Carbon Capture and Storage (CCS) is sometimes claimed to be able to capture up to 90% of the carbon dioxide (CO2) produced by burning fossil fuels like coal or natural gas, and it has been strongly promoted as a major carbon removal option. Certainly there is a lot of interest in it. However, there are some big issues, not least that it rarely achieves anything like 90% removal- the CCS process needs energy to run and producing that generates CO2.
In the case of production of so-called Blue Hydrogen from fossil gas using the Steam Methane Reformation process (SMR) backed up by CCS, flue gasses are also released, which can reduce the overall CO2 saving to 60%. So a review by Pembrina in Canada says that if an SMR facility with CCS ‘captures 80% of its carbon process stream - but only about 60% of carbon is emitted in the process stream – it captures only 48% of the total carbon produced’. That figure was used in a Global Witness report, which also said that total system CO2 savings for a Blue Hydrogen SMR plant in Canada were in fact only 39%- also taking into account emissions from natural gas transmission.
It may of course be possible improve on some of this, for example the auto thermal reforming process sometimes used for ammonia production is claimed to be more efficient. But why not just make green zero carbon hydrogen gas via electrolysis using surplus renewable energy? The costs for that are falling fast, with new more efficient PEM Electrolysers emerging, and large competitive Alkaline units expected by 2030. This green hydrogen can be stored in salt caverns for later use, to make power again when there is a peak in demand and/or a lull in renewable supply. That type of short-to-medium-term operational storage would seem to make more sense than trying to capture fossil-derived CO2 and then store it underground somewhere safely for ever.
Vast volumes of for-ever CO2 storage would also be required for the other main carbon removal option that has been proposed- Direct Air Capture. DAC is being pushed hard at the moment. Sucking CO2 out of the air has a superficial attraction- and DAC plants would take up less room than growing trees to do the same thing. But quite apart from the CO2 storage issue, absorbing CO2 from the air in DAC plants is a costly energy-intensive process, given the low concentration of CO2 in the atmosphere (much lower than in fossil fuel plant exhausts) and, although we might supply that energy with PV solar power, this may not be the best use of zero carbon PV power. Why not use it direct?
Carbon capture and utilisation is another option- CCUS. Given that it is far from clear if we can find room to safely store all the CO2 that DAC might collect, as well as that from fossil fuel CCS and biomass CCS, you could try to convert it to a new synthetic fuel, an idea now being explored in China and elsewhere. But that needs hydrogen. And if we have that why not just use it direct?
CCS and CCUS do have their supporters, the fossil fuel industry included, and there is quite a lot going on in the area. However, although there may be some hard-to-decarbonise industries where it might be useful, as I argued in earlier posts, carbon removal in general has major issues and there is the risk that support for it will deflect money and effort from developing renewables and cutting energy waste- thus, perversely, justifying the need for more CCS/CCUS.
It does seem a long shot. So far, progress on CCS generally has been rather poor. According to a recent study published in Energy Policy Journal, most projects initiated in the past three decades have failed, including the much trumpeted NRG Energy’s Petra Nova plant in Texas. Although some projects are still trying their luck, some are still facing problems, as with Chevron’s Gorgon project in Australia, which has failed to meet the guidelines set for carbon storage. Probably the most successful so far have been Enhanced Oil Recovery (EOC) projects which use captured CO2 to squeeze out the last bits of oil from almost exhausted wells. But, although some argue that EOC can reduce net emissions, it seems to be an odd form of (brief) carbon removal- the oil will eventually be burnt, releasing more CO2 again. Same as with any CCUS synfuels made via fossil CO2 or air captured CO2. None of this helps the planet!
Planting trees might arguably be a safer and cheaper carbon removal bet than any of the artificial CCS/DAC systems and some say that significant gains could in theory be made from forest restoration- storing the equivalent of 25% of the current atmospheric carbon pool. However, there are practical limits to accelerating forest protection, with 1 Giga tonne of CO2 collection p.a. (under 3% of current emissions) seemingly a high hope: fighting de-forestation is hard enough, trying to expand new areas of forestry is even harder. So, sadly, that is unlikely to offer us enough carbon removal.
With emissions still rising, some say therefore that, despite its problems, DAC with storage might still be sensible- as a desperate, and probably expensive, emergency carbon negative option. Certainly some clever new ideas have been emerging, and there have been some positive assessments of DAC. But, quite apart from the CO2 storage issue I mentioned above, putting the DAC energy issue in perspective, Senior Research Fellow at the Grantham Institute, Dr Ajay Gambhir, says that ‘by the end of the century, direct air capture could require the equivalent of over half of today’s global energy needs if it is the dominant carbon dioxide removal technology’.
That’s not going to happen, neither will biomass CCS (BACCS), given the constraints on biomass growing and carbon storage, at least not on a large scale. Some soil sequestration of CO2 by new farming methods can help, as can planting trees, but, centrally, we need to accelerate renewables and energy efficiency- they can do the job at lower cost, replacing the sources of carbon emissions, and avoiding the need for artificial carbon removal and carbon storage technologies.
Will that happen? Well, with renewable costs falling, maybe they will expand faster…and Putin’s war in Ukraine also looks likely to change fossil energy and renewable futures. Indeed, optimistically, Amory Lovins and RMI colleagues recently argued that, with fossil fuel use constrained, it might in the end turn out be good news for renewables and energy saving. We will have to wait to see, and also whether carbon removal will still be needed or prosper much in the new lower-fossil world .
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