Co-combustion Characteristics of coal-Scenedesmus Microalgae Blends and Their Resulting Ash

This study investigated the combustion behavior and evolved greenhouse gases of coal, Scenedesmus microalgae, and coal-Scenedesmus microalgae blends (Coalgae® 5–20%) in air using a thermogravimetric analyzer (TG)-mass spectrometer (MS). Coalgae® refers to a blend of coal fines and microalgae biomass. TG-DTG curves of coal and microalgae confirmed that the combustion behavior of these materials were different. Scanning Electron Micrograph (SEM) morphology images of ash obtained from the combustion of coal and Coalgae® 5–20% confirmed changes in devolatilization and combustion behavior of solid raw fuel. A significant reduction in activation energy of 160.4 kJ/mol, 159.6 kJ/mol, 151.3 kJ/mol, and 134.2 kJ/mol for Coalgae® 5%, Coalgae® 10%, Coalgae® 15% and Coalgae® 20%, respectively, compared to coal (161.3 kJ/mol) was achieved. The lowering of activation energy could be attributed to the relative decrease in fixed carbon. MS data presented a decrease in the emissions of CO₂ (m/e 44), NOx (NO: m/e 30 and NO₂: m/e 46) and SO₂ (m/e 64) from coal to Coalgae® 5–20% due to the complex combustion mechanism in the presence of radicals. The Coalgae® blends showed a synergistic effect due to different combustion characteristics of coal and Scenedesmus microalgae. The results obtained from this work provide a reference to further work on co-combustion of coal and microalgae to some extent.