Coal quality issues addressed at AVS
Part two of a three-step process to tackle coal quality issues at AVS began in August.
Dakota Gasification Company - October 9, 2009
Part two of a three-step process to tackle coal quality issues at the Antelope Valley Station, Beulah, ND, began in August. The first component is almost complete. The third is scheduled to be completed next year.
For the past four years, staff at headquarters and Antelope Valley has been trying to devise a solution that would address changing qualities of lignite coal being delivered to the station. John Jacobs, plant manager, said projections show that the coal coming to Antelope Valley will soon contain as much sodium, sulfur and ash as the plant can handle.
The “sulfur solution” is the second component to begin construction at the 900-megawatt capacity, coal-based power plant. It involves the addition of larger lime handling and processing equipment, called the lime slaking system.
Jacobs said Antelope Valley currently uses a dry scrubber to remove sulfur dioxide from the plant’s exhaust gas. It works like this: pebble lime is fed into a ball mill and mixed with water. The mixture forms a slurry, which is injected into the scrubber. All flue gas passes through the scrubber before moving onto the baghouse. The lime reacts with sulfur dioxide, “scrubbing” it out of the flue gas.
The scrubber keeps the plant running in environmental compliance. When the coal contains greater than 0.85 percent sulfur, Jacobs said every piece of equipment has to be running full-bore to keep up.
Dawn Moore, mechanical engineer III, is coordinating the addition of the lime slaking system. “There’s no redundancy right now. So if the current slaking system goes down, there’s nothing to pick up the slack,” she said. “The new slaking system will take over as the primary system, with the old slaking system as back-up.”
The slaking system’s capacity will be doubled. That means if a higher-sulfur coal is being used, more lime slurry can be injected into the scrubber to keep up.
Moore said construction started in early August, and the focus has been trying to get all the concrete foundations set before winter weather arrives. “We’re about 10 percent complete at this point,” she said. “We also have some structural steel set.”
The other components in the process deal with sodium and ash. The first, which is almost complete addressed the issue of high sodium. The solution was the installation of coal analyzers right on the conveyor belts. The last component is the installation of sonic horns in all the plant’s baghouses to address the issue of higher ash.
The projects are planned for completion in 2010. The cost will be $23 million, to engineer, purchase and install the new technologies.
Read more on all three parts of the project in the September/October 2008 issue of Basin Today. "Sulfur, Sodium and Ash ... Oh my! AVS tackles the challenges that come with lignite coal" is available on www.basinelectric.com.
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