Hennepin Energy Recovery Center

The Hennepin Energy Recovery Center (HERC), located in downtown Minneapolis, is a waste-to-energy facility that burns garbage to generate energy. HERC provides reliable, renewable electricity that is sold to Xcel Energy and steam that supplies the downtown district energy system and Target Field.

HERC facts

  • About 365,000 tons of garbage is burned at HERC to provide enough electricity for 25,000 homes each year. Electricity generated at HERC is sold to Xcel Energy.
  • Through the steam line, HERC provides enough steam for the annual natural gas needs of 1,500 homes to buildings in downtown Minneapolis and Target Field.
  • Residents and businesses in Hennepin County generate more than 1 million tons of garbage every year. According to the state waste management policy, processing waste at HERC is an environmentally preferable alternative to landfilling waste.
  • More than 11,000 tons of ferrous metal are recovered every year at HERC and recycled.
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How HERC converts waste to energy

How is waste converted to energy at HERC?

Garbage trucks coming to HERC dump their waste on the tipping floor. The waste is then pushed into the waste pit with a loader. A crane picks the waste up from the pit and feeds it to the boilers. The loader and crane operators look for and pull out hazardous and problematic wastes, such as appliances, televisions and bulky items, so they can be disposed of properly.

The waste is burned in boilers lined with water-filled tubes. The heat of combustion converts the water in the tubes to steam, which turns a turbine to generate electricity. A portion of the steam produced is extracted after going through the second stage of the turbine and sent to the steam line.

The turbine generator produces enough electricity to power the plant and sell more than 200,000 megawatt-hours of electricity to Xcel Energy. Steam sent through the steam line provides heating and cooling to the downtown Minneapolis district energy system and Target Field.

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

Learn more about waste-to-energy on Covanta Energy's website. Covanta Energy, a leader in the waste-to-energy field, operates and maintains HERC for Hennepin County.

Take a virtual tour of HERC

Learn more about how waste is managed in the county and how HERC generates energy from garbage.

Learn about the scale of waste and energy use by watching the "Waste Not" video projection

As part of the summer 2011 North Spark festival, artist Christopher Baker displayed this video projection, entitled "Waste Not," on the walls of HERC to highlight the true scale of our waste production and energy usage.

HERC wins national waste-to-energy excellence award

In August 2011, HERC received a Waste-to-Energy Excellence Award at the Gold level from the Solid Waste Association of North America (SWANA).

SWANA’s Excellence Awards Program recognizes outstanding solid waste programs and facilities that advance the practice of environmentally and economically sound solid waste management.

Learn more about HERC's Excellence Award.

Controlling air emissions

The HERC facility employs state-of-the-art emission control technology to treat flue gases.  HERC’s air permit requires it to operate under very stringent U.S. EPA and even more restrictive State of Minnesota air pollution regulations. The air emissions are also well below the European Union standards for waste-to-energy facilities.

All air emissions at HERC go through an air pollution control system to minimize and capture pollutants before discharge.

  • Air is injected into the boiler to control nitrogen oxide emissions.
  • Activated carbon is injected to control mercury. HERC was the first waste-to-energy facility in the country to use activated carbon injection to control mercury emissions.
  • Flue gases pass through a dry scrubber, where a lime slurry is injected to control sulfur dioxide and hydrochloric acid.
  • Combustion gases pass through a baghouse containing a series of fabric filters to remove particulate matter, metals and dioxins.

Air emissions are monitored on a continuous basis for multiple pollutants.

Environmental and economic benefits

There are two options for managing waste that cannot be recycled – you can bury it in a landfill or you can burn it for energy. Processing waste at HERC is environmentally and economically preferable to landfilling garbage.

Waste-to-energy is environmentally preferable

Emits fewer greenhouse gas emissions

  • Every ton of trash burned at HERC produces 0.7 fewer tons of greenhouse gas emissions than if it were disposed of in a landfill.
  • Decomposing garbage in landfills produce methane, which is 21 times more potent of a greenhouse gas than carbon dioxide.
  • Waste not delivered to HERC must be hauled to landfills outside of the county. Haulers bringing garbage to HERC travel a shorter distances compared to those bringing waste to a landfill, resulting in avoided vehicle emissions.
  • Electricity generated at HERC offsets the need to produce energy at power plants that use fossil fuels, such as coal and natural gas, to generate electricity.

Recycles more metals

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

Better control of air emissions

  • HERC operates under stringent U.S. EPA and even more restrictive State of Minnesota air pollution regulations.
  • All air emissions at HERC go through an air pollution control system, and air emissions are monitored on a continuous basis for multiple pollutants.
  • Landfills do not have a system to capture all air emissions until the landfill is closed and a final “cover” is in place, which is often after years of decomposition. Landfills do not monitor air emissions on a continuous basis.
  • On a per-kilowatt-hour basis, HERC emits less cadmium, lead, mercury, total particulate, hydrochloric acid and sulfur dioxide than a baseload coal-fired power plant.

More efficient energy production

  • HERC is seven times more efficient at generating energy than a landfill.
  • One ton of trash processed at HERC creates enough electricity to run a house for 3 weeks. One ton of waste disposed of in a landfill creates enough electricity to run a house for 3 days.

Minimizes future environmental impacts

The material remaining after combustion is a stable, inert and nonhazardous ash that is sent to an industrial landfill, where it undergoes no further degradation so poses no problems for future generations. Waste in landfills continues to decompose long after a landfill is closed, producing methane and other organic compounds that make landfills a potential environmental and health risk for decades to come.

HERC is economically preferable

  • HERC employs  more people and in more highly skilled positions than landfills.
  • HERC also generates more than $9 million in revenue for the county, which supports recycling and other environmental programs.

Waste-to-energy is just one component of the county’s integrated waste management system

To reduce the amount of waste generated, the county implements programs to increase reuse, recycling and composting, and properly dispose of hazardous waste.

Increasing recycling and reducing waste

About 42 percent of the waste generated in Hennepin County was recycled in 2011. The county recently updated its Solid Waste Management Master Plan to meet the goal set by the MPCA that Hennepin County reach a recycling and composting rate of 45 percent to 48 percent.

Key strategies to meet this goal:

  • Standardize collection methods and collect more materials for recycling.
  • Increase organics recycling at schools, grocery stores and restaurants.
  • Improve recycling at apartments, events and away-from-home venues.
  • Expand the county's already extensive education and outreach efforts.
  • Offer technical assistance to businesses and encourage product stewardship.
  • Support market development for recyclable materials.

Properly disposing of hazardous waste

The county operates two drop-off facilities and holds several community collection events where residents can properly dispose of household hazardous waste and problem materials.

The county licenses businesses that generate hazardous waste to ensure hazardous wastes are managed properly.

Frequently asked questions

Jump to a frequently asked question:

Why does the county use waste-to-energy to manage garbage?

There are two choices for managing waste that cannot be recycled – you can bury it in a landfill or you can burn it for energy.

Processing waste at a waste-to-energy facility is environmentally and economically preferable to sending waste to landfills. Using waste-to-energy also helps Hennepin County comply the Waste Management Act, a state law that establishes a hierarchy for waste management practices. The waste management hierarchy places preference on using waste-to-energy technology over sending waste to landfills.  

Read more about the environmental and economic benefits of HERC.

How are air emissions controlled at HERC?

HERC has an air emission permit from the Minnesota Pollution Control Agency (MPCA). The MPCA permit imposes strict air emission limits, outlines monitoring and testing requirements, and requires that facility operators undergo annual training. HERC’s air permit requires it to operate under very stringent U.S. EPA and even more restrictive State of Minnesota air pollution regulations.

Air emissions from HERC have consistently been below the MPCA permitted limits.

HERC is a state-of-the-art facility that is designed and operated to minimize air emissions. The flue gases from waste combustion pass through a series of air emission control devices.

  • Air is injected into the boiler to control nitrogen oxide emissions.
  • Activated carbon is injected into the exhaust gases to control mercury.
  • Flue gases then pass through a dry scrubber, where a lime slurry is injected to control sulfur dioxide and hydrochloric acid.
  • Combustion gases pass through a baghouse containing a series of fabric filters to remove particulate matter, metals and dioxins.

Only after this thorough filtration process is air emitted from the facility. Air emissions are monitored on a continuous basis for multiple pollutants.

How does waste-to-energy reduce greenhouse gas emissions?

Burning garbage at HERC reduces greenhouse gas (GHG) emissions in four ways.

  1. Generating electricity from solid waste reduces the need to generate electricity in conventional power plants that use fossil fuels such as coal and oil. An average Midwest power plant generating the same amount of electricity as HERC would produce 33,000 metric tons of carbon dioxide equivalent more each year than HERC.
  2. Metal is separated for recycling, which is more energy efficient than mining virgin materials for the production of new metals such as steel. More than 11,000 tons of metal is recovered and recycled each year.
  3. Less garbage is sent to landfills. Garbage in landfills create methane, which is a greenhouse gas that is 21 times more potent than carbon dioxide. The emissions saved each year by not landfilling the material sent to HERC amounts to 120,000 metric tons of carbon dioxide equivalent.
  4. Haulers bringing garbage to HERC travel a shorter distance compared to those bringing waste to a landfill, resulting in avoided vehicle emissions.

Is waste a renewable resource?

Minnesota defines waste-to-energy as a renewable energy source to help meet the state's goal of producing 25 percent of energy from renewable resources by 2025. Hennepin County has registered HERC with the Midwest Renewable Energy Tracking System to sell or trade renewable energy credits. HERC produces the equivalent electricity for about 220,000 renewable energy credits per year.

How does waste-to-energy affect recycling?

Statistics compiled for more than a decade have proven that waste-to-energy and recycling are compatible.

According to a report from the Integrated Waste Services Association, communities with waste-to energy facilities tend to have higher recycling rates because waste-to-energy is employed as a part of a fully integrated waste system that also includes waste reduction efforts, extensive recycling opportunities and the collection of household hazardous waste. Waste-to-energy also provides an opportunity to recycle ferrous metals that would otherwise end up in landfills.

Instead of sending garbage to HERC, can't we just reduce waste and recycle more?

Hennepin County is a national leader in recycling and waste reduction, and the county is continuously looking for ways to develop new, innovative programs. The county supports curbside recycling programs, operates drop-off facilities for proper disposal of household hazardous wastes, and has programs to encourage waste reduction and reuse opportunities. The county has also worked on developing recycling opportunities for new materials such as organics and mattresses

The county’s Solid Waste Management Master Plan outlines strategies the county will implement to achieve a 45 percent recycling rate by 2015. But even with an increased recycling rate, there will still be some waste that will require disposal through waste-to-energy or landfilling. Garbage not delivered to HERC must be hauled out of the county to landfills. Even with recycling and waste-to-energy, Hennepin County sent 27 percent of the waste produced in the county in 2011 to landfills.

While Hennepin County works with partners to remove barriers to improve recycling in the future, we still need to manage the waste being generated today in the most environmentally preferable manner. That means reducing the amount of waste generated in the first place, recycling as much as possible, and processing garbage at HERC to produce renewable energy.

How is the ash managed?

Burning garbage to generate energy reduces the volume of the waste by 90 percent and the weight by 75 percent. The material remaining after combustion is a non-hazardous ash that is sent to an industrial landfill.

Because organic materials that were present in the garbage have been thermally destroyed, ash from HERC does not decompose and is more stable than landfilled garbage.

What is done to monitor and control odors at HERC?

County staff, known as Nasal Rangers, use a portable odor detecting and measuring device to monitor odors on and around the HERC site. The Nasal Rangers monitor every weekday from April through November.

A variety of measures are in place to keep odors in the building:

  • Traffic patterns for trucks entering and exiting HERC were changed in 2009. Trucks now enter and exit the building through the one door on the 7th Street side of the building (rather than the side that faces Target Field). The pavement closest to Target Field was removed and replaced by landscaping.
  • High speed doors have been installed on the waste tipping hall, minimizing the length of time the doors are open.
  • The tipping floor has negative air pressure. Fans pull air from the tipping floor to be used in the boilers, helping to keep odors inside the facility.
  • A product containing natural ingredients is used to neutralize odors.
  • Roadways are swept and kept clean of debris from trucks.
  • An air lock has been constructed at the entrance to the tipping hall

History

Deciding to build HERC

In 1980, the state passed the Waste Management Act to protect land, air, water and other natural resources and public health by improving waste management. The Act established a hierarchy for solid waste management practices that remains in place today. The waste management practices listed in the statute, in order of preference, are:

  • Waste reduction and reuse
  • Recycling
  • Composting
  • Resource recovery, including waste-to-energy or waste composting
  • Landfilling with methane recovery
  • Landfilling without methane recovery

In 1985, the State of Minnesota prohibited landfilling of unprocessed municipal solid waste generated in the metropolitan area after January 1, 1990.

In response to the establishment of the Waste Management Act and prohibition of landfilling unprocessed waste, the county developed a comprehensive solid waste management system, which includes nationally recognized, award-winning waste reduction and recycling programs.

The county’s commitment to accomplishing the resource recovery portion of the hierarchy included the development of HERC.

Hennepin County has revised its Solid Waste Management Master Plan several times since the Waste Management Act was established in 1980. Each revision
has detailed growth in our solid waste management system with waste-to-energy playing a crucial role in processing waste and reducing landfilling of waste

Construction and opening of HERC

In the mid-1980s, the 12.3 acre site for HERC was selected by the county and the City of Minneapolis because of its proximity to waste sources and the opportunity to clean up and reuse contaminated land. In 1986, Hennepin County demolished the Greyhound Lines, Inc., maintenance garage that previously occupied the site.

Grease, oil and diesel fuel had contaminated the soil and groundwater. Clean up of the site, which began prior to the construction of HERC, was important to redevelopment efforts for the area. Measures taken to clean up the contamination include:

  • Contaminated soils were aerated and used in creating berms as part of the landscaping, which allow bacteria to naturally break down the petroleum in the soil over time.
  • Contaminated groundwater that was removed during construction of the waste pit was routed through on-site treatment ponds prior to moving off-site.
  • Groundwater monitoring wells were installed, and the groundwater was tested until 1998 when the Minnesota Pollution Control Agency allowed Hennepin County to discontinue monitoring.

HERC construction began in 1986, and the plant began operations in the fall of 1989.

Hennepin County owns HERC. Covanta Energy, a leader in the waste-to-energy field, maintains and operates HERC for the county.

Proposal to use the existing capacity of HERC

In an effort to meet state waste management goals of increasing recycling and minimizing the landfilling of waste, the Hennepin County Board has decided to focus on expanding curbside organics recycling and securing more funding from the state solid waste management tax to support local recycling efforts.

The county has withdrawn its request for a permit modification from the City of Minneapolis and for approval from the Minnesota Pollution Control Agency to increase the amount of waste processed at the Hennepin Energy Recovery Center (HERC).

North Loop Community Energy System

Hennepin County is examining the potential to develop a district energy system that will use energy from the Hennepin Energy Recovery Center (HERC) to provide an affordable and sustainable heating and cooling option for businesses and residents in the North Loop neighborhood of downtown Minneapolis.

In this system, heat lost from electricity production at HERC would be captured and distributed for space heating, hot water and space cooling for customers in the North Loop.

Why is this system being developed?

The North Loop neighborhood of downtown Minneapolis is in the midst of unprecedented development. Along with major residential and commercial growth, this community will soon be home to the Interchange, a multi-modal transportation hub and community gathering space.

The development of the North Loop provides the perfect opportunity to use the existing energy assets at HERC to anchor a smarter community energy system. A district heating and cooling system would establish a modern and efficient energy infrastructure to support the growing needs of this neighborhood. This development would also enable HERC to fully utilize combined heat and power (CHP), a process that generates both electricity and heat at the same time, extracting more usable energy from the fuel and increasing overall efficiency.

What are the benefits to the system?

This district energy system will:

  • Make buildings safer, easier and less costly to manage, and help buildings qualify for environmental certifications.
  • Provide building owners with reliable, renewable energy options at a cost that is equal to or less than what they are paying today. The integration of this system will create long-term rate stability for users.
  • Provide a more secure, adaptable and resilient energy source.
  • Use existing energy assets and delivers new economic opportunities to existing commercial and industrial businesses.
  • Improve the efficiency of HERC, maximizing the amount of energy that can be captured from processing waste and further reducing greenhouse gas emissions.

For more information

Find out more about the project and the benefits in the North Loop Community Energy System factsheet (PDF 2MB)

Next steps

Hennepin County is in the development phase for the North Loop Community Energy System. The county and project partners will thoroughly analyze the economic and environmental implications of this project before moving forward with development to ensure that the project meets the long-term needs of the users and the community.

District energy

A 1,600-foot steam line, constructed as a joint venture between Hennepin County and NRG Energy Center, Minneapolis, supplies steam produced at the Hennepin Energy Recovery Center (HERC) to NRG Energy Center's downtown district heating system and Target Field.

The steam line supplies the equivalent annual natural gas needs of 1,500 households to downtown Minneapolis and Target Field.

How does the steam line work?

Solid waste, which is considered a renewable source of energy, is burned at HERC to produce high-pressure steam. Most of this steam is used to turn a turbine that produces electricity. A portion of the steam is diverted to the steam line that connects with the NRG Energy Center’s downtown district heating system.

Benefits of the steam line

  • Producing steam from a renewable and sustainable resource reduces the use of fossil fuels, such as fuel oil and natural gas, to heat and cool buildings. One-third of the steam will be distributed by NRG into the county's district heating system to heat and cool hospital and government buildings.
  • Diverting some of the steam directly to provide heating and cooling - instead of converting it to electricity - improves efficiency of the energy produced at HERC.
  • The steam line creates an interconnected district heating system with energy supplied from multiple sources, increasing the reliability and redundancy of the downtown district heating system and providing a reliable back-up.

The steam line partners

HERC

HERC is located in downtown Minneapolis and burns 365,000 tons of solid waste annually to generate enough electricity to power 25,000 homes. The benefits of energy produced at HERC include:

  • Reducing greenhouse gas emissions. Since opening in 1990, HERC has prevented the release of three million tons of carbon dioxide emissions.
  • Providing valuable renewable energy. The facility helps meet the state’s renewable energy goal of 25 percent of energy from renewable sources by 2025.

NRG Energy Center, Minneapolis

NRG Energy Center’s downtown district heating system provides steam and hot water for space heating, domestic hot water and humidification, and chilled water for air conditioning to more than 100 buildings covering 130 square blocks of downtown Minneapolis through six miles of steam piping and four miles of chilled water piping. The benefits of district heating include:

  • District heating adheres to stricter emission standards than do individual buildings, leading to less air pollution, and can more easily transition to renewable energy sources than can individual buildings.
  • When steam, hot water or chilled water arrives at a building, it is ready to use and 100 percent efficient. Energy produced by burning natural gas or fuel oil on-site is about 80 percent efficient.
  • Individual buildings do not have to store or use fuels, chemicals or refrigerants on-site, making the building safer and more environmentally sound.
  • Individual buildings do not have to install and maintain boilers and chillers, which reduces up-front costs, saves money on maintenance and frees up space that the equipment would otherwise occupy. District energy systems also have the flexibility to use a variety of fuel sources to keep costs down.
  • District heating systems, with built-in interconnections and back-up systems, are typically 99 percent reliable.
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