Particularly, the present invention is directed to an economical filter assembly that removes contaminants from pressurized fluids that produce nonhazardous waste such as liquid. subcritical, or supercritical carbon dioxide. by using an array of small filters that are contained in filter housings having a cross-dimension substantially similar in size to the cross-dimension of the pipe used throughout the fluid system to satisf the needs of the filter assembly in the fluid system.

Further, the present invention relates to a method and system of using the filter assembly to filter pressurized fluid solvents containing undesirable concentrations of contaminants.

Description of Related Art Fluid systems have a wide variety of functions and applications. One such function is to use a fluid system to clean a substrate that can be put into use or re-used after cleaning. Such fluid cleaning systems often utilize a fluid solvent that entrains the contaminants so that they are separated from the substrate. For example, such fluid systems

can be used for cleaning fabrics, delicate electronic components, and similar sensitive substrates. These fluid systems typically use water, perchloroethylene, petroleum, and other low pressure liquid solvents for cleaning the desired substrate.

Such conventional fluid systems generally have been considered satisfactory for their intended purpose. Recently, however, the desirability of employing these conventional fluid systems has been questioned due to environmental, hygienic, occupational hazard, and waste disposal concems, among other things. For example, perchloroethylene frequently is used as a solvent to clean delicate substrates, such as garments and similar fabrics in the process referred to as dry cleaning. The use and disposal of perchloroethylene is regulated by environmental agencies, even though only small amounts of this solvent may be introduced into waste streams. Such regulation results in increased costs to the user, which in turn, are passed to the ultimate consumer. It is therefore advantageous to use a fluid system that cleans substrates utilizing a solvent that does not have the disposal concerns of convei. tior. al solvents like perchloroethylene.

In order to avoid the disposal concerns associated with some conventional solvents. pressurized liquid or'dense fluid"solvents have been used to clean various substrates. Dense fluids are widely understood to encompass gases that are pressurized to either subcritical or supercritical conditions so that they are in a liquid state. In particular, carbon dioxide has been pressurized to a liquid state or a subcritical or supercritical condition so that it can be used as a solvent to clean substrates like clothing and precision metal parts.

Carbon dioxide and other dense fluids do not have all of the handling concerns associated with some conventional solvents, but do require components with considerable structural integi because of the high operating pressures required.

Because the use of dense fluids as cleaning solvents requires a pressurized system, it can be challenging to remove contaminants from the dense fluid so that it can be re-used. For example, expired U. S. Pat. 4, 012,194 issued to Maffei discloses a garrnent cleaning process that uses liquid carbon dioxide. After passing through the garent, the liquid carbon dioxide solvent is circulated through an evaporator for removal of impurities, and then condensed by a refrigerated storage unit before being retumed for further use.

When practiced on a commercial scale, such an eaporation/condensation process has the potential to be capital intensive and to consume a lot of energy in operation. Likewise. U. S.

Pat. 5, 267, 455 and PCT publication \VO 94/01613 to Dewees et al. are directed to a dry cleaning system that uses supercritical carbon dioxide for cleaning clothing. Once cleaning is accomplished by agitation within a vessel, all of the supercritical carbon dioxide within the vessel is drained to a vaporizer vessel for removal of entrained contaminants and then condensed for reuse, As with the technique disclosed by Maffei. this method of cleaning supercritical carbon dioxide also involves potentially costly vaporization and condensation and risks soil redepositin on the substrate during the cleaning process.

In other known processes where a form of carbon dioxide is used as the cleaning solvent, the solvent is not recovered at all. For example, U. S. Pat. 5, 279, 615 issued to Mitchell et. al., is directed to a method of cleaning fabric using dense carbon dioxide. In addition to the dense carbon dioxide, Mitchell et. al. further require the use of a nonpolar cleaning adjunct to clean the fabric. After cleaning, the dense carbon dioxide is directed to an expansion vessel so that the extracted soils can be collected, while the carbon dioxide is apparently vented. Consequently, none of the dense carbon dioxide is recovered by this process and fresh supplies of dense carbon dioxide would be continuously needed. As with the evaporation/condensation processes, this process is not optimal from both a cost and

processing standpoint because it constantly requires a fresh supply of dense carbon dioxide. and also risks soil redeposition on the substrate during the cleaning process.

In U. S. Pat. 5,316, 591 issued to Chao et al., a method of cleaning a substrate by cavitating a liquefied gas, such as liquid carbon dioxide, is disclosed. In the Chao et al. method, the substrate is placed in a cleaning chamber filled with the liquefied gas, and a sonicating horn or similar cavitation-producing means is used to cavitate the liquefied gas for a sufficient time to remove undesired material from the substrate. In one embodiment of Chao et al., the liquefied gas is simply purged after the cleaning process is complete. In another embodiment, a closed loop is specified, such that all of the liquefied gas is recirculated after first being purified by either vaporization, filtration, or an undefined combination of the two. Chao et al. do not provide of a description of the type of filtration contemplated nor do they address any complications that may be encountered by virtue of a pressurized system.

Regardless of whethm the fluid system employs conventional solvents or pressurized solvents, many cleaning methods require that the contaminated substrate be held within a bath of fluid solvent for a specific period of time. These methods may lead to recontamination of the substrate and reduced efficiency if the solvent is not continuously purged of its contaminants as the cleaning process is in progress. Further, the known methods do not address the high capital costs associated with using conventional large-size filters for the filtration of the cleaning solvent. In addition, the methods presently known in the art for cleansing pressurized solvents rely on costly and energ intensive unit operations.

A variez of methods and devices have been developed to filter contaminants from fluids. The contaminated fluid generally is directed through one or more filters that are permeable to the fluid but able to capture and accumulate the contaminants entrained in the

fluid. In this manner, the majority of contaminants become deposited and held in the filter while the fluid flous therethrough. The accumulated contaminants are subsequently removed from the system. A wide range of filters are available, varying in size. design, construction. porosity and filter medium material. The filter, however, must be appropriate for the fluid being used and for the type and amount of contaminants anticipated.

The use of filtration, however, is not without certain operational and/or functional limitations. As contaminants become trapped in the filter, fluid flow eventually may be inhibited because of filter medium clogging. The filter system therefore must be monitored on a regular basis to determine when cleaning or replacement is required. To accommodate the amount of contaminants removed from the fluid, and to obtain prolonged filter system use life, filters having a diameter greater than about 4 inches, are often used to increase the contaminants holding capacity of the filter system before cleaning or replacement is required. Although filters greater than 4 inches in diameter may not be required in fluid systems having low contamination levels. such filters are typically required in fluid systems for cleaning textiles and other substrates.

Furthermore. these larger-sized filters are often utilized where the fluid is considered noxious or hazardous. By prolonging filter life, the frequency with which the filter system must be cleaned or replaced will be lessened and. thus, exposure to the noxious or hazardous fluid is minimized. Use of such large size filters, however, is not without its disadvantages. Large size filters generally require a large vessel or container to hold the filter elements. Large filter vessels become prohibitively more costly because of the structural nature of the pressure-resistant vessels required for filtering pressurized solvents.

This construction cost can surpass whatever savings are derived from using large filters to prolong filter life. For example. as fluid operating pressures increase, filter vessel wall

thickness requirements increase considerably. Vessel lids and covers including hinging and locking mechanisms become commensurately more massive and complex, resulting in prohibitive capital expenditures.

The increased capacity of large size filters can be a disadvantage for maintenance purposes. Cleaning or replacement of the filters requires that the corresponding filter system be drained. This may be an expensive and time consuming process when large size filters are used, and often results in disrupting or precluding operation of the entire fluid solvent system for extended periods of time.

In view of the above, there is a need for an efficient and economical filter assembly and a method for filtering entrained contaminants from pressurized fluid solvents that are used for cleaning fabrics, delicate electronic components, and similar sensitive substrates, without adverseiy impacting the environment or wasting expensive co-solvents and additives. Further, there is a need for a filter assembly that avoids the disadvantages associated with large filters and filter housings.

SUMMARY OF THE INVENTION The purpose and avantage of the present invention will be set forth in and apparent from the description that follows, as well as will be learned by practice of the invention. Additional advantages of the invention will be realized and attained by the filter assemblies and methods particularly pointed out in the written description and claims hereof, as well as from the appended drawings.

To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described, the invention includes an assembly for filtering a pressurized fluid solvent that continuously becomes tainted with contaminants

which must be reduced to acceptable levels. The filter assembly has an upstream connection in fluid communication with the fluid system to remove pressurized fluid solvent therefrom.

An example of a fluid system that could benefit from the filter assembly of the invention is the cleaning vessel of a dry cleaning system used to remove contaminants from textile substrates. At least two filter lines are provided in fluid communication with the upstream connection. Potentially, five to ten filter lines could be utilized depending upon the amount of contaminants anticipated. The filter lines are connected in parallel with each other for flow of the fluid concurrently therethrough.

Each filter line includes one or more filters connected in series, preferably including a strainer and at least one particulate contaminant filter. In the preferred embodiment, the strainer has a porosity greater than that of the filters. The filter assembly also has a downstream connection in fluid communication between the filter lines and the fluid system such that fluid from the fluid system flows from the upstream connection and in parallel through the filter lines before returning to the fluid system through the e downstream connection.

Preferably, the filter housings of the filters have substantially the same cross-dimension as that of the pipe network used to carry the fluid solvent through the fluid system. For example, the cross-dimension would be the diameter of the filter housing and pipe if cylindrical configurations are used. While it is not necessary to practice the invention in this manner, it is desirable to maintain similar cross-dimensions or diameters to avoid the structural requirements and attendant costs if large size filters and filter housings were to be used. The small filter housings of the invention are comprised of a housing cap and a body to which the housing cap is attached. The housing cap is attached to the body either by the engagement of complementary threaded portions or bv a type of union joint. The entry port

to the housing cap of each small filter housing is designed to be connected to another small filter housing or to the filter line. The exit port of the body likewise is designed to be connected to another small filter housing or to the filter line. Two or more small filter housings thereby can be"ganged"together for filtration of the pressurized fluid solvent.

The invention also includes a method of continuously filtering a pressurized liquid or dense fluid solvent used in cleaning a substrate, where the solvent becomes contaminated after contacting the substrate within a vessel, such as a cleaning vessel. A flow of the pressurized fluid to be filtered is removed from the system, and then divided into at least two parallel flow streams. The flow streams are directed through corresponding filter lines connected in parallel with each other for flou of the fluid concurrently therethrough.

Each filter line includes one or more filters connected in series, with the upstream filter of each filter line having a porosity greater than that of the other filter. The flow streams are returned to the fluid system after passing through the filters of the corresponding filter lire.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and are intended to provide further explanation of the invention claimed. The accompanying drawings, which are incorporated in and constitute part of this specification, are included to illustrate and provide a further understanding of the assembly, method, and system of the invention. Together with the description, the drawings serve to explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic representation of the filter assembly of the present invention.

FIG. 2 is an exploded lengthwise cross-section of a representative embodiment of a small filter housing for use in the filter assembly of FIG. 1.

FIG. 3 is a fragmented lengthwise cross-section of another representative embodiment of a small filter housing for use in the filter assembly of FIG. I.

FIG. 4 is an exploded lengthwise cross-section of an additional representative embodiment of a small filter housing for use in the filter assembly of FIG. 1.

FIG. 5 is a schematic representation of filter housings connected together to form parallel filter lines as may be used in the filter assembly of FIG. 1.

FIG. 6 shows a representative embodiment of a particulate contaminant filter element for use in the filter assembly of FIG. I.

FIG. 7 shows another representative embodiment of a particulate contaminant filter element for use in the filter assembly of FIG. I.

FIG. 8 is a schematic representation of an exemplary fluid system, a dry cleaning system, that incorporates the filter assembly of FIG. I.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Reference wilt now be made in detail to the present preferred embodiment of the invention, an example of which is illustrated in the accompanying drawings. The filter assembly, method, and system presented herein may be used for filtering a variety of pressurized fluid solvents for different applications. For purpose of explanation and illustration, and not limitation, an exemplary embodiment of the filter assembly of the invention is shown schematically in FIG. 1 and is designated generally by reference character 100. Descriptions of the method and the system of the invention are provided in conjunction with the description of the various components of the filter assembly 100.

The filter assembly of the invention is intended for fluid systems that become tainted with contaminants that need to be continuously iemoved. In accordance with the invention. the filter assembly includes an upstream connection in fluid communication with the fluid system containing ihe pressurized fluid to be filtered. The upstream connection removes contaminated fluid from the fluid system for subsequent treatment. For example, and as described in detail below, the upstream connection may be provided in fluid communication with the cleaning vessel of a dry cleaning system. In this manner, the fluid may be cycled through the filter assembly immediately after contamination and returned to the cleaning vessel for reuse.

Similarly, the upstream connection may be provided in fluid communication with any one of a variety of other piping components along a fluid system in a conventional manner if desired.

As shown in FIG. 1, and as embodied herein, the upstream connection 110 preferably includes a manifold 105 having an inlet and a plurality of outlets. The manifold 105 may be welded, cast or machined out of metal or a similar durable material to satisfy specific system and space requirements. Alternatively, the upstream connection 110 may be constructed from an assembly of conventional piping components.

The upstream connection 110 embodied herein is indirectly connected to the fluid system through a transition line 14, as shown in FIGs. I and 4. The transition line 14 is a conventional pipe member of sufficient size and construction to remove fluid safely and adequately from the cleaning vessel of the fluid system. If preferred or required due to space requirements, the inlet of the upstream connection may be provided in direct fluid communication with the fluid system.

The filter assembly further includes at least two filter lines provided in fluid communication with the upstream connection. The term"line"used herein is understood to refer to a piping network or any similar conduit configuration capable of conveying a pressurized fluid

including flexible hydraulic hose-tvpe materials. The filter lines are connected in parallel for flow of the fluid concurrently through the lines: the actual orientation of these lines is irrelevant.

The fluid removed from the cleaning vessel therefore is divided into at least two corresponding parallel flow streams. As used herein, the term"parallel"describes the resulting fluid flow. and does not limit the physical orientation of the piping components of the filter lines. For purpose of illustration and not limitation, FIG. I shows a filter assembly having three filter lines, 120, 130, and 140 in parallel, although it is understood that any number of filter lines may be provided in parallel depending upon the needs and requirements of the system. The number of filter lines is dependent on the filter capacity needed to service the fluid system as well as the level and nature of contaminants to be removed from the fluid.

Each filter line of the present embodiment generally includes at least one filter.

The general term"filter"is used to refer broadly to any filter device including but not limited to the strainers and filter elements described below. The number and types of filters used, as well as the order in which the filters are placed along each filter line, may be altered to satisfy the needs and requirements of the fluid system. The number and types of filters also depend on the level and nature of the contaminants. Specifically, the combination of filters as a whole must be selected to satis) the predetermined filtration and capacity requirements of the fluid system.

As further shows in FIG. 1, and as embodied herein, each filter line 120,130. and 140 preferably includes at least two filters connected in series. Particularly, and for purpose of illustration and not limitation, FIG. 1 shows four filters along each filter line 120,130 and 140.

In order to avoid the disadvantages associated with large filters, the present invention uses filters having cross-dimensions that are substantially similar to the cross dimensions of the filter lines and the other piping used throughout the fluid system. Hence, the filters and their housings have cross dimensions that are the same or slightly larger than the cross-dimensions of the filter lines

and other piping. When the cross-dimensions of the filters are approximately the same as the cross-dimension of the filter line, additional structural strength, beyond that needed tc contain the pressurized fluid. is either not necessary or substantially reduced. Further, these áimilarly- sized filters are installed in multiple filter lines connected in parallel to provide sufficient contaminant removal capacity and desirable pressurized fluid solvent flou rates. An additional benefit of parallel filter lines is increased efficiency for servicing, waste disposal and maintenance.

The filters along the filter lines 120,130 and 140 preferably are each housed separately for independent maintenance and replacement. This not only allows for enhanced flexibility and versatility, but also facilitates the use of small, pipe-sized filter housings that are relatively inexpensive to manufacture, avoiding all the disadvantages associated with using large filters and their housings. Each filter line 120,130 and 140 therefore may be constructed of a series of filter housings directly interconnected with each other or, if desired, may even be constructed as a single piping member having a plurality of filter housings formed therein.

Alternatively, and as shows schematically in FIG. 1, a combination of pipe lengths and filter housings may be used. Additional pipe components likewise may be incorporated along each filter line 120,130 and 140. Examples of such additional components include, but are not limited to, pressure regulators, flow meters, relief or control valves and the like.

As explained above, an advantage of the filter assembly of the present invention is the use of filter housings having small volumes; preferably by using a housing having a diameter substantially the same as the diameter of the filter line and of the other piping used throughout the system. One embodiment of a small diameter filter housing 200 in accordance with another aspect of the invention is depicted in FIG. 2. At one end of the filter housing 200 of FIG. 2 is a housing cap 205. The housing cap 205 has an entry port 210 through which the

pressurized fluid solvent enters the filter housing 200. Preferably, the housing cap 205 also has a first threaded portion 215 for connecting the filter housing either to another filter housing or to the filter line although alternat connecting configurations may be used. The housing cap 205 also has a second threaded portion 220 or similar connecting configuration to connect the housing cap 205 to the inlet 230 of the filter housing 200.

The housing cap 205 is easily removable from the filter housing 200 for purposes of performing maintenance or replacing the filter element 235 enclosed within the body 265 of the filter housing 200 as described further below. The housing cap 205 is rotated to engage the second threaded portion 220 with the threads in the interior of the inlet 230. Also provided within the inlet 230 is a sealing ring 225 of conventional construction that prevents leakage of the pressurized fluid solvent. Pressurized fluid solvent flows from the fluid line into the entry port 210 and through the center port 240. The center port 240 includes a closed end, such that the flow of the pressurized fluid solvent is directed to the outer surface of the filter element 235 before flowing radially inward as depicted by the small fluid flow arrows show in FIG. 2. The pressurized fluid solvent flows across the exterior watt and through the filtering media 250 toward the center core 255 of the filter element 235. This path of solvent flow is also depicted by small arrows.

The contaminants entrained within the pressurized fluid solvent having a particle size larger than the porosity of the filtering media 250 are separated from the pressurized fluid solvent as the solvent flows through the filter element 235. The ends of the filter element 235 are closed-offby a sealing gasket 245. The pressurized fluid solvent therefore flows through the center core 255 and exits the filter housing 200 through the exit port 260. The interior of the exit port 260 is threaded for connection with either the filter line or the entry port of another filter housing. The diameter of the filter housing 200 is indicated in FIG. 2 as the line between points

A and B. The diameter of the filter housing 200 is substantially similar to the diameter of the adjacent filter line and. therefore, the filter housing 200 is the same or slightly larger than the filter line. The filter housing 200 is made of sufficiently durable material. The filter housing 200 is manufactured of conventional materials and technoloy as appropriate to satisfy the needs of the system.

Another embodiment of a small diameter filter housing 300 is depicted in FIG.

3. The filter housing 300 of FIG. 3 has a housing cap 305 that is attached to the body 315 by a union joint 310. A trench is used to secure the union joint 310 to the body 315 with the housing cap 305 therebetween. The housing cap 305 has a threaded portion 320 for connecting the filter housing 300 to either the filter line or another filter housing. An"O"Ring-type gasket 325 of conventional construction is provided between the housing cap 305 and the body 315 to prevent leakage of the pressurized fluid solvent.

Pressurized fluid solvent flows into the entry port 330 of the housing cap 305 and through the center ports 335 as depicted in FIG. 3 by the small fluid flow arrows. The center ports 335 direct the flow of solvent around the exterior of the filter element 340. The solvent flows across the exterior wall of the filter element 340 and through the filter media 345 toward the center core 350. Contaminants having a particle size larger than the porosity of the filter media 345 are removed from the pressurized fluid solvent before the solvent reaches the center core 350 of the filter element 340. A gasket 355 is provided at each end of the filter element 340; one between the housing cap 305 and another between the filter element 340 and the housing end to prevent bypass of the contaminated solvent.

As with the filter housing 200 depicted in FIG. 2, the filter housing 300 of FIG.

3 has an exit port (not shown) that can be connected to either the filter line or another filter

housing. As with filter housing 200. the diameter of filter housing 300 is substantially similar to the diameter of the filter line to which it is connected.

FIG. 4 depicts a filter housing 400 having a different type of filter than the filter elements in FIGs. 2 and 3. Filter housing 400 has a housing cap 405 that is coupled with the housing body 410 by a flanged union joint 415. A sealing ring 420 of conventional construction prevents leakage of the pressurized fluid solvent. Unlike the other filters, which use a conventional filter element as will be described, filter housing 400 uses a filter element 425 that includes a woven metal mesh basket containing a woven or non-woven mesh filter sock. Solvent flows through the housing cap 405 and then directly into the mesh filter element 425.

Contaminants having a size larger than the porosity of the mesh filter element 425 remain inside the filter as the solvent flows out through the filter media. The direction of the flow of the pressurized fluid solvent through the filter housing 400 is indicated generally by small arrows in FIG. 4. The solvent exits the filter housing 400 through the exit port 430. As with filter housings 200 and 300. the diameter of filter housing 400 is substantially similar to the same as the diameter of the filter line to which it is connected. In addition to the filter line. the filter housing 400 can be connected to other filters or filter housings.

As explained above, the small diameter housings of the invention can be easily connected to either the filter line or each other. FIG. 5 shows an embodiment of the invention where several filter housings are"ganged"together in series. At the connections, the exit port of each filter housing is coupled with the entry port of an adjacent housing cap. In accordance with another aspect of the invention, a variety of different filters may be provided along each filter line to perform a corresponding variety of different functions. By using small filters on a number of parallel filter lines, and by placing these filters in proper order along each filter line according to the function to be performed, the overall efficiency of the filter assembly is

enhanced greatly. In addition to the efficiency achieved by using one or more parallel filter lines from the manifold 105, the efficiency of the filter assembly can be further increased by using subsets of parallel filter lines as a three-dimensional arras, if desired. For example, and in addition to the"ganging"of filter housings in series, FIG. 5 shows each filter line 120,130 formed as a pair of filter lines 125 127 and 135,! 37. respectively, connected in parallel. The overall number of filter lines is dependent on the filter capacity needed to service the fluid system as well as the level and nature of contaminants to be removed from the pressurized fluid.

Similarly, a variety of filters may be used along each filter line. For example, and as embodied herein, at least one filter along each filter line 120,130 and 140 is a strainer 122, 132 and 142. These strainers 122,132 and 142 preferably are located upstream from the remaining filters along the filter line 120.130 and 140. The strainers 122,132 and 142 are intended to strain or prescreen larger insoluble particles from the fluid. As such, each strainer 122,132 and 142 preferably has? porosity greater than that of the remaining filters downstream on the filter lines 120,130 and 140. respectively, so as to prolong the life of the downstream filters. A porosity of about 100 micron mesh is preferred, although the actual porosity will depend upon the requirements of the system. It is possible, however, that no strainer will be required if substantially no particles greater than about 100 micron are expected to be entrained in the pressurized fluid. Strainers are available in a variety of known configurations and models, including those sized approximately the same as the diameter of conventional filter lines.

Examples of Y-type strainers include, but are not limited to, Yarway Wye-Type No. 863; Mueller Y-type No. 766/766M, 767,767WE, 863/863M, 865/865M, 866/866M; and R-P&C Valve Nos. 602-020,602-030,602-120, and 602-130. In addition, in-line basket. Tee-tope. or angle block strainers can be used and are commercialiy available from Mueller Steam Specialtn of St. Pauls. North Carolina.

Temporary strainers, which include a cone, basket, or plate made of coarse screen. likewise may be used. Such temporary strainers are available from Mueller Steam Specialta of St. Pauls. North Carolina. These temporary strainers are mounted between pipe flanges or a union joint and, therefore, offer the additional avantage of eliminating the need for a housing that has a cross-dimension substantially larger than the cross-dimension of the fluid line and other piping used throughout the fluid system. Eliminating the need for large cross-dimension housings, decreases the need for costly additional structural strength to withstand the pressure at which the filter lines must be kept.

In the illustrative embodiment of FIG. 1, each filter line 120,130 and 140 further includes at least one insoluble contaminant filter 124,134 and 144, respectively. These filters 124,134 and 14 are provided to separate from the fluid and collect insoluble particles that pass the strainers 122.132 and 142. If no strainer is provided, then these filters 124.134 and 144 preferably are located upstream from the remaining filters along the filter line 120.130 and 140.

A variety of insoluble contara : nant filters may be used in accordance with the invention. Such filters generally include filter media having a defined porosity, preferably between 40-60 microns. Nonwoven filter media are preferred for efficiency, durability and cost reasons, although woven mesh and screen filter media satisfying the porosity requirements of the filter assembly may be used as well. Additional structural support for the filter media also may be provided if required or desired.

In-line filters such as disks or socks are preferred filters for the filter assembly 100 of the invention. Such filters are conventional in construction and available from a number of filter media sources, such as Custom Paper Group. The use of these pipe size, in-line filters is particularly advantageous because the need for filter housings substantially larger than the cross-dimension of the filter lines and the other piping of the fluid system is virtually eliminated.

Rather, these pipe size. in-line filters are simply installed in the flow stream of the filter line using conventional union joint or the like of appropriate construction. A swing joint or flexible pipe component further simplifies installation. Cleaning and/or replacement therefore can be performed quickly and easily, thus, reducing costs associated with construction, maintenance and operation. A metal screen or similar structural support also may be installed behind the in-line filter for additional rigidity. Although in-line filters such as filter disks and socks generally have limited contaminant capturing capacity and, therefore, were not previously feasible for systems operating in conditions where high contaminant levels are anticipated, the plurality of the parallel filter lines provided in accordance with the invention enables the use of such filters.

Altematively, small filter cartridges may be used for the filters 124,134 and 144 of the filter assembly 100. The small filter cartridge 620. as shown in FIG. 6, preferably is a hollow structure 622 formed of a pleated nonwoven filter medium, such as paper or the like, although a woven filter medium may be used if desired. The filter cartridges 620 also may include a porous tubular backing 624 within the core of. he hollow pleated structure 622 for additional support and durability if desired. Examples of snall filter cartridges include, but are not limited to, Parker 4C\\J15-070 and 925-835. Similar types of small filter cartridges have been used in hydraulic and chemical systems in which there are relatively low contaminant levels. Conventionally installed, these small filter cartridges are not capable of handling high contamination levels as are continuously encountered in cleaning systems. However, small filter cartridges work well in the filter assembly of the invention in which there is a configuration of parallel filter lines having multiple filters.

Unlike filter disks or socks, but further in accordance with the invention, small filter cartridges may need to be contained in a filter housing that is slightly larger yet substantially similar to the diameter of the filter line. For example the filter line may have a 6

diameter of 1-1/2"and the housing for the small filter cartridge may have a diameter of 2".

However, these housings are significantly smaller than those conventionally required for fluid systems that continuously encounter higher contamination levels. In this manner. costs associated with construction, maintenance and operation likewise are significantly reduced. The relatively small-sized filter housings do not require costly reinforced structural strength to withstand the pressures at which the fluid system may be operated.

In accordance with another aspect of the invention, it is possible to use a basket strainer or the like for filter 124,134 and 144. The basket insert of the basket strainer may be lined with woven or nonwoven filter media to obtain the desired degree of filtration. In this manner, the basket strainer would be installed such that the fluid flows from the inside to the outside of the basket insert. The basket insert also may be pleated to increase the surface area of the filter media for increased efficiency and to prolonp-filter life. Altematively, and in accordance with another aspect of the invention, the basket insert of the basket strainer may be replaced with a small filter cartridge such as one described above. The small filter cartridge and the housing of the basket strainer would be compatible in size. and installed such that the fluid flows from the outside to the inside of the small filter canridsTe.

Another aspect of the invention includes an alternative filter basket insert for use in the filter assembly. This basket insert 630, as shown in FIG. 7, includes a porous metal basket 634 covered with a loose flexible bag 632 of filter material having the desired porosity.

Preferably, the basket 634 has a pleated wall to increase rigidity and surface area. The flexible bag 632 conforms to the pleats of the basket 634 when pressure is applied and fluid flows from the outside toward the inside of the basket 634 during operation. This alternative insert is used in a manner similar to, and therefore may replace, the small filter cartridge described above.

FIG. I shows that the parallel filter lines 120,130 and 140 of the filter assembly 100 embodied herein include additional fitters 126,136 and 146, respectively, to separate and remove insoluble contaminants from the fluid flowing therethrough. Preferably, these additional insoluble contaminant filters 126,136 and 146 each has a porosity less than that of filters 124, 134 and 144 to further enhance the efficiency of each filter line 120, 130 and 140. For example. and as embodied herein, the additional filters 126,136 and 146 each may have a porosity of about 10 microns or less to separate and capture insoluble contaminants not removed by filters 124,134 and 144.

The additional insoluble contaminant filters 126,136 and 146 may be of the same configurations or equivalents thereof as described with regard to filters 124.134 and 144. That is. the additional fillers 126. 136 and 146 may be filter disks, socks, small cartridges or some variation of a basket strainer. It is not necessary, however, that the same type of insoluble contaminant filters be used along each filter line as long as fluid flow remains equally distributed through each filter line.

For example, and for purpose of illustration, filter 124 may be a srnall filter cartridge A, hile filter 126 could be a filter disk. Although preferred, it likewise is not required that each of the additional filters 126,136 and 146 be the same type of filter as that of the other filter lines. As such, filter 124 may be a small filter cartridge while filter 134 may be a variation of a basket type strainer as described above.

If necessary or desired, additional filters (not show) having porosities similar or finer to that of filters 1^-, 6,136 and 146 may be provided downstream to further separate and capture any remaining insoluble contaminants. Again, these filters may be of the same type described above, and may be"mixed and matched"as required to satisfy the demands of the fluid system. Additionally, or alternatively, a centrifuge may be provided to separate large insoluble

particles from the pressurized fluid solvent. Such centrifuges are conventional and known in the art.

As embodied herein, and fur. heur in accordance with the invention, adsorptive filters 128,138 and 148 are provided on filter lines 120.130 and 140 downstream of insoluble contaminant filters 124,126,134,136 144 and 146. The adsorptive filters 128,138 and 148 remove and thereby control undesirable fluid soluble contaminants. Examples of such fluid soluble contaminants include fugitive dyes that are removed from clothing or other substrates during the cleaning process and which dissolve in the pressurized fluid solvent. Known adsorptive filters generally include a housing containing a porous bag, cartridge or similar container filled with adsorptive material. As with the other filters described herein, the housings of the adsorptive filters have cross-dimensions substantially similar to the cross-dimensions of the filter lines 120,130 and 140 and other piping used throughout the fluid system. Satisfactory adsorptive material includes activated carbon, clay or a combination of the two. Alternative adsorptive materials likewise are known and may be selected to accommodate the specific fluid soluble contaminants that are anticipated. Fluid solvent soluble contaminants therefore are adsorbed as the contaminated fluid flows through the adsorptive material in the filter.

Alternatively, a single adsorptive filter may be provided downstream of the downstream connection of the filter assembly as described below.

Further in accordance with the present invention, the filter assembly is provided with a downstream connection in fluid communication with the parallel filter lines to receive the filtered pressurized fluid therefrom. As shown in FIG. l, the downstream connection 150 preferably includes a plurality of inlets connected to the parallel filter lines 120,130 and 140, and an outlet in fluid communication with the system. The downstream connection 150 mav be a manifold 155 that is welded, cast or machined out of metal or a similar durable material to

satis, specific system and space requirements, or may be constructed from an assembly of conventional piping components. Altematively, the downstream connection may be provided as a separate connection between each filter line and the fluid system.

As with the upstream connection HO, the downstream connection 150 may be connected directly to a component of the fluid system, or indirectly through a return line 56 as show in FIG. 8 and described further below. The return line 56 is a conventional pipe member of sufficient size and construction to safely and adequately return filtered fluid to the cleaning vessel. In this manner, pressurized fluid removed from the cleaning vessel flows from the upstream connection I 10 and is directed in parallel through the filter lines 120,130 and 140 before returning to the system through the downstream connection 150 and the return line 56.

Operation and maintenance of the filter assembly is further enhanced by providing control valves along the flow lines. For example, the filter assembly 100 embodied herein includes a master valve ! 08 located proximate the upstream connection 110 and a corresponding valve 160 located proximate the downstream connection 150. The filter assembly 100 as a whole can be opened and closed readily using these master valves 108,160 for operation, maintenance and repair.

Preferably, each filter line 120,130 and 140 likewise includes an upstream control valve 121, 131 and 141, and a downstream control valve 129,139 and 149. These independent control valves further enhance the versatility and operation of the filter assembly 100.

Particularly, fluid flow through each filter line 120,130 and 140 may be opened or closed independently by selected operation of the upstream and downstream valves 121,129,131,139, 141 and 149. In this manner, one or more filter lines may be closed for cleaning or maintenance of the correspondine filters, while the remaining filter lines remain open for operation. Although

not shown, bypass piping configurations also may be provided for independent operation of each filter if desired.

Additionally, and in accordance with another aspect of the invention. each filter of the filter assembly 100 may be provided in fluid communication with a pressure equalization line 20. The pressure equalization line 20 allows fluid to be vented from the filters to a storage vessel or the like during cleaning or maintenance. For purpose of clapit, FIG. 1 only shows pressure equalization lines 20 connected to the filters 142.144.146, 148 along filter line 140, although it is understood that similar pressure equalization lines would extend from the filters of the remaining filter lines. Altematively. it is possible to provide pressure equalization lines in direct communication with the filter lines themselves, so as to reduce the number of fluid connections therebetween.

To clean or replace the filters, the appropriate control valves are closed to secure the entire filter assembly 100, or each filter line independently. The corresponding pressure equalization line 20 is then opened to vent any fluid, including vapors. from the filters for storage and reuse. A condenser may be provided along the pressure equalization line 20 to condense any vapors prior to storage. The filters or pipe connections along the filter line are opened to clean or replace used filter media contained therein. Particularly, and with regard to the embodiment of FIG. 1, the strainers 122.132 and 142 are cleaned using compressed air to force any lodged contaminants therefrom; the filter media of filters 138, 144,146 and 148 may be discarded without any special handling or disposal preparations and simply replaced with new filter media. Because of the small size of the housings of the filters, replacement of filter media is easy because each housing holds only a small volume of solvent.

Reference is now made to FIG. 8. which shows an exemplary fluid system having a filter assembly in accordance with the present invention. Particularly, and for purpose of

illustration. FIG. 8 schematically shows a cleaning system, designated generally by reference character 10, using a pressurized fluid as a cleaning solvent. B'ith regard to this cleaning system. the term"pressurized fluid"is understood to refer to a gas or gas mixture that is maintained at either subcritical or supercritical conditions so as to achieve a liquid or a supercritical fluid having a density approaching that of the liquid state of the solvent. Although a variety of fluids may be used, it is preferred that an inorganic substance such as carbon dioxide, helium, argon, or nitrous oxide is selected for use as the pressurized fluid solvent. For cost and environmental reasons. liquid, supercritical, or subcritical carbon dioxide is preferred. The selected pressurized fluid also must be compatible with the substrate being cleaned.

The cleaning system 10 includes a pressurized cleaning vessel 12 for holding the substrates to be cleaned. Not shown, but understood in the art to be necessary to functionally operate the cleaning system, are components such as, supply and storage tanks for holding pressurized fluid to initially charge the cleaning system 10. and to replace pressurized fluid into the pressurized cleaning vessel 12 that is lost during operation. In addition, the supply and storage tanks receive pressurized fluid from various system components, such as the pressurized cleaning vessel 12 and the filters of the filter assembly 100. As such, pressure equalization lines 20 extend from the storage tank to these various system components.

Once the pressurized fluid contacts the substrate within the pressurized cleaning vessel 12, contaminants from the substrate become entrained in and contaminate the pressurized fluid. The contaminated pressurized fluid therefore must be filtered to remove soluble and insoluble contaminants and therefore prevent recontamination of the substrate. Particularly, and in accordance with the invention, the contaminated pressurized fluid is removed from the cleaning system 10 and directed through the upstream connection 110 of the filter assembly 100 in fluid communication with the cleaning system 10.

As embodied herein for purpose of illustration. and as shown in FIG. 8, a flow line 14 is provided between the pressurized cleaning vessel 12 of the cleaning system 10 and the upstream connection 110 of the filter assembly 100. Altematively, and as noted above, the upstream connection 110 may be directly connected to the pressurized cleaning vessel ! 2. The flow of pressurized fluid solvent is cycled from the pressurized cleaning vessel 12 using a conventional pump 54 and regulator 52. The required flow rate of the fluid will vary depending upon the total volume of the system and the quantity and type of insoluble contaminants present.

In this manner, filtering by the filter assembly 100 may be performed continuously throughout the cleaning process to prevent recontamination of the substrate being cleaned in the pressurized cleaning vessel 12. The use of a single flou line 14 also reduces the number of penetrations in the pressurized cleaning vessel 12 and. thus. the opportunity for leakage or failure.

Alternatively, the pressurized fluid may be cycled through the filter assembly 100 by drawing the fluid from the pressurized cleaning vessel 12 using a pump and flow regulator located downstream of the filter assembly 100. or by any other conventional method. Likewise, cycling of the flow through the filter assembly 100 may be performed intermittently, such as by batch method.

Upon entering the manifold 105 of the upstream connection I 10, the flow of pressurized fluid is divided into parallel flow streams and directed through the corresponding filter lines 120,130 and 140. In addition to piping that may be used to construct the filter lines, the lines exiting the manifold 105 can include flexible reinforced hydraulic-twpe hoses. The use of flexible reinforced hydraulic-type hoses to connect the manifold 105 with the filters increases the ease with which filter elements can be changed. The flexible reinforced hydraulic-type hose permits the operator to allow the housing cap of the filter housing to dangle or be swung away from the body of the filter housing while the element is replaced.

With reference to the filter assembly 100 shon in FIG. 1, for purpose of illustration and not limitation, each filter line includes a strainer at least one insoluble contaminant filter and an adsorptive filter 128,138.148, respectively. The actual number and variety of filter lines and filters used, however, bill depend upon the demands and capacity of the fluid system. In order to minimize the structural reinforcement needed to withstand the pressure requirements of the fluid system, the filters and their housings are substantially similar in size to the filter lines and the other piping used throughout the fluid system. Specifically, the filters and their housings have cross-dimensions substantially similar to the cross-dimension of the filter line in which they are located.

Once filtered. the separate flow streams are returned to the cleaning system 10 for reuse. As previously described, the filter assembly 100 embodied in FIGs. 1 and 8 includes a downstream connection 150 to facilitate the fluid return. Hence, pressurized fluid from the cleaning system 10 flows from the upstream connection 110 and is directed in parallel through the filter lines 120,130 and 140 before returning to the cleaning system 10 through the downstream connection 150. Although FIG. 8 shows a return line 56 to redirect the fluid into the pressurized cleaning vessel 12, the downstream connection 150 may be connected directly to the cleaning system 10 if desired.

Filtration by the filter system 100 reduces the quantity of contaminants in the pressurized fluid to a level sufficient to preclude redeposition of contaminants onto the substrate when the pressurized fluid is reintroduced into the pressurized cleaning vessel 12 via return line 56. Although not show, an auxiliary line also may be provided to direct the filtered pressurized fluid to a storage tank. In this manner, the filtered pressurized fluid can be stored in the storage tank, and cycled back to the pressurized cleaning vessel 12 as needed.

As noted above, maintenance and replacement of the filters in assembly 100 is accomplished by secunng appropriate control valves. Depending upon the control valves provided, the filter assembly 100 as a whole may be secured and cleaned at one time. or individual filter lines may be secured and cleaned independently. Pressure equalization lines 20 further facilitate maintenance and enhance efficiency of the filter assembly 100 as described above.

In a preferred embodiment of the cleaning system 10 of FIG. 8, pressurized fluid such as supercritical carbon dioxide or the like is used as the cleaning solvent, and therefore, maintenance and cleaning is further simplified. Particularly, disposal of the filtering media of the filter assembly 100 typically will not be problematic because of the nature of the solvent that is used. The filtering media therefore may be changed easily and frequently without any special disposal procedures. Additionally, paper and other none, ove filtering media material may be used because pressurized fluid such as supercritical carbon dioxide and the like have low viscosity and lo N surface tension and thus their diffusive nature will easily penetrate the filter media and the solid particulate contaminants deposited thereon. The parallel filter line arrangements of the present invention make the use of paper or nonwoven media feasible, and the use of small filters cost effective. Use of small filters and housings having cross-dimensions substantially similar to the cross-dimensions of the filter lines and other piping used throughout the fluid system reduces costs because structural reinforcement for the filter housings is either not needed or substantially reduced.

It will be apparent to those skilled in the art that various modifications and variations can be made in the filter assembly, method, and system of the present invention without departing from the spirit or scope of the invention. Additionally, the filter assembly may be constructed as a single integral piece. or as a combination of piping components. Thus it is intended that the present invention cover modifications and variations that come within the scope of the appended claims and their equivalents.