District Energy - 2009 3rd Quarter

Courtesy Hennepin County. Photo Pictometry International Corp. Graphic Hennepin County Environmental Services.

The 1,600-ft steam line runs from HERC underneath two bridges on Seventh Street – one over railroad tracks and the other over an interstate highway – to connect with NRG’s district energy system in a vault near the Target Center. An additional connection to Target Field, the new Minnesota Twins ballpark, was recently installed.

By partnering on the steam line, both Hennepin County and NRG have made their respective energy operations even more efficient, cost-effective and reliable. Their partnership shows what can happen when two systems – that some might consider competitors – team up for mutual benefit. Diverting steam from HERC through the new line “is an efficient use of energy that goes directly to downtown instead of going to the grid,” says Durwin Fitch, the facility manager of HERC for Covanta. “In a world of green energy initiatives, this is certainly a good use of energy to support downtown Minneapolis and the ballpark.”

trash and send steam directly to the district energy system without running steam through the turbine. The county plans to take steam off the turbine at two extraction points once the design is approved by Westinghouse, the company that designed and manufactured the turbine.

; Monitoring the system – A telemetry system was installed to monitor the amount, temperature and pressure of steam leaving HERC and the condensate amount and quality returning to HERC. The telemetry can be monitored from the HERC control room by controllers watching the facility operation.

; Connecting to Seventh Street – A pipe bridge carrying the steam line from the HERC building to the Seventh Street bridge was constructed over the road that garbage haulers use to enter and exit HERC. The line was kept above ground for maintenance reasons. The pipe bridge was constructed without any alterations to the road or interfering with hauler traffic.

; Cleaning the returning condensate – Condensate polishing equipment was placed in HERC to clean the return

steam condensate before it can be cycled back into the boiler. The equipment, including a condensate holding tank, piping and chemicals, had to be installed without interrupting facility operation. All equipment was installed in an area that had been used for storage, and room was left for possible system expansion.

Carl J. Michaud, director of
the Department of Environmental
Services for Hennepin County,
Minn., has more than 31 years’
experience in environmental man-
agement. He oversees the county’s
programs for solid and hazardous waste man-
agement, cleanup of contaminated lands, pro-
tection of natural resources, air quality and
energy programs. Michaud previously worked
in the Environmental Planning Division at the
Metropolitan Council, St. Paul, Minn. He received
his undergraduate degree in biology from Illinois
Wesleyan University and a master’s degree in
environmental health from the University of
Minnesota’s School of Public Health.

The Twins’

Target Field

; Minnesota Twins will open their 2010 season in new stadium April 12 vs. Boston Red Sox

Connecting to the Ballpark

To enable HERC to supply energy to Target Field, a connection off the main line was made directly into the ballpark. The project was slated for completion in summer 2009. Target Field – an open-air, natural grass ballpark – will use steam for heating various spaces including offices, locker rooms and restaurants; for hot water throughout the facility; and for heating the field, preventing it from freezing in winter and allowing for a longer grass-growing season.

The primary steam supply for Target Field will come from HERC, although NRG can also provide steam if HERC is unable to do so. (For more on Target Field, see sidebar.)