GB1560327A - Method of removing and preventing biological slime build up - Google Patents

Description

(54) METHOD OF REMOVING AND PREVENTING BIOLOGICAL SLIME BUILD-UP (71) We, NALCO CHEMICAL COMPANY, a Corporation organized and existing under the laws of the State of Delaware, United States of America, of 2901 Butterfield Road, Oak Brook, Illinois, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement:- The present invention relates to a method of removing and preventing slime build-up on the surfaces of cooling systems.

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 water in heat exchangers.

Also, the overall heat transfer efficiency of these units is reduced.

A classic method for preventing slime build-up has been to treat 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 is not feasible to treat these systems with large doses of biocides.

Also, in certain cases, biocides are not completely effective in preventing the growth of slime-forming microorganisms.

If it were possible to readily remove these slime masses from industrial cooling systems and to readily prevent rebuildup by using simple chemicals at low economical doses, a valuable contribution to the art would be made.

The present invention provides a method of removing and preventing biological slime buildup on the surfaces of commercial and industrial cooling systems and the like which comprises treating the water used in the operation of these cooling towers with at least .5 ppm of a propylene oxide-ethylene oxide copolymer, which polymer comprises a polyoxypropylene glycol polymer having a molecular weight of from 1500--2000 which has been reacted with from 53Oo4 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.

In a preferred embodiment of the invention, these copolymers are used in combination 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 biological 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 systems as well as once through cooling units. These latter units normally draw their cooling water from a large body of existing water such as lake, river or a pony pass it in heat exchange relationship with a liquid or gas after which it is returned to its original source without re-use.

The copolymers described above are sold commercially by Wyandotte Chemical Company under the trade name of Pluronics (Pluronics is a Registered Trade Mark). 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 U.S.

2,674,619.

Example 1.

To determine the efficiency of various materials to disperse existing 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: Process Cooled: Experimental Heat Exchanger Tubes Total Capacity: 20 liters Recirculation Rate: 2 gallons per minute Blowdown Rate: 70 cc per minute Make-up Water: Chicago Tap Water AT: 4"C pH Tower Water: 8.5 Hardness: 435 ppm (as calcium carbonate) Temperature: 100"F Make-up Water: 12 gallons per 24 hours To the tower make-up water was added 50 ppm each of ethylene glycol and partially water soluble phosphated mixed esters of oxyalkylated polyols as described in U.S. Patents 3,502,587 and 3,728,420. The tower was allowed to run for 4 days which causes the substantial formation of slime masses on the metallic heat exchange surfaces.

10 ppm of the particular chemical to be tested was added to the water of the tower and allowed to circulate for I 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 described 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.

TABLE I.

10 ppm With I Hour Contact Data Collected with Biometer Chemical % Biomass Change 1. Nonionic (polyol) condensate of ethylene oxide with hydrophobic bases (propylene oxide with propylene glycol) (Pluronic L6l) 66.4% 2. Nonionic polyethoxylated straight chain alcohol 58.5% 3. Tris-cyanoethyl-cocodiamine 47.3% 4. Polyoxyethylene sorbitan ester of fatty and resin acids and alkyl aryl sulfonate blend (nonionic) 45.8% TABLE I.

10 ppm With I Hour Contact Data Collected with Biometer Chemical % Biomass Change 5. Cationic ethylene oxide condensation products of N-Tallow propylene diamine 35.8% 6. Nonionic N,N-dimethyl-stearamide 34.7% 7. *Arneel C 31.3% 8. Sodiumpolyacrylate 31.1% 9. Nonionic -Amine polyglycol condensate 30.0% 10. Cationic -- cocodiamine 25.6% I 1. Nonionic ethoxylated alcohol 21.2% 12. Lignosulfonate -- anionic 10.3% (30 ppm/2 hours) 13. Sodium salt of amphoteric surfactant 5.8% 14. Polyacrylic acid (homopolymer) 4.7% 15. Nonionic octylphenoxy-polyethoxy-ethanol 4.1% 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 below in Table II showed no evidence of biodispersancy.

*Arneel C is a Registered Trade Mark. It is a coconitrile compound manufactured by the Armak Chemical Company.

TABLE II.

Products Showing No Biodispersancy* at 10 ppm Level 1. Onamine RO* 1-(2 hydroxyethyl) 2,n-heptadecenyl-2-imidazoline - cationic 2. Ammonyx 27* alkyl trimethyl ammonium chloride 3. Cyanoethylated cocodiamine* N,1-coco-N,1,3,3,triscyanoethyl propane diamine 4. BTC--2125 M* a material composed of 50% alkyl (60% C--14, 30% C--16, 5% C--12, 5% C--18) dimethylbenzyl ammonium chloride and 50% alkyl (68% C--12, 32% C--14 ethylbenzyl ammonium chloride 5. Surco 5025 nonionic, mixed fatty acid diethanolamide condensate 6. Surfonic N40 nonionic, alkylaryl polyethylene glycol ether 7. Nalco 670 polyacrylamide (Nalco is a Registered Trade Mark) 8. Makon 10 nonionic, alkylphenoxy polyoxy ethylene ethanols *Biocidal effects may mask biodispersancy.

Example III.

In additional laboratory tower testing using standard plate count procedures in place of biometer monitoring techniques, Pluronic L62 was tested and was found to be comparable in its activity to Pluronic L61.

Example IV.

In addition to dispersing existing slime masses, the compositions 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 experimental cooling tower which was in a clean condition. The tower ran 11 days before slime buildup became evident. As was previously indicated in the absence of the compositions, at the end of 4 days, slime became evident.

As previously indicated, the copolymers are quite effective when used in combination with certain water-soluble oxidizing biocides. The most preferred biocide is chlorine which is employed in commercial installations in the form of a chlorine-releasing material, e.g. sodium hypochlorite as chlorine gas or as a waterdispersible 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 combination with organic biocides such as, for instance, methylene-bis-thiocyanate.

As indicated, the preferred biocide to use in combination with the copolymers of the invention to disperse existing biological deposits and to prevent their subsequent build-up is chlorine or a chlorine-releasing compound.

Chlorination practices used to treat industrial cooling waters vary considerably. Most often, the chlorine or chlorine-releasing compound is slug-fed to the system and then allowed to act on the microorganisms present in the system.

As the chlorine acts on the microorganisms and is in contact with organic matter often present in such systems, it is absorbed or chemically reacted to the point that it is no longer detectable as free chlorine. Thus, the systems are treated to provide so-called residual chlorine which, in most cases, rarely exceed 2 ppm and, in most cases, rarely exceed 1 ppm. A typical residual chlorine that would occur from typical chlorination practices would be about 0.2 ppm.

To illustrate the advantages obtained in using the copolymers in combination with chlorine, the following additional examples are presented: Example V.

This test was conducted at a midwestern 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 evaluated: 1. 15 ppm Pluronic L61 single slug with 0.05 ppm Cl2; 2. 5 ppm Pluronic L61 single slug with 12.12 ppm Cl2; 3. Maximum 13.7 ppm Cl2 alone.

The addition of Pluronic L61 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 Figure 1 and Table III.

TABLE III % Maximum C.F.

Treatment Condenser Improvement Time

Pluronic L61 15 ppm Low Pressure 7.24% 6.5 Hrs.

0.05 ppm Cl2 Pluronic L61 15 ppml High Pressure 6.09; 9.5 Hrs.

0.05 ppm Cl2 Pluronic L61 5 ppm Low Pressure 2.61% 6 Hrs.

12.12 ppm Cl2 Pluronic L61 Sppm High Pressure 3.80% 6 Hrs.

12.12 ppm Cl2 No Biodispersant ~ Low Pressure 0.55% 2 Hrs.

12.4 ppm Cl2 No Biodispersant l High Pressure 1.06% 2 Hrs.

12.4 ppm Cl2 Chlorine (Cl2) is measured as HOCI (free chlorine).

Another positive indication of biodispersant activity was the loss of titratable chlorine from recirculating water within two hours in the Pluronic L61 treated system while it takes 9 hours to achieve residual chlorine destruction without the biodispersant. Since Pluronic L61 has no chlorine demand at use concentrations, it can be stated that the biodispersant liberates slime organisms from the cooling system which rapidly react with the available chlorine, reducing 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 condenser 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 recirculating 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 recirculating 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 effective in controlling microbiological deposition in the system.

Analysis of recirculating water and deposit analyses showed that the primary cause of the deposition is microbiological growth. A complete plant survey was conducted to provide baseline date information.

Unit No. 2 instrumentation (i.e., Terminal Difference Thermometers, Vacuum Gauge, Back Pressure [Turbine] manometers, and miscellaneous plant instrumentation) was calibrated.

Based on the above survey, it was established that the unit is presently maintained at 60 Mw (megawatts), a Terminal Difference of lO--120F and a Back Pressure of 3.3-3.5 in. Hg.

Dosage: 30 ppm (residual in the tower) initial dosage to clean up the system.

Maintenance dosage of 1--2 ppm after cleanup. Chemical to be fed during chlorination.

Results: A basic fact was established -- Pluronic L61 reduced terminal difference from 11"F to 4"F and back pressure from 3.3 in. Hg to 2.5 in. Hg.

Pluronic L61 addition was started at 1200 HR simultaneous with chlorination.

At 1600 HR, the TDS reading in the tower increased to 8400 umho from 5800 umho. The water became cloudy and effervescent. indicative 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 pressure levelled off at 4--5"F and 2.5-2.7 in. Hg respectively. This is a reduction of 7"F on terminal difference and 0.8 in. Hg on back pressure.

Back Pressure Reduction: Figure No. 2 and No. 3 show readings taken at 1400 HR and 1700 HR respectively. Back pressure readings decreased from 3.3 in. Hg to 2.5 in. Hg at full load. Back pressure decrease from design indicates the effect of lack of fouling of the condenser. The condenser would be subjecting the turbine to a 2.5 inches of mercury back pressure; hence, increased power output of 0.8%. I in.

Hg in back pressure is equal to 1% loss in power output. Figure No. 2 and No. 3 show readings taken at 1400 HR and 1700 HR respectively, revealing the relative effects of ambient temperature and relative humidity. The 1400 HR reading was assumed as the hottest time of the day, and the 1700 HR reading as the average temperature of the day.

Comparison of the Back Pressure Manometer readings with the Vacuum Chart Recorder and Barometric Pressure Gauge in the plant (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: Figure No. 2 and No. 3 show readings taken at 1400 HR and 1700 HR respectively. This graph plotted Terminal Difference vs. Back Pressure at 60 Mw load (full load). Terminal difference was reduced from 11 .00F to 4"F, or an average reduction of 7"F. However, in spite of the recalibrated thermometers, error in reading the narrow scale expansion of the thermometers would cause an error of +2 F. The most important value of this reading is the fact that it serves as a good indicator of condenser fouling. The fact that the terminal difference decreased indicates that foulants had been 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 500F, based on design absolute pressure converted to saturated steam temperature. The fact that plant terminal readings were decreased to 40F, given an error of f20F, would indicate that the condenser is clean and operating at almost design condition.

'C' CONVERSION Total Count: Total Count (Colonies/ml.) was taken on a limited basis. Figure 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 condenser fouling. TC was too numerous to count (TNTC) at 0900 HR on the day prior to chemical treatment. TC was taken using the portable millipore culture kit. The sample was diluted at 1:1000, using sterilized water and a Glaspak discardit syringe. The sample was then incubated for 24 hours. The colonies which had grown after 24 hours were counted and compared to a comparison chart. Due to limited time and range of comparison charts available, only six ranges could be counted (10K, 30K, 50K, 100K, 300K, and TNTC). However, this was sufficient to establish a microbiological growth trend in the system. TC was reduced to 300K on the 1st day and setted at 50K on the 3rd day. This is an indication that the microbiological growth in the recirculating system has been arrested.

Total Dissolved Solids: Figure No. 4 shows TDS vs. TC. TDS was taken using Nalcometer Model MLN. The meter was standardized using 3000 umho/cm conductance standard solution. TDS readings increased from 6400 umho at 0900 HR to 8400 umho at 1600 HR. This indicates that solids or foulants in the system are being dislodged.

Chlorination: Figure No. 5 shows a comparison of residual-free chlorine in towers before and after Pluronic L61 addition.

Figure No. 5 shows that residual in the tower can only go as high as 0.2 ppm. at 600 pounds/24 HR setting of the chlorinator. The symbol # used in Fig. 5 means pounds. This indicates that a lot of chlorine is being absorbed by foulants in the system. On the first day, at 1,000 pounds/24 HR setting of the chlorinator, residual chlorine in the tower went up to 0.6 ppm and lingered at 0.3 ppm for several hours.

This is an indication that previous foulants in the system have been removed; hence, the increased residual of chlorine in the towers.

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 Cl2 per day.

Pluronic L61 was slug fed at 20 ppm. At the end of 5+ 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 residual chlorine dropped from I ppm to 0 indicating an increased liberation of slime from heat exchange surfaces.

WHAT WE CLAIM IS: 1. A method of removing and preventing biological slime build-up on the surfaces of commercial and industrial cooling systems and the like which comprises treating the water used in the operation of these cooling towers with at least .5 ppm of a propylene oxide -- ethylene oxide copolymer, which polymer comprises a polyoxypropylene glycol polymer having a molecular weight of from 1500--2000 which has been reacted with from 5--309 by weight of ethylene oxide.

2. The method according to claim I where the propylene oxide -- ethylene oxide copolymer is a polyoxypropylene glycol polymer having a molecular weight of about 1750, which polymer has been reacted with 10 or 20 moles of ethylene oxide.

3. A method according to claim I or 2 wherein said polyoxypropylene glycol polymer is reacted with the ethylene oxide and a biocidally active amount of a water-soluble oxidizing biocide.

4. The method according to claim 3 where the water-soluble oxidizing biocide is chlorine.

5. A method of removing and preventing biological slime build-up on the surfaces of commercial and industrial cooling systems and the like substantially as herein described with reference to the examples.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. 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 Cl2 per day. Pluronic L61 was slug fed at 20 ppm. At the end of 5+ 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 residual chlorine dropped from I ppm to 0 indicating an increased liberation of slime from heat exchange surfaces. WHAT WE CLAIM IS:

1. A method of removing and preventing biological slime build-up on the surfaces of commercial and industrial cooling systems and the like which comprises treating the water used in the operation of these cooling towers with at least .5 ppm of a propylene oxide -- ethylene oxide copolymer, which polymer comprises a polyoxypropylene glycol polymer having a molecular weight of from 1500--2000 which has been reacted with from 5--309 by weight of ethylene oxide.

2. The method according to claim I where the propylene oxide -- ethylene oxide copolymer is a polyoxypropylene glycol polymer having a molecular weight of about 1750, which polymer has been reacted with 10 or 20 moles of ethylene oxide.

3. A method according to claim I or 2 wherein said polyoxypropylene glycol polymer is reacted with the ethylene oxide and a biocidally active amount of a water-soluble oxidizing biocide.

4. The method according to claim 3 where the water-soluble oxidizing biocide is chlorine.

5. A method of removing and preventing biological slime build-up on the surfaces of commercial and industrial cooling systems and the like substantially as herein described with reference to the examples.