CN103736394A - Design method of guide plate of reducing flue of SCR (selective catalytic reduction) de-nitration device - Google Patents

Abstract

The invention provides a method for designing a variable-diameter flue deflector of an SCR denitrification device. The method divides the flue gas flowing through the variable-diameter flue by setting a deflector. The deflector is installed at the level of the SCR denitrification device. Inside the variable diameter flue, deflectors change the movement direction of fly ash particles in the variable diameter flue to avoid local enrichment of fly ash particles; The structural parameters and installation positions of the deflectors inside the channel; the structural parameters of the deflectors include: the number n of the deflectors, the length L of the deflectors, the spacing d of the deflectors, and the cross-section clamp between the deflectors and the entrance of the variable-diameter flue angle theta. The invention can improve the uniformity of fly ash particle distribution while satisfying the uniformity of flue gas velocity distribution, thereby avoiding local enrichment of fly ash particles in the catalytic layer and erosion damage to the catalyst.

Description

A design method for variable-diameter flue guide plate of SCR denitrification device

technical field

The invention relates to a design method for a variable-diameter flue guide plate of an SCR denitrification device aimed at adjusting the distribution of fly ash particles, and belongs to the technical field of thermal power environmental protection.

Background technique

Flue gas denitrification methods include selective catalytic reduction (SCR-Selective Catalytic Reduction) technology, selective non-catalytic reduction (SNCR) technology, SNCR/SCR combined flue gas denitrification technology, liquid absorption method, etc. Among the existing thermal power flue gas denitrification methods, SCR denitrification has become the most widely used flue gas purification technology due to its advantages of high denitrification efficiency, good selectivity, and low operating temperature. The main principle of the selective catalytic reduction method is the use of ammonia (NH ₃ ) and nitrogen oxides (NO _x ) in the catalyst composed of V ₂ O ₅ /WO ₃ /TiO ₂ or V ₂ O ₅ /MoO ₃ /TiO ₂ Nitrogen (N ₂ ) and water (H ₂ O) are generated through the redox reaction under the action of the flue gas, thereby removing the harmful NOx in the flue gas. The deflector of the SCR denitrification device is used to adjust the flue gas velocity field and the reducing agent concentration field, so as to control the flue gas velocity distribution and the reducing agent (ammonia) concentration distribution at the catalyst inlet as uniform as possible, such as the first layer of catalyst inlet The relative standard deviation of the smoke velocity distribution on the plane is used to measure the uniformity of the smoke velocity distribution, and this index is required to be less than 15%.

However, the analysis of denitrification devices with catalyst damage accidents shows that when the fly ash content in the flue gas is high, even if the uniformity of the flue gas velocity distribution meets the design requirements, the local enrichment of non-uniformly distributed fly ash particles in the flue gas will This leads to structural damage of the catalyst, which seriously reduces the service life of the catalyst. Therefore, for a high-ash unit, not only the uniformity of velocity distribution but also the dispersion control of fly ash particles should be considered when designing the deflector. Specifically, because the density of fly ash particles is much higher than that of flue gas, it has greater inertia than flue gas under flow conditions. When the fly ash particles move to the variable-diameter flue, it is usually difficult to quickly change the direction of movement, so that after the flue gas leaves the variable-diameter flue, the fly ash particles are enriched, and when they are delayed to the catalytic layer, the local catalyst is highly eroded possibility increases. The enrichment phenomenon of fly ash particles can be eliminated by reasonable design of variable-diameter flue deflectors, and the purpose of prolonging catalyst life can be achieved.

In engineering practice, the deflector used to control the uniformity of the smoke velocity distribution is usually an arc-shaped structure with a radius of R (R≈600mm) and a radian of π/2, and 100-300mm of the arc is connected along the tangential direction at both ends of the arc. Extend the bar. After searching the existing technical literature, it was found that Mao Jianhong, Song Hao, Wu Weihong, etc. published "Design and Optimization of Deflector for SCR Denitrification System of Power Plant Boiler ". This paper analyzes and studies the design scheme of the deflector in the denitration device, and optimizes the position and angle of the deflector, thereby improving the flue gas velocity and the distribution uniformity of ammonia concentration at the catalyst inlet. However, this paper did not analyze and study the distribution of fly ash particles inside the device, and the design of the corresponding deflector did not consider this factor.

Contents of the invention

Aiming at the defects in the prior art, the object of the present invention is to provide a design method for the variable-diameter flue deflector of the SCR denitrification device, which improves the catalyst inlet on the premise that the uniformity of the flue gas velocity distribution of the denitrification device meets the design requirements. The uniformity of fly ash particle distribution can protect the catalyst from local excessive erosion and improve the service life of the catalyst.

In order to achieve the above objectives, the present invention provides a design method for the guide plate of the variable-diameter flue of the SCR denitrification device. In this method, the flue gas flowing through the variable-diameter flue is divided by setting the guide plate. Inside the horizontal variable-diameter flue of the denitration device, the deflector changes the movement direction of fly ash particles in the variable-diameter flue to avoid local enrichment of fly ash particles.

Preferably, the structural parameters of the deflectors include: the number n of the deflectors, the length L of the deflectors, the spacing d of the deflectors, the angle θ between the deflectors and the inlet cross-section of the variable-diameter flue, and these parameters are based on The length, inlet width, and outlet width of the reducing flue are obtained through CFD (computational fluid dynamics) simulation optimization.

Preferably, the deflector divides the variable-diameter flue, which means: when the number of deflectors is n, the bend is divided into (n+1) channels, and the width of each channel entrance is d _i (i=1,2,…,n+1), that is, the distance between the ends of the deflector on the windward side.

Preferably, the angle θ between the deflectors and the inlet cross-section of the variable-diameter flue is the angle between the plane where each deflector is located and the cross-section of the inlet of the variable-diameter flue.

Preferably, the variable-diameter flue is a transitional flue that connects horizontal or vertical flues, has unequal inlet and outlet widths, and non-coinciding central axes.

Preferably, the deflector is a straight plate structure.

Compared with the prior art, the present invention has the following beneficial effects:

The invention can improve the uniformity of fly ash particle distribution on the entrance plane of the catalytic layer on the premise that the flue gas velocity distribution meets the design requirements, and at the same time, it also has an improvement effect on the flue gas velocity distribution, thereby avoiding the local enrichment of fly ash particles in the catalytic layer and its The erosion damage to the catalyst has the effect of prolonging the catalyst life of the SCR denitration system and improving the denitration efficiency.

Description of drawings

Other characteristics, objects and advantages of the present invention will become more apparent by reading the detailed description of non-limiting embodiments made with reference to the following drawings:

Figure 1 is a schematic diagram of the structure of the SCR denitrification device and the variable-diameter flue of the present invention;

In the figure: 1 is the first straight bend, 2 is the second straight bend deflector, 3 is the third straight bend deflector, 4 is the economizer, 5 is the SCR reactor, 6 is the ammonia injection grid, mixing Grille, 7 is variable-diameter flue deflector;

Fig. 2 is the size schematic diagram of variable-diameter flue deflector of the present invention;

Fig. 3 is the tracer fly ash particle distribution diagram at the inlet plane of the catalytic layer when the variable-diameter flue deflector is not installed;

Figure 4 is a distribution diagram of tracer fly ash particles on the entrance plane of the catalytic layer after adding a variable-diameter flue deflector.

Detailed ways

The present invention will be described in detail below in conjunction with specific embodiments. The following examples will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

This embodiment provides a method for designing the guide plate of the variable-diameter flue of the SCR denitrification device used for adjusting the uniformity of fly ash particles. Change the movement direction of fly ash particles in the diameter flue to avoid local enrichment of fly ash particles; according to the length, inlet width, and outlet width of the variable diameter flue, further determine the structural parameters and installation positions of the internal deflectors of the variable diameter flue.

As shown in Figure 1, it is a schematic diagram of the structure of the SCR denitrification device of a coal-fired unit and the variable-diameter flue, 1 is the first straight bend, 2 is the second straight bend deflector, 3 is the third straight bend deflector, 4 is the economizer, 5 is the SCR reactor, 6 is the ammonia injection grid and the mixing grid, and 7 is the variable-diameter flue deflector; the horizontal flue between the economizer 4 and the first straight bend 1 has A section of variable-diameter flue, the variable-diameter flue adopts the deflector designed by the present invention, that is, the variable-diameter flue deflector 7, and the other straight and curved flue places all adopt the arc that is commonly used in engineering with a radian of π/2 Shaped deflector; where:

The length of the variable diameter flue deflector is L _i (i=1,2).

The width of the inlet and outlet of the variable diameter flue is D ₁ and D ₂ respectively, the length is S, the number of deflectors is n (n≥1), and the width of each part of the flue divided by the deflector is d _i (i =1, 2, 3, ...), the angle between each deflector and the cross-section of the variable-diameter flue inlet is θ _i (i = 1, 2, ...) Dimensions are shown in Figure 2.

The above parameters n, L _i , d _i , θ _i are obtained through CFD (computational fluid dynamics) simulation optimization, where:

n=2;

D ₁ =10200mm, D ₂ =11880mm, S=2600mm;

L ₁ =1870mm, L ₂ =1870mm;

d ₁ =3675mm, d ₂ =3900mm, d ₃ =2625mm;

θ ₁ =43°, θ ₂ =40°.

In this example, the flue gas velocity at the inlet of the economizer is 16m/s, the ammonia injection velocity is 77m/s, the static pressure of the flue gas outlet is -1500Pa, the temperature is set at 650K, and the plane size of the catalytic layer inlet is 10.70m x 12.20m. 130.54m ² . The CFD simulation uses Fluent6.3.26 software, and the deflector design scheme commonly used in engineering is used for the position of each bend of the device.

The SCR reactor in Fig. 1 contains two layers, adopts honeycomb catalyst, and the inlet plane of the flue gas entering the SCR reactor is rectangular.

Figure 3 is a top view of the tracer fly ash particle distribution diagram at the entrance of the catalytic layer when no variable-diameter flue deflector is installed. The left side is the side near the boiler. The size of the road is: 10.70m left and right, 12.20m front and rear.

When no guide plate is installed at the trapezoidal diameter reduction of the horizontal flue, the relative standard deviation of the flue gas velocity distribution at the catalyst inlet plane is 12.4%. After the deflector is installed at this position, the relative standard deviation of the corresponding flue gas velocity distribution is reduced to 10.4%. In the above two cases, the relative standard deviation of the flue gas velocity distribution is better than the design standard (<15%), satisfying the velocity distribution Uniformity requirements. However, from the perspective of particle distribution, when no deflector is installed at the trapezoidal diameter reduction, the tracer fly ash particles on the upper surface of the catalyst are obviously enriched on the left side of the catalyst layer (as shown in Figure 3); In the central region of the catalytic layer, the particle distribution is very sparse. Further statistical data shows that within the rectangular strip 2m to the left of the catalyst inlet plane (the rectangular strip is the area between the left boundary and the dotted line in Figure 3, the area is 2m x 12.2m=24.40m ² , accounting for 10% of the total area of the entrance plane 18.69%), and the tracer particle density was 14.3/m ² , much higher than the average tracer particle density (6.4/m ² ) at the entrance plane. In this way, the catalyst in the rectangular strip area will be more strongly eroded by fly ash, which is likely to shorten the service life of the catalyst. After the deflector for particle distribution is installed at the variable-diameter flue, the tracer particle distribution of the corresponding section is shown in Figure 4, and the tracer particle density of the left rectangular strip is reduced to 6.9/m ² , which is close to the average Density, enrichment of tracer particles disappears, while the overall distribution of tracer particles at the inlet plane of the SCR reactor tends to be uniform, especially the sparseness of particles in the central area of Figure 3 disappears.

It can be seen that using the technology of the present invention in the variable-diameter flue can improve the uniformity of the distribution of fly ash particles at the entrance of the catalytic layer, eliminate the local enrichment of particles at the entrance of the catalytic layer, and avoid the problem of uneven distribution of fly ash particles. Excessive wear and erosion of the local catalytic layer plays a role in prolonging the life of the catalyst. At the same time, the technology of the present invention also improves the velocity distribution uniformity of the flue gas passing through the catalytic layer to a certain extent, which is beneficial to improving the denitrification efficiency.

Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art may make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention.

Claims (6)

1. a SCR denitrification apparatus reducing flue deflector method for designing, it is characterized in that, the method is cut apart the flue gas of the reducing flue of flowing through by deflector is set, described deflector is arranged on the horizontal reducing flue inside of SCR denitrification apparatus, this deflector changes the direction of motion of fly ash granule in reducing flue, avoids fly ash granule generation Local enrichment.

2. a kind of SCR denitrification apparatus reducing flue deflector method for designing according to claim 1, it is characterized in that, described deflector, its structural parameters comprise: deflector quantity n, deflector length L, deflector spacing d, deflector and reducing flue entrance cross section angle theta, these parameters obtain by CFD emulation optimizing according to the length of reducing flue, throat width, exit width.

3. a kind of SCR denitrification apparatus reducing flue deflector method for designing according to claim 2, it is characterized in that, described deflector is cut apart reducing flue, specifically refers to: when deflector number is n, bend is divided into (n+1) individual passage, the width of each feeder connection is d _i, i=1,2 ..., n+1,, i.e. spacing between two between deflector windward side end points.

4. a kind of SCR denitrification apparatus reducing flue deflector method for designing according to claim 2, is characterized in that, described deflector and reducing flue flue entrance section angle theta are the angles of each deflector place plane and reducing flue entrance cross section.

5. according to a kind of SCR denitrification apparatus reducing flue deflector method for designing described in claim 1-4 any one, it is characterized in that, described deflector is straight plate structure.

6. according to a kind of SCR denitrification apparatus reducing flue deflector method for designing described in claim 1-4 any one, it is characterized in that, described reducing flue is in horizontal or vertical flue, to play transition flue duct linking effect, that entrance is unequal with exit width, central axis does not overlap.

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