Railroad tracks, looking towards Martin Drake power plant, downtown Colorado Springs CO. Image credit:Flickr,JoeB's stream - excerpted.
End-of-pipe pollution control add-ons are what most coal-fired plant owners in the USA are planning for these days. For example, Martin Drake Power Plant in Colorado (pictured) is trying out a new stack gas scrubber design, with water as a pollutant capturing medium. Later, they could add lime, or ammonia, or suspended charcoal bits...whatever. Let's focus on the water and what's not mentioned: mercury.The story comes to us from the Rocky Mountain News, in Device to make coal plants cleaner passes tests
"We showed that (the device) could capture approximately 90 percent of the sulfur pollutants from the flue gas using only tap water as a capture fluid," Neumann said...Drew Rankin, Colorado Springs Utilities general manager for energy supply, called the results "incredibly encouraging."Bit of a jam up in the sustainability department as soon as you consider that:
Water consumption an issue - but maybe not the deal breaker
The Colorado River is drying up, and Denver-area citizens are competing for the same water to drink and wash with. Equipment to recycle scrubber water costs more money (though it may be a prerequisite of an operating permit).
"End of pipe" ends nothing with coal emissions- moves pollutants around.
USEPA calls this pollution movement dilemma 'media shifting.' With scrubbers in place, less dust, vapor, and gases will go through the baghouse filter and up the stacks; but they will create sulfurous acids, suspended fines, and a precipitate in the scrubber water.
After heavy solids are settled, the awful mix (which can barely biodgrade) may have to be treated to chemically or physically concentrate and dispose of heavy metals and meet pH limits. More money for end-of-pipe technology.
If the spent scrubber water is held in tanks until it can be dumped in fly ash settling ponds to dry in the Denver summer, that adds capital costs.
Mad Hatter's Paradox
Ultimately, there is no "away" for the toxic heavy metals released by burning coal. The more efficient end-of-pipe pollution control is at capturing metals and fly ash and sulfur or nitrogen compounds, the greater the chance that the resulting residues will be classified as hazardous due to metals (from a regulatory standpoint). Mercury epitomizes this risk.
Mercury, as it leaves a coal plant stack, is mostly in vapor form. Mercury vapor can not be captured with just a bag house filter. It has to be cooled, condensed, or chemically trapped by some added end of pipe technology.
The tendency of mercury to leave the boiler stack as a vapor is one reason why fly ash produced by existing coal plants tends not to have very high mercury levels: most of the mercury went up the stacks, passing through the bag house filters; thereafter, it forms aerosols and fall back to the land - miles away.
If a batch of coal has an especially high concentration of mercury, by capturing more of the stack vapors with a new pollution control add on, more mercury becomes more concentrated in the fly ash and/or in a scrubber solution. This "re-partitioning" or "media shifting" of mercury, from the air emissions to fly ash solids, or to water, can mean fly ash can no longer be used for soil amendment, concrete making, and so on. And, it can mean (depending on pollution control designs) that the spent scrubber water can't be discharged.
Risk of 'hazard shifting' to developing nations.
An unintended consequence of an a Federal end-of-pipe approach to mercury emissions controls could be an increase in US market prices for low-mercury coal and a fall off demand for high mercury content coal. That could lead to more exporting of mercury laced coal to developing nations. (Don't ever say "who'd have thought that would ever happen" because it will happen unless end of pipe control regs are thoughtfully worked out.) More paradoxical as we go.
All of this leads to a rather obvious point that I would bet folks in the utility business well recognize but are reluctant to talk about. If EPA were regulate mercury discharges to all media (air, water, land) to the point where public health world-wide is fully protected, coal-fired electricity will lose its current price position and US coal markets will see a loss of revenue. New natural gas and wind and solar powered generators will be easier to permit and far cheaper to operate.
Don't wait for Cap and Trade or carbon taxes to take hold. Just knuckle down on mercury and renewable will move to the front of the pack, helping mitigate the climate crisis at an accelerated pace. That is the opportunity of Mad Hatters Paradox.
Pollution prevention approach?
I know what you engineers are thinking. Sulfurous acids in scrubber blow-down water washes incoming raw coal, reducing mercury vapor emissions from the boiler. Right. Works great until mercury gets concentrated in the coal wash water upstream of the plant, instead of at end-of-pipe. It's still got to be managed and that costs money. See Mad Hatter's Paradox (above) for reference.
Selected and especially relevant coal and mercury posts from our archives.
Coal Released Mercury Ruins Fishing and Duck Hunting
Sundance Festival: The Cove
Plug-Ins Have Higher CO2 Emissions Than Traditional Hybrids Car ...