Innovative Dual Distillation Column Design Enables 91% Ethanol Extraction

A creative two-skids-in-one design allows client to fit a critical distillation system in tight plant footprint.

CLIENT: Fortune 500 Company

INDUSTRY: Alternative Energy

KEY ENGINEERING FEATURES:

• Two distillation columns, comprised of five spools each, rated for 15psig at 250 degrees Fahrenheit
• Reflux loops to achieve higher concentrations of ethanol
• Hot oil system for evaporation of ethanol mixture
• Heat exchanger between reject heat and incoming cold product
• Hydrotesting for entire system to check for leaks
• FEA analysis on skid frame and load bearing members
• Vacuum pump integrated in the design. Lowers required energy inputs by creating a vacuum inside the distillation columns

CORE CHALLENGES:

• Restricted space for skid and a difficult delivery path including several 90 degree turns
• Distillation column design – skid was designed as two separable pieces for individually placement, but worked together to complete the distillation process. Precise measurements for diameter & height and piping & equipment placement were key.
• Distillation modeling and scale-up based on lab data
• Time constraints – distillation system was fabricated as part of a larger system that was simultaneously built through EPIC’s modular process multi-timeline schedule

AN EPIC SOLUTION

Front-End Engineering/Distillation Column Design Engineering

During our proprietary Front-End Engineering (FEE) stage, EPIC reviewed the client provided lab-scale testing data and piping and instrumentation diagrams (P&ID’s). EPIC collaborated with the client to find the correct distillation system layout and made necessary changes to the provided P&ID’s.

A critical visit to the future installation site was completed by EPIC’s project manager and lead CAD designer. Precise measurements for the skid had to be taken due to a tight and complicated installation path. The project engineer had to navigate the installation path for the skids’ final destination. The rigging plan included:

• An immediate turn was required after initial lift
• The system was transported beneath two separate pipe-racks
• Three 90 degrees turns with pass through of a door and hallway.
• Installation between rows of pre-existing tanks
• Tight fit between rows of pre-existing tanks
• Fit tightly to wall for maximum floor space

A two-part design was developed after the initial visit, allowing the system to be split into two independent skids for installation. The system appears to be one seamless skid when fully installed, but can be separated into two independent parts with a few minor changes. Column diameter and height, piping locations and equipment placement were carefully planned for the space and dual-skid parameters.

Detailed distillation column design began after FEE was completed and contract awarded.

Distillation scaleup & modeling were completed by EPIC’s expert distillation consultant, Terry Tolliver. Skid design and layout was finalized by EPIC’s project manager based on the modeled process and experience with similar projects. A Finite Elemental Analysis (FEA) check was performed by an independent source to confirm the skids ability to bear load and stress, especially during installation.

EPIC made the following recommendations during FEE and detailed distillation column design:

• A two column design, with five spools, to achieve the purity of desired ethanol
• Off-site modular skid fabrication performed inside EPIC’s advanced fabrication shop, to ensure quality and safe skid fabrication. The intended installation space was too small to fit equipment, piping, welders, and crew safely.
• A two-part skid that could be split for shipment and installation
• 4.5 psia vacuum in the columns to lower the energy requirements to achieve distillation
• Complete system hydro-testing for leak detection to ensure a constant vacuum
• FEA analysis to certify structural integrity of the completed distillation skid
• Reflux loops on both columns to achieve a higher concentration of ethanol
• Temperature sensors at specific points in the column to monitor temperature profiles per client request.
• A hot-oil system to facilitate evaporation for distillation. Hot oil requires less energy input to reach the required 400 degrees Fahrenheit temperature than alternatives (ex. steam heat).
• A heat exchanger that pre-heats cold solvent entering the first column with heat recycled from hot solvent leaving the column

THE FINAL SOLUTION

A ternary ethanol mixture is fed into the first column and is heated as it falls. Water and ethanol rise to the top of the column and leave as distillate. The remaining ternary solution falls to the bottom of the column and is circulated through a heat-exchanger loop. Fresh solvent is pre-heated before entering the column and reject solvent is cooled before heading to a holding tank.

Water and ethanol are separated, based on boiling point, in the second column. Ethanol leaves the second column as distillate at the top of the column and enters a condenser. Condensed ethanol is sent to a holding tank and leaves the distillation skid.

Reflux loops are used in both columns to cycle the mixture through several intervals. This creates a higher concentration of ethanol in the condenser at the end of the process. A 91% ethanol mix is the final product. Both columns operate under a vacuum to lower the temperature requirements and use less energy to achieve separation.
The distillation module was fabricated and assembled in the EPIC Fabrication Shop. This ensured the skid was assembled under ideal conditions, the project was kept on timeline and construction costs are reduced. Off-site skid fabrication prevented onsite upgrades and skid fabrication from interfering with each other. The time required to build the skid and OSHA exposure hours were both greatly reduced, saving the client money. These are the major advantages that modular design brought to this distillation project.
The client provided their own control system for the skid that EPIC integrated with an experienced automation engineer. EPIC functionally tested all equipment before shipment. The distillation system is a Class 1 Division 1 system. The frame was made of carbon steel in EPIC’s carbon shop, painted, and transferred to the stainless shop where all the piping, tubing and equipment and instrumentation was installed. Hydrotesting was completed on the entire system to double check for leaks and verify the vacuum in the columns.

The client completed three walkthroughs of the skid during fabrication/assembly. On the final walkthrough, a P&ID check was performed.

The finished “plug and play” skid was delivered as two separate framed pieces to the client site and successfully navigated to the installation spot. The two pieces were re-united and start-up was successfully completed.

IMPACT

• 91% ethanol mixture required by client was achieved
• Distillation system was successfully installed in a difficult-to-access area of plant
• Skid was delivered on-time and on-budget due to modular design
• Two-piece skid design allowed for safe transportation and installation
• Overall project timeline shortened due to on-site upgrades and skid fabrication progressing in tandem
• OSHA exposure hours reduced