JP2017012991A - Water treatment apparatus for boiler, and operation method of boiler - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water treatment apparatus for a boiler and an operation method of a boiler using the water treatment apparatus in which a concentration rate of a boiler can be increased while a trouble of scales or corrosion in a boiler can is prevented.SOLUTION: In a water treatment apparatus for a boiler that treats raw water by a reverse osmosis membrane, removal ratio of NaCl of the reverse osmosis membrane is 93% or more and less than 99.4% in the case where evaluation pressure of 0.3 to 1.5 MPa and NaCl solution of 500 to 2000 mg/L are used, and pure water flux is 1.3 m/d or more in the case of evaluation pressure of 0.75 MPa. The treated water is supplied to a boiler after scale dispersant is added to the treated water.SELECTED DRAWING: None

Description

  The present invention relates to a water treatment device for treating water supplied to a boiler, and a boiler operating method using the water treatment device.

  In a normal boiler system, boiler water is manufactured from raw water such as city water, groundwater, industrial water, etc. by removing hardness components, oxygen, etc. using a water treatment device. After injecting boiler treatment agent such as cleansing agent, it is supplied to the boiler.

  As a water treatment apparatus for removing hardness components, a water softener equipped with a cation exchange resin or a desalting apparatus equipped with a filtration membrane such as a nanofiltration membrane or a reverse osmosis membrane (RO membrane) is used. . As a device for performing the deoxidation treatment, a vacuum type, a membrane type or a nitrogen type deoxygenation device or the like is used (Patent Documents 1 to 3).

JP 2005-288219 A Japanese Patent No. 3593723 Japanese Patent Publication No. 7-90220

  The water softener cannot remove impurities other than the hardness component in the raw water, and cannot sufficiently reduce the conductivity and chloride ion concentration of boiler feed water. When the quality of the boiler feed water is poor, it is necessary to operate the boiler at a low concentration rate, which increases heat loss.

  A boiler water treatment apparatus using an RO membrane can remove not only hardness components but also dissolved organic matter, etc., but it needs to be operated at a high pressure and consumes a large amount of energy. When RO membranes, which are called loose RO membranes or nanofiltration membranes, are used to obtain treated water at a relatively low pressure, the removal rate of hardness components and chloride ions is low, and scale may be generated in the boiler. And there is a problem that the concentration ratio cannot be increased.

  The present invention provides a boiler water treatment device capable of increasing the boiler concentration rate while preventing scale and corrosion problems in the boiler can, and a boiler operating method using the water treatment device. Objective.

  The boiler water treatment apparatus of the present invention is a boiler water treatment apparatus that treats raw water with a reverse osmosis membrane. The reverse osmosis membrane uses an evaluation pressure of 0.3 to 1.5 MPa and a NaCl solution of 500 to 2000 mg / L. The reverse osmosis membrane (hereinafter referred to as RO membrane) having a pure water flux of 1.3 m / d or more when the NaCl removal rate is 93% or more and less than 99.4% and the evaluation pressure is 0.75 MPa. It is characterized by the above.

  The calcium membrane removal rate of the RO membrane is preferably 98% or more.

  The operation method of the boiler of this invention has the process of processing raw | natural water with the water treatment apparatus for boilers of this invention, and manufacturing a treated water, and the process of supplying this treated water to a boiler.

  In the boiler operating method of the present invention, it is preferable to add a scale dispersant to the treated water.

  The scale dispersant is a polymer or copolymer containing at least one of acrylic acid, methacrylic acid and maleic acid as a polymerization or copolymerization component or a salt of the polymer or copolymer, and has a weight average molecular weight of 1 , 100,000 to 100,000 are preferred.

  In the boiler water treatment apparatus of the present invention, the removal rate of NaCl when using an evaluation pressure of 0.3 to 1.5 MPa and a NaCl solution of 500 to 2000 mg / L is 93% or more and less than 99.4%, When the evaluation pressure is 0.75 MPa, the raw water is subjected to RO treatment with an RO membrane having a pure water flux of 1.3 m / d or more. This RO membrane has intermediate performance between a loose RO membrane, a nanofiltration membrane and a standard RO membrane, and has a large flux (permeation flux) even at a relatively low pressure. High removal rate. Since the standard RO membrane provides clean treated water, there is a possibility that troubles such as the electrode type level sensor not responding may occur in some cases. Moreover, although the loose RO membrane (NF membrane) has the performance shown in Japanese Patent Publication No. 7-90220, the removal rate of chloride ions and silica is poor, and the boiler concentration rate can be increased. Can not.

  By adding a scale dispersant to the treated water of this RO membrane and then supplying it to the boiler, the trouble of scale and corrosion in the boiler can is prevented, and the boiler concentration rate is increased and efficient operation is performed. be able to.

  Examples of raw water to be treated by the boiler feed water treatment apparatus of the present invention include city water, ground water, and industrial water. The raw water is preferably supplied to the water treatment apparatus after being turbidized by an MF membrane or the like.

  The RO membrane of the water treatment apparatus of the present invention has an NaCl removal rate of 93% or more and less than 99.4% when an evaluation pressure of 0.3 to 1.5 MPa and a NaCl solution of 500 to 2000 mg / L are used. In the case of an evaluation pressure of 0.75 MPa, the RO membrane has a pure water flux of 1.3 m / d or more.

  This evaluation pressure and NaCl removal rate are defined by the following equations. In addition, the density | concentration in a formula represents the density | concentration of NaCl. The feed water is raw water to be treated with the RO membrane, and the treated water is the RO membrane permeate.

Evaluation pressure (MPa) = (feed water pressure + concentrated water pressure) / 2-treated water pressure removal rate (%) = (1-treated water concentration / (((feed water concentration + concentrated water concentration) / 2))) × 100

  If the NaCl removal rate of the RO membrane is less than 93%, the chloride ion concentration in the boiler feed water, which is the RO membrane treated water, becomes high, the concentration rate cannot be increased, and corrosion occurs in the boiler can. It becomes easy. An RO membrane having a NaCl removal rate of 99.3% or more has a high pressure for obtaining treated water.

  The pure water flux of the RO membrane at an evaluation pressure of 0.75 MPa is 1.3 m / d or more, preferably 1.3 to 3.0 m / d, particularly preferably 1.4 to 2.0 m / d. If the pure water flux is less than 1.3 m / d, the operating cost of the RO device increases, which is not preferable. When it is larger than 3.0 m / d, the removal rate is deteriorated and the boiler blow rate cannot be increased.

The removal rate of calcium ions (Ca ²⁺ ) by this RO membrane is preferably 98% or more, although it depends on the state of the RO device and the properties of the liquid to be treated.

The RO membrane module having this RO membrane preferably has a treated water amount of 40 m ³ / d or more when the evaluation pressure is 0.75 MPa. When the amount of treated water is 40 m ³ / d or less, the number of necessary RO membrane modules increases, which is not economical.

  The material and shape of the RO membrane are not particularly limited as long as they satisfy the above performance, but an RO membrane made of aromatic polyamide is preferably used. Examples of the shape include a flat membrane, a spiral, a hollow fiber, and a tubular, and a spiral RO membrane is preferably used.

  When supplying the treated water treated by the boiler water treatment apparatus of the present invention to the boiler, it is preferable to add a scale dispersant. As the scale dispersant, a polymer (homopolymer) or copolymer (copolymer) containing at least one of acrylic acid, methacrylic acid and maleic acid as a polymerization or copolymerization component or a salt of the polymer or copolymer is used. It is preferable to use it.

  Specific examples of the homopolymer include polyacrylic acid, polymethacrylic acid, and polymaleic acid.

  Examples of the copolymer include one or more of acrylic acid, methacrylic acid, and maleic acid, conjugated diene sulfonic acid such as 2-methyl-1,3-butadiene-1-sulfonic acid, and 3-allyloxy-2-hydroxypropane. Unsaturated (meth) allyl ether monomers having a sulfo group such as sulfonic acid and 3-methallyloxy-2-hydroxypropanesulfonic acid, (meth) acrylamide-2-methylpropanesulfonic acid, 2-hydroxy-3-acrylamide Propane sulfonic acid, styrene sulfonic acid, methallyl sulfonic acid, vinyl sulfonic acid, allyl sulfonic acid, isoamylene sulfonic acid, or compounds having a sulfo group such as salts thereof, isobutylene, amylene, acrylamide, N-vinyl formaldehyde, etc. Non-ionic compounds and kuroto Acid, isocrotonic acid, vinyl acetate, atropic acid, fumaric acid, itaconic acid, a copolymer of one or more selected from a compound having a carboxyl group, such as hydroxyethyl acrylate or salts thereof.

  Examples of salts of these homopolymers and copolymers include sodium salts, potassium salts and ammonium salts.

  These polymers, copolymers, or salts thereof preferably have a weight average molecular weight of 1,000 to 100,000, particularly 20,000 to 70,000. When the weight average molecular weight is less than 1,000, a sufficient scale preventing effect may not be obtained. When the weight average molecular weight exceeds 100,000, the scale preventing effect is lowered.

  One type of the above scale dispersant may be added, or two or more types may be added in combination.

  The amount of the scale dispersant comprising these polymers, copolymers, or salts thereof is preferably such that the concentration in the boiler water is 10 to 500 mg / L, and the concentration in the boiler water is 20 to It is more preferably 400 mg / L, further preferably 30 to 300 mg / L, and still more preferably 50 to 250 mg / L. By setting the concentration in the boiler water to 10 mg / L or more, a sufficient scale dispersion effect is easily exhibited. By setting the concentration to 500 mg / L or less, the cost of wastewater treatment due to the increase in COD is prevented, and the cost is reduced. The counter effect can be improved.

  The scale dispersant is preferably added to makeup water or water supply. In addition, when the steam generation facility is a circulation type, it may be added to the condensate.

  In the present invention, as long as the object of the present invention is not impaired, various additive components such as oxygen scavengers, anticorrosives, and scale prevention are provided at any point in the system of the steam generation facility as necessary. An agent or the like may be added. Examples of the scale inhibitor include various phosphates and scale dispersants described above, polymers or copolymers having a low weight average molecular weight that do not satisfy the above-described conditions, water-soluble polymer compounds such as sodium salts thereof, phosphones, and the like. Examples thereof include acid salts and chelating agents.

  In the present invention, it is also preferable to add the following (A) or (B) as the scale dispersant, and both may be used together as in (C). These scale inhibitors of (A) and / or (B) are effective in preventing scale when the RO membrane treated water, particularly water treated with the RO membrane of the present invention is used as the feed water among the scale inhibitors described above. It is also expensive and has the characteristics described below.

(A) Polymethacrylic acid having a weight average molecular weight of 1,000 to 100,000 and / or a salt thereof, and 2-hydroxyethyl-1,2-diphosphonic acid and / or a salt thereof (hereinafter, this combination is referred to as “dispersant ( A) ").
The dispersant (A) is particularly effective when there is a risk of precipitation of zinc-based scale in the boiler water system.

  As 2-hydroxyethyl-1,2-diphosphonate, sodium salt, potassium salt and ammonium salt of 2-hydroxyethyl-1,2-diphosphonic acid can be used. As polymethacrylate, sodium salt, potassium salt, and ammonium salt of polymethacrylic acid can be used.

  The amount of 2-hydroxyethyl-1,2-diphosphonic acid and / or its salt added to the aqueous system varies depending on the water quality (zinc concentration) of the aqueous system to be treated and the precipitation tendency of the zinc-based scale. The concentration of ethyl-1,2-diphosphonic acid and / or a salt thereof as a weight ratio of 2-hydroxyethyl-1,2-diphosphonic acid is not less than 4 times, preferably not less than 6 times the zinc concentration in water. More preferably, it should be added so that the concentration is 8 times or more, and it is preferably 0.1 to 1,000 mg / L, particularly 1 to 500 mg / L. If the addition concentration of 2-hydroxyethyl-1,2-diphosphonic acid and / or its salt is less than the above lower limit, a sufficient addition effect cannot be obtained, and if it exceeds the above upper limit, it is uneconomical in terms of drug cost, Underwater COD increases, which is not preferable in terms of wastewater treatment.

  The preferred amount of polymethacrylic acid and / or salt thereof added to the aqueous system is as described above.

  There is no particular limitation on the ratio of the addition amount of 2-hydroxyethyl-1,2-diphosphonic acid and / or salt thereof to polymethacrylic acid and / or salt thereof, but aqueous 2-hydroxyethyl-1,2-diphosphone is not limited. The concentration ratio of acid and / or salt thereof to polymethacrylic acid and / or salt thereof is 2-hydroxyethyl-1,2-diphosphonic acid and / or salt thereof by weight ratio: polymethacrylic acid and / or salt thereof = 1. It is preferable to add so that it may become the range of 0.01-1: 100, especially 1: 0.01-1: 10, when obtaining the effect by combined use of both.

  2-hydroxyethyl-1,2-diphosphonic acid and / or a salt thereof and polymethacrylic acid and / or a salt thereof may be mixed and added in advance, or may be added separately. When mixing and adding in advance, these may be added as an aqueous solution.

(B) Polymethacrylic acid and / or salt thereof, acrylic acid / 2-acrylamido-2-methylpropanesulfonic acid copolymer and / or salt thereof (hereinafter, this combination is referred to as “dispersant (B)”). .
A dispersing agent (B) is effective when there exists a possibility that an iron-type scale may precipitate in a boiler water system.

  The weight average molecular weight of polymethacrylic acid (hereinafter sometimes referred to as “PMAA”) is as described above.

  The acrylic acid / 2-acrylamido-2-methylpropanesulfonic acid copolymer (AA / AMPS) is a copolymer having acrylic acid and 2-acrylamido-2-methylpropanesulfonic acid as monomer units.

  The weight average molecular weight of AA / AMPS is preferably 1,000 to 200,000, more preferably 2,000 to 80,000, still more preferably 5,000 to 75,000. Most preferably, it is from 5,000 to 50,000. When the weight average molecular weight is 1,000 or more and 200,000 or less, a good iron dispersion effect can be obtained.

  The molar ratio of acrylic acid to 2-acrylamido-2-methylpropanesulfonic acid monomer in AA / AMPS is preferably 99: 1 to 5:95, and 90:10 to 50:50. Is more preferable. By setting AMPS to 1 or more with respect to acrylic acid 99 and AMPS to 95 or less with respect to acrylic acid 5, a good iron dispersion effect can be obtained.

  The salt of AA / AMPS contains acrylate and / or 2-acrylamido-2-methylpropanesulfonate in at least a part of the structural unit of AA / AMPS. That is, in the present invention, the salt of AA / AMPS includes not only a completely neutralized product of AA / AMPS but also a partially neutralized product of AA / AMPS.

  Examples of the AA / AMPS salt include alkali metal salts such as the sodium salt and potassium salt of the above AA / AMPS, ammonium salts, and amine salts. The AA / AMPS salt is preferably such that the base AA / AMPS satisfies the above weight average molecular weight.

  AA / AMPS salt can be obtained, for example, by neutralizing AA / AMPS. Moreover, the acrylic acid and / or 2-acrylamido-2-methylpropane sulfonic acid which are raw material monomers are neutralized, and these are used as acrylate and / or 2-acrylamido-2-methylpropane sulfonate. AA / AMPS salt may be copolymerized.

It is preferable to add polymethacrylic acid and / or a salt thereof and AA / AMPS and / or a salt thereof at a mass ratio of 1: 1 to 10: 1, and 1.5: 1 to 9: 1 It is more preferable to add at a ratio. 1 or more of polymethacrylic acid and / or its salt with respect to AA / AMPS and / or its salt 1, and 10 or less of polymethacrylic acid and / or its salt with respect to AA / AMPS and / or its salt 1 By doing, a high iron dispersion effect can be exhibited with respect to all forms of iron.
In addition, the preferable addition amount of a dispersing agent (B) becomes a preferable addition amount as the above-mentioned scale dispersing agent.

(C) As described above, the dispersant (A) and the dispersant (B) may be used in combination.
Moreover, even if only polyacrylic acid is added, a good effect may be obtained.
In the present invention, it is preferable to use an appropriate scale dispersant in combination with the RO membrane having the performance described above in accordance with the water quality of the boiler water system.

  There are no particular restrictions on the pre-treatment of the RO device, but soft water treatment, turbidity treatment, activated carbon treatment, and the like can be selected as appropriate. When there is a water softener in the previous stage, a bypass valve may be provided between the water softener and the RO device, and when the RO membrane is blocked, the RO device may be bypassed to supply soft water. Also. Since the blow water of the boiler and the recovered water of the steam drain have heat, it may be returned to the previous stage of the RO device to raise the temperature of the RO device feed water. 5-40 degreeC is preferable and the water temperature of RO apparatus feed water has more preferable 20-30 degreeC.

  Examples, reference examples and comparative examples will be described below.

  Table 1 shows RO membranes used in the following Examples, Reference Examples and Comparative Examples.

[Examples 1 to 3]
RO membranes shown in Table 1 after clarification of raw water (electric conductivity: 80 mS / m, M alkalinity 50 mg / L, silica: 10 mg / L) with Cl concentration of 130 mg / L and Ca hardness of 50 mg / L using MF membrane It processed with the water treatment apparatus using. The recovery rate of the RO membrane device was 85%. Thereafter, as a dispersant, a scale dispersant made of polyacrylic acid having a weight average molecular weight of 50,000 was added and introduced into a low-pressure boiler having a retained water amount of 0.2 m ³ . The amount of the scale dispersant added was twice the weight of the calcium hardness component (Ca-H) concentration of the RO membrane treated water.

  Table 2 shows the measurement results of Cl concentration and calcium hardness in the RO membrane treated water, the boiler concentration ratio after 30 days of operation, and the observation results of the presence or absence of scale generation in the boiler can. Table 2 also shows the processing cost when the processing cost of Example 1 is 100%.

[Example 4]
Except that the scale dispersant was not added, the same treatment and boiler operation as in Example 1 were performed. The results are shown in Table 2.

[Comparative Examples 1 and 2]
The same treatment and boiler as in Examples 1 to 3 except that the RO removal rate shown in Table 1 was 85% (Comparative Example 1) or 99.5% (Comparative Example 2). Drove. The results are shown in Table 2.

[Discussion]
According to the first to third embodiments, the boiler can be operated at a high concentration ratio without causing a scale and at a low RO processing cost.

  Although the comparative example 1 is low in the processing cost of the RO device as compared with the first to third embodiments, the boiler concentration is low, the fuel cost is increased, and it is not economical. In Comparative Example 2, the RO device needs to be operated at a high pressure, and the RO processing cost is high, which is not economical. Example 4 was a case where no dispersant was added, but it was confirmed that a trace amount of scale was generated in the boiler can. Although it was not an amount that would cause problems in operation, the heat transfer efficiency deteriorated, resulting in a slightly inferior economic result.

The boiler water treatment apparatus of the present invention is a boiler water treatment apparatus that treats raw water with a reverse osmosis membrane. The reverse osmosis membrane has a calcium ion removal rate of 98% or more and 0.3 to 1.5 MPa. The removal rate of NaCl when using a 500 to 2000 mg / L NaCl solution is 93% or more and less than 99.4%, and when the evaluation pressure is 0.75 MPa, the pure water flux is 1. It is a reverse osmosis membrane (hereinafter also referred to as RO membrane) of 3 m / d or more.

Claims (5)

In a boiler water treatment device that treats raw water with a reverse osmosis membrane,
The reverse osmosis membrane has an evaluation pressure of 0.3 to 1.5 MPa, a NaCl removal rate of 93% or more and less than 99.4% when a 500 to 2000 mg / L NaCl solution is used, and 0.75 MPa. In the case of the evaluation pressure, a boiler water treatment apparatus characterized by being a reverse osmosis membrane having a pure water flux of 1.3 m / d or more.   The boiler water treatment apparatus according to claim 1, wherein a calcium ion removal rate of the reverse osmosis membrane is 98% or more.   A method for operating a boiler, comprising: treating raw water with the boiler water treatment device according to claim 1 or 2 to produce treated water; and supplying the treated water to the boiler.   4. The boiler operation method according to claim 3, wherein a scale dispersant is added to the treated water.   5. The boiler operation method according to claim 4, wherein the scale dispersant is a polymer or copolymer containing at least one of acrylic acid, methacrylic acid and maleic acid as a polymerization or copolymerization component, or the polymer or copolymer. A method for operating a boiler, which is a salt of a polymer and has a weight average molecular weight of 1,000 to 100,000.