The realist’s road to zero: #5 Carbon capture and storage

In discussions about our journey to net-zero by 2050, one phrase tends to come up a lot: “The rest will have to be carbon capture.” Whether you are talking about power generation, cement production, the carbon footprint of an organization, or even the globe as a whole, there is always a portion of the equation marked “carbon emissions we really can’t prevent, no matter how ingenious or efficient our design”.

You might take it from this that CCUS, or carbon capture, utilization and storage, is a done deal, that the necessary bits of kit are already being fitted to chimneys and exhaust flues everywhere, and that those stubborn last few carbon emissions will soon be dealt with permanently. So first, a reality check.

Although carbon capture technology has existed since the 1970s, much of the world’s capacity is still at demonstrator project scale. There are fewer than 30 carbon capture plants on Earth with, in 2021, a total capacity of only 40 million tonnes of CO₂ per annum. To put that in context, the International Energy Agency (IEA) calculates that the world will need a capture capacity of 1.6 billion tonnes, or 40 times the current level, as early as 2030 to align with its pathway to net-zero by 2050. 

Will it happen? To date, the story of CCUS has been one of unfulfilled potential. In 2010, the IEA recorded 65 CCUS projects as “in development” — yet since then, an average of only 1.3 new plants a year have opened. But 2021 has seen unprecedented momentum: more than 100 new CCUS facilities were announced, including major plans such as the world’s largest CCUS-equipped hydrogen production facility in Louisiana, with the capacity to capture more than 5 million tonnes of CO₂ per year.

“The industry has had a few false starts — funding has been promised which hasn’t materialized,” says Tony Alderson, Leeds-based technical lead for carbon capture and storage at WSP, which is leading a consortium advising the UK government on its commercial-scale implementation. “But there is now a genuinely new impetus driven by the clear target of net-zero by 2050. As well as helping to decarbonize power and heavy industries like cement and steel production, CCUS will be vital in the production of hydrogen from natural gas.” Like many countries, the UK has ambitious plans but no functioning CCUS at present. The government’s Committee on Climate Change forecasts a need for up to 175 million tonnes per annum capacity by 2050 — or more than four times the current capacity of the entire world.

Even though carbon capture would seem to be essential if we are to reach the goals advised by the IPCC and ratified at repeated climate conferences, it is far from enjoying the unanimous support of environmental groups. This is partly because its early development has been driven by the fossil fuel industry — most of the CO₂ captured to date has been used for enhanced oil recovery (EOR), in which the gas is pumped underground to help force oil to the surface. There are also fears that its great but as yet unfulfilled promise may deter governments and businesses from embarking on a wider transformation away from carbon-emitting activities, or serve to prop up the status quo. Various reports have highlighted technical challenges and shortfalls in performance.

But no one is claiming that CCUS is a magic bullet. Experts concede it is expensive and energy-intensive, and that though capture rates of over 95% have repeatedly been demonstrated, they have yet to be tested and proven at sufficient scale. However, as things stand, it remains our only hope of getting even close to the net-zero target.

“CCUS is a stop-gap solution, but there is no better one in most of these markets,” says Alderson’s colleague Andy Jackson, head of gas discipline at WSP, based in Manchester. “It’s a means to an end while other, better solutions are brought on stream efficiently and without massive disruption to the world. We won’t get to where we need to be, within the necessary timeframe, without implementing this in some fashion.”

Over the coming decades, this will almost certainly involve the creation of a huge new processing industry and infrastructure, spanning the different stages. “All CCUS starts with capture, which is the most expensive part of the process, accounting for more than half of all the costs involved,” says Alderson. “Obviously there is the capital cost of installing plant, but also significant operational costs because the process is energy intensive.”

The commonest form of capture technology uses amine solvents to absorb CO₂. These then need to be regenerated by heat in a process that, in the case of a power station for example, would typically take up to 20% of the plant’s entire energy output. The efficiency of this process can be improved if the emitting process has suitable spare heat, Alderson adds, such as that which occurs in cement production.

Once captured, CO₂ needs to be transported to a point of use or storage, which also has an energy cost. Electrical energy is required to achieve the necessary compression of 35 bar pressure for a gaseous pipeline, or over 100 bar for dense-phase transportation. Getting CO₂ to its storage site will not always be easy, says Jackson. “In the UK, CO₂ captured near the North Sea coast could be pumped relatively easily via underwater pipeline to sites in depleted offshore oil and gas fields. But where there are no suitable storage sites nearby, other means, such as transport by ship, will be required. Building a 400km pipeline overland would involve significant disruption to the natural and built environment, so shipping would be needed.”

This is another area where CCUS will be relying on capacity that has, to an extent, been developed by the hydrocarbon sector. “The requirements for shipping CO₂ are similar to those for liquid petroleum gas (LPG),” explains Alderson. “Some ships are even dual certified. The immediate problem would be that existing CO₂ ships tend to be quite small — around 2,000 tonnes.” Taking the UK as an example, if only a fraction of the forecast 175 million tonnes of captured CO₂ ends up being shipped, it is clear that existing vessels and designs are not going to be big enough: “The reality is that we’ll need much larger ships which do not yet exist. Plans for 100,000-tonne CO₂ transport ships are still at the drawing board stage.”

Any carbon audit of the CCUS process will also need to take into account emissions from the ships, adds Jackson, as well as the embedded carbon costs of creating infrastructure such as intermediate storage facilities for shipped gas waiting to be taken by pipeline to its ultimate storage location. Mostly, this will be in depleted oil or gas reservoirs, or in saline aquifers within porous rock structures. “Salt water has to be pumped out of aquifers to create space for the CO₂. Again, it is quite an onerous process with a financial and energy cost.”

Environmental groups have raised concerns that over time CO₂ could leak from its storage reservoirs, but Jackson argues that the geology of oil and gas fields will have been well-researched and that monitoring will ensure that it stays put. “Although no storage is molecule-tight, the gas should stay there for thousands of years. Just as natural gas doesn’t leak beyond the cap rock, so the CO₂ shouldn’t either.”

Given the costs of transporting and storing CO₂, putting it to use instead can make economic sense. Captured CO₂ is already used for carbonated drinks, to boost crop yields in greenhouses, and even for inflating body cavities during surgery, though as Jackson says: “In all these cases, the quantities involved are modest, and the gas does still eventually end up in the atmosphere.”

Unsurprisingly, use cases that lock the gas away for good are attracting more attention. CO₂ can, for example be used to “cure” specialized forms of concrete, or to create carbon-negative aggregate through a process known as mineralization. In both cases the carbon becomes a permanent part of the concrete’s chemistry.

Though not yet suitable for all concrete applications, this is still a rather satisfying solution to concrete’s high carbon footprint and, longer term, it seems likely that CO₂ will become embedded in more new commodity supply chains that will develop as a result of net-zero commitments. For example, CO₂ is the working fluid of Allam cycle power plant technology. Though still at demonstration scale, the technology burns natural gas with oxygen to produce power in a way that naturally captures CO₂. Oxygen to supply this process could be provided from the by-products of green hydrogen production via electrolysis.

In the shorter term, however, the CCUS sector suffers from the low intrinsic value of its key commodity. The gas cannot currently be sold for a price which even begins to cover the cost of its capture — so putting a cost on emissions is likely to be more important than finding markets for CO₂. This means, says Alderson, that carbon capture infrastructure can only develop to a useful level with the substantial and continuing assistance of governments worldwide: “The technology exists — but only consistent government support and regulation can make a CCUS industry commercially viable.”