[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).
[4] Oil shale particles are further processed in a horizontal segmented doughnut-shaped traveling-grate retort in the direct or indirect heating mode.
To minimize solubility of aluminium compounds in the oil shale, the heat control is a crucial factor.
The indirect mode is similar; the difference is that combustion of carbonaceous residue takes place in separate vessel.
[4] During retorting, there is no relative movement of oil shale, which avoids dust creation, and therefore increase the quality of generated products.