JP2007209942A - Obtaining method of variation of concentration of dissolved calcium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To use the forcibly caused variation of a liquid property like pH value as an index of the variation of concentration of dissolved calcium. <P>SOLUTION: When removing dissolved calcium in a treating object liquid by aeration with carbon dioxide, addition of alkali is started or stopped within a given pH range, to forcibly raise or lower pH of the treating object liquid. Lowering time of pH in this operation is checked in a Step 100, aeration with carbon dioxide is appropriately controlled in a Step 200 or a Step 300, to correctly determine stopping of addition. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a technique for grasping a change in the concentration of dissolved calcium, and in particular, is a technique that can be effectively applied to a determination at the end of aeration when removing dissolved calcium by aeration of carbon dioxide.

  In the leachate etc. at the final disposal site, it is required that calcium removal is reliably performed in the previous process when wastewater containing a large amount of calcium is treated. This is because the subsequent water treatment may cause a serious failure such as deterioration of the membrane due to the scale or damage to the equipment.

  However, in current water treatment, there is no technique for continuously monitoring changes in calcium concentration in the treatment liquid, and an excess amount multiplied by a safety factor is added to the set amount of chemicals such as sodium carbonate for removing calcium. Therefore, the present situation is that the dissolved calcium can be reliably removed even when the calcium concentration changes to some extent.

  In such a conventional method, since a change in the concentration of dissolved calcium is not monitored, it cannot cope with an unexpected change in the calcium concentration. For this reason, problems such as a delay in response when trouble occurs and an increase in salt concentration due to the addition of an excessive amount of chemicals occur.

The present inventor previously disclosed a technique in Patent Document 1 that allows the concentration of dissolved calcium to be accurately grasped to some extent by tracking the fluctuation range of pH.
JP 2005-161224 A

  When removing dissolved calcium by aeration of carbon dioxide, as a technique for monitoring the change in the calcium concentration in the treatment liquid, there is a technique using the fluctuation range of pH disclosed in Patent Document 1. The method using this fluctuation range can capture the change with high sensitivity to the calcium concentration.

  However, since it is a method that depends on the outcome of the aeration process, there is a problem that it is difficult to exclude the influence of the performance of the device, noise, and the like.

  Therefore, the present inventor has thought that by forcibly causing pH fluctuation, it is possible to monitor dissolved calcium with less influence.

  An object of the present invention is to grasp a change in the concentration of dissolved calcium based on a forced change in liquidity such as pH.

  The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

  Of the inventions disclosed in the present application, the outline of typical ones will be briefly described as follows.

  The present invention is a method for grasping a change in the concentration of dissolved calcium, characterized in that a change in the concentration of dissolved calcium is known from a change in liquidity. In this configuration, the liquid change is a liquid time change. Alternatively, the liquid property change is a liquid property speed change. By using such a configuration, the aeration end point is determined when the dissolved calcium in the solution is removed by aeration with carbon dioxide.

  The present invention is a method for grasping a change in the concentration of dissolved calcium, characterized in that a change in the concentration of dissolved calcium is known from a change in pH. In this configuration, the change in pH is a change in pH over time. The time in the time change of pH is a rising time in a predetermined range of pH or a falling time in a predetermined range of pH. Alternatively, in the above configuration, the change in pH is a change in pH speed. The speed in the rate change of pH is obtained by dividing the amount of change in pH in a predetermined range of pH by the time required to achieve the amount of change.

  In the above configuration, the predetermined pH range is a pH range of 8.5 or more and 9.5 or less. In the above structure, the liquid property is a hydrogen ion concentration, a hydroxide ion concentration, or pOH of the solution.

  Among the inventions disclosed in the present application, effects obtained by typical ones will be briefly described as follows.

  In the present invention, the change in the concentration of dissolved calcium can be monitored and grasped by tracking the liquidity such as pH within a predetermined range by artificially changing it. Thereby, for example, it is possible to easily determine the aeration end point in the removal of dissolved calcium by aeration of carbon dioxide.

  Moreover, since the concentration change of dissolved calcium can be followed in real time, appropriate aeration can be performed and useless addition of alkali can be prevented. According to the present invention, efficient calcium removal can be performed.

  In the present invention, the liquidity such as pH is artificially changed forcibly, so it is easy to exclude the influence of the device or the like on the fluctuation.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  The present invention uses the change in liquidity as an index when grasping the change in the concentration of dissolved calcium. By using such an indicator, it is possible to know the concentration of dissolved calcium, change in concentration, and the like.

As the liquid property, for example, pH (hydrogen ion concentration index) can be used. Alternatively, liquid properties such as hydrogen ion concentration ([H ⁺ ]), pOH (hydroxide ion concentration index), and hydroxide ion concentration ([OH ⁻ ]) may be used. In the following description, pH is taken as an example of liquidity.

  In the present invention, the concentration change of dissolved calcium is known by forcibly raising and lowering the pH in a predetermined pH range and monitoring the fluctuation state. For example, the pH range may be set to 8.5 or more and 9.5 or less. In the setting of such a range, the lower limit was set based on the reason that the abundance ratio of carbonate ions increased from around 8.5, and the upper limit was set based on the reason that excessive addition of alkali was prevented.

  In the present invention, the pH is raised or lowered within the above-mentioned predetermined pH range, but the increase in pH is carried out by adding an alkali. Examples of the alkali include sodium hydroxide and potassium hydroxide. Moreover, use of regenerated alkalis, such as an eco alkali, is also mentioned. The pH may be lowered by aeration of carbon dioxide. Carbon dioxide that can be used for aeration has a concentration in the range of, for example, 0.5% or more and 100% or less. As this carbon dioxide source, any gas containing carbon dioxide such as exhaust gas from combustion engines such as boilers and engines, exhaust gas from facilities such as garbage incinerators, and gas generated from landfills can be used in the present invention. Is possible. Alternatively, artificially mixed carbon dioxide and air may be used.

(Embodiment 1)
In the present embodiment, a case where dissolved calcium in a solution is removed by aeration of carbon dioxide will be described as an example. For example, when reducing the concentration of dissolved calcium in a liquid to be treated, such as a waste liquid, to 100 mg / l or less at which no scale is generated by aeration of carbon dioxide, it is effective when applied to efficiently aeration.

  FIG. 1 shows a situation in which high-low control (also referred to as high-low control) of the present invention is performed with carbon dioxide and alkali in a batch processing system in which carbon dioxide is aerated to precipitate and remove dissolved calcium. It is explanatory drawing which shows. FIG. 2 is an explanatory diagram showing the state of height control in the system in the continuous processing, as in FIG. FIG. 3 is an explanatory diagram showing the transition of the pH fall time in the batch processing system. FIG. 4 is an explanatory diagram showing the transition of the pH fall time in the continuous treatment system. FIG. 5 is an explanatory diagram showing the relationship between the pH fall time and the IC (Inorganic Carbon) concentration in the solution. FIG. 6 is a flowchart showing the procedure of the method for grasping the concentration change of dissolved calcium according to the present invention.

First, experimental facts that are the basis of the present invention will be described. The experiment was performed as a predetermined range of pH between pH 9.0 and pH 9.2 within the set range. In this pH range, a solution having a calcium concentration of 1000 ppm was treated while aerating a gas containing 1 vol% CO ₂ (also referred to as carbon dioxide or carbon dioxide) while performing high-low control. The aeration intensity is, for example, 1.0 vvm.

  In this treatment, dissolved calcium is precipitated as calcium carbonate, a predetermined amount of dissolved calcium is removed from the solution, and the dissolved calcium is suppressed to a predetermined value or less. The target concentration of dissolved calcium was set at 100 mg / l. The value of 100 mg / l is a practical numerical value that is adopted in actual waste liquid treatment or the like as a dissolved calcium concentration that does not generate scale. However, the above numerical values are merely exemplary numerical values, and the application of the present invention can be used for monitoring for preventing scale because, for example, dissolved calcium can be quantified in a concentration range of 200 mg / l or less.

  FIG. 1 shows a batch processing system, and FIG. 2 shows a continuous processing system. The batch process shown in FIG. 1 is a batch process in which a liquid to be processed such as a predetermined amount of waste liquid is precipitated by aeration of carbon dioxide as described above, and then the same volume of liquid to be processed is replaced and processed separately. . On the other hand, the continuous processing is configured such that a predetermined amount of liquid to be processed such as waste liquid is continuously flowed in and a predetermined amount of processed liquid is continuously discharged while maintaining a predetermined capacity. It is what.

In the batch processing system and the continuous processing system, for example, the amount of the liquid to be processed was 2 liters. However, since the aeration itself involves the stirring of the solution, there is no particular stirring in the solution. It was.
Of course, in the actual processing, it is not necessary to stir the solution.

  As shown in FIG. 1, the calcium concentration changed to a target value of 100 mg / l or less around 120 minutes after the start of aeration. The level control in such a system is a technique in which the pH is increased to 9.2 by adding an alkali when the pH is lowered to 9.0 due to aeration of carbon dioxide, and the addition of the alkali is stopped when the pH reaches 9.2. Was used. Of course, the aeration of carbon dioxide is continuously performed including the period between the addition of alkali and the stop of the addition.

  In this way, when the pH becomes 9.0 or 9.2 in a predetermined pH range, for example, the alkali addition and the alkali addition are stopped to forcibly cause the pH to fluctuate. However, strictly speaking, it takes some time until the pH in the solution becomes uniform due to the stirring condition of the solution. Therefore, there is a slight difference from the solution pH at the time when it becomes uniform with respect to the measured pH. Therefore, in FIG. 1, the result is that the pH is 9.0 or less and 9.2 or more.

  As shown in FIG. 1, the pH of the solution does not repeat exactly at 9.0 and 9.2. However, as a control for high and low, alkali addition should be performed when the pH reaches 9.0. The addition of alkali is stopped when the pH reaches 9.2.

  It is confirmed from FIG. 1 that dissolved calcium is effectively precipitated and removed by carbon dioxide to be aerated even when such high and low control is performed. It was found that dissolved calcium can be removed to a target value of 100 mg / l or less, which can prevent the occurrence of scale.

  Such a tendency was also confirmed in the continuous processing system as shown in FIG. Dissolved calcium changed to 100 mg / l or less when a little after 2 hours from the start of aeration. However, in such continuous processing, when 7.2 hours have elapsed, the hydraulic residence time (HRT) is changed from 2.7 hours to 3.6 hours for the purpose of changing the Ca load. did. Therefore, in FIG. 2, a decrease in calcium concentration and an increase in IC (Inorganic Carbon) concentration occur after 7.2 hours.

  In the present invention, as described above, the effectiveness that the dissolved calcium can be effectively removed by aeration of carbon dioxide was confirmed even when such height control was performed. In addition, in the up-and-down fluctuation of the pH obtained by the height control, a case where the dissolved calcium concentration change is grasped and the end point determination in the aeration process of the dissolved calcium is performed will be described below.

  The pH fall time is defined as meaning the time from when the pH starts to decrease until the pH starts to increase when the pH is moving up and down under high and low control.

  Such a pH fall time is considered to be controlled by the following reaction formula.

CO ₂ + H ₂ O → CO ₃ ²⁻ + 2H ⁺ (or HCO ₃ ⁻ + H ⁺ )
CO ₃ ²⁻ + Ca ²⁺ → CaCO ₃
Thus, a decrease in pH occurs due to H ⁺ released by the dissolution of carbon dioxide. If the calcium concentration is high, the equilibrium tends to proceed rightward, and the amount of H ⁺ released is also increased. Therefore, when the calcium concentration is high, the pH fall time is short, and when the calcium concentration is low, the fall time is long. That is, by monitoring the pH fall time, the concentration change of dissolved calcium can be monitored and grasped.

In addition, the change in the IC concentration (generated CO ₃ ²⁻ , HCO ₃ ⁻ ) of the solution when such height control is performed is as shown in FIG. 3 in the batch processing system. It can be seen from FIG. 3 that this tendency is almost linked to the IC concentration in the solution. Incidentally, the measurement of the IC concentration is performed by sampling at regular intervals.

When the dissolved calcium concentration in the solution is initially high, IC dissolved by aeration of CO ₂ is immediately consumed (CO ₃ ²⁻ , HCO ₃ ⁻ ), so that the IC changes at a substantially constant value.

In such a state, when CO ₂ is not sufficiently aerated, CO ₂ is gradually increased and becomes excessive by continuing to aerate CO ₂ . At the same time, the IC concentration and pH fall time in the solution also increase. The case shown in FIG. 3 shows a state in which CO ₂ is aerated to about 300 mg / l with an IC in view of the safety factor.

  Thus, the change in the IC concentration in the solution can also be confirmed by following the pH fall time. Furthermore, it can be said that the concentration change of dissolved calcium can be grasped by tracking the IC concentration in the solution.

  Also, in the case of continuous treatment, it is confirmed that the IC concentration in the solution shows almost the same tendency as the pH fall time as shown in FIG. However, in the case shown in FIG. 4, in order to be able to reproduce assuming the case of continuous processing start, the dissolved calcium is removed to some extent by batch processing of the initial liquid to be processed, and aeration is started from that state. Thereafter, the liquid to be treated is made to flow in.

Therefore, since the initial dissolved calcium concentration is lowered to some extent, the release of H ⁺ by the aeration process is performed relatively slowly, and the pH fall time is long accordingly. Thereafter, the concentration of dissolved calcium is increased by allowing the liquid to be treated to flow, and accordingly, H ⁺ due to the aeration treatment is consumed quickly, and the pH lowering time shows a substantially constant value.

The IC concentration also changes as shown in FIG. 4 in accordance with the above trend. In FIG. 4, the HRT was set as 2.7 hours up to 7.2 hours. Thereafter, for the same reason as described above, the HRT was changed to 3.6 hours so that the CO ₂ due to aeration was slightly excessive to ensure that dissolved calcium was removed.

Thus, for the first time in the present invention, the pH fall time shows almost the same transition as the change in the IC concentration in the solution. This is because, in the above reaction formula, when the calcium concentration is high, the generated IC (CO ₃ ²⁻ , HCO ₃ ⁻ ) is consumed immediately. Therefore, the IC concentration is changing at a constant value. Can be explained. At the same time, it can be said that the pH fall time does not become faster than a certain value because the release of H ⁺ proceeds due to the reaction between calcium and IC.

On the other hand, when the calcium concentration is low, the amount of H ⁺ released decreases as IC increases, and the pH fall time also increases.

  The correlation between the pH fall time and IC is shown in FIG. It became clear that it showed a good correlation. The correlation line is shown as y = 0.8727x + 54.72.

  Thus, the IC concentration shows the opposite tendency reflecting the concentration trend of dissolved calcium in the solution. Therefore, by monitoring the change in the degree of IC using the pH fall time, the concentration of dissolved calcium is indirectly monitored. It can be said that the concentration fluctuation state can be monitored. In this way, the situation can be monitored by the carbon dioxide aeration process.

In this monitoring, as a control index for adding an appropriate amount of alkali addition, a case where the IC concentration is set to 100 mg / l or more and 300 mg / l or less as an appropriate range is shown. Within this range, the pH fall time may be set to 30 seconds or more and 300 seconds or less. More preferably, the end point of the aeration may be determined by setting it as 100 seconds or more and within 200 seconds.
The aeration stop time is
Stop time = HRT / {(Ca concentration of raw water / Ca concentration of treated water) x safety factor}
Can be calculated with

  FIG. 6 is a flow chart showing the procedure for determining the end point of aeration using the pH drop time.

  As shown in FIG. 6, in step S100, the pH drop time of the liquid to be treated such as actual waste liquid is checked. Such a pH fall time is a pH fall time in a unit in which the pH falls after being raised as one unit. For example, the average of the pH fall times in a plurality of units may be taken.

The pH falling time is set in step S001 prior to step S100 by sampling a predetermined amount of the liquid to be treated when actually applied, and using CO ₂ gas adjusted to the gas concentration actually used there. Preliminary testing is performed on a laboratory scale. The CO ₂ gas flow rate to be used and the pH fall time of the target liquid to be treated are defined.

As shown in FIG. 6, in step S001, when the pH fall time is 100 seconds or more and within 200 seconds is an appropriate aeration end point, the pH fall time actually measured in step S100 is the step S200. As shown by the above, when it exceeds 200 seconds, it can be determined that the IC is in a surplus state, that is, CO ₂ aeration is excessive.

  Take measures to stop aeration immediately. Judge that the aeration end point has been reached. For example, in batch processing, it is determined that batch processing has been completed. In the case of continuous treatment, aeration may be stopped for a certain period of time, and then aeration may be resumed to take a treatment that sufficiently removes dissolved calcium.

Also, as shown in step S300, when the pH fall time measured in step S100 is less than 100 seconds, it can be determined that the IC is insufficient, that is, the CO ₂ is not sufficiently aerated. In this case, as shown in FIG. 6, since the dissolved calcium is not sufficiently removed, for example, an alarm is given to the person in charge, for example, equipment inspection or re-inspection such as calcium concentration measurement. The aeration of CO ₂ may be continued after confirming that it is operating normally.

  As described above, the present invention can be used effectively for the determination of the aeration end point when the dissolved calcium in the liquid to be treated such as waste liquid is removed by aeration of carbon dioxide. In particular, in order to prevent the occurrence of scale, it can be used effectively for determining the end point of aeration when the concentration of dissolved calcium is a low concentration of about 100 mg / l.

(Embodiment 2)
In the present embodiment, unlike the above-described embodiment, a case will be described in which the aeration end point is determined using the pH rising time.

  First, the appropriateness of using the pH rise time was confirmed by experiments. As shown in FIG. 7, the solution to be processed was batch-processed by the processing method described in the above embodiment. In Embodiment 1, since the pH fall time is used, the step of raising the pH does not particularly affect the fall time.

  However, in the present embodiment, since it is the pH rise time, it is greatly affected by the alkali used. Therefore, it is necessary to specify the type of alkali used, for example, the type of monoacid base or diacid base. In addition, the use concentration of the alkali greatly affects. Therefore, it is necessary to regulate the concentration of alkali used. Furthermore, it is necessary to determine the specifications of the alkali pump used when adding alkali.

In the case shown in FIG. 7, sodium hydroxide is used as the alkali, and the concentration is 10%. In FIG. 7, as shown in FIG. 3 described in the first embodiment, when the amount of dissolved calcium is large, the pH decrease rate was fast, but the pH increase time for returning such a rapid pH decrease by addition of alkali is also included. Naturally, it becomes faster because of the high H ⁺ concentration. Further, in the state where the dissolved calcium is sufficiently removed, the concentration of H ⁺ is not so high, and accordingly, the pH increase time due to the addition of alkali tends to be delayed.

  FIG. 8 shows the case of continuous processing. In such a case as well, in the same way as the above description, in conjunction with the description of FIG. 4 of the above embodiment, the pH increase time becomes faster in the region where the pH decrease time is early, and the pH increase in the region where the pH decrease time is slow. The time tends to be late.

  In addition, the relationship between the pH rise time and the IC concentration in the solution shows a good correlation as shown in FIG. 9, as in the case of the above embodiment. Incidentally, the correlation line is y = 0.0926x + 12.836.

  Furthermore, the correlation between the pH fall time of the above embodiment and the pH rise time of the present embodiment was examined. The result is shown in FIG. As shown in FIG. 10, the correlation was very good, and y = 0.116x + 10.043.

  Therefore, as described with reference to FIG. 6 of the above embodiment, in the process corresponding to step S001, the optimum range of the pH rise time is determined on the laboratory scale using the sample of the actual liquid to be treated. However, upon such determination, specifications such as the type and concentration of alkali to be used and the flow rate of the alkali pump are determined.

  Thereafter, in the process corresponding to step S100, the actual pH rise time of the liquid to be treated is measured. For example, as can be seen from FIG. 7, if the result is larger than 50 seconds, which is the upper limit of the set value, in the process corresponding to step S <b> 200, it is determined that the result is excessive, and an aerial process is stopped. In the step corresponding to step S300, if the lower limit value is less than 10 seconds, it is determined that the IC is insufficient, and a measure to be reported to the person in charge may be taken.

(Embodiment 3)
In the present embodiment, unlike the first and second embodiments, a case where a change in pH is used as an index as a change in liquidity will be described. That is, a case where the pH decreasing rate or the pH increasing rate is used as an index will be described.

  The rate of change in pH can be defined as the amount of pH change (decrease or increase) divided by the time required for the change. Therefore, the pH decrease rate is defined as the pH decrease amount divided by the time required for the decrease. Similarly, the rate of increase in pH is defined as the amount of increase in pH divided by the time required for the increase.

  For example, in the case of using the pH decrease rate, the decrease rate may be calculated as an arithmetic average of the respective decrease rates at a plurality of measurement points in a predetermined time range before the measurement time point. Although there are various methods for calculating the average, in the present invention, it is optimal to determine the pH decrease rate as the average of a plurality of measurement points in the past predetermined range time at the time of measurement.

  For example, it is assumed that there are n measurement points within a predetermined time range before the measurement time N. In that case, the fall time at the measurement time N is the fall time measured at n measurement points 1 to n. The fall time at the next measurement time N + 1 is an actual measurement value of the fall time at n measurement points from 2 to n + 1.

  On the other hand, when the pH is controlled in the range of 9.2 to 9.0, for example, when the pH is controlled in the range of 9.2 to 9.0, the pH decrease, that is, ΔpH is set to 0, which is obtained by subtracting 9.0 from 9.2. 2. The pH decrease rate can be calculated by dividing ΔpH, which is the amount of pH decrease, by the pH decrease time required to change ΔpH.

  That is, the pH decrease rate at the measurement time N is obtained by dividing the sum of n pH decrease rates, which is a value obtained by dividing each ΔpH corresponding to each actual measurement time measured at 1 to n, by n. Can be calculated as an average value. Similarly, the fall time in the case of the next measurement time N + 1 is an actually measured value of the fall time at n measurement points from 2 to n + 1, and n respective pH fall rates obtained by dividing the corresponding ΔpH. May be calculated as an average value divided by n.

  In order to emphasize this point, the term “moving average of pH lowering speed” may be used. The same applies to the rate of increase in pH, and the term moving average of the rate of increase in pH is sometimes used.

  FIG. 11 shows a case where, for example, the moving average of the pH decrease rate for the past 30 minutes is measured in a continuous processing system. The moving average of the rate of decrease in pH over the past 30 minutes is the average in measurements every 2 seconds. As shown in FIG. 11, it turns out that the transition of the dissolved calcium displayed together and the transition of the moving average of the descent speed show a good agreement.

  In FIG. 12, the result of the moving average of the decreasing rate of pH for the past 5 minutes was shown. Similarly to FIG. 11, it can be said that the moving average of the rate of decrease in pH over the past 5 minutes also reflects the concentration transition of dissolved calcium.

  From experiments, it was found that when using the pH decrease rate as an index for aeration treatment, it is sufficient to use a moving average over a time range of not less than 5 minutes and not more than 30 minutes in the past. If the time is set to less than 5 minutes, a quick response can be made, but the variation becomes large and it is difficult to judge. On the other hand, when the time setting is longer than 30 minutes, unlike the above case, the variation may be small or the response may be delayed. The appropriate time is 5 minutes or more and 30 minutes or less.

It has been confirmed that there is a good correlation as shown in FIG. 13 between the transition of the pH decrease rate and the dissolved calcium concentration. In this connection, the pH decrease rate is a value of a moving average for the past 30 minutes. The correlation line shown in FIG. 13 was y = 7E−05x + 0.0014.
7E-05 here means 7.0 × 10 ⁻⁵ .

  In the moving average of the pH drop time in the past 30 minutes, as shown in FIG. 14, it can be said that the dissolved calcium concentration is 200 mg / l or less, and the transition of dissolved calcium is expressed in good agreement.

  As described above, since the pH decrease rate shows a good correlation with the transition of the dissolved calcium concentration, the pH decrease rate is used as an index as described in the flowchart of FIG. 6 of the first embodiment. As a result, the end point of the aeration process can be determined. For example, in the process assumed in step 001 of the flow in FIG. 6, the sample is sampled, and the pH decrease rate corresponding to the aeration end point is determined to be, for example, 0.001 or more and 0.009 or less on the laboratory scale. .

  In a step corresponding to step S100, the pH drop rate in the actual liquid to be treated is measured. In this case, for example, a moving average of the past 30 minutes may be used as the descending speed.

  In the process corresponding to step S200, when the lower limit of the set value is smaller than 0.001, it is determined that the dissolved calcium is almost zero and the IC is in an excessive state, and the aeration is stopped. In the step corresponding to step S300, when the upper limit is larger than 0.009, it is determined that the calcium concentration is 100 mg / l or more and a measure is reported to the person in charge.

  FIG. 15 shows a comparison of the moving average of the past 30 minutes regarding the pH increase rate and the concentration of dissolved calcium. In FIG. 15 as well, it can be said that the moving average of the pH increase rate in the past 30 minutes sufficiently reflects the transition of the dissolved calcium concentration.

  It was confirmed that there is a good correlation as shown in FIG. 16 in the transition between the rate of increase in pH and the concentration of dissolved calcium. Incidentally, the pH increase rate is the value of a moving average for the past 30 minutes. The correlation line shown in FIG. 16 was y = 0.004x + 0.0048. From these results, it is clear that the end point of the aeration process can be determined by using the rate of increase in pH as an index.

  As mentioned above, the invention made by the present inventor has been specifically described based on the embodiment. However, the present invention is not limited to the embodiment, and various modifications can be made without departing from the scope of the invention. Needless to say.

In the above embodiment, the case where pH is used as a control index has been described, but it goes without saying that hydrogen ion concentration itself, pOH, or hydroxide ion concentration may be used depending on the case. Since there are relational expressions such as pH = −log [H +], [H +] × [OH −] = 10 ⁻¹⁴ , pH + pOH = 14 and the like, mutual conversion is easily determined uniquely, so the pH is used as a control index. This has the same meaning as using the hydrogen ion concentration or pOH or the hydroxide ion concentration as a control index.

  In the above description, the case where the pH fall time, the pH rise time, the pH fall speed, and the pH rise speed of the present invention are applied to the treatment of dissolved calcium by aeration of carbon dioxide has been described. Is also considered to be applicable to the production of calcium carbonate.

  The present invention can be effectively used in the field of removal of dissolved calcium by aeration of carbon dioxide.

It is explanatory drawing which shows the mode in the batch process by the aeration of the carbon dioxide of dissolved calcium at the time of performing height control of one embodiment of this invention. It is explanatory drawing which shows the mode in the continuous process by the aeration of the carbon dioxide of dissolved calcium at the time of performing height control of one embodiment of this invention. ~ It is explanatory drawing which showed transition of pH fall time in the batch processing of one embodiment of this invention in relation to IC concentration. It is explanatory drawing which showed transition of pH fall time in the continuous process of one embodiment of this invention with relation to IC density | concentration. It is explanatory drawing which shows the correlation of pH fall time and IC in one embodiment of this invention. It is a flowchart in case the pH fall time in the aeration process by the carbon dioxide of the dissolved calcium of one embodiment of this invention is used as a parameter | index. It is explanatory drawing which showed transition of the pH rise time in the batch processing of one embodiment of this invention in relation to IC concentration. It is explanatory drawing which showed transition of the pH rise time in the continuous process of one embodiment of this invention by relationship with IC density | concentration. It is explanatory drawing which shows the correlation of pH rise time and IC in one embodiment of this invention. It is explanatory drawing which shows the correlation of pH fall time and pH rise time of one embodiment of this invention. It is explanatory drawing which shows the transition of pH fall rate moving average (30 minute moving average) in the continuous process of one embodiment of this invention, and dissolved calcium. It is explanatory drawing which shows the relationship between the pH fall rate moving average (5-minute moving average) and dissolved calcium in the continuous process of one embodiment of this invention. It is explanatory drawing which shows the correlation with the pH fall speed | rate of one embodiment of this invention, and the density | concentration of dissolved calcium. It is explanatory drawing which showed the pH fall rate moving average of one embodiment of this invention by the relationship with dissolved calcium. It is explanatory drawing which showed transition of the pH increase rate in the continuous process of one embodiment of this invention by the relationship with the density | concentration of dissolved calcium. It is explanatory drawing which showed the correlation with the pH rise rate of one embodiment of this invention, and the density | concentration of dissolved calcium.

Explanation of symbols

S001 Step S100 Step S200 Step S300 Step

Claims (11)

A method for grasping the concentration change of dissolved calcium,
A method for grasping a concentration change of dissolved calcium, characterized by grasping a concentration change of dissolved calcium by a change in liquidity. In the method of grasping the concentration change of dissolved calcium according to claim 1,
The method for grasping a change in the concentration of dissolved calcium, wherein the change in liquidity is a change in liquidity over time. In the method of grasping the concentration change of dissolved calcium according to claim 1,
The method for grasping a change in the concentration of dissolved calcium, wherein the change in liquidity is a change in liquid velocity. In the grasping method of the concentration change of dissolved calcium given in any 1 paragraph of Claims 1-3,
A method for grasping a change in concentration of dissolved calcium, comprising: determining an end point of aeration when the dissolved calcium in a solution is removed by aeration with carbon dioxide by the method for grasping a concentration change of dissolved calcium. A method for grasping the concentration change of dissolved calcium,
A method for grasping a concentration change of dissolved calcium, characterized by knowing a concentration change of dissolved calcium by a change in pH. In the grasp method of the concentration change of the dissolved calcium according to claim 5,
The method of grasping the concentration change of dissolved calcium, wherein the pH change is a time change of pH. In the grasp method of the density | concentration change of the dissolved calcium of Claim 6,
The time for the change in pH with time is an increase time in a predetermined range of pH or a decrease time in a predetermined range of pH. In the grasp method of the concentration change of the dissolved calcium according to claim 5,
The change in pH is a change in the concentration of dissolved calcium, characterized in that the change in pH is a change in pH rate. In the grasp method of the concentration change of the dissolved calcium according to claim 8,
The rate of change in pH rate is obtained by dividing the amount of change in pH within a predetermined range of pH by the time required to achieve the amount of change. . In the grasping method of the concentration change of the dissolved calcium according to claim 7 or 9,
The predetermined range of the pH is a method for grasping a concentration change of dissolved calcium, wherein the pH is in a range of 8.5 or more and 9.5 or less. In the grasping method of the concentration change of dissolved calcium given in any 1 paragraph of Claims 1-4,
A method for grasping a change in the concentration of dissolved calcium, wherein the liquidity is a hydrogen ion concentration, a hydroxide ion concentration, or pOH of the solution.

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