Comment by epistasis | Hacker News Reader

Comment by epistasis | Hacker News Reader

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And to quantify this a bit more, current costs for direct air extraction and sequestration of CO2 are about $6/gallon of gas. Climeworks is charging early customers $600/ton of CO2 [1], and about 100 gallons of gas convert to a ton of CO2.

This sort of direct air capture will be absolutely necessary in the second half of this century for all of our current oaths to keep warming to 1.5C, according to the IPCC SR1.5 report. And though many parts of the supply chain of CO2 direct air capture might get cheaper with time, the actual sequestration part might get harder and more expensive with time.

Chevron had promised to capture only a small amount of CO2 as part of a LNG project in Australia, but is facing massive fines because they didn't understand the geology enough to actually sequester CO2.

So while I'm fairly confident that we could eventually get the tech for CO2 capture down to maybe $1/gallon of gas, the actual sequestration is only going to get more difficult with time.

Every gallon of gas burned today makes 20 pounds of CO2 that will need to be removed in the future we are burdening future generations with an incredibly difficult debt that we don't yet know how to pay down.

[1] https://www.theverge.com/2021/9/9/22663597/largest-direct-ai...

Hey, I've always had a question which perhaps you can answer.

In essence, we're still burning lots and lots of carbon just to extract energy. Thermodynamics says to reverse the process and get carbon from CO2 we need to put all that energy back, with a hefty bonus due to inefficiencies.

So how can it be feasible to afford enough energy to "unburn" a century's worth of burnt carbon if we can't even get enough energy to avoid burning new carbon in the first place? Like, our energy generation might double in a few decades, but this "unburning" would require so much spare energy that it doesn't seem likely to achieve as soon as the second half of this century.

I could be wrong, but I think what you're referring to would be to convert it back to raw carbon. I believe that "carbon capture" would be literally taking out the raw CO2 and leaving it as-is, presumably holding it underground or something, which I don't think would take nearly that much energy.

The physics of storing equivalent weights of gas versus solids - the volume and/or pressure containment required - make it quite impractical to store meaningful amounts (on the scale of billions of tons) of it as gas; the fact that CO2 is just 28% carbon and 72% oxygen is comparably a lesser issue but doesn't help as well.

Perhaps you can avoid "unburning" it by some other chemical process (which is why I was asking this) but simply pumping the CO2 somewhere does not seem a reasonable option, the only place on Earth that can easily hold that much of CO2 gas is the general atmosphere where it already resides.

I agree that sequestering co2 gas is a losing game, and that's why I think all the fossil fuel companies' plans for CCS are pure bunk.

Climeworks' proposal to pump it into basalt caverns, where it chemically reacts and becomes solid, is one way around that.

Carbon Engineering is doing gas to liquids, and claims that they need ~2.25 kWh of electricity to convert atmospheric CO2 to 1 kWh worth of liquid hydrocarbons. We will see.

We will need gigatons/year of sequestration in 2050. It's going to require a ton of innovation to get there.

> So how can it be feasible to afford enough energy to "unburn" a century's worth of burnt carbon if we can't even get enough energy to avoid burning new carbon in the first place?

It isn't, and it won't be. Carbon capture is a pleasing myth we tell ourselves to avoid the massive and immediate actions that would be necessary to avert catastrophe.

We're addicted to fossil fuels, telling ourselves that when we eventually sober up we can undo the damage we've done to ourselves.

Carbon capture will never lead to negative emissions. What it will do is merely capture CO2 at central locations for processes that have no alternative.

I sincerely hope you are wrong, because if you are not, we will never keep to less than 1.5C of warming. Every single pathway for that requires carbon capture above and beyond what we can do with terrestrial processes.

There are several startups trying to come up with ways of sequestering atmospheric carbon in ways that will last for thousands of years. We need something like that to work, and to come up with ways to fund massive deployment in the second half of this century.

Well, we probably will not keep to less than 1.5C of warming, e.g. in the IPCC report even the most optimistic (i.e. unrealistic) scenario has a most likely estimate of 1.6C of warming.

IMHO when estimating future, starting with the desired outcome (or even considering it much) is harmful, as it causes you to accept unrealistic assumptions and estimates for the key items driving your predictions, just so the predictions will come out as "acceptable" to you. You need to consider the impact factors as they are, and have realistic expectations of the effect and likelihood of interventions (especially considering the specific motivation factors of the narrow groups who can make each of those interventions, how that aligns with their interests), and see to what prognosis they lead you.

If we "need to come up with ways" then it means that it's plausible that we won't, and we (in this case, not we-as-the-world but we-as-individuals and we-as-smaller-communities) also need to plan on how to protect our interests in that (quite likely) scenario. An aching desire for something to work does not imply that it's possible in the required timeframe. Especially because there's no single "we"; those that need a solution to climate change and those that could fund it are largely separate groups; you can't look at it as a primarily technical problem when the largest impact factors are political.

Gasoline is high-energy-density using a high-power-density portable quickly-starting/stopping engine. These advantages can overcome the minuses in some applications. (Fewer after the recent advances in batteries, etc.)

My question was more about the fact that we're still burning extreme amounts of carbon purely for energy, not for density of energy or density of power or portability of engines - we're burning coal for electricity, we're burning gas to heat homes.

We'd need to pay back all that energy, but in the coming decades we can't even afford the energy cost of the relatively much simpler solution of "simply" not burning bulk carbon for heat.

I don't think new coal plants are rational at all.

Re gas heating, I sure could've used some just this past winter during the Texas snowpocalypse. My apartment uses electric power for heating/cooking, so electricity was a single point of failure. Resiliency through diversity is a point I missed above.

I like the other answers you got, but will add one observation. Once we get energy fro, non-carbon emitting sources, it’s possible to put energy into capture without emitting more CO2 at the same time. So whether it takes 0.5 kWh or 10 kWh to capture the amount of CO2 that produced 1kWh for us originally, as long as it came from renewable resources, we can largely do it.

My question is more about expectations of scale. If currently renewable energy (not just electricity - heating etc matters a lot) is something like 10% or 12% of total energy; and we need to go to something of 300% or even much more (to cover energy spent not on current needs but solely to cover the "unburning" the excess of previous century, "repaying the debt" much quicker than we accumulated it), then that extreme growth of renewable energy generation doesn't seem plausible to achieve in the timeframe you suggest.

It's been a while since I ran through the napkin math, and I'm on mobile and can't pull up the backing links, unfortunately, but I believe we are just barely on track to replace all energy use with renewables in 15-20 years. After which we should have spare production capacity, assuming there is wind/solar close enough to the carbon sequestration points.

The gist is that if you look at the exponential curves of growth of both wind and solar deployments, and assume that we don't back off from those, you get X amount of TWh/year in 2040. Combine that with conversion of heating and transport to electrification, which provides huge efficiency boosts and requires only 1/3 to 1/4 the energy (most fossil fuel energy is just wasted). Then add in all the parts of the developing world which will increase their energy use to EU/China standards, and we are just barely there.

However I think we are likely to see big gains in production capacity as the developing world ups their game. They will be consuming more electricity, but also be immensely more productive.

Consider that we didn't spend 100 years using electricity at current rates. There was was an s-curve growth that only recently flattened in developed countries.

Thermodynamics says to reverse the process and get carbon from CO2 we need to put all that energy back, with a hefty bonus due to inefficiencies.

The key insight is that you don't need to turn carbon dioxide back into carbon. You just need to store those carbon atoms it in a stable form that keeps them out of the atmosphere. The most plausible way of doing that at large scale is to accelerate the reaction of naturally occurring silicates from rocks with atmospheric CO2.

"From a thermodynamic point of view, inorganic carbonates represent a lower energy state than CO2; hence the carbonation reaction is exothermic..."

That's from chapter 7 of the IPCC Special Report on Carbon Dioxide Capture and Storage, which I recommend reading for more details.

PkG: This is one of the best references I have seen in ages on HN!

Chapter 7 PDF: https://www.ipcc.ch/site/assets/uploads/2018/03/srccs_chapte...

Page 321 has the executive summary with your quote.

Parent page for full book: https://www.ipcc.ch/report/carbon-dioxide-capture-and-storag...

Removing CO2 from the atmosphere doesn't mean unburning it. The CO2 either gets dissolved into the deep ocean, stored underground in deep aquifers, or reacted with silicates to make carbonates.

I'm not 100% sure why you're downvoted, but I don't think we disagree with anything. As I said on my previous post, I was just making up the numbers, and so if it costs $6/gallon-o-gas for CO2 extraction, then my previous point is even more accurate (though I might not have said it very clearly).

Yes, I totally agree with you, did not mean to come across as contradictory in any way.

I do not fear being downvotes at all on this topic. If I'm not getting downvoted by the few persistent anti-climate-change voters here, then IMHO I am not pushing forward the truth enough! People, even here, have a lot more to realize about the technological, economic, and political implications of the transition that we must go through in the coming decades.

Have to say, I've fenced off about nuclear with you before, but thanks for always being up-front about your calculations and really pushing the conversation forward here.

Do you have any more information on the Chevron carbon capture failure? As far as I understand it, the failure had nothing to do with Geology.

  > 100 gallons of gas convert to a ton of CO2

Gasoline is about 87% carbon and 13% hydrogen by weight. And its density is around 700 kg/m^3. 100 gallons is 378.5 liters, which is 265.0 kg. That is 230.5 kg of carbon. C is 12.011 per atom, O is 15.999, thus that converts to 844.6kg, not a ton. Rounding up by >15% to make numbers more impressive is not nice when we are taking science

A gallon of gas converts to 20 pounds of CO2, and there are 2000 pounds in a US ton. My first web search hit, just to make sure my memory was not faulty, was this explanation:

https://climatekids.nasa.gov/review/carbon/gasoline.html

Using imperial units is always unfortunate, but when dealing with the typical unit of gasoline in the US, it's inevitable.

Not sure where you are getting your numbers, perhaps you're using a UK gallon or something?

I gave all my numbers making it trivial to check that I am using the us gallon and. Perhaps a site for kids that you cited isn’t using more than one sig fig?

The kids site is far more correct than yours, and consistently uses two significant figures in its calculations. See, for example, the US federally accepted value of 19.59 pounds or 8.887 kg CO2/gallon burned:

https://www.epa.gov/energy/greenhouse-gases-equivalencies-ca...

Your error appears to be using a single significant figure for the density of gasoline, at 700. Other sources place it from 711 to 749 kg/m3.

Hopefully you will reconsider my comment being "not nice," since you started with one sig fig and ended with four, and then did not consider the two different meanings of ton. And on top of this all, this ignores all the upstream emissions to generate the gasoline, which is greater than the 15% which you said was "not nice."

378.5 * 749/1000 * .87 * (15.999 * 2 + 12.011) / 12.011 = 903.7

still well short of a ton

You seem to be accepting that I was able to find your error on the single significant figure.

However, I already told you that I was using a US ton, 2000 pounds, 907kg:

https://duckduckgo.com/?q=1+ton+in+kg

Additionally, you are not including the 3-6 pounds per gallon in upstream emissions for gasoline.

Let's recall that this all started from the phrase "about 100 gallons of gas convert to a ton of CO2" and that when you quotes, you omitted the "about" so that you could try to make your incorrect quibble relevant. So at this point I would like to call this a very "not nice scientifically" departure from anything relevant, but I'm all ears if you were going somewhere interesting with this.

> Using imperial units is always unfortunate, but when dealing with the typical unit of gasoline in the US, it's inevitable.

Well, no, when dealing with the typical unit of gasoline in the US, Imperial units are irrelevant, and US Customary units are inevitable.

When I search I get a variety of answers, with the bulk being around the same or lower CO2 emissions than your calculation. Why does it the answer vary? Does it change depending on the grade of the fuel?

I have not found a single page with estimates as low as dmitrygr’s 18.6 pounds per gallon. The numbers from the top hits ina web search for me:

19.64 - http://www.patagoniaalliance.org/wp-content/uploads/2014/08/...

20 - https://climatekids.nasa.gov/review/carbon/gasoline.html

20 - https://www.fueleconomy.gov/feg/contentincludes/co2_inc.htm

19.6 (converted from grams) - https://www.epa.gov/energy/greenhouse-gases-equivalencies-ca...

“Just over 19” - https://epicenergyblog.com/2013/05/24/how-many-pounds-of-car...

The next hit isn’t about CO2 from burning Gas, but about the upstream emissions that go into producing gasoline, which it pegs at 3.3 to 6.7 per gallon - https://www.sierraclub.org/sierra/ask-mr-green/hey-mr-green-...

What sort of estimates are you getting?

> Why does it the answer vary? Does it change depending on the grade of the fuel?

Yes, “gasoline” is a family of related fuels of different densities and compositions, and it will also vary based on assumptions about how it is burned. Incomplete combustion will result in more “dirty” pollution and less CO2.

> Gasoline is about 87% carbon and 13% hydrogen by weight. And its density is around 700 kg/m^3.

That density seems to be on the low end; different formulations have different densities, and the sources I’ve found give somewhat different ranges, but the ranges given typically seems to be about 750±35 kg/m³.

Yes and:

IIRC 1 ppm of CO2 is ~1 gigaton of carbon. Roughly the weight of Mt Everest. We're adding ~26 Everests annually.

Mt. Everest has a mass of about 6 trillion tonnes.

Ugh. Stupid brain. Trying to get sense of the challenge, I worked some numbers to try visualizing how much carbon we're talking about. I'll refind my notes or recreate.

Thanks.

1 ppm of C02 ~ 2.13 gigatons of carbon, which is ~ 7.8 gigatons of CO2. (1) We add about 43 gigatons of CO2 to the atmosphere per year 55% of which is absorbed by natural sinks. We're definitely not adding 26 ppm of C02 to the atmosphere each year.

1.https://skepticalscience.com/print.php?r=45

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