Control Efficiencies Boost Ethanol Production

Ethanol producer Mid-Missouri Energy achieves energy savings while increasing production through advanced process control technology.

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In his January State of the Union address, President George W. Bush called for an increase in U.S. production of alternative fuels to 35 billion gallons a year by 2017, or nearly seven times current U.S. capacity.

That prospect—part of a Bush plan to reduce U.S. gasoline consumption by 20 percent over the next 10 years—would seemingly bode well for U.S. ethanol producers. But at the same time, the rising price of corn, ethanol’s primary feed stock, has been cutting sharply into ethanol plant margins. “A year ago, we were often paying less than $2 a bushel for corn, but we’ve paid up to $4 here recently. So the price of corn has doubled,” says Chris Wilson, plant manager at Mid-Missouri Energy Inc., a farmer cooperative-owned ethanol producer in Malta Bend, Mo.

The higher corn prices, along with general energy price volatility, are keeping the pressure on ethanol producers such as Mid-Missouri to be certain that their plants are operating as efficiently as possible.

Mid-Missouri took a big step in that direction last summer, when it installed an advanced process control (APC) application from Pavilion Technologies, an Austin, Texas, software provider. During a five-month period from April through August, Mid-Missouri installed Pavilion’s Ethanol Dryer Control application, one of four modules offered by the vendor for use in ethanol plants.

The Dryer Control application relies on model predictive control (MPC) technology to optimize the process of drying the residue mash, called stillage, which is extracted from the distillation columns that produce alcohol from fermented corn mash. When dried to customer specification, the stillage is converted into what is called dried distillers grains with solubles (DDGS). This material is sold as a high-protein livestock feed ingredient, as a by-product of the ethanol production process.

The MPC technology uses a reference model of the drying process to monitor about 30 different variables to predict future process behavior and calculate an optimum set of control moves, based on real-time sensor data. The same technique is applied to associated evaporators. The resultant commands are fed back every 30 to 60 seconds to Mid-Missouri’s Siemens APACS distributed control system (DCS).  

Compared to Mid-Missouri’s previous manual control method, the Pavilion application affords much tighter control, minimizing natural gas use in the dryers, as well as steam production for the evaporators, both of which save energy, says Wilson. In the Mid-Missouri process, flash steam off the evaporators is also used to drive the distillation process, a step that is likewise optimized by the Pavilion application.

“If you run your distillation columns too cold, you will actually lose alcohol at the bottom of your columns, and that can never be reclaimed,” Wilson explains. Based on data from temperature sensors in the columns, the Pavilion application “allows us to run a real tight control where we’re not overinducing steam or energy into our columns, but we’re putting in just the right amount to keep product from being lost out the bottom,” he says.

Instant benefits

After about six months of operation, Wilson says he has been pleased with the results produced by the Pavilion technology. Benefits from the application “appeared almost instantly” after installation, in the form of improved plant controllability and easing of the control burden on operators, he says. Other benefits also quickly became apparent, he notes, including improved consistency of product and increased plant throughput.

In the end, Wilson says the application is saving Mid-Missouri Energy about 2 percent on energy costs, while increasing ethanol production by about 6 percent. In all, the co-op expects the Pavilion application to produce benefits in excess of $3 million annually, he adds, based on 2006 ethanol market prices.

In fact, Mid-Missouri is now moving ahead with a project to install Pavilion’s full ethanol plant solution. That package, known as the Pavilion8 Ethanol Control Solution, includes modules that apply the same kind of MPC techniques to control of the distillation, water balance and fermentation processes, in addition to the drying process. Installation began last November, and is expected to be completed later this year.

The Mid-Missouri plant—which had a nameplate capacity of 40 million gallons of ethanol per year when it began operations in February 2003—is now producing at a rate of 50 million to 55 million gallons per year, says Wilson. And one goal of installing the plant-wide Pavilion solution is to push that capacity to a consistent 60 million gallons per year. “I believe that’s fully feasible,” says Wilson. “And we’re now putting in the groundwork to make that possible.”  

For more information, search keywords “advanced process control” at www.automationworld.com.

 

To see the accompanying sidebar to this story - "Ethanol APC Market Heats Up" - please visit www.automationworld.com/view-3002

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