KR102367285B1 - Selective catalytic reduction system - Google Patents

Abstract

A selective catalytic reduction system according to an embodiment of the present invention includes an exhaust passage through which exhaust gas moves, and a reactor installed on the exhaust passage and having a catalyst installed therein for reducing nitrogen oxides (NOx) contained in exhaust gas; a heating device for increasing the temperature of the exhaust gas flowing into the reactor; a bypass flow branch branching from the exhaust flow path to bypass the reactor and then rejoining the exhaust flow path; and a branch point with the bypass flow path and the front end of the reactor and a front valve installed on the exhaust passage therebetween. In addition, the catalyst is preheated according to one preheating mode selected from the first catalyst preheating mode and the second catalyst preheating mode that operate differently depending on whether the heating device is normally operated.

Description

Selective Catalytic Reduction System {SELECTIVE CATALYTIC REDUCTION SYSTEM}

The present invention relates to a selective catalytic reduction system, and more particularly, to a selective catalytic reduction system capable of preheating a catalyst used to reduce nitrogen oxides (NOx) contained in exhaust gas.

As industrialization progresses rapidly, the use of various fossil fuels such as petroleum and coal has increased. As a result, various harmful gases emitted during the combustion of fossil fuels cause serious air pollution. Typical examples include smog and acid rain.

The main culprits of air pollution include sulfur oxides (SOx) and nitrogen oxides (NOx) in exhaust gases emitted from engines of vehicles and ships, or from thermal power plants or factories. Among them, a selective catalytic reduction (SCR) system is a representative facility for reducing nitrogen oxides. In the selective catalytic reduction system, the exhaust gas and the reducing agent pass together through a reactor in which the catalyst is installed, and the nitrogen oxides and the reducing agent contained in the exhaust gas are reacted to reduce the nitrogen and water vapor.

When such a selective catalytic reduction system is used in ships, the emission of nitrogen oxides (NOx) emitted from marine diesel engines is regulated by the International Maritime Organization (IMO Tier-III) for engine international air pollution prevention 3rd regulation. Since separate energy is consumed for operation of the selective catalytic reduction system, an effective operation method is required along with a low-cost and high-efficiency denitration facility.

In general, a catalyst used to reduce nitrogen oxides contained in exhaust gas may have an activation temperature within the range of 250 degrees Celsius to 350 degrees Celsius. Here, the activation temperature refers to a temperature at which the catalyst can stably reduce nitrogen oxides without being poisoned. When the catalyst reacts outside the active temperature range, it is poisoned and the efficiency is lowered. Specifically, when exhaust gas having a relatively low temperature of less than 250 degrees Celsius is introduced, sulfur oxide (SOx) of the exhaust gas and ammonia (NH ₄ ) of the reducing agent react to generate a catalyst poisoning material. The catalyst poisoning material may include at least one of ammonium sulfate ((NH4) ₂ SO ₄ ) and ammonium bisulfate (NH ₄ HSO ₄ ). Since such a catalyst poisoning material is adsorbed to the catalyst to decrease the activity of the catalyst, it is required to maintain the temperature of the catalyst within the active temperature range in order to increase the efficiency of the catalyst and minimize losses due to maintenance.

In addition, since the exhaust gas discharged at the initial stage of operation of the engine has a relatively low temperature, a phenomenon in which the catalyst is intensively poisoned at the initial stage of operation or cannot reduce nitrogen oxide to a target value is concentrated. Specifically, the catalyst for reducing nitrogen oxide emitted from the main propulsion diesel engine for a ship is low in the temperature of the exhaust gas discharged from the engine when the ship is set out after anchoring, so the catalyst cannot normally reduce nitrogen oxide, and nitrogen oxide harmful to the human body into the atmosphere. It is difficult to reduce air pollution in ports because

Accordingly, in the conventional selective catalytic reduction system, the catalyst is preheated in advance at the beginning of operation or before full-scale operation. In addition, the catalyst is performed through a separately provided heating device such as an oil burner or an electric heater.

However, when a heating device for preheating the catalyst malfunctions or is not in a steady state, there is a problem in that the catalyst cannot be preheated. For example, when air or fuel for combustion is not stably supplied to the oil burner, stable combustion is not achieved in the oil burner, which not only prevents the catalyst from preheating, but also adversely affects the catalyst.

An embodiment of the present invention provides a selective catalytic reduction system capable of stably preheating a catalyst used to reduce nitrogen oxides (NOx) contained in exhaust gas.

According to an embodiment of the present invention, the selective catalytic reduction system includes an exhaust passage through which exhaust gas moves, and a reactor installed on the exhaust passage and having a catalyst for reducing nitrogen oxides (NOx) contained in the exhaust gas installed therein; a heating device for increasing the temperature of the exhaust gas flowing into the reactor; and a front valve installed on the exhaust passage between the front ends. In addition, the catalyst is preheated according to one preheating mode selected from the first catalyst preheating mode and the second catalyst preheating mode that operate differently depending on whether the heating device is normally operated.

In the first catalyst preheating mode, the catalyst may be preheated by closing the front valve and operating the heating device. In the second catalyst preheating mode, the catalyst may be preheated while the operation of the heating device is stopped and the opening rate is gradually or stepwise increased while the front valve is partially opened.

The selective catalytic reduction system may further include a temperature sensor for measuring the temperature of the exhaust gas flowing into the reactor or the temperature inside the reactor. And in the first catalyst preheating mode, when the temperature measured by the temperature sensor reaches the target temperature, the heating device may be stopped or operated at a level maintaining the target temperature.

The selective catalytic reduction system may further include a bypass valve installed on the bypass passage, and a rear valve installed on the exhaust passage between a junction with the bypass passage and the rear end of the reactor. In the first catalyst preheating mode, the bypass valve may be opened, and the rear valve may be closed or partially opened.

In the first catalyst preheating mode, when the temperature measured by the temperature sensor reaches a target temperature, the opening rate of the front valve may be gradually increased. In addition, after the front valve is opened, the rear valve may also be opened, and the bypass valve may be closed after the rear valve is opened.

When the second catalyst preheating mode is selected, the front valve may be partially opened by 20% or less of the maximum opening.

The selective catalytic reduction system may further include a temperature sensor for measuring the temperature of the exhaust gas flowing into the reactor or the temperature inside the reactor. In addition, in the second catalyst preheating mode, when the rising slope of the temperature measured by the temperature sensor is equal to or greater than a preset slope, the opening rate of the front valve may be increased gradually or stepwise. On the other hand, when the rising slope of the temperature measured by the temperature sensor is less than a preset slope or has a falling slope, the opening rate of the front valve may be maintained as it is or the opening rate may be decreased.

The selective catalytic reduction system may further include a bypass valve installed on the bypass passage, and a rear valve installed on the exhaust passage between a junction with the bypass passage and the rear end of the reactor. And in the second catalyst preheating mode, the bypass valve may be opened, and the rear valve may be closed or partially opened.

In the second catalyst preheating mode, when the temperature measured by the temperature sensor reaches a target temperature, the opening rate of the front valve may be gradually increased. In addition, after the front valve is opened, the rear valve may also be opened, and the bypass valve may be closed after the rear valve is opened.

In addition, in the selective catalytic reduction system, the heating device may be installed on the exhaust passage to directly raise the temperature of the exhaust gas passing through the exhaust passage or to increase the temperature of a separate fluid that joins the exhaust passage. And the heating device may be at least one of a burner or a heater.

According to an embodiment of the present invention, the selective catalytic reduction system can stably preheat the catalyst used to reduce nitrogen oxides (NOx) contained in exhaust gas.

1 is a block diagram showing a selective catalytic reduction system according to an embodiment of the present invention.
Figure 2 is a block diagram showing the operating state of the selective catalytic reduction system of Figure 1.
Figure 3 is a flowchart showing the operation process of the selective catalytic reduction system of Figure 1.

Hereinafter, with reference to the accompanying drawings, the embodiments of the present invention will be described in detail so that those of ordinary skill in the art to which the present invention pertains can easily implement them. The present invention may be embodied in many different forms and is not limited to the embodiments described herein.

It is noted that the drawings are schematic and not drawn to scale. Relative dimensions and proportions of parts in the drawings are shown exaggerated or reduced in size for clarity and convenience in the drawings, and any dimensions are illustrative only and not limiting. And the same reference numerals are used to denote like features to the same structure, element, or part appearing in two or more drawings.

The embodiment of the present invention specifically represents an ideal embodiment of the present invention. As a result, various modifications of the diagram are expected. Accordingly, the embodiment is not limited to a specific shape of the illustrated area, and includes, for example, a shape modification by manufacturing.

Hereinafter, a selective catalytic reduction system 101 according to an embodiment of the present invention will be described with reference to FIG. 1 .

The selective catalytic reduction (SCR) system 101 according to an embodiment of the present invention reduces nitrogen oxides (NOx) contained in exhaust gas discharged from an engine (not shown). Here, the engine may include one or more of a two-stroke low-speed diesel engine used as a main power source for supplying propulsion to a ship or a four-stroke medium-speed diesel engine used as an auxiliary power source for power generation or an auxiliary power source in a ship.

However, one embodiment of the present invention is not limited thereto. The engine may be an internal combustion engine for a plant or an engine for a vehicle. That is, in one embodiment of the present invention, various types of engines known to those of ordinary skill in the art may be used.

In addition, in an embodiment of the present invention, the exhaust gas discharged by the engine has a temperature within the range of 200 degrees Celsius to 500 degrees Celsius, and in some cases may be lowered to 150 degrees Celsius or more and less than 200 degrees Celsius.

As shown in FIG. 1 , a selective catalytic reduction (SCR) system 101 according to an embodiment of the present invention includes an exhaust flow path 610 , a reactor 300 , a heating device 400 , and a bypass. It includes a flow path 620 , and a front valve 711 .

In addition, the selective catalytic reduction system 101 according to an embodiment of the present invention may further include a temperature sensor 500 , a rear valve 712 , and a bypass valve 720 .

The exhaust flow path 610 moves the exhaust gas containing nitrogen oxide (NOx). And the exhaust gas moving along the exhaust flow path 610 is discharged to the outside through the reactor 300 to be described later.

The reactor 300 is installed on the exhaust passage 610 . That is, the reactor 300 receives the exhaust gas containing nitrogen oxide (NOx) through the exhaust passage 610 . And the reactor 300 has a built-in catalyst 350 for reducing nitrogen oxide (NOx) contained in the exhaust gas. The catalyst 350 promotes a reaction between nitrogen oxides (NOx) and a reducing agent contained in exhaust gas to reduce nitrogen oxides (NOx) into nitrogen and water vapor.

In addition, in one embodiment of the present invention, the catalyst 350 installed inside the reactor 300 may be arranged in a multi-layered structure based on the movement direction of the exhaust gas. That is, the catalyst 350 may be provided in the form of a plurality of catalyst modules, and the plurality of catalyst modules may be disposed along the movement direction of the exhaust gas.

The catalyst 350 may be made of various materials known to those skilled in the art, such as zeolite, vanadium, and platinum. For example, the catalyst 350 may have an activation temperature within the range of 200 degrees Celsius to 500 degrees Celsius. Here, the activation temperature refers to a temperature at which the catalyst 350 can stably reduce nitrogen oxides without being poisoned. When the catalyst 350 reacts outside the active temperature range, the catalyst 350 is poisoned and the efficiency is lowered.

For example, when a reduction reaction to reduce nitrogen oxides contained in exhaust gas occurs at a relatively low temperature of 150 degrees Celsius or more and less than 250 degrees Celsius, sulfur oxides (SOx) and ammonia (NH ₃ ) in the exhaust gas react Thus, a catalyst poisoning substance is produced.

Specifically, the poisoning material that poisons the catalyst 350 may include at least one of ammonium sulfate ((NH ₄ ) ₂ SO ₄ ) and ammonium bisulfate (NH ₄ HSO ₄ ). This catalyst poisoning material is adsorbed to the catalyst to reduce the activity of the catalyst 350 . Since the catalyst poisoning material is decomposed at a relatively high temperature, that is, at a temperature within the range of 350 degrees Celsius to 450 degrees Celsius, the catalyst 350 in the reactor 300 may be heated to regenerate the poisoned catalyst 350 .

In addition, the reducing agent used in an embodiment of the present invention may be an aqueous solution of urea (urea, CO(NH ₂ ) ₂ ). When urea is thermally decomposed or hydrolyzed, ammonia (NH ₃ ) and isocyanic acid (HNCO) are produced, and isocyanic acid (HNCO) is again decomposed into ammonia (NH ₃ ) and carbon dioxide (CO ₂ ). . And finally, ammonia (NH ₃ ) produced reacts with nitrogen oxides (NOx) contained in the exhaust gas.

For example, the reducing agent may be injected into the exhaust passage 610 in front of the reactor 300 to be mixed with the exhaust gas. Hereinafter, in the present specification, the front means an upstream direction based on the movement direction of the exhaust gas, and the rear means a downstream direction based on the movement direction of the exhaust gas.

The heating device 400 raises the temperature of the exhaust gas flowing into the reactor 300 . In one embodiment of the present invention, the heating device 400 may be implemented in various forms. Specifically, the heating device 400 may be installed on the exhaust flow path 610 to directly increase the temperature of the exhaust gas passing through the exhaust flow path 610 or to increase the temperature of a separate fluid that joins the exhaust flow path 610 . . In this case, the separate fluid that joins the exhaust passage 610 may be air introduced from the outside or a part of exhaust gas discharged from the engine may be branched.

Further, the heating device 400 may be one of an electric heater, an oil burner, or a plasma burner.

The bypass flow path 620 branches off from the exhaust flow path 610 in front of the reactor 300 , bypasses the reactor 300 , and then rejoins the exhaust flow path 610 at the rear of the reactor 300 .

The front valve 711 is installed on the exhaust passage 610 between the branch point with the bypass passage 620 and the front end of the reactor 300 . The rear valve 712 is installed on the exhaust passage 610 between the junction with the bypass passage 620 and the rear end of the reactor 300 . And the bypass valve 720 is installed on the bypass flow path (620).

The temperature sensor 500 may measure the temperature of the exhaust gas flowing into the reactor 300 or the temperature inside the reactor 300 .

In one embodiment of the present invention, the catalyst 350 is preheated according to any one preheating mode selected from the first catalyst preheating mode and the second catalyst preheating mode that operate differently depending on whether the heating device 400 is normally operated. do.

Therefore, the selective catalytic reduction system 101 according to an embodiment of the present invention stably preheats the catalyst 350 even when the heating device 400 used to preheat the catalyst 350 malfunctions or operates abnormally. can do.

Hereinafter, the operation principle of the selective catalytic reduction system 101 to preheat the catalyst 350 differentially according to the state of the heating device 400 with reference to FIGS. 1 to 3 will be described in detail.

First, as shown in FIGS. 1 and 3 , the first catalyst preheating mode is selected when the heating device 400 operates normally. That is, when the preheating of the catalyst 350 starts, it is checked whether there is an abnormality in the heating device 400 , and if the heating device 400 operates normally, the catalyst 350 is preheated according to the first catalyst preheating mode.

In the first catalyst preheating mode, the catalyst 350 is preheated by basically closing the front valve 711 and operating the heating device 400 . And in the first catalyst preheating mode, the bypass valve 720 may be opened, and the rear valve 712 may be closed or partially opened. At this time, the rear valve 712 prevents the pressure in the reactor 300 from excessively increasing depending on the type of the heating device 400 while the thermal energy is supplied to the reactor 300 through the heating device 400 . Some may be open for

And the temperature sensor 500 measures the internal temperature of the reactor 300 or the temperature of the exhaust gas flowing into the reactor. When the temperature measured by the temperature sensor 500 reaches the target temperature, the heating device 400 may stop operating or may be operated at a level at which the temperature measured by the temperature sensor 500 maintains the target temperature.

At this time, the target temperature may be variously set according to the type of engine that discharges exhaust gas and the overall performance of the selective catalytic reduction system 101 . In addition, the temperature measured by the temperature sensor 500 may vary depending on whether the internal temperature of the reactor 300 or the temperature of the exhaust gas flowing into the reactor 300 .

Also, when the temperature measured by the temperature sensor 500 reaches the target temperature, the opening rate of the front valve 711 is gradually increased. And after the front valve 711 is opened, the rear valve 712 is also opened sequentially. Then, after the rear valve 712 is opened, the bypass valve 720 is sequentially closed.

As described above, when the preheating of the catalyst 350 is finished, the bypass valve 720 is closed and the exhaust gas passes through the reactor 300 , and nitrogen oxides contained in the exhaust gas are effectively reduced.

Next, as shown in FIGS. 2 and 3 , the second catalyst preheating mode is selected when the heating device 400 does not operate normally. That is, if the preheating of the catalyst 350 starts and the heating device 400 is checked for abnormalities, if the heating device 400 malfunctions or becomes inoperable and does not operate normally, the catalyst ( 350) is preheated.

In the second catalyst preheating mode, the catalyst 350 is preheated while the operation of the heating device 400 is basically stopped and the opening rate of the front valve 711 is gradually or stepwise increased while the front valve 711 is partially opened. will do In this case, when the second catalyst preheating mode is selected, the front valve 711 may initially be partially opened by 20% or less of the maximum opening. Also in the second catalyst preheating mode, the bypass valve 720 may be opened, and the rear valve 712 may be closed or partially opened.

And the temperature of the internal temperature of the reactor 300 or the exhaust gas flowing into the reactor 300 is measured through the temperature sensor 500 . When the rising slope of the temperature measured by the temperature sensor 500 is equal to or greater than the preset slope, the opening rate of the front valve 711 may be increased gradually or stepwise. On the other hand, when the rising slope of the temperature measured by the temperature sensor 500 is less than a preset slope or has a falling slope, the opening rate of the front valve 711 may be maintained as it is or the opening rate may be decreased. Here, the preset slope may be variously set according to the type of engine that discharges exhaust gas and the overall performance of the selective catalytic reduction system 101 . In addition, the temperature measured by the temperature sensor 500 may vary depending on whether the internal temperature of the reactor 300 or the temperature of the exhaust gas flowing into the reactor 300 .

When the temperature measured by the temperature sensor 500 reaches the target temperature through this process, the opening rate of the front valve 711 is gradually increased. And after the front valve 711 is opened, the rear valve 712 is also opened sequentially. Then, after the rear valve 712 is opened, the bypass valve 720 is sequentially closed. At this time, the target temperature may be variously set according to the type of engine that discharges exhaust gas and the overall performance of the selective catalytic reduction system 101 . In addition, the temperature measured by the temperature sensor 500 may vary depending on whether the internal temperature of the reactor 300 or the temperature of the exhaust gas flowing into the reactor 300 .

As described above, when the preheating of the catalyst 350 is finished, the bypass valve 720 is closed and the exhaust gas passes through the reactor 300 , and nitrogen oxides contained in the exhaust gas are effectively reduced.

By such a configuration, the selective catalytic reduction system 101 according to an embodiment of the present invention can stably preheat the catalyst 350 used to reduce nitrogen oxides (NOx) contained in exhaust gas.

Although the embodiments of the present invention have been described above with reference to the accompanying drawings, those skilled in the art to which the present invention pertains will understand that the present invention may be embodied in other specific forms without changing the technical spirit or essential characteristics thereof. will be.

Therefore, the embodiments described above are to be understood as illustrative and not restrictive in all respects, and the scope of the present invention is indicated by the following claims, the meaning and scope of the claims, and All changes or modifications derived from the equivalent concept should be construed as being included in the scope of the present invention.

101: selective catalytic reduction system
300: reactor
350: catalyst
400: heating device
500: temperature sensor
610: exhaust flow path
620: bypass euro
711: front valve
712: rear valve
720: bypass valve

Claims (11)

an exhaust passage through which exhaust gas moves;
a reactor installed on the exhaust passage and having a catalyst for reducing nitrogen oxides (NOx) contained in the exhaust gas installed therein;
a heating device for increasing the temperature of the exhaust gas flowing into the reactor;
a bypass passage branching from the exhaust passage to bypass the reactor and then rejoining the exhaust passage;
a front valve installed on the exhaust passage between a branch point with the bypass passage and a front end of the reactor; and
A temperature sensor for measuring the temperature of the exhaust gas flowing into the reactor or the temperature inside the reactor
includes,
The catalyst is preheated according to any one preheating mode selected from a first catalyst preheating mode and a second catalyst preheating mode that operate differently depending on whether the heating device is normally operated,
In the first catalyst preheating mode, the front valve is closed and the heating device is operated to preheat the catalyst,
In the second catalyst preheating mode, the catalyst is preheated while stopping the operation of the heating device and increasing the opening rate gradually or stepwise in a state in which the front valve is partially opened,
In the second catalyst preheating mode, if the rising slope of the temperature measured by the temperature sensor is equal to or greater than a predetermined slope, the opening rate of the front valve is gradually or stepwise increased, and the rising slope of the temperature measured by the temperature sensor is set to a preset slope. Selective catalytic reduction system for maintaining the opening rate of the front valve as it is or reducing the opening rate when the slope is less than the slope or the downward slope. delete The method of claim 1,
In the first catalyst preheating mode, when the temperature measured by the temperature sensor reaches the target temperature, the heating device stops or operates at a level to maintain the target temperature. 4. The method of claim 3,
a bypass valve installed on the bypass passage;
a rear valve installed on the exhaust passage between the junction with the bypass passage and the rear end of the reactor
further comprising,
In the first catalytic preheating mode, the bypass valve is opened, and the rear valve is closed or partially opened. 5. The method of claim 4,
In the first catalyst preheating mode, when the temperature measured by the temperature sensor reaches the target temperature, the opening rate of the front valve is gradually increased, and after the front valve is opened, the rear valve is also opened, and the rear valve Selective catalytic reduction system, characterized in that the bypass valve is closed after the is opened. According to claim 1,
Selective catalytic reduction system, characterized in that when the second catalytic preheating mode is selected, the front valve is partially opened to 20% or less of the maximum opening. delete According to claim 1,
a bypass valve installed on the bypass passage;
a rear valve installed on the exhaust passage between the junction with the bypass passage and the rear end of the reactor
further comprising,
In the second catalyst preheating mode, the bypass valve is opened, and the rear valve is closed or partially opened. 9. The method of claim 8,
In the second catalyst preheating mode, when the temperature measured by the temperature sensor reaches the target temperature, the opening rate of the front valve is gradually increased, and after the front valve is opened, the rear valve is also opened, and the rear valve is opened. Selective catalytic reduction system, characterized in that after the valve is opened, the bypass valve is closed. 10. The method of any one of claims 1, 3 to 6, 8, and 9, wherein
The heating device is installed on the exhaust passage to directly increase the temperature of the exhaust gas passing through the exhaust passage, or a selective catalytic reduction system, characterized in that for raising the temperature of a separate fluid joined to the exhaust passage. 11. The method of claim 10,
The heating device is a selective catalytic reduction system, characterized in that at least one of a burner or a heater.

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