| Corn straws are one of agricultural wastes,and the output of corn straw is huge in China.The application of heat treatment to prepare corn straw biochar can not only alleviate the problem of energy shortage in China,but also solve the environmental pollution caused by corn straw burning,which has important economic and social significance.Based on these,the preparation of biochar from corn straw and their pellets was systematically studied,which provided new ideas for the energy utilizations of corn ststraw.The main research work and achievements are summarized as follows:(1)Based on the study of the influence of hydrothermal carbonation on the conditions(temperature,and time),the characteristics of the hydrochar and the combustion performance from corn straw were analyzed.The results showed that the process of hydrothermal carbonization is mainly dehydration and decarbonylation,and the optimum conditions were 230 ? and 30 min for hydrochar as fuels.The higher heating value,mass yield and energy yield were 20.51 MJ/kg,64.80%and 77.41%,respectively.The physical and chemical properties of the hydrochar were improved.The first order reaction kinetic model and integral method were used to anlayze characteristics of combustion.The activation energy of volatile was 43.0?97.7 kJ/mol,and the activation energy of fixed carbon is 29.6?41.6 kJ/mol,and its activation energy was lower than biochar prepared by pyrolysis.Hydrothermal carbonization is suitable for the preparation of fuels.(2)The activation energy of corn straw was 93.35?186.57 kJ/mol by DAEM model during pyrolysis.The results from TG-FTIR and TG-GC-MS showed that the maximum pyrolysis products of corn straw at 337? were mainly low molecular compounds,and the CO2 yield was the largest.With the increase of temperature,the benzene compounds appeared in the pyrolysis products.At 700?,long chain alkane compounds appeared in the products.(3)The results of gas products showed that the yield of CO2 is more than that of powder when the corn straw pellets was pyrolyzed at 300 ? the yield of H2 and CH4 was more than that of pellets when the corn straw powder was pyrolyzed at 500 ? and 700?.The results of bio-oil by GC-MS showed that the main components of the bio-oil by pyrolysis of corn straw were acid,furan,ketones,aldehydes,phenols,alcohols,and so on.Acids,furans,ketones and phenols were the main products in the pyrolysis process.With the increase of temperature,the content of phenolic compounds becomes larger,but lower than the pyrolysis of corn straw powder.The characteristcs of corn straw biochar pellets showed that the the heat value was increased,the mechanical properties were decreased,the water resistance and hydrophobicity were improved.The combustion kinetics of the biomass pellets and their biochar was analyzed by the first order reaction kinetics model and the integral method.The results showed the activation energy of the combustion stage is 39.34?72.80 kJ/mol,and the activation energy increases with the increase of pyrolysis temperature.(4)During torrefaction,temperature,the heating rate and residence time of torrefaction corn straw pellets were optimized by orthogonal experiment.The result showed that the optimal process conditions are 290 ? of temperature,7.0 ?/min of the heating rate,45 min of the residence time,and the higher heating value and the energy yield are 20.32 MJ/kg and 75.37%,respectively.During pyrolysis,the pyrolysis conditions were optimized by the response surface analysis.The results showed that the optimal process conditions are 432? of temperature,4.0 ?/min of the heating rate,43 min of the residence time,and the higher heating value and the energy yield are 23.89 MJ/kg and 57.88%,respectively. |
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