A non-clogging titanium dioxide waste acid concentration device and concentration process

Abstract

The present invention discloses a titanium dioxide waste acid concentration device and concentration process that is not easy to be blocked, including a heat exchanger, the liquid outlet end of the heat exchanger is connected to a flash chamber through a heat exchanger outlet circulation pipe, the upper side of the flash chamber is provided with an evaporation gas extraction port, the bottom is connected to the inlet of an axial flow pump through a central circulation pipe, and the central circulation pipe is provided with a concentrated acid liquid extraction port; the outlet of the axial flow pump is connected to a crystallizer through a pump outlet circulation pipe, the bottom of the crystallizer is provided with an elutriation leg, the crystallizer is provided with a liquid outlet and connected to a dilution mixing chamber through the liquid outlet, the dilution mixing chamber is connected to the liquid inlet end of the heat exchanger, and the dilution mixing chamber is provided with a dilute acid liquid inlet. The present invention has the advantages of not easy to block the equipment, simple treatment process, small increase in workload, low treatment cost, and high concentration of produced acid.

Description

Technical Field

[0001] The invention relates to a titanium dioxide waste acid concentrating device and a concentrating process, in particular to a titanium dioxide waste acid concentrating device and a concentrating process which are not easy to be blocked. Background Art

[0002] In the sulfuric acid method titanium dioxide production process, for every ton of titanium dioxide produced, about 8 tons of waste sulfuric acid with a mass concentration of about 20% will be produced as a by-product; this part of waste acid usually needs to be concentrated before it can be reused.

[0003] The concentration process generally uses the hot flue gas from the titanium dioxide rotary kiln to contact with 20% waste sulfuric acid to concentrate it to about 30%; then it is concentrated to about 70% through a graphite sulfuric acid concentration evaporation heat exchange device for processing and utilization.

[0004] However, since titanium dioxide waste sulfuric acid contains inorganic salts such as FeSO4, Al(SO4)3, MgSO4 and CaSO4, as well as impurities such as TiO2, soluble titanium, calcium, magnesium and ferrous sulfate crystals are easily precipitated during the waste sulfuric acid concentration process, causing scaling and clogging of the graphite heater tube holes, among which the scaling of titanium, calcium and magnesium is even more difficult to remove. Therefore, usually when the concentration device is in operation for about a month, it is necessary to disassemble and clean the heater as a whole, which is a very large workload and seriously affects the normal operation of the waste acid concentration device. Although there are some concentration processes that reduce the concentration of soluble salts in the waste acid by pretreatment, and then send the treated waste acid to the concentration equipment for concentration, thereby reducing the formation of scaling, it will add a lot of additional processes and workload, and increase costs. In addition, if FeSO4 is pretreated and removed in the early stage, soluble salts such as titanium, calcium and magnesium will directly scale on the tube wall of the heat exchanger in the later stage, which is more difficult to clean. Therefore, the scaling problem of the concentration system has not been fundamentally solved, which is one of the bottlenecks restricting the development of the sulfuric acid titanium dioxide industry. Summary of the invention

[0005] The object of the present invention is to provide a titanium dioxide waste acid concentration device and concentration process that is not easy to clog. The present invention has the characteristics of not easy to clog the equipment, simple treatment process, small additional workload, low treatment cost, and high concentration of produced acid.

[0006] The technical solution of the present invention is: a titanium dioxide waste acid concentration device that is not easy to be clogged, comprising a heat exchanger, the liquid outlet end of the heat exchanger is connected to a flash chamber via a heat exchanger outlet circulation pipe, the upper side of the flash chamber is provided with an evaporation gas production port, the bottom is connected to the inlet of an axial flow pump via a central circulation pipe, and the central circulation pipe is provided with a concentrated acid liquid production port; the outlet of the axial flow pump is connected to a crystallization fluidizer via a pump outlet circulation pipe, the bottom of the crystallization fluidizer is provided with an elutriation leg, the crystallization fluidizer is provided with a liquid outlet and is connected to a dilution mixing chamber via the liquid outlet, the dilution mixing chamber is communicated with the liquid inlet end of the heat exchanger, and the dilution mixing chamber is provided with a dilute acid liquid inlet. In this scheme, by setting the dilute acid inlet on the dilution mixing chamber above the crystallizer, the supersaturated liquid separated by the crystallizer can be diluted by adding dilute acid, and the supersaturation of the waste acid liquid entering the heat exchanger is reduced to the maximum extent, making it unsaturated, ensuring that the acid concentration of the waste acid liquid in the heat exchanger is always the lowest concentration value, thereby greatly reducing the crystallization driving force on the tube wall in the heat exchanger, reducing the scaling tendency, and making the equipment less likely to be blocked; at the same time, through the setting of the crystallizer, the solution containing the crystal outflowing from the flash chamber can be further crystallized and grown, so that The crystal size is continuously enlarged, and thus it settles downward and separates under the action of its own weight, thereby achieving the removal of soluble salts, greatly reducing the amount of soluble salts entering the heat exchanger, and slowing down the speed of heat exchanger blockage; in addition, the crystals in this scheme are mainly formed by FeSO4 precipitated when the waste acid temperature is greater than 115°C and the acid concentration is concentrated to 30-34%, and adsorbing other precipitated soluble salts. Therefore, when concentrating the waste acid, this scheme not only does not require pre-treatment of the soluble salt impurities in the waste acid solution in advance, but also reduces the actual effect of this scheme if the pre-treatment is improper. Therefore, when this scheme is implemented specifically, it can not only delay blockage, but also its process is relatively simple, the additional workload is small, and the processing cost is also low.

[0007] In order to enable the crystallization fluidizer to better achieve the purpose of crystallization separation, the aforementioned titanium dioxide waste acid concentration device that is not easy to clog, the crystallization fluidizer is composed of a straight cylindrical fluidized bed and a conical crystallization chamber arranged outside the straight cylindrical fluidized bed in the form of a jacket, the upper end of the conical crystallization chamber is connected to the outer wall of the straight cylindrical fluidized bed, and the lower end exceeds the lower end of the straight cylindrical fluidized bed; the dilution mixing chamber is connected to the top of the straight cylindrical fluidized bed, and the elutriation leg is connected to the bottom of the conical crystallization chamber. Through the crystallization of the straight cylindrical fluidized bed and the downward sedimentation of the crystals driven by the liquid flow, good separation of crystals is achieved.

[0008] In order to further promote the effect of crystallization separation of the crystallization fluidizer, the aforementioned titanium dioxide waste acid concentration device that is not easy to be blocked is provided with a supernatant separation chamber between the crystallization fluidizer and the dilution mixing chamber. The supernatant separation chamber is provided to further promote the sedimentation of the crystals and achieve the purpose of crystallization separation.

[0009] In order to further promote the effect of crystallization separation of the crystallization fluidizer, the aforementioned titanium dioxide waste acid concentration device that is not easy to be blocked, the supernatant separation chamber is a chamber with a smaller caliber than the crystallization fluidizer and the dilution mixing chamber, and the crystallization fluidizer, the supernatant separation chamber and the dilution mixing chamber form an hourglass-shaped structure. Through the setting of the hourglass-shaped structure, the acid liquid naturally hits the inner wall of the chamber and sinks during the upward flow process, thereby achieving the purpose of separating the crystals.

[0010] The aforementioned titanium dioxide waste acid concentration device which is not easy to be clogged, the heat exchanger is a tubular heat exchanger.

[0011] In order to further reduce costs and energy consumption, the aforementioned titanium dioxide waste acid concentration device that is not easy to clog is provided with a heat exchange jacket outside the tube wall of the heat exchanger, and the heat exchange jacket is provided with a cold dilute acid inlet and a preheated dilute acid outlet, and the preheated dilute acid outlet is connected to the dilute acid inlet. The dilute acid is preheated by recovering the heat dissipated to the air by the heat exchanger, thereby achieving energy conservation and emission reduction and reducing costs.

[0012] In order to further avoid scaling and clogging, the aforementioned titanium dioxide waste acid concentration device that is not easy to be clogged has the heat exchanger outlet circulation pipe connected tangentially to the inner chamber of the flash chamber. The tangential connection allows the liquid to form a circulation and flush the inner wall of the chamber, reducing the formation of scaling.

[0013] In order to further avoid scaling and clogging, the aforementioned titanium dioxide waste acid concentration device that is not easy to be clogged has the pump outlet circulation pipe connected tangentially to the inner chamber of the crystallizer fluidizer. The tangential connection allows the liquid to form a circulation and flush the inner wall of the chamber, reducing the formation of scaling.

[0014] A titanium dioxide waste acid concentration process that is not prone to clogging, wherein the dilute waste acid is sent from the dilute acid inlet into the dilution mixing chamber, and then flows through the heat exchanger and the flash chamber in sequence from the dilution mixing chamber for heating, evaporation and exhaust. The concentrated liquid after exhaust is sent to the crystallization fluidizer for crystallization separation under the action of an axial flow pump, and the supernatant is continuously sent through the dilution mixing chamber to the heat exchanger for circulation and concentration until it is concentrated to the required concentration and discharged through the concentrated acid liquid production outlet.

[0015] Beneficial effects of the present invention

[0016] 1. The present invention utilizes the continuous improvement of the temperature and concentration of the acid solution during the concentration process. When the temperature is greater than 115°C and the concentration is concentrated to 30-34%, a large amount of soluble Fe, Ti, Ca and Mg impurities are precipitated. The researchers of the present invention have confirmed through experiments that when there are ferrous sulfate crystals in the system, the above-mentioned soluble Ti, Ca and Mg impurities will be preferentially adsorbed on the ferrous sulfate crystals, and the ferrous sulfate crystals are relatively easier to remove from the system and are not easy to produce scaling. When the Ti, Ca and Mg impurities that are more likely to produce scaling are attached to the ferrous sulfate crystals and discharged from the system through the crystallization fluidizer, the possibility of scaling in the system is greatly reduced, and the formation of scaling is reduced, thereby making the system less likely to be blocked, especially for the blockage of the heat exchanger. It can be seen from this that the system of the present invention, without the need to pre-treat the impurities in the waste acid in advance, utilizes the characteristics of the impurities in the waste acid itself and the process characteristics of the concentration system, realizes the effective separation of impurities, reduces the phenomenon of scaling and blocking, and also saves the process and cost of the waste acid pretreatment.

[0017] 2. The system of the present invention adopts a process of continuously extracting ferrous sulfate crystals along with the process of concentration and evaporation. Different from the traditional process of adopting cooling crystallization to extract ferrous sulfate crystals in advance in the low concentration stage, the system of the present invention can ensure that ferrous sulfate crystals are always precipitated in the waste acid during the concentration process, and use the ferrous sulfate crystals as a carrier for precipitating Ti, Ca and Mg impurities, which greatly reduces the phenomenon of difficult-to-clean soluble Ca and Mg salts being adsorbed on the equipment, thereby effectively reducing the possibility of scaling and clogging.

[0018] 3. The system of the present invention can achieve a balance between the extraction of crystals and concentrated acid during the concentration process, and can also ensure that the equipment is not easily blocked without pre-treating the soluble salt impurities in advance.

[0019] 4. The concentrated acid liquid extraction port of the device of the present invention is arranged at the front end where the raw material dilute acid enters and the rear end where the concentrated acid evaporates, thereby ensuring that the outlet acid concentration is extracted at the highest point of the system acid concentration, which is about 5% higher than the acid concentration extracted by the traditional method of setting it at the rear end of the feed mixing.

[0020] 5. The heat exchanger of the device of the present invention is provided with a heat exchange jacket outside. The raw material dilute acid is injected into the evaporation device after passing through the heat exchange jacket. While preheating the material, the heat loss (generally about 15%) of the high temperature in the heat exchanger directly facing the atmosphere is avoided. This structure of the device can reduce the heat loss of the system to less than 5%, saving energy, reducing consumption and saving costs.

[0021] 6. The present invention arranges the dilute acid inlet on the dilution mixing chamber above the crystallizer. The supersaturated liquid separated by the crystallizer can be diluted by adding the dilute acid, thereby reducing the supersaturation of the waste acid liquid entering the heat exchanger to the maximum extent, making it unsaturated, and ensuring that the acid concentration of the waste acid liquid in the heat exchanger is always at the lowest concentration value, thereby greatly reducing the crystallization driving force on the tube wall in the heat exchanger, reducing the scaling tendency, and making the equipment less likely to be blocked.

[0022] In summary, the present invention has the advantages of being not easy to clog equipment, having a simple treatment process, less additional workload, lower treatment cost, and high produced acid concentration. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Attached Figure 1 It is a structural schematic diagram of the device of the present invention;

[0024] Attached Figure 2 is a cross-sectional view of a crystallization fluidizer of the present invention;

[0025] Attached Figure 3 For attachment Figure 2 AA view before sectioning;

[0026] Attached Figure 4 It is a schematic structural diagram of the supernatant separation chamber of the present invention;

[0027] Attached Figure 5 A bottom view of a crystallization fluidizer according to the present invention;

[0028] Attached Figure 6 It is a structural schematic diagram of the heat exchanger of the present invention;

[0029] Attached Figure 7 For attachment Figure 1 BB view in;

[0030] Explanation of the reference numerals: 1-heat exchanger, 2-heat exchanger outlet circulation pipe, 3-flash chamber, 4-evaporation gas production outlet, 5-central circulation pipe, 6-concentrated acid liquid production outlet, 7-axial flow pump, 8-pump outlet circulation pipe, 9-crystallization fluidizer, 10-elutriation leg, 11-supernatant separation chamber, 12-dilution mixing chamber, 13-dilute acid liquid inlet, 14-conical crystallization chamber, 15-straight cylindrical fluidized bed, 16-heat exchange jacket, 17-cold dilute acid replenishing inlet, 18-preheated dilute acid discharge outlet. DETAILED DESCRIPTION

[0031] The present invention will be further described below in conjunction with the embodiments, but they are not intended to limit the present invention.

[0032] Embodiments of the present invention

[0033] A titanium dioxide waste acid concentration device that is not easy to clog, as shown in the following Figure 1-7 As shown, it includes a heat exchanger 1, the liquid outlet end of the heat exchanger 1 is connected to a flash chamber 3 through a heat exchanger outlet circulation pipe 2, the upper side of the flash chamber 3 is provided with an evaporation gas production port 4, and the bottom is connected to the inlet of an axial flow pump 7 through a central circulation pipe 5, and the central circulation pipe 5 is provided with a concentrated acid liquid production port 6; the outlet of the axial flow pump 7 is connected to a crystallization fluidizer 9 through a pump outlet circulation pipe 8, the bottom of the crystallization fluidizer 9 is provided with an elutriation leg 10, the crystallization fluidizer 9 is provided with a liquid outlet and is connected to a dilution mixing chamber 12 through the liquid outlet, the dilution mixing chamber 12 is connected to the liquid inlet end of the heat exchanger 1, and the dilution mixing chamber 12 is provided with a dilute acid liquid inlet 13.

[0034] The concentration method is as follows: dilute waste acid with a concentration of about 20% is sent from the dilute acid inlet 13 to the dilution mixing chamber 12, and then the dilution mixing chamber 12 flows through the heat exchanger 1 and the flash chamber 3 in sequence for heating, evaporation and exhaust. The concentrated liquid after exhaust is sent to the crystallization fluidizer 9 for crystallization separation under the action of the axial flow pump 7, and the supernatant is continuously sent to the heat exchanger 1 through the dilution mixing chamber 12 for circulation and concentration until it is concentrated to the required concentration and then discharged through the concentrated acid liquid extraction port 6; during the concentration process, new dilute waste acid is continuously fed from the dilute acid inlet 13, and continuous slag is discharged through the elutriation leg 10, thereby achieving the effect of continuous concentration and extraction. When concentrated to the required concentration, the concentrated sulfuric acid can be extracted from the concentrated acid liquid extraction port 6.

[0035] In another embodiment, as shown in the attached Figure 1-7 As shown, the crystallization fluidizer 9 is composed of a straight cylindrical fluidized bed 15 and a conical crystallization chamber 14 which is arranged outside the straight cylindrical fluidized bed 15 in the form of a jacket, the upper end of the conical crystallization chamber 14 is connected to the outer wall of the straight cylindrical fluidized bed 15, and the lower end exceeds the lower end of the straight cylindrical fluidized bed 15; the dilution mixing chamber 12 is connected to the top of the straight cylindrical fluidized bed 15, and the elutriation leg 10 is connected to the bottom of the conical crystallization chamber 14. When the acid liquid is sent into the crystallization fluidizer 9 from the pump outlet circulation pipe 8, it is located between the outer wall of the straight-cylindrical fluidized bed 15 and the inner wall of the conical crystallization chamber 14, and then flows downward before entering the straight-cylindrical fluidized bed 15. During the flow, larger crystals directly settle downward into the bottom of the conical crystallization chamber 14, while smaller crystals continue to grow in the straight-cylindrical fluidized bed 15. When they grow to a certain weight, they naturally fall, thereby completing the crystallization separation of soluble salts. After a certain amount of crystals have settled, the switch under the elutriation leg 10 is turned on to remove the crystals.

[0036] In another embodiment, as shown in the attached Figure 1-7 As shown, a supernatant separation chamber 11 is provided between the crystallization fluidizer 9 and the dilution mixing chamber 12. When the acid solution with smaller crystal particles flows upward into the supernatant separation chamber 11, growth separation continues, and the large crystal particles are settled into the conical crystallization chamber 14.

[0037] In another embodiment, as shown in the attached Figure 1-7 As shown, the supernatant separation chamber 11 is a chamber with a smaller diameter than the crystallization fluidizer 9 and the dilution mixing chamber 12. The crystallization fluidizer 9, the supernatant separation chamber 11 and the dilution mixing chamber 12 form an hourglass-shaped structure. The hourglass-shaped structure makes the flow channel in the middle faster, and a circulation is formed around it. When the suspended crystal particles hit the top cavity wall, they sink rapidly under the action of the circulation, which can further promote the separation of the crystals.

[0038] In another embodiment, as shown in the attached Figure 1-7 As shown, the heat exchanger 1 is a tubular heat exchanger.

[0039] In another embodiment, as shown in the attached Figure 1-7 As shown, a heat exchange jacket 16 is provided outside the tube wall of the heat exchanger 1, and a cold dilute acid replenishment inlet 17 and a preheated dilute acid discharge outlet 18 are provided on the heat exchange jacket 16, and the preheated dilute acid discharge outlet 18 is connected to the dilute acid liquid inlet 13. The newly replenished cold dilute acid (about 25°C) first enters the heat exchange jacket 16 from the cold dilute acid replenishment inlet 17, absorbs the heat emitted by the heat exchanger 1, thereby increasing the temperature, and when discharged from the preheated dilute acid discharge outlet 18, the temperature can be increased to about 70°C.

[0040] In another embodiment, as shown in the attached Figure 1-7 As shown, the heat exchanger outlet circulation pipe 2 is tangentially connected to the inner chamber of the flash chamber 3. The tangential connection means that the outermost side of the flow direction of water in the heat exchanger outlet circulation pipe 2 is tangential to the peripheral surface of the inner chamber of the flash chamber 3, so that the liquid can enter the inner chamber of the flash chamber 3 tangentially, so that it forms a high-speed circulation in the flash chamber 3, thereby flushing the inner chamber wall of the flash chamber 3.

[0041] In another embodiment, as shown in the attached Figure 1-7 As shown, the pump outlet circulation pipe 8 is tangentially connected to the inner chamber of the crystallization fluidizer 9. The specific structure and principle of this embodiment are the same as above.

[0042] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solutions and inventive concepts of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A titanium dioxide waste acid concentration device that is not easy to clog, characterized in that: The invention comprises a heat exchanger (1), wherein the liquid outlet end of the heat exchanger (1) is connected to a flash chamber (3) via a heat exchanger outlet circulation pipe (2), the upper side of the flash chamber (3) is provided with an evaporation gas extraction port (4), and the bottom is connected to the inlet of an axial flow pump (7) via a central circulation pipe (5), and the central circulation pipe (5) is provided with a concentrated acid liquid extraction port (6); the outlet of the axial flow pump (7) is connected to a crystallization fluidizer (9) via a pump outlet circulation pipe (8), the bottom of the crystallization fluidizer (9) is provided with an elutriation leg (10), the crystallization fluidizer (9) is provided with a liquid outlet and is connected to a dilution mixing chamber (12) via the liquid outlet, and the dilution mixing chamber (12) is provided with a liquid outlet. The mixing chamber (12) is connected to the liquid inlet end of the heat exchanger (1), and a dilute acid liquid inlet (13) is provided on the dilution mixing chamber (12); the crystallization fluidizer (9) is composed of a straight cylindrical fluidized bed (15) and a conical crystallization chamber (14) arranged outside the straight cylindrical fluidized bed (15) in the form of a jacket, the upper end of the conical crystallization chamber (14) is connected to the outer wall of the straight cylindrical fluidized bed (15), and the lower end exceeds the lower end of the straight cylindrical fluidized bed (15); the dilution mixing chamber (12) is connected to the top of the straight cylindrical fluidized bed (15), and the elutriation leg (10) is connected to the bottom of the conical crystallization chamber (14); A supernatant separation chamber (11) is provided between the crystallization fluidizer (9) and the dilution mixing chamber (12); The supernatant separation chamber (11) is a chamber with a smaller caliber than the crystallization fluidizer (9) and the dilution mixing chamber (12); the crystallization fluidizer (9), the supernatant separation chamber (11) and the dilution mixing chamber (12) form an hourglass-shaped structure; The heat exchanger (1) is a tubular heat exchanger. A heat exchange jacket (16) is provided outside the tube wall of the heat exchanger (1). A cold dilute acid inlet (17) and a preheated dilute acid outlet (18) are provided on the heat exchange jacket (16). The preheated dilute acid outlet (18) is connected to the dilute acid inlet (13).

2. The non-clogging titanium dioxide waste acid concentration device according to claim 1, characterized in that: The heat exchanger outlet circulation pipe (2) is tangentially connected to the inner chamber of the flash chamber (3).

3. The non-clogging titanium dioxide waste acid concentration device according to claim 1, characterized in that: The pump outlet circulation pipe (8) is tangentially connected to the inner chamber of the crystallization fluidizer (9).

4. A process for concentrating titanium dioxide waste acid using the device according to claim 1, characterized in that: The dilute waste acid is fed into the dilution mixing chamber (12) from the dilution mixing chamber (13), and then flows through the heat exchanger (1) and the flash chamber (3) in sequence from the dilution mixing chamber (12) to be heated, evaporated and exhausted. The concentrated liquid after exhausting steam is fed into the crystallization fluidizer (9) for crystallization separation under the action of the axial flow pump (7). The supernatant liquid is continuously fed into the heat exchanger (1) through the dilution mixing chamber (12) for circulation and concentration until it is concentrated to the required concentration and then discharged through the concentrated acid liquid extraction port (6).

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