GB2080697A - Filter dehydrator - Google Patents

Abstract

A filter dehydrator for sensing the presence of and separating free water in a transient flow of fluid comprising an inlet and an outlet for the fluid, a mass of water absorptive cellulosic fibers 34 disposed between the inlet and the outlet and surrounded by a rigid porous barrier 35, a filter medium 36 upstream of the absorptive mass for removing solid particles that would block the active surface of the mass and for dispersing water droplets in the fluid. The fibre mass 34 is formed from water-insoluble cross-linked carboxymethyl cellulose fibres which swell in the presence of free water. The barrier 35 may consist of four layers of polyvinyl chloride coated fibre glass mesh screen. <IMAGE>

Description

SPECIFICATION Improved filter dehydrator The present invention relates in general to an improved filter dehydrator useful for removing water from fluids which are water immiscible. For example, a filter dehydrator in accordance with this invention has been successfully used to remove water from the following: liquid hydrocarbons, such as gasoline, diesel fuel, and transformer, insulating, hydraulic, lubricating and turbine oils; synthetic oils; silicones; and various gases.

It is critically important that aviation fuel for today's high-performance aircraft engines be of high quality. Typical aircraft fueling systems include efficient filtration and water separation equipment.

However, it is desirable that a system include a means which will prevent unacceptable fuel from passing into the aircraft. The filter dehydrator in accordance with this invention is ideally suited for the removal of free water from aviation fuel. Therefore, the discussion and examples herein will focus on this particular application of the invention.

Many fuel-water separator systems include some type of coalescer and filter separator elements which retain the solid contaminants contained in the fuel flowing through the system and are effective to coalesce and remove the water content therein. In removing the solid contaminants of the transient fuel, the elements gradually offer increased resistance to the flow of fuel until the attained pressure drop across the element becomes greater than the system pressure can attain. If the element is not replaced before this occurrence, the element will malfunction and discharge into the aircraft fuel tanks a large quantity of contaminants, both solid and water.Also, it has been found that in certain circumstances the fuel being passed through the fuel water separators may contain surfactants and the like, causing the coalescer elements to be inoperative or ineffective in coalescing and removing the water content of fuel.

As a result of the aforementioned problems, water sensitive flow monitors have been designed to block the flow of fuel containing an unacceptable concentration of free water therein. Military specification MIL-M-81380B(AS) dated September 1975 has even been written to specify the effectiveness of such flow monitors.

U.S. Patents 3,528,546 to R. W. McPherson and 3,528,547 to R. E. Adams et el., disclose water sensitive flow monitors containing respectively a grannular bentonite material or an algin material provided in such a water sensitive flow monitor. U.S. Patent 3,572,510 to S. J. Lyda discloses a monitor filter employing a polyethylene oxide between a fiberglass filter tube and a cellulosic fiber confining filter. It has been disclosed to include in a monitor of this general configuration a fail-safe mechanism which automatically shuts off the flow of liquid hydrocarbon fuel.

U.S. Patent 3,710,822 to S. J. Lyda discloses a shutoff valve inside the monitor of the construction of the above referenced Lyda patent. Lyda Patent 3,710,822 also makes reference to other shut-off devices, such as a compressed coil spring held undertension by a strip of hydrophilic paper or a plastic ball acting in conjunction with an aluminum ring.

One such shut-offdevice is described in U.S.

Patent 3,406,827 to G. J. Topol, et al. and is marketed by Keene Corporation under the name "Pet rnguard." This product includes a fiberglass layer surrounding a phenol formaldehyde resin impregnated cellulosic material. The monitor element has a reduced thickness near the hydrophilic paper strip to allow passage of some water to trigger the unit as a fuse. Necessarily, at least some water must pass through the filter element into the outlet in order for the unit to operate as a fuse monitor.

It is the object of the present invention to provide a new improved filter dehydrator which will block the flow of fuel containing an unacceptable concentration of watertherein and remove and retain the water from the fuel.

The present invention is an improved filter dehydrator comprising an element having an inlet for fluid to be filtered and an outletforfiltered fluid; a confined passageway establishing communication between said inlet and said outlet; a mass of water absorptive cellulosic fibers comprising a waterinsoluble cross-linked carboxymethyl celulose fiber medium disposed within said passage permitting the passage of fluids therethrough while swelling upon the presence of free water to block the flow of fluid between said inlet and said outlet; a rigid porous barrier material adjacent and upstream of the absorptive medium, and having pore openings sufficient to allow expansion of the absorptive medium as the said medium retains water; and a filter means disposed within said passage upstream of said water absorptive mass for removing substantially all solid particles that would block the active surface of said mass.

The basic filter dehydrator on which applicant's invention is an improvement is described in United States patent application Serial No. 955,016, filed October 1978 by Estabrooke. It is comprised of layers of water absorptive but insoluble carboxymethyl cellulose fiber and fiberglass. The apparatus simultaneously serves dual functions of a filter and dehydrator.

It has been discovered that the water retention capacity of the cellulosic fibers of a filter dehydrator can be substatially improved by placing a rigid porous material upstream of the water absorbing cellulosic fiber media and the filtering media, such as the fiberglass material. The function of this barrier is to permit the expansion of the water absorption media. Therefore, the barrier must have pore openings sufficiently large to allow such expansion, but insufficient for filter material to transgress the barrier and compress the water absorption media.

In one embodiment the porous barrier consists of four layers of 18 x 14 mesh screen having a total thickness of 0.03 inches (0.0756 centimeters). A polyvinylchloride coated fiberglass is an ideal material for the screen. The screen openings are preferably less than 0.25 inch (.6350 centimeter) and ideally 0.06 inch (.1424 centimeter).

This improvement in the filter dehydrator car tridges doubles the water retention capacity of the filter. Since the filters need to be replaced less fre quently, the costs of filtration are reduced approxi mately 50 percent.

The foregoing and other objectives, features and advantages of the invention will be more readily understood upon consideration of the following detailed description of certain preferred embodi ments of the invention, taken in conjunction with the accompanying drawings wherein the same reference number refers to the same or similar elements in each of the several views.

FIGURE 1 is a schematic elevational view, partially in section, illustrating an embodiment of the present invention.

FIGURE 2 is a schematic enlarged elevational view, partially in section and partially broken away, illustrating one of the improved filter dehydration elements shown in FIGURE 1.

FIGURE 3 is a graph of differential pressure plotted against milliliters of retained water, illustrating the characteristics of the improved filter dehydrator constructed in accordance with the present invention compared to the prior art filter dehydrator.

The present invention has application in a number of possible environments. It can typically be used in conjunction with other conventional fuel-water separator systems or as a single filter dehydrator unit to filter and remove water and solids from a fluid and shut off the flow of fluid before these contaminants exceed acceptable levels.

Referring now with particular reference to FIGURE 1, there is illustrated a filter dehydrator element or assembly 11 as used to filter aviation fuel in the form of a container having a cupshaped housing 12 provided with a lid or cover 13 sealably closing the top of the housing 12, such as by nut and bolt fastening means 14 between the cover 13 and housing 12 and compressing an O-ring 15therebetween.

The housing 12 is provided with an inlet 16 and an outlet 17 and a manifold 18 is mounted in the bottom of housing 12 in communication with the outlet 17.

The manifold 18 is provided with a plurality of openings each for receiving the open end of an elongate upstanding, hollow, cylindrical water sensitive filter dehydrator element 19 open at one end 21 and closed at the other end 22. Each element 19 is sealably engaged in the manifold aperture such as by a friction fit or O-ring seal and typically held in upstanding relation thereto by a support assembly which can include a top retainer plate 23 which is operatively connected to manifold 18 by an upstanding bolt 24 and an associated nut 25 and engages the closed end of the element 19. It will be apparent that access can be had to the interior of assembly 11 by removing the nut and bolt fastening means 14 and removing the cover 13 to expose the assembled elements 19.After removing nut 25 from upstanding bolt 24 the retainer plate 23 can be lifted from the assembly and one or more of the elements 19 removed, inspected and/or replaced in the manifold 18.

The direction of fluid flow through the assembly 11 is indicated by the arrows. Fluid enters through the inlet 16, passes radially inward through the ele ments 19 through the open end 21 into the manifold 18 and exits through the outlet 17.

In operation, the fluid to be treated is caused to enter the housing 12 through the inlet 16 and then caused to flow to the outlet 17 through the filter dehydrator elements 19. Fluid flow is from the outside to the inside of these elements 19 and then to outlet 17 through the manifold 18. The assembly 11 is disposed in fluid communication between a fuel supply and an aircraft to which clean dry fuel is to be delivered. It can be provided in fluid communication between a fuel-water separator unit and an aircraft. it will be appreciated that the assembly 11 can be stationary in nature, or can be mounted in a refueler vehicle and be an integral part of mobile refueling systems. During operation of such a system, the filter dehydrator elements 19 are inert to clean dry fuel containing no undissolved water.When traces or slugs of free water pass into the assembly 11, the elements 19 will absorb water and prevent passage of water into the outlet 17. The elements will sense water and/or solid particle contamination immediately by a build up of water in the water absorptive medium and/or solid particles in the filter medium, and for unacceptable levels of water and/or solid particles the elements 19 will register a practically instantaneous increase in pressure drop or a decrease in flow rate if the housing 12 is not provided with a differential pressure gauge. The pressure drop occurs because the water in the absorptive medium 34 and/or the solid particles in the filter medium 36 form a composite mass cutting off the flow of fuel therethrough. The bursting strength of elements 19 is greater than the average system pressure output.Thus, the filter can provide a filtering function for aviation fuel as well as a dehydrating function which will permit acceptable fuel to pass, but once water contaminated fuel is present, the assembly completely blocks off any flow there through.

The filter dehydrator elements 19 have a structure as shown in FIGURE 2. Each element includes layers of material which operatetogetherto produce water separation and other particle contaminant filtering from a fluid to the point at which the fluid flow is completely shut off by collected water and solids.

The innermost layer is a perforated support tube or grid structure 31 surrounded bya barrier which includes a retaining screen 32 and two layers of a filter paper 33. A water absorptive cellulosic fiber medium 34 is positioned around the filter paper 33 and is surrounded by four layers of a porous barrier 35. The porous barrier 35 is surrounded by a fiberglass filter medium 36. The filter medium 36 is in turn surrounded by a filter media retaining wrap 37 and an outer cover 38. These structural portions of element 19 are held in their wrapped condition by end caps 39 and 40.

It was discovered that in combination with the other structural portions of the element 19 and particularly the fiberglass filter medium 36 water absorptive cellulosic fiber material 34 serves as an excellent water absorptive medium. As mentioned above such water insoluble wet cross-link~d carboxymethyl cellulose fiber matal is described in detail in United States Patent 3,589,364 to W L.

Dean, et al. This material which is sold in powder, fiber or sheet material will absorb approximately 25 times its own weight of water and retain the same even at a centrifugal force of 1600 gravities. In the embodiment illustrated two wrapped layers of sheet material, each approximately .049 inches (.124 centimeters) thick with a ream weight (24 x 36) of 247 grams per square meter are wrapped over one another to avoid thin spots in the material.

It has been discovered that in the filter dehydrator in accordance with the present invention the rate of water takeup in the water absorptive medium 34 must be such that all free water is retained within the transit time of the fluid through the monitor. The rate at which water is retained is a function of the surface activity which is influenced by the ratio of water drop mass to surface area and the display and condition of the surface of the water absorptive medium.

Accordingly a suitable medium or media upstream of the absorptive layer should remove all or substantially all solid materials that would block the active surface, emulsify or disperse the water droplets passing therethrough, and impede the release of water from its exiting surface. Fibers coated with a phenolic or similar resin with a surface energy such as of about 35 ergs/cm2 commercially available as fiberglass, are capable of filtering out solids having a particle size of less than one micrometer by proper selection of fiber size and mass density. Further, this material by its surface activity, deters the release of water drops but permits their migration to the exit surface which is adjacent to the absorptive medium 34. The pore size, formed by appropriate selection of fiber size and control of mass density, emulsifies or disperses water droplets.

The fiberglass filter medium 36 also provides a spring-like expansion space for the water absorptive medium to enable absorption and collection of the large volume of water in the element 19 which the water absorptive medium 34 can hold.

The underlying barrier can also serve to allow swelling of the water absorptive medium but must prevent migration of the water absorptive medium 34 which absorbs water to the point of becoming gelatinous. Consequently the filter paper 33 is selected to have a filter rating to prevent passage of the saturated cellulosic fiber medium 34. The retaining screen 32 keeps the filter paper 33 from breaking through the openings in the support grid 31 at high pressure differential.

The elements 19 are formed by wrapping the layers 32, 33, 34, 35,36, 37 and 38 around the support tube 31 and adding the end caps 39 and 40. The end caps 39 and 40 are formed by disposing the respective end of the wrapped assembly in a suitable quick setting resin material such as a polyester resin which is inert to the fluid being treated.

As an illustrative preferred embodiment of the present invention the innermost tube or grid structure 31 is made of a polypropylene plastic. The retaining screen 32 is a vinyl coated fiberglass insect screen 18 x 14 lines per square inch. The filter paper 33 is two layers of resin impregnated paper stock having a porosity of approximately 75 micrometers.

The water absorptive medium 34 is two sheets of water-insoluble wet cross-linked sodium carboxymethyl cellulosic fiber, each .049 inches (.124 centimeters) thick with the same ream weight given above.

Barrier 35 consists of four layers of polyvinylchloride coated fiberglass mesh screen having 18 x 14 lines per square inch. The openings in the screen are about 1/16 inch square. The thickness of the 4 layer barrier 35 is approximately 1/32 inch.

Four layers of screen have been found to be far superior to a barrier 35 composed of only two layers of screen. The filter cartridge of the four layer barrier held about 52 milliliters (ml) of water as compared to only 30 ml retained by a cartridge having a two layer barrier and 23 ml by a cartridge having no barrier.

The 18 x 14 mesh is idealy suited to maximize the expansion and water absorbing capabilities of medium 34. Larger size mesh does not appear to be as effective.

Since the critical function of barrier 35 is to permit maximum expansion of the absorptive medium 34, it must be placed upstream of the fluid flow, In Figure 2 the fluid flow is from outside the filter dehydrator cartridge and barrier 35 surrounds absorptive medium 34. Obviously, if the fluid flow was from the opposite direction barrier 35 would be placed on the opposite side of absorptive medium 34.

The filter medium 36 can be selected from a variety of suitable materials. For example, resin impregnated cellulose and blends of resin impregnated cel- lulose/fiberglass combinations are suitable. An excellent filter medium can be constructed using two wraps of phenolic resin impregnated onehalf inch loft fiberglass compressed to a mass density of approximately 10 pounds per cubic foot having fiber diameters of approximately .0005 inches (.000127 centimeters). It has been found that in such an embodiment as this, fiberglass compressed to a density of approximately 6 pounds per cubic foot will not provide satisfactory dispersion of water droplets.

Although filter medium 36 fulfills both filtering and dispensing functions, these functions could be performed by separate layers of different materials or even by a series of cartridges.

The retaining wrap 37 is a scrim cloth and the outer cover 38 is a perforated oil board. All materials for the parts of element 19 are inert to the fluid being treated.

FIGURE 3 illustrates the performance of element 19 by comparison of the water retention capabilities of the absorptive medium 34 both in the absence and the presence of barrier 35 between the absorptive medium 34 and the filter medium 36. As shown in the graph, water retention of the absorptive medium 34 is shown in milliliters of water collected in element 19 as pressure builds up thereacross. The graph represents pressure build-up at a jet fuel flow rate of GPM with a water injection rate of 80 parts per million.

Elements 19 having an inside diameter of one inch and an outside diameter of one and three-quarter inch have been constructed to have a flow rate one gallon per minute per inch of length with a differen tial pressure not exceeding 8 psi. Elements thus con structed in accordance with this invention will absorb 17 ml of water per inch of length.

It has been discovered that elements 19 which have been placed in operation and become satu rated with water blocking off flow of fuel can be removed from the housing 12 and dried out. After a drying operation wherein the absorbed water is removed, the element 19 can be put back into service and operate as a successful dehydrator.

Claims (7)

1. A filter dehydrator comprising: (a) an element having an inlet for fluid to be filtered and an outlet for filtered fluid; (b) a confined passageway establishing com munication between said inlet and said outlet; (c) a mass of water absorptive cellulosic fibers comprising a water-insoluble cross-linked carboxymethyl cellulose fiber medium disposed within said passage permitting the passage of fluids therethrough while swelling upon the presence of free water to block the flow of fliud between said inlet and said outlet; (d) a rigid porous barrier material adjacent and upstream of the absorptive medium, and having pore openings sufficient to allow expansion of the absorptive medium as the said medium retains water; and (e) a filter means disposed within said passage upstream of said water absorptive mass for removing substantially all solid particles that would block the active surface of said mass.

2. The filter dehydrator of claim 1 wherein said porous barrier comprises layers of a vinyl coated fiberglass mesh screen having 18 x 14 lines per square inch.

3. The filter dehydrator of claim 2 wherein said porous barrier comprises four layers of the said mesh screen.

4. An improved filter dehydratorfor use in a system for sensing the presence of and separating water in a transient hydrocarbon fluid, the system comprising: (a) a vessel having a fluid inlet and a fluid outlet; (b) a substantially water-insoluble cross-linked sodium carboxymethyl cellulose fiber medium; (c) a filter medium means upstream of said absorptive medium for dispensing water droplets in the stream of hydrocarbon fluid and comprising a fiberglass medium having an average fiber diameter substantially inches inches and a density in the range of substantially 10 pounds per cubic foot; (d) a fiber medium retaining barrier means and a medium support structure downstream of said fiber medium; and (e) a porous barrier surrounding the cellulose fiber medium.

5. The filter dehydrator of claim 4 wherein said porous barrier comprises layers of vinyl coated fiberglass mesh screen having 18 x 14 lines per square inch.

6. The filter dehydrator of claim 5 wherein said porous barrier comprises four layers of the said mesh screen.

7. The filter dehydrator substantially as described herein with reference to the accompanying drawings.