School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemModelling and control of emission from wood flake drying plant( 1999)Factors contributing to emissions from wood flake drying plant were examined and a model constructed of their interdependence. Stack condensate analysis indicated that the emission constituents originate from three different sources: • organic compounds originally present in wood, • products of dryer firebox combustion, • products resulting from the thermo-degradation of wood particles due to overheating. The general condition of the wood flake dryer, whether it exceeded the design capacity of the dryer, the operational regimes used for drying and the choice of fuel all determined the type and the amount of emission. Drying simulations comprising four series of experiments, chemical analysis of the products of thermo-degradation, statistical analysis and mathematical modelling indicate an interdependence of drying temperature, initial moisture content, final moisture content, flake particle size and the residence time. Formation of the products of thermo-degradation of wood including the condensable liquid phase, non-condensable gases, and the solid residue can be predicted when the reaction rate and the reaction input parameters are known. When wood particles are sufficiently small, energy flux high and heat transfer promotes the exothermic type of reactions, conditions for flash pyrolysis may be reached. The mathematical model derived from the simulation experiments may be applied to evaluate different feedstock behaviour during the process of flash pyrolysis. The chemistry of pyrolysis is complex. Small variations in reaction time or temperature radically alter reaction outcomes. The desired products and their relative proportions are obtained from a very narrow-band of control parameters. The theoretical model was used to construct an experimental design for undertaking research into flash pyrolysis. This consisted of: • chemical analytical work, • bench pyrolysis reactor experimentation, • pilot plant design, • commercial implementation. The mathematical model can be used for solving environmental emission control problems, for designing pyrolysis reactors and optimising the production of fine chemicals from flash pyrolysis, which in the past were only obtainable from petroleum.