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The big squeeze

–by Alan Doering

AURI’s agricultural coproduct utilization program seeks utilization ideas for plant and animal coproducts that present environmental and economic opportunities. A coproduct is something that is produced together with or left over during the creation of another product; a great example is the dried distillers grains that are produced during the ethanol production process. Coproducts, such as crop residues, agricultural processing by-products and animal manure, can be used in a variety of agricultural products including fertilizers, renewable fuels, animal feeds and more.

Agricultural processing and energy coproducts, such as cannery waste or digester solids, are typically high in moisture. Many wet biomass feedstocks generally have low value due to the high cost of thermally removing water; increasing the value of these materials in the market often requires an economical big squeeze
called dewatering.

The goal of AURI’s dewatering research, started in 2009, is to identify potential thermal and mechanical drying technologies that can remove water in a cost-effective way, thereby raising the value of these materials. Drier feedstocks would open markets for combustion or gasification of the feedstocks, pelleting material for feed, slow release fertilizer or for use as ground covers. At a minimum, producers or processors using a drier feedstock for feed or land application would be trucking more material and less water.

Recently, AURI, the Northwest Minnesota Foundation and American Crystal Sugar collaborated with PulverDryer USA, Inc., to evaluate the performance of their HydroCellTM technology for dewatering agricultural coproducts. This is one of many various moisture presses entering the market due to their improved water removal efficiency.

Dewatering trials conducted show that the HydroCellTM technology appears to be an efficient method of feasibly dewatering high-moisture coproducts. For this trial, sugar beet tailings and sugar beet pulp were evaluated. A 58.9% liquid extraction was observed in the wet sugar beet tailings and a 44.8% liquid extraction was observed in the wet sugar beet pulp. Although the remaining products still contained 70.5% and 79.2% moisture respectively; the majority of the moisture was removed utilizing mechanical methods. Operational cost assumptions for this technology are estimated to be $6 per wet ton, including a $1.50 to $2.25 per wet ton processing cost.

Dewatering technologies may offer an efficient companion technology to thermal drying, thus increasing the market opportunities for wet feedstocks.

One area of use for these feedstocks is for biomass heating. Biomass refers to any agricultural or forestry product that can be fed into a combustor and burned to generate heat. Biomass can be in bulk form (e.g., straw bales, processing byproducts, wood chips) or densified form (e.g., pucks, pellets, cubes).

For propane users, heating with biomass is a technically and economically feasible option in Minnesota. Minnesota has an adequate supply of biomass; the equipment necessary for its storage, processing and combustion; and the capital, expertise and experience necessary to provide producers an economical alternative for heating applications.