A Densified Decarbonization Strategy

A tag-team effort combining biofuels and biomass expertise aims to commercialize a fuel pathway with the potential to benefit all links in the supply chain.
By Katie Fletcher | August 27, 2016

Afuel pathway management platform is being designed for ethanol producers, corn growers, pellet producers and utilities to capitalize on the potential benefits of using crop residue as densified biomass fuel for cofiring at power plants. Partnering in this endeavor the past five years are Trestle Energy LLC, a low-carbon fuel company that works with Midwestern ethanol producers, and Larksen LLC, a biomass company that provides agricultural residues to Midwestern power plants. After demonstrating its small-scale viability and receiving favorable carbon intensity (CI) ratings from both the California Air Resources Board and the British Columbia Ministry of Energy and Mines, the joint initiative is in a position to focus on commercializing the new approach, but it may be some time before the process becomes commercially feasible.

As a fuel supplier under low-carbon fuel standard (LCFS) programs in California and British Columbia, Trestle is the owner of this coproduct pathway that has the potential of reducing an ethanol plant’s CI rating, as demonstrated by CARB’s and BC’s pathway approvals. Trestle has been speaking to those involved in the ethanol industry about this opportunity.

To implement this pathway, Trestle partnered with Larksen, which has historically collaborated with biomass suppliers and coal plants. Jamie Rhodes, president of the joint initiative, says the companies were founded in 2012 to develop decarbonization pathways for commercialization, with Trestle’s first fuel pathways targeting the potential that crop residues have to decarbonize activities for, in this instance, power and liquid fuel suppliers. Since its founding, the partnership has embarked on the lengthy process of working through data, models, reporting requirements and other verification steps necessary to make commercialization possible, and it currently has a pathway petition pending with the U.S. EPA. A demonstration project was launched in Iowa at the end of 2012 and continued through September 2013 to help support the fuel applications to California and British Columbia. “It was really helpful in validating the assumptions that were built into our model, both the technical and economic assumptions,” Rhodes says.

The joint project integrates two supply chains—one for the grain delivered to the ethanol plant where it’s made into ethanol and delivered to the fuel market, and the other for crop residues used as a fuel, in the corm of pellets, for cofiring at power plants. The latter has long been recognized for its potential, but “has been aspirational up to this point because the economics are just not attractive,” Rhodes says.

Although the economics have been hard to pencil, the process allows the opportunity for both sides of the supply chain to reap emissions reduction benefits. “By making pellets a coproduct of ethanol, the financial benefits of low-carbon fuels can make biomass power a cost-effective option for coal plants to use in meeting their own compliance requirements,” Rhodes says. He adds that the pathway creates economic development opportunities across the agricultural sector, as farmers are able to generate new products and revenue by harvesting their crop residues and selling them to a pellet mill to process and deliver to the power plant.

The fuel pathway is intended to open up LCFS markets domestically and abroad as well. “LCFS markets are one of the few policy tools we have that can drive investments into low-carbon fuel production,” Rhodes says. “Our pathway shows that ethanol can be one of the ways we deliver low-carbon fuels. There are lots of winners under LCFS programs—grain ethanol, cellulosic ethanol, biodiesel, renewable diesel, renewable natural gas—a whole host of opportunities to deliver low-carbon fuel.”

Larksen worked with Iowa-based Cedar Falls Utilities for the demonstration-scale project, which became part of a broader set of test burns that the utility had been working on for nearly a decade. CFU had already been testing the feasibility of various types of densified (cubed or pelletized) biomass as fuel for electricity production in one of its generating units. Rhodes explains that persuading utilities like CFU to open its doors to biomass fuel pellets is one of the limiting factors for producing low-carbon ethanol with Trestle’s fuel pathway. “Utilities are understandably conservative and reticent to do something different that might impact their operations,” he explains. “As a biofuel industry, we should be supporting their regulators, giving them credit for taking in biomass pellets as a way to meet their compliance requirements. They should see a benefit because they are doing a lot of heavy lifting at their facility to let us in the door.”

Supplying much of the fuel-handling, densifying and conveying equipment for Trestle and Larksen’s demonstration effort was Warren & Baerg Manufacturing Inc. They were a natural fit, as they had some limited involvement helping the utility with biomass test burns prior to teaming up for the demonstration.

Warren & Baerg got its start in the hay and animal feed industry, providing equipment for cubing, grinding and handling alfalfa. “When alfalfa prices would rise, less costly crop residues came into the animal feed side of the spectrum,” says Randy Baerg, president of the company. Baerg says this is when the company began getting accustomed to handling corn stover and other biomass residues, and now its equipment has a few different uses in the biomass industry. Spurred by climbing fuel prices in the early 1980s, the company began supplying equipment to the waste industry to densify various materials like low-grade recyclables (paper, cardboard, plastics), as well as wood, straw and stover. In recent years, the company’s grinding, metering and densification equipment has been applicable for cellulosic ethanol production as well.

Other than Warren & Baerg’s equipment, Larksen has considered a wide range of pelleting technologies and found that the commercialization model can be applied to essentially any technology. “We’ve been in discussion with a variety of pellet mill manufacturers, as well as folks who are looking at torrefaction and biochar,” he says. “I think all of those technologies are interesting, and there may be opportunities for each of them.” As a starting point, Rhodes says, they tried to minimize technology risk and energy requirements. For this reason, their default configuration for deployment, subject to the fuel specifications of the coal plant, utilizes equipment like Warren & Baerg’s, which  was originally developed to manufacture feeding cubes from alfalfa and hay. One of the differences between pellets and the stover cubes that his company’s densifying equipment creates, Baerg says, is the reduced cost in grinding. He says wood pellets work much better for the pellet stove and clean wood market, but cubes work well for industrial biomass applications due to the reduced operating cost.

Larksen used a mobile unit for the demonstration project with most of Warren & Baerg’s equipment mounted on a 50-foot truck trailer. “Basically, it’s the complete metering, feeding, cubing system. The additional piece that’s needed separate from the unit is some grinding equipment to run the corn stover through,” Baerg says.

Rhodes conceptualizes a few different options for future commercial fuel processing, but the mobility of the demo unit was an added benefit for this phase. “We’re assuming that most projects would start with permanently installed equipment, like a pellet mill, and that the corn stalk bales would be brought to a centralized facility where they would be processed and loaded into rail cars for delivery to the coal plant,” Rhodes says. “But, the nice thing about the equipment we used for demonstration is you can operate it on a mobile basis—move it around to different sites where you have storage on the field’s edge and then, instead of having to haul bales as far, you can run the cuber right on the field’s edge and then load and haul the pellets in trailers.”

As for what works best, Rhodes says, “It depends on the logistics and feed-handling system at the coal plant.” He adds that the approach they’re taking is to work with the coal plant managers and operators to find out what format is needed  for their boilers, feed-handling systems and overall logistics supply chain. “Larksen worked with us and the fuel user to make the minimal modifications needed,” Baerg says. “That’s always one of the main concerns—whatever fuel they’re running, which is largely coal, they want the densified biomass product to come in and feed and operate well in that same equipment.”

Cedar Falls receives coal delivery by rail with a particular handling and receiving system for coal coming out of the rail cars. Besides hauling the material to a central processing facility, it can also be transported to smaller, decentralized facilities that are spread out through farming communities. Rhodes says they’re expecting to use this more distributed model, comparable to the grain elevator model, with a number of facilities available for local farmers to bring their corn stalks to for densification and then delivery to the coal plant.

Another advantage to a distributed network of facilities is that the equipment that’s been used thus far is widely known in the agricultural sector. “The maintenance and management of the technology is fairly straightforward and robust, which makes it particularly suitable for use in a distributed network and a broader system of facilities,” Rhodes says.

Larksen worked with Warren & Baerg to create a custom set of dies to meet the fuel specifications of the utility’s boilers. What was discovered to burn best was a large-format round pellet about one inch to an inch and a quarter in size, with 15 percent moisture or less. Rhodes says the pellets Larksen supplied for the test burns rated around 7,000 to 8,000 Btu per pound, which puts the fuel on par with low-rank coal, and within the design range of most coal plants. He says every facility will differ as to how much biomass it cofires with coal, but, in general, a large coal plant can burn 5 to 10 percent without too many changes to the plant’s fuel-handling system.

Of course, moving from demonstration to commercial scale depends on a number of factors, including, among others, a utility’s willingness to cofire and the government’s ruling of biomass under carbon-reduction legislation like the Clean Power Plan. “I think when you look at the CPP, although they haven’t come out with definitive rules for how biomass and biofuels will be treated from a carbon accounting perspective, the existing rules hold significant opportunities for coal plants to cofire biomass,” Rhodes says. He adds that some utilities are turning to natural gas, which exposes rate payers to the volatility of these markets. Others are switching to wind, but this creates some management problems with intermittency of supply and the capital-intensive nature of conversions. “I would like to think utilities are pursuing a portfolio approach—not locking themselves into any one technology—and I hope the federal government supports that,” Rhodes says.

Although this fuel pathway involves utilities, ethanol plants could use corn stalk pellets directly at the plant to reduce their CI, Rhodes says. However, many plants are now using natural gas and would need to determine if installing a biomass combined-heat-and-power unit is an efficient option for them. For the time being, Rhodes and his team are optimistic about the initiative’s journey toward commercialization. “We have a whole series of test burning opportunities that could launch for 2017 harvest,” he says. “Since we received the approval, we’ve been speaking with utilities, mainly in the western half of the Midwest, looking at opportunities to commercialize.”

Author: Katie Fletcher
Associate Editor, Biomass Magazine