https://phys.org/news/2019-10-carbon-capture.html
October 25, 2019
Study casts doubt on carbon capture
by Taylor Kubota, Stanford University
One proposed method for reducing carbon dioxide (CO2) levels in the
atmosphere—and reducing the risk of climate change—is to capture carbon
from the air or prevent it from getting there in the first place.
However, research from Mark Z. Jacobson at Stanford University,
published in Energy and Environmental Science, suggests that carbon
capture technologies can cause more harm than good.
"All sorts of scenarios have been developed under the assumption that
carbon capture actually reduces substantial amounts of carbon. However,
this research finds that it reduces only a small fraction of carbon
emissions, and it usually increases air pollution," said Jacobson, who
is a professor of civil and environmental engineering. "Even if you have
100 percent capture from the capture equipment, it is still worse, from
a social cost perspective, than replacing a coal or gas plant with a
wind farm because carbon capture never reduces air pollution and always
has a capture equipment cost. Wind replacing fossil fuels always reduces
air pollution and never has a capture equipment cost."
Jacobson, who is also a senior fellow at the Stanford Woods Institute
for the Environment, examined public data from a coal with carbon
capture electric power plant and a plant that removes carbon from the
air directly. In both cases, electricity to run the carbon capture came
from natural gas. He calculated the net CO2 reduction and total cost of
the carbon capture process in each case, accounting for the electricity
needed to run the carbon capture equipment, the combustion and upstream
emissions resulting from that electricity, and, in the case of the coal
plant, its upstream emissions. (Upstream emissions are emissions,
including from leaks and combustion, from mining and transporting a fuel
such as coal or natural gas.)
Common estimates of carbon capture technologies—which only look at the
carbon captured from energy production at a fossil fuel plant itself and
not upstream emissions—say carbon capture can remediate 85-90 percent of
carbon emissions. Once Jacobson calculated all the emissions associated
with these plants that could contribute to global warming, he converted
them to the equivalent amount of carbon dioxide in order to compare his
data with the standard estimate. He found that in both cases the
equipment captured the equivalent of only 10-11 percent of the emissions
they produced, averaged over 20 years.
This research also looked at the social cost of carbon capture—including
air pollution, potential health problems, economic costs and overall
contributions to climate change—and concluded that those are always
similar to or higher than operating a fossil fuel plant without carbon
capture and higher than not capturing carbon from the air at all. Even
when the capture equipment is powered by renewable electricity, Jacobson
concluded that it is always better to use the renewable electricity
instead to replace coal or natural gas electricity or to do nothing,
from a social cost perspective.
Given this analysis, Jacobson argued that the best solution is to
instead focus on renewable options, such as wind or solar, replacing
fossil fuels.
Efficiency and upstream emissions
This research is based on data from two real carbon capture plants,
which both run on natural gas. The first is a coal plant with carbon
capture equipment. The second plant is not attached to any
energy-producing counterpart. Instead, it pulls existing carbon dioxide
from the air using a chemical process.
Jacobson examined several scenarios to determine the actual and possible
efficiencies of these two kinds of plants, including what would happen
if the carbon capture technologies were run with renewable electricity
rather than natural gas, and if the same amount of renewable electricity
required to run the equipment were instead used to replace coal plant
electricity.
While the standard estimate for the efficiency of carbon capture
technologies is 85-90 percent, neither of these plants met that
expectation. Even without accounting for upstream emissions, the
equipment associated with the coal plant was only 55.4 percent efficient
over 6 months, on average. With the upstream emissions included,
Jacobson found that, on average over 20 years, the equipment captured
only 10-11 percent of the total carbon dioxide equivalent emissions that
it and the coal plant contributed. The air capture plant was also only
10-11 percent efficient, on average over 20 years, once Jacobson took
into consideration its upstream emissions and the uncaptured and
upstream emissions that came from operating the plant on natural gas.
Due to the high energy needs of carbon capture equipment, Jacobson
concluded that the social cost of coal with carbon capture powered by
natural gas was about 24 percent higher, over 20 years, than the coal
without carbon capture. If the natural gas at that same plant were
replaced with wind power, the social cost would still exceed that of
doing nothing. Only when wind replaced coal itself did social costs
decrease.
For both types of plants this suggests that, even if carbon capture
equipment is able to capture 100 percent of the carbon it is designed to
offset, the cost of manufacturing and running the equipment plus the
cost of the air pollution it continues to allow or increases makes it
less efficient than using those same resources to create renewable
energy plants replacing coal or gas directly.
"Not only does carbon capture hardly work at existing plants, but
there's no way it can actually improve to be better than replacing coal
or gas with wind or solar directly," said Jacobson. "The latter will
always be better, no matter what, in terms of the social cost. You can't
just ignore health costs or climate costs."
This study did not consider what happens to carbon dioxide after it is
captured but Jacobson suggests that most applications today, which are
for industrial use, result in additional leakage of carbon dioxide back
into the air.
Focusing on renewables
People propose that carbon capture could be useful in the future, even
after we have stopped burning fossil fuels, to lower atmospheric carbon
levels. Even assuming these technologies run on renewables, Jacobson
maintains that the smarter investment is in options that are currently
disconnected from the fossil fuel industry, such as reforestation—a
natural version of air capture—and other forms of climate change
solutions focused on eliminating other sources of emissions and
pollution. These include reducing biomass burning, and reducing halogen,
nitrous oxide and methane emissions.
"There is a lot of reliance on carbon capture in theoretical modeling,
and by focusing on that as even a possibility, that diverts resources
away from real solutions," said Jacobson. "It gives people hope that you
can keep fossil fuel power plants alive. It delays action. In fact,
carbon capture and direct air capture are always opportunity costs."
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