JP2003269142A - Exhaust emission control method and device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stable and high denitrification rate even to large load variation and to prevent effluence of a unreacted substance, in an exhaust emission control method of an internal combustion engine such as a diesel engine. <P>SOLUTION: A required amount 24 of reducer injection is calculated from an exhaust gas flow rate 21 of the diesel engine 1, an NOx flow rate 22 in the exhaust gas and an exhaust gas or catalyst temperature 23 to control the injection. The exhaust flow rate and the NOx flow rate are calculated from an engine speed 20. An NOx amount can be calculated by actually measuring the exhaust gas flow rate, NOx concentration and the exhaust gas temperature, and all the data of the exhaust gas flow rate, the NOx concentration and the exhaust gas temperature can be obtained from the operation state of the engine. By controlling the reducer injection amount with respect to the NOx amount by the exhaust gas or catalyst temperature, the stable denitrification rate can be realized by a simple technique, and a low-cost operation minimized in effluence of the reducer to the exit can be realized. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for purifying exhaust gas, and more particularly, to efficiently remove nitrogen oxides contained in exhaust gas from internal combustion engines such as mobile engines for automobiles and small diesel engines such as generators. Related to the removal technology.

[0002]

2. Description of the Related Art Diesel engines are widely used in cogeneration systems, automobiles, generators, etc., but in recent years, due to the growing concern about global environment conservation,
The regulations on exhaust gas emitted from these engines are tightened.

Usually, a catalyst for purifying automobile exhaust gas contains NO and NO of carbon monoxide (CO) and hydrocarbons (HC).
A three-way catalyst that simultaneously reduces x (for example, Japanese Patent Publication No. 56-
No. 27295 gazette) is used, but in the case of a lean burn engine or a diesel engine, since it is in an oxygen excess atmosphere, it is difficult to purify NOx with a general three-way catalyst.

Therefore, in order to purify the exhaust gas, the following method, that is, a method of removing particulate pollutants (PM) by a filter and then removing nitrogen oxides, P
A method of reducing NOx using a hydrocarbon as a reducing agent on a catalyst bearing a precious metal such as t (for example, Japanese Patent Laid-Open No. 5-1039).
No. 85), a method using a NOx storage catalyst, and many other methods have been proposed.

[0005]

Of the above-mentioned conventional techniques,
In this method, for example, exhaust gas discharged from a diesel engine is first trapped by a filter carrying a catalyst and the like, and then NH ₃ such as NH ₃ or urea such as urea is used as a reducing agent.
_{This is} a method of surely removing PM and NOx by adding ₃ precursors and catalytically reducing them on a denitration catalyst to convert them into harmless nitrogen and water.

This NOx removing method is a method widely used for removing NOx in exhaust gas discharged from a power plant or the like and can remove NOx stably. However, since unreacted NH ₃ becomes a secondary pollutant, this method has not been widely used for power generation of automobiles and cogeneration systems that are often used in densely populated areas.

Therefore, NH_ThreeTo prevent the outflow of
NH, such as urea, which is harmless as an active ingredient_Three Using a precursor
Is being considered. However, urea is
Reacting NH_ThreeIs used to produce
NH of reaction_ThreeOccurrence of is inevitable.

In order to improve this, using a denitration catalyst having a NH ₃ resolution catalyst, denitration method (e.g. Japanese Patent Application No. 05-109088 capable of reducing agents such as urea be prevented from flowing out to the outlet ) Etc. are also proposed.

In order to prevent the unreacted reducing agent from flowing out due to such fluctuations in the NOx amount, the NOx concentration at the inlet and outlet of the catalyst layer is measured in a denitration device generally used in a power plant or the like, and the value is calculated. A stable denitration rate can be obtained by a method in which the amount of the reducing agent added is controlled in advance.

However, for example, in automobiles, the start and stop of the engine is more frequent than in power plants and the like, and the load variation of the engine is large, so the temperature and emission amount of exhaust gas are likely to vary, and therefore the amount of NOx to be treated is large. Fluctuates greatly.

As described above, when the fluctuation of the NOx emission amount is large, it is difficult to control the supply amount of the reducing agent by the control method which has heretofore been used in the fixed bed. Moreover, in a small engine such as an automobile, using an expensive NOx meter or an advanced control device has been a problem in terms of cost.

The object of the present invention is to eliminate the above-mentioned problems, to obtain a stable high denitration rate even with a large load change, and to remove nitrogen oxides without flowing out unreacted substances. To provide a method.

[0013]

The above object is to provide an exhaust gas purification method for reducing nitrogen oxides in exhaust gas discharged from an internal combustion engine by contacting a catalyst with ammonia or a precursor thereof as a reducing agent to reduce the exhaust gas. Alternatively, it can be achieved by an exhaust gas purification method characterized in that the injection amount of the NOx reducing agent injected into the exhaust gas is controlled by the temperature of the catalyst.

According to the experiments conducted by the present inventors, by using the extremely easy-to-measure data such as the exhaust gas temperature or the catalyst temperature, the result can be obtained without using a complicated control method for supplying the reducing agent, as described later. As a result, a stable denitration rate was obtained, and wasteful outflow of the reducing agent was suppressed.

As a catalyst, NH is used rather than a denitration catalyst.
_It is easier to control using a catalyst having ₃ resolution, but by controlling the injection amount of the reducing agent according to the exhaust gas temperature in both, a stable denitration rate can be obtained without using a complicated control method. In addition, the amount of reducing agent flowing out can be minimized.

The NOx outflow amount in the exhaust gas to be treated is calculated from the exhaust gas amount discharged from the engine and the NOx concentration. The amount of exhaust gas discharged from the engine may be measured using a measuring instrument such as a flow meter, but without using such a device, the operating conditions of the internal combustion engine such as the engine speed and engine intake air amount It is also possible to indirectly request from.

The NOx concentration may be measured by using a concentration detector such as a NOx monitor, but without using such a measuring means, the engine speed,
It is also possible to obtain the relationship between the operating condition of the internal combustion engine such as the engine intake air amount and the exhausted NOx concentration as data in advance, and indirectly obtain the NOx concentration from the operating condition of the engine.

The exhaust gas temperature is the exhaust gas temperature at the engine outlet,
Alternatively, the temperature of the catalyst layer may be measured by a temperature detector such as a thermometer, but this is also indirectly determined from the operating conditions of the internal combustion engine such as the engine speed, cooling water temperature, and engine intake air amount. You can also do it.

The catalyst referred to herein may be an ordinary denitration catalyst, but a denitration catalyst having NH ₃ decomposing ability is particularly preferable because NH ₃ outflow from the outlet is unlikely to occur. NH
_The denitration catalyst having _three resolutions is, for example, Japanese Patent Laid-Open No. 05-
1 selected from titanium (Ti), tungsten (W), and vanadium (V) described in Japanese Patent No. 146634.
A composition comprising an oxide of one or more elements is used as the first component,
Platinum (Pt), Palladium (Pd), Iridium (I
r), one or more noble metals selected from rhodium (Rh), or a catalyst composition containing the noble metal-containing composition previously supported on a porous body such as silica, zeolite or alumina as a second component. It is suitable.

Further, the ordinary denitration catalyst is, for example, titanium (Ti) described in JP-A-50-128681.
In addition to denitration catalysts that are currently widely used in boilers of power plants, such as compositions that consist of oxides of one or more elements selected from tungsten (W), molybdenum (Mo) and vanadium (V), copper , A zeolite carrying iron, cerium, etc. has a denitration function.

When a denitration catalyst having NH ₃ decomposing ability is used as the catalyst, if the detection temperature is 300 ° C. or lower,
The molar ratio of (NH ₃ or NH ₃ precursor) / (nitrogen oxide in exhaust gas) is set to 1 mol / mol or less. When it exceeds 1, unreacted reducing agent may flow out to the outlet, which is not preferable.

At 300 ° C. or higher, the reducing agent is supplied so that the molar ratio is 1 or higher, preferably in the range of 1 to 1.5. If it is 1 mol / mol or less, NOx may flow out to the outlet, and if it exceeds 1.5, unreacted reducing agent may flow out to the outlet.

When a normal denitration catalyst is used as the catalyst, when the detection temperature is 300 ° C. or lower, the molar ratio of (NH ₃ or NH ₃ precursor) / (nitrogen oxide in exhaust gas) is 1 mol / mol. Below. If it exceeds 1 mol / mol, unreacted reducing agent may flow out to the outlet, which is not preferable.

Further, at 300 to 450 ° C., the reducing agent is supplied so that the molar ratio is in the vicinity of 1, preferably in the range of 0.8 to 1.1 mol / mol. If it is less than 1 mol / mol, NOx may flow out to the outlet, and 1.1 mol / mol
If it exceeds the molar amount, unreacted reducing agent flows out to the outlet, which is not preferable.

Further, at 450 ° C. or higher, the reducing agent is supplied in an amount of 1 mol / mol or more, preferably in the range of 1 to 1.5. If it is 1 mol / mol or less, NOx may flow out to the outlet, and if it exceeds 1.5, unreacted reducing agent may flow out to the outlet.

The catalyst shape is such that the catalyst component having the above composition is carried on a porous carrier such as a carrier such as cordierite or zeolite or a honeycomb type carrier in which inorganic fiber woven fabrics are laminated in multiple layers. In addition to the catalyst, any material such as a plate-like material that is usually used as a denitration catalyst, an extruded honeycomb-shaped material, or a granular material may be used.
In a small engine such as an automobile, it is preferable to use a catalyst in which a catalyst component is supported on a narrow-pitch honeycomb carrier because of space problems. The catalyst component loading method is an impregnation method,
Usual catalyst preparation methods such as coating method, slurry coating method and wash coating method can be used.

The reducing agent used here is usually NOx.
In addition to ammonia used for the reduction of ammonia, an ammonia precursor such as urea, cyanuric acid, and melamine can be used. The method of supplying the reducing agent is not particularly limited, and an optimum supplying method for the reducing agent to be used, such as ammonia gas, ammonia water, an aqueous solution state of urea aqueous solution, urea, cyanuric acid, melamine, etc., is used in a granular or powder state. Can be taken. Particularly for automobiles and small engines used in densely populated areas, it is preferable to use a gas other than ammonia gas because there is no risk of explosion.

The following is a description of the operation when each configuration of the present invention is adopted.
I will explain. NH as a reducing agent_Three Or such as urea
NH_ThreeNOx is contained by the denitration catalyst using the precursor of
When the exhaust gas is treated, there is Ti, V, Mo in the catalyst.
Or NH due to the action of W _Three(Or NH_Threeprecursor
NH generated from the body_Three) NO reduction of formula (1)
The reaction proceeds and NOx reduction is achieved.

NH ₃ + NO + 1 / 4O ₂ → N ₂ + 3 / 2H ₂ O ……… (1)

Furthermore, in the denitration catalyst having a NH ₃ resolution, NH ₃ which has not been used for the denitration reaction, by the action of the noble metal component in the catalyst (2) is oxidized with oxygen as shown in formula harmless nitrogen And decomposed into water.

2NH ₃ + 3 / 2O ₂ → N ₂ + 3H ₂ O ……… (2)

FIG. 5 shows a titanium-based denitration catalyst described in JP-B-56-27295 and JP-A-5-146634.
An example of the temperature characteristics of the denitration rate and the NH ₃ oxidation rate of the denitration catalyst having the NH ₃ resolving power described in Japanese Patent Laid-Open Publication is shown.

As is clear from FIG. 5, the denitration activity of the titanium-based denitration catalyst is generally highest in the temperature range of 300 to 450 ° C., lower than 300 ° C., and 450.
It is known that the activity is lower in the temperature range higher than 0 ° C as compared with the above temperature.

This is because at a low temperature, the denitration reaction rate is slow, so that the reaction rate is limited and high performance cannot be obtained. At a high temperature, NH _{3 as} a reducing agent is oxidized and reduced, and NH ₃ necessary for NOx reduction is reduced. This is because there will be a shortage. Also, NH
_The denitration catalyst having ₃ resolution has almost the same denitration characteristics as the denitration catalyst, but the NH ₃ resolution appears at 300 ° C. or higher.

Further, FIG. 6 shows a titanium-based denitration catalyst and
NH_ThreeFor the denitration catalyst with high resolution, the denitration rate is 3
NH at 50 ° C_ThreeAn example of the / NOx molar ratio characteristic is shown.
NH _ThreeWith a denitrification catalyst with high resolution, at temperatures above 300 ° C
NH_ThreeBecause of its high decomposition activity, the molar ratio is 1 mol / mol
Even above is almost NH_ThreeCan't see the leak.

[0036] This means that in the denitration catalyst having a NH ₃ resolution, at the 300 ° C. or higher, if excessively injected reducing agent for variations in NOx emissions, generates little leakage amount of reducing agent from the outlet It means not to let.

Therefore, with the denitration catalyst having the NH ₃ decomposing ability, under the condition that the exhaust gas temperature cannot obtain the NH ₃ decomposing ability of 300 ° C. or lower and the high denitration rate cannot be obtained,
₃ injection amount so that the molar ratio to the NOx outflow amount is 1 mol / mol or less, and under the condition that the exhaust gas temperature is 300 ° C. or higher and NH ₃ decomposition activity and denitration activity are high, the molar ratio is 1 mol / mol. Inject it so that it is more than molar. 300
This is because at a temperature of not less than 0 ° C., leak NH ₃ does not occur even if the reducing agent is excessively injected.

Further, with the denitration catalyst, the exhaust gas temperature is 300
Under conditions in which the NH ₃ resolution cannot be obtained and a high denitrification rate cannot be obtained, the NH ₃ injection amount is injected so that the molar ratio is 1 mol / mol or less with respect to the NOx outflow amount.
Under conditions where the NH ₃ decomposition activity is not obtained but the denitrification activity is high in the exhaust gas temperature range of 300 ° C. to 450 ° C., the injection is performed so that the molar ratio is about 1 mol / mol.

With a normal denitration catalyst, NH
_Since there is no _3- decomposition activity, injection of an excessive reducing agent leads to outflow of the reducing agent to the outlet. Further, under the condition that the exhaust gas temperature is 450 ° C. or higher and the NH ₃ decomposition activity and the denitrification activity are high, the injection is performed so that the molar ratio is 1 mol / mol or more. This is because leak NH ₃ does not occur at this temperature even if the reducing agent is excessively injected.

[0040] As described above, as the catalyst is preferable to use a catalyst having a NH ₃ resolution than used denitration catalyst,
Although it is easier to control, in both cases, by controlling the reducing agent injection amount by the exhaust gas temperature, a stable denitrification rate can be obtained without using a complicated control method, and the reducing agent outflow amount can be minimized. You will be able to hold it down.

[0041]

BEST MODE FOR CARRYING OUT THE INVENTION The outline of an embodiment of the present invention is as follows: exhaust gas flow rate 21 of diesel engine 1 and N in exhaust gas.
The required reducing agent injection amount 24 is calculated from the Ox flow rate 22 and the exhaust gas or catalyst temperature 23 to control the reducing agent injection.

In the specific example 1 (FIG. 1), the exhaust gas flow rate and the NOx flow rate are calculated from the engine speed 20, and the specific example 2
In FIG. 2, the NOx amount is calculated by actually measuring the exhaust gas flow rate, the NOx concentration, and the exhaust gas temperature. In addition, specific example 3 (FIG. 3)
Then, all the data of the exhaust gas flow rate, the NOx concentration, and the exhaust gas temperature can be obtained from the operating state of the engine.

In this way, the NOx amount is calculated by some method or means, and the reducing agent injection amount is calculated as
By controlling the temperature of the exhaust gas or catalyst that is easy to measure, a stable denitration rate can be achieved with a simple method.
Further, it is possible to carry out low-cost operation in which the outflow of the reducing agent to the outlet is minimized.

Specific Example 1 A specific example of a control device for carrying out the method of the present invention will be described below with reference to FIG. In FIG. 1, the exhaust gas discharged from the diesel engine 1 passes through the flue 10 and is introduced into the catalyst layer 4.

The reducing agent is supplied from the reducing agent supply source 3 to the inlet flue of the catalyst layer 4 through the reducing agent injection nozzle, is mixed with the exhaust gas, and NOx is reduced by the reducing agent on the catalyst in the catalyst layer 4, The treated exhaust gas is discharged to the outside of the system. Reference numeral 11 is a control valve for controlling the flow rate of the reducing agent, 5 is a temperature detecting device for detecting the temperature of exhaust gas, and 6 is an engine speed detecting device.

The control method in this example is shown below. Exhaust gas flow rate and NO from engine speed measurement device 6 of engine 1
The calculated value of x concentration is obtained, and the exhaust gas flow rate signal 21 and NOx
The concentration signal 22 is sent to the calculator 8.

The calculator 8 calculates the NOx flow rate in the exhaust gas by using the numerical values obtained from these signals. The obtained NOx flow rate and the temperature signal 23 obtained from the temperature detection device 5.
From the above, the calculator 8 determines the reducing agent injection amount necessary for the reaction, and the reducing agent injection control signal 24 is sent to the control valve 11 to determine the reducing agent injection amount.

The specific operation will be described below using an example of using an aqueous urea solution as a reducing agent. When the numerical value of the engine speed is sent from the engine speed measuring device 6 to the calculator, the exhaust gas flow rate and the NOx concentration are calculated there.
The NOx amount is calculated from these numerical values.

Separately from this, the exhaust gas temperature signal 23 is sent to the calculator 8. When the measured temperature is when the engine is started (for example, 200 ° C.), the reducing agent injection amount from the calculator 8 is (1/2 mol of urea) / NOx mol ratio with respect to the obtained NOx flow rate. A control signal 24 is sent to the control valve 11 so as to be 1 or less (for example, 0.5), and a predetermined amount of urea aqueous solution is sent to the flue through the nozzle.

In this temperature range, neither catalyst has a low denitrification rate and no NH ₃ decomposition rate. Therefore, unreacted urea or a decomposition product of urea discharged to the outlet can be obtained. Some ammonia can be prevented from flowing to the outlet.

The measured temperature is 300 to 450 ° C.
In the case of the normal denitration catalyst, the reducing agent injection amount from the calculator 8 is (1/2 mol of urea) / NOx molar ratio in the vicinity of 1 (for example, 0.
9), the control signal 24 is sent to the control valve 11 and a predetermined amount of urea aqueous solution is sent to the flue through the nozzle.

In the case of a normal denitration catalyst, the denitration performance is high at this temperature, but there is no NH ₃ decomposing ability, so by controlling in this way, a high denitration rate and a low amount of leak reducing agent can be maintained.

Meanwhile, in the case of using a denitration catalyst having a NH ₃ resolution as a catalyst, a reducing agent injection amount from the arithmetic unit 8, the obtained flow rate of NOx, (1/2 moles of urea)
A control signal 24 is sent to the control valve 11 so that the / NOx molar ratio becomes 1 or more (for example, 1.4), and a predetermined amount of aqueous urea solution is sent to the flue through the nozzle.

[0054] NH ₃ when the catalyst with a resolution, because this temperature at high denitrification rate and high NH ₃ decomposition rate is obtained, it is possible to obtain a stable and high NOx removal efficiency if excessive injection of reducing agent, yet reduced Does not allow the agent to flow out.

Furthermore, when the measured temperature is 450 ° C. or higher, the reducing agent injection amount from the computing unit 8 is (1 / urea of urea) with respect to the obtained NOx flow rate for any catalyst.
A control signal 24 is sent to the control valve 11 so that the molar ratio of 2 mol / NOx becomes 1 or more (for example, 1.4), and a predetermined amount of aqueous urea solution is sent to the flue through the nozzle.

At this temperature, all the catalysts have a high denitrification rate and a high NH ₃ decomposition rate, and therefore a stable denitrification rate can be obtained by injecting excessively with the reducing agent and the reducing agent does not flow out. Is. Although urea is shown as the reducing agent in this example, it goes without saying that the same operation can be performed even if the reducing agent is another reducing agent such as NH ₃ water or NH ₃ gas.

Specific Example 2 FIG. 2 is an example of controlling the injection amount of reducing agent by actually measuring the exhaust gas amount, NOx concentration, and exhaust gas temperature to calculate the NOx amount by the exhaust gas purification method of the present invention. The basic flow of this example is the same as that of FIG. 1, and reference numeral 12 is an exhaust gas flow rate detection device, and 7 is a NOx concentration detection device.
In this example, the exhaust gas flow rate is obtained by the exhaust gas flow rate detection device 12, and the NOx concentration is obtained by the NOx concentration detection device 7.

Obtained exhaust gas flow rate signal 21 and NOx
The NOx flow rate in the gas is calculated from the concentration signal 22, and the reducing agent injection amount necessary for the reaction is determined by the calculator 8 from the obtained NOx flow rate and the temperature signal 23 obtained from the temperature detection device 5. The injection control signal 24 is sent to the control valve 11 to determine the reducing agent injection amount.

In this example, the amount of exhaust gas and NOx
Except that the concentration is actually measured and the NOx outflow amount is calculated, the operation is the same as that of the first specific example. Therefore, the operation of this example can be performed in the same manner as the first specific example.

Specific Example 3 FIG. 3 is an example of obtaining all the data of the exhaust gas amount, NOx concentration, and exhaust gas temperature from the operating state of the engine in the exhaust gas purification method of the present invention. The basic flow of this example is the same as in FIG. 1, and in this specific example, the exhaust gas flow rate, NOx concentration,
And the calculated value of the exhaust gas temperature, the exhaust gas flow rate signal 21,
The NOx concentration signal 23 and the temperature signal 23 are sent to the calculator 8.

The calculator 8 calculates the NOx flow rate in the exhaust gas using the numerical values obtained from the exhaust gas flow rate signal 21 and the NOx concentration signal 23, and the calculator 8 reacts based on the obtained NOx flow rate and the temperature signal 23. Is determined, and the reducing agent injection control signal 24 is sent to the control valve 11 to determine the reducing agent injection amount.

In this example, the amount of exhaust gas and NOx
Except that the concentration and the exhaust gas temperature are converted from the operating conditions of the internal combustion engine to calculate the NOx outflow amount, the operation is the same as in the first specific example, and therefore, the operation of this example can be performed in the same manner as the first specific example.

As in the above-mentioned example, the NOx amount is calculated by some method and means, and the reducing agent injection amount for the NOx amount is controlled by the temperature of the exhaust gas or the catalyst, whereby a stable denitration rate can be realized. Further, it is possible to carry out low-cost operation in which the outflow of the reducing agent to the outlet is minimized.

In addition to the examples shown in the concrete examples 1 to 3, the exhaust gas amount is converted from the operating condition of the internal combustion engine, and the NOx concentration is measured by a meter. Needless to say, similar results can be obtained by calculating the NOx amount, and any method is within the scope of the present invention.

[Catalyst Preparation Example 1] Japanese Patent Application No. 2001-216
According to Catalyst Preparation Process 743 JP to obtain a denitration catalyst having a NH ₃ resolution.

[Catalyst preparation example 2] NH of catalyst preparation example 1
₃ except without the Pt component is an exploded component, in the same manner as in Catalyst Preparation Example 1 to obtain a catalyst having only the denitration catalyst component. The composition of the obtained catalyst is shown in Table 1.

[0067]

[Table 1]

[Test Example 1] NH when using the catalyst prepared in Catalyst Preparation Examples 1 and 2 and NH ₃ as a reducing agent
The NH ₃ outflow amount at the outlet when the ₃ / NO molar ratio was changed was measured under the conditions of Table 2.

[0069]

[Table 2]

The measurement results are shown in FIG. N of catalyst preparation example 1
H_ThreeIn the case of a denitration catalyst having resolution (Fig. 4-a), NH
_ThreeAt 200 ℃, which has low decomposition activity and low denitrification rate, a reducing agent
From the vicinity of the / NO molar ratio of 0.5 mol / mol to the outlet
NH_ThreeBegins to flow out, but at 350 ° C and 500 ° C,
NH from the outlet even when the molar ratio is 1 mol / mol or more
_ThreeAlmost no leak was observed.

In a temperature range where the NH ₃ decomposition activity is low, such as 200 ° C., the reducing agent / NO molar ratio is reduced to 1 mol / mol or less, and the NH ₃ decomposition activity is high such as 350 ° C. or 500 ° C. and the denitration rate is high. Then, by setting it to 1 mol / mol or more, a high denitration rate and a low leak NH ₃ can be realized.

Further, in the normal denitration catalyst of Catalyst Preparation Example 2 (FIG. 4-b), the NH ₃ decomposition activity is low, and at a low denitration rate of 200 ° C., the reducing agent / NO molar ratio is 0.5 mol / min. NH ₃ flows out from the vicinity of the mole to the outlet, and at 350 ° C., which has no NH ₃ decomposition activity and a high denitration rate, NH ₃ flows out from the vicinity of 1 mole / mole to the outlet.

Further, in the temperature range where the NH ₃ decomposition activity is high at 500 ° C. and the denitrification rate is high, even at 1 mol / mol or more, NH
₃ never leaks. That is, in the temperature range where the NH ₃ decomposition activity is low, such as 200 ° C., the reducing agent / NO
NH at a molar ratio of 1 mol / mol or less, such as 350 ° C
_{In the} temperature range where there is no decomposition activity and the NOx removal rate is high, 1 mol /
It can be seen that, in the temperature range near the mol, where the NH ₃ decomposition activity is high and the denitration rate is high, such as 500 ° C., a high denitration rate and a low leak NH ₃ can be realized by setting it to 1 mol / mol or more.

As described above, by adopting the exhaust gas purifying method of the present invention, a stable denitration rate can be realized in all temperature ranges, and a low leak NH ₃ amount enables low-cost operation.

[0075]

As described above, according to the present invention, it is possible to obtain a stable high denitrification rate even with a large load change, and a method for removing nitrogen oxides without flowing out unreacted substances. Can be realized.

[Brief description of drawings]

FIG. 1 is a basic configuration diagram showing an embodiment of an exhaust gas purifying apparatus of the present invention.

FIG. 2 is a basic configuration diagram showing another embodiment of the exhaust gas purifying apparatus of the present invention.

FIG. 3 is a basic configuration diagram showing another embodiment of the exhaust gas purifying apparatus of the present invention.

FIG. 4 is a supplementary diagram of each specific example of the present invention.

FIG. 5 is a characteristic diagram of a catalyst used in the present invention.

FIG. 6 is a characteristic diagram of a catalyst used in the present invention.

[Explanation of symbols]

1 diesel engine 3 Reductant supply source 4 Catalyst layer 5 Exhaust gas temperature detector 6 Engine speed detector 7 NOx concentration detector 8 arithmetic unit 10 flue 11 Reducing agent flow control valve 12 Exhaust gas flow rate detector 21 Exhaust gas flow rate signal 22 NOx concentration signal 23 Temperature signal 24 Reductant injection control signal

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F01N 3/28 301 B01D 53/36 ZAB 102B F term (reference) 3G091 AA18 AB04 BA01 BA14 CA17 EA01 EA05 EA21 EA22 EA33 GA01 GA03 GA05 GA06 GB01W GB05W GB06W GB07W GB09X GB10X 4D048 AA06 AA08 AB02 AB03 AC03 AC04 BA07X BA10X BA13X BA23X BA27X BA30X BA31Y BA33Y BA42X BB02 DA01 DA02 DA03 DA05 DA08 DA10 DA13 DA20

Claims (8)

[Claims] 1. An exhaust gas purification method for reducing nitrogen oxide in exhaust gas discharged from an internal combustion engine by bringing ammonia or a precursor thereof into contact with a catalyst as a reducing agent,
An exhaust gas purification method, characterized in that the injection amount of a NOx reducing agent injected into the exhaust gas is controlled by the temperature of the exhaust gas or the catalyst. 2. The amount of NOx contained in the exhaust gas is the amount of exhaust gas measured or converted from the engine speed,
The exhaust gas purifying apparatus according to claim 1, wherein the exhaust gas purifying apparatus is a numerical value calculated from a NOx concentration calculated based on data obtained in advance from a relationship with an engine speed or an engine intake air amount. 3. The exhaust gas purification method according to claim 1, wherein the NOx amount contained in the exhaust gas is a numerical value calculated from the exhaust gas amount and an actual measurement value of the NOx concentration in the exhaust gas. 4. The NOx amount contained in the exhaust gas, the exhaust gas amount and the NOx concentration are calculated based on data obtained in advance from the engine speed of the internal combustion engine or the engine intake air amount, and the exhaust gas amount and the NOx amount are calculated. The exhaust gas purification method according to claim 1, which is a numerical value calculated from the concentration. 5. The catalyst is a denitration catalyst, and when the temperature of the exhaust gas or the catalyst is lower than 300 ° C., the supply amount of the reducing agent to the NOx amount calculated from the exhaust gas amount and the NOx concentration is set to (NH ₃ or the NH ₃ precursor (NH ₃ conversion value) / (NOx in exhaust gas) molar ratio is controlled to be 1 mol / mol or less, and the temperature is 30
In the case of 0 to 450 ° C, the molar ratio is controlled to be around 1 mol / mol, preferably 0.8 to 1.1 mol / mol, and when the temperature is 450 ° C or higher, The exhaust gas purification method according to any one of claims 1 to 4, wherein the molar ratio is controlled to be 1 mol / mol or more. 6. The catalyst is a denitration catalyst having NH ₃ decomposing ability, and the temperature of the exhaust gas or the catalyst is 300.
When the temperature is lower than 0 ° C, the supply amount of the reducing agent with respect to the NOx amount calculated from the exhaust gas amount and the NOx concentration is (NH
₃ or the NH ₃ conversion value of the NH ₃ precursor) / (NOx in the exhaust gas) is controlled to be 1 mol / mol or less, and when the temperature is 300 ° C. or higher, the molar ratio is The exhaust gas purification method according to any one of claims 1 to 4, wherein the exhaust gas purification method is controlled to be 1 mol / mol or more. 7. The denitration catalyst having the ability to decompose NH ₃ has as a first component a composition comprising an oxide of one or more elements selected from titanium (Ti), tungsten (W) and vanadium (V). And one or more kinds of noble metals selected from platinum (Pt), palladium (Pd), iridium (Ir), and rhodium (Rh), or the noble metal-containing composition previously supported by a porous body of silica, zeolite, or alumina. The exhaust gas purification method according to claim 6, which is a catalyst composition containing a substance as a second component. 8. A denitration catalyst having a denitration catalyst or NH ₃ resolution contacting the exhaust gas of an internal combustion engine, a temperature detecting means for detecting a temperature of the exhaust gas, the NOx amount and a NOx concentration of the exhaust gas flow rate and the exhaust gas An exhaust gas purifying apparatus comprising: a calculating unit; a reducing agent injecting unit that injects a reducing agent into the exhaust gas; and a control unit that controls the injection amount of the reducing agent according to the detection value of the temperature detecting unit.