JP2001107723A - Exhaust emission control device for gas engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve NOx removal efficiency in the HC-SCR catalyst device of a multi-cylinder gas engine. SOLUTION: In this gas engine using gas as fuel whose chief ingredient is methane, an exhaust system comprises the turbine section 6a of an exhaust turbine supercharger 6 connected to an exhaust port 5 through an exhaust manifold 3, and an HC-SCR catalyst device 7, which uses hydrocarbon in exhaust gas as reducing agent, connected to the exhaust side upstream of the turbine section 6a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for a gas engine used for removing nitrogen oxides (NOx) in exhaust gas.

[0002]

2. Description of the Related Art Conventionally, as an SCR (selective catalytic reduction) catalyst device for removing nitrogen oxides (NOx), for example, there is a catalyst device in which zeolite or the like is impregnated with copper or the like, and methane is used as a fuel gas. When using natural gas as a main component, the SCR catalyst device can exhibit a catalytic action even at a relatively low temperature (about 350 ° to 400 °),
Therefore, even if the SCR catalyst device is disposed far away from the exhaust port on the exhaust downstream side, for example, on the exhaust downstream side of the exhaust turbine turbocharger, a denitration ratio that does not actually hinder the operation is obtained.

[0003] However, it is a disadvantage that zeolite-based catalyst devices have low durability. In contrast, Ag-based HC-S
Although the CR catalyst device is durable, it has low reactivity with methane and has a characteristic that it is difficult to operate using methane as a reducing agent. In addition, the catalyst does not work effectively unless the temperature is high. Therefore, if the catalyst is disposed downstream of the exhaust gas of the exhaust turbine supercharger as described above, the exhaust gas temperature (350
(About ° -400 °), the temperature is too low, the catalyst does not work effectively, and a high denitration rate cannot be obtained.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to improve the denitration rate of a catalytic device in an exhaust gas purifying device for a gas engine while maintaining the durability of the catalytic device.

[0005]

An invention according to claim 1 of the present application is a gas engine, which comprises an HC-SCR catalyst device,
An exhaust gas purifying apparatus for a gas engine, which is connected to an exhaust gas upstream side of an exhaust turbine supercharger.

According to a second aspect of the present invention, there is provided a multi-cylinder gas engine, wherein HC is provided at an outlet of an exhaust port of each cylinder.
-An exhaust gas purifying device for a gas engine, wherein the exhaust gas purifying device is connected to an SCR catalyst device.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a front view of a stationary multi-cylinder gas engine for a generator to which the invention according to claim 1 of the present application is applied. The engine block 1 and a cylinder head 2 constitute an engine body. In the manifold 3 disposed on one side of the cylinder head 2, each branch pipe is connected to an exhaust port 5 for each cylinder. A selective catalytic reduction catalyst device using hydrocarbon HC as a reducing agent, that is, an HC-SCR catalyst device 7 is provided between a downstream collecting portion (exit portion) 3a of the exhaust manifold 3 and a turbo portion 6a of the supercharger 6. Has been arranged. The downstream outlet of the HC-SCR catalyst device 7 and the exhaust upstream inlet 20 of the turbo unit 6a are connected by an exhaust communication pipe 11. Exhaust pipes 8 and 9 are sequentially connected to the exhaust downstream outlet 21 of the turbo section 6a.

In FIG. 2, which is a view taken in the direction of the arrow II in FIG. 1, an air supply manifold 10 is disposed on the other side of the cylinder head 2, and each branch pipe of the air supply manifold 10 has an air supply port for each cylinder. 11 is connected. The air supply upstream-side gathering portion (entrance portion) of the air supply manifold 10 is connected to the intercooler 13, and the air supply inlet of the intercooler 13 is shown in FIG.
As shown in the figure, the compressor 6b of the supercharger 6 is connected to the compressor 6b through the air supply connection pipe 14. The air inlet of the compressor 6b is connected to a mixer (not shown) for mixing the fuel gas and the air at a predetermined ratio. are doing. Intercooler 1
3, a cooling water inlet pipe 15 and a cooling water outlet pipe 16 are connected for cooling medium distribution.

In such a gas engine, a gas fuel containing methane as a main component is used as a gas fuel, and a durable Ag is used as the HC-SCR catalyst device 7.
A system HC-SCR catalyst device 7 is provided.

[0010]

In FIG. 1, the mixture of fuel gas and air is:
Pressurized by the compressor section 6b of the supercharger 6, supplied to the intercooler 13 via the air supply communication pipe 14,
After being cooled to a predetermined temperature, the air supply manifold 10 shown in FIG.
Is supplied to each supply port 11 and supplied to the combustion chamber of each cylinder via a supply valve.

After the combustion, the exhaust gas discharged from each combustion chamber to the exhaust port 5 is collected from each branch pipe of the exhaust manifold 3 into the exhaust downstream-side collecting section 3a in FIG. Before entering the HC-SCR catalyst device 7, the HC-SCR catalyst device 7 converts nitrogen oxides (NOx) into molecular nitrogen under high temperature and high pressure using hydrocarbon HC in exhaust gas as a reducing agent. To be reduced to

FIG. 5 is a graph showing the effect of the reaction temperature (catalyst inlet temperature) on the denitration rate. The temperature range W2 of the exhaust upstream inlet 20 (FIG. 1) of the turbine section 6a of the supercharger 6 is shown in FIG.
Has a high temperature of 460 ° to 540 °, while the exhaust downstream side outlet 21 of the turbine unit 6a of the supercharger 6 (FIG. 1)
Is in the range of 80 ° to 17 ° from the temperature range W2.
It is 0 ° lower and about 370 ° to 380 °. Looking at the relationship between the curve X1 showing the relationship between the reaction temperature and the denitration rate and the respective temperature ranges W1 and W2, the denitration rate of only about several% can be obtained in the temperature range W1, whereas the temperature range W2 is almost the same. A denitration rate of 50% or more is obtained.
At around °, the denitration rate is the highest at 63%. That is, the temperature is higher on the exhaust gas upstream side of the turbine section 6a of the turbocharger 6, and the denitration rate is higher.

FIG. 8 shows the relationship between the internal pressure of the catalyst and the denitration rate. As the internal pressure of the catalyst increases, the denitration rate increases. However, the turbine section 6a of the supercharger 6 shown in FIG. , An exhaust upstream-side outlet 2 than the exhaust downstream-side outlet 21 communicating with the atmosphere
Since the pressure is higher at 0, the denitration rate is also higher.

As described above, in the structure in which the HC-SCR catalyst device 7 is disposed on the exhaust gas upstream side of the turbine section 6a of the supercharger 6, the distance from the exhaust port 5 to the HC-SCR catalyst device 7 is shortened. Since the exhaust gas reaches the catalyst device 7 while maintaining the temperature (range W2) at which the catalyst works most effectively, and the pressure inside the catalyst is higher than that at the exhaust downstream side of the atmospheric pressure. The denitration rate can be further increased.

[0015]

Second Embodiment FIGS. 3 and 4 show a second embodiment of the present invention.
This is an example to which the described invention is applied, and components having the same names as those in FIGS. 1 and 2 are denoted by the same reference numerals.

In FIG. 3, an exhaust port 5 for each cylinder of the cylinder head 2 is provided with an HC-SCR catalyst device 7 respectively.
Are connected directly to each other. A branch pipe of the exhaust manifold 3 is connected to an exhaust downstream side outlet of each HC-SCR catalyst device 7, and an exhaust downstream side collecting part (exit part) 3a of the exhaust manifold 3 is It is connected to the exhaust upstream inlet 20 of the turbine section 6a of the feeder 6, and the exhaust downstream outlet 21 of the turbine section 6a.
Are connected to exhaust pipes 8 and 9 sequentially.

The structure of the air supply system and other structures are the same as the structures shown in FIGS. 1 and 2, and a description thereof will be omitted.

In such a multi-cylinder gas engine,
As the gas fuel, a gas fuel containing methane as a main component is used, and a durable Ag-based HC-SCR catalyst device 7 is provided as each HC-SCR catalyst device 7.

[0019]

In FIG. 3, the mixture of fuel gas and air is:
After being pressurized by the compressor section 6b of the supercharger 6 and entering the intercooler 13 through the air supply communication pipe 14 and cooled to a predetermined temperature in the intercooler 13, each air supply port is supplied from the air supply manifold 10 in FIG. And supplied to the combustion chamber of each cylinder.

After the combustion, the exhaust gas discharged from the combustion chamber to the exhaust port 5 temporarily remains in the exhaust port 5 and the catalyst device 7 until the exhaust valve is closed and then opened. During this time, nitrogen oxides (NOx) are reduced to molecular nitrogen under high temperature and pressure using hydrocarbon HC in the exhaust gas as a reducing agent. After being purified in this manner, the exhaust gas is discharged from the exhaust manifold 3 through the turbine section 6a of the supercharger 6 and the exhaust pipes 8 and 9.

FIG. 6 shows the relationship between the exhaust gas amount and the exhaust temperature.
It is a graph comparing each part, and the exhaust gas temperature near the exhaust port 5 indicated by the curve X3 is significantly higher than the exhaust gas temperature near the outlet 21 of the turbocharger turbine section 6a indicated by the curve X2. Also, the internal pressure of the catalyst is high. That is, since the HC-SCR catalyst device 7 is connected immediately after the exhaust port 5, the distance until the exhaust gas reaches the catalyst is further reduced, and the internal pressure of the catalyst is maintained at a high pressure. As a result, the denitration rate is improved.

Further, HC-S is provided for each exhaust port 5 of each cylinder.
By arranging the CR catalyst device 7, the exhaust gas flows to the catalyst only during the exhaust stroke. However, the gas composition during the exhaust stroke is not uniform, and the hydrocarbon HC serving as a reducing agent of the HC-SCR catalyst device 7 is used. Is known to increase significantly before the exhaust valve closes, as shown by the dashed curve X4 in FIG. Moreover, as shown in FIG. 9, the correlation between the concentration of hydrocarbon HC and the denitration rate is found to be higher as the concentration of hydrocarbon HC increases. That is, each HC-SCR catalyst device 7
Is connected immediately after each exhaust port 5, each HC-SCR catalyst device 7 comes into contact with exhaust gas containing a high concentration of hydrocarbon (reducing agent), thereby reducing the denitration rate. It is even better.

[0023]

As described above, according to the first aspect of the present invention, since the HC-SCR catalyst device 7 is connected to the exhaust gas upstream side of the exhaust turbine supercharger 6 in the gas engine, Since the distance from the exhaust port 5 to the HC-SCR catalyst device 7 is shortened, the exhaust gas reaches the catalyst device 7 while maintaining the temperature range W2 in which the catalyst works most effectively. Since the pressure is higher than the exhaust pressure downstream of the atmospheric pressure, a sufficiently high denitration rate can be obtained. In addition, by arranging an Ag-based HC-SCR catalyst device, durability can be improved.

According to the second aspect of the present invention, HC-SC
By connecting the R catalyst device 7 immediately after the exhaust port 5, the distance until the exhaust gas reaches the catalyst is further shortened, and the internal pressure of the catalyst is maintained at a high pressure. Denitration rate can be obtained.

Also, HC-SC is provided for each exhaust port of each cylinder.
By providing the R catalyst, the concentration of the hydrocarbon serving as the reducing agent of the HC-SCR catalyst device in the exhaust gas increases, and the exhaust gas contacts the exhaust gas containing the high-concentration hydrocarbon (reducing agent). In addition, the denitration rate is further improved.

[Brief description of the drawings]

FIG. 1 is a front view of a multi-cylinder gas engine to which the invention described in claim 1 of the present application is applied.

FIG. 2 is a view taken in the direction of the arrow II in FIG.

FIG. 3 is a front view of a multi-cylinder gas engine to which the invention described in claim 2 of the present application is applied.

FIG. 4 is a view taken in the direction of arrows IV-IV in FIG. 3;

FIG. 5 is a graph showing a relationship between a reaction temperature and a denitration rate.

FIG. 6 is a graph showing a relationship between an exhaust gas amount and an exhaust temperature for each part.

FIG. 7 is a graph showing a relationship between a crank angle and HC concentration and HC flow rate.

FIG. 8 is a correlation diagram between a pressure in a catalyst and a denitration rate.

FIG. 9 is a correlation diagram between HC concentration and denitration rate.

[Explanation of symbols]

 2 Cylinder head 3 Exhaust manifold 5 Exhaust port 6 Turbocharger 6a Turbine unit 7 HC-SCR catalyst device

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3G004 AA06 BA06 3G091 AA06 AA10 AA19 AA28 AB04 BA14 FB16 GB05W HA03 HB06

Claims (2)

[Claims] 1. An exhaust gas purifying apparatus for a gas engine, wherein an HC-SCR catalyst device is connected to an exhaust gas upstream of an exhaust turbine supercharger. 2. An exhaust gas purifying apparatus for a gas engine, comprising a multi-cylinder gas engine, wherein an HC-SCR catalyst device is connected to an outlet of an exhaust port of each cylinder.