Flotation separation of fine coal particles from ash-forming particles

Abstract

Coal fines are processed by flotation separation to separate coal particles from ash-forming component particles. Coal fines are mixed water under high shear mixing conditions to form an aqueous slurry of coal fines containing between 15 wt. % and 55 wt. % coal fines. The aqueous slurry is introduced into a coal flotation cell to separate coal particles from ash-forming component particles by flotation separation, wherein the coal fines have a particle size less than 500 μm, and more preferably less than 300 μm. Bubbles are generated in the coal flotation cell having a bubble size and bubble quantity selected to float the coal particles and to form a coal-froth containing at least 15 wt. % solid particles. The solid particles include coal particles and ash-forming component particles. The coal-froth is collected for further processing.

1 . A process for separating coal particles from ash-forming component particles comprising:
 generating bubbles within a quantity of water in a flotation cell;   introducing an aqueous slurry of coal fines comprising discrete particles of coal and particles of ash-forming components into the bubbles within the coal flotation cell in a manner that causes the bubbles to capture and float the coal particles and form a coal-froth, wherein the coal fines in the aqueous slurry have a particle size less than about 750 μm; and   collecting the coal-froth, wherein the coal-froth comprises at least 15 wt. % solid particles and wherein the solid particles comprise coal particles and ash-forming component particles, with a flotation efficiency greater than 92%, such that the coal particles in the coal-froth represent a combustible recovery of coal fines greater than 90%.   
     
     
         2 . The process according to  claim 1 , further comprising the steps of:
 stopping the introduction of the aqueous slurry of coal fines into the coal flotation cell; and   continuing to generate bubbles and coal-froth for a period of time to separate coal particles remaining in the quantity of water from ash-forming component particles.   
     
     
         3 . The process according to  claim 2 , further comprising the step of draining the quantity of water in the coal flotation cell. 
     
     
         4 . The process according to  claim 3 , further comprising the step of recovering the solid particles from the drained water for further processing. 
     
     
         5 . The process according to  claim 4 , further comprising the step of recycling the water from which the solid particles are recovered for use in the coal floatation cell. 
     
     
         6 . The process according to  claim 2 , further comprising the step of monitoring a content of solid particles in the quantity of water in the coal flotation cell, wherein the solid particles comprise ash-forming component particles and coal particles, and stopping the introduction of the aqueous slurry of coal fines into the coal flotation cell when the content of solid particles in the quantity of water in the coal flotation cell exceeds a predetermined weight percentage. 
     
     
         7 . The process according to  claim 6 , wherein the predetermined weight percentage of solid particles in the quantity of water is between 3 wt. % and 6 wt. % 
     
     
         8 . The process according to  claim 6 , wherein the content of solid particles in the quantity of water in the coal flotation cell determines a content of ash-forming component particles in the coal-froth. 
     
     
         9 . The process according to  claim 1 , wherein the coal fines in the aqueous slurry have a particle size less than about 500 μm. 
     
     
         10 . The process according to  claim 1 , wherein the coal fines in the aqueous slurry have a particle size less than about 300 μm. 
     
     
         11 . The process according to  claim 1 , wherein the coal fines in the aqueous slurry have a particle size less than about 500 μm, and wherein the bubbles are generated and the aqueous slurry is introduced into the bubbles such that the coal particles in the coal-froth represent a combustible recovery of coal fines greater than 95%. 
     
     
         12 . The process according to  claim 1 , wherein the coal-froth comprises at least 25 wt. % solid particles. 
     
     
         13 . The process according to  claim 1 , wherein the coal-froth comprises at least 45 wt. % solid particles. 
     
     
         14 . The process according to  claim 1 , further comprising the step of balancing an input volume of aqueous slurry to an output volume of coal-froth. 
     
     
         15 . The process according to  claim 1 , wherein the bubbles are generated with one or more bubble generators, wherein the bubble generators comprise a porous material having an average pore size less than 30 μm. 
     
     
         16 . The process according to  claim 1 , wherein the bubbles are generated with one or more bubble generators, wherein the bubble generators comprise a porous material having an average pore size less than 10 μm. 
     
     
         17 . A process for separating coal particles from ash-forming component particles comprising:
 generating bubbles within a quantity of water in a coal flotation cell with one or more bubble generators, wherein the bubble generators comprise a porous material having an average pore size less than 30 μm;   introducing an aqueous slurry of coal fines comprising particles of coal and particles of ash-forming components into the bubbles within the coal flotation cell in a manner that causes the bubbles to capture and float the coal particles and form a coal-froth, wherein the coal fines in the aqueous slurry have a particle size less than about 500 μm, wherein the bubbles are generated and the aqueous slurry is introduced into the bubbles such that the flotation rate of coal fines is greater than 1.5 MTPH/m 3 .   
     
     
         18 . The process according to  claim 17 , wherein the coal fines in the aqueous slurry have a particle size less than about 300 μm. 
     
     
         19 . The process according to  claim 17 , wherein the coal fines in the aqueous slurry have a particle size less than about 150 μm. 
     
     
         20 . The process according to  claim 17 , wherein the aqueous slurry of coal fines contains about 40±15 wt. % coal fines. 
     
     
         21 . The process according to  claim 17 , wherein the bubble generators comprise a porous material having an average pore size less than 10 μm 
     
     
         22 . The process according to  claim 17 , wherein the bubbles are generated and the aqueous slurry is introduced into the bubbles such that the combustible recovery of coal fines is greater than 95%. 
     
     
         23 . An aqueous slurry of coal fines comprising:
 discrete particles of coal;   discrete particles of ash-forming components; and   a quantity of water, wherein the aqueous slurry contains greater than 25 wt. % solid particles comprising particles of coal and particles of ash-forming components, and wherein the particles of coal and particles of ash-forming components collectively have a particle size less than about 500 μm.   
     
     
         24 . The aqueous slurry according to  claim 23 , wherein the aqueous slurry contains greater than 45 wt. % particles of coal and particles of ash-forming components. 
     
     
         25 . The aqueous slurry according to  claim 23 , wherein the particles of coal and particles of ash-forming components collectively have a particle size less than about 300 μm. 
     
     
         26 . The aqueous slurry according to  claim 23 , wherein the particles of coal and particles of ash-forming components collectively have a particle size less than about 150 μm. 
     
     
         27 . A coal-froth generated in a coal flotation cell comprising at least 15 wt. % solid particles and wherein the solid particles comprise coal particles and ash-forming component particles, of which less than 8 wt. % of the solid particles are ash-forming component particles. 
     
     
         28 . The coal-froth according to  claim 27 , wherein the coal-froth comprises at least 25 wt. % solid particles. 
     
     
         29 . The coal-froth according to  claim 27 , wherein the coal-froth comprises at least 35 wt. % solid particles. 
     
     
         30 . The coal-froth according to  claim 27 , wherein the coal-froth comprises at least 45 wt. % solid particles. 
     
     
         31 . The coal-froth according to  claim 27 , wherein less than 5 wt. % of the solid particles are ash-forming component particles. 
     
     
         32 . A process for separating ash-forming component particles from coal particles comprising:
 generating bubbles within a quantity of water in a coal flotation cell;   introducing an aqueous slurry of coal fines comprising particles of coal and particles of ash-forming components into the bubbles within the coal flotation cell in a manner that enables the bubbles to capture and float the coal particles and form a coal-froth; and   maintaining a height of the coal-froth less than about 18 inches (0.45 m).   
     
     
         33 . The process according to  claim 32 , wherein the coal-froth comprises at least 25 wt. % solid particles and wherein the solid particles comprise coal particles and ash-forming component particles, of which less than 8 wt. % of the solid particles are ash-forming component particles. 
     
     
         34 . The process according to  claim 32 , wherein the coal-froth comprises at least 45 wt. % solid particles and wherein the solid particles comprise coal particles and ash-forming component particles, of which less than 8 wt. % of the solid particles are ash-forming component particles.