KR102274546B1 - Method and apparatus for measuring denitration ratio for an internal combustion engine - Google Patents

Abstract

A first zirconia-type NOx sensor capable of detecting the NOx concentration between the engine and the catalytic denitration device in the exhaust gas path, and a second zirconia-type NOx sensor capable of detecting the NOx concentration between the catalytic denitration device and the exhaust gas turbocharger The value detected by the first sensor is referred to as NOx·inlet, and the value detected by the second sensor is referred to as NOx·outlet, and the gas pressure in the detection environment and SOx contained in the exhaust gas affect the detection value of the sensor. Let the correction factor for correcting the influence be α,
Calculate the denitration rate by using the formula (NOx·inlet × α - NOx·outlet × α) / NOx·inlet × α and by removing α by chemical powder.

Description

Measuring method and measuring device of denitration rate for engine {METHOD AND APPARATUS FOR MEASURING DENITRATION RATIO FOR AN INTERNAL COMBUSTION ENGINE}

The present invention relates to a method for measuring a denitration rate for an engine and a measuring device for implementing the method.

Although a two-stroke diesel engine is widely used as an engine for ships, a catalytic denitration device is used to remove nitrogen oxides (NOx) contained in the exhaust gas. is being used In the case of using this catalytic denitration device, urea water is sprayed on the exhaust gas in the denitration device, the sprayed urea component is ammoniated by hydrolysis, and this ammonia reacts with nitrogen oxide by the action of a catalyst to convert it into harmless nitrogen gas and water.

In the case of using such a catalytic denitration device, it is required to control the denitration rate in the denitration device so that the amount of nitrogen oxide in the finally discharged gas is below a limit value.

For example, Patent Document 1 discloses a system in which a supply nozzle for ammonia instead of urea and a catalytic denitration device are installed in the exhaust gas path from the boiler rather than the engine. . In this system, the nitrogen oxide concentration in the exhaust gas path on the upstream and downstream sides of the catalytic denitration device is measured, and the amount of ammonia supplied so that the amount of nitrogen oxide in the finally discharged gas becomes a predetermined emission control value. is controlling

Japanese Patent Laid-Open No. 2003-290630

As described in Patent Document 1, even if a problem does not occur when the source of generation of exhaust gas is a boiler, the following problems occur when the source of generation of exhaust gas is an engine.

That is, in the case of, for example, a two-stroke engine for ships, an exhaust gas turbocharger is generally provided in the exhaust passage from the engine, and the catalytic denitration device is located between the engine and the turbocharger, that is, It is installed on the high-pressure side rather than the turbine of the turbocharger. This is because the catalytic denitration device does not operate sufficiently unless the exhaust gas temperature is higher on the high-pressure side than the turbocharger turbine. On the downstream side of the turbocharger, since the temperature of the exhaust gas is lower, even if a catalytic denitration device is installed, it does not operate sufficiently.

As a result, the sensor for detecting the nitrogen oxide concentration is used in a high-pressure environment. In general, a zirconia type (zirconium dioxide type) NOx sensor is used as a sensor for detecting the nitrogen oxide concentration, but this sensor has a property that its sensitivity varies depending on pressure. For this reason, it is usually necessary to use a pressure sensor together with a zirconia type sensor, and to perform sensitivity correction based on the detection result of the pressure sensor. However, there is a problem in that the system becomes complicated and expensive.

Moreover, since marine fuel contains sulfur, sulfur oxide (SOx) is contained in exhaust gas from a marine engine. However, the zirconia-type NOx sensor also has a problem that its sensitivity is lowered in the presence of sulfur oxides.

Therefore, the present invention solves this problem, and when controlling the operating condition of a catalytic denitration device installed in the exhaust gas path of an engine using a zirconia-type NOx sensor, measured values and The purpose of this is to prevent the occurrence of errors in the control amount.

In order to achieve this object, the method for measuring the denitration rate for an engine of the present invention is to measure the denitration rate in a system in which a catalytic denitration device and an exhaust gas turbocharger are arranged in this order in the exhaust gas path from the engine. A first zirconia type NOx sensor capable of detecting a NOx concentration in a portion between the engine and the catalytic denitration device in the exhaust gas path, and between the catalytic denitration device and the exhaust gas turbocharger in the exhaust gas path Using the second zirconia-type NOx sensor capable of detecting the NOx concentration in the part, the value detected by the first zirconia-type NOx sensor is called NOx·inlet, and the value detected by the second zirconia-type NOx sensor is called NOx·outlet, A correction factor for correcting the effect of the gas pressure in the detection environment and the SOx contained in the exhaust gas on the detection value of the zirconia-type NOx sensor is taken as α, and the equation (NOx·inlet × α - NOx·outlet × α ) / NOx·inlet × α is used, and the denitration rate is obtained by eliminating α by chemical powder.

In the apparatus for measuring the denitration rate for an engine of the present invention, a catalytic denitration device and an exhaust gas turbocharger are arranged in this order in an exhaust gas path from the engine, and between the engine and the catalytic denitration device in the exhaust gas path A first zirconia-type NOx sensor capable of detecting the NOx concentration in a portion of the exhaust gas path, and a second zirconia-type NOx sensor capable of detecting the NOx concentration in a portion between the catalytic denitration device and the exhaust gas turbocharger in the exhaust gas path are installed, , the value detected by the first zirconia type NOx sensor is NOx·inlet, and the value detected by the second zirconia type NOx sensor is referred to as NOx·outlet, and the gas pressure in the detection environment and SOx contained in the exhaust gas are zirconia Formula (NOx·inlet × α - NOx·outlet × α) / NOx·inlet × α Using the equation (NOx·inlet × α - NOx·outlet × α) / NOx·inlet × α, α is reduced by the reduction It is characterized in that a device for measuring the denitration rate is installed.

According to the present invention, both the first and second zirconia-type NOx sensors for measuring the denitration rate are installed in the exhaust gas path upstream of the exhaust gas turbocharger, that is, in the portion containing SOx at high pressure, NOx concentration is detected. For this reason, the pressure and the influence of SOx which these 1st and 2nd zirconia type NOx sensors receive can be made equal. That is, the value of the correction coefficient α in the above equation is the value detected by the first zirconia type NOx sensor (NOx·inlet) and the value detected by the second zirconia type NOx sensor (NOx·outlet) as shown in the above equation. can be made the same in

For this reason, in the above equation, α can be eliminated by a small fraction, and in the end, the above equation cancels the influence of the gas pressure in the detection environment and the SOx contained in the exhaust gas on the detection value of the zirconia-type NOx sensor, that is, The correction factor (α) has been eliminated,

(NOx·inlet - NOx·outlet) / It can be transformed into the form of NOx·inlet.

In addition, the pressure loss caused by exhaust gas passing through the catalytic denitration device is small and negligible. Therefore, it can be considered that the pressures on the upstream side and the downstream side of the exhaust gas path are the same as those of the catalytic denitration device. Based on that premise, the above formula holds.

Also, in reality, the detection value of the second zirconia type NOx sensor is affected by ammonia (leak ammonia) that could not react completely in the catalytic denitration device, but the amount of catalyst charged in the denitration device is appropriate and the urea If a reducing agent such as water or ammonia is not significantly over-administered, the concentration of leak ammonia is very small, so the effect this has on the detection value of the zirconia-type NOx sensor is small and negligible.

According to the present invention, when measuring the denitration rate in a catalytic denitration device using a zirconia-type nitrogen oxide concentration sensor, the sensor sensitivity due to the effect of the exhaust gas pressure in the detection environment and SOx contained in the exhaust gas It is possible to prevent the occurrence of error in the measurement value based on the fluctuation of . In addition, the denitration rate can be measured even when the extent of the influence of the exhaust gas pressure and SOx contained in the exhaust gas on the sensor sensitivity is unknown. Therefore, according to the present invention, when the operation condition of the catalytic denitration device is controlled using the measured value of the denitration rate, it is possible to prevent the occurrence of control errors based on the measurement error of the denitration rate.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the structure of the measuring apparatus of the denitration rate for the engine which concerns on embodiment of this invention.
2 is a graph showing the measurement result of the denitration rate.

In Fig. 1, reference numeral 1 denotes a two-stroke diesel engine for ships, and reference numeral 2 denotes an exhaust gas path from the engine 1. As shown in Figs. A catalytic denitration device (3) is installed in this path (2). And an exhaust gas turbocharger (4) is provided on the downstream side of the denitration device (3). Exhaust gas is supplied to a turbine 4a of the turbocharger 4 and intake air is compressed by a compressor 4b.

Between the engine 1 and the denitration device 3 in the exhaust gas path 2, the first zirconia type (zirconium dioxide type) capable of measuring the NOx concentration in the path 2 of that part NOx sensor (第1 zirconia type NOx sensor) (6) is installed. In the exhaust gas path 2, between the denitration device 3 and the turbocharger 4, a second zirconia type NOx sensor 7 capable of measuring the NOx concentration in the path 2 of that portion is provided. has been

Reference numeral 8 denotes a measurement unit of the denitration rate, a detection signal (NOx·inlet) from the first zirconia-type NOx sensor 6 installed on the inlet side of the denitration device 3 , and a second device installed on the outlet side of the denitration device 3 . Using the detection signal (NOx·outlet) from the 2-zirconia type NOx sensor 7, the denitration rate by the denitration device 3 can be measured by the following equation.

(NOx·inlet × α - NOx·outlet × α) / NOx·inlet × α

In this equation, α is a correction coefficient, and is for correcting the influence of gas pressure in the detection environment, SOx contained in exhaust gas, and the like on the detection values of the zirconia-type NOx sensors 6 and 7 .

As shown in the figure, the first and second zirconia-type NOx sensors 6 and 7 are both a portion upstream of the turbocharger 4 in the exhaust gas path 2, that is, a high pressure, and containing SOx. installed in the part. Further, the pressure loss caused by the exhaust gas passing through the denitration device 3 is small and negligible. For this reason, the pressure and the influence of SOx which these 1st and 2nd zirconia type NOx sensors 6 and 7 receive can be made equal. That is, the value of the correction coefficient α in the above equation is the value detected by the first zirconia type NOx sensor (NOx·inlet) and the value detected by the second zirconia type NOx sensor (NOx·outlet) as shown in the above equation. can do the same in

For this reason, α of the above equation can be reduced, and the above equation shows the effect of the gas pressure in the detection environment and SOx contained in the exhaust gas on the detection values of the zirconia type NOx sensors 6 and 7 After canceling the influence, that is, by canceling the correction factor (α),

It can be transformed into the form of (NOx·inlet- NOx·outlet)/NOx·inlet.

Accordingly, the measurement unit 8 is configured to measure sensor sensitivity fluctuations due to the influence of the exhaust gas pressure in the detection environment of the first and second zirconia-type NOx sensors 6 and 7, SOx contained in the exhaust gas, and the like. After preventing the occurrence of error, the measured value of the denitration rate can be obtained.

In the system shown in Fig. 1, urea water is sprayed on exhaust gas from the catalytic denitration device 3, but the spray amount is controlled based on the measured value of the denitration rate by the measuring unit 8. By employing the feedback control system, it is possible to set the emission amount of nitrogen oxides in the finally exhausted gas to a predetermined emission control value. For this reason, the illustrated system can be operated by setting the denitration rate to, for example, 80%.

[Example]

The case where feedback control is performed using the measurement values based on the present invention as described above, the case where feedforward control is performed without using the NOx sensor, and the inlet and outlet sides of the catalytic denitration device In addition to using a zirconia-type NOx sensor, a pressure sensor is used in the denitration device to perform feedback control using a signal obtained by pressure correction of the NOx sensor signal will be described.

Figure 2 shows a graph of the result of controlling with the target of the denitration rate of 80% by the three methods described above. The horizontal axis represents the load factor of the engine and the vertical axis represents the achieved denitration ratio.

As shown in this graph, when feedback control was performed using the measured value based on the present invention, the result was closest to the target value of 80%.

In the case of feedforward control that does not use the NOx sensor, the result deviates from the target value in the high load region. In this case, with respect to the measured value of NOx generated when the engine is operated, the amount of urea water for reducing it by 80% is calculated, and control is performed to actually administer the urea water by feed-forward control. This is due to the difference between the ambient conditions such as temperature and humidity when NOx emission data from the engine body is previously collected for feedforward control and the ambient conditions when the main denitration operation is performed. It is thought to be a control error that occurred. This change in ambient conditions is a phenomenon that occurs frequently in ships, especially ships used for international shipping.

In the case of feedback control using the pressure-corrected signal, there was a tendency to deviate from the target as a whole, and the tendency was particularly remarkable in the high load region where the exhaust gas pressure was high. This is considered to be because the precision of the value of the pressure correction coefficient α was not high.

From the above, the following conclusions can be drawn. That is, it is difficult to accurately predict the amount of nitrogen oxide (NOx) generated in the engine because it fluctuates due to various condition changes such as changes in conditions around the engine and changes in fuel components, which are typified by changes in climate. In order to cope with this, it is judged that feedback control using the NOx concentration detection value at the inlet and outlet of the catalytic denitration device is effective. A zirconia type sensor is used to detect the concentration of NOx, but since this sensor's detection value is particularly affected by the exhaust gas pressure, some countermeasure is required. Therefore, in the present invention, in order to remove the influence of the exhaust gas pressure or the like from the detected value, it is possible to cancel the influence by installing both the sensor on the inlet side and the sensor on the outlet side of the denitration device in a place with high gas pressure. For this reason, when measuring the denitration rate, it is possible to prevent the occurrence of errors in measurement values based on fluctuations in sensor sensitivity due to the influence of exhaust gas pressure in the detection environment.

1: diesel engine
2: exhaust gas path
3: Catalytic denitration device
4: Turbocharger
4a: turbine
4b: Compressor
6: 1st zirconia type (RSD type) NOx sensor
7: Second zirconia type (RSD type) NOx sensor

Claims (2)

In a system in which a catalytic denitration device and an exhaust gas turbocharger are arranged in this order in the exhaust gas path from the engine In measuring the denitration rate (脫硝率),
a first zirconia type NOx sensor capable of detecting the NOx concentration in a portion between the engine and the catalytic denitration device in the exhaust gas path, and a catalytic denitration device in the exhaust gas path; Using a second zirconia type NOx sensor that can detect the NOx concentration in the part between the exhaust gas turbochargers,
The value detected by the first zirconia type NOx sensor is referred to as NOx·inlet, and the value detected by the second zirconia type NOx sensor is referred to as NOx·outlet, and is included in the gas pressure and exhaust gas in the detection environment. A correction factor for correcting the effect of the SOx on the detection value of the zirconia-type NOx sensor as α,
Formula (NOx·inlet × α - NOx·outlet × α) / NOx·inlet × α
A method of measuring the denitration rate for an engine, characterized in that the denitration rate is obtained by using and eliminating α by a small fraction.
A catalytic denitration device and an exhaust gas turbocharger are arranged in this order in the exhaust gas path from the engine,
A first zirconia-type NOx sensor capable of detecting the NOx concentration in a portion between the engine and the catalytic denitration device in the exhaust gas path, and a portion between the catalytic denitration device and the exhaust gas turbocharger in the exhaust gas path A second zirconia-type NOx sensor capable of detecting the NOx concentration is installed,
The value detected by the first zirconia type NOx sensor is NOx·inlet, and the value detected by the second zirconia type NOx sensor is referred to as NOx·outlet, and the gas pressure in the detection environment and SOx contained in the exhaust gas are zirconia type NOx Let α be the correction factor for correcting the effect on the detection value of the sensor,
Formula (NOx·inlet × α - NOx·outlet × α) / NOx·inlet × α
A device for measuring the denitration rate for an engine, characterized in that a device for measuring the denitration rate is installed by using and removing α by chemical powder.

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