Study On The Combustion Characteristics Of Typical Biomass Samples

In this paper, four kinds of typical biomass fuels were studied, including red pine, corn straw, Bermuda grass and bamboo. In China, pine is one of the most widely planted woods, corn is the main crop in the north, Bermuda grass is a common lawn grass, and bamboo grows in a large area in the south, the latter three samples belong to the herbs.For the biomass studied, the industrial components and heat values were measured. Through themogravimetric analysis method, the combustion characteristics of the three stages were analyzed, including water evaporation, removal and combustion of volatile matters, and char combustion. Biomass is more likely to ignite and suitable for burning in lower temperature range, whose reaction is more intense than bituminous coal.The thermal kinetic parameters of the samples were calculated by using a first order model for the global process and for the separate stage. A modified model was proposed based on the two-stage reaction kinetic scheme, whose linear correlation of the regression curve is very good. This method is simple and accurate, which can be used to calculate the kinetic parameters of the global process for actual combustion, based on which, the activation energy was calculated to be in range of 123.4-140.3 kJ/mol.The combustion for volatile matters of biomass was treated as diffusion combustion in an open system. According to the dimensionless heat release rate and the dimensionless heat absorption rate, the impact on combustion of volatile matters from various factors was analyzed. In regards to the char combustion, the comprehensive formula of combustion rate and reaction time for the char particle was obtained. The impacts on the combustion of biomass char from internal pores and melting point were discussed.The impact on biomass combustion from water concentration was examined. The instability from moist air combustion is due to condensation and evaporation of water, which results in fluctuation of heat load in furnace. Additionally, the impact from heating rate was investigated. Thermal hysteresis occurs when the heating rate is too large, affecting the characteristic temperature, mass loss rate and the residual mass percentage. Moreover, the impact from oxygen concentration was studied. Because of high oxygen concentration, the mass transfer of oxygen to the solid layer is strengthened, volatile matters and solid fuels are burning simultaneously, making the burning rate increase while the burnout temperature decrease.The deformation temperature of corn straw and pine were obtained to be higher than 1100℃, and that of Bermuda grass and bamboo were lower than 1100℃. For Bermuda grass and bamboo, the sintering phenomena occurs when the samples are ashed at 600℃, which is more serious at 815℃. The melting point of biomass is higher for a larger ashing temperature. Lastly, the ash fusion characteristics of corn straw mixed with bituminous coal were investigated, with increasing the content of the corn straw, melting temperature is first decreased and then increased.