Liquid purification or separation – Recirculation – Serially connected distinct treating or storage units
Reexamination Certificate
2001-12-28
2004-07-20
Walker, W. L. (Department: 1723)
Liquid purification or separation
Recirculation
Serially connected distinct treating or storage units
C210S251000, C210S257200, C210S261000, C210S295000, C210S314000, C210S321640
Reexamination Certificate
active
06764598
ABSTRACT:
CROSS-REFERENCES TO RELATED APPLICATIONS
Not Applicable
SEQUENCE LISTING, TABLE OR COMPUTER PROGRAM
Not Applicable
FIELD OF THE INVENTION
This invention relates to filtration to remove emulsified water from various types of liquid hydrocarbons, such as fuels and other solvents, where the emulsification is accomplished through the use of surfactants.
BACKGROUND OF THE INVENTION
When water is present in a fuel or other solvent, the preferred method of removal is through the use of a hydrophobic filter screen that prevents the passage of water. Such a screen can become covered with water, and the covering prevents the passage of fuel through the filter. Water may then be removed by backflushing or sweeping the surface with a flow to carry away the trapped water. However, the need for backflushing imparts an additional function that suspends the action of the filter for a period of time.
Other methods have used hydrophobic prefilters, but these suffer from the same need to backflush or sweep with a flow to remove the water on the filter surface.
In order to obviate the need to backflush, hydrophilic filters are often chosen for the first filter in a system. The hydrophilic filter will allow the passage of water into its interior, where the particles are absorbed onto the filter medium surface and there they coalesce into larger globules of water. These then eventually break free and pass into the gap separating the first filter from the second filter. There a stream of fuel carries away the water that has passed the first filter. However, when the fuel being filtered contains an emulsifying agent, the particles of water will remain suspended and pass through the first filter without coalescing, and continue on to the second filter. The emulsified water will then pass through this last filter under pressure, and continue to contaminate the fuel.
In this typical construction of the prior art used to remove water from jet fuel, a conventional fuel-water separator is usually comprised of two different filter cartridges. The two cartridges are arranged in series. The first is a water-coalescing cartridge, and the second is a water-separating cartridge. This latter cartridge is hydrophobic and operates to exclude water as described. Fuel contaminated with water passes through the coalescing filter cartridge first, which has a pore size range of 1 &mgr;m to 100 &mgr;m, preferably in the range of 1 &mgr;m to 20 &mgr;m. The coalescing cartridge usually has a pleated design or a string wound design utilizing hydrophilic material, such as cotton. Fine water droplets are absorbed by the filter fibers due to their hydrophilic surface property. As more and more water is absorbed in the filter cartridge, agglomeration occurs and larger water globules (greater than 100×100 mesh typically used) are formed. The jet fuel flowing through this first cartridge then carries these away. Then the jet fuel containing water globules flows into the separation cartridge, which is made from 100×100 mesh PTFE screen. In the prior art, the mesh size must be this large to prevent the buildup of water on the surface, which will occur with smaller mesh sizes. The jet fuel freely passes through the screen, but, due to its hydrophobic surface property, the PTFE screen retains the water globules and prevents their passage. The retained water globules then settle down to the bottom of the water collection chamber.
Surfactant fuel additives are often added to jet fuel for the purpose of cleaning the aircraft fuel system and allowing the engine components to operate more effectively and efficiently at higher temperatures. One particularly useful additive is SPEC-AID 8Q462, as sold by BetzDearborn In., Trevose, Pa., which is known as a +100 additive because it allows engine operation temperature to be increased by up to 100 degrees Fahrenheit. However, the side effect of surfactant fuel additives is that they break down the water droplets to much smaller sizes (1 &mgr;m to 10 &mgr;m), forming a stable water emulsion in the jet fuel. Each water droplet is surrounded by surfactant, the molecules of which consist of a hydrophilic head functional group (hydrophilic head) and a hydrophobic tail functional group (hydrophobic tail). The hydrophilic heads of the surfactant molecules attach to the water droplet and the hydrophobic tails face outward, where they are solvated by the jet fuel and form a stable emulsion. Very small droplets of water bound by surfactant thus characterize this emulsion. Since the surfactant-coated water droplets are thus hydrophobic at their surface, they will not be absorbed in the hydrophilic coalescing filter cartridge of the prior art. Therefore, there will be no water coalescing effect in the coalescing filters. Consequently, the jet fuel and the fine surfactant-bound water droplets freely pass through the first filter without coagulation, remain dispersed in the flow stream and reach the PTFE screen filter cartridge, where, due to the much larger pore size of the screen, they pass through and continue to contaminate the fuel.
In the instant invention, the filter medium is chosen to be hydrophobic in contrast to the accepted prior art. However, since the water molecules are bound with surfactant, and are now functionally hydrophobic, the water is not repelled by the hydrophobic filter medium, and passes into the filter. Because the tail of the surfactant molecule is hydrophobic, it is attracted to the surface of the hydrophobic filter medium. At the surface of the hydrophobic filter, the surfactant-bound water attaches and waits until a larger build-up occurs. As the surfactant-bound water molecules pass into and build up on the surface of the hydrophobic filter, the water agglomerates, breaking the boundary of the surfactant. The coagulated water then passes out of the filter into the stream between the first and second filter.
Similar to the conventional fuel-water separator, the instant invention is also comprised of two filter cartridges: A water coagulation cartridge and a hydrophobic water separation cartridge. But here the similarity ends. The water coagulation cartridge of the instant invention is a hydrophobic depth filter cartridge. The filter medium can be nylon, polyester, polyvinylidene difluoride or polypropylene. As discussed above, the surfactant-coated water droplets have a hydrophobic surface when surfactant fuel additives are present in the jet fuel. As the jet fuel and the now “hydrophobic water droplets” flow through the hydrophobic filter cartridge, the “hydrophobic water droplets” attempt to be absorbed by the hydrophobic filter fibers and become contained within the filter. As more water droplets are absorbed in the cartridge, multi-layer water/additive globules are formed and, when they become large enough, are carried away by the jet fuel flow. A globule of water/additive is comprised of multiple water droplets. Its size is usually 5 to 10 times larger than that of a single emulsified water droplet, which would typically be in the range of 1 &mgr;m to 10 &mgr;m. This action within the filter greatly reduces the degree of water emulsification in the jet fuel. However, the globules are still in the range of micron sizes and don't settle down easily. The second function of the water coagulation filter is to separate dirt, bacteria, and other suspended solids from the jet fuel.
Next the jet fuel and water/additive globules flow to the water separation filter cartridge, which is formed with a hydrophobic membrane (e.g., PTFE) of 0.1 &mgr;m pore size, which is approximately three orders of magnitude smaller than used in prior art technology. Use of a filter with such a small pore size with the technology taught in the prior art will result in rapid blocking of the filter surface by water and shut down of the fuel flow. A bypass-flow or cross-flow is maintained on the membrane surface at the feed side. The cross-flow is used to sweep the membrane surface with high shear motion and to carry the suspension away from the filter surface, while the fuel componen
Jen Chang-Wei
Thierry Montfort
Yu Guanghua
Filtration Solutions, Inc.
Menon Krishnan S.
Myers & Kaplan LLC
Walker W. L.
Williamson, III Thomas
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