Abstract:
A method of water treatment comprising: providing an electrolysis device comprising an electrolysis vessel; providing feed streams to the first salt water chamber of the vessel, second salt water chamber of the vessel, acidic chamber of the vessel, and alkalic chamber of the vessel, the acidic chamber producing an acidic solution and the alkalic chamber producing an alkalic solution; directing at least a portion of the contents of the first and second salt water chambers into a precipitation tank; directing at least a portion of the alkalic solution into the precipitation tank, thereby increasing the pH in the precipitation tank to produce precipitate; and removing the precipitate from the precipitation tank.

Description:
RELATED APPLICATION 
       [0001]    U.S. application Ser. No. 12/123,521, filed May 20, 2008, and assigned to General Electric Company, which is herein incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention is related to the use of an electrolysis device for water treatment. 
       DESCRIPTION OF RELATED ART 
       [0003]    The presence of scale forming species in aqueous systems, such as brackish water and cooling tower make up or blowdown, lead to an increase in system maintenance and a decrease in system yield. Accordingly, a need exists to decrease the presence of scale forming species in aqueous systems. 
       SUMMARY OF THE INVENTION 
       [0004]    One embodiment of the present invention concerns a method of water treatment comprising: providing an electrolysis device comprising an electrolysis vessel; providing feed streams to the first salt water chamber of the vessel, second salt water chamber of the vessel, acidic chamber of the vessel, and alkalic chamber of the vessel, the acidic chamber producing an acidic solution and the alkalic chamber producing an alkalic solution; directing at least a portion of the contents of the first and second salt water chambers into a precipitation tank; directing at least a portion of the alkalic solution into the precipitation tank, thereby increasing the pH in the precipitation tank to produce precipitate; and removing the precipitate from the precipitation tank. 
         [0005]    Another embodiment of the present invention concerns an electrolysis device comprising a pair of electrodes arranged in the electrolysis vessel, serving as a positive electrode and a negative electrode, respectively; and a cell unit arranged between the positive and negative electrodes, the cell unit comprising a bipolar membrane element and at least one cation exchangeable membrane, the bipolar membrane element having a cation exchangeable side and an anion exchangeable side, the cation exchangeable side being closer to the negative electrode than the anion exchangeable side, the at least one cation exchangeable membrane being arranged between the anion exchangeable side of the bipolar membrane element and the positive electrode, so as to define an alkalic chamber between the bipolar membrane element and the cation exchangeable membrane; wherein the cation exchangeable membrane is selective. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    These and other aspects of the invention will be understood from the description and claims herein, taken together with the drawings showing details of construction and illustrative embodiments, wherein: 
           [0007]      FIG. 1  schematically illustrates one embodiment of the bipolar membrane; 
           [0008]      FIG. 2  schematically illustrates a method of operating bipolar membrane of  FIG. 1 ; 
           [0009]      FIG. 3  schematically illustrates a method of operating bipolar membrane of  FIG. 1 ; 
           [0010]      FIG. 4  schematically illustrates a method of operating bipolar membrane of  FIG. 1 ; 
           [0011]      FIG. 5  schematically illustrates a method of operating bipolar membrane of  FIG. 1 ; 
           [0012]      FIG. 6  schematically illustrates a method of operating bipolar membrane of  FIG. 1 ; 
           [0013]      FIG. 7  schematically illustrates a method of operating bipolar membrane of  FIG. 1 ; and 
           [0014]      FIG. 8  schematically illustrates a method of operating bipolar membrane of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0015]    Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about”, is not limited to the precise value specified. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Range limitations may be combined and/or interchanged, and such ranges are identified and include all the sub-ranges stated herein unless context or language indicates otherwise. Other than in the operating examples or where otherwise indicated, all numbers or expressions referring to quantities of ingredients, reaction conditions and the like, used in the specification and the claims, are to be understood as modified in all instances by the term “about”. 
         [0016]    “Optional” or “optionally” means that the subsequently described event or circumstance may or may not occur, or that the subsequently identified material may or may not be present, and that the description includes instances where the event or circumstance occurs or where the material is present, and instances where the event or circumstance does not occur or the material is not present. 
         [0017]    As used herein, the terms “comprises”, “comprising”, “includes”, “including”, “has”, “having”, or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a process, method, article or apparatus that comprises a list of elements is not necessarily limited to only those elements, but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. 
         [0018]    The singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise. 
         [0019]    Cooling towers are widely used in industries to remove heat in processes, such as oil refinery, chemical processes, and power generation plants. Cooling towers are also used in the HVAC systems common in commercial, institutional, and hospital buildings. Water consumption in cooling tower operation constitutes the largest water withdrawal from natural water sources in many countries. Water scarcity has become an increasing concern worldwide. According to the data published by Global environment outlook, 5% of population was facing water scarcity problems in 2000, mainly in the middles east area. However, by year 2030, nearly half of world population will be water stressed. 
         [0020]    In addition to the limited water resources, environment regulation becomes increasingly restricted to disposal of industrial wastewaters. Cost of treating wastewater before discharge to environment is continuously increased in recent years. 
         [0021]    Water shortage worldwide and stringent environment regulations have led to increasing water conservation effort in all industries. Inevitably, it has significant impact on industry water use, especially on huge water consumption industries. Cooling water system conservation efforts have focused on replacing fresh water with treated municipal effluent, reusing plant wastewater, and reducing water discharge by operating at higher cycles of concentration, such as greater than about 7 cycles. 
         [0022]    With increasing cycles of concentration, the tendency for deposition increased due to high concentration of Ca, alkalinity, SiO 2 , silt, Fe, Al, etc. Likewise, the tendency for corrosion increased with increasing cycles due to high conductivity and high concentration of Cl −  and SO 4   2− . 
         [0023]    Common approach to treat cooling towers operating at high cycles is to add acid to reduce alkalinity, operating cooling towers at lower pH, therefore, decreasing the tendency of deposition or precipitation in cooling systems. This usually requires adding a high dose of chemicals such as anionic polymers and corrosion inhibitors to cooling towers. However, handling and storage of strong acid posed a danger to workers and environment, especially in commercial and institutional buildings. Increasing usage of chemicals also results in increasing overall cost of the treatment. 
         [0024]    In one embodiment, the present invention is directed toward a method of treating water from cooling towers operating at a high cycle of concentration using an electrolysis device, such as a bipolar membrane or its combination with a nanofiltration unit. Cooling tower water is provided to the electrolysis device. An acidic solution generated from the electrolysis device is added to cooling towers to reduce alkalinity and pH. An alkalic solution generated from the electrolysis device is added to a portion of cooling tower blowdown stream in a separation apparatus to precipitate calcium, silica and other scale forming species. The water after precipitates removal in the separation apparatus is softened and returned to cooling tower. This method allows cooling tower to operate at high cycles of concentration and/or achieve zero liquid discharge, thus significantly reducing water consumption and water treatment chemical usage. 
         [0025]    Referring to  FIG. 1 , a first embodiment of the electrolysis device  2  for producing an acidic solution and alkalic solution includes a pair of electrodes respectively acting as a positive electrode  21  and a negative electrode  22 , at least one cell unit  23  between the positive and negative electrodes  21 ,  22 , and a vessel  24  for housing the electrodes  21 ,  22  and the cell unit  23  therein. The positive and negative electrodes  21 ,  22  respectively connect with an anode and a cathode of a DC power supply  25 . The vessel  24  includes at least a first inlet  243 , second inlet  244 , third inlet,  245 , and fourth inlet  246  for inducing a feed stream to flow through the electrolysis device  2 . The cell unit  23  includes at least one alkalic chamber  236  and at least one acidic chamber  235  defined between ion exchangeable membranes, which will be discussed in detail below. 
         [0026]    The cell unit  23  of the vessel  24  of electrolysis device  2  according to the first embodiment, shown in  FIG. 1 , comprises a bipolar membrane element  230 , a cation exchangeable membrane  231 , and an anion exchangeable membrane  232 . The bipolar membrane element  230  has a cation exchangeable side  233  and an anion exchangeable side  234 , and is used as a water splitter. The cation exchangeable side  233  of the bipolar membrane element  230  is closer to the positive electrode  21  than the anion exchangeable membrane  232 . The cation exchangeable membrane  231  is arranged between the anion exchangeable side  234  and the positive electrode  21 . The anion exchangeable membrane  232  is arranged between the cation exchangeable side  233  and the negative electrode  22 . 
         [0027]    A direct current from the power supply  25  flows through the bipolar membrane element  230  causing the water to split with OH −  ions being produced on the anion exchangeable side  234  and a corresponding number of H +  ions being produced on the cation exchangeable side  233  of the bipolar membrane element  230 . The generated OH −  and H +  ions are prevented from moving further by the cation exchangeable membrane  231  and the anion exchangeable membrane  232 , respectively. 
         [0028]    Cation exchangeable membrane  231  is selective and only passes univalent cationic ions. Anion exchangeable membrane  232  is selective and only passes univalent anionic ions. Accordingly, Na +  ions from the salt water received by second inlet  244  move through cation exchangeable membrane  231  toward the negative electrode  22 , while Ca 2+ , Mg 2+ , Ba 2+ , Fe 2+ , Fe 2+ , and Al 2+  do not move through cation exchangeable membrane  231 . Further, Cl −  ions from the salt water received by first inlet  243  move through anion exchangeable membrane  232  toward the positive electrode  21 , while CO 3   2− , SO 4   2−  and PO 4   2−  do not move through the anion exchangeable membrane  232 . 
         [0029]    Thus an alkalic chamber  236  is defined between the bipolar membrane element  230  and the cation exchangeable membrane  231 , and an acidic chamber  235  is defined between the bipolar membrane element  230  and the anion exchangeable membrane  232 . 
         [0030]    A first salt water chamber  237  is defined between negative electrode  22  and anion exchangeable membrane  232 . A second salt water chamber  238  is defined between positive electrode  21  and cation exchangeable membrane  231 . 
         [0031]    A first inlet  243  provides a feed stream to the first salt water chamber  237 , a second inlet  244  provides a feed stream to the second salt water chamber  238 , a third inlet  245  provides a feed stream to the acidic chamber  235 , and a fourth inlet  244  provides a feed stream to the alkalic chamber  236 . The feed streams provided to first salt water chamber  237  and second salt water chamber  238  may be comprised of at least one of cooling tower make up water, cooling tower blow down water, or low quality water 
         [0032]    The vessel  24  further includes an acidic outlet  241  and an alkalic outlet  242  respectively for the alkalic solution of alkalic chamber  236  and the acidic solution of acidic chamber  235  to flow out of. The vessel  24  also includes a first salt water outlet  247  and a second salt water outlet  248  respectively for the salt water of first salt water chamber  237  and second salt water chamber  238  to flow out of. 
         [0033]    The feed stream entering the acidic chamber  235  through inlet  245  can be one or both of pure water or the acidic solution exiting acidic outlet  241  of the vessel  24 . The feed stream entering alkalic chamber  236  through inlet  246  can be one or both of pure water or the alkalic solution exiting alkalic outlet  242  of vessel  24 . 
         [0034]    The alkalic solution produced at alkalic outlet  242  can be used to create a high pH environment to precipitate hardness and other species in aqueous systems, such as CaCO 3 , CaMg(CO 3 ) 2 , Ca 3 (PO 4 ) 2 , Ca 5 (PO 4 ) 3 OH, CaSO 4 , Fe(OH) 3 , Al(OH) 3 , MgSiO 3  etc. The acidic solution produced in acidic chamber  235  can be used to adjust pH of cooling tower water and clean hardness off membranes or electrodes in the vessel  24 . 
         [0035]    The bipolar membrane element  230  has a water splitting feature to split water directly into H +  and OH − . 
         [0036]    The application of the bipolar membrane element  230  greatly improves the efficiency of the electrolysis device  2  for producing alkalic solution and acidic solution from the water. The bipolar membrane element  230  may be a bipolar membrane which includes a cation exchangeable layer and an anion exchangeable layer, or a bipolar module formed by a combination of anion and cation exchangeable membranes which functions as a bipolar membrane. 
         [0037]    In one embodiment, the positive and negative electrodes  21 ,  22  are made from highly porous carbon materials selected from any of activated carbon, carbon black, carbon nanotubes, graphite, carbon fiber, carbon cloth, carbon aerogel, or combination thereof. Surface area of the carbon material is in a range of from about 500 to 2000 square meters per gramme as measured by nitrogen adsorption BET method. high porous positive and negative electrodes  21 ,  22  each have a shape, size or configuration that is a plate, a block, a cylinder, or a sheet. It is also anticipated that positive and negative electrodes  21 ,  22  can be made of any metal or porous material deemed suitable by a person having ordinary skill in the art, such as activated carbon. 
         [0038]      FIG. 2  discloses one embodiment in which electrolysis device  2  is used to generate acid solution for cooling tower water pH adjustment or cleaning of electrolysis device  2  and to generate base for hardness precipitation. In this configuration, the output of salt water tank  301  is provided as a feed stream to said first salt water chamber  237  and second salt water chamber  238  of vessel  24 . Salt water tank  301  can contain one or more of cooling tower make up water, cooling tower blow down water, or low quality water. Low quality water is any water that needs to be treated to soften and/or remove undesirable ion species, such as brackish water. Water is provided as a feed stream to the acidic chamber  235  and alkalic chamber  236 . The output of acidic chamber  235  is provided to cooling towers. The output of alkalic chamber  236  is provided to precipitation tank  304 , and the output of the first and second salt water chambers  237  and  238  is also provided to the precipitation tank  304 . Accordingly, the addition of the alkalic solution from alkalic chamber  236  into precipitation tank  304  increases the pH in precipitation tank  304  to a desired value to precipitate metal salts and metal hydroxides, such as CaCO 3 , MgCO 3 , CaSO 4 , Mg(OH) 2 , etc. After the precipitate is removed from precipitation tank  304 , the treated water from precipitation tank  304  is provided to a water storage tank or to cooling towers. In one embodiment, the desired pH value in precipitation tank  304  after the addition of alkalic solution from electrolysis device  2  is between about 7 to 14, preferably between about 8 to 13 and more preferably between about 9 to 12. 
         [0039]    Further, as is shown in  FIG. 3 , it is also contemplated that in some embodiments all or part of the acidic solution produced in acidic chamber  235  can be returned to acidic chamber  235  as a feed stream. Further, all or part of the alkalic solution produced in alkalic chamber  236  can be returned to alkalic chamber  236  as a feed stream. This would allow for the concentration of the acid and base solutions to be increased with time within acidic chamber  235  and alkalic chamber  236 . Further, this would allow for the pH within the precipitation tank  304  increases to enhance precipitation. 
         [0040]      FIG. 4  discloses another embodiment in which electrolysis device  2  is used to generate an acidic solution for cooling tower water pH adjustment or cleaning of electrolysis device and to generate a base solution for hardness precipitation. In this embodiment, cooling tower blowdown is delivered to selective membrane  501 , which outputs a divalent ion stream that is provided to precipitation tank  502 . Selective membrane  501  may be a nanofiltration unit. The divalent ion stream contains one or more divalent ions, such as Ca 2+ , Mg 2+ , Ba 2+ , Fe 2+ , Fe 3+ , Al 3+ , CO 3   2− , SO 4   2−  and PO 4   3− , etc. Selective membrane  501  outputs a univalent ion stream that is provided to the first and second salt water chambers  237  and  238  of vessel  24 . The univalent ion stream contains one or more univalent ions, such as Na + , Cl − , etc. Further, a water feed stream is provided to the acidic chamber  235  and alkalic chamber  236  of vessel  24 . 
         [0041]    The alkalic solution output of the alkalic chamber  236  is provided to the precipitation tank  502 , which increases the pH in precipitation tank  502  to a desired value to precipitate metal salts and metal hydroxides, such as CaCO 3 , MgCO 3 , CaSO 4 , Mg(OH) 2 , etc. In one embodiment, the desired pH value in precipitation tank  304  after the addition of alkalic solution from vessel  24  is between about 7 to 14, preferably between about 8 to 13 and more preferably between about 9 to 12. 
         [0042]    The precipitates are then removed from precipitation tank  502  and the remaining treated water contained in precipitation tank  502  is used as cooling tower make up water or for other industrial processes. The output of the first and second salt water chambers  237  and  238  is combined with the remaining treated water from the precipitation tank  302  as cooling tower make up water or for other industrial processes, The acidic solution output of the acidic chamber  235  can be used to adjust pH of cooling tower water and/or adjust the pH of treated water stream exiting from precipitation tank  502 , and to clean membranes of vessel  24 . Returning the remaining water from precipitation tank  502  to the cooling tower reduces water consumption and reduces or eliminates the waste water discharged to a sewer or river. Further, the use of high quality water in the cooling tower reduces the amount of chemicals required to treat the water in the cooling tower, thus reducing disposal cost and impact on the environment. 
         [0043]    Further, as is shown in  FIG. 5 , it is also contemplated that in some embodiments all or part of the acidic solution output of acidic chamber  235  can be returned to acidic chamber  235  as a feed stream. Further, all or part of the alkalic solution output of alkalic chamber  236  can be returned to alkalic chamber  236  as a feed stream. This would allow for the concentration of acid and base solutions to be increased with time within acidic chamber  235  and alkalic chamber  236 . Additionally, the output of salt chambers  237  and  238  is combined with the remaining treated water from the precipitation tank after precipitate removal as cooling tower make up water or for other industrial processes. 
         [0044]      FIG. 6  discloses another embodiment in which electrolysis device  2  is used to generate acidic solution for cooling tower water pH adjustment, the cleaning of electrolysis device  2 , and/or to generate base for hardness precipitation. In this embodiment, a feed stream of low quality water, such as brackish water, is delivered to selective membrane  601 , which outputs a divalent ion stream that is provided to precipitation tank  602 . However, it is contemplated that the feed stream can be comprised of at least one of cooling tower make up water, cooling tower blow down, or low quality water. The divalent ion stream contains one or more divalent ions, such as ca 2+ , mg 2+ , Ba 2+ , Fe 2+ , Fe 3+ , Al 3+ , CO 3   2− , SO 4   2− , PO 4   3 , etc. Selective membrane  601  outputs a univalent ion stream that is provided to the first and second salt water chambers  237  and  238  of electrolysis device  2 . Selective membrane  601  may be a nanofiltration unit. The univalent ion stream contains one or more univalent ions, such as Na + , Cl − , etc. Further, a water feed stream is provided to the acidic chamber  235  and alkalic chamber  236  of vessel  24 . 
         [0045]    The output of the alkalic chamber  236  is provided to the precipitation tank  602 , which increases the pH in precipitation tank  602  to a desired value to precipitate Ca and Mg salts and metal hydroxides. In one embodiment, the desired pH value in precipitation tank  602  after the addition of alkalic solution from vessel  24  is between about 7 to 14, preferably between about 8 to 13 and more preferably between about 9 to 12. The precipitates are then removed from precipitation tank  602  and the remaining treated water contained in precipitation tank  602  is used as cooling tower make up water or for other industrial processes. The output of first and second salt water chambers  237  and  238  is combined with the remaining treated water from the precipitation tank and used as cooling tower make up water or for other industrial processes. The acidic solution output of the acidic chamber  235  can be used to adjust the pH of cooling tower water, adjust the pH of the treated water stream exiting from precipitation tank  602 , and/or clean membranes of vessel  24 . 
         [0046]    Further, as is shown in  FIG. 7 , it is also contemplated that in some embodiments all or part of the output of acidic chamber  235  can be returned to acidic chamber  235  as a feed stream. Further, all or part of the output of alkalic chamber  236  can be returned to alkalic chamber  236  as a feed stream. This would allow for the concentration of acid solution and base solution to be increased with time within acidic chamber  235  and alkalic chamber  236 . The output of first salt water chambers  237  and  238  is combined with the remaining treated water from the precipitation tank and used as cooling tower make up water or for other industrial processes. 
         [0047]    Turning to  FIG. 8 , in one embodiment of this invention, a first portion of blowdown from a cooling tower operating at a high cycle of concentration, greater than about 7 cycles, and pure water are provided to an electrolysis unit. The electrolysis unit uses the first portion of blowdown and pure water to generate an acidic solution in acid chamber  235 , an alkalic solution in alkalic chamber  236 , and a salt water solution in first and second chambers  237  and  238 . The acidic solution is provided to the cooling tower to reduce the alkalinity and pH of the water circulating through the cooling tower. The alkalic solution is mixed with a second portion of blowdown in precipitation tank  702  to precipitate and remove calcium and other scaling forming species from the second portion of blowdown, thereby softening the second portion of blowdown. The softened second portion of blowdown is then returned to the cooling tower as make up water. 
         [0048]    In one embodiment, the blowdown is filtered by a nanofiltration unit  701  after leaving the cooling tower. After nanofiltration, the first portion of blowdown is comprised of one or more univalent ions and the second portion of blowdown is comprised of one or more divalent ions. In some embodiments, the salt water solution is added to the softened second portion of blowdown and returned to the cooling tower as makeup water. 
         [0049]    While this invention has been described in conjunction with the specific embodiments described above, it is evident that many alternatives, combinations, modifications and variations are apparent to those skilled in the art. Accordingly, the preferred embodiments of this invention, as set forth above are intended to be illustrative only, and not in a limiting sense. Various changes can be made without departing from the spirit and scope of this invention. Therefore, the technical scope of the present invention encompasses not only those embodiments described above, but also all that fall within the scope of the appended claims. 
         [0050]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated processes. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. These other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.