1. Differences in Core Principles

Single-effect low-temperature evaporation

Only one evaporation process is used. External steam (or hot water) heats the material to generate secondary steam, which is directly condensed and discharged, with no heat recovery. The entire system has only one evaporation unit and the simplest structure.

Multi-effect low-temperature evaporation

Multiple evaporators are connected in series. The secondary steam generated by the previous effect serves as the heating source for the next effect, and the waste heat is utilized sequentially. Generally, 2 to 4 effects are common. The more effects there are, the more times the heat is utilized, resulting in better energy efficiency.

Heat pump low-temperature evaporation

Through a compressor or steam ejector, low-temperature secondary steam is directly heated and pressurized, and then sent back to the heating chamber for reuse as a heat source, which is equivalent to "recycling" the steam. Typical forms are MVR (Mechanical Vapor Recompression) and TVR (Thermal Vapor Recompression), which have the highest energy utilization efficiency.

2. Differences in Energy Consumption and Operating Costs

Single-effect evaporation has the highest energy consumption. Evaporating 1 ton of water requires approximately 1 ton of heating steam, with almost no heat recovery. It is only suitable for small water volumes and intermittent operation.

Multi-effect evaporation utilizes the latent heat of steam multiple times, and energy consumption decreases as the number of effects increases. The steam consumption per ton of water for double-effect is about 0.5-0.6 tons, and for triple-effect is about 0.3-0.4 tons, which is significantly more energy-efficient than single-effect. However, after exceeding 4 effects, the energy-saving benefits diminish, and the complexity of the equipment increases significantly.

Heat pump evaporation has the strongest energy-saving effect. MVR almost does not require fresh steam, only consuming a small amount of electrical energy to drive the compressor. The energy consumption per ton of water is much lower than that of multi-effect evaporation, resulting in the lowest long-term operating costs, making it suitable for large water volumes and continuous working conditions.

3. Differences in Equipment Structure and Investment

Single-effect evaporation has the simplest structure, with only one set of evaporator, condenser, and vacuum pump. It has the lowest investment, small floor space, quick installation, and easy operation.

Multi-effect evaporation requires multiple sets of evaporators, multi-stage vacuum systems, complex pipelines, and interlocking controls. The equipment investment is much higher than that of single-effect, the system is larger, and the control difficulty is higher.

Heat pump evaporation requires additional compressors, frequency conversion systems, anti-surge devices, precise automatic control, etc., resulting in the highest equipment investment. However, the system is compact, and the overall floor space is often less than that of multi-effect evaporation.

4. Differences in Vacuum and Temperature Control

All three belong to low-temperature evaporation and operate under vacuum, but their control focuses are different.

Single-effect evaporation control is simple, mainly requiring stable vacuum and heating temperature.

Multi-effect evaporation requires step-by-step control of pressure, temperature, and liquid level to ensure pressure difference and heat transfer matching between each effect; otherwise, operation is prone to disorder.

Heat pump evaporation requires the most precise control of temperature, pressure, and superheat. It must accurately match the compressor load, maintain a stable heat transfer temperature difference, and prevent liquid hammer, surge, and material leakage.

5. Differences in Applicable Scenarios

Single-effect low-temperature evaporation

Suitable for scenarios with small water volumes, intermittent operation, low steam costs, and limited investment, such as small-scale wastewater, laboratory concentration, and scattered waste liquid treatment.

Multi-effect low-temperature evaporation

Suitable for medium to large water volumes, continuous operation, and situations with cheap steam sources, especially more economical in chemical plants, thermal power plants, and other places with sufficient by-product steam.

Heat pump low-temperature evaporation

Suitable for scenarios with large evaporation capacity, long-term continuous operation, and high sensitivity to energy consumption, such as industrial wastewater concentration, landfill leachate, and high-salt wastewater, with the best comprehensive economy.

6. Brief Summary

Single-effect: The simplest and cheapest, but the most steam-consuming, suitable for small water volumes.

Multi-effect: Reuses heat through multiple effects, with moderate energy savings and complex equipment.

Heat pump type: Recycles steam through a compressor, with the strongest energy savings, high investment but the most economical operation.