Absorber: In the absorber column the refrigerated feed gas and lean oil are intermingled at a temperature of minus 35 deg F to allow the lean oil to absorb the LPG products of propane and heavier components from the gas and become a rich oil.
Rich oil still column/hot oil system: In the rich oil still, lean oil is separated by distillation from the absorbed LPG products.
The lean oil shale layer, lying under the rich oil shale, has the average thickness of about 30 m.
The rich oil shale has specific gravity lower than 2.4, while that of the lean oil shale exceeds 2.4.
Based on the Fischer Assay of 42 bore samples of the Fushun west pit oil shale, the average shale oil yield of rich oil shale accounts for 4.18-7.61%, that of lean oil shale 1.11-4.35%.
For normal operation, open-pit mining includes two mining systems: one for preparation work, i.e., stripping process, including hole drilling, blasting, quarrying, transporting, and dumping (to the dumping yard with sand, rocks, lean oil shale, etc.); the other for exploitation work, including quarrying and transportation of rich oil shale to the retorting plant.
The process is suitable for retorting high-calorific oil shales (over 15% of Fischer assay oil) and bituminizing oil shales as well as for lean oil shales.
In experiments of processing lean oil shale by vertical retorts in Kivioli with cross-flow of heat carrier, their average daily throughput remained low (160-180 tpd) compared to concentrated oil shale at Kohtla-Jarve (200 tpd).
A serious problem in using large deposits of lean oil shale is the development of vertical retorts designed for high throughput.
The main specific property of organic lean oil shales as technological feed is their relatively high thermomechanical strength, but also absence or formation of bitumen even in negligible quantities on heating of oil shale.
Thus, the processing of lean oil shale makes possible: