Abstract:
A solvent separator apparatus having a vertical accumulator tank with a top end and a bottom end, the accumulator tank being serially connected to a vertical reservoir tank having a top end and a bottom end; a down tube vertically positioned in the accumulator tank having a top end nearest the top end of the accumulator tank and a bottom end nearest the bottom end of the accumulator tank, with an inlet at the top end of the down tube and an outlet at the bottom end of the down tube; an inlet conduit connected to the inlet of the down tube, the inlet conduit entering the bottom end of the accumulator tank and defining an upward flow path within the accumulator tank to the inlet at the top end of the down tube; a heat exchanger in communication with the down tube for withdrawing heat therefrom; and a transfer conduit defining a downward flow path from the top end of the accumulator tank to the bottom end of the reservoir tank. Systems in which the apparatus is combined with a dry cleaning machine are also disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    The present application is a Continuation of International Application No. PCT/US00/05289 filed Feb. 26, 2000, which, in turn, claims priority benefit of U.S. Provisional Application Serial No. 60/121,793, filed Feb. 26, 1999. The disclosures of both applications are incorporated herein by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The present invention relates to an apparatus for separating solvents having a limited degree of miscibility. In particular, the present invention relates to an apparatus for the removal of water from glycol ether dry cleaning solvents. The present invention further relates to a system in which the apparatus of the present invention is used in combination with a dry-cleaning machine, which cleans fabrics and other materials with a glycol ether dry cleaning solvent, to remove water that accumulates in the solvent during the dry cleaning process.  
           [0003]    In a dry-cleaning machine, the clothing or other fabric to be cleaned is tumbled or agitated in the presence of a liquid solvent that removes dirt, oil, grease and other soiling substances from the fabric. Garments entering a dry cleaning plant contain significant quantities of water in the form of moisture. The water is removed from the fabric by the solvent along with the soiling substances.  
           [0004]    Traditionally, dry cleaning solvents, such as perchloroethylene, are water-immiscible and have a density greater than that of water. Thus, when the perchloroethylene is returned to the solvent tank of a dry cleaning machine, the water removed from the fabric floats to the surface, with any soil dissolved therein, where it is easily removed. The other soiling substances are removed either by filtration or, alternately, by distillation of the dry cleaning solvent.  
           [0005]    Because perchloroethylene poses a hazard to health and the environment, substitute solvents have been developed. EP 479,146 discloses the use of propylene glycol monomethyl ether as a safe alternative to perchloroethylene. The use of propylene glycol tertiary butyl ether (PTB) and propylene glycol n-butyl ether (PNB) as dry cleaning solvents is disclosed by WO 98/45523. Other glycol ethers have been identified as potential replacements for perchloroethylene as a dry cleaning solvent. The glycol ethers, especially PTB and PNB, possess the requisite detergency for dry cleaning without damaging garments and other fabrics. The glycol ethers also dry at temperatures suitable for use with fine fabrics. From the standpoint of health and safety, glycol ethers are non-carcinogenic, non-toxic and biodegradable.  
           [0006]    Glycol ethers also differ from perchloroethylene by being marginally miscible with water, particularly at the temperatures employed with dry cleaning. Consequently, the glycol ether is diluted by clothing moisture during the dry cleaning process, reducing the cleaning ability of the solvent. This can be restored by replenishment of the glycol ether through distillation.  
           [0007]    WO 98/45523 discloses that water can be removed from PTB and PNB by distillation. However, the energy required for distillation of glycol ethers is also costly. Ideally, distillation should be reserved for reclaiming heavily soiled solvent.  
           [0008]    U.S. Pat. Nos. 3,674,650; 5,069,755; and 5,236,580 disclose distillation systems for use with dry cleaning machines to purify perchloroethylene. U.S. Pat. No. 4,191,651 discloses an apparatus for separating two immiscible liquids. However, such a device would not efficiently separate liquids having even a limited degree of miscibility.  
           [0009]    There remains a need for an energy efficient means by which water can be separated and removed from modern glycol ether dry cleaning solvents.  
         SUMMARY OF THE INVENTION  
         [0010]    This need is met by the present invention. The present invention provides an apparatus for separating two miscible liquids with a high degree of energy efficiency. The apparatus cools the mixture to a temperature below which the two liquids are miscible and then employs gravity separation to partition the two liquids. The apparatus may be used to separate essentially any mixture of two miscible solvents.  
           [0011]    Therefore, according to one aspect of the present invention, an apparatus is provided, including:  
           [0012]    a vertical accumulator tank having a top end and an bottom end, with the accumulator tank being serially connected to a vertical reservoir tank having a top end and a bottom end;  
           [0013]    a down tube vertically positioned in the accumulator tank and having a top end nearest the top end of the accumulator tank and a bottom end nearest the bottom end of the accumulator tank, and with an inlet at the top end of the down tube and an outlet at the bottom end of the down tube;  
           [0014]    an inlet conduit connected to the inlet of the down tube, the inlet conduit entering the bottom end of the accumulator tank and defining an upward flow path within the accumulator tank to the inlet at the top end of the down tube;  
           [0015]    a heat exchanger in communication with the down tube for withdrawing heat therefrom; and  
           [0016]    a transfer conduit defining a downward flow path from the top end of the accumulator tank to the bottom end of the reservoir tank.  
           [0017]    The apparatus is most effective for the separation of liquids that are miscible above and immiscible below a temperatures of about 60° C. The apparatus can be used to separate liquid mixtures that remain miscible at temperatures as low as room temperature, so that the apparatus may be used to separate heated liquid mixtures that are immiscible at room temperature (room temperature defined as being about 22° C.).  
           [0018]    The apparatus is particularly useful in dewatering glycol ethers used as the cleaning solvents in modern dry cleaning equipment. Therefore, according to another aspect of the present invention, a system is provided in which a dry cleaning machine adapted to cleaning clothing or other fabrics with glycol ethers, and having a cleaning section in communication with a glycol ether storage tank, is combined with the apparatus of the present invention. Glycol ethers from the storage tank are pumped to the apparatus where they are dewatered. After dewatering, the glycol ethers are then pumped back to the solvent storage tank.  
           [0019]    Some water will always be bound to the glycol ether as an azeotrope. However, the removal of excess water from the glycol ether is critical in order to control the shrinkage of woolens and other fabrics.  
           [0020]    Typical dry cleaning systems have three or more solvent tanks, one of which is used to store reclaimed, distilled solvent, with the others being designated work tanks, which supply dry cleaning solvent to the cleaning sections of the dry cleaning machine, which then returns the solvent to the work tanks. The present invention therefore also includes an apparatus in which the accumulator tank is compartmentalized into individual cells, each dedicated to a separate solvent tank of a dry cleaning machine. Therefore, according to another aspect of the present invention, an apparatus is provided in which the accumulator tank is divided vertically into a plurality of isolated compartments, each compartment having a down tube vertically positioned therein. The apparatus further includes a plurality of inlet conduits, each entering the bottom end of an individual compartment and defining an upward flow path within each compartment and connected to the top inlet of each down tube. Each down tube is provided with a heat exchanger, and each compartment has a separate transfer conduit defining a downward flow path to the bottom end of the reservoir tank. The purpose of rising to the top and then back to the bottom is to limit the amount of loss from the cell should there be a failure of the input tube.  
           [0021]    A single reservoir tank may be used to collect dewatered solvent from the plurality of accumulator tank compartments, which is then supplied to the plurality of dry cleaning machine solvent tanks from the single reservoir tank. Alternatively, the reservoir tank may also be divided vertically into a plurality of isolated compartments, each compartment corresponding to a compartment of the accumulator tank. Each of a plurality of transfer conduits would define a downward flow path from the top end of an accumulator tank compartment to the bottom end of the reservoir tank corresponding thereto. Each reservoir tank compartment is then dedicated to a solvent tank of the dry cleaning machine and each of a plurality of outlet conduits defines a flow path exiting the bottom end of its reservoir tank compartment and returning to the dry cleaning machine solvent tank corresponding thereto.  
           [0022]    The apparatus of the present invention may also be used in other end use applications for glycol ethers in which dewatering is required. Such applications include, but are not limited to, dyeing processes in which glycol ethers are used as the solvents, processes for scouring raw wool and milling the scoured raw wool, and processes in which glycol ethers are used to clean or degrease metal parts or electronic components. Furthermore, the apparatus of the present invention may be applied to essentially any end use application in which it is desirable to obtain the separation of two miscible solvents.  
           [0023]    The foregoing and other objects, features and advantages of the present invention are more readily apparent from the detailed description of the preferred embodiments set forth below, taken in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]    [0024]FIG. 1 is a side, cross-sectional view of an apparatus according to one embodiment of the present invention;  
         [0025]    [0025]FIG. 2 is a front perspective view of the apparatus of FIG. 1; and  
         [0026]    [0026]FIG. 3 is a schematic view of one embodiment of a system according to the present invention in which an apparatus according to another embodiment of the present invention is used in combination with a dry-cleaning machine. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0027]    The apparatus  1  depicted on FIG. 1 consists of tank  3  divided along its entire length by wall  5  into accumulator tank  7  and reservoir tank  9 . Inlet conduit  11  enters the bottom end  13  of accumulator tank  7  and defines an upward flow path  15  through the accumulator tank. The inlet conduit  11  is connected via a down tube  17  to exit ports  29  and  30  in the down tube  17 . Anti-siphon valve  23  prevents the liquid mixture from being siphoned back into inlet conduit  11 .  
         [0028]    The coil  28  cools the outbound liquid from  29  and  30 , which in the embodiment of FIG. 1 is a heat exchanger cooling coil through which a coolant flows, typically water from inlet  27  through the coil to outlet  25 . However, when colder temperatures are required, a refrigerant may be used. Essentially any means for withdrawing heat from the down tube  17  may be employed.  
         [0029]    In the depicted embodiment water is supplied to the coil  28  at inlet  27  and withdrawn at outlet  25 . Cold fresh water may be continuously supplied to the heat exchanger, or, alternatively, the outlet water may be cooled by a refrigerator (not shown) and returned to the heat exchanger by way of inlet  27 .  
         [0030]    The portion  21  of the down tube  17  within the coil  28  has perforations  29  in the depicted embodiment. This permits the liquid to flow over the coils of the heat exchanger when exiting the down tube, which increases cooling efficiency. Transfer conduit  33  defines a downward flow path  36  from the top end  31  of accumulator tank  7  to the bottom end  35  of the reservoir tank  9 . Outlet conduit  39  is positioned vertically in the reservoir tank and has a top end  38  with an inlet  42  positioned near the top end  37  of the reservoir tank. The outlet conduit defines a downward flow path  40  exiting the bottom  35  of the reservoir tank. In the depicted embodiment, outlet  41  at the end  44  of outlet conduit  39  is in communication with a solvent return line. Liquid at the bottom  35  of reservoir tank  9  is recirculated by line  51  to inlet conduit  11  via filter unit  53 .  
         [0031]    The apparatus of FIG. 1 may be modified depending upon the physical characteristics of the liquid mixture to be separated. The apparatus cylinder may be jacketed so that a coolant may be circulated through the jacket to pre-cool the cylinder contents. For example, a heat exchanger employing a cryogenic refrigerant may be used, or the apparatus cylinder may be pressurized to maintain volatile materials in the liquid state.  
         [0032]    With reference to FIG. 1, the apparatus of the invention operates as follows:  
         [0033]    A mixture L 3  of two miscible liquids L 1  and L 2  is supplied to the accumulator tank  7  via inlet conduit  11 . The mixture is transferred to the accumulator tank by a pump  57  after being passed through the filter element  59  of filter  53  to remove particulate matter. Conduit  56  delivers the mixture from the filter  53  to the pump  57 . The mixture is supplied to the filter  53  from a solvent tank (not shown)by conduit  55 .  
         [0034]    The mixture is delivered by the inlet conduit  11  through the bottom  13  of the accumulator tank upwardly through the tank to the top end of down tube  17 . The mixture then flows to the outlet  29  and the bottom end  30  of the cooling column, passing through coil  28 , which draws heat from the mixture, lowering the temperature of the mixture below the temperature range within which L 1  and L 2  are miscible. L 1  and L 2  separate, with the denser liquid, for purposes of illustration, L 2 , remaining at the bottom end  13  of the accumulator tank  7  upon discharge from the outlet  29  of the cooling column, and the lower density liquid, L 1 , floating to the top end  31  of the accumulator tank.  
         [0035]    The lower density liquid L 1  is then drawn into the inlet  32  of transfer conduit  33  at the top end of the accumulator tank. The transfer conduit delivers the lower density liquid through the reservoir tank  9 , where it is discharged through outlet  34  at the bottom  35  of the tank  9 . Any remaining quantities of the denser liquid L 2  sink to the bottom of the reservoir tank, so that the liquid at the top of the reservoir tank is the lower density liquid L 1  essentially free of the denser solvent L 2 .  
         [0036]    The lower density liquid L 1  is then drawn from the top end  37  of the reservoir tank into the opening  38  of outlet conduit  39 . The lower density liquid L 1  is delivered by the outlet conduit through the bottom  35  of the reservoir tank after which the essentially pure liquid is either collected or recirculated (not shown). The denser liquid L 2  is discharged from the accumulator tank through outlet  47 , and from the reservoir tank through outlet  51 . The denser liquid will be essentially free of the lower density liquid L 1 .  
         [0037]    Outlet  51  returns the denser solvent L 2  to inlet conduit  11  of accumulator tank  7  via filter unit  53 . Referring to FIG. 2 (from which the filter unit has been omitted for purposes of clarity), outlets  47   a,    47   b  and  47   c  deliver solvent L 2  from the respective bottoms of accumulator tanks  7   a,    7   b  and  7   c  to manifold  65 . The outlets  47   a,    47   b  and  47   c  contain solenoid-controlled drain valves (not shown) to prevent balancing between the tanks when one or more are being drained. Solenoid valve  67  controls the delivery of solvent L 2  from the manifold  65  to a water separator (not shown) by conduit  61 . Solenoid valve  67  is controlled by microprocessor  75  providing instructions by way of electrical conduit  71 . Solenoid valve  69  controls the delivery of solvent L 2  to a solvent distillation apparatus (not shown) by conduit  63 . Solenoid valve  69  is controlled by microprocessor  75  providing instructions by way of electrical conduit  73 .  
         [0038]    Drain valve  77  on the manifold  65  allows the total system (and accumulator tanks) to be drained. Check valve  79  prevents the backflow of the solvent to the manifold unit.  
         [0039]    The purpose of the solenoid valve  67  and  69  is to permit small quantities of the denser solvent L 2  to be drawn from the bottom of the accumulator tank. The microprocessor opens each solenoid valve to permit a small amount of the denser liquid L 2  to pass to either the water separator or the distillation apparatus, depending upon the solenoid valve that is opened. The heights of conduits  61  and  63  are set lower than the total column height of the accumulator tank, so that the amount of liquid removed will be limited to the height of its corresponding conduit. Thus, the height of conduit  61  is selected so that essentially only the denser liquid drawn therethrough upon the opening of valve  67 . The height of column  63  is selected so that only denser contaminate levels of the lower density liquid are therethrough upon the opening of valve  69 .  
         [0040]    Referring again to FIG. 1, reservoir tank  9  has a small drain fitting at the lowest point to drain any accumulation of the denser solvent L 2  through conduit  51 , which connects the drain fitting to the filter unit  53 , thus ensuring that the denser solvent L 2  is removed and the pump  57  is constantly primed. The height of the filter unit  53  is set above the column height of the reservoir tank  9  to prevent overflow. The center tube  60  of the filter unit  53  acts as a drain and allows the reservoir tank  9  to drain back to the solvent tank (not shown) in the event that the filter were to leak air at the top. The height of the tube  60  is selected to limit the amount of solvent that can return to the solvent tank.  
         [0041]    Normally, a small amount of liquid is pulled from the bottom of the reservoir tank  9  to the filter housing  53  on the clean side of the filter  59  through the pump  57  and back into the separation cycle of the accumulator tank  7 . This ensures that the denser solvent L 2  does not accumulate in the reservoir tank  7  and also ensures that the pump  57  re-primes after each cleaning of the filter  59 . A restriction (not shown) is preferably introduced onto conduit  51  to limit the flow of liquid from the reservoir tank  9 , so that essentially only the denser solvent is removed unless greater quantities of liquid are needed to keep the filter  59  flooded and the pump  57  primed.  
         [0042]    The apparatus of the present invention may be used to separate a mixture of two liquids in which the recovery or recirculation of both liquids is desired. Alternatively, the apparatus may be used to remove a lower density liquid contaminant from a denser liquid or a denser liquid contaminant from a lower density liquid. Particulate and soluble contaminants may also be removed with the liquid contaminant phase.  
         [0043]    A liquid mixture containing more than two liquids may be employed. The mixture will separate into a substantially more polar liquid or liquid mixture and a substantially less polar liquid or liquid mixture.  
         [0044]    The apparatus of the present invention is particularly well suited for the dewatering of glycol ethers used in modern dry-cleaning machines. A system in which an apparatus according to another embodiment of the present invention is operated in combination with a dry-cleaning machine is shown in FIG. 3.  
         [0045]    The system depicted in FIG. 3 consists of a dry-cleaning machine, only the solvent tank  102  of which is shown. The solvent tank consists of work tanks  104   a  and  104   b  and clean tank  106 . The glycol ether solvent S contained in each tank becomes contaminated with water, as well as with dirt particles, fatty acids, fats, oils and grease as it is circulated through the dry cleaning machine.  
         [0046]    Pump  157   a  draws solvent S 1  from work tank  104   a  through solvent inlet line  156   a  and filter  153   a.  Pump  157   b  draws solvent S 2  from work tank  104   b  through solvent inlet line  156   b  and filter  153   b,  and so forth. The lines enter each pump through compression fittings, for example, fittings  114  and  116  of pump  157   c.  Pump  157   a  then pumps solvent S 1  through solvent line  118   a  to cylinder  103 . Pump  157   b  pumps solvent S 2  through solvent line  118   b  to the cylinder, and so forth.  
         [0047]    Cylinder  103  is an apparatus according to another embodiment of the present invention. In this embodiment, the accumulator tank  107  is separated into compartments  107   a,    107   b  and  107   c.  Likewise, reservoir tank  109  is separated into compartments  109   a,    109   b  and  109   c.  Each compartment  107   a,    107   b,    107   c  is configured like the accumulator tank  7  of the apparatus depicted in FIG. 1. Each compartment  109   a,    109   b  and  109   c  is configured like the reservoir tank  9  depicted in FIG. 1.  
         [0048]    Each compartment has its own down tube from which heat is withdrawn by a heat exchanger (not shown). Solvent line  118   a  enters the bottom of compartment  107   a  and defines an upward flow path to the top of compartment  107   a  where it discharges into the top of a down tube; solvent line  118   b  enters the bottom of compartment  107   b  and defines an upward flow path to the top of compartment  107   b  where it discharges into the top of a down tube; and so forth.  
         [0049]    A transfer conduit (not shown) defines a downward flow path from the top end of compartment  107   a  to the bottom end of reservoir tank compartment  109   a.  Likewise, another transfer conduit (not shown) defines a downward flow path from the top end of compartment  107   b  to the bottom end of reservoir tank compartment  109   b;  and so forth. Each reservoir tank compartment has an outlet conduit positioned vertically therein with the inlet end situated near the top end of its compartment. Each outlet conduit defines a downward flow path through its compartment and exiting the bottom thereof.  
         [0050]    Openings in each outlet conduit at  141   a,    141   b,    141   c  connect to solvent return line  120   a,    120   b,    120   c,  respectively, to define return flow paths to tanks  104   a,    104   b  and  106 , respectively.  
         [0051]    Openings in the bottom of each accumulator tank compartment and reservoir tank compartment of the type depicted in FIGS. 1 and 2 are employed to drain the bottom of each compartment.  
         [0052]    Referring again to FIG. 3, the system of the present invention operates as follows:  
         [0053]    Solvent S 1 , S 2 , S 3  is drawn from tanks  104   a,    104   b,    106  through inline filters  153   a,    153   b,    153   c  via respective pumps  157   a,    157   b,    157   c  and then into respective accumulator compartments  107   a,    107   b  and  107   c.  The pumps force the solvent to rise in the upward flow paths defined by the inlet conduit in each accumulator tank compartment, after which the solvents then drain into the corresponding down tube of each compartment. Heat exchangers in each compartment withdraw heat from each down tube, reducing the temperature of the solvent in each compartment. The heat exchangers also cool the contents of each compartment, so that the liquid within each compartment functions as a highly effective heat sink, cooling and separating the solvent mixture in each inlet conduit and down tube.  
         [0054]    Exiting the down tubes, the temperature reduction in the solvent causes moisture to precipitate, and, being heavier than solvent, it falls to the bottom of each accumulator compartment. When water precipitates and falls to bottom, any water soluble contaminants, particulate matter, fatty acids, oils, greases and residual perchloroethylene (from previous dry cleaning) sink to the bottom as well. The lighter solvent rises in each accumulator compartment and overflows to the transfer conduit for each accumulator compartment, each of which transfers solvent to the corresponding and adjacent reservoir compartment.  
         [0055]    The reservoir tank and compartments thereof serve to isolate the dewatered solvent from moisture in the accumulator tank. The reservoir tank and reservoir compartments also serve to retain the dewatered solvent for recirculation to the dry cleaning machine solvent tanks. Therefore, the present invention also includes an embodiment in which the accumulator tank is compartmentalized but the reservoir tank is not. Instead, transfer conduits from each accumulator tank compartment discharge solvent to a single reservoir tank.  
         [0056]    Any moisture remaining in the solvent not bound thereto as an azeotrope precipitates to the bottom of the reservoir tank or the compartments thereof. Referring to FIG. 3, each reservoir compartment has an outlet conduit, each of which drains the dewatered solvent from the top end of a compartment through the bottom end of the reservoir tank. The outlet conduits drain from the top end of each compartment in order to prevent any water that may settle to the bottom of a compartment from being drawn into an outlet conduit.  
         [0057]    Each outlet conduit drains dewatered solvent back to one of tank  104   a,    104   b,    106  by way of solvent return line  120   a,    120   b,    120   c.  Each compartment of the accumulator and reservoir tank is drained periodically, preferably daily, of the water and other contaminants that have settled to the bottom.  
         [0058]    The system of the present invention represents a significant advancement in the replacement of perchloroethylene as a dry cleaning solvent. The apparatus of the present invention makes feasible the use of glycol ethers as dry cleaning solvents in commercial applications, which, unlike perchloroethylene, do not pose a hazard to health or the environment.  
         [0059]    The foregoing description of the preferred embodiments should be taken as illustrating, rather than as limiting, the present invention as defined by the claims. Numerous variations and combinations of the features described above can be utilized without departing from the present invention.