by David Kolstad, Pentair
December 17, 2011

Using mass transfer principles, a filter-dehydration system effectively diffuses

Using mass transfer principles, a filter-dehydration system effectively diffuses moisture from oil to the dry air in the system's membrane contactor.

First, oil is pumped from its reservoir into the system's high efficiency particle filter, which cleans the oil beyond the levels attained by most full flow filtration circuits. The oil then flows through the inside of the patented hollow fiber membrane contactor, while dry air sweeps the exterior surface of the membrane. This promotes the diffusion of moisture through the contactor and into the sweep air. The air, which now contains dissolved moisture, vents out of the system to atmosphere with no bulk water or other disposables generated in the process, and the clean, dry oil returns to the reservoir.

This filter-dehydration system operates at ambient oil temperature with no heat or post-process cooling required, preventing thermal degradation. It enables customers to cost-effectively remove contaminants-minimizing equipment wear for improved process uptime and performance.

Another benefit of this filter-dehydration system is its simplicity. It requires no routine operator intervention, no moving parts and no liquid level controls or water drains. Since the only routine replacement component is the system's coreless particle filter, it saves maintenance costs. Once moved into position near a reservoir, simple connections are made for oil supply, oil return, power and compressed air. In operation, the only things to be monitored are the differential pressure gauge (for particulate filter condition), and the moisture level in the oil (to determine when conditioning is complete).

In one example, the main lube reservoir at a paper mill had been typically averaging a moisture level of 290 to 530 ppm, with excursions as high as 3,770 ppm on occasion. Given the high cost of replacing journal bearings and associated downtime, the overall cost to the facility was more than $100,000 per year. If a failure resulted in lost production, the cost would escalate to $5,000 to $10,000 per hour. Since a dedicated filter-dehydration system was installed, the oil has averaged 50 to 100 ppm-potentially tripling the paper mill equipment's operational life.


A filter-dehydration system removes free, emulsified and dissolved water, as well as particulates and gases, from petroleum- based and synthetic oils. The system can serve a wide variety of applications within pulp and paper mills, power plants, hydraulic presses (such as stamping and plastic injection molding), steel and roll mills, etc. It decreases water concentration, down to 25 ppm, and improves particulate filtration, as low as ISO 13/10 (or lower). The system reduces oil contamination and minimizes wear, maintenance expenses and downtime for extended hydraulic and lubricated system life.

The system is cost-effective, conveniently sized and easy to maintain. With no moving parts or flow/level controls to adjust, specialized operator training is unnecessary. A filter-dehydration system is suited for periodic use on reservoirs throughout an entire facility.

It may also be dedicated to a particular reservoir to provide continuous conditioning, ensuring that oil is optimized without the fluctuations in water concentration that occur with periodic oil reconditioning.

 Reducing moisture content in oil significantly reduces equipment wear. Reducing

Reducing moisture content in oil significantly reduces equipment wear. Reducing water concentration from 250 to 40 ppm, for example, can potential triple equipment life.


Pumps & Systems, January 2010