GB1015812A - Improvements relating to the treatment of particulate material, to separate components of different specific gravities - Google Patents

Abstract

1,015,812. Pneumatic separators. HEAD WRIGHTSON & CO. Ltd. Sept. 8, 1964 [Sept. 16, 1963], No. 36419/63. Heading B2H. [Also in Division F4] Components of different specific gravities are separated from particulate material, e.g. small coal, by delivering the material into a fluidized bed of discrete solid particles comprising an exogenous medium composed of controlled proportions of at least two materials of markedly different specific gravities, and by maintaining the bed in fluidized condition by a gaseous medium applied thereto in such a manner as to give, and retain in, the bed a specific gravity effective to cause separation of the particulate material into two fractions of different specific gravities, continuous measurement of the effective specific gravity of the fluidized bed being made. The fluidized bed materials may be selected from sand, magnetite and ferrosilicon. The gaseous medium may be in the form of a hot or unheated gas and may be applied to the bed in a continuous or pulsed manner. The apparatus, which may also serve to dry the particulate material, is substantially as described in Fig. 7 of Specification 971,583 with the following modifications: (i) The gas supply for feed line 13 is combustion gases from a furnace 17 whereas that for feed lines 12 and 15 is air supplied from a blower 23 and heated in a heat exchanger 22 by the combustion gases. The line 15 may have an independent air supply. The line 51 is a bypass for air not passed along the lines 12, 15. (ii) Only one cyclone 21 is used to separate dust from the hot gas. (iii) Bunkers 40, 42 serve to supply the fluidized bed materials (in this case two) to the hopper 38 via feed control devices 43, 44, e.g. rotary seals or electromagnetically vibrated feeders. The devices 43, 44 are in turn controlled through a mass flow rate indicator 45. In operation, the mass flow rate of fluidizing gas lies within predetermined limits and the devices 43, 44 are set to deliver from the bunkers 40, 42 the necessary proportions of materials to maintain the bed at the required specific gravity. When dip-tubes 27 detect an increase or decrease in the specific gravity, a controller 26 causes the valve 25 respectively to open or close in order to vary the flow rate of fluidizing gas so as to restore the specific gravity to its desired value. If, in order to maintain the desired specific gravity, the mass flow rate of gas has been automatically reduced below, or increased above, the predetermined limits, as the indicator 45 moves below the lower control limit, or above the upper control limit, a control signal automatically actuates the feed control device 43 and/or device 44 to vary the relative proportions of the fluidized bed materials thereby requiring an increased or decreased mass flow rate of fluidizing gas to produce the required specific gravity. As soon as the mass flow rate has increased above the lower control limit or decreased below the upper control limit, the devices 43, 44 revert to their original settings. The hopper 38 may be equipped with upper and lower level controllers which, by automatic control of the devices 43, 44, ensure that the necessary amount of fluidized bed particles is present in the circuit.