Sulfuric acid process titanium dioxide waste acid concentration system and method

Abstract

The invention discloses a sulfuric acid process titanium dioxide waste acid concentration system and method, the system comprises a preheating device, an MVR heating evaporation device, a cooling curing device and a vacuum device, the preheating device is communicated with the MVR heating evaporation device, the vacuum device is communicated with the MVR heating evaporation device, the MVR heating evaporation device comprises a heater, an evaporator, a vapor compressor and a first circulating pump, and the first circulating pump is communicated with the MVR heating evaporation device. The heater is communicated with the first circulating pump, the heater is communicated with the evaporator, the evaporator is communicated with the cooling and curing equipment, circulating ports of the preheating equipment and the evaporator are communicated to the first circulating pump, the evaporator is communicated with the steam compressor, the steam compressor is communicated to the heater, and the heater is communicated to the condensate water tank. Secondary steam is pressurized and heated again to serve as a heat source of the heater to be recycled, condensate water generated in the production process is recycled to be used for preheating waste acid, the whole production process is short in flow and low in production cost, and the production targets of saving energy, reducing emission, reducing cost, improving efficiency and protecting the environment are effectively achieved.

Description

Technical Field

[0001] The invention relates to the technical field of sulfuric acid concentration production, and in particular to a sulfuric acid process titanium dioxide waste acid concentration system and method. Background Art

[0002] When titanium dioxide is produced by the sulfuric acid method, waste acid with a concentration of 20% to 25% will be generated. For every ton of titanium dioxide produced, 6-7 tons of waste acid will be discharged. For the treatment of waste acid, the main waste acid treatment methods used in the titanium dioxide industry are simple neutralization and recycling after concentration. Among them, simple neutralization produces a large amount of gypsum, and the technical difficulty of resource utilization is relatively large, the process is immature, and the economic efficiency is low, which not only causes waste of resources, but also easily produces secondary pollution. The waste acid concentration technology such as single effect, double effect, and multiple effect is generally used for recycling after concentration, but the waste acid of titanium dioxide has a high water content, many impurities, and strong corrosiveness, resulting in high requirements and high energy consumption of the existing waste sulfuric acid concentration process equipment, resulting in large investment and high operating costs. The overall effect is not ideal, which seriously affects the further application of this method in industry. Therefore, there is an urgent need for a production process that is environmentally friendly, economically beneficial, highly efficient, and low in energy consumption. Summary of the invention

[0003] The main purpose of the present invention is to overcome the defects of the above-mentioned background technology and provide a system and method for concentrating waste acid of titanium dioxide produced by sulfuric acid process.

[0004] To achieve the above-mentioned purpose, the sulfuric acid process titanium dioxide waste acid concentration system proposed in the present invention includes a preheating device, an MVR heating evaporation device, a cooling and maturation device and a vacuum device. The preheating inlet of the preheating device is connected to the waste acid pipeline to be treated, the preheating outlet of the preheating device is connected to the feed inlet of the MVR heating evaporation device, the discharge port of the MVR heating evaporation device is connected to the inlet of the cooling and maturation device, the vacuum device is connected to the MVR heating evaporation device and provides a vacuum working environment for the MVR heating evaporation device. The MVR heating evaporation device includes a heater, Evaporator, steam compressor and first circulation pump, the feed port of the heater is connected to the outlet of the first circulation pump, the discharge port of the heater is connected to the feed port of the evaporator, the discharge port of the evaporator is connected to the cooling and maturation equipment, the preheating outlet of the preheating equipment and the circulation port of the evaporator are both connected to the inlet of the first circulation pump, the gas-liquid outlet of the evaporator is connected to the inlet of the steam compressor, the outlet of the steam compressor and the external raw steam pipeline are both connected to the hot medium inlet of the heater, and the cold medium outlet of the heater is connected to the condensed water tank. The secondary steam generated in the production process of the MVR heating evaporation equipment is re-pressurized and heated by the steam compressor, and then sent to the heater as the heating heat source of the heater for recycling, which effectively reduces the consumption of steam energy. The production of 1 ton of 50% acid only consumes about 0.13 tons of steam, which effectively reduces the production cost. The forced circulation heating evaporation by the first circulation pump solves the problem of easy clogging of the heater and effectively improves the system operation efficiency.

[0005] Furthermore, the sulfuric acid titanium dioxide waste acid concentration system also includes an alkali washing device, which is connected in series with the gas-liquid outlet of the evaporator and the inlet pipeline of the steam compressor. The alkali washing device includes an alkali washing tower and a first gas-liquid separator. The cleaning inlet of the alkali washing tower is connected to the gas-liquid outlet of the evaporator, the cleaning outlet of the alkali washing tower is connected to the inlet of the first gas-liquid separator, the steam outlet of the first gas-liquid separator is connected to the inlet of the steam compressor, the liquid outlet of the first gas-liquid separator is connected to the liquid seal tank, the cleaning liquid inlet and outlet of the alkali washing tower are connected to the alkaline water tank and circulated alkaline washing is performed through a spray pump, and the alkaline water tank is connected to the raw steam pipeline. Since the secondary steam is acidic steam, it is easy to cause equipment corrosion if it is directly recompressed and reused without treatment. The acidic secondary steam is washed by the alkali washing equipment to become neutral secondary steam, which can avoid equipment corrosion and extend the service life of the equipment. During alkali washing, the temperature of the washing alkaline water is maintained at a high temperature of 85 to 95°C, which will not affect the temperature of the secondary steam and effectively improve the energy utilization rate.

[0006] Furthermore, the vacuum equipment includes a vacuum pump, a vacuum tank, a second gas-liquid separator and a condenser, the vacuum pump's air outlet is connected to the vacuum tank's air outlet, the vacuum tank's air inlet is connected to the gas outlet of the second gas-liquid separator, the second gas-liquid separator's liquid outlet is connected to the liquid seal groove, the second gas-liquid separator's inlet is connected to the gas outlet of the condenser, the condenser's gas inlet is connected to the heater and the condensed water tank respectively, and the condenser's liquid outlet is connected to the liquid seal groove. The vacuum degree of the entire system is maintained within the range of 50 to 80 KPa by the vacuum equipment, and the vacuum balance ensures the stability of the system operation.

[0007] Furthermore, the preheating equipment includes a hot water tank, a preheating tank, a hot water preheater, a steam preheater and a second circulation pump, the feed port of the hot water preheater is connected to the waste acid pipeline to be treated, the discharge port of the hot water preheater is connected to the inlet of the preheating tank, the circulation port of the preheating tank is connected to the inlet of the second circulation pump, the outlet of the second circulation pump is connected to the feed port of the steam preheater, the discharge port of the steam preheater is connected to the inlet of the preheating tank, the heat medium inlet of the steam preheater is connected to the raw steam pipeline, the condensate outlet of the steam preheater and the outlet of the condensate tank are both connected to the hot water tank, and the water outlet of the hot water tank is connected to the heat medium inlet of the hot water preheater. By collecting the condensate generated during the operation of the system into the hot water tank and using it as a heat source for the hot water preheater to preheat the waste acid, the energy utilization rate is increased and the energy consumption is reduced.

[0008] Furthermore, the waste acid pipeline to be treated is connected with a mixing tank, and the discharge port of the evaporator is connected with the mixing tank through a circulation pipeline. By introducing the concentrated high-temperature 50% waste acid into the mixing tank to mix with 20% to 25% waste acid, the concentration of the waste acid before entering the preheating equipment is increased, so that the waste acid precipitates ferrous sulfate monohydrate and calcium sulfate to precipitate solid large particles before entering the MVR heating evaporation equipment, avoiding the slow precipitation of metal salts in the waste acid and adhering to the inner wall of the hot water preheater pipeline to form scale, affecting the heat exchange efficiency.

[0009] Furthermore, the circulation pipeline is connected to a shunt pipeline, which is connected to the preheating tank, and the bottom of the preheating tank is connected to the filtering device. After the waste acid enters the preheating tank, under high temperature and high concentration conditions, ferrous sulfate monohydrate and calcium sulfate of the waste acid are further precipitated in large quantities, and metatitanic acid crystals are also precipitated. The crystalline solid particles are precipitated at the bottom of the preheating tank and then extracted to the filtering device for solid-liquid separation. In the continuous concentration process of the waste acid, scaling of the inner wall of the pipeline can be effectively avoided, and there is no need to stop the machine for descaling and maintenance, which effectively improves the operating efficiency.

[0010] The present invention also provides a method for concentrating waste acid of titanium dioxide produced by a sulfuric acid process, which uses the above-mentioned waste acid concentrating system of titanium dioxide produced by a sulfuric acid process to concentrate 20% to 25% of the waste acid, comprising the following steps:

[0011] S1. Start the MVR heating evaporation equipment and the vacuum equipment, and sequentially pass the waste acid to be treated into the hot water preheater and the steam preheater on the preheating equipment for preheating. The waste acid is circulated and preheated in the steam preheater and the preheating tank by the second circulation pump until the preheating temperature reaches the set temperature;

[0012] S2, the waste acid reaching the set temperature is sent to the heater through the discharge pump for heating, the heated waste acid is sent to the evaporator for evaporation and concentration, and the first circulation pump is used for circulating heating and evaporation during evaporation and concentration, until the waste acid concentration reaches 50-55% of the process requirement, and is sent to the cooling and maturation equipment, the waste acid with a temperature of 100-105° C. is cooled to below 55° C., and the waste acid after maturation and cooling is sent back to the titanium dioxide production leaching process for recycling;

[0013] S3. In the initial stage of operation, the steam preheater and the heater need to continuously pass saturated raw steam through the raw steam pipeline to heat the waste acid. The condensed water produced by the steam preheater and the heater enters the hot water tank and is used to pass into the hot water preheater to preheat the waste acid.

[0014] S4. During the start-up operation, the secondary acidic steam generated by evaporation of the evaporator is introduced into the alkali washing tower and sprayed with alkaline water with a temperature of 85-95°C and a pH value of 8-12 for cleaning. The neutral steam obtained after separation treatment in the first gas-liquid separator enters the steam compressor for pressurization and temperature increase, and is then sent to the heater for heating the waste acid.

[0015] S5. During the start-up operation, the non-condensable gas generated by the heater and the condensed water tank is pumped to the condenser for cooling. The cooled gas enters the second gas-liquid separator and the vacuum tank in turn and is discharged through the exhaust port of the vacuum pump. The condensed water generated in the condenser, the second gas-liquid separator and the first gas-liquid separator enters the liquid seal tank.

[0016] S6. During the start-up process, when the system's feed rate, water evaporation rate, and discharge rate are balanced, and the system's pressure, temperature, and discharge concentration are stable, gradually close the steam valve of the saturated raw steam that enters the steam preheater and heater through the raw steam pipeline.

[0017] Furthermore, in step S6, the system has a waste acid feed rate of 5 to 6 t / h, a water evaporation rate of 3 t / h, a waste acid discharge rate of 2.5 to 3.0 t / h, a vacuum degree of 50 to 80 KPa, a waste acid discharge concentration of 50% to 55%, a waste acid feed temperature of 25°C, a waste acid discharge temperature below 55°C, a hot water preheating temperature of 40°C to 55°C, a preheating tank control temperature of 75°C to 85°C, and an MVR heating evaporation equipment operating liquid temperature of 100°C to 105°C.

[0018] Furthermore, during the start-up operation, a part of the waste acid with a concentration of 50% to 55% coming out of the evaporator is sent back to the mixing tank through the circulation pipeline to be mixed with the waste acid with a concentration of 20% to 25%, so that the concentration of the waste acid is adjusted to 33%, and a part of calcium sulfate and ferrous sulfate monohydrate solid large-particle crystals are precipitated, and the solid large-particle crystals mixed with the waste acid are sent to the hot water preheater for preheating.

[0019] Furthermore, during the start-up process, the waste acid with a concentration of 50% to 55% in the circulation pipeline is sent into the preheating tank through the diversion pipeline, the waste acid concentration in the preheating tank is adjusted to 38%, and the precipitate at the bottom of the preheating tank is led out to the filtering equipment to filter out the large solid particle crystals.

[0020] The beneficial effects of the present invention include: by pumping the secondary steam generated in the circulating heating and evaporation process in the MVR heating and evaporation equipment to the steam compressor for re-pressurization and temperature increase, the secondary steam is recycled as a heating heat source for the heater; the forced circulation action of the first circulating pump effectively solves the problem of easy clogging of the heater; by recycling the condensed water generated in the production process of the MVR heating and evaporation equipment and using it to preheat the waste acid, the steam consumption is effectively reduced, and only about 0.13 tons of steam are consumed for each ton of 50% acid produced; and the entire system has a short process flow, low power consumption, and low production cost, which effectively achieves the goals of energy conservation and emission reduction, cost reduction and efficiency improvement, and environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a process flow chart of the sulfuric acid process titanium dioxide waste acid concentration system in an embodiment of the present invention.

[0022] Figure 2 It is a flow chart of the method for concentrating waste acid of titanium dioxide produced by sulfuric acid process in an embodiment of the present invention.

[0023] Figure numerals: 1 cooling and maturing equipment; 2 pipeline for waste acid to be treated; 3 heater; 4 evaporator; 5 steam compressor; 6 first circulation pump; 7 raw steam pipeline; 8 condensate tank; 9 alkali washing tower; 10 first gas-liquid separator; 11 liquid seal tank; 12 alkali water tank; 13 spray pump; 14 vacuum pump; 15 vacuum tank; 16 second gas-liquid separator; 17 condenser; 18 hot water tank; 19 preheating tank; 20 hot water preheater; 21 steam preheater; 22 second circulation pump; 23 circulation pipeline; 24 filtering equipment; 25 diversion pipeline; 26 mixing tank; 27 hot water pump; 28 feed pump; 29 discharge pump; 30 high-pressure pump; 31 finished product pump. DETAILED DESCRIPTION

[0024] In order to make the technical problems, technical solutions and beneficial effects to be solved by the embodiments of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0025] It should be noted that when a component is referred to as being "fixed to" or "disposed on" another component, it can be directly on the other component or indirectly on the other component. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or indirectly connected to the other element. In addition, connection can be used for both fixing and circuit connection.

[0026] It should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0027] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the embodiments of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0028] Example 1

[0029] See also Figure 1 and Figure 2The sulfuric acid method titanium dioxide waste acid concentration system disclosed in the present invention comprises a preheating device, an MVR heating evaporation device, a cooling and maturing device 1 and a vacuum device. The preheating inlet of the preheating device is connected to the waste acid pipeline 2 to be treated, and is used to inject 20% to 25% of the waste acid into the preheating device at a certain flow rate for preheating. The waste acid with a feed temperature of 25°C reaches a temperature of 75°C to 85°C after two-stage preheating. The preheating outlet of the preheating device is connected to the feed inlet of the MVR heating evaporation device, and the preheated waste acid is sent to the MVR heating evaporation device for heating and evaporation for concentration. The discharge port of the MVR heating evaporation device is connected to the inlet of the cooling and maturing device 1. The concentrated waste acid is sent to the cooling and maturing device 1 for cooling and maturation, and then sent back to the titanium dioxide production leaching. The process is recycled, the vacuum equipment is connected with the MVR heating evaporation equipment and provides a vacuum working environment with a vacuum degree of 50-80KPa for the MVR heating evaporation equipment, the MVR heating evaporation equipment includes a heater 3, an evaporator 4, a steam compressor 5 and a first circulation pump 6, the feed port of the heater 3 is connected with the outlet of the first circulation pump 6, the discharge port of the heater 3 is connected with the feed port of the evaporator 4, the discharge port of the evaporator 4 is connected with the cooling and maturation equipment 1, the preheating outlet of the preheating equipment and the circulation port of the evaporator 4 are both connected to the inlet of the first circulation pump 6, the gas-liquid outlet of the evaporator 4 is connected with the inlet of the steam compressor 5, the outlet of the steam compressor 5 and the external raw steam pipeline 7 are both connected to the heat medium inlet of the heater 3, the heater The cold medium outlet of 3 is connected to the condensed water tank 8. Specifically, the vacuum equipment includes a vacuum pump 14, a vacuum tank 15, a second gas-liquid separator 16 and a condenser 17. The air suction port of the vacuum pump 14 is connected to the air outlet of the vacuum tank 15, the air inlet of the vacuum tank 15 is connected to the gas outlet of the second gas-liquid separator 16, the liquid outlet of the second gas-liquid separator 16 is connected to the liquid sealing groove 11, the inlet of the second gas-liquid separator 16 is connected to the gas outlet of the condenser 17, the gas inlet of the condenser 17 is connected to the heater 3 and the condensed water tank 8 respectively, the liquid outlet of the condenser 17 is connected to the liquid sealing groove 11, the non-condensable gas generated in the heater 3 and the condensed water tank 8 is cooled by the condenser 17 and separated by the second gas-liquid separator 16, so that the waste acid reaches To the boiling state, the gas enters the vacuum tank 15 for buffering and then enters the exhaust port of the vacuum pump 14 for discharge. In this process, in order to ensure the vacuum balance of the system, the generated condensed water enters the liquid seal tank 11 to ensure that the vacuum degree of the system is maintained stable in the range of 50-80KPa. The preheating equipment includes a hot water tank 18, a preheating tank 19, a hot water preheater 20, a steam preheater 21 and a second circulating pump 22. The feed port of the hot water preheater 20 is connected to the waste acid pipeline 2 to be treated, the discharge port of the hot water preheater 20 is connected to the inlet of the preheating tank 19, the circulation port of the preheating tank 19 is connected to the inlet of the second circulating pump 22, the outlet of the second circulating pump 22 is connected to the feed port of the steam preheater 21, and the discharge port of the steam preheater 21 is connected to the inlet of the preheating tank 19.The heat medium inlet of the steam preheater 21 is connected to the raw steam pipeline 7, the condensate outlet of the steam preheater 21 and the condensate outlet of the condensate tank 8 are both connected to the hot water tank 18, the water outlet of the hot water tank 18 is connected to the heat medium inlet of the hot water preheater 20, the hot water tank 18 collects the condensed hot water generated in the process of heating the waste acid by the steam preheater 21 and the heater 3, the collected condensed hot water has a temperature of 60-70°C, and then is pumped into the hot water preheater 20 by the hot water pump 27 to perform the first stage preheating of the waste acid, the waste acid is heated to 40-50°C in the hot water preheater 20 and then enters the preheating tank 19, the waste acid in the preheating tank 19 is pumped into the steam preheater 21 through the second circulation pump 22 to perform the second stage preheating of the waste acid, when the feed liquid temperature rises to a temperature close to the boiling point of 50% dilute sulfuric acid, it is pumped into the first circulation pump 6 inlet of the MVR heating evaporation equipment through the feed pump 28 and enters the heater 3 for Heating, the waste acid is heated and evaporated through the heater 3 and the evaporator 4 under the forced circulation of the first circulation pump 6, until the concentration of the feed liquid reaches 50%, and then it is pumped into the cooling and maturation equipment 1 through the discharge pump 29. In this embodiment, the secondary steam generated during the circulating heating and evaporation of the waste acid in the MVR heating and evaporation equipment is pumped to the steam compressor 5 for re-pressurization and heating, and then it is used as the heating heat source of the heater 3 for recycling. The steam compressor 5 is a three-stage steam compressor. After the secondary steam is pressurized and heated, it is used as the heating heat source of the heater 3 for recycling. Only about 0.13 tons of steam are consumed for each ton of 50% acid produced. The forced circulation of the first circulation pump 6 can effectively solve the problem of easy clogging of the heater 3. In addition, the process flow of the entire system is short, the power consumption is not high, and the production cost is low, which effectively achieves the goals of energy conservation, emission reduction, cost reduction, efficiency improvement and environmental protection.

[0030] Example 2

[0031] Please continue reading Figure 1 and Figure 2Since the secondary steam generated during the circulating heating and evaporation process in the MVR heating evaporation equipment is acidic steam, in order to avoid the acidic secondary steam from corroding the steam compressor 5 and affecting the working efficiency of the steam compressor 5, this embodiment adds an alkali washing device on the basis of Embodiment 1. The alkali washing device is connected in series between the gas-liquid outlet of the evaporator 4 and the inlet pipeline of the steam compressor 5. The alkali washing device includes an alkali washing tower 9 and a first gas-liquid separator 10. The cleaning inlet of the alkali washing tower 9 is connected to the gas-liquid outlet of the evaporator 4, the cleaning outlet of the alkali washing tower 9 is connected to the inlet of the first gas-liquid separator 10, the steam outlet of the first gas-liquid separator 10 is connected to the inlet of the steam compressor 5, the liquid outlet of the first gas-liquid separator 10 is connected to the liquid seal tank 11, the cleaning liquid inlet and outlet of the alkali washing tower 9 are both connected to the alkaline water tank 12 and circulated alkaline washing is performed through a spray pump 13, and the alkaline water tank 12 is connected to the raw steam pipeline 7. The temperature and pH in the alkaline water tank 12 are controlled in a chain manner to ensure that the liquid alkali temperature is controlled at 85-95°C and the pH is within the range of PH=8-12. The alkaline water is then pumped into the alkaline washing tower 9 through the spray pump 13 to wash the acidic secondary steam. Since the alkaline water temperature is maintained at a high temperature of 85-95°C, the temperature loss of the neutral secondary steam obtained after washing is not large. The secondary steam enters the steam compressor 5 at a higher temperature for efficient pressurization and heating, and is then recycled to the heater 3, which effectively reduces the use of raw steam and improves energy utilization.

[0032] Example 3

[0033] Please continue reading Figure 1 and Figure 2In order to further avoid the problem of blockage of the hot water preheater 20, the steam preheater 21, the heater 3 and the system pipelines, this embodiment adds a mixing tank 26, a circulation pipeline 23 and a shunt pipeline 25 on the basis of Example 2. The waste acid pipeline 2 to be treated is connected with the mixing tank 26, and the discharge port of the evaporator 4 is connected with the mixing tank 26 through the circulation pipeline 23. The circulation pipeline 23 is connected with the shunt pipeline 25, and the shunt pipeline 25 is connected to the preheating tank 19. The bottom of the preheating tank 19 is connected with a filtering device 24, and the filtering device 24 adopts any one or more combinations of a membrane filter, a filter press or a cyclone separator. The high-temperature 50% waste acid that has not been cooled and concentrated is partially diverted and introduced into the mixing tank 26 to be mixed with 20% to 25% waste acid, thereby increasing the concentration of the waste acid before it enters the preheating device. As the concentration of the waste acid increases, the concentration of sulfate ions gradually increases, the common ion effect is enhanced, the dissolution equilibrium of ferrous sulfate ions and calcium sulfate moves in the opposite direction, the solubility of ferrous sulfate monohydrate and calcium sulfate decreases, and part of the ferrous sulfate monohydrate and calcium sulfate precipitate solid large-particle crystals. The solid large-particle crystal mixed waste acid is pumped into the hot water preheater 20 through the high-pressure pump 30 to exchange heat with the hot water in the hot water tank 18. , the solid large particle crystals flow at high speed through the inner wall of the pipe of the hot water preheater 20 without adhesion. Of course, in order to make full use of the heat of the hot water in the hot water tank 18, a hot water preheating circulation pipe can be added to the discharge port of the hot water preheater 20 to send the liquid after hot water preheating back to the mixing tank 26 for circulation preheating; because the metal salts of the waste acid in the mixing tank 26 at the current concentration have been partially precipitated and crystallized, the maximum heat exchange temperature of the hot water preheater 20 is 55°C. Under this maximum temperature condition, although the concentration of calcium sulfate will continue to decrease and precipitate crystals, the change gradient is small (calcium sulfate is greatly affected by sulfuric acid concentration and temperature). The concentration of ferrous sulfate changes less (although temperature affects the concentration of ferrous sulfate, the concentration has a greater impact), while the concentration of titanyl sulfate remains unchanged (temperature will not affect the hydrolysis of titanyl sulfate to generate metatitanic acid or saturation and precipitation), which avoids the slow precipitation of metal salts in the waste acid and adhesion to the inner wall of the pipeline to form scale; after the solid large particles of ferrous sulfate monohydrate and calcium sulfate precipitated and the waste acid enter the preheating tank 19, as the temperature continues to rise (75°C-85°C), and the concentrated high-temperature 50% waste acid part directly enters the preheating tank 19 through the diversion pipe 25, the waste acid concentration continues to increase, under high temperature and high concentration conditions Under the above conditions, most of the ferrous sulfate monohydrate and calcium sulfate in the waste acid continue to precipitate in large quantities. At the same time, the ferrous sulfate monohydrate and calcium sulfate crystals serve as seeds, which reduce the temperature at which titanyl sulfate hydrolyzes and increase the hydrolysis rate of titanyl sulfate, causing titanyl sulfate to hydrolyze and generate metatitanic acid crystals that precipitate. The precipitated solid particles are deposited at the bottom of the preheating tank 19. The preheating tank 19 is a vertical flow sedimentation tank structure. The solid particles are precipitated at the bottom and then pumped out to the filtration equipment 24 for solid-liquid separation. In the continuous concentration process of the waste acid, scaling of the inner wall of the pipeline can be effectively avoided, and there is no need to stop for descaling and maintenance, thereby effectively improving the operating efficiency.

[0034] Example 4

[0035] Please continue reading Figure 1 and Figure 2 The method for concentrating waste acid of titanium dioxide produced by sulfuric acid process disclosed in this embodiment uses the waste acid concentrating system of titanium dioxide produced by sulfuric acid process in Examples 1 to 3 to concentrate 20% to 25% of waste acid, and comprises the following steps:

[0036] S1, start the MVR heating evaporation equipment and the vacuum equipment, and pass the waste acid to be treated into the hot water preheater 20 and the steam preheater 21 on the preheating equipment in turn for preheating, and the waste acid is circulated and preheated in the steam preheater 21 and the preheating tank 19 by the second circulation pump 22 until the preheating temperature reaches the set temperature (75°C-85°C); during the preheating start-up operation, a part of the waste acid with a concentration of 50% to 55% coming out of the evaporator 4 is sent back to the mixing tank 26 through the circulation pipeline 23 to be mixed with the waste acid with a concentration of 20% to 25% in the waste acid pipeline 2 to be treated in the mixing tank 26. The waste acid concentration is adjusted to 33%. At a relatively low temperature, as the waste acid concentration increases, the sulfate ion concentration gradually increases in the mixing tank 26, the common ion effect is enhanced, the dissolution equilibrium of ferrous sulfate ions and calcium sulfate moves inversely, the solubility of ferrous sulfate monohydrate and calcium sulfate decreases, and some of the ferrous sulfate monohydrate and calcium sulfate precipitate solid large-particle crystals. The solid phase generated by the agglomeration of the solid large-particle crystals is suspended in the solution and is pumped into the hot water preheater 20 by the high-pressure pump 30 to exchange heat with the hot water in the hot water tank 18. The solid large-particle crystals flow at a high speed through the pipe of the hot water preheater 20. After preheating in the hot water preheater 20, part of the waste acid enters the preheating tank 19, and part of it is continuously forced to circulate between the hot water preheater 20 and the mixing tank 26. The waste acid with a concentration of 50% to 55% in the circulation pipeline 23 is sent to the preheating tank 19 through the shunt pipeline 25, and the waste acid concentration in the preheating tank 19 is adjusted to 38%. The second circulation pump 22 continuously circulates and heats the waste acid between the preheating tank 19 and the steam preheater 21, so that the temperature in the preheating tank 19 is controlled to 75°C-85°C. Most of the ferrous sulfate monohydrate and calcium sulfate in the waste acid continue to precipitate in large quantities, and at the same time, the ferrous sulfate monohydrate Iron and calcium sulfate crystals are used as seeds, which reduce the temperature at which titanyl sulfate hydrolyzes and increase the hydrolysis rate of titanyl sulfate, causing titanyl sulfate to hydrolyze and generate metatitanic acid crystals. The precipitated solid particles are deposited at the bottom of the preheating tank 19, and then extracted to the filtration equipment 24 for solid-liquid separation. The solid titanium dioxide contained in the original waste acid causes the metatitanic acid particles generated by the hydrolysis of soluble titanium at high temperature and high concentration. It is easy to agglomerate with the crystallized ferrous sulfate and calcium sulfate to form solid phases during system operation or start-up and shutdown. The solid phase has a density difference with the solution and is suspended in the solution, resulting in blockage of some tubes. Therefore, before the waste acid enters the MVR heating evaporation equipment, it is necessary to remove the solid titanium dioxide and other sulfates in the waste acid to the maximum extent, which can effectively avoid scaling of the inner wall of the pipeline during the continuous concentration of the waste acid, and there is no need to stop the system for descaling and maintenance, which effectively improves the operation efficiency.

[0037] S2, the waste acid reaching the set temperature is sent to the heater 3 through the discharge pump for heating, and the heated waste acid is sent to the evaporator 4 for evaporation and concentration. During evaporation and concentration, the first circulation pump 6 is used for forced circulation heating and evaporation to avoid easy blockage of the heater 3; until the waste acid concentration reaches 50-55% of the process requirement, it is sent to the cooling and aging equipment 1, and the waste acid with a temperature of 100-105° C. is cooled to below 55° C. The waste acid after aging and cooling is sent back to the titanium dioxide production leaching process for recycling through the finished product pump 31;

[0038] S3. In the initial stage of operation, the steam preheater 21 and the heater 3 need to continuously pass saturated raw steam through the raw steam pipeline 7 to heat the waste acid. The condensed water produced by the steam preheater 21 and the heater 3 enters the hot water tank 18 and is used to pass into the hot water preheater 20 to preheat the waste acid.

[0039] S4. During the start-up operation, the secondary acidic steam generated by evaporation of the evaporator 4 is introduced into the alkali washing tower 9 and sprayed with alkaline water with a temperature of 85-95°C and a pH value of 8-12 for washing. The neutral steam obtained after separation treatment by the first gas-liquid separator 10 enters the steam compressor 5 for pressurization and temperature increase, and then is sent to the heater 3 for heating the waste acid; the secondary acidic steam is converted into neutral secondary steam by alkali washing to avoid acidic steam corrosion of the steam compressor 5. The temperature of the alkaline water by alkali washing is maintained at 85-95°C and the pH value is in the range of PH=8-12 to avoid the alkali washing process affecting the temperature of the secondary steam and causing the intake temperature of the steam compressor 5 to decrease. The secondary steam is pressurized and heated by the three-stage steam compressor 5 and used as a heating heat source for the heater 3 to recycle the steam. Only about 0.13 tons of steam are consumed to produce 1 ton of 50% acid, effectively reducing the production cost.

[0040] S5. During the start-up operation, the non-condensable gas generated by the heater 3 and the condensed water tank 8 is pumped to the condenser 17 for cooling. The cooled gas enters the second gas-liquid separator 16 and the vacuum tank 15 in turn and is discharged through the exhaust port of the vacuum pump 14. The condensed water generated in the condenser 17, the second gas-liquid separator 16 and the first gas-liquid separator 10 enters the liquid seal tank 11 to ensure the vacuum pressure balance of the system.

[0041] S6. During the start-up process, when the system's feed rate, water evaporation rate, and discharge rate are in balance, and the system's pressure, temperature, and discharge concentration are stable, gradually close the steam valve of the saturated live steam entering the steam preheater 21 and the heater 3 through the live steam pipeline 7. The system's waste acid feed rate is 5-6 t / h, water evaporation rate is 3 t / h, waste acid discharge rate is 2.5-3.0 t / h, vacuum degree is 50-80 KPa, waste acid discharge concentration is 50%-55%, waste acid feed temperature is 25°C, waste acid discharge temperature is below 55°C, hot water preheating temperature is 40°C-55°C, preheating tank 19 control temperature is 75°C-85°C, and MVR heating evaporation equipment operating liquid temperature is 100°C-105°C.

[0042] The applicant completed the sulfuric acid titanium dioxide waste acid concentration and put it into production in November 2023. The system design capacity is: daily consumption of 23% waste acid 160t / d, output of 50% waste acid 74t / d. The device will be in operation until June 2024, and the actual capacity is as follows:

[0043]

[0044] The system has been running continuously for 7 months, with an actual operating efficiency of about 90%, basically meeting the design conditions.

[0045] The above content is a further detailed description of the present invention in combination with specific / preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, without departing from the concept of the present invention, they can also make several substitutions or modifications to these described embodiments, and these substitutions or modifications should be regarded as belonging to the protection scope of the present invention. In the description of this specification, the description of reference terms "an embodiment", "some embodiments", "preferred embodiments", "examples", "specific examples" or "some examples" means that the specific features, structures, materials or characteristics described in combination with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily target the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In the absence of mutual contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples. Although the embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions and modifications can be made herein without departing from the scope of protection of the patent application.

Claims

1. A sulfuric acid process titanium dioxide waste acid concentration system, characterized in that: The invention comprises a preheating device, an MVR heating evaporation device, a cooling and maturation device and a vacuum device, wherein the preheating inlet of the preheating device is connected to the waste acid pipeline to be treated, the preheating outlet of the preheating device is connected to the feed inlet of the MVR heating evaporation device, the discharge port of the MVR heating evaporation device is connected to the inlet of the cooling and maturation device, the vacuum device is connected to the MVR heating evaporation device and provides a vacuum working environment for the MVR heating evaporation device, the MVR heating evaporation device comprises a heater, an evaporator, a steam compressor and a first circulating pump, the feed inlet of the heater is connected to the outlet of the first circulating pump, the discharge port of the heater is connected to the feed inlet of the evaporator, the discharge port of the evaporator is connected to the cooling and maturation device, the preheating outlet of the preheating device and the circulation port of the evaporator are both connected to the inlet of the first circulating pump, the gas-liquid outlet of the evaporator is connected to the inlet of the steam compressor, the outlet of the steam compressor and the external raw steam pipeline are both connected to the hot medium inlet of the heater, and the cold medium outlet of the heater is connected to the condensed water tank.

2. The sulfuric acid process titanium dioxide waste acid concentration system according to claim 1, characterized in that: It also includes an alkali washing device, which is connected in series with the gas-liquid outlet of the evaporator and the inlet pipeline of the steam compressor. The alkali washing device includes an alkali washing tower and a first gas-liquid separator. The cleaning inlet of the alkali washing tower is connected to the gas-liquid outlet of the evaporator, the cleaning outlet of the alkali washing tower is connected to the inlet of the first gas-liquid separator, the steam outlet of the first gas-liquid separator is connected to the inlet of the steam compressor, the liquid outlet of the first gas-liquid separator is connected to a liquid seal tank, the cleaning liquid inlet and outlet of the alkali washing tower are both connected to an alkaline water tank and circulated alkaline washing is performed through a spray pump, and the alkaline water tank is connected to the raw steam pipeline.

3. The sulfuric acid process titanium dioxide waste acid concentration system according to claim 2, characterized in that: The vacuum equipment includes a vacuum pump, a vacuum tank, a second gas-liquid separator and a condenser. The vacuum port of the vacuum pump is connected to the gas outlet of the vacuum tank, the gas inlet of the vacuum tank is connected to the gas outlet of the second gas-liquid separator, the liquid outlet of the second gas-liquid separator is connected to the liquid seal groove, the inlet of the second gas-liquid separator is connected to the gas outlet of the condenser, the gas inlet of the condenser is respectively connected to the heater and the condensed water tank, and the liquid outlet of the condenser is connected to the liquid seal groove.

4. The sulfuric acid process titanium dioxide waste acid concentration system according to claim 3, characterized in that: The preheating equipment includes a hot water tank, a preheating tank, a hot water preheater, a steam preheater and a second circulation pump. The feed port of the hot water preheater is connected to the waste acid pipeline to be treated, the discharge port of the hot water preheater is connected to the inlet of the preheating tank, the circulation port of the preheating tank is connected to the inlet of the second circulation pump, the outlet of the second circulation pump is connected to the feed port of the steam preheater, the discharge port of the steam preheater is connected to the inlet of the preheating tank, the heat medium inlet of the steam preheater is connected to the raw steam pipeline, the condensate outlet of the steam preheater and the outlet of the condensate tank are both connected to the hot water tank, and the water outlet of the hot water tank is connected to the heat medium inlet of the hot water preheater.

5. The sulfuric acid process titanium dioxide waste acid concentration system according to claim 4, characterized in that: The waste acid pipeline to be treated is connected with a mixing tank, and the discharge port of the evaporator is connected with the mixing tank through a circulation pipeline.

6. The sulfuric acid process titanium dioxide waste acid concentration system according to claim 5, characterized in that: The circulation pipeline is connected with a diversion pipeline, the diversion pipeline is connected to the preheating tank, and the bottom of the preheating tank is connected to the filtering equipment.

7. A method for concentrating waste acid from titanium dioxide produced by a sulfuric acid process, characterized in that: The sulfuric acid process titanium dioxide waste acid concentration system according to any one of claims 1 to 6 is used to concentrate 20% to 25% of the waste acid, comprising the following steps: S1. Start the MVR heating evaporation equipment and the vacuum equipment, and sequentially pass the waste acid to be treated into the hot water preheater and the steam preheater on the preheating equipment for preheating. The waste acid is circulated and preheated in the steam preheater and the preheating tank by the second circulation pump until the preheating temperature reaches the set temperature; S2, the waste acid reaching the set temperature is sent to the heater through the discharge pump for heating, the heated waste acid is sent to the evaporator for evaporation and concentration, and the first circulation pump is used for circulating heating and evaporation during evaporation and concentration, until the waste acid concentration reaches 50-55% of the process requirement, and is sent to the cooling and maturation equipment, the waste acid with a temperature of 100-105° C. is cooled to below 55° C., and the waste acid after maturation and cooling is sent back to the titanium dioxide production leaching process for recycling; S3. In the initial stage of operation, the steam preheater and the heater need to continuously pass saturated raw steam through the raw steam pipeline to heat the waste acid. The condensed water produced by the steam preheater and the heater enters the hot water tank and is used to pass into the hot water preheater to preheat the waste acid. S4. During the start-up operation, the secondary acidic steam generated by evaporation of the evaporator is introduced into the alkali washing tower and sprayed with alkaline water with a temperature of 85-95°C and a pH value of 8-12 for cleaning. The neutral steam obtained after separation treatment in the first gas-liquid separator enters the steam compressor for pressurization and temperature increase, and is then sent to the heater for heating the waste acid. S5. During the start-up operation, the non-condensable gas generated by the heater and the condensed water tank is pumped to the condenser for cooling. The cooled gas enters the second gas-liquid separator and the vacuum tank in turn and is discharged through the exhaust port of the vacuum pump. The condensed water generated in the condenser, the second gas-liquid separator and the first gas-liquid separator enters the liquid seal tank. S6. During the start-up process, when the system's feed rate, water evaporation rate, and discharge rate are balanced, and the system's pressure, temperature, and discharge concentration are stable, gradually close the steam valve that allows saturated raw steam to enter the steam preheater and heater through the raw steam pipeline.

8. The method for concentrating waste acid of titanium dioxide produced by sulfuric acid process as claimed in claim 7, characterized in that: In step S6, the system has a waste acid feed rate of 5-6 t / h, a water evaporation rate of 3 t / h, a waste acid discharge rate of 2.5-3.0 t / h, a vacuum degree of 50-80 KPa, a waste acid discharge concentration of 50%-55%, a waste acid feed temperature of 25°C, a waste acid discharge temperature below 55°C, a hot water preheating temperature of 40°C-55°C, a preheating tank control temperature of 75°C-85°C, and an MVR heating evaporation equipment operating liquid temperature of 100°C-105°C.

9. The method for concentrating waste acid of titanium dioxide produced by sulfuric acid process as claimed in claim 8, characterized in that: During the start-up process, part of the waste acid with a concentration of 50% to 55% coming out of the evaporator is sent back to the mixing tank through a circulation pipeline to be mixed with the waste acid with a concentration of 20% to 25%, so that the waste acid concentration is adjusted to 33%, and part of the solid large-particle crystals of calcium sulfate and ferrous sulfate monohydrate are precipitated. The solid large-particle crystals mixed with the waste acid are sent to the hot water preheater for preheating.

10. The method for concentrating waste acid of titanium dioxide produced by sulfuric acid process as claimed in claim 9, characterized in that: During the start-up process, the waste acid with a concentration of 50% to 55% in the circulation pipeline is sent to the preheating tank through the diversion pipeline, the waste acid concentration in the preheating tank is adjusted to 38%, and the sediment deposited at the bottom of the preheating tank is led out to the filtering equipment to filter out the large solid particles.

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