JP3486696B2 - Desulfurization method using gas containing sulfurous acid gas as gas to be treated - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a desulfurization method using a gas containing sulfurous acid gas as a gas to be treated.

[0002]

2. Description of the Related Art In order to remove sulfurous acid gas (SO ₂ ) contained in exhaust gas such as various combustion exhaust gas and factory exhaust gas, the exhaust gas is brought into contact with an aqueous slurry liquid of limestone to remove S in the exhaust gas.
The method of absorbing and reacting O ₂ with the limestone water slurry is widely used. In such a desulfurization method, the desulfurization rate of SO _{2 in} the exhaust gas is usually about 90 to 95%, and when desulfurization is performed at a higher desulfurization rate, for example, a desulfurization rate of 99 to 100%, the device There is a problem in that the size of the vehicle will become extremely large and the required power will increase significantly. Therefore, in the conventional desulfurization method, as described above, about 9
Currently, desulfurization is performed at a desulfurization rate of 0 to 95%. On the other hand, in recent years, from the viewpoint of global environment protection, regulations regarding SO ₂ concentration in exhaust gas discharged to the atmosphere have become increasingly strict, and thorough removal of SO ₂ in exhaust gas has been demanded. If SO ₂ in exhaust gas is to be thoroughly removed by a conventional desulfurization device, as described above, the device must be extremely large and the required power must be greatly increased. Not desirable. Therefore, the low concentration SO discharged from the conventional desulfurization equipment
_It would be very meaningful to develop a method that could economically remove its SO ₂ from a gas containing ₂ .

Conventionally, in order to remove SO _{2 in} combustion exhaust gas, a method is known in which exhaust gas at 100 to 130 ° C. is directly supplied to an activated carbon layer to be adsorbed and removed at a high temperature (Hitachi Review, Vol. 49). , No. 11, pp. 54-57, 196.
7 years). In this method, high-concentration SO ₂ in the combustion exhaust gas is adsorbed by activated carbon, then converted to sulfuric acid by reacting with oxygen and moisture, and adsorbed on activated carbon in the state of sulfuric acid. This adsorptive separation method using activated carbon is very simple in operation since exhaust gas only needs to be passed through the activated carbon packed bed, but avoids the problem of adsorbent regeneration, which is an essential drawback of adsorption separation. It is not possible. That is, when the adsorption operation is performed for a certain period of time, SO ₂ breakthrough occurs, and in order to regenerate the activated carbon at the time of this breakthrough, a regeneration operation such as washing or heating of the activated carbon is required. Due to the necessity of this regenerating operation, the adsorption separation method using activated carbon is hardly adopted. It is also known to use an activated carbon fiber layer instead of the activated carbon layer (“catalyst” vol 32, N).
o 2, p. 105, 1990 and "Chemistry.
Letters ", No. 11, 1899, 199
3 years).

In the former document (“catalyst”), the typical combustion exhaust gas composition is SO _{2 at} 1,000 ppm, and
A desulfurization test was performed using PAN-based, cellulose-based, kinol-based or pitch-based activated carbon fibers, coconut shell activated carbon, activated coke or brown coal char, and all carbonaceous substances other than PAN-based activated carbon fibers were destroyed immediately after the reaction started. It was described that the desulfurization performance of the carbonaceous material showed very little, and that the carbonaceous materials did not show any improvement in the desulfurization performance even after the calcination treatment. Also, SO
_{2 The} removal capacity is determined by the saturation of the generated sulfuric acid that covers the active sites of sulfuric acid adsorption, and it is clear that desulfurization by carbonaceous substances in this desulfurization test is a method based on the principle of adsorption. In the latter document, it is recognized that carbonaceous materials other than PAN-based materials do not give high desulfurization performance,
SO ₂ 1,000vol using PAN-based activated carbon fiber
A desulfurization test under the condition of ppm is being studied. In this latter document, in order to improve the desulfurization performance of the PAN-based activated carbon fiber, in consideration of how to extend the time until breakthrough by heat-treating it, for a short time of about 60 hours, It has been shown that complete adsorption of SO ₂ is carried out in the presence of supersaturated water at operating temperature and that sulfuric acid dripping occurs during this, which is a phenomenon unique to PAN-based activated carbon fibers. And the SO in this activated carbon fiber
_2The removal effect is said to be improved by further heat treating it to give it a special surface structure. On the other hand, as for activated carbon, as described above, this one has a small desulfurization performance, and its properties are greatly different from those of activated carbon fiber, and it is difficult for sulfuric acid to drop under normal desulfurization conditions, and the adsorption rate is also very high. It was considered to be unsuitable for practical use because of the delay ("Flue gas desulfurization technology", Chemical Industry Co., Ltd., pp. 90-94). Therefore, when desulfurizing SO ₂ , desulfurization test such as continuously separating sulfuric acid from the activated carbon layer has never been attempted.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for continuously removing SO ₂ from a gas containing a low concentration of SO ₂ for a long time. Another object of the present invention is to provide a method for separating SO ₂ based on a new separation principle instead of adsorption separation.
Still another object of the present invention is to provide a method for desulfurizing SO ₂ containing gas, which utilizes a catalytic function for SO ₂ oxidation of activated carbon. Still another object of the present invention is to provide a method for economically desulfurizing low-concentration sulfur dioxide contained in a desulfurization treatment gas discharged from a flue gas desulfurization apparatus. Still another object of the present invention is to provide a method for economically desulfurizing low-concentration sulfur dioxide gas contained in a desulfurization treatment gas discharged from a limestone-gypsum flue gas desulfurization device. Other subjects of the present invention will be clearly understood from the following description.

[0006]

The present inventors have completed the present invention as a result of intensive studies to solve the above problems. As a result of earnest studies to solve the above problems, the present inventors have found that, as shown in the above-mentioned document (“catalyst”), under the condition of SO ₂ 1,000 ppm, breakthrough begins immediately after the start of the reaction. In the steady state of the reaction, even if the activated carbon showed an extremely small desulfurization rate, when the activated carbon having a large catalytic sulfation rate R described later is used, the desulfurization rate is remarkably improved when the SO ₂ concentration in the gas to be treated decreases. However, it was found that when used under a low concentration condition of 100 ppm or less, an extremely high desulfurization rate was exhibited. That is, S
Under low O ₂ concentration conditions, even activated carbon having a low SO ₂ adsorption capacity is not used as an adsorbent for adsorbing and separating SO ₂ , but a catalyst that does not require regeneration operation by reacting SO ₂ with oxygen. It has been found that a sufficiently high desulfurization rate can be obtained by using the above. The present invention has been completed based on these findings.

According to the present invention, in the desulfurization method using a gas containing sulfurous acid gas, oxygen and water vapor as the gas to be treated, (i) the sulfur dioxide gas concentration in the gas to be treated is 100 v
(ii) A gas to be treated is circulated through an activated carbon layer, and sulfur dioxide gas and oxygen are catalytically oxidized in the activated carbon layer to be converted into sulfur trioxide, and the sulfur trioxide is reacted with water. To produce dilute sulfuric acid, (iii) to continuously separate the dilute sulfuric acid content produced in the activated carbon layer from the activated carbon layer, and (iv) the catalytic sulfation rate R of the activated carbon forming the activated carbon layer is 5 μmmol / g /
(v) Catalytic desulfurization rate Y of the gas to be treated obtained by circulating the gas to be treated through the activated carbon layer
Is at least 80%, and a method for desulfurizing a gas containing a low concentration of sulfurous acid gas is provided.

Further, according to the present invention, there is provided a method of using the desulfurization treatment gas discharged from the flue gas desulfurization apparatus as the gas to be treated in the above desulfurization method. Further, according to the present invention, a wet limestone-gypsum method flue gas for performing a neutralization reaction step of reacting an aqueous limestone slurry liquid with sulfurous acid gas and an oxidation reaction step of oxidizing the neutralized product to produce gypsum The desulfurization treatment gas discharged from the desulfurization device is subjected to the secondary desulfurization treatment by the desulfurization method, and the dilute sulfuric acid separated from the activated carbon layer during the secondary desulfurization treatment is introduced into the oxidation reaction process part in the flue gas desulfurization device. A desulfurization method characterized by the above is provided.

The activated carbon used in the present invention acts as a catalyst for the oxidation of SO ₂ , and various conventionally known carbonaceous substances usually called activated carbon can be used.
Examples thereof include various activated carbons such as coconut shell activated carbon, activated carbon derived from wood, activated carbon derived from coal tar pitch, activated carbon derived from petroleum pitch, activated carbon derived from coal, and activated coke. In general,
A specific surface area of 50 to 2000 m ² / g is used.
These activated carbons can be used after firing at 500 to 1000 ° C., if necessary. As the activated carbon used in the present invention, it is preferable to use activated carbon having a sufficiently high catalytic sulfation rate R defined later.

Next, the present invention will be described with reference to the drawings.
FIG. 1 shows a schematic view of an activated carbon packed tower used in the present invention. In FIG. 1, 1 is a treated gas supply pipe, 2 is an activated carbon layer, 3
Is a processing gas discharge pipe, 4 is a dilute sulfuric acid container, 5 is a dilute sulfuric acid discharge pipe, 6 is a cleaning liquid spray pipe, 7 is a cleaning liquid supply pipe, and 10 is an activated carbon packed tower. In order to carry out the method of the present invention using the activated carbon packed tower, the gas to be treated is introduced into the tower 10 through the supply pipe 1 thereof, and is circulated in the activated carbon layer 2, and then the desulfurization gas is discharged. Withdraw through the tube 3 to the outside of the tower 10. From the spray pipe 6, the cleaning liquid introduced from the cleaning liquid supply pipe 7 is continuously or intermittently sprayed onto the upper surface of the activated carbon layer, and the cleaning liquid is caused to flow downward in the activated carbon layer 2 to thereby form a gas to be treated. The solid fine particles that are entrained and collected in the activated carbon layer flow out downward from the activated carbon layer together with the cleaning liquid.

In the activated carbon layer 2, SO ₂ contained in the gas is oxidized on the surface of the activated carbon to SO ₃ by the catalytic action of the activated carbon, and this SO ₃ reacts with the water adsorbed on the surface of the activated carbon to generate H ₂ It becomes SO ₄ , and this H ₂ SO ₄ is diluted with the water adsorbed on the surface of the activated carbon to become dilute sulfuric acid. In the present invention, the activated carbon layer 2 is not the SO ₂ as an adsorbent layer for adsorbing separator, characterized by using as a catalyst layer for reacting SO ₂ and oxygen. In the conventional desulfurization method using activated carbon, activated carbon is handled as an adsorbent for adsorbing and separating SO ₂ from the gas, and an activated carbon packed column is also designed as an SO ₂ adsorption / separation column. Therefore, the packed tower has three stages of drying, adsorption, and water washing.
It is operated by repeating this cycle with the process as a reference cycle (Hitachi Review, Vol. 49, No. 11).
No., pp. 54-57). On the other hand, in the present invention,
Activated carbon is handled as a catalyst, and the activated carbon packed tower is designed as a catalyst packed tower. Therefore, in the case of the present invention, the activated carbon packed column does not require a step of drying or washing for the purpose of regeneration, and can be continuously operated for a long time. In the case of the present invention, the continuous operating time of the activated carbon packed tower depends on the performance deterioration of the activated carbon as a catalyst, but is usually 10
It is more than 00 hours, and the activated carbon packed tower of the present invention can be stably operated over such a long time.

In the present invention, the dilute sulfuric acid produced in the activated carbon layer during the flow reaction of the gas to be treated is continuously separated from the activated carbon layer. When the dilute sulfuric acid is not continuously separated from the activated carbon layer or when the separation is insufficient, the smooth oxidation reaction of SO ₂ does not occur. That is, the dilute sulfuric acid produced in the activated carbon layer needs to be continuously separated from the activated carbon layer by the amount produced in the reaction.

In the activated carbon packed tower shown in FIG. 1, the dilute sulfuric acid produced in the activated carbon layer 2 flows down and is accommodated in the dilute sulfuric acid accommodating portion 4 arranged below the layer 2. Further, in the case of the activated carbon packed tower shown in FIG. 1, since the gas to be treated flows downward in the activated carbon layer, the downward flow of the dilute sulfuric acid generated in the activated carbon layer is caused by the downward flow of the object to be treated. It is facilitated by the gas flow, so that a smooth separation of the dilute sulfuric acid from the activated carbon layer 2 is achieved. Dilute sulfuric acid is used as the storage unit
The dilute sulfuric acid stored in the storage unit 4 is withdrawn through the discharge pipe 5 continuously or intermittently.

The activated carbon used for forming the activated carbon layer 2 may have various shapes such as columnar shape, cylindrical shape, granular shape, spherical shape, and honeycomb shape. In the case of granules or spheres, the dimension is 0.1 to 20 mm, preferably 1 to 20 mm.
In the case of a columnar shape or a cylindrical shape, the diameter is 0.1 to 20 mm, preferably 1 to 10 mm, and the length is 0.1 to 20 mm, preferably 1 to 10 mm. If the size of the activated carbon is too small, the dilute sulfuric acid generated in the activated carbon layer will not flow down easily, and the pressure loss of the activated carbon will increase, which is not preferable.On the other hand, if the size of the activated carbon is too large, the inside of the activated carbon will contact the contact surface. Since it cannot be effectively used as the above, and the dilute sulfuric acid does not smoothly flow out from the inside of the activated carbon, it is preferable that the size is within the above range. Activated carbon is usually packed in the tower while being retained by a mesh or plastic mesh that does not pass through it.

According to the research conducted by the present inventors, 1,000 v
When a gas containing SO ₂ at a high concentration of about olppm is circulated through the activated carbon layer together with oxygen and water vapor, the desulfurization rate is 100% at the start of the operation as shown in FIG. Was confirmed to be extremely low. On the other hand, when a gas containing a low concentration of SO ₂ of about 100 volppm was circulated through the activated carbon layer together with oxygen and water vapor, it broke through as shown in FIG. 3 and had a sufficiently high desulfurization rate even after the desulfurization rate of 100% was not maintained. It was confirmed that the rate was maintained for an extremely long time of 1,000 hours or more. Further, the desulfurization rate Y that continues over these long periods of time is
It was confirmed that it changes depending on the type of activated carbon, and also changes depending on the SO ₂ concentration in the gas to be treated and the supply rate of the gas to be treated. The desulfurization rate Y achieved by the catalytic function of this activated carbon is defined as the catalytic desulfurization rate Y in this specification. In the present invention, the catalytic desulfurization rate Y is at least 80%,
It is preferably 90 to 100%. This contact desulfurization rate Y
Is the supply rate of the gas to be treated to the activated carbon layer, or conversely,
It can be controlled by the capacity of the activated carbon layer with respect to the gas to be treated.

Further, in the present invention, the catalytic function of the activated carbon exhibiting the catalytic desulfurization rate Y differs depending on the type of the activated carbon. Therefore, the production rate of dilute sulfuric acid formed on the surface of the activated carbon (defined as the catalytic sulfation rate R in this specification). It also depends on the type of activated carbon. Therefore, when the gas to be treated is brought into contact with the activated carbon layer for desulfurization according to the present invention, it is important to select an activated carbon having a large catalytic sulfation rate R of the activated carbon. In the conventional adsorption separation, activated carbon with a long breakthrough time was selected as an excellent adsorbent, but the activated carbon used in the present invention requires a catalytic function, which is different from the conventional adsorption concept. It is selected according to the standard. That is, the breakthrough time, which was the conventional adsorbent selection standard, is insufficient for selecting the activated carbon of the present invention, and the catalytic sulfation rate R is used as the selection standard. This shows the magnitude of SO ₂ removal performance of activated carbon in a steady state, because the present invention uses activated carbon as a catalyst. Therefore, as the activated carbon, the pore structure of the activated carbon and the affinity with water, which are related to the removal performance of the dilute sulfuric acid generated in the pores, are more important than the SO ₂ adsorption performance related to the breakthrough time. Is evaluated as the catalytic sulfation rate R, and the larger the value, the higher the activated carbon having catalytic desulfurization performance. In the relationship between the catalytic desulfurization rate Y and the feed rate F of the gas to be treated as shown in FIG. 4, the catalytic sulfidation rate R defined in the present specification is the largest catalytic desulfurization rate Y of 100%. It is calculated by the following equation (1) using the supply rate (F ₁₀₀ ) of the processing gas. In this case, in order to standardize the catalytic sulfation rate R as a characteristic value specific to the activated carbon applied to the activated carbon layer, the activated carbon used is 18.5 to 8.6 mesh, and the gas to be treated is , SO ₂ : 40vo
1 ppm, oxygen: 5 vol%, steam: 9.4 vol
%, Balance: A gas consisting of nitrogen gas is used as a standard gas, and the standard contact temperature between the standard gas and activated carbon is 45
C was used. R = F ₁₀₀ × X _S /(22.4×W) (1) R: catalytic sulfation rate (μmol / g / hr) F ₁₀₀ : supply of the largest gas to be treated with a catalytic desulfurization rate Y of 100% Velocity (Nl / hr) X _S : SO ₂ concentration (volppm) of the gas to be treated W: Weight of activated carbon (g) In the present invention, the catalytic sulfation rate R is usually 5 μmol / g / hr or more, preferably 10 μmol /
g / hr or more, more preferably 20 μmol / g / hr
Activated carbon with the above values is used. As such activated carbon, commercially available products such as activated carbon manufactured by Toyo Calgon Co., Ltd. (trade name: "F30 / 470"), activated carbon manufactured by Tsurumi Coal (trade name: "4GV"), activated carbon manufactured by Kuraray Chemical Co., Ltd. (Product name: “4GS”) and the like. This catalytic sulfation rate R is a characteristic value specific to activated carbon, and this R can be obtained by conducting a desulfurization experiment. This catalytic sulfation rate R is 5 μmol / g /
If activated carbon smaller than hr is used, the desulfurization device becomes large, which is not economically suitable.

In the desulfurization method of the present invention, as can be seen from FIG. 5, the catalytic desulfurization rate Y depends on the SO ₂ concentration in the gas to be treated, and greatly increases as the SO ₂ concentration in the gas to be treated decreases. improves. Therefore, the desulfurization method of the present invention uses S
When it is applied to the SO ₂ -containing gas to be treated, which has a low O ₂ concentration of 100 volppm or less, a remarkable effect is exhibited. The SO ₂ concentration in the gas to be used in the present invention is 100 volppm or less, preferably 50 volp
It is pm or less. Further, the oxygen concentration in the gas to be treated is 0.
It is 1 vol% or more, preferably 1 vol% or more, and more preferably 2 vol% or more. The upper limit of the oxygen concentration is usually 21 vol%. The water vapor concentration is 5 to 100%, preferably 40 to 100, expressed as relative humidity.
%, More preferably 70 to 100%. When the oxygen concentration and the water vapor concentration in the gas to be treated are too low, those gases can be added from the outside.

The desulfurization operation temperature of the present invention is an average temperature of the activated carbon layer 2 of 100 ° C. or lower, preferably 80 ° C. or lower, more preferably 50 ° C. or lower. The lower limit is usually 10 ° C
Is.

The desulfurization device used in the present invention is not limited to the activated carbon packed column as described above, and any gas-solidifying device having an activated carbon layer can be used. For example, a horizontal type gas having an activated carbon layer can be used. Fastening devices can also be used.
In this case, this gas-solidifying device is provided with a dilute sulfuric acid storage portion at the bottom thereof to continuously separate the dilute sulfuric acid generated in the activated carbon layer during the desulfurization treatment of the gas to be treated from the activated carbon layer, and to react this. It is important that the structure is such that the device is continuously or intermittently withdrawn.

The desulfurization method of the present invention is advantageously applied as a secondary desulfurization method for desulfurization treatment gas discharged from various flue gas desulfurization devices, and preferably an aqueous slurry of limestone and S
_Two types of desulfurization treatment gas from a wet limestone-gypsum flue gas desulfurization device for performing a neutralization reaction step of reacting with O ₂ and an oxidation reaction step of oxidizing the neutralized product (calcium sulfite) to generate gypsum It is applied as the next desulfurization method. Figure 6
FIG. 1 shows an example of a flow sheet when the desulfurization method of the present invention is applied to the secondary desulfurization of the desulfurization treatment gas from the wet limestone-gypsum flue gas desulfurization apparatus.

In FIG. 6, the exhaust gas at 130 to 150 ° C. containing SO ₂ discharged from the combustion equipment such as a boiler is
This is supplied to the gas / gas heat exchanger 12 via the conduit 11, desulfurized as described later, and cooled by heat exchange with the desulfurization gas after flue gas desulfurization supplied in the conduit 22 and then cooled. It is introduced into the exhaust gas cooling tower 14 by 13. To the cooling tower 14, the absorption liquid (aqueous solution of limestone) after separating gypsum particles as described later is supplied by a conduit 32,
The exhaust gas cooled by the absorption liquid supplied by the conduit 15 and the water spray supplied by the conduit 38 is introduced into the lower part of the desulfurization tower 17 by the conduit 16. On the other hand, in the upper part of the desulfurization tower 17, a limestone-gypsum-containing aqueous slurry liquid (hereinafter abbreviated as an absorption liquid) having a pH of 5 to 6 is supplied from a lower part of the desulfurization tower by a conduit 18 and dispersed by means such as a spray to desulfurize. Most of the SO ₂ in the exhaust gas (usually 90 to 95%) is removed by making countercurrent contact with the rising exhaust gas in the column 17. The exhaust gas from which most of SO ₂ was removed in the desulfurization tower 17 is the demister 1 installed at the upper part of the desulfurization tower 17.
9, the mist and solid matter entrained in the exhaust gas are removed here. The exhaust gas from which most of SO ₂ was removed in the desulfurization tower 17 was introduced into the activated carbon packed tower 10 through the conduit 20, and SO ₂ remaining in the exhaust gas was several ppm or less or completely removed by contact with the activated carbon. After that, it is reheated to 90 to 110 ° C. by heat exchange with the exhaust gas supplied from the conduit 11 in the gas / gas heat exchanger 12 via the conduit 22, and is discharged to the outside of the system via the conduit 23.

The dilute sulfuric acid flowing out from the activated carbon packed tower 10 is
It is supplied to the lower portion of the desulfurization tower 17 (calcium sulfite oxidation reaction process section) through a conduit 36, where it reacts with limestone to produce gypsum. The absorption liquid that has absorbed most of SO _{2 in} the desulfurization tower 17 comes into contact with an oxygen-containing gas, for example, air, which is supplied by a conduit 37 in the lower portion of the desulfurization tower 17, and the sulfurous acid in the absorption liquid is oxidized to form gypsum. To do.

In the present invention, the dilute sulfuric acid flowing out of the activated carbon layer of the activated carbon packed tower 10 oxidizes the neutralized product (CaSO ₃ ) of the wet limestone-gypsum flue gas desulfurization unit to produce gypsum (CaSO ₄ ). It is effective to introduce it into the oxidation reaction process section. In this oxidation reaction process part, it is desirable to maintain the pH of the absorbing solution at a low value of around 4.5 in order to accelerate the oxidation of sulfurous acid, so the introduction of dilute sulfuric acid flowing out from the activated carbon packed column 10 serves as a pH adjuster. It is extremely effective.

In FIG. 6, the case where there is an oxidation step in the lower part of the desulfurization tower has been described, but in order to remove unreacted limestone and obtain high quality gypsum, an oxidation tower is installed separately and sulfuric acid is added to this oxidation tower. Although oxidation may be performed at a low pH, dilute sulfuric acid separated from the activated carbon layer can be used as the sulfuric acid also in this case, which is extremely effective.

The absorption liquid containing gypsum is sent to the gypsum separator 25 by the conduit 24, where the gypsum is separated. The absorption liquid after separating the gypsum is stored in the filtrate tank 27 by the conduit 26, is further sent to the limestone slurry tank 29 by the conduit 28, slurries the limestone supplied from the conduit 30, and then the desulfurization tower 17 by the conduit 31. Will be returned to the bottom of. A part of the absorption liquid in the filtrate tank 27 is sent to the exhaust gas cooling tower 14 by the conduit 32, used for cooling the exhaust gas, and then sent to the wastewater treatment process 34 by the conduit 33 to remove harmful substances, Conduit 35
Released by.

When the desulfurization treatment is carried out as described above, a minute amount of fine solid matter that has passed through the demister 19 is adhered and deposited on the activated carbon layer of the activated carbon packed tower 10, whereby the catalytic function of the activated carbon is gradually increased. It may decrease. In order to prevent such a decrease in the catalytic function of the activated carbon, water is continuously or intermittently supplied to the activated carbon packed tower 10 from the conduit 21 or an aqueous solution, for example, from the filtrate tank 27 by the conduit 39. It is effective to continuously or intermittently supply an absorption liquid (limestone aqueous solution) containing no solid matter such as gypsum, and wash the activated carbon layer with these liquids. The supply of these liquids is also effective for cleaning and removing dilute sulfuric acid generated in the activated carbon layer. The desulfurization method of the present invention is not only a secondary desulfurization method of a desulfurization treatment gas from a wet limestone-gypsum flue gas desulfurization apparatus, but also a gas obtained by treating the present invention with a gas containing a low concentration of sulfurous acid gas. It includes a method of converting sulfuric acid into gypsum based on the principle of the wet limestone-gypsum method.

[0027]

INDUSTRIAL APPLICABILITY The present invention is a method for catalytically oxidizing and removing SO ₂ contained in a gas to be treated by utilizing a catalytic function of SO ₂ for oxidizing reaction of SO _2. The regeneration treatment of activated carbon required for the desulfurization method by separation is not required. Therefore, in the present invention, SO ₂ in the gas to be treated can be removed continuously and for a long time at a stable desulfurization rate. The present invention is based on SO ₂
It can be applied as a desulfurization method for various gases containing a low concentration of. Examples of the gas to be treated include desulfurization treatment gas obtained from various desulfurization devices, fluidized bed boiler exhaust gas, incinerator exhaust gas, and the like. These gases contain 10 to 1 SO ₂
Although it contains about 100 volppm, in the present invention, SO ₂ in these gases can be made 1 volppm or less or completely zero.

When the desulfurization treatment gas discharged from the flue gas desulfurization apparatus is desulfurized by the desulfurization method of the present invention, it is released to the atmosphere without requiring an extremely large size of the flue gas desulfurization apparatus or a large increase in power consumption. The SO ₂ concentration in the exhaust gas can be made almost zero. Moreover, since the desulfurization method of the present invention can be carried out using an activated carbon packed column having a simple structure, its operation is simple, and its treatment cost is low, and it is economical.

[0029]

EXAMPLES Next, the present invention will be described in more detail by way of examples.

Example 1 A reactor having an activated carbon layer having a structure shown in FIG. 7 was used as a desulfurizer. This reactor has an inner diameter of 26 mm and a length of 1
A 50 mm glass reaction tube 41 was filled with 12 cc of commercially available activated carbon to form an activated carbon layer 42, and a dilute sulfuric acid extraction valve 45 was attached to the gas supply tube 43 at the upper end and a dilute sulfuric acid extraction valve 45 at the lower end. A pipe 44 is provided, a process gas outlet 46 is provided below the activated carbon layer 42 of the reaction tube, and a hot water introducing pipe 47 is provided on the outer peripheral surface of the reaction tube.
And a heating jacket 49 having a hot water discharge pipe 48 for adjusting the reaction temperature. As the activated carbon,
A commercial product (trade name "F30 / 470" manufactured by Toyo Calgon Co., Ltd., surface area of about 1500 m ² / g) using coal as a raw material was divided into nodes and the particle size thereof was adjusted to 18.5 to 8.6 mesh. The catalytic sulfation rate R of this product is 38 μmol
It was / g / hr.

A gas inlet pipe 43 at the upper end of the reactor
A desulfurization test was conducted by flowing a gas to be treated having the following composition downward at a reaction rate of 45 ° C. at a supply rate of 60 N liter / hr. In this case, the dilute sulfuric acid generated in the activated carbon layer was discharged to the outside by letting it flow down to the bottom and intermittently operating the dilute sulfuric acid extraction valve 45. (Treated gas _{composition) SO 2: 1000 volppm O 2} : 5 vol% CO 2: 12 vol% H 2 O: 45 ℃ saturated, about 9.5 vol% N _2: the remaining portion

In this desulfurization test, the desulfurization rate was 100% and SO ₂ was not present in the desulfurization treatment gas until about 4 o'clock after passing the gas, but after about 4 hours, an excessive amount of gas began to pass and the passing gas was passed. After 12 hours, the catalytic desulfurization rate Y was a constant value of 18%. The relationship between the desulfurization rate and the operation time in this case is shown in FIG. The SO ₂ concentration in the gas was continuously increased to 200 volpp
When the catalytic desulfurization rate Y was measured while lowering m and 40 volppm, the catalytic desulfurization rates Y = 68% and 100% were obtained, respectively. The measurement results of these catalytic desulfurization rates Y are shown in FIG. 5 in relation to the SO ₂ concentration (vol ppm) in the gas to be treated. Next, the SO ₂ concentration in the gas was fixed at 40 volppm, and the gas to be treated was supplied at a rate of 110 Nl / h.
r, 222 Nl / h and 331 Nl / h
The catalytic desulfurization rate Y was measured while changing to r. FIG. 4 shows the relationship between the catalytic desulfurization rate Y and the supply rate (Nl / hr) of the gas to be treated.

Example 2 A reactor having the same structure as shown in Example 1 except that it has an activated carbon layer composed of 12 cc of new activated carbon similar to that shown in Example 1 was prepared. A continuous desulfurization experiment was carried out by flowing downward a flue gas desulfurization outlet simulation gas having the following composition at a supply rate of 60 Nl / hr from the gas introduction pipe 43 at the upper end of the reactor to a temperature of 45 ° C. (FGD outlet simulated exhaust gas _{composition) SO 2: 40 volppm O 2} : 5 vol% CO 2: 12 vol% H 2 O: 45 ℃ saturated, about 9.5 vol% N _2: the remaining part the desulfurization experiments Is a desulfurization rate of 100 from the beginning of passing gas.
%, And after about 250 hours, dilute sulfuric acid started to flow out from the activated carbon layer, and this was continuously separated from the activated carbon layer.
In this way, the desulfurization rate was maintained at 100% even if the desulfurization experiment was continued for 1000 hours or longer. Therefore, it is understood that the catalytic desulfurization rate Y in this experiment is 100%.

Example 3 A reactor having the same structure as shown in Example 1 except that it has an activated carbon layer consisting of 12 cc of new activated carbon similar to that shown in Example 2 was prepared. A gas to be treated having the following composition was made to flow downward from the gas introduction pipe 43 at the upper end of the reactor at a temperature of 45 ° C. at a supply rate of 60 Nl / hr,
A continuous desulfurization experiment was conducted. (Processed gas composition) SO ₂ : 100 volppm O ₂ : 5 vol% CO ₂ : 12 vol% H ₂ O: saturated at 45 ° C., about 9.5 vol% N ₂ : balance The result of this desulfurization experiment is shown in FIG. As shown in Fig. 1, a desulfurization rate of 100% was obtained at the beginning of passing gas, but it started to break through after 45 hours and showed a constant desulfurization rate of 87% after 132 hours. The desulfurization rate was maintained. Therefore, it is understood that the catalytic desulfurization rate Y in this experiment is 87%.

Example 4 In Example 1, as the activated carbon, another commercially available product (trade name “4GV”, manufactured by Tsurumi Coal Co., Ltd., raw material of coconut shell, surface area of 1200 m ² / g) was sieved to have a particle size of 18 .5
〜8.6 mesh (R = 43 μmol / g
/ Hr), and the same experiment was conducted except that the SO ₂ concentration in the gas to be treated was set to 100 volppm. In this case, the desulfurization rate at the beginning of passing gas is 10
Although it was 0%, breakthrough occurred about 30 hours after passing the gas, and after 160 hours after passing the gas, the catalytic desulfurization rate Y was a constant value of 87%. Then, the SO ₂ concentration in the gas to be treated is adjusted to 40 v
When it was set to olppm, the result of the catalytic desulfurization rate Y = 100% was obtained.

Example 5 In Example 2, at a time of 1000 hours after passing the gas, a temperature of 45 simulating the wet limestone-gypsum process waste liquid desulfurization absorption liquid was used.
50 ml of a saturated aqueous solution of gypsum at 0 ° C. was gradually supplied together with the gas to be treated from the gas introduction pipe 43 of the reactor to wash the activated carbon layer. It was confirmed that even after this washing operation, the activated carbon layer had a sufficient catalytic function and showed a catalytic desulfurization rate Y of 100%.

[Brief description of drawings]

FIG. 1 shows a schematic view of an activated carbon packed tower.

FIG. 2 shows the relationship between the desulfurization rate and the operating time when the target gas containing SO ₂ at a high concentration is circulated in the activated carbon layer for desulfurization and the dilute sulfuric acid generated at that time is continuously separated. .

FIG. 3 shows the relationship between the desulfurization rate and the operating time when a target gas containing SO ₂ at a low concentration is circulated in an activated carbon layer for desulfurization and the dilute sulfuric acid generated at that time is continuously separated. .

FIG. 4 shows the relationship between the catalytic desulfurization rate Y and the space velocity of the gas to be treated.

FIG. 5 shows the relationship between the catalytic desulfurization rate Y and the SO ₂ concentration in the gas to be treated.

FIG. 6 shows an example of a flow sheet when the desulfurization method of the present invention is applied to the secondary desulfurization gas of the desulfurization gas discharged from the wet limestone-gypsum flue gas desulfurization apparatus.

FIG. 7 shows a structural diagram of a desulfurization device used in Examples.

[Explanation of symbols]

1 Processing gas supply pipe 2 activated carbon layer 3 Process gas exhaust pipe 4 Dilute sulfuric acid storage 5 Dilute sulfuric acid extraction tube 6 Cleaning liquid spray tube 7 Cleaning liquid supply pipe 10 Activated carbon packed tower 12 Gas / gas heat exchanger 14 Cooling tower 17 Desulfurization tower 19 Demister 20 Process gas supply line 25 gypsum separator 27 Filtrate tank 29 Limestone slurry tank 36 Dilute sulfuric acid extraction line

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Takashi Kimura Inventor Takashi Kimura 2-12-1, Tsurumi Chuo, Tsurumi-ku, Yokohama-shi, Kanagawa Chiyoda Kakoh Construction Co., Ltd. (56) Reference JP-A-61-86929 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) B01D 53/86 B01D 53/50 B01D 53/81 B01J 21/18

Claims (7)

(57) [Claims] 1. A desulfurization method using a gas containing sulfurous acid gas, oxygen and steam as a gas to be treated, wherein (i) the concentration of sulfurous acid gas in the gas to be treated is 100 volppm or less, and (ii) the gas to be treated is activated carbon. Distribute the layers,
In the activated carbon layer, sulfur dioxide gas and oxygen are catalytically oxidized to be converted into sulfur trioxide, and this sulfur trioxide is reacted with water to generate dilute sulfuric acid,
(Iii) continuously diluting the dilute sulfuric acid content generated in the activated carbon layer from the activated carbon layer, (iv) the catalytic sulfation rate R of the activated carbon forming the activated carbon layer is 5 μmol / g / hr or more (v ) The catalytic desulfurization rate Y of the gas to be treated obtained by circulating the gas to be treated through the activated carbon layer is at least 80.
%, A method for desulfurizing a gas containing sulfur dioxide at a low concentration. 2. A to-be-processed gas is supplied into the tower from a position above the activated carbon layer to an activated carbon packed column having a structure in which an activated carbon layer is provided inside and a diluted sulfuric acid accommodation section is disposed below the activated carbon layer. The desulfurization treatment gas is extracted from the position below the activated carbon layer to the outside of the tower, dilute sulfuric acid is allowed to flow down from the bottom of the activated carbon layer into the dilute sulfuric acid storage section, and the diluted sulfuric acid is extracted from the dilute sulfuric acid storage section. The method of claim 1, wherein: 3. The concentration of sulfurous acid gas in the gas to be treated is 50.
The method according to claim 1 or 2, which is less than or equal to volppm. 4. The method according to claim 1, wherein the gas to be treated is a desulfurization treatment gas discharged from a flue gas desulfurization device. 5. A wet limestone for carrying out a neutralization reaction step of reacting an aqueous limestone slurry liquid with sulfurous acid gas, and an oxidation reaction step of oxidizing the neutralized product to produce gypsum.
Desulfurization treatment gas discharged from the gypsum method flue gas desulfurization device,
A desulfurization method comprising performing a secondary desulfurization treatment by the method according to claim 1 or 2, and introducing dilute sulfuric acid separated from an activated carbon layer during the secondary desulfurization treatment into an oxidation reaction process section of the flue gas desulfurization apparatus. . 6. The method according to claim 5, wherein the activated carbon layer is continuously or intermittently washed with water, and the cleaning effluent obtained by the cleaning at that time is introduced into the oxidation reaction step section of the flue gas desulfurization apparatus. 7. An activated carbon layer is continuously or intermittently formed with an aqueous solution after separating suspended particles contained therein from an aqueous slurry liquid containing gypsum and limestone discharged from a wet limestone-gypsum flue gas desulfurization apparatus. The method according to claim 5, wherein the cleaning waste liquid obtained by the cleaning at that time is introduced into the oxidation reaction process section of the flue gas desulfurization apparatus.