# Patent

## Title
NOx removal catalyst management unit for NOx removal apparatus and method for managing NOx removal catalyst

## Abstract

To provide an NOx removal catalyst management unit for use with an NOx removal apparatus, the management unit detecting an NOx removal catalyst layer that is actually deteriorated, whereby the deteriorated catalyst layer can be effectively replaced by a new catalyst layer, and to provide a method for managing the NOx removal catalyst. The management unit for managing a plurality of NOx removal catalyst layers provided in a flue gas NOx removal apparatus includes NOx measurement means 16A through 16E for determining NOx concentrations on the inlet and outlet sides of respective NOx removal catalyst layers 14A through 14D; NH3 measurement means 17A through 17E for determining NH3 concentrations on the inlet and outlet sides of the same NOx removal catalyst layers; and percent NOx removal determination means 18 for determining percent NOx removal (η) on the basis of an inlet mole ratio (i.e., inlet NH3/inlet NOx).

## Background
TECHNICAL FIELD
The present invention relates to an NOx removal catalyst management unit for use with an NOx removal apparatus, the management unit being provided for carrying out performance management on an NOx removal catalyst included in a flue gas NOx removal apparatus installed in a facility such as a thermal power station, and to a method for managing the NOx removal catalyst.
BACKGROUND ART
Conventionally, boilers provided in thermal power stations and a variety of large-scale boilers employing a fuel such as petroleum, coal, or fuel gas, waste incinerators, and similar apparatuses have been equipped with a flue gas NOx removal apparatus which contains a plurality of NOx removal catalyst layers.
The above employed NOx removal catalysts assume the form of honeycomb, plate, etc. During use, the catalytic performance of the catalysts is problematically deteriorated with elapse of time as a result of deposition, on the surface of the catalyst, of a substance which deteriorates the catalytic performance (hereinafter referred to as deteriorating substance) or through migration of the dissolved deteriorating substance into the catalyst.
Conventionally, the performance of the NOx removal catalysts has been managed by measuring NOx concentration and unreacted NH3 concentration on the inlet and outlet sides of respective catalysts. When a drop in total performance of a catalyst system is confirmed, old catalysts are replaced with new catalysts or regenerated catalysts in order of use age, and such replacement is carried out periodically.
Generally, NOx removal catalysts are very expensive. Thus, there has been proposed one approach for prolonging the service life of the NOx removal catalysts to as long a duration as possible by assessing the performance of each unit catalyst (Japanese Patent Publication (kokoku) No. 7-47108).
However, the aforementioned catalyst managing method has a drawback. According to the method, NOx concentration and unreacted NH3 concentration of each catalyst layer are determined, and percent NOx removal and percent contribution of each catalyst layer are calculated from the determined NOx concentration. On the basis of these values, performance-deteriorated catalysts are replaced with new catalysts in order of degree of deterioration. In this case, when the catalytic performance is evaluated by the percent contribution calculated on the basis of the NOx concentration, the catalyst layer(s) having actually deteriorated performance cannot be detected correctly.
In view of the foregoing, an object of the present invention is to provide an NOx removal catalyst management unit for use with an NOx removal apparatus, the management unit detecting an NOx removal catalyst layer that is actually deteriorated, whereby the deteriorated NOx removal catalyst layer can be effectively replaced by a new catalyst layer. Another object of the invention is to provide a method for managing the NOx removal catalyst.
DISCLOSURE OF THE INVENTION
In order to attain the aforementioned objects, a first mode of the present invention provides an NOx removal catalyst management unit for use with an NOx removal apparatus, the management unit being provided for managing a plurality of NOx removal catalyst layers provided in a flue gas NOx removal apparatus, characterized in that the management unit comprises NOx measurement means for determining NOx concentrations on the inlet and outlet sides of respective NOx removal catalyst layers; NH3 measurement means for determining NH3 concentrations on the inlet and outlet sides of the same NOx removal catalyst layers; and percent NOx removal determination means for determining percent NOx removal (η) on the basis of an inlet mole ratio (i.e., inlet NH3/inlet NOx).
According to the first mode, NOx concentrations and NH3 concentrations are determined on the inlet and outlet sides of respective NOx removal catalyst layers, and the percent NOx removal (η) is determined on the basis of an inlet mole ratio. Therefore, the percent NOx removal, which is enhanced as the mole ratio increases, can be evaluated on an absolute basis and correctly.
A second mode of the present invention is drawn to a specific embodiment of the NOx removal catalyst management unit of the first mode for use with an NOx removal apparatus, wherein the percent NOx removal (η) is determined on the basis of NH3 concentrations.
According to the second mode, the percent NOx removal (η) of each and every NOx removal catalyst layer is determined on the basis of NH3 concentrations rather than on the basis of NOx concentrations. Therefore, the catalytic performance can be detected with smaller variation.
A third mode of the present invention is drawn to a specific embodiment of the NOx removal catalyst management unit of the second mode for use with an NOx removal apparatus, wherein the percent NOx removal (η) is determined on the basis of the following equation (1):

η={(inlet NH3−outlet NH3)/(inlet NH3−outlet NH3+outlet NOx)}×100×(evaluation mole ratio/inlet mole ratio)  (1).

According to the third mode, the percent NOx removal (η) of respective NOx removal catalyst layers can be detected without variation and correctly, thereby managing respective NOx removal catalysts successfully and effectively.
A fourth mode of the present invention is drawn to a specific embodiment of the NOx removal catalyst management unit of any of the first to third modes for use with an NOx removal apparatus, which management unit further includes transmission means for transmitting concentration values determined by the NOx measurement means and the NH3 measurement means to the percent NOx removal determination means, wherein the percent NOx removal determination means determines the percent NOx removal (η) of respective NOx removal catalyst layers included in a plurality of flue gas NOx removal apparatuses.
According to the fourth mode, NOx removal catalysts included in a plurality of flue gas NOx removal apparatuses can be collectively managed, thereby effectively managing NOx removal catalysts.
A fifth mode of the present invention provides a method for managing an NOx removal catalyst for use with an NOx removal apparatus, the method being provided for managing a plurality of NOx removal catalyst layers provided in a flue gas NOx removal apparatus, characterized in that the method comprises determining NOx concentrations and NH3 concentrations on the inlet and outlet sides of respective NOx removal catalyst layers; determining percent NOx removal (η) on the basis of an inlet mole ratio (i.e., inlet NH3/inlet NOx); and evaluating performance of respective NOx removal catalyst layers on the basis of the percent NOx removal (η).
According to the fifth mode, NOx concentrations and NH3 concentrations are determined on the inlet and outlet sides of respective NOx removal catalyst layers, and the percent NOx removal (η) is determined on the basis of an inlet mole ratio. Therefore, the percent NOx removal, which is enhanced as the mole ratio increases, can be evaluated on an absolute basis and correctly.
A sixth mode of the present invention is drawn to a specific embodiment of the method for managing an NOx removal catalyst of the fifth mode for use with an NOx removal apparatus, wherein the percent NOx removal (η) is determined on the basis of NH3 concentrations.
According to the sixth mode, the percent NOx removal (η) of respective NOx removal catalyst layers is determined on the basis of NH3 concentrations rather than on the basis of NOx concentrations. Therefore, the catalytic performance can be detected without variation.
A seventh mode of the present invention is drawn to a specific embodiment of the method for managing an NOx removal catalyst of the sixth mode for use with an NOx removal apparatus, wherein the percent NOx removal (η) is determined on the basis of the following equation (1):

η={(inlet NH3−outlet NH3)/(inlet NH3−outlet NH3+outlet NOx)}×100×(evaluation mole ratio/inlet mole ratio)  (1).

According to the seventh mode, the percent NOx removal of each NOx removal catalyst layer can be detected without variation and correctly, thereby managing respective NOx removal catalysts successfully and effectively.
An eighth mode of the present invention is drawn to a specific embodiment of the method for managing an NOx removal catalyst of any of the fifth to seventh modes for use with an NOx removal apparatus, wherein the method further comprises performing restoration treatment of an NOx removal catalyst layer having a catalytic performance deteriorated to a predetermined level, on the basis of results of performance evaluation of the respective NOx removal catalyst layers.
According to the eighth mode, the percent NOx removal of each NOx removal catalyst layer is determined without variation and correctly, and the performance restoration treatment is carried out on the basis of the results. Thus, respective NOx removal catalysts can be effectively used.
A ninth mode of the present invention is drawn to a specific embodiment of the method for managing an NOx removal catalyst of the eighth mode for use with an NOx removal apparatus, wherein the performance restoration treatment is replacement of the NOx removal catalyst layer with a new NOx removal catalyst layer, replacement of the NOx removal catalyst layer with a regenerated NOx removal catalyst layer, replacement of the NOx removal catalyst layer with an NOx removal catalyst layer inverted with respect to the direction of the flow of discharge gas, or replacement of the NOx removal catalyst layer with an NOx removal catalyst layer from which a deteriorated portion has been removed.
According to the ninth mode, the performance of deteriorated NOx removal catalysts can be restored through any of the above treatments.
A tenth mode of the present invention is drawn to a specific embodiment of the method for managing an NOx removal catalyst of any of the fifth to ninth modes for use with an NOx removal apparatus, wherein the method further comprises determining the percent NOx removal of respective NOx removal catalyst layers included in a plurality of flue gas NOx removal apparatuses and evaluating catalytic performance of respective NOx removal catalyst layers included in a plurality of flue gas NOx removal apparatuses.
According to the tenth mode, NOx removal catalysts included in a plurality of flue gas NOx removal apparatuses can be collectively managed, thereby effectively managing NOx removal catalysts.
As described hereinabove, the present invention employs an NOx removal catalyst management unit for use with an NOx removal apparatus, which management unit comprises NOx measurement means for determining NOx concentrations on the inlet and outlet sides of respective NOx removal catalyst layers; NH3 measurement means for determining NH3 concentrations on the inlet and outlet sides of the same NOx removal catalyst layers; and percent NOx removal determination means for determining percent NOx removal (η) on the basis of an inlet mole ratio (i.e., inlet NH3/inlet NOx). Therefore, the management unit detects an NOx removal catalyst layer that is actually deteriorated, whereby the deteriorated catalyst layer can be effectively replaced by a new catalyst layer.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 schematically shows a configuration of a flue gas NOx removal apparatus equipped with an NOx removal catalyst management unit according to an embodiment of the present invention.



BEST MODES FOR CARRYING OUT THE INVENTION
FIG. 1 schematically shows a configuration of a flue gas NOx removal apparatus equipped with an NOx removal catalyst management unit according to an embodiment of the present invention. Actually, the flue gas NOx removal apparatus is provided in a thermal power station. However, no particular limitation is imposed on the facility that includes the NOx removal catalyst management unit of the embodiment.
As shown in FIG. 1, a flue gas NOx removal apparatus 10 includes an exhaust duct 12 and a treated gas duct 13. The exhaust duct 12 is in communication with a boiler unit installed in a thermal power station that is connected with an apparatus body 11 on the upstream side. The treated gas duct 13 is connected with the apparatus body 11 on the downstream side. In the apparatus body 11, a plurality of NOx removal catalyst layers (4 layers in this embodiment) 14A to 14D are disposed at predetermined intervals. The NOx removal catalyst layers 14A to 14D are arranged so that a discharge gas introduced through the exhaust duct 12 is sequentially passed therethrough, and reduce the level of nitrogen oxide (NOx) of the discharge gas through contact with the discharge gas passing through the catalyst layers. Notably, to the exhaust duct 12 communicating with the boiler unit, NH3 is injected in an amount in accordance with the amount of the discharge gas fed from the boiler body.
No particular limitation is imposed on the type, shape, etc. of the catalysts 14A to 14D. Generally, each catalyst is composed of TiO2 serving as a carrier and V2O5 serving as an active component. The catalysts assume the form of honeycomb, plate, etc.
In the present embodiment, each catalyst layer employs a catalyst in the form of columnar honeycomb, and a plurality of catalyst layers are arranged in combination, thereby forming the catalyst layers 14A to 14D.
An NOx removal catalyst management unit 20 of the present embodiment is provided with gas sampling means 15A through 15E on the inlet and outlet sides of respective NOx removal catalyst layers 14A through 14D. The gas sampling means 15A through 15E are connected with NOx concentration measurement means 16A through 16E and with NH3 concentration measurement means 17A through 17E. The data obtained by the measurement means are transferred to a percent NOx removal determination means 18 for calculating percent NOx removal and percent NOx removal contribution of the respective NOx removal catalyst layers 14A through 14D.
The gas sampling means 15A through 15E sample, via sampling tubes, a gas to be sampled in a desired amount and at a desired timing, and subsequently feed the sampled gas to the NOx concentration measurement means 16A through 16E and to the NH3 concentration measurement means 17A through 17E. Notably, the sampling tubes and similar parts which are in contact with a gas to be sampled are required to be made of a material which has a predetermined heat resistance and which is inert to the corresponding gas. In the present embodiment, the gas sampling means 15A through 15E feed the sampled gas to the NOx concentration measurement means 16A through 16E and to the NH3 concentration measurement means 17A through 17E. However, needless to say, each of the NOx concentration measurement means 16A through 16E and the NH3 concentration measurement means 17A through 17E may be provided with gas sampling means.
No particular limitation is imposed on the timing for sampling a gas by the gas sampling means 15A through 15E. Generally, sampling is carried out during usual operation of the power station, preferably at the nominal load where the amount of gas reaches the maximum, if possible. The interval between sampling operations may be prolonged to about six months, and the interval is sufficient for managing the performance of the NOx removal catalyst layers 14A through 14D. However, if the interval is shortened, precision in management is enhanced. Thus, the sampling is preferably carried out, for example, once every one to two months. Particularly, in a catalyst layer placed on the downstream side, variation of obtained data increases due to decrease in NH3 concentration. Thus, in order to attain better management and evaluation, preferably, determination of NH3 concentration is performed at short intervals, and percent NOx removal is calculated from an averaged NH3 concentration value.
No particular limitation is imposed on the NOx concentration measurement means 16A through 16E and the NH3 concentration measurement means 17A through 17E, so long as the measurement means can determine the NOx concentration measurement and the NH3 concentration of the sample gas. Although an automated measuring apparatus is preferred, manual analysis means may also be employed. Needless to say, the NOx concentration and the NH3 concentration may be directly determined by means of a sensor without sampling the gas.
As described above, the NOx concentration and the NH3 concentration of the sampled gas are determined. In addition, oxygen or other components may also be determined, if required.
According to the present embodiment, NOx measurement means and NH3 measurement means are provided on the inlet and outlet sides of respective NOx removal catalyst layers 14A through 14D. Alternatively, a single NOx concentration measurement means and a single NH3 concentration measurement means are provided, and NOx concentrations and NH3 concentrations on the inlet and outlet sides of respective NOx removal catalyst layers 14A through 14D may be analyzed sequentially. In this case, sampling of gas may be performed sequentially in accordance with measurement. Although time lags occur during sampling, they would not be any problem so long as the NOx removal operation proceeds consistently. However, it is preferred that sampling be simultaneously performed and the sampled gases be sequentially fed to the corresponding measurement means for analysis.
The percent NOx removal determination means 18 collects the measurement data from the NOx concentration measurement means 16A through 16E and the NH3 concentration measurement means 17A through 17E, and calculates, from the measurement data, percent NOx removal and percent NOx removal contribution of respective NOx removal catalyst layers 14A through 14D. No particular limitation is imposed on the method of calculating percent NOx removal, and any method may be employed so long as the percent NOx removal is calculated on the basis of an inlet mole ratio (i.e., inlet NH3/inlet NOx) of the NOx removal catalyst layers 14A through 14D.
The reason for taking the inlet mole ratio into consideration is as follows. NH3 is fed into an NOx removal apparatus in the vicinity of NOx removal catalysts on the upstream side in an amount proportional to that of the gas to be treated. The rate determining step of NOx removal reaction is a step of adsorbing NH3 onto the catalysts. Therefore, it is most critical to detect NH3 concentrations on the inlet and outlet sides of the NOx removal catalyst layers 14A through 14D upon management of the performance of the NOx removal catalyst layers 14A through 14D on the basis of NH3 concentrations.
When calculated on the basis of an inlet mole ratio, the percent NOx removal may be calculated from NOx concentration or NH3 concentration. However, NH3-basis calculation provides percent NOx removal values of higher precision suitable for management.
An exemplary procedure of deriving percent NOx removal will next be described. The percent NOx removal (η) is determined on the basis of the following equation (2) employing NOx concentrations:

η={(inlet NOx−outlet NOx)/(inlet NOx)}×100×(evaluation mole ratio/inlet mole ratio)  (2).

As used herein, the term “evaluation mole ratio” refers to a mole ratio which is predetermined for the purpose of evaluating an NOx removal catalyst. The evaluation mole ratio may be predetermined to an arbitrary value; for example, 0.8, which is almost equal to a mole ratio typically employed for operating a power station.
Although the percent NOx removal (η) is determined on the basis of the equation employing NOx concentrations, target catalysts can be evaluated on the basis of a percent NOx removal value actually reflecting the conditions of a catalyst, since the equation employs an inlet mole ratio. In general, since the percent NOx removal increases with NH3/NOx, the percent NOx removal must be derived on the basis of the inlet mole ratio so as to evaluate catalysts in an actual state.
The percent NOx removal (η) is also determined on the basis of the following equation (1) employing NH3 concentrations:

η={(inlet NH3−outlet NH3)/(inlet NH3−outlet NH3+outlet NOx)}×100×(evaluation mole ratio/inlet mole ratio)  (1).

Since the percent NOx removal (η) is determined on the basis of the equation employing NH3 concentrations, variation in the obtained percent NOx removal values is smaller as compared with the case in which the equation employing NOx concentrations is used, which is advantageous. Thus, catalysts can be evaluated on the basis of percent removal values with smaller variation.
According to the present invention, percent NOx removal (η) of respective NOx removal catalyst layers 14A through 14D is determined through a technique on the basis of the inlet mole ratio, and the performance of the catalysts is managed on the basis of the determined percent NOx removal values. Specifically, when the percent NOx removal of a certain catalyst drops below a predetermined level, the catalyst having deteriorated performance undergoes performance restoration treatment. According to the invention, a catalyst which has been most deteriorated or a catalyst having a lowered percent NOx removal value below a predetermined level is exclusively subjected to performance restoration treatment. Therefore, NOx removal catalysts can be effectively used without performing unnecessary restoration treatment.
As used herein, the term “performance restoration treatment” generally refers to replacement of deteriorated catalysts with new catalysts, replacement of deteriorated catalysts with catalysts which have been regenerated by washing, or replacement of deteriorated catalysts with catalysts which have undergone regeneration treatment. Particularly when a honeycomb catalyst is used, a regenerated or un-regenerated NOx removal catalyst is placed such that the catalyst is inverted with respect to the direction of the flow of discharge gas, or a deteriorated NOx removal is replaced with a new NOx removal catalyst from which a deteriorated portion has been removed, whereby performance of the catalyst is restored. Notably, such restoration treatments are conceived on the basis of the finding of the present applicant that the upstream side of the discharge gas flow exclusively plays a great role in NOx removal reaction.
In the aforementioned embodiment, NOx removal catalysts of one flue gas NOx removal apparatus are managed by means of a single NOx removal catalyst management unit. Alternatively, NOx removal catalysts of a plurality of flue gas NOx removal apparatuses may also be managed by means of a single NOx removal catalyst management unit. Specifically, the percent NOx removal data obtained by the percent NOx removal determination means 18 may be transmitted in a wired or wireless manner to a central control system, whereby the percent NOx removal data are collectively controlled. Alternatively, concentration data obtained by NOx concentration measurement means 16A to 16E and NH3 concentration measurement date 17A to 17E may be transmitted to a central control system, whereby the percent NOx removal data are collectively controlled. In any case, total performance evaluation of catalysts can be performed through collective management of a plurality of flue gas NOx removal apparatuses, thereby reliably attaining total management and effective performance management of NOx removal catalysts.
WORKING EXAMPLE
Table 1 shows the results of NOx concentration measurement and NH3 concentration measurement on the inlet and outlet sides of four respective NOx removal catalyst layers (similar to FIG. 1) of a flue gas NOx removal apparatus installed in an actual thermal power station. The measurement was carried out seven times: 1st (starting), 2nd (about 2 months after starting), 3rd (about 5 months after starting), 4th (about 7 months after starting), 5th (about 12 months after starting), 6th (about 24 months after starting), and 7th (about 30 months after starting).
As mentioned above, percent NOx removal on the basis of NOx concentration of each catalyst layer was calculated from measured NOx concentrations and NH3 concentrations, and the results are shown in Table 2. Percent NOx removal on the basis of NH3 concentrations of each catalyst layer was calculated in a similar manner, and the results are shown in Table 3.
Measurement was also performed with respect to the case where a portion of the second NOx removal catalyst layer had been replaced with a regenerated catalyst (regenerated by washing with water; having catalytic performance equivalent to that of an unused product, confirmed by a performance test). In a similar manner, NOx concentration and NH3 concentration were measured on the inlet and outlet sides of the replaced portion of the second catalyst layer. The results are also shown in Table 1. In addition, percent NOx removal on the basis of NOx concentration of each catalyst layer was calculated from measured NOx concentrations and NH3 concentrations, and percent NOx removal on the basis of NH3 concentrations of each catalyst layer was calculated in a similar manner. The results are shown in Tables 2 and 3, respectively.
COMPARATIVE EXAMPLE
Percent NOx removal and percent NOx removal contribution of each catalyst layer were calculated on the basis of the following equation (3):

η={(inlet NOx−outlet NOx)/(inlet NOx)}×100  (3),

from NOx concentrations measured on the inlet and outlet sides of the catalyst layer in the Working Example. Table 4 shows the results. This technique is based on the method disclosed in Japanese Patent Publication (kokoku) No. 7-47108.

















TABLE 1









2nd
3rd
4th
5th 12
6th 24
7th 30




1st
2 months
5 months
7 months
months
months
months



Measurement
starting
after
after
after
after
after
after
























NOx
1st layer
148.7
166.6
208.3
228.1
221.6
166.7
175.9


concentration
inlet


(ppm)
2nd layer
65
72.3
85.7
111.4
94.4
78.8
78.9



inlet



3rd layer
44.6
46.4
44.7
51.8
48.6
47.6
44.0



inlet



4th layer
42.4
44.9
41.1
48.8
45.6
45.4
40.2



inlet



4th layer
39.4
39.4
36.9
44.2
43.3
42.3
38.0



outlet


Ammonia
1st layer
106.3
110.4
151.2
146.8
147.0
117.3
139.1


concentration
inlet


NH3 (ppm)
2nd layer
23.9
25.9
31.8
36.2
46.1
28.9
37.0



inlet



3rd layer
3
4
2.8
2.9
6.9
4.0
5.0



inlet



4th layer
3.2
2.2
2.3
1.8
5.4
3.0
2.0



inlet



4th layer
0.7
1.8
0.7
0.5
1.7
0.5
0.8



outlet


Regenerated
2nd layer
66.2
72.1
75.9
92.8
85.9
81.3
75.2


layer (2nd
inlet


layer) NOx
2nd layer
46.4
47.7
50.3
58.0
55.2
56.9
46.8


concentration
outlet


Ammonia
2nd layer
24.1
27.8
29.5
36.4
39.9
28.4
41.9


concentration
inlet


NH3 (ppm)
2nd layer
6.8
9.2
9.1
11.2
16.1
10.4
10.5



outlet

























TABLE 2









2nd
3rd
4th
5th 12
6th 24
7th 30




1st
2 months
5 months
7 months
months
months
months



Measurement
starting
after
after
after
after
after
after
























Reduced to
1st layer
63.0%
68.3%
64.9%
63.6%
69.2%
59.9%
55.8%


mole ratio
2nd layer
68.3%
80.0%
103.3%
131.8%
79.6%
86.5%
75.5%


0.8
3rd layer
58.7%
30.0%
101.6%
81.5%
34.9%
42.7%
60.2%


NOx
4th layer
75.0%
200.0%
147.6%
201.2%
33.1%
82.7%
90.9%


Regenerated
NOx
65.7%
70.4%
69.3%
76.5%
61.5%
68.9%
54.3%


layer


(2nd layer)

























TABLE 3









2nd
3rd
4th
5th 12
6th 24
7th 30




1st
2 months
5 months
7 months
months
months
months



Measurement
starting
after
after
after
after
after
after
























Reduced to
1st layer
62.6%
65.1%
64.2%
61.9%
62.3%
60.1%
57.1%


mole ratio
2nd layer
69.4%
71.6%
84.9%
96.3%
73.2%
75.1%
71.8%


0.8
3rd layer
−5.6%
35.8%
15.7%
31.9%
18.1%
19.6%
49.7%


NH3
4th layer
63.2%
16.4%
60.9%
63.6%
53.6%
66.5%
48.1%


Regenerated
NH3
59.6%
58.2%
59.4%
61.8%
51.9%
55.1%
57.7%


layer


(2nd layer)

























TABLE 4









2nd
3rd
4th
5th 12
6th 24
7th 30




1st
2 months
5 months
7 months
months
months
months



Measurement
starting
after
after
after
after
after
after























Total percent NOx
73.5%
76.4%
82.3%
80.6%
80.4%
74.6%
78.4%


removal















Percent
1st layer
76.6%
74.1%
71.5%
63.4%
71.3%
70.7%
70.3%


contribution
2nd layer
18.7%
20.4%
23.9%
32.4%
25.7%
25.1%
25.3%



3rd layer
2.0%
1.2%
2.1%
1.6%
1.7%
1.7%
2.7%



4th layer
2.7%
4.3%
2.5%
2.5%
1.2%
2.5%
1.6%



Total
100.0%
100.0%
100.0%
100.0%
100.0%
100.0%
100.0%









<Performance Evaluation>

As is clear from Tables 1 to 4, percent NOx removal values of the third layer and the fourth layer calculated on the basis of only NOx concentrations (Comparative Example) are very small from the first measurement. The Test Example mentioned below has revealed that these small values do not reflect the actual states of the catalyst layers.
In contrast, according to the method of the Working Example employing mole ratios (NH3/NOx) (inlet mole ratio and evaluation mole ratio), percent NOx removal values on the basis of NH3 concentrations and those on the basis of NOx concentrations were found to assess the actual states of the catalyst layers.
Through statistical processing of the data shown in Tables 2 and 3 of the Working Example so as to determine variation in a specific data set, percent NOx removal values calculated on the basis of NH3 concentrations were found to have less variation. This was confirmed through the following procedure.
In the Working Example, since the evaluation mole ratio was set to 0.8, the theoretical percent NOx removal was 0 to 80% on the basis of the evaluation mole ratio. The incident of the values falling outside the above range was counted in Tables 2 and 3. Table 5 shows the results.
A simple average was calculated for percent NOx removal values obtained from the first measurement to seventh measurement shown in Tables 2 and 3, and the incident of the simple average values exceeding the theoretical percent NOx removal was counted. The results are shown in Table 6.
From the data in Tables 2 and 3, unbiased variance in percent NOx removal of each catalyst layer was calculated, and the obtained variance values were averaged. The percent NOx removal values falling outside the theoretical range were removed from the data shown in Tables 2 and 3, and approximate equations were derived from the remaining data through the least squares method. Pearson's product-moment correlation coefficients of the equations (r), r2 (RSQ), and averaged values thereof were calculated. Table 7 shows the results.










TABLE 5









Outside the




theoretical range











Catalyst layers
NH3
NOx















1st layer
0
0



2nd layer
2
3



3rd layer
1
2



4th layer
0
5



2nd layer
0
0



(regenerated)





Total
3
10




















TABLE 6









Average












Catalyst layers
NH3
NOx







1st layer
61.9%
 63.5%



2nd layer
77.5%
 89.3%



3rd layer
23.6%
 58.5%



4th layer
53.2%
118.6%



2nd layer
57.7%
 66.7%



(regenerated)



Outside the
0
2



theoretical range




















TABLE 7









r2 (RSQ)/least














Catalyst
Variance

squares method














layers
NH3
NOx
NH3
NOx

















1st layer
0.0007
0.0022
0.812
0.537



2nd layer
0.0094
0.0470
0.034
0.028



3rd layer
0.0310
0.0668
0.302
0.027



4th layer
0.0304
0.4260
0.031
0.168



2nd layer
0.0011
0.0050
0.167
0.351



(regenerated)



Average
0.0145
0.1094
0.269
0.222










As is clear from Table 5, the incident of values falling outside the theoretical percent NOx removal range is larger in NOx than in NH3.
As is clear from Table 6, the incident of simple average values falling outside the theoretical percent NOx removal range is larger in NOx than in NH3.
As is clear from Table 7, variance in NOx-based percent NOx removal values is larger than variance in NH3-based percent NOx removal values. From Table 7, the averaged RSQ in relation to the least squares method is greater in the case of NH3 than in the case of NOx, indicating that NH3-based percent NOx removal values have high correlation. In the cases of the fourth layer and the regenerated second layer, RSQ values are lower in the case of NH3 than in the case of NOx. However, these values were obtained at unsatisfactory measurement precision, and the averaged correlation value is higher in the case of NH3. Therefore, NH3-basis data are concluded to have less variance.
As is clear from Tables 5 to 7, time-dependent change in percent NOx removal of each NOx removal catalyst layer is smaller in the case of NH3-concentration-basis percent NOx removal values than in the case of NOx-concentration-basis percent NOx removal values.
From the NH3-concentration-basis percent NOx removal values shown in Table 3, the percent NOx removal values falling outside the theoretical range were removed, and approximate equations were derived from the data falling within the theoretical range through the least squares method. On the basis of these approximate equations, percent NOx removal of each catalyst layer (12 months after the start of measurement) was calculated. Table 8 shows the results.










TABLE 8







Catalyst layers
5th (after 12 months)









1st layer
62%



2nd layer
74%



3rd layer
28%



4th layer
60%



2nd layer (regenerated)
58%










As is clear from Table 8, the most deteriorated NOx removal catalyst layer is estimated to be the third layer. At the fifth point in time of measurement, the degree of deterioration has been found to be in the sequence of the third layer, the regenerated second layer, the fourth and the first layers (approximately equal to each other), and the second layer.
In contrast, the results of the Comparative Example appear to indicate that the percent contribution of the first layer decreased and that of the second layer increased, thereby maintaining the performance of the NOx removal apparatus. That is, the first layer is concluded to be deteriorated.
TEST EXAMPLE
A portion of each of the catalyst layers employed in the Working Example was sampled, and the sample was evaluated in performance through the following method.
A portion (50 mm×50 mm×100 mm in length) was cut from the inlet side of the each NOx removal catalyst layer, and set in a performance test machine. The test gas was fed under the conditions which match the design values of an actual NOx removal apparatus, and percent NOx removal was determined by measuring NOx concentration and NH3 concentration on the outlet side of the catalyst sample. The results are shown in Table 9.
The results indicate a certain degree of deterioration of catalyst layers, and are almost identical to the aforementioned deterioration evaluation results.
As is clear from the above results, performance evaluation of NOx removal catalysts carried out in the Working Example reflects actual deterioration status; however, performance evaluation carried out in the Comparative Example does not coincide with actual performance evaluation.












TABLE 9





Catalyst
1st
2nd
3rd
4th
2nd layer


layers
layer
layer
layer
layer
(regenerated)




















Percent NOx
78.5%
80.2%
69.1%
79.4%
77.7%


removal


Order of
3
5
1
4
2


deterioration

## Claims

1. A NOx removal catalyst management unit comprising:
a NOx measurement means for determining NOx concentrations on the inlet and outlet sides of respective NOx removal catalyst layers;
a NH3 measurement means for determining NH3 concentrations on the inlet and outlet sides of the same NOx removal catalyst layers; and
a percent NOx removal determination means for determining percent NOx removal (η) on the basis of an inlet mole ratio (i.e., inlet NH3/inlet NOx), which percent NOx removal (η) is determined on the basis of the following equation (1):





  
    
      
        η
        =
        
          
            (
            
              
                (
                
                  
                    inlet
                    ⁢
                    
                      
                    
                    ⁢
                    
                      NH
                      3
                    
                  
                  -
                  
                    outlet
                    ⁢
                    
                      
                        
                      
                      ⁢
                      
                        
                      
                    
                    ⁢
                    
                      NH
                      3
                    
                  
                
                )
              
              
                (
                
                  
                    inlet
                    ⁢
                    
                      
                        
                      
                      ⁢
                      
                        
                      
                      ⁢
                      
                        
                      
                    
                    ⁢
                    
                      NH
                      3
                    
                  
                  -
                  
                    outlet
                    ⁢
                    
                      
                    
                    ⁢
                    
                      NH
                      3
                    
                  
                  +
                  
                    outlet
                    ⁢
                    
                      
                    
                    ⁢
                    
                      NO
                      x
                    
                  
                
                )
              
            
            )
          
          ×
          100
          ×
          
            
              evaluation
              ⁢
              
                
                  
                
                ⁢
                
                  
                
              
              ⁢
              mole
              ⁢
              
                
              
              ⁢
              ratio
            
            
              inlet
              ⁢
              
                
              
              ⁢
              mole
              ⁢
              
                
              
              ⁢
              ratio
            
          
        
      
    
    
      
        (
        1
        )
      
    
  



wherein:
the inlet mole ratio is derived from a NOx concentration as measured on the inlet side by means of said NOx measurement means and an NH3 concentration as measured on the inlet side by means of said NH3 measurement means;
the inlet NH3 concentration is an NH3 concentration as measured on the inlet side;
the outlet NH3 concentration is an NH3 concentration as measured on the outlet side;
the outlet NOx concentration is a NOx concentration as measured on the outlet side; and
the evaluation mole ratio is predetermined for the purpose of evaluating respective NOx removal catalyst layers or plurality of NOx catalyst layers.

2. A NOx removal catalyst management unit according to claim 1, which management unit further includes transmission means for transmitting concentration values determined by the NOx measurement means and the NH3 measurement means to the percent NOx removal determination means, wherein the percent NOx removal determination means determines the percent NOx removal (η) of respective NOx removal catalyst layers included in a plurality of flue gas NOx removal apparatuses.

3. A method for managing a NOx removal catalyst comprising:
determining NOx concentrations and NH3 concentrations on the inlet and outlet sides of respective NOx removal catalyst layers;
determining percent NOx removal (η) on the basis of an inlet mole ratio (i.e., inlet NH3/inlet NOx); which percent NOx removal (η) is determined on the basis of the following equation (1):





  
    
      
        η
        =
        
          
            (
            
              
                (
                
                  
                    inlet
                    ⁢
                    
                      
                    
                    ⁢
                    
                      NH
                      3
                    
                  
                  -
                  
                    outlet
                    ⁢
                    
                      
                    
                    ⁢
                    
                      NH
                      3
                    
                  
                
                )
              
              
                (
                
                  
                    inlet
                    ⁢
                    
                      
                    
                    ⁢
                    
                      NH
                      3
                    
                  
                  -
                  
                    outlet
                    ⁢
                    
                      
                        
                      
                      ⁢
                      
                        
                      
                    
                    ⁢
                    
                      NH
                      3
                    
                  
                  +
                  
                    outlet
                    ⁢
                    
                      
                    
                    ⁢
                    
                      NO
                      x
                    
                  
                
                )
              
            
            )
          
          ×
          100
          ×
          
            
              evaluation
              ⁢
              
                
                  
                
                ⁢
                
                  
                
              
              ⁢
              mole
              ⁢
              
                
              
              ⁢
              ratio
            
            
              inlet
              ⁢
              
                
              
              ⁢
              mole
              ⁢
              
                
              
              ⁢
              ratio
            
          
        
      
    
    
      
        (
        1
        )
      
    
  



wherein:
the inlet NH3 concentration is an NH3 concentration as measured on the inlet side;
the outlet NH3 concentration is an NH3 concentration as measured on the outlet side;
the outlet NOx concentration is a NOx concentration as measured on the outlet side;
the inlet mole ratio is derived from a NOx concentration as measured on the inlet side and an NH3 concentration as measured on the inlet side; and
an evaluation mole ratio is predetermined for the purpose of evaluating respective NOx removal catalyst layers or plurality of NOx catalyst layers; and
evaluating performance of respective NOx removal catalyst layers on the basis of the percent NOx removal (η).

4. A method according to claim 3 for managing a NOx removal catalyst, wherein the method further comprises performing restoration treatment of a NOx removal catalyst layer having a catalytic performance deteriorated to a predetermined level, on the basis of results of performance evaluation of the respective NOx removal catalyst layers.

5. A method according to claim 4 for managing a NOx removal catalyst, wherein the performance restoration treatment is replacement of the NOx removal catalyst layer with a new NOx removal catalyst layer, replacement of the NOx removal catalyst layer with a regenerated NOx removal catalyst layer, replacement of the NOx removal catalyst layer with an NOx removal catalyst layer inverted with respect to the direction of the flow of discharge gas, or replacement of the NOx removal catalyst layer with an NOx removal catalyst layer from which a deteriorated portion has been removed.

6. A method according to any of claims 3 and 4 for managing a NOx removal catalyst, wherein the method further comprises determining the percent NOx removal of respective NOx removal catalyst layers included in a plurality of flue gas NOx removal apparatuses and evaluating catalytic performance of respective NOx removal catalyst layers included in a plurality of flue gas NOx removal apparatuses.

7. A method according to claim 5 for managing a NOx removal catalyst, wherein the method further comprises determining the percent NOx removal of respective NOx removal catalyst layers included in a plurality of flue gas NOx removal apparatuses and evaluating catalytic performance of respective NOx removal catalyst layers included in a plurality of flue gas NOx removal apparatuses.