MVR vs Multi-Effect Evaporation: Steam, Power and the Real Cost Split
MVR (mechanical vapour recompression) and multi-effect evaporation do the same job with different energy inputs. MVR consumes electricity to compress vapour; multi-effect consumes steam and cooling water. The correct choice is an economic one, not a technical preference — and it flips depending on your local power and steam prices.
Comparison at equal capacity
| Item | MVR | Triple-effect |
|---|---|---|
| Specific steam demand | Near zero after start-up (electric drive) | ~0.4 kg steam per kg evaporated |
| Specific power | ~20–40 kWh per tonne evaporated, depending on ΔT | ~2–6 kWh per tonne (pumps, vacuum) |
| Capex | Higher (compressor, larger motor, switchgear) | Lower (three vessels, no compressor) |
| Footprint | Compact — one vessel plus compressor | Large — three vessels in series |
| Turndown | Poor below ~60%; compressor surge limits | Good — can run on fewer effects |
| Scaling sensitivity | High — ΔT is small, fouling eats it quickly | Moderate — larger ΔT per effect |
| Best fit | Cheap power, expensive steam, stable load | Cheap steam, variable load, scaling liquors |
The break-even calculation you should run
Take the annual evaporation duty (tonnes of water). Multiply by 0.4 to get steam tonnes saved per year by MVR, then multiply by your delivered steam cost per tonne. That is the annual saving. Divide the capex difference by that saving to get a simple payback. In most markets a payback under three years justifies MVR; over five years, multi-effect is safer because it also tolerates load swings and fouling.
Do not forget the compressor’s own risk. A large MVR compressor is a single point of failure with a long lead time. Plants that must run 8,000 hours a year often keep a steam-driven fallback or accept multi-effect for that reason alone.
Scaling is the hidden variable
MVR runs on a small temperature difference between boiling and condensing. A 1 mm scale layer can consume a significant share of that ΔT, and throughput falls before anyone notices. If your liquor is near saturation for gypsum, carbonate or sulphate, multi-effect with a larger per-effect ΔT and easier mechanical cleaning is usually the more honest choice.
Send your evaporation duty, steam price, power price and liquor analysis, and we will return both configurations with utility consumption and a payback estimate.