Biomass Fuel: Worse for Climate than Coal?

The crackling log fire, flickering in an open hearth, may win the day for romance or Christmas cards. From the modern viewpoint of efficiency and good health, it’s more of a horror-show. Our ancestors, living in unvented huts lit and warmed by open fires, wheezed and coughed their way to early death. Burning wood still releases an old-timey scented bouquet of toxins: nitrogen oxides, sulfur dioxides, carbon monoxide, volatile organic compounds, dioxin, and a couple dozen other chemicals classified as hazardous air pollutants, along with ultra-fine particles of super-toxic soot that go deep into the lungs. As a 2007 Health Canada review put it, “Even though wood smoke is natural, it is not benign.”

For that reason, a well-run modern biomass-burning power plant is much less smoky than a fireplace. High-tech smoke scrubbers with multisyllabic names like "electrostatic precipitator" and "regenerative thermal oxidizers" scrub the exhaust, and operators work continually to bring down pollution levels, tweaking temperatures and fuels. The state-of-the-art may be UBC’s $34-million Bioenergy Research and Demonstration Facility reported on in the first installment in this series: what comes out of its smokestack is even cleaner than emissions from most natural-gas plants.

That achievement is likely exceptional. In the United States, a Wall Street Journal review of 107 biomass-fueled power plants found that 79 per cent had been cited in the previous five years for violating air or water-pollution standards. Prompted by health concerns, the American Lung Association, Massachusetts Medical Society, and Florida Medical Association have all come out against large-scale wood-burning to produce energy.

Technology, as the UBC facility shows, can keep harmful wood smoke out of the air. But there’s a much bigger question hanging over the wildfire popularity of capturing energy from British Columbia’s forests. As reported yesterday, for all its accomplishments in keeping the air clear, UBC’s high-tech burner nonetheless still emits about 5,000 tons of climate-changing carbon dioxide a year -- about the same amount as the natural-gas power it replaces.

So, how can UBC claim that the new facility has reduced its emissions by that amount?

The answer to that question holds both the promise and the temptation of burning plant matter -- biomass, whether it comes from trees or straw -- for energy. The promise is that plants grow, capturing carbon from the atmosphere as they do. That means that when we burn one tree, releasing its carbon, the tree that replaces it will capture that carbon again: a fuel that cleans up after itself!

But all that takes time: the clean-up of the carbon released by burning the tree may take decades. Meanwhile, temptation arises to consider biomass energy "zero-carbon" from the day it’s trucked out of the forest. (See infographic at the top of this story.)

British Columbia has put energy from wood at the heart of its Bioenergy Strategy, aimed at reducing the province’s greenhouse gas emissions by a third by 2020 and by 80 per cent by 2050. In Europe, former coal power plants are being converted to burn woody biomass instead, allowing several countries to claim to be meeting their targets for emission cuts under Kyoto Protocol rules that consider all biomass energy as zero-carbon today. Selling B.C. wood in pellet form to many of those plants has turned the province into a major exporter of biomass energy.

In reality, however, wood combustion produces unavoidable quantities of climate-changing carbon dioxide. And while some or all of that may be taken up into trees that grow in the future, “anything that comes out of a smokestack is still going to have an impact,” notes Ananda Tan, the Vancouver-based Canada/U.S. regional coordinator for the Global Alliance for Incinerator Alternatives.

So has UBC really cut its emissions by 5,000 tons, or not? And what about all those European countries?

Three key dynamics

Three dynamics affect the answer. One is the difference in the energy density (the amount of energy produced from a given amount of fuel) between wood and fossil fuels like coal or oil. Another is whether new trees do in fact recapture the carbon released by burning previously harvested trees -- and how quickly.

A third is particularly relevant to British Columbia, where 18 million hectares of forests have been infested so far by the mountain pine beetle -- and the felling of those trees has doubled in the last few years. The common wisdom is that those trees are going to die, disintegrate and release their carbon anyway, so why not burn them and get some juice for the grid out of them instead? But is that assumption right?

Let’s start with the density problem. Burning a kilogram of coal produces more energy than burning a kilo of wood. Which means that you need to burn more wood to get the same amount of electricity as you would from a smaller amount of ancient carbon in the form of coal or oil, releasing more actual carbon to the atmosphere.

The Intergovernmental Panel on Climate Change confirmed the inference in a 2006 document that evaluated carbon dioxide releases compared to energy produced for 53 different fuels. It determined that wood and wood wastes had a greenhouse emission factor roughly 20 per cent higher than coal. Even after biomass is “densified” in pellets, the U.S. Department of Energy’s Biomass Energy Data Book, determined, “the bulk density (and hence energy density) of most biomass feedstocks is... between about 10 and 40 per cent of the bulk density of most fossil fuels.”

As a result, according to one study by the Manomet Center for Conservation Studies for the Massachusetts Department of Environmental Conservation, burning wood to produce electricity produces 46 per cent more emissions, kilowatt-hour-for-kilowatt-hour than burning coal. Yes! Burning coal actually produces fewer climate-altering emissions than burning wood.

This startling fact was confirmed again this month, when the Pelham, Mass., based Partnership for Policy Integrity and American Lung Association analyzed 88 biomass power plants in more than two-dozen U.S. states from California to Maine, and reported that on average they emitted 50 per cent more greenhouse gasses per kilowatt of electricity generated than coal plants did. (They also released eight times as much other air pollution as the cleanest fossil fuel, natural gas.)

There are other factors. Wood has to be dried before it can be burned. How’s that done? By burning more wood to heat improbably large dryers. “Think of your clothes drier at home multiplied by about a thousand times,” says Gordon Murray, executive director of the Revelstoke-based Wood Pellet Association of Canada. Then, wood is bulky. It takes more energy, and emissions, to deliver pellets than coal to generate a needed amount of power.

But if new growing trees are recapturing all the carbon expended in harvesting, drying, shipping and burning woody biomass, the volume that’s being cut, shipped and burned shouldn’t make a difference, right? It’s all net-carbon-zero in the end.

Are new trees cleaning up after old?

That gets us to the second question: will new growing trees actually recapture the carbon released when the last generation was burned? UBC researchers who monitored carbon emissions from forests regenerating on Vancouver Island found that three years after being logged, a hectare of regenerating Douglas Fir seedlings, far from capturing carbon, was releasing 22 tons of it over a year. Even 18 years after being logged, another area was still releasing 5 tons of carbon dioxide per hectare.

That’s assuming new forests are planted. The carbon “offset” certificates that many companies buy to cancel out their fossil-fuel emissions by capturing an equivalent amount of carbon in a growing forest, typically meet detailed standards to ensure that the carbon is really being removed from the atmosphere.

The same careful accounting doesn’t apply to biomass destined for fuel: British Columbia has struggled historically to ensure that Crown forests are replanted once their trees are cut down, much less that they actually balance out carbon-wise. The number of natural resource officers on the provincial payroll tumbled by 46 per cent between 2009 and 2012, with actual inspections of forestry operations falling by two-thirds. In 2012, British Columbia’s auditor-general found that provincial ministries were failing to ensure reforestation kept up a sustainable pace with timber harvesting.

Lastly, there are all those trees dead and dying from the beetle plague. They’re marked to supply nearly half the additional renewable electricity produced under B.C.’s Bioenergy Strategy through 2020. And after all, they’re just going to decompose and release their carbon anyway, so why not?

Because, says David Moore of the University of Arizona, dead forests don’t actually give up all that much carbon, at least right away. Moore tracked carbon dioxide coming off of forests in Colorado for 10 years after they were hit by beetles. “We didn’t see a big release,” Moore said. “Over this 10-year period, [carbon]’s not going anywhere. It’s just staying there.”

It’s not only that standing trees hold a lot of carbon still tied up in their trunks and branches. It’s also that once the trees die they stop hosting the billions of underground fungi and microbes that suckled on the living trees’ roots, and exhaled carbon dioxide. Dead trees equal fewer fungi and microbes, equals less CO2 being exhaled. Once trees do fall over, some of the carbon released as they decay gets absorbed into the soil, rather than into the air.

Of course, standing dead trees are also potential fuel for forest fires, which release their carbon as certainly as if they were burned as fuel, only without any benefit to the economy.

Seeking the carbon-neutral point

Still, if enough young trees are planted when we burn today’s biomass harvest, then at some point several decades out, the carbon released from burning that wood will have been recaptured in trees. At that point, if tree-growing and burning are in perfect balance, the climate effect of using wood for fuel will indeed be neutral.

But we’re a long way from that today, with no guarantee we’ll ever reach a balance of burning and growing. Doing all the sums to calculate the point when today’s carbon emissions from biomass will have been recaptured is a daunting task.

The Manomet Centre’s study for the state of Massachusetts tried. It calculated, based on in-state data, that even a switch from coal to biomass fuel in power generation today would still take at least 20 years and probably more like 50 before moving into the positive column for the climate by becoming truly carbon neutral. If wood were chosen in place of natural gas to substitute for coal, the climate break-even point doesn’t come until the 22nd century.

Other research, reported in the latest IPCC climate impacts report, suggests the same goes for Europe. Continental claims of reduced emissions from conversion to biomass energy will be “offset partly or entirely for decades or centuries,” the report said, because of increased carbon releases from logged-over land.

The forest or the trees

That conclusion sparks vigorous rebuttal from Michael Weedon, executive director of the BC Bioenergy Network, an industry group supported primarily by provincial and other government grants. “That’s a seriously flawed report,” Weedon says. Mainly, he adds, Manomet’s assumption that whole trees would be cut to generate electricity overlooked mill residues -- the source of more than half of B.C.’s anticipated biomass energy.

European and North American trade groups have taken up the same chorus, sponsoring a report contesting Manomet’s findings on similar grounds. Eighty-five per cent of B.C. fuel biomass, that report added, comes from sawmill waste, with the rest coming from logs judged unsuitable for lumber.

The proportion of harvested wood that’s classified as unsuitable for lumber and therefore eligible to become biomass fuel -- 15 to 20 per cent of what’s cut, according to industry estimates -- has been a contested issue in British Columbia’s forests in the past. It may become contentious again, if the findings of researcher Caren Dymond are factored into decisions about whether to burn those “unsuitable” trees for energy.

Dymond, a staff scientist with the B.C. Ministry of Forests, worked on the first comprehensive study to break down the “carbon budget” of B.C.’s biomass energy industry. She looked specifically at whether cutting down beetle-infested trees for power makes sense for the climate.

Her finding: if 85 per cent or more of the trees in a forest are fatally infested and dead or dying, it’s better for the climate to clear them out for fuel and replant new saplings that will suck up carbon. But if as few as one tree in five in a forest stand will survive the beetles, cutting it for fuel is a net minus for the climate. Even if the wood replaces dirty coal in power production, more carbon will be retained by leaving the dead trees standing than by burning their biomass.

UBC’s climate claims for its new power plant may nonetheless have some validity. Although the plant releases about as much greenhouse gas as the one it replaces, much of the biomass it burns is urban wood waste. In the past, that might have been sent to the landfill where, decomposing beneath tons of other trash in the absence of oxygen, it would have released methane, a greenhouse gas 21 times more potent than carbon dioxide. (Although nowadays landfills almost uniformly neutralize the methane; some even produce power from it.)

But the UBC plant is far from typical. Worldwide, a huge amount of biomass energy is obtained from wood not by converting it to syngas but rather the old-fashioned way: simply by burning the stuff. “Bioenergy from biomass is not carbon neutral,” Dymond said. “And the emissions need to be calculated and accounted for over time.”

That raises some big questions about whether B.C.’s ability to supply the world with growing volumes of biomass from climate-friendly energy forests, can live up to its promise.

Those questions will be tackled in the final part of this series, running tomorrow on The Tyee.