Method and system for treating ferric phosphate mother liquor and washing water

Abstract

The present invention provides a method and system for treating iron phosphate mother liquor and washing water, the method comprising: S110, using the mother liquor to be treated to absorb gaseous ammonia to obtain a process liquid, using the washing water to be treated to absorb gaseous ammonia to obtain ammonia absorbing liquid, and using the process water to absorb gaseous ammonia to obtain ammonia water; wherein, gaseous ammonia is produced by gasifying liquid ammonia by heat released by the mother liquor in the process of absorbing gaseous ammonia; S120, using ammonia water to condition the process liquid and the ammonia absorbing liquid; S130, performing one or more operations of evaporation concentration, centrifugation, solid-liquid separation, drying and cooling crystallization on the conditioned process liquid and the ammonia absorbing liquid to obtain a product fertilizer. Using gaseous ammonia can reduce the amount of water to be treated in subsequent evaporation and crystallization; and the mother liquor after absorbing gaseous ammonia is cooled successively by circulating water and liquid ammonia gasification, making full use of the heat absorption of liquid ammonia gasification to reduce the consumption of circulating water, while increasing the ammonia recovery rate and increasing the concentration of the mother liquor and washing water, further reducing the amount of water to be treated by evaporation and crystallization, thereby reducing the investment and operation costs of treating the mother liquor and washing water.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater treatment in the new energy industry, and in particular to a method and system for treating iron phosphate mother liquor and wash water. Background Art

[0002] With the rapid development of the new energy market, the demand for power batteries, energy storage materials or equipment is increasing. Correspondingly, the demand for iron phosphate, the precursor of lithium iron phosphate for the preparation of battery positive electrode materials, is also increasing. At present, iron phosphate is generally prepared from ferrous sulfate, monoammonium phosphate and hydrogen peroxide through oxidation, synthesis, filtration, sintering, washing and other processes. The synthetic mother liquor and washing water in the preparation process contain different concentrations of ammonium ions, metal ions, sulfate ions (SO4 2- ), phosphate (hydrogen) ion (H2PO4 - )'s high-salt inorganic wastewater, if discharged directly, does not meet the discharge standards of industrial wastewater and will cause serious pollution and damage to the surrounding environment. Therefore, the wastewater needs to be treated for recycling or to meet the discharge standards.

[0003] Iron phosphate is mainly used to produce positive electrode material lithium iron phosphate, which is made by combining iron phosphate precursor and battery-grade lithium hydroxide. The reaction equation is:

[0004] 2FePO4+2LiOH+C→2LiFePO4+H2O+CO.

[0005] There are currently two methods for producing iron phosphate: one is to use phosphoric acid and iron salt to react, and the other is to recycle lithium iron phosphate batteries. Both of the above iron phosphate treatment methods will produce iron phosphate wastewater.

[0006] At present, the mainstream methods for treating wastewater from iron phosphate production include lime precipitation, magnesium salt treatment and membrane treatment:

[0007] 1) Lime precipitation method

[0008] A large amount of limestone and lime is added to the wastewater, and the gaseous ammonia is recovered and the supernatant is directly discharged without considering the total salt exceeding the standard. This method will produce a large amount of difficult-to-handle sludge and does not take into account the discharge and disposal of salt.

[0009] 2) Stripping of high concentration ammonia nitrogen and precipitation of magnesium ammonium phosphate

[0010] Magnesium oxide and magnesium hydroxide are added to the wastewater to generate magnesium ammonium phosphate (struvite); the remaining ammonia gas / ammonium salt is then stripped and absorbed by sulfuric acid to generate ammonium sulfate. However, this method has a long process flow, consumes a large amount of magnesium salt and steam, has high treatment costs, and it is difficult for the wastewater to meet discharge standards.

[0011] 3) Combined process of membrane method and multi-effect evaporation

[0012] Ammonium sulfate and monoammonium phosphate fertilizers are produced, and the distilled water can also be recycled, but the process is complicated and the investment cost is high.

[0013] Furthermore, the Chinese invention patent application with publication number CN114105392A discloses a method for treating iron phosphate wastewater, comprising:

[0014] S1, pre-treating the ferric phosphate mother liquor to obtain a clarified filtrate of the mother liquor, adding ammonia water to adjust the pH of the mother liquor in the ferric phosphate production process to 7-8, pre-treating the ferric phosphate washing water to obtain concentrated water A, and adding ammonia water to adjust the pH of the washing water in the ferric phosphate production process to 7-8 before concentration;

[0015] S2, mixing the clarified filtrate of the mother liquor and concentrated water A, and evaporating and concentrating them to obtain concentrated water B;

[0016] S3, concentrated water B is centrifuged and cooled for crystallization to obtain a solid product which is then dried to obtain fertilizer products such as ammonium sulfate, ammonium hydrogen phosphate and magnesium sulfate.

[0017] This method has the following problems:

[0018] 1) The demand for ammonia water is large, and the cost of transportation and storage is high.

[0019] 2) The use of ammonia water for conditioning will increase the amount of mother liquor and wash water treated by 5-20%, increasing the investment and operating costs of subsequent MVR evaporation and crystallization.

[0020] Therefore, how to reduce the treatment cost of mother liquor and wash water in the production process of ferric phosphate has become a technical problem that needs to be solved urgently. Summary of the invention

[0021] The technical problems of high treatment cost or incomplete treatment of mother liquor and wash water in the production process of ferric phosphate are addressed.

[0022] The present invention provides a method for treating iron phosphate mother liquor and wash water, the method comprising:

[0023] S110, using the mother liquid to be treated to absorb gaseous ammonia to obtain process liquid, using the washing water to be treated to absorb gaseous ammonia to obtain ammonia absorbing liquid, and using the process water to absorb gaseous ammonia to obtain ammonia water; wherein the gaseous ammonia is produced by gasifying liquid ammonia by heat released by the mother liquid during the process of absorbing gaseous ammonia;

[0024] S120, using ammonia water to condition the process liquid and the ammonia absorbing liquid;

[0025] S130, subjecting the conditioned process liquid and the ammonia absorbing liquid to one or more operations of evaporation concentration, centrifugation, solid-liquid separation, drying and cooling crystallization to obtain a product fertilizer.

[0026] Preferably, S110 further includes cooling the process liquid by circulating water and liquid ammonia gasification, and the ratio of heat transferred by the circulating water and liquid ammonia gasification is 1:(2-10).

[0027] Preferably, in S110, the mass ratio of the mother liquor, wash water and process water absorbed ammonia is 1:(0.10-0.35):(0.15-0.50).

[0028] Preferably, in S110, the concentration of ammonia water obtained after the process water absorbs gaseous ammonia is 17.7%-22.3%.

[0029] Preferably, in S110, the mother liquor and the wash water are in a flowing state, wherein the flow rate of the mother liquor is 50-600m 3 / h, washing water flow rate is 80-1200m 3 / h, and the volume ratio of mother liquor to washing water is 1:(1.3-2.5).

[0030] Preferably, in S120, the pH of the process liquid before conditioning is 4.2-5.3, and the pH after conditioning is 6.8-8.4; the pH of the ammonia absorbing liquid before conditioning is 4.5-5.6, and the pH after conditioning is 7-8.8; the ratio of the process liquid to the ammonia absorbing liquid absorbing ammonia water is 1:(0.5-2.0).

[0031] Preferably, in S130, the product fertilizer includes ammonium sulfate and monoammonium phosphate; wherein the monoammonium phosphate is obtained by subjecting part of the centrifuged mother liquor of ammonium sulfate to one or more operations of cooling crystallization, solid-liquid separation, and drying.

[0032] Preferably, after S130, the method further comprises: S140, dissolving monoammonium phosphate in water, and further reacting with ammonia water to obtain diammonium phosphate.

[0033] As a parallel solution, the present invention also provides a method for treating iron phosphate mother liquor and wash water, the method further comprising:

[0034] S210, using the mother liquid to be treated to absorb gaseous ammonia to obtain process liquid, using the washing water to be treated to absorb gaseous ammonia to obtain ammonia absorbing liquid, and using the process water to absorb gaseous ammonia to obtain ammonia water; wherein the gaseous ammonia is produced by gasifying liquid ammonia by heat released by the mother liquid during the process of absorbing gaseous ammonia;

[0035] S220, performing operations including but not limited to evaporation and concentration on the ammonia absorbing liquid, and then mixing the ammonia absorbing liquid with the process liquid to obtain a mixed liquid;

[0036] S230, conditioning the mixed solution using aqueous ammonia and potassium dihydrogen phosphate;

[0037] S240, performing one or more operations of evaporation concentration and hot air drying on the conditioned mixed liquid to obtain a product compound fertilizer.

[0038] The present invention also provides a system for treating ferric phosphate mother liquor and wash water, which is applied to the above-mentioned method for treating ferric phosphate mother liquor and wash water and the parallel scheme, and the system comprises:

[0039] Mother liquor ammonia absorption cooling equipment, used for mother liquor to absorb gaseous ammonia to prepare process liquid, and to cool the process liquid; and

[0040] Wash water ammonia absorption equipment, used for washing water to absorb gaseous ammonia to prepare ammonia absorption liquid;

[0041] Ammonia water preparation equipment, used for absorbing gaseous ammonia from process water to prepare ammonia water;

[0042] Liquid ammonia gasification equipment, used to utilize the heat released by the mother liquid absorbing gaseous ammonia to gasify liquid ammonia, and to provide gaseous ammonia to the mother liquid ammonia absorption cooling equipment, the wash water ammonia absorption equipment and the ammonia water preparation equipment through the gaseous ammonia pipeline;

[0043] Conditioning equipment, respectively connected to the mother liquor ammonia absorption cooling equipment, the wash water ammonia absorption equipment and the ammonia water preparation, for conditioning the process liquid and the ammonia absorption liquid with ammonia water; or, respectively connected to the mother liquor ammonia absorption cooling equipment, the wash water ammonia absorption equipment and the ammonia water preparation, for conditioning the mixed liquid of the process liquid and the ammonia absorption liquid with ammonia water and potassium dihydrogen phosphate;

[0044] The fertilizer production equipment is connected to the conditioning equipment and is used to prepare the finished fertilizer after filtering, evaporating and concentrating, centrifuging, separating solid from liquid, drying and cooling and crystallizing the conditioned process liquid and ammonia absorbing liquid.

[0045] In summary, the lithium iron phosphate mother liquor and wash water treatment method and system provided by the present invention utilize the heat released by the mother liquor absorbing gaseous ammonia to gasify liquid ammonia into gaseous ammonia, and then use the mother liquor to absorb gaseous ammonia to prepare process liquid, use the wash water to absorb gaseous ammonia to prepare ammonia absorbing liquid, and use the ammonia water obtained by absorbing gaseous ammonia with the process water to condition the process liquid and the ammonia absorbing liquid, and then obtain the product fertilizer or product compound fertilizer through operations such as evaporation concentration, separation and drying.

[0046] Among them, the use of gaseous ammonia can reduce the cost of transporting ammonia water and the amount of water for subsequent evaporation and crystallization. Furthermore, the mother liquor absorbs gaseous ammonia to continuously release heat to vaporize liquid ammonia, thereby eliminating the need for a liquid ammonia storage tank with great safety hazards. The mother liquor after absorbing gaseous ammonia is cooled successively by circulating water and liquid ammonia vaporization. The heat absorption of liquid ammonia vaporization can be fully utilized to reduce the consumption of circulating water, improve the ammonia recovery rate, and increase the concentration of mother liquor and washing water, further reducing the amount of water for evaporation and crystallization. The mother liquor and washing water are recovered into fertilizer efficiently and at low cost, reducing the investment and operation costs of treating mother liquor and washing water. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0048] Figure 1 : A flow chart of a method for treating a ferric phosphate mother liquor and wash water provided by an embodiment of the present invention;

[0049] Figure 2 : A process diagram of a method for treating a ferric phosphate mother liquor and wash water provided in an embodiment of the present invention;

[0050] Figure 3 : A flow chart of a method for treating a ferric phosphate mother liquor and wash water provided by an embodiment of the present invention;

[0051] Figure 4 : A flow chart of a method for treating a ferric phosphate mother liquor and wash water provided by an embodiment of the present invention;

[0052] Figure 5 : A process diagram of a method for treating a ferric phosphate mother liquor and wash water provided in an embodiment of the present invention;

[0053] Figure 6 : A device diagram of a system for processing iron phosphate mother liquor and wash water to produce product fertilizers provided by an embodiment of the present invention;

[0054] Figure 7 : Equipment diagram of a system for processing iron phosphate mother liquor and wash water for producing compound fertilizer products provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0055] In order to make the above and other features and advantages of the present invention more clear, the present invention is further described below in conjunction with the accompanying drawings. It should be understood that the specific embodiments given herein are for the purpose of explaining to those skilled in the art and are only exemplary and not restrictive.

[0056] In the following description, many specific details are set forth to provide a thorough understanding of the present invention. However, it is apparent to one of ordinary skill in the art that specific details need not be adopted to practice the present invention. In other cases, well-known steps or operations are not described in detail to avoid obscuring the present invention.

[0057] In order to reduce the treatment cost of mother liquor and wash water in the production process of ferric phosphate, the present invention provides a method for treating ferric phosphate mother liquor and wash water, such as Figure 1 As shown, the method includes:

[0058] S110, using the mother liquid to be treated to absorb gaseous ammonia to obtain process liquid, using the washing water to be treated to absorb gaseous ammonia to obtain ammonia absorbing liquid, and using process water to absorb gaseous ammonia to obtain ammonia water; wherein, gaseous ammonia is produced by gasifying liquid ammonia by heat released by the mother liquid during the process of absorbing gaseous ammonia.

[0059] like Figure 2 As shown, in the present application, the heat released by the liquid ammonia absorption mother liquor in the process of absorbing gaseous ammonia is used to gasify and generate gaseous ammonia, and the gaseous ammonia is respectively transported to the mother liquor, wash water and process water for absorption through the gaseous ammonia pipeline. The gaseous ammonia generated by the gasification of liquid ammonia is used to treat the mother liquor and wash water instead of using ammonia water, thereby reducing the transportation cost and the amount of water to be treated in subsequent operations such as evaporation and crystallization.

[0060] Specifically, the liquid ammonia gasification and mother liquid ammonia absorption and process liquid cooling equipment are integrated equipment. In the preferred scheme, the lower part is a liquid ammonia gasifier, and the gas ammonia obtained by liquid ammonia gasification is connected to the upper mother liquid ammonia absorption device through an internal pipeline to prepare the process liquid, and then the process liquid is cooled by the middle circulating water cooler and the lower liquid ammonia gasifier. Among them, the gas ammonia temperature after liquid ammonia gasification is -5-10°C, the pressure is 0.3-1.5MPa, and the gas ammonia can be directly sent to the washing water and process water ammonia absorption tower. In the preferred scheme, the circulating water and liquid ammonia gasification cool the process liquid, and the ratio of the heat transferred by the two parts is 1: (2-10). Thereby, the amount of gas ammonia produced by liquid ammonia gasification is guaranteed, and the heat absorption of liquid ammonia gasification is fully utilized, which reduces the circulating water consumption of the cooling process liquid. Further, due to the two-stage cooling of circulating water and liquid ammonia gasification, the liquid ammonia gasification cold capacity is fully utilized, so that the heat can be removed in time to prevent ammonia from escaping, the recovery rate of ammonia can be improved, and the secondary pollution of ammonia can also be reduced.

[0061] In some preferred schemes, the mass ratio of mother liquor, wash water, and process water to absorb gas ammonia is 1:(0.10-0.35):(0.15-0.50). According to the mother liquor and wash water components and conditioning requirements, the amount of ammonia used is accurately controlled to minimize the amount of ammonia water used, thereby increasing the concentration of the process liquid, reducing the amount of process liquid treated, and also reducing the investment and operating costs of subsequent MVR evaporation crystallization.

[0062] In other preferred solutions, the concentration of ammonia water obtained after the process water absorbs gaseous ammonia is 17.7%-22.3%. By accurately controlling the concentration of ammonia water, the processing volume of mother liquor and washing water can be guaranteed, and it is also beneficial to adjust the pH of the process liquid and ammonia absorbing liquid later, thereby reducing the processing volume of the conditioned process liquid and ammonia absorbing liquid as much as possible.

[0063] In a preferred embodiment, the mother liquor and the wash water are in a flowing state, wherein the mother liquor flow rate is 50-600m 3 / h, washing water flow rate is 80-1200m 3 / h, and the volume ratio of mother liquor to washing water is 1:(1.3-2.5). By accurately controlling the flow rate of mother liquor and washing water, as well as the volume ratio of mother liquor to washing water, the efficiency of treating mother liquor and washing water can be fully guaranteed.

[0064] In some more preferred schemes, wash water and process water absorb gaseous ammonia by spraying in an absorption tower, the liquid-to-gas ratio in the absorption tower for preparing ammonia absorbing liquid from wash water is 0.18-0.35L / L, and the number of spraying layers is at least 2 layers, and the liquid-to-gas ratio in the absorption tower for preparing ammonia water from process water is 0.02-0.1L / L, and the number of spraying layers is at least 2 layers.

[0065] S120, use ammonia water to condition the process liquid and ammonia absorption liquid.

[0066] Specifically, the pH of the process liquid before conditioning is 4.2-5.3, and the pH after conditioning is 6.8-8.4; the pH of the ammonia absorbing liquid before conditioning is 4.5-5.6, and the pH after conditioning is 7-8.8; the two-stage pH control can not only prevent a large amount of metal ions from precipitating during the absorption of gaseous ammonia, affecting the absorption effect, but also reasonably distribute the amount of metal ion precipitation in the two stages to make the metal ion precipitation more thorough. Furthermore, during the conditioning process, the ratio of the process liquid to the ammonia absorbing liquid to absorb ammonia water is 1: (0.5-2.0), and the amount of ammonia water used is accurately controlled. While meeting the conditioning requirements, the processing volume of the process liquid and ammonia absorbing liquid after conditioning is minimized.

[0067] After conditioning, the ammonium ion concentration in the process liquid is 15-30g / L, the sulfate ion concentration is 50-100g / L, the phosphate (hydrogen) ion concentration is 0.5-2g / L, and the metal ion concentration is 1.1-4g / L; the ammonium ion concentration in the ammonia absorbing liquid is 5-10g / L, the sulfate ion concentration is 15-40g / L, the phosphate (hydrogen) ion concentration is 1.5-5g / L; the metal ion concentration is 0.25-1g / L.

[0068] S130, subjecting the conditioned process liquid and the ammonia absorbing liquid to one or more operations of evaporation concentration, centrifugation, solid-liquid separation, drying and cooling crystallization to obtain a product fertilizer.

[0069] Specifically, the product fertilizer includes ammonium sulfate and monoammonium phosphate; the conditioned process liquid and the centrifugal liquid obtained by evaporation and crystallization of the ammonia absorption liquid are separated by solid-liquid separation equipment and then dried by drying equipment to obtain the product ammonium sulfate; wherein the nitrogen content in the ammonium sulfate is ≥20%, and the sulfur content is ≥23%. Furthermore, part of the ammonium sulfate solid-liquid separation mother liquor is cooled, crystallized, solid-liquid separated, and dried by cooling crystallization equipment to obtain the product monoammonium phosphate.

[0070] like Figure 3 As shown, after S130, the method further includes: S140, dissolving monoammonium phosphate in water, and further reacting with ammonia water to obtain diammonium phosphate.

[0071] After monoammonium phosphate is obtained, it can be recycled to prepare iron phosphate as needed, or further reacted with ammonia water to produce diammonium phosphate product.

[0072] As a parallel solution of the present application, the present application also provides a method for treating iron phosphate mother liquor and wash water, such as Figure 4 As shown, the method also includes:

[0073] S210, using the mother liquid to be treated to absorb gaseous ammonia to obtain a process liquid, using the wash water to be treated to absorb gaseous ammonia to obtain ammonia absorbing liquid, and using the process water to absorb gaseous ammonia to obtain ammonia water;

[0074] Among them, gaseous ammonia is produced by gasifying liquid ammonia with the heat released by the mother liquor in the process of absorbing gaseous ammonia;

[0075] like Figure 5 As shown, in the present application, the heat released by the liquid ammonia absorption mother liquor in the process of absorbing gaseous ammonia is used to gasify and generate gaseous ammonia, and the gaseous ammonia is respectively transported to the mother liquor, wash water and process water for absorption through the gaseous ammonia pipeline. The gaseous ammonia generated by the gasification of liquid ammonia is used to treat the mother liquor and wash water instead of using ammonia water, thereby reducing the transportation cost and the amount of water to be treated in subsequent operations such as evaporation and crystallization.

[0076] Specifically, the liquid ammonia gasification and mother liquid ammonia absorption and process liquid cooling equipment are integrated equipment. In the preferred scheme, the lower part is a liquid ammonia gasifier, and the gas ammonia obtained by liquid ammonia gasification is connected to the upper mother liquid ammonia absorption device through an internal pipeline to prepare the process liquid, and then the process liquid is cooled by the middle circulating water cooler and the lower liquid ammonia gasifier. Among them, the gas ammonia temperature after liquid ammonia gasification is -5-10°C, the pressure is 0.3-1.5MPa, and the gas ammonia can be directly sent to the washing water and process water ammonia absorption tower. In the preferred scheme, the circulating water and liquid ammonia gasification cool the process liquid, and the ratio of the heat transferred by the two parts is 1: (2-10). Thereby, the amount of gas ammonia produced by liquid ammonia gasification is guaranteed, and the heat absorption of liquid ammonia gasification is fully utilized, which reduces the circulating water consumption of the cooling process liquid. Further, due to the two-stage cooling of circulating water and liquid ammonia gasification, the liquid ammonia gasification cold capacity is fully utilized, so that the heat can be removed in time to prevent ammonia from escaping, the recovery rate of ammonia can be improved, and the secondary pollution of ammonia can also be reduced.

[0077] In some preferred schemes, the mass ratio of mother liquor, wash water, and process water absorption gas ammonia is 1:(0.1-0.35):(0.15-0.5). According to the mother liquor and wash water components and conditioning requirements, the amount of ammonia used is accurately controlled to reduce the amount of ammonia water used as much as possible, thereby increasing the concentration of the process liquid, reducing the amount of process liquid treated, and also reducing the investment and operating costs of subsequent MVR evaporation crystallization.

[0078] In other preferred solutions, the concentration of ammonia water obtained after the process water absorbs gaseous ammonia is 17.7%-22.3%. By accurately controlling the concentration of ammonia water, the processing volume of mother liquor and washing water can be guaranteed, and it is also beneficial to adjust the pH of the process liquid and ammonia absorbing liquid later, thereby reducing the processing volume of the conditioned process liquid and ammonia absorbing liquid as much as possible.

[0079] In a preferred embodiment, the mother liquor and the wash water are in a flowing state, wherein the mother liquor flow rate is 50-600m 3 / h, washing water flow rate is 80-1200m 3 / h, and the volume ratio of mother liquor to washing water is 1:(1.3-2.5). By accurately controlling the flow rate of mother liquor and washing water, as well as the volume ratio of mother liquor to washing water, the efficiency of treating mother liquor and washing water can be fully guaranteed.

[0080] S220, performing operations including but not limited to evaporation and concentration on the ammonia absorbing liquid, and then mixing the ammonia absorbing liquid with the process liquid to obtain a mixed liquid;

[0081] S230, conditioning the mixed solution using aqueous ammonia and potassium dihydrogen phosphate;

[0082] S240, performing one or more operations of evaporation concentration and hot air drying on the conditioned mixed liquid to obtain a product compound fertilizer.

[0083] Specifically, in this scheme, ammonia water is not used to condition the ammonia absorbing liquid, but the ammonia absorbing liquid is concentrated and directly mixed with the process liquid, and the mixed liquid is mixed and conditioned with ammonia water and potassium dihydrogen phosphate, and then the mixed liquid is further concentrated and hot air dried to obtain the product compound fertilizer. The content of N, P2O5 and K2O in the product compound fertilizer is 40-50%, wherein the N content is ≥15%, the P2O5 content is ≥16%, and the K2O content is ≥9%.

[0084] In summary, the method provided by the present invention has the following advantages:

[0085] 1) The use of gaseous ammonia reduces the transportation cost of ammonia water and the amount of water for evaporation and crystallization treatment, improves the ammonia recovery rate, and increases the concentration of mother liquor and washing water, reducing the investment and operating costs of evaporation and crystallization.

[0086] 2) Make full use of the heat absorption of liquid ammonia gasification to reduce the consumption of circulating water.

[0087] 3) Liquid ammonia is directly vaporized and absorbed by process water / wash water / mother liquor, and there is no need for a liquid ammonia storage tank with great safety hazards.

[0088] 4) The temperature of the process liquid can be reduced to 20-30℃ after two-stage cooling by circulating water and liquid ammonia gasification, making full use of the cooling capacity of liquid ammonia gasification, removing heat in time, preventing ammonia escape, improving ammonia recovery rate and reducing secondary pollution.

[0089] 5) Strictly control the proportion of ammonia used in each step, the pH after ammonia use, the liquid-to-gas ratio of the absorber and other parameters to ensure the quality of the products ammonium sulfate and monoammonium phosphate, and efficiently and low-costly recycle the mother liquor and washing water into fertilizers. The monoammonium phosphate can be reused for the preparation of iron phosphate or further processed into diammonium phosphate products as needed.

[0090] 6) Reduce investment and operating costs, floor space, and improve operational stability.

[0091] 7) The mother liquor and washing water can be conditioned separately or together. After being conditioned together with ammonia water and potassium dihydrogen phosphate, a compound fertilizer with a total content of N, P2O5 and K2O of 40-50% can be produced, wherein the N content is ≥15%, the P2O5 content is ≥16%, and the K2O content is ≥9%, thereby increasing the added value of the product, reducing the investment and operation costs, and improving the product structure.

[0092] In order to demonstrate the advantages of the method provided by the present invention, it is described below in conjunction with specific embodiments.

[0093] Embodiment 1

[0094] The mother liquor absorbs the heat of ammonia to vaporize the liquid ammonia into gaseous ammonia. After the liquid ammonia is vaporized, the temperature of the gaseous ammonia is 0°C and the pressure is 1MPa. The vaporized liquid ammonia is absorbed by the mother liquor, washing water and process water respectively, and the absorption mass ratio is 1:0.25:0.35.

[0095] The temperature of the mother liquor after absorbing ammonia is 60°C. The mother liquor after absorption is cooled down successively by circulating water and liquid ammonia gasification, and the heat ratio of the two parts is 1:3; the temperature of the process liquid after cooling down is 25°C.

[0096] The concentration of ammonia water obtained after the process water absorbs gaseous ammonia is 20%.

[0097] Ammonia water was used to condition the process liquid. The pH before conditioning was 4.5 and the pH after conditioning was 7.

[0098] Ammonia water was used to condition the ammonia absorbing liquid. The pH before conditioning was 4.8 and the pH after conditioning was 7.3.

[0099] Among them, the ratio of process liquid and ammonia absorbing liquid to ammonia water is 1:1.35.

[0100] After conditioning, the concentration of ammonium ions in the process liquid is 22 g / L, the concentration of sulfate ions is 65 g / L, the concentration of phosphate (hydrogen) ions is 1.1 g / L, and the concentration of metal ions is 1.1 g / L;

[0101] The ammonium ion concentration in the ammonia absorption solution is 7g / L, the sulfate ion concentration is 20g / L, the phosphate (hydrogen) ion concentration is 3g / L; the metal ion concentration is 0.3g / L.

[0102] The tempered process liquid and the centrifugal liquid obtained by evaporation and crystallization of the ammonia absorption liquid are separated by solid-liquid separation equipment and then dried by drying equipment to obtain the product ammonium sulfate; part of the ammonium sulfate solid-liquid separation mother liquor is cooled, crystallized, solid-liquid separated and dried by cooling crystallization equipment to obtain the product monoammonium phosphate.

[0103] Among them, the mother liquor flow rate is 180m 3 / h, washing water flow rate 360m 3 / h; liquid ammonia consumption 1t / h, product ammonium sulfate output 20t / h, product monoammonium phosphate output 0.5t / h.

[0104] Embodiment 2

[0105] The mother liquor absorbs the heat of ammonia to vaporize the liquid ammonia into gaseous ammonia. After the liquid ammonia is vaporized, the temperature of the gaseous ammonia is 3°C and the pressure is 1.3MPa. The vaporized liquid ammonia is absorbed by the mother liquor, washing water and process water respectively, and the absorption mass ratio is 1:0.3:0.4.

[0106] The temperature of the mother liquor after absorbing ammonia is 75°C. The mother liquor after absorption is cooled down successively by circulating water and liquid ammonia gasification, and the heat ratio of the two parts is 1:5; the temperature of the process liquid after cooling down is 28°C.

[0107] The concentration of ammonia water obtained after the process water absorbs gaseous ammonia is 21%.

[0108] Ammonia water was used to condition the process liquid. The pH before conditioning was 4.9 and the pH after conditioning was 7.6.

[0109] Ammonia water was used to condition the ammonia absorbing liquid. The pH before conditioning was 5.2 and the pH after conditioning was 8.

[0110] Among them, the ratio of process liquid and ammonia absorbing liquid to ammonia water is 1:1.35.

[0111] After conditioning, the concentration of ammonium ions in the process liquid is 27 g / L, the concentration of sulfate ions is 74 g / L, the concentration of phosphate (hydrogen) ions is 1.75 g / L, and the concentration of metal ions is 1.6 g / L;

[0112] The ammonium ion concentration in the ammonia absorption solution is 9g / L, the sulfate ion concentration is 27g / L, the phosphate (hydrogen) ion concentration is 4.2g / L; the metal ion concentration is 0.6g / L.

[0113] The tempered process liquid and the centrifugal liquid obtained by evaporation and crystallization of the ammonia absorption liquid are separated by solid-liquid separation equipment and then dried by drying equipment to obtain the product ammonium sulfate; part of the ammonium sulfate solid-liquid separation mother liquor is cooled, crystallized, solid-liquid separated, and dried by cooling crystallization equipment to obtain the product monoammonium phosphate; further, the obtained monoammonium phosphate is dissolved in water, and further reacted with ammonia water, and then cooled, crystallized, solid-liquid separated, and dried by cooling crystallization equipment to obtain diammonium phosphate.

[0114] Among them, the mother liquor flow rate is 180m 3 / h, washing water flow rate 360m 3 / h; liquid ammonia consumption 1.5t / h, product ammonium sulfate output 25t / h, product diammonium phosphate output 2t / h.

[0115] Embodiment 3

[0116] This embodiment is a parallel scheme of embodiment 1, in which ammonia water is not used to condition the ammonia absorbing liquid 2. The ammonia absorbing liquid 2 is directly concentrated and mixed with the process liquid, and then mixed and conditioned with ammonia water and potassium dihydrogen phosphate to obtain a mixed liquid. After the mixed liquid is further concentrated, hot air drying is performed to obtain the product compound fertilizer.

[0117] Among them, the mother liquor flow rate is 180m 3 / h, washing water flow rate 360m 3 / h; liquid ammonia consumption 1.6t / h, potassium dihydrogen phosphate consumption 12t / h, compound fertilizer output 40t / h. The total content of N, P2O5 and K2O in the compound fertilizer is 47.5%, N content is 19%, P2O5 content is 21%, and K2O content is 11%.

[0118] The present application also provides a system for treating ferric phosphate mother liquor and wash water, which is applied to the method for treating ferric phosphate mother liquor and wash water of the present application, and the system comprises:

[0119] Mother liquor ammonia absorption cooling equipment, used for mother liquor to absorb gaseous ammonia to prepare process liquid, and to cool the process liquid; and

[0120] Wash water ammonia absorption equipment, used for washing water to absorb gaseous ammonia to prepare ammonia absorption liquid;

[0121] Ammonia water preparation equipment, used for absorbing gaseous ammonia from process water to prepare ammonia water;

[0122] Liquid ammonia gasification equipment, used to utilize the heat released by the mother liquid absorbing gaseous ammonia to gasify liquid ammonia, and to provide gaseous ammonia to the mother liquid ammonia absorption cooling equipment, the wash water ammonia absorption equipment and the ammonia water preparation equipment through the gaseous ammonia pipeline;

[0123] Conditioning equipment, respectively connected to the mother liquor ammonia absorption cooling equipment, the wash water ammonia absorption equipment and the ammonia water preparation, for conditioning the process liquid and the ammonia absorption liquid with ammonia water; or, respectively connected to the mother liquor ammonia absorption cooling equipment, the wash water ammonia absorption equipment and the ammonia water preparation, for conditioning the mixed liquid of the process liquid and the ammonia absorption liquid with ammonia water and potassium dihydrogen phosphate;

[0124] The fertilizer production equipment is connected to the conditioning equipment and is used to prepare the finished fertilizer after filtering, evaporating and concentrating, centrifuging, separating solid from liquid, drying and cooling and crystallizing the conditioned process liquid and ammonia absorbing liquid.

[0125] Specifically, Figure 6 and Figure 7 As shown, the liquid ammonia vaporizer, the mother liquid ammonia absorber, and the process liquid cooler are integrated equipment. The lower part is the liquid ammonia vaporizer. The gaseous ammonia obtained by gasifying the liquid ammonia is connected to the upper mother liquid ammonia absorber through an internal pipeline, and then cooled by the middle circulating water cooler and the lower liquid ammonia vaporizer and connected to the process liquid conditioning equipment. Therefore, the liquid ammonia can be directly gasified after unloading, so there is no need to set up a liquid ammonia storage tank. Among them, the liquid ammonia vaporizer is the liquid ammonia gasification equipment, and the mother liquid ammonia absorption cooling equipment includes the mother liquid ammonia absorber and the circulating water cooler. Figure 6 Among them, the conditioning equipment includes a process liquid conditioning tank and a conditioning tank, and the fertilizer production equipment includes a filter 1, a filter 2, an evaporator, a centrifuge and a dryer; Figure 7 Among them, the conditioning equipment includes a neutralization reactor and a preparation tank, and the fertilizer production equipment includes a filter, an evaporator, a centrifuge and a dryer.

[0126] The washing water ammonia absorption equipment includes an absorption tower 1, and the ammonia water preparation equipment includes an absorption tower 2. The liquid-gas ratio in the absorption tower 1 is 0.18-0.35L / L, and the number of spray layers is at least 2. The liquid-gas ratio in the absorption tower 2 is 0.02-0.1L / L, and the number of spray layers is at least 2.

[0127] The evaporation and concentration equipment includes 4-5 effect steam evaporation equipment, 3 effect MVR evaporation equipment, and 3 effect MVR evaporation equipment; among which, the temperature rise of the steam compressor is not less than 16°C, and the 3 effect MVR evaporation equipment is preferably a double effect falling film (rising film) evaporation equipment and a single effect forced circulation equipment.

[0128] Furthermore, to prevent corrosion of the equipment, the evaporation equipment is made of 316L stainless steel, 2205 stainless steel, 2507 stainless steel, titanium or nickel alloy. The double-effect falling film evaporation equipment is preferably made of 2205 stainless steel, and the single-effect forced circulation evaporation equipment is preferably made of TA2 titanium.

[0129] In order to implement the specific embodiments of the method of the present invention, the corresponding system embodiments are provided below.

[0130] Embodiment 4

[0131] This embodiment can realize the treatment method of the iron phosphate mother liquor and the washing water of the first embodiment and the second embodiment.

[0132] Specifically, Figure 6 As shown, a system for treating iron phosphate mother liquor and wash water provided in this embodiment includes: a liquid ammonia gasifier, a mother liquor ammonia absorber, a process liquid cooler, an absorption tower 1, an absorption tower 2, a wash water concentration device, a tempering tank, a process liquid tempering tank, a filter 1, a filter 2, an evaporator, a centrifuge and a dryer.

[0133] Among them, the liquid ammonia vaporizer, the mother liquid ammonia absorber and the process liquid cooler are integrated equipment. The lower part is the liquid ammonia vaporizer. The gaseous ammonia obtained by gasifying the liquid ammonia is connected to the upper mother liquid ammonia absorber through an internal pipeline, and then cooled by the middle circulating water cooler and the lower liquid ammonia vaporizer and connected to the process liquid tempering tank.

[0134] The branch of the gas ammonia pipeline of the liquid ammonia gasifier is also connected to absorption tower 1 and absorption tower 2 to provide gas ammonia for absorption tower 1 and absorption tower 2; wherein, absorption tower 1 is used to absorb gas ammonia with process water to prepare ammonia water, and absorption tower 2 is used to absorb gas ammonia with wash water to prepare ammonia absorption liquid.

[0135] The wash water concentration equipment is connected to the absorption tower 2 and the conditioning tank respectively, so as to concentrate the ammonia absorption liquid prepared in the absorption tower 2 and then transport it to the conditioning tank.

[0136] The process liquid conditioning tank is connected to the mother liquid ammonia absorber to receive the process liquid prepared in the mother liquid ammonia absorber.

[0137] The absorption tower 1 is connected to the conditioning tank and the process liquid conditioning tank respectively, so as to use the ammonia water prepared in the absorption tower 1 to condition the ammonia absorbing liquid in the conditioning tank and the process liquid in the process liquid conditioning tank.

[0138] The filter 1 is connected to the tempering tank to filter the metal precipitates in the tempering tank and transport the filtered ammonia absorbing liquid to the evaporator.

[0139] The filter 2 is connected to the process liquid conditioning tank to filter the metal precipitates in the process liquid conditioning tank and transport the filtered process liquid to the evaporator.

[0140] The evaporator is also connected with a centrifuge and a dryer in sequence to perform operations such as evaporation, crystallization, centrifugation and drying on the ammonia absorption liquid and the process liquid.

[0141] Embodiment 5

[0142] This embodiment can realize the method for treating the iron phosphate mother liquor and wash water of the third embodiment.

[0143] Specifically, Figure 7 As shown, a system for treating iron phosphate mother liquor and wash water provided in this embodiment includes: a liquid ammonia gasifier, a mother liquor ammonia absorber, a process liquid cooler, an absorption tower 1, an absorption tower 2, a wash water concentration device, a neutralization reactor, a preparation tank, a filter, an evaporator, a centrifuge and a dryer.

[0144] Among them, the liquid ammonia vaporizer, the mother liquid ammonia absorber and the process liquid cooler are integrated equipment. The lower part is the liquid ammonia vaporizer. The gaseous ammonia obtained by gasifying the liquid ammonia is connected to the upper mother liquid ammonia absorber through an internal pipeline, and then cooled by the middle circulating water cooler and the lower liquid ammonia vaporizer and connected to the neutralization reactor.

[0145] The branch of the gas ammonia pipeline of the liquid ammonia gasifier is also connected to absorption tower 1 and absorption tower 2 to provide gas ammonia for absorption tower 1 and absorption tower 2; wherein, absorption tower 1 is used to absorb gas ammonia with process water to prepare ammonia water, and absorption tower 2 is used to absorb gas ammonia with wash water to prepare ammonia absorption liquid.

[0146] The wash water concentration equipment is connected to the absorption tower 2 and the neutralization reactor respectively, so as to concentrate the ammonia absorption liquid prepared in the absorption tower 2 and then transport it to the neutralization reactor.

[0147] The neutralization reactor is also connected to the mother liquor ammonia absorber to receive the process liquid prepared in the mother liquor ammonia absorber.

[0148] The absorption tower 1 is connected to the neutralization reactor and the preparation tank respectively, and the preparation tank is also connected to the neutralization reactor, so as to use the ammonia water prepared in the absorption tower 1 and the potassium dihydrogen phosphate configured in the preparation tank to condition the mixed liquid of the process liquid and the ammonia absorption liquid in the neutralization reactor.

[0149] The filter is connected to the neutralization reactor to filter the metal precipitate precipitated in the neutralization reactor and transport the filtered mixed liquid to the evaporator.

[0150] The evaporator is also connected to the centrifuge and the dryer in sequence to perform operations such as evaporation, crystallization, centrifugation and drying on the mixed liquid.

[0151] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for treating ferric phosphate mother liquor and wash water, characterized in that: The method comprises: S110, using the mother liquid to be treated to absorb gaseous ammonia to obtain process liquid, using the wash water to be treated to absorb gaseous ammonia to obtain ammonia absorbing liquid, and using the process water to absorb gaseous ammonia to obtain ammonia water; wherein the gaseous ammonia is produced by gasifying liquid ammonia by heat released by the mother liquid in the process of absorbing gaseous ammonia; the mass ratio of the mother liquid, the wash water, and the process water absorbing gaseous ammonia is 1:(0.10-0.35):(0.15-0.50); ​​the concentration of the ammonia water obtained after the process water absorbs gaseous ammonia is 17.7%-22.3%; S120, using the ammonia water to condition the process liquid and the ammonia absorbing liquid; the pH of the process liquid before conditioning is 4.2-5.3, and the pH after conditioning is 6.8-8.4; the pH of the ammonia absorbing liquid before conditioning is 4.5-5.6, and the pH after conditioning is 7.0-8.8; the ratio of the process liquid to the ammonia water absorbed by the ammonia absorbing liquid is 1:(0.5-2.0); S130, subjecting the conditioned process liquid and the ammonia absorbing liquid to one or more operations of evaporation concentration, centrifugation, solid-liquid separation, drying and cooling crystallization to obtain a product fertilizer.

2. The method for treating iron phosphate mother liquor and wash water according to claim 1, characterized in that: S110 also includes cooling the process liquid by using circulating water and liquid ammonia gasification, and the ratio of the heat transferred by the circulating water and the liquid ammonia gasification is 1:(2-10).

3. The method for treating iron phosphate mother liquor and wash water according to claim 1, characterized in that: In S110, the mother liquor and the wash water are in a flowing state, wherein the flow rate of the mother liquor is 50-600m 3 / h, the washing water flow rate is 80-1200m 3 / h, and the volume ratio of the mother liquor to the wash water is 1:(1.3-2.5).

4. The method for treating iron phosphate mother liquor and wash water according to claim 1, characterized in that: In S130, the product fertilizer includes ammonium sulfate and monoammonium phosphate; wherein the monoammonium phosphate is obtained by performing one or more operations of cooling crystallization, solid-liquid separation, and drying on a part of the centrifuged mother liquor of the ammonium sulfate.

5. The method for treating iron phosphate mother liquor and wash water according to claim 4, characterized in that: After S130, the method further includes: S140, dissolving the monoammonium phosphate in water, and further reacting the monoammonium phosphate with the ammonia water to obtain diammonium phosphate.

6. A system for treating ferric phosphate mother liquor and washing water, applied to the treatment method according to any one of claims 1 to 5, characterized in that: The system comprises: A mother liquid ammonia absorption cooling device is used for the mother liquid to absorb gaseous ammonia to prepare a process liquid, and to cool the process liquid; and Wash water ammonia absorption equipment, used for washing water to absorb gaseous ammonia to prepare ammonia absorption liquid; Ammonia water preparation equipment, used for absorbing gaseous ammonia from process water to prepare ammonia water; Liquid ammonia gasification equipment, used to utilize the heat released by the mother liquid absorbing gaseous ammonia to gasify liquid ammonia, and provide gaseous ammonia to the mother liquid ammonia absorption cooling equipment, the wash water ammonia absorption equipment and the ammonia water preparation equipment through gaseous ammonia pipelines; a conditioning device, respectively connected to the mother liquor ammonia absorption cooling device, the wash water ammonia absorption device and the ammonia water preparation device, for conditioning the process liquid and the ammonia absorption liquid using the ammonia water; or, respectively connected to the mother liquor ammonia absorption cooling device, the wash water ammonia absorption device and the ammonia water preparation device, for conditioning the mixed liquid of the process liquid and the ammonia absorption liquid using the ammonia water and potassium dihydrogen phosphate; The fertilizer production equipment is connected to the conditioning equipment and is used to prepare the product fertilizer after filtering, evaporating and concentrating, centrifuging, solid-liquid separation, drying and cooling crystallization of the conditioned process liquid and the ammonia absorbing liquid.

Images