There are wet and dry methods of cleaning pulverized coal lor thermal power stations. However, it may be desirable to list- ;i thy process because dewatering finely pulverized coal is clifl'iaili and expensive, and burning wet coat reduces the thermal efficiency of the combustion process. The largest advantage is that dry cleaning methods require the lowest initial capital investment and have the lowest maintenance costs of ail currently used methods of upgrading fine coal. Also, influencing the choice of dry cleaning benefieiation is the lack of sufficient water in arid regions, localities of high altitude or cold climates. It has been shown that high gradient magnetic fillers can be constructed which will extract micron-sized paramagnetic particles from a pulverized coal-air stream passing through the filter. Conventional magnetic separators are generally restricted to separating strongly magnetic materials, such as iron and magnetite. High gradient magnetic filters are capable of separating weakly paramagnetic particles, Ilie magnetic force being proportional to the product of field strength and gradient. Superconducting magnets can produce extremely intense and uniform magnetic fields, of up to 20 Tesla or more, with gradients of 70 Tesla/m or more. A high gradient magnetic cleaning device consists of a matrix made of fine ferromagnetic fibers located in a high magnetic field. The fine wire of the matrix provides high magnetic gradient sites for the capture of paramagnetic particles which there-lore can be separated from an incoming coal and impurities mixture. The presence of wire of high magnetic susceptibility in air of low susceptibility results in a highly nonuniform -magnetic field with large magnetic gradients. The finer the wire, the smaller the distance over which the field changes and thus the higher the gradient. Only superconducting magnets are currently economic to generate sufficiently large background magnetic fields of, say, more than 2 Tesla, over the volumes required for the desulfurization of coal.
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