Carbon sequestration

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 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.

Current projects

All the projects in this section are funded and active except where noted.

  1. 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.
  2. 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.
  3. 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.
  4. 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 USGS[8]. Liquid 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.
  5. 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 inauguration.
  6. CO2SINK: small-scale test trapping of CO2 in a saline aquifer in Germany has started.
  7. RECOPOL: small scale injection of CO2 in deep seated coal layers in Poland has started.
  8. 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 rates.

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.

Planned projects

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.

Sequestration summary

Some ideas, such as extracting the carbon dioxide from the gasses emerging from gas wells and re-injecting it, look pretty reasonable.

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.