CN114195316A - Iron phosphate wastewater treatment system and treatment method - Google Patents
Iron phosphate wastewater treatment system and treatment method Download PDFInfo
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- CN114195316A CN114195316A CN202111673882.4A CN202111673882A CN114195316A CN 114195316 A CN114195316 A CN 114195316A CN 202111673882 A CN202111673882 A CN 202111673882A CN 114195316 A CN114195316 A CN 114195316A
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- iron phosphate
- phosphate wastewater
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- flash evaporation
- forced circulation
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- WBJZTOZJJYAKHQ-UHFFFAOYSA-K iron(3+) phosphate Chemical compound [Fe+3].[O-]P([O-])([O-])=O WBJZTOZJJYAKHQ-UHFFFAOYSA-K 0.000 title claims abstract description 101
- 229910000398 iron phosphate Inorganic materials 0.000 title claims abstract description 93
- 238000004065 wastewater treatment Methods 0.000 title claims abstract description 38
- 238000000034 method Methods 0.000 title claims abstract description 20
- 238000001704 evaporation Methods 0.000 claims abstract description 102
- 230000008020 evaporation Effects 0.000 claims abstract description 101
- 238000002425 crystallisation Methods 0.000 claims abstract description 66
- 230000008025 crystallization Effects 0.000 claims abstract description 66
- 239000011552 falling film Substances 0.000 claims abstract description 63
- 239000002351 wastewater Substances 0.000 claims abstract description 62
- 239000012452 mother liquor Substances 0.000 claims abstract description 47
- BFNBIHQBYMNNAN-UHFFFAOYSA-N ammonium sulfate Chemical compound N.N.OS(O)(=O)=O BFNBIHQBYMNNAN-UHFFFAOYSA-N 0.000 claims abstract description 40
- 229910052921 ammonium sulfate Inorganic materials 0.000 claims abstract description 40
- 235000011130 ammonium sulphate Nutrition 0.000 claims abstract description 40
- LFVGISIMTYGQHF-UHFFFAOYSA-N ammonium dihydrogen phosphate Chemical compound [NH4+].OP(O)([O-])=O LFVGISIMTYGQHF-UHFFFAOYSA-N 0.000 claims abstract description 34
- 229910000387 ammonium dihydrogen phosphate Inorganic materials 0.000 claims abstract description 34
- 235000019837 monoammonium phosphate Nutrition 0.000 claims abstract description 34
- 239000006012 monoammonium phosphate Substances 0.000 claims abstract description 34
- 239000007788 liquid Substances 0.000 claims description 111
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 39
- 238000000926 separation method Methods 0.000 claims description 23
- 239000002562 thickening agent Substances 0.000 claims description 22
- 238000005406 washing Methods 0.000 claims description 18
- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 claims description 13
- 229910019142 PO4 Inorganic materials 0.000 claims description 10
- 239000012530 fluid Substances 0.000 claims description 10
- 238000009835 boiling Methods 0.000 claims description 8
- 238000003860 storage Methods 0.000 claims description 6
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 abstract description 10
- 239000003337 fertilizer Substances 0.000 abstract description 5
- 229910052757 nitrogen Inorganic materials 0.000 abstract description 5
- 239000002994 raw material Substances 0.000 abstract description 4
- 150000001875 compounds Chemical class 0.000 abstract description 3
- 239000000463 material Substances 0.000 description 15
- 239000007789 gas Substances 0.000 description 14
- 238000004806 packaging method and process Methods 0.000 description 14
- 150000003839 salts Chemical class 0.000 description 12
- 239000005955 Ferric phosphate Substances 0.000 description 8
- 229940032958 ferric phosphate Drugs 0.000 description 8
- 229910000399 iron(III) phosphate Inorganic materials 0.000 description 8
- 238000004519 manufacturing process Methods 0.000 description 7
- 238000001514 detection method Methods 0.000 description 6
- 239000013078 crystal Substances 0.000 description 5
- 238000010586 diagram Methods 0.000 description 5
- 239000007787 solid Substances 0.000 description 5
- 238000001035 drying Methods 0.000 description 4
- 238000004064 recycling Methods 0.000 description 4
- 235000008733 Citrus aurantifolia Nutrition 0.000 description 3
- 235000011941 Tilia x europaea Nutrition 0.000 description 3
- 150000002500 ions Chemical class 0.000 description 3
- 239000004571 lime Substances 0.000 description 3
- 239000002245 particle Substances 0.000 description 3
- 239000010452 phosphate Substances 0.000 description 3
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 description 2
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 2
- OSGAYBCDTDRGGQ-UHFFFAOYSA-L calcium sulfate Chemical compound [Ca+2].[O-]S([O-])(=O)=O OSGAYBCDTDRGGQ-UHFFFAOYSA-L 0.000 description 2
- 238000004140 cleaning Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000005265 energy consumption Methods 0.000 description 2
- 239000010408 film Substances 0.000 description 2
- 239000011521 glass Substances 0.000 description 2
- 239000011344 liquid material Substances 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 229910052698 phosphorus Inorganic materials 0.000 description 2
- 239000011574 phosphorus Substances 0.000 description 2
- 239000000047 product Substances 0.000 description 2
- 238000005086 pumping Methods 0.000 description 2
- 238000010992 reflux Methods 0.000 description 2
- 238000009751 slip forming Methods 0.000 description 2
- 239000007921 spray Substances 0.000 description 2
- QGZKDVFQNNGYKY-UHFFFAOYSA-O Ammonium Chemical compound [NH4+] QGZKDVFQNNGYKY-UHFFFAOYSA-O 0.000 description 1
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 description 1
- 229910000147 aluminium phosphate Inorganic materials 0.000 description 1
- 239000006227 byproduct Substances 0.000 description 1
- 239000001506 calcium phosphate Substances 0.000 description 1
- 229910000389 calcium phosphate Inorganic materials 0.000 description 1
- 235000011010 calcium phosphates Nutrition 0.000 description 1
- 239000003153 chemical reaction reagent Substances 0.000 description 1
- 239000012141 concentrate Substances 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000013461 design Methods 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000007599 discharging Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 238000000605 extraction Methods 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- 239000000618 nitrogen fertilizer Substances 0.000 description 1
- 229940085991 phosphate ion Drugs 0.000 description 1
- 239000007774 positive electrode material Substances 0.000 description 1
- 239000002243 precursor Substances 0.000 description 1
- 230000002035 prolonged effect Effects 0.000 description 1
- 239000007858 starting material Substances 0.000 description 1
- 239000011232 storage material Substances 0.000 description 1
- QORWJWZARLRLPR-UHFFFAOYSA-H tricalcium bis(phosphate) Chemical compound [Ca+2].[Ca+2].[Ca+2].[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O QORWJWZARLRLPR-UHFFFAOYSA-H 0.000 description 1
- 239000002918 waste heat Substances 0.000 description 1
Images
Classifications
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- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F9/00—Multistage treatment of water, waste water or sewage
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B25/00—Phosphorus; Compounds thereof
- C01B25/16—Oxyacids of phosphorus; Salts thereof
- C01B25/26—Phosphates
- C01B25/28—Ammonium phosphates
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01C—AMMONIA; CYANOGEN; COMPOUNDS THEREOF
- C01C1/00—Ammonia; Compounds thereof
- C01C1/24—Sulfates of ammonium
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/008—Control or steering systems not provided for elsewhere in subclass C02F
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/02—Treatment of water, waste water, or sewage by heating
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/02—Treatment of water, waste water, or sewage by heating
- C02F1/04—Treatment of water, waste water, or sewage by heating by distillation or evaporation
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/02—Treatment of water, waste water, or sewage by heating
- C02F1/04—Treatment of water, waste water, or sewage by heating by distillation or evaporation
- C02F1/06—Flash evaporation
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F1/00—Treatment of water, waste water, or sewage
- C02F1/02—Treatment of water, waste water, or sewage by heating
- C02F1/04—Treatment of water, waste water, or sewage by heating by distillation or evaporation
- C02F1/08—Thin film evaporation
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2101/00—Nature of the contaminant
- C02F2101/10—Inorganic compounds
- C02F2101/105—Phosphorus compounds
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2101/00—Nature of the contaminant
- C02F2101/10—Inorganic compounds
- C02F2101/20—Heavy metals or heavy metal compounds
- C02F2101/203—Iron or iron compound
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
- C02F2103/34—Nature of the water, waste water, sewage or sludge to be treated from industrial activities not provided for in groups C02F2103/12 - C02F2103/32
-
- C—CHEMISTRY; METALLURGY
- C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
- C02F2209/00—Controlling or monitoring parameters in water treatment
- C02F2209/02—Temperature
Abstract
The invention discloses a system and a method for treating iron phosphate wastewater. The iron phosphate wastewater treatment system comprises a preheating unit, a falling film evaporation unit, a forced circulation crystallization unit and a flash evaporation crystallization unit which are connected in sequence; the forced circulation crystallization unit comprises a forced circulation heater and a forced circulation crystallizer which are connected in sequence; the side wall of the forced circulation crystallizer shell is provided with a mother liquor overflow port, a circulation feed inlet and a circulation discharge port from top to bottom, and the circulation discharge port is positioned at the bottom end; a circulating feeding pipe is nested from the circulating feeding port to the inner cavity of the shell; the outlet end of the circulating feeding pipe is arranged above the mother liquor overflow port; the flash evaporation crystallization unit comprises a flash evaporation crystallizer, and a feed inlet of the flash evaporation crystallizer is connected with a mother liquor overflow port. The invention can continuously and stably produce ammonium sulfate and monoammonium phosphate with higher purity by using the wastewater treatment system, and the separated ammonium sulfate and monoammonium phosphate are used as raw materials of industrial nitrogen fertilizers and compound fertilizers.
Description
Technical Field
The invention relates to a system and a method for treating iron phosphate wastewater.
Background
The iron phosphate is a precursor for producing the iron phosphate positive electrode material, and along with the rapid development of the electric automobile industry, the market demand of the iron phosphate is more and more large, and the demand on the battery-grade iron phosphate raw material is increased year by year. A large amount of wastewater is generated in the production process of iron phosphate, and according to the estimation of the pilot production of battery-grade iron phosphate by new crystal technology limited in Guangxi, about 50 tons of wastewater is generated for every 1 ton of battery-grade iron phosphate.
The iron phosphate production wastewater has the characteristics of high sulfate radical concentration, high ammonium ion concentration, high total phosphorus concentration and low pH value, and is mainly treated by the processes of lime pretreatment and evaporation at present. Phosphate radical, sulfate radical and lime in the wastewater react to generate calcium phosphate and calcium sulfate; the lime pretreatment effluent is subjected to advanced treatment by adopting an evaporation process, and finally the effluent reaches the national relevant discharge standard and the byproduct ammonium sulfate is generated. The iron phosphate wastewater treatment system in the prior art reports little about how to separate and crystallize high-purity ammonium sulfate and monoammonium phosphate. This technical problem is yet to be solved.
Disclosure of Invention
The invention mainly aims to overcome the defect that the ferric phosphate wastewater cannot be effectively treated in the prior art, and provides a ferric phosphate wastewater treatment system and a treatment method. The wastewater treatment system disclosed by the invention can be used for recycling the ferric phosphate wastewater, and can be used for continuously and stably producing the high-purity ammonium sulfate crystal salt and monoammonium phosphate.
The invention mainly solves the technical problems through the following technical scheme.
The invention provides a ferric phosphate wastewater treatment system, which comprises a preheating unit, a falling film evaporation unit, a forced circulation crystallization unit and a flash evaporation crystallization unit which are sequentially connected;
the forced circulation crystallization unit comprises a forced circulation heater and a forced circulation crystallizer which are connected in sequence;
the forced circulation crystallizer comprises a shell, wherein a mother liquor overflow port, a circulation feed inlet and a circulation discharge port are formed in the side wall of the shell from top to bottom, and the circulation discharge port is positioned at the bottom end of the shell;
a circulating feeding pipe is nested from the circulating feeding port to the inner cavity of the shell;
the outlet end of the circulating feeding pipe is arranged above the mother liquid overflow port;
the flash evaporation crystallization unit comprises a flash evaporation crystallizer, and a feed inlet of the flash evaporation crystallizer is connected with a mother liquid overflow port.
In the invention, preferably, the shell comprises an upper shell and a lower shell, the upper shell and the lower shell are connected in a nested manner, and the diameter of the upper shell is smaller than that of the lower shell; the bottom end of the upper shell is positioned below the mother liquid overflow port and is spaced from the wall surface of the inner cavity of the lower shell.
Wherein, in the process that the feed liquid enters the inner cavity of the shell from the circulating feed inlet, ammonium sulfate crystallized salt is continuously formed in the feed liquid. The nested connection arrangement of the upper shell and the lower shell ensures that the area of the upper shell nested to the lower shell can prevent ammonium sulfate particles formed in feed liquid entering from the outlet end of the circulating feed pipe from entering the mother liquid overflow port, so that the purity of monoammonium phosphate crystallized in the flash evaporation crystallization unit is higher. When the mass concentration of phosphate ions in the feed liquid entering the inner cavity of the shell from the outlet end of the circulating feeding pipe reaches 20-25%, a valve of the mother liquid overflow port is opened, and the feed liquid in the inner cavity of the shell flows to the mother liquid overflow port from a gap between the bottom end of the upper shell and the wall surface of the inner cavity of the lower shell.
In the invention, preferably, the forced circulation heater is provided with the forced circulation pipeline, and the forced circulation pipeline is provided with a forced circulation pump for pumping the feed liquid entering the forced circulation crystallization unit into the forced circulation heater.
In the invention, preferably, the preheating unit comprises a condensate water preheater, a tail gas preheater and a steam preheater which are connected in sequence, and a hot fluid channel of the condensate water preheater is communicated with a condensate water outlet of the falling film evaporation unit and a condensate water outlet of the forced circulation crystallization unit; a hot fluid channel of the tail gas preheater is communicated with a tail gas outlet of the falling film evaporation unit and a tail gas outlet of the forced circulation crystallization unit; a hot fluid channel of the steam preheater is communicated with each steam outlet of the iron phosphate wastewater treatment system; used for preheating the iron phosphate wastewater to be treated.
Preferably, the condensed water preheater is used for preheating the iron phosphate wastewater to be treated to a set temperature, such as 85 ℃; the condensate water preheater reduces the outlet water temperature of the condensate water to the maximum extent while preheating the iron phosphate wastewater, and facilitates the recycling production of the condensate water.
Preferably, the tail gas preheater is used for further preheating the iron phosphate wastewater to be treated to a set temperature, such as 88 ℃; and the tail gas preheater is used for recovering waste heat generated in the iron phosphate wastewater treatment system, so that the energy consumption loss is reduced.
Preferably, the steam preheater is used for further preheating phosphoric acid extraction wastewater to be treated to a boiling point; steam heater with falling liquid film evaporation unit links to each other, can guarantee that ferric phosphate waste water reaches the boiling feeding, improves when ferric phosphate waste water treatment system to stability, the maximize guarantees falling liquid film throughput.
In the invention, preferably, the falling film evaporation unit comprises a falling film heater and a falling film separator which are connected in sequence; the falling film heater is also provided with two falling film circulating pipelines, and each falling film circulating pipeline is provided with a falling film circulating pump. The falling film heater is used for further heating and concentrating preheated iron phosphate wastewater, and meanwhile, the high-concentration section and the low-concentration section are arranged through the two falling film circulating pumps to realize the on-line switching of two concentrations, so that the iron phosphate wastewater entering the falling film circulating heater is guaranteed to reach a boiling point. The falling film separator is used for gas-liquid separation, steam is discharged through a secondary steam outlet on the falling film separator and enters the steam washing unit, and liquid flows back to the falling film heater.
In the invention, preferably, the iron phosphate wastewater treatment system further comprises a first solid-liquid separation unit, wherein the first solid-liquid separation unit comprises a first thickener and a first centrifuge which are sequentially connected; the first thickener is connected with the circulating discharge port through a pipeline, and a discharge pump is arranged on the pipeline; the first centrifugal machine is provided with an ammonium sulfate discharge port and a first mother liquor discharge port; and the first mother liquid discharge port is in reflux connection with the forced circulation crystallizer through a first mother liquid pump. The first solid-liquid separation unit enables the thick liquid obtained by thick separation of the liquid material sent from the circulating discharge port through the thickener to enter a first centrifuge, clear liquid enters a first mother liquid tank, the first centrifuge separates the thick liquid material into ammonium sulfate solid and mother liquid, the ammonium sulfate solid enters an ammonium sulfate packaging system for drying, and the mother liquid enters the first mother liquid tank and then flows back to the forced circulation crystallization unit for further concentration and crystallization.
In the invention, preferably, a buffer storage tank is arranged on a pipeline connecting a feed inlet of the flash evaporation crystallization unit and the mother liquor overflow port.
In the present invention, preferably, the flash evaporation crystallization unit further includes a flash evaporation circulation pipeline connecting the feed port of the flash evaporation crystallizer and the discharge port of the flash evaporation crystallizer, and the flash evaporation circulation pipeline is provided with a flash evaporation circulation pump. In the invention, the flash evaporation crystallizer is preferably a continuous flash evaporation crystallizer, and flash evaporation crystallization can be continuously performed by a structure connected with the forced circulation crystallizer and the buffer storage tank.
In the invention, preferably, the iron phosphate wastewater treatment system further comprises a second solid-liquid separation unit, and the second solid-liquid separation unit comprises a second thickener and a second centrifuge which are sequentially connected; the second thickener is connected with a discharge port of the flash evaporation crystallizer through a pipeline, and a discharge pump is arranged on the pipeline; the second centrifuge is provided with a monoammonium phosphate discharge port and a second mother liquor discharge port; and the second mother liquor discharge port is connected with the forced circulation crystallizer in a backflow mode through a second mother liquor pump. The second solid-liquid separation unit enables the feed liquid sent out from the discharge port of the flash evaporation crystallization unit to pass through a second thickener, thick liquid obtained through thick separation is fed into a second centrifuge, clear liquid is fed into a second mother liquid tank, the second centrifuge separates the thick feed liquid into monoammonium phosphate solid and mother liquid, the monoammonium phosphate solid is fed into a monoammonium phosphate packaging system for drying, and the mother liquid is fed into the second mother liquid tank and then flows back to the forced circulation crystallization unit for further concentration and crystallization.
In the invention, preferably, the iron phosphate wastewater treatment system further comprises a steam washing unit, wherein the steam washing unit comprises a steam washing tower, a first MVR compressor and a second MVR compressor which are sequentially connected; a secondary steam inlet is arranged on the steam washing tower; and the secondary steam inlet is respectively connected with a secondary steam outlet at the top end of the forced circulation crystallizer and a secondary steam outlet at the top end of the falling film separator. And a first steam outlet is arranged on the second MVR compressor, and the first steam outlet is respectively connected with the first steam inlet of the falling film heater and the first steam inlet of the forced circulation heater and used for recycling the steam after the steam washing unit washes the steam to the falling film heater and the forced circulation heater.
In the invention, the iron phosphate wastewater treatment system preferably further comprises a detection unit comprising a temperature detection unit and an ion concentration detection unit, and the detection unit is used for detecting the feed liquid temperature of each unit in the iron phosphate wastewater and the concentration of ions in the feed liquid so as to accurately control the feed liquid inlet and outlet temperature and the inlet and outlet concentration.
The invention also provides a method for treating the iron phosphate wastewater, which adopts the iron phosphate wastewater treatment system to carry out process treatment; which comprises the following steps:
sequentially introducing iron phosphate wastewater to be treated into the preheating unit, the falling film evaporation unit and the forced circulation crystallization unit;
and when the mass concentration of phosphate ions in the iron phosphate wastewater entering the circulating feed port is 20-25%, opening a valve at the mother liquor overflow port.
The concentration of phosphate ions in the mother liquor entering the flash evaporation crystallization unit must be strictly controlled; otherwise, the purity of the monoammonium phosphate product is seriously influenced. Too low concentration of phosphate ions in the feed liquid can cause the purity of the monoammonium phosphate crystal salt to be greatly reduced, and if too high, part of phosphate can enter the ammonium sulfate crystal product to influence the purity of the ammonium sulfate.
In the invention, the iron phosphate wastewater to be treated can be washing liquor and mother liquor generated in the conventional iron phosphate production process in the field.
In the invention, the liquid level of the feed liquid entering the inner cavity of the forced circulation crystallizer can be above the circulation discharge pipe, and the region where the feed liquid is located is a crystallization region. Those skilled in the art will appreciate that the momentum of the feed liquid entering from the outlet end of the circulation feed pipe is greater, and that the feed liquid will not flow out of the outlet end of the circulation feed pipe due to the momentum of the feed liquid in the interior cavity of the housing above the outlet end of the circulation feed pipe.
In the invention, preferably, when the mass concentration of phosphate ions in the iron phosphate wastewater entering the circulating feed port is 22-24%, the valve at the mother liquor overflow port is opened.
In the present invention, the iron phosphate wastewater to be treated preferably comprises the following components: NH (NH)4 +：40700～50000mg/L；PO4 3-: 16000-19600 mg/L and SO4 2-：98300～120000mg/L。
Wherein, the NH4 +The concentration of (b) is preferably 43000-47000 mg/L, for example 45251 mg/L.
Wherein, the PO4 3-The concentration of (b) is preferably 169900 to 18700mg/L, for example 17844 mg/L.
Wherein the SO4 2-The concentration of (b) is preferably 104000-115000 mg/L, such as 109329 mg/L.
In the invention, the TDS in the iron phosphate wastewater to be treated is 155500-19000 mg/L, such as 172800 mg/L. The TDS may be as conventionally understood in the art and is generally referred to as a dissolved solid.
In the invention, the iron phosphate wastewater to be treated can also comprise trace amounts of other ions, such as F-、Mg2 +、Ca2+One or more of (a).
Wherein, F is-The concentration of (b) is preferably 140 to 170 mg/L.
Wherein said Mg2+The concentration of (B) is preferably 1 to 2 mg/L.
Wherein, the Ca2+The concentration of (B) is preferably 1 to 2 mg/L.
In the invention, the temperature of the iron phosphate wastewater to be treated is generally 10-40 ℃, for example 35 ℃.
In a specific embodiment of the present invention, the iron phosphate wastewater to be treated includes NH4 +：45251mg/L；PO4 3-：17844mg/L；SO4 2-: 109329 mg/L; and in the iron phosphate wastewater to be treated, the TDS is 172800 mg/L; the pH value of the iron phosphate wastewater to be treated is 5.
In the present invention, the mass concentration of the solute in the iron phosphate wastewater to be treated is preferably 10 to 20%, for example, 16%, where the percentage is the percentage of the mass of the solute to the total mass of the iron phosphate wastewater to be treated.
In the present invention, the mass concentration of the iron phosphate wastewater after the concentration and conveyed to the forced circulation crystallization unit is preferably 40 to 45%, for example, 42%. When the treatment method is carried out, the concentration of concentration is in the range of 41-43% and is the most stable data point in operation, if the concentration is too high, the wastewater treatment system has risks, and if the concentration is too low, the energy consumption of the system is increased, and the investment is increased.
On the basis of the common knowledge in the field, the above preferred conditions can be combined randomly to obtain the preferred embodiments of the invention.
The reagents and starting materials used in the present invention are commercially available.
The positive progress effects of the invention are as follows: according to the invention, through the forced circulation crystallizer, the mother liquor with lower phosphate ion concentration can form ammonium sulfate in the forced circulation crystallizer, and when the mother liquor reaches a certain concentration, the mother liquor is sent into the flash evaporation crystallizer by utilizing the height difference to form monoammonium phosphate, and the connection relationship among the preheating unit, the falling film evaporation unit, the forced circulation crystallization unit and the flash evaporation crystallization unit is combined, so that the ammonium sulfate and the monoammonium phosphate with higher purity can be continuously and stably produced (for example, the nitrogen content of the ammonium sulfate is more than or equal to 21 wt.%, the water content of the ammonium sulfate is less than or equal to 0.2 wt.%, the purity of the monoammonium phosphate produced from a monoammonium phosphate packaging system is more than or equal to 90%, and the water content of the monoammonium phosphate is less than or equal to 0.2 wt.%), the separated ammonium sulfate and monoammonium phosphate can be used as raw materials of industrial nitrogen fertilizers and compound fertilizers, and zero emission in real sense is realized.
Drawings
FIG. 1 is a schematic view of the process flow of the iron phosphate wastewater treatment system in example 1.
FIG. 2 is a process flow diagram of the ferric phosphate wastewater treatment system in example 1.
FIG. 3 is a structural view of a forced circulation crystallizer in example 1.
FIG. 4 is a block diagram of the flash crystallizer of example 1.
Description of reference numerals: the reference numerals in fig. 1 illustrate: 12 a feed lift pump; 21 condensate water preheater; 21-1 cooler; 22 a tail gas preheater; 22-1 condenser; 23 a steam preheater; 23-1 evaporating and condensing water tank;
31 a falling film heater; 32 a first falling film circulation pump; 33 a second falling film circulation pump; 33-1 material passing pump; 34 a falling film separator;
41 forced circulation heater; 42 forced circulation crystallizer; 43 forced circulation pump;
51 a first discharge pump; 52 a first thickener; 53 a first centrifuge; 54 a first mother liquor tank; 55 a first mother liquor pump;
61 caching middle storage material tanks; 62 flash feed pump; 63 a flash crystallizer; 64 flash circulation pump; 65 a vacuum system;
71 a second discharge pump; 72 second thickener; 73 a second centrifuge; 74 a second mother liquor tank; 75 a second mother liquor pump;
81 steam washing tower; 82 a first MVR compressor; 83 a second MVR compressor;
100 ammonium sulfate packaging systems; 200 monoammonium phosphate packaging system;
the reference numerals in fig. 3 illustrate: n1 cleaning fluid port; SG1 middle view mirror; a TE1 temperature sensor; an N2 mother liquor overflow port; n3 circulation feed inlet; n4 circular discharge port; an N6 secondary steam outlet; an M1 manhole;
the reference numerals in fig. 4 illustrate: a P1 secondary steam outlet; a P2 feed inlet; a discharge port P3; a P4 salt outlet; a P5 condensate inlet; a P6 spray opening; SG2 sight glass; TE2 temperature sensor.
Detailed Description
The invention is further illustrated by the following examples, which are not intended to limit the scope of the invention. The experimental methods without specifying specific conditions in the following examples were selected according to the conventional methods and conditions, or according to the commercial instructions.
Example 1
The composition of the iron phosphate wastewater treated in this example is shown in table 1 below. In the embodiment, the iron phosphate wastewater to be treated is concentrated to a solute mass concentration of 16% by using a washing liquid and a mother liquid generated by an iron phosphate production process.
TABLE 1
| Serial number | Item | Numerical value |
| 1 | NH4 + | 45251mg/L |
| 2 | PO4 3- | 17844mg/L |
| 3 | SO4 2- | 109329mg/L |
| 4 | TDS | 172800mg/L |
| 5 | pH | 5±0.2 |
| 6 | Temperature of inlet water | 35℃±1℃ |
| 7 | Boiling point | 91℃±2℃ |
The effect of the device used in this example is shown in Table 2 below
TABLE 2
1. The present embodiment provides an iron phosphate wastewater treatment system, and fig. 1 is a schematic process flow diagram of the iron phosphate wastewater treatment system in the present embodiment. FIG. 2 is a process flow diagram of the ferric phosphate wastewater treatment system in this embodiment. The system comprises a preheating unit, a falling film evaporation unit, a forced circulation unit and a flash evaporation crystallization unit which are connected in sequence; the system also comprises a first solid-liquid separation unit connected with the forced circulation crystallization unit and a second solid-liquid separation unit connected with the flash evaporation crystallization unit.
The preheating unit comprises a condensate water preheater 21, a tail gas preheater 22 and a steam preheater 23 which are sequentially connected, and a hot fluid channel of the condensate water preheater 21 is communicated with a condensate water outlet of the falling film evaporation unit and a condensate water outlet of the forced circulation crystallization unit; a hot fluid channel of the tail gas preheater 22 is communicated with a tail gas outlet of the falling film evaporation unit and a tail gas outlet of the forced circulation crystallization unit; a hot fluid channel of the steam preheater 23 is communicated with each steam outlet of the iron phosphate wastewater treatment system; the method is used for preheating the iron phosphate wastewater to be treated to a boiling point; the condensed water preheater 21 is used for raising the temperature of the iron phosphate wastewater to be treated to 85 ℃; be equipped with the feed line on the comdenstion water preheater 21, be equipped with feeding elevator pump 12 on the feeding pipeline, feeding elevator pump 12 is used for sending pending waste water into comdenstion water preheater 21 and preheats. The condensate water preheater 21 is also connected with a cooler 21-1 for maintaining the temperature of the condensate water preheater 21 stable. The iron phosphate wastewater treatment system also comprises an evaporation condensate water tank 23-1 which is used for recovering condensate water generated by the steam preheater 23, the falling film heater 31 and the forced circulation heater 41 and returning the condensate water to the condensate water preheater 21. The tail gas preheater 22 is used for further raising the temperature to 88 ℃, and the tail gas preheater 22 is also connected with a condenser 22-1 for maintaining the temperature of the tail gas preheater 22 to be stable; the steam preheater 23 is used to raise the temperature to 91 ℃.
The falling film evaporation unit is used for concentrating the iron phosphate wastewater preheated to the boiling point until the mass concentration of the iron phosphate wastewater in a solute is 42%, and comprises a falling film heater 31 and a falling film separator 34 which are sequentially connected, wherein the falling film separator 34 is used for separating secondary steam generated in a feed liquid of the falling film heater 31. The falling film heater 31 is provided with two falling film circulating pipelines, namely a first falling film circulating pump 32 and a second falling film circulating pump 33, and each falling film circulating pipeline is provided with a falling film circulating pump. The two falling film circulating pipelines arranged in the embodiment correspond to a high-concentration section (93 ℃) and a low-concentration section (91 ℃) respectively, and a sectional type concentration mode is adopted, so that the free switching of high-concentration feed liquid and low-concentration feed liquid is realized, the operation period is prolonged, and the utilization rate of a unit area is improved. And a discharge pipeline is connected to the falling film circulating pipeline and communicated with the forced circulation crystallization unit, a material passing pump 33-1 is arranged on the discharge pipeline, and when the mass concentration of the material liquid on the falling film circulating pipeline reaches 42%, the material passing pump 33-1 is started, so that the material liquid is conveyed to the forced circulation crystallization unit from the discharge pipeline.
Fig. 3 is a structural view of the forced circulation crystallizer in this embodiment. The forced circulation crystallization unit comprises a forced circulation heater 41 and a forced circulation crystallizer 42 which are sequentially connected, wherein a forced circulation pipeline is arranged on the forced circulation heater 41, and a forced circulation pump 43 is arranged on the forced circulation pipeline; the feed liquid led out from the discharge pipeline is led into a forced circulation heater 41 through a forced circulation pump 43 to be heated and concentrated, and then enters a forced circulation crystallizer 42 for crystallization. The forced circulation crystallizer 42 comprises a shell, wherein the side wall of the shell is provided with a mother liquor overflow port N2, a circulation feed port N3 and a circulation discharge port N4 from top to bottom, and is also provided with a cleaning solution port N1, a middle view mirror SG1, a temperature sensor TE1 and a manhole M1; the circular discharge port N4 is positioned at the bottom end of the shell; a circulating feed pipe is nested from the circulating feed inlet N3 to the inner cavity of the shell; the outlet end of the circulating feeding pipe is arranged above the mother liquor overflow port N2; the horizontal plane of the rearview mirror SG1 is flush with the liquid level of feed liquid in the inner cavity of the shell, the shell comprises an upper shell and a lower shell, the upper shell and the lower shell are connected in a nested manner, and the diameter of the upper shell is smaller than that of the lower shell; the bottom end of the upper shell is positioned below the mother liquor overflow port and is spaced from the wall surface of the inner cavity of the lower shell. Wherein, in the process that the feed liquid enters the inner cavity of the shell from the circulating feed inlet, ammonium sulfate crystallized salt is continuously formed in the feed liquid. The nested connection arrangement of the upper shell and the lower shell ensures that the region of the upper shell nested to the lower shell can prevent ammonium sulfate particles formed in feed liquid entering from the outlet end of the circulating feed pipe from entering the mother liquid overflow port N2, so that the purity of monoammonium phosphate crystallized in the flash evaporation crystallization unit is higher. When the mass concentration of phosphate ions in the feed liquid entering the inner cavity of the shell from the outlet end of the circulating feed pipe reaches 20-25%, a valve of the mother liquid overflow port is opened, the feed liquid in the inner cavity of the shell flows to the mother liquid overflow port N2 from a gap between the bottom end of the upper shell and the wall surface of the inner cavity of the lower shell, and the flow direction of the feed liquid from the outlet end of the circulating feed pipe to the mother liquid overflow port is shown in figure 3.
The first solid-liquid separation unit is used for separating ammonium sulfate generated in the feed liquid led out from the forced circulation crystallizer 42, enabling the mother liquid to flow back to the forced circulation crystallization unit for continuous concentration and crystallization to obtain ammonium sulfate crystal salt until the mass concentration of phosphate ions in the mother liquid separated from the first solid-liquid separation unit is 22-24%, enabling the mother liquid to enter the forced circulation crystallizer 42, opening a valve of a mother liquid overflow port N2, and closing a circulation discharge port N4 at the same time, and enabling the mother liquid to enter the flash evaporation crystallization unit. The first solid-liquid separation unit comprises a first thickener 52 and a first centrifuge 53 which are connected in sequence, a first discharge pipeline communicated with the first thickener 52 is arranged on the forced circulation crystallizer 42, and a first discharge pump 51 is arranged on the first discharge pipeline. The first solid-liquid separation unit further comprises a first mother liquor tank 54, and the first mother liquor tank 54 is connected with the first thickener 52 and the first centrifuge 53 and is used for collecting mother liquor discharged from the first thickener 52 and the first centrifuge 53. The first centrifuge 53 is provided with an ammonium sulfate outlet, and the ammonium sulfate outlet is connected with the ammonium sulfate packaging system 100.
Wherein the flash evaporation crystallization unit comprises a flash evaporation feed pump 62, a flash evaporation crystallizer 63, a continuous flash evaporation circulating pipeline and a vacuum system 65; as shown in fig. 4, which is a structural diagram of the flash evaporation crystallizer in this embodiment, the flash evaporation crystallizer 63 is a continuous flash evaporation crystallizer 63, a condensed water inlet P5, a spray port P6, a sight glass SG2 and a temperature sensor TE2 are arranged on a side wall of a casing of the continuous flash evaporation crystallizer 63, a salt outlet P4 is arranged at a bottom end of the casing, and a feed inlet of the flash evaporation crystallizer 63 is connected with a mother liquor overflow port N2; a pipeline connecting the feed inlet of the flash evaporation crystallizer 63 with the mother liquid overflow port N2 is provided with a storage tank 61 in the buffer memory, and the storage tank 61 in the buffer memory is used for storing the feed liquid flowing out from the mother liquid overflow port N2. The flash evaporation circulating pipeline is connected with a feed inlet P2 of the flash evaporation crystallizer 63 and a discharge outlet P3 of the flash evaporation crystallizer 63, and a flash evaporation circulating pump 64 is arranged on the flash evaporation circulating pipeline; a flash feed pump 62 is used to deliver mother liquor to the flash circulation line and further to the continuous flash crystallizer 63 via a flash circulation pump 64. A vacuum system 65 is used to maintain a vacuum in the flash crystallizer 63. After the monoammonium phosphate is separated out from the flash evaporation crystallizer 63, the mass concentration of the monoammonium phosphate in the mother liquor is 8-9%.
The second solid-liquid separation unit is used for separating out monoammonium phosphate generated in the feed liquid led out from the flash evaporation crystallizer 63, and the mother liquid is refluxed to the forced circulation crystallization unit for continuous concentration and crystallization. The second solid-liquid separation unit comprises a second thickener 72 and a second centrifuge 73 which are sequentially connected, a second discharge pipeline communicated with the second thickener 72 is arranged on the flash crystallizer 63, and a second discharge pump 71 is arranged on the second discharge pipeline. The second solid-liquid separation unit further comprises a second mother liquor tank 74, and the second mother liquor tank 74 is connected with the second thickener 72 and the second centrifuge 73 and is used for collecting mother liquor discharged from the second thickener 72 and the second centrifuge 73. And a monoammonium phosphate discharge port is formed in the second centrifuge 73 and connected with the monoammonium phosphate packaging system 200.
The iron phosphate wastewater treatment system of the embodiment further comprises a steam washing unit, wherein the steam washing unit comprises a steam washing tower 81, a first MVR compressor 82 and a second MVR compressor 83 which are sequentially connected; a secondary steam inlet is arranged on the steam washing tower 81; the secondary steam inlet is respectively connected with a secondary steam outlet N6 at the top end of the forced circulation crystallizer 42 and a secondary steam outlet P1 at the top end of the falling film separator 34. The second MVR compressor 83 is provided with a first steam outlet, and the first steam outlet is respectively connected to the first steam inlet of the falling film heater 31 and the first steam inlet of the forced circulation heater 41, and is used for recycling the steam washed by the steam washing unit to the falling film heater 31 and the forced circulation heater 41.
2. The embodiment also provides a method for treating iron phosphate wastewater, which is carried out in the iron phosphate wastewater treatment system, wherein after the iron phosphate wastewater to be treated is sequentially introduced into a preheating unit, a falling film evaporation unit and a forced circulation crystallization unit, a feed liquid containing ammonium sulfate is produced, pumping the feed liquid into a first solid-liquid separation unit through a first discharge pump 51, packaging the separated ammonium sulfate, refluxing the mother liquid to a forced circulation crystallization unit to continuously concentrate and crystallize until the mass concentration of phosphate ions in the feed liquid centrifuged by the first solid-liquid separation unit is 22-24%, opening a valve of a mother liquid overflow port N2 when the feed liquid enters the forced circulation crystallization unit again, so that the feed liquid at the height of the mother liquid overflow port N2 is discharged to the flash evaporation crystallization unit to crystallize monoammonium phosphate, and the ammonium sulfate crystallized salt continuously crystallized and grown in the feed liquid below the mother liquid overflow port N2 is discharged through the circulating discharge port N4 to be continuously separated and concentrated.
In the embodiment, the evaporation temperature of the falling film evaporation unit is 88 ℃, the evaporation pressure is-0.03377 MpaG, the material concentrated by the falling film evaporation unit is subjected to online density detection, and the discharge concentration is strictly controlled and adjusted, so that the stable operation of the system is ensured. Qualified materials are sent into an FC crystallization evaporation unit (also called a forced circulation crystallization unit) through a material pump 33-1, the evaporation temperature of the FC crystallization evaporation unit is 88 ℃, the evaporation pressure is-0.03377 MpaG, and the material temperature is 100 ℃. The material is continuously concentrated and crystallized in an FC crystallization evaporation unit. When a certain magma concentration is reached, the magma is conveyed to the first thickener 52 through the discharge pump to be thickened and finally conveyed to the first centrifuge 53, and the first centrifuge 53 is a horizontal spiral concentration discharge centrifuge. The water content of the ammonium sulfate dry salt discharged from the centrifuge is controlled within 0.2 percent, and the ammonium sulfate dry salt is directly sent into a sulfate packaging system without drying. The centrifuged mother liquor is collected by a first mother liquor tank, and is pumped into an FC evaporation crystallization unit through a first mother liquor pump 55 to continue concentration evaporation and crystallization. Continuously crystallizing, centrifuging and packaging the ammonium sulfate. When the phosphate radical in the feed liquid entering the FC crystallizer reaches the mass concentration of 22-24%, the high-concentration phosphorus-containing mother liquid entering the FC crystallizer is discharged into a storage tank 61 in the cache through the height difference, and is sent into a flash evaporation crystallizer 63 through a flash evaporation feed pump 62. After entering the system, the high-temperature material is mixed with the circulating material, a lower superheat degree is kept, the mixture enters a continuous flash evaporation crystallizer 63, flash evaporation crystallization is carried out in the crystallizer, the design temperature of the flash evaporation crystallizer 63 is 40-50 ℃, and the pressure is about-0.092 MpaG. Finally, a large amount of monoammonium phosphate and a small amount of ammonium sulfate are separated out. When the material reaches the crystallization temperature point, the material is conveyed into a second thickener 72 through a second discharge pump 71 to be thickened and then conveyed into a second centrifuge 73, and the second centrifuge 73 is a double-pushing-and-discharging centrifuge. Because the particle size entering the second centrifuge 73 is low, the moisture content of the salt (monoammonium phosphate) discharged from the second centrifuge 73 is 3% -5%. The wet salt is conveyed into a vibrated fluidized bed for drying through a screw conveyer. Ensuring that the water content of the discharged material is within 0.2 percent. The mother liquor enters a second mother liquor tank 74 for collection, and is pumped into an FC evaporation crystallization unit through a second mother liquor pump 75 for further concentration, so that a circulation loop in the system is realized.
Through detection, the nitrogen content of the ammonium sulfate produced from the ammonium sulfate packaging system 100 in the embodiment is more than or equal to 21 wt.%, and the water content is less than or equal to 0.2 wt.%; the purity of the monoammonium phosphate produced from the monoammonium phosphate packaging system 200 is greater than or equal to 92%, and the water content is less than or equal to 0.2 wt.%. The embodiment can continuously and stably produce the ammonium sulfate and the monoammonium phosphate with higher purity, the separated ammonium sulfate and the monoammonium phosphate are used as raw materials of the industrial nitrogen fertilizer and the compound fertilizer, and the evaporated condensate water is recycled for production, so that zero emission of real significance is realized. In the implementation process, when the mass concentration of phosphate ions in the iron phosphate wastewater entering the circulating feed port is further selected to be 23%, a valve of a mother liquor overflow port is opened to enable the iron phosphate wastewater to enter a flash evaporation crystallization unit, and the nitrogen content and the water content of ammonium sulfate produced from an ammonium sulfate packaging system 100 are respectively more than or equal to 21 wt.% and less than or equal to 0.2 wt.%; the purity of the monoammonium phosphate produced from the monoammonium phosphate packaging system 200 can be as high as 95% and the water content is less than or equal to 0.2 wt.%.
Claims (10)
1. The iron phosphate wastewater treatment system is characterized by comprising a preheating unit, a falling film evaporation unit, a forced circulation crystallization unit and a flash evaporation crystallization unit which are sequentially connected;
the forced circulation crystallization unit comprises a forced circulation heater and a forced circulation crystallizer which are connected in sequence;
the forced circulation crystallizer comprises a shell, wherein a mother liquor overflow port, a circulation feed inlet and a circulation discharge port are formed in the side wall of the shell from top to bottom, and the circulation discharge port is positioned at the bottom end of the shell;
a circulating feeding pipe is nested from the circulating feeding port to the inner cavity of the shell;
the outlet end of the circulating feeding pipe is arranged above the mother liquid overflow port;
the flash evaporation crystallization unit comprises a flash evaporation crystallizer, and a feed inlet of the flash evaporation crystallizer is connected with a mother liquid overflow port.
2. The iron phosphate wastewater treatment system of claim 1, wherein the housing comprises an upper housing and a lower housing, the upper housing and the lower housing are nested together, and the diameter of the upper housing is smaller than that of the lower housing; the bottom end of the upper shell is positioned below the mother liquid overflow port, and a space is reserved between the bottom end of the upper shell and the wall surface of the inner cavity of the lower shell;
and/or the preheating unit comprises a condensate water preheater, a tail gas preheater and a steam preheater which are sequentially connected, wherein a hot fluid channel of the condensate water preheater is communicated with a condensate water outlet of the falling film evaporation unit and a condensate water outlet of the forced circulation crystallization unit; a hot fluid channel of the tail gas preheater is communicated with a tail gas outlet of the falling film evaporation unit and a tail gas outlet of the forced circulation crystallization unit; a hot fluid channel of the steam preheater is communicated with each steam outlet of the iron phosphate wastewater treatment system; used for preheating the iron phosphate wastewater to be treated;
and/or the falling film evaporation unit comprises a falling film heater and a falling film separator which are connected in sequence.
3. The iron phosphate wastewater treatment system according to claim 2, wherein two falling film circulating pipelines are arranged on the falling film heater, and a falling film circulating pump is arranged on each falling film circulating pipeline.
4. The iron phosphate wastewater treatment system according to claim 1, wherein a buffer storage tank is arranged on a pipeline connecting the feed inlet of the flash evaporation crystallizer and the mother liquid overflow port;
the flash evaporation crystallization unit further comprises a flash evaporation circulating pipeline, the flash evaporation circulating pipeline is connected with the feed inlet of the flash evaporation crystallizer and the discharge outlet of the flash evaporation crystallizer, and a flash evaporation circulating pump is arranged on the flash evaporation circulating pipeline.
5. The iron phosphate wastewater treatment system according to claim 1, further comprising a first solid-liquid separation unit comprising a first thickener and a first centrifuge connected in series; the first thickener is connected with the circulating discharge port through a pipeline, and a discharge pump is arranged on the pipeline; the first centrifugal machine is provided with an ammonium sulfate discharge port and a first mother liquor discharge port; the first mother liquor discharge port is connected with the forced circulation crystallizer in a backflow mode through a first mother liquor pump;
and/or the iron phosphate wastewater treatment system further comprises a second solid-liquid separation unit, wherein the second solid-liquid separation unit comprises a second thickener and a second centrifuge which are sequentially connected; the second thickener is connected with a discharge port of the flash evaporation crystallizer through a pipeline, and a discharge pump is arranged on the pipeline; the second centrifuge is provided with a monoammonium phosphate discharge port and a second mother liquor discharge port; and the second mother liquor discharge port is connected with the forced circulation crystallizer in a backflow mode through a second mother liquor pump.
6. The iron phosphate wastewater treatment system of claim 2, further comprising a steam washing unit, wherein the steam washing unit comprises a steam washing tower, a first MVR compressor and a second MVR compressor which are connected in sequence;
a secondary steam inlet is arranged on the steam washing tower;
and the secondary steam inlet is respectively connected with a secondary steam outlet at the top end of the forced circulation crystallizer and a secondary steam outlet at the top end of the falling film separator.
7. A method for treating iron phosphate wastewater, which is characterized by adopting the iron phosphate wastewater treatment system according to any one of claims 1 to 6 for treatment;
which comprises the following steps: sequentially introducing iron phosphate wastewater to be treated into the preheating unit, the falling film evaporation unit and the forced circulation crystallization unit;
and when the mass concentration of phosphate ions in the iron phosphate wastewater entering the circulating feed port is 20-25%, opening a valve of the mother liquid overflow port to enable the iron phosphate wastewater to enter the flash evaporation crystallization unit.
8. The iron phosphate wastewater treatment method according to claim 7, wherein when the mass concentration of phosphate ions in the iron phosphate wastewater entering the circulating feed inlet is 22-24%, such as 23%, a valve of the mother liquid overflow port is opened to enable the iron phosphate wastewater to enter the flash evaporation crystallization unit;
and/or the iron phosphate wastewater to be treated comprises the following components: NH (NH)4 +：40700～50000mg/L；PO4 3-: 16000-19600 mg/L and SO4 2-：98300～120000mg/L；
Wherein, the NH4 +The concentration of (b) is preferably 43000-47000 mg/L, such as 45251 mg/L;
wherein, the PO4 3-The concentration of (b) is preferably 169900-18700 mg/L, such as 17844 mg/L;
wherein the SO4 2-The concentration of (b) is preferably 104000-115000 mg/L, such as 109329 mg/L;
and/or the TDS concentration in the iron phosphate wastewater to be treated is 155500-19000 mg/L, such as 172800 mg/L;
and/or F is also contained in the iron phosphate wastewater to be treated-、Mg2+、Ca2+One or more of;
wherein, F is-The concentration of (b) is preferably 140-170 mg/L;
wherein said Mg2+The concentration of (b) is preferably 1 to 2 mg/L;
wherein, the Ca2+The concentration of (B) is preferably 1 to 2 mg/L.
9. The iron phosphate wastewater treatment method according to claim 7 or 8, wherein the pH value of the iron phosphate wastewater to be treated is 4.5-5.5, such as 5;
and/or the mass concentration of the solute in the iron phosphate wastewater to be treated is 10-20%, such as 16%;
and/or the temperature of the iron phosphate wastewater to be treated is 10-40 ℃, for example 35 ℃;
and/or the preheating unit is used for preheating the iron phosphate wastewater to be treated to a boiling point;
wherein the boiling point of the iron phosphate wastewater to be treated is preferably 88-100 ℃, for example 91 ℃ or 93 ℃;
and/or the falling film evaporation unit is used for increasing the mass concentration of solutes in the preheated iron phosphate wastewater to 40-45%, such as 41%, 42% or 43%.
10. The iron phosphate wastewater treatment method according to claim 7, wherein the iron phosphate wastewater to be treated comprises:
NH4 +：45251mg/L；
PO4 3-：17844mg/L；
SO4 2-：109329mg/L；
and in the iron phosphate wastewater to be treated, the TDS is 172800 mg/L;
the pH value of the iron phosphate wastewater to be treated is 5.
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