Turning sugar beets into electricity

Sugar beet waste
The trimmings from the top and bottom of the sugar beet are transformed from nuisance waste to fuel.
MPR Photo/Dan Gunderson

Your average beet is about the size of a softball. To cook it, you cut off the top and the tail. Then you peel it.

It's ready to slice and cook to remove the sugar, and there are a couple of big handfuls of peelings to toss in the garbage.

Now, consider the pile of peelings from several million tons of sugar beets.

Just one processing plant generates 400 tons -- about a dozen semi truck loads -- of what are called tailings every day.

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Paul Lane
University of Florida engineer Paul Lane helped design the American Crystal Sugar biodigester.
MPR Photo/Dan Gunderson

University of Florida engineer Paul Lane, who helped design the system to turn that waste into methane, explains how sugar beet tailings are dumped into a series of big tanks filled with carefully selected bacteria.

"What we do here is try to make a really nice environment for the bacteria to decompose the material we're putting in there," Lane said. "We make it the right temperature, the right ph and we make it damp. They're happy under those conditions and they just work for us."

It takes the happy bacteria about a week to turn the sugar beet tailings into methane, carbon dioxide and a pile of compost.

The methane can be burned in the sugar beet factory boilers, or they can power a generator to make electricity.

American Crystal Sugar Company Director of Business Development Dave Malmskog says the company started looking at a biodigester several years ago as a way to get rid of waste. The tailings are now spread on fields or sold to farmers for cattle feed.

American Crystal Sugar factory
If the biofuels pilot project is successful, American Crystal Sugar could save millions of dollars in energy costs.
MPR Photo/Dan Gunderson

The company pays thousands of dollars to dispose of the waste. So the idea of turning it into energy caught the attention of Crystal Sugar executives.

"Over the course of the last few years as energy prices have skyrocketed, it's turned out that it might be very good timing. It could come to fruition just the time when we need it the most," said Malmskog.

This experiment is funded by a $1 million grant from Xcel Energy.

The pilot project will get a shakedown run this month, and will go into full operation in the fall when the sugar beet harvest starts.

American Crystal's Dave Malmskog says if all goes well with the pilot project, a full-scale operation could be producing methane in two years.

Malmskog says it all depends on future prices for natural gas and electricity, and the cost of constructing a full-size plant. But he's optimistic American Crystal is on to a good thing.

"The best scenario for us would be if we eliminate the cost of disposing of the tailings, and we either use electricity in our plant or sell the electricity, plus generate some carbon credits, some green credits. It actually looks as if that's achievable," said Malmskog.

Preliminary numbers, and they're only based on laboratory tests, show American Crystal saving nearly $10 million a year at each of its five sugar processing plants.

Bacteria in these tanks turn the sugar beet scraps into methane and compost.
MPR Photo/Dan Gunderson

University of Florida researchers say the process is simple. Bacteria do all the work. The digester generates four times more energy as it uses.

Bill Sheehan, director of environmental systems at the Commercial Space Technology Center at the University of Florida, says that's far more efficient than ethanol production.

He says the process being used at American Crystal was developed for NASA, as a possible way to produce fuel on Mars.

NASA isn't using the technology, but Sheehan thinks it has a bright future here on earth.

"People ought to be looking at this, I think, more generally than they are right now," said Sheehan, "rather than all this ethanol push, where it's taking away from our food supply and converting to other things. It's like a no- brainer anyplace you have a waste product, to try and do something like this."

If the sugar beet-to-methane project is successful, American Crystal will look for other waste products that could be added to the sugar beet tailings.

Researchers say there are many options for creating methane from waste. The corn mash left over when ethanol is made, or the glycerin that's a byproduct of soy diesel, could easily be turned in to methane using the biodigester.