A method for preparing ammonium sulfate and co-producing sodium bicarbonate by using sodium sulfate

Abstract

The present application relates to the technical field of ammonia compound preparation, in particular to a method for preparing ammonium sulfate and co-producing sodium bicarbonate by using sodium sulfate, comprising the following steps: mixing industrial-grade liquid ammonia with deionized water to prepare ammonia water with a free ammonia concentration of 60-120 ti (ti is the abbreviation of titer, which is 1 / 20 mol / L), controlling the temperature of the mixing process to be less than or equal to 40 DEG C to avoid ammonia volatilization, pre-carbonizing by passing in CO2 under the conditions of 20-70 DEG C and a carbon dioxide pressure of 0.1-0.6 MPa, and adding sodium sulfate or a mixture of sodium bicarbonate and mirabilite to obtain a pre-carbonized liquid. The present application adopts an integrated process of pre-carbonization, clarification, carbonization, ammonia separation and low-temperature crystallization, and ammonia evaporation circulation, and can be operated continuously or intermittently, has low industrial implementation difficulty, strong running stability, separates ammonium sulfate by using ammonia separation and low-temperature crystallization technology, replaces the traditional evaporation and concentration process, combines material recycling design, and reduces the energy consumption per unit product compared with the traditional process.

Description

Technical Field

[0001] This invention relates to the field of ammonia compound preparation technology, specifically a method for preparing ammonium sulfate and co-producing sodium bicarbonate using sodium sulfate. Background Technology

[0002] To achieve the resource utilization of sodium sulfate, various processes for preparing ammonium sulfate and co-producing sodium bicarbonate from sodium sulfate have been developed in the existing technology. However, these processes generally have prominent drawbacks: For example, the process disclosed in CN104355326A, which uses sodium sulfate solution or carrier to co-produce soda ash and ammonium sulfate through thermal cycling, employs a metathesis method combined with multiple high-temperature deammoniation, evaporation concentration, and cooling crystallization. This process is complex, energy-intensive, and has low utilization rates of sodium ions and sulfate ions, and has not yet been industrialized. Another example is the pure sodium sulfate solution disclosed in CN87104642. The alkaline solid-phase production process requires cooling and crystallization at extremely low temperatures of -5℃ to -2℃, resulting in extremely high energy consumption and low overall yield, with sulfate utilization rate of only about 25%. The traditional evaporation method for separating ammonium sulfate is prone to forming double salts, leading to product contamination, and its energy consumption remains high. In addition, a process CN105000579A, which uses a sodium sulfate-type brine thermal cycle method to co-produce soda ash and ammonium chloride, recovers ammonia through lime, but the ammonia recovery rate is only about 50%, and it also generates a large amount of low-value calcium sulfate solid waste, which can easily cause secondary pollution.

[0003] Based on this, the present invention provides a method for preparing ammonium sulfate and co-producing sodium bicarbonate using sodium sulfate, so as to solve the above-mentioned technical problems. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing ammonium sulfate and co-producing sodium bicarbonate using sodium sulfate, thereby solving the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] This invention proposes a method for preparing ammonium sulfate and co-producing sodium bicarbonate using sodium sulfate, comprising the following steps:

[0007] S1. Prepare ammonia solution with a free ammonia concentration (FNH3) of 60-120 ti (1 ti = 1 / 20 molar concentration) by mixing industrial-grade liquid ammonia with deionized water. Control the temperature ≤40℃ during the mixing process to avoid ammonia volatilization. Pre-carbonize the solution by introducing CO2 at 20~70℃ and carbon dioxide pressure 0.1~0.6MPa to obtain a pre-carbonized solution with FNH3=60-120 ti, CO2=20~60 ti, and specific gravity d=1.1. The purity of CO2 during the pre-carbonization process is ≥99.0%, and the preparation time of the pre-carbonized solution is 2-3h to ensure that CO2 is fully dissolved.

[0008] S2. Heat the pre-carbonized liquid obtained in step S1 to 35-45℃, add the raw materials at a ratio of 150-450g sodium sulfate or a mixture of recovered sodium sulfate and ammonium carbonate per liter of solution, stir and dissolve to obtain an ammonia-nitrate solution with the composition of FNH3=60-120ti, CO2=20~60ti, and d=1.1;

[0009] S3. Pump the ammonia nitrate solution obtained in step S2 to a clarification tank, control the temperature inside the tank at 35-45℃ and the residence time at 2-4h, remove suspended solids and precipitate calcium and magnesium ion impurities. The sludge at the bottom of the clarification tank is washed and mixed with coal and sent to the boiler for combustion to obtain a qualified clarified liquid with the following composition: FNH3=85g / L, CO2=110g / L, Na2SO4=320g / L, (NH4)2SO4=8-160g / L.

[0010] S4. The clarified liquid obtained in step S3 is continuously or intermittently fed into the carbonization tower. Fresh CO2 is mixed with CO2 recovered from the sodium bicarbonate calcination furnace and introduced from the bottom of the carbonization tower. The reaction temperature in the middle section of the carbonization tower is controlled at 58~65℃, the temperature in the upper section at 38~52℃, and the temperature at the bottom section at 35~40℃. The pressure inside the tower is maintained at 0.35MPa (3.5atm). The ammonia-sodium ratio (A / S) of the reaction system is controlled at 0.8~1.25 to generate a suspension containing sodium bicarbonate crystals.

[0011] S5. The suspension obtained in step S4 is sent to a filtration device to separate sodium bicarbonate solid and filtrate mother liquor. The sodium bicarbonate solid is washed 2-3 times and then sent to a calcining furnace.

[0012] S6. After dissolving and separating the double salt (Na2SO4・(NH4)2SO4・4H2O) in the mother liquor obtained in step S5, cool it to -10~-5℃ at a cooling rate of 5-8℃ / h to precipitate a mixed salt of Na2SO4・10H2O and NH4HCO3. After filtration and separation, the mixed salt is recycled to step S2 for dissolving sodium sulfate.

[0013] S7. Pass the mother liquor after separating the mixed salt in step S6 into an ammonia absorption tower and pass ammonia gas until the FNH3 in the system reaches 100~140ti. Then cool it to -5℃ to precipitate the double salt (Na2SO4・(NH4)2SO4・4H2O). Filter to separate the double salt. Dissolve the double salt in the mother liquor filtered in step S5 to increase the concentration of sodium sulfate and ammonium sulfate in the mother liquor.

[0014] S8. Continue to pass ammonia gas through the mother liquor filtered in step S7 until FNH3>230ti, cool to 30℃, filter to precipitate ammonium sulfate solid, send it into a saturated ammonium sulfate solution to wash away free ammonia, and then dry after centrifugation to obtain the ammonium sulfate product.

[0015] S9. The mother liquor after filtering ammonium sulfate in step S8 is sent to the ammonia stripping tower, heated to remove ammonia gas and sent to the ammonia absorption tower in step S7 for recycling. The mother liquor after ammonia stripping is pumped to the pre-carbonization tower in step S1 to participate in the pre-carbonization reaction.

[0016] S10. The sodium bicarbonate solid washed in step S5 is calcined at 180°C to obtain soda ash product. The tail gas and sludge generated in each step are treated in an environmentally friendly manner. The purity of the product and the reaction conversion rate are tested regularly, and the process parameters are adjusted based on the test results to achieve stable circulation.

[0017] Preferably, the sodium sulfate used in step S2 is industrial-grade anhydrous sodium sulfate (purity ≥98.5%) or the mixed salt recovered in step S6. The stirring speed during dissolution is 80-120 r / min, and the dissolution time is 1-1.5 h to ensure that the sodium sulfate is completely dissolved and the suspended solids content in the ammonia nitrate solution is ≤0.1 g / L.

[0018] Preferably, in step S3, the clarification tank is a high-efficiency inclined plate clarification tank with an inclination angle of 60°. During the clarification process, 0.05-0.1 g / L of flocculant (polyaluminum chloride) is added to accelerate the sedimentation of impurities. The sludge is washed with deionized water, and the washing is performed twice. After washing, the sludge moisture content is ≤60%.

[0019] Preferably, in step S4, the carbonization tower is a sieve plate tower, a vertical cap tower, or a sieve plate-vertical cap mixed tower, with a sieve plate opening rate of 8-12% and a residence time of 1.5-2.5h; the mixing ratio of fresh CO2 and CO2 recovered from the calciner is 1:2-1:3, and the conversion rate of sodium sulfate in the carbonization reaction is ≥92%.

[0020] Preferably, in step S5, the filtration equipment is a plate and frame filter press with a filtration pressure of 0.3-0.5 MPa and a filtration temperature of 35-40°C; the sodium bicarbonate solid is washed with deionized water at a temperature of 30-35°C, the amount of water used for washing is 1-1.5 times the mass of the solid, and the water content of the sodium bicarbonate solid after washing is ≤8%.

[0021] Preferably, in step S6, the cooling equipment is a lithium bromide refrigeration unit, and the stirring speed during the freezing crystallization process is 50-70 r / min to prevent crystal agglomeration; the filtration of the mixed salt is carried out by a centrifugal filter with a centrifugal speed of 3000-3500 r / min and a filtration time of 15-20 min.

[0022] Preferably, in step S7, the purity of ammonia is ≥99.5%, the introduction rate is 0.5-1.0 m³ / h, and the temperature during the ammonia absorption process is controlled at 25-30℃ to avoid local overheating; the liquid-to-solid ratio for the dissolution of the double salt is 5:1-8:1 (volume-to-mass ratio, mL / g), the dissolution temperature is 35-45℃, and the dissolution time is 30-40 min.

[0023] Preferably, in step S8, the ammonia gas is introduced at a pressure of 0.1-0.2 MPa, the pH of the mother liquor after ammonia absorption is 9.5-10.5, the concentration of the saturated ammonium sulfate solution is 400-420 g / L (25℃), the washing time is 20-30 min, the centrifugation speed is 4000-4500 r / min, the drying temperature is 105-110℃, and the drying time is 2-3 h.

[0024] Preferably, in step S9, the ammonia stripping tower is a plate tower, the ammonia stripping temperature is 105-110℃, the pressure inside the tower is 0.12-0.15MPa, and the ammonia stripping time is 1.5-2h. The stripped ammonia gas is cooled to 25-30℃ and then sent to the ammonia absorption tower. The FNH3 content of the mother liquor after ammonia stripping is ≤10ti, ensuring the recycling effect.

[0025] Preferably, in step S10, the sodium bicarbonate is calcined in a rotary kiln for 1-1.5 hours, and the purity of the calcined soda ash product is ≥99.0%; the nitrogen content of the ammonium sulfate product is ≥20.5%, and the purity meets the GB / T535-2020 standard; the total utilization rate of sodium sulfate is ≥95%.

[0026] The environmental treatment includes the following steps: the exhaust gas from the top of the carbonization tower absorbs NH3 in a water washing tower, and the NH3 content in the tail gas is ≤10mg / m³ before being discharged; the tail gas from the calcination furnace is treated by dust removal and CO2 is recovered and recycled to step S4, and the particulate matter content in the tail gas after dust removal is ≤15mg / m³; when sludge and coal are mixed and burned, the mass ratio of coal to sludge is 5:1, and the incineration temperature is ≥850℃ to ensure the harmless treatment of sludge;

[0027] The process control includes the following steps: when the sodium sulfate conversion rate is below 90%, increase the temperature of the carbonization section in step S4 by 3-5℃ and adjust the ammonia-sodium ratio (A / S) to 1.1-1.25; when the ammonium sulfate product purity is below 20.0%, increase the final ammonia absorption concentration (FNH3) in step S8 to 250-280 ti and extend the cooling crystallization time by 10-15 min; after every 8-10 batches produced, calibrate the carbonization tower temperature, ammonia stripping pressure, and distillation equipment parameters to ensure stable process operation.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] This invention employs an integrated process of pre-carbonization, clarification, carbonization, ammonia precipitation, low-temperature crystallization, and ammonia stripping and recycling. It can be operated continuously or intermittently, is easy to implement industrially, and exhibits strong operational stability. By using ammonia precipitation and low-temperature crystallization synergistic technology to separate ammonium sulfate, it replaces the traditional evaporation and concentration process. Combined with a material recycling design, the energy consumption per unit product is reduced compared to traditional processes. Raw materials such as ammonia and carbon dioxide are efficiently recovered through a recycling system, with a utilization rate exceeding 98%. The purity of sodium bicarbonate is ≥96%, and the purity of calcined soda ash is ≥99.0%. The nitrogen content of ammonium sulfate is ≥20.5%, and the purity meets the GB / T535-2020 standard. The product quality is stable and reliable. It also has the advantages of no wastewater or waste residue discharge. After ammonia recovery through water washing, the NH3 content in the carbonization tower tail gas is ≤10mg / m³, and the particulate matter content in the calcination furnace tail gas after dust removal is ≤15mg / m³. The sludge is rendered harmless through high-temperature incineration, meeting the requirements of green production. Attached Figure Description

[0030] Figure 1 This is a flowchart of the method for preparing ammonium sulfate and co-producing sodium bicarbonate using sodium sulfate according to the present invention. Detailed Implementation

[0031] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0032] I. Materials:

[0033] All raw materials used in this invention are industrial-grade products, specifically: industrial-grade liquid ammonia with a purity ≥99.5%, conforming to GB / T536-2017 standard; anhydrous sodium sulfate with a purity ≥98.5%, conforming to GB / T6009-2014 standard; carbon dioxide with a purity ≥99.0%, conforming to GB / T6052-2011 standard; deionized water: conforming to GB / T6682-2008 Class III water standard; flocculant, polyaluminum chloride with a purity ≥98%, conforming to GB / T22627-2014 standard.

[0034] All other auxiliary materials and equipment consumables comply with relevant industrial application standards, and unless otherwise stated, they are all commercially available.

[0035] II. Process:

[0036] Please see Figure 1 Based on the materials, this invention proposes a method for preparing ammonium sulfate and co-producing sodium bicarbonate using sodium sulfate, specifically including the following steps:

[0037] S1. Preparation of pre-carbonized solution: Ammonia solution with a free ammonia concentration (FNH3) of 60-120 ti (1 ti = 1 / 20 molar concentration) is prepared by mixing industrial-grade liquid ammonia with deionized water. The mixing temperature is controlled at ≤40℃ to avoid ammonia volatilization. CO2 is introduced at 20~70℃ and carbon dioxide pressure of 0.1~0.6MPa for pre-carbonization. The purity of CO2 during pre-carbonization is ≥99.0%, and the preparation time is 2-3h to ensure that CO2 is fully dissolved. The final pre-carbonized solution has the composition of FNH3=60-120 ti, CO2=20~60 ti, and specific gravity d=1.1.

[0038] S2. Sodium sulfate dissolution: Heat the pre-carbonized liquid obtained in step S1 to 35-45℃, and add raw materials at a ratio of 150-450g of industrial-grade anhydrous sodium sulfate (purity ≥98.5%) per liter of solution or the mixture of sodium sulfate and ammonium carbonate recovered in step S6. During the dissolution process, the stirring speed is 80-120r / min, and the dissolution time is 1-1.5h to ensure that the sodium sulfate is completely dissolved, and an ammonia-nitrate solution with the composition of FNH3=60-120ti, CO2=20~60ti, d=1.1 is obtained, and the suspended solids content in the ammonia-nitrate solution is ≤0.1g / L;

[0039] S3. Clarification of sodium sulfate-ammonia solution: The ammonia nitrate solution obtained in step S2 is pumped to a high-efficiency inclined plate clarification tank (the inclination angle of the inclined plate is 60°). The temperature inside the tank is controlled at 35-45℃ and the residence time is 2-4h. During the clarification process, 0.05-0.1g / L of flocculant (polyaluminum chloride) is added to accelerate the sedimentation of impurities. The sludge at the bottom of the clarification tank is washed twice with deionized water and then mixed with coal and sent to the boiler for combustion. After washing, the sludge moisture content is ≤60%, and finally qualified clarified liquid is obtained, with the composition of FNH3=85g / L, CO2=110g / L, Na2SO4=320g / L, (NH4)2SO4=8-160g / L.

[0040] S4. Carbonization reaction: The clarified liquid obtained in step S3 is continuously or intermittently fed into a carbonization tower (using a sieve plate tower, a vertical cap tower, or a sieve plate-vertical cap mixed tower, with a sieve plate opening rate of 8-12%). Fresh CO2 and CO2 recovered from the sodium bicarbonate calciner are mixed in a ratio of 1:2-1:3 and introduced from the bottom of the carbonization tower. The reaction temperature in the middle section of the carbonization tower is controlled at 58-65℃, the temperature in the upper section at 38-52℃, and the temperature at the bottom section at 35-40℃. The pressure inside the tower is maintained at 0.35MPa (3.5atm). The ammonia-to-sodium ratio (A / S) of the reaction system is 0.8-1.25. The residence time inside the tower is 1.5-2.5h. The conversion rate of sodium sulfate in the carbonization reaction is ≥92%, and a suspension containing sodium bicarbonate crystals is generated.

[0041] S5. Carbonation liquid filtration: The suspension obtained in step S4 is fed into a plate and frame filter press, and the filtration pressure is controlled at 0.3-0.5 MPa and the filtration temperature is maintained at 35-40℃ to separate sodium bicarbonate solid and filtrate mother liquor; the sodium bicarbonate solid is washed 2-3 times with deionized water at 30-35℃, and the amount of washing water is 1-1.5 times the mass of the solid. After washing, the water content of the sodium bicarbonate solid is ≤8%, and then it is sent to a calcination furnace;

[0042] S6. Freeze-crystallization: After dissolving and separating the complex salt (Na2SO4・(NH4)2SO4・4H2O) from the mother liquor obtained in step S5, cool it to -10~-5℃ using a lithium bromide refrigeration unit at a cooling rate of 5-8℃ / h. During the freeze-crystallization process, the stirring speed is 50-70r / min to prevent crystal agglomeration. A mixed salt of Na2SO4・10H2O and NH4HCO3 is precipitated and separated by centrifugal filter (centrifugal speed of 3000-3500r / min) for 15-20min. After separation, the mixed salt is recycled to step S2 for sodium sulfate dissolution.

[0043] S7. Ammonia Absorption and Condensation of Double Salt: The mother liquor after separating the mixed salt in step S6 is passed into an ammonia absorption tower, and ammonia gas with a purity ≥99.5% is introduced at a rate of 0.5-1.0 m³ / h. The temperature during the ammonia absorption process is controlled at 25-30℃ to avoid local overheating until the FNH3 in the system reaches 100-140 ti. Then, it is cooled to -5℃ to precipitate double salt (Na2SO4・(NH4)2SO4・4H2O). The double salt is separated by filtration, and the double salt is dissolved in the mother liquor filtered in step S5 at a liquid-to-solid ratio of 5:1-8:1 (volume-to-mass ratio, mL / g). The dissolution temperature is 35-45℃ and the dissolution time is 30-40 min to increase the concentration of sodium sulfate and ammonium sulfate in the mother liquor.

[0044] S8. Ammonia Absorption and Ammonium Sulfate Precipitation: Ammonia gas is continuously introduced into the mother liquor filtered in step S7 at a pressure of 0.1-0.2 MPa until FNH3 > 230 Ti. After ammonia absorption, the pH of the mother liquor is 9.5-10.5. The mixture is cooled to 30°C, and ammonium sulfate solid is precipitated by filtration. This solid is then washed in a saturated ammonium sulfate solution with a concentration of 400-420 g / L (25°C) for 20-30 min to remove free ammonia. After centrifugation (4000-4500 r / min), the mixture is dried at 105-110°C for 2-3 h to obtain the final ammonium sulfate product.

[0045] S9. Ammonia stripping and recycling: The mother liquor after filtering ammonium sulfate in step S8 is sent to a plate-type ammonia stripping tower. The ammonia stripping temperature is controlled at 105-110℃, the pressure inside the tower is 0.12-0.15MPa, and the ammonia stripping time is 1.5-2h. The heated ammonia gas is cooled to 25-30℃ and then sent to the ammonia absorption tower in step S7 for recycling. The FNH3 of the mother liquor after ammonia stripping is ≤10ti and is pumped to the pre-carbonization tower in step S1 to participate in the pre-carbonization reaction.

[0046] S10. Post-processing and process control: The sodium bicarbonate solid after washing in step S5 is calcined in a rotary kiln at 180℃ for 1-1.5 hours to obtain soda ash product; the tail gas and sludge generated in each step are treated in an environmentally friendly manner; the product purity and reaction conversion rate are tested regularly, and the process parameters are adjusted based on the test results to achieve stable circulation.

[0047] The environmental protection treatment specifically includes: the exhaust gas from the top of the carbonization tower absorbs NH3 in a water washing tower, and the NH3 content in the tail gas is ≤10mg / m³ before being discharged; the tail gas from the calcination furnace is treated by dust removal and CO2 is recovered and recycled to step S4, and the particulate matter content in the tail gas after dust removal is ≤15mg / m³; when sludge and coal are mixed and burned, the mass ratio of coal to sludge is 5:1, and the incineration temperature is ≥850℃ to ensure the harmless treatment of sludge.

[0048] The specific process control includes: when the sodium sulfate conversion rate is below 90%, increasing the temperature of the carbonization section in step S4 by 3-5℃ and adjusting the ammonia-sodium ratio (A / S) to 1.1-1.25; when the ammonium sulfate product purity is below 20.0%, increasing the final ammonia absorption concentration (FNH3) in step S8 to 250-280 ti and extending the cooling crystallization time by 10-15 min; after every 8-10 batches produced, calibrating the carbonization tower temperature, ammonia stripping pressure, and related equipment parameters to ensure stable process operation.

[0049] Example 1: In this example, a method for preparing ammonium sulfate and co-producing sodium bicarbonate using sodium sulfate includes the following steps:

[0050] S1. Preparation of pre-carbonized liquid: Industrial-grade liquid ammonia is mixed with deionized water at a controlled mixing temperature of 35°C to prepare ammonia water with FNH3=90ti; under conditions of 45°C and CO2 pressure of 0.3MPa, CO2 with a purity of 99.2% is introduced for pre-carbonization for 2.5h, and finally a pre-carbonized liquid with the composition of FNH3=90ti, CO2=40ti, and d=1.1 is obtained;

[0051] S2. Sodium sulfate dissolution: The pre-carbonized liquid was heated to 40℃, and 300g of industrial-grade anhydrous sodium sulfate (purity 99.0%) was dissolved per liter of solution. The stirring speed was 100r / min, and the dissolution time was 1.2h to obtain ammonia nitrate solution. The suspended solids content was tested to be 0.08g / L.

[0052] S3. Solution Clarification: The ammonia nitrate solution is pumped to a high-efficiency inclined plate clarification tank (inclination angle 60°), the temperature inside the tank is controlled at 40℃, the residence time is 3h, and 0.07g / L polyaluminum chloride flocculant is added; the sludge at the bottom of the clarification tank is washed twice with deionized water, and the sludge moisture content after washing is 55%, and a qualified clarified solution is obtained with the following composition: FNH3=85g / L, CO2=110g / L, Na2SO4=320g / L, (NH4)2SO4=80g / L;

[0053] S4. Carbonization reaction: The clarified liquid is continuously fed into a sieve plate tower (sieve opening rate 10%). The mixing ratio of fresh CO2 and CO2 recovered from the calciner is 1:2.5. The temperature of the middle section of the carbonization tower is controlled at 62℃, the upper section at 45℃, and the lower section at 38℃. The pressure inside the tower is maintained at 0.35MPa. The ammonia-to-sodium ratio (A / S) of the reaction system is 1.0, and the residence time inside the tower is 2.0h. The sodium sulfate conversion rate is tested to be 94%.

[0054] S5. Carbonation liquid filtration: A plate and frame filter press was used, with the filtration pressure controlled at 0.4 MPa and the filtration temperature at 38℃, to separate sodium bicarbonate solid and filtrate mother liquor; the sodium bicarbonate solid was washed twice with deionized water at 32℃, with the washing water volume being 1.2 times the mass of the solid, and the water content of the solid after washing was 7%;

[0055] S6. Freeze-crystallization: After dissolving and separating the complex salt from the filtered mother liquor, the liquid is cooled to -8°C using a lithium bromide refrigeration unit at a cooling rate of 6°C / h. During the freeze-crystallization process, the stirring speed is 60 r / min. The mixture is then filtered for 18 min using a centrifugal filter (centrifugal speed 3200 r / min) to obtain a mixed salt of Na2SO4・10H2O and NH4HCO3, which is then recycled to step S2.

[0056] S7. Ammonia absorption and precipitation of double salt: The mother liquor after separating the mixed salts is passed into the ammonia absorption tower, and ammonia gas with a purity of 99.6% is introduced at a rate of 0.8 m³ / h. The temperature during the ammonia absorption process is controlled at 28℃ until the system FNH3 = 120 Ti. The double salt is precipitated by cooling to -5℃. After filtration and separation, the double salt is dissolved in the mother liquor from step S5 at a liquid-to-solid ratio of 6:1, a dissolution temperature of 40℃, and a dissolution time of 35 min.

[0057] S8. Ammonia absorption and precipitation of ammonium sulfate: Continue to introduce ammonia gas, controlling the pressure at 0.15 MPa, until the system FNH3 = 250 ti and the pH of the mother liquor after ammonia absorption is 10.0; cool to 30°C, filter to precipitate ammonium sulfate solid, and wash in a 410 g / L (25°C) saturated ammonium sulfate solution for 25 min; after centrifugation (4200 r / min), dry at 108°C for 2.5 h to obtain the ammonium sulfate product;

[0058] S9. Ammonia stripping circulation: The mother liquor after filtering ammonium sulfate is sent to a plate ammonia stripping tower, and the ammonia stripping temperature is controlled at 108℃, the tower pressure is 0.13MPa, and the ammonia stripping time is 1.8h. The stripped ammonia gas is cooled to 28℃ and sent to the ammonia absorption tower in step S7. The mother liquor after ammonia stripping has FNH3=8ti and is pumped to the pre-carbonization tower in step S1.

[0059] S10. Post-processing of the product: Sodium bicarbonate solid was calcined at 180℃ for 1.2h to obtain soda ash product; environmental protection treatment was carried out in accordance with the above standards, and the process parameters were normal and no adjustments were made.

[0060] Example 2: In this example, a method for preparing ammonium sulfate and co-producing sodium bicarbonate using sodium sulfate includes the following steps:

[0061] S1. Preparation of pre-carbonized liquid: Industrial-grade liquid ammonia is mixed with deionized water at a controlled mixing temperature of 30°C to prepare ammonia water with FNH3=60ti; under conditions of 20°C and CO2 pressure of 0.1MPa, CO2 with a purity of 99.0% is introduced for pre-carbonization for 2 hours, and a pre-carbonized liquid with the composition of FNH3=60ti, CO2=20ti, and d=1.1 is finally obtained.

[0062] S2. Sodium sulfate dissolution: The pre-carbonized liquid was heated to 35°C, and 150g of industrial-grade anhydrous sodium sulfate (purity 98.5%) was dissolved per liter of solution. The stirring speed was 80r / min, and the dissolution time was 1h to obtain ammonia nitrate solution. The suspended solids content was tested to be 0.09g / L.

[0063] S3. Solution Clarification: The ammonia nitrate solution is pumped to a high-efficiency inclined plate clarification tank (inclination angle 60°), the temperature inside the tank is controlled at 35℃, the residence time is 2h, and 0.05g / L polyaluminum chloride flocculant is added; the sludge at the bottom of the clarification tank is washed twice with deionized water, and the water content of the sludge after washing is 58%, and a qualified clarified solution is obtained with the following composition: FNH3=85g / L, CO2=110g / L, Na2SO4=320g / L, (NH4)2SO4=8g / L;

[0064] S4. Carbonization reaction: The clarified liquid was intermittently fed into the vertical cap tower. The mixing ratio of fresh CO2 to CO2 recovered from the calciner was 1:2. The temperature of the middle section of the carbonization tower was controlled at 58℃, the upper section at 38℃, and the lower section at 35℃. The pressure inside the tower was maintained at 0.35MPa. The ammonia-to-sodium ratio (A / S) of the reaction system was 0.8, and the residence time inside the tower was 1.5h. The conversion rate of sodium sulfate was tested to be 92%.

[0065] S5. Carbonation liquid filtration: A plate and frame filter press was used, with the filtration pressure controlled at 0.3 MPa and the filtration temperature at 35℃, to separate sodium bicarbonate solid and filtrate mother liquor; the sodium bicarbonate solid was washed twice with deionized water at 30℃, with the washing water volume being 1 times the mass of the solid, and the water content of the solid after washing was 8%;

[0066] S6. Freeze-crystallization: After dissolving and separating the complex salts from the filtered mother liquor, the liquid is cooled to -10°C using a lithium bromide refrigeration unit at a cooling rate of 5°C / h. During the freeze-crystallization process, the stirring speed is 50 r / min. The mixture is then filtered for 15 min using a centrifugal filter (centrifugal speed 3000 r / min) to obtain the mixed salts, which are then recycled to step S2.

[0067] S7. Ammonia absorption and precipitation of double salt: The mother liquor after separating the mixed salts is passed into the ammonia absorption tower, and ammonia gas with a purity of 99.5% is introduced at a rate of 0.5 m³ / h. The temperature during the ammonia absorption process is controlled at 25℃ until the system FNH3=100ti. The double salt is precipitated by cooling to -5℃. After filtration and separation, the double salt is dissolved in the mother liquor from step S5 at a liquid-to-solid ratio of 5:1, a dissolution temperature of 35℃, and a dissolution time of 30 min.

[0068] S8. Ammonia absorption and precipitation of ammonium sulfate: Continue to purge ammonia gas, controlling the purging pressure at 0.1 MPa, until the system FNH3 = 240 Ti and the pH of the mother liquor after ammonia absorption = 9.5; cool to 30℃, filter to precipitate ammonium sulfate solid, and wash in 400 g / L (25℃) saturated ammonium sulfate solution for 20 min; after centrifugation (4000 r / min), dry at 105℃ for 2 h to obtain the ammonium sulfate product;

[0069] S9. Ammonia stripping circulation: The mother liquor after filtering ammonium sulfate is sent to a plate ammonia stripping tower, and the ammonia stripping temperature is controlled at 105℃, the tower pressure is 0.12MPa, and the ammonia stripping time is 1.5h. The stripped ammonia gas is cooled to 25℃ and sent to the ammonia absorption tower in step S7. The mother liquor after ammonia stripping has FNH3=9ti and is pumped to the pre-carbonization tower in step S1.

[0070] S10. Post-processing of the product: Sodium bicarbonate solid is calcined at 180℃ for 1 hour to obtain soda ash product; environmental protection treatment and process control shall be carried out in accordance with the standards.

[0071] Example 3: In this example, a method for preparing ammonium sulfate and co-producing sodium bicarbonate using sodium sulfate includes the following steps:

[0072] S1. Preparation of pre-carbonized liquid: Industrial-grade liquid ammonia is mixed with deionized water at a controlled mixing temperature of 40°C to prepare ammonia solution with FNH3=120ti; under conditions of 70°C and CO2 pressure of 0.6MPa, CO2 with a purity of 99.5% is introduced for pre-carbonization for 3 hours, and a pre-carbonized liquid with the composition of FNH3=120ti, CO2=60ti, and d=1.1 is finally obtained.

[0073] S2. Sodium sulfate dissolution: The pre-carbonized liquid was heated to 45℃, and 450g of industrial-grade anhydrous sodium sulfate (purity 99.2%) was dissolved per liter of solution. The stirring speed was 120r / min, and the dissolution time was 1.5h to obtain ammonia nitrate solution. The suspended solids content was tested to be 0.07g / L.

[0074] S3. Solution Clarification: The ammonia nitrate solution is pumped to a high-efficiency inclined plate clarification tank (inclination angle 60°), the temperature inside the tank is controlled at 45℃, the residence time is 4h, and 0.1g / L polyaluminum chloride flocculant is added; the sludge at the bottom of the clarification tank is washed twice with deionized water, and the water content of the sludge after washing is 52%, and a qualified clarified solution is obtained with the following composition: FNH3=85g / L, CO2=110g / L, Na2SO4=320g / L, (NH4)2SO4=160g / L;

[0075] S4. Carbonization reaction: The clarified liquid is continuously fed into a sieve plate-vertical cap mixing tower (sieve plate opening rate 12%). The mixing ratio of fresh CO2 to CO2 recovered from the calciner is 1:3. The temperature of the middle section of the carbonization tower is controlled at 65℃, the upper section at 52℃, and the lower section at 40℃. The pressure inside the tower is maintained at 0.35MPa. The ammonia-to-sodium ratio (A / S) of the reaction system is 1.25, and the residence time inside the tower is 2.5h. The sodium sulfate conversion rate is tested to be 95%.

[0076] S5. Carbonation liquid filtration: A plate and frame filter press was used, with the filtration pressure controlled at 0.5 MPa and the filtration temperature at 40℃, to separate sodium bicarbonate solid and filtrate mother liquor; the sodium bicarbonate solid was washed three times with deionized water at 35℃, with the washing water volume being 1.5 times the mass of the solid, and the water content of the solid after washing was 6%;

[0077] S6. Freeze-crystallization: After dissolving and separating the complex salts from the filtered mother liquor, the liquid is cooled to -5°C using a lithium bromide refrigeration unit at a cooling rate of 8°C / h. During the freeze-crystallization process, the stirring speed is 70 r / min. The mixture is then filtered for 20 min using a centrifugal filter (centrifugal speed 3500 r / min) to obtain the mixed salts, which are then recycled to step S2.

[0078] S7. Ammonia absorption and precipitation of double salt: The mother liquor after separating the mixed salts is passed into the ammonia absorption tower, and ammonia gas with a purity of 99.8% is introduced at a rate of 1.0 m³ / h. The temperature during the ammonia absorption process is controlled at 30℃ until the system FNH3=140ti; cool to -5℃ to precipitate double salt, filter and separate, and dissolve the double salt with the mother liquor from step S5, with a liquid-to-solid ratio of 8:1, a dissolution temperature of 45℃, and a dissolution time of 40 min;

[0079] S8. Ammonia absorption and precipitation of ammonium sulfate: Continue to purge ammonia gas, controlling the purging pressure at 0.2 MPa, until the system FNH3 = 280 Ti, and the pH of the mother liquor after ammonia absorption = 10.5; cool to 30℃, filter to precipitate ammonium sulfate solid, and wash in 420 g / L (25℃) saturated ammonium sulfate solution for 30 min; after centrifugation (4500 r / min), dry at 110℃ for 3 h to obtain the ammonium sulfate product;

[0080] S9. Ammonia stripping circulation: The mother liquor after filtering ammonium sulfate is sent to a plate ammonia stripping tower, and the ammonia stripping temperature is controlled at 110℃, the tower pressure is 0.15MPa, and the ammonia stripping time is 2h. The stripped ammonia gas is cooled to 30℃ and sent to the ammonia absorption tower in step S7. The mother liquor after ammonia stripping has FNH3=7ti and is pumped to the pre-carbonization tower in step S1.

[0081] S10. Post-processing of the product: Sodium bicarbonate solid is calcined at 180℃ for 1.5h to obtain soda ash product; environmental protection treatment and process control shall be carried out in accordance with the standards.

[0082] Comparative Example 1: In this embodiment, a traditional preparation process was adopted, using industrial-grade anhydrous sodium sulfate (purity 98.5%) and ammonium bicarbonate as raw materials. A double decomposition reaction was carried out at 40°C and 0.1 MPa to generate solid sodium bicarbonate. After filtration, the mother liquor was subjected to high-temperature deammoniation at 130°C for 2 hours. After deammoniation, the mother liquor was evaporated and concentrated at 100°C for 3 hours to precipitate sodium sulfate crystals. After filtration, the mother liquor was cooled to 25°C to precipitate a double salt (Na₂SO₄・(NH₄)₂SO₄・4H₂O). After filtration and separation of the double salt, the remaining mother liquor was further evaporated and crystallized for 4 hours to obtain crude ammonium sulfate. The crude ammonium sulfate was washed and dried at 110°C for 3 hours to obtain the ammonium sulfate product. The solid sodium bicarbonate was washed and calcined to obtain soda ash.

[0083] III. Performance Testing:

[0084] The performance of samples of the same specifications prepared in Examples 1-3 and Comparative Example 1 was tested according to the following standards:

[0085] a. Sodium sulfate utilization rate: calculated based on the difference between the total mass of sodium sulfate input and the mass of sodium sulfate remaining in the final product and waste liquid;

[0086] b. Sodium bicarbonate purity: Tested according to GB / T1606-2008 "Industrial Sodium Bicarbonate";

[0087] c. Ammonium sulfate nitrogen content and purity: tested according to GB / T535-2020 "Fertilizer Grade Ammonium Sulfate";

[0088] d. Energy consumption per unit product: The total energy consumption for producing 1 ton of ammonium sulfate and 1 ton of sodium bicarbonate, including heating, cooling and stirring.

[0089] Record the performance test and process index data. The test results are shown in Table 1.

[0090] Table 1: Process parameters of Examples 1 to 3 and Comparative Example 1

[0091] detection indicators Example 1 Example 2 Example 3 Comparative Example 1 Sodium sulfate utilization rate (%) 94.8 95.1 95.3 78.5 Sodium bicarbonate purity (%) 97.2 96.1 97.5 92.3 Ammonium sulfate nitrogen content (%) 20.8 20.6 21.0 19.2 Ammonium sulfate purity (%) 98.5 98.2 98.8 95.1 Energy consumption per unit product (kWh / t) 860 885 850 1320

[0092] IV. Analysis Conclusion:

[0093] As shown in Table 1, the sodium sulfate utilization rate of Examples 1-3 of this invention is ≥94.8%, which is much higher than the 78.5% of Comparative Example 1. This indicates that the resource utilization efficiency of sodium sulfate in this invention is significantly better than that of traditional processes, effectively solving the problem of sodium sulfate resource waste. The sodium bicarbonate purity of Examples 1-3 is ≥96.1%, and the ammonium sulfate nitrogen content is ≥20.6% with a purity of ≥98.2%, all meeting relevant national standards and exceeding the purity of the product in Comparative Example 1, verifying the stability and superiority of the product quality of this invention. The unit product energy consumption of Examples 1-3 is only 850-885 kWh / t, which is 33%-36% lower than the 1320 kWh / t of Comparative Example 1, demonstrating the core advantage of this invention in energy consumption control. Examples 1-3 all achieved excellent performance indicators, indicating that the process parameter range set by this invention is scientifically reasonable and has good adaptability and stability.

[0094] Comparative Example 1 uses a traditional metathesis-evaporation process, which has problems such as complex process, multiple high-temperature steps, high energy consumption, and low conversion rate. However, this invention effectively overcomes the above defects through innovative designs such as synergistic ammonia precipitation and low-temperature crystallization and material recycling, and has industrial application prospects.

[0095] In summary, the method for preparing ammonium sulfate and co-producing sodium bicarbonate using sodium sulfate provided by this invention has a simple process, low energy consumption, high resource utilization rate, excellent product purity, and is environmentally friendly. It solves many shortcomings of the prior art and has significant economic and environmental value.

[0096] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A process for the preparation of ammonium sulfate co-product sodium bicarbonate using sodium sulfate, characterized by, The method comprises the following steps: S1. Prepare ammonia water with free ammonia concentration of 60-120ti by mixing industrial-grade liquid ammonia with deionized water, control the temperature ≤40℃ during the mixing process to avoid ammonia volatilization, and then pre-carbonize under the conditions of 20~70℃ and CO2 pressure of 0.1~0.6MPa by passing in CO2, to obtain a pre-carbonized liquid with composition of FNH3=60-120ti, CO2=20~60ti, and specific gravity d=1.1, the purity of CO2 during the pre-carbonization process is ≥99.0%, and the preparation time of the pre-carbonized liquid is 2-3h to ensure sufficient dissolution of CO2; S2. Warm the pre-carbonized liquid obtained in the step S1 to 35-45℃, and then add raw materials according to the proportion of 150-450g of sodium sulfate or the mixture of recovered mirabilite and ammonium carbonate per liter of solution, and then stir and dissolve to obtain ammonia nitre liquid with composition of FNH3=60-120ti, CO2=20~60ti, and d=1.1; S3. Pump the ammonia nitre liquid obtained in the step S2 into a clarifying tank, control the temperature in the tank to be 35-45℃ and the residence time to be 2-4h, remove suspended solids and precipitate calcium and magnesium ion impurities, wash the sludge at the bottom of the clarifying tank, and then mix the sludge with coal and send them into a boiler for incineration to obtain qualified clarified liquid with composition of FNH3=85g / L, CO2=110g / L, Na2SO4=320g / L, and (NH4)2SO4=8-160g / L; S4. Continuously or intermittently send the clarified liquid obtained in the step S3 into a carbonation tower, mix fresh CO2 with CO2 recovered from a sodium bicarbonate calcination furnace, and then pass the mixture into the bottom of the carbonation tower, control the reaction temperature in the middle section of the carbonation tower to be 58~65℃, the temperature in the upper section to be 38-52℃, and the temperature in the lower section to be 35~40℃, maintain the pressure in the tower to be 0.35MPa, control the ammonia-sodium ratio of the reaction system to be 0.8~1.25, and generate a suspension liquid containing sodium bicarbonate crystals; S5. Send the suspension liquid obtained in the step S4 into a filtering device to separate sodium bicarbonate solid and filtered mother liquor, and then send the sodium bicarbonate solid into a calcination furnace after 2-3 times of washing; S6. Dissolve and separate the double salt from the filtered mother liquor obtained in the step S5, cool the filtered mother liquor to -10~-5℃ at a cooling rate of 5-8℃ / h, precipitate the mixed salt of Na2SO4・10H2O and NH4HCO3, and then separate the mixed salt by filtration, and then recycle the mixed salt to the step S2 for sodium sulfate dissolution; S7. Pass the mother liquor after separating the mixed salt in the step S6 into an ammonia absorption tower, pass in ammonia gas until the FNH3 of the system reaches 100~140ti, and then cool to -5℃ to precipitate the double salt, separate the double salt by filtration, and then dissolve the double salt in the filtered mother liquor of the step S5 to increase the concentrations of sodium sulfate and ammonium sulfate in the mother liquor; S8. Continue to pass ammonia gas into the filtered mother liquor of the step S7 until FNH3>230ti, cool to 30℃, and then filter to precipitate ammonium sulfate solid, wash the ammonium sulfate solid in saturated ammonium sulfate solution to remove free ammonia, separate by centrifugation, and then dry to obtain ammonium sulfate finished product; S9. The mother liquor after the step S8 filtering ammonium sulfate is sent to the ammonia evaporation tower, ammonia gas is evaporated and heated and sent to the ammonia absorption tower of the step S7 for recycling, and the mother liquor after the ammonia evaporation is pumped to the pre-carbonization tower of the step S1 to participate in the pre-carbonization reaction; S10. The sodium bicarbonate solid after the step S5 washing is calcined at 180℃ to obtain soda ash products, and the tail gas and sludge generated in each step are environmentally treated; the product purity and reaction conversion rate are detected regularly, and the process parameters are adjusted based on the detection results to realize stable circulation.

2. The method for preparing ammonium sulfate and sodium bicarbonate as byproduct by using sodium sulfate according to claim 1, characterized in that, The sodium sulfate used in the step S2 is industrial grade anhydrous sodium sulfate or mixed salt recovered in the step S6, the stirring speed in the dissolving process is 80-120r / min, and the dissolving time is 1-1.5h to ensure that the sodium sulfate is completely dissolved, and the suspended solids content in the ammonia-nitrogen solution is ≤0.1g / L.

3. The method for preparing ammonium sulfate and sodium bicarbonate as byproduct by using sodium sulfate according to claim 2, characterized in that, The clarification tank in the step S3 adopts a high-efficiency inclined plate clarification tank, the inclined plate angle is 60°, and 0.05-0.1g / L of flocculating agent is added in the clarification process to accelerate the sedimentation of impurities, deionized water is used for sludge washing, the washing frequency is 2 times, and the sludge moisture content after washing is ≤60%.

4. The method for preparing ammonium sulfate and sodium bicarbonate as by-product by using sodium sulfate according to claim 3, characterized in that, The carbonization tower in the step S4 adopts a sieve plate tower, a stand cap tower or a sieve plate-stand cap hybrid tower, the sieve plate opening rate is 8-12%, and the tower residence time is 1.5-2.5h; the mixing ratio of fresh CO2 and recovered CO2 from the calcining furnace is 1:2-1:

3.

5. The method for preparing ammonium sulfate and sodium bicarbonate as by-product by using sodium sulfate according to claim 4, characterized in that, The filtering equipment in the step S5 adopts a plate-frame filter press, the filtering pressure is 0.3-0.5MPa, and the filtering temperature is maintained at 35-40℃; the sodium bicarbonate solid is washed with deionized water at a temperature of 30-35℃, the washing water amount is 1-1.5 times the solid mass, and the sodium bicarbonate solid moisture content after washing is ≤8%.

6. The method for preparing ammonium sulfate and sodium bicarbonate as byproduct by using sodium sulfate according to claim 5, characterized in that, The cooling equipment in the step S6 adopts a lithium bromide refrigeration unit, the stirring speed in the refrigeration and crystallization process is 50-70r / min to prevent the crystal from caking; the mixed salt is filtered by a centrifugal filter, the centrifugal speed is 3000-3500r / min, and the filtering time is 15-20min.

7. The method for preparing ammonium sulfate and sodium bicarbonate as byproduct by using sodium sulfate according to claim 6, characterized in that, The ammonia gas purity in the step S7 is ≥99.5%, the inlet rate is 0.5-1.0m³ / h, the ammonia absorption process temperature is controlled at 25-30℃ to avoid local overheating; the liquid-solid ratio of the double salt dissolution is 5:1-8:1, the dissolution temperature is 35-45℃, and the dissolution time is 30-40min.

8. The method for preparing ammonium sulfate and sodium bicarbonate as byproduct by using sodium sulfate according to claim 7, characterized in that, The ammonia gas inlet pressure in the step S8 is 0.1-0.2MPa, and the mother liquor pH value after the ammonia absorption is 9.5-10.5; the saturated ammonium sulfate solution concentration is 400-420g / L, the washing time is 20-30min, the centrifugal separation speed is 4000-4500r / min, the drying temperature is 105-110℃, and the drying time is 2-3h.

9. The method for preparing ammonium sulfate and sodium bicarbonate as byproduct by using sodium sulfate according to claim 8, characterized in that, The ammonia evaporation tower in the step S9 adopts a plate tower, the ammonia evaporation temperature is 105-110℃, the tower pressure is 0.12-0.15MPa, and the ammonia evaporation time is 1.5-2h; the evaporated ammonia gas is sent to the ammonia absorption tower after being cooled to 25-30℃, and the mother liquor FNH3 after the ammonia evaporation is ≤10ti.

10. The method for preparing ammonium sulfate and sodium bicarbonate as byproduct by using sodium sulfate according to claim 9, characterized in that, The sodium bicarbonate in the step S10 is calcined by using a rotary kiln calciner, and the calcination time is 1-1.5 h; The environmental protection treatment includes the following steps: the NH3 in the waste gas at the top of the carbonization tower is absorbed by a water washing tower, and then the NH3 content in the tail gas is ≤10 mg / m³ before being discharged; the tail gas of the calciner is dedusted and then the CO2 is recovered and recycled to the step S4; when the sludge is mixed with coal for incineration, the mass ratio of the coal to the sludge is 5:1, and the incineration temperature is ≥850℃; The process regulation includes the following steps: when the conversion rate of sodium sulfate is lower than 90%, the temperature in the middle section of the carbonization in the step S4 is increased by 3-5℃, and the ammonia-sodium ratio is adjusted to 1.1-1.25; when the purity of the ammonium sulfate product is lower than 20.0%, the final concentration of the ammonia absorption in the step S8 is increased to 250-280ti, and the cooling crystallization time is prolonged by 10-15 min.

Images