GB1101105A - Improvements in or relating to the control of mechanical stokers - Google Patents

Abstract

1,101,105. Controlling fuel and air supply to furnaces. HODGKINSON BENNIS Ltd. 10 Aug., 1966 [14 Aug., 1965], No. 34904/65. Heading F4B. In a furnace for heating a boiler and having automatic fuel feeding means and a fan or fans creating draught and having a time lag between the starting of the fans and the commencement of fuel feed and a similar lag when the fuel feed and fans are stopped there is provided means responsive to the temperature of the heated fluid which controls the fuel feed, an automatic damper regulating the draught is also provided. The furnace 2 has a combustion chamber 3 and an underfed grate 6 supplied with solid fuel from a hopper 8 by a screw conveyer 10 driven by an electric motor 11. Forced draught is provided in a duct 16 by a fan 12 driven by an electric motor 14 and an induced draught is generated by a fan 18 driven by a motor 20, either fan may be dispensed with. Two feed screws may be provided arranged in series or in parallel. A chain grate or ram stoker could alternatively be provided. A damper flap (24, Fig. 2, not shown), is mounted in the duct 16 and is controlled by a solenoid. The damper is balanced to float against the draught in the halfopen position with the solenoid de-energized and when the fan is stopped the damper falls to give maximum obstruction; counterweights enable the degree of float to be adjusted. The electric control circuit (Fig. 3, not shown), comprises an overriding control (A) which cuts-off the whole circuit if the temperature in the boiler 4 or system 5 reaches a predetermined maximum, a control stat controlling a contact (B<SP>1</SP>) ensuring that the temperature is maintained between upper and lower limits and which may be a thermostat in a flow pipe or heat exchanger, contacts (B<SP>3</SP>) for a programme clock and further contacts (B<SP>3</SP>) for an idling clock which runs the stoker for a few minutes at given intervals during the night when the programme clock breaks the normally made contact (B<SP>2</SP>). This circuit ensures that fuel and draught are supplied when the temperature falls and withdrawn as the temperature rises and that the damper is correspondingly adjusted and includes thermal switches providing a time delay so that fuel is fed to the grate before the draught is increased. Similarly, the fans continue to run after the fuel feed has ceased to burn up fuel more quickly and eliminate smoke. The circuit also includes a regulator stat that enables fuel to be fed at a higher or lower rate as required by a thermostat in the flow pipe.