Study On Removal Of Carbon Dioxide From Simulated Biogas

Biogas is a source of clean and renewable energy. It could replace other non-renewable energy sources, which would relieve the energy crisis and protect the environment. Biogas is a mixture of gases comprising methane and carbon dioxide as the main ingredients (60-70and30-40%, respectively). However, it also contains many other impurities such as hydrogen sulfide. So hydrogen sulfide must be reduced to acceptable levels before use.In this paper, rice straw, grass, mixtures of rice straw and kitchen waste were used as raw materials and biogas slurry was used as inoculum to produce biogas by anaerobic batch fermentation at35±1or55±1℃. The hydrogen sulfide in biogas was be removed using micro-oxygenation technology (supplying limited air or oxygen to the anaerobic fermentation tank). The control experiment (R0) and experiments (R1-R7) were supplied with O×,0.5×,1.0×,2.0×,3.0×,4.0×,5.0×and10.0×the theoretical oxygen or air demand respectively to explore the feasibility and applicability of micro-oxygenation technology, the diversity of biogas production and the influence of different oxygen sources to micro-oxygenation technology.The experimental results showed the feasibility and applicability (different raw materials, different fermentation temperature(35±℃,55±1℃) or different oxygen sources) of micro-oxygenation technology as method to remove the hydrogen sulfide in biogas. There were no obvious changes in biogas production and methane concentration with the addition of limited oxygen or air. The oxygen residues could be controlled to below 0.5%when the oxygen or air supplied was2.0×3.0×and4.0×the theoretical oxygen or air demand. The average hydrogen sulfide concentration was lower, and the desulfurization efficiency was higher than92%.Although micro-oxygenation technology was applicable to different raw materials, mesophilic and thermophilic fermentation. There were diversity of biogas production with different raw materials and fermentation temperature. Daily biogas production of a gas peak and cumulative biogas production were both greater with grass or mixtures of rice straw and kitchen waste than with rice straw, and compared with rice straw as raw material, grass or mixtures of rice straw and kitchen waste as raw materials led to a higher concentration of hydrogen sulfide and a faster speed of reaching gas peak (mixtures of rice straw and kitchen waste more so). Gas production rate and yield were greater in thermophilic fermentation than in mesophilic fermentation. In thermophilic fermentation, methane concentration remained stable, while in mesophilic fermentation the methane concentration gradually increased to a stable value.Micro-oxygenation technology was applicable to different oxygen sources, Nitrogen content was higher with oxygen than with nitrogen. But the height of calorific value was inversely proportional to the content of nitrogen. The low calorific value may affect the utilization efficiency. While micro-oxygenation technology was a good desulfurization method with air as oxygen source if the requirement of calorific value was low for the utilization of biogas.