Ohio Valley residents can breathe easier, according to American
Electric Power’s Wayne Irons, since emissions controls were installed
at the company’s Mitchell Power Plant a year ago.
The Mitchell plant installed its first sulfur dioxide-catching scrubber
about one year ago and added a second last April, plant manager Irons
said. And he is pleased with their performance.
“We are making better than designed capture,” he said. “We are at about 98 percent capture of SO2.”
Wheeling News-Register - Sunday, February 10, 2008
MOUNDSVILLE — Ohio Valley residents can breathe easier, according to
American Electric Power’s Wayne Irons, since emissions controls were
installed at the company’s Mitchell Power Plant a year ago.
The Mitchell plant installed its first sulfur dioxide-catching scrubber
about one year ago and added a second last April, plant manager Irons
said. And he is pleased with their performance.
“We are making better than designed capture,” he said. “We are at about 98 percent capture of SO2.”
That success, coupled with the installation of Selective Catalytic
Reduction Systems that remove nitrogen oxides produced in the
coal-burning process, has made the air cleaner for area residents. It
also is reducing acid rain conditions for residents of the northeast
part of the country, he claimed.
According to ecologist and Wheeling Jesuit University professor of
biology Ben Stout, having this clean air technology in place “will have
a positive effect, especially when we have an atmospheric inversion.”
He said the SO2 and nitrogen oxides are both strong acids. Removing
them in the coal-burning process is a good thing.
“Every little bit helps,” he said.
Irons agreed. “If we were the problem in the past, we should be seeing
a major reduction in acid rain in the Northeast. Cars and steel mills
also contribute to the problem, but our reductions do have effects
locally as well as regionally.”
Irons said during the first year of scrubber operation, there have been
no forced outages due to the scrubbers or the SCR systems, which remove
about 90 percent of nitrogen oxides. The SCRs use ammonia gas to create
a chemical reaction that converts nitrogen oxide into nitrogen and
water.
The nitrogen oxides, he said, are a contributing factor to ozone
depletion. Because SCRs are temperature-dependent, they are not running
year-round at this time, but they are expected to be shortly. At the
present time, SCR technology is the best available technology for
making significant reductions in nitrogen oxide emissions, according to
Irons.
“We have had no major problems with either system — just a few minor
things which you could expect. Nothing major. No show stoppers. They
have been good equipment,” he added.
The Mitchell Power Plant is a 1,600-megawatt generating facility. It
has twin 800-megawatt generating units and started producing
electricity in 1971.
It is jointly managed with the neighboring Kammer facility, which began
operation in the early 1950s and has no scrubbers. No plans are being
made to install them at that plant because of its age. It is required
to use exclusively low-sulfur coal.
Electricity from both plants is put into an electric grid. Where the
power goes depends on where it is needed. Much of it goes to Ohio.
Since the installation of the emissions-cleaning scrubbers at the
Mitchell Plant, Irons said, there has been about a 4-percent reduction
in the plant’s electric output.
According to Irons, no plans are being made at this time to upgrade the
plant with higher-efficiency turbines to make up for the lost output.
He noted one of the two units at the plant was upgraded about two and a
half years ago — before the scrubbers were installed.
AEP invested $900 million to put the scrubbers and SCRs in place at the
Mitchell facility. The cost included more than 3 miles of new conveyor
belts and structures to transport limestone from the Ohio River where
it is unloaded, coal for blending and to carry gypsum. Gypsum is a
by-product of the scrubbing process, and it is sent to the new
CertainTeed Plant across W.Va. 2, where it is now being stockpiled for
future use in the production of building products such as drywall.
During the “scrubbing,” chemical and mechanical processes remove sulfur
dioxide from gas produced by burning coal. Exhaust gas from a
coal-fired unit’s steam generator is routed through absorber vessels,
where chemical reactions take place and the sulfur dioxide is removed.
In the absorbers, flue gas passes through a mixture, or slurry, of
pulverized limestone and water, which is sprayed into the flue gas
stream.
The sulfur dioxide then reacts with the slurry and forms the gypsum. A
dewatering system, consisting of a vacuum belt filter, literally sucks
most of the water from the mixture leaving just the gypsum, which is
able to be used without additional treatment.
“Our gypsum quality has remained in line with their (CertainTeed’s)
specifications. It’s real good. We have very little waste. It’s been
very encouraging.” Irons said. “We’ve totally met their specifications.
They are taking 100 percent of it, which is great. It means we don’t
have to landfill it and it’s a good deal.”
A railroad spur also was installed across W.Va. 2 to connect the two facilities.
“Carbon dioxide is also an emerging issue, as well as how to reduce it
effectively,” Irons added. “It’s a lot bigger issue than most people
realize. We can’t reduce carbon dioxide output. We can capture it, but
it is not efficient or cost-effective. The only process is to pump it
underground, and it’s very expensive.”
The Mitchell plant uses on average more than11,000 tons of a medium
sulfur mixed blend of locally mined high- and low-sulfur coal daily.
Irons said the mix is used to generate the greatest efficiency from the
scrubbers. The average annual coal use at the plant is more than 4
million tons. The Kammer Plant uses an average 6,120 tons of low-sulfur
coal on a daily basis.
Irons also noted limestone used in the scrubbers is brought in from the Oglebay Norton Co. in Michigan by river.
“I don’t think people fully realize just how big of a project this was,” he concluded.
