Billets Heat Treatment using Flue Gas for Energy Efficiency and Batching Cycle Time Reduction

Exhaust gas temperature in natural gas reverberatory furnaces can reach 700 - 900 °C at the furnace's chimney exit, carrying 40% to 65% of the total input energy. This study meant to investigate the utilization of the exhaust flue gas waste energy to preheat aluminum billets before homogenization process in batch homogenizers. Currently, the heat from flue gas can be retrieved by installing an extra heat exchanger, at the exit. This paper proposes a novel strategy replace the natural gas fired burners with flue gas waste heat extracted from exit from the recuperator. Also, the flue gas heat can replace the natural gas-fired power, resulting in better energy savings and the reduction of heat treatment cycle times. Thermodynamically case studies based on heat flue gas recycling and re-using through the heat exchanger and preheater into furnaces are performed on billets. The exhaust flue gas temperature on billets preheating process and efficiency is studied, as well as the effects of aluminum billets preheating process on homogenizing cycle time. The results indicate an excellent performance of the novel strategy, with a decrease in energy loss and improvement in heat transfer characteristics. The use of the heat flue gas equivalent of the novel approach can save nearly 32% of time compared to the system using conventional process. Our achievements provide a promising heat recovery method of the utility flue gas.