Whatever happened to carbon capture?

05 Sep 2018 Dave Elliott

(Courtesy: iStock/Pgiam)

There was a time when carbon capture and storage (CCS) was seen as a major way ahead, allowing fossil fuels to be burnt with impunity – just add a CCS unit to the power plant. So the UK government had scenarios heavy on gas and even coal use, with CCS taking care of the emissions. Renewables were relegated to being “also rans”, alongside nuclear. However, while nuclear is still in the mix in a recent UK government Department for Business, Energy and Industrial Strategy (BEIS) scenario, at 13 GW by 2035, renewables now dominate with 45 GW by 2035, and CCS is all but forgotten – 1 GW by 2035 at most, with gas use declining rapidly and coal gone entirely.

CCS involves several difficult stages – the capture of the carbon dioxide produced from fossil fuel combustion via chemical absorption and then its release, with the gas being compressed and pumped along pipes for hopefully indefinite storage in empty undersea oil and natural gas wells or other geological strata. It is sometimes claimed that CCS can reduce CO2emissions from the use of fossil fuels by 80-90%, although in practice its overall efficiency may be more like 60-70%, since the various CCS processes use energy, and supplying that adds more emissions. Although some of the CO2 emission processing technology associated with CCS may help reduce some other emissions, such as acid gases and particulates, CCS cannot realistically be used for road vehicles, much less aircraft, and the social and ecological impacts and risks of coal mining, oil and gas extraction, and the transport of these fuels, remain unchanged.

Why use renewables to keep sucking CO2 out while still adding more – it’s endless!Dave Elliott

CCS has increasingly been seen as expensive and uncertain – the UK abandoned its £1 bn CCS power plant competition in 2015. It’s the same elsewhere. The flagship US Kemper coal CCS project has been halted. Norway, a CCS pioneer with its enhanced oil recovery technology, has now cut its CCS funding. Some work on CCS is still continuing, and there are around 17 projects running worldwide, although all but two of them are industrial gas processing or chemical plants, not power plants, and only four have dedicated geological CO2storage. While CCS may have some important industrial applications, as far as the power sector is concerned the overall message seems to be that for the moment it is “game over”for CCS, in the EU especially, with renewables offering a cheaper option.READ MORE

Negative carbon not on

This means that, as noted in my last post, hopes for the development of negative-carbon biomass with carbon capture and storage (BECCS) have also been stymied. Burning biomass can be (roughly) carbon neutral, but if the CO2 produced is then captured and stored, it is overall carbon negative. At one point the Energy Technologies Institute estimated that BECCS could supply around 10% of UK power along with a substantial net carbon reduction, servicing around 10 GW of power generation and other industrial sources fitted with CCS. However, its progress clearly depended on the success of CCS, as well as the development of bioenergy technology and the necessary sustainable sources – its wide-scale use implies a significant increase in biomass production and associated land and water use.

Using utilization

While CCS and BECCS now look like long shots, there is a bit more interest in a linked idea – carbon capture and utilization (CCU), which could also be used with biomass (BECCU). This approach avoids the need to store captured CO2, which would reduce some costs and risks. Instead, the CO2 is used as a feedstock for chemical conversion, using hydrogen, to synfuels or other products. If these products are valuable, that can offset the cost of CCU and the subsequent conversion process. However, it needs hydrogen.

Hydrogen is mostly produced at present from the high-temperature “steam reformation” of fossil gas so, as well as an energy cost, there is a CO2 output to deal with. To reduce that, we would have to go back to CCS again; we would be no further forward. But, even though it is currently more expensive, the availability of non-fossil hydrogen from the electrolysis of water, using surplus renewable electricity, might give CCU a boost at some point, enabling conversion of CO2 to methane, methanol or whatever without more CO2 resulting from the hydrogen production. Although costs are still high, that is already being done with renewable hydrogen in some power-to-gas projects in Germany and elsewhere, with the methane being used for power generation, heating or in vehicles. Of course, burning the methane creates CO2, but since that was initially captured from a power plant exhaust, the overall process can be roughly carbon neutral.

Straight from the air

Capturing carbon dioxide from power or industrial plants is not the only option. Carbon dioxide can also be captured direct from the air. In direct “air capture” CCU systems, air is sucked through large filters in towers, with a recyclable chemical absorbent like NaOH to separate out the CO2. That can then be released and stored, making the process carbon negative. Or it can be used for synfuel production, although then it is no longer carbon negative, since CO2 is produced when the synfuel is burnt. But it can be carbon neutral if the energy to make the hydrogen needed for synfuel production comes from a green source.

The main advantage air capture has over conventional power plant/industrial CCS/CCU apart from, potentially, being carbon negative in the case of CCS, is that it can be done anywhere. It does not have to be at or near a power plant. It is also much more efficient at capturing CO2 than bio-photosynthesis, so it takes up less land area. However, given that it does requires energy, it seems unlikely to be cheaper to extract CO2 from air than to avoid its production by using renewable energy-powered devices, such as wind turbines, directly for power. In theory, renewable energy sources could power the air capture process, but it is not clear if that is the best use for their output in carbon-saving terms. Why use renewables to keep sucking CO2 out while still adding more – it’s endless!That said, the proportion of CO2 in air is very much lower than in the exhausts of power plants, so this approach has a fundamental problem compared with conventional CCS or CCU, although some see it as viable. Bill Gates has supported the development of one such system. And tests on prototypes are under way.

Where next?

Clearly, ideas continue to emerge for carbon capture. Some of them are quite clever and might cut CCS costs. Others might take us in another direction. However, as with many of the negative carbon technologies looked at in my last post, for the moment it all seems some way off, with mainstream CCS mostly stalled. There are still some small projects underway, with the emphasis more on CO2 utilization and storage as a possible extra. For example, the UK government has just announced a £15m programme for work on “carbon capture use and storage”. But otherwise the idea that CCS might play a major and early role in carbon reduction seems somewhat less credible.READ MORE

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So what’s the bottom line? CCS might play a role in Asia, where coal use seems likely to continue for some while, as an interim measure while renewables are developed fully. And as I will be exploring in my next post, there are also some possible interim strategic complementarities between, and synergies from, the use of carbon capture and renewables. However, the basic CCS idea of trying to store an unwanted by-product forever seems inelegant: instead, we should not be producing it. Finding a use for it, via CCU, makes a bit more sense economically but doesn’t deal with all the other social and environmental problems associated with fossil fuel extraction and transport. CCS/CCU and Air Capture might have a role in the short term in some locations, allowing us to continue to use fossil fuels a bit longer, but that doesn’t avoid the need to develop clean energy generation systems.

Dave Elliott is emeritus professor of technology policy at the Open University, UK, and writes a regular column for Physics World on sustainable energy technologies

8/9/2018 FROM PHYSICSWORLD.COM