For years, optimists have talked up carbon capture and storage (CCS) as an essential part of taking emissions out of electricity generation. Yes, build wind and solar farms, they have said, but they can’t be relied on to produce enough power all the time. So we’ll still need our fleet of fossil-fuel-burning power stations; we just need to stop them pumping carbon dioxide (CO₂) into the atmosphere.
Most of their emphasis has been on post-combustion capture. This involves removing CO₂ from power station flue gases by absorbing them into an aqueous solution containing chemicals known as amines.
You then extract the CO₂, compress it into a liquid and pump it into a storage facility – the vision in the UK being to use depleted offshore oil and gas fields. One of the big attractions with such a system is it could be retrofitted to existing power stations.
The big let-down
But ten years after the UK government first announced a £1 billion competition to design CCS, we’re not much further forward.
The reason is summed up by the geologist Lord Oxburgh in his contribution to the government-commissioned report on CCS published last year:
There is no serious commercial incentive and it will stay that way unless the state demonstrates there is a business there.
The problem is that the process is costly and energy intensive. For a gas-fired power station, you typically have to burn 16% more gas to provide the capture power. Not only this, you end up with a 16% increase in emissions of other serious air pollutants like sulphur dioxide, nitrogen oxides and particulate matter.
Concerns have also been expressed about the potential health effects of the amine solvent used in the carbon capture.
You then have to contend with the extra emissions from processing and transporting 16% more gas. And all this before you factor in the pipeline costs of the CO₂ storage and the uncertainties around whether it might escape once you’ve got it in the ground. Around the world, the only places CCS looks viable are where there are heavy state subsidies or substantial additional revenue streams, such as from enhanced oil recovery from oilfields where the CO₂ is being pumped in.
Well, say the carbon capture advocates, maybe another technology is the answer. They point to oxy-combustion, a system which is close tor eaching fruition at a plant in Texas, USA.
First proposed many years ago by British engineer Rodney Allam, this involves separating oxygen from air, burning the oxygen with the fossil fuel, and using the combustion products – water and CO₂ – to drive a high-pressure turbine and produce electricity.
The hot CO₂ is pressurised and recycled back into the burners, which improves thermal efficiency. It has the additional advantage that CO₂ is also available at pressures suitable for pipeline transportation.
It is, according to some enthusiasts, the “holy grail” of CCS. Admittedly it looks promising, but I wouldn’t go that far. It’s not suitable for retrofitting existing power stations. With many existing stations viable for several decades, this will do little for immediate emissions. And you are still obtaining and moving fossil fuels in large quantities, with the resultant emissions along the way. Finally, my experience would indicate that there is always very significant cost growth with new technology scaled up to industry.
One UK post-combustion CCS project that was cancelled earlier this year was the joint-venture between SSE and Shell at the Peterhead gas-fired ation in northeast Scotland. It aimed to capture 10m tonnes of CO₂ over a 10-year period and store it 2km under the North Sea.
Let’s put this saving into context. The diagram below summarises the amount of power produced and used in the UK. It shows that the country uses 108 terawatt hours (TWhrs) of domestic electricity per annum.
UK electricity generation/consumption
Of this domestic usage, 16% goes to cooking. Boiling kettles makes up 34% – that’s 5.9TWhrs per annum, the equivalent of a 670MW power station. Domestic kettle use is particularly inefficient as we regularly overfill our kettles. We could save at least half the energy if we boiled only what we need to make tea and coffee.
That would negate the need for 335MW of power. Now compare that to what CCS would have saved from Peterhead – 85% of a 400MW gas turbine, or 340MW. Simply by not overfilling our kettles, we could remove about the same amount of CO₂. Unlike CCS, let alone oxy-combustion, we could do this immediately, for free, and cut our electricity bills and remove various air pollutants at the same time.
Of course, being kettle smart will only deliver a fraction of the UK’s required carbon reduction goals. It’s only about 3TWhrs out of the approximately 170TWhrs produced by gas-fired power in the UK each year. But it hopefully illustrates why energy efficiency is a much smarter way of reducing carbon and other harmful air emissions than CCS.
If we took the same approach to lighting, computer monitors, TVs on stand-by, running water and everything else, it becomes a very different proposition. If we could achieve the aim of a carbon-neutral house, we could shut down half the UK’s existing gas-fired power stations. And if industry and other non-domestic consumers made energy savings of the order of 20%, that would bring down the gas-fired power requirement by a corresponding percentage.
Is 20% realistic? As a chemical engineer with a 40-year industrial career, I am confident it is. Key areas to be considered would be pump and compressor efficiency, energy use in separation processes, combined heat and power, furnace fuel management, green concrete and energy integration.
Together with the government giving greater priority to renewable energy like offshore wind and solar, you have a viable plan for delivering the UK’s carbon goals. CCS may still have its place, but as a means of removing carbon emissions from burning things like wood and rubbish as opposed to fossil fuels. Suffice to say it looks more promising on that front.
But in short, it is time for governments to stop wasting time and money on technologies like CCS that aren’t working.
They need to finally get serious about leading a major drive for energy efficiency instead.
Tom Baxter is Senior Lecturer in Chemical Engineering at Aberdeen University.
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