Energy considerations for a SSF-based softwood ethanol plant

Area of Science:

• Biomass Conversion
• Chemical Engineering
• Sustainable Energy

Background:

• Ethanol production from softwood via steam pretreatment and simultaneous saccharification and fermentation (SSF) is established.
• Low final ethanol concentrations in SSF lead to high energy demands in downstream processing.

Purpose of the Study:

• To technically and economically evaluate alternatives for reducing energy consumption in softwood-to-ethanol downstream processing.
• To model and optimize the overall process for cost-effective bioethanol production.

Main Methods:

• Process modeling using Aspen Plus based on experimental data.
• Technical-economic evaluation using Icarus process evaluator.
• Comparison of a base case (distillation and multi-effect evaporation) with alternatives like mechanical vapor recompression and anaerobic digestion.

Main Results:

• The base case process (3.5% ethanol feed) required 19.0 MJ/L steam and cost 4.14 SEK/L.
• Mechanical vapor recompression and anaerobic digestion alternatives reduced steam demand to 10.2 MJ/L and 9.8 MJ/L, respectively.
• These alternatives lowered production costs to 3.82 SEK/L and 3.84 SEK/L, respectively.

Conclusions:

• Mechanical vapor recompression and anaerobic digestion are promising alternatives for reducing energy consumption and production costs in softwood ethanol production.
• Optimizing downstream processing is crucial for the economic viability of bioethanol from lignocellulosic feedstocks.