JP2007000830A - Method for desulfurizing exhaust gas - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for desulfurizing exhaust gas in which sulfurous acid gas can be removed stably by using an activated carbon catalyst for stack gas desulfurization over a long period of time without poisoning the activated carbon catalyst by hydrogen sulfide gas when sulfurous acid gas in exhaust gas, in which there is some chance that hydrogen sulfide gas is mixed, is removed/recovered as sulfuric acid. <P>SOLUTION: The method for desulfurizing exhaust gas comprises a hydrogen sulfide concentration adjusting step 1, which is carried out when the concentration of hydrogen sulfide in exhaust gas exceeds 50 volume ppm and used for adjusting the concentration of hydrogen sulfide in exhaust gas to ≤50 volume ppm, and a desulfurization step 2 of bringing exhaust gas containing sulfurous acid gas, water and oxygen into contact with the activated carbon catalyst for stack gas desulfurization to recover sulfurous acid gas in exhaust gas as sulfuric acid. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust gas desulfurization method in which an exhaust gas containing sulfurous acid gas is contacted with an activated carbon catalyst for flue gas desulfurization, and the sulfurous acid gas is recovered and removed as sulfuric acid.

  There is a case where toxic sulfurous acid gas is contained in a large amount of combustion exhaust gas discharged from a boiler for thermal power generation. In order to remove sulfurous acid gas from such exhaust gas, there is a dry desulfurization method in which sulfurous acid gas in exhaust gas is contacted with an activated carbon adsorbent under dry conditions at a relatively high temperature (about 150 to 400 ° C.).

  However, in the dry desulfurization method as described above, the adsorptive capacity of activated carbon gradually decreases. Therefore, it is indispensable to perform a regeneration process such as water washing and drying on the activated carbon whose adsorptive capacity has decreased. For this reason, the implementation system of the dry desulfurization method has to repeat adsorption and regeneration of exhaust gas with respect to the activated carbon in the adsorption tower by providing two or more adsorption towers and switching the adsorption tower through which the exhaust gas passes. There is a problem of complexity.

  Therefore, low-temperature wet flue gas desulfurization that recovers sulfurous acid gas as sulfuric acid under relatively low temperature and high humidity conditions using activated carbon catalyst as a method that enables continuous treatment of exhaust gas without regenerating activated carbon. Methods have been proposed (Patent Documents 1 to 4). In such a low temperature wet flue gas desulfurization method, exhaust gas is introduced at a relatively low temperature into a catalyst packed tower packed with an activated carbon catalyst, and the sulfurous acid gas in the exhaust gas is catalytically oxidized by oxygen gas in the exhaust gas on the activated carbon catalyst. Let it be sulfur trioxide. This sulfur trioxide reacts with moisture in the exhaust gas and is further converted into sulfuric acid, and is adsorbed and held on the activated carbon catalyst. Then, the sulfuric acid that can no longer be held by the activated carbon catalyst is separated from the activated carbon catalyst by gravity and collected at the lower part of the catalyst packed tower.

  By the way, heavy oil is used as a fuel to be burned in a boiler for thermal power generation. Before using heavy oil as a fuel, all sulfur components such as mercaptans and thiophenes contained therein are used with hydrogen. From the viewpoint of preventing air pollution, it is essential to reduce to hydrogen sulfide and recover it as elemental sulfur using the Claus reaction in a sulfur recovery device. Since the exhaust gas generated in such a sulfur recovery device contains sulfurous acid gas and hydrogen sulfide, after absorbing and removing them with an aqueous solution containing an amine compound, the exhaust gas is combusted with an incinerator. It is necessary to convert the hydrogen sulfide into sulfurous acid gas and perform the above-described flue gas desulfurization treatment on the exhaust gas from the insulator containing the sulfurous acid gas.

Japanese Patent No. 3272366 Japanese Patent Laid-Open No. 10-230129 Japanese Patent Laid-Open No. 10-314586 JP-A-11-290688

  However, when the exhaust gas from the sulfur recovery device is combusted with an incinerator, the hydrogen sulfide gas contained therein is converted to sulfurous acid gas, and when flue gas desulfurization is performed under relatively low temperature and high humidity conditions, There was a problem that the desulfurization performance of the activated carbon catalyst for desulfurization deteriorated. It was also confirmed that hydrogen sulfide gas was occasionally mixed in the exhaust gas that should have been burned by the insulator.

  The present invention is intended to solve the above-described problems of the prior art. By contacting an exhaust gas containing sulfurous acid gas, moisture and oxygen with an activated carbon catalyst for flue gas desulfurization, the sulfurous acid gas in the exhaust gas is converted into sulfuric acid. In the exhaust gas desulfurization method to be recovered and removed, even if the exhaust gas contains hydrogen sulfide gas, the desulfurization performance of the activated carbon catalyst for flue gas desulfurization is not lowered, and the activated carbon for flue gas desulfurization is not regenerated. The object is to enable continuous treatment of exhaust gas.

  As a result of earnest research under the hypothesis that the above-mentioned problem is very closely related to the hydrogen sulfide concentration, the present inventor has found that when the hydrogen sulfide concentration in the exhaust gas exceeds 50 ppm by volume, The present inventors have found that the catalytic ability of the activated carbon catalyst for flue gas desulfurization in contact with such exhaust gas is drastically reduced, and the present invention has been completed.

  That is, the present invention relates to an exhaust gas desulfurization method having a desulfurization step of recovering sulfur dioxide gas in exhaust gas as sulfuric acid by contacting exhaust gas containing sulfur dioxide gas, moisture and oxygen with an activated carbon catalyst for flue gas desulfurization. An exhaust gas desulfurization method characterized by having a hydrogen sulfide concentration adjusting step of adjusting the hydrogen sulfide concentration in the exhaust gas to 50 ppm by volume or less before the desulfurization step when the hydrogen sulfide gas concentration in the exhaust gas exceeds 50 ppm by volume I will provide a.

  In the exhaust gas desulfurization method of the present invention, in order to prevent a decrease in the desulfurization performance of the activated carbon catalyst for flue gas desulfurization due to hydrogen sulfide gas that may be mixed into the exhaust gas, the hydrogen sulfide concentration in the exhaust gas is set to 50 ppm by volume or less. And a hydrogen sulfide concentration adjusting step. Therefore, exhaust gas having a hydrogen sulfide concentration exceeding 50 ppm by volume can be prevented from coming into contact with the activated carbon catalyst for flue gas desulfurization, so that a reduction in catalytic ability can be prevented. For this reason, exhaust gas can be continuously desulfurized without performing regeneration treatment of the activated carbon catalyst, and sulfurous acid gas can be stably removed from the exhaust gas over a long period of time.

  As shown in FIG. 1, the present invention includes a desulfurization step 2 in which an exhaust gas containing sulfurous acid gas, moisture, and oxygen is brought into contact with an activated carbon catalyst for flue gas desulfurization to recover the sulfurous acid gas in the exhaust gas as sulfuric acid. This is an exhaust gas desulfurization method. In the present invention, in order to prevent deterioration of the desulfurization performance of the activated carbon catalyst for flue gas desulfurization due to hydrogen sulfide gas that may be mixed into the exhaust gas, when the concentration of hydrogen sulfide in the exhaust gas exceeds 50 ppm by volume, such In order to prevent the exhaust gas from coming into contact with the activated carbon catalyst for flue gas desulfurization, a hydrogen sulfide concentration adjusting step 1 for setting the hydrogen sulfide concentration in the exhaust gas to 50 ppm by volume or less is provided before the desulfurization step 2. The reason why the catalytic ability of the activated carbon catalyst for flue gas desulfurization decreases when the hydrogen sulfide concentration in the exhaust gas exceeds 50 ppm by volume is considered as follows. That is, if the hydrogen sulfide concentration in the exhaust gas exceeds 50 ppm by volume, even if the hydrogen sulfide gas concentration is lower than the concentration of sulfurous acid gas, the hydrogen sulfide gas is on the activated carbon catalyst for flue gas desulfurization, This is because elemental sulfur, polysulfide, or polythionic acid that becomes a catalyst poison is easily generated exponentially. The reason for this is not clear, but low-concentration hydrogen sulfide of 50 ppm or less by volume is oxidized to sulfuric acid. However, if it exceeds 50 ppm by volume, sulfurous acid gas and hydrogen sulfide gas react on the catalyst to react with elemental sulfur. This is because it is considered to be easy to generate.

  If the concentration of hydrogen sulfide in the exhaust gas does not exceed 50 ppm by volume, even if such exhaust gas is introduced into the desulfurization step 2, the catalytic performance of the flue gas desulfurization activated carbon catalyst is not significantly reduced. Although it is not necessary to carry out the treatment in the hydrogen concentration adjusting step 1, it is preferable to carry out the treatment so as to be 10 ppm by volume or less in order to almost completely prevent the deterioration of the catalytic ability.

  Examples of the exhaust gas containing sulfurous acid gas, which is an object of the exhaust gas desulfurization method of the present invention, include exhaust gases from various combustion in which hydrogen sulfide gas may be mixed. For example, in order to convert hydrogen sulfide in a hydrogen sulfide-containing gas into sulfurous acid gas, exhaust gas obtained by burning the hydrogen sulfide-containing gas in a combustion furnace can be targeted. Therefore, even exhaust gas in which hydrogen sulfide gas is always mixed can be targeted. In the exhaust gas desulfurization method of the present invention, before the exhaust gas is brought into contact with the activated carbon catalyst for flue gas desulfurization in the desulfurization step 2, the hydrogen sulfide concentration can be adjusted to 50 ppm by volume or less in the hydrogen sulfide concentration adjustment step 1. Because it is possible.

  Further, in the desulfurization step 2, the sulfurous acid gas is oxidized on the activated carbon catalyst for flue gas desulfurization to become sulfur trioxide and further to sulfuric acid. For this purpose, oxygen reacts with sulfurous acid gas and sulfur trioxide. I need water. The oxygen and water originally contained in the exhaust gas can be used, but when they are not contained or insufficient, the oxygen and water may be supplied to the exhaust gas from the outside. In addition, as this water, the normal industrial water and the dilute sulfuric acid aqueous solution containing the sulfuric acid produced | generated by the desulfurization process can be used preferably.

  In the present invention, specific operations of the hydrogen sulfide concentration adjusting step 1 include (a) a method using a combustion furnace, (b) a method using an adsorbent, (c) a method using an absorbent, (d ) A method by catalytic oxidation and the like.

  (A) The method using a combustion furnace is a method of burning and oxidizing hydrogen sulfide gas to sulfurous acid gas while burning fuel (for example, methane gas) in the combustion furnace in the presence of oxygen. If the oxygen concentration in the exhaust gas after combustion oxidation is too low, combustion is insufficient, and a short pass of hydrogen sulfide gas and elemental sulfur are likely to be generated. Is in the range of 0.5% to 15% by volume. The range is more preferably 1.5% by volume or more and 5% by volume or less from the viewpoint of securing the combustion reaction temperature, preventing a decrease in combustion efficiency, and suppressing the generation of NOx. Oxygen may be contained in the exhaust gas. However, when oxygen is not contained in the exhaust gas or when the absolute amount is insufficient, it may be supplied as combustion air from the outside to the combustion furnace. Good.

  Since the conversion of hydrogen sulfide gas in exhaust gas to sulfurous acid gas depends on the oxidation reaction rate of hydrogen sulfide, the conversion rate depends on the hydrogen sulfide concentration, furnace temperature (reaction temperature), residence time (reaction time), etc. Determined by the element. The exhaust gas containing hydrogen sulfide gas may be introduced into the furnace in the vicinity of the burner or in the combustion chamber as long as the necessary furnace temperature (reaction temperature) and residence time (reaction time) can be secured. Here, if the concentration of hydrogen sulfide in the exhaust gas to be treated is high, it is necessary to convert the hydrogen sulfide gas to sulfurous acid gas at a high conversion rate. Therefore, the furnace temperature (reaction temperature) is relatively increased and stayed. It is necessary to lengthen the time (reaction time).

  If the furnace temperature (reaction temperature) is too low, it is necessary to lengthen the residence time (reaction time), and the mixing state of the combustion gas and exhaust gas in the furnace varies, and the hydrogen sulfide concentration is 50 ppm by volume. It is difficult to maintain a low hydrogen sulfide concentration. Moreover, coupled with the long residence time, the gas phase Claus reaction proceeds and elemental sulfur (gas) is likely to be generated, which may reduce the activity of the catalyst in the desulfurization step 2. Further, if the reaction temperature is too high, the cost of maintaining the temperature becomes high, and the hydrogen sulfide gas concentration becomes 1 volume ppm or less in a short time, so that the unused portion of the furnace increases, and the utilization efficiency of the combustion furnace increases. descend.

  If the residence time (reaction time) is too short, the mixing state of the combustion gas and exhaust gas in the furnace becomes insufficient, making it difficult to maintain a low hydrogen sulfide concentration. If it is too long, the furnace is too large. This means that usage efficiency is reduced.

  On the other hand, the hydrogen sulfide concentration of the exhaust gas treated by the method (a) using the combustion furnace in the hydrogen sulfide concentration adjusting step 1 is generally 5 to 50% by volume.

  Therefore, assuming that such an exhaust gas having a hydrogen sulfide concentration of 5 to 50% by volume, particularly 30% by volume or less, is treated, the furnace temperature (reaction temperature) when treating the exhaust gas by a method using a combustion furnace is: , Preferably 300 to 1000 ° C., more preferably 500 to 800 ° C., and the residence time (reaction time) is preferably 0.1 to 5.0 seconds, more preferably 0.3 to 2.0 seconds. However, when the furnace temperature is relatively low within the aforementioned temperature range, the residence time is preferably relatively long within the aforementioned time range. Further, it is preferable to raise the temperature of the combustion furnace as the concentration of hydrogen sulfide in the exhaust gas to be introduced into the combustion furnace increases.

  When exhaust gas with a hydrogen sulfide concentration of less than 5% by volume is treated by a method using a combustion furnace, the hydrogen sulfide concentration is low, so the conversion rate of hydrogen sulfide gas to sulfurous acid gas is low, and the oxidation reaction Although the speed is inevitably slow, it is preferable to treat under the same conditions as those for the exhaust gas having a hydrogen sulfide concentration of 5 to 50% by volume described above.

(B) The method using an adsorbent is an iron-based adsorbent capable of adsorbing hydrogen sulfide gas, activated carbon, or an impregnated activated carbon containing an oxidizing agent or an alkali compound (for example, KMnO ₄ , NaOH) and an exhaust gas. By doing so, the hydrogen sulfide gas is adsorbed and removed. Known adsorbents can be used as these adsorbents. For example, as the iron-based adsorbent, a material mainly composed of FeO or Fe ₂ O ₃ and formed into a porous pellet can be used.

  Further, as a specific operation of the adsorption treatment, exhaust gas at 30 to 200 ° C. is continuously introduced into the adsorbent packed tower filled with the adsorbent and brought into contact with the adsorbent. These adsorbents can also be regenerated according to conventionally known methods.

  In addition, the hydrogen sulfide concentration of the exhaust gas treated by the method (b) using the adsorbent in the hydrogen sulfide concentration adjusting step 1 is generally 10 to 1000 ppm by volume.

(C) In addition, the method using an absorbent includes at least an iron-based compound (for example, Fe ₂ O ₃ , FeCl ₃ , Fe (OH) ₃ ), an alkali compound (for example, NaOH, lime), an oxidation absorbent (for example, Hydrogen sulfide gas absorption liquid containing sodium hypochlorite, potassium permanganate, hydrogen peroxide water, ozone-added water) and / or amine compounds (for example, monoethanolamine, diisopropanolamine) and exhaust gas Thus, hydrogen sulfide gas is absorbed and removed. As these absorbents, known ones can be used. For example, an aqueous absorbent obtained by dissolving monoethanolamine, which is an amine compound, in water can be used.

  In addition, as a specific operation of the absorption treatment, the absorbent is allowed to flow down from the upper part of the absorption tower filled with a resin packing (Terraret, Nippon Steel Chemical Industries, Ltd.), and preferably at a temperature of 40 to 90 ° C. For example, exhaust gas is introduced into the absorption tower from below and brought into contact with the absorption liquid. This method of regenerating the absorbent can also be performed according to a conventionally known method.

  In addition, the hydrogen sulfide concentration of the exhaust gas treated by the method (c) using the absorbent in the hydrogen sulfide concentration adjusting step 1 is generally 1 to 50% by volume.

  (D) Further, as a method by catalytic oxidation, for example, in the presence of oxygen, exhaust gas is brought into contact with an oxidation catalyst in which a catalyst metal such as vanadium or platinum is supported on a silicon nitride carrier and contained in the catalyst. Hydrogen sulfide is oxidized to sulfurous acid gas catalytically. Such an oxidation catalyst is, for example, a catalyst metal deposited on a porous silicon nitride granular support with a thickness of 5 to 15 nm, or an anodized aluminum and a noble metal such as platinum supported on the surface of alumina. It has been made. Such an oxidation catalyst can be prepared by a conventionally known method.

  As a specific operation for the catalytic oxidation treatment, exhaust gas is introduced into the oxidation catalyst layer, and hydrogen sulfide gas is oxidized to sulfurous acid gas with oxygen. The necessary oxygen in the catalytic oxidation method is preferably about 1.05 to 1.2 times the theoretical amount with respect to the amount of hydrogen sulfide introduced into the oxidation catalyst layer. When oxygen is insufficient in the exhaust gas, a necessary amount of air, preferably pure oxygen, may be introduced from the outside. In addition to exhaust gas, a fuel such as methane can be introduced into the oxidation catalyst layer to ensure stable combustion. In that case, an oxygen amount necessary for fuel combustion is also introduced. If the reaction temperature is too low, it is advantageous for adsorption, but the reaction rate is controlled by an oxidation reaction. Conversely, if the reaction temperature is too high, the adsorption rate is controlled.

  In addition, the hydrogen sulfide concentration of the exhaust gas treated by the method (d) by catalytic oxidation in the hydrogen sulfide concentration adjusting step 1 is generally 0.1 to 5% by volume.

  The desulfurization step 2 of the exhaust gas desulfurization method of the present invention is to recover the sulfurous acid gas in the exhaust gas as sulfuric acid by bringing the exhaust gas containing sulfurous acid gas, water and oxygen into contact with the activated carbon catalyst for flue gas desulfurization.

  The activated carbon catalyst for flue gas desulfurization is a catalyst for adsorbing and oxidizing the sulfurous acid gas when it comes into contact with exhaust gas containing sulfurous acid gas, water and oxygen, and recovering and removing it as sulfuric acid. As such an activated carbon catalyst for flue gas desulfurization, fibrous activated carbon, granular activated carbon, non-woven activated carbon, or high-temperature baking treatment or water repellent (for example, water-repellent resin such as tetrafluoroethylene resin) addition treatment using these as raw materials Activated carbon processed by the above method can be preferably used, and these can be combined with a reinforcing material made of thermoplastic resin fibers such as polypropylene, non-woven fabric or board (for example, pasting or blending) to increase the What strengthened can be used preferably.

  Specific examples of the activated carbon catalyst for flue gas desulfurization include activated carbon catalyst (Japanese Patent Laid-Open No. 10-314586, claims 1 to 5) formed by supporting activated carbon powder with fluororesin particles or a fluororesin dispersion, inorganic fibers, Activated carbon catalyst (Japanese Patent Laid-Open No. 2000-263678) in which activated carbon fiber papermaking sheets are laminated on both sides of a core material sheet made of polymer fiber, activated carbon formed by kneading activated carbon powder and fluororesin while applying shearing force Catalyst (JP-A-11-290688, claims 1-6), water-repellent treated product of activated carbon catalyst in which fine activated water repellent material is supported on granular activated carbon (JP-A-10-314585, claims 1-6) 4) etc. can be used preferably. Moreover, as the activated carbon catalyst for flue gas desulfurization, a catalyst molded into a dust-through structure such as a honeycomb structure can be preferably used.

  A specific operation example of the desulfurization process in the desulfurization step 2 will be described below. That is, the exhaust gas from the hydrogen sulfide concentration adjusting step 1 is introduced into the catalyst packed tower packed with the activated carbon catalyst for flue gas desulfurization at a relatively low temperature (preferably 100 ° C. or less, more preferably 20 to 80 ° C.), Sulfurous acid gas in the exhaust gas is catalytically oxidized on the activated carbon catalyst with oxygen gas in the exhaust gas to form sulfur trioxide. This sulfur trioxide is further reacted with moisture in the exhaust gas to convert it into sulfuric acid. To adsorb and hold. Then, the sulfuric acid that can no longer be held by the flue gas desulfurization activated carbon catalyst is separated from the activated carbon catalyst for flue gas desulfurization by gravity. In the desulfurization step 2, the regeneration treatment of the activated carbon catalyst for flue gas desulfurization is not necessary in principle. Note that the sulfuric acid separated from the activated carbon catalyst for flue gas desulfurization by gravity is recovered in the lower part of the catalyst packed tower.

  In the exhaust gas desulfurization method of the present invention, the hydrogen sulfide concentration of the exhaust gas is measured before the hydrogen sulfide concentration adjustment step 1, between the hydrogen sulfide concentration adjustment step 1 and the desulfurization step 2, or at one or more places after the desulfurization step 2. . According to the measurement result, the processing conditions of the hydrogen sulfide concentration adjusting step 1 are controlled so that the hydrogen sulfide concentration of the exhaust gas introduced into the desulfurization step 2 is 50 ppm by volume or less, preferably 10 ppm by volume or less.

  For example, when it is measured before the hydrogen sulfide concentration adjustment step 1, the hydrogen sulfide concentration of the exhaust gas before the treatment is measured. When it exceeds 50 ppm by volume, depending on the hydrogen sulfide concentration The hydrogen sulfide concentration is adjusted under the processing conditions determined in advance. That is, the relationship between the treatment conditions at a certain hydrogen sulfide concentration of the exhaust gas introduced into the hydrogen sulfide concentration adjusting step 1 and the hydrogen sulfide concentration after treatment is obtained as a calibration curve, and the treatment conditions are determined according to the calibration curve. Is preferred. Further, when the measurement is performed between the hydrogen sulfide concentration adjusting step 1 and the desulfurization step 2, the hydrogen sulfide concentration of the exhaust gas itself introduced into the desulfurization step 2 is measured, so that it exceeds 50 ppm by volume. Therefore, it is possible to immediately change the processing conditions of the hydrogen sulfide concentration adjusting step 1 in a direction in which the hydrogen sulfide concentration decreases. Therefore, the hydrogen sulfide concentration of the exhaust gas introduced into the desulfurization step 2 can be more reliably maintained at 50 ppm by volume or less. Further, when measured after the desulfurization step 2, the hydrogen sulfide concentration of the exhaust gas after the desulfurization treatment is measured, but when it exceeds 50 ppm by volume, the hydrogen sulfide concentration is previously determined according to the hydrogen sulfide concentration. The hydrogen sulfide concentration is adjusted under the determined processing conditions. Also in this case, it is preferable to prepare a calibration curve in advance.

  As a specific method for measuring the hydrogen sulfide concentration, a known method can be used. For example, an ultraviolet absorption method, a gas chromatograph method, a coulometric titration method, a detector tube method, a potentiometric titration method, an ion electrode method, methylene blue It can be measured by using an absorption light passing method, etc., and it can be adopted by an automatic continuous measuring instrument or a manual measurement.

  In the exhaust gas desulfurization method of the present invention, as shown in FIG. 2, a temperature for controlling the temperature and relative humidity of the exhaust gas introduced into the desulfurization step 2 between the hydrogen sulfide concentration adjustment step 1 and the desulfurization step 2. -It is preferable to provide the humidity control process 3. By controlling the temperature and relative humidity of the exhaust gas, high desulfurization performance can be obtained efficiently.

  In the temperature / humidity control step 3, control is performed with emphasis on sufficiently increasing the humidity of the exhaust gas. The higher the relative humidity, the better the performance of the activated carbon catalyst for flue gas desulfurization. Therefore, it is preferably 60% or more, more preferably 80% or more, and particularly preferably 90% or more. Specific examples of the adjustment of the relative humidity include adjusting the water vapor partial pressure in the exhaust gas, or washing the activated carbon catalyst for flue gas desulfurization with water or a sulfuric acid aqueous solution.

  As the temperature control device and the humidity control device used in the temperature / humidity control step 3, those according to the object of the present invention can be used from known devices.

  In the exhaust gas desulfurization method of the present invention, as shown in FIG. 2, a bypass line 4 for the desulfurization step 2 can be provided. Thereby, even when the hydrogen sulfide concentration in the exhaust gas to be introduced into the desulfurization step 2 exceeds 50 ppm by volume, preferably even when it exceeds 10 ppm by volume, the exhaust gas is introduced into the bypass line 4 to Can be prevented from entering the desulfurization step 2. Such a bypass line 4 is preferably branched from between the temperature / humidity control step 3 and the desulfurization step 2. The bypass line 4 can be branched from between the hydrogen sulfide concentration adjusting step 1 and the temperature / humidity controlling step 3.

  Hereinafter, the present invention will be specifically described by way of examples.

Reference example 1
To 90 parts by weight of granular activated carbon (manufactured by Takeda Pharmaceutical Co., Ltd.), a polytetrafluoroethylene aqueous dispersion (resin solid content: 60% by weight) (manufactured by Daikin Industries) is mixed to a solid content concentration of 10 parts by weight, After kneading using a pressure kneader, a flat sheet having a thickness of 0.8 mm was prepared using a roll. Half of the flat sheet was processed into a corrugated shape with a gear-shaped roll, and laminated with the flat sheet to obtain a honeycomb-shaped activated carbon catalyst for flue gas desulfurization.

The obtained honeycomb-shaped activated carbon catalyst for flue gas desulfurization 0.001 m ³ was packed in a catalyst packed tower having a cross section of 50 mm square to form a catalyst layer. For this catalyst layer, a simulated exhaust gas at 50 ° C. consisting of 1000 vol ppm of sulfurous acid gas not containing hydrogen sulfide gas, 5 vol% oxygen concentration, 10 vol% carbon dioxide, 98% humidity at a flow rate of 1 m ³ / hr It was desulfurized by passing through for a time. The desulfurization rate was stable at 95% over 1000 hours.

Example 1
As in Reference Example 1, simulated exhaust gas under the same conditions as in Reference Example 1, except that the activated carbon catalyst for flue gas desulfurization is packed in the square catalyst packed tower and the catalyst layer contains hydrogen sulfide gas at the concentration shown in Table 1. The desulfurization performance after 1000 hours of passing gas was measured. The results are shown in Table 1 and plotted in FIG.

  As is apparent from Table 1 and FIG. 3, it can be seen that a high desulfurization rate can be maintained if the hydrogen sulfide gas is 50 ppm by volume or less.

Example 2
The oxygen concentration of the furnace outlet gas is set to 2.5% by volume, the furnace gas temperature near the furnace outlet is set as shown in Table 2, and hydrogen sulfide gas is placed near the burner of the combustion furnace where methane is burned by the burner. A simulated exhaust gas containing 10% by volume was introduced, the concentration of hydrogen sulfide contained in the exhaust gas at the furnace outlet at that time was measured, and the results are shown in Table 2. The residence time (design calculation) of the exhaust gas in the furnace was 0.5 seconds.

  As can be seen from Table 2, under the combustion conditions of Example 2, the furnace gas temperature was between 450 ° C. and 550 ° C. (approximately 500 ° C.) or higher, and the hydrogen sulfide concentration in the exhaust gas flow at the furnace outlet was It turns out that it falls remarkably.

Example 3
In Example 2, a part of the exhaust gas treated at a furnace gas temperature of 650 ° C. was branched, and the branched gas was treated in the same manner as in Example 1. The desulfurization rate after 1000 hours of gas passage was 94 to 95% with almost no decrease compared to the desulfurization rate immediately after gas passage.

Comparative Example 1
In Example 2, the exhaust gas was treated under the same conditions except that the furnace gas temperature was 600 ° C. and the residence time in the furnace was 0.05 seconds. At this time, the concentration of the hydrogen sulfide gas contained in the exhaust gas near the combustion furnace outlet was 140 ppm by volume.

Example 4
A simulated exhaust gas containing 1500 vol ppm of sulfurous acid gas, 100 vol ppm of hydrogen sulfide gas, and 4 vol% oxygen concentration is placed in an adsorption tower (inner diameter 50 mm, adsorption height 1000 mm) filled with iron oxide pellets (diameter 2 mm, length 3 mm). When gas was passed at a flow rate of 1 m ³ / hr, the hydrogen sulfide concentration at the outlet of the adsorption tower was 1 ppm by volume or less. When this adsorption exhausted simulated exhaust gas was desulfurized in the same manner as in Example 1, the desulfurization rate after 1000 hours of passing gas was 95%, just after the passing of gas. In addition, the exchange of iron oxide pellets was performed in a timely manner when the gas was passed for 1000 hours.

Example 5
A simulated exhaust gas containing 2000 ppm by volume of sulfurous acid gas and 100 ppm by volume of hydrogen sulfide gas is passed through an absorption tower filled with a resin filler (Terraret, Nippon Steel Corporation) at a flow rate of 1 m ³ / h for absorption. An aqueous NaOH solution controlled to pH 7-8 was allowed to flow from the top of the column to wash it. As a result, the concentration of sulfurous acid gas at the outlet of the absorption tower was 1200 to 1400 ppm by volume, and the concentration of hydrogen sulfide gas was 30 to 40 ppm by volume. When this absorption-treated simulated exhaust gas was desulfurized in the same manner as in Example 1, sulfurous acid gas could be removed to 60 to 80 ppm by volume.

Example 6
Similar to Reference Example 1, a square catalyst packed tower is packed with an activated carbon catalyst for flue gas desulfurization, and the catalyst layer contains water having a concentration shown in Table 3 at 50 vol ppm of hydrogen sulfide gas. The simulated exhaust gas was passed under the same conditions as in Example 1, and the desulfurization performance after 1000 hours of gas passage was measured. The results are shown in Table 3 and plotted in FIG.

  As is apparent from Table 3 and FIG. 4, it can be seen that a high desulfurization rate can be maintained when the relative humidity is 60% or more, preferably 80% or more.

  According to the exhaust gas desulfurization method of the present invention, when the sulfurous acid gas in the exhaust gas in which hydrogen sulfide gas may be mixed is removed as sulfuric acid and recovered, the activated carbon catalyst for flue gas desulfurization is poisoned with hydrogen sulfide gas. However, sulfurous acid gas can be removed stably over a long period of time.

It is a flowchart of the exhaust gas desulfurization method of this invention. It is a flowchart of another aspect of the exhaust gas desulfurization method of this invention. FIG. 3 is a graph showing the relationship between the hydrogen sulfide concentration and the desulfurization rate of exhaust gas passed through the activated carbon catalyst for flue gas desulfurization in Example 1. It is a related figure of the relative humidity of the waste gas which passed the activated carbon catalyst for flue gas desulfurization in Example 6, and a desulfurization rate.

Explanation of symbols

1 Hydrogen sulfide concentration adjustment process 2 Desulfurization process 3 Temperature / humidity control process 4 Bypass line

Claims (14)

  In an exhaust gas desulfurization method having a desulfurization step of recovering sulfur dioxide gas in exhaust gas as sulfuric acid by contacting exhaust gas containing sulfurous acid gas, moisture and oxygen with an activated carbon catalyst for flue gas desulfurization, the concentration of hydrogen sulfide gas in the exhaust gas When the amount exceeds 50 ppm by volume, the exhaust gas desulfurization method is characterized by having a hydrogen sulfide concentration adjusting step for setting the hydrogen sulfide concentration in the exhaust gas to 50 ppm by volume or less before the desulfurization step.   The exhaust gas desulfurization method according to claim 1, wherein the hydrogen sulfide concentration is adjusted to 10 ppm by volume or less in the hydrogen sulfide concentration adjusting step.   The hydrogen sulfide concentration of the exhaust gas is measured before the hydrogen sulfide concentration adjustment step, between the hydrogen sulfide concentration adjustment step and the desulfurization step, or after the desulfurization step, and the hydrogen sulfide concentration of the exhaust gas introduced into the desulfurization step is 50 ppm by volume. The exhaust gas desulfurization method according to claim 1 or 2, wherein the processing conditions of the hydrogen sulfide concentration adjusting step are controlled so as to be as follows.   The exhaust gas desulfurization method according to claim 3, wherein the treatment conditions of the hydrogen sulfide concentration adjustment step are controlled so that the hydrogen sulfide concentration of the exhaust gas introduced into the desulfurization step is 10 ppm by volume or less.   5. A temperature / humidity control step for controlling the temperature of exhaust gas introduced into the desulfurization step to 100 ° C. or less and the relative humidity to 60% or more between the hydrogen sulfide concentration adjustment step and the desulfurization step. The exhaust gas desulfurization method according to any one of the above.   The exhaust gas according to any one of claims 1 to 5, further comprising a bypass line for the desulfurization step, wherein the exhaust gas is introduced into the bypass line when the hydrogen sulfide concentration in the exhaust gas to be introduced into the desulfurization step exceeds 50 ppm by volume. Desulfurization method.   The exhaust gas desulfurization method according to claim 6, wherein the exhaust gas is introduced into the bypass line when the concentration of hydrogen sulfide in the exhaust gas to be introduced into the desulfurization step exceeds 10 ppm by volume.   The exhaust gas desulfurization method according to any one of claims 1 to 7, wherein in the hydrogen sulfide concentration adjusting step, the hydrogen sulfide gas is burnt and oxidized into sulfurous acid gas in a combustion furnace in the presence of oxygen.   The exhaust gas desulfurization method according to claim 8, wherein hydrogen sulfide gas is oxidized into sulfurous acid gas in a combustion furnace in the presence of oxygen under conditions of a temperature of 300 ° C to 1000 ° C and a residence time of 0.1 to 5.0 seconds.   The exhaust gas desulfurization method according to claim 9, wherein control is performed to increase the temperature of the combustion furnace in the presence of oxygen as the concentration of hydrogen sulfide in the exhaust gas to be introduced into the combustion furnace increases.   In the hydrogen sulfide concentration adjusting step, the hydrogen sulfide gas is adsorbed and removed by bringing the exhaust gas into contact with an iron-based adsorbent capable of adsorbing hydrogen sulfide gas, activated carbon, or an impregnated activated carbon containing an oxidizing agent or an alkali compound. The exhaust gas desulfurization method according to any one of claims 1 to 7.   In the hydrogen sulfide concentration adjusting step, hydrogen sulfide gas is obtained by contacting exhaust gas with an absorbing solution capable of absorbing hydrogen sulfide gas containing at least an iron-based compound, an alkali compound, an oxidation absorbent, and / or an amine compound. The exhaust gas desulfurization method according to any one of claims 1 to 7, wherein absorption and removal are performed.   The exhaust gas desulfurization method according to any one of claims 1 to 7, wherein in the hydrogen sulfide concentration adjusting step, exhaust gas is brought into contact with an oxidation catalyst in the presence of oxygen to oxidize hydrogen sulfide gas to sulfurous acid gas. The exhaust gas desulfurization method according to any one of claims 1 to 13, wherein the activated carbon catalyst for flue gas desulfurization includes fibrous activated carbon, granular activated carbon, activated carbon processed using these as raw materials, and a reinforcing material.

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