[7] The Kiviter retort is a vertical cylindrical vessel that heats coarse oil shale with recycled gases, steam, and air.
[8] To supply heat, gases (including produced oil shale gas) and carbonaceous spent residue are burnt within the retort.
Pyrolysis is completed in the lower section of the retort, where the spent shale contacted with more hot gas, steam and air is heated to about 900 °C (1,650 °F) to gasify and burn the residual carbon (char).
[9][10] The Kiviter process is used by the Estonian Viru Keemia Grupp's subsidiary VKG Oil.
[8][11] The company operates several Kiviter retorts, the largest of them having a processing capacity of 40 tonnes per hour of oil shale feedstock.