JPH0739719A - Method and apparatus for wet type exhaust gas desulfurization - Google Patents

Abstract

PURPOSE:To omit a thickener, to decrease load of a dehydrator and to achieve more higher desulfurization properties. CONSTITUTION:A separation apparatus 16 for removing needle-like particles in solid particles included in an absorbing soln. from a circulation system (a circulation pump 5 and a drawing pipe 10) of a desulfurization tower main body 1 is provided. In an absorbing soln. with a solid concn., viscosity of an absorbing soln. contg. more needle-like solid particles is higher than that of a absorbing soln. contg. more nearly spherical solid particles and decrease in desulfurization properties caused by absorption of SO2 is large. Then, as viscosity of the absorbing soln. becomes lower than that of the absorbing soln. contg. needle-like solid particles at the same solid concn. by removing the needle-like solid particles from the absorbing soln. by means of a separation apparatus 16, circulation inside a liq. drop becomes easier and absorption properties of SO2 are improved.

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 method and apparatus, and in particular, by removing needle-like solid particles contained in an absorbent, a thickener can be omitted while maintaining high desulfurization performance. The present invention relates to a wet flue gas desulfurization method and apparatus.

[0002]

2. Description of the Related Art Sulfur oxides, especially sulfur dioxide (SO ₂ ), in flue gas generated by burning fossil fuels in thermal power plants and the like is a cause 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 flue gas desulfurization apparatus have become extremely important subjects. Although various processes have been proposed as the flue gas desulfurization method,
The wet method is the mainstream. This wet method includes 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. Among these, the soda method is excellent in 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 for a flue gas desulfurization apparatus such as a large-scale boiler for power generation.

Flue gas desulfurization systems using this calcium compound as an absorbing liquid are roughly classified into three types, a spray type, a wet wall type and a bubbling type, depending on the difference in the gas-liquid contacting method. Each method has its own characteristics,
The spray method, which has a proven track record and is highly reliable, is widely used worldwide. This spray-type flue gas desulfurization system has traditionally been a cooling tower that cools and removes exhaust gas,
It consisted of three towers: an absorption tower that sprays the absorbing liquid and reacts with SO ₂ in the exhaust gas, and an oxidation tower that oxidizes the calcium sulfite produced in the absorption tower. However, in recent years, the development of a single tower desulfurization tower (in-tank oxidation method) in which the absorption tower has functions of cooling and oxidation has progressed, and recently, the single tower flue gas desulfurization system has become the mainstream of the spray method. It's starting.

FIG. 10 shows an example of a conventional one-column type flue gas desulfurization system by a spray method. The single tower type desulfurization tower mainly includes a tower body 1, an inlet duct 2, an outlet duct 3, a spray nozzle 4, an absorbing liquid pump 5, an oxidizing tank 6, an agitator 7, an air blowing device 8, a mist eliminator 9, and an absorbing member. It is composed of a liquid extraction pipe 10, a gypsum extraction pipe 11, a limestone supply pipe 12, a thickener 13, a dehydrator 14, and the like. A plurality of spray nozzles 4 are installed in the horizontal direction, and a plurality of spray nozzles 4 are installed in the height direction. Also, the agitator 7 and the air blowing device 8
Is installed in the oxidation tank 6 in the lower part of the desulfurization tower where the absorbing liquid remains, and the mist eliminator 9 is installed in the uppermost part of the absorption tower or in the outlet duct 3.

Exhaust gas discharged from the boiler is introduced into the desulfurization tower main body 1 through the inlet duct 2 and discharged through the outlet duct 3. During this time, the desulfurization tower is sprayed with the absorption liquid sent from the pump 5 through the absorption liquid extraction pipe 10 from the plurality of spray nozzles 4, and the absorption liquid and the exhaust gas are brought into gas-liquid contact. At this time, the absorbing liquid selectively absorbs SO ₂ in the exhaust gas and forms calcium sulfite. The absorption liquid that has generated calcium sulfite is accumulated in the oxidation tank 6, and while being stirred by the stirrer 7, the calcium sulfite in the absorption liquid is oxidized by the air supplied from the air blowing device 8 to generate gypsum. Desulfurizing agents such as limestone are used for limestone supply pipe 12
More is added to the absorbing liquid in the oxidation tank 6. A part of the absorption liquid in the oxidation tank 6 in which calcium carbonate and gypsum coexist is sent to the spray nozzle 4 again from the absorption liquid extraction pipe 10 by the absorption liquid pump 5, and a part of the absorption liquid 1
Part 1 is sent to the dehydrator 14 via the thickener 13, and a part of the water dehydrated is returned to the desulfurization tower through a pipe line (not shown). Further, among the atomized absorption liquid sprayed from the spray nozzle 4, those having a small droplet diameter are entrained in the exhaust gas, but are recovered by the mist eliminator 9 provided at the upper part of the desulfurization tower.

The absorption rate of SO ₂ is influenced by the concentration of alkali (for example, limestone) in the absorption liquid, and naturally, the higher the concentration of limestone in the absorption liquid, the higher the absorption rate of SO ₂ (desulfurization rate). However, a part of the absorbed liquid extracted is dehydrated and then used as gypsum, so it is not possible to raise the ratio of limestone to gypsum in the extracted liquid in order to prevent deterioration of the quality of gypsum. Not possible (after extraction, it is possible to turn excess limestone into gypsum with sulfuric acid, etc., but this is not economical). Therefore, by increasing the concentration of gypsum in the absorption liquid (the solid content in the absorption liquid is mostly gypsum, the solid concentration will be increased), so that the limestone concentration will be high without degrading the quality of the extracted gypsum. However, a method of improving the desulfurization performance can be considered. further,
Increasing the solid concentration of such an absorbing solution is an effective method from the viewpoint of omitting the thickener 13 and reducing the load on the dehydrator used for dehydrating the absorbing solution. But,
As a result of examination by the present inventors, it was found that even if the solid concentration and limestone concentration of the absorbing solution were increased, the desulfurization performance was not necessarily improved.

[0007]

The above prior art does not consider the influence of the shape of the solid particles in the absorbing liquid on the desulfurization reaction by the limestone slurry in the desulfurization tower, and cannot obtain high desulfurization performance. There was a problem. An object of the present invention is to eliminate the thickener, reduce the load on the dehydrator, and achieve higher desulfurization performance.

[0008]

The above object of the present invention can be achieved by the following constitutions. That is, in a wet flue gas desulfurization method of treating sulfur oxides in exhaust gas by contacting the exhaust gas discharged from a combustion device such as a boiler with the absorption liquid circulated and supplied, among solid particles contained in the absorption liquid. Is a wet flue gas desulfurization method for selectively removing the acicular particles outside the circulation supply system of the absorbing liquid. It is desirable that the shape factor of the acicular particles removed to the outside of the circulation supply system is 3 or more. Further, the absorption liquid from which the needle-shaped particles are removed can be returned to the absorption liquid circulation supply system and reused.

The above object of the present invention can be achieved by the following constitutions. That is, the exhaust gas discharged from a combustion device such as a boiler is contacted with an absorbent that is circulated and supplied in a desulfurization tower, and the sulfur oxides in the exhaust gas are absorbed in the absorbent to be recovered in an absorbent tank. In a wet flue gas desulfurization device that circulates and supplies a part of the absorption liquid in the tank to the absorption tower and removes the other part from the desulfurization tower circulation supply system, needle-shaped particles in the solid particles contained in the absorption liquid. It is a wet flue gas desulfurization apparatus provided with a separator for removing particles from the desulfurization tower circulation supply system.

[0010]

[Function] Alkaline slurry such as limestone slurry is SO
_{When 2} is absorbed, the pH of the surface of the droplet is lowered and the SO ₂ absorption performance is lowered to some extent. However, since alkali such as limestone exists in the droplets and circulation occurs due to the difference in relative velocity with the exhaust gas inside the droplets, the once lowered pH is recovered and the SO ₂ absorption performance is also increased again. . However, when the concentration of solid particles such as gypsum in the absorption liquid becomes high, the viscosity of the absorption liquid becomes high, and it becomes difficult for the liquid droplets to circulate due to the difference in the relative velocity with the exhaust gas, so the pH once lowered cannot be recovered. , SO ₂ absorption performance is not improved.
In particular, when many needle-shaped solid particles are contained, the viscosity becomes high, so that circulation inside the liquid droplets is less likely to occur, and the desulfurization performance is greatly reduced. It is considered that this is because the acicular particles occupy the same volume as the sphere having the maximum diameter as the diameter in the absorbing liquid.
For this reason, the viscosity of the absorbing liquid containing many needle-shaped solid particles even with the same solid concentration is higher than that of the absorbing liquid containing many solid particles having a shape close to a sphere, and the desulfurization performance by SO ₂ absorption is high. The decrease is large. In the present invention, since the needle-shaped solid particles are removed from the absorption liquid, the viscosity of the absorption liquid becomes lower than that of the absorption liquid containing the needle-shaped solid particles even at the same solid concentration, so that the circulation inside the droplet is likely to occur. The SO ₂ absorption performance is also improved.

[0011]

The present invention will be explained in more detail by the following examples, but it should not be construed as being limited thereto. Example 1 An example according to the present invention is shown in FIG. Similar to the conventional desulfurization tower shown in FIG. 10, the desulfurization tower of the flue gas desulfurization apparatus of the present embodiment 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, It is composed of a stirrer 7, an air blowing device 8, a mist eliminator 9, and the like. However, in the embodiment according to the present invention, unlike the desulfurization tower of FIG. 10, a part of the absorbing liquid in the oxidation tank 6 in which calcium carbonate and gypsum coexist is sent to the separating device 16 from the gypsum withdrawing pipe 11. Here, the slurry containing many needle-shaped gypsum particles is separated from the absorbing liquid and sent to the dehydrator 14,
The other absorption liquid is returned to the oxidation tank 6. The exhaust gas discharged from the boiler is discharged from the inlet duct 2 into the desulfurization tower body 1
And is discharged from the outlet duct 3. During this time, the desulfurization tower is sprayed with the absorbing liquid sent from the pump 5 from the plurality of spray nozzles 4, and the absorbing liquid and the exhaust gas are brought into gas-liquid contact. At this time, the absorbing liquid selectively absorbs SO ₂ in the exhaust gas and forms calcium sulfite. The absorbing liquid that produced calcium sulfite is stored in the oxidation tank 6 and is stirred by the agitator 7.
While being stirred by, the calcium sulfite in the absorbing liquid is oxidized by the air supplied from the air blowing device 8 to produce gypsum. Tank 6 in which limestone and gypsum coexist
A part of the absorbing liquid therein is sent again to the spray nozzle 4 from the absorbing liquid extracting pipe 10 by the absorbing liquid pump 5, and a part of the absorbing liquid is sent to the separating device 16 from the gypsum extracting pipe 11.

An example of the flow of the separating device 16 used in this embodiment is shown in FIG. A slurry containing gypsum particles is supplied from a line 18 to a settling tank (water sieving) 19, large particles or needle-shaped particles are easily settled, and fine particles are difficult to settle, so that they can be separated. The large-sized particles and the needle-shaped particles are sent to the wet cyclone 20, the needle-shaped particles are discharged from the vertical pipe 21, and the particles having a shape close to a sphere are discharged from the lower discharge pipe 22. In this way, needle-shaped particles can be separated. Further, if necessary, the fine particles discharged from the settling tank 19 can also be separated by the wet cyclone 20 according to the particle shape. Pure crystals of gypsum (dihydrate) belong to the monoclinic system, but in actual flue gas desulfurization equipment, many of them have rounded corners due to grinding with a pump or a spray nozzle. However, here, the shape of the gypsum particles is approximated as shown in FIG. 3, and the ratio of the maximum diameter to the minimum diameter is defined as the shape factor.
In the example shown in FIG. 3, the shape factor is the maximum diameter (= height (b)).
/ Minimum diameter (= depth (c)).

A desulfurization test was conducted using the apparatus according to this example. However, the concentration of sulfurous acid gas in the exhaust gas at the inlet of the desulfurization tower is 1000 ppm, and the total amount of limestone supplied from the limestone supply pipe 12 is about 0.97 times the equivalent amount of sulfurous acid gas in the exhaust gas, but strictly speaking, The ratio of limestone and gypsum in the absorption liquid (hereinafter referred to as limestone excess ratio) is 1% in molar ratio
The limestone supply was adjusted to maintain Further, by adjusting the amount of the absorbing liquid extracted from the gypsum withdrawing pipe 11 and the amount of water in the limestone slurry supplied from the limestone supplying pipe 12, the solid concentration of the absorbing liquid inside the oxidation tank 6 (the gypsum per unit weight of the absorbing liquid slurry, The ratio of solid particles such as limestone and calcium sulfite, the same shall apply hereinafter)
The average shape factor of the solid particles in the oxidation tank 6 was changed by adjusting the operating conditions of the separator 16 while changing the range of 30% by weight.

FIG. 4 shows the relationship between the average shape factor of particles and the desulfurization rate at a solid concentration of 30%. From this figure, the shape factor is 3
It can be seen that the desulfurization rate decreases significantly when the above is exceeded.
FIG. 5 shows the relationship between the desulfurization rate and the ratio of particles having a shape factor of 3 or more when the solid concentration in the absorbing liquid is changed to 10 to 30% by weight. However, the vertical axis represents a relative value when the desulfurization rate is 1 when particles having a shape factor of 3 or more are contained in an amount of 10% by weight.
As shown in FIG. 5, the desulfurization rate increases as the proportion of particles having a shape factor of 3 or more decreases. It was also found that the higher the solid concentration, the greater the effect of the particle shape factor on the desulfurization performance. On the other hand, FIG. 6 shows the relationship between the proportion of particles having a shape factor of 3 or more in the gypsum particles sent to the dehydrator 14 and the processing capacity of the dehydrator 14. However, the vertical axis represents a relative value when the treatment amount when particles containing a shape factor of 3 or more is 10% by weight is set to 1. As the proportion of particles having a shape factor of 3 or more increases, the processing capacity of the dehydrator 14 also increases. As described above, according to this example, since the average shape factor of the gypsum particles sent to the dehydrator 14 becomes large, not only the desulfurization performance but also the throughput of the dehydrator can be increased.

Example 2 Using the same flue gas desulfurization apparatus as in Example 1, the same desulfurization test as in Example 1 was conducted. However, the sulfur dioxide gas concentration in the exhaust gas in the inlet duct 2 of the desulfurization tower was 3000 ppm. FIG. 7 shows the relationship between the desulfurization rate and the ratio of particles having a shape factor of 3 or more when the solid concentration in the absorbing liquid is changed to 10 to 30% by weight. Similar to Example 1, the smaller the proportion of particles having a shape factor of 3 or more, the higher the desulfurization rate. It was also observed that the higher the solid concentration, the greater the effect of the particle shape factor on the desulfurization performance. Furthermore, the inlet duct 2 of the desulfurization tower
Concentration of sulfur dioxide in exhaust gas at 100-5000pp
The same result was obtained although the value was changed to m.

Example 3 In Example 1, as a method for adjusting the particle size of the solid particles contained in the absorbing liquid which comes into contact with the sulfurous acid gas in the exhaust gas, the slurry extracted from the oxidation tank 6 is separated and the shape factor Only small particles were returned to the oxidation tank 6. The same effect as this
It can also be obtained by the flow shown in FIG. In FIG. 8, the devices having the same numbers as those in FIG. 1 have the same functions, and the description thereof will be omitted. In the flow shown in FIG. 8, the circulation line 17
A separator 16 is installed in the middle of, and an absorbing liquid containing particles having a small shape factor is sprayed from the spray nozzle 4. Separator 1
The solid particles having a large shape factor (acicular shape) separated in 6 are sent to the thickener 13 or the dehydrator 14. Using the flow of this example, the relationship between the desulfurization performance and the dehydrator treatment capacity when the sulfur dioxide gas concentration in the exhaust gas and the solid concentration in the absorbing liquid were changed was the same as in Example 1 or Example 2. Results were obtained.

Embodiment 4 In FIG. 9, a separator 16 is installed in the middle of the circulation line 17,
A flow in which solid particles having a large shape factor (acicular shape) are returned to the oxidation tank 6 and an absorbing solution containing particles having a small shape factor is sprayed is shown. In FIG. 9, the devices having the same numbers as those in FIG. 1 have the same functions, and the description thereof will be omitted. Also in the flow of this example, the relationship between the desulfurization performance and the dehydrator treatment capacity when the sulfur dioxide gas concentration in the exhaust gas and the solid concentration in the absorption liquid were changed was the same as that in the case of Example 1 or Example 2. was gotten. In the above-described embodiment of the present invention, a device combining a settling tank and a wet cyclone is used as the needle-shaped particle separating device 16, but other methods may be used as long as they can separate particles having different shapes. It is possible. Further, it goes without saying that the method of the present invention can be applied not only to the flue gas desulfurization apparatus of the spray type, but also to other flue gas desulfurization apparatuses of the wet wall type and the like.

[0018]

According to the present invention, the thickener is omitted,
The processing capacity and desulfurization performance of the dehydrator can be increased.

[Brief description of drawings]

FIG. 1 is a diagram showing a flow of a wet flue gas desulfurization apparatus of Example 1 and Example 2 according to the present invention.

FIG. 2 is a diagram showing a flow of a separation device used in the method of the present invention.

FIG. 3 is a diagram schematically showing the shape of gypsum particles.

FIG. 4 is a diagram showing experimental data regarding desulfurization performance of Example 1 of the present invention.

FIG. 5 is a diagram showing experimental data regarding desulfurization performance of Example 1 of the present invention.

FIG. 6 is a diagram showing experimental data regarding desulfurization performance of Example 1 of the present invention.

FIG. 7 is a diagram showing experimental data on desulfurization performance of Example 2 of the present invention.

FIG. 8 is a diagram showing a flow of a wet flue gas desulfurization apparatus according to a third embodiment of the present invention.

FIG. 9 is a diagram showing a flow of a wet flue gas desulfurization apparatus according to a fourth embodiment of the present invention.

FIG. 10 is a diagram showing a flow of a conventional wet flue gas desulfurization apparatus.

[Explanation of reference numerals] 1 ... Tower body, 2 ... Inlet duct, 3 ... Exit duct, 4 ... Spray nozzle, 5 ... Absorbing liquid pump, 6 ... Oxidation tank, 7
... Stirrer, 8 ... Air blowing device, 9 ... Mist eliminator, 10 ... Absorbing liquid withdrawing pipe, 11 ... Gypsum withdrawing pipe, 12
… Limestone supply pipe, 13… Thickener, 14… Dehydrator, 1
6 ... Separator, 17 ... Circulation line, 18 ... Line, 19
... Settling tank, 20 ... Wet cyclone, 21 ... Vertical tube, 22
... Discharge pipe

Continuation of front page (51) Int.Cl. ⁶ Identification number Reference number in the agency FI Technical indication location B01D 53/34 125 Q (72) Inventor Narihito Takamoto 3 36 Takaracho, Kure-shi, Hiroshima Babcock-Hitachi Kure Co., Ltd. In the laboratory

Claims (4)

[Claims] 1. In a wet flue gas desulfurization method for treating sulfur oxides in exhaust gas by bringing exhaust gas discharged from a combustion device such as a boiler into contact with absorption liquid circulatingly supplied, solids contained in the absorption liquid. A wet flue gas desulfurization method, characterized in that needle-like particles in the particles are selectively removed to the outside of the circulation system of the absorbing liquid. 2. The wet flue gas desulfurization method according to claim 1, wherein the shape factor of the needle-shaped particles to be removed to the outside of the circulation supply system is 3 or more. 3. The wet flue gas desulfurization method according to claim 1, wherein the absorbing liquid from which the acicular particles have been removed is used in a circulation supply system. 4. Exhaust gas discharged from a combustion device such as a boiler is brought into contact with an absorbent that is circulated and supplied in a desulfurization tower, and sulfur oxides in the exhaust gas are absorbed in the absorbent and recovered in an absorbent tank. In a wet flue gas desulfurization device that circulates and supplies a part of the absorption liquid in the absorption liquid tank to the absorption tower and removes the other part from the desulfurization tower circulation supply system, the solid particles contained in the absorption liquid A wet flue gas desulfurization apparatus comprising a separator for removing needle-shaped particles from the desulfurization tower circulation supply system.