Measurement of char burning kinetics of torrefied biomass with imaging two-colour pyrometry: Statistical burning rates of non-spherical particles

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Co-firing of biomass is a promising concept to reduce CO2-emissions from pulverized coal fired power plants. However, the use of raw biomass in pc-boilers is limited due to several problems. The fibrous structure of the most biomasses reduces their ability to be grinded into typical particle sizes, so that larger particles (in the range of millimetres, coal dust particles: 100 µm) with large aspect ratios appear. Furthermore, the heating value is lower than that of most coals, and the elementary and proximate composition is different from typical coal properties. A possible solution to shift a biomass into the property range of coal is the torrefaction process. In this process, thermochemical treatment is used to change the structure of biomass, so that the heating value and the carbon content increase and the grinding properties are improved.Sound design of pc-boilers requires detailed knowledge of the reaction rate of solid carbon, as this step dominates the particle conversion and energy release. The measurement of reaction rates of single burning torrefied biomass particles will be carried in a flat flame burner with a laminar gas flow. The necessary parameters, particle temperature, diameter and shape, will be measured with a high speed imaging two colour pyrometer. The measurement of temperature and diameter of burning particles enables to calculate the energy balance around single burning particles and to calculate burning rates and global burning kinetics of the cahr burning process. Scope of the project is the derivation of reaction rate parameters for the char of torrefied biomasss. For the first time, the particle shape will be considered, which is necessary especially for larger particles with high aspect ratios, which is typical for biomass particles. A statistical approach will be used to consider for the parameters of the kinetic models used here. The experimental data will include all stages of char burning in respect of reduced burning rates with proceeding burn out.