Tubular triple-effect evaporator

1. Core Concept Explanation: What is a "Tube-Type" Evaporator?

A "tube-type" evaporator refers to an evaporator whose heating chamber uses a shell-and-tube structure. This is the heart of the evaporator, its function being to provide the heat required for material evaporation.

Basic Structure: It consists of a large shell and an internal bundle of parallel heat transfer tubes.

Working Principle: Typically, heating steam or secondary steam from the pre-effect condenses in the shell side, releasing a large amount of latent heat; while the material to be evaporated flows through the tubes in the tube side, absorbing heat and experiencing a temperature increase or partial vaporization.

Material Selection: Depending on the corrosiveness and scaling tendency of the material, heat transfer tubes can be made of 316L stainless steel, 2205/2507 duplex stainless steel, titanium, Hastelloy, etc.

Triple-effect evaporation refers to connecting three such tube-type evaporator units in series according to a specific flow pattern (co-current, counter-current, and parallel flow) to achieve three-stage reuse of thermal energy.

2. Working Principle and Process 

The working principle of a tubular triple-effect evaporator is based on a combination of multi-effect evaporation and tubular heat exchange. Its energy-saving core lies in the reuse of secondary steam.

Taking a common co-current process as an example:

First-Effect Evaporation: Live steam enters the shell side of the first-effect heating chamber, condensing and releasing heat. The material passes through the tube side and is heated to boiling. At this time, the first effect operates at a relatively high temperature/pressure.

Secondary Steam Transfer: The secondary steam generated by the first-effect evaporation is introduced into the shell side of the second-effect heating chamber, serving as a heat source for the second effect.

Second and Third-Effect Evaporation: The concentrate from the first effect enters the second effect under pressure differential. Because the operating pressure of the second effect is maintained lower through a vacuum system, the boiling point of its material is also lower, so the secondary steam from the first effect is sufficient to make it boil. This process is repeated between the second and third effects, with the secondary steam from the second effect serving as a heat source for the third effect.

Condensation and Discharge: The secondary steam generated by the third effect enters the final-effect condenser and is completely condensed by cooling water. After being concentrated in three stages, the material reaches the desired concentration and is discharged from the system by a discharge pump.

3. Technical Features of Falling Film Tubular Triple-Effect Evaporator:

High Heat Transfer Efficiency: Thin liquid film, high turbulence, and large heat transfer coefficient.

Short Residence Time: Material passes through in a single pass, suitable for heat-sensitive materials such as juice, milk, biological products, and pharmaceuticals.

Low Static Liquid Column: No boiling point elevation due to liquid column static pressure, resulting in a large effective temperature difference.

High Scale Prevention Requirements: Suitable for clean or lightly scaled materials, requiring a rapid CIP cleaning system.

Core Component: The precision distributor is crucial for success; it must ensure uniform film distribution in each tube to prevent dry wall scaling.