What are the types of concentrated brine evaporation and crystallization devices?

Concentrated brine evaporation and crystallization devices come in various types, which can be classified according to four dimensions: "evaporator type," "crystallization method," "steam utilization method," and "whether membrane technology is coupled." The mainstream types currently available in the domestic market, commercially viable, and expected to operate stably around 2025 are summarized as follows:

I.Classification by Evaporator Structure

1.Single-Effect Evaporator: The simplest structure, utilizing fresh steam in a single pass, with a steam consumption of approximately 1 ton of water. Suitable for small water volumes (≤3 t/h) or scenarios where enterprises have inexpensive waste heat/low-pressure waste steam.

2.Multi-Effect Evaporator: 3–8 effects connected in series, with subsequent effects utilizing secondary steam from previous effects, producing 0.25–0.35 t of steam per ton of water. Moderate investment, high operational stability, and a mainstay device for early zero-emission projects.

3.MVR Evaporator: Centrifugal/Roots compressors heat secondary steam to 18–25℃ for reuse, consuming only 25–35 kWh of electricity per ton of water, requiring almost no fresh steam. Evaporation capacities of 1–150 t/h are modular, making them the preferred energy-saving solution for capacities >5 t/h.

4.Falling/Rising Film Evaporator: The feed liquid forms a film inside a vertical tube, resulting in a high heat transfer coefficient and small footprint; when coupled with an MVR, power consumption per ton of water can be further reduced by 10–15%. Suitable for low-viscosity, non-scaling concentrated brine, such as NaCl-type desulfurization wastewater.

5.Forced Circulation Evaporator: High flow velocity (2–4 m/s) washes the heating surface, providing strong anti-scaling ability; often combined with an MVR and crystallizer for high-solids, easily crystallizing sodium sulfate and phosphoric acid wastewater.

II.Classification by Crystallization Section Type

1.DTB (DraftTube & Baffle) Crystallizer: Built-in guide tube + annular settling zone, adjustable particle size 0.6–1.2 mm, high capacity, suitable for fractional crystallization of sodium chloride and sodium sulfate.

2.SL (Krystal) Fractional Crystallizer: Crystals grow in suspension within the fractionating legs, resulting in low mother liquor supersaturation and more uniform product particle size. Commonly used for high-purity industrial salts.

3.Forced Circulation Flash Crystallizer: Flash cooling + external circulation heating, suitable for heat-sensitive materials or systems requiring two-stage crystallization (e.g., MgS₄·7H₂).

4.Surface Cooling/Vacuum Cooling Crystallizer: Heat is removed via vacuum or plate heat exchangers. No evaporation section; can be connected in series with an evaporation unit to reduce the final mother liquor volume.

III.Classification by Steam/Heat Source Utilization Method

1.Fresh Steam Multi-Effect Crystallizer: Driven by boiler steam, high energy consumption but no need for a high-power motor, suitable for northern industrial parks with high electricity prices and low steam prices.

2.MVR Electric Compression Type (Mainstream): Fully electric drive, can be coupled with photovoltaic, off-peak electricity, and in-plant waste heat power generation, with the lowest operating cost and smallest footprint.

3.TVR (Thermal Vapor Recompression) + Multi-Effect Hybrid Type: Utilizes high-pressure fresh steam to induce secondary steam, with lower power consumption than MVR, but still requires approximately 30% fresh steam. Suitable for plants with steam pressure ≥ 0.6 MPa.

4.Low-Temperature Heat Source Membrane Distillation-Crystallization Coupling Device: 40–70℃ hot water/waste heat + hydrophobic microporous membrane. Membrane distillation concentration is performed first, followed by salt precipitation in a crystallizer. Power consumption is 8–15 kWh per ton of water. Currently, this is mostly in the demonstration stage.

IV.Classification by Integrated "Membrane + Evaporation Crystallization" Process

1.NF (Nanofiltration) Salt Separation + MVR Evaporation Crystallization: First separates divalent/monovalent salts, then feeds them separately into the evaporator, obtaining NaCl and Na₂S₄ with a purity > 97% and a miscellaneous salt rate < 5%.

2.High-Pressure R/DTR Ultimate Concentration + Evaporation Crystallization: Concentrates TDS from 50,000 mg/L to 180,000–220,000 mg/L, a 70% reduction, before feeding it into the evaporator, significantly reducing evaporation investment.

3.Forward Osmosis (F) + Membrane Distillation (MD) + Crystallization: Concentrates TDS at ambient temperature and pressure using F, then recovers the driving liquid using MD and crystallizes. Suitable for temperature-sensitive or high-CD pharmaceutical wastewater.

V.Specialized Devices for Special Scenarios

1.Flue Gas Waste Heat Spray Drying-Crystallization Tower: Utilizes 150–200℃ flue gas to directly atomize concentrated brine. After water evaporation, salt dust is collected by a dust collector, resulting in no liquid discharge. Low investment but lower salt quality.

2.Solar Energy/Interfacial Evaporation-Crystallization Floating Device: A carbon-based photothermal film floats on the surface of a water tank, evaporating under sunlight. Crystallization occurs at the bottom. Suitable for water- and power-deficient mining areas or islands. Processing capacity is generally <1 t/d.

3.Freezing Crystallizer: The temperature is first lowered to −5–5℃. Utilizing the low-temperature crystallization characteristics of Na₂S₄, Glauber's salt and NaCl are separated. It is often combined with the evaporation section to reduce energy consumption and increase the added value of the salt.

VI.Summary of Selection Points

1.Water volume <3t/h, abundant steam – select single-effect or multi-effect crystallizers;

2.Water volume 5–100t/h, reasonable electricity price – MVR forced circulation is preferred;

3.High requirements for crystal particle size and purity – use DTB/SL crystallizers;

4.Contains divalent/monovalent mixed salts and requires resource recovery – first use NF for salt separation, then dual evaporation lines;

5.Has low-temperature waste heat or flue gas – consider falling film + TVR, membrane distillation, or flue gas spray drying.

All of the above-mentioned devices have been industrialized in domestic coal chemical, power plant desulfurization, lithium battery wastewater, metallurgical and chemical industrial parks. Enterprises can choose the "single technology" or "coupled process" route according to water quality, heat source/power source structure, salt resource utilization goals and one-time investment budget to achieve the goals of "reduction-crystallization-resource utilization" and "zero emission" of concentrated brine.