The retorting of shale requires an operation combining very good heat and fuel economy with low capital investment. In order to meet these demands the Union Oil Company developed its novel underfeed retorting method, which was publicly demonstrated in 1950 in a 50-ton per day unit. The retorting unit employs countercurrent flow of shale and air in a kiln utilizing bottom feed of solids. Ash and clinkers are removed overhead, and the oil drained from the bottom of the unit is cooled by countercurrent heat exchange with the incoming shale. No water is required for process operation. Movement of the shale through this unit is effected by a hydraulically operated underfeed mechanism. The shale kiln employs an external retorting section with cowling to direct air flow over the fins and to control shell temperature. Unlike conventional retorts, fusion of ash is not considered a problem in the operation of the Union retort since specially designed sodium-filled plows carry out a scraping action in the plastic ash-fusion zone, maintaining uniform bed porosity and size range of the discharged ash. It has been estimated that a typical commercial shale mine can produce approximately 20,000 tons per day of shale. The shale-retorting plant designed to handle this production would employ a battery of retorts, each having a capacity of 1000 tons per day, and centralized gas-handling and hydraulic power-supply systems.

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