WTUI – HEPA Filters

1. HEPA filters eliminate compressor washing

Alliance Pipeline relies on 19 DLE-equipped base-load gas turbines from Solar, Siemens, and GE to power compressors on its 1857-mile system of 3-ft-diam pipe that extends from gas fields in British Columbia to customer receipt points just west of Chicago.

   The environment surrounding these units dictates water washing each spring, summer, and fall. In sum, each round of engine washing takes more than 1000 man-hours and consumes more than 3200 gal of demineralized water and 30 gal of soap, which must be disposed of in an environmentally acceptable manner.

   The pipeline’s Rob McMahon told attendees of the Western Turbine Users’ 22nd Annual Conference and Exhibition  that his company had tested hydrophobic HEPA filters from W L Gore & Associates Inc, Newark, Del, on two engines for nearly two years before deciding to equip its entire fleet with those filters, thereby eliminating water washing and 57 outages from the company’s annual schedule.

   Alliance learned about the Gore filter from TransCanada Corp’s experience at its Grandview Power Plant (access www.ccj-online.com, use the search function to find Grandview Power Plant).

   Alliance began testing the filters in April 2010 at two locations with different operating environments: the LM2500+G4 in the Windfall pumping station at the start of the main line, the largest engine in the company’s fleet, and a midstream LM2500 at Kerrobert in west-central Saskatchewan. Both engines showed a total system pressure drop of less than 1.5 in. of water with the new filters.

  Six months (4300 operating hours) later, a borescope inspection of the Kerrobert HP compressor revealed pristine airfoils (Fig 1). With the top case removed for maintenance, McMahon said the compressor rotor was so clean it was as if had just returned from a shop overhaul (Fig 2). Generally, after six months of operation, the bell mouth and blades and vanes in Stages 1-5 would have been very dirty.

 

   After one year of operation with the new filters, a borescope inspection of the Windfall G4 showed the bell mouth and visible stages of the HP compressor were clean (Figs 3, 4). An offline water wash was conducted but the wash fluid was white rather than the usual dark gray or black.

   McMahon said that a water wash when the unit was equipped with conventional filters would have resulted in an efficiency increase of from about 1% to 2%. There was no improvement following washing when the Gore filters were installed. Reason: There was not dirt to remove, thus no performance loss had been incurred.

   Based on the first two years of operation with the original Gore filters, expectations are that the filters should last at least another two years without replacement, making their service life comparable to that of the less efficient filters used previously. CCJ