Patent ID: 7452203

Claim:
A method for processing solid material comprising: (A) combusting fuel and primary oxidant in a kiln in a combustion zone within said kiln which extends lengthwise along the longitudinal axis of the kiln from the base of the combustion zone toward its free end, wherein the stoichiometric ratio of oxygen to fuel in said combustion zone is 0.3 to 0.9; (B) feeding a plurality of streams of staging oxidant into the kiln into the space between said combustion zone and the inner surface of said kiln in the direction extending from the base of the combustion zone to the free end of said combustion zone, along said longitudinal axis of the kiln, wherein said streams are fed at a sufficient velocity and orientation that the fraction of the staging oxidant that has been entrained into the combustion zone between the base of the combustion zone and any point along the direction of flow of the staging oxidant is equal to or less than the fraction of primary oxidant that has entered into the combustion between the base of the combustion zone and said point, whereby staging oxidant is entrained into said combustion and combusts therein with unburned fuel or products of incomplete combustion of said fuel; wherein all oxygen entering said kiln from all sources constitutes 27.5 vol. % to 72.5 vol. % of all gas entering said kiln, and wherein the overall stoichiometric ratio of all oxygen entering said kiln to fuel entering said kiln is greater than 1.0 and not greater than 1.30; and (C) passing said solid material into, through, and out of said kiln while rotating the kiln so that the solid material passes along the length of the kiln from the point at which it enters the kiln to the point of its passage out of the kiln, wherein said solid material is exposed to heat of combustion of said fuel while it is passing through the kiln.