A test burn proved that shelled corn could be burned in Corn Belt’s Wisdom Unit 1 coal-fired boiler. The utility is now looking at other fuels that might serve as an alternative to coal. (Photo by Corn Belt Power Cooperative)

To turn corn into an alternative to fossil fuel, you can process it into ethanol, or you can do what Corn Belt Power Cooperative did last winter and just toss the ear into a boiler.

More precisely, the Northern Iowa generation and transmission cooperative fed 470 bushels of shelled corn into its pulverized coal-fired Wisdom Unit 1 boiler on February 16. Burning a mix of 20 percent corn and 80 percent bituminous coal, the plant reached approximately 96 percent of its gross output level. “We plan to conduct a more extensive test soon,” said Mike Thatcher, Corn Belt's vice president of generation.

The idea of the test burn came up at a Corn Belt directors' meeting. Discussions centered on the rising costs of buying and transporting coal and the increasing expense of sulfur dioxide allowances. Someone casually suggested that it would be cheaper to burn Iowa corn. "Sometimes, the price of coal is actually higher than corn," said Thatcher. "When the price of corn goes down, the other expenses associated with burning coal make corn a cost-effective alternative."   

Corn, after all, is grown in Corn Belt's service territory, by co-op members. The grain's sulfur content is lower than coal's, so emissions allowances would cost less. "It was worth looking into," Thatcher concluded.

Emissions, equipment questions

Cost was only one of the issues that had to be addressed. Corn Belt's air operating permit allows the plant to burn only coal, so the utility had to apply to the Iowa Department of Natural Resources for a variance. The agency stopped short of giving permission, instead issuing the opinion that corn was likely to give off fewer emissions than coal. The variance allowed Corn Belt to do a limited burn, "but on the basis of comparable emissions, I think DNR would probably grant a permit for regular burns," said Thatcher.

The type of equipment presented potential challenges, too. Thatcher had read about stoker-fired units burning corn, and knew that nearby Cedar Falls Utilities had tested several types of biomass in its 16-MW Streeter #6 stoker boiler. "Pulverized-coal units, however, have fewer options," said Thatcher.

Corn might not run through the grinder as easily as coal, and more corn would have to be pulverized because its heat content is lower than coal. "And that takes energy," said Thatcher.

The grinder handled the corn with little difficulty, and the corn ash—stickier than coal ash—did not gum up the sides of the boiler. The test did reveal that corn requires specialized storage. Some of the corn stored in the coal bunker began to sprout, "and sprouts get mushy," observed Thatcher. "You can't store corn in the bunker for a long time like coal."

On the day of the test burn, Wisdom 1's sulfur dioxide emissions were lower than usual, while nitrogen oxide was slightly higher. "But that could be fixed with some equipment adjustments," added Thatcher.

Other fuels considered

In spite of the initial success of the test, Corn Belt won't be substituting shelled corn for coal in the Wisdom 1 boiler because corn is generally more expensive. However, the test burn opened up other fuel possibilities.

A Des Moines demolition company has offered Corn Belt waste left over from deconstructing houses. Thatcher said that construction waste might not be a problem for the coal mill, but raised some concern about air quality. "The big challenge with refuse-derived fuel is making sure that it is free of potentially hazardous material," Thatcher explained.

Waste seed corn was another alternative fuel source that would otherwise wind up in a landfill. It is a local product like shelled corn, but less expensive because its germination date has expired, so it has no use to growers. The DNR is researching the environmental implications of the proposal, because the corn has been treated with fungicide. "It would have to be burned at high enough temperature to mitigate potential hazardous emissions," said Thatcher.

Diversity is the key to success when substituting biomass for conventional fuels, confirmed Cedar Falls Project Manager David Rusley. "Boilers consume huge quantities of fuel—our 16-MW unit would require the output of 50,000 acres if it was fired only with cornstalks," he said. "And if it's a wet fall, we can't harvest. You have to have options."

Utilities like Cedar Falls and Corn Belt Power are exploring their options with test burns. In the process, they are learning that just as there are more energy resources than fossil fuels, there is more than one way to squeeze energy from corn.