The Tosco process of retorting oil shales
The Tosco process of retorting oil shales employs a cocurrent flow of hot alumina ball and oil shale in a rotating drum means. The oil shale takes up heat from the balls, and the oil vapors produced are drawn off into a collection system,leaving a spent shale admixed with the balls. The spent shale is transferred to a furnace where residue-carbon is burned off to provide reheating of the balls. The main advantages of the Tosco system are the relatively high throughput rates achieved inproportion to the size of equipment, and the production of high-BTU off-gas since there is no dilution thereof by combustion products. However, one serious disadvantage of the Tosco process has been just how to separate the alumina ball from the spentshale.
In an alternative method, finely divided high-alumina refractory and water are admixed, but without the iron, and formed in an extruder to provide cylinders of suitable size. These cylinders are tumbled in a rotary drum so as to provide a firstsized wet raschig ring. These first-sized wet alumina balls are admixed with iron filings or shot in a second rotary drum step, so as to coat the first formed balls with the iron filings. These iron-filing coated alumina balls then are admixed withfurther water and further high-alumina, such as in further rotary drum step, so as to provide, in effect, a ball with a ceramic core, an iron filing coating thereover, and over that additional alumina.