2108.     ----------------.  [LEWIS, W. K.]  Kinetics of the Reactions of Steam and Carbon Dioxide With Carbon.  Chem. and Eng. News, vol. 25, No. 39, 1947, pp. 2815-2818.

        New fluidized powder technique for the efficient combustion and gasification of coal is described in the Priestley medal address.  In this method, finely powdered coal, actually suspended by a stream of air entering at the bottom of the retort, is subjected to air and steam and converted into a mixture of CO and H₂ gases.  Combining with O₂ in the air, CO₂ is formed, and heat is evolved.  In the upper part of the retort the CO₂ and heat encounter more C, in the form of powdered coal and steam.  3 important reactions then take place, during which heat is absorbed, while the CO₂ is transformed into CO and H₂.  Rapid and even heat distribution is the basis for the success of the method, compared with the older processes in which heat is difficult to control.  A great advantage of fluidized powder technique is that all grades of coal can be used.  Other advantages are the reduction of operating difficulties owing to elimination of excessive temperatures; prevention of slag formation; reduction of unburned fuel in the refuse and in handling both the coal fed and the ash removed by the fluidized powder technique; high conversion with low CO₂ and undecomposed steam in the product; a definite, though limited, improvement in thermal efficiency; and the reduction in tar formation and its complete utilization.  The most serious limitation of the operation is its relatively low capacity; this limit is set by the gas velocity, which cannot be allowed to rise to levels above those necessary for good fluidization.  Fluctuations in the gas velocity must also be kept to a minimum.  One of its first uses probably will be in the manufacturing of better and cheaper producer gas for industrial purposes.  The production of synthesis gas for the Fischer-Tropsch reaction will also be carried out by some modification of this method.  The same applies to the synthesis of combustion gases of high heating value.

        ----------.  See abs. 1097.