VTDigger: Biomass: A sustainable, but “never carbon neutral” resource

Jun 29, 2011 No Comments by

Reposted here from VTDigger.

As farmers have abandoned fields over the last 150 years, Vermont’s landscape has dramatically shifted from a largely agricultural terrain to forests that now blanket three-quarters of the state. Forest is still converted to fuel here: Many residents burn cordwood in rural areas as a primary source of heat.


Recently, though Vermonters have begun to think about forest fuel in a new way – as “biomass,” or renewable energy from wastewood products that can be used to heat homes, college campuses and even enormous 19th and early 20th century structures that house the seat of state government in Montpelier.


Several municipalities are considering district biomass heating systems, and big electricity generation build-outs like the Beaver Wood Energy plant in Fair Haven remain on the table.


Forests are the latest fuel in a long-running debate: How much of the region’s woodlands can–or should–be harvested?


Some experts worry that Vermont is trending toward a denuded future. “There is a conventional wisdom in the region that wood is abundant and cheap,” said Bob De Geus, a forester for the Vermont Department of Forests, Parks and Recreation. “There is a lot of indication that it is neither.”


Adam Sherman, program director for the Biomass Energy Resource Center, says biomass generation requires trade-offs, but he argues that it’s worth it.


“It was short-term thinking that got us into the current climate debt,” he said. Regionally harvested biomass fuel curbs use of oil, coal, and natural gas while promoting local autonomy, for better and worse, according to Sherman. “Having it in our backyard, being our own watchdogs, seeing the impacts of what our demand is, it’s the only way we can manage that resource sustainably.”


Supply chain: The Montpelier microcosm

Montpelier’s future biomass district heating project relies on a Combined Heat and Power plant, an upgrade and expansion of existing boilers located on State Street. Woodchips are trucked in by Limlaw Pulpwood and Chipping, a West Topsham logger who specializes in the screened chips suited to biomass heating, often called “bolewood.”


Biomass power plants like Burlington’s McNeil Generating Station and Ryegate, which average around 25 percent efficiency after thermal loss from steam generation, can burn low-grade “whole-tree chips,” which BERC describes as “tops and stems from harvested logs, processed in the forest into various-sized chips that also contain bark, and sometimes forest debris.”


Biomass heating plants like Montpelier’s, however, usually burn bolewood chips to maintain their potential 75 percent to 80 percent efficiency. As small-scale biomass heating blossomed in Vermont in the 1980s, as public schools adopted the technology, plants could purchase wastewood from sawmills processing logs into dimensional lumber. Those milled corners and smoothed ends produced a byproduct suited to biomass heating without significantly increasing tree harvesting.


With sawmills and papermills shuttering over the past two decades–causing declines in the demand for pulpwood as well as the availability of milled wastewood, pegged at around 200,000 tons per year in Vermont–Limlaw capitalized on the market’s dearth of quality woodchips, upgrading his logging operation to provide screened chips for biomass heaters.


That shift, mirrored by loggers and haulers around the region, signified a new direction in forest harvesting that’s seen in the supply chain for Montpelier’s plant. A 2008 BERC Feasibility Study conducted for the city found that as wastewood and milling residues become scarce, loggers harvest wood for chip fuel as a primary product: “While some wood fuel sourced for the Montpelier CHP system may be a by-product, a majority of the supply will come directly from harvesting.”


Forests, by the ton

A raft of studies on regional forests preceded Montpelier’s CHP plan, and state foresters, the University of Vermont and the Biomass Energy Resource Center regularly parse statistics to monitor the state’s woodlands. While most agree that Vermont can sustain current harvest levels, consensus fragments over the future.


Looking specifically at low-grade wood–the kind harvested for biomass and sometimes for firewood–Vermont’s forests produce around 900,000 green tons per year beyond current demand, a figure that both state foresters and BERC agree upon.


Zeroing in on Montpelier’s estimated 20,000 tons-per-year burn, an April 2010 study by Innovative Natural Resource Solutions, a Maine company previously hired by the Vermont Land Trust and the Vermont Timberland Owners Association, found that within 30 miles of Montpelier, 650,000 tons of timber growth exceeded harvest levels annually. Montpelier officials claim 360,000 tons within 50 miles, and a recent Biomass Energy Resource Center study found 283,000 excess tons available within 25 miles.


It’s this type of discrepancy that’s at the heart of debates over Vermont’s sylvan future.


“Montpelier will defend its project by pointing out that they have paid for a professional fuel supply study, showing that they’ll have an adequate and even ample supply of affordable wood,” De Geus said. “But it’s very, very difficult to forecast future supply.”


De Geus cautions that the means to forecast forest growth “aren’t particularly robust.” The national program tracking growth–USDA Forest Inventory and Analysis studies–remains the benchmark dataset for most organizations, including the Innovative Natural Resource Solutions and Biomass Energy Resource Center studies for Montpelier and Vermont. While the study is good at measuring forest area and volume of trees, says De Geus, it is a less accurate predictor of growth rates: “When it gets to growth, [the study] is relatively weak as an estimate, with a broad confidence interval” or margin of error.


“If you factor in the range, being responsible,” he cautions, “then you’re faced with the reality that you may be seeing your forest grow in the negative, losing volume.”


A 2011 report from the Cary Institute of Ecosystem Studies, co-authored with the University of Vermont, concluded that “the magnitude of the sustainable forest biomass supply is far smaller than most previous studies have suggested.” All of the forests in New England and New York could supply less than 6 percent of the region’s energy use, even with current, efficient technology like Combined Heat and Power systems.


A February letter to Sen. Bernie Sanders, I-Vt., from a coalition of academics from Tufts, Williams College and the Partnership for Policy Integrity stated that current wood demand from biomass in Vermont, coupled with new construction of proposed biomass facilities, would create a future demand of more than double Vermont’s forest capacity.


Adam Sherman, BERC’s program director, says that any measurement of forest growth vs. forest loss (which he puts at a 2-to-1 ratio right now) depends on a baseline comparison. He argues that the decline of Vermont’s pulpwood market over the past 20 years has been precipitous, tracking with mill closures in Quebec and Maine. Increasing the current harvest may not represent an overall increase when compared to historic levels. “It’s just swapping one for another.”


De Geus applauds Montpelier–“the people involved are more sensitive to the risks than just about anyone else”—but he maintains that larger operations, such as the proposed Fair Haven power plant and pellet manufacturers, will incur problems no matter what the historical baseline. “When you ramp up demand, we can’t really look to the past to indicate whether problems will emerge, because we’ve never been at that level of demand.”


Local, but not necessarily carbon neutral

Wrapped up in the question of how deeply Vermont should tap its forests is climate change. The proposed district heating plant in Montpelier, called a “low carbon option,” will produce double the heat generated at the current state facility while releasing “in total fewer regulated air contaminants,” according the city’s Voter Guide.


Harold Garabedian, the city’s project manager and a former deputy director at the state’s Air Pollution Control Division, says electrostatic precipitators will scrub some of the worst-case 80 tons of pollutants emitted annually from the new facility. While a medley of emissions is possible, it’s the greenhouse gas carbon dioxide that garners the most attention.


“Biomass emits more carbon dioxide than fossil fuels per unit of energy produced, and is never a ‘carbon neutral’ fuel,” assert Professors William Moomaw, Lara Shore-Sheppard, and Mary Booth in their letter to Sanders.


They cite a 2010 study by the Manomet Center for Conservation Sciences, commissioned by the Massachusetts Department of Energy Resources to look at the potential for biomass in the state. (Massachusetts Gov. Deval Patrick recently proposed that any new biomass plant must conduct a life-cycle study showing a reduction in greenhouse gas emissions by 50 percent or more over 20 years, and must operate at 60 percent efficiency.) Interpretations of the widely-read study remain controversial.


“There’s a lot of nuance to that idea of net [carbon] neutrality,” said Adam Sherman, whose organization participated in the Manomet study. Two BERC staffers were among the authors, including Chris Recchia, the now-deputy secretary of the Vermont Agency of Natural Resources.


The study took up the relationship between carbon debt and carbon dividends, or the amount of carbon emitted from harvesting and burning biomass vs. the amount of carbon re-sequestered by forests. While myriad factors influence the rate of carbon sequester, like forest health, logging practices, and the type of forest, the idea is simple: burning wood emits carbon instantaneously, and sequestering it takes time–“ten, twenty, or thirty years” for small-scale, efficient, thermal-only combined heat and power plants like Montpelier’s, allege the authors of the Sanders letter.


“I think a lot of people get hung up on whether there’s an initial carbon debt and the dividend doesn’t kick in until down the line,” said Sherman. “If we say we’re not going to employ things that don’t have immediate dividends on carbon reductions, then we run the risk of continuing to burn coal, oil, natural gas, which is a way one way street.” He points out that the amount of time it takes to capture carbon in petroleum fuels is on the scale of millions of years, while forests can capture carbon within years or decades.


The biological balancing act of managing forest harvests and burn rates with an eye toward sequestering carbon is, at least partially, at the mercy of the markets.


Montpelier’s biomass advocates cite the low cost of woodchips as a primary benefit to the updated district heating plant. Fuel oil would have to drop to $1.14 a gallon to compete with current per-ton rates for bole chips, hovering around $56/ton. Over the projected 30-year lifespan of the CHP–a lifespan very much tied to the plant’s carbon footprint–the cost of woodchips could skyrocket with the increased demand from future biomass plants.


“If Randolph, for instance, succeeds with a community district energy system, and a few other municipalities do likewise in the Central Vermont area, then we go from a situation of relative ease of access of fuel to relative restriction,” said De Geus. That’s of concern to an estimated 81,000 home-based wood-burners, many of whom are low-income residents who rely on firewood as their sole source of heat through the winter.


Although Sherman argues that a price increase won’t necessarily follow–“I don’t think we’ve really seen a dramatic increase from 20 years ago to today,” even as biomass has seen “huge increases”–he said that paying more for woodchips would encourage better forestry practices in Vermont, similar to buying more costly organic milk.


Despite the contested drawbacks, concludes Sherman, biomass needs to remain a part of Vermont’s manifold energy future. When it comes to tackling climate change, “there’s no silver bullet,” he said. “There are little pieces of silver buckshot.”


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