Plasma Desulfurization of Coal

The total sulfur content of coal varies in the range of 0.2—11 wt%, although inmost cases it is between 1 and 3 wt %293). A large part of the sulfur is in the form of FeS2. The amount of organic sulfur is usually one-half to one-third of the total sulfur294). 

The two depolymerization methods which have been used most are pyrolysis and hydrogenation. Thiophenes and sulfides were the major sulfur components of tars from coal pyrolysis hydrogen sulfide and the lower mercaptans and sulfides were found in the volatiles299. Hydrogen sulfide and thiophenes were practically the only sulfur products of coal hydrogenation300 hydrogen sulfide is produced in char hydrodesulfurization301.  

There are few direct measurements of the sulfur removed from coals treated in plasmas. Zavitsanos and Bleiler305 reported that coal could be desulfurized without loss of heating value by exposing coal particles of 0.1—4 cm size in 1.5-2 cm layers to 2.45 GHz microwaves for 40 s in air at 1—5 torr pressure. The coal temperature did not exceed 420 K and the sulfur content was reduced from 4.11 to 1.91%. However, Scott et al.224 did not observe any significant change in S content (2%) of bituminous coals as a result of exposure to 60 Hz discharges in the annular space of a Siemens tube. 

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