| Process type | Chemical |
|---|---|
| Industrial sector(s) | Chemical industry oil industry |
| Feedstock | oil shale |
| Product(s) | shale oil |
| Leading companies | Superior Oil Company |
| Developer(s) | Superior Oil Company |
TheSuperior multimineral process (also known as theMcDowell–Wellman process orcircular grate process) is an above groundshale oil extraction technology designed for production ofshale oil, a type ofsynthetic crude oil. The process heatsoil shale in a sealed horizontal segmented vessel (retort) causing its decomposition into shale oil,oil shale gas andspent residue. The particularities of this process is a recovery of salineminerals from the oil shale, and a doughnut-shape of the retort. The process is suitable for processing of mineral-rich oil shales, such as in thePiceance Basin. It has a relatively high reliability and high oil yield. The technology was developed by the American oil companySuperior Oil.
The multimineral process was developed bySuperior Oil Company, now part ofExxonMobil, for processing of thePiceance Basin's oil shale.[1] The technology tests were carried out in pilot plants inCleveland, Ohio.[2][3] In the 1970s, Superior Oil planned a commercial-size demonstration plant in the northern Piceance Basin area with a capacity of 11,500 to 13,000 barrels (1,830 to 2,070 m3) of shale oil per day; however, because of low crude oil price these plans were never implemented.[4][5]
The process was developed to combine the shale oil production with production ofsodium bicarbonate,sodium carbonate, andaluminum fromnahcolite anddawsonite, occurring in oil shales of the Piceance Basin.[1][3][4] In this process, the nahcolite is recovered from the raw oil shale by crushing it to lumps smaller than 8 inches (200 mm). As a result, most of the nahcolite in the oil shale becomes a fine powder what could screened out. Screened oil shale lumps are further crushed to particles smaller than 3 inches (76 mm).[4] Oil shale particles are further processed in a horizontal segmented doughnut-shaped traveling-grate retort in the direct or indirect heating mode.[4][5][6] The retort was originally designed by Davy McKee Corporation foriron orepelletizing and it also known as theDravo retort. In the direct retort, oil shale moves pastducts through which are provided hot inert gas for heating the raw oil shale, air for combustion of carbon residue (char or semi-coke) in thespent oil shale, and cold inert gas for cooling the spent oil shale.[5] The oil pyrolysis takes place in the heating section. To minimize solubility of aluminium compounds in the oil shale, the heat control is a crucial factor. Necessary heat for pyrolysis is generated in the carbon recovery section by combustion of carbon residue (char or semi-coke) remained in the spent oil shale. While blowing inert gases through the spent oil shale, the spent oil shale is cooled and gases are heated to cause pyrolysis. The indirect mode is similar; the difference is that combustion of carbonaceous residue takes place in separate vessel. The last section is for discharging of oil shale ash.Aluminium oxide andsodium carbonate are recovered from calcined dawsonite and calcined nahcolite in the oil shale ash.[4]
The traveling-grate retort allows close temperature control, and therefore better control of dawsonite's solubility during the burning stage.[4] During retorting, there is no relative movement of oil shale, which avoids dust creation, and therefore increase the quality of generated products.[5] Theoil recovery yields greater than 98%Fischer Assay. The technology has also a relatively high reliability. The sealed system of this process has environmental advantage as it prevents gas and mist leakage.[6]