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?
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.
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?
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".
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.
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.
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?