CN104096477B - A kind of static mixer for selective catalytic reduction flue gas denitration system - Google Patents

Abstract

The invention discloses a static mixer used in a selective catalytic reduction flue gas denitrification system. The static mixer is installed in the flue of the denitrification system and includes a plurality of mixing units with the same structure, wherein each mixing unit consists of eight Congruent right-angled triangular structures are spliced together around the same center point, and these eight right-angled triangular structures are divided into four groups, each of which includes two right-angled triangular structures connected to each other by a right-angled side, and then adjacent groups The hypotenuses of the right-angled triangular plate structure are completely connected to each other; in addition, the center points of each mixing unit are respectively located directly above the circle centers of the nozzles of the flue ammonia injection grille. Through the present invention, the mixing degree of ammonia gas and flue gas can be significantly improved, the uniformity of ammonia-nitrogen molar ratio can be improved, a small system pressure loss can be generated, and short-distance mixing can be realized. At the same time, it has obvious turbulence effect, compact overall structure, and is easy to process. and installation features.

Description

A static mixer for selective catalytic reduction flue gas denitrification system

technical field

The invention belongs to the technical field of flue gas denitrification devices in coal-fired power plants, and more specifically relates to a static mixer used in a selective catalytic reduction (SCR) flue gas denitrification system.

Background technique

At present, my country has increasingly strict requirements on the emission control of nitrogen oxides from coal-fired power plants. Selective Catalytic Reduction (SCR) flue gas denitrification method is an efficient and mature technology, and the highest denitrification efficiency can reach more than 90%. It has been widely used in the field of nitrogen oxide pollutant control in power plants at home and abroad.

In the SCR reaction system, an important part of the ammonia/air mixing system, the ammonia nitrogen molar ratio directly affects the denitrification efficiency and ammonia slip rate. If ammonia gas and NOx are mixed unevenly, the incompletely reacted ammonia gas will escape directly from the reactor; NH ₃ reacts with SO ₃ and H ₂ O in the flue gas to form NH ₄ HSO ₄ , which will aggravate the cooling of the air preheater. segment corrosion, resulting in severe clogging of the air preheater. When the blockage is serious, the resistance will increase by 30% to 50%, which will have a great impact on the safe and economical operation of the unit.

At present, in the SCR denitrification system of the power plant, the ammonia injection grid is mainly used to perform the ammonia mixing process. Due to the limitation of the reactor space, the gas mixing distance is limited, resulting in uneven mixing of ammonia gas and flue gas. For this reason, a mixer is added in the prior art to make the ammonia gas and the flue gas mix evenly. However, further studies have shown that the traditional mixer has defects such as poor mixing effect, large system pressure loss, and complicated processing, so it is necessary to make further improvement or improvement in this field.

Contents of the invention

In view of the above defects or improvement needs of the prior art, the present invention provides a new type of static mixer for selective catalytic reduction flue gas denitrification system, wherein the structure of its key components and its arrangement are studied, Correspondingly, it can significantly improve the mixing degree of ammonia gas and flue gas, improve the uniformity of ammonia-nitrogen molar ratio, generate small system pressure loss, realize short-distance mixing, and at the same time have obvious turbulence effect, compact overall structure, easy processing and installation, etc. characteristics, so it is especially suitable for the mixed use of ammonia/flue gas in the SCR reaction system.

In order to achieve the above object, according to the present invention, a static mixer for selective catalytic reduction flue gas denitrification system is provided, the static mixer is installed in the flue of the denitrification system, and includes multiple A hybrid unit arranged horizontally in the cross-sectional direction of the road, characterized in that:

Each hybrid unit is composed of eight congruent right-angled triangular plate structures jointly spliced around the same center point, and the splicing is performed in the following way: The eight right-angled triangular plate structures are divided into four groups, each of which includes two right-angled Triangular structures, and these two right-angled triangle structures are completely connected to each other through their respective right-angled sides; then, adjacent groups are completely connected to each other through the hypotenuses of the right-angled triangular plate structure;

In addition, the central points of each mixing unit are respectively located directly above the center of each nozzle of the ammonia injection grid in the flue, in this way, when the ammonia gas is injected into the flue through the nozzle of the ammonia injection grid, the The center of the mixing unit is divided into eight parts by the tank bottom formed by the splicing of the right-angled triangular plate structure, and then flows through the hypotenuse of the right-angled triangle structure to generate a vortex, which leads to a greater degree of uniform mixing of ammonia and flue gas.

As a further preference, for the above-mentioned static mixer, the sum of the projected areas of all right-angled triangular plate structures on the horizontal plane is set to be less than 35% of the cross-section of the flue, so as to avoid excessive pressure drop.

As a further preference, the three sides of the right-angled triangular plate structure are preferably unequal.

As a further preference, the mixing units are all welded on stainless steel pipes, and then fixed to the side wall of the flue through the stainless steel pipes.

As a further preference, the distance between the center point of each mixing unit and the nozzles of the ammonia injection grid is preferably set at 0.3m˜1m.

Generally speaking, compared with the prior art, the above technical solution conceived by the present invention mainly has the following technical advantages:

1. By adopting a plurality of right-angled triangular plate structures to splice the mixing unit together and studying the splicing method, the test shows that the ammonia gas will generate a vortex when it passes through this time, which will cause the gas to perform the maximum mixing in the shortest distance. In addition, the process The spoiler effect is remarkable, and the pressure drop is small;

2. By setting other key performance parameters of the above-mentioned static mixer, such as the projected area, the height from the ammonia nozzle, etc., it is verified by using the fluid dynamics calculation software that it can quickly perform mixing for each strand of ammonia gas, greatly Improve the mixing efficiency and realize the uniform mixing between ammonia and flue gas;

3. The new static mixer according to the present invention is compact in structure, easy to process and install, and has strong applicability. At the same time, it has the characteristics of effectively reducing ammonia escape and improving denitrification efficiency, so it is especially suitable for ammonia in various existing SCR denitrification systems. Gas/fume mixed use.

Description of drawings

Fig. 1 is a three-dimensional schematic diagram of a mixing unit constructed according to a preferred embodiment of the present invention;

Fig. 2 is the front view when static mixer according to the present invention is installed in flue;

Fig. 3 is a schematic diagram of the main structure used for exemplary illustration when the static mixer according to the present invention is used in an existing SCR flue gas denitrification system;

Throughout the drawings, the same reference numerals are used to designate the same elements or structures, wherein:

1- Economizer 2- Ammonia injection grid 3- Static mixer 4- Baffle plate 5- Rectification grid 6- Catalyst layer 31- Mixing unit 32- Right angle triangular plate structure 33- Stainless steel tube

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not constitute a conflict with each other.

Fig. 3 is a schematic diagram of the main structure for exemplarily explaining when the static mixer according to the present invention is used in an existing SCR flue gas denitrification system. As shown in Figure 3, after leaving the economizer 1, the high-temperature flue gas turns downwards along the flue through 90 degrees to enter the horizontal section, and after being rectified by two sets of deflectors, it turns to the vertical section. An ammonia injection grid 2 (AIG) is arranged near the downstream of the vertical flue, and a static mixer 3 according to the present invention is installed above the ammonia injection grid 2, for example, 0.5m. This static mixer 3 is made up of a plurality of identical mixing units of structure, and as shown in Figure 2, is welded on a stainless steel tube 33 and arranges horizontally along the cross-sectional direction of flue, and its quantity is the same as that of the ammonia spraying grid. The number of nozzles in the grid is the same, for example, 80. After the ammonia gas is injected into the flue through the AIG nozzle, it hits the center of each mixing unit 31, the diluted ammonia gas is quickly disturbed, and at the same time entrained by the smoke from the upstream and fully diffused; then continues to pass through the top of the vertical flue Two turns take place, passing down the fairing grille 5 . The fully mixed ammonia and flue gas enter the catalyst layer 6 for a catalytic reduction reaction, and the denitrated clean flue gas flows to the downstream air preheater.

The novel static mixer according to the present invention will be specifically described below with reference to FIG. 1. FIG. As shown in FIG. 1 , each mixing unit 31 is formed by splicing together eight congruent, i.e. completely overlapping right-angled triangular plate structures 32 around the same central point, wherein the three sides of each right-angled triangular plate structure 32 are respectively are not equal, and the splicing is performed in the following manner: the eight right-angled triangular plate structures are divided into four groups, wherein each group respectively includes two right-angled triangular structures, and the two right-angled triangular structures are completely connected to each other by their respective right-angled sides; Then, the adjacent groups are completely connected to each other through the hypotenuses of the right-angled triangular plate structure. For further convenience of observation, it needs to be pointed out that the group directly in front of Figure 1 presents an inwardly concave structure, while the group directly behind protrudes toward the reader; these four groups are similar to double wings It is in the form of a sheet, and can form an inclination angle of 35° to 45° with the horizontal plane, and the specific angle can be adjusted according to the actual gas flow rate.

In addition, the center points of each mixing unit 31 are respectively located directly above the circle centers of the nozzles of the ammonia injection grid 2 in the flue. The center of the mixing unit 31 is divided into eight parts by the bottom of the tank formed by the splicing of the right-angled triangular plate structure, and then flows through the hypotenuse of the right-angled triangle structure to generate a vortex, which causes the gas to be mixed to the greatest extent in the shortest distance. The mixing unit The surrounding airflow interacts to accelerate the uniform distribution of ammonia. The single mixed airflow after the turbulence is diffused to a wider space in a very short distance, the turbulence effect is remarkable, and the pressure drop is minimal.

More specifically, the hypotenuse of each right-angled triangular plate is preferably set to 150 mm to 400 mm, and the thickness is preferably 6 mm, which can be determined according to the cross-sectional area of the flue and the number of nozzles of the ammonia injection grid. According to a preferred embodiment of the present invention, for the above-mentioned static mixer, the sum of the projected areas of all right-angled triangular plate structures on the horizontal plane is set to be less than 35% of the cross-section of the flue, so as to avoid excessive pressure drop.

According to another preferred embodiment of the present invention, the center point of each mixing unit is set at a distance of 0.3m-1m from the nozzle of the ammonia injection grid. The simulation verification of fluid dynamics calculation software shows that the above working parameters can realize the rapid mixing of each ammonia gas in a short distance, effectively improve the mixing efficiency, and enhance the turbulence interference, and finally ensure the separation between ammonia gas and flue gas. Uniform response.

In addition, according to the present invention, the number of mixing units is determined by the cross section of the flue, and the arrangement can be determined according to the nozzles of the matching ammonia injection grid, as long as the center point of the mixing units is directly above the center of the nozzle.

The practical effect of the present invention is verified by using a numerical simulation method, and it is calculated that the velocity distribution deviation in front of the catalyst in the first layer of the SCR reactor can reach 8.7%. In addition, before the mixer was installed, the concentration deviation of the ammonia nitrogen molar ratio was 7.5%. After the mixer was installed, the deviation value was 4.3%, and the resulting system resistance was 72pa, which was in line with the engineering design goal. The above actual test results showed that The static mixer of the invention has great application value.

It is easy for those skilled in the art to understand that the above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, All should be included within the protection scope of the present invention.

Claims (4)

1. A static mixer for a selective catalytic reduction flue gas denitrification system, which is installed in the flue of the denitrification system and includes a plurality of mixing units with the same structure and arranged horizontally along the cross-sectional direction of the flue , characterized by: Each hybrid unit is composed of eight congruent right-triangular structures joined together around the same center point, and the joining is performed in the following way: The eight right-triangular structures are divided into four groups, each of which consists of two right triangles structure, and these two right-angled triangular structures are completely connected to each other through their respective right-angled sides; then, adjacent groups are completely connected to each other through the hypotenuses of the right-angled triangular plate structure; In addition, the central points of each mixing unit are respectively located directly above the center of each nozzle of the ammonia injection grid in the flue, in this way, when the ammonia gas is injected into the flue through the nozzle of the ammonia injection grid, the The center of the mixing unit is divided into eight parts by the tank bottom formed by the splicing of the right-angled triangular plate structure, and then flows through the hypotenuse of the right-angled triangle structure to generate a vortex, which leads to a greater degree of uniform mixing of ammonia and flue gas. 2. The static mixer according to claim 1, characterized in that the sum of the projected areas of all right-angled triangular plate structures on the horizontal plane is set to be less than 35% of the cross-section of the flue, so as to avoid excessive pressure drop. 3. The static mixer according to claim 1 or 2, wherein the three sides of the right-angled triangular plate are not equal. 4. The static mixer according to claim 3, characterized in that, the distance between the center point of each mixing unit and the nozzles of the ammonia injection grid in the flue is set at 0.3m-1m.