GB1093025A - The smokeless combustion of bituminous caking and non-caking coals - Google Patents

Abstract

1,093,025. Boiler furnace. COAL INDUSTRY (PATENTS) Ltd. March 12, 1965 [March 17, 1964], No. 11220/64. Heading F4B. A boiler for burning bituminous caking or non-caking coals comprises a combustion chamber 4 defined by an inclined grate 2, an inclined refractory roof 6 and refractory walls 7, 8, there being a feed inlet slot 9 for downward entry of fuel into the chamber 4 and a pneumatic thermosensitive probe 15, 17 for determining and effecting adjustment of the fuel bed level 16. The fuel fed by a screw (not shown) falls on to the bed 16 where it is carbonized and burnt by an undergrate air blast from duct 13 which comprises 15-30% of the total combustion air requirement, the evolved volatiles being burnt in chamber 4 by overgrate air from air inlets 14 in the refractory roof 6 which is inclined between 30 and 45 degrees. The evolved gases flow through passage 11 to flue 12 heating the water in the jackets 10. A reciprocable declinkering ram 18 is provided to discharge grate ash to ash box 21. Alternatively a reciprocable grate 22 may be used. In operation fuel is fed into the combustion chamber 4 in excess of the rate of combustion to increase the bed level 16. This obstructs the outlet of conduit 15 through which air is delivered, so reducing the hot gas intake into conduit 17 which houses temperature sensitive means, since the conduits 15, 17 are joined at a point remote from the combustion chamber. The temperature sensitive means respond to the temperature drop due to the decreased flow of hot gases past them by stopping the fuel feed. When the fuel bed level falls below a predetermined level, more air can pass along conduit 15, consequently more gas is drawn along conduit 17 so the temperature rises and the temperature-sensitive means restores the fuel feed. When operating at a reduced output, all air supplies are shut off till the temperature falls to a predetermined value. Undergrate air only is then supplied to burn away the fuel bed until a temperature of 700‹ C. has been reached. The pneumatic thermosensitive probe 15, 17 is then switched on and initiates the supply of fuel and overgrate air which continues until the desired bed level has been reached when all the air supplies are again switched off to return the cycle to its starting point.