Comment by telotortium | Hacker News Reader

Comment by telotortium | Hacker News Reader

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None of these carbon conversion companies ever talk about how they obtain their CO2 supplies, probably because it would reveal them as greenwashers. Although they attempt to imply that they are climate tech, they don't ever describe a solution for extracting carbon dioxide from the atmosphere, because they know it's economically infeasible. These carbon capture processes need a concentrated stream of CO2.

Let's compare carbon capture to the currently existing product that needs concentrated CO2, dry ice. Dry ice usually captures some concentrated stream of CO2 from an industrial process that creates it. The global market for dry ice is on the order of half a million tons per year. Meanwhile, the CO2 equivalent for global annual jet fuel consumption is on the order of 300 million tons. So it seems infeasible for carbon capture technology to replace even jet fuel, let alone all the other uses of fossil fuels needed for processes that require heat.

You can make dry ice directly from air, by cooling and compressing it, because after the condensation of water the other gases have much lower boiling temperatures than carbon dioxide.

Obviously, the efficiency of the cycle is lower when starting from air instead of from pure carbon dioxide, but the input energy is unlimited, as it comes from solar or wind energy.

This does not compete directly with batteries, which have very good cycle efficiency but poor mass, volume and maximum storage time. It competes only with other energy storage technologies that can also store energy for many years and/or which have comparable energy per mass and energy per volume ratios.

To judge whether the technology of this company can be competitive, we need some numbers that they do not provide. Nevertheless, it is also impossible to dismiss it a priori, because there are good chances for it to have a good enough efficiency.

What they say about having a better efficiency than the 2-step process through carbon monoxide is plausible, and even the indirect Fischer-Tropsch synthesis has been economically viable in the past, in the absence of enough fossil fuels, despite the fact that it is not competitive today, as long as the fossil fuels are still cheaper.

> Obviously, the efficiency of the cycle is lower when starting from air instead of from pure carbon dioxide, but the input energy is unlimited, as it comes from solar or wind energy.

What sort of energy inputs are required for a kg of CO2? If the process is so inefficient that e-fuels contain only a few percent of the energy inputs, then it's pretty unlikely to be a good use of electricity (even excess renewable energy).

That's the pivotal number. kWh per kg of CO2. It needs to be reasonable.

Ultimately only 0.04% of the air is CO2. You need to process a lot of air to extract large amounts of CO2.

If you look through your window, it is likely that you will see the proof of concept that the energetic efficiency of extracting the 0.04% of CO2 from air and the hydrogen from water, and of converting both of them into hydrocarbons can be high enough to allow you to breathe and to satisfy your hunger.

The artificial alternatives already have better efficiency for capturing the solar light and for extracting the hydrogen. It remains necessary to improve the efficiency of the CO2 capture and of the conversion to hydrocarbons.

Air has a bit over 400 parts per million CO2. Extracting CO2 from air in meaningful amounts involves pumping a lot of air.

The preferred source of CO2 for most carbon capture schemes is the exhaust fumes of those burning fossil fuels. Basically how this works is that you burn some dead dinosaur juice/lumps/gas, you capture (a fraction of) the CO2, use lots of energy to turn that into synthetic dinosaur juice/gas, and when you burn that, 100% of the CO2 ends up in the atmosphere. That's right, 100% CO2 comes from fossil deposits and at the end of the process 100% of it ends up in the air.

And 100% of the CO2 found in fossil deposits also originated from the atmosphere, many, many years ago (I.e when the fossils were not in the ground, that quantity of CO2 pre-existed in the air). Let us pause and think about that.

There’s already a trial of CO2 capture at a trash burning facility in Oslo. I could see trash burning + CO2 capture becoming viable over time. Especially if that CO2 capture is paid for by carbon credits. (Yeah, reuse and recycle first, but eventually everything degrades and burning is in the end the best option , especially as modern processes lets us filter out heavy metals and toxic chemicals circulating in our materials)

I could also see e-fuels become competitive for larger remote islands that would otherwise import fuels. Could make them self sustaining. If they don’t go all-electric that is.

The jet fuels will be largely offset by battery electric flights IMO. Most miles flown are short range. It’s still a couple of decades out but I’m certain battery electric will be viable for short range flight eventually. The main challenge is designing the plane from the ground up to get the efficiency advantages of electric flight.

So I really don’t think we’ll end up needing all that much CO2. It’s basically fuel for a subset of planes and ships, and feedstock for some chemicals. That’s a minor part of the oil/gas usage and CO2 emissions today.

Notably they've quit building regional jets

https://en.wikipedia.org/wiki/Bombardier_CRJ

https://en.wikipedia.org/wiki/Embraer_ERJ_family

which will eventually lead to a crisis for small airports like

http://www.airnav.com/airport/KITH

It's already a big problem in economic development that many cities are stuck with airports with terrible service. Many organizations in Ithaca believe that the airport is a competitive disadvantage. Airlines are refusing to adopt next generation small aircraft like

https://en.wikipedia.org/wiki/Embraer_E-Jet_E2_family

even though the lower operating costs and better comfort (e.g. people who are riding an E2-Jet to get on a 737 would be shocked that the regional jet is a lot more comfortable than mainstream narrowbody airliners.)

Since regional jets are going extinct there will be a market for something else, maybe electric aircraft, because the competition from legacy aircraft isn't there. See also

https://www.raa.org/wp-content/uploads/2023/02/1Q23-Small-Co...

If we're being realistic, the road to a circular economy is going to be long.

We're still going to produce non-recyclable garbage in 50 years (you could potentially even reform that to hydrogen and carbon monoxide, lowering the energy requirements relative to synth fuel production from CO2), and the world will still be running gas turbine peaker plants for those wind-less winter days.

We might be running gas peaker plants in 50 years but there’s no way they will run on natural gas. The reduced scale, and gas being harder to find, will obliterate the economies of scale.

We’ll be running them on hydrogen produced from excess electricity on days with a lot of wind and sun.

There’s even some serious talks about delivering hydrogen over existing gas lines. Like all the off shore platforms in the northern sea can become hubs for off shore wind (super strong and stable wind all the way out there) that power electrolysis to send hydrogen to Germany.

I really hope it works out like this.

But right now, the technological challenges (electrolysis cells are expensive at GW scale, transporting and storing hydrogen is dangerous and expensive) are substantial.

I just don't see a scale where a hydrogen electrolysis facility that only runs on days with excess electricity production is more economically feasible than running a thermal hydrogen reformer of a natural gas pipeline and using the natural gas itself for the applications where you end up just burning it anyway.

Gigantic taxes on CO2 emission could fix this, but ever then hydrogen would need a couple of breakthroughs to make it more economical than carbon capture and storage.

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