Control method for freezing crystallization of lithium carbonate through LNG gasification cold energy

Abstract

The invention discloses an energy-saving control method for lithium carbonate freezing crystallization through LNG gasification cold energy. According to the LNG gasification cold energy recovery method, propane serves as an intermediate heat exchange medium to exchange heat with LNG and an ethylene glycol solution, and the ethylene glycol solution obtained after heat exchange cools materials in the lithium carbonate freezing crystallization process. According to the invention, the refrigerant adopting the ethylene glycol solution for cold energy recovery can absorb cryogenic cold energy of LNG by utilizing the lower freezing point temperature of the refrigerant, and the part of cold energy is used in the lithium carbonate freezing crystallization process, so that steam used during LNG vaporization can be avoided, and the refrigerant can be combined with the lithium carbonate freezing crystallization process, so that the cold energy is fully and reasonably utilized, and the energy consumption is reduced. The energy consumption is reduced, the method is more environment-friendly, the energy consumption and carbon emission of the whole production process are reduced, the use of factory liquefied natural gas and the lithium carbonate freezing crystallization process form good energy utilization and recovery, and the production cost is reduced.

Description

Technical Field

[0001] This application belongs to the technical field of lithium carbonate crystallization, and specifically relates to a control method for using LNG gasification cold energy for lithium carbonate freezing crystallization. Background Technique

[0002] With the rapid development of power batteries and energy storage devices in the new energy field, the demand for lithium carbonate as an important raw material is increasing day by day. Among them, extracting lithium from lithium ore is an important way to obtain lithium carbonate industrially. In the process of extracting lithium from lepidolite ore, the mother liquor after lithium precipitation is first adjusted for acid removal and decarbonization, and then pumped by a raw material pump into an evaporation crystallizer for evaporation crystallization, and part is used to dissolve sodium sulfate decahydrate. The material evaporated by the evaporation crystallizer enters a centrifuge for centrifugal separation. The separated crystals go to the drying process, and the separated mother liquor returns to the evaporation crystallizer for continuous evaporation crystallization. After the lithium is enriched by evaporation crystallization, it enters a flash crystallizer for flash crystallization. The material of the flash crystallization enters a centrifuge for centrifugal separation. The separated crystals are washed by a washing liquid and enter the drying process, and the separated mother liquor enters a freezing crystallizer for freezing crystallization. The freezing crystallization material undergoes primary and secondary flash evaporation to reduce the material temperature from 90°C to 35°C, and then is frozen to -5°C by a freezing unit for crystallization. The crystallized mirabilite is melted by heat and then sent to a sodium sulfate evaporation crystallization device, and after drying, by-product sodium sulfate is obtained. The potassium and sodium mixed salts crystallized by freezing are dried and returned to the roasting workshop for recycling. From the temperature requirements of this process, it can be seen that the required freezing energy is large and the energy consumption is high.

[0003] In industrial applications, a refrigerator is usually used to exchange heat with a refrigerant, and the refrigerant exchanges heat with the crystallization material to make the freezing crystallization material reach the material crystallization temperature, so as to complete the crystallization and growth of the crystals. After being melted by heat, it is then sent to a sodium sulfate evaporation crystallization device, and after drying, by-product sodium sulfate is obtained. In the traditional freezing crystallization process, the temperature of the first flash material is reduced from 90°C to 45°C, and the steam flashed out is cooled by circulating water to obtain condensed water; the temperature of the second flash material is reduced from 45°C to 35°C, and the steam flashed out exchanges heat with the refrigerant coming out of the refrigerator and is cooled to obtain condensed water. The freezing crystallization material exchanges heat and is cooled by the refrigerant coming out of the refrigerator, and the temperature is reduced from 35°C to -5°C to crystallize mirabilite. After being melted by heat, it is then sent to a sodium sulfate evaporation crystallization device, and after drying, by-product sodium sulfate is obtained. This production process requires a large amount of cold energy consumption, a large carbon footprint, and a large refrigerant circulation volume. Therefore, how to reduce the energy consumption of freezing crystallization is of great significance for the lithium carbonate freezing crystallization process. Summary of the Invention

[0004] In view of the above problems, this application provides a control method for using LNG gasification cold energy for lithium carbonate freezing crystallization, which can solve the problems of large energy consumption and low production efficiency in the freezing process during the production of lithium carbonate.

[0005] The present application provides a control method for using the cold energy of LNG gasification for lithium carbonate freezing crystallization, including the following steps: S1. Feed LNG stored at normal pressure of -162°C to -160°C into the upper part of the IFV heat exchanger, and conduct vapor-phase heat exchange with the vapor-phase heat exchange medium located in the upper part to condense the heat exchange medium into a liquid state. S2. Feed the ethylene glycol solution into the lower part of the IFV heat exchanger, and conduct liquid-phase heat exchange with the liquid-phase heat exchange medium located in the lower part to evaporate the heat exchange medium into a vapor state. After heat exchange, the ethylene glycol solution obtains an outlet temperature of -22°C to -18°C. S3. The ethylene glycol solution in step S2 enters the ethylene glycol mixing tank and is mixed with the ethylene glycol solution in the ethylene glycol return pipe after freezing crystallization heat exchange to form an ethylene glycol solution of about -10°C to -8°C. S4. The ethylene glycol solution in step S3 is precisely controlled in temperature by a refrigeration unit, and then enters the freezing crystallization heat exchanger to conduct heat exchange with the freezing crystallization material, so that the freezing crystallization material reaches the material crystallization temperature, thereby completing the crystallization and growth process of the crystal.

[0006] In some embodiments, the heat exchange medium is propane or R507, R410 refrigerant, and the ethylene glycol solution is an ethylene glycol solution with a mass fraction of 50% to 60%; the inlet temperature of LNG in step S1 is -162°C to -160°C, the outlet temperature in step S2 is -22°C to -18°C, and the mixing temperature in step S3 is about -10°C to -8°C.

[0007] In some embodiments, in step S4, the refrigeration unit starts or stops operating according to the amount of freezing crystallization material or the demand for cold energy, so as to achieve precise control of the crystallization temperature.

[0008] In some embodiments, after step S4, a part of the ethylene glycol solution enters the condenser to conduct heat exchange with the secondary flash steam, and is stored in the ethylene glycol storage tank, and then is pumped back to the IFV heat exchanger of LNG by a delivery pump to recover cold energy; another part enters the reflux mixing in step S3.

[0009] In some embodiments, the temperature of the ethylene glycol solution after heat exchange with the secondary flash steam is about 2°C to 5°C.

[0010] The beneficial effects of the present invention: In view of the defects existing in the existing freezing crystallization process, such as large energy consumption, large carbon emissions, and large refrigerant circulation volume, the present invention creatively proposes an energy-saving method for applying LNG cold energy to lithium carbonate freezing crystallization. First, the ethylene glycol solution enters the IFV heat exchanger and exchanges liquid heat with the heat exchange medium, causing the heat exchange medium to evaporate and become gaseous. Then, -162°C LNG enters the IFV heat exchanger and exchanges gaseous heat with the heat exchange medium, causing the heat exchange medium to condense and become liquid. In this way, the heat exchange medium continuously undergoes the transformation from liquid to gas and from gas to liquid. The gas rises to the upper part of the IFV heat exchanger, and the liquid descends to the lower part of the IFV heat exchanger, converting the vaporization cold energy of LNG to the ethylene glycol solution and making the temperature of the heat-exchanged ethylene glycol solution -22°C to -18°C. The ethylene glycol solution at -22°C to -18°C is transported to the ethylene glycol mixing tank and mixed with the 0°C ethylene glycol solution after freezing crystallization heat exchange to form an ethylene glycol solution at -10°C to -8°C. This solution passes through the refrigeration unit and automatically starts or stops operating according to the amount of freezing crystallization material or the demand for cold energy, while ensuring that the temperature of the ethylene glycol solution at the outlet of the refrigeration unit is -10°C. The -10°C ethylene glycol solution enters the freezing crystallization heat exchanger and exchanges heat with the freezing crystallization material, causing the freezing crystallization material to reach the material crystallization temperature, thereby completing the crystallization and growth process of the crystals. A part of the 0°C ethylene glycol solution after freezing crystallization heat exchange enters the condenser to exchange heat with the secondary flash steam, heating the flashed steam to make it condensate into water. After exchanging heat with the secondary flash steam, the ethylene glycol solution at about 2°C to 5°C enters the storage tank and is pumped back to the LNG vaporizer to recover cold energy. This cold energy utilization method uses ethylene glycol solution as the refrigerant for cold energy recovery. It can absorb the cryogenic cold energy of LNG using its low freezing point temperature and utilize this part of the cold energy in the lithium carbonate freezing crystallization process. This not only eliminates the steam used during LNG vaporization but also combines with the lithium carbonate freezing crystallization process, enabling full and reasonable utilization of cold energy, reducing energy consumption, being more environmentally friendly, reducing the energy consumption and carbon emissions of the entire production process, making the use of liquefied natural gas in the factory and the lithium carbonate freezing crystallization process form a good energy utilization and recovery, and reducing production costs.

[0011] The above description is only an overview of the technical solution of this application. In order to be able to understand the technical means of this application more clearly, it can be implemented according to the content of the specification. And in order to make the above and other purposes, features, and advantages of this application more obvious and understandable, the following specifically describes the embodiments of this application. Brief Description of the Drawings

[0012] Upon reading the following detailed description of the preferred embodiments, various other advantages and benefits will become apparent to those of ordinary skill in the art. The drawings are only for the purpose of showing the preferred embodiments and are not considered to be a limitation of the present application. Moreover, in all the drawings, the same reference numerals are used to denote the same components. In the drawings: Figure 1 It is a schematic flow diagram of a control method for using the cold energy of LNG gasification for lithium carbonate freezing crystallization in the present application.

[0013] The reference numerals in the specific embodiments are as follows: 1. IFV heat exchanger; 11. Heat exchange tank; 12. Upper layer heat exchange tubes; 13. Lower layer heat exchange tubes; 2. Ethylene glycol mixing tank; 3. Refrigeration unit; 4. Freezing crystallization heat exchanger; 5. Condenser; 6. Ethylene glycol storage tank; 7. Transfer pump; 8. Ethylene glycol return pipe. Specific embodiments

[0014] Hereinafter, embodiments of the technical solution of the present application will be described in detail with reference to the drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application and therefore are only examples and cannot be used to limit the protection scope of the present application.

[0015] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above drawings are intended to cover non-exclusive inclusion.

[0016] In the description of the embodiments of the present application, technical terms such as "first" and "second" are only used to distinguish different objects and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity, specific order or primary-secondary relationship of the indicated technical features. In the description of the embodiments of the present application, "a plurality" means more than two unless otherwise specifically defined.

[0017] Reference to "an embodiment" herein means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the present application. The phrase appears in various places in the specification and does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art will explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0018] In the description of the embodiments of the present application, the term "and / or" is merely a description of the relationship between associated objects, indicating that there can be three relationships. For example, A and / or B can represent three situations: A exists alone, A and B exist simultaneously, and B exists alone. Additionally, in this text, the character " / " generally indicates that the associated objects before and after are in an "or" relationship.

[0019] In the description of the embodiments of the present application, the term "multiple" refers to two or more (including two). Similarly, "multiple groups" refers to two or more groups (including two groups), and "multiple pieces" refers to two or more pieces (including two pieces).

[0020] In the description of the embodiments of the present application, the orientation or positional relationship indicated by technical terms such as "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the embodiments of the present application and simplifying the description, rather than indicating or implying 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 construed as a limitation on the embodiments of the present application.

[0021] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installation", "connection", "connection", "fixation", etc. should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can also be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to specific circumstances.

[0022] Such as Figure 1 , an energy-saving device for a control method of using LNG vaporization cold energy for lithium carbonate freezing crystallization, including an IFV heat exchanger 1, an ethylene glycol mixing tank 2, a refrigeration unit 3, a freezing crystallization heat exchanger 4, a condenser 5, and an ethylene glycol storage tank 6 that are connected in sequence through pipelines, and a refrigeration pump between the ethylene glycol mixing tank 2 and the refrigeration unit 3 and a transfer pump 7 between the ethylene glycol storage tank 6 and the IFV heat exchanger 1. The IFV heat exchanger 1 is filled with a heat exchange medium, and the LNG pipeline is communicated with the IFV heat exchanger 1; the ethylene glycol solution circulates in the IFV heat exchanger 1, the ethylene glycol mixing tank 2, the refrigeration unit 3, the freezing crystallization heat exchanger 4, the condenser 5, and the ethylene glycol storage tank 6; the freezing crystallization material is cooled through the freezing crystallization heat exchanger 4, and the LNG is vaporized through the IFV heat exchanger 1.

[0023] In some embodiments, the IFV heat exchanger 1 is provided with a double-layer heat exchange tube and a heat exchange tank 11. The double-layer heat exchange tube includes an upper heat exchange tube 12 and a lower heat exchange tube 13. The upper heat exchange tube 12 is arranged in the upper part of the heat exchange tank 11, and the lower heat exchange tube 13 is arranged in the lower part of the heat exchange tank 11. The inlet and outlet of the upper heat exchange tube 12 are communicated with the inlet and outlet pipelines of LNG. The inlet of the lower heat exchange tube 13 is communicated with the delivery pump 7, and the outlet is communicated with the ethylene glycol mixing tank 2.

[0024] The heat exchange medium realizes heat exchange with LNG through the upper heat exchange tube 12 in the IFV heat exchanger 1, and the heat exchange medium is liquefied into a low-temperature liquid. The heat exchange medium is located in the lower heat exchange tube 13 at the lower part of the heat exchange tank 11; the low-temperature heat exchange medium realizes heat exchange with the ethylene glycol solution through the lower heat exchange tube 13; at the same time, the heat exchange medium vaporizes and rises to the upper heat exchange tube 12 at the upper part of the heat exchange tank 11. In this way, the cold energy of LNG is transferred to the ethylene glycol solution through the heat exchange medium.

[0025] In some embodiments, the boiling point of the heat exchange medium is -52°C to -40°C. In some embodiments, the heat exchange medium is propane or R507, R410 refrigerant.

[0026] In some embodiments, the ethylene glycol solution is an ethylene glycol solution with a mass fraction of 50 - 60%.

[0027] In some embodiments, an ethylene glycol return pipe 8 is provided between the freezing crystallization heat exchanger 4 and the ethylene glycol mixing tank 2.

[0028] A control method for using the cold energy of LNG gasification for lithium carbonate freezing crystallization includes the following steps: (1) Recover the cold energy of LNG; (2) Apply the recovered cold energy to the lithium carbonate freezing crystallization process; The energy-saving method for applying the cold energy of LNG to lithium carbonate freezing crystallization includes the following steps: S1. Feed a 50 - 60% ethylene glycol solution into the IFV heat exchanger 1 for cooling, so that the outlet temperature of the 50 - 60% ethylene glycol solution is -22°C to -18°C; S2. Feed LNG at -162°C to -160°C into the IFV heat exchanger 1 for vaporization; S3. The 50 - 60% ethylene glycol solution at -22°C to -18°C exchanges heat with the freezing crystallization material.

[0029] In step S1, the method for feeding the 50 - 60% ethylene glycol solution into the IFV heat exchanger 1 for cooling includes the following steps: S1-1. Feed the 50 - 60% ethylene glycol solution into the lower heat exchange tube 13 at the lower part of the IFV heat exchanger 1 for liquid heat exchange with the liquid heat exchange medium propane located at the lower part; After the heat exchange medium propane exchanges heat with a 50-60% ethylene glycol solution, the heat exchange medium propane evaporates and becomes gaseous, rising to the upper part of the IFV heat exchanger 1.

[0030] After heat exchange, the outlet temperature of the 50-60% ethylene glycol solution is -22°C to -18°C.

[0031] In step S2, the method for the LNG to enter the IFV heat exchanger 1 for vaporization includes the following steps: S2-1: The -162°C to -160°C LNG enters the upper-layer heat exchange tubes 12 of the upper part of the IFV heat exchanger 1 and exchanges heat in a gaseous state with the gaseous heat exchange medium propane located in the upper part. After the heat exchange medium propane exchanges heat with the -162°C to -160°C LNG, the heat exchange medium propane condenses and becomes liquid, descending to the lower part of the IFV heat exchanger 1.

[0032] In step S3, the method for the 50-60% ethylene glycol solution at -22°C to -18°C to exchange heat with the freeze-crystallized material includes the following steps: S3-1: The 50-60% ethylene glycol solution at -22°C to -18°C enters the ethylene glycol mixing tank 2 and is mixed with the approximately 0°C 50-60% ethylene glycol solution after freeze-crystallization heat exchange to form a 50-60% ethylene glycol solution at about -10°C to -8°C. S3-2: The 50-60% ethylene glycol solution at about -10°C to -8°C passes through the refrigeration unit 3 and enters the freeze-crystallization heat exchanger 4 to exchange heat with the freeze-crystallized material, enabling the freeze-crystallized material to reach the material crystallization temperature, thereby completing the crystallization and growth process of the crystals. S3-3: The refrigeration unit 3 starts or stops operating according to the amount of the freeze-crystallized material or the demand for cooling capacity. S3-4: A part of the approximately 0°C 50-60% ethylene glycol solution after freeze-crystallization heat exchange enters the condenser 5 to exchange heat with the secondary flash steam, exchanging heat with the flashed steam to turn the steam into condensed water. After exchanging heat with the secondary flash steam in the condenser 5, the 50-60% ethylene glycol solution at about 2-5°C enters the storage tank and is pumped back to the LNG vaporizer to recover cold energy.

[0033] In step (1), the IFV heat exchanger 1 is used to vaporize the -162°C LNG and recover the vaporization cold energy as a 50-60% ethylene glycol solution at -22°C to -18°C.

[0034] In step (2), a 50-60% ethylene glycol solution at -22°C to -18°C for cold energy recovery exchanges heat with the freeze-crystallized material to bring the freeze-crystallized material to the material crystallization temperature, thereby completing the crystallization and growth process of the crystals.

[0035] In step S3, a 50-60% ethylene glycol solution at -22°C to -18°C enters the ethylene glycol mixing tank 2 and is mixed with a 50-60% ethylene glycol solution at 0°C that has undergone freeze-crystallization heat exchange to form a 50-60% ethylene glycol solution at around -10°C to -8°C; the 50-60% ethylene glycol solution at around -10°C to -8°C passes through the refrigeration unit 3 and enters the freeze-crystallization heat exchanger 4 to exchange heat with the freeze-crystallized material, bringing the freeze-crystallized material to the material crystallization temperature, thereby completing the crystallization and growth process of the crystals.

[0036] In step S3, the refrigeration unit 3 starts or stops operating according to the amount of the freeze-crystallized material or the demand for cold energy; a part of the 50-60% ethylene glycol solution at 0°C after freeze-crystallization heat exchange enters the condenser 5 to exchange heat with the secondary flash steam, exchanging heat with the flashed steam to turn the steam into condensed water; after passing through the condenser 5 and exchanging heat with the secondary flash steam, the 50-60% ethylene glycol solution at around 2°C to 5°C enters the ethylene glycol storage tank 6 and is pumped back to the IFV heat exchanger 1 to recover cold energy. The temperature of the secondary flash steam is around 30°C to 45°C; after undergoing temperature-raising treatment, it can enable the ethylene glycol solution to recover more cold energy when exchanging heat with LNG, making full use of the cold energy of LNG.

[0037] In other embodiments, in order to accurately control the crystallization temperature, a PID controller or a fuzzy controller can be further introduced to monitor the temperature change of the freeze-crystallized material in real time and automatically adjust the temperature and flow rate of the ethylene glycol solution to ensure the stability of the crystallization process.

[0038] Specifically, the input parameters are defined as follows: the flow rate of the freeze-crystallized material is Q material , the initial temperature of the freeze-crystallized material is T initial , the target temperature of the freeze-crystallized material is T target , the current temperature of the ethylene glycol solution is T glycol , the current power of the refrigeration unit is P current ; the output parameters are as follows: the circulation volume of the ethylene glycol solution is Q glycol , the target power of the refrigeration unit is P target .

[0039] The cold energy required for the freeze-crystallized material is: ; where c material is the specific heat capacity of the material.

[0040] And the heat transfer capacity of the ethylene glycol solution satisfies: ; where c glycol is the specific heat capacity of the ethylene glycol solution.

[0041] Adjust the circulation rate of the ethylene glycol solution and the power of the refrigeration unit according to the cooling capacity required for freeze crystallization of the material and the heat transfer capacity of the ethylene glycol solution: , where η chiller is the energy efficiency ratio of the refrigeration unit.

[0042] In one of the embodiments, a PID controller is introduced to achieve precise control of the temperature of the freeze-crystallized material, specifically as follows: Define the parameters as follows: The input parameters include: the current temperature T of the freeze-crystallized material current ; the target temperature T of the freeze-crystallized material target ; the current temperature T of the ethylene glycol solution glycol ; The output parameters include: the power adjustment amount ΔP of the refrigeration unit and the circulation rate adjustment amount ΔQ of the ethylene glycol solution.

[0043] First, calculate the temperature error as follows: .

[0044] Then calculate the integral and differential of the temperature error: .

[0045] According to the PID control formula, calculate the control quantity: , where K p , K i , K d are the proportional, integral, and differential coefficients respectively.

[0046] Finally, according to the control quantity u(t), adjust the power of the refrigeration unit and the circulation rate of the ethylene glycol solution: , where α and β are adjustment coefficients.

[0047] As a further improvement, the adjustment coefficients α and β can be adjusted and confirmed through experience. Specifically: Set the values of α and β according to experience; then, run the system and observe the response curve of temperature control. If the system response is too slow, α and β can be appropriately increased; if the system response is too fast or there is oscillation, α and β can be appropriately decreased. Iterate repeatedly: Through multiple tests, gradually adjust α and β until the system response meets the design requirements.

[0048] Embodiment The embodiments of the present application will be described below. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as a limitation to the present application. For those techniques or conditions not specified in the embodiments, they shall be carried out according to the techniques or conditions described in the literature in the field or according to the product specification. For the reagents or instruments whose manufacturers are not specified, they are all conventional products that can be obtained through commercial purchase.

[0049] Example 1 A control method for using the cold energy of LNG vaporization for lithium carbonate freezing crystallization, specifically, lithium mica concentrate particles made from lithium mica concentrate are used for lithium extraction, including the following steps: S1. Feed the 50% ethylene glycol solution into the lower part of the IFV heat exchanger, and conduct liquid heat exchange with the liquid propane located in the lower part of the heat exchange medium IFV heat exchanger; S2. After the heat exchange medium propane exchanges heat with the 50% ethylene glycol solution, the heat exchange medium propane evaporates and becomes gaseous, and rises to the upper part of the IFV heat exchanger.

[0050] S3. The outlet temperature of the 50% ethylene glycol solution after heat exchange is -20°C.

[0051] S4. Feed the LNG stored at -162°C under normal pressure into the upper part of the IFV heat exchanger, and conduct gaseous heat exchange with the gaseous heat exchange medium propane located in the upper part of the IFV heat exchanger; S5. After the heat exchange medium propane exchanges heat with the -162°C LNG, the heat exchange medium propane condenses and becomes liquid, and descends to the lower part of the IFV heat exchanger.

[0052] S6. The 50% ethylene glycol solution at -20°C enters the ethylene glycol mixing tank, and is mixed with the 50% ethylene glycol solution at 0°C after freezing crystallization heat exchange to form a 50% ethylene glycol solution at about -10°C; S7. The 50% ethylene glycol solution at about -10°C passes through the refrigeration unit and enters the freezing crystallization heat exchanger, and exchanges heat with the freezing crystallization material, so that the freezing crystallization material reaches the material crystallization temperature, and then completes the crystallization and growth process of the crystal; S8. The refrigeration unit starts or stops operating according to the amount of the freezing crystallization material or the demand for cold energy; S9. A part of the 50% ethylene glycol solution at 0°C after freezing crystallization heat exchange enters the condenser to conduct heat exchange with the secondary flash steam, and exchanges heat with the flashed steam to turn the steam into condensed water; S10. After the heat exchange with the secondary flash steam in the condenser, the 50% ethylene glycol solution at about 2°C - 5°C enters the ethylene glycol storage tank and is pumped back to the IFV heat exchanger to recover the cold energy.

[0053] Using the refrigerant at -10°C provided by the refrigeration mechanism, the operating temperature of the freeze crystallization heat exchanger is accurately controlled at -5°C to -4°C; specifically, the feed temperature of the freeze crystallization material is 20 to 25°C, the temperature of the freeze crystallization heat exchanger is 0 to 5°C, the temperature of the refrigerant (ethylene glycol solution) is -10°C, the inlet temperature of the refrigerant in the external cooler is -5°C, the outlet temperature of the refrigerant in the external cooler is -4°C, the pressure is atmospheric pressure, and the salt output is 10000 - 12000 Kg / h.

[0054] As can be seen from the above results, in the control method for using the cold energy of LNG gasification in the freeze crystallization of lithium carbonate of the present invention, first, LNG at -162°C is heat-exchanged with propane, and then propane transfers the cold energy to the 50% ethylene glycol solution, avoiding the crystallization of the ethylene glycol solution caused by direct heat exchange. The 50% ethylene glycol solution at -20°C enters the freeze crystallization system and exchanges heat with the freeze crystallization material, so that the freeze crystallization material reaches the material crystallization temperature, and then the crystallization and growth process of the crystal is completed. The 50% ethylene glycol solution at about 5°C after heat exchange is pumped back to the LNG vaporizer for cold energy recovery in a cycle. This energy-saving method can not only eliminate the steam used during LNG vaporization, but also be combined with the lithium carbonate freeze crystallization process, making full and reasonable use of the cold energy, reducing energy consumption and being more environmentally friendly.

[0055] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should all be covered within the scope of the claims and the description of the present application. In particular, as long as there is no structural conflict, the technical features mentioned in each embodiment can be combined in any way. The present application is not limited to the specific embodiments disclosed in the text, but includes all technical solutions falling within the scope of the claims.

Claims

1. A control method for using the cold energy of LNG vaporization in lithium carbonate freezing crystallization, comprising the following steps: S1. Feed LNG at -162°C to -160°C into the upper part of the IFV heat exchanger, and conduct vapor-phase heat exchange with the vapor-phase heat exchange medium located in the upper part of the IFV heat exchanger, so that the heat exchange medium condenses into a liquid and descends to the lower part of the IFV heat exchanger; S2. Feed the ethylene glycol solution into the lower part of the IFV heat exchanger, and conduct liquid-phase heat exchange with the liquid heat exchange medium located in the lower part of the IFV heat exchanger, so that the heat exchange medium evaporates into a vapor and rises to the upper part of the IFV heat exchanger. The ethylene glycol solution obtains an outlet temperature of -22°C to -18°C after heat exchange; S3. The ethylene glycol solution in step S2 enters the ethylene glycol mixing tank and is mixed with the ethylene glycol solution in the ethylene glycol return pipe after freezing crystallization heat exchange to form an ethylene glycol solution at -10°C to -8°C; S4. The ethylene glycol solution in step S3 is precisely controlled in temperature by the refrigeration unit, and then enters the freezing crystallization heat exchanger to conduct heat exchange with the freezing crystallization material, so that the freezing crystallization material reaches the material crystallization temperature, and then completes the crystallization and growth process of the crystal.

2. The energy-saving control method for lithium carbonate freezing crystallization using the cold energy of LNG gasification according to claim 1, characterized in that, The heat exchange medium is propane, R507 refrigerant or R410 refrigerant, and the ethylene glycol solution is an ethylene glycol solution with a mass fraction of 50% to 60%; the inlet temperature of LNG in step S1 is -162°C to -160°C, the outlet temperature in step S2 is -22°C to -18°C, and the mixing temperature in step S3 is -10°C to -8°C.

3. The energy-saving control method for cryogenic crystallization of lithium carbonate using the cold energy of LNG gasification according to claim 1, characterized in that, In step S4, the refrigeration unit starts or stops operating according to the amount of the freezing crystallization material or the demand for cold energy, so as to achieve precise control of the crystallization temperature.

4. The energy-saving control method for lithium carbonate freezing crystallization using the cold energy of LNG gasification according to claim 1, wherein After step S4, a part of the ethylene glycol solution enters the condenser to conduct heat exchange with the secondary flash steam, and is stored in the ethylene glycol storage tank, and then is pumped back to the IFV heat exchanger of LNG by the delivery pump to recover the cold energy; another part enters the reflux mixing in step S3.

5. The energy-saving control method for lithium carbonate freezing crystallization using the cold energy of LNG gasification according to claim 1, characterized in that, The temperature of the ethylene glycol solution after heat exchange with the secondary flash steam is 2°C to 5°C.

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