JP7468570B2 - Steam condensate recovery method - Google Patents

Description

The present invention relates to a method for recovering steam condensate (drain) in steam generating equipment such as a boiler.

Thermal energy from steam is the most widely used energy source in industry. Approximately 80% of the total heat of steam is effectively utilized, the latent heat of vaporization, and the remaining sensible heat is often discarded as drain. If drain is recovered and effectively used as boiler feed water, it can contribute to reducing boiler fuel, reducing _CO2 emissions, and saving water.

However, there are many cases where drain water quality is poor and it is not recovered. For example, if the drain water contains a large amount of metal ions and oxides of iron, copper, zinc, etc. due to corrosion of the steam pipes or heat exchanger, these are known to be carried into the boiler and accumulate at the bottom of the boiler, causing secondary corrosion, or to adhere as scale to the evaporator tubes, causing heat transfer problems, etc. For this reason, there have been cases where drain recovery had to be abandoned.

Patent Document 1 discloses a condensate supply method and water supply device for a boiler system that measures the drain water quality and water temperature at regular intervals and determines whether the drain can be recovered. In Patent Document 1, if it is determined that the drain water quality or water temperature does not meet the standards, the drain is discarded.

JP 2003-343807 A

In Patent Document 1, drain that does not meet the standards for water quality and water temperature is not recovered, so water savings, heat recovery, and reduction in boiler blow water through drain recovery are insufficient.

In addition, in Patent Document 1, the iron ion concentration and copper ion concentration in the drain are measured, but there is no inexpensive device that can continuously measure metal concentration on-site. Therefore, to measure the iron ion concentration and copper ion concentration, it is necessary to bring a condensate sample back from the site and analyze the respective metal ions at an analysis laboratory. Therefore, in Patent Document 1, drain recovery cannot be performed in response to changes in the drain water quality quickly.

The objective of the present invention is to provide a method for recovering steam condensate (drain) that can be appropriately recovered.

In order to solve the above problems, the present invention provides the following:

[1] A method for recovering steam condensate in a steam generating facility that recovers drainage, measuring the turbidity of the drainage and adding a scale inhibitor to the water supply to the steam generating facility based on the turbidity.

[2] In a steam generating facility that recovers drain, an approximation equation of a positive correlation between the turbidity of the drain and a concentration of at least one metal selected from iron, copper, and zinc in the drain is obtained,
A method for recovering steam condensate, comprising determining a metal concentration in the drain from a turbidity measurement value and the approximation formula, and adding a scale inhibitor to the water supplied to the steam generating facility based on the metal concentration.

[3] The method for recovering steam condensate according to [1], in which the scale inhibitor is a polymethacrylate having a weight-average molecular weight of 1,000 to 100,000.

[4] The method for recovering steam condensate according to [2], in which the scale inhibitor is a polymethacrylate having a weight-average molecular weight of 1,000 to 100,000, and the amount of scale inhibitor added is 0.5 to 10 times the metal concentration calculated from the turbidity measurement value and the approximation formula.

[5] A method for recovering steam condensate in a steam generation facility that recovers drainage, measuring the turbidity of the drainage and determining whether or not the drainage can be recovered based on the turbidity.

[6] A method for recovering steam condensate in a steam generating facility that recovers drainage, measuring the turbidity of the drainage, recovering the drainage as is if the turbidity is lower than a predetermined value a, and recovering the drainage after improving its quality using a water quality improvement device if the turbidity is within a predetermined range a to b (where b > a).

[7] The steam generating equipment is equipped with a water supply tank that stores softened water obtained by softening raw water, and the drain is collected in the water supply tank. [6] A method for recovering steam condensate.

[8] The steam generating facility includes a raw water tank for storing raw water for supplying the steam generating facility,
The method for recovering steam condensate according to [6], wherein drain is recovered in the raw water tank when the turbidity is higher than b.

[9] In a steam generating facility that recovers drain, an approximation equation of a positive correlation between the turbidity of the drain and a concentration of at least one metal selected from iron, copper, and zinc in the drain is obtained,
A steam condensate recovery method in which the metal concentration in the drain is calculated from the turbidity measurement value and the approximation formula, and whether or not the drain can be recovered is determined based on this metal concentration.

[10] In a steam generating facility that recovers drain, an approximation equation of a positive correlation between the turbidity of the drain and a concentration of at least one metal selected from iron, copper, and zinc in the drain is obtained,
This steam condensate recovery method determines the metal concentration in the drain from the turbidity measurement value and the approximation formula, and if the metal concentration is lower than a predetermined value c, recovers the drain as is, and if the metal concentration is within a predetermined range c to d (where d > c), improves the quality of the drain using a water quality improvement device before recovering it.

[11] The steam generation facility is equipped with a water supply tank that stores softened water obtained by softening raw water, and the drain is collected in the water supply tank. [10] A method for recovering steam condensate.

[12] The steam generating facility includes a raw water tank for storing raw water to be supplied to the steam generating facility,
The method for recovering steam condensate according to [10], wherein when the metal concentration is higher than d, drain is recovered in the raw water tank.

[13] The method for recovering steam condensate according to [6] or [10], wherein the water quality improvement device is a device for removing metal oxides or metal ions.

As a result of extensive research conducted by the inventors to achieve the above-mentioned objective, they discovered that there is a positive correlation between the concentration of metals in drain and turbidity. By continuously monitoring the turbidity and recovering drain or adding a scale inhibitor according to the turbidity value, it is possible to effectively suppress the formation of scale on the metals brought into the boiler. It is also possible to prevent energy loss caused by the adhesion of scale to the boiler's heat transfer surfaces, and to reduce energy costs by recovering the water and heat from the drain.

FIG. 2 is a flow diagram of the boiler facility. 1 is a graph showing the results of an example. 1 is a graph showing the results of an example. 1 is a graph showing the results of an example. 1 is a graph showing the results of an example.

As mentioned above, there is a positive correlation between the concentration of metals contained in drain (including all forms of metal oxides and metal ions) and turbidity. For example, as shown in the examples below, there is a positive correlation between the turbidity of drain and the concentrations of iron, copper, and zinc. In particular, there is a strong correlation between the concentration of iron, which is found in large amounts in drain, and turbidity. There is also a strong correlation between the total concentration of iron, copper, and zinc and turbidity. Specifically, there is a relationship between concentration Y and turbidity X: Y = α·X (α: constant).

The present invention is based on such findings, and in one aspect of the present invention, in a steam generating facility such as a boiler that recovers drainage, the turbidity of the drainage is measured, and depending on the turbidity, measures are taken such as adding a scale inhibitor to the water supply to the steam generating facility, improving the water quality of the drainage, or determining whether or not the drainage can be recovered.

When taking action based on the drain turbidity measurement, for example, if the drain turbidity is 50 or less, drain recovery is performed, and if the turbidity is over 50, for example 51 or more, the drain is discarded or the water quality is improved and the drain is recovered.

In another aspect of the present invention, the metal concentration in the drain is calculated from an approximation (correlation equation) of the positive correlation between drain turbidity and metal concentration, and measures such as adding a scale inhibitor, improving the drain water quality, or determining whether or not to recover the drain are taken depending on the metal concentration.

In the present invention, the turbidity measuring device is not particularly limited as long as it can determine the turbidity in the drain. For example, the transmitted light turbidity, scattered light turbidity, and integrating sphere turbidity tests specified in JIS K0101:2017 can be used.

In the present invention, when water quality is improved, a water quality improvement device can be provided in the drain recovery line, or the water can be returned to the raw water tank and treated for water quality improvement. As a device for improving water quality, a device that removes metal oxides and metal ions is preferably used. As this device, for example, ion exchange resin, hollow fiber membrane, RO membrane, filter material, thread-wound filter, metal filter, or a combination thereof can be used.

The scale inhibitors used in the present invention include polymethacrylic acid and/or its salts, polyacrylic acid and/or its salts, polymaleic acid and/or its salts, polyitaconic acid and/or its salts, and copolymers and terpolymers obtained by copolymerizing at least two of the monomer components constituting these homopolymers.

In addition, copolymers (AA-HAPS, AA-AMPS, etc.) of at least one of the monomer components (acrylic acid (AA), maleic acid (MA), etc.) constituting the homopolymer with sodium 3-allyloxy-2-hydroxypropanesulfonate (HAPS) or sodium 2-acrylamido-2-methylpropanesulfonate (AMPS), bis(poly-2-carboxyethyl)phosphinic acid and/or its salts, carboxymethylcellulose (CMC) in which carboxymethyl groups are bonded to some of the hydroxy groups of the glucopyranose monomers constituting the cellulose backbone, 1-hydroxyethylidene-1,1-diphosphonic acid (hereinafter abbreviated as HEDP), etc. can also be used.

The above scale inhibitors can be used alone or in combination of two or more.

Among these, from the viewpoint of the effect of preventing iron scale in the water-side can of the boiler, poly(meth)acrylic acid compounds such as polyacrylic acid and/or its salts, polymethacrylic acid and/or its salts are preferred, with polymethacrylic acid and/or its salts being more preferred. The weight-average molecular weight of polyacrylic acid and/or its salts may be, for example, 1,000 to 100,000, preferably 1,000 to 40,000, and more preferably 1,000 to 20,000. The weight-average molecular weight of polymethacrylic acid and/or its salts may be, for example, 1,000 to 100,000, preferably 1,000 to 50,000, more preferably 5,000 to 50,000, and particularly preferably 5,000 to 20,000.

In one aspect of the present invention, the amount of scale inhibitor added is determined based on the metal concentration calculated from the approximation formula of the above correlation. For example, the turbidity and the metal concentrations of iron, copper, and zinc (including all forms of metal oxides and metal ions) are analyzed at the site where the scale inhibitor is to be applied in advance to calculate an approximation formula, and the metal concentration in the drain water is calculated from the approximation formula. The amount of scale inhibitor added may be a specified multiple of the calculated metal concentration (total value of the metal concentrations of iron, copper, and zinc), for example, 0.1 to 20 times, preferably 0.5 to 10 times, more preferably 1 to 10 times, even more preferably 3 to 10 times, and particularly preferably 5 to 10 times.

It is preferable to monitor the relationship between turbidity and metal concentration and update the approximation formula.

To more effectively prevent the above-mentioned scale, it is preferable to control the recovery according to the turbidity of the drain. For example, consider a case where the drain piping is heavily contaminated with metals that have eluted during start-up of the boiler after a factory holiday. In this case, a threshold value is set for the turbidity to determine whether or not the drain can be recovered. If the turbidity of the drain is 50 or less, the above-mentioned drain recovery is performed, and if the turbidity is 51 or more, the drain is discarded or the water quality is improved before recovery. If the water quality is to be improved, it can be treated by passing it through a water quality improvement device, or returned to the raw water tank for treatment.

In addition to the scale inhibitor, additive components used in conventional boiler scale inhibitors and anticorrosive agents, such as alkaline agents, oxygen scavengers, anticorrosive agents, and condensate treatment agents, may be added as necessary, provided that the effects of the present invention are not impaired. For example, the addition of oxygen scavengers and condensate treatment agents can increase the anticorrosive effect in the steam and drain piping in the steam generation equipment and suppress the metal concentration in the drain water.

In the present invention, the turbidity, temperature, and flow rate of drain, and the temperature and flow rate of boiler make-up water and/or feed water may be continuously measured and monitored on the web. Also, the drain recovery rate, fuel reduction effect, _CO2 reduction effect, and water saving effect may be estimated from each of these pieces of information, and the data collected from each factory may be benchmarked and displayed on the web so that it can be arbitrarily compared by factory size or type of industry.

An example of a boiler facility to which the present invention can be applied is shown in Figure 1.

The raw water for the boiler feed is softened through the raw water tank 1, iron removal device 2, and softener 3, and then introduced into the feed water tank 4. The water in the feed water tank 4 is fed from the deaerator 5 through the feed water piping 6 to the boiler 7. The feed water piping 6 is provided with a chemical injection device 19 for a scale inhibitor.

The steam generated in the boiler 7 is supplied to the steam-using equipment 9 via the steam header 8. The drain generated in the steam-using equipment 9 flows out into the pipe 10. The pipe 10 branches into pipes 12, 13, and 14 via a switching valve 11. The pipe 12 is connected to the water supply tank 4. The pipe 13 is connected to the water quality improvement device 15, and the water from the water quality improvement device 15 is introduced into the water supply tank 4. The pipe 14 is connected to the raw water tank 1.

The piping 10 is provided with a thermometer 21, a flowmeter 22, and a turbidity meter 23. These detection signals are input to a control device 24. The control device 24 controls the switching valve 11 and the scale inhibitor dosing device 19 based on the turbidity and the metal concentration calculated from the approximation formula.

The control of the switching valve 11 and the chemical injection device 19 by the control device 24 is as described above.

For example, if the turbidity of the drain is equal to or lower than a predetermined value a, the drain is sent to the water supply tank 4, if it is equal to or higher than a but equal to or lower than b (a<b), the drain is sent to the water quality improvement device 15, and if it exceeds b, the drain is sent to the raw water tank 1. Also, the amount of chemicals to be injected from the chemical injection device 19 (e.g., the number of revolutions of the chemical injection pump) is controlled according to the turbidity.

Similarly, if the metal concentration calculated from the turbidity of the drain is equal to or lower than a predetermined value c, the drain is sent to the water supply tank 4, if it is equal to or higher than c but equal to or lower than d (c<d), the drain is sent to the water quality improvement device 15, and if it exceeds d, the drain is sent to the raw water tank 1. Also, the amount of chemicals injected from the chemical injection device 19 is controlled according to the metal concentration calculated from the turbidity.

[Experimental Example 1]
At a factory that uses a low-pressure small-scale once-through boiler for soft water supply, drain water was continuously sampled and analyzed for iron concentration and turbidity to verify whether there was a correlation.
<Experimental conditions>
Soft water supply: M alkalinity 30 mg as CaCO ₃ /L
Boiler pressure: 0.6 MPa
Steam drain flow rate: 5 L/min
Steam and drain piping materials: Steel is used; copper and zinc are not used.
Material of steam equipment: Steel only Timing of water collection: Start the boiler two days after the boiler operation is stopped, and then run the water to the feedwater tank.
Once drain water starts coming out of the drain collection pipe,
Water was collected from the area.
Iron concentration: The iron concentration in the drain water, including both iron oxides and iron ions, was analyzed.
The collected drain water contains iron oxide and iron ions.
Add hydrochloric acid to the mixture, heat it, dilute it if necessary, pretreat it, and then use a flame atomic absorption spectrometer.
It was analyzed by spectrophotometry.
Turbidity: Analyzed using a transmitted light type turbidimeter.
Number of drainage samples: 60 samples

<Results and Discussion>
The relationship between turbidity and iron concentration (total iron concentration including iron oxide and iron ions; the same applies below) is shown in FIG.

As shown in FIG. 2, it was confirmed that there is a positive correlation between turbidity and iron concentration in the turbidity range of 0.1 to 501 and the iron concentration range of 0.01 to 135 mg/L.
Approximation Y (iron concentration) = 0.2469X (turbidity), correlation coefficient ^R2 = 0.9592

Figure 3 shows the change in turbidity and iron concentration over time. It can be seen from Figure 3 that the turbidity and iron concentration in the drain water rise sharply immediately after the boiler is started up, and then gradually decrease over time. This shows that, depending on the timing of boiler operation and drain recovery, there are times when there is a lot of iron contamination, and therefore measures are needed to prevent scale formation inside the boiler.

[Experimental Example 2]
At other factories that use low-pressure small-scale flow-through boilers for soft water supply, drain samples were taken multiple times and the metal concentrations and turbidity were analyzed to verify whether there was a correlation.
<Experimental conditions>
Soft water supply: M alkalinity 10-60 mg as CaCO ₃ /L
Boiler pressure: 0.7 MPa
Steam drain flow rate: 100 L/min
Steam and drain pipe materials: Steel was mainly used, with some zinc used. Steam equipment materials: Steel and copper. Water sampling timing: Water was sampled five times at hourly intervals for each factory.
Metal concentration: Analyzes the metal concentration in drain water, including all metal oxides and metal ions
Hydrochloric acid was added to the collected drainage water, heated, and diluted as necessary.
After treatment, the mixture was analyzed by flame atomic absorption spectrometry.
Turbidity: Analyzed using a transmitted light type turbidimeter.
Number of factories: 14 Number of drainage samples: 70

<Results and Discussion>
The results are shown in Figures 4 and 5 and Table 1. From Figure 4 and Table 1, looking at the individual metals, the correlation between turbidity and iron was the highest, followed by the correlation between turbidity and copper, and the correlation between turbidity and zinc was the lowest.

Furthermore, Figures 4 and 5 and Table 1 show that turbidity is more strongly correlated with the total metal concentration than with the concentration of each individual metal.

[Comparative Examples 1 to 13, Examples 1 to 17]
＜Overview＞
Using a boiler facility having the configuration shown in FIG. 1 and equipped with a low-pressure small-scale once-through boiler with a soft water supply (however, two boilers are installed in parallel), the scale prevention effect was evaluated in the following cases: when no scale inhibitor was added (Comparative Example 1), when a fixed amount of scale inhibitor was constantly injected (Comparative Examples 2 to 13), and when the turbidity of drain water was continuously measured and the injection of scale inhibitor was controlled in accordance with the value (Examples 1 to 17).

The iron, copper, and zinc concentrations in the drain water rose sharply immediately after drain collection to simulate the actual equipment, and the water quality was adjusted so that they dropped to normal concentrations after one hour.

Sludge recovery balance (SRB) was used to determine the effectiveness of scale prevention. SRB is an index that shows how much of the metals in the boiler's feed water are discharged into the boiler's blow water, and the higher the value, the better the scale prevention is considered to be. The average SRB% in Table 2 was calculated by finding the values for five water samples using the SRB% formula below, and then averaging them.

<Experimental conditions>
Soft water supply: M alkalinity 30 mg as CaCO ₃ /L, silica 15 mg/L, hardness less than 1 mg as CaCO ₃ /L Boiler pressure: 0.6 MPa
Boiler water supply: 250L/h - 1 boiler Drain recovery rate: 99%
Boiler concentration ratio: 10 times. Materials of steam-using equipment: Stainless steel material was used to prevent the drain water from becoming dirty.
Timing of water sampling: For metal concentration measurement, water was collected from the drain and collected 5 times at 15-minute intervals.
The boiler water was also sampled.
Metal concentration: Analyzes the metal concentration in drain water, including all metal oxides and metal ions
Hydrochloric acid was added to the collected drainage water, heated, and diluted as necessary.
After treatment, the mixture was analyzed by flame atomic absorption spectrometry.
Turbidity: The turbidity of the drain water was continuously measured using a transmitted light turbidity meter.
Adjustment of each metal concentration: Iron concentration was adjusted using iron oxide and iron chloride. Copper concentration was adjusted using
Copper oxide and copper chloride were used. The zinc concentration was adjusted using zinc chloride.
there was.
Iron concentration in drain water: Adjusted in the range of 0.05 to 15 mg/L.
Start the injection and adjust so that the concentration decreases by 1.25 mg/L every 5 minutes.
Adjusted.
Copper concentration in drain water: Adjusted in the range of 0.01 to 2.0 mg/L.
The drug administration was started so that the concentration decreased by 0.17 mg/L every 5 minutes.
was adjusted to.
Zinc concentration in drain water: Adjusted in the range of 0.01 to 1.0 mg/L.
The drug administration started at 0.08 mg/L every 5 minutes.
It was adjusted as follows.
Scale inhibitor: The ones shown in Table 2 were used.
Amount of scale inhibitor added: In the comparative example, each scale inhibitor was added at 5 mg/L regardless of turbidity.
A constant amount was continuously injected.
From the value of the degree, the approximate formula of [Example 2] (y = 0.3375x,
y is the metal concentration, x is the turbidity)
Ten-fold amounts were added as shown in the table.
SRB%: SRB% = {boiler metal concentration / (feedwater metal concentration x concentration factor)} x 100
Boiler water pH adjuster: NaOH and KOH make the boiler water pH 11.5
It was adjusted as follows.

<Results and Discussion>
The results are shown in Table 2. It was found from Table 2 that a high metal scale inhibition effect can be obtained when a scale inhibitor is added according to the metal concentration calculated from the turbidity value. In particular, it was found that an excellent metal scale inhibition effect can be obtained when sodium polymethacrylate having a weight average molecular weight of 5,000 to 50,000 is used as the scale inhibitor and the amount added is 0.5 to 10 times the metal concentration.

In addition, even if the metal concentration in the drain water changes due to changes in the drain recovery rate or recovery of drain after a shutdown period, and high concentrations of metals are fed to the boiler, the metal concentration in the drain can be estimated by continuously monitoring the turbidity, and a scale inhibitor can be added according to that concentration, providing excellent metal scale prevention effects and allowing the drain to be recovered.

The symbols in Table 2 are as follows:
PAA: Sodium polyacrylate
PMA: Sodium polymethacrylate
AA-HAPS: Sodium 3-allyloxy-2-hydroxypropanesulfonate of acrylic acid
AA-AMPS: Sodium acrylic acid-2-acrylamido-2-methylpropanesulfonate
CMC: Carboxymethyl cellulose
HEDP: 1-hydroxyethylidene-1,1-diphosphonic acid

REFERENCE SIGNS LIST 1 raw water tank 4 feed water tank 7 boiler 11 changeover valve 15 water quality improvement device 19 chemical injection device 21 thermometer 22 flowmeter 23 turbidity meter

Claims (4)

In a steam generating facility that recovers drain, an approximate equation for a positive correlation between the turbidity of the drain and the total metal concentration of iron, copper, and zinc in the drain is obtained,
A method for recovering steam condensate, comprising the steps of: determining a total metal concentration of iron, copper and zinc in the drain from a turbidity measurement value and the approximation formula; and adding a scale inhibitor to the water supplied to the steam generating facility based on the total metal concentration;
The scale inhibitor is a polymethacrylate having a weight average molecular weight of 1,000 to 100,000, and the amount of the scale inhibitor added is 0.5 to 10 times the metal concentration calculated from the turbidity measurement value and the approximation formula,
A steam condensate recovery method in which, when the metal concentration calculated from the turbidity measurement value and the approximation formula is lower than a predetermined value c, the drain is recovered as is, and, when the metal concentration is within a predetermined range c to d (where d > c), the drain is recovered after its quality is improved using a water quality improvement device. The steam generation facility is provided with a water supply tank that stores softened water obtained by softening raw water, and the drain is collected in the water supply tank. The steam condensate recovery method of claim 1. The steam generating facility includes a raw water tank that stores raw water to be supplied to the steam generating facility,
2. The method for recovering steam condensate according to claim 1, further comprising recovering drain in said raw water tank when said metal concentration is higher than said d. The steam condensate recovery method according to any one of claims 1 to 3, wherein the water quality improvement device is a device for removing metal oxides or metal ions.

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