TransCanada Pipelines pumps natural gas through underground pipelines from production facilities in western Canada to consumers in eastern Canada and Midwestern United States. Gas generators (themselves powered by natural gas) drive power turbines, which in turn drive compressors that compress natural gas to transmit it across the country.
Pipeline engineers learned long ago that these gas generators run more efficiently with their inlet air above 70ºF.
“Once you hit cold weather, you lose efficiency,” Marie Standing said, senior mechanical engineer with TransCanada.
To remedy this, they installed an air-to-air heat exchanger on a turbine exhaust at the Compressor Station in Saskatchewan. The heat exchanger recovered heat from the turbine exhaust and used it to preheat a portion of the inlet air to 385ºF. This in turn mixed with the remaining cold inlet air to bring the entire inlet airstream up to 75ºF, allowing the turbine to gain hundreds of horsepower.
However, TransCanada also learned that because the turbines ramp up quickly to an operating temperature of over 1000ºF, turbine operation created a severe environment for heat exchangers. They originally used a heat exchanger from another manufacturer, but it failed after only three months of operation. The quick ramp-up was inherent in turbine operation and hard to control, and in addition, TransCanada couldn’t reduce the startup rate because it would have held back operations on each startup.
In response, Munters designed a special heat exchanger, a modified Thermo-Z™ that accommodates rapid thermal expansion. A heat exchanger that can withstand such severe conditions is uncommon in the industry. TransCanada now uses the heat exchanger for three to five months out of the year.
“It may not sound like much, but when you add up the number of days, it’s quite a bit,” Standing said.
With the success of this trial, the company plans to add a heat exchanger to other compressor station turbines.
About Thermo-Z
The Thermo-Z™ all-welded heat exchanger, offers modular design with heave gauge, welded-plate construction, and guaranteed leakage rates less than 0.01% factory tested. Thermo-Z™ offers integral thermal expansion compensation and an insulated shell with an all-welded outer casing for increased performance. Both crossflow and counterflow configurations are available. Variable plate spacing is utilized to optimize performance, pressure drop, and service requirements, providing the most efficient and maintenance free heat recovery equipment available.
Welded construction eliminates the possibility of premature failure and increased leakage caused by particulate build-up in the compression seals of a non-welded unit.
Tel: (800) 843-5360 | E-mail: dhinfo@munters.com