Optimizing Waste Heat Recovery in the Post-combustion Chamber of a Sponge Iron Plant

The hot gases from the rotary kiln used for sponge iron production enter the post-combustion chamber (PCC) placed next to the kiln. These gases (1023–1223 K) contain unused carbon monoxide (CO) and unburnt coal, along with other components. Since carbon and CO cannot be released into the atmosphere, these are combusted by adding air into the PCC, and if gases are overheated, they are cooled by water to the required temperature. The PCC’s output flue gases’ temperature and volume determine energy consumption and waste heat recovery for optimal power generation. To minimize power generation fluctuations, exit gas temperatures must be kept in an optimal window. The water guns for cooling gases are operated by PID controllers. An optimization program is required to feed P, I, and D inputs to the controllers. The present work focuses on the development of optimal control programs through energy balance, mass transfer, and heat transfer calculations. These calculations are described in the present work along with the predicted values of air and water to be added to PCC. This study employs a simple genetic algorithm (SGA) to determine the appropriate air and water levels for PCC continuously. This kind of dynamic energy balance-based control is the first attempt of its kind for a sponge iron plant. It has industrial importance because nearly 30 million tons of sponge iron is produced in India through this route presently.