JPH06210126A - Method and device for treating waste gas - Google Patents

Abstract

PURPOSE:To secure high desulfurizing performance even when a slurry absorbent contains chloride of high concentration by detecting the pH and the chloride concentration of the slurry absorbent to control the quantity of organic acid or salt of organic acid to be added by the detected values. CONSTITUTION:The chloride concentration and the pH of slurry in a circulation tank are measured by a chloride concentration measuring instrument 20 and a pH measuring instrument 21, respectively. When a slurry absorbent, such as limestone slurry is prepared from gypsum separated mother liquor 16 and limestone 7 in a limestone slurry tank 8, a prescribed quantity of an organic acid such as acetic acid or formic acid or a salt of organic acid, is added to the circulation tank based on both the measurement signals. Then the dissolving velocity of limestone in the slurry absorbent is controlled and sulfite generated by waste gas treatment is recovered as gypsum while being oxidized in an absorber circulating tank, allowing desulfurizing reaction to be maintained with high efficiency.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of treating exhaust gas, and particularly to a sulfur oxide (S) contained in exhaust gas even when a high concentration of chloride is contained in an absorbent slurry using limestone.
The present invention relates to a wet exhaust gas treatment method and apparatus suitable for efficiently absorbing and removing Ox) and recovering gypsum as a by-product.

[0002]

2. Description of the Related Art Environmental problems have been discussed from a global perspective, but the main substance as a pollution source is nitrogen oxide (NO).
x) and sulfur oxides (SOx). At thermal power plants in Japan, measures are taken to reduce the concentration levels of pollutants such as NOx and SOx in exhaust gas to below a specified level. However, except for some regions such as Europe and the United States, Such measures are far behind and cause serious acid rain problems. Japan has already had a track record of 20 years or more in environmental pollution control equipment and has high technical reliability, but it is necessary to reduce the cost of the equipment in order to spread it worldwide. Explaining only to sulfur oxides (SOx), the exhaust gas of a coal or a heavy oil-fired boiler usually contains several hundred ppm of SO _2, and by treating this with a desulfurizer, it is several tens of ppm from the stack. The most common desulfurization method is to release an exhaust gas containing some SO ₂ . At present, a typical method of a wet flue gas desulfurization apparatus targeting boiler exhaust gas in a thermal power plant is a method in which limestone slurry is used as an SO ₂ absorbent and gypsum is finally produced as a by-product and recovered. Among the wet desulfurization methods by the limestone-gypsum method, the one-tower type desulfurization method which is becoming the mainstream at present is shown in FIG.
Will be explained. As a conventional wet flue gas desulfurization device, for example, Japanese Patent Publication No. 61-16491 can be cited. In FIG. 4, the exhaust gas 1 is guided to the absorption tower 2. In the absorption tower 2, cooling and dust removal are mainly performed in the lower part thereof, while desulfurization reaction proceeds in the upper part of the absorption tower 2. The exhaust gas that has passed through the absorption tower 2 is subjected to heat exchange with the exhaust gas 1 introduced into the absorption tower 2 by the gas / gas heater 4 after removing entrained mist by the demister 3, and then discharged as purified gas 5 from the chimney 6 to the atmosphere. To be done. On the other hand, the limestone 7 serving as the absorbent slurry is supplied to the limestone slurry tank 8 and becomes the limestone slurry. A predetermined amount of limestone slurry is supplied from the limestone slurry supply pump 9 to the absorption tower circulation tank 1
Supplied to zero. The supply of limestone slurry is largely determined by the amount of sulfur oxide (SOx) that is treated. The absorbent slurry is taken out of the tank by the absorption tower circulation / extraction pump 11 and sprayed in the absorption tower 2 to fall into the absorption tower circulation tank 10 while coming into gas-liquid contact with the exhaust gas rising in the absorption tower 2. Return. Absorption tower circulation tank 10
The absorbent slurry at the time of returning to No. ₂ contains calcium sulfite generated by the absorption of SO ₂ , but in the system shown in FIG. 4, the agitator 13 that disperses the air 12 as fine bubbles in the slurry 13 Since it is installed in the absorption tower circulation tank 10, the generated calcium sulfite is oxidized to gypsum. In this way, the sulfite in the absorbent slurry that has fallen into the absorption tower circulation tank 10 is rapidly oxidized, so that most of the solid substances in the slurry in the absorption tower circulation tank 10 become gypsum, and limestone and sulfite. The content of is small. A predetermined amount of the slurry in the absorption tower circulation tank 10 is sent to the gypsum separator 14 by the absorption tower circulation / extraction pump 11, and the powder gypsum 15 is recovered. The gypsum separation mother liquor 16 generated in the gypsum separator 14 is temporarily stored in a drainage tank 17 as needed, and a predetermined amount thereof is introduced into a limestone slurry tank 8 by a pump 18 and used for preparing limestone slurry. In the absorption part of the wet flue gas desulfurization device, hydrogen chloride (HCl), hydrogen fluoride (HF), etc. in the exhaust gas are absorbed and removed, while the gypsum separation mother liquor 16 generated in the gypsum recovery system is circulated to the absorption system. Therefore, the concentration of chloride (Cl-) in the absorption system increases significantly unless a predetermined amount of drainage is performed. Increasing the chloride concentration in the slurry causes corrosion of the equipment materials and lowers the purity of the gypsum as a by-product, but keeps the chloride concentration in the absorbent slurry at a low level. The operation has a problem that the amount of water to be supplied to the desulfurizer is increased and the waste water treatment facility becomes large. Therefore, when strict regulations are imposed on securing of water or dumping (discharging) of waste water, the device must be operated with the Cl-concentration in the desulfurization system being as high as possible. In an extreme case, there is a demand for a system that does not discharge wastewater at all, or does not discharge waste in a solution state by drying and solidifying the wastewater. By the way, the increase of Cl-concentration in the absorbent slurry means that calcium ion (Ca2
+) Means increase. Therefore, when the Ca2 + concentration increases, there arises a problem that the reactivity (dissolution reaction) of limestone containing Ca as a common component is lowered and the desulfurization performance of the entire desulfurization apparatus is lowered.

[0003]

The object of the present invention is to improve the desulfurization performance as the concentration of chloride (Cl-) in the absorbent slurry containing limestone used in the above-mentioned conventional wet flue gas desulfurization method is increased. An object of the present invention is to provide a method for treating exhaust gas and an apparatus for the same, which can solve the problem of deterioration and can ensure high desulfurization performance even when the absorbent slurry contains a high concentration of Cl-.

[0004]

In order to achieve the above-mentioned object of the present invention, an absorbent slurry containing a high concentration of chloride (Cl-) is used to absorb acidic substances such as sulfur oxides in exhaust gas. In the removal method, the chloride concentration in the slurry is detected together with the pH of the absorbent slurry, and the amount of organic acid or acid salt added is adjusted according to the detected value to adjust the dissolution rate of limestone in the absorbent slurry. The desulfurization reaction is maintained at high efficiency by controlling and recovering the sulfite generated by the exhaust gas treatment as gypsum while oxidizing it in the absorption tower circulation tank. The present invention is a method for treating exhaust gas, wherein an acidic substance contained in exhaust gas is absorbed and removed using an absorbent slurry containing limestone and an organic acid or an organic acid salt. It is a method for treating exhaust gas in which the amount is adjusted and controlled by the concentration of chloride contained in the absorbent slurry, the pH value of the absorbent slurry, or both. As the organic acid or organic acid salt added to the absorbent slurry of the present invention, at least one selected from acetic acid, formic acid, adipic acid, succinic acid, tartaric acid, citric acid or salts thereof can be used. . The amount of organic acid or organic acid salt added is such that the pH value of the absorbent slurry is 4.5 or less and the chloride concentration is 0, 0.5, 1.0, 1.5 or 2.0 mol. , Respectively, 0, 0.2, 0.3, 1.0 or 1.8
It is preferable that the content is at least mmol. Further, when the pH value of the absorbent slurry is 5.0 or less and the chloride concentration is 0, 0.5, 1.0, 1.5 or 2.0 mol, respectively, 0, 0.2, It is preferable to contain 0.7, 3.0 or 13 mmol or more. Furthermore, p of the absorbent slurry
H value is less than 5.5, chloride concentration is 0, 0.5,
In the case of 1.0, 1.5 or 2.0 mol, 0,
It is preferable to contain 0.8, 2.0, 6.0 or 20 mmol or more. The present invention is an absorption method for absorbing and removing acidic substances such as sulfur oxides, chlorides, and fluorides contained in exhaust gas by gas-liquid contact while circulating an absorbent slurry containing limestone and an organic acid or an organic acid salt. A tower, an absorbent slurry circulation tank provided under the absorption tower, and means for supplying air into the absorbent slurry circulation tank to oxidize sulfite generated by absorption of sulfur oxides to form gypsum. In a wet exhaust gas treatment apparatus having, a chloride concentration measuring device in the absorbent slurry in the absorbent slurry circulation tank,
The amount of the organic acid or the organic acid salt added is determined from the pH measuring device of the absorbent slurry and the chloride concentration detection value from the chloride concentration measuring device or the pH detection value from the pH measuring device or both detection values. It is an exhaust gas treatment device comprising at least means for adjusting and controlling.

[0005]

The method of treating exhaust gas according to the present invention is characterized in that an organic acid or an organic acid salt (adsorbent slurry containing a high concentration of chloride (the main component of solid is gypsum and a small amount of limestone other than that) is added to an organic acid or an organic acid salt ( (Hereinafter, simply referred to as an organic acid salt) is made to coexist, but this organic acid salt is shown below (Chemical formula 1) to the dissolution reaction of limestone in the absorbent slurry in the absorption tower circulation tank. It is considered that the reaction of (Chemical Formula 8) controls the dissolution reaction of limestone. The dissolution reaction of limestone (CaCO ₃ ) is considered to proceed as follows when viewed microscopically. CaCO ₃ = Ca 2+ + CO ₃ 2 -... (Chemical formula 1) CO ₃ 2- + H ₂ O = HCO _3- + OH -... (Chemical formula 2) CO ₃ ^2- + H + = HCO ₃ -... (Chemical formula ₃ ) HCO _3- + H + = H ₂ CO ₃ (Chemical formula 4) H ₂ CO ₃ = CO ₂ + H ₂ O (Chemical formula 5) OH- + H + = H ₂ O (Chemical formula 6) On the particle surface of limestone in the absorbent slurry ( Although the reaction of Chemical formula 1) proceeds, the liquid near the surface and the liquid body do not mix instantaneously, but the carbonate ion (CO ₃ 2−) concentration near the surface of the limestone particles is higher than that in the liquid body. In order for the dissolution reaction of limestone to proceed, the reaction of (Chemical formula 1) must proceed to the right. For this purpose, the CO ₃ 2- removal reaction, and therefore the reactions of (Chemical formula 2) to (Chemical formula 6) must proceed to the right. In other words, CO ₃ 2- is decomposed by hydrogen ions (H +) present in the absorbent slurry and scattered as CO ₂ in the gas phase, whereby the reaction of (Chemical Formula 1) proceeds. The effect of adding an organic acid salt to promote the dissolution reaction of CaCO ₃ can be explained as follows. That is, the organic acid (RH) causes a dissociation reaction as in (Chemical formula 7), and the concentration of each chemical species (represented by []) is determined by the acid dissociation constant ka (Chemical formula 8). Exists. RH = R- + H + (Chemical formula 7) ka = [R-] [H +] / [RH] (Chemical formula 8) When H + is added, the organic acid ion (R-) in the liquid becomes H + When H + is consumed, H + is supplied after the RH undergoes an acid dissociation reaction. In addition, p near the particle surface of limestone is higher than the liquid body.
In the H condition, when RH approaches this portion, H + is released by the reaction of (Chemical formula 7). Therefore, the dissolution rate of limestone is higher when the organic acid salt is present. When R-generated by releasing H + near the particle surface of limestone diffuses back to the liquid body and returns to (Chemical formula 8), H + in the liquid is deprived to increase the amount of RH. The reaction proceeds in the direction. This means a decrease in H + concentration in the liquid, that is, an increase in pH, in which case a new acid is added. In this way, the organic acid ion (R-) acts as a carrier of H + and catalytically acts on the dissolution reaction of limestone. It is a well known fact that organic acid salts such as acetate and formate improve desulfurization performance, while the presence of chloride (Cl-) reduces desulfurization performance. Therefore, in a desulfurization method using a limestone-containing slurry having a high Cl-concentration, it is easily understood that the desulfurization performance is improved by adding an organic acid salt. By the way, it is the absorption tower circulation tank that finally determines the utilization rate of limestone in the absorbent slurry in the flue gas desulfurization apparatus, unless reaction (behavior) is performed so that the residual amount of limestone in the tank decreases. However, it is not possible to secure the desired utilization rate of limestone in the entire desulfurization equipment. In consideration of the above-mentioned dissolution control reaction of limestone, the present inventors have developed a flue gas desulfurization method suitable when a high Cl-concentration absorbent slurry is used. That is, in the circulation tank, limestone reacts with the acid in the slurry, and the H + of this acid originally exists in the sulfite ion (HSO _3- ) generated when SO ₂ was absorbed by the CaCO ₃ -containing slurry. H +. H + in HSO _3- is CaC
There are two types of reactions that can be passed to O ₃ . Part 1
One is that HSO ₃ − forms CaSO between Ca 2+ in the slurry.
_The reaction shown in (Chemical Formula 9) when ₃ · ½H ₂ O is precipitated, and the reaction shown in (Chemical Formula 10) when HSO ₃ − is oxidized to sulfuric acid. Since the reaction itself between CaCO ₃ and H + proceeds promptly, the consumption rate of CaCO ₃ in the absorption tower circulation tank depends on the rate of the H + release reaction (Formula 9) in the preceding stage. 2HSO ₃ − + Ca 2+ + H ₂ O = CaSO ₃ · ½H ₂ O + 2H + (Chemical formula 9) 2HSO ₃ − + O ₂ = 2SO ₄ 2 − + 2H + (Chemical formula 10) The reaction shown in the (Chemical formula 10) of the latter is , The speed can be adjusted artificially, and it progresses faster than the former.
That is, H + can be rapidly generated by oxidizing HSO ₃ − generated by absorption of SO ₂ , and thereby CaCO in the absorption tower circulation tank can be produced.
The consumption (dissolution) rate of ₃ will increase. If Cl-is present in the absorbent slurry, limestone (CaCO ₃ )
The reaction rate between H + and H + decreases, but in order to increase this reaction rate, it is premised that H + which is the decomposing agent is rapidly supplied. Therefore, it is desirable to oxidize sulfite to rapidly release H + in order to enhance the reactivity with limestone. Also, the effect of adding the organic acid salt is notable only when H + is supplied at a sufficient rate. When the reaction of releasing H + from HSO ₃ − generated by the desulfurization reaction is linked to the precipitation of CaSO ₃ · 1 / 2H ₂ O as shown in (Chemical formula 9), a bent organic acid salt is added. However, the effect cannot be fully exerted. When the Cl-concentration is high as described above, it is effective to operate with the sulfite concentration in the absorbent slurry being reduced as much as possible, and the addition effect of the organic acid salt is also effective for the sulfite concentration in the absorbent slurry. Becomes remarkable when the engine is operated in a state in which is reduced as much as possible. In addition,
In order to add the organic acid salt more efficiently, the amount of the organic acid salt to be added should be adjusted depending on the Cl-concentration in the liquid and the pH. Ie Cl-concentration and pH
The reactivity of limestone varies depending on the type of limestone, and in order to ensure the desired desulfurization performance, the amount of organic acid salt added should be adjusted and controlled according to the Cl-concentration and pH. This is the basic principle of the exhaust gas treatment method of the present invention.

[0006]

Embodiments of the present invention will be described below in more detail with reference to the drawings. <Embodiment 1> FIG. 1 is a schematic diagram showing the configuration of the exhaust gas treating apparatus exemplified in this embodiment. Exhaust gas treatment method of the present invention, the absorbent component adjustment of the slurry, namely the organic acid salt can be contained added absorbent slurry, also be one characterized by a method for determining the amount added, such as SO ₂ The absorption can be carried out in the same manner as the conventional device. SO ₂ in the exhaust gas 1 is removed by contacting with the exhaust gas by supplying an absorbent slurry was withdrawn by the absorption tower circulating-extraction purpose pump 11 to the absorber tower 2, SO ₂ absorption conditions, the absorption tower The exhaust gas treatment method of the present invention is not restricted by the sulfite oxidation method in the circulation tank 10. Among them, regarding the oxidation of sulfite, it is easy to supply fine air into the tank 10 and a method of generating bubbles of fine air is to supply air 12 near the stirring blades of the stirrer 13. Can be achieved. In addition, in FIG.
It is the figure which showed the flow of the device at the time of recovering gypsum using limestone as an O ₂ absorbent, but when gypsum is not recovered by the method using limestone 7, the part corresponding to the gypsum recovery in FIG. 1 is omitted. The exhaust gas treatment method of the present invention can also be carried out in the form. The exhaust gas treatment method of the present invention is characterized by controlling the addition amount of the organic acid salt according to the chloride concentration in the absorbent slurry and the pH value. The invention is not restricted. Organic acid salts include acetic acid, formic acid,
An acid such as adipic acid, succinic acid, tartaric acid or citric acid, or a salt corresponding to these organic acids can be supplied in the solid or liquid state into the absorption tower circulation tank 10 or the limestone slurry tank 8. In the method of the present invention, chloride concentration and pH in the absorbent slurry are
And add the corresponding amount of organic acid salt,
The chloride concentration and pH are basically measured on the slurry in the absorption tower circulation tank 10. Instead of measuring the chloride concentration in the slurry, it is also possible to measure the hydrogen chloride (HCl) concentration in the exhaust gas and add the organic acid salt accordingly. In FIG. 1, chloride concentration and pH of the slurry in the circulation tank are measured by a chloride concentration measuring device 20 and a pH measuring device 21, respectively,
Both measurement signals show a flow when a predetermined amount of organic acid salt 19 is added when preparing limestone slurry from gypsum separation mother liquor 16 and limestone 7 in limestone slurry tank 8. The proper amount of organic acid salt is
It is rational to make the amount of the organic acid salt necessary to give the reactivity of the limestone equivalent to that when the slurry in the absorption tower circulation tank 10 having a predetermined pH is virtually unaffected by chloride. This is also a basic guideline in the exhaust gas treatment method of the present invention. That is, the reactivity of limestone in the absorbent slurry is affected by the Cl-concentration and pH, but in the method of the present invention, the reactivity of a given limestone does not depend on the Cl-concentration when the pH is constant. Organic acid salts can be added as obtained. The chloride concentration is 6
When it is less than 0 mM (mmol), the effect on the reactivity of limestone is small. However, since the effect of adding the organic acid salt on the reactivity of limestone appears remarkably, it is possible to make the SO ₂ absorption section and the absorption tower circulation tank section compact by adding the organic acid salt.

By adjusting and controlling the addition amount of the organic acid salt according to the method of the present invention, the desulfurization reactivity of a given limestone can be secured regardless of the level of Cl-concentration. , Or lowering the pH of the absorbent slurry under the condition that the amount of organic acid salt added is constant,
It is clear that the desulfurization reactivity of limestone is further increased. However, the addition of an organic acid salt increases COD in wastewater and is not preferable in terms of wastewater treatment, and adding a large amount naturally causes an economical problem. On the other hand, operating under low pH conditions causes problems with the corrosion of equipment materials and the quality of gypsum produced as a by-product, so appropriate operating conditions for exhaust gas treatment are the pH of the absorbent slurry and the amount of organic acid salt added. It is necessary to make a decision considering both. When the wet exhaust gas desulfurization treatment is continuously operated according to FIG. 1, chlorides are accumulated in the absorbent slurry. If the concentration of chloride exceeds a predetermined value, corrosion of equipment materials will proceed and the desulfurization performance itself will deteriorate. Therefore, a measure is taken to discharge a part of the gypsum separation mother liquor 16 out of the system. Even in the method of the present invention, it is necessary to discharge the gypsum separation mother liquor 16 containing the organic acid salt to the outside of the system at a predetermined ratio, and even if the organic acid salt is circulated, the concentration in the absorbent slurry is constantly kept at a predetermined level. It is necessary to add (make up) and adjust so as to maintain at. Thus, the exhaust gas treatment method of the present invention, in order to constantly supply the organic acid salt,
It is not economical to add unnecessarily to make the concentration high. The concentration of the organic acid salt is practically the upper limit of about 20 mM (mmol), and it is clear from the examples shown below that a sufficient effect is exhibited with the amount added in this range.

<Embodiment 2> Next, an exhaust gas treating method of the present invention will be described based on specific experimental results. 100m
90 ml of water was placed in a 1 (milliliter) beaker and immersed in a constant temperature water bath. Stirring was continued with a magnetic stirrer, and when it was confirmed that the liquid temperature reached 50 ° C., 2 mmol of limestone having an average particle diameter of 10 μm (moleol .... alkali content basis) and 0.4 g of gypsum were added. PH of liquid
1N sulfuric acid was added dropwise using an automatic titrator until the pH reached 4.5, and then 1N so that the pH of the solution was maintained at 4.5.
Sulfuric acid was continuously added dropwise (pH stat method). Similarly,
A pH stat titration experiment was carried out at pHs of 5.0, 5.5 and 6.0. The residual amount C of limestone dissolved was plotted against the reaction time t, and the results were organized assuming that the relationship of (Equation 1) holds between C and t. C = C ₀ exp (−kt) (Equation 1) As a result, k values at pH of 4.5, 5.0, 5.5 and 6.0 were 4.19, 2.55, 1.41 and 0.4, respectively. 75h ~ ¹ was obtained. Next, the influence of chloride concentration on the reaction between limestone and acid at a given pH was investigated. However, in this case, a solution containing a predetermined amount of calcium chloride (CaCl ₂ ) to which gypsum and limestone were added was used as a sample solution (absorbent slurry). The dissolution rate index k of the obtained limestone is shown in FIG. pH 4.5
In the case of, the reactivity of limestone is not affected up to a chloride concentration of 20 mM, but the reactivity of limestone is gradually decreased at chloride concentrations above 0.2 mM, 0.2, 1.0 and 2.0 M (mol) In the case of, the k values were 3.29, 2.78 and 2.09, respectively. In this way, when the chloride concentration is as high as 2.0 M, it is less than half the k value (4.19) in the absence of chloride. The same is true for pH 5.0 and 5.5, and it is clear that the reactivity of limestone gradually decreases when the chloride concentration is several tens of mM or more. Moreover, it is shown that the reactivity of limestone is higher when the pH is lower. In the same manner as above, pH 4.5, chloride concentration 2.0M (C
In the case of aCl ₂ of 1.0 M), the addition of sodium acetate at 1, 5 and 10 mM gave k values of 3, respectively.
52, 6.19 and 6.91 were obtained. The k value was plotted against the acetate concentration, and the addition concentration of acetate required to show the same k value as the k value in the absence of chloride (hereinafter referred to as "minimum organic acid addition concentration") was 1 .8
mM was obtained. Similarly, as the minimum addition concentration of the organic acid salt when the chloride concentration is 0.5, 1.0 and 1.5M,
0.2, 0.3 and 1.0 mM respectively were obtained. Curve A shown in FIG. 3 is obtained by the above method. In the same manner, the relationship between the chloride concentration and the minimum addition amount of the organic acid salt was determined in the same manner for pH 5.0 and 5.5. The results are shown in curves B and C of FIG. As is clear from the above results, the amount of addition of the organic acid salt required to obtain the reactivity of limestone equivalent to that in the case where no chloride is present in the slurry solution containing chloride at a predetermined concentration is obtained from FIG. be able to. According to the exhaust gas treatment method of the present invention, the decrease in reactivity of limestone due to the Cl-concentration can be compensated for by adding an organic acid salt. In addition, Cl-
When the concentration and the pH are constant, a larger amount of organic acid salt than the amount calculated from FIG. 3 is added, or the amount of the organic acid salt is set to the amount determined from FIG.
It is clear that the reactivity of limestone is higher than that of the control group (when the Cl-concentration is not contained at a given pH) when the value of is decreased.

[0009]

As described in detail above, according to the exhaust gas treatment method of the present invention, the absorption of a high chloride concentration can be achieved by adding an organic acid or an organic acid salt to the absorbent slurry to control the pH. Even with an agent slurry, the rate of dissolution of limestone in the slurry can be increased, so desulfurization performance is improved,
A highly efficient exhaust gas desulfurization system can be realized.
Further, since the low drainage operation can be performed, the cost of the exhaust gas desulfurization device can be reduced.

[Brief description of drawings]

FIG. 1 is a system diagram showing a configuration of a wet exhaust gas desulfurization apparatus exemplified in an embodiment of the present invention.

FIG. 2 is a graph showing the relationship between the concentration of calcium chloride in the absorbent slurry and the dissolution rate index of limestone exemplified in the examples of the present invention.

FIG. 3 is a graph showing the relationship between the chloride concentration of the absorbent slurry and the minimum addition concentration of the organic acid salt exemplified in the examples of the present invention.

FIG. 4 is a system diagram showing a configuration of a conventional wet exhaust gas desulfurization device.

[Explanation of symbols]

 1 ... Exhaust gas 2 ... Absorption tower 3 ... Demister 4 ... Gas / gas heater 5 ... Purified gas 6 ... Chimney 7 ... Limestone 8 ... Limestone slurry tank 9 ... Limestone slurry supply pump 10 ... Absorption tower circulation tank 11 ... Absorption tower circulation / extraction Pump 12 ... Air 13 ... Stirrer 14 ... Gypsum Separator 15 ... Gypsum 16 ... Gypsum separation mother liquor 17 ... Drainage tank 18 ... Pump 19 ... Organic acid salt 20 ... Chloride concentration measuring instrument 21 ... pH measuring instrument

Claims (6)

[Claims] 1. A method for treating exhaust gas, wherein an acidic substance contained in the exhaust gas is absorbed and removed by using an absorbent slurry containing limestone and an organic acid or an organic acid salt. A method for treating exhaust gas, characterized in that the amount of addition is adjusted and controlled by the concentration of chloride contained in the absorbent slurry, the pH value of the absorbent slurry, or both. 2. The organic acid or organic acid salt to be added to the absorbent slurry according to claim 1, wherein at least one selected from acetic acid, formic acid, adipic acid, succinic acid, tartaric acid, citric acid or salts thereof. A method for treating exhaust gas, which comprises a seed. 3. The addition amount of an organic acid or organic acid salt according to claim 1 or 2, wherein the pH value of the absorbent slurry is 4.5 or less, and the chloride concentration is 0, 0.5, 1.0,
In the case of 1.5 or 2.0 mol, respectively 0, 0.2,
A method for treating exhaust gas, characterized by containing 0.3, 1.0 or 1.8 mmol or more. 4. The addition amount of an organic acid or organic acid salt according to claim 1 or 2, wherein the pH value of the absorbent slurry is 5.0 or less, and the chloride concentration is 0, 0.5, 1.0,
In the case of 1.5 or 2.0 mol, respectively 0, 0.2,
A method for treating exhaust gas, characterized by containing 0.7 or more or 3.0 or 13 mmol or more. 5. The addition amount of an organic acid or an organic acid salt according to claim 1 or 2, wherein the pH value of the absorbent slurry is 5.5 or less and the chloride concentration is 0, 0.5, 1.0,
In the case of 1.5 or 2.0 mol, 0, 0.8,
A method for treating exhaust gas, characterized by containing 2.0, 6.0 or 20 mmol or more. 6. A sulfur oxide, a chloride contained in exhaust gas,
An absorption tower that absorbs and removes acidic substances such as fluorides by gas-liquid contact while circulating an absorbent slurry containing limestone and an organic acid or organic acid salt, and an absorbent slurry circulation provided under the absorption tower In a wet exhaust gas treatment device having a tank and a means for supplying air into the absorbent slurry circulation tank to oxidize sulfite generated by absorption of sulfur oxides to form gypsum, in the absorbent slurry circulation tank, Chloride concentration measuring device in absorbent slurry, pH measuring device of the absorbent slurry, detection of chloride concentration from the chloride measuring device or detection of pH from the pH measuring device, or both An exhaust gas treatment apparatus comprising at least means for adjusting and controlling the addition amount of an organic acid or an organic acid salt based on the value.