Experimental Study Of Biomass Pyrolysis Characteristics Based On Components Analysis

The human society is currently facing two major problems of energy shortage and environmental pollution. Development and utilization of biomass energy is one of the most important means of achieving sustainable development. Among many technologies, pyrolysis has been widespread concern. Physical and chemical properties of biomass are very complicated. Proximate and ultimate analysis methods are difficult to apply to biomass pyrolysis. Some scholars have explored biomass thermal decomposition mechanism from the perspective of cellulose, hemicellulose, and lignin. But it is still controversial whether the biomass pyrolysis behavior is equal to the simple superposition of the three components. Therefore, the main subject of this thesis is to explore the mechanism of interactions between three components and the influence to the original biomass pyrolysis characteristics. The experimental study are based on two typical biomass: pinewood, ricestraw and three components: cellulose, xylan, lignin. The mass loss of biomass could be described by superposition of three components. This thesis reveals the light gas release mechanism based on structural relationship of the three components and the influence of interactions between three components on pyrolysis tar products. This exploration provides a new way for studying biomass pyrolysis and also a theoretical basis for the application of biomass pyrolysis technologies.Firstly, we used TG-MS to investigate the weight loss characteristics superisition law of three components and biomass pyrolysis and the kinetics model. Through the comparisons of experimental results and the literature: biomass weight loss curves could not be obtained by superposition law under lower temperature (3℃00) , w hile at higher temperatures (800°C) the law could be adapted well. There were interactions between components in the original biomass. This interactions could not be ignored under lower temperature. However, the higher temperature environment provided enough energy to destroy these interactions. Thus, the error between experimental and calculated weight loss under lower temperature was lower than the higher temperature.Secondly, in order to explore the light gas(H₂, CH₄, H₂O, CO, CO₂ ) release characteristics of pinewood, rice straw and three components, experimental investigation were done through TG-MS combined with fixed-bed reactor. The contributions of three components to the biomass light gas products was studied.It was found that the side chains of xylan prone to rupture molecular gas, yield most gas. Cross-linking reaction of Guaiacyl units from lignin produce char and H2O, so yield list gas. Pinewood produced more gas than ricestraw under higher temperature because of higher lignin content. There was only one single release peak for light gas of original biomass, while there were two peaks separated from each other in the calculated MS curves. This was because that lignin surrounded the cellulose and hemicelluloses in the plant cell wall, thus hindered volatile releasing, resulting in the longer residence time, higher release temperature, an increase of gas yield. Component superimposed on the gas yield was less than the original biomass pyrolysis results, verifing the above analysis.Lastly, the pyrolysis tar of biomass and components was detected through GC-MS. Levoglucosan and its derivatives were the main cellulose-tar. The xylan-tar were furfural, ketones, acids and phenols. Lignin produced more guaiacol, toluene, xylene, etc. The most of pinewood and ricestraw pyrolysis tar came from lignin. This phenomenon could be explained by the synergistic mechanism of lignin and cellulose: small aromatictar of lignin won H radicals from levoglucosan to generate more small molecule aromatic compounds, as to levoglucosan, the loss of H radicals induced the its cracking into small molecular gas.