155.    BATCHELDER, H. R., DRESSLER, R. G., TENNEY, R. F., SKINNER, L. C., AND HIRST, L. L.  Role of Oxygen in the production of Synthetic Liquid Fuels From Coal.  Bureau of Mines Rept. of Investigations 4775, 1951, 15 pp.

                   Steps in the production of O₂ by the liquefaction and fractionation of air are discussed.  All commercial designs involve the following basic steps:  (1) Supply of air into the plant apparatus; (2) refrigeration of the apparatus; (3) heat transfer between ingoing air and outgoing products; (4) removal of impurities from the air supply; (5) fractionation of liquefied air into components N₂ and O₂ and delivery of both as product gases; (6) removal of C₂H₂.  Characteristics of 4 commercial-size plants in this country for the production of O₂ are presented, and the type and size of 4 other plants under construction are listed.  The relationship of O₂-plant size to plant cost and to O₂ cost is discussed.  Increases in O₂ cost are quite rapid as the size of the plant is reduced:  $7.00 for a 100-ton plant; $4.80 for 300 tons; and $3.50 for 1,000 tons.  The function of O₂ in the production of synthetic liquid fuels is primarily the gasification of coal with O₂ to produce mixtures of CO+H₂, which then may be used directly, in the case of the Fischer-Tropsch synthesis, or as a source of H₂ for coal hydrogenation.  Among the potential advantages of the substitution of O₂ for air in the coal-gasification step are the following:  (1) Fuel economy; (2) increased capacity of equipment; (3) wider range of possible fuels; (4) greater adaptability to pressure operation; and (5) higher range of attainable temperatures.  The amount of O₂ necessary to produce synthetic fuel by Fischer-Tropsch is about 690 lb. per bbl. of liquid fuel.  This amount of O₂ at $5.00 per ton would amount to $1.72 per bbl. and at $3.00 to $1.03.  Each change of $1.00 per ton for O₂ will change the cost per bbl. of synthetic fuel from this process by about $0.35.  In the coal-hydrogenation process, a relatively large part of the required H₂ is to be recovered from the tail gases by low-temperature separation and produced by reforming the product CH₄ with steam.  Thus, the O₂ requirement for coal gasification is only a fraction of that for Fischer-Tropsch.  About 90 lb. of O₂ will be required to make 1 bbl. of synthetic fuel by coal hydrogenation.  At $5.00 per ton, the O₂ cost would amount to about $0.22 per bbl. of oil and at $3.00 to about $0.14.  Each change of $1.00 per bbl. in O₂ cost will change the cost per bbl. by about $0.04.