An algorithm for optimization of the air distribution in direct reduction process in rotary kilns akin to the SL/RN process is proposed, based on Pontryagin's continuous maximum principle. The optimum air distribution has been obtained for given operating conditions. The optimum air distribution has been found to have a definite pattern with small changes due to variation in process conditions. Air distribution has been found to be the most important parameter, which could be suitably chosen to obtain desired operating conditions. The influence of operating parameters, such as iron and carbon concentration in the charge, oxide and coal reactivity, have been studied and the process behaviour has been analyzed. Performance of the process has been observed to improve for an increase in oxide and coal reactivity and iron and carbon concentrations in the charge.