Energy Savings in Multi-Effect Evaporators
Jetomat thermocompressors improve evaporator steam economy by recompressing vapour from a downstream effect and reusing it as heating steam.
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Introduction
Multi-effect evaporators (MEEs) are steam-hungry. Whether you’re concentrating sugar juice, whey permeate, gelatin liquor, or salt brine, the KPI that rules the day is steam economy—how many kilograms of water you evaporate per kilogram of live steam. A smart way to lift economy without adding a new effect is to fit a Jetomat steam ejector (a controllable thermocompressor) between effects. It takes lower-pressure vapour from a downstream effect and boosts it to the pressure of an upstream effect—like adding an extra half-effect at very low cost.
The result: lower energy use, fewer plumes, and a tighter, calmer evaporation train.
What is a thermocompressor (Jetomat) in an MEE
A Jetomat is a steam jet ejector (a thermal vapour recompressor) with a controllable nozzle. High-pressure motive steam expands through a shaped nozzle, producing a high-velocity jet that creates a vacuum to entrain low-pressure vapour (from a lower effect). In the diffuser, velocity is converted back to pressure, delivering mixed steam at the higher effect’s setpoint. That’s the classic steam jet ejector principle—momentum exchange with no rotating machinery (only the nozzle spindle moves).
In MEE terms: vapour from Effect N+1 (lower pressure) is recompressed to serve as part of the heating steam for Effect N (higher pressure). Less live steam is needed at the front of the train, so steam economy increases.
Components of the Jetomat inter-effect link
Controllable Motive Nozzle (with actuator)
Pneumatic or electric actuator moves the spindle to modulate throat area and motive mass flow.
Typical rangeability 3:1–5:1 for stable operation from low to peak load.
Good nozzle design keeps the jet stable across seasonal boiler-pressure swings.
Suction Inlet & Mixing Chamber
Pulls vapour from the lower-pressure effect’s vapour space or calandria outlet.
Provides intensive mixing; protects entrainment across turndown.
Diffuser (pressure recovery)
Rebuilds pressure to match the target effect.
The thermocompressor design (nozzle + diffuser) sets feasible entrainment ratio (ω = suction flow ÷ motive flow) and compression ratio (π = mixed pressure ÷ suction pressure).
Instrumentation & Controls
Primary loop: mixed-steam pressure (or Effect-N calandria temperature) → actuator.
Optional: suction pressure/temperature; motive pressure.
Easy tie-in to PLC/DCS; supports recipes for different products.
(Optional) A steam separator downstream is rarely needed for calandrias (they accept saturated steam), but include one if a specific instrument demands very dry steam.
How a Jetomat Adds “Half an Effect”
In a simple 4-effect evaporator
Before: Live steam feeds Effect-1; its vapour heats Effect-2; and so on. Steam economy might be ~4.0 kg water/kg Steam.
After (with Jetomat): Vapour from Effect-3 (say 0.25 bar abs) is recompressed to help heat Effect-2 (say 0.45 bar abs). That reduces live steam to Effect-1 and raises economy toward ~4.6–5.0—an “extra half-effect” in practical terms.
Key performance variables
Entrainment ratio ω often 0.5–1.2 in MEE service.
Compression ratio π commonly 1.3–2.0 for a single stage (service-dependent).
Stability: With a controllable nozzle, mixed pressure typically holds ±0.05 bar, and calandria temperature ±0.5 K even as feed rate and solids change.
Worked example
Duty: 4-effect falling-film evaporator concentrating cane juice
Throughput evaporation: 30 t/h water removed
Baseline live steam (to Effect-1): 7.5 t/h → Steam Economy = 30 / 7.5 = 4.0
Jetomat between Effect-3 (suction) and Effect-2 (mixed)
Motive header: 9–10 bar(g)
Suction: 0.25 bar abs vapour from Effect-3
Target mixed: 0.45 bar abs to Effect-2
Selected operating point: ω ≈ 0.8
Result
Live steam drops to ~6.0 t/h (the balance made up by recompressed vapour).
New economy = 30 / 6.0 = 5.0 (+25% improvement).
Boiler firing, make-up water, and chemical dosing fall proportionally; visible vents subside.
If your baseline economy is already high, the bump is smaller; evaporators with significant venting or PRV throttling gain the most.
Industry scenarios where this pays back fast
Sugar refining
Large, steady evaporation with variable feed Brix.
Jetomat smooths calandria pressure across rate changes—fewer condensate pockets and better heat flux.
Dairy (whey, milk, permeate)
Frequent turndown and CIP cycles.
Controllable nozzle keeps suction during low load.
Salt Brine Concentrators / Chemicals
Brine carryover risks and fouling favour no rotating machinery.
Jetomat provides compact heat recovery between effects, best where the inter-effect ΔT is modest.
Why thermocompression beats “bigger effects”
Capex light: One ejector/line is far cheaper than adding a whole new effect.
No rotating machinery — only the nozzle spindle moves: Rugged and low-maintenance—ideal for harsh services.
Real energy recycling: Instead of venting or condensing flash steam, you reuse it at process pressure.
Control under variability: A fixed ejector works at one point; a controllable Jetomat maintains entrainment across product, season, and boiler swings—no loss of suction, no over-compression.
Control & integration
Setpoint: Hold Effect-N calandria pressure/temperature (e.g., 0.45 bar abs, ~76–80 °C, product-dependent).
Response: With a modern actuator, <2–5 s to stabilise after feed/concentration steps.
Loop tuning: Start with pressure control; add temperature cascade if you want tighter product outlet °Brix control.
Piping: Keep suction runs short, insulated, and pocket-free; ensure proper drainage to avoid slugging.
Turndown: Design 3:1–5:1; verify stability at night/weekend low-rate operation.
Benefits
Steam economy up: More kg water evaporated per kg live steam.
Fuel & utilities down: Lower boiler firing; reduced steam and condensate losses; less make-up water & chemicals.
Process stability: Flatter calandria temperatures; improved heat transfer from steadier condensate removal (thinner films).
Simplicity & reliability: No rotor or bearings; the ejector works on pure fluid dynamics.
Scalable: One unit can upgrade a 3–6 effect train; multiple units can step-ladder larger systems.
Practical checklist
Data Pack: Motive header P/T; Effect-N and N+1 pressures/temperatures; vapour flows; allowable Δp to calandrias.
Sizing Targets: Pick feasible ω and π; confirm with vendor maps for nozzle/diffuser geometry.
Suction Piping: Short, clean, insulated; add a knock-out pot only if carryover is likely.
Controls: Mixed-pressure control with motive trim; add temperature cascade if quality critical.
KPIs to trend: Live steam flow, economy (kg/kg), product rate, calandria ΔT, vent flows, and boiler load.
Conclusion
A Jetomat thermocompressor between effects is a compact, low-risk way to lift steam economy—more evaporation per unit of live steam. In sugar, dairy, and brine concentration, that translates to rapid payback, calmer operation, and measurable energy savings without adding a full effect.
How to proceed
Identify the effect pair with the largest pressure gap and steady vapour source.
Gather one week of pressures/flows and product rates.
Request a thermocompressor design check (entrainment ratio, compression ratio, nozzle and diffuser geometry, turndown).
Pilot and document: live-steam reduction, economy, and product stability over 2–4 weeks.
Scale to other trains once the numbers confirm the gain.
