Method and apparatus for classifying viscous slurries

Claim 2

IN A METHOD OF OPERATING A SYSTEM FOR SHARPLY CLASSIFYING WET SLURRIES FOR SHARPLY SEPARATING FINE PARTICLES FROM COARSE PARTICLES IN AT LEAST THREE STAGES, COMPRISING THE STEP OF DELIVERY A SLURRY WITH PARTICLES WHICH ARE TO BE CLASSIFIED SUSPENDED THEREIN TO A FIRST STAGE, CENTRIFUGALLY SEPARATING FINE PARTICLES FROM COARSE PARTICLES IN THE SLURRY AT THE FIRST STAGE, DELIVERING THE COARSE PARTICLES SEPARATED AT THE FIRST STAGE TO A SECOND STAGE, GRAVIATATIONALLY SEPARATING COARSE FORM FINE PARTICLES AT SAID SECOND STAGE, DELIVERING THE FINE PARTICLES IN THE SLURRY WHICH ARE SEPARATED AT THE SECOND STAGE TO A THIRD STAGE, SEPARATING FINE FROM COARSE PARTICLES AT THE THIRD STAGE AND RETURNING THE FINE PARTICLES SEPARATED AT THE THIRD STAGE BACK TO THE FIRST STAGE, WHILE PROVIDING FOR AN OUTPUT MADE UP OF THE COARSE PARTICLES DERIVED IN THE SLURRY FROM THE THIRD STAGE AND AT LEAST PART OF THE FINE PARTICLES CENTRIFUGALLY SEPARATED FROM THE COARSE PARTICLES AT THE FIRST STAGE.

Claim 3

In a method as recited in claim 1 and including the steps of delivering slurry with centrifugally separated fine particles suspended therein and separated from coarse particles at the first stage to a fourth stage, separating fine from coarse particles at the fourth stage, and combining slurries having suspended therein coarse particles derived from the fourth stage and coarse particles derived from the third stage.

Claim 4

In a method as recited in claim 2 and wherein the slurry at the fourth stage is subjected to a wet classification which separates fine particles in a size range of from 5 to 40 microns from the remaining particles at the fourth stage which form the coarse particles thereof providing part of the output of the system.

Claim 5

In a method as recited in claim 1 and wherein a slurry having suspended therein fine particles centrifugally separated at the first stage is almost in its entirety combined with a slurry having suspended therein having coarse particles derived from the third stage to provide the output of the entire system.

Claim 6

In a method as recited in claim 1 and including the step of milling particles suspended in a slurry prior to delivery of the latter to said first stage for increasing the concentration of fine particles in the output of the system.

Claim 7

In a method as recited in claim 5 and wherein said milling is carried out at least in part on coarse particles derived from the second stage.

Claim 8

In an apparatus for treating viscous slurries to sharply separate fine particles from coarse particles suspended therein, liquid cyclone means forming a first wet classification stage for centrifugally separating fine particles from coarse particles, pump means communicating with said liquid cyclone means for delivering a slurry thereto, sump means communicating with said pump means for feeding a slurry thereto to be pumped thereby to said liquid cyclone means, gravitational wet classification means forming a second wet classification stage and communicating with said liquid cyclone means for receiving therefrom a slurry with coarse particles suspended therein, said gravitational classification means of said second stage gravitationally separating coarse particles from fine particles in the slurry received from said first stage, third wet classification means forming a third classification stage and communicating with said second stage for receiving therefrom a slurry with fine particles suspended therein, said third classification means separating fine from coarse particles in the slurry having suspended therein fine particles separated at said second stage, said third classification means communicating with said sump means for delivering thereto slurry with fine particles separated at said third stage, so that the latter slurry with the fine particles therein will be returned to the first stage, the slurry with coarse particles therein as derived from the third stage and at least part of the slurry with fine particles therein as derived from the first stage forming an output.

Claim 9

In an apparatus for treating viscous slurries to sharply separate fine particles from coarse particles suspended therein, liquid cyclone means forming a first wet classification stage for centrifugally separating fine particles from coarse particles, pump means communicating with said liquid cyclone means for delivering a slurry thereto, sump means communicating with said pump means for feeding a slurry thereto to be pumped thereby to said liquid cyclone means, gravitational wet classification means forming a second wet classification stage and communicating with said liquid cyclone means for receiving therefrom a slurry with coarse particles suspended therein, said gravitational classification means of said second stage gravitationally separating coarse particles from fine particles in the slurry received from said first stage, third wet classification means forming a third classification stage and communicating with said second stage for receiving therefrom a slurry with fine particles suspended therein, said third classification means separating fine from coarse particles in the slurry having suspended therein fine particles separated at said second stage, said third classification means communicating with said sump means for delivering thereto slurry with fine particles separated at said third stage, so that the latter slurry with the fine particles therein will be returned to the first stage, the slurry with coarse particles therein as derived from the third stage and at least part of the slurry with fine particles therein as derived from the first stage forming an output.

Claim 10

The combination of claim 7 and wherein a milling means communicates with said second stage and with said sump means for receiving gravitationally separated coarse particles from said second stage and reducing the size thereof before delivering the coarse particles frOm the second stage back to said sump means to be again returned as part of the input to said first stage.

Claim 11

The combination of claim 8 and wherein a spiral or rake classifier forms part of said gravitational wet classification means of said second stage for removing coarse particles therefrom for delivery to said milling means.

Claim 12

The combination of claim 8 wherein said milling means is a ball or rod mill.

Claim 13

The combination of claim 8 and wherein a supply means communicates with said sump means for delivering raw material thereto for delivery from said sump means by said pump means to said liquid cyclone means.

Claim 14

The combination of claim 11 and wherein a second milling means forms part of said supply means for comminuting particles suspended in the slurry of the raw material before the latter reaches said sump means.

Claim 15

The combination of claim 7 and wherein the wet classification means of said third stage is in the form of a lamina thickener.

Claim 16

The combination of claim 13 and wherein said thickener has baffles in a zig-zag arrangement.

Claim 17

The combination of claim 7 and wherein said gravitational wet classification means of said second stage is a multi-stage horizontal wet classifier having its stages interconnected in a phalanx arrangement.

Claim 18

The combination of claim 7 and wherein a fourth classification stage includes a fourth wet classification means communicating with said liquid cyclone means of said first stage for receiving therefrom slurry with fine particles suspended therein and separated at said first stage and for separating particles in the latter slurry into fine and coarse particles with a slurry having suspended therein the latter coarse particles derived from the fourth stage being combined with the slurry having suspended therein the coarse particles of the third stage to provide the output.

Claim 19

The combination of claim 16 and wherein said fourth classification means includes a lamina thickener.

Claim 20

The combination of claim 17 and wherein said thickener has baffles in a zig-zag arrangement.