- Buyer's Guide
The oil storage room at the Elrama Generating Station in Elrama, Pa., was located in a separate building specifically made to house the oil at the plant (Figure 1). Oil drums were stocked on racks, and an overhead crane lifted full drums to pour into steel containers that stored the oil for plant distribution (Figure 2). These storage tanks were open to atmospheric conditions and were typically left open as the manually operated oil pump dripped for several hours after use. These tanks were an entry point for contamination into the system. No filtering took place. The lubricant was placed into containers, bottles and buckets – another entry point for contamination. But, that was then. This is now.
Figure 1. Here’s a snapshot of the old lubricant storage area. It was not set up to achieve lubrication excellence.
Figure 2. This is a visual diagram of the previous practice used to store and distribute oil.
The reconfigured storage room today consists of oil in stacked plastic totes in a quantity representative to the SAP stocking level (Figure 3). Drums are not stored in the room unless an oil analysis is in process. The drums are pumped through 25- and 3-micron filters on a filtering cart into the plastic totes. The totes are sealed from the atmosphere and use a desiccant breather to dry the air that enters the tote when draining the oil into filling bottles.
Figure 3. Today, oil is stored in stacked plastic totes.
Totes are labeled with the oil manufacturer’s information to prevent pumping into the wrong tote (Figure 4). Color- and shape-coordinated labels also identify the oil type and help prevent cross-contamination (Figure 5). The overall process is shown in Figure 6.
Figure 4. Totes are labeled to show oil type and the manufacturer.
Oil analysis indicates that new oil from the supplier is received on site with an average ISO cleanliness code of 18/17/13. This is consistent with the manufacturer’s claims and advertising. This is not something a person can see with the naked eye, so the pictures in Figure 7 have been magnified 100 times to give you a better look.
Figure 5. Labels have a color and shape system to prevent misuse.
Transferring into the old storage tanks made the oil dirtier than new. Oil samples from these tanks showed an increase in the ISO cleanliness code to 19/18/14, or 50 percent dirtier than when we first purchased the oil (Figure 8). Using this oil following an oil change, we would never meet recommended cleanliness targets. Meeting these targets would maximize equipment and component life.
Figure 6. This is a visual diagram of the current practice used to store and distribute oil.
Installation of the new storage totes and filtering the oil before placing it into the tote dropped the cleanliness code by 2/2/2 from the drum and 3/3/3 from the old storage system. The amount of particles in this oil is 87 percent lower than before. This allows for extended equipment life and maximized oil life.
Figure 7. Pictures of oil samples taken from a fresh oil drum (left), after transferral into the old storage tanks (center) and after the changes.
Using a life extension table created by Noria Corporation to compare machine oil cleanliness, we saw that a three-level reduction in cleanliness code extends the life of gearboxes by a factor of 1.5 and journal bearing machines by a factor of 1.8 times. The Noria chart makes a couple of assumptions in that you must maintain the oil cleanliness level at that level for the life of the machine, which is very difficult and almost never practical. It does show, however, that if the oil is cleaner (and all other variables are equal), longer equipment life will be the result. The question you should ask yourself is, “How much of your budget do you use to repair oil-lubricated machines?” If that amount is greater than $100,000 per year, then cleaner oil would be a huge benefit to your bottom line.
Figure 8. What oil do you want protecting your machines?
An additional benefit of starting with cleaner oil is that oil change intervals can be extended if the reason for changing the oil is high particle counts. If you extend oil change intervals, your plant will consume less oil during any measured period. This will result in an overall savings and increased profit margin. If you extend the oil change intervals on average by 20 percent and the annual plant oil expenditure was $100,000, the savings would be $20,000 in reduced oil purchases, plus the cost of labor for those oil changes, which could easily double that amount, for a total savings of $40,000 per year. I won’t account for any benefit that a machine sees with extended life because of the number of variables that exist.
Best practices indicate that setting individual machine cleanliness targets should be followed to maximize the life of lubricated surfaces. Figure 9 represents targets for common machines and machine elements.
If any of these targets are followed, then filtering the oil from the drums is mandatory since the new drum oil will not meet any of these targets. Clean oil storage hardware and techniques are the key components to keep these targets low.
Figure 9. Here is a sampling of base cleanliness targets for common machines and machine elements.
The cost of the Elrama oil storage tanks was $45,000. The cost of your lube room is dependent on a number of factors. How many lubricants do you use on site? Do you need spill protection? Are you going to use filter carts or individual rack-mounted pumps with filters? Filter carts give you the added flexibility to roll around the plant and filter larger oil reservoirs, such as boiler feed pumps and pulverizer gearboxes. Storage totes come in many different sizes, from 65 to 240 gallons. Some oil storage areas have their own spill containment units.
The cost to filter and store four different lubricants for a gas turbine plant may be in the $5,000 to $15,000 range, and the cost to filter and store 10 different lubricants at a coal-fired plant may be in the $30,000 to 45,000 range.
We conservatively calculate $40,000 as the annual benefit from extended oil changes. This doesn’t take into account lost margin from any unit derate or outages, nor does it take into account benefits from reduced maintenance due to extended machinery life. We also conservatively calculate $45,000 for costs on an oil storage area, with 12 percent as a discount rate and a 20-year life expectancy. The net present value (NPV) is calculated at $208,778.
New oil arrives on site in varying degrees of cleanliness. It easily can be improved with the use of sealed storage tanks and by filtering the oil before storage. A minimum removal of 75 percent of all particulate contaminates can be expected with filtering.
New oil is not clean enough to use if cleanliness targets are implemented and maintained. The NPV shows a positive figure of $208,788 for a 20-year life cycle; the benefit-to-cost ratio is 4.6 when a discount rate of 12 percent is used.
These storage tanks should be used at every power plant facility. This is a case of proactive maintenance contributing to machine reliability and the company’s bottom line.