 and caused by the hot furnace gases to rock a shaft 158 on which are mounted two plates 153, 155 carrying mercury switches. Springs 156, 157 produce sufficient friction to cause the plates 153, 155 to move with the shaft 158 until stopped by abutments, the rear plate engaging fixed abutments 159, 171 and the front plate engaging adjustable abutments 166, 172. Fig. 5 shows a suitable circuit for operating and controlling the burner apparatus under the influence of a room thermostat 121. When the main switch 122 is closed current can pass through a switch 135 to energize the primary winding 123 of a transformer 124 having two secondary windings 123<1>, 168. If the room thermostat 121 is in the " cold " position, as shown, a current will pass from the secondary winding 123<1> through a switch 126 and a resistance 130. This current energizes an electromagnet 136 thereby causing pivoted armature 136<1> to move a switch 137 to the closed position. The switch 137 completes the circuit from the mains to a motor 89 operating the fuel feeding apparatus 66 and through a switch 144 carried by the plate 155 to the gas valve 46 and the primary winding of the ignition transformer 27. If ignition is not established within a short period of time the heat generated at the resistance 130 causes an element 164 to expand and operate a trip device 163 to open a switch 135. The fuel supply is thereby stopped and can only be restarted after the trip device has been reset. If ignition is established the heat of the flue gases acting on the element 120 causes the plate 153 to move into engagement with the abutment 159, thereby closing a switch 154 which short-circuits the resistance 130. As the stack element 120 becomes further heated the carrier 155 is moved into engagement with the abutment 166 thereby opening the switches 126 and 144 and breaking the circuits to the resistance 130, the gas valve 46, and the ignition transformer 27. When the predetermined maximum room temperature is reached the room thermostat 121 operates to break the circuit from the secondary winding 123<1> and to close the circuit of the secondary winding 168 at contacts 167 through the switch 154 and a resistance 160. The current through the secondary winding is insufficient to energize the electromagnet .136 and consequently the switch 137 opens and the fuel feeding apparatus stops. As the stack element 120 cools, the switch 154 opens and the switches 126, 144 close. The switches are then in position for restarting when the room temperature reaches the lower limit. If, under abnormal conditions, the stack switch 118 is not operated when the maximum room temperature is reached the resistance 160 becomes heated sufficiently to operate the trip device 163 and open the switch 135. A solenoid 97 operating to increase the fuel supply at starting, as described in Specification 440,418, may be provided. In a modified circuit shown in Fig. 8 the resistance 130 is used as a safety device both during the starting period and at the end of the running period, the resistance 160 being placed in series with the resistance 130 to prevent it from reaching a temperature sufficient to operate the trip device 163 during the running period. Fig. 8 also shows a switch 128, which is carried by the plate 153, inserted between the switch 126 and the resistance 130 so as to enable the gas burner to be maintained alight for a period after the current passing through the resistance 130 has been reduced to prevent the operation of the trip device 163. Modifications of the above two circuits are described. If it is desired to maintain the gas burner alight during the whole of the time pulverized fuel is being burnt the circuit to the electromagnet operating the valve 46 is arranged to be controlled only by the switch 137.