Advanced fine coal cleaning techologies such as column flotation have seen poor adoption rates in industry. These processes produce a slurry containing 25% fine coal (~35 microns). Vacuum drying can reduce the water content to only 25-30%. A second thermal drying stage is needed to extract water in capillaries within the filter cake to make a usable product containing less than 20% moisture. This drying stage is energy intensive. Dewatering of fine coal slurry constitutes a significant portion of the total cost of cleaning fine coal. When fine coal cannot be successfully dewatered, it is often discarded, representing a substantial loss of energy.

Both vacuum and pressure treatment for dewatering of fine coal have been used previously in industry. However, the two processes have not yet been succesfully combined. Current research at the University of Kentucky indicates that a two-stage process combining both vacuum and high pressure treatment can produce usable fine coal with less than 20% moisture.

Researchers have found that filter cakes formed under vacuum have a porous structure, and that when high pressure is applied, up to half the contained water is released from capillaries within the cake.

They have also demonstrated that the process is even more efficient when the cake is broken up mechanically before being pressure treated.

A two-stage vacuum-pressure treatment process offers a promising pathway for producing fine coal containing less than 20% moisture. This process will increase recovery of fine coal, thus saving the energy that would be lost if fines were discarded. Also a major energy and environmental savings comes from the elimination of coal drying, which is energy intensive and contributes fine particles to air pollution resulting in a safety hazard. Lower moisture content of fine coal will also lower the transportation cost per ton by moving more coal and less water from mines to power plants.

• Provide an efficient and low-cost dewatering process for ultra-fine coal slurries

• Eliminate the need for thermal coal drying

• Develop basic understanding of the morphology of fine coal filter cakes

• Reduce the mositure content of fine coal filter cake to less than 20%

• Lower transportation costs by reducing the water content of fine coal

Goal: To develop and optimize a process for dewatering of fine coal to improve coal recovery and reduce the energy used in coal processing.

Since the new hybrid process combines two operations that are already common in the industry, adoption of this technology is expected to be relatively swift. Capital expenditures and operational issues will be minimized by the use of familiar equipment and procedures.

• Collect and characterize samples of fine coal slurries from at least two different industrial preparation plants

• Optimize the dewatering process through laboratory studies of vacuum and pressure filtration processes

• Develop a concept design of a continuous dewatering unit with preliminary economic and technical evaluations

From:http://www.vipeakmill.com/