A system for purifying exhaust gas from aluminum ash treatment

Abstract

This invention relates to a waste gas purification system for aluminum ash treatment, comprising a falling film absorption unit, an ammonia absorption unit, and a neutralization unit. The falling film absorption unit includes a falling film absorber, which, from top to bottom, has an inlet section, a film distribution section, an absorption cooling section, and a gas-liquid separation section. The inlet section is connected to the waste gas input pipe, and the cooling absorption section contains multiple vertical absorption pipes. This application incorporates a falling film absorber before a three-stage acid spray tower. The falling film absorber absorbs hydrogen chloride from the waste gas and cools the waste gas to facilitate subsequent ammonia absorption. After the falling film absorber absorbs the hydrogen chloride, the waste gas sequentially passes through a three-stage acid spray tower to absorb ammonia, then through an alkaline spray tower to absorb residual hydrogen chloride and sulfuric acid, and finally through a water spray tower to meet emission standards, thus achieving waste gas purification in the aluminum ash acid leaching process for manufacturing polyaluminum chloride.

Description

Technical Field

[0001] This invention relates to the field of waste gas purification technology, specifically to a waste gas purification system for aluminum ash treatment. Background Technology

[0002] Aluminum ash is a solid waste residue generated during the smelting and processing of aluminum. On one hand, aluminum ash contains sulfur (F). - CN - Harmful ions and heavy metals such as Cr, Cd, and Pb can pollute soil and groundwater if not properly handled, causing environmental pollution problems. On the other hand, aluminum ash contains a large amount of metallic aluminum and aluminum compounds, which have high industrial recycling and reuse value. The comprehensive utilization of aluminum ash resources involves using aluminum ash as the main raw material to extract valuable components. This approach can turn aluminum ash into a valuable resource, creating economic value while reducing environmental pollution.

[0003] The acid dissolution method for producing polyaluminum chloride from aluminum ash is one of the most widely used, low-cost, and simplest manufacturing methods in China. Aluminum and its compounds (Al₂O₃ and γ-Al₂O₃) in aluminum ash can undergo a vigorous exothermic reaction with hydrochloric acid, which can be divided into three processes: dissolution, hydrolysis, and polymerization. Some aluminum ash contains α-Al₂O₃, which has very low reactivity and is difficult to dissolve in hydrochloric acid, thus reducing the dissolution rate. As aluminum dissolves and hydrochloric acid is consumed, the pH value gradually increases, promoting the hydrolysis of the coordinated water. The hydrochloric acid produced by hydrolysis further promotes the dissolution reaction of aluminum. During the continuous hydrolysis, OH-bridging polymerization occurs between adjacent aluminum hydrolysis forms. The polymerization reduces the concentration of hydrolysis products, thus promoting further hydrolysis. Dissolution, hydrolysis, and polymerization alternately promote each other, driving the reaction towards high aluminum concentration, high basicity, and high degree of polymerization. By controlling the reaction feed ratio and reaction time, a polyaluminum chloride solution with acceptable alumina content and basicity can be obtained.

[0004] In the process of manufacturing polyaluminum chloride using the acid leaching method with aluminum ash, the generated waste gas typically contains pollutants. For example, during the denitrification process, aluminum nitride in the aluminum ash undergoes a hydrolysis reaction, releasing ammonia gas along with a large amount of water vapor. During the acid leaching process, hydrochloric acid, when heated, produces acid mist, which is mainly composed of hydrogen chloride and water vapor. Direct emission of these waste gases into the atmosphere would cause environmental pollution; therefore, purification of these waste gases is necessary. Summary of the Invention

[0005] The technical problem to be solved by this invention is to provide a waste gas purification system for aluminum ash treatment, addressing the above-mentioned shortcomings. This application can sequentially remove hydrogen chloride and ammonia from the waste gas, and then neutralize the waste gas with acids and alkalis to ensure that the waste gas meets emission standards.

[0006] To solve the above technical problems, the present invention adopts the following technical solution: A waste gas purification system for aluminum ash treatment includes a falling film absorption unit, an ammonia absorption unit, and a neutralization unit. The falling film absorption unit includes a falling film absorber, which is provided with an inlet section, a film distribution section, an absorption cooling section, and a gas-liquid separation section from top to bottom. The inlet section is connected to a waste gas input pipe. The cooling absorption section is provided with multiple vertical absorption pipes, which are connected to the film distribution section and the gas-liquid separation section. The falling film absorption unit is used to allow the first absorbent and waste gas to pass through the absorption pipes from top to bottom to absorb hydrogen chloride in the waste gas, and to allow cooling water to pass through the cooling absorption section to reduce the temperature of the waste gas. The ammonia absorption unit includes multiple acid spray towers connected in series. The gas inlet of the first acid spray tower is connected to the gas-liquid separation section of the falling film absorber. The ammonia absorption unit is used to absorb ammonia from the waste gas in sequence. The neutralization unit includes an alkaline spray tower and a water spray tower. The gas inlet of the alkaline spray tower is connected to the gas outlet of the last acid spray tower, and the gas inlet of the water spray tower is connected to the gas outlet of the alkaline spray tower. The neutralization unit is used to neutralize residual acidic gases and wash waste gases.

[0007] Furthermore, the falling film absorption unit includes an absorbent storage tank and an absorbent pump. The output end of the absorbent storage tank is connected to the film distribution section, and the absorbent pump is used to transport the first absorbent in the absorbent storage tank to the film distribution section. The liquid outlet of the gas-liquid separation section is connected to the input end of the absorbent storage tank.

[0008] Furthermore, the falling film absorption unit includes a cooling tower and a cooling water pump. The hot medium inlet and cold medium outlet of the cooling tower are respectively connected to the cooling water outlet and cooling water inlet of the cooling absorption section. The cooling water pump is used to drive the cooling water to flow through the cooling absorption section and back to the cooling tower.

[0009] Furthermore, the falling film absorber includes a shell and absorption tubes. The shell is provided with an upper partition and a lower partition. Multiple absorption tubes vertically penetrate the upper partition and the lower partition. An absorption and cooling section is formed between the upper partition and the lower partition. A film-forming section and an air inlet section are formed above the upper partition, and a gas-liquid separation section is formed below the lower partition. The top of the absorption tube is located above the upper partition plate. The membrane section is provided with a distribution ring and a guide tube. The outer shell is provided with an absorbent inlet communicating with the membrane section. The upper part of the distribution ring and the first end of the guide tube are both connected to the absorbent inlet. The distribution ring is located inside the outer shell. The bottom of the distribution ring is provided with multiple first liquid outlet holes communicating with the membrane section. The second end of the guide tube extends to the middle of the upper partition plate. The second end of the guide tube is located below the top of the absorption tube.

[0010] Furthermore, the second end of the guide tube is provided with a guide shroud, which is funnel-shaped, and the bottom of the guide shroud is provided with multiple second liquid outlet holes.

[0011] Furthermore, an overflow device is provided at the top of the absorption tube. The overflow device consists of a partition ring and a spiral overflow plate. Multiple spiral overflow plates are evenly arranged circumferentially on the outer side of the top of the absorption tube. The top of the spiral overflow plate extends to the top of the absorption tube. The partition ring is located at the bottom of the spiral overflow plate and is located above the upper partition plate.

[0012] Furthermore, both the acid spray tower and the alkali spray tower are equipped with a first demister at their top. The first demister includes a central column, a second guide plate, and a liquid-blocking ring. Multiple second guide plates are evenly arranged circumferentially on the outer side of the central column, forming multiple spiral channels between the multiple second guide plates. There is a gap between the outer side of the second guide plate and the inner wall of the acid spray tower or the alkali spray tower. The liquid-blocking ring is disposed on the inner wall of the acid spray tower or the alkali spray tower and is located above the gap.

[0013] Furthermore, the second guide plate is composed of an inlet section, a swirl guide section, and an outlet section connected sequentially from bottom to top. The outlet angle of the outlet section gradually increases from the side closer to the central column to the side farther from the central column, and the distance between the outlet section and the inlet section gradually increases from the side closer to the central column to the side farther from the central column.

[0014] Furthermore, a baffle plate is provided on the side of the guide section facing the tangential rotation direction of the airflow, and the width of the baffle plate gradually increases from the side closer to the central column to the side farther away from the central column.

[0015] Furthermore, all the water tanks of the acid spray towers are connected to the first storage tank, which is used to store the second absorbent discharged from the acid spray tower.

[0016] Compared with the prior art, the present invention, by adopting the above technical solution, has the following advantages: This application incorporates a falling film absorber before the three-stage acid spray tower. The falling film absorber absorbs hydrogen chloride from the waste gas and cools the gas, facilitating subsequent ammonia absorption. After the falling film absorber absorbs the hydrogen chloride, the waste gas sequentially passes through the three-stage acid spray tower to absorb ammonia. It then passes through an alkaline spray tower to absorb residual hydrogen chloride and sulfuric acid. Finally, the waste gas is washed by a water spray tower to meet emission standards, thus achieving waste gas purification in the aluminum ash acid leaching process for manufacturing polyaluminum chloride.

[0017] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. Attached Figure Description

[0018] Figure 1This is a schematic diagram of the structure of the exhaust gas purification system in the embodiments of this application; Figure 2 This is a cross-sectional view of the falling film absorber in an embodiment of this application; Figure 3 for Figure 2 Enlarged view of point C; Figure 4 This is a schematic cross-sectional view of the falling film absorber located in the film section in an embodiment of this application; Figure 5 This is a front view of the acid spray tower in an embodiment of this application; Figure 6 This is a cross-sectional view of the acid spray tower in an embodiment of this application; Figure 7 This is an enlarged view of the acid spray tower located at the first demister in an embodiment of this application; Figure 8 This is a three-dimensional structural diagram of the first demister in an embodiment of this application; Figure 9 This is a three-dimensional structural diagram of the first demister from another angle in an embodiment of this application; Figure 10 This is a three-dimensional structural diagram of the second guide plate in an embodiment of this application; Figure 11 These are front (left) and right (right) views of the second guide vane in an embodiment of this application. Figure 12 This is a cross-sectional view of the water spray tower in an embodiment of this application.

[0019] The attached diagram lists the components represented by each number as follows: 11. Falling film absorption unit; 12. Ammonia absorption unit; 13. Neutralization unit; 2. Falling film absorber; 21. Inlet section; 22. Film distribution section; 221. Distribution ring; 2211. First liquid outlet; 222. Guide pipe; 223. Guide hood; 2231. Second liquid outlet; 23. Absorption cooling section; 231. First guide plate; 24. Gas-liquid separation section; 25. Outer shell; 251. Upper baffle; 252. Lower baffle; 26. Absorption pipe; 27. Overflow device; 271. Spacing ring; 272. Spiral overflow ring; 3. Waste gas input pipe; 4. Acid spray tower; 41. First storage tank; 42. 43. Tower body; 44. Water tank; 45. First circulating pump; 46. Grating plate; 47. Spray pipe; 48. Chemical replenishment tank; 5. Alkali spray tower; 51. Second storage tank; 62. Absorbent storage tank; 63. Absorbent pump; 64. Cooling tower; 65. Cooling water pump; 76. Second demister; 77. First demister; 78. Central column; 79. Second guide plate; 70. Inlet section; 71. Swirl guide section; 72. Outlet section; 72. Baffle plate; 73. Baffle ring; 74. Gap; 75. Upper fixed frame; 76. Lower fixed frame; 8. Water spray tower; 91. Exhaust fan; 92. Discharge tower. Detailed Implementation

[0020] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0021] In the description of this invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", "clockwise" and "counterclockwise" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0022] Example 1 like Figure 1 As shown, this embodiment discloses an aluminum ash treatment waste gas purification system, including: a falling film absorption unit 11, an ammonia absorption unit 12, and a neutralization unit 13 connected in sequence. The falling film absorption unit 11 is used to allow waste gas and a first absorbent to flow along the membrane tube 26 to absorb hydrogen chloride in the waste gas and cool it down. The ammonia absorption unit 12 absorbs ammonia in the waste gas through a second absorbent as the waste gas passes through a three-stage acid spray tower. Finally, the waste gas passes through an alkaline spray tower and a water spray tower in the neutralization unit 13 to absorb hydrogen chloride and sulfuric acid, and to wash the waste gas to meet emission standards. The purified waste gas is then discharged through a 15m emission tower 92.

[0023] The falling film absorption unit 11 includes a falling film absorber 2, an absorbent storage tank 61, an absorbent pump 62, a cooling tower 63, and a cooling water pump 64. In this embodiment, there are two falling film absorbers 2, which are arranged in parallel. The exhaust gas inlet pipe 3 is connected to the gas inlet of the two falling film absorbers 2. The falling film absorber 2 is provided with an inlet section 21, a film distribution section 22, a cooling absorption section 23, and a gas-liquid separation section 24 from top to bottom. The falling film absorber 2 has a gas inlet, a gas outlet, an absorbent inlet, a liquid outlet, a cooling water inlet, and a cooling water outlet. The gas inlet is connected to the top of the inlet section 21, the gas outlet is connected to the middle of the gas-liquid separation section 24, the absorbent inlet is connected to the film distribution section 22, the liquid outlet is connected to the bottom of the gas-liquid separation section 24, the cooling water inlet is connected to the bottom of the cooling absorption section 23, and the cooling water outlet is connected to the top of the cooling absorption section 23.

[0024] The falling film absorption unit 11 also includes a second demister 65, and the gas outlets of the two falling film absorbers 2 are connected to the input end of the second demister 65.

[0025] The output end of the absorbent storage tank 61 is connected to the absorbent inlet, and the liquid outlet is connected to the input end of the absorbent storage tank 61. The absorbent pump 62 is used to transport the first absorbent in the absorbent storage tank 61 to the membrane section 22. The cold medium outlet of the cooling tower 63 is connected to the cooling water inlet, and the hot medium inlet of the cooling tower 63 is connected to the cooling water outlet. The cooling water pump 64 is used to drive the cooling water to flow through the cooling absorption section 23 and then return to the cooling tower 63.

[0026] The ammonia absorption unit 12 includes three acid spray towers 4 and a first storage tank 41. The three acid spray towers 4 are connected in series, and the gas inlet of the first acid spray tower 4 is connected to the output end of the second demister 65. Figure 5 and Figure 6 As shown, the acid spray tower 4 includes a tower body 42, a water tank 43, and a first circulating pump 44. The top and bottom of the tower body 42 are respectively provided with a gas outlet and a gas inlet. The water tank 43 is located at the bottom of the tower body 42 and is connected to the bottom of the tower body 42. Three grid plates 45 are arranged sequentially from bottom to top inside the tower body 42. The two lower grid plates 45 are filled with packing material (the first acid spray tower 4 uses rosette packing, and the latter two use Pall ring packing). Spray pipes 46 are installed below the two upper grid plates 45. A first demister 7 is installed on the uppermost grid plate 45. The first circulating pump 44 is used to transport the second absorbent liquid in the water tank 43 to each spray pipe 46, and then spray the second absorbent liquid onto the packing material below through the spray pipes 46 to absorb ammonia in the waste gas. A first storage tank 41 is connected to the output end of the water tank 43 of the three acid spray towers 4.

[0027] Neutralization unit 13 includes an alkaline spray tower 5 and a water spray tower 8. The structure of the alkaline spray tower 5 is basically the same as that of the acid spray tower 4, and will not be described in detail here. The output end of the water tank of the alkaline spray tower 5 is connected to the second storage tank 51. The gas inlet of the alkaline spray tower 5 is connected to the gas outlet of the last acid spray tower 4, and the gas inlet of the water spray tower 8 is connected to the gas outlet of the alkaline spray tower 5. The gas outlet of the water spray tower 8 is sequentially connected to an induced draft fan 91 and an exhaust tower 92. The induced draft fan 91 is used to drive the exhaust gas sequentially through the falling film absorber 2, the three acid spray towers 4, the alkaline spray tower 5, and the water spray tower 8, and finally discharges upward through the exhaust tower 92.

[0028] Specifically, the first absorbent is water, the second absorbent is dilute sulfuric acid solution, and the third absorbent used in the alkaline spray tower 5 is sodium hydroxide solution.

[0029] The purification system also includes a water supply pipeline and a drainage pipeline. The water supply pipeline is connected to the water tanks of the absorbent storage tank 61, cooling tower 63, acid spray tower 4, alkali spray tower 5, and water spray tower 8. The drainage pipeline is connected to the drain outlets of the cooling absorption section 23, cooling tower 63, and water spray tower 8.

[0030] The purification system also includes a control unit, and the output end of the absorbent storage tank 61 is equipped with a first pH meter for monitoring the pH value of the first absorbent; a thermometer is installed at the cooling water outlet to monitor the temperature of the cooling water flowing out from the cooling absorption section 23.

[0031] The first pH meter, thermometer, absorbent pump 62, and cooling water pump 64 are all electrically connected to the control unit. The control unit can control the valve between the water supply line and the absorbent storage tank 61 to open based on the pH value of the first pH meter, thus supplying water to the absorbent storage tank 61 (e.g., when the pH value of the absorbent drops below 3, water is supplied to the absorbent storage tank 61). The first absorbent in the absorbent storage tank 61 needs to be periodically drained. The control unit can adjust the power of the cooling water pump 64 based on the thermometer value to change the flow rate of the cooling water entering the absorption cooling section 23 (e.g., increasing the cooling water flow when the temperature rises), thereby maintaining the cooling effect on the exhaust gas and the first absorbent. When the ambient temperature rises, the cooling effect of the cooling tower 63 deteriorates, and cannot be controlled by increasing the cooling water flow rate, the control unit can also open the valve at the outlet of the cold medium in the water supply line to supply cooling water through the water supply line, further reducing the temperature of the cooling water. Simultaneously, the cooling tower 63 needs to discharge some cooling water into the drain line.

[0032] The first absorbent is mainly used to absorb hydrogen chloride in the waste gas, and it will also dissolve some of the ammonium chloride produced by the reaction of ammonia and hydrogen chloride. The first absorbent in the absorbent storage tank 61 needs to be discharged periodically, and the hydrogen chloride and ammonium chloride in the first absorbent can be separated by crystallization or thermal decomposition.

[0033] Preferably, the pH value of the first absorbent is maintained above 3 to maintain the absorption efficiency of hydrogen chloride; the temperature of the cooling water is maintained at 20~30℃ to reduce the absorption of ammonia and facilitate the subsequent absorption of ammonia by the second absorbent.

[0034] Each acid spray tower 4 / alkali spray tower 5 is equipped with a chemical replenishment tank 47, which is connected to a water tank 43. A second pH meter is installed on the water tank 43 or at the output end of the circulating pump 44 to detect the pH value of the second / third absorbent. A chemical pump is installed on the chemical replenishment tank 47 to transport the chemical solution in the chemical replenishment tank 47 to the water tank 43. The drain outlet of the water tank 43 is connected to the first storage tank 41 / second storage tank 51, and a level gauge is installed on the water tank 43 to monitor the liquid level in the water tank 43.

[0035] The first circulation pump 44, the second pH meter, the chemical pump, and the water level gauge are all electrically connected to the control unit. During operation, the absorbent in the water tank 43 is periodically discharged into the first storage tank 41 / second storage tank 51. The water level gauge monitors the water level in the water tank 43 and uploads the water level data to the control unit. The control unit controls the valve on the water supply pipeline to replenish fresh water to the water tank 43 based on the water level data. The second pH meter monitors the pH value of the absorbent in the water tank 43 and uploads the pH value data to the control unit. The control unit controls the chemical pump to replenish the chemical solution to the water tank 43 based on the pH value data to maintain the absorption efficiency of the absorbent.

[0036] Working principle: Waste gas containing hydrogen chloride and ammonia is transported to the falling film absorber 2 through the waste gas inlet pipe 3 and flows downward along the absorber pipe 26. During the flow, the first absorbent forms a liquid film on the inner wall of the absorber pipe 26, which absorbs the hydrogen chloride in the waste gas. The waste gas and the first absorbent separate at the bottom of the falling film absorber 2. After passing through the second demister 65, the waste gas enters the third-stage acid spray tower, where the second absorbent absorbs the ammonia in the waste gas. Subsequently, the waste gas enters the alkaline spray tower 5, where the third absorbent neutralizes the residual acidic gas in the waste gas. Finally, the waste gas is washed by the water spray tower 8 to complete the purification of the waste gas. The purified gas is discharged through the discharge tower 92.

[0037] Example 2 This embodiment is an improvement on embodiment 1, with the improvement being in the specific structure of the falling film absorber 2.

[0038] like Figure 2 As shown, the falling film absorber 2 includes a housing 25 and absorption tubes 26. The housing 25 is a hollow cylinder. Inside the housing 25, there is an upper partition 251 and a lower partition 252. An air inlet section 21 and a film distribution section 22 are formed above the upper partition 251. A cooling absorption section 23 is formed between the upper partition 251 and the lower partition 252. A gas-liquid separation section 24 is formed below the lower partition 252. Multiple absorption tubes 26 are vertically arranged inside the housing 25. The top end of the absorption tube 26 penetrates the upper partition 251 and extends above the upper partition 251, and the bottom end of the absorption tube 26 penetrates the lower partition 252.

[0039] Preferably, a plurality of first guide plates 231 are provided in the cooling absorption section 23 from top to bottom. The plurality of first guide plates 231 are arranged in an alternating manner to form an "S"-shaped cooling flow channel in the cooling absorption section 23, so that the cooling water can fully exchange heat with the exhaust gas and the first absorbent liquid flowing in the absorption pipe 26.

[0040] like Figure 3 and Figure 4 As shown, the distribution section 22 is provided with a distribution ring 221 and a guide tube 222. The upper part of the distribution ring 221 and the first end of the guide tube 222 are both connected to the absorbent inlet. The distribution ring 22 is located inside the outer shell 25. The bottom of the distribution ring 22 has multiple first liquid outlet holes 2211 that communicate with the membrane section 22. All the first liquid outlet holes 2211 are evenly distributed along the circumference of the distribution ring 22. The second end of the guide tube 222 extends to the middle of the upper partition 251, and the bottom end of the guide tube 222 is provided with a guide shroud 223. The guide shroud 223 is funnel-shaped, and the outer diameter of the bottom of the guide shroud 223 is larger than the outer diameter of the top. The bottom of the guide shroud 223 has multiple second liquid outlet holes 2231, and all the second liquid outlet holes 2231 are evenly distributed along the circumference of the guide shroud 223. The distribution ring 221 and the guide pipe 222 can simultaneously input the first absorbent into the middle and the periphery of the membrane section 22, so that the first absorbent is evenly distributed in the membrane section 22.

[0041] like Figure 4As shown, preferably, an overflow device 27 is provided at the top of the absorption pipe 26. The overflow device 27 consists of a partition ring 271 and a spiral overflow plate 272. Three spiral overflow plates 272 are fixedly provided on the outer side of the top of the absorption pipe 26. The three spiral overflow plates 272 are evenly distributed along the circumference of the absorption pipe 26, and the top of the spiral overflow plates 272 is located above the absorption pipe 26 (the distance between the two is 2~3mm). The partition ring 271 is fixedly provided at the bottom of the spiral overflow plate 272, and there is a gap between the partition ring 271 and the upper partition plate 251. The partition ring 271 is horizontally arranged. Multiple absorption tubes 26 are evenly distributed in a triangular pattern within the outer casing 25. Multiple spacer rings 271 form a water-blocking layer below the top of the absorption tubes 26, and uniform gaps are formed between the spacer rings 271, allowing the absorbent liquid to be evenly distributed around all the absorption tubes 26. When the water level of the absorbent liquid rises to the top of the spiral overflow plate 272, it will swirl along the spiral overflow plate 272 into the absorption tubes 26 to form a uniform film within the absorption tubes 26, thereby improving the absorption rate of the falling film absorber. Furthermore, the absorbent liquid flows out from the gaps between the spacer rings 271, providing better anti-clogging performance compared to the holes on conventional distributors.

[0042] Example 3 This embodiment is an improvement on embodiment 1, with the improvement being in the demister structure inside the acid spray tower 4 and the alkali spray tower 5.

[0043] like Figure 7 , Figure 8 and Figure 9 As shown, in this embodiment, the first demister 7 includes a central column 71, a second guide plate 72, and a liquid-blocking ring 73. The central column 71 is placed on the uppermost grid plate 45 of the acid spray tower 4 or the alkaline spray tower 5, and the central column 71 is located in the middle of the tower body. Multiple second guide plates 72 are arranged circumferentially on the outer side of the central column 71. The multiple second guide plates 72 are distributed at equal angles and form multiple spiral channels distributed circumferentially in the tower body. There is a gap 74 between the outer side of the second guide plate 72 and the inner wall of the tower body. The liquid-blocking ring 73 is fixedly arranged on the outermost side of the second guide plate 72 and is located at the top of the second guide plate 72.

[0044] It should be noted that the inner side of the second guide plate 72 is fixedly connected to the central column 71. The top and bottom of the second guide plate 72 are respectively provided with annular upper fixing frame 75 and lower fixing frame 76. The upper fixing frame 75 and lower fixing frame 76 are fixedly connected to all the second guide plates 72 to limit the included angle between adjacent second guide plates 72.

[0045] like Figure 10 and Figure 11As shown, the second guide plate 72 consists of an inlet section 721, a swirl guide section 722, and an outlet section 723 connected sequentially from bottom to top. The outlet angle of the outlet section 723 gradually increases from the side closer to the central column 71 to the side farther away from the central column 71, with a maximum outlet angle of 35°. The distance between the outlet section 723 and the inlet section 721 gradually increases from the side closer to the central column 71 to the side farther away from the central column 71. This distance refers to the horizontal distance between the outlet section 723 and the inlet section 721 at the same distance from the central column. A baffle plate 724 is provided on the side of the swirl guide section 722 facing the tangential rotation direction of the airflow. The width of the baffle plate 724 gradually increases from the side closer to the central column 71 to the side farther away from the central column 71, and the cross-section of the baffle plate 724 is arc-shaped.

[0046] In this embodiment, the demister combines centrifugal force to remove water mist from the exhaust gas. In the middle stage of the exhaust gas purification system (acid spray tower and alkali spray tower), it has high separation efficiency for small droplets, moderate pressure drop, and allows for a moderate gas velocity.

[0047] Working principle: When the exhaust gas passes through the first demister 7 from bottom to top, the exhaust gas will spiral up along the spiral channel to make the airflow rotate. Under the centrifugal force, the water mist (water droplets) will be thrown to the outside of the second guide plate 72 because the density is greater than that of the gas. Among them: (1) the water mist located inside and in the middle of the second guide plate 72 will move a certain distance to the outside of the second guide plate 72 and collide with the second guide plate 72 or be captured by the baffle plate 724; (2) a part of the water mist located outside the second guide plate 72 will move a certain distance to the outside of the second guide plate 72 and collide with the second guide plate 72 or be captured by the baffle plate 724; (3) another part of the water mist located in the second guide plate 72 will be thrown out of the gap 74 and adhere to the inner wall of the tower body, or be directly captured by the baffle ring 73.

[0048] After passing through multiple spray towers, the dust content in the exhaust gas is reduced, and the gas is clean. For example... Figure 12 As shown, the demister at the top of the water spray tower 8 can be a wire mesh demister to perform final demisting of the exhaust gas and intercept smaller droplets in the exhaust gas.

[0049] The above description provides examples of the preferred embodiments of the present invention. Parts not detailed herein are common knowledge to those skilled in the art. The scope of protection of the present invention is determined by the claims. Any equivalent modifications based on the technical teachings of the present invention are also within the scope of protection of the present invention.

Claims

1. A system for purifying exhaust gas from aluminum ash treatment, characterized in that, The system includes a falling film absorption unit (11), an ammonia absorption unit (12), and a neutralization unit (13). The falling film absorption unit (11) includes a falling film absorber (2). The falling film absorber (2) is provided with an inlet section (21), a film distribution section (22), an absorption cooling section (23), and a gas-liquid separation section (24) from top to bottom. The inlet section (21) is connected to the waste gas input pipe (3). The cooling absorption section (23) is provided with multiple vertical absorption pipes (26). The absorption pipes (26) are connected to the film distribution section (22) and the gas-liquid separation section (24). The falling film absorption unit (11) is used to allow the first absorbent liquid and waste gas to pass through the absorption pipes (26) from top to bottom to absorb hydrogen chloride in the waste gas and to allow cooling water to pass through the cooling absorption section to reduce the temperature of the waste gas. The ammonia absorption unit (12) includes multiple acid spray towers (4), which are connected in series. The gas inlet of the first acid spray tower (4) is connected to the gas-liquid separation section (24) of the falling film absorber (2). The ammonia absorption unit (12) is used to absorb ammonia in the waste gas in sequence. The neutralization unit (13) includes an alkaline spray tower (5) and a water spray tower (8). The gas inlet of the alkaline spray tower (5) is connected to the gas outlet of the last acid spray tower (4). The gas inlet of the water spray tower (8) is connected to the gas outlet of the alkaline spray tower (5). The neutralization unit (13) is used to neutralize residual acidic gases and wash waste gas.

2. The aluminum ash treatment waste gas purification system according to claim 1, characterized in that, The falling film absorption unit (11) includes an absorbent storage tank (61) and an absorbent pump (62). The output end of the absorbent storage tank (61) is connected to the membrane section (22). The absorbent pump (62) is used to transport the first absorbent in the absorbent storage tank (61) to the membrane section (22). The liquid outlet of the gas-liquid separation section (24) is connected to the input end of the absorbent storage tank (61).

3. The aluminum ash treatment waste gas purification system according to claim 1, characterized in that, The falling film absorption unit (11) includes a cooling tower (63) and a cooling water pump (64). The hot medium inlet and cold medium outlet of the cooling tower (63) are respectively connected to the cooling water outlet and cooling water inlet of the cooling absorption section (23). The cooling water pump (64) is used to drive the cooling water to flow through the cooling absorption section (23) and return to the cooling tower (63).

4. The aluminum ash treatment waste gas purification system according to claim 1, characterized in that, The falling film absorber (2) includes a shell (25) and absorption tubes (26). The shell (25) is provided with an upper partition (251) and a lower partition (252). Multiple absorption tubes (26) vertically penetrate the upper partition (251) and the lower partition (252). An absorption cooling section (23) is formed between the upper partition (251) and the lower partition (252). A film-forming section (22) and an air inlet section (21) are formed above the upper partition (251). A gas-liquid separation section (24) is formed below the lower partition (252). The top of the absorption tube (26) is located above the upper partition plate (251). The membrane section (22) is provided with a distribution ring (221) and a guide tube (222). The outer shell (25) is provided with an absorbent inlet that communicates with the membrane section (22). The upper part of the distribution ring (221) and the first end of the guide tube (222) are both connected to the absorbent inlet. The distribution ring (221) is located inside the outer shell (25). The bottom of the distribution ring (221) is provided with a plurality of first outlet holes (2211) that communicate with the membrane section (22). The second end of the guide tube (222) extends to the middle of the upper partition plate (251). The second end of the guide tube (222) is located below the top of the absorption tube (26).

5. The aluminum ash treatment waste gas purification system according to claim 4, characterized in that, The second end of the guide tube (222) is provided with a guide shroud (223), which is horn-shaped, and the bottom of the guide shroud (223) is provided with a plurality of second liquid outlet holes (2231).

6. The aluminum ash treatment waste gas purification system according to claim 4, characterized in that, An overflow device (27) is provided at the top of the absorption tube (26). The overflow device (27) consists of a partition ring (271) and a spiral overflow plate (272). Multiple spiral overflow plates (272) are evenly arranged circumferentially on the outer side of the top of the absorption tube (26). The top of the spiral overflow plate (272) extends to the top of the absorption tube (26). The partition ring (271) is located at the bottom of the spiral overflow plate (272) and is located above the upper partition plate (251).

7. The aluminum ash treatment waste gas purification system according to claim 1, characterized in that, The top of both the acid spray tower (4) and the alkali spray tower (5) is provided with a first demister (7). The first demister (7) includes a central column (71), a second guide plate (72) and a liquid-blocking ring (73). Multiple second guide plates (72) are uniformly arranged circumferentially on the outer side of the central column (71). Multiple spiral channels are formed between the multiple second guide plates (72). There is a gap (74) between the outer side of the second guide plate (72) and the inner wall of the acid spray tower (4) or the alkali spray tower (5). The liquid-blocking ring (73) is arranged on the inner wall of the acid spray tower (4) or the alkali spray tower (5) and is located above the gap (74).

8. The aluminum ash treatment waste gas purification system according to claim 7, characterized in that, The second guide plate (72) is composed of an inlet section (721), a swirl guide section (722), and an outlet section (723) connected sequentially from bottom to top. The outlet angle of the outlet section (723) gradually increases from the side closer to the central column (71) to the side farther away from the central column (71). The distance between the outlet section (723) and the inlet section (721) gradually increases from the side closer to the central column (71) to the side farther away from the central column (71).

9. The aluminum ash treatment waste gas purification system according to claim 7, characterized in that, The guide section (722) is provided with a baffle plate (724) on the side facing the tangential rotation direction of the airflow. The width of the baffle plate (724) gradually increases from the side closer to the central column (71) to the side farther away from the central column (71).

10. The aluminum ash treatment waste gas purification system according to claim 1, characterized in that, All the water tanks of the acid spray towers (4) are connected to the first storage tank (41), which is used to store the second absorbent discharged from the acid spray towers (4).

Images