Research On Biomass Baking-Pyrolysis-Gasification Graded Gasification Process

Biomass gasification technology has the potential to significantly enhance the utilization efficiency of biomass energy by converting low-energy-density biomass into high-quality,high-calorific-value,and easily storable combustible gases.However,the use of biomass as feedstock in gasification applications is limited by several inherent challenges,including high moisture content,high oxygen content,complex structure,low energy density,and low calorific value.To provide experimental data support for the development of industrial biomass classification gasification technology and equipment.Recent research has shown that biomass torrefaction,which involves the thermal treatment of biomass under controlled conditions,can significantly reduce storage and transportation costs,improve energy density,and enhance grindability.As a pre-treatment step for biomass gasification,torrefaction can improve the quality of gasification products and enhance process operability.This study investigates the impact of torrefaction on the physicochemical properties,pyrolysis behavior,and gasification performance of biomass,and proposes an optimized biomass gasification process.The proposed optimized gasification process provides a potential pathway for the commercialization of biomass gasification technology,which has important implications for the sustainable utilization of biomass resources and the transition to a low-carbon economy（1）Investigate the effects of different roasting temperatures on the physicochemical properties of corn stalks.Thermogravimetric analysis revealed that the thermal decomposition rate of pretreated corn stover was higher than that of the raw material in the lower temperature range,with little change in the Dmax value below 250°C and a slight variation in the Tmax value within the range of 319.3-325.2°C.At 275°C,the decrease in Dmax and Tmax values indicated the onset of cellulose degradation.With an increase in the torrefaction temperature,the Tmax value rose from 323.5°C to 379.8°C.Pyrolysis gas chromatography/mass spectrometry analysis showed a change in the composition distribution of the pyrolysis liquid products.The relative contents of acid and ketone in the original corn stover were 23.48%and 7.69%,respectively.In the 300°C torrefaction-treated samples,they decreased to 8.43%and 5.88%,respectively,while the relative content of phenol increased from 10.91%to 18.75%.Using a self-designed biomass continuous baking-pyrolysis coupled system,we investigated the effects of baking temperature and residence time on the properties of pyrolysis products from corn stover.In the biomass continuous baking-pyrolysis coupled system experiment,as the residence time of corn stover increased in the baking furnace,the carboxylic acid content decreased,for example,from 27.5%to 11.9%at 300°C.The phenol content in CS-275-240 and CS-275-480 was higher than that of baking pre-treated samples,reaching 39.7%and 40.5%,respectively,while in CS-300-480,the phenol content reached its maximum value of 47.7%.At CS-300,the trend of each component was similar to that of CS-275.As the residence time of corn stover raw materials increased,the ketone yield gradually increased.The baking-pyrolysis coupled system significantly increased the content of high-value compounds in the liquid product.At higher pyrolysis temperatures and baking residence times of 480,the CO content tended to increase,while the CO₂ content decreased.In addition,the release of H₂increased slightly with the degree of baking.The volume fraction of the main gas products CO₂ranged from 44.42 vol%to 47.37 vol%,while CO ranged from 36.33 vol%to 38.12 vol%.（2）Investigation of the effect of roasting pretreatment on the pyrolysis characteristics of corn stalk and optimization of the pyrolysis processThe baking pretreatment significantly affected the pyrolysis properties of corn stover.The thermogravimetric（TG）curves showed a smoother profile with a gradual disappearance of the shoulder peak and a more symmetrical curve.（DTG）shows the rate of thermal decomposition of corn stover,which was higher in the lower temperature range of pretreated corn stover than the raw material.below 250°C,Dmax values did not vary much and Tmax values varied slightly in the range of 319.3°C to 325.2°C.at 275°C,Dmax and Tmax values decreased indicating the onset of cellulose degradation.As the baking temperature increased,the Tmax values increased from 323.5°C to 379.8°C,and the product composition distribution of the pyrolysis solution changed,with a decrease in the relative content of acids and ketones and an increase in the relative content of phenols.The relative contents of acids and ketones in the original corn stover were 23.48%and 7.69%,respectively,which decreased to 8.43%and 5.88%,respectively,in the pretreated samples baked at 300°C,while the relative content of phenols increased from10.91%to 18.75%.In the experiments with the coupled biomass continuous baking-pyrolysis system,the carboxylic acid content decreased with increasing residence time of corn stover in the baking heater,from 27.5%to 11.9%at 300°C.The phenol content of CS-275-240 and CS-275-480 was higher than the baking pretreatment,reaching 39.7%and 40.5%.At CS-300°C,the trend of the components was similar to CS-275°C.The carboxylic acid content decreased and the ketone yield gradually increased with increasing residence time of corn stover feedstock.The phenol content reached a maximum of 47.7%in CS-300-480.The coupled baking-pyrolysis system significantly increased the content of high-value compounds in the liquid product.Higher pyrolysis temperatures and a baking residence time of 480 s tended to increase the CO content and decrease the CO₂ content.the release of H₂ increased slightly with increasing baking degree.The average volume fractions of the main gas products ranged from 44.42 vol%to 47.37 vol%for CO₂ and 36.33 vol%to 38.12 vol%for CO.（3）Investigation of the effects of Baking Pretreatment on Gasification Characteristics of Corn Stalk and Optimization of Gasification ProcessDuring the gasification of unbaked treated corn stover,the hydrogen content increased with time,the carbon monoxide content gradually decreased,the carbon dioxide content gradually increased,and the methane concentration gradually decreased.The total gas yield of gasification products was 2.07 Nm³/kg,which decreased after baking pretreatment.The baking pretreatment reduced the moisture and oxygen content in the biomass,increased the carbon monoxide concentration in the syngas,and decreased the carbon dioxide yield.The calorific value of corn stover gasification products decreased with time and was close before and after15 min baking pretreatment.Using a self-designed biomass continuous baking-pyrolysis-gasification coupling system,the study investigated the effects of the coupling process on the gasification reaction gas product composition,calorific value,and synthetic gas ratio of corn stalks.In the experiments of the biomass continuous baking-pyrolysis-gasification coupling system,higher concentrations of H₂and CO were generated compared to direct gasification at 700°C.The H₂ concentration at direct gasification and coupling system with baking temperatures of 250°C and 275°C was 37.38%,40.67%,and 42.96%,lower than 43.90%,47.91%,and 49.93%at the gasification temperature of 850°C.As the gasification temperature increased,the yield of H₂ increased,resulting in an increase in the H₂/CO ratio.The biomass continuous baking-pyrolysis-gasification coupling system enhances the gasification process by improving the gas quality and cold gas efficiency.The study showed that the coupling system reduced tar production,thus reducing downstream gas cleaning costs and workload,and produced higher H₂/CO ratios in the gas product,making it suitable for biofuel production applications with higher H₂/CO ratios and lower tar content in the gas product.