Modelling of pulverised wood combustion using a functional group model

Modelling of pulverised wood flames in a laboratory vertical furnace was carried out. The aim was to gain deeper understanding of the combustion process and to validate a mathematical model to simulate the process. Pulverised wood combustion involves many different processes such as two-phase flow dynamics, drying and devolatilisation of the particles, oxidation of the volatile and formation and oxidation of char. It is desirable to know which are the most dominating/sensitive processes that control the combustion behaviour and in particular the emissions of unburned hydrocarbons and carbon monoxide. To achieve this goal, a comprehensive devolatilisation model based on the functional group concept is applied to predict the details of the devolatilisation products including tar. The solid-gas coupling is made using the Eulerian/Lagrangian approach. A ‘rocket force’ model is developed to account for the influence of drying and devolatilisation on the particle motion. The present mathematical model successfully simulated the flame temperature and detailed species distributions including CH4 and CO. These two species were shown to be sensitive to the fate of tar. Major paths for the CO formation were identified as the devolatilisation of the wood particles and the char oxidation. Influences of the initial functional group yield, the char oxidation and gasification reactions, the turbulence mixing rate and the fuel particle size on the flame structures andb emissions were examined.

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