Thermal Oxidation of Ventilation Air Methane in a Flow Reversal Reactor: Comparison of Heat Recovery between Central Cooling and Hot Gas Withdrawal.

Thermal oxidation of ventilation air methane in a flow reversal reactor has attracted more attention due to its low operation cost and high grade of heat. However, there is still controversy over the waste heat recovery and utilization. A detailed one-dimensional heterogeneous model was designed, and the performances of the two heat recovery schemes, namely, central cooling and hot gas withdrawal, were systematically compared. Numerical results show that in the studied cases, the permissible ventilation air methane flow rate and methane concentration for central cooling are 2000-18,000 m3/h and 0.4-1.2 vol % with heat recovery efficiency around 55%, while those for hot gas withdrawal are 2000-10,000 m3/h and 0.6-1.2 vol % with a heat recovery efficiency of 46-76%. Theoretically, the heat recovery efficiency is independent of the heat recovery scheme. Due to the long switching time of the central cooling, it shows a higher overall methane conversion. Temperature fluctuation at the reactor center is 520 °C for hot gas withdrawal, while that for central cooling is 280 °C, which reduces the thermal shock to the bed and slows down the pulverization of the filler. Thus, central cooling seems a favorable heat recovery scheme in terms of its larger permissible flow rate, wider methane concentration range, higher methane conversion, and less thermal shock.