JPH07238851A - Correcting method for nox sensor and denitration device - Google Patents

Abstract

PURPOSE:To realize a high reliability of NOx density detection while correcting adequately a NOx sensor which is liable to generate an error with the passage of time, in a simple structure. CONSTITUTION:When a NOx sensor 20 provided to a denitration device 1 to denitration process the exhaust gas from a combustion engine 5 in the three- dimensional catalyst method is corrected, the NOx sensor 20 is corrected by an air-fuel ratio to function a three-dimensional catalyst provided to the denitration device 1 effectively, by making the gas before the denitration process as the standard gas for correction, in the condition that the combustion engine 5 is being operated at a specific constant load.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for correcting a Knox sensor for detecting the Knox concentration for performance monitoring and feedback control of a denitration apparatus adopting a three-way catalyst system provided in a combustion engine such as an internal combustion engine, And a denitration device equipped with this type of Knox sensor.

[0002]

2. Description of the Related Art Conventionally, when a Knox sensor is used, standard gas is regularly supplied from a standard gas cylinder (gas concentration is registered in a memory in the device) to the Knox sensor, and the output of the Knox sensor is automatically output. The concentration was corrected to match the gas concentration of the standard gas. That is, conventionally, the Knox sensor incorporates an arithmetic unit for performing such a correction. This correction needs to be performed about every 24 hours, although it depends on the sensor type, and if not corrected, an error of about ± 2% occurs after 24 hours. Therefore, as shown in FIG. 4, the standard gas cylinder 200 is currently relatively expensive and costly.
Is corrected for the exhaust gas treatment system including the Knox sensor 20.

[0003]

However, in the case of the above-mentioned prior art, it is necessary to always prepare an expensive standard gas cylinder, which not only increases the cost but also raises the problem of high-pressure gas management.

Therefore, an object of the present invention is to provide a method for correcting a Knox sensor and a NOx removal device, which are capable of highly reliable Knox concentration detection, while appropriately correcting a Knox sensor, which is susceptible to errors over time, with a simple structure. Is to get.

[0005]

In order to achieve this object, the characteristic means of the correction method of the Knox sensor provided in the denitration device for denitrifying the exhaust gas from the combustion engine according to the present invention by the three-way catalyst system is With the air-fuel ratio at which the three-way catalyst provided in the denitrification device works effectively, and before the denitrification treatment exhaust gas discharged from the combustion engine is used as a correction reference gas when the combustion engine is operating at a predetermined constant load, a Knox sensor Is to correct. In this case, it is preferable that the correction is made up of the following steps. The first step of obtaining a reference Knox concentration, which is the concentration of Knox contained in the correction reference gas, by a previously corrected analyzer, the air-fuel ratio at which the three-way catalyst effectively works, and the combustion engine has the predetermined constant value. When operating under load,
The second step of introducing the exhaust gas before denitration treatment to the Knox sensor to obtain the pre-treatment sensor output concentration, and the third step of obtaining the coefficient for correcting the pre-treatment sensor output concentration to the reference Knox concentration.
Step, a correction output step of correcting and outputting the sensor output density from the Knox sensor based on the coefficient obtained through such a step.

Further, in a denitration device equipped with a Knox sensor for measuring the concentration of Knox in the exhaust gas passage, a catalyst arrangement part having a catalyst for denitrifying exhaust gas from a combustion engine by a three-way catalyst system is provided. The characteristic configuration of the present invention in this is that it has an untreated exhaust gas introducing passage for guiding the exhaust gas before denitration treatment to the Knox sensor, the air-fuel ratio at which the three-way catalyst effectively works, and the combustion engine is operated at a predetermined constant load. Storage means for storing the nox concentration contained in the exhaust gas generated from the combustion engine in the state as the reference nox concentration, and the exhaust gas before denitration treatment from the pretreatment exhaust gas introduction path to the nox sensor to obtain the pretreatment sensor output concentration, And a coefficient deriving means for obtaining a coefficient for correcting the unprocessed sensor output density to the reference Knox density, and based on the coefficient obtained by the coefficient deriving means. There is to be configured with an output means for outputting the corrected sensor output density from Knox sensor. Then, in the method for correcting the Knox sensor, in the denitration device, the air-fuel ratio at which the three-way catalyst works effectively is included in the denitration-treated exhaust gas when the air-fuel ratio of the mixed gas supplied to the combustion engine is changed. It is preferable that the air-fuel ratio is when the Knox concentration rapidly changes. The actions and effects of these are as follows.

[0007]

That is, in this correction method, the untreated exhaust gas from the combustion engine that uses the three-way catalyst is selected as the correction reference gas, and the Knox sensor is corrected according to the Knox concentration of this gas. . Now, the state of untreated exhaust gas from a combustion engine that employs such a three-way catalyst will be described. When this combustion engine is in a predetermined constant load state, the air-fuel ratio (1 2) when operating under the condition
As shown in (the same figure shows the relationship between the air-fuel ratio λ and the concentration of Knox contained in the exhaust gas, the solid line shows the Knox concentration of the exhaust gas that is the correction reference gas in the present application before denitration treatment, and Indicates the nox concentration of the exhaust gas that is generally the detection target of the NOx sensor after the denitration treatment), and the nox concentration contained in the exhaust gas before the denitration treatment is stable. And this concentration is hard to change with time. Therefore, this Knox density can be selectively used as a correction reference. Specifically, the stage at which the Knox concentration in the exhaust gas discharged from the combustion engine was measured in advance with a corrected device (analyzer) and stored as the reference Knox concentration, and the Knox sensor needed to be corrected. Then, guide the exhaust gas before denitration treatment to the Knox sensor, measure this concentration, obtain the pretreatment sensor output concentration, obtain the coefficient so that the pretreatment sensor output concentration matches the reference Knox concentration, and then The output from the Knox sensor is corrected and output.

Further, in the denitration apparatus of the present application, the above-mentioned reference Knox concentration is stored in the storage means, and the exhaust gas before denitration treatment is guided to the Knox sensor through the pretreatment exhaust gas introduction passage, and at the time of this introduction. The above-mentioned unprocessed sensor output density, which is the output from the Knox sensor, is obtained. Then, the coefficient deriving unit obtains the coefficient according to the above method, and the correct Knox concentration is output in the state corrected by the output unit.

Here, when the air-fuel ratio is changed to the air-fuel ratio in which the NOx concentration contained in the denitration-treated exhaust gas changes rapidly when the air-fuel ratio of the mixed gas supplied to the combustion engine is changed, Since the NOX concentration in the exhaust gas in this state can be specified exactly (specified from the configuration of the engine), highly accurate KNOX concentration measurement can be performed.

[0010]

Therefore, by adopting this method and configuration, control such as monitoring of NOX of the denitration system and fine adjustment of the air-fuel ratio can be performed based on the accurate NOX concentration, and long-term A three-way catalyst system that can purify exhaust gas stably can be provided.

[0011]

Embodiments of the present application will be described with reference to the drawings. FIG. 1 shows a configuration example of a three-way catalyst system 2 equipped with the denitration device 1 of the present application. The system 2 is configured to include a city gas supply passage 3 for supplying a city gas which is a fuel gas and an air passage 4 for supplying an air which is an oxygen-containing gas for combustion, and a mixed gas obtained by mixing these gases. A mixed gas passage 6 leading to the gas engine 5 and an exhaust gas passage 7 through which exhaust gas from the gas engine 5 flows are provided. An actuator 8 for controlling the air-fuel ratio is provided between the city gas supply passage 3 and the mixed gas passage 6, and an actuator for combustion load control for adjusting the supply amount of the mixed gas to the mixed gas passage 6. 9 is provided. Exhaust gas path 7 above
Is provided with a catalyst arrangement portion 10 in which a three-way catalyst is arranged, and an oxygen sensor 11 is provided on the upstream side of the catalyst arrangement portion 10. Then, the output from this sensor is collected in the ECU 13 for engine control and is used for the operation of the gas engine 5.

The above is the schematic structure of the three-way catalyst system 2. The structure relating to the Knox sensor 20 in which the correction method of the Knox sensor of the present application is adopted will be described below. The Knox sensor 20 has a first guide for guiding the exhaust gas after the denitration treatment to the sensor for the purpose of ordinary monitoring.
A post-treatment exhaust gas introduction passage 22 provided with a solenoid valve 21 and a pre-treatment exhaust gas introduction passage 24 provided with a second solenoid valve 23 that guides the exhaust gas before denitrification treatment required at the time of correction to the sensor 20 are provided, and will be described below. An arithmetic unit 25 that performs arithmetic processing for performing the correction and a display unit 26 that displays the result obtained by the arithmetic unit 25 are provided. Further, a transmission cable 27 for transmitting the detection signal from the arithmetic unit 25 to the engine control ECU 13 is provided. Then, the arithmetic unit 25 described above uses, as the reference Knox concentration, the Knox concentration contained in the exhaust gas generated from the combustion engine in the state where the combustion engine is operated at a predetermined constant load with the air-fuel ratio at which the three-way catalyst works effectively. Storage means 25a for storing
And a coefficient deriving means 25b for guiding the exhaust gas before denitration treatment from the untreated exhaust gas introduction path 24 to the Knox sensor 20 to obtain the untreated sensor output concentration, and for obtaining a coefficient for correcting the untreated sensor output concentration to the reference Knox concentration. And the output means 25c for correcting and outputting the sensor output density from the Knox sensor based on the coefficient obtained by the coefficient deriving means 25b.

By adopting the above configuration, normally,
In detecting the purification state of the exhaust gas, the first solenoid valve 21
Is opened and the second solenoid valve 23 is closed to detect the Knox concentration in the exhaust gas, and it is converted into an electric signal V, and the value of the electric signal is converted into the Knox concentration C by the arithmetic unit 25 and displayed. Here, the output V from the Knox sensor 20 and the display C
The relationship between and is expressed by the following equation.

## EQU1 ## C = f (V) f (x) is a function of x. F (x) may be, for example, a linear function as shown in the following Expression 2 or other approximated functions. Is also good. It may also be a value read from the table. Furthermore, a timer (not shown) is provided in the arithmetic unit 25 described above.
Or an external input device (not shown) is provided, and at each time when the characteristics of the Knox sensor 20 are predicted to change, or
When you want to know the exact Knox concentration
A configuration is adopted in which a correction operation can be performed by inputting a command to. In this correction operation,
The exhaust gas from the gas engine before the denitration process is used as the correction reference gas.

The details of the correction operation will be described below.
This correction includes initial correction at the time of the initial rise of the Knox sensor system and sequential correction that is sequentially performed after a predetermined time has elapsed from the start of measurement. The correction procedure will be described with the flowchart shown in FIG. Each correction procedure is listed below. A Initial Correction 1 While the first solenoid valve 21 is open, the actuator 8 for controlling the air-fuel ratio is controlled, and the air-fuel ratio is shifted from the rich side to the lean side (from the side where the value of λ is low to the side where it is high). The air-fuel ratio λ _a is set so as to rise rapidly. (This operation is based on the air-fuel ratio range (0.95
It is almost unnecessary for ~ 1.01), but it is performed when accuracy is required. 2) The corrected NOx analyzer 100 is used to measure the Knox concentration C0 in the exhaust gas before the denitration treatment (this is referred to as the reference Knox concentration), and this value is stored in a part of the memory (storage means 25a of the arithmetic unit 25. (This is called the first step). 3 The first solenoid valve 21 is closed and the second solenoid valve 23 is opened to guide the exhaust gas before denitration treatment to the Knox sensor 20, and the output signal value V0 of the Knox sensor 20 at that time (this is called the pretreatment sensor output concentration). Is stored (this stage is called the second stage). 4 From the measured V0 and C0, the above relation f (V)
The coefficients a and b are obtained from the following equation 2 as
This operation is performed by the coefficient deriving means 25b described above, and this stage is called the third stage).

[Formula 2] C = a × V + b However, initial a and b are

## EQU00003 ## C0 = a.times.V0 + b is satisfied, and it is determined by specifying the sensor. Regarding b, when the sensor output is 0 when the Knox concentration is zero, b = 0, and when the engine is stopped, V0 of the following equation 4, which is the zero point output, is measured, and It is also possible to obtain a and b from the equation 4.

## EQU00004 ## 0 = aV1 + b When performing this zero point correction, the engine may be stopped as described above, or clean air may be introduced into the Knox sensor from the third solenoid valve 28 shown in FIG. 5 After the determination of a and b by the above operation, the Knox concentration is measured based on the equation 2.

The above is the details of the initial correction, but in the following correction, the above first step is omitted and correction is performed. In this case, the exhaust gas before the denitration process is used as the correction reference gas. Work Procedure for Performing Correction Again 1 The Knox concentration C0 (reference Knox concentration) in the exhaust gas before the denitration process stored in the initial correction stage is used as it is (corresponding to the first stage). 2 The first solenoid valve 21 is closed, the second solenoid valve 23 is opened, the exhaust gas before denitration treatment is guided to the Knox sensor 20, and the output signal value Vk of the Knox sensor 20 at that time (the sensor output concentration before treatment) is stored. (Second stage). 3 From the measured Vk and the stored C0, f
The coefficients a and b are obtained from the following equation 5 as (V) (third stage).

## EQU00005 ## C0 = a.times.Vk + b Here, as for b, when the sensor output is 0 when the NOx concentration is zero, b =
It is possible to set it to 0, and when the engine is stopped or when the clean air is introduced from the third solenoid valve 28, the zero point output V2 of the equation 6 is measured, and a and b can be obtained from the equation 5 and the equation 6. .

## EQU6 ## 0 = a.times.V2 + b.sub.4 After the determination of a and b by the above operation, the Knox concentration is measured based on the equation 2. Further, even when a function other than the above formula is used, the function formula is changed or the values in the table are replaced by the above process.

Through such a correction procedure, initial correction, 2
00 hours, 400 hours, 600 hours, 1000 hours, 2
Table 1 shows the result of correction of the Knox sensor at 000 hours. In Table 1, V is a sensor output in units of volts, the correction display is the sensor output concentration from the Knox sensor 20 whose characteristics may change, and the analyzer value is actually measured by the analyzer 100 before denitration treatment. It is a measurement of the Knox concentration in the exhaust gas. In the present application, when such verification is not necessary, the Knox concentration of the exhaust gas before the denitration treatment may be measured once at the initial stage. Further, regarding the exhaust gas after the denitration treatment, the measurement results of the Knox sensor 20 and the analyzer 100 are also shown.

[0017]

[Table 1]

Equation 2 was used as f (V) in the arithmetic unit. However, since the sensor outputs 0 when there is no Knox, b = 0 in Equation 2 and C0 is 2800p.
In pm, the sensor type is potentiostatic electrolysis Knox sensor. Furthermore, in the table, the value "before" was measured after the lapse of a predetermined time without changing the values of a and b (without correction), and the value of the analyzer and each display due to the characteristic change of the Knox sensor. The value of will be different. Here, the correction operation is performed, and the display becomes the display described in the “after” column. As a result, the value of a was corrected and changed from 500 to 560 after 2000 hours. When no correction is made, this Knox sensor has a characteristic change of 11%, and the error exceeds ± 11%. On the other hand, in the case of the present application in which the correction was performed, the value was within ± 5%.

[Other Embodiments] (a) In the above embodiments, a gas engine is shown as an example of a combustion engine, but the present invention is applicable to any structure as long as it produces nitrogen oxides. Can be adapted. That is, it can be suitably applied to denitration treatment of internal combustion engines such as gas engines and gasoline engines. (B) As the Knox sensor, any NOx sensor such as a potentiostatic electrolysis sensor, a semiconductor sensor, a chemiluminescence NOx analyzer, an infrared absorption NOx sensor, or the like may be used. (C) In the above embodiment, an example is shown in which correction is performed when the gas engine, which is a combustion engine, operates at a predetermined constant load. Therefore, in the flow shown in FIG. 3, the condition is that the engine is operating in a constant load state. And, in a combustion engine, like a cogeneration facility, the load is usually constant (80%).
It is possible to satisfy this condition because some of them are operated within a range that can be regarded as 100%). However, in order to deal with the full load for the operation with load fluctuation, a function C0 (load) as the reference Knox concentration that changes with the changing load is introduced, and C0 (x) = g (x ); X = load, g (x) is first obtained, and at the time of correction, C0 (x ₁ ) is a value adjusted to the load (x ₁ ) at the time of correction, and C0 (x ₁ ) in the flow of correction described above. It suffices to replace with and correct. In the case of adopting such a configuration, even when the load varies, the correction can be appropriately performed and the Knox concentration can be satisfactorily detected.

It should be noted that reference numerals are added to the claims for convenience of comparison with the drawings, but the present invention is not limited to the configurations of the accompanying drawings by the entry.

[Brief description of drawings]

FIG. 1 is a diagram showing the configuration of a three-way catalyst system equipped with a Knox sensor.

FIG. 2 is a diagram showing the relationship between air-fuel ratio and Knox concentration in a three-way catalyst system.

FIG. 3 is a flowchart of a correction process.

FIG. 4 is a diagram showing a three-way catalyst system having a conventional Knox sensor correction configuration.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Denitration device 5 Combustion engine 7 Exhaust gas passage 20 Knox sensor 24 Pretreatment exhaust gas introduction passage 25a Storage means 25b Coefficient deriving means 25c Output means 100 Analyzer

Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location B01D 53/94 F01N 3/08 ZAB Z

Claims (5)

[Claims] 1. A method for correcting a NOx sensor (20) provided in a denitration device (1) for denitrifying exhaust gas from a combustion engine (5) by a three-way catalyst method, the denitration device (1) comprising: The exhaust gas before denitration treatment discharged from the combustion engine (5) is used as a correction standard when the combustion engine (5) is operated at a predetermined constant load with an air-fuel ratio at which the provided three-way catalyst works effectively. A method for correcting a Knox sensor for correcting the Knox sensor (20) as gas. 2. A first step of obtaining a reference Knox concentration, which is a concentration of Knox contained in the correction reference gas, by a previously corrected analyzer (100), and an air-fuel ratio at which the three-way catalyst works effectively. A second stage in which exhaust gas before denitration treatment is introduced to the Knox sensor (20) to obtain a pre-treatment sensor output concentration while the combustion engine (5) is operating at the predetermined constant load; A third step of obtaining a coefficient for correcting the sensor output density to the reference Knox density, and based on the obtained coefficient, the Knox sensor (2
The sensor output density from 0) is corrected and output.
Correction method for the described Knox sensor. 3. When the air-fuel ratio at which the three-way catalyst works effectively changes the air-fuel ratio of the mixed gas supplied to the combustion engine (5), the NOx concentration contained in the exhaust gas after the denitration treatment is reduced. The method for correcting a Knox sensor according to claim 1 or 2, wherein the air-fuel ratio is a value when abruptly changing. 4. A catalyst arrangement part (10) equipped with a catalyst for denitrifying exhaust gas from a combustion engine (5) by a three-way catalyst system is provided in the exhaust gas passage (7), and the nox in the exhaust gas passage (7) is provided. A NOx sensor (20) provided with a NOx sensor (20) for measuring the concentration of NOx, wherein the NOx sensor (20) measures the exhaust gas before the NOx treatment.
The exhaust gas is introduced from the combustion engine (5) in a state in which the combustion engine (5) is operated at a predetermined constant load at an air-fuel ratio at which the three-way catalyst effectively works. Storage means (25 for storing the nox concentration contained in the exhaust gas as the reference nox concentration)
a) and exhaust gas before denitrification treatment from the pretreatment exhaust gas introduction path (24) to the Knox sensor (20) to obtain the pretreatment sensor output concentration, and the pretreatment sensor output concentration to the reference Knox concentration. Coefficient deriving means (2) for obtaining the coefficient to be corrected
5b), and a denitration device including an output means (25c) for correcting and outputting the sensor output density from the Knox sensor (20) based on the coefficient obtained by the coefficient deriving means (25b). 5. When the air-fuel ratio at which the three-way catalyst works effectively changes the air-fuel ratio of the mixed gas supplied to the combustion engine (5), the NOx concentration contained in the exhaust gas after denitration treatment is The denitration device according to claim 4, wherein the air-fuel ratio is that when it changes abruptly.