System for producing caustic soda

Abstract

The utility model relates to the technical field of caustic soda production process devices, in particular to a system for producing caustic soda, which comprises a crude salt preparation unit, a primary brine preparation unit, a secondary refined brine preparation unit, an electrolysis unit, an evaporation unit, a brine preparation unit, a chlorine hydrogen treatment unit and a hydrochloric acid synthesis unit, the caustic soda solutions with different mass concentrations are obtained on the same production line, the solid flaky caustic soda is obtained at the same time, and byproducts such as chlorine, hydrogen, hydrochloric acid, sodium hypochlorite and mirabilite with recycling value are obtained; according to the utility model, the salt dissolving water preparation unit is reasonably and orderly communicated with the other units, and materials such as waste water generated by each unit are recycled, so that the purposes of energy conservation and efficiency improvement are achieved.

Description

Technical Field

[0001] This utility model relates to the technical field of caustic soda production process equipment, and in particular to a system for producing caustic soda. Background Technology

[0002] Caustic soda, scientifically known as sodium hydroxide, is an inorganic compound with the chemical formula NaOH. Along with soda ash, caustic soda is one of the "three acids and two alkalis" in the chemical industry, belonging to the salt chemical industry and being one of the foundational industries of modern industry. As an important basic raw material, caustic soda has a wide range of downstream applications, mainly including alumina, chemical fibers, chemicals, papermaking and dyeing, food industry, glass, and water treatment. Caustic soda production processes include the causticization method and the electrolysis method. The electrolysis method can be further divided into the mercury method, the diaphragm method, and the ion exchange membrane method. The ion exchange membrane method is the mainstream production method in the world today, accounting for approximately 99%. However, the existing ion exchange membrane method suffers from high energy consumption and high cost, and these are technical problems that urgently need to be solved. Utility Model Content

[0003] To solve the above-mentioned technical problems, this utility model provides a system for producing caustic soda, including a raw salt preparation unit, a primary brine preparation unit, a secondary refined brine preparation unit, an electrolysis unit, an evaporation unit, a brine preparation unit, a chlorine hydrogen treatment unit, and a hydrochloric acid synthesis unit.

[0004] The primary brine preparation unit includes a magnesium ion removal unit, a calcium ion removal unit, and a ceramic membrane filtration unit.

[0005] The ceramic membrane filtration unit includes a ceramic membrane filter, wherein the membrane used in the ceramic membrane filter is a tubular ceramic membrane, and the tubular ceramic membrane has annularly distributed membrane pores on its axial cross-section, and the diameter of the membrane pores is 40-50 nm.

[0006] The electrolysis unit and the evaporation unit are used to prepare a caustic soda solution with a mass content of 30-62% and caustic soda flakes with a mass content of 98-99%.

[0007] The brine preparation unit is connected to the raw salt preparation unit, the primary brine preparation unit, the secondary refined brine preparation unit, the electrolysis unit, and the evaporation unit, respectively. It is used to receive wastewater generated from the primary brine preparation unit, the secondary refined brine preparation unit, the electrolysis unit, and the evaporation unit, and to prepare brine from the wastewater as raw material in the brine preparation unit. The brine is then sent to the raw salt preparation unit for salt preparation.

[0008] Furthermore, the porosity of the tubular ceramic membrane is 35-55%.

[0009] Furthermore, the internal flow channel of the tubular ceramic membrane is spiral-shaped, with a pitch of 5-10 mm and a spiral angle of 30-60°.

[0010] Furthermore, the raw salt preparation unit includes a salt treatment tank for obtaining saturated crude brine;

[0011] The salt treatment tank includes a raw salt inlet located above the salt treatment tank, a brine inlet located below the salt treatment tank, and a saturated crude brine outlet.

[0012] In the raw salt preparation unit, raw salt is fed into the salt dissolving tank through the raw salt inlet, and brine is fed into the salt dissolving tank through the brine inlet. The brine and raw salt are contacted countercurrently to dissolve the salt, resulting in the saturated crude brine. The saturated crude brine is then sent to the primary brine preparation unit from the crude brine outlet.

[0013] Furthermore, the raw salt preparation unit also includes a brine heater for heating the brine entering the brine tank, thereby increasing the dissolution rate of the raw salt and improving production efficiency.

[0014] Furthermore, a filter device is also provided at the outlet of the crude brine to prevent unmelted raw salt from entering other units and affecting subsequent processes.

[0015] Furthermore, the primary brine preparation unit is used to obtain primary brine.

[0016] Furthermore, the magnesium ion removal unit includes a sodium hydroxide solution high-level tank and a magnesium ion removal tank;

[0017] The sodium hydroxide solution stored in the high-level sodium hydroxide solution tank is sent to the magnesium ion removal tank, where it reacts with the saturated crude brine that has entered the magnesium ion removal tank. The magnesium ions in the saturated crude brine are removed by generating magnesium hydroxide precipitate, resulting in magnesium-removed crude brine.

[0018] Furthermore, the calcium ion removal unit includes a sodium carbonate solution high-level tank and a calcium ion removal tank;

[0019] The sodium carbonate solution stored in the high-level sodium carbonate solution tank is sent to the calcium ion removal tank, where it reacts with the magnesium-removed crude brine that has entered the calcium ion removal tank. The calcium ions in the magnesium-removed crude brine are removed by generating calcium carbonate precipitate, thus obtaining refined brine.

[0020] Furthermore, the magnesium ion removal unit and / or the calcium ion removal unit also include a precipitation filtration device for filtering the precipitate generated during the reaction, the precipitate including magnesium hydroxide and / or calcium carbonate.

[0021] Furthermore, the pore size selection of the membrane pore structure in the ceramic membrane filtration unit can effectively trap impurities such as suspended solids, colloids, and microorganisms in the refined brine, and even has a good trapping effect on some nano-sized particles, thereby reducing the turbidity of the refined brine and providing high-quality primary brine for subsequent electrolysis processes.

[0022] Furthermore, in order to ensure the high filtration capacity and low filtration resistance of the tubular ceramic membrane filter, it is necessary to perform chemical regeneration every 3-12 months using hydrochloric acid with a mass content of 15%.

[0023] Furthermore, the slurry produced by the ceramic membrane filter is discharged into a slurry tank and then fed into a plate and frame filter press. After filtration, the filtrate and filter cake are obtained. The filtrate is then sent as a raw material for brine preparation to the brine preparation unit to prepare the brine.

[0024] Furthermore, the secondary refined brine preparation unit includes at least one ion exchange resin tower to further reduce the metal ion content in the primary brine, thereby obtaining secondary refined brine.

[0025] Furthermore, the number of ion exchange resin towers is three, with two connected in series during use and the third used for regeneration;

[0026] The content of each metal ion in the secondary brine is less than or equal to 20 wtppb, and the metal ions include, but are not limited to, magnesium ions and calcium ions.

[0027] Furthermore, the secondary refined brine preparation unit also includes a brine heater for heat exchange between the primary brine and / or the secondary refined brine during operation, utilizing and / or recovering the energy therein.

[0028] Furthermore, after each ion exchange resin tower operates at full load for 24 hours, the ion exchange resin needs to be regenerated using ion exchange membrane caustic soda and hydrochloric acid. After regeneration, waste brine, acidic wastewater and / or alkaline wastewater are discharged.

[0029] The waste brine enters the waste brine storage tank through a resin collector, and is then sent to the brine preparation unit as raw material for the brine preparation.

[0030] The acidic and / or alkaline wastewater is sent to a neutralization and equalization tank for neutralization before being discharged.

[0031] Furthermore, the electrolysis unit includes an electrolytic cell for electrolyzing the secondary refined brine to generate brine and chlorine gas in the anode region and a first caustic soda solution and hydrogen gas in the cathode region.

[0032] Furthermore, the electrolysis unit also includes a hydrochloric acid addition device for adding hydrochloric acid to the anode region to reduce the oxygen content of the generated chlorine gas.

[0033] Furthermore, the electrolysis unit also includes an anolyte separator for separating the brine and wet chlorine gas generated in the anode region;

[0034] The brine is sent as a raw material for the brine preparation unit to prepare the brine.

[0035] The dry basis purity of the wet chlorine gas is 98.5-99.0 vol.

[0036] Furthermore, the electrolysis unit also includes a cathode liquid cooler, which uses cooling water to cool the first caustic soda solution generated in the cathode region.

[0037] Furthermore, the electrolysis unit also includes a cathode liquid separator for separating the first caustic soda solution and wet hydrogen gas generated in the cathode region;

[0038] The mass content of the first sodium hydroxide solution is 30-35%;

[0039] The dry basis purity of the wet hydrogen gas is greater than or equal to 99.9 vol.

[0040] Furthermore, the evaporation unit includes one or more of the following: a triple-effect evaporator, a double-effect evaporator, a single-effect evaporator, a falling film concentrator, and a final concentrator, to obtain caustic soda solutions and / or solid flake caustic soda with different mass contents.

[0041] Furthermore, the first caustic soda solution is evaporated in the triple-effect evaporator to obtain a second caustic soda solution, the second caustic soda solution having a mass content of 36-37%.

[0042] Furthermore, the second caustic soda solution is evaporated in the double-effect evaporator to obtain a third caustic soda solution, the third caustic soda solution having a mass content of 40-43%.

[0043] Furthermore, the third caustic soda solution is evaporated in the single-effect evaporator to obtain a fourth caustic soda solution, the fourth caustic soda solution having a mass content of 50-55%.

[0044] Furthermore, the fourth caustic soda solution is pre-concentrated in the falling film concentrator to obtain a fifth caustic soda solution, the fifth caustic soda solution having a mass content of 60-62%.

[0045] Furthermore, the fifth caustic soda solution is heated with hot salt in the final concentrator to obtain flake caustic soda, the flake caustic soda having a mass content of 98-99%.

[0046] Furthermore, the final concentrator includes, but is not limited to, a molten salt furnace.

[0047] Furthermore, the condensate generated during the evaporation and / or concentration process of the evaporation unit is sent as raw material for the brine to the brine preparation unit to prepare the brine.

[0048] Furthermore, the brine preparation unit is connected to the raw salt preparation unit, the primary brine preparation unit, the secondary refined brine preparation unit, the electrolysis unit, and the evaporation unit to recover brine raw materials from each unit except the raw salt preparation unit, and send them to the raw salt preparation unit for use after treatment including but not limited to dechlorination and denitrification, thereby achieving the effects of recycling and cost saving.

[0049] Furthermore, the brine preparation unit includes a dechlorination unit and a denitrification unit.

[0050] Furthermore, the dechlorination unit includes a dechlorination brine tank and / or a dechlorination tower;

[0051] Sodium sulfite is added to the brine raw material in the dechlorinated brine tank to remove free chlorine from the brine raw material and produce dechlorinated brine containing sulfate ions;

[0052] And / or the brine raw material is added from the top of the dechlorination tower, and the free chlorine in the brine raw material is extracted by the dechlorination vacuum pump to obtain wet chlorine gas, which is then sent to the chlorine-hydrogen treatment unit.

[0053] Furthermore, the denitrification unit includes a membrane denitrification device for denitrifying the dechlorinated brine. The resulting permeate is sent as brine to the raw salt preparation unit for preparing saturated crude brine. The resulting concentrate is used to recover sodium sulfate and denitrified brine through a refrigeration denitrification device. The denitrified brine is sent as brine to the raw salt preparation unit for preparing saturated crude brine.

[0054] Furthermore, the brine preparation unit also includes a brine storage tank for storing the brine.

[0055] Furthermore, the brine preparation unit also includes at least one filtration device for filtering solid particles contained in the substances produced by each unit.

[0056] Furthermore, the brine preparation unit also includes online monitoring instruments to ensure the indicators of the brine.

[0057] Furthermore, in the caustic soda production system, materials are transported between each other via pumps and / or pipelines.

[0058] Furthermore, the chlorine-hydrogen treatment unit includes a chlorine treatment unit and a hydrogen treatment unit.

[0059] Furthermore, the chlorine treatment unit is connected to the electrolysis unit and / or the brine preparation unit to dry the wet chlorine gas.

[0060] Furthermore, the chlorine treatment unit includes one or more of the following: a chlorine scrubbing tower, a titanium tube cooler, a first water mist collector, a primary packed drying tower, a secondary packed drying tower, a bubble cap tower, an acid mist collector, and a chlorine compressor.

[0061] Further, the wet chlorine gas is washed and cooled to 40-45°C with chlorine water in the chlorine scrubbing tower, then enters the titanium tube cooler and is cooled to 15°C with chilled water at 5-7°C. After removing condensate droplets from the wet chlorine gas by the first water mist collector, it sequentially enters the primary packed drying tower and the secondary packed drying tower, where sulfuric acid is sprayed from the top of the tower to dry the chlorine gas again. The sulfuric acid used has a mass content of 75%. The dried chlorine gas is then further dried in the bubble cap tower with concentrated sulfuric acid with a mass content of 98%, so that the water content of the dried chlorine gas exiting the tower is less than 20 ppm. After the dried chlorine gas passes through the acid mist collector to remove acid mist droplets, it enters the chlorine compressor to obtain chlorine gas.

[0062] Furthermore, the hydrogen processing unit is connected to the electrolysis unit to dry the wet hydrogen.

[0063] Furthermore, the hydrogen processing unit includes one or more of the following: a hydrogen scrubbing tower, a hydrogen compressor, a hydrogen cooler, and a second water mist collector.

[0064] Furthermore, the wet hydrogen gas is directly sprayed and cooled to 30-45°C by the hydrogen scrubbing tower, compressed by the hydrogen compressor, cooled by 5°C water in the hydrogen cooler, and then obtained as hydrogen gas by the second water mist collector.

[0065] Furthermore, the hydrochloric acid synthesis unit includes a four-in-one hydrochloric acid synthesis furnace.

[0066] Furthermore, chlorine and hydrogen from the chlorine-hydrogen treatment unit generate hydrogen chloride gas in the four-in-one hydrochloric acid synthesis furnace, while steam is produced as a byproduct.

[0067] Furthermore, the pressure of the steam is 0.2-0.6 MPa, and the steam generation is calculated based on 0.65 tons of low-pressure steam generated from 1 ton of hydrogen chloride.

[0068] Furthermore, the system for producing caustic soda also includes a chlorine liquefaction unit.

[0069] Furthermore, the chlorine liquefaction unit is connected to the chlorine hydrogen treatment unit.

[0070] Furthermore, the chlorine liquefaction unit includes a chlorine liquefaction tank.

[0071] Furthermore, the chlorine gas enters the chlorine liquefaction tank, where the refrigeration unit liquefies the chlorine gas.

[0072] Furthermore, the refrigerant used in the refrigeration unit includes, but is not limited to, Freon.

[0073] Furthermore, the system for producing caustic soda also includes a sodium hypochlorite preparation unit.

[0074] Furthermore, the sodium hypochlorite preparation unit is connected to the chlorine hydrogen treatment unit and / or chlorine liquefaction unit to process the chlorine-containing tail gas generated by the chlorine hydrogen treatment unit and / or chlorine liquefaction unit to produce sodium hypochlorite.

[0075] The beneficial effects of this utility model are as follows:

[0076] 1. This utility model discloses a system for producing caustic soda, comprising a raw salt preparation unit, a primary brine preparation unit, a secondary refined brine preparation unit, an electrolysis unit, an evaporation unit, a brine preparation unit, a chlorine treatment unit, and a hydrochloric acid synthesis unit. In the primary brine preparation unit, a tubular ceramic membrane with a pore size of 40-50 nm is specifically selected to filter the refined brine, effectively trapping suspended solids, colloids, microorganisms, and other impurities, and even showing good trapping effect on some nano-sized particles, thereby reducing the turbidity of the refined brine and preparing it for subsequent electrolysis. The process provides high-quality primary brine, which, in conjunction with other units and specific connection sequences of components, enables the production line to obtain caustic soda solutions with different and precise mass contents (e.g., mass contents of 30-35%, 36-37%, 40-43%, 50-55%, 60-62%). These solutions can be used for different industrial production needs. Simultaneously, solid flake caustic soda (mass content of 98-99%) can be obtained, making it easier to store, and byproducts such as chlorine, hydrogen, hydrochloric acid, sodium hypochlorite, and sodium sulfate, which have recycling value, can also be obtained.

[0077] 2. In the caustic soda production system, the present invention specifically selects a tubular ceramic membrane with a pore size of 45-50nm. Compared with other filtration methods in the prior art, the tubular ceramic membrane has better chemical stability, thermal stability and mechanical strength, and can more effectively remove impurities in brine, improve the brine purification effect, thereby improving the quality of caustic soda products and reducing production costs.

[0078] 3. The brine preparation unit in this utility model is rationally and orderly connected with the other units. Multiple units, such as the raw salt preparation unit and the brine preparation unit, are combined with a specific primary brine preparation unit (including a specific ceramic membrane filtration unit) to form an organic whole. The units cooperate and work together to achieve a more efficient and stable caustic soda production process. At the same time, the brine preparation unit can also recycle the wastewater generated by each unit as brine raw material, achieving the purpose of energy saving and efficiency improvement. Attached Figure Description

[0079] Figure 1 This is a schematic diagram of the system for producing caustic soda according to this utility model;

[0080] Figure 2 This is a schematic diagram of the structure of the tubular ceramic membrane of this utility model;

[0081] Figure 3 This is a schematic diagram of the internal flow channel of this utility model.

[0082] The labels in the diagram are:

[0083] 1. Raw salt preparation unit; 2. Primary brine preparation unit; 3. Secondary refined brine preparation unit; 4. Electrolysis unit; 5. Evaporation unit; 6. Chemical brine preparation unit; 7. Chlorine hydrogen treatment unit; 8. Hydrochloric acid synthesis unit; 9. Chlorine liquefaction unit; 10. Sodium hypochlorite preparation unit; 11. Tubular ceramic membrane; 12. Membrane pores; 13. Internal flow channel. Detailed Implementation

[0084] Example 1

[0085] like Figure 1 As shown, this embodiment provides a system for producing caustic soda, including a raw salt preparation unit 1, a primary brine preparation unit 2, a secondary refined brine preparation unit 3, an electrolysis unit 4, an evaporation unit 5, a brine preparation unit 6, a chlorine hydrogen treatment unit 7, and a hydrochloric acid synthesis unit 8.

[0086] The primary brine preparation unit 2 includes a magnesium ion removal unit, a calcium ion removal unit, and a ceramic membrane filtration unit.

[0087] The ceramic membrane filtration unit includes a ceramic membrane filter, and the membrane used in the ceramic membrane filter is a tubular ceramic membrane. The tubular ceramic membrane has a uniform membrane pore structure. In this embodiment, as shown... Figure 2 As shown, the pore size 12 of the tubular ceramic membrane 11 is 40-45 nm. In some embodiments, the pore size 12 of the tubular ceramic membrane 11 is 45-50 nm or between 40-50 nm.

[0088] The pore size selection of the membrane structure in the ceramic membrane filtration unit can effectively trap impurities such as suspended solids, colloids, and microorganisms in the refined brine, and even has a good trapping effect on some nano-sized particles, thereby reducing the turbidity of the refined brine and providing high-quality primary brine for subsequent electrolysis processes.

[0089] To ensure the high filtration capacity and low filtration resistance of the ceramic membrane filter, it needs to be chemically regenerated every 6 months using hydrochloric acid with a mass content of 15%, or regenerated periodically according to actual production needs, in order to extend the life of the tubular ceramic membrane.

[0090] The tubular ceramic membrane has a porosity of 55%. The porosity, in conjunction with the membrane pores 12, can precisely control the passage of molecules or particles, and can effectively intercept or allow the passage of target substances of specific particle sizes, thereby enabling the ceramic membrane filtration unit to achieve good separation, purification, and filtration effects.

[0091] like Figure 3 As shown, in some embodiments, the internal flow channel 13 of the tubular ceramic membrane 11 is spiral-shaped with a pitch of 8 mm and a spiral angle of 40°. The spiral flow channel causes the fluid to rotate and twist when flowing in the internal flow channel 13, resulting in more thorough mixing and exchange between fluids at different locations. Compared to a direct-flow channel, this spiral structure can effectively break the laminar boundary layer of the fluid, causing stronger turbulence in both the radial and axial directions, thereby improving mass transfer efficiency and making the mass transfer between different substances during the separation process more efficient, which helps to improve the separation effect. Furthermore, the spiral internal flow channel 13 extends the flow path of the fluid in the membrane, increasing the residence time of the fluid in the membrane. This provides more time for the separation process, which is beneficial for the interaction between the solute and the membrane surface, improving the separation effect. This enables the ceramic membrane filtration unit to have higher filtration efficiency, further improving the purity of the brine, and thus enabling subsequent units to meet the requirements of precise concentration for preparing caustic soda.

[0092] The brine preparation unit 6 is connected to the raw salt preparation unit 1, the primary brine preparation unit 2, the secondary refined brine preparation unit 3, the electrolysis unit 4, and the evaporation unit 5, respectively. It is used to receive wastewater generated from the primary brine preparation unit 2, the secondary refined brine preparation unit 3, the electrolysis unit 4, and the evaporation unit 5, and to prepare brine from the wastewater as raw material in the brine preparation unit 6. The brine is then sent to the raw salt preparation unit 1 for salt preparation.

[0093] The raw salt preparation unit 1 includes a salt treatment tank for obtaining saturated crude brine;

[0094] The salt treatment tank includes a raw salt inlet located above the salt treatment tank, a brine inlet located below the salt treatment tank, and a saturated crude brine outlet.

[0095] In the raw salt preparation unit 1, raw salt is added into the salt dissolving tank through the raw salt inlet, and brine is introduced into the salt dissolving tank through the brine inlet. The brine and raw salt are in countercurrent contact to dissolve the salt, resulting in the saturated crude brine. The saturated crude brine is sent to the primary brine preparation unit from the crude brine outlet.

[0096] The raw salt preparation unit 1 also includes a brine heater for heating the brine entering the brine tank, thereby increasing the dissolution rate of the raw salt and improving production efficiency.

[0097] In this embodiment, a filter device is also provided at the crude brine outlet to prevent unmelted raw salt from entering other units and affecting subsequent processes.

[0098] The primary brine preparation unit 2 is used to obtain primary brine.

[0099] The magnesium ion removal unit includes a sodium hydroxide solution high-level tank and a magnesium ion removal tank.

[0100] A 32% sodium hydroxide solution stored in the high-level sodium hydroxide solution tank is sent to the magnesium ion removal tank, where it reacts with the saturated crude brine entering the tank to remove magnesium ions from the saturated crude brine by generating magnesium hydroxide precipitate, thus obtaining magnesium-removed crude brine. In some embodiments, the mass content of the sodium hydroxide solution can be adjusted according to actual production conditions.

[0101] The calcium ion removal unit includes a sodium carbonate solution high-level tank and a calcium ion removal tank.

[0102] The saturated sodium carbonate solution stored in the high-level sodium carbonate solution tank is sent to the calcium ion removal tank, where it reacts with the magnesium-removed crude brine that has entered the calcium ion removal tank. Calcium ions in the saturated crude brine are removed by forming calcium carbonate precipitate, yielding refined brine. In some embodiments, the mass content of the sodium carbonate solution can be adjusted according to actual production conditions.

[0103] In this embodiment, the sodium carbonate used meets the requirements of GB / T 210-2022.

[0104] The magnesium ion removal unit and the calcium ion removal unit also include a precipitation filtration device for filtering the precipitate generated during the reaction. In this embodiment, the precipitate includes magnesium hydroxide and calcium carbonate.

[0105] The slurry produced by the ceramic membrane filter is discharged into a slurry tank and then pumped into a plate and frame filter press. After filtration, the filtrate and filter cake are obtained. The filtrate is then sent as a raw material for brine preparation to the brine preparation unit 6 to prepare the brine.

[0106] In this embodiment, the secondary refined brine preparation unit 3 includes three ion exchange resin towers to further reduce the metal ion content in the primary brine to obtain secondary refined brine. During use, two towers are connected in series, and the third tower is used for regeneration. In some embodiments, the number of ion exchange resin towers can be adjusted according to actual production needs.

[0107] The content of each metal ion in the secondary brine is less than or equal to 20 wtppb, and the metal ions include, but are not limited to, magnesium ions and calcium ions.

[0108] The secondary refined brine preparation unit 3 further includes a brine heater for heat exchange between the primary brine and / or the secondary refined brine during operation, utilizing and / or recovering the energy therein.

[0109] Each of the ion exchange resin towers needs to be regenerated with ion exchange membrane caustic soda and hydrochloric acid after 24 hours of full-load operation. After regeneration, waste brine, acidic wastewater and / or alkaline wastewater are discharged.

[0110] The waste brine enters the waste brine storage tank via a resin collector, and is then sent to the brine preparation unit 6 as raw material for brine preparation to prepare the brine.

[0111] The acidic and / or alkaline wastewater is sent to a neutralization and equalization tank for neutralization before being discharged.

[0112] The electrolysis unit 4 includes an electrolytic cell, which electrolyzes the secondary refined brine to generate brine and chlorine gas in the anode region and a first caustic soda solution and hydrogen gas in the cathode region.

[0113] The electrolysis unit 4 also includes a hydrochloric acid addition device for adding hydrochloric acid to the anode region to reduce the oxygen content of the generated chlorine gas.

[0114] The electrolysis unit 4 also includes an anolyte separator for separating the brine and wet chlorine gas generated in the anode region;

[0115] The brine is sent as a raw material for ionized water to the ionized water preparation unit 6 to prepare the ionized water.

[0116] The dry basis purity of the wet chlorine gas is 98.5 vol.

[0117] The electrolysis unit 4 also includes a cathode liquid cooler, which uses cooling water to cool the first caustic soda solution generated in the cathode region.

[0118] The electrolysis unit 4 also includes a cathode liquid separator for separating the first caustic soda solution and wet hydrogen gas generated in the cathode region;

[0119] The mass content of the first sodium hydroxide solution is 32%;

[0120] The dry basis purity of the wet hydrogen gas is 99.9 vol.

[0121] In this embodiment, the first caustic soda solution can also be partially recycled back to the high-level tank of sodium hydroxide solution for the removal of magnesium ions.

[0122] The evaporation unit 5 includes a triple-effect evaporator, a double-effect evaporator, a single-effect evaporator, a falling film concentrator, and a final concentrator. In this embodiment, it is used to obtain caustic soda solutions with different mass contents and solid flake caustic soda.

[0123] The first caustic soda solution is evaporated in the triple-effect evaporator to obtain a second caustic soda solution, the second caustic soda solution having a mass content of 36.8%.

[0124] The second caustic soda solution is evaporated in the double-effect evaporator to obtain a third caustic soda solution, the third caustic soda solution having a mass content of 42%.

[0125] The third caustic soda solution is evaporated in the single-effect evaporator to obtain a fourth caustic soda solution, the fourth caustic soda solution having a mass content of 50%.

[0126] The fourth caustic soda solution is pre-concentrated in the falling film concentrator to obtain the fifth caustic soda solution, the fifth caustic soda solution having a mass content of 61%.

[0127] The fifth caustic soda solution is heated with hot salt in the final concentrator molten salt furnace to obtain flake caustic soda, the flake caustic soda having a mass content of 98%.

[0128] The condensate generated during the evaporation and concentration process in the evaporation unit is sent as raw material for the brine preparation unit 6 to prepare the brine.

[0129] The brine preparation unit 6 is connected to the raw salt preparation unit 1, the primary brine preparation unit 2, the secondary refined brine preparation unit 3, the electrolysis unit 4, and the evaporation unit 5. It is used to recover the brine raw materials in each unit except the raw salt preparation unit 1, and after treatment including but not limited to dechlorination and denitrification, it is sent to the raw salt preparation unit 1 for use, so as to achieve the functions of recycling and cost saving.

[0130] The brine preparation unit 6 includes a dechlorination unit and a denitrification unit.

[0131] The dechlorination unit includes a dechlorination tower;

[0132] The brine raw material is added from the top of the dechlorination tower, and the free chlorine in the brine is extracted by the dechlorination vacuum pump to obtain wet chlorine gas, which is then sent to the chlorine-hydrogen treatment unit 7.

[0133] In some embodiments, the dechlorination unit further includes a dechlorination brine tank, into which sodium sulfite is added to the brine raw material to remove free chlorine from the brine and produce dechlorinated brine containing sulfate.

[0134] In this embodiment, the sodium sulfite used meets the requirements of GB 1886.8 2015.

[0135] The denitrification unit includes a membrane denitrification device for denitrifying the dechlorinated brine. The resulting permeate is sent as brine to the raw salt preparation unit for preparing saturated crude brine. The concentrate is used to recover sodium sulfate and denitrified brine through a refrigeration denitrification device. The denitrified brine is sent as brine to the raw salt preparation unit for preparing saturated crude brine.

[0136] The brine preparation unit 6 also includes a brine storage tank for storing the brine.

[0137] In this embodiment, the brine preparation unit 6 further includes a filtration device for filtering solid particles contained in the substances produced by each device. In some embodiments, the number of filtration devices can be adjusted according to filtration needs.

[0138] The brine preparation unit 6 also includes online monitoring instruments to ensure the various indicators of the brine.

[0139] In this embodiment, the caustic soda production system uses pumps and pipelines to transport the various materials between each other.

[0140] The chlorine-hydrogen treatment unit 7 includes a chlorine treatment unit and a hydrogen treatment unit.

[0141] The chlorine treatment unit 7 is connected to the electrolysis unit 4 and the brine preparation unit 6 to dry the wet chlorine gas.

[0142] The chlorine treatment unit 7 includes a chlorine scrubbing tower, a titanium tube cooler, a first water mist collector, a primary packed drying tower, a secondary packed drying tower, a bubble cap tower, an acid mist collector, and a chlorine compressor.

[0143] The wet chlorine gas is washed and cooled to 45°C with chlorine water in the chlorine scrubbing tower, then enters the titanium tube cooler and is cooled to 15°C with chilled water at 6°C. After removing condensate droplets from the wet chlorine gas by the first water mist collector, it sequentially enters the primary packed drying tower and the secondary packed drying tower, where sulfuric acid is sprayed from the top of the tower to dry the chlorine gas again. The sulfuric acid used has a mass content of 75%. The dried chlorine gas is then further dried in the bubble cap tower with concentrated sulfuric acid with a mass content of 98%, so that the water content of the dried chlorine gas exiting the tower is less than 20 ppm. After the dried chlorine gas passes through the acid mist collector to remove acid mist droplets, it enters the chlorine compressor to obtain chlorine gas.

[0144] In this embodiment, the concentrated sulfuric acid with a mass content of 98% meets the requirements of the national standard GB / T 534-2014; the product parameters of the chlorine gas are shown in Table 1.

[0145] Table 1. Product parameter values ​​for chlorine gas.

[0146]

[0147] The hydrogen processing unit is connected to the electrolysis unit 4 and is used to dry the wet hydrogen.

[0148] The hydrogen processing unit includes a hydrogen scrubbing tower, a hydrogen compressor, a hydrogen cooler, and a second water mist collector.

[0149] The wet hydrogen gas is directly sprayed and cooled to 40°C by the hydrogen scrubbing tower with washing water, then compressed by the hydrogen compressor and cooled with 5°C water in the hydrogen cooler, and finally obtained as hydrogen gas by the second water mist collector.

[0150] The product parameters of the hydrogen are shown in Table 2:

[0151] Table 2. Parameter values ​​of hydrogen gas

[0152]

[0153] The hydrochloric acid synthesis unit 8 includes a four-in-one hydrochloric acid synthesis furnace.

[0154] Chlorine and hydrogen from the chlorine-hydrogen treatment unit 7 are converted into hydrogen chloride gas in the four-in-one hydrochloric acid synthesis furnace, while steam is produced as a byproduct.

[0155] The pressure of the steam is between 0.4 and 0.5 MPa, and the steam generation is calculated as 0.65 tons of low-pressure steam generated from 1 ton of hydrogen chloride.

[0156] In this embodiment, the generated hydrogen chloride gas is dissolved in water to form a hydrochloric acid solution. The product parameter values ​​of the hydrochloric acid solution are shown in Table 3.

[0157] Table 3. Product parameter values ​​for hydrochloric acid solution

[0158]

[0159] In this embodiment, the system for producing caustic soda further includes a chlorine liquefaction unit 9.

[0160] The chlorine liquefaction unit 9 is connected to the chlorine hydrogen treatment unit 7.

[0161] The chlorine liquefaction unit 9 includes a chlorine liquefaction tank.

[0162] The chlorine gas enters the chlorine liquefaction tank, and the refrigeration unit liquefies the chlorine gas to obtain liquid chlorine according to user requirements and the methods recorded in the existing chlorine liquefaction tank operation manual.

[0163] The product parameters of the liquid chlorine are shown in Table 4:

[0164] Table 4 Product Parameter Values ​​for Liquid Chlorine

[0165]

[0166] The refrigeration unit uses Freon as its refrigerant.

[0167] In this embodiment, the system for producing caustic soda further includes a sodium hypochlorite preparation unit 10.

[0168] The sodium hypochlorite preparation unit 10 is connected to the chlorine hydrogen treatment unit 7 and the chlorine gas liquefaction unit 9, and is used to process the chlorine-containing tail gas generated by the chlorine hydrogen treatment unit 7 and the chlorine gas liquefaction unit 9 to produce sodium hypochlorite.

[0169] The product parameters of the sodium hypochlorite are shown in Table 5:

[0170] Table 5 Product Parameters of Sodium Hypochlorite

[0171]

[0172] In addition to the devices in the above system, the three types of waste generated in this embodiment are also equipped with existing waste treatment devices to prevent environmental pollution.

[0173] The system for producing caustic soda in this embodiment specifically selects a tubular ceramic membrane with a pore size of 40-50 nm in the primary brine preparation unit to filter the refined brine. This effectively removes suspended solids, colloids, microorganisms, and other impurities from the refined brine, and even has a good retention effect on some nano-sized particles. This reduces the turbidity of the refined brine, providing high-quality primary brine for subsequent electrolysis processes. Finally, by combining the devices in other units and the specific connection sequence of the devices, the same production line can obtain caustic soda solutions with different and precise mass contents. For example, caustic soda with a mass content of 30-35%, 36-37%, 40-43%, 50-55%, or 60-62% can be used to meet different industrial production needs. It can also produce solid flake caustic soda (mass content of 98-99%), which is easier to store, and produce by-products such as chlorine, hydrogen, hydrochloric acid, sodium hypochlorite, and sodium sulfate with recycling value. Furthermore, the brine preparation unit in this embodiment is rationally and orderly connected with the other units, and the wastewater and other materials generated by each unit are recycled to achieve the purpose of energy saving and efficiency improvement.

[0174] It should be understood that this utility model is not limited to the content already described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this utility model is limited only by the appended claims.

Claims

1. A system for producing caustic soda, characterized by, The system comprises a raw salt preparation unit (1), a primary brine preparation unit (2), a secondary refined brine preparation unit (3), an electrolysis unit (4), an evaporation unit (5), a brine preparation unit (6), a chlorine and hydrogen treatment unit (7), a hydrochloric acid synthesis unit (8); The primary brine preparation unit (2) comprises a magnesium ion removal unit, a calcium ion removal unit and a ceramic membrane filtration unit. The ceramic membrane filtration unit comprises a ceramic membrane filter, wherein the membrane used in the ceramic membrane filter is a tubular ceramic membrane (11), and the tubular ceramic membrane (11) is provided with annularly and uniformly distributed membrane holes (12) in the axial cross section thereof, and the diameter of the membrane holes (12) is 40-50 nm. The brine preparation unit (6) is connected with the raw salt preparation unit (1), the primary brine preparation unit (2), the secondary refined brine preparation unit (3), the electrolysis unit (4) and the evaporation unit (5) respectively.

2. The system for producing caustic soda according to claim 1, characterized by, The raw salt preparation unit (1) comprises a salt dissolving tank.

3. The system for producing caustic soda according to claim 1, characterized by, The secondary refined brine preparation unit (3) comprises at least one ion exchange resin tower.

4. The system for producing caustic soda according to claim 1, characterized by, The electrolysis unit (4) comprises an electrolysis tank.

5. The system for producing caustic soda according to claim 1, characterized by, The evaporation unit (5) comprises one or more of a triple-effect evaporator, a double-effect evaporator, a single-effect evaporator, a falling film concentrator and a final concentrator.

6. The system for producing caustic soda according to claim 1, characterized by, The brine preparation unit (6) comprises a dechlorination unit and a denitration unit.

7. The system for producing caustic soda according to claim 1, characterized by, The chlorine and hydrogen treatment unit (7) comprises a chlorine treatment unit and a hydrogen treatment unit.

8. The system for producing caustic soda according to claim 1, characterized by, The hydrochloric acid synthesis unit (8) comprises a four-in-one hydrochloric acid synthesis furnace.

9. The system for producing caustic soda according to claim 1, characterized by, The system for producing caustic soda further comprises a chlorine liquefaction unit (9).

10. The system for producing caustic soda according to claim 1, characterized by, The system for producing caustic soda further comprises a sodium hypochlorite preparation unit (10).

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