Patent EA-004721-B1 (EA)
Title: Apparatus and method for high speed dewatering of slurries
Inventor: HODGES MICHAEL KENT
IPC: C02F11/12
Filed: 2001-05-04
Abstract: 1. A method of dewatering a stream of slurry, comprising the steps of: (a) continual or continuous determination of one or more parameters; (b) addition of a flocculating agent to the stream of slurry in response to the determined parameter or parameters; (c) mixing the flocculating agent with the slurry, to afford a stream of flocculated slurry; (d) delivering the flocculated slurry through a diffuser onto a tracking screen; and (e) filtering the flocculated slurry through the tracking screen to afford solids and a filtrate; wherein the parameters are: the flow rate of the slurry, the pulp density of the slurry and the pulp density of the filtrate. 2. A method according to claim 1, wherein the mixing in step (c) is controlled in response to the determined parameter or parameters. 3. A method according to claims 1 or 2, wherein said flocculating agent comprises an anionic, cationic, or non-ionic polymer or a polyacrylamide or a mixture of polyacrylamides. 4. A method according to any of claims 1 to 3, wherein a diffuser comprises a vertically disposed conduit rising from a base having the inlet for the stream of flocculated slurry to an upper portion where the stream of flocculated slurry is delivered to the tracking screen, said conduit having a horizontal sectional area that remains constant or increases from said base to said upper portion. 5. A method according to claim 4, wherein said base has a horizontal section of relatively low aspect ratio of from 1:1 to 4:1, and said upper portion has a horizontal section of relatively high aspect ratio of from 40:1 to 100:1, the ratio of the horizontal sectional areas at the upper portion and the base being from 1:1 to 3:1. 6. A method according to any of claims 1 to 5, wherein said tracking screen comprises two screens mounted on an A-frame. 7. A method according to any of claims 1 to 6, further comprising the steps of: clarification of the filtrate and/or dewatering of the solids. 8. A method according to any of claims 1 to 7, wherein the addition of the flocculating agent is controlled by a programmable logic control in communication with the means to determine the parameter or parameters, and in communication with the means for adding the flocculating agent. 9. An apparatus for dewatering a stream of slurry, comprising: (i) means to continually or continuously determine one more parameters; (ii) means for adding the flocculating agent to the slurry; (iii) means responsive to the determined parameter or parameters to control the rate of addition of the flocculating agent by the means for adding; (iv) a mixer to mix the flocculating agent with the slurry to generate a stream of flocculated slurry; (v) a tracking screen to filter the flocculated slurry to afford solids and a filtrate; and (vi) a diffuser to deliver the flocculated slurry onto the tracking screen; wherein the parameters are: the flow rate of the slurry; the pulp density of the slurry; and the pulp density of the filtrate. 10. An apparatus according to claim 9, wherein the assembly comprising the diffuser and the tracking screen is mounted on a support, the support being adjustably mounted on a transportation means, so that the assembly can be moved relative to the transportation means so as to allow solids to be removed from the tracking screen by means of gravity. 11. A diffuser for delivery of a stream of flocculated slurry to a tracking screen, comprising a vertically disposed conduit rising from a base having the inlet for the stream of flocculated slurry to an upper portion where the stream of flocculated slurry is delivered to the tracking screen, said conduit having a horizontal sectional area that remains constant or increases from said base to said upper portion, and an extension that substantially increases from said base to said upper portion. 12. A diffuser according to claim 11, wherein said base has a horizontal section of relatively low aspect ratio of from 1:1 to 4:1, and said upper portion has a horizontal section of relatively high aspect ratio of from 40:1 to 100:1, the ratio of the horizontal sectional areas at the upper portion and the base being from 1:1 to 3:1. 13. An assembly comprising a tracking screen according to claim 6 and a diffuser according to any one of claims 11 or 12. 14. An apparatus for collecting filter cake from a separation screen, comprising: a pair of elongate spaced sidewalls having opposite ends and a bottom wall extending therebetween; a plurality of plates extending inwardly from at least one of said sidewalls; said plates establishing a plurality of heights forming a ladder for breaking a fall of said filter cake from said screen to said bottom wall. 15. An apparatus according to claim 14, wherein: said bottom wall inclines downwardly to an aperture for enabling said filter cake to flow out of said apparatus; said sidewalls extend downwardly toward said aperture; and downward inclination of said bottom wall in cooperation with said sidewalls causes said apparatus to have greater depth adjacent said aperture than at an opposite end from said aperture.