JPS6147159B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a scale control agent for preventing scale and sludge from forming in boilers, cooling water systems, etc., and for removing scale and sludge that have once adhered. On heat transfer surfaces such as boilers and cooling water systems, adhesion of scale or sludge often causes various operational problems such as a reduction in thermal efficiency and local corrosion. The reason for the formation of scale or sludge is that impurities such as calcium, magnesium, iron, or silica in water are concentrated under high temperature conditions, and the solubility of calcium carbonate, hydroxyapatite, iron oxide, or magnesium silicate is reduced. This is because it precipitates on the heat transfer surface that comes into contact with water. Furthermore, in recent years, medium- and low-pressure boilers have become more packaged and have higher performance, and as a result, the unit heat transfer surface evaporation rate and furnace heat load have become much higher than in conventional boilers. Due to this increase in heat load on heat transfer surfaces, impurities in water are becoming more concentrated, making it easier for scale to adhere than before, and even if a small amount of scale adheres, it is difficult to evaporate. tube bulge,
Scaling failure is becoming a serious problem as it can lead to accidents such as explosions. Substances that cause such scaling problems include calcium carbonate, hydroxyapatite, iron oxide, and magnesium silicate, and most of these scales are dissolved in inorganic acids such as hydrochloric acid. Therefore, the conventional method for removing scale has been to temporarily stop the operation of the boiler, lower the temperature, and clean it with an inorganic acid such as hydrochloric acid. However, this acid cleaning has disadvantages such as temporary severe corrosion of the plant by the acid, handling risks due to the use of strong acids, and the troublesome process of discharging the acid waste liquid. In order to overcome these drawbacks, chelating agents such as nitrilotriacetates have come into use, although their scale-dissolving power is inferior to that of inorganic acids. However, this type of chelating agent has disadvantages such as giving off a strange odor to the steam, being corrosive to metals, and making operation management difficult. The inconvenience of having to blow out the entire amount could not be avoided. On the other hand, in recent years, a method has been proposed that uses polyacrylate to remove scale without stopping the operation of the boiler. However, although polyacrylates are effective to some extent in removing scales mainly composed of calcium carbonate and calcium silicate, they are hardly effective in removing scales mainly composed of hydroxyapatite, which are most commonly found in boilers. It had the fatal flaw of being completely powerless. This invention applies to calcium carbonate, hydroxyapatite,
Related to scale control agents that can prevent the precipitation of scales such as iron oxide and magnesium silicate, and can also remove scales mainly composed of the above components that have formed and adhered without stopping plant operation. It is characterized in that it contains a copolymer of itaconic acid and another unsaturated carboxylic acid and/or an unsaturated monomer other than the unsaturated carboxylic acid, or a water-soluble salt thereof. Examples of other unsaturated carboxylic acids (B) to be copolymerized with itaconic acid (A) described above include (meth)acrylic acid (referred to as acrylic acid or methacrylic acid. The same description will be used hereinafter), maleic acid, etc. Ru. Note that the unsaturated carboxylic acid (B) may be an anhydride.
Examples of unsaturated monomers other than unsaturated carboxylic acids include unsaturated sulfonic acids such as styrene sulfonic acid and vinyl sulfonic acid, hydroxyalkyl (meth)acrylates such as hydroxyethyl methacrylate, (meth)acrylamides such as acrylamide, and methyl. Unsaturated carboxylic acid esters such as (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate, vinyl esters such as vinyl acetate, unsaturated nitriles such as acrylonitrile, and aromatic substances such as styrene. Examples include group vinyl compounds. Among these, preferred are unsaturated sulfonic acids. When the unsaturated monomer to be copolymerized is another unsaturated carboxylic acid, the amount of itaconic acid in the itaconic acid copolymer is 75 mol% or more, preferably more than 95 mol%, and the remainder is another unsaturated carboxylic acid. In addition, when the unsaturated monomer to be copolymerized is an unsaturated monomer other than an unsaturated carboxylic acid, it is usually more than 90 mol% of itaconic acid, preferably 91 mol% or more of itaconic acid, and more preferably 95 mol% or more of itaconic acid.
The remainder is an unsaturated monomer other than the unsaturated carboxylic acid at mol% or more. If the amounts of itaconic acid and unsaturated monomer in the copolymer are outside the above range, the scale prevention and removal effects in high-temperature water will be poor. Itaconic acid copolymer is made of, for example, itaconic acid and other unsaturated monomers that can be copolymerized with itaconic acid.
Usually at 40 to 150°C, preferably in the presence of a conventional polymerization initiator such as a peroxide type such as benzoyl peroxide, an azo type such as azobisisobutyronitrile, or a persulfate type such as sodium persulfate. can be obtained by polymerizing at 50 to 90°C, and known examples of the polymerization method include aqueous solution polymerization. The molecular weight of the itaconic acid copolymer used in this invention is usually in the range of 1,000 to 200,000, preferably 3,000 to 50,000. The itaconic acid copolymer used in this invention may be a water-soluble salt thereof, and water-soluble salts include salts of alkali metals such as sodium, potassium, and lithium, ammonium salts, and salts of amines such as triethanolamine. Salts and mixtures thereof are mentioned. In order to obtain a water-soluble salt of an itaconic acid copolymer, a monomer may be made into a salt in advance and then polymerized, or the monomer may be polymerized and then made into a salt. The scale control agent of this invention may be added continuously to the target water system at all times, or may be added intermittently at short intervals. Further, it may be added all at once after reaching the limit allowable amount of scaly adhesion. The amount of the scale control agent of the present invention added varies depending on the type of scale component and the amount of scale, but is generally about 1 to 1000 mg/. When the purpose is removal, the amount tends to be larger than when the purpose is prevention. Target water systems include systems where scale generally forms, such as boiler supply water systems, cooling circulation water systems, seawater evaporation systems, waste liquid concentration systems, and waste gas dust collection water systems. When the scale control agent of the present invention is used, for example, to remove scale from a boiler, it is of course possible to temporarily stop the operation of the boiler and remove the scale by a conventional method as in the conventional method; The biggest advantage is that you can remove scale from the boiler without stopping it. In other words, when the boiler in operation reaches the time to be cleaned, by adding the scale control agent of the present invention to the boiler water supply for a certain period of time while the boiler continues to operate, it is possible to obtain steam completely free of any offensive odor caused by chemicals. At the same time, scales whose main components are calcium carbonate, iron oxide, calcium silicate, hydroxyapatite, etc. are sufficiently removed by the action and effect of the scale control agent.
These scales are discharged from the system together with the blow water. In general, boilers are cleaned once a year, and when using the scale control agent of the present invention, cleaning can be done in accordance with this, and preferably, the scale control agent is cleaned once a month or once every few months. It is more effective to increase the frequency of addition of scale because it can be removed when the amount of scale precipitated is small. When the scale control agent of the present invention is added to the system from the beginning and used for scale prevention, the precipitation of scale is almost prevented, and even if a small amount of scale is precipitated, the amount of the control agent added during the cleaning period is adjusted to the appropriate amount for scale removal. The scale can be easily removed by simply changing to On the other hand, if the pesticidal agent of the present invention is used for scale removal and continues to be used after cleaning, scale precipitation will be prevented, and in either case, operational management will be significantly easier. Note that polyitaconic acid may also be used as a scale control agent, but polyitaconic acid is difficult and expensive to produce, whereas itaconic acid copolymers have the advantage of being easy to produce. The scale control agent of the present invention includes conventional boiler chemicals,
Can be used in combination with cooling water-based chemicals, such as alkaline agents such as sodium hydroxide, potassium hydroxide, morpholine, and cyclohexylamine, anticorrosive agents such as phosphates, hydrazine, triethanolamine, and organic acid salts, and hypochlorite. Can also be used with disinfectants such as acid salts. The scale control agent of this invention prevents the generation of scale and sludge in water systems, and can also be used to prevent scale and sludge from forming and adhering to normal scales, as well as scales whose main component is hydroxyapatite, without stopping plant operation. Since it can be effectively removed, safe operation can be continued without reducing the thermal effect. Next, examples of the present invention will be shown. Example 1 An internally heated autoclave equipped with a steam outlet, make-up water inlet, and electric heater was used to test the performance of a scale control agent. Autoclave operation requires iron oxide 10 as water supply.
The experiment was carried out for 20 days using softened water from Yokohama city water to which mg/mg was added, under conditions of a concentration ratio of 8 times and a pressure of 15 kg/cm ² . As scale control agents, those shown in Table 1 were used (molecular weight 4000-8000). The iron oxide concentration in the boiler water during operation was measured, and the dispersion rate was determined using the following formula. A high dispersion rate indicates a high scale prevention rate. Dispersion rate = Iron oxide concentration in boiler water (mg/) / Iron oxide concentration in feed water (mg/) x Concentration rate x 100

[Table] As can be seen from the table, the scale preventive agent of the present invention has the same preventive effect as the conventional scale preventive agent polyacrylate. Example 2 An internally heated autoclave equipped with a steam outlet, make-up water inlet, and electric heater tube was used to test the performance of a scale control agent. First, while supplying Yokohama city water containing 200 mg of sodium hydroxide as make-up water, the concentration factor was 10.
It was operated for 3 days under the conditions of 10 kg/cm ² and a pressure of 10 kg/cm 2 . The PH of the water inside the autoclave was maintained at 11.5-11.7. Three days later, when the heater tube was removed, it was observed that hard scale containing 65% calcium carbonate, 15% calcium silicate, 8% magnesium silicate, etc. had adhered to the entire surface. Next, the make-up water will be Yokohama City Water Softened Water, and
After continuously adding 100mg/scale control agent with a molecular weight of 4000 to 8000 shown in Table 2 and operating for 2 days,
The scale removal rate was calculated. In the scale removal test, the same operation as above was repeated for each drug each time. Table showing the scale removal rate of each scale control agent.
Shown in 2. From this, the scale control agent of the present invention has calcium carbonate,
It can be seen that the removal of scale mainly composed of calcium silicate is comparable or superior.

[Table] Example 3 In Example 2, the performance of a scale control agent having a molecular weight of 4000 to 8000 was tested under the same operating conditions as in Example 2, except that 100 mg/trisodium phosphate was further added to the make-up water. The hard scale produced in this case contained 67% hydroxyapatite, 13% magnesium silicate, etc. The results are shown in Table-3. As can be seen, the scale control agent of the present invention exhibits superior effects compared to polyacrylates.

[Table] Therefore, when the scale control agent of the present invention is consistently used for the purpose of preventing and removing scale, it is possible to obtain a scale prevention effect equivalent to that of polyacrylates, and to remove the scales that polyacrylates cannot completely remove. The same scale removal effect can be obtained even for different types of scale, and the same chemical can be used to control scale without stopping the operation of the boiler or the like.

Claims (1)

[Claims] 1 75 mol% or more of itaconic acid (A) and 25 mol% or less of another unsaturated carboxylic acid (B) and/or an unsaturated monomer other than the unsaturated carboxylic acid (C) A scale control agent comprising an itaconic acid copolymer or a water-soluble salt thereof. 2. The scale control agent according to claim 1, wherein (C) is an unsaturated sulfonic acid. 3. The scale control agent according to claim 1 or 2, wherein the amount of (C) is less than 10 moles based on the total monomers. 4 The molecular weight of itaconic acid copolymer is 1000 to 200000
The scale control agent according to any one of claims 1 to 3.