It is recommended to use MVR evaporation (or triple-effect evaporation) and continuous crystallization production processes for lithium sulfate evaporation and concentration. This complete set of equipment mainly processes the pure lithium sulfate solution obtained after extraction and impurity removal. The purpose of lithium sulfate evaporation and concentration is to achieve a supersaturated state after high-temperature evaporation and dehydration. The evaporated and concentrated saturated solution enters the continuous crystallization system to produce lithium sulfate crystal products; the lithium sulfate evaporation and concentration system equipment is installed and arranged in the workshop, and the factory building and platform adopt a steel structure.

1. Medium parameters (based on a feed flow rate of 5.5 t/h)

2. Capacity design: The feedstock feed rate of the lithium sulfate evaporation and concentration system is 7.32 m³/h (excluding the return of mother liquor). The device design requires an evaporation capacity of no less than 5.5 T/h. The evaporation system can operate normally under a load of 70% to 100% of the design evaporation capacity.

3. Detailed technical requirements:

1) The evaporation and concentration processes both adopt MVR evaporation (or triple-effect evaporation), and the crystallization process adopts continuous crystallization;

2) Secondary condensate water requirements

3) A reasonably designed crystallization system can temporarily store lithium sulfate slurry produced by the system for no less than 14 hours, for centralized centrifugal drying in the subsequent daytime shift;

4) Except for normal maintenance, shutdown, or planned maintenance, the equipment can operate continuously and stably 24 hours a day, all year round, under humid and acidic conditions.

5) Devices and measures to prevent material blockage in the pipelines from the evaporator outlet to the continuous crystallizer, from the crystallizer to the thickener, and from the thickener to the centrifuge shall be designed separately.

6) Equipment design and operation requirements:

(1) Requires 24-hour operation daily, with an annual operating rate of no less than 8000 hours, and equipped with an operating timer;

(2) Design life: The main equipment is no less than 10 years (the main equipment mainly refers to the evaporator, heat exchanger, separator, compressor, crystallizer, thickener, and pipelines between them);

(3) All lithium sulfate solution flow parts and evaporator shell sides in the lithium sulfate MVR (or triple-effect evaporation) evaporation and concentration system use 2205 material.

Process flow and description of MVR equipment: Turn on the raw material liquid feed pump to allow the material to enter the evaporator after passing through the preheater. The material level rises under the action of the feed pump; when the liquid level rises to the design value, turn on the circulation transfer pump for circulation, and the material in the evaporator is controlled by the liquid level meter; at this time, turn on the live steam valve to allow live steam to enter the compressor for sealing, and turn on the compressor to compress the steam to increase the temperature for heat exchange with the material in the heater, and then condense into condensate. After the material reaches the boiling point temperature, it enters the evaporator for flash evaporation, and the water is continuously vaporized into water vapor. The secondary steam is continuously extracted and compressed by the compressor; the liquid level decreases due to the discharge, at which time the material is automatically replenished into the evaporator under the action of the feed pump controlled by the liquid level meter and the connected material pipe. The replenishment speed of the material is controlled by the liquid level meter, thereby achieving the purpose of automatically controlling the liquid level of each effect in the evaporator.

1. Introduction to Lithium Sulfate Triple-Effect Evaporation and Concentration Process

1) In actual industrial production, the evaporation amount of lithium sulfate solution is large, and the concentration is low. The evaporation endpoint generally requires a concentration lower than the saturation concentration. Considering the comprehensive operating costs and one-time investment, the evaporation and concentration process generally selects a quadruple-effect falling film evaporator with high evaporation intensity, high heat transfer coefficient, and low power consumption for evaporation and concentration operations; Shanghai Qike Environmental Protection Equipment Engineering Co., Ltd. has designed a superior evaporation and concentration technical solution based on the actual evaporation situation of lithium sulfate solution.

(1) Following the principle of effective energy utilization, the raw material liquid is preheated by a condensate preheater before entering the first-effect evaporation device for concentration. The concentrated liquid is fed to the second-effect evaporation device for further concentration by the first-effect circulation pump. The concentrated liquid is fed to the third-effect evaporation and concentration device for further evaporation and concentration by the second-effect circulation pump; the concentrated liquid is fed to the fourth-effect evaporation and concentration device by the third-effect circulation pump to complete the evaporation and concentration operation; the concentrated finished liquid is fed to the next process by the fourth-effect discharge pump.

(2) Steam and condensate flow: Live steam from the steam cylinder enters the shell side of the first-effect heating chamber to exchange heat with the solution in the tube side and condense. The condensate enters the condensate preheater to preheat the raw materials and then returns to the boiler room; the secondary steam generated during the evaporation process in the first-effect separation chamber enters the shell side of the second-effect heating chamber to exchange heat with the solution in the tube side and condense. The condensate enters the third-effect heating chamber to heat the material; the secondary steam generated during the evaporation process in the second-effect separation chamber enters the shell side of the third-effect heating chamber to exchange heat with the material in the tube side and condense. The condensate enters the fourth-effect heating chamber to heat the material; the secondary steam generated during the evaporation process in the third-effect separation chamber enters the shell side of the fourth-effect heating chamber to exchange heat with the material in the tube side and condense. The condensate enters the condensate tank and is discharged by the condensate pump; the secondary steam generated during the evaporation process in the fourth-effect separation chamber enters the indirect condenser for condensation, and the condensate enters the condensate tank. Non-condensable gas is extracted by a vacuum pump and discharged into the atmosphere.

2) Introduction to triple-effect falling film evaporator:

(1) A triple-effect falling film evaporator is a highly efficient membrane-type evaporation device. It features high heat transfer efficiency, low temperature difference loss, short material heating time, and small equipment volume. Its working principle is to add the feed liquid from the upper header of the heating chamber. After passing through the liquid distribution and film-forming device, it is evenly distributed into each heat transfer tube. Under the action of gravity, vacuum induction, and airflow, it flows downwards in a uniform film; during the flow process, it is heated and vaporized by the shell-side heating medium. The generated steam and liquid phase enter the separation chamber of the evaporator together. After sufficient separation of gas and liquid, the steam enters the next effect evaporator as a heating medium, and the liquid phase is discharged from the separation chamber.

(2) The liquid distributor is a key component of the falling film evaporator. The heat exchange intensity and production capacity of the falling film evaporator are essentially determined by the uniformity of the liquid distribution along the heat transfer tube; the so-called uniform distribution not only means that the liquid must be evenly distributed into each tube, but also evenly distributed along the entire periphery of each tube and maintain its uniformity over the entire length of the tube. When the liquid cannot uniformly wet the inner surface of all heating tubes, the surface with insufficient liquid may become scaled due to drying. The scaled surface, in turn, hinders the flow of the liquid film, thus further deteriorating the heat transfer conditions in the nearby area.