U.S. patent application number 12/895314 was filed with the patent office on 2011-05-12 for electrochemical liquid treatment system using dose control.
Invention is credited to Dennis E. Bahr, Ajit K. Chowdhury, Brian R. Hale, Karl W. Marschke, James A. Tretheway, Jeremy J. Vogel.
Application Number | 20110108438 12/895314 |
Document ID | / |
Family ID | 43416654 |
Filed Date | 2011-05-12 |
United States Patent
Application |
20110108438 |
Kind Code |
A1 |
Tretheway; James A. ; et
al. |
May 12, 2011 |
Electrochemical Liquid Treatment System Using Dose Control
Abstract
The invention herein provides an apparatus and method of
controlling an electrochemical treatment process where treatment is
performed in a flow cell to ensure that a controlled dose of
electrical energy or current is delivered to all volumes of the
liquid being treated. In addition the invention provides for
further optimization of the dose based on other factors and sensor
inputs. This invention also provides a method to estimate, display
and record a forecast of process efficacy such as disinfection,
oxidation or other desired treatment that otherwise cannot be
measured in an online manner.
Inventors: |
Tretheway; James A.;
(Madison, WI) ; Hale; Brian R.; (Lake Mills,
WI) ; Bahr; Dennis E.; (Madison, WI) ;
Chowdhury; Ajit K.; (Madison, WI) ; Vogel; Jeremy
J.; (Fort Atkinson, WI) ; Marschke; Karl W.;
(Madison, WI) |
Family ID: |
43416654 |
Appl. No.: |
12/895314 |
Filed: |
September 30, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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61248077 |
Oct 2, 2009 |
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Current U.S.
Class: |
205/743 ;
204/228.1; 204/228.3; 204/228.6; 205/788 |
Current CPC
Class: |
C02F 1/4672 20130101;
C02F 2201/003 20130101; Y02E 60/366 20130101; C02F 2303/04
20130101; C02F 2209/06 20130101; A23L 3/325 20130101; C02F
2001/46142 20130101; C02F 2201/4613 20130101; Y02E 60/36 20130101;
C02F 1/46104 20130101; C02F 2301/043 20130101; C02F 2103/343
20130101; C02F 2103/42 20130101; C02F 2301/046 20130101; C02F
1/4674 20130101; C02F 2201/46115 20130101; C02F 2103/22 20130101;
C02F 2103/32 20130101; A61L 2/035 20130101; C02F 2209/04 20130101;
C02F 2101/305 20130101; C02F 2201/4611 20130101; C02F 2209/29
20130101 |
Class at
Publication: |
205/743 ;
204/228.1; 204/228.3; 204/228.6; 205/788 |
International
Class: |
C02F 1/467 20060101
C02F001/467 |
Claims
1. A liquid treatment system comprising a treatment cell containing
at least two electrodes through which a liquid to be treated may
flow; a power supply providing power to the electrodes; at least
one sensor to measure at least one parameter of the liquid being
treated and providing sensor data on that parameter; and a control
system that adjusts power delivered to the treatment cell based
upon the sensor data.
2. The liquid treatment system of claim 1 further including a flow
meter measuring treatment liquid flow and wherein the control
system adjusts the power delivered to the treatment cell to provide
a predetermined dose of energy to each volume element of the liquid
stream being treated.
3. The liquid treatment system of claim 1 further including a flow
meter measuring treatment liquid flow and wherein the control
system adjusts the power delivered to the treatment cell to provide
a predetermined dose of current to each volume element of the
liquid stream being treated.
4. The liquid treatment system of claim 1 wherein the at least one
sensor measures a voltage and current delivered to the treatment
cell, and wherein the control system calculates an apparent
conductivity of the liquid in the treatment cell and adjusts the
power delivered to the treatment cell to provide a predetermined
dose of energy to each volume element of the liquid stream being
treated.
5. The liquid treatment system of claim 1 wherein the at least one
sensor measures a voltage and current delivered to the treatment
cell, and wherein the control system calculates an apparent
conductivity of the liquid in the treatment cell and adjusts the
power delivered to the treatment cell to provide a predetermined
dose of current to each volume element of the liquid stream being
treated.
6. The liquid treatment system of claim 1 wherein the at least one
sensor measures liquid properties selected from the group
consisting of oxidation-reduction potential, salinity, chlorine
concentration, and pH provide sensor data to the control system to
adjust the power applied to the electrodes for treatment of the
liquid.
7. A method of controlling electrical power delivered to electrodes
in an electrochemical liquid treatment system of a type providing a
treatment cell containing at least two electrodes through which a
liquid to be treated may flow, a power supply providing power to
the electrodes; and at least one sensor to measure at least one
parameter of the liquid being treated to provide sensor data on
that parameter; the method comprising the steps of: passing a
liquid through the electrochemical treatment cell; monitoring at
least one parameter of the liquid being treated with a sensor to
provide sensor data; adjusting the power delivered to the treatment
cell based upon the sensor data.
8. The method of claim 7 wherein the liquid treatment system
further includes a flow measuring device and wherein the method
adjusts the power delivered to the treatment cell to provide a
predetermined dose of energy to each volume element of the liquid
stream being treated.
9. The method of claim 7 wherein the liquid treatment system
further includes a flow measuring device and wherein the method
adjusts the power delivered to the treatment cell to provide a
predetermined dose of current to each volume element of the liquid
stream being treated.
10. The method of claim 7 further including the steps of:
monitoring voltage and current delivered to the treatment cell,
calculating an apparent conductivity of the liquid in the treatment
cell, and wherein the step of adjusting, modulates the power
delivered to the treatment cell to provide a predetermined dose of
energy to each volume element of the liquid stream being
treated.
11. The method of claim 7 further including the steps of:
monitoring voltage and current delivered to the treatment cell,
calculating an apparent conductivity of the liquid in the treatment
cell, and wherein the step of adjusting, adjusts the power
delivered to the treatment cell to provide a predetermined dose of
current to each volume element of the liquid stream being
treated.
12. The method of claim 7 wherein the step of adjusting modulates
an electrical dose delivered to a liquid in a treatment cell based
on sensor information selected from the group consisting of
oxidation-reduction potential, treatment liquid salinity, chlorine
measurements, and pH.
13. A method of providing a real-time estimate of treatment
efficacy of an electrochemical process comprising the steps of:
passing a liquid through an electrochemical treatment cell;
monitoring at least two parameters selected from the group
consisting of: power delivery and liquid characteristics;
calculating and reporting an estimate of treatment efficacy based
on the parameters measured.
14. The method of claim 13 wherein treatment efficacy is estimated
based on at least two process parameters from the group consisting
of: dose delivered to the liquid, oxidation reduction potential of
the liquid and an apparent conductivity of the liquid in the
treatment cell.
15. The method of claim 13 wherein an expected effective treatment
performance operating range for least one process parameter is
determined by a use of minimum and maximum setpoints for the
range.
16. The method of claim 13 wherein a marginally effective treatment
range is determined as a variance from a minimum and maximum
setpoints.
17. The method of claim 13 wherein a marginally effective treatment
range is established through a use of at least one setpoint.
18. The method of claim 13 wherein a color change on at least one
element of a user interface is used to indicate a change in an
expected liquid treatment process efficacy.
19. The method of claim 13 wherein an alarm is provided based on a
change in the expected liquid treatment process efficacy.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application 61/248,077 filed Oct. 2, 2009 hereby incorporated by
reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to an apparatus and method of
controlling the power delivered to an electrochemical process
taking place in a treatment cell so that each unit volume of liquid
passing through the treatment cell receives the same specified
treatment dose, which dose may be a specified amount of electrical
energy or electrical current, sometimes both. The invention also
includes an apparatus and method which may modify the treatment
dose based on chemical sensor measurements such as those for
oxidation-reduction potential, calculated apparent liquid
conductivity in the electrochemical cell, or other parameters.
[0003] Electrochemistry is a basis for many industrial processes.
Some of these occur in fixed baths, such as electroplating
applications, wherein a tank contains a conductive solution, the
electrolyte, in which the desired coating material is either
dissolved in the conductive solution itself or is on the surface of
an electrode. This electrode, the anode, is connected to the
positive terminal of a direct current power supply. The part to be
plated is attached to the negative terminal of the power supply and
becomes a cathode in an electrochemical reaction that takes place
once the part is submerged in the electrolyte. Ions from the
coating material are attracted to the cathode where they are
reduced to metal atoms on the part being coated, for example chrome
on an automobile grill.
[0004] Another application of electrochemistry is to generate
chemicals from liquids containing precursor compounds. One
industrial application, the chlor-alkali process, treats highly
concentrated sodium chloride salt water by DC electrolysis to
generate chlorine gas at the anode and a sodium hydroxide solution
at the cathode. Such applications are not plating ones, so the
anodes may be made out of conductive carbon or catalytic metal
oxide surfaces, generally from the platinum group metals, and the
cathodes can be conductors such as iron, mild steel, stainless
steel or similar materials. In applications like this, the
treatment cell may have an inlet and outlet to permit a process
loop whereby salt is replenished in the water and is returned to
the treatment cell to maintain the reaction.
[0005] In yet another electrolysis application, similar in many
ways to the second one, a clean salt solution is circulated through
a treatment cell to generate chlorine species, which include the
hypochlorite ion and hypochlorous acid. This solution is then
injected into another liquid stream and the chlorine species
disinfect bacteria and other pathogens contained therein. These
devices are commonly called hypochlorite generators.
[0006] In all of these applications, the magnitude of electrical
current controls the reaction rate. The mass of metal that deposits
on the cathode or the quantity of chemicals generated is directly
proportional to the number of electrons provided by the power
supply. For example, sodium chloride salt (NaCl) is a strong
electrolyte that completely ionizes when dissolved in water. This
NaCl solution will conduct electricity due to the mobility of the
positive cations (Na+) and negative anions (Cl-). This ionization
is represented by:
NaCl(s).fwdarw.Na.sup.+(aq)+Cl.sup.-(aq)
[0007] The anion (Cl.sup.-) is attracted to the treatment cell
anode, or positively charged plate, where chloride ions are
oxidized (donate electrons) to form chlorine gas as follows.
2Cl.sup.-.fwdarw.Cl.sub.2(g)+2e.sup.-
[0008] One ampere of electrical current is equivalent to
6.242.times.10.sup.18 electrons per second. To generate chlorine,
the anode donates two electrons to form one molecule of chlorine
gas.
6.242 .times. 10 18 electrons s 2 electrons Cl 2 = 3.121 .times. 10
18 Cl 2 s = 1 ampere ##EQU00001## Cl 2 = 70.9 g / mole
##EQU00001.2## 1 mole = 6.02 .times. 10 23 molecules ( Avagadro ' s
number ) ##EQU00001.3## 70.9 g 1 mole 1 mole 6.02 .times. 10 23
molecules 3.121 .times. 10 18 molecules 1 s = 367.6 .times. 10 - 6
g / s = 0.3676 mg / sec ##EQU00001.4##
[0009] Assuming 100% efficiency and non-reversible reactions,
approximately 0.37 mg of chlorine gas will be created each second
for each ampere. In reality, the electrochemistry of chlorine
generation is more complicated because many parallel reactions may
take place in the liquid being treated. For example, some of the
electrical energy in a salt solution may be used to oxidize water
and generate oxygen. In addition, for each oxidation reaction that
takes place at the anode, an equal reduction reaction takes place
at the cathode. For example, when water is oxidized to generate
oxygen on the anode, hydrogen is evolved on the cathode. Efforts to
optimize efficiency have led to the development of various metal
oxide formulations used to coat the anodes that favor one reaction
over another.
[0010] Since current and not power determines the rate of the
electrochemical reactions, in almost all disinfection applications
to date the electrode plates have been placed very close together
to reduce resistive losses across the electrolyte between the
electrode plates. Liquids with suspended solids cannot be treated
at all without fine filtration beforehand, and those with
significant dissolved solids could not be treated due to the rapid
fouling of the electrodes from charged elements, compounds,
proteins and other organic and inorganic matter.
[0011] Many electrochemical liquid treatment processes exist,
including electrowinning, electrocoagulation, electroflocculation,
electroprecipitation, and electrooxidation. One specific liquid
treatment application of electrochemistry focuses on a direct
current process to generate sodium hypochlorite and hypochlorous
acid in a very clean salt water stream. These chemicals are
disinfectants and oxidizing agents. The treated liquid is then
injected into a dirty or contaminated liquid such as ship bilge
water to disinfect and oxidize the contaminants contained therein.
The described electrolytic reaction takes place in a liquid that
normally has relatively constant salinity and conductivity along
with a relatively constant flow rate.
[0012] Traditionally, the direct current power used in such
electrolytic applications has been controlled in a relatively
simple manner. Over time equipment manufacturers have determined an
optimum current density for a particular anode material and
application that balances production rate with anode life. Knowing
this and the conductivity of the liquid in the treatment cell, a
voltage can be set to deliver this current density. If these
systems experience an increase in the flow rate through the
treatment cell, the power delivered will remain unchanged and will
cause an equivalent reduction in the energy delivered to each unit
volume of the flow. This can result in reduced treatment efficacy,
such as disinfection and oxidation of the contaminants in the flow
streams. If the flow rate were to go down, unplanned overtreatment
of the liquid stream would take place, wasting energy and perhaps
causing other undesired changes in the liquid. The net result in
flow variations is uneven treatment of the liquid.
SUMMARY OF THE INVENTION
[0013] The invention herein provides an apparatus and method of
automated control of an electrochemical process, referred to as
"dose control", which is designed to modulate the power delivered
to an electrolytic flow-through treatment cell so that each unit
volume of liquid passing through the treatment cell receives a
specified uniform dose of electrical energy. Dose control may be
used with alternating current, direct current, polarity switched
direct current, or pulse width modulated current power
supplies.
[0014] The inventors have determined that treatment efficacy for a
liquid stream is directly proportional to the energy delivered to a
given volume of liquid and this energy level varies by the specific
properties of the liquid stream being treated. As such, if the flow
rate or liquid conductivity changes, the applied power must be
adjusted to maintain the predetermined dose of energy to each unit
of liquid volume.
[0015] Dose is defined as power divided by flow. One way to express
it is as a kilowatts (kW) per million gallons (mgal) per day or
kW/mgd. This can be expressed simply by the following
equations:
Dose ( kW mgd ) = Power flow = V * I 1.44 * gpm ##EQU00002## Power
= kW W 1000 = V * I 1000 ##EQU00002.2## Flow = mgd gallons min * 1
1 / 1440 day = 1440 day * M gallons 10 6 = .00144 mgd
##EQU00002.3## Flow .00144 * gpm = mgd ##EQU00002.4##
[0016] Power supplies well known in the art can be controlled by
setting boundary limits for output voltage (V) and current (I). The
impedance of the load (R) determines whether the unit is voltage or
current controlled. Under dose control, the current limit is set to
a high level and is allowed to follow the non-linear impedance of
the electrochemical treatment cell. The set voltage corresponds to
the desired dose by the following relation.
Voltage(V)= {square root over (Dose*gpm*R*1.44)}
[0017] A microprocessor or other controller receives information
from process sensors, calculates the voltage required to maintain
the delivery of the desired energy dose to the liquid stream as the
flow varies, and adjusts the power supply to deliver this
voltage.
[0018] It is thus a feature of at least one embodiment of this
invention to control an electrochemical process to maintain a
predetermined amount of energy delivered to each unit of liquid
volume under varying conditions of operation.
[0019] Traditionally, electrochemical processes have been
controlled to maintain a fixed level of current in a liquid stream.
Yet many industrial liquid streams may vary significantly in flow
rate during the course of operation. For example, in food
processing liquid streams with inline strainers, flow goes down as
solids build up on the strainer screens, increasing their pressure
drops. Two strainers may be installed in parallel with one running
at a time, and operators may suddenly switch over to the clean
strainer so that they can clean the dirty one. This can cause flow
to suddenly increase again. Any electrochemical treatment of such
liquid streams, for example disinfection, could suddenly have
reduced efficacy due to the additional flow. Raising power to avoid
this would waste energy and compromise the lifetime of the
electrodes.
[0020] It is thus a feature of at least one embodiment of this
invention to use a flow measurement means to adjust the power
delivered to the electrodes to maintain a predetermined dose to
each unit of liquid volume of the liquid being treated irrespective
of flow rate.
[0021] The impedance of an electrochemical treatment cell and thus
the apparent conductivity is not constant. Depending on the
electrode materials, especially catalytic electrodes, the treatment
cell may not conduct electricity at all until a certain critical
minimum voltage is reached. Once the voltage reaches this level,
the electrodes will begin to conduct. As the voltage and
corresponding current density increase and gases evolve from the
electrodes, the apparent conductivity may continue to change.
[0022] The impedance of the treatment cell is calculated using
measured values of voltage and current together with Ohm's law. The
inverse of impedance is called conductance. The conductivity of the
treatment cell can be calculated using this conductance combined
with the treatment cell geometry factor. A treatment cell geometry
factor is calculated using the electrode plate area (A), the
distance between each electrode plates (d), and number of treatment
channels (N) in the cell and will be different depending on the
electrode configuration. For example, if alternating electrodes are
each connected to opposite polarities of the power supply in a
monopolar configuration, the treatment cell geometry factor is
calculated as follows.
treatment cell geometry factor = d A N ##EQU00003##
[0023] If only the end electrodes are connected to the power supply
with unconnected electrodes in between in a bipolar configuration,
the treatment cell geometry factor is calculated as follows.
treatment cell geometry factor = d N A ##EQU00004##
[0024] For a hybrid monopolar/bipolar configuration, a combination
of the above equations would be used to calculate the treatment
cell geometry factor.
[0025] Once the treatment cell geometry factor is calculated, it
can be used to calculate the apparent conductivity as follows.
Apparent conductivity=treatment cell geometry
factor.times.conductance
[0026] It is important to note that this conductivity, as measured
within the treatment cell and referred to as the apparent
conductivity, may be significantly different from that measured
outside the treatment cell, referred to herein as the inherent
conductivity.
[0027] As an additional complication, commercial liquid streams may
vary in conductivity quite significantly over time as organic and
inorganic loads change. This can have a dramatic effect on the
actual treatment dose delivered if not otherwise corrected.
[0028] It is thus a feature of at least one embodiment of this
invention to directly calculate the apparent conductivity in the
treatment cell and use this to adjust voltage and current to
maintain the desired dose to each unit of liquid volume of the
liquid being treated.
[0029] As described earlier, for certain electrode materials,
especially catalytic electrodes, electrical current may not begin
to flow in the treatment cell until a certain minimum voltage is
reached, called the activation voltage.
[0030] The activation voltage can vary depending on temperature,
liquid property variations and for other reasons and operating near
this limit can result in highly varied dose delivery. Consistent
control of dose delivery is very difficult to do if the desired
dose requires operating close to the activation voltage.
[0031] Pulse width modulation is a technique that turns power on
and off for fractions of a second at a time on a repeated basis to
modulate current flow and power use while avoiding the need to
adjust voltage. Many incandescent light dimmers use this
technique.
[0032] The inventors have determined that pulse width modulation
provides a robust method of maintaining a consistent treatment dose
when continuous power delivery otherwise would require operating at
voltages close to the activation limit. Voltages are set somewhat
higher than the activation voltage and the width of the "on" time
pulse is adjusted to deliver the treatment dose desired.
[0033] It is thus a feature of at least one embodiment of this
invention to use pulse width modulation to permit the delivery of a
consistent low treatment dose while maintaining electrode voltage
above the activation voltage.
[0034] The invention further relates to methods of recording and
reporting various operating parameters on a display screen, printed
report or database so that an estimate of process efficacy,
specifically disinfection efficacy is provided, which may not
otherwise be available on an online basis due to the laboratory
delays associated with such tests. Depending on the process liquid
being treated, several key parameters can be monitored and
integrated to make this process efficacy estimate.
[0035] Regulating bodies such as the U.S. Department of Agriculture
and Food and Drug Administration monitor the food safety controls
used by food processors. They need to know what steps plants are
taking to control pathogens. They also need to know if the
intervention is working or not. Unfortunately there is no online
measurement for bacteria count, and lab tests take 24-48 hours to
provide accurate disinfection results.
[0036] It is thus a feature of at least one embodiment of this
invention to monitor key parameters including, but not limited to;
treatment dose, liquid flow rate, oxidation reduction potential,
apparent conductivity, and chlorine levels. Acceptable operating
ranges for each parameter can be set. If the parameter falls out of
the acceptable range, the user will be notified by visual and
audible means. If necessary, the microcontroller can control
external chemical disinfectant pumps as a failsafe measure.
[0037] These particular objects and advantages may apply to only
some embodiments falling within the claims and thus do not define
the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] FIG. 1 is a perspective view of a liquid treatment system in
one embodiment of the present invention showing a main housing
holding opposed planar electrodes between liquid inlets and
outlets, a power distribution module, and a control unit;
[0039] FIG. 2 is a detailed block diagram of the components of FIG.
1 showing the electrodes as flat plates;
[0040] FIG. 3 is a graph showing the voltage and current curves of
electrically conductive catalytic electrodes;
[0041] FIG. 4 illustrates pulse width modulation techniques;
[0042] FIG. 5 illustrates the capacitive effect of electrode plates
upon removal of power from these plates; and
[0043] FIG. 6 shows a touchscreen interface displaying a real-time
estimate of treatment efficacy.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0044] Referring now to FIGS. 1 and 2, a liquid treatment system 10
per the present invention may include a treatment unit 12 providing
a liquid inlet 14 and outlet 16 to conduct liquid across internal
electrodes 28. The electrodes 28 are contained in an insulating
housing 18 supported on frame 20 and may be, for example, carbon,
metals such titanium or stainless steel or the like, and optionally
coated with catalytic materials such as platinum group metal
consisting of platinum, palladium, rhodium, iridium, osmium, and
ruthenium, or similar materials.
[0045] A power distribution module 22 provides electrical
connections 24 to the internally contained electrodes 28 for power
received from a control unit 26. The control unit 26 has a
touchscreen user interface 27 for the display and entry of data
including critical operation parameters.
[0046] Referring now to FIG. 2, the treatment unit 12 includes two
or more generally planar and parallel electrodes 28 held in a
channel 36 between the inlet 14 and the outlet 16. The electrodes
28 are separated along an axis 30 generally perpendicular to the
flow of liquid by gaps 32 to receive liquid 34 therethrough. The
separation of the electrodes 28 will be greater than 5 mm to permit
the passage of untreated liquid 34 without undue risk of
clogging.
[0047] One or more chemical sensors 40 may be positioned in sensor
fitting 38 downstream from the electrodes 28 and channel 36 to
measure chemical properties of the liquid and/or a flow sensor 42
may be positioned in the stream of liquid 34 to measure the flow
across the electrodes 28. The chemical sensors 40 may include those
measuring pH, oxidation-reduction potential, chlorine level, free
chlorine level, or total chlorine level.
[0048] The amount of flow through the channel 36 may be controlled
by an electrically driven pump 44 and/or valve 46 alone or in
combination.
[0049] The electrodes 28 are electrically isolated from each other
as held by the housing 18 but may be joined by the connections 24
from power distribution module 22 so that some or all of the
electrodes 28 are electrically connected to electrical conductors
48a and 48b. In some configurations alternating electrodes may be
connected to opposite power polarities. In other configurations
some electrodes 28 may not be directly connected to the electrical
conductors 48a and 48b but instead become electrically activated by
the ionic currents in the liquid 34 being treated, resulting in
each side of such intermediate electrodes 28 having opposite
polarities, an arrangement known as bipolar mode.
[0050] Conductors 48a and 48b are connected to a switching unit 50
contained in the control unit 26 that may alternate the electrical
polarity or limit the current to the electrodes 28. The switch is
depicted logically as a double pole, triple throw electrical switch
and will be typically implemented by solid-state electronics
controllable by control line 51. One pole connects to a positive
voltage line 52 from a voltage controllable DC power supply 58 and
the other pole connects to a negative voltage line 53 from the
voltage controllable DC power supply 58. The voltage controllable
DC power supply 58 receives power from electrical mains 62.
[0051] The throws of the switching unit 50 are controllable so that
one conductor 48a or 48b may be connected to a given voltage
(positive or negative) while the other conductor 48a or 48b is
connected to the opposite voltage. The switching unit may also
limit the power delivered to the electrodes by modulating at a
specific frequency and duty cycle.
[0052] The positive voltage line 52 may connect to a current sensor
54 and voltage sensing point 56, both of which are connected to
inputs of a controller 60, the latter being a special-purpose
computer, for example, a programmable logic controller executing a
stored program to control of the process as will be described. A
similar current sensor 54 and voltage sensing point 56 (not shown)
may be provided on negative voltage line 53. Sensors 52 and 54 may
also be built into the power supply 58. The programmable controller
60 also receives signals from the chemical sensors 40 and flow
sensor 42 and may provide control signals to the pump 44 and valve
46. In addition, the controller 60 communicates with the
touchscreen 27 or alternative user input device which may be a
keyboard or other means known in the art.
[0053] The controller 60 includes a processor 70 and a control
program 72, the latter contained in the memory 81 communicating
with the processor 70 as is generally understood in the art. In
operation, the program 72 will read various parameters of the
process including the electrode current from current sensors 54,
the electrode voltage from voltage sensing points 56, user entered
parameters through touchscreen 27, chemical environment sensing
from the chemical sensors 40, and/or the flow rate from the flow
sensor 42, and will provide output signals on control line 51
controlling the switching unit 50 and the power supply 58. In
addition, output signals controlling the pump 44 and valve 46 and
providing information on the touchscreen 27 may be provided.
[0054] Pump 44 or the valve 46 may be used as the flow controller.
Pump 44 may be a variable flow pump and valve 46 may be a
continuously adjustable valve.
[0055] The control program 72 run by the processor 70 is designed
to maintain a specified dose to the liquid being treated. The user
provides basic setup by entering on the touchscreen 27 two key
pieces of information, desired treatment dose and initial apparent
conductivity. The initial apparent conductivity is used by the
control program 72 as a default value if the calculated value falls
out of a valid range or when the system starts. Dose is the
controlling parameter in the system. The control program utilizes
dose, flow, and apparent conductivity to determine the voltage or
current to apply. Dose may be set as a given power, current or
voltage or any of these measures on a per volume of flow basis.
Further, dose may be adjusted over time based on other sensor
readings indicating efficacy of the dose.
[0056] The power supply 58 can be either voltage or current
controlled. If voltage controlled, the current is allowed to float
within a range depending on the impedance of the treatment unit 12
to provide a given voltage across the liquid. If current
controlled, voltage is allowed to float to maintain the desired
current level through the liquid.
[0057] Referring now to FIG. 2, FIG. 3 and FIG. 4 together, when
the desired treatment dose would otherwise require a voltage at the
electrodes below or only somewhat above the activation voltage 302
of the electrode plates (determined by the chemical composition of
the plates as is understood in the art), the controller 60 uses
pulse width modulation 400 to maintain voltage on the electrode at
a minimum voltage that is somewhat greater than the activation
voltage 302 of the electrode plates 28.
[0058] Referring now to FIG. 3, graph line 300 shows the idealized
activation voltage curve, with no current flowing until activation
voltage 302 is reached. Thereafter current rises in a linear
fashion with voltage increases. Graph line 304 shows the actual
curve of an approximate 50% saturated brine solution from the work
of the inventors.
[0059] Referring to FIG. 4, this graph provides a simplified view
of pulse width modulation, which can take several forms and this
invention is not intended to be limited by this illustrative
figure. Graph line 400 illustrates pulse width modulation where the
power is on 10% of the time. This power-on time is referred to as
the duty cycle. This would allow the voltage to be set an
appropriate level above the activation voltage to provide stable
power delivery level while delivering only approximately 10% of the
treatment dose that would be delivered with continuous power
delivery at that voltage. Graph lines 402 and 404 illustrate 50%
and 90% duty cycles, which would deliver a corresponding higher
dose at the same voltage.
[0060] Referring now to FIG. 2, FIG. 4 and FIG. 5 together, the
inventors have determined that when voltage 500 is removed at time
504 from the electrode plates 28, the electrical circuit maintains
the voltage on the electrode plates 28 near the activation voltage
502 for a period of time after power has been removed from the
electrodes. The voltage discharge follows a capacitive discharge
curve 506 until the voltage goes to zero at time 508. The time
period of this capacitive discharge 510 is input via touchscreen 27
or obtained from a database. Control program 72 adjusts the
frequency of pulse width modulation 400 so that the time with no
power applied to electrode plates 28 during the pulse width
modulation duty cycle does not fully discharge the electrode plates
to avoid ramp up time delays at the start of the next duty cycle
and reduces voltage shock effects on the electrode plates that
could adversely affect electrode plate life.
[0061] The control program 72 constantly reads and records data
from field and locally mounted devices. It filters this data and
feeds it back into the equations controlling the voltage or current
out. Power is constantly adjusted in this manner to maintain the
set dose regardless of flow rate or conductivity.
[0062] Referring now to FIG. 6, this is an example of a touchscreen
27 display of online estimated process efficacy. This is meant to
be an illustrative example only and is not meant to limit the
claims. This screen provides a real-time estimate of the
disinfection efficacy, shown here as disinfection strength 600, of
the electrochemical process. In this specific case three variables
602 are used in the calculation: oxidation reduction potential
(ORP), treatment dose, and relative (apparent) conductivity of the
liquid being treated.
[0063] ORP indicates the ability of a liquid stream to oxidize the
liquid. This is directly related to disinfection power for a given
liquid stream and salinity level. A minimum level 604 and a maximum
level 606 are set. Below the minimum, effective treatment becomes
marginal. Above the maximum and unwanted byproducts may be
produced, such as trichloramines which can cause negative effects
on plant operators.
[0064] Treatment dose is the energy requirement per unit of volume
that in the past has been demonstrated to deliver consistently
acceptable disinfection results. It confirms that the power supply
is operating properly. As with ORP, a minimum value is set as well
as a maximum, above which power would be wasted or that may
indicate a faulty sensor.
[0065] For a given liquid stream, changes in relative (apparent)
conductivity substantially relates to changes in the salinity or
chloride content of the liquid. If salinity were to drop, the
balance between molecular oxygen, reactive oxygen species, and
reactive chlorine species would change, affecting disinfection
performance. If the salinity level were to rise too high, unwanted
byproducts such as trichloramines may be produced.
[0066] The control program for online process efficacy monitors
whether the selected variables 602 are in the acceptable range and
displays an estimate of disinfection strength 600 of "OK" or
language with a similar meaning if all three are in range. In
addition, the disinfection strength indicator 600 and the variables
all have a green background to provide a quick indicator of system
efficacy to plant personnel who may be at a distance.
[0067] If one or more variables 602 falls or rises outside of the
range determined by the minimum value 604 and maximum value 606 but
does so by less than a predetermined amount or percentage, such as
ten percent, the indicator for that variable 602 changes color to
yellow and the disinfection strength indicator 600 changes to
yellow. The disinfection strength indicator also changes text to
read "LOW" or to language with a similar meaning. Again, this color
change permits plant operators to monitor expected process efficacy
and operational status at a distance.
[0068] Finally, if one or more of the variables 602 falls or rises
by more than the predetermined amount or percentage described
previously, such as the ten percent in the example, the indicator
for that variable 602 changes color to red and the disinfection
strength indicator 600 changes to red. The disinfection strength
indicator also changes text to read "VERY LOW" or to language with
a similar meaning. The red color may also blink. Again, this color
change permits plant operators to monitor expected process efficacy
and operational status at a distance. In some installations a
warning horn may also be sounded to draw attention to the out of
limits condition.
[0069] The inventors do not intend to limit this control
methodology to minimum and maximum set points, and the use of
intermediate (marginal performance) set points has already been
tested. The inventors also envision control programs that adjust
one monitored variable in response to changes in another, such as
increasing treatment dose if relative (apparent) conductivity
levels fall.
[0070] The present invention has been described in terms of the
preferred embodiment, and it is recognized that equivalents,
alternatives, and modifications, aside from those expressly stated,
are possible and within the scope of the appending claims.
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