JP4277170B2 - Exhaust gas purification method and apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas purification technology, and more specifically, in exhaust gas that is discharged from a combustion apparatus such as a turbine, a boiler, and an internal combustion engine and contains nitrogen oxides (NOx) but does not contain sulfur oxides (SOx). The present invention relates to an exhaust gas purification method and apparatus for decomposing NOx.
[0002]
[Prior art]
As a technique for reducing nitrogen oxide (NOx) in an oxygen-excess atmosphere and converting it into harmless nitrogen, ammonia (NH₃NOx selective catalytic reduction method (NH) using as a reducing agent₃-SCR) is known. According to this technique, NOx can be reduced and removed efficiently with a simple apparatus, but NH used as a reducing agent₃Storage, maintenance management, appropriate safety management, etc. are necessary, and these lead to an increase in denitration costs.
[0003]
A technique for decomposing NOx into nitrogen and oxygen without using a reducing agent is currently being researched and developed, but no method has yet emerged that can achieve practical results.
[0004]
A denitration method (HC-SCR) using unburned hydrocarbons contained in combustion exhaust gas as a reducing agent has been studied, but this has not yet been put into practical use.
[0005]
As one of the HC-SCR technologies, a method of decomposing NOx under an oxygen-excess atmosphere using methane as a reducing agent and a catalyst used therefor have been disclosed (see Patent Document 1 below).
[0006]
[Patent Document 1]
JP 2000-61308 A (Claims, Examples, etc.)
[0007]
[Problems to be solved by the invention]
However, in the case of the above method, the NOx conversion rate, which was about 60% at the beginning of the reaction, was 52% after 30 hours, 45% after 50 hours, and 35% after 88 hours, gradually with time. The NOx conversion rate stable for a long time is not obtained (see Example 1 of Patent Document 1 and FIG. 1).
[0008]
In view of the above points, an object of the present invention is to provide an exhaust gas purification method and apparatus that can stably decompose NOx for a long period of time using a hydrocarbon such as methane as a reducing agent in an oxygen-excess atmosphere.
[0009]
[Means for Solving the Problems]
In the denitration method disclosed in Patent Document 1, it is considered that the selective reduction denitration reaction of NOx with methane proceeds by the following mechanism.
That is, methane adsorbed on the catalyst active site is remarkably activated and reacts rapidly with the catalyst lattice oxygen without waiting for the arrival and activation of oxygen molecules from the gas phase.
At the same time, the NOx adsorbed on the catalyst is reduced by being deprived of oxygen by the catalyst in which oxygen defects are generated by the reaction with methane as described above, and desorbed as nitrogen gas.
[0010]
Here, the functions desired for the catalyst are as follows.
a. Adsorption and activation of methane
b. Providing lattice oxygen that is easy to react with activated methane
c. Suppression of reaction between oxygen defects and gas phase oxygen
d. NOx adsorption and NO bond breakage
e. Acceleration of the reaction between oxygen ions or radicals generated by decomposition of NOx and oxygen defects
[0011]
Therefore, when the activity of the catalyst shown in Patent Document 1 was examined from the physical properties, the activity was expressed by the interaction of the special crystals of zirconia obtained by calcination of zirconium hydroxide and the platinum and palladium supported thereon. It has been found that the activity decreases as the unstable zirconia crystal surface changes.
[0012]
Desirable crystals can be obtained when sulfate groups coexist during the formation of zirconia crystals. However, sulfate groups are detached during a long-time reaction, and the crystal surface changes accordingly.
[0013]
On the other hand, if the activity of the catalyst is considered from the reaction surface, the violent activation of methane decreases as the crystal surface changes, and the adsorbed methane reacts with gas-phase oxygen according to a general oxidation reaction mechanism. That is, it is considered that the methane that has reached the catalyst surface is not consumed effectively for the reaction with NOx, and the denitration performance is lowered.
[0014]
In other words, it is considered that the added sulfate radical suppresses the oxidation of methane by gas phase oxygen and improves the selectivity of the reaction between methane and NOx. The drawback of the catalyst described in Patent Document 1 is a decrease in the denitration performance due to such elimination of sulfate radicals.
[0015]
Based on the above research results, when the present inventors decompose NOx by using hydrocarbons such as methane as a reducing agent in an oxygen-excess atmosphere, if sulfur oxides coexist in the exhaust gas, the activity of the catalyst is suppressed. I found it effective. This is presumably because the desorption of sulfate radicals from the catalyst surface was suppressed due to the relationship between the adsorption and desorption equilibrium between the sulfur oxides in the exhaust gas and the catalyst surface, and the crystal structure was less likely to change.
[0016]
That is, in the exhaust gas purification method according to the present invention, a catalyst in which at least one of ruthenium, palladium and platinum is supported on a metal oxide support is brought into contact with exhaust gas, and the hydrocarbon is used as a reducing agent in an exhaust gas atmosphere in an oxygen-excess atmosphere. In the exhaust gas purification method for decomposing nitrogen oxides, the nitrogen oxides in the exhaust gas are decomposed in the presence of sulfur oxides.
[0017]
As the metal oxide support of the catalyst, it is preferable to use a zirconia support containing a sulfate group. The carrier may support at least one of ruthenium, palladium and platinum, but preferably a carrier supporting palladium and platinum is used.
[0018]
The hydrocarbon as the reducing agent is preferably methane. However, hydrocarbons other than methane, such as ethane and propane, can be used as the reducing agent. In the present invention, in addition to the case where the hydrocarbon contained in the exhaust gas is used as the reducing agent, the hydrocarbon supplied from outside the system may be used as the reducing agent.
[0019]
In the exhaust gas purification method according to the present invention, as a first means for allowing sulfur oxides to coexist, the sulfur oxides desorbed from the catalyst accompanying the decomposition of nitrogen oxides in the exhaust gas are collected and reused. Can be mentioned.
[0020]
As one of the above means, a sulfur oxide adsorbent layer is disposed on both sides of the catalyst layer via a cooler, and only the cooler on the downstream side of the two coolers is selectively operated. There is a method in which sulfur oxides desorbed from the upstream adsorbent layer and the catalyst layer are adsorbed and collected by the downstream adsorbent layer, and the exhaust gas flow is sequentially switched in the reverse direction in accordance with a decrease in the denitration performance of the catalyst layer.
[0021]
In this method, first, exhaust gas flows through the first adsorbent layer on the upstream side, so that sulfur oxides desorbed therefrom are mixed into the exhaust gas. The first cooler following the first adsorbent layer is left unactuated. In the catalyst layer, NOx in the exhaust gas is decomposed using hydrocarbon as a reducing agent in an oxygen-excess atmosphere and in the presence of sulfur oxides. Along with the decomposition of NOx, sulfur oxides are also desorbed from the catalyst layer. The exhaust gas containing sulfur oxide is lowered in temperature by the second cooler on the downstream side, and then reaches the second adsorbent layer on the downstream side, where the sulfur oxide is adsorbed and collected. Then, when desulfurization of the sulfur oxide has progressed and the NOx removal performance of the catalyst layer has deteriorated, the exhaust gas flow is switched in the reverse direction, and the operation of the second cooler is stopped to operate the first cooler. This time, the second adsorbent layer that adsorbs sulfur oxide is upstream, and the first adsorbent layer from which sulfur oxide is desorbed is downstream. Below, the decomposition process of NOx is performed. By repeating the switching operation of the exhaust gas flow direction as described above, NOx can be stably decomposed for a long period of time.
[0022]
In the above case, the temperatures of the upstream adsorbent layer and the catalyst layer are preferably 400 to 500 ° C. Thereby, desorption of sulfur oxides from the upstream adsorbent layer and the catalyst layer is efficiently performed, and high denitration performance is maintained in the catalyst layer.
[0023]
On the other hand, the temperature of the downstream side adsorbent layer is preferably set to room temperature to 300 ° C. Thereby, adsorption | suction of the sulfur oxide to a downstream adsorbent layer is performed efficiently. The temperature of the downstream adsorbent layer is adjusted by controlling the temperature of the exhaust gas in the cooler on the downstream side.
[0024]
As the adsorbent layer, at least one of zeolite, titania, zirconia, silica, alumina, and silica-alumina is preferably used.
[0025]
As another method for collecting and reusing the sulfur oxide desorbed from the catalyst, two catalyst layers are arranged via a cooler, and the sulfur oxide desorbed from the upstream catalyst layer is removed. There is one that adsorbs and collects in the downstream catalyst layer and sequentially switches the exhaust gas flow in the reverse direction in accordance with a decrease in the denitration performance of the upstream catalyst layer.
[0026]
In this method, first, in the first catalyst layer on the upstream side, NOx in the exhaust gas is decomposed using hydrocarbon as a reducing agent in an oxygen-excess atmosphere. As NOx is decomposed, sulfur oxides are desorbed from the upstream catalyst layer. The exhaust gas containing the sulfur oxide is lowered in temperature by the cooler, and then reaches the second catalyst layer on the downstream side, where the sulfur oxide is adsorbed and collected. And when desorption | desorption of sulfur oxide advances and the denitration performance of an upstream catalyst layer falls, an exhaust gas flow is switched to a reverse direction. This time, the second catalyst layer that adsorbs sulfur oxide is upstream, and the first catalyst layer from which sulfur oxide is desorbed is downstream. , NOx decomposition processing is performed. By repeating the switching operation of the exhaust gas flow direction as described above, NOx can be stably decomposed for a long period of time.
[0027]
In said case, it is preferable that the temperature of an upstream catalyst layer shall be 400-500 degreeC. Thereby, desorption of sulfur oxides from the upstream catalyst layer is efficiently performed, and high denitration performance is maintained in the upstream catalyst layer.
[0028]
On the other hand, the temperature of the downstream catalyst layer is preferably from room temperature to 300 ° C. Thereby, adsorption | suction of the sulfur oxide to a downstream catalyst layer is performed efficiently. The temperature of the downstream catalyst layer is adjusted by controlling the temperature of the exhaust gas in the cooler.
[0029]
As described above, when sulfur oxides desorbed from the catalyst due to decomposition of nitrogen oxides in the exhaust gas are collected and reused, the sulfur content may be intermittently supplied from outside the system. Good. This is effective as an auxiliary means when the denitration performance of the catalyst layer is not sufficiently exhibited.
[0030]
In the exhaust gas purification method according to the present invention, as a second means for allowing the sulfur oxide to coexist, supplying a sulfur content from outside the system can be mentioned.
[0031]
The sulfur component supplied from outside the system is, for example, at least one of hydrogen sulfide, sulfur oxide, and an aqueous solution containing a sulfur component.
[0032]
In the above case, the gaseous sulfur content may be mixed with the hydrocarbon supplied as the reducing agent and supplied. Moreover, when hydrocarbon is not supplied as a reducing agent, the gaseous sulfur content may be diluted with a diluent gas such as air.
[0033]
In the above case, an aqueous solution containing a sulfur content may be vaporized in advance to form a gaseous sulfur oxide, which is then mixed with a hydrocarbon supplied as a reducing agent. Further, when hydrocarbon is not supplied as a reducing agent, an aqueous solution containing a sulfur content may be vaporized in advance to form a gaseous sulfur oxide, which is then diluted with a diluent gas such as air.
[0034]
The concentration of the sulfur component supplied from outside the system is preferably 0.1 to 100 ppm.
[0035]
It is sufficient to supply the sulfur content from outside the system when the denitration performance of the catalyst is not sufficiently exhibited. Therefore, the supply of the sulfur content from outside the system may be intermittently performed when the denitration performance of the catalyst is not sufficiently exhibited.
[0036]
In the above case, it is preferable to collect and reuse those sulfur components supplied from outside the system that have not been used for decomposition of nitrogen oxides.
[0037]
Next, an exhaust gas purifying apparatus according to the present invention includes a catalyst layer formed by supporting at least one of ruthenium, palladium and platinum on a metal oxide support, and passing exhaust gas through the catalyst layer, thereby allowing an oxygen-excess atmosphere. In the case where nitrogen oxides in exhaust gas are decomposed using hydrocarbon as a reducing agent, a sulfur oxide adsorbent layer is provided on both sides of the catalyst layer via a cooler, and an exhaust gas flow direction switching means is provided. It is characterized in that only the cooler on the downstream side of the two coolers can be operated.
[0038]
In the above apparatus, first, exhaust gas flows through the first adsorbent layer on the upstream side, so that sulfur oxides desorbed from the first adsorbent layer are mixed into the exhaust gas. The first cooler following the first adsorbent layer is left unactuated. In the catalyst layer, NOx in the exhaust gas is decomposed using hydrocarbon as a reducing agent in an oxygen-excess atmosphere and in the presence of sulfur oxides. Along with the decomposition of NOx, sulfur oxides are also desorbed from the catalyst layer. The exhaust gas containing sulfur oxide is lowered in temperature by the second cooler on the downstream side, and then reaches the second adsorbent layer on the downstream side, where the sulfur oxide is adsorbed and collected. Then, when desulfurization of the sulfur oxide has progressed and the NOx removal performance of the catalyst layer has deteriorated, the exhaust gas flow is switched in the reverse direction, and the operation of the second cooler is stopped to operate the first cooler. This time, the second adsorbent layer that adsorbs sulfur oxide is upstream, and the first adsorbent layer from which sulfur oxide is desorbed is downstream. Below, the decomposition process of NOx is performed. By repeating the switching operation of the exhaust gas flow direction as described above, NOx can be stably decomposed for a long period of time.
[0039]
In the above apparatus, as the exhaust gas flow direction switching means, a catalyst layer, two adsorbent layers and two coolers are formed in series, and branched from the exhaust gas inlet toward both ends of the exhaust gas main channel. And an exhaust gas introduction passage having a switching valve at a branch point, and an exhaust gas discharge passage formed in a confluence from both ends of the exhaust gas main passage toward the exhaust gas outlet and having a switching valve at the junction. There is a case where the exhaust gas flow in the exhaust gas main channel is switched in the reverse direction by the switching operation of the switching valves of the introduction channel and the exhaust gas discharge channel.
[0040]
According to the above configuration, the direction of the exhaust gas flow can be easily and quickly switched by simultaneous operation of the two switching valves.
[0041]
In the above apparatus, the two coolers may be common devices.
[0042]
The exhaust gas purifying apparatus according to the present invention includes one in which two catalyst layers are provided via a cooler and an exhaust gas flow direction switching means is provided.
[0043]
In the second apparatus, first, in the upstream first catalyst layer, NOx in the exhaust gas is decomposed using hydrocarbons as a reducing agent in an oxygen-excess atmosphere and in the presence of sulfur oxides. As NOx is decomposed, sulfur oxides are desorbed from the upstream catalyst layer. The exhaust gas containing the sulfur oxide is lowered in temperature by the cooler, and then reaches the second catalyst layer on the downstream side, where the sulfur oxide is adsorbed and collected. Then, when the desulfurization of the upstream catalyst layer is reduced due to the progress of desorption of the sulfur oxide, the exhaust gas flow is switched in the reverse direction. This time, the second catalyst layer adsorbing the sulfur oxide is upstream. Since the first catalyst layer from which the sulfur oxide is desorbed is on the downstream side, the NOx decomposition treatment is performed in the presence of the sulfur oxide as described above. By repeating the switching operation of the exhaust gas flow direction as described above, NOx can be stably decomposed for a long period of time.
[0044]
In the second apparatus, as the exhaust gas flow direction switching means, an exhaust gas main flow path in which two catalyst layers and a cooler are arranged in series, and a branch formed from the exhaust gas inlet toward both ends of the exhaust gas main flow path and branched An exhaust gas introduction flow path having a switching valve at a point, and an exhaust gas discharge flow path formed in a confluence from both ends of the exhaust gas main flow path toward the exhaust gas outlet and having a switching valve at the merge point. In some cases, the exhaust gas flow in the exhaust gas main flow path can be switched in the reverse direction by the switching operation of the switching valve of the exhaust gas exhaust flow path.
[0045]
According to the above configuration, the direction of the exhaust gas flow can be easily and quickly switched by simultaneous operation of the two switching valves.
[0046]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a first embodiment of an exhaust gas purifying apparatus according to the present invention. This device (11) includes a catalyst layer (2) formed by supporting palladium and platinum on a sulfate group-containing zirconia support. Sulfur oxide adsorbent layers (3A) (3B) are provided on both sides of the catalyst layer (2) in the exhaust gas flow direction via coolers (4A) (AB), respectively. The device (11) is provided with exhaust gas flow direction switching means. Of the two coolers (4A) and (AB), only the cooler on the downstream side is operated.
[0047]
The exhaust gas flow direction switching means includes an exhaust gas main flow path (L1) in which a catalyst layer (2), two adsorbent layers (3A) (3B) and two coolers (4A) (AB) are arranged in series, and exhaust gas An exhaust gas introduction channel (L2) that is branched from the inlet toward both ends of the exhaust gas main channel (L1) and has a switching valve (5) at the branch point, and from both ends of the exhaust gas main channel (L1) to the exhaust gas outlet The exhaust gas discharge passage (L3) is formed in a confluence state and has a switching valve (5) at the confluence. By the switching operation of the switching valve (5) of the exhaust gas introduction channel (L2) and the exhaust gas discharge channel (L3), the exhaust gas flow in the exhaust gas main channel (L1) is switched in the reverse direction.
[0048]
In the apparatus (11), in the initial state, as shown in FIG. 1 (a), first, exhaust gas flows through the first adsorbent layer (3A) on the upstream side, so that sulfuric acid desorbed therefrom is removed. Roots are mixed in the exhaust gas. The first cooler (4A) following the first adsorbent layer (3A) is not operated. In the catalyst layer (2), NOx in the exhaust gas is decomposed using methane as a reducing agent in an oxygen-excess atmosphere and in the presence of sulfur oxides. With the decomposition of NOx, the sulfate radical is detached from the catalyst layer (2). The exhaust gas containing sulfate radicals is cooled by the second cooler (4B) on the downstream side and reaches the second adsorbent layer (3B) on the downstream side, where the sulfate radicals are adsorbed and captured. Be collected. Then, when the desulfurization performance of the catalyst layer (2) decreases due to the progress of desorption of sulfate radicals, the exhaust gas flow is switched in the reverse direction by the switching operation of the switching valve (5), and the second cooler (4B) And the first cooler (4A) is activated. Then, as shown in FIG. 1B, this time, the second adsorbent layer (3B) that adsorbs the sulfate radical is upstream, and the first adsorbent layer (3A) from which the sulfate radical is desorbed is downstream. As in the case described above, the NOx decomposition treatment is performed in the presence of sulfur oxides.
[0049]
Next, Example 1 of the present invention using the device (11) is shown together with Comparative Example 1.
Example 1
Catalyst preparation
150 g of zirconium hydroxide was immersed in 150 ml of an aqueous solution in which 15 g of ammonium sulfate was dissolved for 10 hours. This immersion body was dried and then calcined at 550 ° C. for 3.5 hours to obtain sulfate zirconia.
[0050]
0.011 g of palladium nitrate solution as Pd and 0.068 g of tetraammineplatinum nitric acid aqueous solution containing 1.47% by weight as Pt are mixed and stirred, and the resulting mixed solution is diluted to 10 ml with the addition of pure water. Got.
[0051]
In this immersion liquid, 10 g of the sulfate zirconia was mixed and stirred and immersed for 10 hours. After the immersion, the sulfate zirconia was dried and then calcined at 500 ° C. for 9 hours to prepare a 0.05% Pd-0.01% Pt / sulfate zirconia catalyst.
[0052]
After this catalyst was formed into a disk shape, this was pulverized and sized into meshes 22 to 42, and filled into the catalyst layer (2).
[0053]
Preparation of adsorbent
150 g of H-type mordenite (silica / alumina ratio 16) was washed with water and dried to obtain an adsorbent.
[0054]
After forming this adsorbent into a disk shape, this was pulverized and sized into meshes 22 to 42, and filled into adsorbent layers (3A) and (3B).
[0055]
Catalytic activity test
A simulated exhaust gas obtained by mixing 50 ppm of sulfur dioxide, 150 ppm of nitric oxide, 2000 ppm of methane, 10% of water vapor, and the remaining air in the exhaust gas purifying apparatus (11) shown in FIG. 1 in the exhaust gas flow direction shown in FIG. Introduced. The exhaust gas temperature in the first adsorbent layer (3A) and the catalyst layer (2) was set to 450 °. Further, the second cooler (4B) was operated so that the exhaust gas temperature in the second adsorbent layer (3B) was 200 °. The space velocity (SV) in the adsorbent layers (3A) (3B) and the catalyst layer (2) is 30000 h, respectively.^-1It was. Under the above conditions, the NOx concentration at the inlet and outlet of the catalyst layer (2) was measured with a chemiluminescent NOx analyzer.
[0056]
The denitration rate was 72% at the beginning of the reaction, but gradually decreased as the reaction time elapsed, and decreased to 55% after 20 hours.
[0057]
Therefore, when the exhaust gas flow is switched to the direction shown in FIG. 1B by the switching valve (5) and the operating cooler is switched to the first cooler (4A), the denitration rate rises again, and 3 hours Later it recovered to 70%.
[0058]
The measurement results when the switching of the exhaust gas flow direction by the switching valve (5) and the switching of the coolers (4A) and (4B) to be operated are repeated about every 20 to 30 hours are shown in FIG. In FIG. 2, the downward arrows indicate the direction of exhaust gas flow and the time for switching the coolers (4A) and (4B) to be operated.
[0059]
As shown in FIG. 2, the NOx removal rate was maintained at 55% or more for 100 hours or more by repeating the exhaust gas flow direction and the switching operation of the coolers (4A) and (4B) to be operated.
[0060]
(Comparative Example 1)
The sulfur oxide adsorbent layers (3A) (3B) and the coolers (4A) (4B) were removed from the exhaust gas purification device (11) shown in FIG. 1 to obtain only the catalyst layer (2). Then, after the catalyst layer (2) was molded into the same shape as the catalyst used in Example 1, it was pulverized and sized and packed into meshes 22 to 42. A catalytic activity test was conducted under the same conditions. The test results are indicated by dotted lines in FIG.
[0061]
As shown in FIG. 2, the denitration rate, which was 72% at the beginning of the reaction, decreased to 55% after 8 hours.
[0062]
Therefore, although the exhaust gas flow was switched to the direction shown in FIG. 1B by the switching valve (5), the denitration rate further decreased to 50% after 100 hours, and the denitration rate continued to decrease thereafter.
[0063]
FIG. 3 shows a second embodiment of the exhaust gas purifying apparatus according to the present invention. This device (12) is provided with two catalyst layers (2A) (2B) each having palladium and platinum supported on a sulfate group-containing zirconia support via a cooler (4). The device (12) is provided with exhaust gas flow direction switching means.
[0064]
The exhaust gas flow direction switching means includes an exhaust gas main flow path (L1) in which two catalyst layers (2A) (2B) and a cooler (4) are arranged in series, and an exhaust gas inlet to both ends of the exhaust gas main flow path (L1). The exhaust gas introduction flow path (L2) having a switching valve (5) formed at the branch point and the exhaust gas main flow path (L1) from both ends of the exhaust gas flow path to the exhaust gas outlet and switching to the merge point And an exhaust gas discharge passage (L3) having a valve (5). By the switching operation of the switching valve (5) of the exhaust gas introduction channel (L2) and the exhaust gas discharge channel (L3), the exhaust gas flow in the exhaust gas main channel (L1) is switched in the reverse direction.
[0065]
In the above apparatus (12), in the initial state, as shown in FIG. 3 (a), first, in the upstream first catalyst layer (2A), methane is produced in an oxygen-excess atmosphere and in the presence of sulfur oxides. As a reducing agent, NOx in the exhaust gas is decomposed. Along with the decomposition of NOx, the sulfate radical is detached from the first catalyst layer (2A). The exhaust gas containing sulfate radicals is lowered in temperature by the cooler (4) and then reaches the second catalyst layer (2B) on the downstream side, where the sulfate radicals are adsorbed and collected. Then, when the desulfurization performance of the first catalyst layer (2A) is reduced due to the progress of desorption of sulfate radicals, the exhaust gas flow is switched in the reverse direction by the switching operation of the switching valve (5). Then, as shown in FIG. 3B, the second catalyst layer (2B) that has adsorbed the sulfate radical is now upstream, and the first catalyst layer (2A) from which the sulfate radical has been released is downstream. As in the case described above, the NOx decomposition treatment is performed in the presence of sulfur oxides.
[0066]
Next, Example 2 of the present invention using the above device (12) is shown together with Comparative Example 2.
(Example 2)
Catalyst preparation
In the same manner as in Example 1, a 0.05% Pd-0.01% Pt / sulfate zirconia catalyst was prepared.
[0067]
After this catalyst was formed into a disk shape, it was pulverized and sized into meshes 22 to 42, and filled in two catalyst layers (2A) and (2B).
[0068]
Catalytic activity test
  A simulated exhaust gas obtained by mixing 50 ppm of sulfur dioxide, 150 ppm of nitric oxide, 2000 ppm of methane, 10% of water vapor, and the remaining air into the exhaust gas purification device (12) shown in FIG.3It was introduced in the exhaust gas flow direction shown in (a). The exhaust gas temperature in the first catalyst layer (2A) was set to 450 °. Further, the cooler (4) was operated so that the exhaust gas temperature in the second catalyst layer (2B) was 250 °. The space velocity (SV) in both catalyst layers (2A) and (2B) is 30000 h, respectively.^-1It was. Under the above conditions, the NOx concentrations at the inlet and outlet of the first catalyst layer (2A) on the upstream side were measured with a chemiluminescent NOx analyzer.
[0069]
The denitration rate showed 70% or more at the beginning of the reaction, but gradually decreased as the reaction time passed, and decreased to 55% after 20 hours.
[0070]
Therefore, when the exhaust gas flow was switched to the direction shown in FIG. 3B by the switching valve (5), the denitration rate increased again and recovered to about 70% after several hours.
[0071]
  Fig. 5 shows the measurement results when the switching of the exhaust gas flow direction using the switching valve (5) is repeated approximately every 20 to 30 hours.4Is shown by a solid line. Figure4The middle and downward arrows indicate the time when the exhaust gas flow direction is switched.
[0072]
  Figure4As shown in FIG. 4, the NOx removal rate could be maintained at 55% or more for 100 hours or more by repeating the switching operation of the exhaust gas flow direction.
[0073]
(Comparative Example 2)
  A catalytic activity test was performed under the same conditions as in Example 2 except that the measurement was continuously performed without switching the exhaust gas flow. Figure of test results4Is indicated by a dotted line.
[0074]
  Figure4As shown in FIG. 5, the denitration rate, which was 70% or more at the beginning of the reaction, decreased to 55% after 8 hours and continued to decrease thereafter.
[0075]
Examples 3 and 4 of the present invention are shown together with Comparative Example 3.
(Comparative Example 3)
Catalyst preparation
In the same manner as in Example 1, a 0.05% Pd-0.01% Pt / sulfate zirconia catalyst was prepared.
[0076]
Catalytic activity test
After the catalyst was formed into a disk shape, it was pulverized and sized into meshes 22 to 42, and filled into a reaction tube. In this reaction tube, a simulated exhaust gas obtained by mixing 150 ppm of nitric oxide, 2000 ppm of methane, 0% or 10% of water vapor, and the remaining air, was reacted at a reaction temperature of 450 ° and a space velocity (SV) of 30000 h.^-1The catalyst activity was tested by measuring the NOx concentration at the inlet and outlet of the catalyst layer with a chemiluminescent NOx analyzer. The test results are shown in FIG.
[0077]
When water vapor is not included in the simulated exhaust gas, the 0.05% Pd-0.01% Pt / sulfate zirconia catalyst shows a high denitration performance of 53% at the beginning of the reaction, but 48% after 10 hours, After 20 hours, it decreased to 44% over time.
[0078]
On the other hand, when 10% of water vapor is contained in the simulated exhaust gas, the catalyst causes a significant deterioration in activity at a denitration rate of 38% at the beginning of the reaction, and the denitration rate is 30% after 10 hours and 25 after 20 hours. % Over time.
[0079]
(Example 3)
A catalyst similar to that in Comparative Example 3 is filled in a reaction tube, and a simulated exhaust gas obtained by mixing sulfur dioxide 0 to 200 ppm, nitrogen monoxide 150 ppm, methane 2000 ppm, water vapor 0% or 10%, and the remaining air is mixed in the reaction tube. , Reaction temperature 450 °, space velocity (SV) 30000h^-1The catalytic activity was tested under the following conditions. The measurement was carried out after confirming the stability for 5 hours or more from the time when 10 hours or more passed after the start of gas flow. FIG. 6 shows the measurement results obtained by changing the sulfur dioxide concentration with respect to nitrogen monoxide 150 ppm and methane 2000 ppm from 0 ppm to 200 ppm in each case of 0% and 10% steam.
[0080]
When water vapor was not included in the simulated exhaust gas, the denitration rate increased up to a sulfur dioxide concentration of 5 ppm, but when it exceeded that, the denitration rate decreased and was below the denitration rate when the sulfur dioxide concentration was 0 ppm.
[0081]
On the other hand, in the case of 10% water vapor, the denitration rate increases rapidly as the sulfur dioxide concentration is increased from 0 ppm to 25 ppm. When the sulfur dioxide concentration is increased to 25 ppm or more, the initial activity when the denitration rate is 0% water vapor Gradually descended.
[0082]
(Example 4)
A catalyst similar to that in Comparative Example 3 was filled in a reaction tube, and a simulated exhaust gas obtained by mixing 5 ppm of sulfur dioxide, 150 ppm of nitric oxide, 2000 ppm of methane, 0% of water vapor, and the remaining air was added to this reaction tube at a reaction temperature of 450 ° C. , Space velocity (SV) 30000h^-1The catalytic activity was tested under the following conditions. The measurement results are shown in FIG.
[0083]
As shown in FIG. 7, no change in the denitration rate over time was observed even at a reaction time of 20 hours.
[0084]
It should be noted that the above embodiment is merely an example, and it is of course possible to implement the present invention with appropriate modifications without departing from the scope of the present invention described in the claims.
[0085]
【The invention's effect】
According to the exhaust gas purification method and apparatus of the present invention, the coexistence state of sulfur oxide is maintained, and thereby NOx can be stably decomposed for a long period of time.
[Brief description of the drawings]
FIG. 1 is a diagram showing a first embodiment of an exhaust gas purifying apparatus according to the present invention.
2 is a graph showing the relationship between the denitration rate and elapsed time in Example 1 and Comparative Example 1. FIG.
FIG. 3 is a view showing a second embodiment of the exhaust gas purifying apparatus according to the present invention.
4 is a graph showing the relationship between the denitration rate and elapsed time in Example 2 and Comparative Example 2. FIG.
5 is a graph showing the relationship between the denitration rate and reaction time in Comparative Example 3. FIG.
6 is a graph showing the relationship between the denitration rate and the sulfur oxide concentration in Example 3. FIG.
7 is a graph showing the relationship between the denitration rate and the reaction time in Example 4. FIG.
[Explanation of symbols]
(11): Exhaust gas purification device
(2): Catalyst layer
(3A): First sulfur oxide adsorbent layer
(3B): Second sulfur oxide adsorbent layer
(4A): First cooler
(4B): Second cooler
(12): Exhaust gas purification device
(2A): First catalyst layer
(2B): Second catalyst layer
(4): Cooler
(5): Switching valve
(L1): Exhaust gas main flow path
(L2): Exhaust gas introduction flow path
(L3): Exhaust gas discharge flow path

Claims (10)

A catalyst comprising at least one of ruthenium, palladium and platinum supported on a sulfate group-containing zirconia support is brought into contact with exhaust gas, and nitrogen is oxidized in the exhaust gas using a hydrocarbon as a reducing agent in an oxygen-excess atmosphere and in the presence of sulfur oxides. In the exhaust gas purification method for decomposing substances, a sulfur oxide adsorbent layer is disposed on both sides of the catalyst layer via a cooler, and only the downstream cooler of the two coolers is selectively operated. The sulfur oxide desorbed from the upstream adsorbent layer and the catalyst layer is adsorbed and collected by the downstream adsorbent layer, and the exhaust gas flow is sequentially switched in the reverse direction in accordance with the reduction in the denitration performance of the catalyst layer. An exhaust gas purification method. Upstream adsorbent layer and the temperature of the catalyst layer and 400 to 500 ° C., characterized by the temperature of the downstream adsorbent layer and the normal temperature to 300 ° C., the exhaust gas purification method according to claim 1. The exhaust gas purification method according to claim 1 or 2 , wherein the adsorbent layer comprises at least one of zeolite, titania, zirconia, silica, alumina, and silica-alumina. A catalyst comprising at least one of ruthenium, palladium and platinum supported on a sulfate group-containing zirconia support is brought into contact with exhaust gas, and nitrogen is oxidized in the exhaust gas using a hydrocarbon as a reducing agent in an oxygen-excess atmosphere and in the presence of sulfur oxides. In the exhaust gas purification method for decomposing substances, two catalyst layers are arranged via a cooler, and sulfur oxides desorbed from the upstream catalyst layer are adsorbed and collected by the downstream catalyst layer, and the upstream catalyst layer and switches sequentially in a direction opposite the exhaust gas flow in accordance with the denitration performance degradation, the exhaust gas purification method. The exhaust gas purification method according to claim 4 , wherein the temperature of the upstream catalyst layer is 400 to 500 ° C, and the temperature of the downstream catalyst layer is normal temperature to 300 ° C. A sulfate layer-containing zirconia support is provided with a catalyst layer in which at least one of ruthenium, palladium and platinum is supported, and by passing exhaust gas through the catalyst layer, nitrogen in the exhaust gas using hydrocarbon as a reducing agent in an oxygen-excess atmosphere In the exhaust gas purifying apparatus in which oxide is decomposed, a sulfur oxide adsorbent layer is provided on both sides of the catalyst layer via a cooler, and an exhaust gas flow direction switching means is provided, and two coolers Only the cooler on the downstream side is selectively operated, and sulfur oxides desorbed from the upstream adsorbent layer and catalyst layer are adsorbed and collected by the downstream adsorbent layer, and the denitration performance of the catalyst layer According to the exhaust gas flow, the exhaust gas flow is sequentially switched in the reverse direction, whereby the decomposition of nitrogen oxides in the exhaust gas is performed in the presence of sulfur oxides. Purifying device. As exhaust gas flow direction switching means, an exhaust gas main flow path in which a catalyst layer, two adsorbent layers and two coolers are arranged in series, and a branch point formed from the exhaust gas inlet toward both ends of the exhaust gas main flow path An exhaust gas introduction flow path having a switching valve, and an exhaust gas discharge flow path formed in a confluence from both ends of the exhaust gas main flow path toward the exhaust gas outlet and having a switching valve at the junction, The exhaust gas purification apparatus according to claim 6 , wherein the exhaust gas flow in the exhaust gas main flow path is switched in the reverse direction by switching operation of the switching valve of the exhaust gas exhaust flow path. The exhaust gas purifier according to claim 6 or 7 , wherein the two coolers are common devices. A catalyst layer formed by supporting at least one of ruthenium, palladium, and platinum on a sulfate group-containing zirconia support , and passing exhaust gas through the catalyst layer allows hydrocarbons to be used as a reducing agent in an oxygen-excess atmosphere to reduce nitrogen in the exhaust gas. In the exhaust gas purification apparatus in which oxide is decomposed, two catalyst layers are provided via a cooler, and an exhaust gas flow direction switching means is provided, and sulfur oxides desorbed from the upstream catalyst layer Is absorbed and collected by the downstream catalyst layer, and the exhaust gas flow is sequentially switched in the reverse direction in accordance with the denitration performance degradation of the upstream catalyst layer, so that the decomposition of nitrogen oxides in the exhaust gas is performed in the presence of sulfur oxides. An exhaust gas purifying apparatus, characterized in that it is designed to be As an exhaust gas flow direction switching means, an exhaust gas main flow path in which two catalyst layers and a cooler are arranged in series, and an exhaust gas formed in a branched shape from the exhaust gas inlet toward both ends of the exhaust gas main flow path and having a switching valve at the branch point It is provided with an introduction flow path, and an exhaust gas discharge path formed in a confluence from both ends of the exhaust gas main flow path toward the exhaust gas outlet and having a switching valve at the junction, and switching of the exhaust gas introduction flow path and the exhaust gas discharge flow path The exhaust gas purification apparatus according to claim 9 , wherein the exhaust gas flow in the exhaust gas main flow path is switched in the reverse direction by a valve switching operation.

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