CN111348665A - Membrane method freezing denitration method and production device - Google Patents
Membrane method freezing denitration method and production device Download PDFInfo
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- CN111348665A CN111348665A CN201811582322.6A CN201811582322A CN111348665A CN 111348665 A CN111348665 A CN 111348665A CN 201811582322 A CN201811582322 A CN 201811582322A CN 111348665 A CN111348665 A CN 111348665A
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- 238000000034 method Methods 0.000 title claims abstract description 141
- 239000012528 membrane Substances 0.000 title claims abstract description 129
- 238000007710 freezing Methods 0.000 title claims abstract description 81
- 230000008014 freezing Effects 0.000 title claims abstract description 81
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 35
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 245
- AMXOYNBUYSYVKV-UHFFFAOYSA-M lithium bromide Chemical compound [Li+].[Br-] AMXOYNBUYSYVKV-UHFFFAOYSA-M 0.000 claims abstract description 88
- 229910000041 hydrogen chloride Inorganic materials 0.000 claims abstract description 57
- IXCSERBJSXMMFS-UHFFFAOYSA-N hydrogen chloride Substances Cl.Cl IXCSERBJSXMMFS-UHFFFAOYSA-N 0.000 claims abstract description 57
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 claims abstract description 55
- 230000008569 process Effects 0.000 claims abstract description 42
- 239000003513 alkali Substances 0.000 claims abstract description 16
- 238000006243 chemical reaction Methods 0.000 claims abstract description 5
- 239000007788 liquid Substances 0.000 claims description 157
- 239000012267 brine Substances 0.000 claims description 127
- HPALAKNZSZLMCH-UHFFFAOYSA-M sodium;chloride;hydrate Chemical compound O.[Na+].[Cl-] HPALAKNZSZLMCH-UHFFFAOYSA-M 0.000 claims description 127
- 229910002651 NO3 Inorganic materials 0.000 claims description 125
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 claims description 123
- 238000011084 recovery Methods 0.000 claims description 80
- FGIUAXJPYTZDNR-UHFFFAOYSA-N potassium nitrate Chemical compound [K+].[O-][N+]([O-])=O FGIUAXJPYTZDNR-UHFFFAOYSA-N 0.000 claims description 79
- 238000001816 cooling Methods 0.000 claims description 71
- 238000000926 separation method Methods 0.000 claims description 71
- 238000003786 synthesis reaction Methods 0.000 claims description 47
- 230000015572 biosynthetic process Effects 0.000 claims description 42
- 235000010333 potassium nitrate Nutrition 0.000 claims description 31
- 150000003839 salts Chemical class 0.000 claims description 31
- 239000003507 refrigerant Substances 0.000 claims description 29
- 238000002425 crystallisation Methods 0.000 claims description 25
- 230000008025 crystallization Effects 0.000 claims description 25
- PMZURENOXWZQFD-UHFFFAOYSA-L Sodium Sulfate Chemical compound [Na+].[Na+].[O-]S([O-])(=O)=O PMZURENOXWZQFD-UHFFFAOYSA-L 0.000 claims description 23
- 239000006228 supernatant Substances 0.000 claims description 22
- 239000010446 mirabilite Substances 0.000 claims description 21
- 239000001257 hydrogen Substances 0.000 claims description 13
- 229910052739 hydrogen Inorganic materials 0.000 claims description 13
- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 claims description 12
- 239000000460 chlorine Substances 0.000 claims description 12
- 229910052801 chlorine Inorganic materials 0.000 claims description 12
- 239000013078 crystal Substances 0.000 claims description 12
- 238000001704 evaporation Methods 0.000 claims description 11
- 230000008020 evaporation Effects 0.000 claims description 11
- 239000000243 solution Substances 0.000 claims description 11
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 claims description 10
- 238000004064 recycling Methods 0.000 claims description 10
- 150000002823 nitrates Chemical class 0.000 claims description 9
- 230000002194 synthesizing effect Effects 0.000 claims description 6
- 238000005057 refrigeration Methods 0.000 claims description 5
- 238000004062 sedimentation Methods 0.000 claims description 5
- 238000001035 drying Methods 0.000 claims description 4
- 239000007789 gas Substances 0.000 claims description 4
- 238000002360 preparation method Methods 0.000 claims description 4
- 230000001174 ascending effect Effects 0.000 claims description 3
- 239000000126 substance Substances 0.000 claims description 2
- 238000005265 energy consumption Methods 0.000 abstract description 8
- 239000002699 waste material Substances 0.000 abstract description 5
- 238000003912 environmental pollution Methods 0.000 abstract description 3
- QAOWNCQODCNURD-UHFFFAOYSA-L Sulfate Chemical compound [O-]S([O-])(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-L 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- FAPWRFPIFSIZLT-UHFFFAOYSA-M Sodium chloride Chemical compound [Na+].[Cl-] FAPWRFPIFSIZLT-UHFFFAOYSA-M 0.000 description 3
- 238000010521 absorption reaction Methods 0.000 description 3
- 239000000498 cooling water Substances 0.000 description 3
- 238000007599 discharging Methods 0.000 description 3
- 150000002431 hydrogen Chemical class 0.000 description 3
- 239000000047 product Substances 0.000 description 3
- 239000011780 sodium chloride Substances 0.000 description 3
- 229910052938 sodium sulfate Inorganic materials 0.000 description 3
- 235000011152 sodium sulphate Nutrition 0.000 description 3
- 239000008399 tap water Substances 0.000 description 3
- 235000020679 tap water Nutrition 0.000 description 3
- 238000009826 distribution Methods 0.000 description 2
- 230000007613 environmental effect Effects 0.000 description 2
- 239000012535 impurity Substances 0.000 description 2
- 230000007246 mechanism Effects 0.000 description 2
- 239000011259 mixed solution Substances 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 238000007781 pre-processing Methods 0.000 description 2
- 230000009467 reduction Effects 0.000 description 2
- 239000007787 solid Substances 0.000 description 2
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 description 1
- KZBUYRJDOAKODT-UHFFFAOYSA-N Chlorine Chemical compound ClCl KZBUYRJDOAKODT-UHFFFAOYSA-N 0.000 description 1
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 1
- 230000008901 benefit Effects 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 239000011575 calcium Substances 0.000 description 1
- 229910052791 calcium Inorganic materials 0.000 description 1
- 125000004122 cyclic group Chemical group 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000010612 desalination reaction Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000005868 electrolysis reaction Methods 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 238000007701 flash-distillation Methods 0.000 description 1
- 238000009776 industrial production Methods 0.000 description 1
- 239000011777 magnesium Substances 0.000 description 1
- 229910052749 magnesium Inorganic materials 0.000 description 1
- 238000010979 pH adjustment Methods 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
- C01D3/00—Halides of sodium, potassium or alkali metals in general
- C01D3/14—Purification
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01D—COMPOUNDS OF ALKALI METALS, i.e. LITHIUM, SODIUM, POTASSIUM, RUBIDIUM, CAESIUM, OR FRANCIUM
- C01D3/00—Halides of sodium, potassium or alkali metals in general
- C01D3/22—Preparation in the form of granules, pieces, or other shaped products
- C01D3/24—Influencing the crystallisation process
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/80—Compositional purity
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Engineering & Computer Science (AREA)
- Materials Engineering (AREA)
- Inorganic Chemistry (AREA)
- Separation Using Semi-Permeable Membranes (AREA)
Abstract
The invention provides a membrane method freezing denitration method and a production device, wherein heat generated by synthetic reaction in a hydrogen chloride synthetic furnace is recycled by water, low-pressure steam flashed out is introduced into a steam lithium bromide refrigerating unit, low-temperature water of 4-7 ℃ is prepared by the steam lithium bromide refrigerating unit, and the low-temperature water of 4-7 ℃ is used for providing cold energy for a membrane method freezing denitration process to realize freezing denitration. The invention not only solves the problem of high-level cold quantity requirement of membrane method freezing denitration, reduces energy consumption, saves production cost, but also solves the problem of waste of steam emptying of the hydrogen chloride synthetic furnace in the chlor-alkali production process, and reduces environmental pollution.
Description
Technical Field
The invention belongs to the technical field of chlor-alkali production, and particularly relates to a membrane method freezing denitration method and a production device.
Background
High-nitrate brine with high sodium sulfate concentration can be generated in the production process of chlor-alkali, wherein sodium sulfate is mainly removed by adopting a membrane method for freezing denitration, and the method comprises the following steps: the high nitrate water is treated by heat recovery, pH adjustment, solid impurity filtration and the like, and then enters a membrane separator for membrane separation, and the concentrated nitrate water obtained by separation enters a concentrated nitrate water tank, and enters a crystallizer after being subjected to heat exchange and temperature reduction by a precooler. And circularly cooling the concentrated nitre solution in the crystallizer to 3-10 ℃ through a freezing heat exchanger, separating out mirabilite, obtaining a clear solution with low nitre content at the upper part, and obtaining mirabilite solid and low-nitre light brine through solid-liquid centrifugal separation of the concentrated nitre solution at the lower part.
However, this denitration method has the following disadvantages: the refrigerant of the condensed nitrate liquid freezing and circulating heat exchanger usually adopts low-temperature chilled water with the temperature of minus 10 to minus 13 ℃, has higher requirements on energy consumption and causes high-level cold quantity waste.
Meanwhile, in the production process of chlor-alkali, hydrogen and chlorine are used for synthesizing hydrogen chloride in a synthesis furnace to react to generate a large amount of heat, and the generated products are cooled to generate a large amount of steam which is discharged outwards, so that energy is wasted, and the surrounding environment is thermally polluted.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a membrane method freezing denitration method and a production device aiming at the defects in the prior art, which can solve the problem of high-order cold quantity requirement in the membrane method freezing denitration process and the problem of waste of steam emptying of a hydrogen chloride synthetic furnace in the chlor-alkali production process, greatly reduce the energy consumption in the denitration process, reduce the production cost and reduce the environmental pollution.
The technical scheme of the membrane freezing denitration method adopted for solving the technical problems is as follows:
a membrane method freezing denitration method comprises pretreatment, membrane separation and freezing denitration of nitrate-containing dilute brine, wherein low-temperature water of 4-7 ℃ is prepared by a steam lithium bromide refrigerating unit, and the low-temperature water of 4-7 ℃ is used for providing cold energy for a membrane method freezing denitration process to realize freezing denitration.
Preferably, the steam lithium bromide refrigerating unit is used for refrigerating and preparing low-temperature water at the temperature of 4-7 ℃ by using low-pressure steam generated by recycling heat generated by a synthesis reaction in a hydrogen chloride synthesis furnace by using water.
Further, the membrane method freezing denitration method provided by the invention specifically comprises the following steps:
(1) preparing low-temperature water: recycling heat generated by the synthetic reaction of hydrogen and chlorine in the hydrogen chloride synthetic furnace by using water, introducing low-pressure steam flashed out into a steam lithium bromide refrigerating unit, and refrigerating by using the steam lithium bromide refrigerating unit to prepare low-temperature water at the temperature of 4-7 ℃;
(2) pretreating the nitrate-containing dilute brine: the low-temperature water prepared in the step (1) is used for providing cold energy for the membrane method freezing denitration process, and the temperature of the nitrate-containing dilute brine is reduced by introducing the cold energy into a pretreatment unit;
(3) membrane separation: after the pressure of the pretreated nitrate-containing light salt water is increased by a high-pressure pump, the nitrate-containing light salt water passes through a separation membrane by adopting a membrane separation method, and denitrated salt water and concentrated nitrate salt water are obtained by separation;
(4) nitrate and liquid separation of concentrated nitrate brine: and (2) introducing the low-temperature water prepared in the step (1) into a cooling crystallization unit to circularly cool the concentrated saltpeter water subjected to membrane separation, crystallizing, and performing saltpeter-liquid separation to obtain mirabilite and a centrifugal clear liquid.
Preferably, the preparation of low-temperature water in the step (1) provides cold for the membrane method freezing denitration process, and specifically comprises the following steps:
(1-1) heat recovery: drying hydrogen and chlorine produced by a chlor-alkali electrolytic cell, feeding the dried hydrogen and chlorine into a hydrogen chloride synthesis furnace through a pipeline, and combusting to obtain hydrogen chloride gas, wherein heat generated by the synthesis furnace is recovered by using water to obtain high-temperature water;
(1-2) low-temperature water preparation: introducing the high-temperature water obtained in the step (1-1) into a flash evaporation tank for flash evaporation to obtain low-pressure steam, introducing the low-pressure steam into a steam lithium bromide refrigerating unit for work refrigeration to prepare low-temperature water with the temperature of 4-7 ℃ and the refrigerant of desalted water;
(1-3) introducing low-temperature water with the temperature of 4-7 ℃ into a cooling crystallization unit in the membrane method freezing and denitration process to provide cold energy for the membrane method freezing and denitration process;
(1-4) returning the low-temperature water subjected to heat exchange to a steam lithium bromide refrigerating unit to be used as a refrigerant medium for recycling so as to prepare refrigerant low-temperature water; when the recycled refrigerant medium is insufficient, proper amount of desalted water of the refrigerant in the step (1-2) can be supplemented;
and (4) continuously preparing the low-temperature water of the refrigerant at the temperature of 4-7 ℃ by repeating the step (1-2), the step (1-3) and the step (1-4).
Preferably, the nitrate and liquid separation of the concentrated nitrate brine in the step (4): the circulating cooling, crystallization and separation of the concentrated saltpeter water specifically comprise the following steps:
(4-1) separating the concentrated nitrate water into upper clear liquid and middle-lower concentrated nitrate liquid in a crystallizer through sedimentation, boosting the upper clear liquid in the crystallizer by using a circulating pump, conveying the upper clear liquid to a circulating cooler, exchanging heat with low-temperature water at 4-7 ℃, reducing the temperature of the upper clear liquid to 4-10 ℃, and returning the upper clear liquid to the middle position of the crystallizer;
(4-2) cooling the concentrated nitre liquid at the middle lower part of the crystallizer by using the low-temperature upper clear liquid returned after cooling in the step (4-1), and simultaneously, ascending the clear liquid and settling the concentrated nitre liquid through settling;
(4-3) repeating the steps (4-1) and (4-2) on the supernatant to gradually cool and crystallize the concentrated mirabilite liquid to generate mirabilite crystals, and then performing mirabilite-liquid separation by using a centrifuge to obtain mirabilite and a centrifuged supernatant;
and (4-4) conveying the centrifugal clear liquid into a clear liquid cold energy recovery heat exchanger for reducing the temperature of the concentrated saltwater generated by the membrane separation in the step (3), and conveying the centrifugal clear liquid subjected to heat exchange with the concentrated saltwater to a position where the saltwater-containing dilute brine is pretreated in the step (2) to be converged with the saltwater-containing dilute brine for circular denitration.
Preferably, the cold quantity in the process of the membrane method freezing denitration method is mainly provided by the low-temperature water with the temperature of 4-7 ℃ prepared in the step (1): firstly, transferring cold energy to upper clear liquid in a circulating cooler by low-temperature water at 4-7 ℃; then transferring the concentrated nitre solution to the middle lower part of the crystallizer; then transferring to the centrifugal clear liquid; then, after the centrifugal clear liquid is conveyed to a clear liquid cold energy recovery heat exchanger, part of cold energy is transmitted to the concentrated saltwater, and the other part of cold energy is converged with the saltwater-containing light saltwater along with the centrifugal clear liquid, and the cold energy is transmitted to the saltwater-containing light saltwater, so that the temperature of the saltwater-containing light saltwater is reduced; and finally, separating the nitrate-containing light salt brine into denitrated salt brine and concentrated nitrate salt brine in a membrane separator, wherein the denitrated salt brine is conveyed into a heat recovery heat exchanger to provide cold energy for reducing the temperature of the nitrate-containing light salt brine when the nitrate-containing light salt brine is pretreated in the step (2).
The invention provides a membrane method freezing denitration production device, which is used for the membrane method freezing denitration method and comprises the following steps: a low-temperature water unit, a pretreatment unit, a membrane separation unit and a cooling crystallization unit,
the low-temperature water unit is used for preparing low-temperature water and providing cold energy for the membrane method freezing denitration process;
the pretreatment unit is used for cooling the nitrate-containing dilute brine;
the membrane separation unit is connected with the pretreatment unit and is used for pressurizing the nitrate-containing light brine and then separating the nitrate-containing light brine into denitrated brine and concentrated nitrate brine by adopting a membrane separation method;
the cooling crystallization unit is connected with the membrane separation unit and used for cooling, crystallizing and separating the concentrated nitrate salt water, and is also connected with the low-temperature water unit and used for receiving the refrigerant low-temperature water provided by the low-temperature water unit and providing the cooling capacity required by the cooling crystallization unit for the crystallization of the concentrated nitrate salt water, and transmitting the cooling capacity to the membrane separation unit and the pretreatment unit.
Preferably, the low temperature water unit includes: a hydrogen chloride synthetic furnace, a heat recovery device and a steam lithium bromide refrigerating unit,
the hydrogen chloride synthesis furnace and the heat recovery equipment prepare low-pressure steam by utilizing heat generated by synthesizing hydrogen chloride;
and the steam lithium bromide refrigerating unit is connected with the hydrogen chloride synthesis furnace and the heat recovery equipment, and is used for preparing the refrigerant low-temperature water and providing cold energy for the membrane method freezing and denitration process.
Preferably, the pretreatment unit includes: a heat recovery heat exchanger and a circulating water heat exchanger,
the heat recovery heat exchanger is used for introducing nitrate-containing light salt water, is connected with the membrane separator and is used for receiving the denitration salt water as a cold source to recover heat of the nitrate-containing light salt water so as to cool the nitrate-containing light salt water;
and the circulating water heat exchanger is connected with the heat recovery heat exchanger and is used for further cooling the saltpeter-containing dilute brine.
Preferably, the cooling crystallization unit comprises a clear liquid cold energy recovery heat exchanger, a crystallizer, a circulating pump, a circulating cooler and a centrifuge,
the clear liquid cold energy recovery heat exchanger is connected with the membrane separation unit (namely connected with a membrane separator of the membrane separation unit) and is also connected with the centrifuge, and is used for recovering the cold energy of the centrifuged clear liquid and further reducing the temperature of the concentrated saltwater discharged by the membrane separation unit.
The crystallizer is connected with the clear liquid cold energy recovery heat exchanger and is used for cooling, crystallizing and separating the concentrated nitrate brine;
the circulating pump is connected with the crystallizer and is used for conveying the supernatant in the crystallizer to the circulating cooler to provide power for the circulation of the supernatant;
the circulating cooler is connected with the steam lithium bromide refrigerating unit of the low-temperature water unit and used for carrying out cold cooling treatment on the upper clear liquid and returning the cooled upper clear liquid to the crystallizer;
the centrifuge is connected with the crystallizer and is used for separating the crystal substances output from the crystallizer.
According to the invention, heat generated by a synthesis reaction of a hydrogen chloride synthesis furnace in a chlor-alkali industrial process is recycled by using water, high-temperature water after heat absorption is subjected to flash evaporation to obtain low-pressure steam, the low-pressure steam is introduced into a steam lithium bromide refrigerating unit for refrigeration to prepare low-temperature water at 4-7 ℃, and the low-temperature water at 4-7 ℃ is used as a cold source to provide cold energy for a membrane method freezing and denitration process, so that freezing and denitration are realized. Compared with the prior art, the invention not only solves the problem of high-level cold quantity requirement of membrane method freezing denitration, reduces energy consumption and saves production cost, but also solves the problem of waste caused by steam emptying generated by cooling a hydrogen chloride synthesis furnace and synthesizing products in the production process of chlor-alkali, and reduces environmental thermal pollution.
Drawings
FIG. 1 is a process flow diagram of a membrane-process freezing denitration production apparatus in example 1;
FIG. 2 is a schematic view showing the production process of the membrane process freezing denitration method in example 1;
in the figure: 1-nitrate-containing dilute saline; 2-heat recovery heat exchanger; 3-circulating water heat exchanger; 4-a high pressure pump; 5-a membrane separator; 6-denitrified brine; 7-denitrified brine; 8-clear liquid cold energy recovery heat exchanger; 9-centrifuging the clear solution; 10-concentrated saltpeter brine; 11-a crystallizer; 12-crystallizer supernatant; 13-a circulation pump; 14-a circulation cooler; 15-centrifuge downcomer; 16-a centrifuge; 17-mirabilite; 18-hydrogen; 19-chlorine gas; 20-desalted water; a 21-hydrogen chloride synthesis furnace and heat recovery equipment; 22-hydrogen chloride; 23-low pressure steam; 24-steam lithium bromide refrigeration unit; low temperature water of 25-4 to 7 ℃.
Detailed Description
In order to make the technical solutions of the present invention better understood, the present invention will be further clearly and completely described below with reference to the accompanying drawings and specific examples of the present invention.
In the prior art, the membrane method freezing denitration process has high requirement on a refrigerant, needs high-level cold quantity, and has the problems of high energy consumption, high cost and the like; meanwhile, the hydrogen chloride synthesis furnace has the problems of environmental pollution caused by steam emptying and the like in the industrial production process of chlor-alkali. Therefore, the invention provides a membrane method freezing denitration method, which comprises the following steps:
the method is characterized in that a steam lithium bromide refrigerating unit is used for refrigerating steam generated by heat of a hydrogen chloride synthesis furnace to prepare low-temperature water at the temperature of 4-7 ℃, and the low-temperature water at the temperature of 4-7 ℃ is used as a cold source to provide cold energy for the membrane method freezing and denitration process, so that freezing and denitration are realized.
Correspondingly, the invention also provides a membrane method freezing and denitration production device, which is used for the membrane method freezing and denitration method and comprises the following steps: a low-temperature water unit, a pretreatment unit, a membrane separation unit and a cooling crystallization unit,
the low-temperature water unit is used for preparing low-temperature water, the low-temperature water is used as a cold source to provide cold energy for the membrane method freezing denitration process,
the pretreatment unit is used for cooling the nitrate-containing dilute brine;
the membrane separation unit is connected with the pretreatment unit and is used for pressurizing the nitrate-containing light brine and then separating the nitrate-containing light brine into denitrated brine and concentrated nitrate brine by adopting a membrane separation method;
the cooling crystallization unit is connected with the membrane separation unit and used for cooling, crystallizing and separating the concentrated nitrate brine, and is also connected with the low-temperature water unit and used for receiving the low-temperature water provided by the low-temperature water unit as a cold source, providing cold energy required by cooling and crystallizing for crystallizing the concentrated nitrate brine by the cooling crystallization unit, and transmitting the cold energy to the membrane separation unit and the pretreatment unit.
Example 1
As shown in fig. 2, this embodiment provides a membrane method for freezing and denitration, which includes pretreatment of a dilute brine containing nitrate, membrane separation, cooling and denitration, and further includes preparing low-temperature water: the heat generated by the synthesis reaction in the hydrogen chloride synthesis furnace and the heat recovery equipment 21 is recovered and reused by using water, the low-pressure steam flashed out is introduced into the steam lithium bromide refrigerating unit 24, the steam lithium bromide refrigerating unit 24 refrigerates to prepare 4-7 ℃ low-temperature water, and the 4-7 ℃ low-temperature water 25 is used as a cold source to provide cold for the membrane method freezing denitration process, so that freezing denitration is realized.
The membrane method freezing denitration method in the embodiment specifically comprises the following steps:
Specifically, the method for preparing low-temperature water in the step (101) to provide cold for the membrane method freezing denitration process further comprises the following steps:
(1-1) heat recovery: drying hydrogen 18 and chlorine 19 produced by a chlor-alkali industrial electrolytic cell, conveying the dried hydrogen and chlorine into a hydrogen chloride synthesis furnace through a pipeline, combusting the hydrogen chloride to obtain hydrogen chloride 22 gas, introducing water into heat recovery equipment of the hydrogen chloride synthesis furnace to recover heat generated by the hydrogen chloride synthesis reaction to obtain high-temperature water, introducing the high-temperature water into a flash evaporation tank in the heat recovery equipment to carry out flash evaporation to obtain low-pressure steam 23;
further, in order to avoid the formation of scale in the flash tank when low-pressure steam 23 is flashed off during the recovery of heat from the hci synthesis furnace, the water used in this example is desalted water 20. Firstly, removing impurities such as calcium, magnesium and the like from water to obtain desalted water 20, then introducing the desalted water 20 into heat recovery equipment of a hydrogen chloride synthesis furnace, and recovering heat generated by a hydrogen chloride synthesis reaction in the hydrogen chloride synthesis furnace. The specific production process of the low-salt steam 23 is as follows: the desalted water 20 enters heat recovery equipment of a hydrogen chloride synthesis furnace to absorb heat released during hydrogen chloride synthesis to obtain high-temperature desalted water, the high-temperature desalted water is introduced into a flash evaporation tank, part of the high-temperature desalted water absorbs heat and then becomes low-pressure saturated steam, the rest desalted water enters the synthesis furnace again to continue circulating heat absorption and flash evaporation, and the pressure of the generated low-pressure steam 23 is 0.3-0.5 MPa.
(1-2) low-temperature water preparation: and (2) introducing the high-temperature water obtained in the step (1-1) into a flash evaporation tank for flash evaporation to obtain low-pressure steam 23, introducing the low-pressure steam into a steam lithium bromide refrigerating unit 24 for work refrigeration to obtain low-temperature water 25 with the temperature of 4-7 ℃, and taking the low-temperature water 25 with the temperature of 4-7 ℃ as a cold source for the membrane freezing denitration process. In the embodiment, in order to prevent equipment scaling, desalted water is adopted as refrigerant water in the steam lithium bromide refrigerating unit, and the temperature of the refrigerant water is reduced by absorbing a large amount of heat of the refrigerant water, so that refrigerant low-temperature water at 4-7 ℃ is obtained.
(1-3) introducing low-temperature water 25 at the temperature of 4-7 ℃ into a circulating cooler 14 in a cooling crystallization unit in the membrane method freezing and denitration process to provide cold energy for the membrane method freezing and denitration process;
(1-4) returning the low-temperature water 25 subjected to heat exchange to the steam lithium bromide refrigerating unit 24 to be used as refrigerant water for recycling, so as to prepare 4-7 ℃ low-temperature refrigerant water; when the recycled refrigerant medium is insufficient, the refrigerant in the step (1-2) can be supplemented in a proper amount, namely desalted water is supplemented;
and (3) continuously preparing the refrigerant low-temperature water at the temperature of 4-7 ℃ by repeating the step (1-2), the step (1-3) and the step (1-4), so that sufficient cold energy can be provided for the membrane method freezing denitration process.
Further, low-temperature water 25 at 4-7 ℃ enters the circulation cooler 14 from the steam lithium bromide refrigerating unit 24 to provide sufficient cold for the circulation cooler 14, and the low-temperature water 25 exchanges heat with upper clear liquid 12 (hereinafter referred to as upper clear liquid) of the crystallizer in the circulation cooler 14 and returns to the steam lithium bromide refrigerating unit 24 for cyclic utilization, so that the cold utilization rate can be improved, and the loss in the cold circulation process can be reduced.
Specifically, the nitrate-containing dilute brine 1 used in this embodiment is a dilute brine containing nitrate with high sodium sulfate concentration in the production process of chlor-alkali, the pressure is 0.05 to 0.1MPa, and the temperature is 60 to 90 ℃. Inputting the nitrate-containing dilute brine 1 from the heat recovery heat exchanger 2, exchanging heat between the nitrate-containing dilute brine 1 and the denitrated brine 6 discharged from the membrane separator 5 in the heat recovery heat exchanger 2, and reducing the temperature of the nitrate-containing dilute brine 1 to 40-60 ℃; and then conveying the mixed solution into a circulating water heat exchanger 3, and exchanging heat between the nitrate-containing dilute brine 1 and cooling water in the circulating water heat exchanger 3 to further reduce the temperature of the nitrate-containing dilute brine 1 to 25-35 ℃. The cooling water in the circulating heat exchanger can be tap water, the tap water is introduced into the circulating heat exchanger, and the tap water is discharged after heat exchange. In this embodiment, the circulating heat exchanger is connected to a circulating water cooling system in a plant to realize cooling water circulation.
specifically, in order to improve the membrane separation effect, the pressure of the dilute brine 1 containing nitrate at 25-35 ℃ output in the step 102 is increased to 2.0-2.8 MPa by using the high-pressure pump 4, and then the dilute brine is conveyed to the membrane separator 5. The nitrate-containing dilute brine 1 is separated by a membrane method in a membrane separator 5 to obtain denitrated brine 6 and concentrated nitrate brine 10. Wherein the sulfate ion concentration of the denitrified brine 6 is 1-2 g/L, the temperature is 25-35 ℃, the sulfate ion concentration of the concentrated nitrate brine 10 is 50-80 g/L, and the temperature is 25-35 ℃.
Further, conveying the concentrated nitrate brine 10 at the temperature of 25-35 ℃ to a clear liquid cold energy recovery heat exchanger 8, further cooling to reduce the temperature of the concentrated nitrate brine 10 to 10-20 ℃, and then conveying to a crystallizer 11.
Further, the denitration brine 6 with the temperature of 25-35 ℃ is conveyed to the heat recovery heat exchanger 2 to recover the heat of the denitration brine 1, and the denitration brine 7 obtained after heat exchange with the denitration brine 1 is discharged to the water distribution tank for recycling, so that the cold energy can be fully utilized, the water can be saved, and the production cost is reduced.
step (4-1): after entering a crystallizer 11, the concentrated nitrate brine 10 is separated into upper clear liquid 12 and middle-lower concentrated nitrate liquid through sedimentation, the upper clear liquid 12 in the crystallizer 11 is pressurized by a circulating pump 13 and then is conveyed to a circulating cooler 14, after heat exchange is carried out with low-temperature water 25 at 4-7 ℃, the temperature of the upper clear liquid 12 is reduced to 4-10 ℃, and then the upper clear liquid is returned to the crystallizer 11 from the middle position of the crystallizer 11;
specifically, the pressure of the supernatant 12 in the crystallizer 11 is raised to 0.2 to 0.5MPa by the circulation pump 13, and the supernatant is sent to the circulation cooler 14. In a circulating cooler 14, heat exchange is carried out between the upper clear liquid 12 and low-temperature water 25 at 4-7 ℃, the temperature of the upper clear liquid 12 is reduced to 4-10 ℃, and then the upper clear liquid is returned to a crystallizer 11; the low-temperature water 25 is heated after heat exchange, and then returns to the steam lithium bromide refrigerating unit 24 to be used as a refrigerant medium for recycling, so as to prepare the refrigerant low-temperature water.
Step (4-2): and (4) cooling the concentrated nitre liquid at the middle lower part in the crystallizer 11 by using the upper clear liquid 12 returned after cooling in the step (4-1), and simultaneously ascending the clear liquid and descending the concentrated nitre liquid through sedimentation.
Step (4-3): repeating the step (4-1) and the step (4-2) on the supernatant liquid 12, gradually cooling the concentrated mirabilite liquid, crystallizing to generate mirabilite 17 crystals, discharging the mirabilite 17 crystals from the bottom of the crystallizer 11 to a centrifuge 16, and performing mirabilite-liquid separation by using the centrifuge 16 to obtain mirabilite 17 and a centrifugal clear liquid 9;
specifically, the temperature of the supernatant 12 returned to the crystallizer 11 is 4-10 ℃, the temperature of the concentrated saltpeter at the middle-lower part of the crystallizer 11 is 10-20 ℃, heat exchange is carried out between the supernatant and the concentrated saltpeter, the temperature of the concentrated saltpeter is gradually reduced, the step (4-1) and the step (4-2) are continuously repeated on the supernatant 12, the temperature of the concentrated saltpeter is reduced to 4-10 ℃, mirabilite 17 crystals are separated out through crystallization, then the concentrated saltpeter enters a centrifuge 16 through a crystallizer liquid descending pipe 15 connected to the bottom of the crystallizer 11, and the mirabilite 17 and the centrifuge supernatant 9 are obtained through separation in the.
Step (4-4): and (3) conveying the centrifugal clear liquid 9 into a clear liquid cold energy recovery heat exchanger 8 for reducing the temperature of the concentrated saltwater 10 generated by the membrane separation in the step (3), and conveying the centrifugal clear liquid 9 subjected to heat exchange with the concentrated saltwater 10 to be converged with the saltwater-containing dilute saltwater 1 output by the circulating water heat exchanger 3 for circulating denitration.
Specifically, the crystal separated by the centrifuge 16 is mirabilite 17; the sulfate radical concentration of the centrifugal clear liquid 9 is 10-30 g/L, the temperature is 4-10 ℃, the centrifugal clear liquid is conveyed into a clear liquid cold energy recovery heat exchanger 8 through a pipeline and is used for further cooling the concentrated nitrate water 10 separated by the membrane separator 5, and the temperature of the concentrated nitrate water 10 is reduced to 10-20 ℃. The centrifugal clear liquid 9 is delivered from the clear liquid cold energy recovery heat exchanger 8 and then delivered to the nitrate-containing dilute brine 1 to be merged (in this embodiment, the centrifugal clear liquid 9 is merged with the nitrate-containing brine from the delivery pipeline of the circulating water heat exchanger, and may be merged with the nitrate-containing dilute brine from other positions of the pretreatment unit, which is not further limited in this embodiment), so as to perform the circulating denitration. By the aid of the method, the cold energy utilization rate can be improved, energy consumption is reduced, and the denitration effect can be improved.
In the embodiment, the cold quantity in the process of the membrane method freezing denitration method is mainly provided by the low-temperature water 25 with the temperature of 4-7 ℃ prepared in the step (1), and the specific cold quantity transmission process is as follows:
firstly, the cold energy is transferred to the upper clear liquid 12 in the circulating cooler 14 from low-temperature water 25 at 4-7 ℃; the concentrated nitre solution is delivered to the crystallizer 11 again; then transferred to the centrifuged supernatant 9; then, after the centrifugal clear liquid 9 is conveyed to a clear liquid cold energy recovery heat exchanger 8, part of cold energy is transmitted to concentrated nitrate brine 10, the other part of cold energy is converged with nitrate-containing brine 1 along with the centrifugal clear liquid 9, and the cold energy is transmitted to nitrate-containing dilute brine 1 again, so that the temperature of the nitrate-containing brine 1 is reduced; finally, the nitrate-containing dilute brine 1 is separated into denitrated brine 6 and concentrated nitrate brine 10 in a membrane separator 5, wherein the denitrated brine 6 is conveyed into a heat recovery heat exchanger 2 to provide cold for reducing the temperature of the nitrate-containing dilute brine 1 when the nitrate-containing dilute brine 1 is pretreated in the step (2).
Example 2
As shown in fig. 1, the present embodiment provides a membrane-process freezing and denitration production apparatus, including: a low-temperature water unit, a pretreatment unit, a membrane separation unit and a cooling crystallization unit,
the low-temperature water unit is used for preparing low-temperature water, and the low-temperature water is used as a cold source to provide cold energy for the membrane method freezing denitration process;
the pretreatment unit is used for carrying out cooling and pressure boosting treatment on the nitrate-containing dilute brine 1;
the membrane separation unit is connected with the pretreatment unit and is used for pressurizing the nitrate-containing dilute brine 1 and then separating the nitrate-containing dilute brine 1 into denitrated brine 6 and concentrated nitrate brine 10 through a separation membrane by adopting a membrane separation method;
the cooling crystallization unit is connected with the membrane separation unit and used for cooling, crystallizing and separating the concentrated saltpeter water 10, and is also connected with the low-temperature water unit and used for receiving the low-temperature water provided by the low-temperature water unit as a cold source, providing cold energy required by cooling and crystallizing for the cooling crystallization unit to crystallize the concentrated saltpeter water 10, and transmitting the cold energy to the membrane separation unit and the pretreatment unit.
Further, the low temperature water unit includes: a hydrogen chloride synthesis furnace and heat recovery device 21, a steam lithium bromide refrigerating unit 24; the membrane separation unit comprises a high-pressure pump 4 and a membrane separator 5; the preprocessing unit includes: a heat recovery heat exchanger 2 and a circulating water heat exchanger 3; the cooling crystallizer comprises a clear liquid cold energy recovery heat exchanger 8, a crystallizer 11, a circulating pump 13, a circulating cooler 14 and a centrifuge 16. The devices are connected through flanges and pipelines.
Specifically, the hydrogen chloride synthesis furnace and heat recovery device 21 includes a hydrogen chloride synthesis furnace and a heat recovery device, wherein the heat recovery device includes a flash tank. The hydrogen chloride synthesis furnace is connected with the hydrogen gas 18 and the chlorine gas 19 produced by the chlor-alkali electrolytic cell through pipelines, and is used for synthesizing hydrogen chloride 22 and generating a large amount of heat to provide a heat source for preparing low-pressure steam 23 in the hydrogen chloride synthesis furnace and the heat recovery equipment 21. Introducing water into a hydrogen chloride synthesis furnace and a heat recovery device 21 to absorb heat generated during hydrogen chloride synthesis to obtain high-temperature water, and flashing the high-temperature water subjected to heat absorption in a flash tank to prepare low-pressure steam 23, wherein the pressure level of the low-pressure steam 23 is 0.3-0.5 MPa.
The water used to produce the low pressure steam 23 in this example is desalted water 20. The desalination has the advantage that scaling can be avoided when water flashes off low-pressure steam in the synthesis furnace.
Specifically, the steam lithium bromide refrigerating unit 24 is connected with the hydrogen chloride synthesis furnace 21, and is used for preparing the low-temperature water 25 and providing cold energy for the membrane method freezing denitration process.
The steam lithium bromide refrigerating unit 24 is connected with the outlets of the flash tanks in the hydrogen chloride synthesis furnace and the heat recovery equipment 21, receives low-pressure steam prepared by the hydrogen chloride synthesis furnace and the heat recovery equipment 21, namely receives low-pressure steam 23 flashed out of the flash tanks, and prepares low-temperature water 25 at 4-7 ℃ by utilizing the production mechanism of the steam lithium bromide refrigerating unit 24. The steam lithium bromide refrigerating unit 24 is also connected with the circulating cooler 14, low-temperature water 25 with the temperature of 4-7 ℃ is provided for the circulating cooler 14, sufficient cold energy is provided for the membrane method freezing denitration process, the low-temperature water 25 discharged from the circulating cooler 14 returns to the steam lithium bromide refrigerating unit 24 to continuously prepare the low-temperature water 25 with the temperature of 4-7 ℃, and low-temperature water circulation is achieved.
Specifically, the preprocessing unit includes: the heat recovery heat exchanger 2 and the circulating water heat exchange 3 are used for cooling the nitrate-containing dilute brine 1. Wherein:
the heat recovery heat exchanger 2 is a nitrate-containing light salt water heat recovery heat exchanger, is connected with the membrane separator 5, and is used for receiving the denitration salt water 6 to provide cold for the denitration salt water, recovering the heat of the nitrate-containing salt water 1, and performing primary cooling treatment on the nitrate-containing light salt water 1;
the circulating water heat exchanger 3 is connected with the heat recovery heat exchanger 2, the cold energy of the circulating water heat exchanger is provided by normal temperature water, and the nitrate-containing dilute brine 1 is subjected to further water cooling treatment in the circulating water heat exchanger 3;
specifically, the high-pressure pump 4 is connected with the circulating water heat exchanger 3 and is used for increasing the pressure of the nitrate-containing dilute brine 1 in the output pipeline of the circulating water heat exchanger 3 to 2.0-2.8 MPa and providing power for the membrane separator 5 to separate the nitrate-containing dilute brine.
Specifically, the membrane separator 5 is a membrane concentration separator connected to the high-pressure pump 4, and is configured to separate the nitrate-containing dilute brine 1 into a denitrated brine 6 and a concentrated nitrate brine 10, where: the denitration brine 6 is conveyed into the heat recovery heat exchanger 2 to provide cold for the denitration brine and is used for recovering the heat of the denitration-containing dilute brine 1; the concentrated saltpeter water 10 is conveyed to a clear liquid cold energy recovery heat exchanger 8 for further temperature reduction treatment.
Specifically, the clear liquid cold recovery heat exchanger 8 is a centrifugal clear liquid cold recovery heat exchanger, and the clear liquid cold recovery heat exchanger 8 is connected with the centrifuge 16 and used for receiving the centrifugal clear liquid 9 obtained in the centrifuge 16 and recovering the cold of the centrifugal clear liquid 9; and is also connected with the membrane separator 5 and is used for receiving the concentrated saltwater 10 separated by the membrane separator 5. In the clear liquid cold energy recovery heat exchanger 8, the centrifugal clear liquid 9 and the concentrated saltpeter water 10 exchange heat, the centrifugal clear liquid 9 provides cold energy, the temperature of the concentrated saltpeter water 10 discharged by the membrane separator 5 is further reduced, and the cooled concentrated saltpeter water 10 is conveyed into a crystallizer 11. The clear liquid cold energy recovery heat exchanger 8 is also connected with the pretreatment unit and is used for conveying the centrifuged clear liquid 9 back to the nitrate-containing dilute brine 1 for circular denitration. In this embodiment, the clear liquid cold recovery heat exchanger 8 is connected to the output pipeline of the circulating water heat exchanger 3 (of course, the clear liquid cold recovery heat exchanger may be connected to any other position in the pretreatment unit where the centrifugal clear liquid and the nitrate-containing brine are joined, which is not further limited in this embodiment), so that the centrifugal clear liquid 9 is joined to the nitrate-containing dilute brine 1, thereby realizing the circulating denitration.
Further, a crystallizer 11 is connected with the clear liquid cold energy recovery heat exchanger 8 and used for crystallizing and separating the concentrated saltwater 10. Specifically, the concentrated saltpeter water 10 in the clear liquid cold recovery heat exchanger 8 enters from the middle lower part of the crystallizer 11, so that the concentrated saltpeter water 10 in the crystallizer 11 can be precipitated and then the crystal mirabilite 17 is separated more completely in the processes of cooling and crystallizing. If entering from the upper part of the crystallizer 11, the time for separating and settling is long, and the content of the nitre in the supernatant liquid 12 can rise, so that the supernatant liquid 12 is crystallized in the circulating cooler 14 during the cooling process of circulating cooling, and the blockage is caused. In the crystallizer 11, the concentrated saltpeter brine 10 is separated and settled into upper clear liquid 12 and lower concentrated saltpeter liquid, the upper clear liquid 12 rises to the upper part of the crystallizer 11, and then continuously circularly flows among the crystallizer 11, the circulating pump 13 and the circulating cooler 14, so that the temperature of the concentrated saltpeter liquid is reduced and the concentrated saltpeter liquid is crystallized.
Specifically, the circulating pump 13 is connected with the upper part of the crystallizer 11 and is used for conveying the upper clear liquid 12 in the crystallizer 11 to the circulating cooler 14, the upper clear liquid 12 is pressurized to 0.2-0.5 MPa by the circulating pump 13 and then enters the circulating cooler 14, and the circulating pump 13 mainly provides power for continuous circulating flow of the upper clear liquid among the crystallizer 11, the circulating pump 13 and the circulating cooler 14, so that the effects of cooling and crystallizing the concentrated nitre liquid are achieved. The recycle cooler 14 is connected to a steam lithium bromide refrigerator unit 24 for cooling the supernatant liquid 12. The circulating cooler 14 is further connected with the middle part of the crystallizer, and precisely, the height of the joint of the circulating cooler 14 and the crystallizer 11 is 40-80 cm below the height of the joint of the circulating pump 13 and the crystallizer 11, and preferably, the position is far away from the joint of the circulating pump 13 and the crystallizer 11, so that the arrangement can ensure that the upper clear liquid 12 coming out of the circulating cooler 14 cannot be directly pumped away by the circulating pump 13, and the separation and sedimentation of the concentrated saltpeter and saltpeter water in the crystallizer 11 into the upper clear liquid 12 and the concentrated saltpeter liquid cannot be influenced. In the circulating cooler 14, heat exchange is carried out between the low-temperature water 25 at the temperature of 4-7 ℃ and the upper clear liquid 12, and the low-temperature water 25 after heat exchange returns to the steam lithium bromide refrigerating unit 24 to be used as a refrigerant medium for circularly preparing the low-temperature water 25 at the temperature of 4-7 ℃ so as to realize low-temperature water circulation; the temperature of the upper clear liquid 12 is reduced to 4-10 ℃, and then the upper clear liquid is returned to the middle part of the crystallizer 11 for cooling the concentrated nitre liquid at the middle and lower parts. The cooling and crystallization of the concentrated nitrate salt water are realized through the continuous circulation of the supernatant liquid 12.
Further, a centrifuge 16 is connected with the crystallizer 11 through a crystallizer liquid dropping pipe 15 and is used for separating the crystal of the crystallizer 11 to obtain mirabilite 17 and a centrifugal clear liquid 9. The centrifugal clear liquid 9 is conveyed to the clear liquid cold recovery heat exchanger 8 through a pipeline to provide cold for the clear liquid cold recovery heat exchanger 8, and then is conveyed to be converged with the nitrate-containing dilute brine 1, so that the circular denitration is realized. By the aid of the method, the cold energy utilization rate can be improved, circulating denitration can be realized, and the denitration effect is improved.
Referring to fig. 1 and 2, the production process of membrane-method freezing denitration by the membrane-method freezing denitration production apparatus provided in this embodiment is exemplified by a nitrate-containing dilute brine 1 with a pressure of 0.05 to 0.1MPa and a temperature of 60 to 90 ℃, and is detailed as follows:
(1-1) drying hydrogen 18 and chlorine 19 produced by a chlor-alkali electrolysis cell, conveying the dried hydrogen and chlorine to a hydrogen chloride synthesis furnace through a pipeline, and combusting the hydrogen chloride to obtain hydrogen chloride gas 22 and generate a large amount of heat;
(1-2) conveying desalted water 20 to a hydrogen chloride synthesis furnace and heat recovery equipment 21 for recovering and utilizing heat in the hydrogen chloride synthesis furnace to obtain low-pressure steam 23 with the pressure of 0.3-0.5 MPa;
(1-3) introducing the low-salt steam 23 into a steam lithium bromide refrigerating unit 24 to do work, obtaining low-temperature water 25 at 4-7 ℃ by utilizing a production mechanism of the steam lithium bromide refrigerating unit, and then conveying the low-temperature water 25 at 4-7 ℃ to a circulating cooler 14 to provide sufficient cold for the membrane method freezing denitration process.
(2-1) conveying the nitrate-containing dilute brine 1 to a heat recovery heat exchanger 2 (a dilute brine heat recovery heat exchanger), and reducing the temperature of the nitrate-containing dilute brine 1 to 40-60 ℃;
(2-2) conveying the mixed solution to a circulating water heat exchanger 3, and further reducing the temperature of the nitrate-containing dilute brine 1 to 25-35 ℃;
(3-1) the pressure of the nitrate-containing dilute brine 1 is raised to 2.0-2.8 MPa by a high-pressure pump 4, and then the nitrate-containing dilute brine is conveyed to a membrane separator 5.
(3-2) in a membrane separator 5, the pressure provided by a high-pressure pump 4 is used as the power for membrane separation, so that the nitrate-containing dilute brine 1 passes through a separation membrane, and the nitrate-containing dilute brine 1 is separated into denitrated brine 6 with the sulfate ion concentration of 1-2 g/L and concentrated nitrate brine 10 with the sulfate ion concentration of 50-80 g/L.
(3-3) conveying the denitration brine 6 into the heat recovery heat exchanger 2 to provide cold energy for the denitration brine, and finally discharging the denitration brine into a water distribution tank for recycling;
(3-4) conveying the concentrated saltpeter water 10 to a clear liquid cold energy recovery heat exchanger 8, further reducing the temperature of the concentrated saltpeter water 10 to 10-20 ℃ by utilizing cold energy provided by the centrifugal clear liquid 9, and then conveying the concentrated saltpeter water to a crystallizer 11.
(4-1) boosting the pressure of the upper clear liquid 12 in the crystallizer 11 by a circulating pump, then boosting the pressure to 0.2-0.5 MPa, and conveying the pressure to a circulating cooler 14;
(4-2) in the circulating cooler 14, exchanging heat between the upper clear liquid 12 and the low-temperature water 25 at 4-7 ℃, reducing the temperature of the upper clear liquid 12 to 4-10 ℃, and returning the upper clear liquid to the crystallizer 11;
(4-3) cooling the concentrated nitrate solution at the middle-lower part of the crystallizer 11 at the temperature of 10-20 ℃ by using the upper clear liquid 12 at the temperature of 4-10 ℃;
(4-4) continuously repeating the step (4-1) to the step (4-3) on the supernatant 12, so as to realize circulating cooling, and finally stably reducing the temperature of the concentrated nitre solution to 4-10 ℃;
(4-5) crystallizing the concentrated nitre solution, discharging crystals from the bottom of the crystallizer, and separating the crystals by using a centrifuge 16 to obtain mirabilite 17 and a centrifugal clear liquid 9 with sulfate radical concentration of 1-2 g/L;
(4-6) conveying the centrifugal clear liquid 9 to a clear liquid cold recovery heat exchanger 8 to provide cold for the clear liquid, and then conveying the clear liquid to be converged with the nitrate-containing dilute brine for circulating denitration.
The heat that the synthetic reaction of hydrogen chloride synthetic furnace produced among the chlor-alkali industrial process was retrieved through the water to this embodiment, carries out the flash distillation to the high temperature water after absorbing the heat again, obtains low pressure steam, prepares 4 ~ 7 ℃ low temperature water through letting in low pressure steam to steam lithium bromide refrigerating unit, uses 4 ~ 7 ℃ low temperature water as the cold source, provides cold volume for the freezing denitration process of embrane method, realizes freezing the denitration. The embodiment solves the problem that membrane method freezing denitration needs high-order cold quantity, reduces energy consumption, saves production cost, solves the problem that steam generated by cooling a hydrogen chloride synthesis furnace and synthesizing products in the production process of chlor-alkali generates waste, reduces environmental heat pollution, can greatly reduce the energy consumption in the membrane method freezing denitration process, and saves production cost.
It will be understood that the foregoing is only a preferred embodiment of the invention, and that the invention is not limited thereto. It will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention, and these changes and modifications are to be considered as within the scope of the invention.
Claims (10)
1. A membrane method freezing denitration method comprises pretreatment, membrane separation and freezing denitration of nitrate-containing dilute brine, and is characterized in that: the method comprises the steps of preparing low-temperature water of 4-7 ℃ by a steam lithium bromide refrigerating unit, and providing cold energy for the membrane freezing and denitration process by using the low-temperature water of 4-7 ℃ to realize freezing and denitration.
2. The membrane-method freezing denitration method according to claim 1, characterized in that: the steam lithium bromide refrigerating unit is used for refrigerating low-temperature water at 4-7 ℃ by using low-pressure steam generated by recycling heat generated by synthetic reaction in a hydrogen chloride synthetic furnace by using water.
3. The membrane-method freezing denitration method according to claim 2, specifically comprising the steps of:
(1) preparing low-temperature water: recycling heat generated by the synthetic reaction of hydrogen and chlorine in the hydrogen chloride synthetic furnace by using water, introducing low-pressure steam flashed out into a steam lithium bromide refrigerating unit, and refrigerating by using the steam lithium bromide refrigerating unit to prepare low-temperature water at the temperature of 4-7 ℃;
(2) pretreating the nitrate-containing dilute brine: the low-temperature water prepared in the step (1) is used for providing cold energy for the membrane method freezing denitration process, and the temperature of the nitrate-containing light salt water is reduced by introducing the cold energy into a pretreatment unit of the nitrate-containing light salt water;
(3) membrane separation: after the pressure of the pretreated nitrate-containing light salt water is increased by a high-pressure pump, the nitrate-containing light salt water passes through a separation membrane by adopting a membrane separation method, and denitrated salt water and concentrated nitrate salt water are obtained by separation;
(4) nitrate and liquid separation of concentrated nitrate brine: and (2) introducing the low-temperature water prepared in the step (1) into a cooling crystallization unit to circularly cool the concentrated saltpeter water subjected to membrane separation, crystallizing, and performing saltpeter-liquid separation to obtain mirabilite and a centrifugal clear liquid.
4. The membrane-method freezing denitration method according to claim 3, characterized in that: the method is characterized in that the low-temperature water prepared in the step (1) is used for providing cold energy for the membrane method freezing denitration process, and specifically comprises the following steps:
(1-1) heat recovery: drying hydrogen and chlorine produced by a chlor-alkali electrolytic cell, feeding the dried hydrogen and chlorine into a hydrogen chloride synthesis furnace through a pipeline, and combusting to obtain hydrogen chloride gas, wherein heat generated by the synthesis furnace is recovered by using water to obtain high-temperature water;
(1-2) low-temperature water preparation: introducing the high-temperature water obtained in the step (1-1) into a flash evaporation tank for flash evaporation to obtain low-pressure steam, introducing the low-pressure steam into a steam lithium bromide refrigerating unit for work refrigeration to prepare low-temperature water with the temperature of 4-7 ℃ and the refrigerant of desalted water;
(1-3) introducing low-temperature water with the temperature of 4-7 ℃ into a cooling crystallization unit in a membrane method freezing denitration process to provide cold energy for the freezing denitration process;
(1-4) returning the low-temperature water subjected to heat exchange to a steam lithium bromide refrigerating unit to be used as a refrigerant medium for recycling so as to prepare refrigerant low-temperature water;
and (4) continuously preparing the low-temperature water of the refrigerant at the temperature of 4-7 ℃ by repeating the step (1-2), the step (1-3) and the step (1-4).
5. The membrane-method freezing denitration method according to claim 3, wherein the step (4) is a nitrate-liquid separation of concentrated nitrate brine: the circulating cooling, crystallization and separation of the concentrated saltpeter water specifically comprise the following steps:
(4-1) separating the concentrated nitrate brine into upper clear liquid and middle-lower concentrated nitrate liquid in a crystallizer through sedimentation, boosting the upper clear liquid in the crystallizer by using a circulating pump, conveying the upper clear liquid to a circulating cooler, exchanging heat with refrigerant low-temperature water at 4-7 ℃, reducing the temperature of the upper clear liquid to 4-10 ℃, and returning the upper clear liquid to the middle position of the crystallizer;
(4-2) cooling the concentrated nitre liquid at the middle lower part of the crystallizer by using the low-temperature upper clear liquid returned after cooling in the step (4-1), and simultaneously, ascending the clear liquid and settling the concentrated nitre liquid through settling;
(4-3) repeating the step (4-1) and the step (4-2) on the supernatant liquid, gradually cooling the concentrated mirabilite liquid, crystallizing to generate mirabilite crystals, and performing mirabilite-liquid separation by using a centrifuge to obtain mirabilite and a centrifuged supernatant liquid;
and (4-4) conveying the centrifugal clear liquid into a clear liquid cold energy recovery heat exchanger for reducing the temperature of the concentrated saltwater generated by the membrane separation in the step (3), and conveying the centrifugal clear liquid subjected to heat exchange with the concentrated saltwater to a position where the saltwater-containing dilute brine is pretreated in the step (2) to be converged with the saltwater-containing dilute brine for circular denitration.
6. The membrane-method denitration method according to claim 5, wherein the cold quantity in the process of the membrane-method freezing denitration method is mainly provided by the low-temperature water of 4-7 ℃ prepared in the step (1): firstly, transferring cold energy to upper clear liquid in a circulating cooler by low-temperature water at 4-7 ℃; then transferring the concentrated nitre solution to the middle lower part of the crystallizer; then transferring to the centrifugal clear liquid; then, after the centrifugal clear liquid is conveyed to a clear liquid cold energy recovery heat exchanger, part of cold energy is transmitted to the concentrated saltwater, and the other part of cold energy is converged with the saltwater-containing light saltwater along with the centrifugal clear liquid, and the cold energy is transmitted to the saltwater-containing light saltwater to reduce the temperature of the saltwater-containing light saltwater; and finally, separating the nitrate-containing light salt water into denitrated salt water and concentrated nitrate salt water in a membrane separator, wherein the low-temperature denitrated salt water is conveyed into a heat recovery heat exchanger to provide cold for reducing the temperature of the nitrate-containing light salt water when the nitrate-containing light salt water is pretreated in the step (2).
7. A membrane-method freezing and denitration production apparatus used for the membrane-method freezing and denitration method according to any one of claims 1 to 6, comprising: a low-temperature water unit, a pretreatment unit, a membrane separation unit and a cooling crystallization unit,
the low-temperature water unit is used for preparing low-temperature water and providing cold energy for the membrane method freezing denitration process;
the pretreatment unit is used for cooling the nitrate-containing dilute brine;
the membrane separation unit is connected with the pretreatment unit and is used for pressurizing the nitrate-containing light brine and then separating the nitrate-containing light brine into denitrated brine and concentrated nitrate brine by adopting a membrane separation method;
the cooling crystallization unit is connected with the membrane separation unit and used for cooling, crystallizing and separating the concentrated nitrate salt water, and is also connected with the low-temperature water unit and used for receiving the refrigerant low-temperature water provided by the low-temperature water unit, providing the cooling capacity required by cooling and crystallizing for crystallizing the concentrated nitrate salt water by the cooling crystallization unit, and transmitting the cooling capacity to the membrane separation unit and the pretreatment unit.
8. The membrane-method freezing denitration production apparatus according to claim 7, wherein the low-temperature water unit includes: a hydrogen chloride synthetic furnace, a heat recovery device and a steam lithium bromide refrigerating unit,
the hydrogen chloride synthesis furnace and the heat recovery equipment prepare low-pressure steam by utilizing heat generated by synthesizing hydrogen chloride;
and the steam lithium bromide refrigerating unit is connected with the hydrogen chloride synthesis furnace and the heat recovery equipment, and is used for preparing the refrigerant low-temperature water and providing cold energy for the membrane method freezing and denitration process.
9. The membrane-method freezing denitration production apparatus according to claim 7, wherein the pretreatment unit includes: a heat recovery heat exchanger and a circulating water heat exchanger,
the heat recovery heat exchanger is used for introducing nitrate-containing light salt water, is connected with the membrane separation unit, and is used for receiving the denitration salt water as a cold source to recover heat of the nitrate-containing light salt water so as to cool the nitrate-containing light salt water;
and the circulating water heat exchanger is connected with the heat recovery heat exchanger and is used for further cooling the saltpeter-containing dilute brine.
10. The membrane-method freezing denitration production device according to claim 7, wherein the cooling crystallization unit comprises a clear liquid cold recovery heat exchanger, a crystallizer, a circulating pump, a circulating cooler and a centrifuge,
the clear liquid cold energy recovery heat exchanger is connected with the membrane separation unit and the centrifuge and is used for recovering the cold energy of the centrifuged clear liquid and further reducing the temperature of the concentrated saltwater brine discharged by the membrane separation unit;
the crystallizer is connected with the clear liquid cold energy recovery heat exchanger and is used for cooling, crystallizing and separating the concentrated nitrate brine;
the circulating pump is connected with the crystallizer and is used for conveying the supernatant in the crystallizer to the circulating cooler to provide power for the circulation of the supernatant;
the circulating cooler is connected with the steam lithium bromide refrigerating unit of the low-temperature water unit and used for carrying out cold cooling treatment on the upper clear liquid and returning the cooled upper clear liquid to the crystallizer;
the centrifuge is connected with the crystallizer and is used for separating the crystal substances output from the crystallizer.
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| CN117146483A (en) * | 2023-09-06 | 2023-12-01 | 内蒙古伊东集团东兴化工有限责任公司 | Heat exchange device and heat exchange method of denitration refrigerating unit by substituted membrane method |
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| CN117146483B (en) * | 2023-09-06 | 2024-03-26 | 内蒙古伊东集团东兴化工有限责任公司 | Heat exchange device and heat exchange method of denitration refrigerating unit by substituted membrane method |
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