A 10t/h MVR evaporator for sodium sulfate and lithium sulfate.

I. Project Overview

In the lithium battery industry chain, the evaporation and concentration of lithium sulfate solution and the recovery and treatment of byproducts such as sodium sulfate are crucial links in ensuring lithium salt quality and comprehensive resource utilization. This project is a supporting facility for a lithium battery material company, designed to process 10 t/h of a mixed sodium sulfate/lithium sulfate solution through evaporation and concentration. The raw material is sourced from the mother liquor recovery system in the battery-grade lithium carbonate production process.

The project requires the system to have continuous and stable operation capabilities, with an annual effective operating time of no less than 7200 hours. The concentrated solution must meet the feed requirements of downstream crystallization or drying processes, while simultaneously achieving the recycling of condensate.

II. Process Background and Challenges Analysis

2.1 Material Characteristics

The mixed solution processed in this project has the following characteristics:

Complex Composition: The solution contains both lithium sulfate and sodium sulfate. Their solubilities change differently with temperature, requiring the avoidance of co-crystallization or localized supersaturation leading to scaling.

Concentration Fluctuations: The concentration of incoming materials from upstream processes fluctuates due to production conditions, necessitating a wide load adjustment range for the system.

Corrosivity: The solution is weakly acidic (pH 4–6) and contains a small amount of sulfate ions, requiring corrosion-resistant equipment materials.

2.2 Technical Challenges

1. Salt Separation and Scale Prevention: Sodium sulfate has low solubility in low-temperature regions, easily precipitating and forming scale on heat exchange surfaces, affecting heat transfer efficiency and continuous operation cycle;

2. Load Adaptability: The 10t/h processing capacity needs to match fluctuations in the upstream mother liquor production, and the system needs to operate stably within a load range of 50%–110%;

3. Energy Consumption Control: Although the mother liquor processing capacity is less than the main production line, long-term energy consumption still needs to be effectively reduced through MVR technology;

4. Automated Operation and Maintenance: With limited on-site operators, the system requires a high degree of automation to reduce manual intervention.

III. Solution and Process Route

To address the above requirements, our company adopts an integrated process solution of "MVR forced circulation evaporation + online scale prevention," with the core process as follows:

3.1 Feed Pretreatment

After mechanical impurities are removed by a precision filter, the incoming mother liquor is pumped to the preheating system. The preheater utilizes the waste heat from the system's condensate to gradually raise the temperature of the feed, recovering low-grade heat energy.

3.2 MVR Forced Circulation Evaporation

The preheated solution enters the MVR forced circulation evaporator. The evaporator uses a vertical shell-and-tube heat exchanger. Driven by a circulating pump, the solution flows through the heated tube bundle at a high velocity, creating turbulent flow and effectively inhibiting sodium sulfate deposition and scaling on the tube walls. The secondary steam generated by evaporation is compressed and heated by a high-efficiency steam compressor and then reused as a heating source, forming a closed-loop thermal energy cycle.

3.3 Gas-Liquid Separation and Condensation

The concentrated liquid and secondary steam after evaporation undergo gas-liquid separation in a separator. The secondary steam is recycled by the compressor, and the condensate is collected and reused in the production system or discharged after meeting standards.

3.4 Concentrated Liquid Discharge

The lithium sulfate/sodium sulfate mixture concentrated to the target concentration is continuously discharged by a discharge pump and transported to the downstream crystallization or drying section for further processing.

IV. Key Equipment and Technical Parameters

Design Evaporation Capacity: 10 t/h

Feed Composition: Lithium sulfate + sodium sulfate mixed solution (concentration depends on front-end conditions)

Evaporation Process: MVR forced circulation evaporation

Separator Type: Vertical gas-liquid separator

Circulation Pump Type: Axial flow forced circulation pump

Steam Compressor: High-efficiency centrifugal/Roots steam compressor

Main Body Material: 2205 duplex steel / 316L stainless steel for flow parts

Evaporation Water Consumption per Ton: Approximately 30-40 kWh

Design Annual Operating Time: ≥ 7200 h

Load Adjustment Range: 50%-110%

Automation Control: PLC full-process automatic monitoring, online detection of key parameters

V. Project Highlights

5.1 Significant Energy Saving Effect

Adopting MVR mechanical vapor recompression technology, the latent heat of secondary steam is fully recovered and utilized. Compared with traditional single-effect evaporation, the overall energy saving rate can reach 50%-60%, significantly reducing steam consumption and operating costs.

5.2 Anti-scaling Design

The forced circulation evaporator, coupled with a reasonable circulation velocity (≥1.5 m/s), creates sufficient turbulence within the heating tubes, effectively inhibiting the deposition of salts such as sodium sulfate on the tube walls.

The system includes an online cleaning interface, supporting non-stop chemical cleaning and extending continuous operation cycles.

5.3 Strong Load Adaptability

Both the steam compressor and circulation pump are designed with variable frequency drives, automatically adjusting operating parameters according to fluctuations in feed concentration and output, maintaining stable evaporation efficiency within a load range of 50%–110%.

5.4 Reliable Materials

Key components such as the evaporator heating tubes, separator, and flow piping are made of 2205 duplex steel or 316L stainless steel, possessing excellent resistance to pitting and stress corrosion. The main equipment is designed for a service life of no less than 10 years.

5.5 High degree of automation 

The system is equipped with online monitoring instruments for temperature, pressure, liquid level, density and conductivity. The PLC control system realizes automatic feeding, automatic adjustment, automatic discharge and fault alarm. Daily operation and maintenance only requires inspection, which greatly reduces the labor intensity.

VI. Operational Results
Since its commissioning, the system has operated stably and reliably, with the following key indicators:

* Evaporation Capacity: Stably reaches the design load of 10t/h, with timely adjustment response to load fluctuations;

* Energy Consumption: Electricity consumption per ton of water evaporated is controlled within 30-40 kWh, meeting the energy efficiency expectations of the MVR system;

* Continuous Operation Cycle: With reasonable maintenance, the single-cycle continuous operation time meets the production cycle requirements of the lithium battery industry;

* Condensate Quality: The conductivity of the condensate meets the reuse standards, achieving the recycling of production water;

* Automation Level: The system achieves unattended automatic operation with a low failure rate and convenient maintenance.

VII. Conclusion
The successful implementation of this project demonstrates the applicability and economic efficiency of MVR evaporation technology in mother liquor recovery and by-product treatment in the lithium battery industry. The 10t/h processing capacity not only meets the actual needs of medium-capacity enterprises but also achieves the dual goals of energy saving, consumption reduction, and automated operation through MVR technology. Leveraging our accumulated engineering experience in the field of evaporation and concentration, our company provides customers with stable and reliable system solutions, helping lithium battery material production achieve efficient resource utilization and green manufacturing.