For this study, waste coal fines were treated with live microalgae slurry at varying biomass ratios to form coal-microalgae blends. The parent samples and the coal-microalgae blends were analysed for their proximate, ultimate and calorific values. Thermogravimetric experiments were performed on the parent samples and coal-microalgae blends under inert conditions. The aim was to investigate the effects of loading live microalgae slurry onto the waste coals with respect to the overall chemical and thermal characteristics of the coal. Based on the analysed results, the blending of microalgae slurry with coal has been shown to enhance thermal decomposition of coal. Coal-microalgae blends have a higher hydrogen content and volatile matter content than coal. Moreover, the presence of microalgae results in faster rates of decomposition at lower temperatures (200–400 ºC), and lower residual mass fraction. The blending of microalgae slurries with waste coal appears to be suitable for enhancing the thermal reactivity of waste coal as well as improving the thermal conversion of waste coal.

No abstract

Combustion of South African discard ultra-fine coal (i.e. coal dust), charcoal, microalgae biomass, and composites of the three under air were studied. The study involves to find out the effect of Scenedesmus microalgae biomass on the comprehensive combustion characteristics of the ultra-fines. Coal dust is considered as waste material, but it could be modified and combusted for energy. The composites were designed with Design Expert, and unlike blending with the dry microalgae biomass, fresh slurry was blended with the ultra-fine coal and charcoal. Non-isothermal combustion was carried out at heating rate of 15 C/min from 40 – 900 ºC and at flow rate of 20 ml/min, O2/CO2 air. Combustion properties of composites were deduced from TG-DTGA and analysed using multiple regression. On combustion, the interaction of coal-charcoal-microalgae was antagonistic (b = - 1069.49), while coal-microalgae (b = 39.17), and coal-charcoal (b = 80.37), was synergistic (p = 0.0061). The coal-microalgae (Coalgae®) indicated first order reaction mechanism unlike, coal, and the charcoal. Comprehensive combustion characteristics index of Coalgae®, (S-value = 4.52E8) was superior relative to ultra-fine (S-value = 3.16E8), which indicated high quality fuel. This approach to combusting ultra-fine coal with microalgae biomass is partly renewable, and it would advance the production of heat and electricity. Key words: coal-dust, combustion, s-value, Coalgae®, renewable.

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.

Co-processing of coal and biomass has been a focus of several research studies aimed at addressing the negative environmental attributes associated with thermal processing of coal alone, as well as improving the thermal behaviour of coal. Biomass materials are regarded as a clean, renewable source, so thermal co-processing of biomass with coal is considered an effective way to utilise coal in a sustainable manner. In this study, coal fines were blended with Scenedesmus microalgae slurry to form a coal-algae composite. Pyrolytic topping of coal-algae composite was performed at 450 ºC on a batch reactor. Parent fuels and resultant chars were analysed for their proximate properties using an Eltra thermostep TGA; a Vario EL cube Elementar was used to determine the elemental composition of the chars and oils. A simulated distillation (SimDis) method was used to determine the boiling point distribution of the produced oils. The objective of the study was to examine the effects of microalgae slurry on the pyrolytic behaviour of waste coal fines with respect to product yields, composition and quality. Results showed that the yields of volatile components from pyrolysis of coal-algae composite were high compared with those from pyrolysis of coal alone. A significant degree of deoxygenation, dehydrogenation and denitrification was observed in coal-algae char than coal char. SimDis results showed that the fossil bio-crude oil has different boiling point characteristics from coal tar. The study has shown that microalgae slurry has potential to influence the pyrolytic behaviour of waste coal under mild inert conditions.