Multi-component Kinetic Modeling On Biomass Pyrolysis

Biomass, mainly referring to straw, agricultural residue and firewood, has its typical feature for substituted energy production. Its utilization is an effective way to solve the increasing problem caused by energy shortage and to improve environmental protection. One important way is to convert the biomass energy thermally, in which pyrolysis is regarded as a significant technology because it acts not only as an essential step in biomass gasification and combustion, but also as an independent technology resulting in high energy density products. Because the pyrolysis of biomass, the complicated polymer, is a quite complex physico-chemical process, the basis kinetic research is applied to present the internal transformations, and therefore improve the exploitation and utilization of biomass energy finally. A summarization of the representative work on pyrolysis research for biomass and related components was given in this thesis.Experiments on pyrolysis kinetics of pure cellulose were done on a thermo-gravimetric analyzer(TGA) coupled with a Fourier Transform Infrared spectrometry(FTIR). A consecutive competitive reaction mode was obtained to describe the cellulose pyrolysis process, on the basis of stage division of thermal degradation and relevant product formation. The Broido-Shafizadeh kinetic model is widely accepted to describe the cellulose pyrolysis process, but the special cellulose pyrolysis in a close environment confirmed that the competitive-consecutive reaction mode also appeared in volatile formation, and therefore the Broido-Shafizadeh model was advanced with addition of secondary reaction of volatiles.The TGA-FTIR analysis system was also applied to pyrolysis of lignin and xylan, the modeling material of hemicellulose. Lignin behaved rather particularly both in microstructure and in pyrolysis process. A detailed analysis was made to the releasing process of major volatiles during pyrolysis process, and a two-stage global model was used to simulate xylan pyrolysis.The pyrolysis of three typical wood was analyzed on TGA-FTIR system, thermal results of which were contrasted on basis of distinct components content. On the assumption that three main components in biomass underwent individual thermo-degradation, a multi-component kinetic model was developed. The parameters in the model were obtained on thermogravimetric analysis of Pterocarpus indicus. The thermo-degradation of other two samples, Cunninghamia lanceolata and Fraximus mandshurica, was also simulated with this new model, which is well accordance with experimental result. It was confirmed that the thermal progress were related to the progressive changes of the chemical content of the wood.