Ash to asphalt: one use for mountains of coal waste
The confluence of the environmental movement of the 1960s and the energy crisis of the 1970s has left a powdery legacy: millions of tons of coal ash. Today, imbibing the entrepreneurial spirit of the 1980s, electric utilities are looking increasingly at this monumental waste problem as a potential resource. Already, several companies have managed to turn a major liability into a modest asset.
When coal is burned, almost 10 percent ends up as ash. Before strict environmental regulations, most of this went up power plant stacks. But increasingly efficient pollution-control equipment now captures almost all of this fly ash. Combined with the oil-crisis-inspired renaissance of coal burning, this has led to growing ash piles at the nation's coal-fired power plants.
With six such power plants, Detroit Edison alone generates enough of the stuff annually to fill a box the size of a football field 70 stories high.
The amount of ash being generated by the nation's utilities has jumped from 39 million tons in 1970 to 68 million tons in 1981, according to the National Ash Foundation. Nearly another doubling in the quantity is expected by 1990.
That's the bad news. The good news is that since 1970 the proportion of ash put to beneficial use has risen from 13 to 24 percent over the same period and is expected to increase to over 45 percent by 1990. While not enough to keep up with the anticipated growth in the ash generated, converting this waste into a resource could substantially ease the nation's ash disposal problem.
Over the years, enterprising utilities have found a number of uses for their ash. Some manufacturers add it to cement to make concrete blocks. When added to ready-mix concrete, fly ash makes the mixture flow easier so it can be pumped easier, has a smoother finish, and forms better corners. Ash has also been added to asphalt on highways and airport runways and in roofing materials. It's also used as a fine mud for lubricating oil drilling rigs. Gritty bottom ash left in the bottom of the boiler when coal is burned has been used to control ice on roads.
A more exotic possibility, which the Electric Power Research Institute (EPRI) intends to study, is the extraction of aluminum from ash. There is as much aluminum in all the coal ash as the United States currently imports, says EPRI's John Maulbetsch. So if an inexpensive method could be developed to extract this valuable mineral, it might be possible to reduce the nation's foreign dependence in this area.
EPRI decided recently to spend $200,000 for an ash utilization program to help member utilities find markets for their wastes.
''We have an old quarry that we have been putting ash in for many, many years. One day we may mine it,'' jokes John F. Anderson, assistant vice-president of Detroit Edison, which has been selling its ash ever since 1933 .
''My strategic plan is to get to the place where we are marketing all of our ash,'' he says seriously. Currently, it is selling about one-sixth of its ash and is using the rest on its own construction projects.
Detroit Edison itself has developed a couple of new fly-ash based products. One is called cement-stabilized ash. This is a mixture of 95 percent fly ash and 5 percent Portland cement. It has the consistency of modeling clay and will dry even under water.
According to Mr. Anderson, the material, used to fill in a trench that was dug for large cooling water pipes of a new power plant, saved the company $750, 000 because it was cheaper than backfilling the trench with dirt and tamping it down.
''This has a lot of the benefits of concrete at a much lower cost,'' he says enthusiastically.
The utility is also working with a local foundry to spin melted fly ash into something resembling fiberglass. It is considering marketing it for production of sound-deadening panels in automobiles.
The path to coal ash utilization is not smooth, however. Coal is less uniform than any other fossil fuel, and its ash can vary significantly in its chemical composition. If this is not properly accounted for, it can cause side effects such as weakening concrete, Anderson acknowledges.
For this reason, utilities are particularly interested in uses where the ash quality does not make much difference.