Coal produces lots of carbon dioxide no matter how it is used.
The currently hyped solution for large, fixed coal-powered plant,
e.g. electricity generation, synthetic petrol or oil production,
is carbon sequestration. This means that the carbon dioxide is
separated from the plant's exhaust gases, compressed and pumped
into exhausted coal mines or depleted oil and gas wells. It
sometimes seems that supporters of carbon sequestration visualise
a nice, shiny new power station with its chimney bent over and
vanishing, together with the carbon dioxide, into the ground.
Sorry, but it ain't so neat.
Some of the points that must be considered are:
- the economics of sequestration: apart from the capital
costs there are energy costs for separating, compressing and
transporting the carbon dioxide to the storage site. Estimates
of the energy used for sequestration range from 10% to 40% of
the plant's output.
- what proportion of the total emissions of the energy
production cycle can be captured. A detailed estimate by Peter
Viebahn of the German Aerospace Centre (DLR, Stuttgart) shows
that, at best, carbon sequestration can capture 67% of the
total emissions from coal burning energy production, which
makes a coal burning plant with carbon sequestration at best
comparable with a modern CCGT generator burning natural
- the costs of building and maintaining the transport system.
This is minimal if the consuming plant is close to the disposal
site. However depleted oil wells are not usually close to coal
mines, so either the fuel or the waste carbon will have to be
shipped elsewhere. As a concrete example, Montana is currently
promoting the idea that, by making synthetic oil from its vast
coal seams, the USA will be freed from any dependence on Middle
Eastern oil. Montana's coal is in shallow seams, so it would be
extracted from open cast mines. You can't sequester anything in
a worked-out open-cast mine for more than a few seconds, so
sequestration would have to be off-site. I think the nearest
depleted oil wells are in central California....
- the carbon dioxide will probably be piped away, so the
pipeline needs to be duplicated unless the source plant is to
be shut down whenever the pipeline needs maintenance. If the
disposal is in undersea wells the pipeline maintenance gets
harder and more expensive. These pipelines will not be small or
cheap. Every tonne of coal burnt generates 3.67 tonnes of
carbon dioxide, which must be removed just as fast as more coal
is shipped in. In addition, carbon dioxide can only be
liquified at room temperature at a pressure of 5.1 atmospheres
so the pipes will either need to be large, to carry the gas at
atmospheric pressure, or strong enough to be capable of
handling the high pressure needed to keep the carbon dioxide in
liquid form. Last but not least, the pipes and pumping
equipment must be made of materials that are not attacked by
carbon dioxide, even in the presence of water vapour.
- the sequestration site must guarantee to hold the
compressed carbon dioxide for millions of years. It must be
stored for far longer than nuclear waste has to be kept
because, unlike nuclear waste, sequestrated carbon dioxide
never loses its power to harm the ecosphere.
- some other questions that need attention are:
- can a worked-out coal mine ever be made
gas-tight, let alone for the forseeable future?
- an oil or gas well was gas tight when it was tapped,
but has it subsided and cracked its impermeable rock cap
while it was being emptied?
- did fracturing the oil-bearing rock, commonly done to
improve extraction rates, cause the impermeable cap to
- were the test and production bore holes all catalogued
- can they all be found?
- can they all be sealed well enough to guarantee no
leaks for millions of years?
- how is a leak to be detected?
- how can the leak be repaired without losing significant
amounts of carbon dioxide?
- if all carbon is to be sequestered, every fossil fuel
carbon atom extracted must be replaced with a molecule of
carbon dioxide. Carbon dioxide molecules weigh 3.67 times
as much as as a carbon atom. It has 2.26 times the volume
of a carbon atom or 2.07 time the volume of the
CH2 repeating unit in hydrocarbons (oil). What
are the geological consequences of replacing carbon or
CH2 units with the equivalent number of carbon
- undersea wells contain water. Carbon dioxide dissolves
in water to form carbonic acid. Can we guarantee that this
will not damage the impermeable rock cap or borehole seals
over geologic ages? Indications are that we can't. See the
Texan Gulf coast injection experiment
- the oil reservoirs may have been sealed since the
Carboniferous era but can we guarantee that the refilled
reservoirs remain sealed through future geological ages and
tectonic shifts? Bear in mind that not all oil-bearing regions
are geologically stable. California and Iran spring to mind
here. Some projects appear to be ignoring this point. See the
BP and the Edison Mission Group project
The most promising separation method is to gassify coal,
extract the carbon dioxide from the resulting syngas and use this
to drive combined cycle gas turbine generators. The extracted
carbon dioxide would be dried, compressed and shipped off to the
storage facility. This is not a zero carbon system: some carbon
dioxide will remain in the turbine's fuel and this will be
exhausted to the atmosphere. The energy cost of extracting the
carbon dioxide is 15-20%, giving an overall thermal efficiency of
35-40% - about the same as current coal-fired plant. This
information came the report of the Cycles for
Low Carbon Dioxide Production conference, held at
Cranfield University in March, 2003.
Carbon sequestration is future technology. Here's a sample
showing the general state of play at July 2006. The projects and
results were found in online EU reports and New Scientist.
All the projects in this section are funded and active except
- natural gas extracted from the Sleipner gas field in the
North Sea, Norway, is 9% carbon dioxide. This component is
removed from the extracted gas and re-injected into a deep
saline formation consisting of a 200 m thick sandstone layer at
a depth of 1040 m. Re-injection started in 1996. Approximately
1 million tonnes of carbon dioxide have been re-injected per
year, replacing the 4 million tonnes of gas extracted.
- BP, Sonatrach and Statoil started a similar injection
project in 2004 at In Salah, Algeria, where the targeted
injection rate is 1.1 million tonnes per year. So far it has
stored 0.8 million tonnes of carbon dioxide.
- Weyburn in Saskatchewan, Canada has a similar scheme to the
one at In Salah, with a target injection rate of about 4.5
megatonnes per year. Both of these inject carbon dioxide into
existing oil wells to help the extraction process.
- Texan Gulf coast
injection experiment. An old, brine-filled oil reservoir in
the Upper Frio sandstone formation on the Texan Gulf coast has
been the site of a carbon dioxide injection experiment that
started in October 2004. This experiment is being run by the
and gas samples have been periodically taken for analysis,
starting before injection began. Recent samples taken in mid
2006, under two years since the experiment started, have a
composition suggesting that minerals, including carbonates, are
being dissolved out of the surrounding rock by the mixture of
carbon dioxide and salt water in the reservoir. If this
continues it may destroy the reservoir's seals, allowing the
carbon dioxide to escape into the atmosphere. This is likely to
be a general problem: many oil drilling sites have
carbonate-filled cracks in the impermeable layer that prevents
the oil and gas from escaping.
- the world's largest carbon dioxide postcombustion capture
was inaugurated on 15 March, 2006 at the Elsam coal-fired power
station near Esbjerg, Denmark. This is a pilot
project that doesn't seem to have done anything at all since
- CO2SINK: small-scale test trapping of CO2 in a saline aquifer in Germany has
- RECOPOL: small scale injection of CO2 in deep seated coal layers in Poland has
Basalt sequestration is being investigated by the Battelle Memorial Institute.
Lab-scale experiments show that if carbon dioxide is injected
into volcanic rock, it combines with the minerals in basalt to
form calcite. A larger field trial to inject 3000 tonnes of
carbon dioxide, the daily emission from a 150 MW coal-fired
power plant, into a Columbia River Baisin basalt body is being
planned. Another feasibility
study is being planned at the Wallula paper mill in Idaho.
This is potentially a good sequestration method since calcite
is a permanent, solid means of storing carbon dioxide and costs
will be comparable with simple carbon dioxide storage. However,
there may be unquantified consequences from forming large
amounts of calcite within a stable rock stratum and the
reaction that converts CO2 into CaCO3
(calcite) is 30-40 times slower than likely injection
Only the first three of these are up and running, giving a
total sequestration capacity of 6.5 megatonnes. The rest are at
either either purely experimental or apparently moribund pilot
projects (Esbjerg). Current emissions due to power stations and
industrial plant total about 8 billion tonnes per year, so the
much hyped sequestration currently handles 0.075% of this.
There is a lot of hot air being emitted about sequestration
projects, so I've listed only projects which have projected
operational dates and that indicate the technology to be used for
carbon capture and storage, together with some indication that
its transport has been considered.
- BP, ConocoPhillips, Shell and Scottish & Southern
Energy have started planning the world's first industrial-scale
project to generate low-carbon electricity from hydrogen. The
Peterhead Hydrogen Power project in Scotland would
"decarbonise" natural gas to produce hydrogen to power a 475MW
generator. 90% of the carbon dioxide would be re-injected into
the depleted Miller field in the North Sea. This should allow
the enhanced recovery of oil that would otherwise have remained
underground. It could be operational by the end of 2009.
- BP and the
Edison Mission Group project. This project is planning to
generate 500 Mw of low-carbon electricity in California by
gasifying petroleum coke and avoiding 4 million tonnes/year
CO2 emissions. This plant
could be operational by 2011. The carbon dioxide would be
injected into depleted oil fields in the Los Angeles basin to
recover oil that would otherwise remain trapped in the
- FutureGen is a commercial scale project in Matoon,
Illinois that promises near-zero emissions from the use of
carbon sequestration. On 30 January 2008 the Bush
administration cancelled funding for the project. It was
subsequently restarted on 12 June 2009 by the Obama
administration. On 3 October 2010 the domain name
had lapsed and not been renewed.
- Kingsnorth, on the Medway in Kent started planning in
2006 for two replacement coal-fired generators with vague plans
for retrofitting carbon capture systems at some unspecified
time in the future. In March 2009 the UK Government postponed a
decision on carbon capture indefinitely. The project is now on
hold and all references to carbon capture have
been removed from the web site.
Some ideas, such as extracting the carbon dioxide from the
gasses emerging from gas wells and re-injecting it, look pretty
However, I am not at all convinced that the current plot for
burying all those megatonnes of carbon dioxide produced by
burning coal in disused coal mines and oil wells is a safe or
permanent solution. Some, such as the Montana scheme, look
distinctly harebrained. The Texan Gulf Coast injection experiment
may well show that many otherwise suitable brine-filled
reservoirs can't be used.
There seems to be too much sequestration hype coming from the
ignorant, the lazy-minded, politicians and oil companies who
smell a revenue stream from dead oil wells. The fate of FutureGen and Kingsnorth tend to
reinforce this view.
If the carbon dioxide cannot be gotten rid of coal may be
usable for steam trains but not much else.