JP2013208568A - Water quality control method of circulating cooling water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water quality control method of circulating cooling water by which a phosphoric acid component in recycled water can be utilized for corrosion prevention of water system members and scale deposition in the water system can be also suppressed.SOLUTION: In a water quality control method of circulating cooling water that uses phosphoric acid-containing recycled water at least as a part of makeup water, concentration is controlled so that phosphoric acid concentration in the cooling water may be 20 to 25 mg PO/L, 10 to 20 mg/L of a scale prevention polymer is added and pH of the cooling water is controlled between 7.0 and 7.5, calcium hardness in the cooling water is made to be 1,500 mg CaCO/L or less, Clconcentration is made to be 2,500 mg/L or less and SOconcentration is made to be 2,500 mg/L or less.

Description

  The present invention relates to a water quality management method for circulating cooling water, and more particularly to a water quality management method using recovered water as at least a part of makeup water.

  In an open circulation cooling water system, makeup water is supplied to the water system in an amount commensurate with the evaporation and scattering of water.

  In order to make effective use of water, recovered water is used as at least part of makeup water (for example, paragraph 0009 of Patent Document 1 and paragraph 0007 of Patent Document 2).

JP2011-224455A JP2008-249275

  The recovered water from municipal wastewater or industrial wastewater contains phosphoric acid components. This phosphate component has an anticorrosive action, but generates a calcium phosphate scale.

  An object of this invention is to provide the water quality management method of the circulating cooling water which can suppress the precipitation of scale in an aqueous system while using the phosphoric acid component in recovered water for corrosion prevention of an aqueous member.

The water quality management method for circulating cooling water according to the present invention is a water quality management method for circulating cooling water using recovered water containing phosphoric acid in at least a part of makeup water, wherein the phosphoric acid concentration in the cooling water is 20 to 25 mg PO ₄ ^3−. Concentration is controlled to be 10 / L, 10-20 mg / L of scale preventing polymer is added, pH of cooling water is controlled to 7.0-7.5, and calcium hardness in cooling water is 1500 mgCaCO ₃ / L or less , Cl ⁻ concentration is 2500 mg / L or less, and SO ₄ ²⁻ concentration is 2500 mg / L or less.

According to the present invention, the water-based member can be prevented from being corroded by phosphoric acid derived from recovered water, and scale can be prevented by adding a scale preventing polymer, pH control and calcium hardness, Cl ⁻ , SO ₄ ²⁻ concentration control ( Including suppression).

It is a flowchart of a test apparatus. It is a flowchart of a test apparatus. It is a graph which shows a test result. It is a graph which shows a test result.

  Hereinafter, the present invention will be described in more detail.

  The present invention is applied to the case where recovered water is used as at least a part of makeup water in an open circulation cooling water system as shown in FIG.

Examples of the recovered water include, but are not limited to, recovered water from municipal wastewater treated water or factory wastewater treated water. It is preferred as the phosphoric acid concentration of the recovered water is 3~7mgPO ₄ ^3- / L especially 4~6mgPO ₄ ^3- / about L.

  FIG. 1 is a flow diagram of a circulating cooling water system used in the examples described later. Water in a pit 1 a of the cooling tower 1 is passed through a water pump 2, a pipe 3, a flow meter 4, a heat exchanger 5, and a pipe 6. Water is sprinkled from the sprinkling nozzle 7 in the upper part of the cooling tower 1 to the filler 8, cooled by latent heat of vaporization, and dropped into the pit 1a.

  It is possible to supply makeup water to the pit 1 a via the makeup water pipe 10 and the ball tap 11.

The electrical conductivity of the water in the pit 1a as measured by electrical conductivity meter 20, calcium hardness, Cl ^- concentration and _SO ^{4 2-calcium} concentration, respectively hardness meter 21, Cl ^- ion sensor 22 and _SO ^{4 2-ion} sensor 23, and the blow pump 25 is controlled by a controller (not shown). The chemical injection pump 26 is controlled so that the polymer concentration in the aqueous system falls within a predetermined range. The polymer concentration in the water system is calculated from the chemical injection amount, the blow amount, and the scattering loss amount. Reference numeral 27 indicates a tank of the scale preventing polymer aqueous solution.

  Further, the pH of the water in the pit 1a is measured by the pH meter 30, and the sulfuric acid in the sulfuric acid tank 31 is injected into the pit 1a by the chemical injection pump 32 so that the pH is in the range of 7.0 to 7.5. To do. Since FIG. 1 shows a test apparatus, cooling water is separated from the pipe 3 into the pipe 40 and is passed through the test container 42 via the flow rate adjustment valve 41, and a test piece (not shown) in the test container 42. A line for returning to the pipe 6 via the pipe 43 is also provided.

In the present invention, the phosphoric acid concentration in the cooling water is 20 to 25 mg PO ₄ ³⁻ / L, the calcium hardness is 1500 mg CaCO ₃ / L or less, the Cl ⁻ concentration is 2500 mg / L or less, and the SO ₄ ²⁻ concentration is 2500 mg. Concentrate and manage to be less than / L That is, operation is performed at as high a concentration rate as possible within a range where these values detected by the respective sensors do not exceed the upper limit value, and thereby the phosphoric acid concentration is set to 20 mg PO ₄ ³⁻ / L or more. If any one of the items of calcium hardness, Cl ⁻ concentration, and SO ₄ ²⁻ concentration exceeds the above upper limit value, the blow pump 25 is operated to blow and make-up water is introduced.

In addition, when the phosphoric acid concentration does not reach 20 mg PO ₄ ³⁻ / L even when the high concentration magnification operation is performed, a phosphoric acid scale inhibitor is added.

  As described above, sulfuric acid is poured into the solution so that the pH is 7.0 to 7.5. When the pH is lower than 7.0, an alkaline agent is added.

  Further, in order to suppress the formation of calcium phosphate scale, a scale preventive polymer (polymer scale inhibitor) is added. The polymer scale inhibitor is one selected from the group consisting of 2-hydroxy-3-allyloxy-1-propanesulfonic acid (HAPS), maleic acid, and 2-acrylamido-2-methylpropanesulfonic acid (AMPS). Or a homopolymer or copolymer having an average molecular weight of about 5,000 to 20,000, wherein two or more monomers are polymerized, or these are copolymerized with acrylic acid (AA) and / or methacrylic acid (MA). Is preferred.

  By managing the cooling water system as described above, it is possible to prevent corrosion of the water system member by utilizing the phosphoric acid derived from the recovered water, and scale adhesion is also suppressed.

[Example 1]
In the test apparatus shown in FIG. 1, concentration management was performed under the following conditions using synthetic makeup water having the following water quality. During the test period, a part of the cooling water was poured into the container 42 and brought into contact with the iron test piece stored in the container 42, and the corrosion rate was measured from the corrosion weight loss of the test piece.
<Supply water>
To tap water Tochigi Prefecture Nogi-machi, the orthophosphate with adding 5 mg / L, so that the CaCl ₂ becomes calcium hardness 300mg / LasCaCO _3, NaCl so as to have a chloride ion concentration 500 mg / L, Na ₂ SO ₄ added to a sulfate ion concentration of 500 mg / L.
<Concentration multiple>
The concentration factor was 2, 3, 4, 5 or 6 times.
<PH>
The pH was adjusted to 7.0 to 7.5 with sulfuric acid.
<Polymer>
12 mg-solid / L of AA / HAPS polymer (weight average molecular weight 10,000) and AA / AMPS polymer (weight average molecular weight 10,000) were added.

  The corrosion rate of the test piece (iron) at the end of the test is shown in FIG. The anticorrosion effect became favorable by managing the concentration factor and maintaining the phosphorus concentration at 20 to 25 mg / L. On the other hand, it was found that the corrosion rate increases when the phosphorus concentration is low (current treatment) or excessively, and the effect is insufficient in a high salt concentration aqueous system.

[Test Example 1]
The adhesion rate to the heat transfer surface was measured using a high heat load test apparatus (FIG. 2). In FIG. 2, test water corresponding to the following water quality (hereinafter referred to as make-up water) is supplied into a tank 50, and this make-up water is circulated and supplied to a test tank 52 by a pump 51. A steel tube (outer diameter 30 mm, length 300 mm) 53 with an electric heater 54 inserted therein was accommodated. The water temperature was 30 ° C., and the surface temperature of the tube 53 was 80 ° C. by the electric heater 54. The residence time was continuously supplied so as to be 80 hours. The test period was 48 hours, and the amount of adhesion was measured after 48 hours withdrawing the tube. As a comparative example, the evaluation with conventionally known N = 2 equivalent water (pH 8.0, calcium hardness 500 mg / L, T-PO ₄ 10 mg / L) was also performed.

<Supply water equivalent test water>
A 5% M alkaline solution (Na bicarbonate solution) is added to pure water so that the M alkalinity is 100 mg / LasCaCO _3, and AA / HAPS polymer (80/20, molecular weight 5,000) and AA / AMPS are added. System polymer (80/20, molecular weight 10,000) is added at 12 mg-solid / L, orthophosphoric acid is added so that the phosphorous concentration is 20 mg PO ₄ / L, and CaCl ₂ is added with a calcium hardness of 1,200 mg / LasCaCO ₃ . NaCl was added to a chloride ion concentration of 2500 mg / L, Na ₂ SO ₄ was added to a sulfate ion concentration of 1000 mg / L, and the pH was adjusted to 7.0 to 8.0 with sulfuric acid. Adjusted.

  The adhesion rate measurement results are shown in FIG. As shown in FIG. 4, many scales are observed when the pH is 7.8 or higher. However, when pH is 7.5 or lower, the adhesion is light, and the amount of adhesion is lighter than the conventional treatment.

1 Cooling Tower 5 Heat Exchanger 11 Ball Tap 25 Blow Pump

Claims (2)

In the water quality management method for circulating cooling water using recovered water containing phosphoric acid in at least a part of makeup water,
Concentration is controlled so that the phosphoric acid concentration in the cooling water is 20 to 25 mg PO ₄ ³⁻ / L, 10-20 mg / L of the scale prevention polymer is added, and the pH of the cooling water is controlled to 7.0 to 7.5. A water quality management method for circulating cooling water, characterized in that the calcium hardness in the cooling water is 1500 mg CaCO ₃ / L or less, the Cl ⁻ concentration is 2500 mg / L or less, and the SO ₄ ²⁻ concentration is 2500 mg / L or less. The water quality management method for circulating cooling water according to claim 1, wherein the concentration of phosphoric acid in the recovered water is ³ to 7 mg P ₄ ³ / / L.

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