At most plants, oil reclamation is not fully supported due to a lack of technical knowledge and availability of technologies, processes and applications. Why should reclamation be considered? The process has evolved over the years through rigorous oil testing and compatibility analysis of in-field trials. The advances and scientific support now available have led to robust reclamation technologies and processes. However, it is important to understand the limits and boundaries.
Past experiences and practices often lead to oil being changed on a timed interval or based on oil analysis results. Few managers want to be accountable for the risk of using new and emerging methods. Therefore, changing the oil and flushing the system are frequently the chosen approach.
Lubricating oils in large-volume systems can have a long service life. Some may be in service for 15 to 20 years. Many of these oils are made from Group I or II base stocks, unlike the more robust Group III or polyalphaolefin (PAO) base stocks. What makes these lubricants last so long? A historical review of the data from these systems reveals the oils operated within the set parameters, specifically temperature and contamination. Additive content remained healthy and the base oil was protected. The oils also were not significantly stressed.
Other systems that experienced significant problems were also reviewed. These included labyrinth seal issues, higher temperatures, filter decay and breakdown, process gas and steam ingress and poor maintenance practices. In these cases, the oils operated in highly stressed environments and were exposed to heat, water, solid contaminants and chemicals. Costly firefighting strategies were also employed, such as filtration systems, vacuum dehydrators and “sweetening” of the oils.
For organizations desiring to mitigate further problems, there is good news. Some solutions have a much longer duration than others, depending on operations, availability of spare parts, maintenance plans and the establishment of long-term objectives. For lube oil, detailed analysis is required to determine its life. Some oils will be fit for use, while others must be changed.
Unfortunately, few companies are focused on reclaiming their oils when the base oil is not compromised, which can only be verified through base oil testing. Reclamation normally will involve the removal of precursors along with the addition of additives, typically antioxidants for turbine oils. The addition of these antioxidants should be validated by compatibility testing. Three case-study examples are detailed below.
Case Study #1: Petrochemical Plant Turbine A
The reservoir size of this particular turbine was 2,800 gallons. The lube oil system was well maintained and had a nitrogen purge on the headspace. The system filtration used 5-micron absolute filters. Oil was changed based on a timed interval and supported with routine oil analysis. The rotating pressure vessel oxidation test (RPVOT), remaining useful life evaluation routine (RULER) and membrane patch colorimetry (MPC) are conducted twice a year. The system has been in service for 12 years with no oil changes. Typical results would include an RPVOT value greater than 1,100, more than 55% remaining useful life on the RULER test and an MPC value of less than 10.
Case Study #2: Petrochemical Plant Turbine B
The reservoir size of this reservoir was 2,200 gallons. The lube oil system was more than 30 years old. The system’s filtration used 25-micron nominal cotton-wound cartridges. The reservoir headspace had a dehumidifier, which had been problematic. Due to a labyrinth seal problem, there was a constant steam leak. The system experienced significant lube oil challenges. Typical results included an RPVOT value of 700, 30% remaining useful life, an MPC value of 35 and a viscosity change of more than 3% every six months.
“Sweetening” of the lube oil was frequent. Varnish was prevalent. The system had a vacuum dehydrator and a balanced charged agglomeration varnish removal unit. The dehydrator significantly reduces moisture to below 300 parts per million (ppm) and varnish below 20. Without the vacuum dehydrator, moisture will increase significantly and has exceeded 10,000 ppm. Operators have daily noted, a strong ammonia scent from the dehydrator’s vacuum pump exhaust.
Case Study #3: A Centrifugal Compressor
The in-service oil of this compressor did not meet specifications as required by the original equipment manufacturer (OEM). Oil analysis results showed an RPVOT value of 900, 50% remaining useful life and an MPC value of 15. The company did extensive testing on the compatibility of the oil with the addition of an antioxidant. The lab results were very favorable. Antioxidant was added under the supervision of the supplier. Oil testing was conducted for a period of one year with favorable results.
Analysis
Case study #1 is a clear example of a well-maintained system. The system was well designed with best practice methodologies. Opportunities for ingress have been eliminated. But more importantly, the system is well maintained. Abnormalities were addressed with urgency. Reclamation was not required. Decontamination has been maintained by the system’s filtration. The company has invested in training, certification and has partnered with equipment OEMs for maintenance.
Case study #2 identifies a situation that is chronic. Other factors unknown are the availability of spare parts or the availability of resources to address issues. The situation is a common “firefighting” situation with no clear objectives. Viscosity changes are forcing “oil sweetening” strategy to be executed periodically. Reclamation cannot be considered as the base oil has been damaged. The equipment is the oldest of these three scenarios.
Case study #3 identifies a system problem that has been allocated resources to identify the root cause, with intervention of a long-term solution. The cost associated with this process is considerably higher than scenario two but has lower cost of ownership. Again, it is important to consider all factors including context. The reclamation strategy examined the addition of antioxidant under robust supervision of the management team in partnership with the supplier. This strategy is still uncommon but is gaining momentum as references are increasing worldwide. It is an option that is available for consideration for large turbine oil users; something that would not have been considered many years ago.
In summary, reclamation is becoming visible to turbine oil users. As references increase, the risk reduces and users explore their options. It is mandatory that lube oils are tested to ensure they are fit for reclamation as well as to ensure that the reclamation process has been successful.
Decontamination
Decontamination has been a focus for many in the past with great emphasis on filtration technologies from numerous vendors worldwide. Some have benefitted significantly while others have been “stuck in the middle” with no clear objectives. Some lack understanding of decontamination processes and technologies available.
Some of the more common contaminants frequently found in lube oil systems are water/moisture, solid particles, process gases, high temperatures and varnish deposits. Ingress of these contaminants has detrimental effects on lubricants and equipment components. Most times these effects are long term with progressive deterioration that can potentially lead to failure. However, some consequences are immediate and can be catastrophic.
Using best practices, systems can be designed or modified to exclude contaminant ingress. Among the areas of contaminant ingress to review include gaskets, worn or damaged seals, open hatches and pipes, dirty hoses, dirty top-up containers and dirty new oil.
Focus is required on the types of contamination that is in a lube oil system. Firstly, examine oil analysis reports and review any abnormalities. Look for data changes and trends (both increasing and decreasing). If a report provides cautionary or critical warnings, it must be investigated further. Resample and retest the lube oil. A retest will confirm accuracy of the results and can prevent unnecessary actions.
In the absence of oil analysis reports, take alternative options such as using your senses. This is by no means best practice. Use your sense of touch to feel for tacky, thin or solid material. Use your sense of smell to detect fuel, process gases, burnt, foul or pungent odors. Use your vision to look for water, foam, air bubbles or a cloudy or dark appearance.
For solid contaminants, another alternative is to conduct a field patch test. This provides a great snapshot of solid contaminants in the lube oil sample. However, particle counting is the best practice available. Particle counting provides counts of actual particles identified in the range numbers of the ISO code. This is very helpful in selecting filters required to remove solid particles.
Once contaminants are determined, it is imperative to remove these as soon as possible. Following are some of the most popular methods for removing these contaminants.
Water
Water and heavy solid particles will naturally settle at the bottom of reservoirs. If oil analysis results identify high levels of moisture beyond specified limits, it must be reduced. For applications with large ingress of water, a centrifuge will be very effective. However, it will not remove moisture below the saturation point. For lube oils, it is best to remove moisture to as low as reasonably possible. Therefore, in most situations, a vacuum dehydrator is used to remove large volumes of water and to meet moisture limits of the oil. In the situation where there is a coolant leak or steam leak, moisture ingress maybe continuous. A balance will have to be achieved with a vacuum dehydrator to ensure that moisture limits are maintained. Dry air and nitrogen are best suited for maintaining lube oils with existing low moisture levels.
For vacuum dehydrators, the technology has evolved significantly. Most systems utilize low wattage density heaters. This prevents lube oils from becoming burnt as it passes over these heaters. Vacuum pumps have improved significantly resulting in more reliable operations. Foam sensors have also been included with controls to avoid foaming. This reduces the risk of vacuum pump failure and oil spills. Vacuum chambers’ designs have been improved resulting in improved mass transfer efficiency. Vacuum dehydrators are becoming more reliable in the industry.
Gases
Most times these gases are directly related to process gases. They are typically dissolved and can be easily removed using vacuum dehydration. Note that some gases are dangerous. In this case, the vacuum pump exhaust must be vented to a flare.
Solid Particles
These particles are removed via filter media. The choice of media can be challenging, as they vary in performance. However, a logical process should be adopted where filters are selected on the type and number of particulates to be removed.
There isn’t a simple process to the selection. However, obtain a current particle count with particle distribution. This will give you an indication of particle size and quantity.
If filtration is offline with easy access to change filters, then lower cost filters can be explored. Start with the micron size in abundance and remove these particles. Then replace with a lower micron size. Change filter based on recommended differential pressure or filter indicator. Repeat process until particle count is acceptable. This will avoid using depleted multiple smaller micron filters which typically are more costly.
For pipeline flushing, screen mesh or surface media can be used initially to remove the bulk contaminants followed by standard filtration.
Efficiency or beta ratio is sometimes not well understood. Some manufacturers state their filters are high efficiency or absolute rated. Unfortunately, there is no standard that identifies an absolute rated filter. Best practice recommendation is to review performance curves of each filter. Higher efficient filter will capture more particle of a specific micron size in one pass. This type of filter is necessary if lube oils will be pump directly to lube oil components after the filter. They are not recommended for recirculation systems.
Dirt-holding capacity can be used to determine the cost of filtration based on the number of filters expected to be used.
High Temperature
For systems with high temperature, many factors need to be reviewed. These include the use of vibration analysis, infrared thermography and airborne ultrasound. Related symptoms are normally beyond the lube oil system. However, the coolant system periodically clogs with minerals. In this case, the coolant system must be flushed.
Varnish
Varnish has become prominent in many lube oil systems. There are many precursors to the development of varnish from high heat, contaminants and base oil stocks. In many systems, varnish deposits on machine surfaces can be identified by a very thin dark layer on tank walls, bearings/journals, valve spools and filters. This layer acts as an insulator leading to high temperatures. The effects can be devastating. To reduce varnish, many companies focus on varnish removal equipment. Note, many systems may not show any visible signs of varnish unless the system is shut down. Varnish can dissolve at higher temperatures. When the system is shut down the lube oil cools leading to varnish deposits on machine surfaces. Systems designed to remove varnish must be evaluated and considered with temperature in mind. It is recommended to conduct lube oil testing and analysis to determine varnish potential. Varnish can be reduced using technologies such as balance charged agglomeration, depth cellulose media and ion exchange. These technologies are available in units similar to offline filtration systems.
Roadmap Forward
A road map is provided as guidance to making decisions with large reservoir turbine oil systems. Both short- and long-term steps are provided.
Short Term
Step 1: Obtain oil analysis data and determine current issues.
Step 2: Based on existing KPIs, determine requirements to address current issues. These may include the operations schedule and budget, the maintenance schedule and budget, the required resources and associated costs.
Step 3: Obtain and implement the relevant resources. Test the lube oil and analyze the results. Repeat until the desired results are achieved.
Long Term
Step 4: Reassess existing KPIs and long-term objectives, such as oil testing, best practices, varnish mitigation, oil reclamation, filtration/dehydration, cooler performance, parts replacement and equipment modifications. Determine the resources required to implement recommended best-practice solutions. These might include training and certification, standardize procedures, parts replacement, equipment modification and implementation and the deployment of oil reclamation strategies. Finally, seek the allocation of funds for oil testing and analysis inclusive of varnish testing, additive health and base oils.
Step 5: Obtain budget approval.
Step 6: Implement resources.
Step 7: Monitor and reassess. Review the current oil analysis reports, maintenance and operations costs and program performance.
Summary
Turbine oils are critical to companies’ operations. If not monitored and supported effectively, increased costs and potential failure remains eminent. Oil analysis is critical to understanding the health of lube oils and equipment. In some cases, the lube oil life has been exhausted. In many applications, lube oils can be reclaimed using detailed oil analysis together with the current technologies and solutions available today. It is mandatory that equipment users consider options to monitor and maintain lube oil health. Life extension and equipment reliability will be achieved and will become the new norm. Companies will be able to manage their core business at peak profitability.
About the Author
Managing Director at CASL
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