Another way to reduce atmospheric CO2

There have been several ideas about using limestone to absorb carbon dioxide. If experts are convinced that the chemistry really would work like that, I'd like to see any of them tried out on a large scale.

My main hesitation was that several commenters on that site questioned the basic chemistry. If they are right, then none of these approaches would work for very long. So I'd want to see that verified or not. The gist was that the simple chemical equilibrium they posited (that the resulting solution would be mostly bicarbonate with a small amount of carbonate formed) might not hold up in sea water because the carbonate is much less soluble. If it precipitates out of the surface waters, that shifts the equilibrium toward producing more carbonate, and in the long run it all ends up as calcium carbonate again, spread thinly on the ocean floor. With zero net sequestration. So I'd like to see a study of the actual lifetime of the excess bicarbonate in ocean water first. Could be that's wrong, could be it'll take 10,000 years to happen, no idea. But I'd like to see that addressed definitively. Otherwise none of the carbonate rock ideas make much sense.

But if the basic chemistry is right, then there are several proposals out there that would use limestone to sequester carbon.

I've seen a couple of proposals for just spreading limestone dust around. The weathering converts it to bicarbonate, and you get the same effect. One was cited in the discussion. And that one addressed the transportation costs, coming up with $4/ton of carbon removed, though I have no idea if that's reasonable or not. They also noted that limestone dust that's a waste product of current US quarrying could offset 20% of US C02 emissions. If that works that seems like a pretty good idea -- use existing waste products to absorb C02.

ScienceDirect - Energy : Reducing energy-related CO2 emissions using accelerated weathering of limestone

Here is a scheme to put the ground up limestone in power plant flue gas stream, then take the resulting bicarbonate solution and dump it in the ocean. Basically the same concept. They even call it "accelerated weathering".

University of California - UC Newsroom | Patented technology captures carbon dioxide from power plants

 

Even if it is possible it is certainly uneconomical. The Department of Energy’s lowest estimate of the cost of CCS, $120 per ton of CO2, is equivalent to more than $35 per ton of carbon captured. In contrast a fossil fuel tax of $30 per ton of fossil carbon content would immediately make today’s non-fossil energy sources (including nuclear, wind, and Solar) cheaper than fossil energy sources. We must stop wasting time, money, and political will on pointless diversions such as CCS. The only practical way of using coal to mitigate global warming is to leave it in the ground.

 

Well, yes and no.

Fundamentally, sure, a large budget-neutral carbon tax would make a large part of the problem resolve itself over time. And the ultimate cost would not be the $30/ton, it would only be the loss of efficiency from using the higher-cost energy sources. The tax dollars themselves could be used to (e.g.) reduce marginal income tax rates, keeping Federal spending at the same share of GDP as it has been (plus or minus a percent or two or a war or two) since Eisenhower.

So, fundamentally, I agree. Just make clean energy cheaper and swallow the loss of efficiency. You'd pretty much be done with it, eventually.

But I think there are at least two rational reasons for pursing alternatives as well.

First, maybe the Congress will have the sense to implement a large carbon tax in the near future. That's possible. But the carbon-tax-is-it strategy says, in effect, let the fate of the planet rest entirely on the good sense of the US Congress. That strikes me as a rather slender reed. I'd rather hedge my bets.

Second, even with a tax, the speed of changeover may be slow, and the changeover may be incomplete, for a variety of reasons. We are certainly constrained in how fast we could build the alternatives, and to some degree, on the extent to which renewables can be used. So there's a technical constraint.

There are also economic factors that would moderate the speed of the transition. These don't get discussed much. With the carbon tax, you could clearly make it so that building new coal plants wouldn't make sense (assuming there were no technical barriers to using renewable alternatives). But it's not clear that a moderate tax would make it profitable to shut down existing functional coal-fired power generators. The reason is that the capital cost of the coal-fired plant is a sunk cost -- it doesn't go away. So, for the decision to replace a functioning coal plant with a new renewables-based plant, you'd compare the total cost of renewable plant to the marginal cost of the coal and maintenance to keep the coal plant going. I couldn't find a good reference quickly, but I think that capital cost of modern coal plants accounts for one-third to one-half the average cost per KWH for electrical production. My point is that you'd have to push up the price of coal enough so that the marginal cost of running the coal plant (excluding the sunk cost of the capital) exceeds the average cost of new renewable electricity. Maybe $30/ton would be enough, for the average plant, and maybe not. And clearly some plants (located close to coal mines, say, since the shipping is a big chunk of the cost) would continue to be run at $30/ton tax.

So, while I think you have correctly characterized the the big-dollar high-profile Rube-Goldberg-on-steroids approach of the DOE clean coal initiative as basically a waste of time, and possibly an intentional waste of time, that's not the only thing on the table for sequestration. I kind of liked the concept of spreading limestone dust at $4/ton. Not as an alternative to stopping burning fossil fuels, but something that cheap and feasible in the short run. Kind of the complete opposite of the DOE. No idea whether there's anything to that, once you look into the details, but I wouldn't dismiss cheap sequestration out-of-hand.