Abstract: An improved process for retorting a solid carbonaceous material at elevated temperatures wherein a portion of the spent solids withdrawn from the retort is heated to a temperature within the range from about 1600.degree. F. to about 2400.degree. F. and then recycled to the retort as a source of heat at a temperature within the range from about 650.degree. F. to about 1600.degree. F. When the improved process of this invention is operated in this manner, the amount of liquid product obtained is maximized and the amount of gaseous product minimized. Moreover, the integrity of the particles thus recycled is improved and the amount of fines in the liquid product correspondingly reduced.

Abstract: Oil shale, coal, inert heat transfer material and other carbon-containing solids of varying sizes are preheated with a gas in a transfer line by first separating the solids into a plurality of size fractions and then separately introducing the size fractions into the transfer line at predetermined distances from the transfer line inlet. The predetermined distances are inversely related to the size of the particles comprising each fraction of solids so that the fraction of solids containing the largest particles is introduced nearest to the gas inlet and the fraction of solids containing the smallest particles is introduced at a point furthest away from the transfer line inlet. Normally, solids withdrawn from the transfer line will have been heated to a temperature below which any liquids or gases evolve and are ready for further processing in downstream conversion units such as oil shale retorts, coal gasifiers and the like.