SUMMARYForest residues are renewable materials for bioenergy conversion that have the potential to replace fossil fuels beyond electricity and heat generation. A challenge hindering the intensified use of forest residues for energy production is the high cost of their supply chain. Previous studies on optimal design of forest residue supply chains focused on biofuel or bioenergy production separately, mostly with a single time period approach. We present a multi-period mixed integer linear programming model that optimizes the supply chain of forest residues for the production of bioenergy and biofuels simultaneously. The model determines (i) the location, type and size of the technologies to install and the period to install them, (ii) the mix of biofuel and bioenergy products to generate, (iii) the type and amount of forest residues to acquire and the sourcing points, (iv) the amount of forest residues to transport from sources to facilities and (v) the amount of product to transport from facilities to markets. The objective of the model is to maximize the net present value of the supply chain over a 20-year planning horizon with yearly time steps. We applied the model to a case study in British Columbia, Canada, to investigate the production of heat, electricity, pellets and pyrolysis bio-oil from available forest harvesting residues and sawmill wastes. Based on current energy generation costs in the region and the predicted operating costs of new conversion plants, the results of our model recommended the installation of small biomass boilers coupled with steam turbines for electricity production (0.5 and 5 MW) and pyrolysis plants with a capacity of 200 and 400 odmt day
À1. We performed a sensitivity analysis to evaluate the sensitivity of the optimal result to changes in the demand and price of products, as well as the availability and cost of forest residues.
Utilization of forest and wood residues as bioenergy feedstock in some remote communities could reduce environmental burdens and increase development opportunities. In a thorough bioenergy project planning, in addition to the economic performance, the potential greenhouse gas (GHG) emissions from investment alternatives should be considered. We present an economic assessment and a life cycle analysis of GHG emissions of alternative bioenergy systems, which include four combustion and gasification technologies with different capacities (0.5 MW, 2 MW and 5 MW), in two remote communities in British Columbia, Canada. In the analysis, all stages from harvesting to energy production are included, and the GHG emissions of the baseline system in each community (the current situation with all the products and services it provides) is used as the reference for comparison. Results of this study show that for small scale alternatives (0.5 MW and 2 MW), cogenerating plants using boiler/steam turbines generate the cheapest electricity, while for larger scale alternatives (5 MW), the most economical plant alternative is a gasification cogeneration system. In the community where all energy needs are currently satisfied using fossil fuels, and all biomass residues (forest and sawmill residues) are currently disposed by burning, net reductions of up to 40,909 t of CO 2 equivalent GHG emissions could be achieved with the installation of a 5 MW boiler/steam turbine cogenerating heat and electricity. In the community where the current energy mix is mostly supplied from other renewable sources (i.e. hydro), and where forest residues are disposed by burning and sawmill residues are landfilled, the net GHG emission reductions that can be achieved with a bioenergy system are considerably lower (2,535 t of CO 2 equivalent emissions with a 5 MW cogenerating gasification system) or null, since the carbon capture of current biomass disposal in landfill outweighs the carbon emission reduction of most bioenergy alternatives.
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