Yep, exactly! The world needs CaO for cement. We have a carbon neutral process for making it. It's actually overall negative as not all carbonates we extract are usable in cement production. But as far as cement producers are concerned it's carbon neutral.
A way to help explain this to people is that it's the equivalent of rapidly growing trees and burning those for fuel instead of burning fossil fuels.
You do the same with limestone, rapidly creating it by capturing atmospheric CO2 (indirectly, via the ocean) so it can then be burned in cement production instead of the naturally occurring kind. In both cases, CO2 is released into the air at the end when the product is burned, but because the released CO2 had just now been sucked out of the air anyway (instead of having previously been sequestered in natural limestone) you're not adding to the total amount of CO2 in circulation in the system, making the process neutral.
A followup question... how do you regenerate the alkaline sorbent? It gets acidified in the process of extracting CaO from the water and needs to be made alkaline again somehow.
why does removing carbonates cause the ocean to absorb more CO2, though? Calcium and magnesium oxide aren't just floating around the ocean waiting to absorb more CO2. Removing salts does not lower oceanic acidity.
The ocean and the atmosphere exist in an equilibrium there is a 'balance' of relative concentration of CO2. Because CO2 can dissolve in water as CO3 and HCO3 the concentration is skewed to a higher concentration in oceans. When we take out CO2 from the oceans we lower the relative concentration, so we shift it out of balance. So the entire ocean becomes the surface area for re-absorbing CO2 from the atmosphere to re-establish that balance!
But the re-absorbed CO2 will come from new limestone dissolving into calcium bicarbonate, not from atmospheric CO2.
You'll be adding more CO2 to the air -increasing oceanic acidification- while increasing the ocean's ability to dissolve more CaCO3. Far from fighting global warming it sounds like this will put exactly as much CO2 into the atmosphere and double the leaching impact on shellfish and coral.
I am shit at chemistry and would really like cement to not release CO2, but I don't understand this.
Same question! As I understand it:
CO2 pulled out of the ocean is replenished by atmospheric CO2, because limestone in the ocean dissolves too slowly to make up for the imbalance and it more readily comes in from the air.
But if that's true, then the calcium will actually not be replenished quickly in the ocean (not sure what the significance of this is)!
If it were true that the calcium is dissolved fast enough to replenish, then there must also be CO2 released from underwater limestone? Which means extracting Ca and CO2 will not remove any atmospheric CO2 really.
Alternatively, we do end up extracting Ca from the ocean that is not replenished (there's probably so much we don't care) and rely on the atmospheric CO2 to correct ph balance of the ocean?
Wait, no, why? As far as I understand the process of limestone dissolving into oceans is the long term (on the scale of millions of years) process and is based on rivers dissolving limestone so would not be affected by the ocean changes; in the short term (days/years/centuries) it would be balanced simply by CO2 exchange between the atmosphere and what's dissolved in the ocean.
Yeah absolutely, the CO2 balance comes from re-equilibration with the atmosphere. The rivers replenish calcium content on a longer time scale. But as you point out we're in no danger of running out of calcium in the oceans
so there is no more additional burning of limestone needed? instead your process directly produces the lime, CaO? and that then binds the CO2 when curing?
to my limited understanding cement production emits CO2 in two ways: by splitting limestone into lime and co2 and by burning carbon based fuels to split the limestone.
your method addresses both sources of co2 from cement production? or just one of them?
> so there is no more additional burning of limestone needed? instead your process directly produces the lime, CaO? and that then binds the CO2 when curing?
The OP says they'll make money by selling synthetic limestone ("We make money from selling synthetic limestone to cement producers..."), so I think the CO2 still needs to be burned off of it before the cement is produced. However they say they already (indirectly) pulled that same CO2 out of the air, instead of the ground, so overall the process is carbon neutral.
> they say they already (indirectly) pulled that same CO2 out of the air, instead of the ground, so overall the process is carbon neutral.
I find that difficult to understand. If the output is CaCO3 that still needs to kilned to make CaO, then CO2 gets emitted. Even if that volume of CO2 was obtained from dissolved CO2 in the ocean, one would have had to expend energy to extract that CO2 from the ocean and that energy would have generated emissions as well.
If the output of this is just CaCO3 again, then I fail to see how this is a better solution than carbon capture using a clay geopolymer technique that goes directly to a concrete like structural material. What I mean is, wouldn't it be better to just skip all of this and go focus on rediscovering the technology for "creating" rock like what was possibly achieved at Cuzco (Hatun Rumiyoc) or Pumapunku? Or more realistically in the short term, using fly ash and silica flume or slag to make concrete without requiring CaO?
> one would have had to expend energy to extract that CO2 from the ocean and that energy would have generated emissions as well.
I suppose they could planning to use renewable energy?
> If the output of this is just CaCO3 again, then I fail to see how this is a better solution than carbon capture using a clay geopolymer technique that goes directly to a concrete like structural material.
I don't have a horse in this race, but one possibility is that concrete is a better understood material than some novel "concrete like structural material," so it's more acceptable in safety critical situations (e.g. people know how it fails, how to detect failures, how to remediate problems, etc.).
> one possibility is that concrete is a better understood material than some novel "concrete like structural material," so it's more acceptable in safety critical situations (e.g. people know how it fails, how to detect failures, how to remediate problems, etc.).
Your explanation and argument looks correct to me. However, I should point out that concrete structures fail regularly and frequently, and sadly with great loss of human life, most recently in Miami. I should also point out that I've seen this argument used as a tactical trick. I watched a Microsoft rep using this argument successfully convince a management team that they should use Embedded Windows instead of Linux because, just as you pointed out, "we know how it fails", "we know how to detect failures", "we know how to remediate problems".
I think the difference between materials and software through is that with materials, there's definitely a better understanding that comes with actual aging that you can't really get otherwise.
With some new material, they'd probably need to rely significantly on accelerated aging tests (at least for a few decades), and there's always the question with those of how accurately those actually model real aging under real conditions.
That's not to say they shouldn't try new materials, just that the rollout probably should be slower, and maybe not so good for tackling climate change. For that reason, I can see the benefit of a less carbon intensive way to produce an existing material, since that could be rolled out/scaled up immediately without some of the concerns of alternatives.
yes that kilning is what bothers me, not for the co2 that is captured at sea, released in the kiln. that is then recaptured when curing, isn't it?
what bothers me is the 1400°C needed in the kiln. to my understanding the ratio of limestone-to-lime co2 to fuel-for-the-process co2 is 2:3. you need lots of co2 intensive energy for that kiln.
Our process produces calcium carbonate, CaCO3, which cement producers can then burn to make quicklime, CaO. This does release CO2 but that CO2 has been captured from the atmosphere in the process of making that calcium carbonate. We only address process emissions (ie. splitting CO2 from CaCO3), but we do also produce hydrogen on-site, which can be used to replace fossil fuels in generating the requisite heat
ok so your cement does not expose additional co2 from the lime-to-quicklime transformation, instead it takes co2 from the oceans.
that is released to zhe athmosphere during cement production. and that co2 from the air is then recaptured by the ocean. so your process creates a ocean-co2 -> air -> ocean cycle.
and when and where the hydrogen is replacing some carbon based fuels, somehwere, that counterbalances the carbon based fuel used in the cement furnace.
now I get how it becomes carbon neutral overall.
do you guys have data points at hand how long it takes for an ocean to recapture the co2?
