AAPG Explorer - American Association of Petroleum Geologists

AAPG
EXPLORER
Mobile filter unit gets field test
Putting the ‘Clean’ in Coal Technology
By BARRY FRIEDMAN, EXPLORER Correspondent
Clean coal technology is one of those
concepts that in theory work for
everyone: environmentalists, the
industry at large, coal producing states,
American consumers.
It also is, however, an illusive and
expensive concept, often argued about.
How clean is clean? How much clean
can we afford? Does it even exist?
The devil really is in the details – in
this case, in the coal. Literally.
Simply put, the dirtier the coal, the
tougher it is to clean; the more it’s
cleaned, the more expensive the energy
AMBROSE
derived from it becomes.
AAPG member William Ambrose,
who presented a paper on clean coal
20 JULY 2011 WWW.AAPG.ORG
“Carbon capture and storage
isn’t cheap and isn’t easy, but
is worth it.”
technology at the recent AAPG Annual
Convention and Exhibition, admits that
“CCS” (the catchall phrase for “carbon
capture and storage”) isn’t cheap and
isn’t easy, but is worth it.
“Coal-gasification technology can
achieve reductions in mercury, arsenic
and sulfur up to 80 percent, as well as
CO2 capture at levels of as much as 90
percent.”
More importantly, says Ambrose, who
is a research scientist for the Bureau of
Economic Geology at the University of
Texas, Austin, as well as a past president
of AAPG’s Energy Minerals Division,
there’s so much coal available, we owe it
to ourselves to use it.
“The United States has a
superabundance of coal, with almost
six quintillion BTU of energy-equivalent
resources,” he said, “more than Eastern
Europe and the former Soviet Union
(FSU) combined.”
The Price Is Right?
Cleaning coal involves stripping
of minerals and other impurities via
high-temperature and high-pressure
gasification with capture of CO2 and
hydrogen. Minerals and impurities that
are stripped from coal are oxides of
nitrogen and sulfur (referred to as NOx
and SOx), mercury, sulfur, arsenic, metals
such as lead and cadmium, and ash.
Here’s the catch, though. It comes, as
Ambrose admits, with an “appreciable
price tag.”
The costs of capture, transport and
storage of CO2 range, he estimates, from
$25 to more than $50 per metric ton.
This depends on a variety of factors,
including:
u Pre- versus post-combustion carbon
capture.
u New plant versus retrofitted plant.
u Type of gasifier feedstock.
u Distance of new plants from user
electric load.
Operational costs, too, will increase
the cost $15 per metric ton.
The net result is that the overall
energy penalty of installing CO2-capture
equipment could reduce plant efficiency
by as much as 40 percent.
“And when one figures in the
additional costs on new construction of
new CO2 pipelines or pumping costs
associated with CO2 sequestration in
deep, brine-bearing formations, the cost
of electricity could go up by 25 to 50
percent or more,” Ambrose said.
To put those cost increases in
perspective, he added, while $50 per
metric ton may not seem like a great
amount, the state of Texas, for instance,
accounted for 152 million metric tons (Mt)
from coal-fired power plants in 2008. To
capture and sequester all this CO2 would
cost $7.6 billion per year.
So why bother?
Ambrose is clear.
“Harnessing these vast resources
could help the U.S. to lessen its
dependence on foreign energy sources.”
Clean, Right Now
And it’s not like it isn’t already being
done effectively.
“Actually, clean coal processes
have been under way in the United
Continued on next page