Abstract: A specific feature of the disclosed apparatus comprising burners disposed along the generatrix of the shell of the kiln and provided each with a plurality of nozzles each whereof is located in the refractory lining of the kiln, consists of a cylindrical portion the outlet wherefrom is provided in the form of converging as well as diverging cones and accommodates an axially disposed hollow movable rod which is provided with perforations within a portion passing through a gas chamber and is linked up with a drive by way of a means of actuation is that the gas chamber is fixed outside the nozzle the cylindrical portion, the converging cone and the diverging one whereof are located coaxially and successively looking in the direction wherein the mixture of steam, gas and air flows, the rod is spring-loaded in the axial direction and provided at its end facing the outlet from the nozzle with a hollow valve head pierced with through passages to obtain communication with the space inside the cylindrical portion of th