Even if capturing uses more energy than emitting, it can still be useful since we can Maxwell's Demon the whole process.

We can decide only to emit CO2 at the times when we don't have clean energy ready to use and decide to recapture CO2 when we do have clean energy to use.

Unfortunately we have collectively decided that solving hashes is a better use for clean energy

Maybe we could start minting coins or NFTs from captured CO2?

There is already similar stuff being done as part of tracking for carbon credits. i.e https://www.forbes.com/sites/forbestechcouncil/2021/08/16/th...

This would be an interesting approach! Not sure how it would work in practice, but it's a fun thought...

And there could be inherent value there, especially as a carbon capture tax credit. Instead of proof of work or proof of state, it's proof of capture. You'd have to put together some kind of distributed capture hardware, but... That's maybe possible with current tech?

Unfortunately the fact that it has a clearly measurable value means it's price is pegged to that value.

If this token gets you $100 worth of carbon emissions, it's hard to justify a price higher than $100. If the token gets you absolutely nothing, then the value is absolutely arbitrary - enabling spectacular rise

What if you tied it to a desktop carbon capture device (understood that these don't really exist currently)? Doesn't even have to be particularly efficient, nor tied to carbon credits.

The reason we don't have clean energy ready to use is that the cost of renewable generation plus storage is currently higher than the cost of burning natural gas. If you add the cost of capture to the cost of natural gas, that's plausibly not going to be the case anymore. And then it's more cost effective to build storage than capture.

That's the point though? You use carbon-capture as energy storage (when you have excess clean energy), and you can release CO2 when you don't have enough clean energy. In an idealized process, you basically produce coal as a form of "energy storage".

No. That doesn't follow at all, and I wish people would stop repeating this overclever "proof".

Burning fossil fuels for energy: hydrocarbon + O2 -> atmospheric CO2 + other stuff

Sequestration: atmospheric CO2 -> not-amospheric-CO2 e.g. solid C + other stuff

Notice that those are not exact reverses of each other, so there is no requirement that the energy released in one be the same quantity as the energy absorbed in the other.

Hydrocarbon fuels have very high Gibbs free energy. Solid carbon does not. We're only trying to get the CO2 out of the atmosphere, not return it to the form of the original fuel that was burned. Therefore, sequestration can potentially require less energy than was originally released from burning the hydrocarbons.

Combustion is an energetic oxidation. The primary chemical energy change is combining the oxygen with other stuff to produce stuff-oxide. If you want the stuff back out in its pure form you absolutely do have to put in more energy in to remove the oxygen than the combustion result produced. Now, depending on the chemical reaction, sometimes the "more energy in" is "waaay more energy in", which can certainly be improved with catalysts and the like, but that can only create improvements like 100x to 1.1x, which is great!, but always >1.

It's not a general rule for all capture processes, but on the case of solid carbon you do need to put back most of the energy yo get by burning the fuel.

Solid carbon is basically coal. It has more usable energy per mass than any hydrocarbon, and just a little bit less per carbon.

> you do need to put back most of the energy yo get by burning the fuel.

And we can get this energy from sunlight.

Well, we can. But it would make no sense to deploy something like this before our electricity generation is decarbonized. Other capture processes do not share that issue.

But nobody is planning on deploying something like it currently anyway.

Sure, but dont underestimate the inefficiency of power production and sequestration.

Take take the gallium example, for atmospheric levels of CO2, is 400:1. Add the thermodynamic minimum to reverse GalliumOxide to Gallium and O2, and its 800:1, at an absolute minimum. This crushes the difference to methane.

More importantly its a pointless argument, we have practically endless nuclear fuel available, enough to supply the world with power entirely for millions of years. So it does not matter if its inefficient, its climate neutral anyways as long as we stop being idiots and use what we have better. That said there are way simpler more cost effective methods than using a rare earth metal.

You're on to something.

To make it concrete, let's look at methane, the hydrocarbon with most hydrogen.

One kg of methane contains 0.75 kg of C and 0.25 kg of H. When it burns it realeases 55.6 MJ (per wikipedia [1]). Carbon's energy density is 32.7 MJ/kg, so the 750 g release 24.6 MJ. More importantly, you could in principle split the CO2 for the cost of 24.6 MJ and be left with a net of 31 MJ. Q.E.D.

Well, except in real life nothing is done with 100% efficiency. You can't just use all the 55.6 MJ released by burning CH4, you first convert it to electricity, and the best you get is 63%, so you make 35 MJ of electricity. If you get 70% efficiency in splitting CO2, you get exactly the 24.6 MJ you need. But you don't get that efficiency. But let's just say you get even more than that, let's say you get a whooping 85%. That means you need 30 MJ for the splitting, and you are left with a net of 5 MJ of electricity. Which is another way of saying you increased the cost of electricity you generate by a factor of 6 (=30/5), this ignoring altogether the capital cost associated with the splitting of CO2.

But all is not lost.

If we get back to 1kg CH4 = 0.75 kg C + 0.25 kg H2, burning the CH4 we get 55.6 MJ, burning the C and H2 separately, we get 24.6 MJ + 35.5 MJ = 60.1 MJ, which is 4.5 MJ more. That's a different way of saying you need 4.5 MJ to split CH4 into C and H2. That reaction is called methane pyrolysis [2]. Let's say you manage to deliver this with only 30% efficiency, i.e. for 15 MJ. You are left with 35.5-15=20.5 MJ net energy. If you convert this to electricity you get about 13 MJ, which is not that great. But hydrogen is valuable in itself. If we move towards the hydrogen economy, this method of generating hydrogen may be the winner.

[1] https://en.wikipedia.org/wiki/Energy_density

[2] https://en.wikipedia.org/wiki/Pyrolysis#Methane_pyrolysis_fo...

Agreed, the only way this can be useful is to do both: stop burning carbon; use processes like this to recover the carbon from processes where there isn't a good alternative to producing CO2 output. Cement production, perhaps.

There are a number of marine processes which permanently bind carbon, and they do increase with increased CO2 concentration. Problem is that they are overwhelmed by current production. If we reduce CO2 production to zero, the earth will mostly bounce back on its own in a century or two.

Yes, recapturing CO2 at the powerplant is pointless because of conservation of energy. It's always better not to burn the carbon in the first place.

But recapturing CO2 from air isn't pointless - because we can use surplus renewable energy to do so (and then burn C later as fuel). Basically it would use air as infinite capacity (but low-efficiency) rechargeable battery. I've seen estimates of about 13% efficiency over the whole cycle (capturing + burning).

Is there any known or predicted capture technology that does this more efficiently than by growing plants or algae and then burying them underground and/or using them as biofuels?

Inducement of massive algea blooms is extremely cost effective, can store massive amounts of carbon very quickly, and horrendously damaging to large lake, and ocean ecosystems, where you can use them. There are two problems, the first is that its only effective as storage if you make it damaging enough to ensure mostly anoxic decomposition, so the damage is required. Its reusable though, so if you waste a huge lake, there is no reason not to do this over and over again. The second problem is that if you do it in oceans, then ensuring it sinks to the bottom, becomes key, though this is straightforward if you do it on a scale to solve global warming in a single sweep. Though you would sacrifice an ocean and everyone living nearby for decades. The one time someone tried it, it was a far more massive success than anticipated, but also killed the fishing and tourism industry on several nearby, and not so nearby islands, for several years.

A slower variant is to build artificial floating reefs, increasing the amount of marine snow. That improves the ecosystem, but requires significant investment.

According to this guy [1] in less than a decade it will be cheaper to produce hydrocarbons out of air and water + surplus renewable energy than by pumping them out of ground. Which is in turn cheaper than biofuels.

[1] https://caseyhandmer.wordpress.com/2021/11/01/scaling-carbon...

Yes. CO2 can be frozen out of the air as snow at sufficiently low temperatures.

This could be done at scale in central Antarctica using enormous refrigerating complexes[1], but it would be the most ambitious engineering project ever undertaken by humanity.

Generally this is not seriously discussed by experts as a solution to global warming not because it is not feasible, but because it would diminish the sense of urgency and discourage the much more prudent and affordable approach of simply reducing emissions.

[1] https://journals.ametsoc.org/view/journals/apme/52/2/jamc-d-...

> it would diminish the sense of urgency and discourage the much more prudent and affordable approach of simply reducing emissions.

If air capture costs more, then simple economics will keep us more focused on reducing emissions. If it somehow costs less, then doing the air capture is a win.

Most likely, air capture will cost more in some cases (power plant emissions), and less in other cases (long-haul jets). Ideally we'd set a price on carbon, award credits for verifiable air capture/sequestration, and let the market sort all this out.

> Generally this is not seriously discussed by experts as a solution to global warming not because it is not feasible, but because it would diminish the sense of urgency

Let us say it is not being discussed because it is not feasible. Unless of course we build massive nuclear power plants in Antarctica with all what that entails. We are not any time soon in a position where we can produce any nontrivial amount of solar or wind energy in the hostile environment of that continent, plus it's dark night down there for half a year each year. Meaning the only remaining option would be to ship coal or oil down there to burn it so we can cool air to –140°C, obviously a non-starter if there ever was one.

> and discourage the much more prudent and affordable approach of simply reducing emissions.

This. The entire plan is madness: you'd burn two tons of oil and coal to get rid of part of what burning one ton of oil and coal leave behind in the atmosphere. It is not clear to me at this point if it is at all feasible to use fossil fuel to get more CO2 out of the atmosphere than burning it puts into the atmosphere in the first place. Because in this household we obey the laws of thermodynamic. And if it's possible at all it's not easy to see why continuing to burn oil and coal and capturing the CO2 at other sites should be better than not burning part of those fuels and capturing the CO2 right at their point of emission should be the better option. It is a hare-brained plan.

> Let us say it is not being discussed because it is not feasible. Unless of course we build massive nuclear power plants in Antarctica with all what that entails.

Maybe it really is because it's not feasible, I concede that's not something I can really know. But nuclear power plants are not necessary. As the paper sets out, there is abundant wind energy in Antarctica. Setting up a medium-size (1200 MW) wind farm on the Antarctic coast is actually not a crazy proposal, since the construction can be undertaken by ship alone.

Moreover it's very clear that the energy required to freeze one ton of CO2 is substantially less than the useful energy obtained by its combustion (this is intuitive from the magnitude difference between heat of combustion and enthalpy of sublimation: combusting one mol of pure coal to CO2 liberates 393 kJ, freezing one mol of CO2 out of the air consumes 26 kJ). In no way does that violate thermodynamics; the CO2 still exists, it just isn't doing any harm.

This project would not just ameliorate global warming, it could allow useful exploitation of all the remaining global fossil fuels.

Maybe perpetually shaded area would work even without active refigeration? Sun never rises overhead in Antarctica. But yes it's still about building a megastructure in very harsh environment.

I'm not sure if it's more efficient than the methods you mentioned, but Project Vesta makes some pretty bold claims using the carbonate-silicate cycle. More details:

https://news.ycombinator.com/item?id=20403570

https://www.vesta.earth/

> surplus renewable energy

is where you lost me. Hell coal is projected to get burned by the megaton for another half century or so because China and India have those resources and that demand. Mankind does not currently have surplus renewable energy.

There isn't a single global account of electricity generation and expenditures. If your windmills are humming in Montana, and demand for electricity relatively nearby right now is already met, you have surplus energy to either use or store; China doesn't factor into it.

Maybe if you were allocating resources across the world's economies, it would be better to invest in solar panels in Shanghai than capture carbon in Billings, but that's not the actual situation.

> Mankind does not currently have surplus renewable energy.

On the contrary - we have a lot of surplus renewable energy, and it's a problem [1].

Energy isn't fungible. 1 MWh in Texas at 12:00 on 4th July is not the same as 1MWh in London at 23:30 on 25th December.

Energy consumption vary a lot through the day and year. Energy production of solar and wind vary a lot as well, and these variances aren't correlated with each other.

Most big scale energy grids are created with the assumption that every millisecond energy produced == energy consumed. When this isn't true - frequency in the grid rises or drops. If it drops too much you just have blackouts, if it rises too much - devices blow up AND you have blackouts until you replace the blown up devices.

Even if a grid as a whole has energy deficit - it's often true that one part of the network is producing too much but the power lines between them might not be "thick" enough to transfer all that energy to the part of the grid that has deficit at the moment.

If we moved completely away from fossil fuels towards renewables - to serve energy needs of customers we would need a lot of overcapacity (because you can't count on sun and wind producing at 100% power all the time). Usually the overcapacity for wind is 2x and for solar is 10x compared to traditional sources. Better batteries might change that, but it still won't be 1x. So when there's a very good weather grids with a lot of renewables will by definition produce too much energy.

There's a lot of factors, and in practice even in countries with less than 50% renewable power installed - often they have too much renewable energy. This will only get worse as we replace more energy production with renewables.

Big batteries like the one in Australia are very profitable and solve short-term (sub-hour) balancing, but aren't big enough to shift the solar production peak in the noon to the consumption peak late evening.

So indeed we have a lot of surplus renewable power already that gets wasted every day and causes problems, and it will only get worse.

[1] https://www.sierraclub.org/sierra/what-do-we-do-too-much-ren...

Yeah, I was about to say... as great as this seems like it may be, surely turning CO2 into coal isn't a net gain versus not burning the coal.

But there are plenty of point emitters of CO2, so if we imagine a grid that's actually renewable sure. Capture though? It could always be paired with another capture method to concentrate it first, it's usually cheap to concentrate things a little and expensive to concentrate them a lot.

Even if we stop all emissions right now, the CO2 already in the air will stay there for a while. We need some way to recapture it if we want to return to pre-industrial levels.

And that might take centuries to do, so we'll probably end up doing some kind of geo-engineering to interrupt the buildup of heat to give us time to extract the carbon.

Or, pessimistically, we’ll do the geo-engineering step without ever reigning in the new emissions and call it done.

As someone who has been growing plants for years underwater (aquascaping) IMO geo-engineering is the only answer. We are already doing it by proxy, we need to have it front and center though. Every action has a reaction. We cannot consider a single project for its merits without the context of the larger whole. We need to not only stuff more air into that supercharged engine, we also need the correct mix of fuel, strong spark, and correct timing.

The natural way to of carbon sequestion on a planetary scale is - life ( plants / organisms / microbes etc). The catch is that if we fuck it up, and you know we will, we will pay a hefty price (like we do now with red tides, dead zones, bleeching). The added bonus is that we just do not sequester carbon, but we supercharge all the plantatary processes.

You reminded me of a "midnight thought" on the topic. I wonder if Tesla starlink process could be used to create satellites with sails that block sunlight opening/closing as needed until we can remove enough carbon to do it right? The ring of satellites could be some distance above our current satellite flight paths.

Have you ever seen the shadow of a satellite passing overhead?

For that matter, if it did work, would the satellites not reflect IR back to Earth? They might even hurt more than they help because they would be blocking sunlight on one side of the Earth only but would be blocking IR escaping on both sides.

Read about solar radiation management. Space based approaches aren't necessary. You can put the equivalent of sunblock in the upper atmosphere or seed more low clouds. It's relatively cheap but there is a lot of opposition to the science.

@dr_shiv & @DemocracyFTW (I don't recall if HN notifies of mentions)

Is the "opposition" mainly that the process as stated isn't reversible? Is there a way to improve the original idea to make it reversible in a short order?

Well, marine cloud brightening is small scale and involves lofting salt water in the air. It is immediately reversable.

The opposition comes from political signaling and tribalism.

Read more:

https://www.nature.com/articles/d41586-021-02290-3

Thank you so much - very helpful

That's not "opposition to the science", that's a sane response to a madman's proposal to intentionally f*k with the biosphere at the grandest scale.

Considering the psychological effects of no sunlight, this is a terrible idea.

It doesn't require darkened skies --a reduction in incoming light is all you need. 10% reduction would be a lot.

Oh, you'll still get sunlight, assuming you pay your monthly sunlight bill to spacex.

My response isn't a HN "appropriate" comment, more Reddit - but this is gold! Made me laugh thinking of it.

I was suggesting, more like.... if they were programmed (for instance) to open over deserts, or barren U.S. lands, etc for short periods of time. Some parts of the globe might have some small amount of light blocked for 10 mins, 1 hour, etc - whatever. It would be like a cloudy "hour", etc.

Not sure how to phrase this, but: Are you aware of clouds? (The ones in the sky, not at FAANG...)

That outcome isn't necessarily bad. It's somewhat arrogant of us to assume that we understand enough about a system as complex as the Earth's biosphere and atmosphere to know for sure a larger percentage of CO2 will necessarily be bad long term. It's feasible that it could be better, even if only after a painful transition.

I for one find the future where we're not actively managing the Earth's climate in some way to be the more pessimistic outcome. It indicates that civilization has failed to continue advancing, probably isn't spacefaring, and that the light of consciousness will eventually twinkle out once the Earth becomes uninhabitable in about 500 million years.

We'll see.

We know that, at least, thousands of species, including many not catalogged, will be driven to extinction, that large currently inhabited areas will become uninhabitable, that tens or hundreds of millions of those inhabitants will be converted to refugees unable to provide for themselves, and the influx of those refugees will drive temperate nation governments to fascism. If that is not bad enough, I can go on.

The "everything is so uncertain, we must do nothing" line has worn out its welcome. It was dishonest 30 years ago, and is reprehensible today.

Rather as in the pandemic, the attention paid to models is remarkable. You can cherry pick a model to suit your predilections. They certainly cover a wide range of possibilities. I do wonder what your view is of the utter lack of any concerted action by countries in response to these models? If we're off to hell in a handbasket, it does seem that few in power, with access to the best authorities available, are really concerned. How is that? Extinction Rebellion are certainly logical on the basis of their belief in the views of some climate scientists. They sound and act rather like people who'd say yes to O'Brien's question in 1984 when he asks Winston if he's prepared to do some pretty horrible things in pursuance of the objective of overthrowing Big Brother. But when it comes down to it, no one is convinced. Example: Coal is now back on the menu when power shortages loom.

I'm pretty sure the models are right, and that we will hit +4C on time, that politicians are aware of this, and they wont do much about it. They want to, but all real solutions have massive conflicts of interest, and they are aware voters dont really care much about global warming compared to other issues like house prices and jobs.

In forums like this, where everyone has a well paying job and fuck you money, it is important to preserve the planet, just not enough that more than 1% here would approve a build permit for a windfarm next door to their house. Arguably we mostly care about preserving the nice nature we now enjoy for free, and this is as good as it gets. The vast majority of people who specifically feel climate change is important still dont think the near guarantee of climate change is more important than the negligible risks of nuclear power.

Basically, politicians are representing the true interests of the population, which to be fair is their job. We just arent who we want to pretend we are.

Alarm about climate is overwhelming greater among voters than politicians. But US politicians (and the US Supreme Court) have arranged not to need to care if voters are alarmed, so long as lobbyists are not.

The two party system of the US occlude the matter so lets look at the rich well functioning democracies of Europe instead. Better education means there isn't anything resembling the climate denial movement of the us, and on average people are place climate concerns higher on their list of priorities. Every single one of these countries has a green party or similar whose primary purpose is the preventing ecological damage and climate change, and most argue it can be done without or with a minimum of loss of wealth and productivity. Not a single one of these countries is in a majority and most are around 10%. The ones which acknowledge that preventing a 4C rise requires massive investments and outright forced unpleasant changes will be required usually fail to go above 5%. And this is in the richest countries, the poorer countries dont give a rats ass about it, and the green parties are token efforts that idealists vote for knowing that their representatives will mostly make the others feel bad, while helping pass policy which supports the economy at the cost of eg climate as long as a token effort to minimize the negatives are used.

This shows that the vast majority of people in these countries, while publicly concerned, and privately mildly alarmed about climate change, prioritize other things and that their politicians are responding to their constituent priorities. Why would this be different in the US? everything from median education to city planning, predicts that US population cares much less about environmental impact. Poor people living on welfare in some Nordic country sometimes care about climate change, but mostly dont, certainly much less so than average citizens. The number of poor in the US who prioritize climate change over saving 5 bucks on gas so their kid can eat that night is zero.

When people aren't lying to themselves, its easy to see that preventing climate change is a policy favored by, and forced upon the public, by elites. Speaking as one, if of the lowest possible level, obviously we should do it. I'm certainly willing to sacrifice the poor both abroad and at home, but I think tigers are cool, that nature is nice to look at, and I would like to keep it that way. On the rare occasion I happen to meet some of my old friends turned politicians, I naturally point this out. And they listen, far more than they should, given neither my phd nor my career is in an applicable field. The few times I meet 0.001%ers, they have been more concerned than I. They haven't needed to status signal for decades, certainly not in private to someone like me, and they all had significant interests in industry which would be negatively affected.

This changes the story of who is preventing such policy and of if its democratic. There isn't a conspiracy by the elite to prevent climate change from being solved, if anything its the opposite, and the problem is that common people aren't stupid enough to let us get away with it.

With enough counterfactuals, you can support any claim.

The argument loses all interest, but the questions remain why the argument is being made, and who wants it made.

Your claim is that politicians prioritize global warming less than their constituents. If this was true, then in countries with multi party systems we would expect to see green parties become larger than parties which prioritize other issues. However in reality, most green parties get fewer votes than other niche voter issues like anti immigration. They are much much smaller than parties which focus on issues the voters actually prioritized, such as economy, jobs, and welfare.

People in power expect to be dead before the chickens come home to roost. They didn't get where they are by caring about what happens to anybody else. Provided civilization doesn't wholly collapse before then, they are insulated from all consequences.

All the accepted models point in the direction of mass extinctions to varying degrees.

Arrogant? It's arrogant?

You might want to read up on the effects of higher CO2 levels on human cognition. It's not pretty. And it completely blows your comment out of the water.

We already know that the CO2 levels that are forecast this century are going to be catastrophic. This isn't a "we'll see" situation anymore. We have seen. The only question is whether we will do something about it before it is far, far too late.

You need to worry about the next 50 years before you start worrying about 500 million years.

> It's somewhat arrogant of us to assume that we understand enough about a system as complex as the Earth's biosphere and atmosphere to know for sure a larger percentage of CO2 will necessarily be bad long term. It's feasible that it could be better, even if only after a painful transition.

That's the problem. Maybe it's better, maybe it's worse, and there is only one way to find out. But if it's worse, finding out is very bad. And there is no way to know ahead of time.

I think we can and should be confident about the short-medium term negative effects of high CO2 on human civilization. You can always spread doubt about anything that's long-term(say more than 2 decades) but it doesn't help to hope long-term it works, and short-term let it hurt as much as possible.

> And that might take centuries to do

How many efforts at international cooperation have survived for centuries?

A lot of the comments upthread seem to be assuming that we live under some kind of World Government.

> We need some way to recapture it if we want to return to pre-industrial levels

To return we probably need to capture well below the "safe" boundary of 350 ppm of CO2, to engage all the feedback loops that will refreeze the arctic etc.

But also, why bother? Biggest problems from climate change are due to the fast change, which causes destruction of ecosystems (including human habitat). Even if we refreeze, we won't revert these losses.

That's why we do solar radiation management first (e g., Marine cloud brightening), to prevent the rapid change. Then we try to fix the atmospheric carbon balance. That will take a while.

> solar radiation management first [...] Marine cloud brightening

you mean, like, throwing a spanner into a machinery we hardly understand and see whether "it sticks"? Give me a hundred planets and start the trials!

Maybe read about it: https://www.nature.com/articles/d41586-021-02290-3

That's a good reason not to apply this technology to smokestacks, since that would make a power plant into a power consumer.

However, in some cases it's quite difficult to stop burning C. Long-haul jets are one example. So for those, it makes sense to make carbon-neutral liquid fuels, even though there's an energy penalty. Pull CO2 from the atmosphere, use renewables or nuclear as an energy source to turn it into fuel. CO2 emissions from steel plants might be another good application.

Ideally we might be better off using clean energy sources to displace fossil plants, but that doesn't happen as fast as we'd like for all sorts of political and economic reasons. So we might as well get started now on other reductions, because it'll still help some, and we can get it scaled up by the time we've decarbonized the energy grid and want to decarbonize everything else.

We don't burn pure C to make CO2 though. We burn hydrocarbons. I am not sure what the effects of the longer carbon chain is. But I feel certain the other extra parts of hydrocarbons leave more energy on the table.

The output might be quite low. But I doubt it would be negative.

Coal is pure carbon more or less. You are right that the math is a bit different for gas and oil.

He's not talking about perpetual motion. The input energy into this hypothetical spherical-cow process is concentrated reflected insolation. Unfortunately, getting the Ga2O back to being liquid Ga is probably the problem.

How is it smelted from ore in the first place? Quick look suggests that it starts out as an oxide, and is a byproduct of aluminum production.

> getting the Ga2O back to being liquid Ga is probably the problem

guess, the same way we got it - bath, electricity, cathode and anode

Luckily there are these rocks which get hot just lying around, more so if you concentrate them, and we have millions of years of current power consumption of those to use. Perfectly CO2 free too.

Unless you're Australia, where we shut down our geothermal trials after some early success.

Ignore those rocks that are already hot, let's keep digging up these black ones and burning them!

There are some industrial processes like blast furnaces where it's hard to come up with a better heat source than fire. That might be a place where this tech could help.

I think a better example might be cement production. For a blast furnace you don't just need heat, you need to chemically react some reducing agent with the iron ore. Generally that's either coal coke or methane reacting with the iron oxide to produce iron and carbon dioxide. There's technologies on the horizon that could enable electrolytic refining of iron much like how aluminum is refined. With cement production there's no potential method to eliminate the carbon dioxide. You still have the extreme heat of the process so natural gas and coal are a pretty good fit but even if you sidestepped that and heated it through other means, you're ultimately taking calcium carbonate and calcining it to calcium oxide. Even if you eliminated all coal usage you'd at best cut the amount of CO2 released by half. With a good carbon capture system connected to cement kilns you could actually use concrete to capture CO2 from the air. Concrete naturally forms calcium carbonate over time as it ages so you could use it to have concrete production effectively be a net negative for atmospheric CO2. Concrete production currently accounts for 8% of CO2 emissions globally and direct atmospheric capture has been something that's historically difficult due to the low concentration of CO2 in the atmosphere so you could kill two birds with one stone.

> With cement production there's no potential method to eliminate the carbon dioxide.

Please have a look at Limestone Calcined Clay Cement: https://lc3.ch/

This is only one of the cement alternatives I believe.

Either way, point stands: there are industrial processes that are very carbon-intensive in ways that are difficult to replace with electrical power. Carbon-capture in the exhaust system sounds like an excellent solution for these.

Are there any chemical carbon configurations more stable than CO2 which are solid?

Yes, carbonates of alkaline earth metals (e.g. magnesium and calcium) are solids at STP and more stable than carbon dioxide. See section 7.2.2 "Chemistry of mineral carbonation" in this IPCC report:

https://www.ipcc.ch/site/assets/uploads/2018/03/srccs_chapte...

Even at the low partial pressure of atmospheric CO2 and at ambient temperature, carbonation of metal oxide bearing minerals occurs spontaneously, though on geological time scales (Robie et al., 1978; Lasaga and Berner, 1998). Limitations arise from the formation of silica or carbonate layers on the mineral surface during carbonation that tend to hinder further reaction and to limit conversion (Butt et al., 1996) and from the rate of CO2 uptake from the gas phase in the case of aqueous reactions. The challenge for mineral carbonation is to find ways to accelerate carbonation and to exploit the heat of reaction within the environmental constraints, for example with minimal energy and material losses.