JPS6357810A - Method for eliminating nox of diesel engine - Google Patents

Abstract

PURPOSE:To enable good elimination of NOX in exhaust gas by detecting NOX in exhaust gas, mixing a prescribed amount of NH3 gas based on the detected result and making it in contact with TiO2 catalyst at the prescribed temperature. CONSTITUTION:In driving of a diesel engine, for example, by measuring the generation amount of NOX at the change of engine speed and the change of engine load, NOX in exhaust gas is detected based on the measured result of the engine speed and the engine load, using a previously formed and stored prescribed map. And 0.3-0.9mol of NH3 is mixed, to the detected 1mol of NOX, and TiO2 catalyst is brought in contact with it at the temperature of 250-500 deg.C. By this, efficient deoxidation of NOX can be attempted.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention provides a method for removing nitrogen oxides from a diesel engine;
More specifically, the present invention relates to a method for removing nitrogen oxides (NOx) from a diesel engine, which can effectively remove nitrogen oxides (NOx) from the exhaust gas of a diesel engine using a catalyst.

[Technical background of the invention]

Nitrogen oxides (hereinafter referred to as N) in the exhaust gas of diesel engines
As a method of reducing M (referred to as Ox), there is a known method of preventing the generation of NOx by slightly delaying the fuel injection timing of a diesel engine and combusting the fuel (so-called timing retard). That is,
Since a large amount of NOx is generated when fuel is combusted at a high temperature, by performing timing retard as described above, the fuel is combusted at a lower temperature to suppress the generation of NOx.

However, according to this timing retard method, N
Although the generation of Ox is suppressed, there are disadvantages in that not only the combustion efficiency deteriorates but also the generation of black smoke increases.

For the removal of NOx as described above, a method of reducing and removing NOx once generated by a catalyst as in the case of a gasoline engine may be considered.

However, compared to gasoline engines, diesel engines have a characteristic that there is more residual oxygen in the exhaust gas, and the drawback is that it cannot be reduced using the reducing agents used in gasoline engines, such as hydrogen and carbon oxides. was there. In other words, in a gasoline engine, it is possible to burn the air-fuel at a stoichiometric mixing ratio, and the oxygen in the exhaust gas is almost zero, but in the case of a diesel engine, the air-fuel mixing ratio is kept at a stoichiometric ratio even at full engine load. It is necessary to have an excess of air, about 1.3:1 (volume mixing ratio), and therefore a considerable amount of residual oxygen is mixed in the exhaust gas. For this reason, common reducing agents such as hydrogen,
- Even if a reducing agent such as carbon oxide is added to the exhaust gas in the presence of a catalyst, it will react with oxygen first, making it impossible to reduce NOx. For this reason, at present, a method for removing exhaust gas from diesel engines by catalytic reaction has not been put to practical use.

Recently, as a method for removing NOx from combustion gas from thermal power generation, a method has been developed in which N113 is used as a reducing agent to reduce NOx from oxygen-rich combustion gas in the presence of a catalyst.

However, NO in diesel engine exhaust gas
This technique cannot be directly used to reduce x. That is, (1) in the thermal power generation, the temperature of the combustion gas is almost constant in order to reduce the combustion gas in a steady state, but in the case of a diesel engine, the temperature of the exhaust gas changes significantly depending on the engine load; ■Since the thermal power generation is in a steady state, the amount of NOx is almost constant, but in the case of a diesel engine, the amount of NOx changes depending on the engine load; ■N) I3 mentioned above.
However, since it is toxic and has a strong pungent odor, the amount of NHaO is strictly controlled in accordance with the amount of NOx, and 14H3 is added to the exhaust gas.
This is because there are various conditions such as the need to ensure that no residue remains.

[Summary of the invention]

The present invention has been made in view of the above points, and is based on NI+3.
It is an object of the present invention to provide a method for reducing and removing NOx from a diesel engine by using NOx as a reducing agent and using a catalyst.

Therefore, the method for removing nitrogen oxides from a diesel engine according to the present invention is a method for removing nitrogen oxides from diesel engine exhaust gas.
The amount of Ox is detected, and NH
While mixing 0.3 to 0.9 moles of 3 gases, 250
The NO
It is characterized by reducing x.

According to the present invention, N113 is used as a reducing agent, and Ti05! which is active at relatively high temperatures as a catalyst! By using this method, it becomes possible to reduce and remove NOx in the oxygen-rich exhaust gas of a diesel engine, which has the advantage of being practical as a method for removing NOx from a diesel engine.

[Detailed description of the invention]

The present invention will be explained in more detail.

The method for removing nitrogen oxides from a diesel engine according to the present invention begins by detecting the amount of NOx in exhaust gas.

The method of detecting the amount of NOx in the exhaust gas is not fundamentally limited in the present invention. For example, a map may be prepared by measuring the amount of NOx generated under changes in engine speed and load in advance, and the amount of NOx generated may be estimated and detected by measuring the engine speed and load. Good too. Further, it is also possible to know the amount of NOx by detecting the fuel injection amount by utilizing the fact that about 2% by weight of the fuel is oxidized to NOx. Of course, it is also possible to use a NOx sensor.

The NOx is added to the exhaust gas whose NOx amount has been detected as described above.
Add NH3 gas corresponding to x amount. As mentioned above, the amount of Ni13 gas added is 0.3 per mole of NOx.
~0.9 mol. That is, when the amount of NHa added is 0.
If it is less than 3 moles, NOx will not be reduced sufficiently, while if it is more than 0.9 moles, there will be too much unreacted N113 gas and a large amount of N113 will be released into the atmosphere.

4 NO+4 N1(3+02 ←4N 2 +6H
t O・・・・・・(116NO2+8 NI+3 7
N t +12Ht O-・-・-・(2) In the present invention, Ti0 is used as a catalyst for causing such a reaction.
2 catalysts are used. For example, the noble metal catalyst Pt
, Catalysts such as Pd also cause the above reaction, but
Such a catalyst is characterized by having good activity at a relatively low temperature of 200 to 300°C. However, at such low temperatures the amount of NOx in the exhaust gas is limited (if the fuel burns at a relatively low temperature)
(the amount of NOx generated is small), there is little need to reduce and remove NOx.

Therefore, the present invention uses TiO2, which is inexpensive and active at relatively high temperatures. This is because when the exhaust gas is at a relatively high temperature, even if carbon is adsorbed on the TiO2 catalyst, it will be burned by heat and will not reduce the activity of the catalyst.

Such a Ti02 catalyst is active at a relatively high temperature of 250 to 500°C. Therefore, the temperature of the exhaust gas treated in the catalyst is 250 to 500°C.
Adjust to. When the exhaust gas temperature is less than 250°C,
This is because the activity of the catalyst is low, and there is a possibility that the NOx cannot be reduced sufficiently. On the other hand, if the temperature exceeds 500°C, there is a possibility that the catalyst deteriorates and loses its activity.

In the case of a diesel engine, the exhaust gas is 70
Although it may reach a high temperature of 0° C., in this case, the temperature is lowered by means such as mixing air, and the exhaust gas is brought into contact with the TiO2 catalyst. On the other hand, when the temperature of the exhaust gas is less than 250° C., the amount of NOx is relatively low in concentration, so it may be released into the atmosphere without contacting the TiO2 catalyst.

The changes in the amount of NOx generated with changes in the rotational speed and engine load of a diesel engine with an exhaust capacity of 113.7 tt were prepared. This map is shown in Figure 1.

Using this engine, the rotation speed and load of the diesel engine were measured based on the map shown in FIG. 1, and the amount of NOx generated was detected. N1 (3) can be added to the exhaust gas according to the operating conditions of the diesel engine so that the volumetric mixing ratio is 0.5 for the NOx generation amount 1 detected by the above detection method, and When the temperature is measured and the exhaust gas exceeds 500°C, air is replenished and the exhaust gas reaches 25°C.
After adjusting the temperature to be in the range of 0 to 500°C, it was passed through a catalytic converter filled with a Ti02 catalyst.

In the figure, the numbers written on the graph indicate NO4 degrees (g/hour). By changing NH31 based on the above map and mixing it into the exhaust gas and passing it through the Ti02 catalyst, the reduction efficiency was shown to be almost constant at each load, and approximately 50% of NOx was reduced to nitrogen. Understood.

It was also revealed that the exhaust gas after reducing and removing NOx had no irritating odor and contained almost no N113.

On the other hand, when N113 was added at a volumetric mixing ratio of 0.9 to the amount of NOx generated and a test similar to the above was conducted, the reduction efficiency was approximately 85%. contained some NH3, but it was within an acceptable range.

〔Effect of the invention〕

As explained above, according to the method for removing nitrogen oxides from a diesel engine according to the present invention, by using TiO2 as a catalyst and NH3 as a reducing agent, it is possible to remove nitrogen oxides from diesel engine exhaust gas, which was previously impossible. It has the advantage of being able to remove nitrogen oxides well. Therefore, there is no need to delay the injection timing as in the conventional method, and the fuel can be burned efficiently, and there are also advantages in that the generation of black smoke can be suppressed.

[Brief explanation of drawings]

FIG. 1 is a map showing changes in the amount of NOx generated with respect to changes in the rotational speed and load of the diesel engine.

Claims (2)

[Claims] (1) Detect the amount of NO_x in the exhaust gas of a diesel engine, mix 0.3 to 0.9 mol of NH_3 gas to 1 mol of NO_x detected, and mix 250 to 5 mol of NH_3 gas.
Contact with the TiO_2 catalyst at a temperature of 00°C, and the NO_
A method for removing nitrogen oxides from a diesel engine, the method comprising reducing x. (2) A patent characterized in that the detection of NO_x is performed by creating a map of changes in the amount of NO_x generated due to changes in the rotation speed and load of the diesel engine, and measuring the rotation speed and engine load. A method for removing nitrogen oxides from a diesel engine according to claim 1.