Abstract:
A method of improving electrocoagulation (“EC”) treatment processes for treating waste water and similar applications. The method includes providing a variable power supply that outputs an alternating current (“AC”) to one or more EC treatment cells. The alternating current from the variable power supply is rectified before delivery to the EC cell. As an intermediate step between the variable power supply and rectification, the method described and claimed here uses a variable step down transformer to modify the output delivered to the EC cell.

Description:
TECHNICAL FIELD 
     The invention disclosed here generally relates to hydraulic fracturing methods for enhancing the production of a natural gas well. More specifically, the invention is directed to a method of enhancing the fracturing and natural gas release process by pre-treating water used in the fracturing fluid and/or recycling treated flow back fluid or source water previously used in the hydraulic fracturing process. 
     BACKGROUND OF THE INVENTION 
     “Hydraulic fracturing” is a common and well-known enhancement method for stimulating the production of natural gas. The process involves injecting fluid down a well bore at high pressure. The fracturing fluid is typically a mixture of water and proppant (the term “proppant” includes sand and synthetics). Other chemicals are often added to the proppant to aid in proppant transport, friction reduction, wetability, pH control and bacterial control. 
     Varying amounts of water are required in a typical hydraulic fracturing operation. Water is usually trucked to the well head site from other locations, typically in large quantities. The water may come from a variety of sources that include untreated water from rivers, lakes, or water wells. Once delivered to the well head site, the water is mixed with the proppant particulates and then pumped down the well bore. 
     During the fracturing process, the fracturing fluid penetrates producing formations (sometimes called “subterranean formations”) at sufficient hydraulic pressure to create (or enhance) underground cracks or fractures—with the proppant particulates supporting the fracture for “flow back.” Sometimes the process is repeated a multiple number of times at the well site. When this is done, the well head is closed between stages to maintain water pressure of the fracturing fluid for a period of time. 
     The process creates a significant amount of fluid “flow back” from the producing formation. Untreated flow back often is not recyclable in subsequent fracturing operations because of the contaminants it contains. Flow back is normally hauled away and treated off-site relative to the geographic location of the well head. 
     Hydraulic fracturing is very important to companies involved in the production of natural gas. These companies have made large investments in looking for ways to improve upon all phases of the fracturing operation. One obvious drawback to fracturing involves the high cost of hauling water to the well head site followed by retrieving and hauling away the flow back by-product for off-site treatment and subsequent disposal. 
     There have been many attempts at improving gas production that results from fracturing operations by varying the make-up and use of the fracturing fluid. Attempts at stimulating natural gas production via fracturing generally falls in two categories: hydraulic fracturing and “matrix” treatments. 
     Fracturing treatments stimulate gas production by creating more flow paths or pathways for natural gas to travel up the well bore for retrieval. Matrix treatments are different in that they are intended to restore natural permeability of the underground formation following damage. The make-up of the fracturing fluid is often designed to address different situations of this kind by making adjustments in the material and chemical content of the fluid and proppant particulates. 
     The methods and processes disclosed here involve the quality of the water used to make up the fracturing fluid and treatment of flow back and other water-based fluids produced from hydraulic fracturing or other source waters for gas retrieval operations. There are many advantages to the methods disclosed here: First, the disclosed methods provide a means for significantly reducing trucking costs to and from the well head site that directly relate to the large quantities of water typically needed for hydraulic fracturing. Second, the disclosed methods offer a viable way to recycle the water used as the fracturing fluid in an energy efficient treatment process at the well head site. Third, because of the nature of the treatment process, for reasons explained below, the delivered or recycled water component in the fracturing fluid improves flow back and increases the quantity of natural gas produced that results from the fracturing operation. 
     In sum, the methods and processes disclosed below serve to improve natural gas production at a lower water treatment cost. 
     SUMMARY OF THE INVENTION 
     The invention disclosed here involves methods and processes for improving natural gas release from a well following a hydraulic fracturing operation. The method involves first introducing a hydraulic fracturing fluid into a producing subterranean formation via conventional means. The typical hydraulic fracturing fluid includes a mixture of water and other proppant particulates (or fracturing components). After the pressure on the fluid is released, at least a portion of the hydraulic fracturing fluid is captured from the subterranean formation (preferably, as much as possible). As indicated above, this is typically referred to as “flow back.” 
     The captured fluid or flow back is separated from residual proppant particulates and then introduced to an electrocoagulation (“EC”) treatment process. The EC treatment separates the water in the flow back from much of the inherent subterranean contaminants as well as other fracturing fluid components. Thereafter, the treated water is clean of contaminants and may be recycled into the fracturing fluid that is used in subsequent fracturing operations. 
     The EC treatment serves to reduce the viscosity of the fracturing fluid, which makes it function better in the underground or producing formation. Part of the viscosity improvement obtained via the EC treatment process relates to bacterial content removal and reduction in turbidity, in addition to removal of other particulates. 
     It is conceivable that the same type of EC treatment can be used to treat fresh water delivered to the well head from off-site locations. Even though it is relatively clean, newly delivered fresh water may still contain bacterial or other contaminants that impede the fracturing process. Therefore, EC treatment of water newly delivered to the well head site may be beneficial before it is mixed with proppant particulates and used to initiate a fracturing operation. 
     The EC system uses the combination of a variable power supply, step-down transformer(s), and an AC to DC rectifier to produce the required treatment conditions (proper electric current level). The design reduces the overall power consumed by EC cells in order to achieve clarity in the treated water over a wide range of water conductivity. 
     The variable power supply outputs an alternating current (“AC”) typically in the range of 0 to 480 volts AC (“VAC”). The precise level is determined or controlled by a programmable logic controller (“PLC”) that sets the VAC output. The VAC output from the power supply is then delivered to the variable step-down transformer, which has a series of “taps” that further adjust the AC output prior to delivery to the rectifier. The taps are adjusted upwardly or downwardly depending on whether or not the desired operating current (or targeted current) is received by the EC cells within the system. The adjustment is made by monitoring the ratio of AC current to DC current. 
     The EC treatment cells are tubular in shape and have an arrangement of stacked circular plates with alternating positive and negative charges across the array of plates (i.e., one plate will be positive with plates on either side charged negatively). The polarity of all the plates within the stack is reversed at preset intervals. 
     Because the plates are closely spaced, it is desirable to create as much turbulence in flow passing between the plates as possible. In this case, turbulence is created by generating an asymmetric, “vortex”-like flow relative to the center-line axis of the cell. 
     Based on results to date, the methods and processes disclosed here will significantly reduce conventional transportation and disposal costs attributable to water hauling and treatment in hydraulic fracturing operations. Moreover, the desired water quality is achieved at lowered electrical cost relative to known EC systems. Finally, use of the methods and processes disclosed here appear to generate better flow back return from the well, and increased natural gas production, because EC treatment at the well head site decreases the volume of particles in the fluid that would otherwise be trapped in the fracture. EC treatment at the well head site also helps to reduce the ability of the water to form scales and precipitants while reacting with formation and other metals and minerals in the fracturing water. Not only does it immediately enhance production but it also improves the production life of the well. EC treatment provides other potential benefits such as overall reduction in proppant/chemical use and minimizing environmental impact because of better point-source control of contaminated water. 
     While the foregoing description is made in the context of hydraulic fracturing operations, the EC treatment system described here may have useful applications in other kinds of waste water treatment environments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings, like reference numerals refer to like parts throughout the various views, unless indicated otherwise, and wherein: 
         FIG. 1  is a schematic view of a well head site and illustrates the general treatment and recycling of fluid (“flow back”) from the well head; 
         FIG. 2  is a schematic that is to be taken with  FIGS. 3 and 4  and shows a pre-treatment storage tank for holding the flow back captured from the hydraulic fracturing fluid process prior to EC treatment; 
         FIG. 3  is a schematic of a series of parallel EC treatment cells that receive fluid from the pre-treatment tank shown  FIG. 2 ; 
         FIG. 4  is to be taken with  FIGS. 2 and 3  and is a schematic showing a plurality of settling or “flocculation” tanks that receive fluid processed by the EC cells in  FIG. 3 , with the fluid being passed onto final stage processing through media filters; 
         FIG. 5  is a block schematic diagram showing the operational control of the EC system; 
         FIG. 6  is a block schematic diagram that illustrates electric current control for the EC system; 
         FIG. 7  is related to  FIG. 6  and is a block diagram illustrating control of the tap settings in a transformer that makes up a portion of the EC system; 
         FIG. 8  is similar to  FIG. 1 , but illustrates treatment of water delivered to the well head site before its initial use in a fracturing operation; 
         FIG. 9  is an exploded view of an “EC” cell constructed in accordance with the invention disclosed here; 
         FIG. 10  is a view like  FIG. 9 ; 
         FIG. 11  is an exploded view of the back of the cell; 
         FIG. 12  is a view like  FIG. 11 ; 
         FIG. 13  is a view like  FIG. 12 , but is taken from a different angle; 
         FIG. 14  is a pictorial view of the center plate in the cell set; 
         FIG. 15  is a side view of the plate shown in  FIG. 14 ; 
         FIG. 16  is a perspective view of the plate that is on each side of the center plate; 
         FIG. 17  is a side view of the plate shown in  FIG. 16 ; 
         FIG. 18  is a schematic view of flow through of an EC treatment cell; and 
         FIG. 19  is a view like  FIG. 18 , but illustrating the electric field within the cell. 
     
    
    
     DETAILED DESCRIPTION 
     Referring first to  FIG. 1 , the general process will now be described. The process described in the present application centers around the use of a portable electrocoagulation (“EC”) system  10  (further described below) that is brought to a natural gas well head site  12 . The EC system  10  is small enough to rest on a truck trailer bed (not shown in the drawings). While this description focuses on hydraulic fracturing operations at natural gas well heads, it is to be understood that it may be useful in other applications. 
     Referring to  FIG. 8 , as an example, water that is to be used in the hydraulic fracturing operation is delivered to the well head site, as schematically indicated at  14  (by truck or other means). Newly delivered water (reference  13 ) is processed by the EC system  10  and then mixed with proppant particulates. It is then pumped (as illustrated at  16 ) down the bore at the well head location, thus introducing a hydraulic fracturing fluid into a subterranean formation (indicated at  17 ). This basic fracturing process is well-known in the gas industry, with the exception of using EC technology. Likewise, many different variations on the make-up and delivery of fracturing fluids and proppants have been used in the industry such as, for example, the materials described in U.S. Pat. No. 7,621,330 issued to Halliburton Energy Services, Inc. (“Halliburton”). 
     As a person familiar with hydraulic fracturing operations would know, when the fracturing process is deemed to be completed, pressure is released at the well head  12 , thus resulting in flow back of the fracturing fluid back up through the well head  12 . Referring again to  FIG. 1 , the hydraulic fracturing fluid that makes up the flow back is captured, (indicated at  18 ) and passed directly to the EC system  10 . Natural gas is retrieved (indicated at  15 ) and piped to a storage facility (indicated at  19 ). 
     The EC system  10 , which will be further described in greater detail below, uses an EC treatment process to separate the water from other components in the flow back. The EC-treated water is then held in a storage tank  20 . Thereafter, it is mixed with new proppant particulates and recycled (indicated at  22 ) for subsequent hydraulic fracturing operations. 
     For reasons described later, the EC system  10  will significantly reduce flow back parameters like turbidity and bacteria to very low levels. With the exception of sodium and chloride contaminants, other chemicals in the flow back are likewise reduced via the EC treatment process. 
     Moreover, recycling the EC-treated water by subsequent mixing with conventional proppant particulates is beneficial to the hydraulic fracturing or fracking process. Processing the flow back (or delivered fresh water) via the EC process  10  and recycling it in subsequent operations positively affects viscosity of the fracking fluid (by reducing viscosity) and, consequently, affects the release of natural gas from the subterranean formation. 
     The EC process reduces viscosity (μ) in Darcy&#39;s general equation: 
     
       
         
           
             Q 
             = 
             
               
                 
                   
                     - 
                     κ 
                   
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   A 
                 
                 μ 
               
               ⁢ 
               
                 
                   ( 
                   
                     
                       P 
                       b 
                     
                     - 
                     
                       P 
                       a 
                     
                   
                   ) 
                 
                 L 
               
             
           
         
       
     
     The reduction in μ is particularly acute with respect to diminishing imbibition in rocks less than 1 milli-Darcy. By reducing μ and, consequently, imbibition, the fractured interface is significantly less damaged, which benefits the recovery of the fracturing fluid (i.e., the flow back) and improves gas recovery from the well head. 
     The total discharge, Q (units of volume per time, e.g., m 3 /s) is equal to the product of the permeability (κ units of area, e.g. m 2 ) of the medium, the cross-sectional area (A) to flow, and the pressure drop (Pb−Pa), all divided by the dynamic viscosity μ (in SI units, e.g., kg/(m·s) or Pa·s), and the physical length L of the pressure drop. 
     The negative sign in Darcy&#39;s general equation is needed because fluids flow from high pressure to low pressure. If the change in pressure is negative (e.g., in the X-direction) then the flow will be positive (in the X-direction). Dividing both sides of the above equation by the area and using more general notation leads to: 
     
       
         
           
             q 
             = 
             
               
                 
                   - 
                   κ 
                 
                 μ 
               
               ⁢ 
               
                 ∇ 
                 P 
               
             
           
         
       
     
     where q is the filtration velocity or Darcy flux (discharge per unit area, with units of length per time, m/s) and ∇P is the pressure gradient vector. This value of the filtration velocity (Darcy flux) is not the velocity which the water traveling through the pores is experiencing. 
     The pore (interstitial) velocity (V) is related to the Darcy flux (q) by the porosity (φ). The flux is divided by porosity to account for the fact that only a fraction of the total formation volume is available for flow. The pore velocity would be the velocity a conservative tracer would experience if carried by the fluid through the formation. 
     Water treated by EC is likely to provide better flow rates underground in pressure-driven fracturing operations according to the following version of Darcy&#39;s law (relating to osmosis): 
     
       
         
           
             J 
             = 
             
               
                 
                   Δ 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   P 
                 
                 - 
                 ΔΠ 
               
               
                 μ 
                 ⁡ 
                 
                   ( 
                   
                     
                       R 
                       f 
                     
                     + 
                     
                       R 
                       m 
                     
                   
                   ) 
                 
               
             
           
         
       
     
     where,
         J is the volumetric flux (m.s −1 ),   ΔP is the hydraulic pressure difference between the feed and permeate sides of the membrane (Pa),   ΔΠ is the osmotic pressure difference between the feed and permeate sides of the membrane (Pa),   μ is the dynamic viscosity (Pa·S),   R f  is the fouling resistance (m −1 ), and   R m  is the membrane resistance (m −1 ).       

     In both the general and osmotic equations, increased discharge or volumetric flow is proportionate to decreased viscosity. Therefore, any treatment method that is likely to reduce viscosity in a fracturing fluid is also likely to improve the outcome of the fracturing process in terms of improvements to natural gas production. 
     Once again, water that is delivered to the fracturing or well head site may come from a variety of sources. Using river water, as an example, the water may be relatively clean but it will still contain varying amounts of contaminants. Therefore, it may be desirable to use the EC system  10  for a threshold treatment of the water as it is delivered (thus reducing viscosity) and before mixing with sand or chemicals. As indicated above; the EC system  10  is otherwise self-contained so that it is easy to move to and from the well head  12 .  FIGS. 2 and 3  illustrate the basic operating parameters of the system  10 . 
     In the recycling scenario, the flow back  18  is delivered to a pretreatment holding tank  24  (see  FIG. 2 ). From there, the flow back is passed to a manifold feed system  28  (see  FIG. 3 ) via line  26 . The manifold system  28  distributes the flow back to a series of parallel EC treatment cells, indicated generally at  30 . Each EC treatment cell has an internal configuration of charged plates that come into contact with the flow back. 
     EC treatment cells with charged plate configurations have been in general use with EC systems for a long time. However, to the extent possible, it is desirable to select plate and flow-through configurations that create turbulent flow within each cell (further described below). It is undesirable to generate significant amounts of flocculation within the cells  30  themselves. After treatment by the cells  30 , the flow back is returned to a series of settling tanks  32  (see  FIG. 2 ) via line  34 . 
     The EC treatment in the cells causes flocculent to be subsequently generated in the settling tanks  32 . There, the contaminants are removed from the water via a settling out process. Solid materials are removed from the settling tanks  32  and trucked off-site for later disposal in a conventional manner. The clarified water is then passed through sand media  36  (usually sand or crushed glass). Thereafter, the EC-treated water is passed onto the storage tank  20  ( FIG. 1 ) for recycling in subsequent fracturing operations. Once again, the EC treatment positively improves the viscosity of the fluid (by reducing viscosity). Various pumps  37  are used at different points in the EC process to move the flow from one stage to the next. 
     There will be some variables in the overall EC treatment process from one site to the next because of chemical and similar differences in the fracturing fluid or flow back. Similarly, there may be variations that are dependent on the content of delivered water in those situations where the EC treatment process is used initially to treat incoming water before it is used in a fracturing operation. 
       FIG. 5  is a schematic that illustrates the control logic for the EC system  10  illustrated in  FIGS. 1-3 . The EC system  10  utilizes an adjustable power supply  44 . Three-phase power is delivered to the power supply  44  at  480  volts AC (“VAC”) (schematically indicated at  46  in  FIG. 4 ). The output of the power supply  44  (indicated generally at  48 ) is a variable that is adjusted from 0 to 480 VAC by a controller  50 . The power supply output  48  is delivered to a variable step transformer  51  that further steps down the AC voltage from the power supply  40  before delivering it to a three-phase rectifier  52 . 
     Both the power supply  44  and transformer  51  are conventional power system components when standing alone. The transformer  51  includes a series of “taps,” which would be familiar to a person having knowledge of transformer systems. The “taps” provide different set points for stepping down the voltage across the transformer according to the power current level needed by the EC system  10 . 
     The three-phase rectifier  52  converts the output (see  54 ) from the transformer  50  to direct current (“DC”). The three-phase rectifier  52  is also a conventional component, standing alone. 
     The transformer  51  evens out or prevents current “spikes” that are typical to the way adjustable power supplies work. The EC system  10  is adjusted to operate at a target current that maximizes EC cell operation. Part of this process involves imparting a charge to the fluid being treated without instigating significant amounts of flocculation in individual cells. 
     That is, the target current is conducted through the flow back (or other fluid under treatment) in the EC treatment cells  30  via the charged plates. (further described below) within the cells. The target current may be set manually by the EC system operator, depending on the water quality of the flow back after EC treatment. Alternatively, it may be set automatically via an algorithm described below:
 
 I   target   =I   user −((Turb out −Turb goal )+(Turb in −Turb cal ))×(1/Flow)
 
     Where: 
     I target =Current system will maintain and hold to provide treatment 
     I user =Current set point user has specified to provide the gross level of treatment 
     Turb out =Turbidity out of treatment train 
     Turb goal =Desired turbidity out of the system 
     Turb in =Turbidity of the water to be treated 
     Turb cal =Turbidity value to which the system is baseline 
     Flow=Flow rate through the treatment cells 
     The controller  50  is a conventional programmable logic controller. The basic control of current to the treatment cells  30  will now be described by referring to  FIG. 6 . 
     The controller  50  ramps up to the target current  56  as follows. Reference numeral  58  (in  FIG. 5 ) reflects the controller&#39;s constant monitoring of DC current (I DC ) and AC current (I Ac ) output from the transformer  51  and three-phase rectifier  52 . The EC system  10  uses a proportional integral derivative algorithm (PID) to maintain cell current to a set point defined by the user, as shown at  60 . PIDs are generic algorithms that are well-known. 
     Unique to the present invention, the control logic includes a “power quality” (“PQ”) calculation that is based on the following equation: 
     
       
         
           
             PQ 
             = 
             
               
                 
                   I 
                   AC 
                 
                 
                   I 
                   DC 
                 
               
               × 
               100 
             
           
         
       
     
     Both the AC (I AC ) and DC (I DC ) current values are sensed following rectification. The DC current (I DC ) is the averaged direct output from the rectifier  52 . The AC current (I AC ) is the residual alternating current from the rectifier  52 . The DC and AC values reflect different characteristics from the same wave form output by the rectifier  52 . 
     The tap settings in the transformer  51  are adjusted, as shown at  62 , depending on the power quality (“PQ”) value. If the PQ is equal to or greater than 60 (as an example), or alternatively, if the sensed current is less than the target current, then the controller  50  adjusts the transformer tap settings (reference  64 ). 
     The control logic for the tap adjustment  64  is further illustrated in  FIG. 6 . Transformer taps are adjusted either upwardly or downwardly depending on the PQ calculation (referenced at  66 ). If PQ is equal to or greater than 60, for example, then the controller shuts down the power supply  68  (see, also, reference  44  in  FIG. 4 ) for a brief period. At that point in time, the transformer taps are adjusted downwardly (item  70 ). As a skilled person would know, if the transformers have a set of five taps, then they are selected one at a time in the direction that steps voltage down another step (with the process repeated iteratively until the desired result is achieved. If PQ is not equal to or greater than 60, then the power supply is similarly shut down (see item  72 ), but the transformer taps are instead adjusted upwardly (reference  74 ). 
     Returning to  FIG. 5 , if the current set point is not outside the range specified in control logic block  62  (that is, the current setting is acceptable), then the controller  50  checks the polarity timing function  76 . In preferred form, the EC system  10  is set to maintain polarity across a set of plates inside the EC treatment cells  30  for a specified period of time. The control logic will loop through the sequence just described until the next polarity time-out is reached. At that point in time, the controller  50  once again shuts down the power supply (see item  80 ) and switches the polarity  82  of the plates inside the treatment cells to run until the next time-out period. 
     Referring again to  FIG. 5 , the controller  50  may also monitor incoming and outgoing flow rate ( 86 ) pH ( 88 ,  89 ), turbidity ( 90 ,  91 ), and other factors relating to the flow back via conventional sensor control logic  84 . The pH of the flow back may need to be adjusted upstream of the EC cells so that no flocculation occurs in the flow back before it reaches and passes through the treatment cells  30 . Flow rates and pH and turbidity factors  86 ,  88 ,  89 ,  90 ,  91  may be continually and automatically monitored by the controller  50 . Depending on the quality of the output from the settling tanks  32 , and after filtering (see  36 ,  FIG. 4 ), the treated flow back could be recirculated through the system (not shown) until the EC system&#39;s operation is stabilized. Otherwise, the treatment water is discharged (reference  92 ) to the water tank  20  for recycling in the next hydraulic fracturing operation. Once again, the same basic treatment process is used if delivered water is treated prior to any use as a fracturing fluid. 
     The use of EC technology to enhance hydraulic fracturing in natural gas applications offers many advantages. The benefits of reduced viscosity were previously described. In addition, EC creates significant bacterial kill in the treated water—whereas bacteria in fracturing fluid is otherwise known to be undesirable. The direct field current generated in the EC cells  30  serves to kill bacteria (see  FIG. 19 ). If aluminum plates are used in the cells  30 , they will also generate aluminum hydrate which also affects certain bacterial types. It is believed other kinds of metal besides aluminum may be well-suited for certain kinds of EC cells  30 . 
     In preferred form, stable operation of the EC system  10  involves no or minimum chemical adjustment to the flow, with the treatment relying on the cell plate charge delivered by current control. It is preferred to deliver target currents in the range of 100 to 140 amps DC. These high currents can be achieved because of proper impedance matching provided by the variable step-down transformer  51  described above. It is also more power efficient to use a 3-phase rectifier (reference  52 ) in lieu of single-phase rectification. Different EC cell designs are possible. However, it is desirable to use cell designs that are capable of dissipitating the heat potentially generated by putting high current loads on the plates. 
     Referring now to  FIG. 9 , shown generally at  100  is an EC cell constructed in accordance with the foregoing. Cell  100  consists of a series of circular plate sets, indicated generally at  102 . Each plate set or configuration consists of one central plate  104  that is sandwiched between plates  106 ,  108  on each side. The outer diameter of the central plate  104  is close to the inner diameter of a tubular cell housing (not shown) that holds the array of plate sets that make up the cell  100 . The sidewalls of the tubular housing are illustrated schematically at  109  in  FIGS. 18 and 19 . 
     Referring now to  FIG. 14 , the center plate  104  has a central opening  110  that is laterally offset relative to the plate&#39;s center point  111 . Each plate  106 ,  108  on opposite sides of the center plate  104  will be spaced a small distance from the center plate  104 . This allows waste water to pass around the edges of the smaller plates  106 ,  108  as it flows through the cell. The center point  113  of the smaller plates is on the same axis of symmetry as the larger plate  104 . The cell&#39;s overall center-line axis of symmetry is generally illustrated at  115  in  FIG. 12 . 
     In operation, waste water passes through the plate array in the general direction indicated by arrow  112  (see  FIG. 1 ). The waste water first passes around the outer peripheral edge of a smaller plate  108 ; then radially inward, in between the smaller plate  108  and the center plate  104 ; and then through the opening  110  of the center plate  104  to the plate  106  below. This generates a serpentine, in-and-out flow (in the gaps  117  between the plates—see  FIG. 18 ). For reasons described below, this structural arrangement creates a “vortex” flow along the EC cell&#39;s axial length. The vortex flow is schematically indicated at  124  in  FIG. 10 . The plates are suspended on rods  114 ,  116  which carry electrical current and put a charge on the plates. The plates are also tied together by rods  118 ,  120 ,  122 . Tie rods  118 ,  120 ,  122  are not in electrical contact with the plates (described later). 
     A person skilled in the art will appreciate that the plates are closely packed with a relatively large flow rate passing between the narrow spacing  117  defined by the distance between plates  104 ,  106 ,  108  (insulated plate spacers are shown at  125  in  FIG. 9 ). The vortex flow through cell  30 , in combination with the other process controls described above, will help enable desirable flow rates and throughputs (for treating large quantities of water) without clogging the cell. 
     In general, the EC cells  30  in the system  10  are typically connected together in series. As described above, each EC cell has a sandwiched plate pattern  106 ,  104 ,  108  consisting of alternating plate diameters. Referring to  FIGS. 9 and 10 , for example, different plate diameters are generally shown at  126 ,  128  (see also  FIGS. 18 and 19 ). 
     Each plate carries an electrical charge (positive or negative) that is provided by rods  114 ,  116 , respectively. With respect to the reference numbers used to describe plate set  102 , one rod  114  is electrically connected to all of the larger diameter plates (e.g.,  104 ) while the other is connected to the smaller diameter plates (e.g.,  106 ,  108 ). This allows one plate (e.g., plate  104 ) to be charged positively while the plates on each side ( 106 ,  108 ) are charged negatively (or vice versa). These charges reverse when the polarity is changed in accordance with the foregoing description. 
     As the waste water passes through the cell, the contaminants in the waste water (i.e., particulates and the like) acquire charges from the cell plates. The negative/positive combination of charges initiates particulate coagulation that causes the particulates to mass into larger particles upon exiting the cell  30 . The larger masses gather weight and sink to the bottom of a holding tank, or clarifying tank, or the like. 
     To further describe the above, attention is now directed to the schematics shown in  FIGS. 18 and 19 . These figures illustrate the vortex flow  124  previously described, with the in-and-out nature of flow between the plates illustrated at  117 . 
     Because the openings  110  in the larger plates  104  are offset (for enabling one changing rod to pass through the arrangement of plates without touching the larger ones), the vortex flow through the cell  30  is not symmetric along the cell&#39;s line of symmetry or center-line axis of symmetry (item  115  in  FIG. 12 ). Instead, it becomes “asymmetric” along the center-line axis of symmetry  115 . This creates the “vortex”-like effect through the cell  30  just described and, it is believed, alters the boundary layer next to the surfaces of the cell plates  104 ,  106 ,  108  in a favorable way. 
     The fluid flow between the plates  104 ,  106 ,  108  themselves will be perpendicular to much of the electric field (indicated by arrows  130  in  FIG. 19 ) that is created between the plates. This was described above and is also believed to favorably enhance the EC treatment process. 
     The positive and negative charges on plates  104 ,  106 ,  108  (which alternate, as described above) are schematically indicated on  FIG. 19 . In essence, the plates  104 ,  106 ,  108  create a capacitance effect, setting up the electric field  130  generally perpendicular to flow. The field direction changes as chargers alternate. The capacitance effect is believed to be important because it reduces heat generation and enhances cell performance. 
     The plate sets  106 ,  104 ,  108  within the cell are metal. They are directly connected to rods  114 ,  116 , which place charges on alternating plates (it should be understood that alternating the charge across the rods  114 ,  116  likewise alternates plate charges). Heat generation within the cell  30  is an issue because the cell housing is typically non-metal. One way to reduce heat generation at the electric inputs  136 ,  138  to cell  30  involves use of a bar  140  (see  FIG. 12 ) that splits the current input at the point of delivery to rods  114 ,  116 . This minimizes local overheating at the points on the cell&#39;s cap where the rod ends are connected (see items  142 ,  144  in  FIG. 12 ). 
     Both the large  104  and small  108  plates have rod openings  119  for electrically connecting rods  114 ,  116  to the respective plates. The small plates  108  have a smaller opening  121  for holding an insulating member  123  (see  FIG. 18 ) to prevent electrical conduction with the rod passing through that particular opening  121 . Obviously, there are different ways and insulator arrangements that could be used to accomplish this purpose. There are other plate openings  127  that are used for the non-conducting tie rods  118 ,  120 ,  122  that hold the plate arrangement together. 
     The foregoing description is not intended to limit the scope of the patent right. Instead, it is to be understood that the scope of the patent right is limited solely by the patent claim or claims that follow, the interpretation of which is to be made in accordance with the established doctrines of patent claim interpretation.