Carbon Dioxide and Coal Power

I've been giving it some thought, and I think I have a cost-effective solution for the carbon dioxide and other air pollutants produced by using coal in power plants. It's a pretty simple idea, but I don't know how helpful it will actually be. Before I get to that though, I'd like to include a little background on my thought process.

Renewable energy is The Future - Who cares about coal?

Given the increase in renewable power sources, why should anyone care about coal fired power plants? Well, I can think of several reasons:

  1. The United States has huge amounts of coal available domestically. Using it for power generation would reduce reliance on oil imports.
  2. Developing nations like China and India are using more and more coal to provide power. Since the U.S. has shown them how to pollute the air, it would be logical to help them avoid repeating our mistakes.
  3. I'm cheap, and the thought of all that carbon dioxide going to waste offends the hell out of me if there's another use for it.
  4. I'm cheap, and the thought of all the heavy metals in coal going to waste offends the hell out of me if there's a way to collect it.

The problem of coal (the short version)

With the advent of plug-in hybrids and other electric vehicles, our need for electricity is only going to rise. Burning coal is a tried and true technology for generating power. It's here, it works, and it doesn't have the high costs and training requirements of a nuclear plant. Though things like cellulosic ethanol, wind power, and solar power are promising, they're still too young to solve the problem, and fail to provide the constant, steady power our modern infrastructure requires.

But there are also many problems associated with coal combustion. Probably the biggest are the release of heavy metals like lead and mercury into the atmosphere and greenhouse gas emissions. This is a complex problem, so I'm going to focus on only a few possible solutions that I think are the most likely to provide the best return on investment for the owners and operators of coal fired power plants.

Capturing heavy metals and particulate pollution

One of the key complaints about the use of coal for power production is the fact that burning coal releases particles of heavy metals into the air, along with "particulate pollution" - dust and other crud that causes respiratory problems for people. Now the interesting thing about the heavy metals that are released is that most of them have some industrial applications. The Wikipedia article mentions the following heavy metals by name: arsenic, lead, mercury, nickel, sulphur, vanadium, beryllium, cadmium, barium, chromium, copper, molybdenum, zinc, selenium and radium. A little more research into some of these metals shows their various industrial uses, which I've summarized in the following list. All this information is from the English language version of Wikipedia.

Gallium arsenide is an important semiconductor material, used in integrated circuits. Circuits made using the compound are much faster (but also much more expensive) than those made in silicon. Unlike silicon it is direct bandgap, and so can be used in laser diodes and LEDs to directly convert electricity into light.
Lead is a major constituent of the lead-acid battery used extensively in car batteries.
Lead is used as projectiles for firearms and fishing sinkers because of its density, low cost compared to alternative products and ease of use due to relatively low melting point.
Lead is used as shielding from radiation, e.g. in x-ray rooms.
Molten lead is used as a coolant, eg. for lead cooled fast reactors.
Lead is added to brass to reduce machine tool wear.
Nickel is chiefly valuable for the alloys it forms, especially many superalloys, and particularly stainless steel.
The electronics industry, electrical power transmission.
It is primarily used as a hardening agent in alloys, most notably beryllium copper. Commercial use of beryllium metal presents technical challenges due to the toxicity (especially by inhalation) of beryllium-containing dusts.
Beryllium is a relatively rare element in both the Earth and the universe, because it is not formed in conventional stellar nucleosynthesis.
Has the sixth-highest melting point of any element, and for this reason it is often used in high-strength steel alloys.
Zinc is the fourth most common metal in use, trailing only iron, aluminium, and copper in annual production
Zinc is used to galvanize steel to prevent corrosion
Zinc is the primary metal used in making American cents since 1982
a catalyst in many chemical reactions and is widely used in various industrial and laboratory syntheses
power DC surge protection, where the superior energy capabilities of selenium suppressors make them more desirable
Sheets of amorphous selenium convert x-ray images to patterns of charge in xeroradiography and in solid-state flat panel x-ray cameras.
When mixed with beryllium it is a neutron source for physics experiments.
Radium (usually in the form of radium chloride) is used in medicine to produce radon gas which in turn is used as a cancer treatment. The isotope 223Ra is currently under investigation for use in medicine as cancer treatment of bone metastasis.

So it's pretty clear that most of the heavy metals in the coal plant exhaust have industrial uses. It sure would be nice to gather all that material together and sell it to industrial metalyards, wouldn't it? Well, I think we can do it pretty easily.

While I was watching the Peterbilt episode of Ultimate Factories on the National Geographic channel, I saw that their painting operation uses a downdraft paint booth to pull extra paint particles out of the air and into a water bath to prevent defects in the paint job. (Please see References below for patent information.)

CLICK! The lightbulb went off in my head. Put a similar downdraft system going into a water bath on the exhaust side of a coal fired power plant. The downdraft would pull all the heavy metal particles down to the water bath, trapping them before they escape into the air. If the tank is structured like a septic system, so all the solids are trapped in a deep well while all the liquids flow over a thin gap at the top into another well, it would be easier for an industrial recycler or HAZMAT team to go in and collect the metals. (I should really put an image here to illustrate the point.)

So that would reduce the heavy metal in air pollution problem I mentioned earlier. In addition, since the downdraft is pulling down everything that's in the air, this system would remove all the particulate pollution. So all the people who have respiratory problems are happy because the power plant has helped them reduce their medical bills. How's that for some good public relations?

And that particulate pollution, formally known as fly ash, is actually a pretty good substance for a lot of applications. It's used in cement, concrete, asphalt, and as an engineering soil amendment. Capturing this and selling it provides the power plant owner with an additional revenue stream, and turns a problem into an asset.

Update July 2, 2008

I just read this story on Slashdot that links to this article claiming that certain elements and materials will be "extinct" by 2017. Here's a relevant quotation:

But now comes word that it isn’t just wildlife that can go extinct. The element gallium is in very short supply and the world may well run out of it in just a few years. Indium is threatened too, says Armin Reller, a materials chemist at Germany’s University of Augsburg. He estimates that our planet’s stock of indium will last no more than another decade. All the hafnium will be gone by 2017 also, and another twenty years will see the extinction of zinc. Even copper is an endangered item, since worldwide demand for it is likely to exceed available supplies by the end of the present century.

Though I am not in a position to judge how accurate this theory is, it seems to be another good reason for implementing the particulate collection mechanism I proposed earlier.

Carbon dioxide and greenhouse gases

Of course, the downdraft system doesn't really address the carbon dioxide and other greenhouse gases released. I mean some of the CO2 will be captured and put in the water, but not a huge amount. Since coal combustion accounts for 40% of all the carbon dioxide released, that's a big problem.

To deal with the carbon dioxide problem, my proposal is this: Set up a series of greenhouses that take the exhaust gases that have passed through the downdraft system and let the plants convert the carbon dioxide into oxygen through photosynthesis. I'm picturing a structure similar to a maze, lined with plants and carbon dioxide sensors to show how effective the plants are, but probably a wide open greenhouse would work just as well.

One possible use for the plants grown in these greenhouses is as a feedstock for cellulosic ethanol. Once that technology is perfected, we'll need source crops that are not derived from corn and other foodstuffs. This greenhouse seems like a good source for that. If we don't want to wait on cellulosic ethanol, how about growing plants that can be used as a soil amendment and shipping them out to various farming businesses? That might prove cost effective. And if nothing else, well, I'm sure there are a lot of endangered trees and plants that could be grown in a protected environment to help preserve biological diversity. Maybe the power plant could receive a charitable contribution tax credit for supplying a nature preserve.

I don't think that the greenhouse should grow food crops, though, at least at first. There's too much chance of heavy metals or some other Bad Thing getting into the system. Though that can be dealt with by installing filters, but I'm trying to keep costs low so someone builds the darn thing.

Water, both hot and blocked

I didn't realize this until I read the article, but power plants don't care about the temperature of the steam they use as their working fluid. They're interested in the pressure of the steam. That pressure is used to turn the turbines in the plant. Though combined cycle power plants are starting to change this, that basically remains true. So you have a lot of cold water going into the plant, and a lot of hot water coming out of it.

This is a real problem on rivers, where certain species have their environments changed dramatically. The temperature change is enough to drive away some types of aquatic life. A related problem for river-fed plants is the blockage of rivers, and the accidental "fish suckage" - fish and frogs and other aquatic life being sucked into the powerplant and killed. I'm pretty sure that no one in the power industry wants this to happen. Setting aside all the moral arguments for a minute, it just has to be hell on the turbines and other equipment to get fish scales and guts grinding all the parts together.

One possible solution for this is to stop using rivers. Figure out how much water a power plant uses per day and build a storage reservoir that holds 15 days worth of water in a closed tank. This means that the power plant is no longer beholden to the whimsy of Mother Nature. Drought? Who cares? The plant still has a half month's supply of water available. And no one can complain about fish and aquatic life getting hurt, because there isn't anything living in the feed water!

That solves the input side of the plant's water needs. Now how do we handle the output? What do we do with all the hot water and steam? Well, we could make sure that our greenhouses are hydroponic, and use them to condense the steam and cool the water. Of course that means the greenhouse is limited to plants that can handle high-temperature water. That's doable, but I'm not happy with that solution. There has to be a better way.

Since the steam exits the power generation process after it spins the turbine, it makes sense to assume that the coal exhaust leave via a different path. This means we don't have to worry about coal exhaust contaminating the steam and water. For that reason, I think a series of ground loop heat exchangers placed under parking lots, administration building, or some other "wasted space" would be a great solution. The temperature difference between the steam and the surrounding earth makes the steam condense into liquid water.

It might even be possible to use the main feed reservoir as the heat sink. I'm thinking of a large copper pipe bent into a giant spring shape, like the stills used by Appalachian moonshiners or Hawkeye Pierce and B.J. Hunnicut on the M*A*S*H TV series. That would probably work pretty well, right?

And there's another benefit to using the source pond: The steam will raise the temperature of the water. This means that less coal is needed to raise the temperature of the water, which saves the plant owners money.

Any water that is lost for some reason could be replaced with water from rain or snowmelt. In fact, if the cooling loops for the water system are run through the parking lot concrete, that could raise the temperature of the slab to the point that snow and ice will melt. So there's another cost savings because the money that would go into clearing snow out of the parking lot is now available for another use. And another environmental benefit is that there's no salt or other anti-ice treatment needed. So our theoretical power plant is green in a lot of unanticipated ways.

Alternatively, the condenser loops could be part of a radiant-floor heating system in the administration building. That would reduce the HVAC costs of the plant. Well, in winter anyway.

But again, I'm getting into the pricey end of things. If the system just dumps the water into the source tank, or the condenser pipes are just sunk about eight feet (~2.5 meters) underground and allowed to feed the water into the source pond, that would do the job pretty well too.


Some patents turned up by Google's Patent search when searching for "downdraft paint booth water"