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Thermochemical conversion of cashew nut shells, palm nut shells and peanut shells char with CO2 and/or steam to aliment a clay brick firing unit

Diedhiou, Ansoumane, Ndiaye, Lat-Grand, Bensakhria, Ammar, Sock, Oumar
Renewable energy 2019 v.142 pp. 581-590
activation energy, baking, biomass, bricks, carbon, carbon dioxide, cashew nuts, clay, equations, gasification, heat, models, particle size, peanut hulls, peanuts, renewable energy sources, steam, temperature
Experimental gasification studies are reported for highly reactive peanuts, palm and cashew nut shells chars from Ziguinchor area in order to aliment a local clay brick baking unit. The gasification tests were operated in a fixed bed reactor under steam and/or carbon dioxide at three different temperatures (950 °C, 1000 °C and 1050 °C), in order to investigate the experimental conditions of three samples at different particle size. The gasification of char conversion at different temperatures is found to be dependent on gasifying agent, nature of the sample, and can be explained by the Arrhenius equation, thus suggesting the use of three different models: Volume Reaction Model (VRM), Random Pore Model (RPM), and Shrinking Core Model (SCM) in order to interpret the carbon conversion data and to determine the kinetics parameters.From the results obtained, temperature has a positive effect on the kinetic conversion. Further, the gasification under mixed atmosphere of steam and carbon dioxide showed that the reactivity of the different chars depends on the increase of steam concentration in the mixture. The gasifying char types has some effects in the determination of the kinetic parameters (activation energies obtained ranged between 110 and 126 kJ/mol for peanut shell, 104–125 kJ/mol for the cashew shell and 116–150 kJ/mol for the palm shell). By using different models, the experimental results shows that the kinetics reaction of the cashew shells char, and peanuts shells char, are faster than those from palm shells char. At the same time, results showed that the char-steam reactivity, char - CO2 reactivity and their mixture (char-steam and char - CO2) are different. The experimental measurements also show the influence of temperature on the Lower Heating Values (LHV) of the gas. The LHV of gas obtained are between (8–12 MJ/Nm3) and that, these values (LHV) are inversely proportional to the particles size of the biomass. While, based on the Europe Environment and Energy Management Agency (ADEME) standards on Lower Heating Value of gas, these gases obtained under all experimental conditions can be safely used to operate motor functioning with to gas.