GB844721A - Improvements in or relating to underfeed stokers for boilers, furnaces and similar apparatus - Google Patents

Abstract

844,721. Controlling underfeed stoker furnaces. HODGKINSON (SALFORD) Ltd., J. March 23, 1959 [June 26, 1958], No 20487/58. Class 51 (1). In a furnace having an underfeed stoker and forced draught fan controlled by a thermostat, a time lag is introduced between the stopping of the fuel feed and the stopping of the fan, and be tween the starting of the far and the starting of the fue feed. A delay may be introduced in the starting circuits of the motors driving the fue feed and the fan, or both the motors may be started or stopped together, and a clutch in the fuel feed drive introduces the delay. In one form of control circuit, Fig. 3, the contacts 19 of a programme clock 7 in series with overload circuit breakers for both the fan and fuel feed motors are in series with an on-off switch 4 and an emergency switch 3. When the stoker is switched on, the coil 10 of the fan contactor is energized through normally closed contacts 8, 9 of a change-over switch on the stoker contactor to start the fan. A delayed switch 11, 12 on the fan contactor closes after a suitable delay to energize the stoker contactor coil 14 and close contacts 15, 16 to by-pass the fan contacts 11, 12, open contacts 8, 9 and close contacts 9, 17. The stoker runs intermittently under the control of a timer 13 set to regulate the amount of fuel feed, but the delay on the changeover switch 9, 17 holds the fan running until the circuit is switched off the programme clock 7 or switch 4, when the stoker motor stops and after a suitable delay, the changeover switch 8, 9, 17 acts to de-energize the fan. An overriding switch 18 by-passes the programme clock 7 and a "hold-fire" timer 5 operates to start the air and fuel feed at intervals to maintain a low fire when the circuit is switched off, by-passing both the programme clock 7 and the on-off switch 4, but not the emergency switch.