Impact of Increased Renewable Gases in Natural Gas on Combustion Performance of Self-aspirating Flames
The depletion of fossil fuels and the urgency of reducing greenhouse gas emissions demonstrate a pressing need for alternative energy sources. Currently, natural gas consumption is a major contributor to global warming, not only due to the carbon dioxide emissions in the combustion products but also due to natural gas leakage in the mining, transmission and storage facilities. Therefore, replacing the pipeline natural gas with renewable gas can decrease greenhouse gas emissions as well as reduce dependence on fossil fuels. This dissertation investigated the feasibility of blending renewable gases (i.e., biogas, hydrogen), into existing natural gas transmission and distribution pipelines from the perspective of fuel properties and combustion performance of residential appliances.
The fuel interchangeability technical barriers and challenges were first investigated, including fuel properties, flowrate control, flame performance, etc.. Moreover, the source of reddish hydrogen flame color was also investigated experimentally. The results indicated that hydrogen cracking and embrittlement could be a concern influencing flame appearance. A multi-fuel blending system was fabricated under this dissertation to generate fuel mixtures of various percentages. Burner configurations of existing residential burners were investigated, and representative self-aspirating burners were selected to conduct fuel interchangeability testing on different fuel classes. Monitored combustion performance included ignition behaviors, blowoff/flashback limits, emissions (CO, UHCs, NO, NO2, N2O, NH3, etc.), efficiency, burner temperature, combustion noise, etc.. It was found that CO and UHCs emissions and the risk of flame blow-off increase significantly when the CO2 percentage in the fuel exceeds 5 vol%. Self-aspirating burners were found to have distinct H2 tolerance levels with a limiting factor of the flashback, which is more inclined to occur at ignition conditions. This limited the H2 injection limits below 20 vol%. At a low level of H2 addition to natural gas, most of the combustion performance of the tested self-aspirating devices didn’t differ much and some of them were improved, which shows a positive sign for natural gas replacement with renewable hydrogen for self-aspirating flames