An important part of the purification process is “Filtration”.  In plant filtration of any industrial fluids can be a literal lifesaver for that company’s expensive equipment.  Today’s high performance components are very expensive, and the price of skilled labor required to replace components continues to escalate.  But the biggest cost to most companies in the event of system shutdown is the downtime itself.  Filtration is the separation of a liquid / solids mixture.  Filtration involves passing a liquid through a barrier that retains the solids, or prevents the solids from being carried through the barrier with the liquid.  The barrier may be made from many different types of materials, and made in the form of a screen, or a bed of solids.  CFE designs a wide range of stationary and portable filtration systems to meet our customer’s needs for complete filtration.  These filtration systems may be designed for either automatic or manual operation.  Many filtration systems require the use of pumps, motors, heaters, control valves, electrical control center, conduit, piping, and more.  To achieve more effective removal of contaminants, filtration equipment is often combined with other methods of purification, such as coalescing, separation by settling, separation by absorption, chemical separation by air   stripping, chemical separation by vacuum dehydration or chemical separation by vacuum distillation.

Industrial oils are most commonly concaminted by water, dissolved hydrocarbons and solids. Water in oil can exist in the form of free water, emulsified water and dissolved water. Dissolved hydrocarbons can enter the oil via leaking compressor seals, while solids can consist of rust particles suspended in the oil.

 

Dissolved gases can cause the following undesirable effects in lubricating oil:

• Lowering of flash point, causing an explosion hazard
• Lowering of the viscosity, which lowers the lubricating capacity
• Increased rates of corrosion

There are four methods of dehydrating oils:

• Centrifuging
• Coalescing
• Air stripping
• Vacuum dehydration 

Centrifuging and Coalescing can remove almost all water but they cannot remove dissolved water. They also cannot remove dissolved hydrocarbons or hydrogen sulfide.

 

Vacuum Dehydration & Air Stripping

Vacuum dehydration and Air Stripping employ two methods that remove free, emulsified and dissolved water, entrained air, dissolved light hydrocarbons and hydrogen sulfide.

 

The vacuum dehydration unit consists mainly of a vacuum vessel with the vacuum being pulled by a vacuum pump, typically to 750 mm (29.6 Hg).

 

A positive displacement inlet pump circulates contaminated oil from a reservoir through a pre-filter that removes solids.  The oil continues through a pre-heater, which raises the oil temperature to approximately 170 degrees F. The flow-through heater is specifically designed to prevent localized hot spots and carbonization of the oil.

 

The heated oil then proceeds, still under pump pressure, to the vacuum vessel. In this vessel, which remains under 26” to 29.9” of vacuum, the oil creates a film with turbulent flow characteristics, which combined with heat and vacuum, promotes dehydration, de-aeration and de-gasification. A valve, which is controlled by level switch, maintains the level in the vacuum vessel by re-circulating excess flow back to the inlet pump.

 

Water, hydrocarbons and other condensables are flashed off and condensed downstream in a refrigerated condenser before they reach the vacuum pump. The condensate is automatically drained from the unit, while the water vapor is vented though the vacuum pump exhaust. A second positive displacement outlet pump feeds the conditioned oil back to the reservoir in a continuous cycle. A constantly flooded suction enables the outlet pump to pull against the vacuum at the rated capacity of the unit. A final step in the process often consists of a 0.5 micron polishing filter to remove any fines remaining in the oil.

 

Conditioning is controlled on a timed basis and samples are taken before and after conditioning for laboratory analysis to confirm that the oil has returned to its original specifications. The entire process is normally automatically controlled by a programmable logic controller (PLC), but manually controlled units are also available.

 

If an abnormal amount of water or volatiles is encountered, the temperature and vacuum sensors may signal a valve to divert the flow back to the conditioner for further processing or the process may be slowed by other means.

 

This process generally will remove solids and sludge down to five microns (or less if required) and water content from more than two percent down to ten ppm. Air and dissolved gases can be removed from ten percent down to 0.1 percent by volume.

 

While most lubricating oils contain less than 1% by weight of additives, such as calcium, phosphorus, sulfur, zinc, molybdenum, silicones and polymers, etc., the oil conditioning process will not remove any additives that were previously in the oil. The purification process will also significantly decrease the acidity as is evidenced by a decrease in the total acid number.

 

Coalescer/Separator System

 

Description of the process

The coalescence of droplets can occur whenever two or more droplets collide and remain in contact long enough for the continuous-phase film, which exists around each droplet, to become so thin that the hole develops and allows the liquid droplets to become one body. Clean systems with high interfacial tension will generally coalesce rapidly. Particulates and polymeric films tend to accumulate at the droplet surfaces and reduce the rate of coalescence. This can lead to build-up of coalescence, which can significantly enhance the rate of mass-transfer between phases.

 

Coalescers

The small drops of fine may be caused to coalesce and thus become larger by passing the dispersion through a Coalescer. The enlarged drops then settle more rapidly. Coalescers are mats, beds or layers of porous or fibrous solids whose properties are especially suited for this purpose. It has been found in studies that coalescence is promoted by decreased fiber diameter. A minimum bed density is required to achieve complete coalescence, depending on the system characteristics. Wetting of the fibers by droplets of the dispersed phase is not necessary for good coalescence.

 

The Filter/Coalescer/Separator System

The Custom Filtration Equipment Coalescer system removes free and emulsified water down to saturation level. The saturation level is a function of the type of oil, the kinds of additives in the oil and the temperature of the oil. For typical ISO 32 turbine light oil at 100 deg. F the saturation level is approximately 150 ppm.

 

The Pre-filter

The oil first passes through either a 0.5-micron or a 5-micron pre-filter. The pre-filter removes 98% of dirt particles larger than 0.5 or 5 micron respectively. This prevents the Coalescer cartridge from being plugged pre-maturely.

 

The Coalescer Element

From the pre-filter, the oil then flows to the Coalescer / Separator housing, where it enters from the bottom, mobbing through the Coalescer cartridges. The oil travels from the inside to the outside of the cartridge.

 

The Coalescer cartridges filter any remaining dirt particles down to 10 micron and then coalesce (join together) all emulsified and free water particles into droplets large enough to settle out of the oil. The water collects on the outside of the cartridge.

 

Coalescer cartridges are made of fiberglass material, which separates immiscible liquids with different densities such as water from oil. Large (coalesced) water droplets break away from the cartridge surface and sink to the bottom of the filter housing, where they are automatically drained by a dual-specific gravity drain valve.

 

The Separator Element

The oil continues through the separator cartridge, which are in the same housing as the Coalescer cartridges. The oil passes from the outside to the inside of the separator cartridges.

 

The separator cartridge is a Teflon-coated screen, which repels 100% of any suspended water from passing through it with the oil. The oil is thus separated from any remaining water.

 

The Optional Final Filter

The optional final filter is a 0.5-micron water-absorbing cartridge, which removes any free or emulsified water remaining in the oil, as well as any dirt particles over 0.5 microns.