Fast Beds for Combustion Affording Low Pressure Drop

Fast Beds for Combustion (Affording Low Pressure Drop) 

fluidization data did not reach the open literature until 1949 (Lewis et ai), and it remained for Wilhelm and Kwauk (1948) to provide a report whereby one may infer that fine powders aggregate when buoyed by a rising current of air—clustering to a degree such that velocities to buoy the particles, or transport them upward, were far higher than single-particle terminal velocities (see, especially, Leo Friend s comment on the Wilhelm-Kwauk paper). 

Kellogg s fast-bed reactors for Sasol received negligible attention in the European or U.S. engineering literature, and Sasol s engineering achievements in implementing Kellogg s concept attracted little notice. 

Accordingly, I could not be surprised when Lothar Reh told me that the M.I.T. data at high gas velocities, as well as the Sasol fast-bed reactor, were far from his thoughts when he invented the Lurgi fast bed for calcining alumina (Reh, 1971 Reh and Rosenthal, 1971). (See Fig. 6.) 

Primary air flow, supplied at the bottom of the bed, is insufficient for complete combustion of the fuel. The zone below the elevation of secondary-air jets is endothermic, cracking oil to yield carbon and fuel gas species. These burned in the upper, exothermic zone. Alumina product is withdrawn from a standpipe receiving solid from the upper zone, and burn-off of carbon in this zone is sufficient to yield a product that is acceptably white. Fluidizing-gas velocity being lower in the primary combustion zone than in the secondary, density is higher. Provision of the two zones accomplishes two purposes (1) affording a sufficient solid residence time in the primary zone and (2) reducing horsepower needed for air compression. 

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