Implementation of a Fixed Bed Solid Fuel Combustor for the Purpose of Macroalgal Biomass Co-firing Studies

Abstract

Coal-fired power plants represent the majority share of fossil fuel based electricity generation facilities. Due to their numerous negative environmental impacts, however, they are targeted for reduction and eventual replacement. Algal biomass is a promising third generation biofuel that could reduce coal usage through co-firing in the near future and possibly replace coal in the more distant future. Unlike another popular co-combustion biomass, woody biomass, little is known about direct algae firing and co-firing. As a result, a solid fuel combustor is created and instrumented with the intent of burning pelleted mixtures of pine, macroalgae, and coal in order to determine algae’s properties as a direct firing and co-firing fuel. In keeping with this vision, a normalization study is conducted using various mixtures of pine and algae, finding that increasing algae content yielded higher exhaust temperatures with more nitrogen oxides and sulfur oxides emissions than pine. Emissions of carbon dioxide are reduced with increasing algae content, however. A normalization study is also proposed using coal-biomass fuel blends, but technical issues required that a separate accelerant study be made. It is found that 10 mL of petroleum distillate added to the fuel just before attempting ignition greatly improved the combustion characteristics of the coal-containing pellets. However, increased air flow rates from the biomass mixtures are also required to begin shifting the coal-containing mixture to thorough and complete combustion. The adjustments to the air flow rates provided to the burner prompted further modifications of the setup and the experimental procedures to ensure the safety and sustainability of the experimentation. An optimization study is also begun, yielding a simple but accurate mass burned calculator that can be used to augment and improve further experiments. Tangent to this optimization study is a flow validation study which ultimately failed in its intended goal of validating the Alicat reported air flow rates. Despite its difficulties, however, this study provided significant insight regarding the sizing and design of the pipe diameters and lengths employed in a Pitot-tube based system.