644.    CRENTZ, W. L., DOHERTY, J. D., AND DONATH, E. E.  Coal Preparation for Synthetic Liquid Fuels.  Min. Eng., Trans. Am. Inst. Min. and Met. Eng., vol. 187, 1950, pp. 507-510.

      Principal washing problems in preparing coal for the synthetic fuel industry may be stated as:  (1) Ash removal for the Bergius process; and (2) S removal for the Fischer-Tropsch process.  A study is made of the effect of ash on oil losses during the elimination of the nonliquefiable portions of the coal in the hydrogenation process.  The oil loss increases with ash content of the coal and results in increased consumption of coal, H₂, and power.  Quantitatively, it is estimated that the oil loss due to ash amounts to about 9 lb. of oil for each % of ash in 1 ton of the hydrogenated coal.  Cost comparison is made of the economic advantages resulting from the use of 2.3% ash coal and a 6% ash coal in a 30,000 bbl./day hydrogenation plant.  In the Fischer-Tropsch process, the quantity of ash in the raw-coal feed is not as critical as in the Bergius process.  The problem here is the amount of S that the synthesis gas contains.  The economic advantage, however, lies with the cleaning of the coal used to make synthesis gas to a low S content if the S can be removed by mechanical cleaning.  It is estimated that it costs $1.15/ton of gasified coal to remove S from synthesis gas when the coal contains 3% S.  Increase in the S content of the coal from 3 to 5% would impose an additional cost of $0.37/ton.

     CRITTENDEN, E. D.  See abs. 36, 3748.