GB862837A - Improvements in or relating to the production of smoke from sawdust - Google Patents

Abstract

862,837. Smoke-producing apparatus and methods. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Oct. 10, 1957 [July 10, 1956], No. 21379/56. Addition to 781,591. Class 81 (1). In the production of smoke from sawdust by partially burning or otherwise decomposing it by heat while it is maintained as a fluidized bed as described in the parent Specification the apparatus comprises a diverging fluidization chamber of annular form. As shown in Fig. 1, the apparatus comprises a Venturi tube 11, 12 with an inserted body consisting of two cones 13, 14 base to base, the maximum diameter coming at the Venturi throat 15 at which is also provided the grid 15A to prevent the sawdust falling lower. The remainder of the apparatus, not illustrated, for the supply of air or other gas and sawdust, the heating of the gas and the removal of charred residue may be as described in the parent Specification. Instead of the lower cone 14, a rounded body may be used. As shown in Fig. 2 instead of the tapering lower section 12 a cylindrical lower section 16 may be used, the central body as before being two cones 13, 14 base to base or a cone and a rounded body, with a maximum diameter at the junction of the cylinder 16 and the diverging walled chamber 11, the entry section 16 being made double walled, the air or gas being blown e.g. by an electric fan in at 17 between the walls near their upper end, then escaping below the lower edge of the inner wall 18 and sweeping past vertically arranged electric heaters 19. The double-walled entry and the diverging chamber may be surrounded by insulating material 23 within a cylindrical casing 24, a section 25 of which in the neighbourhood of the junction with the diverging chamber being removable to permit access to the diverging chamber and the double-coned body 13, 14 which may be of hollow metal. A conical hood 26 arranged over the upper end of the diverging chamber 11, and terminating in a cylindrical skirt 27 causes the suspended particles to fall downwardly while smoke rises outside the skirt, the whole being arranged within a cylindrical outer casing 28 from which a junction pipe 29 leads at the top to carry away smoke, while at the lower end a hopper 31 is provided through which the charred particles may be discharged continuously or from time to time. The sawdust is delivered from a hopper 36 in which two sides only at a time converge to a metering device comprising a worm 35 in a chamber 39 having an opening 38 through which the sawdust falls in front of an air nozzle 41 and is then discharged through an injecting tube 34. According to another feature a layer of a granular inert material e.g. sand or alumina having a melting point above 500‹ C. which does not react with air or sawdust at say 400‹ C. is used below the sawdust, the material having a particle size and density such that it requires a higher velocity for fluidization than does the sawdust.