JP2004066070A - Method of producing denitrification catalyst, denitrification catalyst, and denitrification system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily denitrify exhaust gas at a low cost even at a low temperature. <P>SOLUTION: A denitrification catalyst comprising cobalt oxide and zirconium oxide is used. By the use of the denitrification catalyst, a denitrification system having the first and second denitrification reaction chambers 11 and 12 is constituted. The exhaust gas is introduced alternately into the first and second denitrification reaction chambers 11 and 12, and the occlusion process and release process of NOx in the exhaust gas are repeated in the chambers 11 and 12. In this way, NOx in the exhaust gas is occluded in ether one of denitrification reaction chambers, and a reducing gas is introduced into the other chamber to release the occluded gas. The released NOx, after being burned by a burner 16, is discharged. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a denitration catalyst, a method for producing a denitration catalyst, and a denitration system applied to a heat engine such as an internal combustion engine or a gas turbine used in automobiles, boilers, and the like.
[0002]
[Prior art]
Various measures have been studied for air pollution caused by heat engines such as internal combustion engines and gas turbines used in automobiles and boilers, but the situation is still severe. In exhaust gas discharged from an internal combustion engine of an automobile, nitrogen oxides (NO _X ) such as nitrogen monoxide (NO) and nitrogen dioxide (NO ₂ ) are contained together with water and carbon dioxide as combustion products. Yes. This NO _X affects the human body and not only increases the incidence of diseases such as respiratory diseases, but is also one of the causes of acid rain that has been regarded as a problem in terms of global environmental conservation.
[0003]
For this reason, various regulations are performed on the exhaust gas from the heat engine as described above, and the regulations are strengthened year by year. For example, the emission limit value for automobiles is set by the Director-General of the Environment Agency as an allowable limit for the amount of automobile exhaust gas based on the Air Pollution Control Law, and the Minister of Transport sets safety standards for road transport vehicles so that this limit value can be secured. . However, problems due to NO _X, which continues to remain a serious situation due to an increase in automobile equipped with a diesel engine, has been speculated that the further strengthening of measures future is made.
[0004]
Various denitration techniques for efficiently removing NO _X in exhaust gas have been developed, and ammonia or urea water is used as a reducing agent, for example, NO _X in exhaust gas is passed through a catalyst such as titanium (TiO ₂ ). A selective catalytic reduction method for reducing to harmless nitrogen (N ₂ ) or water (H ₂ O) is known. When ammonia is used as the reducing agent, by contacting the catalyst by spraying the ammonia gas in the exhaust gas is located downstream direction (discharging direction) of the exhaust gas to decompose NO _X in the exhaust gas to N ₂ and H _{2 O} To denitrate. Also, when urea water is used as the reducing agent, ammonia gas is generated by hydrolyzing the urea water in a predetermined temperature atmosphere (a temperature at which urea can be hydrolyzed), and the ammonia gas is added to the exhaust gas. To denitrate.
[0005]
In general, the selective catalytic reduction method and the separation denitration method are applied to denitrate exhaust gas at a temperature of about 320 to 550 ° C.
[0006]
[Problems to be solved by the invention]
However, the selective catalytic reduction method as described above has a problem that the running cost due to the reducing agent increases. In addition, when the exhaust gas is denitrated at a temperature of about 320 ° C. or less by the above methods, NO _X and ammonia in the exhaust gas react to produce ammonium nitrate, or SO _X and ammonia in the exhaust gas are Reaction may cause ammonium sulfate. The ammonium nitrate and ammonium sulfate are powdered and adhere to the catalyst, and the activity of the catalyst is reduced with the lapse of time of the denitration reaction. That is, depending on the amount of ammonium nitrate or ammonium sulfate adhering to the catalyst, it takes time and effort to periodically remove and clean or replace the catalyst, resulting in high running costs.
[0007]
The present invention has been made in view of the above, and a denitration catalyst and a denitration catalyst that can efficiently denitrate NO _x in exhaust gas even at low temperatures (eg, 320 ° C. or less) without using a reducing agent such as ammonia. The present invention provides a method and a denitration system using the denitration catalyst.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a method for producing a denitration catalyst for storing NO _x in exhaust gas, wherein cobalt nitrate and zirconium oxynitrate are mixed in a molar ratio of cobalt nitrate: oxyoxynitrate. Zirconium is used at a ratio of 1: 1 to prepare an aqueous solution (for example, prepared by dissolving cobalt nitrate and zirconium oxynitrate in distilled water), and water in the aqueous solution is removed by evaporation (for example, stirring at a temperature of 80 ° C. The residue obtained by evaporation is calcined in a reducing gas (for example, calcined in H ₂ gas at a temperature of 450 ° C.).
[0009]
The invention according to claim 2 is the method for producing a denitration catalyst according to claim 1, wherein activated alumina is added to the aqueous solution.
[0010]
The invention according to claim 3, after immersing honeycomb activated alumina (for example, 30 to 100 cells) in the aqueous solution (for example, immersing at room temperature for 0.5 to 6 hours), It is characterized by being dried and fired in a reducing gas.
[0011]
A fourth aspect of the invention is a denitration catalyst manufactured by any one of the first to third aspects of the invention.
[0012]
According to a fifth aspect of the present invention, in the denitration system, exhaust gas is alternately introduced into two denitration reaction chambers equipped with the denitration catalyst produced according to any of the first to third aspects of the present invention, and at room, absorbing a step of storing the NO _X in the exhaust gas, a step of releasing the occluded NO _X, by repeatedly performing the NO _X in the exhaust gas either at one of the denitration reaction chamber At the same time, reducing gas is introduced into the other denitration reaction chamber to release the stored NO _X, and the released NO _X is burned.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a denitration catalyst, a method for producing a denitration catalyst, and a denitration system in an embodiment of the present invention will be described in detail with reference to the drawings.
[0014]
It was found that NO ₂ in the exhaust gas can be occluded by an occlusion substance such as ZrO _X as shown in the following formula even at a low temperature of 320 ° C. or lower.
[0015]
NO ₂ → ZrO · (NO ₃ ) ₂ (1)
In addition, in NO in exhaust gas, by using an oxidation catalyst such as manganese or cobalt, even at a low temperature of 320 ° C. or lower, it is oxidized to NO ₂ as shown in the following formula and then stored in a storage material such as ZrO _X I knew that I could occlude.
[0016]
NO → NO ₂ → ZrO. (NO ₃ ) ₂ (2)
Further, the ZrO. (NO ₃ ) ₂ occluded as described above releases NO _X as shown in the following formula by reducing with a reducing gas such as butane, propane gas or H ₂ (hydrogen gas). I understand.
[0017]
ZrO. (NO ₃ ) ₂ → ZrO _X + NO _X (3)
Therefore, in this embodiment, cobalt nitrate is used as the oxidation catalyst, zirconium oxynitrate is used as the occlusion material, and the cobalt nitrate and zirconium oxynitrate are oxidized to produce a denitration catalyst (first to third examples). Thus, it was studied to efficiently store and release NO _X in the exhaust gas for denitration treatment. Further, constitute a denitration system comprising a denitration reaction chamber 2 group, the sample gas containing NO _X with occluded in each denitration reaction chamber of the, by burning process releases its occluded NO _X examined the reduction of the NO _X discharged from the heat engine to the atmosphere (outside the system of the heat engine).
[0018]
(First embodiment)
In the first embodiment, first, cobalt nitrate and zirconium oxynitrate are used in a molar ratio of 1: 1, and these cobalt nitrate and zirconium oxynitrate are added to distilled water and stirred at a temperature of about 80 ° C. An aqueous solution was obtained. Next, the water in the aqueous solution is removed by evaporation, and the residue is calcined in a reducing gas (hydrogen gas in the first to third embodiments) at a temperature of about 450 ° C. for about 2 to 6 hours. By oxidizing zirconium nitrate, an amorphous (powdered) denitration catalyst composed of cobalt oxide and zirconium oxide was produced.
[0019]
By passing the exhaust gas through the denitration catalyst, NO _{2 in} the exhaust gas is occluded by zirconium oxide in the denitration catalyst as shown in the above formula (1) even at a low temperature of 320 ° C. or less. ZrO can be converted to ZrO. (NO ₃ ) ₂ . Further, NO in the exhaust gas can be occluded by zirconium oxide in the denitration catalyst after being oxidized to NO ₂ with cobalt oxide in the denitration catalyst as shown in the above formula (2).
[0020]
When denitrification processes NO _X in the exhaust gas in this manner, but the denitration catalyst activity decreases with increasing of the NO _X storage amount, together with the NO _X is absorbed and concentrated, butane gas, propane gas and H _Since it can be reduced and released by a reducing gas such as ₂ as shown in the above formula (3), the activity of the denitration catalyst can be easily recovered in a short time.
[0021]
(Second embodiment)
In the second embodiment, as in the first embodiment, cobalt nitrate and zirconium oxynitrate are added to distilled water (molar ratio: cobalt nitrate: zirconium oxynitrate = 1: 1), and then a denitration catalyst with respect to distilled water. Activated alumina (γ-Al ₂ O ₃ ) was added as a carrier for the above, followed by stirring and mixing at a temperature of about 80 ° C. to obtain an aqueous solution. Then, as in the first embodiment, the water in the aqueous solution is removed by evaporation to obtain a residue, which is then calcined in a reducing gas at a temperature of about 450 ° C. for about 2 to 6 hours to obtain cobalt nitrate and zirconium oxynitrate. Oxidation produced an amorphous (powdered) denitration catalyst composed of cobalt oxide and zirconium oxide.
[0022]
As in the second embodiment, by preparing a denitration catalyst by supporting cobalt oxide and zirconium oxide on a carrier, the amount of NO that can be occluded while maintaining the activity of the denitration catalyst (hereinafter referred to as the occlusion allowable amount). ) Can be made larger than in the first embodiment.
[0023]
(Third embodiment)
In the third example, first, activated alumina and a binder (for example, an organic binder) were added to distilled water and mixed and kneaded as a denitration catalyst carrier, and the resulting kneaded product was extruded. Thereafter, the extrudate is dried by conditioning and then fired at a temperature of about 800 ° C. to obtain a honeycomb-shaped carrier having a columnar structure (for example, 30 to 100 cells having a columnar structure of 65 mm × 65 mm × 130 mm). It was. Further, about 100 to 200 grams (preferably about 125 to 150 grams) of cobalt nitrate and zirconium oxynitrate are used, and these cobalt nitrate and zirconium oxynitrate are added to about 0.9 liter of distilled water and mixed to form an aqueous solution. Got.
[0024]
Next, the honeycomb-shaped carrier was immersed in the aqueous solution and allowed to stand at room temperature for about 0.5 to 6.0 hours (preferably about 1 to 2 hours). Thereafter, the honeycomb-shaped carrier is taken out from the aqueous solution, dried, and calcined at a temperature of about 450 ° C. for about 4 hours to oxidize cobalt nitrate and zirconium oxynitrate, thereby forming a honeycomb shape composed of cobalt oxide and zirconium oxide. A denitration catalyst (hereinafter referred to as a honeycomb catalyst) was prepared.
[0025]
As in the third embodiment, when the honeycomb catalyst is produced by supporting cobalt oxide and zirconium oxide on the honeycomb-shaped carrier, the allowable storage amount of the honeycomb catalyst can be made larger than that in the second embodiment. it can.
[0026]
(Denitration test)
Next, a honeycomb catalyst (a 30-cell honeycomb having a supporting rate of 10.5%) was prepared based on the third embodiment, and a test for confirming the characteristics of the denitration catalyst was performed using 20 g of the pulverized sample as a sample. It was.
[0027]
The test device, the processing vessel heater is attached (stainless steel), a gas inlet tube for introducing the gas and connecting the gas discharge pipe for discharging the gas, NO _X concentration analyzer (drilling downstream of the gas discharge pipe This is a configuration in which a portable gas analyzer PG-250) is installed, and the sampled denitration catalyst 20g is housed in a stainless steel mesh case, which is then inserted into the processing vessel. -The installed one was used.
[0028]
In the test, a sample gas obtained by mixing NO (1500 ppm) and 13% O ₂ and adjusting with N ₂ gas was used to denitrate the sample gas and measure the NO _X concentration after the denitration treatment to determine NO. _This was done by confirming the removal rate of _X. At this time, the operating temperature of the denitration catalyst was 300 ° C., and the W / F of the denitration catalyst was 2 g · s · cm ⁻³ . The measurement results are shown in the characteristic diagram of the NO _X removal rate with respect to time change of FIG.
[0029]
As shown in FIG. 1, it was confirmed that about 100% of NO _x was removed over about 30 minutes from the start of the test.
[0030]
Then, NO _X removal rate After 30 minutes gradually decreased, it remained horizontally at about 20%. When checking this phenomenon, a portion of NO in the sample gas passes through the test apparatus are changed to NO _2, since the measurement target of the NO _X concentration analyzer is only NO, it changes to NO ₂ the amount (about 20%) was found to be due to not measured at nO _X concentration analyzer.
[0031]
From the above results, in the test conducted under these conditions, NO _X can be removed for about 30 minutes by reduction and occlusion by the denitration catalyst, and then the activity of the denitration catalyst is gradually lost and removed. The rate decreased, and it was confirmed that NO _X was not removed at all after 1 hour.
[0032]
In the state where the activity of the denitration catalyst was lost, when N ₂ gas adjusted with C ₃ H ₈ (5000 ppm) as a reducing gas was introduced into the test apparatus, NO (high concentration) stored in the denitration catalyst was introduced. NO) was reduced to NO _X and released from the denitration catalyst, and it was confirmed that the denitration catalyst regained its activity. At this time, the time required for the denitration catalyst to completely recover the activity was slightly shorter than about 30 minutes during which occlusion was possible.
[0033]
Therefore, using the above-mentioned test apparatus, NO (1500 ppm) and 13% O ₂ were mixed and adjusted with N ₂ gas to perform denitration (NO _X occlusion) for about 30 minutes and then test It repeated carrying out the release of about 30 minutes NO _X those switching the gas supplying device to the _C 3 _H 8 to (5000 ppm) was _{N 2} gas conditioning as a reducing gas and subjected to repeated experiments occlusion and release of the NO _X . The results of this experiment are shown in the characteristic diagram of the switching times and the amount of NO _X / mol of occluding and releasing FIG.
[0034]
As shown in FIG. 2, even when repeated occlusion and release, about 1.2 × 10 ⁻³ mol of NO _X is stably occluded during occlusion, and about 9.5 × 10 ⁻³ mol of NO _X is released during occlusion. It can be confirmed that the gas is stably released, and about 100% of NO _X contained in the sample gas is occluded. If 20% of NO not measured by the above-mentioned NO _x concentration analyzer is taken into consideration, the occluded NO _{X It} can be seen that 100% of _X is released.
[0035]
(Denitration system)
Next, a denitration system that continuously removes NO _X in the exhaust gas using the denitration catalysts of the first to third embodiments will be described.
[0036]
FIG. 3 is a schematic explanatory diagram of a denitration system using the denitration catalyst of the first to third embodiments. In FIG. 3, reference numerals 11 and 12 denote first and second denitration reactors each filled with a denitration catalyst (not shown), and reference numeral 13 denotes exhaust gas discharged from a heat engine (not shown). Is a three-way valve for introducing either one of the first and second denitration reaction chambers 11 and 12. By controlling the three-way valve 13, the exhaust gas from the heat engine can be alternately introduced into the first and second denitration reaction chambers 11 and 12.
[0037]
The exhaust gas that has passed through the first and second denitration reaction chambers 11 and 12 is discharged to the outside of the heat engine through the three-way valve 14 or burner (high concentration NO _x through the on-off valves 15a and 15b, respectively. Are introduced into a denitration burner 16 for burning the gas. As shown in the figure, it is assumed that a reducing gas can be introduced into the first and second denitration reaction chambers 11 and 12 via the on-off valves 17a and 17b, respectively.
[0038]
Next, an operation example of the denitration system shown in FIG. 3 will be described. First, the three-way valve 13 is controlled to introduce exhaust gas discharged from the heat engine into the first denitration reaction chamber 11, and NO _X in the exhaust gas is reduced by the denitration catalyst in the first denitration reaction chamber 11 and occluded. As a result, NO _{X in} the exhaust gas is removed. Its NO _X exhaust gas has been removed is discharged from the system of the heat engine via the three-way valve 14.
[0039]
After the activity of the denitration catalyst in the first denitration reaction chamber 11 begins to decrease with the passage of time of the denitration reaction, the three-way valve 13 is controlled to introduce exhaust gas from the heat engine into the second denitration reaction chamber 12, similar to the first denitration reaction chamber 11 of the at denitration catalyst is occluded after reducing the NO _X in the exhaust gas, the NO _X exhaust gas removed is discharged from the system of the heat engine via the three-way valve 14 .
[0040]
Further, during the period in which the exhaust gas is introduced into the second denitration reaction chamber 12, a reducing gas is introduced into the first denitration reaction chamber 11 via the on-off valve 17a, and the first denitration reaction is performed. NO (high concentration NO) occluded in the denitration catalyst in the chamber 11 is reduced to NO _X and released, and the reduced denitration catalyst activity in the first denitration reaction chamber 11 is recovered. The released NO _X is introduced into the burner 16 and combusted together with fuel and combustion air, so that it is reduced or decomposed and discharged out of the system of the heat engine.
[0041]
Then, after the activity of the denitration catalyst in the second denitration reaction chamber 12 starts to decrease with the passage of time of the denitration reaction, the three-way valve 13 is controlled to introduce the exhaust gas from the heat engine into the first denitration reaction chamber 11 again. and, the activity was recovered denitration catalyst occludes after reducing the NO _X in the exhaust gas, and discharges the exhaust gas to remove the NO _X to the outside of the heat engine via the three-way valve 14.
[0042]
Further, by introducing the reducing gas into the second denitration reaction chamber 12 through the on-off valve 17b during the period in which the exhaust gas is introduced into the first denitration reaction chamber 11, the first denitration reaction chamber 12 is introduced. As in the case of the first denitration reaction chamber 11, the reduced denitration catalyst activity in the second denitration reaction chamber 12 is recovered, and the released NO _x is combusted by the burner 16, reduced or decomposed, and then removed from the heat engine system. To discharge.
[0043]
As described above, a denitration system is configured, and exhaust gas from the heat engine is alternately introduced into the first and second denitration reaction chambers, and in each of the first and second denitration reaction chambers, an occlusion process and a discharge process are performed. By repeating the above, it is possible to continuously denitrate the exhaust gas from the heat engine and maintain the activity of the denitration catalyst in the denitration system. Further, according to this denitration system, it is not necessary to take out the denitration catalyst for cleaning or replacement, and the running cost can be reduced.
[0044]
In the denitration system shown in FIG. 3, but the emitted NO _X is reduced or decomposed configured combusted by the burner, for example, recirculated to the heat engine with combustion air emitted NO _X of the Or a combustion means such as a recombustion boiler or duct burner is provided between the heat engine and the denitration system, and the released NO _X is combusted together with the combustion air in the combustion means. Also good.
[0045]
The three-way valves 13 and 14 and the on-off valves 15a, 15b, and 17a are also considered in consideration of the NO _X amount that can be discharged, the storage capacity of the denitration catalyst, the reaction rates in the first and second denitration reaction chambers 11 and 12, and the like. , 17b can be used to automate the denitration system, and the size of the denitration system can be reduced by minimizing the amount of reducing gas to be used and the denitration catalyst (and each denitration reaction chamber). it can. Furthermore, the denitration reaction chamber in the denitration system may be increased according to the scale of the heat engine, the amount of exhaust gas, and the like.
[0046]
Furthermore, according to the denitration catalyst shown in the first to third embodiments, the operating temperature of the denitration reaction chamber capable of absorbing NO and NO ₂ in the exhaust gas even one hundred to three hundred and twenty ° C. (NO ₂ at room temperature under But it can be occluded). When the operating temperature is 100 ° C. or lower, NO cannot be occluded due to a decrease in the oxidizing power of cobalt oxide, and therefore a converter or the like for oxidizing NO may be provided.
[0047]
Although the present invention has been described in detail only for the specific examples described above, it is obvious to those skilled in the art that various changes and modifications can be made within the scope of the technical idea of the present invention. Of course, such variations and modifications fall within the scope of the appended claims.
[0048]
For example, by using a desulfurization device between each denitration reaction chamber and heat engine of the denitration system shown in the present embodiment, A heavy oil or C heavy oil that discharges not only NO _X but also high concentration SO _X is used. Can be applied to the heat engine that was.
[0049]
【The invention's effect】
As described above in detail, according to the present invention, NO _x in exhaust gas can be occluded even at a low temperature of 320 ° C. or less by a denitration catalyst comprising cobalt oxide and zirconium oxide. Further, by the denitration catalyst, NO _X in the exhaust gas can be recovered and concentrated to a to be occluded, the activity of the denitration catalyst is easily releases NO _X in a short time with a reducing gas. Further, the denitration system 2 group using the denitration catalyst, as well as absorbing the NO _X in the exhaust gas, it is possible to burn and releases the occluded NO _X, can denitration successively the exhaust gas denitration system The activity of the denitration catalyst in the inside can be maintained.
[0050]
Therefore, denitration treatment of exhaust gas can be easily performed at low cost even at low temperatures.
[Brief description of the drawings]
[1] Time NO _X removal rate characteristic diagram for change.
[Figure 2] characteristic diagram of the switching frequency and _the amount of NO _X occluded release.
FIG. 3 is a schematic explanatory diagram of a denitration system in the present embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 ... 1st denitration reaction chamber 12 ... 2nd denitration reaction chamber 13, 14 ... Three-way valve 15a, 15b, 17a, 17b ... On-off valve 16 ... Burner

Claims (5)

In a method for producing a denitration catalyst that stores NO _X in exhaust gas,
An aqueous solution is prepared using cobalt nitrate and zirconium oxynitrate in a molar ratio of cobalt nitrate: zirconium oxynitrate = 1: 1, and the residue obtained by evaporating and removing the water in the aqueous solution is calcined in a reducing gas. A method for producing a denitration catalyst. 2. The method for producing a denitration catalyst according to claim 1, wherein activated alumina is added to the aqueous solution. 2. The method for producing a denitration catalyst according to claim 1, wherein the activated alumina is dipped in the aqueous solution, and then the activated alumina is dried and calcined in a reducing gas. A denitration catalyst produced by the production method according to claim 1. The exhaust gas is alternately introduced into the two denitration reaction chambers equipped with the denitration catalyst produced by the production method according to claim 1,
In each of the denitration reaction chambers, by repeatedly storing the NO _X in the exhaust gas and releasing the stored NO _X ,
Either at one of the denitration reaction chamber while storing the NO _X in the exhaust gas, by introducing a reducing gas into the other of the denitration reaction chamber to release occluded NO _X,
A NOx removal system characterized in that the released NO _X is subjected to a combustion treatment.

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