Deliver Clean Lube Four Ways
Ken Bannister | November 18, 2018
Depending on space and needs, there are four recirculating-oil-decontamination system variations that will keep an asset’s moving parts lubricated with fresh oil.
By Ken Bannister, MEch Eng (UK), CMRP, MLE, Contributing Editor
In the “end to end” process and manufacturing world, industries such as pulp and paper, petrochemical, energy, and steel employ equipment that favors large, centralized recirculating-oil lubrication and hydraulic systems designed to move hundreds of gallons of oil per minute. This requires large reservoirs designed to hold hundreds to many thousand of gallons of oil.
Recirculating-oil systems deliver lubricating oil on a continual basis to many hundreds of lubricating points that are designed to allow the oil to flow across the bearing point and return back to the reservoir to be decontaminated, cooled and, once again, delivered to the bearing. This repetitive cycle can continue around the clock.
Because systems are sometimes operating in non-controlled environments, i.e., open to air, many contaminants such as production process material, moisture, and plain old silica dirt regularly make their way into the lubricant. These contaminants must be dealt with before the lubricant is resent on its next lubrication cycle. If not dealt with quickly, contamination will abrade bearing surfaces, deplete the oil’s additive package, oxidize the oil, and render it harmful to the very bearings it is designed to protect.
To combat contamination, oil can be changed on a regular-to-accelerated basis, based on its cleanliness—as is the practice in small to mid-sized recirculating systems. However, with very large hydraulic and recirculating systems, the time taken to perform an oil change can greatly affect the uptime utilization of an asset. At the same time, an oil change can easily cost tens of thousands of dollars to purchase oil, store and pre-filter the oil to the required cleanliness standard, and responsibly dispose of the used oil. With the cost of downtime, it is not unusual to experience six-figure costs per oil change.
To significantly reduce the amount of oil changes required on large recirculating systems, there are four major “in service” decontamination (sometimes referred to purification) processes designed to offset maintenance, reliability, and excessive downtime issues.
In all systems, the return oil will usually first pass through a low-pressure gravity filter on the return line prior to entering the reservoir. A baffled reservoir will act as a first-stage cooling process prior to the oil passing through a suction filter into one of four decontamination-system designs:
Continuous Full Flow
In continuous full-flow decontamination systems, the entire oil volume is pumped from the reservoir, through a strainer to take out large solid contaminants, then on through the primary filter element (usually a bag-style filter) to remove smaller contaminants before passing through a cooler on its way to the machine element or bearing (See Fig. 1). In 24/7 industries, the filter can be duplexed (as shown) and, depending on the control design, manually or automatically switched to the secondary filter once the working-filter pressure differential indicates the media is saturated with contaminant.
If no decontamination system exists, and/or tight real estate does not allow for an inline “built in” full-flow decontamination system, a continuous auxiliary decontamination system can be used. In this system, an independent pump draws lubricant from the reservoir and, depending on the design requirement, can then pass it through a number of decontamination processes that may include a centrifuge to extract water; a large-micron filter for large contaminants; or a small-micron, fine-contaminant, depth-type filter (analogous to pushing fluid through a toilet-paper-roll-style filter media, compared to a gross-contaminant filter similar to a screen-style nylon stocking). An additional option is to use any combination of these filter types. Once passed through the filter, the oil is returned to the main oil-recirculation system for cooling prior to release to the bearings.
When the working-environment air is filtered and the temperature controlled, the contamination risk is significantly reduced. In these circumstances a simpler continuous-bypass decontamination system might be preferred.
In this system, the main oil flow is screened and pumped continuously through an adjustable pressure-control valve that can allow as much as 75% of the fluid to pass directly to the cooler. The remaining oil passes continuously into a bypass loop in which the lubricant is filtered, similar to a full-flow system, and returned to the delivery system for distribution through the cooler and then the bearings.
A variation of this system allows for a full-flow-through filter circuit with a continuous bypass circuit plumbed to allow a small percentage of the oil to pass through a depth-type polishing filter that is once again returned into the primary delivery circuit.
When no permanently plumbed decontamination filtration circuit exists and oil is contained in a smaller footprint, it’s possible to use a periodic batch-decontamination process. In this process, the machine is shut down and oil evacuated to a mobile tank and decontaminated in a separate area or off site by a third-party contractor. This system works well when there are numerous machines using the same oil. In this case, oil cleaned off site from another machine can be used by a machine undergoing oil evacuation. Its used oil can then be cleaned and polished, ready for the next oil change out, significantly reducing the oil-change cost. For large turbines, oil can be made to last for decades using this process.
Oil is an integral component of any machine or process. Decontamination systems treat the oil as an asset, not a consumable, resulting in financial benefits for a machine’s life cycle and the corporate bottom line. EP
Contributing editor Ken Bannister is co-author, with Heinz Bloch, of the book Practical Lubrication for Industrial Facilities, 3rd Edition (The Fairmont Press, Lilburn, GA). As managing partner and principal consultant for Engtech Industries Inc., Innerkip, Ontario, he specializes in the implementation of lubrication-effectiveness reviews to ISO 55001 standards, asset-management systems, and training. Contact him at firstname.lastname@example.org, or telephone 519-469-9173.