The Other Stuff
by Devilstower
Sun Jan 11, 2009 at 06:04:24 AM PDT
In the 1960s, my mother helped build the Paradise Steam Plant in Western Kentucky. Every day, she was up at dawn and off for her job in the construction phase of the massive project.
Massive was just the right word. The plant has three enormous generator units, each of which is cooled by a hyperbolic tower the size of a 40-story building. The central smokestack is over 800' tall. If it was a building, that monster chimney would easily be among the fifty tallest in the United States. As a kid we told all the same death-by-falling-penny stories about it that kids in New York whispered about the Empire State Building. Everything about the plant is built to such enormous scale that you really can't appreciate it until you're standing inside and gawping up at the Land of the Giants set around you. In an area where the tallest building tops out at four-floors, the size of the plant rising up over the streets the neighboring town seemed surreal.
At the time, Paradise Steam Plant was the largest coal-fired plant in the world. It's still near the top, with boilers that consume 20,000 tons of coal a day and generators that crank out enough electricity for nearly a million homes. Despite John Prine's lyrics, it wasn't really Mr. Peabody's coal trains that hauled the town of Paradise away. Instead, Mr. Tennessee Valley Authority built a big power plant right next to the place and ran everyone out. There was certainly plenty of mining around it, though. River Queen, Sinclair... at the time, these were the largest mines in the world, built to match the world's largest steam plant.
In 1970, Paradise Steam Plant rumbled to life. Not long after that, the paint peeled off my mom's car. Dime-sized holes would appear overnight, where the enamel of her Pontiac was mysteriously missing. The holes went right down to shiny metal (on a 60s GM product, that metal was soon rusty). Occasionally she'd even get these odd melted spots in her clothing. Right at the center of each spot was a tiny fleck of fly ash.
Just as tossing a log in your fireplace leaves you with ash to clean up, so does burning coal in a power plant. Coal is mostly carbon, but it's not all carbon (you can't make a diamond out of coal, no matter how hard Superman squeezes). Bituminous coal, the kind found in the Midwest, is 60-80% carbon. About 10% of what remains is simply water, and the rest is made up of various compounds -- silca, calcite, iron sulfide, clays, salts, you name it. Midwestern coal originated in a massive swampy area that stretched across a good part of Illinois, Indiana, Ohio, and Kentucky around 320 million years ago. What's left now is what you get when you take giant ferns, cycads, horsetails, and a hundred other kinds of plants, mix in varying amounts of fresh water, brackish water, and plain old mud, then leave it to stew for a long, long time. You get a lot of nice, flammable hydrocarbons, but some other stuff, as well.
When you burn the coal, the water, most of the carbon, and volatile compounds are removed. What doesn't burn is that other stuff. That stuff becomes ash. Anyone who has ever walked beside an old railroad track and found something that looks like the product of a volcano has some idea what coal ash is like, only power plants don't produce big "clinkers" like an old steam loco. For peak efficiency, most coal burned in power plants is crushed to pea-size, or better yet, pulverized to a fine powder. That exposes the maximum surface area so you burn every bit of the coal that you possibly can. The ash from this pulverized coal is equally tiny. Don't think grains of sand. Think flecks of flour.
In the early days of Paradise and its contemporaries, these itsy-bitsy specks were literally allowed to fly from the smoke stack. Hence the name -- fly ash.
For bituminous coal, the fuel that plants like Paradise gulped for the first couple of decades, ash generally runs between 5-15% of the coal. 10% is a good average. So if you're burning 20,000 tons of coal each day, you get 2,000 tons of ash (a bit more, actually, for some fun with chemistry reasons, but we'll skip that for now). What was in the coal is now in the ash -- only its essentially concentrated 10x. If there was 1% iron in your coal, it's roughly 10% in the ash. Again, I'm playing fast and loose with the math, but we're in the ball park. Some materials, like sulfur, readily combine with oxygen and a good part of the SO2 heads up the smokestack. Still, Western Kentucky coal is around 3% sulfur, what's left in the ash was plenty to help eat those holes in my mother's car.
About half the ash heads up the smokestack in a typical plant. You'll be happy to know that very little of that ash is now allowed to fly free across the countryside and ruin the paint job of autos three states away. Electrostatic precipitators and other means are used to send the fly ash down to join the not-so-flighty "bottom ash" in storage. Which leaves one question: what do you do with it?
Fly ash can be used to make construction materials. Treat it like fine silt, adjust your mix to account for the amount of metals and acids in the stuff, and you can make concrete, or asphalt, or any of dozens of other materials. Many plants make a considerable effort at this, but there are problems.
Fly ash isn't the only ingredient in any of these products, so you have to have a plant with access to limestone, shale, or whatever other components you need. Almost every power plant is on rail line, but cars that are bringing in limestone aren't bringing in coal, so it takes some juggling. Plus, hauling low-value materials around can drive up the price of the material so that it's hard to compete. Get past that, and assuming that your fly ash is suitable, there's the simple matter of scale. 2,000 tons of fly ash a day is enough for up to 7,000 tons of concrete (less if you're making a high percentage fly ash product, but not all ash is suitable). That works out to better than 3,000 cubic yards a day of concrete. That's a big plant -- big enough to provide all the concrete for the Empire State building a bit over a month -- and in a lot of areas you're going to have a hard time finding buyers for that material. Fly ash is also commonly used as a fill material (think watery concrete mixed with soil). If you've been driving past the new strip mall in your area and wondering how they built that seventy-five degree slope in front of the Applebees without the whole thing sliding onto the highway, now you know.
Coal-fired plants really work at using fly ash in any way they can. Of the 78 million metric tons of fly ash produced annually by coal-fired plants in the United States, 40% gets reused in some kind of product. That's a huge change from those days when Paradise the town was replaced by Paradise the steam plant. Still, the rest of the fly ash produced in the United States -- 47 million tons a year -- ends up in storage. Fly ash averages right at a ton per cubic yard. So that 47 million tons is enough to cover Manhattan about two feet deep. Or to pile up some really enormous heaps next to the power plants.
Most of whats in fly ash is simply the same as what's in sand -- silica, calcite, aluminum oxide, but it's not really sand. It's glass, tiny bits of glass. Some of it is little glass beads. Other parts are tiny little shards of sharp, nasty glass that's abrasive to machinery and worse for lungs. That aspect of fly ash is why so many places are quick to stop it from flying by keeping it wet and storing it as a slurry. Adding water keeps the fly ash grounded -- but it also lets all those materials that were concentrated when the rest of the coal was burned away seep into the water. Sulfates and other materials help to make sure the mixture is acidic. That helps to free up materials like mercury, arsenic, and selenium. Now that more plants are burning coal from the Powder River Basin in Wyoming, the mixture even includes a dash of uranium and thorium.
Engineers monitor the stuff, but it sits there for year after year, filling one containment pond after another. It's not as toxic as the material at most superfund sites. It's not as nasty as the material parked outside many nuclear plants. But there's a whole, whole, whole lot of it, and a lot more of it all the time.
Researchers working on what to do with fly ash will tout the material as an "environmentally friendly product" because it's recyclable and, since it's already around, it takes less energy to produce than the material it replaces in many product mixes. That's stretching the idea of "environmentally friendly" further than a piece of saltwater taffy, but it might have some validity, except there's so much ash that doesn't get recycled and isn't likely to.
It's much more likely that ash will eventually do what the holding pond at TVA's Kingston plant did the week before Christmas. That one failure spilled a billion gallons of slurry containing more than 5 million cubic yards of ash across the landscape and into streams and rivers. Homes were destroyed. Fields, forests, and waterways ruined. A whole town left unlivable.
The Kingston spill made the news mostly because it was 100 times the size of the oil spill from the Exxon Valdez, but smaller spills occur with regularity. Smaller spills -- mere tens or hundreds of thousands of gallons -- don't make the national press, but they certainly make an impact on communities near the facilities. Even the Kingston plant leaked slurry on several occasions before the big spill.
Devastating spills associated with coal mining aren't even limited to fly ash. In 2000, an impoundment at a Massey Energy in Eastern Kentucky released more than 300 million gallons of coal slurry across two states, turning a stretch of the Ohio River black with sludge. They spilled another 135,000 gallons two years later. It's little wonder, when Massey alone violated Clean Water Act permits 4,500 times between January 2000 and December 2006. In 1972,a slurry impoundment at Pittson Coal failed, releasing 132 million gallons. At least 125 people were killed, and over 4,000 were left homeless as the slurry flattened five small towns in West Virginia.
What's the worst thing about all this material piling up around coal mines and coal-fired steam plants? We know it's hazardous. We know that eventually it'll end up flowing through communities and in the water people drink. The EPA and other agencies have argued for years that these slurries should be treated like hazardous waste, because that's what they are. We don't do that, because handling fly ash and coal slurry the way it should be handled would drive up the price of electricity. It would force us all to absorb more of the real cost behind our "cheapest electricity source."
Right now most of that cost is paid by the people in small towns like Kingston, TN and Larado, WV and Inez, KY. It's the towns near the plants that stockpile ash, and the towns near the mines that impound sludge. Towns like the one where I grew up. That's where people pay the price so that politicians can talk about "clean coal."
Further reading
Fly ash facts for highway engineers
Coal ash described as "environmentally friendly"
Time: Ash spill reveals the truth behind "clean coal"
Toxic spills in the Appalachians
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