CN115346610A - Ammonia injection optimization method, device and medium based on SCR reaction kinetic model - Google Patents

Ammonia injection optimization method, device and medium based on SCR reaction kinetic model Download PDF

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CN115346610A
CN115346610A CN202210892294.8A CN202210892294A CN115346610A CN 115346610 A CN115346610 A CN 115346610A CN 202210892294 A CN202210892294 A CN 202210892294A CN 115346610 A CN115346610 A CN 115346610A
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ammonia
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卢志民
闫超
唐雯
李博航
钟尚文
姚顺春
陈后虎
杨建民
杨杰
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Guangdong Honghaiwan Power Generating Co ltd
South China University of Technology SCUT
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Abstract

The invention discloses an ammonia injection optimization method, device and medium based on an SCR reaction kinetic model, wherein the method comprises the following steps: acquiring smoke data; according to the obtained flue gas data, verifying a CFD model of the SCR denitration system, and sprayingCarrying out visual analysis on the track and the influence area of the ammonia fluid, defining the influence coefficient of ammonia injection flow, and determining the corresponding relation between different partitions/nozzles of an ammonia injection grid and the upstream section area of the catalyst; solving the SCR reaction kinetic model to obtain the upstream section NH of the catalyst 3 A mathematical relational expression corresponding to the concentration and the concentration of NOx at the outlet of the SCR; and coupling the optimization matrix equations of the ammonia injection flow influence coefficients of different partitions/nozzles, and quantitatively solving to obtain the optimized ammonia injection amount corresponding to the ammonia injection grating with the aim of most uniform concentration distribution of NOx at the outlet of the SCR. The method can quantitatively solve the ammonia injection grating corresponding optimized ammonia injection amount according to the outlet NOx concentration distribution characteristic. The invention can be widely applied to the technical field of flue gas SCR denitration.

Description

Ammonia injection optimization method, device and medium based on SCR reaction kinetic model
Technical Field
The invention relates to the technical field of flue gas SCR denitration, in particular to an ammonia injection optimization method, an ammonia injection optimization device and an ammonia injection optimization medium based on an SCR reaction kinetic model.
Background
Nitrogen oxides (NOx) are one of the main pollutants in the atmosphere, and in order to implement stricter environmental protection standards, the emission concentration of the NOx is required to be not more than 50mg/Nm under the condition that the reference oxygen content is 6 percent 3 . Selective Catalytic Reduction (SCR) denitration is a flue gas denitration technology mainly applied to domestic power plants at present, NOx removal efficiency can be improved by increasing ammonia injection amount under the requirement of ultralow emission, ammonia escape amount of partial areas exceeds the standard, and air preheater blockage and SCR Catalytic Reduction (SCR) are increasedRisk of drug poisoning. Adjusting the ammonia injection amount of different areas of the ammonia injection grid is an important measure for improving the mixing matching degree of the ammonia nitrogen concentration in the flue, and the reasonable ammonia nitrogen mixing equivalence ratio can ensure that the SCR denitration reaction is complete and improve the distribution uniformity of the concentration of NOx at an outlet, so that the partition ammonia injection fine adjustment needs to be carried out on an SCR denitration system.
At present, the actual ammonia spraying regulation process of engineering is mostly carried out by means of manual experience, blindness is large, theoretical guidance is lacked, the flue gas fluid track and the influence area of the flue gas fluid track can be visualized by means of a CFD numerical simulation technology, and theoretical reference is provided for the optimization work of on-site ammonia spraying grille ammonia spraying; in the existing research, researchers use a CFD numerical simulation technology to perform ammonia injection optimization work, the proposed optimization strategy usually focuses on solving the problem of uniformity of the concentration distribution of ammonia-nitrogen mixture at the upstream of a first-layer catalyst, ammonia injection amount adjustment of equal ammonia-nitrogen ratio is performed according to the minimization of relative deviation of ammonia-nitrogen ratio at the upstream section of the catalyst, and the result shows that the concentration of NOx at an SCR outlet cannot meet the requirement of optimal distribution, and the problems of large deviation of the concentration of the NOx at the outlet, large escape of local ammonia and the like still exist after optimization; meanwhile, in most simulation optimization research works, the corresponding ammonia injection grid partition ammonia injection amount under the optimal ammonia injection strategy can be obtained through multiple trial calculation, the adjustment work has certain blindness, and the simulation time is long. In the prior art, no researchers analyze the corresponding influence relationship of the ammonia injection amount of different partitions of the ammonia injection grid on the concentration distribution of the NOx at the outlet of the SCR, so that a clear mathematical relational expression cannot be given according to the concentration distribution characteristics of the NOx at the outlet to quantitatively calculate the ammonia injection amount required by different partitions of the ammonia injection grid, the accuracy and pertinence of the existing adjusting strategy are poor, and the ammonia injection adjustment is high in blindness.
Disclosure of Invention
In order to solve at least one of the technical problems in the prior art to a certain extent, the invention aims to provide an ammonia injection optimization method, an ammonia injection optimization device and an ammonia injection optimization medium based on an SCR reaction kinetic model.
The technical scheme adopted by the invention is as follows:
an ammonia injection optimization method based on an SCR reaction kinetic model comprises the following steps:
acquiring smoke data;
according to the obtained flue gas data, verifying a CFD model of the SCR denitration system, performing visual analysis on the track and the influence area of the ammonia injection fluid, defining the influence coefficient of ammonia injection flow, and determining the corresponding relation between different partitions/nozzles of the ammonia injection grid and the upstream section area of the catalyst;
solving the SCR reaction kinetic model to obtain the upstream section NH of the catalyst 3 A mathematical relational expression corresponding to the concentration and the concentration of NOx at the outlet of the SCR;
and coupling optimization matrix equations of the ammonia injection flow influence coefficients of different partitions/nozzles, and quantitatively solving to obtain the optimized ammonia injection amount corresponding to the ammonia injection grating with the purpose of most uniform concentration distribution of NOx at the outlet of the SCR.
Furthermore, the whole structure of the SCR system comprises an inlet and outlet flue, an ammonia injection grid, a guide plate, a static mixer, a guide flow grid, a catalyst layer and the like.
Further, the acquiring of smoke data comprises:
measuring the flow field characteristic of the inlet measuring section of the SCR system to obtain smoke data; wherein, the flue gas data comprises a velocity field of the inlet measuring section, a concentration field of the inlet measuring section, a temperature field of the inlet measuring section and inlet parameters of the CFD numerical simulation.
Further, the step of establishing the CFD model of the SCR denitration system comprises the following steps:
a standard k-epsilon model is adopted as a turbulence model;
simulating the mixing and transportation of a plurality of gas components in the flue gas by adopting a component transportation model; wherein the gas components include NO and NH 3 、H 2 O、CO 2 、O 2 And N 2 ；
And selecting a standard SCR reaction to represent the whole reaction process, and verifying the CFD model by combining the smoke data to reflect the smoke flow of the SCR system.
Further, the defining an ammonia injection flow influence coefficient includes:
analyzing the influence of the inlet ammonia spraying amount on the ammonia concentration of the first-layer catalyst inlet by means of Fluent flow field simulation quantitative analysis, and providing ammonia flow schematic diagrams of different ammonia spraying grids for ammonia spraying to analyze the flow rule of an ammonia trace;
in order to determine the correspondence between the different zones/nozzles of the ammonia injection grid and the upstream cross-sectional area of the catalyst, the following definitions of the ammonia injection flow influence coefficient are given:
Figure BDA0003768086060000021
in the formula, a i For different ammonia injection zones/nozzles, m i The ammonia injection for a single zone/nozzle affects the ammonia concentration in a zone upstream of the catalyst, and m is the total ammonia injection concentration for a single zone/nozzle.
Further, solving the SCR reaction kinetic model to obtain the catalyst upstream section NH 3 A mathematical relationship relating concentration to SCR outlet NOx concentration comprising:
obtaining upstream section NH of the catalyst by solving an SCR reaction kinetic model 3 And calculating the ammonia concentration distribution of different partitions of the inlet section of the catalyst by using a mathematical relation formula corresponding to the concentration and the outlet NOx and taking the minimum relative deviation of the SCR outlet NOx concentration distribution uniformity as a target.
Further, the optimization matrix equation is:
Figure BDA0003768086060000031
in the formula, a i,j Expressing the influence coefficient of the i-th subarea of the ammonia injection grid on a certain j area in the upstream area of the catalyst by injecting ammonia; y is i Both represent the ammonia concentration demand in the ith zone of the zone upstream of the catalyst; x i The ammonia spraying amount of the corresponding subarea/nozzle at the ammonia spraying grid to be obtained is shown.
Further, the quantitative solution to obtain the optimized ammonia injection amount corresponding to the ammonia injection grid with the aim of most uniform distribution of the concentration of the NOx at the outlet of the SCR comprises:
determining the concentration distribution of NH3 at the inlet of the first-layer catalyst by using the mathematical relation between the concentration of NH3 at the upstream section of the catalyst and the concentration of NOx at the outlet, wherein the most uniform concentration distribution of NOx at the outlet of the SCR is taken as an optimization target;
and establishing a quantitative calculation correlation between the ammonia injection amount of different zones of the ammonia injection grid and the outlet NOx concentration distribution characteristic by combining the obtained optimization matrix equation based on the ammonia injection flow influence coefficients of different zones/nozzles, and calculating by using the correlation to obtain the optimized ammonia injection amount.
Further, the calculating the optimized ammonia injection amount by using the correlation comprises the following steps:
by analyzing the corresponding influence relationship of the ammonia injection amount of different partitions of the ammonia injection grid on the concentration distribution of the outlet NOx, the matlab is used for solving the optimization matrix equation by using a gradient descent method, and the optimized ammonia injection amount corresponding to different partitions/nozzles of the ammonia injection grid with the most uniform concentration distribution of the outlet NOx is obtained.
The invention adopts another technical scheme that:
an ammonia injection optimization device based on an SCR reaction kinetic model comprises:
at least one processor;
at least one memory for storing at least one program;
when executed by the at least one processor, cause the at least one processor to implement the method described above.
The invention adopts another technical scheme that:
a computer readable storage medium in which a processor executable program is stored, which when executed by a processor is for performing the method as described above.
The invention has the beneficial effects that: the method aims at obtaining the NH of the upstream section of the catalyst based on the standard SCR reaction kinetic model by taking the optimal concentration distribution uniformity of the outlet NOx as a target 3 The concentration and the outlet NOx concentration mathematical relation can quantitatively solve the ammonia injection amount correspondingly optimized by the ammonia injection grating according to the outlet NOx concentration distribution characteristic. In addition, the SCR reaction kinetic model is simple and is easy to modelThe mathematical relation formula of quantitative calculation of the ammonia injection amount of the ammonia injection grid and the concentration of the NOx at the outlet improves the calculation efficiency.
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In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following description is made on the drawings of the embodiments of the present invention or the related technical solutions in the prior art, and it should be understood that the drawings in the following description are only for convenience and clarity of describing some embodiments in the technical solutions of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to these drawings without creative efforts.
FIG. 1 is a flow chart of an ammonia injection simulation optimization method for an SCR denitration system in an embodiment of the present invention;
FIG. 2 is a schematic diagram of a three-dimensional overall SCR denitration system according to an embodiment of the present invention;
FIG. 3 is a schematic diagram showing the flow trajectory of ammonia in the case of 5 zones separately injecting ammonia according to the embodiment of the present invention;
FIG. 4 is a cloud plot of NOx concentration profiles across a section of an SCR system outlet measurement in an embodiment of the present invention;
FIG. 5 is a statistical plot of NOx concentration for 18 zones at the outlet of an SCR system in an embodiment of the present invention;
FIG. 6 is a flowchart illustrating steps of a method for optimizing ammonia injection based on an SCR reaction kinetic model according to an embodiment of the present invention.
Reference numerals in fig. 2: 1. an inlet of an SCR denitration system; 2. a baffle; 3. an inlet measurement cross-section; 4. an ammonia injection grid; 5. a static mixer; 6. a guide flow grating; 7. a catalyst layer; 8. outlet measurement cross section; 9. and (4) an SCR system outlet.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are illustrative only for the purpose of explaining the present invention, and are not to be construed as limiting the present invention. The step numbers in the following embodiments are provided only for convenience of illustration, the order between the steps is not limited at all, and the execution order of each step in the embodiments can be adapted according to the understanding of those skilled in the art.
In the description of the present invention, it should be understood that the orientation or positional relationship referred to in the description of the orientation, such as the upper, lower, front, rear, left, right, etc., is based on the orientation or positional relationship shown in the drawings, and is only for convenience of description and simplification of description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus, should not be construed as limiting the present invention.
In the description of the present invention, a plurality of means is one or more, a plurality of means is two or more, and greater than, less than, more than, etc. are understood as excluding the essential numbers, and greater than, less than, etc. are understood as including the essential numbers. If there is a description of first and second for the purpose of distinguishing technical features only, this is not to be understood as indicating or implying a relative importance or implicitly indicating the number of technical features indicated or implicitly indicating the precedence of technical features indicated.
In the description of the present invention, unless otherwise explicitly limited, terms such as arrangement, installation, connection and the like should be understood in a broad sense, and those skilled in the art can reasonably determine the specific meanings of the above terms in the present invention in combination with the specific contents of the technical solutions.
The prior art has the following disadvantages:
(1) When the load of the boiler changes, the NOx concentration field changes, the actual ammonia injection adjustment process of the project is mostly carried out by means of manual experience, the blindness is high, theoretical guidance is lacked, and the debugging work takes long time.
(2) At present, ammonia injection adjustment simulation work of an SCR denitration system is to perform ammonia injection amount optimization of equal ammonia nitrogen ratio according to minimization of relative deviation of ammonia nitrogen ratio of upstream section of a catalyst, and results show that the concentration of NOx at an SCR outlet cannot meet the requirement of optimal distribution, and the problems of large deviation of the concentration of the NOx at the outlet, large local ammonia escape and the like still exist after optimization.
(3) The CFD numerical simulation technology is used for carrying out SCR ammonia injection optimization research work, most scholars often need to try calculation for many times to determine the corresponding ammonia injection grid partition ammonia injection amount under the optimal ammonia injection strategy, adjustment work has certain blindness, calculation efficiency is low, and simulation time is long.
(4) In the existing research, the corresponding influence relationship of the ammonia injection amount of different partitions of the ammonia injection grid on the concentration distribution of the NOx at the outlet of the SCR cannot be analyzed, and a definite mathematical relational expression cannot be given according to the concentration distribution characteristics of the NOx at the outlet to quantitatively calculate the ammonia injection amount required by the different partitions of the ammonia injection grid, so that the accuracy and pertinence of the existing adjusting strategy are poor, and the blindness of ammonia injection adjustment is high.
(5) According to the existing technical scheme, the ammonia injection optimization method based on the influence factors aims at achieving the most uniform distribution of the ammonia-nitrogen ratio at the inlet of the first-layer catalyst, the adjustment of an ammonia injection valve is guided only by establishing the influence factors of different partition ammonia injection amounts on the ammonia-nitrogen ratio at the inlet of the first-layer catalyst, and the optimization aim is not to achieve the minimum relative deviation of the concentration distribution of the NOx at the outlet of an SCR (selective catalytic reduction), so that the concentration of the NOx at the outlet of the SCR cannot meet the requirement of the optimal distribution, and the problems of large deviation of the concentration of the NOx at the outlet, large escape of local ammonia and the like still exist after the optimization.
(6) In another existing technical scheme, an SCR reaction mathematical model is obtained based on 6 groups of highly nonlinear coupling differential equations and is used for outputting the mathematical relation between the concentration of NOx at an outlet and the influence factors at an inlet, the model is too complex, the modeling difficulty is high, the calculation steps are more complicated, and NH on the upstream section of a catalyst cannot be directly given 3 The concentration and the SCR outlet NOx concentration are calculated by a one-step mathematical relation, so that the quantitative calculation correlation of the ammonia injection amount and the outlet NOx concentration distribution characteristic of different sections/nozzles of the ammonia injection grid is difficult to directly establish.
Based on one of the above problems, referring to fig. 1 and fig. 6, the present embodiment provides an ammonia injection optimization method based on an SCR reaction kinetic model, comprising the following steps:
s1, acquiring smoke data.
As an alternative embodiment, the smoke data is obtained by field performance testing. The performance test adopts measuring equipment to measure the flow field characteristics of the inlet measuring section of the SCR system, obtains the velocity field, the concentration field and the temperature field of the inlet measuring section, and provides inlet parameters for CFD numerical simulation.
S2, verifying a CFD model of the SCR denitration system according to the obtained flue gas data, performing visual analysis on the track and the influence area of the ammonia injection fluid, defining the ammonia injection flow influence coefficient, and determining the corresponding relation between different partitions/nozzles of the ammonia injection grid and the upstream section area of the catalyst.
As an alternative embodiment, referring to fig. 2, the establishment of the overall structure model of the scr denitration system includes structures such as an inlet and outlet flue, an ammonia injection grid 4, a guide plate 2, a static mixer 5, a guide flow grid 6, and a catalyst layer 7.
As an optional implementation manner, the CFD model building process mainly includes the following steps: selecting a standard k-epsilon model as a turbulence model; simulating NO and NH in flue gas by adopting component transport model 3 、H 2 O、CO 2 、O 2 And N 2 Mixing and transporting 6 gas components without considering the influence of fly ash; the standard SCR reaction was chosen to represent the whole reaction process, ignoring the ammonia adsorption, desorption and oxidation reactions. After the CFD model is verified by combining with the field measured data in the step S1, the actual flue gas flow of the SCR system can be truly reflected.
As an optional embodiment, the influence coefficient of the ammonia injection flow is used for quantitatively analyzing the influence of the ammonia injection amount at the inlet on the ammonia concentration at the inlet of the first-layer catalyst by means of Fluent flow field simulation, and an ammonia flow schematic diagram of different ammonia injection grids for ammonia injection is given to analyze the flow rule of the ammonia trace. To determine the correspondence between the different sections/nozzles of the ammonia injection grid and the upstream cross-sectional area of the catalyst, the following definitions of the ammonia injection flow influence coefficients are given:
Figure BDA0003768086060000061
in the formula: a is i For different ammonia injection zones/nozzles, m i Ammonia sparging for individual zones/nozzles to affect a zone upstream of the catalystM is the total concentration of ammonia sprayed by the individual zones/nozzles.
S3, solving the SCR reaction kinetic model to obtain the catalyst upstream section NH 3 And (3) a mathematical relation corresponding to the concentration and the SCR outlet NOx concentration.
Specifically, according to an SCR reaction kinetic model given by a standard SCR chemical reaction global kinetic mechanism, solving the model to obtain the NH of the upstream section of the catalyst 3 And calculating the ammonia concentration distribution of different partitions of the inlet section of the catalyst by taking the minimum relative deviation of the uniformity of the concentration distribution of the NOx at the outlet of the SCR as a target according to a mathematical relation corresponding to the concentration and the NOx at the outlet.
As an alternative embodiment, the catalyst is V 2 O 5 -WO 3 /TiO 2 Monolithic honeycomb catalysts.
Further as an alternative embodiment, the V 2 O 5 -WO 3 /TiO 2 The kinetic model involved in the monolithic honeycomb catalyst is as follows:
Figure BDA0003768086060000071
catalyst upstream section NH obtained by solving according to model integral 3 The mathematical relationship between concentration and outlet NOx is expressed as follows:
Figure BDA0003768086060000072
wherein: c NH3 、C NO Respectively NH in the flue gas 3 And the concentration of NO; k is a radical of NO Is the denitration reaction rate constant.
Figure BDA0003768086060000073
And
Figure BDA0003768086060000074
measuring NH of different sections of the cross-section for the outlet respectively 3 And the concentration of NO;
Figure BDA0003768086060000075
and
Figure BDA0003768086060000076
respectively NH corresponding to a section of the upstream side of the catalyst 3 And the concentration of NO.
And S4, coupling optimization matrix equations of ammonia injection flow influence coefficients of different partitions/nozzles, and quantitatively solving to obtain the optimized ammonia injection amount corresponding to the ammonia injection grating with the most uniform concentration distribution of NOx at the outlet of the SCR serving as a target.
The optimization matrix equation is defined as:
Figure BDA0003768086060000077
in the formula: a is i,j Expressed as the influence coefficient of the i section of the ammonia injection grid for injecting ammonia to a certain j area in the upstream area of the catalyst; y is i Both represent the ammonia concentration demand in the ith zone of the zone upstream of the catalyst; x i The ammonia spraying amount of the corresponding subarea/nozzle at the ammonia spraying grid to be obtained is shown.
The method is characterized in that the most uniform distribution of the concentration of NOx at the outlet of an SCR is taken as an optimization target, the concentration distribution of the NH3 at the inlet of a first-layer catalyst is determined by utilizing the mathematical relation between the concentration of the NH3 at the upstream section of the catalyst based on the standard SCR reaction kinetic model and the concentration of the NOx at the outlet obtained in the step S3, and meanwhile, the quantitative calculation correlation between the ammonia injection amount of different partitions of an ammonia injection grid and the concentration distribution characteristic of the NOx at the outlet can be established by combining the optimization matrix equation based on different partition/nozzle ammonia injection flow influence coefficients obtained in the step S4.
Further, by analyzing the corresponding influence relationship of the ammonia spraying amount of different partitions of the ammonia spraying grid on the outlet NOx concentration distribution, the optimized matrix equation in the step S4 is solved by utilizing matlab and a gradient descent method, so that the optimized ammonia spraying amount corresponding to different partitions/nozzles of the ammonia spraying grid with the most uniform outlet NOx concentration distribution is obtained.
The optimized ammonia spraying amount can be regarded as a relative value to be subjected to equal proportion conversion, and guidance is provided for scale adjustment of an ammonia spraying butterfly valve by combining with the on-site ammonia spraying valve debugging experience.
The above method is explained in detail below with reference to the drawings and the specific embodiments.
An ammonia injection optimization method based on an SCR reaction kinetic model comprises the following steps:
s101, measuring flue gas flow field characteristics of 12 x 3 grid points of an inlet measuring section of the SCR system under 100% load by using measuring equipment, obtaining a velocity field, a concentration field and a temperature field of the inlet measuring section, and providing inlet parameters for CFD numerical simulation. The average velocity at the inlet of the SCR system was 2.9m/s, and the calculated ammonia injection rate per nozzle was 0.046kg/s, with a 2.35% volume fraction of ammonia.
S102, as shown in FIG. 2, taking the A-side reactor as an example for explanation, carrying out geometric modeling on the whole structure of the SCR system, and carrying out targeted zoning on an ammonia injection grid. Then, carrying out grid division, adopting unstructured grids at the ammonia spraying grid, the guide plate and the mixer, and encrypting the position of a nozzle; other regular areas employ structured grids.
S103, performing numerical simulation on the whole SCR denitration system model, wherein the numerical simulation comprises a turbulent flow model, a component transportation and chemical reaction model and the like, selecting a proper mathematical model and parameter values in Fluent to ensure that a reliable simulation result can be obtained, and selecting a standard k-epsilon model as the turbulent flow model; simulating NO and NH in flue gas by adopting component transport model 3 、H 2 O、CO 2 、O 2 And N 2 Mixing and transporting 6 gas components without considering the influence of fly ash; the standard SCR reaction is selected to represent the whole reaction process, the adsorption and desorption processes and the oxidation reaction of ammonia are neglected, and the actual flue gas flow of the SCR system is truly reflected. The 3 catalyst layers were set as porous media zones and the drag coefficients were set from actual pressure drop calculations.
And S104, according to the NOx concentration and temperature distribution of the inlet measurement section of the performance test, reversely simulating the NOx concentration and temperature distribution of the inlet section. And (4) performing numerical calculation in Fluent, comparing the calculation result with the test data after the calculation determines convergence, and verifying the reliability of the CFD model.
S105, explaining an ammonia injection simulation optimization method of the SCR denitration system under 100% load, but the method is also suitable for other working conditions. According to the simulation report result in the early stage, the flow field of the whole SCR system is relatively uniform, the internal flow guide device is reasonably arranged, and the design requirement of the flow field is met. When the denitration reaction simulation was performed by the uniform ammonia injection method, the result of the uniformity of the outlet NOx concentration distribution is shown in fig. 4 (a). When the uniform ammonia spraying mode is adopted, the ammonia nitrogen concentration equivalence ratio in the catalytic reactor is not matched, and the ammonia spraying amount in the right area of the reactor is excessive, so that the concentration of NOx at an outlet in the area is low, and the risk of ammonia escape exists; meanwhile, the concentration of NOx at the outlet of the left partial area is higher and exceeds 50mg/Nm 3 The engineering requirements of (1). The uniformity of the NOx concentration distribution of the outlet measuring section is poor, the relative standard deviation is as high as 40.14%, and the unreasonable ammonia nitrogen mixing equivalence ratio of each subarea in the reactor can cause the serious and uneven distribution of the outlet NOx concentration, so that the subarea ammonia injection optimization of the ammonia injection grid is needed to improve the uniformity of the outlet NOx concentration. Fig. 4 (a) is a cloud chart of outlet NOx concentration distribution under the uniform ammonia injection method, fig. 4 (b) is a cloud chart of outlet NOx concentration distribution under the 5-partition optimization method, and fig. 4 (c) is a cloud chart of outlet NOx concentration distribution under the 42-nozzle optimization method.
S106, the influence of the ammonia spraying amount at the inlet on the ammonia concentration distribution at the inlet of the first-layer catalyst is quantitatively analyzed by means of Fluent flow field simulation, and the inlet section of the first-layer catalyst is divided into 6 multiplied by 3=18 areas named as C11, C12 \8230, 8230, C62 and C63 by taking an actual power plant as an example, and corresponds to 18 areas for outlet NOx gridding sampling. Flow field visual analysis is performed on ammonia gas flowing out of 5 different partitions of the ammonia injection grid, fig. 3 is a schematic flow diagram of an ammonia trace of the ammonia injection grid, and because a flow guide structure in a flue limits mixed diffusion of NH3 injected by branch pipes in the flue, and the mixing distance is limited, ammonia concentration of 18 areas of an inlet of a catalyst is influenced by ammonia injection of each partition/nozzle is distributed in a certain area, therefore, in order to determine the corresponding relation between different partitions/nozzles of the ammonia injection grid and an upstream cross section area of the catalyst, the following definition of an ammonia injection flow influence coefficient is given:
Figure BDA0003768086060000091
in the formula: a is i For different ammonia injection zones/nozzles, m i The ammonia injection for a single zone/nozzle affects the ammonia concentration in a zone upstream of the catalyst, and m is the total ammonia injection concentration for a single zone/nozzle.
S107, according to the definition of the ammonia injection flow influence coefficient of the formula (1), the influence coefficients of the 5 subareas of the ammonia injection grid on the 18 areas of the catalyst inlet are obtained and are shown in the table 1. The influence coefficient of each subarea on 18 areas of the catalyst inlet is different, taking subarea 1 as an example, the subarea sprayed with ammonia mainly influences areas from inlets C11 to C13 and C23, the influence coefficient is more than 0.1, and the influence coefficient on other areas is smaller. Since the ammonia injection flow influence coefficient of the space relation of 42 nozzles is omitted, the solution method is consistent with the 5 partition optimization methods.
TABLE 1 influence of the flow of the zoned ammonia injection
Figure BDA0003768086060000092
S108, in order to achieve the optimization goal of the most uniform NOx concentration distribution of the outlet measurement section, the corresponding relation between the NOx concentrations of different partitions of the outlet section and the ammonia concentration distribution of 18 partitions of the upstream section of the catalyst needs to be further determined. The standard SCR chemical reaction global kinetic mechanism adopted is expressed as reaction equation (2):
4NO+4NH 3 +O 2 →4N 2 +6H 2 O (2)
v represented by the following equation (3) 2 O 5 -WO 3 /TiO 2 Kinetic model involved in monolithic honeycomb catalysts:
Figure BDA0003768086060000093
in solving the model, assume N in the reactionO and NH 3 The same consumption rate, i.e. according to (4); substituting the initial data into the formula (3) to obtain the catalyst upstream section NH through integral solution 3 And (6) a mathematical relation of concentration to outlet NOx.
Figure BDA0003768086060000101
Figure BDA0003768086060000102
Figure BDA0003768086060000103
Wherein: c NH3 、C NO Respectively NH in the flue gas 3 And the concentration of NO; k is a radical of formula NO Is the denitration reaction rate constant. k is a pre-exponential coefficient; ea is the apparent activation energy representing the reaction speed; t is the temperature of the denitration reactor; r represents a gas constant; t is the reaction residence time.
Figure BDA0003768086060000104
And
Figure BDA0003768086060000105
NH with 18 sections of outlet measurement cross-section 3 And the concentration of NO;
Figure BDA0003768086060000106
and
Figure BDA0003768086060000107
NH of 18 zones corresponding to the upstream cross section of the catalyst 3 And the concentration of NO.
S109, defining a matrix equation according to the ammonia injection influence coefficient as follows:
Figure BDA0003768086060000108
the invention carries out two kinds of optimization of subarea and nozzle, therefore, in the formula 7: 1) If 5 partitions are optimized, then a i,j (i =1, 5, j = 1) is expressed as the influence coefficient of the i-th zone of the ammonia injection grid for injecting ammonia on a certain j zone in 18 zones upstream of the catalyst; 2) If the optimization is carried out according to 42 nozzles, a i,j (i =1:42,j = 1); in both cases, Y i Both represent the i-th zone ammonia concentration demand in the 18 zones upstream of the catalyst; x i Indicating the ammonia injection amount of the corresponding subarea/nozzle at the ammonia injection grid to be obtained.
S110, taking the most uniform outlet NOx concentration distribution as an optimization target, and obtaining the NH of the upstream section of the catalyst based on a standard SCR reaction kinetic model 3 Determining first-layer catalyst inlet NH by using a mathematical relation between concentration and outlet NOx concentration 3 The standard SCR reaction kinetic model is simple, a mathematical relation for quantitatively solving the ammonia injection amount is easy to model, the accuracy and pertinence of ammonia injection adjustment can be improved, the blindness of adjustment work is reduced, and the calculation efficiency is improved.
S111, on the basis of analyzing the corresponding influence relationship of the ammonia injection amount of different partitions of the ammonia injection grid on the concentration distribution of the NOx at the outlet, keeping the average value of the concentration of the NOx at the section of the outlet to be constant (lower than 50 mg/Nm) 3 Engineering standard) assuming a target outlet NOx concentration for each zone of 41.7mg/Nm cross-sectional average 3 (0.0004458mol/m 3 ) To achieve a minimum of relative deviation of outlet NOx concentration. By catalyst upstream section NH 3 The first layer catalyst inlet NH is obtained by the back-stepping calculation of the mathematical relation (6) of the concentration and the outlet NOx concentration 3 Concentration distribution, inlet NH of different zones 3 Required amount of concentration distribution Y i Substituting into an optimization matrix equation (7), and solving by utilizing matlab and a gradient descent method to obtain the ammonia spraying grid with the outlet NOx concentration distribution most uniformOptimized ammonia injection amount X corresponding to different sections of grids i . And substituting the optimized ammonia injection amount of different subareas into Fluent to perform simulation calculation, wherein the specific simulation result is shown in a NOx concentration distribution cloud chart of the measured section of the SCR system outlet in the figure 4 and a NOx concentration statistical chart of 18 subareas at the SCR system outlet in the figure 5.
S112, after 5-partition ammonia spraying optimization, the distribution uniformity of the concentration of the NOx at the outlet is improved, the areas of the low NOx concentration region at the right side and the high NOx concentration region at the upper left side are reduced, the relative standard deviation is reduced to 33.0%, and compared with a uniform ammonia spraying mode, the optimization effect of the distribution uniformity of the concentration of the NOx at the outlet is improved by 17.7%. In order to further optimize the distribution uniformity of the outlet NOx concentration, a more refined ammonia injection optimization adjustment method is needed, and after the NOx concentration in 18 subareas at the outlet is optimized by 42 nozzles, the average value of the cross section of the NOx concentration tends to be 40mg/Nm 3 The risk of low NOx concentration, excessive ammonia injection and excessive ammonia escape emission does not exist, and the emission standard of 50mg/Nm is not exceeded 3 The area of (3) can realize that NOx line pressing discharge meets the environmental protection requirement, avoids the area that denitration efficiency is too high and low excessively to appear again, has reached the purpose that improves export NOx concentration distribution uniformity.
S113, assuming that the initial valve opening is 70 under the condition of uniform ammonia spraying, and the valve opening range is 0-100. The optimized ammonia injection amount of the 42 nozzles under the 100% load condition is compared with that under the uniform ammonia injection condition, and the opening degree adjustment relative values of the optimized 42 ammonia injection valves are obtained, as shown in table 2. Compared with the opening sizes of 42 valves under the uniform ammonia spraying strategy, the opening of the valve A4-3 needs to be reduced by 17.5, namely the valve is the minimum opening 52.5, the opening of the valve A14-1 needs to be increased by 13.8, namely the valve is the maximum opening 83.8, after the openings of the 42 optimized ammonia spraying valves are obtained, the ammonia spraying valves are adjusted by combining the field ammonia spraying valve debugging experience and the outlet NOx concentration gridding measurement result, and therefore the purposes of optimizing ammonia spraying and improving the outlet NOx concentration distribution uniformity of the SCR denitration system are achieved.
TABLE 2 relative values of the opening adjustment of the 42 ammonia injection valves
Figure BDA0003768086060000111
Figure BDA0003768086060000121
S113, when the load of the boiler changes, the corresponding relation between different partitions/nozzles of the ammonia injection grid and the concentration distribution characteristics of NOx at the section of the outlet can be determined by establishing flue gas flow and reaction models under different working conditions and repeating the calculation steps, the debugging efficiency of the ammonia injection control regulating valve under different working conditions can be obviously helped and improved, and theoretical reference is provided for actual ammonia injection optimization regulation test and operation.
In summary, compared with the prior art, the method of the embodiment has the following advantages and beneficial effects:
(1) The invention adopts the simulated inlet boundary condition based on the test measured value to reflect the whole flue gas flow of the SCR system more truly, can carry out visual analysis on the flue gas flow, ammonia nitrogen mixing and denitration reaction characteristics to obtain the flow rule of an ammonia gas trace, finds the area range of the ammonia concentration distribution of the downstream SCR inlet and the area range of the NOx concentration distribution of the SCR outlet after reaction, provides theoretical reference for the actual ammonia injection optimization adjustment test and operation, and reduces the blindness of the adjustment work.
(2) The method aims at obtaining the NH of the upstream section of the catalyst based on the standard SCR reaction kinetic model by taking the optimal concentration distribution uniformity of the outlet NOx as a target 3 Determining the first-layer catalyst inlet NH according to a mathematical relation between the concentration and the outlet NOx concentration 3 The concentration distribution is combined with an optimization matrix equation based on different subareas/nozzle ammonia injection flow influence coefficients, a quantitative calculation correlation formula of the ammonia injection amount of different subareas of the ammonia injection grating and the outlet NOx concentration distribution characteristic is established, the corresponding optimized ammonia injection amount of the ammonia injection grating according to the outlet NOx concentration distribution characteristic can be solved quantitatively, a standard SCR reaction kinetic model is simple, the quantitative calculation mathematical relation formula of the ammonia injection amount of the ammonia injection grating and the outlet NOx concentration is obtained easily through modeling, and the calculation efficiency is improved.
(3) According to the invention, through the optimized ammonia spraying method which is obtained through simulation and enables the concentration distribution of NOx at the outlet of the SCR to be most uniform, the partitioned ammonia spraying amount control of the ammonia spraying grid can be carried out, the method can be more finely applied to the control and regulation valve of each nozzle in the ammonia spraying grid, and the optimized ammonia spraying amount obtained through simulation is subjected to equal proportion conversion of the opening of the valve by combining with the debugging experience of the site, so that the adjustment of the ammonia spraying control valve is guided.
(4) The optimization method can be suitable for different working conditions, the corresponding relation between different partitions/nozzles of the ammonia injection grid and the concentration distribution characteristics of NOx at the section of the outlet can be determined by establishing flow and reaction models under different working conditions and repeating the calculation steps, and the debugging efficiency of the ammonia injection control regulating valve under different working conditions can be remarkably improved.
The embodiment also provides an ammonia injection optimization device based on the SCR reaction kinetic model, which includes:
at least one processor;
at least one memory for storing at least one program;
when executed by the at least one processor, cause the at least one processor to implement the method of fig. 6.
The ammonia injection optimization device based on the SCR reaction kinetic model can execute the ammonia injection optimization method based on the SCR reaction kinetic model, can execute any combination of implementation steps of the method embodiments, and has corresponding functions and beneficial effects of the method.
The embodiment of the application also discloses a computer program product or a computer program, which comprises computer instructions, and the computer instructions are stored in a computer readable storage medium. The computer instructions may be read by a processor of a computer device from a computer-readable storage medium, and executed by the processor, causing the computer device to perform the method illustrated in fig. 6.
The embodiment also provides a storage medium, which stores instructions or a program capable of executing the ammonia injection optimization method based on the SCR reaction kinetic model, and when the instructions or the program are executed, the instructions or the program can execute any combination of the method embodiments to implement steps, and have corresponding functions and beneficial effects of the method.
In alternative embodiments, the functions/acts noted in the block diagrams may occur out of the order noted in the operational illustrations. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality/acts involved. Furthermore, the embodiments presented and described in the flow charts of the present invention are provided by way of example in order to provide a more thorough understanding of the technology. The disclosed methods are not limited to the operations and logic flows presented herein. Alternative embodiments are contemplated in which the order of various operations is changed, and in which sub-operations described as part of larger operations are performed independently.
Furthermore, although the present invention is described in the context of functional modules, it should be understood that, unless otherwise stated to the contrary, one or more of the described functions and/or features may be integrated in a single physical device and/or software module, or one or more functions and/or features may be implemented in a separate physical device or software module. It will also be understood that a detailed discussion of the actual implementation of each module is not necessary for an understanding of the present invention. Rather, the actual implementation of the various functional modules in the apparatus disclosed herein will be understood within the ordinary skill of an engineer given the nature, function, and interrelationships of the modules. Accordingly, those skilled in the art can, using ordinary skill, practice the invention as set forth in the claims without undue experimentation. It is also to be understood that the specific concepts disclosed are merely illustrative of and not intended to limit the scope of the invention, which is to be determined from the appended claims along with their full scope of equivalents.
The functions, if implemented in the form of software functional units and sold or used as a stand-alone product, may be stored in a computer readable storage medium. Based on such understanding, the technical solution of the present invention may be embodied in the form of a software product, which is stored in a storage medium and includes instructions for causing a computer device (which may be a personal computer, a server, or a network device) to execute all or part of the steps of the method according to the embodiments of the present invention. And the aforementioned storage medium includes: a U-disk, a removable hard disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a magnetic disk or an optical disk, and other various media capable of storing program codes.
The logic and/or steps represented in the flowcharts or otherwise described herein, e.g., an ordered listing of executable instructions that can be considered to implement logical functions, can be embodied in any computer-readable medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. For the purposes of this description, a "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device.
More specific examples (a non-exhaustive list) of the computer-readable medium would include the following: an electrical connection (electronic device) having one or more wires, a portable computer diskette (magnetic device), a Random Access Memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disc read-only memory (CDROM). Further, the computer-readable medium could even be paper or another suitable medium upon which the program is printed, as the program can be electronically captured, via for instance optical scanning of the paper or other medium, then compiled, interpreted or otherwise processed in a suitable manner if necessary, and then stored in a computer memory.
It should be understood that portions of the present invention may be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, the various steps or methods may be implemented in software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, any one or combination of the following techniques, which are known in the art, may be used: a discrete logic circuit having a logic gate circuit for implementing a logic function on a data signal, an application specific integrated circuit having an appropriate combinational logic gate circuit, a Programmable Gate Array (PGA), a Field Programmable Gate Array (FPGA), or the like.
In the foregoing description of the specification, reference to the description of "one embodiment/example," "another embodiment/example," or "certain embodiments/examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
While embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that: various changes, modifications, substitutions and alterations can be made to the embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.
While the preferred embodiments of the present invention have been illustrated and described, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (10)

1. An ammonia injection optimization method based on an SCR reaction kinetic model is characterized by comprising the following steps:
acquiring smoke data;
according to the obtained flue gas data, verifying a CFD model of the SCR denitration system, performing visual analysis on the track and the influence area of the ammonia injection fluid, defining the influence coefficient of ammonia injection flow, and determining the corresponding relation between different partitions/nozzles of the ammonia injection grid and the upstream section area of the catalyst;
solving the SCR reaction kinetic model to obtain the catalyst upstream section NH 3 A mathematical relation corresponding to the concentration and the concentration of NOx at the outlet of the SCR;
and coupling the optimization matrix equations of the ammonia injection flow influence coefficients of different partitions/nozzles, and quantitatively solving to obtain the optimized ammonia injection amount corresponding to the ammonia injection grating with the aim of most uniform concentration distribution of NOx at the outlet of the SCR.
2. The method of claim 1, wherein the obtaining of flue gas data comprises:
measuring the flow field characteristic of the inlet measuring section of the SCR system to obtain smoke data; wherein, the flue gas data comprises a velocity field of the inlet measuring section, a concentration field of the inlet measuring section, a temperature field of the inlet measuring section and inlet parameters of the CFD numerical simulation.
3. The method of claim 1, wherein the step of establishing the CFD model of the SCR denitration system comprises:
a standard k-epsilon model is adopted as a turbulence model;
simulating the mixing and transportation of a plurality of gas components in the flue gas by adopting a component transportation model; wherein the multiple gas components include NO and NH 3 、H 2 O、CO 2 、O 2 And N 2 ；
And selecting a standard SCR reaction to represent the whole reaction process, and verifying the CFD model by combining the smoke data to reflect the smoke flow of the SCR system.
4. The method of claim 1, wherein the defining the ammonia injection flow impact coefficient comprises:
analyzing the influence of the inlet ammonia spraying amount on the ammonia concentration of the first-layer catalyst inlet by means of Fluent flow field simulation quantitative analysis, and providing ammonia flow schematic diagrams of different ammonia spraying grids for ammonia spraying to analyze the flow rule of an ammonia trace;
in order to determine the correspondence between the different zones/nozzles of the ammonia injection grid and the upstream cross-sectional area of the catalyst, the following definitions of the ammonia injection flow influence coefficient are given:
Figure FDA0003768086050000011
in the formula, a i For different ammonia injection zones/nozzles, m i The ammonia injection for a single zone/nozzle affects the ammonia concentration in a zone upstream of the catalyst, and m is the total ammonia injection concentration for a single zone/nozzle.
5. The method of claim 1, wherein the SCR reaction kinetics model is solved to obtain a catalyst upstream cross section NH 3 The mathematical relationship of concentration and SCR outlet NOx concentration includes:
obtaining upstream section NH of the catalyst by solving an SCR reaction kinetic model 3 And calculating the ammonia concentration distribution of different partitions of the inlet section of the catalyst by using a mathematical relation formula corresponding to the concentration and the outlet NOx and taking the minimum relative deviation of the SCR outlet NOx concentration distribution uniformity as a target.
6. The method of claim 1, wherein the optimization matrix equation is as follows:
Figure FDA0003768086050000021
in the formula, a i,j Expressing the influence coefficient of the i-th subarea of the ammonia injection grid on a certain j area in the upstream area of the catalyst by injecting ammonia; y is i Both represent the i-th zone ammonia concentration demand in the upstream zone of the catalyst; x i Indicating the ammonia injection amount of the corresponding subarea/nozzle at the ammonia injection grid to be obtained.
7. The method of claim 1, wherein the quantitative solution of the optimal ammonia injection amount corresponding to the ammonia injection grid with the objective of most uniform SCR outlet NOx concentration distribution comprises:
determining the concentration distribution of NH3 at the inlet of the first-layer catalyst by using the mathematical relation between the concentration of NH3 at the upstream section of the catalyst and the concentration of NOx at the outlet, wherein the most uniform concentration distribution of NOx at the outlet of the SCR is taken as an optimization target;
and establishing a quantitative calculation correlation between the ammonia injection amount of different zones of the ammonia injection grid and the outlet NOx concentration distribution characteristic by combining the obtained optimization matrix equation based on the ammonia injection flow influence coefficients of different zones/nozzles, and calculating by using the correlation to obtain the optimized ammonia injection amount.
8. The method of claim 7, wherein the calculating an optimized ammonia injection amount by using a correlation comprises:
by analyzing the corresponding influence relationship of the ammonia injection amount of different partitions of the ammonia injection grid on the concentration distribution of the outlet NOx, the matlab is used for solving the optimization matrix equation by using a gradient descent method, and the optimized ammonia injection amount corresponding to different partitions/nozzles of the ammonia injection grid with the most uniform concentration distribution of the outlet NOx is obtained.
9. An ammonia injection optimization device based on an SCR reaction kinetic model is characterized by comprising:
at least one processor;
at least one memory for storing at least one program;
when executed by the at least one processor, cause the at least one processor to implement the method of any one of claims 1-8.
10. A computer-readable storage medium, in which a program executable by a processor is stored, wherein the program executable by the processor is adapted to perform the method according to any one of claims 1 to 8 when executed by the processor.
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