CA1233722A - Method of controlling scale in pressurised boilers - Google Patents
Method of controlling scale in pressurised boilersInfo
- Publication number
- CA1233722A CA1233722A CA000469567A CA469567A CA1233722A CA 1233722 A CA1233722 A CA 1233722A CA 000469567 A CA000469567 A CA 000469567A CA 469567 A CA469567 A CA 469567A CA 1233722 A CA1233722 A CA 1233722A
- Authority
- CA
- Canada
- Prior art keywords
- copolymer
- water
- scale
- boiler
- phosphate
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F5/00—Softening water; Preventing scale; Adding scale preventatives or scale removers to water, e.g. adding sequestering agents
- C02F5/08—Treatment of water with complexing chemicals or other solubilising agents for softening, scale prevention or scale removal, e.g. adding sequestering agents
- C02F5/10—Treatment of water with complexing chemicals or other solubilising agents for softening, scale prevention or scale removal, e.g. adding sequestering agents using organic substances
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F5/00—Softening water; Preventing scale; Adding scale preventatives or scale removers to water, e.g. adding sequestering agents
- C02F5/08—Treatment of water with complexing chemicals or other solubilising agents for softening, scale prevention or scale removal, e.g. adding sequestering agents
Abstract
ABSTRACT
METHOD OF CONTROLLING SCALE IN PRESSURISED BOILERS
The formation of scale in aqueous pressurised boiler systems is inhibited by the addition of a copolymer of maleic acid or anhydride or fumaric acid and allyl or vinyl sulphonic acid or a water soluble salt thereof.
These copolymers have the great advantage that they actually cause the removal of existing scale in such pressurised boiler systems and may be added in combination with a water soluble, hardness precipitating agent such as a carbonate or phosphate.
METHOD OF CONTROLLING SCALE IN PRESSURISED BOILERS
The formation of scale in aqueous pressurised boiler systems is inhibited by the addition of a copolymer of maleic acid or anhydride or fumaric acid and allyl or vinyl sulphonic acid or a water soluble salt thereof.
These copolymers have the great advantage that they actually cause the removal of existing scale in such pressurised boiler systems and may be added in combination with a water soluble, hardness precipitating agent such as a carbonate or phosphate.
Description
"METHOD OF CONTROLLING SCALE IN PRESSURlSED BOILERS"
~ This invention relates to the treatment of a~ueous : systems used in pressurised boilers.
The water used in steam generating boilers, cooling :~ ~ towers, desalination units and other industrial aqueous ! 5 systems contains various impurities. The impurities typically include alkaline earth cations, principally ; ~ calcium and:magnesium, and several anions including : ~ bicarbonate, carbonate, sulphater oxalate, phosphate, silicate and~fluoride~ The most common impurities in ~ 10 industrial water supplies are the water hardening calcium, : : magnesium and carbonate ions although sulphate is usually ~ ~ also present. The salts of these metal ions, especislly , ,: :
, ,, .
~33~2 the carbonates, tend to precipitate forming solid accumulations on the surfaces of the system and these accumulations can give rise to the formation of scale on hot surfaces. The water may also contain various solids such as mud, clay, iron oxides, silt, sand and other mineral matter as well as microbiological debris which accumulate as sludge in the system. Naturally sludge and scale deposits greatly reduce heat transfer efficiency by settling at low flow points in the system and thus limiting the circulation of the water and insulating it from the heat transfer surfaces. In addition, corrosion of metal surfaces under the deposits is facilitated since corrosion control agents are unable to contact the surfaces effectively. Again, the deposits harbour bacteria. Removal of the deposits can cause expensive delays and shutdown of the system.
Since prior treatments such as softening, coagulation and filtration do not adequately remove solids and solid forming substances various chemicals have been used to counteract the adverse effects of scale and sludge in aqueous systems. In cooling water systems and desalination plants the chemicals are commonly added in order to increase the threshold at which precipitation occurs; it has also been thought that the chemical forms a 25 film on the hot surfaces where scale formation is likely ....
~L;233~
to occ~r thereby preventing scale forming material from adhering to the hot surfaces in question. A variety of different chemicals have been used for this purpose including pGlycarboxylates and other soluble, polar polymers such as acrylate and methacrylate polymers. The presence of small quantities of these polymers can have a marked effect on the system.
Although these various chemicals are quite effective in industrial cooling towers and desalination plants and the like quite different problems arise in water which is used in pressurised boilers due to the much higher temperatures involved; the boiler point of water at the lowest pressure normally used, 80 psig, is already 324F
(about 162~C)~
Because of the greater problems involved, the water : used for such pressurised boilers is first subjected to a deioniser or to base exchange, the former being the more effective~ Even so these treatments are not always f~lly effective with the result that some calcium and magnesium ions, in particular, remain in the boiler feedwater along with their associated anions.
In view of the higher temperatures involved, it is not practical to try and keep the calcium in solution as is : the case with cooling water; an exception to this is the ,, ,-use of chelants but these present some other problems of application in particular correct dosing. Likewise, it is much more difficult to prevent the solid deposits from contacting the very hot surfaces thereby giving rise to scaling.
As a result, different techniques have to be adopted for the prevention of scale in pressurised boiler systems.
For boilers which are subjected only to low (up to, say, 150 psig) pressures it is not unusual to add a water soluble carbonate to the feed water in order to cause all the calcium present to precipitate as carbonate and to add also a dispersant to prevent the precipitated material from settling on the hot surfaces. This is, of course, in complete contrast with the situation with cooling water where the aim is to keep the carbonate concentration to a minimum and to keep that concentration in solution.
Calcium sulphate is very much more soluble than calcium carbonate so that it does not present a significant problem in cooling water and desalination systems. In pressurised boilers, however, scaling due to calcium sulphate can occur so that it is desirable to ensure that all the calcium is precipitated.
. , , ,. ..
~2~3~2;~
Inevitably~ however, dosing with carbonate is not fully effective with the result that some scale does still form. Over a period, scale can accumulate to such an extent that the hoiler has to be shut down and the scale removed. This is essential since scale deposits can cause localised overheating and even rupture in the boiler.
With moderate (e.g. 15D to 600 psig) or high (above 600 psig) pressure ~oilers, dosing the feed water with carbonate is not satisfactory since at the water boiler point under these pressures the carbonate will tend to decompose giving rise to carbon dioxide; at these temperatures carbon dioxide has a very corrosive effect on the metal surfaces. Accordingly, for such boilers and, indeed, for low pressure boilers as well (instead of carbonate addition) it is usual to add a soluble phosphate, typically sodium phosphate eOg. disodium phosphate, or trisodium phosphate to the feed water, although potassium phosphate and other phosphates including polyphosphates e.g. sodium hexametaphosphate and fluorophosphates can also be used. This ensures that all the calcium present precipitates as calcium phosphate which is then dispersed with a dispersant as before. This material can be removed periodically, as in the other systems, with the water drained from the boiler by :
~'33~22 blowdown where the sludge containing boiler water is removed through a valve by rapidly reducing the pressure within the boiler. Nevertheless, not all the calcium phosphate i5 removed in this way with the result that a scale of calcium phosphate forms which, in due course, has to be removed after shutting down the boiler.
In practice, one adds more than the stoichiometric amount of phosphate needed to reach with the calcium in the water. The aim is to add sufficient phosphate to give an exces~ at all times, e.g. 10 to 20 ppm in the boiler;
the excess required can be established by consulting authoritative guidelines such as British Standard 2486.
Such standards also specify the degree of alkalinity needed, generally a pH of 9.5 to 12. This alkalinity is needed for seYeral reasons. First, by keeping the pH
sufficiently high one ensures that all the calcium phosphate precipitates as hydroxy apatite, a basic calcium phosphate which is easy to condition and also ensures low solubility of the calcium phosphate. Second, alkaline conditions prevent corrosion. Third, such a pH ensures that any magnesium ions present are precipitated as magnesium hydroxide.
This illustrates a further difference between the way in which one tackles scale in cooling water and desalination systems, on the one hand, and pressurised boiler systems, on the other. In cooling water systems, ~L233722 scaling due to magnesium is seldom significant because the magnesium stays in solution in the water which rarely exceeds a temperature of about 50C. In desalination systems magnesium scaling does become a significant problem because temperatures rise to 100C and because salt water contains a much higher magnesium content than does ordinary industrial water and, as a result, special steps have to be taken~ In effect the magnesium bicarbonate is first converted to carbon dioxide and magnesium carbonate which is hydrolysed by the hot water to magnesium hydroxide; due to the high magnesium content the solubility product is exceeded with a result that it starts to come out of solution. In contrast to the situation with pressurised boiler feed water, salt water is not significantly alkaline with the result that the magnesium hydroxide has a greater tendency to stay in solution. At a pH of 9.5 to 12, however magnesium hydroxide will precipitate even in the cold so that at the high temperatures involved in pressurised boilers there is usually no chance of scaling due to magnesium hydroxide.
It is also of interest to note that in cooling water systems it is not uncommon to add acid (rather than alkali) in order to try and keep more calcium carbonate in solution.
3~
It has now surprisingly been found that certain specific sulphonate copolymers are effective for controlling the formation of scale in pressurised boilers~ It will be appreciated that by ~pressurised boilers~ we mean boilers operating at a pressure of at least 50 psig, generally at least 80 psig, typically 80 to 150 psig (low pressure), generally 150 to 600 psig ~moderate pressure) and above 600 and up to, say 2000 psig (high pressure). In such boilers the water will be at its boiling point which will vary from about 298F at 80 PSIG, to about 324~F at 80 PSIG, to about 366F at 150 PSIG, to about 489F at 600 PSIG to about 637F at 2000 PSIG.
Furthermore, it has been found that these particular copolymers provide the very real practical advantage that they will, in factl when present in the boiler water, actually remove scale which is already presentO In other words, these specific copolymers have an "in service"
cleaning effect. This cleaning effect i5 not specific to the particular scale which has been deposited from the feed water currently in use; in other words the copolymers will also remove scale which may have formed from previous operation of the boiler using a different feed water.
Thus if a boiler has been operated incorrectly by allowing the composition of the feed water to vary without adequate controls and, as a result calcium phosphate scale allowed 33~22 to form, that is there is old scale present, regardless of the additive which may have been used, then by dosing the feed water with the specific copolymers used in the present invention the scale can be removed while the boiler is operating under load.
It should be added that this surprising in service cleaning effect is only observed when using the high temperatures involved in pressurised boilers. Thus, these same copolymers are not effective for removing scale from c~oling systems even though they may be effective in ~ inhibiting the formation of fresh scale.
According to ~he present invention there is provided a method of controlling scale in a pressurised boiler which comprises adding to the boiler at least a scale controlling amount of a copolymer which possesses recurring units of the formula - CH - CH-COOH COOH
; : and the formula ~ -CH2- CH -z : 20 where Z represents -SO3H or -CH2SO3H, or a water soluble salt thereof, typically an alkali metal salt such as the sodium salt, although potassium, ammonium, zinc and lower amine salts and other water soluble salts may be :~3~3~2~
~ 10 --used. The free acids may also be used and all of the acid hydrogens need not be replaced nor need the cation be the same for those replaced. Thus, the cation may be any one of or a mixture of NH~, E, Na, K. etc. In another aspect the present invention provides a method of removing scale from a scaled pressurised boiler which comprises adding to the aqueous system of said boiler a scale removing amount of the specified copolymer. The invention further provides a composition suitable for addition to a pressurised boiler water system which comprises a copolymer which possesses xecurring units of the formula - C~ - CH -COOH COOH
and of the formula where Z represents ~SO3H or -CH2S03H, or a water soluble salt thereof, and a water soluble calcium precipitating agent.
The copolymers are conveniently prepared by polymerising maleic acid or anhydride or fumaric acid with the vinyl or allyl sulphonic acid or an alkali metal salt thereof using conventional procedures. Thus con~entional addition polymerisation methods using light or free radical initiators may be employed. Generally, the copolymerisation may be effected at from about 30 to about 120C using a peroxide catalyst such as hydrogen peroxide or ben20yl peroxide in an inert medium. The copolymer may be derived, for example, ",J
~;~33~
- lOa -by solution polymerisation of maleic acid and sodium allyl sulphonate in the presence of hydrogen peroxide. The salts can of course be obtained using conventional methods.
The relative proportions of sulphonate and carboxylate components depend on some extent upon the degree of scaling to be treated. The copolymer generally contains ~,~33~
from about 10 to about 80 mol per cent of sulphonate moieties and correspondingly rom 90 ~o abou~ 20 mol percent of the carboxylate moieties. Preferably, the sulphonate moieties comprise about 25 ~o about 75 mol per cent of the copolymer and the carboxylate moieties comprise from about 75 to about 25 mol per cent. For the vinyl sulphonate copolymer, the sulphonate moieties especially comprise about 50 to about 75 mol per cent of the copolymer and the carboxylate moieties from about 50 to about 25 mol per cent.
The average molecular weight of the copolymer is not critical 50 long as the polymer is water soluble.
Generally, the weight average molecular weight ranges from about 500 to about 100,000. The molecular weight is preferably from about 800 to about 25,000 and especially is from about 1,000 to about 15,000. A copolymer having a mol ratio of maleic acid or anhydride to allyl sulphonic acid of about 1:1 and a molecular weight of about 2,000 is especially preferred. Other preferred copolymers include those havin9 a mol ratio of maleic acid or anhydride to vinyl sulphonic acid of about 1:1.5 or about 1:3, and a molecular weight of about 7,000 to 9,000. Although the best results are generally obtained with the 1:3 mole ratio, in practice because of the relatively high cost of the vinyl sulphonic acid, a mole ratio 1:1.5 is generally preferred eYen though the results are not quite so good.
Jl~.t~
It will be appreciated that it will sometimes be simpler to dose the feed water simultaneously with the specific copolymer and the water soluble carbonate, typically sodium carbonate, or phosphate such as those specified above or other hardness precipitating agent as appropriate to the temperatures and pressures to be used in the boiler; the pH will normally be adjusted if necessary to 9.5 to 12, preferably 10 to 11. This pH can be achieved by maintaining the recommended alkalinity value for the particular boiler employed by adding appropriate quantities of caustic soda. This alkalinity value can be determined using well known methods, such as by titration against standard acid. Accordingly, the present invention also provides a composition suitable for the addition to a pressurised boiler water system which comprises a copolymer having recurring units of the formulae set out above and a water soluble hardness precipitating agent. Typically the copolymer is added as an aqueous solution generally containing 0.1 to 50%, preferably 2.5 to lD~, especially 3 to 5~ by weight (active) of the copolymer. The amount of hardness precipitating agent in the solution is suitable from 5 to 50% (or solubility limit) preferably from 15 to 35~, especially 25 to 35~, by weight. Thus the relative weight proportions of the copolymer and hardness precipitating ~;33'~
agent are suitably from 0.1:50 ~o 10:1, preferably from 1:15 to 2:3, especially from 1:11 to 1:3.
Of course other conventional additives can also be incorporated in the water including alkalis, lignin derivatives, other polymers, tannins, biocides and corrosion inhibitors.
The copolymer may be introduced at any location where it will be quickly and efficiently mixed with the water of the system although it will generally be most convenient to add it to the make-up or feed water lines through whish the water enters the boiler. Typically, an injector calibrated to deliver a predetermined amount periodically or continuously to the make-up water is employed.
The amount of the copolymer added to the water is a 15 substoichiometric amount that is-effective to control, i.e., inhibit and remove the scale and naturally this depends on the nature of the aqueous system to be treated, especially its calcium content. The amount depends to ; some extent on the concentration o~ suspended solids and 20 existing levels of solids build up in the system.
Typically, amounts from about 0.1 to about 400 ppm, preferably from about 1 to about BO ppm and especially from about 5 to about 50 ppm active in the boiler water are used. In general, as the amount of precipitating 25 agent needed for the calcium increases so does the amount . :
" .
~hddal~ I
- i4 -of copolymer. Typically for an especially preferred composition the amount of composition added will be about 20 to about 2500 ppm.
The following Examples further illustrate the present invention. In these Examples the properties of the additives were evaluated in a small laboratory boiler which had three removable tubes as described in the proceedings of the 15th Annual Water Con~erence, Engineers Society of the Western Pennsylvania, pages 87-102 (1954).
The feed water for the laboratory boiler was prepared by diluting Lake Zurich, Illinois, tap water with distilled water to 40 ppm total hardness as CaCO3 and adding calcium chloride tD provide a 6:1 elemental calcium to magnesium ratio. The feed water and chemical treatment solutions were fed to t~e boiler in a ratio of 3 volumes of feed water to 1 volume of solution giving a feed water total hardness of 30 ppm CaCO3. The-scaling tests for all the treatment solutions were conducted by adjusting boiler blow-d~wn -to 10~ of the boiler feed water giving an 20 approximately 10 fold concentration of the boiler water salines and adjusting the composition of the treatment solution to give a boiler water after the 10 fold concentration haYing the composition shown in Table I.
. , , 33~
TABLE I
Sodium Hydroxide as NaOH 258 ppm Sodium Carbonate as Na2CO3 120 ppm Sodium Chloride as ~aCl 681 ppm Sodium Sulfite as Na2SO3 50 ppm Sodium Sulfate as Na2SO4 819 ppm Silica zs SiO2 less than 1 ppm Iron as Fe less than 1 ppm Phosphate as PO4 10-20 ppm In the first series of tests, the boiler was run for 45 hours at a boiler water pressure of 400 psigO At the completion of each test, the boiler tubes were individually removed from the boiler and the scale or deposit present on 6" of the central length of each tube was removed by scraping, collected in a tared vial, and weighed. The results obtaioed are shown in Taùle II.
;:
:
TABLE II
Run Additives Active Scaling Scale No. Dosage Rate Reduction, in the g/ft2/hr Boiler Water ppm 1 None - 0.213
~ This invention relates to the treatment of a~ueous : systems used in pressurised boilers.
The water used in steam generating boilers, cooling :~ ~ towers, desalination units and other industrial aqueous ! 5 systems contains various impurities. The impurities typically include alkaline earth cations, principally ; ~ calcium and:magnesium, and several anions including : ~ bicarbonate, carbonate, sulphater oxalate, phosphate, silicate and~fluoride~ The most common impurities in ~ 10 industrial water supplies are the water hardening calcium, : : magnesium and carbonate ions although sulphate is usually ~ ~ also present. The salts of these metal ions, especislly , ,: :
, ,, .
~33~2 the carbonates, tend to precipitate forming solid accumulations on the surfaces of the system and these accumulations can give rise to the formation of scale on hot surfaces. The water may also contain various solids such as mud, clay, iron oxides, silt, sand and other mineral matter as well as microbiological debris which accumulate as sludge in the system. Naturally sludge and scale deposits greatly reduce heat transfer efficiency by settling at low flow points in the system and thus limiting the circulation of the water and insulating it from the heat transfer surfaces. In addition, corrosion of metal surfaces under the deposits is facilitated since corrosion control agents are unable to contact the surfaces effectively. Again, the deposits harbour bacteria. Removal of the deposits can cause expensive delays and shutdown of the system.
Since prior treatments such as softening, coagulation and filtration do not adequately remove solids and solid forming substances various chemicals have been used to counteract the adverse effects of scale and sludge in aqueous systems. In cooling water systems and desalination plants the chemicals are commonly added in order to increase the threshold at which precipitation occurs; it has also been thought that the chemical forms a 25 film on the hot surfaces where scale formation is likely ....
~L;233~
to occ~r thereby preventing scale forming material from adhering to the hot surfaces in question. A variety of different chemicals have been used for this purpose including pGlycarboxylates and other soluble, polar polymers such as acrylate and methacrylate polymers. The presence of small quantities of these polymers can have a marked effect on the system.
Although these various chemicals are quite effective in industrial cooling towers and desalination plants and the like quite different problems arise in water which is used in pressurised boilers due to the much higher temperatures involved; the boiler point of water at the lowest pressure normally used, 80 psig, is already 324F
(about 162~C)~
Because of the greater problems involved, the water : used for such pressurised boilers is first subjected to a deioniser or to base exchange, the former being the more effective~ Even so these treatments are not always f~lly effective with the result that some calcium and magnesium ions, in particular, remain in the boiler feedwater along with their associated anions.
In view of the higher temperatures involved, it is not practical to try and keep the calcium in solution as is : the case with cooling water; an exception to this is the ,, ,-use of chelants but these present some other problems of application in particular correct dosing. Likewise, it is much more difficult to prevent the solid deposits from contacting the very hot surfaces thereby giving rise to scaling.
As a result, different techniques have to be adopted for the prevention of scale in pressurised boiler systems.
For boilers which are subjected only to low (up to, say, 150 psig) pressures it is not unusual to add a water soluble carbonate to the feed water in order to cause all the calcium present to precipitate as carbonate and to add also a dispersant to prevent the precipitated material from settling on the hot surfaces. This is, of course, in complete contrast with the situation with cooling water where the aim is to keep the carbonate concentration to a minimum and to keep that concentration in solution.
Calcium sulphate is very much more soluble than calcium carbonate so that it does not present a significant problem in cooling water and desalination systems. In pressurised boilers, however, scaling due to calcium sulphate can occur so that it is desirable to ensure that all the calcium is precipitated.
. , , ,. ..
~2~3~2;~
Inevitably~ however, dosing with carbonate is not fully effective with the result that some scale does still form. Over a period, scale can accumulate to such an extent that the hoiler has to be shut down and the scale removed. This is essential since scale deposits can cause localised overheating and even rupture in the boiler.
With moderate (e.g. 15D to 600 psig) or high (above 600 psig) pressure ~oilers, dosing the feed water with carbonate is not satisfactory since at the water boiler point under these pressures the carbonate will tend to decompose giving rise to carbon dioxide; at these temperatures carbon dioxide has a very corrosive effect on the metal surfaces. Accordingly, for such boilers and, indeed, for low pressure boilers as well (instead of carbonate addition) it is usual to add a soluble phosphate, typically sodium phosphate eOg. disodium phosphate, or trisodium phosphate to the feed water, although potassium phosphate and other phosphates including polyphosphates e.g. sodium hexametaphosphate and fluorophosphates can also be used. This ensures that all the calcium present precipitates as calcium phosphate which is then dispersed with a dispersant as before. This material can be removed periodically, as in the other systems, with the water drained from the boiler by :
~'33~22 blowdown where the sludge containing boiler water is removed through a valve by rapidly reducing the pressure within the boiler. Nevertheless, not all the calcium phosphate i5 removed in this way with the result that a scale of calcium phosphate forms which, in due course, has to be removed after shutting down the boiler.
In practice, one adds more than the stoichiometric amount of phosphate needed to reach with the calcium in the water. The aim is to add sufficient phosphate to give an exces~ at all times, e.g. 10 to 20 ppm in the boiler;
the excess required can be established by consulting authoritative guidelines such as British Standard 2486.
Such standards also specify the degree of alkalinity needed, generally a pH of 9.5 to 12. This alkalinity is needed for seYeral reasons. First, by keeping the pH
sufficiently high one ensures that all the calcium phosphate precipitates as hydroxy apatite, a basic calcium phosphate which is easy to condition and also ensures low solubility of the calcium phosphate. Second, alkaline conditions prevent corrosion. Third, such a pH ensures that any magnesium ions present are precipitated as magnesium hydroxide.
This illustrates a further difference between the way in which one tackles scale in cooling water and desalination systems, on the one hand, and pressurised boiler systems, on the other. In cooling water systems, ~L233722 scaling due to magnesium is seldom significant because the magnesium stays in solution in the water which rarely exceeds a temperature of about 50C. In desalination systems magnesium scaling does become a significant problem because temperatures rise to 100C and because salt water contains a much higher magnesium content than does ordinary industrial water and, as a result, special steps have to be taken~ In effect the magnesium bicarbonate is first converted to carbon dioxide and magnesium carbonate which is hydrolysed by the hot water to magnesium hydroxide; due to the high magnesium content the solubility product is exceeded with a result that it starts to come out of solution. In contrast to the situation with pressurised boiler feed water, salt water is not significantly alkaline with the result that the magnesium hydroxide has a greater tendency to stay in solution. At a pH of 9.5 to 12, however magnesium hydroxide will precipitate even in the cold so that at the high temperatures involved in pressurised boilers there is usually no chance of scaling due to magnesium hydroxide.
It is also of interest to note that in cooling water systems it is not uncommon to add acid (rather than alkali) in order to try and keep more calcium carbonate in solution.
3~
It has now surprisingly been found that certain specific sulphonate copolymers are effective for controlling the formation of scale in pressurised boilers~ It will be appreciated that by ~pressurised boilers~ we mean boilers operating at a pressure of at least 50 psig, generally at least 80 psig, typically 80 to 150 psig (low pressure), generally 150 to 600 psig ~moderate pressure) and above 600 and up to, say 2000 psig (high pressure). In such boilers the water will be at its boiling point which will vary from about 298F at 80 PSIG, to about 324~F at 80 PSIG, to about 366F at 150 PSIG, to about 489F at 600 PSIG to about 637F at 2000 PSIG.
Furthermore, it has been found that these particular copolymers provide the very real practical advantage that they will, in factl when present in the boiler water, actually remove scale which is already presentO In other words, these specific copolymers have an "in service"
cleaning effect. This cleaning effect i5 not specific to the particular scale which has been deposited from the feed water currently in use; in other words the copolymers will also remove scale which may have formed from previous operation of the boiler using a different feed water.
Thus if a boiler has been operated incorrectly by allowing the composition of the feed water to vary without adequate controls and, as a result calcium phosphate scale allowed 33~22 to form, that is there is old scale present, regardless of the additive which may have been used, then by dosing the feed water with the specific copolymers used in the present invention the scale can be removed while the boiler is operating under load.
It should be added that this surprising in service cleaning effect is only observed when using the high temperatures involved in pressurised boilers. Thus, these same copolymers are not effective for removing scale from c~oling systems even though they may be effective in ~ inhibiting the formation of fresh scale.
According to ~he present invention there is provided a method of controlling scale in a pressurised boiler which comprises adding to the boiler at least a scale controlling amount of a copolymer which possesses recurring units of the formula - CH - CH-COOH COOH
; : and the formula ~ -CH2- CH -z : 20 where Z represents -SO3H or -CH2SO3H, or a water soluble salt thereof, typically an alkali metal salt such as the sodium salt, although potassium, ammonium, zinc and lower amine salts and other water soluble salts may be :~3~3~2~
~ 10 --used. The free acids may also be used and all of the acid hydrogens need not be replaced nor need the cation be the same for those replaced. Thus, the cation may be any one of or a mixture of NH~, E, Na, K. etc. In another aspect the present invention provides a method of removing scale from a scaled pressurised boiler which comprises adding to the aqueous system of said boiler a scale removing amount of the specified copolymer. The invention further provides a composition suitable for addition to a pressurised boiler water system which comprises a copolymer which possesses xecurring units of the formula - C~ - CH -COOH COOH
and of the formula where Z represents ~SO3H or -CH2S03H, or a water soluble salt thereof, and a water soluble calcium precipitating agent.
The copolymers are conveniently prepared by polymerising maleic acid or anhydride or fumaric acid with the vinyl or allyl sulphonic acid or an alkali metal salt thereof using conventional procedures. Thus con~entional addition polymerisation methods using light or free radical initiators may be employed. Generally, the copolymerisation may be effected at from about 30 to about 120C using a peroxide catalyst such as hydrogen peroxide or ben20yl peroxide in an inert medium. The copolymer may be derived, for example, ",J
~;~33~
- lOa -by solution polymerisation of maleic acid and sodium allyl sulphonate in the presence of hydrogen peroxide. The salts can of course be obtained using conventional methods.
The relative proportions of sulphonate and carboxylate components depend on some extent upon the degree of scaling to be treated. The copolymer generally contains ~,~33~
from about 10 to about 80 mol per cent of sulphonate moieties and correspondingly rom 90 ~o abou~ 20 mol percent of the carboxylate moieties. Preferably, the sulphonate moieties comprise about 25 ~o about 75 mol per cent of the copolymer and the carboxylate moieties comprise from about 75 to about 25 mol per cent. For the vinyl sulphonate copolymer, the sulphonate moieties especially comprise about 50 to about 75 mol per cent of the copolymer and the carboxylate moieties from about 50 to about 25 mol per cent.
The average molecular weight of the copolymer is not critical 50 long as the polymer is water soluble.
Generally, the weight average molecular weight ranges from about 500 to about 100,000. The molecular weight is preferably from about 800 to about 25,000 and especially is from about 1,000 to about 15,000. A copolymer having a mol ratio of maleic acid or anhydride to allyl sulphonic acid of about 1:1 and a molecular weight of about 2,000 is especially preferred. Other preferred copolymers include those havin9 a mol ratio of maleic acid or anhydride to vinyl sulphonic acid of about 1:1.5 or about 1:3, and a molecular weight of about 7,000 to 9,000. Although the best results are generally obtained with the 1:3 mole ratio, in practice because of the relatively high cost of the vinyl sulphonic acid, a mole ratio 1:1.5 is generally preferred eYen though the results are not quite so good.
Jl~.t~
It will be appreciated that it will sometimes be simpler to dose the feed water simultaneously with the specific copolymer and the water soluble carbonate, typically sodium carbonate, or phosphate such as those specified above or other hardness precipitating agent as appropriate to the temperatures and pressures to be used in the boiler; the pH will normally be adjusted if necessary to 9.5 to 12, preferably 10 to 11. This pH can be achieved by maintaining the recommended alkalinity value for the particular boiler employed by adding appropriate quantities of caustic soda. This alkalinity value can be determined using well known methods, such as by titration against standard acid. Accordingly, the present invention also provides a composition suitable for the addition to a pressurised boiler water system which comprises a copolymer having recurring units of the formulae set out above and a water soluble hardness precipitating agent. Typically the copolymer is added as an aqueous solution generally containing 0.1 to 50%, preferably 2.5 to lD~, especially 3 to 5~ by weight (active) of the copolymer. The amount of hardness precipitating agent in the solution is suitable from 5 to 50% (or solubility limit) preferably from 15 to 35~, especially 25 to 35~, by weight. Thus the relative weight proportions of the copolymer and hardness precipitating ~;33'~
agent are suitably from 0.1:50 ~o 10:1, preferably from 1:15 to 2:3, especially from 1:11 to 1:3.
Of course other conventional additives can also be incorporated in the water including alkalis, lignin derivatives, other polymers, tannins, biocides and corrosion inhibitors.
The copolymer may be introduced at any location where it will be quickly and efficiently mixed with the water of the system although it will generally be most convenient to add it to the make-up or feed water lines through whish the water enters the boiler. Typically, an injector calibrated to deliver a predetermined amount periodically or continuously to the make-up water is employed.
The amount of the copolymer added to the water is a 15 substoichiometric amount that is-effective to control, i.e., inhibit and remove the scale and naturally this depends on the nature of the aqueous system to be treated, especially its calcium content. The amount depends to ; some extent on the concentration o~ suspended solids and 20 existing levels of solids build up in the system.
Typically, amounts from about 0.1 to about 400 ppm, preferably from about 1 to about BO ppm and especially from about 5 to about 50 ppm active in the boiler water are used. In general, as the amount of precipitating 25 agent needed for the calcium increases so does the amount . :
" .
~hddal~ I
- i4 -of copolymer. Typically for an especially preferred composition the amount of composition added will be about 20 to about 2500 ppm.
The following Examples further illustrate the present invention. In these Examples the properties of the additives were evaluated in a small laboratory boiler which had three removable tubes as described in the proceedings of the 15th Annual Water Con~erence, Engineers Society of the Western Pennsylvania, pages 87-102 (1954).
The feed water for the laboratory boiler was prepared by diluting Lake Zurich, Illinois, tap water with distilled water to 40 ppm total hardness as CaCO3 and adding calcium chloride tD provide a 6:1 elemental calcium to magnesium ratio. The feed water and chemical treatment solutions were fed to t~e boiler in a ratio of 3 volumes of feed water to 1 volume of solution giving a feed water total hardness of 30 ppm CaCO3. The-scaling tests for all the treatment solutions were conducted by adjusting boiler blow-d~wn -to 10~ of the boiler feed water giving an 20 approximately 10 fold concentration of the boiler water salines and adjusting the composition of the treatment solution to give a boiler water after the 10 fold concentration haYing the composition shown in Table I.
. , , 33~
TABLE I
Sodium Hydroxide as NaOH 258 ppm Sodium Carbonate as Na2CO3 120 ppm Sodium Chloride as ~aCl 681 ppm Sodium Sulfite as Na2SO3 50 ppm Sodium Sulfate as Na2SO4 819 ppm Silica zs SiO2 less than 1 ppm Iron as Fe less than 1 ppm Phosphate as PO4 10-20 ppm In the first series of tests, the boiler was run for 45 hours at a boiler water pressure of 400 psigO At the completion of each test, the boiler tubes were individually removed from the boiler and the scale or deposit present on 6" of the central length of each tube was removed by scraping, collected in a tared vial, and weighed. The results obtaioed are shown in Taùle II.
;:
:
TABLE II
Run Additives Active Scaling Scale No. Dosage Rate Reduction, in the g/ft2/hr Boiler Water ppm 1 None - 0.213
2 Allyl sulphonic 5 D.063 ~0.4 acid and maleic acid copolymer ~1 1; wt.av.M.W. = about 2,000)
3 Sodium vinyl 5 0.046 78.4 sulfonate and maleic acid copolymer (1.5:1; wt.av.M.W. = about 7,000 to 9,000)
4 Sodium 10 0.094 55.9 vinyl sulfonate and fumaric acid copolymer (1.5:1; wt.av.M.W. = about 7,000 - 9,000) Allyl sulphonic 10 0.006 97.2 acid and maleic acid copolymer (as in Example 2) 6 Sodium vinyl 10 0.014 93.4 sulfonate and maleic acid copolymer (as in Example 3) These results show that the copolymers used in the present invention are effective ~or reducing the rate of scaling in a pressurised boiler.
In a second series of tests, the system was first run for 45 hours without any addition of polymer and then one of the three tubes was taken out and replaced by a clean tube. The system was then run for a further 45 hours but this time with polymer added.
After this further period of 45 hours the scale in the three tubes , , . ~
~ ~33~
~f~O
is weighed as before. Thus comparison of the results of this test with those of an untreated blank (no polymer added during the second 45 hour period) enables one to assess whether the polymer is capable sf r~moving scale and also preventing the formation of scale on a clean tube. The results obtained are shown in following Table III.
TABLE III
Run Additives Active Dosage Scale No. in the Boiler Reduction Water, ppm %
7 Allyl sulphonic 30 112.0 acid and maleic acid copolymer (as in Example 2) 8 Sodium vinyl sulfonate 30 108.8 and maleic acid copolymer ~as in Example 3) 9 Sodium vinyl sulfonate and 30 123.9 maleic acid copolymer (3:1; wt.av.M.W. = about 6,000) It is clear therefore,-that the use of these polymers is effective not only in inhibition of scale formation but also, since the scale reduction is greater than 100~, in removing existing scale.
In order to assess the inservice cleaning ability of the copolymers in a coolln~ water system a clean metal heater was fixed in a glass t~be assembly through which water heated to 60C. was circulated by means of a pump. The assembly formed part of a .~,..
~:Z33~:%
closed system provided with an expansion tank open to the atmosphere. The heater was removed and placed in dilute acid to ~ remove the scale thereon. The acid solution was then titrated with ; a standard EDTA solution to determine the amount of calcium carbonate scale (as Ca ) from which the weight of calcium carbonate scale was determined.
In the first test, a synthetic water adjusted to 400 ppm of calcium and 400 ppm alkalinity (as bicarbonate) was circulated for 6 hours. On weighing the heater it was found that 780 milligrams 1~ Of calcium carbonate scale had formed.
The test was then repeated, after 6 hours 10 ppm of a copolymer of maleic acid and allyl sulphonic acid (as in Example 2) was added and circulation continued for 45 hours. ~he heater was then removed and tested as above; it was again found that 7B0 1~ milligrams of calcium carbonate scale had formed. It is apparent, therefore, that the copolymer did not remove any scale under these conditions.
~:
:
In a second series of tests, the system was first run for 45 hours without any addition of polymer and then one of the three tubes was taken out and replaced by a clean tube. The system was then run for a further 45 hours but this time with polymer added.
After this further period of 45 hours the scale in the three tubes , , . ~
~ ~33~
~f~O
is weighed as before. Thus comparison of the results of this test with those of an untreated blank (no polymer added during the second 45 hour period) enables one to assess whether the polymer is capable sf r~moving scale and also preventing the formation of scale on a clean tube. The results obtained are shown in following Table III.
TABLE III
Run Additives Active Dosage Scale No. in the Boiler Reduction Water, ppm %
7 Allyl sulphonic 30 112.0 acid and maleic acid copolymer (as in Example 2) 8 Sodium vinyl sulfonate 30 108.8 and maleic acid copolymer ~as in Example 3) 9 Sodium vinyl sulfonate and 30 123.9 maleic acid copolymer (3:1; wt.av.M.W. = about 6,000) It is clear therefore,-that the use of these polymers is effective not only in inhibition of scale formation but also, since the scale reduction is greater than 100~, in removing existing scale.
In order to assess the inservice cleaning ability of the copolymers in a coolln~ water system a clean metal heater was fixed in a glass t~be assembly through which water heated to 60C. was circulated by means of a pump. The assembly formed part of a .~,..
~:Z33~:%
closed system provided with an expansion tank open to the atmosphere. The heater was removed and placed in dilute acid to ~ remove the scale thereon. The acid solution was then titrated with ; a standard EDTA solution to determine the amount of calcium carbonate scale (as Ca ) from which the weight of calcium carbonate scale was determined.
In the first test, a synthetic water adjusted to 400 ppm of calcium and 400 ppm alkalinity (as bicarbonate) was circulated for 6 hours. On weighing the heater it was found that 780 milligrams 1~ Of calcium carbonate scale had formed.
The test was then repeated, after 6 hours 10 ppm of a copolymer of maleic acid and allyl sulphonic acid (as in Example 2) was added and circulation continued for 45 hours. ~he heater was then removed and tested as above; it was again found that 7B0 1~ milligrams of calcium carbonate scale had formed. It is apparent, therefore, that the copolymer did not remove any scale under these conditions.
~:
:
Claims (26)
1. A method for the treatment of scale in a pressurised boiler water system which comprises adding to the system at least a scale controlling amount of a copolymer which possesses recurring units of the formula and of the formula where Z represents -SO3H or -CH2SO3H, or a water soluble salt thereof.
2. A method according to claim 1 in which the copolymer is a copolymer of maleic acid and allyl sulfonic acid.
3. A method according to claim 1 in which the copolymer contains from about 25 to about 75 mole per cent sulphonate moieties and correspondingly from about 75 to about 25 per cent carboxylate moieties.
4. A method according to claim 3 in which the copolymer is derived from vinyl sulfonic acid and contains from about 50 to about 75 per cent sulphonate moieties and correspondingly from about 50 to about 25 percent carboxylate moieties.
5. A method according to claim 2 in which the said copolymer has a mol ratio of allyl sulphonic acid to maleic acid or anhydride of about 1:1 and has a molecular weight of about 800 to about 25,000.
6. A method according to claim 4 in which the said copolymer has a mol ratio of vinyl sulphonic acid to maleic acid or anhydride of about 1.5:1 and has a molecular weight of about 800 to about 25,000.
7. A method according to claim 1 in which the copolymer is added in an amount from 0.1 to about 400 ppm.
8. A method according to claim 7 in which the copolymer is added in an amount of about 1 to about 80 ppm.
9. A method according to claim 1 in which a water soluble precipitating agent is also added to the system.
10. A method according to claim 9 in which a water soluble carbonate or phosphate is added to the system.
11. A method according to claim 10 in which disodium or trisodium phosphate or sodium metaphosphate is added to the system.
12. A method according to claim 1 in which the feed water for the system is adjusted to a pH of 9.5 to 12.
13. A method for the inhibition and removal of scale in a pressurised boiler water system which comprises adding to the feed water for the system a water soluble phosphate in an amount in excess of the stoichiometric amount needed to neutralise the calcium in the water and a copolymer of maleic acid or anhydride and allyl sulphonic acid or a water-soluble salt thereof in an amount sufficient to provide about 0.1 to about 400 ppm of the copolymer in the boiler water and, if necessary, adjusting the pH of the water to 10 to 11 by addition of caustic soda.
14. A composition suitable for addition to a pressurised boiler water system which comprises a copolymer which possesses recurring units of the formula and of the formula where Z represents -SO3H or -CH2SO3H, or a water soluble salt thereof, and a water soluble calcium precipitating agent.
15. A composition according to claim 14 in which the copolymer is a copolymer of maleic acid and allyl sulfonic acid.
16. A composition according to claim 14 in which the copolymer contains from about 25 to about 75 mol per cent sulphonate moieties and correspondingly from about 75 to about 25 per cent carboxylate moieties.
17. A composition according to claim 16 in which the copolymer is derived from vinyl sulphonic acid and contains from about 50 to about 75 mol per cent sulphonate moieties and correspondingly from about 50 to about 25 mol per cent carboxylate moieties.
18. A composition according to claim 15 in which the copolymer has a mol ratio of allyl sulphonic acid to maleic acid or anhydride of about 1:1 and has a molecular weight of about 800 to 25,000.
19. A composition according to claim 17 in which the copolymer has a mol ratio of vinyl sulphonic acid to maleic acid or anhydride of about 1.5:1 and has a molecular weight of about 800 to about 25,000.
20. A composition according to claim 14 in which the water soluble hardness precipitating agent is a water soluble carbonate or phosphate.
21. A composition according to claim 20 in which the water soluble hardness precipitating agent is di-sodium or tri-sodium phosphate or sodium metaphosphate.
22. A composition according to claim 14 which is an aqueous solution containing from about 0.1 to 50% by weight of the copolymer.
23. A composition according to claim 22 which is an aqueous solution containing from about 2.5 to 10% by weight of said copolymer and from about 5 to 50% by weight of the said hardness precipitating agent.
24. A composition according to claim 14 which also contains at least one water treatment additive selected from the group consisting of alkalis, lignin derivatives, other polymers, tannins, biocides and corrosion inhibitors.
25. A method according to claim 10 wherein the copolymer is a copolymer of a maleic acid or anhydride and allyl sulfonic acid having a molecular weight between 500 and 100,000 and a mole ratio of maleic moieties to allyl sulfonic acid moieties between 3:1 and 1:3, or a water-soluble salt of said copolymer, and wherein the copolymer is added to a boiler system in which the boiler water contains calcium and reaches operating temperatures of at least about 298°F and in which more than the stoichio-metric amount of phosphate needed to react with said calcium is maintained in the boiler water such that scale comprising calcium phosphate is formed, the copolymer addition being made in an amount between 0.1 ppm and 400 ppm effective to remote previously-formed calcium phosphate scale while operating temperatures of the boiler water are being attained.
26. A method according to claim 10 wherein the copolymer is a copolymer of maleic acid or anhydride and vinyl sulfonic acid having a molecular weight between 500 and 100,000 and a mole ratio of maleic moieties to vinyl sulfonic acid moieties between 3:1 and 1:3, or a water-soluble salt of said copolymer, and wherein the copolymer is added to a boiler system in which the boiler water contains calcium and reaches operating temperatures of at least about 298°F
and in which more than the stoichiometric amount of phosphate needed to react with said calcium is maintained in the boiler water such that scale comprising calcium phosphate is formed, the copolymer addition being made in an amount between 0.1 ppm and 400 ppm effective to remove previously-formed calcium phosphate scale while operating temperatures of the boiler water are being attained.
and in which more than the stoichiometric amount of phosphate needed to react with said calcium is maintained in the boiler water such that scale comprising calcium phosphate is formed, the copolymer addition being made in an amount between 0.1 ppm and 400 ppm effective to remove previously-formed calcium phosphate scale while operating temperatures of the boiler water are being attained.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB08332800A GB2152919B (en) | 1983-12-08 | 1983-12-08 | Method of controlling scale in pressurised boilers |
| GB8332800 | 1983-12-08 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1233722A true CA1233722A (en) | 1988-03-08 |
Family
ID=10553025
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000469567A Expired CA1233722A (en) | 1983-12-08 | 1984-12-07 | Method of controlling scale in pressurised boilers |
Country Status (13)
| Country | Link |
|---|---|
| JP (1) | JPS60139397A (en) |
| AU (1) | AU572235B2 (en) |
| CA (1) | CA1233722A (en) |
| DE (1) | DE3444679A1 (en) |
| ES (1) | ES538357A0 (en) |
| FR (1) | FR2556334B1 (en) |
| GB (1) | GB2152919B (en) |
| IT (1) | IT1177376B (en) |
| NL (1) | NL8403714A (en) |
| NZ (1) | NZ210446A (en) |
| PH (1) | PH21200A (en) |
| SE (1) | SE456675B (en) |
| ZA (1) | ZA849464B (en) |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4600524A (en) * | 1983-12-08 | 1986-07-15 | W. R. Grace & Co. | Composition and method for inhibiting scale |
| GB8728162D0 (en) * | 1987-12-02 | 1988-01-06 | Albright & Wilson | Threshold treatment |
| ES2035534T3 (en) * | 1988-08-01 | 1993-04-16 | Calgon Corporation | METHOD TO CONTROL THE DEPOSITION OF INCRUSTATIONS IN AQUEOUS SYSTEMS USING ALYL SULPHONATE-MALEIC ANHYDRIDE POLYMERS. |
| US6020297A (en) * | 1999-04-06 | 2000-02-01 | National Starch And Chemical Investment Holding Corporation | Colorless polymaleates and uses thereof in cleaning compositions |
| US6333005B1 (en) * | 1999-06-16 | 2001-12-25 | Hercules Incorporated | Methods of preventing scaling involving inorganic compositions in combination with copolymers of maleic anhydride and isobutylene, and compositions therefor |
| FI20096408A (en) * | 2009-12-30 | 2011-07-01 | Kemira Oyj | The dispersion composition, its use and the coating composition comprising it and a method for improving the viscosity properties of the coating composition or slurry |
Family Cites Families (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3639278A (en) * | 1967-12-27 | 1972-02-01 | Grace W R & Co | Composition and method for inhibiting and removing scale using glycolic acid and lignosulfonic acid |
| US3879288A (en) * | 1970-07-01 | 1975-04-22 | Frederick Herman Siegele | Process of inhibiting scale formation on walls of structures containing an aqueous system |
| GB1575173A (en) * | 1977-02-07 | 1980-09-17 | American Cyanamid Co | Mixtures of polycationic and polyanionic polymers for scale control |
| US4342652A (en) * | 1978-09-25 | 1982-08-03 | American Cyanamid Company | Process for scale inhibition in evaporative desalination units |
| ZA793301B (en) * | 1978-09-25 | 1980-06-25 | American Cyanamid Co | Process for scale inhibition in evaporative desalination units |
| JPS57174194A (en) * | 1981-04-17 | 1982-10-26 | Deiaaboon Chem Ltd | Treatment of aqueous system |
| DE3230291A1 (en) * | 1981-08-18 | 1983-03-03 | Dearborn Chemicals Ltd., Widnes, Cheshire | COMPOSITION FOR PREVENTING KETTLE IN AQUEOUS SYSTEMS |
| JPS5881494A (en) * | 1981-11-11 | 1983-05-16 | Toagosei Chem Ind Co Ltd | Composition for water purifying agent |
| JPS59162999A (en) * | 1983-03-07 | 1984-09-13 | カルゴン・コ−ポレ−シヨン | Synergistic scale and corrosion control mixture containing carboxylic acid/sulfonic acid polymer |
| EP0210590A3 (en) * | 1983-03-07 | 1988-02-17 | Calgon Corporation | Polymeric additives for water |
-
1983
- 1983-12-08 GB GB08332800A patent/GB2152919B/en not_active Expired
-
1984
- 1984-12-05 ZA ZA849464A patent/ZA849464B/en unknown
- 1984-12-05 NZ NZ210446A patent/NZ210446A/en unknown
- 1984-12-06 NL NL8403714A patent/NL8403714A/en not_active Application Discontinuation
- 1984-12-06 SE SE8406203A patent/SE456675B/en unknown
- 1984-12-06 AU AU36348/84A patent/AU572235B2/en not_active Ceased
- 1984-12-06 IT IT23950/84A patent/IT1177376B/en active
- 1984-12-07 JP JP59257766A patent/JPS60139397A/en active Pending
- 1984-12-07 CA CA000469567A patent/CA1233722A/en not_active Expired
- 1984-12-07 FR FR848418771A patent/FR2556334B1/en not_active Expired - Lifetime
- 1984-12-07 DE DE19843444679 patent/DE3444679A1/en active Granted
- 1984-12-07 ES ES538357A patent/ES538357A0/en active Granted
- 1984-12-07 PH PH31551A patent/PH21200A/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| JPS60139397A (en) | 1985-07-24 |
| ES8601330A1 (en) | 1985-11-01 |
| ES538357A0 (en) | 1985-11-01 |
| AU572235B2 (en) | 1988-05-05 |
| DE3444679C2 (en) | 1992-08-06 |
| AU3634884A (en) | 1985-06-13 |
| NZ210446A (en) | 1988-01-08 |
| FR2556334A1 (en) | 1985-06-14 |
| NL8403714A (en) | 1985-07-01 |
| FR2556334B1 (en) | 1990-05-04 |
| DE3444679A1 (en) | 1985-06-20 |
| GB2152919A (en) | 1985-08-14 |
| SE8406203L (en) | 1985-06-09 |
| GB8332800D0 (en) | 1984-01-18 |
| GB2152919B (en) | 1987-08-26 |
| SE456675B (en) | 1988-10-24 |
| IT1177376B (en) | 1987-08-26 |
| ZA849464B (en) | 1985-08-28 |
| IT8423950A0 (en) | 1984-12-06 |
| SE8406203D0 (en) | 1984-12-06 |
| PH21200A (en) | 1987-08-19 |
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