Abstract: A stream of hot primary gas rising from the gasification region in a slag bath generator passes through an after-gasification region and thence into a cooling region. The stream of hot gas is cooled in the cooling region by injecting purified and cooled primary gas through tangentially-arranged nozzles at an outlet velocity of between 1 and 8 meters per second. Below the tangentially-arranged nozzles, other gas-cooling nozzles inject cooled and purified primary gas into the hot gas stream upwardly at an angle within 10.degree.-60.degree. , preferably at 45.degree. and at an outlet velocity of between 10 and 160 meters per second. The upwardly-inclined gas injection nozzles are carried by the inner wall of an annular duct. The inner wall extends between a lining of cooling tubes surrounding the vertical gas flow space.