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
alumina ball. 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.
Another alternative mode of preparation includes admixing the finely divided refractory-grade alumina and water, but without any iron, to form a thick mixture which is passed through a roll-type briquetting machine, pelleting mill, or tabletingpress. Prior to passing the
alumina ball into the cavities of the mill or press, an iron particle such as a burr is inserted into each cavity and can be held in the cavity by such as a cleat or small magnet. The iron-particle containing pellets aresubsequently treated to produce balls in effect with an internal iron piece or burr.
