No abstract

This study investigated the effect of coal–Scenedesmus microalgae (with blending ratios of 100:0 (coal), 95:5 (Coalgae® 5%), 90:10 (Coalgae® 10%), 85:15 (Coalgae® 15%) and 80:20 (Coalgae® 20%)) on combustion temperature, mass loss, the formation of CO2, SO2 and NOx gases, and ash content under constant atmospheric air flow. Coalgae® refers to a material formed after blending coal and microalgae. The results showed that NOx came mainly from Coalgae® 10% and 15%, and this observation could be attributed to a variable air concentration level (O2 level) in the environment that could influence NOx during the combustion process, irrespective of the blending ratios. CO2 emission reductions (12%, 17%, 21% and 29%) and SO2 emission reductions (3%, 12%, 16% and 19%) increased with the increasing coal-microalgae blending ratio (Coalgae® 5–20%), respectively. Bubble-like morphology was observed in the ash particles of coal–microalgae blends through SEM, while the TEM confirmed the formation of carbon-based sheets and graphitic-based nanocomposites influenced by the microalgae amounts. Ash residues of the coal–microalgae blends contained high amounts of fluxing compounds (Fe2O3, K2O, CaO and MgO), which resulted in an increased base/acid ratio from 0.189 (coal) to 0.568 (Coalgae® 20%). Based on the above findings, the co-firing of coal–Scenedesmus microalgae led to a reduction in CO2, SO2, and NOx emissions. As such, lower Coalgae® blends can be considered as an alternative fuel in any coal-driven process for energy generation.

No abstract

South Africa is heavily depended on coal to meet its energy requirements. There is therefore a significant incentive to develop and implement clean coal combustion technologies that would reduce the environmental impact of energy generation from coal. For power generation, the co-firing of renewable biomass fuels at conventional coal-fired power stations is recognised as one of the lowercost, lower-risk options to achieve significant greenhouse gas (GHG) emission reductions. The aim of study was to evaluate the GHG emission reduction potential through the co-firing of coal and microalgae biomass. Coal to microalgae mass ratios of 95:5 and 90:10 were prepared, combusted in a fixed-bed reactor and compared to pure coal. The emission concentration of CO2 (%), NOx (ppm) and SO2 (ppm) of coal and Coalgae ® blends (a composite material containing coal and microalgae biomass) were measured during the combustion of the three materials using Lancom 4 portable flue gas analyser. The results have shown significant reduction in CO2, SO2 and NOx levels when Coalgae ® was burned. Emission reductions of 8.4%, 17.5% and 10.4% for CO2, SO2 and NOx were achieved with Coalgae ® 5%, respectively. Reductions of 10.7%, 21.4% and 15.4% for CO2, SO2 and NOx were achieved with Coalgae ® 10%, respectively. Moreover, the combustion efficiency of Coalgae ® was maintained at 97.60% slightly below 99.26% (1.7% difference) obtained from the pure coal. Based on the above findings, the co-firing of coal and microalgae biomass was necessary for the reduction of GHG emissions. As such, Coalgae ® can be considered as an alternative fuel in any coal driven process for energy generation.