Abstract: The rate of calcining carbonaceous material in a rotary kiln is increased by introducing oxygen into the inlet of air fans mounted on the kiln. The introduction of oxygen is effected during a predetermined portion of each kiln revolution and is effective to enrich the oxygen content of air supplied to the kiln to approximately 23-25% oxygen. By so enriching the interior kiln atmosphere during calcining of material such as petroleum coke, greater temperatures are obtained than will be obtained by the use of air alone thereby accelerating the evolution and combustion of volatile materials during calcination. The accelerated evolution and combustion of such volatiles enables the rate at which carbonaceous materials can be calcined in a kiln of a predetermined length to be increased.