Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/1222953
24 | March - April 2020 | www . machinerylubrication.com In regard to the air supply, the maximum consumption is 30 standard cubic feet per minute (SCFM) for a large system that would serve 50 to 80 pieces of equipment. Should the air supply system go down, there likely would be many more issues to be concerned with, as the process unit or plant would be shutting down. A typical oil mist system uses 2 gallons of oil per 24 hours. A fully instrumented oil mist generator has a 9-gallon misting chamber and a 75-gallon bulk reserve. Many process plant installations include an additional 110-gallon bulk oil tank, thus providing an oil supply of approximately 200 days of continuous operation. Dry Sump or Pure Mist? Dry sump or pure mist is the preferred lubrication method for most rolling-element bearings, including pumps, motors and pillow-block bearing applications. Pure oil mist can also provide superior lubrication over traditional oil sump or grease lubrication. Where there is no oil level in the bearing housing, oil mist is the only means of lubrication. e preferred flow of oil mist is through the bearings, side to side or top to bottom. Pump and motor manufacturers are quite aware of oil mist systems, and most have designed their equipment for use with this type of lubrication. Current API standards also support the use of oil mist for equipment lubrication and preservation. Technical Risks Oil mist systems are relatively simple, operating at 0.73 pounds per square inch with a flow rate of 20-24 feet per second. With no moving parts to wear out or fail, many systems in the refining industry have exceeded 40 years of operation. Turnkey installations can be provided by the supplier. Training for operations and maintenance personnel normally is offered onsite, along with customer support and service. Routine main - tenance contracts are common in most facilities. Case Study e Petronor oil refinery in northeastern Spain recently installed pure oil mist in the pillow block of a gas blower that originally was equipped with an oil console. e final conversion involved a dual pillow-block bearing arrangement for an air blower in the refinery's sulfur unit. All the rotating machines in the plant were lubricated by oil mist except for this blower, which was a requirement of the plant licensor. Since its startup, the blower had experienced multiple lubrication issues related to the oil console, such as oil clean- liness deficiencies and clogged oil injectors. e main pump also failed because the bearing's pillow block had a very small oil volume and no constant-level oiler, so even a slight drop in the oil level put the pump and machine at risk. After the system was studied by a design engineer, it was concluded that the oil console was unnecessary and too complicated to lubricate the pillow block. Oil mist, which already was installed on the surrounding machines, was deter - MAINTENANCE AND RELIABILITY Figure 3. The upgraded lubrication system incorporating oil mist (Ref. Hydrocarbon Processing Magazine) Figure 4. A gas blower lubricated by oil mist. mined to be the best option for simplifying the system and boosting the reliability of the blower. During the upgrade, the oil console and related instrumentation were dismantled. e system's current design (Figure 3) is much simpler. Now, the blower works much better than before, and the conversion cost was less than $6,000. Lessons Learned What can be learned from this case study is that reliability engineers often need to question the original design of their lubri- cation systems and refute underlying assumptions to improve reliability. System designs frequently are complex without justifi- cation. Complicated systems do not always mean reliable systems. Finally, consider oil mist as a possible lubrication method based on its proven ability to reduce equipment failure rates while increasing availability and throughput. ML