North Dakota's Subterranean Fuel Feedstock
When the advanced biofuel industry thinks feedstocks, ideas may drift toward dried corn stover on a freshly harvested field, or swathes of switchgrass or miscanthus swaying in the breeze. In the Red River Valley and Drift Prairie regions of North Dakota, however, the next advanced biofuel might be found below the ground in the form of sugar beets. But why sugar beets?
“Why not sugar beets,” replies David Ripplinger, assistant professor at the agribusiness and applied economics department at North Dakota State University. The feedstock has several benefits to both growers and biofuel producers. For growers, the plant improves soil health with its deep tap root, yields relatively high numbers and can gain access to nutrients available in lower soil depths, he explains. “It’s also relatively high-yielding. If you did an ethanol yield per acre, it’s about twice that of corn.”
Farmers also gain a nitrogen credit due to the left-behind plant tops, he adds. “That ends up being quite a bit of nitrogen on a per acre basis.”
From a biofuel producer standpoint, the beets are a sugar-rich source that can be processed and handled more easily than food-grade sugar. “It’s a sugar crop, so you don’t have to go through the effort of converting starch or cellulose into sugar,” Ripplinger says. “It’s already in that form.” The sugar being used in the process would not be necessarily taken away from the food production chain since food-grade sugar producers prefer beets with a sugar content greater than 12 percent, whereas this project could utilize beets under the threshold."
Additionally, North Dakota is one of the few locations where beet production remains fairly steady, Ripplinger says. According to the USDA Economic Research Service, the upper Midwest, which includes only North Dakota and Minnesota, harvests the most sugar beets. North Dakota alone harvested 225,000 acres of sugar beets during the 2013-’14 growing season, more than the totals reported from the Great Plains and Great Lakes regions.
Converting the beets to a usable material does not come without its challenges, Ripplinger explains. “You’re essentially re-engineering the front-end, even though it’s not as many pieces or quite as delicate as a process,” he says. “Making sure that everything works individually, as well as together, and scaling from bench-scale to commercial scale, that’s still a pretty big deal.”
The crop is also relatively delicate when it comes to herbicide carryover from field applications. For instance, herbicides containing sulfentrazone can have rotational restrictions of 24 months or longer, while other chemicals, such as imazethapyr, has 40-month rotational restrictions, according to Ripplinger. “You can certainly grow with the right chemical regime,” he says. “But some growers, who grow certain crops or certain practices, you have to let them know years in advance because the carryover for certain chemicals can be significant.”
Converting beets to edible sugars requires roughly 38 different steps, Ripplinger says, whereas converting it to an industrial sugar requires four steps. The beets are run through a hammer mill, a modified ribbon mixer with hot water spray, and a chamber filter press. Afterward, the beet pulp can be used for pellet production, while the sugary beet juice can be used in biofuel production.
Based on a life-cycle analysis at NDSU, the beets could potentially qualify as an advanced biofuel feedstock, Ripplinger says. In October 2011, a petition was submitted to the U.S. EPA to establish its use as an advanced biofuel pathway, however, the agency’s evaluation revamp has put it and other potential pathways in a slight delay, he says.
Although the petition delay presents a challenge in the project, it has not stopped the project partners from evaluating sites across North Dakota. Last October, the project developers saw the promise behind the project and decided to develop criteria for a site location process, Ripplinger recalls. “Initially, they thought there would be no more than a few sites,” he adds. “By the time they were done, they realized there were five sites that were possibilities.”
The project developers toured the sites in January and March, evaluating possible locations and engaging sugar beet growers on the possibility of growing the beets as an industrial crop. “The purpose of both of those meetings was really to gauge grower interest,” Ripplinger says. “Without growers willing to commit, there really isn’t a project because it’s dependent on locally available feedstocks. There is no alternative, you can’t easily store and transport them, so that became a key.”
The proposed 20-MMgy refinery would require roughly 750,000 tons of beets primarily sourced within 20 miles of the facility, and is expected to be built as soon as 2016. The project developers hope to finalize processing and commercialization strategies, which includes feedstock commitments and capitalization.
Author: Chris Hanson
Staff Writer: Biomass Magazine