Raw Material Rationale
Top quality pellets can be made from hardwood, softwood or a blending of the two, and every pellet plant has a reason for the raw material it chooses. On the other hand, consumers may not have concrete reasons for their pellet of choice, and it seems to vary by region. In the Northeast, consumers prefer hardwoods for their heating needs, but in the Pacific Northwest, softwood seems to be the fuel pellet choice.
One is not necessarily better than another, however, because it all has to do with perception and tradition, according to Michael Scanlon, national account sales manager of American Wood Fibers, which has plants in Circleville, Ohio, and Marion, Va. “Plus, the performance of a brand of pellet has a lot to do with the appliance you are heating with,” says Scanlon. “There are some very good quality hardwoods on the market, and some very good quality softwoods. People will swear by whatever it is they burn, and there’s no real hard and fast rules about what’s the better choice.”
When choosing one option over the other, not all species are the same. Softwoods like Southern Yellow Pine don’t yield the same quality as a White Pine, and a Western Spruce and Douglas-fir both have better ash content than other softwoods. For hardwoods, maple and birch are much different when comparing Btu and ash content as well.
According to Chris Sharron, president of West Oregon Wood Products Inc. in Colombia City, Ore., making quality comparisons in terms of hardwood versus softwood isn’t the best scientific approach, as quality is more relative to specific species. Furthermore, quality is also relative to the cleanliness of the wood fiber being used and the quality of the manufacturer’s process, regardless of the quality of species. “Some hardwoods contain more heat (Btu) value per pound than some softwoods, likewise, some softwoods contain more heat value per pound than some hardwoods. So, heat value truly is species specific,” says Sharron. “Some hardwoods have higher ash content per pound than some softwoods, and vice-versa. So, ash content truly is species specific.”
West Oregon Wood Products uses primarily Douglas-fir for its pellets, and while it’s known as one of the best softwoods, it wasn’t entirely a conscious choice. “We’re somewhat blessed that Douglas-fir is indigenous to the Pacific Northwest and abundant around the sawmills in our area, as it’s one of the highest breeds of species for making pellets,” says Sharron. “It creates an extremely high heat and extremely low ash content. Ash that doesn’t want to fuse or form any type of clinker in the fire part of a pellet stove.”
American Wood Fibers uses both hardwood and softwood for its pellets, producing 80,000 tons of hardwood in its two plants and 10,000 tons of softwood in only its Marion plant. “The availability of raw materials is a primary factor, but the perception that hardwood is better still creeps into some psyche,” says Scanlon. “I think it’s based on the fact that everyone was always told in wood stoves not to burn pine and softwood, but when you pelletize the wood, it doesn’t matter. Hardwood and softwood offer the same density, and there’s no sap to worry about.”
Truth be told, softwood usually does burn hotter and creates a lot less ash, almost half as much. At American Wood Fibers, its hardwood comes in at under 0.5 percent of ash, while its softwood is 0.25. Meanwhile, its hardwood pellets are around 8,200 Btu, and softwood pellets are around 8,700 Btu. “Both products perform perfectly well as a fuel pellet, as long as you have a clean stream of raw materials,” says Scanlon. “The raw materials are a little higher for softwood, and some people think the extra cost for more heat and less work is fine.”
New England Wood Pellet operates three manufacturing plants, in Jaffrey, N.H., and Schuyler and Deposit, N.Y., and turned out over 204,000 tons of wood pellets last year. The company uses an 85-15 hardwood-softwood blend, including a combination of hardwoods from oak, maple, beech, birch, cherry and other species common to the Northeast, and softwoods including white pine, hemlock, and occasionally some spruce and fir. “This blend recipe is what we found works best for us,” says Charlie Niebling, the company’s general manager. “It is a reflection of the range of species and wood available to us to some extent, but we’ve also found that having a softwood component in our pellet optimizes the performance of our pellet mills. We have everything dialed in around this blend, and it’s become synonymous with our brand identity and consumer familiarity.”
By blending in softwoods, Niebling reveals it creates a better performance at the mills themselves and helps for a longer die life.
Matt O’Malley, president of O’Malley Timber Products in Tappahannock Va., says his company uses sawmill residue as a feedstock for its pellet mills to produce a 100 percent hardwood pellet. “We generate over 60,000 U.S. tons of hardwood chips and sawdust a year as a byproduct from our sawmills,” he says. “We decided to put in our pellet mills in an effort to become more vertically integrated. By having our own feedstock for our pellet mills, we can control the quality of our pellets very closely. By not having to purchase outside raw materials, we feel we gain a significant advantage over other mills because we are not paying any freight on our raw material.”
The hardwood pellets O’Malley Timber Products produces has 5 to 8 percent moisture content, 350,000 Btu per cubic foot, and an ash content that runs between 0.5 and 0.7 percent.
While hardwood logs are drier than softwood logs, and the low-moisture content result in a cleaner, hotter burn, once in the manufacturing process, the moisture content for both will be reduced 3 to 4 percent leaving only cellulose, lignin and resins. “It should be realized that in the process of manufacturing pellets, extreme heat and pressure completely change the structure of the wood fiber and a density of approximately 40 pounds per cubic foot is achieved, using either hardwoods or softwoods,” says Sharron. “Therefore, if the relative densities of hardwood and softwood pellets are comparable, they will experience equal burn time, assuming equal amounts of combustion air.”
Once pelletized, the difference between softwood and hardwood fiber is minimal. In fact, it’s the density of the pellet that makes a bigger difference than the species of wood does. According to Niebling, cellulose has the same heating value regardless of whether it originated from hardwood or softwood, but because resin has a higher heating value than cellulose, and softwood has a higher percentage of resin content than hardwood, softwood pellets will burn hotter and faster in most cases.
The main factor that impacts the quality of a wood pellet is the ash content. Low ash is a result of using clean wood—no bark or dirt—and a quality manufacturing process, not the type of wood used.
And while it’s true that more softwood species have a lower absolute mineral content so they offer a lower ash content—the Lodgepole Pine is especially known for this—total ash content is still dependent on the quality of the wood coming in. “It’s not so much an issue of what percentage of hardwood or softwood, but more than anything, it has to do with bark content and the amount of dirt that gets into a feedstock supply,” says Niebling. “Any company that’s focused on the quality of the pellet is working to eliminate contamination and reduce bark content and generally work for the cleanest and best wood supply that they can.”
The difference between hardwood and softwood from a production standpoint is that softwoods are pelletized at a higher rate than dense hardwoods. This is why many manufacturers inject or blend in softwoods to its hardwoods, because it helps lubricate the dyes and make the production run smoother. Pellet plants in the Northeast are more commonly turning to blends, adding little softwood injections into its hardwood pellets. White Pine is one softwood that is indigenous in the area, and pellet manufacturers are seeing the positive effects a blend can offer, raising the heat value and lowering the ash content. “It actually runs through the mill better because the pine helps grease the skids so to speak in the manufacturing process,” says Sharron. “It helps oak pelletize easier, has better production per horse power and improves the quality of the finished product.”
Not all blends work, however. While a certain species of softwood might make a great pellet and another species of hardwood might equally make a great pellet, they can be a disaster when combined. There are certain chemical reactions that can occur in the combustion process relative to the blend based on the chemical and elemental makeup of both, so tests need to be done on any combination. As an example, Sharron uses the hardwood Alder, which is indigenous to Oregon and might be blended with its Douglas-fir softwood. A test of 100 percent Alder comes back at 7,900 Btu and 0.75 percent ash content. Comparably, the Douglas-fir results in 8,400 Btu and 0.25 percent ash content.
“Alder pelletizes kind of roughly, doesn’t get good production relative to horse power and doesn’t make that good of a fuel, but would we blend it? Possibly,” says Sharron. He admits it doesn’t make a bad fuel, and if the economics and sawmill operation make sense, it might be a recipe worth trying.
There are so many variables that have to be closely evaluated, according to Sharron. “It starts with a good supply. If you don’t have a good sustainable supply, it doesn’t really matter. If you’re confident that you will for years to come, roll up your sleeves and really evaluate the product and whether or not it will make a good pellet. Evaluate the species. Inspect the cleanliness and contamination, because it doesn’t matter how well it pelletizes, if it’s contaminated. It’s not rocket science. It all makes sense, but you can’t just wish it to happen.”
Author: Keith Loria
Pellet Mill Magazine freelance writer