JP2013002355A - Denitration device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain the temperature of a denitration catalyst at a high temperature, and avoid reduction in scavenging pressure to an engine, without causing use of a separate electric motor.SOLUTION: This denitration device 200 includes a supercharger 250 having a first valve 256 for introducing exhaust gas upstream of a turbine 252, the denitration catalyst 214 for reducing the exhaust gas passed through the turbine of the supercharger, a first bypass pipe 210 branched off from an exhaust passage upstream of the turbine for bypassing the exhaust gas upstream of the turbine to the exhaust passage downstream of the turbine, a second valve 220 for adjusting a flow rate of the exhaust gas introduced to the first bypass pipe between a branch point to the first bypass pipe of the exhaust passage and a confluent point to the exhaust passage, a temperature detecting part 224 for detecting the temperature of an inlet of the denitration catalyst, and a valve adjusting part 226 for adjusting opening of the first valve and opening of the second valve based on the temperature detected by the temperature detecting part.

Description

  The present invention relates to a denitration device that reduces nitrogen oxides contained in engine exhaust gas to nitrogen using a reducing agent.

  Combustion exhaust gas (exhaust gas) is generated when fossil fuel is burned in an engine such as a ship or a vehicle. This exhaust gas contains nitrogen oxides (hereinafter simply referred to as NOx). In order to remove such NOx, a denitration device may be provided on the downstream side of the exhaust passage.

As a denitration apparatus, a selective catalytic reduction denitration apparatus that includes a denitration catalyst that promotes NOx reduction and a reducing agent that reduces NOx has become widespread. When NOx is decomposed using a denitration device, exhaust gas and a reducing agent are mixed, and the mixed gas is passed through a denitration catalyst so that the reducing agent reduces (decomposes) NOx in the exhaust gas. To do. Ammonia (NH ₃ ) is considered as the reducing agent, but urea is widely used as a precursor of ammonia because ammonia is highly toxic. Therefore, in order to supply ammonia to the denitration catalyst, the urea water inlet is installed upstream of the denitration catalyst.

  On the other hand, when the denitration catalyst is at a predetermined temperature (for example, about 270 ° C.) or less, there is a problem that the NOx reduction efficiency is lowered. In addition, ammonium sulfate produced by sulfur and ammonia contained in exhaust gas (hereinafter simply referred to as ammonium sulfate) may poison the denitration catalyst, so it is necessary to keep the denitration catalyst above the decomposition temperature of ammonium sulfate. There is. Since exhaust gas is circulated through the denitration catalyst, the temperature of the exhaust gas is such that the temperature at which NOx can be sufficiently reduced (hereinafter simply referred to as the activation temperature) and the decomposition temperature of ammonium sulfate (hereinafter simply referred to as the ammonium sulfate decomposition temperature). The NOx removal catalyst does not need to be heated.

  However, when adopting a configuration in which a turbocharger turbine is provided in the exhaust path of the engine, the heat of the exhaust gas is consumed by the turbine. Therefore, the temperature of the exhaust gas downstream of the turbine depends on the activation temperature of the denitration catalyst and the ammonium sulfate. The decomposition temperature may not be reached. Therefore, as a technique for maintaining the denitration catalyst at the activation temperature or the ammonium sulfate decomposition temperature in the denitration device, the exhaust gas upstream of the turbocharger turbine is diverted and the diverted diverted exhaust gas is introduced into the denitration catalyst. Thus, a technique for increasing the temperature of the denitration catalyst to prevent the production of ammonium sulfate is disclosed (for example, Patent Document 1).

  However, if the technique of Patent Document 1 described above is used, the flow rate of the exhaust gas upstream of the turbine of the supercharger is reduced to reduce the rotational speed of the turbine, and the compression that scavenges the engine using the rotation of the turbine. The machine output drops. Therefore, a technique is disclosed in which a separate electric motor is provided in the compressor of the supercharger, so that the compressor is energized by the electric motor and the scavenging pressure is maintained while the exhaust gas upstream of the turbine is bypassed ( For example, Patent Document 2).

Patent No. 2915687 JP 2010-185349 A

  However, in the technique of Patent Document 2 described above, electric power for driving the electric motor is required, and the efficiency of the entire engine system is deteriorated. In addition, it is necessary to secure a separate space for installing the electric motor.

  Furthermore, if the motor is too close to the compressor, the motor may block the compressor inlet, and scavenging from the compressor to the engine may be difficult, so the motor and the compressor are separated to some extent. It is necessary to install it. In this case, the rotating shaft that connects the electric motor and the compressor must be lengthened, and additional space is required to install the long rotating shaft. Moreover, if the rotating shaft is lengthened, there is a possibility that vibration is generated by the rotation of the rotating shaft.

  In view of such problems, the present invention maintains the temperature of the denitration catalyst at the activation temperature and the ammonium sulfate decomposition temperature, and avoids reducing the scavenging air pressure to the engine without using a separate electric motor. An object of the present invention is to provide a denitration apparatus capable of performing the above-mentioned.

  In order to solve the above problems, a denitration apparatus of the present invention has a first valve that introduces exhaust gas upstream of a turbine into a turbine provided in an exhaust path of the engine, and uses the rotation of the turbine for the engine. A turbocharger that introduces air; a denitration catalyst that reduces exhaust gas that has passed through the turbine of the turbocharger; and a branch from the exhaust path upstream of the turbine, and the exhaust gas upstream of the turbine is sent to an exhaust path downstream of the turbine A first bypass pipe to be bypassed, a second valve for adjusting a flow rate of exhaust gas introduced into the first bypass pipe between a branch point of the exhaust path to the first bypass pipe and a junction point to the exhaust path, and denitration A temperature detection unit that detects the temperature of the inlet of the catalyst, and a valve adjustment unit that adjusts the opening of the first valve and the opening of the second valve based on the temperature detected by the temperature detection unit. To.

  The valve adjusting unit may reduce the opening of the first valve when increasing the opening of the second valve.

  According to the present invention, the temperature of the denitration catalyst is maintained at the activation temperature and the ammonium sulfate decomposition temperature, and reduction in scavenging pressure to the engine can be avoided without using a separate electric motor.

It is explanatory drawing for demonstrating a denitration system. It is explanatory drawing for demonstrating the relationship between the engine load in a 2 stroke engine, and the temperature of exhaust gas. It is explanatory drawing for demonstrating the relationship between the scavenging pressure by a supercharger, and an engine load. It is explanatory drawing for demonstrating the 1st valve | bulb of a turbine.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The dimensions, materials, and other specific numerical values shown in the embodiments are merely examples for facilitating the understanding of the invention, and do not limit the present invention unless otherwise specified. In the present specification and drawings, elements having substantially the same function and configuration are denoted by the same reference numerals, and redundant description is omitted, and elements not directly related to the present invention are not illustrated. To do.

  In large ships such as container ships and tankers, a uniflow type two-cycle engine (two-stroke engine), which is advantageous in terms of cost because it has high thermal efficiency and low-quality fuel oil (heavy oil) can be used, is widely used. Combustion of fuels such as fossil fuels such as gasoline, light oil, heavy oil, liquefied natural gas (LNG), and liquefied petroleum gas (LPG) in such engines results. The exhaust gas contains NOx. Hereinafter, the denitration system 100 that reduces NOx in the exhaust gas discharged from the engine will be described. In the following embodiments, a uniflow type two-stroke engine will be described as an example of an engine used in the denitration system 100. However, the denitration system 100 may be adopted in other types of two-stroke engines.

(Denitration system 100)
FIG. 1 is an explanatory diagram for explaining a denitration system 100 according to the present embodiment. As shown in FIG. 1, the denitration system 100 includes an engine 110 and a denitration device 200. In FIG. 1, the flow of substances (exhaust gas, reducing agent) is indicated by solid lines, and the flow of signals is indicated by broken lines.

  The engine 110 includes a cylinder 110a, a piston 110b, an exhaust valve 110c, and an exhaust collecting pipe 112. The engine 110 reciprocates in the direction shown by the white arrow in FIG. 1 so that the piston 110b connected to the crosshead (not shown) can slide in the cylinder 110a through the processes of scavenging, compression, combustion, and exhaust. To do. In such a crosshead type piston 110b, the stroke in the cylinder 110a can be formed relatively long, and the crosshead receives the side pressure acting on the piston 110b, so that the output of the two-stroke engine can be increased. Can do. Further, since the cylinder 110a and the crank chamber in which the crosshead is accommodated are isolated, it is possible to prevent fouling deterioration even when low quality fuel oil is used. The exhaust collecting pipe 112 collects a plurality of exhaust passages communicating with the cylinder 110 a through the plurality of exhaust valves 110 c provided in the engine 110.

  The denitration apparatus 200 reduces the NOx contained in the exhaust gas X1 to nitrogen by causing ammonia to act on the exhaust gas X1 discharged from the exhaust collecting pipe 112.

  In this way, the exhaust gas X1 exhausted from the engine 110 is introduced into the denitration apparatus 200, NOx is reduced, and exhausted to the outside as the exhaust gas X2. Hereinafter, the denitration apparatus 200 according to the present embodiment will be described in detail.

(Denitration device 200)
In the denitration apparatus 200 according to the present embodiment, a selection is made such that a reducing agent is introduced into the exhaust gas X1, and NOx contained in the exhaust gas X1 is reduced by a denitration catalyst downstream of the introduction position of the reducing agent to generate nitrogen. The catalytic reduction method is adopted.

  As shown in FIG. 1, the denitration apparatus 200 includes a first bypass pipe 210, a first reducing agent introduction unit 212, a denitration catalyst 214, a supercharger 250, a NOx detection unit 216, and a reducing agent adjustment unit 218. And a second valve 220, a second reducing agent introduction unit 222, a temperature detection unit 224, and a valve adjustment unit 226.

  The first bypass pipe 210 is branched from the exhaust passage 202 a upstream of the turbine 252 of the supercharger 250, and bypasses the exhaust gas X 1 upstream of the turbine 252 to the exhaust passage 202 b downstream of the turbine 252.

  The first reducing agent introduction unit 212 introduces the reducing agent (urea water) into the first bypass pipe 210 between the junction point P from the branch point P from the exhaust path 202a to the first bypass pipe 210 to the exhaust path 202b. (Spray). In the present embodiment, the first reducing agent introduction unit 212 introduces urea water into the first bypass pipe 210 on the downstream side of the second valve 220 described later.

  It should be noted that the urea water introduction position by the first reducing agent introduction section 212 and the position of the second valve 220 are preferably as upstream as possible in the first bypass pipe 210. For example, the temperature of the exhaust gas X1 upstream of the turbine 252 is 270 ° C., and it takes 1 second to vaporize and decompose urea water at 270 ° C., and the flow rate of the exhaust gas X1 is 10 m / second. Then, in order to vaporize and decompose urea water, a 10 m flow path is required. Therefore, the time for vaporizing and decomposing the urea water (by making the introduction position of the urea water by the first reducing agent introduction unit 212 and the position of the second valve 220 as upstream as possible in the first bypass pipe 210 ( (Pipe length) can be earned, and it is not necessary to wastefully lengthen the pipe length to the denitration apparatus 200.

  The denitration catalyst 214 is made of a metal such as vanadium, tungsten, or molybdenum or an oxide thereof and titanium oxide, and reduces NOx in the exhaust gas X1 that has passed through the turbine 252 of the supercharger 250.

  As described above, uniflow type two-stroke engines are widely used in large ships, but the two-stroke engines are more efficient and have a higher ratio of air to fuel than the four-stroke engines. Often the temperature is low. Accordingly, when a uniflow type two-stroke engine is adopted as the engine 110 and the turbine 252 of the supercharger 250 is provided in the exhaust path of the engine 110, the heat of the exhaust gas X1 is consumed by the turbine 252. The temperature of the exhaust gas X1 downstream of 252 may not reach the activation temperature of the denitration catalyst 214 and the ammonium sulfate decomposition temperature.

  FIG. 2 is an explanatory diagram for explaining the relationship between the engine load and the temperature of the exhaust gas X1 in a two-stroke engine. In FIG. 2, the temperature of the exhaust gas X1 at the inlet of the turbine 252 is indicated by a solid line, and the temperature of the exhaust gas X1 at the outlet of the turbine 252 is indicated by a broken line.

  As shown in FIG. 2, when the engine load is high, the work amount of the turbine 252 increases, that is, the heat of the exhaust gas X1 is consumed in the turbine 252, and thus the temperature of the exhaust gas X1 at the outlet of the turbine 252 is increased. descend. For example, as the engine load increases from 25% to 75%, the work amount of the turbine 252 increases, so the temperature of the exhaust gas X1 at the outlet of the turbine 252 gradually decreases to about 250 ° C., exceeding 75%. However, it remains at about 250 ° C. Therefore, when the engine load exceeds 67%, the temperature is lower than 270 ° C. which is a temperature necessary for vaporization and decomposition of urea water.

  Here, since the outlet of the turbine 252 and the denitration catalyst 214 are close to each other, the temperature of the exhaust gas X1 at the outlet (downstream) of the turbine 252 can be regarded as the temperature of the inlet of the denitration catalyst 214. Therefore, if the temperature of the exhaust gas X1 downstream of the turbine 252 is lowered, that is, the temperature of the denitration catalyst 214 is lowered and has not reached the activation temperature and the ammonium sulfate decomposition temperature (for example, about 270 ° C.), the denitration catalyst 214 cannot sufficiently reduce NOx.

  In the present embodiment, the denitration apparatus 200 is provided with the first bypass pipe 210 described above, and the exhaust gas X1 having a high temperature upstream of the turbine 252 is bypassed immediately before the denitration catalyst 214, whereby the temperature of the denitration catalyst 214 is increased. Can be raised. Therefore, by appropriately adjusting the pipe diameter of the first bypass pipe 210 and the flow rate of the exhaust gas X1 to be bypassed by the first bypass pipe 210, the temperature of the denitration catalyst 214 reaches the activation temperature and the ammonium sulfate decomposition temperature. Therefore, it is possible to prevent the formation of ammonium sulfate in the denitration catalyst 214.

  However, if the exhaust gas X1 upstream of the turbine 252 is simply bypassed downstream of the turbine 252 by the first bypass pipe 210, the flow rate of the exhaust gas X1 upstream of the turbine 252 decreases, and the rotational speed of the turbine 252 decreases. The output of the compressor 254 that scavenges the engine 110 using the rotation of the turbine 252, that is, the scavenging air pressure, drops.

  FIG. 3 is an explanatory diagram for explaining the relationship between the scavenging pressure by the supercharger and the engine load. As shown in FIG. 3, the scavenging air pressure of the supercharger increases as the engine load increases. That is, in order to increase the engine load, it is also necessary to increase the scavenging air pressure. However, if the exhaust gas X1 upstream of the turbine 252 is bypassed downstream of the turbine 252 by the first bypass pipe 210, the rotational speed of the turbine 252 is reduced, and the scavenging air pressure is lowered accordingly, thereby increasing the engine load. Even if it cannot be done or can be raised, the engine will become hot and affect the normal operation of the engine.

  More specifically, the scavenging amount (air amount) decreases when the scavenging pressure decreases, but the fuel amount for obtaining a predetermined output hardly changes. For this reason, the combustion temperature rises, and the temperature of the components constituting the combustion chamber such as the cylinder head and cylinder liner constituting the cylinder 110a, the exhaust valve 110c, the piston 110b, and the piston ring constituting the piston 110b rises.

  When the temperature of the parts constituting the combustion chamber rises, the material strength of the parts decreases, the wear of the sliding parts (cylinder 110a, piston 110b, exhaust valve 110c) accelerates, the parts deform due to thermal expansion, and the parts fail to seal. (Gas leaks) may occur. Therefore, it is conceivable to manufacture the parts constituting the combustion chamber with a material having high heat resistance, but the cost becomes high. In addition, although a configuration for cooling the parts is conceivable, the apparatus becomes large and a large design change is forced.

  Further, when the scavenging air pressure decreases, the scavenging amount (air amount) decreases, so that the combustion state deteriorates due to air shortage (the fuel is not sufficiently oxidized) and unburned components such as soot increase.

  The supercharger 250 includes a turbine 252 and a compressor 254 that is coaxial with the turbine 252. The turbine 252 is rotated by the exhaust gas X1 discharged from the engine 110, and the compressor 254 utilizes the rotation of the turbine 252, and an active gas (oxidant such as oxygen and ozone, or a mixture thereof) introduced from the outside. (E.g., air) is compressed to increase the scavenging pressure to the engine 110. By doing so, the output of the engine 110 can be improved.

  Further, the turbine 252 of the present embodiment has a first valve 256 for introducing the exhaust gas X1 upstream of the turbine 252. That is, the supercharger 250 according to the present embodiment is a variable capacity supercharger. Note that the opening degree (flow rate) of the first valve 256 is, for example, an opening degree (setting) that satisfies the relationship between the engine load and the scavenging air pressure shown in FIG. 3 while the second valve 220 described later is closed. Value).

  4 is an explanatory diagram for explaining the first valve 256 of the turbine 252. FIGS. 4A and 4B are views of the turbine 252 as viewed from the upstream side, and FIG. FIG. 3 is an explanatory diagram for explaining the relationship between the flow rate of exhaust gas X1 flowing into the turbine 252 and the pressure ratio according to the opening degree of the first valve 256. In FIG. 4C, the vertical axis represents the pressure ratio πt, and the horizontal axis represents the turbine corrected flow rate. Here, W is the flow rate (kg / s) of the gas flowing through the turbine, T3 is the turbine inlet temperature (K), P3 is the turbine inlet pressure (Pa), and P4 is the ter-part outlet pressure (Pa). .

  As shown in FIG. 4 (c), when the opening degree of the first valve 256 of the turbine 252 as shown in FIG. 4 (a) is small, the first valve of the turbine 252 as shown in FIG. 4 (b). Compared with the case where the opening degree of 256 is large, the pressure of the exhaust gas X1 flowing into the blade portion (impeller) constituting the turbine 252 becomes higher. That is, when the opening degree of the first valve 256 is reduced (throttle), the pressure of the exhaust gas X1 flowing into the wing part increases and the rotation speed of the wing part increases.

  The NOx detector 216 detects the concentration of NOx in the exhaust gas X1 upstream of the turbine 252. Here, since the NOx concentration has a correlation with the engine load, the NOx detecting unit 216 may estimate the NOx concentration from the engine load without measuring the actual NOx concentration.

  The reducing agent adjusting unit 218 is introduced by the first reducing agent introducing unit 212 based on the concentration of NOx detected by the NOx detecting unit 216 and the opening degree (flow rate) of the second valve 220 by the valve adjusting unit 226 described later. The amount of urea water to be adjusted and the amount of urea water introduced by the second reducing agent introduction unit 222 are adjusted.

  Due to the configuration provided with the NOx detection unit 216 and the reducing agent adjustment unit 218, urea water is introduced wastefully when the NOx in the exhaust gas X1 is small, and ammonia is not oxidized in the denitration catalyst 214 and discharged outside. It is possible to avoid a situation where the amount of urea water is necessary to reduce the NOx when the amount of NOx is large.

  The second valve 220 is disposed between the junction P to the exhaust passage 202b from the branch point P to the first bypass pipe 210 in the exhaust passage 202a. The opening degree of the second valve 220 is adjusted by the valve adjustment unit 226, and the valve adjustment unit 226 adjusts the flow rate of the exhaust gas X1 introduced into the first bypass pipe 210.

  The second reducing agent introduction unit 222 introduces (sprays) urea water downstream of the junction point Q in the exhaust path 202b. In the present embodiment, the second reducing agent introduction unit 222 is in a period during which the second valve 220 is closed, that is, the entire amount of the exhaust gas X1 passes through the turbine 252 according to control by the valve adjustment unit 226. The urea water is introduced downstream of the confluence point Q only during the period.

  The temperature detector 224 detects the temperature at the inlet of the denitration catalyst 214. As can be understood with reference to FIG. 2, since the temperature of the exhaust gas X1 at the outlet of the turbine 252 and the engine load have a correlation, the temperature detector 224 measures the actual inlet temperature of the denitration catalyst 214. At least, if the engine load, for example, the engine load is 67% or more, the temperature may be estimated from the engine load such that the temperature at the inlet of the denitration catalyst 214 is lower than 270 ° C.

Table 1 is a table showing the relationship between the engine load and the rotation speed of the crank. As shown in Table 1, since there is a correlation between the engine load and the rotation speed of the crank, the temperature detection unit 224 does not measure the actual inlet temperature of the denitration catalyst 214, but the rotation speed of the crank. From this, the engine load may be estimated, and the temperature may be estimated from the estimated engine load. That is, the temperature at the inlet of the denitration catalyst 214 can be uniquely determined from the rotation speed of the crank.

  The valve adjustment unit 226 adjusts the opening degree of the second valve 220 based on the temperature detected by the temperature detection unit 224, and adjusts the opening degree of the first valve 256 accordingly. Specifically, when the opening degree of the second valve 220 provided in the first bypass pipe 210 is increased based on the temperature detected by the temperature detection unit 224, the valve adjustment unit 226 causes the turbine 252 of the supercharger 250 to When the opening degree of the first valve 256 provided is reduced and, conversely, when the opening degree of the second valve 220 is reduced, the opening degree of the first valve 256 provided in the turbine 252 of the supercharger 250 is increased. .

  When the engine load is high, the temperature of the exhaust gas X1 downstream of the turbine 252 is decreased, and the temperature of the inlet of the denitration catalyst 214 has not reached the activation temperature and the ammonium sulfate decomposition temperature, the first bypass pipe 210 is Therefore, it is necessary to heat the denitration catalyst 214 by bypassing the high-temperature exhaust gas X1 upstream of the turbine 252.

  Therefore, the valve adjustment unit 226 adjusts the opening degree of the second valve 220 when it is determined that the temperature detected by the temperature detection unit 224 is lower than the activation temperature of the denitration catalyst 214 and lower than the ammonium sulfate decomposition temperature. Then, the flow rate of the hot exhaust gas X1 to be bypassed is adjusted. As a result, the temperature of the denitration catalyst 214 can reach the activation temperature and the ammonium sulfate decomposition temperature, and NOx contained in the exhaust gas X1 can be reliably reduced.

  However, as described above, when the denitration catalyst 214 is heated, the valve adjustment unit 226 increases the opening of the second valve 220 to increase the flow rate of the exhaust gas X1 to the first bypass pipe 210. The flow rate of the exhaust gas X1 upstream of the turbine 252 of the supercharger 250 is reduced, and the rotational speed of the turbine is reduced.

  Therefore, when the opening of the second valve 220 is increased, that is, when the flow rate of the exhaust gas X1 upstream of the turbine 252 is decreased, the valve adjustment unit 226 is provided with the first one provided in the turbine 252 of the supercharger 250. The opening degree of the valve 256 is reduced. Then, as described above, the rotational speed of the blades of the turbine 252 increases, and the scavenging air pressure of the compressor 254 that decreases due to a decrease in the flow rate of the exhaust gas X1 upstream of the turbine 252 is maintained at a desired value. Can do.

  Further, when the opening of the second valve 220 is reduced, that is, when the flow rate of the exhaust gas X1 upstream of the turbine 252 does not decrease, the valve adjusting unit 226 increases the opening of the first valve 256 and sets the opening. Move closer to the value. As a result, the exhaust gas X1 sufficiently passes through the turbine 252, so that the scavenging pressure of the compressor 254 can be maintained at a desired value.

  As a result, it is possible to avoid a situation in which the scavenging air pressure to the engine 110 decreases and the engine load decreases or the engine 110 becomes hot.

  Further, if the engine load is low and the temperature of the denitration catalyst 214 has reached the activation temperature and the ammonium sulfate decomposition temperature, it is not necessary to pass the exhaust gas X1 upstream of the turbine 252 through the first bypass pipe 210. Therefore, the valve adjustment unit 226 is a temperature (for example, 370 ° C. that is 100 ° C. higher than 270 ° C.) that can be regarded as the activation temperature of the denitration catalyst 214 without bypassing the high temperature exhaust gas X1 in the first bypass pipe 210. Is determined, the second valve 220 is closed, and the high-temperature exhaust gas X1 upstream of the turbine 252 is not bypassed. Further, the valve adjustment unit 226 returns the opening degree of the first valve 256 to a set value. If the upstream exhaust gas X1 is not bypassed, the exhaust gas X1 sufficiently passes through the turbine 252. Therefore, the situation where the flow rate of the exhaust gas X1 passing through the turbine 252 decreases and the output of the compressor 254 decreases is avoided. It becomes possible to do.

  Further, when the temperature detected by the temperature detection unit 224 is a high temperature that decomposes ammonia, the valve adjustment unit 226 closes the second valve 220 and discharges the high-temperature exhaust gas X1 upstream of the turbine 252. Do not bypass. As a result, the exhaust gas X1 upstream of the turbine 252 is too hot. By bypassing the exhaust gas X1, the temperature of the denitration catalyst 214 rises too much, decomposing ammonia and reducing the NOx decomposition efficiency. This can avoid the situation.

  While the valve adjustment unit 226 closes the second valve 220, the reducing agent adjustment unit 218 stops the introduction of urea water to the first reducing agent introduction unit 212, and the NOx detection unit 216 detects the NOx detected. Based on the concentration, the amount of urea water introduced by the second reducing agent introduction unit 222 is adjusted.

  As described above, according to the denitration apparatus 200 according to the present embodiment, the bypass amount of the exhaust gas X1 upstream of the turbine 252 is adjusted according to the temperature of the denitration catalyst 214, and based on the adjustment of this bypass amount. Thus, the opening degree of the first valve 256 of the turbine 252 is adjusted so that the scavenging air pressure of the compressor 254 does not decrease. Therefore, while maintaining the temperature of the denitration catalyst 214 at the activation temperature and the ammonium sulfate decomposition temperature, it is possible to avoid a reduction in scavenging air pressure to the engine 110 without using a separate electric motor.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to this embodiment. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Is done.

  INDUSTRIAL APPLICABILITY The present invention can be used for a denitration device that reduces nitrogen oxides contained in engine exhaust gas to nitrogen using a reducing agent.

DESCRIPTION OF SYMBOLS 200 ... Denitration apparatus 210 ... 1st bypass pipe 214 ... Denitration catalyst 216 ... NOx detection part 220 ... 2nd valve 224 ... Temperature detection part 226 ... Valve adjustment part 250 ... Supercharger 252 ... Turbine 254 ... Compressor 256 ... 1st valve

Claims (2)

A turbocharger having a first valve that introduces exhaust gas upstream of the turbine into a turbine provided in an exhaust path of the engine, and that introduces air into the engine using rotation of the turbine;
A denitration catalyst that reduces exhaust gas that has passed through the turbocharger turbine;
A first bypass pipe branched from the exhaust passage upstream of the turbine and bypassing exhaust gas upstream of the turbine to the exhaust passage downstream of the turbine;
A second valve for adjusting a flow rate of exhaust gas introduced into the first bypass pipe between a branch point to the first bypass pipe in the exhaust path and a junction point to the exhaust path;
A temperature detector for detecting the temperature of the inlet of the denitration catalyst;
A valve adjusting unit that adjusts the opening of the first valve and the opening of the second valve based on the temperature detected by the temperature detection unit;
A denitration apparatus comprising:   The denitration apparatus according to claim 1, wherein the valve adjustment unit reduces the opening degree of the first valve when the opening degree of the second valve is increased.

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