Seems like a simple enough question. It gets asked thousands of times a day in restaurants around the world. But in generating plants powered by gas turbines, it takes on a whole different meaning. These engines are very sensitive to salt, and there are strict limits on its ingestion. Just a few parts-per-million can quickly lead to a multi-million-dollar repair bill. That’s all good to know, but the fact of the matter is that our plants get sited where they make functional and fiscal sense, not on the druthers of equipment manufacturers. We have learned from work done in Hungary’s Institute for Atmospheric Physics (by L Horvath, E Mfiszaros, and E Antal) and Central Institute for Meteorology (by A Simon), that marine air basically contains two kinds of aerosol particles: Those with radii larger than about 0.5 microns composed of sea salt (NaCl), and smaller particles of mostly sulfur species formed in the air by gas-to-particle conversion (excess sulfate). These particles are found in the atmosphere up to 11 miles from the seashore. OEMs frown on sodium (Na) and sulfur (S) entering their engines, but just how much sodium are we really talking about here? Sure, you can taste the salt in the air when you’re at the beach, but how dense can it really be 11 miles inland? So, let’s take the mid-point—5.5 miles—from the shore for illustrative purposes. Assume the gas turbine at that location is an unfiltered LM2500 (base model with a single annular combustor). Based on the work of the Hungarian researchers and the amount of air the example engine swallows during an 8200-fired-hour base-loaded year, the GT would ingest a little more than 5 lb of salt. Even if you don’t add the sodium that enters the engine through other vectors (fuel, steam, water injection), you are way over the limit GE recommends for this machine. Managing salts and sulfur in the non-air vectors can—and usually is—done through a combination of contractual obligations and plant processes. Managing the air is really down to one tool: filtration. The design, installation, operation, and maintenance of the combustion-air filtration system is the sole line of defense. What about them should we be concerned with if we find ourselves in a plant sited within 11 miles of a saltwater coastline? Well, here are a few thoughts: Design. Some packagers only have one combustion-air filtration option, but others have multiple options that are designed for specific environments (desert, marine, etc). If options are available, ticking the appropriate box is a great first step. If options are not available, consider asking for a customized unit, or deleting the inappropriate unit and seeking options in the aftermarket (they are available). Installation. When the construction team is assembling the combustion-air intake, some oversight/sign-off hold points are a good idea. Pay particular attention to the following:
- Make sure the structure’s bolted flanges are made up tight, and that the gasketing is centered up on the bolt line as it should be.
- Check the structural alignment and grouting of the support legs to ensure that there isn’t going to be any sagging or tweaking of the structures that could lead to cracking of welds or flange separations.
- Verify the proper alignment of any expansion joints or bellows in the ductwork; no binding allowed. And make sure there are no gaps or tears in these components that would allow air (and contaminants) to enter.
- Check the interior materials and coatings—especially downstream of the high-efficiency filter elements—to ensure they are in good condition and sufficiently robust to withstand the corrosive effects of a marine environment.
- Check the man-doors to be sure they are hung straight and square to promote good sealing.
- Inspect door gaskets for proper attachment; also, that latches are adjusted for firm closure. Same for inspection hatches—straight, square, and good tight gaskets.