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Getting serious about climate changeDr Jon Gibbins, Principal Investigator for the UK Carbon Capture and Storage Consortium, suggets a fundamental change in the way we use fossil fuels that can help save the planet before it is too late. CAPTURING the carbon dioxide produced when fossil fuels are used and placing it securely back in the earth’s crust offers a unique approach to the problem of human-induced climate change. Carbon capture and storage (CCS) technologies are probably the key to unlocking climate change negotiations and making a successful transition to a low-carbon global energy economy. Currently CCS is being picked up by the oil industry as a way to get extra oil as well as to reduce CO2 emissions. But when the urgency of tackling climate change is outstripping the ability of governments alone to respond it is important to use every opportunity at hand to get this game-changing technology deployed at a global scale as soon as possible. Global needFossil fuels, although a dwindling resource, are not dwindling fast enough for the climate. The Intergovernmental Panel for Carbon Change (IPCC) estimates that up to 5000 Gt of fossil fuel carbon could still be emitted, 10 times the amount since the start of the Industrial Revolution and much more than is currently expected to lead to irreversible ‘tipping point’ events. While there are still many uncertainties, it is clear either that significant amounts of fossil fuels will have to be left unused, essentially for ever, or that they will have to be used in such a way that the resulting carbon dioxide doesn’t do any harm – with carbon dioxide capture and storage.
Alternatively, the fuel can first be gasified and reformed to produce hydrogen and carbon dioxide. The CO2 is then removed and the hydrogen burned in a conventional gas turbine power plant (instead of natural gas) to generate ‘decarbonised’ electricity. The hydrogen may also be used directly, for example in future hydrogen vehicles. Initial designs for capture plants, based on conventional power and chemical plant technologies, are expected to add an extra 1-3p/kWh to the cost of electricity with CCS. Practical experience might lead to this cost penalty being halved through innovation and development. For geological storage, the captured CO2 is compressed to around 100 atmospheres, forming a liquid with about the same density as water. The liquid CO2 is then injected into porous rock layers a kilometer or more underground with impermeable rock sealing layers on top of them. Depleted oil (and gas) reservoirs are good places to store CO2, provided old wells are plugged properly. The rock seals have already held gases for millions of years and it is easy to calculate how much dense phase CO2 they can hold. Ideal storageBut there are also many saline aquifers with suitable seals on top. Preliminary estimates are that these could store much more CO2, probably enough to hold the emissions from all or most of the world’s fossil fuels. Injecting CO2 into ageing oil fields can also wash out extra oil, a process known as enhanced oil recovery (EOR). Especially with higher oil prices, revenue from EOR can cover at least some of the costs of capturing, transporting and injecting the CO2. These CCS+EOR projects are important to get CCS deployed as quickly and widely as possible during an interim period while carbon prices are still too low to make most storage-only schemes viable. Also EOR is probably the only legal offshore CO2 storage option, until the OSPAR and London Conventions’ rulings on placing substances under the seabed can be brought up to date. If the additional oil from EOR displaces other oil production then the net increase in emission rates is likely to be small. With suitable incentives, projects can usually be planned to give long term CO2 storage significantly in excess of CO2 from incremental oil. Many new CCS+EOR projects are now at the planning stage – in the USA, Canada, China, Norway and the Middle East as well as in the UK. In one of the first such projects, BP and Scottish and Southern Energy announced plans a year ago to generate low-CO2 electricity at Peterhead Power Station in Scotland and send the captured CO2 through an existing pipeline to the offshore Miller oilfield. A smaller number of ‘pure’ CCS schemes with CO2 injection into aquifers or depleted natural gas wells are also being considered, using either lowcost CO2 sources or direct government subsidies to get satisfactory project economics. For the next 15–20 years large numbers of fossil fuel plants will, however, continue to be built without CCS, especially in rapidly-developing economies such as China and India and for urgent replacement of worn-out 60s’ and 70s’ infrastructure in Europe and the USA. It is important that these are at least made ‘capture ready’, so that capture equipment can be retrofitted later without extensive downtime and unnecessary expenditure. Only minor up-front costs are involved, for additional space on site and some small design modifications.
Key contributorsImperial College and 13 other universities and research institutes are participating in the UK Carbon Capture and Storage Consortium (UKCCSC), funded by the Research Councils’ ‘Towards a Sustainable Energy Economy’ (TSEC) programme. Work so far has included a paper at the Exeter G8 Climate Change conference, showing how CCS could be used to address the UK’s 2020 generation and emission gaps. UKCCSC members have also contributed to the Science and Technology Select Committee’s recent inquiry on CCS. If the ongoing energy review supports current proposals from BP, E.ON and others for CCS projects in the UK, an outcome that seems likely, given the critical importance of CCS for global climate change mitigation efforts, then UKCCSC will have a major role to play in developing the necessary knowledge and skills, and also in helping to transfer these to key overseas users such as China. Useful web addresses for more on CCS and climate change:
JON GIBBINS is a Senior Lecturer in the Energy Technology for Sustainable Development Group within Mechanical Engineering. He is raising awareness of CCS’s possible role as part of a more sustainable UK and global energy supply, with participation in a number of industrial projects on new CCS developments, several invited presentations to parliamentary groups and inputs to academic and professional meetings and the media in the UK and abroad. He has recently given oral evidence to the Science and Technology Committee inquiry on CCS (as part of a UKCCSC group) and to the UK Energy Review. Jon is especially interested in integrating power cycles with post combustion and oxyfuel CO2 capture equipment, in order to improve overall performance, and in ‘capture ready’ concepts for all types of plant. |
Carbon dioxide can be captured
from conventional power plants
by washing the flue gases with
CO2-specific solvents before they are
vented to the atmosphere. 