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Every year the city of Duluth burns more than 50,000 tons of coal at its downtown steam plant. That's enough coal to fill one of the 1,000-foot cargo ships that ply the waters of nearby Lake Superior. 

But this year, as part of a new pilot project announced Wednesday, the city is poised to cut that amount of coal burned by more than 40 percent by switching to natural gas at the plant, which provides heat to 200 buildings in the city's downtown core. 

The seven-month pilot project is expected to cut the plant's carbon emissions by 15 percent, or about 13,000 tons. 

"We are really excited about how this advances our commitment to decrease greenhouse gases 80 percent by 2050," said Duluth Mayor Emily Larson, who laid out aggressive carbon emission goals in her recent State of the City address, including cutting emissions by 15 percent during her first term. 

"I feel strongly we have a responsibility. We own a stream plant that's powered on coal."

The plant next to Interstate 35 was built in 1932. It pulls in 90 million gallons of water from nearby Lake Superior every year, burns coal in four boilers to heat that water under high pressure to 300 degrees, and then sends the steam through a network of underground pipes throughout downtown. 

Over the past year the city has spent about $500,000 to upgrade two of the boilers to allow them to burn natural gas.  

Officials believe the switch will be cost-neutral because of electricity and other cost savings. 

"We will test and analyze and learn how the system can perform under natural gas during the spring and summer," said Ken Smith, CEO of Ever-Green Energy, which runs the steam plant for the city of Duluth. 

In the short term the plant will need to burn coal during the winter's coldest months, officials said. But if the pilot is effective, the hope is to eliminate the use of coal at other times of the year. 

The project is tied to the city's plan to convert the steam plant to a closed-loop, hot water system. 

Currently, after buildings use the steam from the plant, they discharge the hot water left over into the sewer system, which runs back into Lake Superior. 

The city wants to change that to a system where the water is circulated back to the plant, saving it the expense of heating water from Lake Superior, where the average temperate is 42 degrees. 

Duluth officials are banking on $21 million from the state Legislature to help fund the project. 

If that's approved and the project moves forward, the city plans to utilize other energy sources to heat the water, including solar and biomass harvested from northeastern Minnesota forests. A permit application to burn biomass is currently pending with the Pollution Control Agency. 

The overall objective, said Larson, is to reduce greenhouse gas emissions, but to do it in a way that also could boost the area's economy. 

"Our real strong hope," she said, "is that the opportunity to decrease coal usage can be an opportunity for our region.

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Dan Kraker

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The city's switch at its steam plant from coal to natural gas is expected to cut the city's carbon emissions by 10 percent this year.

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