Pyrolytic topping of coal-algae composite under mild inert conditions

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

Influences of microalgae biomass on the thermal behaviour of waste coal fines

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

An investigation of the combustion kinetics of coal-microalgae composite

Coal mining and handling generate sizeable quantities of ultra-fine coal particles which are heaped as discard material. Use of the ultra-fine coal for co-firing with microalgae biomass appears to be a promising option that would improve combustion of the discard. There is no available traditional biomass binder that can be used to agglomerate, reclaim, and co-fire the discard ultra-fine coal to generate heat. In a recent research, microalgae biomass was identified as an effective natural binder for discard ultra-fine coal. Biomass is a renewable resource, and many have been co-fired on a large scale except microalgae biomass. Researchers have studied co-firing of dry mixed coal-microalgae, however, the kinetics of a wet mix of microalgae biomass and ultra-fine coal, “Coalgae®” patented recently by the Nelson Mandela University needs to be explored. The study aimed at investigating in some detail the oxidation mechanism of coal-microalgae composites. The objective is to understand the impact of microalgae on the kinetic properties of coal which will inform on the application of “Coalgae®”. It involves correlating the small and large-scale combustion properties that will establish the co-firing option on an industrial scenario. The goal is to utilize all grades of discard ultra-fine resource using microalgae biomass as binder and a renewable component which enhances the combustion of coal to supply heat and electricity. The use of microalgae for fuel preparation and upgrading is on the increase due to its high growth potential, reactivity, and ability to store energy more than other biomasses. This research hypothesized that blending of discard ultra-fine coal with live microalgae biomass would improve the kinetic properties of the coal more than expected from linear combination of the dry materials. Thermogravimetric combustion of “Coalgae®” was studied under non-isothermal conditions from 40 °C to 900°C at a heating rate of 15 °C/min and air flow rate of 20 ml/min. The thermogravimetric combustion properties i.e. small-scale was related to the large-scale, John Thompson’s fixed-bed reactor under the above condition. Thermal profiles were transformed into a differential function to reveal overlapped combustion events. The Coat-Redferns kinetic model was applied on the non-de-Ejesieme, O.V. PhD Chemistry (Research), Nelson Mandela Univ. Email: [email protected] , [email protected] convoluted reactions set to obtain some of kinetic parameters. The Fraser-Suzuki equation was used to de-convolute the overlapped combustion. Then, rate law combined with Arrhenius equation was used to derive the activation energy E a and pre-exponential factor A, while the integral form of solid states reaction model, g (∝) was applied to deduce the oxidation mechanism. The composite formed a strong and partly renewable blend under controlled temperature conditions, unlike assorted dried biomass mixed with coal. Microalgae biomass upgraded the fuel and kinetics properties of ultra-fine coal more than what was expected from a linear combination. It released heat that promoted the oxidation mechanism of the discard coal. The main effect is that the “Coalgae®” is significantly (p = 0.0570) more reactive than the coal. The co-firing approach is partly renewable and contributes to the utilization of high and low-quality available discard ultra-fine coal. It advances the combustion of coal resources and reduces carbon dioxide, CO2 emission attributed to global warming as well as preserves the natural biomass sources. The combustion of “Coalgae® “will improve economy, environment, and health, heat, and electricity supply to the society

Reclamation of ultra-fine coal with scenedesmus microalgae and comprehensive combustion property of the Coalgae® composite

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