Co-pyrolysis Behavior And Coal Char Quality Of Biomass Blended With Coal

The heavy consumption of fossil energy has aggravated the environmental pollution.The biomass has attracted much attention due to its huge reserves,carbon neutral characteristics and renewability.Despite the disadvantages such as low density,small calorific value and low heating efficiency,the similarities of utilization with coal makes biomass an ideal cost-saving additive to mitigate coal consumption and environmental pollution.As an initial step of co-utilization,the co-pyrolysis process has a great influence on the subsequent procedure.The damage effect of tar,a main by-product of co-pyrolysis,should never be neglect for the existing harmful substances like aromatics.Coal char regard as the solid products resulted from coal pyrolysis,has been widely used in industrial manufacture,and its quality and structure characteristics deserves further investigation.Therefore,it is significant to study the co-pyrolysis behavior between biomass and coal,and influence on coal char structure caused by biomass.Firstly,pyrolysis characteristics of biomass?poplar?and fat coal under individual pyrolysis and co-pyrolysis processes were studied by thermogravimetric analysis technology.The interactions and its degree were investigated during co-pyrolysis,the kinetics was also calculated in the pyrolysis process.The results show that biomass was easier pyrolysis than the fat coal,which generated 3 times the total weight loss of the fat coal and 5 times the maximum weight loss rate of the fat coal.Their pyrolysis temperature range was overlapped slightly.In the co-pyrolysis process,the calculated values were greater than experimental values for TG curves and the deviation increased with the increase of temperature.The maximum weight loss rate was higher than the calculated values in the main pyrolysis of biomass and was lower than the calculated values in the main pyrolysis ranges of fat coal,both of above deviation increased with increasing addition of biomass.The variation both of co-pyrolysis apparent activation energy E_a and frequency factor A were inversely proportional to the amount of biomass,both of E_a and A were lower than that of biomass when the addition mass ratio is 16%.There was interaction in the co-pyrolysis process,which mainly occurred in the main pyrolysis region of biomass and fat coal,and present promotion effect and inhibition effect with the increase of temperature,which is related to chemical reaction and physical action respectively.Secondly,composition and structural characteristics of co-pyrolysis tar were analyzed separately by gas chromatography mass spectrometry,attenuated total reflection-Flourier transformed infrared spectroscopy and ¹H-nuclear magnetic resonance analysis technology.The results show that the fat coal tar was characterized by more components,more complex structure and higher pollution than that of biomass.The oxygenated and aromatic compounds accounted for more than 90%of the total tar for all samples.Some compounds containing carbonyl and methoxyl in the biomass tar were can't detected in the co-pyrolysis tar.With the increase of biomass,the oxygenated compounds showed a tendency of decreasing first and then increasing,and the degree of increase and decrease of alcohol/ester/ether were higher than that of phenol compounds.The aromatic compounds showed a tendency of increasing first and then decreasing,and the degree of benzene compounds increased a higher range.The order of aliphatic C-H stretching vibration content ranging from many to fewer was asymmetric-CH₂-,asymmetric-CH₃,symmetric-CH₂-and symmetric-CH₃-.And these functional groups showed a variation tendency of increasing,decreasing,decreasing and increasing with the addition of biomass,respectively.While the functional groups of C=O and aromatic C=C stretching vibration showed a tendency with decreasing first and then increase with the addition of biomass.Biomass tar had the largest hydrocarbon-generating potential,carbonyl contribution,aromaticity and the shortest aliphatic chain.The structural parameters showed a change tendency of increasing first and then decreasing with the addition of biomass.Compared to the calculated values,the biomass greatly promoted the formation of aldehyde C=O and carboxylic acid C=O,and had a slight inhibition effect on the aromatic C=C.These phenomena indirectly affected the aromaticity most.The classification of hydrogen protons was more accurate,causing acenaphthene and fluorene hydrogen protons to be detected in the biomass tar.The addition of biomass was beneficial to the increase of aromatic hydrogen protons and aliphatic hydrogen protons in?in tar,while opposite to aliphatic hydrogen protons in?.Finally,the crucible cokes containing biomass were prepared by crucible.The evolution of coal char structure in thermoplastic region was studied.The thermal properties and microstructure of coal char were evaluated.The results show that the strength of functional group of C=C came from co-pyrolysis coal char was lower than that of biomass and fat coal.The synergistic effect caused functional groups of C=O,aromatic ether C-O-C,phenol C-O and ester C-O-O-C stretching vibration to disappear,which indirectly increase the hydrogen-generating potential and thermal maturity,and decrease the length of aliphatic chains and the aromaticity of coal-char.The quality of bio-coke reduced compared with conventional coke.The addition of biomass makes the evolution of coal-char microstructure favorable to reactivity.