Integrated anaerobic digestion and gasification processes for upgrade of ethanol biorefinery residues

摘要

The upgrading of the biorefineries residues is a possible way to increase the overall process efficiency while attaining economical revenues from wastes that otherwise would be discarded. In this sense, anaerobic digestion and gasification represent interesting alternatives to convert organic residues into biofuels, electricity or other bioproducts. However, few studies have explored energy integration possibilities between those options or evaluated various final product pathways. Thus, in this work, various scenarios aimed at capitalizing the main residues of the sugarcane ethanol industry (vinasse and bagasse) are investigated. Two process layouts combining anaerobic digestion and gasification are proposed for each desired product (methane, hydrogen or power). The highest exergy efficiency (48%) was obtained for the configuration focused on methane production and using a combined cycle, since it requires fewer resources and separation steps to convert feedstock into exportable products. On the other hand, exergy was primarily destroyed in vinasse disposal, since a significant fraction of its organic wastes are inert to anaerobic digestion, followed by the bagasse gasifier and utility systems, due to the irreversible reactions occurring in these processes. In short, this study points to some improvement opportunities and reinforces the advantages of the waste capitalization concept.