2576.     PARRY, V. F., WAGNER, E. O., KOTH, A. W., AND GOODMAN, J. B.  Gasification of Subbituminous Coal and Lignite in Externally Heated Retorts.  Ind. Eng. Chem., vol. 40, 1948, pp. 627-641; Chem. Abs., vol. 42, 1948, p. 3929.

        During the war the Bureau of Mines conducted experimental work on 2 pilot plants for gasification of low-grade fuels.  The experimental data resulting from operation of the externally heated alloy retorts for a total of 3,500 hr. are summarized in graphs and tables, and the fundamental theories of gasification therein are presented.  It is shown that CO+H₂ can be made at the rates of 65-70 ft.³ per hr. per ft.² of heated surface in retorts heated to 1,900° F.  The performance of various processes for production of CO+H₂ is compared on the basis of ft.³ per hr. per ft.² of fuel-bed area.  The Lurgi and Winkler generators, respectively, make 1,000-8,600 ft.³ of CO+H₂ per ft.², while externally heated processes make 1,000-2,300 ft.³  Various grades of water gas having H₂:CO ratios ranging from 1.9-10 were made in the pilot plants, but it is indicated that lowest-cost gases and highest efficiency and capacity are attained when making gases 2.0:2.5 H₂:CO ratio.  The performances of 3 externally heated processes, the Didier-Bubiag, the Freilberger, and the annular retort, are reported with operating data.  The Didier-Bubiag process was operated in Germany and supplied about 7% of the  gas converted to liquid fuel by the Fischer-Tropsch process.  This retort employs refractory chambers and each unit makes about 17,500 ft.³ of gas per hr. at an efficiency of about 78%.  The 48-in. diameter annular alloy retort at Grand Forks has about the same capacity and has a present indicated efficiency of 71%.  Calculations given show that the efficiency of externally heated continuous retorts should be about 80% when equipped with heat-recovery devices.  In considering the economics of externally heated retorts, it is shown that the cost of alloy is about $0.01 per 1,000 ft.³ of CO+H₂, assuming that a 0.25-in.-thick alloy plate will have an average life of 10,000 hr. at 1,900° F.  It is therefore indicated that, when making CO+H₂ at a rate of 70 cu. ft./hr./sq. ft. in the externally heated retort, the equivalent cost of O₂ to make the same gas in an internally heated process would be $0.03-$0.05 per 1,000 ft.³