Ammonia spraying grid structure for short-distance mixing of SCR (Selective Catalytic Reduction) denitration system of heating furnace

Abstract

The invention relates to an ammonia spraying grid structure for short-distance mixing of a heating furnace SCR denitration system, and belongs to the field of petrochemical industry flue gas treatment. Comprising a flue gas and ammonia gas mixing chamber, two flue gas turbulent flow pipelines and an ammonia spraying grid, wherein the flue gas and ammonia gas mixing chamber is of a rectangular pyramid shell structure which is vertically placed; the two flue gas turbulent flow pipelines are horizontally and symmetrically arranged on the two sides of the flue gas and ammonia gas mixing chamber, and the flue gas turbulent flow pipelines are communicated with an inner cavity of the flue gas and ammonia gas mixing chamber; the ammonia spraying grid horizontally extends into an inner cavity of the flue gas and ammonia gas mixing chamber from the side wall of the bottom end of the flue gas and ammonia gas mixing chamber; the small opening end of the flue gas and ammonia gas mixing chamber is upward and is a flue gas outlet of the heating furnace; the large opening end of the flue gas and ammonia gas mixing chamber faces downwards and is a flue gas inlet of the heating furnace; the device is applied to the upstream of the SCR denitration reactor so as to ensure that NH3 molecules can be uniformly distributed on the section of a flue, and full and uniform mixing of ammonia gas and low-speed flue gas can be realized in a relatively small space. Ammonia escape is reduced; and the denitration efficiency is improved.

Description

Technical Field

[0001] This invention belongs to the field of petrochemical flue gas treatment and relates to an ammonia injection grid structure for short-distance mixing in a heating furnace SCR denitrification system. Background Technology

[0002] Nitrogen oxides (NOx) are one of the main pollutants emitted from thermal power plants, industrial furnaces, and ships. Large amounts of NOx emitted into the air cause a series of environmental problems. To effectively prevent environmental pollution, NOx treatment of flue gas is necessary. Among current flue gas NOx technologies, Selective Catalytic Reduction (SCR) is widely used due to its low reaction temperature and high NOx removal efficiency. Various forms and structures of ammonia injection grids are developed to achieve uniform mixing of ammonia and flue gas and improve NOx removal efficiency.

[0003] As a core component of denitrification units, the ammonia injection grid is typically located at the front end of the SCR reactor. It includes ammonia injection pipes, nozzles, supports, and accessories. Ammonia gas enters the injection pipes upstream and is injected into the flue gas duct through the nozzles to mix with the flue gas. While the arrangement of multiple ammonia injection pipes and numerous nozzles in the flue gas duct cross-section ensures ammonia injection coverage, it can also lead to weak diffusion of ammonia gas upstream of the injection grid, affecting the denitrification effect. Flue gas velocity is also a crucial factor affecting denitrification efficiency. Higher flue gas velocities result in greater gas turbulence within the flue gas duct, leading to better mixing after the flue gas passes through the injection grid. Conversely, lower flue gas velocities result in insufficient mixing with ammonia, negatively impacting the flue gas denitrification treatment effect. Summary of the Invention

[0004] The technical problem solved by this invention is to overcome the shortcomings of existing technologies and propose an ammonia injection grid structure for short-distance mixing in a heated furnace SCR denitrification system. This structure is applied upstream of the SCR denitrification reactor to ensure that NH3 molecules are uniformly distributed across the flue gas cross-section, achieving thorough and uniform mixing of ammonia and low-velocity flue gas within a smaller space. This reduces ammonia slip and improves denitrification efficiency.

[0005] The solution of the present invention is:

[0006] An ammonia injection grid structure for short-distance mixing in a heating furnace SCR denitrification system includes a flue gas ammonia mixing chamber, two flue gas turbulence pipes, and an ammonia injection grid.

[0007] The flue gas ammonia mixing chamber is a vertically placed four-sided pyramidal shell structure; two flue gas turbulence pipes are horizontally and symmetrically arranged on both sides of the flue gas ammonia mixing chamber, and the flue gas turbulence pipes are connected to the inner cavity of the flue gas ammonia mixing chamber; the ammonia injection grid extends horizontally from the bottom side wall of the flue gas ammonia mixing chamber into the inner cavity of the flue gas ammonia mixing chamber.

[0008] In the aforementioned ammonia injection grid structure for short-distance mixing in an SCR denitrification system for a heating furnace, the small end of the flue gas ammonia mixing chamber faces upward and is defined as the flue gas outlet of the heating furnace; the large end of the flue gas ammonia mixing chamber faces downward and is defined as the flue gas inlet of the heating furnace; thus realizing that the flue gas of the heating furnace enters from the flue gas inlet of the heating furnace and exits from the flue gas outlet of the heating furnace.

[0009] In the above-mentioned ammonia injection grid structure for short-distance mixing in a heating furnace SCR denitrification system, the characteristic feature is that the flue gas turbulence pipe includes a main flue gas inlet pipe and n flue gas inlet branch pipes.

[0010] Among them, the main flue gas inlet pipe is horizontally parallel to the corresponding side wall of the flue gas ammonia mixing chamber; n flue gas inlet branch pipes are evenly arranged along the axial direction of the main flue gas inlet pipe; and n flue gas inlet branch pipes are perpendicular to the main flue gas inlet pipe.

[0011] In the aforementioned ammonia injection grid structure for short-distance mixing in an SCR denitrification system for a heating furnace, the main flue gas inlet pipe is a cylindrical structure with one end open and the other closed; the flue gas inlet branch pipes are all cylindrical structures; one axial end of the flue gas inlet branch pipe is connected to the main flue gas inlet pipe; the other axial end of the flue gas inlet branch pipe is connected to the flue gas ammonia mixing chamber; n is a positive integer not less than 5.

[0012] In the aforementioned ammonia injection grid structure for short-distance mixing in a heating furnace SCR denitrification system, the flue gas from the heating furnace enters the flue gas inlet main pipe from the open end of the flue gas inlet main pipe, and then enters the flue gas ammonia mixing chamber through n flue gas inlet branch pipes.

[0013] In the above-mentioned ammonia injection grid structure for short-distance mixing in a heating furnace SCR denitrification system, the ammonia injection grid includes an ammonia main pipe, m ammonia branch pipes, and m×k pairs of conical nozzles.

[0014] The ammonia main pipe is placed horizontally; m ammonia branch pipes are evenly arranged along the axial direction of the ammonia main pipe; one end of the ammonia branch pipe is connected to the inner cavity of the ammonia main pipe; the other end of the ammonia branch pipe extends into the inner cavity of the flue gas ammonia mixing chamber; and k pairs of conical nozzles are evenly arranged along the axial direction on each ammonia branch pipe.

[0015] In the aforementioned ammonia injection grid structure for short-distance mixing in an SCR denitrification system for a heating furnace, the ammonia main pipe is a horizontally placed T-shaped cylindrical structure; the short arm section of the T-shaped ammonia main pipe has an opening; both ends of the long arm section of the T-shaped ammonia main pipe are blocked; the long arm section of the ammonia main pipe is arranged parallel to the side wall of the flue gas ammonia mixing chamber; the short arm section of the ammonia main pipe is arranged perpendicular to the middle of the long arm section; one end of the ammonia branch pipe is connected to the long arm section, and the other end extends into the cavity of the flue gas ammonia mixing chamber.

[0016] In the aforementioned ammonia injection grid structure for short-distance mixing in a heating furnace SCR denitrification system, ammonia gas enters from the opening of the short arm section and passes sequentially through the short arm section, the long arm section, the ammonia branch pipe, and the conical nozzle, before being ejected from the flue gas ammonia mixing chamber.

[0017] In the aforementioned ammonia injection grid structure for short-distance mixing in an SCR denitrification system for a heating furnace, k pairs of conical nozzles are evenly distributed along the axial direction of the ammonia branch pipe and are all located at the top of the ammonia branch pipe; m is a positive integer not less than 6; k is a positive integer not less than 6.

[0018] In the aforementioned ammonia injection grid structure for short-distance mixing in an SCR denitrification system for a heating furnace, each pair of conical nozzles includes two conical nozzles; the two conical nozzles are symmetrically distributed at an angle; each conical nozzle is an inverted cone structure.

[0019] The advantages of this invention compared to the prior art are:

[0020] (1) The ammonia-air mixture of the present invention first enters the ammonia injection main pipe and is then diverted to the ammonia injection branch pipe. The alternating arrangement of nozzles on the ammonia injection branch pipe ensures the injection coverage of the upper area of ​​the grid. The ammonia gas sprayed from the inclined nozzles provides a hybrid power of horizontal and vertical mixing for the flue gas, and also generates a significant secondary contact zone, prolonging the contact time between the flue gas and the ammonia gas, making the mixing more uniform.

[0021] (2) The flue gas of the present invention is horizontally injected into the gas mixing zone through the symmetrically distributed flue gas turbulence main pipe and branch pipe. After the two airflows meet and collide in the middle, the convergence and relative movement of the two gases intensify the degree of gas disorder, especially intensifying the disturbance of the gas above the ammonia injection grid, further promoting the mixing of flue gas and ammonia.

[0022] (3) The dual configuration of the ammonia injection grid and flue gas turbulence tube group in this invention provides multiple disturbance forces for the gas mixing area, and the COV value is less than 0.05 in the inlet of the first catalyst layer. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the overall structure of the ammonia injection grid of the present invention;

[0024] Figure 2 This is a schematic diagram of the ammonia injection grid of the present invention;

[0025] Figure 3 This is a schematic diagram of the conical nozzle of the present invention. Detailed Implementation

[0026] The present invention will be further described below with reference to the embodiments.

[0027] This invention provides an ammonia injection grid for short-distance uniform mixing in an SCR denitrification system, comprising a flue gas ammonia mixing zone, an ammonia injection grid, and flue gas turbulence ducts. The gas mixing zone has a square or irregular shape. The ammonia injection grid is located at the bottom layer of the gas mixing zone. The ammonia injection grid includes a delivery pipe, a main ammonia injection pipe, and branch ammonia injection pipes. The branch ammonia injection pipes have nozzles at a certain angle distributed alternately and equidistantly. The nozzles are conical nozzles, which can entrain the flue gas at the conical section, increasing the mixing of ammonia and flue gas. Above the ammonia injection grid are two sets of symmetrically distributed flue gas turbulence ducts, each including a turbulence main pipe and turbulence branch pipes.

[0028] Ammonia injection grid structure for short-distance mixing in SCR denitrification systems of heating furnaces, such as Figure 1 As shown, it specifically includes a flue gas-ammonia mixing chamber, two flue gas turbulence ducts, and an ammonia injection grille. The flue gas-ammonia mixing chamber is a vertically placed four-sided pyramidal shell structure; the two flue gas turbulence ducts are horizontally and symmetrically arranged on both sides of the flue gas-ammonia mixing chamber, and the flue gas turbulence ducts are connected to the inner cavity of the flue gas-ammonia mixing chamber; the ammonia injection grille extends horizontally from the bottom side wall of the flue gas-ammonia mixing chamber into the inner cavity of the flue gas-ammonia mixing chamber.

[0029] The small opening of the flue gas-ammonia mixing chamber faces upward and is defined as the flue gas outlet 2 of the heating furnace; the large opening of the flue gas-ammonia mixing chamber faces downward and is defined as the flue gas inlet 1 of the heating furnace; thus, the flue gas of the heating furnace enters from the flue gas inlet 1 and exits from the flue gas outlet 2 of the heating furnace.

[0030] The flue gas turbulence duct includes a main flue gas inlet pipe 3 and n flue gas inlet branch pipes 4. The main flue gas inlet pipe 3 is horizontally parallel to the corresponding side wall of the flue gas ammonia mixing chamber; the n flue gas inlet branch pipes 4 are evenly arranged along the axial direction of the main flue gas inlet pipe 3; and the n flue gas inlet branch pipes 4 are perpendicular to the main flue gas inlet pipe 3.

[0031] The main flue gas inlet pipe 3 is a cylindrical structure with one open end and one closed end; the flue gas inlet branch pipes 4 are all cylindrical structures; one axial end of the flue gas inlet branch pipe 4 is connected to the main flue gas inlet pipe 3; the other axial end of the flue gas inlet branch pipe 4 is connected to the flue gas ammonia mixing chamber; n is a positive integer not less than 5. After the flue gas from the heating furnace enters the main flue gas inlet pipe 3 through the open end, it enters the flue gas ammonia mixing chamber through n flue gas inlet branch pipes 4.

[0032] like Figure 2 As shown, the ammonia injection grid includes an ammonia main pipe 7, m ammonia branch pipes 8, and m×k pairs of conical nozzles 9. The ammonia main pipe 7 is placed horizontally; the m ammonia branch pipes 8 are evenly arranged along the axial direction of the ammonia main pipe 7; one end of each ammonia branch pipe 8 is connected to the inner cavity of the ammonia main pipe 7; the other end of each ammonia branch pipe 8 extends into the inner cavity of the flue gas ammonia mixing chamber; and each ammonia branch pipe 8 has k pairs of conical nozzles 9 evenly arranged along its axial direction.

[0033] The ammonia main pipe 7 is a horizontally placed T-shaped cylindrical structure; the short arm of the T-shaped ammonia main pipe 7 has an opening; both ends of the long arm of the T-shaped ammonia main pipe 7 are blocked; the long arm of the ammonia main pipe 7 is set parallel to the side wall of the flue gas ammonia mixing chamber; the short arm of the ammonia main pipe 7 is set perpendicular to the middle of the long arm; one end of the ammonia branch pipe 8 is connected to the long arm, and the other end extends into the cavity of the flue gas ammonia mixing chamber.

[0034] Ammonia gas enters through the opening in the short arm section and passes sequentially through the short arm section, the long arm section, the ammonia branch pipe 8, and the conical nozzle 9 before being ejected from the flue gas ammonia mixing chamber.

[0035] like Figure 3 As shown, k pairs of conical nozzles 9 are evenly distributed along the axial direction of the ammonia branch pipe 8, and are all located at the top of the ammonia branch pipe 8; m is a positive integer not less than 6; k is a positive integer not less than 6. Each pair of conical nozzles 9 includes 2 conical nozzles 9; the 2 conical nozzles 9 are symmetrically distributed at an angle; each conical nozzle 9 is an inverted cone structure.

[0036] Ammonia gas enters the main injection pipe upstream and is evenly distributed into the branch injection pipes. It is then injected obliquely upwards into the gas mixing zone through nozzles on the branch pipes. Low-velocity flue gas flows upwards into the gas mixing zone and mixes with the injected ammonia gas. The flue gas is then diverted into the branch pipes through two symmetrical sets of flue gas turbulence main pipes and injected horizontally into the gas mixing zone. The two airflows with the same speed but opposite directions collide in the middle of the gas mixing zone, moving upwards and downwards respectively. The convergence and relative movement of the two gas streams intensify the gas turbulence, especially the disturbance of the gas above the ammonia injection grid, further promoting the mixing of flue gas and ammonia. The ammonia flow rate can be adjusted according to the flue gas volume to achieve a balance between the mixing effect and economy of flue gas and ammonia.

[0037] This invention achieves uniform mixing of ammonia and flue gas in a relatively small space, saving on investment costs. The ammonia-air mixture first enters the main ammonia injection pipe and is then branched to the branch ammonia injection pipes. The alternating arrangement of nozzles on the branch ammonia injection pipes ensures the injection coverage of the upper area of ​​the grid. The ammonia injected by the inclined nozzles provides a hybrid mixing of lateral and longitudinal gases for the flue gas, and also creates a significant secondary contact zone, extending the contact time between the flue gas and ammonia, resulting in a more uniform mixture.

[0038] The dual setup of the ammonia injection grid and the flue gas turbulence tube assembly provides multiple disturbance forces for the gas mixing zone, resulting in a non-uniform COV value of less than 0.05 before the inlet of the first catalyst layer.

[0039] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by utilizing the methods and techniques disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the protection scope of the technical solutions of the present invention.

Claims

1. A structure of ammonia injection grid for short-distance mixing of a heating furnace SCR denitration system, characterized in that: The device comprises a flue gas ammonia mixing chamber, two flue gas disturbance pipelines and an ammonia injection grid. The flue gas ammonia mixing chamber is a vertical four-prism-pyramid shell structure; the two flue gas disturbance pipelines are symmetrically arranged horizontally on the two sides of the flue gas ammonia mixing chamber and are in communication with the inner cavity of the flue gas ammonia mixing chamber; the ammonia injection grid extends horizontally from the bottom end of the sidewall of the flue gas ammonia mixing chamber into the inner cavity of the flue gas ammonia mixing chamber.

2. The ammonia injection grid structure for short-range mixing of a heating furnace SCR denitration system according to claim 1, characterized in that: The small end of the flue gas ammonia mixing chamber is upward, which is defined as the flue gas outlet (2) of the heating furnace; the large end of the flue gas ammonia mixing chamber is downward, which is defined as the flue gas inlet (1) of the heating furnace; the flue gas of the heating furnace is introduced from the flue gas inlet (1) and discharged from the flue gas outlet (2).

3. The ammonia injection grid structure for short-range mixing of a heating furnace SCR denitration system according to claim 1, characterized in that: The flue gas disturbance pipeline comprises a flue gas inlet main pipe (3) and n flue gas inlet branch pipes (4). The flue gas inlet main pipe (3) is horizontally parallel to the corresponding sidewall of the flue gas ammonia mixing chamber; the n flue gas inlet branch pipes (4) are uniformly arranged along the axial direction of the flue gas inlet main pipe (3); the n flue gas inlet branch pipes (4) are perpendicular to the flue gas inlet main pipe (3).

4. The ammonia injection grid structure for short-range mixing of a heating furnace SCR denitration system according to claim 3, characterized in that: The flue gas inlet main pipe (3) is a cylindrical structure with one end open and the other end closed; the flue gas inlet branch pipes (4) are all cylindrical structures; the axial end of the flue gas inlet branch pipe (4) is in communication with the flue gas inlet main pipe (3); the other axial end of the flue gas inlet branch pipe (4) is in communication with the inner cavity of the flue gas ammonia mixing chamber; n is a positive integer not less than 5.

5. The ammonia injection lattice structure for short-range mixing of a heating furnace SCR denitration system according to claim 4, characterized in that: After the flue gas of the heating furnace enters the flue gas inlet main pipe (3) from the open end of the flue gas inlet main pipe (3), it enters the inner cavity of the flue gas ammonia mixing chamber through the n flue gas inlet branch pipes (4).

6. The ammonia injection lattice structure for short-range mixing of a heating furnace SCR denitration system according to claim 1, characterized in that: The ammonia injection grid comprises an ammonia mother pipe (7), m ammonia branch pipes (8) and m×k pairs of conical nozzles (9). The ammonia mother pipe (7) is horizontally placed; the m ammonia branch pipes (8) are uniformly arranged along the axial direction of the ammonia mother pipe (7); one end of the ammonia branch pipe (8) is in communication with the inner cavity of the ammonia mother pipe (7); the other end of the ammonia branch pipe (8) extends into the inner cavity of the flue gas ammonia mixing chamber; k pairs of conical nozzles (9) are uniformly arranged along the axial direction on each ammonia branch pipe (8).

7. The ammonia injection grid structure for short mixing distance of heating furnace SCR denitration system according to claim 6, characterized in that: The ammonia mother pipe (7) is a horizontally placed T-shaped cylindrical structure; the short arm segment of the T-shaped ammonia mother pipe (7) is provided with an opening; the long arm segment of the T-shaped ammonia mother pipe (7) is blocked at both ends; the long arm segment of the ammonia mother pipe (7) is parallel to the sidewall of the flue gas ammonia mixing chamber; the short arm segment of the ammonia mother pipe (7) is perpendicular to the middle part of the long arm segment; one end of the ammonia branch pipe (8) is in communication with the long arm segment, and the other end extends into the inner cavity of the flue gas ammonia mixing chamber.

8. The ammonia injection lattice structure for short-range mixing of a heating furnace SCR denitration system according to claim 7, characterized in that: The ammonia enters the short arm segment from the opening of the short arm segment, sequentially passes through the short arm segment, the long arm segment, the ammonia branch pipe (8) and the conical nozzle (9), and is sprayed in the inner cavity of the flue gas ammonia mixing chamber.

9. The ammonia injection lattice structure for short mixing distance of heating furnace SCR denitration system according to claim 7, characterized in that: The m×k pairs of conical nozzles (9) are uniformly distributed along the axial direction of the ammonia branch pipe (8) and are located at the top of the ammonia branch pipe (8); m is a positive integer not less than 6; k is a positive integer not less than 6.

10. The ammonia injection lattice structure for short-range mixing of a heating furnace SCR denitration system according to claim 7, characterized in that: Each pair of conical nozzles (9) comprises two conical nozzles (9); the two conical nozzles (9) are symmetrically distributed at an included angle; each conical nozzle (9) is an inverted conical cylinder structure.

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