Cost Optimization of Ethanol Distillation
- 1. Cost Optimization of Ethanol Distillation Samantha Butler, Michael DePietro, Connor Medlang, Maxwell Miller Case Western Reverse University: Department of Chemical and Biomolecular Engineering April 25, 2016 Project Description Junior year, in Case Westerns separations course, ECHE 361, I was a member of a team that created an Aspen simulation that distilled ethanol from a multitude of different products. In particular, one of the separations was between ethanol and butanal, these two compounds form an azeotrope at the pressure we ran the columns at. For this project our professor, Dr. Jesse Wainwright, gave the group 6 different distillation sequences to choose from, each based on different heuristic characteristics, and each member of the group was tasked with simulating 1 sequence. Once all 4 sequences had been created, 1 sequence was selected to be thermally optimized to reduce the cost of building and operating that process. The PFD below gives the operating conditions for each column. Notably, no column could be run lower than atmospheric pressure, making the azeotrope somewhat difficult to separate. A brief summary of the sequence is given as follows. A five component mixture containing: acetaldehyde, butanal, ethanol, butanol, and hexanol (components volatility were given in order, with acetaldehyde being the most volatile) was feed to the 1st distillation column. Acetaldehyde was taken off in the 1st column, the 2nd stage split ethanol and butanol. The 3rd stage separated butanal from ethanol and then the heavies from column 2, butanol and hexanol were separated in column 4. The executive summary below gives a synopsis out our projects outcomes. The executive summary and PFD were taken directly from our group’s final report.
- 2. Executive Summary Our group chose to optimize and thermally integrate sequence B for part B of the project. We found two opportunities to couple the duties of condenser and reboiler pairs for sequence B (reboiler of column 1 with condenser of C4 and reboiler of column 3 with condenser of column 2) which greatly reduced the cost of the overall sequence. The initial cost of sequence B from part A was $5.15 million. By employing various thermal integration techniques, the final cost of the optimized sequence dropped 36.5% to $3.27 million. In the final design, all hot product streams were used to heat the original feed stream to reduce the cost of the cooling units that were used to cool final product streams. This thermal integration also ended up lowering the reboiler duty required in column 1. From part A, the majority of the $5.15M in part A came from the steam costs of the reboilers. To eliminate steam costs, the reboiler from column 3 was coupled with the condenser from column 2, saving $1.3M. While each column had at least one condenser or reboiler coupled with another, the main controlling cost of the system is still the steam cost for column 2. After thermal integration, the operating cost for the column 2 is $1.5M, over twice the cost of any other individual column in the sequence. The steam required to heat the reboiler for column 2 accounts for 83% of the total cost of that column. In comparison to the entire sequence, this steam accounts for 40% of the entire cost after thermal integration. Future studies into the reduction of steam costs in column 2 would be the next step in optimization of sequence B. However, $1.88M was successfully saved on sequence B through the thermal integration techniques described in detail later in this report.