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Life Cycle Analysis Issues on Separation and Dehydration Steps of Bio-Ethanol Production

Life Cycle Analysis Issues on Separation and Dehydration Steps of Bio-Ethanol Production

Authors: 
Colombo, M. - Presenter, Universidad Nacional de Tucuman
Mele, F. D., Universidad Nacional de Tucuman
Gatica, J. E., Cleveland State University
Hern√°ndez, M. R., Universidad Nacional de Tucuman
Bio-ethanol production is a rapidly growing market due to the possible uses of the anhydrous product in energy generation. This production however, is weighed down by energetic demands and environmental effects.

A new chapter for bioenergy products associated with sugar manufacturing was opened from the Law 26.093 of biofuels and the requirement to mix gasoline with 5 % ethanol. In this new scenario, particularly ethanol production is a large consumer of energy and generates large quantities of effluent with high organic load and high salt content. This situation is very difficult to solve because Tucuman’s soil has also high salt content, so it is necessary to redesign processes configuration, using tools like simulation and optimization that allow a systematic analysis leading to obtain the best combination the process variables.

This paper examines the distillation and dehydration steps of a bio-ethanol production plant complementing a sugar mill. The distillation step is optimized by performing rigorous energy analysis and heat integration on the process utilizing the resources made available by the sugar mill, while an ad-hoc pervaporation module is used in the dehydration step.

Also, we have analyzed the situation in a classic distillery of Tucuman using the UniSim® simulator. Alternative schemes of varying complexity are proposed for reducing energy consumption and effluent generation. To this end, it has been proposed an approximate index of environmental impact, which combines power consumption with effluent generation, and it has been used as objective function for the optimization of operational variables seeking for an operating window with lower energy consumption and environmental impact.

The explicit consideration of environmental issues offers an alternative route to explore trade-offs between environmental and economic aspects. In this regard, Life Cycle Assessment (LCA) is used in this work with the support of SimaPro® software. This approach belongs to a research line that has been growing a few years ago with the aim at designing more sustainable processes (Guillén-Gosálbez et al., 2008).

In this paper, a life cycle analysis is performed on the distillation and dehydration steps of a bio-ethanol production plant complementing a sugar mill. The two parts of the process are first studied and optimized independently, heat integration is performed on both steps, the two are then combined and a life cycle analysis is performed on the resulting process.

The results of this LCA analysis are compared with the results provided by the approximate index of environmental impact, in order to validate its use in this process.

Alternative schemes that meet the same specifications of purity and recovery in effluent streams are examined in this paper. Of particular relevance is the assessment of costs and environmental impact of these processes. A baseline case is defined in our case-study, and structural and parametric changes are made. Different scenarios with respect to economic and environmental issues are proposed taking into account the specifications of the final product. Near-optimal scenarios are formulated by defining an operating window for some of environmentally friendly technologies available. The impact of different operating policies for the production of anhydrous alcohol on the environment is examined in detail.

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