White cloud indicates startup of new scrubber

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By The Staff



Cleaner emissions from TVA’s Kingston Fossil plant will come in the form of a big white cloud of steam.

The first of two scrubber units will be online this week at the plant. All units are scheduled to be online by spring 2010.

Scrubbers, the units being put in place around the TVA system, are another step the plant is making toward cleaner air under the Clean Air Act.

“The purpose of the scrubber is to remove the sulfur dioxide,” said Bob Rehberg, maintenance manager.

Together, the scrubbers can remove around 95 percent of the sulfur dioxide in the flue gas before it is released.

Gypsum, a byproduct of the scrubbers, is planned to be stored onsite.

A pond will be initially a wet storage facility for the gypsum until a dry storage facility is made.

“We’re going to add a gypsum dewatering system,” Rehberg said. The system will be built in 18-24 months.

“In the meantime, we are going to be sluicing that gypsum out to the pond wet,” Rehberg said.

There are a lot of variables, but Rehberg said in the worst-case scenario, if all nine units were going all the time the plant could produce up to 300,000-400,000 tons of gypsum a year.

Rehberg said the bottom of the pond is set up to dry out the gypsum.

When the gypsum is sent to the dewatering facility, what will be left is a sort of gypsum cake, which will be piled up and hauled to the pond, officials said.

“It’s a tradeoff,” said Ron Nash, TVA scrubber program manager. “In order to clean the air up, you create a landfill.”

Little public outcry was heard when the plans for a gypsum pond was first discussed in the measures to clean the air.

A Roane County News story last year said the scrubbers were a year away, planned for early to mid-November.

In the wake of the December 2008 fly ash spill because of a failed containment pond, some safety concerns about the gypsum pond have been voiced.

Officials are hopeful the housing market goes back up, helping them find a buyer for the gypsum to ideally use it for wall board production.

Most of the gypsum is used for wall board in this country, officials said.

“Once you dry it, you can do anything with it,” Nash said. “It just gives us more options.”

Residents may also be concerned about a white plume they will begin seeing from the plant this week.

Rehberg said it’s nothing to worry about. He explained that water vapor will make it more visible.

Scrubbers use a limestone slurry to “clean” the sulfur dioxide from the flue gas.

Powdered limestone is injected into million-gallon tanks of water where high-powered pumps turn over the mixture.

The slurry created is sprayed into the air to interact with the flue gas.

The interaction causes a chemical reaction, creating calcium sulfate, or gypsum.

The system  uses a variety of tools to make cleaner emissions.

The first mechanism the flue gas goes through is the SCRs, pollution control devices that remove nitrogen oxide.

Next it goes through precipitators that remove particulate ash from the flue gas.

The first scrubber unit to go online will be for boiler units 6-9.

The second scrubber unit, when it goes online will be for boiler units 1-5.

On most days the only stack that will be in use is the new 400-foot one that is part of the scrubber facility.

Of the two tall stacks currently in use, the north stack will be blocked off.

The south stack will have a bypass damper. It will only be used if there is a reason the plant needs to bypass the scrubber unit.

Rehberg said it would act as a sort of release valve to protect the ductwork.

Kingston Fossil Plant is currently shut down.

Plant manager Leslie Nale said it is a combination of getting ready to hook into the scrubber and because of no energy demand.

“We shut the last unit down on Oct. 10 to start that construction,” Nale said.