JPH08257366A - Regeneration of used carbonaceous catalyst - Google Patents

Abstract

PURPOSE: To improve the desulfurizing and denitrating performance of a regenerated catalyst by adding ammonia to an inert gas which is to be supplied to an inert gas introducing region and utilized in the case of regeneration of used carbonaceous catalyst, e.g. activated carbon used for a dry desulfurizing and denitrating process to purify exhaust gas from a boiler. CONSTITUTION: After ammonia gas is introduced to an inlet of a cross-flow type fluidized-bed reactor R, exhaust gas from a boiler is introduced to the reactor R and sulfur oxides in the gas are absorbed as sulfuric acid and ammonium sulfate in a carbonaceous catalyst C. Meanwhile, nitrogen oxides in the exhaust gas are reduced to nitrogen gas by reduction reactions. After that, in the case used carbonaceous catalyst C is regenerated, the catalyst C is supplied to a regenerating apparatus 1 by a valve V1 , flows down in a thermally conductive tube 5..., and is heated by a heated gas 6 to release desorbed substances, e.g. sulfur dioxide, hydrogen chloride, and ammonia, and the desorbed substances are parted from the catalyst C by an inert gas 8 containing ammonia and discharged out of a line 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for regenerating an activated carbonaceous catalyst such as activated carbon or activated coke used in a dry desulfurization denitration method for combustion exhaust gas from a boiler or the like.

[0002]

2. Description of the Related Art A dry desulfurization denitration method in which ammonia is injected and mixed into exhaust gas from a boiler or the like containing sulfur oxides and nitrogen oxides and the mixture is brought into contact with a carbonaceous catalyst such as activated carbon or activated coke is a method of oxidizing sulfur from exhaust gas. It has an advantage that the substance and the nitrogen oxide can be removed simultaneously. In this case, the sulfur oxides in the exhaust gas are adsorbed on the carbonaceous catalyst as sulfuric acid, acidic ammonium sulfate, ammonium sulfate and the like. On the other hand, nitrogen oxides are decomposed into nitrogen and water by the action of ammonia as a reducing agent. Therefore, the carbonaceous catalyst used in the dry desulfurization and denitration method gradually inactivates due to the accumulation of sulfuric acid or sulfate on the catalyst surface as the contact time with the exhaust gas elapses, but the carbon thus inactivated. The quality catalyst can be reused for the above-mentioned exhaust gas treatment if it is heated and regenerated at an appropriate time. It is well known that a relatively high concentration of sulfur dioxide gas is obtained during this heating regeneration, and sulfuric acid, sulfur, gypsum, etc. can be recovered from this gas.

By the way, as a method for regenerating an inactivated carbonaceous catalyst as described above, a method is known in which an inactivated carbonaceous catalyst is heated in an inert gas atmosphere. No. 55-121907. The regeneration method disclosed in the above publication mixes an inert gas with an inactivated carbonaceous catalyst, and causes this mixture to flow indirectly downward to a heating region while indirectly exchanging heat with the heating gas flowing upward in the region. The mixture is heated by means of this heating, the desorbed substances leaving the deactivated carbonaceous catalyst by this heating are purged with an inert gas in the mixture, and the desorbed substance-containing inert gas is separated in the separation region located below the heating region. Is separated from the carbonaceous catalyst. According to this method, the desorbed substances separated from the inactivated carbonaceous catalyst are purged by an inert gas flowing in parallel with the carbonaceous catalyst and moved to a higher temperature side. Therefore, there is an advantage that the desorbed product is not recondensed, but there is a problem in that ammonia is mixed in the desorbed product purged with an inert gas. That is, when the deactivated carbonaceous catalyst is heated and regenerated, a relatively high concentration of sulfur dioxide gas is by-produced as described above, so it is usual to recover sulfuric acid or sulfur from this by-product gas.
In this case, it is not preferable that ammonia is contained in the by-product gas.

Therefore, the present inventors can obtain the gas by-produced when the inactivated carbonaceous catalyst is heated and regenerated as described above in a state where ammonia is not substantially contained, and the inactivated carbonaceous catalyst is also obtained. Invented a method (see Japanese Examined Patent Publication No. 6-59408) that can recycle the waste gas for reuse in exhaust gas treatment. In this method, as shown in FIG. 2, the inactivated carbonaceous catalyst C is passed downward to the heated side of the heat exchange zone 4 of the regenerator 1, and indirectly with the heating gas flowing upward on the heating side of the zone. The inactivated carbonaceous catalyst is heated and regenerated by heat exchange and made to flow into the inert gas introduction region 7a located below the heat exchange region 4, and the inactivated carbon is supplied to this region by the inert gas supplied from the line 8a. The desorbed substances from the high quality catalyst, the inert gas accompanied with the desorbed substances is raised on the heated side of the heat exchange region 4, and the desorbed substances are separated in the separation region 3 located above the heat exchange region 4. The ammonia gas therein is adsorbed on the deactivated carbonaceous catalyst and separated from the desorbed matter, and the desorbed matter (sulfur dioxide gas) containing no ammonia is taken out as a by-product gas from the desorbed gas line 9 together with the inert gas. It was done like this.

[0005]

However, according to the method of the above Japanese Patent Publication No. 6-59408, a high concentration sulfur dioxide gas containing no ammonia can be obtained, but the desulfurization activity and denitrification activity of the regenerated carbonaceous catalyst are high. Is not enough. Therefore, the present invention aims to obtain a by-product gas containing no ammonia and to improve the desulfurization and denitration performance of the regenerated carbonaceous catalyst.

[0006]

[Means for Solving the Problems] The inactivated carbonaceous catalyst used in a dry desulfurization and denitration apparatus is heated and regenerated by indirect heat exchange with a heating gas in a heat exchange region of a regenerator. , It is made to flow down to an inert gas introduction region located below the heat exchange region, and the desorbed substances from the inactivated carbonaceous catalyst are purged and the carbonaceous catalyst is activated by the inert gas supplied to this region. , The inert gas accompanied by the desorbed product is raised on the heated side of the heat exchange region, and the desorbed product is separated from the deactivated carbonaceous catalyst together with the inert gas in the separation region located above the heat exchange region. The regeneration method is characterized in that the inert gas supplied to the inert gas introduction region contains ammonia.

[0007]

The method of the present invention will be described with reference to FIG. R is a known cross-flow moving bed reactor for treating exhaust gas from a boiler or the like by a dry desulfurization and denitration method, and the main body of the reactor R is filled with a carbonaceous catalyst such as activated carbon or activated coke. Exhaust gas from a boiler or the like is introduced into the reactor R by injecting ammonia gas into the exhaust gas at the inlet of the cross flow type moving bed reactor R. Then, the sulfur oxides in the exhaust gas are adsorbed on the carbonaceous catalyst in the form of sulfuric acid or ammonium sulfate salt. Further, the nitrogen oxides in the exhaust gas are reduced to nitrogen gas by a reduction reaction, the sulfur oxides and nitrogen oxides are removed and become clean gas, which is released from the reactor R into the atmosphere. Thus, the carbonaceous catalyst C, which has been used for a long time and deactivated in the reactor R, is supplied into the regenerator ₁ through the top valve V ₁ of the regenerator 1.

The inert carbonaceous catalyst supplied to the regenerator 1 flows down as a moving bed through a plurality of heat transfer tubes 5 arranged substantially vertically in a heat exchange area 4 via a storage area 2 and a separation area 3. . On the other hand, since the heating gas supplied from the line 6 is passed upward on the heating side in the heat exchange region 4, that is, outside the heat transfer tube 5, the inactivated carbonaceous catalyst C flowing down in the heat transfer tube 5 is It is heated to a regeneration temperature of about 300 to 600 ° C. by indirect heat exchange with this heating gas. The inert carbonaceous catalyst heated to the regeneration temperature releases desorbed substances such as sulfur dioxide, sulfur trioxide, hydrogen chloride and ammonia, and is regenerated to move to the inert gas introduction region 7. An inert gas containing ammonia gas (for example, carbon dioxide gas, steam, nitrogen gas, or a gas having a low oxygen content such as a mixed gas thereof) is supplied to the region 7 through the line 8, and the ammonia gas-containing inert gas is supplied. The active gas purges the above-mentioned desorbed substances from the inactivated carbonaceous catalyst from the carbonaceous catalyst, rises in the heat transfer tube 5 with these desorbed substances, and the inactivated carbonaceous catalyst at a relatively low temperature stays there. The separation area 3 is reached.

In general, an inert carbonaceous catalyst that is subjected to heating regeneration usually has a surplus capacity for adsorption, so that the desorbed matter which has reached the separation region 3 due to the inert gas and Ammonia in the inert gas as sulfate,
Sulfur trioxide is captured as sulfuric acid on the inactivated carbonaceous catalyst. Therefore, a high-concentration sulfur dioxide gas containing neither ammonia nor sulfur trioxide can be taken out from the separation region 3 through the line 9 and taken out as a by-product gas.
The gas that has risen to the separation region 3 along with the desorbed substances is stored in the storage region 2
If it invades, the corrosion of the regenerator due to dew condensation or the like may occur. In such a case, an inert gas is additionally supplied from the line 8 ′ to the vicinity of the rectifying body 10 provided in the storage area 2. As a result, it is possible to prevent the gas accompanied with the desorbed substances from entering the storage region 2. Even if gas invades, dew condensation can be prevented by installing a heater (not shown) near the rectifying body 10.

In the present invention, 300 to 60 are provided below the heat transfer tube 5.
By bringing the ammonia-containing inert gas into contact with the carbonaceous catalyst heated to the regeneration temperature of 0 ° C., the chemical properties of the surface of the carbonaceous catalyst are changed and the catalytic activity (desulfurization activity and denitration activity) is improved. Although the reason is not clear, it is considered that a nitrogen compound is generated on the surface of the carbonaceous catalyst, which improves the catalytic activity. If the ammonia concentration in the inert gas is 0.5% or less, the effect of activating the catalyst is small, and if it is 15% or more, the effect of improving the activation is alleviated and wasted. Separation area 3
Therefore, it is difficult to capture ammonia, and there is a problem that ammonia is mixed in the desorbed gas taken out through the line 9, so 0.5 to 15% is preferable. Also,
Since the improvement of the catalytic activity becomes more remarkable as the amount of the adsorbed sulfur dioxide and the amount of adsorbed ammonium sulfate of the deactivated carbonaceous catalyst becomes more remarkable, it is possible to mix the oxygen-containing gas (air, exhaust gas, etc.) in the line 8 '. In the storage area 2 and the separation area 3, the sulfur dioxide in the desorbed gas is oxidized to sulfuric acid to increase the adsorption amount of sulfur dioxide on the inactivated carbonaceous catalyst,
By regenerating this carbonaceous catalyst in the heating regeneration region, the activation of the regenerated catalyst can be further improved. Thus, the carbonaceous catalyst that has been heated and regenerated in the heat transfer tube 5 and released the desorbed substances in the ammonia gas-containing inert gas introduction region 7 flows down to the cooler 11 and exchanges heat with the cooling fluid from the line 14. After being cooled, it is taken out from the bottom valve V ₂ of the regenerator 1 and conveyed to the reactor R to be reused for exhaust gas treatment. The sulfuric acid and the sulfate on the inactivated carbonaceous catalyst in the heat transfer tube 5 are decomposed and desorbed by the chemical reactions represented by the chemical formulas (1) to (3) of general formula 1, and the inactivated carbonaceous catalyst is It is considered to be regenerated. Further, the ammonia mixed in the desorbed gas causes the chemical reactions represented by the chemical formulas (4) and (5) of Chemical formula 1 in the separation region 3 and is adsorbed by the deactivated carbonaceous catalyst, so that the ammonia does not contain high ammonia. It is believed that a concentration of sulfur dioxide gas will be obtained.

[0011]

Embedded image

[0012]

According to the present invention, the activation of the regenerated catalyst could be improved by bringing the ammonia-containing inert gas into contact with the carbonaceous catalyst heated to the regeneration temperature. Furthermore, by supplying the oxygen-containing gas to the storage region 2, the activation of the regenerated catalyst could be further improved.

[0013]

【Example】

Example 1 A coal-fired boiler exhaust gas containing 500 ppm of sulfur oxides and 50 ppm of nitrogen oxides was taken out at a flow rate of 1000 Nm ³ / h and mixed with 300 ppm of ammonia gas.
It was introduced into a cross-flow moving bed reactor at 5 ° C. In this case, the charged amount of activated carbon in the reactor is set to 2.5 m ³ , and the residence time of activated carbon is set to 70 hours. The activated carbon used in the reactor and deactivated was placed in the regenerator 1 shown in Fig. 1 at 25 kg / h.
It was supplied and regenerated. The residence time of the carbonaceous catalyst in the heat transfer tube 5 was 7 hours, and the temperature of the finally obtained regenerated activated carbon catalyst was 450 ° C. The supply amount of the inert gas containing ammonia gas (5% NH ₃ + N ₂ ) from the line 8 is 0.5 Nm.
³ / h, and the amount of inert gas (N ₂ ) supplied from the line 8 ′ was 0.5 Nm ³ / h. At this time, the composition of the desorbed gas obtained in the line 9 is SO ₂ : 16.6%, CO ₂ :
2.8%, CO: 0.2%, H ₂ O: 38.2%, N
_{H 3: 0.002%, HCl:} 1%, N 2: was 41.2%. In addition, each gas concentration is a wet standard display. The regenerated activated carbon was returned to the top of the cross flow type moving bed reactor R and continuously operated. As a result of exhaust gas treatment under the above conditions, the desulfurization rate of the treated gas was 99% and the denitration rate was 70%. Example 2 In Example 1, air was injected into the line 8'to obtain oxygen 1
As a result of operating under the same conditions except that 0.5 Nm ³ / h of nitrogen gas containing 0% was supplied, the desulfurization rate in the reactor R was 100.
%, And the denitration rate was 80%. Comparative Example 1 The operation was performed under the same conditions as in Example 1 except that an inert gas containing only nitrogen was used in place of the ammonia gas-containing inert gas in the regenerator 1. The composition of the desorbed gas at this time is SO
₂ : 16.4%, CO ₂ : 2.8%, CO: 0.2%, H
₂ O: 38%, NH ₃ : 0.001%, HCl: 1%,
N ₂ : It was 41.6%. The desulfurization rate in the reactor R was 97.5%, and the denitration rate was 57%.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a regenerator for carrying out the method of the present invention.

FIG. 2 is a vertical sectional view of a known regenerator.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Regenerator 2 Storage area 3 Separation area 4 Heat exchange area 5 Heat transfer tube 6 Heating gas line 7 Ammonia gas-containing inert gas introduction area 7a Inert gas introduction area 8 Ammonia gas-containing inert gas line 8a Inert gas line 8 ' Inert gas line 9 Desorbed gas line 10, 12, 13 Rectifier 11 Cooler 14 Cooling fluid line C Inactivated carbonaceous catalyst R Cross flow type moving bed reactor V ₁ , V ₂ valve

Claims (3)

[Claims] 1. A carbon dioxide catalyst used in a dry desulfurization and denitration apparatus is inactivated by heating the inactivated carbonaceous catalyst by indirect heat exchange with a heating gas in a heat exchange area of a regenerator, and a heat exchange area. Flow into an inert gas introduction area located below
With the inert gas supplied to this region, the desorbed substances from the inactivated carbonaceous catalyst are purged and the carbonaceous catalyst is activated, and the inert gas accompanied with the desorbed substances is supplied to the heated side of the heat exchange region. In a separation region located above the heat exchange region, the desorbed product is separated from the deactivated carbonaceous catalyst together with the inert gas in a regeneration method, in which the inert gas is supplied to the inert gas introduction region. A method for regenerating an inactivated carbonaceous catalyst characterized by containing ammonia. 2. The method for regenerating an inactivated carbonaceous catalyst according to claim 1, wherein the amount of ammonia contained in the inert gas is 0.5 to 15% of the inert gas. 3. The method for regenerating an inactivated carbonaceous catalyst according to claim 2 or 3, wherein an inert gas and / or an oxygen-containing gas is supplied to the inactivated carbonaceous catalyst storage area of the regenerator. .