Abstract:
The inventive subject matter provides apparatus, systems and methods in which a feed fluid entering a filtration system is mixed with a portion of a reject fluid. The re-introduced reject fluid is preferably pressurized using a positive displacement pump, and more preferably using a work exchange pump having a translatable piston. The re-introduced reject fluid is preferably pressurized to within 10 psi, or more preferably to within 5 psi, of the uncombined feed fluid. The filtration system can have one or more filters.

Description:
[0001]    This application claims priority to U.S. provisional patent application Ser. No. 61/587538 filed Jan. 17, 2012, the disclosure of which is incorporated herein in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The field of the invention is filtration systems and methods. 
       BACKGROUND 
       [0003]    To reduce the energy requirements of a reverse osmosis pump system, it is known to include a pumping system that can conserve a portion of the pressure of an incoming stream to thereby increase the pressure of a second stream. See, e.g., U.S. pat. publ. no. 2008/0296224 to Cook, et al. (publ. Dec. 2008). However, such system requires electricity to operate the pumping system, which increases the overall energy use of the system. 
         [0004]    Cook and all other extrinsic materials discussed herein are incorporated by reference in their entirety. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply. 
         [0005]    To further reduce the energy requirements of filtrations systems, it is known to utilize a work exchange pump, such as that discussed in U.S. pat. publ. no. 2005/0035048 to Chancellor et al. (publ. February 2005) and U.S. Pat. No. 6,017,200 to Childs, et al. However, such systems are complex, which increases the maintenance and energy costs of the systems. 
         [0006]    Thus, there is still a need for filtration systems having reduced energy requirements. 
       SUMMARY OF THE INVENTION 
       [0007]    The inventive subject matter provides apparatus, systems and methods in which a feed fluid entering a filtration system is mixed with a portion of a reject fluid. The re-introduced reject fluid is preferably pressurized using a positive displacement pump, and more preferably using a work exchange pump having a translatable piston. The re-introduced reject fluid is preferably pressurized to within 10 psi, or more preferably to within 5 psi, of the uncombined feed fluid. The filtration system can have one or more filters. 
         [0008]    Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0009]      FIG. 1A  is a schematic of a positive displacement energy recovery unit for a pressurized filtration system. 
           [0010]      FIG. 1B  is a schematic of the positive displacement energy recovery unit of  FIG. 1 , at a different point in operation of the energy recovery unit. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    One embodiment of a filtration system  100  is shown in  FIGS. 1A and 1B . System  100  can receive a feedwater stream  102  that can flow past one or both of pumps P 1  and P 2 , which thereby increase a pressure of the feedwater stream  102  to approximately 125-200 psi, and more preferably at least about 150 psi, although the specific pressure can vary depending upon the application. For example, the pressure of a feedwater stream comprising brackish water will likely be less than that of a feedwater stream comprising salt water because the brackish water will require less pressure to operate the filter. 
         [0012]    System  100  can include a first filter  110  configured to receive at least a portion of feedwater stream  102  and produce a permeate stream  104 A and reject stream  106 , which can then be fed into a second filter  112  to produce a second permeate stream  104 B and a reject stream  108 . In this manner, the feedwater stream  102  can be passed through multiple filters to remove a larger percentage of impurities from the stream  102  and it is contemplated that the stream  102  could be passed serially through three or more filters although the specific number of filters will depend upon the application. In alternative embodiments, the feedwater stream  102  could be separated into two or more streams and each stream could be passed through one or more filters in parallel. 
         [0013]    Permeate streams  104 A and  104 B can optionally be merged downstream of the filters  110  and  112  as combined stream  104 . 
         [0014]    Preferred filters include reverse osmosis (RO) filters, and especially preferred RO filters include a filter element and a casing formed about the filter element, such as those described in U.S. utility application titled “Water Purification System With Entrained Filtration Elements” having Ser. No. 13/263819 filed on Oct. 10, 2011. As used herein, the term “filter element” is defined to include all commercially suitable filters including, for example, sand, charcoal, paper, and other media, and any membrane capable of filtering a fluid. The filter element could be of any type, size or manufacturer, and preferably the filter element is selected based upon the commercial application. 
         [0015]    A first portion  111  of the reject stream  108  can bypass pump P 3  to increase its pressure before it is merged with the feedwater stream  102  downstream of pump P 2 . By using a smaller pump P 3  rather than pump P 2  to pressurize the reject stream  108 , less energy is advantageously consumed. P 2  is used primarily to boost pressure of reject stream  108  and re-circulate feed fluid  108  back into the feed fluid stream  103   a  (i.e., P 2  discharge). 
         [0016]    A second portion  109  of the reject stream  108  can be diverted upstream of pump P 3  and fed into a lower portion of energy recovery unit. In preferred embodiments, the energy recovery unit comprises a positive displacement pump  118  having a cylindrical unit  120  and piston  122 . As shown in  FIG. 1A , the higher pressure reject stream  109  causes a piston  122  within pump  118  to translate leftward, which thereby expels a feedwater stream  126  from a left side outlet of pump  118  through mechanical check valve  128 . In this manner, the pressure of the feedwater stream  126  can be increased via work exchange with the reject stream  109 , which advantageously eliminates a need for an additional in-line pressure booster pump, and its associated energy costs. Preferably, piston  122  is a zero-buoyancy piston to reduce blowby around the piston  122 , and also to reduce the pressure loss and friction between the piston  122  and unit  120 . 
         [0017]    The feedwater stream  126  can be fed into a venturi valve  140  as a result of the negative pressure created as stream  108  flows through the venturi valve  140 . This advantageously reduces the energy costs of system  100 , as the reject stream  108  does not require a pump between valve  140  and pump  118 . It is especially preferred that the positive displacement pump  120  be disposed vertically with respect to a ground level, such that the feedwater stream  128  flowing from pump  118  has a pressure near (preferably with 10 psi, and more preferably within 5 psi) that of feedwater stream  102  without the need for an additional pump. 
         [0018]    To reduce the amount of fluids exchanged between opposite sides of piston  122 , it is preferred that the difference in pressure between the fluids on each side is less than 10 psi. 
         [0019]    After piston  122  reaches a desired left side position within pump  120 , a sensor can send a signal to cause L-diverter valve  125  to be rotated to stop flow of the portion  109  of the reject stream  108  to the pump  118 , as shown in  FIG. 1B . Although valves  128  and  129  are shown as separate valves, it is contemplated that a three-way valve could be substituted for the valves  128  and  129  to thereby further reduce the complexity of system  100 . In addition, rather than using L-diverter valve  125 , any commercially suitable valve(s) could be used including, for example, actuated gate valves, and ball valves. Separate valves could also be used in place of valve  125  to regulate flow into and out from the pump  118 , respectively. 
         [0020]    With valve  129  opened and valve  128  closed, a portion  103  of the feedwater stream  102  can be removed upstream of pump P 2  and fed into pump  118 . As shown in  FIG. 1B , the higher pressure feedwater stream  103  causes piston  122  to translate downwardly, which thereby expels the lower pressure reject stream  124  from a lower outlet of pump  118  through valve  125 . After the piston  122  reaches a lower portion of the pump  118 , a sensor can send a signal to cause L-diverter valve  125  to be rotated to allow the flow of portion  109  of the reject stream  108  to the pump  118 , as shown in  FIG. 1B . 
         [0021]    As used herein, and unless the context dictates otherwise, the term “coupled to” is intended to include both direct coupling (in which two elements that are coupled to each other contact each other) and indirect coupling (in which at least one additional element is located between the two elements). Therefore, the terms “coupled to” and “coupled with” are used synonymously. 
         [0022]    It should be apparent to those skilled in the art that many more modifications besides those already described are possible without departing from the inventive concepts herein. The inventive subject matter, therefore, is not to be restricted except in the scope of the appended claims. Moreover, in interpreting both the specification and the claims, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the terms “comprises” and “comprising” should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced. Where the specification claims refers to at least one of something selected from the group consisting of A, B, C . . . and N, the text should be interpreted as requiring only one element from the group, not A plus N, or B plus N, etc.