Combustion performance of low calorific gas enriched by oxygen and ozone

Abstract

Biomethane produced via anaerobic digestion or thermochemical process is one of alternatives, which could substitute fossil fuel and reduce carbon footprints. However, during biomethane preparation for end-users, the waste gas stream could be formed during biogas upgrade/methanation. As these gases consists of few to 30 vol% of methane in CO2, the waste gas stream should be utilized instead of emission to atmosphere. Aside, to achieve clean and stable combustion of such gases, innovative methods are required as high concentrations of CO2 causes the decreased flame temperature and burning velocity.This study concerns the low calorific gas combustion enhancement by oxygen enriched air and plasma-produced ozone. The ozone-assisted combustion was investigated by burning various composition waste gases (30–15 vol% of CH4 in CO2) in a low swirl burner under different oxygen enrichment levels, from 28 to 80 vol%. It was determined that the combustion enhancement by ozone is related to methane concentration in the mixture and to oxygen enrichment level. Moreover, at lower oxygen enrichment levels, the combustion enhancement by the ozone addition was more pronouncing than at higher oxygen enrichment levels. The flame lift-off was reduced by 0.9–25.9% due to the ozone addition and the flame stability improved, but NOx emissions increased by 2–10 ppm compared to cases without O3 addition. Considering the combustion efficiency in terms of flame lift-off height, NOx and CO emissions, the ozone-assisted combustion of WG25 and WG20 was the most efficient under oxygen enrichment of 40 vol% compared to other cases.