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2 2019

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

Nogueira Nakashima Rafael, Flórez-Orrego Daniel, Oliveira, Jr Silvio de

Journal of Power Technologies

2019

Vol. 99, nr 2

104--114

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.

Methodology for Energy Efficiency and Sustainability Improvement of Batch Production Systems on the Example of Autothermal Thermophilic Aerobic Digestion Systems

Vaklieva-Bancheva Natasha, Vladova Rayka, Kirilova Elisaveta

Journal of Ecological Engineering

2019

Vol. 20, nr 9

103--115

The present study proposes a methodology for energy efficiency and sustainability improvement of the operating conditions of batch production systems. The methodology involves applying a conventional system for municipal wastewater treatment using the process of Autothermal Thermophilic Aerobic Digestion (ATAD) of sludge. Its sustainable operation is essential for the quality of the treated sludge and the reduction of environmental impact. An analysis of the possibilities for energy integration of processes in ATAD systems was performed. The structures for indirect energy integration of processes using storage tanks and mathematical models for describing energy integration for the studied object were proposed. The models are included within a two-stage stochastic optimization problem together with constraints on the physical, technical and technological feasibility of the integration frameworks and temperature constraints with an optimization criterion minimum redesign cost. The obtained results show significant energy savings as a result of energy integration and sustainability to temperature conditions in bioreactors.