Prediction of concentration in the pyrolysis of biomass material. II

In this work, a prediction of concentration profiles in the case of pyrolysis of different lignocellulosic materials in isothermal and non-isothermal conditions has been made. The operative temperature ranges from 573 to 973 K for isothermal conditions and, for non-isothermal conditions, the heating rate ranges from 5 to 80 K/min. Concentrations for these conditions were previously predicted by Srivasta et al. for various biomass components, viz. cellulose, hemicellulose and lignin. Based on the concentration profiles of different biomass materials, it was possible to predict pyrolysis behavior over a wide range of temperatures under isothermal and non-isothermal conditions for a large number of biomass materials. The simulation model utilizes a fourth order Runge-Kutta Predictor-Corrector method to solve the coupled ordinary differential equations. Based on thermogravimetric analysis done elsewhere by Koufopanos et al., it was observed that temperature and time have a linear relationship. The above technique enables the prediction of concentration profiles of different biomass materials for the entire range of pyrolysis. In the earlier mathematical model of Srivastava et al., the concept of an “intermediate” was introduced, which was very difficult to define physically. Consequently, it was not possible to measure this concentration experimentally. Therefore, another mathematical model has been developed elsewhere by Srivastava et al. without utilizing the concept of an intermediate. Instead, char and volatiles are considered to have been formed in an intermediate stage and converted to char and volatiles of different types. The concentration profiles were predicted using the same numerical scheme used earlier for a particular type of biomass for which experimental kinetic data were available in the literature.