Feasibility study of biomass-based combined heat and power project in Canadian sawmill plant

This aim of this dissertation is to investigate the feasibility of biomass-based CHP generation at a specific sawmill located in Alberta, Canada. Although sawmills consume a relatively modest amount of energy compared to other heavy industries, they are uniquely positioned to benefit from combined heat and power (CHP) systems: a ready supply (in many cases an excess of) cheap fuel fiber is available as a by-product of lumber production; the heat produced can be used in the lumber drying process and the electrical energy generated can be used directly in mill operations or exported to the grid for profit; the entire process can reduce mill GHG emissions and generate additional revenue in the form of carbon credits. The focus of this paper is to understand and quantify energy use and excess biomass availability at the West Fraser Timber Ltd. sawmill in Sundre Alberta, conduct a technical review of biomass conversion and power generation technologies for the mill, and use this knowledge to carry out a technical and economic feasibility study to determine the best overall CHP project for the site. The Sundre sawmill has a considerable inventory of residuals on site: like many sawmills in Alberta, the combination of changing markets, a slow economy and increasingly stringent environmental regulations have created challenges for Sundre around wood waste utilization and disposal. Technologies exist to deal with this situation: Sundre’s existing direct combustion furnace with thermal fluid heat transfer (TFH) system has capacity to consume surplus fibre; other newer, more advanced technologies such as gasification are also able to efficiently and cost-effectively convert biomass to heat for power generation. Organic Rankine Cycle (ORC) engines are shown to be economical in utilizing excess thermal energy from these TFH’s to produce electrical power. However, most other power generation technologies utilizing biomass as feedstock are not feasible for Sundre due to the requirement for complex and costly biogas cleaning (for internal combustion or gas turbine engines) or high operating costs and an inability to cost-effectively size for the site (steam turbines, Stirling engines). This paper shows that an ORC installation in the range of 1.5MW is economically attractive for Sundre. If feedstock supply increases significantly in the future (due to mill expansion, market changes or equipment changes), it is marginally viable to add more TFH capacity (either furnace or gasification style) to utilize this feedstock. It was noted however that careful consideration must be given to fibre allocation to the CHP system to ensure high-value sales revenues are preserved and return on investment is maximized