MVR (Mechanical Vapor Recompression) evaporative crystallization system and evaporative crystallization method for coarsely preparing lithium sulfate monohydrate

Abstract

The invention provides an MVR (Mechanical Vapor Recompression) evaporative crystallization system and an evaporative crystallization method for coarsely preparing lithium sulfate monohydrate. The lithium sulfate MVR evaporative crystallization system is composed of a feeding pump, a first condensate water preheater, a non-condensable gas preheater, a lithium sulfate crystallizer, a vacuum pump, a first gas-liquid separator, a steam washing tower gas-liquid separator, a condensate water pump, a condensate water tank, a mother liquor discharge pump, a discharging pump, a mother liquor pump, a mother liquor tank, a thickener, a lithium sulfate centrifugal machine, a drying machine, a packaging machine, a steam compressor and a gas washing tower. And a scrubber tower circulating pump. According to the lithium sulfate MVR evaporative crystallization system and the lithium sulfate MVR evaporative crystallization method provided by the invention, the problems of system equipment scaling and evaporation gas-liquid entrainment can be reduced, and meanwhile, the crystal granularity is large and uniform.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ore water treatment, and relates to a lithium sulfate monohydrate evaporation crystallization system and method, and specifically relates to an MVR evaporation crystallization system and an evaporation crystallization method for crude lithium sulfate monohydrate. Background Art

[0002] With the development of electronic products and new energy vehicles, the demand for basic lithium salts in new energy batteries is increasing day by day. At present, there are two main methods for preparing crude lithium sulfate monohydrate at home and abroad: sulfuric acid method and lithium carbonate method.

[0003] The sulfuric acid method is a method of obtaining lithium sulfate monohydrate by subjecting spodumene concentrate or other lithium-containing ores to a series of treatments. The method mainly includes the following steps:

[0004] 1. Ore dressing and crushing: The lithium ore is coarsely crushed by a jaw crusher, then crushed by a cone crusher, and then subjected to gravity separation, flotation and magnetic separation to separate the lithium-containing ore.

[0005] 2. Sulfate roasting: The dried lithium ore is reacted with concentrated sulfuric acid to obtain a lithium sulfate solution. This step requires controlling the reaction temperature and reaction time to ensure the reaction effect.

[0006] 3. Impurity removal: The lithium sulfate solution is subjected to impurity removal treatment to remove impurity ions in the solution, such as by chemical precipitation impurity removal and resin adsorption impurity removal, to obtain a lithium sulfate purified solution.

[0007] 4. Evaporation concentration and crystallization: Take the lithium sulfate purified liquid for evaporation concentration, then cool and crystallize, and filter to obtain lithium sulfate wet material.

[0008] 5. Washing and drying: Wash the wet lithium sulfate material to remove impurities attached to the surface of the crystals, and then dry to obtain the lithium sulfate monohydrate product.

[0009] The lithium carbonate method is a reaction between lithium carbonate and sulfuric acid. The specific steps include:

[0010] 1. Reaction process: Add lithium carbonate solution into the reactor, and slowly add sulfuric acid under stirring to react. The reaction equation is: Li2CO3+H2SO4→Li2SO4+H2O+CO2↑.

[0011] 2. Evaporation concentration and crystallization: The solution after the reaction is evaporated and concentrated to reach a supersaturated state, and then cooled and crystallized to obtain crystals of lithium sulfate monohydrate.

[0012] 3. Centrifugal separation and drying: The crystals are separated from the mother liquor by centrifugal separation, and then the crystals are dried to obtain the final lithium sulfate monohydrate product.

[0013] Both the sulfuric acid method and the lithium carbonate method produce lithium sulfate monohydrate products by evaporation concentration + cooling crystallization. The entire process path is long, with high steam consumption, high operating costs, large floor space, complex operations, high labor costs, and difficult to control evaporation and freezing process parameters.

[0014] Therefore, it is necessary to develop a lithium sulfate monohydrate preparation process with low preparation equipment investment cost, low energy consumption and short process path. Summary of the invention

[0015] In order to solve the above problems, the object of the present invention is to provide an MVR evaporation crystallization system for crude lithium sulfate monohydrate, which has low investment cost, low energy consumption and short process path.

[0016] Another object of the present invention is to provide an MVR evaporation crystallization method for crude lithium sulfate monohydrate.

[0017] In order to achieve the above object, the present invention provides an MVR evaporation and crystallization system for crude lithium sulfate monohydrate, which is composed of a feed pump, a condensate preheater, a non-condensable gas preheater, a vacuum pump, a first gas-liquid separator, a gas-liquid separator of a steam scrubber, a condensate pump, a condensate tank, a lithium sulfate crystallizer, a mother liquor discharge pump, a discharge pump, a mother liquor pump, a mother liquor tank, a thickener, a lithium sulfate centrifuge, a dryer, a packaging machine, a steam compressor, a scrubber, and a scrubber circulating pump;

[0018] Wherein, the first gas-liquid separator is arranged above the lithium sulfate crystallizer, and a baffle demister is arranged on the upper part of the first gas-liquid separator; the upper part of the lithium sulfate crystallizer is a mother liquor clarification zone, and the middle and lower parts are crystal growth zones; a central circulation pipe is vertically arranged in the center of the lithium sulfate crystallizer; the top of the central circulation pipe is connected to the bottom of the first gas-liquid separator; the side wall of the first gas-liquid separator is connected to one end of the tube side of a forced circulation heater through an upper circulation pipeline, and the upper circulation pipeline goes deep into the first gas-liquid separator, and a cross-shaped liquid distributor is arranged at the end of the upper circulation pipeline; the other end of the tube side of the forced circulation heater is connected to the mother liquor clarification zone of the lithium sulfate crystallizer through a lower circulation pipeline, and a forced circulation pump is arranged on the lower circulation pipe;

[0019] One end of the feed pump is connected to the raw material pipeline outside the system through a pipeline, and the other end of the feed pump is connected to the tube side inlet of the condensate preheater through a pipeline. The tube side outlet of the condensate preheater is then connected to the tube side inlet of the non-condensable gas preheater through a pipeline. The condensate pump and the condensate tank are sequentially arranged between the shell side inlet of the condensate preheater and the forced circulation heater, and are connected through pipelines; the shell side of the non-condensable gas preheater is also connected to the shell side of the forced circulation heater through a pipeline; the shell side outlet of the condensate preheater is connected to the condensate network outside the system through a pipeline; the shell side outlet of the non-condensable gas preheater is connected to the gas-liquid separator of the steam washing tower through a pipeline; the gas-liquid separator of the steam washing tower is also connected to the vacuum pump and the condensate tank through pipelines respectively; The vacuum pump is connected to the condensate network outside the system through a pipeline; the lower circulation pipeline is connected to the mother liquor pump through a pipeline, and the mother liquor pump is connected to the mother liquor tank through a pipeline; the pipe outlet of the non-condensable gas preheater is connected to the mother liquor tank through a pipeline; the mother liquor clarification zone of the lithium sulfate crystallizer is connected to one end of the mother liquor discharge pump through a pipeline; the other end of the mother liquor discharge pump is connected to the outside of the system through a pipeline; the lower part of the lithium sulfate crystallizer is connected to the discharge pump through a pipeline, and the other end of the discharge pump is connected to the thickener through a pipeline; the thickener is connected to the lithium sulfate centrifuge through a pipeline, and the lithium sulfate centrifuge is connected to the dryer through a pipeline; the dryer is connected to the packaging machine through a pipeline; the lithium sulfate centrifuge is also connected to the mother liquor tank through a pipeline;

[0020] The first gas-liquid separator is connected to the scrubber through management; a wire mesh demister is arranged inside the scrubber; a scrubber circulating pump is arranged outside the scrubber, and both ends of the scrubber circulating pump are respectively connected to the upper part and the bottom part of the scrubber to drive the liquid inside the scrubber to circulate; the scrubber is connected to the steam compressor through a pipeline, and the steam compressor is connected to the forced circulation heater through a pipeline, and a cooling and pressure reducing steam input pipeline is also connected to the pipeline between the steam compressor and the forced circulation heater for inputting the pressure reducing steam outside the system.

[0021] Furthermore, the condensate preheater is a plate heat exchanger; and the non-condensable gas preheater is a plate heat exchanger.

[0022] The present invention also provides an MVR evaporation crystallization method for crude lithium sulfate monohydrate, using the above-mentioned MVR evaporation crystallization system for crude lithium sulfate monohydrate, comprising the following process:

[0023] 1) The raw material liquid enters the condensate preheater through the feed pump for the first preheating, raising the temperature from 40°C to 90°C; then enters the non-condensable gas preheater for the second preheating, raising the temperature from 90°C to 92°C;

[0024] 2) The raw material liquid preheated twice enters the mother liquid tank from the non-condensable gas preheater, and then enters the lower circulation pipeline from the mother liquid tank through the mother liquid pump; then enters the forced circulation heater from the lower circulation pipeline; and then enters the first gas-liquid separator from the upper circulation pipeline after being heated in the forced circulation heater;

[0025] 3) The steam after the raw material liquid is heated in the first gas-liquid separator moves upward through the baffle demister and enters the scrubber; the concentrated mother liquor after the raw material liquid is heated in the first gas-liquid separator moves downward along the central circulation pipe, and the lithium sulfate in the concentrated mother liquor gradually crystallizes and settles at the bottom of the lithium sulfate crystallizer during the movement to form lithium sulfate slurry; the lithium sulfate slurry enters the thickener through the discharge pump for concentration; the concentrated lithium sulfate slurry enters the lithium sulfate centrifuge for centrifugation to separate the lithium sulfate crystals and the solution part, and the lithium sulfate crystals are dried in the dryer and then enter the packaging machine for packaging; the solution part returns to the mother liquid tank; the uncrystallized mother liquor moves upward along the outside of the central circulation pipe, and is discharged from the boundary area outside the mother liquor clarification area through the mother liquor discharge pump;

[0026] 4) The steam coming out of the scrubber passes through the wire mesh demister and then enters the steam compressor. The steam compressed by the steam compressor returns to the forced circulation heater. The scrubber circulation pump installed outside the scrubber can ensure the steam circulation.

[0027] 5) The outlet water of the non-condensable gas preheater enters the second gas-liquid separation tank, and then is discharged through the vacuum pump into the condensate network; the outlet water of the condensate preheater directly enters the condensate network; the condensate of the second gas-liquid separation tank enters the condensate tank, and the condensate of the forced circulation heater also enters the condensate tank.

[0028] The present invention is characterized in that:

[0029] In conventional designs, mother liquor is drawn out from the mother liquor after the centrifuge. At present, various types of centrifuges will have material penetration, resulting in the mother liquor discharged from the outside carrying more lithium sulfate particles, resulting in a decrease in the recovery rate of crystallized salt and affecting the subsequent operation. At the same time, the flushing operation of the centrifuge may also dilute the components of the mother liquor. In order to avoid taking mother liquor out of the centrifuged mother liquor, the present invention specially designs a clarification zone in the crystallizer clarification zone to reduce the system impurity salt rate and improve the product yield.

[0030] The evaporation crystallization system provided by the present invention directly mixes the preheated raw material with the centrifugal mother liquor. The concentration of the raw material is low, and the mother liquor is saturated and has fine permeation crystals. The purpose of mixing the raw material with the mother liquor is that the particle size of lithium sulfate is less than 200 mesh and the particle size is fine. The centrifuge permeation is serious and a small amount of crystals enter the mother liquor tank. Therefore, they are diluted with the raw material liquid and dissolved. At this time, when the mother liquor pump is used to return to the crystallizer, the system crystal nucleus will be reduced, thereby increasing the crystal particle size.

[0031] In the evaporation and crystallization system provided by the present invention, in the face of the situation that foam may be generated during the evaporation of lithium sulfate, the wire mesh demister designed in the scrubbing tower is used to remove foam, and the design of the gas-liquid separator can prevent the secondary steam from escaping from the liquid surface, thereby ensuring that the secondary steam condensate is clean and preventing alkali, salt and foam from entering the compressor.

[0032] According to the raw material characteristics, the boiling point of lithium sulfate will rise by 5-6°C during evaporation and crystallization. The compressor should be a centrifugal compressor with a temperature rise of 18°C. Since the raw material temperature is relatively low (40-45°C), it needs to be preheated before entering the evaporation feeding process.

[0033] In the evaporation crystallization system provided by the present invention, since the raw materials have been pre-treated to remove calcium and magnesium ions before entering the MVR evaporation crystallization system, the preheater can adopt a plate preheater with higher heat transfer performance, which can effectively reduce the preheating area and preheating steam volume.

[0034] The evaporation crystallization system provided by the present invention is driven by a steam compressor to form a heat energy cycle, and the generated steam can be recycled, with almost no energy waste, thereby achieving the purpose of energy saving and consumption reduction.

[0035] The beneficial effects of the present invention are:

[0036] The present invention provides an MVR evaporation crystallization system and an evaporation crystallization method for crude lithium sulfate monohydrate. The evaporation crystallization system adopts a long tube evaporator, the installed power of the device is small, and the failure rate of the equipment is low. The evaporation crystallization system provided by the present invention adopts a condensate preheater to preheat the raw materials, which can reduce the consumption of raw steam to achieve the purpose of saving energy. The flushing water or boiling water in the evaporation crystallization method provided by the present invention adopts high-temperature condensed water to ensure that the feed temperature is not reduced, so as to reduce the consumption of raw steam. The evaporation crystallization method provided by the present invention makes full use of the sensible heat of steam, saves the consumption of raw steam, and reduces the operating cost of the equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a schematic structural diagram of the MVR evaporation and crystallization system for crude lithium sulfate monohydrate provided by the present invention.

[0038] Figure 2 A cross-sectional view of a Pozidriv liquid distributor of an MVR evaporation and crystallization system for crude lithium sulfate monohydrate provided by the present invention.

[0039] Reference numerals

[0040] 1: Feed pump; 2: Condensate preheater; 3: Non-condensable gas preheater; 4: Mother liquor tank; 5: Mother liquor pump; 6: Forced circulation heater; 7: First gas-liquid separator; 8: Lithium sulfate crystallizer; 9: Discharge pump; 10: Thickener; 11: Lithium sulfate centrifuge; 12: Dryer; 13: Packaging machine; 14: Condensate pump; 15: Condensate tank; 16: Gas-liquid separator of steam washing tower; 17: Vacuum pump; 18: Mother liquor discharge pump; 19: Gas washing tower; 20: Gas washing tower circulation pump; 21: Steam compressor; 191: Wire mesh demister; 61: Upper circulation pipeline; 611: Pozidriv liquid distributor; 62: Lower circulation pipeline; 71: Baffle demister; 81: Central circulation pipe; A: Raw material pipeline outside the system; B: Condensate network outside the system; C: Condensate network outside the system; D: Outside the system; E: Cooling and pressure reduction steam outside the system. DETAILED DESCRIPTION

[0041] The embodiments of the present invention will be described in detail and comprehensively below so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more definite definition of the protection scope of the present invention.

[0042] The MVR evaporation crystallization system for crude lithium sulfate monohydrate provided by the present invention is as follows: Figure 1 As shown, it is composed of a feed pump 1, a condensate preheater 2, a non-condensable gas preheater 3, a lithium sulfate crystallizer 8, a vacuum pump 17, a first gas-liquid separator 7, a steam washing tower gas-liquid separator 16, a condensate pump 14, a condensate tank 15, a mother liquor discharge pump 18, a discharge pump 9, a mother liquor pump 5, a mother liquor tank 4, a thickener 10, a lithium sulfate centrifuge 11, a dryer 12, a packaging machine 13, a steam compressor 21, a gas washing tower 19, and a gas washing tower circulation pump 20;

[0043] Among them, the first gas-liquid separator 7 is arranged above the lithium sulfate crystallizer 8, and a baffle demister 71 is arranged on the upper part of the first gas-liquid separator 7; the upper part of the lithium sulfate crystallizer 8 is a mother liquor clarification zone, and the middle and lower parts are crystal growth zones; a central circulation pipe 81 is vertically arranged in the center of the lithium sulfate crystallizer 8; the top of the central circulation pipe 81 is connected to the bottom of the first gas-liquid separator 7; the side wall of the first gas-liquid separator 7 is connected to one end of a forced circulation heater 6 through an upper circulation pipe 61, and the upper circulation pipe 61 penetrates into the first gas-liquid separator 7, and a cross-shaped liquid distributor 611 is arranged at the end of the upper circulation pipe 61, such as Figure 2 The figure shows a cross-sectional view of a crisscross liquid distributor made of a stainless steel plate, wherein the circular dotted line in the figure indicates the end section of the upper circulation pipeline 61; the other end of the forced circulation heater 6 is connected to the mother liquor clarification zone of the lithium sulfate crystallizer 8 through a lower circulation pipeline 62;

[0044] One end of the feed pump 1 is connected to the raw material pipeline A outside the system through a pipeline, and the other end of the feed pump 1 is connected to the condensate preheater 2 through a pipeline, and the condensate preheater 2 is further connected to the non-condensable gas preheater 3 through a pipeline, and the condensate pump 14 and the condensate tank 15 are sequentially arranged between the shell side inlet of the condensate preheater 2 and the forced circulation heater 6, and are connected through pipelines; the shell side outlet of the condensate preheater 2 is connected to the condensate network B outside the system through a pipeline; the non-condensable gas preheater 3 is also connected to the forced circulation heater 6 through a pipeline; the non-condensable gas preheater 3 is connected to the steam washing tower gas-liquid separator 16 through a pipeline; the steam washing tower gas-liquid separator 16 is also connected to the vacuum pump 17 and the condensate tank 15 through pipelines respectively; the vacuum pump 17 is connected to the outside of the system through a pipeline Condensate pipe network C; the lower circulation pipe 62 is connected to the mother liquor pump 5 through a pipe, and the mother liquor pump 5 is connected to the mother liquor tank 4 through a pipe; the non-condensable gas preheater 3 is connected to the mother liquor tank 4 through a pipe; the mother liquor clarification zone of the lithium sulfate crystallizer 8 is connected to one end of the mother liquor discharge pump 18 through a pipe; the other end of the mother liquor discharge pump 18 is connected to the outside of the system D through a pipe; the lower part of the lithium sulfate crystallizer 8 is connected to the discharge pump 9 through a pipe, and the other end of the discharge pump 9 is connected to the thickener 10 through a pipe; the thickener 10 is connected to the lithium sulfate centrifuge 11 through a pipe, and the lithium sulfate centrifuge 11 is connected to the dryer 12 through a pipe; the dryer 12 is connected to the packaging machine 13 through a pipe; the lithium sulfate centrifuge 11 is also connected to the mother liquor tank 4 through a pipe;

[0045] The first gas-liquid separator 7 is connected to the scrubber 19 through management; a wire mesh demister 191 is arranged inside the scrubber 19; a scrubber circulating pump 20 is arranged outside the scrubber 9, and both ends of the scrubber circulating pump 20 are respectively connected to the upper and bottom parts of the scrubber 191, driving the liquid inside the scrubber 19 to circulate; the scrubber 19 is connected to the steam compressor 21 through a pipeline, and the steam compressor 21 is connected to the forced circulation heater 6 through a pipeline, and a cooling and reducing steam input pipeline 22 is also connected to the pipeline between the steam compressor 21 and the forced circulation heater 6 for inputting reduced-temperature and reduced-pressure steam E outside the system to supplement the insufficient steam in the system.

[0046] Example 1

[0047] This embodiment is implemented in a project in the Democratic Republic of the Congo. The raw material liquid is a crude lithium sulfate solution, and the specific composition is shown in Table 1.

[0048] Table 1 Composition of crude lithium sulfate solution

[0049]

[0050] Taking production fluctuations into consideration, equipment selection is based on 1.2 times the evaporation capacity.

[0051] The specific steps are:

[0052] 1) The raw material liquid enters the condensate preheater 2 through the feed pump 1 for the first preheating, raising the temperature from 40°C to 90°C; then enters the non-condensable gas preheater 3 for the second preheating, raising the temperature from 90°C to 92°C.

[0053] 2) The raw material liquid that has been preheated twice enters the mother liquid tank 4 from the non-condensable gas preheater 3, and then enters the lower circulation pipe 62 from the mother liquid tank 4 through the mother liquid pump 5; then enters the forced circulation heater 6 from the lower circulation pipe 62; and then enters the first gas-liquid separator 7 from the upper circulation pipe 61 after being heated by the forced circulation heater 6; wherein the flow rate is controlled to be 2m / s by the forced circulation pump.

[0054] The lower the flow rate in the pipe, the easier it is to scale. The scaling material unloading rate increases with the increase of flow rate. The scaling rate decreases with the increase of flow rate. However, too high flow rate in the pipe will affect crystal formation. Therefore, the forced circulation pump uses a large flow, low speed axial flow pump to control the flow rate in the pipe to reduce the scaling rate while reducing interference with the crystal formation process, so as to better form lithium sulfate crystals.

[0055] 3) The steam after the raw material liquid is heated in the first gas-liquid separator 7 moves upward through the baffle demister 71 into the scrubber 19; the concentrated mother liquor after the raw material liquid is heated in the first gas-liquid separator 7 moves downward along the central circulation pipe 81, and the lithium sulfate in the concentrated mother liquor gradually crystallizes and settles at the bottom of the lithium sulfate crystallizer 8 as it is oversaturated during the movement to form lithium sulfate slurry, and the lithium sulfate concentration in the slurry can reach 330g / L; the lithium sulfate slurry enters the thickener 10 for concentration through the discharge pump 9; the concentrated lithium sulfate slurry enters the lithium sulfate centrifuge 11 for centrifugation to separate the lithium sulfate crystals and the solution part, and the lithium sulfate crystals are dried by the dryer 12 and then enter the packaging machine 13 for packaging; the solution part returns to the mother liquid tank 4; the uncrystallized mother liquor moves upward along the outside of the central circulation pipe 81, and is discharged from the boundary area outside the mother liquor clarification area through the mother liquor discharge pump 18;

[0056] Among them, the baffle demister 71 set in the first gas-liquid separator and the wire mesh demister 191 set in the scrubber 19 are used to improve the gas-liquid separation efficiency and reduce the entrainment loss of mist and foam. In particular, the wire mesh demister 191 effectively prevents the corrosion of the steam compressor 21 and the adhesion of salt, and greatly improves the water quality of the condensed water. The secondary steam generated by evaporation enters the condenser for condensation after defoaming, and the conductivity of the final evaporated condensed water is ≤60us / cm.

[0057] In the above process, since the raw material liquid enters the first gas-liquid separator to release supersaturation after being heated by the forced circulation heater, the concentrated mother liquor containing lithium sulfate continuously precipitates lithium sulfate crystals due to the supersaturation of the mother liquor during the downward movement along the central circulation pipe, and reaches the bottom of the lithium sulfate crystallizer. The mother liquor passes through the crystal growth zone upward along the outside of the central circulation pipe, and the precipitated lithium sulfate crystals reversely pass through the mother liquor according to gravity, and precipitate downward to the bottom of the lithium sulfate crystallizer, and during the sinking process, the newly precipitated lithium sulfate tends to attach to the crystallized lithium sulfate as a crystal nucleus, and avoids attaching to the inner wall of the lithium sulfate crystallizer, thereby reducing the possibility of scaling on the inner surface of the lithium sulfate crystallizer and extending the cleaning cycle of the lithium sulfate crystallizer. The mother liquor running upward gradually becomes clear as the lithium sulfate crystals sink, and is discharged from the upper part of the lithium sulfate crystallizer through the mother liquor discharge pump. The lithium sulfate crystals deposited at the bottom of the lithium sulfate crystallizer are sucked out by the discharge pump, while avoiding the formation of scale in the tube after precipitation in the first circulation tube and the second circulation tube, which affects the heat transfer efficiency.

[0058] When lithium sulfate in the mother liquor is continuously crystallized and precipitated, the mother liquor in the mother liquor clarification area enters the lower circulation pipeline and finally returns to the first gas-liquid separator for gas-liquid separation, so that the sodium ions and other impurity ions in the mother liquor are continuously concentrated, and the sodium ion concentration is continuously increased, which will reduce the evaporation amount of the lithium sulfate system. At this time, it is necessary to discharge the mother liquor to reduce the enrichment concentration of sodium ions in the system.

[0059] 4) The steam from the scrubber 19 passes through the wire mesh demister 191 and enters the steam compressor 21, and the steam compressed by the steam compressor returns to the forced circulation heater; the scrubber circulating pump arranged outside the scrubber can ensure the steam circulation;

[0060] The wire mesh demister can remove the tiny droplets entrained in the steam. The steam compressor can raise the steam temperature by 18°C, converting the low-potential steam into high-potential steam, which is input into the shell side of the forced circulation heater to heat the internal mother liquor. The steam after heating the mother liquor is condensed into condensed water at about 113°C, enters the condensate tank, and enters the shell side of the condensate preheater through the condensate pump to preheat the raw liquid.

[0061] 5) The outlet water of the non-condensable gas preheater 3 enters the second gas-liquid separation tank 16, and then is discharged through the vacuum pump 17 into the condensate network; the outlet water of the condensate preheater 2 directly enters the condensate network; the condensate of the second gas-liquid separation tank 16 enters the condensate tank 15, and the condensate of the forced circulation heater 6 also enters the condensate tank 15.

[0062] The chemical composition of the prepared lithium sulfate product shall comply with the requirements of Table 2.

[0063] Table 2

[0064]

[0065] The product Li2SO4·H2O of this embodiment is tested to be white crystalline particles with fluidity and no visible inclusions. Its content meets the standards in Table 2.

[0066] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. An MVR evaporation crystallization system for crude lithium sulfate monohydrate, characterized in that: It consists of a feed pump, a condensate preheater, a non-condensable gas preheater, a lithium sulfate crystallizer, a vacuum pump, a first gas-liquid separator, a gas-liquid separator of a steam washing tower, a condensate pump, a condensate tank, a mother liquid discharge pump, a discharge pump, a mother liquid pump, a mother liquid tank, a thickener, a lithium sulfate centrifuge, a dryer, a packaging machine, a steam compressor, a gas washing tower, and a gas washing tower circulation pump; Wherein, the first gas-liquid separator is arranged above the lithium sulfate crystallizer, and a baffle demister is arranged on the upper part of the first gas-liquid separator; the upper part of the lithium sulfate crystallizer is a mother liquor clarification zone, and the middle and lower parts are crystal growth zones; a central circulation pipe is vertically arranged in the center of the lithium sulfate crystallizer; the top of the central circulation pipe is connected to the bottom of the first gas-liquid separator; the side wall of the first gas-liquid separator is connected to one end of the tube side of a forced circulation heater through an upper circulation pipeline, and the upper circulation pipeline goes deep into the first gas-liquid separator, and a cross-shaped liquid distributor is arranged at the end of the upper circulation pipeline; the other end of the tube side of the forced circulation heater is connected to the mother liquor clarification zone of the lithium sulfate crystallizer through a lower circulation pipeline, and a forced circulation pump is arranged on the lower circulation pipe; One end of the feed pump is connected to the raw material pipeline outside the system through a pipeline, and the other end of the feed pump is connected to the tube side inlet of the condensate preheater through a pipeline. The tube side outlet of the condensate preheater is then connected to the tube side inlet of the non-condensable gas preheater through a pipeline. The condensate pump and the condensate tank are sequentially arranged between the shell side inlet of the condensate preheater and the shell side of the forced circulation heater, and are connected through pipelines; the shell side outlet of the condensate preheater is connected to the condensate network outside the system through a pipeline; the shell side of the non-condensable gas preheater is also connected to the shell side of the forced circulation heater through a pipeline; the shell side outlet of the non-condensable gas preheater is connected to the gas-liquid separator of the steam washing tower through a pipeline; the gas-liquid separator of the steam washing tower is also connected to the vacuum pump and the condensate tank through pipelines respectively. The vacuum pump is connected to the condensate network outside the system through a pipeline; the lower circulation pipeline is connected to the mother liquor pump through a pipeline, and the mother liquor pump is connected to the mother liquor tank through a pipeline; the non-condensable gas preheater is connected to the mother liquor tank through a pipeline; the mother liquor clarification zone of the lithium sulfate crystallizer is connected to one end of the mother liquor discharge pump through a pipeline; the other end of the mother liquor discharge pump is connected to the outside of the system through a pipeline; the lower part of the lithium sulfate crystallizer is connected to the discharge pump through a pipeline, and the other end of the discharge pump is connected to the thickener through a pipeline; the thickener is connected to the lithium sulfate centrifuge through a pipeline, and the lithium sulfate centrifuge is connected to the dryer through a pipeline; the dryer is connected to the packaging machine through a pipeline; the lithium sulfate centrifuge is also connected to the mother liquor tank through a pipeline; The first gas-liquid separator is connected to the scrubber via a pipeline; a wire mesh demister is arranged inside the scrubber; a scrubber circulating pump is arranged outside the scrubber, and both ends of the scrubber circulating pump are respectively connected to the upper part and the bottom part of the scrubber to drive the liquid inside the scrubber to circulate; the scrubber is connected to the steam compressor via a pipeline, and the steam compressor is connected to the forced circulation heater via a pipeline, and a temperature-reducing and pressure-reducing steam input pipeline is also connected to the pipeline between the steam compressor and the forced circulation heater for inputting pressure-reducing steam outside the system.

2. The MVR evaporation and crystallization system for crude lithium sulfate monohydrate according to claim 1, characterized in that: The condensate preheater is a plate heat exchanger; the non-condensable gas preheater is a plate heat exchanger.

3. The MVR evaporation and crystallization system for crude lithium sulfate monohydrate according to claim 1, characterized in that: The forced circulation pump is an axial flow pump.

4. The MVR evaporation and crystallization system for crude lithium sulfate monohydrate according to claim 1, characterized in that: The static liquid column pressure of the upper circulation pipeline is greater than the steam pressure under the working pressure state.

5. A MVR evaporation crystallization method for crude lithium sulfate monohydrate, characterized in that: The MVR evaporation crystallization system using the crude lithium sulfate monohydrate as claimed in any one of claims 1 to 4 comprises the following process; 1) The raw material liquid is controlled at pH 8-9 and temperature 30-55°C. It enters the condensate preheater through the feed pump for the first preheating, raising the temperature from 40°C to 90±2°C; then enters the non-condensable gas preheater for the second preheating, raising the temperature from 90°C to 92±1°C; 2) The raw material liquid preheated twice enters the mother liquid tank from the non-condensable gas preheater, and then enters the lower circulation pipeline from the mother liquid tank through the mother liquid pump; then enters the forced circulation heater from the lower circulation pipeline; and then enters the first gas-liquid separator from the upper circulation pipeline after being heated in the forced circulation heater; 3) The steam from the raw material liquid heated in the first gas-liquid separator moves upward through the baffle demister and enters the scrubber; the concentrated mother liquor from the raw material liquid heated in the first gas-liquid separator moves downward along the central circulation pipe, and during the movement, the lithium sulfate in the concentrated mother liquor gradually crystallizes and settles at the bottom of the lithium sulfate crystallizer to form lithium sulfate slurry; the lithium sulfate slurry enters the thickener through the discharge pump for concentration; the concentrated lithium sulfate slurry enters the lithium sulfate centrifuge for centrifugation to separate the lithium sulfate crystals and the solution part, and the lithium sulfate crystals are dried in the dryer and then enter the packaging machine for packaging; the solution part returns to the mother liquid tank; The uncrystallized mother liquor moves upward along the outside of the central circulation pipe and is discharged from the system through the mother liquor discharge pump in the mother liquor clarification area; 4) The steam coming out of the scrubber passes through the wire mesh demister and then enters the steam compressor. The steam compressed by the steam compressor returns to the shell side of the forced circulation heater. The scrubber circulating pump installed outside the scrubber is used to ensure the cleanliness of the secondary steam generated. 5) Some non-condensed gas in the shell side of the forced circulation heater passes through the non-condensable gas preheater and is partially condensed before entering the second gas-liquid separation tank, where the gas and liquid are separated. The gas is then pumped out by a vacuum pump, and the condensed liquid is cached in the condensate tank.

6. The MVR evaporation crystallization method of crude lithium sulfate monohydrate according to claim 5, characterized in that: Step 2) The forced circulation pump is an axial flow pump, and the forced circulation pump controls the flow rate to be 1.8-2.5m / s.

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