5 ms·

I did some lengthy analysis behind the chemistry / economics and wrote it up here. https://www.moderndescartes.com/essays/carbon_neutral_concrete/ https://www.

by brilee 5y ago

I did some lengthy analysis behind the chemistry / economics and wrote it up here. https://www.moderndescartes.com/essays/carbon_neutral_concrete/ 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...

dang 5y ago
Wow, that's the most in-depth response to a Launch HN I've ever seen. This is probably the most substantive Launch HN thread (I mean of the official YC startup launches at https://news.ycombinator.com/launches https://news.ycombinator.com/launches) that we've yet seen. And it was very little work to put together.
- brilee 5y ago
  The secret is apparently to be slightly cagey about your tech and nerd snipe half of HN into trying to figure out if your thing actually works or not...
  - rossjudson 5y ago
    The other secret is to not be using investor money to pay low wage gig workers while you build out a "platform" for the future when you take all the business from everyone because they are too dumb to possibly compete with you.
- marcuslima 5y ago
  Agreed!
go_elmo 5y ago
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?
- marcuslima 5y ago
  Same idea for iron!
thereisnospork 5y ago
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/Chem_1202/Unit_6%3A_Electrochemistry/6.8%3A_Industrial_Electrolysis_Processes https://chem.libretexts.org/Courses/Mount_Royal_University/C... [2] Saturated near room temp, don't have a better source handy.
- 5y ago
marcuslima 5y ago
Impressive analysis! Missed out on a couple details, but I'll take that as a thoroughly researched/analyzed endorsement. Most importantly, we'll be scaling up a lot faster. Our current 1t/yr is just a demo. Our current roadmap is scaling up to a 300t/yr pilot in the next few months before setting up building a commercial plant (10kt+) in the second half of next year. Any chance we can poach you from Google? ;)
- m12k 5y ago
  What's the status on your current 1t/yr demo? (i.e. is it fully operational?) What did you learn from it and what are the technical challenges to scale it up to bigger plants?
thinkcontext 5y ago
Interesting, thanks. The chemistry you discuss sounds a lot like this Rau, G.H., Willauer, H.D. & Ren, Z.J. The global potential for converting renewable electricity to negative-CO2-emissions hydrogen. Nature Clim Change 8, 621–625 (2018). https://www.nature.com/articles/s41558-018-0203-0?WT.feed_name=subjects_biogeochemistry https://www.nature.com/articles/s41558-018-0203-0?WT.feed_na...
philipkglass 5y ago
I love your approach but I think that you've made a mistake. $70.00 of electricity at $0.13/kWh is 538 kWh, or 1937 MJ. Hydrogen has a higher heating value of 142 MJ/kg. If you could actually get 36 kg of electrolytic hydrogen from 538 kWh of electricity, that's getting 5112 MJ of chemical energy from 1937 MJ of electrical energy. That can't be done. At first I thought maybe I was overlooking some consumable electrodes in the scheme, but it appears not. Rule of thumb for electrolytic water splitting is 50 kWh per kg of hydrogen. That would mean about 0.29 as much H2 as estimated in the blog post. If you scale all salable products by 0.29 (not sure if that's sensible since I haven't identified the root error) it would still yield $142 of products from $70 of electricity. And good news there is that industrial scale electricity can be had for well under $0.13/kWh.
nextaccountic 5y ago
> More than just profitability, can they make a dent in our carbon problem? The scale of our carbon problem is on the order of 30 billion tons of CO2, of which maybe 1 billion tons are due to lime production. Heimdal is currently at the scale of 1 ton per year - nine orders of magnitude away from making a difference. Assuming continuous Silicon Valley ridiculous growth rates of 50% year over year, they will take 50 years to grow to a point where they are actually making a dent in our carbon problem. I wish them good luck. They don't need to do it all alone. If this idea is solid, a lot of different companies and nations could be doing this. I'm excited for China to have carbon-neutral cement. If they do, it will probably be of their own making and not tied to this company growth.

by brilee 5y ago

dang 5y ago

Wow, that's the most in-depth response to a Launch HN I've ever seen. This is probably the most substantive Launch HN thread (I mean of the official YC startup launches at https://news.ycombinator.com/launches https://news.ycombinator.com/launches) that we've yet seen. And it was very little work to put together.

brilee 5y ago
The secret is apparently to be slightly cagey about your tech and nerd snipe half of HN into trying to figure out if your thing actually works or not...
- rossjudson 5y ago
  The other secret is to not be using investor money to pay low wage gig workers while you build out a "platform" for the future when you take all the business from everyone because they are too dumb to possibly compete with you.
marcuslima 5y ago
Agreed!

go_elmo 5y ago

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?

marcuslima 5y ago
Same idea for iron!

thereisnospork 5y ago

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/Chem_1202/Unit_6%3A_Electrochemistry/6.8%3A_Industrial_Electrolysis_Processes https://chem.libretexts.org/Courses/Mount_Royal_University/C... [2] Saturated near room temp, don't have a better source handy.

5y ago

marcuslima 5y ago

Impressive analysis! Missed out on a couple details, but I'll take that as a thoroughly researched/analyzed endorsement. Most importantly, we'll be scaling up a lot faster. Our current 1t/yr is just a demo. Our current roadmap is scaling up to a 300t/yr pilot in the next few months before setting up building a commercial plant (10kt+) in the second half of next year. Any chance we can poach you from Google? ;)

m12k 5y ago
What's the status on your current 1t/yr demo? (i.e. is it fully operational?) What did you learn from it and what are the technical challenges to scale it up to bigger plants?

thinkcontext 5y ago

Interesting, thanks. The chemistry you discuss sounds a lot like this Rau, G.H., Willauer, H.D. & Ren, Z.J. The global potential for converting renewable electricity to negative-CO2-emissions hydrogen. Nature Clim Change 8, 621–625 (2018). https://www.nature.com/articles/s41558-018-0203-0?WT.feed_name=subjects_biogeochemistry https://www.nature.com/articles/s41558-018-0203-0?WT.feed_na...

philipkglass 5y ago

I love your approach but I think that you've made a mistake. $70.00 of electricity at $0.13/kWh is 538 kWh, or 1937 MJ. Hydrogen has a higher heating value of 142 MJ/kg. If you could actually get 36 kg of electrolytic hydrogen from 538 kWh of electricity, that's getting 5112 MJ of chemical energy from 1937 MJ of electrical energy. That can't be done. At first I thought maybe I was overlooking some consumable electrodes in the scheme, but it appears not. Rule of thumb for electrolytic water splitting is 50 kWh per kg of hydrogen. That would mean about 0.29 as much H2 as estimated in the blog post. If you scale all salable products by 0.29 (not sure if that's sensible since I haven't identified the root error) it would still yield $142 of products from $70 of electricity. And good news there is that industrial scale electricity can be had for well under $0.13/kWh.

nextaccountic 5y ago

> More than just profitability, can they make a dent in our carbon problem? The scale of our carbon problem is on the order of 30 billion tons of CO2, of which maybe 1 billion tons are due to lime production. Heimdal is currently at the scale of 1 ton per year - nine orders of magnitude away from making a difference. Assuming continuous Silicon Valley ridiculous growth rates of 50% year over year, they will take 50 years to grow to a point where they are actually making a dent in our carbon problem. I wish them good luck. They don't need to do it all alone. If this idea is solid, a lot of different companies and nations could be doing this. I'm excited for China to have carbon-neutral cement. If they do, it will probably be of their own making and not tied to this company growth.