| Biomass energy is the only renewable energy which can be converted into liquid fuels, and biomass indirect liquefaction technology is one of the most potential technologies in the future. Gasification technology is the base and key of indirect liquefaction. Due to the complexity of biomass, high oxygen and low calorific value, biomass gasification especially staged-gasification is still insufficient understanding in the gasification characteristics, staged-gasification mechanism and energy efficiency research. Based on the Special Funds for Major State Basic Research Projects of China (2007CB210208) and the State Key Program of National Natural Science of China (no.51336008), the fundamental task about biomass staged-gasification was investigated through theoretical analysis and experimental research.Firstly, the research of mixed-gasification on entrained flow bed was completed. Secondly, a technical route of staged-gasification for high quality syngas based on mixed-gasification was proposed. The three steps staged-gasification using MATLAB software was completed, and influencing factors of staged-gasification were proposed, and gave a guide for the staged gasification test. Finally, exergy loss of the whole system was calculated by Aspen Plus software, it maybe optimize the biomass staged-gasification system.In order to investigate the characteristics of biomass staged-gasification, a lab-scale biomass staged-gasification system with three steps was designed and set up. Experiments were performed to analyze the production distribution, sygas composition, carbon conversion, cold gas efficiency and C/H transformation rules. The results showed that:on the thermal stability of biomass, cellulose is first, lignin take the second, and half fiber is the worst. In three kinds of biomass, the H2/CO ratio of sawdust gasification reached1.21, the highest increase was up to23.5%; Carbon conversions of three biomass were similar, but the increase of change is not the same. Rice straw at the beginning was the largest, reaching12.8%. In order to understand the staged-gasification mechanism and forecast the test result, the paper established a biomass staged-gasification model. Through the matlab programming, the paper can realize solving control equations of gasification kinetics model, and conduct the gasification characteristics research. Results show that H2/CO ratio is the largest, reached1.2at a gasification time of0.6s. With the increase of O/B, H2/CO ratio is increasing after reducing. It reached1.19about at0.2s. The appropriate O/B is an important factor for efficient directional gasification.In the experimental study on staged-gasification with three steps, the research of pyrolysis temperature, gasification temperature, first gasification time, the position of water vapor into the gasifier, and tar content carried out for the influence of parameters on gasification characteristics. Results show that the gasification and pyrolysis temperature rise can help to improve the quality of syngas. At1100℃H2yield reached the maximum of52.8g/kg biomass, at the same time H2/CO also reached the maximum of1.42. As the extension of a gasification time, gasification efficiency an d carbon conversion rate took a trend of convex type, the maximum was respectively75%and96.3%at0.6s. At the distance of1.12m to the top of1.12m is bubbled into water vapor, staged-gasification effect best, H2content have reached the maximum57.2%, the maximum was also up to2.64H2/CO at the same time.On the basis of above research, biomass gasification system model was set up by Aspen Plus software, and exergy balance and exergy analysis research were carried out exergy analysis results show that energy utilization rate of the staged-gasification system is only41.5%. Among the system parts, the highest exergy efficiency is pyrolysis unit, accounted for80.78%of all system exergy loss. Exergy efficiency rises with temperature increasing, reaching48.82%at the1100℃.In the optimization of gasification system, increase the waste heat recovery unit, and implements the system since the hot, but the corresponding reduced exergy efficiency, optimize system exergy efficiency up to8.14%. |
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