Study On H₂/Co₂ Biological Methanation Process

As the natural gas energy demand is increasing as well as non-renewable energy of natural gas reserves to reduce gradually,environmentally friendly energy methane gradually appears in the line of sight of people,and is gradually to the attention of the people.The high content of carbon dioxide in the traditional biogas will reduce its calorific value.Therefore,how to produce biogas with high purity methane effectively and quickly has become one of the research focuses in various countries.H₂/CO₂ biological methanation process is not as the traditional biogas purification methods like physicochemical?in-site or ex-site purification to reduce the CO₂ content of biogas,but to convert H₂ and CO₂ to CH₄ under medium temperature or high temperature via microbial metabolism of enriched hydrotrophic methanogens.The main research contents and conclusions are as follows:?1?In the batch type experiments,the operating temperature of shaking table is37?,the stirring speed is 200 rpm.The experimental results show that when the volumetric flow rate ratio of H₂ and CO₂ is in the range of 3.5⁴.5,the higher is beneficial to the start of the reaction,but before starting the experiments have to go through a certain adaptation period of time.Hydrogen is completely consumed in the process of experiment according to the examination results.?2?On the base of the existing CSTR devices in laboratory,a continuous air intake device is modified and installed.Carry out the biomethanation of H₂ and CO₂short-term experiments under the temperature of 37?,the air input ratio of H₂ and CO₂is kept at 4:1.Measure the biogas composition,the change of single acid content and the microbial community structure in in the process of reaction through changing the volumetric flow rate and stirring intensity.The judgment of the change of this process can lays the foundation for the follow-up long-term experiment.The experimental results show that the biomethanation of H₂ and CO₂ can be effectively conducted in the CSTR device.The gas intake of hydrogen in the stable stage reaches 3.3 L/L/d biogas slurry,and the content of biogas respectively are 1.18±0.48%?H₂?,88.92±0.17%?CH₄?and 9.98±0.60%?CO₂?.There is no significant inhibitory effect in this process,and the range of pH was 7.74±0.07⁸.19±0.08.In the end,the biogas produces contains about 10%of CO₂.?3?Carry out a long-term experimental study on the biomethanation system of H₂and CO₂ with a new set of CSTR reactor,to enrich a hydrotrophic methane-producing fermentation system and obtain biogas with high methane purity by changing the operation parameters of air intake,intake ratio and stirring intensity.During the experiment,the pH is adjusted by regulating the intake ratio of H₂ and CO₂.What's more,no additional nutrients or nutrients are added in the whole experiment.In the stable stage I of the long-term experimental,when V_hydrogen=1.48 L/L/d biogas slurry,H₂/CO₂=3.6,and the stirring speed is 250 rpm,the acquire methane concentration is95.79±1.11%,while the hydrogen utilization rate is 99.46±0.26%.In stable stage II,when V_hydrogen=1.03 L/L/d biogas slurry,H₂/CO₂=2.5,and the stirring speed is 200 rpm,the acquire methane concentration is 97.94±2.33%.It is confirmed that the pH of biomethanation system of H₂/CO₂ can be regulated by changing the intake ratio of H₂and CO₂.When the air intake exceeds the load of the system,the gas production will be seriously affected,and it can be effectively restored to a stable state by changing the operating conditions.There is no inhibition phenomenon caused by hydrogen gas liquid mass transfer limitation is found in long-term experiments.Moreover,the reaction system forms a self-sealing nutrition system,and microbial residues can maintain the nutrient cycle of the system through other microbial metabolism,without the need to add additional nutrients.Microbial results show that,due to change of metabolic substrate,the structure,number and diversity of H₂/CO₂ biological methanation happen great change.In archaea bacteria,Methanosarcina richness declines,the richness of Methanoculleus which only with H₂ and CO₂ as the metabolic substrate gradually increases and eventually become the dominant archaea bacteria in the biomethanation system of H₂ and CO₂.