The Red-Hot Sands of Winnebago

For a year now, Corn Plus has been successfully combusting its solubles—the syrup normally added to distillers dried grains—in a fluidized bed system. EPM takes a look at the technology behind the power, and the innovative southern Minnesota ethanol plant taking advantage of this widely available energy feedstock.
By Ron Kotrba | June 01, 2006
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It was about one year ago when Corn Plus, a 44 MMgy ethanol plant in Winnebago, Minn., came on line with its fluidized bed reactor. When the company announced plans to burn its concentrated stillage from the evaporation stage of the ethanol production process—more commonly called "syrup," or the "soluble" fractions usually dried along with distillers grains to commonly make distillers dried grains with solubles (DDGS)—it very well could have been the impetus needed to spark an energy revolution in the ethanol industry.

Energy Products of Idaho (EPI), a design-engineer company in operation since the early 1970s, has more than 90 of its fluidized bed energy systems working in a variety of industries, says Kent Pope, business development manager for EPI. Pope says EPI has recently put an emphasis on expanding its presence in the ethanol industry. "EPI's energy systems are fueled by hundreds of renewable and fossil fuels, such as wood chips, cow manure, paper sludge, municipal wastes, agricultural residues, chipped tires, coal and many other fuels," Pope tells EPM.

In particular, EPI has extensive experience in the broad application of fluidized systems, from fluidized bed gasifiers to the retrofitting of existing boilers with fluidized bed technologies. "The term ‘fluidized bed' refers to the area of an energy system that accepts the fuel and converts it into a usable energy," Pope says. "This bed is generally a sand-like material that is made to act like a fluid by blowing air up through the sand."

The energy from a fluidized bed system can be introduced directly to the dryers as hot gas to reduce natural gas consumption in drying distillers grains, or the energy can fuel a boiler to make process heat and steam for the plant.

According to Pope, if a plant has a boiler originally designed for solid fuel, retrofitting that boiler with a fluidized bed can greatly increase the fuel flexibility of that boiler and improve emissions at the same time. "The retrofit is accomplished by removing the grate and replacing it with a fluidized bed bottom section," he tells EPM. "A gas-fired boiler is not designed to accept and remove the ash associated with solid fuels."

EPI is working with several ethanol plants on their energy needs, but no names could be mentioned in this stage of development. In Minnesota, however, Corn Plus is an ethanol producer already leading the way in implementing fluidized bed technology.

First in Line, First On Line
With Von Roll Ltd.'s technology and Harris Mechanical's hands-on expertise, Corn Plus came on line with its cost-saving fluidized bed system last year. Von Roll's manager of technology, Brian Copeland, tells EPM how it all started.

Copeland had been developing his fluidized bed technology since the 1970s, but it wasn't until years later—in the 1990s—when the economics made enough sense to successfully sell his innovative energy design to Von Roll, which incorporated the design, and Copeland, into its arsenal of technological offerings.

According to Copeland, Von Roll and a Colorado-based company developed and built a pilot-scale fluidized bed reactor between the late 1990s and 2000. "I can't recall the exact date, but it was before 9/11, I'm sure of that," he says.

Corn Plus got in on the ground floor with this technology, which now appears ready to explode onto the ethanol scene. "In 2000, we were using some of Corn Plus' syrup for the pilot system," Copeland tells EPM. "They were supplying materials for us, and they were very interested in the process." Moreover, he says, Corn Plus saw economic sense in burning a coproduct from the ethanol production process, getting away from the rising cost of natural gas.

Corn Plus General Manager Keith Kor describes to EPM the process his plant uses, from the extraction of its syrup to commoditizing the remaining ash from the fluidized bed system.

"From the evaporators, [the syrup] goes into a holding tank," Kor tells EPM. "Then from the holding tank, we meter the amount of syrup into the fluid bed."

But the introduction of the syrup doesn't occur until the 60 tons of sand at the bottom of the system are heated with natural gas to the red-hot temperature of 1,350 degrees Fahrenheit. "Our syrup combusts as a fuel, and then the natural gas valves close down," Kor explains. "The heat that is generated [from combustion] goes into a waste-heat recovery boiler, and that boiler generates all the steam throughout the plant."

Kor says the stack gases from the dryers are also pulled into the fluid bed, helping to incinerate the plant's emissions—essentially acting as a thermal oxidizer, too. "After the boilers, the emissions go through our baghouse to collect all of the particulates and ash."

On that note, 24 tons per day of ash are produced in Corn Plus' fluidized bed system. Corn Plus has been giving the ash to farmers to test its effectiveness as fertilizer. "The ones I've talked to really like it," Kor says.

Future Plans at Corn Plus
Corn Plus has a couple of different projects on the drawing table for this summer, one of which will improve the logistics of marketing the two dozen tons of ash being produced every day.

"We're going to put in a pelletizing plant right next to our existing ash pile, and then we're going to start marketing the ash," Kor says. "We're hoping to have [the pelletizing plant] up and running by October."

Kor says he's looking to further improve the plant's energy efficiency. Since the new energy system was put in place, Corn Plus has reduced its consumption of natural gas by up to 54 percent through the energy created by the fluidized bed system for process steam and in reducing the amount of natural gas needed to dry the DDG (DDGS minus the solubles), according to Kor. This reduction in natural gas use amounts to approximately $750,000 in savings per month for the 44 MMgy ethanol plant, Copeland says. With help this summer from Harris Mechanical and Von Roll, Kor intends to further reduce the plant's natural gas use by an additional 10 percent, boosting savings even closer to the $1 million-per-month mark.

Using the fluid bed system alone, the plant can be run at only 75 percent capacity, so Corn Plus has two conventional natural gas boilers to supply the necessary additional energy for the production process, plus heat for drying its DDG. "We're limited right now in how much syrup we can burn because our boiler is maxed out," Kor tells EPM. "We're looking at Von Roll and Harris to take some of the waste heat prior to going to the boiler and using that to either help dry the DDG or preheat the combustion air for the fluid bed."

According to Copeland, Corn Plus' unit produces more steam than currently needed —an extra 10 MMBtus per hour, he says—so rather than blowing off that steam, the plant will utilize a heat exchanger to recover that energy in the form of hot air.

Bids are being finalized for this project now, and Kor says he anticipates its completion by October or November.

Even though Corn Plus' DDG looks more appealing—a bright, golden color—without the solubles, the product still commands the same price as DDGS on the market, according to Kor. "For the month of March, we got around $67 a ton for the DDG," he says. "As DDG gets cheaper and cheaper, it might lead us to put in another fluid bed to burn our wet cake, and a turbine for generating electricity to run the plant. That's another option we're looking at."

Ron Kotrba is an Ethanol Producer Magazine staff writer. Reach him at or (701) 746-8385.