3387.     --------------.  [THAU, A.]  [Water-Gas Production With External Heating.]  Gas- u. Wasserfach, vol. 84, 1941, pp. 509-513; Chem. Abs., vol. 36, 1942, p. 5334.

        Water-gas reaction, being endothermic, requires a continuous supply of heat if it is to be maintained as a continuous process.  Heat can be supplied in various ways, for example, continuous supply of O₂ in place of air, direct supply of superheated steam, and external heating of the generator.  Processes involving an externally heated generator, for example, those of Heller, Herzberg and Bueb, are reviewed.  The Didier-Bubiag process, in which an externally heated and continuous vertical retort is used, is described.  In this the gas outlet is moved from the top of the retort to about halfway down.  The raw, weakly or noncoking, coal before entering the retort passes through a drying chamber, which can also be adapted to submit the coal to a preliminary low-temperature carbonization.  Superheated steam is introduced toward the bottom of the retort, the lowest section of which is not heated and serves to cool the issuing coke.  The coal in passing down the retort is progressively carbonized in the zone above the gas outlet, and the carbonization gases must pass downward to reach the outlet; in doing so the tarry vapors are cracked.  Water gas is produced in the lower half of the retort and passes upward to the same gas outlet.  The operation is adjusted so that just enough coke leaves the retort to supply producer gas for external heating.  Conditions can be varied to yield either a rich gas or synthesis gas.  If lignite briquets are used, subjected to low-temperature carbonization in the pretreatment chamber, and the tarry vapors are led down through the top of the retort, C₆H₆ containing 16-25% of toluene can be recovered.