▁burn . ▁At ▁the ▁same ▁time ▁the ▁air ▁injection ▁continued ▁bringing ▁temperature ▁in ▁the ▁burning ▁part ▁to ▁about ▁. ▁ ▁The ▁he ated ▁gas ▁caused ▁a ▁py ro ly s is ▁on ▁the ▁lower ▁part ▁of ▁oil ▁sh ale ▁and ▁produced ▁sh ale ▁oil ▁and ▁oil - sh ale ▁gas ▁are ▁escaped ▁from ▁the ▁ret ort ▁through ▁exhaust ▁pipe ▁at ▁the ▁bottom ▁of ▁ret ort . ▁The ▁py ro ly s is ▁occurred ▁at ▁the ▁temperature ▁about ▁. ▁ ▁By ▁time - be ing , ▁the ▁comb ust ion ▁zones ▁moved ▁down ward , ▁and ▁the ▁char ▁( sem i - co ke ) ▁produced ▁as ▁a ▁solid ▁resid ue ▁of ▁py ro ly s is , ▁ign ited ▁to ▁burn ▁as ▁additional ▁fuel ▁for ▁comb ust ion . ▁This ▁caused ▁the ▁py ro ly s is ▁zone ▁to ▁move ▁down ward ▁to ▁the ▁lower ▁parts ▁of ▁ret ort . ▁After ▁comb ust ion ▁zone ▁reached ▁to ▁the ▁bottom ▁of ▁ret ort , ▁air ▁injection ▁was ▁stopped ▁to ▁stop ▁comb ust ion . ▁After ▁burning ▁of ▁char , ▁the ▁sh ale ▁oil ▁production ▁ceased ▁and ▁only ▁spent ▁oil ▁sh ale ▁ash ▁remained ▁in ▁the ▁ret ort . ▁The ▁bottom ▁of ▁ret ort ▁could ▁opened ▁for ▁removal ▁of ▁the ▁oil ▁sh ale ▁ash ▁after ▁ret ort ing ▁process . ▁ ▁Oper ating ▁ ▁the ▁N T U ▁ret ort ▁with ▁nom inal ▁capacity ▁of ▁ 4 0   ton ▁of ▁raw ▁oil ▁sh ale , ▁the ▁full ▁process ▁cycle ▁took ▁about ▁ 4 0