Plate Evaporator
Plate Evaporators
Plate evaporators are compact, highly efficient thermal separators that concentrate solutions using plate heat exchangers instead of traditional tube bundles. The feed liquid flows through channels between plates while heating medium (steam or hot water) flows in alternating channels, causing rapid evaporation. Plate evaporators offer superior heat transfer, small footprint, low hold-up volume, and easy maintenance — making them ideal for heat-sensitive, viscous, or fouling-prone products in food, dairy, pharmaceuticals, chemicals, and wastewater applications.
System Design & Key Components
Plate evaporators use gasketed or welded plate packs (typically stainless steel) arranged in a frame. Key components include:
- Plate pack with alternating product and heating channels
- Product inlet/outlet nozzles and distribution system
- Heating medium inlet/outlet (steam/hot water)
- Vapor-liquid separator (cyclone or baffle type) for phase separation
- Condenser and vacuum system (for low-temperature operation)
- Frame with tightening bolts for easy disassembly and cleaning
Plates are corrugated to enhance turbulence and heat transfer. Gasketed designs allow easy plate replacement; welded designs handle higher pressures/temperatures.
Plate Evaporation Process
The continuous process follows these steps:
- Feed Entry & Distribution — Liquid feed enters the plate pack and flows through product channels in a thin layer.
- Heating & Evaporation — Heating medium in adjacent channels transfers heat through the plates; solvent evaporates rapidly from the product side.
- Two-Phase Flow — Vapor bubbles form and mix with the liquid, creating high turbulence and excellent heat transfer.
- Separation — Vapor-liquid mixture exits the plate pack into a separator where vapor is disengaged and routed to the condenser.
- Concentrate Discharge — Concentrated liquid collects and is discharged; part may be recirculated for higher concentration ratios.
- Condensation & Vacuum — Vapor is condensed (often under vacuum) to recover solvent or heat; vacuum lowers boiling point and protects heat-sensitive products.
Comparisons
| Feature | Plate Evaporator | Falling Film Evaporator |
|---|---|---|
| Heat Transfer Coefficient | Extremely high (4,000–6,000 W/m²·K) | High (2,000–5,000 W/m²·K) |
| Residence Time | Very short (seconds) | Short (seconds to minutes) |
| Fouling Tendency | Low to moderate (high turbulence) | Low (thin film flow) |
| Footprint | Very compact | Moderate (tall tubes) |
| Maintenance | Easy plate pack disassembly | Tube cleaning required |
| Best For | Heat-sensitive, viscous, space-limited | Heat-sensitive, clean to moderate fouling |
| Feature | Plate Evaporator | Forced Circulation Evaporator |
|---|---|---|
| Residence Time | Very short | Longer (recirculation) |
| Fouling Handling | Good (high turbulence) | Excellent (high velocity) |
| Viscosity Limit | Moderate to high | Very high |
| Energy Use | Low (no recirculation pump) | Higher (pump energy) |
| Footprint | Very compact | Larger (recirculation loop) |
| Best For | Heat-sensitive, compact installations | High-viscosity, scaling/crystallizing solutions |
Typical Operating Parameters
| Parameter | Typical Range | Notes |
|---|---|---|
| Evaporation Rate | 1–50 tons water/h | Scales with plate area and number of plates |
| Operating Temperature | 40–120 °C | Low under vacuum for heat-sensitive |
| Operating Pressure | 0.05–2 bar (vacuum to atmospheric) | Vacuum common |
| Residence Time | Seconds to minutes | Short due to thin channels |
| Heat Transfer Coefficient | 3,000–6,000 W/m²·K | Very high due to corrugated plates and turbulence |
| Viscosity Limit | Up to 10,000–20,000 cP | Handles higher viscosities than falling film |
Common Applications & Advantages
| Industry / Application | Typical Process | Primary Goal |
|---|---|---|
| Food & Beverage | Juice, milk, sugar syrup concentration | Gentle concentration, flavor preservation |
| Dairy | Milk evaporation, whey concentration | High-quality concentrate for powder |
| Pharmaceuticals | API solutions, herbal extracts | Minimal thermal degradation |
| Chemicals | Brine, organic solutions | Efficient solvent removal |
| Wastewater / ZLD | Brine minimization | Water recovery, volume reduction |
Key Advantages of Plate Evaporators
- Extremely high heat transfer coefficients and compact size
- Short residence time — excellent for heat-sensitive products
- Easy disassembly and CIP cleaning
- Low hold-up volume — fast startup/shutdown
- Handles moderate viscosity and fouling better than falling film
- Energy efficient in multi-effect or MVR configurations
Also check out, "Rising Falling Film Evaporator"