https://www.theguardian.com/environment/2025/jun/26/global-shipping-emissions-invention-clean-up-cargo-fleets-net-zero

The idea here is to use quicklime (Calcium oxide, CaO) to absorb CO2 from the exhaust of ship engines, generating calcium carbonate (CaCO3, limestone, chalk etc).

And they speak of using renewable energy to power the kilns that generate the quicklime.

But, er, the kilns generate CaO by driving off CO2 from calcium carbonate. So all you've done with this proposed technology is move your CO2 from the ship to the shore; you still now need to dispose of it, somehow. I don't see in the article where this issue is addressed.

Does anyone know more about this? Is this idea designed to work in conjunction with CCS, perhaps, i.e. disposing of the CO2 in depleted oil and gas fields? If so I suppose it could have a role as a bridging technology, before shipping is converted to ammonia or something. But then CCS is yet to prove itself, so a number of imponderables here.

Edited June 26Jun 26 by exchemist

Just now, exchemist said:

https://www.theguardian.com/environment/2025/jun/26/global-shipping-emissions-invention-clean-up-cargo-fleets-net-zero

The idea here is to use quicklime (Calcium oxide, CaO) to absorb CO2 from the exhaust of ship engines, generating calcium carbonate (CaCO3, limestone, chalk etc).

And they speak of using renewable energy to power the kilns that generate the quicklime.

But, er, the kilns generate CaO by driving off CO2 from calcium carbonate. So all you've done with this proposed technology is move your CO2 from the ship to the shore; you still now need to dispose of it, somehow. I don't see in the article where this issue is addressed.

Does anyone know more about this? Is this idea designed to work in conjunction with CCS, perhaps, i.e. disposing of the CO2 in depleted oil and gas fields? If so I suppose it could have a role as a bridging technology, before shipping is converted to ammonia or something. But then CCS is yet to prove itself, so a number of imponderables here.

Sounds to me like a typical account's greenwashing.

CaO + CO₂ = CaCO₃

56 + 44 = 100

So for every ton of carbon dioxide removed from the fuel, the ship will have to carry 1.3 tons of calcium oxide and make space for 2.3 tons of carbonate storage.

And carbon dioxide is a very significant proportion of the weight of the fuel.

If the 2.3 tons is then 'dumped' at some location outside the home port or country it will not count there.

19 minutes ago, studiot said:

Sounds to me like a typical account's greenwashing.

CaO + CO₂ = CaCO₃

56 + 44 = 100

So for every ton of carbon dioxide removed from the fuel, the ship will have to carry 1.3 tons of calcium oxide and make space for 2.3 tons of carbonate storage.

And carbon dioxide is a very significant proportion of the weight of the fuel.

If the 2.3 tons is then 'dumped' at some location outside the home port or country it will not count there.

Hmm, interesting to look at it this way. A cargo ship may burn of the order of 50mt/day of RFO, 85% of which is carbon. So roughly speaking it will produce 150mt/day CO2, generating over 300mt/day of limestone! There's going to have to be an awful lot of both quicklime and limestone on this ship for a voyage from Singapore to Antwerp.

29 minutes ago, exchemist said:

Does anyone know more about this? Is this idea designed to work in conjunction with CCS, perhaps, i.e. disposing of the CO2 in depleted oil and gas fields? If so I suppose it could have a role as a bridging technology, before shipping is converted to ammonia or something. But then CCS is yet to prove itself, so a number of imponderables here.

"Yet to prove itself" seems to me like understatement. More like "ridiculous scam," that would be insanely expensive to implement on any scale that matters - money that could be hastening the vitally important transition to renewables. The only reason oil companies were interested in this was because CO2 injection into oil wells could help to extract more oil (you are probably familiar with this, but I'll post a link for those who might not be) while greenwashing at the same time.

Greenpeace International

The Great Carbon Capture Scam — Rex Weyler - Greenpeace I...

Oil companies hid knowledge of global heating for decades, but the captains of petroleum also schemed to turn the ecological crisis into a profit centre.

1 minute ago, exchemist said:

Hmm, interesting to look at it this way. A cargo ship may burn of the order of 50mt/day of RFO, 85% of which is carbon. So roughly speaking it will produce 150mt/day CO2, generating over 300mt/day of limestone! There's going to have to be an awful lot of both quicklime and limestone on this ship for a voyage from Singapore to Antwerp.

😆

Oil would be extracted, processed, stored and distributed, all of which involve a CO2 cost.

The on board absorbtion process would not only involve space for the necessary plant, but obviously greatly increase the fuel requirement for journey.

Yes the conversion to carbonate would offset the CO2 generated but it is obvious that cargo capacity of the ship would be greatly reduced and other not offset costs would be involved.

19 minutes ago, TheVat said:

"Yet to prove itself" seems to me like understatement. More like "ridiculous scam," that would be insanely expensive to implement on any scale that matters - money that could be hastening the vitally important transition to renewables. The only reason oil companies were interested in this was because CO2 injection into oil wells could help to extract more oil (you are probably familiar with this, but I'll post a link for those who might not be) while greenwashing at the same time.

Greenpeace International

The Great Carbon Capture Scam — Rex Weyler - Greenpeace I...

Oil companies hid knowledge of global heating for decades, but the captains of petroleum also schemed to turn the ecological crisis into a profit centre.

😆

Hmph. I don't trust anything emanating from Greenpeace. I know for a fact that they are happy to misrepresent the truth for publicity purposes cf. Brent Spar. They are also one of the prime actors seeking to blame the fossil fuel industry for our carbon-intensive lifestyle, a deeply hypocritical exercise in blame shifting to a suitable "other" we can settle back and safely hate, as we carry on driving our petrol cars, heating our homes with gas and whining about the price of "gasoline".

Oil and gas companies are willing to do CCS because they know how to do it and have the depleted reservoirs to hand. Secondary extraction is not intrinsic to the economics. But it is not cheap, that's true enough. When I was at Shell we had a pilot project to do this for the UK government about 20years ago, but they pulled out after we had spent $1m on it. No secondary recovery featured in that.

It's not greenwashing, it is real and it might help to bridge the gap during the technology transition. However I would always be worried that CO2 buried in this way might somehow find its way back to the surface over time, so I wouldn't want to see it become a major component of the moves to carbon neutrality.

4 minutes ago, exchemist said:

Hmph. I don't trust anything emanating from Greenpeace. I know for a fact that they are happy to misrepresent the truth for publicity purposes cf. Brent Spar. They are also one of the prime actors seeking to blame the fossil fuel industry for our carbon-intensive lifestyle, a deeply hypocritical exercise in blame shifting to a suitable "other" we can settle back and safely hate, as we carry on driving our petrol cars, heating our homes with gas and whining about the price of "gasoline".

Oil and gas companies are willing to do CCS because they know how to do it and have the depleted reservoirs to hand. Secondary extraction is not intrinsic to the economics. But it is not cheap, that's true enough. When I was at Shell we had a pilot project to do this for the UK government about 20years ago, but they pulled out after we had spent $1m on it. No secondary recovery featured in that.

It's not greenwashing, it is real and it might help to bridge the gap during the technology transition. However I would always be worried that CO2 buried in this way might somehow find its way back to the surface over time, so I wouldn't want to see it become a major component of the moves to carbon neutrality.

I have seen the critique from more neutral sources than Greenpeace, so sorry to use them for a quick link. It seems like greenwashing to me mainly because only oil companies are pushing it - usually not a good sign. I was tempted to counter your "hmph" with "hmph, I don't trust anything emanating from oil companies." I will agree that a more economical implementation of CCS might be a bridge, but the potential for future leakage is there and quite scary.

As for hypocrisy, yes organizations like GP and Sierra Club do a lot of that. I prefer groups like The Nature Conservancy which seem more practical and about The Art of the Possible.

35 minutes ago, TheVat said:

I have seen the critique from more neutral sources than Greenpeace, so sorry to use them for a quick link. It seems like greenwashing to me mainly because only oil companies are pushing it - usually not a good sign. I was tempted to counter your "hmph" with "hmph, I don't trust anything emanating from oil companies." I will agree that a more economical implementation of CCS might be a bridge, but the potential for future leakage is there and quite scary.

As for hypocrisy, yes organizations like GP and Sierra Club do a lot of that. I prefer groups like The Nature Conservancy which seem more practical and about The Art of the Possible.

Yeah I just get tired of the facile scapegoating, when CO2 emissions are due as much if not more to Henry Ford and his successors as to Rockefeller and his.

After all it's not like cigarettes when the product is inessential and promoted by the manufacturer as a fashionable lifestyle accessory. We objectively need oil and gas. Weaning ourselves off it is a huge collective effort in which all, including oils and gas companies, have a part to play. Demonising one industry to make the rest of us all feel better gets us nowhere fast. In fact, it just delays the realisation that we all need to make changes. Also if these companies have a role to play, let's encourage them to play it, not chuck bricks at them all the time.

On CCS, I think it is pushed by various CO2-intensive industries, including fossil fuel power gen plants, cement, glass, steel, etc. All of them of course would prefer not to have to change their fuel source or, in the case of iron smelting, the whole chemical process, especially if government might subsidise the process.

The thing that stands out to me, and this applies to shipping too, is the alternatives very largely require hydrogen. (Ammonia for ship fuel is a way of handling large quantities of hydrogen more safely, basically: you burn it to N2 and water.) The really transformative technology we desperately need is high efficiency electrolysis.