CHP Offers Reliable and Affordable Biproducts

Intelligent Flow Control Supports Clean, Low Cost Energy

Engineering, June 7, 2016

Major urban areas have markets for both products of a cogeneration operation: electricity and heating/cooling energy, and “district heating and cooling” is commonly used worldwide to serve commercial and residential customers.

As an example, NRG Energy Center Omaha has delivered reliable and affordable steam and chilled water thermal energy services to its customers in Downtown Omaha for 50 years.

omaha chp map
NRG Energy Center Omaha’s service area. (Image courtesy of NRG.)

Three NRG district energy plants in Omaha deliver steam and chilled water through an extensive pipeline network. Each building is instrumented to monitor usage for billing purposes.

Steam measurement was originally by pressure and temperature measurementthrough an orifice plate, along with a BTU meter. Chilled water was measured with simple positive displacement flow measurement, temperature monitoring and BTU meters. Circular chart recorders generated paper records of measurements.

Although state-of-the-art when installed, the original metering systems had limitations. The orifice plate system had a limited “rangeability” (turndown ratio) as the system dealt with wide variations in flow, a problem shared with the chilled water positive displacement flowmeters.

And as the original BTU meter vendor ended support for that legacy product, a system upgrade was ideal. NRG replaced the orifice plate devices with Endress+Hauser Prowirl 73F vortex flow meters, Cerabar PMP71 pressure transmitters and TH13 HART Smart temperature transmitters.

Chilled water flow is measured using Promag 53W Magnetic flow meters. NRG rounds out the system with an RMS621 Steam Flow Computer/Energy Manager and RSG30 Paperless Recorder/Multi-channel display.

Results have been excellent, with improved accuracy and reliability, and an additional benefit of lower pumping costs with the vortex and magnetic flow meters. The RSG30 has eliminated the storage and tracking issues of paper charts, and the systems is managed by an Endress+Hauser ReadWin 2000 system for billing.

An added advantage is that the new system’s instrumentation is traceable to NIST standards. The new technology was initially implemented for NRG’s new customers but now existing equipment is being upgraded to take advantage of the lower costs and improved accuracy of the automation.

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Image credit: Mattia Luigi Nappi