GB1368284A - Operation of jet mills - Google Patents

Abstract

1368284 Jet mills; pneumatic and centrifugal separators ALPINE AG 16 Aug 1971 [14 Aug 1970] 38403/71 Headings B2A B2H and B2P A jet mill comprises a nozzle 3, Fig. 1, arranged at the bottom of a container 2 and receiving, e.g. compressed air via a chamber 4. A bed of material 5 is kept in continuous motion, e.g. by vibrating the container 2 by means of a vibrator 9, so that material continuously flows into the jet and ground material flows away from it. The disposition of the nozzle beneath the bed is such that the kenitic energy of the jet is substantially absorbed within the bed, comminuted material being fed to a separator or sifter operated independantly of the jet and arranged above the level of the bed of material. In a second embodiment, the bed is kept in motion by fluidising it, Fig. 2 (not shown), and the bed may be wide enough to prevent material being flung through the bed by the jet. The bed may be kept in motion by an agitator 17, Fig. 5, or by a bucket elevator 22 and chute 23, Fig. 6 or by a pneumatic conveyor, Fig. 7 (not shown). Various known separators may be used using bladed rotors, Fig. 9 (not shown), an arrangement of zig-zag pipes, Fig. 10 (not shown), a chamber 70 including adjustable guide blades 30, Fig. 8, with screw feed for material to be ground, or a chamber including propellant jets 41, Fig. 12. A simple riser tube may also be used as a separator, Fig. 13 (not shown). A rotary separator including a rotor and stator forming between them a zig-zag path (as seen in section) may be used, Fig. 14a. The nozzle may be closed by a pneumatically-actuated needle valve, Fig. 16 (not shown), when the mill is stopped or the supply of comminuting gas ceases. The nozzle 63 may be in the form of an adjustable slot, varied by displacing a plate 65 by means of a screw 66, Fig. 17. Alternatively a known annular slot nozzle may be used, Fig. 18 (not shown). The level of material may be detected by a probe or baffle plate controlling a switch, Fig. 19, (not shown). This may in turn regulate the rate of feed. The jet may be developed by the use of a gas turbine.