阅读说明：本技术 一种SCR脱硝出口混合及分区烟气NOx浓度检测系统及其方法 (SCR denitration outlet mixing and partition flue gas NOx concentration detection system and method thereof ) 是由 钟洪玲 赵喆 尹二新 刘国栋 张军 徐浩 张聪涛 张浩亮 于 2019-09-26 设计创作，主要内容包括：本发明公开了一种SCR脱硝出口混合及分区烟气NOx浓度检测系统及其方法,所述检测系统包括烟气采样装置、烟气缓冲置换装置及烟气NOx浓度检测装置；所述烟气采样装置设置于SCR反应器出口不同位置,其所抽取的分区烟气的一路与混合烟气采样电动门连接,另一路与分区烟气采样电动门连接,通过电动门的开关实现气路切换；所述烟气缓冲置换装置与电动门控制的气路相连通,所述烟气NOx浓度检测装置与所述烟气缓冲置换装置连接,所述电动门的开关切换以转换混合烟气NOx浓度及分区烟气NOx浓度的检测。本发明提供的技术方案,其结构合理,公用一套CEMS进行混合烟气NOx浓度及分区烟气NOx浓度的检测,有效降低了分区测量精准喷氨系统的建设成本。(the invention discloses a system and a method for detecting NOx concentration of mixed and zoned flue gas at an SCR (selective catalytic reduction) denitration outlet, wherein the detection system comprises a flue gas sampling device, a flue gas buffer replacement device and a flue gas NOx concentration detection device; the smoke sampling devices are arranged at different positions of the outlet of the SCR reactor, one path of the extracted subarea smoke is connected with the mixed smoke sampling electrically operated gate, the other path of the extracted subarea smoke is connected with the subarea smoke sampling electrically operated gate, and the gas circuit switching is realized through the switch of the electrically operated gate; the flue gas buffering and replacing device is communicated with a gas path controlled by the electric door, the flue gas NOx concentration detection device is connected with the flue gas buffering and replacing device, and the switch of the electric door is switched to convert the detection of the concentration of the mixed flue gas NOx and the concentration of the partitioned flue gas NOx. The technical scheme provided by the invention has a reasonable structure, and a set of CEMS is used for detecting the NOx concentration of the mixed flue gas and the NOx concentration of the partitioned flue gas, so that the construction cost of the partitioned-measurement accurate ammonia spraying system is effectively reduced.)

1. A system for detecting NOx concentration of mixed and zoned flue gas at an SCR denitration outlet is characterized by comprising a flue gas sampling device, a flue gas buffer replacement device and a flue gas NOx concentration detection device; the smoke sampling devices are arranged at different positions of the outlet of the SCR reactor, one path of the extracted subarea smoke is connected with the mixed smoke sampling electrically operated gate, the other path of the extracted subarea smoke is connected with the subarea smoke sampling electrically operated gate, and the gas circuit switching is realized through the switch of the electrically operated gate; the flue gas buffering and replacing device is communicated with a gas path controlled by the electric door, the flue gas NOx concentration detection device is connected with the flue gas buffering and replacing device, and the switch of the electric door is switched to convert the detection of the concentration of the mixed flue gas NOx and the concentration of the partitioned flue gas NOx.

2. the system for detecting the concentration of NOx of claim 1, further comprising a gas circuit selection and numerical processing unit, wherein the gas circuit selection and numerical processing unit is connected with the flue gas NOx concentration detection device and sends input signals required by a total amount control strategy and a partition leveling control strategy according to corresponding mixed flue gas NOx concentration signals and partition flue gas NOx concentration signals.

3. The system for detecting the concentration of NOx of claim 2, wherein the total amount control strategy adjusts the total ammonia injection amount according to the received mixed flue gas NOx concentration value, and the subarea leveling control strategy adjusts the opening degree of the ammonia injection branch pipes according to the received deviation signal of the concentration of NOx in each subarea flue gas and the mixed flue gas NOx concentration.

4. The NOx concentration detection system according to claim 2, characterized in that the switching order of opening and closing the electrically operated gate is:

V_MIX,V_prt(1),V_MIX,V_prt(2),V_MIX,V_prt(3),V_MIX,…,V_prt(n-1),V_MIX,V_prt(n)

So as to alternately measure the concentration of NOx in the mixed flue gas at the SCR outlet and the concentration of NOx in the subarea flue gas,

wherein, V_MIXElectric door V for mixing flue gas at SCR outlet_prt(1)～V_prtAnd (n) is a subarea smoke sampling valve.

5. The NOx concentration detection system of claim 1, wherein the detection system sends the input signals required for the total amount control strategy and the zone leveling control strategy based on the zone NOx concentration and the mixed flue NOx concentration at adjacent times.

6. the NOx concentration detection system of claim 1, wherein the mixed flue gas NOx concentration and the zoned flue gas NOx concentration are detected by a common set of CEMS.

7. The NOx concentration detection system of claim 3, wherein the zoned leveling control strategy is based on a deviation of the SCR outlet mixed flue gas NOx concentration and the zoned flue gas NOx concentration at adjacent times.

8. a method for detecting NOx concentration of mixed and zoned flue gas at an SCR denitration outlet is characterized by comprising the following steps:

S1, arranging a CEMS detection device at the outlet of the SCR denitration reactor to alternately measure the concentration of NOx in the mixed flue gas at the outlet of the SCR and the concentration of NOx in the zoned flue gas;

s2, taking the NOx concentration of the mixed and partitioned flue gas obtained at the adjacent moment as an input signal of a partitioned leveling control strategy;

And S3, when the concentration of the NOx in the partitioned flue gas is measured in a circulating mode, compensating the concentration of the NOx in the partitioned flue gas obtained in the circulating mode according to the deviation between the concentration of the NOx in the partitioned flue gas obtained by the previous circulating measurement and the concentration of the NOx in the mixed flue gas obtained at the adjacent moment of the partitioned flue gas obtained by the previous circulating measurement, and obtaining an outlet mixed flue gas NOx concentration signal required by the ammonia injection total amount control system.

9. The method for detecting the concentration of NOx of claim 8, wherein the NOx concentration detection system is provided with a non-disturbance switching link for the outlet mixed flue gas NOx concentration signal received by the ammonia injection total amount control system when the NOx concentration of the flue gas in the measurement subarea is switched to the NOx concentration of the mixed flue gas or when the NOx concentration of the mixed flue gas is switched to the NOx concentration of the measurement subarea.

10. The method according to claim 9, wherein the undisturbed switching is performed by filtering a difference between the NOx concentration of the mixed flue gas measured at the current time of the current cycle and the NOx concentration of the mixed flue gas calculated at the current time of the current cycle.

Technical Field

the invention belongs to the technical field of denitration engineering, and relates to a system and a method for detecting NOx concentration of mixed and zoned flue gas at an SCR (selective catalytic reduction) denitration outlet.

background

SCR denitration is the main form of thermal power unit flue gas denitration, and its control system generally adopts the single-point measurement value of SCR export flue gas NOx concentration as the control target, adjusts the ammonia injection total volume, and then reaches flue gas NOx emission concentration standard's purpose. Due to the fact that a flow field in the SCR denitration system is complex, the average NOx concentration of the flue gas at the outlet of the SCR cannot be accurately reflected by a single-point measured value of the NOx concentration of the flue gas, the control system cannot accurately calculate the total ammonia injection amount, and control quality of the control system is reduced. In order to ensure that the emission concentration of the NOx in the flue gas reaches the standard, the power plant has to perform excessive ammonia injection, and meanwhile, the problems of catalyst poisoning, blockage of an air preheater, dust deposition of a dust remover and the like caused by excessive ammonia injection are more serious.

In order to solve the problems, an accurate ammonia injection system for partition measurement is gradually popularized, an SCR denitration system is divided into A, B two sides, and a single side is taken as an example, the whole structure diagram of the accurate ammonia injection system for partition measurement is changed into an electric door, as shown in figure 1, the system changes a manual door of an ammonia injection branch pipe at an inlet of an SCR reactor into an electric door, and simultaneously, a single set or a plurality of sets of measuring devices for measuring the concentration of NOx in partition flue gas are additionally arranged at an outlet of the SCR reactor, namely, the system applies one set of CEMS device to measure the concentration of mixed flue gas NOx at an outlet of the single side, and then applies one set or a plurality of sets of CEMS devices to measure the concentration. The control system controls the total ammonia injection amount according to the concentration of mixed flue gas NOx, and simultaneously adjusts the opening degree of the ammonia injection branch pipe valve according to the deviation condition of the concentration of the NOx of the subarea flue gas and the concentration of the mixed flue gas NOx, so that the uniformity of the concentration of the NOx of each subarea is leveled.

Therefore, a system and a method for detecting NOx concentration in mixed and zoned flue gas at an SCR denitration outlet are needed to solve the existing technical problems.

Disclosure of Invention

The invention aims to solve at least part of technical problems in the prior art to a certain extent, and provides the system and the method for detecting the NOx concentration of the mixed and partitioned flue gas at the SCR denitration outlet.

In order to solve the technical problem, the invention provides a system for detecting NOx concentration in mixed and partitioned flue gas at an SCR (selective catalytic reduction) denitration outlet, which comprises a flue gas sampling device, a flue gas buffer replacement device and a flue gas NOx concentration detection device; the smoke sampling devices are arranged at different positions of the outlet of the SCR reactor, one path of the extracted subarea smoke is connected with the mixed smoke sampling electrically operated gate, the other path of the extracted subarea smoke is connected with the subarea smoke sampling electrically operated gate, and the gas circuit switching is realized through the switch of the electrically operated gate; the flue gas buffering and replacing device is communicated with a gas path controlled by the electric door, the flue gas NOx concentration detection device is connected with the flue gas buffering and replacing device, and the switch of the electric door is switched to convert the detection of the concentration of the mixed flue gas NOx and the concentration of the partitioned flue gas NOx.

In some embodiments, the detection system further comprises a gas path selection and numerical processing unit, and the gas path selection and numerical processing unit is connected with the flue gas NOx concentration detection device and sends input signals required by the total amount control strategy and the partition leveling control strategy according to the corresponding mixed flue gas NOx concentration signal and the partition flue gas NOx concentration signal.

in some embodiments, the total amount control strategy adjusts the total ammonia injection amount according to the received mixed flue gas NOx concentration value, and the subarea leveling control strategy adjusts the opening degree of the ammonia injection branch pipe according to the received deviation signal of the NOx concentration of each subarea flue gas and the mixed flue gas NOx concentration.

In some embodiments, the switching sequence of the electric door is:

V_MIX,V_prt(1),V_MIX,V_prt(2),V_MIX,V_prt(3),V_MIX,…,V_prt(n-1),V_MIX,V_prt(n)

So as to alternately measure the concentration of NOx in the mixed flue gas at the SCR outlet and the concentration of NOx in the subarea flue gas,

Wherein, V_MIXelectric door V for mixing flue gas at SCR outlet_prt(1)～V_prtand (n) is a subarea smoke sampling valve.

In some embodiments, the detection system sends the input signals required by the gross control strategy and the zone leveling control strategy based on the zone NOx concentration and the mixed flue NOx concentration at adjacent times.

in some embodiments, the mixed flue gas NOx concentration and the zoned flue gas NOx concentration are detected using a common set of CEMS.

In some embodiments, the zonal leveling control strategy is based on deviations of SCR outlet mixed flue gas NOx concentrations and zonal flue gas NOx concentrations at adjacent times.

Simultaneously, the application also discloses a method for detecting NOx concentration of mixed and zoned flue gas at the SCR denitration outlet, which comprises the following steps:

s1, arranging a CEMS detection device at the outlet of the SCR denitration reactor to alternately measure the concentration of NOx in the mixed flue gas at the outlet of the SCR and the concentration of NOx in the zoned flue gas;

S2, taking the NOx concentration of the mixed and partitioned flue gas obtained at the adjacent moment as an input signal of a partitioned leveling control strategy;

and S3, when the concentration of the NOx in the partitioned flue gas is measured in a circulating mode, compensating the concentration of the NOx in the partitioned flue gas obtained in the circulating mode according to the deviation between the concentration of the NOx in the partitioned flue gas obtained by the previous circulating measurement and the concentration of the NOx in the mixed flue gas obtained at the adjacent moment of the partitioned flue gas obtained by the previous circulating measurement, and obtaining an outlet mixed flue gas NOx concentration signal required by the ammonia injection total amount control system.

in some embodiments, the NOx concentration detection system sets a non-disturbance switching link for the outlet mixed flue gas NOx concentration signal received by the ammonia injection total amount control system when switching from measuring the zoned flue gas NOx concentration to measuring the mixed flue gas NOx concentration or from measuring the mixed flue gas NOx concentration to measuring the zoned flue gas NOx concentration.

In some embodiments, the undisturbed switching element is configured to perform filtering processing on a difference between a mixed flue gas NOx concentration measured at the moment of the current cycle and a mixed flue gas NOx concentration calculated at the moment of the current cycle.

the invention has the beneficial effects that:

The invention provides a system and a method for detecting NOx concentration of mixed and zoned flue gas at an SCR (selective catalytic reduction) denitration outlet, which are used for acquiring original measurement data by adopting a mode of alternately measuring NOx concentration of mixed flue gas at the SCR outlet and NOx concentration of zoned flue gas, designing a corresponding signal processing method according to the requirements of a total ammonia injection amount control system and a zoned leveling control system on received signals, and finally realizing that a set of CEMS (continuous emission monitoring system) device is applied to simultaneously provide measurement signals for an ammonia injection total amount control system and a zoned leveling control system, thereby effectively reducing the investment cost of a zoned-measurement accurate ammonia injection system and having good popularization value.

Drawings

The above advantages of the present invention will become more apparent and more readily appreciated from the detailed description set forth below when taken in conjunction with the drawings, which are intended to be illustrative, not limiting, of the invention and in which:

FIG. 1 is a diagram of a single-side conventional zoned measurement accurate ammonia injection system in the prior art;

FIG. 2 is a diagram of a SCR denitration outlet mixing and zone-dividing flue gas NOx concentration detection system;

FIG. 3 is a sample valve switching sequence according to the present invention;

FIG. 4 is a graph of deviation finding and signal transmission for SCR outlet mixed flue gas NOx concentration and zoned flue gas NOx concentration at adjacent times according to the present invention;

FIG. 5 is a flow chart of the acquisition of the mixed flue gas NOx concentration signal during the cyclic measurement of the zone concentration according to the present invention;

FIG. 6 is a flow chart of the acquisition of the NOx concentration signal of the mixed flue gas during the cyclic measurement of the mixed concentration according to the present invention;

FIG. 7 is a flow chart of the method for detecting NOx concentration in mixed and zoned flue gas at an SCR denitration outlet according to the present invention;

FIG. 8 is a schematic illustration of an SCR reactor outlet section in an embodiment of the present invention.

in the drawings, the reference numerals denote the following components:

The system comprises a 1-ammonia spraying main pipe adjusting door, a 2-ammonia spraying branch pipe adjusting door, a 3-partition flue gas sampling manual door, a 4-mixed flue gas sampling electric door, a 5-partition flue gas sampling electric door and a 6-partition flue gas sampling isolation door.

Detailed Description

Fig. 1 to 8 are related schematic diagrams of an SCR denitration outlet mixing and zoned flue gas NOx concentration detection system and method according to the present application, and the present invention will be described in detail below with reference to specific embodiments and accompanying drawings.

The examples described herein are specific embodiments of the present invention, are intended to be illustrative and exemplary in nature, and are not to be construed as limiting the scope of the invention. In addition to the embodiments described herein, those skilled in the art will be able to employ other technical solutions which are obvious based on the disclosure of the claims and the specification of the present application, and these technical solutions include technical solutions which make any obvious replacement or modification for the embodiments described herein.

The drawings in the present specification are schematic views to assist in explaining the concept of the present invention, and schematically show the shapes of respective portions and their mutual relationships. It is noted that the drawings are not necessarily to the same scale so as to clearly illustrate the structures of the various elements of the embodiments of the invention. Like reference numerals are used to denote like parts.

The structural schematic diagram of the SCR denitration outlet mixing and partition flue gas NOx concentration detection system described in the present application is shown in fig. 2, and includes a flue gas sampling device, a flue gas buffer replacement device, and a flue gas NOx concentration detection device; the smoke sampling devices are arranged at different positions of the outlet of the SCR reactor, one path of the extracted subarea smoke is connected with the mixed smoke sampling electrically operated gate, the other path of the extracted subarea smoke is connected with the subarea smoke sampling electrically operated gate, and the gas circuit switching is realized through the switch of the electrically operated gate; the flue gas buffering and replacing device is communicated with a gas path controlled by the electric door, the flue gas NOx concentration detection device is connected with the flue gas buffering and replacing device, and the switch of the electric door is switched to convert the detection of the concentration of the mixed flue gas NOx and the concentration of the partitioned flue gas NOx.

In the embodiment shown in fig. 2, a plurality of flue gas sampling devices are arranged at different positions of the outlet of the SCR reactor, the partitioned flue gas extracted by each sampling pipe is divided into two paths, one path is connected to the mixed flue gas sampling electric door, the other path is connected to the partitioned flue gas sampling electric door, the gas path switching is realized by opening and closing the electric doors, in the switching process, except that the valve corresponding to the selected measuring passage is in an open state, the valves corresponding to the other sampling passages are kept in a closed state, and in other words, the flue gas NOx concentration detection device is immediately kept to only measure the flue gas NOx concentration of the passage corresponding to the selected electric door. In the invention, the time interval for carrying out primary valve switching is called a moment, the smoke of a selected passage replaces the measured smoke at the previous moment in a smoke buffer replacement device and then is sent to a smoke NOx concentration detection device, a gas path selection and numerical value processing unit respectively sends corresponding mixed and subarea smoke NOx concentration signals to a total amount control strategy and a subarea leveling control strategy according to the NOx concentration detected by the smoke NOx concentration detection device and a data processing method corresponding to the selected passage, the total amount control strategy adjusts the total ammonia injection amount according to the received mixed smoke NOx concentration value, and the subarea leveling control strategy adjusts the opening degree of an ammonia injection branch pipe according to the received deviation signals of the NOx concentration of each subarea smoke and the NOx concentration of the mixed smoke.

components such as a flue gas sampling and filtering device, a drying device, a cooling device, a flowmeter, a sampling pump and the like which are not mentioned in the system structure refer to the existing partitioned measurement accurate ammonia spraying system.

The invention summarizes, the number of the SCR outlet partitions is n, each partition is numbered according to the cycle test requirement, the partitioned flue gas sampling valves can be numbered according to the sampling space positions, the partitions can also be numbered at intervals according to the requirement, and each partitioned valve is named as V after being numbered_prt(1)～V_prt(n); electric door named V for extracting mixed smoke at SCR outlet_MIX. After the system is started, the gas path selection and numerical value processing unit is circularly opened according to the following valve sequence, and the unselected valves are in a closed state:

V_MIX,V_prt(1),V_MIX,V_prt(2),V_MIX,V_prt(3),V_MIX,…,V_prt(n-1),V_MIX,V_prt(n)

The method is characterized in that factors such as the measurement time of the NOx concentration detection device, the flue gas replacement time of the flue gas buffer replacement device, the length of a flue gas extraction pipeline and the like are comprehensively considered, the switching time intervals of all valves are determined, the intervals can be the same or different, and after one round of cycle measurement is finished, a new round of cycle is restarted according to the same valve switching sequence. The sampling valve switching sequence is as shown in fig. 3.

the acquisition process of the zoned flue gas NOx concentration signal is briefly described as follows:

In the accurate ammonia injection system for the zone measurement, a zone leveling control strategy needs to adjust the opening degree of an ammonia injection branch pipe valve at an SCR inlet according to the difference between a zone flue gas NOx concentration signal and the concentration of mixed flue gas NOx at an SCR outlet. Because frequent change of the opening degree of the ammonia injection branch pipe valve can generate adverse effect on the ammonia injection total amount control system, the control precision and stability of the ammonia injection total amount control system are reduced, and meanwhile, the timeliness requirement of the SCR denitration system on the NOx concentration subarea leveling is considered to be not high. In an actual accurate ammonia injection system for zoning measurement, in order to ensure the accuracy and stability of total ammonia injection amount control, after a plurality of rounds of circulation measurement are generally carried out on zoning concentration, the deviation conditions of mixed flue gas NOx concentration and zoning flue gas NOx concentration at the same time in each circulation are comprehensively evaluated, and the opening of an ammonia injection branch pipe is adjusted once, namely after the NOx concentration is measured for a plurality of times in zoning, the opening of the ammonia injection branch pipe is adjusted once.

The application uses one set of CEMS device to measure the mixed flue gas NOx concentration at the SCR outlet and the concentration of the partitioned flue gas NOx in turn, the timeliness requirement on the partitioned leveling of the NOx concentration in the running process of the SCR denitration system is not high, and the working condition of the system is not changed greatly in a short time, so the deviation of the mixed flue gas NOx concentration at the SCR outlet and the concentration of the partitioned flue gas NOx at the adjacent moment can be used as the basis for the partitioned flue gas NOx concentration leveling, according to the valve switching sequence shown in figure 3, after a plurality of cycles, the deviation condition is comprehensively evaluated by a partitioned leveling control system, and the opening of an ammonia injection branch pipe is adjusted once, namely the partitioned flue gas NOx concentration and the mixed flue gas NOx concentration at the adjacent moment are used in the application, and the partitioned flue gas NOx concentration and the mixed flue gas NOx concentration at the same moment obtained by using two or more sets of CEMS systems in the. And (3) calculating the deviation of the mixed flue gas NOx concentration and the subarea flue gas NOx concentration at the SCR outlet at the adjacent moments and transmitting signals, as shown in FIG. 4.

Setting the system to perform branch pipe opening adjustment once every m rounds, wherein the number of SCR outlet partitions is n, each round of cycle measurement comprises 2n moments, and the moment of cycle measurement of the jth partition in the ith round after the opening adjustment of the kth ammonia injection branch pipe is as follows:

k*m*2n+(i-1)*2n+2j

At this time, the flue gas measured by the CEMS is the flue gas of the j-th zone, and the measured NOx concentration is as follows:

ρ(k*m*2n+(i-1)*2n+2j)

The previous moment of the ith round of cycle measurement of the jth subarea moment after the opening degree of the kth ammonia injection branch pipe is adjusted is as follows:

k*m*2n+(i-1)*2n+2j-1

At this time, the flue gas measured by the CEMS is mixed flue gas, and the measured NOx concentration is as follows:

ρ(k*m*2n+(i-1)*2n+2j-1)

After the opening degree of the ammonia injection branch pipe is adjusted for the kth time, the signal received by the partition leveling control strategy for the kth +1 th time from the cycle of the i-th cycle is as follows:

i belongs to (1, m) j belongs to (1, N), k belongs to N, and N represents a nonnegative integer.

The total signal d (k +1) received by the (k +1) th sub-partition leveling control strategy can be expressed as:

k ∈ N, N representing a nonnegative integer.

The acquisition process of the mixed flue gas NOx concentration signal is briefly described as follows:

because the ammonia injection total amount control system needs to control the ammonia injection total amount in real time according to the concentration of NOx in mixed flue gas at an SCR outlet, the system needs to continuously provide the concentration of NOx in the mixed flue gas. According to the method, a set of CEMS devices are used for measuring the concentration of NOx in mixed flue gas at an SCR outlet and the concentration of NOx in partitioned flue gas in turn, so that the concentration of NOx in mixed flue gas is not always measured by the CEMS, and if the concentration of NOx in mixed flue gas is required to be continuously obtained, CEMS measurement signals need to be processed. In the following description, the concentration of the mixed flue gas NOx received by the ammonia injection total amount control system is generally referred to as "mixed flue gas NOx concentration" and is denoted by ρ_mix(ii) a The mixed flue gas NOx concentration signals are divided into two types, one type is a mixed flue gas NOx concentration signal obtained by carrying out undisturbed switching on the concentration signal after the CEMS device measures the mixed flue gas NOx concentration and is called as a mixed flue gas NOx concentration measuring signal, and the other type is a mixed flue gas NOx concentration signal obtained by carrying out mathematical calculation on the partition flue gas NOx concentration value and other related data after the CEMS device measures the partition flue gas NOx concentration and is called as a mixed flue gas NOx concentration calculating signal.

1) Acquisition of mixed flue gas NOx concentration signal during measurement of zoned flue gas NOx concentration

as shown in fig. 5, when measuring the concentration of the zoned flue gas NOx, taking the difference between the concentration of the mixed flue gas NOx measured at the last moment of the zoned moment according to the last round of the cycle measurement and the concentration of the zoned flue gas NOx measured at the last round of the cycle measurement as a compensation step, and adding the value obtained in the compensation step and the concentration of the zoned flue gas NOx measured at the current moment of the cycle as a predicted mixed flue gas NOx concentration signal at the moment; furthermore, in order to avoid signal jump between the predicted mixed flue gas NOx concentration and the mixed flue gas NOx concentration obtained by the moment measurement on the current cycle, filtering is carried out after the deviation part of the predicted mixed flue gas NOx concentration and the mixed flue gas NOx concentration obtained by the moment measurement on the current cycle is multiplied by an adjustment coefficient K, a first-order or high-order inertia link with a small inertia time constant is generally selected by a filter, the filtered numerical value is added to the mixed flue gas NOx concentration obtained by the moment measurement on the current cycle, and the calculated mixed flue gas NOx concentration is obtained.

Referring to fig. 5, the system is designed to adjust the opening degree of the branch pipe once every m rounds, if the number of the SCR outlet partitions is n, each round of the system includes 2n moments, and the moment of the ith round of the system after the opening degree of the kth ammonia injection branch pipe is adjusted is:

k*m*2n+(i-1)*2n+2j

the flue gas measured by CEMS at this moment is the flue gas of the j section, and the measured NOx concentration is as follows:

ρ(k*m*2n+(i-1)*2n+2j)

the previous moment of the ith round of cycle measurement of the jth subarea moment after the opening degree of the kth ammonia injection branch pipe is adjusted is as follows:

k*m*2n+(i-1)*2n+2j-1

At this time, the flue gas measured by the CEMS is mixed flue gas, and the measured NOx concentration is as follows:

ρ(k*m*2n+(i-1)*2n+2j-1)

Then there is a mixed flue gas NOx concentration signal rho received by the ammonia injection total amount control strategy at that moment_mixcomprises the following steps:

i belongs to the element of (2, m), j belongs to the element of (1, N), k belongs to the element of N, and N represents nonnegative integer.

2) Initialization of compensation link after opening adjustment of ammonia injection branch pipe valve

after a plurality of cycles, the opening degree of the ammonia injection branch pipe is adjusted once by the zone leveling control strategy, after adjustment, the zone concentration distribution of NOx at the outlet of the SCR is greatly changed due to the change of the ammonia injection amount of each zone at the inlet of the SCR, and a concentration compensation link designed according to the difference value of the zone NOx concentration and the mixed concentration obtained at the adjacent moment of the zone in the last cycle has no reference significance any more, so that after each adjustment of the ammonia injection branch pipe, a compensation value needs to be initialized. The aim of adjusting each ammonia injection branch pipe is to make the NOx concentration of each zone of the SCR outlet uniform, namely: the concentration of NOx in the smoke of each subarea at the SCR outlet is close to the concentration of NOx in the mixed smoke at the SCR outlet, so that after each ammonia injection branch pipe is adjusted, the adjustment of the opening degree of the ammonia injection branch pipe can be assumed to enable the concentration of NOx in the smoke of each subarea to be the same as the concentration of NOx in the mixed smoke, and the compensation link C can be initialized to be zero at the moment, namely in the first round of measurement after the ammonia injection branch pipe is adjusted, when the concentration of NOx in the mixed smoke is calculated by applying the concentration of NOx in the smoke of a certain subarea, the deviation between the concentration of NOx in the smoke of the subarea obtained by the previous round of circulation measurement and the concentration of NOx in.

Referring to 1), in the calculation process, the system is set to perform branch pipe opening adjustment once every m rounds, if the number of SCR outlet partitions is n, each round of circulation measurement comprises 2n moments, and the moment of the 1 st round of circulation measurement of the jth partition after the opening adjustment of the kth ammonia injection branch pipe is as follows:

k*m*2n+2j

the flue gas measured by CEMS at this moment is the flue gas of the j section, and the measured NOx concentration is as follows:

ρ(k*m*2n+2j)

The previous moment of the 1 st round of circulation measurement j section moment after the opening degree of the kth ammonia injection branch pipe is adjusted is as follows:

k*m*2n+2j-1

At this time, the flue gas measured by the CEMS is mixed flue gas, and the measured NOx concentration is as follows:

ρ(k*m*2n+2j-1)

then the mixed flue gas NOx concentration signal received by the ammonia injection total amount control strategy at the moment is as follows:

i is 1, j belongs to (1, N), k belongs to N, and N represents a nonnegative integer.

3) and acquiring a mixed flue gas NOx concentration signal when the mixed flue gas NOx concentration is measured circularly.

when the mixed concentration is measured circularly, if no special requirement exists, the measured value can be directly sent to an ammonia spraying total amount control system. In addition, considering that the mixed flue gas NOx concentration signal received by the ammonia injection total amount control system needs to be continuously switched between the calculation of the mixed flue gas NOx concentration and the measurement of the mixed flue gas NOx concentration, the switching process can cause the mixed NOx concentration signal received by the ammonia injection total amount control system to have step jump, when a control strategy of the system has a differential or other control loop section sensitive to the step change of the signal, the control system can have fluctuation or even instability, under the condition, a undisturbed switching function needs to be added to the process of switching the mixed NOx concentration signal from the calculation of the mixed flue gas NOx concentration to the measurement of the mixed flue gas NOx concentration signal, as shown in fig. 6, the difference between the mixed flue gas NOx concentration measured at this moment of the cycle and the mixed flue gas NOx concentration calculated at the moment of the cycle is filtered, and a first-order or high-order inertia link with a smaller inertia time constant can be generally used as a filter, and summing the filtered numerical value and the mixed flue gas NOx concentration obtained by calculation at the moment on the cycle to obtain the final measured mixed flue gas NOx concentration, sending the signal to a total amount control system, and calculating the total ammonia injection amount by the total amount control system according to the value. The processing process can accurately reduce the NOx concentration value of the mixed flue gas obtained by CEMS measurement, and can ensure the undisturbed signal switching process.

referring to fig. 6, the system is designed to adjust the opening degree of the branch pipe once every m rounds, if the number of the SCR outlet partitions is n, each round of the system includes 2n moments, and the moment of the ith round of the system after the opening degree of the kth ammonia injection branch pipe is adjusted is:

k*m*2n+(i-1)*2n+2j

The flue gas measured by CEMS at this moment is the flue gas of the j section, and the measured NOx concentration is as follows:

ρ(k*m*2n+(i-1)*2n+2j)

The previous moment of the ith round of cycle measurement of the jth subarea moment after the opening degree of the kth ammonia injection branch pipe is adjusted is as follows:

k*m*2n+(i-1)*2n+2j-1

At this time, the flue gas measured by the CEMS is mixed flue gas, and the measured NOx concentration is as follows:

ρ(k*m*2n+(i-1)*2n+2j-1)

then there is a mixed flue gas NOx concentration signal rho received by the ammonia injection total amount control strategy at that moment_mixcomprises the following steps:

i ∈ (1, m), j ∈ (1, N), k ∈ N, and i ∈ 1, j ∈ 1, k ∈ 0 do not hold at the same time, N represents a nonnegative integer.

4) initialization of mixed flue gas NOx concentration after system startup

after the system is started, firstly measuring the concentration of the mixed flue gas NOx, according to the description in 3) and referring to FIG. 6, the concentration of the mixed flue gas NOx obtained by measuring the concentration of the mixed flue gas NOx needs to be calculated at the moment of the cycle, at the moment, the system is just started, the concentration of the mixed flue gas NOx obtained by calculating the moment of the cycle does not exist, and the system is generally required to be in a stable running state when the ammonia injection total amount control system is automatically put into operation, so that the concentration of the mixed flue gas NOx obtained by calculating the moment of the cycle can be set to be equal to the concentration of the mixed flue gas NOx measured at the moment of the cycle when the system is started.

instant rho_mix(0) And (2) rho (1), wherein the concentration of NOx in the mixed flue gas obtained at the moment of 1 cycle measurement of the first round after the system is started is as follows:

i＝1，j＝1，k＝0

after substitution, the following can be obtained:

ρ_mix(1)＝ρ(1)i＝1，j＝1，k＝0。

5) Maintenance of mixed flue gas NOx concentration signal after gas circuit switching

Because processes such as NOx concentration detection, flue gas buffer replacement, flue gas extraction and delivery all need to consume certain time, therefore switch to obtaining new measurement result from the gas circuit, need certain time, the mixed flue gas NOx concentration that ammonia injection total amount control system received in this time quantum, need to keep the mixed flue gas NOx concentration of measurement that the moment got or calculate mixed flue gas NOx concentration value, promptly: if the system measures the concentration of the mixed flue gas NOx at the moment, the mixed flue gas NOx concentration signal received by the ammonia injection total amount control system keeps the calculated mixed flue gas NOx concentration value at the previous adjacent moment before the measurement result is obtained, and if the system measures the concentration of the flue gas NOx in the subarea at the moment, the mixed flue gas NOx concentration signal received by the ammonia injection total amount control system keeps the measured mixed flue gas NOx concentration value at the previous adjacent moment before the measurement result is obtained.

meanwhile, the invention also discloses a method for detecting the concentration of NOx in mixed and zoned flue gas at an SCR denitration outlet, and the flow chart is as shown in FIG. 7, and comprises the following steps:

s1, arranging a CEMS detection device at the outlet of the SCR denitration reactor to alternately measure the concentration of NOx in the mixed flue gas at the outlet of the SCR and the concentration of NOx in the zoned flue gas;

s2, taking the NOx concentration of the mixed and partitioned flue gas obtained at the adjacent moment as an input signal of a partitioned leveling control strategy;

And S3, when the concentration of the NOx in the partitioned flue gas is measured in a circulating mode, compensating the concentration of the NOx in the partitioned flue gas obtained in the circulating mode according to the deviation between the concentration of the NOx in the partitioned flue gas obtained by the previous circulating measurement and the concentration of the NOx in the mixed flue gas obtained at the adjacent moment of the partitioned flue gas obtained by the previous circulating measurement, and obtaining an outlet mixed flue gas NOx concentration signal required by the ammonia injection total amount control system.

The following description will be given, with reference to specific examples, of a method for detecting NOx concentration in mixed and zoned flue gas at an SCR denitration outlet, specifically implemented as follows:

Certain 600MW unit adopts SCR denitration outlet mixing and subarea flue gas NOx concentration detection of shared CEMSthe measuring method obtains the NOx concentration of mixed and partitioned flue gas, the number n of partitions is 4, the mixed and partitioned flue gas is numbered according to the spatial position sequence of the SCR outlet section, the sectional partition diagram is shown in figure 8 when the flue gas is seen along the flow direction, and the valve corresponding to each partition is V_prt(1)，V_prt(2)，V_prt(3)，V_prt(4) (ii) a Electric door named V for extracting mixed smoke at SCR outlet_MIX. After the system is started, the gas path selection and numerical value processing unit is circularly opened according to the following valve sequence, and the unselected valves are in a closed state:

V_MIX,V_prt(1),V_MIX,V_prt(2),V_MIX,V_prt(3),V_MIX,V_prt(4)

and selecting the switching time interval of each valve as 90s, and restarting a new cycle according to the same valve switching sequence after one cycle of cycle selection is finished.

the results of the first 5 cycles performed by the system after the system was started up, which are shown in the following table, were obtained by adjusting the opening of the ammonia injection branch pipe once every 4 cycles:

(1) Acquisition of zoned flue gas NOx concentration signals

in this embodiment, the time when the ith cycle measures the jth sub-area after the opening of the kth ammonia injection branch pipe of the system is adjusted is m-4, n-4:

32k +8(i-1) +2j i ∈ (1,4), j ∈ (1,4), k ∈ N, N represents a nonnegative integer.

Let the NOx concentration measured by CEMS at this time be:

Rho (32k +8(i-1) +2j) i ∈ (1,4), j ∈ (1,4), k ∈ N, and N represents a nonnegative integer.

after the opening degree of the ammonia injection branch pipe is adjusted for the kth time, the signal received by the partition leveling control strategy for the kth +1 th time from the cycle of the i-th cycle is as follows:

Represents a non-negative integer.

the total signal d (k +1) received by the (k +1) th sub-partition leveling control strategy can be expressed as:

And N represents a non-negative integer.

taking round-trip test 1 to 4 as an example, referring to table 1, it can be obtained that each subarea deviation signal received by the subarea leveling control strategy when the branch pipe is adjusted for 1 st time is:

In the same way, the deviation signals of all the subareas received by the subarea leveling control strategy when other branch pipes are adjusted can be obtained.

(2) Acquisition of mixed flue gas NOx concentration signal

1) Acquisition of mixed flue gas NOx concentration signal during cyclic measurement of zone concentration

in this embodiment, m is 4, n is 4, and the inertia time constant T of the filtering element₁Filter order n of 10₁when the adjustment coefficient K is equal to 1, the time when the ith round of cycle measurement of the jth subarea after the opening degree of the kth ammonia injection branch pipe is adjusted is as follows:

32k+8(i-1)+2j

the flue gas measured by CEMS at this moment is the flue gas of the j section, and the measured NOx concentration is as follows:

ρ(32k+8(i-1)+2j)

Then the signals received by the ammonia injection total amount control strategy at the moment are as follows:

j is equal to (1,4), k is equal to N, and N represents a nonnegative integer.

i belongs to the group of 2 and 4, j belongs to the group of 1 and 4, and k belongs to the group of N and N represents nonnegative integers.

2) Acquisition of mixed flue gas NOx concentration signal during cyclic measurement of mixed concentration

The inertial time constant T of the link filter₂filter order n of 10₂When the system is started, let ρ be 2_mix(0) and (1), receiving signals according to the ammonia injection total amount control strategy at the moment of measuring the mixed concentration as follows:

ρ_mix(1)＝ρ(1)i＝1j＝1k＝0

i ∈ (1,4), j ∈ (1,4), k ∈ N, and i ∈ 1, j ∈ 1, k ∈ 0 do not hold at the same time, N represents a nonnegative integer.

Compared with the defects and shortcomings of the prior art, the SCR denitration outlet mixing and partition flue gas NOx concentration detection system and the method thereof provided by the invention have the advantages that the original measurement data are obtained by adopting a mode of alternately measuring the SCR outlet mixing flue gas NOx concentration and the partition flue gas NOx concentration, the corresponding signal processing method is designed according to the requirements of the total ammonia injection amount control system and the partition leveling control system on the received signals, and finally, the purpose of applying a set of CEMS device and simultaneously providing the measurement signals for the ammonia injection total amount control system and the partition leveling control system is realized, so that the investment cost of the partition measurement accurate ammonia injection system is effectively reduced, and the popularization value is good.

The present invention is not limited to the above embodiments, and any other products in various forms can be obtained by the teaching of the present invention, but any changes in the shape or structure thereof, which are the same as or similar to the technical solutions of the present invention, fall within the protection scope of the present invention.