JPS637120B2 - - Google Patents

Description

[Detailed description of the invention]

Introduction One of the greatest challenges in boiler water treatment lies in the development of simple, easily monitored and easily controlled programs. Ideally it would be a compound that can prevent scaling, provide protection to heat transfer surfaces, and protect the condensate system. However, implementation of that technology has not been able to meet this challenge. For example, chelating agent programs are capable of eliminating stubborn deposits. However, they are also known to cause corrosion under certain conditions. While chelating agents have the ability to solubilize hard metal ions, their strong affinity for iron ions may actually be a corrosion mechanism. Excess residual chelating agent not only prevents magnetite formation, but also flakes off the boiler with its protective magnetite film. It is an object of the present invention to (1) develop a program that provides exceptional scale protection without the corrosion potential; (2) a program that provides the same scale protection ability as a chelating agent without the corrosion potential associated with the application of the chelating agent. The goal is to develop These purposes include the use of certain water-soluble anionic vinyl polymers, either alone or in combination with certain low molecular weight water-soluble polymeric dispersions, including sulfonate-containing hard-dispersed polymers, in specified dosage ranges. achieved. Invention The present invention provides a method for preventing and removing scale caused by hard substances present in boiler water, which is formed on a heat transfer surface in contact with the hard substances present in boiler water and such water. A method for treating such scale comprising at least 30% and preferably from 70% to 100% by weight of such water having a molecular weight ¹ in the range of 500 to 50,000. The amount is 1 to 30 ppm per 1 ppm of hardness material present in boiler water.
treatment with a water-soluble anionic vinyl polymer sufficient to provide a The term "hardness material" is meant to include soluble and insoluble compounds such as calcium, magnesium, iron, copper, aluminum, and the like. In addition to the above properties, water-soluble anionic vinyl polymers must also interact with hardness ions in order to sequester metal ions. The sequestration must be of such a magnitude as to give a chelation value of at least 200 when measured by the specified ionic electrode. In a preferred embodiment of the invention, the molecular weight of the carboxylate polymer ranges from 1000 to
In the range of 30000. In another preferred embodiment, in combination with the anionic water-soluble vinyl polymer, the ability to act as a dispersant for some excess hardness materials not acted upon by the sequestering anionic water-soluble vinyl polymer is provided. Another water-soluble polymer with dispersing properties is used, such as certain sulfonate-containing polymers. ¹ molecular weight is the average molecular weight. Water-soluble sequestering anionic vinyl polymers As noted, these polymers
and the preferred molecular weight range is within the range of 1,000 to 30,000. The polymer may be a homopolymer or copolymer of vinyl carboxylate containing monomers. "Carboxylate-containing monomer" means that the carboxylic acid group is in the free acid form or a water-soluble salt thereof with an alkali metal, ammonia or an amine. In the case of acrylic acid polymers, it contains amides. In this way, acrylic acid, methacrylic acid,
Homopolymers of maleic acid, fumaric acid, itaconic acid, etc. may also be used. Polyacrylamide is
When added to boiler water, it undergoes hydrolysis to convert some or all of the amide groups to carboxylate groups and is also included as such. In addition to using these homopolymers, water-soluble copolymer forms may also be used. When the copolymer is used, the amount of carboxylate should be at least 30% monomer weight ratio for the copolymer. A preferred group of carboxylate polymers are those derived by hydrolysis of the corresponding polyacrylamides. These materials will contain between about 10 and 30% by weight of amide groups after either caustic or acid hydrolysis. The most preferred group of carboxylate polymers are those obtained by polymerizing acrylic acid with acrylamide in a monomer weight ratio of 3:1. As indicated, the amount of polymer used to treat hardness substances contained in boiler water (canned water) should be between 1 and 30 ppm for 1 ppm of hardness substances. Preferred water-soluble anionic vinyl polymers are
It must exhibit a chelation value greater than 200, preferably greater than 300. When applied to the present invention,
Chelation value refers to the average chelation value from both calcium and magnesium measurements. Chelation Value Chelation Value is defined as mg of calcium or magnesium expressed in terms of calcium carbonate complexed by 1 g of active sequestering agent. Here it is measured by specific ion electrode technology. Known increments of sequestering agent are added to a system containing a known amount of free (uncomplexed) calcium or magnesium. Then calcium/
The decrease in magnesium activity (concentration) is a direct measurement of the complexed species. This amount is then converted (expressed as a ratio) to give the chelation value. Effective moles can also be calculated using this information. The equivalent weight for sequestering agent is determined by dividing the chelation number by 100,000. If the molecular weight is known, then the molar ratio is obtained by dividing the molecular weight by the equivalent weight.
For EDTA and NTA the value should be close to 1. For polymers, this number varies with molecular weight and is generally greater than one. High Molecular Weight Dispersant In a preferred method of the invention, the carboxylate polymer is used in conjunction with a water-soluble polymer capable of dispersing hard materials. The high molecular weight dispersant used in this preferred method of the invention is an anionic water soluble vinyl polymer. To be effective, they must be capable of dispersing suspended solids that normally occur in boiler water. They may be further characterized as containing either carboxylate or sulfonate functional units. Further, they may be characterized as having a molecular weight of at least 500 to about 50,000. Water-soluble dispersion polymers useful in this invention include carboxylic vinyl polymers such as vinyl sulfonate-acrylic acid copolymers, vinyl sulfonate-methacrylic acid copolymers, sulfonated styrene-maleic anhydride copolymers, and acrylamide/acrylate copolymers. You can choose from the rates. A preferred water-soluble dispersion polymer is a vinyl sulfonate copolymer comprised of vinyl sulfonate and acrylic acid. The dispersant molecules generally contain 5 to 25 mole percent vinyl sulfonate or its alkali metal (preferably Na) salt and 95 to 25 mole percent vinyl sulfonate or its alkali metal (preferably Na) salt.
Contains 75 mole percent acrylic acid and its water-soluble alkali metal or ammonium salts. Preferably the acrylic acid-vinyl sulfonate copolymer is
It contains 10-20 mol% vinyl sulfonate and 90-80 mol% acrylic acid. The molecular weights of these preferred dispersed polymers range from about 500 to about 50,000. A molecular weight range of 750 to 50,000 is preferred, particularly a molecular weight range of approximately 900 to 15,000. Ideally the molecular weight is 1000~
In the range of 6000. It is surprising that these dispersant molecules, which may or may not be chelating or sequestering agent molecules, could be required if throughput were to be dramatically increased. Another class of high molecular weight dispersants are low molecular weight polyacrylic acids and their water soluble salts. These materials have a molecular weight range of 1000-5000.
The ratios in which these materials are used with the carboxylate polymer are the same as described above for the acrylic acid-vinyl sulfonate copolymer. Another class of high molecular weight dispersants are low molecular weight sulfonated copolymers of styrene and maleic anhydride. These materials are preferably present as sodium salts of sulfonated copolymers of styrene and maleic anhydride and are
It is typically known as the TL-3 ² product and is sold commercially. Other sulfonated copolymers of styrene and maleic anhydride also prove useful in this application when combined with the carboxylate polymers with sequestering agents. ² Registered Trademark of National Starch and Chemical Co., Ltd. To make a statement regarding the most preferred method of operation, to prevent and remove scale caused by such hard materials present in boiler water in contact with heat-conducting surfaces. A preferred method of treating hardness materials that contain such water comprises (a) a water-soluble anionic vinyl polymer containing at least 30% by weight of carboxylate functional units and having a molecular weight within the range of 500 to 50,000; polymer, and (b) a second anionic water-soluble vinyl polymer dispersant. To make a general comment regarding the most preferred polymeric dispersants, the boiler water preferably contains the sequestering agents (chelating agents) water-soluble anionic vinyl polymers as well as carboxylate-containing, water-soluble vinyl polymers, vinyl sulfonate-acrylic acid. copolymer, a vinyl sulfonate-methacrylic acid copolymer, a sulfonated styrene-maleic anhydride copolymer, and another anionic water-soluble vinyl polymer dispersant selected from the group consisting of an acrylamide-acrylic acid copolymer; may also be stated. Most anionic vinyl polymers of chelating or sequestering agents exhibit the ability to disperse solids in boiler water systems if the throughput is less than or equal to that required to chelate hardness material ions. It is of particular interest to note that. As a result of this observation, the chelating or sequestering polymer may be used in amounts greater than or equal to that required to chelate all of the hardness materials initially found in boiler systems. In this way, some of the hardness ions or scale present in the boiler system can be removed from the system and the additional chelating polymer can act as a dispersant and also as a sequestering agent against hardness contamination. It was observed that. Thus, the expression and related matters regarding the addition of a dispersant of another anionic water-soluble vinyl polymer in combination with a sequestering agent polymer are consistent with the aforementioned phenomena, i.e., the addition of an excess of metal to provide both sequestering properties and dispersibility. the use of sequestering polymers,
It means to include. Sequestering agent polymer to dispersant polymer ratio The ratio of carboxylate polymer to acrylic acid-vinyl sulfonate copolymer when they are used ranges from 30:1 to 1:30;
A preferred range is 20:1 to 30:1, with 20:1 being most preferred. Generally the ratio of sequestrant carboxylate polymer to dispersant polymer is also between 30:1 and
It is within the range of 1:30. The preferred ratio of sequestrant polymer to dispersant polymer is 30:1
~10:1, with the most preferred ratio of sequestrant polymer to dispersant polymer being 20:1.
It is 1. In all cases, this ratio is on a weight:weight basis. To illustrate the many advantages of the invention, the following is given by way of example. EXPERIMENTAL To understand the following tests, a series of different polymers and known boiler water treatment chemicals were evaluated.
These evaluations were conducted using two series of test programs. The initial test program involved determination of the chelation value of various polymers in order to determine by initial screening the potential of each polymer to act suitably as a boiler transport material. The experimental design used to test the chelation value of a series of polymers was as follows: Solutions of calcium or magnesium ions were titrated with solutions of other sequestrants of various polymers. The residual unsequestered metal ion concentration (or more precisely, the activity) is measured using a Specific Ion Electrode (now SI
Measured by method E.). This data was ultimately translated into a graphical illustration of sequestering agent performance. The performance of the sequestering agent against Ca ions was measured using a calcium ratio electrode model 93-20 manufactured by Orion Research. The response of the electrode is measured when the sequestering agent solution is added incrementally to the hardness material solution. The desired solution PH is maintained automatically by feeding potassium hydroxide solution from a Mettler DV10 controlled by a Mettler DK10/11 system. A short period of time is allowed after each sequestering agent addition before reading to allow the electrode to equilibrate with the solution. Noise levels are typically ±0.2 higher with mechanical stirring than with magnetic stirrers.
mV. Before each titration, set the SIE to 1000, 100, 10 and
Calculated using a standard solution containing 1 ppm calcium or magnesium. SIE responds to activity rather than concentration. For calcium measurements, a high and constant ionic strength is maintained by adding 6 g/potassium chloride to all solutions (i.e. standards, sequestrants and calcium samples). It maintains a constant activity coefficient towards calcium ions. The divalent detection electrode used for magnesium measurements is subject to interference from sodium and potassium ions at fairly low concentrations, so no ionic strength buffers can be used in this case. Typical operating conditions are (in all cases) 100ml
It was 2 or 3 g/active high molecular weight sequestering agent titrated against 100 ppm metal ions. Under these conditions, most titrations range from 40 to
After addition of 50 ml of sequestering agent it was essentially complete. Usually 2 to 3 ml of sequestrant solution
increments. The sequestering agent was added slowly to avoid the formation of bubbles that could get trapped in the base of the electrode and result in false readings. All measurements were performed at room temperature (measurements above about 40°C will result in rapid electrode degradation). Data from these experiments were displayed graphically or converted into an easy-to-use form, preferably by computer programs written specifically for these experiments. The computer program iteratively obtains the best straight line fitted through the program origin using a least squares approximation and allows calculation of chelation values for each polymer type. For calcium measurements, a pH of 10 was used in most cases. Early studies gave results indicating greater chelation than theory. At PH of 9,
The results were in good agreement with theory. The discrepancy in PH10 may be due to competitive reactions (eg magnesium hydroxide formation). All magnesium measurements were made at a pH of 9 from now on. An attempt was made to correct the magnesium results for the effects of some sodium present. However, the correction obtained from the sodium chloride solution
"Corrected" when applied to NTA.Na ₃ .H ₂ O titration
The results were extremely unreasonable (much greater than theoretical chelation). No further attempts were made to correct for sodium. The chelation value was determined from the initial slope of the titration curve, which plots the percent metal ion sequestered against grams of active polymer added. This calculation gives competing equilibrium effects or different stability constants to the effective chelation value with no consideration given to the complexes formed. In the case of the polymers being considered, a comparison of chelation values may be useful if a simple comparison of chelation values is not necessarily a good guide to performing chelation.
This may be more reasonable than would be the case with strong complexing agents such as EDTA or NTA. No evidence of a "marginal effect" was seen for some of the polymers tested. As the later results show, the chelation value for high molecular weight sequestering agents must be greater than 200 to be effective as a transport agent in boilers, and the test solution of both calcium and magnesium ions A clear solution must be given to the The preferred average chelation value is 300 or more. Most polymers tested appeared to sequester magnesium ions better than they could sequester calcium ions. However, to obtain good results, the polymer must have a chelation value of 200 or higher, preferably 300 or higher, as mentioned above, sequestering both calcium and magnesium ions to give a clear solution. must be able to do so. The data in the table compares the chelation values obtained using various sequestering agents and the test described above. As can be seen from this table, the sequestrants tested include known complexing agents such as EDTA and NTA as well as high molecular weight sequestrants as well as other sequestrants. As will be shown later, only those sequestering agents with a chelation number of 200 or higher can be shown to act as effective transport agents in boiler systems. Other sequestering agents in the table are not satisfactory as transport agents due to known thermal degradation in boiler systems. Such agents are the phosphate-containing compounds listed in the table. The table identifies each polymer type tested. The table describes the results for the high molecular weight sequestrants of the present invention, as well as other more common sequestrants, for magnesium ions. Also, as can be seen, the high molecular weight sequestrants that have a chelation value of 200 or more and are thermally stable give excellent results in boiler transport. Of particular note in the table are the results for citric acid. Even though extremely high chelation values are obtained, this material does not effectively transport magnesium or calcium hardness substances when tested in a boiler. It is believed that these results are due to the fact that citric acid decomposes thermally when exposed to boiler operating conditions. This benefits very well the carboxylate polymers of the present invention, which are low molecular weight polymers which, at appropriate dosages, provide thermal stability while retaining sequestering activity towards hard material ions. It is what it is. What is particularly noteworthy in the table is that polymer C
gives a chelation value in excess of 200, but gives a somewhat cloudy solution with magnesium at a pH of 9, and is not expected to perform as well as other carboxylate-containing polymeric sequestering agents of the present invention. That's true. This problem may be solved by increasing the concentration of this polymer or by combining this polymer with other materials that provide improved results. Polymeric materials that did not perform well with calcium were not tested against magnesium. This is because both ions must be complexed before a suitable boiler transport system can be achieved.

[Table] ** Produces cloudy solution

【table】

【table】

[Table] ★Ratio is monomer weight ratio

Table: Some of the more promising carboxylate-containing polymers with chelation numbers above 200 have been tried in experimental boiler water systems. The experimental boiler is a paper presented at the 41st Annual Meeting of the International Water Congress, Pittsburgh, Pennsylvania, October 20-22, 1980, Paper No. IWC-80-10, JAKelly.
PT Colombo & G.W.Flasch in "Study of Delamination and Corrosion Mechanisms Using Process Simulation". The table points out the formulations and sequestering polymers selected to be tested in the experimental boiler program. Included in these tests are phosphorus-containing sequestering agents and water-soluble polymers that do not contain measurable amounts of carboxylate functional units.

[Table] Experimental-scale boilers: 1000psig, 110000Btu/ft ² −hr for most experiments
of heat flux and 10 concentration cycles. The polymer of the composition was tested more extensively at 250, 600 and 1500 psig. This laboratory boiler is covered by U.S. patent no.
It is of the type described in No. 3296027. The water supply is typically 1 ppm Ca, 0.5 ppm Mg,
and deionized water containing 0.5 ppm SiO ₂ .
Residual SO ^-- 25±5ppm at 600psig and 1000psig
was maintained at 10±5ppm. The alkalinity of boiler water "0" was maintained at 160-180 ppm. of polymer
The pH was adjusted to 9. Laboratory Scale Boiler Results A Dose Distribution Dose distributions for a number of polymers were obtained under three conditions. The following is clear from FIG. 1. The recommended dosage of the combination polymer of the composition for hardness material control is about 5.3 ppm active polymer to ppm of total hardness material at 1000 psig, and 2. Polymer selectively Ca rather than Mg ions
It means transporting ions. Figures 1, 2 and ³ point out that the composition or compositions and compositions have marginal suppression capacity for Ca ions at low doses and chelate hardness ions at high throughputs. ing. In general, all tested acrylate, acrylamide and vinyl sulfonate based polymers give excellent hardness control at high dosages, as long as they contain sufficient carboxylate functional units. Among them the compositions and are the most effective. The results are listed below. ³ Sequestration is a more specific term, however chelation appears to be mechanistic. Condition 1: Boiler pressure = 1000psi, heat flux = 110000Btu/
ft ² −hr, Ca = 1 ppm, Mg = in the feed water
0.5ppm, SiO ₂ =ppm.

[Table] Condition 2: Boiler pressure = 1000psi, heat flux = 250000Btu/
ft ² −hr, the feed water contains 1 ppm Ca, 0.5 ppm Mg and
Contains 0.5ppm _SiO2 .

【table】

[Table] Condition 3: Boiler pressure = 600psi, heat flux = 110000Btu/hr
−ft ² , Ca=1ppm, Mg= in the feed water
0.5ppm, SiO ₂ =0.5ppm.

TABLE B Composition Efficacy at 1500 psig Higher recommended dosages are required for control of hard materials at higher boiler pressures. The increase in throughput is likely due to polymer degradation. As the data below points out, the dose required for complete hardness material recovery increased at 1500 psig. The corrosion rate as measured by iron content did not increase during blowdown. In the supply water, Ca = 1ppm, Mg = 0.5ppm,
SiO ₂ = 0.5ppm, pressure = 1500psig, heat flux =
110000Btu/ ^ft2 −hr. Polymer Treatment Ratio % Ca Recovery % Mg Recovery Composition 15.75 89 105 21.0 99 108 26.25 99 107 C Efficacy of Composition at 250 psig The combination polymers had no problems controlling hardness materials in low pressure (250 psi) boiler applications. The heat flux was 110,000 Btu/ft ² −hr. Condition 1: Feed water is Ca=3ppm, Mg=1.5ppm, Na ₂ SO ₄
=42.6ppm, NaCl=10ppm, SiO ₂ =5ppm, Fe=
1ppm and M alkalinity 40ppm in feed water
contained enough NaHCO ₃ to give an M alkalinity of 400 ppm in the boiler water and SO ₃ ⁼ 30 ppm in the blowdown.

Table Condition 2: Feed water contained 3 ppm Mg and all other components listed in 1.

[Table] D. Effect of the hard material and silica in the composition The treatment agent of the composition can be recovered from the moderately hard material, silica and the treating agent in the confused state. Condition 1: Boiler pressure = 1000 psig, heat flux =
110000Btu/hr−ft ² , initial hardness material is 1ppm
With Ca and 0.5 ppm Mg, the treatment ratio of the composition was 7.88 ppm polymer/hard material. The total polymer was kept constant throughout the test as the hardness material was changed.

[Table] Condition 2: Response to Ca/Mg/SiO ₂ three-way variation 1000psi and 250000Btu/hr-ft ²

【table】

[Table] Condition 3 - For composition: Feed water contains 1 ppm Ca, 0.5 ppm Mg, and
Contains 2.5ppm _SiO2 . 1000psi and
110000Btu/hr− ^ft2 . Treatment ratio Ca recovery % Mg recovery % SiO ₂ recovery % 7.88 100 97 103 15.75 106 149 102 E Scale removal using the composition Descaling using the composition can be carried out if hard materials and silica can be discharged by blowdown. It seems possible to implement it. Treatment agents of suitable composition are capable of transporting boiler deposits in addition to hardness materials in the feed water. It enhanced the passivation of the boiler heat transfer surface and formed a black magnetite film. Condition 1: Feed water is Ca=1ppm, Mg=1.5ppm, and SiO ₂
= Contains 0.5ppm. Pressure = 1000psig, heat flux =
110000Btu/hr− ^ft2 ,

[Table] Condition 2: Feed water contained no hardness substances or silica, and the boiler was extremely dirty. Pressure = 1000psig, heat flux = 110000Btu/hr- ^ft2 ,

[Table] Condition 3: The feed water contained no hardness substances or silica, and the boiler was relatively clean. Pressure = 1000psig, heat flux =
110000Btu/hr-ft ² , treatment agent is completely hardened material =
Assuming 1ppm, for 1ppm of total hardness material
The composition was 23.63 ppm.

TABLE F Effect of Heat Flux on Performance of Compositions Heat flux in the range of 110,000 to 250,000 Btu/hr-ft ² had little effect on hard material recovery. Heat fluxes greater than 300,000 Btu/hr- ^ft2 resulted in thin film deposits on the heat transfer surfaces. Test conditions: 1000psi Feed water contains 1ppm Ca, 0.5ppm Mg, and
Contains 0.5ppm _SiO2 .

Table G Implementation of Other Combination Polymers Although the composition/composition combination polymers are less effective than the compositions,
Provided satisfactory hardness material control at 1000 psig. This combination polymer could be used in _NH3 sensitive applications. Conditions: Ca=1ppm, Mg=0.5ppm in feed water,
SiO ₂ = 0.5ppm, pressure = 1000psig, heat flux =
110000 Btu/ft ² , treatment ratio % Ca recovery % Mg recovery 7.88 86 91 10.5 99 111 13.12 102 108 Experimental Boiler Results Combined polymer composition at 7.9 ppm activator dosage for 1 ppm total hardness material , initially added to the boiler. The dose was maintained for 8 days. The average calcium and magnesium recoveries were 118% and 101%, respectively. The initial hydrogen level was 11 ppb, which dropped to 1.5 ppb on the same day. It averaged out to 0.4ppb. 1.0~1.2ppb
The value of hydrogen is equivalent to the background level. A high initial build-up of hydrogen occurs in the boiler that has just been brought onto the line. Furthermore, the first two
Residual SO ₃ ^-- for 3 days was lower than desired and contributed to hydrogen evolution. Iron in blowdown is 2
It started high at ~3 ppm and decreased to 1.1 ppm after 8 days. The condensate often had a PH greater than 9 and contained small amounts of ammonia. At this point, reduce the polymer dosage to 3.9;
The test continued under these conditions for 6 days. This amount of processing is less than two-thirds of what was recommended. The average calcium and magnesium recoveries during this period were
They were 96% and 81%. It was expected from the experimental scale boiler results that hardness recovery would be reduced and that magnesium would be more affected than calcium. Hydrogen drops to 0.3ppb, iron
It decreased to 0.3ppm. The temperature of the high heat flux surface was kept constant and no peeling was observed. At this point the polymer dosage was further reduced to 2.6 and held at this condition for 3 days. Calcium and magnesium recovery is 89% and 79% respectively
On the other hand, the amounts of hydrogen and iron decreased little by little. During the low level treatment, the temperature in the horizontal specimen increased by 30°, indicating that scale was being deposited. The polymer dosage was then returned to the original level of 7.9 for 15 days. Within the first day, the temperature of the horizontal specimen decreased by 30°. As expected, calcium and magnesium recovery increased dramatically;
The average values were 122% and 111%, respectively. These high recovery values suggest that the program of the polymer treatment agent is to remove previously deposited deposits when under treatment. It was also assumed at the beginning of this test that the 118% calcium recovery was due to the removal of boiler deposits left in the system from the previous test. Hydrogen and iron remained at relatively low levels. Figures 4, 5, and 6 depict the percent hardness recovery, amount of _H2 , and amount of iron in blowdown as a function of test days. Polymer treatment then 7
I stopped it for a day. Only trace amounts of calcium and magnesium were recovered over this period, while hydrogen and iron remained virtually unchanged. During the remainder of the study, 7.9 polymer doses were alternated without treatment. In the presence of the polymer, calcium and magnesium recoveries averaged 115% and 106%, respectively.

[Brief explanation of the drawing]

Figure 1 shows 1000 psig for the composition;
The relationship between the processing ratio and hardness material recovery % at 110000 Btu/hr-ft ² is shown. FIG. 2 shows the relationship between treatment ratio and % hardness recovery at 600 psig and 110,000 Btu/hr-ft ² for the composition. FIG. 3 shows the relationship between treatment ratio and % hardness recovery at 600 psig and 110,000 Btu/hr-ft ² for the composition.
Figure 4 shows the composition in the experimental boiler;
The percent hardness material recovery obtained with 600 psig treatment is shown as a function of test days. FIG. 5 shows the composition in the experimental boiler, the amount of H ₂ (ppb) obtained with 600 psig treatment as a function of the number of test days. FIG. 6 shows the composition, iron content (PPM) in the boiler obtained with 600 psig treatment as a function of test days.

Claims (1)

Claims: 1. A method of treating hard materials present in boiler water in contact with heat transfer surfaces to prevent scale formation and remove existing scale, wherein said treatment % of carboxylate functional units, has a chelation number of at least 200, and has a molecular weight in the range of 500 to 50,000, present in the boiler water. hardness substance
Use in an amount within the range of 1 to 30 ppm per 1 ppm,
It consists of treating boiler water, thereby sequestering hard substances in the boiler water, and
A method characterized in that it prevents the formation of scales on heat transfer surfaces and removes scales already present on heat transfer surfaces. 2. The method of claim 1, wherein the water-soluble anionic vinyl polymer sequestering agent has a chelation value of at least 300. 3. The method of claim 1, wherein the water-soluble anionic vinyl polymer sequestering agent has a molecular weight in the range of 1,000 to 30,000. 4. The method of claim 1, wherein the water-soluble anionic vinyl polymer sequestering agent is added to the boiler water in a range of 3 to 15 ppm per 1 ppm of hardness material present in the boiler water. 5. The water-soluble anionic vinyl polymer sequestering agent comprises: (a) a homopolymer of a member of the group consisting of acrylic acid, methacrylic acid, maleic acid and fumaric acid; (b) acrylic acid, methacrylic acid, maleic acid and fumaric acid; Copolymers consisting of two or more members of the group consisting of acids; (c) Copolymers of acrylamide and one or more members of the group consisting of acrylic acid, methacrylic acid, maleic acid and fumaric acid; (d) Acrylic acid, methacrylic acid and maleic acid. and (e) a hydrolyzed polyacrylamide. 6. A method of treating boiler water in contact with a heat transfer surface, wherein said treatment comprises at least 30% by weight of carboxylate functional units and at least
A water-soluble anionic vinyl polymer sequestering agent having a chelation value of 200 and a molecular weight ranging from 500 to 50,000 is added at a concentration of 1 to 30 ppm per ppm of hardness material present in the boiler water. It is used in large amounts to sequester hard materials in boiler water, thus preventing scale formation on heat transfer surfaces and removing scale already present on heat transfer surfaces, as well as to separate boiler water. A method characterized by treating with a water-soluble anionic vinyl polymer dispersant. 7. The method of claim 6, wherein the ratio of water-soluble anionic vinyl polymer sequestering agent to water-soluble anionic vinyl polymer is within the range of 30:1 to 1:30 on a weight basis. 8 Another anionic water-soluble vinyl polymer dispersant is a carboxylate-containing water-soluble vinyl polymer,
vinyl sulfonate-acrylic acid copolymer, vinyl sulfonate-methacrylic acid copolymer,
7. The method of claim 6, wherein the polymer is selected from the group consisting of sulfonated styrene-maleic anhydride copolymers and acrylamide-acrylic acid copolymers. 9. The boiler water is selected from the group consisting of (a) a water-soluble acrylic acid-vinyl sulfonate copolymer having a molecular weight in the range between 900 and 15,000, and (b) an acrylic acid polymer having a molecular weight in the range between 2,000 and 4,000. 7. The method of claim 6, wherein the method is simultaneously treated with an anionic water-soluble vinyl polymer dispersant. 10 Another anionic water-soluble vinyl polymer dispersant comprising (a) 5 to 25 mole % vinyl sulfonate; (b) 95 to 75 mole % acrylic acid; and (c) a water soluble vinyl polymer having a molecular weight in the range of 1000 to 6000. 10. The method according to claim 9, wherein the copolymer is a polyacrylic acid-vinyl sulfonate copolymer. 11. The method of claim 9, wherein the other anionic water-soluble vinyl polymer dispersant is an acrylic acid polymer having a molecular weight in the range of 2,000 to 4,000.