Because the ethanol process is several times more complicated than the simple one product/single step process system, the process has several stages of unit operations. Cardinal implemented MPC to address these complex challenges, such as numerous equipment/process stream constraints, ethanol and DDGS specification constraints and a 65-hour process time from grind of corn to the final products, alcohol and DDGS.
All the variables and their dynamic responses to changes in feed flow, energy and qualities were built in from plant data collected during testing and historical data from the Cardinal Ethanol facility. It took three months of testing and nine months to commission all components. Once the system was online, it stabilized the plant by reducing variation in the process, enabling transitions to happen smoothly and unifying the plant operating facility between operating teams and the day/night shift. This significantly reduced fluctuations in the facility.
The Pavilion8 MPC technology was installed in three stages: plant testing, modeling and commissioning/optimization. The project required a server networked to the distributed control system (DCS), but did not require the purchase of additional hardware. The MPC system unified the plant controls from grain (grind) to the 200-proof production.
The system stabilized the drop glucose levels in the fermenters and then drove it to a minimum level through precision control of fermentation feed, temperatures and enzymes (plus enzymes addition timing). This increased conversion of starch to ethanol on a consistent basis, essentially yielding more ethanol for the same amount of corn, and added to the bottom line of the plant, thus increasing the facility's sustainability.
The MPC made improvements that originally seemed difficult to obtain at the start of the project, since all operations were striving for efficiency improvements through hourly and daily best practices. However, the Rockwell Software Pavilion8 MPC solution improved plant stability and reduced variability on all key process variables, especially the batch fermentation operations. As a result, the following benefits have demonstrated a successful project:
- Ethanol yield increase - 2.2%
- Ethanol production increase – 10%
- Energy/gallon reduction - 8.2%
- Great operator acceptance
- Payback in under 12 months
In summary, the project met and exceeded the expectations of Cardinal Ethanol and the plant learned some key lessons through the implementation of this project:
- MPC projects help a plant uncover process factors that may be restricting higher production, yield or energy efficiency.
- Good control instruments are an integral part of an MPC project.
- The MPC system significantly reduced the carbon footprint of ethanol production, therefore increasing the sustainability index of the biofuel.