Abstract: In a method of recovering heat from flue gas resulting from the combustion of chlorinated organic compounds at 900.degree. to 1300.degree. C. at a pressure of 0.9 to 1.5 bar absolute whereby the flue gas is cooled with the recovery of heat and hydrogen chloride is processed, the improvement comprising (a) cooling the flue gas in a first step to a temperature of 250.degree. to 350.degree. C. with a contact time of 0.05 to 0.15 seconds, (b) cooling the flue gas in a second step to a minimum of 140.degree. C. with a contact time of 1.3 to 2.0 seconds, the cooling medium in both stages being water flowing at an initial temperature of 100.degree. to 140.degree. C. in step (b) counter to the flue gas flow direction and added to cooling stage (a) at a temperature of 200.degree. to 220.degree. C. and (c) cooling the flue gas in a third stage to its dew point and scrubbing it with water to recover the hydrogen chloride therein in solution.