Titanium white waste acid concentration system and method

Abstract

The invention discloses a titanium dioxide waste acid concentration system and method, and belongs to the technical field of sulfuric acid process titanium dioxide production or similar waste acid concentration. The system comprises a primary concentration and ferrous separation module and a secondary concentration and ferrous separation module. The primary concentration and ferrous separation module realizes primary concentration and solid-liquid separation of waste acid through an evaporation concentration kettle, a flash tank and a primary diaphragm filter press; and the secondary concentration and ferrous separation module is used for carrying out deep concentration and secondary separation on the waste acid through a scraper evaporator and a secondary diaphragm filter press. The system adopts the technologies of ultrasonic descaling, stepped concentration and solid removal, partition temperature control film evaporation and the like, and is matched with a mirror surface level inner wall scraper evaporator and an adjustable rapping device, so that the problem of scaling blockage in the waste acid concentration process is effectively solved. The method can increase the concentration of waste acid to 60% or above, realizes continuous automatic operation, and has the advantages of low equipment investment, low operation cost, environmental friendliness, high resource recovery rate and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of titanium dioxide production by sulfuric acid method or similar waste acid concentration, and particularly relates to a system and method for concentrating waste acid of titanium dioxide. BACKGROUND

[0002] At present, the concentration of waste acid after hydrolysis in a titanium dioxide plant by sulfuric acid method is generally about 20%, and the waste acid is neutralized by calcium carbonate and slaked lime in some plants, which results in a large amount of solid waste accumulation and more consumption of sulfuric acid for products, thereby bringing heavy burden to enterprises and great damage to the environment.

[0003] Some enterprises adopt multi-effect evaporation concentration, or frozen iron removal + multi-effect evaporation concentration, or frozen iron removal + MVR evaporation, or resin purification + calcination tail gas concentration + MVR concentration and the like to recover waste acid.

[0004] The multi-effect evaporation concentration has not solved the problem of serious scaling and plugging of equipment, and frequent switching and cleaning are required, so that more standby system equipment is needed, which not only has large investment, but also has large labor intensity and long time.

[0005] The frozen iron removal + multi-effect evaporation (MVR) concentration requires a higher specification of frozen station, a higher cost of public engineering such as vacuum system, a long concentration process, high investment and operation cost, less performance, and the key equipment plugging problem is not fundamentally solved.

[0006] The resin purification + calcination tail gas concentration + MVR concentration has a long process, short service life of resin, high investment and operation cost, and the plugging problem is not completely solved. SUMMARY

[0007] In view of the problems in the background art, the application provides a system and method for concentrating waste acid of titanium dioxide, which adopts a combined process of evaporation concentration + flash evaporation concentration + scraper evaporation concentration, uses ultrasonic descaling, step concentration and solid removal, and partition temperature control thin film evaporation technology, and not only concentrates the waste acid of titanium dioxide efficiently, but also completely solves the problem of scaling and plugging of waste acid, and realizes automatic operation in the whole process, and has low investment and operation cost.

[0008] The application uses ultrasonic descaling, step concentration and solid removal, and partition temperature control thin film evaporation technology, and through a unique combination of equipment systems, completely solves the plugging problem in the concentration process of waste acid of titanium dioxide, and can increase the concentration of waste acid to more than 60% and greatly reduce the soluble salt content.

[0009] The purpose of the application can be achieved by the following technical scheme: A system for concentrating waste acid of titanium dioxide, comprising a first concentration and ferrous ion separation module and a second concentration and ferrous ion separation module. The primary concentration and ferrous separation module includes an evaporation and concentration kettle, which is sequentially connected to a waste acid pump, a flash tank, a flash-cooled waste acid liquid sealing tank, a primary filter press feed tank, a primary filter press feed pump, a primary diaphragm filter press, and a primary concentrated waste acid tank. The secondary concentration and ferrous separation module includes a scraped evaporator connected to the primary concentration waste acid tank via an evaporation feed pump. The scraped evaporator is sequentially connected to a scraped evaporator liquid seal tank, a secondary filter press feed tank, a secondary filter press feed pump, and a secondary diaphragm filter press. The system is also equipped with a first condenser and a second condenser, which are used to condense the steam generated by the evaporation and concentration kettle and the flash tank, respectively. Both the primary and secondary diaphragm filter presses are equipped with hoppers and belt conveyors below them for separating and conveying solid ferrous sulfate containing impurities.

[0010] Furthermore, the outlet of the secondary diaphragm filter press is connected to a finished waste acid tank.

[0011] Furthermore, the evaporation and concentration vessel is equipped with a stirrer, an ultrasonic transmitter, and a removable steam heating coil, which is made of stainless steel lined with titanium.

[0012] Furthermore, the flash tank is made of stainless steel lined with titanium.

[0013] Furthermore, the first and second condensers are made of 316L stainless steel.

[0014] Furthermore, several rappers with adjustable rapping frequencies are evenly arranged in the circumferential direction between the two jackets on the outside of the scraped evaporator; the surface roughness Ra of the inner wall and the guide tube of the scraped evaporator is ≤0.05μm; the scraped evaporator has an adjustable speed scraper built in it, the surface roughness Ra of the scraper and the bearing it is connected to is ≤0.05μm, and the distance between the scraper and the inner wall of the evaporator is ≤1.5mm.

[0015] Furthermore, the upper and lower jackets of the scraped evaporator are heated by saturated steam at 0.6 MPaG and 0.8 MPaG respectively; the operating pressure inside the scraped evaporator cylinder is ≤ -0.054 MPaG.

[0016] Furthermore, a cooling coil and an ultrasonic transmitter are provided in the secondary filter press feed tank.

[0017] Another object of the present invention is to provide a method for concentrating titanium dioxide waste acid, which is carried out using the above-mentioned system and includes the following steps: Step 1: Primary Concentration and Ferrous Separation The waste acid from titanium dioxide is introduced into an evaporation and concentration kettle, and evaporated and concentrated to a concentration of 40%-50% at a pressure of ≤-0.054MPaG and a temperature of 100℃. Then it is sent to a flash tank for flash cooling. The waste acid after flash evaporation is separated from the impurity ferrous sulfate by a primary diaphragm filter press, and the filtrate enters the primary concentrated waste acid tank. Step 2: Secondary concentration and ferrous separation The waste acid in the primary concentrated waste acid tank is sent to a scraped evaporator and evaporated and concentrated to a concentration of over 60% under a pressure of ≤-0.054MPaG. After concentration, the waste acid is separated again by a secondary diaphragm filter press to remove impurities such as ferrous sulfate. The filtrate is the finished waste acid product.

[0018] Furthermore, the acidic gases generated by the evaporation and concentration kettle and the flash tank are condensed by the first condenser and the second condenser, respectively, and the acidic demineralized water obtained from the condensation is collected and reused.

[0019] The beneficial effects of this invention are: 1) High efficiency and continuous operation: By combining the processes of evaporation concentration, flash concentration and scraper evaporation concentration, along with ultrasonic descaling, step-by-step concentration and solid removal and zoned temperature-controlled thin film evaporation technology, the scaling and clogging problems in the waste acid concentration process are fundamentally solved, significantly extending the continuous operation cycle of the equipment and reducing the frequency of cleaning and downtime.

[0020] 2) High concentration efficiency and stable product concentration: The system can efficiently concentrate titanium dioxide waste acid to more than 60% and significantly reduce the soluble salt content, meeting the concentration requirements for reuse or further treatment, and improving the resource utilization value of waste acid. Attached Figure Description

[0021] The invention will now be further described with reference to the accompanying drawings.

[0022] Figure 1 This is a schematic diagram of the structure of a system for concentrating waste acid from titanium dioxide according to the present invention.

[0023] In the diagram: 1. Evaporation and concentration kettle; 2. Waste acid pump; 3. Flash evaporator; 4. Flash cooling waste acid liquid seal tank; 5. Primary filter press feed tank; 6. Primary filter press feed pump; 7. Primary diaphragm filter press; 8. Primary concentration waste acid tank; 9. Evaporation feed pump; 10. Scraped evaporator; 11. Scraped evaporator liquid seal tank; 12. Secondary filter press feed tank; 13. Secondary filter press feed pump; 14. Secondary diaphragm filter press; 15. Finished product waste acid tank; 16. Finished product waste acid pump; 17. Cleaning waste acid pump; 18. First condenser; 19. Second condenser; 20. First vacuum pump; 21. Second vacuum pump; 22. First hopper; 23. Second hopper; 24. Condenser liquid seal tank; 25. Acidic water pump; 26. Belt conveyor. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] A system for concentrating waste acid from titanium dioxide, such as Figure 1 As shown, it includes a primary concentration and ferrous iron separation module and a secondary concentration and ferrous iron separation module; The primary concentration and ferrous separation module includes an evaporation and concentration kettle 1. The outlet of the evaporation and concentration kettle 1 is connected to the inlet of the flash tank 3 through a waste acid pump 2. The steam outlet of the evaporation and concentration kettle 1 is connected to a first condenser 18 through a pipeline. The outlet of the flash tank 3 is connected to the inlet of the flash-cooled waste acid seal tank 4, and the steam outlet of the flash tank 3 is connected to the second condenser 19 through a pipeline. The outlet of the flash-cooled waste acid sealing tank 4 is connected to the inlet of the primary filter press feed tank 5 via a pipeline. The outlet of the primary filter press feed tank 5 is connected to the inlet of the primary diaphragm filter press 7 via the primary filter press feed pump 6. A first hopper 22 is provided below the primary diaphragm filter press 7. A belt conveyor 26 is provided at the outlet end of the first hopper 22. The ferrous sulfate containing impurities separated by the primary diaphragm filter press 7 is guided to the belt conveyor 26 via the first hopper 22 and transferred to the outside via the belt conveyor 26. The outlet of the primary diaphragm filter press 7 is connected to the inlet of the primary concentrated waste acid tank 8. The filtrate of the primary diaphragm filter press 7 enters the primary concentrated waste acid tank 8.

[0026] The outlets of the first condenser 18 and the second condenser 19 are connected to the inlet of the condenser liquid seal tank 24. The acidic demineralized water produced by the two condensers is introduced into the condenser liquid seal tank 24 through pipelines. The other outlets of the first condenser 18 and the second condenser 19 are respectively connected to the first vacuum pump 20 and the second vacuum pump 21. The non-condensable gas after being condensed by the first condenser 18 and the second condenser 19 is discharged through the first vacuum pump 20 and the second vacuum pump 21 respectively.

[0027] The outlet of the evaporation and concentration kettle 1 is also connected to a secondary pressure filter feed tank 12 via a cleaning waste acid pump 17. After the evaporation and concentration pump 1 completes cleaning, the generated waste acid is sent into the secondary pressure filter feed tank 12 via the cleaning waste acid pump 17. The secondary concentration and ferrous sulfate separation module includes a scraped evaporator 10 connected to the outlet of the primary concentration waste acid tank 8 via an evaporation feed pump 9. The outlet of the scraped evaporator 10 is connected to a scraped evaporator liquid seal tank 11. The outlet of the scraped evaporator liquid seal tank 11 is connected to the inlet of the secondary filter press feed tank 12 via a pipe. The outlet of the secondary filter press feed tank 12 is connected to the inlet of the secondary diaphragm filter press 14 via a secondary filter press feed pump 13. A second hopper 23 is provided below the secondary diaphragm filter press 14. The outlet end of the second hopper 23 is located above the belt conveyor 26. The ferrous sulfate containing impurities separated by the secondary diaphragm filter press 14 is guided to the belt conveyor 26 via the second hopper 23 and then transferred by the belt conveyor 26. The filtrate from the secondary diaphragm filter press 14 enters the finished waste acid tank 15.

[0028] The evaporation and concentration kettle 1 is equipped with a stirrer, an ultrasonic transmitter and a removable steam heating coil. The equipment is made of stainless steel lined with titanium. One spare evaporation and concentration kettle 1 needs to be considered for use in rotation. When in standby mode, the finished waste acid can be sent into it and ultrasonic descaling can be activated. The flash tank 3 is made of stainless steel lined with titanium. The first condenser 18 and the second condenser 19 are made of 316L stainless steel. The outer upper and lower jackets of the scraped evaporator 10 are heated by saturated steam at 0.6 MPaG and 0.8 MPaG, respectively.

[0029] Several vibrators are evenly arranged in the circumferential direction between the two outer jackets of the scraper evaporator 10, and the vibration frequency is adjustable. The power source is compressed air or electricity.

[0030] The inner wall and guide tube of the scraped evaporator 10 both meet the industrial-grade mirror finish requirement of Ra≤0.05μm.

[0031] The scraped evaporator 10 features a built-in adjustable-speed scraper, and the surfaces of both the scraper and the connected bearings meet the industrial-grade mirror finish requirement of Ra≤0.05μm. The bottom of the scraper bearing uses a tapered scraper. The distance between all scrapers and the inner wall of the evaporator is controlled to be ≤1.5mm.

[0032] The operating pressure inside the 10-cylinder scraped evaporator is ≤-0.054 MPaG.

[0033] The secondary filter press feed tank 12 is equipped with a cooling coil and an ultrasonic transmitter; A spare unit should be considered for the secondary filter press feed tank 12, which can be used in rotation. When in standby mode, the finished waste acid can be sent into it and ultrasonic descaling can be activated.

[0034] A method for concentrating waste acid from titanium dioxide, using the above-mentioned system, includes the following steps: Primary concentration and ferrous separation: Titanium dioxide waste acid from outside the boundary is introduced into evaporation and concentration kettle 1. The operating temperature of evaporation and concentration kettle 1 is 100℃ and the operating pressure is ≤-0.054MpaG. Under the action of steam heating and negative pressure, the waste acid is concentrated to 40%-50% and then sent to flash tank 3 through waste acid pump 2. The operating temperature of flash tank 3 is 50~100℃ and the operating pressure is ≤-0.054MpaG. After the waste acid is flash concentrated and cooled in a vacuum environment, it enters flash-cooled waste acid liquid sealing tank 4. The acidic gas distilled from the evaporation and concentration kettle 1 enters the first condenser 18, and after being cooled by demineralized water spray, it is discharged through the first vacuum pump 20. The gas flashed out of flash tank 3 enters the second condenser 19, and after being cooled by demineralized water spray, it is discharged by the second vacuum pump 21. The operating temperature of the first condenser 18 and the second condenser 19 is 50~100℃, and the operating pressure is ≤-0.054MpaG; The acidic demineralized water collected by the first condenser 18 and the second condenser 19 enters the condenser liquid seal tank 24, and then is sent to the external metatitanic acid washing section for reuse via the acidic water pump 25. Waste acid overflows from flash-cooled waste acid liquid sealing tank 4 to primary filter press feed tank 5, and is sent to primary diaphragm filter press 7 via primary filter press feed pump 6 to separate ferrous sulfate containing impurities. The ferrous sulfate containing impurities is guided to belt conveyor 26 via first hopper 22, and belt conveyor 26 transfers it to the outside. The resulting filtrate enters primary concentrated waste acid tank 8.

[0035] Secondary concentration and ferrous separation: The primary concentrated waste acid is sent to the scraped evaporator 10 via the evaporation feed pump 9. The concentrated waste acid completes the evaporation process from top to bottom in the scraped evaporator 10, and after the waste acid concentration is increased to more than 60%, it enters the liquid seal tank 11 of the scraped evaporator. The waste acid concentrated by the scraper evaporator overflows from the liquid seal tank 11 of the scraper evaporator into the secondary filter press feed tank 12. After cooling in the secondary filter press feed tank 12, it is sent to the secondary diaphragm filter press 14 via the secondary filter press feed pump 13 to separate the ferrous sulfate containing impurities. The filtrate, i.e., the finished waste acid, enters the finished waste acid tank 15 and is then sent off-site for reuse via the finished waste acid pump 16.

[0036] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A system for concentrating titanium white spent acid, characterized in that, The system comprises a primary concentration and ferrous separation module and a secondary concentration and ferrous separation module. The primary concentration and ferrous separation module comprises an evaporation concentration kettle (1) connected with a waste acid pump (2), a flash tank (3), a flash cooling waste acid liquid sealing tank (4), a primary pressure filtration feed tank (5), a primary pressure filtration feed pump (6), a primary diaphragm pressure filter (7) and a primary concentrated waste acid tank (8) in sequence. The secondary concentration and ferrous separation module comprises a scraped surface evaporator (10) connected with the primary concentrated waste acid tank (8) through an evaporation feed pump (9), and the scraped surface evaporator (10) is connected with a scraped surface evaporator liquid sealing tank (11), a secondary pressure filtration feed tank (12), a secondary pressure filtration feed pump (13) and a secondary diaphragm pressure filter (14) in sequence. The system is further provided with a first condenser (18) and a second condenser (19) for condensing the steam generated by the evaporation concentration kettle (1) and the flash tank (3) respectively. A hopper and a belt conveyor (26) are arranged below the primary diaphragm pressure filter (7) and the secondary diaphragm pressure filter (14) for separating and conveying the impurity-containing ferrous sulfate.

2. The system of claim 1, wherein, The discharge port of the secondary diaphragm pressure filter (14) is connected with a finished product waste acid tank (15).

3. The system of claim 1, wherein, The evaporation concentration kettle (1) is provided with a stirrer, an ultrasonic transmitter and a pullable steam heating coil, and is made of stainless steel lined with titanium.

4. The system of claim 1, wherein, The flash tank (3) is made of stainless steel lined with titanium.

5. The system of claim 1, wherein, The first condenser (18) and the second condenser (19) are made of 316L stainless steel.

6. The system of claim 1, wherein, A plurality of beaters with adjustable beat frequency are evenly arranged in the circumferential direction between the two outer jackets of the scraped surface evaporator (10); the surface roughness Ra of the inner wall of the scraped surface evaporator (10) and the surface roughness Ra of the surface of the flow guide cylinder are both ≤0.05 μm; the scraped surface evaporator (10) is provided with an adjustable rotating speed scraper, and the surface roughness Ra of the scraper and the connected bearing is ≤0.05 μm; the distance between the scraper and the inner wall of the scraped surface evaporator is ≤1.5 mm.

7. The system of claim 1, wherein, The upper and lower jackets of the scraped surface evaporator (10) are heated by 0.6 MPaG and 0.8 MPaG saturated steam respectively; the operating pressure in the cylinder of the scraped surface evaporator (10) is ≤-0.054 MPaG.

8. The system of claim 1, wherein, The secondary pressure filtration feed tank (12) is provided with a cooling coil and an ultrasonic transmitter.

9. A method for concentrating titanium white waste acid, performed using the system according to any one of claims 1 to 8, characterized in that, The system comprises the following steps: Step one, primary concentration and ferrous separation Titanium white waste acid is introduced into the evaporation concentration kettle (1), and is evaporated and concentrated to a concentration of 40%-50% under a pressure of ≤-0.054 MPaG and a temperature of 100°C, and then is sent into the flash tank (3) for flash cooling; the waste acid after the flash cooling is separated from the impurity-containing ferrous sulfate by the primary diaphragm pressure filter (7), and the filtrate enters the primary concentrated waste acid tank (8); Step two, secondary concentration and ferrous separation The waste acid in the primary concentrated waste acid tank (8) is sent into the scraped surface evaporator (10), and is evaporated and concentrated to a concentration of more than 60% under a pressure of ≤-0.054 MPaG, and the concentrated waste acid is separated from the impurity-containing ferrous sulfate again by the secondary diaphragm pressure filter (14), and the filtrate is the finished product waste acid.

10. The method of claim 9, wherein, The acid gas generated by the evaporation concentration kettle (1) and the flash tank (3) is condensed by the first condenser (18) and the second condenser (19) respectively, and the acid desalted water obtained by condensation is collected and reused.

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