PAH/VOC Abatement in Water and Hydrogen Flows at MILD Combustion Conditions

PAH and/or VOC emission control from industrial processes is realized through several techologies, i.e thermal or catalytic oxidation, absorption or condensation in dependence of pollutants concentration and physical properties. Thermal oxidizers are designed to achieve from 95% to 99% of removal efficiency [1,2]. The typical combustion chamber temperatures range from of 950K up to 1100K. The low concentration of PAH in the exhaust gases implies temperatures do not sufficient for sustaining the reaction process. Therefore, an auxiliary fuel is needed. Unfortunately, the contemporary use of an auxiliary fuel and reactant pre-heating can lead to the potential formation of undesirable by-products, such as NOx. However, for a pre-heating of reactants at a temperature higher than the PAH autoignition temperature, thermal oxidation can fall in the Mild Combustion regime if mixtures sufficiently diluted are used. In this case both the clean and cleaning characteristics of the Mild combustion are simultaneously effective in the same process. Moreover, the suitable choice of the diluent can improve the abatement efficiency of the system. This is the case of water diluted Mild Combustion where the diluent can favor the PAH oxidation for its propensity to give radicals in these thermal conditions. The use of a fuel enhancer, such as hydrogen, can play the same role increasing the efficiency of the system by reducing the characteristic time of the process. Furthermore, the water used as diluent allows for separating particles from flue gas in a downstream condensation unity. In this framework, the paper aims to show a preliminary analysis of PAH oxidation in Mild combustion regime. The effect of diluent has been evaluated by comparing results obtained using both nitrogen and/or water as diluent.