Unveiling the Anti-fouling Design of Evaporators—The Synergy of Flow Rate, Surface Shear, and Circulation Mode

In the operation of evaporation systems such as MVR evaporators, scaling problems severely affect equipment efficiency, operating cycle, and energy consumption. Especially in the processing of materials with high salt, high hardness, and high organic content, anti-scaling design becomes crucial for the successful application of evaporators. The synergistic effect of flow rate, surface shear force, and circulation method is the core technological key to solving the scaling problem in evaporators.

I. Scale Formation Mechanism and Hazards

• Formation Mechanism: During evaporation, dissolved salts, organic matter, colloids, etc., reach supersaturation as their concentration increases, precipitating crystals or forming an adhesion layer that adheres to the heat exchange surface, forming scale.

• Hazards: Scale reduces heat transfer efficiency, increases energy consumption, and in severe cases, leads to equipment blockage, corrosion, frequent shutdowns for cleaning, and shortens equipment lifespan.

II. Core Elements of Anti-Scale Design—Flow Rate, Surface Shear, and Circulation Mode

1. Flow Rate Control—Scrubbing and Crystallization Inhibition

• High-speed fluid scouring: Increasing the flow rate of the material within the heat exchange tubes/plates enhances the fluid scouring effect, reducing the residence and adhesion of crystals or impurities on the surface.

• Optimizing the Flow Rate Range: Too low a flow rate easily leads to deposition, while too high a flow rate increases pressure loss and energy consumption. An economical and reasonable flow rate should be designed based on material characteristics, particle size, viscosity, etc. (e.g., forced circulation evaporation typically uses 1.5-3 m/s).

• Flow Rate Uniformity: Preventing localized dead zones caused by excessively low flow rates; optimizing the flow channel structure to ensure a uniform flow field distribution.

2. Surface Shear Force – Peeling and Anti-Adhesion

• Enhanced Shear Force: High-velocity fluids generate significant shear force on the heat exchange surface, effectively peeling away microcrystals or sticky impurities that are about to deposit, inhibiting scale formation.

• Optimized Surface Structure: Surface structure designs such as grooves, corrugations, and spirals enhance heat exchange and shear force, improving fluid turbulence and self-cleaning capabilities.

• Material Selection: Smooth, hydrophilic, and corrosion-resistant heat exchange surfaces (such as titanium, duplex steel, and Teflon coating) reduce adhesion and improve anti-fouling performance.

3. Synergistic Circulation Methods – Forced Circulation Combined with Falling/Rising Film

• Forced Circulation Design: Suitable for high-concentration, high-viscosity materials with a high tendency to foul. Driven by a high-flow-rate circulation pump, it ensures high-speed material circulation, inhibiting localized supersaturation and deposition.

• Crystallizing materials often use external circulation or flash tank designs, ensuring that crystallization mainly occurs within the separator or crystallizer, protecting the heat exchange surface.

• Synergistic Effect of Falling/Rising Film Evaporation: Falling film evaporation features a thin liquid film, high flow rate, and high shear force, which is beneficial for inhibiting scaling; rising film evaporation has strong gas-liquid two-phase flow turbulence, resulting in good flushing effect.

• Combined with forced circulation, the advantages of each are leveraged to improve both heat transfer efficiency and anti-scaling capability.

• Optimized Circulation Path: A rational layout of the feed, circulation, and separation flow paths avoids dead zones and short circuits, achieving efficient circulation and timely separation.

III. Synergistic Optimization and Engineering Practice Cases

Case 1: MVR Forced Circulation Anti-Scale Design for High-Salinity Wastewater

A high-speed forced circulation pump (flow rate 2.5 m/s), combined with titanium heat exchange tubes and a corrugated surface structure, significantly enhances surface shear force.

Optimized circulation path with no dead zones ensures that crystallization mainly occurs in the separation chamber, resulting in no significant scaling on the heat exchange tube surface during long-term operation, extending the cleaning cycle to 3-6 months.

Case Study 2: Application of Falling Film Evaporators in Dairy Concentration Falling film evaporation involves a thin liquid film flowing at high speed over a smooth stainless steel heat exchange surface. The strong surface shear force prevents milk protein and salt from adhering.

Combined with online CIP automatic cleaning, it ensures stable operation, low energy consumption, and high product quality.

IV. Auxiliary Anti-fouling Measures

Pretreatment: Softening, hardening removal, and flocculation filtration remove easily fouling ions and impurities.

Chemical Scale Inhibition: Adding scale inhibitors and dispersants inhibits crystal growth and aggregation.

Online Cleaning (CIP): Regular automatic cleaning ensures long-term stable operation.

Intelligent Monitoring: Real-time monitoring of temperature difference, pressure drop, and heat transfer coefficient changes provides early warning of fouling trends and dynamically optimizes operating parameters.

V. Summary 

The key to anti-fouling design of evaporators lies in the synergistic optimization of flow rate, surface shear force, and circulation mode. By using high-speed fluid flushing, enhanced surface shear, and appropriate circulation mode selection, combined with material optimization and pretreatment, online cleaning, and other auxiliary measures, the risk of fouling can be significantly reduced, and the operating efficiency and stability of the evaporator can be improved. In the future, with the development of surface engineering, fluid dynamics simulation and intelligent control technologies, the anti-fouling performance of evaporators will continue to improve, helping to achieve efficient, energy-saving and long-cycle operation of evaporation treatment for difficult materials.