Sweeter still Beet sugar makes corn ethanol processing more efficient 

By E. M. Morrison

Sugar makes corn-based ethanol sweeter still.

Demonstration tests at Corn Plus in Winnebago, Minn. showed that by adding 1.5 percent beet sugar to corn silage shortened fermentation time by nearly three hours and boosted ethanol yields by 1,500 gallons a batch.  The research could lead to greater efficiency in corn ethanol processing.  It could also inform the debate on renewable fuel policies.

AURI’s Center for Producer-Owned Energy sponsored the research on behalf of the Southern Minnesota Beet Sugar Cooperative, a 570-member farmer-owned co-op based in Renville, Minn.

When the project started, SMBSC growers were looking for additional sugar markets to run their plant at full capacity. After the 2002 Farm Bill became law, the co-op’s federally-supported sugar allotment dropped to 70 percent of the factory’s production capacity. (Federal production controls, called allotments, shore up sugar prices. Allotments are administered through USDA nonrecourse loans, with a 22.9 cents-per-pound price guarantee. The policy discourages excess domestic supplies, while tariffs and trade agreements limit imports of cheaper foreign sugar.)

SMBSC’s granulated beet-sugar capacity is 7.5 million hundredweights (cwt), but the coop could only market 5.5 million cwt at the federally-supported price. Any excess sugar has to be sold at world market prices, which  are usually less than half of Midwest beet sugar prices. “It was our hope that we could find a process for using sugar that would have a return similar to domestic sugar,” says John Richmond, CEO of SMBSC. 

Last fall, however, SMBSC bought a California company that had a larger sugar allocation than it could fulfill. “We can use the surplus allocation here,” Richmond says. “So we’ll be producing at full capacity this year.” The company will slice three million tons of beets grown on 120,000 acres. 

Still, Minnesota farmers, who grow more than one-third of the U.S. beet crop, “would like to produce more sugar,” says Dennis Timmerman, AURI project director. “They have the land and they have the processing capacity.” Using sugar to enhance corn based ethanol manufacturing “might be a way for co-ops to profitably produce sugar beyond their federal allotments,” he says.

A ‘spoonful’ of sugar

A series of bench-top experiments last year evaluated the effects of adding up to 5 percent refined sugar to corn mash. A 1.5 percent sugar-inclusion rate produced optimum results, improving corn- starch fermentation and yield, Timmerman says. Higher sugar inclusion rates did not produce
additional efficiencies.

Three commercial-scale trials were carried out last August, September and October at Corn Plus, a 44-million-gallon corn dry mill in south central Minnesota. Corn Plus has adopted a number of cutting-edge technologies, such as combusting corn solubles in a fluidized bed reactor and pelletizing reactor ash for fertilizer.

The sugar trials were performed under Corn Plus’s normal operating conditions, using 342,950-gallon fermenters with 12,000 pounds of granulated sugar added to each test batch. Each experiment included a control batch. Results were collected using high-performance liquid chromatography.

Researchers wanted to find out if sugar would inhibit corn mash’s yeast activity, says Keith Kor, Corn Plus manager. In fact, “we found better yeast viability with the sugar.” Sugar pushed up average ethanol yields by 1.48 percentage points compared to the controls — a 10 percent improvement.

Fermentation time dropped by 2.6 hours, to an average of 40 hours — a 6 percent improvement.

What’s that worth to an ethanol plant

It depends on ethanol’s price, Timmerman says. At $1.90-per-gallon ethanol, for example, the additional yield from sugar adds about 12 cents of value per pound of sugar, he says. That’s three times the value of corn as a fermentable carbohydrate, Richmond notes. “But it’s only about half of what’s needed to encourage U.S. growers to produce sugar for ethanol.”

The cost of producing sugar in North America approaches 20 cents a pound, Richmond says. So it’s unlikely that domestic sugar will be used for fuel production, at least in the near term, he says.

Demand squeeze

But the equation could change in the coming decades, Kor says, if rising demand for ethanol squeezes corn supplies. “There’s good potential for making ethanol from sugar if the economics work out,” says Kor, who used to manage a small Iowa ethanol plant that converted scrap sugar to ethanol. “It depends on the price of sugar. During times when the U.S. sugar industry struggles to get rid of excess product, there might be an opportunity.” And as the ethanol industry expands, he adds, sugar could supplement corn feedstocks, helping the country meet ambitious renewable fuel goals.

As the country formulates renewable-fuel policy, Richmond adds, there could be future “encouragements to use sugar for ethanol, especially at times when the U.S. has more sugar than it can consume, or if the government wants to encourage the importation of sugar from Third World countries, to help their economies.”■

Source: Center for Producer-Owned Energy trials
8-21-06; 9-21-06; 10-18-06 at Corn Plus.