Cleaning and dewatering fine coal
Fine coal is cleaned of its mineral matter impurities and dewatered by mixing the aqueous slurry containing both with a hydrophobic liquid, subjecting the mixture to a phase separation. The resulting hydrophobic liquid phase contains coal particles free of surface moisture and droplets of water stabilized by coal particles, while the aqueous phase contains the mineral matter. By separating the entrained water droplets from the coal particles mechanically, a clean coal product of substantially reduced mineral matter and moisture contents is obtained. The spent hydrophobic liquid is separated from the clean coal product and recycled. The process can also be used to separate one type of hydrophilic particles from another by selectively hydrophobizing one.
1. A method of removing water and mineral matter impurities from an aqueous slurry containing fine coal particles of 1.0 mm in diameter and smaller, said water, and said mineral impurities, comprising the steps of:
mixing a hydrophobic liquid with said aqueous slurry, said mixing step allowing said fine coal particles to be transferred into said hydrophobic liquid along with the small water droplets formed during said mixing step, while said mineral matter impurities remain in said aqueous slurry, and thereby producing a mixture;
phase separating said mixture produced in said mixing step, said phase separating step producing a first phase containing said hydrophobic liquid, said fine coal particles, and said water droplets, and a second phase containing said aqueous media and said mineral matter impurities;
retrieving said first phase after said phase separating step;
separating said water droplets from said hydrophobic liquid in said first phase, along with the residual mineral matter impurities dispersed in said water droplets; and
removing said hydrophobic liquid from said fine coal particles to obtain a clean coal product with reduced mineral impurities and moisture content.
2. The method of claim 1 further comprising the step of recycling said hydrophobic liquid removed in said removing step.
3. The method of claim 1 wherein said hydrophobic liquid is selected from ligroin, naphtha, petroleum naphtha, petroleum ether, kerosene, diesel fuel, heating oil, and mixtures thereof.
4. The method of claim 3 wherein said hydrophobic liquid is used in the amount of 5 to 56% by weight of fine coal feed.
5. The method of claim 1 wherein said hydrophobic liquid is selected from shorter-chain n-alkanes and n-alkenes, both unbranched and branched, cycloalkanes and cycloalkenes, with carbon numbers of less than eight, and liquid carbon dioxide.
6. The method of claim 5 wherein said hydrophobic liquid has a contact angle on the surface of fine coal in water, as measured through said water in excess of 90°.
7. The method of claim 1 wherein said separating step is performed with a size-size separator.
8. The method of claim 7 wherein said size-size separator includes a screen.
9. The method of claim 1 wherein said separating step is performed with a solid-liquid separator.
10. The method of claim 9 wherein said solid-liquid separator is a filter.
11. The method of claim 9 wherein said solid-liquid separator is a centrifuge.
12. The method of claim 1 wherein said separating step includes an application of mechanical means to dislodge said tine coal from said entrained water droplets so that said fine coal is dispersed in the hydrophobic liquid, while the water drops free of said fine coal separate from the first phase.
13. The method of claim 12 wherein said mechanical means includes one or more of the sonic vibrator, ultrasonic vibrator, magnetic vibrator, and grid vibrator.
14. The method of claim 1 wherein said fine coal is selected from bituminous coal, anthracite, and subbituminous coal.