JPH09290129A - Method for exhaust gas desulfirization and its apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve utilization efficiency of an absorbing liq. and to make the whole size of an exhaust gas desulfurization apparatus small by assembling an oxidation column in an absorption column. SOLUTION: In an exhaust gas desulfurization apparatus wherein exhaust gas is cleaned with an absorbing liq. in an absorption column, an absorbing liq. tank 14 for storing an absorbent and an oxidation tank 22 for oxidation processing of the absorbent are provided in parallel in the absorption column and the vol. of the absorbing liq. tank 14 is made approximately 2-5% of the amt. of circulation of the absorbing liq. per hr. The absorbing liq. in the absorbing liq. tank 14 is circulated thereby 50-20 times per hr.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an absorbent containing 1 to
The present invention relates to a flue gas desulfurization method and a device using light burned magnesia (MgO) having a relatively wide particle size distribution of several tens of microns.

[0002]

2. Description of the Related Art Among the technologies for performing flue gas desulfurization, the absorption method using a slurry containing magnesium hydroxide (Mg (OH) ₂ ) is relatively inexpensive for magnesium hydroxide and has a relatively small apparatus. Therefore, in particular, it is often used as a flue gas desulfurization device for small and medium-sized combustion equipment.

Here, as magnesium hydroxide, those produced from seawater are often used, but in recent years, in order to further reduce the cost, it is a finely calcinated product of a magnesite ore (MgCO ₃ ). A technique has been developed that uses a light burned magnesia (MgO) directly as an absorbent.

Along with the development of flue gas desulfurization technology using light burned magnesia as an absorbent, various researches and developments have been made on the peripheral technology. For example, JP-A-6
JP-A-246129 proposes a technique in which light burned magnesia is used as an absorbent, and the supply of this absorbent to the bottom of an absorption tower can be directly introduced as light burned magnesia without hydration treatment. . In addition, JP-A-3-143
Japanese Patent Laid-Open No. 527 and Hei 4-78419 propose a technique of collecting unreacted coarse particles and returning them to the absorption tower again in order to increase the utilization rate of light-burned magnesia.

Now, a conventional flue gas desulfurization apparatus will be described with reference to FIG. FIG. 2 is a schematic view of a conventional flue gas desulfurization apparatus. In FIG. 2, 10 is an absorption tower, which takes in exhaust gas from the inlet flue section 11 and
Then, a part of the industrial water or the absorbing liquid is dispersed in the exhaust gas by a cooling means (not shown). 12 is a disperser for absorbing liquid,
Reference numeral 13 is a gas-liquid contact portion, and a gas-liquid contact portion or a filling material is generally used. The absorbing liquid is dispersed from the disperser 12 with respect to the exhaust gas passing through the gas-liquid contact portion 13. This allows
The exhaust gas comes into contact with the absorbent, is cooled, desulfurized, and has its dust removed, and is exhausted from the exhaust port. On the other hand, the dispersed absorption liquid absorbs the sulfur oxides in the exhaust gas and absorbs the sulfur oxides in the absorption tower 14 at the bottom of the absorption tower.
To fall.

Although the absorbing solution is circulated and used, it is necessary to withdraw a part of the absorbing solution out of the system in order to prevent the salt concentration of the sulfur compound generated in the absorbing solution from increasing and the salt from precipitating. There is. Here, if the absorbent is excessively contained in the absorbent, the unreacted absorbent is extracted out of the system, so that the utilization rate of the absorbent is lowered.

As a remedy for this, a pipe line L2 for the extracted liquid is used.
There is proposed a system in which a wet separator 15 is provided in the above to collect the coarse particle absorbent and return it to the absorption tower. Here, a liquid cyclone is generally adopted as the wet separator, but a large number of wet separators are required to pass all of the required amount of liquid to be extracted. Therefore, the remaining extracted liquid is sent to the oxidation tower 30 via the line L3, and in this oxidation tower 30, the COD-related part of the sulfite or bisulfate tower is oxidized to sulfate by the air sent from the blower 35. COD is lowered.

However, since the soot dust component remains in this treatment liquid, it cannot be discharged as it is to the water area. Therefore, the suspended suspended substances are removed by the filter 40 and then discharged. In addition, since the filtration machine 40 causes clogging of the filtration cloth, the oxidation tower 30 is used while the filtration cloth is being replaced.
Continue operation of the flue gas desulfurization equipment while storing in.

[0009]

By the way, although light-burning magnesia has a coarser particle size than magnesium hydroxide produced from seawater, commercially available light-burning magnesia for absorbent has an average particle size of about 16 microns. And very fine. Here, assuming a liquid cyclone as a wet separator, the particle size that can be collected by the liquid cyclone is at most about 10 microns, and in order to collect these particles, the diameter of the liquid cyclone is about 10 cm. It is necessary to reduce the size, and as a practical matter, a considerably large amount of incidental equipment is required to be effective in a large-scale device.

Further, since the oxidation tower 30 needs to be sufficiently air-oxidized to surely prevent the generation of pollution,
The tower is large in size and the second largest in the flue gas desulfurization apparatus after the absorption tower 10. For this reason, there has been a problem that the installation area for installing the flue gas desulfurization device and the entire device become large.

The present invention has been made in view of the above circumstances, and a flue gas desulfurization method for increasing the circulation rate of the absorbent to improve the utilization rate of the absorbent, and an oxidizing tank and / or a filtering machine supply tank. It is an object of the present invention to provide a flue gas desulfurization apparatus in which the inside of the absorption tower is incorporated to reduce the scale of the entire apparatus.
The present invention can be suitably applied not only when light burned magnesia is used as an absorbent, but also when applied to a flue gas desulfurization device that uses magnesium hydroxide as an absorbent.

[0012]

The present invention also relates to a flue gas desulfurization technique using light burned magnesia as an absorbent, and in a storage tank for absorbing liquid in order to effectively utilize coarse particles in the absorbent as the absorbent. The present invention relates to a technique for improving the utilization efficiency of an absorbent by reducing the residence time and increasing the ratio of the contact time at the gas-liquid contact portion.

That is, in the flue gas desulfurization method of the present invention in which the absorbing liquid is circulated to wash the exhaust gas, the absorbing liquid is circulated about 20 to 50 times per hour, and preferably the absorbing liquid is used. The amount of absorbent therein is adapted to follow the pH value of the absorbent.

Further, in the flue gas desulfurization apparatus of the present invention for cleaning the exhaust gas with the absorbing liquid in the absorbing tower, the absorbing liquid tank for storing the absorbing liquid inside the absorbing tower and the absorbing agent are oxidized. For this purpose, an oxidizing tank and / or a filtration machine supply tank are provided side by side, and the volume of the absorption liquid tank is set to about 2 to 5% of the absorption liquid circulation amount per hour. Further, in the device of the present invention, a new absorbent is directly supplied to the circulation system from the absorption liquid tank to the disperser, and preferably, a sensor for measuring the pH value inside the absorption tower and a signal from this sensor are used. The new absorbent flow control valve is controlled based on the above.

As a result, the fresh absorbent is directly sent to the absorbent disperser and dispersed in a state of being not diluted very much.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below. In the flue gas desulfurization apparatus of this embodiment, the residence time of the absorbent circulation system is shortened to improve the responsiveness of the pH control of the absorbent so that the amount of treated gas in the absorption tower and the load of the sulfur oxide concentration also change. It is configured to avoid a state where the absorbent is excessively present and to maintain a situation where the absorbent is effectively consumed. As a result, light burned magnesia is effective as an absorbent without installing auxiliary equipment for collecting coarse particles of unreacted absorbent in the extraction liquid of the absorption liquid required in the prior art and returning it to the absorption tower. Can be used for

First, an embodiment of a flue gas desulfurization apparatus will be described with reference to FIG. FIG. 1 is a schematic view of a flue gas desulfurization apparatus according to an embodiment. Since the partial structure of the absorption tower is the same as that of the conventional example, detailed description of the same parts as those of the conventional example will be omitted. In the flue gas desulfurization apparatus of this embodiment, an absorption liquid tank 14 for temporarily storing an absorbent, an oxidation tank 22 and a filter machine supply tank 23 are formed below the absorption tower 10. Specifically, the upper and side surfaces are surrounded by a partition plate 21 at the lower part of the absorption tower 10 to form a space portion independent of the space portion of the absorption tower 10 (the bottom surface is surrounded by the bottom surface of the absorption tower). The independent space is used as an oxidation tank 22 and a filtration machine supply tank 23.

Here, the volume of the absorption liquid tank 14 is equal to that of the absorption tower 1.
It is set to about 2 to 5% of the absorption liquid circulation amount per hour at 0. With such a volume ratio, the absorption liquid circulates efficiently, the responsiveness of the pH control of the absorption liquid is improved, and the frequency with which the absorption liquid comes into contact with the exhaust gas at the gas-liquid contact portion increases. The usage rate of the agent is high. If the volume of the absorption liquid tank 14 is smaller than 2% of the absorption liquid circulation amount per hour, the circulation pump may be empty when the liquid level changes due to insufficient absorption liquid, and if it is larger than 5%, the utilization efficiency of the absorbent is increased. May decrease.

The oxidation tank 22 has an air supply unit 24 provided at the bottom thereof.
Is sending air for oxidation. The oxidation tank 22 adopts an overflow system in order to secure a stable aeration effect and sufficiently oxidize the absorbing liquid, and to stably and sufficiently increase the liquid level of the tank.
The absorption liquid overflowing from the oxidation tank 22 enters the filter machine supply tank 23. In the present embodiment, air is also sent from the air supply unit to the absorbent tank 14 and the filter machine tank 23.
The purpose is to both reduce the load on the oxidation tank 22 and prevent sedimentation and accumulation of solid particles. Therefore, a stirrer may be provided and the introduction of air may be omitted.

In the filtration machine 40, the cake grows on the filter cloth with the passage of time, and the liquid passing amount decreases. Therefore, when the liquid flow rate becomes a certain amount or less, the supply of the absorbent from the filter machine supply tank 23 is stopped, and the water is drained and the cake is removed. When cleaning the filter machine, lower the liquid level of the filter tank 23 in advance, and during cleaning,
The operation of the absorption tower 10 is continued by raising the liquid level of the filtration machine supply tank 23.

On the other hand, in the absorbent tank 14, the absorbent that has been washed in by the exhaust gas and flowed through the inclined upper partition plate is stored. The liquid level of the absorption liquid tank 14 must satisfy reqNPSH (liquid level height required from the pump suction condition) of the circulation pump 19 and the air oxidation effect by air aeration is increased to some extent. The height is ensured. The liquid level height in this case is adjusted by controlling the circulating amount (withdrawal amount) of the absorbing liquid.

In this absorbing liquid tank 14 as well, air is sent from the lower part, but the absorbing liquid tank 14 is the oxidizing tank 2.
Since it is integrally provided adjacent to the inside of the absorption tower 2 and the inside of the absorption tower 10, it can be performed by using the common air supply part 24. According to the flue gas desulfurization device having such a configuration,
It is possible to reduce the residence time of the absorbing liquid in the storage tank and to reduce the ground contact area of the flue gas desulfurization device by incorporating the oxidizing tank and the filter supply tank inside the absorption tower.

Further, in the flue gas desulfurization apparatus of the present embodiment, the new absorbent supply path has the gas-liquid contact portion 13 of the disperser 1
It is directly connected to the circulation path 16 connected to 2. As a result, the absorbent that is not diluted with the new absorbent is dispersed from the disperser 12 and effectively comes into contact with the exhaust gas, which enhances the cleaning effect.

A flow rate control valve 17 is provided in the new absorbent supply passage. On the other hand, the absorption tower 10 is provided with a sensor (pH meter) 18 for measuring the pH value of the absorbing liquid, and a control signal is sent from the sensor 18 to the flow control valve 17. As a result, the opening degree and / or the opening / closing operation time of the flow rate control valve 17 are controlled according to the pH value inside the absorption tower 10.

Further, in the absorption tower 10 of the present embodiment, for example, the gas-liquid contact portion 13 has at least two perforated plates each having a hole of 10 mm to 30 mm and an opening ratio of 20 to 60%. The structure is such that they are laminated at intervals of up to 200 mm, and the exhaust gas and the absorbing liquid are vigorously brought into gas-liquid contact in the gas-liquid contact space formed between these perforated plates.

According to the flue gas desulfurization apparatus of this embodiment having such a structure, the absorbent such as light burned magnesia is directly sent to the circulation path 16 and mixed with the circulating absorption liquid to be dispersed from the disperser 12. It is dispersed inside the absorption tower 10. The dispersed absorption liquid is violently in gas-liquid contact with the exhaust gas mainly in the gas-liquid contact portion 13 to perform cooling, desulfurization and dust removal,
It is dropped into the absorbing liquid tank 14, flows into it, and is stored.

Here, it is preferable that the number of circulations of the absorbing liquid in the absorbing liquid tank 19 is about 20 to 50 times per hour. In this way, the utilization rate of the absorbent can be improved. Here, if the circulation number is less than 20 times, the utilization efficiency of the absorbent is lowered, and if it is more than 50 times, the circulation pump will be drained when the liquid level changes due to insufficient absorption liquid.

Further, based on the signal from the sensor (pH meter) 18, the flow rate control valve 17 is controlled to supply a new absorbent into the absorption liquid circulated to the disperser 12. Specifically, the pH meter 18 shown in FIG. 1 detects the pH immediately after the absorption liquid circulation line or gas-liquid contact, and the pH is controlled by operating the flow rate control valve 17 for the absorbent with this signal. It Generally, the flow control valve 17 is controlled by adjusting the on / off operation time or the opening degree.

As a result, since the new absorbent is not diluted so much, the absorbent is dispersed from the disperser 12 to the gas-liquid contact portion, so that the dead time in pH control of the absorbent can be greatly reduced. This makes it possible to enhance the effect of avoiding the generation of an environment in which the absorbent is excessively present in the absorbent.

The absorbing liquid is air-oxidized by aeration of air in the absorbing liquid tank 14 and then sent to the circulation path 16 again. At this time, the liquid level of the absorbing liquid in the absorbing liquid tank 14 is kept high enough to oxidize air and to send it to the circulation path 16 (suction of the circulation pump 19).

A part of the absorption liquid sent to the circulation path 16 is sent to an oxidation tank 22 formed inside the absorption tower 10 and adjacent to the absorption liquid tank 14, where air oxidation is carried out and the absorbent is absorbed. The concentration of the sulfur oxide in the inside is adjusted. After that, the absorbent overflows from the oxidation tank 22 and the filtration machine supply tank 2
3 where it is further air-oxidized and then discharged via the filter 40.

The present invention is not limited to the above-mentioned embodiments, but includes various modifications within the scope of the gist. For example, there is no limitation on the positional relationship between the absorption liquid tank 14 and the oxidation tank 22, and an absorption liquid tank is formed in the center of the inside of the absorption tower, and a ring-shaped oxidation tank is formed by a partition plate on the outer periphery (one side half is an air aeration tank. , The other half of one side to form a filtration machine supply tank) is also included.

When the oxidation tank 22 functions as a buffer tank and also serves as a filter machine supply tank, the filter machine supply tank 23 can be omitted. Furthermore, the filter machine supply tank 23 can be omitted.
When the tank also serves as the oxidation tank 22, the oxidation tank 22 may be omitted.

[0034]

EXAMPLE In the apparatus shown in FIG. 1, a desulfurization tower 10 has an inner diameter of 150 mm, a gas-liquid contactor in which a perforated plate having a hole diameter of 20 mm and a porosity of 36% is loaded in one stage, and a circulating amount of an absorbing liquid of 200 l is used. / h, circulation times 20 times (5 times the circulation amount per hour)
%), SO ₂ 700-800vol p
Air containing pm was added to p using air burned magnesia slurry.
The desulfurization rate and the effective utilization rate of the absorbent were measured while controlling to H6.2 ± 0.1. As a result, the desulfurization rate was 92% and the effective utilization rate was 99%.

As for the desulfurization rate, a performance of 98% or more can be achieved by increasing the number of stages of the desulfurization rate.
It was confirmed that a sufficiently high absorbent utilization rate can be achieved unless pH is controlled and an environment in which the absorbent is excessive is created. The fact that the effective utilization rate of the absorbent is 99% means that it is not necessary to take a measure for improving the utilization rate of the absorbent by collecting the coarse particles of the absorbent such as a hydrocyclone as in the prior art.

[0036]

As described above, according to the flue gas desulfurization method of the present invention, it is possible to improve the utilization efficiency of the absorbing liquid (agent) by increasing the circulation rate of the absorbing liquid (agent). Further, according to the flue gas desulfurization apparatus of the present invention, since the oxidation tank is integrally incorporated inside the absorption tower together with the absorption liquid tank, the scale of the entire apparatus can be reduced.

Furthermore, since the new absorbent is supplied to the circulation path to the disperser instead of being supplied to the absorbing liquid tank, the new absorbent is directly dispersed from the disperser to the gas-liquid contact portion, Effectively contacts exhaust gas to enhance cleaning effect.

[Brief description of drawings]

FIG. 1 shows a schematic configuration diagram of an embodiment of a flue gas desulfurization apparatus of the present invention.

FIG. 2 shows a schematic configuration diagram of an embodiment of a conventional flue gas desulfurization apparatus.

[Explanation of symbols]

 10 Absorption Tower 12 Absorption Liquid Disperser 13 Gas-Liquid Contact Portion 14 Absorption Liquid Tank 16 Circulation Line 17 Flow Control Valve 18 pH Meter 20 Oxidation Tank 21 Partition Plate 22 Air Aeration Tank 23 Filtration Machine Supply Tank

Claims (6)

[Claims] 1. A flue gas desulfurization method in which an absorbing solution is circulated to wash exhaust gas, the absorbing solution being contained in an amount of 20 to 20 per hour.
A flue gas desulfurization method characterized by being circulated 50 times. 2. The flue gas desulfurization method according to claim 1, wherein the amount of the absorbent in the absorbent is made to follow the pH value of the absorbent in the absorption tower. 3. A flue gas desulfurization apparatus for cleaning exhaust gas with an absorption liquid in an absorption tower, an absorption liquid tank for storing an absorbent inside the absorption tower, and an oxidation tank for oxidizing the absorbent. And / or a filtration machine supply tank is installed side by side, and the volume of the absorption liquid tank is set to 2 to 5 times the absorption liquid circulation amount per hour.
A flue gas desulfurization device characterized by the percentage. 4. The flue gas desulfurization apparatus according to claim 3, wherein fresh absorbent is supplied to the circulation system from the absorption liquid tank to the disperser. 5. A sensor for measuring the pH value inside the absorption tower,
The flue gas desulfurization apparatus according to claim 3 or 4, further comprising a flow rate control valve that adjusts a supply amount of the new absorbent based on a signal from the sensor. 6. The flue gas desulfurization apparatus according to claim 3, 4 or 5, wherein the oxidation tank has a function as a filtration machine supply tank.