A method and system for regeneration of a magnesium-based desulfurizer based on in-situ electrochemical production of alkali

Abstract

This invention discloses a method and system for regenerating magnesium-based desulfurizers based on electrochemical in-situ alkali production. The system includes solid-liquid separation of desulfurization byproduct slurry to obtain a liquid-phase regenerated liquid; the liquid-phase regenerated liquid is introduced into the front zone of a partitioned electrochemical reactor, where in-situ alkali production at the cathode is used for synergistic pretreatment to achieve pH adjustment, calcium salt precipitation, and organic matter coagulation and flocculation removal; the pre-treated liquid-phase regenerated liquid is then introduced into the rear zone of the partitioned electrochemical reactor, where in-situ alkali production at the cathode further increases the alkalinity of the liquid phase, converting magnesium ions into magnesium hydroxide slurry. The magnesium hydroxide slurry is then processed by a regenerated slurry collection unit and used as a magnesium-based desulfurizer in a flue gas desulfurization absorption tower for recycling. The magnesium hydroxide slurry obtained by this method has a purity of up to 99%, which reduces the use of lime-based agents as the main regenerator, lowers salt accumulation and sludge burden, improves the continuous stability of the magnesium-based desulfurizer regeneration process, and enables controllable particle size of the regenerated magnesium hydroxide slurry.

Description

Technical Field

[0001] This invention relates to the fields of flue gas desulfurization, by-product liquid resource utilization, and electrochemical water treatment technology. In particular, it relates to a method and system for regenerating magnesium-based desulfurizing agents based on electrochemical in-situ alkali production. Background Technology

[0002] Wet flue gas desulfurization (FGD) is an important technical route for controlling sulfur dioxide emissions from industrial flue gas such as coal combustion, metallurgy, and chemical industries. In magnesium-based FGD processes, the absorbent typically participates in the absorption reaction in the form of magnesium oxide or magnesium hydroxide slurry. After absorbing sulfur dioxide, it gradually generates magnesium sulfite and magnesium bisulfite, which are further converted into magnesium sulfate and other components under oxidizing conditions. To reduce the consumption of magnesium-based absorbent and improve system economy, it is usually necessary to regenerate the magnesium components in the desulfurization byproduct slurry or liquid into magnesium hydroxide and return it to the absorption tower for recycling. Therefore, how to achieve efficient, continuous, and low-consumption regeneration of magnesium-based desulfurizing agents has always been a key issue in the application of magnesium-based FGD engineering.

[0003] Existing magnesium-based desulfurizer regeneration routes mostly use lime-based alkaline agents as the main regenerator, converting magnesium ions in the system into magnesium hydroxide precipitate by adding lime or slaked lime. While this method can achieve a certain degree of magnesium regeneration, it typically has the following drawbacks in engineering applications: First, the continuous introduction of calcium sources can easily form new calcium salt byproducts in the system, increasing the burden of sludge or byproduct solids treatment; second, the addition of chemical alkali increases operating chemical consumption and may lead to equipment scaling, pipeline blockage, and increased burden on subsequent solid-liquid separation; third, for desulfurization byproduct liquids with complex compositions, relying solely on a single-step chemical regeneration often makes it difficult to simultaneously achieve effective magnesium recovery, removal of organic interference, and quality control of the returned slurry.

[0004] On the other hand, desulfurization by-product slurry or liquid is usually not a single magnesium salt system. In addition to magnesium salts, sulfites, and sulfates, it may also contain calcium salts, suspended particles, organic matter, and other impurities. These components increase the difficulty of nucleation, precipitation, solid-liquid separation, and continuous operation control during subsequent regeneration. Without effective pretreatment or regenerated liquid conditioning steps, single-stage regeneration often struggles to balance regeneration efficiency, product quality, and stable system operation.

[0005] To reduce reliance on externally added chemical alkalis, electrochemical in-situ alkali production technology has attracted attention in recent years. This type of technology typically utilizes cathode electrolysis to generate hydroxide ions in situ, thereby increasing the alkalinity of the system, inducing metal ion precipitation, or softening and removing hardness. Existing research on electrochemical softening or resource recovery mostly focuses on softening high-hardness water, scale control, or magnesium resource recovery. The processing time is generally long (approximately 60 minutes), and the magnesium hydroxide products generated in the reaction generally suffer from low purity and severe impurity entrainment, making it difficult to meet the reuse requirements of desulfurization absorbents.

[0006] Furthermore, while electrochemical in-situ alkali production generates alkalinity, it is often accompanied by side reactions and produces a certain amount of process waste liquid, which adversely affects subsequent resource recovery and system water balance. Simultaneously, the precipitates generated by traditional electrochemical systems are mostly nano-sized particles. Due to their excessive fineness, these particles easily lead to increased slurry viscosity, causing scaling on the packing, nozzle, and pipe wall surfaces, making it difficult to simultaneously meet the actual reuse requirements of flue gas desulfurization absorbents for suitable particle size, good settling performance, and high desulfurization efficiency. For the more complex flue gas desulfurization by-product liquid system with more clearly defined reuse requirements, there is still a lack of a systematic process scheme that combines "short-term conditioning in the front end, continuous regeneration in the back end, reduced lime main regeneration, and adjustable particle size of the slurry returned to the tower."

[0007] Therefore, it is still necessary to provide a new method and system for regenerating magnesium-based desulfurizers to reduce the use of lime-based agents as the main regenerator, thereby reducing new salt accumulation and sludge burden. At the same time, before entering the main regeneration zone, the desulfurization by-product slurry or liquid should be subjected to short-term synergistic pretreatment to remove some interfering components and organic matter, thereby creating liquid phase conditions more suitable for subsequent magnesium hydroxide regeneration and precipitation. Furthermore, by adjusting the electrochemical operating parameters, the particle size of the regenerated magnesium hydroxide slurry can be controlled, making it more suitable for recycling back to the absorption tower for flue gas desulfurization. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the present invention aims to provide a magnesium-based desulfurizer regeneration system based on electrochemical in-situ alkali production. This system removes large-particle-size or high-density solid impurities from the desulfurization by-product slurry through a solid-liquid separation unit. Then, it utilizes a partitioned electrochemical reactor to produce alkali in-situ at the cathode, creating different alkali environments in the front and rear zones. The partitioned electrochemical reactor employs an electrode structure that isolates the anolyte from the main liquid and connects the cathode to the main liquid, enabling the regeneration process to use electrochemical in-situ alkali production at the cathode as the main alkali supply method. This achieves efficient regeneration of magnesium ions in the desulfurization by-product slurry, solving problems such as the existing magnesium-based desulfurizer regeneration process mainly relying on lime-based agents, continuous salt accumulation, large sludge production, the influence of organic matter and calcium and magnesium interference components in complex desulfurization by-product slurries on the regeneration effect, and the difficulty in balancing the particle size of the regenerated slurry with its performance in return to the tower.

[0009] Another objective of this invention is to provide a method for regenerating magnesium-based desulfurizers based on electrochemical in-situ alkali production.

[0010] To achieve the above objectives, the present invention is accomplished through the following technical solutions.

[0011] A magnesium-based desulfurizing agent regeneration system based on electrochemical in-situ alkali production includes a desulfurization by-product slurry conveying unit 1, a solid-liquid separation unit 2, a zoned electrochemical reactor 3, a regenerated slurry collection unit 4, and a return-to-tower conveying unit 5.

[0012] The desulfurization by-product slurry conveying unit 1 is connected to the inlet of the solid-liquid separation unit 2, and the outlet of the solid-liquid separation unit 2 is connected to the liquid inlet 3-1 of the partitioned electrochemical reactor 3. The liquid outlet 3-6 (or the rear zone discharge outlet 3-3) of the partitioned electrochemical reactor 3 is connected to the regenerated slurry collection unit 4, and the regenerated slurry collection unit 4 is connected to the return tower conveying unit 5. The partitioned electrochemical reactor 3 includes: a liquid inlet 3-1, a front zone discharge port 3-2, a rear zone discharge port 3-3, two support legs 3-4, N electrode assemblies 3-5, a liquid outlet 3-6, a tank body 3-7, and a flow baffle 3-8. The tank 3-7 is vertically equipped with a flow baffle 3-8, which divides the tank 3-7 into a front zone and a rear zone. The front zone and the rear zone can be connected through the flow baffle 3-8. The liquid phase regeneration liquid flows through the front zone and the rear zone sequentially along the length of the tank. The front zone of the tank 3-7 has inlet ports 3-1 at both ends or on the outer wall, and the rear zone has outlet ports 3-6 at both ends or on the outer wall. The front zone has a discharge port 3-2 at the bottom of the front zone, and the rear zone has a discharge port 3-3 at the bottom of the rear zone. Support legs 3-4 are provided below the front zone discharge port 3-2 and the rear zone discharge port 3-3 respectively. The tank 3-7 contains N electrode assemblies 3-5, where N≥2. At least one electrode assembly 3-5 is provided in the front and rear areas to form a pretreatment electrochemical unit and a regeneration electrochemical unit, respectively. The front and rear areas are connected to independent power circuits to form different alkalization intensities. The electrode assemblies are arranged in sequence along the water flow direction as the first electrode assembly, the second electrode assembly, ..., the Nth electrode assembly, and the first to the Nth electrode assemblies are interconnected. The electrode assembly 3-5 includes: a fastening mold 3-5-1, a first anode 3-5-2, a second anode 3-5-3, a first cathode 3-5-4, a second cathode 3-5-5, two diaphragms 3-5-6, an anode cavity inlet 3-5-7, and an anode cavity outlet 3-5-8; The fastening mold 3-5-1 is used to fix the first anode 3-5-2, the second anode 3-5-3, the first cathode 3-5-4, and the second cathode 3-5-5; the first anode 3-5-2 and the second anode 3-5-3 are arranged opposite each other perpendicular to the liquid flow direction and spaced apart, forming an anode cavity with the fastening mold 3-5-1; the first cathode 3-5-4 and the second cathode 3-5-5 are respectively arranged outside the first anode 3-5-2 and the second anode 3-5-3, and are separated from the corresponding anodes by a diaphragm 3-5-6; The anode cavity inlet 3-5-7 is located on the outer side wall of the fastening mold 3-5-1, and the anode cavity outlet 3-5-8 is located on the opposite outer side wall of the fastening mold 3-5-1; The anode cavities of the first electrode assembly to the Nth electrode assembly are interconnected, and the first cathode and the second cathode of the first electrode assembly to the Nth electrode assembly are in contact with the liquid entering the partitioned electrochemical reactor 3.

[0013] In the above technical solution, the regenerated slurry collection unit 4 is used to collect the magnesium hydroxide slurry generated in the rear zone, and the return tower conveying unit 5 is used to convey the collected magnesium hydroxide slurry back to the flue gas desulfurization absorption tower for recycling as an absorbent.

[0014] In the above technical solution, the front area is provided with at least one electrode assembly 3-5 to form a pretreatment electrochemical unit for synergistic pretreatment of the liquid phase regenerated liquid, and the rear area is provided with at least one electrode assembly 3-5 to form a regeneration electrochemical unit for regenerating magnesium hydroxide slurry; the spacing between each electrode assembly is ≥5cm.

[0015] In the above technical solution, the trough 3-7 is a continuous flow trough structure.

[0016] In the above technical solution, the front discharge port 3-2 is used to collect the settled calcium salts and organic matter for coagulation and flocculation; the rear discharge port 3-3 is used to collect the settled magnesium hydroxide slurry.

[0017] In the above technical solution, the liquid inlet 3-1 and the liquid outlet 3-6 are used to realize continuous liquid inlet and continuous liquid outlet operation.

[0018] In the above technical solution, the aspect ratio of the first anode 3-5-2, the second anode 3-5-3, the first cathode 3-5-4, and the second cathode 3-5-5 is (2.8~5.6):1.

[0019] In the above technical solution, the first anode 3-5-2 and the second anode 3-5-3 are titanium-based noble metal oxide coated electrodes, and the first cathode 3-5-4 and the second cathode 3-5-5 are one or more of stainless steel, iron, copper, titanium, nickel and aluminum.

[0020] In the above technical solution, the diaphragm 3-5-6 is one of the following: ion exchange membrane, nylon mesh, polytetrafluoroethylene mesh, polyester nonwoven composite diaphragm, and polyester.

[0021] In the above technical solution, the overflow baffle 3-8 is one of the overflow plate, the perforated baffle, and the flow guide baffle.

[0022] In the above technical solution, the front zone forms a relatively mild alkalization and conditioning environment for synergistic pretreatment of the liquid phase regenerated liquid, and the rear zone forms a magnesium regeneration environment with a high alkalization intensity, thereby improving the overall process zoning control capability for regenerating magnesium hydroxide slurry.

[0023] In the above technical solution, the electrode assembly 3-5 is also provided with a support frame and positioning structure to facilitate installation, disassembly and maintenance.

[0024] In the above technical solution, the fastening mold 3-5-1 is a frame-shaped structure, with solid walls on one side and frame-like flow walls on the other side.

[0025] In the above technical solution, the first anode 3-5-2 and the first cathode 3-5-4, and the second anode 3-5-3 and the second cathode 3-5-5 respectively constitute two sets of electrode pairs arranged symmetrically.

[0026] In the above technical solution, it is preferable that the front area and the rear area each have two sets of electrode assemblies independently.

[0027] In the above technical solution, the anode cavity outlet 3-5-8 of the first electrode assembly is connected to the anode cavity inlet 3-5-7 of the second electrode assembly; and the anode cavity inlet 3-5-7 of the first electrode assembly or the anode cavity outlet 3-5-8 of the Nth electrode assembly is connected to an external device to introduce or export anolyte.

[0028] In the above technical solution, the external device is one of an external circulation device, a pumping device, and a liquid storage device.

[0029] In the above technical solution, the solid-liquid separation unit 2 is one or more combinations of a sedimentation tank, an inclined plate sedimentation device, a filter, and a centrifugal separator.

[0030] A method for regenerating magnesium-based desulfurizers based on electrochemical in-situ alkali production includes the following steps: The desulfurization by-product slurry was subjected to solid-liquid separation to obtain a liquid-phase regenerated liquid; at 5~100 mA / cm 2 Under a current density of 0.05–10 L / h, the liquid-phase regenerated liquid is introduced into the front zone of the partitioned electrochemical reactor 3. The hydraulic retention time in the front zone is 1.5–20 min, and the pH is 8.5–10.5. Then, at a current density of 10–400 mA / cm², the liquid phase regenerated liquid is introduced into the front zone of the partitioned electrochemical reactor 3. 2 At a current density, the liquid phase regenerated liquid after pretreatment is introduced into the rear zone of the partitioned electrochemical reactor 3 at a liquid flow rate of 0.05~10 L / h. The hydraulic residence time in the rear zone is 0.01~3.5 h, and the pH is 9.5~11.8, to obtain magnesium hydroxide slurry. The magnesium hydroxide slurry is then processed by the regenerated slurry collection unit 4 and sent to the flue gas desulfurization absorption tower for recycling as a magnesium-based desulfurizing agent.

[0031] In the above technical solution, the desulfurization by-product slurry is a slurry containing magnesium, sulfate and / or sulfite discharged from the flue gas desulfurization absorption tower during the magnesium-based flue gas desulfurization process.

[0032] In the above technical solution, the preferred hydraulic residence time in the front zone is 5 to 15 minutes, and more preferably 8 to 12 minutes.

[0033] In the above technical solution, the liquid phase regenerated liquid is introduced into the front zone of the partitioned electrochemical reactor 3, and the pH is adjusted to 8.5~10.5 by utilizing the in-situ alkali production effect of the cathode, so as to complete the preliminary precipitation of calcium salt interference components and the removal of organic matter by coagulation and flocculation.

[0034] In the above technical solution, the pH of the liquid phase regeneration solution in the front zone is preferably 9.0~10.0.

[0035] In the above technical solution, the preliminary precipitation of the calcium salt interference components and the removal of organic matter by coagulation and flocculation include: sedimentation, filtration, slag scraping or sludge discharge.

[0036] In the above technical solution, the liquid phase regenerated liquid enters the rear zone from the front zone of the partitioned electrochemical reactor 3. The alkalinity of the liquid phase in the rear zone is increased by the in-situ alkali production at the cathode, and the pH is controlled at 9.5~11.8, so that the magnesium ions in the liquid phase are converted into magnesium hydroxide slurry, which is then used as a magnesium-based desulfurizing agent for regeneration.

[0037] In the above technical solution, the pH of the back-zone liquid phase regeneration solution is preferably 10.0~11.5.

[0038] In the above technical solution, the preferred back-region current density is 20~150 mA / cm². 2 This promotes the regeneration and precipitation of magnesium hydroxide slurry.

[0039] In the above technical solution, the operations of the recycled slurry collection unit 4 include: filtration, drying or centrifugation.

[0040] In the above technical solution, the magnesium hydroxide slurry can be operated by the regenerated slurry collection unit 4 according to actual needs.

[0041] In the above technical solution, the mass concentration of magnesium hydroxide slurry returned to the flue gas desulfurization absorption tower is 5~150 g / L, preferably 10~80 g / L.

[0042] In the above technical solution, the particle size distribution of magnesium hydroxide slurry can be adjusted by the current density and the liquid flow rate in the back zone. When the current density of the independent power supply circuit in the back zone is 10~40 mA / cm², the particle size distribution of the magnesium hydroxide slurry can be adjusted accordingly. 2 When the liquid flow rate in the rear zone is 0.05~0.08 L / h, the particle size distribution is 1~10 μm, and the current density of the independent power supply circuit in the rear zone is 40~400 mA / cm². 2 When the liquid flow rate in the back zone is 0.08~10 L / h, the particle size distribution is 0.1~1 μm.

[0043] In the above technical solution, the preferred current density of the independent power supply circuit in the rear area is 20~40mA / cm². 2 When the liquid flow rate in the rear zone is 0.05~0.08 L / h, the particle size distribution is 1~10 μm, and the current density of the independent power supply circuit in the rear zone is 40~150 mA / cm². 2 When the liquid flow rate in the back zone is 0.20~8.00L / h, the particle size distribution is 0.1~1 μm.

[0044] The method of this invention utilizes the electrochemical conditions to generate magnesium hydroxide, where the nucleation and crystal growth behavior is influenced by parameters such as current density, magnesium ion concentration, and liquid flow rate. High current density and high liquid flow rate result in finer magnesium hydroxide particles, while low current density and low liquid flow rate lead to relatively larger particles. This allows for effective control of magnesium hydroxide particle size over a wide range, resulting in adjustable particle size distribution and surface properties of the obtained magnesium hydroxide slurry. Furthermore, the solubility and absorption performance of magnesium-based desulfurizers are closely related to particle size, dispersibility, and mass transfer conditions. Therefore, combining the controllable regeneration of magnesium hydroxide particles with electrochemical parameter regulation with synergistic pretreatment in the desulfurization byproduct pretreatment zone is more conducive to achieving continuous regeneration and recycling of magnesium-based absorbents.

[0045] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The present invention uses in-situ alkali production at the electrochemical cathode as the main alkali supply method for magnesium hydroxide slurry, which makes the magnesium hydroxide slurry highly pure, with a purity of over 90% and reaching up to 99%. It can be directly used as a magnesium-based desulfurizer for regeneration, reducing or avoiding the use of lime-based alkaline agents as the main regeneration method. This helps to reduce the accumulation of new salts, reduce agent consumption, and alleviate the burden of sludge or by-product solid treatment.

[0046] (2) The present invention sets up a front-zone synergistic pretreatment zone, so that the desulfurization by-product liquid can complete the conditioning of regenerated liquid, the initial precipitation of calcium salt interference components and the removal of organic matter by coagulation and flocculation within a short residence time, thereby creating more favorable liquid phase conditions for magnesium regeneration in the back zone and improving the continuous stability of the overall process.

[0047] (3) The present invention enables the regenerated magnesium hydroxide slurry to have controllable particle size by synergistic regulation of the back zone current density and liquid flow rate: submicron particles can be obtained under high current and high flow rate conditions, and micron particles can be obtained under low current and low flow rate conditions. It can be controlled to the submicron to micron range according to the application requirements of the return tower, which is beneficial to improving the specific surface area, reactivity and slurry mass transfer characteristics.

[0048] (4) This invention integrates solid-liquid separation, zoned electrochemical regeneration and regenerated slurry return to the tower in a closed loop, forming a complete process chain with good continuous operation capability and engineering implementation value.

[0049] (5) In the anode cavity formed by the anode of the present invention, sulfate and sulfite ions will be attracted by positive electric attraction. Sulfite ions will be reacted by the anode to form sulfate ions. Electrolysis of water will also produce hydrogen ions, resulting in an acidic solution with pH=1.5. This acidic solution can be used as dilute sulfuric acid in the flue gas plant to realize the green recycling of by-products. Attached Figure Description

[0050] Figure 1 This is a schematic diagram of the process flow of the magnesium-based desulfurizer regeneration method based on electrochemical in-situ alkali production according to the present invention. Figure 2 This is a schematic diagram of the magnesium-based desulfurizer regeneration system based on electrochemical in-situ alkali production according to the present invention. Figure 3 This is a schematic diagram of the overall structure of the partitioned electrochemical reactor 3 of the present invention; Figure 4 This is a schematic diagram of the main view of the partitioned electrochemical reactor 3 of the present invention; Figure 5 This is a top view schematic diagram of the partitioned electrochemical reactor 3 of the present invention; Figure 6 This is a three-dimensional structural schematic diagram of the electrode assembly 3-5 of the present invention; Figure 7 This is a front view schematic diagram of electrode assembly 3-5 of the present invention; Figure 8 This is a cross-sectional schematic diagram of the electrode assembly 3-5 of the present invention; Figure 9 This is an exploded structural diagram of the electrode assembly 3-5 of the present invention; Figure 10 Scanning electron microscope image of magnesium hydroxide in the magnesium-based desulfurizer prepared by the method in Example 1; Figure 11 Scanning electron microscope image of magnesium hydroxide in the magnesium-based desulfurizer prepared by the method in Example 5; Among them, 1: desulfurization by-product slurry conveying unit, 2: solid-liquid separation unit, 3: zoned electrochemical reactor, 4: regenerated slurry collection unit, and 5: return tower conveying unit; 3-1: Liquid inlet, 3-2: Front discharge port, 3-3: Rear discharge port, 3-4: Support leg, 3-5: Electrode assembly, 3-6: Liquid outlet, 3-7: Tank body, 3-8: Flow baffle; 3-5-1: Fastening mold, 3-5-2: First anode, 3-5-3: Second anode, 3-5-4: First cathode, 3-5-5: Second cathode, 3-5-6: Diaphragm, 3-5-7: Anode cavity inlet, 3-5-8: Anode cavity outlet. Detailed Implementation

[0051] The following examples are intended to enable those skilled in the art to more fully understand the present invention, but do not limit the invention in any way.

[0052] Unless otherwise specified, the materials used in the embodiments of the present invention can be obtained commercially or prepared according to conventional methods known to those skilled in the art.

[0053] In the following examples, the desulfurization by-product slurry is a slurry containing magnesium salts, sulfites, sulfates, suspended particles, and other impurities discharged from the flue gas desulfurization absorption tower during the magnesium-based flue gas desulfurization process. The slurry has a magnesium ion concentration of 7 g / L, a calcium ion concentration of 0.3 g / L, and a total organic carbon (TOC) content of 55 mg / L.

[0054] Example 1 A magnesium-based desulfurizer regeneration system based on electrochemical in-situ alkali production, the process flow diagram is shown below. Figure 1 As shown, the system structure diagram is as follows: Figure 2 As shown, it includes a desulfurization by-product slurry conveying unit 1, a solid-liquid separation unit 2, a zoned electrochemical reactor 3, a regenerated slurry collection unit 4, and a return-to-tower conveying unit 5; The desulfurization by-product slurry conveying unit 1 is connected to the inlet of the solid-liquid separation unit 2, and the outlet of the solid-liquid separation unit 2 is connected to the inlet 3-1 of the partitioned electrochemical reactor 3. The discharge port 3-3 of the partitioned electrochemical reactor 3 is connected to the regenerated slurry collection unit 4, which collects the magnesium hydroxide slurry generated in the latter zone. The regenerated slurry collection unit 4 is connected to the return tower conveying unit 5, which transports the collected magnesium hydroxide slurry back to the flue gas desulfurization absorption tower for recycling as an absorbent. The solid-liquid separation unit 2 uses a settling tank-filter combination process. If the supernatant discharged from the outlet 3-6 contains sediment, it can be sent to the regenerated slurry collection unit 4 for static separation of the magnesium hydroxide slurry.

[0055] A schematic diagram of the overall structure of the partitioned electrochemical reactor 3 is shown below. Figure 3 As shown, the main view diagram is as follows: Figure 4 As shown in the top view diagram Figure 5 As shown, the partitioned electrochemical reactor 3 includes: inlet 3-1, front zone discharge port 3-2, rear zone discharge port 3-3, two support legs 3-4, N electrode assemblies 3-5, outlet 3-6, tank body 3-7, and flow baffle 3-8.

[0056] Tank 3-7 is a continuous flow tank structure. A flow baffle 3-8 is vertically installed in tank 3-7. The flow baffle 3-8 is an overflow plate that divides tank 3-7 into a front zone and a rear zone. The front zone and the rear zone can be connected through the flow baffle 3-8. The liquid phase regenerated liquid overflows into the front zone and the rear zone sequentially along the length of the tank through the upper edge of the baffle. The front zone is mainly used for the co-pretreatment of the liquid phase regenerated liquid, and the rear zone is mainly used for the regeneration of magnesium hydroxide slurry.

[0057] The tank body 3-7 has an inlet 3-1 on the outer wall of the front section and an outlet 3-6 on the outer wall of the rear section to enable continuous liquid inflow and outflow. A discharge port 3-2 is located at the bottom of the front section, and a discharge port 3-3 is located at the bottom of the rear section. Support legs 3-4 are located below both the discharge port 3-2 and the discharge port 3-3.

[0058] The tank 3-7 contains N electrode assemblies 3-5, where N=4. Two electrode assemblies are installed in the front zone and two in the rear zone, forming two pretreatment electrochemical units and two regeneration electrochemical units, creating a four-unit structure. The electrode assemblies 3-5 in the front zone are primarily used to increase the pH of the liquid regeneration solution, induce initial precipitation of calcium salts, and promote the coagulation and flocculation of organic matter. The electrode assemblies 3-5 in the rear zone are primarily used to increase the alkalinity of the liquid phase and promote the conversion of magnesium ions into magnesium hydroxide slurry. The front and rear zones are connected to independent power circuits to create different alkalinization intensities. This allows for a milder alkalinization and conditioning environment in the front zone and a higher alkalinity magnesium regeneration environment in the rear zone, thereby improving the overall process's zonal control capability. The electrode assemblies are arranged sequentially along the water flow direction as the first electrode assembly, the second electrode assembly, the third electrode assembly, and the fourth electrode assembly, with a spacing of 5 cm between each assembly.

[0059] A schematic diagram of the three-dimensional structure of electrode assembly 3-5 is shown below. Figure 6 As shown, the main view diagram is as follows: Figure 7 As shown in the schematic cross-sectional view... Figure 8 As shown in the diagram, the exploded structure is as follows: Figure 9 As shown, electrode assembly 3-5 includes: a fastening mold 3-5-1, a first anode 3-5-2, a second anode 3-5-3, a first cathode 3-5-4, a second cathode 3-5-5, two diaphragms 3-5-6, an anode chamber inlet 3-5-7, and an anode chamber outlet 3-5-8. Both the first anode 3-5-2 and the second anode 3-5-3 are titanium-based noble metal oxide coated electrodes, and both the first cathode 3-5-4 and the second cathode 3-5-5 are stainless steel meshes. Diaphragm 3-5-6 is an ion exchange membrane. The aspect ratio of the first anode 3-5-2, the second anode 3-5-3, the first cathode 3-5-4, and the second cathode 3-5-5 is 4.2:1.

[0060] The fastening mold 3-5-1 has a frame-like structure with a length-to-width ratio of 1:1. It is made of PVC and has two solid side walls and two openwork side walls for fixing the first anode 3-5-2, the second anode 3-5-3, the first cathode 3-5-4, and the second cathode 3-5-5. The first anode 3-5-2 and the second anode 3-5-3 are perpendicular to the liquid flow direction and are spaced apart, forming an anode cavity with the solid wall of the fastening mold 4-1. The first cathode 3-5-4 and the second cathode 3-5-5 are respectively located outside the first anode 3-5-2 and the second anode 3-5-3, and are separated from the corresponding anodes by a diaphragm 3-5-6. That is, the first anode 3-5-2 and the first cathode 3-5-4, and the second anode 3-5-3 and the second cathode 3-5-5 respectively form two symmetrically arranged electrode pairs. The anode cavity inlet 3-5-7 is located on the outer side wall of the solid wall of the fastening mold 3-5-1, and the anode cavity outlet is located on the outer side wall of the opposite solid wall of the fastening mold 3-5-1. Both are connected to the inside of the anode cavity. In the aforementioned partitioned electrochemical reactor 3, the anode outlet 3-5-8 of the preceding electrode assembly is connected to the anode inlet 3-5-7 of the following electrode assembly; the anode cavities of the first electrode assembly to the Nth electrode assembly are interconnected, and the first cathode and the second cathode of the first electrode assembly to the Nth electrode assembly are in contact with the liquid entering the partitioned electrochemical reactor 3.

[0061] The liquid-phase regenerated liquid enters the front area of ​​tank 3-7 through inlet 3-1. The liquid-phase regenerated liquid (i.e., the main liquid) contacts the outer cathode, connecting the first cathode 3-5-4 and the second cathode 3-5-5 in each electrode assembly 3-5. Part of the liquid-phase regenerated liquid (i.e., the anolyte) is pumped into the anode cavity of the first electrode assembly through a pumping device from the anode cavity inlet 3-5-7. The anolyte flows sequentially through the first electrode assembly to the anode cavity of the fourth electrode assembly, and is then discharged from the anode cavity outlet 3-5-8 of the fourth electrode assembly through an external pipeline. The first anode 3-5-2 and the second anode 3-5-3 are isolated from the main liquid by the diaphragm 3-5-6, thus forming an electrode structure where the anolyte is isolated from the main liquid, and the cathode side is connected to the main liquid. With this structure, acidic products generated on the anode side can be promptly discharged through an independent circuit, while the cathode side continuously provides hydroxide ions to the main liquid, thereby creating a continuous alkaline environment in the main liquid and reducing the direct neutralization of acid produced at the anode and alkali produced at the cathode in the main liquid.

[0062] In the anode cavity of the present invention, the positive charge attracts sulfate and sulfite ions. The sulfite ions are reacted by the anode to form sulfate ions. Electrolysis of water also produces hydrogen ions, resulting in an acidic solution with pH=1.5. This acidic solution can be used as dilute sulfuric acid in situ at the flue gas plant.

[0063] Examples 2 to 7 A method for regenerating magnesium-based desulfurizers based on electrochemical in-situ alkali production includes the following steps: Step 1: The desulfurization by-product slurry discharged from the flue gas desulfurization absorption tower is subjected to solid-liquid separation. After removing coarse particulate suspended matter, a liquid phase regenerated liquid is obtained. The liquid phase regenerated liquid is continuously fed into the front zone of the partitioned electrochemical reactor 3. The pH is adjusted by the in-situ alkali production of the cathode to complete the preliminary precipitation of calcium salt interference components and the coagulation and flocculation removal of organic matter.

[0064] Step 2: The liquid phase regenerated liquid after the pre-zone treatment in Step 1 is introduced into the rear zone of the partitioned electrochemical reactor 3; in the rear zone, the alkalinity of the liquid phase is further increased by in-situ alkali production at the cathode, so that the magnesium ions in the liquid phase are preferentially converted into magnesium hydroxide slurry to form reusable magnesium hydroxide slurry. The magnesium hydroxide slurry obtained in the rear zone is processed by the regenerated slurry collection unit 4 and then sent to the flue gas desulfurization absorption tower for recycling as a magnesium-based desulfurizing agent.

[0065] Table 1 shows the liquid flow rate, hydraulic residence time, current density, corresponding effluent pH, magnesium hydroxide slurry mass concentration, median particle size, magnesium hydroxide purity, and conversion rate used in Examples 2 to 7.

[0066] Table 1

[0067] Comparative Example 1 A method for regenerating magnesium-based desulfurizers based on electrochemical in-situ alkali production includes the following steps: The desulfurization by-product slurry discharged from the flue gas desulfurization absorption tower undergoes solid-liquid separation to remove coarse particulate suspended solids, yielding a liquid-phase regenerated liquid. This liquid-phase regenerated liquid is continuously fed into the downstream zone of the partitioned electrochemical reactor to form a reusable magnesium hydroxide slurry. The magnesium hydroxide slurry obtained in the downstream zone is collected and returned to the flue gas desulfurization absorption tower. The system processing flow rate (corresponding to the downstream zone liquid flow rate) is 500 L / h, the downstream zone hydraulic retention time is 20 min, and the downstream zone current density is controlled at 40 mA / cm² (at which point the pH of the downstream effluent is 10.8).

[0068] The magnesium hydroxide slurry obtained by the method in Comparative Example 1 has a mass concentration of 10 g / L and a purity of 87.3%.

[0069] Example 8 Exploring the synergistic pretreatment in the front zone: This invention utilizes the in-situ alkali production at the cathode to design a zoned electrochemical reactor front zone for synergistic pretreatment of the liquid phase regenerated liquid, enabling the liquid phase regenerated liquid to complete pH adjustment, preliminary precipitation of calcium salt interference components, and removal of organic matter through coagulation and flocculation.

[0070] As shown in Table 1, in Example 2, the hydraulic retention time in the front zone was set to 10 min, the pH of the effluent in the front zone was controlled at about 9.4, calcium carbonate appeared in the front zone (magnesium hydroxide was rarely seen), and there was obvious flocculation. The total organic carbon (TOC) of the effluent in the front zone was reduced by about 70% compared with the influent in the front zone.

[0071] The results indicate that the front zone not only performs a simple calcium precipitation function, but also simultaneously completes the conditioning of the regenerated solution, the removal of some calcium salt interference components, and the synergistic removal of organic matter within a short residence time, creating favorable conditions for magnesium regeneration in the back zone.

[0072] Furthermore, the magnesium hydroxide slurry obtained by the regeneration method in Comparative Example 1 had a mass concentration of only 10 g / L and a purity of 87.3%. This slurry not only had a low content of effective components and poor product purity, but also contained a large number of impurities, which would directly affect the subsequent desulfurization effect and product quality.

[0073] Therefore, the hydraulic residence time of the front zone is controlled to be 3~20 min in this invention, and the front zone can simultaneously achieve the following functions: (1) Rapidly increase the pH of the liquid phase by in-situ alkali production at the cathode.

[0074] (2) Taking advantage of the difference in pH between magnesium hydroxide and calcium carbonate precipitation (the former precipitates significantly at higher pH, while the latter precipitates completely at lower pH), the calcium salt interference components in the system are induced to undergo initial precipitation. (3) Organic matter is coagulated and flocculated through adsorption, bridging and sweeping on the surface of precipitated particles; (4) Reduce the interference of organic matter and impurities in the main regeneration stage of the back zone.

[0075] Example 9 Investigating the regeneration of magnesium hydroxide in the back zone: By controlling the current density in the back zone to be 25–400 mA / cm² 2 To increase the alkalization intensity in the back zone, the pH of the effluent in the back zone is controlled at 10.4~11.5, which can preferentially convert magnesium ions in the liquid phase into magnesium hydroxide precipitate, forming a reusable magnesium hydroxide slurry.

[0076] As shown in Table 1, the magnesium hydroxide slurry prepared by the regeneration process in Examples 2 and 3 has a suitable mass concentration of 24-30 g / L and a purity of over 90%. After collection, the slurry can be returned to the absorption tower and used directly as a flue gas desulfurization absorbent. Throughout the regeneration process, there is no need to add lime or slaked lime to convert magnesium ions in the system into magnesium hydroxide precipitate; therefore, lime-based alkaline agents are no longer used as the main regeneration agent.

[0077] In Example 4, the TOC in the liquid phase of the back zone was approximately 30 mg / L; the median particle size (D50) of the obtained magnesium hydroxide product was approximately 1 μm. Further analysis of the obtained magnesium hydroxide slurry showed that the moisture content of the formed wet magnesium hydroxide slurry was approximately 97%, and the purity of magnesium hydroxide on a dry basis was approximately 99%. This meets the metallurgical industry standard YB / T 4378-2014 "Passivating Magnesium for Desulfurization of Molten Iron" which specifies Mg ≥ 92.0% (dry basis). The magnesium hydroxide slurry can be further processed through a regenerated slurry collection unit to reduce its moisture content, allowing it to be used directly as a magnesium-based desulfurizing agent.

[0078] Example 10 Exploring Controllable Particle Size Regeneration: Table 1 shows that the particle size distribution of regenerated magnesium hydroxide particles can be controlled by adjusting the current density and liquid flow rate in the rear zone. As shown in Example 1, micron-sized magnesium hydroxide particles with a D50 of 10 μm can be obtained under low current density of 25 mA / cm² and low liquid flow rate of 0.05 m / s. Scanning electron microscope images are shown below. Figure 10 As shown; however, in Example 5, under a higher current density of 120 mA / cm² and a higher liquid flow rate of 0.25 m / s, submicron-sized magnesium hydroxide particles with a D50 of 800 nm were obtained, as shown in the corresponding scanning electron microscope image. Figure 11 As shown.

[0079] In summary, this invention can control the particle size distribution of regenerated magnesium hydroxide particles by adjusting the current density and liquid flow rate in the rear zone: at a lower current density (25~40 mA / cm²), 2 Micron-sized magnesium hydroxide particles with a D50 of 1–10 μm can be prepared under conditions of low liquid flow rate (0.05–0.08 L / h); and under high current density (100–400 mA / cm²), micron-sized magnesium hydroxide particles with a D50 of 1–10 μm can be prepared. 2 When combined with a relatively high liquid flow rate (0.20~8.00 L / h), submicron-sized magnesium hydroxide particles with a D50 of 0.1~1 μm (excluding 1 μm) can be obtained. The former, micron-sized particles, are more conducive to slurry settling and circulation, while the latter, submicron-sized particles, are more conducive to increasing specific surface area and absorption reactivity. The latter region of this invention not only enables magnesium regeneration but also allows for directional control of the particle size of the regenerated product through process parameter adjustment.

[0080] The above embodiments are merely preferred embodiments of the present invention and are not intended to limit the implementation. The scope of protection of the present invention should be determined by the scope defined in the claims. Other variations or modifications can be made based on the above description. Obvious variations or modifications derived therefrom are still within the scope of protection of the present invention.

Claims

1. A magnesium-based desulfurizer regeneration system based on electrochemical in-situ alkali production, characterized in that, It includes a desulfurization by-product slurry conveying unit (1), a solid-liquid separation unit (2), a zoned electrochemical reactor (3), a regenerated slurry collection unit (4), and a return-to-tower conveying unit (5); The desulfurization by-product slurry conveying unit (1) is connected to the inlet of the solid-liquid separation unit (2); the outlet of the solid-liquid separation unit (2) is connected to the inlet (3-1) of the partitioned electrochemical reactor (3); The liquid outlet (3-6) or the back zone discharge port (3-3) of the partitioned electrochemical reactor (3) is connected to the regenerated slurry collection unit (4), and the regenerated slurry collection unit (4) is connected to the return tower conveying unit (5). The partitioned electrochemical reactor (3) includes: a liquid inlet (3-1), a front zone discharge port (3-2), a rear zone discharge port (3-3), two support legs (3-4), N electrode assemblies (3-5), a liquid outlet (3-6), a tank body (3-7), and a flow baffle (3-8). The tank (3-7) is vertically equipped with a flow baffle (3-8) to divide the tank (3-7) into a front zone and a rear zone. The front zone and the rear zone can be connected through the flow baffle (3-8). The liquid phase regeneration liquid flows through the front zone and the rear zone sequentially along the length of the tank. The front zone of the tank (3-7) has inlets (3-1) at both ends or on the outer side wall, and the rear zone has outlets (3-6) at both ends or on the outer side wall. The front zone has a discharge port (3-2) at the bottom of the front zone, and the rear zone has a discharge port (3-3) at the bottom of the rear zone. Support legs (3-4) are provided below the front zone discharge port (3-2) and the rear zone discharge port (3-3). The tank (3-7) contains N electrode assemblies (3-5), where N≥2. At least one electrode assembly (3-5) is provided in the front and rear regions to form a pretreatment electrochemical unit and a regeneration electrochemical unit, respectively. The front and rear regions are connected to independent power supply circuits to form different alkalization intensities. The electrode assemblies are arranged in sequence along the water flow direction as the first electrode assembly, the second electrode assembly, ..., the Nth electrode assembly. The electrode assembly (3-5) includes: a fastening mold (3-5-1), a first anode (3-5-2), a second anode (3-5-3), a first cathode (3-5-4), a second cathode (3-5-5), two diaphragms (3-5-6), an anode chamber inlet (3-5-7), and an anode chamber outlet (3-5-8). The fastening mold (3-5-1) is used to fix the first anode (3-5-2), the second anode (3-5-3), the first cathode (3-5-4), and the second cathode (3-5-5); the first anode (3-5-2) and the second anode (3-5-3) are arranged perpendicular to the liquid flow direction and are spaced apart, forming an anode cavity with the fastening mold; the first cathode (3-5-4) and the second cathode (3-5-5) are respectively arranged outside the first anode (3-5-2) and the second anode (3-5-3), and are separated from the corresponding anode by a diaphragm (3-5-6); The anode cavity inlet (3-5-7) is located on the outer side wall of the fastening mold (3-5-1), and the anode cavity outlet (3-5-8) is located on the opposite outer side wall of the fastening mold (3-5-1). The anode cavities of the first electrode assembly to the Nth electrode assembly are interconnected, and the first cathode (3-5-4) and the second cathode (3-5-5) of the first electrode assembly to the Nth electrode assembly are in contact with the liquid entering the partitioned electrochemical reactor (3).

2. The magnesium-based desulfurizer regeneration system according to claim 1, characterized in that, The front region is provided with at least one electrode assembly (3-5) to form a pretreatment electrochemical unit for synergistic pretreatment of the liquid phase regenerated liquid, and the rear region is provided with at least one electrode assembly (3-5) to form a regeneration electrochemical unit for regenerating magnesium hydroxide slurry; the distance between each electrode assembly is ≥5cm; The aspect ratios of the first anode 3-5-2, the second anode 3-5-3, the first cathode 3-5-4, and the second cathode 3-5-5 are all (2.8~5.6):

1.

3. The magnesium-based desulfurizer regeneration system according to claim 1, characterized in that, The first anode (3-5-2) and the second anode (3-5-3) are titanium-based noble metal oxide coated electrodes, and the first cathode 3-5-4 and the second cathode (3-5-5) are one or more of stainless steel, iron, copper, titanium, nickel and aluminum; The diaphragm (3-5-6) is one of the following: ion exchange membrane, nylon mesh, polytetrafluoroethylene mesh, polyester nonwoven composite diaphragm, and polyester. The overflow baffle (3-8) is one of the following: overflow plate, perforated baffle, and flow guide baffle.

4. The magnesium-based desulfurizer regeneration system according to claim 1, characterized in that, The electrode assembly (3-5) is also provided with a support frame and a positioning structure; The anode cavity outlet (3-5-8) of the preceding electrode assembly is connected to the anode cavity inlet (3-5-7) of the following electrode assembly; and the anode cavity inlet (3-5-7) of the first electrode assembly or the anode cavity outlet (3-5-8) of the Nth electrode assembly is connected to an external device for introducing or exporting anolyte. The external device is one of an external circulation device, a pumping device, and a liquid storage device; The solid-liquid separation unit (2) is one or more combinations of a sedimentation tank, an inclined plate sedimentation device, a filter, and a centrifugal separator.

5. The magnesium-based desulfurizer regeneration system according to claim 1, characterized in that, Ideally, both the front and rear regions should have two sets of electrode assemblies set independently.

6. A method for regenerating magnesium-based desulfurizing agents based on electrochemical in-situ alkali production, characterized in that, Includes the following steps: The desulfurization by-product slurry was subjected to solid-liquid separation to obtain a liquid-phase regenerated liquid; at 5~100 mA / cm 2 At a current density of 0.05–10 L / h, the liquid regenerated liquid was introduced into the front zone of the partitioned electrochemical reactor (3). The hydraulic retention time in the front zone was 1.5–20 min, and the pH was 8.5–10.

5. Then, at a current density of 10–400 mA / cm², the liquid phase regenerated liquid was introduced into the front zone of the partitioned electrochemical reactor (3). 2 At a current density of 0.05 to 10 L / h, the liquid phase regenerated liquid after the pre-treatment is introduced into the rear zone of the partitioned electrochemical reactor (3). The hydraulic residence time in the rear zone is 0.01 to 3.5 h, and the pH is 9.5 to 11.

8. Magnesium hydroxide slurry is obtained. After being treated by the regenerated slurry collection unit (4), the magnesium hydroxide slurry is sent to the flue gas desulfurization absorption tower for recycling as a magnesium-based desulfurizing agent.

7. The method for regenerating magnesium-based desulfurizer according to claim 6, characterized in that, The desulfurization by-product slurry is a slurry containing magnesium, sulfate, and / or sulfite discharged from the flue gas desulfurization absorption tower during the magnesium-based flue gas desulfurization process.

8. The method for regenerating magnesium-based desulfurizer according to claim 6, characterized in that, The hydraulic residence time in the front zone is 5-15 minutes; The liquid phase regenerated liquid is introduced into the front zone of the partitioned electrochemical reactor (3) and the pH is adjusted by the in-situ alkali production at the cathode; the pH of the liquid phase regenerated liquid in the front zone is 9.0~10.0; The liquid-phase regenerated liquid enters the rear zone from the front zone of the partitioned electrochemical reactor (3), and the alkalinity of the liquid phase in the rear zone is increased through in-situ alkali production at the cathode. Preferably, the pH of the liquid-phase regenerated liquid in the rear zone is 10.0~11.5; preferably, the current density in the rear zone is 20~150 mA / cm. 2 .

9. The method for regenerating magnesium-based desulfurizer according to claim 6, characterized in that, The operations handled by the recycled slurry collection unit (4) include: filtration, drying or centrifugation.

10. The method for regenerating magnesium-based desulfurizer according to claim 6, characterized in that, When the current density in the back region is 10~40 mA / cm 2 When the liquid flow rate in the back zone is 0.05~0.08 L / h, the particle size distribution of magnesium hydroxide is 1~10 μm, and when the current density in the back zone is 40~400 mA / cm². 2 When the liquid flow rate in the back zone is 0.08~10 L / h, the particle size distribution of magnesium hydroxide is 0.1~1 μm.

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