A desulfurization and denitrification system for coal-fired boilers

Abstract

The present invention relates to the field of separation technology. The present invention discloses a desulfurization and denitrification system for coal-fired boilers, comprising a water droplet air barrier and a stepped spray mechanism arranged at the center of the flue gas duct. The water droplet air barrier comprises a wind-blocking spherical portion and a tangent special-shaped portion. The top of the wind-blocking spherical portion has a horizontal circular section. The diameter of the circular section is smaller than the diameter of the wind-blocking spherical portion. The tangent special-shaped portion is fixedly connected to the top surface of the circular section. The arc-shaped circumferential side surface of the tangent special-shaped portion is tangent to the spherical surface of the wind-blocking spherical portion. The water droplet air barrier is used to divide the flue gas flow into turbulent flow and laminar flow, and the tangent special-shaped portion is used to form turbulent flow and laminar flow to achieve dynamic gradient spraying. A dynamic mass transfer method is used in which low-kinetic energy atomized liquid is used in conjunction with turbulent flow for mass transfer, and high-kinetic energy atomized liquid is used to penetrate into laminar flow for mass transfer. Improving the gas-liquid mass transfer efficiency can improve the separation efficiency and separation quality.

Description

Technical Field

[0001] The present invention relates to the field of separation technology, in particular to a desulfurization and denitrification system for coal-fired boilers. Background Art

[0002] During flue gas denitrification, an oxidant is used to convert NO into easily absorbable NO₂. The resulting NO₂ is then absorbed by water or an alkaline solution, forming nitric acid or nitrous acid, thereby achieving denitrification. Similarly, desulfurization requires spraying lime powder, slurry, or water into the flue gas. This section clearly demonstrates that the most important factor in flue gas desulfurization and denitrification is the gas-solid-liquid mass transfer efficiency, which directly affects the amount of substances released from the flue gas.

[0003] The most common way to improve the mass transfer efficiency of gas is to generate turbulence, such as using the Bernoulli theorem to prepare the Venturi tube. The laminar high-speed flue gas passes through the constriction to generate a vacuum turbulent zone and form an adsorption state, and the subsequent tail flow is in a turbulent state. Before the gas forms a turbulent state, liquid or powder is added to the laminar flow area. If you want to improve the mass transfer efficiency, the dispersion is better when the liquid is in an atomized state. However, the atomized droplets are light in mass and low in kinetic energy. Because the laminar high-speed flue gas will drive the atomized liquid to flow upward rapidly, it is difficult for the atomized liquid to completely cover the laminar flue gas area. The laminar flue gas mixed with the unevenly distributed atomized liquid is accelerated through the Venturi tube and becomes turbulent. In the turbulent state, the atomized liquid gradually disperses evenly with the turbulent flue gas. Therefore, the Venturi tube needs to have a length that satisfies the turbulent flue gas to evenly distribute the uneven atomized liquid.

[0004] If the droplets are large and the kinetic energy at the droplet outlet is high, the possibility of the droplets passing through the high-speed laminar flue gas increases. Although the droplets are better dispersed in the high-speed laminar flow area, the specific surface area of ​​the droplets is small, which is not conducive to gas-liquid mass transfer.

[0005] Atomizing spray is set in the turbulent area of ​​flue gas. If the kinetic energy of the atomized droplets is increased, the atomized droplets will affect the gas turbulence. If the kinetic energy of the atomized droplets is reduced, the impact of the atomized droplets on the gas turbulence is reduced, but the distribution uniformity of the atomized droplets in the turbulent gas is also reduced. Summary of the Invention

[0006] The purpose of the present invention is to provide a desulfurization and denitrification system for coal-fired boilers, in which a water droplet gas barrier is arranged in the flue gas duct, and the flue gas passes through the front end of the water droplet head, and the flue gas forms a turbulent flow area and a laminar flow area behind the water droplet head. The shape of the tangent special-shaped portion is utilized to form a ring-shaped spraying area with an inverted triangle cross-section, which does not destroy the turbulence while forming a turbulent and laminar stepped spraying surface. The mass transfer efficiency between the flue gas and the separation liquid is improved, thereby improving the flue gas desulfurization and / or denitrification efficiency. It can also be used as a pre-treatment for the flue gas entering the venturi tube or for independent treatment to solve the problems raised in the above-mentioned background technology.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] A desulfurization and denitrification system for a coal-fired boiler, comprising a water droplet gas barrier and a stepped spray mechanism arranged at the center of a flue gas duct;

[0009] The water droplet air blocking obstacle comprises a wind-blocking spherical portion and a tangent special-shaped portion, wherein the top of the wind-blocking spherical portion has a horizontal circular cross-section, the diameter of the circular cross-section is smaller than the diameter of the wind-blocking spherical portion, and the tangent special-shaped portion is fixedly connected to the top surface of the circular cross-section;

[0010] The arc-shaped circumferential side surface of the tangent special-shaped portion is tangent to the spherical surface of the wind-blocking spherical portion, the top diameter of the tangent special-shaped portion is smaller than the bottom diameter of the tangent special-shaped portion, and the stepped spraying mechanism is arranged at the tangent special-shaped portion. The stepped spraying mechanism sprays the liquid through the arc-shaped circumferential side surface of the tangent special-shaped portion to the turbulent flow zone and the laminar flow zone.

[0011] As a further solution of the present invention: the stepped spray mechanism includes a main pipe and a branch pipe assembly, the main pipe is vertically arranged inside the tangent special-shaped portion, and the branch pipe assemblies are equidistantly distributed on the outer wall of the main pipe along the axial direction of the main pipe, and the single pipe length of the branch pipe assembly increases from top to bottom along the circumferential side curve of the tangent special-shaped portion.

[0012] As a further solution of the present invention: the angle a between the axis of the single tube of the branch pipe assembly and the main pipe increases from top to bottom, and the maximum angle a between the axis of the single tube of the branch pipe assembly and the main pipe is 90 degrees.

[0013] As a further solution of the present invention: the number of the branch pipe assemblies gradually increases from top to bottom.

[0014] As a further solution of the present invention: the sum of the cross-sectional areas of the single-tube channels of the plurality of branch pipe assemblies is not greater than the channel cross-sectional area of ​​the main pipe.

[0015] As a further solution of the present invention: the wind-blocking spherical portion includes a wind-blocking hemisphere and a separation spherical surface, the wind-blocking hemisphere is located at the air intake end, and the peripheral side surfaces of the wind-blocking hemisphere and the tangent special-shaped portion are circumscribed to the peripheral side surfaces of the separation spherical surface.

[0016] As a further solution of the present invention: the diameter of the wind-blocking hemisphere is smaller than the diameter of the pipe, and an annular channel is formed between the wind-blocking hemisphere and the smoke pipe.

[0017] As a further solution of the present invention: a connecting pipe is provided in the flue gas duct, the connecting pipe extends to the outside of the duct, and the connecting pipe is communicated with the main duct.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] Water droplet barriers are used to divide the flue gas flow into turbulent and laminar flows, and tangential profiles are used to create turbulent and laminar flows, achieving dynamic gradient spraying. This dynamic mass transfer method utilizes low-kinetic energy atomized liquid to transfer mass with turbulent flow, while high-kinetic energy atomized liquid penetrates into laminar flow for mass transfer. Improving gas-liquid mass transfer efficiency can improve separation efficiency and quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0021] Figure 1 A schematic diagram of the area where flue gas passes through a water droplet gas barrier in a desulfurization and denitrification system for a coal-fired boiler;

[0022] Figure 2 It is a three-dimensional schematic diagram of a stepped spray mechanism in a desulfurization and denitrification system for a coal-fired boiler;

[0023] Figure 3 A schematic diagram of a stepped spray mechanism in a desulfurization and denitrification system for a coal-fired boiler;

[0024] Figure 4 A three-dimensional schematic diagram of a water droplet gas barrier in a desulfurization and denitrification system for a coal-fired boiler;

[0025] Figure 5 A schematic diagram of a curved tangent line of a water droplet gas barrier in a desulfurization and denitrification system for a coal-fired boiler;

[0026] Figure 6 This is a schematic diagram of the pressure of airflow passing through a circular obstacle;

[0027] Figure 7 for Figure 6 Schematic diagram of fluid separation in part A;

[0028] In the figure: 100, water droplet air-blocking obstacle; 101, wind-blocking spherical portion; 1011, wind-blocking hemisphere; 1012, separation spherical surface; 102, tangent special-shaped portion; 103, circular cross-section; 200, stepped spray mechanism; 201, main pipeline; 202, branch pipeline assembly; 300, connecting pipe. DETAILED DESCRIPTION

[0029] Example 1:

[0030] See also Figure 1-Figure 7 : This embodiment makes the following improvements to achieve the purpose of dividing the laminar flue gas into turbulent and laminar regions, and dividing the cylindrical airflow into annular airflow for spraying:

[0031] The improvements include: a water droplet air-blocking obstacle 100 and a stepped spray mechanism 200 arranged at the center of the flue gas duct. The water droplet air-blocking obstacle 100 includes a wind-blocking spherical portion 101 and a tangent special-shaped portion 102. The wind-blocking spherical portion 101 includes a wind-blocking hemisphere 1011 and a separation spherical surface 1012. The diameter of the wind-blocking hemisphere 1011 is smaller than the diameter of the duct, and an annular channel is formed between the wind-blocking hemisphere 1011 and the flue gas duct.

[0032] Improvement principle: Please refer to Figure 1 The water droplet air barrier 100 is set on the central axis of the pipe, and the pipe and the water droplet air barrier 100 form an annular channel. The flue gas moves in a laminar flow in the pipe. When the flue gas reaches the water droplet air barrier 100, it can only flow around the water droplet air barrier 100, and the flow cross section is reduced. Figure 6 , where the smoke passes through the circular surface, the red line is the positive pressure area. The blue area behind the circular obstacle is the negative pressure area. Figure 6-Figure 7 The flue gas flows along the circular surface on the windward side and gradually leaves the surface on the leeward side, resulting in boundary layer separation and the formation of a low-speed, low-pressure region behind the circle. The flow velocity in this region is usually chaotic and may contain vortex flow in laminar or turbulent flow. To generate turbulence behind the circle, it is only necessary to increase the gas velocity. Increasing the gas velocity increases the Reynolds number, thus forming turbulence.

[0033] Based on the above, it can be seen that the area where the gas is separated from the circular surface is located at the arc surface near the rear of the circular midline. Therefore, it is necessary to further improve the shape of the water droplet gas blocking barrier 100:

[0034] See also Figure 1The top of the wind-blocking spherical portion 101 has a horizontal circular section 103. The diameter of the circular section 103 is smaller than the diameter of the wind-blocking spherical portion 101. The wind-blocking spherical portion 101 is an incomplete sphere. The shape of the wind-blocking spherical portion 101 is formed by cutting a portion of the sphere through a horizontal cutting line. Therefore, the wind-blocking spherical portion 101 can be divided into a wind-blocking hemisphere 1011 and a separation spherical surface 1012. The wind-blocking hemisphere 1011 is the windward area. No separation phenomenon occurs within the interface of the wind-blocking hemisphere 1011. The separation phenomenon of gas occurs at the separation spherical surface 1012. Therefore, please refer to Figure 1 The turbulent zone is mainly located behind the separation spherical surface 1012, that is, the surrounding area of ​​the tangent profiled portion 102.

[0035] In order to reduce the loss of flue gas kinetic energy and the interference with the flue gas flow direction, the following improvements have been made:

[0036] The tangent profiled portion 102 is fixedly connected to the top surface of the circular section 103 , the arc-shaped circumferential side surface of the tangent profiled portion 102 is tangent to the spherical surface of the wind-blocking spherical portion 101 , and the top diameter of the tangent profiled portion 102 is smaller than the bottom diameter of the tangent profiled portion 102 .

[0037] The peripheral side surface of the tangent profiled portion 102 has an arc, and the peripheral side surface of the tangent profiled portion 102 is tangent to the water droplet air blocking obstacle 100 to avoid obstruction and increase surface smoothness. The turbulent area occurs on the peripheral side of the tangent profiled portion 102.

[0038] To increase the range of turbulent area, the following improvements are made:

[0039] The wind-blocking hemisphere 1011 is located at the air inlet end, and the peripheral side surfaces of the wind-blocking hemisphere 1011 and the tangent special-shaped portion 102 are circumscribed to the peripheral side surfaces of the separation spherical surface 1012 .

[0040] pass Figure 1 It can be seen that when the peripheral side surface of the tangent profiled portion 102 is circumscribed to the peripheral side surface of the separation spherical surface 1012, the volume of the annular space between the peripheral side of the tangent profiled portion 102 and the inner wall of the pipe is larger, and the turbulent area of ​​the flue gas is larger.

[0041] The stepped spray mechanism 200 is positioned at the tangential profile 102. It sprays liquid through the arcuate circumferential side of the tangential profile 102 into the turbulent and laminar flow zones. Using the tangential profile 102 as a carrier and the arcuate circumferential side of the tangential profile 102 as a spray surface, the liquid is sprayed into the turbulent and laminar flow zones. The narrow annular flue gas passageway allows the atomized liquid to more easily cover the flue gas.

[0042] Example 2:

[0043] See also Figure 1-Figure 7Based on the first embodiment, this embodiment couples the water droplet air barrier 100 with the stepped spray mechanism 200, making the spray ring cross-section of the stepped spray mechanism 200 an inverted triangle, thereby reducing the impact on the turbulent zone. This embodiment makes the following improvements:

[0044] In this embodiment, the stepped spray mechanism 200 includes a main pipe 201 and a branch pipe assembly 202. The main pipe 201 is vertically arranged inside the tangent special-shaped portion 102, and the branch pipe assembly 202 is equidistantly distributed on the outer wall of the main pipe 201 along the axial direction of the main pipe 201. The single pipe length of the branch pipe assembly 202 increases from top to bottom along the circumferential side curve of the tangent special-shaped portion 102.

[0045] See also Figure 1 The tangent profiled portion 102 is narrow at the top and wide at the bottom. The stepped spray mechanism 200 is embedded in the tangent profiled portion 102, and the ends of the branch pipe assembly 202 are flush with the side surfaces of the tangent profiled portion 102. When the tangent profiled portions 102 are arranged vertically, the length of a single pipe in the upper tangent profiled portion 102 must be shorter than the length of a single pipe in the lower tangent profiled portion 102.

[0046] As can be seen from the parallel pipes, the flow rate and water pressure in main pipe 201 remain constant. The longer the branch pipe, the greater the friction affecting the flow of liquid within it. The longer the branch pipe, the greater the flow resistance, and the lower the water pressure in the branch pipe. The lower the water pressure, the closer the spray distance of the atomizing nozzle at the end of branch pipe assembly 202. This creates a triangular, annular spray area.

[0047] The design of the tangent profile 102 not only increases the area of ​​the turbulent flow region, but also reduces the kinetic energy of the water mist generated by the branch pipe assembly 202 as the branch pipe assembly 202 is closer to the water droplet-blocking gas obstacle 100 and the spray distance of the atomizing nozzle of the branch pipe assembly 202 is shorter and the length of the branch pipe assembly 202 is longer. This reduced kinetic energy of the water mist has a minimal impact on turbulence, thereby reducing the impact on gas turbulence.

[0048] See also Figure 1 After the airflow passes through the water droplet barrier 100, laminar flow still exists outside the turbulent region. The laminar flow converges after passing through the turbulent region behind the water droplet barrier 100. Furthermore, the turbulent region gradually widens from the water droplet barrier 100 toward the stepped spray mechanism 200. This configuration coincides with the triangular cross-section of the annular spray zone, achieving the following specific effects:

[0049] As the turbulent zone widens from narrow to wide, the kinetic energy and range of the atomized droplets gradually increase. This dynamic design aligns the kinetic energy with the formation of the turbulent zone, preventing high-kinetic energy droplets from forming at the starting point of the turbulent zone and affecting the gas turbulence effect.

[0050] As the turbulent region narrows from wide to narrow, the laminar flow region moves closer to the pipe axis, increasing its width. At this point, the kinetic energy and range of the atomized droplets gradually increase. The droplet kinetic energy reaches the laminar flow region, and no matter how wide the laminar flow region increases, it remains smaller than the pipe radius, ensuring that the gas passing through the water droplet gas barrier 100 covers the flue gas flow after it passes through the water droplet gas barrier 100.

[0051] The formation of the atomization triangle cannot be controlled by simply changing the length of the branch pipe assembly 202. The branch pipe assembly 202 can be further improved. The improvements are as follows: the angle a between the axis of the single tube of the branch pipe assembly 202 and the main pipe 201 increases from top to bottom, and the maximum angle of the angle a between the axis of the single tube of the branch pipe assembly 202 and the main pipe 201 is 90 degrees.

[0052] Improvement Principle: The horizontal distance between the topmost main pipe 201 and the tangentially shaped portion 102 is short, making it difficult to install the nozzle. Therefore, the topmost branch pipe assembly 202 is arranged at an angle a with the main pipe 201. Angle a increases the length of the branch pipe assembly 202 and is less than 90 degrees. The fluid resistance generated by the topmost branch pipe assembly 202 is smaller than that of the bottommost branch pipe assembly 202. Therefore, adjusting the angle allows for nozzle installation and further adjusts the pipe resistance.

[0053] Based on the above improvements, further improvements are made as follows: the number of branch pipe assemblies 202 gradually increases from top to bottom.

[0054] Principle of improvement: Since the branch pipe assembly 202 near the windward area is long and the coverage range of the branch pipe assembly 202 near the windward area is short, the more branch pipe assemblies 202 near the windward area there are, the wider the area covered by the nozzle at the end of the branch pipe assembly 202 near the windward area for spraying smoke in the turbulent area.

[0055] Supplementary explanation: The sum of the cross-sectional areas of the single pipes of the multiple branch pipe assemblies 202 is not greater than the cross-sectional area of ​​the main pipe 201. This is to avoid the problem that the pipe of one of the branch pipe assemblies 202 cannot divert liquid.

[0056] Supplementary explanation: A connecting pipe 300 is provided in the flue gas duct. The connecting pipe 300 extends to the outside of the duct and is connected to the main duct 201 .

[0057] The connecting pipe 300 extends to the outside of the pipeline and can pass through the curved portion of the pipeline. The connecting pipe 300 transports the external liquid into the main pipeline 201 .

[0058] In summary:

[0059] The contents of Examples 1 and 2 can be used for flue gas pretreatment. Compared to high-speed laminar direct injection, this method splits the airflow into turbulent and laminar flows, leveraging these two flows to achieve dynamic gradient spraying. This dynamic mass transfer method utilizes low-kinetic energy atomized liquid in conjunction with turbulent flow for mass transfer, while high-kinetic energy atomized liquid penetrates the laminar flow for mass transfer. This improved gas-liquid mass transfer efficiency can enhance separation efficiency and quality.

[0060] Furthermore, Example 1 and Example 2 can be combined with a Venturi tube. If the flue gas volume is insufficient and the flow rate is insufficient during the use of the Venturi tube, bed collapse may easily occur. The contents of Example 1 and Example 2 can be used for the pre-treatment of flue gas entering the Venturi tube. When the flue gas volume is insufficient, the low-flow flue gas can be independently processed by pressurizing and mass transferring through Example 1 and Example 2. When the flue gas volume is sufficient, the liquid is dispersed into the flue gas through Example 1 and Example 2. Because the dispersion rate of the liquid in the flue gas through Example 1 and Example 2 is improved compared to the dispersion rate of directly injecting high-speed laminar flue gas. The turbulent channel length of the Venturi tube can be shortened, and the flue gas treated through Example 1 and Example 2 continues to be turbulent and promote mass transfer after being accelerated through the Venturi tube, thereby achieving the purpose of improving the separation effect.

[0061] The above is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with this technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solutions and inventive concepts of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A desulfurization and denitrification system for a coal-fired boiler, characterized by: It comprises a water droplet gas blocking obstacle (100) and a stepped spray mechanism (200) arranged at the center of the flue gas duct; The water droplet air blocking obstacle (100) comprises a wind-blocking spherical portion (101) and a tangent special-shaped portion (102); the top of the wind-blocking spherical portion (101) has a horizontal circular section (103); the diameter of the circular section (103) is smaller than the diameter of the wind-blocking spherical portion (101); and the tangent special-shaped portion (102) is fixedly connected to the top surface of the circular section (103); The arc-shaped circumferential side surface of the tangent profiled portion (102) is tangent to the spherical surface of the wind-blocking spherical portion (101); the top diameter of the tangent profiled portion (102) is smaller than the bottom diameter of the tangent profiled portion (102); the stepped spraying mechanism (200) is arranged at the tangent profiled portion (102); the stepped spraying mechanism (200) sprays liquid through the arc-shaped circumferential side surface of the tangent profiled portion (102) to the turbulent flow zone and the laminar flow zone; The stepped spray mechanism (200) comprises a main pipe (201) and a branch pipe assembly (202), wherein the main pipe (201) is vertically arranged inside the tangent profiled portion (102), and the branch pipe assemblies (202) are equidistantly distributed on the outer wall of the main pipe (201) along the axial direction of the main pipe (201), and the length of a single pipe of the branch pipe assembly (202) increases along the circumferential side curve of the tangent profiled portion (102) from top to bottom.

2. A desulfurization and denitrification system for a coal-fired boiler according to claim 1, characterized in that: The included angle a between the axis of the single pipe of the branch pipe assembly (202) and the main pipe (201) increases in equal angles from top to bottom, and the maximum included angle a between the axis of the single pipe of the branch pipe assembly (202) and the main pipe (201) is 90 degrees.

3. The desulfurization and denitrification system for a coal-fired boiler according to claim 1, characterized in that: The number of the branch pipe components (202) gradually increases from top to bottom.

4. The desulfurization and denitrification system for a coal-fired boiler according to claim 1, characterized in that: The sum of the cross-sectional areas of the single-tube channels of the plurality of branch pipeline assemblies (202) is not greater than the channel cross-sectional area of ​​the main pipeline (201).

5. The desulfurization and denitrification system for a coal-fired boiler according to claim 1, characterized in that: The wind-blocking spherical portion (101) comprises a wind-blocking hemisphere (1011) and a separation spherical surface (1012); the wind-blocking hemisphere (1011) is located at the air inlet end; and the peripheral side surfaces of the wind-blocking hemisphere (1011) and the tangent special-shaped portion (102) are circumscribed to the peripheral side surfaces of the separation spherical surface (1012).

6. A desulfurization and denitrification system for a coal-fired boiler according to claim 5, characterized in that: The diameter of the wind-blocking hemisphere (1011) is smaller than the diameter of the pipe, and an annular channel is formed between the wind-blocking hemisphere (1011) and the smoke pipe.

7. The desulfurization and denitrification system for a coal-fired boiler according to claim 1, characterized in that: A connecting pipe (300) is provided in the flue gas duct, the connecting pipe (300) extending to the outside of the duct, and the connecting pipe (300) is in communication with the main duct (201).

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