Single-effect, double-effect, triple-effect, MVR: How much can the evaporation energy efficiency limit be improved?

With carbon emissions targets and soaring steam prices, energy consumption in evaporation processes now accounts for over 30% of manufacturing costs in industries such as chemicals, pharmaceuticals, and food. Traditional single-effect, double-effect, and triple-effect evaporation achieves tiered energy savings through "series steam utilization," while the new generation of mechanical steam recompression (MVR) technology directly "turns waste into treasure" with secondary steam. From single-effect to MVR, how much higher can the energy efficiency limit be pushed? We provide an objective answer with data.

I.The "Ceiling" of Traditional Multi-Effect Vaporization

Single-effect evaporation is the simplest: 1 ton of live steam ≈ 1 ton of water evaporated, with a steam consumption ratio of 1.1. A second-effect evaporation reuses the secondary steam from the first effect, reducing the steam consumption ratio to 0.6. A third-effect evaporation continues in series, with a steam consumption ratio of approximately 0.4, reducing energy consumption by 60% compared to single-effect. However, as the number of effects increases further, temperature difference losses expand exponentially. Four-effect and five-effect evaporations only reduce energy consumption by about 10% further, while equipment investment increases exponentially. In industry, ≥4-effect evaporations are extremely rare. It can be said that multi-effect technology has reached its physical and economic "ceiling."

II.The "Limited Leap" of MVR

MVR uses electricity to drive a centrifugal compressor, compressing and heating secondary steam by 8–12°C before immediate reuse, theoretically eliminating the need for external live steam. Taking a 15t/h amino acid concentration project as an example, under the same evaporation capacity, the heat required by MVR is only 24% of that of a triple-effect compressor, saving 85.7% of standard coal equivalent, and annually saving 7.83 million yuan in steam costs. Another comparison for a 5t/h sodium sulfate solution shows that the annual operating cost of a single-effect compressor is 7 million yuan, a triple-effect compressor is 2.8 million yuan, while MVR is as low as 1.5 million yuan, further reducing energy costs by 46%. The data speaks for itself: MVR reduces the "operating cost per ton of water" from 100 yuan for a triple-effect compressor to 22 yuan, increasing energy efficiency by nearly 80%.

III.Three Key Mechanisms Behind Energy Efficiency Improvement

1.Upgraded Thermodynamic Cycle: Multi-effect evaporators only use steam in stages, while MVR achieves a closed-loop heat pump cycle, repeatedly utilizing the latent heat of secondary steam and minimizing system energy loss.

2.Zero Temperature Difference Loss: Multi-effect evaporators lose 3-5°C of effective temperature difference with each additional effect, while MVR compensates for the boiling point increase through compression, stabilizing the evaporation temperature difference at 7-10°C, and reducing the heat transfer area by 20-30%.

3.Near-Zero Cooling Water Consumption: Triple-effect evaporation requires 40t of cooling water per ton of water, while MVR eliminates the final-effect condenser, resulting in approximately zero circulating water consumption and a simultaneous decrease in auxiliary power consumption.

IV.Objective Boundaries and Applicable Scenarios

MVR is not a "panacea." When the boiling point of the material increases by >18°C, is prone to scaling, or has a solids content >20%, the compressor power consumption increases significantly, requiring coupling with forced circulation or a scraper crystallizer. Furthermore, the initial investment for MVR is 30-50% higher than that of triple-effect evaporators, and it places higher demands on grid capacity and operational precision. For regions with low steam prices and power shortages, triple-effect evaporators remain a safe choice; however, for high-salt wastewater, heat-sensitive materials, and zero-emission projects, the extreme energy saving and concentration limits (up to 1400 kg/m³) of MVR are virtually irreplaceable.

V.Conclusion

From single-effect to triple-effect evaporation, evaporation technology uses a "series" connection to reduce the steam consumption ratio to 0.4, improving energy efficiency by approximately 60%; MVR, through "compression and reuse," cuts heat demand to one-quarter of that of triple-effect evaporators, further pushing the energy saving potential upwards by 80%, approaching the energy efficiency limit of current industrial evaporation technology. In the future, with the maturity of high-temperature heat pumps and magnetic levitation compressors, MVR is expected to further increase overall energy efficiency by 5-8%, but the technological leap curve of "single-effect → double-effect → triple-effect → MVR" clearly shows that the limit is not a concept, but verifiable data—85% coal, 7.83 million yuan in steam costs, and zero cooling water are the tangible benefits that enterprises can achieve today.