JP3590856B2 - Exhaust gas desulfurization method - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a method for desulfurizing an exhaust gas containing a sulfurous acid gas.
[0002]
[Prior art]
In order to desulfurize the exhaust gas containing sulfurous acid gas, the exhaust gas and oxidizing air are blown into an absorbing solution consisting of a water-based slurry solution containing gypsum and a calcium-based absorbent reactive to sulfurous acid gas. A method of fixing sulfurous acid gas as gypsum is widely used.
In such an exhaust gas desulfurization method, a part of the absorbent is extracted, and a fresh absorbent is supplied to the absorbent accordingly. Conventional supply of a fresh absorbent is performed by ejecting the absorbent as a water slurry liquid into the absorbent through a liquid ejection nozzle.
However, in such a method for supplying a fresh absorbent, since the pH of the fresh absorbent is high, the pH of the absorbent in the vicinity of the nozzle from which the fresh absorbent is jetted rises to 7 or more, and the fresh absorbent is dissolved in the absorbent. The gypsum precipitates as fine crystal particles, and the carbon dioxide gas in the exhaust gas is absorbed in the portion where the pH of the absorbing solution becomes 7 or more, and reacts with calcium ions contained in the absorbing solution to form fine crystals of calcium carbonate. This causes a problem that the liquid ejection hole of the liquid supply nozzle is closed and scale is generated in the exhaust gas dispersion pipe and the like in the vicinity thereof.
[0003]
[Problems to be solved by the invention]
The present invention prevents the precipitation of gypsum and calcium carbonate fine crystal particles that occur when a fresh absorbent is supplied to an absorbent, and causes a problem of clogging of a liquid ejection hole of a liquid supply nozzle and generation of scale in an exhaust gas dispersion pipe and the like. Is to solve the problem.
[0004]
The present inventors have conducted intensive studies to solve the above problems, and as a result, completed the present invention.
That is, according to the present invention, an exhaust gas containing sulfurous acid gas and oxidizing air are blown into an absorbent comprising a water-based slurry solution containing calcium-based absorbent and gypsum reactive with sulfurous acid gas to convert the sulfurous acid gas into gypsum. In the desulfurization method for exhaust gas to be fixed as: (i) stirring the absorbing liquid with a stirring blade, and (ii) supplying a water slurry liquid of a calcium-based absorbent into the liquid through a plurality of liquid ejection nozzles. (Iii) the position of the liquid ejection nozzle hole is at a height between the position of the stirring blade disposed in the absorbent and the position of the lower end of the exhaust gas dispersion pipe disposed in the absorbent. it, (iv) solution that but the number of ejection nozzles is a ratio of one per absorbing fluid 20~500m ^3, (v) liquid supply amount of ejection nozzles per calcium-based absorbent mixed solution of 0. 5-20kgmol / h And (vi) a method for desulfurizing exhaust gas, wherein the molar ratio of gypsum and calcium-based absorbent contained in the calcium-based absorbent-containing absorbent is in the range of 0.5 to 20. .
[0005]
Next, the present invention will be described with reference to the drawings.
FIG. 1 shows a schematic diagram of an exhaust gas desulfurization device. In this figure, 1 is a desulfurizer, 1 'is a closed tank, 2 is a first partition, 3 is a second partition, 4 is a top plate, 5 is a first chamber, 6 is a second chamber, and 7 is a third chamber. A chamber, 8 is an exhaust gas introduction duct, 9 is an exhaust gas dispersion pipe, 10 is an exhaust gas riser, 11 is an exhaust gas outlet duct, 12 is a stirrer, 13 is an oxidizing air supply pipe, 14 is an oxidizing air jet nozzle, and 15 is an absorption pipe. A liquid discharge pipe, 16 is a pump, 17 is an absorbing liquid discharge pipe, 18 and 20 are absorbing liquid pipes, 19 is an absorbent supplying pipe, 21 is a liquid ejection nozzle, L is an absorbing liquid, S is a stationary liquid level of the absorbing liquid, A shows a floss layer composed of a mixture of exhaust gas bubbles and an absorbing liquid.
[0006]
The exhaust gas desulfurization treatment apparatus 1 shown in FIG. 1 is composed of a large-sized closed tank 1 ′, and the inside of the tank is divided into a first chamber 5 and a first chamber 5 by a first partition 2 and a second partition 3 located above the first partition 2. It is divided into a second chamber 6 adjacent above one chamber and a third chamber 7 adjacent above the second chamber. The upper space of the third chamber is closed by the top plate 4. The first partition 2 can be horizontal or slightly inclined. The second partition 3 can be horizontal or inclined, and the inclination angle is not particularly limited.
The first chamber 5 contains the absorbing liquid L. Further, in the first chamber, a stirrer 12 and an oxidizing air jet nozzle 14 for supplying oxygen into the absorbing liquid L are provided.
An exhaust gas inlet is provided on the peripheral wall of the second chamber 6, and an exhaust gas introduction duct 8 is connected to this inlet.
An exhaust gas outlet is provided in the third chamber 7, and an exhaust gas outlet duct 11 is connected to this outlet.
[0007]
The first partition plate 2 is provided with a large number of through-holes communicating between the first chamber 5 and the second chamber 6, and each of the through-holes has a tip end extending into the absorbent in the first chamber. A pipe 9 is provided vertically. The exhaust gas dispersion pipe 9 has a gas ejection hole on the peripheral wall surface at the lower end. The first partition 2 and the second partition 3 are provided with openings for disposing the exhaust gas riser 10, and these openings are configured to receive the exhaust gas existing in the upper space of the first chamber 5. An exhaust gas riser 10 for introduction into the third chamber 7 is connected. The cross-sectional shape of the exhaust gas ascending cylinder can be various shapes such as a circle, a square, and a rectangle.
[0008]
An absorption liquid extraction pipe 15 is provided below the first chamber 5, and an absorption liquid pipe 18 is connected to the absorption liquid extraction pipe 15 via a pump 16. Further, an absorbent supply pipe 19 is connected to the absorbing liquid pipe 18, and the tip of the absorbing liquid pipe 18 is introduced into the absorbing liquid L, and a liquid jet nozzle 21 is connected via the absorbing liquid pipe 20. .
The position of the liquid ejection nozzle hole is preferably arranged at a height between the position of the upper end of the stirring blade of the stirrer 12 and the position of the lower end of the exhaust gas dispersion pipe 9. In this case, it is preferable that the stirrer has a structure in which the absorbing liquid flows downward. Further, it is preferable that the position of the liquid ejection nozzle hole be set not at the upper part of the stirring blade but at a position which is laterally separated by a certain distance (0.5 to 10 m) from the position of both ends of the stirring blade. When the absorbing liquid mixed with the absorbent is supplied into the absorbing liquid from the liquid discharging nozzle hole arranged as described above, the absorbing liquid mixed with the absorbent ejected from the liquid discharging nozzle hole is absorbed by the absorbing liquid formed around the stirrer. Riding on the upward flow of the liquid, the liquid smoothly moves into and reacts with the floss layer A formed of a mixture of bubbles of the exhaust gas formed above the absorbing liquid and the absorbing liquid.
[0009]
In order to treat the exhaust gas using the apparatus shown in FIG. 1, the exhaust gas is introduced into the second chamber 6 through the exhaust gas introduction duct 8, and from there, the exhaust gas is dispersed in the first chamber 5 through the exhaust gas dispersion pipe 9. Blow into absorption liquid L. The exhaust gas blown into the absorbing liquid L rises as bubbles, and a floss layer A composed of a mixed phase of the bubbles and the absorbing liquid is formed above the gas outlet of the dispersion pipe. While the exhaust gas rises as bubbles in the absorbing solution, contaminants such as sulfur dioxide and dust contained in the exhaust gas are captured by the absorbing solution and removed from the exhaust gas.
[0010]
The exhaust gas thus purified is radiated from the floss layer A to the upper space, and is introduced into the third chamber 7 through the exhaust gas ascending cylinder 10 and passes through the exhaust gas outlet duct 11 provided in the third chamber. The gas is then discharged out of the tank and introduced into a mist eliminator (not shown), where the absorbing liquid particles and the like contained in the gas are removed and then released to the atmosphere.
On the other hand, in the lower part of the first chamber 5, the oxidizing air supplied through the oxidizing air supply pipe 13 is jetted out of the jet nozzle 14 into the absorbing solution, and the sulfurous acid gas absorbed in the absorbing solution is plastered. Immobilized as
[0011]
In the present invention, a part of the absorbing liquid existing in the first chamber 5 is withdrawn by the pump 16 through the absorbing liquid extracting pipe 15, and a part of the absorbing liquid is discharged through the absorbing liquid discharging pipe 17 to the outside of the system. Is ejected from the liquid ejection nozzle 21 located in the absorption liquid L through the pipes 18 and 20 into the absorption liquid. In this case, the absorbing liquid to be ejected from the liquid ejecting nozzle 21 together with the absorbent into the absorbing liquid L may be a mother liquor after separating solids such as gypsum contained therein. In the present invention, the absorbent is mixed with the absorbent circulated through the pipe 18 through the supply pipe 19, and is ejected from the liquid ejection nozzle 21 through the pipe 20 into the absorbent. The absorbent L contained in the first chamber 5 is a water slurry containing an absorbent and gypsum, and a part of the absorbent exists in a dissolved state, and most of the calcium sulfate is gypsum (CaSO ₄ .2H). ₂ O) present as solid particles, with only a small portion of the calcium sulfate present in the dissolved state. Therefore, in the absorbing solution, calcium sulfate generated by the reaction between the sulfurous acid gas, the absorbing agent and oxygen precipitates as gypsum in the absorbing solution.
[0012]
Gypsum precipitated in the absorbing solution as described above must be removed from the absorbing solution, and on the other hand, it is necessary to supply the absorbing agent corresponding to the absorbent consumed in the reaction to the absorbing solution. In the case of the invention, for this purpose, a part of the absorbing liquid is withdrawn from the first chamber 5 and a part of the absorbing liquid is discharged out of the system. Circulate to The supplied absorbent is a calcium-based absorbent such as CaCO ₃ and / or Ca (OH) ₂ , and this absorbent is usually mixed into the circulating absorbent as a 10 to 30 wt% aqueous slurry liquid. The amount of the absorbing solution discharged out of the system through the absorbing solution discharge pipe 17 is an amount corresponding to the amount of the sulfurous acid gas immobilized as gypsum in the absorbing solution. Is the amount corresponding to the absorbent consumed by the reaction with The amount of the absorbing liquid circulated into the absorbing liquid L through the absorbing liquid pipe 18 is 0.2 to 10 times, preferably 0.5 to 10 times the amount of the absorbing liquid discharged through the absorbing liquid discharging pipe 17. 5 times the weight. It is not always necessary to discharge a part of the absorbing liquid passing through the absorbing liquid pipe 18 when the absorbing liquid is discharged outside the system. Another pipe is connected to the first chamber 5 and discharged through the pipe to the outside of the system. You can also. In addition, the absorbent supplied from the absorbent supply pipe 19 can be directly supplied to the absorbent L in the first chamber via the liquid jet nozzle 21 without mixing with the circulating absorbent.
[0013]
As the liquid jet nozzle for jetting the absorbent mixed with the absorbent into the absorbent L, a normal liquid jet nozzle having a liquid jet hole at the tip is used. In this case, the diameter of the ejection hole is 20 to 100 mm, preferably 25 to 75 mm. The number of liquid ejection nozzles disposed in the absorption liquid as much as possible often preferred, in general, per absorbing fluid 20 to 500 m ^3, which is accommodated in the first chamber 5, preferably 30～300M ³ per It is one ratio. Further, the amount of the absorbent ejected from the liquid ejection nozzle is 0.5 to 20 kg mol / h, preferably 1 to 10 kg mol / h per liquid ejection nozzle. As described above, when a plurality of liquid ejection nozzles are provided and the absorbent is ejected from the liquid ejection nozzles as a mixture with the absorbent, the absorbent can be dispersed in the absorbent in a short time. It is possible to prevent the generation of scale on the liquid ejection nozzle or the exhaust gas dispersion pipe and the decrease in desulfurization performance due to the local pH rise of the liquid.
[0014]
Mixing amount of absorbent mixed with the absorption liquid circulation, the molar ratio A / B of the gypsum _{(CaSO 4 · 2H 2 O)} A in the absorbing agent-mixed absorbent solution as absorbent B 0.1 to 20 The ratio is preferably in the range of 1 to 10. When such a liquid mixed with an absorbent is ejected from the liquid ejecting nozzle into the absorbing liquid, fine gypsum crystal particles are deposited and CO ₂ and calcium ions in the exhaust gas are removed because there is no local increase in pH near the nozzle. The precipitation of fine crystal particles of CaCO ₃ due to the reaction is prevented, and even if these fine crystals precipitate, these fine crystals precipitate on the gypsum crystal surface and become coarse crystals. Blocking trouble and scaling to the exhaust gas dispersion pipe 9 and the like are prevented.
[0015]
【Example】
Next, the present invention will be described in more detail with reference to examples.
Example 1
The exhaust gas desulfurization treatment apparatus 1 having the structure shown in FIG. 1 was used to treat flue gas containing SO ₂ : 1000 vol ppm, O ₂ : 5 vol%, and CO ₂ : 11 vol%.
The device conditions in this case are as follows.
(1) Diameter of closed tank 1 ': 10m, height: 10m
(2) Diameter of exhaust gas dispersion pipe 9: 4 inches and number: 800 (3) Number of liquid ejection nozzles 21: 8 (4) Height of stationary liquid surface of absorbent in first chamber 5: 5 m
The tip hole diameter of the liquid jet nozzle 21 was 50 mm.
[0016]
A water slurry having a gypsum concentration of 20% by weight and a CaCO ₃ concentration of about 0.001% by weight is previously stored in the first chamber 5 of the closed tank 1 ′ having the structure shown in FIG. I let it.
Next, smoke was supplied from the exhaust gas introduction duct 8 of the device into the second chamber 6 at a supply amount of 300,000 Nm ³ / h. In this case, air was jetted at 4000 Nm ³ / h from the oxidizing air jet nozzle 14 disposed at a position 2500 mm below the stationary liquid level of the absorbing liquid, and the agitator 12 was rotated to stir the absorbing liquid.
A part of the absorbing liquid L in the first chamber 5 was withdrawn at a rate of 30,000 kg / h through a pipe 15, and 11,000 kg / h of the liquid was discharged out of the system through a pipe 17. On the other hand, the remaining 19,000 kg / h of the absorbing solution is ejected from the liquid ejection nozzle 21 into the absorbing solution L through the pipe 18, and the CaCO ₃ is added to the absorbing solution passing through the pipe 18 at a concentration of 20% by weight. The added water slurry was mixed at 6,400 kg / h. The gypsum concentration in the absorbent mixed with CaCO ₃ thus formed was 15% by weight, the CaCO ₃ concentration was 5% by weight, and the molar ratio of CaSO ₄ .2H ₂ O / CaCO ₃ was 22/13. there were. The amount of the absorbent ejected from the liquid ejection nozzle 21 was 1.6 kg mol / h per liquid ejection nozzle.
[0017]
As a result of desulfurizing the flue gas as described above, a high desulfurization rate of 95% could be obtained. In addition, even in the continuous operation for 12 months, no blocking trouble of the liquid ejection nozzle 21 occurred.
On the other hand, for comparison, the circulation of the absorbent through the pipe 18 was stopped, and the operation of seven of the liquid jet nozzles 21 was stopped directly without mixing the aqueous slurry of CaCO ₃ into the absorbent, When only one of them was jetted into the absorbing liquid, a desulfurization rate of 92% was obtained, but in this case, the liquid jet nozzle 21 was clogged with the operation for one month. Further, in this case, scaling was observed in the exhaust gas dispersion pipe 9 and the like near the liquid ejection nozzle.
[0018]
【The invention's effect】
According to the present invention, when the absorbent supplied to the absorbing liquid is ejected into the absorbing liquid through the liquid ejecting nozzle, the absorbing agent is ejected as a mixture with the absorbing liquid. There is no local pH rise, and the precipitation of fine gypsum crystal particles and calcium carbonate particles is prevented, and the problem of clogging of the liquid ejection nozzle and scaling on the inner wall of the exhaust gas dispersion pipe near the liquid ejection nozzle are effectively prevented for a long time. .
[Brief description of the drawings]
FIG. 1 is a schematic view showing one example of an exhaust gas desulfurization treatment apparatus used in the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Exhaust gas desulfurization apparatus 1 'Closed tank 2 1st partition 3 2nd partition 4 Top plate 5 1st chamber 6 2nd chamber 7 3rd chamber 8 Exhaust gas introduction duct 9 Gas dispersion pipe 10 Exhaust gas riser cylinder 11 Desulfurization exhaust gas lead-out duct Reference Signs List 12 Stirrer 13 Oxidation air supply pipe 14 Gas ejection nozzle 15 Absorption liquid extraction pipe 16 Pump 17 Absorption liquid discharge pipe 18, 20 Absorption liquid pipe 19 Absorbent supply pipe 21 Liquid ejection nozzle

Claims (3)

A method for desulfurizing exhaust gas by immobilizing sulfurous acid gas as gypsum by blowing exhaust gas containing sulfurous acid gas and oxidizing air into an absorbent consisting of a water slurry containing calcium-based absorbent and gypsum reactive to sulfurous acid gas (I) stirring the absorbing liquid with a stirring blade, (ii) supplying a water slurry liquid of a calcium-based absorbent into the liquid through a plurality of liquid discharging nozzles, (iii) liquid discharging nozzle holes Is located at a height between the position of the stirring blade provided in the absorbing solution and the position of the lower end of the exhaust gas dispersion pipe provided in the absorbing solution, (iv) the liquid jet nozzle it but the number of the fraction absorbing fluid 20 to 500 m ³ per 1, (v) solution that the supply amount of the ejection nozzle per a calcium-based sorbent entrained liquid is 0.5~20kgmol / h And (vi) mosquito A method for desulfurizing exhaust gas, wherein the molar ratio of gypsum and calcium-based absorbent contained in the absorption liquid mixed with a lucium-based absorbent is in the range of 0.5 to 20 . 2. The method according to claim 1, wherein the liquid jet nozzle is disposed in a vertical direction, and the calcium-based absorbent water slurry liquid is supplied from above to the absorbent through the liquid jet nozzle. A part of the absorbing solution is discharged, a calcium-based absorbing agent is mixed into the absorbing solution to form a calcium-based absorbing agent-containing absorbing solution, and the liquid is supplied into the absorbing solution through a plurality of liquid ejection nozzles. Any one of the methods 1-2.

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