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On Board with Energy Crops

300 140 Miguel Ángel Martínez

Near the Columbia River just outside of eastern Oregon’s Boardman sits the state’s last operating coal plant, a 600-MW facility built in the late 1970s. Though the plant has plenty of years left in it, the state’s decision to phase out coal left Portland General Electric exploring its options.

In 2010, PGE was approved to continue to burn coal at Boardman until 2020, with some temporary emissions controls upgrades. After that, $500 million in additional pollution controls would be required to comply with federal and state sulfur, nitrogen and mercury rules, thus enabling the plant to continue operations until at least 2040.

Ultimately, PGE faced three possibilities—closing by 2020, making costly upgrades, or switching to another fuel source. If closed, it would make history as the youngest coal plant in the U.S. to shut down as a result of air quality regulations, but doing so and building a new plant elsewhere makes more economic sense than keeping it open for upgrades.

With the upgrade option ruled out, the fate of the plant rests on the feasibility of using torrefied energy crops as fuel, and PGE has spent the past several years conducting in-depth research and rigorous testing to determine what the possibilities are.

Exploring Options

Initially, PGE looked into repowering with natural gas, but rendered that option unfeasible. “We did a study on natural gas and found the area didn’t have a gas line, but that wasn’t the real issue,” says Jaisen Mody, PGE projects manager. “The issue was that the Boardman boiler was designed for coal combustion, and using gas in the existing boiler made it highly inefficient. The cost wasn’t conducive to running the plant long-term, as we would have to change out the boiler. We decided that converting an old Rankine cycle coal boiler wasn’t the way to go because of the capital expenditure.”

Basically, it boiled down to the notion of using gas meant building a new gas plant, adds Steve Corson, PGE spokesman.

When PGE began evaluating biomass back in 2010, wood pellets were tested but gummed up the plant’s pulverizers. Crop research began at that point, and arundo donax was chosen as a fuel of interest due to its great growth potential. It’s been found to produce upwards of 35 dry tons per acre per year, compared to switchgrass, which will yield 4 to 13 dry tons per acre per year.

PGE has been growing arundo test plots around the Boardman area for the past couple of years—about 92 acres—and has harvested it a few times, storing the crop for test burns, Mody says. He adds that while the initial emphasis was mostly on arundo, that’s changed a bit.

On one hand, a single energy crop is attractive because it’s dedicated to producing feedstock volumes needed, but reliance on a single fuel source is risky for a number of reasons, including harsh weather, natural disasters or pests. “So we’re also investigating other biomass sources, including sorghum and ag waste,” says Mody.

One thing that’s certain is that if energy crops and biomass are used at Boardman, they will be torrefied first. “Torrefaction is the right way to repower Boardman with biomass, because we’re anticipating no changes to plant equipment,” Mody says.

Corson adds that torrefaction would allow the plant to pulverize the fuel just as it is doing with coal, but green biomass would require a lot of changes. Additionally, researchers have found that torrefied biomass is more hydrophobic than Powder River Basin coal, which is currently used at Boardman.

Later this year, PGE is installing a torrefier at Boardman, and will then begin its test burns, according to Mody. “These test burns are critical for us,” he says. “We think running this test will prove to us that we can run torrefied biomass through the plant, and we’ll also collect emissions data. Then we’ll sit down and figure out what it’ll take to run the plant for air permitting and the economics of that.”

Mody notes that each feedstock tested—arundo or sorghum—could have a different effect on the boiler, slagging or fouling it, so close attention will be paid as to what source is torrefied and how.

According to a study done in 2012 by researchers at the University of Washington, Washington State and Oregon State University, operating at 300 MW and producing power under optimal economic conditions, about 1.25 million tons of torrefied arundo would be used by Boardman, based on the Btu content of torrefied arundo (10,400 Btu per pound). About 94 dry tons of arundo would produce 52.7 tons of torrefied chips, the researchers found, so a total of 67.6 thousand acres of arundo would be required to produce 1.25 million tons of torrefied chips and support torrefaction, assuming 33 dry tons per acre per year.

Of course, while multiple sources would be used, Mody admits obtaining necessary quantities remains PGE’s biggest challenge in the quest to repower with biomass.

Moving Foward

“It’s [repowering] always been one issue—the source of biomass,” says Mody. “How can we procure and move enough in an economic manner that would sustain a large plant? The production of biomass, whether we’re growing or buying it, remains our biggest challenge. That’s why we’re looking at diversity now—one species isn’t the answer. It’s about what we can grow at a reasonable price, and what’s available out there.”

If the torrefaction test burns are successful, more work has to be done to calculate the economics and emissions profiles of a full-scale torrefier. Once that data is complete, PGE will bring it to its integrated resource planning process, which is a comprehensive plan presented to the public utility commission that lays out its generating portfolio resource requirements.

At that time, the next step for Boardman will be decided, Corson adds. “At this point, what we’ll really be saying is, okay, we know we can do this, is it better than the other options?”

Arundo Is Better than Switchgrass for Biomass Power Generation

484 309 Miguel Ángel Martínez

Arundo donax, the ancient species of Giant Reed that may have hidden Moses along the Nile River more than 3500 years ago, could also go a long way in solving the U.S.’ 21st century biomass to energy needs. That is, if it can overcome regulatory hurdles and environmentalists bent on characterizing this tall grass as an “out of control” invasive species.

In the U.S., Arundo’s biggest challenge remains whether the Environmental Protection Agency (EPA) will ultimately grant the Giant Reed a Renewable Identification Number (RIN).  A RIN would enable biofuel refiners and fossil fuel blenders to receive credits for complying with the 2005 federally-mandated Renewable Fuels Standard (RFS).

“The EPA hasn’t announced a timetable for RIN approval,” said Wil Glenn, communications director for the Biofuels Center of North Carolina.  “But the agency has already recognized the Giant Reed (Arundo donax) as a crop that can reduce Greenhouse Gas (GHG) emissions by up to 80 percent.”

However, environmentalists note that Arundo has already transformed a significant amount of native southern California riparian habitat into pure stands of this weed-like grass.  In fact, it’s estimated that tens of thousands of acres of Arundo now line southern California drainage systems, after being intentionally introduced nearly two hundred years ago as a hedge against soil erosion.

Originally, native to the grasslands and wetlands of East Asia, its hollow, bamboo-like stems can reach heights of more than 25 feet producing 20 dry tons of biomass per acre.  That’s compared to Switchgrass, which only averages up to 8 tons an acre annually.

But although fast growing and drought-tolerant, Arundo’s seeds are sterile.  Thus, its stems and underground bulb-like rhizomes only propagate via cultivation or movement by forces of nature like hurricanes and flooding.

Despite such cultivation challenges, Arundo’s potential as a biofuel feedstock is already recognized in Europe.

Since late last year, Beta Renewables, whose partners are Chemtex, Novozymes and TPG, has been operating a 20-million gallon a year ethanol production facility in Crescintino, Italy using Arundo donax and wheat straw as feedstock.

“In Italy, we use enzymatic hydrolysis fermentation,” said Delane Richardson, a chemical engineer at Chemtex in Medina, Ohio.  “You extract the sugar from the biomass and the enzymes take the long chain sugars and cut them into digestible C5 and C6 sugars that are then exposed to a patented ethanologen microorganism to produce ethanol.  We want a facility just like it in North Carolina.”

Although the EPA has yet to get onboard, the North Carolina Dept. of Agriculture recently decided against putting Arundo on the noxious weed list, leaving the door open to cultivation.

Richardson says Chemtex would like to build a biomass to ethanol plant in Clinton, North Carolina that would operate on a combination of Arundo, Switchgrass, Fiber Sorghum, Miscanthus, and Rye at a delivered aggregate biomass feedstock cost of $50 or less per dry ton.  However, the largest single component would be 100,000 tons of Arundo, which would account for 7 million gallons (or at least a third) of the Clinton facility’s annual ethanol production.

If the plant’s local biomass supply chains were firmed up, Richardson says the North Carolina facility could be operational by mid-2015.

Richardson says that while the conversion process uses the Arundo’s sugars, as much as 60 percent of the harvested reed is leftover.  It’s this leftover lignin that is generally converted to electricity.  Richardson notes that Beta Renewables’ Italian facility has enough converted electrical power to supply its own needs as well as sell a portion to local utilities.  Chemtex hopes to do something similar with its planned North Carolina facility.

On the other side of the country, however, Portland General Electric (PGE) is running a study to determine whether Oregon’s Boardman coal-fired electric plant can be converted to a total biomass facility after the year 2020.  That’s the deadline for the plant to meet a regulatory ultimatum dictating that the facility cease burning coal.

If it successfully makes the transition to biomass, the 585 MW Boardman plant, which already provides PGE with 15 percent of its electricity, or some 65 percent (374 MW) of the plant’s output, would become the U.S.’ largest biomass-fueled electric generator.

But to do so, PGE would have to have some 8,000 tons of biomass for every day the biofuel generator was operational.  An Arundo test crop, being grown on 90 acres of Morrow County, Oregon farmland, will be harvested, pulverized and then torrefied in a charring process before the Boardman plant actually tests the crop in its facility next year.

“The goal in the test burn is to determine whether it’s feasible to convert this coal-fired power plant to [biomass],” said PGE spokesman Steve Corson.  “Arundo would only be only one of several feedstocks for such a biomass plant.”

Still, it’s estimated that Arundo would produce about 10,000 Btu/lb compared to 8500 Btu/lb for Boardman’s coal operations.

As for the risk of invasiveness in Oregon?

Tim Butler, a weed scientist at the Oregon Dept. of Agriculture, says mitigation control against Arundo invasivity would include strict monitoring of fields; restrictions on how close it could be planted to water; and attention in cleaning farm equipment leaving its fields.

The Giant Reed has been sold in Oregon as an ornamental for decades, says Butler, and thus far, the state appear to be free of wild Arundo stands.

However, Lauren Quinn, an invasive plant ecologist at the University of Illinois at Urbana-Champaign, says that every Weed Risk Assessment (WRA) published for Arundo has indicated high risk.  “We worry about extreme climatic events such as hurricanes moving rhizomes out of cultivation [areas] and about abandonment of plantations after leases expire or if the industry fails,” said Quinn.  She notes there is also a risk of escape via transportation of rhizomes to production fields or bio-refineries.

As weed scientist Joe DiTomaso at the University of California at Davis notes, Arundo is the “weediest” of all the plants being considered for biofuel and, as such, has taken over a lot of stream banks.  Its root fragments can also can spread down river corridors via flooding events, where they eventually create new Arundo colonies.

But when planted on farmland, DiTomaso says Arundo is easy to manage because it doesn’t produce any viable seeds.  Because its only means of spreading are via stem nodes and rhizomes, he says when planted in confined areas away from water, it remains at low risk of invasivity.

“The good news is that Arundo is one of the few crops that meets the yield threshold that we believe is going to make it attractive for farmers to plant,” said Richardson.  “The bad news is that a hundred years ago it was mishandled and became invasive in some environments.”

But at this point, without the RIN, Richardson says the economics for Chemtex’ North Carolina project don’t look promising.  Even so, Richardson says Chemtex is looking at other potential Arundo biofuel plant locations in the Southeast including Virginia, Kentucky and Georgia.  The idea is to target former strip-mining areas, as well as low-production agricultural lands, such as former tobacco-growing areas for Arundo acreage.

“Arundo can be grown on very contaminated soils without herbicides or pesticides and a minimal amount of fertilizer,” said Richardson.  “Plant it once and it lasts 15 years.  That’s versus a corn crop where you’re pushing a tractor through a field five times a year.

Arundo is a win, win, win.”


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