Hennepin Energy Recovery Center

Located in downtown Minneapolis, the Hennepin Energy Recovery Center (HERC) burns garbage to create energy. HERC uses the latest technologies to reduce environmental and taxpayer costs and is part of the county's integrated waste management system.

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How HERC converts waste to energy

Waste is delivered

Garbage trucks deliver waste from Minneapolis and surrounding communities to HERC. About 75 percent of the waste delivered to HERC comes from Minneapolis; the remaining 25 percent comes from suburban Hennepin County.

Waste is burned

The waste is pushed into the waste pit with a loader. A crane picks the waste up from the pit and feeds it to the boilers. Operators look for and pull out hazardous and problematic wastes, such as appliances, televisions and bulky items, so they can be disposed of properly.

Heat generates steam

The waste is burned in boilers lined with water-filled tubes. The heat of combustion converts the water in the tubes to steam that turns a turbine to generate electricity. HERC produces enough electricity to power 25,000 homes. The electricity is sold to Xcel Energy.

A portion of the steam produced is extracted after going through the second stage of the turbine and sent to the steam line. This steam provides heating and cooling to the downtown Minneapolis district energy system and Target Field. District energy is a network of pipes that aggregates the heating and cooling needs for 100 downtown buildings. District energy systems are more efficient than buildings operating their own boilers and chillers.

The steam is then condensed back to water and circulated back to the boiler, completing a closed-loop. 

Controlling air emissions, recycling metals and disposing of ash

Air emissions are cleaned and treated so that emissions are consistently below the Minnesota Pollution Control Agency permitted levels.

The combustion process reduces the volume of waste by 90 percent. The material remaining after combustion is non-hazardous ash that is disposed of in a landfill.

Metals are removed and recycled before the ash is sent to a landfill. HERC recovers more than 11,000 tons of scrap metal each year, which is more than double the amount of metal collected in curbside recycling programs in the county.

Learn more

See a diagram of how HERC converts waste to energy (JPG).

Air pollution control equipment

Air emissions at HERC are cleaned and treated before being released. HERC’s air permit requires it to operate under stringent U.S. EPA and State of Minnesota air pollution regulations. The air emissions are also well below the European Union standards for waste-to-energy facilities.

HERC uses the following state-of-the-art air emission control technology:

  • Air is injected into the boiler to control nitrogen oxide (NOx) emissions. Additional NOx control equipment was added in 2015.
  • Activated carbon is injected to control mercury and other metals.
  • Flue gases pass through a scrubber, where a lime slurry is injected to control sulfur dioxide and hydrochloric acid.
  • Combustion gases pass through fabric filters to remove particulate matter, metals and dioxins
Air pollution control equipment is monitored continuously to ensure it is operating effectively. HERC's air emissions in 2014 were on average 80 percent below permitted levels from the Minnesota Pollution Control Agency. See HERC's 2014 air emissions (PDF).

HERC is environmentally preferable to landfills

How waste is managed in Hennepin County

Hennepin County residents and businesses generate more than one million tons of waste each year. Add up all this waste and it's enough to fill Target Field more than 11 times. Processing 365,000 tons of waste at HERC each year is just one part of the county's waste management efforts that emphasize waste prevention, reuse, recycling and composting. 

About 45 percent of the waste generated in Hennepin County is recycled or composted. The county is committed to making recycling as convenient as possible and expanding opportunities to compost. Learn more about the county's solid waste management plans and recycling and organics recycling programs.

The trash remaining after recycling and composting can either be buried in the ground or burned for energy.

HERC is environmentally preferable to landfills

HERC is better for the environment than landfills for the following reasons.

Better air pollution controls and fewer air emissions

  • HERC has an air pollution control system to capture pollutants. This equipment is monitored 24/7.
  • Waste delivered to HERC is being processed close to where it is produced, minimizing the transportation of waste and associated truck emissions.
  • Pollution control measures at landfills are buried, meaning it can take years to detect and find a leak in a liner.
  • Waste in landfills continues to decompose, producing methane and organic compounds. This makes landfills an environmental and health risk for decades.

More energy generated

  • A ton of waste processed at HERC creates electricity to run a house for 21 days, plus steam to heat Target Field and downtown Minneapolis.
  • A ton of waste buried in a landfill creates electricity to run a house for 3 days.

Fewer greenhouse gas emissions

  • Every ton of trash burned at HERC produces fewer tons of greenhouse gas emissions than if it were disposed of in a landfill because decomposing garbage in landfills produces methane. Methane is over 20 times more potent of a greenhouse gas than carbon dioxide over 100 years.

More metal recycled

  • More than 11,000 tons of scrap metal is recovered from the waste stream delivered to HERC and recycled annually.
  • Metals are not recovered from the waste at landfills.

More jobs created

  • It takes 45 high-wage jobs to operate HERC.
  • It takes 18 lower-wage jobs to operate a landfill.
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