Device and method for dechlorinating gypsum and separating fly ash

Abstract

The invention relates to the technical field of solid waste treatment and resource utilization, in particular to a gypsum dechlorination and coal ash separation device and method. A gypsum raw material containing chlorine and fly ash is prepared into an emulsion, the emulsion is placed in a reactor, direct current is applied for electrochemical treatment, and chloride ions are removed through anodic oxidation; after electrifying is stopped, gravity settling layering is carried out by utilizing density difference, and supernate, fly ash slurry and bottom layer purified gypsum are separated in sequence. The device comprises a reactor, an electrochemical system and a layered discharge device, and a nickel-molybdenum oxide catalyst can be selected to improve the dechlorination efficiency. According to the method, dechlorination and impurity separation are integrated in the same process, a large amount of water washing is not needed, high-chlorine wastewater is avoided, the chlorine content of the gypsum can be remarkably reduced, the fly ash is effectively separated, the purity and whiteness of the desulfurized gypsum are greatly improved, and efficient resource utilization of solid waste is achieved.

Description

Technical Field

[0001] This invention relates to the field of solid waste treatment and resource utilization technology, specifically to an apparatus and method for gypsum dechlorination and fly ash separation. Background Technology

[0002] Wet flue gas desulfurization (FGD) in coal-fired power plants is a major technology for controlling sulfur dioxide emissions, and its byproduct, desulfurized gypsum (mainly composed of calcium sulfate dihydrate, CaSO4·2H2O), is produced in huge quantities. Theoretically, desulfurized gypsum is a high-grade, high-quality resource that can replace natural gypsum in the production of gypsum board, gypsum mortar, cement retarders, and other building materials. However, in practical applications, the resource utilization rate of desulfurized gypsum is not ideal, with large quantities being stockpiled and disposed of, occupying valuable land resources and posing environmental risks.

[0003] The main bottleneck limiting its high-value utilization lies in its impurities, the most harmful of which is chloride ions (Cl). - ) and fly ash.

[0004] The hazards of chloride ions: Chloride ions in desulfurized gypsum mainly originate from coal combustion and process water. High chloride ion content (reaching over 10,000 ppm in some areas) can cause a series of serious problems for downstream products and production processes. Impact on product quality: Chlorides such as calcium chloride and magnesium chloride have strong hygroscopic properties, which can cause gypsum products (such as gypsum board and plaster plaster) to exhibit a "re-efflorescence" phenomenon, that is, the surface absorbs moisture, frosts, and water, which in turn leads to problems such as blackening, mold, and peeling of the finishing layer, seriously affecting the aesthetics and durability of the building.

[0005] Corrosion of Equipment and Reinforcing Steel: During the production process, high concentrations of chloride ions can severely corrode metal equipment such as mixers and molds, shortening their lifespan. More seriously, when used in the preparation of concrete admixtures or plastering mortar, chloride ions in the gypsum can migrate and corrode the reinforcing steel in buildings, posing a long-term threat to structural safety.

[0006] The impact of fly ash and other impurities: Fly ash is fine particulate matter produced during coal combustion. Some of it enters the desulfurization system with the flue gas and mixes with gypsum. The main impacts of the presence of fly ash are: Product purity and whiteness: The addition of fly ash directly reduces the purity of gypsum, and its color is usually grayish-black, which significantly reduces the whiteness of gypsum products, making them unable to meet the color requirements of high-grade building materials or chemical raw materials.

[0007] Product performance: Unburned carbon and other components in fly ash may affect key performance indicators of gypsum products such as setting time and mechanical strength.

[0008] To address the aforementioned problems, existing technologies primarily employ water washing. While water washing can remove some chloride ions, it suffers from the following drawbacks: it consumes a huge amount of water, generating large quantities of difficult-to-treat high-chlorine wastewater, causing secondary pollution; its removal efficiency for chloride ions adsorbed on the surface of gypsum crystals is limited; and it is difficult to effectively separate fine fly ash particles similar in size to gypsum particles. Therefore, developing an economical, efficient, and environmentally friendly gypsum purification technology to achieve simultaneous removal of chloride ions and fly ash has become a pressing technical challenge for the industry. Summary of the Invention

[0009] In view of the shortcomings of the prior art, the purpose of this invention is to provide a device for gypsum dechlorination and fly ash separation, which organically combines the two processes of dechlorination and impurity separation into one core device. The process flow is short, the operation and control are relatively simple, and it can be designed for intermittent or continuous production to meet the needs of different scales.

[0010] Another objective of this invention is to provide a method for gypsum dechlorination and fly ash separation, which can significantly improve the purity and quality of gypsum, reduce the negative impact on the environment, and realize the high-value and resource utilization of solid wastes such as desulfurized gypsum.

[0011] This invention is achieved using the following technical solution: The method for gypsum dechlorination and fly ash separation includes the following steps: a) Mix gypsum raw materials containing chlorine and fly ash with water to prepare gypsum emulsion; b) The gypsum emulsion is placed in a reactor, and a direct current is applied to the gypsum emulsion through the cathode and anode set in the reactor to perform electrochemical treatment on the gypsum emulsion to remove chloride ions from the gypsum emulsion, thereby obtaining a treated mixture; c) After the application of DC current is stopped, the treated mixture is subjected to gravity sedimentation stratification; d) Separate the layered material to obtain purified gypsum.

[0012] Specifically, according to a first aspect of the present invention, a method for gypsum dechlorination and fly ash separation is provided, comprising the following steps: a) Emulsion Preparation: Gypsum raw materials containing chlorine and fly ash (such as desulfurized gypsum) are mixed with water and prepared into a gypsum emulsion with a certain degree of fluidity through stirring and other methods. This step aims to transform the solid gypsum raw materials into a liquid suspension system, creating conditions for subsequent electrochemical treatment and physical separation.

[0013] b) Electrochemical treatment: The gypsum emulsion is placed in a reactor, and a direct current is applied through the cathode and anode located within the reactor. Under the influence of the electric field, ions in the emulsion undergo directional migration, including negatively charged chloride ions (Cl...). -Chloride ions will migrate towards the anode. At the anode surface, chloride ions undergo oxidation reactions (e.g., 2Cl₂). - -2e - →Cl2↑), which is separated from the emulsion in gas or other forms, thereby achieving dechlorination. At the same time, the microbubbles generated during the electrolysis process have a certain flotation and agitation effect, which helps to remove impurities attached to the surface of gypsum particles.

[0014] c) Gravity Sedimentation and Stratification: After the electrochemical treatment is completed, power supply and stirring are stopped, allowing the mixture in the reactor to settle. Due to the density differences between calcium sulfate dihydrate (density approximately 2.3 g / cm³), fly ash (density typically between 1.9-2.2 g / cm³, and some are hollow microspheres), and water (density approximately 1.0 g / cm³), the mixture will naturally stratify. Typically, the densest pure gypsum particles will settle to the bottom of the reactor, the less dense fly ash particles will remain suspended in the middle layer, and the top layer will be a mostly clear supernatant.

[0015] d) Separation and recovery: After the material is clearly separated into layers, physical methods are used to separate the material into layers, and finally purified gypsum product is obtained.

[0016] To further optimize the method of the present invention, the electrochemical treatment process in step b) further includes allowing the gypsum emulsion to flow through or contact a catalyst disposed between the cathode and anode. The introduction of the catalyst aims to enhance the efficiency and selectivity of the electrochemical reaction. For example, the catalyst can reduce the overpotential of the anodic chlorine evolution reaction, suppress side reactions such as oxygen evolution, thereby achieving higher dechlorination efficiency with lower energy consumption, and effectively suppress the "armoring" phenomenon caused by scaling on the electrode surface, extending electrode life.

[0017] The catalyst is preferably a mixture of nickel and molybdenum oxides. These materials have been shown to exhibit good electrocatalytic activity and stability for the chlorination reaction. The preferred mixing ratio (mass or molar ratio) of nickel to molybdenum is 1:1, at which the catalytic activity is likely optimal. To increase the contact area between the catalyst and the emulsion and facilitate fixation, the catalyst can be loaded onto a ceramic honeycomb support. The honeycomb structure allows the emulsion to pass through smoothly while providing a large specific surface area, thus enhancing the catalytic effect.

[0018] The applied DC power energy density ranges from 1 mW / L to 2 kW / L. This range covers various operating modes, from low energy consumption and long processing time to high energy consumption and short processing time, and can be flexibly adjusted according to raw material characteristics and production needs to achieve a balance between treatment effectiveness and economic cost. The processing time ranges from 10 seconds to 1200 seconds, which is matched to the applied energy density to ensure that the dechlorination process is completed within a reasonable production cycle.

[0019] In step d), the separation process sequentially discharges the upper supernatant, the middle fly ash slurry, and the bottom gypsum slurry. This stratified discharge method is simple to operate and can effectively achieve the separate collection of the three materials, ensuring the purity of the final product.

[0020] According to a second aspect of the present invention, an apparatus is provided for implementing the above-described method for gypsum dechlorination and fly ash separation. The apparatus comprises: Reactor body: a tank or vessel that serves as the core container for holding and processing gypsum emulsion.

[0021] Electrochemical system: This system is the core of the dechlorination function and consists of two parts: 1) Electrode assembly, which includes at least one pair of cathodes and anodes arranged in parallel or concentrically in the reactor to establish an electric field; 2) DC power supply, which provides adjustable DC power to the electrode assembly.

[0022] Separation and discharge device: A mechanism used to accurately discharge materials from different layers at different heights after settling and stratification, such as discharge valves set at different heights of the reactor, liftable siphon pipes, or inclined discharge structures.

[0023] It also includes a catalytic system containing a catalyst positioned between the cathode and the anode. This corresponds to an improvement in the method, enabling the device to perform catalytic-electrochemical synergistic processing to enhance processing efficiency.

[0024] The catalytic system is preferably defined with the catalyst being a mixture of nickel-molybdenum oxides supported on a ceramic honeycomb carrier. This defines a highly efficient and stable catalytic module structure.

[0025] The electrode assembly can be made of one or more of the following materials: nickel, molybdenum, silver, copper, platinum, stainless steel, carbon steel, carbon, or graphite. This selection of materials balances conductivity, corrosion resistance, electrocatalytic activity, and cost, providing a variety of feasible options for the actual fabrication of the device.

[0026] The gypsum raw material containing chloride and fly ash described in this invention can be either stockpiled or purchased desulfurization gypsum solid waste, or it can be directly derived from the existing wet desulfurization system of a coal-fired power plant. In application scenarios with existing desulfurization systems, the method of this invention can be seamlessly integrated with the front-end desulfurization process, in which case the independent raw material pretreatment and slurry preparation steps (i.e., step a) can be omitted; the desulfurizing agent slurry rich in chloride ions and fly ash impurities discharged from the desulfurization tower (or gypsum slurry after preliminary cyclone concentration) can be directly introduced as feed into the reactor of this invention for subsequent electrochemical dechlorination and gravity sedimentation separation. This integrated approach not only simplifies the process flow and reduces equipment investment and operating costs, but also enables online real-time purification of desulfurization byproducts, further improving the resource utilization efficiency of the entire desulfurization system.

[0027] Compared with the prior art, the beneficial effects of the present invention are: (1) This invention can fundamentally remove chloride ions through electrochemical treatment, with a dechlorination efficiency far higher than that of traditional water washing methods. It can reduce the chloride content of high-chlorine gypsum to extremely low levels (e.g., from thousands of ppm to tens of ppm), effectively solving problems such as efflorescence and corrosion caused by chloride ions. At the same time, by utilizing gravity sedimentation, fly ash impurities can be effectively separated, significantly improving the purity and whiteness of gypsum.

[0028] (2) This invention not only transforms the originally difficult-to-use desulfurized gypsum into high-quality building materials or chemical raw materials, realizing "turning waste into treasure"; at the same time, the separated fly ash has a calorific value due to the presence of a certain amount of residual carbon, and can be recycled as a low-grade fuel or building material admixture, realizing the comprehensive and high-value utilization of solid waste.

[0029] (3) This invention organically combines dechlorination and impurity separation processes into a single core device, resulting in a short process flow and relatively simple operation and control. It can be designed for intermittent or continuous production to meet different scale requirements. Compared to water washing, this invention does not require a large amount of fresh water and avoids the problem of generating large amounts of high-chlorine wastewater. The treated supernatant has a low chlorine content and can be recycled for the preparation of new gypsum emulsions, minimizing water consumption and wastewater discharge, thus providing excellent environmental benefits. This invention provides both a catalyst-free basic solution and a catalyst-containing high-efficiency solution. Users can choose the most suitable solution based on a comprehensive consideration of treatment efficiency, energy consumption, and investment costs, demonstrating strong engineering application flexibility. Attached Figure Description

[0030] Figure 1 This is a flowchart of the gypsum dechlorination and fly ash separation device of the present invention; Figure 2 This is a schematic diagram of the structure at the electrode of the present invention; In the diagram: 1. Modulation power supply; 2. Cathode plate; 3. Anode plate; 4. Catalyst. Detailed Implementation

[0031] The present invention will now be described in detail with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Various modifications and improvements made without departing from the spirit and scope of the present invention should fall within the scope of protection of the present invention.

[0032] Raw material description: Unless otherwise stated, the desulfurized gypsum raw materials used in all embodiments and comparative examples are taken from the same batch, and their basic components are as follows: Main component (CaSO4·2H2O): Approximately 88.5% Fly ash content: approximately 3.1% Initial chloride ion content: 978 ppm Moisture content: Approximately 8% Test method description: Chloride ion content: Detected by silver nitrate titration or ion chromatography.

[0033] Fly ash content: calculated using differential thermal-thermogravimetric analysis or based on chemical composition analysis.

[0034] Purity (CaSO4·2H2O content): Calculated based on chemical analysis results.

[0035] like Figure 1-2 As shown, the modulated power supply 1 is used to provide energy, and the catalyst 4 is located between the cathode plate 2 and the anode plate 3, closer to the side of the cathode plate 2.

[0036] Example 1: A method for dechlorinating gypsum and separating fly ash includes the following steps: Emulsion preparation: Take 100 kg of the above-mentioned desulfurized gypsum raw material, add 300 kg of tap water (solid-liquid ratio 1:3), and stir in a reactor equipped with a stirring device for 10 minutes to form a uniform gypsum emulsion.

[0037] Electrochemical treatment: The reactor is equipped with parallel stainless steel electrode plates (anode) and carbon steel electrode plates (cathode), with a plate spacing of 30 mm. A DC power supply is turned on, applying DC current to the electrode assembly, controlling the energy density within the reactor to 260 W / L, with a treatment time of 10 minutes (600 seconds). Stirring is maintained throughout the treatment process, and the reaction temperature is kept at room temperature (approximately 25°C).

[0038] Sedimentation and Separation: After treatment, power supply and stirring are stopped, and the mixture is allowed to stand for 1 hour. Once the mixture has clearly separated into layers, the supernatant, the fly ash slurry in the middle layer, and the gypsum slurry at the bottom layer are discharged sequentially through valves at different heights on the side wall of the reactor.

[0039] Post-processing: The obtained gypsum slurry is sent to a filter press for dewatering, and then dried at 80°C to obtain the final purified gypsum product.

[0040] Product testing results: Chloride ion content of the treated gypsum: 130 ppm; The fly ash content of the treated gypsum was 2.8%. The purity of the treated gypsum (CaSO4·2H2O) is approximately 90.3%.

[0041] Example 2: Except for the electrochemical treatment conditions in step 2), the other steps are the same as in Example 1.

[0042] Step 2) Electrochemical treatment: Control the energy density in the reactor to increase to 850 W / L, and the treatment time is shortened to 3 minutes (180 seconds).

[0043] Product testing results: Chloride ion content of the treated gypsum: 52 ppm; The fly ash content of the treated gypsum is 2.55%. The purity of the treated gypsum (CaSO4·2H2O) is approximately 90.8%.

[0044] Example 3: Except for the electrochemical treatment conditions in step 2), the other steps are the same as in Example 1.

[0045] Step 2) Electrochemical treatment: A ceramic honeycomb structure loaded with a nickel-molybdenum oxide catalyst (Ni:Mo mass ratio 1:1) is placed between the anode and cathode. The DC power supply is turned on, and the energy density is controlled at 260 W / L (same as in Example 1), with a treatment time of 10 minutes (600 seconds).

[0046] Product testing results: Chloride ion content of the treated gypsum: 35 ppm; The fly ash content of the treated gypsum was 2.6%. The purity of the treated gypsum (CaSO4·2H2O) is approximately 90.7%.

[0047] Comparative Example 1: A method for dechlorinating gypsum and separating fly ash includes the following steps: Washing: Take the same weight (100 kg) of desulfurized gypsum raw material as in Example 1, add the same amount of tap water (300 kg), and stir for 10 minutes in the same reactor.

[0048] Settling and Separation: After stirring, let stand for 1 hour. Then drain the supernatant and the bottom gypsum slurry through the valve (at this time, the fly ash and gypsum are mixed together and cannot be effectively separated).

[0049] Post-processing: The obtained gypsum slurry was subjected to the same pressure filtration and drying process as in Example 1.

[0050] Product testing results: Chloride ion content of the treated gypsum: 450 ppm The fly ash content of the treated gypsum is 3.0%. The purity of the treated gypsum (CaSO4·2H2O): approximately 88.8% Comparative Example 2: A method for dechlorinating gypsum and separating fly ash includes the following steps: Emulsion preparation: The gypsum emulsion was prepared in the same manner as in Example 1.

[0051] Settling: Without electrochemical treatment, the well-stirred emulsion is allowed to stand for 1 hour.

[0052] Separation observation: Observations revealed that although some gypsum settled, the stratification was not obvious. A large number of fine fly ash particles were mixed with gypsum particles, making effective separation impossible through simple stratification and discharge. The fly ash content of the bottom layer of gypsum slurry obtained by forced separation was almost not reduced after treatment.

[0053] Product testing results: Chloride ion content of the treated gypsum: 970 ppm; The fly ash content of the treated gypsum is 3.05%.

[0054] The test data for Examples 1-3 and Comparative Examples 1-2 are shown in Table 1.

[0055] Table 1: Test data of Examples 1-3 and Comparative Examples 1-2

[0056] As shown in Table 1, compared with Example 1 and Comparative Example 1, under the same solid-liquid ratio and treatment time, the basic electrochemical method of this invention significantly outperforms the traditional water washing method in removing chloride ions. This proves that electrochemical oxidation is a more thorough dechlorination pathway than physical dissolution. Comparing Example 1 and Comparative Example 2, it can be seen that the gypsum emulsion without electrochemical treatment is difficult to achieve clear gravity stratification. This may be because the microbubbles and electric field generated during the electrochemical process disrupt the agglomeration or electrostatic adsorption between gypsum and fly ash particles, playing a pretreatment role similar to "electrocoagulation / electroflotation," thus making subsequent density difference separation possible. Comparing Example 1 and Example 2, with similar total energy consumption, using higher energy density and shorter treatment time can achieve better dechlorination and fly ash separation effects. This indicates that the process parameters of this invention are adjustable and can be optimized according to production cycle and quality requirements. Comparing Examples 1 and 3, under identical energy density and processing time conditions, the addition of a nickel-molybdenum oxide catalyst reduced the residual chloride ion content by approximately 73%, and increased the dechlorination rate from 86.7% to 96.4%. This strongly demonstrates the synergistic enhancing effect of the catalyst in this invention, which can significantly improve reaction efficiency, enabling deep dechlorination to be achieved with lower energy consumption.

[0057] In summary, the gypsum dechlorination and fly ash separation method proposed in this invention, through an innovative process combining electrochemical treatment and gravity sedimentation, not only achieves dechlorination efficiency far exceeding that of traditional methods, but also creatively solves the technical problem of difficult fly ash separation. Furthermore, its performance can be further optimized by adjusting energy density or introducing catalysts, demonstrating significant technological progress and broad industrial application prospects.

Claims

1. A method for dechlorination of gypsum and separation of fly ash, characterized in that, Includes the following steps: a) Mix gypsum raw materials containing chlorine and fly ash with water to prepare gypsum emulsion; b) The gypsum emulsion is placed in a reactor, and a direct current is applied to the gypsum emulsion through the cathode and anode set in the reactor to perform electrochemical treatment on the gypsum emulsion to remove chloride ions from the gypsum emulsion, thereby obtaining a treated mixture; c) After the application of DC current is stopped, the treated mixture is subjected to gravity sedimentation stratification; d) Separate the layered material to obtain purified gypsum.

2. The method for gypsum dechlorination and fly ash separation according to claim 1, characterized in that, In step b), the electrochemical treatment further includes causing the gypsum emulsion to flow through or contact with a catalyst disposed between the cathode and the anode.

3. The method for gypsum dechlorination and fly ash separation according to claim 2, characterized in that, The catalyst is a mixture of nickel and molybdenum oxides.

4. The method for gypsum dechlorination and fly ash separation according to claim 3, characterized in that, In the nickel-molybdenum oxide mixture, the mass ratio or molar ratio of nickel to molybdenum is 1:1; the catalyst is supported on a ceramic honeycomb carrier.

5. The method for gypsum dechlorination and fly ash separation according to claim 1, characterized in that, The energy density of the applied DC current in step b) is 1 mW / L to 2 kW / L; the processing time for applying the DC current in step b) is 10 seconds to 1200 seconds.

6. The method for gypsum dechlorination and fly ash separation according to claim 1, characterized in that, The separation step described in step d) specifically includes: sequentially discharging the supernatant from the upper layer after sedimentation and stratification, the fly ash slurry from the middle layer, and the gypsum slurry from the bottom layer.

7. A device for gypsum dechlorination and fly ash separation, characterized in that, include: The main body of the reactor is used to contain the gypsum emulsion; Electrochemical systems, including: The electrode assembly includes at least one pair of cathodes and anodes disposed within the reactor body; A DC power supply, electrically connected to the electrode group, is used to supply power to the electrode group; The separation and discharge device is used to discharge the settled and stratified material in layers after the treatment is completed.

8. The apparatus for gypsum dechlorination and fly ash separation according to claim 7, characterized in that, It also includes a catalytic system comprising a catalyst disposed between the cathode and the anode.

9. The apparatus for gypsum dechlorination and fly ash separation according to claim 8, characterized in that, The catalyst is a mixture of nickel and molybdenum oxides and is supported on a ceramic honeycomb carrier.

10. The apparatus for gypsum dechlorination and fly ash separation according to claim 7, characterized in that, The materials of the cathode and anode are selected from one or more of nickel, molybdenum, silver, copper, platinum, stainless steel, carbon steel, carbon, or graphite.

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