JP5190396B2 - Denitration equipment - Google Patents

Description

  The present invention relates to a denitration device that supplies a reducing agent such as urea water to combustion exhaust gas discharged from a combustion device such as an engine, and decomposes NOx contained in the combustion exhaust gas.

NOx is contained in the combustion exhaust gas generated when combustion is performed by a combustion apparatus such as a cogeneration engine. NOx is a cause of photochemical smog and acid rain, and there are places that are regulated by regulations in urban areas. Therefore, it is necessary to decompose NOx into harmless N ₂ or the like, and a denitration device comprising a reducing agent supply device that supplies a reducing agent such as urea water or ammonia water and a denitration catalyst that promotes the reduction reaction should be installed. Is widely practiced. In this denitration device, a reducing agent is sprayed into combustion exhaust gas, and NOx is reacted with ammonia in a denitration catalyst, whereby NOx is decomposed into harmless N ₂ and H ₂ O.

  In the case of denitration by a denitration apparatus, it is necessary to appropriately control the supply amount of the reducing agent. If the amount of reducing agent supplied is small, the amount of NOx discharged into the atmosphere will increase, and if the amount of reducing agent supplied is too large, ammonia that could not be reacted will be discharged into the atmosphere. Therefore, as described in Japanese Patent No. 3051442, means for appropriately controlling the reducing agent supply amount has been studied. Basic adjustment of the reducing agent supply amount is performed based on the engine load factor (engine output value). As the engine output increases, the amount of combustion exhaust gas generated increases, and the amount of NOx contained in the combustion exhaust gas also increases. Therefore, the reducing agent supply amount is changed in proportion to the fluctuation of the engine load factor.

  Even if the engine continues constant combustion, the NOx concentration in the combustion exhaust gas discharged from the engine increases and decreases as the temperature and humidity fluctuate. Therefore, if the reducing agent supply is controlled only by proportional control with respect to the output value of the engine, the reducing agent supply amount becomes excessive or insufficient. Therefore, it has been considered that the NOx value in the combustion exhaust gas is detected and the reducing agent supply amount is controlled based on the NOx value.

  Therefore, it has been considered that the NOx concentration in the combustion exhaust gas is detected and the reducing agent supply amount is controlled based on the NOx concentration. Considering simply, if the NOx concentration before denitration (denitration device inlet) is detected and the reducing agent supply amount is controlled based on the inlet NOx concentration, appropriate control should be possible. However, even if the predetermined reducing agent supply amount is determined based on the inlet NOx concentration, the NOx concentration after denitration does not become a predetermined value, and a deviation occurs. In addition, when the capacity of the reducing agent supply pump is reduced, an assumed amount of reducing agent cannot be supplied, and the outlet NOx concentration increases. Therefore, it is necessary to operate the reducing agent supply amount based on the outlet NOx concentration, detect the outlet NOx concentration that appears as a result of the operation, and perform feedback control to further operate the reducing agent supply amount.

  In the invention described in Japanese Patent No. 3051442, control of the reducing agent supply amount based on the inlet NOx value and control of the reducing agent supply amount based on the outlet NOx value are performed. In this case, by performing control based on both the inlet NOx value and the outlet NOx value, the reducing agent supply amount is adjusted to be appropriate, the exhaust NOx value is stably kept low, and ammonia is discharged. It is described that it can be suppressed. However, when the control is performed based on the NOx concentrations of both the inlet NOx value and the outlet NOx value, it is necessary to install the NOx value measuring device at both the inlet portion and the outlet portion of the denitration device. When the NOx value measuring devices are installed at two locations, there is a drawback that the device cost increases.

  In the case of a system in which a plurality of engines are installed, the same number of exhaust gas passages as the engine are required, and the same number of denitration devices as the engine is required. Although it is unavoidable that the device cost increases as the number of devices increases, there has been a desire to reduce the device cost as much as possible even when the number of devices of the denitration device increases.

Japanese Patent No. 3051442

  The problem to be solved by the present invention is to reduce the number of parts by reducing the number of parts and to reduce the apparatus cost when a plurality of denitration apparatuses are installed.

  The invention according to claim 1 is provided with a plurality of devices that generate combustion exhaust gas, such as an engine, and a plurality of installations in which NOx in the combustion exhaust gas is decomposed by providing a denitration device in each of a plurality of exhaust gas flow paths. A denitration apparatus, wherein one end of a sample tube is connected to a portion downstream of the denitration apparatus in each exhaust gas passage, and the other end of the sample tube is connected to a common NOx value measurement device. In the denitration device provided in each exhaust gas passage, when the NOx value measuring device measures the outlet NOx value of the exhaust gas passage, it is measured. When the reducing agent supply amount is adjusted based on the outlet NOx value that is being discharged and the NOx value measuring device is not measuring the outlet NOx value of the exhaust gas passage, the NOx value is measured. The outlet NOx value at the time of measuring the outlet NOx value of the exhaust gas passage is stored as the previous final value, and the reducing agent supply amount is adjusted based on the previous final value. Switching of the exhaust gas passage for measurement is performed by switching the exhaust gas passage for measuring the NOx value when the switching condition time has passed since the previous switching and the condition that the outlet NOx value is stable is satisfied. It is characterized by having done.

  According to the second aspect of the present invention, in the above-described multiple installation denitration apparatus, the fact that the outlet NOx value is stable means that the difference between the maximum value and the minimum value of the outlet NOx value within the predetermined time immediately before is the stability determination amplitude. Less than, the average value of the outlet NOx value in the immediately preceding predetermined time is within the stability determination target range, and the reducing agent supply amount correction value calculated based on the outlet NOx value in the immediately preceding predetermined time is within the stability determining correction value. The present invention is characterized in that one or a plurality of conditions are satisfied.

  When the present invention is implemented, since the NOx value measuring device is shared, the required number of NOx value measuring devices is smaller than the number of NOx removal devices installed. Therefore, the number of NOx value measuring devices installed can be reduced, and the device cost can be reduced. In addition, since the requirement that the outlet NOx value is stable is included as a switching condition, measurement of the outlet NOx value is stopped when the outlet NOx value fluctuates, and subsequent fluctuations in the outlet NOx value are supported. Thus, it becomes possible to prevent the reducing agent supply amount from being excessive or insufficient by making it impossible to adjust the reducing agent supply amount. Furthermore, as a condition for switching, when the switching condition time has passed since the previous switching, it is possible to prevent the switching apparatus from being consumed excessively due to excessive switching of the apparatus and shortening the life of the apparatus. Can do.

Flow chart of denitration apparatus for carrying out the present invention Explanatory drawing explaining the situation of urea water supply amount calculation Flowchart in the embodiment of the present invention The graph which shows the exit NOx value measured in order to confirm the effectiveness of this invention Flow chart of denitration apparatus in another embodiment

  An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a flow chart of a denitration apparatus for carrying out the present invention, FIG. 2 is an explanatory diagram in which a reducing agent supply amount obtained from a correction value based on an engine output value (%) and an outlet NOx value is graphed, and FIG. The flowchart in an Example, FIG. 4 is a graph which shows the exit NOx value measured in order to confirm the effectiveness of this invention, FIG. 5 is the flowchart of the denitration apparatus in another Example.

  FIG. 1 shows a flow of a denitration device for removing NOx contained in combustion exhaust gas discharged from two engines 1a1b. The two systems are distinguished from each other by adding ab, and are named a system and b system, respectively. Since two engines 1 are installed in FIG. 1, the exhaust gas passage 2 is provided with 2a and 2b, and the reducing agent spray nozzle 3 and the reducing agent supply unit 4 are also provided in two systems. As a reducing agent for reducing NOx, urea is easier to handle than ammonia, so urea water is used in the examples.

  In the case of system a, combustion exhaust gas generated in the engine 1a is discharged through an exhaust gas passage 2a connected to the engine 1a. In the middle of the exhaust gas passage 2a, a reducing agent spray nozzle 3a and a denitration catalyst 5a are installed in order from the upstream side of the combustion exhaust gas flow. The reducing agent spray nozzle 3a has a tip installed in the exhaust gas passage 2a, and the other end is connected to a reducing agent supply unit 4a including a urea water pump and a urea water tank, and is supplied from the reducing agent supply unit 4a. The urea water is sprayed into the exhaust gas passage 2a. A pulse-type metering pump is used for the urea water pump of the reducing agent supply unit, and the urea water supply amount can be adjusted by changing the number of pulses per minute. The a-system denitration apparatus 10 including the reducing agent spray nozzle 3a, the reducing agent supply unit 4a, and the denitration catalyst 5a is set as a denitration apparatus 10a.

  A sample tube 8a for extracting exhaust gas from the exhaust gas passage 2a is connected to the exhaust gas passage 2a downstream of the denitration catalyst 5a. The sample tube 8a is also connected to a NOx value measuring device 6 for measuring the NOx value in the combustion exhaust gas. Keep it. A sample valve 9a is provided in the middle of the sample pipe 8a, and by opening the sample valve 9a, a part of the combustion exhaust gas exhausted through the exhaust gas passage 2a is extracted and sent to the NOx value measuring device 6 to obtain the NOx value. The measurement device 6 measures the outlet NOx value in the exhaust gas passage 2a.

  In the case of the b system, the configuration is the same as that of the a system, and the combustion exhaust gas generated in the engine 1b is discharged through the exhaust gas passage 2b connected to the engine 1b. In the middle of the exhaust gas passage 2b, a reducing agent spray nozzle 3b and a denitration catalyst 5b are installed in order from the upstream side of the combustion exhaust gas flow. The reducing agent spray nozzle 3b has a tip installed in the exhaust gas passage 2b, and the other end is connected to a reducing agent supply unit 4b including a urea water pump and a urea water tank, and is supplied from the reducing agent supply unit 4b. The urea water is sprayed into the exhaust gas passage 2b. A pulse-type metering pump is used for the urea water pump of the reducing agent supply unit, and the urea water supply amount can be adjusted by changing the number of pulses per minute. The b-system denitration apparatus 10 including the reducing agent spray nozzle 3b, the reducing agent supply unit 4b, and the denitration catalyst 5b is set as a denitration apparatus 10b.

  A sample tube 8b for extracting exhaust gas from the exhaust gas passage 2b is connected to the exhaust gas passage 2b downstream of the denitration catalyst 5b, and the sample tube 8b is also connected to a NOx value measuring device 6 for measuring the NOx value in the combustion exhaust gas. Keep it. A sample valve 9b is provided in the middle of the sample pipe 8b, and by opening the sample valve 9b, a part of the combustion exhaust gas exhausted through the exhaust gas passage 2b is extracted and sent to the NOx value measuring device 6 to obtain the NOx value. The measuring device 6 measures the outlet NOx value in the exhaust gas passage 2b.

  Operation control of the denitration device 10a and the denitration device 10b is performed by the denitration control device 7. The denitration control device 7 is connected to the engine 1a, the engine 1b, the reducing agent supply unit 4a, the reducing agent supply unit 4b, the sample valve 9a, the sample valve 9b, and the NOx value measuring device 6. The denitration control device 7 captures information (engine output value) such as an engine load factor from the engine 1 a and the engine 1 b and also captures the NOx value measured by the NOx value measuring device 6.

  In the denitration control device 7, the urea water basic supply amount calculated from the engine load factor (engine output value) and the urea water supply amount correction value for increasing / decreasing from the basic supply amount calculated earlier based on the outlet NOx value are set. Determine and adjust the urea water supply. In the denitration control device 7, a basic supply amount calculation formula for calculating the basic supply amount of urea water and a correction value calculation formula for calculating a correction value based on the outlet NOx value measured by the NOx value measurement device 6 are set. Keep it. Further, the denitration control device 7 also performs opening / closing control of the sample valve 9a and the sample valve 9b.

The load factor of the engine and the amount of flue gas emission are in a substantially proportional relationship. When the NOx concentration in the flue gas is constant, the amount of flue gas and the amount of NOx are also proportional. Further, since the NOx amount and the urea water requirement amount are substantially proportional to each other, the urea water requirement amount increases proportionally as the engine load factor increases. Therefore, in order to keep the NOx concentration in the exhaust gas discharged to the atmosphere at a predetermined value, the engine output value is detected, and urea water for decomposing NOx is increased as the engine output value increases. That's fine.

  However, even if the engine output value is the same, the NOx value in the flue gas fluctuates due to changes in temperature and humidity due to seasonal changes. The urea supply amount control based on the basic supply amount calculation formula is effective when the NOx value is constant and only the combustion exhaust gas amount changes, but when the NOx value fluctuates, the urea water supply amount is controlled appropriately. Can not do it. For this reason, in the case of urea water supply with only the basic supply amount based on the engine output value, excess or deficiency occurs in the supply amount. When the urea water supply amount is insufficient, the amount of NOx discharged into the atmosphere increases, and when the urea water supply amount becomes excessive, ammonia components that could not be reacted are discharged into the atmosphere. Therefore, it is necessary to control the urea water supply amount to be appropriate.

  Therefore, correction for increasing or decreasing the urea water supply amount is performed based on the outlet NOx value measured by the NOx value measuring device 6. The correction value is calculated from the difference between the outlet NOx value measured by the NOx value measuring device 6 and the target value of the outlet NOx value set in advance. The correction value determines how many pulses of urea water are to be increased or decreased per minute from the basic supply amount, and supplies the urea water in an amount obtained by adding the correction value to the basic supply amount.

  FIG. 2 is an explanatory diagram that graphs how the urea water supply amount is determined from the basic supply amount obtained from the engine output value (%) and the correction value obtained from the outlet NOx value. The basic supply amount calculation formula can calculate the basic supply amount by multiplying the engine output value by a predetermined constant. For example, if the engine output value is X%, the basic supply amount is set to supply urea water of Y pulses / minute.

  The correction value can be obtained by a calculation formula of correction amount = coefficient × (exit NOx value−target value). When the outlet NOx value is larger than the target value, the NOx value is higher than the target value because the urea supply amount is smaller than the required amount. In this case, the correction value becomes a positive value, and the correction value becomes larger as the outlet NOx value becomes higher than the target value. When the correction value is positive, the urea water supply amount increases by adding the correction value calculated by the correction value calculation formula to the basic supply amount, and therefore the outlet NOx value decreases toward the target value. . Conversely, when the outlet NOx value is smaller than the target value, the NOx value is lower than the target value because the urea supply amount is larger than the required amount. In this case, the correction value becomes a negative value, and the correction value becomes larger in the minus direction as the exit NOx value becomes lower than the target value. When the correction value is negative, the urea water supply amount decreases by adding the correction value calculated by the correction value calculation formula to the basic supply amount, so the outlet NOx value increases toward the target value. .

  The coefficient of the correction value calculation formula is determined from the relationship between the urea water supply amount and the outlet NOx value. If the capacity of the engine 1 is large and the amount of combustion exhaust gas is large, even if the difference between the outlet NOx value and the target value is small, the amount of urea water that increases is large. Conversely, if the amount of combustion exhaust gas is small, even if the difference between the outlet NOx value and the target value is the same, the amount of urea water that increases is small. When the correction amount of the urea water supply amount has to be increased with respect to the difference between the outlet NOx value and the target value, the coefficient is set to a large value, and the urea water supply amount is corrected with respect to the difference between the outlet NOx value and the target value. When the quantity is small, the coefficient is set to a small value. This coefficient differs for each denitration device.

  For example, when the exit NOx value is substituted into the equation of correction amount = coefficient × (exit NOx value−target value), it is assumed that a value of correction value = + Z is obtained. As shown in FIG. 2, when the basic supply amount determined from the engine output value (X%) is Y pulses / minute and the correction value based on the outlet NOx value is + Z pulses / minute, the urea water supply amount is Since it is a value obtained by adding the correction value Z obtained from the outlet NOx value to the basic supply amount Y obtained from the engine output value, Y + Z pulses / minute. This means that the correction value is + because the outlet NOx value is higher than the target value at the present time. By decreasing the outlet NOx value by increasing the urea water supply amount, The exit NOx value is brought close to the target value.

  Next, a description will be given along the flowchart for determining the correction amount of the urea water supply amount shown in FIG. The correction amount is calculated based on the outlet NOx value. Since the exhaust gas passage 2 has two systems, the a system and the b system, and the NOx value measuring device 6 is one, the NOx value measuring device 6 alternates between the two systems. To measure. First, urea water supply control in the denitration apparatus 10a of the a system is performed by feedback control based on the outlet NOx value of the exhaust gas passage 2a. In this case, in step S1, the sample valve 9a is opened and the sample valve 9b is closed. When the sample valve 9a is opened and the sample valve 9b is closed, only the combustion exhaust gas flowing through the exhaust gas passage 2a is extracted and sent to the NOx value measuring device 6, so that the NOx value measured in step S2 is The exhaust gas passage 2a is used. In the next step S3, a correction value for the urea water supply amount is calculated. Since the outlet NOx value in the exhaust gas passage 2a is detected in the immediately preceding step S2, the correction value for the denitration device 10a is obtained by substituting the detected outlet NOx value into the correction value calculation formula. At this time, if the correction value is calculated by using the measured value of the outlet NOx value by the NOx value measuring device 6 as it is, the correction value is strongly affected when an abnormal value such as noise is generated. An average value is calculated, and the denitration control device 7 sets the average value as the outlet NOx value. Although the NOx value is detected by the NOx value measuring device 6 at short intervals such as every second, the NOx value handled by the denitration control device 7 is set to a relatively long time such as a moving average value for 5 minutes. deep.

  Further, the correction value is required not only for the denitration apparatus 10a but also for the denitration apparatus 10b. When the NOx value measuring device 6 detects the outlet NOx value of the exhaust gas passage 2a and does not measure the outlet NOx value of the exhaust gas passage 2b, the NOx value is removed by substituting the current outlet NOx value into the correction value calculation formula. The correction value of the device 10b cannot be calculated. In this case, the final value (final value of the moving average value) when the outlet NOx value in the exhaust gas passage 2b is being measured is stored and calculated from the final value. In this case, since the final value is fixed, the correction value is also fixed, and the correction value for the outlet NOx value cannot be calculated in real time. However, by appropriately switching the outlet NOx value by the NOx value measuring device 6, the urea water supply amount can be appropriately maintained even if the outlet NOx value is not measured.

  In the next step S4, it is determined whether or not the denitration apparatus that performs feedback control is switched from the a-system denitration apparatus 10a to the b-system denitration apparatus 10b. Switching is performed when all of the following conditions A to D are satisfied. Condition A: The time during which feedback control based on the outlet NOx value is performed is equal to or longer than the switching condition time. Condition B: The difference between the maximum value and the minimum value of the outlet NOx value in the immediately preceding predetermined time is less than the stability determination amplitude. Condition C: The average value of the outlet NOx values within the immediately preceding predetermined time is within the stability determination target range. Condition D: The reducing agent supply amount correction value calculated based on the outlet NOx value within the predetermined time immediately before is within the correction value range for stability determination.

  The following settings are made as specific switching conditions. Condition A: Feedback control based on the outlet NOx value of the exhaust gas passage 2a is continued for 30 minutes or more, or feedback control based on the outlet NOx value of the exhaust gas passage 2b is continued for 30 minutes or more. Condition B: The fluctuation range (the difference between the maximum value and the minimum value) of the outlet NOx value in the previous five minutes is smaller than the stability determination amplitude set to 30% with respect to the average value of the outlet NOx value during that period. Condition C: The average value of the outlet NOx values in the immediately preceding 5 minutes is within the target range for stability determination in the range of + 5% to -11% with respect to the target value. Condition D: The correction value for the last 5 minutes is within the correction value range for stability determination of the correction value average value for 5 minutes−maximum urea water supply pump value × 10% to the correction value average value + urea water supply pump × 10%. is there. If any one of these conditions is not satisfied, the process returns to step S1 without switching. In this case, the opening of the sample valve 9a and the closing of the sample valve 9b are continued, the outlet NOx value of the a system is measured in step S2, and the feedback control of the a system is performed.

  When the switching condition is satisfied in step S4, the process proceeds to step S5, and the control is switched to the feedback control in the b system. In step S5, contrary to step S1, the sample valve 9a is closed and the sample valve 9b is opened. When the sample valve 9a is closed and the sample valve 9b is opened, only the combustion exhaust gas flowing through the exhaust gas passage 2b is sent to the NOx value measuring device 6, so the NOx value measured in step S6 is the exhaust gas passage 2b. Will be. In the next step S7, a correction value for the urea water supply amount is calculated. In the calculation of the correction value, since the outlet NOx value of the exhaust gas passage 2b is detected in the immediately preceding step S6, in the calculation of the correction value for the denitration device b, the detected outlet NOx value (moving average value) is a correction value calculation formula. By substituting into, the correction value is obtained. Further, when calculating the correction value for the denitration apparatus a, the measurement of the outlet NOx value in the exhaust gas passage 2a is not performed in step S6, so the correction value is substituted with a fixed value. This fixed value is a value calculated from the final value by storing the final value when the outlet NOx value in the exhaust gas passage 2a is being measured. Since the final value does not change during feedback control on the other side, the correction value during this period is constant.

  In step S8, it is determined whether or not to switch the outlet NOx value measurement target from the exhaust gas passage 2b to the exhaust gas passage 2a. The switching condition is the same as in step S4. If any of these conditions is not satisfied, the process returns to step S5 without switching. If the switching condition is satisfied in step S8, the process proceeds to step S1, and feedback control is performed in the a system.

  FIG. 4 is a graph showing the results of tests performed to determine the validity of switching control. When the present invention is implemented, since the number of NOx value measuring devices 6 installed is smaller than that of the denitration device 10, a time when feedback control for calculating a correction value based on the outlet NOx value in real time cannot be performed occurs. If the outlet NOx value deviates significantly from the target value at a time when the feedback control cannot be performed, this control cannot be performed. Therefore, the outlet NOx value can be stabilized even when the feedback control is not performed. Check if you can. The graph of FIG. 4 shows the urea water supply amount calculation method in both ab systems, the changes in the outlet NOx value in the exhaust gas passage 2a, and the urea water supply amount in the denitration apparatus 10a. In actual control, at the time of feedback control in the system b, the outlet NOx value in the exhaust gas passage 2b is measured and the outlet NOx value in the exhaust gas passage 2a is not measured, but in this figure, the correction value is a fixed value. Since it is for evaluation in the case, the outlet NOx value of system a is described.

  The switching conditions in the present embodiment are as follows. Condition A: Feedback control based on the outlet NOx value of the exhaust gas passage 2a is continued for 30 minutes or more, or feedback control based on the outlet NOx value of the exhaust gas passage 2b is continued for 30 minutes or more. Condition B: The fluctuation range (the difference between the maximum value and the minimum value) of the outlet NOx value in the immediately preceding 5 minutes is smaller than the stability determination amplitude set to 30% of the average value of the outlet NOx value during that period. Condition C: The average value of the outlet NOx value in the immediately preceding 5 minutes is within the target range for stability determination in the range of + 5% to -11% with respect to the target value. Condition D: The correction value for the last 5 minutes is within the correction value range for the stability determination of the correction value average value for 5 minutes−the maximum value of urea water supply pump × 10% to the correction value average value + the maximum value of urea water supply pump × 10%. It is in.

In this embodiment, the target value of the outlet NOx value is set to 150 ppm (the NOx value is a value converted to O ₂ = 0%, and the same applies hereinafter), and the target range for stability determination in the range of + 5% to −11% is 133%. ˜158 ppm. The urea water supply pump has a maximum value of 360 pulses / min. In this case, the urea water supply pump maximum value × 10% and the −urea water supply pump maximum value × 10% are 36 pulses / minute, respectively. Min and -36 pulses / min.

  In this embodiment, the correction value for the a system is initially calculated based on the outlet NOx value, and the correction value for the b system is calculated from the final value when the outlet NOx value in the previous exhaust gas passage 2b was measured. The fixed value obtained is used. However, the description of the outlet NOx value and the urea water supply amount in the b system is omitted, and only the outlet NOx value and the urea water supply amount in the system a are described in the graph.

In the case of the present embodiment, the outlet NOx value is stable, but since the condition A is for 30 minutes, the denitration device 10a calculates a correction value based on the outlet NOx value of the exhaust gas passage 2a for 30 minutes. Feedback control to adjust the urea water supply amount. After that, since the switching condition is satisfied when 30 minutes have elapsed, the denitration apparatus that performs feedback control based on the outlet NOx value is switched from the denitration apparatus 10a to the denitration apparatus 10b. In this case, the time-related switching condition A is satisfied because 30 minutes have passed. Further, the maximum value of the outlet NOx value in the immediately preceding 5 minutes was 154 ppm, and the minimum value was 135 ppm. In this case, the difference is 19 ppm and the fluctuation range is 13%. Since 13% of the fluctuation range is smaller than the stability determination amplitude 30% of the condition B, the switching condition B regarding the fluctuation range of the outlet NOx value is satisfied.
The average value of the outlet NOx value in the last 5 minutes was 149 ppm. In this case, since the average value of the outlet NOx value is within the range of 133 to 158 ppm which is the target range for stability determination, the switching condition C regarding the average value of the outlet NOx value is satisfied. The correction value in the last 5 minutes was +108 to +110 pulses / minute, and the average value was 109 pulses / minute. Correction value average value−urea water supply pump maximum value × 10% ˜correction value average value + urea water supply pump maximum value × 10% The correction value range for stability determination is 73 to 145 pulses / min. The switching condition D regarding stability is satisfied.

  During the time axis from 0:30 to 1:00, the correction value calculation by the food back control is performed by the denitration apparatus b, and the correction value is set to a fixed value in the denitration apparatus a. In actual control, the NOx value in the exhaust gas passage 2b is measured in order to perform feedback control in the denitration device b during this period, but how the outlet NOx value changes when the correction value is fixed. In the graph, the outlet NOx value of the exhaust gas passage 2a is described. In this case, the feedback control of the correction value based on the outlet NOx value is not performed in the a system, and the correction value is a fixed value. Since the engine output is also constant at 100%, the basic supply amount is also constant. Accordingly, the urea water supply amount obtained by adding the basic supply amount and the correction amount does not change at all. However, it can be seen that there is no significant disturbance in the outlet NOx value of the exhaust gas passage 2a, and it is effective even if the correction value is fixed. However, if the period during which the feedback control is not performed becomes longer, the possibility that the outlet NOx value departs from the target value increases, and therefore switching is determined again after 30 minutes. In this case, it is confirmed whether the outlet NOx value in the exhaust gas passage 2b is stable. If the outlet NOx value in the exhaust gas passage 2b is stable, switching is performed, and feedback control in the a system is resumed.

  Conditions for switching the exhaust gas passage detected by the NOx value measuring device include that the outlet NOx value is stable within the target value and that the correction value is stable, resulting in fluctuations in the NOx value. If not, switching is not performed. If the outlet NOx value is not stable, the outlet NOx value may continue to fluctuate thereafter. Therefore, the control for measuring the outlet NOx value and determining the correction value is continued, and after the outlet NOx value is stabilized. Switch. The conditions B to D are all for determining the stability of the outlet NOx value, so the stability can be determined only from the conditions B to D under the condition 1 or 2. . Conversely, as the number of conditions increases, the stable time of the outlet NOx value can be determined with higher accuracy, so conditions other than conditions B to D may be added.

  Further, if the switching interval is set too short, the sample valve 9a and the sample valve 9b are frequently opened and closed, so that the consumption becomes severe. If the switching interval is set too long, the possibility that the outlet NOx value deviates from the target value increases. . For this reason, it is necessary to set a balanced value, and in this embodiment, 30 minutes is set as a balanced condition.

  FIG. 5 is a flowchart of a denitration apparatus in another embodiment. In FIG. 5, the engine 1a, the engine 1b, and the engine 1c are installed, and the control of the denitration device 10a, the denitration device 10b, and the denitration device 10c is based on the outlet NOx value measured by the common NOx value measurement device 6. Do. In this case as well, as in the previous embodiment, sample tubes 8 are connected to the exhaust gas passages 2, respectively, so that the NOx value measuring device 6 can sequentially measure the outlet NOx values of the exhaust gas passages 2. ing. The denitration apparatus shown in FIG. 5 differs from the denitration apparatus of FIG. 1 in that it has three systems, but the concept is the same. The outlet NOx value of each exhaust gas passage 2 is measured by opening and closing the sample valve 9a, the sample valve 9b, and the sample valve 9c provided in each sample pipe 8 in order. For the denitration device 10 in the exhaust gas passage 2 being measured, a correction value is calculated from the measured NOx value, and for the other denitration devices 10, a correction value is calculated from the previous final value.

DESCRIPTION OF SYMBOLS 1 Engine 2 Exhaust gas passage 3 Reductant spray nozzle 4 Reductant supply unit 5 Denitration catalyst 6 NOx value measuring device 7 Denitration control device 8 Sample pipe 9 Sample valve 10 Denitration device

Claims (2)

A plurality of installed denitration devices in which a plurality of devices for generating combustion exhaust gas such as an engine are installed, and NOx in the combustion exhaust gas is decomposed by providing a denitration device in each of the multiple exhaust gas flow paths, each exhaust gas passage One end of the sample tube is connected to the downstream portion of the denitration device in FIG. 1, and the other end of the sample tube is connected to a common NOx value measuring device, and the NOx value measuring device detects the outlet NOx value in each exhaust gas passage. In the denitration device provided in each exhaust gas passage, when the NOx value measuring device measures the outlet NOx value of the exhaust gas passage, the reduction is performed based on the measured outlet NOx value. If the NOx value measuring device is not measuring the outlet NOx value of the exhaust gas passage, the NOx value measuring device adjusts the exhaust gas supply amount. The outlet NOx value at the time when the outlet NOx value was measured was stored as the previous final value, the reducing agent supply amount was adjusted based on the previous final value, and the exhaust gas passage for measuring the outlet NOx value The switching of the exhaust gas passage for measuring the NOx value is performed when the condition that the switching condition time has passed since the previous switching and the outlet NOx value is stable is satisfied. Denitration equipment with multiple installations. In the multiple NOx removal apparatus according to claim 1, that the outlet NOx value is stable means that the difference between the maximum value and the minimum value of the outlet NOx value in the immediately preceding predetermined time is less than the stability determination amplitude. Either the average value of the outlet NOx value within the predetermined time is within the target range for stability determination, the reducing agent supply amount correction value calculated based on the outlet NOx value within the predetermined time immediately before is within the correction value for stability determination, or A denitration apparatus of a plurality of installations characterized in that a plurality of conditions are satisfied.

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