Sensible heat in the hot effluent gas stream leaving a partial oxidation gas generator for the production of raw synthesis gas, reducing gas, or fuel gas is used at its maximum temperature to produce a continuous stream of superheated steam at a pressure which may exceed the pressure in the gas generator. The by-product superheated steam may be used as a dispersant or carrier of the fuel feed to the generator or as a temperature moderator. Optionally, a portion of the by-product superheated steam may be used as the working fluid in a turbine to produce mechanical work or electrical energy or both. The high steam superheat temperature results in a higher conversion efficiency. A shell and tube heat exchanger in which a stream of steam or cleaned generator gas is continuously bled from inside the tubes to the outside, or the reverse is employed. The bleed stream mixes with the effluent gas stream passing through the heat exchanger. By this means a continuously flowing protective sheath or curtain of comparatively cooler bleedstream is placed between the surfaces of the tubes and headers, if any, in the heat exchanger and the surrounding hot effluent gas stream from the gas generator, which enters the heat exchanger at maximum temperature. The surfaces of the tubes and headers, if any, are thereby protected against corrosive gas attack and deposits of ash, slag, and soot.