Determination of pyrolysis temperature for charring materials

An energy and mass balanced method of determining the pyrolysis temperature is proposed. The concept is to find the pyrolysis temperature that consumes the same amount of energy to produce the same amount of mass when using the pyrolysis front model as when using finite rate kinetics models for the entire charring process. The resulting pyrolysis temperature has the form of pyrolysis rate weighted average temperature. Comparisons between finite rate kinetics and pyrolysis front models for various boundary conditions, geometries, heats of decomposition, kinetic parameters and assumptions used in the literature were made to assess the proposed method. Models using energy and mass balanced pyrolysis temperature show good agreement with finite rate models and the experiments. Extensive numerical studies on various factors influencing the charring material pyrolysis show that heat flux, sample size, heat of decomposition and kinetic parameters are the most important factors for determining an appropriate pyrolysis temperature. Thermal conductivity, specific heat and density have a lesser effect on the pyrolysis temperature. For practical application, a non-dimensional correlation is developed to determine the appropriate pyrolysis temperature without solving the problem by using finite rate models. With this correlation the energy and mass balanced pyrolysis temperature can be determined with a standard deviation of 7.6 K. These predictions are validated by comparison with measurements of wood cylinder pyrolysis. A good agreement suggests that simpler pyrolysis front models yield practically useful and accurate results given an appropriate pyrolysis temperature.