[walnutclosefarm]

There are no energy free ways to resequester atmospheric CO2. If you accept that we will have to do so to meet the world's climate change goals, then the question is really, how energy efficient can you make your process, and where can you get carbon-free energy. This company has a credible approach, although as soon as you look at any of the mechanisms being considered, the scaling problem is daunting.

[ImPostingOnHN]

Honestly, the low tech nature of grinding up rocks, baking them, and setting them out in a pile makes this seem pretty easy to scale, given any money

[walnutclosefarm]

I'm really thinking of the energy scaling. Suppose you want to use such a technology to offset burning oil for some purpose. Even for highly efficient processes, you're going to get generate a ton of CO2 for a MWh of usable energy. You're then going to use 2 MWh of electrical energy to recapture the CO2. So, you've tripled the energy we need to produce for that process. That's really raising the bar on carbon neutral energy production.

[ImPostingOnHN]

energy production is orthogonal to CO2 production, neither requires the other to happen

so, imagine you want to absorb a ton of CO2 from the air to prevent the planet from further spiraling into uninhabitability: you could electrically bake the rock with renewable energy, then use it to absorb CO2

[eppp]

Isn't this just portland cement at that point?

[natch]

The CO2 in the limestone was already sequestered by nature. They are freeing it, which is the opposite of what is needed. Leave the limestone alone and that CO2 remains sequestered, no additional energy needed. This sounds like a way to just capture CO2 on paper.

[walnutclosefarm]

Obviously, you didn't read how it is intended to work. Baking the rock gives them a stream of nearly pure CO2, which can be sequestered underground. The powdered rock then efficiently captures CO2 from the air (where it is of course, very low in concentration). That CO2 can then be baked off, sequestered, and the rock cycled to the air again. In an industrial plant, you'd have a continuous process of rock being baked, exposed, baked again, with a continous stream CO2 being sequestered geologically.

[aydyn]

How can one sequester CO2 “geologically”?

[ttyprintk]

There are two natural geologies I know of:

Oil fields often have dissolved CO2 and methane contaminants. Those gasses are captured and pressurized to force more oil out. Those empty caverns are the largest opportunity for capture.

At ocean depth, CO2 is trapped under hydrate caps. This is best-known around geothermal “smokers”, but the ocean floor is largely unknown. So, there is significant risk allowing the hydrate caps to melt.

[natch]

>Those empty caverns are the largest opportunity for capture

How large?

We have 42,592 trillion cubic feet of CO2 in the atmosphere, and the projected total natural gas that can be extracted going forward in the US over the next 85 years is 2,973 trillion cubic feet.

First, will we even extract that much? I've heard that using that much will create more CO2 than we can handle.

And, taking the wild assumption that we do extract that much, how much of that natural gas will come from fracking, and how much from caverns?

Let's be generous and say that 50% comes from caverns. So now we have 2973 times 0.5 which gives 1486 trillion cubic feet of space we can eventually use for the plan you describe, if we use more natural gas than we safely can use.

And that's making again another overly generous assumption in favor of your plan which is that these caverns are somehow left in a state of vacuum before we start putting in CO2.

And let's be fair and assume we only want to sequester say 20% of the CO2, so we want to squeeze 8,518 trillion cubic feet of CO2 into this idealized generously estimated 1,486 trillion cubic feet.

Naturally the gas will be injected under pressure.

I imagine this gets incredibly complex, and there will be leakage, and it will be the province of huge contracting companies that historically have shown themselves to be mainly interested in getting to a finish line such that they can get paid by the taxpayers, with help from their bought-and-paid-for lawmakers, long term results and consequences be damned (see: oil and gas industry, nuclear industry).

I don't feel very good about this plan.

But I can envision the ear-to-ear grins at the contracting companies when they found out "the libs" are going to make tax dollars rain on them for continuing to extract oil and gas out of the ground using some paperwork and a variation of a process they were already doing, even though it probably won't achieve the ends those libs want.

[adammarples]

You can inject it into coal beds and it should adsorb into the coal

[natch]

You do realize that coal then gets dug up and burned, right?

Also, have you heard of fracking? It's a blend of the words "cracking" and "fracture" and why is that? Like virtually any geology, there are cracks, through which, for example, gasses, like methane or in this case CO2, can escape. Coal beds also happen to be riddled with fractures and cracks. So even if you don't dig up the coal, "should absorb" is pretty weak for something we would be betting our future on.