Coal separation techniques at preparation plants

Coal preparation images

Several different mechanisms are used to separate unwanted rocks and minerals from coal at preparation plants. Prior to separation, float-sink (also called washability) tests are run on raw (run-of-mine, ROM) coal samples at different sizes and different densities to test the optimum preparation sizes and separation techniques needed to reach the desired quality of prepared coal.

Preparation plants are designed to separate coal and rock or mineral impurities at different particle sizes. Run-of-mine (ROM) material is passed through a series of breakers, crushers, and mills to break down the material to manageable sizes. Impurities in the ROM material can occur as large rocks or as very thin rock layers or laminae (partings) in or attached to the coal itself. Other impurities may be tiny (even microscopic) within the coal particles. After breaking down the rock material to sizes of several inches (or smaller), screens of different sizes and classifiers allow specific ranges of particle sizes to pass through to different processing routes or "circuits" in the preparation plant. Each circuit is designed with different technologies to optimally separate coal from rock at that particle size range. Different plants use different technologies based on the product specifications for which they were designed (Nunenkamp, 1976; Gibbs and Hill, 1978; McCandless and Shaver, 1978; Singh and Peterson, 1979; Honaker and others, 2007; Luttrell and Honaker, 2012).

Schematic diagram of a typical eastern Kentucky coal preparation plant. Different plants use different combinations of sizing, separation and dewatering processes and may use different technologies than shown. The different paths are called processing circuits, and are based on different ranges of particle sizes. Not all plants have all circuits or separate to all of the particle sizes shown (modified from Figure 3.1, Gluskoter and others, 2009; Fig. 1, Honaker and others, 2007; and Fig. 2, Luttrell and Honaker, 2012).
>Schematic diagram of a typical eastern Kentucky coal preparation plant. Different plants use different combinations of sizing, separation and dewatering processes and may use different technologies than shown. The different paths are called processing circuits, and are based on different ranges of particle sizes. Not all plants have all circuits or separate to all of the particle sizes shown (modified from Figure 3.1, Gluskoter and others, 2009; Fig. 1, Honaker and others, 2007; and Fig. 2, Luttrell and Honaker, 2012).

For each particle size separated, a mixed stream of particles goes into a process designed to separate the coal from other particles of similar size. The product is a stream of cleaned coal and a reject stream of rocks and minerals separated from the coal. Coal preparation refuse (reject rock particles) at different stages of preparation are disposed of according to federal and state regulations. Different methods are used for different sizes of reject particles.

Sized and washed or "cleaned" product coal is dried through the use of drain and rinse screens, centrifuges or by driers/heaters and sold. Many washed coals are blended prior to sale, although blending may take place at sites other than the preparation facility.

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Last Modified on 2024-04-22
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