A multiple-effect evaporator is a combination of multiple sets of evaporator stages or effect, the core principle is utilizing the secondary steam generated by the evaporation in the previous effect as the heat source for the next effect to achieve the purpose of saving energy.
Evaporation can be classified into single-effect and multiple-effect evaporation based on whether the secondary steam is used as the heating steam for another evaporator. When several evaporators are connected in a certain configuration, and the secondary steam from one evaporator is used as the heating steam for the next, this is called multiple-effect evaporation. The primary purpose of using multiple-effect evaporation is to reduce the consumption of heating steam and save thermal energy.
During the evaporation process, a large amount of secondary steam is generated, which contains significant latent heat. To maximize energy efficiency, this secondary steam should be recovered and utilized. In a multiple-effect evaporator, the secondary steam produced in one effect is directed into the heating chamber of the next effect. As long as the operating pressure and boiling point of the solution in the subsequent effect are lower than those of the preceding one, the secondary steam can still serve effectively as a heating source.
This cascading reuse of steam across successive stages significantly enhances thermal efficiency, resulting in notable energy savings and reduced operating costs.
The multiple-effect evaporator consists of multiple evaporator stages or “effects”, a condenser, vacuum system and auxiliary equipments, operating in a series to form the multiple-effect system, with each stage designed to progressively utilize the residual energy from the preceding one. The system adopts a continuous input-output method, enabling stable and uninterrupted production.
Multiple-effect evaporators can be configured in various forms, including forced circulation, natural circulation, falling film, rising film, and plate-type evaporators. Additionally, hybrid combinations of these types can be employed to optimize performance based on process requirements, feed properties, and energy efficiency targets.
The typical values of steam economy (W/D) for multiple-effect evaporators are as follows.
| Number of Effects | Single -effect | Double -effect | Triple-effect | Four-effect | Five-effect |
| W/D | 0.91 | 1.75 | 2.5 | 3.33 | 3.70 |
| Note: W/D= Water evaporated/ Direct steam used | |||||
A higher W/D ratio means more water is evaporated per unit of fresh steam, indicating better energy efficiency. Because the steam economy of multiple-effect evaporation is relatively high, multiple-effect evaporators are widely used for evaporating large amounts of water. However, the table also shows that although the W/D value increases with the number of effects, it does not increase proportionally to the number of effects.
1) Energy Efficiency: The most significant benefit is the great reduction in steam consumption, translating into lower energy costs and a smaller carbon footprint.
2) Reduced Environmental Impact: Lower energy consumption translates to reduced carbon footprint, aligning with sustainability goals.
3) High Concentration Ratios: They can achieve high solute concentrations, making them ideal for industries requiring high-purity products.
4) Operational Flexibility: These systems can be designed to accommodate varying feed compositions and production requirements.
Multiple-effect evaporators are employed across diverse sectors to remove solvent, typically water, from a solution or slurry to concentrate the solute. The efficiency and scalability of multiple-effect evaporators make them suitable for a wide range of applications, including:
– Desalination : Removing salt from seawater to produce potable water.
– Food and Beverage Industry : Concentrating fruit juices, dairy products, and other liquids.
– Chemical Industry:Concentration of chemicals, solvents, and industrial wastewater treatment.
– Pulp and Paper Industry: Concentrating black liquor for energy production.
– Pharmaceuticals: Concentrating active pharmaceutical ingredients and intermediates.
– Environmental protection: treatment of industrial wastewater in industries like chemical, pharmaceutical, metallurgy, mining, petrochemical, rare earths, lithium batteries, and hazardous waste.
When designing a multiple-effect evaporator system, our engineers consider several critical factors to optimize its operation. These include the specific needs for heat recovery, the potential for automatic online cleaning to ensure long-term efficacy, and the choice among various process configurations such as forced or natural circulation and falling or rising film evaporation. The selection is tailored to meet the unique requirements of each application, ensuring the system’s maximum efficiency and reliability.
If any demands on evaporator and crystallizers, pls feel free to contact us.
