Application of microwave plasma to biogas reformulation

To utilize biogas effectively, microwave plasma was applied to partial oxidation reforming of biogas. The reformulation characteristics of biogas were investigated by experiments using two circular nozzles of different sizes. With the smaller nozzle, stable reformulation of biogas stably occurred over a wider range of equivalence ratio than with the larger nozzle, because the damping of microwaves was inhibited. The concentrations of H₂ and CO increased, and CO₂ concentration decreased with increasing equivalence ratio. In this method, CO₂ is decomposed, and in the high equivalence ratio region the amount of CO₂ in the reformulation gas is less than the amount of supplied CO₂. When CH₄ is completely reformed into H₂ and CO, cold gas efficiency is about 95%. However, the maximum value of cold gas efficiency is approximately 110% with the smaller nozzle, because CO₂, which does not have calorific value, is decomposed into CO, which does have calorific value.