Note: Descriptions are shown in the official language in which they were submitted.
CA 02738286 2011-04-28
IMPROVED ELECTROCOAGULATION TREATMENT PROCESS
Technical Field
[0001] 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
[0002] "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.
[0003] 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.
[0004] 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
1
CA 02738286 2011-04-28
head is closed between stage'S to mintain water pressure of the fracturing
fluid for a
period of time.
[0005] 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.
[0006] 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.
[0007] 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.
[0008] 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.
[0009] 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
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CA 02738286 2011-04-28
retrieval operations. There a're 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.
[0010] In sum, the methods and processes disclosed below serve to improve
natural gas production at a lower water treatment cost.
Summary of the Invention
[0011] 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."
[0012] 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,
3
CA 02738286 2011-04-28
the treated water is clean of contaminants and may be recycled into the
fracturing
fluid that is used in subsequent fracturing operations.
[0013] 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.
[0014] 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.
[0015] 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.
[0016] 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
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CA 02738286 2011-04-28
the EC cells within the system. The adjustment is made by monitoring the ratio
of
AC current to DC current.
[0017] 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.
[0018] 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.
[0019] 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.
CA 02738286 2011-04-28
[0020] While the forego' ing 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
[0021] In the drawings, like reference numerals refer to like parts throughout
the various views, unless indicated otherwise, and wherein:
[0022] 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;
[0023] 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;
[0024] Fig. 3 is a schematic of a series of parallel EC treatment cells that
receive fluid from the pre-treatment tank shown Fig. 2;
[0025] 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;
[0026] Fig. 5 is a block schematic diagram showing the operational control of
the EC system;
[0027] Fig. 6 is a block schematic diagram that illustrates electric current
control for the EC system;
[0028] 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;
[0029] 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;
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CA 02738286 2011-04-28
[0030] Fig. 9 is an exploded View of an "EC" cell constructed in accordance
with the invention disclosed here;
[0031] Fig. 10 is a view like Fig. 9;
[0032] Fig. 11 is an exploded view of the back of the cell;
[0033] Fig. 12 is a view like Fig. 11;
[0034] Fig. 13 is a view like Fig. 12, but is taken from a different angle;
[0035] Fig. 14 is a pictorial view of the center plate in the cell set;
[0036] Fig. 15 is a side view of the plate shown in Fig. 14;
[0037] Fig. 16 is a perspective view of the plate that is on each side of the
center plate;
[0038] Fig. 17 is a side view of the plate shown in Fig. 16;
[0039] Fig. 18 is a schematic view of flow through of an EC treatment cell;
and
[0040] Fig. 19 is a view like Fig. 18, but illustrating the electric field
within the
cell.
Detailed Description
[0041] 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.
[0042] 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
7
CA 02738286 2011-04-28
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. Patent No. 7,621,330
issued to
Halliburton Energy Services, Inc. ("Halliburton").
[0043] 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).
[0044] 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.
[0045] 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.
8
CA 02738286 2011-04-28
[0046] 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.
[0047] The EC process reduces viscosity (p) in Darcy's general equation:
[0048] ¨KA (Pb -- Pa)
Q ¨
[0049] The reduction in p is particularly acute with respect to diminishing
imbibition in rocks less than 1 milli-Darcy. By reducing p 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.
[0050] The total discharge, Q (units of volume per time, e.g., m3/s) is equal
to
the product of the permeability (K units of area, e.g. m2) of the medium, the
cross-
sectional area (A) to flow, and the pressure drop (Pb - Pa), all divided by
the
dynamic viscosity p (in SI units, e.g., kg/(m.$) or Pas), and the physical
length L of
the pressure drop.
[0051] The negative sign in Darcy's general equation is needed because fluids
flow from high pressure to low pressure. If the change in pressure is negative
(e.g.,
in the X-direction) then the flow will be positive (in the X-direction).
Dividing both
sides of the above equation by the area and using more general notation leads
to:
9
CA 02738286 2011-04-28
[0052] ¨lc VP
= ______________________________
.11
[0053] where q is the filtration velocity or Darcy flux (discharge per unit
area,
with units of length per time, m/s) and VP is the pressure gradient vector.
This
value of the filtration velocity (Darcy flux) is not the velocity which the
water traveling
through the pores is experiencing.
[0054] The pore (interstitial) velocity (V) is related to the Darcy flux (q)
by the
porosity (w). The flux is divided by porosity to account for the fact that
only a fraction
of the total formation volume is available for flow. The pore velocity would
be the
velocity a conservative tracer would experience if carried by the fluid
through the
formation.
[0055] Water treated by EC is likely to provide better flow rates underground
in pressure-driven fracturing operations according to the following version of
Darcy's
law (relating to osmosis):
[0056] j = AP ¨ All
Rn2)
where,
= J is the volumetric flux (m.s -1),
= AP is the hydraulic pressure difference between the feed and permeate
sides
of the membrane (Pa),
= All is the osmotic pressure difference between the feed and permeate
sides
of the membrane (Pa),
= p is the dynamic viscosity (Pa.$),
= Rf is the fouling resistance (m-1), and
= Rm is the membrane resistance (m -1).
[0057] In both the general and osmotic equations, increased discharge or
volumetric flow is proportionate to decreased viscosity. Therefore, any
treatment
CA 02738286 2015-10-19
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.
[0058] 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.
[00591 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.
[0060] 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, e.g. Fig.
4) via line 34.
[0061]The EC treatment in the cells causes flocculent to be subsequently
generated in the settling tanks 32. There, the contaminants are removed from
the
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CA 02738286 2015-10-19
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.
[0062] 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.
[0063] Fig. 5 is a schematic that illustrates the control logic for the EC
system
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. 5). 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.
[0064] 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
12
CA 02738286 2011-04-28
across the transformer according to the power current level needed by the EC
system 10.
[0065] 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.
[0066] 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.
[0067] 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:
[0068] !target = luser(gurbout oal,-Turbg 1+(Turb,n-Turbcal))x(1/Flow)
[0069] Where:
[0070] !target = Current system will maintain and hold to provide treatment
[0071] luser = Current set point user has specified to provide the gross level
of
treatment
[0072] Turbo = Turbidity out of treatment train
[0073] Turbgoal = Desired turbidity out of the system
[0074] Turb,n = Turbidity of the water to be treated
[0075] Turboa, = Turbidity value to which the system is baseline
[0076] Flow = Flow rate through the treatment cells
13
CA 02738286 2011-04-28
[0077] 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.
[0078] The controller 50 ramps up to the target current 56 as follows.
Reference numeral 58 (in Fig. 5) reflects the controller's constant monitoring
of DC
current (IDc) and AC current (lAc) 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.
[0079] Unique to the present invention, the control logic includes a "power
quality" ("PQ") calculation that is based on the following equation:
[0080]IAC
PQ - X loo
T
[0081] Both the AC (lAc) and DC (IDc) current values are sensed following
rectification. The DC current (IDc) is the averaged direct output from the
rectifier 52.
The AC current (lAc) 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.
[0082] 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).
[0083] 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
14
CA 02738286 2015-10-19
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).
[0084] Returning to Fig. 6), 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
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.
[0085] 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's
operation
CA 02738286 2011-04-28
,
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.
[0086] 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.
[0087]1n 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.
[0088] 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
16
CA 02738286 2011-04-28
,
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.
[0089] Referring now to Fig. 14, the center plate 104 has a central opening
110 that is laterally offset relative to the plate'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's
overall center-line axis of symmetry is generally illustrated at 115 in Fig.
12.
[0090] 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-
outflow
(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'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).
[0091] 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
17
CA 02738286 2011-04-28
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.
[0092] 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).
[0093] 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.
[0094] 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.
[0095] To further describe the above, attention is now directed to the
schematics shown in Fig. 18 and 19. These figures illustrate the vortex flow
124
18
CA 02738286 2011-04-28
i
previously described, with the in-and-out nature of flow between the plates
illustrated
at 117.
[0096] 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'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.
[0097] 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.
[0098j 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.
[0099] 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
19
CA 02738286 2011-04-28
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's cap where the rod ends are connected
(see
items 142, 144 in Fig. 12).
[00100] 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.
[00101] 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.
