A method and device for recovering ammonium chloride from desalting mother liquor produced by thermal method

Abstract

The invention discloses a method and device for recovering ammonium chloride from a desalting mother liquor for preparing ammonium chloride by a thermal method, comprising the following steps: 1) collecting the desalting mother liquor: using the mother liquor containing ammonium chloride and sodium chloride produced in the production process of baking soda as raw material to prepare ammonium chloride by a thermal method, and collecting the desalting mother liquor obtained by separation into a deammonium chloride mother liquor storage tank; 2) cold precipitation crystallization and centrifugal dehydration; 3) salting out crystallization; 4) ammonium chloride crystal separation: overflowing the saturated brine produced after the salting out crystallization from the upper overflow port of the salting out kettle into a thickening tank, so that the ammonium chloride crystals and the crystal slurry composed of salt in the saturated brine sink to the bottom of the thickening tank; 5) salt separation; 6) mother liquor recycling: collecting the brine produced by the centrifugal dehydration in step 2) and the supernatant saturated brine in the thickening tank in step 4) and returning them to the double decomposition reaction system for preparing baking soda for recycling. The method and device can reduce the energy consumption of ammonium chloride recovery in the desalting mother liquor, and greatly reduce the recovery cost of ammonium chloride.

Description

Technical Field

[0001] The invention relates to the technical field of recycling mother liquor of ammonium chloride prepared by thermal method, and in particular to a method and device for recycling ammonium chloride from desalted mother liquor of ammonium chloride prepared by thermal method. Background Art

[0002] Baking soda, also known as sodium bicarbonate, is mainly made from brine and ammonium bicarbonate through double decomposition reaction, followed by washing, dehydration and drying. In the production process, the mother liquor separated after washing and dehydration contains a large amount of ammonium chloride, sodium chloride and ammonium bicarbonate. Therefore, recovering ammonium chloride and sodium chloride from the mother liquor can turn waste into treasure and protect the environment.

[0003] At present, there are two main methods for recovering ammonium chloride from the mother liquor separated by double decomposition reaction: hot method and cold method. Among them, the hot method is to concentrate the mother liquor by evaporation, and utilize the different solubility of ammonium chloride and sodium chloride with temperature to precipitate respectively, so as to achieve the purpose of separation. It mainly includes three steps: deammonium, desodium chloride and deammonium chloride.

[0004] There are many methods for recovering ammonium chloride from mother liquor by thermal method in the prior art, such as the process for recovering ammonium chloride and sodium chloride from waste water containing ammonium chloride and sodium chloride with patent application number CN200910068695.6, which adopts ammonia distillation, evaporation, crystallization and separation process. The evaporation adopts multi-effect, heat pump and vacuum evaporation process, and selects three-effect mixed flow process. Sodium chloride is crystallized during evaporation, and ammonium chloride is crystallized at 35-60°C after evaporation. Then the ammonium chloride suspension is thickened by thickener II and separated by centrifuge II to obtain the finished ammonium chloride. The mother liquor after separating ammonium chloride from centrifuge II and the overflow liquid of thickener II are collected and flowed into the mother liquor exhaust steam preheater, and then sent to the third effect evaporator and mixed with the third effect evaporation liquid for cyclic evaporation.

[0005] In the process of recovering ammonium chloride and sodium chloride, the mother liquor formed by the overflow liquid of centrifuge II and thickener II is a desalted mother liquor separated in the process of preparing ammonium chloride by thermal method using the mother liquor containing ammonium chloride and sodium chloride produced in the process of producing baking soda by double decomposition reaction of brine and ammonium bicarbonate as raw materials. The desalted mother liquor also contains a large amount of sodium chloride (120g / L) and ammonium chloride (50g / L). Therefore, the method further returns the separated desalted mother liquor to the third effect evaporator (46-65°C), the first effect evaporator (95-125°C), and the second effect evaporation crystallizer (80-110°C) for continuous cyclic evaporation and crystallization. Since the crystallization temperature of ammonium chloride is 35-60°C, the desalted mother liquor separated by crystallization needs to be heated to above 95-125°C when entering the subsequent evaporator for evaporation, which increases the energy consumption of 35-90°C. The desalted mother liquor returns to the evaporator for cyclic evaporation, which consumes a large amount of heat energy, greatly increasing the recovery cost of ammonium chloride. Summary of the invention

[0006] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method and a device for recovering ammonium chloride from a desalting mother liquor produced by a thermal process. The method and the device can reduce the energy consumption of recovering ammonium chloride from the desalting mother liquor and greatly reduce the recovery cost of ammonium chloride.

[0007] The technical solution adopted by the present invention to solve the technical problem is: a method for recovering ammonium chloride from a desalting mother liquor for preparing ammonium chloride by a thermal method, comprising the following steps: 1) collecting the desalting mother liquor: using the mother liquor containing ammonium chloride and sodium chloride generated in the production process of baking soda as a raw material and separating the desalting mother liquor obtained in the process of preparing ammonium chloride by a thermal method as a raw material, and collecting the desalting mother liquor into a deammonium chloride mother liquor storage tank; 2) cold precipitation crystallization and centrifugal dehydration; 3) salting out crystallization; 4) ammonium chloride crystal separation: allowing the saturated brine generated after the salting out crystallization to overflow from the upper overflow port of the salting out kettle into a thickening tank, so that the ammonium chloride crystals in the saturated brine and the crystal slurry composed of the salt remaining on the ammonium chloride crystals sink to the bottom of the thickening tank; 5) salt separation; 6) recycling of the mother liquor: the brine generated by the centrifugal dehydration in step 2) and the supernatant saturated brine in the thickening tank in step 4) are collected and returned to the double decomposition reaction system for preparing baking soda for recycling.

[0008] The method of the invention has simple process, adopts cold precipitation crystallization and salting-out crystallization methods to treat the desalted mother liquor separated when preparing ammonium chloride by thermal method, so that the desalted mother liquor generated by preparing ammonium chloride by thermal method no longer needs to be returned to the system for cyclic evaporation after repeated heating, thus saving the energy required for the desalted mother liquor to be returned to the system for cyclic evaporation, greatly reducing the energy consumption of recovery and saving the recovery cost of ammonium chloride on the premise of ensuring full recovery of ammonium chloride.

[0009] The present invention adopts the step of separating ammonium chloride crystals after salting out crystallization, further separates the ammonium chloride crystals in the saturated brine produced after the salting out crystallization from the brine, effectively recovers the ammonium chloride remaining in the saturated brine, and improves the yield of ammonium chloride; and the saturated brine after centrifugal dehydration and separation of ammonium chloride crystals after cold crystallization is directly sent to the double decomposition reaction system for preparing baking soda for recycling, without the need for circulating evaporation, thereby reducing energy consumption and greatly saving the cost of preparing baking soda.

[0010] Furthermore, the specific operation steps of step 2) are: conveying the desalted mother liquor to the crystallization kettle, adding the divalent anion accelerator ammonium sulfate to the crystallization kettle, the crystallization kettle is circulated and connected through a heat exchanger, and the supernatant is conveyed to the heat exchanger for heat exchange with low-temperature cold water, so that the temperature in the crystallization kettle is reduced to 20°C-25°C, ammonium chloride crystals are precipitated, and the obtained ammonium chloride is dehydrated and packaged.

[0011] Furthermore, the specific operation steps of step 3) are as follows: the overflow liquid generated after cold crystallization overflows from the crystallization kettle to the salting-out kettle, and sodium chloride is added to the salting-out kettle at the same time, the temperature is controlled at 10°C~12°C, and the salting-out is performed for 6 h~8 h, and ammonium chloride is further crystallized and precipitated, and settles to the crystal paddle outlet of the salting-out kettle, and then the ammonium chloride crystal paddle at the crystal paddle outlet is returned to the crystallization kettle of step 2).

[0012] Furthermore, the specific operation steps of step 5) are: the crystal slurry settled to the bottom of the thickening tank is transported to the salt separation kettle, the sodium chloride remaining on the ammonium chloride crystals sinks to the bottom of the salt separation kettle and dissolves and then returns to the salting-out kettle for recycling, and the ammonium chloride crystals float to the slurry taking port of the salt separation kettle and return to the crystallization kettle of step 3) from the slurry taking port, and are collected with the ammonium chloride crystals frozen and precipitated in the crystallization kettle, and centrifuged for dehydration.

[0013] The present invention also provides a device for recovering ammonium chloride from a desalted mother liquor for preparing ammonium chloride by a thermal method as described above, comprising a desalted ammonium chloride mother liquor storage tank, a cold precipitation device, and a salting-out device connected in sequence by pipelines, wherein the salting-out device comprises a salting-out kettle and a salt feeding device connected to the salting-out kettle, an upper side wall of the salting-out kettle is provided with an upper overflow port, and a lower side wall thereof is provided with a slurry outlet, wherein both the feed end and the slurry outlet are connected to the cold precipitation device, and the cold precipitation device is also connected to an ammonium chloride treatment device, the desalted ammonium chloride mother liquor storage tank is connected to a first thickener and a centrifuge in a system for preparing ammonium chloride by a thermal method, the upper overflow port of the salting-out kettle is connected to a thickening tank by a pipeline, the bottom of the thickening tank is connected to a salting kettle by a pipeline, the side wall of the salting kettle is connected to the cold precipitation device by a pipeline, and the bottom thereof is connected to the salting-out kettle by a pipeline.

[0014] Furthermore, a liquid outlet is provided on the upper side wall of the thickening tank, and the liquid outlet is connected to a brine tank through a pipeline, and the brine tank is also connected to an ammonium chloride treatment device through a pipeline.

[0015] Furthermore, the cold separation device includes a crystallization kettle and a heat exchanger cyclically connected to the crystallization kettle, the heat exchanger is cyclically connected to a cold water tank through a pipeline, a replacement tank is connected to the bottom of the heat exchanger, and the replacement tank is connected to the crystallization kettle through a pipeline.

[0016] Furthermore, the overflow port of the crystallization kettle is connected to the feed end of the salting-out kettle, and the top of the crystallization kettle is connected to the slurry outlet of the salting-out kettle and the side wall of the salt separation kettle.

[0017] Furthermore, the ammonium chloride processing device includes a second thickener, a centrifuge and a packaging machine which are connected in sequence.

[0018] Furthermore, a liquid outlet is provided on the upper side wall of the second thickener, and the liquid outlet and the centrifuge are both connected to the brine tank through a pipeline.

[0019] Beneficial effects of the method and device for recovering ammonium chloride from desalted mother liquor produced by thermal method of ammonium chloride of the present invention:

[0020] (1) The method of the present invention is simple in process. The desalted mother liquor separated during the thermal preparation of ammonium chloride is treated by cold precipitation crystallization and salting-out crystallization. The desalted mother liquor produced by the thermal recovery of ammonium chloride no longer needs to be returned to the system for cyclic evaporation. Therefore, the desalted mother liquor does not need to be heated to reach the temperature of the evaporation process. The energy required for multiple heating of the desalted mother liquor returned to the system for cyclic evaporation is saved. Under the premise of ensuring sufficient recovery of ammonium chloride, the energy consumption of recovery is greatly reduced, and the recovery cost of ammonium chloride is saved.

[0021] (2) The method of the present invention adds a step of separating ammonium chloride crystals during salting-out crystallization, which can further separate the ammonium chloride crystals in the saturated brine produced after salting-out crystallization from the brine, effectively recovering the ammonium chloride remaining in the saturated brine, avoiding the loss of this part of ammonium chloride, and improving the yield of ammonium chloride; and the saturated brine after centrifugal dehydration and separation of ammonium chloride crystals after cold crystallization is directly fed into the double decomposition reaction system for preparing baking soda for recycling, without the need for cyclic evaporation, thereby reducing energy consumption and greatly saving the cost of preparing baking soda;

[0022] (3) The device of the present invention is simple. By using a de-ammonium chloride mother liquor storage tank to connect the first thickener and the centrifuge in the thermal process for preparing ammonium chloride with the cold separation device, the desalted mother liquor obtained by separation by the first thickener and the centrifuge in the thermal process for preparing ammonium chloride can be first stored in the de-ammonium chloride mother liquor storage tank, and then transported to the cold separation device and the salting-out device in sequence for crystallization and recovery of ammonium chloride, so that the part of the desalted mother liquor no longer needs to be returned to the system for circulation and evaporation, saving the energy required for multiple heating of the desalted mother liquor returned to the system for circulation and evaporation, greatly reducing the energy consumption of recovery, and saving the cost of ammonium chloride recovery;

[0023] (4) The device of the present invention adds a thickening tank between the salting-out kettle and the salt separation kettle, so that the saturated brine overflowing from the upper overflow port of the salting-out kettle can be transported to the thickening tank, so that the ammonium chloride remaining in the saturated brine can be further separated from the brine, thereby avoiding the loss of ammonium chloride in this part of the brine and greatly improving the yield of ammonium chloride. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 — is a schematic diagram of the overall structure of the desalted mother liquor produced by the heat recovery method of the device of the present invention;

[0025] Figure 2 — is a schematic structural diagram of a device for recovering ammonium chloride from desalted mother liquor produced by thermal process of the present invention.

[0026] The above figure numbers: 1-deammonium removal system, 2-sodium chloride removal system, 3-deammonium chloride removal system, 4-ammonium chloride recovery device, 5-deammonium chloride mother liquor storage tank, 6-first thickener, 7-first centrifuge, 8-first liquid delivery pump, 9-crystallization kettle, 10-heat exchanger, 11-cold water pump, 12-cold water tank, 13-replacement tank, 14-replacement pump, 15-second thickener, 16-second centrifuge, 17-packaging machine, 18-salting out kettle, 19-bucket elevator, 20-salt transfer tank, 21-weighing scale, 22-salt slurry pump, 23-thickening tank, 24-brine tank, 25-salt separation kettle, 26-slurry delivery pump, 27-second liquid delivery pump. DETAILED DESCRIPTION

[0027] The present invention is further described below in conjunction with the accompanying drawings and examples, but these specific implementation schemes do not limit the protection scope of the present invention in any way.

[0028] Example 1

[0029] See also Figure 1-2 A method for recovering ammonium chloride from a desalted mother liquor obtained by thermal production of ammonium chloride, comprising the following steps:

[0030] 1) Collecting desalted mother liquor: using the mother liquor containing ammonium chloride and sodium chloride produced in the process of baking soda production as a raw material and separating the desalted mother liquor obtained in the process of preparing ammonium chloride by thermal method as a raw material, and collecting it into a deammonium chloride mother liquor storage tank 5; the desalted mother liquor is the mother liquor separated from the first thickener 6 and the first centrifuge 7 in the deammonium chloride system 3 of the thermal method for preparing ammonium chloride (comprising the deammonium system, the sodium chloride removal system 2 and the deammonium chloride removal system 3 in sequence), the temperature of which is 45°C, and contains 110 g / L of NaCl and 10 g / L of NH4Cl2;

[0031] 2) Cold crystallization and centrifugal dehydration: The desalted mother liquor in the ammonium chloride mother liquor storage tank 5 is pumped into the crystallization kettle 9 by the first liquid delivery pump 8 for cold crystallization, and the divalent anion accelerator ammonium sulfate is added to the crystallization kettle 9. The crystallization kettle 9 is circulated and connected through the heat exchanger 10, and the supernatant thereof is pumped into the heat exchanger 10 by the N axial flow pump, and heat is exchanged with the low-temperature cold water (20°C) pumped into the heat exchanger 10 from the cold water tank 12 by the cold water pump 11 in the heat exchanger 10. The solution after heat exchange enters the replacement tank 13 connected to the bottom of the heat exchanger 10, and then the solution is sent to the crystallization kettle 9 by the replacement pump 14, so that the temperature of the solution in the crystallization kettle 9 is reduced to 20°C-25°C, and ammonium chloride crystals are precipitated. The obtained ammonium chloride slurry is input into the second thickener 15, and the ammonium chloride slurry at the bottom discharge port of the second thickener 15 is transported to the second centrifuge 16 for dehydration and then sent to the packaging machine 17 for packaging to obtain the finished ammonium chloride;

[0032] 3) Salting out crystallization: the overflow liquid from the overflow port of the crystallization kettle 9 enters the salting out kettle 18, and sodium chloride is added to the salting out kettle 18 through the salt feeding device (specific operation: sodium chloride is sent to the salt transfer tank 20 by the bucket elevator 19, and then sent to the salting out kettle 18 after being measured by the weighing scale 21), the temperature is controlled at 10°C~12°C, the salting out is carried out for 6 h~8h, and ammonium chloride is further crystallized and precipitated, and settled to the crystal paddle outlet of the salting out kettle 18, and then the ammonium chloride crystal paddle at the crystal paddle outlet is sent to the crystallization kettle 9 of step 2) by the salt slurry pump 22;

[0033] 4) Separation of ammonium chloride crystals: The saturated brine produced after salting out and crystallization overflows from the upper overflow port of the salting out kettle 18 into the thickening tank 23, and the slurry composed of ammonium chloride crystals and salt sinks to the bottom of the thickening tank 23. The saturated brine enters the brine tank 24 from the liquid outlet on the upper side wall of the thickening tank 23, so that the saturated brine is further separated from the ammonium chloride crystals and salt;

[0034] 5) Salt separation: The crystal slurry settled to the bottom of the thickening tank 23 is transported to the salt separation kettle 25, and the sodium chloride remaining on the ammonium chloride crystals sinks to the bottom of the salt separation kettle 25 and dissolves, and is then sent back to the salting-out kettle 18 by the slurry pump 26 for recycling, and the ammonium chloride crystals float to the slurry outlet of the salt separation kettle 25 and return from the slurry outlet to the crystallization kettle 9 in step 3), and are collected with the ammonium chloride crystals frozen and precipitated in the crystallization kettle 9;

[0035] 6) Recycling of mother liquor: The mother liquor discharged from the supernatant of the second thickener 15 through the liquid outlet of the upper side wall in step 2), the mother liquor separated by centrifugation in the second centrifuge 16, and the supernatant saturated brine discharged from the liquid outlet of the upper side wall of the thickening tank 23 in step 4) are all transported to the brine tank 24 for collection, and then the collected brine (containing NaCl 300g / L, NH4Cl 60g / L) is sent back to the double decomposition reaction system for preparing baking soda by the second liquid delivery pump 28 for recycling.

[0036] A device for recovering ammonium chloride from a desalting mother liquor produced by a thermal process corresponding to the above method comprises a desalting mother liquor storage tank 5, a cooling device, and a salting device which are sequentially connected by pipelines.

[0037] The feed port of the deammonium chloride mother liquor storage tank 5 is connected to the first thickener 6 and the first centrifuge 7 in the deammonium chloride system 3 of the thermal ammonium chloride preparation system (which includes the deammonium system, the sodium chloride removal system 2 and the ammonium chloride removal system 3 in sequence), and is used to collect the mother liquor separated by the first thickener 6 and the first centrifuge 7 in the thermal ammonium chloride preparation system, and the mother liquor is the desalted mother liquor;

[0038] The cold precipitation device is used to cold-precipitate and crystallize the desalted mother liquor in the deammonium chloride mother liquor storage tank 5, and comprises a crystallization kettle 9 and a heat exchanger 10 circulatedly connected to the crystallization kettle 9, wherein the heat exchanger 10 is circulatedly connected to a cold water tank 12 through a pipeline, and a replacement tank 13 is connected to the bottom of the heat exchanger 10, and the replacement tank 13 is connected to the crystallization kettle 9 through a pipeline, and the overflow port of the crystallization kettle 9 is connected to the feed end of the salting-out kettle 18, and is used to transport the overflow liquid discharged from the crystallization kettle 9 to the salting-out kettle 18 for salting-out crystallization, and an ammonium chloride treatment device is connected to the lower side wall through a pipeline, and the ammonium chloride treatment device comprises a second thickener 15, a centrifuge 7 and a packaging machine 17 which are connected in sequence, and the ammonium chloride crystallized by the crystallization kettle 9 is first input into the second thickener 15, and then dehydrated by the second centrifuge 16 and then enters the packaging machine 17 for packaging. The upper side wall of the second thickener 15 is provided with a liquid outlet, and the liquid outlet and the second centrifuge 16 are connected to a brine tank 24 through a pipeline, which is used to transport the mother liquor separated by the second thickener 15 and the second centrifuge 16 to the brine tank 24, and then return it to the double decomposition reaction system for preparing baking soda for recycling by a liquid delivery pump 278.

[0039] The salting-out device comprises a salting-out kettle 18 and a salt feeding device (comprising a bucket elevator 19, a salt transfer tank 20 and a weighing scale 21 connected in sequence) connected to the salting-out kettle 18. The salting-out kettle 18 comprises a clear liquid section, a connecting section and a suspension section from top to bottom. The upper side wall (i.e., the side wall of the clear liquid section) of the salting-out kettle 18 is provided with an upper overflow port, and the lower side wall (i.e., the side wall of the suspension section) is provided with a slurry outlet, the feed end of which is connected to the overflow port of the crystallization kettle 9, and the slurry outlet is connected to the feed end of the crystallization kettle 9. The upper overflow port of the salting-out kettle 18 is also connected to a thickening tank 23 through a pipeline for transferring the overflow of the salting-out kettle 18 to the thickening tank 23. The saturated brine overflowing from the outlet is transported to the thickening tank 23. Since the density of ammonium chloride crystals and salt is greater than that of brine, the ammonium chloride crystals and salt will sink to the bottom of the thickening tank 23, and the brine will be located at the upper part of the thickening tank 23, so that the brine and the ammonium chloride crystals are further separated, and the ammonium chloride crystals in the saturated brine are effectively recovered; the upper side wall of the thickening tank 23 is provided with a liquid outlet, and the liquid outlet is connected to the brine tank 24 through a pipeline, which is used to transport the supernatant saturated brine separated from the upper part of the thickening tank 23 to the brine tank 24, and then sent back to the double decomposition reaction system for preparing baking soda by the second liquid delivery pump 27 for recycling.

[0040] The bottom of the thickening tank 23 is connected to the salt separation kettle 25 through a pipeline. The middle part of the side wall of the salt separation kettle 25 is provided with a slurry outlet. The slurry outlet of the salt separation kettle 25 is connected to the top of the crystallization kettle 9 through a pipeline, and is used to transport ammonium chloride crystals into the crystallization kettle 9, provide ammonium chloride crystal nuclei for the crystallization kettle 9, promote the growth of ammonium chloride crystals in the crystallization kettle 9, and quickly precipitate ammonium chloride crystals in the crystallization kettle 9, thereby saving energy and time. The bottom of the thickening tank 23 is connected to the salting-out kettle 18 through a pipeline.

[0041] When the desalting mother liquor obtained by thermal preparation of ammonium chloride is 700M 3 / day, if the desalted mother liquor is circulated into the evaporation system for preparing ammonium chloride by thermal method according to the method in the prior art, the temperature required for cyclic evaporation is 30°C. When the method and device of the present invention are used to recover ammonium chloride in the desalted mother liquor, the temperature is 700M 3 Calculated on the basis of mother liquor per day, 72 tons of standard coal can be saved and CO2 emission reduction can reach 191.52 (72*2.66) tons / day. Under the premise of ensuring the quality of ammonium chloride, the evaporation-free ammonium chloride product can be increased by 200 tons per day, which not only improves the yield of ammonium chloride, but also reduces energy consumption and the recovery cost of ammonium chloride.

[0042] The deammonium removal system, desalination system and ammonium chloride removal system in the present invention are respectively steps of removing ammonium bicarbonate, sodium chloride and ammonium chloride from the mother liquor containing ammonium chloride and sodium chloride produced in the process of producing baking soda by double decomposition reaction of brine and ammonium bicarbonate. The devices and corresponding methods adopted by each system can adopt the devices and methods for recovering ammonium chloride in the mother liquor containing ammonium chloride and sodium chloride produced in the process of producing baking soda by double decomposition reaction of brine and ammonium bicarbonate by thermal method in the prior art. Again, the devices and methods adopted by the deammonium removal system, desalination system and first-level ammonium chloride removal system will not be described one by one.

[0043] It should be noted that the terms "primary", "secondary", "first", "second", "third", "fourth", etc. are used herein to describe various elements, but these elements should not be limited by these terms. These terms are only used to distinguish one element from another.

[0044] The words "upper", "lower", "left", "right", "front", "back", "vertical", "inside", "outside", etc. used in this article to describe the orientation or position are for the convenience of explanation and are based on the orientation or position relationship shown in the drawings. In the actual device, these orientations may be different due to the placement of the device. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be understood as a limitation on the present invention.

[0045] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technician familiar with this profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for recovering ammonium chloride from a desalted mother liquor obtained by thermal production of ammonium chloride, characterized in that: The following steps are involved: 1) Collecting desalted mother liquor: using the mother liquor containing ammonium chloride and sodium chloride generated in the production process of baking soda as raw material and separated in the process of preparing ammonium chloride by thermal method as raw material, collecting the desalted mother liquor into a deammonium chloride mother liquor storage tank; 2) Cold precipitation crystallization and centrifugal dehydration; 3) Salting out crystallization; 4) Ammonium chloride crystal separation: allowing the saturated brine generated after salting out crystallization to overflow from the upper overflow port of the salting out kettle into the thickening tank, so that the ammonium chloride crystals in the saturated brine and the crystal slurry composed of the salt remaining on the ammonium chloride crystals sink to the bottom of the thickening tank; 5) Salt separation; 6) Recycling of mother liquor: the brine generated by centrifugal dehydration in step 2) and the supernatant saturated brine in the thickening tank in step 4) are collected and returned to the double decomposition reaction system for preparing baking soda for recycling.

2. A method for recovering ammonium chloride from a desalted mother liquor prepared by thermal method as claimed in claim 1, characterized in that: The specific operation steps of step 2) are: conveying the desalted mother liquor to the crystallization kettle, adding divalent anion accelerator ammonium sulfate to the crystallization kettle, the crystallization kettle is circulated and connected through a heat exchanger, and the supernatant is conveyed to the heat exchanger for heat exchange with low-temperature cold water, so that the temperature in the crystallization kettle is reduced to 20°C-25°C, ammonium chloride crystals are precipitated, and the obtained ammonium chloride is dehydrated and packaged.

3. A method for recovering ammonium chloride from a desalted mother liquor prepared by thermal method as claimed in claim 1, characterized in that: The specific operation steps of step 3) are as follows: the overflow liquid generated after cold crystallization overflows from the crystallization kettle to the salting-out kettle, and sodium chloride is added to the salting-out kettle at the same time, the temperature is controlled at 10°C~12°C, and the salting-out is performed for 6 h~8 h, and ammonium chloride is further crystallized and precipitated, and settles to the crystal paddle outlet of the salting-out kettle, and then the ammonium chloride crystal paddle at the crystal paddle outlet is returned to the crystallization kettle of step 2).

4. A method for recovering ammonium chloride from a desalted mother liquor prepared by thermal method as claimed in claim 1, characterized in that: The specific operation steps of step 5) are as follows: the slurry settled to the bottom of the thickening tank is transported to the salt separation kettle, the sodium chloride remaining on the ammonium chloride crystals sinks to the bottom of the salt separation kettle and dissolves and then returns to the salting-out kettle for recycling, the ammonium chloride crystals float to the slurry taking port of the salt separation kettle and return to the crystallization kettle of step 3) from the slurry taking port, and are collected with the ammonium chloride crystals frozen and precipitated in the crystallization kettle, and centrifuged for dehydration.

5. A device for recovering ammonium chloride from a desalted mother liquor prepared by a thermal method as claimed in any one of claims 1 to 4, comprising a desalted ammonium chloride mother liquor storage tank, a cold precipitation device, and a salting-out device connected in sequence by pipelines, wherein the salting-out device comprises a salting-out kettle and a salt feeding device connected to the salting-out kettle, wherein the upper side wall of the salting-out kettle is provided with an upper overflow port, and the lower side wall thereof is provided with a slurry outlet, wherein the feed end and the slurry outlet are both connected to the cold precipitation device, wherein the salting-out kettle comprises a clear liquid section, a connecting section, and a suspension section from top to bottom, wherein the cold precipitation device is also connected to an ammonium chloride treatment device, characterized in that: The deammonium chloride mother liquor storage tank is connected to the first thickener and the centrifuge in the thermal method for preparing ammonium chloride. The upper overflow port of the salting-out kettle is connected to a thickening tank through a pipeline. The bottom of the thickening tank is connected to a salting-out kettle through a pipeline. A slurry taking port is provided in the middle of the side wall of the salting-out kettle. The side wall is connected to the cold precipitation device through a pipeline, and the bottom is connected to the salting-out kettle through a pipeline.

6. A device for recovering ammonium chloride from a desalted mother liquor obtained by thermal production of ammonium chloride as claimed in claim 5, characterized in that: The upper side wall of the thickening tank is provided with a liquid outlet, and the liquid outlet is connected to a brine tank through a pipeline, and the brine tank is also connected to an ammonium chloride treatment device through a pipeline.

7. A device for recovering ammonium chloride from desalted mother liquor produced by thermal process as claimed in claim 5, characterized in that: The cold separation device includes a crystallization kettle and a heat exchanger circulatedly connected to the crystallization kettle. The heat exchanger is circulatedly connected to a cold water tank through a pipeline, and a replacement tank is connected to the bottom of the heat exchanger. The replacement tank is connected to the crystallization kettle through a pipeline.

8. A device for recovering ammonium chloride from desalted mother liquor produced by thermal process as claimed in claim 7, characterized in that: The overflow port of the crystallization kettle is connected to the feed end of the salting-out kettle, and the top of the crystallization kettle is connected to the slurry outlet of the salting-out kettle and the side wall of the salt separation kettle.

9. A device for recovering ammonium chloride from a desalted mother liquor obtained by thermal production of ammonium chloride as claimed in claim 6, characterized in that: The ammonium chloride processing device comprises a second thickener, a centrifuge and a packaging machine which are connected in sequence.

10. A device for recovering ammonium chloride from desalted mother liquor produced by thermal process as claimed in claim 9, characterized in that: The upper side wall of the second thickener is provided with a liquid outlet, and the liquid outlet and the centrifuge are both connected to the brine tank through a pipeline.

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