This is the simplest modelling approach in that the model is based on the overall mass balance as shown in equation M.1.

biomass — > a char + b liquid + g gas M.1

Such model provides a simple stoichiometry specific to the reactor conditions used and are therefore highly specific and of limited use. functional or empirical relationships between yield and the process parameters may be derived but requires a substantial amount of experimental data.

2.3.3 Kinetic Modelling

Kinetic models are usually derived from particles with the hope that the Arrhenius type equations derived will represent the intrinsic reaction rates of pyrolysis. With small particles mass transport effects will be minimal and may therefore be neglected.

The complexity of the pyrolysis process implies that there are numerous homogeneous and heterogeneous reactions occurring either simultaneously and/or consecutively depending on the reactor conditions. Kinetic modelling is

therefore an attempt to represent the overall kinetics as individual reaction pathways are very difficult to determine.