Calcination treatment method of titanium dioxide

Abstract

The invention relates to a calcination treatment method of titanium dioxide, which comprises the following steps: carrying out segmented calcination treatment on a moisture-containing titanium dioxide raw material, the calcination process comprising a dehydration treatment stage and a desulfurization and crystal form conversion stage; in the dehydration treatment stage, a heat source is used for heating the raw materials to evaporate water to generate water vapor tail gas; the water vapor tail gas is condensed and recycled, and obtained condensed water is used for a follow-up process; carrying out high-temperature calcination on the dehydrated raw materials in the desulfurization and crystal form conversion stages to generate tail gas containing sulfur oxides; and carrying out catalytic oxidation and absorption treatment on sulfur oxides in the tail gas, and reusing the obtained absorption liquid in the production process of titanium dioxide. The technical problems that in the titanium dioxide calcination process, the water content of tail gas is high, sulfur oxide is difficult to efficiently absorb, and resource utilization of by-products is insufficient are solved.

Description

Technical Field

[0001] The present invention is a calcination treatment method for titanium dioxide. Background Art

[0002] In the production process of titanium dioxide, the calcination link is a key step to realize the transformation of materials from the precursor to the final product, and a rotary kiln is usually used for calcination. This process is generally divided into three stages: the first stage is the dehydration stage, which is used to remove the crystal water and part of the free water in the raw materials; the second stage is the desulfurization stage, and the main goal is to decompose the sulfate ions in the raw materials and release gases such as sulfur dioxide (SO2) and sulfur trioxide (SO3); the third stage is the crystal form transformation stage, in which the raw materials are transformed into titanium dioxide finished products with a stable crystal form. The temperature control of the above-mentioned stages is usually achieved by introducing natural gas for combustion from the kiln head and adjusting the flame length and intensity.

[0003] In actual production, in order to meet the environmental protection emission standards, the tail gas generated during the calcination process needs to be desulfurized. The traditional method mainly uses sodium hydroxide solution or lime water as absorbents to convert SO2 and SO3 in the tail gas into sodium sulfate or calcium sulfate. These by-products are usually stored as solid waste after treatment, which not only causes waste of resources but also increases the environmental protection burden.

[0004] There is also a significant problem in the current process: due to the low solid content of the slurry after pressure filtration (about 40%), a large amount of water vapor is released during the calcination process, which greatly increases the difficulty of tail gas treatment after entering the tail gas system. Traditional tail gas treatment equipment is inefficient in simultaneously treating high-concentration water vapor and SO2 / SO3, and can only rely on liquid-phase absorption methods to remove polluting gases, which easily causes an increase in system load and equipment corrosion.

[0005] Therefore, the existing technology has significant defects in tail gas treatment, mainly manifested in: on the one hand, the mixed existence of water vapor and sulfur oxides is not conducive to efficient absorption; on the other hand, the by-products cannot be recycled, resulting in waste. Summary of the Invention

[0006] The purpose of the present invention is to solve the above deficiencies of the prior art and provide a calcination treatment method for titanium dioxide.

[0007] A calcination treatment method for titanium dioxide, comprising:

[0008] Performing segmented calcination treatment on the wet titanium dioxide raw materials, and the calcination process includes a dehydration treatment stage and a desulfurization and crystal form transformation stage;

[0009] In the dehydration treatment stage, heating the raw materials with a heat source to evaporate water and generate water vapor tail gas;

[0010] Condense and recover the water vapor tail gas, and the obtained condensed water is used for subsequent processes;

[0011] In the desulfurization and crystal form conversion stage, the dehydrated raw material is calcined at a high temperature to generate a tail gas containing sulfur oxides;

[0012] Catalytically oxidize and absorb the sulfur oxides in the tail gas, and the obtained absorption liquid is recycled to the titanium dioxide production process.

[0013] Furthermore, the heat source is the waste heat from other high-temperature processes in the titanium dioxide process flow.

[0014] Furthermore, the calcination temperature in the dehydration treatment stage is controlled within the range of 100°C to 300°C.

[0015] Furthermore, the condensation recovery is realized by a condenser and a cooling water circulation system.

[0016] Furthermore, the calcination temperature in the desulfurization and crystal form conversion stage is controlled within the range of 800°C to 1100°C.

[0017] Furthermore, the catalytic oxidation step is carried out in a fixed-bed reactor using V2O5 as a catalyst.

[0018] Furthermore, 93% sulfuric acid is used as the absorption liquid for the absorption treatment.

[0019] Furthermore, the absorption liquid is used in the acid digestion section to decompose the titanium concentrate raw material.

[0020] Furthermore, the staged calcination treatment is realized by arranging two rotary kilns in sequence, corresponding to the dehydration section and the desulfurization and crystal form conversion section respectively.

[0021] Furthermore, the water after condensing the water vapor tail gas is transported to the washing or filtration system in a closed-loop circulation manner.

[0022] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0023] Improve energy efficiency and resource utilization rate. By dividing the rotary kiln calcination process into a dehydration section and a desulfurization / crystal form conversion section, the present invention effectively realizes energy zoning management. Among them, the dehydration section can be heated by using the waste heat generated in the production line, avoiding the waste of high-grade energy and significantly reducing the energy consumption per unit product.

[0024] In addition, a large amount of water vapor generated during the dehydration process is condensed and recovered and then re-entered into the production system, avoiding the resource waste caused by direct discharge, realizing the recycling of water resources, and contributing to the realization of the overall water-saving goal of the factory.

[0025] Optimizing tail gas treatment and reducing the environmental load, the present invention effectively alleviates the problems of low absorption efficiency and large treatment load caused by high humidity of tail gas in traditional rotary kiln calcination through segmented collection and quality-separated treatment of tail gas.

[0026] Specifically, the dry SO2 tail gas generated in the desulfurization section is catalytically oxidized and converted into SO3, and absorbed by 93% sulfuric acid. This not only enables the up-to-standard treatment of tail gas, but also the generated sulfuric acid can be recycled and used in the acid hydrolysis reaction link, realizing the resource recycling of SO2 and completely getting rid of the environmental problem of the storage of by-products after absorption by lime water or alkali solution.

[0027] Improving product quality and process controllability, through segmented calcination, the temperature control in the kiln is more targeted, which is conducive to realizing the precise regulation of the key temperature zone in the crystal form transformation stage, thereby improving the crystal form purity and particle size uniformity of titanium dioxide products and improving product quality.

[0028] At the same time, since the length of the high-temperature reaction section is shortened (for example, the length of the desulfurization / crystal form section is controlled at about 25 m), the structure of the entire rotary kiln is more compact, the response of the temperature control system is faster, which helps to improve the process stability and the level of automation control.

[0029] Saving equipment investment and reducing operation and maintenance costs, in the structure of the present invention, the rotary kiln is shortened, the tail gas system is modularized, and the recycling path is clear. Compared with the traditional calcination tail gas system, it can greatly reduce the layout of equipment pipelines and the floor area of tail gas purification facilities, and simplify the operation and maintenance process.

[0030] In addition, the recovery of sulfur resources into the main process system saves the external purchase cost of acid-consuming materials and improves economic benefits.

[0031] Promoting green production, through the separate recovery of water vapor and SO2, and the efficient separation of hydrothermal and harmful gases, the present invention reduces emissions from the source and realizes the recycling of tail gas resources, significantly improving the clean production level of the titanium dioxide industry, and having good environmental adaptability and popularization prospects. Brief Description of the Drawings

[0032] Figure 1 It is a flow chart of a calcination treatment method for titanium dioxide. Detailed Embodiments

[0033] To deepen the understanding of the present invention, the following will further elaborate on the present invention in combination with embodiments and drawings. The embodiments are only used to explain the present invention and do not constitute a limitation on the protection scope of the present invention.

[0034] A calcination treatment method for titanium dioxide includes the following steps:

[0035] The wet titanium dioxide raw material is subjected to staged calcination. The calcination process includes a dehydration treatment stage and a desulfurization and crystal form conversion stage. In the dehydration treatment stage, the raw material is heated by a heat source to evaporate water, generating water vapor tail gas.

[0036] The water vapor tail gas is condensed and recovered, and the obtained condensed water is used for subsequent processes.

[0037] In the desulfurization and crystal form conversion stage, the dehydrated raw material is calcined at a high temperature, generating tail gas containing sulfur oxides.

[0038] The sulfur oxides in the tail gas are catalytically oxidized and absorbed, and the obtained absorption liquid is recycled to the titanium dioxide production process.

[0039] This method uses a staged calcination strategy to improve the thermal efficiency and product quality of the calcination process. In the dehydration stage, the raw material is heated by a heat source to evaporate water, forming water vapor tail gas, and the water vapor tail gas is cooled by a condensation device to form condensed water. In the high-temperature calcination stage, crystal form conversion is promoted and sulfur-containing tail gas is discharged under conditions above 800 °C. The tail gas is then converted into sulfuric anhydride or SO3 by a catalyst and absorbed by the absorption liquid.

[0040] This method effectively improves the thermal energy utilization rate and tail gas treatment level in the titanium dioxide calcination process, realizes resource recycling and pollution control, and reduces the consumption of water resources and raw materials.

[0041] In this process, the condensed water can be used for filtration, washing or other sections; the absorption liquid can be used as a reaction medium in raw material acidolysis. This method is applicable to various titanium dioxide production systems and has good adaptability and engineering application potential.

[0042] In a possible implementation, the heat source is the waste heat from other high-temperature processes in the titanium dioxide process flow.

[0043] In this implementation, the calcination system is connected to high-temperature equipment such as a roasting furnace and a chlorination reactor through a pipeline system, and the waste heat is guided to the calcination section for water evaporation or raw material preheating.

[0044] This technical solution realizes the recovery and reuse of thermal energy between processes, reduces the overall energy consumption of the system, and improves the energy utilization efficiency.

[0045] In an alternative solution, the high-temperature flue gas from other processes can also be indirectly utilized through a heat exchanger to further expand the range of heat source selection.

[0046] In a possible implementation, the calcination temperature in the dehydration treatment stage is controlled within the range of 100 °C to 300 °C.

[0047] Ensure that the temperature in the dehydration section is maintained within a safe range by the temperature control system, which can efficiently dehydrate without causing crystal form changes or raw material decomposition. The common temperature range is 150°C to 250°C.

[0048] This solution can avoid raw material caking or pre-reaction caused by overheating, and improve the calcination uniformity and subsequent processing efficiency.

[0049] Electric heating, hot air circulation, etc. can be used to replace the external heat source method, and the specific selection is determined according to energy efficiency and process conditions.

[0050] In a possible implementation, the condensation recovery is achieved by a condenser and a cooling water circulation system.

[0051] The water vapor tail gas is cooled and condensed after heat exchange with the external circulating water system through a shell-and-tube condenser. The condenser material is preferably corrosion-resistant metal, such as stainless steel or titanium.

[0052] This system operates stably and reliably, has high condensation efficiency, and is convenient for system closed-loop operation and water resource recovery.

[0053] In alternative solutions, condensation devices with different structural forms, such as spray towers and plate heat exchangers, can be used, depending on the existing conditions of the factory.

[0054] In a possible implementation, the calcination temperature in the desulfurization and crystal form transformation stage is controlled within the range of 800°C to 1100°C.

[0055] By controlling the temperature in the second calcination section within an appropriate range, anatase is promoted to transform into rutile, and sulfides are oxidized to form SOx and discharged.

[0056] This temperature range is conducive to crystal maturation, particle size stability, and improvement of crystal form purity, which is the key guarantee for the production of high-quality titanium dioxide.

[0057] According to the properties of the raw materials, the set temperature can be adjusted within this range to achieve the best thermal conversion efficiency and gas emission control.

[0058] In a possible implementation, the catalytic oxidation step is carried out in a fixed-bed reactor with V2O5 as the catalyst.

[0059] Tail gases such as SO2 are introduced into the fixed-bed reactor by a fan. V2O5 is loaded on the carrier and reacts with SO2 to generate SO3. The temperature of the catalytic bed is maintained at 350°C to 450°C.

[0060] This catalytic device has a high reaction rate, good stability, is easy to operate continuously for a long time, and V2O5 has high activity, which is suitable for industrial applications.

[0061] Alternative solutions include fluidized bed or moving bed forms, and single tower or multi-tower series structures can also be selected according to the gas volume.

[0062] In a possible implementation, 93% sulfuric acid is used as the absorption liquid for the absorption treatment.

[0063] The SO3 gas enters the absorption tower and reacts with concentrated sulfuric acid to form fuming sulfuric acid or diluted sulfuric acid products, which are cooled by a heat exchanger and then transported to the acid digestion system or the storage system.

[0064] High-concentration sulfuric acid has high absorption efficiency and low volatility, which can ensure high conversion rate and low emission of sulfur oxides in the tail gas.

[0065] In some systems, sulfuric acid or other absorption media with different concentrations can be used according to product requirements.

[0066] In a possible implementation, the absorption liquid is used in the acid digestion section to decompose ilmenite raw materials.

[0067] The sulfuric acid obtained by absorption is directly used for the acid digestion reaction of ilmenite or high-titanium slag, and as a reaction medium, the Ti element is converted into a soluble state.

[0068] The internal recycling and reuse of sulfur resources are realized, reducing the consumption of externally purchased acid and the discharge of waste acid.

[0069] In the alternative process, the sulfuric acid concentration can also be adjusted to adapt to the acid digestion characteristics or reaction conditions of different raw materials.

[0070] In a possible implementation, the staged calcination treatment is realized by arranging two rotary kilns in sequence, corresponding to the dehydration section and the desulfurization and crystal form transformation section respectively.

[0071] The temperature of the first-stage rotary kiln is controlled at 100°C to 300°C for dehydration, and the second stage is heated to 800°C to 1100°C for crystal form transformation and desulfurization. The raw materials are sequentially processed during continuous transportation.

[0072] The rotary kiln has good structural continuity, large processing capacity and strong controllability, and is suitable for large-scale industrial applications.

[0073] A preheater or a cooling section can be selected to further improve the thermal efficiency and product quality.

[0074] In a possible implementation, the water after condensing the water vapor tail gas is transported to the washing or filtration system in a closed-loop cycle manner.

[0075] The recovered condensed water is sent to the washing equipment or the slurry filtration system through the pipeline system, avoiding waste of resources and reducing the demand for fresh water replenishment.

[0076] The closed-loop system realizes automatic control and water quality adjustment through water quality monitoring and circulation pumps, improving the operation safety and sustainability.

[0077] If there are concentrated impurities in the system, an on-line purification device can be added to maintain the stability of water quality.

[0078] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A calcination treatment method for titanium dioxide, characterized in that, Comprising: Subjecting the wet titanium dioxide raw material to staged calcination, wherein the calcination process includes a dehydration treatment stage and a desulfurization and crystal form transformation stage; In the dehydration treatment stage, heating the raw material with a heat source to evaporate water and generate water vapor tail gas; Condensing and recovering the water vapor tail gas, and using the obtained condensed water for subsequent processes; In the desulfurization and crystal form transformation stage, subjecting the dehydrated raw material to high-temperature calcination to generate tail gas containing sulfur oxides; Catalytically oxidizing and absorbing the sulfur oxides in the tail gas, and recycling the obtained absorption liquid to the titanium dioxide production process.

2. The method according to claim 1, characterized in that, The heat source is the waste heat from other high-temperature processes in the titanium dioxide process flow.

3. The method according to claim 1, wherein The calcination temperature in the dehydration treatment stage is controlled within the range of 100°C to 300°C.

4. The method according to claim 1, characterized in that, The condensation recovery is realized by a condenser and a cooling water circulation system.

5. The method according to claim 1, wherein The calcination temperature in the desulfurization and crystal form transformation stage is controlled within the range of 800°C to 1100°C.

6. The method according to claim 1, wherein The catalytic oxidation step is carried out in a fixed-bed reactor using V2O5 as a catalyst.

7. The method according to claim 1, wherein The absorption treatment uses 93% sulfuric acid as the absorption liquid.

8. The method according to claim 1, characterized in that, The absorption liquid is used in the acid digestion section to decompose the titanium concentrate raw material.

9. The method according to claim 1, characterized in that, The staged calcination treatment is realized by arranging two rotary kilns in sequence, corresponding to the dehydration section and the desulfurization and crystal form transformation section respectively.

10. The method according to claim 1, wherein The water after condensing the water vapor tail gas is transported to the washing or filtration system in a closed-loop circulation manner.

Images