Abstract: The rate of calcining carbonaceous material in a rotary kiln is increased by enriching with oxygen air supplied into the kiln by fans. 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 of volatile materials and the combustion of such volatiles during calcination. The accelerated evolution and combustion of volatiles enables the rate at which carbonaceous material is calcined in a kiln of a given length to be increased.