The Characteristic Study Of Synthesis Gas Bio-methanation

With the development of the world economy,fossil fuel consumption intensified,and promoted the exploration and development of new energy at home and abroad,the world of unconventional energy sources such as biogas,coal bed methane,coke oven gas and so on,had became a hot spot.The traditional catalytic methanation technology is an important way to convert syngas into natural gas,which can effectively improve the energy efficiency.However,this process normally involves high pressure and/or temperature,may be poisoning of the catalyst when impurities are present,and tend to have low product specificity,so the bio-methanation technology is a simple operation and does not use of industrial catalysts is attracting more and more attention.According to the special energy structure of"rich coal,less oil,poor gas"and rich biomass energy resources in China,this project focuses on the bio-methanation process combined with gasification technology and anaerobic fermentation technology was to produce methane.For this purpose,it is important to study the anaerobic fermentation process of simulated syngas.In this study,the simulated synthesis gas(SSG)is prepared from the syngas components obtained from the fixed-bed gasification technology.Continuous lab-scale experiments,and full scale trials were carried out.The main research contents and conclusions are as follows:(1)Exploring experiment of bio-methanation of SSG:According to the results of the gasification technology found that fixed-bed gasification technology is more suitable for the process of syngas convert to methane via microbial anaerobic fermentation because of the daily gas production and gas composition,and then the content of simulated synthesis gas is determined as H2:CO:CH4:CO2=35:30:15:20(vol%)according to the gas product composition of fixed-bed gasification technology process.In this experiment,the anaerobic digestion process of SSG is explored by adjusting the stirring speed,gas retention time and H2/CO ratio to determine the feasibility of biogasification of syngas.The results showed:the SSG can be rapidly converted to biogas in an anaerobic fermentation system after domestication at a certain experimental temperature(37°C),stirring speed and gas retention time,which indicating that the experiment is feasible;with the increase of stirring speed and gas retention time,the methane content is increasing and the speed has a greater effect on the gas production.However,the H2/CO ratio in the feed gas is not as high as possible,and it has been found that the system pH>8.0 when an excess of hydrogen,which will affect the conversion efficiency.From the data of continuous anaerobic fermentation process during 110 days,it can be seen that the system has a good running stability and can achieve long-term stable transformation process.(2)Semi-continuous experiment of anaerobic digestion of SSG:according to the results of exploring experiment,the conditions optimization experiments about synthesis gas convert to methane via anaerobic digestion process was studied,which is setting different of temperature(37,45 and 55 ~oC)and stirring speed(120 and 400 rpm).The results show that utilizing SSG as feed gas,and gas composition was H2:CO:CH4:CO2(35:30:15:20,vol%),fermentation temperature was 37°C and at the stirring speed of 400rpm,the methane concentration was highest in bio-methanation of SSG system.After 90 days of anaerobic digestion process of SSG,the pH value of inoculum fluctuation was small,and it has strong buffering ability and long-term operation stability.At the same time,compared with the effect of results at different experiment parameters,it is found that the gas-liquid mass transfer rate is the main limiting factor in the bio-methanation process of SSG.(3)In the continuous experiment of SSG bio-methanation system,the mainly research contents involved compare the conversion rates and gas production at mesophilic and thermophilic fermentation.Results showed that when the feed gas content was 50%H2,40%CO and 10%CO2(on volume basis),gas flow rate was 10mL/min(ccm),the gas production has a best quality at stirring speed of 500rpm in thermophilic fermentation system,which contained 49.7±0.4%CH4,49.9±0.4%CO2and 0.3±0.0%CO,the CO and H2 conversion efficiency can achieved 99.3%and 100%,respectively.And the methane daily production was 6.66±1.33L/d,the lower calorific value of generated gas increased 23.8%than that of feed gas,which indicated that anaerobic digestion was a effectively method of syngas convert to methane.With the increase of feed gas flow rate,we can see the methane content of generated gas was reduced to about 45%and CO2 content increased,which indicated that although the system has the ability to convert syngas to methane when the feed gas flow rate increased,but also produce more CO2,and then led to the gas production quality was reduced.And we think the best processing power in thermophilic fermentation system was 3.6L SSG/L/d.