JP2020025934A - Regeneration method of adsorbent for exhaust gas treatment - Google Patents

Abstract

To provide a regeneration method of adsorbent for exhaust gas treatment which is efficient for effectively preventing corrosion deterioration of a heat transfer pipe existing on a heating part and a cooling part of a regenerating column.SOLUTION: In such a regeneration method of adsorbent that the adsorbent discharged from an adsorption column is conveyed to a regeneration column composed of a multi-tube heat exchanger structure and is heated, thereby, a substance regulated by a law such as Clean Air Act is decomposed and removed, at the same time, is cooled and is regenerated and, thereafter, the adsorbent after regeneration is flowed back to the adsorption column and is used again, upon cooling after heating regeneration of the adsorbent on the regeneration column, temperature of the regeneration adsorbent on an outlet part of the regeneration column cooling part is regulated into a temperature range capable of avoiding a sulfuric acid dew point corrosion region by regulating a cooling air quantity.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a regeneration method that is effective for heating and regenerating an adsorbent that has adsorbed a substance regulated by laws such as the Air Pollution Control Law such as sulfur oxides (SOx) in exhaust gas and reusing it.

  For example, sintering exhaust gas generated during the production (sintering) of sinter ore may contain many substances regulated by laws such as the Air Pollution Control Law such as sulfur oxides (SOx). Are known. Conventionally, as a method of treating such exhaust gas, the exhaust gas is introduced into an adsorption tower filled with a granular adsorbent, and the exhaust gas is brought into contact with the adsorbent to be regulated by laws such as the Air Pollution Control Law. While adsorbing and removing the substances to be used, the used adsorbent is led to a regeneration tower to be heated and regenerated, and then the regenerated and cooled adsorbent is circulated again to the adsorption tower and reused. Processing techniques are known. (See Patent Document 1)

  The technology of adsorbing and removing substances regulated by laws such as the Air Pollution Control Law mentioned above is based on the fact that adsorbents such as activated carbon and activated coke filled in a moving bed reactor are packed in a reactor (adsorption tower). When the exhaust gas flowing counter-currently contacts the packed bed of adsorbent while moving downward from above while forming a substance, the adsorbent adsorbs substances regulated by laws and regulations such as the Air Pollution Control Law. It is a method of removing by removing.

  In this technique, sulfuric acid and the like are gradually accumulated in the adsorbent due to contact with exhaust gas, and the ability to remove (desulfurize) the adsorbent gradually decreases with time. Therefore, it is necessary to regenerate the adsorbent. That is, the adsorbent, whose desulfurization capacity has temporarily decreased, is conveyed to a regeneration tower mainly comprising a heating section and a cooling section having, for example, a multi-tubular heat exchanger structure, and from above to below (from the heating section to the cooling section). The heat is regenerated and cooled in the process of moving to the adsorption tower.

  The adsorbent (activated coke) that has undergone such a heat treatment for regeneration is generally cooled to a temperature of about 50 ° C., and then discharged from the bottom of the regeneration tower (lower end of the cooling unit), and then re-moved. It is returned to the top of the adsorption tower composed of a bed reactor or the like and is provided for recycling. As described above, when circulating and recycling the adsorbent for exhaust gas treatment, some of the adsorbent may be powdered when performing the regeneration treatment, but these are difficult to reuse in the packed bed. Therefore, it is separated and removed together with dust by a process such as sieving.

  The prior art described above is an exhaust gas treatment for adsorbing and removing substances regulated by laws and regulations such as the Air Pollution Control Law in an adsorption tower. Is recycled in the regeneration tower and recycled for recycling, so that the exhaust gas treatment can be performed efficiently.

JP 2007-83222A (Section 2-7, FIG. 1)

  In the above-described conventional technology, substances regulated by laws and regulations such as the Air Pollution Control Law, such as sulfuric acid, adsorbed on the adsorbent are decomposed and removed in the heating section when introduced into the regeneration tower. On the other hand, after the adsorbent is regenerated by heating, when cooled in the cooling section and sent to the adsorption tower, the adsorbent is controlled to have a temperature of about 50 ° C. for circulation reuse. I have. However, such temperature control causes, for example, the SOx gas to be quickly changed to sulfuric acid, and particularly to the corrosion and deterioration of the heat transfer tube itself of the multi-tube heat exchanger in the cooling section and the heating section, and eventually the hole is broken. In addition, there is a problem that the adsorbent is chemically consumed and the adsorption capacity is reduced.

  Therefore, an object of the present invention is to propose a new technique of a method for regenerating an adsorbent for removing substances regulated by laws and regulations such as the Air Pollution Control Act, which can solve the above-mentioned problems of the prior art. is there.

  In order to solve the problems of the related art (Reference 1) related to the present invention and to achieve the object, the inventor has arrived at the present invention according to the following gist configuration. That is, in the present invention, an exhaust gas from a steel mill containing a substance regulated by laws and regulations such as the Air Pollution Control Act is first filled with an adsorbent for removing substances regulated by laws and regulations such as the Air Pollution Control Act. Introduced into the adsorption tower to adsorb substances regulated by laws and regulations such as the Air Pollution Control Law in the exhaust gas, and then discharge the adsorbent discharged from the adsorption tower from the multi-tube heat exchanger structure By transporting the adsorbent to a regeneration tower and heating it to decompose and remove the substances regulated by laws and regulations such as the Air Pollution Control Law, simultaneously cool and regenerate the adsorbent, and then recirculate the adsorbent after regeneration to the adsorption tower. In the method for regenerating the adsorbent, the regenerated adsorbent at the outlet of the regenerating tower cooling unit is adjusted by adjusting the amount of cooling air in cooling after heating and regenerating the adsorbent in the regenerating tower. Sulfuric acid dew point temperature A method for regenerating an exhaust gas treatment for adsorbing material and adjusting the temperature can be avoided region.

  In addition, research by the inventor has revealed that it is desirable that the temperature range of the regenerated adsorbent to avoid the sulfuric acid dew point corrosion region is a temperature of 84 ° C. or more and 120 ° C. or less.

  According to the present invention, by passing exhaust gas through an adsorption tower filled with an adsorbent, substances regulated by laws and regulations such as the Air Pollution Control Law such as sulfur oxides (SOx) in exhaust gas are adsorbed and removed. When the adsorbent thus obtained is heated and cooled for regeneration, the temperature of the adsorbent in the cooling section of the regeneration tower having the multi-tube heat exchanger structure is adjusted to a temperature at which the sulfuric acid dew point corrosion area can be avoided by adjusting the cooling air flow, for example, 84 Since the temperature is adjusted to be in the range of ≦ ° C. ≦ adsorbent temperature at the outlet of the regenerator ≦ 120 ° C., it is possible to at least prolong the service life of the heat transfer tubes constituting the multi-tube heat exchanger of the regenerator. Become like

It is an approximate line figure showing an example of an exhaust gas processing equipment. It is a figure which shows the temperature transition in the general regeneration tower cooling part estimated from the temperature of the adsorbent and cooling air at the entrance / exit of the regeneration tower cooling part. FIG. 4 is a schematic diagram illustrating a temperature measurement position in a regeneration tower cooling unit. It is a temperature transition analysis diagram in a regeneration tower cooling part when a sulfuric acid dew point corrosion area is generated. It is a temperature transition analysis diagram in a regeneration tower cooling part when cooling air volume is reduced by 25%. It is a temperature transition analysis diagram in the regeneration tower cooling part when the cooling air volume is reduced by 50%. It is a figure which shows the relationship between the amount of cooling air, and the adsorbent temperature at the outlet of a regeneration tower.

  The present invention relates to an adsorbent such as activated coke (hereinafter abbreviated as "AC") which is repeatedly circulated and used, and is provided with laws and regulations (such as the Air Pollution Control Act such as sulfur oxides (SOx) in exhaust gas from steelworks). Adsorbs various substances regulated by the Environmental Law), transports them to a regeneration tower having a multi-tube heat exchanger structure, and heats them to decompose sulfuric acid derived from sulfur oxides and remove gas. After cooling and regenerating the adsorbent after the removal, the temperature of the adsorbent to be cooled is properly controlled by controlling the amount of cooling air supplied to the cooling unit in the regeneration tower. This is a method for maintaining the temperature of the adsorbent after regeneration on the outlet side in a temperature range that can avoid the sulfuric acid dew point corrosion region. In the present invention, as the temperature range that is the sulfuric acid dew point corrosion area, in addition to the upper limit (120 ° C.), the lower limit (84 ° C.) is set and managed. Damage due to dew point corrosion can be avoided, and a longer life of the cooling unit piping (heat transfer tube) can be realized.

  FIG. 1 is a schematic diagram showing a main part of a sintering exhaust gas treatment facility using activated coke as an adsorbent. 1 is an adsorption tower 1 (upper part 1a, lower part 1b) filled with an adsorbent such as activated coke (AC) using a plurality of units in parallel, and 2 is used to heat the adsorbent. A heating unit 2a for gasifying and decomposing and removing substances regulated by laws such as the Air Pollution Control Law such as sulfur oxides adhering to the adsorbent, and a cooling unit 2b for adsorbent for reuse It is a regeneration tower.

  In addition, reference numeral 3 denotes a conveyance pipe for pneumatically feeding the adsorbent from the adsorption tower 1 to the regeneration tower 2, and reference numeral 4 circulates the adsorbent regenerated by heating and cooling from the regeneration tower 2 to the adsorption tower 1. This is a recirculation pipe for re-use.

  5 is an adsorbent hopper, 6 is a storage bin for the adsorbent, 7 is a booster, 8 is a chimney, 9 is a vibrating sieve, 10 is a powdered adsorbent hopper, and A is exhaust gas.

  Here, in the case of the heating unit 2a, deterioration of the heat transfer tube of the multi-tube heat exchanger structure constituting the heating unit 2a and the cooling unit 2b of the regeneration tower 2 is mainly caused by grain boundary cracking due to sensitization. On the other hand, in the case of the cooling part, there is no sensitization due to the low temperature, but damage (holes) due to sulfuric acid dew point corrosion.

  The adsorbent heated to a temperature of about 340 ° C. or higher during the heat regeneration in the regeneration tower 2 is gradually cooled by coming into contact with the cool air when descending in the heat transfer tube of the cooling unit 2 b, and finally is cooled. It is generally considered that the temperature at the outlet at the lower end of the heat transfer tube becomes about 50 ° C.

In the cooling unit 2b, the adsorbent (AC) generates SO ₂ gas until the adsorbent (AC) is cooled to about 230 ° C. at a point of 1.1 to 1.4 m from the top. It does not condense. However, while the temperature is cooled to an acid dew point temperature of 145 ° C. (a temperature at which sulfuric acid dew point corrosion starts), sulfuric acid is condensed on the surface of the heat transfer tube, and sulfuric acid dew point corrosion proceeds.

  Therefore, in the present invention, by adjusting the flow rate of the cooling air supplied to the cooling unit 2b heat transfer tube, the temperature of the heat transfer tube is kept from falling below the acid dew point temperature of 145 ° C, and the adsorbent is moved to the sulfuric acid dew point corrosion area. We decided not to reach. By performing such management, the temperature of the adsorbent at the outlet (at the time of discharge) of the cooling unit 2b can be set to 120 ° C. or less, which is suitable for regeneration circulation. As described above, as the temperature of the adsorbent at the outlet (at the time of discharge) of the cooling unit 2b increases, the temperature at the entrance of the adsorption tower 1 increases, and the adsorption efficiency in the adsorption tower decreases. The temperature of the adsorbent at the outlet of the cooling unit 2b (during discharge) is desirably 120 ° C. or lower because the demand for heat resistance of the material of the members constituting the reflux path 4 increases.

  According to the knowledge of the inventor, if the intended rated air volume is allowed to flow as it is without adjusting the temperature of the adsorbent at the outlet of the cooling section 2b, the sulfuric acid dew-point corrosion region cannot be reliably avoided. I understand. The reason is that the supply of the cooling air at the rated air volume does not allow the temperature of the adsorbent at the outlet of the cooling section 2b of the adsorbent to fall within a temperature range that can sufficiently avoid the sulfuric acid dew point corrosion area. Therefore, in the present invention, the temperature is finally adjusted to be higher than the conventional general temperature (about 50 ° C.) (about 84 ° C. according to the knowledge of the present inventors), whereby the transfer is performed. The temperature of the heat tube does not become too low, and the sulfuric acid dew point corrosion region can be avoided. The details will be described below.

  FIG. 2 shows the actual temperature 11 of the adsorbent (AC) at the upper end (inlet) of the cooling unit 2b and the actual temperature 12 of the cooling air from the inlet side to the outlet side with respect to the cooling section 2b of the regeneration tower 2 having the multi-tube heat exchanger structure. It is the graph which estimated temperature transition 13 of the adsorbent and temperature transition 14 of the heat exchanger tube of a heat exchanger. In this figure, the temperature 15 at which sulfur oxides (SOx) and the like volatilize from the adsorbent and the sulfuric acid dew point 16 are calculated and displayed from the environment inside the regeneration tower 2. As shown in this figure, when a region including a range 17 in which sulfur oxides and the like volatilize from the adsorbent is volatilized and a sulfuric acid dew point range 18 is defined as a sulfuric acid dew point corrosion region 19, according to studies by the inventors, the cooling unit 2b It was found that the distance from the upper end (inlet) coincided with the corrosion damage part of the actual machine.

  Then, the inventors studied a cooling method for avoiding the sulfuric acid dew point corrosion region 19 described above. In this study, in order to ensure consistency with the actual machine, the heat transfer tube temperature and the cooling air temperature of the heat exchanger shown in FIG. 3 were actually measured, and the physical property values were determined so as to match the analysis values. In FIG. 3, reference numeral 20 indicates a flow straightening plate, reference numeral 21 indicates a flow of cooling air, reference numeral 22 indicates an actual measurement location of the cooling air temperature, and reference numeral 23 indicates an actual measurement location of the adsorbent temperature.

  FIG. 4 shows the actual temperature of the adsorbent at the inlet / outlet of the cooling section 2b of the regeneration tower 2, the actual temperature of the cooling air, and the temperature of the adsorbent in the regeneration tower 2 calculated from the rated air flow rate at the rated time. It is the figure which showed transition 13 and temperature transition 14 of a heat exchanger tube. Also in this case, it was confirmed that the sulfuric acid dew point corrosion area 19 described above was generated.

  Therefore, by controlling the amount of cooling air in accordance with the method of the present invention, the respective temperature transitions 13 and 14 in the cooling section 2b in the regeneration tower 2 were controlled as shown in FIG. That is, when the cooling air flow is reduced by 25% from the rated air flow, the temperature transition 14 of the heat transfer tube is a temperature that avoids the aforementioned sulfuric acid dew point corrosion area 19 (about 1.2 m to 1.7 m as a distance from the upper end). Good results were obtained, indicating a drop. On the other hand, if the cooling air volume is reduced by 50% from the rating as shown in FIG. 6, the temperature of the adsorbent at the outlet of the regenerator cooling section 2b can be reduced from the adsorbent even in the vicinity of 1.2 m to 1.7 m. It was found that the temperature exceeded the temperature at which the sulfur oxides volatilized (230 ° C.) and became equal to or higher than the sulfuric acid dew point.

  FIG. 7 summarizes the desirable relationship between the flow rate of cooling air (input) and the temperature of the adsorbent (output) at the outlet of the regeneration tower cooling unit 2b based on the above analysis results. That is, this figure is according to the present invention when the upper limit of the temperature of the adsorbent at the outlet of the regeneration tower cooling unit 2b (120 ° C.) is 24 and the upper limit of the cooling air flow that can avoid the sulfuric acid dew point corrosion area is 25. It shows the relationship between the temperature of the adsorbent at the outlet of the cooling unit 2b and the amount of cooling air calculated by the analysis, 27 is a preferable temperature of the adsorbent at the outlet of the regenerator cooling unit 2b, and 28 is the above relationship. Is a range of a preferable cooling air flow for maintaining the cooling air flow.

  According to the present invention, in the relationship shown in FIG. 7, the amount of cooling air is controlled to control the temperature of the adsorbent that has been cooled and regenerated at the outlet of the cooling unit 2b. It turns out that managing is effective. That is, in addition to the control upper limit temperature of the sulfuric acid dew point corrosion area: 120 ° C. or less, the lower limit temperature (84 ° C.) is also controlled, so that the heat regeneration that avoids the sulfuric acid dew point corrosion area 19 shown in FIG. -Cooling can be performed, and as a result, corrosion deterioration of the heat exchanger can be prevented, and a longer life of the heat transfer tube can be realized.

  In the above description, the control value of the temperature of the adsorbent after cooling is set to the upper limit: 120 ° C. and the lower limit: 84 ° C. However, the temperature control value of the adsorbent 2 at the outlet of the cooling unit 2 b is determined from the adsorbent. Since it differs depending on the sulfuric acid dew point corrosion area 19 defined from the sulfur oxide volatilizing area 17 and the sulfuric acid dew point corrosion area 18, the temperature of the regenerated adsorbent is set to a temperature within the range avoiding the sulfuric acid dew point corrosion area. It is necessary to.

(Comparative Example 1)
In the prior art, the temperature of the adsorbent at the outlet of the regeneration tower cooling unit 2b was set to about 50 ° C. FIG. 4 shows the temperature transition of the heat transfer tube and the adsorbent in the regeneration tower cooling section. From the temperature change, it is predicted that the sulfuric acid volatilized at the position indicated by 19 in FIG. 4 will condense on the surface of the heat transfer tube and cause corrosion. When the heat transfer tube was partially sampled and its cross section was investigated, the adsorbent and The inner surface of the heat transfer tube in contact was completely corroded and reduced in thickness, and the service life was estimated to be less than 10 years.

(Example 1)
As an embodiment conforming to the present invention, first, the air volume of the cooling air supplied to the regeneration tower cooling unit (2b) is reduced by 25% from Comparative Example 1 in which the operation is performed at the rated air volume, so that the air volume at the outlet of the adsorbent is reduced. Was raised to 84 ° C. The temperature transition of the heat transfer tube and the adsorbent in the regeneration tower cooling section is as shown in FIG. In this case, the volatilization of sulfuric acid occurs in the range indicated by the line 17 of the temperature transition in FIG. 5, but since the temperature of the heat transfer tube is higher than the dew point in that range, it is predicted that corrosion due to dew condensation is suppressed. Was. Then, when the heat transfer tube was partially sampled and the cross section was examined, no corrosion of the inner surface of the heat transfer tube observed in Comparative Example 1 was observed at all, and it was found that the service life was 20 years or more.

(Example 2)
As another embodiment conforming to the present invention, the flow rate of the cooling air supplied to the regeneration tower cooling section (2b) is reduced by 50% from Comparative Example 1, which is operated at the rated flow rate, so that the outlet portion of the adsorbent is reduced. Temperature was increased to 115 ° C. The temperature transition of the heat transfer tube and the adsorbent in the regeneration tower cooling section is as shown in FIG. In this case, the volatilization of sulfuric acid occurs in the range indicated by the line 17 of the temperature transition in FIG. 6, but since the temperature of the heat transfer tube in this range is higher than the dew point, it is predicted that corrosion due to dew condensation is suppressed. Was done. Then, when the heat transfer tube was partially sampled and its cross section was examined, no corrosion of the heat transfer tube inner surface observed in Comparative Example 1 was observed at all, and it was found that the service life was 20 years or more.

  Although the present invention has been described with reference to the example of removing substances regulated by laws and regulations such as the Air Pollution Control Act from sintering machine generated exhaust gas in the above-described example, it includes sulfur oxides and the like, in addition to other exhaust gas generated in steel works. It is also effective for the treatment of other similar exhaust gas.

DESCRIPTION OF SYMBOLS 1 Adsorption tower 1a Adsorption tower upper part 1b Adsorption tower lower part 2 Regeneration tower 3 Conveyance pipeline from adsorption tower to regeneration tower 4 Recirculation pipeline from regeneration tower to adsorption tower 5 Adsorbent hopper 6 Adsorbent storage bin 7 Booster 8 Chimney 9 Vibrating sieve 10 Powder adsorbent hopper 11 Actual temperature of adsorbent 12 Actual temperature of cooling air 13 Temperature transition of adsorbent 14 Temperature transition of heat transfer tube 15 Temperature at which sulfur oxides volatilize from adsorbent 16 Sulfuric acid dew point temperature 17 Range where sulfur oxides evaporate from the adsorbent 18 Sulfuric acid dew point range of heat transfer tube 19 Sulfuric acid dew point corrosion area 20 Rectifier plate 21 Cooling air flow 22 Cooling air temperature actual measurement point 23 Adsorbent temperature actual measurement point 24 Upper limit of regenerator outlet adsorbent temperature Value 25 Upper limit of air volume that can avoid sulfuric acid dew point corrosion area 26 Relationship calculated by analysis 27 Adsorbent temperature range at cooling tower outlet of regeneration tower 28 Adsorbent temperature range Cooling air volume range A flue gas to protect

Claims (2)

Emissions from steelworks containing substances regulated by laws such as the Air Pollution Control Act,
First, the substance is introduced into an adsorption tower that is filled with an adsorbent for removing substances regulated by laws such as the Air Pollution Control Law, and the substances regulated by laws such as the Air Pollution Control Law in the exhaust gas are introduced. Adsorb,
Next, the adsorbent discharged from the adsorption tower is conveyed to a regeneration tower having a multitubular heat exchanger structure and heated to decompose and remove substances regulated by laws and regulations such as the Air Pollution Control Act. Simultaneously cool and regenerate,
Thereafter, in the method for regenerating an adsorbent, the regenerated adsorbent is recirculated to the adsorption tower and used again.
In cooling after heating and regeneration of the adsorbent in the regeneration tower, the temperature of the regeneration adsorbent at the outlet of the regeneration tower cooling unit is adjusted to a temperature range that can avoid the sulfuric acid dew point corrosion region by adjusting the amount of cooling air. A method for regenerating an adsorbent for exhaust gas treatment, characterized by comprising:   2. The method for regenerating an adsorbent for exhaust gas treatment according to claim 1, wherein the temperature of the regenerated adsorbent is 84 ° C. or more and 120 ° C. or less, which is a temperature range in which a sulfuric acid dew point corrosion region can be avoided.

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