Dry superconducting magnetic cleaning of pulverized coal

There are wet and dry methods of cleaning pulverized coal for thermal power stations. However, it may be desirable to use a dry process because dewatering finely pulverized coal is difficult and expensive, and burning wet coal reduces the thermal efficiency of the combustion process. It has been shown that high gradient magnetic filters 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, the magnetic force being proportional to the product of field strength and 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. These experimental tests indicated that the dry magnetic desulfurization process was able to remove up to 69% of the pyritic sulfur and 33% of the ash content from a typical pulverized coal in a vertically upward airstream rig, and the heating value recovery is 97%. Increasing magnetic fields increases the percentage of reductions of pyritic sulfur, total sulfur, and ash. The penalty for the improved sulfur removals was the reduced heating value recoveries.