JP2000046821A - Method and apparatus for measuring concentration of carbonate in slurry - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately measure the concentration of CaCO3 in a slurry within a short time even if the concentration of CaCO3 in the slurry is suddenly changed. SOLUTION: The pH values of a slurry A are detected at two or more places after an acid B is added by pH meters 10, 10' and, corresponding to the respective measured values and the difference between them, the addition amount of the acid B is changed. More preferably, the addition amount of the acid is changed corresponding to the pH measured values before and after a dissolved CO2 concentration meter 9 and the difference between them and, further concretely, when the difference between the pH measured values is larger than a certain set value, the addition amount of the acid A is increased and, when the difference between them is smaller than the certain set value, the addition amount of the acid B is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring a carbonate concentration in a slurry containing a carbonate, and more particularly to an automatic continuous measuring method.

[0002]

2. Description of the Related Art As a method for measuring a carbonate concentration in a slurry containing a carbonate such as CaCO ₃ , JISR910
Although the method defined in No. 1 is well known, this method is a manual analysis and requires several tens of minutes for measurement. Several patents relating to continuous measurement have been filed (for example, Japanese Patent Publication No. 3-52826, Japanese Patent Application Laid-Open No. 2-195).
253 publication).

[0003] In the method disclosed in the patent publication,
An acid is added to the slurry containing carbonate and heated, and C
This is a method of calculating the carbonate concentration by measuring the CO ₂ in the gas by releasing O ₂ . However, although these methods are automatic continuous analyses, it takes time to completely release CO ₂ into the gas phase, resulting in a longer measurement time.

A flue gas desulfurization device is used as a field using a slurry containing CaCO _3, which is used in a thermal power plant or the like to generate sulfur oxides in flue gas generated by fossil fuel combustion, especially sulfur dioxide. This is an apparatus for absorbing and removing (SO ₂ ) with an absorbent slurry containing CaCO ₃ . In flue gas desulfurization equipment, depending on the boiler load and changes in the properties of the fuel used, Ca
The supply amount of CO ₃ was adjusted, and CaCO ₃ in the absorbent slurry was adjusted.
The concentration is adjusted to an optimal value (for example, the amount of exhaust gas or SO _{2 in} exhaust gas).
It is necessary to maintain economical and high desulfurization performance by controlling the concentration of CaCO ₃ in the absorbent slurry as the concentration increases.

However, in the conventional technique, it takes a long time to measure CaCO ₃ in the absorbent slurry, and it is impossible to adjust the supply amount of CaCO ₃ in response to a sudden change in boiler load or a change in properties of fuel used. there were.

[0006] Against this background, the present inventors have proposed a method for continuously measuring the CaCO ₃ concentration in a slurry in a short time (Japanese Patent Laid-Open No. 9-101296). FIG. 5 shows a flow of the embodiment of the present invention proposed by the present inventors.

The slurry A sent from the line 1 to the acid addition tank 3 by the pump 2 is supplied from the acid tank 4 into the acid addition tank 3 through the acid addition line 5 in accordance with the indicated value of the pH meter 10 by the acid addition pump 12. Hydrochloric acid B is added, and the slurry A is sent into the measuring tank 8 after being stirred by the line mixer 7 installed in the middle of the line 6.

In the measuring tank 8, the dissolved CO ₂ concentration and pH are measured by a dissolved CO ₂ meter 9 and a pH meter 10, respectively. The flow rate of the acid addition pump 12 is adjusted by the calculator 13 so that the measured value of the pH meter 10 falls within a predetermined range.
The slurry A for which the measurement has been completed is discharged from the line 11.
The addition of acid B to the slurry A CaCO ₃ and equimolar CO ₂ in the slurry A is generated, equal to or less than the solubility CO ₂ is dissolved in water. Therefore, if the dissolved CO ₂ concentration in the slurry A is measured, the same molar amount of CaCO 2 is added before the acid B is added.
₃ was present, and the CaCO ₃ concentration can be easily obtained. .

As a result of measuring the CaCO ₃ concentration in the desulfurization slurry A used in the flue gas desulfurization apparatus according to this method, the same value was obtained in almost all cases within the range of measurement error as in the method specified in JISR9101. However, slurry A
If the CaCO ₃ concentration in the medium fluctuates suddenly, it takes time to completely replace the slurry in the acid addition tank 3 and the measurement tank 8, and the true CaCO ₃ concentration is not measured until then.

Further, if the place where the acid B is added is far from the place where the pH is measured, the pH value fluctuates (hunts) when the CaCO ₃ concentration in the slurry A fluctuates. And an accurate CaCO ₃ concentration is not measured. In particular, in a flue gas desulfurization apparatus, the supply amount of CaCO ₃ is adjusted according to the change in the boiler load and the properties of the fuel used, and the concentration in the absorption liquid slurry A is controlled to an optimal value, thereby achieving economical and high desulfurization. Because it is necessary to maintain performance,
Often, the CaCO ₃ concentration in the slurry A increases and decreases in a short time.
It is not possible to measure the O ₃ concentration accurately.

As one method for solving such a problem, as shown in FIG. 6, acid B is added to the line 1 and a pH measuring tank 14 (only the pH meter detector 10A is installed in the tank). Therefore, it is possible to prevent the pH value after the acid addition from oscillating (hunting) in the measuring tank 8). However, in such a method, CaCO ₃ in the slurry is sent into the measuring tank 8 without completely reacting, and the dissolved CO ₂ concentration is measured by the dissolved CO ₂ meter 9, which may cause an error. There was found.

As described above, in the prior art, when the volume of the slurry A from the addition of the acid B to the pH measurement is reduced, the slurry A
Although the response time when the concentration of CaCO _{3 in the} medium fluctuates can be shortened and the hunting of pH can be prevented, the CaCO ₃ in the slurry A is sent into the measuring tank 8 without completely reacting, and an error occurs. There was a problem.

[0013]

In the above prior art, when the CaCO ₃ concentration in the slurry A suddenly fluctuates, the true C
There has been a problem that it takes time to detect the aCO ₃ concentration or an error occurs. The object of the present invention is to solve the above-mentioned problems of the prior art, and to accurately determine the CaCO ₃ concentration in a slurry in a short time even if the CaCO ₃ concentration in a slurry such as an absorption liquid slurry of a flue gas desulfurization device fluctuates rapidly. It is to propose a method that can be measured.

[0014]

The object of the present invention is to detect the pH of a slurry at two or more places after the addition of an acid,
The addition amount of the acid is changed according to each measured value and the difference between the two pH measured values, more preferably, the dissolved C
Measured pH values before and after the O ₂ concentration detector
Changing the amount of acid added according to the difference between the measured H values, and even more specifically, increasing the amount of acid added when the difference between the measured values of the two pH values is greater than a certain set value; If it is smaller than the set value, it is achieved by decreasing the amount of acid added.

The method of measuring the concentration of dissolved CO ₂ in the slurry is as follows: (a) a method using a thermal conductivity detecting element separated from the slurry by a gas permeable membrane; A method using a phenomenon in which the fluorescence intensity is changed by dissolving CO ₂ in the slurry into the isolated fluorescent dye solution, or (c) CO ₂ in the slurry is separated from the slurry by a gas-permeable membrane. Any known method such as a method utilizing a phenomenon in which the pH of a solution changes by dissolution can be used.

[0016]

[Action] CaCO₃Due to the reaction when hydrochloric acid is added to
As shown in equation (1), CaCO₃And equimolar CO₂
Occurs. CO₂Is soluble in water.
If there is dissolved CO₂Slurry by measuring concentration
CaCO in₃The concentration can be determined. For example,
Existed CO₂If the concentration is X (g / L), CO ₂Minute
Since the amount of particles is 44, CaCO in the slurry₃The concentration is X /
44 (mol / L).

CaCO ₃ + 2HCl = CaCl ₂ + CO ₂ + H ₂ O (1) In order to obtain an accurate CaCO ₃ concentration in the slurry, it is necessary to react all CaCO ₃ in the slurry with an acid.
The CaCO ₃ in the slurry is sent into the measuring tank 8 without completely reacting, and the dissolved CO ₂ concentration is measured by the dissolved CO ₂ meter 9, which may cause an error. It is necessary to adjust while measuring the pH of the slurry.

Suitable pH values include, for example, limestone (C
It varies depending on the particle size and reactivity of the (aCO ₃ ) particles (the amount of impurities and deposits on the particle surface), and also the stirring state after the addition of the acid and the time until measurement. According to the study of the present inventors, it has been found that it is usually preferable to add an acid so that the pH becomes about 2 to 4. If the pH is 2 or less, there is no problem in the measurement accuracy, but it is not economical because the amount of acid added increases.

When the CaCO ₃ concentration in the slurry fluctuates, the amount of acid added changes. For example, CaC in slurry
When the O ₃ concentration fluctuates suddenly, the amount of acid added is increased after detecting that the value measured by the pH meter has increased,
In the prior art shown in FIG. 5, it takes time to detect an accurate CaCO ₃ concentration. In the prior art shown in FIG. 6, CaCO _{3 in} the slurry is sent to the measuring tank 8 without completely reacting with the acid, and the dissolved C ₂ is measured by the dissolved CO ₂ meter 9.
Since the O ₂ concentration is measured, an error occurs (true CaCO 2).
₃ values lower than the density).

On the other hand, in the method of the present invention, when the CaCO ₃ concentration in the slurry fluctuates, the amount of acid added is increased or decreased more quickly by the pH meter on the upstream side, and the difference from the pH meter on the downstream side is further increased. Thus, it can be determined whether or not CaCO ₃ in the slurry has completely reacted with the acid. Therefore, even when the CaCO ₃ concentration in the slurry fluctuates suddenly, it is possible to obtain an accurate CaCO ₃ concentration in a short time.

This is because the amount of acid added is sufficient and the C
When aCO ₃ completely reacts with the acid, the reaction shown in the above formula (1) does not proceed any more, and the difference between the indicated values of the pH meter between the upstream side and the downstream side is small. Thus, it can be seen whether CaCO ₃ in the slurry has completely reacted with the acid. Even when the amount of acid added is extremely small and the reaction of the above formula (1) is completed in a short time, the difference between the indicated values of the pH meter between the upstream side and the downstream side becomes small. Value (pH 4.0 or higher), CaCO _{3 in} the slurry
Is not completely reacted with the acid.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in more detail by the following embodiments, but is not limited by the following examples.

Embodiment 1 FIG. 1 shows an embodiment of the present invention. 5 and 6
As in the prior art shown in FIG. 1, an acid addition tank 3, an acid tank 4, a line mixer 7, a measuring tank 8, a dissolved CO ₂ meter 9 and a pH meter 1
However, in the example shown in FIG. 1, pH meters 10 and 10 ′ are further provided before and after the dissolved CO ₂
The amount of acid to be added can be changed by the calculator 13 and the acid additive pump 12 according to the difference between the measured value and the dissolved CO ₂ measured value.

The slurry A sent from the line 1 to the acid addition tank 3 by the pump 2 is fed into the acid addition tank 3 from the acid tank 4 through the acid addition line 5 by the acid addition pump 12 in response to a signal from the computer 13. Hydrochloric acid B is added, and the slurry A is stirred by the line mixer 7 installed in the middle of the line 6, and then the pH is measured by the pH meter 10 in the pH measuring tank 14.

Next, the slurry is sent into the measuring tank 8 where the dissolved CO ₂ concentration is measured by the dissolved CO ₂ meter 9, and then the pH meter 10 ′ is further measured in the pH measuring tank 14 ′.
Measures the pH. Measured value of pH meter 10 and pH
The flow rate of the acid addition pump 12 is adjusted by the calculator 13 so that the difference between the measured values in the total 10 ′ falls within a predetermined range. The slurry A for which the measurement has been completed is discharged from the line 11.

Specifically, the measured value of the pH meter 10 is 2.4.
At ~ 2.6, the flow rate of the acid addition pump 12 was adjusted so that the difference between the measured values at the pH meters 10 and 10 'would be 0.2-0.3. Measured value of pH meter 10 and pH meters 10 and 1
When any one of the measured value differences at 0 'was larger than the set value, the flow rate of the acid addition pump 12 was increased.

Using the measuring apparatus shown in FIG. 1, the response time of the measuring apparatus when the CaCO ₃ concentration in the slurry A was increased or decreased in a stepwise manner was examined. The curve a in FIG.
A curve b shows the result of measurement of the concentration when the aCO ₃ concentration was increased or decreased in a step-like manner, using the measurement apparatus shown in FIG.

The value of the curve a in FIG. 2 is a result of sampling the slurry A and measuring the CaCO ₃ concentration by the manual analysis method specified in JISR9101. The vertical axis indicates CaCO in slurry A from the detected value of dissolved CO ₂ 9
_{3 The} result was calculated by converting the concentration (unit: mmol /
L). Curve a and curve b agree well, and Ca in slurry A
It can be seen that even if the CO ₃ concentration fluctuates, the measuring device of FIG. 1 has a small time delay. In addition, pH meter 10 and pH meter 10 '
In the method of adjusting the flow rate of the acid addition pump 12 in the case where the difference between the measured values is larger than the set value, as shown in FIG. It goes without saying that it is possible.

Comparative Example 1 The concentration of CaCO ₃ in the same slurry A was measured with the measuring device based on the prior art shown in FIG. 5 under the same conditions as the device shown in FIG. The result is shown by curve c in FIG. The time lag when the CaCO ₃ concentration of the slurry A fluctuates relatively is larger than that of the apparatus shown in FIG. In particular, the responsiveness when the CaCO ₃ concentration suddenly decreases is poor. This is because it takes time for the slurry A having a relatively high CaCO ₃ concentration in the acid addition layer 3 and the measuring tank 8 to be replaced with the slurry A having a relatively low CaCO ₃ concentration.

Comparative Example 2 The CaCO ₃ concentration in the same slurry A was measured under the same conditions as in FIG. 1 using a measuring device based on the prior art shown in FIG. The result is shown by a curve d in FIG. Although the time delay is smaller than that of Comparative Example 1, the measured value is oscillating (hunting).

In the apparatus shown in FIG. 1, FIG. 5, and FIG. 6, hydrochloric acid B is used as the acid, but it goes without saying that other acids such as sulfuric acid that reacts with CaCO ₃ can be used other than hydrochloric acid.

[0032] In the example shown in FIG. 1 measures the pH of the before and after of dissolved CO ₂ meter 9, dissolved CO ₂ as shown in FIG. 4
It is also possible to install two pH meters 10, 10 'before the total 9. However, it is more preferable to measure the pH before and after the dissolved CO ₂ measurement.

[0033]

According to the present invention, CaCO _{3 in} the slurry
Even if the concentration fluctuates suddenly, the CaCO ₃ concentration in the slurry can be accurately measured in a short time.

[Brief description of the drawings]

FIG. 1 is a flowchart of a CaCO ₃ concentration measuring device according to an embodiment of the present invention.

FIG. 2 shows a CaCO ₃ concentration measuring apparatus shown in FIG. 1 and Comparative Example 1
Is experimental data.

FIG. 3 shows a CaCO ₃ concentration measuring apparatus shown in FIG. 1 and Comparative Example 2
Is experimental data.

FIG. 4 is a flowchart of a CaCO ₃ concentration measuring device according to an embodiment of the present invention.

FIG. 5 is a flow chart of a CaCO ₃ concentration measuring device in a conventional technique.

FIG. 6 is a flow chart of a CaCO ₃ concentration measuring device in the prior art.

FIG. 7 is an example of an operation method of an acid addition pump.

[Explanation of symbols]

1, 6, 11 line 2 pump 3 acid addition tank 4 acid tank 5 acid addition line 7 line mixer 8 measuring tank 9 dissolved CO ₂
Total 10, 10 'pH meter 12 Acid additive pump 13 Computer 14 pH measuring tank A Slurry B Hydrochloric acid

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Seiji Takamoto 3-36 Takara-cho, Kure-shi, Hiroshima Pref. Inside the Kure Research Laboratory, Babcock Hitachi Co., Ltd. (72) Inventor Shigeru Nozawa 6-9 Takara-cho, Kure-shi, Hiroshima Pref. F-term in the Kure factory (reference) 2G042 AA01 BB03 BB05 CA10 CB04 FA01 HA07 4D002 AA02 BA02 DA05 DA16 GA02 GB08 GB09

Claims (4)

[Claims] 1. A method for measuring the concentration of carbonate present in a slurry by adding an acid while flowing a slurry containing a carbonate through a cell and then measuring the concentration of dissolved CO _{2 in the} slurry. The pH of the slurry is detected in two or more slurry streams on the downstream side after adding the acid, and the respective measured values and both pH values are measured.
A method for measuring a carbonate concentration in a slurry, wherein an amount of an acid added is changed according to a difference between measured values. 2. The method according to claim 1, wherein the addition amount of the acid is changed according to the measured value of the pH value in the slurry flow before and after the dissolved CO ₂ concentration detection site and the difference between the measured pH values. A method for measuring the concentration of carbonate in the slurry described. 3. The method according to claim 1, wherein when the difference between the measured values of the two pH values is larger than a certain set value, the amount of acid added is increased, and when the difference is smaller than a certain set value, the added amount of acid is decreased. Item 3. The method for measuring a carbonate concentration in a slurry according to Item 1 or 2. Added 4. A cell flowing slurry containing carbonate, an acid adding means for adding an acid to the cell, and the dissolved CO ₂ meter for measuring the dissolved CO ₂ concentration in the slurry after acid addition, the acid PH of the slurry in two or more cells downstream of the site
And a calculator for calculating the difference between the measured value of each of the pH meters and the measured pH value, and the amount of the acid added according to the measured value of the calculator and the difference between the measured pH values. And a pump for changing the pressure of the slurry.