U.S. patent application number 09/947469 was filed with the patent office on 2002-01-17 for method of treating water in a water system.
This patent application is currently assigned to KURITA WATER INDUSTRIES LTD.. Invention is credited to Iseri, Hajime, Takahashi, Kuniyuki, Yoneda, Yutaka.
Application Number | 20020005384 09/947469 |
Document ID | / |
Family ID | 18559727 |
Filed Date | 2002-01-17 |
United States Patent
Application |
20020005384 |
Kind Code |
A1 |
Iseri, Hajime ; et
al. |
January 17, 2002 |
Method of treating water in a water system
Abstract
According to the method of treating water in a cooling water
system, adhesion of fouling is on-line monitored by a compact and
inexpensive apparatus and a slime control treatment is intensified
according to the result of on-line monitoring. The water treatment
is intensified in response to the change of electric potential of a
sensor monitoring microbial fouling 11 made of sensitized metallic
material. When the electric potential of the sensor exceeds a
threshold value, an agent is added through both chemical feeding
pumps 15 and 17. When the electric potential lowers to the normal
value, the agent is added only through the pump 15.
Inventors: |
Iseri, Hajime; (Tokyo,
JP) ; Yoneda, Yutaka; (Tokyo, JP) ; Takahashi,
Kuniyuki; (Tokyo, JP) |
Correspondence
Address: |
KANESAKA AND TAKEUCHI
1423 Powhatan Street
Alexandria
VA
22314
US
|
Assignee: |
KURITA WATER INDUSTRIES
LTD.
|
Family ID: |
18559727 |
Appl. No.: |
09/947469 |
Filed: |
September 7, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09947469 |
Sep 7, 2001 |
|
|
|
PCT/JP00/08476 |
Nov 30, 2000 |
|
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Current U.S.
Class: |
210/660 |
Current CPC
Class: |
C02F 1/50 20130101; G01N
17/008 20130101; C02F 2209/04 20130101; C02F 1/008 20130101; G01N
33/1866 20130101; C02F 2103/023 20130101 |
Class at
Publication: |
210/660 |
International
Class: |
B01D 015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 14, 2000 |
JP |
2000-35544 |
Claims
What is claimed is:
1. A method of treating water in a water system including steps of
monitoring the water system by a sensor and treating the water
based on the result of monitoring, wherein said sensor includes
metallic material sensitized and monitors microbial fouling adhered
thereon, and the water is treated according to the change of
electric potential of the sensor.
2. A method as claimed in claim 1, wherein the metallic material
has at least one welded spot and at least one crevice.
3. A method as claimed in claim 1 or 2, wherein the water is
treated by adding at least one agent into the water system.
4. A method as claimed in claim 3, wherein the agent includes at
least one slime control chemical.
5. A method as claimed in claim 1 or 2, wherein the water is
treated by an apparatus for eliminating microbial fouling.
6. A method as claimed in claim 5, wherein said apparatus generates
at least one chemical for sterilizing microbes.
7. A method as claimed in any one of claims 1 through 6, wherein
the temperature in the water system is in a range of 5-50.degree.
C.
8. A method as claimed in any one of claims 1 through 6, wherein
the surface of said sensor contacting the water is heated by a
heater to the temperature higher than that of the water system.
9. A method as claimed in claim 8, wherein the surface of the
sensor contacting the water is heated to 5-50.degree. C. by said
heater.
10. A method as claimed in claim 3 or 4, wherein the additive
amount of the slime control agent is increased when the electric
potential of the sensor exceeds a predetermined value.
11. A method as claimed in claim 3 or 4, wherein another slime
control agent different in kind from the ordinary one is added into
the water system when the electric potential of the sensor exceeds
a predetermined value.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This is a continuation application of PCT/JP00/08476 filed
on Nov. 30, 2000.
FIELD OF THE INVENTION
[0002] The present invention relates to a method of treating water
in a water cooling system, pulp manufacturing process, and so on,
in which microbial fouling on a metal pipe and the like contacting
water is monitored and an appropriate water treatment is carried
out based on the result of monitoring. More particularly, the
present invention relates to a water treatment system in which
microbial fouling on a metal pipe and the like is predicted early
and precisely by monitoring change of corrosion potential of a
sensor having a sensitized metal and contacting the water, and thus
an appropriate water treatment is carried out based on the
prediction.
BACKGROUND OF THE INVENTION
[0003] Some problems of a water system are associated with slime.
Slime which is formed by microbes in water causes decreasing a heat
transfer efficiency of a heat exchanger, clogging of pipes, and
corrosion of pipes and the like. To prevent such problems, various
slime control treatments are done; for example, a microbicide is
added into the water system. Moreover, according to an amount of
slime adhered on the pipes, a slime removing agent is added into
the water to eliminate slime adhered on pipes and the like ("Manual
for Protecting Pipes from Corrosion", edited by Kajima Construction
Co., Ltd. and Kurita Water Industries Ltd., and published by Nippon
Kogyo Publishing Company in 1987).
[0004] According to a conventional method of monitoring microbial
fouling in a water system, a rubber plate is immersed in water of a
water system, and the rubber plate is measured periodically on an
amount of a fouling component adhered to the rubber plate. Another
method is disclosed in NACE Standard RPO189-89, "Standard
Recommended Practice On-line Monitoring of Cooling waters", NACE
International, Houston, 1996, in which microbial fouling is
detected by a change of pressure difference in a tube.
[0005] In natural seawater, stainless steel becomes to have an
extremely high corrosion potential when microbes adhere thereto (R.
Johnsen, Corrosion, 41:296, 1985). The same phenomenon occurs in a
cooling water system (Hirano et. al: 38th corrosion-corrosion
prevention debate, 1991).
[0006] Japanese patent publication H6-201637A and Japanese Patent
2794772 disclose methods of monitoring microbial fouling by
measuring a natural electrode potential. Japanese patent
publication H10-142219A and Japanese patent publication 2000-9674A
disclose a method of controlling addition of an agent based on
measured results of a corrosion potential.
[0007] In a conventional slime control treatment, an appropriate
slime control agent is selected for a water system and an amount of
the agent to be added is predetermined or controlled so that the
concentration of the agent in the water system would be in a
predetermined range. Lately, a slime control treatment has been
carried out with using a controlling apparatus to meet the
requirements of ecology, safety handling, better workability, and
so on. However, because of various external factors such as the
deterioration of water quality, a sufficient treatment may not be
accomplished by adding usual amounts of agents or by controlling
concentrations of agents in the water system. Then, microbial
fouling adhere to the system and cause various problems.
[0008] In order to prevent such problems, more amount of a slime
controlling agent may be added according to a fouling level of a
water system which is measured by monitoring adhesion of
contaminants. It is desirable to monitor the adhesion of fouling
all the time and to add more amount of slime controlling agent soon
after the adhesion of fouling is detected. However, at the present
time, the slime controlling agent is increased in its additive
amount manually based on the fouling level monitored from time to
time.
[0009] It is desirable to control the addition of agents
automatically based on the result of on-line monitoring. However,
the aforementioned method using a rubber plate can not be an
on-line monitoring method.
[0010] The other aforementioned method measuring differential
pressure of a tube can be an on-line monitoring method. However, a
fouling level measured as a change of the differential pressure is
considerably affected by the way of adhesion of fouling elements to
a tube, that is, whether the fouling elements adhere to the tube
evenly or unevenly. Furthermore, there is an disadvantage to
install a monitor of this type in each cooling water system. In
addition, expensive parts such as a differential pressure gauge
must be equipped and a monitoring apparatus needs a large space to
be installed because the tube needs enough length for measuring
differential pressure. Since a differential pressure should be
measured under a condition of a constant flow velocity of cooling
water in a tube, the water flow in the tube is adjusted by a
constant flow valve or the like. An obtained value of differential
pressure is often affected by a small change in the flow velocity
caused by fouling in the valve.
[0011] The surface of a plate sensor used in a conventional method
of monitoring the corrosion potential is so smooth that its
sensitivity is not good enough.
[0012] As mentioned above, there are a lot of problems in each
conventional method in which the addition of agents or the
operation of an apparatus is controlled based on the monitoring
result of microbial fouling.
[0013] When a slime control treatment is not accomplished
sufficiently and a large quantity of slime adheres to a water
system, the slime should be removed off. However, when the water
system is not monitored all the time, the fouling level in the
system is unclear and the slime is retained in the water system for
a long time.
[0014] When slime is removed from the water system by adding a
removing agent automatically at regular intervals controlled by a
timer, the water system is saved from fouling. However, in this
case, the removing agent may be added even if there is no fouling.
That is a waste of the agent. A necessary treatment should be done
at a necessary time to reduce treatment cost and to meet the
ecological requirements.
SUMMARY OF THE INVENTION
[0015] It is an object of the present invention to provide a method
of water treatment in which microbial fouling onto metallic pipes
and the like is detected early and precisely and an appropriate
water treatment is carried out according to the detection.
[0016] A method of water treatment in a water system of the present
invention employs at least one sensor having a sensitized metal
piece for monitoring microbial fouling, and the water is treated
according to a change of electric potential of the metallic
sensor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 shows sensitivities to microbial fouling of test
pieces in Example 1.
[0018] FIG. 2 is a schematic diagram of a cooling water system used
in Example 2.
[0019] FIG. 3 shows the change of corrosion potential with the
passage of time when the method in Example 2 is carried out.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] A monitoring sensor for detecting fouling caused by microbes
is made of sensitized metallic material. The metal may be
sensitized by annealing it in an electric furnace, but it can be
sensitized by another method. The sensitized metal may be a
metallic piece having at least one welded spot and at least one
crevice. Such a metallic piece with a crevice can detect the
microbial fouling with a very high sensitivity.
[0021] The metal to be sensitized may be stainless steel or nickel
alloy, but is not limitative thereto.
[0022] A metallic piece with a crevice for a sensor may be prepared
by overlapping two plates of the same kind of metal each other and
welding them so as to make at least one welded spot and at least
one crevice. The metal pieces may have any shape.
[0023] The plates may be welded by spot welding, but not limitative
thereto. It is recommended to use a metallic piece having no
expulsion in welding. Two metallic pieces are preferably welded at
1 to 3 spots.
[0024] The welded plates with a crevice may have a surface area
excluding welded area larger than a welded area. It makes no
difference if post weld treatments (stress relief and so on) are
done around a welded area or not. An opening width of an air gap
between two welded metallic plates is preferably one tenth of an
opening depth or smaller.
[0025] Coated wire may be connected to the sensitized metallic
plate of the sensor and an electric potential is measured via this
coated wire. The metallic plate may be connected with the coated
wire through a solderless terminal which is attached to the coated
wire and screwed on the metallic plate. Instead thereof, the
metallic plates may be connected with the coated wire by soldering
or the like.
[0026] When the water temperature in a water system is in a range
that microbes can grow, the metallic material of the sensor does
not need to be heated. When the water temperature in the water
system is too low for the growth of microbes, a heating plate may
be attached to the metallic plate of the sensor in order to
stimulate the growth of microbes on the surface of the sensor. The
temperature of the surface of the sensor contacting the water is
preferably in a range of 5-50.degree. C., more preferably in a
range of 10-40.degree. C.
[0027] When the metallic plate of the sensor has the crevice
described above, the heating plate is preferably attached to the
exterior surface of the larger metallic plate of two. When the area
of the two metallic plates are equal, the heating plate can be
attached to either one.
[0028] The surface of the heating plate may be coated with
insulating resin or the like to electrically insulate the heating
plate from the metallic material of the sensor.
[0029] When the heating plate heats the metallic plate of the
sensor in water, heating surface of the plate has preferably a
temperature in a range where microbes can grow, preferably in a
range of 10-50.degree. C. In order to keep the temperature in the
above range, the heating plate is preferably equipped with a
thermostat such as a liquid expansion thermostat, a bimetal
thermostat, a temperature controlling system using a thermocouple
temperature sensor, and the like. The heating plate may be composed
of an electric resistance composition having a positive temperature
coefficient (PTC), that is, a property of having a drastic change
in electric resistance responding to a change in temperature. When
the sensor is provided with the heating plate composed of the
composition having the positive temperature coefficient (PTC); an
exterior temperature sensor is not necessary, the amount of
electric power consumption is small, and it is not overheated even
in a failure.
[0030] The size and shape of the heating plate are determined
according to those of the surface of the metallic plate to which
the heating plate is attached.
[0031] The heating plate can be attached to the metallic plate with
an adhesive, a double-sided tape, or the like. The adhesive should
not be degraded by heat from the heating plate.
[0032] It is preferable that the sensitized metallic plate of the
sensor is in contact with water only at a part thereof for
monitoring, and that other part of the metallic plate is not in
contact directly with water. Accordingly, the other part of the
metallic plate is preferably coated with insulating resin such as
silicone resin at its entire surface except for the area for
monitoring the potential.
[0033] The electric potential of the sensor having the sensitized
metallic plate rises when microbial fouling adheres thereto in a
water system. This phenomenon is also observed in a metallic plate
which is made of the same kind of metallic material but not
sensitized. However, the unsensitized plate has much lower
sensitivity for fouling than that of the sensitized plate.
Particularly, sensitized metallic plates having the welded spot(s)
and the crevice is extremely sensitive to the fouling and detects
microbial fouling with a very high sensitivity so as to make it
possible to perform an appropriate slime control treatment.
[0034] When the sensor is in contact with water in a water system
which is treated properly by a slime controlling treatment, an
electric potential of the sensor is almost constant. When the slime
controlling treatment is not appropriate, the electric potential of
the sensor tends to rise. When a tendency of rising potential is
detected, the slime controlling treatment is controlled
automatically so as to treat the water system more sufficiently.
For example, when the electric potential of the sensor exceeds a
threshold value, the slime controlling treatment is intensified, or
an apparatus for eliminating the microbial fouling is started to
operate.
[0035] Examples of the apparatus for eliminating microbial fouling
include an apparatus having a membrane for eliminating microbes, an
apparatus which sterilizes microbes by ultraviolet light, and an
apparatus which adds at least one chemical for sterilizing microbes
such as ozone, chlorine, hypochlorous acid, hydrogen peroxide,
chlorine dioxide, active oxygen in the form of the radical species,
and the like.
[0036] A threshold value can be determined suitably according to a
value of the electric potential which is observed right after the
sensor is immersed in a water system, that is, when the sensor is
not affected by fouling in the water system. It is preferable to
set the threshold value in a range of 100-300 mVvs.Ag/AgCl/sat.KCl
for a usual cooling water system.
[0037] For intensifying the slime controlling treatment, it is
desirable to add a larger amount of the agent than usual or to add
another kind of agent additionally together with the agent usually
used. When the usual slime controlling agent is added continuously
by a chemical feeding pump, an larger amount of the agent can be
added only by increasing the amount of the agent, or by installing
another chemical feeding pump to add an extra amount of the agent
in addition to the pump in the ordinary operation. An extra amount
of the agent can be added either continuously or intermittently.
When the slime controlling agent is intermittently added at a usual
operation, a larger amount of the agent than usual can be added by
increasing the frequency of addition of the agent, or by increasing
an amount of the agent added at one time.
[0038] When another kind of slime controlling agent which is
different from the ordinary one is added additionally, it is
desirable to install a chemical feeding pump for the other agent
and to control it according to a signal from the sensor. The agent
can be added either continuously or intermittently. Both the
treatments, adding the agent and eliminating the microbial fouling
by the apparatus, can be carried out at the same time. Or either
one of them can be carried out.
[0039] The intensified slime control treatment is continued until
the value of the electric potential signaled from the sensor lowers
to the value of normal electric potential, that is, the value of
electric potential of the sensor not affected by fouling. The value
of the normal electric potential can be set according to the water
system.
[0040] A method of the releasing slime includes installing a pump
and adding a predetermined amount of an agent for releasing slime
in batch operation. The release treatment is usually carried out
only once.
[0041] When the electric potential of the sensor does not lower to
the normal electric potential for a definite period of time after
the treatment is started to be intensified or after the release
treatment is started, an emergency signal is preferably sent.
[0042] Once the emergency signal is sent, a malfunction of the
sensor is checked, and furthermore, a fouling level in the water
system is estimated from the result of water analysis, other
monitoring methods, and so on. When it becomes certain that fouling
in the water system is serious, it is necessary to perform a
further release treatment and to take a drastic measure.
[0043] Adding an oxidizing agent such as chlorine for the slime
control treatment may cause a problem in monitoring microbial
fouling because the electric potential of the sensor depends on the
concentration of the oxidizing agent. However the method of the
water treatment of this invention can be applied to a water system
in which an oxidizing agent is added as the slime control agent, if
the concentration of the oxidizing agent in the water system is
kept constant. An example of the method to keep the concentration
of the oxidizing agent constant is monitoring the concentration of
the oxidizing agent automatically and adjusting an amount of the
oxidizing agent to add according to the result of monitoring.
[0044] An oxidizing agent can be added to intensify the slime
control treatment. However, the electric potential of the sensor
may be affected by the concentration of the oxidizing agent when it
becomes high and there may be a concern about the corrosion of
materials in the system. Accordingly, it is preferable to add a
non-oxidizing agent instead of the oxidizing agent. Even in a case
that an apparatus is used to eliminate microbial fouling, the
oxidizing agent is controlled desirably to be kept at a low
concentration.
[0045] The electric potential of the sensor can be detected by any
method. A chemical feeding pump and an apparatus for eliminating
the microbial fouling can be controlled by any controlling system.
The system may include a computer. It is preferable to measure the
electric potential of the sensor not less than 6 times a day, but
not limitative thereto.
[0046] It is desirable to exchange the sensor to a new one
periodically, at least once a year. It is also desirable to
exchange the sensor after an emergency signal is detected.
[0047] There is no limitation to the number of sensors to be
installed. Two or more sensors can be installed to detect the
electric potential at an improved precision. The sensors having
different sensitivities, for example, a sensor made of sensitized
metallic material of this invention and a sensor made of not
sensitized metallic material, make it possible to perform the
intensified treatment more appropriately. Water treatment can be
intensified when a rise of electric potential occurs in the
sensitive sensor followed by a rise in the less sensitive one.
EXAMPLE 1
[0048] The sensitivities of the sensors to microbial fouling were
measured and the results are shown in FIG. 1
[0049] Contaminants including slime collected in a practical water
cooling system was added into circulating cooling water having a
temperature of 30.degree. C. to prepare sample water. Three kinds
of test pieces A, B, and C in the following were immersed into the
sample water and electric potentials of them were measured;
[0050] A: a test piece made of type 304 stainless steel
(SUS304),
[0051] B: a test piece made of SUS304 sensitized at 650.degree. C.
for 24 hours, and
[0052] C: a test piece having a crevice prepared by joining two
metal plates in different sizes made of SUS304 through spot welding
followed by sensitizing at 650.degree. C. for 24 hours.
[0053] As shown in FIG. 1, after immersed into the sample water,
the electric potential of the test piece C rose at a high rate. The
electric potential of the test piece B rose at a low rate. The
electric potential of the test piece A had just slight changes
during this experiment.
[0054] This means that the sensitivity of the sensitized metallic
material to microbial contaminants is high and that of the
sensitized metallic sensor with a crevice is even higher.
[0055] It was confirmed that the electric potential of the test
piece A, B, or C did not have any drastic changes while the test
piece was immersed into the water system containing no
contaminant.
EXAMPLE 2
[0056] In a model plant of a cooling water system shown in FIG. 2,
a corrosion potential of metal (SUS304) was monitored by detecting
the electric potential of the test piece C of Example 1 immersed in
the cooling water, and the water treatment was carried out based on
the result of monitoring.
[0057] In the water system, water in a cooling tower 20 having a
cooling fan 18 and a pit 19 was sent to a heat exchanger 23 via a
water pump 21 and a pipe 22 and returned to the cooling tower 20
via a pipe 24. A pipe for collecting sample water 25 was branched
off from the pipe 22. Collected sample water having a temperature
of 30.degree. C. was sent to a test tube 26 via the pipe 25 and
returned to the cooling tower 20 or to the pipe 22 or 24.
[0058] The test tube 26 had a sensor 11 and a reference electrode
(Ag/AgCl/sat.KCl electrode) 12. Signals from the sensor 11 and from
the reference electrode 12 were sent to a control device 13. The
control device 13 measured an electric potential of the sensor 11
referring to an electric potential of the reference electrode 12.
Controlling signals from this control device 13 were sent to a
chemical feeding pumpl7.
[0059] A slime control agent in a tank 16 is added into the pit 19
by chemical feeding pumps 15, 17.
[0060] When the sensor 11 did not detect fouling, the agent was
added only through the chemical feeding pump 15 for ordinary use.
When the sensor 11 detected fouling, the agent was added through
both pumps 15 and 17 in order to intensify the slime control
treatment.
[0061] FIG. 3 shows changes in the electric potential of the sensor
11 with the elapsed time under the experimental condition that the
chemical feeding pump 15 was stopped and contaminants including
slime collected in a practical cooling water system regularly. The
electric potential exceeded the upper limit (0.20V) on the eleventh
day since the experiment started, and an organic slime control
agent was added automatically through the pump 17. The electric
potential lowered to the lower limit (0.17V) in about a day and
then the pump 17 stopped adding the slime control agent
automatically.
[0062] Industrial Applicability
[0063] The system of the present invention detects the microbial
fouling by the sensor precisely and performs the slime control
treatment appropriately by controlling an additive amount of the
agent(s) or by controlling the apparatus for the treatment, and
thus the condition of the water system is kept good.
[0064] According to the method of the present invention, the
compact and inexpensive on-line monitor monitors the fouling, and
the slime control treatment can be intensified based on the result
of monitoring. Fouling by slime in the water system can be
prevented by detecting the fouling early and perform the treatment
promptly. Furthermore, since the slime control treatment is
intensified only at a necessary time, no agent is wasted and the
effect of the agent on the environment can be minimized. With
respect to the treatment by an apparatus, the apparatus is operated
only if necessary to decrease the amount of the power consumption
and to lower the maintenance cost.
* * * * *