Oops...There's Fly-Ash In The Clean Coal Ointment
by John Laumer, Philadelphia on 09.19.07
A few months back we reported on why we felt coal-fired utilities have so strongly resisted stringent air emission standards for mercury: it, or other heavy metals captured in pollution control devices, could potentially cause fly ash to become regulated as a hazardous waste in the US. All coal contains a variety of heavy metals; and, mercury, a heavy metal ubiquitous among coals, is especially dangerous to human health. The less mercury that is allowed to go up the stack as vapor, or attached to particulates, the more mercury is transferred to fly-ash, bottom ash, or wastewater discharged from coal-burning plants. There absolutely is no "away" for mercury. Even if you could somehow capture all of it in elemental form, there is no market; nor should there be one for mercury. Lead and arsenic have similar risks, although there are indeed markets for these.
However, it made sense when a commenter reminded us that fly ash could simply be deposited in spent coal mines, and that this has been a common practice where mines are close enough to the coal fired generators. Now comes the news:
"Pennsylvania calls putting fly ash waste from coal-fired power plants into abandoned coal mines a "beneficial use," but a coalition of national environmental groups has issued a report showing the widespread practice does much more harm than good."
"The report released yesterday by the Clean Air Task Force and Earthjustice says at 10 of the 15 mines it examined in the state, nearby ground water and streams contained levels of arsenic, lead, cadmium, selenium and other pollutants above safe standards. In addition, at six of nine mines where ash is used to treat acid mine drainage, the acid in the groundwater has increased.""
"Clean coal" technology and C02 sequestration cost-effectiveness are increasingly looking like moot points unless and until this issue is solved. There are projections now of 400+ years of coal in the US, and strongly increased demand projected for electricity generation. If the increased amounts of fly-ash waste produced to meet this demand are going to become regulated as hazardous waste, fly ash can longer go into municipal landfills. This could be especially problematic for utilities located far from the mines. And, managing fly ash will become much more expensive if many mines are found to be unacceptable repositories. USEPA, state regulators, and utilities can't continue to just look the other way, or assume that they will become magically exempt from the hazwaste regs.
Update:
"And the Maryland Department of the Environment has been aware of the problem since the companies first identified it, but has continuously allowed fly ash to be dumped at the mine and approved plans to deposit the substance at more sites in Gambrills. In the meantime, fly ash -- a by-product of the combustion of coal -- has seeped into the water supply beneath the site, contaminating wells in at least 23 nearby homes with dangerous amounts of heavy metals, sometimes more than 10 times above the federal Environmental Protection Agency's levels for safe water."
Via:: Pittsburg Post-Gazette and Update via::Maryland Gazette 9/19/07. Image credit:: Muscoid fly (house fly) (6.25x), by Charles Krebs, Charles Krebs Photography, Issaquah, WA, Hobnob Blog
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Not all "clean coal" technologies produce ash. U-gas technology, currently owned by ConnocoPhillips, melts the ash into a vitreous slag that passes leach tests. The mercury in most gasification based designs are trapped in an activated carbon bed which (in theory) can be safely disposed of in clay-lined landfills.
==== author's response follows ===
Good point about the vitrification option. But would that not parasitize some more of the coal energy which otherwise would go to electricity?
There are two problems with using activated carbon for capturing heavy metals. Carbon is excellent at grabbing organic solvents and aromatics and organic acids, but not very efficient at capturing inorganics. Which means that, for capturing coal plant air emissions, the carbon beds will have to be large and changed out frequently enough to prevent metal breakthrough, at some expense. The second problem is the bigger one, however.
Using carbon to capture coal emitted metals is like a game of musical chairs. To manufacture activated carbon, coal is washed in a mineral acid to leach out some of the heavy metals, neutralized with a strong base, washed, pelletized with nasty additives, dried, and then heated to high temp in an oxygen starved refractory to drive off the organics and more of the remaining metals, while creating a pore structure. This last step is energy intensive, consuming large amounts of natural gas. The activated carbon process wastewater and air emission streams contain...you guessed it: mercury, lead, antimony, etc. These have to be treated and disposed of. Were it not for an exemption obtained by the mining industry when RCRA was being written, these carbon waste streams might well be classed as hazardous waste today.
Back to our chairs. We feed the coal plant emissions through the bed of activated carbon to get back to square one: metal contaminated carbon - just like the original coal, except very likely with higher concentrations. The C02 foot print of this operation is large. And it is as, I say ,an insane merry-go-round of media shuffling of toxic materials.
With an organics-laden spent activated carbon you could at least dry it out and burn it for energy in an incinerator. With heavy metal laden carbon you'd just be back to media shuffling again if you burned it.
I also have my doubts about heavy metal laden carbon being permitted in a non-hazardous waste landfill in large amounts.
The second aspect of this issue does not involve gasification and herein lies the lions share of the problem. I speak of plants that intend to inject carbonates ammonia etc into the combustion off-gas stream to capture heavy metals and pull them into a bag house as particulates or scrub them into a wet stream. These would end up as fly ash ordinarily, but now with much higher metal levels.
I am confused now. An episode of "Eco-Tech" the other night said they could used fly ash instead of cement in concrete. Would this be a bad use of fly ash then?
=== author's response follows ====
Per the earlier post on this subject, about a third of fly ash produced now goes into concrete as an "amendment." In other words it replaces some of the sand, thus lightening up the concrete without compromising strength much.
THe point of this post is that if more heavy metals go in that some of the fly ash that once was used in concrete may no longer be suitable for such economic uses.