Full evaporation crystallization system of aluminum electrolysis flue gas desulfurization wastewater

Abstract

The utility model discloses a kind of full evaporation crystallization systems of aluminum electrolysis flue gas desulfurization wastewater.The system includes wastewater supply and concentration unit, crystallization unit, filtration unit and flue gas supply unit.It utilizes aluminum electrolysis flue gas self heat, first desulfurization wastewater is concentrated in concentration tower and flue gas direct contact heat exchange concentration, then concentrated liquid is atomized and full evaporation crystallization in evaporation crystallization tower, crystallization salt is captured by dust collector, water vapor returns desulfurization system with flue gas.The utility model realizes zero discharge and resource of wastewater, energy saving and environmental protection, and low operating cost.

Description

Technical Field

[0001] This utility model relates to the field of aluminum electrolysis flue gas purification technology, specifically to a full evaporation crystallization system for aluminum electrolysis flue gas desulfurization wastewater, which is applied to the treatment of wastewater generated by the wet desulfurization system of aluminum electrolysis flue gas, realizing zero discharge and resource utilization of wastewater. Background Technology

[0002] In recent years, to meet increasingly stringent air pollutant emission standards, the domestic aluminum smelting industry has widely adopted calcium-based wet desulfurization devices in its flue gas purification systems. While this technology boasts high desulfurization efficiency and reliable operation, it continuously generates a certain amount of desulfurization wastewater during the process. This wastewater is complex in composition, not only with high suspended solids content but, more importantly, rich in high concentrations of soluble chlorides, fluorides, and trace heavy metals, exhibiting strong corrosiveness and environmental hazards. Currently, the industry primarily employs physicochemical treatment methods such as "three-stage treatment tanks" for this type of desulfurization wastewater. After treatment using these processes, suspended solids and some heavy metals in the effluent are removed, meeting the direct discharge limits of the "Integrated Wastewater Discharge Standard." However, the total dissolved solids content in the treated wastewater remains extremely high, mainly due to the inability to effectively remove soluble salts such as chloride ions. This results in the wastewater quality failing to meet the discharge standards of municipal wastewater treatment plants or industrial park wastewater treatment stations, leading to its widespread rejection. Furthermore, direct discharge poses risks of soil salinization and groundwater pollution. Evaporation crystallization technology is currently recognized as a key terminal technology for achieving "zero discharge" of industrial wastewater. However, setting up a separate evaporator consumes a huge amount of energy and has high operating costs. This greatly limits its large-scale application and promotion in the treatment of desulfurization wastewater from large-scale aluminum electrolysis flue gas. Therefore, there is an urgent need to develop an efficient and low-cost desulfurization wastewater treatment solution. Utility Model Content

[0003] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a full evaporation crystallization system for desulfurization wastewater from aluminum electrolysis flue gas. This system utilizes the waste heat from aluminum electrolysis flue gas as the sole heat source to achieve full evaporation of wastewater and separation of crystallized salts, ultimately achieving zero emissions.

[0004] To achieve the above technical objectives, the following technical solutions were adopted: This utility model provides a full evaporation crystallization system for desulfurization wastewater from aluminum electrolysis flue gas, including a wastewater supply and concentration unit, a crystallization unit, a filtration unit, and a flue gas supply unit; The wastewater supply and concentration unit includes a wastewater tank and a concentration tower, and the wastewater tank is connected to the concentration tower through a circulating spray device. The crystallization unit includes a concentrated brine tank, a fully automatic spray device, and an evaporation crystallization tower; the concentrated liquid outlet at the bottom of the concentrated tower is connected to the inlet of the fully automatic spray device via the concentrated brine tank; the outlet of the fully automatic spray device is connected to an atomizing nozzle located at the top of the evaporation crystallization tower. The filtration unit includes a dust collector, the flue gas inlet of which is connected to the flue gas outlet of the evaporation crystallization tower, for capturing crystalline salts carried by the flue gas; The flue gas supply unit includes a first flue gas branch pipe and a second flue gas branch pipe arranged in parallel; the two ends of the first flue gas branch pipe are respectively connected to the flue gas inlet and outlet of the concentration tower, and the two ends of the second flue gas branch pipe are respectively connected to the flue gas inlet of the evaporation crystallization tower and the flue gas outlet of the dust collector.

[0005] Furthermore, the circulating spray device includes a variable frequency circulating pump, a circulating nozzle, and a replenishing nozzle; the inlet of the variable frequency circulating pump is connected to the liquid pool at the bottom of the concentration tower through a pipe, and its outlet is connected to the circulating nozzle located at the top of the concentration tower through a pipe; the replenishing nozzle is located in the lower middle part of the concentration tower and is used to introduce fresh wastewater from the wastewater tank.

[0006] Furthermore, a variable frequency wastewater pump is installed on the replenishment pipe connecting the wastewater tank and the replenishment nozzle.

[0007] Furthermore, the top of the concentration tower is equipped with a demister, and the bottom of the concentration outlet is equipped with a waste liquid regulating valve.

[0008] Furthermore, the dust collector is a bag filter or cartridge filter, and its bottom is equipped with an ash discharge valve and a material box for collecting and temporarily storing crystallized salt.

[0009] Furthermore, a first flue gas valve, a first inlet temperature measuring instrument, and a first booster fan are sequentially installed on the pipe connecting the first flue gas branch pipe and the flue gas inlet of the concentrator; a first outlet temperature measuring instrument is installed on the pipe connecting the flue gas outlet of the concentrator and the first flue gas branch pipe. A second flue gas valve and a second inlet temperature measuring instrument are installed sequentially on the pipeline connecting the second flue gas branch pipe and the flue gas inlet of the evaporation crystallization tower; a third temperature measuring instrument is installed on the pipeline connecting the flue gas outlet of the evaporation crystallization tower and the flue gas inlet of the dust collector; and a second outlet temperature measuring instrument and a second booster fan are installed sequentially on the pipeline connecting the flue gas outlet of the dust collector and the second flue gas branch pipe.

[0010] Furthermore, the system also includes multiple flow detection instruments; the multiple flow detection instruments include a first flow detection instrument installed on the replenishment pipeline connecting the wastewater tank and the concentration tower, a second flow detection instrument installed on the discharge pipeline connecting the concentration tower and the concentrated brine tank, and a third flow detection instrument installed on the pipeline connecting the fully automatic spraying device and the atomizing nozzle.

[0011] Compared with existing technologies, this invention provides a full evaporation crystallization system for desulfurization wastewater from aluminum electrolysis flue gas. It has the following significant advantages: 1. Energy-saving and efficient with extremely low operating costs: This utility model uses the waste heat of aluminum electrolysis flue gas as the sole heat source, which is directly used for the evaporation and crystallization process of wastewater. There is no need to introduce external steam or configure a high-energy-consuming independent evaporator, thus eliminating the bottleneck problem of huge energy consumption in traditional evaporation and crystallization technology and significantly reducing the system operating cost.

[0012] 2. Achieve zero wastewater discharge and completely eliminate secondary pollution: Through the process of "concentration + full evaporation crystallization", the final product is only solid crystalline salt and water returned to the desulfurization system in the form of water vapor. There is no discharge of any liquid wastewater, which completely solves the risk of soil salinization and groundwater pollution caused by high-salt desulfurization wastewater, resulting in significant environmental benefits.

[0013] 3. Resource utilization and turning waste into treasure: On the one hand, the water in the wastewater is converted into water vapor and reused in the wet desulfurization system, realizing the internal circulation of water resources; on the other hand, the dissolved salts in the wastewater are converted into solid crystalline salts, which can be sent to the electrolytic aluminum plant's dedicated solid waste storage yard for centralized and compliant storage as general industrial solid waste, realizing the stabilization and resource utilization path of pollutants.

[0014] 4. Good crystallization effect and stable system operation: During the crystallization stage, the inherent alumina and other small particles in the aluminum electrolysis flue gas are used as condensation nuclei to induce the growth of crystallized salt on its surface, which helps to form crystals with larger particle size and stable properties. This not only improves the collection efficiency of the subsequent dust collector, but also avoids problems such as fine crystallized salt adhering to the tower wall or clogging the nozzle, ensuring the long-term stable operation of the system.

[0015] 5. Low investment and easy to promote: The main equipment of this system can be arranged in conjunction with the existing aluminum electrolysis flue gas purification system, making full use of the resources and conditions of the existing process links. There is no need to build a separate complex and expensive treatment facility. It is particularly suitable for the technical transformation of the desulfurization system of the existing aluminum electrolysis plant and the supporting construction of new projects. It has broad prospects for promotion and application. Attached Figure Description

[0016] The present invention will now be described in conjunction with the accompanying drawings.

[0017] Figure 1 This is a process flow diagram of the system of this utility model.

[0018] In the diagram: 1-First flue gas branch pipe; 2-Second flue gas branch pipe; 31-First flue gas valve; 32-Second flue gas valve; 41-First inlet temperature measuring instrument; 42-First outlet temperature measuring instrument; 43-Second inlet temperature measuring instrument; 44-Second outlet temperature measuring instrument; 45-Third temperature measuring instrument; 5-Wastewater tank; 6-Concentration tower; 71-Variable frequency circulating pump; 72-Variable frequency wastewater pump; 8-Circulation nozzle; 9-Replenishment nozzle; 10-Demister; 11-Waste liquid regulating valve; 12-Concentrated brine tank; 13-Fully automatic spray device; 14-Evaporation crystallization tower; 15-Atomizing nozzle; 16-Dust collector; 17-Ash discharge valve; 18-Material bin; 191-First flow detection instrument; 192-Second flow detection instrument; 193-Third flow detection instrument; 20-First booster fan; 21-Second booster fan. Detailed Implementation

[0019] The following specific embodiments illustrate the implementation of this utility model. Those skilled in the art can easily understand other advantages and effects of this utility model from the content disclosed in this specification. The described embodiments are merely some embodiments of this utility model, not all embodiments. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of this utility model.

[0020] like Figure 1 As shown, the present invention discloses a total evaporation crystallization system for desulfurization wastewater from aluminum electrolysis flue gas, comprising a wastewater supply and concentration unit, a crystallization unit, a filtration unit, and a flue gas supply unit.

[0021] The wastewater supply and concentration unit includes a wastewater tank 5 and a concentration tower 6. The wastewater tank 5 is connected to the concentration tower 6 via a circulating spray system. The circulating spray system includes a variable frequency circulating pump 71, circulating nozzles 8, and a replenishing nozzle 9. The inlet of the variable frequency circulating pump 71 is connected to the liquid pool at the bottom of the concentration tower 6 via a pipe, and its outlet is connected to the circulating nozzles 8 via a pipe. The replenishing nozzle 9 is located in the lower part of the concentration tower 6 and is used to introduce fresh wastewater from the wastewater tank 5. A variable frequency wastewater pump 72 is installed on the replenishing pipe connecting the wastewater tank 5 to the replenishing nozzle 9. A demister 10 is installed at the top of the concentration tower 6, and a wastewater regulating valve 11 is installed at the bottom concentrate outlet.

[0022] The crystallization unit includes a concentrated brine tank 12, a fully automatic spray device 13, and an evaporation crystallization tower 14. The concentrated liquid outlet at the bottom of the concentration tower 6 is connected to the inlet of the fully automatic spray device 13 via the concentrated brine tank 12. The outlet of the fully automatic spray device 13 is connected to an atomizing nozzle 15 located on the upper part of the evaporation crystallization tower 14.

[0023] The filtration unit includes a dust collector 16 (such as a bag filter or cartridge filter), whose flue gas inlet is connected to the flue gas outlet of the evaporation crystallization tower 14. The bottom of the dust collector 16 is equipped with an ash discharge valve 17 and a material bin 18 for collecting and temporarily storing the crystallized salt.

[0024] The flue gas supply unit includes a first flue gas branch pipe 1 and a second flue gas branch pipe 2 connected in parallel. The two ends of the first flue gas branch pipe 1 are connected to the flue gas inlet and outlet of the concentrator 6, respectively. The two ends of the second flue gas branch pipe 2 are connected to the flue gas inlet of the evaporation crystallization tower 14 and the flue gas outlet of the dust collector 16, respectively. A first flue gas valve 31, a first inlet temperature measuring instrument 41, and a first booster fan 20 are sequentially installed on the pipe connecting the first flue gas branch pipe 1 and the flue gas inlet of the concentrator 6; a first outlet temperature measuring instrument 42 is installed on the pipe connecting the flue gas outlet of the concentrator 6 and the first flue gas branch pipe 1. A second flue gas valve 32 and a second inlet temperature measuring instrument 43 are sequentially installed on the pipeline connecting the second flue gas branch pipe 2 and the flue gas inlet of the evaporation crystallization tower 14; a third temperature measuring instrument 45 is installed on the pipeline connecting the flue gas outlet of the evaporation crystallization tower 14 and the flue gas inlet of the dust collector 16; a second outlet temperature measuring instrument 44 and a second booster fan 21 are sequentially installed on the pipeline connecting the flue gas outlet of the dust collector 16 and the second flue gas branch pipe 2.

[0025] The system also includes multiple flow detection instruments; the multiple flow detection instruments include a first flow detection instrument 191 installed on the replenishment pipeline connecting the wastewater tank 5 and the concentration tower 6, a second flow detection instrument 192 installed on the discharge pipeline connecting the concentration tower 6 and the concentrated brine tank 12, and a third flow detection instrument 193 installed on the pipeline connecting the fully automatic spraying device 13 and the atomizing nozzle 15.

[0026] The working process of this utility model is as follows: S1. Concentration Stage Work Process Desulfurization wastewater is pumped from wastewater tank 5 through variable frequency wastewater pump 72 and replenishment pipe to replenishment nozzle 9 at the lower part of thickening tower 6. Simultaneously, variable frequency circulating pump 71 extracts wastewater from the bottom of thickening tower 6 and forms a circulating spray at the top of thickening tower 6 through circulating nozzle 8. The first stream of aluminum electrolysis flue gas enters the bottom of thickening tower 6 through the first flue gas branch pipe 1, contacting the falling wastewater droplets countercurrently. The sensible heat in the flue gas is transferred to the wastewater, causing the water to evaporate. Demister 10 at the top of thickening tower 6 removes the droplets entrained in the flue gas. The concentrated flue gas, with its temperature monitored by the first outlet temperature measuring instrument 42 (controlled above the dew point temperature), returns to the rear end of the first flue gas branch pipe 1. The replenishment water volume is monitored by the first flow meter 191, and the flow rate of variable frequency circulating pump 71 and the opening of the first flue gas valve 31 are controlled by feedback from the first outlet temperature measuring instrument 42 to maintain system water and heat balance. When the TDS concentration of the wastewater at the bottom of the tower reaches a certain level, the waste liquid regulating valve 11 is opened, and the concentrate is discharged into the concentrated brine tank 12.

[0027] S2. Crystallization Stage Working Process The concentrated brine in the concentrated brine tank 12 is delivered to the atomizing nozzle 15 at the top of the evaporation crystallization tower 14 via a fully automatic spray device 13. The nozzle atomizes the concentrated brine into fine droplets of 50-100 μm, greatly increasing the evaporation area. A second stream of aluminum electrolysis flue gas enters from the top of the evaporation crystallization tower 14 through the second flue gas branch pipe 2, and mixes thoroughly with the falling atomized droplets. Under the heat of the flue gas, the water in the droplets evaporates rapidly, and dissolved salts crystallize out. Notably, the crystallization process uses particulate matter carried in the second flue gas as condensation nuclei, promoting the formation of crystalline salts. The outlet flue gas temperature of the evaporation crystallization tower 14 is monitored by a third temperature measuring instrument 45 (controlled above the dew point temperature), and the spray volume of the fully automatic spray device 13 and the opening of the second flue gas valve 32 are adjusted accordingly to ensure complete evaporation of water.

[0028] S3. Separation and Recovery Stage Work Process Flue gas carrying crystalline salt particles enters the bag filter from the outlet of the evaporation crystallization tower 14. Inside the dust collector 16, the crystalline salt is captured and separated by the filter bags. After being monitored by the second outlet temperature measuring instrument 44, the purified flue gas is sent back to the rear end of the second flue gas branch pipe 2 by the second booster fan 21.

[0029] The entire system achieves closed-loop control through multiple temperature measuring instruments and flow detection instruments: The outlet temperature of the concentration tower 6 is monitored by the first outlet temperature measuring instrument 42, which adjusts the circulating spray volume and the first flue gas volume; the outlet temperature of the evaporation crystallization tower 14 is monitored by the third temperature measuring instrument 45, which adjusts the spray volume and the second flue gas volume; the liquid flow rate of each unit is monitored and adjusted by the corresponding flow detection instrument.

[0030] Other aspects of this utility model that are not detailed herein are all conventional techniques known to those skilled in the art.

[0031] It should be noted that the terms “comprising,” “including,” or any other variations are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0032] The scope of protection of this utility model is not limited to the technical solutions disclosed in the specific embodiments. Any modifications, equivalent substitutions, improvements, etc., made to the above embodiments based on the technical essence of this utility model shall fall within the scope of protection of this utility model.

Claims

1. A total evaporation crystallization system for desulfurization wastewater from aluminum electrolysis flue gas, characterized in that: It includes a wastewater supply and concentration unit, a crystallization unit, a filtration unit, and a flue gas supply unit; The wastewater supply and concentration unit includes a wastewater tank (5) and a concentration tower (6), wherein the wastewater tank (5) is connected to the concentration tower (6) through a circulating spray device; The crystallization unit includes a concentrated brine tank (12), a fully automatic spray device (13), and an evaporation crystallization tower (14); the concentrated liquid outlet at the bottom of the concentration tower (6) is connected to the inlet of the fully automatic spray device (13) via the concentrated brine tank (12); the outlet of the fully automatic spray device (13) is connected to an atomizing nozzle (15) located on the upper part of the evaporation crystallization tower (14). The filtration unit includes a dust collector (16), the flue gas inlet of which is connected to the flue gas outlet of the evaporation crystallization tower (14) for capturing crystalline salt carried by the flue gas. The flue gas supply unit includes a first flue gas branch pipe (1) and a second flue gas branch pipe (2) arranged in parallel; the two ends of the first flue gas branch pipe (1) are respectively connected to the flue gas inlet and outlet of the concentration tower (6), and the two ends of the second flue gas branch pipe (2) are respectively connected to the flue gas inlet of the evaporation crystallization tower (14) and the flue gas outlet of the dust collector (16).

2. The total evaporation crystallization system for desulfurization wastewater from aluminum electrolysis flue gas according to claim 1, characterized in that: The circulating spray device includes a variable frequency circulating pump (71), a circulating nozzle (8), and a replenishing nozzle (9); the inlet of the variable frequency circulating pump (71) is connected to the liquid pool at the bottom of the concentration tower (6) through a pipe, and its outlet is connected to the circulating nozzle (8) located at the top of the concentration tower (6) through a pipe; the replenishing nozzle (9) is located in the lower part of the concentration tower (6) and is used to introduce fresh wastewater from the wastewater tank (5).

3. The total evaporation crystallization system for desulfurization wastewater from aluminum electrolysis flue gas according to claim 2, characterized in that: A variable frequency wastewater pump (72) is installed on the replenishment pipe connecting the wastewater tank (5) and the replenishment nozzle (9).

4. The total evaporation crystallization system for desulfurization wastewater from aluminum electrolysis flue gas according to claim 3, characterized in that: The concentration tower (6) is equipped with a demister (10) at the top and a waste liquid regulating valve (11) at the outlet of the concentrate at the bottom.

5. The total evaporation crystallization system for desulfurization wastewater from aluminum electrolysis flue gas according to claim 1, characterized in that: The dust collector (16) is a bag filter or cartridge filter, and its bottom is equipped with an ash discharge valve (17) and a material box (18) for collecting and temporarily storing crystallized salt.

6. The total evaporation crystallization system for desulfurization wastewater from aluminum electrolysis flue gas according to claim 1, characterized in that: On the pipe connecting the first flue gas branch pipe (1) and the flue gas inlet of the concentrator (6), a first flue gas valve (31), a first inlet temperature measuring instrument (41) and a first booster fan (20) are installed in sequence; on the pipe connecting the flue gas outlet of the concentrator (6) and the first flue gas branch pipe (1), a first outlet temperature measuring instrument (42) is installed. On the pipeline connecting the second flue gas branch pipe (2) and the flue gas inlet of the evaporation crystallization tower (14), a second flue gas valve (32) and a second inlet temperature measuring instrument (43) are installed in sequence; on the pipeline connecting the flue gas outlet of the evaporation crystallization tower (14) and the flue gas inlet of the dust collector (16), a third temperature measuring instrument (45) is installed; on the pipeline connecting the flue gas outlet of the dust collector (16) and the second flue gas branch pipe (2), a second outlet temperature measuring instrument (44) and a second booster fan (21) are installed in sequence.

7. The total evaporation crystallization system for desulfurization wastewater from aluminum electrolysis flue gas according to claim 1, characterized in that: The system also includes multiple flow detection instruments; the multiple flow detection instruments include a first flow detection instrument (191) installed on the replenishment pipe connecting the wastewater tank (5) and the concentration tower (6), a second flow detection instrument (192) installed on the discharge pipe connecting the concentration tower (6) and the concentrated brine tank (12), and a third flow detection instrument (193) installed on the pipe connecting the fully automatic spraying device (13) and the atomizing nozzle (15).

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