Is wood pellet-based electricity less carbon-intensive than coal-based electricity? It depends on perspectives, baselines, feedstocks, and forest management practices
P Dwivedi, M Khanna, and Madisen Fuller
Some studies suggest that the carbon intensity of electricity generated in the United Kingdom by using imported wood pellets from the southern United States is higher than that of coal-based electricity, whereas other studies suggest that the use of wood pellet-based electricity reduces carbon emissions significantly, relative to coal-based electricity. We developed the Forest Bioenergy Carbon Accounting Model (ForBioCAM 1.0) to analyze factors that influence the carbon intensity of wood pellet-based electricity, using a common set of assumptions and the same system boundary. We show that widely differing assessments of the carbon intensity of wood pellet-based electricity depend on the choice of forest management perspectives (landscape or stand), baselines (no harvest, or harvesting for the manufacture of traditional finished wood products), feedstocks (whole trees, pulpwood, or logging residues), forest management practices (change in rotation age), and the duration of the analysis itself. Unlike with a stand perspective, we demonstrate conditions under which a landscape perspective results in carbon savings net of avoided emissions from coal-based electricity. Our results also suggest that the two perspectives of forest management converge in their assessment of the positive carbon effects of various feedstock types used to manufacture wood pellets relative to a no-harvest baseline, and that the use of whole trees for wood pellets results in net carbon savings after a break-even period of about three years relative to a no-harvest scenario. The results of this study can guide future policy deliberations on the use of wood pellets as a renewable energy source worldwide.
By Oscar Holland
Stefano Boeri’s tree-covered towers in Milan won critical acclaim. Now he’s taking his urban forests global.
Architect Stefano Boeri has always been obsessed with trees. The Italian traces his fascination back to a novel he read as a child, “Il Barone Rampante” (“The Baron in the Trees”), in which a young boy climbs up into a world of trees and vows to never to return.
“I think trees are individuals,” Boeri said in a phone interview. “Each has its own evolution, its own biography, its own shape.”
Unsurprisingly, there is child-like wonder to the architect’s best-known building, Il Bosco Verticale, or the Vertical Forest. Built in his home city of Milan, the celebrated complex teems with greenery, its facades transformed into living, breathing organisms.
The project’s two residential towers — measuring 80 meters (262 feet) and 112 meters (367 feet) respectively — play host to around 20,000 trees, shrubs and plants. They spill out from irregularly placed balconies and crawl up the structures’ sides. By Boeri’s estimates, there are two trees, eight shrubs, and 40 plants for each human inhabitant.
The purported benefits of this garden architecture transcend aesthetics. Greenery, supposedly, provides shade to apartments, psychological benefits to residents and a home to wildlife. (There are, Boeri said, “hundreds of birds, more than 15 different species” nesting on the towers’ various floors.)
But the architect’s proudest claim is that the buildings absorb 30 tons of carbon dioxide and produce 19 tons of oxygen a year, according to his research, with a volume of trees equivalent to more than 215,000 square feet of forestland…
In September, Vertical Forest was named among four finalists for the RIBA International Prize, a biennial award honoring the world’s best new buildings. Amid the plaudits, Boeri claims the project’s real success is that it serves as a prototype.
The architect has far more ambitious designs. His firm has already unveiled plans for new Vertical Forest buildings in European cities including Treviso in Italy, Lausanne in Switzerland and Utrecht in the Netherlands.
In the Chinese city of Liuzhou, Guangxi province, he has masterminded an entire “Forest City,” scheduled for completion in 2020, which comprises tree-covered houses, hospitals, schools and office blocks over a sprawling 15-million-square-foot site. (Boeri said that he’s also been approached about producing similar “cities” in Egypt and Mexico.)
In July 2014, DECC published the Bioenergy Emissions and Counterfactual (BEAC) model, which investigates the impact on carbon emissions of various ways of sourcing woody biomass from North America to produce electricity in the UK. The calculator estimates the greenhouse gas intensity by taking into account the counterfactual land use for the scenario (i.e. what the land or wood would have been used for if it was not used for bioenergy). BEAC shows that some scenarios could save considerable carbon emissions compared to fossil fuels, whilst if others occurred they could cause emissions greater than fossil fuels. BEAC did not assess the likelihood of particular scenarios so, in spring 2015, DECC commissioned an independent study (led by Ricardo-AEA and including North American forestry experts) to assess the likelihood that the most carbon intensive BEAC scenarios are happening now or if they might happen in the future, and what might drive or constrain them.
The study found that the majority of the high carbon scenarios identified in the BEAC report are unlikely to occur, but there are four that may be already happening or may happen in the future, although their scale is likely to be limited or uncertain.
The research identified economic decision making as driving forestry practices: the main value of a tree is in sawtimber, not biomass for wood pellet production. It is therefore unlikely that demand for biomass would cause foresters to change behaviour to harvest sooner than they intended, or to switch to supplying wood for bioenergy, but they may increase the intensity with which they manage forests.
As the world works to replace fossil fuels, wood pellets are playing a key role in decarbonizing power grids. European nations, in particular, have invested heavily in pellets for both heating and electricity generation. To supply this increased demand, global trade in pellets has doubled since 2012, with U.S., Canadian and European producers all playing a role. How this supply stream may evolve is the focus of the European Pellet Supply and Cost Analysis, a new study from RISI, an information provider for the global forest products industry.
ACS Sustainable Chem. Eng., 2016, 4 (12), pp 6355–6361
The use of renewable biomass for production of heat and electricity plays an important role in the circular economy. Degradation of wood biomass to produce heat is a clean and novel process proposed as an alternative to wood burning, and could be used for various heating applications. So far, wood degradation has mostly been studied at ambient temperatures. However, the process needs to occur at elevated temperatures (40–55 °C) to produce useable heat. Our objective was to study wood degradation at elevated temperatures for its potential application on heat production. Two (a thermotolerant and a thermophilic) fungi with different degradation strategies were chosen: lignin-degrading Phanerochaete chrysosporium and cellulose-degrading Chaetomium thermophilum. Each fungus was inoculated on nonsterile and sterile birch woodblocks to, respectively, study their wood degradation activity with and without natural biota (i.e., microorganisms naturally present in wood). The highest wood decay rates were found with C. thermophilum in the presence of natural biota, followed by P. chrysosporium under sterile conditions. The estimated theoretical value of heat production with C. thermophilum under nonsterile conditions was 0.6 W kg–1 wood. In conclusion, C. thermophilum seems to be a promising fungus to degrade wood together with natural biota, as sterilization of wood is not feasible in practice. Further testing on a larger scale is needed to implement the obtained results and validate the potential of biological wood degradation for heat production.
By DONG Energy
For the past 18 months, Avedøre Power Station has been converting its coal-fired power station unit, and the entire combined-heat-and-power plant is now able to produce electricity and heat based on wood pellets and straw, rather than coal and gas.
“Following the conversion of unit 1 at Avedøre Power Station, we can produce heat for more than 215,000 Danish households in the Greater Copenhagen area without using coal or gas. The conversion is a major contribution to achieving a green district heating system in the Greater Copenhagen area as well as a green electricity system, supplementing solar and wind power,” says Thomas Dalsgaard, executive vice president at DONG Energy.
FutureMetrics recently published a white paper, titled “The Lowest Cost Solution for Maximum Decarbonization of the Power Sector While Maintaining Grid Reliability,” that compares two scenarios for powering carbon emissions in the power generation sector.
The first scenario assumes coal plants are retired and replaced with new combined cycle natural gas generation stations. The second assumes that existing pulverized coal plants are modified to use wood pellets rather than coal. Within the paper, author William Strauss notes his analysis shows converting coal plants to wood pellets is the solution that provides significantly higher carbon dioxide reduction at a lower net monetary cost per avoided ton.
As wood pellet imports in Japan begin to accelerate, industry professionals offer cautious optimism that an Asian market opportunity for North American producers has arrived.
In July, Japan imported 52,000 tons of wood pellets, eclipsing the previous monthly high of 51, 500 tons set in December 2015. Additionally, monthly volumes in 2016 have been more consistent in contrast to the peaks and valleys that defined 2014 and 2015. As a result, Japan is expected to finish 2016 having imported between 350,000 and 400,000 tons of wood pellets and producers around the world are optimistic that Japan’s wood pellet demand is set to rise steadily to 1 million tons per year within the next handful of years.
Maine is poised to finally begin shipping wood chips to Europe for power generation next year if plans underway at Eastport and Searsport stay on schedule.
After years of false starts, these developments would be especially welcome now, as the ongoing decline of the paper and in-state biomass power industries has hit hundreds of loggers and truckers who used to harvest and move fiber to Maine mills and generators. The value of U.S.-based wood fuel sent to the European Union in 2015 exceeded $684 million, according to export research firm WISERtrade, but none of it came from Maine.
The state’s first opportunity could come next year in Eastport, where the port authority has been working on export plans since 2009. A company it has partnered with is building special equipment that processes the chips to standards required in Europe. Chris Gardner, the authority’s director, said that while the equipment may be ready by year’s end, he thinks it’s more realistic to begin exporting wood chips in 2017.
US utility company Duke Energy Carolinas (DEC) has issued a request for 750,000MWh of energy located in its territory, including biomass and landfill gas installations.
Results from the request for proposals (RFP) will help DEC meet North Carolina’s 2007 Renewable Energy and Energy Efficiency Portfolio Standard (REPS), which mandates the company generate 12.5% of its retail sales in the state by renewable energy or energy efficiency programmes by 2021.
The RFP is open to biomass, landfill gas, solar, wind, and other facilities that qualify as a renewable energy resource under REPS requirements, excluding swine and poultry waste.