The chemical industry relies on very special processing to manufacture many of its products and often times include the use of compressors to achieve the special process conditions required. The selection of a lubricant is not always as easy as relying on the equipment manufacturer's recommendations. This issue of the Molykote Smart Lubrication Series highlights some of the potential scenarios that can occur and why selecting the best lubricant is so important for compressors used in the Chemical Industry. The Molykote product line has in it, specialty oils designed for many of these exact applications.
Compressor Oils for the Chemical Industry
Compressors in a chemical plant can be subjected to very demanding applications and as such, the lubricant used is also subject to very harsh conditions that most lubricants are not designed to stand up to. Two of the key constituents of a finished lubricant are the base oil and the additive package.
While the base oil is very important for compatibility with the application, it is often times the additive package that determines a lubricant's success in an application. All oils are not created equal. Gear oil is not hydraulic oil, a spindle oil is not a compressor oil which is not a motor oil and so forth. Gear oils will have anti-wear or extreme pressure additives in them. Compressor oils may have completely different additive packages with special rust and oxidation inhibitors. Motor oils will have detergents among other additives not found in most other oils.
Many industrial processes are not thought to experience major problematic conditions because the process is for the most part inert, this is the case for standard compressors which are compressing air for general plant use. Chemical plant compressors can be part of very complex and reactive, process gas handling systems which are designed to drive and isolate the process, protect the environment and the people surrounding it. Given a process such as this, isn't it reasonable to think the lubricant may be affected adversely by the same harsh process gases we are trying to protect the environment and people from? The answer is yes. Information on a lubricant's base oil is typically well published or advertised but the additive package is much the opposite and as such makes it easy to ignore in the lubricant selection process.
Without knowledge in hand, the end user relies on brand familiarity or the trusted lubricant they have used in many other applications, not realizing that the chemical process before them can be doomed with the lubricant selected because it was selected without regard to additive package. Unknowingly the end user proceeds and soon experiences failure of a compressor because of deposits on the internal surfaces because of possible salt precipitating out of the oil. Failure mode is often times determined to be simply "contamination" all while a fruitless chase ensues to identify the cause of the apparent contamination.
Compressors and vacuum pumps used in process gas systems like anhydrous hydrochloric acid (HCl) need to have lubricants which are completely free of many additives found in multi-purpose oils or motor oils. Even oils labeled as compressor or vacuum pump oil can have additives that will react adversely with the process gas stream.
These reactions can form deposits which quickly promote excessive bearing wear and even more serious wear on larger rotating components such as rotary screws and compression chamber walls. Deterioration of these components can lead to the onset of reduced capacity and ultimate failure of the equipment.
Downtime combined with repair or replacement costs for the equipment can easily kill a budget for a reliability/maintenance professional. Seldom is the lubricant thought to be the suspected culprit until one with lubrication knowledge and process gas experience is able to uncover the mystery. Even the use of the most appropriate lubricant can bring some unwanted features. By using a lubricant which is less reactive because of additive package, it may be the case that life expectancy may be limited for the lubricant.
For example, an absence or reduction in an antioxidant may lead to more rapid base oil oxidation and thus oil changes may need to be done more frequently. This is typically a small price to pay versus the alternatives to the potential scenarios discussed earlier.
To maximize the overall cost effectiveness and promote improved uptime numbers, maintenance based on condition monitoring is always a good option. Oil analysis is one such conditional approach in determining when to perform maintenance activity such as an oil change.
Smart Lubrication Tips
Problem: You see short service life due to varnish built up with the air compressor in your chemical plant.
Solution: You would need to switch to a high-performance industrial lubricant for compressors and vacuum pumps with good oxidation and thermal stability like the Molykote® L-1246 synthetic compressor oil.
This information has been sourced, reviewed and adapted from materials provided by Dow Corning.
For more information on this source, please visit Dow Corning.