Fortune Brainstorm Green

An unusually interesting discussion of 'clean coal'

Posted by David Roberts at 5:08 PM on 21 Apr 2008

Read more about: coal | energy | carbon sequestration | renewable energy

Earlier today I attended a small roundtable discussion about clean coal. Most of the people there were basically pro-clean coal: people from NRG energy, railroad companies, venture capital firms, and David Hawkins from NRDC. Some other folks were uncommitted. In the anti column were me and Mike Brune from Rainforest Action Network. Also in attendance: Fred Krupp of EDF and eco-oldtimer Stewart Brand.

There were pockets of agreement. To his credit, the guy from NRG lamented that the term "clean coal" had been used as a marketing trick -- he said the only thing that should qualify is a coal plant that actually sequesters CO2. There was general agreement that building new pulverized coal plants is a very bad idea, and that the immediate priority should be efficiency.

The disagreements were where you'd expect: can renewables scale up. Is coal getting (or asking for) unfair subsidies. Is it realistic to bury hundreds of millions of tons of CO2 all across the country.

I remain unconvinced that it's worth subsidizing new forms of coal plants -- I still overwhelmingly think that our short-term goal should be to stop the building of new coal plants, period.

But one argument I did find compelling is the utility of post-combustion carbon capture -- the kind of technology that can capture carbon out of the smokestack of a traditional coal plant (or use the CO to grow algae, or whatnot). It makes sense to me to fund that technology and try to drive the expense (which is enormous) down. The fact is, there are going to be lots and lots of coal plants in the world for the foreseeable future, even if we don't build any more. However expensive post-combustion capture may be, it's less expensive than tearing a plant down.

More on this stuff later.

For story: Fortune Brainstorm Green
5 Comments | Post a Comment

Capture isn't the hard part

In the end, it all comes down to biodiversity. Poison Darts--Protecting the biodiversity of our world

by biodiversivist at 5:31 PM on 21 Apr 2008

Capture isn't feasible

David,

There is a fundamental problem with capture - namely, that end-of-pipe control is only viable for really low concentration species (and then only with mandates). Thus, we can mandate technologies to take NOx emissions from 1000 ppm (0.1%) to 50 ppm (0.05%) with a relatively small imposed cost. CO2 is totally different. When you burn coal, you get CO2. The only other species in the exhaust is nitrogen, purely as a byproduct of the fact that the air with the oxygen is mostly nitrogen. But CO2 is a massive percent of the exhaust. Which means you have to invest massive amounts of capital and energy in pulling that CO2 out. There's just no getting around this.

In this vein, it is way easier to pull the carbon out of the fuel. Just as the route to reduced SOx emissions is to go to lower sulfur fuels - and the route to lower airborne lead emissions is to pull out lead additives - the route to lowering CO2 is to go to less carbon intensive fuels. Pick which one you want: natural gas, oil, biomass, solar... but by any measure, coal is directionally flawed.

And as you've often pointed out, "clean" coal is about more than just carbon. Separating and sequestering CO2 from an IGCC coal plant imposes something on the order of 20% parasitic loads. Meaning that we pull the coal out of the ground 20% faster, cut down that many more mountain tops that many more trains, etc. Whatever that is, it isn't clean. And it isn't economically smart, since those costs all drive up the cost of energy. You only do it if you have the luxury of public equity guarantees. But no private company is taking that risk, nor will they.

At the end of the day, this isn't a technology-development issue - it's a basic heat and mass balance around a coal plant.

by Sean Casten at 6:08 PM on 21 Apr 2008

Isn't IGCC underground?

Sean, my understanding is that IGCC means In Ground Coal Combustion, which implies we don't actually mine the coal, but inject gases, and use other gases for the above ground part of the process. In paper, at least unless there is a volumetric change above ground should be relatively unaffected. Nevertheless there is still a substantial additional capital cost, and ultimately more coal consumed per joule of output than a nonsequestered plant -and that is not counting disposal costs.

In general I have to agree with the logic of David's last paragraph. Assuming it is possible to generate power from "clean coal" cheaper than renewables/nuclear, then even if we choose not to pursue that path, developing economies may choose the cheapest path for economic reasons. Having a viable CCS option could be crucial for limiting/reducing future emissions.

by bigTom at 9:06 PM on 21 Apr 2008

The acronym means ...

Integrated Gasification Combined Cycle

by katakanadian at 10:29 PM on 21 Apr 2008

BigTom

katakhandian is right. It has nothing to do with being in the ground. IGCC is simply the process of gasifying coal (e.g., converting it into gas prior to combustion) and then running it through a gas turbine - as compared to a conventional coal plant which burns a solid fuel to make steam and runs the resulting steam through a steam turbine. (The gasification process makes an IGCC as much a chemical processing plant as a power plant, which accounts for some of it's higher costs/complexity.) The key point though is that an IGCC per se doesn't have any impact on CO2 emissions, other than a - theoretically - slight increase in overall power plant efficiency. The reason why IGCC technology is a part of the CCS conversation is that the CO2 ends up in a relatively more concentrated form than it otherwise would, thus making it easier to later come out and retrofit CCS onto. This is why some refer to IGCC as "carbon capture ready", but this doesn't make it inevitable. (When I was 16, I was "ready" to make sweet love to Paulina Porizkova. Putting CCS on an IGCC is only marginally more certain.)

The issue is that once you get to that end-of-pipe control, you sail directly into the initial problem I described. Namely, it takes a ton of energy to pull all that CO2 out. Coal is just about pure carbon. CO2 is carbon plus two oxygens. Purely on a mass basis, that means that you have 3.7 times as much stuff to bury underground as you pulled out in the first place. Worse, the stuff you pulled out of the ground was a dense solid while the stuff you're trying to re-bury is a diffuse gas - which means that you have to add a huge amount of energy to compress that gas before you bury it.

This basic technical reality (dense, light carbon gets converted into diffuse, heavy CO2) bedevils any technology to sequester CO2, and as a result ensures that any coal plant that sequesters CO2 will be much less energy efficient than one that doesn't - which means that it will use a lot more coal to make power than the current fleet. (Current IGCC + CCS models have about a 20% efficiency penalty against the conventional approach.) Looking at the problem narrowly from the context of CO2, that's OK (so long as the CO2 remains buried). But on every other metric, it's a bad idea. Since we're burning more coal, it raises the price of power. Virtually every renewable technology out there is cheaper than IGCC + CCS on a cents/kWh basis. Since we're burning more coal, we're cutting down mountaintops faster with all the commensurate environmental damage.

It simply isn't rational. Should we study this in the hopes that a breakthrough technology might come along someday? That depends on whether you think that the benefit with respect to CO2 outweighs the other environmental and economic costs, and reasonable people may disagree. But we should not delude ourselves into thinking that there is any scenario in which a strategy based on increased coal consumption per MWh is going to be more cost effective than one that uses less (renewables, efficiency, etc.) In other words, the focus has to be on getting the carbon out of the fuel rather than out of the exhaust.

by Sean Casten at 7:36 AM on 22 Apr 2008
[ Parent ]

ADVERTISING POLICY

You are not logged in. Thus, you cannot post a comment. If you have an account, log in. If you don't have an account, well, by all means go make one! Meet you back here in five.