Preparation method for producing large-particle ammonium sulfate by utilizing phosphogypsum

Abstract

The invention relates to the technical field of comprehensive utilization of ardealite, and particularly discloses a preparation method for producing large-particle ammonium sulfate by utilizing ardealite, which comprises six steps of raw material preparation and treatment, ammonium sulfate preparation, neutralization, evaporative crystallization, ammonium sulfate sphere preparation, finished product drying and the like. The ammonium sulfate crystal slurry separated out through complete crystallization is subjected to extrusion forming and pelletizing, and high-strength large-particle ammonium sulfate is formed through later drying, so that the production cost of large-particle ammonium sulfate is reduced, and the technical problem that ammonium sulfate produced from ardealite in the prior art is mostly powdery or small-particle ammonium sulfate crystals and is prone to caking in the transportation and storage process is solved.

Description

Technical Field

[0001] The invention relates to the technical field of comprehensive utilization of phosphogypsum, and in particular to a preparation method for producing large-particle ammonium sulfate by utilizing phosphogypsum. Background Art

[0002] The comprehensive utilization of phosphogypsum is an inevitable technical problem in the phosphorus chemical industry. The degree of resource utilization of phosphogypsum directly affects the high-quality development of the phosphorus chemical industry.

[0003] The comprehensive utilization of phosphogypsum includes its use in construction and building materials, soil improvement and agriculture, feed additives, and the production of chemical products. Among them, the use of phosphogypsum to produce ammonium sulfate is one of the effective ways to achieve the comprehensive utilization of phosphogypsum resources. It can reuse the calcium and sulfur resources contained in phosphogypsum, which not only reduces the problem of stacking phosphogypsum as solid waste, but also helps alleviate resource shortages and reduces the production cost of ammonium sulfate.

[0004] In the prior art, when phosphogypsum is used to produce ammonium sulfate products, the produced ammonium sulfate is usually produced by spray granulation or crystallization in a crystallization kettle for evaporation and crystallization, and the formed ammonium sulfate is mainly in the form of powder or small-particle ammonium sulfate crystals. For example, the patent document with application number: CN201210099988.2 discloses a method for producing ammonium sulfate with ammonium bicarbonate as the main raw material, which uses evaporation and crystallization. For example, the patent document with application number: CN201210230645.5 discloses a method for preparing granulated ammonium sulfate and calcium carbonate by low-temperature conversion of chemical gypsum, which is spray granulation.

[0005] Although the above-mentioned method and technology can realize resource utilization of ammonium sulfate produced from phosphogypsum, the powdered or small-particle ammonium sulfate crystals have low strength, are inconvenient to transport and store, and are easily deliquesced and recrystallized with moisture in the air to form crystal bridges, causing small particles to become large particles and aggregate together to form agglomerates with greater hardness. This requires the ammonium sulfate to be crushed when used, which limits the use of ammonium sulfate. Summary of the invention

[0006] The object of the present invention is to provide a method for producing large-particle ammonium sulfate using phosphogypsum, so as to solve the technical problem that the ammonium sulfate produced by phosphogypsum in the prior art mentioned above is mostly powdery or small-particle ammonium sulfate crystals, which are easy to agglomerate during transportation and storage.

[0007] In order to solve the above problems, the technical solution adopted by the present invention is as follows: A preparation method for producing large-particle ammonium sulfate using phosphogypsum comprises the following steps:

[0008] Step 1, raw material preparation and processing: slurrying the phosphogypsum, filtering and washing to obtain purified phosphogypsum, and preparing an ammonium carbonate solution;

[0009] Step 2, preparing ammonium sulfate: mixing the ammonium carbonate solution in step 1 with the purified phosphogypsum, mixing them evenly to carry out double decomposition reaction, and obtaining a mixed slurry of calcium carbonate and ammonium sulfate after the reaction is completed; filtering and washing the mixed slurry to obtain a solid phase calcium carbonate and a liquid phase ammonium sulfate solution;

[0010] Step 3, neutralization: add an appropriate amount of sulfuric acid to neutralize the ammonium sulfate solution obtained by filtering in step 2, and convert a small amount of ammonia and ammonium carbonate in the solution into ammonium sulfate;

[0011] Step 4, evaporation crystallization: the neutralized ammonium sulfate solution is concentrated by a triple-effect evaporation crystallizer to obtain ammonium sulfate slurry;

[0012] Step 5, preparing ammonium sulfate spheres: conveying the ammonium sulfate slurry to a double-roll extruder to prepare spherical large-particle ammonium sulfate;

[0013] Step 6, drying the finished product: the large-particle ammonium sulfate is dried by a drum dryer to obtain a large-particle ammonium sulfate finished product.

[0014] The beneficial effects of this embodiment are:

[0015] 1. In the production process of ammonium sulfate produced by phosphogypsum in the prior art, evaporation crystallization and spraying crystallization are used for crystallization, so that the crystallized ammonium sulfate is powdery or small-particle ammonium sulfate crystals with a large specific surface area, which is easy to deliquesce and recrystallize with moisture in the air. The recrystallization process forms a crystal bridge, causing small particles to become large particles and gather together to form a hard agglomerate. After the application uses a triple-effect evaporation concentration crystallizer to concentrate it into a slurry, it is first made into a sphere by a double-roll extruder, and then dried and crystallized. The ammonium sulfate produced is a spherical large-particle ammonium sulfate. The spherical large-particle ammonium sulfate reduces the specific surface area of ​​​​ammonium sulfate, so the same weight of ammonium sulfate has a reduced area in contact with the air, and its moisture absorption capacity is reduced, so the degree of recrystallization is reduced, and it is not easy to agglomerate.

[0016] 2. Prepare the completely dried and crystallized ammonium sulfate crystals into pellets to reduce the area of ​​moisture absorption. In theory, it can also reduce the probability of recrystallization. However, when granulating after the ammonium sulfate crystals are precipitated, the ammonium sulfate crystals have already crystallized, resulting in large particles of ammonium sulfate formed by the adsorption force during the extrusion process. The internal strength is low. During transportation or storage, the ammonium sulfate needs to be bagged. When stacking, the large particles of ammonium sulfate stacked at the bottom are crushed by extrusion due to insufficient strength, so that they are destroyed into small particles or powdery structures, the specific surface area is increased, and moisture absorption and recrystallization occur. This is an important reason why the ammonium sulfate at the bottom of most stored ammonium sulfate is easily hardened. In this regard, the present application does not perform extrusion granulation after the ammonium sulfate is completely crystallized, but performs extrusion granulation after the evaporation crystallization reaches a certain degree and the slurry is formed, so that the formed pellets contain unprecipitated ammonium sulfate in an ionic state. The ammonium sulfate in an ionic state is distributed among the precipitated ammonium sulfate crystals and adsorbed on their surfaces. During the final drying, this part of the ammonium sulfate is precipitated. The precipitated ammonium sulfate is close enough to the crystal molecules of other ammonium sulfate, so various connection relationships such as van der Waals force, adsorption force, crystal bridge and embedded connection are generated, so that the large-particle ammonium sulfate of the present application has high strength. According to actual testing, the average compressive strength of the large-particle ammonium sulfate of the present application is ≥30N. It is not easy to be crushed by external extrusion force. It is more stable during transportation and storage, and is not easy to harden after moisture absorption and recrystallization.

[0017] 3. Granulation adopts extrusion granulation, which can reduce equipment investment and energy consumption compared with spraying equipment, so its production cost is lower. Taking the 250,000 tons / year device for producing granulated ammonium sulfate from phosphogypsum as an example, the consumption of ammonium sulfate granulation equipment and public works is compared. The maximum diameter of the spray granulation dryer is 4.75 meters. When used for ammonium sulfate granulation, the production capacity of a single device is 10-12.5 tons / hour. The size of a single set of spray granulation dryer is large and difficult to transport. Its transportation method adopts segmented transportation and welding and assembly at the factory. The device occupies a large area and has high operating costs. The ex-factory price of a single set of spray granulation dryer (size: Φ4.75×18m, net weight: ~200t, power: 315+11kW) is about 4 million yuan. A 250,000 tons / year device requires three sets of spray granulation dryers (Φ4.75×18m), totaling 12 million yuan (excluding hot air furnace, tail gas treatment facilities, and product cooler).

[0018] The capacity of a single roll extruder granulator (size: 1260×700×1600mm, net weight: ~800kg, power: 15kW) is 0.8-1.2 tons / hour. A 250,000-ton / year device requires 40 roll extruder granulators to form a granulation drying and cooling unit, which costs a total of 6 million yuan (including hot air furnace, tail gas treatment facilities, product drying and cooler). The maintenance of any roll extruder granulator does not affect the normal operation of other equipment. It has great operational flexibility and low energy consumption. The following table shows the comparison of utility consumption of spray granulation and extrusion granulation (tons of product)

[0019] Technology Power consumption natural gas Phosphoric acid Exhaust emissions Spray granulation 80kWh 100Nm3 50kg 15,000m3 Extrusion granulation 20kWh 3Nm3 0 2500m3

[0020] 4. The roller extrusion granulator uses the extrusion force of two relatively rotating rollers to form granules. The surfaces of the two steel rollers have evenly arranged hemispherical pit models, which are directly on the surface of the steel cylinder. The powder enters between the two rollers from the feeding port. After the two corresponding hemispherical molds on the rollers are filled with material, they are squeezed relative to each other, and the two hemispheres are combined into an oblate spherical particle. It is a pure physical granulation, and no adhesive is required.

[0021] Furthermore, the ammonium carbonate solution in step 1 is an ammonium carbonate solution prepared by countercurrent absorption of carbon dioxide, ammonia and water, and water is circulated and absorbed during the absorption process so that its concentration reaches more than 30%.

[0022] Furthermore, the countercurrent absorption process of carbon dioxide, ammonia and water is divided into two-stage absorption. The second stage utilizes washing water to cyclically absorb carbon dioxide and ammonia to form 5-10% dilute ammonium carbonate, and the first stage utilizes the dilute ammonium carbonate solution prepared in the second stage to cyclically absorb carbon dioxide and ammonia to form 30%-45% concentrated ammonium carbonate. The carbon dioxide and ammonia of the second stage come from the tail gas absorbed in the first stage.

[0023] Furthermore, during the secondary circulation absorption process, the temperature is controlled to be 40-60° C. and the gas pressure is controlled to be 40-80 kPa.

[0024] Furthermore, in the step 4, the temperature of the first-effect evaporator of the triple-effect evaporation concentration crystallizer is 105-110°C, the temperature of the second-effect evaporator is 85-90°C, and the temperature of the third-effect evaporator is 60-65°C.

[0025] Furthermore, the water content of the ammonium sulfate slurry prepared in step 4 is 5-10%.

[0026] Furthermore, the molding die of the roll extruder in step 5 includes sizes of φ3.2, 3.6, 3.8, 4.5, 5.0, 5.5, and 6.0 mm. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is the process flow chart of the present invention,

[0028] Figure 2 It is a diagram of the ammonium carbonate synthesis reaction system of the present invention. DETAILED DESCRIPTION

[0029] The following is further described in detail through specific implementation methods:

[0030] The reference numerals in the drawings of the specification include: a washing water tank 11, a primary washing pump 12, an ammonium carbonate synthesis reactor 13, an ammonium carbonate circulation pump 14, an ammonium carbonate cooler 15, an exhaust gas absorber 16, a secondary washing pump 17, an ammonium carbonate solution tank 18, and an ammonium carbonate delivery pump 19.

[0031] Implementation example Figure 1-2 As shown:

[0032] A method for producing large-particle ammonium sulfate using phosphogypsum comprises the following steps:

[0033] Step 1, raw material preparation and processing: slurrying the phosphogypsum, filtering and washing to obtain purified phosphogypsum, and preparing an ammonium carbonate solution;

[0034] After the phosphogypsum and washing water are mixed and stirred evenly, they are sent to the vacuum belt filter for filtration, washing, and hot air drying to obtain purified phosphogypsum. The purpose of washing phosphogypsum is to control the concentration of free P2O5 within 0.3% to avoid the formation of colloids during the double decomposition reaction of phosphogypsum and ammonium carbonate, which affects the reaction conversion rate. The solid content of phosphogypsum mixed with washing water is 20% to 30%, and the water content of purified phosphogypsum obtained by filtration with the vacuum belt filter is 15% to 30%. The vacuum belt filter can realize continuous feeding, filtration, washing, drying, and filter cloth regeneration functions. The washing can be collected in sections, and can be washed in reverse or downstream.

[0035] Wherein, the ammonium carbonate solution in step 1 is ammonium carbonate prepared by carbon dioxide, ammonia and water in an ammonium carbonate synthesis reactor equipped with fillers, and the ammonium carbonate synthesis reaction system is as follows: Figure 2 As shown:

[0036] Ammonia and carbon dioxide enter from the lower part of the ammonium carbonate synthesis reactor 13, and dilute ammonium carbonate solution enters from the top of the ammonium carbonate synthesis reactor 13. In the ammonium carbonate synthesis reactor 13, ammonia and carbon dioxide flow upward, and dilute ammonium carbonate solution flows downward. The two flow in countercurrent contact to react and generate ammonium carbonate. Unreacted reaction tail gas comes out from the top of the tower and enters the tail gas absorber 16. The tail gas absorption tower 16 is provided with a secondary washing pump 17. The secondary washing pump 17 is used to circulate and wash the tail gas. The washing water uses acidic washing water. The washing water absorbs enough ammonia and carbon dioxide in the process of repeated washing to form a dilute ammonium carbonate solution and is pumped into the washing water tank 11. The primary washing pump 12 is used to pump it into the ammonium carbonate synthesis reactor 13 as primary washing water. The ammonium carbonate synthesis reactor 13 is also provided with an ammonium carbonate circulation pump 14, which pumps the ammonium carbonate at the bottom of the ammonium carbonate synthesis reactor 13 into the top of the ammonium carbonate synthesis reactor 13 to repeatedly absorb carbon dioxide and ammonia to increase the concentration. Since the entire absorption process is an exothermic reaction, when the temperature is too high, the pressure of carbon dioxide and nitrogen is too large, and the absorption process is easy to slow down. Therefore, an ammonium carbonate cooler 15 is arranged on the ammonium carbonate circulation pipeline to ensure that the ammonium carbonate reaching the top of the ammonium carbonate synthesis reactor 13 is always kept at a low temperature. When the ammonium carbonate is concentrated into 30% to 45% ammonium carbonate solution, it is pumped into the ammonium carbonate solution tank 18 for temporary storage, and an ammonium carbonate delivery pump 19 is used to deliver it to the double decomposition reaction section of step 2.

[0037] The ammonium carbonate synthesis process utilizes the above-mentioned ammonium carbonate synthesis reaction system to adopt a two-stage absorption reaction.

[0038] The first stage is an ammonium carbonate synthesis reactor 13. The dilute ammonium carbonate solution formed after the second stage absorption is used as washing water at the top of the tower. It flows downward to absorb carbon dioxide and ammonia and is converted into a concentrated ammonium carbonate solution. The concentration of the ammonium carbonate solution can reach up to 45%, which greatly reduces the load of subsequent concentration and evaporation and reduces production costs.

[0039] The second stage uses acidic washing water such as washing water to absorb the tail gas of the first reaction, fully absorbs the ammonia in the tail gas, reduces the consumption of ammonia and thus reduces the production cost. The ammonia conversion rate is above 99.5%. The washing water from the second stage absorption is sent to the first stage absorption supplementary water, and the process water of the entire production system is reused.

[0040] Ammonia, water and carbon dioxide react to form ammonium carbonate solution. The reaction equation is as follows:

[0041]

[0042] The ammonium carbonate synthesis reaction releases heat. The higher the temperature, the higher the evaporation pressure of ammonia and carbon dioxide, which is not conducive to the conversion rate of ammonia. Therefore, the ammonium carbonate circulating liquid is cooled to 50°C and the synthesis reaction temperature is 40-60°C.

[0043] The reaction equation for secondary absorption is as follows:

[0044] 2yH3+H2SO4→(NH4)2SO4

[0045] The design of the secondary absorption makes the conversion rate of ammonia in the preparation process of ammonium carbonate of the present application to be above 99.5%. The pressure control range of the ammonium carbonate synthesis reactor in the secondary absorption process is 40-80 kPa, the reaction temperature control range is 40-60°C, the mass ratio of carbon dioxide to ammonia feed is 1.35-1.45:1, and the concentration of ammonium carbonate generated by the reaction is 30%-45%. The filler in the ammonium carbonate synthesis reactor is ball ring.

[0046] Step 2, preparing ammonium sulfate: mixing the ammonium carbonate solution in step 1 with the purified phosphogypsum, mixing them evenly to carry out double decomposition reaction, and obtaining a mixed slurry of calcium carbonate and ammonium sulfate after the reaction is completed; filtering and washing the mixed slurry to obtain solid calcium carbonate and liquid ammonium sulfate solution.

[0047] Purified phosphogypsum and ammonium carbonate solution are added to a cyclone mixer in a mass ratio of 1.45-1.55:1 for mixing. After being mixed into a balanced slurry in the cyclone mixer, they are introduced into a double decomposition reactor. The reaction temperature of the double decomposition reactor is controlled between 60 and 80° C., the speed of the reactor stirrer is 60-80 r / min, and the reaction is carried out for 3-4 hours. In order to convert all calcium sulfate into calcium carbonate, the material reaction residence time shall not be less than 3 hours. After the reaction, the mixed slurry of calcium carbonate and ammonium sulfate is discharged from the double decomposition reactor.

[0048] The mixed slurry after the double decomposition reaction is completely sent to a vacuum belt filter for filtration, washing and drying to obtain solid calcium carbonate and liquid ammonium sulfate solution.

[0049] The vacuum belt filter can realize continuous feeding, filtration, washing, drying and filter cloth regeneration. The washing can be collected in sections and can be washed in reverse or downstream.

[0050] Step 3, neutralization: add an appropriate amount of sulfuric acid to neutralize the ammonium sulfate solution obtained by filtering in step 2, and convert a small amount of ammonia and ammonium carbonate in the solution into ammonium sulfate;

[0051] The mass fraction of ammonium sulfate in the ammonium sulfate filtrate obtained in step 2 is 30% to 45%, and there is also excess unreacted ammonium carbonate and a small amount of free ammonia in the filtrate. In order to increase the ammonium sulfate concentration, dilute sulfuric acid is added to the ammonium sulfate solution.

[0052] Step 4, evaporation crystallization: the neutralized ammonium sulfate solution is concentrated by a triple-effect evaporation crystallizer to obtain ammonium sulfate slurry;

[0053] The ammonium sulfate solution enters the triple-effect evaporation concentration crystallizer, the temperature of the first-effect evaporator is 105-110°C, the temperature of the second-effect evaporator is 85-90°C, and the temperature of the triple-effect evaporator is 60-65°C. The solid content of the crystal slurry discharged from the crystallization system is 20-30%. Each effect evaporation concentration crystallizer is an Oslo-type continuous crystallizer. The crystal slurry containing 20-30% of ammonium sulfate crystals is continuously separated by a centrifuge to finally obtain ammonium sulfate crystal slurry with a water content of 5-10%, and the mother liquor returns to the triple-effect evaporation concentration crystallization system.

[0054] Step 5, preparing ammonium sulfate spheres: conveying ammonium sulfate slurry with a water content of 5-10% to a double-roll extruder to prepare spherical large-particle ammonium sulfate;

[0055] Ammonium sulfate slurry is fed into the double-roll extrusion granulator to obtain spherical large-particle ammonium sulfate. The particle size of the product particles can be adjusted by replacing the mold (φ3.2, 3.6, 3.8, 4.5, 5.0, 5.5, 6.0 mm). The double-roll extrusion granulator is a dry granulation machine that granulates at room temperature and forms the particles in one step.

[0056] Step 6, drying the finished product: the large-particle ammonium sulfate is dried by a drum dryer to obtain a large-particle ammonium sulfate finished product.

[0057] Large-particle ammonium sulfate is precipitated during the drying process of the drum dryer, and the ammonium sulfate precipitated later generates various connection relationships such as van der Waals force, adsorption force, crystal bridge and embedded connection with the ammonium sulfate precipitated in step 4, forming a spherical large-particle ammonium sulfate product with high strength. The water content of the spherical large-particle ammonium sulfate product is ≤0.15%. The heat source of the drum dryer is hot air, and the rotation speed is 6r / min.

[0058] The above is only an embodiment of the present invention, and the common knowledge such as the known specific structure and characteristics in the scheme is not described in detail here. It should be pointed out that for those skilled in the art, several deformations and improvements can be made without departing from the structure of the present invention, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for producing large-particle ammonium sulfate using phosphogypsum, characterized in that: The following steps are involved: Step 1, raw material preparation and processing: slurrying the phosphogypsum, filtering and washing to obtain purified phosphogypsum, and preparing an ammonium carbonate solution; Step 2, preparing ammonium sulfate: mixing the ammonium carbonate solution in step 1 with the purified phosphogypsum, mixing them evenly to carry out double decomposition reaction, and obtaining a mixed slurry of calcium carbonate and ammonium sulfate after the reaction is completed; filtering and washing the mixed slurry to obtain a solid phase calcium carbonate and a liquid phase ammonium sulfate solution; Step 3, neutralization: add an appropriate amount of sulfuric acid to neutralize the ammonium sulfate solution obtained by filtering in step 2, and convert a small amount of ammonia and ammonium carbonate in the solution into ammonium sulfate; Step 4, evaporation crystallization: the neutralized ammonium sulfate solution is concentrated by a triple-effect evaporation crystallizer to obtain ammonium sulfate slurry; Step 5, preparing ammonium sulfate spheres: conveying the ammonium sulfate slurry to a double-roll extruder to prepare spherical large-particle ammonium sulfate; Step 6, drying the finished product: the large-particle ammonium sulfate is dried by a drum dryer to obtain a large-particle ammonium sulfate finished product.

2. The method for producing large-particle ammonium sulfate using phosphogypsum according to claim 1, characterized in that: The ammonium carbonate solution in step 1 is an ammonium carbonate solution prepared by countercurrent absorption of carbon dioxide, ammonia and water, and water is circulated and absorbed during the absorption process so that its concentration reaches more than 30%.

3. The method for producing large-particle ammonium sulfate using phosphogypsum according to claim 2, characterized in that: The countercurrent absorption process of carbon dioxide, ammonia and water is divided into two stages of absorption. The second stage utilizes washing water to cyclically absorb carbon dioxide and ammonia to form 5-10% dilute ammonium carbonate. The first stage utilizes the dilute ammonium carbonate solution prepared in the second stage to cyclically absorb carbon dioxide and ammonia to form 30%-45% concentrated ammonium carbonate. The carbon dioxide and ammonia in the second stage come from the tail gas absorbed in the first stage.

4. The method for producing large-particle ammonium sulfate by using phosphogypsum according to claim 3, characterized in that: During the secondary circulation absorption process, the temperature is controlled at 40-60° C. and the gas pressure is controlled at 40-80 kPa.

5. The method for producing large-particle ammonium sulfate using phosphogypsum according to claim 1, characterized in that: In the step 4, the temperature of the first-effect evaporator of the triple-effect evaporation concentration crystallizer is 105-110°C, the temperature of the second-effect evaporator is 85-90°C, and the temperature of the third-effect evaporator is 60-65°C.

6. The method for producing large-particle ammonium sulfate using phosphogypsum according to claim 5, characterized in that: The water content of the ammonium sulfate slurry prepared in step 4 is 5-10%.

7. The method for producing large-particle ammonium sulfate using phosphogypsum according to claim 6, characterized in that: The molding die of the roller extruder in step 5 includes sizes of φ3.2, 3.6, 3.8, 4.5, 5.0, 5.5, and 6.0 mm.

Images