Patent GB-731000-A (GB)
Title: Improved method of countercurrently contacting solids with liquids
IPC: B03B5/62
Filed: 1953-02-24
Abstract: <PICT:0731000/III/1> <PICT:0731000/III/2> In a method of obtaining continuous counter-current contact in catalyst-liquid contacting operations and in the extraction of vegetable oils from seeds &c., the liquid is introduced into an apparatus having an upper and a lower compartment separated by a screen and the flow is maintained in one direction, solid particles (catalyst or seeds) being fed to the upper compartment remote from the point at which the liquid enters and being removed from the upper compartment at a point remote from that at which they are fed into the apparatus; the solids are caused to traverse above the screen in a direction opposite to that of the overall flow of the liquid, and are continuously contacted with the liquid as a result of alternate upward and downward liquid movement, by imparting a motion to either compartment or to the screen, the screen being moved steadily upward and forward relatively to the lower compartment, thereby causing liquid to drain steadily out of the upper into the lower compartment, and being then caused to descend suddenly downward and backward, thereby causing liquid to surge suddenly from the lower into the upper compartment.  A sufficiently close seal is maintained between the relatively movable abovementioned parts of the apparatus to ensure adequate movement of the liquid through the screen.  The upper compartment, which may carry the screen, may be movable, and the lower compartment may be stationary or vice versa, or the screen may be moved in relation to the two compartments.  As shown, feed liquid FL enters a trough 11 in which a box 1 having a bottom constituted by a perforated plate or other screen 10 is suspended from inclined bell cranks 3 pivoting on a rigid frame 4 and connected to a rotating shaft 9 and arranged so that the box can be steadily lifted and then sharply dropped under its own weight at a rate such as 60-200 strokes per minute.  The feed liquid enters at one end and leaves over a weir 12 at the other.  The solid particles to be contacted with the liquid are fed on to the screen plate through a hopper 13 at the end remote from the liquid feed inlet, and are removed from a sump 20 into which they fall over a weir 19.  As the screen box drops in the liquid in the trough it also swings forward, carrying the bed of solids with it, and liquid rapidly surges through the screen and fluidizes the particles.  When the box reaches the end of its stroke and commences to rise upwards and backwards, the bed of particles continues forward under its own inertia until the particles settle as a compact bed upon the screen a little in advance of their previous position, flexible rubber flaps 13A being provided to seal the end clearances.  A layer 21 of solid particles, e.g. galena, magnetite, emery or quartz sand, having a sedimentation velocity considerably greater than that of the particles to be contacted, may be placed above the screen plate and retained by transverse partitions 22 to prevent it moving along the screen plate with the feed particles, promote even liquid distribution throughout the screen area and, if its specific gravity is greatly in excess of that of the particles being contacted and its particle size is not too different from that of the feed solids, to function as "heavy media" preventing the particles from coming in contact with the screen. Alternatively, instead of the layer of solid particles, a number of screen layers in place of one single layer may be used.  In a modification shown in Fig. 3 the solid particles are propelled by using links 14 to lift the screen box 1 and a radius link 15 with a shifting fulcrum 16.  At the commencement of the downstroke the screen falls freely for up to approximately 1/8 inch on to a bearing plate 17, thus causing the bed to be fluidized by the upward surge of liquid through the screen, the screen box continuing to swing about the fulcrum and thus move backwards under the fluidized bed.  At the commencement of the upstroke the screen box is first lifted substantially vertically, the pivot point being transferred from the bearing plate 17 to a bearing plate 18, and then swings upward and forward carrying the bed with it.  In a further modification shown in Fig. 5, the screen box 1 is sealed to a base plate 25 by a flexible diaphragm 26, thus forming a bottom compartment, the base plate being suspended, to eliminate twisting of the diaphragm, on long hangers 27 to allow it free motion in the horizontal plane but to limit its vertical motion.  The process may be applied to counter-currently contacting liquid with a mixture of solid species which differ in their sedimentation velocities, in which case the solids segregate into different layers and, after being contacted with the liquid, may be withdrawn as individual streams of the various solid species.  The method may be modified for handling solids lighter than the liquid so that the solids are retained in a lower compartment beneath a screen and are contacted with liquid passing through the screen from an upper compartment. Specification 721,062 is referred to.