Abstract:
An ion exchange apparatus includes at least one fluid passage that extends between an inlet and an outlet for transporting a fluid having ions therein. At least one cartridge includes an ion exchange material and the cartridge has an ion removal rate of removing the ions from the fluid that varies in response to a concentration of the ions in the fluid.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates to ion exchange reactors and, more particularly, to an ion exchange reactor having low pressure loss and a variable ion removal rate. 
         [0002]    Conventional ion exchange reactors are used to remove ions from a fluid, such as water, to maintain electric resistivity, neutral pH, or both. Typical ion exchange reactors circulate fluid through a container filled with closely packed ion exchange media. The close packing of the media produces tortuous flow paths for the fluid as it flows between the media particles. The tortuous flow paths maximize the exposure of the fluid to ionically active surfaces of the media and minimize a diffusion distance that the ions must travel through the water to the ionically active surfaces. In this manner, conventional ion exchange reactors efficiently remove essentially all of the ions from the fluid in one pass through the reactor. 
         [0003]    Although effective for ion removal, conventional ion exchange reactors that utilize packed ion exchange media have the disadvantage that the tortuous paths slow the velocity of the fluid and thereby cause a significant pressure drop between incoming fluid and outgoing fluid. The pressure drop can be overcome in part by using a larger, more powerful pump to move the fluid through the reactor. However, using a larger pump adds size and expense to the system. Further, since conventional reactors essentially remove all of the ions, control over the electric resistivity or pH of the fluid is limited. 
         [0004]    Accordingly, there is a need for an ion exchange reactor that provides control over ion removal, and in turn over electric resistivity and pH, while achieving a relatively low pressure drop. 
       SUMMARY OF THE INVENTION 
       [0005]    An example ion exchange apparatus includes at least one fluid passage that extends between an inlet and an outlet for transporting a fluid having ions. One or more cartridges include an ion exchange material. The cartridge has an ion removal rate that varies in response to a concentration of the ions in the fluid and the fluid velocity through the reactor. 
         [0006]    An example method of controlling ion removal from a fluid flowing through the ion exchange apparatus includes the steps of establishing a first ion removal rate when a concentration of ions in the fluid is at a first ion concentration, and establishing a second, lower ion removal rate when the concentration of ions is at a second, lower ion concentration. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows. 
           [0008]      FIG. 1  is an example cooling system utilizing an ion exchange reactor. 
           [0009]      FIG. 2  is an example of the ion exchange reactor of  FIG. 1 . 
           [0010]      FIG. 3  is an exploded view of the example ion exchange reactor. 
           [0011]      FIG. 4  is an exploded view of an example cartridge for use in the ion exchange reactor. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0012]      FIG. 1  illustrates selected portions of an example cooling system  10 , such as an ultra-pure water cooling system. In this example, the cooling system  10  includes a heat exchanger  12  arranged within a cooling loop  14 . The cooling loop  14  circulates a coolant, such as water, between the heat exchanger  12  and a device  16  that the coolant maintains at a desired temperature. The cooling loop  14  employs an ion exchange reactor  18  to maintain the coolant in a desired pure state. For example, the ion exchange reactor  18  removes ions from the coolant to maintain a desired level of electrical resistivity and/or a desired coolant pH. It is to be understood that the above described coolant system  10  is an example, and that other types of systems will also benefit from the ion exchange reactor  18 . 
         [0013]      FIG. 2  illustrates an example of the ion exchange reactor  18 , which includes an outer container  30  having an inlet  32  and an outlet  34 . Although the container  30  is cylindrically shaped in this example, any number of different shapes may be used. The container  30  encloses at least one cartridge  36  for removing the ions from the coolant. In the illustrated example, a plurality of the cartridges  36  are used. However, it is to be understood that the number of cartridges  36  may be varied depending upon the ion removal needs of a particular system. 
         [0014]    Referring also to the exploded view in  FIG. 3 , the cartridges  36  are spaced apart such that there are fluid passages  38  that extend between the cartridges  36 . The amount of spacing between the cartridges  36  depends upon the desired ion removal performance, as will be described. The cartridges  36  vary in size. For example, a cartridge  36   a  located radially outwards from a centerline A of the container  30  is smaller than a cartridge  36   b  located closer to the centerline A. That is, the cartridge  36   a  includes less interfacial surface area exposed to the fluid passages  38  than the cartridge  36   b.    
         [0015]    The container  30  includes stepped grooves  40  for retaining and positioning the cartridges  36 . In this example, the stepped grooves  40  position a first set of cartridges  36   c  parallel and end-to-end with a second set of cartridges  36   d . Alternatively, only one set of cartridges  36  could be used, or a greater number than two sets of cartridges may be used, depending upon the ion removal needs of a particular system. 
         [0016]    The stepped grooves  40  also position the cartridges  36  approximately parallel to a flow direction  42  ( FIG. 2 ) through the ion exchange reactor  18 . Thus, the fluid passages  38  extend linearly between the ends of the cartridges  36  and provide little or no resistance to coolant flow between the cartridges  36 . 
         [0017]      FIG. 4  illustrates an exploded view of an example cartridge  36 . In this example, the cartridge  36  includes a frame  52 . The frame is a rectangular ring defining an interior open space. It is to be understood however, that the shape of the frame  52  may vary from the disclosed example, depending upon design factors, such as the size requirements of a particular system. Optionally, the frame  52  also includes an opening  54  and a seal  56  that removably fits within the opening  54 . The opening  54  provides access the interior of the frame  52  to permit filling or removal of an ion exchange media  58  into the cartridge  36 . 
         [0018]    A porous screen  60  is attached on each planar side of the frame  52  between porous covers  62  that are secured to the frame  52 . In this example, fasteners  64  extend through the porous covers  62  and into the frame  52  to secure the porous screens  60  between the porous covers  62  and the frame  52 . Once assembled, the porous covers  62  and porous screen  60  permit water flow there through from the fluid passages  38  to the ion exchange media  58 . The porosity of the porous screens  60  and the porous covers  62  limits the flow of coolant into and out of the cartridge  36 . 
         [0019]    The ion exchange media  58  includes an ion exchange resin. For example, the resin includes anionic active sites  66  and cationic active sites  68  for, respectively, removing anions and cations from the coolant. Alternatively, the ion exchange media  58  may be another type of ion exchange media suited for the particular system. 
         [0020]    The cartridges  36  and their arrangement within the container  30  provide the benefit of an ion removal rate that varies with the concentration of the ions in the coolant. In the illustrated example, the open fluid passages  38  between the cartridges  36  establish a diffusion distance for the ions to travel to the ion exchange media  58 . That is, for the ions to be removed from the coolant, the ions must move through the coolant within the fluid passages  38 , through openings in the porous cover  62 , through openings in the porous screen  60 , and to an active site  66 ,  68  of the ion exchange media  58 . The diffusion of ions per unit of time, or mass transfer, is proportional to the concentration and the interfacial surface area of the cartridges  36 . That is, increasing concentration and interfacial surface area increases mass transfer. The inverse occurs for decreasing concentration and decreasing interfacial surface area. 
         [0021]    At relatively higher concentrations, a portion of the ions diffuse into the cartridges  36  for removal, which results in a relatively high ion removal rate that requires few passes through the reactor  18  to remove a significant amount of the ions. Conversely, at relatively lower concentrations, fewer ions diffuse into the cartridges  36  for removal, which results in a relatively low ion removal rate that requires many passes through the reactor  18  to remove remaining ions. The specific ion removal rates of a particular system will vary, depending on a variety of factors such as the types of ions, coolant flow rate, system corrosion etc. 
         [0022]    The ion removal rate is also proportional to the interfacial surface area of the cartridges  36 . That is, the rates shift in proportion to the interfacial surface area. For example, if the arrangement in the disclosed example is changed such that the cartridges  36  are closer together, the size of the fluid passages  38  would decrease and the effective interfacial surface area of the cartridges  36  would increase. This would result in a shorter diffusion distance between the fluid passages  38  and the ion exchange material  58 , and a corresponding greater ion removal rate. Conversely, if the cartridges  36  where farther apart than in the illustrated example, the size of the fluid passages  38  would increase. This would result in a greater diffusion distance and a corresponding lower ion removal rate. Thus, the spacing between the cartridges  36  at least partially determines the amount of effective interfacial surface area and can be designed to achieve a desired ion removal rate. For example, the spacing of the cartridges  36  can be predetermined through experimentation for desirable ion removal rates. 
         [0023]    The variation in ion removal rate provides the benefit of establishing an equilibrium ion concentration level above zero rather than removing essentially all of the ions. At progressively lower concentrations, the ion removal rate approaches zero order and is too slow to remove the remaining ions. By allowing some of the ions to remain in the coolant, the electric resistivity and pH can be controlled to a desired level. For example, a particular equilibrium resistivity and pH may be achieved by using particular sizes and numbers of cartridges  36  and by using a particular spacing of cartridges  36 . In the illustrated example, the electrical resistivity is maintained between 0.2 and 5.0 Mohm-cm during operation of the coolant system  10 . Controlling the electrical resistivity and the pH of the coolant provides the opportunity to tailor the electrical resistivity and pH of the coolant to the coolant system  10 . For example, in coolant systems  10  that utilize ultra pure water, it may be desirable to maintain the resistivity within the above range to prevent current leakage within the device  16  or elsewhere within the coolant system  10 . Similarly, controlling the pH to a desired level may provide better control over corrosion within the coolant system  10 . 
         [0024]    The disclosed example ion exchange reactor  18  provides the benefit of a relatively low pressure drop compared to previously known reactors, and the ability to control the electrical resistivity and pH of a coolant. For example, the open, linear fluid passages  38  allow relatively free flow of the coolant through the ion exchange reactor  18  to thereby produce low pressure drop. Additionally, the arrangement of the cartridges  36  within the container  30  permits variation of the ion removal rate such that the ion exchange reactor  18  becomes more efficient in removing ions at high concentrations and less efficient in removing ions at low concentrations. 
         [0025]    Although a combination of features is shown in the illustrated examples, not all of them need to be combined to realize the benefits of various embodiments of this disclosure. In other words, a system designed according to an embodiment of this disclosure will not necessarily include all of the features shown in any one of the Figures or all of the portions schematically shown in the Figures. Moreover, selected features of one example embodiment may be combined with selected features of other example embodiments. 
         [0026]    The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this disclosure. The scope of legal protection given to this disclosure can only be determined by studying the following claims.