UBC Theses and Dissertations
Logistics of wood chips supply and performance analysis of an industrial updraft gasifier Oveisi-Fordiie, Ehsanollah
In the published literature, there is a lack of detailed data relevant to full-scale gasification plants that operate on variable quality of biomass feedstock, especially those originating from urban sources. The objectives of this study are to characterize the spatial and temporal variations in the physical properties of waste wood supplied to the UBC industrial gasification system; and to conduct an analysis of variations in fuel properties vs. gasifier performance in terms of system reliability, steam production, syngas quality, tar formation, and gasification efficiencfy. The measured values of fuel properties were in compliance with the fuel specifications. Large variation in steam production during the earlier years of operation was attributed partly to the variations in feedstock moisture content and particle size. Subsequent data collection and analysis revealed that fuel moisture content affects the production of steam the most. Fuel moisture content (mc), gasifier bed temperature, and fuel feeding rate were identified to be the key factors that affect syngas quality, tar formation, and gasifier efficiency. Multi-variable regression models were developed to quantify these relationships. Despite a wide variation of the data collected from the industrial gasifier, our results are in line with the trends reported in the literature based on lab-scale and pilot-scale studies. Research findings indicated that even for a commercial updraft gasifier, syngas quality and steam production would be enhanced if the fuel moisture content could be maintained around 20% (wb). With air as the gasifying agent, when fuel moisture content decreased to 20%, the carbon monoxide (CO) concentration (~30%) and calorific value (>4 MJ/m³) would be higher, whereas tar concentration (<60–70 g/m³) would be lower. This near-optimal level of fuel moisture content (20% wb) is recommended for the operation of BRDF. The 20% mc also coincides with the typical equilibrium moisture content of air-dried wood fuel under ambient air conditions in Vancouver if the fuel is protected from rain. As such, high temperature drying of the wood chips can be avoided for saving energy. The higher CO concentration in syngas is also beneficial when the syngas is used to produce other industrial and chemical products.
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