Abstract:
Method and apparatus for adjusting the salinity and/or hardness of a process waste stream so that the stream may be electrolyzed to form an oxidant or disinfectant. Also an electrolytic cell having certain features such as widely spaced electrodes, flushing capabilities, and insulating dividers that can accommodate waste streams that have varying salinity, hardness, and dissolved solids content.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to and the benefit of filing of U.S. Provisional Patent Application Ser. No. 61/605,929, entitled “Waste to Product On Site Generator,” filed on Mar. 2, 2012, the specification and claims of which are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention (Technical Field) 
         [0003]    The present invention relates to methods and apparatuses for electrolytic processing of waste brine solutions produced by water purification or other industrial processes, thereby producing one or more oxidants and/or disinfectants. 
         [0004]    2. Background Art 
         [0005]    Note that the following discussion refers to a number of publications and references. Discussion of such publications herein is given for more complete background of the scientific principles and is not to be construed as an admission that such publications are prior art for patentability determination purposes. 
         [0006]    Electrolytic technologies utilizing dimensionally stable anodes have been developed to produce oxidant solutions from brine solutions, and these technologies have grown in market presence and interest across a variety of applications. Dimensionally stable anodes are described in U.S. Pat. No. 3,234,110 to Beer, entitled “Electrode and Method of Making Same,” wherein a noble metal coating is applied over a titanium substrate. Electrolytic cells have had wide use for the production of chlorine and mixed oxidants for the disinfection of water. Some of the simplest undivided electrolytic cells are described in U.S. Pat. No. 4,761,208, entitled “Electrolytic Method and Cell for Sterilizing Water”, and U.S. Pat. No. 5,316,740, entitled “Electrolytic Cell for Generating Sterilizing Solutions Having Increased Ozone Content.” One limitation of these technologies is the operating cost associated with the feedstock of this process, consisting of sodium chloride and other dissolved salts which are converted into solutions comprising at least one oxidant. It is well accepted that one of the major failure mechanisms of undivided electrolytic cells is the buildup of unwanted films on the surfaces of the electrodes. The source of these contaminants can be either from the feed water to the on-site generation process, or contaminants in the salt that is used to produce the brine solution feeding the system. Typically these unwanted films consist of manganese, calcium carbonate, silica, or other unwanted substances. If buildup of these films is not controlled or they are not removed on a fairly regular basis, the electrolytic cells will lose operating efficiency and will eventually catastrophically fail (due to localized high current density, electrical arcing or some other event). Typically, manufacturers protect against this type of buildup by incorporating a water softener on the feed water to the system to prevent these contaminants from ever entering the electrolytic cell. However, these contaminants will enter the process over time from contaminants in the salt used to make the brine. High quality salt is typically specified to minimize the incidence of cell cleaning operations. U.S. Pat. No. 7,922,890 describes methods and apparatuses of creating low maintenance, highly reliable electrolytic cells for creating oxidants. However, this type of approach typically only works for lower hardness waters (&lt;20 grains/gallon for example) and higher quality salts (&gt;99.5% dry). 
         [0007]    Many water purification processes produce a brine solution containing enough dissolved salts to be suitable for processing into a disinfectant/oxidant. Specifically, reverse osmosis, evaporation, distillation, chemical softening, and ion exchange technologies have waste streams with high concentrations of salts. Typically, however, these waste streams also have high concentrations of contaminants (typically measured as hardness) that would foul most electrolytic cells quickly, resulting in premature electrolytic cell failure. 
         [0008]    More recently, though, solutions providers such as GE or Veolia Water have developed offerings such as the HERO or OPUS® technologies, where waste water is pretreated to reduce the hardness prior to exposing them to the RO membranes. This makes this waste stream from the RO membranes much more desirable as a possible feedstock for electrolytic generation of an oxidant from that waste stream, as most of the undesirable contaminants for electrolysis are removed via the pretreatment process. 
       SUMMARY OF THE INVENTION (DISCLOSURE OF THE INVENTION) 
       [0009]    An embodiment of the present invention is a method for producing an oxidant, the method comprising adjusting the salinity and/or hardness of a waste stream thereby forming a brine solution; and electrolyzing the brine solution to produce at least one oxidant. The adjusting step preferably comprises measuring the salinity and/or hardness of the waste stream. The adjusting step optionally comprises adding water or processed water to the waste stream to reduce the salinity of the waste stream and preferably further comprises varying the relative flow rates of the waste stream and the water or processed water being input into an electrolytic cell. The adjusting step optionally comprises adding a saturated or near saturated salt solution to the waste stream to increase the salinity of the waste stream and preferably further comprises varying the relative flow rates of the waste stream and the saturated or near saturated salt solution being input into an electrolytic cell. The adjusting step preferably comprises treating the waste stream by a method selected from the group consisting of softening, ion exchange, filtering, and reverse osmosis. The brine solution preferably has a salinity between approximately 10 g/L and 40 g/L. The adjusting step preferably reduces a cleaning frequency of the electrolytic cell. 
         [0010]    Another embodiment of the present invention is a method for cleaning an electrolytic cell, the method comprising measuring a salinity and hardness of a waste stream to be electrolyzed, calculating a frequency for cleaning the electrolytic cell based on the measured salinity and hardness of the waste stream and a spacing between electrodes of the electrolytic cell, and cleaning the electrolytic cell in accordance with the calculated frequency. The cleaning step preferably comprises reversing a polarity of the electrolytic cell and/or flushing solid contaminants from the electrolytic cell. The flushing is preferably performed once or twice a day or after the electrolytic cell was cleaned by reversing the polarity of the electrolytic cell. The method preferably further comprises adjusting the salinity and/or hardness of the waste stream, thereby reducing the cleaning frequency. 
         [0011]    Another embodiment of the present invention is an electrolytic cell for electrolyzing a waste stream, the electrolytic cell comprising one or more devices for adjusting a flow rate of the waste stream entering an electrolytic cell; one or more dispersion tubes for transporting the waste stream into the electrolytic cell; a plurality of holes in the dispersion tubes, the holes angled to direct a flow of the waste stream toward bottom edges of the electrolytic cell; and one or more insulators substantially parallel to electrodes in the electrolytic cell and extending from a bottom of the electrolytic cell to at least a level of bottoms of the electrodes. The additive stream may comprise water, processed water, a saturated salt solution, or a near saturated salt solution. At least one of the devices can preferably flush the cell with the waste stream or water at a flushing flow velocity higher than (preferably at least twice) the operational flow velocity of the waste stream. Spacing between adjacent holes is preferably between approximately 0.5″ and approximately 2″. The electrolytic cell preferably comprises electrodes which are spaced more widely than electrodes in an electrolytic cell designed to produce a similar quantity and strength of oxidants from a controlled brine stream. The electrolytic cell preferably comprises intermediate electrodes, wherein spacing between adjacent intermediate electrodes is preferably between approximately 0.15″ and approximately 0.5″, and more preferably 0.25″+/−0.1″. 
         [0012]    Objects, advantages, novel features, and further scope of applicability of the present invention will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The accompanying drawings, which are incorporated into and form a part of the specification, illustrate an embodiment of the present invention and, together with the description, serve to explain the principles of the invention. The drawings are only for the purpose of illustrating various embodiments of the invention and are not to be construed as limiting the invention. In the drawings: 
           [0014]      FIG. 1  is a schematic showing brine waste at a high salinity being converted electrochemically into usable oxidant. 
           [0015]      FIG. 2  is a schematic showing brine waste at a low salinity being converted electrochemically into usable oxidant. 
           [0016]      FIG. 3  is a schematic showing brine waste with a very high hardness to salinity ratio, where divalent cations are removed prior to electrolysis making the brine waste appropriate for electrolysis. 
           [0017]      FIG. 4  is a high level schematic of an on-site electrolytic generator for converting brine waste to oxidant. 
           [0018]      FIG. 5  is a cross section of an electrolytic cell for converting brine waste to oxidant. 
           [0019]      FIG. 6  is a 3D representation of an electrolytic cell for converting brine waste to oxidant. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    Embodiments of the present invention electrolize the waste stream from an industrial process, such as reverse osmosis, ion exchange softening, chemical softening, evaporation, distillation, produced or flowback water from oil and gas wells, to produce an oxidant and/or disinfectant. This waste stream may be highly variable in salt content, presenting a unique challenge for consistent oxidant production. For example, a water source with low dissolved salt may be injected into the electrolyte for a high salinity waste stream at a rate determined by the operating current of the electrolytic cell. When the operating current is high, more water with low dissolved salt is preferably injected to reach the target operating current of the cell. Conversely, when the operating current is low, the water with low dissolved salts may be replaced with a concentrated brine solution injection to raise the current to the desired operating condition. 
         [0021]    As used throughout the specification and claims, the term “waste stream” means an aqueous byproduct of an industrial process or application, including but not limited to frac water, produced water from oil and gas operations, cooling towers, desalination, or evaporation, the byproduct having a sodium chloride content of greater than approximately 1 g/L. 
         [0022]    Embodiments of the present invention utilize an electrochemical process to convert a waste brine stream into a usable oxidant; one such process is shown in  FIG. 1 . In  FIG. 1 , raw water  1  is first treated via softening process equipment  2  to remove divalent cations (typically those acknowledged as hardness) and other contaminants. Softened waste water  3  is then put through purification processing equipment  4 , such as reverse osmosis or other membrane processing equipment, to remove monovalent cations (i.e. salts) to create processed water  5  and brine waste  6 . Processed water  5  can often be used for industrial processes, is appropriate for discharge, and/or can even potentially be used as potable water. Brine waste  6  is then processed and electrolyzed in on-site electrolytic generator  7  into oxidant  8 . Oxidant  8  can either be stored in a tank or directly used for a variety of applications (not shown). To produce a desired concentration of oxidant  8  (for example 100 to 1000&#39;s mg/L) and/or provide electrolyte with the proper salinity for electrolysis, dilution water  9  may optionally be used to dilute brine waste  6  in the on-site electrolytic generator if brine waste  6  is too salty. 
         [0023]    Raw water  1  can be from virtually any source. However, certain sources have, or certain industrial processes produce a waste stream that has, a somewhat higher incidence of dissolved salts in the raw water, such as seawater, produced and/or flowback water from oil and gas operations, ground water, surface water, waste from industrial processes, waste water from municipalities, potable water, etc. 
         [0024]    Brine waste  6  is often at a fairly high salinity, often greater than approximately 40 g/L but less than that for saturated brine (317 g/L). In the event that the salinity is greater than approximately 40 g/L, dilution water  9  may be used to dilute the brine waste to a lower level that is more appropriate for electrolysis, typically between approximately 10 g/L and 40 g/L. A small percentage of processed water  5  may optionally be used as the dilution water  9 . 
         [0025]    Depending on the nature of the raw water  1  and the purification processing equipment  4 , if not required softening process equipment  2  may not be included in order to reduce cost and complexity of the system. 
         [0026]    Some industrial processes produce a brine waste that does not require complicated purification processing equipment  4  because the brine waste has the appropriate hardness to salinity ratio in the brine solution that it can be electrolyzed. Examples of this are waste water remediation and/or flowback or produced waters from oil and gas operations. Thus, in one embodiment of the invention, there is no processed water  5 , and the purification processing equipment comprises or consists essentially of a simple filter to remove large particles (typically &gt;20 microns, but preferably &gt;100 microns) from brine waste  6 . 
         [0027]      FIG. 2  shows another embodiment of the invention. In the event that the salinity of the waste brine  6  is low, less than approximately 10 g/L for example, solid brine storage tank  11  may be utilized. In the solid brine storage tank, solid salt is saturated in water, creating a brine solution  10  at or near saturation (approximately 317 g/L). In this event, a small amount of saturated brine solution  10  is combined with the brine waste  6  for electrolysis by on-site electrolytic generator  7 . 
         [0028]    Another embodiment of the invention is shown in  FIG. 3 . In this embodiment, divalent cations are removed from brine waste  6  using selective ion exchange process equipment  12 , leaving a brine solution suitable for electrolytic generation of oxidant in on-site electrolytic generator  7 . 
         [0029]    Compared to existing commercially available on-site electrolytic generators, embodiments of that required to convert waste to oxidant in accordance with the present invention are substantially different.  FIG. 4  shows a high level schematic of an embodiment of on-site electrolytic generator  7 . The electrolytic generator takes brine waste  6  and either dilution water  9  or saturated brine solution  10  and generates oxidant  8  by electrolyzing it in electrolytic cell  14 . Depending on the salt concentration of brine waste  6 . the relative flow rates of brine waste  6  and/or dilution water  9  or saturated brine solution  10  are preferably controlled by integrated controls  15 , preferably via devices  13  such as pressure mechanisms, pumps, or valves. These input rates and the current and/or voltage applied to the electrolytic cell are preferably varied to maintain a controlled oxidant concentration. 
         [0030]    During operation, devices  13  can be controlled to intermittently flush the electrolytic cell with very high flow rates (preferably greater than approximately two times the operational flow rate) of water or waste stream  6 . If the latter is used, flushing can occur during the electrolysis process. This flushing prevents or reduces deposits from accumulating at the bottom of the electrolytic cell. Integrated controls  15  also preferably control reversing the polarity of the cell, which removes deposits from the electrode surfaces. This process is more fully described in U.S. Patent Application Publication No. 20090229992. 
         [0031]    Despite being exposed to high levels of hardness, suspended solids, dissolved solids, and contaminants such as silica, electrolytic cell  14  is preferably designed such that it is robust and has an adequate lifetime.  FIG. 5  shows a cross section of an embodiment of a bipolar electrolytic cell useful for the current invention. Primary electrodes  15  and intermediate electrodes  16  are preferably coated with Dimensionally Stable Anode (DSA) material, such as ruthenium, iridium, palladium, or other materials known in the art. Both the primary anode and preferably cathode are coated with DSA so that the polarity of the cell can be intermittently reversed to remove any deposits on the electrodes. A series of intermediate electrodes  16  are disposed between primary electrodes  15 . The spacing from one electrode to the next is wider than on most typical electrolytic cells, preferably greater than 0.15″ but less than approximately 0.5″, preferably 0.25″+/−0.1″. In general, the wider the spacing the more inefficient the cell is, but wider spacing is useful with the present invention to prevent elevated contaminants from the incoming brine waste  6  from depositing on intermediate electrodes  16  and creating an electrical short circuit and arcing and/or premature cell failure. Brine waste  6  is introduced to the electrolytic cell via dispersion tube  18 , which comprises holes which direct the brine waste towards the bottom of electrolytic cell  14 , and more preferably, to the bottom corners of the electrolytic cell  14 . The size, angles, and spacing of these holes down the length of the dispersion tube are preferably chosen to increase the velocity of the fluid, such that particles are less likely to settle into the bottom of the cell. By accelerating the brine waste  14  and angling it down and substantially towards the corners of the bottom of the electrolytic cell, any contaminants and/or particles that have begun to settle into the bottom of the cell can be accelerated and re-suspended up and between electrodes  16  and out of the electrolytic cell  14 . This design makes it particularly easy to flush larger particles and/or contaminants out of the bottom of the cell by performing intermittent flushing, preferably 1-2 times a day, preferably at high flow rates either while the cell is energized or not. During operation, brine waste  6  stream through dispersion tubes  18  and out of the holes, where its flow is directed to agitate any particles that may have settled. The brine waste stream then travels up between the electrodes, and, when power is applied to primary electrodes  15 , it is electrolyzed to form oxidant  8  which leaves the electrolytic cell. 
         [0032]    Electrolytic cell preferably comprises one or more electrical isolator blocks  17 , which preferably extend from the bottom of the cell at least up to the bottom of the electrodes. One isolator block is preferably present every few intermediate electrodes  16 , which prevents loss of electrical efficiency and also protects the electrodes from being exposed to voltages beyond their breakdown voltages, for example due to high salinity of the brine waste. Thus the use of these blocks enables particles to build up in the cell without arcing between electrodes taking place. Typically electrical isolator blocks  17  are spaced every 5-10 electrodes, but depending on the chemistry desired in the oxidant and the salinity of brine waste  6 , one electrical isolator block  17  could be present every 3 electrodes or even up to every 40 electrodes. As shown in the perspective view of electrolytic cell  14  shown in  FIG. 6 , dispersion tubes  18  preferably distribute the brine waste  6  into the cell through an array of holes as described above. The holes are preferably spaced apart between approximately 0.5″ and approximately 2″, preferably 1″+/−0.25″. 
         [0033]    The characteristics of the brine waste vary considerably with different waste applications, which has implications on the frequency with which the electrolytic cell is cleaned. Specifically, the ratio of divalent cations to monovalent cations is particularly important. For a given ratio, the growth rate of contaminants on the electrodes is calculated, and for a given electrode spacing, the required cleaning frequency of the cell to prevent arcing between electrodes can be determined, after applying a given safety factor. From this cleaning frequency the expected life of an electrolytic cell can then be predicted given a certain number of cycles to failure. Thus, treating the waste stream so that the salinity and/or hardness are in optimal ranges can greatly increase the lifetime of the cell by reducing required cleaning frequency. By controlling these parameters, as well as flow rate, voltage, and current in the electrolysis cell, the system can be optimized for energy conversion efficiency as salt is a waste product for various industrial processes and is therefore is extremely inexpensive. 
       Example 1 
       [0034]    A waste brine stream was created by a system very similar to the system shown in  FIG. 1 , in which the softening water processing equipment was an ion exchange resin softener, and the purification process equipment was a membrane based reverse osmosis filter. The salinity of the waste brine stream was measured at 40 g/L, and had 100 grains/gallon hardness. Electrolyzing this waste brine stream was completed yielding an oxidant with 3400 mg/L FAC, with a required cell cleaning frequency of about 7 days corresponding to an expected cell life well over 10 years. 
       Example 2 
       [0035]    A waste brine stream consisting of produced water from an oil and gas operation was created by a system similar to the one shown in  FIG. 1 , with the exception that the softening water processing equipment was not present and the process equipment was a simple filter to remove particles &gt;80 microns. The salinity of the waste brine stream was 17 g/L, and the hardness was 24 grains, and electrolyzing it yielded an oxidant with 2200 mg/L FAC, with a cell cleaning frequency of 12 days and an expected cell life well over 10 years. 
       Example 3 
       [0036]    A waste brine stream from a desalination plant was created with a system similar to the one depicted in  FIG. 1 , with no softening processing equipment. The desalination plant relied on reverse osmosis to process the water. The waste brine stream had a salinity of 210 g/L (typically too salty for effective electrolysis) and a hardness of 2800 grains/gallon. The waste brine stream was recombined with a side stream of RO permeate as described herein to deliver a salinity of approximately 15 g/L to the electrolytic cell. Electrolysis of this stream yielded an oxidant with 4200 mg/L FAC, with a cell cleaning frequency of 1.3 days and an expected cell life of 3.9 years. 
       Example 4 
       [0037]    Waste blowdown from a cooling tower had approximately 4 g/L salt and a hardness of 180 grains/gallon. This waste blowdown was directly electrolyzied, yielding an oxidant with 650 mg/L FAC with a cleaning frequency of 0.4 days and an expected cell life of 1.2 years. When combined with a solid brine source as shown in  FIG. 2 , the salinity was increased to 15 g/L, lengthening the cleaning frequency to 1.5 days and increasing expected cell life to over 5 years. In both instances, the oxidant produced was used to disinfect the cooling tower. 
         [0038]    Although the invention has been described in detail with particular reference to the disclosed embodiments, other embodiments can achieve the same results. Variations and modifications of the present invention will be obvious to those skilled in the art and it is intended to cover all such modifications and equivalents. The entire disclosures of all patents and publications cited above are hereby incorporated by reference.