Forced-Circulation MVR Evaporator

1.Forced-Circulation Principle

In a forced-circulation evaporator, liquid is circulated through the heat exchanger tubes by a circulation pump at high velocity. This prevents crystallization, scaling, and fouling on the heat transfer surfaces, making it suitable for:

• High-viscosity liquids

• Heat-sensitive materials

• Solutions prone to scaling, fouling, or crystallization

Unlike natural circulation evaporators (which rely on density differences between the heated and unheated liquid), forced circulation provides stable, controlled flow, ensuring uniform heating and high heat transfer efficiency.

2.Structure and Components

A typical forced-circulation MVR evaporator consists of:

• Circulation pump – Ensures high flow velocity through the heating tubes.

• Heat exchanger (calandria or shell-and-tube) – Provides the surface for evaporation.

• Separator (flash chamber) – Separates vapor from the concentrated liquid.

• Mechanical vapor compressor – Compresses secondary steam to raise temperature and pressure for reuse.

• Demister – Removes entrained droplets to ensure clean vapor.

• Piping, valves, and control systems – For automation and process stability.

3.Working Process

• The feed liquid enters the circulation loop.

• The circulation pump forces liquid through the heat exchanger tubes.

• Secondary steam generated in the separator is drawn into the MVR compressor, where it is compressed to a higher temperature and pressure.

• The compressed vapor is then sent back to the heat exchanger shell side, serving as the heating medium.

• This vapor transfers heat to the circulating liquid, generating more vapor while conserving energy.

• The process continues until the desired concentration is reached, with product discharged from the bottom of the separator.

4.Advantages

Energy efficiency: Up to 90% lower steam consumption compared to conventional evaporators.

Stable operation: Forced circulation prevents scaling and maintains heat transfer efficiency.

Wide applicability: Handles viscous, corrosive, or crystallizing solutions.

Compact footprint: MVR reduces or eliminates the need for external boilers or cooling towers.

Environmentally friendly: Lower CO₂ emissions due to reduced energy demand.

5.Typical Applications

Food industry: Concentration of fruit juice, dairy, sugar, starch hydrolysates.

Pharmaceuticals: Extraction liquid concentration, recovery of solvents.

Chemical industry: Sodium sulfate, sodium chloride, caustic soda, ammonium salts.

Wastewater treatment: High-salinity or high-COD wastewater concentration and zero-liquid discharge (ZLD).

Desalination: Brine concentration and water recovery.

In short, a forced-circulation MVR evaporator is an energy-saving, efficient, and reliable evaporation system that combines mechanical vapor recompression with forced liquid circulation, making it especially suitable for challenging industrial applications where scaling, viscosity, or crystallization are issues.