Hoovering Up CO2 with CCS-equipped Biomass Power Plants
Last year's update from the Intergovernmental Panel on Climate Change identified biomass-fired power plants that capture their carbon—and thus sequester atmospheric CO2—as one of the most critical tools available for stabilizing climate change by the end of this century. Last week, researchers at the University of California at Berkeley reported that carbon-capturing bio-power plants could go two steps further, rendering the entire Western North American power grid carbon-negative by 2050.
The idea behind bioenergy with carbon capture and storage, or BECCS, is to capture carbon emissions from a combustion power plant's effluent using the same equipment and methods employed by a few CCS-equipped coal-fired power plants. Once such plant, which started up in September in Saskatchewan, is the world's first commercial-scale coal power plant to capture over 90 percent of its carbon.
But whereas power plants that capture and sequester fossilized carbon can, at best, achieve carbon-neutral performance, BECCS can be carbon-negative. That's because the carbon in the wood and other biofuels they burn was sucked from the atmosphere as the plants grew. Storing that atmospheric carbon underground is tantamount to generating electricity while actually doing Earth's climate a favor.
Last week's report, in the journal Nature Climate Change, purports to be the first detailed simulation of how BECCS would play out in a particular region. The research team, led by Daniel Kammen, director of the Renewable and Appropriate Energy Laboratory at UC Berkeley, simulated BECCS deployment on the Western power system (which interconnects most of the U.S. and Canada west of the Rockies, plus Mexico's Baja California). Their SWITCH-WECC model is a standard power grid model augmented with information about the location and cost of biomass fuel sources.
After screening the sustainability of biomass resources available in the region from forestry, agriculture, and municipal wastes, the researchers identified enough biomass to meet between 7 and 9 percent of projected electricity demand for 2050. But they found that pushing BECCS to that level had an outsize impact on total power sector emissions.
By combining BECCS with aggressive deployment of renewable energy and fossil-fuel emission reductions, they projected that grid-wide carbon emissions could be reduced by 145 percent in 2050 relative to 1990 levels. In that scenario, with BECCS providing carbon-negative baseload power to complement solar, wind, hydropower and other renewable installations, overall emissions from the Western N.A. grid come in at -135 megatons of CO2 per year. That's enough to offset all of the emissions from Alberta's unconventional oil drilling, twice over.
No doubt critics will question the validity and relevance of Berkeley's findings, starting with the alleged carbon benefits. Many critics argue that bioenergy production leads to changes in land use—such as clearing of forests—that can generate large carbon releases and thus undercut the notion of negative emissions.
Then there is the cost of capturing carbon from power plant emissions. The Saskatchewan coal plant's CCS equipment has been so pricey to install and operate that it may cost more per kilowatt-hour to run than the 12 cents that its operator, SaskPower, gets for selling the electricity it generates.
In SaskPower's case, it pencils out because they can sell the captured CO2 to a nearby oil and gas operator, which uses it to stimulate oil production in the process of storing the CO2 underground. But the scale of BECCS contemplated by UC Berkeley's study is well beyond what oil markets will support. That means massive cost reductions must be achieved in the decades ahead.
The third major question facing all future carbon capture and storage operations, whether they capture atmospheric or fossil CO2, is how securely the CO2 can be sequestered underground. Five years ago, one of the world’s largest CCS operations experienced large surface deforming, raising the spectre that rock layers expected to keep injected CO2 underground could fracture. No CO2 escaped from that remote Algerian site, but operators prematurely terminated CO2 injection there, and anxiety over CO2 leakage has paralyzed a number of CCS projects.
According to the IPCC, these concerns are valid but, at least at present, none appear to be showstoppers. The international scientific body judges the challenge of stabilizing climate to be too large and important to eliminate BECCS from consideration. Berkeley's study is likely to strengthen that argument.