Study On Co-pyrolysis Kinetics And Pyrolysis Products Of Agricultural Biomass

Traditional fossil energy consumption and global carbon emissions are increasing,and the world is falling into a new energy crisis.Efficient development and utilization of renewable energy is an inevitable requirement to cope with the sudden shortage of energy and alleviate the pain of new and old energy transformation.As the only renewable carbon source,biomass has become one of the most preferred alternatives to traditional fossil energy.Biomass pyrolysis can most efficiently realize the conversion of biomass raw materials to high-grade energy.Co-pyrolysis technology can better improve the quality of pyrolysis products and improve energy conversion efficiency.In this paper,three typical agricultural biomasses of rice husk,peanut shell and wheat straw were selected to carry out the thermogravimetric and small-scale experiments of single sample and mixed samples with different mass blending ratios.By comparing the TG,DTG and DSC curves,the variation of single pyrolysis and co-pyrolysis weight loss process was analyzed.The kinetic parameters of co-pyrolysis were calculated by FWO method and CR method,and the reaction models of co-pyrolysis of different kinds of biomass under different blending ratios were determined.The coke appearance and tar components were analyzed by scanning electron microscopy and gas chromatography-mass spectrometry,and the three-phase product yield was determined.The results showed that :(1)The single pyrolysis process and co-pyrolysis process are similar,which can be divided into three stages : drying and preheating stage,main weight loss stage and residual solid carbonization stage.The co-pyrolysis DSC curve has more endothermic and exothermic peaks than the single pyrolysis process.The enthalpy of the co-pyrolysis process is larger,the heat transfer process is more complex,and the synergistic effect of the co-pyrolysis process is significant.(2)FWO method and CR method were used to fit : when the mixing ratio of rice husk peanut shell was 1 : 1,the co-pyrolysis activation energy and mechanism function were 76.3 k J / mol,and the second-order reaction model F2;when the blending ratio is 2 :1,the co-pyrolysis activation energy and mechanism function are 70.1 k J / mol,and the first-order reaction model F1;when the blending ratio is 1 : 2,the co-pyrolysis activation energy and mechanism function are 79.8 k J / mol,and the two-dimensional diffusion model D2;when the blending ratio is 3 : 1,the co-pyrolysis activation energy and mechanism function are 66.9 k J / mol,and the first-order reaction model F1;when the blending ratio is1 : 3,the activation energy and mechanism function of co-pyrolysis are 85.5 k J / mol and one-dimensional diffusion model D1.When the blending ratio of rice husk and wheat straw is 1 : 1,the co-pyrolysis activation energy and mechanism function are 64.0 k J / mol,and the two-dimensional diffusion model D2;when the blending ratio is 2 : 1,the co-pyrolysis activation energy and mechanism function are 66.4 k J / mol,and the first-order reaction model F1;when the blending ratio is 1 : 2,the co-pyrolysis activation energy and mechanism function are 63.4 k J / mol and the third-order reaction model F3;when the blending ratio is 3 : 1,the co-pyrolysis activation energy and mechanism function are 67.1k J / mol,and the three-dimensional diffusion model D3;when the blending ratio is 1 : 3,the co-pyrolysis activation energy and mechanism function are 61.7 k J / mol and the first-order reaction model F1.When the blending ratio of peanut shell and wheat straw was1 : 1,the activation energy and mechanism function of co-pyrolysis were 74.5 k J / mol and the first-order reaction model F1.When the blending ratio is 2 : 1,the co-pyrolysis activation energy and mechanism function are 78.9 k J / mol,and the one-dimensional diffusion model D1;when the blending ratio is 1 : 2,the co-pyrolysis activation energy and mechanism function are 71.3 k J / mol,and the second-order reaction model F2;when the blending ratio is 3 : 1,the co-pyrolysis activation energy and mechanism function are 81.5k J / mol,and the second-order reaction model F2;when the blending ratio is 1 : 3,the co-pyrolysis activation energy and mechanism function are 70.0 k J / mol and the first-order reaction model F1.(3)The rice husk-peanut shell co-pyrolysis char is black block or granular,the section is dense and uniform,showing anisotropy;the co-pyrolysis char of peanut shell-wheat straw gradually presents a porous lamellar structure with the increase of wheat straw blending ratio.The lamellar structure of rice husk-wheat straw co-pyrolysis char is more obvious,and the fracture surface shows the morphological characteristics of glassy amorphous body.(4)A total of 58 main organic compounds were detected in the pyrolysis tar obtained by co-pyrolysis at different blending ratios.The main components were phenols,alcohols,sugars,pyridines,ketones,esters,acids,alkanes and other organic compounds.The organic compounds with higher relative content were : phenol,tetrahydrofurfuryl alcohol,guaiacol,o-cresol,p-cresol,3-furanmethanol,2-methoxy-4-methylphenol,γ-butyrolactone,o-diphenol,2,6-dimethoxyphenol.The relative contents of ketones,alcohols and esters increased with the increase of peanut shell blending mass.The relative contents of pyridine,furan and alkanes increased with the increase of rice husk blending quality.The relative contents of acids,pyridines and ketones increased with the increase of wheat straw blending ratio.(5)In the pyrolysis of single biomass,the yield of rice husk solid product was the highest,the yield of peanut shell tar was the highest,and the gas yield of wheat straw was the highest.The solid product yield increased with the increase of rice husk blending ratio.The tar yield increased with the increase of peanut shell blending ratio.The gas production rate increased with the increase of wheat straw blending ratio.