"Making money" is the biggest Co2 unleashing endeavour by far. Trapping science in hic-ups bursts in a linear narrative is not explanatory. Be well, the World is dumbed down enough to take your desires for solutive. You might reach for local fame and hoaxy glory. The Co2 in your case is released by your approach.
Launch HN: Heimdal (YC S21) – Carbon neutral cement
171–180 of 227 posts
Re: Launch HN: Heimdal (YC S21) – Carbon neutral cement
#172Taking bicarbonate to carbonate releases about 0.8 moles of CO2. This has the opposite effect of what you are intending. See the below link for a discussion of the mechanism for how taking carbonate (i.e. limestone) to bicarbonate sequesters carbon. Please don't just run this reaction in reverse. That's almost as bad as our current process for making cement. If you're doing something different (e.g. adding a counteri…
It seems what they do is Ocean Water + Sorbent -> Leaches Carbonates for use in Cement -> Heated in Kiln -> Releases C02 -> Captured and redissolved in Ocean water. This still has to be proved how to reabsorb such large amounts of c02 in ocean water.
Absorbing large amounts of CO2 happens every second since 2-3 centuries at this point, and is the main driver of ocean acidification and subsequent coral bleaching, loss of wildlife, etc. If the mentioned process could "recycle" the CO2 needed for lime production, then it could be a big win for a very hard to decarbonize sector.
What is still to be checked is how more expensive this lime will be, and how it will stack up compared with traditional limestone+carbon tax
Re: Launch HN: Heimdal (YC S21) – Carbon neutral cement
#173How many orders of magnitude separate your current cost per ton of limestone from the popular status quo methods? You're talking about ancillary products and regulatory credits, which is a fine business model; but I'm asking about the core industrial process. Trying to get a sense of how much more efficient your scale-up needs to be, before your process is in the black.
Our current cost per tonne is in the same order of magnitude when including the carbon value from the European ETS. The key success criteria for making large plants profitable will be connecting to cheap electricity at <$50/MWh we're in the black
Cheap green electricity at less than 50 $/MWh should not be a problem, most PPAs are already getting signed at costs substantially lower than that.
Re: Launch HN: Heimdal (YC S21) – Carbon neutral cement
#174I did some lengthy analysis behind the chemistry / economics and wrote it up here. https://www.moderndescartes.com/essays/carbon_neutral_concre... TL;DR: ignoring all sources of overhead/inefficiency and purely on consideration of thermodynamic costs, $70 of electricity can generate $100 of lime, $300 of chlorine gas, and $75 of hydrogen gas. Much more details on the chemistry and economics in the blog post...
Thanks for the analysis, interesting to read!
What about the lime-burning for cement, does it imply "only" net-carbon neutral as all the captured carbon is released upon cement production? And what about iron smeltering? I suppose most carbon is also released in that process?
Re: Launch HN: Heimdal (YC S21) – Carbon neutral cement
#175I did some lengthy analysis behind the chemistry / economics and wrote it up here. https://www.moderndescartes.com/essays/carbon_neutral_concre... TL;DR: ignoring all sources of overhead/inefficiency and purely on consideration of thermodynamic costs, $70 of electricity can generate $100 of lime, $300 of chlorine gas, and $75 of hydrogen gas. Much more details on the chemistry and economics in the blog post...
Some comments and expansion on your analysis, which I enjoyed reading and provided a nice excuse to dust some mental cobwebs.
I'd also like to clarify up front that I'm limiting my analysis to the proposed electrochemical mechanism, and have no information on the specifics of Heimdal's proposed implementation - which may vary significantly and materially:
The theoretically minimum electrical energy input (often) winds up being set by one of the reaction intermediates, rather than the overall reaction enthalpy. Typically these analyses are done via determining the corresponding half cell potentials, then counting electrons and computing power via P = IV.[0] So we only need to consider H2O (and its dissociation -0.83[1]) and Cl- to Cl2 at 1.36). That sums to approx 2.19V for the cell, and 2 electrons to do 2H2O + 2Cl- -> H2 + 2OH- + Cl2. That the formed OH-'s pair with Ca2+, and/or CO2 is immaterial to the theoretical electrical efficiency of the cell. Accordingly, the cell energy requirement is on a molar basis identical to the chloralkali process. The only difference is the presence of 2Na+ vs. Ca2+.
Less concretely the lower reactant concentrations have two specific negative effects: Cell potential is adversely affected (per the Nernst equation) and Cell current can be adversely affected if/when depletion occurs. At 0.01M of Ca2+, vs. 6+M Na+[2], current densities could be 1-3 orders of magnitude lower. Cell count (CAPEX) is inversely proportional to current density.
Ultimately making CaCO3 this way (and CaO) winds up substituting a 400$/tonne product in NaOH for an approx 40$/tonne product in CaCO3. It is a very technically feasible approach for turning $$$ into sequestered carbon via non emission from natural limestone.
The analyzed approach reminds me a lot of Calera, who had an apparently similar electrochemical approach to CaCO3.
[0]Not that it can't be done from Gibb's energies, indeed the standard potentials for a reaction can be computed from the delta Gibbs, but the specific species the electrons are being pulled from/pushed into matters. Phrased a different way: electrical energy and overall reaction enthalpy are not necessarily fungible. e.g. (at a simple level) the reaction of CO2 with Ca(OH)2 doesn't affect the electrical energy requirement, nor does CaCO3 --> CaO because neither reaction involves electrons. Any exotherm just winds up 'wasted' as heat, instead of lowering the electrical demand.
[1]Per 2H2O + 2e- --> H2(g) + 2OH-(aq) #6.8.11 https://chem.libretexts.org/Courses/Mount_Royal_University/C...
[2] Saturated near room temp, don't have a better source handy.
Re: Launch HN: Heimdal (YC S21) – Carbon neutral cement
#176Earlier quoted context omitted.
Well understood! The ocean is supersaturated in the ocean (ie. there is about 20x more of it dissolved than you would expect). In fact it's the single largest deposit of calcium in the world. Risk of running out is zero. Calcium in the ocean comes from dissolved limestone (this does not emit CO2)
How will reducing the amount of dissolved calcium and CO2 in the ocean affect organisms like shellfish and crabs. Could there be local zones around your extraction points where these organisms can no longer produce shells?
The ocean is 20x supersaturated with calcium and is constantly being replenished by geological stores of the stuff coming in through rivers. As long as the ecosystem remains supersaturated this shouldn't be a problem for any marine life. Though a slight dislcaimer there is i'm not a marine scientist!
Re: Launch HN: Heimdal (YC S21) – Carbon neutral cement
#177Earlier quoted context omitted.
Well understood! The ocean is supersaturated in the ocean (ie. there is about 20x more of it dissolved than you would expect). In fact it's the single largest deposit of calcium in the world. Risk of running out is zero. Calcium in the ocean comes from dissolved limestone (this does not emit CO2)
What sort of waste water do you produce? What is the local ecosystem impact? Edit: Also, it’s great that your de-carbonating the ocean as part of this project. Ecological damage to the ocean is out of sight, and usually out of mind.
All 'waste' we produce we either consume in our process or we're able to sell as a commercial product!
Not bad tackling ocean acidifcation to boot
Re: Launch HN: Heimdal (YC S21) – Carbon neutral cement
#178Earlier quoted context omitted.
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.
I'm probably missing something obvious. > The world needs CaO for cement. We have a carbon neutral process for making it vs > We make synthetic limestone using atmospheric CO2, such that when it is used to make cement, the process is carbon neutral. Do you make CaO or CaCO3?
We make CaCO3, I mention CaO here because that's what cement producers ultimately need. They heat up limestone (CaCO3) to make CaO
Re: Launch HN: Heimdal (YC S21) – Carbon neutral cement
#179Earlier quoted context omitted.
> 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…
> 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 energ…
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.
Re: Launch HN: Heimdal (YC S21) – Carbon neutral cement
#180Earlier quoted context omitted.
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 c…
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