Triple-effect forced circulation evaporator

Core Concepts and Working Principles

1. Multi-Effect Evaporation: Its core is the cascade utilization of energy. Live steam (primary energy) first enters the heating chamber of the first effect, heats the material, and then condenses into water. The secondary steam generated in the first effect is then introduced into the heating chamber of the second effect as a heat source, and so on. In this way, 1 ton of live steam can evaporate approximately 3 tons of water, significantly improving thermal energy utilization.

2. Forced Circulation: Unlike natural circulation, it uses a high-flow-rate circulation pump between the evaporation chamber and the heating chamber of each effect. This pump forces the material to flow through the heating tubes at a high velocity (typically 1.5~3.5 m/s), resulting in two key effects:

Inhibition of Scaling and Crystallization: The high-speed material flow washes over the tube walls, greatly reducing solute deposition and scaling on the heating surface.

Enhanced Heat Transfer: The high flow velocity disrupts the laminar boundary layer of the tube walls, enhancing turbulence and improving the heat transfer coefficient.

Main Components of the System

• A typical triple-effect forced circulation evaporation system includes:

• Heating Chamber: A shell-and-tube heat exchanger, the core component for heat exchange between steam and material.

• Evaporation Separation Chamber: The material flashes here, separating the secondary steam from the concentrate.

• Forced Circulation Pump: The "heart" of the system, providing power for material circulation; a critical piece of equipment.

• Preheater: Utilizes the waste heat of condensate or secondary steam to preheat the feed.

• Vacuum System: Typically located in the last effect. Lowers the boiling point of the last effect, thereby increasing the overall temperature difference driving force of the system and further reducing steam consumption.

• Condenser: Condenses and discharges the secondary steam generated in the last effect.

• Control System: Automates the control of material flow rate, concentration, liquid level, temperature, and pressure at each effect.

Key Advantages and Applicable Scenarios

Advantages:

1. Extremely high thermal economy: This is its most significant advantage. Steam consumption is far lower than in single-effect evaporation, resulting in significant energy savings and low operating costs.

2. High processing capacity and wide applicability: Particularly suitable for processing high-viscosity, easily scaling, and crystallizing materials. Examples include: salts in the chemical industry (such as sodium chloride and sodium sulfate), fructose syrup in the food industry, extracts in the pharmaceutical industry, and industrial wastewater (containing saline wastewater) in the environmental protection industry.

3. Anti-scaling and long operating cycle: The high-speed flushing action of forced circulation makes the equipment less prone to scaling, ensuring long-term stable heat transfer efficiency and extending the cleaning cycle.

4. High operational flexibility: By adjusting the flow rate of the circulating pump and the inter-effect pressure, it can adapt to different feed conditions and concentration requirements.

Disadvantages:

1. High investment cost: Due to the large number of effects and the need for high-power circulating pumps, the initial equipment investment and installation costs are high.

2. High energy consumption: Forced circulation pumps are high-power equipment, and their power consumption is one of the main operating costs of the system, offsetting the benefits of steam savings to some extent.

3. Potential shearing effect on materials: For some materials sensitive to shear forces (such as certain polymers or biological products), high-speed circulation pumps may cause product degradation or changes in properties.

Process Flow (Co-current Example)

Taking a co-current process where the material and steam flow in the same direction as each other as an example:

1. The raw material liquid, after preheating, enters the first effect.

2. Live steam heats the material in the first effect, and the generated secondary steam enters the heating chamber of the second effect.

3. The concentrated liquid from the first effect, driven by a circulating pump, partially enters the second effect.

4. The secondary steam generated in the second effect enters the third effect, and its concentrated liquid also enters the third effect.

5. The third effect operates under vacuum, achieving the lowest boiling point. The final concentrated liquid, meeting the requirements, is discharged from the bottom of the third effect.

6. The secondary steam generated in the third effect enters the condenser and is completely condensed.

Summary: 

The triple-effect forced circulation evaporator perfectly balances energy efficiency, stability, and adaptability through ingenious "tiered energy use" and "forced circulation" technologies. Although its initial investment and power consumption are relatively high, its outstanding performance in handling difficult materials and extremely low steam consumption make it irreplaceable in large-scale industrial production and one of the preferred processes for rapid, energy-saving evaporation and concentration in many industries.