Experimental Study Of Biomass Pyrolysis And Gasification In A Circulating Dual Bed

The extensive use of fossil energy has brought about environmental problems,climate change,and energy crisis,and biomass energy,as a mainstay of renewable energy,is of great significance for the achievement of carbon neutrality goal in China.In this experiment,a 50 kg/h pyrolysis and gasification circulating fluidized dual bed with a height of about 5.7 m and a width of 3 m was used to investigate the pyrolysis and gasification behavior of beech wood particle（BP）at different pyrolysis and gasification temperatures.（1）The rapid fluidization gas velocity of the bed material in the device was calculated,and the working gas volume of the gasifier was selected as 75Nm³/h,which corresponds to a particle circulation rate Gs of about 89.31kg/（m²·s）.The pressure in the cycling stage of both one-step and two-step experiments was in the range of 5～12 k Pa,and the average pressure difference between the gasifier and pyrolyzer increased from 0.011 k Pa in the no-load stage to 1.83 k Pa in the cycling stage during the experiment,and the temperature of the pyrolyzer increased rapidly,which realized the dynamic relative isolation between the gasifier and the pyrolyzer,and the reaction time of the one-step method was shorter and operationally more suitable for subsequent industrialization..（2）The beech wood particle were pyrolyzed into three stages by Thermogravimetric analysis.Stage 2（160～510°C）was the main stage with62.81 wt.%weight loss,when the complex reactions such as dehydroxylation,decarboxylation,decarbonylation and demethoxylation of cellulose were mainly carried out.As the pyrolysis temperature increases,the sp²hybridized carbon atoms in biochar gradually transformed to sp³hybridized and defective carbon,and the C-O changes had little relationship with the changes of pyrolysis and gasification temperature,which was favorable to promote the decarboxylation reaction in biochar,while the content of amorphous carbon structure increased.The one-step method showed little change in the chemical binding state of the two biochars compared to the two-step method（3）Beech particle bio-oil had the highest yield of 32.88%at the pyrolyzer temperature of 550°C and the gasifier of 800°C.Phenols and benzene derivatives were the main components in bio-oil,which were produced from the cracking of broken chains of guaiacyl,p-hydroxy phenyl and syringyl in lignin to deoxygenate and demethylate.The non-condensable gases are mainly CO₂,CO,CH₄and H₂.Oxygen and water vapor can promote the water gas reaction as well as methane formation and the oxidation of gasification of char.（4）The energy analysis of the whole equipment showed that the energy yield reached 56.52%～82.68%,among which the highest energy yield of bio-oil reached 18.64%～52.45%,followed by biochar with 22.13%～33.62%and the least pyrolysis gas between 1.46%～15.75%and methylene blue and iodine adsorption experiments were also conducted on the produced biochar.The adsorption values of methylene blue increased from 184.04 mg/g to 261.38mg/g and iodine adsorption values increased from 80.28 mg/g to 99.72 mg/g when the pyrolysis temperature was increased from 450°C to 600°C at a gasifier temperature of 800°C.In the one-step method,the adsorption values of methylene blue and iodine further increased to 327.24 mg/g and 117.46mg/g due to the extension of the cycle time.