Liquid purification or separation – Processes – Liquid/liquid solvent or colloidal extraction or diffusing...
Reexamination Certificate
2001-08-22
2003-02-11
Fortuna, Ana (Department: 1723)
Liquid purification or separation
Processes
Liquid/liquid solvent or colloidal extraction or diffusing...
C210S644000, C095S045000
Reexamination Certificate
active
06517725
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to the lubrication and hydraulic industry, and particularly to an apparatus and a process used for the removal of free, emulsified, or dissolved water from oil, and more generally, from liquids of low volatility.
2. Discussion of the Related Art
Oil is used in lubrication and hydraulic systems. It is widely recognized that the presence of water has deleterious effects on the oil in such systems, the components in the systems, and the operation of the systems. It is well known that corrosion; oil oxidation, chemical wear and tear, reduced bearing fatigue life, and loss of lubricity may result when water contamination enters a lubrication or hydraulic system. These deleterious effects can be directly attributed to water present in free, emulsified or dissolved form.
Consequently, significant efforts have been made to remove water from oil in order to provide optimal performance of lubrication and hydraulic systems. The devices and systems that have been used to remove water contamination include settling tanks or reservoirs, centrifuges, water absorbing filters, and vacuum dehydration oil purifiers. However, these have had significant limitations in either their water removal capabilities, ease of operation, capital costs, or operating costs, as will be discussed.
Settling tanks remove bulk quantities of “free” water from oil based on the difference in their densities and gravitational settling. To be effective in removing “free” water, settling tanks require large residence times and a significant amount of floor space. However, they are ineffective in separating oil-water emulsions and are not capable of removing dissolved water.
Centrifuges accelerate the gravitational settling of water from oil by imposing centrifugal force on the fluid that, in effect, elevates the gravitational force. Centrifuges are effective in removing free water from the oil. However, these centrifuges are generally expensive, and have limited capability of separating oil-water emulsions. They cannot remove dissolved water from the oil.
Water absorbing filters use special filter media that absorbs water from the oil. As the water is absorbed, the media swells, the flow is restricted, and the pressure drop across the filter rises. When the pressure drop reaches a predetermined level, the water absorbing filter is removed, disposed of, and a new filter is installed. These water-absorbing filters are effective in removing free water but have marginal effect in removing emulsified or dissolved water from the oil. In addition, water-absorbing filters have a limited capacity for water. Therefore, they must be replaced once they are saturated with water. Consequently, they are typically only used in applications where trace amounts of water are present. In applications where water concentrations are higher, the cost of continuously replacing water-absorbing filters becomes very high. Several types of vacuum dehydration oil purifiers have been used for oil dehydration. These generally operate under the principle of vacuum distillation, mass transfer of moisture from the oil to dry air, or a combination of the two.
In vacuum distillation, a vacuum is applied to reduce the boiling point of the water. For example, while the boiling point of water is 100° C. (212° F.) at 1013 mm H
2
O (29.92″ Hg) barometric pressure (standard atmospheric pressure), its boiling point at 100 mm H
2
O (approximately 26″ Hg of vacuum) is only 50° C. (122° F.). By applying a sufficient vacuum relative to the temperature of the oil, the water in the oil will evaporate from the oil into the low-pressure air (vacuum), thus dehydrating the oil.
Flowing the oil into a contactor vessel which has a vacuum applied to it by means of a vacuum pump is the typical means by which this is achieved. In order to maximize the water vaporization rate in a given vessel, large surface area-to-volume ratios of oil are preferred. This can be accomplished by means of flowing the oil over structured packing, random packing, cascading plates, spinning discs, or other methods well known in the vacuum distillation and contactor fields. The oil usually enters at the top of the contactor and flows gravitationally downward over the packing, spreading into relatively thin films. The oil collects in the bottom of the vessel where it must be pumped out by means of an oil pump. Examples of these are U.S. Pat. No. 4,604,109 by Koslow and U.S. Pat. No. 5,133,880 by Lundquist, et al. Heat may be added to the oil in order to reduce the amount of vacuum needed.
Vacuum is applied to lower the water boiling point, and to increase the water removal rate. Heat may also be applied to increase the water removal rate. However, great care must be taken in not applying too much heat and/or vacuum because more and more of the lower molecular weight hydrocarbons in the oil will also be vaporized as the temperature and/or vacuum is increased to levels below their boiling points. It should be understood that any liquid with a boiling point less than water will also be removed. This may, or may not be desirable, depending upon the application.
Mass transfer-based systems use similar contactor vessels. However, rather than relying on distillation for removal of the water, dry air or gas is continuously passed countercurrently upwards across the oil that flows downward. Water molecules in the oil will move via a concentration gradient into the relatively drier air. The now humid air is drawn from the contactor by a vacuum pump or blower and exhausted to atmosphere. It is not necessary to heat the oil more than the boiling point of water in order for the water to vaporize. Therefore, less heat and/or vacuum can be used for water removal with a mass transfer-based system than in vacuum distillation systems.
While vacuum distillation and mass transfer systems do remove free, emulsified and dissolved water, they have several drawbacks that have prevented their widespread use. In both systems, liquid level controls are used within the vessel in order to ensure that the oil level does not become so low so that the oil pump runs dry. The liquid level controls also function to ensure that the oil level does not become so high that the vacuum vessel fills with oil. This would reduce or eliminate the water removal efficiency of the vessel and may even lead to the oil entirely filling the vessel and overflowing into the vacuum pump.
Vacuum purifiers are also subject to foaming within the vessels as water is vaporized within the oil. This foam has a lower specific gravity than the oil and can cause malfunctioning of the liquid level controls and a reduction in the performance of the purifier.
Due to the very nature of the use of heaters, controls, pumps, etc., purifiers are relatively complex pieces of equipment. In addition, the type of packing used, the viscosity of the oil, and the airflow rate, limit the flow rates through contactor vessels. This usually results in very large vessels being used relative to the amount of flow. When packaged with all of the necessary oil pumps, vacuum pumps, heaters, controls, electrical panels and connections, the system becomes quite large and expensive. With the number of components and complexity of these systems, the maintenance and operating costs are usually quite high as well.
Due to their ability to remove free, emulsified or dissolved water from oil, vacuum dehydration oil purifiers have become the desired method for water removal from oil. However, the drawbacks associated with vacuum oil purifiers have prohibited these purifiers from being widely used and/or are not practical on the majority of lubrication or hydraulic systems. Because of their relatively large size and costs, they are limited to non-mobile, stationary applications, and are not practical for, use on mobile equipment.
Due to their high capital cost, they are typically not permanently installed in a system unless it is a relatively large, expensive lubrication or hydraulic system. Ins
Burban John H.
Spearman Michael R.
Thundyil Mathews
Zia Majid
Fortuna Ana
Marshall & Melhorn LLC
Porous Media
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