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Impacts of retrofitting analysis on first generation ethanol production: process design and techno-economics


More than half of the bioethanol plants in operation today use corn or grains as raw materials. The downstream processing of mash after fermentation to produce ethanol and distiller grains is an energy-demanding process, which needs retrofitting for optimization. In addition, the fluctuation in the ethanol and grain prices affects the overall profitability of the plant. For this purpose, a process simulation was performed in Aspen Plus® based on an existing industrial plant located in Sweden. The simulations were compared using different scenarios including different concentrations of ethanol, using the stillage for biogas production to produce steam instead of distiller grains as a by-product, and altering the purity of the ethanol produced. Using stillage for biogas production, as well as utilizing the steam, reduced the overall energy consumption by 40 % compared to the plant in operation. The fluctuations in grain prices had a high impact on the net present value (NPV), where grain prices greater than 349 USD/ton reached a zero NPV. After 20 years, the plant in operation producing 41,600 tons ethanol/year can generate a profit of 78 million USD. Compared to the base case, the less purified ethanol resulted in a lower NPV of 30 million USD.

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Dried distillers grains with soluble


Total solids


Net present value


Payback period


Cumulative cash position


Non -fermentable dissolved solids


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The authors would like to thank the Swedish Energy Agency for their financial support and Lantmännen Agroetanol AB, Sweden for sharing the data of the plant. We also acknowledge Thomas Södergren for his computer support.

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Correspondence to Karthik Rajendran.

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Rajendran, K., Rajoli, S., Teichert, O. et al. Impacts of retrofitting analysis on first generation ethanol production: process design and techno-economics. Bioprocess Biosyst Eng 38, 389–397 (2015).

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  • Process design
  • Retrofitting analysis
  • Ethanol
  • Aspen plus
  • Techno-economic analysis