(615d) Co-Gasification of Sugarcane Bagasse with Cane Leaves/Tops: Role of Potassium Migration on Char Reactivity

Co-gasification of biomass with petroleum coke is known to enhance the reactivity of less reactive petroleum coke by the alkali and alkaline earth metals present in a more reactive biomass char (synergy). Since biomass species differ in their ash content and composition, there is a possibility of enhancement in the reactivity of less reactive biomass char by a more reactive biomass char during co-gasification of two different types of biomass. Also, an added incentive for co-gasification of two or more biomass is the potential improvement in the economy of scale and fuel availability. In this study, the focus is on co-gasifying two kinds of sugarcane residue, bagasse and sugarcane leaves/tops (SCT) chars. The Brazilian bagasse used in this study has a much higher content of potassium, and thus much higher overall char reactivity, than the Brazilian SCT char. Thus, co-gasification was expected to improve the reactivity of SCT char by the synergistic effect, which is the main focus of this study.

Contrary to expectations, the experimental results during co-gasification of bagasse and SCT chars showed that for conversions below 75%, the observed reactivity of the mixture is lower than the predicted reactivity based on no interaction between bagasse and SCT chars (inhibition). When the char conversion exceeds 75%, the ash from bagasse char starts to enhance the reactivity of SCT char in a mixture (synergy). The initial inhibition effect is attributed to migration of potassium from K-rich bagasse char to SCT char, followed by the reaction of some of the migrated potassium with silicates in SCT char to form inactive potassium aluminosilicates. Potassium migration was confirmed by SEM-EDX technique. Addition of SCT ash to bagasse char lowered the reactivity of bagasse char, while the addition of bagasse ash to SCT char enhanced the reactivity of SCT char. Based on these results, different flow schemes for co-processing of bagasse and SCT chars are suggested to maximize the char reactivity.