Ethanol Plant Boosts Operating Margin

Model predictive control enables plantwide optimization.

By Maina Macharia, Rockwell Automation

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The Batch Fermentation Control application adjusted temperature conditions and helped ensure an optimal dynamic ratio of enzyme to feedstock and the best trajectories to respond to changes in feedstock quality. This led to a cut of more than 40% in the average of residual sugars and a drop in excess of 70% in the standard deviation. A higher conversion of starch to ethanol yielded more ethanol for the same amount of corn, the key factor in the overall margin increase.

The MPC technology identified energy inefficiencies in separating and purifying ethanol. Optimizing energy trade-offs between the sieve and distillation operations allowed the Distillation and Dehydration Control application to reduce energy use variability by more than 50%.

The Dryer and Evaporator application, which controls evaporator solids and dryer moisture while managing stillage inventory and syrup usage, improved both DDGS quality and yield, and minimized energy use.

Since its installation was completed in February 2011, the Pavilion8-based MPC solution has greatly improved overall plant stability and reduced variability of all crucial process parameters — especially in the batch fermentation operations.  Key gains include:

• 2.2% increase in ethanol yield per bushel of corn;
• 7.2% boost in overall ethanol production;
• 7.7% decrease in energy consumption per gallon;
• better stability of all key process variables;
• 40–70% reduction in the standard deviation for each variable, and
• payback of less than 12 months.

In addition, it has achieved operator acceptance.

Overall, the project exceeded the expectations of Cardinal Ethanol. Due to its success, the company contracted with Rockwell Automation for sustained solution support. This will enable incorporating minor plant-configuration changes into the optimization solution. Today, the service factor of the system exceeds 99% for all variables. The significant increase in operating margin has helped ensure that Cardinal Ethanol is a well-positioned, low-cost producer. In addition, the optimization has cut its carbon footprint to below the industry average.

MAINA MACHARIA is Austin, Texas-based biofuels industry manager for Rockwell Automation. E-mail him at

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