By John Kemp
LONDON Feb 11 Following President Barack
Obama's second inaugural address, which reaffirmed his
commitment to clean energy, there has been mounting speculation
the administration will impose stricter emission standards on
existing coal-fired power plants across the United States.
Cutting emissions from existing coal-fired plants is
essential to the administration's goal of limiting carbon
dioxide (CO2) emissions.
New power plants built after 2014 will already be subject to
tougher emissions limits under draft regulations published by
the Environmental Protection Agency (EPA).
EPA's Carbon Pollution Standard for New Power Plants,
published in 2012, will in effect prohibit construction of new
coal-fired plants unless they are eventually fitted with carbon
capture and storage (CCS) technology.
However, the standard's impact is likely to be limited. Even
before it was published, few if any power generating companies
were planning to add coal plants because burning natural gas is
currently much cheaper. Its main practical effect will be to
prevent new coal plants being built if the price of gas
The new rules will not apply to the existing fleet of 1,400
coal-fired power plants across the United States that accounted
for 37 percent of all electricity generated in the 12 months to
These long-lived plants will still account for nearly a
quarter of the country's generating capacity by 2040, according
to the Energy Information Administration (EIA)'s 2013 "Annual
In theory there are a wide range of options for cutting
emissions from coal-fired power stations, ranging from the
installation of integrated gasification and combined cycle
(IGCC) systems and highly-efficient supercritical boilers to
post-combustion CO2 scrubbers and oxyfuel combustion systems.
But IGCC systems are largely unproven, complex, and would
require the construction of an entirely new generation of
coal-fired power plants. Replacing subcritical boilers with a
new generation of supercritical ones would essentially mean
rebuilding existing power plants from scratch.
So in practice the options for retrofitting the existing
fleet come down to two: post-combustion CO2 capture and oxyfuel
Post-combustion CO2 capture has a proven track record, but
only in natural gas processing plants, steam methane reformers,
ethanol plants and other chemicals facilities, which produce a
relatively concentrated stream of CO2 in their exhaust gases or
as a by-product.
In contrast, the CO2 in the exhaust gases from a
utility-scale power plant is much more diluted, mixed with large
amounts of other gases, particularly nitrogen, which makes up
almost 80 percent of the air the plant takes in to burn the
The low concentration of CO2 in power station exhaust
requires large absorption systems that use a lot of energy and
water and substantially reduce the net energy output of the
Oxyfuel combustion plants solve this problem by burning coal
in a concentrated stream of oxygen rather than air.
Oxyfuel requires an expensive and energy-intensive air
separation unit (ASU) to produce the oxygen for combustion, but
the exhaust gases contain a much higher concentration of CO2,
without nitrogen, so the post-combustion absorption system can
be smaller, cheaper and use less energy.
Oxyfuel is the least-developed of the main options for
carbon capture. There are just two small pilot plants in
operation at Vattenfall's Schwarze Pumpe coal-fired power
station in Germany and Total's pilot project in Lacq, France.
"Despite being the least developed of the CO2 capture
options, oxyfuel combustion is perhaps the CO2 capture option
that the traditional electric power industry likes best,"
according to the authors of the "Global Energy Assessment 2012."
"This is most likely due to the lack of chemical processing
compared to the simple chemical processing of post-combustion
capture (systems) and especially the complex chemical processing
of pre-combustion CO2 capture," they wrote.
Oxyfuel continues to gain interest and development spending.
More than two dozen projects, ranging from laboratory scale
tests to pilot plants, have been undertaken or are planned,
examining how to make oxyfuel boilers work efficiency and
separate out the oxygen needed using less energy.
The Department of Energy is funding FutureGen 2.0, a
demonstration project that involves retrofitting an existing
coal-fired power plant in Illinois with oxyfuel technology to
capture more than 90 percent of its CO2 emissions, and store
them underground in a nearby saline aquifer.
FutureGen was originally conceived as an IGCC plant but
changed to oxyfuel in part because it could provide more useful
experience for retrofitting the rest of the country's existing
On Feb 4, the Energy Department announced that it was moving
ahead with Phase II of the FutureGen project.
"In cooperation with the FutureGen project partners, the
Department of Energy is investing in the upgrade of a coal-fired
power plant in Meredosia, Illinois, with oxy-combustion
technology ... This project will test oxygen separation
technology and exhaust processing technology ... at power plant
scales," the Department explained.
Phase II will including preliminary design, pre-construction
and engineering for the retrofitted power plant.
The main barrier to the commercial deployment of oxyfuel
combustion at utility scale is the ability to make large amounts
of oxygen cheaply and without using too much energy in the
"For oxy-combustion to be a cost-effective power generation
option, a low-cost supply of pure oxygen is required," according
to the U.S. Department of Energy's National Energy Technology
"In the most frequently proposed version of this concept, a
cryogenic air separation unit is used to supply high purity
oxygen to the boiler. This commercially available technology is
both capital and energy-intensive and could raise the cost of
electricity from coal-fired plants considerably, in addition to
degrading the overall plant efficiency," NETL explains on its
New supercritical coal-fired power plants can achieve a
thermal efficiency of 40 percent (40 percent of the energy
originally present in the coal is turned into usable
But if it is fitted with oxyfuel technology, even the most
advanced supercritical power plant will see thermal efficiency
drop to just 32 percent the Congressional Research Service (CRS)
explained in a report to Congress ("Carbon Capture: A Technology
Assessment" July 2010).
Oxyfuel plants would consume up to 25 percent more coal per
kilowatt of electricity produced. The main source of extra fuel
consumption is the air separation unit, which CRS estimates
would account for about 60 percent of the additional energy
"The most compelling need -- and a major focus for research
and development -- is for improved, lower-cost processes to
deliver large quantities of high-purity oxygen, the major cost
in current oxyfuel schemes," CRS wrote.
Praxair and BOC Group, both of which are
major manufacturers of industrial gases and equipment, have been
working on projects aimed at separating oxygen much more cheaply
and using less energy.
But oxyfuel plants are still a long way from commercial
deployment, let alone being cost-competitive with natural
New EPA regulations could give oxy-combustion technology a
much-needed push towards realisation. But the Obama
administration needs to take care its race to mandate CCS does
not outpace development of the technology.