阅读说明：本技术 一种scr催化剂多层串联的脱硝效率预测方法 (Denitration efficiency prediction method for SCR catalyst multilayer series connection ) 是由 谢新华 宋玉宝 马云龙 姚燕 周健 王乐乐 卢承政 孔凡海 于 2021-08-02 设计创作，主要内容包括：本发明涉及一种SCR催化剂多层串联的脱硝效率预测方法,包括：对多层催化剂分别进行取样,对每层催化剂的参数进行检测；计算催化剂骨架微孔结构的有效扩散系数；根据催化剂参数、有效扩散系数计算脱硝反应速率常数；根据脱硝反应速率常数计算脱硝反应的活化能和指前因子；根据脱硝入口NH-(3)和NO浓度、催化剂脱硝反应活化能和指前因子计算该层催化剂在工程应用中MR<1时的出口脱硝效率；逐层计算获得催化剂多层串联时的脱硝效率。通过本发明的准确预测,可以合理制定催化剂再生或更换计划,有效预防发生因催化剂活性不足导致的NOx排放浓度或氨逃逸超标问题,为进一步的脱硝运行优化和设计优化奠定了基础。(The invention relates to a method for predicting denitration efficiency of SCR catalysts in multi-layer series connection, which comprises the following steps: respectively sampling the multiple layers of catalysts, and detecting the parameters of each layer of catalyst; calculating the effective diffusion coefficient of the microporous structure of the catalyst framework; calculating a denitration reaction rate constant according to the catalyst parameters and the effective diffusion coefficient; calculating denitration reaction rate constantActivation energy and pre-finger factor of nitro reaction; according to denitration inlet NH 3 Calculating MR of the catalyst layer in engineering application by using concentration of NO, activation energy of denitration reaction of the catalyst and pre-exponential factor<Outlet denitration efficiency at 1 hour; and calculating layer by layer to obtain the denitration efficiency of the catalysts when the catalysts are connected in series in a multi-layer mode. Through accurate prediction of the method, a catalyst regeneration or replacement plan can be reasonably formulated, the problem that the NOx emission concentration or ammonia escape exceeds the standard due to insufficient catalyst activity is effectively prevented, and a foundation is laid for further denitration operation optimization and design optimization.)

1. A denitration efficiency prediction method for SCR catalysts in multi-layer series connection is characterized by comprising the following steps: the method comprises the following steps:

1) respectively sampling the multiple layers of catalysts, and detecting the parameters of each layer of catalyst;

2) calculating the effective diffusion coefficient D of the microporous structure of the catalyst framework_e；

3) According to the catalyst parameters detected in 1), the effective diffusion coefficient D in 2)_eComputational denitrationA reaction rate constant k;

4) calculating and calculating activation energy E and pre-indication factor A of the denitration reaction according to the denitration reaction rate constant k in the step 3);

5) according to denitration inlet NH₃Calculating MR of the layer of catalyst in engineering application by using concentration of NO, activation energy E of denitration reaction of the catalyst and pre-exponential factor A<Outlet denitration efficiency η of 1 hour_MR＜1；

6) And calculating layer by layer to obtain the denitration efficiency of the catalyst when the catalysts are connected in series in a multi-layer mode.

2. The method of predicting denitration efficiency of an SCR catalyst in multi-layer series connection according to claim 1, characterized in that: in 2): effective diffusion coefficient D in catalyst framework microporous structure_eCalculated by the following formula:

in the above formula, D_beA dominant effective diffusion coefficient; d_keIs the effective micropore diffusion coefficient.

3. The method of predicting denitration efficiency of an SCR catalyst in multi-layer series connection according to claim 2, characterized in that: effective diffusion coefficient of host D_beEffective micropore diffusion coefficient D_keCalculated by the following formula:

in the above formula, D_ijIs the molecular diffusion coefficient of gas component i in gas j; theta is the catalyst framework porosity; τ is a tortuosity factor;is the average pore diameter of the micropores; t is the temperature; m is relative molecular weight.

4. The method of predicting denitration efficiency of an SCR catalyst in multi-layer series connection according to claim 3, characterized in that: coefficient of molecular diffusion D_ijCalculated by the following formula:

in the above formula, T is the temperature of the diffusion system; m is the relative molecular mass; p is the absolute pressure of the diffusion system; σ is the kinetic diameter of the molecule; omega_DIs a collision integral function.

5. The method of predicting denitration efficiency of an SCR catalyst in multi-layer series connection according to claim 4, characterized in that: collision integral function omega_DCalculated by the following formula:

in the above formula, A, B, C, K, E, F, G, H is a constant; t is the normalized gas temperature T/(ε/k).

6. The method of predicting denitration efficiency of an SCR catalyst in multi-layer series connection according to claim 1, characterized in that: in 3): the denitration reaction rate constant k is calculated by the following formula:

in the above formula, eta_MR＝1Denitration efficiency of the single-layer catalyst when activity detection is carried out for MR 1; sigma is the wet period of the catalyst pore channel; l is the length of the single-layer catalyst; u is the gas velocity in the catalyst pore channel; the sectional area of the catalyst pore channel X; alpha is the microcosmic specific surface area of the catalyst; d_eIs the effective diffusion coefficient within the microporous structure of the catalyst; phi is Thiele modulus; h is the catalyst half wall thickness.

7. The method of predicting denitration efficiency of an SCR catalyst in multi-layer series connection according to claim 1, characterized in that: in 4): the catalyst denitration reaction activation energy E and the pre-exponential factor A are calculated by the following formula:

in the above formula, T is temperature; r is a molar gas constant.

8. The method of predicting denitration efficiency of an SCR catalyst in multi-layer series connection according to claim 7, characterized in that: and substituting denitration reaction rate constants k at two different temperatures when calculating the catalyst denitration reaction activation energy E and the pre-indication factor A.

9. The method of predicting denitration efficiency of an SCR catalyst in multi-layer series connection according to claim 1, characterized in that: in 5): eta_MR＜1And η_MR＝1The relation of (A) is as follows:

10. the method of predicting denitration efficiency of an SCR catalyst in multi-layer series connection according to claim 1, characterized in that: in 1): the parameters of the catalyst comprise catalyst density, geometric characteristic parameters of the catalyst, microscopic specific surface area and pore volume of the catalyst, and catalyst activity parameters at a plurality of temperatures.

Technical Field

The invention relates to the technical field of denitration, in particular to a method for predicting denitration efficiency of SCR catalysts in multi-layer series connection.

Background

Coal fired power plants generally adopt high-temperature high-dust type SCR denitrification facilities to realize denitration in order to control NOx emission concentration. The SCR denitration device is arranged between the economizer and the air preheater, and due to the reasons of flying ash contamination, blockage, abrasion, poisoning, sintering and the like, the denitration activity of the SCR catalyst is continuously reduced in the service process, so that the utilization rate of the amino reducing agent is reduced, and the ammonia escape is increased. When NH is present₃/SO₃At an equivalence ratio of <1, unreacted NH₃With SO in flue gas₃、H₂And (3) generating Ammonium Bisulfate (ABS) through the O reaction, wherein the ammonium bisulfate is in a sticky liquid state at a low temperature section (about 147-230 ℃) of the air preheater, so that the ABS of the air preheater is polluted and blocked, and the safe and economic operation of a unit is threatened.

Therefore, in the operation process, the catalyst activity detection is required to be carried out regularly, a catalyst regeneration or replacement plan is reasonably formulated, and the problem that the NOx emission concentration or ammonia escape exceeds the standard due to insufficient catalyst activity is actively prevented. According to relevant requirements, a full-scale performance evaluation device is adopted for engineering application simulation evaluation and third-party catalyst detection evaluation, and due to the high detection cost, the content and working condition arrangement of catalyst activity detection are few, and the full-scale performance evaluation device mainly comprises physicochemical performance, single-layer denitration activity and multilayer series performance under a design working condition. In engineering-oriented application, a high-precision prediction model of the performance of a multilayer series SCR catalyst is urgently needed, and a theoretical basis and a calculation method are provided for carrying out denitration variable-working-condition operation optimization and design optimization with high efficiency and low cost.

The SCR denitration device is a large-scale fixed bed reactor, and a plurality of layers of formed catalysts are arranged inside the SCR denitration device. In calculating NH of SCR denitration device₃-DeNO_xIn performance, the NO of each layer of catalyst can be calculated one by one along the direction of air flow_xRemoval rate to obtain NO of the whole SCR reactor_xAnd (4) removing rate. Early derivation of NO for each catalyst based on catalyst activity_xThe removal rate can be expressed as:

in the formula eta_iNO of the i-th catalyst_xThe removal rate;

MR_i,inNH from catalyst inlet of i-th layer₃/NO_xA molar ratio;

K_iin situ NH of catalyst of the i-th layer₃-DeNO_xActivity, Nm/h;

AV_i-the surface velocity, Nm/h, of the flue gas flowing through the catalyst of the i-th bed.

The denitration catalyst has the capability of playing a catalytic role in the reaction process of an amino reducing agent and NOx, and the single-layer catalyst is characterized in NH₃the/NOx molar ratio MR is 1, and the comprehensive denitration performance under the specific smoke condition is realized. The catalyst activity when MR is 1 in the formula (1) was used to calculate MR<The denitration efficiency at 1 is not strict, which causes a large calculation error.

Disclosure of Invention

The invention aims to provide a method for predicting denitration efficiency of SCR catalysts in a multi-layer series connection mode.

In order to achieve the purpose, the invention adopts the technical scheme that:

a denitration efficiency prediction method for SCR catalyst multilayer series connection comprises the following steps:

1) respectively sampling the multiple layers of catalysts, and detecting the parameters of each layer of catalyst;

2) calculating the effective diffusion coefficient D of the microporous structure of the catalyst framework_e；

3) According to the catalyst parameters detected in 1), the effective diffusion coefficient D in 2)_eCalculating a denitration reaction rate constant k;

4) calculating and calculating activation energy E and pre-indication factor A of the denitration reaction according to the denitration reaction rate constant k in the step 3);

5) according to denitration inlet NH₃Calculating MR of the layer of catalyst in engineering application by using concentration of NO, activation energy E of denitration reaction of the catalyst and pre-exponential factor A<Outlet denitration efficiency η of 1 hour_MR＜1；

6) And calculating layer by layer to obtain the denitration efficiency of the catalyst when the catalysts are connected in series in a multi-layer mode.

Preferably, in 2): effective diffusion coefficient D in catalyst framework microporous structure_eCalculated by the following formula:

in the above formula, D_beA dominant effective diffusion coefficient; d_keIs the effective micropore diffusion coefficient.

Further preferred isGround, bulk effective diffusion coefficient D_beEffective micropore diffusion coefficient D_keCalculated by the following formula:

in the above formula, D_ijIs the molecular diffusion coefficient of gas component i in gas j; theta is the catalyst framework porosity; τ is a tortuosity factor;is the average pore diameter of the micropores; t is the temperature; m is relative molecular weight.

Further preferably, the molecular diffusion coefficient D_ijCalculated by the following formula:

in the above formula, T is the temperature of the diffusion system; m is the relative molecular mass; p is the absolute pressure of the diffusion system; σ is the kinetic diameter of the molecule; omega_DIs a collision integral function.

Further preferably, the collision integral function Ω_DCalculated by the following formula:

in the above formula, A, B, C, K, E, F, G, H is a constant; t is the normalized gas temperature T/(ε/k).

Preferably, in 3): the denitration reaction rate constant k is calculated by the following formula:

in the above formula, eta_MR＝1Denitration efficiency of the single-layer catalyst when activity detection is carried out for MR 1; sigma is the wet period of the catalyst pore channel; l is the length of the single-layer catalyst; u is the gas velocity in the catalyst pore channel; the sectional area of the catalyst pore channel X; alpha is the microcosmic specific surface area of the catalyst; d_eIs the effective diffusion coefficient within the microporous structure of the catalyst; phi is Thiele modulus; h is the catalyst half wall thickness.

Preferably, in 4): the catalyst denitration reaction activation energy E and the pre-exponential factor A are calculated by the following formula:

in the above formula, T is temperature; r is a molar gas constant.

Further preferably, the denitration reaction rate constants k at two different temperatures are substituted when the catalyst denitration reaction activation energy E and the pre-indication factor a are calculated.

Preferably, in 5): eta_MR＜1And η_MR＝1The relation of (A) is as follows:

preferably, in 1): the parameters of the catalyst comprise catalyst density, geometric characteristic parameters of the catalyst, microscopic specific surface area and pore volume of the catalyst, and catalyst activity parameters at a plurality of temperatures.

Due to the application of the technical scheme, compared with the prior art, the invention has the following advantages:

the invention realizes the accurate prediction of the multilayer catalyst series variable working condition denitration efficiency when the MR is less than 1 by using the single-layer catalyst activity detection data when the MR is less than 1, can reasonably make a catalyst regeneration or replacement plan according to the prediction result, effectively prevents the problem of NOx emission concentration or ammonia escape standard exceeding caused by insufficient catalyst activity, and lays a foundation for further denitration operation optimization and design optimization.

Drawings

FIG. 1 is a schematic flow chart of the present embodiment.

Detailed Description

The technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings, and it should be understood that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

A method for predicting denitration efficiency of SCR catalysts in multi-layer series connection specifically comprises the following steps:

step 1:

respectively sampling the multilayer catalysts, and detecting the parameters of each layer of catalyst, wherein: the parameters of the catalyst comprise catalyst density, geometric characteristic parameters of the catalyst, microscopic specific surface area and pore volume of the catalyst, and catalyst activity parameters at a plurality of temperatures.

Table 1: parameters of the catalyst

Serial number	Parameter(s)	Unit of
			1	Number of pores of catalyst	Hole x hole
2	Transverse length L of cross sectionA	mm
			3	Longitudinal length of cross section LB	mm
4	Length of unit body	mm
			5	Thickness of inner wall	mm
6	Pore diameter	mm
			7	Open porosity	％
8	Geometric specific surface area	m2/m3
			9	Density of catalyst	kg/m3
10	Micro specific surface area	m2/g
			11	Micro pore volume	cm3/g
12	Dough velocity AV in Activity detection	m/h
			13	Temperature of flue gas	℃
14	Ammonia nitrogen molar ratio MR during activity detection	--
			15	Inlet NOx content at activity detection	mg/m36% O on a dry basis2
16	O in flue gas2Content (wt.)	% dry basis
			17	H in flue gas2Content of O	％
18	Denitration efficiency during activity detection	％

Wherein: the serial numbers 1-10 are geometric characteristic parameters of the catalyst, and the serial numbers 12-18 are activity parameters of the catalyst.

Step 2:

calculating NH₃Effective diffusion coefficient D of NO in microporous structure of catalyst framework_eIn units of cm²And s. In this step, first, NH is performed₃And calculating the molecular diffusion coefficient of NO in the smoke, and then calculating the effective diffusion coefficient of NO in the microporous structure of the catalyst framework.

For NO, NH₃Diffusion in flue gas can be simplified to that they are in N₂The diffusion coefficient D of the component i in the component j is calculated based on the kinetic theory of fluid molecules₁₂In units of cm²The/s can be calculated by:

in the above formula, T is the temperature of the diffusion system in K; m is the relative molecular mass; p is the absolute pressure of the diffusion system in bar; σ is the kinetic diameter of the molecule in unitsσ_ij＝(σ_i+σ_j)/2；Ω_DAs a collision integral function, calculated by the following formula:

in the above equation, A, B, C, K, E, F, G, H is a constant, and in this embodiment: a is 1.06036; b-0.15610; c-0.19300; k-0.47635; e-1.03587; f-1.52996; g-1.76474; h-3.89411; t is the normalized gas temperature T/(ε/k). The gas physical property parameters such as M, sigma, epsilon/k and the like related to the gas physical property parameters are calculated and obtained by looking up a manual.

Next, the subject effective diffusion coefficient D is calculated_beIn units of cm²(s), effective micropore (Knudsen) diffusion coefficient D_keIn units of cm²And/s, calculated by the following formula:

in the above formula, D_ijIs the molecular diffusion coefficient of gas component i in gas j, in cm²S; theta is the porosity of the catalyst framework and is obtained by multiplying the microscopic pore volume by the framework density; tau is a tortuosity factor and has a value range of 2.0-2.3;the average pore diameter of the micropores is equal to 4 times of the volume of the micropores divided by the specific surface area of the micropores in cm; t is temperature, in K; m is relative molecular weight.

Finally, calculating the effective diffusion coefficient D in the microporous structure of the catalyst framework_eIn units of cm²And/s, calculated by the following formula:

in the above formula, D_beIs the main effective diffusion coefficient in cm²/s；D_keIs the effective micropore diffusion coefficient in cm²/s。

And step 3:

according to the detected catalyst parameters and the effective diffusion coefficient D_eCalculating a denitration reaction rate constant k by the following formula:

in the above formula, eta_MR＝1Denitration efficiency of the single-layer catalyst when activity detection is carried out for MR 1; sigma is the wet period of the catalyst pore channel and the unit cm; l is the length of the single-layer catalyst and is in cm; u is the air flow speed in the pore channel of the catalyst, and the unit is cm/s; cross-sectional area of X catalyst pore canal in cm²(ii) a k is a denitration reaction rate constant in the unit of cm/s; alpha is the microscopic specific surface area of the catalyst and the unit cm²/cm³；D_eIs the effective diffusion coefficient in the microporous structure of the catalyst in cm²S; phi is Thiele modulus; h is the half wall thickness of the catalyst in cm.

And 4, step 4:

according to the catalyst denitration reaction rate constant k at the two different temperatures, an Arrhenius equation is utilized:

in the above formula: t is the temperature; r is a molar gas constant, R-8.314J/(mol x K).

Solving the activation energy E and the pre-exponential factor A of the denitration reaction. In order to ensure the accuracy of denitration efficiency prediction under variable working conditions, the catalyst activity detection temperature for solving the denitration reaction activation energy E and the pre-indication factor A covers the service temperature range of the catalyst.

And 5:

according to denitration inlet NH₃Calculating MR of the layer of catalyst in engineering application by using concentration of NO, activation energy E of denitration reaction of the catalyst and pre-exponential factor A<Outlet denitration efficiency η of 1 hour_MR＜1。

According to NH₃Effect of concentration and MR on denitration efficiency, η_MR＜1And η_MR＝1The relationship (c) is represented by the following formula.

In the above formula, n is 5-50 ppm.Entrance MR<1, flowing to NH in the catalyst layer along the flue gas₃the/NOx molar ratio is becoming smaller. In order to ensure the calculation accuracy, each layer of catalyst needs to be divided into a plurality of small sections with the length of 1cm for calculation of the MR inlet and the denitration efficiency, and NH at the outlet of each small section₃And NO concentration is NH of the next segment of inlet₃And NO concentration.

Step 6:

when multiple layers are connected in series, the NH at the outlet of the catalyst of the first layer is calculated from the first layer₃And NO concentration is NH at the inlet of the second layer catalyst₃And the concentration of NO is calculated layer by layer along the flow direction of the flue gas to obtain the final NH at the outlet when the catalysts are connected in series in a multi-layer manner₃And NO concentration, denitration efficiency.

The method provided by the embodiment is adopted to predict the denitration efficiency of 4 new catalysts and 2 old catalysts in series, and the results are shown in table 2, wherein the absolute errors are all below 1.5%.

Table 2: prediction result of series performance of catalyst

The above embodiments are merely illustrative of the technical ideas and features of the present invention, and the purpose thereof is to enable those skilled in the art to understand the contents of the present invention and implement the present invention, and not to limit the protection scope of the present invention. All equivalent changes and modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.