GB735639A - Improvements in and relating to the roasting of mineral substances - Google Patents

Abstract

<PICT:0735639/III/1> A fluidized bed furnace for roasting mineral substances, e.g. sulphide minerals, has a combustion chamber 10 formed with a charging duct 15, discharging ducts 17 and 19, banks of water-cooled tubes 20 extending through the fluidized bed A and a hopper-shaped wind-box 12, the combustion chamber 10 being separated from an expansion chamber 23 by an arched wall 21 formed with a rectangular opening 22 of smaller cross-sectional area than the combustion chamber. Dust deposited in the chamber 23 by sudden expansion of the gases through the opening 22 is discharged from a hopper 25, either back to the fluidized bed or into the discharged treated material. The returned dust is fed into the chamber 10 immediately above the fluidized bed A, either by a screw feed, Fig. 4 (not shown), or by pressure air or gas through tangentially disposed injectors, creating a whirling of the gases in the chamber, Fig. 5 (not shown). The hot gases pass immediately from the expansion chamber to a waste-heat boiler 27 formed with a further dust-collecting hopper 29. Material falling through the grate 11 collects in the wind-box 12 and is discharged at 14.