Coal-Scenedesmus Microalgae Co-Firing in a Fixed Bed Combustion Reactor: A Study on CO2, SO2 and NOx Emissions and Ash
Nokuthula Ethel Magida, Gary Dugmore, Adeniyi S. Ogunlaja
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.