Measuring lube oil humidity can help control water contamination

In a turbine-driven blower, it was found that multiple failures showed traditional approaches were not fast enough to protect this machine from damage due to high water in the lube oil.

High water contamination of lube oil damaged a turbine driven process blower on multiple occasions. The traditional solution would have been monitoring oil for milky appearance; draining free water from reservoir, but oil stays saturated.

A better solution would be installing a 4-20 mA on-line humidity monitor plus dry gas purge. Humidity sensors give numbers to alarm & troubleshoot. Dry gas purges vent moisture and oil stays below saturation.

This article has excerpts from, "Continuous Control of Lube Oil Water Contamination – Never get Surprised Again" by Steve Locke of The Chemours Co. presented at the 2016 Turbomachinery Symposium.

In a turbine-driven blower, it was found that multiple failures showed traditional approaches were not fast enough to protect this machine from damage due to high water in the lube oil

Turbine steam seals are a continuous source of water contamination in bearings and lube oil system. Bearing housings normally run at a slight vacuum due to oil drainage flow which pulls seal steam in & accumulates condensate. Lube reservoir vent runs slightly positive. • This blower had two episodes of severe Lube cooler leaks. The outdoor installation also has rain exposure risks.

Bearing housings run slightly negative due to oil drainage. Some steam gets pulled in and condenses in the cooler oil.

Dry air purges were added to the middle of each of the bearing housings on the turbine and the blower. We usually purge into the center of bearing laby seals, but time and resources did permit this extra step on this blower. Rotameters were provided to control purge rate. These rotameters are sized for a peak flow of 6 SCFM.

Use of a back pressure device on the reservoir raises bearing housing pressure to atmospheric to retard steam induction. A clever instrument tech used a small hydrostatic head to raise bearing housing pressure to atmospheric.

An oil humidity sensor was added to continuously monitor the water concentration in DCS with high alarm set at 80% Trend history can be valuable in troubleshooting to correlate any high water events with changes in process or other conditions such as weather.

Use of dry gas (instrument air) absorbs water entry from the turbine steam seals and any other sources. A 4-20 mA oil humidity sensor provides continuous DCS history to alarm & troubleshoot before reaching 100% saturation in the oil. Rotameter air purges allow operators to add more air if needed to help arrest water entry. Back pressuring the bearing housings retards steam flow into the turbine and blower bearing housings.

The above combination of control steps has stopped water entry into the lube oil system of this turbine driven blower. The turbine-driven blower has run for over seven years with no repeat failures from water contaminated oil.