Sulfuric acid method titanium dioxide waste acid resource reutilization process

Abstract

The invention provides a sulfuric acid method titanium dioxide waste acid resource reutilization process, and belongs to the technical field of waste acid recovery. Sulfuric acid in the sulfuric acid waste liquid is effectively recovered and impurities in the sulfuric acid are separated through filtering, preheating, multi-stage concentration, flash evaporation and protective separation of the sulfuric acid waste liquid generated in the preparation of titanium dioxide, so that the purity of the sulfuric acid is ensured; by means of multi-stage preheating and recycling, especially MVR evaporation combined equipment, the energy utilization efficiency is greatly improved, energy consumption is reduced, and meanwhile the operation cost is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of waste acid recovery and relates to a process for resource recycling of waste acid from titanium dioxide produced by a sulfuric acid process. Background Art

[0002] In the sulfuric acid process of preparing titanium dioxide, the generation of a large amount of sulfuric acid waste liquid leads to two major problems. First, the treatment and disposal of these waste liquids involve significant environmental risks and compliance issues, because improper treatment may lead to serious environmental pollution. The common practice is to use limestone neutralization process to treat sulfur-containing wastewater. This method uses limestone (mainly calcium carbonate) to react with sulfuric acid in wastewater to generate calcium sulfate precipitation (i.e. gypsum) and carbon dioxide. Although this treatment method is quite effective in removing harmful substances, the main disadvantages of this method are: large reagent consumption, no sulfuric acid recovery, neutralized wastewater still contains some heavy metal elements and cannot be recycled because it is saturated with calcium sulfate; the amount of gypsum after neutralization is large, and 5 tons of gypsum are produced as a by-product for each ton of titanium dioxide. Since gypsum has few uses, it is difficult to sell it; currently most of the smaller titanium dioxide companies in China use this method to treat waste acid, and the cost of producing red gypsum by treating waste acid with limestone in China is 700-800 yuan / t titanium dioxide, which will increase the production cost of titanium dioxide by sulfuric acid process by 10%-15%.

[0003] Secondly, direct treatment or disposal of these waste streams results in a huge waste of sulfuric acid, as they usually contain reusable sulfuric acid. Since sulfuric acid is a precious resource, this not only increases production costs, but also runs counter to the growing goals of environmental protection and resource sustainability.

[0004] Therefore, it is particularly important to provide an economical and environmentally friendly solution to recycle and reuse the sulfuric acid waste liquid from the sulfuric acid process of titanium dioxide production. Summary of the invention

[0005] The purpose of the present invention is to address the above-mentioned problems in the existing technology and to propose a process for recycling waste acid from titanium dioxide produced by the sulfuric acid process.

[0006] The purpose of the present invention can be achieved by the following technical scheme: a process for recycling waste acid of titanium dioxide produced by sulfuric acid process, the process for recycling waste acid of titanium dioxide produced by sulfuric acid process is used to treat the waste sulfuric acid liquid generated in the preparation of titanium dioxide by sulfuric acid process, the sulfuric acid concentration in the waste sulfuric acid liquid is 20-25%; the sulfuric acid liquid obtained after treatment is used in the titanium dioxide acidolysis section; the process for recycling waste acid of titanium dioxide produced by sulfuric acid process comprises the following steps:

[0007] S1 filtration: After the sulfuric acid waste liquid is filtered, the pre-treated sulfuric acid waste liquid is obtained;

[0008] S2 preheating: preheating the pretreated sulfuric acid waste liquid with water using preheating equipment 1, preheating the mixed steam using preheating equipment 2, and preheating the fresh steam using preheating equipment 3 to obtain preheated material;

[0009] The role of preheating is as follows: Improve thermal efficiency: Preheating is to gradually heat the sulfuric acid waste liquid to raise its temperature to the boiling point. This can significantly reduce the energy required in the subsequent evaporation and concentration steps because the liquid has been preheated to close to the evaporation temperature. This not only saves energy, but also helps to quickly start the evaporation process.

[0010] Reduce the heat load of the equipment: If the low-temperature sulfuric acid waste liquid is directly fed into the evaporator, the evaporator needs to consume more energy to heat the liquid to the evaporation temperature. By preheating, the heat load of the evaporator is reduced, thereby reducing energy consumption and extending the service life of the equipment.

[0011] Reduced operating costs: The preheating step can reduce energy consumption and thus operating costs by recovering and reusing the heat energy in the system (e.g., using non-condensable steam and condensed water for preheating).

[0012] In summary, preheating not only optimizes the recovery efficiency of sulfuric acid, but also helps save energy, protect equipment and improve the economy of the entire process.

[0013] S3 first stage concentration: Use MVR evaporation combination equipment to evaporate and concentrate the preheated material until the sulfuric acid concentration in the material reaches the designed concentration, and then end the evaporation and concentration operation to obtain the initial mixed material;

[0014] As the feed liquid is continuously evaporated and concentrated in the MVR evaporator, the concentration of sulfuric acid is gradually increased, and at the same time, salts such as ferrous sulfate contained in the feed liquid reach saturation concentration and crystallize out.

[0015] The MVR evaporation combined equipment includes an MVR evaporator and an evaporation compressor. In the evaporation and concentration operation, the MVR evaporator is first heated by fresh steam to evaporate the moisture of the material in the MVR evaporator to obtain secondary steam. The secondary steam is pressurized and heated by the evaporation compressor to obtain secondary compressed steam. Finally, the MVR evaporator is heated by fresh steam and secondary compressed steam to reduce the use of fresh steam.

[0016] Reasons for choosing MVR evaporation combination equipment: 1. MVR evaporator mechanically compresses the steam generated secondary (i.e., the water vapor released during the evaporation process) and reuses the steam as a heating source. In this way, MVR technology can significantly reduce the demand for external energy, such as fresh steam supply, because it mainly relies on the recovered steam energy to maintain the evaporation process. The energy consumption of this technology mainly comes from the electricity to drive the compressor, rather than the large amount of heat energy required for traditional evaporation. 2. Cost-effectiveness: Although the MVR system has a higher initial investment, its operating cost is much lower than that of traditional multi-effect evaporation systems or single-effect evaporation systems. Because the MVR system greatly reduces the additional heat energy input, it saves a lot of fuel costs and maintenance costs. In long-term operation, this energy-saving effect can significantly reduce the energy consumption and operating costs of the entire plant.

[0017] The choice of using an MVR evaporation combination in the first stage concentration step is based on the following key considerations: 1. Efficiency requirements in the initial concentration stage: In the treatment of sulfuric acid waste liquid, the initial concentration stage is the most critical step because it involves increasing the sulfuric acid in the waste liquid from a lower concentration (20-25%) to a higher concentration. The MVR evaporator provides the required heat energy for effective concentration by recovering and compressing the steam generated during the evaporation process. This step has a high energy demand, so the use of an MVR system can significantly improve energy efficiency and is the most suitable choice. 2. Reduce initial energy consumption and costs: By using MVR in the first stage of concentration, the energy consumption of the entire system can be reduced in the initial stage of operation. Although MVR equipment requires electricity to drive, the cost of electricity is usually lower and the operation is more controllable than the large amount of steam required for direct heating. This is crucial to the economy and sustainability of the entire production process.

[0018] S4 Second stage concentration: Use a single-effect evaporator to evaporate and concentrate the initial mixture until the sulfuric acid concentration in the material reaches the designed concentration, and then end the evaporation and concentration operation to obtain an intermediate mixture;

[0019] The choice of using a single-effect evaporator over other types of evaporators is based on the following key considerations: 1. Process requirements and concentration targets: In step S3, the MVR evaporator is used to increase the sulfuric acid concentration from 20-25% to about 45%. Thereafter, the goal in step S4 is to further increase the sulfuric acid concentration to 48%. The use of a single-effect evaporator in this step is based on its ability to accommodate intermediate sulfuric acid concentrations, effectively increasing the concentration from 45% to 48%. An energy-efficient MVR system is not required at this stage because the sulfuric acid concentration is already high and the energy required for evaporation is relatively low. 2. Energy efficiency and cost considerations: Although the single-effect evaporator is slightly less energy-efficient than the multi-effect or MVR evaporator, the difference in energy efficiency is not significant when dealing with sulfuric acid that is already relatively high in concentration. In addition, the equipment cost, maintenance cost, and operational complexity of the single-effect evaporator are generally lower than those of the MVR evaporator. When achieving the intermediate target of 48% design concentration, the use of a single-effect evaporator is a cost-effective choice.

[0020] 3. Ease of operation: The single-effect evaporator is relatively simple to operate and is suitable for this stage of the sulfuric acid concentration process. It can provide stable and controllable operating conditions. At this stage of sulfuric acid concentration, the thermal sensitivity and corrosiveness of the material are already relatively high, and the use of a single-effect evaporator can better control these risks. 4. System integration and process continuity: From the perspective of the entire process flow, the use of a single-effect evaporator in step S4 can serve as a transition stage to prepare for the final flash operation (step S5). In the final concentration and purification stage of sulfuric acid, the flash evaporator will handle higher concentrations of sulfuric acid, so the use of a single-effect evaporator in step S4 helps to balance the energy consumption and efficiency of the entire system.

[0021] S5 flash evaporation: Use a flash evaporator to flash the intermediate mixture until the sulfuric acid concentration in the material reaches the designed concentration, then end the flash evaporation operation to obtain a concentrated sulfuric acid mixture;

[0022] During the flash evaporation process, the flash evaporator is set at a lower pressure. When the material enters the flash evaporator, due to the sudden drop in pressure, part of the water in the feed liquid is vaporized and evaporated, the feed liquid temperature is reduced, and the sulfuric acid concentration is increased. At the same time, due to the evaporation of water, salts such as ferrous sulfate are further crystallized from the solution.

[0023] The choice of using a flash evaporator to flash the intermediate mixture is based on the following key process, energy efficiency and economic considerations: 1. Process requirements and evaporation efficiency: In the concentration process of sulfuric acid, achieving a higher concentration requires improving the concentration efficiency while maintaining low energy consumption. This can be effectively achieved using a flash evaporator because the flash evaporator evaporates the water in the solution quickly by rapidly reducing the pressure, thereby achieving the purpose of rapidly increasing the concentration. This process is particularly suitable for treating sulfuric acid that is already relatively highly concentrated, because the traditional evaporation process becomes slow and energy-intensive at high concentrations. 2. Optimization of temperature and pressure. In step S5, the parameter setting indicates that the gas phase pressure of the flash evaporator is 10kpa (A) and the gas phase temperature is 45°C, which indicates that operating at lower temperature and pressure can minimize heat loss and improve energy efficiency. 3. Energy efficiency: A major advantage of flash operation is energy recovery and energy efficiency optimization. Through flash evaporation, the heat energy of the material itself can be used to achieve evaporation, thereby reducing the need for external energy. In addition, the heat obtained from the previous stage (single-effect evaporator) can be reused in the flash process, further optimizing the overall energy consumption.

[0024] 5. Cost-effectiveness: Although the initial investment may be higher than that of traditional evaporation equipment, the high energy efficiency and low energy consumption of the flash evaporator in operation can save more costs in long-term operation. In addition, due to its operating characteristics, the flash evaporator usually has a higher processing capacity and lower operating costs.

[0025] In summary, the use of flash evaporators is to achieve the final concentration goal efficiently and economically while ensuring the energy efficiency of the process is optimized. This choice meets the requirements for the preparation of high-purity sulfuric acid, ensuring product quality and optimizing operating costs.

[0026] S6 protective separation: After the concentrated sulfuric acid mixture is subjected to cooling operations and solid-liquid separation operations in sequence, sulfuric acid liquid and precipitated salt are obtained.

[0027] In the process of resource recycling of waste acid from titanium dioxide produced by the sulfuric acid process, a steam manufacturing device is used to provide fresh steam and heating water. The steam manufacturing device is connected to preheating device 1 through a heating water delivery pipeline, connected to preheating device 2 through a fresh steam delivery pipeline 1, connected to preheating device 3 through a fresh steam delivery pipeline 2, connected to an MVR evaporator through a fresh steam delivery pipeline 3, and connected to a single-effect evaporator through a fresh steam delivery pipeline 4;

[0028] The MVR evaporator is connected to the preheating device 2 through the non-condensable steam delivery pipeline 1 and is connected to the preheating device 1 through the condensed water delivery pipeline 1;

[0029] The preheating device 3 is connected to the preheating device 2 via the non-condensable steam delivery pipeline 2, and is connected to the preheating device 1 via the condensed water delivery pipeline 2;

[0030] The preheating device 2 is connected to the preheating device 1 via a condensed water delivery pipeline 3;

[0031] The preheating device 1 is connected to a water storage unit of the steam production device through a return pipeline, and the water storage unit is used to provide a water source for the steam production device.

[0032] Preferably, in the filtering operation, a filtering system consisting of multiple units is used for filtering.

[0033] Design of the filtration system: Primary coarse filtration unit: This stage uses a larger pore size filter medium (containing tantalum alloy, Hastelloy, monel, polytetrafluoroethylene or synthetic fiber filter material) to capture and remove larger particulate matter and obvious solid impurities in the waste liquid. This helps protect downstream filtration equipment from damage by large particles.

[0034] Intermediate fine filtration unit: After the primary coarse filtration, a medium pore size filter material (such as a sand filter bed or sand shell filter) is used. This level of filtration is designed to further remove medium-sized suspended particles and a portion of poorly soluble sediments.

[0035] Final microfiltration unit: Uses filter materials with fine pore sizes (such as porous ceramics or high-efficiency polymer filters) to remove tiny particles and residual tiny sediments.

[0036] Through such a multi-stage filtration system, sulfuric acid waste liquid can be efficiently treated to provide clean, high-quality sulfuric acid raw materials for the next preheating and concentration operations.

[0037] Preferably, in the fresh steam preheating operation, the preheating equipment 3 receives fresh steam provided by the steam manufacturing equipment through the fresh steam delivery pipeline 2. The fresh steam is converted into condensed water and non-condensable steam after heat exchange. The condensed water is delivered to the preheating equipment 1 through the condensed water delivery pipeline 2, and the non-condensable steam is delivered to the preheating equipment 2 through the non-condensable steam delivery pipeline 2.

[0038] During the fresh steam preheating, after the fresh steam is converted into condensed water and non-condensed steam, the condensed water is transported back to the preheating equipment 1 for reuse, and is used for water preheating of the subsequent pretreatment of sulfuric acid waste liquid, and the non-condensed steam is transported to the preheating equipment 2 for mixed steam preheating of the subsequent pretreatment of sulfuric acid waste liquid; these by-products are reused to achieve energy saving.

[0039] Preferably, in step S3, fresh steam and secondary compressed steam are converted into condensed water and non-condensable steam after heat exchange; the condensed water is transported to the preheating equipment 1 through the condensed water transport pipeline 1; the non-condensable steam is transported to the preheating equipment 2 through the non-condensable steam transport pipeline 1.

[0040] Preferably, in the mixed steam preheating operation, the heating fluid used to heat the preheating device 2, the portion that becomes condensed water after heat exchange is transported to the preheating device 1 through the condensed water transport pipeline 3, and the uncondensed portion is discharged.

[0041] In the mixed steam preheating operation, the first batch of sulfuric acid waste liquid is heated using fresh steam as the heating fluid; with the start of the fresh steam preheating step and the start of the first stage concentration operation, in the subsequent heating, the heating fluids used are fresh steam, non-condensable steam generated in the fresh steam preheating step, and non-condensable steam generated in the first stage concentration operation.

[0042] Preferably, the sulfuric acid concentration in the sulfuric acid waste liquid is 20-25%; the fresh steam parameters are as follows: temperature 126°C, pressure 130kpa; the target temperature of the water preheating operation is 78-80°C; the target temperature of the mixed steam preheating operation is 93-95°C; the target temperature of the fresh steam preheating operation is 110-115°C;

[0043] In step S3, the parameters are set as follows: MVR liquid phase maintenance temperature is 106-110°C, gas phase pressure is -50kpa, sulfuric acid design concentration is 45%, secondary compression steam temperature is 126°C, secondary compression steam pressure is 0.239MPa(A).

[0044] In step S4, the parameters are set as follows: the gas phase pressure of the single-effect evaporator is controlled to be -50 kPa; the liquid phase temperature of the single-effect evaporator is maintained at 110-112° C.; and the designed concentration of sulfuric acid is 48%.

[0045] In step S5, the parameters are set as follows: the flash evaporator gas phase pressure is maintained at 10 kpa (A), the flash gas phase temperature is maintained at 45° C.; and the designed concentration of sulfuric acid is 50%.

[0046] In the process of making titanium dioxide, the concentration of sulfuric acid in the sulfuric acid waste liquid ranges from 20% to 25%. In most cases, for every 1t of titanium dioxide produced, about 5-6t of waste acid with a sulfuric acid concentration of about 22% is produced. In the process of resource recycling of waste acid from titanium dioxide produced by sulfuric acid method, the determination of parameters involves a complex process that comprehensively considers equipment performance, processing efficiency, cost control and environmental factors. The setting of the provided parameters is based on the following considerations:

[0047] Steam temperature and pressure settings: In the fresh steam parameters, the temperature of 126°C and the pressure of 130kpa are set mainly to take into account the boiling point of the sulfuric acid solution and the required heat input. This temperature and pressure can ensure that the steam provides sufficient heat energy in each preheating and concentration stage while maintaining the thermal efficiency and safety of the system.

[0048] Preheating target temperature: The target temperature of 78-80℃ for water preheating, 93-95℃ for mixed steam preheating and 110-115℃ for fresh steam preheating are selected based on the specific heat capacity of sulfuric acid solution and the expected heat transfer efficiency. These temperature settings help effectively improve preheating efficiency while reducing heat energy loss.

[0049] Parameters in MVR evaporator and single-effect evaporator: MVR evaporator liquid phase maintenance temperature is 106-110℃, gas phase pressure is -50kpa, secondary compression steam temperature is 126℃ and pressure is 0.239MPa(A). These parameters are selected based on the working principle of the evaporator and the thermodynamic properties of the material. By adjusting the temperature and pressure, the evaporation process can be optimized to achieve the desired concentration effect and minimize energy consumption.

[0050] The settings in step S5: The flash evaporator gas phase pressure of 10 kpa (A) and the gas phase temperature of 45 ° C are set to utilize the rapid evaporation caused by the pressure drop to more efficiently separate more concentrated sulfuric acid. This step ensures that the sulfuric acid concentration is maximized while controlling the operating conditions to protect the equipment and ensure safe operation.

[0051] These parameters are set based on experimental data, simulation results and existing process knowledge. Through these strictly controlled operating conditions, efficient recovery of sulfuric acid waste liquid can be achieved while ensuring the economy of the entire process.

[0052] The process of obtaining parameters is as follows: 1. Establish process model: Process simulation software: Use process simulation software ASPENPlus to establish the model; input all involved material characteristics, reaction kinetics, physical properties and equipment parameters.

[0053] Model setup: input feedstock composition, flow rates and initial conditions, set operating parameters, and define product and by-product flows at each stage;

[0054] 2. Thermodynamics and material balance calculations: Thermodynamic model: Select the thermodynamic model NRTL to describe the behavior of the liquid and vapor phases; Material balance: Perform material balance calculations for each process unit.

[0055] 3. Perform dynamic and static simulations: Static simulation: Preliminarily run the model to perform steady-state simulation, adjust various parameters to meet the design indicators, and evaluate the impact of key parameters such as temperature, pressure, and concentration.

[0056] Dynamic Simulation: Perform dynamic simulation to understand the system response to startup, shutdown, and disturbances. Adjust control strategies to optimize process stability.

[0057] 4. Sensitivity analysis and optimization: Sensitivity analysis: Analyze the impact of key operating parameters (temperature, pressure) on sulfuric acid recovery, energy consumption, and product quality. Optimization process: Use the optimization tool MATLAB, integrated in the simulation software to find the best operating conditions to minimize energy consumption and cost and maximize output and product quality.

[0058] 5. Validation and Experimentation: Use field test data to verify the accuracy of simulation results. Adjust model parameters to better fit actual observation data.

[0059] Pilot Run: Conduct a small-scale pilot run in a plant environment to validate the operating conditions predicted by the model and make adjustments based on actual operating results.

[0060] Preferably, in step S6, during the cooling operation, the cooling target temperature is 45-50°C.

[0061] The target temperature of the material is set at 45-50°C. There are several key reasons:

[0062] 1. Reduce corrosiveness: Sulfuric acid is significantly more corrosive at high temperatures. By reducing the temperature to 45-50°C, the risk of corrosion to subsequent processing equipment (such as solid-liquid separation equipment) can be greatly reduced. The corrosive effect of sulfuric acid on metals and other materials increases with increasing temperature, so controlling the lower temperature is to protect the integrity of the entire system and extend the service life of the equipment.

[0063] 2. Promote salt precipitation: When sulfuric acid is used as a solvent in the preparation of titanium dioxide, waste liquid containing salts such as ferrous sulfate will be formed. The solubility characteristics of ferrous sulfate salts at different temperatures are crucial for the cooling step of the sulfuric acid recovery process. When the final sulfuric acid solution concentration reaches 50%, the cooling process has the following aspects to promote the precipitation of salts: 1. The relationship between solubility and temperature: The solubility of ferrous sulfate in sulfuric acid solution varies greatly with temperature. Under high temperature conditions, the solubility of ferrous sulfate is higher, which means that more ferrous sulfate will remain in solution. However, when the temperature is reduced, the solubility of ferrous sulfate decreases, prompting it to precipitate from the solution. This is because the solubility of most salts decreases with decreasing temperature, and ferrous sulfate is no exception. 2. The relationship between cooling and precipitated salts: In the treatment of sulfuric acid waste liquid, when the liquid is cooled from a higher temperature to 45-50°C, not only ferrous sulfate, but also other possible salts, will be affected. Since the solubility of these salts decreases after cooling, they will precipitate from the solution to form solid particles. This temperature control strategy exploits the temperature dependence of solubility to optimize the solid-liquid separation process.

[0064] 3. Interaction between sulfuric acid concentration and salt precipitation: When the sulfuric acid concentration is increased to 50%, the ionic strength of the solution increases, which will further affect the solubility of salts. A high concentration of sulfuric acid environment will reduce the solubility of other salts through the so-called "salt effect". Therefore, when a higher sulfuric acid concentration is reached, some salts may begin to precipitate even at higher temperatures. However, when the temperature is reduced to 45-50°C, this effect will be more significant, because the dual effects of temperature and ionic strength further reduce the solubility, which is more conducive to salt precipitation.

[0065] Therefore, when treating sulfuric acid waste liquid containing ferrous sulfate, cooling to 45-50°C not only helps reduce equipment corrosion, but also promotes effective precipitation of salts by utilizing the lower solubility of ferrous sulfate and other salts at lower temperatures. This helps to remove more insoluble and poorly soluble salts in the solid-liquid separation step, clean the sulfuric acid solution, and meet the sulfuric acid concentration requirements of the acid hydrolysis stage.

[0066] Compared with the prior art, the process of recycling waste acid from titanium dioxide produced by sulfuric acid process has the following beneficial effects:

[0067] 1. Resource recycling: The present invention can effectively recycle and reuse the waste sulfuric acid liquid generated in the titanium dioxide production process, reducing the demand and production of new sulfuric acid, which not only reduces production costs, but also reduces dependence on and exploitation of natural resources.

[0068] 2. Improve the purity of sulfuric acid: By using multi-stage filtration technology, multi-stage concentration and flash evaporation process, impurities in sulfuric acid can be effectively separated, ensuring the purity and quality of sulfuric acid.

[0069] 3. Efficient energy utilization: Through multi-stage preheating and recycling, especially the use of MVR evaporation combined equipment, the energy utilization efficiency is greatly improved. MVR equipment reduces the need for additional energy by recycling and recompressing steam while maintaining the thermal efficiency of the system. This method not only reduces energy consumption, but also reduces operating costs.

[0070] 4. Optimization of temperature and pressure control: The temperature and pressure of each step in the process are strictly controlled to ensure that each stage operates under optimal operating conditions, which helps to improve energy efficiency and product quality while reducing energy waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] Figure 1 It is a schematic flow chart of the process for resource recycling of waste acid from titanium dioxide produced by the sulfuric acid process in a specific embodiment. DETAILED DESCRIPTION

[0072] The following are specific embodiments of the present invention and the accompanying drawings to further describe the technical solution of the present invention, but the present invention is not limited to these embodiments.

[0073] like Figure 1 As shown, a process for recycling waste acid from titanium dioxide produced by the sulfuric acid process is used to treat the waste sulfuric acid liquid generated in the preparation of titanium dioxide by the sulfuric acid process; the sulfuric acid liquid obtained after treatment is used in the titanium dioxide acidolysis section; in the process for recycling waste acid from titanium dioxide produced by the sulfuric acid process, steam manufacturing equipment is used to provide fresh steam and heating water; the specific steps of the process for recycling waste acid from titanium dioxide produced by the sulfuric acid process are as follows:

[0074] S1 filtration: After filtering the sulfuric acid waste liquid, a pretreated sulfuric acid waste liquid is obtained; after testing, the temperature of the pretreated sulfuric acid waste liquid is 50° C., and the sulfuric acid content in the pretreated sulfuric acid waste liquid is 22%;

[0075] S2 preheating: preheating the pretreated sulfuric acid waste liquid with water using preheating equipment 1, preheating the mixed steam using preheating equipment 2, and preheating the fresh steam using preheating equipment 3 to obtain preheated material;

[0076] In water preheating operation, the target temperature is 78°C; in mixed steam preheating operation, the target temperature is 93°C; in fresh steam preheating operation, the target temperature is 112°C;

[0077] S3 first stage concentration: use MVR evaporation combination equipment to evaporate and concentrate the preheated liquid to obtain an initial mixed material; the initial mixed material contains precipitated salts;

[0078] The MVR evaporation combined equipment includes an MVR evaporator and an evaporation compressor. In the first stage of heating treatment, the MVR evaporator is first heated by fresh steam to evaporate the moisture of the material in the MVR evaporator to obtain secondary steam. The secondary steam is pressurized and heated by the evaporation compressor to obtain secondary compressed steam. The MVR evaporator is heated by fresh steam and secondary compressed steam to reduce the use of fresh steam.

[0079] The parameters are as follows: MVR liquid phase maintenance temperature is 108°C, gas phase pressure is -50kpa, sulfuric acid design concentration is 45%, secondary compression steam temperature is 126°C, secondary compression steam pressure is 0.239MPa(A).

[0080] S4 The second stage of concentration: Use a single-effect evaporator to evaporate and concentrate the initial mixture to obtain an intermediate mixture; the intermediate mixture includes precipitated salts;

[0081] The parameters are as follows: the gas phase pressure of the single-effect evaporator is controlled at -50kpa; the liquid phase temperature of the single-effect evaporator is maintained at 110℃; the design concentration of sulfuric acid is 48%;

[0082] S5 flash evaporation: flash evaporator is used to flash the intermediate mixture to obtain a refined concentrated sulfuric acid mixture; after testing, the temperature of the refined concentrated sulfuric acid mixture is 80°C; the refined concentrated sulfuric acid mixture includes precipitated salts;

[0083] The flash evaporation operation parameters are as follows: the flash evaporator gas phase pressure is maintained at 10 kpa (A), the flash gas phase temperature is 45 ° C; the sulfuric acid design concentration is 50%;

[0084] S6 protection separation: The concentrated sulfuric acid liquid is cooled by a refrigeration system to 45°C; after solid-liquid separation by a solid-liquid separation device, 50% sulfuric acid liquid and precipitated salt are obtained;

[0085] In the process of resource recycling of waste acid from titanium dioxide produced by the sulfuric acid process, a steam manufacturing device is used to provide fresh steam and heating water. The steam manufacturing device is connected to preheating device 1 through a heating water delivery pipeline, connected to preheating device 2 through a fresh steam delivery pipeline 1, connected to preheating device 3 through a fresh steam delivery pipeline 2, connected to an MVR evaporator through a fresh steam delivery pipeline 3, and connected to a single-effect evaporator through a fresh steam delivery pipeline 4;

[0086] The MVR evaporator is connected to the preheating device 2 through the non-condensable steam delivery pipeline 1 and is connected to the preheating device 1 through the condensed water delivery pipeline 1;

[0087] The preheating device 3 is connected to the preheating device 2 via the non-condensable steam delivery pipeline 2, and is connected to the preheating device 1 via the condensed water delivery pipeline 2;

[0088] The preheating device 2 is connected to the preheating device 1 via a condensed water delivery pipeline 3;

[0089] The preheating device 1 is connected to a water storage unit of the steam production device through a return pipeline, and the water storage unit is used to provide a water source for the steam production device.

[0090] In the fresh steam preheating operation, the preheating equipment 3 receives the fresh steam provided by the steam production equipment through the fresh steam transmission pipeline 2. The fresh steam is converted into condensed water and non-condensable steam after heat exchange. The condensed water is transported to the preheating equipment 1 through the condensed water transmission pipeline 2, and the non-condensable steam is transported to the preheating equipment 2 through the non-condensable steam transmission pipeline 2.

[0091] Fresh steam and secondary compressed steam are converted into condensed water and non-condensable steam after heat exchange; condensed water is transported to preheating equipment 1 through condensed water transport pipeline 1; non-condensable steam is transported to preheating equipment 2 through non-condensable steam transport pipeline 1.

[0092] In the mixed steam preheating operation, the heating fluid used to heat the preheating device 2 is converted into condensed water after heat exchange and transported to the preheating device 1 through the condensed water transport pipeline 3, and the uncondensed part is discharged.

[0093] Practice 1 (traditional method): The feed liquid containing 22% sulfuric acid passes through distilled water and enters the first-effect evaporator for concentration. The heat source used in the first-effect evaporator is the secondary steam generated by the second-effect evaporator; the feed liquid discharged from the first-effect evaporator enters the second-effect evaporator for evaporation and concentration. The heat source used in the second-effect evaporator is fresh steam. The feed liquid transferred from the second-effect evaporator enters the single-effect evaporator for final concentration to obtain a 50% sulfuric acid solution containing ferrous sulfate crystal slurry. The heat source used in the single-effect evaporator is fresh steam.

[0094] Energy consumption comparison: The comparison is made for the stage with the highest energy consumption in the treatment of sulfuric acid waste liquid. The comparison results are as follows:

[0095] Standard coal conversion: equivalent heat of 1kW·h electric energy = 0.12303kg standard coal; equivalent coal quantity of 1ton saturated steam = 97.14kg standard coal;

[0096] Traditional method: In the two-effect evaporator, steam consumption: 0.6 tons of saturated steam are required to evaporate 1 ton of water; energy consumption conversion: 0.6 tons of steam × 97.14 kg of standard coal / ton of steam = 58.284 kg of standard coal;

[0097] In a specific embodiment, an MVR combined device is used in the first stage of concentration: Power consumption: 45 kW·h is required for every ton of water used; Energy consumption conversion: 45 kW·h×0.12303 kg standard coal / kW·h=5.53635 kg standard coal;

[0098] Energy saving ratio: Savings: 58.284kg standard coal - 5.53635kg standard coal = 52.74765kg standard coal

[0099] Savings percentage: 52.74765 / 58.284≈90.5%.

[0100] Economic benefits: The selling price of concentrated sulfuric acid (98%) is 600 yuan / ton. Taking the annual production of 10,000 tons of titanium dioxide as an example, it is conservatively estimated that 50,000 tons of titanium dioxide waste acid (H2S04 accounts for 22%, FeS04 accounts for 12%) will be produced. After treatment, the purity of 50% sulfuric acid liquid is more than 98%. After calculation, the cost of sulfuric acid can be saved by about 6,654,492 yuan per year; in addition, the precipitated ferrous sulfate can be sold to downstream companies for use, including: as a flocculant and reducing agent in the water treatment industry; used in the production of ferrite pigments in the pigment and coating industry; as a micro-fertilizer component in the fertilizer industry; and as a surface treatment agent in metallurgy and mining.

[0101] Comprehensive analysis shows that compared with the method of using limestone to neutralize waste acid and produce red gypsum, the cost of treating waste acid to produce red gypsum is 700-800 yuan / ton of titanium dioxide, so this treatment method has obvious economic benefits.

[0102] Purity detection: After detection, the purity of the sulfuric acid liquid recovered by the method provided in the specific embodiment is higher than 98%, and the content of impurities that have an impact on the acid decomposition stage of titanium dioxide is far lower than the required standard.

[0103] Specific data that meets the requirements of the titanium dioxide acid hydrolysis section for the recovery of impurities in sulfuric acid solution,

[0104]

[0105] Remarks: The control of iron and aluminum ions is very important because their content will directly affect the whiteness and purity of titanium dioxide. The content of manganese and chloride ions needs to be strictly controlled to avoid product color and interference in the production process. Fluoride ions and other heavy metals (such as copper and zinc) should also be controlled at low concentrations to ensure product quality.

[0106] The specific data of impurities in the sulfuric acid solution recovered by the method provided in the specific embodiment are as follows:

[0107]

[0108] The above test results show that the purity and impurity content of the sulfuric acid liquid after being treated by the recovery process of the specific embodiment have reached the use requirements of the titanium dioxide acid decomposition section.

[0109] The specific embodiments described herein are merely examples of the spirit of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in similar ways without departing from the spirit of the present invention or exceeding the defined scope.

Claims

1. A process for recycling waste acid from titanium dioxide produced by sulfuric acid process, characterized in that: The process for recycling waste acid from titanium dioxide produced by the sulfuric acid process is used to treat the waste sulfuric acid liquid generated in the preparation of titanium dioxide by the sulfuric acid process. The treated sulfuric acid liquid is used in the titanium dioxide acidolysis process. The process for recycling waste acid from titanium dioxide produced by the sulfuric acid process includes the following steps: S1 filtration: After the sulfuric acid waste liquid is filtered, the pre-treated sulfuric acid waste liquid is obtained; S2 preheating: preheating the pretreated sulfuric acid waste liquid with water using preheating equipment 1, preheating the mixed steam using preheating equipment 2, and preheating the fresh steam using preheating equipment 3 to obtain preheated material; S3 first stage concentration: Use MVR evaporation combination equipment to evaporate and concentrate the preheated material until the sulfuric acid concentration in the material reaches the designed concentration, and then end the evaporation and concentration operation to obtain the initial mixed material; The MVR evaporation combined equipment includes an MVR evaporator and an evaporation compressor. In the evaporation and concentration operation, the MVR evaporator is first heated by fresh steam to evaporate the moisture of the material in the MVR evaporator to obtain secondary steam. The secondary steam is pressurized and heated by the evaporation compressor to obtain secondary compressed steam. Finally, the MVR evaporator is heated by fresh steam and secondary compressed steam to reduce the use of fresh steam. S4 Second stage concentration: Use a single-effect evaporator to evaporate and concentrate the initial mixture until the sulfuric acid concentration in the material reaches the designed concentration, and then end the evaporation and concentration operation to obtain an intermediate mixture; S5 flash evaporation: flash evaporator is used to flash the intermediate mixture until the sulfuric acid concentration in the material reaches the designed concentration, and the flash evaporation operation is terminated to obtain a refined concentrated sulfuric acid mixture; S6 protection separation: The concentrated sulfuric acid mixture is subjected to cooling operation and solid-liquid separation operation in sequence to obtain sulfuric acid liquid and precipitated salt; In the process of resource recycling of waste acid from titanium dioxide produced by the sulfuric acid process, a steam manufacturing device is used to provide fresh steam and heating water. The steam manufacturing device is connected to preheating device 1 through a heating water delivery pipeline, connected to preheating device 2 through a fresh steam delivery pipeline 1, connected to preheating device 3 through a fresh steam delivery pipeline 2, connected to an MVR evaporator through a fresh steam delivery pipeline 3, and connected to a single-effect evaporator through a fresh steam delivery pipeline 4; The MVR evaporator is connected to the preheating device 2 through the non-condensable steam delivery pipeline 1 and is connected to the preheating device 1 through the condensed water delivery pipeline 1; The preheating device 3 is connected to the preheating device 2 via the non-condensable steam delivery pipeline 2, and is connected to the preheating device 1 via the condensed water delivery pipeline 2; The preheating device 2 is connected to the preheating device 1 via a condensed water delivery pipeline 3; The preheating device 1 is connected to a water storage unit of the steam production device through a return pipeline, and the water storage unit is used to provide a water source for the steam production device.

2. The process for recycling waste acid from titanium dioxide produced by sulfuric acid process as claimed in claim 1, characterized in that: In the fresh steam preheating operation, the preheating equipment 3 receives fresh steam from the steam production equipment through the fresh steam transmission pipeline 2. The fresh steam is converted into condensed water and non-condensable steam after heat exchange. The condensed water is transported to the preheating equipment 1 through the condensed water transmission pipeline 2, and the non-condensable steam is transported to the preheating equipment 2 through the non-condensable steam transmission pipeline 2.

3. The process for recycling waste acid from titanium dioxide produced by sulfuric acid process as claimed in claim 1, characterized in that: In step S3, fresh steam and secondary compressed steam are converted into condensed water and non-condensable steam after heat exchange; condensed water is transported to preheating equipment 1 through condensed water transport pipeline 1; non-condensable steam is transported to preheating equipment 2 through non-condensable steam transport pipeline 1.

4. The process for recycling waste acid from titanium dioxide produced by sulfuric acid process as claimed in claim 1, characterized in that: In the mixed steam preheating operation, the heating fluid used to heat the preheating device 2 is converted into condensed water after heat exchange and transported to the preheating device 1 through the condensed water transport pipeline 3, and the uncondensed part is discharged.

5. The process for recycling waste acid from titanium dioxide produced by sulfuric acid process as claimed in claim 1, characterized in that: The sulfuric acid concentration in the sulfuric acid waste liquid is 20-25%; the fresh steam parameters are as follows: temperature 126°C, pressure 130kpa; the target temperature of the water preheating operation is 78-80°C; the target temperature of the mixed steam preheating operation is 93-95°C; the target temperature of the fresh steam preheating operation is 110-115°C; In step S3, the parameters are set as follows: MVR liquid phase maintenance temperature is 106-110°C, gas phase pressure is -50kpa, sulfuric acid design concentration is 45%, secondary compression steam temperature is 126°C, secondary compression steam pressure is 0.239MPa(A). In step S4, the parameters are set as follows: the gas phase pressure of the single-effect evaporator is controlled to be -50 kPa; the liquid phase temperature of the single-effect evaporator is maintained at 110-112° C.; and the designed concentration of sulfuric acid is 48%. In step S5, the parameters are set as follows: the flash evaporator gas phase pressure is maintained at 10 kpa (A), the flash gas phase temperature is maintained at 45° C.; and the designed concentration of sulfuric acid is 50%.

6. The process for recycling waste acid from titanium dioxide produced by sulfuric acid process as claimed in claim 1, characterized in that: In step S6, during the cooling operation, the cooling target temperature is 45-50°C.

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