JP3202299B2 - Wet flue gas desulfurization tower - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wet flue gas desulfurization apparatus, and more particularly, to an improvement in the efficiency of sulfur oxide absorption by increasing the oxidation rate at a gas-liquid contact portion between exhaust gas and an absorbent in a desulfurization tower. Further, the present invention relates to a wet flue gas desulfurization tower capable of reducing the capacity of an oxidation tank.

[0002]

2. Description of the Related Art Sulfur oxides, particularly sulfur dioxide (SO ₂ ), in flue gas generated by the combustion of fossil fuels in thermal power plants, etc., are a major source of global environmental problems such as air pollution and acid rain. It is one of the main causes. Therefore, research on a flue gas desulfurization method for removing SO ₂ from flue gas and development of a desulfurization apparatus have become extremely important issues.

As the above desulfurization method, a simple dry desulfurization apparatus with a low cost and a simple system has recently been developed. Dominates the mainstream. In this wet method,
There are a soda method using a soda compound as an absorbent, a calcium method using a calcium compound, and a magnesium method using a magnesium compound. Of these, the soda method has excellent reactivity between the absorbent and SO ₂ , but the soda used is very expensive. For this reason, a method using a relatively inexpensive calcium compound such as calcium carbonate is most often used in a flue gas desulfurization apparatus such as a large boiler for power generation.

[0004] Desulfurization systems using this calcium compound as an absorbing solution are roughly classified into three types, a spray system, a wet wall system, and a bubbling system, depending on the gas-liquid contact method. Although each method has its own characteristics, spray methods that have a good track record and high reliability are widely used worldwide. As this spray type desulfurization system,
BACKGROUND ART Conventionally, a cooling tower for cooling and removing dust from an exhaust gas, an absorption tower for spraying an absorbing liquid to react with SO ₂ in the exhaust gas, and an oxidizing tower for oxidizing calcium sulfite generated in the absorption tower have been used. However, in recent years, the development of a single-column desulfurization tower having cooling and oxidation functions in an absorption tower has been advanced, and recently, the single-column desulfurization system has been becoming the mainstream of the spray method.

FIG. 9 shows an example of a conventional single-column desulfurization apparatus using a spray method. The single-column desulfurization tower is mainly composed of a tower body 1 and an inlet duct 2 into which exhaust gas discharged from a combustion device is introduced, an outlet duct 3 from which desulfurized exhaust gas is discharged, and an inlet duct 2 and an outlet duct 3. A spray nozzle 4 arranged in the space in the tower, an absorbent pump 5 for sending the absorbent to the spray nozzle 4, an oxidation tank 6 provided at a lower portion of the tower body 1, and an absorbent in the oxidation tank 6. A stirrer 7 for stirring, an air blowing device 8 for blowing air into the absorption liquid in the oxidation tank 6, and a mist eliminator 9 provided at the top of the absorption tower or in the outlet duct 3.
Etc. Here, a plurality of spray nozzles 4 are provided in a horizontal direction, and a plurality of spray nozzles are provided in a height direction.

Exhaust gas discharged from a boiler (not shown) is introduced into the desulfurization tower main body 1 from an inlet duct 2 and discharged from an outlet duct 3. During this time, the absorbent containing calcium carbonate sent from the absorbent pump 5 is sprayed from the plurality of spray nozzles 4 into the desulfurization tower, and gas-liquid contact between the absorbent and the exhaust gas is performed. At this time, the absorbing liquid selectively absorbs SO ₂ in the exhaust gas as shown in the formula (1) and generates calcium sulfite.

[0007]

Embedded image

[0008] The absorption liquid that has generated calcium sulfite accumulates in the oxidation tank 6 and is stirred by the stirrer 7.
Calcium sulfite in the absorbing solution is oxidized by air supplied from the air blowing device 8 to produce gypsum. The reactions in the circulation tank 6 are shown in equations (2) and (3).

[0009]

Embedded image

A part of the absorbing solution in the oxidation tank 6 where calcium carbonate and gypsum coexist is sent again to the spray nozzle 4 by the absorbing solution pump 5, and a part of the absorbing solution is discharged from the absorbing solution discharge pipe 10.・ Sent to the gypsum collection system. Of the absorbing liquid atomized from the spray nozzle 4 and atomized, those having a small droplet diameter are entrained in the exhaust gas, but the mist eliminator 9 provided in the upper part of the desulfurization tower is used.
Will be recovered by

The absorption rate of SO ₂ increases as the pH of the absorbing solution increases. However, absorbing liquid drops sprayed from the spray nozzle 4, the diffusion inside the droplets is rate-limiting, SO ₂
When calcium sulfite is formed on the surface of the droplet by reacting with, the pH value of the surface of the droplet decreases. For this reason, the absorption droplet SO
The reactivity with ₂ drops sharply. In other words, the absorbing liquid reacts with SO ₂ as soon as it is sprayed, but once the p
When H decreases, it falls into the oxidation tank 6 while absorbing almost no SO ₂ .

Therefore, if the pH can be restored until the absorbing droplets reach the oxidation tank 6, that is, while the absorbing droplets are in contact with the exhaust gas, the absorbing droplets will again absorb the SO ₂ And the oxidation tank 6
Until it reaches SO ₂ , so that the absorption rate is improved. As a method of recovering the pH of the absorbing droplet once lowered, there are a method of renewing the surface of the absorbing droplet and a method of oxidizing calcium sulfite present on the surface of the absorbing droplet. As these specific means, for example,
In the apparatus described in Japanese Utility Model Publication No. Sho 62-46424, a net is installed directly below the lowermost stage of the spray nozzle group, and the absorbing droplets that fall are attached to the net to mix the droplets.
The re-dispersion and the renewal of the surface of the absorbing droplet are attempted. However, it is difficult to attach all the absorbing droplets falling on the net, and the effect of renewing the droplet surface cannot be increased. Further, in the apparatus described in the above publication, no consideration is given to the recovery of pH due to the oxidation of calcium sulfite. Actually, it is not enough to simply recover the pH by renewing the surface of the absorbing droplets, and it is not possible to expect a significant improvement in desulfurization performance.

Therefore, if another means can be used to improve the surface of the absorbing droplet and greatly promote the oxidation of calcium sulfite in the absorbing droplet, the pH can be sufficiently recovered,
Absorbent droplets had lost activity regained high absorption capacity again, so further to absorb SO _2. This allows
Even if the spray amount of the absorbing liquid with respect to the liquid / gas ratio, that is, the exhaust gas amount, is reduced, high desulfurization performance can be maintained,
It is possible to reduce operating costs.

[0014] Further, the spray type wet flue gas desulfurization apparatus is compared with those of the wet wall type and the bubbling type.
Since the contact time between the exhaust gas and the absorbent is short, the natural oxidation rate in the spray reaction section in the desulfurization tower is low. For this reason, in the spray method, the load of the oxidation treatment in the oxidation tank 6 increases, and the capacity of the oxidation tank 6 tends to increase compared to other methods in order to increase the residence time of the absorbing solution in the oxidation tank 6. There is a tendency. Therefore, if the oxidation rate in the spray reaction section can be increased, the load of the oxidation treatment in the oxidation tank 6 can be reduced, and the capacity of the oxidation tank 6 can be reduced.

[0015]

In the above prior art, the oxidation of calcium sulfite in the absorbing solution whose pH has been lowered by reacting with SO ₂ in the spray reaction section of the desulfurization tower, ie, p
No consideration is given to improving the desulfurization performance due to the recovery of H, and in order to obtain high desulfurization performance, there has been a problem that the operation cost is high and the apparatus scale is large.

[0016] It is an object of the present invention to greatly promote the oxidation of calcium sulfite in absorbing droplets in a spray reaction section, so that high desulfurization performance can be maintained even when the spraying amount of absorbing droplets is reduced. An object of the present invention is to reduce the capacity of the oxidation tank by reducing the load of the oxidation treatment in the oxidation tank.

[0017]

The above object of the present invention is achieved by the following main structure. That is, in a wet flue gas desulfurization tower that treats sulfur oxides in exhaust gas by contacting the exhaust gas discharged from the combustion device with the absorbent discharged from the spray nozzle group, the absorbent discharged from the spray nozzle group is removed. This is a wet type flue gas desulfurization tower in which a storage section for temporarily collecting and a perforated pipe having an air ejection hole are installed in the storage section, and air is supplied to the perforated pipe.

[0018]

[Action] value of pH of the absorption liquid droplets sprayed from the spray nozzle to produce calcium sulfite to droplet surface reacts with SO ₂ in the flue gas droplet surface is lowered. For this reason, the reactivity of the absorbing droplets with SO ₂ is sharply reduced, and the absorbing droplets fall into the oxidation tank with the pH lowered. However, this pH
By placing a storage unit in the desulfurization tower that temporarily collects the absorbed liquid whose absorption has decreased, all of the absorbed droplets are once collected in this storage unit, and mixing / redispersion and surface renewal of the absorbed droplets are performed. It is done reliably.

Further, since air is constantly ejected from the porous pipe installed in the storage section, a bubble layer of air is formed in the absorbing solution in the storing section, and oxygen in the bubbles is converted into sulfurous acid in the absorbing solution. Oxidizes calcium. In particular, the concentration of calcium sulfite in the absorption liquid collected in the storage is higher than that in the absorption liquid in the oxidation tank, so the oxidation rate in the storage naturally increases, and the oxidation rate in the oxidation tank is higher than that in the oxidation tank. It is oxidized efficiently. The absorption liquid whose pH has been recovered by the oxidation of calcium sulfite overflows from the storage part, flows down from the lower part of the storage part, becomes an absorbing droplet again, and contains S in the exhaust gas.
It falls while absorbing O ₂ and enters the oxidation tank.

However, since the absorbing liquid flowing down from the storage section has a large droplet diameter, the gas-liquid contact area is small, and the contact time with the exhaust gas is short. Does not absorb SO ₂ sufficiently. Therefore, the pH of the absorbent finally entering the oxidation tank is higher than that of the prior art method, the load of the oxidation treatment in the oxidation tank is reduced, the capacity of the oxidation tank can be reduced, and the height of the desulfurization tower is reduced, Compactness can be achieved.

Further, in addition to the absorption of SO ₂ by the spray absorbing solution between the spray nozzle and the oxidation tank, the absorbing solution whose absorption capacity has been recovered by oxidation in the storage section overflows and the exhaust gas falls while falling into the oxidation tank. to absorb the SO ₂ in. For this reason, the SO ₂ absorption capacity per unit absorption liquid is increased, and even if the spray amount of the absorption liquid at the spray nozzle is reduced, a high desulfurization rate equivalent to the conventional method can be maintained.

If the exhaust gas drifts in the desulfurization tower, the liquid-gas ratio locally changes, which adversely affects the desulfurization performance. However, in the case of the present invention, since the flow resistance is generated by installing the storage unit in the tower, a rectifying effect of the exhaust gas is obtained, and the drift of the exhaust gas in the tower can be prevented.

[0023]

【Example】

Embodiment 1 An embodiment according to the present invention is shown in FIG. The desulfurization tower shown in FIG. 1 is the same as the prior art desulfurization tower shown in FIG. 9, and has a tower body 1, an inlet duct 2, an outlet duct 3, a spray nozzle 4, an absorbent pump 5, an oxidation tank 6, an agitator 7, air It comprises a blowing device 8, a mist eliminator 9, and the like. In the embodiment, a plurality of collectors 11, which are arranged in parallel below the lowermost stage of the spray nozzles 4 as a storage unit for temporarily collecting the absorbing liquid, Further, a perforated pipe 12 provided at a portion of the collector 11 where the absorbing liquid is stored, an air blower 13 for supplying air to the perforated pipe 12, and an air supply pipe 14 are additionally provided. FIG. 2 is a view taken along the line AA ′ in FIG. In the present embodiment, the collectors 11 and the perforated pipes 12 are arranged in a staggered manner in two upper and lower stages.

Exhaust gas discharged from a boiler (not shown) is introduced into the desulfurization tower main body 1 from an inlet duct 2 and discharged from an outlet duct 3. During this time, the absorbing liquid sent from the absorbing liquid pump 5 is sprayed from the plurality of spray nozzles 4, and gas-liquid contact between the absorbing liquid and the exhaust gas is performed. At this time, the absorbing liquid selectively absorbs SO ₂ in the exhaust gas and generates calcium sulfite. Calcium sulfite is generated and surface p
The absorbing liquid droplets whose H has decreased fall toward the oxidation tank 6.

However, in this embodiment, since the collector 11 is installed immediately below the lowermost stage of the spray nozzles 4 of the desulfurization tower 1, it reacts with SO ₂ as shown in FIG.
Absorbent liquid 17 whose concentration has decreased is once collected by the collector 11 and mixed / redispersed and the surface of the absorbed liquid droplets is renewed. In addition, since air is constantly ejected from the air ejection holes 15 of the porous pipe 12 provided in the portion of the collector 11 where the absorption liquid 17 is stored, air is contained in the absorption liquid 17 in the collector 11 as shown in FIG. Bubble layer 18 is formed,
The oxygen in the bubble layer 18 oxidizes the calcium sulfite in the absorbing solution 17. In particular, the concentration of calcium sulfite in the absorbing solution 17 collected by the collector 11 is higher than that of the absorbing solution in the oxidation tank 6, so that it naturally flows down from the lower end of the collector 11, becomes an absorbing droplet again, and contains SO 2 in the exhaust gas. _It falls while absorbing ₂ and enters the oxidation tank 6.

FIG. 4 shows the relationship between the pH of the absorbing solution and the SO ₂ absorbing ability in order to easily understand the phenomenon occurring at this time. In the conventional method, when the absorbing liquid 17 sprayed from the spray nozzle 4 absorbs SO ₂ in the exhaust gas, the pH decreases. Therefore, the absorption liquid 17 shifts from the point A to the point B, and enters the oxidation tank 6 with the absorption capacity being reduced. Therefore, in the oxidation tank 6, the pH must be restored by oxidizing the calcium sulfite, and the pH must be raised again from the point B to the point A to restore the absorption capacity of the absorbing solution 17. The processing load was increasing.

On the other hand, in the embodiment, when the absorbing liquid 17 sprayed from the spray nozzle 4 absorbs SO ₂ , the point A
From the point B to the point B, the absorption capacity is temporarily lost.
The absorption capacity is immediately raised to point C by the oxidation at However, the absorption liquid 17 whose absorption ability has been recovered has a short contact time with the exhaust gas, and the absorption liquid flowing down from the collector 11 is large, so that the absorption efficiency is deteriorated and the SO ₂ is absorbed only up to the point D. Accordingly, the load of the oxidation tank processing is reduced by about 30%, and the capacity of the oxidation tank 6 can be reduced to about two-thirds that of the prior art. As a result, the tower height is reduced, and the desulfurization tower can be made compact.

FIG. 5 shows the results of comparison of the spraying amount of the absorbing solution necessary for making the desulfurization rate in this embodiment 95% with the conventional method. The amount of SO ₂ absorbed from the time when the absorbing liquid 17 is sprayed from the spray nozzle 4 to the time when the absorbing liquid 17 enters the oxidation tank 6 is equivalent to the point A to the point B in the conventional method as shown in FIG. in addition to the absorption of the equivalent between points A- point B in the example, to absorb after the SO ₂ equivalent between points C- point D oxidized at the collector 11. This means that the SO ₂ absorption capacity per unit absorption liquid has increased. Therefore, according to the embodiment, the absorption liquid 17
The desulfurization rate equivalent to that of the conventional method can be maintained even if the spray amount is reduced by about 20%, and the operating cost can be reduced by about 20% by reducing the power of the absorbent pump 5.

If the exhaust gas drifts in the tower, the liquid-gas ratio changes locally, which adversely affects the desulfurization performance. However, since the flow resistance is generated by installing the collector 11 in the tower as in the present embodiment, a rectifying effect of the exhaust gas is obtained, and the drift of the exhaust gas in the tower can be prevented.

Further, in this embodiment, a liquid discharge hole 16 (FIG. 3) is provided on the bottom surface of the collector 11 to prevent a problem such as scaling caused by the absorption liquid 17 remaining in the collector 11 when the operation is stopped. It is considered so that it can be prevented.

In this embodiment, in order to increase the efficiency of collecting the absorbing solution 17, the collector 11 and the porous pipe 12 are used.
Are arranged in a staggered manner in two upper and lower stages, but the present invention is not limited to this embodiment and FIGS. 1 to 3. For example, three or four stages are provided so as to further increase the collection efficiency. As described above, they may be arranged in a staggered manner. Further, although the collection efficiency of the absorbing solution is slightly reduced, the collector 11 is not staggered,
Several stages may be arranged on the same vertical, or several stages may be arranged in the cross direction. Further, as a simple method, only one collector 11 may be arranged.

Embodiment 2 FIG. 6 shows another embodiment of the present invention. FIG. 7 is a view taken along the line BB ′ in FIG. The difference from the first embodiment is
The perforated plate 19 is used instead of the collector 11 as a storage unit for temporarily collecting the absorbing liquid, and all other components are the same. FIG. 8 shows a detailed view of the perforated plate. Exhaust gas ventilation holes 20 of the perforated plate 19 have weirs 21
The absorption liquid flows down from the weir 21 and forms droplets and enters the oxidation tank 6. The operation and effect of this embodiment are the same as those of the first embodiment. In the present embodiment, the storage unit for temporarily collecting the absorbing liquid is constituted by one stage of the porous plate 19, but may be constituted by two or more stages.

[0033]

According to the present invention, it is possible to increase the SO ₂ absorption amount of the absorbing solution from the time when the absorbing solution is sprayed from the spray nozzle in the desulfurization tower to the time when the absorbing solution falls into the oxidation tank. Since the pH of the absorbing solution can be increased, the operating cost can be reduced, the desulfurization tower can be made compact, and the gas drift in the tower can be reduced.

[Brief description of the drawings]

FIG. 1 is a view showing a single-column wet flue gas desulfurization tower according to an embodiment of the present invention.

FIG. 2 is a view taken in the direction of arrows A-A 'in FIG.

FIG. 3 is a diagram showing an oxidized state at the collector of FIG. 1;

FIG. 4 is a diagram showing the relationship between the pH of an absorbing solution and the absorbing solution capacity of an example according to the present invention.

FIG. 5 is a diagram showing a comparison between a conventional method and an example of the present invention with respect to a spray amount of an absorbing solution for obtaining a desulfurization rate of 95%.

FIG. 6 is a view showing a single-column wet flue gas desulfurization tower according to another embodiment of the present invention.

FIG. 7 is a view taken along the line B-B 'in FIG.

FIG. 8 is a detailed view of the perforated plate of FIG.

FIG. 9 is a diagram showing a single-column wet-type flue gas desulfurization tower according to a conventional technique.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Tower main body, 2 ... Inlet duct, 3 ... Outlet duct, 4 ... Spray nozzle, 5 ... Absorbent pump, 6 ... Oxidation tank, 7
... Agitator, 8 ... Air blowing device, 9 ... Mist eliminator, 10 ... Absorbent extraction pipe, 11 ... Collector 12 ... Perforated pipe, 13 ... Air blower, 14 ... Air supply pipe, 15 ... Air ejection hole, 16 ... Liquid Exhaust hole, 17: Absorbing liquid, 18: Bubble layer, 19: Perforated plate, 20: Exhaust gas ventilation hole, 21: Weir

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Yasuyuki Nishimura 3-36 Takara-cho, Kure City, Hiroshima Prefecture Inside the Kure Research Institute, Inc. (72) Inventor Hirofumi Yoshikawa 3-36 Takaracho Kure City, Hiroshima Prefecture Babcock Date Inside Kure Research Institute Co., Ltd. (56) References JP-A-1-83427 (JP, U) JP-A 4-110127 (JP, U) JP-A 1-163535 (JP, U) (58) Fields surveyed ( Int.Cl. ⁷ , DB name) B01D 53/50 B01D 53/18 B01D 53/77

Claims (5)

(57) [Claims] In a wet flue gas desulfurization tower for treating sulfur oxides in exhaust gas by bringing exhaust gas discharged from a combustion device into contact with absorbing liquid ejected from a group of spray nozzles, the exhaust gas is ejected from a group of spray nozzles. A wet-type flue gas desulfurization tower, comprising: a storage section for temporarily collecting an absorbing liquid; and a porous pipe having an air ejection hole in the storage section, and supplying air to the porous pipe. 2. The wet flue gas desulfurization tower according to claim 1, wherein the absorption liquid storage section and the perforated pipe are installed immediately below a lowermost stage of a spray nozzle group. 3. The wet flue gas desulfurization tower according to claim 1, wherein a plurality of absorption liquid discharge holes are provided on a bottom surface of the absorption liquid storage section. 4. The wet flue gas desulfurization tower according to claim 1, wherein the absorption liquid storage section comprises a plurality of gutter members arranged in parallel. 5. The wet flue gas desulfurization tower according to claim 1, wherein the absorption liquid storage section is constituted by a perforated plate provided with a weir.