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Comment by Lariscus | Hacker News Reader

Carbon capture isn't real (as advertised). If you take green energy out of the supply to capture carbon, a carbon producing power plant will have to make up for it.

[1] https://www.youtube.com/watch?v=nJslrTT-Yhc

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You can run carbon capture by burning natural gas and still capture more carbon than you release because compressed CO2 + H2O is a lower energy state than O2 + hydrocarbon compounds.

Wow, interesting

Is this true? Sounds exciting if so.

It's true in a naive sense but the natural gas must also be extracted, refined, transported and the infrastructure to convert it into electricity and to perform the carbon capture must be built.

So yes carbon capture using fossil fuels isn't outright impossible because of physics, but practically speaking it's not real because the rest of the chain lowers the already marginal efficiency.

It's not really marginal efficiency. It's ~60% efficiency for a natural gas system, higher for a system with point-source capture on that natural gas. I'm not sure how exactly it pans out with the inefficiency of extraction but as I understand it those are fairly minor.

That's not to say that I think DAC is a silver bullet or something - it's obviously not because the CAPEX costs are huge at the moment.

Yeah for sure, you're right that I shouldn't have said marginal as the situation wrt natural gas is decent (though that is the best case fossil fuel). It's important to be accurate about these things.

Yes, we need to decarbonize.

But that doesn't mean we can't also try to accelerate the removal of carbon from our atmosphere.

You have a machine that if you turn it on, it removes carbon from the air. But, to power it you release a greater amount of carbon into the air.

Should you turn on the machine? No, you should leave it off.

Only when your power sources are green should you turn on the machine.

No, carbon capture powered by fossil fuels releases less carbon than it captures. For direct air capture, it takes somewhere around 2,000 kWh to capture a ton of CO2 [1]. You can generate those 2,000 kWh using natural gas and release about 0.4 tons of CO2 (about 0.8 if you use coal). [2] You can be even more efficient by burning natural gas in the sorbent re-generator (avoiding inefficiencies of power generation and transmission).

[1]: https://www.wri.org/insights/direct-air-capture-resource-con...

[2]: https://ourworldindata.org/grapher/carbon-dioxide-emissions-...

Out of curiosity, do those figures account for the carbon released during manufacture of the carbon-capture and power-generation equipment you're using? Do they include the carbon emissions of extracting, refining, and delivering the fuels, as well as the emissions from actually using them?

There have been some detalied life-cycle analysis of certain carbon capture methods/plants. As one of the most famous (& funded), Climeworks have had a third party study published to break this down[1]

[1] https://www.nature.com/articles/s41560-020-00771-9

They don't, that's just my napkin math.

The machines must result in more capture & storage than they produce - net negative emissions.

For example, using a machine to heat waste biomass with fast pyrolysis turns the biomass into bio-oil. Bio-oil can then be pumped underground resulting in long-term, stable storage. The machine produced far fewer emissions than were captured naturally by the plants.

Eventually, sure - but in the short term, carbon removal is an inefficient way of allocating resources.

But we have to allocate some resources to start the development process now (and hopefully make it more efficient and effective).

Why? Carbon is awesome. Life is made out of it. I want more.

This is only potentially true up to the point where you reach 100% energy generation using zero emission sources.

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