Multiple Effect Evaporator (MEE)
A multiple effect evaporator connects 2–7 evaporator bodies in series so that vapour generated in each effect serves as the heating medium for the next lower-pressure effect — recovering and reusing latent heat. Processing 500–500,000 kg/h with steam economy of 1.5–6.5 kg water per kg steam consumed, it achieves the lowest energy consumption per unit of water removed — the production standard for dairy, sugar, pulp, and chemical concentration.
A multiple effect evaporator connects 2–7 evaporator bodies in series so that vapour generated in each effect serves as the heating medium for the next lower-pressure effect — recovering and reusing latent heat. Processing 500–500,000 kg/h with steam economy of 1.5–6.5 kg water per kg steam consumed, it achieves the lowest energy consumption per unit of water removed — the production standard for dairy, sugar, pulp, and chemical concentration.
Steam enters Effect 1 (highest pressure); vapour from Effect 1 heats Effect 2; Effect 2 vapour heats Effect 3 — continuing through the train. Feed flows forward, backward, or mixed depending on viscosity and scaling tendency. Each effect increases solids concentration. Final vapour is condensed by cooling water or MVR. Steam economy improves linearly with effect count — a 7-effect system evaporates approximately 6.5 kg water per kg steam consumed.
- Boiling Point Elevation Reducing Effective ΔT Across Train: High-solids feeds elevate boiling point — reduces available temperature driving force in later effects.
- Fouling Intensification in High-Concentration Final Effects: Scaling rates highest in last effect where solids and viscosity are maximum.
- Complex Control of Multi-Body Level and Pressure Balance: Instability in one effect propagates through train — requires multi-loop PLC cascade control.
- High Capital Cost for 5–7 Effect Systems: Each additional effect requires full evaporator body, heat exchanger, separator, and controls.
- Non-Condensable Gas Accumulation in Later Effects: Dissolved air released from feed accumulates in steam chest — reduces U-value.
- Backward Feed for High-Viscosity Products (Last Effect Highest Temperature): Backward feed ensures highest-viscosity product contacts highest ΔT — restores driving force.
- Dedicated CIP Line to Final Effects (Higher Frequency Clean Cycle): Final effects cleaned 2–3× more frequently — scale removed before U-value degradation.
- Multi-Loop PLC with Model Predictive Control (MPC): MPC anticipates interaction between effects — maintains stable level and pressure balance.
- Mechanical Vapour Recompression (MVR) to Supplement Last Effect: MVR reduces required steam input by 60–80% — near-zero marginal steam cost.
- Venting of Non-Condensables at Each Effect Steam Chest (Timed Purge): Timed vent valve purges non-condensable build-up — maintains design U-value per effect.
- Dairy: Milk and whey evaporation before spray drying — 3–7 effect standard for large plants.
- Sugar: Thin juice evaporation (5–6 effects), cane juice concentration, beet sugar processing.
- Pulp & Paper: Black liquor evaporation before recovery boiler — 6–7 effects standard in kraft mills.
- Chemical: Caustic soda, phosphoric acid, ammonium nitrate, sodium sulphate concentration.
- Desalination: Multi-effect distillation (MED) for seawater and brackish water desalination.
Indicative values. Steam economy = N − 1 approximately (N = number of effects); actual economy depends on boiling point elevation, heat losses, and feed condition. Total heating area = sum of all effect areas. MVR option reduces steam consumption 60–80%.
Multiple Effect Evaporator (MEE) — Models & Capacities | ||||||||||||
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Model | Scale | Effects(N) | EvaporationCapacity [kg/h] | Total HeatingArea [m²] | SteamConsumption [kg/h] | Steam Economy[kg/kg steam] | Effect 1 Temp[°C] | Last EffectTemp [°C] | Last EffectVacuum [mbar] | MVROption | InstalledPower [kW] | Weight[t] |
MEE-2E-LAB | Lab | 2 | 100–1,000 | 2 | 55–550 | ~1.8 | 110 | 65 | 250 | Optional | 2.2 | 3 |
MEE-2E-PIL | Pilot | 2 | 500–5,000 | 10 | 280–2,800 | ~1.8 | 110 | 65 | 200 | Optional | 5.5 | 12 |
MEE-3E-PIL | Pilot | 3 | 800–8,000 | 20 | 300–3,000 | ~2.7 | 120 | 60 | 150 | Optional | 7.5 | 25 |
MEE-3E-P | Production | 3 | 2,000–20,000 | 50 | 750–7,500 | ~2.7 | 125 | 55 | 100 | Optional | 18.5 | 65 |
MEE-4E-P | Production | 4 | 5,000–50,000 | 120 | 1,300–13,000 | ~3.6 | 130 | 50 | 80 | Optional | 30 | 160 |
MEE-5E-P | Production | 5 | 10,000–100,000 | 250 | 2,200–22,000 | ~4.5 | 140 | 45 | 50 | Standard | 55 | 380 |
MEE-6E-LP | Large Prod | 6 | 20,000–200,000 | 550 | 3,500–35,000 | ~5.4 | 150 | 40 | 30 | Standard | 90 | 850 |
MEE-7E-LP | Large Prod | 7 | 50,000–500,000 | 1,200 | 8,000–80,000 | ~6.4 | 160 | 35 | 15 | Standard | 160 | 2,100 |
Common Technical Specifications — All Evaporator Types | |
|---|---|
Parameter | Specification — All Evaporator Types |
Evaporation Mechanism | Conduction through tube/cylinder wall → phase change at liquid-vapour interface under applied vacuum or atmospheric pressure |
Heating Medium | Steam (0.5–10 bar gauge); hot water; thermal oil (up to 200°C); MVR recompressed vapour (60–80% steam saving) |
Vacuum System | Liquid-ring pump (down to 30 mbar); steam jet ejector (down to 1 mbar); turbomolecular pump (WFE: to 0.001 mbar) |
Condenser Type | Surface condenser (shell-and-tube or plate heat exchanger); barometric condenser; internal coaxial condenser (WFE short-path) |
MVR Option | Mechanical Vapour Recompression compressor — increases steam economy by 60–80%; available on FFE, MEE, and WFE |
Product Contact Material | SS 316L all wetted surfaces; Ra <0.8 µm (food/pharma); Ra <0.4 µm (sterile/WFE); PTFE wiper blades (WFE) |
GMP Compliance | FDA 21 CFR Part 211; EU GMP Annex 1 and 15; EN 10204 3.1 material traceability; GAMP 5 (control system) |
CIP Compatibility | Full CIP — NaOH 2% (75°C, 20 min) + HNO₃ 0.5% (60°C, 15 min) + WFI rinse; spray ball on all wetted surfaces |
Control System | PLC-PID with cascade level, temperature, and vacuum loops; MPC for MEE multi-body; VFD on all pumps and compressors |
Safety Interlocks | Low-level cutout; high-temperature alarm; vacuum loss alarm; non-condensable vent; product concentration limit |
Scale-Up Parameter | Heat transfer area [m²] scales linearly with evaporation duty at constant U-value and ΔT; pilot-scale data required for U-value |
Typical U-Values | Falling film: 1,500–3,000 W/m²·°C; Rising film: 1,200–2,500; MEE (per effect): 1,000–2,500; WFE: 300–1,000 W/m²·°C |
Documentation | FAT/SAT protocol; IQ/OQ/PQ; heat and mass balance report; EN 10204 3.1; GAMP 5; thermal performance test certificate |