Coal- Scenedesmus Microalgae Co-Firing in a Fixed Bed Combustion Reactor: A Study on CO 2 , SO 2 and NOx Emissions and Ash.

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. [ABSTRACT FROM AUTHOR]