A system for producing lithium dihydrogen phosphate by low-temperature evaporation crystallization through heat pump-steam coupling

Abstract

The present application relates to a kind of lithium dihydrogen phosphate production systems of heat pump steam coupling low temperature evaporation crystallization, including the heat pump steam system of reverse Carnot cycle and two-effect forced circulation evaporation crystallization system;Wherein heat pump steam system includes the refrigerant evaporator, compressor, refrigerant condenser, hot water circulating pump, expansion valve and chilled water pump for refrigerant circulation of pipeline connection;Evaporation crystallization system includes one-effect heater, one-effect separator, two-effect heater, two-effect separator, water vapor condenser and vacuum system of pipeline connection, this system includes a low temperature two-effect evaporation crystallizer, using DTB or Oslo crystallizer, in second effect low temperature evaporation, crystallization, continuous crystallization obtained lithium dihydrogen phosphate is obtained than flash crystallization lithium dihydrogen phosphate The particle is large, facilitate subsequent solid-liquid separation;This system uses reverse Carnot cycle heat pump negative pressure steam generator, using refrigerant recovers the heat of condenser, produces negative pressure steam, realizes the reuse of energy.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of evaporative crystallization product preparation, and relates to a system for producing lithium dihydrogen phosphate by using a heat pump steam coupling low-temperature evaporative crystallization. BACKGROUND

[0002] Lithium dihydrogen phosphate is an important inorganic salt, which is mainly used for preparing positive electrode materials (such as LiFePO4). Lithium dihydrogen phosphate has high electrochemical stability and good solubility, which helps to improve the capacity and cycle life of the battery.

[0003] There are mainly the following methods for preparing lithium dihydrogen phosphate:

[0004] 1. Direct synthesis method: lithium source (such as lithium carbonate or lithium hydroxide) and phosphoric acid source (such as orthophosphoric acid or pyrophosphoric acid) are mixed in a certain proportion, and lithium dihydrogen phosphate is directly synthesized at high temperature. The disadvantage of this method is that the temperature is high and the energy consumption is large.

[0005] 2. Double decomposition method: the double decomposition reaction of phosphoric acid solution and lithium hydroxide solution generates lithium dihydrogen phosphate and lithium hydroxide. This method needs to control the reaction temperature and pH value to ensure the stability of the product purity and yield.

[0006] The above methods all obtain lithium dihydrogen phosphate solution, usually with a concentration of about 40%. If lithium dihydrogen phosphate crystals are to be further obtained, the excess water needs to be evaporated. Since the solubility of lithium dihydrogen phosphate is very large, the relationship between the solution concentration and the temperature is as shown in Figure 1 From the figure, it can be seen that the solubility of lithium dihydrogen phosphate in water is very large, and the solubility increases with the increase of temperature. Therefore, lithium dihydrogen phosphate is usually obtained by evaporating a dilute solution to obtain a high-concentration solution, such as a single-effect or multi-effect evaporator. Due to the temperature limitation of the summer cooling water tower (usually the temperature is greater than 30℃), the concentrated solution obtained from the single-effect or multi-effect evaporator is usually greater than 50℃. Then, the high-temperature and high-concentration lithium dihydrogen phosphate solution is cooled and crystallized or flash evaporated to obtain lithium dihydrogen phosphate crystals, as shown in Figure 2

[0007] The present patent adopts an inverse Carnot cycle heat pump unit, which provides a 70-100℃ low-pressure steam (heat source) and a 10-30℃ chilled water (cold source) at the same time. The conventional single-effect or multi-effect evaporator needs an external cooling water tower, especially in summer when the temperature is high, the cooling water temperature of the cooling water tower is high, so the conventional single-effect or multi-effect production is greatly affected by the environment. The two-effect evaporator configured with the inverse Carnot cycle heat pump unit is a relatively closed system, which is not affected by the external environment. At the same time, since the chilled water temperature is low, the direct evaporative crystallization of lithium dihydrogen phosphate can be realized, and lithium dihydrogen phosphate crystals are obtained at the same time. SUMMARY​

[0008] Therefore, the present application provides a system for producing lithium dihydrogen phosphate by heat pump steam coupling low-temperature evaporation crystallization to solve the problems of the above-mentioned existing lithium dihydrogen phosphate preparation method, that is, the evaporation crystallization process is greatly affected by the environment, and the obtained lithium dihydrogen phosphate particles are not uniform and the product quality is poor.

[0009] To achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0010] A system for producing lithium dihydrogen phosphate by heat pump steam coupling low-temperature evaporation crystallization, comprising a heat pump steam system of reverse Carnot cycle and an evaporation crystallization system of two-effect forced circulation.

[0011] The heat pump steam system comprises a refrigerant evaporator, a compressor, a refrigerant condenser, a hot water circulating pump, an expansion valve and a chilled water pump connected by pipelines to realize refrigerant circulation.

[0012] The evaporation crystallization system comprises a one-effect heater, a one-effect separator, a two-effect heater, a two-effect separator, a water vapor condenser and a vacuum system connected by pipelines, the temperature and absolute pressure of the one-effect heater are 70-100 DEG C and 30-100 KPa respectively, the temperature and absolute pressure of the two-effect heater are 50-60 DEG C and 12-20 KPa respectively, and the temperature and absolute pressure of the water vapor condenser are 25-40 DEG C and 3-8 KPa respectively; the one-effect separator is connected with a raw material tank provided with a feeding pump, low-pressure steam generated by the refrigerant evaporator enters the one-effect separator after heat exchange in the one-effect heater to perform one-effect flash evaporation on the material flow, and the material is concentrated; the two-effect separator is provided with a DTB crystallizer, secondary steam generated by the one-effect separator enters the two-effect separator after heat exchange in the two-effect heater to perform two-effect evaporation crystallization on the material flow, condensed water in the two-effect heater is discharged into the water vapor condenser, secondary steam generated by the two-effect separator enters the water vapor condenser, is condensed into water and then discharged, the refrigerant evaporator and the water vapor condenser are connected by pipelines to realize reutilization of the heat of the secondary steam of the two-effect, and the vacuum system connected with the water vapor condenser adopts a Roots pump+water ring vacuum pump or a screw vacuum pump, and the absolute vacuum degree reaches 0.5-3 KPa to ensure high vacuum degree of the two-effect separator.

[0013] Further, the refrigerant condenser is provided with an upper pipe box at the top and a lower pipe box at the bottom, and the hot water circulating pump is connected between the upper pipe box and the lower pipe box to realize water circulation in the refrigerant condenser.

[0014] Further, the refrigerant condenser is provided with a refrigerant gas phase inlet at the upper portion and a refrigerant liquid phase outlet at the lower portion, and the refrigerant evaporator, the compressor, the expansion valve and the chilled water pump are connected between the refrigerant gas phase inlet and the refrigerant liquid phase outlet to realize refrigerant circulation.

[0015] Further, the low-pressure steam outlet, the low-pressure steam condensate return water outlet and the pure water supply outlet are arranged on the upper pipe box of the refrigerant condenser.

[0016] Further, the one-effect heater upper portion is arranged with the one-effect heater steam inlet connected with the low-pressure steam outlet, and the one-effect heater lower portion is arranged with the one-effect heater condensate outlet connected with the low-pressure steam condensate return water outlet, and the low-pressure steam condensate water temperature sensor is arranged on the connecting pipeline.

[0017] Further, the refrigerant condenser lower pipe box is arranged with the refrigerant condenser lower pipe box liquid level meter, the one-effect separator is arranged with the one-effect separator liquid level meter for observing the liquid level in the one-effect separator, and the two-effect separator is arranged with the two-effect separator liquid level meter for observing the liquid level in the two-effect separator.

[0018] Further, the one-effect automatic feeding valve is arranged on the pipeline connecting the one-effect separator upper portion with the feeding pump, the one-effect heater and the one-effect separator are arranged with the one-effect forced circulation pump connected with the one-effect heater and the one-effect separator, the one-effect forced circulation pump is used to push the steam circulation in the one-effect heater and the material circulation heat exchange in the one-effect separator for flash evaporation, so that the material is concentrated, and the one-effect automatic feeding valve is coordinated with the one-effect separator liquid level meter to adjust the liquid level in the one-effect separator to be stable.

[0019] Further, the two-effect heater and the two-effect separator are arranged with the two-effect forced circulation pump connected with the two-effect heater and the two-effect separator, the one-effect forced circulation pump and the two-effect forced circulation pump are connected through the pipeline with the one-effect to two-effect material transfer automatic valve, the material flows from the one-effect forced circulation pump outlet to the two-effect forced circulation pump inlet through the one-effect to two-effect material transfer automatic valve, and then is transported to the two-effect separator, and the one-effect to two-effect material transfer automatic valve is coordinated with the two-effect separator liquid level meter to adjust the liquid level in the two-effect separator to be stable.

[0020] Further, the two-effect separator bottom portion is connected with the two-effect material outlet pump, and the middle portion is connected with the solid-liquid separation system with the two-effect material outlet automatic valve, after the material is evaporated and crystallized in the two-effect, the lithium dihydrogen phosphate crystals enter the DTB crystallizer, and part of the crystals is circulated in the two-effect through the two-effect material outlet pump, and part of the crystals is discharged into the solid-liquid separation system through the two-effect material outlet automatic valve.

[0021] Further, the material sampling valve is arranged on the pipeline connecting the two-effect material outlet pump with the two-effect separator, and the crystal content in the two-effect separator can be periodically sampled and analyzed through the material sampling valve.

[0022] Further, the water vapor condenser is further connected with the condensate negative pressure pump, so that the condensate in the water vapor condenser is discharged through the condensate negative pressure pump.

[0023] Further, the one-effect heater is provided with a one-effect heater pressure sensor and a one-effect heater temperature sensor for observing the steam temperature and pressure in the one-effect heater, and the two-effect heater is provided with a two-effect heater pressure sensor and a two-effect heater temperature sensor for observing the steam temperature and pressure in the two-effect heater.

[0024] The present application has the following advantages:

[0025] 1. The system for producing lithium dihydrogen phosphate by heat pump steam coupling low-temperature evaporation crystallization comprises a heat pump system of reverse Carnot cycle and a two-effect forced circulation evaporation crystallization system. The heat pump system of reverse Carnot cycle simultaneously provides low-pressure steam at 70-100 DEG C and chilled water at 10-30 DEG C. The low-pressure steam serves as the heat source of the two-effect heater in the evaporation crystallization system, and the chilled water serves as the cold source of the condenser. Due to the low temperature of the chilled water, a Roots-water ring or screw vacuum system is adopted to realize evaporation at 35-50 DEG C in the second effect under high vacuum condition, and lithium dihydrogen phosphate crystals are obtained by crystallization at the same time. Since evaporation and crystallization are carried out simultaneously, the obtained lithium dihydrogen phosphate particles are large and uniform, which facilitates subsequent solid-liquid separation and improves product quality. Compared with the traditional evaporation-cooling crystallization, one cooling crystallization step is saved, and the process is simpler and easier to operate.

[0026] 2. The system for producing lithium dihydrogen phosphate by heat pump steam coupling low-temperature evaporation crystallization comprises a heat pump system of reverse Carnot cycle and a two-effect forced circulation evaporation crystallization system. The heat pump system of reverse Carnot cycle simultaneously provides low-pressure steam at 70-100 DEG C and chilled water at 10-30 DEG C. The low-pressure steam serves as the heat source of the two-effect heater in the evaporation crystallization system, and the chilled water serves as the cold source of the condenser. Due to the low temperature of the chilled water, a Roots-water ring or screw vacuum system is adopted to realize evaporation at 35-50 DEG C in the second effect under high vacuum condition, and lithium dihydrogen phosphate crystals are obtained by crystallization at the same time. Since evaporation and crystallization are carried out simultaneously, the obtained lithium dihydrogen phosphate particles are large and uniform, which facilitates subsequent solid-liquid separation and improves product quality. Compared with the traditional evaporation-cooling crystallization, one cooling crystallization step is saved, and the process is simpler and easier to operate.

[0027] Other advantages, objects, and features of the present application will be apparent to those skilled in the art from the following specification, which is to be taken in conjunction with the accompanying drawings, or can be learned from the practice of the application. The objects and other advantages of the present application can be achieved and obtained by means of the features and combinations hereinafter more fully described. BRIEF DESCRIPTION OF DRAWINGS

[0028] In order to make the objectives, technical solutions and advantages of the present application clearer, the preferred embodiments of the present application will be described in detail below with reference to the accompanying drawings, in which:

[0029] Figure 1 A concentration-temperature relationship diagram of lithium dihydrogen phosphate in the prior art;

[0030] Figure 2 A process diagram for preparing lithium dihydrogen phosphate by evaporation-cooling crystallization in the prior art;

[0031] Figure 3 This is a schematic diagram of the structure of the heat pump steam coupling low-temperature evaporation crystallization system for producing lithium dihydrogen phosphate according to the present invention;

[0032] Figure 4 for Figure 3 Schematic diagram of a medium-temperature heat pump steam system;

[0033] Figure 5 for Figure 3 A schematic diagram of the structure of the evaporation crystallization system.

[0034] Figure labels: 1 for refrigerant evaporator, 2 for compressor, 3 for refrigerant vapor inlet, 4 for refrigerant condenser upper tube box, 5 for refrigerant condenser, 6 for refrigerant liquid outlet, 7 for refrigerant condenser lower tube box level gauge, 8 for refrigerant condenser lower tube box, 9 for hot water circulation pump, 10 for low-pressure steam outlet, 11 for low-pressure steam condensate return port, 12 for pure water makeup port, 13 for first-effect automatic feed valve, 14 for low-pressure steam temperature sensor, 15 for low-pressure steam condensate temperature sensor, 16 for first-effect heater condensate outlet, 17 for first-effect heater non-condensable gas outlet, 18 for first-effect heater pressure sensor, 19 for first-effect heater temperature sensor, 20 for first-effect heater steam inlet, 21 for first-effect... 22 is a heater, 23 is a level gauge for a first-effect separator, 24 is a second-effect heater, 25 is a pressure sensor for a second-effect heater, 26 is a temperature sensor for a second-effect heater, 27 is an automatic valve for transferring material from the first to the second effect, 28 is a second-effect separator, 29 is an automatic discharge valve for the second effect, 30 is a steam condenser, 31 is a solid-liquid separation system, 32 is a level gauge for a second-effect separator, 33 is a liquid storage device for a first-effect separator, 34 is a DTB crystallizer, 35 is a vacuum system, 36 is a condensate negative pressure pump, 37 is a discharge pump for the second effect, 38 is a forced circulation pump for the second effect, 39 is a forced circulation pump for the first effect, 40 is a feed pump, 41 is a raw material tank, 42 ​​is a discharge sampling valve, 43 is a chilled water pump, and 44 is an expansion valve. Detailed Implementation

[0035] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0036] The drawings are only used for exemplary illustration, and the representation is only a schematic diagram, and cannot be understood as a limitation on the present application; in order to better illustrate the embodiments of the present application, some components of the drawings will be omitted, enlarged or reduced, and do not represent the size of the actual product; for those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings can be omitted.

[0037] The same or similar reference numerals in the drawings of the embodiments of the present application correspond to the same or similar components; in the description of the present application, it should be understood that if the orientations or positional relationships indicated by the terms "upper", "lower", "left", "right", "front", "back" and the like are based on the orientations or positional relationships shown in the drawings, they are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, therefore the terms describing the positional relationship in the drawings are only used for exemplary illustration, and cannot be understood as a limitation on the present application, and for those skilled in the art, the specific meanings of the above terms can be understood according to the specific circumstances.

[0038] Embodiment

[0039] As Figures 3 to 5 shown in a system for producing lithium dihydrogen phosphate by a heat pump steam coupling low-temperature evaporation crystallization, including a heat pump steam system using an inverse Carnot cycle and a two-effect forced circulation evaporation crystallization system, the inverse Carnot cycle heat pump steam system provides 70-100℃ negative pressure low-temperature steam as the heat source of the two-effect heater in the evaporation crystallization system, and at the same time provides 10-30℃ chilled water as the cold source of the water vapor condenser 30 in the evaporation crystallization system. The heat pump steam system provides 70-100℃ saturated negative pressure water vapor, and the absolute pressure of the steam is 30-100Kpa, which is a non-pressure container.

[0040] The heat pump steam system includes a refrigerant evaporator 1, a compressor 2, a refrigerant condenser 5, an expansion valve 44 and a chilled water pump 43 connected by pipelines for refrigerant circulation, the refrigerant condenser 5 is provided with a refrigerant gas phase inlet 3 at the upper part and a refrigerant liquid phase outlet 6 at the lower part, the compressor 2 is connected with the refrigerant gas phase inlet 3, the expansion valve 44 is connected with the refrigerant liquid phase outlet 6, and the refrigerant evaporator 1 is connected with the water vapor condenser 30 in the evaporation crystallization system through A / B ports to realize refrigerant circulation, the water vapor condenser 30 provides heat for the refrigerant evaporator 1, and pure water is used as a heat carrier to realize the reuse of heat in the evaporation crystallization system. The pure water is continuously circulated under the action of the chilled water pump 43, enters the water vapor condenser 30 from the A port of the water vapor condenser 30, and exits from the B port of the water vapor condenser 30, and the temperature difference between the inlet and outlet is about 5℃, so that the heat of the two-effect secondary steam in the water vapor condenser 30 is continuously transported to the refrigerant inverse Carnot cycle heat pump steam system.

[0041] The top of the refrigerant condenser 5 is a refrigerant condenser upper pipe box 4, and the bottom is a refrigerant condenser lower pipe box 8, and a hot water circulating pump 9 is connected between the refrigerant condenser upper pipe box 4 and the refrigerant condenser lower pipe box 8 to realize water circulation in the refrigerant condenser 5.

[0042] A low-pressure steam outlet 10, a low-pressure steam condensate water return port 11 and a pure water supplement port 12 are arranged on the refrigerant condenser lower pipe box 8. The low-pressure steam generated by the refrigerant condenser 5 is provided to the two-effect evaporation system through the low-pressure steam outlet 10, the low-pressure steam condensate water return port 11 is used to return the condensed water after condensation of the one-effect heater 21, and the pure water entering the refrigerant condenser 5 from the pure water supplement port 12 is continuously circulated under the action of the hot water circulating pump 9, and heat is obtained through the refrigerant condenser 5, so that low-pressure steam is continuously generated to supply the two-effect evaporator.

[0043] A refrigerant condenser lower pipe box liquid level meter 7 for observing the liquid level in the refrigerant condenser 5 is arranged on the refrigerant condenser lower pipe box 8 at the bottom of the refrigerant condenser 5.

[0044] The two-effect forced circulation evaporation crystallization system is a one-effect forced circulation system without a crystallizer and a two-effect forced circulation system with a DTB crystallizer, and the material is evaporated and crystallized in the two-effect system.

[0045] The evaporation crystallization system comprises a one-effect heater 21, a one-effect separator 22, a two-effect heater 24, a two-effect separator 28, a water vapor condenser 30 and a vacuum system 35 connected by pipelines. The temperature and absolute pressure of the one-effect heater 21 are 70-100 DEG C and 30-100 KPa respectively, the temperature and absolute pressure of the two-effect heater 24 are 50-60 DEG C and 12-20 KPa respectively, and the temperature and absolute pressure of the water vapor condenser 30 are 25-40 DEG C and 3-8 KPa respectively. A one-effect heater steam inlet 20 is arranged on the upper portion of the one-effect heater 21 and connected to the low-pressure steam outlet 10, a one-effect heater condensate water outlet 16 is arranged on the lower portion of the one-effect heater 21 and connected to the low-pressure steam condensate water return port 11, a low-pressure steam condensate water temperature sensor 15 is arranged on the connecting pipeline, low-pressure steam is connected to the one-effect heater steam inlet 20 through the low-pressure steam outlet 10 and the connecting pipeline, and a low-pressure steam temperature sensor 14 is arranged on the connecting pipeline. After heat exchange in the one-effect heater 21, the low-pressure steam becomes condensate water, is discharged from the one-effect heater 21 through the one-effect heater condensate water outlet 16 and is returned to the low-pressure steam condensate water return port 11. A one-effect heater pressure sensor 18 and a one-effect heater temperature sensor 19 are further arranged on the one-effect heater 21 to observe the steam temperature and pressure in the one-effect heater 21.

[0046] The upper pipe of the first separator 22 is connected with the raw material tank 41 with the feed pump 40, and a first automatic feed valve 13 is installed on the pipe. The top gas outlet of the first heater 21 is connected with the first separator 22. A first forced circulation pump 39 is arranged below the first heater 21 and the first separator 22, and is connected with both the first heater 21 and the first separator 22. The first forced circulation pump 39 is used to push the steam in the first heater 21 and the material in the first separator 22 to circulate and exchange heat, so that the material is concentrated by flash evaporation. The first separator 22 is provided with a first separator liquid level meter 23 for observing the liquid level in the first separator 22. The first automatic feed valve 13 is coordinated with the first separator liquid level meter 23 to stabilize the liquid level in the first separator 22 within a certain range.

[0047] The DTB crystallizer 34 or Oslo crystallizer is installed in the second separator 28. The secondary steam generated by the first separator 22 enters the second separator 28 after heat exchange in the second heater 24 to evaporate and crystallize the material in the second separator 28. The top gas outlet of the second heater 24 is connected with the second separator 28. The second heater 24 is also provided with a second heater pressure sensor 25 and a second heater temperature sensor 26 for observing the steam temperature and pressure in the second heater 24. A second forced circulation pump 38 is arranged below the second heater 24 and the second separator 28, and is connected with both the second heater 24 and the second separator 28. The first forced circulation pump 39 and the second forced circulation pump 38 are connected through a pipe with a first-to-second transfer automatic valve 27. The material flows from the outlet of the first forced circulation pump 39 to the inlet of the second forced circulation pump 38 through the first-to-second transfer automatic valve 27, and then is transported to the second separator 28. The second separator 28 is provided with a second separator liquid level meter 32 for observing the liquid level in the second separator 28. The first-to-second transfer automatic valve 27 is coordinated with the second separator liquid level meter 32 to stabilize the liquid level in the second separator 28 within a certain range. The second separator 28 is connected with a second discharge pump 37 at the bottom and a solid-liquid separation system 31 with a second discharge automatic valve 29 in the middle. After the material is evaporated and crystallized in the second separator 28, the lithium dihydrogen phosphate crystals enter the DTB crystallizer 34. Part of the crystals circulate in the second separator 28 by the second discharge pump 37, and part of the crystals are discharged into the solid-liquid separation system 31 through the second discharge automatic valve 29. A discharge sampling valve 42 is arranged on the pipe connecting the second discharge pump 37 with the second separator 28. The crystal content in the second separator 28 can be regularly sampled and analyzed through the discharge sampling valve 42.

[0048] The lower part of the two-effect heater 24 is provided with a two-effect heater condensate outlet connected with the water vapor condenser 30. The secondary steam generated by the two-effect separator 28 enters the water vapor condenser 30, is condensed into water and discharged. The refrigerant evaporator 1 is connected with the water vapor condenser 30 in pipeline to reuse the heat of the two-effect secondary steam. The vacuum system 35 is connected with the water vapor condenser 30. The vacuum system 35 adopts a Roots pump + water ring vacuum pump or a screw vacuum pump, and the absolute vacuum degree reaches 0.5-3 Kpa to ensure the high vacuum degree of the two-effect separator 28. The water vapor condenser 30 is also connected with a condensate negative pressure pump 36 to facilitate the discharge of the condensate in the water vapor condenser 30 through the condensate negative pressure pump 36.

[0049] The negative pressure steam generated by the refrigerant reverse Carnot cycle heat pump steam system needs a vacuum environment, which is provided by the vacuum system 35 of the two-effect evaporator. The refrigerant reverse Carnot cycle heat pump steam system is connected with the two-effect forced circulation evaporation crystallization system through the non-condensable gas outlet 17 of the primary heater, and the connection is adjusted through the valve behind the non-condensable gas outlet 17.

[0050] The material flow and control in the heat pump steam coupled low-temperature evaporation crystallization system for producing lithium dihydrogen phosphate are as follows. The material is pumped into the primary separator 22 from the raw material tank 41 through the feed pump 40, and the feed inlet is above the liquid level of the primary separator liquid storage 33. The material is heated in the primary heater 21 under the push of the primary forced circulation pump 39, flashed in the primary separator 22, and concentrated. The primary automatic feed valve 13 is linked with the primary separator liquid level gauge 23 to realize the stability of the liquid level in the primary separator within a certain range through the opening size / opening and closing of the primary automatic feed valve 13. The material flows from the outlet of the primary forced circulation pump 39 to the inlet of the secondary forced circulation pump 38 through the primary-to-secondary transfer automatic valve 27. The primary-to-secondary transfer automatic valve 27 is linked with the secondary separator liquid level gauge 32 to realize the stability of the liquid level in the secondary separator within a certain range through the opening size / opening and closing of the primary-to-secondary transfer automatic valve 27. After evaporation crystallization in the secondary evaporator, the lithium dihydrogen phosphate crystals enter the DTB crystallizer 34, and part of them is circulated in the secondary evaporator through the secondary discharge pump 37, and part of them is discharged into the solid-liquid separation system 31 through the secondary discharge automatic valve 29. The internal crystal content of the secondary evaporator can be periodically sampled and analyzed through the discharge sampling valve 42. The material of the two-effect evaporation crystallization system adopts a flow-through mode, i.e. the material enters the system from the primary evaporator, flows into the secondary evaporator from the primary evaporator, and then is discharged from the system through the secondary discharge pump 37 after evaporation crystallization in the secondary evaporator.

[0051] The secondary steam and condensed water flow as follows: the secondary steam generated by the primary separator 22 is used as the heat source of the secondary heater 24, and is condensed into water in the secondary heater 24, which is discharged into the water vapor condenser 30. The secondary steam generated by the secondary separator 28 enters the water vapor condenser 30 and is condensed into water. All the condensed water is discharged by the condensed water negative pressure pump 36. The vacuum system 35 uses a Roots pump + water ring vacuum pump or a screw vacuum pump, and the absolute vacuum degree is as high as 0.5-3 Kpa, so as to ensure that the secondary separator 28 works at a higher vacuum degree.

[0052] Finally, it should be pointed out that the above embodiments are only used to illustrate the technical solutions of the present application and not to limit the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced equivalently without departing from the purpose and scope of the technical solutions, and all should be covered in the scope of the claims of the present application.

Claims

1. A system for the production of lithium dihydrogen phosphate by heat pump vapor coupled cryogenic evaporation crystallization, characterized in that, The heat pump steam system comprises a refrigerant evaporator (1), a compressor (2), a refrigerant condenser (5), a hot water circulating pump (9), an expansion valve (44) and a chilled water pump (43) connected by pipelines to realize refrigerant circulation; the evaporation crystallization system comprises a one-effect heater (21), a one-effect separator (22), a two-effect heater (24), a two-effect separator (28), a water vapor condenser (30) and a vacuum system (35) connected by pipelines; the one-effect heater (21) has a temperature of 70-100 DEG C and an absolute pressure of 30-100 KPa, the two-effect heater (24) has a temperature of 50-60 DEG C and an absolute pressure of 12-20 KPa, and the water vapor condenser (30) has a temperature of 25-40 DEG C and an absolute pressure of 3-8 KPa; the one-effect separator (22) is connected with a raw material tank (41) provided with a feeding pump (40); low-pressure steam generated by the refrigerant evaporator (1) is heated in the one-effect heater (21) and then enters the one-effect separator (22) to perform one-effect flash evaporation on the material flow, so that the material is concentrated; the DTB crystallizer (34) is installed in the two-effect separator (28); the secondary steam generated by the one-effect separator (22) is heated in the two-effect heater (24) and then enters the two-effect separator (28) to perform two-effect evaporation crystallization on the material flow; the condensed water in the two-effect heater (24) is discharged into the water vapor condenser (30), the secondary steam generated by the two-effect separator (28) enters the water vapor condenser (30) and is condensed into water and then discharged; the refrigerant evaporator (1) is connected with the water vapor condenser (30) to reuse the heat of the secondary steam in the two-effect separator (28); the vacuum system (35) connected with the water vapor condenser (30) is a Roots pump+water ring vacuum pump or a screw vacuum pump, and has an absolute vacuum degree of 0.5-3 KPa to ensure high vacuum degree of the two-effect separator (28); The refrigerant condenser (5) has a refrigerant condenser upper pipe box (4) at the top and a refrigerant condenser lower pipe box (8) at the bottom, and the hot water circulating pump (9) is connected between the refrigerant condenser upper pipe box (4) and the refrigerant condenser lower pipe box (8) to realize water circulation in the refrigerant condenser (5); The refrigerant condenser (5) is provided with a refrigerant gas phase inlet (3) at the upper portion and a refrigerant liquid phase outlet (6) at the lower portion, and the refrigerant evaporator (1), the compressor (2), the expansion valve (44) and the chilled water pump (43) are connected between the refrigerant gas phase inlet (3) and the refrigerant liquid phase outlet (6); the refrigerant condenser lower pipe box (8) is provided with a low-pressure steam outlet (10), a low-pressure steam condensate water return port (11) and a pure water supplement port (12). ​ ​ The upper part of the one-effect heater (21) is provided with a one-effect heater steam inlet (20) connected with the low-pressure steam outlet (10), the lower part of the one-effect heater (21) is provided with a one-effect heater condensate water outlet (16) connected with the low-pressure steam condensate water return (11) and a low-pressure steam condensate water temperature sensor (15) is installed on the connecting pipeline, and a low-pressure steam temperature sensor (14) is installed on the pipeline connecting the low-pressure steam outlet (10) with the one-effect heater steam inlet (20).

2. The system for producing lithium dihydrogen phosphate according to claim 1, wherein The lower pipe box (8) of the refrigerant condenser is provided with a refrigerant condenser lower pipe box liquid level meter (7), the one-effect separator (22) is provided with a one-effect separator liquid level meter (23) for conveniently observing the liquid level in the one-effect separator (22), and the two-effect separator (28) is provided with a two-effect separator liquid level meter (32) for conveniently observing the liquid level in the two-effect separator (28).

3. The system for producing lithium dihydrogen phosphate according to claim 2, wherein The upper part of the one-effect separator (22) is provided with a one-effect automatic feeding valve (13) installed on the pipeline connected with the feeding pump (40), the lower part of the one-effect heater (21) and the one-effect separator (22) is provided with a one-effect forced circulation pump (39) connected with the one-effect heater (21) and the one-effect separator (22), the one-effect forced circulation pump (39) is used for driving the steam in the one-effect heater (21) and the material in the one-effect separator (22) to circulate and exchange heat to perform flash evaporation, so that the material is concentrated, and the one-effect automatic feeding valve (13) is coordinated with the one-effect separator liquid level meter (23) to adjust the stable liquid level in the one-effect separator (22).

4. The system for producing lithium dihydrogen phosphate according to claim 3, wherein The lower part of the two-effect heater (24) and the two-effect separator (28) is provided with a two-effect forced circulation pump (38) connected with the two-effect heater (24) and the two-effect separator (28), the one-effect forced circulation pump (39) and the two-effect forced circulation pump (38) are connected through a pipeline provided with a one-effect to two-effect material transfer automatic valve (27), the material flows from the outlet of the one-effect forced circulation pump (39) to the inlet of the two-effect forced circulation pump (38) through the one-effect to two-effect material transfer automatic valve (27) and is then transported to the two-effect separator (28), and the one-effect to two-effect material transfer automatic valve (27) is coordinated with the two-effect separator liquid level meter (32) to adjust the stable liquid level in the two-effect separator (28).

5. The system for producing lithium dihydrogen phosphate according to claim 4, wherein The bottom of the two-effect separator (28) is connected with a two-effect material outlet pump (37), and the middle part is connected with a solid-liquid separation system (31) provided with a two-effect material outlet automatic valve (29), after the material is evaporated and crystallized in the two-effect separator (28), lithium dihydrogen phosphate crystals enter a DTB crystallizer (34), part of the lithium dihydrogen phosphate crystals is circulated in the two-effect separator (28) by the two-effect material outlet pump (37), and part of the lithium dihydrogen phosphate crystals is discharged into the solid-liquid separation system (31) through the two-effect material outlet automatic valve (29).

6. The system for producing lithium dihydrogen phosphate according to claim 5, wherein The pipeline connecting the two-effect material outlet pump (37) with the two-effect separator (28) is provided with a material sampling valve (42), and the water vapor condenser (30) is connected with a condensate water negative pressure pump (36).

7. The system for producing lithium dihydrogen phosphate according to claim 1, wherein The primary heater (21) is provided with a primary heater pressure sensor (18) and a primary heater temperature sensor (19) for observing the temperature and pressure of the steam in the primary heater (21), and the secondary heater (24) is provided with a secondary heater pressure sensor (25) and a secondary heater temperature sensor (26) for observing the temperature and pressure of the steam in the secondary heater (24).

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