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UBC Theses and Dissertations

Optimization of a wood-waste fuelled, indirectly-fired gas turbine cogeneration plant for sawmill applications Zaradic, Andrea Melissa


Forests are a primary natural resource in the province of British Columbia. Harvested trees are delivered to sawmills which produce lumber for domestic and export markets, wood chips for the pulp and paper industry and large volumes of wood waste. Traditionally, wood waste has been disposed of by open incineration. The government of British Columbia has mandated that by 1996, all forms of open burning must be eliminated. In the past this form of biomass waste had very limited economic value due to its limited application and use. The most common use for forest residues was in pulp and paper mills where it was utilized as a fuel for steam boilers for generating both heat and electricity. Until recently, very little incentive existed for manufacturers of wood wastes to generate electricity and/or heat due to the very low electricity and natural gas prices. This scenario is beginning to change due to increased environmental standards. Cogeneration with wood waste, i.e. the simultaneous production of heat and electricity, is proposed as a viable alternative for supplying the heat and power requirements of a sawmill. Cogeneration has been utilized in the past, in the pulp and paper sector, but has had very limited application in the sawmill industry. In analyzing the application of a cogeneration system the amount of heat and power to be produced must be determined. In some cases, the system is sized to match the electrical power requirements, while in other cases it is sized to meet the thermal requirements. In order to achieve the best economic return from the system, both heat and power must be produced accordingly. These amounts are not intuitively obvious and an optimization technique known as linear programming has been incorporated in this analysis to determine the optimum production levels of heat and power. In general it was found that cash flow was maximized when the cogeneration system was sized to meet the thermal requirements of the sawmill. Production of electricity was not particularly attractive due to low electricity rates. The overall conclusions indicate that cogeneration is an economically attractive option for disposing of wood wastes for those sawmills which require large amounts of process heat, typically in the range of 20,000 kW (68 MMBtu/hr).

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