Reducing our CO2 emissions is something toward which civilization must strive; but there is no denying that, in our struggle to come to terms with a massive, vague goal, practically unattainable for almost everyone, it ceases to be a mere engineering matter, instead taking on a certain ethereal, puritanical significance.
Occasionally this can be self-defeating: for example, environmentalist opposition to high-speed rail projects. Carbon capture and storage (CCS) – extracting CO2 and burying it underground – is another technology which comes in for this treatment.
Indeed, at first it appears a kind of cheat – a shortcut, sidestepping intervention or upheaval on moral grounds. As Rebecca Wicker, MSc, PhD candidate in environmental biotechnology and member of Extinction Rebellion (XR) Scientists, puts it: “Think of it like heart disease. You can take medication to mitigate some of the symptoms, but it is still going to kill you if you do not cut back on the McDonald’s. Carbon capture is medication, but system change is the cure.”
Wicker is correct: CCS cannot solve climate change by itself. But almost none of its advocates argue that it can. It is best deployed as a short-term measure to eat into the CO2 emissions from existing industrial processes – those which humanity cannot afford to dispense with. One of these? Shipping.
If it works…
In late 2019, MIT postdoc Sahag Voskian developed a new concept dubbed “Faradaic electro-swing reactive adsorption for CO2 capture”. It involves running exhaust over a set of charged electrochemical plates, coated with a carbon-reactive compound called polyanthraquinone, which “has either a high affinity [for CO2] or no affinity whatsoever,” depending on its state of electric charge.
Each plate would alternately absorb CO2 from exhaust, and later release it. If applied on a vessel, the installation would comprise two sets of cells operating in parallel, with exhaust being directed at one or the other in turn, to match their bind-release cycles.
“For example, if the desired end-product is pure carbon dioxide… then a stream of the pure gas can be blown through the plates,” explained Voskian. “The captured gas is then released from the plates and joins the stream.”
The method is estimated to use one tenth the energy of today’s equivalents. Voskian envisions polyanthraquinone being fabricated in large rolls, for tens of dollars-per-m3 of electrode.
“Shipping cannot do this alone”
A recent study into CCS on a large vessel showed that the technology was viable – with some caveats. Mitsubishi Heavy Industries (MHI) estimates that adding four cooling towers, a liquefaction plant, and carbon storage tanks – a system dubbed CC-Meth (carbon capture-methanation cycle) – to a VLCC would offset 2% of cargo capacity, and add a capex cost of $45m for a newbuild. Kazuki Saiki, MHI Deputy Manager, Ship & Ocean Engineering, said that for the solution to work, other industries “beyond ours…” would need to “bear the costs… shipping cannot do this alone.”
Soon after, in late 2020, MHI entered into an agreement to fit a small-scale CCS unit to K-Line vessel Corona Utility, with backing from the Maritime Bureau of Japan’s Ministry of Land, Infrastructure, Transport and Tourism (MLIT). Dubbed Carbon Capture on the Ocean (CC-Ocean), the unit, to be installed later this year, will be used “not only [to] verify the efficacy of capturing and storing CO2 from a vessel’s gas emissions, but also the operability and safety of CO2 capture facilities at sea.”
Similarly, with considerable effort has gone into developing scrubbers, for removing sulfur from ship exhaust; according to Wärtsilä, it is “technically viable” for this technology to remove CO2, as well. To test this, Wärtsilä is installing a 1MW pilot plant at its test facility in Moss, Norway.
Wärtsilä believes that CCS could play a vital role in decarbonising existing tonnage without having to build an entirely new fleet from scratch – which, although the fact is oft-forgotten, has a massive CO2 cost of its own.
“CCS onboard vessels is clearly a substantial undertaking, but one that we believe we are well placed to pioneer,” said Sigurd Jenssen, Director, Exhaust Treatment at Wärtsilä, adding that it would “enable us to safeguard existing assets as we move to a cleaner mode of operating.”