JPH0433492B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for regenerating a carbonaceous adsorbent that has been inactivated and used in an apparatus for dry desulfurization or dry denitrification of combustion exhaust gas. More specifically, the present invention relates to a method that can stably regenerate a carbonaceous adsorbent without any trouble even when the carbonaceous adsorbent that has been exhausted and inactivated has adsorbed a halogen component. [Prior art and its problems] A dry flue gas treatment method in which ammonia is injected and mixed into exhaust gas containing sulfur oxides, nitrogen oxides, and hydrogen halides, and this gas is brought into contact with a carbonaceous adsorbent such as activated carbon. is sulfur oxide from exhaust gas,
It has the advantage of being able to remove nitrogen oxides and hydrogen halides at the same time. In this case, sulfur oxides in the exhaust gas are adsorbed as sulfuric acid or its ammonium salt, and hydrogen halides are adsorbed as ammonium halides, respectively, while nitrogen oxides react with ammonia due to the catalytic action of the adsorbent, resulting in nitrogen and is converted into water. When an adsorbent comes into contact with exhaust gas for a long period of time, the above-mentioned sulfuric acid and ammonium salts accumulate on the surface of the adsorbent, so that it becomes gradually inactivated. but,
This inactivated adsorbent can be regenerated by heating it, and the regenerated adsorbent can be used again for the non-smoke treatment described above. When the inactivated adsorbent is heated and regenerated, high-concentration sulfur dioxide gas is produced as a by-product, and sulfuric acid, elemental sulfur, and the like can also be recovered from this gas. By the way, a common method for regenerating carbonaceous adsorbents that have been exhausted and inactivated during flue gas treatment is to heat the adsorbents in an inert gas atmosphere.One preferred example of such a regeneration method is This was proposed in Patent No. 1315878 (Special Publication No. 60-37047). The regeneration method of this patent involves mixing an inert adsorbent with an inert gas and heating the mixture by flowing the mixture downward into a heating zone while indirectly exchanging heat with the heating gas flowing upward through the zone. The desorbed substances that leave the inactivated adsorbent due to this heating are purged with an inert gas in the mixture, and in the separation area located below the heating area, the desorbed substances are regenerated with the inert gas containing the desorbed substances. This separates the adsorbent from the adsorbent. According to this regeneration method, the desorbed material from the inactivated adsorbent is purged with an inert gas flowing in parallel with the adsorbent and moves to a higher temperature side, so hydrogen halide is contained in the desorbed material. Even in the case where the regenerator is used, there is no fear that the regenerator will be clogged by the formation of ammonium halides, and there is no risk of corrosion.
However, this regeneration method has the disadvantage that a relatively high concentration of ammonia is mixed in the desorbed product-containing inert gas separated from the regenerated adsorbent. Incidentally, as mentioned above, the above-mentioned inert gas containing desorbed products, which is produced as a by-product during thermal regeneration of the inactivated adsorbent, is normally subjected to a sulfuric acid or elemental sulfur recovery process. If ammonia is present in the gas, it is troublesome that the ammonia in the gas must be removed by washing with water or the like before recovering sulfuric acid or elemental sulfur. Patent No. 1313219 (Special Publication No. 60-34413)
While the inactivated adsorbent is flowing down in two moving beds, upper and lower, the inactivated adsorbent and the first gas stream are brought into contact with each other at a temperature of about 150 to 350°C in the upper moving bed to remove SO in the first gas stream. By trapping ₃ and ammonia in the inactivated adsorbent, highly concentrated sulfur dioxide gas that does not substantially contain _{SO 3 and} ammonia is recovered. The adsorbent is transferred to a moving bed and regenerated by contacting it with an inert gas at an elevated temperature of about 300 to 650°C, and SO ₂ , SO ₃ and ammonia, etc., which are desorbed from the adsorbent during regeneration, are entrained in the inert gas. , discloses a method for regenerating inactivated adsorbent which is fed to the upper moving bed as the first gas stream. One of the aims of this method is to capture SO ₃ and ammonia desorbed from the inactivated adsorbent in the lower moving bed into the inactivated adsorbent in the upper moving bed. The purpose of this method is to prevent SO ₃ and ammonia from being mixed into the high-concentration sulfur dioxide gas that is generated. However, when this method is applied to regenerating inactivated adsorbents containing halogen components, it may cause clogging of the regenerator or Corrosion must be a concern. This is because if the inactivated adsorbent contains a halogen component, the hydrogen halide will be desorbed during heating and regeneration of the inactivated adsorbent, so naturally the first gas flow will contain hydrogen halide. are also mixed. This first gas stream is brought into contact with the inactivated adsorbent in the upper moving bed at a temperature of about 150 to 350°C, but the temperature of the inactivated adsorbent used for regeneration is generally about 90 to 110°C. Therefore, in the upper moving bed, a temperature region that is higher than the set temperature tends to occur in some parts, and when this occurs, the hydrogen halide in the first gas stream reacts with ammonia to generate ammonium halide, which can clog the regenerator. Otherwise, it may cause corrosion. JP-A No. 62-23440 also proposes a method for regenerating inactivated adsorbents that can obtain sulfur dioxide-containing gas, which is produced as a by-product during heating and regeneration of inactivated adsorbents, without ammonia being mixed therein. has been done. In this method, the inactivated adsorbent is passed downward to the heated side of the heat exchange area, and the inactivated adsorbent is heated and regenerated by indirect heat exchange with the heated gas flowing upward in the heated side of the area. The adsorbent is caused to flow down into the inert gas introduction area located below the heat exchange area, and the inert gas supplied to this area purges the desorbed substances from the adsorbent, and the inert gas accompanied by the desorbed substances is removed. The method is characterized in that the active gas is raised on the heated side of the heat exchange region, and the inert gas accompanied by desorbed products is separated from the adsorbent in the separation region located above the heat exchange region. However, when this method is applied to the regeneration of an inactivated adsorbent containing a halogen component, as in the case of the regeneration method described in the previous patent No. 1313219,
There is concern about blockage or corrosion of the regenerator due to the formation of ammonium halides.
In other words, in the regeneration method of JP-A No. 62-23440, the inert gas containing desorbed substances from the adsorbent is separated from the adsorbent by moving it to the separation area where the temperature is lower. This is because the hydrogen halide and ammonia in the gas react again and tend to generate ammonium halide. In other words, in a method for regenerating an inactivated adsorbent used to treat combustion exhaust gas containing hydrogen halides, inert gas containing desorbed products from the inactivated adsorbent is transferred to a relatively high temperature side. If the inert gas is separated from the adsorbent, there is no need to worry about clogging or corrosion of the regenerator caused by the formation of ammonium halides, but a large amount of ammonia (several thousand to tens of thousands of ppm) will be entrained in the inert gas. There is a drawback that it can be done. On the other hand, if the inert gas containing desorbed products from the inactivated adsorbent is separated from the adsorbent at a relatively low temperature, the amount of ammonia accompanying this gas can be reduced. However, it is not possible to sufficiently suppress the production of ammonium halides that cause blockage or corrosion of the regenerator. Therefore, an object of the present invention is to regenerate the inactivated adsorbent stably without worrying about clogging or corrosion of the equipment, even if the inactivated adsorbent to be regenerated contains a halogen component. The object of the present invention is to provide a method for regenerating an inactivated adsorbent, which can also maintain the amount of ammonia in the desorbed inert gas by-produced during regeneration at a low level of about 500 ppm or less. [Means for Solving the Problems] The method of the present invention is a method for regenerating a carbonaceous adsorbent that has been inactivated by being used in a dry flue gas treatment method. Flowing downward into the heated side of the zone, the inactivated adsorbent is preheated by indirect heat exchange with the heated gas flowing on the heated side of this zone, and the inactivated adsorbent is transferred below the first heat exchange zone. The inactivated adsorbent is made to flow down through a separation region located at After heating and regenerating the adsorbent, the inert adsorbent is transferred to the inert gas introduction area located below the second heat exchange area, and the inert gas introduced into this area removes the desorbed substances generated during the heating regeneration of the inert adsorbent. While purging, the regenerated adsorbent is taken out from the lower part of the inert gas introduction region, and the inert gas with desorbed products is guided to the separation region by raising the heated side of the second heat exchange region, where it is desorbed. It is characterized by the separation of inert gases accompanied by substances from inert adsorbents. A specific example of the present invention will be explained in more detail with reference to _FIG . supplied within. This inactivated adsorbent passes through the storage area 2 and flows down to the first heat exchange area 3. In this heat exchange area, a plurality of heat transfer tubes 4 are arranged almost vertically, and the inactivated adsorbent flows down into the first heat exchange area 3. In other words, it flows down the inside of the heat exchanger tube, using the heated side of the first heat exchange area 3 as a moving bed. On the other hand, the heated gas supplied from the line 5 is allowed to pass upward through the heating side of this heat exchange region, that is, the outside of the heat transfer tube, so that the inactivated adsorbent flowing down inside the heat transfer tube 4 is mixed with this heated gas. preheated to approximately 150-220°C by indirect heat exchange. The preheated inactivated adsorbent is then transferred to separation zone 6
and flows down to the second heat exchange area 7. In this region, like the first heat exchange region, a plurality of heat exchanger tubes 8 are arranged substantially vertically, and the inactivated adsorbent flows down as a moving bed inside the heat exchanger tubes. On the other hand, since the heated gas supplied from the line 9 is allowed to pass upwardly to the outside of the heat transfer tube 8, that is, to the heating side of the second heat exchange area, by indirect heat exchange with this heated gas, The inactivated adsorbent within the tube is heated to a regeneration temperature of approximately 350-500°C. Therefore, the inactivated adsorbent is regenerated by releasing SO ₂ , SO ₃ , hydrogen halide, ammonia, etc. while flowing down the pipe, and moves to the inert gas introduction region 10 . Line 1 in area 10
Inert gas is supplied from 1, and this inert gas is
Separation in which desorbed substances such as SO ₂ , SO ₃ , hydrogen halides, and ammonia are purged from the adsorbent, and they rise in the heat exchanger tube 8 while being accompanied by them, and the inactivated adsorbent remains at about 150 to 220°C. After being supplied to the region 6, it is taken out from the apparatus through a line 12. In addition, if the gas that has risen to the separation region 3 along with the desorbed materials enters the storage region 2 through the heat transfer tube 4,
There is a concern that the regenerator will corrode due to dew condensation, etc., but in such a case, the flow regulator 13 installed in the storage area 2
By additionally supplying an inert gas from the line 14 in the vicinity of the inert gas, it is possible to prevent gases accompanied by desorbed products from entering the storage region. The regenerated adsorbent freed from the desorbed material in the inert gas introduction zone 10 flows down to the cooling zone 15, where it is cooled by indirect heat exchange with a suitable coolant and then removed via valve _V2 . , reused for flue gas treatment. [Operation] The most important feature of the method of the present invention is that the inert gas containing the desorbed product from the inactivated adsorbent is removed in the separation region located between the first heat exchange region and the second heat exchange region. at the point where it is separated from the adsorbent. As is clear from the above, the temperature in the area where the inert gas containing desorbed products is separated from the adsorbent is set to prevent clogging and corrosion of the regenerator and to reduce the amount of ammonia in the inert gas containing desorbed products. Although this is an important factor in keeping the temperature to a low level, the present inventors have determined that the temperature of the separation region is 150 to 220°C, preferably 170 to 190°C.
It was confirmed that the intended purpose could be achieved by maintaining the temperature within the range of ℃. According to the method of the invention, the inactivated adsorbent is preheated to 150-220°C, preferably 170-190°C in the first heat exchange zone, and then flows down into the second heat exchange zone after passing through the separation zone; Here it is heated to a regeneration temperature of 350-500°C. This heating inactivates the sulfuric acid in the adsorbent,
Ammonium sulfate, ammonium halides, etc. are decomposed according to the following formula and desorbed from the adsorbent. 2H ₂ SO ₄ +C→2SO ₂ +CO ₂ +2H ₂ O (1) 3NH ₄ HSO ₄ →NH ₃ +3SO ₂ +N ₂ +6H ₂ O (2) 3(NH ₄ ) ₂ SO ₄ →4NH ₃ +3SO ₂ +N ₂ +6H ₂ O ( ₃ ) NH ₄
It is thought that it is partially converted to nitrogen in the reaction according to the following. 2NH ₃ +3(0)→N ₂ +3H ₂ O (5) The adsorbent that has flowed down from the second heat exchange area to the inert gas introduction area is purged from the desorbed material by the inert gas introduced into this area. is removed from the bottom of the regenerator via a cooling area. Since this adsorbent has recovered its adsorption capacity, it can be used again for flue gas treatment. On the other hand, the desorbed material from the inactivated adsorbent ascends through the second heat exchange region accompanied by the inert gas and reaches the separation region, but this region is separated from the first heat exchange region and the second heat exchange region. Because the temperature is between 150 and 220 degrees Celsius, the temperature does not exceed 150 to 220 degrees Celsius. Therefore, the ammonia that has reached this separation zone reacts with the sulfuric acid in the inactivated adsorbent flowing down from the first heat exchange zone according to the following formula, and a part of it is absorbed by the inactivated adsorbent. NH ₃ + H ₂ SO ₄ →NH ₄ HSO ₄ NH ₄ HSO ₄ +NH ₃ → (NH ₄ ) ₂ SO ₄ . Incidentally, FIG. 2 is a graph showing the relationship between the temperature of the separation region and the ammonia concentration in the gas discharged from the region to the outside of the system, and as is clear from this graph, as long as the method of the present invention is followed,
The ammonia concentration in the gas in the separation region can be maintained within a range of 500 ppm, which does not pose a practical problem. Regarding hydrogen halide in the gas in the separation region, in general, in the heating regeneration method of inert adsorbent, the concentration of hydrogen halide contained in the inert gas used for purging is Although it varies depending on the hydrogen halide concentration present in the gas, the flue gas treatment equipment, etc., it is in the range of several thousand to tens of thousands of ppm. The relationship between the theoretical equilibrium temperature of the reaction in which ammonium chloride is produced from hydrogen halide, typically hydrogen chloride, and ammonia, and the production rate of ammonium chloride is as shown in Figure 3. As the concentration decreases, the production rate of ammonium chloride increases. However, according to the regeneration method of the present invention, the ammonia concentration in the gas phase of the separation region is maintained within a range of about 500 ppm or less, as described above.
Moreover, the temperature of the separation region is preferably 150 to 220℃.
Since the temperature is maintained in the range of 170 to 190°C, the ammonium chloride produced in this region is at most only a few percent of the ammonia in the gas. Therefore, blockage and corrosion of the regenerator due to large amounts of ammonium halides produced in the separation area can be avoided.
This can be substantially avoided with the present invention. [Example] A regenerator configured as shown in Fig. 1 was incorporated into a 3000Nm ³ /hr boiler exhaust gas treatment device, activated carbon was circulated through the system at a rate of 65Kg/hr, and the lower end of the second heat exchange area 7 was heated. The temperature of the activated carbon was maintained at 390° C., and the amount of inert gas supplied to lines 11 and 14 was maintained at a total of 10 Nm ³ /hr to carry out long-term operation of the flue gas treatment device and regeneration device. In this case, in cases 1 and 2, the first heat exchange area 3
Stop the supply of heating gas to the inactivated activated carbon passing through and set the temperature of the inactivated activated carbon to 90°C.
In steps 4, 5, and 6, heating gas is supplied to the first heat exchange area 3, and the inactivated activated carbon is heated to 140°C, 150°C, and 150°C, respectively.
Preheated to 170℃, 190℃, and 220℃. In Cases 1 and 2, the internal pressure in the second heat exchange area rose sharply after about one month and about two months, respectively, causing problems with operation.As a result of stopping operation and conducting an open inspection of the separation area, the problem occurred. Blockage due to large amounts of ammonium chloride crystal precipitation was observed in the area and gas outlet line. In Case 3, when the separation area was inspected after about two months, it was found that the ammonium chloride precipitation in this area was not large enough to cause any problems in operation. No abnormality was found in case 4 when the separated area was opened and inspected after about 3 months, and cases 5 and 6 after about 1 month. In each of the above cases, the analysis results of the gas discharged from the separation zone are shown in sequence along with the preheating temperature of the inactivated activated carbon.

[Table] [Effects of the Invention] In the present invention, the components desorbed from the inactivated adsorbent during heating regeneration of the inactivated adsorbent are entrained in the inert gas to raise the second heat exchange region, and the second heat exchange region is raised. Since the desorption-containing inert gas is separated from the adsorbent in the separation zone located above the first heat exchange zone and below the first heat exchange zone, the generation of ammonium halide in this zone is minimized. Therefore, blockage or corrosion of the regenerator due to overproduction of ammonium halide can be avoided. In addition, in the method of the present invention, some of the ammonia desorbed from the inactivated adsorbent in the second heat exchange area is captured by the inactivated adsorbent in the separation area, so it is removed from the system from the separation area. The concentration of ammonia in the gas emitted can also be kept low.

[Brief explanation of drawings]

FIG. 1 is a longitudinal sectional view of a regeneration device suitable for carrying out the method of the invention. FIG. 2 is a graph showing the relationship between the separation region temperature and the ammonia concentration in the gas discharged from the region. FIG. 3 is a graph showing the relationship between the theoretical equilibrium temperature of the reaction in which ammonium chloride is produced from hydrogen chloride and ammonia and the production rate of ammonium chloride. DESCRIPTION OF SYMBOLS 1... Regenerator, 2... Storage area, 3... First heat exchange area, 4... Heat exchanger tube, 6... Separation area, 7...
...Second heat exchange region, 8...Heat transfer tube, 10...Inert gas introduction region, 13...Regulating fluid, 15...Cooling region.

Claims (1)

[Claims] 1. In a method for regenerating a carbonaceous adsorbent that has been inactivated by being used in a dry flue gas treatment method, heating the first heat exchange area while flowing the inactivated adsorbent downward to the heated side of the first heat exchange area. The inactivated adsorbent is preheated by indirect heat exchange with a heated gas flowing along the side, and the inactivated adsorbent is transferred via a separation zone located below the first heat exchange zone to a second heat exchange zone located below it. After the inactivated adsorbent is heated and regenerated by indirect heat exchange with the heated gas flowing downward to the heated side of the heat exchange area and flowing upward on the heating side of this area, the inactivated adsorbent is placed below the second heat exchange area. The regenerated adsorbent is transferred from the lower part of the inert gas introduction area to the inert gas introduction area, and the inert gas introduced into this area purges the desorbed substances generated during heating and regeneration of the inactivated adsorbent. The inert gas accompanied by the desorbed product is guided to the separation region by raising the heated side of the second heat exchange region, where the inert gas accompanied by the desorbed product is separated from the inert adsorbent. A method for regenerating an inactivated adsorbent, characterized by: