WO2015046666A1

WO2015046666A1 - Selective catalytic reduction system and selective catalytic reduction method

Info

Publication number: WO2015046666A1
Application number: PCT/KR2013/011296
Authority: WO
Inventors: 이균; 이재문; 이창희; 최낙원
Original assignee: 두산엔진주식회사
Priority date: 2013-09-30
Filing date: 2013-12-06
Publication date: 2015-04-02
Also published as: KR101497828B1

Abstract

An embodiment of the present invention relates to a selective catalytic reduction system. The selective catalytic reduction system comprises: a main exhaust flow path in which an exhaust gas containing a nitrogen oxide moves; a reactor installed in the main flow path and including a catalyst for reducing the nitrogen oxide contained in the exhaust gas; a urea decomposition chamber for decomposing urea and generating ammonia; an ammonia injection part for injecting the ammonia generated from the urea decomposition chamber into the exhaust gas to be introduced into the reactor; a urea direct injection part for directly injecting the urea into the exhaust gas to be introduced into the reactor; a urea supply part for supplying urea to the urea decomposition chamber or supplying urea to the urea direct injection part; a diverging flow path which diverges from the main exhaust flow path in the front of the reactor and is connected to the urea decomposition chamber; a blower, installed in the diverging flow path, for adjusting the flow rate of the exhaust gas flowing in the diverging flow path; a heater, installed in the diverging flow path, for adjusting the temperature of the exhaust gas flowing in the diverging flow path; and a controller for controlling the blower, the heater and the urea supply part.

Description

Selective Catalytic Reduction System and Selective Catalytic Reduction Method

Embodiments of the present invention relate to a selective catalytic reduction system and a selective catalytic reduction method for reducing nitrogen oxides contained in exhaust gases by using a selective catalytic reduction reaction.

In general, a selective catalytic reduction (SCR) system is a system for reducing nitrogen oxides by purifying exhaust gases generated from diesel engines, boilers, and incinerators.

In the selective catalytic reduction system, the nitrogen gas contained in the exhaust gas and the reducing agent react with each other while passing the exhaust gas and the reducing agent together in a reactor in which the catalyst is installed therein, and the reduction process is performed with nitrogen and water vapor.

The selective catalytic reduction system is used by directly spraying urea (Urea) as a reducing agent to reduce nitrogen oxides or by spraying ammonia (NH ₃ ) generated by hydrolysis of urea.

However, when urea is directly injected into an exhaust gas having a temperature of less than 250 degrees Celsius, biuret, cyanuric acid, melamine, and ammeline, which are produced as the urea decomposes, etc. There is a problem that the nozzle is clogged by the same by-product or obstructs the flow of exhaust gas.

In addition, in order to hydrolyze the urea to generate ammonia, since the internal temperature of the hydrolysis chamber must be raised to the hydrolysis reaction temperature by using an electric heater or a burner, a large amount of energy is separately consumed for hydrolysis.

Embodiment of the present invention is to selectively spray the urea used in the reduction reaction to reduce the nitrogen oxides contained in the exhaust gas as a whole to reduce the amount of energy consumed and the amount of ammonia slip remaining after the reduction reaction (selective catalytic reduction) A system and selective catalytic reduction method are provided.

According to an embodiment of the present invention, the selective catalytic reduction system is a catalyst for reducing the nitrogen oxide contained in the exhaust gas is installed on the main exhaust passage, the main exhaust passage to which the exhaust gas containing nitrogen oxides (NOx) is moved A reactor comprising a, urea decomposition chamber to decompose urea (Urea) to produce ammonia (NH ₃ ), ammonia injection unit for injecting ammonia generated in the urea decomposition chamber to the exhaust gas to be introduced into the reactor, the reactor Urea direct injection unit for directly injecting urea into the exhaust gas to be introduced, urea supply unit for supplying urea to the urea decomposition chamber or urea supply unit for urea injection unit, branched from the main exhaust flow path in front of the reactor and the urea decomposition chamber A branch flow passage connected to the branch flow passage and installed on the branch flow passage to flow the branch flow passage; A blower for regulating the flow rate of the exhaust gas, is provided on the branch flow path and a heating device, and a control unit for controlling parts of the heating device and the urea supply and the blower to control the temperature of the exhaust gas flowing in the branch channel.

The control unit calculates the amount of heat required to decompose urea, calculates the amount of heat that the exhaust gas has, and in consideration of the amount of heat of the exhaust gas, urea to be injected through the urea direct injection unit and injection of ammonia to be injected through the ammonia injection unit. The ratio can be determined. The controller may control the operation of the blower, the heating device, and the urea supply unit according to the determined ratio to generate ammonia in the urea decomposition chamber or to directly inject urea into the urea direct injection unit.

The ratio of urea to be injected through the urea direct injection unit is the total amount of heat required to decompose the total amount of urea for generating ammonia necessary to reduce nitrogen oxides (NOx) in the reactor to the amount of heat of the exhaust gas flowing into the reactor. It can be divided by.

The urea decomposition chamber may generate ammonia by decomposing the remaining urea by limiting the amount of urea injected through the urea direct injection unit in the total amount of urea for producing ammonia required to reduce nitrogen oxides (NOx) in the reactor. have.

The selective catalytic reduction system may further include a front branch temperature sensor and a rear branch temperature sensor respectively installed in the branch passages before and after the heating apparatus. And when the blower maintains a constant flow rate of the exhaust gas supplied to the urea decomposition chamber through the branch flow path, the control unit controls the branch flow path according to the information received from the front branch temperature sensor and the rear branch temperature sensor. The exhaust gas supplied to the urea decomposition chamber may control the operation of the heating device to supply the amount of heat required to generate ammonia in the urea decomposition chamber.

Meanwhile, the selective catalytic reduction system may further include a rear branch temperature sensor installed in the branch flow path behind the heating device and a branch flow meter installed behind the blower. And when the heating device maintains a constant temperature of the exhaust gas supplied to the urea decomposition chamber through the branch flow path, the control unit is the through the branch flow path according to the information received from the branch temperature sensor and the branch flow meter. The operation of the blower can be controlled so that the exhaust gas supplied to the urea decomposition chamber supplies the amount of heat required to produce ammonia in the urea decomposition chamber.

The urea supply unit may include a urea tank for storing urea, a urea transfer device for transferring urea stored in the urea tank, and a control valve for controlling the supply amount and supply direction of urea.

The selective catalytic reduction system may further include a main mass flow meter installed in the main exhaust flow path and measuring a mass flow rate of the exhaust gas and a main temperature sensor measuring the temperature of the exhaust gas.

In addition, according to an embodiment of the present invention, the selective catalytic reduction method is required to calculate the flow rate of the exhaust gas containing nitrogen oxides (NOx), and to remove the nitrogen oxides containing the exhaust gas through a reduction reaction Calculating a total amount of urea, calculating a total amount of heat required to decompose the total amount of urea into ammonia, calculating a heat amount of the exhaust gas, and considering the amount of heat of the exhaust gas, Determining the proportion of urea to be injected directly into the exhaust gas and then directly injecting a corresponding amount of urea into the exhaust gas, and limiting the amount of urea to be directly injected from the total amount of the urea, remaining urea in a separate urea decomposition chamber Decompose to produce ammonia and spray the ammonia produced in the urea decomposition chamber to the exhaust gas Includes the steps.

In the selective catalytic reduction method, a part of the exhaust gas is branched and supplied to the urea decomposition chamber, and the amount of heat required to decompose urea in the urea decomposition chamber is increased by raising the branched exhaust gas or adjusting a supply flow rate. Can be.

In the selective catalytic reduction method described above, when the reduction efficiency of the nitrogen oxide contained in the exhaust gas and the measured value of the ammonia slip after the reduction reaction are less than the reference value, the ratio of urea to be directly injected into the exhaust gas can be readjusted.

According to an embodiment of the present invention, the selective catalytic reduction system and the selective catalytic reduction method optimize the injection of urea used in the reduction reaction to reduce nitrogen oxides contained in the exhaust gas, and the energy consumed as a whole and the ammonia slip remaining after the reduction reaction ( Ammonia slip can be minimized.

1 is a block diagram showing a selective catalytic reduction system according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration for injecting urea into the main exhaust passage of FIG. 1 and a configuration for injecting urea into the urea decomposition chamber.

3 is a configuration diagram illustrating a modification of FIG. 2.

4 is a block diagram showing a selective catalytic reduction system according to a second embodiment of the present invention.

5 is a flowchart illustrating a selective catalytic reduction method using a selective catalytic reduction system according to embodiments of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the present invention. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

In addition, in various embodiments, components having the same configuration will be described in the first embodiment by using the same reference numerals, and in the second embodiment, only the configuration different from the first embodiment will be described. Shall be.

It is noted that the figures are schematic and not drawn to scale. The relative dimensions and ratios of the parts in the figures have been exaggerated or reduced in size for clarity and convenience in the figures and any dimensions are merely exemplary and not limiting. And the same reference numerals are used to refer to similar features in the same structure, element or part shown in more than one figure.

Embodiments of the invention specifically illustrate ideal embodiments of the invention. As a result, various modifications of the drawings are expected. Thus, the embodiment is not limited to the specific form of the illustrated region, but includes, for example, modification of the form by manufacture.

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

The selective catalytic reduction system 101 according to the first embodiment of the present invention reduces the nitrogen oxide content of the exhaust gas by removing nitrogen oxide (NOx) contained in the exhaust gas discharged from the engine 900 through a reduction reaction. . Here, the engine 900 may be a low speed or medium speed diesel engine used in a ship.

However, the selective catalytic reduction system 101 according to the first embodiment of the present invention is not limited to the exhaust gas discharged from the engine 900 and may be used in various fields such as a plant.

As shown in FIG. 1, the selective catalytic reduction system 101 according to the first embodiment of the present invention includes a main exhaust passage 210, a reactor 100, a urea decomposition chamber 300, and an ammonia injection unit 430. , A urea direct injection unit 410, a urea supply unit 500, a branch flow path 220, a blower 610, a heating device 620, and a control unit 700.

In addition, the selective catalytic reduction system 101 according to the first embodiment of the present invention includes a rear branch temperature sensor 811, a front branch temperature sensor 812, a main mass flow meter 851, a main temperature sensor 815, and The mixer may further include a mixer 450.

The main exhaust passage 210 serves as a passage through which the exhaust gas containing nitrogen oxides (NOx) moves.

The reactor 100 is installed on the main exhaust flow path 210. The reactor 100 includes a catalyst for reducing nitrogen oxides (NOx) contained in the exhaust gas. The catalyst catalyzes the reaction between the nitrogen oxide (NOx) contained in the exhaust gas and the reducing agent to reduce the nitrogen oxide (NOx) to nitrogen and water vapor. At this time, ammonia (NH ₃ ) may be used as the final reducing agent to be reduced by reacting with nitrogen oxide (NOx).

The catalyst may be made of various materials known to those skilled in the art, such as zeolite, vanadium, platinum and the like. In one example, the catalyst may have an active temperature in the range of 250 degrees Celsius to 350 degrees Celsius. Here, the active temperature refers to a temperature at which the catalyst can be stably reduced without poisoning the catalyst. If the catalyst reacts outside the active temperature range, the catalyst is poisoned and the efficiency is lowered. Specifically, the poisoning substance for poisoning the catalyst may include one or more of ammonium sulfate (NH ₄ ) ₂ SO ₄ ) and ammonium bisulfate (NH ₄ HSO ₄ ). These catalyst poisoning substances are adsorbed on the catalyst to lower the activity of the catalyst. Since the catalyst poisoning substance decomposes at a relatively high temperature, the catalyst can be regenerated by raising the temperature.

In addition, the housing of the reactor 100, for example, may be made of stainless steel (stainless steel) material.

The urea decomposition chamber 300 decomposes urea (urea, CO (NH ₂ ) ₂ ) to produce ammonia (NH ₃ ) used as a reducing agent to reduce nitrogen oxides (NOx).

When urea (urea, CO (NH ₂ ) ₂ ) is decomposed in the urea decomposition chamber 300, isocyanic acid (HNCO) is generated together with ammonia (NH ₃ ). Isocyanic acid is decomposed again to ammonia. That is, urea may be decomposed to finally produce ammonia.

The ammonia injection unit 430 injects ammonia (NH ₃ ) generated in the urea decomposition chamber 300 to the exhaust gas to be introduced into the reactor 100. The injected ammonia is mixed with the exhaust gas to reduce the nitrogen oxide contained in the exhaust gas while passing through the catalyst of the reactor 100.

Specifically, the ammonia injection unit 430 includes an ammonia injection nozzle 431 installed in the main exhaust flow path 210, and an ammonia injection flow path 435 connecting the ammonia injection nozzle 431 and the urea decomposition chamber 300. can do.

That is, the ammonia injection unit 430 may inject ammonia NH ₃ toward the exhaust gas passing through the main exhaust flow path 210 in front of the reactor 100.

In the present specification, the front means an upstream side and the rear means a downstream side based on the flow of exhaust gas.

The urea direct injection unit 410 directly injects urea to the exhaust gas to be introduced into the reactor 100.

Specifically, the urea direct injection unit 410 may include a urea injection nozzle 411 installed in the main exhaust flow path 210 and a urea injection flow path 415 for supplying urea to the urea injection nozzle 411. have.

That is, the urea direct injection unit 410 may directly inject unresolved urea toward the exhaust gas passing through the main exhaust passage 210 in front of the reactor 100.

The urea injected from the urea direct injection unit 410 may be mixed with the exhaust gas and decomposed into ammonia by the heat amount of the exhaust gas. The ammonia thus produced, like ammonia injected from the ammonia injection unit 430, reduces nitrogen oxide contained in the exhaust gas while passing through the catalyst of the reactor 100.

In the first embodiment of the present invention, the ammonia injection portion 430 is located closer to the reactor 100 than the urea injection portion 410. That is, the urea injection unit 410 injects urea toward the exhaust gas at a position relatively far from the reactor 100. The urea injected from the urea injection unit 410 is to ensure the time and space to be mixed with the exhaust gas and decomposed into ammonia by the heat of the exhaust gas.

The mixer 450 is installed on the main exhaust flow path 210 between the ammonia injection unit 430 and the reactor 100. The mixer 450 evenly mixes the exhaust gas with ammonia, which is a reducing agent, before the exhaust gas enters the reactor 100.

The urea supply unit 500 supplies urea to the urea decomposition chamber 300 or supplies urea to the urea direct injection unit 410.

Specifically, the urea supply unit 500 is a urea tank 550 for storing urea, a urea transfer device 530 for transferring urea stored in the urea tank 550, and a control valve for controlling the supply amount and supply direction of urea 510 may be included.

In addition, the urea supply unit 500 may further include a urea supply passage 515 connected to the urea transfer device 530 to supply urea to the urea decomposition chamber 300.

That is, the control valve 510 may be installed on the urea supply flow path 515, and the urea injection flow path 415 of the urea direct injection unit 410 may connect the control valve 510 and the urea injection nozzle 411. have.

In addition, the control valve 510 may proportionally control urea to be supplied to the urea direct injection unit 410 and urea to be supplied to the urea decomposition chamber 300.

For example, the control valve 510 may be a proportional control valve or a plurality of solenoid valves.

Branch flow path 220 is branched from the main exhaust flow path 210 in front of the reactor 100 is connected to the urea decomposition chamber 300.

The blower 610 is installed on the branch flow path 220. The blower 610 adjusts the flow rate of the exhaust gas flowing through the branch flow path 220. That is, the blower 610 adjusts the flow rate of the exhaust gas flowing into the urea decomposition chamber 300 through the branch flow path 220.

The heating device 620 is installed on the branch flow path 220 to adjust the temperature of the exhaust gas flowing through the branch flow path 220. That is, the heating device 620 adjusts the temperature of the exhaust gas flowing into the urea decomposition chamber 300 through the branch flow path 220.

In addition, in the first embodiment of the present invention, the heating device 620 may be a burner. In detail, the heating device 620 may include a fuel supply device, a control device for controlling a supply fuel amount for heating temperature control, and a stabilizer.

In addition, the heating device 620 may be a plasma burner having improved performance by using plasma.

In addition, although not shown in FIG. 1, the selective catalytic reduction system 101 according to the first embodiment of the present invention may further include an outside air supply device for supplying outside air to assist combustion of the heating device 620. That is, the outside air supply device may supply oxygen to the heating device 620.

The rear branch temperature sensor 811 is installed in the branch flow path 220 behind the heating device 620, and the front branch temperature sensor 812 is installed in the branch flow path in front of the heating device 620.

The main mass flow meter 851 is installed in the main exhaust flow path 210 to measure the mass flow rate of the exhaust gas, and the main temperature sensor 815 is installed in the main exhaust flow path 210 to measure the temperature of the exhaust gas.

In this case, the main mass flow meter 851 may be installed in the main exhaust flow path 210 before the branch flow path 220 branches. However, the first embodiment of the present invention is not limited thereto, and the main mass flow meter 851 may be omitted. When the main mass flow meter 851 is omitted, the mass flow rate of the exhaust gas flowing through the main exhaust flow path 210 may be estimated by mapping the exhaust gas emissions according to the load variation of the engine 900.

The control unit 700 calculates the amount of heat required to decompose urea, calculates the amount of heat that the exhaust gas has, and then takes the urea and ammonia injection unit 430 to be injected through the urea direct injection unit 410 in consideration of the amount of heat of the exhaust gas. Determine the injection rate of ammonia to be injected through.

The control unit 700 controls the operation of at least one of the blower 610, the heating device 620, and the urea supply unit 500 according to the determined ratio to generate ammonia in the urea decomposition chamber 300 or the urea direct injection unit ( The urea may be directly injected into the exhaust gas flowing through the main exhaust passage 210 through 410.

The ratio of urea to be injected through the urea direct injection unit 410 decomposes the total amount of urea to generate ammonia necessary to reduce nitrogen oxides (NOx) in the reactor to the amount of heat of the exhaust gas flowing into the reactor 100. It can be divided by the total calories required.

Specifically, the controller 700 may calculate the amount of heat that the exhaust gas has through the temperature of the exhaust gas and the mass flow rate of the exhaust gas. And it is possible to calculate the amount of heat required to decompose the total amount of urea required to reduce the nitrogen oxides contained in the exhaust gas.

The controller 700 determines the injection ratio of urea to be directly injected into the exhaust gas flowing through the main exhaust flow path 210 through the urea direct injection unit 410 by dividing the heat amount of the exhaust gas by the amount of heat required to decompose the total amount of urea. The controller 700 controls the urea supply unit 500 and the urea direct injection unit 410 according to the determined injection ratio to directly inject the urea into the main exhaust flow path 210.

In addition, the control unit 700 limits the amount of urea injected through the urea direct injection unit 410 in the total amount of urea for producing ammonia required to reduce nitrogen oxides (NOx) in the reactor 100 to urea remaining urea The blower 610 and the heating device 620 are controlled to decompose in the decomposition chamber 300 to generate ammonia.

In particular, in the first embodiment of the present invention, the control unit 700 controls the blower 610 to maintain a constant flow rate of the exhaust gas supplied to the urea decomposition chamber 300 through the branch flow path (220).

And the control unit 700 is the exhaust gas supplied to the urea decomposition chamber 300 through the branch flow path 220 in accordance with the information received from the front branch temperature sensor 812 and the rear branch temperature sensor 811 is a urea decomposition chamber ( The operation of the heating device 620 is controlled to supply the amount of heat required to generate ammonia in 300. That is, the mass flow rate is fixed in the calorie calculation formula and the temperature difference is controlled by a variable.

As described above, according to the first embodiment of the present invention, the amount of fuel consumed by the heating device 620 may be controlled according to the temperature change of the exhaust gas. That is, the amount of fuel consumed by the heating device 620 can be reduced.

In addition, as shown in FIG. 2, the urea transfer device 530 of the urea supply unit 500 includes a urea transfer pump 531 for transferring urea and

mass flow controllers

536 and 537 for quantitatively controlling the transfer amount of urea. ) May be included.

Specifically, in the first embodiment of the present invention, the urea transfer device 530 is one of the urea transfer pump 531, the first mass flow controller 536 for supplying urea to the urea decomposition chamber 300, And a second mass flow controller 537 for supplying urea to be directly injected into the main exhaust passage 210.

However, the first embodiment of the present invention is not limited thereto. 3 shows a modification of the first embodiment of the present invention. As shown in FIG. 3, the urea transfer device 530 of the urea supply unit 500 supplies urea to the first urea transfer pump 532 and the urea direct injection unit 410 that supplies urea to the urea decomposition chamber 300. It may also include a second urea transfer pump 533 to supply. In this case, the

mass flow meters

536 and 537 may be omitted using the quantitative control pump as the first urea transfer pump 532 and the second urea transfer pump 533.

In addition, the urea supply unit 500 includes a manifold for supplying urea to a plurality of urea decomposition injection nozzles 517 for injecting urea into the urea decomposition chamber 300 and a plurality of urea decomposition injection nozzles 517, respectively. , 516 may be further included.

Since the urea decomposition chamber 300 is relatively small in volume and size in comparison with the main exhaust flow path 210, it is more effective to use a plurality of small-capacity injection nozzles than to use one large-capacity injection nozzle.

By such a configuration, the selective catalytic reduction system 101 according to the first embodiment of the present invention optimally injects urea used for the reduction reaction to reduce the nitrogen oxides contained in the exhaust gas and the reduction reaction as a whole. The remaining amount of ammonia slip can be minimized.

Specifically, in the process of purifying exhaust gas, the efficiency of energy use may be improved by adjusting the ratio of direct injection urea and ammonia to be used according to the heat amount of the exhaust gas.

In addition, the amount of fuel consumed by the heating device 620 for providing heat to the urea decomposition chamber 300 can be reduced.

Hereinafter, the selective catalytic reduction system 102 according to the second embodiment of the present invention will be described with reference to FIG. 4.

As shown in FIG. 4, the selective catalytic reduction system 102 according to the second embodiment of the present invention is a branch flow meter 952 installed behind the blower 610 instead of the front branch temperature sensor 812 of the first embodiment. ). That is, the front branch temperature sensor 812 of the first embodiment may be omitted in the second embodiment.

In the second embodiment of the present invention, the control unit 700 controls the heating device 620 to maintain a constant temperature of the exhaust gas supplied to the urea decomposition chamber 300 through the branch flow path (220). That is, the temperature difference is fixed in the calorie calculation formula and the mass flow rate is controlled by the variable.

In one example, the heating device 620 may constantly increase the temperature of the exhaust gas to the urea decomposition chamber 300 via the branch flow path 220 to 290 degrees Celsius.

Decomposition of urea at temperatures below 250 degrees Celsius results in the formation of by-products such as biuret, cyanuric acid, melamine, and ammeline, which are produced by the decomposition of urea, clogging the nozzles. Or obstruct the flow of exhaust gases. Therefore, it is appropriate to maintain the temperature of the urea decomposition chamber 300 at 250 degrees Celsius or more.

And the control unit 700 is the exhaust gas supplied to the urea decomposition chamber 300 through the branch flow path 220 in accordance with the information received from the rear branch temperature sensor 811 and the branch flow meter 952 urea decomposition chamber 300 Control the operation of the blower 610 to supply the amount of heat required to produce ammonia in the.

As described above, according to the second embodiment of the present invention, the power consumed to operate the blower 610 may be controlled according to the temperature change of the exhaust gas. That is, the power consumed by the blower 610 can be reduced.

By such a configuration, the selective catalytic reduction system 102 according to the second embodiment of the present invention optimally injects urea used for the reduction reaction to reduce the nitrogen oxides contained in the exhaust gas and the reduction reaction as a whole. The remaining amount of ammonia slip can be minimized.

In addition, the power consumed to operate the blower 610 for providing heat to the urea decomposition chamber 300 can be reduced.

Hereinafter, referring to FIG. 5, a selective catalytic reduction method using the selective

catalytic reduction systems

101 and 102 according to the first and second embodiments of the present invention will be described.

First, as shown in FIG. 5, the flow rate of the exhaust gas is calculated to calculate the urea dosing rate required to reduce the nitrogen oxide contained in the exhaust gas (S100). The total amount of urea required is calculated based on the flow rate of the exhaust gas to calculate the urea dosing rate (S200). As an example, if the mass flow rate of the exhaust gas is calculated to be 110,000 kg / h, the urea dosing rate may be determined 270 kg / h.

Next, the amount of heat required to decompose the urea to be supplied according to the urea dosing rate, that is, the amount of heat required to decompose the total amount of urea into ammonia is calculated (S300). Then, the amount of heat of the exhaust gas flowing along the main exhaust flow path is calculated (S400). At this time, the heat amount of the exhaust gas can be calculated through the temperature and the flow rate of the exhaust gas.

Next, the ratio of direct urea injection to be directly injected into the exhaust gas is determined in consideration of the heat amount of the exhaust gas (S500).

The urea direct injection ratio is the ratio of directly injecting urea, not ammonia, into the exhaust gas to reduce the nitrogen oxide content in the total amount of urea to be used according to the urea dosing rate.

For example, if the amount of heat for decomposing the total amount of urea is calculated to be 190,531 kcal / h, and the amount of heat of the exhaust gas is calculated to be 98,260 kcal / h, the urea direct injection ratio may be 51.6%.

The urea is directly injected into the exhaust gas according to the urea direct injection ratio.

Next, to determine the ammonia generation rate to be generated by decomposing the remaining urea in a separate urea decomposition chamber except for the urea directly injected according to the urea direct injection ratio (S600).

For example, when the urea direct injection ratio is 51.6%, the urea injected directly is 139.32 kg / h and the urea to be divided in a separate urea decomposition chamber is 130.68 kg / h.

The ammonia is generated at optimum efficiency by determining an operation rate of the heating device and the blower based on the temperature and flow rate of the fluid supplied to the urea decomposition chamber to generate ammonia according to the ammonia generation rate (S700). The ammonia thus produced is injected into the exhaust gas.

Here, a part of the exhaust gas may be branched into a fluid supplied to the urea decomposition chamber. The branched exhaust gas may be heated up or the supply flow rate may be adjusted to provide the amount of heat required to break down the urea in the urea cracking chamber.

At this time, the amount of heat required for the production of ammonia in the urea decomposition chamber is controlled by adjusting the temperature rise temperature of the heating device while maintaining a constant operating flow rate of the blower, or by maintaining the temperature rising temperature of the heating device constant and adjusting the operating flow rate of the blower. Can provide.

In addition, by monitoring the reduction efficiency of the nitrogen oxides contained in the exhaust gas and the amount of ammonia slip after the reduction reaction (S800), when the measured value is less than the reference value, the ratio of urea to be directly injected into the exhaust gas may be readjusted ( S900).

By this selective catalytic reduction method, it is possible to minimize the amount of energy consumed to reduce nitrogen oxides contained in the exhaust gas and the amount of ammonia slip remaining after the reduction reaction by optimally injecting urea used in the reduction reaction. .

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 can understand that the present invention can be implemented in other specific forms without changing the technical spirit or essential features. 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 represented by the following detailed description, and the meaning and scope of the claims and All changes or modifications derived from the equivalent concept should be interpreted as being included in the scope of the present invention.

100: reactor

101, 102: selective catalytic reduction system

210: main exhaust flow path 220: branch flow path

300: urea decomposition chamber 410: urea direct injection unit

430: ammonia injection unit 450: mixer

500: urea supply part 510: control valve

530: urea transfer device 550: urea tank

610: blower 620: heating device

700: control unit 811: rear branch temperature sensor

812: forward branch temperature sensor 815: main temperature sensor

851: main mass flow meter 900: engine

952: branch flow meter

Claims

A main exhaust flow path through which exhaust gas containing nitrogen oxides (NOx) moves;

A reactor installed on the main exhaust passage and including a catalyst for reducing nitrogen oxides contained in the exhaust gas;

A urea decomposition chamber that decomposes urea to produce ammonia (NH 3 );

An ammonia injection unit for injecting ammonia generated in the urea decomposition chamber to exhaust gas to be introduced into the reactor;

A urea direct injection unit for directly injecting urea into the exhaust gas to be introduced into the reactor;

A urea supply unit supplying urea to the urea decomposition chamber or supplying urea to the urea direct injection unit;

A branch passage branched from the main exhaust passage in front of the reactor and connected to the urea decomposition chamber;

A blower installed on the branch passage to adjust a flow rate of the exhaust gas flowing through the branch passage;

A heating device installed on the branch flow path to adjust a temperature of exhaust gas flowing through the branch flow path; And

Control unit for controlling the blower, the heating device and the urea supply unit

Selective catalytic reduction system comprising a.
In claim 1,

The control unit calculates the amount of heat required to decompose urea, calculates the amount of heat that the exhaust gas has, and in consideration of the amount of heat of the exhaust gas, urea to be injected through the urea direct injection unit and injection of ammonia to be injected through the ammonia injection unit. Determine the ratio,

And the control unit controls the operation of the blower, the heating device, and the urea supply unit according to the determined ratio to generate ammonia in the urea decomposition chamber or directly spray urea to the urea direct injection unit.
In claim 2,

The ratio of urea to be injected through the urea direct injection unit is the total amount of heat required to decompose the total amount of urea for generating ammonia necessary to reduce nitrogen oxides (NOx) in the reactor to the amount of heat of the exhaust gas flowing into the reactor. Selective catalytic reduction system divided by.
In claim 3,

The urea decomposition chamber limits the amount of urea injected through the urea direct injection unit in the total amount of urea for producing ammonia required to reduce nitrogen oxides (NOx) in the reactor to selectively decompose the remaining urea to produce ammonia. Catalytic reduction system.
In claim 4,

Further comprising a front branch temperature sensor and a rear branch temperature sensor respectively installed in the branch flow paths in front of and behind the heating device,

When the blower maintains a constant flow rate of the exhaust gas supplied to the urea decomposition chamber through the branch flow path,

The control unit is configured to supply the amount of heat required to generate ammonia in the urea decomposition chamber by the exhaust gas supplied to the urea decomposition chamber through the branch flow path according to the information received from the front branch temperature sensor and the rear branch temperature sensor. Selective catalytic reduction system to control the operation of the heating device.
In claim 4,

Further comprising a rear branch temperature sensor installed in the branch flow path behind the heating device and a branch flow meter installed behind the blower,

When the heating device maintains a constant temperature of the exhaust gas supplied to the urea decomposition chamber through the branch passage,

The control unit operates the blower so that the exhaust gas supplied to the urea decomposition chamber through the branch flow path supplies the amount of heat required to generate ammonia in the urea decomposition chamber according to the information received from the branch temperature sensor and the branch flow meter. Selective catalytic reduction system to control the.
In claim 1,

The urea supply unit selective catalytic reduction system including a urea tank for storing urea, a urea transfer device for transferring the urea stored in the urea tank, and a control valve for controlling the supply amount and supply direction of the urea.
The method according to any one of claims 1 to 7,

And a main mass flow meter installed in the main exhaust flow path and measuring a mass flow rate of the exhaust gas and a main temperature sensor measuring the temperature of the exhaust gas.
Calculating a flow rate of the exhaust gas containing nitrogen oxides (NOx);

Calculating a total amount of urea required to remove nitrogen oxides contained in the exhaust gas through a reduction reaction;

Calculating a total amount of heat required to decompose the total amount of urea into ammonia;

Calculating a heat amount of the exhaust gas;

Determining a ratio of urea to be directly injected into the exhaust gas in consideration of the heat amount of the exhaust gas, and then directly injecting a corresponding amount of urea into the exhaust gas; And

Limiting the amount of urea to be directly injected from the total amount of urea, dissolving the remaining urea in a separate urea decomposition chamber to generate ammonia, and injecting the ammonia generated in the urea decomposition chamber to the exhaust gas.

Selective catalytic reduction method comprising a.
In claim 9,

Branching a portion of the exhaust gas and supplying it to the urea decomposition chamber,

And selectively heating the branched exhaust gas or adjusting a feed flow rate to provide the amount of heat required to decompose urea in the urea decomposition chamber.
In claim 9,

Selective catalytic reduction method that readjusts the ratio of urea to be directly injected into the exhaust gas when the measured reduction efficiency of the nitrogen oxide contained in the exhaust gas and the measured amount of ammonia slip after the reduction reaction are less than the reference value.