Tuyere blocks of vertical reactor furnaces

A tuyere block to be positioned in a vertical wall defining a furnace or reactor interior, for defining a passage in which a tuyer or burner can be mounted, said tuyere block consisting of a plurality of prefabricated elements which each has a first surface to be positioned in said vertical wall of said furnace or reactor interior, each of said elements being made of molded refractory concrete and being provided with a protective lining, said protective lining being composed of a plurality of identical ceramic refractory keys united to said concrete and consisting essentially of grains of at least one of corundum and silicon carbide bonded by a nitride or sialon binder, said elements being positioned together such that said ceramic refractory keys form a passage in which a tuyere or burner can be mounted.