Dissociation characteristics and anthropogenic emissions from the combustion of double gas hydrates

Abstract

Gas hydrates are an alternative and environmentally friendly energy source increasingly in the focus of scientific attention. The physicochemical processes behind gas hydrate combustion are studied experimentally and numerically with a view to improving the combustion efficiency and reducing gas emissions. It is important to estimate the pollutant emission concentrations in the context of combustion conditions. The research deals with the dissociation and combustion behavior of double gas hydrates in a tubular muffle furnace. Gas hydrates of different composition are considered: methane, methane-ethane, methane-propane and methane-isopropanol. Double gas hydrates are characterized by more stable combustion compared to methane hydrate. It is also shown that the double gas hydrate dissociation rate increases by 15–30% with increasing temperature. Dissociation and combustion processes were also modeled as part of the research, accounting for phase transitions in a gas hydrate layer. According to the simulation results, the total dissociation rate of gas hydrate increases by 3 times with an about 2.5-times increase in the powder layer thickness. Our experiments also focused on the impact of furnace temperature and gas hydrate composition on concentrations of anthropogenic gas emissions. We have found that the presence of heavy hydrocarbons such as ethane, propane and isopropanol in double gas hydrates reduce unburned CH4 emissions by 60%. Also, an increase in the combustion efficiency of double gas hydrates, accompanied by a decrease in the concentrations of unburned CH4 and CO, affects the yield of CO2, which increased by 13–35%. When we increased the temperature in the furnace from 750 °C to 1050 °C, concentrations of nitrogen oxides and carbon dioxide increased by up to five times. Thus, the resulting correlations between the key parameters of these processes and a set of the main inputs illustrate the possibility to predict the optimal conditions for the combustion of gas hydrates.