Multi-stage cooling cycle freezing crystallization system and crystallization process thereof

Abstract

The present invention discloses a multi-stage cooling cycle freezing crystallization system. The multi-stage cooling cycle freezing crystallization system includes a freezing heat exchanger, a freezing discharge tank, a freezing circulation pump, a freezing slurry pump, a first cyclone separator, a freezing crystal growing tank, a freezing discharge pump, a second cyclone separator, a freezing centrifuge buffer tank, and a freezing centrifuge; the number of the freezing heat exchangers is at least two, and the plurality of freezing heat exchangers are arranged in parallel, the freezing heat exchanger is connected to the freezing discharge tank, and the freezing discharge tank, the freezing slurry pump, the first cyclone separator, the freezing crystal growing tank, the freezing discharge pump, the second cyclone separator, the freezing centrifuge buffer tank, and the freezing centrifuge are connected in sequence; the freezing discharge tank is also connected to each of the freezing heat exchangers via the freezing circulation pump. The multi-stage cooling cycle freezing crystallization system achieves efficient, stable, and long-term operation of freezing crystallization while ensuring the purity and resource utilization rate of the crystallized salt.

Description

Technical Field

[0001] The invention belongs to the field of water treatment, and in particular relates to a multi-stage cooling cycle freezing crystallization system and a crystallization process thereof. Background Art

[0002] At present, with the improvement of national environmental protection policies, enterprises have changed their wastewater treatment from the initial comprehensive utilization of wastewater to zero discharge, and the treatment technology has also evolved from simple chemical dosing treatment, ion exchange treatment, and membrane treatment to complex advanced oxidation, nanofiltration, electrocatalysis, high-pressure reverse osmosis, high-pressure nanofiltration, evaporative crystallization, frozen crystallization, etc. The technology is constantly innovating and the process is constantly lengthening.

[0003] Through the combined optimization of the above-mentioned various process technologies, the full recycling of water has been basically achieved, and the separation and resource utilization of crystallized salt in wastewater have been achieved. However, these methods still cannot efficiently separate sodium chloride and sodium sulfate in wastewater, and cannot simultaneously guarantee the purity and resource utilization rate of crystallized salt, resulting in an increase in mixed salt that cannot be reused. Although the combination of hot and cold methods can achieve the simultaneous guarantee of the purity and resource utilization rate of crystallized salt, due to the small number of frozen crystallization projects and the lack of experience of design and manufacturing personnel, frozen crystallization has caused problems such as easy clogging, the temperature cannot be reduced to the design value, the operation cycle is short, the cleaning and maintenance time is long, and the sulfate ion in the mother liquor exceeds the standard after treatment, ultimately increasing the output of mixed salt.

[0004] Mixed salt has many impurities and complex composition, cannot be utilized as a resource, and is difficult to handle. Currently, it is often disposed of by stacking or landfilling, which not only easily causes secondary pollution, but also requires a lot of manpower and financial resources, which is not worth the cost. Summary of the Invention

[0005] Based on this, it is necessary to provide a multi-stage cooling cycle freezing crystallization system and its crystallization process that realizes efficient, stable and long-term operation of freezing crystallization while ensuring the purity and resource utilization rate of the crystallized salt.

[0006] A multi-stage cooling cycle freezing crystallization system includes a refrigerated heat exchanger, a refrigerated discharge tank, a refrigerated circulation pump, a refrigerated crystal slurry pump, a first cyclone separator, a refrigerated crystal growing tank, a refrigerated discharge pump, a second cyclone separator, a refrigerated centrifuge buffer tank and a refrigerated centrifuge; the refrigerated heat exchanger is provided in plurality and the plurality of refrigerated heat exchangers are arranged in parallel, the refrigerated heat exchanger is connected to the refrigerated discharge tank, the refrigerated discharge tank, the refrigerated crystal slurry pump, the first cyclone separator, the refrigerated crystal growing tank, the refrigerated discharge pump, the second cyclone separator, the refrigerated centrifuge buffer tank and the refrigerated centrifuge are connected in series in sequence; the refrigerated discharge tank is also connected to each of the refrigerated heat exchangers through the refrigerated circulation pump to form a circulation path.

[0007] In one embodiment, the refrigeration heat exchanger has a feed-liquid interface, a heat exchanger exhaust port, a refrigeration cycle inlet, a cleaning water inlet, a refrigeration liquid outlet, a refrigeration external mother liquid outlet, a refrigeration external mother liquid inlet, a refrigeration liquid inlet, a cleaning water outlet and a refrigeration cycle outlet; the refrigeration cycle outlet of each of the refrigeration heat exchangers is connected to the feed port of the refrigeration discharge tank, and the discharge tank outlet of the refrigeration discharge tank is connected to the refrigeration cycle inlet of each of the refrigeration heat exchangers through the refrigeration circulation pump.

[0008] In one embodiment, the refrigeration heat exchanger also has a temperature transmitter interface and a liquid level meter interface.

[0009] In one embodiment, the discharge port of the frozen discharge tank is connected to the first cyclone separator through the frozen slurry pump, the liquid outlet of the first cyclone separator is connected to the frozen crystal growing tank, and the clear liquid outlet of the first cyclone separator is connected to the slurry dilute liquid feed port of the frozen discharge tank through the refrigeration circulation pump.

[0010] In one embodiment, the liquid outlet of the second cyclone separator is connected to the refrigerated centrifuge buffer tank, and the clear liquid outlet of the second cyclone separator is connected to the refrigerated effluent mother liquid inlet of each of the refrigerated heat exchangers and the sodium sulfate solution feed pipe of each of the refrigerated heat exchangers.

[0011] In one embodiment, there are one or more refrigeration circulation pumps, and multiple refrigeration circulation pumps are arranged in parallel.

[0012] All the pumps involved are considered to be able to complete the task with just one pump, so they are changed to one or more pumps. The advantage of choosing multiple pumps is that they can be switched online at any time, which is easier to ensure continuous operation than shutting down due to a failure of one pump.

[0013] In one embodiment, there are one or more refrigerated slurry pumps. When there are multiple refrigerated slurry pumps, the multiple refrigerated slurry pumps are arranged in parallel.

[0014] In one embodiment, there are one or more refrigerated discharge pumps. When there are multiple refrigerated discharge pumps, the multiple refrigerated discharge pumps are arranged in parallel.

[0015] In one embodiment, the multi-stage cooling cycle freezing crystallization system also includes a freezing mother liquor tank and a freezing mother liquor pump. The overflow port of the freezing centrifugal buffer tank is connected to the freezing mother liquor tank, and the freezing mother liquor tank is connected to the freezing crystal growing tank through the freezing mother liquor pump.

[0016] In one embodiment, there are one or more refrigerated mother liquid pumps. When there are multiple refrigerated mother liquid pumps, the multiple refrigerated mother liquid pumps are arranged in parallel.

[0017] In one embodiment, a stirring mechanism is provided on the refrigerated heat exchanger, the refrigerated discharge tank, the refrigerated crystal growing tank, the refrigerated centrifuge buffer tank, and the refrigerated mother liquor tank.

[0018] A crystallization process of the multi-stage cooling cycle freezing crystallization system comprises the following steps:

[0019] The sodium sulfate solution is added to the first refrigerated heat exchanger from the feed-liquid interface, and is cooled by heat exchange with the frozen effluent mother liquid entering from the frozen effluent mother liquid inlet of the first refrigerated heat exchanger to form a pre-cooled sodium sulfate solution, and is discharged from the refrigeration cycle outlet of the first refrigerated heat exchanger and enters the frozen discharge tank. After the frozen effluent mother liquid is heated by heat exchange, it is discharged from the frozen effluent mother liquid discharge outlet of the first refrigerated heat exchanger. The first refrigerated heat exchanger acts as a precooler to achieve heat exchange between the frozen effluent mother liquid and the sodium sulfate solution;

[0020] The pre-cooled sodium sulfate solution is pumped from the discharge tank outlet of the refrigerated discharge tank through the refrigeration circulation pump and the refrigeration circulation inlet of the second refrigerated heat exchanger into the second refrigerated heat exchanger, and the pre-cooled sodium sulfate solution is heat-exchanged and cooled again with the refrigerated liquid entering from the refrigerated liquid inlet of the second refrigerated heat exchanger, and then enters the refrigerated discharge tank to produce and enrich the sodium sulfate;

[0021] The mirabilite slurry in the freezing discharge tank is pumped into the first cyclone separator by a freezing slurry pump to achieve solid-liquid separation. The mirabilite slurry separated by the first cyclone separator enters the freezing crystal growing tank. The freezing liquid enters the jacket of the freezing crystal growing tank and exchanges heat with the mirabilite slurry in the freezing crystal growing tank to achieve secondary cooling and freezing.

[0022] The mirabilite slurry in the frozen crystal growing tank is pumped into the second cyclone separator through a frozen discharge pump to achieve solid-liquid separation. The mirabilite slurry separated by the second cyclone separator enters a refrigerated centrifuge through a refrigerated centrifuge buffer tank. The refrigerated centrifuge is used to centrifuge the mirabilite slurry to achieve separation of mirabilite and mother liquor.

[0023] In one embodiment, the following steps are also included:

[0024] The clear liquid separated by the first cyclone separator enters the freezing discharge tank and then enters the freezing heat exchanger through the freezing circulation pump.

[0025] In one embodiment, the following steps are also included:

[0026] The dilute slurry separated by the second cyclone separator is pumped into the first refrigeration heat exchanger for heat exchange with the sodium sulfate solution, or the dilute slurry separated by the second cyclone separator is pumped from the feed-liquid interface into the first refrigeration heat exchanger for reheat exchange and refrigeration.

[0027] In one embodiment, the following steps are also included: the supernatant overflowing from the refrigerated centrifuge buffer tank enters the refrigerated mother liquor tank, and is pumped into the refrigerated crystal growing tank through the refrigerated mother liquor pump, so that the mirabilite slurry in the refrigerated crystal growing tank is cooled and crystallized again, so that the fine mirabilite particles in the mirabilite slurry recrystallize and grow, and at the same time, the uncrystallized sodium sulfate is converted into mirabilite.

[0028] The multi-stage cooling cycle freezing crystallization system of the present invention achieves efficient, stable, and long-term operation of freezing crystallization, while ensuring the purity and resource utilization rate of the crystallized salt. The present invention optimizes the combination of a freezing heat exchanger, a freezing crystal growing tank, a freezing cyclone separator, a freezing centrifugal buffer tank, and a freezing mother liquor tank to achieve efficient, stable, and long-term operation of freezing crystallization, while ensuring the purity and resource utilization rate of the crystallized salt.

[0029] The multi-stage cooling cycle freezing crystallization of the present invention can effectively shorten the cleaning cycle of the freezing heat exchanger and ensure the stability of operation. Specifically, (1) during operation, if the current of the freezing circulation pump increases or the pump outlet pressure increases, at least two groups of freezing heat exchangers can be switched. The first freezing heat exchanger originally used for pre-cooling is used as a freezing cooling crystallization heat exchanger, and the second freezing heat exchanger originally used for freezing cooling crystallization is used as a pre-cooling heat exchanger. The first heat exchanger only needs to discharge the frozen effluent mother liquor in the shell side and rinse it with condensed water, and then the frozen liquid enters the shell side. The second heat exchanger only needs to discharge the frozen liquid in the shell side and rinse it with condensed water, and then the sodium sulfate feed liquid enters the tube side, and the frozen effluent mother liquor enters the shell side. The complete reversal of the two groups of heat exchangers is achieved. In this way, the first freezing heat exchanger originally used for pre-cooling is used as a freezing crystallization heat exchanger to pass the cold material to freeze, while the second freezing heat exchanger originally used for freezing crystallization is used as a pre-cooling heat exchanger to pass the hot material to pre-cool, so that the blockage of the heat exchange tubes in the two groups of freezing heat exchangers can be avoided.

[0030] (2) During operation, if the current of the refrigeration circulation pump increases or the pump outlet pressure increases, the valve of the refrigeration discharge mother liquor pipeline can be switched to allow the refrigeration discharge mother liquor to bypass and be discharged directly out of the refrigeration system without exchanging heat with the first refrigeration heat exchanger. At the same time, the circulation of the refrigerant in the second refrigeration heat exchanger is stopped. In this way, the sodium sulfate solution entering the first refrigeration heat exchanger is not pre-cooled but directly enters the second refrigeration heat exchanger, which can increase the temperature of the second refrigeration heat exchanger and reduce or even eliminate the risk of heat exchange tube blockage.

[0031] (3) During operation, if the circulating pump current increases or the pump outlet pressure increases, the refrigeration heat exchanger can be stopped and the refrigeration cycle outlet (raw steam pipeline valve) of the refrigeration heat exchanger can be opened to allow the raw steam to enter the refrigeration heat exchanger from the refrigeration cycle outlet to heat it. This will cause the blocked heat exchange pipe to dissolve the mirabilite due to the increased temperature and thus be unblocked. The above three measures can be operated separately or in combination, which can fully shorten the refrigeration cleaning cycle and ensure the operation cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a schematic diagram of a multi-stage cooling cycle freezing crystallization system according to one embodiment of the present invention;

[0033] Figure 2 for Figure 1 Schematic diagram of a freezing heat exchanger of a multi-stage cooling cycle freezing crystallization system shown in FIG;

[0034] Figure 3 for Figure 1 Schematic diagram of the freezing discharge tank of the multi-stage cooling cycle freezing crystallization system shown in;

[0035] Figure 4 for Figure 1 Schematic diagram of the freezing crystal growing tank of the multi-stage cooling cycle freezing crystallization system shown in.

[0036] Description of Reference Numerals

[0037] 10: Multi-stage cooling cycle freezing crystallization system; 100: Refrigeration heat exchanger; 101: Feed-liquid interface; 102: Heat exchanger exhaust port; 103: Refrigeration cycle inlet; 104: Washing water inlet; 105: Refrigeration liquid outlet; 106: Refrigeration cycle outlet; 107: Refrigeration mother liquor outlet; 108: Refrigeration mother liquor inlet; 109: Refrigeration liquid inlet; 110: Washing water outlet; 200: Refrigeration discharge tank; 201: Feed inlet; 202: Discharge port; 203: Discharge port; 204: Mixer Structure; 205: slurry inlet; 300: refrigerated circulation pump; 400: refrigerated slurry pump; 500: first cyclone separator; 600: refrigerated crystal growing tank; 601: feed inlet; 602: exhaust port; 603: discharge port; 604: refrigerated liquid inlet and outlet; 605: liquid level meter interface; 606: thermometer interface; 700: refrigerated discharge pump; 800: second cyclone separator; 900: refrigerated centrifuge buffer tank; 1000: refrigerated centrifuge; 1100: refrigerated mother liquor tank; 1200: refrigerated mother liquor pump. DETAILED DESCRIPTION

[0038] To facilitate understanding of the present invention, the present invention will be described more fully below with reference to the accompanying drawings. Preferred embodiments of the present invention are shown in the accompanying drawings. However, the present invention may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the present disclosure.

[0039] It should be noted that when an element is considered to be “connected to” another element, it can be directly connected to the other element or there may be an intervening element at the same time.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this invention pertains. The terms used herein in the specification of the present invention are for the purpose of describing specific embodiments only and are not intended to limit the present invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0041] See also Figure 1 As shown, an embodiment of the present invention provides a multi-stage cooling cycle freezing crystallization system 10. The multi-stage cooling cycle freezing crystallization system 10 includes a refrigeration heat exchanger 100, a refrigeration discharge tank 200, a refrigeration circulation pump 300, a refrigeration slurry pump 400, a first cyclone separator 500, a refrigeration crystal growing tank 600, a refrigeration discharge pump 700, a second cyclone separator 800, a refrigeration centrifuge buffer tank 900, and a refrigeration centrifuge 1000.

[0042] The number of refrigerated heat exchangers 100 is at least two, and multiple refrigerated heat exchangers 100 are arranged in parallel. The refrigerated heat exchangers 100 are connected to the refrigerated discharge tank 200. The refrigerated discharge tank 200, the refrigerated slurry pump 400, the first cyclone separator 500, the refrigerated crystal growing tank 600, the refrigerated discharge pump 700, the second cyclone separator 800, the refrigerated centrifuge buffer tank 900, and the refrigerated centrifuge 1000 are sequentially connected via pipelines. The refrigerated discharge tank 200 is also connected to each refrigerated heat exchanger 100 via a refrigerated circulation pump 300 through pipelines to form a circulation path.

[0043] Please also refer to Figure 2-Figure 4As shown, in one embodiment, the refrigeration heat exchanger 100 has a feed-liquid interface 101, a heat exchanger exhaust port 102, a refrigeration cycle inlet 103, a wash water inlet 104, a refrigerant outlet 105, a refrigerated external mother liquid outlet 107, a refrigerated external mother liquid inlet 108, a refrigerant inlet 109, a wash water outlet 110 and a refrigeration cycle outlet 106, wherein the wash water outlet 110 is used as a common outlet for refrigerant wash water and refrigerated external wash water, and the refrigeration cycle outlet 106 also serves as a raw steam inlet; valves are provided on each pipeline connected to the feed-liquid interface 101, the heat exchanger exhaust port 102, the refrigeration cycle inlet 103, the wash water inlet 104, the refrigerant outlet 105, the refrigerated external mother liquid outlet 107, the refrigerated external mother liquid inlet 108, the refrigerant inlet 109, the wash water outlet 110 and the refrigeration cycle outlet 106.

[0044] The freezing discharge tank 200 has a feed port 201 , a discharge port 202 , a discharge port 203 , a stirring mechanism 204 , and a slurry dilute liquid inlet 205 .

[0045] Each discharge tank feed port 201 is connected to the refrigeration cycle outlet 106. The discharge port 203 of the refrigeration discharge tank 200 is connected to the refrigeration cycle inlet of each refrigeration heat exchanger 100 through a pipeline via a refrigeration cycle pump 300.

[0046] See also Figure 1 As shown, the refrigeration heat exchanger 100 also has a temperature transmitter interface and a liquid level meter interface. Further, the freezing crystal growing tank 600 has a feed inlet 601, an exhaust port 602, a discharge port 603, a freezing liquid inlet and outlet 604, a liquid level meter interface 605 and a thermometer interface 606.

[0047] Furthermore, the discharge port 202 of the frozen discharge tank 200 is connected to the first cyclone separator 500 through the frozen slurry pump 400, the liquid outlet of the first cyclone separator 500 is connected to one of the feed ports 601 of the frozen crystal growing tank 600, and the clear liquid outlet of the first cyclone separator 500 is connected to the slurry dilute liquid feed port 205 of the frozen discharge tank 200. The clear liquid from the first cyclone separator 500 first enters the frozen discharge tank 200 and then enters the frozen heat exchanger 100 through the refrigeration circulation pump 300.

[0048] Furthermore, the liquid outlet of the second cyclone separator 800 is connected to the refrigerated centrifuge buffer tank 900, and the clear liquid outlet of the second cyclone separator 800 is connected to the refrigerated effluent mother liquid inlet 108 of each refrigerated heat exchanger 100 via a pipeline. The clear liquid outlet of the second cyclone separator 800 is also connected to the sodium sulfate solution feed pipe of each refrigerated heat exchanger 100. By controlling the amount of effluent mother liquid, the effluent mother liquid is recirculated and refrigerated. The sodium sulfate solution feed pipe shares the liquid interface 101, which serves as both a sodium sulfate solution feed interface and an inlet for the clear liquid from the second cyclone separator 800 to enter the refrigerated heat exchanger 100.

[0049] Preferably, see Figure 1 As shown, in one embodiment, the number of the refrigeration circulation pumps 300 is one or more. When the number of the refrigeration circulation pumps 300 is multiple, the multiple refrigeration circulation pumps 300 are arranged in parallel.

[0050] Preferably, see Figure 1 As shown, in one embodiment, the number of the refrigerated slurry pumps 400 is one or more. When the number of the refrigerated slurry pumps 400 is multiple, the multiple refrigerated slurry pumps 400 are arranged in parallel.

[0051] Preferably, see Figure 1 As shown, in one embodiment, there are one or more refrigerated discharge pumps 700. When there are multiple refrigerated discharge pumps 700, the multiple refrigerated discharge pumps 700 are arranged in parallel. The number of each pump is one or more. The advantage of using multiple pumps is that they can be switched online at any time. Compared with a single pump, this avoids failure shutdowns and helps ensure continuous operation.

[0052] Furthermore, the multi-stage cooling cycle freezing crystallization system 10 also includes a freezing mother liquor tank 1100 and a freezing mother liquor pump 1200. The overflow port of the freezing centrifugal buffer tank 900 is connected to the freezing mother liquor tank 1100 through a pipeline, and the freezing mother liquor tank 1100 is connected to another crystal growing tank feed port 601 of the freezing crystal growing tank 600 through a pipeline via the freezing mother liquor pump 1200.

[0053] Each of the above pipelines is provided with a valve.

[0054] Preferably, see Figure 1 As shown, in one embodiment, the number of the refrigerated mother liquid pump 1200 is one or more. When the number of the refrigerated mother liquid pump 1200 is more than one, the multiple refrigerated mother liquid pumps 1200 are arranged in parallel.

[0055] Furthermore, a stirring mechanism 204 is provided on the refrigerated heat exchanger 100 , the refrigerated discharge tank 200 , the refrigerated crystal growing tank 600 , the refrigerated centrifuge buffer tank 900 , and the refrigerated mother liquor tank 1100 .

[0056] The multi-stage cooling cycle freezing crystallization system 10 of the present invention achieves efficient, stable, and long-term operation of freezing crystallization while ensuring the purity and resource utilization rate of the crystallized salt. The present invention optimizes the combination of the freezing heat exchanger 100, the freezing crystal growing tank 600, the freezing cyclone separator, the freezing centrifugal buffer tank 900, and the freezing mother liquor tank 1100 to achieve efficient, stable, and long-term operation of freezing crystallization while ensuring the purity and resource utilization rate of the crystallized salt.

[0057] It should be noted that all valves in this embodiment can be either manual or automatic.

[0058] This embodiment also provides a crystallization process using a multi-stage cooling cycle freezing crystallization system 10. The multi-stage cooling cycle freezing crystallization process includes the following steps:

[0059] The sodium sulfate solution enters the first refrigerated heat exchanger 100, and is cooled by heat exchange with the frozen effluent mother liquor entering from the frozen effluent mother liquor inlet 108 of the first refrigerated heat exchanger 100 to form a pre-cooled sodium sulfate solution, and is discharged from the refrigeration cycle outlet 106 of the first refrigerated heat exchanger 100 and enters the frozen discharge tank 200. After the frozen effluent mother liquor is heated by heat exchange, it is discharged from the frozen effluent mother liquor outlet 105 of the first refrigerated heat exchanger 100. The first refrigerated heat exchanger 100 acts as a precooler to realize heat exchange between the frozen effluent mother liquor and the sodium sulfate solution, and the precooling temperature is 30-40°C.

[0060] The pre-cooled sodium sulfate solution is pumped into the second refrigerated heat exchanger 100 from the discharge port 203 of the refrigerated discharge tank 200 through the refrigeration circulation pump 300 and the refrigeration circulation inlet of the second refrigerated heat exchanger 100. The pre-cooled sodium sulfate solution is heat exchanged with the refrigerated liquid entering from the refrigerated liquid inlet 109 of the second refrigerated heat exchanger 100 and then enters the refrigerated discharge tank 200 again to produce and enrich Glauber's salt; the refrigerated liquid can be CaCl2 or anhydrous ethylene glycol, and the freezing temperature is -5-5°C.

[0061] The Glauber's salt slurry in the freezing discharge tank 200 is pumped into the first cyclone separator 500 through the freezing slurry pump 400 to achieve solid-liquid separation. The Glauber's salt slurry separated by the first cyclone separator 500 enters the freezing crystal growing tank 600, and the frozen liquid enters the jacket of the freezing crystal growing tank 600 to exchange heat with the Glauber's salt slurry in the freezing crystal growing tank 600 to achieve secondary cooling and freezing; the clear liquid separated by the first cyclone separator 500 enters the freezing discharge tank 200 and then enters the freezing heat exchanger 100 through the freezing circulation pump 300.

[0062] The Glauber's salt slurry in the frozen crystal growing tank 600 is discharged through the discharge port 603 and pumped into the second cyclone separator 800 through the frozen discharge pump 700 to achieve solid-liquid separation. The Glauber's salt slurry separated by the second cyclone separator 800 enters the refrigerated centrifuge 1000 through the refrigerated centrifuge buffer tank 900. The refrigerated centrifuge 1000 is used to centrifuge the Glauber's salt slurry to achieve separation of Glauber's salt and mother liquor.

[0063] The dilute slurry separated by the second cyclone separator 800 (also known as the refrigerated mother liquor) re-enters the first refrigerated heat exchanger 100 through the refrigerated mother liquor inlet 108 thereof to exchange heat with the sodium sulfate feed solution. The purpose of exchanging heat between the dilute slurry separated by the second cyclone separator 800 and the sodium sulfate solution in the first refrigerated heat exchanger 100 is to fully utilize energy, both pre-cooling the sodium sulfate solution and heating the refrigerated mother liquor, thereby reducing energy consumption.

[0064] Alternatively, the slurry liquid (i.e., the frozen discharged mother liquor) separated by the second cyclone separator 800 can also enter the first refrigeration heat exchanger 100 through the feed-liquid interface 101 for re-cooling and freezing. The purpose of this is to control the amount of discharged mother liquor, increase the production of Glauber's salt, and reduce the production of miscellaneous salts.

[0065] The supernatant overflowing from the refrigerated centrifuge buffer tank 900 enters the frozen mother liquor tank 1100 and is pumped into the frozen crystal growing tank 600 through the crystal growing tank feed port 601 by the frozen mother liquor pump 1200. This cools and crystallizes the thenardite slurry in the frozen crystal growing tank 600 again, causing the fine thenardite particles in the thenardite slurry to recrystallize and grow. This also converts the uncrystallized sodium sulfate into thenardite. The crystal growing tank is set to a freezing temperature of -5-5°C.

[0066] When the refrigeration heat exchanger 100 needs to be cleaned, clean water can be introduced through the cleaning water inlet 104 of the refrigeration heat exchanger 100 , and the wastewater after cleaning can be discharged through the cleaning water outlet 110 .

[0067] The multi-stage cooling cycle freezing crystallization of the present invention can effectively shorten the cleaning cycle of the freezing heat exchanger 100 and ensure operational stability. Specifically, (1) during operation, if the current of the freezing circulation pump 300 increases or the pump outlet pressure increases, at least two groups of freezing heat exchangers 100 can be switched, and the first freezing heat exchanger 100 originally used for pre-cooling is used as a freezing cooling crystallization heat exchanger, and the second freezing heat exchanger 100 originally used for freezing cooling crystallization is used as a pre-cooling heat exchanger. The first heat exchanger 100 only needs to discharge the frozen effluent mother liquor in the shell side and flush it with condensed water, and then the frozen liquid enters the shell side. The second heat exchanger 100 only needs to discharge the refrigerant in the shell side and flush it with condensed water. Then the sodium sulfate liquid enters the tube side, and the frozen discharged mother liquor enters the shell side, realizing the complete swapping of the two sets of heat exchangers. In this way, the first refrigerated heat exchanger 100 originally used for pre-cooling is used as a frozen crystallization heat exchanger to pass cold material for freezing, while the second refrigerated heat exchanger 100 originally used for freezing crystallization is used as a pre-cooling heat exchanger to feed hot material for pre-cooling, so that the blockage of the heat exchange tubes in the two sets of refrigerated heat exchangers 100 can be avoided.

[0068] (2) During operation, if the current of the refrigeration circulation pump 300 increases or the pump outlet pressure increases, the valve of the refrigeration discharge mother liquid pipeline can be switched to allow the refrigeration discharge mother liquid to bypass and directly discharge from the refrigeration system without exchanging heat with the first refrigeration heat exchanger 100, and at the same time stop the circulation of the refrigeration liquid in the second refrigeration heat exchanger 100. In this way, the sodium sulfate solution entering the first refrigeration heat exchanger is not pre-cooled but directly enters the second refrigeration heat exchanger 100, which can increase the temperature of the second refrigeration heat exchanger 100 and reduce or even eliminate the risk of heat exchange tube blockage.

[0069] (3) During operation, if the circulating pump current increases or the pump outlet pressure increases, the refrigeration heat exchanger 100 can be stopped and the refrigeration cycle outlet 106 (raw steam pipeline valve) of the refrigeration heat exchanger 100 can be opened to allow raw steam to enter the refrigeration heat exchanger 100 from the refrigeration cycle outlet 106 to heat the refrigeration heat exchanger 100. This will cause the blocked heat exchange pipe to dissolve the mirabilite due to the increased temperature and thus be unblocked. The above three measures can be used individually or in combination to fully shorten the refrigeration cleaning cycle and ensure the operating cycle.

[0070] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0071] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A multi-stage cooling cycle freezing crystallization system, characterized in that: It includes a refrigerated heat exchanger, a refrigerated discharge tank, a refrigerated circulation pump, a refrigerated crystal pump, a first cyclone separator, a refrigerated crystal growing tank, a refrigerated discharge pump, a second cyclone separator, a refrigerated centrifuge buffer tank and a refrigerated centrifuge; there are multiple refrigerated heat exchangers and the multiple refrigerated heat exchangers are arranged in parallel, the refrigerated heat exchanger is connected to the refrigerated discharge tank, the refrigerated discharge tank, the refrigerated crystal pump, the first cyclone separator, the refrigerated crystal growing tank, the refrigerated discharge pump, the second cyclone separator, the refrigerated centrifuge buffer tank and the refrigerated centrifuge are connected in series in sequence; the refrigerated discharge tank is also connected to each of the refrigerated heat exchangers through the refrigerated circulation pump to form a circulation path, there are multiple refrigerated crystal pumps, there are multiple refrigerated circulation pumps, and the multiple refrigerated circulation pumps are arranged in parallel.

2. The multi-stage cooling cycle freezing crystallization system according to claim 1, characterized in that: The refrigeration heat exchanger has a feed-liquid interface, a heat exchanger exhaust port, a refrigeration cycle inlet, a cleaning water inlet, a refrigeration liquid outlet, a refrigeration external mother liquid outlet, a refrigeration external mother liquid inlet, a refrigeration liquid inlet, a cleaning water outlet and a refrigeration cycle outlet; the refrigeration cycle outlet of each of the refrigeration heat exchangers is connected to the feed port of the refrigeration discharge tank, and the discharge tank outlet of the refrigeration discharge tank is connected to the refrigeration cycle inlet of each of the refrigeration heat exchangers through the refrigeration circulation pump.

3. The multi-stage cooling cycle freezing crystallization system according to claim 2, characterized in that: The discharge port of the frozen discharge tank is connected to the first cyclone separator through the frozen slurry pump, the liquid outlet of the first cyclone separator is connected to the frozen crystal growing tank, and the clear liquid outlet of the first cyclone separator is connected to the slurry dilute liquid feed port of the frozen discharge tank.

4. The multi-stage cooling cycle freezing crystallization system according to claim 2, characterized in that: The liquid outlet of the second cyclone separator is connected to the refrigerated centrifugal buffer tank, and the clear liquid outlet of the second cyclone separator is connected to the refrigerated effluent mother liquid inlet of each refrigerated heat exchanger and the sodium sulfate solution feed pipe of each refrigerated heat exchanger.

5. The multi-stage cooling cycle freezing crystallization system according to any one of claims 1 to 4, characterized in that: When there are multiple refrigerated slurry pumps, the multiple refrigerated slurry pumps are arranged in parallel.

6. The multi-stage cooling cycle freezing crystallization system according to any one of claims 1 to 4, characterized in that: There are one or more refrigeration discharge pumps. When there are multiple refrigeration discharge pumps, the multiple refrigeration discharge pumps are arranged in parallel.

7. The multi-stage cooling cycle freezing crystallization system according to any one of claims 1 to 4, characterized in that: The multi-stage cooling cycle freezing crystallization system also includes a freezing mother liquor tank and a freezing mother liquor pump. The overflow port of the freezing centrifugal buffer tank is connected to the freezing mother liquor tank, and the freezing mother liquor tank is connected to the freezing crystal growing tank through the freezing mother liquor pump.

8. The multi-stage cooling cycle freezing crystallization system according to claim 7, characterized in that: There are one or more refrigerated mother liquid pumps. When there are multiple refrigerated mother liquid pumps, the multiple refrigerated mother liquid pumps are arranged in parallel.

9. The multi-stage cooling cycle freezing crystallization system according to claim 7, characterized in that: The refrigerated heat exchanger, the refrigerated discharge tank, the refrigerated crystal growing tank, the refrigerated centrifuge buffer tank, and the refrigerated mother liquid tank are all provided with stirring mechanisms.

10. A crystallization process of a multi-stage cooling cycle freezing crystallization system according to any one of claims 1 to 9, characterized in that: The steps include: The sodium sulfate solution is added to the first refrigerated heat exchanger from the feed-liquid interface, and is cooled by heat exchange with the frozen effluent mother liquid entering from the frozen effluent mother liquid inlet of the first refrigerated heat exchanger to form a pre-cooled sodium sulfate solution, and is discharged from the refrigeration cycle outlet of the first refrigerated heat exchanger and enters the frozen discharge tank. After the frozen effluent mother liquid is heated by heat exchange, it is discharged from the frozen effluent mother liquid discharge outlet of the first refrigerated heat exchanger. The first refrigerated heat exchanger acts as a precooler to achieve heat exchange between the frozen effluent mother liquid and the sodium sulfate solution; The pre-cooled sodium sulfate solution is pumped from the discharge port of the refrigerated discharge tank into the second refrigerated heat exchanger through a refrigeration circulation pump and a refrigeration circulation inlet of the second refrigerated heat exchanger. The pre-cooled sodium sulfate solution is heat-exchanged and cooled again with the refrigerated liquid entering from the refrigerated liquid inlet of the second refrigerated heat exchanger, and then enters the refrigerated discharge tank to produce and enrich the sodium sulfate. The mirabilite slurry in the freezing discharge tank is pumped into the first cyclone separator by a freezing slurry pump to achieve solid-liquid separation. The mirabilite slurry separated by the first cyclone separator enters the freezing crystal growing tank. The freezing liquid enters the jacket of the freezing crystal growing tank and exchanges heat with the mirabilite slurry in the freezing crystal growing tank to achieve secondary cooling and freezing. The thenardite slurry in the frozen crystal growing tank is pumped into the second cyclone separator through a frozen discharge pump to achieve solid-liquid separation. The thenardite slurry separated by the second cyclone separator enters the refrigerated centrifuge through a refrigerated centrifuge buffer tank. The refrigerated centrifuge is used to centrifuge the thenardite slurry to achieve separation of the thenardite and the mother liquor; The dilute slurry separated by the second cyclone separator is pumped into the first refrigeration heat exchanger for heat exchange with the sodium sulfate solution, or the dilute slurry separated by the second cyclone separator is pumped from the feed-liquid interface into the first refrigeration heat exchanger for reheat exchange and refrigeration.

11. The multi-stage cooling cycle freezing crystallization process according to claim 10, characterized in that: The following steps are also included: The clear liquid separated by the first cyclone separator enters the freezing discharge tank and then enters the freezing heat exchanger through the freezing circulation pump.

12. The multi-stage cooling cycle freezing crystallization process according to claim 10, characterized in that: The method further includes the following steps: the supernatant overflowing from the refrigerated centrifuge buffer tank enters a refrigerated mother liquor tank, and is pumped into the refrigerated crystal growing tank through the refrigerated mother liquor pump, so that the mirabilite slurry in the refrigerated crystal growing tank is cooled and crystallized again, so that the fine mirabilite particles in the mirabilite slurry recrystallize and grow, and at the same time, the uncrystallized sodium sulfate is converted into mirabilite.

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