CO2 Gasification of Sugarcane Bagasse Char: Consideration of Pyrolysis Temperature, Silicon and Aluminum Contents, and Potassium Addition for Recirculation of Char

In sugarcane bagasse gasification, char recirculation to the gasifier improves the syngas quality and process efficiency. To determine the effect of char properties on the reaction kinetics, in this work, the pregasification pyrolysis temperature, particle size, and catalyst (potassium) loading were varied. Char samples were prepared at 750–900 °C via pyrolysis and gasified isothermally in a thermogravimetric analysis unit at 850 °C with CO2, and gasification data were modeled using the random pore and extended random pore models. Increasing pyrolysis temperatures did not affect the char morphology and surface composition but did reduce the surface area, as determined by N2 adsorption, decreasing initial gasification rates, and the overall fitted rate constants. Reduction of the particle size via ball milling decreased the time required for complete conversion and changed the shape of the rate versus conversion curves from monotonically decreasing to concave down. The char sample prepared via pyrolysis at 900 °C was an exception, having a maximum rate at ∼10% conversion without ball milling. After ball milling of the char sample prepared at 750 °C, there was an accumulation of ash (Al and Si) on the surface of the particles and a reduction in the surface area, consistent with the ash blocking pores—the porosity in these samples increased during the initial stages (up to ∼20% conversion) of gasification. The gasification behavior was generally well modeled by the extended random pore model. Although the addition of KOH (K/Al mass ratio ∼ 0.2–1.25) enhanced the gasification rates, too much K—from the addition of KOH or after 90% conversion—created mass-transfer limitations resulting in lower gasification rates.
potassium, reaction products, adsorption, pyrolysis, Gasification