Plate Evaporators

Overview of Plate Evaporators

A plate evaporator is a high-efficiency evaporation device that uses metal plates as heat transfer elements. It achieves thin-film evaporation of liquids through narrow flow channels between the plates. Compared to traditional tubular evaporators, it has significant advantages such as compact structure, high heat transfer efficiency, and small footprint, and is widely used for concentrating heat-sensitive materials in the food, pharmaceutical, and chemical industries.

Main Types and Working Principles

1. Rising Film Plate Evaporator

Working Principle: The material enters from the middle of the lower end of the plate, is heated and boils in the flow channels between the plates, forming an upward-rising liquid film. The steam carries the liquid upward, and the vapor-liquid mixture is discharged from the upper outlet. Alternatively, heating steam enters from the upper end of the plate, flowing counter-currently with the material, and condensate is discharged from the lower end.

Features: High heat transfer efficiency, suitable for low-viscosity, easily foaming materials, but not suitable for high-viscosity liquids.

2. Falling Film Plate Evaporator

Working Principle: Material enters from both sides of the upper end of the plates, descends along the plate wall in a film form under gravity, and evaporates. The vapor-liquid mixture is discharged from the lower end. Heating steam enters from the middle of the upper end, flowing in the same direction as the material.

Features: Short residence time (suitable for heat-sensitive materials), energy consumption is 15%-20% lower than rising film evaporators, but requires high uniformity of liquid distribution.

3. Rising Film Plate Evaporator

Working Principle: Each group consists of 4 plates forming 4 flow channels. Material first flows in rising film in the first and second channels, then enters the third and fourth channels in falling film flow after passing through the plates, combining the advantages of both methods.

Features: Suitable for materials with large viscosity changes during evaporation, combining high heat transfer rate and short residence time.

4. Scraped (Stirred Thin Film) Plate Evaporator

Working Principle: Rotating scrapers force high-viscosity material to be evenly distributed on the heating plate surface to form a thin layer. Mechanical stirring enhances heat transfer and prevents coking and scaling. Features: Can handle materials with viscosities up to 50,000 cP with residence times of only a few seconds, but the equipment is expensive and maintenance is complex.

Material Selection

The plate material for plate evaporators needs to be selected based on the material characteristics:

Stainless steel (304/316L): Commonly used in the food and pharmaceutical industries; corrosion resistant and easy to clean.

Titanium: Resistant to highly corrosive media.

Nickel-based alloys: High temperature resistant and acid/alkali resistant.

PTFE (Polytetrafluoroethylene): Used in scraper systems; has extremely high corrosion resistance.

Epoxy resin coating: Commonly used in household refrigeration; improves corrosion resistance.

Sealing gasket materials include fluororubber (conventional) and PTFE (corrosion resistant).

Advantages and Disadvantages Comparison

Core Advantages of Plate Evaporators:

High heat transfer coefficient, small temperature difference requirement (effective operation with small temperature differences)

High product quality, no reflux required, short flow path, low liquid retention

Modular design, can be freely combined and expanded like "building blocks"

Easy to check heat transfer area, suitable for frequent cleaning scenarios

Main Limitations:

Large sealing gasket area, requires regular maintenance to prevent leakage

Pre-treatment (e.g., filtration) is required for high-viscosity materials and materials containing solids

Relatively limited pressure resistance, not suitable for high-pressure conditions

Application Areas

1. Food Industry: Dairy product concentration (milk concentration from 12% solids to 45%), fruit juice concentration (citrus juice), coffee extract concentration, syrup preparation, honey and jam processing

2. Pharmaceutical Industry: Vitamin production, gelatin concentration, traditional Chinese medicine extract concentration, separation of heat-sensitive drug components

3. Chemical Industry: Seawater desalination pretreatment, polymer monomer removal, solvent recovery, catalyst recovery, ethylene glycol recovery

4. Environmental Engineering: MVR (Mechanical Vapor Recompression) energy-saving systems, TVR (Thermal Vapor Recompression) systems, high-salinity wastewater treatment

5. Refrigeration Systems: Household refrigerators, commercial freezers, ice cream display cases, ice-making equipment

Plate evaporators, with their high efficiency, energy saving, and compact design, have become important equipment in modern evaporation processes, especially in fields requiring the protection of heat-sensitive components and pursuing high-quality products, where they possess irreplaceable advantages.