 During the pyrolysis process, oil shale is decomposed to shale coke (char), which together with the ascending air-steam is burnt in the lower part of the retort to heat gases necessary for pyrolysis.These gases are recirculated; after leaving retort, they are cooled in a condensation system, where shale oil is condensed, and re-heated in a heating furnace about to before reinserting into the retort.The shale ash exits from a rotating water dish that acts as a seal and cooler at the bottom of the retort.