Abstract
In this work, the co-pyrolysis of coal and algae is explored with special emphasis on decomposition kinetics and the possibility of the existence of synergistic effects. Modelling and kinetics analysis based approaches were used for the investigation of the existence of synergistic effects. The co-pyrolysis kinetics was studied using the model-free, Coats–Redfern integral method. The kinetics were evaluated for 1st and 2nd order reaction models. Results reveal that Scenedesmus microalgae is characterised by a two stage decomposition process that occurs at temperature ranges of 200–400 °C and 500–700 °C with activation energy of 145.5 and 127.3 kJ/mol, respectively. Bituminous coal has a two stage, slow decomposition process that occurs at temperature ranges of 400–700 °C and above 750 °C with an activation energy of 81.8 and 649.3 kJ/mol, respectively. Furthermore, co-pyrolysis of coal and microalgae is characterised by three stages whose kinetics are dominated by the pyrolysis of the individual materials. For the studied range of coal/algae ratios, the three pyrolysis stages occur in the approximate temperature ranges of 200–400 °C, 430–650 °C and above 750 °C, with activation energies in the ranges of 131–138, 72–78 and 864.5–1235 kJ/mol, respectively. Modelling and kinetics study showed that there is strong evidence of interactions between coal and microalgae that manifest as synergistic effects especially in the second and third stages of decomposition.
Highlights
The use of coal as the main energy source is expected to decline due to two major reasons
Results reveal that Scenedesmus microalgae is characterised by a two stage decomposition process that occurs at temperature ranges of 200–400 °C and 500–700 °C with activation energy of 145.5 and 127.3 kJ/mol, respectively
23.4 high hydrogen to carbon (H/C) ratio of biomass generates more hydrogen and other light compounds that interact with coal
Summary
The use of coal as the main energy source is expected to decline due to two major reasons. Biomass is a promising alternative commercial fuel source but has a major drawback due to its low energy density This has inspired a number of studies on the simultaneous use of coal and biomass such as co-pyrolysis (Meesri and Moghtaderi 2002; Kirtania and Bhattacharya 2013; Azizi et al 2017; Baloyi and Dugmore 2019). The Coats–Redfern method is a common model fitting technique that can be used to evaluate kinetic parameters from a single mass loss curve if a reaction order is guessed accurately (Coats and Redfern 1964; Ebrahimi-Kahrizsangi and Abbasi 2007; Ramukutty and Ramachandran 2014). The Coats– Redfern model fitting technique will be used for this study
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