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Pulp Frequency

Microwaves could sweeten the value of Minnesota sugar beet pulp.

An industrial microwave dryer in Iowa is being tested by AURI scientists as a potential low-energy alternative to natural-gas dryers.

Beet pulp, the vegetable matter remaining after sugar is extracted from sliced beets, is typically dried then sold as a nutritious, high-fiber livestock feed. However, because of beet pulp’s high-moisture content, it is difficult to transport or store unless it is dried first.

AURI scientists Alan Doering and Kevin Hennessy recently tested a microwave dryer at Biomass Energy Conversion in Nevada, Iowa. They fed wet-pressed beet pulp from the Southern Minnesota Beet Sugar Cooperative in Renville, Minn., into a microwave system and recorded variations in pulp throughout the drying process.

Microwave drying technology could save a significant amount of energy. Traditional dryers, powered with natural gas, typically require 1,400 to 2,200 British thermal units to evaporate a pound of moisture. Microwave drying may be able to evaporate as much using only 1,000 Btus or less. Also, microwave drying could retain more of the pulp’s fiber and protein available for higher quality livestock feed.

“Microwave drying technology is also very safe,” says Doering, head of AURI’s coproducts lab in Waseca, Minn. The 100 kilowatt system — “about 100 times more (powerful) than the average kitchen microwave,” is designed not to leak, Doering says. “The microwave uses an industrial frequency of 915 megahertz,” about the same frequency as older cell phones.

In the next project phase, AURI will evaluate equipment costs and the dried pulp’s nutrient content. Results will be available this summer.