JPH03229910A - Method to remove nitrogen oxide from diesel engine exhaust - Google Patents

Abstract

PURPOSE:To improve the cleaning performance of NOx when the NOx in the exhaust of an engine with a supercharger is reduced and removed by using a catalyst in a reaction receptacle under the existence of ammonia, by controlling the flow of ammonia on the basis of the measured values of a fuel consumption and intake air humidity. CONSTITUTION:An exhaust cleaning device A is provided with an intake air compression supercharger 4 and a reaction receptacle 5 on the exhaust pipe 3 of an engine main body 1. Also, an ammonia container 10 is connected to an ammonia injection nozzle 6 provided at the exhaust gas flow passage 3a on the upper stream side of the supercharger 4 through an ammonia regulating valve 8 and an ammonia transport pipe 7 provided interveniently with an ammonia flow meter 9. In this instance, a fuel flow meter 11 that measures the consumption quantity of fuel, and a humidity detector 12 that measures the humidity of intake air, are provided, and the total discharge quantity of NOx is calculated by means of an operator 13 on the basis of these outputs, and the quantity of ammonia to be supplied is determined by means of a ratio setter 14 on the basis of the calculation outcome of the above, and the ammonia regulating valve 8 is controlled through an ammonia flow controller 15.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for removing nitrogen oxides from diesel engine exhaust gas. In detail, it is possible to remove nitrogen oxides in response to fluctuations in the properties of the exhaust gas emitted without interfering with the operation of the diesel engine, and at the same time, it is possible to remove ammonia contained in the exhaust gas after nitrogen oxide removal as much as possible. The present invention relates to a controllable method for removing nitrogen oxides.

(Prior art) Conventionally, as a method for removing nitrogen oxides in an oxidizing atmosphere, a selective reduction denitrification method using ammonia as a reducing agent has been used.
Because nitrogen oxides and ammonia react selectively without being affected by the oxygen concentration in the exhaust gas, it is an effective method even in oxidizing atmospheres, and can be used at fixed sources such as boilers and heating furnaces in thermal power plants. It has been widely applied to exhaust gas purification.

On the other hand, various examples have been disclosed in which the ammonia selective reduction method is applied to reduce nitrogen oxides in exhaust gas from internal combustion engines. For example, a method in which nitrogen oxides are removed by supplying ammonia into exhaust gas in proportion to fuel consumption and passing the resulting mixed gas through a reactor filled with pellet catalyst (Japanese Patent Publication No. 511-501001) (see official bulletin) etc. have been disclosed.

However, in the case of a diesel engine, the engine load fluctuates significantly compared to a boiler, and the amount of exhaust gas and nitrogen oxide concentration change rapidly accordingly. The above-mentioned conventional techniques are not sufficient to control the amount of nitrogen oxides contained in the exhaust gas, and there remains a problem in removing nitrogen oxides from the exhaust gas with high efficiency while at the same time controlling the amount of ammonia discharged as much as possible.

Further, the removal rate of nitrogen oxides in the exhaust gas is related to the reaction efficiency in the reactor, and the relationship between the two is almost proportional. In order to increase the efficiency of this reaction, it is important that the ammonia supplied to the exhaust gas be uniformly mixed with the nitrogen oxides in the exhaust gas.

For this purpose, mixing methods using baffle plates, venturis, packing materials, etc. are adopted for boat fishing, and a large number of nozzle ports are installed in the exhaust pipe on the upstream side of the reactor between the supercharger and the ammonia. Although methods for supplying ammonia and methods for supplying ammonia by using an injection nozzle at the supply port are used, the mixing method and device must not cause any harm to the lungin itself.

In this respect, the mixing method using a baffle plate, venturi, or filler causes a large pressure loss, leading to a decrease in engine output in a diesel engine, resulting in poor fuel efficiency of the engine, and causing harm to the engine itself.

In addition, in the mixing method in which ammonia is supplied by providing a large number of nozzles in the exhaust gas flow path on the upstream side of the reactor between the turbocharger and the reactor, it is difficult to uniformly mix ammonia into the exhaust gas, and the The removal efficiency of nitrogen oxides in the exhaust gas only decreases and does not increase, and it is difficult to say that the reaction efficiency is high.

Also, in the mixing method where ammonia is supplied from an injection nozzle,
Die-cast particles contained in the exhaust gas adhere to the injection port, causing the nozzle to become blocked, which may cause ammonia blockage, requiring frequent nozzle cleaning or replacement.

Furthermore, in the case of relatively small diesel engines, it is also important that the exhaust gas treatment system is inexpensive.

(Problems to be Solved by the Invention) The object of the present invention is to mix nitrogen oxides in diesel engine exhaust gas with ammonia sufficiently uniformly before reaching the denitration catalyst, and then bring them into contact with the catalyst. Increases the reaction efficiency in the reactor without hindering the work,
It can efficiently remove nitrogen oxides even in the face of sudden changes in exhaust gas properties, and it can also respond to changes in the amount of nitrogen oxides due to changes in engine combustion performance.At the same time, it can control ammonia contained after nitrogen oxide removal as much as possible. An object of the present invention is to provide an economically inexpensive method for removing nitrogen oxides from diesel engine exhaust gas.

(Means for Solving the Problems) In order to achieve the above-mentioned object, the present invention has a first invention in which nitrogen oxides in the exhaust gas of a diesel engine having a supercharger in the middle of the exhaust gas flow path are removed in the presence of ammonia. When reducing and removing ammonia using a catalyst in the reactor, the engine's fuel consumption and intake air humidity are measured, the flow rate of ammonia is controlled based on these measurements, and the ammonia is supplied to the exhaust gas inlet side of the supercharger. It is characterized by

In the second invention, when nitrogen oxides in the exhaust gas of a diesel engine having a supercharger in the exhaust gas flow path are reduced and removed using a catalyst in a reactor in the presence of ammonia, the fuel consumption of the engine, It is characterized by measuring the temperature of the engine supply air and the humidity of the intake air, controlling the flow rate of ammonia based on these measured values, and supplying the ammonia to the exhaust gas inlet side of the supercharger.

According to the studies conducted by the present inventors, the total amount of nitrogen oxides emitted from diesel engines is
As shown in the figure, it increases and decreases almost in proportion to the fuel consumption and engine intake air temperature, but it was also found that it decreases and increases in proportion to the humidity of the intake air, as shown in Figure 3. .

That is, as shown in FIG. 1, since the amount of nitrogen oxide emissions is proportional to the amount of fuel consumed, it is possible to control the amount of ammonia supplied by supplying ammonia in accordance with the amount of fuel consumed. The concentration of nitrogen oxides is greatly affected by atmospheric conditions, that is, not only the temperature of the engine's supply air but also the humidity of the intake air. based on,
It is important to further correct for nitrogen oxide emissions.

Therefore, the total amount of nitrogen oxides emitted from the engine is determined by the fuel consumption, the humidity of the intake air, and the amount of ammonia that can be directly determined by measuring the engine air supply temperature. Determine supply amount.

As a result, even if the emission amount and concentration of nitrogen oxides change rapidly, the optimum amount of ammonia is accurately supplied without any time delay in proportion to the emission amount and concentration, and nitrogen oxide in the exhaust gas is oxidized. This test confirmed that nitrogen oxides can be effectively removed and that residual ammonia in the exhaust gas after nitrogen oxide removal can be suppressed as much as possible.

In addition, by supplying the ammonia with a controlled flow rate into the exhaust gas inlet side of the supercharger, nitrogen oxides and ammonia in the exhaust gas are sufficiently mixed before reaching the reactor.
This confirms that it is possible to further increase the reaction efficiency and the removal efficiency of nitrogen oxides.

(Function) The amount of ammonia supplied is determined in proportion to the amount and concentration of nitrogen oxide in the exhaust gas, which is determined based on the engine's fuel consumption, intake air humidity, and intake air temperature measurements. , the more accurate optimal amount of ammonia is supplied to the exhaust gas inlet side of the turbocharger in the exhaust gas flow path with respect to the total amount of nitrogen oxides in the exhaust gas, and the ammonia is supplied sufficiently and uniformly in the process of passing through the turbocharger. After being mixed, it flows into the reactor.

As a result, nitrogen oxides are constantly and efficiently removed in response to the engine load, with the diesel engine functioning unimpeded and the reaction efficiency in the reactor being made highly efficient. This means that residual ammonia is suppressed as much as possible.

(Example) The present invention will be explained in detail below.

The exhaust gas purification device (A) provided in the engine body (1) shown in FIG. A supercharger (4) for compressing intake air and a reactor (5) are provided in the exhaust pipe (3) communicating with the exhaust pipe (3).

This supercharger (4) has a known mechanical structure that compresses air supplied to the engine using the pressure of exhaust gas so as to increase the output of the engine, and has a turbine blade on the exhaust gas flow path (3a) side. and the blower blade on the air supply side are connected by a shaft, and when the turbine blade on the exhaust gas flow path (3a) side rotates due to the pressure of the exhaust gas, the blower blade on the air supply side also rotates, and the intake air is drawn into the engine. It compresses air.

In addition, an ammonia injection nozzle (6) installed in the exhaust gas flow path (3a) on the upstream side of the supercharger (4) in the exhaust pipe (3)
) is connected to an ammonia transport pipe (7), and this ammonia transport pipe (7) is provided with an ammonia regulating valve (8) and an ammonia flow meter (9), and is connected to an ammonia container (10). There is.

The fuel flow meter (11) that is supplied to the engine body (1) and measures the amount of fuel consumed and the humidity detector (12) that measures the humidity of the intake air of the engine body (1) are connected to the computer (13). The arithmetic unit (13) is in communication with the ammonia regulating valve (8) through a ratio setter (14) and an ammonia flow rate controller (15).

0 That is, in response to the load amount of the engine body (1), each signal from the fuel flow meter (11) and the intake air humidity detector (12) is input to the computing unit (13).

The calculation unit (13) calculates the total amount of nitrogen oxide emissions, sends this signal to the ratio setter (14), and supplies the ammonia/nitrogen oxide ratio preset by the ratio setter (14). Determine the amount of ammonia to be added.

The output of the ratio setting device (14) is input as an ammonia flow rate signal to an ammonia flow rate controller (15), which controls the opening and closing of the ammonia regulating valve (8), and controls the opening and closing of the ammonia regulating valve (8).
) to control the amount of ammonia mixed into the exhaust gas flowing into the reactor (5).

The exhaust gas flows from the manifold (2) through the exhaust pipe (3) and the supercharger (4) in the middle to the reactor (5) filled with a denitrification catalyst (16).

Ammonia passes from the ammonia container (10) through the ammonia transport pipe (7), is controlled to an optimal flow rate by the ammonia regulating valve (8), and is fed to the supercharger (
4), ammonia 1 is mixed into the exhaust gas by the ammonia injection nozzle (6), sufficiently mixed and stirred with the exhaust gas by the turbine blade of the supercharger (4), and if necessary, by the gas distribution plate (17). After being mixed and dispersed, it reaches a reactor (5), passes through a catalyst (16), and reduces and removes nitrogen oxides in the exhaust gas.

The exhaust gas purification device (A,) provided in the engine body (1) shown in FIG. Since it has basically the same configuration as the illustrated exhaust gas purification device (A), the explanation of the common configuration will be omitted, and the different configuration will be explained below.

A supply air temperature detector (19) is provided in the supply air pipe (18) that connects the exhaust pipe gas turbine (4) with the engine body (1), and this supply air temperature detector (19) is connected to the fuel flow meter (11).
) and the humidity detector (12) as well as the computing unit (13).

This exhaust gas purification device (A1) responds to the load amount of the engine body (1) and calculates each signal from the fuel flow meter (11), humidity detector (12), and supply air temperature detector (19). input into the device (13). The calculator (13) calculates the total amount of nitrogen oxides discharged, inputs this signal to the ratio setter (14), and supplies the ammonia/nitrogen oxides ratio preset by the ratio setter (14). Determine the amount of ammonia to be added. The output of this ratio setting device (14) is input as an ammonia flow rate signal to an ammonia flow rate controller (15), which controls the opening and closing of the ammonia regulating valve (8), thereby controlling the ammonia mixed in the exhaust gas flowing into the reactor (5). Control quantity.

Thereby, the ammonia is controlled to an optimal flow rate by the ammonia regulating valve (8), and the ammonia injection nozzle (
6) is mixed into the exhaust gas, thoroughly mixed and stirred with the exhaust gas by the turbine blade of the supercharger (4), mixed and dispersed by the gas distribution plate (17) if necessary, and then transferred to the reactor (5).
The exhaust gas then passes through a catalyst (16) to reduce and remove nitrogen oxides in the exhaust gas.

Further, in the present invention, examples of the shape of the catalyst used include pellet-like, bi-spherical, bi-granular, plate-like, pipe-like, and honeycomb-like shapes.

In particular, a honeycomb shape is preferred because the required amount of catalyst is small due to its large geometric surface area, and the pressure loss in the catalyst layer is small.

There is no particular reason to limit the composition of the catalyst that is the object of the present invention, but catalysts containing titanium as a main component and zeolite catalysts are preferred.

In particular, the A component is an oxide containing titanium, and this is 60~
Contains 99.5% by weight of vanadium, tungsten, molybdenum, manganese, copper, iron, and cobalt.

The B component is an oxide of at least one element selected from the group consisting of cerium and tin.
A catalyst comprising a range of % by weight gives favorable results.

Favorable results can be obtained if the catalyst A component is an oxide containing titanium, such as titanium oxide or a binary composite oxide of titanium and silicon (hereinafter referred to as TiO2-8iO7). Examples include binary composite oxides of titanium and zirconium, and ternary composite oxides consisting of titanium, silicon, and zirconium. Preferable results are obtained when the specific surface area of component A is 10i/g or more, particularly 20rrf/g or more.

The reducing agent used in the present invention includes ammonia gas,
Ammonium salts such as aqueous ammonia, other urea, and ammonium salts that thermally decompose into ammonia such as ammonium sholate are used.

The composition of the exhaust gas discharged from the diesel engine that is the object of the present invention is usually 10 to 1,0 ammonia.
00ppm, oxygen 2-21% by volume, carbon dioxide 5-15% by volume, moisture 5-15% by volume, dust 0.02-1g/Nm
3, and about 200 to 3,000 ppm of nitrogen oxides, but the composition range is not particularly limited as long as it is an exhaust gas discharged from an internal combustion engine such as a diesel engine or a gas engine.

The processing conditions include a reaction temperature of 150°C to 650°C;
Particularly preferred is 200°C to 600°C.

The space velocity is preferably in the range of 200 (1-100,000 t++-1, particularly -5,000 to 5 (1,0OOh+-1).

5. The amount of ammonia added is 0.0% per part by volume of nitrogen oxide.
Although 3 to 1.2 parts by volume is preferable, it is particularly preferable to use the ammonia/nitrogen oxide molar ratio of 1 or less because it is usually necessary to suppress unreacted ammonia as much as possible.

The present invention will be explained in more detail with reference to specific examples below, but the present invention is not limited to these specific examples.

Specific example ■ Using the exhaust gas purification device (A) illustrated in Fig. 4, the reactor (5) communicating with the exhaust pipe (3) of a diesel engine for power generation contains 52% by weight of V2O and 37% by weight of WO. T i O2-based honeycomb catalyst (150 mm square equivalent diameter 3.2 mm, cell wall thickness 0.5 mm.

450 mm in length) were packed in two layers of 6 x 6 pieces.

Using the same device (A), operate the calculator (13) and the ratio setter (14) so that the ammonia/nitrogen oxide molar ratio is 0.85, and inject ammonia into the exhaust gas in the exhaust pipe, Exhaust gas processing amount 3500-550ON/h
+, exhaust gas The engine was operated while varying the exhaust gas temperature in the range of 0 to 4306 and the oxide concentration in the range of 700 to 950 ppm.

At that time, the denitrification rate was 83-86%, and the ammonia concentration in the exhaust gas at the reactor outlet was 0.5-1. It was Oppm.

Specific Example ■ Using the exhaust gas purification apparatus (A1) illustrated in FIG. 5, a denitrification reaction was carried out in the same manner as in the specific example.

The denitrification rate at this time was 82-85%, and the ammonia concentration in the exhaust gas at the reactor outlet was 0.4-1. It was lppm.

The denitrification methods described in Specific Examples I and (2) can remove nitrogen oxides with high efficiency with a small fluctuation range in the denitrification rate, and at the same time release extremely little ammonia, which can cause secondary pollution, and the reaction efficiency in the reactor is also This is an excellent method because the nitrogen oxides and ammonia in the exhaust gas are sufficiently and uniformly mixed in advance, resulting in high reaction efficiency on the denitrification catalyst.

(Effect of the invention) Therefore, the present invention has the following advantages.

7. Nitrogen oxides can be removed efficiently at a high level by quickly responding to sudden changes in the amount of nitrogen oxides due to changes in exhaust gas properties and changes in engine load. The amount of ammonia in the gas that is released together with the exhaust gas can be suppressed to a minimum, and there is no need to worry about secondary pollution, which is of great practical benefit.

(2) According to claim 1, the above-mentioned effects can be obtained especially with the two-term measurement factor, which is effective in saving labor of the apparatus.

■Since no new pressure loss is caused to the diesel engine, the output of the diesel engine will not be reduced.

- Since the injection nozzle of the ammonia supply port can be selected to any size, there is no need to worry about the injection nozzle being blocked by dust in the exhaust gas, and maintenance such as cleaning is unnecessary.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between diesel engine fuel consumption and nitrogen oxide emissions. Figure 2 is a graph showing the relationship between the intake air temperature and nitrogen oxide concentration of the De8 easel engine. Figure 3 is a graph showing the relationship between the absolute humidity and nitrogen oxide concentration of the intake air of a diesel engine. 4 and 5 are schematic diagrams of a diesel engine equipped with an exhaust gas purification device for carrying out the method of the present invention. In the figure (1), the engine body (3) is the exhaust pipe (3B), the exhaust gas flow path (4) is the supercharger (5), the reactor (6) is the ammonia injection nozzle (7), the ammonia transport pipe (8) is ) is the ammonia regulating valve (9) is the ammonia flow meter (10) is the ammonia container (11) is the fuel flow meter (12) is the humidity detector (13) is the calculator 9 is the ratio setting device is the ammonia flow controller is the catalyst The supply air pipe is the supply air temperature detector

Claims (2)

[Claims] (1) When nitrogen oxides in the exhaust gas of a diesel engine with a supercharger in the exhaust gas flow path are reduced and removed using a catalyst in a reactor in the presence of ammonia, the amount of fuel consumed by the engine and the amount of intake air are reduced. Measure the humidity,
A method for removing nitrogen oxides from diesel engine exhaust gas, which comprises controlling the flow rate of ammonia based on these measured values and supplying the ammonia to the exhaust gas inlet side of a supercharger. (2) When nitrogen oxides in the exhaust gas of a diesel engine with a supercharger in the exhaust gas flow path are reduced and removed using a catalyst in a reactor in the presence of ammonia, engine fuel consumption and engine air supply A method for removing nitrogen oxides from diesel engine exhaust gas, which comprises measuring the temperature and humidity of intake air, controlling the flow rate of ammonia based on these measured values, and supplying the ammonia to the exhaust gas inlet side of a supercharger.