Thermo-microwave Energy Coupled Pyrolysis And Gasification Of Crop Straw For Syngas And Biochar

Biomass can be transformed into the valuable oil,gas and char products by pyrolysis and gasification.However,traditional pyrolysis has the disadvantages of low heat transfer efficiency and poor product quality.Microwave heating is fast and efficient in overall heat production,but it also has some problems such as poor absorption performance of biomass and degraded use of high-grade electric energy.The study presented a novel approach—microwave pyrolysis or gasification coupled with conventional pre-pyrolysis to dispose of the stalk for syngas and biochar.A two-step pyrolysis method with conventional heat as the first stage and microwave-assistant heat as the second stage were adopted for straw thermo-chemical conversion.The cascade matching utilization of energy was realized,and the bottleneck problems inherent in traditional pyrolysis such as high energy consumption,poor heat transfer and long processing time were solved.Meanwhile,the product distribution was optimized and the product quality was improved.In this paper,based on the coupling of thermal energy and microwave energy,the characteristics and reaction path of coupled pyrolysis,the product characteristics and influencing factors of coupled steam gasification,and the characteristics and catalytic mechanism of coupled catalytic gasification were studied.Finally,coupled pyrolysis response surface model was established to optimize the process conditions,the engineering application design of the mobile coupled pyrolysis system was carried out,and the technical and economic evaluation was completed.Study on characteristics of microwave pyrolysis coupled with conventional pre-pyrolysis.The effects of coupling temperature,mixing ratio and microwave power on the temperature rise and product distribution of coupled pyrolysis were investigated in a thermo-microwave coupling experiment system.The results were compared with directly conventional or microwave pyrolysis.The matching mechanism of thermal energy and microwave energy and reaction mechanism were revealed by product characterization analysis.The results showed that the initial time for rapid temperature ramp in coupled pyrolysis was distinctly advanced from 124 s to within 20 s.Compared with direct microwave pyrolysis,the biochar yield from coupled pyrolysis was significantly increased from 24.19%to 33.24%,and the content of H₂ in microwave syngas reaches 64.65 vol%.The BET specific surface area of biochar reached141.69 m²/g.Conventional low temperature pyrolysis retained the complete carbon skeleton structure of biochar,while microwave deep pyrolysis promoted hydrogen production and improved the degree of biochar aromatization.Compared with conventional pyrolysis at different temperatures（500-800°C）,coupled pyrolysis had higher carbon yield and H₂selectivity.Study on microwave steam gasification coupled with conventional pre-pyrolysis for hydrogen-rich syngas.Based on the coupled pyrolysis,steam was introduced into the microwave part to further optimize the product distribution.The effects of different preheating temperature,steam ratio,gasification temperature and gasification time on the gasification characteristics and product distribution were investigated.The coupling gasification mechanism was revealed by analyzing the characteristics of gasification coke and syngas products.The results were as follows:the gas yield reached 1.14 Nm³/kg after preheating,which was 62.86%higher than that of direct microwave gasification,and the H₂ yield increased from 13.63 mmol/g to 31.62 mmol/g,and H₂/CO reached 1.95.Coupled gasification biochar had more oxygen-containing functional groups and lower aromatization degree,providing more active sites for gasification reaction.The increase of steam ratio,gasification temperature and gasification time can optimize the distribution of gas products,and the gasification temperature was the most important factor.Synthesis of Ni-based and Fe-based supported catalysts and optimization of syngas quality from biomass coupled gasification..Ni/Fe-basedγ-Al₂O₃ supported catalysts were prepared by the impregnation-deposition method.The effects of calcination temperature,urea doping and other preparation conditions on precursor components,catalyst synthesis path and structural characteristics were investigated.The catalytic effects of supported catalysts,dolomite,K₂CO₃and other common gasification catalysts in coupled gasification were explored,and compared with direct microwave catalytic gasification.The results were as follows:the results showed that the specific surface area of the nickel-based catalyst was 117.25 m²/g after calcination at400°C with urea as precipitant.The nickel oxide grain size was generally small and relatively uniform,and the carrier was Al O（OH）.The catalyst had the best catalytic effect in coupled catalytic gasification,and the H₂ yield reached 42.04 mmol/g.The syngas yield reached 1.41Nm³/kg and H₂/CO value was 2.02.In coupled gasification,the tar yield was low and the catalyst was difficult to deactivate.The catalytic effect was obviously better than direct microwave gasification.Coupling pyrolysis process optimization and mobile system design.Based on the experimental data,a response surface model of coupled pyrolysis of rice straw was established,and the effects of various process parameters on product distribution were investigated.According to the design indexes,the optimal process conditions were selected.On this basis,a mobile coupled pyrolysis system was designed,and its energy consumption analysis,structure calculation and economic analysis were carried out.The results are as follows:among the coupling pyrolysis parameters,the coupling temperature has the most significant influence,followed by the final temperature,and the conventional pyrolysis time has the least influence.According to the parameters of the pyrolysis model,the optimal conditions were obtained as follows:coupling temperature 325.86°C,microwave duration 7.35 min,final reaction temperature 793.58°C,preheating duration 22.11 min.The mobile coupled pyrolysis system can realize the co-production of biochar,heavy oil and wood vinegar liquid,and the combustion of pyrolysis gas and light oil for power generation.The system was self-sufficient in energy,and the thermal efficiency reached 85.9%.At the same time,the total volume of the system was14.7 m³.It had great industrialization potential and bright application prospects.