The Real Burning Question: Are Liquid Fuels the best use of Non-Woody Biomass?

David Malakoff, Science Writer (Photo Credit: PortWorks)

If Roger Samson had a coat of arms, it might be a flickering flame encircled by a wreath of grass.

For decades now, the Canadian agriculture expert has been talking up the environmental and economic benefits of burning non-woody biomass – such as pellets made from perennial grasses – to produce heat and electricity. And he’d won some converts: Policymakers, industry executives and farmers in the United States and Canada were warming to the idea, conducting research and starting pilot projects.

Recently, however, Samson has had a harder time getting people to listen. “All everyone wants to talk about is dealing with climate change by making ethanol from corn and switchgrass,” he says. “The money and interest got focused on liquid biofuels.”

That’s a big mistake, Samson and his allies believe. The push to ramp up ethanol production will be costly and do relatively little to ease climate problems, they predict – and it could end creating other problems, from higher food prices to habitat destruction. Instead of pushing the idea of using non-woody biomass to brew biofuels, they say policymakers should be promoting ways to burn it.

“In many settings, direct combustion just makes more economic and thermodynamic sense,” says Samson, the executive director of the nonprofit Resource Efficient Agricultural Production Canada (REAP, www.reap-canada.com). And a growing number of studies back him up: Some show that burning switchgrass, for instance, could produce two to three times more usable energy than using new technologies to convert it into a liquid fuel.

Such numbers, however, don’t appear to have impressed policymakers. They are set to pump tens of billions of research and subsidy dollars into ethanol production over the next decade – including unproven “cellulosic” technologies that have yet to be developed. In part, that’s because they say there are few other climate-friendly options for powering cars and trucks. Also, however, “ethanol backers have a huge, well-funded and politically-potent lobbying effort,” says an aide to a U.S. Senator from a major corn- and soybean-growing state. “Biomass combustion folks, on the other hand, don’t have much political muscle. They aren’t as visible.”

That could be changing. In February, Congress and President Barack Obama included nearly $800 million to promote biomass energy in the new economic stimulus program (Bioenergy Business, 2009); some of that money is expected to go to burning projects. It also includes hefty tax breaks for consumers who buy heaters that burn biomass. And in March, nine companies founded the Biomass Thermal Energy Council (BTEC, www.biothermalenergy.org) to give combustion advocates a higher profile in Washington. One goal, says BTEC director Jeffrey Serfass, is to make burning biomass – including non-woody plants – “an important component of the Obama Administration’s new energy policy.”

From Prairie to Pellet

The idea of burning non-woody biomass – which can include everything from clumps of grass to crop residues and food-processing waste – isn’t new. When European settlers fanned out across North America’s grasslands, for instance, they quickly learned from Native Americans that bunches of dried prairie grass could warm up a winter night (Cherney et al., 2006).

For industrial purposes, however, wood has long overshadowed grass and other non-woody plants. In northern climes, for example, wood-fired furnaces routinely provide heat and produce electricity to businesses and homeowners. Still, while biomass is a major energy player in the developing world, it has played a minor role in industrialized nations during the fossil fuel era. In the United States, for instance, the federal Energy Information Administration estimates that biomass provides less than 3% of the total energy supply (Porter et al., 2008).

Concerns about climate change and energy security, however, are now prompting a fresh look at biomass. And although wood continues to win a lion’s share of the attention, worries about adequate timber supplies and the environmental damage associated with logging have brightened the spotlight on non-woody resources such as cultivated switchgrass and wild-growing prairie grasses. A single acre of switchgrass, for instance, could produce enough biomass to meet the space and water heating needs of a typical household, concluded a 1999 study by researchers at Kansas State University in Manhattan (Porter et al., 2008).

Combustion advocates, however, say they do face some challenges. Non-woody biomass can be expensive to harvest and transport, for instance, and difficult to store when it is not needed. Variations in geography and weather can make it challenging to grow adequate supplies with consistent qualities – often a must for large energy producers, such as electric utilities (Samson, 2008).

Then, there is the challenge posed by basic chemistry. “The main historic problem with the use of these materials has been that, unlike wood, they are not easy to burn over sustained periods because of their chemical properties,” REAP’s Samson and his colleagues note in a 2007 analysis (Samson et al., 2007). Grasses, for instance, can contain high levels of potassium and chorine. When burned, these elements promote metal corrosion and the formation of “clinker,” a slag-like material that can jam furnaces.

Clinker isn’t a showstopper, however. Experts say they are overcoming that problem by tweaking burner technologies, carefully choosing grass varieties, and using some practical tricks – like harvesting mature grasses in the fall or the following spring, when tissue levels of problem chemicals are low. Even simple fixes like increasing the rate at which a burner automatically sweeps ash off combustion grates can make a major difference (Samson et al., 2008).

Another trick for burning grasses and other non-woody biomass efficiently is to compress them into dense, easy-to-manage pellets. Already, companies sell more than 2 million tons of biomass pellets annually in the U.S. and Canada, notes a June 2008 report — Growing Wisconsin Energy – that examines the potential of using non-woody biomass for energy (Porter et al., 2008). The pellet-making process is fairly well understood for wood, the report concludes, but researchers are still studying a range of factors “commonly known to affect the success of pelleting” grass. A material’s moisture content, density, particle size and fiber strength can all make a difference, notes the report, which was prepared by the Agrecol Corporation of Madison, which makes pellets and produces grass seed. Pellet makers may also have to add binders — such as oils or starch – to hold the pellets together, and heat the raw material to high temperatures to “bake” a durable pellet.

A number of research teams in North America and abroad are working on developing just the right recipes for making and burning pellets. One leader is Cornell University in Ithaca, New York, where agronomist Jerry Cherney has demonstrated the practicality of an array of pellet burners for home heating (www.GrassBioenergy.org). In New England, the Maine Technology Institute has given a small grant to X Café, a coffee maker, to fine-tune burning pellets made from waste coffee grinds (Christiansen 2009). In Minnesota, the nonprofit Agricultural Utilization Research Institute (www.auri.org) has been testing pellet machines – in part because several Midwestern utilities are thinking about burning biomass pellets in their coal-fired power plants in order to meet new renewable energy requirements. Despite these efforts, however, pellet making is still “more of an art than it is a science,” Agrecol president Mark Doudlah recently told Biomass Magazine (Christiansen 2009).

Better than Brewing?

Still, he and other biomass advocates believe that biomass burning technology can be perfected – and that the immediate economic and environmental payoff would be greater than, say, promoting the conversion of corn to ethanol.

For instance, “the simple act of planting grass is a surprisingly effective tool for reducing global warming emissions,” notes the Growing Wisconsin report, drawing on studies done by biogeochemist Phil Robertson of Michigan State University in East Lansing and Chris Kucharik of the University of Wisconsin, Madison. “A field converted from high input corn to low input perennial grass and kept in grass for 10 years would decrease emissions by 13.2 metric tons,” it concludes, adding that a “100,000 acre switchgrass biomass project would be equal to removing 240,000 cars from the road” (Porter et al., 2008).

Other researchers note that favoring grass over row crops can also bring a host of non-energy benefits – from increased habitat for everything from birds to bees, to less erosion and better water quality, since grasses typically need lower inputs of fertilizer and farm chemicals (Landis 2008).

Once harvested and pelletized, the grass could have a number of uses. A growing corps of researchers, for instance, is examining how switchgrass might be used to reduce greenhouse gas emissions from power plants. One, by Xiaoyun Qin and colleagues at Texas A&M University, found that simply replacing some coal with switchgrass quickly brings significant, relatively easy reductions in emissions. But costs are still relatively high, the study warned, and “a mix of technological, market and policy actions are needed to enhance biomass feedstock competitiveness” (Qin et al., 2006). (A tax on carbon, for instance, could make switchgrass fuels much more competitive.)

Burning grass biomass should also produce more energy than converting it into ethanol with new “cellulosic” technologies, which are still largely theoretical. In a recent article in Alternatives Journal, for instance, Samson and several colleagues estimated that a unit of energy used to convert switchgrass to cellulosic ethanol will return 4.4 to 6.1 units (other researchers have arrived at somewhat lower and higher estimates). In contrast, converting the grass to pellets and burning them would at least double the return – to 12.8 units of energy – and produce up to 90% less greenhouse gas emissions (Purdon et al., 2009). “Switchgrass, even when grown on marginal sub-prime land, produces more than nine times the energy per acre of land than does the leading biofuels technology of corn (grain) ethanol,” concludes the Growing Wisconsin study (Porter et al., 2008).

Combustion advocates also note that big isn’t necessarily better when it comes to burning biomass. While many ethanol advocates have grand global dreams of producing lakes of liquid fuels, combustion promoters tend to think locally. “Combustion works at a lot of scales,” says Samson. “You can heat a home or small business, fuel a district heating system, put biomass in a regional power plant. So you don’t necessarily need a huge, centralized investment.” Some cities in Minnesota and Wisconsin, for instance, are talking about producing their own pellets from waste material, and using them in municipal facilities. And even some corn-to-ethanol plants in the Midwest have been exploring how to produce energy from their own non-woody biomass (Morey 2009).

If big economies-of-scale are desirable, however, burning advocates predict that supersizing their technology would be simply cheaper than many alternatives. It should cost about $9 million to establish a commercial-scale grass pelleting plant, for instance, concludes an analysis by Ken Campbell of the Minnesota Agricultural Utilization Research Institute (Porter et al., 2008). That’s a fraction of the costs associated with wood pelleting and celluslosic ethanol facilities, according to industry statistics.

No consensus

Other energy analysts don’t necessarily dispute those figures. They just argue that they are beside the point.

“Liquid fuels aren’t easy to replace with other forms of energy – unfortunately, you can’t just burn biomass to run a car or truck,” says Lee Lynd, an environmental engineer at Dartmouth University in New Hampshire who has been developing cellulosic technologies (http://engineering.dartmouth.edu/faculty/regular/leelynd.html). He believes biomass will play a role in combating climate change. But he also argues that while there are lots of climate-friendly ways to produce heat and electricity – from wind to solar – there are just a few ways to produce green liquid fuels.

“Biomass is uniquely suited to producing sustainable transportation fuels — there aren’t a lot of options,” he says. The bottom line, he believes, is that “the highest, best use” of non-woody biomass like switchgrass is likely to be liquid fuels, assuming cellulosic technologies pan out.

In the meantime, however, combustion advocates see little harm in moving ahead. “A case can certainly be made that the energy provided by switchgrass pellets cannot be directly put into a car and used as fuel,” notes the Growing Wisconsin study, for instance. But it also notes that the U.S. is using “approximately 6% of its petroleum for heating oil and is also importing increasing amounts of natural gas. Switchgrass pellets can be used to displace these fuels and increase available fuel for the transportation sector.” No matter how you look at it, the authors argue, burning biomass is “a compelling option” for producing green energy (Porter et al., 2008).

From dream to reality

Making that compelling option a reality, however, will take more than persuasive data. In Europe, for instance, governments have provided a combination of regulatory sticks and carrots to “stand up” its biomass burning industry – from special air pollution rules and technical standards for factories and home heaters that burn biomass to tax credits and direct funding for everyone from farmers and pellet makers to consumers and researchers (AEBIOM 2008).

In the U.S., however, such efforts are still nascent – or nonexistent. That’s something the new Biomass Thermal Energy Council hopes to change. Over the next few years, it hopes to persuade federal and state officials to pump more funds into offsetting the costs of installing biomass heaters, for instance, and to tweak renewable energy plans to make high-efficiency biomass fuels more attractive. It also wants to make sure that current tax incentives – such as a 30% federal credit for the buyers of certain kinds of biomass-related equipment – are sustained, and perhaps expanded. And it will urge Congress to recognize the “carbon neutral” nature of renewable biomass fuels (which store as much carbon as they release) when it comes to writing new climate change laws. And the group is bullish on its future. “Thermal energy from biomass has enormous growth potential,” says BTEC head Serfass.

In Canada, REAP’s Samson is also seeing reasons for optimism. “Some government officials are reconsidering their enthusiasm for liquid ethanol,” he says, “and there are some very large farms interested in growing grass for heating fuel.” In part, that’s because several Canadian utilities have announced plans to experiment with burning biomass along with coal in their electricity plants. Ontario Hydro, for instance, is out shopping for 2 million tons of pellets, Samson says, creating a potentially lucrative market for grass pellets.

Like many other combustion advocates, Samson says that policymakers are still a bit drunk on the promise of liquid ethanol – but that the inevitable hangover is coming. “The Canadian and U.S. governments have really been taken astray by the lobbyists on the whole liquid fuels thing,” he says almost mournfully. “There is no science to justify the skewed spending allocations right now. So we just need to keep putting the data out there and making the case.”

Eventually, he believes, policymakers will see the light – and it will be from the flickering flame of a pellet made of grass.

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