Abstract:
A cooling tower water management system is disclosed. A water treatment module is positioned in a water circulation line in a cooling tower. The water treatment module comprises a treatment cell having a cathodic tube and an anodic rod within the tube. A controller and power supply create a pulsed electrical potential across water in the treatment cell from the cathode to the anode to perform electrolysis on the water. Suspended and dissolved solids in the water are built up on a surface within the treatment cell. The controller can initiate a regeneration cycle to remove the built up solids from the surface. The regeneration comprises switching the electrical contact from the anode to a portion of the cathodic tube.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Application No. 61/281,339, filed on Nov. 16, 2009 and incorporated herein by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    This disclosure relates to an electrolytic water treatment module and associated systems and methods for use with cooling towers. 
       BACKGROUND 
       [0003]    Water-based cooling towers are commonly used to remove excess heat from buildings, factories, and industrial equipment. The water absorbs unwanted heat, and the heated water is piped to a cooling tower where the water transfers the heat to the air through a system of evaporators, louvers, etc. Frequently the cooling towers are placed on a roof of a building where they can be seen venting heat and steam into the air. The cooling towers use the relatively high latent heat of evaporation of water to transfer heat into the air. Cooling towers cool water through evaporative and convection cooling principles. At the actual point of heat exchange with the process medium there will be some loss of water due to evaporation. The tower return water containing heat picked up at the point of heat exchange with the chillers or process load is cooled for return to the tower fill/supply reservoir or sprays. This water is distributed uniformly over the tower system. The tower breaks up the water to small droplets which flow through the fill. At the same time air is flowed across the water. As the air and water contact each other evaporation takes place. During the evaporation process, heat is removed from the cooling tower water equivalent to the latent heat of vaporization, which in turn cools the process medium. 
         [0004]    The latent heat of evaporation is equivalent to 1,000 BTU per pound of water evaporation. In general this is equivalent to 1 degree F. drop in cooling water for each 0.1% of water evaporated. The following formula is used to determine evaporation in a cooling tower system: 
         [0000]      Evaporation=0.1%×delta  T ×Recirculation Rate,GPM
       E=0.001×delta T×R, where delta T=Temperature Drop and R=recirculation rate of the condenser water pumps in GPM.       
 
         [0006]    The following is an example of tower evaporation with tower return temperature at 950 F and discharge temperature at 850 F. The tower water recirculation rate is 3,000 GPM. 
         [0007]    E=0.001×(950 F-850 F)×3,000 GPM 
         [0008]    E=0.001×10×3000 GPM 
         [0009]    E=30 GPM 
         [0010]    The water in these cooling towers is generally supplied by the municipal water supply, and so it carries solids and other suspended or dissolved substances. The water that evaporates into the air does not, however, carry any of these substances with it. As the water cycles through the cooling tower, the concentration of these substances in the water increases. Gradually, the efficiency of the cooling tower decreases and the concentration of suspended or dissolved solids in the water increases. Make-up water is needed to compensate for the evaporated water, but in many applications water is expensive or difficult to obtain. The following relationships exist between make-up water, evaporation, and bleed-off: 
         [0000]      Make-up (contains impurities)=Evaporation (no impurities)+Bleed-off (contains concentrated impurities) 
         [0000]      Or: 
         [0000]      Make-up=Evaporation+Bleed-off 
         [0000]    The equation for bleed-off is then: 
         [0000]      Bleed-off=Evaporation/(cycles of concentration−1)
 
         [0000]    Thus for a system used above and concentrating the solids three times the bleed-off rate would be: 
         [0011]    Bleed-off=30/(3−1)=15 GPM or 
         [0012]    Make-up=30 GPM Evaporation+15 GPM Bleed-off 
         [0013]    Make-up=45 GPM 
         [0014]    In general terms, there are problems presented by operations of the type just described. When water is bled off it is discharged into the municipal water system, this is a waste of water and requires introducing an amount of makeup water to the cooling tower supply resulting in an overall increase in the volume of water required for the operation of the cooling tower. Moreover, the water being discharged returns dissolved and suspended solids to municipal water system, and in a more concentrated form than when withdrawn from the municipal water system. 
         [0015]    Even with water treatment as discussed above there are constraints on time of additive exposure in the water and on the quantity of the particular additive which must be adhered to insure against solids coming out of solution. In most cases, these additives are undesirable as unwanted chemicals and their concentration in the water supply must be closely monitored, especially as it is discharged to the municipal water system. 
         [0016]    Current water treatment programs fall into two categories: acid-based and carbonate-based. In acid-based systems, the acid normally used is sulfuric and is either used as a straight additive or mixed with inhibitors and dispersants or polymers. Acid based systems have limits based on forming calcium sulfate deposits. Carbonate-based systems use polymers and dispersants to keep contaminants in system water in solution. This program has limits based on system water alkalinity and hardness levels. 
         [0017]    Typical current cooling tower systems operate at between 2.5-5 cycles of concentrations before the water should be rejuvenated. More particularly, a cycle is determined by dividing the amount of water that has been used as make up water by amount that has bled off. Many applications are based on a time cycle, independent of any monitoring of the condition of the water in the system. For example, some systems are rejuvenated once per day, regardless of the condition of the water. This is an inefficient way to proceed because either the water concentration is high and rejuvenation should be performed more frequently, or the water concentration is low so rejuvenation should be performed less frequently. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0018]      FIG. 1  is a partially schematic diagram of a cooling tower system and water treatment module configured in accordance with the present disclosure. 
           [0019]      FIG. 2  is a schematic illustration of a treatment cell for use with a water treatment module configured in accordance with the present disclosure. 
           [0020]      FIG. 3  is a graph of voltage and amperage according to a control routine of the present disclosure. 
           [0021]      FIG. 4  is an illustration of a wall of a treatment cell configured in accordance with the present disclosure. 
           [0022]      FIG. 5  is an isometric illustration of a portable water treatment module configured in accordance with the present disclosure. 
           [0023]      FIG. 6  is a flow chart diagram of a control routine for use with a water treatment module configured in accordance with the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]      FIG. 1  is a schematic illustration of a water management system  10  in accordance with embodiments of the present disclosure. The system  10  includes a network of piping  14  within a housing  12 . A process medium flows through the network of piping  14 , and is cooled by water that is drawn from a source such as municipal water system and is propelled through piping  18   a ,  18   b ,  18   c ,  18   d , and  18   e  to the upper portion of a cooling tower  15  by a pump  16 . 
         [0025]    The cooling tower  15  includes an array of pipes  20  with spray nozzles  22  above the piping  14 . The details of the cooling tower  15  are not fully given here, but are generally understood in the art. Some of the water evaporates into the atmosphere and is lost. Water not lost through evaporation returns to a reservoir  24  and is recycled through the system  10 . The water in the reservoir  24  is returned to the main water supply via piping  25   a  and  25   b  as desired and controlled by a valve  27 . To compensate for water evaporated or otherwise lost in the cooling operation, make-up water is periodically introduced into the system as needed through make-up piping  26  that can lead to the reservoir  24  or to another part of the cycle. 
         [0026]    The water that evaporates is pure, but the make-up water is not. Overtime, the water in the system becomes highly concentrated with deleterious suspended and dissolved materials. In conventional systems the cooling water is periodically purged from the system and into the municipal water system. This purging is inefficient, costly, and has a negative effect on the quality of the municipal water supply. Moreover, as the frequency of the purging increases the inefficiency, lack of cost, and the negative impact is compounded. 
         [0027]    The system  10  can include a water treatment module  30 . The water treatment module  30  can have an inlet  60  that receives water from piping  18   b , and an outlet  66  that returns the water after treatment back to the piping  18   c . Water from the main water supply is diverted to the cell  32  by conduits  60 , pump  62 , and conduits  64   a ,  64   b , and  64   c . The power source  50  can be used to drive the pump  62  through a line  70 . The module includes one or more cells  32 . Four cells are illustrated in  FIG. 1 , but any suitable number of cells  32  can be used depending on the needs of the system  10 . The power source  50  can be electrically connected to the cells through electrical lines  52  and  54 . In some embodiments the module  30  is portable and can be moved from location to location and incorporated into piping of a cooling tower as needed. A portable version of the module  30  is shown mounted on skids in  FIG. 5 . 
         [0028]      FIG. 2  illustrates a water treatment cell  32  of the water treatment module  30  shown with reference to  FIG. 1  above in accordance with embodiments of the present disclosure. The water treatment module  30  can include any suitable number of cells  32 . For purposes of brevity, a single cell  32  is described. The cell  32  includes a cylinder  36  and a rod  34  supported on the centerline of the cylinder  36 . The rod  34  is made from a mixed metal alloy, for example a titanium core coated with a rare earth material. The rare earth coating allows the rod to give of an electron during an electrolysis process without disintegrating. The cylinder  36  is made of a conductive material such as stainless steel. The power source  50  is electrically connected through a line  52  to a fitting  40  which is in turn connected to the rod  34 . The power source  50  is also electrically connected to the cylinder  36  by another fitting  38  through another line  54 . In embodiments having multiple cells  32 , individual cells  32  can be taken online or offline individually for cleaning or maintenance or repair without affecting other cells  32  in the module  30 . 
         [0029]    When the power source applies a voltage, the rod  34  is an anode and the tube  36  is a cathode. As the water flows from one end of the cylinder  36  to the other end while the voltage is applied, the water undergoes an electrolytic process that breaks water down. In some embodiments, the voltage is between approximately 10-100 volts generating 10-20 amps. At the anode, hydrogen (H) is generated as a gas that can be vented from the cell and captured for disposal or use elsewhere. At the cathode, hydroxide (OH) is generated. The hydroxide reacts with caustic materials in the water, such as calcium and magnesium, to form calcium and magnesium carbonate. The calcium and magnesium carbonates adhere to the inner wall of cylinder  36  and form a gummy, paste-like substance. Organics in the water will also bind with the calcium and magnesium carbonate and thus are desirably removed from the cooling water supply. The treated water leaves the cell  32  cleaner, softer, and less prone to producing scale, corrosion or other harmful effects. 
         [0030]    Some of the organics are captured in the carbonates at the cathode (cylinder  36 ). In addition, municipal water usually contains some amount of salt (NaCL). The hydroxide generated in the cell will react to come degree with the salt and generate an amount of sodium hydroxide (NaOH) and chlorine (CL). That chlorine is then available for use in treating some of organics contained in water. Since that chlorine is coming from a source that was already present in the water supply it is not considered a negative. Furthermore, since the system reduces or eliminates the need to discharge cooling water to the municipal water system, the overall contribution of contaminants is reduced compared to conventional systems. 
         [0031]    In some cooling tower installations, the treatment of organics inherent in the use of this disclosure and as described hereinabove is sufficient to treat any organics that may be present in the water supply. If additional organic treatment is necessary the system of this disclosure can be used conveniently with apparatus such as those described in U.S. Pat. Nos. 6,126,820 and 6,325,944 B1, which are incorporated herein in their entirety. 
         [0032]    The power source  50  can deliver a pulsed voltage to the cells  32  as opposed to constant voltage. The pulsed voltage can be a series of alternating ramp-up and ramp-down periods. The pulse width can vary.  FIG. 4  illustrates a coating  100  on walls of the cylinder  36  is a constant voltage supply is used. The irregular thickness requires more power for proper operation as compared to a coating of relatively uniform thickness. The need for a higher amperage degrades the operation and also shortens the time between cell regeneration. A pulsed power source  50 , however, results in a coating of relatively uniform thickness, shown by the dotted line  102  in  FIG. 4 . In an embodiment, the pulsed power source  50  can be a Micro-Star SCR type power source. 
         [0033]      FIG. 3  illustrates a relationship between build-up and voltage, with voltage represented along the x-axis and build-up represented by the y-axis. The more build-up on the cylinder walls, the more voltage is required to maintain a desirable, constant amperage. There is a range A between lines B and C in which a preferred result is achieved. 
         [0034]      FIG. 6  illustrates a control routine  80  for initiating and terminating a regeneration cycle in accordance with embodiments of the present disclosure and according to the relationship shown in  FIG. 3 . The routine  80  can be executed by a controller  53  shown schematically in  FIG. 1 . The controller  53  can be a programmable logic controller or another equivalent device. At step  81 , the control routine  80  can begin. At step  82 , the controller  53  can determine whether the voltage required by the system to maintain a constant amperage has reached a predetermined threshold value. The controller  53  can include appropriate amp and voltage sensors and measuring equipment. The actual value of the threshold can vary with the size and configuration of the module  30 . If the voltage is below the threshold, the routine  80  can wait a certain time before checking the voltage level again. In areas where the municipal water supply is relatively free from solids, this process can extend much longer than in other areas. This is an advantage over other systems that regenerate based on time alone, without determining a need for the regeneration cycle. It is also more cost-effective than directly measuring the dissolved or suspended solids currently present in the water. 
         [0035]    If the predetermined voltage threshold is met, the control routine  80  can begin a regeneration cycle  83 . In some embodiments, the regeneration cycle can be performed by switching the lead  52  ( FIG. 2 ) from the anode to a portion of the cylinder  36 . This causes a “dead short” between the power source  50 , the lines  52 , and  54 , and the cylinder  36 . The dead short knocks the build-up off the walls of the cylinder  36  and into the water. The water in the treatment cell  32  can then be disposed of properly. 
         [0036]    In some embodiments, the routine  80  can run the regeneration cycle  83  for a predetermined period of time and then refresh the routine at step  81 . In other embodiments, during the regeneration cycle  83 , the controller  53  can monitor a voltage level in the treatment cell  32 . At step  84 , if the voltage has not dropped below a predetermined voltage threshold, the regeneration cycle can continue at step  85 . Otherwise, once the voltage drops below the threshold the regeneration cycle can be terminated  86  and the routine  80  can terminate at step  87 . In embodiments in which the regeneration cycle  83  is performed by the dead short, step  84  can include switching the lead  52  back to the anode and running current for a short time to measure voltage across the electrolytic gap between the anode and cathode. If the voltage is not below the threshold, the lead  52  can switch back to the cathode and continue the dead short operation. 
         [0037]    Using the water treatment module  30  maintains the concentration of dissolved and suspended solids in the cooling water at a lower, more tolerable level and the same water can be used for more cycles before requiring a purge than other cooling tower systems. In some embodiments, the purge and replacement cycles can be eliminated. The water management system is more sustainable because the only make-up water needed is equal to an amount lost through evaporation. The need to discharge water having a high concentration of solids after use in cooling tower is reduced or eliminated. The actual volume of water discharged is reduced and what is discharged contains fewer contaminants. The load on the municipal water system is reduced. 
         [0038]    The substances that builds up within the cells is collected in the cells and must be discharged periodically. This can be done by taking the cell offline and flushing with water and/or a suitable cleansing agent. The removed deposits are easily captured and contained for safe disposal. The deposits and the flushing water can be directed to a drain  69  ( FIG. 1 ) through an outlet pipe  67  into either the municipal water system or to a container for capture. 
         [0039]    From the foregoing, it will be appreciated that specific embodiments of the disclosure have been described herein for purposes of illustration, but that various modifications may be made without deviating from the spirit and scope of the disclosure. Additionally, aspects of the disclosure described in the context of particular embodiments or examples may be combined or eliminated in other embodiments. Although advantages associated with certain embodiments of the disclosure have been described in the context of those embodiments, other embodiments may also exhibit such advantages. Additionally not all embodiments need necessarily exhibit such advantages to fall within the scope of the disclosure.