Wipe Film Evaporators
Wiped Film Evaporators
Wiped film evaporators (also called thin film evaporators or agitated thin film evaporators) are high-performance, short-residence-time thermal separators designed for concentrating heat-sensitive, viscous, fouling-prone, or high-boiling-point liquids. A rotating wiper system continuously spreads the feed into a thin film on the heated inner wall, allowing rapid evaporation with minimal thermal degradation. They are widely used in pharmaceuticals, food & beverage, chemicals, essential oils, polymers, and wastewater treatment where product quality, high concentration ratios, or solvent recovery are critical.
System Design & Key Components
Wiped film evaporators consist of a vertical cylindrical vessel with a heated jacket (steam, thermal oil, or hot water). Inside, a central rotor with wiper blades (or rollers) rotates at moderate speed (100–500 RPM). The feed enters at the top, is spread into a thin film (~0.5–2 mm) on the heated wall, evaporates rapidly, and vapor exits the top while concentrate flows downward to the bottom discharge. Key components include:
- Heated evaporator body (jacketed cylinder)
- Rotor with wiper blades/rollers (PTFE, carbon, or stainless steel)
- Condenser (external or internal)
- Vacuum system (to lower boiling point)
- Feed distribution ring and bottom concentrate discharge
Wiped Film Evaporation Process
The continuous process follows these steps:
- Feed Introduction — Liquid feed enters at the top through a distribution ring or nozzle, forming a uniform film on the heated wall.
- Thin Film Formation — Wiper blades continuously spread and agitate the liquid into a thin, turbulent film, enhancing heat transfer and preventing fouling.
- Rapid Evaporation — Solvent evaporates quickly due to high heat flux and low film thickness; vapor rises to the top.
- Vapor Separation — Vapor is separated from entrained liquid droplets via centrifugal force or a mist eliminator and exits to the condenser.
- Concentrate Discharge — Concentrated liquid flows downward along the wall and is discharged at the bottom.
- Condensation & Vacuum — Vapor is condensed (often under vacuum) to recover solvent or heat; vacuum lowers boiling point and protects heat-sensitive products.
Comparisons
| Feature | Wiped Film Evaporator | Falling Film Evaporator |
|---|---|---|
| Residence Time | Very short (seconds to minutes) | Short (minutes) |
| Heat Sensitivity | Excellent (minimal exposure) | Good |
| Fouling Tendency | Very low (continuous wiping) | Moderate (can foul at low flow) |
| Viscosity Handling | High viscosity & fouling products | Low to moderate viscosity |
| Energy Efficiency | High (short contact) | High |
| Best For | Heat-sensitive, viscous, fouling, high-value products | Clean, low-viscosity, high-volume evaporation |
| Feature | Wiped Film Evaporator | Forced Circulation Evaporator |
|---|---|---|
| Residence Time | Very short | Longer (due to recirculation) |
| Fouling Handling | Excellent (wiping action) | Excellent (high velocity) |
| Viscosity Limit | Very high (up to 100,000 cP) | High (up to 10,000–50,000 cP) |
| Energy Use | Moderate (mechanical wiping) | Higher (recirculation pump) |
| Best For | Heat-sensitive, high-viscosity, fouling products | High-viscosity, scaling/crystallizing solutions |
Typical Operating Parameters
| Parameter | Typical Range | Notes |
|---|---|---|
| Evaporation Rate | 1–50 kg/h per m² of heating surface | Scales with rotor size |
| Operating Temperature | 40–200 °C | Low under vacuum for heat-sensitive |
| Operating Pressure | 0.001–1 bar (deep vacuum to atmospheric) | Vacuum lowers boiling point |
| Residence Time | 5–60 seconds | Extremely short → minimal degradation |
| Rotor Speed | 100–500 RPM | Controls film thickness & turbulence |
| Viscosity Handling | Up to 100,000 cP or higher | Excellent for viscous/pasty products |
Common Applications & Advantages
| Industry / Application | Typical Process | Primary Goal |
|---|---|---|
| Pharmaceuticals | API concentration, solvent recovery | Gentle handling of heat-sensitive compounds |
| Food & Beverage | Essential oils, fruit extracts, monoglycerides | High-quality concentrate, flavor preservation |
| Chemicals | High-boiling solvents, polymers, resins | Concentration, solvent recovery |
| Biotechnology | Fermentation broth concentration | Product concentration without degradation |
| Wastewater / ZLD | Brine concentration, solvent stripping | Volume reduction, water recovery |
Key Advantages of Wiped Film Evaporators
- Extremely short residence time — minimal thermal degradation
- Handles high-viscosity, fouling, and heat-sensitive products
- Continuous operation with high evaporation rates
- Excellent fouling resistance due to continuous wiping
- High concentration ratios possible in one pass
- Low hold-up volume — fast startup/shutdown
Also check out, "Falling Film Evaporators"