KR101699594B1 - Selective catalytic reuction system and method for checking performance of the smae - Google Patents

Abstract

The present invention relates to a selective catalytic reduction system for reducing nitrogen oxides contained in exhaust gas of an engine having a variable load, and a selective catalytic reduction system according to an embodiment of the present invention includes an exhaust catalytic converter A second concentration sensor provided on the exhaust passage in the rear of the reactor, and a second concentration sensor provided on the exhaust passage in front of the reactor, A reducing agent supply passage for connecting the decomposition chamber and the reducing agent injecting section, and a reducing agent supply passage for supplying the reducing agent to the reducing agent supply passage, A temperature sensor provided in the first concentration sensor, and a temperature sensor provided in the second concentration sensor, And a control unit for calculating a nitrogen oxide reduction efficiency of the exhaust gas passing through the reactor, wherein the control unit receives information from the temperature sensor and determines that the nitrogen oxide reduction efficiency is lowered, Or by the supply of reducing agent.

Description

TECHNICAL FIELD [0001] The present invention relates to a selective catalytic reduction system and a method for diagnosing performance thereof. BACKGROUND OF THE INVENTION < RTI ID = 0.0 >

The present invention relates to a selective catalytic reduction system for reducing nitrogen oxides (NOx) contained in exhaust gases using a selective catalytic reduction reaction and a method for diagnosing its performance.

In general, the selective catalytic reduction (SCR) system is a system for purifying exhaust gas generated from a diesel engine, a boiler, and an incinerator to reduce nitrogen oxides contained in the exhaust gas.

The selective catalytic reduction system reacts the nitrogen oxides contained in the exhaust gas with the reducing agent while passing the exhaust gas and the reducing agent together in the reactor equipped with the catalyst, thereby reducing the nitrogen and the water vapor.

The selective catalytic reduction system uses ammonia (NH ₃ ) generated by directly spraying urea as a reducing agent to reduce nitrogen oxides or by hydrolyzing urea.

The selective catalytic reduction system uses urea or ammonia (NH ₃ ) as a reducing agent to reduce nitrogen oxides. That is, ammonia (NH ₃ ) produced by hydrolysis of urea is used as a reducing agent for reducing nitrogen oxides.

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

In order to improve the hydrolysis efficiency of the urea, a fluid heated through a separate electric heater or a burner is supplied to the decomposition chamber to raise the internal temperature of the decomposition chamber to the hydrolysis reaction temperature, and the urea is decomposed stably And ammonia (NH ₃ ) and isocyanic acid (HNCO) produced by the reaction are fed to the reactor

In addition, the selective catalytic reduction system mainly utilizes a high-temperature active catalyst having an active temperature range of 250 ° C to 400 ° C in consideration of economical efficiency and radioactivity regulation.

However, when an exhaust gas having a temperature of 250 DEG C or less flows into a reactor equipped with a high-temperature active catalyst, the catalyst is poisoned by the sulfur component contained in the fuel of the diesel engine, and the activity of the catalyst is continuously deteriorated.

Therefore, the NOx removal efficiency is calculated by measuring the NOx concentration before and after the selective catalytic reduction reaction, and the catalyst poisoning is determined according to the change of the NOx reduction efficiency to determine the catalyst regeneration point.

However, in the case of a marine low-speed diesel engine, the emission amount of the exhaust gas changes depending on the load fluctuation of the diesel engine, and it is difficult to cope with the change of the emission amount of the exhaust gas immediately following the supply amount of the reducing agent.

Therefore, it is difficult to accurately determine whether the change in nitrogen oxide reduction efficiency calculated by measuring the nitrogen oxide concentration before and after the selective catalytic reduction reaction is due to poisoning of the catalyst, the load fluctuation of the engine, or an abnormality in the supply of the reducing agent .

Thus, conventionally, since it is not possible to accurately determine whether the catalyst is poisoned, it is difficult to determine the regeneration timing of the catalyst.

An embodiment of the present invention provides a selective catalytic reduction system and its performance diagnosis method capable of accurately grasping the cause of the reduction of the nitrogen oxide reduction efficiency to determine the regeneration timing of the catalyst.

According to the embodiment of the present invention, a selective catalytic reduction system for reducing nitrogen oxides contained in the exhaust gas of an engine whose load is varied includes an exhaust gas passage through which the exhaust gas of the engine is exhausted, A first concentration sensor provided on the exhaust passage in front of the reactor; a second concentration sensor provided on the exhaust passage in the rear of the reactor; A reducing agent spraying unit installed on the exhaust passage and spraying a reducing agent to the exhaust gas moving to the reactor; a decomposition chamber for generating a reducing agent to be supplied to the reducing agent spraying unit; and a reducing agent supply unit for connecting the decomposition chamber and the reducing agent spraying unit A temperature sensor provided on the reducing agent supply passage, and a temperature sensor provided on the reducing agent supply passage, 2 concentration sensor, and calculates a nitrogen oxide reduction efficiency of the exhaust gas passing through the reactor. In addition, if it is determined that the nitrogen oxide reduction efficiency is lowered, the controller receives information from the temperature sensor to determine whether the decrease in the nitrogen oxide reduction efficiency is due to poisoning of the catalyst installed in the reactor or an abnormality in the supply of the reducing agent .

Wherein the control unit determines that the reduction of the nitrogen oxide reduction efficiency is caused by the poisoning of the catalyst when the temperature measured by the temperature sensor falls within the range of about 250 degrees Celsius to about 500 degrees Celsius, To 500 deg. C, it can be judged that an abnormality has occurred in the supply of the reducing agent.

The control unit may stop the calculation of the NOx reduction efficiency temporarily when the load of the engine fluctuates and calculate the nitrogen oxide reduction efficiency again after the supply amount of the reducing agent is followed in correspondence with the exhaust amount of the exhaust gas changed in accordance with the load variation of the engine .

According to an embodiment of the present invention, there is provided a method for diagnosing the performance of a selective catalytic reduction system for reducing nitrogen oxide contained in exhaust gas of an engine whose load is varied by using a reducing agent and a catalyst, Comparing the nitrogen oxide reduction efficiency data with a reference reduction efficiency range, extracting a transient section and a stable section according to a load variation of the engine separately from each other, and extracting nitrogen oxide reduction efficiency data for trend analysis in the stable section; Calculating a moving average value of the nitrogen oxide reduction efficiency in the stable section; calculating a moving average value when the moving dispersion value is out of an allowable error range; Comparing the nitrogen oxide reduction efficiency with the target value of nitrogen oxide reduction efficiency, Determining that the performance is in a normal state when the nitrogen oxide reduction efficiency target value is not less than the target value and determining that the performance is abnormal if the moving average value is less than the nitrogen oxide reduction efficiency target value.

The nitrogen oxide reduction efficiency data can be obtained by measuring the nitrogen oxide concentration before and after the selective catalytic reduction reaction.

Wherein the reference reduction efficiency range is set to a predetermined upper and lower percentages based on a nitrogen oxide reduction set value, and a section in which the nitrogen oxide reduction efficiency data is out of the reference reduction efficiency range is regarded as an excessive section, The section in which the efficiency data is within the reference reduction efficiency range can be regarded as the stable section and can be extracted.

The moving average value may be calculated by calculating a moving average of nitrogen oxide reduction efficiency for a predetermined time.

The tolerance range may be set to a predetermined upper limit or lower limit based on the moving average value.

The reducing agent is generated in the decomposition chamber and supplied through the reducing agent injection unit. If the performance is judged to be abnormal, the temperature between the decomposition chamber and the reducing agent injection unit is measured. If the temperature is within the normal temperature range, It can be determined that an abnormality has occurred in the supply of the reducing agent when the temperature is outside the normal temperature range.

The normal temperature range may range from 250 degrees Celsius to 500 degrees Celsius.

According to the embodiment of the present invention, the selective catalytic reduction system and its performance diagnosis method can accurately grasp the cause of the degradation of the nitrogen oxide reduction efficiency to determine the regeneration point of the catalyst.

1 is a block diagram illustrating a selective catalytic reduction system according to an embodiment of the present invention.
FIG. 2 is a flowchart illustrating an operation procedure of a performance diagnosis method of a selective catalytic reduction system according to an embodiment of the present invention.
FIG. 3 and FIG. 4 are graphs showing a part of a process of a performance diagnosis method of the selective catalytic reduction system according to an embodiment of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings, which will be readily apparent to those skilled in the art to which the present invention pertains. The present invention may be embodied in many different forms and is not limited to the embodiments described herein.

The drawings are schematic and illustrate that they are not drawn to scale. The relative dimensions and ratios of the parts in the figures are exaggerated or reduced in size for clarity and convenience in the figures, and any dimensions are merely illustrative and not restrictive. And to the same structure, element or component appearing in more than one drawing, the same reference numerals are used to denote similar features.

The embodiments of the present invention specifically illustrate ideal embodiments of the present invention. As a result, various variations of the illustration are expected. Thus, the embodiment is not limited to any particular form of the depicted area, but includes modifications of the form, for example, by manufacture.

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

The selective catalytic reduction system 101 according to an embodiment of the present invention is used to effectively reduce the nitrogen oxides contained in the exhaust gas of an engine (not shown) whose load is varied.

1, a selective catalytic reduction system 101 according to an embodiment of the present invention includes a reactor 300, an exhaust passage 600, a decomposition chamber 550, a reducing agent supply passage 530, A first density sensor 410, a second density sensor 420, and a temperature sensor 450. The first density sensor 410, the second density sensor 420,

In addition, the selective catalytic reduction system 101 according to an embodiment of the present invention may further include a control unit 700 and an information processing unit 750.

The exhaust passage 600 discharges exhaust gas containing nitrogen oxides (hereinafter referred to as "NOx") exhausted from the engine.

The reactor 300 is installed on the exhaust passage 600. The reactor 300 includes a catalyst for reducing the NOx contained in the exhaust gas. The catalyst catalyzes the reaction of the reducing agent with the NOx contained in the exhaust gas to reduce NOx to nitrogen and water vapor. At this time, ammonia (NH ₃ ) may be used as a final reducing agent to react with and reduce NO x.

The catalyst may be made of a variety of materials known to those skilled in the art, such as zeolite, vanadium, and platinum. In one example, the catalyst may have an active temperature in the range of 250 degrees Celsius to 350 degrees Celsius. Here, the activation temperature refers to a temperature at which the catalyst can be stably reduced without being poisoned. When the catalyst reacts outside the activation temperature range, the catalyst is poisoned and the efficiency is lowered. Specifically, the poisoning substance that poisons the catalyst may include at least one of ammonium sulfate (NH ₄ ) ₂ SO ₄ and ammonium hydrogen sulfite (NH ₄ HSO ₄ ). Such a catalyst poisoning material is adsorbed on the catalyst to lower the activity of the catalyst. Since the catalyst poisonous substance decomposes at a relatively high temperature, the poisoned catalyst can be regenerated by raising the temperature of the catalyst.

Also, the housing of the reactor 300 can be made of, for example, stainless steel.

The first concentration sensor 410 is installed in the exhaust passage 600 in front of the reactor 300 and the second concentration sensor 420 is installed in the exhaust passage 600 in the rear of the reactor 300. The first concentration sensor 410 and the second concentration sensor 420 measure the concentration of NOx contained in the exhaust gas.

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

The decomposition chamber 550 generates ammonia (NH ₃ ) which is used as a reducing agent for reducing nitrogen oxide (NOx) by decomposing the urea (CO (NH ₂ ) ₂ ), which is a reducing agent precursor, from the outside.

If specifically, the temperature in the decomposition chamber 550 maintained within Celsius 300 degrees to degrees Celsius to 500 degrees, urea (urea, CO (NH _{2) 2)} is as easily hydrolyzed ammonia (NH ₃₎ and isocyanate ( Isocyanic acid, HNCO). And isocyanate (HNCO) is decomposed again into ammonia (NH ₃ ) and carbon dioxide (CO ₂ ). That is, when urea is decomposed, ammonia may finally be generated.

The reducing agent spraying unit 510 receives the reducing agent generated in the decomposition chamber 550 and injects the reducing agent in the exhaust gas passage 600. That is, the reducing agent spraying unit 510 injects the reducing agent into the exhaust gas to be introduced into the reactor 300. The injected reducing agent is mixed with the exhaust gas to reduce the NOx contained in the exhaust gas through the catalyst in the reactor 300.

The reducing agent supply passage 530 connects the decomposition chamber 550 and the reducing agent spraying unit 510.

The temperature sensor 450 is installed on the reducing agent supply passage 530. That is, the temperature sensor 450 is installed at the rear end of the decomposition chamber 550.

The control unit 700 can calculate the NOx reduction efficiency of the exhaust gas through the reactor 300 through the selective catalyst reduction reaction by receiving information from the first concentration sensor 410 and the second concentration sensor 420 .

Also, the control unit 700 can receive information from the temperature sensor 450 to determine whether the decrease in the NOx reduction efficiency is due to the poisoning of the catalyst or the supply of the reducing agent.

The information processing unit 750 receives the information signal from the control unit 700, processes information about the cause of the occurrence of the abnormality and the abnormality, records it, and displays the warning.

In addition, the information processing unit 750 can set various reference values to be used as a determination criterion, and can monitor the current situation in real time.

Specifically, the information processing unit 750 may include an operation recording unit 751 and a monitor 752. [

With such a structure, the selective catalytic reduction system 101 according to an embodiment of the present invention can accurately grasp the cause of the degradation of the nitrogen oxide reduction efficiency to determine the regeneration timing of the catalyst.

Hereinafter, a method for diagnosing performance of the selective catalytic reduction system 101 according to an embodiment of the present invention will be described in detail with reference to FIGS. 2 to 4. FIG.

That is, a method for diagnosing the performance of the selective catalytic reduction system 101 for reducing the nitrogen oxides contained in the exhaust gas of the engine whose load is varied will be described in detail.

As shown in FIG. 2, when the performance of the selective catalytic reduction system according to an embodiment of the present invention starts, all data are initialized (S100).

Next, the NOx reduction efficiency data is obtained (S200). NOx reduction efficiency data can be obtained by measuring the NOx concentration before and after the selective catalytic reduction reaction.

Specifically, the NOx reduction efficiency can be calculated by comparing the NOx concentration measured by the first concentration sensor 410 with the NOx concentration measured by the second concentration sensor 420. [

Then, the NOx reduction efficiency data is compared with the reference reduction efficiency range (S300), and the transient section and the stable section according to the engine load variation are distinguished from each other,

The reference reduction efficiency range is set to a predetermined upper and lower percentages based on the NOx reduction set value. That is, the reference reduction efficiency range is increased or decreased based on the NOx reduction set value in consideration of the deviation, and the target NOx reduction efficiency value to be described later falls within the reference reduction efficiency range.

The reference reduction efficiency range can be appropriately determined depending on the type of the engine, the surrounding environment, and the selective catalytic reduction system. For example, the reference reduction efficiency range may be set in the upper and lower limits of 10% of the NOx reduction set value.

The section in which the NOx reduction efficiency data deviates from the reference reduction efficiency range is regarded as an excessive section and the section in which the NOx reduction efficiency data is within the reference reduction efficiency range is regarded as the stable section as shown in FIG.

If it is determined that the NOx reduction efficiency data corresponds to the transient section, the data is initialized and the NOx reduction efficiency data is obtained again.

The transient section is generated because the exhaust gas emission amount of the engine temporarily changes when the load of the engine changes and the reducing agent is not supplied immediately following the amount of the reducing agent required for the changed exhaust gas emission amount. As described above, the amount of the reducing agent supplied temporarily becomes lower or higher than the amount of the reducing agent depending on the load variation of the engine, and NOx reduction efficiency data is not an accurate basis for determining whether the catalyst is poisoned.

Therefore, the NOx reduction efficiency data determined as the transient section is initialized and the NOx reduction efficiency data is obtained again.

On the other hand, if it is determined that the NOx reduction efficiency data corresponds to the stable period, the moving average value of the NOx reduction efficiency is calculated for the trend analysis in the stable period (S400).

The moving average is a method of taking a series of time series, calculating the average value of them, and connecting them to create a trend line. The moving average value is calculated by calculating a moving average of the NOx reduction efficiency for a predetermined time. For example, the predetermined time may be 10 minutes. That is, the moving average value of the NOx reduction efficiency for 10 minutes is calculated.

Then, the moving dispersion value of the NOx reduction efficiency in the stable section is calculated (S500).

Next, it is determined whether the calculated moving dispersion value is out of the allowable error range (S600).

That is, to determine whether or not the average NOx reduction efficiency converges within the tolerance range, the movement dispersion of the NOx reduction efficiency is compared with the tolerance range.

The tolerance range is set to a predetermined upper / lower limit percentage based on the moving average value. The tolerance range can be appropriately changed depending on the type of the engine, the surrounding environment, and the selective catalytic reduction system. For example, the tolerance range may be set to a range of up to 5% of the moving average value.

If the mobile dispersion value deviates from the tolerance range, it is determined that the average NOx reduction efficiency has not converged within the allowable error range, and the process returns to the initialization step.

When the moving dispersion value is within the tolerance range, that is, when the average NOx reduction efficiency converges within the tolerance range, as shown in FIG. 4, the moving average value and the NOx reduction efficiency target value (S700).

If the moving average value is equal to or more than the NOx reduction efficiency target value, it is determined that the performance is in a normal state, and the data is made fresh and new NOx reduction efficiency data is obtained.

That is, while maintaining the operation of the selective catalytic reduction system 101, the NOx reduction efficiency data is constantly obtained, and the presence or absence of the performance abnormality is repeatedly confirmed.

If the moving average value is less than the NOx reduction efficiency target value, it is determined that the performance is abnormal.

If it is determined that the performance is abnormal, the temperature of the reducing agent supply passage 530 between the decomposition chamber 550 and the reducing agent injection portion 510 is measured (S800). If the measured temperature is within the normal temperature range, the catalyst is poisoned to judge that the performance is deteriorated, and it is notified as the catalyst regeneration time (S900).

On the other hand, if the measured temperature is out of the normal temperature range, it is determined that an abnormality has occurred in the reducing agent supply, and the reductant supply abnormality is notified (S950).

Here, the normal range temperature can range from 250 degrees Celsius to 500 degrees Celsius.

The urea in the liquid state is decomposed and gasified in the decomposition chamber 550. If the decomposition chamber 550 is less than 250 degrees Celsius, it is not completely gasified and remains as a solid material, so that the reducing agent does not normally react with NOx, .

Further, even when the decomposition chamber 550 is excessively higher than the hydrolysis reaction temperature, that is, the decomposition chamber 550 exceeds 500 deg. C, decomposition of urea may not proceed effectively.

Thus, the temperature at the downstream end of the decomposition chamber 550 can be measured to determine whether the reduction in NOx reduction efficiency is due to the supply of reducing agent.

The rear end of the decomposition chamber 550 includes a reducing agent supply passage 530 behind the decomposition chamber 550.

If it is determined that the decrease in the NOx reduction efficiency is not due to poisoning of the catalyst, the operator does not unnecessarily regenerate the catalyst, and the operator checks the abnormality of the heating apparatus for supplying the thermal energy to the decomposition chamber 550 It can take measures.

Through such a method, the performance diagnostic method of the selective catalytic reduction system 101 according to an embodiment of the present invention can accurately determine the cause of the degradation of the nitrogen oxide reduction efficiency to determine the regeneration point of the catalyst.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. will be.

It is therefore to be understood that the embodiments described above are to be considered in all respects only as illustrative and not restrictive, the scope of the invention being indicated by the appended claims, It is intended that all changes and modifications derived from the equivalent concept be included within the scope of the present invention.

101: Selective Catalytic Reduction System
300: reactor
410: first density sensor
420: second density sensor
450: Temperature sensor
510: Reducing agent dispensing part
530: Reducing agent supply channel
550: decomposition chamber
600:
700:
750: Information processing unit

Claims (10)

A selective catalytic reduction system for reducing nitrogen oxides contained in an exhaust gas of an engine whose load is varied,
An exhaust passage through which the exhaust gas of the engine is discharged;
A reactor provided on the exhaust passage and provided with a catalyst therein for reducing nitrogen oxides contained in the exhaust gas;
A concentration sensor provided on the exhaust passage;
A reducing agent spraying unit installed on the exhaust flow path and spraying a reducing agent to the exhaust gas moving to the reactor;
A decomposition chamber for generating a reducing agent to be supplied to the reducing agent spraying unit;
A reducing agent supply passage connecting the decomposition chamber and the reducing agent injection unit;
A temperature sensor provided on the reducing agent supply passage; And
A control unit for receiving the information from the concentration sensor and calculating the nitrogen oxide reduction efficiency of the exhaust gas passing through the reactor,
/ RTI >
If the temperature of the reducing agent supply passage measured by the temperature sensor falls within a predetermined normal temperature range, a decrease in the nitrogen oxide reduction efficiency may be detected in the catalyst installed in the reactor When the temperature of the reducing agent supply passage is out of the predetermined normal temperature range, it is determined that the reduction of the nitrogen oxide reduction efficiency is caused by the supply of the reducing agent,
Wherein the control unit stops the calculation of the NOx reduction efficiency when the load of the engine fluctuates and the NOx reduction efficiency is calculated again after the supply amount of the reducing agent is followed in correspondence with the exhaust amount of the exhaust gas changed in accordance with the load variation of the engine system. The method of claim 1,
Wherein the predetermined normal temperature range falls within a range of from about 250 degrees Celsius to about 500 degrees Celsius. delete A method for diagnosing the performance of a selective catalytic reduction system for reducing nitrogen oxides contained in exhaust gas of an engine whose load is varied by using a reducing agent and a catalyst,
Obtaining nitrogen oxide reduction efficiency data;
Extracting the nitrogen oxide reduction efficiency data by comparing the nitrogen oxide reduction efficiency data with a reference reduction efficiency range and separating a transient section and a stable section according to a load variation of the engine;
Calculating a moving average value of the nitrogen oxide reduction efficiency for the trend analysis in the stable period;
Calculating a moving dispersion value of the nitrogen oxide reduction efficiency in the stable section;
If the moving dispersion value of the nitrogen oxide reduction efficiency is out of the tolerance range and the moving dispersion value of the nitrogen oxide reduction efficiency does not converge, initializing the data;
Comparing the moving average value with the nitrogen oxide reduction efficiency target value when the moving dispersion value of the nitrogen oxide reduction efficiency is within an allowable error range and the moving dispersion value of the nitrogen oxide reduction efficiency converges; And
Determining that the performance is in a steady state when the moving average value is equal to or higher than the target value of nitrogen oxide reduction efficiency and determining that the performance is abnormal if the moving average value is less than the target value of nitrogen oxide reduction;
/ RTI >
The reducing agent is generated in the decomposition chamber and supplied through the reducing agent injection unit,
If the temperature is within the normal temperature range, it is determined that the performance of the catalyst is deteriorated. If the temperature is outside the normal temperature range, the reducing agent supply unit And determining that an abnormality has occurred in the selective catalytic reduction system. 5. The method of claim 4,
Wherein the nitrogen oxide reduction efficiency data is obtained by measuring the nitrogen oxide concentration before and after the selective catalytic reduction reaction. 5. The method of claim 4,
The reference reduction efficiency range is set to a predetermined upper and lower percentages based on the nitrogen oxide reduction set value,
A selective catalytic reduction system in which the section in which the nitrogen oxide reduction efficiency data is out of the reference reduction efficiency range is regarded as an excessive section and the section in which the nitrogen oxide reduction efficiency data is within the reference reduction efficiency range is regarded as the stable section, Performance Diagnostic Method. 5. The method of claim 4,
Wherein the moving average value is calculated by calculating a moving average of nitrogen oxide reduction efficiency for a predetermined time. 5. The method of claim 4,
Wherein the tolerance range is set as a predetermined upper / lower limit percentage based on the moving average value. delete 5. The method of claim 4,
Wherein the normal temperature range is within the range of 250 degrees Celsius to 500 degrees Celsius.

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