Sounds impressive, doesn't it?

A story from the Business section of yesterday's Western Mail caught my eye:

Biggest carbon capture test planned for Aberthaw Power Station
By Aled Blake

Aberthaw Power Station could host the UK’s biggest carbon dioxide capture pilot project connected to a working power station.

RWE, the power station’s owner, has applied for planning permission to construct a plant capable of testing the capture process on emissions direct from the power station.

At 3 MW in size the plant will be at least eight times the size of existing post-combustion projects in the UK and will operate for twice as long. It will be capable of capturing up to 50 metric tonnes of CO2 per day.

Western Mail, 10 November 2009

Impressive, eh? Well, that's obviously what RWE would like you to think. All you need to say is "Wales leads the world" and a tame reporter from the local rag (sorry, the National Newspaper of Wales) will lap it up unquestioningly. Aled Blake certainly seems to have re-worked their press release without thinking to put these figures into any sort of perspective.

But as he might not accept it from me, I'll let his fellow reporter Lisa Jones do it instead:

Aberthaw is Wales’ biggest polluter
By Lisa Jones

A power station in the Vale of Glamorgan has been revealed as Wales’ biggest polluter.

Aberthaw Power Station tops the league tables of the 10 dirtiest sites in Wales, based on Environment Agency information.

Last year the coastal power station between Barry and Llantwit Major pumped out more than 7.4 million tonnes of carbon dioxide, the gas which is a major contributor to climate change.

It also belched out 28,325 tonnes of nitrogen dioxide and 30,953 tonnes of sulphur dioxide – both gases which help to create acid rain.

South Wales Echo, 8 December 2007

We can all do the maths for ourselves. Aberthaw produces over 20,000 tonnes of CO2 per day. This new plant will collect less than a quarter of one percent of it!

This should act as a sobering reminder that the words "clean coal" are, in any practical terms, just gobbledygook. They sound impressive, but will not deliver.

That's not to say that it can't be done. It can be done, but it requires a different approach. What RWE are proposing is to retrofit a post-combustion capture plant. This will be almost useless.

The problem is that, at present, the UK government seems to think that it is possible to retrofit post-combustion capture to any new plant, such as Kingsnorth, by allowing space for it at the design stage. That is not quite as misleading, but nearly as much so. At full scale I'm sure it will capture more than 0.25% ... but still not nearly enough to make a significant difference.


In my opinion the only way to really make clean coal work is with pre-combustion capture: a process in which the coal is first gassified, the CO2 separated from the resulting syngas, and the hydrogen which remains burnt in very much the same way as natural gas but without producing CO2. Doing it this way also makes the power plant very much more flexible, because the output of electricity can be tailored to suit variations in demand. Burning coal directly only works well for continuous base load generation.

This means that power stations like Aberthaw are hopelessly doomed (it's had a good run for its money, but needs to be put out of its misery sooner rather than later) ... but it also means that new coal power stations such as the one proposed for Kingsnorth are fatally flawed from the outset.

By diverting money into projects of this nature the UK Government is failing to put sufficient emphasis on developing the sorts of technologies that will make a big difference, most notably tidal energy. We in Wales can produce all the electricity we need from renewable sources, but the Assembly can't develop it on any scale because it is not a devolved matter. Instead we are locked into an agenda that suits England's energy needs rather than our own.

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Anonymous said...

Don't be too hard on them. It is only a test. If it works they can scale it up.

MH said...

Yes, it's only a test. But that was my point: that we're still nowhere near able to talk about using this sort of capture at a large enough scale to make any real difference.

The technology of the process is fine. Although the story doesn't give details, I'd guess it's by a cycle of chemical absorption in one chamber, with the CO2 released in another chamber by heating the mixture up. It then has to be cooled before it can do the cycle over again. The CO2 also has to be cooled or compressed to make it transportable. It takes energy to do this.

This test plant uses 3MW of energy to capture 0.25% of the CO2. If that process were scaled up, it would take 400 times the energy to capture all the CO2, some 1,200 MW. The total output of the plant is only about 1,400MW. It would take 86% of the energy Aberthaw produces!

Now of course there would be economies of scale which would make everything more efficient, but how much more efficient? It is not doing it that's the problem, but doing it efficiently.

Anonymous said...

Aled, regrettably you are factually incorrect about pre-combustion capture. It is not flexible at all and it has very poor availability, which are the two reasons why the large UK generators do not support this technology in the UK.

First let me explain what availability means. We need 40GW of new power plant in the coming 20 years to replace only plant and meet rising demand. Gasification plant, which is at the core of pre-combustion capture, has a diabolical availability record for generation having, on average, less than 50% availability. That means that for half the time you want the plant on it wont work.

Secondly your statement about flexibility is absolutely the opposite of the truth. When you add carbon capture to a gasifier in the form of pre-combustion capture, you make the plant less flexible and it is not very flexible to start with. Whether you like it or not, the commercial situation in the UK is that fossil plant must be flexible - it is the only plant that can be turned down in off-peak hours. Wind is not dispatchable, which means you cannot call upon it whenever you wish because the wind may not be there. Nuclear cannot be turned on and off and there is no proven method of storing sufficient energy to capture the excess generation between peak and off-peak demand. The poor flexibility of pre-combustion capture means it will never be commercially viable on a small island like the UK with limited grid connections. Only small companies who effectively want the Government to subsidise their entry into the market are proposing this technology. Generators that have tens of millions of customers need to consider simply could never take the risk.

Pre-combustion might be barely viable in countries where there is a massive interconnecting grid and a large surplus of plant but that is unlikely to be the case in the UK for 50 years. Last but not least, as you claim to be knowledgeable about the technology, you probably also know that no one has yet built a hydrogen burning turbine that will match the theoretical efficiencies quoted by university academics that are needed to make the technology viable. Ask a supplier if you don't believe me and see if you can get a quote to supply one. Pre-combustion capture is no panacea for generating clean electricity from coal and it’s misleading to write an informed article suggesting otherwise.

MH said...

I presume your comment was addressed to me, Anon.

You've not grasped the basic point ... which is not your fault, since I took it for granted as something obvious rather than saying it explicitly.

I was not talking about pre-combustion capture and generation as a continuous process. The crucial point is that the gas can be stored. When it is then burned to generate electricity, it has the same inherent flexibility as burning natural gas, meaning that the electricity produced can be ramped up very quickly in response to changes in demand.

I would also pick you up on you point that fossil fuel power stations are "the only plant that can be turned down in off peak hours". Yes, that does apply to gas, which might take a matter of minutes to get up to full production; but not nearly so much to coal, which might take hours to do so. Hydro is even more flexible in that it can be turned down and ramped up in a matter of only seconds. Wales has plenty of opportunities for more hydro and pumped hydro, and the same principle can be used in interconnected tidal lagoons.

As for burning hydrogen, I'd appreciate something to back up your claim. In theory burning either hydrogen or syngas should be more thermodynamically efficient. But even if it were marginally less efficient, that drawback would be more than balanced by the additional flexibility.

For me, flexibility is the most important factor in the energy mix. In order to make maximum use of intermittent renewables such as wind (and yesterday's news about Round 3 shows we are progressing wind very quickly, which is good, but unbalanced) we need to have readily available, quickly switched in, back-up. Pre-combustion capture can provide that in a way that post-combustion capture can't.

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