U.S. patent application number 12/282742 was filed with the patent office on 2009-12-31 for device for measuring permeate flow and permeate conductivity of individual reverse osmosis membrane elements.
This patent application is currently assigned to HYDRANAUTICS. Invention is credited to Craig Bartels, Rich Franks, Norio Ikeyama, Mark Wilf.
Application Number | 20090320563 12/282742 |
Document ID | / |
Family ID | 38522905 |
Filed Date | 2009-12-31 |
United States Patent
Application |
20090320563 |
Kind Code |
A1 |
Wilf; Mark ; et al. |
December 31, 2009 |
DEVICE FOR MEASURING PERMEATE FLOW AND PERMEATE CONDUCTIVITY OF
INDIVIDUAL REVERSE OSMOSIS MEMBRANE ELEMENTS
Abstract
The present disclosure relates to a system comprising integrated
sensors (169, 170) for measurement of permeate flow and permeate
conductivity of individual membrane elements (163) while they are
in operation in an RO unit. The flow and conductivity measuring
integrated sensors (169, 170) are of a small size that enables them
to be inserted into the permeate tube (172) of connected membrane
elements (163) during RO unit operation. Measured flow and
conductivity information is transferred to the recording device
(174) through electric wires or through wireless transmission.
Inventors: |
Wilf; Mark; (San Diego,
CA) ; Franks; Rich; (Fallbrook, CA) ; Bartels;
Craig; (San Diego, CA) ; Ikeyama; Norio;
(Osaka, JP) |
Correspondence
Address: |
KNOBBE MARTENS OLSON & BEAR LLP
2040 MAIN STREET, FOURTEENTH FLOOR
IRVINE
CA
92614
US
|
Assignee: |
HYDRANAUTICS
Oceanside
CA
|
Family ID: |
38522905 |
Appl. No.: |
12/282742 |
Filed: |
March 12, 2007 |
PCT Filed: |
March 12, 2007 |
PCT NO: |
PCT/US2007/006152 |
371 Date: |
April 6, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60781858 |
Mar 13, 2006 |
|
|
|
Current U.S.
Class: |
73/38 ;
73/204.11 |
Current CPC
Class: |
B01D 65/02 20130101;
B01D 65/104 20130101; B01D 2311/06 20130101; B01D 2321/40 20130101;
B01D 61/12 20130101; B01D 2311/06 20130101; B01D 2311/16 20130101;
B01D 2311/06 20130101; B01D 2311/243 20130101; B01D 61/025
20130101; B01D 63/12 20130101; Y02A 20/131 20180101 |
Class at
Publication: |
73/38 ;
73/204.11 |
International
Class: |
G01N 15/08 20060101
G01N015/08; G01F 1/68 20060101 G01F001/68 |
Claims
1. A system that permits assessment of performance of a reverse
osmosis membrane element, comprising: said reverse osmosis membrane
element; a permeate tube within said reverse osmosis membrane
element; an elongated probing tube within the permeate tube of said
reverse osmosis membrane element; at least one sensor configured to
measure a value used to assess said performance and disposed at an
inlet side of said probing tube; and a recording device in
electronic communication with said sensor so as to record results
of said measurement.
2. The system of claim 1, wherein said sensor configured to measure
a value used to assess said performance comprises a sensor for
measuring permeate flow.
3. The system of claim 2, wherein said sensor for measuring
permeate flow comprises a thermal anemometer sensor.
4. The system of claim 1, further comprising a sensor for measuring
permeate conductivity.
5. The system of claim 4, wherein said sensor for measuring
permeate conductivity comprises a conductivity cell with an
integrally mounted thermocouple.
6. The system of claim 1, wherein a power source powers said
sensor.
7. The system of claim 6, wherein said power source comprises at
least one radio frequency identification (RFID) tag.
8. The system of claim 1, wherein said electronic communication is
conducted via wiring connecting said recording device and said
sensor.
9. The system of claim 1, wherein said electronic communication is
conducted via a wireless connection connecting said recording
device and said sensor.
10. The system of claim 1, wherein said sensor is additionally
provided with an RFID tag, and said value is linked to a reverse
osmosis membrane element via communication between said REID tag
and an RFID tag mounted on said element.
11. A method of assessing performance of reverse osmosis membrane
elements, said method comprising: a) providing a system in
accordance with claim 1 in a pressure vessel containing at least
one said element; b) measuring at least one said value; c)
transmitting results of said measurement to said recording device;
and d) assessing said performance based on said results.
12. A method of assessing performance of reverse osmosis membrane
elements in accordance with claim 11, wherein said at least one
value comprises data relating to permeate flow.
13. A method of assessing performance of reverse osmosis membrane
elements in accordance with claim 12, wherein said at least one
value additionally comprises data relating to permeate
conductivity.
14. A method of assessing performance of reverse osmosis membrane
elements in accordance with claim 11, wherein said sensor is
additionally provided with an RFID tag, and said value is linked to
a reverse osmosis membrane element via communication between said
RFID tag and an RFID tag mounted on said element.
15. A method of assessing performance of reverse osmosis membrane
elements in accordance with claim 11, additionally comprising: e)
replacing said element if said assessment indicates replacement is
required to improve system performance.
Description
RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional
Application No. 60/781,858, filed Mar. 13, 2006, the entirety of
which is hereby incorporated by reference herein.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present disclosure relates to a measuring device and
system that allows convenient and simultaneous measurement of flow
and conductivity of permeate produced by reverse osmosis elements
while they are installed in a pressure vessel and operated in an RO
train.
[0004] 2. Description of the Related Art
[0005] Spiral wound reverse osmosis membrane elements are widely
used for the desalination of water in plants of increasingly higher
capacity. A commercial membrane element measures 1000 mm (40
inches) in length and 200 mm (8 inches) in diameter and weighs
about 16 kg (40 lbs). A single element produces a permeate flow of
12 m.sup.3/d-24 m.sup.3/day (3200-6400 gallons per day). A single
desalination plant producing 200,000 m.sup.3/day (50 million
gallons of water per day) of permeate may require as many as 15,000
such spiral wound elements to produce the designed permeate
capacity. The individual elements are loaded into fiberglass
pressure vessels arranged in racks to form a single RO train. In
large RO systems one train may consist of 100-200 pressure vessels.
Several trains may operate independently in any single desalination
plant. Six to eight elements are loaded into a single pressure
vessel. Accordingly, 600 to 1600 elements may operate in a single
train. Once loaded in the pressure vessels, membrane elements are
only removed at the time of element replacement (usually every 3-10
years of operation) or when required for special testing. Removal
of membrane elements from pressure vessels requires the complete
shut down of RO train operation.
[0006] The performance of individual elements is usually known
prior to installation in the RO system. After installation, the
performance of elements may change due to membrane fouling. The
effect of membrane performance deterioration is observed by
measuring the permeate flow, permeate conductivity and pressure
drop of a complete RO train. In some cases, the permeate
conductivity of individual pressure vessels can be measured.
Measurement of permeate flow and permeate conductivity of
individual elements is not practical with current technology in a
commercial RO unit. Usually, the effect of fouling on element
performance is not uniform through the system. After performance of
an RO system has deteriorated to a certain level, a performance
improvement can be achieved by membrane cleaning or partial or
complete replacement with new elements. The major obstacle to
efficient element replacement is the absence of a convenient method
for measuring the performance of individual elements while they are
installed and operating in an RO train.
SUMMARY OF THE INVENTION
[0007] In an aspect, a system that permits assessment of
performance of a reverse osmosis membrane element is provided that
comprises: the reverse osmosis membrane element; a permeate tube
within the reverse osmosis membrane element; an elongated probing
tube within the permeate tube of the reverse osmosis membrane
element; at least one sensor configured to measure a value used to
assess the performance and disposed at an inlet side of the probing
tube; and a recording device in electronic communication with the
sensor so as to record results of the measurement.
[0008] In a further aspect, the sensor configured to measure a
value used to assess the performance comprises a mechanism for
measuring permeate flow.
[0009] In a further aspect, the sensor for measuring permeate flow
comprises a thermal anemometer sensor.
[0010] In a further aspect, the system also comprises a sensor for
measuring permeate conductivity.
[0011] In a further aspect, the sensor for measuring permeate
conductivity comprises a conductivity cell with an integrally
mounted thermocouple.
[0012] In a further aspect, a power source powers the sensor.
[0013] In a further aspect, the power source comprises at least one
radio frequency identification (RFID) tag.
[0014] In a further aspect, the electronic communication is
conducted via wiring connecting the recording device and the
sensor.
[0015] In a further aspect, the electronic communication is
conducted via a wireless connection connecting the recording device
and the sensor.
[0016] In a further aspect, the sensor is additionally provided
with an RFID tag, and the value is linked to a reverse osmosis
membrane element via communication between the RFID tag and an RFD
tag mounted on the element.
[0017] In an aspect, a method of assessing performance of reverse
osmosis membrane elements is provided, the method comprising:
providing a system in a pressure vessel, the system comprising a
reverse osmosis membrane element, a permeate tube within the
reverse osmosis membrane element, an elongated probing tube within
the permeate tube of the reverse osmosis membrane element, at least
one sensor configured to measure a value used to assess the
performance and disposed at an inlet side of the probing tube, and
a recording device in electronic communication with the sensor so
as to record results of the measurement; measuring at least one
value; transmitting results of the measurement to the recording
device; and assessing the performance based on the results.
[0018] In a further aspect of this method, at least one value
comprises data relating to permeate flow.
[0019] In a further aspect of this method, at least one value
additionally comprises data relating to permeate conductivity.
[0020] In a further aspect of this method, the sensor is
additionally provided with an RFID tag, and the value is linked to
a reverse osmosis membrane element via communication between the
RFID tag and an RFID tag mounted on the element.
[0021] In a further aspect of this method, the method additionally
comprises replacing the element if the assessment indicates
replacement is required to improve system performance.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a partial schematic and partial block diagram of
one embodiment of a thermal anemometer that may be employed in the
measurement system.
[0023] FIG. 2 is a graph illustrating the cyclic operation of the
probe in the thermal anemometer.
[0024] FIG. 3 is a graph of the characteristic temperature decay of
a thermocouple probe.
[0025] FIG. 4 is a semi-log plot of the normalized temperature
decay of a thermocouple probe.
[0026] FIG. 5 is a block diagram of one logic circuit that may be
employed in a thermal anemometer useful in a measurement system in
accordance with an embodiment.
[0027] FIGS. 6-10 are embodiments of sheath type probes that may be
employed in the thermal anemometer.
[0028] FIG. 11 is a flow chart of the operation of the thermal
anemometer.
[0029] FIG. 12 shows a schematic view of an arrangement of reverse
osmosis membrane elements in a pressure vessel.
[0030] FIG. 13 shows the configuration of an integrated thermal
anemometer sensor and conductivity sensor device mounted on a
support.
[0031] FIG. 14 shows a schematic view of an arrangement of a
thermal anemometer sensor mounted on a support tubing inserted in
the permeate tube of an RO membrane element.
[0032] FIG. 15 shows a schematic block diagram of a conductivity
probe that may be used in a measuring system in accordance with an
embodiment.
[0033] FIG. 16 shows a schematic diagram of temperature
compensation circuits of the conductivity probe of FIG. 15.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0034] Embodiments comprise an integrated sensor device that
enables simultaneous measurement of permeate flow and permeate
conductivity inside the permeate tube of membrane elements, while
the elements are in operation in the RO unit. Particularly
preferred embodiments comprise a thermal anemometer sensor and
conductivity sensor mounted on an elongated small diameter support
tubing. This sensor device can be inserted through a permeate port
of a pressure vessel into permeate tubes of membrane elements
operating and connected together in a pressure vessel. As the
sensor is moved along the permeate tube it generates electric
signals that are related to the permeate flow rate and permeate
conductivity at various points along the pressure vessel. The
electric signal is either transmitted through the wires connecting
the sensors with an outside recording device or by generating and
sending a wireless transmission of the measured data.
[0035] The electric energy required to power the thermal anemometer
sensor and conductivity sensor (collectively described as the
"measuring devices") can be supplied by radio frequency radiation,
a rechargeable battery, power transformed from a radio frequency
identification (RFID) tag, electromagnetic energy, energy from a
turbine mounted on the small diameter support tubing, or other
forms of energy supply known to those skilled in the art. The
measuring devices of preferred embodiments are preferably powered
by RFID tags. The RFID tags are preferably activated by
electromagnetic energy emitted by devices that retrieve information
from RFID tags, such as a receiver situated inside or outside the
pressure vessel. When activated, the RFID tags preferably transmit
power to the measuring devices, which take their measurements. In
particularly preferred embodiments, the data is stored in the RFID
tags, which may be instantaneously and/or later retrieved. In other
preferred embodiments, the measuring devices are powered by
rechargeable batteries. For example, such batteries include, but
are not limited to, nickel cadmium batteries, lithium ion
batteries, and other batteries known to those skilled in the art.
In preferred embodiments the batteries may be recharged by energy
transmitted from activated RFID tags. In other preferred
embodiments, the measuring devices may be activated by radio
frequency (RF) energy from an outside source. Further embodiments
comprise measuring devices which are powered by magnetic energy,
electromagnetic energy, or other forms of energy known to those
skilled in the art.
Permeate Flow Measurement
[0036] In an embodiment of the device, the permeate flow is
measured using a thermal anemometer. Examples of such devices are
disclosed in U.S. Pat. Nos. 5,271,138; 4,794,794; 4,848,147;
4,621,929; and 4,537,068, which are incorporated in their entirety
by reference.
[0037] In general, a thermal anemometer measures fluid velocity by
sensing the changes in heat transfer from a small,
electrically-heated element exposed to the fluid.
[0038] If a wire is immersed in a fluid and is heated by an
electric current, the temperature of the wire increases and the
power input is:
I.sup.2R.sub.w=h.sub.wS.sub.w(T.sub.w-T.sub.f) (1)
Where:
[0039] I: value of electric current,
[0040] R.sub.w: resistance of the wire
[0041] h.sub.w: heat transfer coefficient of the wire
[0042] S.sub.w: the surface area of the wire
[0043] T.sub.w: temperature of the wire
[0044] T.sub.f: temperature of the fluid
[0045] The resistance of the wire is also a function of
temperature:
R.sub.w=R.sub.0[1+.alpha.(T.sub.w-T.sub.0)] (2)
Where:
[0046] R.sub.o is resistance of the wire at the reference
temperature
[0047] .alpha. is coefficient of thermal resistance of the wire
[0048] T.sub.0 is the reference temperature
[0049] The heat transfer coefficient of the wire h.sub.w is a
function of the fluid velocity v.sub.f according to the following
equation:
h.sub.w=a+bv.sub.f.sup.c (3)
where a, b and c are coefficients obtained by calibration.
[0050] Combining the above three equations we can eliminate heat
transfer coefficient hw and rearrange to solve for fluid
velocity:
V.sub.f={(I.sup.2R.sub.0[1+.alpha.(T.sub.w-T.sub.0)]/S.sub.w(T.sub.w-T.s-
ub.0)-.alpha.)/b}.sup.1/c (4)
[0051] The cooling effect produced by the flow passing over the
element is balanced by the electrical current to the element, so
that the element is held at a constant temperature. The change in
current due to a change in flow velocity shows up as a voltage at
the anemometer output.
[0052] An embodiment of a thermal anemometer suitable for use in
the device for measuring permeate flow and permeate conductivity
will now be described. Referring to FIG. 1, one embodiment of a
thermal transient anemometer fluid flow measuring device useful in
preferred embodiments is designated generally by the reference
numeral 10. The device 10 includes a thermocouple sensing probe 12
which can be inserted into a fluid flow path, illustrated by arrows
14 to measure the flow velocity.
[0053] The fluid flow 14 can be contained in a conduit or duct 16,
such as a permeate tube. The thermocouple probe 12 includes a pair
of calibration wires 20, 22 which are connected to form a
conventional thermocouple junction 24 located adjacent to the end
of the probe 12.
[0054] In this embodiment, the thermocouple 12 is illustrated as
being a sheath type probe, specific examples of which are
illustrated in FIGS. 6-10. An unsheathed probe also could be
utilized. The sheath protects the junction 24 from the effects of
the fluid flow 14.
[0055] A simple, preferably electronic, control unit 26 is
illustrated in block form. The control unit 26 may be located at a
site remote from the thermocouple probe 12, as shown for example in
FIG. 14, in which the thermocouple probe is located at the distal
end of support tube 173 and control unit 26 may be located within
recording device 174. The unit 26 includes a power supply 28 which
is coupled to one of the wires 22 through a pulsing switch 30.
[0056] The unit includes a voltage measuring instrument 32, which
is coupled to a voltage versus time recorder 34. The voltage and
time measurements are coupled to a calculation unit 36, which
correlates the fluid flow velocity from the temperature decay or
time constant of the probe 12. The calculation unit 36 is coupled
to an output or display unit 38, which can generate a visual and/or
hard copy output.
[0057] The cyclic operation of the device 10 and the probe 12 is
best illustrated with respect to FIG. 2. At a time t.sub.-1, the
pulse switch 30 is closed, coupling a relatively high voltage pulse
across the wires 20 and 22 for a time period of (t.sub.0-t.sub.-1).
The temperature of the probe 12 near the junction 24 is raised by
resistance heating to a temperature above that of the fluid to be
measured. For example, in typical fluid flow measurements, the
temperature of the probe can be raised 5 to 10.degree. F. above
that of the fluid. As described hereinafter, the power pulse does
not require accurate control or measurement.
[0058] At time t.sub.0, the switch 30 is opened to remove the power
from the wires 20, 22. When the power is removed, the temperature
distribution in the thermocouple 12 begins to relax. At time
t.sub.1, the temperature T.sub.1 of the junction 24 is measured by
the instrument 32 which couples the measurement to the recorder 34.
At a second time t.sub.2, the temperature T.sub.2 of the junction
24 again is measured by the instrument 32 and again is coupled to
the recorder 34.
[0059] The two measurements, T.sub.1 and T.sub.2, then are utilized
in the unit 36 to calculate the corresponding flow velocity of the
flow 14 in accordance with the analysis provided hereinafter with
respect to FIGS. 3 and 4. At time t.sub.3, the cycle again can be
repeated if desired. The temperatures T.sub.1 and T.sub.3 are
totally unrelated and do not need to be the same value. A second
conventional reference thermocouple junction may be required where
the fluid bulk temperature is not substantially constant.
[0060] A mathematical analysis of the temperature decay of the
junction 24 is characterized by the graph illustrated in FIG. 3.
Initially, at time t.sub.0, the junction 24 has some arbitrary
temperature profile described by a temperature function, f(r).
Modeling the probe 12 as an infinitely long, homogeneous solid
cylinder, the temperature distribution as functions of radius `r`
and time `t` can be described by the classical series solution of
equation 5 below. This discussion is made under the zero reference
theory, where the fluid temperature is assumed to be zero, so that
the probe temperature "T" actually represents a difference from the
reference temperature. In actual practice, the fluid temperature
would be measured and known, so that the corresponding measured
difference between the fluid and probe temperatures could easily be
correlated mathematically.
T = 2 a 2 n = 1 .infin. - k .alpha. n 2 t [ .alpha. n 2 J o (
.alpha. n r ) ( h 2 + .alpha. n 2 ) J o 2 ( .alpha. n a ) ] .intg.
0 .alpha. rf ( r ) J o ( .alpha. n r ) r ( 5 ) ##EQU00001##
Where:
[0061] T=temperature differential between probes and fluid at given
radius and time
[0062] r=radius
[0063] a=outside radius of cylinder
[0064] t=time
[0065] H=convective coefficient at cylinder surface
[0066] h=H/K
[0067] k=K/.rho.C
[0068] .rho.=density
[0069] C=heat capacity
[0070] K=thermal conductivity within the cylinder
[0071] Jo=Bessel function of order zero
[0072] .alpha..sub.n=roots of the transcendental equation 2
.alpha.J.sub.o'(a.alpha.)+hJ.sub.o(a.alpha.)=0 (6)
[0073] After a sufficient decay time, t.sub.0-t.sub.1, the initial
temperature conditions in the probe 12 relaxes and all terms, in
the same series, approach zero, accept one. The decay equation
after time, t.sub.1, can be approximated by:
T = A 1 - k .alpha. 1 2 t where A 1 = 2 a 1 2 a 2 J o ( .alpha. 1 r
o ) ( h 2 + .alpha. 1 2 ) J o 2 ( .alpha. 1 , a ) .intg. 0 a rf ( r
) J o ( .alpha. 1 r ) r . ( 7 ) ##EQU00002##
[0074] A.sub.1 is a constant for fixed initial conditions, flow
conditions and radial position, r; and .alpha..sub.1, is the
smallest root (eigenvalue) of the transcendental equation 6.
[0075] A semi-log plot of equation 7 starting at time, t.sub.1, and
normalized to T.sub.1, is shown in FIG. 4. The slope of this curve
is constant and approximated by equation 8. Significantly, the
initial conditions cancel and, therefore, the slope is independent
of the power pulse's shape, duration, radial position and
magnitude. Utilizing equation 8 and from equation 6 recognizing
that H is a function of .alpha..sub.1, the convective coefficient,
H, can be determined by using equation 8A.
ln T 2 / T 1 t 2 - t 1 = - k .alpha. 1 2 = Slope or ( 8 ) .alpha. 1
= - .rho. C K .times. slope ( 8 A ) ##EQU00003##
[0076] From fluid dynamic considerations, the convective
coefficient at the surface of the probe can be approximated using a
correlation for fluid cross flow over a cylinder in the form of
equation 9.
H=CRe.sup.n (9)
Where
Re=vd/.gamma.(Reynolds Number) (9A)
d=outside diameter of cylinder v=local fluid velocity
.gamma.=dynamic viscosity and C and n are known empirical constants
over large ranges of Re numbers. Substituting equation 9A into
equation 9 yields equation 10.
v = .gamma. d ( H C ) 1 / n ( 10 ) ##EQU00004##
[0077] Thus, with measured temperature values, T.sub.1 and T.sub.2,
the local flow velocity, v, can be calculated using equations 6, 8A
and 10.
[0078] For small internal thermal resistances (Biot #=hd<1)
local fluid velocity is approximately related to the slope in
equation 8 utilizing equation 11. Hence, for fixed fluid and probe
properties, a log-log plot of v vs. slope, results in a straight
line with slope n.
v.sup.n=Slope.times.Constant For Biot #<1 (11)
[0079] The above constant is a calibration constant dependent upon
fixed probe and fluid properties. A database for different fluids
and/or fluid temperatures can then be developed. The exponent `n`
is a known constant over large ranges of Re numbers and is given as
0.466 for the range of Re numbers from 40 to 4,000.
[0080] Thus, with measured normalized slope values (from equation
8) the local flow velocity, v, can be calculated using equation 11.
The total flow in the duct 16 based upon the local velocity reading
or readings then can be calculated utilizing fluid conditions, duct
size, probe location, etc. as utilized in many conventional flow
measurement methods.
[0081] A generalized block and schematic logic circuit of another
embodiment of an anemometer which may be used in an embodiment is
designated generally by the reference numeral 40 in FIG. 5. A
thermocouple junction 42 is coupled by a pair of calibration wires
44 and 46 to an amplifier 48. The wire 44 conveniently can be
grounded and the wire 46 is coupled to a pulse switch 50 via a line
52. The pulse switch 50 is coupled to a power supply 54 via a line
56.
[0082] The amplifier 48 is coupled via wires 58 and 60 to an
analog-to-digital converter (A/D) 62. The output of the A/D
converter 62 is coupled to a processor 64 via a line 66. The
processor 64, such as a microcomputer or microprocessor, also is
coupled via a line 68 to the switch 50 and via a line 70 to a
display 72. Although not illustrated, appropriate filtering can be
provided at the input to the amplifier 48 to isolate the amplifier
48 from the transient power pulses applied to the junction 42, if
desired.
[0083] In the device 40, the processor 64 controls the timing of
the pulses applied to the junction 42 by the pulse switch 50 and
the power supply 54. The voltage from the junction 42 is amplified
by the amplifier 48 and converted into digital signals to be
utilized by the digital process which then can be displayed in the
display 72. Although digital signals are most preferable along with
the utilization of a microprocessor for the processor 64, an analog
logic processor also could be utilized in which case the processor
64 and associated circuitry could be eliminated.
[0084] The devices 10 and 40 have good stability, repeatability and
sensitivity. The devices 10 and 40 readily can be adapted for
simultaneous multiple flow measurement techniques. Thermocouples
have an established history of reliability, accuracy and durability
and the devices 10 and 40 benefit from the incorporation of the
thermocouple concept. Specific thermocouple designs are illustrated
in FIGS. 6-10.
[0085] In conventional thermocouples, the entire thermocouple
length is heated by applying sufficient power thereto. A decrease
in power consumption can be obtained by heating only the tip area
of the thermocouple around the thermocouple junction. The following
probes described especially in FIGS. 6-10 are designed to utilize
standard fabrication techniques to minimize manufacturing costs.
The utilization of sheath type thermocouples allows their
established history of reliability, accuracy and durability to be
incorporated into the devices 10 and 40. Further, the thermocouples
are modified to minimize the power requirements for decreasing
operating costs and to enhance portable battery powered
applications.
[0086] Referring to FIG. 6, a first embodiment of a sheath type
thermocouple probe 74 is best illustrated. The probe 74 includes a
sheath outer body 76 ending in a closed tip 78. A first calibration
wire 80 is formed to have a relatively low electrical resistance by
forming the wire 80 from a highly conductive material and/or a
large wire diameter. A second calibration wire 82 is formed to have
a relatively high electrical resistance by forming the wire 82 from
a poor conductive material and/or a small wire diameter.
[0087] A junction 84 is formed adjacent the tip 78 and the wire 82
is grounded to the tip 78 and hence the sheath body 76. The tip 78
is locally heated adjacent the junction 84. The local heating of
the tip 78 is accomplished by applying a relatively high voltage
across the low resistance wire 80 and the sheath body 76. The
current thus flows through the wire 80 to the junction 84 with
negligible resistance heating. From the junction 84, the current
flows through the high resistance wire 82 to the grounded tip 78.
The wire 82 is thus heated between the junction 84 and the tip 78
to locally heat the tip 78. The current flow through the sheath
body 76 generates a minimal or negligible resistance heating. The
temperature sensing of the probe 74 is performed by utilizing the
Seebeck effect between the wires 80 and 82 at the junction 84.
[0088] A second embodiment of a sheath type thermocouple probe 86
is illustrated in FIG. 7. The probe 86 includes a sheath body 88
with a tip 89. A first low resistance calibration wire 90 is
connected at a junction 92, just prior to the tip 89, to a high
resistance wire portion 94 which is grounded to the tip 89. A
second low resistance calibration wire 96 is also grounded to the
tip 89.
[0089] The local heating of the tip 89 during the applied power
pulse is accomplished by applying a relatively high voltage across
the wires 90 and 96. Due to the high electrical conductivity of the
wires 90 and 96, the only significant resistance heating occurs in
the high resistance wire portion 94 adjacent the tip 89. The
temperature sensing of the probe 86 is accomplished by utilizing
the Seebeck effect between the wires 90 and 96. The wire 96 also
can be eliminated and the voltage then can be applied across the
wire 90 and the sheath body 88.
[0090] A third sheath type thermocouple probe embodiment is
designated generally by the numeral 98 in FIG. 8. The probe 98 also
has a low resistance sheath body 100, however, the probe 98 has a
tip 102 formed from a high electrical resistance material. A pair
of low resistance calibration wires 104 and 106 are grounded to the
tip 102. The tip 102 is locally heated by applying a relatively
high voltage across the wires 104 and 106 which are of high
conductivity causing the only significant resistance heating to
occur in the tip 102. Temperature sensing is again accomplished by
utilizing the Seebeck effect between the wires 104 and 106.
Alternatively the voltage can be applied across the sheath body 100
and one of the calibration wires, which eliminate the need for the
other calibration wire to be formed of a low resistance wire.
[0091] Another sheath type probe embodiment 108 is illustrated in
FIG. 9. The probe 108 includes a sheath body 110 having a tip 112.
A pair of relatively low resistance wires 114 and 116 are connected
adjacent the tip 112 by a portion of high resistance wire 118. The
tip 112 is locally heated by applying a relatively high voltage
pulse across the pair of wires 114 and 116 which resistance heats
the portion 118 to in turn heat the tip 112. Temperature sensing of
the probe 108 again is accomplished by utilizing the Seebeck effect
between the pair of wires 114 and 116.
[0092] A fifth embodiment of a sheath type thermocouple probe 120
is illustrated in FIG. 10. The probe 120 includes a sheath body 122
having a tip 124. A low electrical resistance wire 126 is grounded
to the tip 124. To accomplish local heating of the tip 124, either
the tip 124 can be a high resistance material such as the tip 102
(FIG. 8) or the wire 126 can include a high resistance portion at
the tip such as the wire portion 94 (FIG. 7). A pair of calibration
wires 128 and 130 are utilized for temperature sensing by utilizing
the Seebeck effect between the wires 128 and 130.
[0093] Alternatively, four or more multi-wire configurations also
can be utilized. For example, two wires can be utilized for
providing the power pulse and two separate calibration wires can be
utilized for the Seebeck effect temperature sensing. Another
alternative is leaving the calibration wires 128 and 130 ungrounded
in a similar fashion to a conventional ungrounded thermocouple.
[0094] A flow diagram of the operation of the flow measuring device
10 is illustrated in FIG. 11. The thermocouple (t/c) 12 is first
pulsed as indicated by a block 146 such, as over time period
t.sub.0-t.sub.- in FIG. 2. The temperature is then measured, as
indicated by a block 148, at least twice, such as at times t.sub.1,
t.sub.2, etc. in FIG. 2, as the junction temperature decays. The
slope of the decay curve is then calculated as indicated by a block
150, in accordance with Equation 8. The fluid velocity then is
determined from the slope, as indicated by a block 152 in
accordance with Equation 11.
[0095] The velocity determined from each power pulse set of
measurements then can be displayed as indicated by a block 154.
Alternatively or in addition, the velocity determined by a power
pulse can be stored and averaged with succeeding pulse
measurements, as indicated by a block 156. Each velocity value can
be displayed, and the average also can be displayed, or only the
average velocity need be displayed. The average can be a running
average or can be for a fixed time period. After each velocity is
determined, the sequence again can be repeated as indicated by a
line 158.
[0096] Modifications and variations are possible in light of the
above teachings. The heating of the probes can be effected as
described by electrical resistance heating (Joule heating). The
heating or cooling of the probes relative the fluid also can be
effected by Peltier heating or cooling. The sheath type probes can
include a conventional potting material if desired. The calibration
wires generally are formed from thermocouple alloys. The addition
in some probe embodiments of a separate wire portion or the probe
tip between the calibration wires, does not affect the measurement
as long as the junctions are maintained substantially at the same
temperature. It is therefore to be understood that thermal
anemometers useful in preferred embodiments include those that are
otherwise than as specifically described.
[0097] Alternate embodiments of the flow meters comprise rotatable
members. Such liquid flow meters can comprise an impeller or
turbine mounted in the liquid flow path and the inlet end of the
support tube, wherein the number of rotations of the impeller or
turbine provide a measure of the liquid flow volume therethrough.
The liquid flow meters may provide an electrical circuit for
detecting the rotation of movement of the impeller or turbine,
wherein it is typical to connect a magnetic element to the
rotatable shaft and to provide a coil or inductive pickup circuit
in proximity to the magnet, wherein the rotating magnet generates
varying magnetic fields to influence the circuitry coupled to the
pickup, and to thereby generate electrical signals representative
of shaft rotation. The electrical signals are subsequently
amplified and converted to drive signals for energizing some form
of indicating device, such as an RFID tag.
[0098] One embodiment comprises a liquid flow meter, wherein a
magnet is affixed to the rotatable impeller shaft. A magnetic field
sensor, in the form of a ferromagneto resistive circuit, is placed
in physical proximity to the rotatable magnet, and the magnetic
field induces an electrical signal in the sensor, which signal is
amplified and shaped to drive a suitable logic network, the logic
network serving to both count the sensed signals and to calculate a
corresponding flow volume indication.
[0099] Another embodiment of the flow meter utilizes magnets. For
example, a first magnet is affixed to the rotatable impeller shaft,
and a second magnet is placed in proximity to the first magnet, but
outside of the liquid flow chamber. Rotation of the second magnet
is induced by the rotating field of the first magnet, and the
rotating field generated by the second magnet is detected by an
inductive sensor to generate an electrical signal representative of
the shaft rotation. The electrical signal is then utilized to drive
an indicator circuit to provide a readout of the volume flow
detected by the device.
[0100] Another embodiment comprises a flow meter utilizing
shaft-mounted magnets. For example, a meter has a first magnet
attached to a rotor shaft and a second magnet attached to an
indicator shaft, the second magnet being rotatably and magnetically
coupled to the first magnet, so as to provide corresponding
rotation of the indicator shaft when the rotor shaft is rotated by
the flow of fluid through the meter housing.
[0101] Another embodiment comprises a liquid flow meter of the
rotating turbine or impeller type, wherein liquid flow through the
meter results in positive rotatable displacement of a shaft made
from a nonmagnetic material. A permanent magnet is embedded
proximate one end of the shaft, and the impeller end shaft is
rotatably mounted in a housing made from nonmagnetic materials. A
magnetically-operated reed switch is positioned outside the housing
proximate the shaft end embedding the permanent magnet, and each
complete revolution of the shaft causes two magnetically-induced
closures of the reed switch. The reed switch is electrically
coupled to a battery-operated logic circuit, including counters and
an electronic readout, so that switch closures of the reed switch
are converted into flow volume data provided to an RFID tag, for
example.
[0102] The internal design of the rotatable impeller and flow meter
cavity are controlled to provide predetermined volumetric
displacement characteristics, wherein each revolution of the
impeller is matched to the logic circuit so as to provide a
predetermined fractional relationship between the liquid flow
volume passed during a single revolution of the shaft and the unit
of measure in which the logic circuit and display are adapted to
count and display units. The unit of measurement may therefore be
modified by merely changing one linear dimension of the rotatable
turbine or impeller.
Permeate Conductivity Measurement
[0103] Preferred embodiments also comprise measuring devices which
monitor the electrical properties of the permeate stream. The
operation of devices that measure water conductivity are preferably
based on a measurement of the water resistivity between two
electrodes. A resistivity measuring sensor can preferably be
mounted at the some position as the flow measuring device. As
described above, the permeate flow is measured using a thermal
anemometer.
[0104] Preferred embodiments of a permeate conductivity measuring
device comprise measuring devices which monitor the electrical
properties of a liquid. The operation of devices that measure water
conductivity are preferably based on measurement of liquid
resistivity between two electrodes. A device that measures current
flow between at least two electrodes can preferably be located on
or within in a core tube of a reverse osmosis filter device and/or
system. Examples of such devices are disclosed in U.S. Pat. Nos.
3,867,688, and 4,132,944, which are hereby incorporated in their
entirety by reference. Electric energy required to power such
devices can be supplied by radio frequency radiation, a
rechargeable battery, power transferred from an RFID tag,
electromagnetic energy, or other forms of energy known to those
skilled in the art.
[0105] The permeate conductivity measuring device of the preferred
embodiments consists of a conductivity cell which has an integrally
mounted thermocouple. As shown in FIG. 13, the electrodes of the
conductivity measuring device 170 are installed within open shield
171 of the measuring device. When the conductivity cell is
connected across an a.c. sine wave excitation source, the resulting
current is proportional to the cell admittance. This current is
resolved into two orthogonal components: a charging current which
leads the excitation voltage by 90.degree. and is proportional to
the dielectric constant (k) of the liquid between the electrodes of
the conductivity cell, and an ohmic current which is in phase with
the excitation voltage and is proportional to the reciprocal of the
resistance, or conductance, of the liquid.
[0106] Temperature compensation for the real component of the
admittance (conductance) can be based on the Arrhenius absolute
rate model. Accordingly, conductance is preferably a function of
the thermal energy (RT), and the activation energy
.DELTA.E.sup..noteq. which separates equilibrium positions of the
conducting species. The conductance G at a process temperature T
may be corrected to a conductance G.sub.o at the reference
temperature T.sub.o by the equation:
G.sub.o=G10.sup.b(T.sub.o-T) (12)
or,
Log G.sub.o=log G+b(T.sub.o-T)
[0107] where:
[0108] b=.DELTA.E.sup..noteq./[2.303 R T.sub.ok.sup.2], in
which
[0109] .DELTA.E.sup..noteq.=activation energy in calories/mole
[0110] R=the gas constant in calories/(mole .degree. K.), and
[0111] T.sub.ok=T.sub.o in degrees Kelvin
[0112] The thermocouple embedded in the permeate conductivity
measuring device produces a signal proportional to the process
liquid temperature T, while constant signals analogous to the
reference temperature T.sub.o and to b are generated by appropriate
circuitry. These analog signals proportional to T, T.sub.o and b,
are combined to form a signal representing the expression
b(T.sub.o-T). The log G function is generated from the signal
representative of the conductance G, added to the signal
representing b (T.sub.o-T), and sent to an antilog amplifier, whose
output signal is representative of the desired conductance value
G.sub.o of the liquid.
[0113] The imaginary component of the admittance when divided by
the excitation frequency in radians per second is the capacitance C
of the liquid at the processing temperature T. Based on the simple
volume expansion for the liquid and the Debye model for dilute
solutions of polar molecules, the temperature dependence of the
dielectric constant k of the liquid takes the form
k=k.sub.o-.alpha.(T-T.sub.o), (13)
as reported in the National Bureau of Standards circular 514. In
terms of measured capacitance,
C.sub.o=C-aC(T.sub.o-T), (14)
where C.sub.o is the capacitance of the liquid at the reference
temperature T.sub.o, K.sub.o is the dielectric constant of the
liquid at the reference temperature T.sub.o, .alpha. is the volume
expansion coefficient, and a=.alpha./K.sub.o.
[0114] This equation assumes that the capacitance C'.sub.o of the
cell in air at the reference temperature T.sub.o is approximately
equal to the capacitance C of the liquid at the measured process
temperature T divided by the dielectric constant k of the liquid at
the process temperature T. This assumption was made to allow the
use of different conductivity cells having different C'.sub.o
values, without changing any of the circuit values, and is accurate
so long as the dielectric constant variation with temperature is no
more than plus or minus ten percent, which is the case for water at
the temperatures and pressures normally found in RO filtration
systems.
[0115] A signal proportional to a(T.sub.o-T) is generated by the
same method used to form the b(T.sub.o-T) term in the conductance
compensation circuit. The signal proportional to the capacitance C
of the liquid and the signal proportional to a(T.sub.o-T) are
supplied to an analog multiplier which generates a signal
proportional to the product of these two signals, aC(T.sub.o-T).
This product signal is then electrically subtracted from the
capacitance signal C to produce a signal proportional to the
capacitance C.sub.o of the liquid at the reference temperature
T.sub.o.
[0116] For example, in one preferred embodiment of a permeate
conductivity measuring device, as shown in FIG. 15, a quadrature
oscillator 217 generates a 1000 Hz sine wave voltage, which is
amplified by an amplifier 218 and applied to a conductivity cell
219 of a liquid sensor probe immersed in the liquid being processed
through shielded lines. The current flowing through the
conductivity cell 219 is converted into a proportional voltage by a
current transducer 222, and amplified by a narrow band amplifier
223. This amplified voltage signal is then divided into two signals
of opposite polarity by the phase splitter 224, which are supplied
to respective circuits of a first multiplier 225 and a second
multiplier 226.
[0117] In the first multiplier 225, the phase splitter output
signals are preferably multiplied by a square wave voltage signal
generated by the quadrature oscillator 217 which is in phase with
the voltage applied across the conductivity cell 219, to produce an
output signal proportional to the real component of the current
flowing through the conductivity cell 219, and thus proportional to
the conductance G of the liquid.
[0118] In the second multiplier 226, the phase splitter signals are
preferably multiplied by a second square wave voltage signal,
generated by the quadrature oscillator 217, which is 90.degree.
out-of-phase with the voltage applied across the conductivity cell
219, to produce an output signal proportional to the imaginary
component of the current flowing through liquid in the conductivity
cell 219, and thus proportional to the capacitance C of the liquid
at its processing temperature T.
[0119] The liquid sensor probe also preferably includes a
thermocouple 228 embedded in it, which produces a signal
proportional to the temperature of the liquid at the probe. This
temperature signal is amplified, and made linear with temperature
in an amplifier and compensation circuit 230.
[0120] In preferred embodiments, this compensated temperature
signal is directly proportional to the liquid process temperature
T, and is utilized in the temperature compensation circuit of FIG.
16, together with a signal proportional to the reference
temperature T.sub.o, to convert the signals proportional to the
conductance G and the capacitance C of the liquid at the measured
temperature T to respective signals proportional to the conductance
G.sub.o and the capacitance C.sub.o of the liquid at the reference
temperature T.sub.o In most applications of this monitoring
apparatus, the reference temperature T.sub.o is selected to be
about the average temperature of the liquid during the processing
operation, so that temperature compensation is only made over the
range from the highest to the lowest temperature of the liquid
during the processing operation.
[0121] In FIG. 16, an amplifier is preferably used to produce a
signal proportional to the reference temperature T.sub.o, from
which the signal proportional to the process liquid temperature T
can be electrically subtracted. An input of the amplifier 232 is
connected to a positive voltage source through the reference
voltage resistor 234, and a feedback resistor 236 is connected
between the input and the output of the amplifier and is directly
proportional to the reference temperature T.sub.o, the value of the
reference temperature resistor 234 is inversely proportional to the
reference temperature T.sub.o, and can be a variable resistor, to
allow selection of the reference temperature T.sub.o. Also, since
the output signal from the amplifier 232 must be equal to the
output temperature signal from the thermocouple amplifier at the
selected temperature T.sub.o, the value of the feedback resistor
236 is determined by the signal characteristics of the thermocouple
amplifier 230. Assuming the voltage output signal of the
thermocouple amplifier 230 is 10 volts at 500.degree. C., and
varies with the temperature T at a rate of 0.02 volts per degree
C., the output voltage signal of the reference temperature
amplifier 232 is preferably proportional to 0.02 (-T.sub.o) volts.
Thus, if the positive voltage source is 15 volts, and the value of
the temperature resistance 234 is selected to equal
1/T.sub.o.times.10.sup.7 ohms, the value of the feedback resistor
236 is preferably approximately 13,300 ohms (13.3 K) to produce an
output signal of 0.02 (-T.sub.o) volts.
[0122] This 0.02 (-T.sub.o) voltage signal is preferably supplied
to an input of a summing amplifier 238 through a 10K resistor, and
the 0.02 (T) voltage signal from the thermocouple amplifier 230 is
also supplied to the same input of the amplifier through another
10K resistor 242. A 100K feedback resistor 244 is connected between
the input and the output of the amplifier 238, to produce an output
temperature compensation signal of 0.2 (T.sub.o-T) volts, which is
supplied to both the conductance and capacitance compensation
circuits. When the measured liquid temperature T is equal to the
reference temperature T.sub.o, there will be no temperature
compensation signal.
[0123] This 0.2 (T.sub.o-T) temperature compensation signal is
preferably supplied to an input of the amplifier 246 through a
conductance compensation resistor 248, having a value of
1/b.times.10.sup.2 ohms, which may be a variable resistor to allow
this apparatus to be used with different liquids having different
"b" values. A 10K feedback resistor 250 is preferably connected
between its input and output. The output of the amplifier 246,
representing 20b(T.sub.o-T), is supplied to an input of the summing
amplifier 252 through a 200K scaling resistor 254.
[0124] The output signal from the first multiplier 225, which is
proportional to the liquid conductance G, is preferably supplied to
the input of a log amplifier 258 through a resistor 260. Assuming
that the maximum value of this conductance signal is +5 volts full
scale, the resistor 260 can be selected to have an ohmic value of
50K, to thus allow a maximum input current of 100 .mu.A to the log
amplifier 258, and the log amplifier 258 may be selected to have a
transfer function of .mu. log (Amperes input current/100 .mu.A), so
that the voltage output of the log amplifier 258 will preferably be
-log G volts.
[0125] In preferred embodiments, this -log G signal is also
supplied to the input of the summing amplifier 252 through a 10K
resistor 255, to produce an output signal of log G+b (T.sub.o-T)
volts or log G.sub.o volts, since, as discussed earlier, log
G.sub.o=log G+b (T.sub.o-T). This log G.sub.o voltage signal is
preferably supplied to an input of an amplifier 256 through a 10K
resistor 259, and a 10K feedback resistor 260 is connected between
this input and the output of the amplifier 256, to invert the input
signal and produce an output signal from the amplifier 256 of -log
G.sub.o volts. This -log G.sub.o signal is then supplied to the
input of antilog amplifier 262 having a transfer function of
10.times.10.sup.-x, where x is the input signal, to produce an
output signal of 0 to 10 volts that is directly proportional to the
conductance G.sub.o of the liquid.
[0126] In this permeate conductivity measuring device, the maximum
value of the capacitance signal from the second multiplier 226 is
-5 volts, and since a full scale positive output of 10 volts
proportional to the capacitance C.sub.o of the liquid is desired,
the input signal from the second multiplier 226 is shown as -C/2
volts.
[0127] The 0.2 (T.sub.o-T) volt temperature compensation signal
from the amplifier 238 is also supplied to an input of another
amplifier 264 through a capacitance compensation resistor 266,
having an ohmic value of 1/a.times.10.sup.2. This capacitance
compensation resistor 266 can be a variable resistor, which can be
adjusted for use with different liquids having different "a"
values. A 5K amplifier feedback resistor 268 is preferably
connected between the input and the output of the other amplifier
264, to produce an output signal of that amplifier of -10 [a
(T.sub.o-T)] volts, which is supplied to a first input of an analog
multiplier 270. The -C/2 volt signal from the second multiplier 226
is supplied to a second input of the analog multiplier 270. The
analog multiplier 270 has a transfer function of one-tenth of the
product of the two input signals, to produce an output signal of a
(T.sub.o-T) C/2 volts. This output signal of the analog multiplier
is supplied to an input of a summing amplifier 272 through a 10K
resistor 274. The -C/2 volt signal from the second multiplier 226
is also supplied to the same input of the amplifier 272 through a
10K resistor 276. A 20K feedback resistor 278 is preferably
connected between the input and the output of the amplifier, to
produce an output voltage signal proportional to C-aC(T.sub.o-T),
or to the capacitance C.sub.o of the liquid, since, as discussed
earlier, C.sub.o=C-aC(T.sub.o-T).
[0128] In a preferred embodiment of a permeate conductivity
measuring device, a relatively high frequency of 1000 Hz is
selected for the voltage applied across the electrodes of the
conductivity cell to reduce the effects of charge transfer kinetics
(Faradaic impedance) and electrode polarization, and to enhance the
capacitive coupling of the electrodes with the liquid (double layer
capacitance). Also, the operational amplifiers and other electronic
components used in this embodiment are readily available
commercially at this operating frequency. However, the present
disclosure is not limited to devices employing this frequency, any
frequency within an approximate range of 100 Hz to 10.sup.7 Hz may
be used. Also, the nominal operating temperature range, maximum
deviation of the process temperature T from the reference
temperature T.sub.o, and the maximum absolute signal correction is
preferably determined by the choice of circuit components.
[0129] In another embodiment of a permeate conductivity measuring
device, conductance is measured by an electrodeless device. In such
a device, noncontact measurement of the conductance of the liquid
is obtained by charging a capacitor in series with the primary
winding of a first transformer ring core. The capacitor is
periodically discharged so that across the primary winding, a
damped oscillatory signal is produced as a result of the capacitor,
the inductance of the winding, and inherent resistivity. A loop
including for at least a portion of its path the liquid acts as a
one-turn secondary winding for the first ring core and as a
one-turn primary winding for a second transformer ring core. At the
instant the discharge is initiated, a constant voltage appears
across by loop regardless of the resistance of the loop so that by
measuring the peak current in a secondary winding of the second
core, which will appear at the initiation of discharge and which
corresponds to the current in the loop at the initiation of the
discharge, the conductance of the liquid can be determined using
Ohm's law.
[0130] It should be appreciated that the conductivity measurement
described above is not limited to an assessment of the salinity of
the liquid passing through the RO filtration device, but may as
easily be applied by those of skill in the art to the measurement
of total dissolved solids (TDS).
[0131] Additionally, it is not absolutely necessary that the
conductance of the liquid be obtained in order to measure salinity
or TDS; other means known in the art, such as the density method,
or the refractance method, may be employed.
Permeate Flow and Permeate Conductivity Measuring Device
[0132] The system of this disclosure may be employed in the
pressure vessel shown in FIG. 12. The pressure vessel is a
cylindrical pipe 161 with number of membrane elements 163 inside.
The elements are connected to the end plates using adaptors 162 and
to each other through interconnectors 164. The pressure vessel has
feed and concentrate ports 165 & 166. Permeate leaves the
pressure vessel through permeate ports 167. One permeate port is
closed with a cap 168. The pressure vessel could be a part of a
pressure vessel assembly (RO train), which may contain a large
number of pressure vessels connected in parallel. As shown in FIG.
12, membrane elements are enclosed in a pressure vessel, which
operates under a pressure of 100-1200 psi. During operation of the
RO train the membrane elements are not accessible. Therefore, any
complete measurement of element performance has to be conducted by
stopping the RO train, removing elements from the pressure vessel
and testing them individually in a separate test unit. During
operation it is possible to measure the conductivity of the
combined permeate from the pressure vessel. It is also possible to
measure composite conductivity along the pressure vessel by
inserting a small-diameter probing tube through cap 168. Samples of
permeate collected at the other end of the probing tube correspond
to specific locations in the pressure vessel. However, conductivity
results alone are not sufficient to calculate element performance.
To calculate element performance, the values of permeate flow along
the pressure vessel are required as well. The results of a
measurement of permeate flow, permeate conductivity and data of
feed pressure, concentrate pressure, feed salinity and temperature
enable the calculation of normalized element performance. There has
been up to now no convenient way to measure permeate flow of
individual membrane elements while they are in operation in an RO
unit.
[0133] In an embodiment, an integrated sensor, shown in FIG. 13,
comprises a thermal anemometer probe 169 and conductivity probe 170
mounted on a small diameter pipe and protected by an open flow
shield 171. As shown in FIG. 14, to conduct measurement, the
integrated probe mounted on the supporting small diameter tube 173
is inserted through a small opening in plug 168 into a permeate
tube 172. The sensor is connected via wiring to at least one
recording device 174. In a preferred embodiment, the recording
device is an RFID tag attached to the individual reverse osmosis
membrane element in which the inlet side of the probing tube is
located. Alternatively, the sensor can generate a signal and send
it wirelessly to the recording device. The opening in the plug 168
is normally closed with a small diameter ball valve. Permeate
leaves the pressure vessel through the permeate port on the other
end of the pressure vessel, which is connected to the permeate
manifold. This arrangement enables inserting the probe through the
opening of the valve during plant operation while assuring a
minimal amount of permeate water leaking outside during the flow
and conductivity measurement process. The supporting tubing, with
the sensors mounted thereon, is progressively moved inside the
connected permeate tubes of the adjacent elements, and permeate
flow and conductivity readings are recorded and can be related to
specific positions inside the length of the pressure vessel. This
may be accomplished in a variety of ways known in the art. For
example, the sensors may transmit data to the closest RFID tag,
which would be the tag associated with the element in which the
inlet side of the probe then resided. Alternatively,
electromagnetic radiation generated by a recording device located
on a track outside the pressure vessel could be used to serially
activate the RFID tags of the individual elements, which would then
receive data from the sensors as the probe passed through each
element. Such communication would enable the measured values to be
linked directly to the individual element in which the sensors were
located, which would facilitate the determination of the
performance of the individual elements. Alternatively, the measured
values could be linked to the individual elements by measuring the
length to which the support tubing was inserted into a pressure
vessel.
[0134] The permeate flowing inside the connected permeate tubes of
membrane elements in the pressure vessel has an aggregate rate of
permeate flow and permeate conductivity. By taking measurements
along the length of connected permeate tubes, it is possible to
calculate the contribution of the permeate to the combined flow and
conductivity at a given point. The measured values, combined with
historical data of the past performance of an element, is important
in determining the current condition of the elements in the system.
It also provides information required for the selection of elements
that have to be replaced to improve system performance.
[0135] Because conductivity of the permeate corresponding to
specific locations in the pressure vessel may be measured at the
outlet end of the probing tube, it is not necessary that
conductivity be measured at the inlet end of the probing tube. In
an embodiment, the probing tube comprises only a mechanism for
measuring permeate flow at the inlet end, while permeate
conductivity is measured at the outlet end.
[0136] Although all possible embodiments are not listed, the
present disclosure encompasses different embodiments that
incorporate various changes, corrections and modifications based on
the knowledge of those skilled in the art. It should be clearly
understood that the forms of the present disclosure are
illustrative only and not intended to limit the scope thereof.
Modifications to these embodiments are also included in the scope
of the present disclosure, as long as they do not deviate from the
spirit of the disclosure.
* * * * *