Method and apparatus for purifying acid regeneration off-gas

Abstract

The application provides a method and device for purifying acid regeneration flue gas emission, comprising the following steps: injecting hydrochloric acid solution into a ferrous chloride washing tower of an acid regeneration unit, mixing with circulating liquid in the tower to adjust the concentration of free acid in the circulating liquid, and obtaining circulating liquid containing free acid; delivering the circulating liquid containing free acid to a pre-concentrator for dissolving scale at the throat of the pre-concentrator or inhibiting the scale from growing at the throat; before switching the running state of the acid regeneration unit, supplementing the acid solution into the ferrous chloride washing tower to maintain the acidic environment in the washing tower, and achieving the purpose of purifying flue gas. The method and device are simple and convenient to operate, do not need to add large equipment or complex facilities, can be directly implemented by relying on the existing flue gas treatment equipment for optimization, have strong process compatibility, can realize closed-loop automatic control, reduce the manual operation and maintenance intensity, and have a good industrial application prospect.

Description

Technical Field

[0001] This invention belongs to the field of metallurgical and chemical waste gas treatment technology, and particularly relates to a method and apparatus for purifying acid regeneration flue gas emissions. Background Technology

[0002] In the pickling process of cold-rolled steel, the hydrochloric acid regeneration unit recovers regenerated acid by roasting waste acid, but also generates flue gas containing pollutants such as HCl, iron oxide powder, and chlorine. Existing acid regeneration flue gas treatment systems typically employ a multi-stage process of "double cyclone separator + pre-concentrator + absorption tower + ferrous chloride scrubbing tower + pure water scrubbing tower." While this achieves a certain degree of pollutant removal, it suffers from several common problems in actual production. For example, severe scaling at the pre-concentrator throat increases flue gas resistance, reduces waste acid treatment capacity, and affects flue gas emission performance. Furthermore, blockage of the packing in the ferrous chloride scrubbing tower significantly reduces the gas-liquid contact area, leading to the failure of dechlorination and particulate matter removal functions. Additionally, the "red smoke" emission during startup not only affects production stability but also risks exceeding environmental standards and resulting in production shutdowns for rectification.

[0003] In existing technologies, the main approach to improving the aforementioned problems is through additional investment, such as adding multi-stage scrubbing equipment, flue gas condensation systems, or independent flue gas treatment systems. While these methods can improve emissions, they generally suffer from drawbacks such as high investment and operating costs, large footprint, and limited effectiveness in addressing "red smoke" and scaling issues. Therefore, this invention provides a method and apparatus for purifying acid regeneration flue gas emissions to solve the problems of severe scaling, "red smoke" generation, and high costs associated with existing acid regeneration flue gas treatment systems. Summary of the Invention

[0004] The main objective of this invention is to provide a method and apparatus for purifying acid regeneration flue gas emissions, aiming to solve the technical problems of severe scaling, "red smoke" generation, and high cost in existing acid regeneration flue gas treatment systems.

[0005] To achieve the above objectives, the present invention provides a method for purifying acid regeneration flue gas emissions, comprising the following steps: S1: Inject hydrochloric acid solution into the ferrous chloride scrubbing tower of the acid regeneration unit and mix it with the circulating liquid in the tower to adjust the concentration of free acid in the circulating liquid and obtain a circulating liquid containing free acid.

[0006] S2: The circulating liquid containing free acid is transported to the pre-concentrator to dissolve the scale at the throat of the pre-concentrator or to inhibit the growth of the scale at the throat.

[0007] S3: Before switching the operating status of the acid regeneration unit, add the hydrochloric acid solution to the ferrous chloride scrubbing tower to maintain the acidic environment inside the scrubbing tower.

[0008] According to an embodiment of this application, the hydrochloric acid solution contains 10-30% hydrochloric acid by mass.

[0009] The concentration of free acid in the circulating fluid is 5~10 g / L.

[0010] According to the embodiments of this application, after being treated by the method for purifying the flue gas emissions from acid regeneration, the flue gas emitted by the acid regeneration unit does not contain red smoke.

[0011] According to embodiments of this application, the injection method of the hydrochloric acid solution includes: Before the acid regeneration unit is started, the hydrochloric acid solution is added to the ferrous chloride scrubbing tower at a first flow rate. The addition is stopped when the liquid level in the ferrous chloride scrubbing tower reaches level H.

[0012] During the water-operation mode, gradually reduce and then stop adding the hydrochloric acid solution.

[0013] During the operation phase when switching from water operation mode to acid operation mode, the free acid concentration in the ferrous chloride scrubbing tower is maintained at 5~10g / L with the hydrochloric acid solution at a second flow rate.

[0014] During the shutdown phase of the acid regeneration unit, after the acid operation mode is switched to the water operation process, the addition of the hydrochloric acid solution is gradually reduced to maintain the stability of the acidity in the tower.

[0015] According to an embodiment of this application, the first flow rate is 150~300L / h.

[0016] The second flow rate is 100~150L / h.

[0017] According to the embodiments of this application, the operation state switching includes one or more of the following modes: acid regeneration unit start-up, shutdown, heating, load adjustment, acid operation, and water operation.

[0018] According to an embodiment of this application, during the shutdown phase of the acid regeneration unit, the addition of hydrochloric acid solution to the ferrous chloride scrubbing tower is stopped after the water operation mode ends, so as to maintain the low acidity of the circulating liquid in the tower under the water operation mode.

[0019] The present invention also provides an apparatus for purifying acid regeneration flue gas emissions, comprising: The flue gas treatment unit includes a dual cyclone separator, a pre-concentrator, an absorption tower, an exhaust gas fan, a ferrous chloride scrubbing tower, a pure water scrubbing tower, a chimney, and an exhaust gas fan flushing water collection tank connected in sequence.

[0020] The acid circulation and addition system includes an acid storage tank, an acid transfer pump, a ferrous chloride circulation pump, and an acid transfer pipeline connecting the acid storage tank and the ferrous chloride scrubbing tower.

[0021] The control unit includes a flow control valve, a flow meter, and an acid concentration detection device. The flow meter and the acid concentration detection device are signal-connected to the flow control valve and are used to monitor the acid flow rate and acid concentration in real time and provide feedback to adjust the opening of the flow control valve.

[0022] The bottom of the ferrous chloride washing tower is connected to the pre-concentrator via the ferrous chloride circulation pump, which is used to circulate the ferrous chloride solution to the pre-concentrator.

[0023] According to an embodiment of this application, the acid delivery pipeline includes a DN25 PPH pipe.

[0024] The flow control valve includes a solenoid ball valve.

[0025] The flow meter includes an electromagnetic flow meter.

[0026] The acid concentration detection device includes a densitometer, a conductivity meter, a thermometer, and corresponding correction software.

[0027] The flow control valve and the flow meter are installed on the acid delivery pipeline.

[0028] The acid concentration detection device is installed on the branch line of the circulating pump pressure end of the ferrous chloride washing tower.

[0029] According to an embodiment of this application, the control unit further includes a closed-loop control circuit formed with an electromagnetic ball valve on the circulating liquid outlet pipe of the ferrous chloride scrubbing tower to adjust the acidity of the circulating liquid.

[0030] The free acid concentration of the circulating liquid is 5~10 g / L.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows: The aforementioned method and apparatus for purifying acid regeneration flue gas emissions achieves targeted enrichment and recycling of regenerated acid within the system by injecting hydrochloric acid solution into the ferrous chloride scrubbing tower to adjust the free acid concentration in the circulating liquid, effectively improving the acid resource recovery efficiency. Simultaneously, the stable acidic environment inhibits the oxidative hydrolysis of ferrous ions, reducing the formation of ferric hydroxide colloidal precipitates, thereby lowering the scaling rate inside the scrubbing tower and extending the continuous operation cycle of the equipment. Furthermore, the circulating liquid rich in free acid is introduced into the pre-concentrator, where the chemical dissolution effect of the free acid is used to perform in-situ cleaning of existing scale, effectively dissolving or inhibiting scale buildup. The scale buildup at the throat of the ferrous chloride scrubber fundamentally solves the blockage problem and completely eliminates the "red smoke" phenomenon from the chimney during start-up and shutdown. It also prevents the structured packing material inside the ferrous chloride scrubber from becoming clogged and yellowed by sediment, restoring the packing to its original color and maintaining intact pores. This significantly improves liquid-gas contact efficiency and mass transfer, resulting in cleaner flue gas emissions and ensuring smooth production processes while meeting environmental protection requirements. Finally, hydrochloric acid solution is proactively added before switching the operating status of the acid regeneration unit to maintain the acidic environment inside the ferrous chloride scrubber, ensuring the stability of the scrubber's treatment efficiency during start-up, shutdown, and load adjustments. Through the coordinated efforts of these steps, closed-loop utilization of acid resources and continuous stability of flue gas purification efficiency are achieved.

[0032] Moreover, the method and apparatus of the present invention are simple and easy to operate. They do not require the addition of large-scale equipment or complex facilities. They can be implemented by optimizing existing flue gas treatment equipment. They have strong process compatibility, can realize closed-loop automatic control, reduce the intensity of manual operation and maintenance, and have good prospects for industrial application. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0034] Figure 1 This is a schematic diagram of the apparatus for purifying acid regeneration flue gas emissions according to Embodiment 1 of the present invention; Figure 2 The images show a comparison of the structured packing material in the ferrous chloride scrubbing tower of Example 1 of the present invention with that of the prior art structured packing material; wherein, (a) is the structured packing material of the present invention; and (b) is the structured packing material of the prior art. Figure 3 The images show a comparison of the Venturi throat scale of the pre-concentrator in Embodiment 1 of the present invention and the Venturi throat scale of the pre-concentrator in the prior art; wherein, (a) the Venturi throat scale of the present invention; and (b) the Venturi throat scale of the prior art. Figure 4 This is a physical image of the structured packing material in the ferrous chloride scrubbing tower of Comparative Example 2 of the present invention during shutdown inspection. Figure 5 This is a graph showing the relationship between the emission concentration and different free acid concentrations in Example 1 of the present invention.

[0035] The attached figures are labeled as follows: 1. Double cyclone separator; 2. Pre-concentrator; 3. Absorption tower; 4. Exhaust gas fan; 5. Ferrous chloride scrubbing tower; 6. Pure water scrubbing tower; 7. Chimney; 8. Regenerated acid tank; 9. Exhaust gas fan flushing water collection tank; 10. Solenoid ball valve; 11. Flow meter; 12. Regenerated acid pump; 13. Ferrous chloride solenoid ball valve; 14. Ferrous chloride circulation pump; 15. Acid concentration detection device.

[0036] The realization of the objective, functional characteristics and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0037] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0039] In existing technologies, to ensure that the atmospheric emissions of acid regeneration units meet national emission standards, common environmental protection designs for acid regeneration units are as follows: A dual cyclone separator effectively removes 40% of iron oxide particles from the flue gas by utilizing changes in airflow velocity; a pre-concentrator effectively reduces the flue gas temperature by using high-intensity jet cooling at the Venturi throat, facilitating flue gas absorption; an absorption tower uses structured packing to increase the gas-liquid contact area, absorbing 98% of HCl and 30% of iron oxide particles; a ferrous chloride scrubbing tower also uses structured packing to effectively remove chlorine and remaining particulate matter from the flue gas by increasing the gas-liquid contact area; finally, a pure water scrubbing tower uses demineralized water at the Venturi taper for final washing, after which qualified flue gas is discharged into the atmosphere.

[0040] However, in actual production and application, the above design has the following drawbacks: Scaling (a combination of ferric hydroxide and iron powder) easily forms at the Venturi throat of the pre-concentrator, affecting the acid regeneration waste acid treatment capacity and flue gas emission efficiency; iron powder easily accumulates on the structured packing of the ferrous chloride scrubbing tower, which oxidizes upon contact with the ferrous chloride solution sprayed from above, forming ferric hydroxide-like sludge-like precipitates, thus clogging the scrubbing tower packing and reducing the contact area between the sprayed liquid and the flue gas, causing the ferrous chloride scrubbing tower to fail in its environmental protection functions of dechlorination and flue gas absorption; during the acid regeneration operation mode switching process, the probability of "red smoke" appearing on the exhaust chimney within half an hour increases significantly. Based on this, the present invention provides a method and apparatus for purifying acid regeneration flue gas emissions to reduce the frequency of scaling at the pre-concentrator throat, ensuring no impact on treatment capacity and emission efficiency; effectively dissolving precipitates to ensure the porosity of the structured packing of the ferrous chloride scrubbing tower, guaranteeing the gas-liquid contact area; and eliminating the "red smoke" problem during the start-up, shutdown, and abnormal conditions of the acid regeneration unit.

[0041] To achieve the above objectives, the present invention provides a method for purifying acid regeneration flue gas emissions, comprising the following steps: S1: Inject hydrochloric acid solution into the ferrous chloride scrubbing tower of the acid regeneration unit and mix it with the circulating liquid in the tower to adjust the concentration of free acid in the circulating liquid and obtain a circulating liquid containing free acid.

[0042] In some embodiments, hydrochloric acid solution is injected into the ferrous chloride scrubbing tower of the acid regeneration unit and mixed with the circulating liquid inside the tower. The valve opening of the hydrochloric acid solution is adjusted by an online concentration meter to inject the required flow rate of free acid, thereby obtaining a circulating liquid containing free acid.

[0043] In some embodiments, by adding hydrochloric acid solution to the ferrous chloride scrubbing tower and mixing it with the circulating liquid, the concentration of free acid in the circulating liquid is precisely adjusted, and a stable free acid circulating liquid that meets the process requirements is obtained, ensuring the stability of subsequent flue gas purification and system operation.

[0044] In existing technology, the original liquid in the ferrous chloride scrubbing tower is a ferrous chloride solution. After a period of production, iron powder in the flue gas is easily deposited on the structured packing and adsorbed by the ferric hydroxide generated after the oxidation of ferrous chloride. This easily forms precipitates on the packing, which significantly reduces the porosity of the packing and thus affects the gas-liquid contact area. At the same time, when switching from water operation to acid operation, the liquid in the pre-concentrator and ferrous chloride scrubbing tower is rinsing water, which has almost no ability to dissolve iron powder. When switching from acid operation to water operation, the liquid in the pre-concentrator and ferrous chloride scrubbing tower gradually changes from treatment acid to rinsing water, which also leads to a decrease in the ability to dissolve iron powder. Therefore, the chimney will show a "red smoke" phenomenon.

[0045] Therefore, in some embodiments, by adding an appropriate amount of hydrochloric acid solution to the ferrous chloride scrubbing tower, the formation of ferric hydroxide can be reduced, preventing a decrease in the porosity of the packing. Simultaneously, the ferrous chloride solution with a certain acidity, injected into the pre-concentrator and circulated, can significantly reduce scaling in the furnace throat. Furthermore, during mode switching, adding hydrochloric acid solution to the ferrous chloride scrubbing tower in advance can increase the acidity of the liquid, thereby effectively preventing the generation of "red smoke."

[0046] In some embodiments, by adding a DN25 (with an automatic valve and flow meter) regeneration acid pipeline at the bottom of the ferrous chloride scrubbing tower, 10-30% hydrochloric acid solution is continuously added to the ferrous chloride scrubbing tower during actual production and mode switching. The chemical properties of hydrochloric acid are used to help dissolve iron powder particles in the flue gas. During normal production, the circulating liquid is kept at a certain acidity, thereby ensuring that the structured packing in the ferrous chloride scrubbing tower and the throat in the pre-concentrator are not prone to scaling.

[0047] S2: The circulating liquid containing free acid is transported to the pre-concentrator to dissolve the scale at the throat of the pre-concentrator or to inhibit the growth of the scale at the throat.

[0048] In some embodiments, a circulating liquid containing free acid is fed into a pre-concentrator. The acidic environment effectively dissolves the scale that has formed at the throat of the pre-concentrator and continuously inhibits the formation of new scale, preventing throat blockage, ensuring smooth flue gas flow at the throat of the acid regeneration unit, and reducing equipment maintenance frequency and downtime risk.

[0049] S3: Before switching the operating status of the acid regeneration unit, add the hydrochloric acid solution to the ferrous chloride scrubbing tower to maintain the acidic environment inside the scrubbing tower.

[0050] In some embodiments, before the acid regeneration unit switches its operating state, the hydrochloric acid solution is added to or adjusted in the ferrous chloride scrubbing tower to maintain an acidic environment in the scrubbing tower; this can effectively absorb solid particles such as iron oxide powder and dust carried in the flue gas before the production mode switch, thereby achieving the purpose of purifying the flue gas.

[0051] In some embodiments, hydrochloric acid solution is added in advance before the acid regeneration unit switches operating status to maintain a continuous and stable acidic environment in the scrubbing tower, preventing a decrease in purification efficiency, aggravated scaling, or abnormal equipment corrosion due to pH fluctuations, thereby achieving continuous, stable, and efficient operation of the acid regeneration flue gas purification process.

[0052] The aforementioned method for purifying acid regeneration flue gas emissions achieves targeted enrichment and recycling of regenerated acid within the system by injecting hydrochloric acid solution into the ferrous chloride scrubbing tower to adjust the free acid concentration in the circulating liquid, effectively improving acid resource recovery efficiency. Simultaneously, the stable acidic environment inhibits the oxidative hydrolysis of ferrous ions, reducing the formation of ferric hydroxide colloidal precipitates, thereby lowering the scaling rate inside the scrubbing tower and extending the continuous operation cycle of the equipment. Furthermore, the circulating liquid rich in regenerated acid is introduced into the pre-concentrator, where the chemical dissolution effect of the free acid is used to clean existing scale in situ, effectively dissolving or inhibiting scale buildup. The removal of scale at the venturi throat fundamentally solves the clogging problem and completely eliminates the "red smoke" phenomenon from the chimney. It also prevents the structured packing material inside the ferrous chloride scrubbing tower from becoming clogged and yellowed by sediment, restoring the packing to its original color and maintaining intact pores. This significantly improves liquid-gas contact efficiency and mass transfer, resulting in cleaner flue gas emissions and ensuring smooth production processes while meeting environmental protection requirements. Finally, hydrochloric acid solution is proactively added before switching the operating status of the acid regeneration unit to maintain the acidic environment inside the ferrous chloride scrubbing tower, ensuring the stability of the scrubbing tower's processing efficiency during start-up, shutdown, and load adjustments. Through the coordinated efforts of these steps, closed-loop utilization of acid resources and continuous stability of flue gas purification efficiency are achieved.

[0053] In some embodiments, the hydrochloric acid solution contains 10-30% hydrochloric acid by mass.

[0054] In some embodiments, the hydrochloric acid solution contains 15-20% hydrochloric acid by mass.

[0055] In some embodiments, the concentration of free acid in the circulating liquid is 5-10 g / L.

[0056] In some embodiments, after being treated by the method for purifying the flue gas emissions from acid regeneration, the flue gas emitted by the acid regeneration unit does not contain red smoke.

[0057] In some embodiments, the hydrochloric acid solution is injected in the following manner: Before the acid regeneration unit is started, the hydrochloric acid solution is added to the ferrous chloride scrubbing tower at a first flow rate. The addition is stopped when the liquid level in the ferrous chloride scrubbing tower reaches level H.

[0058] During the water-operation mode, gradually reduce and then stop adding the hydrochloric acid solution.

[0059] During the operation phase when switching from water operation mode to acid operation mode, the free acid concentration in the ferrous chloride scrubbing tower is maintained at 5~10g / L with the hydrochloric acid solution at a second flow rate.

[0060] During the shutdown phase of the acid regeneration unit, after the acid operation mode is switched to the water operation process, the addition of the hydrochloric acid solution is gradually reduced to maintain the stability of the acidity in the tower.

[0061] In some embodiments, before the acid regeneration unit starts pumping, hydrochloric acid solution is added to the ferrous chloride scrubbing tower at a first flow rate. When the liquid level in the ferrous chloride scrubbing tower reaches level H, the addition is stopped to ensure that the ferrous chloride scrubbing tower can maintain a certain acid concentration during the heating process of the calcining furnace. This can effectively dissolve iron oxide powder in the flue gas, which is generated on the flue during shutdown, thereby reducing the risk of red smoke when starting up.

[0062] During the water-operated phase, the addition of the hydrochloric acid solution is stopped.

[0063] In some embodiments, during the water-operated phase, since no reaction occurs in the roasting furnace, the flue gas mainly consists of water vapor and carries some hydrogen chloride gas. During this phase, the addition of the hydrochloric acid solution is gradually reduced and stopped.

[0064] During the shutdown phase of the acid regeneration unit, the addition of hydrochloric acid solution should be reduced or stopped after the acid and water processes are completed in order to maintain stable acidity in the tower.

[0065] In some embodiments, the addition of hydrochloric acid solution is completely stopped during the pure water operation until the shutdown phase.

[0066] In some embodiments, to ensure operational accuracy, when the acid regeneration unit is started, if a certain amount of demineralized water needs to be re-injected after the liquid in the ferrous chloride scrubbing tower is drained, a certain amount of hydrochloric acid solution (16-20% hydrochloric acid by mass) is added to the ferrous chloride scrubbing tower 5-15 minutes before pump start-up. The free acid concentration in the ferrous chloride scrubbing tower is ensured to be 5-10 g / L by volume ratio or online acid concentration meter display, and the liquid level is ensured to reach position H.

[0067] In some embodiments, such as after the liquid in a ferrous chloride scrubbing tower is drained, hydrochloric acid solution must be injected before starting the tower.

[0068] In some embodiments, the first flow rate is 150~300L / h.

[0069] The second flow rate is 100~150L / h.

[0070] In some embodiments, the operation state switching includes one or more of the following modes: acid regeneration unit start-up, shutdown, load adjustment, heating operation, acid operation, and water operation.

[0071] In some embodiments, the operation state switching includes one or two of the following modes: acid regeneration unit start-up, shutdown, load adjustment, heating operation, acid operation, and water operation.

[0072] In some embodiments, during the shutdown phase of the acid regeneration unit, the addition of hydrochloric acid solution to the ferrous chloride scrubbing tower is stopped after the water operation is completed, in order to maintain the acidity of the circulating liquid in the tower and prevent abnormal flue gas emissions when the acid regeneration unit is started up later.

[0073] In some embodiments, during the shutdown phase of the acid regeneration unit, the addition of hydrochloric acid solution to the ferrous chloride scrubbing tower is stopped after the water operation is completed, so as to maintain the low acidity of the circulating liquid in the tower under water operation mode and prevent abnormal emission of hydrogen chloride gas in the flue gas due to excessively high acidity when the acid regeneration unit is started later.

[0074] The method and apparatus of this invention are simple and easy to operate. They do not require the addition of large-scale equipment or complex facilities. They can be implemented by optimizing existing flue gas treatment equipment. They have strong process compatibility, can realize closed-loop automatic control, reduce the intensity of manual operation and maintenance, and have good prospects for industrial application.

[0075] The present invention also provides an apparatus for purifying acid regeneration flue gas emissions, comprising: The flue gas treatment unit includes a dual cyclone separator, a pre-concentrator, an absorption tower, an exhaust gas fan, a ferrous chloride scrubbing tower, a pure water scrubbing tower, a chimney, and an exhaust gas fan flushing water collection tank connected in sequence.

[0076] The acid circulation and addition system includes an acid storage tank, an acid transfer pump, a ferrous chloride circulation pump, and an acid transfer pipeline connecting the acid storage tank and the ferrous chloride scrubbing tower.

[0077] The control unit includes a flow control valve, a flow meter, and an acid concentration detection device. The flow meter and the acid concentration detection device are signal-connected to the flow control valve and are used to monitor the acid flow rate and acid concentration in real time and provide feedback to adjust the opening of the flow control valve.

[0078] The bottom of the ferrous chloride washing tower is connected to the pre-concentrator via the ferrous chloride circulation pump, which is used to circulate the ferrous chloride solution to the pre-concentrator.

[0079] In some embodiments, the acid delivery pipeline includes a DN25 PPH pipe.

[0080] The flow control valve includes a solenoid ball valve.

[0081] The flow meter includes an electromagnetic flow meter.

[0082] The concentration detection device includes a densitometer, a conductivity meter, a thermometer, and compatible correction software.

[0083] The flow control valve and the flow meter are installed on the acid delivery pipeline.

[0084] The concentration detection device is installed on the branch line at the pressure end of the circulating pump of the ferrous chloride washing tower.

[0085] In some embodiments, during acid operation, since the ferrous chloride scrubbing tower has a stable supply flow rate, the opening of the solenoid ball valve is controlled so that the flow meter parameter is 100~150L / h; or, by using an online acid concentration detection device, in conjunction with the opening of the ferrous chloride solenoid ball valve connected to the bottom of the ferrous chloride scrubbing tower, a closed-loop control is formed with the opening of the acid replenishment solenoid ball valve to ensure that the free acid concentration in the ferrous chloride solution in the ferrous chloride scrubbing tower is 5~10g / L.

[0086] In some embodiments, when the acid regeneration unit is shut down, at the end of the pure water operation mode, since the ferrous chloride scrubbing tower has a certain acidity, if no maintenance or venting is performed, the acid operation can be directly performed before the next startup.

[0087] In some embodiments, a DN25 PPH pipeline for regenerated acid is added below the ferrous chloride scrubbing tower, equipped with a DN25 solenoid ball valve and a flow meter. Simultaneously, an acid concentration detection device is added at the pump pressure end. The opening of the solenoid ball valve is controlled by feedback from the measured acid concentration data to ensure controlled flow.

[0088] In some embodiments, the flow control valve and flow meter are not specifically limited, as long as they can be used to monitor the flow rate. For example, a common ball valve (manual opening) or a float flow meter can be selected.

[0089] In some embodiments, the control unit further includes a closed-loop control circuit formed with an electromagnetic ball valve on the circulating liquid outlet pipe of the ferrous chloride scrubbing tower, wherein the acidity of the circulating liquid is adjusted by proportionally adjusting the opening degree of the two valves.

[0090] The free acid concentration of the circulating liquid is 5~10 g / L.

[0091] To further illustrate the present invention, the following examples are provided: It should be noted that, prior to the emission of the acid regeneration flue gas of this invention, the content of each substance as determined by a third-party environmental protection test was: HCl gas 15 mg / m³. 3 Iron powder particles 13mg / m³ 3 Cl2 gas 20mg / m³ 3 Example 1 A method for purifying flue gas emissions from acid regeneration includes the following steps: S1: Inject hydrochloric acid solution (acid solution) into the ferrous chloride scrubbing tower of the acid regeneration unit and mix it with the circulating liquid in the tower to adjust the concentration of free acid in the circulating liquid, thus obtaining a circulating liquid containing free acid; the mass fraction of hydrochloric acid in the hydrochloric acid solution is 18%; the acid solution is injected as follows: during the start-up phase of the acid regeneration unit, 10 minutes before switching from water operation mode to acid operation mode, add acid solution to the ferrous chloride scrubbing tower at a first flow rate to make the free acid concentration in the ferrous chloride scrubbing tower 10g / L, with a first flow rate of 200L / h; during the operation phase of acid operation mode, maintain the free acid concentration in the ferrous chloride scrubbing tower with a second flow rate of 100L / h.

[0092] During the shutdown phase of the acid regeneration unit, after the water operation is completed, the addition of acid to the ferrous chloride scrubbing tower is stopped in order to maintain the acidity of the circulating liquid in the tower at 10 g / L, so as to prevent abnormal flue gas emissions when the acid regeneration unit is started later.

[0093] S2: The circulating liquid containing regenerated acid is delivered to the pre-concentrator to dissolve or inhibit scale buildup at the throat of the pre-concentrator.

[0094] S3: Before switching the operating status of the acid regeneration unit, add acid to the ferrous chloride scrubbing tower so that the liquid level in the scrubbing tower reaches position H, in order to maintain the acidic environment inside the scrubbing tower.

[0095] A device for purifying flue gas emissions from acid regeneration, see [link / reference]. Figure 1 ,for: The flue gas treatment unit consists of a dual cyclone separator, a pre-concentrator, an absorption tower, an exhaust gas fan, a ferrous chloride scrubbing tower, a pure water scrubbing tower, a chimney, and an exhaust gas fan flushing water collection tank connected in sequence.

[0096] The acid circulation and addition system includes an acid storage tank, an acid delivery pump, a ferrous chloride circulation pump, and an acid delivery pipeline connecting the acid storage tank and the ferrous chloride scrubbing tower. The acid delivery pipeline is a DN25 PPH pipe. The control unit consists of a flow control valve, a flow meter, and an acid concentration detection device. The flow control valve is a solenoid ball valve, the flow meter is an electromagnetic flow meter, and the acid concentration detection device comprises a densitometer and a conductivity meter. The acid concentration corresponds to the set flow rate. The flow meter is signal-connected to the flow control valve for real-time monitoring of the acid flow rate and feedback adjustment of the flow control valve opening. The bottom of the ferrous chloride scrubbing tower is connected to a pre-concentrator via the ferrous chloride circulation pump to circulate the ferrous chloride solution to the pre-concentrator. The control unit forms a closed-loop control circuit with the detection results from the acid concentration device and the solenoid ball valve on the acid replenishment pipeline at the bottom of the ferrous chloride scrubbing tower circulation liquid to adjust the free acid concentration of the circulating liquid.

[0097] After modifying the acid regeneration flue gas, the above-mentioned method and device for purifying acid regeneration flue gas, as tested by a third-party environmental protection agency, showed the following content of various substances: HCl gas 6.7 mg / m³. 3 Iron powder particles 7.7 mg / m³ 3 Cl2 gas 8mg / m 3 Furthermore, see Figure 2 In Example 1, the structured packing of the ferrous chloride scrubbing tower regained its initial color and maintained intact pores, effectively ensuring the liquid-gas contact area. In contrast, the structured packing of the prior art appeared yellow, with pores blocked by precipitates. (See also...) Figure 3 In this application, the pre-concentrator has no deposits or scale at the Venturi throat; in the prior art, iron powder and ferrous chloride easily combine at the Venturi throat of the pre-concentrator to form deposits. These deposits become extremely hard after cooling and gradually grow along the wall, eventually blocking the entire throat and affecting production capacity; and in this embodiment 1, the chimney does not emit any "red smoke".

[0098] Comparative Example 1 Compared to Example 1, the hydrochloric acid solution was replaced with a nitric acid solution or a sulfuric acid solution, while the other steps were the same as in Example 1.

[0099] The above-mentioned method and device for purifying acid regeneration flue gas emissions, after modification of the acid regeneration flue gas, showed the following content of various substances as determined by third-party environmental testing: HCl gas 7 mg / m³ 3 Iron powder particles 10mg / m³ 3 Cl2 gas 7.6 mg / m³ 3 .

[0100] Although the structured packing of the ferrous chloride scrubbing tower in Comparative Example 1 recovered its initial color and the pores remained intact, effectively ensuring the liquid-gas contact area, and there were no deposits or scale at the Venturi throat of the pre-concentrator; and no "red smoke" was emitted from the chimney of Comparative Example 1, after a period of operation, nitric acid and sulfuric acid would mix in the system. On the one hand, this would increase the nitrogen oxide or sulfur oxide content in the by-product iron oxide powder, resulting in impure iron powder quality; on the other hand, nitric acid and sulfuric acid would corrode the impeller of the iron powder conveying fan, affecting the system's pumping capacity, impacting normal unit production, and even leading to production interruption.

[0101] Comparative Example 2 Compared to Example 1, the concentration of free acid in the ferrous chloride scrubbing tower was changed.

[0102] In Comparative Example 2, the free acid concentration in the ferrous chloride scrubbing tower was 15 g / L, and the other steps were the same as in Example 1.

[0103] After modifying the acid regeneration flue gas, the above-mentioned method and device for purifying acid regeneration flue gas, as tested by a third-party environmental protection agency, showed the following content of various substances: HCl gas 10.5 mg / m³.3 Iron powder particles 7.5mg / m³ 3 Cl2 gas 8.1 mg / m³ 3 The emission of HCl gas exceeds the ultra-low emission standard.

[0104] Although the structured packing of the ferrous chloride scrubbing tower in Comparative Example 2 recovered its initial color and the pores remained intact, effectively ensuring the liquid-gas contact area, a shutdown inspection and extraction of the structured packing revealed localized areas of yellow sludge. (See [link to relevant documentation]). Figure 4 In Comparative Example 2, the pre-concentrator had no deposits or scale at the venturi throat, and no red smoke was emitted from the chimney.

[0105] Comparative Example 3 Compared to Example 1, hydrochloric acid solution was not injected into the ferrous chloride scrubbing tower of the acid regeneration unit, while the other steps were the same as in Example 1.

[0106] The content of each substance, as determined by third-party environmental testing, is as follows: HCl gas 15 mg / m³ 3 Iron powder particles 13mg / m³ 3 Cl2 gas 20mg / m³ 3 Among them, HCl gas and iron powder particles did not meet the ultra-low emission standards, and the emission of Cl2 gas was relatively high.

[0107] The structured packing in Comparative Example 3 is yellow, and the pores are blocked by precipitates. The iron powder and ferrous chloride in Comparative Example 3 tend to combine at the venturi throat of the pre-concentrator to form an adhering substance. This substance becomes extremely hard after cooling and gradually grows along the wall, eventually blocking the entire throat and affecting the production capacity. In addition, the chimney of Comparative Example 3 emits "red smoke".

[0108] Analysis example 1 Compared to Example 1, the concentration of free acid in the ferrous chloride scrubbing tower was changed.

[0109] In Example 1, the free acid concentrations in the ferrous chloride scrubbing tower were analyzed at five sets of data: 3 g / L, 13 g / L, 15 g / L, 18 g / L, and 20 g / L. These data, along with the flue gas composition measured by a third-party environmental protection agency, were combined with data from Example 1 and Comparative Examples 1-3. (See [reference needed]). Figure 5 , Figure 5 This is a graph showing the relationship between emission concentrations and different free acid concentrations.

[0110] from Figure 5 As can be seen, for free acid concentrations below 5 g / L, the structured packing appears yellow, and the pores are more or less blocked by precipitates; for free acid concentrations above 10 g / L, the emission of HCl gas exceeds the ultra-low emission standard.

[0111] The aforementioned method and apparatus for purifying acid regeneration flue gas emissions achieves targeted enrichment and recycling of regenerated acid within the system by injecting acid into the ferrous chloride scrubbing tower to adjust the free acid concentration in the circulating liquid, effectively improving acid resource recovery efficiency. Simultaneously, the stable acidic environment inhibits the oxidative hydrolysis of ferrous ions, reducing the formation of ferric hydroxide colloidal precipitates, thereby lowering the scaling rate inside the scrubbing tower and extending the continuous operation cycle of the equipment. Furthermore, the circulating liquid rich in regenerated acid is introduced into a pre-concentrator, where the chemical dissolution effect of the free acid is used to clean existing scale in situ, effectively dissolving or... Suppressing scale buildup at the venturi throat fundamentally solves the clogging problem and completely eliminates the "red smoke" emission from the chimney. It also prevents the structured packing in the ferrous chloride scrubbing tower from becoming clogged and yellowed by sediment, restoring the packing to its original color and maintaining intact pores. This significantly improves liquid-gas contact efficiency and mass transfer, resulting in cleaner flue gas emissions and ensuring smooth production processes while meeting environmental requirements. Finally, proactive acid replenishment before switching the acid regeneration unit's operating status maintains the acidic environment within the ferrous chloride scrubbing tower, ensuring stable processing efficiency during start-up, shutdown, and load adjustments. Through the coordinated efforts of these steps, closed-loop utilization of acid resources and continuous stability of flue gas purification efficiency are achieved.

[0112] Moreover, the method and apparatus of the present invention are simple and easy to operate. They do not require the addition of large-scale equipment or complex facilities. They can achieve ultra-low emission requirements by directly optimizing existing flue gas treatment equipment. They have strong process compatibility, can realize closed-loop automatic control, reduce the intensity of manual operation and maintenance, and have good prospects for industrial application.

[0113] In summary, the above-described technical solutions of the present invention are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. All equivalent structural transformations made using the contents of the present invention's specification and drawings under the technical concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for purifying flue gas emissions from acid regeneration, characterized in that, Includes the following steps: S1: Inject hydrochloric acid solution into the ferrous chloride scrubbing tower of the acid regeneration unit and mix it with the circulating liquid in the tower to adjust the concentration of free acid in the circulating liquid and obtain a circulating liquid containing free acid. S2: The circulating liquid containing free acid is transported to the pre-concentrator to dissolve the scale at the throat of the pre-concentrator or to inhibit the growth of the scale at the throat. S3: Before switching the operating status of the acid regeneration unit, add the hydrochloric acid solution to the ferrous chloride scrubbing tower to maintain the acidic environment inside the scrubbing tower.

2. The method for purifying acid regeneration flue gas emissions according to claim 1, characterized in that, The hydrochloric acid solution contains 10-30% hydrochloric acid by mass. The concentration of free acid in the circulating fluid is 5~10 g / L.

3. The method for purifying acid regeneration flue gas emissions according to claim 1, characterized in that, After being treated by the method described above for purifying the flue gas emissions from acid regeneration, the flue gas emitted by the acid regeneration unit does not contain red smoke.

4. The method for purifying acid regeneration flue gas emissions according to claim 1, characterized in that, The hydrochloric acid solution is injected in the following ways: Before the acid regeneration unit is started, the hydrochloric acid solution is added to the ferrous chloride scrubbing tower at a first flow rate. When the liquid level in the ferrous chloride scrubbing tower reaches level H, the addition is stopped. During the water-operation mode, gradually reduce and then stop adding the hydrochloric acid solution; During the operation phase when switching from water operation mode to acid operation mode, the free acid concentration in the ferrous chloride scrubbing tower is maintained at 5~10g / L with the hydrochloric acid solution at the second flow rate; During the shutdown phase of the acid regeneration unit, after the acid operation mode is switched to the water operation process, the addition of the hydrochloric acid solution is gradually reduced to maintain the stability of the acidity in the tower.

5. The method for purifying acid regeneration flue gas emissions according to claim 4, characterized in that, The first flow rate is 150~300L / h; The second flow rate is 100~150L / h.

6. The method for purifying acid regeneration flue gas emissions according to claim 1, characterized in that, The operation status switching includes one or more of the following modes: start-up, shutdown, heating, load adjustment, acid operation, and water operation of the acid regeneration unit.

7. The method for purifying acid regeneration flue gas emissions according to claim 1, characterized in that, During the shutdown phase of the acid regeneration unit, the addition of hydrochloric acid solution to the ferrous chloride scrubbing tower is stopped after the water operation mode ends, in order to maintain the low acidity of the circulating liquid in the tower under the water operation mode.

8. A device for purifying flue gas emissions from acid regeneration, characterized in that, include: The flue gas treatment unit includes a dual cyclone separator, a pre-concentrator, an absorption tower, an exhaust gas fan, a ferrous chloride scrubbing tower, a pure water scrubbing tower, a chimney, and an exhaust gas fan flushing water collection tank connected in sequence. An acid circulation and addition system includes an acid storage tank, an acid transfer pump, a ferrous chloride circulation pump, and an acid transfer pipeline connecting the acid storage tank and the ferrous chloride scrubbing tower. The control unit includes a flow control valve, a flow meter, and an acid concentration detection device. The flow meter and the acid concentration detection device are signal-connected to the flow control valve and are used to monitor the acid flow rate and acid concentration in real time and provide feedback to adjust the opening of the flow control valve. The bottom of the ferrous chloride washing tower is connected to the pre-concentrator via the ferrous chloride circulation pump, which is used to circulate the ferrous chloride solution to the pre-concentrator.

9. The apparatus for purifying acid regeneration flue gas emissions according to claim 8, characterized in that, The acid delivery pipeline includes a DN25 PPH pipe; The flow control valve includes a solenoid ball valve; The flow meter includes an electromagnetic flow meter; The acid concentration detection device includes a densitometer, a conductivity meter, a thermometer, and phase-adaptive correction software. The flow control valve and the flow meter are installed on the acid delivery pipeline; The acid concentration detection device is installed on the branch line of the circulating pump pressure end of the ferrous chloride washing tower.

10. The apparatus for purifying acid regeneration flue gas emissions according to claim 8, characterized in that, The control unit also includes a closed-loop control circuit formed with the electromagnetic ball valve on the circulating liquid outlet pipe of the ferrous chloride scrubbing tower to adjust the acidity of the circulating liquid. The free acid concentration of the circulating liquid is 5~10 g / L.

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