Pellet Ingenuity

While wood and crop residue pellets have largely the same end uses, vast differences surface in comparing their energy content, feedstock pricing and production components.
By Lisa Gibson | February 22, 2011

None of the customers interested in licensing pelletizing systems from Nebraska-based Pellet Technology will be pelletizing wood. Instead they will be pelletizing a resource that is more abundant, cheaper and requires less manpower to harvest. Corn stover, along with some other agricultural residues, is becoming more plentiful with the increase in yields of traditional crops. Pellet Technology has equipment capable of pelletizing wood, switchgrass, wheat and soybean stubble but corn stover is by far the company’s primary material.

Every pound of corn leaves a little more than a pound of biomass, says Russ Zeeck, Pellet Technology president and COO, and harvesting that residue can help farmers solve build-up problems that come with excessive accumulation. “We can pelletize wood for those people who want it, but with the numbers and cost, users are focused on stover,” he says. The company serves industrial cogeneration users, mainly in Europe.

Process, Pricing and Equipment

While pellet mill processes are generally similar, the inner workings can differ with the type of feedstock. “Ours is patented and a completely different design,” Zeeck says of Pellet Technology’s proprietary system. “While you still have a pellet mill machine, th

e die and feed system of that pellet machine vary [with wood versus crop residue feedstock].”
The equipment requirements in handling systems are different for the two raw materials, and added drying equipment is necessary at most wood pellet plants. Because of those variations on the basic design, wood pelletizing facilities have a capital cost around 40 percent higher than that of agricultural residues, Zeeck says. Ballparking, he says a 175,000 ton-per-year wood pellet plant could cost between $20 million and $25 million, compared with $15 million to $17 million for a similar-sized stover pelletizing plant.

Subsequent to contrasts in essential equipment comes a change in permitting requirements and timelines. The lack of drying systems in a corn stover pellet plant means those facilities can be permitted in 90 days. “You have a much more limited permitting requirement,” Zeeck says.

Those benefits and others, including price stability, influenced heavily by demand in existing and future markets, contributed to Pellet Technology’s decision to feature corn stover in its applications.For example, raw wood feedstocks currently have competition in the pulp and paper industry as well as the housing industry and off-shore uses, Zeeck explains. “That puts a lot of pressure on a feedstock,” he says. “And if you step back and look at the volume needed, and if we were to complete 50 percent of the liquid fuel pilot plants that have been announced, that biomass demand shoots up dramatically.” On the other hand, though, with that wood demand and multiple end uses comes a market that’s better developed.

But corn stover’s superior price stability comes into play once again when considering financing for plant construction. The feedstock takes at least one risk variable out of the development process with its longer-term price security. “We can work with customers and lock stover in for a secure price for seven years,” Zeeck says. “Our financing groups like that because of the fact that the feedstock has a fixed price.” Wood prices become difficult to secure past one or two years because of their variability, he adds.

Energy and Ash

If that doesn’t satisfy curiosity about Pellet Technology’s choice to feature corn stover systems, Zeeck would add that the feedstock brings with it a consistent chemistry profile that helps stabilize the entire pelletizing process. “If you take a White Scotch Pine that is in Arkansas versus one that is in Oregon, you are going to have a totally different chemistry makeup of the wood itself because they bring their nutrients from the soil,” he says. But farmers maintain a certain chemistry profile for their corn, regardless of the state it’s grown in, translating to stabilized per pound Btu values between 7,100 and 7,300. “All this comes down to the chemistry, especially in the combustion world,” he says. “For the past three years, we’ve stayed very consistent on that Btu value.” In addition, corn stover feedstock realizes an 85 percent net Btu gain between energy going into the pelletizing process and energy coming out, as it uses about 60 to 70 percent of the energy required in wood pelletizing processes.

But neither wood nor corn stover wins the comparison across the board. While stover offers consistency in Btu, that value falls well short of some wood species. Not to be outdone, wood can offer a Btu value of between 7,000 and 11,000, according to Jim Brown, salesman with Wood Grain Mill Works and former project manager of Atlas Pellets. “Almost all wood fiber has higher Btu content than agricultural pellets,” he says. “There may be some switchgrass varieties that come close, but typically wood has more Btu.” In addition, wood pellets have consistently lower ash content.

Earthtech Energy Inc. ran into problems with ash content in most of the recipes it concocted for ag residue pellets, according to CEO Marion Mast. “Most of them burned but would not come to the 1 percent ash requirement,” he says, adding that issues in transporting the crop residues to the plant can make the feedstock unusable. The company had a list of resources it had hoped to use at its own crop residue pellet plant, but hit a wall with the U.S. EPA when trying to sell to district heating companies, he says. The EPA requires a stack test for all new formulas and each test needs about 200 tons of feedstock. Because of that and other factors, Earthtech does not make its own pellets. Instead, the company offers consultation on processes and equipment for solid biofuels.

As Earthtech Energy learned, pelletizing agricultural residue isn’t always as simple as pelletizing wood. Corn stover is particularly hard to densify because of its light bulk density once it is ground, Zeeck explains. “It’s kind of a unique animal,” he says, adding that a multitude of attempts by numerous companies to pelletize the material have failed. “We’ve been able to come up with a design that allows a process to pelletize seven days a week, 24 hours a day, 365 days a year, which is really what is needed, especially in liquid fuels and electric utility industries,” he explains. “They need a product that’s at their door seven days a week, 24 hours a day.” The company’s proprietary process also makes particle sizing customization possible, which is crucial for a consistent quality parameter, he adds.

Lagging Behind

Even with such efficient systems available, the U.S. has yet to realize a substantial uptake in the pellet market beyond residential use. Europe has the most extensive industrial and commercial pellet use and Asia is following suit. “There is very little commercial or industrial use of pellets in the Americas,” Brown laments, adding that the U.S. government incentives currently favor liquid biofuels over other biomass applications. “There seems to be very little help in the biomass area and until that attitude changes; until natural gas triples its current pricing, there probably won’t be much commercial or industrial pellet use. So I don’t see a big need for agricultural pellets.”

Mast echoes the complaint about meager government investments of both money and effort, saying the lack of a solid biofuels infrastructure is the U.S.’s shortfall, stemming from resistance to promote them on a government level. “There is huge potential in solid biofuels but also some yellow flags that need to be addressed [including] maintaining commodity pricing, EPA testing, service centers and certification of products,” he says, adding that it will take more than just one person or company to establish the necessary infrastructure.

But in the meantime, slow progress is better than none and more feedstock options could help develop that infrastructure and increase pellet use in electrical and thermal applications. Infrastructure is not so much an issue with corn stover pellets, as they can use existing storage and transportation means, Zeeck says. “Once this product is pelletized, that allows easy transportation through existing corn grain infrastructure systems,” he says.

An increase in biofuel facilities will increase demand for pellets from both wood and agricultural feedstocks, and the supply needs to be closely evaluated and reviewed, Zeeck cautions. He adds that Pellet Technology evaluates projects on a case-by-case basis to determine which feedstock is appropriate.

While residential users would undoubtedly see more benefits with wood pellets because of their higher Btu value and less ash, industrial users will want to weigh those factors against the cheaper cost of crop residue pellets, Brown says. “You’re going to have to buy ag pellets at ‘x’ amount cheaper to justify higher ash and lower Btu.”

It’s clear that pellets made from wood and those from crop residue take turns leading the race to an efficient and desirable feedstock, but they seem to finish neck and neck. “There are a lot of positives both ways,” Zeeck says.

Author: Lisa Gibson
Associate Editor, Biomass Power & Thermal
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