JPH06130049A - Method for sequential analysis of concentration of carbonate and sulfite in liquid - Google Patents

Abstract

PURPOSE:To enhance the analytical accuracy of the title method and to reduce the consumption of an acid by a method wherein an operation which separates a liquid under test into a solid and a liquid and which finds the concentration of a sulfite and an operation which finds the concentration of a carbonate without separating the liquid under test into the solid and the liquid are changed over and performed alternately. CONSTITUTION:A sample A under test is separated into two lines, i.e., a line in which a filtrate is supplied to a changeover valve 30 via a liquid cyclone 29 by a pump 28 and a line in which a filtrate is sent directly to the changeover valve 30 via a pump 31. The liquid which has been supplied to the valve 30 is supplied to a reaction container 5 via a heater 2 through a flow-rate control valve 33. The valve 30 is changed over at a definite time interval by a signal *3 from a regulator 34 provided with a timer mechanism, and the two divided liquids are supplied alternately to the container 5 via the valve 33. A flow-rate signal *4 from a flow-rate controller 35 is sent to a carbonate-concentration arithmetic unit 20 and a sulfite-concentration arithmetic unit 26, and it is processed together with an air flow-rate signal *1. In this manner, an operation which separates the liquid under test into a solid and a liquid and which supplies only the filtrate to the container 5 and an operation which sends the filtrate directly without separating the liquid under test into the solid and the liquid are changed over and performed alternately.

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 absorbing solution 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 device 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 an agitated continuous reaction vessel which is isolated from the outside air, The following reaction forms carbonate and sulfite into CO ₂ and SO ₂ , 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 using sulfuric acid) 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) Air is blown into the reaction solution to degas it, and C in the degassed gas
The amounts of O ₂ and SO ₂ are detected, and the concentrations of carbonate and sulfite contained in the liquid are calculated.

The conventional method will be described with reference to FIG. In FIG. 2, the sample solution A containing carbonate and sulfite is sampled by the metering pump 1, and the temperature of the retained liquid 6 in the reaction vessel 5 is adjusted to a predetermined temperature by a temperature detector. The temperature is detected in step 4, and the temperature is supplied to the reaction vessel 5 after heating via the heater 2 whose heat source is controlled by the signal from the temperature controller 3.

The stagnant liquid 6 in the reaction vessel 5 is a pH detector 14
PH is detected by the pH controller 15, the micro pump 12 is controlled by a signal from the pH controller 15, and sulfuric acid (or hydrochloric acid) C is added to the reaction vessel 5.
PH is controlled by injecting into
Further, at that time, reaction formulas (3) to (4) (or (1)
- (2) in order to smoothly degassing of CO ₂ and SO ₂ generated in accordance), flow indicator by operating portion or a dispensing valve 22 of the air B, which is controlled to a required flow rate at a flow rate adjusting meter 11 The stagnant liquid 6 is blown into the stagnant liquid 6 via 17 and an air blowing pipe 8, and the stagnant liquid 6 in the reaction container 5 is stirred by a stirrer 7 driven by a motor 10 via a sealing material 9.

Next, an increase in the amount of the stagnant liquid 6 due to the supply of the sample liquid A from the metering pump 1 is discharged from the overflow pipe 23 to the liquid sealer 13, and in the liquid sealer 13, the reaction container 5 is discharged.
The tip of the overflow pipe 23 is at the tip of the liquid in the liquid sealer 13 so that the gas E containing CO ₂ and SO ₂ in the inside of the overflow container 23 does not leak along with the overflow liquid so that the internal pressure of the reaction container 5 is overcome. It is submerged in the same liquid sealer 13
The surplus 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 evaporated water from the air blowing pipe 8 joins the air 16 bypassing the reaction vessel 5 and is then discharged as the exhaust gas F. , Part of the exhaust F is the dehumidifier 2
The water contained in 4 is removed as drain H and then sucked by the air pump 18, and the CO ₂ analyzer 19 and S
It is sent to the O ₂ analyzer 25, and the same CO ₂ analyzer 19 and S
The CO ₂ concentration and the SO ₂ concentration are measured by the O ₂ analyzer 25, and the exhaust gas G is discharged. CO ₂ analyzer 1
9 and the respective measurement signals of 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 a liquid sampling flow rate signal. * 2 and the air flow rate signal * 1 are calculated and the concentration of carbonate and sulfite in the liquid is calculated by the following formula. The carbonate concentration is measured by the concentration indicator 21 and the sulfite concentration is measured by the concentration indicator 27. Each is instructed by. Carbonate concentration [mol / l] _{= x 1 × Q / (100} -x 1 -x 2) × 22.4 × L ··· (5) sulfite concentration [mol / l] = x ₂ × Q / ( 100-x ₁ -x ₂ ) × 22.4 × L (6) x ₁ : CO ₂ concentration [volume%] x ₂ : SO ₂ concentration [volume%] Q: Air for injection and mixture Total flow rate [N liter / minute] L: Liquid sampling flow rate [liter / minute]

[0007]

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

That is, as described above, since the sulfite concentration and the carbonate concentration level in the absorbing liquid are greatly different, in order to improve the detection accuracy, the concentration is usually low, that is, the stirring is performed according to the sulfite concentration level. It was necessary to adjust the amount of absorbing liquid supplied to the continuous reaction vessel. That is, when the amount of the absorbing liquid is small, the x ₂ : SO ₂ concentration [volume%] shown in the above formula (6) becomes lower than the lower limit of detection, and in other words, the SO ₂ concentration can be measured accurately. It becomes impossible. Therefore, it is necessary to increase the supply amount of liquid 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 reactions of the above formulas (1) and (2) (or (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.

In view of the above-mentioned state of the art, the present invention sequentially analyzes the concentrations of carbonate and sulfite in a liquid which can solve the conventional drawback that a large amount of acid is consumed for detecting low concentration of sulfite. It is intended to provide a method.

[0011]

In the present invention, it is noted that carbonate exists mainly as a solid, and sulfite exists as a solution. After solid-liquid separation of carbonate, the filtrate is converted into a low-concentration sulfite. It was found that the consumption of the acid can be reduced with high precision by supplying a sufficient amount to the stirring type continuous reaction vessel to generate SO ₂ by the acid, and the present invention was completed based on this finding. It was

That is, according to the present invention, when the concentration of carbonate and sulfite in a liquid containing carbonate and sulfite is continuously detected, the liquid is continuously and quantitatively sampled, and this is continuously stirred with the outside air. The solution in the reaction vessel is heated to 50 ° C. or higher and sulfuric acid or hydrochloric acid is mixed with air and blown into the solution in the reaction vessel to remove the carbonate and sulfite in the solution and the acid. CO ₂ and S produced by the reaction
A method of extracting O ₂ from the same reaction vessel, and obtaining the carbonate concentration and sulfite concentration in the liquid from the CO ₂ and SO ₂ concentrations contained in the extracted gas, and the liquid sampling flow rate and the blown air flow rate. In, the liquid is subjected to solid-liquid separation, only the filtrate is supplied to the stirring type continuous reaction vessel to determine the sulfite concentration by the means, and the liquid is separated into the stirring type continuous reaction vessel without solid-liquid separation. It is a method for sequentially analyzing the concentrations of carbonate and sulfite in a liquid, which is characterized in that the operations of supplying and determining the carbonate concentration by the above 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 solution A is overflowed from the pump 28 through the hydrocyclone 29, that is, the filtrate is supplied to the switching valve 30 and the line is directly sent to the switching valve 30 via the pump 31 into two lines. Will be divided. The underflow of the liquid cyclone 29 is discharged to the outside of the system through the line 32. The test solution supplied to the switching valve 30 passes through the flow rate control valve 33, the heater 2, and the post-heating reactor 5
Is supplied to. Here, the switching valve 30 has a function of being switched at a constant time interval by a signal * 3 from a controller 34 having a timer mechanism so that the two divided test solutions are alternately supplied to the reaction vessel 5 via the flow control valve 33. Have. Signal *
3, the liquid amount set value of the flow rate controller 35 of the flow rate control valve 33 is switched. Specifically, when the overflow liquid of the hydrocyclone 29 flows through the flow rate control valve 33, the flow rate setting value is increased, and when the sample liquid that has passed through the pump 31 flows, the flow rate setting value is decreased.

The flow rate signal * 4 from the flow rate 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 rate signal * 1, the above (5) and (6).
It is calculated by an expression. The switching interval of the switching valve 30 can be arbitrarily set by the timer mechanism of the controller 34 according to the detection time interval requirement of the carbonate and the sulfite in the sample liquid.

[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) 〇 Carbonate 0.051 0.020 〇 Sulfite 0.0021 0.047 〇 Hydrochloric acid supply 2.03 [mL / min] However, the carbonate and sulfite concentrations show the values when a sample is taken through the pump 31 and the liquid cyclone 29, respectively.

The composition of the standard sample and other conditions were as follows. 〇 Standard sample composition: Calcium carbonate 0.051
[Mole / liter] Calcium sulfite 0.0022 [mol / liter] (Sulfurous acid was all present in the liquid phase.) 〇 Amount of sample collected: Amount of sample collected through the pump 31 0.12 [liter / min. ] Amount of sample to be sampled through the hydrocyclone 29 1.0 [liter / minute] ○ Flow rate of blown air: 7 [Nliter / minute] ○ Total air flow rate: 20 [Nliter / minute] ○ Reaction temperature setting: 75 [ ℃] 〇 Reaction pH setting: 2.5 [-] 〇 Flow path switching time interval: 5 [minutes] 〇 Type of supplied acid: hydrochloric acid 〇 Concentration of acid: 6 normal

[Comparative Example] A timer was adjusted so as to collect a sample through the pump 31 only in the same apparatus as in Example, and the same standard sample as in Example was measured, and the following results were obtained. Average concentration [mol / liter] Coefficient of variation (10-point average) (standard deviation / average) 〇 Carbonate 0.051 0.024 〇 Sulfite 0.0017 0.24 〇 Hydrochloric acid supply 2.26 [mL / min] The amount of sample to be collected, the flow rate of blown air, the total flow rate of 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.

Comparing the examples and the comparative examples, there is no difference in analysis accuracy because the average concentration and the coefficient of variation of the carbonate concentration are almost the same, but regarding the sulfite concentration,
Since the average value of the comparative example has a large difference from the true value and the coefficient of variation is also large, it is clear that the analysis accuracy is improved by the present invention. Moreover, the amount of hydrochloric acid consumed is smaller in the method of the present invention than in the comparative example.

[0020]

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to analyze the extremely low concentration of sulfite dissolved in a test solution with high accuracy as compared with the conventional method and without increasing the amount of acid consumption. Is possible.

[Brief description of drawings]

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

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

Claims (1)

[Claims] 1. When continuously detecting the concentrations of carbonate and sulfite in a liquid containing carbonate and sulfite, the liquid is continuously and quantitatively sampled, and the liquid is transferred to an agitated continuous reaction vessel which is shielded from the outside air. The temperature of the liquid in the reaction vessel is raised to 50 ° C. or higher, and sulfuric acid or hydrochloric acid is mixed with air and blown into the liquid in the reaction vessel, which is produced by the reaction between the carbonate and sulfite in the liquid and the acid. CO ₂ and SO ₂ are extracted from the reaction vessel, and the concentration of CO ₂ and SO ₂ contained in the extracted gas and the respective values of the liquid sampling flow rate and the blowing air flow rate are used to determine the concentration of carbonate and sulfite in the liquid. In the method for determining the concentration, the liquid is subjected to solid-liquid separation, and only the filtrate is supplied to the stirring type continuous reaction vessel to determine the sulfite concentration by the means, and the stirring type is used without solid-liquid separation of the liquid. Supply to 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.