Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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I~TRODUCTION
Industrial cooling systems such as cooling towers and once
through heat exchange coolers often develop large masses of biological
slimes which adhere to heat transfer surfaces. These slimes reduce
the flow of the water in heat excnangers. Also, the overall heat
transfer efficiency of these units is reduced.
~ A classic method for preventing slime buildup has been to trea
¦the water in these systems with industrial biocides. While this has
¦met with a measure of success, it does not cope with the problem of
¦removing existing deposits. Also, in certain cases, it i5 not feasib~
to treat these systems with large doses of biocides. Also, in
¦certain cases, biocides are not completely effective in preventing
¦the gxowth of slime-forming microorganisms.
¦ If it were possible to xeadily remove these slime masses from
¦industrial cooling systems and to readily prevent rebuildup by usin~
¦simple chemicals at low economical doses, a valuable contribution to I
the art would be made.
¦ THE INVENTION
¦ In accordance with the invention, it has been found that
biological slime buildup may be removed and, once removed, prevented I
on the surface of cooling towers and heat exchange equipment associa~¦
~ ted therewith which comprises treating the water utilized in such
¦ cooling towers and heat exchange equipment with at least .5 ppm of a
propylene oxide--ethylene oxide copolymer, which polymers comprise a
polyoxy-propylene glycol polymer having a molecular weight of from
1 1500 - 2000 which has been reacted wit~l from 5 - 30~ by weight of
¦ ethylene oxide.
In a preferred embodiment of the invention, these polymers are
employed at a dosage rate varying between .5 - 50 ppm, and, most
preferably, 5 - 30 ppm.
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In a preferred embodiment of the invention, these copolymers are
used in com~ination with biocides, particularly oxidizing biocides, to aid
in preventing microbiological growth from reoccurring and to sterilize areas
which have been rendered deposit-free by the action of the copolymers. In
certain instances, it is believed that the copolymers act in concert with the
oxidizing biocides to provide not only improved dispersancy of existing bi-
ological deposits but to allow the biocide to exert its full effectiveness.
; The invention is capable of treating microbiological deposits which
occur on the heat exchange surfaces of both recirculating cooling tower sys-
tems as well as once through cooling units. These latter units normally draw
their cooling water from a large body of existlng water such as a lake, river
or a pond, pass it in heat exchange relationship with a liquid or gas after
which it is returned to its original source without reuse.
The copolymers described above are sold commercially by Wyandotte
Chemical Company under the trade name of Pluronics*. Particularly useful
Pluronics that may be used in the practice of the invention are Pluronic L61*
' and Pluronic L62*. These two Pluronic* materials have a polyoxypropylene
- glycol base molecule which has a molecular weight of about 1750. In the case
of Pluronic L61*, this polyoxypropylene glycol base is reacted with 10% by
weight of ethylene oxide and has an average molecular weight of about 2000.
Pluronic L62* reacts the polyoxypropylene glycol base with 20% by weight of
ethylene oxide and has an average molecular weight of about 2500. A further
description of these materials and their method of preparation is set forth
in United States 2,674,619.
Example 1
To determine the efficiency of various materials to disperse exist-
ing biologically produced slimes, a laboratory scale forced draft single cell
cooling tower was used. The basic characteristics of this cooling tower and
; its environment are set forth below:
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E~rocess Cooled: Experimental Heat
Exchanger Tubes
Total Capacity: 20 liters .
Recirculation Rate: 2 gallons per minute
Blowdown Rate: 70 cc per minute
Make-up Water: Chicayo Tap Water
aT: 4C
l Concentration: 3
I ¦ pH Tower Water: 8.S
¦ Hardness: 435 ppm (as calcium carbonate)
Temperature: 100F
. ¦ Make-up Water: 12 gals. per 24 hours .
¦ To the tower makeup water was added 50 ppm each of ethylene
glycol and a source of organic phosphorus in the form of a phosphate
ester. The tower was allowed to run for 4 days which caused the
¦ substantial formation of slime masses on the mPtallic heat exchange
surfaces.
! lo ppm of the particular chemical to be tested was added to
¦ the water of the tower and allowed to circulate for l-hour. At the
¦end of that period of time, a bio mass assay was made of the basin
¦ water using a duPont biometer which is descri~ed in the duPont
¦ publication entitled, duPont 760 Luminescence Biometer, December,
: 1970. It is also described in U.S. 3,359,973~ .
The results of these tests are set forth in Table I.
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TABLE I
- 10 ppm With 1 Hour Contact
Data Collected ~ith Biometer
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Chemical Z Biomass Chanpe
1. Nonionic (polyol) condensate of
ethylene oxide with hydrophobic
bases (propylene oxide with
propylene glycol) (Pluronic L-61) * 66.4%
2. ~onionic polyethoxylated straight
chain alcohol 58.5%
3. Tris cyanoethyl cocodiamine47.3%
. 4. Polyoxyethylene sorbitan ester of
: fatty and resin acids and alkyl
'; aryl sulfonate~ blend (nonionic) 45.8%
5. Cationic ethylene oxide condensation
., products of N-Tallow propylene diamine 35~8~D
- 6. Nonionic N, N-dimethyl stearamide34.7%
7. Monoamine (cationic) (cocomononitrile) 31.3%
:: 8. Sodium polyacrylate 31.1%
9. Nonionic - amine polyglycol condensate 30.0%
10. Cationic - cocodiamine 25.6Z
onionic ethoxylated alcohol 21~2%
12. Lignosulfonate - anionic 10.3%
(3Q ppm~2 hours)
13. Sodium salt of amphoteric surfactant 5~8%
14. Polyacrylic acid (homopolymer)4.7%
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~ 15. ~onionic octylphenox7 polyethoxy ethanol 4.1%
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Example II
¦ In addition to the above, additional commercially available
surfactants and dispersants were tested at the 10 ppm level. Some of
¦these materials were known to possess bacteriacidal activity. This
particular group of materials which is set forth below in Table II
showed no evidence of biodispersancy.
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TABLE II
Products Showing No Biodispersancy at 10 ppm Level
1. Onamine RO* l-t2 hydroxyethyl) 2,n-hepta-
decenyl-2-imidazoline - cationic
2. Ammonyx 27* alkyl trimethyl ammonium chloride
3. Cyanoethylated
cocodiamine (mono-diamine)
4. BTC-2125 M* Onyx dual quat - catlonic
:: 5. Surco 5024* nonionic, mixed fatty acid
diethanolamide condensate
6. Surfonic N-40* nonionic, alkylaryl polyethylene
' glycol ether
7. Nalco 670* polymer
8. Makon 10* nonionic, alkylphenoxy polyoxy
ethylene ethanols
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: Note. In the case of items 1, 2, 3 and 4 biocidal effects may
. mask biodispersancy.
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¦ E~ample III
¦ In additional laboratory tower testing using standard plate
¦count procedures in place of biometer monitorirg techniques, Pluronic
L62 was tested and was found to be comparable in its activity to
¦IPluronic L61.
Example IV
In addition to dispersing existing slime masses, the composi-
tions used in the invention are capable of preventing slime buildup.
In another series of tests using the chemical of the invention, the
material was maintained at a dosage level of 10 ppm in the experi-
mental cooling tower which was in a clean condition. The tower ran
11 days before slime buildup became evident. As was previously ~ -
indicated, at the end of 4 days, slime became evident.
As previously indicated, the copolymers are quite effective
~hen used in combination with certain water-soluble oxidizing bio-
cides. T~e most preferred biocide is chlorine which is employed in
commercial installations in the form of a chlorlne-releasi:ng material,
e~g. sodium hypochlorite as chlorine gas or as a water-dispersible
organic compound which is capable of releasing chlorine
Also, it should be noted that certain beneficial effects can
be obtained by using the copolymers of the invention in com~ination
with organic biocides such as, for instance, methylene ~is thio-
cyanate.
As indicated, the preferred biocide to use in combination with
the copolymers of the invention to disperse e~isting biological
deposits and to prevent their subsequent buildup is chlorine or a
chlorine-releasing co~pound.
Chlorination practices used to treat indust~ial cooling waters
vary considerably. Most often, the chlorine or chlorine-releasing
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~compo~lnd is slug-fed to the system and then ~llowed to act on the
¦microorganisms present in the system. As the chlorine acts on the
.icroorganisms and is in contact with organic matter often present
¦in such systems, it is absorbed or c'nemically reacted to the point
I that it is no longer detectable as free chlorine. Thus, the systems
are treated to provide so-called chlori~e residuals which, in most
l cases, rarely exceed 2 ppm and, in most cases, rarely exceed 1 ppm.
¦ A typical chlorine residual that would occur from typîcal chlorinatio
practices would ~e aboui 0.2 ppm.
l To illustrate the advantages obtained in using the copolymers
¦ in combination with chlorine, the following addîtional examples are
~presented:
Example V
¦ This test was conducted at a mid~estern atomic energy power
¦plant. The particular tower chosen had a history of slime deposits
¦on the decks as well as decreased cooling efficiency as monitored by
!¦condenser cleanliness factors.
¦ Three dosage parameters were e~aluated:
1. 15 ppm Pluronic L61*single slug with o~a5 ppm C12~
2. 5 ppm Pluronic L~l single slug with 12.12 ppm Cl2;
3. Maximum 13.7 ppm Cl2 alone. ~
The addition of Pluronic L~l in conjunction with chlorination
demonstrated an improvement in the % Cleanliness Factor (CF) in both
the high and low pressure condensers. The results of this test are
¦ set forth in Fig. 1 and Ta~le III.
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Table III
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Treatment Condenser % Maximum C.F. Time
Improvement
Pluronic L61 15 ppml Low Pressure 7.24% - 6.5 Hrs.
0.05 ppmC12 J : ~
Pluronic L61 15 PPml High Pressure 6.09% 9.5 Hrs.
0.05 pp~C12 J
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Pluronic L61 * 5 PPml Low Pressure 2.61% 6 Hrs.
12.12 ppmC12 J . .
Piuronic L61 * 5 ppm~ High Pressure 3.80% 6 Hrs.
12.12 ppmCl2 J
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No Biodispersant 1 Low Pressure 0.55% 2 Hrs
12.4 ppm C12 ~
~o Biodispersant 1 High Pressure 1.06X - . 2 Hrs.
12.4 ppm Cl2 J _ ~ _
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Arlother positive indication of biodispersant activity ~as ~he
loss of titratable chlorine from recirculating water within two hours
in the Pluronic L61 treated system while it ta~es 9 hours to achieve ¦
chlorine residual destruction witnout the biodispersant. Since
Pluronic L61 has r.o chlorine demand at use concentrations, it can ~e
¦stated that the biodispersant liherates slime organisms from the
cooling system which rapidly react with the available chlorine, reduc-
ing it to 0 level.
Example VI
The situs for this test was a cooling tower located at a
midwestern power company. This company had been experiencing con-
denser fouling for the past several years due to microbiological
growth in the recirculating water system. The microbiological growth
¦is due to the municipal sewer water effluent used in the recirculat-
ing water system. This sewer water effluent contains a high level of
microorganisms and organic-nutrients for the microorganisms - hence
the tremendous potential for microbiological growth in the recirculat-
ing water system. Chlorination before and after the lime softener,
phosphate removal, chlorination at the cooling towers and intermittent
additions of commercial biocides have not been effec~ive in control-
ling microbiological depos;tion in the system.
Analysis of recirculating water and deposit analyses showed
that the pr;mary cause o~ the deposition is microhiological growth.
A complete plant survey was conducted to provide ~aseline date
information.
Unit No. 2 instrumentation (i.e., Terminal Difference Thermo-
meters, Vacuum Gauge, Back Pressure [Turbine} manometers, ana miscel~
laneous plant instrumentation) was calibrated.
Based on the above survey, it was established that the unit
is presently maintaining at 60MW, a Terminal Difference of 10 - 12~F
and a Back Pressure of 3.3 - 3.5 in. Hg.
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Dosa~e: 30 ppm (residual in the tower) initlal dosage to
l¦cl~an up the system. ~aintenance dosage o~ 1 - 2 ppm after cleanup.
¦IChemical to be fed during chlorination.
Results: A basic fact was established--Pluronic L61 reduced
¦terminal difference from 11F to 4F and bacX pressure from 3.3 in.
!¦~lg to 2.5 in. Hg.
i¦ Pluronic L6~ addition was started at 1200 HR simultaneous with
¦chlorination. At 1600 HR, t~e TDS reading in the tower increased to
¦8400 umho from 5800 umho. The water became cloudy and effervescent,
¦indicati~e of the quick dispersive property of Pluronic L61.*
On the first day, the terminal difference and back pressure
started to decrease.
On the 2nd and 3rd day, the terminal difference and back
l pressure plateaud at 4 - 5F and 2.5 - 2.7 in. Hg respectively.
;This is a reduction of 7F on terminal difference and 0.8 in. Hg on
back pressure.
Back Pressure Reduction: Fig. No. 2 and No. 3 show readings
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taken at 1400 HR and 1700 HR respectively. Bac~ pressure readings
¦¦decreased from 3.3 in. Hg. to 2.5 in. Hg at full load. Bac~ pressure
¦¦decrease from design indicates the effect of lac~ of fouling of the
¦~condenser. The condenser would be su~jecting the turbine to a 2 5
¦ inches of mercury ~ack pressure; hence, increased power output of
¦0.8%. 1 in. Hg in back pressure is e~ual to 1% loss in power outpu~.
I Fig. No. 2 and No. 3 show-readings taken at 140Q HR and 1700 HR
i~! respectively, revealing the relative effects of a~bient temperature
! and relative humidity. The 1400 HR reading was assumed as the hot-
¦ test time of the day, and the 1700 HR readin~ as the average
I temperature of the day.
j~ Comparison of the Back Pressure Manometer readin~s ~7ith the
I! Vacuum Chart Recorder and Barometric Pressure Gauge in the plant
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I(Barometric Pressure minus Vacuum equals Back Pressure), showed close
¦correlation. Hence, the Back Pressure Manometer reading is a more
¦reliable measure for indication of condenser fouling.
¦ Terminal Difference: Fig. No. 2 and No. 3 show readings taken
~at 1400 HR and 1700 ~R respectively. This graph plotted Terminal
Difference ~s. Back Pressure at 60 Mw load (full load). Terminal
Idifference was reduced from 11.0F to 4F, or an average reduction of
¦7F. However, in spite of the recalibrated thermometers, error in
¦reading the narrow scale expansion of the thermometers would cause an
¦error of +2F. The most important value of this reading is the fact
¦ that it serves as a good indicator of condenser ouling. The fact
¦ that the terminal difference decreased indicates that foulants had
¦~een removed. More accurate terminal difference data may be taken
using a Thermocouple temperature measurement device. The Unit No. 2
¦ is designed for a terminal difference of 5~ - 6F, based on design
absolute pressure converted to saturated steam temperature. The
fact that plant terminal readings were decreased to 4F, given an
error of +2FI would indicate that the condenser is clean and
operating at almost design condition. -
Total Count: Total Count tColonies/ml ~ was taken on alimited basis. Fig. No. 4 shows TC vs. TDS. Total Count was taken
prior to the start of chemical treatment, in order to confirm
presence of microbiological growth as the primary cause of the con-
denser fouling. TC was too numerous to count ~T~TC~ at 0900 HR on
¦ the day prior to chemical treatment. TC was taken using the portahle
¦ millipore culture kit. The sample was diluted at 1:1000, using
¦ sterilized water and a Glaspak discardit syringe. The sample was
¦I then incubated for 24 hours. The colonies which had grown a~ter
I 24 hours were counted and compared to a comparison chart. Due to
limited time and range of comparison charts available, only six
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¦ranges could b~ counted (lOK, 30K, 50K, lOOK, 300~, and TNTC).
EIo~ever, this was sufficient to establish a micro~iological gro~7th
trend in the system. TC was reduced to 300~ on the 1st day and
¦settled at 50~ on the 3rd day. This is an indication that the
micro~iological growth in the recirculating system has been arrested.
Total Dissolved Solids: Fig. No. 4 shows TDS vs. TC. TDS
i was taken using ~alcometer Model ~LN. The meter was standardized
¦~sing 3000 umbo/cm con~uctance standard solution. TDS readings
¦increased from 6400 umho at 0900 HR to 8400 u~ho at 1600 HP~. This
jindicates that solids or foulants in the system are being dislodged~
Chlorination: Fig. No. 5 shows a comparison of residual-free
chlorine in towers before and after Pluronic L61 addition.
Fig. No. 5 shows that residual in the tower can only go as
high as 0.2 ppm. at 600~/24 HR setting of the-chlorinator. This
indicates that a lot of chlorine is heing absorbed by foulants in the
system. On the first day, at l,OOO~/24 HR setting of the chlorinator,
residual chlorine in the tower went up to 0.6 ppm and lingered at
Q.3 ppm for several hours. This is an indlcation that previous
foulants in the system have been removed; hence, the increased
¦residual of chlorine i~ the towers.
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Example VII
This test was a once through cooling system located
at a chemical plant in the southeastern part of the United
States. The water source was an empounding pond which contained
chlorinated sewage from a major city. Prior to the test, the
water was treated with between 750 - 1200 pounds of chlorine,
as C12 per day.
Pluronic L61* was slug fed at 20 ppm. At the end of
5-1/2 hours, the total count had increased from 2,750,000 to
7,300,000. The iron content of the water was increased by 2 ppm.
The chlorine residual dropped from 1 ppm to 0 indicating an
increased liberation of slime from heat exchange surfaces.
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