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.

Description

BACKGROUND OF THE INVENTION[0001]This disclosure relates to systems and methods for the flotation separation of fine coal particles from ash-forming component particles, thereby enabling the recovery of fine coal particles to be processed into upgraded, commercially valuable coal products.BACKGROUND[0002]Coals are ranked primarily based on the carbon makeup of the material (e.g. macerals and fixed carbon vs. volatile matter) and BTU value as a function of the ash-forming mineral and moisture content:[0003]Anthracite is the highest ranking coal and is used by the steel industry as a coke substitute through processes such as pulverized coal injection in metallurgical coal applications. It is a dense, hard rock with a metallic luster. It contains between 85% and 98% fixed carbon by weight. Anthracite coal contains approximately 14,000+BTU / lb (32+MJ / Kg).[0004]Bituminous is the second highest ranking coal and used for both electric power generation and coke production. It is a relatively...

AI Technical Summary

Benefits of technology

[0053]In one aspect of the disclosed process, a flotation aid is added to the aqueous slurry of coal fines. Flotation aids are known in the art of mineral flotation. Some flotation aids include frothers and collectors. Frothers aid in fine air bubble formation. Frothers are typically surfactants that control and reduce bubble size and provide froth-building capacity. Collectors increase the natural hydrophobicity of the coal particle surface, increasing the separability of hydrophobic coal particles and hydrophilic ash-forming component particles. Collectors are especially useful where the surface of the coal particles may be partially oxidized and have hydrophilic oxygen-containing “groups.” Non-limiting examples of such oxygen-containing groups include hydroxyl, ketone, carboxylic acid, and ether groups. The flotation aid may be mixed with the aqueous slurry of coal fines. Any mixing process may be used that adequately disperses the flotation aid with the water and coal fines. The mixing process should enable collectors to adequately coat the coal fines.

[0054]In one non-limiting embodiment, the flotation aid is mixed with the coal fines under high energy mixing conditions. This is especially beneficial for collector flotation aids because high energy mixing helps to ensure uniform, complete coating of the coal particles with the collector to enhance the hydrophobicity of the coal particles and thereby enhance flotation of the coal particles.

Problems solved by technology

The current industrial process to recover coal particles less than 1 mm in size is more expensive than other coal processing.

The smaller the particles, the greater the processing cost.

Further, there are no current commercial processes to recover and sell particles less than 100 microns (0.1 mm).

While coal fines are the same chemical composition of the larger-size mined coal product, it is considered waste because the conventional coal recovery process is not designed to handle small particles.

The waste coal fines are left unused because they are typically too wet to burn, too dirty to be worth drying, and too fine to transport.

They are often impounded as environmentally hazardous.

Of particular challenge in the coal industry is the burning of coal with typical ash-forming components.

The components are the major source of most harmful emissions, such as SOx, and reduce energy value and heat transfer efficiency.

While coal fines separation, classification and drying technologies are known, they are too inefficient and expensive with particles less than 150 microns to be commercially feasible.

Further significant money is being wasted in the transportation and handling of the moisture fraction and the ash-forming mineral fraction of the coal.

However, reports in literature and patents have not demonstrated theory, instead they show combustible recovery increased with increasing particle size [Yoon 1995, Vapur 2010, Peng 2013].

Even with recent advances in some coal processes, including attempts to recover coal fines via coal flotation processes, the coal industry does not have an effective process for upgrading and handling coal fines less than 500 microns (0.5 mm), more specifically less than 300 microns (0.3 mm), less than 150 microns (0.15 mm), less than 100 microns (0.1 mm), and certainly less than 50 microns (0.05 mm).

These massive amounts of fine waste are inefficient and are an environmental and disposal problem.

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