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Getting Steamed: Mega-Plume Blossoms in Cold Weather at St. Paul Energy Plant

By District Energy posted 01-13-2020 10:22


Post Bulletin


Almost everyone in the metro area has seen St. Paul’s largest thermometer. The enormous plume from the St. Paul District Energy plant rises and falls with every change in temperature. On a cold day, it’s like a colossus towering over the dozens of lesser plumes scattered at its feet. That’s when Nina Axelson sometimes has to explain that, no, the giant cloud is not smoke. It’s water vapor, and it’s getting bigger because the plant is getting greener — burning more water-bearing wood.

“It’s an exciting time. The bar is being set high for all of us,” said Axelson, vice president of sustainability and outreach for District Energy and its subsidiary, Ever-Green Energy.

It’s the water in the wood that makes the steam-cloud so huge, even though the plant itself is not the biggest in the state. There is now more local wood to burn, said Axelson, because of the epidemic of emerald ash borers that is killing ash trees.The plant heats 80 percent of the buildings in downtown St. Paul, about 33 million square feet — more than a square mile of office space.

Mike Burns, Ever-Green’s senior vice president of operations, explained that the plume isn’t actually steam.Steam is hot air containing invisible water — which condenses into water vapor as it cools. It’s water vapor — not steam — that forms clouds, creates fog and rises from coffee cups. The oversized plume is a sign — visible for 20 miles — that the plant is burning wood.

The plant’s shift to greener fuels began in 2003, when it started to burn wood.The plant stopped burning coal in 2019.

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