- Associated Press - Monday, December 8, 2014

BEULAH, N.D. (AP) - Once coal has been removed from the Earth, it becomes a key cog in producing electricity to power North Dakota.

At the Antelope Valley Station, Basin Electric Cooperative produces 900 megawatts of electricity, enough power to light up 720,000 homes. Antelope Valley is Basin Electric’s largest power plant in North Dakota and second largest plant throughout the Basin operation, the Minot Daily News (https://bit.ly/12lh7kL ) reported.

And it all begins with coal. The plant uses 700 tons of coal every hour.

“For all this to work together, we use coal that comes from the coal mine,” said Audrey Vind. “When the coal comes in by truck, we put it on a conveyor.”

The conveyor moves the coal to nine coal silos, each designed to hold 700 tons of coal. At the electric plant, the coal is pulverized into a fine powder, which is then forced by air into a massive boiler. Inside the boiler, the coal is constantly burned, keeping the boiler at a temperature of more than 2,000 degrees.

Inside the boiler, which stands taller than the Capitol building in Bismarck and weighs as much as 36 million pounds, there are also 55 miles of carbon steel tubing. While coal is burned to keep the boiler at 2,000 degrees, water is piped into the steel pipes. The combination of high heat and water creates intense steam, which is then used to spin turbines at speeds of up to 3,600 revolutions per minute.

The Antelope Valley Station was built starting in 1978 at a cost of $1.9 billion. At one time, the plant went 16 months without a tube leak, but as the plant has gotten older, leaks have become more common. When the steel tubes do breach, the boiler has to be shut down and it takes eight to 10 hours to cool down enough for repairs to be made.

When the steam is fed into the turbines, the plant uses a three-tier approach to make electricity. Most of the power comes from the first tier when the high-pressure steam turns the turbine at 3,600 RPM. As the steam cools, it turns a second turbine slower, and it finally moves to a third turbine that returns the steam to water, which is recycled and put back to use at the plant.

Every minute the plant is in operation, two employees sit in the operations room, monitoring the equipment. Usually the most experienced employees keep a constant eye to make sure things are working properly.

“These guys do not leave their station,” said Paige Fleck. “We always say a good day is a boring day. If they look like they have nothing to do, that’s OK.”

While the goal is to have both stations at the plant running nonstop, Fleck said every three years they do get a reprieve. Once every three years, a unit is turned off for eight weeks for maintenance. Once the work is done, the unit is fired back up with a goal of running it nonstop for the next 148 weeks.

While making electricity is the No. 1 goal at the plant, limiting the impact on the environment also requires a big effort. All emissions other than steam that leave the plant are sent through a scrubber house that reduces carbon dioxide emissions by 90 percent. In the scrubbers, lime is used to absorb the CO2. At Antelope Valley, 300 tons of lime is used every day to keep the air clean.

Another byproduct of the process is tons of ash created when the coal is burned. The ash is sent to a baghouse, where 8,064 bags that are 35 feet tall and one foot in diameter are used to capture and remove the ash. This process removes 99 percent of the ash.

Most of the ash is deposited in a landfill near the plant, while some is used to make roads and buildings.

At Antelope Valley, 210 employees work around the clock with one goal — keeping the electricity flowing to nine states and 137 co-ops that count on Basin for electricity.

___

Information from: Minot Daily News, https://www.minotdailynews.com


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