Disclosure of Invention
The invention aims to provide an evaluation method of the activity of a denitration system catalyst, which aims to solve the problem that the evaluation process of the existing method is complex.
The second purpose of the invention is to provide a method for correcting denitration efficiency of a denitration system.
In order to achieve the purpose, the technical scheme of the method for evaluating the activity of the denitration system catalyst is as follows:
a method for evaluating the activity of a denitration system catalyst comprises the following steps:
1) obtaining NO in inlet flue gas of SCR reactorxReduced concentration (reduced to standard state, dry basis, 6% oxygen content, the same applies below), oxygen content, and ammonia slip concentration at the outlet of the SCR reactor, NO in the outlet clean flue gasxReduced concentration (reduced to standard state, dry basis, 6% oxygen content, the same applies below);
2) substituting the data obtained in the step 1) into the formulas (1) to (3) to calculate the denitration correction efficiency:
in formulae (1) to (3), η
Repair theThe denitration correction efficiency is percent, which reflects the state of the catalyst, and η is the denitration efficiency is percent;
ammonia slip concentration, ppm; c
NOIs the concentration of NO in the inlet flue gas, ppm;
for NO in inlet flue gas
xReduced concentration of (d), mg/Nm
3;
For discharging NO in clean flue gas
xReduced concentration of (d), mg/Nm
3;O
2Is the oxygen content of the inlet flue gas,%;
3) and (4) monitoring the change trend of the denitration correction efficiency on line, and if the denitration correction efficiency moves downwards, indicating that the activity of the catalyst is reduced.
The traditional denitration efficiency calculation formula does not take the influence of ammonia escape concentration into account, and still has higher efficiency when the ammonia injection excess ammonia escape concentration seriously exceeds the standard, and the catalyst activity is difficult to reflect faithfully only by monitoring the ammonia injection excess ammonia escape concentration. The method for evaluating the catalyst activity provided by the invention is mainly used for carrying out online evaluation on the catalyst activity based on the correction of the denitration efficiency, and is less influenced by the ammonia/nitrogen molar ratio when ammonia is excessively sprayed, so that the actual activity of the catalyst can be reflected more stably and accurately.
NO at SCR reactor outlet (denitration outlet)
xThe CEMS (flue gas on-line monitoring system) measuring point is often influenced by a flue gas flow field, an operation load, a coal mill combination mode and the like to cause the problem of poor representativeness (the average NO of a flue is difficult to reflect)
xConcentration), if the denitration efficiency calculated by using the method is easy to be distorted, in order to improve the calculation accuracy of the denitration efficiency, the NO in the clean flue gas at the outlet of the desulfurization system is preferably used
xHas a reduced concentration of
With NO at the desulfurization outlet
xFor the basis of calculation, the flue gas has been mixed by further mixing of denitration downstream equipment and stirring of a draught fan, the measurement point representativeness is stronger, and therefore the real denitration efficiency can be reflected more accurately.
Generally, each coal-fired power generating unit has two SCR reactors, which are conventionally called A side and B side in the industry, in order to more accurately obtain the test data of the corresponding parameters, preferably, the denitration system comprises an A side SCR reactor and a B side SCR reactor, η,
C
NO、
O
2The average of the data for the A-side SCR reactor and the B-side SCR reactor.
In order to better warn the activity condition of the catalyst, preferably, the method is carried out according to NO in the smoke at the SCR inletxLong-term average data of converted concentration, SCR outlet flue gas NOxAnd substituting the design value of the converted concentration and the early warning value of the ammonia escape concentration into the formulas (1) to (3) to calculate the early warning value of the denitration correction efficiency. Under the condition that the activity of the catalyst is normal, the denitration correction efficiency is maintained to be higher than an early warning value along with NO at the denitration inlet and the desulfurization outletxThe converted concentration fluctuates due to fluctuation, and once the converted concentration is reduced to an early warning value, the maintenance, activity test and other work of the catalyst need to be considered. Considering the aspects of efficient and economic operation of the SCR system, the early warning value of the ammonia escape concentration needs to be determined according to the coal quality characteristics for combustion, the increase speed of the differential pressure on the smoke side of the air preheater and other factors, and can be set to be 3-10 ppm if the early warning value is determined.
The technical scheme of the method for correcting the denitration efficiency of the denitration system is as follows:
a method for correcting denitration efficiency of a denitration system comprises the following steps:
1) obtaining NO in inlet flue gas of SCR reactorxReduced concentration and oxygen content of the SCR, ammonia escape concentration at the outlet of the SCR reactor and clean flue gas at the outletNOxThe reduced concentration of (c);
2) substituting the data obtained in the step 1) into the formulas (1) to (3) to calculate the denitration correction efficiency:
in formulae (1) to (3), η
Repair theThe denitration correction efficiency is percent, which reflects the state of the catalyst, and η is the denitration efficiency is percent;
ammonia slip concentration, ppm; c
NOIs the concentration of NO in the inlet flue gas, ppm;
for NO in inlet flue gas
xReduced concentration of (d), mg/Nm
3;
For discharging NO in clean flue gas
xReduced concentration of (d), mg/Nm
3;O
2Is the oxygen content of the inlet flue gas,%.
According to the method for correcting the denitration efficiency of the denitration system, the denitration efficiency under the conditions of excessive ammonia injection amount and over-standard ammonia escape rate is corrected by counting the ammonia escape concentration, the influence of the ammonia/nitrogen molar ratio is small, and the actual activity of the catalyst can be reflected more stably and accurately.
For increasing NO in outlet clean flue gas
xThe accuracy of the calculation of the reduced concentration is preferably determined by the NO content in the clean flue gas at the outlet of the desulfurization system
xHas a reduced concentration of
In order to more accurately obtain the test data of the corresponding parameters, it is preferable that the denitration system includes an A-side SCR reactor and a B-side SCR reactor, η,
C
NO、
O
2The average of the data for the A-side SCR reactor and the B-side SCR reactor.
Detailed Description
The activity of the catalyst is evaluated mainly by correcting the actual denitration efficiency of the SCR system, corresponding measured point data are all actual working condition data, and the method offsets the influence degree of the denitration efficiency under the ammonia/nitrogen molar ratio when the ammonia injection is excessive as much as possible by taking the influence of the ammonia escape rate into account, so that the corrected denitration efficiency can more accurately reflect the current actual activity of the catalyst, and the denitration correction efficiency trend is continuously evaluated on line and early-warning is carried out, thereby being beneficial to reasonably arranging SCR maintenance work.
The calculation formula of the original denitration efficiency is as follows:
NO in SCR reactor inlet flue gas
xReduced concentration, mg/Nm
3;
NO in the SCR reactor outlet flue gas
xReduced concentration, mg/Nm
3。
In the SCR operation, the denitration efficiency is increased along with the gradual increase of the molar ratio of ammonia to nitrogen, and the ammonia slip rate is obviously increased after the reaction capacity of the catalyst is exceeded. Generally, the denitration efficiency should be evaluated under the premise that the ammonia slip rate does not exceed 3ppm, and the denitration efficiency at this time can reflect the actual state and the reaction capability of the catalyst. And under the conditions that the ammonia injection amount is too large and the ammonia escape rate exceeds the standard, the SCR can obtain higher denitration efficiency, but the denitration efficiency is distorted at the moment and cannot reflect the actual state of the catalyst.
The corrected denitration efficiency is influenced by the ammonia escape rate, and can be relatively less influenced by the ammonia/nitrogen molar ratio when the ammonia injection is excessive, so that the actual activity of the catalyst can be more stably and accurately reflected.
The following examples are provided to further illustrate the practice of the invention.
In the following examples, NOxThe conversion concentration calculation formula is as follows:
in the formula (4), the reaction mixture is,
is NO in flue gas
xReduced concentration (reduced to standard state, dry basis, 6% oxygen content), mg/Nm
3;C’
NOThe concentration of NO in the dry flue gas is actually measured, ppm; o's'
2Is the oxygen content of the flue gas,%.
The specific embodiment of the method for evaluating the activity of the catalyst of the denitration system comprises the following steps of:
1) obtaining inlet flue gas NO of SCR (selective catalytic reduction) reactors at side A and side B according to a Distributed Control System (DCS) of a power plantxReduced concentration, mg/Nm3(ii) a Oxygen content, (volume)%; the ammonia escape concentration of the SCR reactor outlets of the side A and the side B is ppm; clean flue gas NO at outlet of desulfurization systemxReduced concentration, mg/Nm3;
2) Displaying a calculation result of calculating the denitration correction efficiency on the DCS by using the data acquired in the step 1), wherein the denitration correction efficiency is calculated according to the formula (1) to the formula (5):
ηrepair theCorrecting the efficiency,%, for denitration, reflecting the state of the catalyst;
η is the average denitration efficiency of the SCR reactor at the A side and the B side in percent;
the average ammonia escape concentration of the SCR reactor at the side A and the side B is ppm;
CNOaverage NO concentration of inlets of SCR reactors at the side A and the side B is ppm;
average NO at the inlet of the A-side and B-side SCR reactors
xReduced concentration, mg/Nm
3;
For the clean flue gas NO of the desulfurization outlet
xReduced concentration, mg/Nm
3;
O2Average oxygen content at inlets of SCR reactors at the side A and the side B,%;
respectively an A side SCR reactor and a B side SCR reactorKouNO
xReduced concentration, mg/Nm
3;
O2,A、O2,BThe oxygen content at the inlet of the SCR reactor at the side A and the inlet of the SCR reactor at the side B are respectively percent.
The ammonia escape concentration at the outlets of the SCR reactors at the side A and the side B, and the NO at the inlets of the SCR reactors at the side A and the side BxWhen the number of DCS on-line measuring points such as the converted concentration, the oxygen content of inlets of the SCR reactors at the side A and the side B is more than 1, the average value of all the measuring points is taken in the calculation so as to improve the representativeness of the measuring points and the accuracy of the calculation of the denitration correction efficiency.
3) Denitration inlet flue gas NO of generator setxLong term average data of reduced concentration (e.g. monthly average data, actually 450mg/Nm3) And denitration outlet flue gas NOxDesign value of reduced concentration (e.g., 45 mg/Nm)3) And substituting the early warning value (such as 8ppm) of the ammonia escape concentration into the formulas (1) to (3) to calculate the early warning value of the denitration correction efficiency, continuously evaluating the denitration correction efficiency on line, and if the denitration correction efficiency is reduced to the early warning value, sending out a catalyst maintenance early warning.
It is easily understood that the method for evaluating the activity of the catalyst of the denitration system of the present invention is applicable to a case where the following two conditions are simultaneously satisfied: (1) NO in inlet flue gasxThe reduced concentration of (a) reaches or exceeds a long-term average value; (2) the evaporation capacity of the boiler reaches the rated load. Taking the above embodiment as an example, the inlet flue gas NO of the denitration systemxThe long-term average of the converted concentration was 450mg/Nm3. When the evaporation capacity of the boiler is close to or reaches the rated load: NO in inlet flue gasxThe reduced concentration is 600mg/Nm3On the other hand, the method can be used for evaluating the activity of the catalyst simply and effectively; such as an inlet concentration (e.g., 300mg/Nm in some cases)3) If the average value is lower than the long-term average value, the SCR reactor is indicated to operate under the standard load, the actual denitration efficiency obtained through calculation under the condition may be lower, but the processing capacity of the catalyst is still surplus under the condition, and the activity of the catalyst can be evaluated by referring to whether the ammonia escape concentration exceeds the early warning value or not. In a word, when the two conditions cannot be met simultaneously, the denitration correction efficiency can not be monitored on line for the moment, and the monitoring is continued when the next boiler operation condition is met.
The specific embodiment of the method for correcting the denitration efficiency of the denitration system of the present invention is the same as the step 1) and the step 2) in the above evaluation method, and will not be described in detail.