Expermental Study On Agricultural Straw Torrefaction And High-quality Applications

Biomass as a sufficient, clean energy, with high-quality applications, attracts widespread attention. However, due to the widely spatial distribution, high moisture content, low energy density and uneasy storage of biomass, the development of biomass large-scale industrialization conversion is blocked. While the torrefaction treatment can effectively reduce the moisture content and enhance the energy density. Repeatedly, the characteristics of torrefaction and the influences on pyrolysis and gasification of the agricultural straw were investigated here with the support of 973 program"The fundamental research on the conversion of biomass to high-quality fuel". It supplies important reference for the optimization of torrefaction technology. It is significance for the high-quality applications of biomass.Firstly, several typical agriculture straws were involved in to study the torrefaction characteristics and the influences of different torrefaction temperature (200,230,260 and 290℃) to the torrefaction process by using the TG- FTIR analyzer with the three components of biomass. Meanwhile, the torrefaction kinetics was analyzed by a two-step degradation mode with parallel reactions. It was found that it is mainly the dehydration of straw(<200℃) , decomposition of hemicellulose as well as the conversion of trace amount of lignin and cellulose during biomass torrefaction. The decomposition of hemicellulose was much faster than lignin and cellulose degradation. Furthermore, the torrefaction velocity increased greatly with final temperature enhancing. The gas products of the torrefaction were mainly H2O,CO2, with a small amount of C=O, C-O-C oxygenated organic carbohydrates.Secondly, the evolution properties of torrefaction products and the torrefaction mechanism was studied based on the macroscopical physical structure and microcosmic chemical composition using a fixed bed torrefaction system coupled with laser particle size analyzer,FT-IR,GC-MS and BET analyzer etc. The results showed that straw changed to brown and darker from yellow color gradually, the morphology changed from fibrous to spherical, and the particle size is much more uniform after grinding. It is benefit for the transportation and utilization of the biomass straw. Simultaneously, the oxygen content decreased obviously, while the carbon content increased distinctly, which led to the great improvement of the heating value. The porosity characteristic of straw was enhanced after torrefaction, and microscopic chemical structure indicated that the oxygen-containing organic functional groups reduced visibly, and it is great for the upgrading of biomass pyrolysis and gasification products.Finally, the influence of torrefaction on the high-quality conversion was researched with the chemical dynamics simulation and experiment. It was found that the process of biomass pyrolysis was accelerated after torrefaction, and the water and oxygen contained hydrocarbon content decreased visibly, the quality of the products were enhanced. Regards to biomass gasification, the reaction rate of fixed carbon was enhanced, and the content of CO,CH4 increased visibly(30%), the heating value of the gas raised evidently after torrefaction. Meanwhile, the combustion property was studied and the straw was more combustible, and the heating value enhanced greatly with torrefaction.It indicates that biomass torrefaction contributes greatly to the efficiency promotion of the products quality during the pyrolysis,gasification and combustion, which plays an important role in the highly efficient and commercialized utilization of biomass materials.