JP3015604B2 - Method for sequential analysis of carbonate and sulfite concentrations in liquid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for sequentially analyzing and measuring the concentrations of carbonate and sulfite in an absorbent in a wet flue gas desulfurization apparatus using a calcium salt as an alkali source.

[0002]

2. Description of the Related Art Conventionally, in a continuous measuring apparatus for the concentration of carbonate and sulfite in a liquid, a liquid containing carbonate and sulfite is reacted with hydrochloric acid or sulfuric acid in a stirred continuous reaction vessel which is shielded from the outside air. Carbonate and sulfite are converted into CO ₂ and SO ₂ by the following reaction, respectively (when hydrochloric acid is used): CaCO ₃ + 2HCl → CaCl ₂ + CO ₂ ↑ + H ₂ O (1) CaSO ₃ + 2HCl → CaCl ₂ + SO ₂ ↑ + H ₂ O (2) (when sulfuric acid is used) CaCO ₃ + H ₂ SO ₄ → CaSO ₄ + CO ₂ ↑ + H ₂ O (3) CaSO ₃ + H ₂ SO ₄ → CaSO ₂ + SO ₂ ↑ + H ₂ O (4) This is blown into the reaction solution by air, and degassed.
The amounts of O ₂ and SO ₂ are detected, and the concentrations of carbonate and sulfite contained in the liquid are calculated.

A conventional method will be described with reference to FIG. In FIG. 2, a test solution A containing a carbonate and a sulfite is collected by a metering pump 1, and the temperature of the staying solution 6 in the reaction vessel 5 is measured by a temperature detector so that the temperature of the staying solution 6 becomes a predetermined temperature. At 4, the temperature is raised to the reaction vessel 5 through the heater 2 controlled by the heat source by the signal from the temperature controller 3.

[0004] The retained liquid 6 in the reaction vessel 5 is supplied to a pH detector 14.
To detect the pH and control the micropump 12 with a signal from the pH controller 15 to transfer sulfuric acid (or hydrochloric acid) C to the reaction vessel 5.
PH is controlled so that the required pH is obtained by injecting
In that case, the reaction formulas (3) to (4) (or (1)
(2)) In order to smoothly remove CO ₂ and SO ₂ generated according to (2)), a part of the air B controlled to a required flow rate by the flow controller 11 or the distribution valve 22 or the flow indicator is operated. 17 and the stagnation liquid 6 in the reaction vessel 5 is blown into the stagnation liquid 6 through the air blowing pipe 8, and is stirred by the stirrer 7 driven by the motor 10 through the sealing member 9.

Next, an increase in the amount of the stagnant solution 6 due to the supply of the sample solution A from the metering pump 1 is discharged from the overflow pipe 23 to the liquid sealing device 13, where the reaction vessel 5
The tip of the overflow tube 23 is connected to the liquid in the liquid sealer 13 so that the CO ₂ and SO ₂ -containing gas E in the inside does not leak out along with the overflow liquid so that the liquid depth overcomes the internal pressure of the reaction vessel 5. The liquid sealing device 13 is immersed in
The excess liquid amount of the overflow liquid flowing into is discharged as waste liquid D.

Reaction formulas (3) to (4) (or (1) to
The CO ₂ or SO ₂ generated according to (2)) and the mixed gas E of the air and the evaporating moisture from the air blowing pipe 8 merge with the air 16 bypassing the reaction vessel 5 and then are discharged as exhaust F. , Part of the exhaust F is dehumidifier 2
After removing the water contained in 4 as drain H, the water is sucked by the air pump 18 and the CO ₂ analyzer 19 and S ₂
It is sent to the O ₂ analyzer 25 and the CO ₂ analyzer 19 and S
After the CO ₂ concentration and the SO ₂ concentration are measured by the O ₂ analyzer 25, the gas is released as exhaust gas G. CO ₂ analyzer 1
9 and the respective measurement signals from the SO ₂ analyzer 25 are sent to a carbonate concentration calculator 20 and a sulfite concentration calculator 26 for calculating the carbonate concentration and the sulfite concentration in the liquid, and the liquid sampling flow signal * 2 and the values of the air flow rate signal * 1 are processed and the concentrations of carbonate and sulfite in the liquid are calculated by the following equation. The carbonate concentration is measured by the concentration indicator 21 and the sulfite concentration is measured by the concentration indicator 27. Is indicated in each. Carbonate concentration [mol / liter] = x ₁ × Q / (100−x ₁ −x ₂ ) × 22.4 × L (5) Sulfite concentration [mol / liter] = x ₂ × Q / ( 100−x ₁ −x ₂ ) × 22.4 × L (6) x ₁ : CO ₂ concentration [vol%] x ₂ : SO ₂ concentration [vol%] Q: Air for blowing and mixing Total flow rate [N liter / min] L: Liquid sampling flow rate [L / min]

[0007]

The carbonate contained in the absorbent in the wet flue gas desulfurization apparatus to be detected in the present invention is calcium carbonate, and its solubility is small, so that it is usually suspended in liquid as a solid. Sulfite is present as calcium sulfite, but in the so-called tank oxidation type process, which has recently become mainstream, air is directly blown into the circulating fluid tank to obtain an oxidation rate close to 100%.
The concentration is not high until the solid precipitates out, and is mostly present only as an ion in the solution. When such an absorbing solution is to be detected, the following problems have been encountered when employing a method of directly supplying the absorbing solution to a continuous stirring type reaction vessel as in the conventional method.

That is, as described above, since the sulfite concentration and the carbonate concentration level in the absorbing solution are significantly different, to improve the detection accuracy, usually the stirring is performed in accordance with the lower concentration side, that is, the sulfite concentration level. It was necessary to adjust the amount of the absorbing solution supplied to the continuous reaction vessel. That is, when the amount of the absorbing solution is small, the x ₂ : SO ₂ concentration [% by volume] shown in the above equation (6) becomes lower than the detection lower limit, and in other words, the accurate measurement of the sulfite concentration in the absorbing solution in terms of the SO ₂ concentration. It will be impossible. Therefore, it is necessary to increase the supply liquid amount so that sufficient accuracy can be maintained, but in this case, the following inconvenience occurs.

That is, sulfuric acid (or hydrochloric acid) is injected into a continuous reaction vessel to cause the reaction of the above formulas (1) and (2) (or formulas (3) and (4)) to produce CO ₂ and SO _2.
Although to generate a _2, disadvantageously large amount of sulfuric acid by the neutralization of the calcium carbonate concentration present in significantly higher concentrations in comparison with the case sulfite concentration in the absorbing liquid (or hydrochloric acid) is consumed occurs.

[0010] In view of the state of the art, the present invention sequentially analyzes the concentrations of carbonate and sulfite in a liquid which can solve the conventional disadvantage that a large amount of acid is consumed for detecting the low concentration of sulfite. It seeks to provide a way.

[0011]

The present invention focuses on the fact that carbonate is mainly present as a solid and sulfite is present as a solution. After solid-liquid separation of the carbonate, the filtrate is reduced to a low-concentration sulfite. by generating the SO ₂ with an acid to provide a sufficient amount corresponding to a stirred continuous reaction vessel, it found that can be accurately moreover reduced as much as possible the consumption of acid, thereby completing the present invention based on this finding Was.

That is, according to the present invention, when the carbonate and sulfite concentrations in a solution containing carbonate and sulfite are continuously detected, the solution is continuously quantitatively sampled, and the solution is continuously stirred and shut out from the outside air. The solution in the reaction vessel is heated to a temperature of 50 ° C. or higher, and sulfuric acid or hydrochloric acid is mixed with air and blown into the solution in the reaction vessel. CO ₂ and S generated by the reaction
A method of extracting O ₂ to the outside of the reaction vessel and obtaining the carbonate concentration and the sulfite concentration in the liquid from the CO ₂ and SO ₂ concentrations contained in the extracted gas and the respective values of the liquid sampling flow rate and the blown air flow rate In the operation, the liquid is separated into solid and liquid, only the filtrate is supplied to the stirred continuous reaction vessel, and the sulfite concentration is determined by the means, and the liquid is separated into solid and liquid by the stirred continuous reaction vessel. A method for sequentially analyzing the concentrations of carbonate and sulfite in a liquid, characterized in that the supply and the operation for obtaining the carbonate concentration by the means are alternately switched.

[0013]

The structure and operation of the present invention will be described in more detail with reference to FIG. FIG. 1 is an explanatory diagram of an embodiment of the present invention. In the description of FIG. 1, only the points different from the conventional method shown in FIG. 2 will be described, and the description of the configuration according to the conventional method will be omitted.

In FIG. 1, the test liquid A overflows from a pump 28 through a liquid cyclone 29, that is, a line where the filtrate is supplied to a switching valve 30 and a line which is directly sent to a switching valve 30 via a pump 31 and is sent to two lines. Divided. The underflow of the hydrocyclone 29 is discharged out of the system via the line 32. The test liquid supplied to the switching valve 30 passes through the flow rate control valve 33, passes through the heater 2, and then rises in temperature in the reactor 5.
Supplied to Here, the switching valve 30 is switched at a fixed time interval by a signal * 3 from the controller 34 having a timer mechanism, and has a function of alternately supplying the two divided test liquids to the reaction vessel 5 through the flow control valve 33. Have. Also signal *
From 3, the set value of the liquid amount of the flow controller 35 of the flow control valve 33 is switched. Specifically, when the overflow liquid of the hydrocyclone 29 flows through the flow control valve 33, the flow rate setting value is increased, and when the test liquid flowing through the pump 31 flows, the flow rate setting value is decreased.

The flow signal * 4 from the flow controller 35 is sent to the carbonate concentration calculator 20 and the sulfite concentration calculator 26, and together with the value of the air flow signal * 1, the above (5) and (6)
The arithmetic processing is performed by the formula. The switching interval of the switching valve 30 can be arbitrarily set by a timer mechanism of the controller 34 in accordance with a request for a detection time interval of carbonate and sulfite in the test solution.

[0016]

EXAMPLE A standard sample prepared by the method of the present invention shown in FIG. 1 was measured, and the following results were obtained. Average concentration [mol / liter] Coefficient of variation (10-point average) (standard deviation / average value) 〇carbonate 0.051 0.020 硫酸 sulfite 0.0021 0.047 〇 hydrochloric acid supply 2.03 [ml / min However, the carbonate and sulfite concentrations indicate values obtained when the sample was collected via the pump 31 and the liquid cyclone 29, respectively.

Here, the composition of the standard sample and other conditions were as follows. 〇Standard sample composition: Calcium carbonate 0.051
[Mol / liter] Calcium sulfite 0.0022 [mol / liter] (Sulfurous acid was all present in the liquid phase.) 採取 Sample collection amount: Sample collection volume via pump 31 0.12 [liter / min. ] Sampling amount through the liquid cyclone 29 1.0 [liter / min] 〇Blowing air flow rate: 7 [N liter / min] 〇Total air flow rate: 20 [N liter / min] 〇Reaction temperature setting: 75 [ ° C] 〇Reaction pH setting: 2.5 [-] 〇Flow switching time interval: 5 [min] 〇Supply acid type: hydrochloric acid 〇Acid concentration: 6N

[Comparative Example] The same apparatus as in the example was used to adjust the timer so as to collect the sample only through the pump 31. The same standard sample as in the example was measured, and the following results were obtained. Average concentration [mol / liter] Coefficient of variation (10-point average) (standard deviation / average value) 〇carbonate 0.051 0.024 硫酸 sulfite 0.0017 0.24 〇hydrochloric acid supply 2.26 [milliliter / min The amount of the sample to be collected, the flow rate of the blown air, the flow rate of the total air, the reaction temperature setting, the reaction pH setting, the type of the supplied acid, and the acid concentration are the same as those in the examples.

When comparing the example and the comparative example, the average concentration and the coefficient of variation are almost the same for the carbonate concentration, so that there is no difference in the analysis accuracy.
Since the average value of the comparative example has a large difference from the true value and a large coefficient of variation, the improvement of the analysis accuracy according to the present invention is apparent. Further, the consumed amount of hydrochloric acid is smaller in the method of the present invention than in the comparative example.

[0020]

According to the present invention, it is possible to analyze a very low concentration of a sulfite dissolved in a test solution with higher accuracy than that of a conventional method and without increasing acid consumption. Becomes possible.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of one embodiment of the present invention.

FIG. 2 is an explanatory view of one embodiment of a method for analyzing carbonate and sulfite concentrations in an absorbent in a conventional wet flue gas desulfurization apparatus using a calcium salt as an alkali source.

Continuation of the front page (56) References JP-A-62-129757 (JP, A) JP-A-60-154158 (JP, A) JP-A-60-154157 (JP, A) JP-A-60-36956 (JP) JP-A-59-150339 (JP, A) JP-A-60-36955 (JP, A) JP-A-60-36957 (JP, A) JP-A-4-190831 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01N 31/00

Claims (1)

(57) [Claims] When detecting the concentration of carbonate and sulfite in a solution containing carbonate and sulfite continuously, the solution is continuously quantitatively collected and transferred to a stirred continuous reaction vessel which is shielded from outside air. Supply the liquid in the reaction vessel at a temperature of 50 ° C. or higher and mix sulfuric acid or hydrochloric acid with air and blow into the reaction vessel liquid to form a reaction between the carbonate and sulfite in the liquid and the acid. CO ₂ and SO ₂ to be extracted from the reaction vessel, and from the CO ₂ and SO ₂ concentrations contained in the extracted gas and the respective values of the liquid collection flow rate and the blown air flow rate, the carbonate concentration and the sulfite concentration in the liquid are determined. In the method for determining the concentration, the liquid is subjected to solid-liquid separation, only the filtrate is supplied to the stirring type continuous reaction vessel, and the sulfite concentration is determined by the means, and the stirring is performed without solid-liquid separation of the liquid. To the continuous reaction vessel How to sequentially analyze the concentration of carbonate and sulfite in the liquid, characterized in that performing an operation for obtaining the carbonate concentration by serial means alternately switched.