Abstract: In a method of mixing two or more gas flows, the gas flows are passed through an array of at least three parallel adjacent guide conduits so as to emerge from said conduits into a mixing zone as a corresponding array of parallel adjacent streams flowing in the same direction. The gas flows are distributed alternatingly in said conduits so that each said stream has, as each of its neighbors, a gas stream from a different said gas flow. To improve mixing and shorten the required length of the mixing zone, the streams derived from the respective gas flows have different velocities at their emergence from the guide conduits into the mixing zone.

Abstract: A recuperative heat exchanger for gas-gas heat exchange at a temperature above 700.degree. C., comprising a refractory lined vessel having a vertically extending steel shell closed at top and bottom by respective ends, wherein the space within the vessel is divided into respective top and bottom end chambers and a heat-exchange chamber therebetween by top and bottom apertured refractory plates and the end chambers are connected by a plurality of substantially vertical tubes of refractory ceramic material extending between said plates.