operation nearly 20 years ago, HERC has
prevented the release of 3 million tons of
carbon dioxide emissions, thereby reducing
the county’s impact on climate change.
Each year more than 11,000 tons of ferrous
metal are recovered from the waste stream
at HERC and recycled.
The steam line further helps reduce
environmental impact. Producing steam
from solid waste – a renewable and sustainable resource – reduces the use of
fossil fuels such as fuel oil and natural
gas to heat and cool buildings. The steam
line will help Hennepin County cut greenhouse gas emissions by 80 percent by
2050 – a goal shared by many counties
participating in the nationwide Cool
County Initiative (see sidebar p. 10).
“The steam line represents the latest
part of Hennepin County's strong effort
to ‘go green,’” says Hennepin County
Board Chair Mike Opat. “Not all of us can
discern the nuances of steam engineering,
but I think everyone recognizes the long-term benefits of expanding this reliable
and sustainable energy resource.”
In addition, the steam line creates
an interconnected district heating system
further increasing the reliability and
redundancy of the downtown district
heating system. The line provides the
opportunity for the county and NRG
systems to back each other up with
emergency steam, if needed.
Deciding to Construct
the Steam Line
Constructing a steam line from HERC
has been a possibility since the plant
opened. When the plant was constructed
in the late 1980s, the county had to decide
whether it would produce steam to be
used in a district energy system or high-pressure steam that would turn a turbine
to produce electricity. Based on the economics at the time, the county chose to
produce electricity at HERC. But the bridges
on Seventh Street, also built in the late
1980s, had been designed to accommodate
a steam line, so the possibility to add
one later remained.
In 2005, with natural gas prices on
the rise, the county began discussing a
partnership with NRG to construct a steam
line from HERC. HDR Inc., an architectural
and engineering consulting firm, conducted
two studies in 2005 assessing the possibility of diverting some steam produced
at HERC to NRG Energy Center Minneapolis,
Courtesy Hennepin County Public Affairs. Photo Teresa Schafer.
and ultimately to the Hennepin County
Energy Center (HCEC). These studies
determined that some steam could indeed
be diverted for district energy use and
still meet the county’s existing contractual
commitments for electricity production.
The ability to use steam generated from
solid waste burning would help both NRG
and HCEC offset their fuel cost increases.
The Hennepin County Energy Center
is a county-owned facility (separate from
HERC) in downtown Minneapolis that
generates steam from natural gas or fuel
oil for the county’s own district energy
system. This system supplies steam for
space heating, hot water and chilled water
to downtown county buildings – including
the main county government center,
Hennepin County Medical Center, Hennepin
County Juvenile Justice Center and
Hennepin County Public Safety Facility –
other government buildings and several
private customers. The Hennepin County
Energy Center is designed to produce and
supply up to 360,000 lb/hr of steam and
up to 14,400 lb/hr of chilled water.
NRG provides downtown customers
with steam and hot water for space heating,
domestic hot water and humidification,
and chilled water for air conditioning. The
A crane picks up the solid waste from the pit at HERC and feeds it to the boilers to produce steam.
The steam line creates an
interconnected district heating
system with energy supplied
from multiple sources, further
increasing the reliability and
redundancy of the downtown
district heating system.