JPH03229911A - 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 within a reaction receptacle under the existence of ammonia, by conducting the flow control of ammonia on the basis of the measured values of an engine output, exhaust temperature and intake air humidity. CONSTITUTION:An exhaust cleaner A is provided with an intaken air compression supercharger 6 and a reaction receptacle 7 at the exhaust pipe 4 of an engine main body 1. Also, an ammonia container 12 is connected to an ammonia injection nozzle 8 provided at an exhaust gas flow passage 4a on the upper stream side of the supercharger 6 through an ammonia regulating valve 10 and an ammonia transport pipe 9 provided interveniently with an ammonia flow meter 11. In this instance, an output meter 2 or an output proportion signaler 2a, an exhaust temperature detector 5 and an intaken air humidity detector 13 are provided, and the total discharge quantity of NOx is calculated by means of an operator 14 on the basis of these outputs, and the quantity of ammonia to be supplied is determined by means of a ratio setter 15 on the basis of this calculation outcome, and the ammonia requlating valve 10 is controlled through an ammonia flow controller 16.

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 of controlling the flow rate of ammonia supplied to exhaust gas based on an engine fuel regulating governor, intake air temperature, and intake air amount (Japanese Patent Laid-Open No. 52-48722
(Refer to the Publication No.) 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 this reaction efficiency, it is important that the ammonia supplied to the exhaust gas is uniformly mixed with the nitrogen oxides in the same gas.

For this purpose, mixing methods using baffle plates, venturis, and packing materials are used 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. A method of supplying ammonia or a method of supplying ammonia by using an ammonia supply port as an injection nozzle are used. The mixing method and device must not cause any harm to the engine 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,
As the injection port becomes blocked by dust contained in the exhaust gas, the ammonia injection condition not only worsens, but the nozzle may also become clogged, requiring frequent nozzle cleaning or nozzle 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 purpose of the present invention is to mix nitrogen oxides in diesel engine exhaust gas sufficiently uniformly with ammonia before reaching the denitrification 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 rapid 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. Moreover, it is an object of the present invention to provide a method for removing nitrogen oxides from diesel engine exhaust gas that can be carried out economically and at low cost.

(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 output, exhaust gas temperature, and intake air humidity are measured, and the flow rate of ammonia is controlled based on these measurements, and the ammonia is delivered to the exhaust gas side of the supercharger. It is characterized by supplying.

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, engine output and exhaust gas temperature are determined. , the temperature of the engine supply air and the humidity of the intake air are measured, and the flow rate of ammonia is controlled based on these measured values, and the ammonia is supplied to the exhaust gas inlet side of the supercharger.

According to studies conducted by the present inventors, the total amount of nitrogen oxides emitted from a diesel engine is approximately proportional to the engine output, engine exhaust gas temperature, and intake air temperature, as shown in Figures 1 to 3. However, as shown in FIG. 4, it was found that the humidity also decreased and increased in proportion to the humidity of the intake air.

In other words, as shown in Figures 1 and 2, the amount of nitrogen oxide emissions is proportional to engine output and exhaust gas temperature, so ammonia can be supplied by supplying ammonia in accordance with engine output and exhaust gas temperature. Although it is possible to control the amount of nitrogen oxides, the concentration of nitrogen oxides is greatly affected by atmospheric conditions, that is, not only the engine intake air temperature but also the intake air humidity. It is important to measure the humidity of the air and further correct the nitrogen oxide emissions based on the measured value.

In particular, when controlling the ammonia supply amount based on engine output, the correlation between nitrogen oxide emissions and output changes over time due to dirt in the engine or supercharger, so engine exhaust gas It is necessary to measure the temperature and correct the nitrogen oxide emissions based on the measured value.

Therefore, the total amount of nitrogen oxides emitted from the engine depends on the engine output, exhaust gas temperature, and intake air humidity.
In addition, the amount of ammonia supplied is determined in proportion to the total amount of nitrogen oxide emissions, which can be directly determined by measuring the engine air supply temperature.

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 flow-controlled ammonia to the exhaust gas inlet side of the supercharger, nitrogen oxides and ammonia in the exhaust gas are sufficiently mixed before reaching the reactor, increasing reaction efficiency and reducing nitrogen This confirms that the removal efficiency of oxides can be further increased.

(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 measured values of engine output, exhaust gas temperature, intake air humidity, and supply air temperature. As a result, a more accurate and 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 process of passing through the turbocharger is sufficient and After being uniformly 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. Output proportional signal device (2a) of meter (2) or driven machine (1a)
), and an exhaust gas temperature detector (
5), a supercharger (6) for compressing intake air, and a reactor (7).

This supercharger (6) has a known mechanical structure that compresses the 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 (4a) 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 (4a) 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.

Moreover, an ammonia injection nozzle (8) installed in the exhaust gas inlet side flow path (4a) of the supercharger (6) in the exhaust pipe (4).
An ammonia transport pipe (9) is connected to the ammonia transport pipe (9), which is equipped with an ammonia regulating valve (10) and an ammonia flow meter (11), and is connected to an ammonia container (12). There is.

The output meter (2) or the output proportional signal device (2a), the exhaust gas temperature detector (5), and the humidity detector (13) that measures the humidity of the intake air of the engine body (1) are connected to the computing unit (14).
This calculator (14) is connected to the ratio setter (15).
and communicates with an ammonia regulating valve (1o) through an ammonia flow controller (16).

That is, in response to the load on the engine body (1), each signal from the engine output meter (2) or output proportional signal device (2a), exhaust gas temperature sensor (5), and intake air humidity sensor (13) is The signal is input to the calculator (14). Arithmetic unit (14
), calculate the total amount of nitrogen oxide emissions, input this signal to the ratio setter (15), and set the amount of ammonia to be supplied according to the ammonia/nitrogen oxide ratio set in advance by the ratio setter (15). decide.

The output of the ratio setter (15) is input as an ammonia flow rate signal to the ammonia flow rate controller (16), which controls the opening and closing of the ammonia regulating valve (1o), and then passes through the supercharger (6). The amount of ammonia mixed into the exhaust gas flowing into the reactor (7) is controlled.

Exhaust gas flows from the manifold (3) through an exhaust pipe (4) and an intermediate supercharger (6) to a reactor (7) filled with a catalyst (17).

Ammonia passes through the ammonia transport pipe (9) from the ammonia container (12), is controlled to an optimal flow rate by the ammonia regulating valve (10), and is delivered to the inlet side of the supercharger (6) in the exhaust gas flow path (4a). , ammonia injection nozzle (8)
is mixed into the exhaust gas by the turbine blades of the supercharger (6), mixed and dispersed by the gas distribution plate (18) if necessary, and then reaches the reactor (7) where the catalyst (17) to reduce and remove nitrogen oxides in the exhaust gas.

The exhaust gas purification device (A1) provided in the engine body (1) shown in FIG. 6 is an example of one developed to carry out the second invention of the present invention, and the second configuration is 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 (20) is provided in the supply air pipe (19) that connects the exhaust pipe gas turbine (6) with the engine body (1), and this supply air temperature detector (20) is connected to the output meter (2). Alternatively, the output proportional signal device (2a), the exhaust gas temperature detector (5), and the humidity detector (13) are connected to the computing unit (14).

This exhaust gas purification device (A1) responds to the load amount of the engine main body (1) and includes an engine output meter (2) or an output proportional signal device (2a), an exhaust gas temperature detector (5), and a humidity detector (
13) and the supply air temperature detector (20) are input to the calculator (14). The calculator (14) calculates the total amount of nitrogen oxides discharged, inputs this signal to the ratio setter (15), and supplies ammonia according to the ammonia/nitrogen oxide ratio preset by the ratio setter (15). Determine the amount. The output of this ratio setter (15) is input as an ammonia flow rate signal to the ammonia flow rate controller (16), which controls the opening and closing of the ammonia regulating valve (10) and is mixed into the exhaust gas flowing into the reactor (7). Control the amount of ammonia used. Thereby, the ammonia is controlled to the optimum flow rate by the ammonia regulating valve (10), and the ammonia is
6), it is mixed into the exhaust gas by the ammonia injection nozzle (8), sufficiently mixed with the exhaust gas by the turbine blade of the supercharger (6), and if necessary, the gas distribution plate (
After being mixed and dispersed by 18), it reaches a reactor (7), passes through a catalyst (17), and reduces and removes nitrogen oxides in the exhaust gas.

In addition, in the present invention, the shape of the catalyst used is as follows:
Examples include pellet shape, two spheres, one grain shape, plate shape, pipe shape, and honeycomb shape.

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 catalyst composition to which the present invention is applied, but patented catalysts featuring titanium and zeolite-based 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 T i O2S i O2).

Examples include binary composite oxides of titanium and zirconium, ternary composite oxides consisting of titanium, silicon, and zirconium, and the like. Preferably, the specific surface area of component A is 10 ffl/g or more, particularly 20 rrf/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.

5 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.
00 pHm, 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.

Space velocity is 2000-100.000 hr-1, especially 5
．． The range of 000 to 50000h+-1 is preferable.

The amount of ammonia added is 0.00% 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 by giving specific examples below, but the present invention is not limited to these specific examples.

Specific example I Using the exhaust gas purification device (A) illustrated in Fig. 5, the reactor (7) communicating with the exhaust pipe (4) of a diesel engine for power generation contains ■2052% by weight and 27% by weight of WO. TiO2-based honeycomb catalyst (150 mm square equivalent diameter 3.
2mm, cell wall thickness 0.5mm.

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

Using the same device (A), operate the calculator (14) and the ratio setter (15) 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
t, exhaust gas temperature 380-430℃ inlet nitrogen oxide concentration 7
The engine was operated with the concentration varied within the range of 0.00 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 device (A1) illustrated in Figure 6, 1 A denitrification reaction was carried out in the same manner as in Example I.

The denitrification rate at this time was 84 to 86%, and the ammonia concentration in the exhaust gas at the reactor outlet was 0.5 to 0.8 ppm.

The denitrification methods described in specific examples (1) and (2) have a small fluctuation range in the denitrification rate and can remove nitrogen oxides with high efficiency. At the same time, the release of ammonia that can cause secondary pollution is extremely small, and the reaction efficiency in the reactor is also low. 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.

In response to rapid changes in exhaust gas properties and the amount of nitrogen oxides caused by fluctuations in engine load,
Nitrogen oxides can be removed efficiently at a high level, and the amount of ammonia released in the exhaust gas after nitrogen oxide removal can be minimized, making it practical for practical use without worrying about secondary pollution. It is highly profitable.

8 ■ 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 can be eliminated.

[Brief explanation of drawings]

Figure 1 is a graph showing the relationship between diesel engine output and nitrogen oxide emissions. Figure 2 is a graph showing the relationship between exhaust gas temperature and nitrogen oxide emissions. Figure 3 is a graph showing the relationship between the intake air temperature and nitrogen oxide concentration of a diesel engine. FIG. 4 is a graph showing the relationship between the absolute humidity of intake air of a diesel engine and the concentration of nitrogen oxides. 5 and 6 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) is the engine body (2) is the output meter 9 (2a) is the output proportional signal device (4) is the exhaust pipe (4a) is the exhaust gas flow path (5) is the exhaust gas temperature detector (6) is the supercharging The machine (7) is the reactor (8), the ammonia injection nozzle (9) is the ammonia transport pipe (0), the ammonia regulating valve (11) is the ammonia flow meter (12), the ammonia container (13) is the humidity detector (4) ) is the calculator (5) is the ratio setter (6) is the ammonia flow rate controller (7) is the catalyst (9) is the supply air pipe (20) 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 the reaction path in the presence of ammonia, engine output, exhaust gas temperature, and intake air A method for removing nitrogen oxides from diesel engine exhaust gas, the method comprising: measuring the humidity of each gas, 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 reducing and removing nitrogen oxides in the exhaust gas of a diesel engine with a supercharger in the exhaust gas flow path using a catalyst in a reactor in the presence of ammonia, engine output, exhaust gas temperature, engine supply A method for removing nitrogen oxides from diesel engine exhaust gas, which is characterized by measuring air 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. .