A plugged or damaged nozzle can also be returned to the manufacturer for cleaning and reworking.Įxcessive nozzle plugging can occur if carbon steel or galvanized pipefittings or components are installed in the flow path of demineralized water. Most fog nozzles have an integral filter, which can be replaced in the field. Any nozzles that are plugged or have deformed spray plumes-usually none or less than one percent-should be replaced. While fog nozzles typically require little maintenance, they should be visually checked at least once per year. If compressor fouling occurs, it may be because the compressor is suctioning dirty water from the duct walls and floor. If this process is skipped, dirt or other material that has accumulated on duct surfaces and silencer panels can be carried to the compressor, leading to compressor fouling. This includes recoating duct surfaces that have rust or a compromised coating.

Prior to restarting a fog system that has been off-line for a long period of time, inlet duct surfaces and silencer panels should be thoroughly cleaned. Mee recommends using demineralized water with less than one part per million of total dissolved minerals-conductivity of 2 mS/cm or less. Key needs: pure water, clean ductsįogging systems require that demineralized water be used to prevent mineral build-up on compressor blades or hot-gas-path corrosion that could be caused by the dissolved minerals present in untreated water. True fog droplets do not cause compressor erosion, but if large secondary droplets exist in the airflow, or if water is allowed to accumulate near the compressor inlet where it can be suctioned into the compressor as large droplets, blade erosion can occur. Systems used primarily for overspray or wet compression should have them located close to the compressor inlet.

In fog systems used primarily for evaporative cooling, nozzles should be located in the filter house to allow maximum evaporation time. Mee notes the importance of installing nozzles in the proper locations in the inlet duct. Furthermore, because there is usually not sufficient time for all droplets to fully evaporate, any that don’t evaporate must be small enough to not cause compressor blade erosion. Small droplets ensure that water evaporates quickly without causing excessive accumulation in the inlet ducts. Droplets that impact on silencer panels or duct walls can also create flowing and pooling water on inlet duct walls or on the floor. This accumulated water can be stripped off by high-velocity airflow in the form of very large secondary droplets with a diameter of one millimeter (1000 microns) or more. If fog droplets impact on duct-support struts or trash screens, water will accumulate. Also, larger droplets are more likely to collect on duct obstructions or settle to the duct floor. Large droplets not only take more time to evaporate, they are less able to follow airflow around obstructions such as inlet-silencer panels and duct-support structures. The most important factor for proper operation of a fog system, Mee says, is to use nozzles that make very small water droplets. Fogging equipment expert Thomas Mee offers the following advice for keeping these systems-and in turn, the turbines with which they are associated-in top shape. While these systems usually require little maintenance and operate trouble-free for many years, they must be installed and maintained properly to produce the desired result. Inlet fogging boosts turbine output by cooling the air, especially on hot afternoons when demand is often at peak.

Since their introduction more than two decades ago, gas-turbine inlet-air-fogging systems have been used with turbines across industry, including those found in power-generation applications. These turbine-output boosters work well with little maintenance, but require proper installation and regular monitoring.

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