Eliminate Oil Contamination in Wind Turbine Gear Boxes with Drytech Membrane Dryers |
The ANSI/AGMA/AWEA 6006-A 03 standard provides guidelines for design and manufacturing of wind turbine gear boxes. Specifically paragraph F.5.3.3.2 talks to the harmful effects of water contamination in gear box lubricant. It confirms that moisture levels should be kept below saturation point which for many oils is less than 500 PPM depending upon oil type and temperature; it further recommends that desiccant breathers be used.
Should this standard not be maintained, manufacturers and users may see:
- Lubricant degradation
- Degradation of internal gear box component
- Corrosion of metallic component
- Accelerated metal fatigue
Problem
Gearboxes present the biggest challenge to wind turbine reliability due to the extreme stresses imposed by the turbine blades directly connected to the gearbox assembly. These problems are further exacerbated by lubricant degradation caused by moisture, particulate, viscosity issues and acidity. Once liquid water is adsorbed into oil it emulsifies and can never be removed, despite the use of cellulose filter systems.
Moisture Intrusion
Moisture intrusion occurs during diurnal exchanges of air caused by temperature variations during the day. Moisture is inhaled into the gearbox through polyurethane and/or PTFE seals and gaskets by leaks and moisture vapor transmission (MVTR). In cases where a desiccant breather is used, inhale will take place through the breather but these units are generally inadequate in both size and capacity to handle the significant levels of moisture.
Currently desiccant breathers are used in various configurations, but as it can be seen from prior paragraphs, the volume of available desiccant is inadequate for required desiccant life cycle of 6 months before change out and in extreme cases could only provide protection for a month before saturation and the gearbox starting to see contamination from moisture at levels of a cup of moisture per week. |
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Example |
- Typical inhale of air into a 10 cubic ft. gearbox free air space under a diurnal temperature swing of 115° F represents 5.7 grams of moisture/day.
- Typical MVTR of urethane seals represents approximately 2.0 grams of moisture/day.
- Typical change out of desiccant breather every 6 months. 183 days @ 7.7 grams/day = 1409.10 grams to be adsorbed (3.1 lbs.).
- Typical adsorbtion capability of 3 lb. desiccant breather is 476 grams (1.05 lbs.).
Therefore under these conditions a 3 lb. desiccant breather will last approximately 2 months. |
Solution |
Recognizing that desiccant breathers provide inadequate protection for the large wind turbines being produced (1-3MW range). Drytech has developed a stand alone continuous air drying membrane system, GenDry™, that will provide an on going source of dry air <-30° F Dew Point (<400 ppm) to envelop the gearbox free airspace, preventing oil contamination from moisture.
The GenDry™ system will not require maintenance not desiccant change outs and provide a MTBF of 3-5 years and are designed for rigorous and harsh environments such as offshore or tropical applications where moisture and salt air will accelerate gearbox degradation.
The GenDry™ system design utilizes two pneumatic cylinders in parallel acting as air pumps and driven by a heavy-duty linear actuator.
Essentially, the actuator drives the air pumps and generates a volume of compressed air, which is stored in an air reservoir (accumulator). This accumulator will store all of the pressurized atmospheric air produced by the pump cylinder stroke cycle(s) thus minimizing the amount of cycles (3-4 strokes/hour) extending the life of the system to 3-5 years before maintenance.
The stored air is continuously released from the accumulator at a given flow and pressure into a coalescer to take out liquid water and then downstream into the membrane filter which removes the moisture and provides <400 ppm air (<-30° DP) into the gearbox.
This design will supply a constant purge supply of low humidity air to the gearbox or other enclosures requiring moisture protection.
| Model No. |
Part No. |
Windturbine |
Gear Box Free Air Volume |
Air Dryer |
Gear Box Air Exchange |
| ppm |
°C dp |
| GenDry™ 10 |
1DT70600-10 |
1.0-1.5 MW |
10 cu. ft. |
<400 |
<-30 |
min. 3/hour |
| GenDry™ 20 |
1DT70600-20 |
1.5-2.5 MW |
20 cu. ft. |
<400 |
<-30 |
min. 3/hour |
| GenDry™ 30 |
1DT70600-30 |
3 MW |
30 cu. ft. |
<400 |
<-30 |
min. 3/hour |
For more products and information on desiccants for alternative energy please visit our newest venture, www.wind-dry.com |
