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Evaporator Mass & Steam Balance Calculator

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Evaporator Mass & Steam Balance Calculator

Water evaporation rate, concentrate flow and steam consumption

Services Calculators
Online evaporator mass balance and steam economy calculator for dairy.

Calculate water evaporation rate, concentrate flow and steam consumption for single, multi-effect and MVR systems
Need help with evaporator mass & steam balance design, validation, or troubleshooting? Discuss your project →

The Formula

Evaporator design uses a simple total mass and solids balance:

F × XF = C × XC   (solids balance)
F = C + V   (total mass balance)
⇒ C = F × XF / XC  |  V = F − C F = feed flow (kg/hr), C = concentrate flow, V = evaporation rate, X = solids fraction (F=feed, C=concentrate)

Steam consumption depends on the configuration. Steam Economy (SE) = kg water evaporated per kg steam:

Steam = V / SE Illustrative assumptions: 1-effect 0.9, 2-effect 1.8, 3-effect 2.5, 4-effect 3.2, 5-effect 3.8. Use measured or supplier data for your plant and duty boundary.

Multi-effect evaporators use the vapour from one effect to heat the next, with each effect operating at progressively lower temperature and vacuum. MVR (Mechanical Vapour Recompression) uses a compressor to raise vapour pressure for reuse as heating medium, requiring compressor electricity. Calculate that electrical demand separately from any additional steam; it is not represented by an assumed steam economy of 25.

Worked Example

Problem: A skim milk concentrate (SMC) line at a dairy receives 25,000 kg/hr of milk feed at an assumed 12% TS and must produce concentrate at 48% TS for spray drying. The plant uses a triple-effect falling-film evaporator. Calculate the water evaporation rate, concentrate output and steam consumption.

Step 1. Solids balance: Solids in = Solids out. 25,000 × 12% = 3,000 kg solids/hr must end up in the concentrate at 48% TS.
Step 2. Concentrate flow: C = 3,000 / 48% = 6,250 kg/hr of concentrate at 48% TS
Step 3. Water evaporated: V = F − C = 25,000 − 6,250 = 18,750 kg/hr of water evaporated
Step 4. Steam consumption (triple-effect, SE ≈ 2.5): Steam = 18,750 / 2.5 = 7,500 kg/hr
Comparison: at an assumed SE of 0.9, steam demand is 20,833 kg/h, or 2.78 times the triple-effect example. This is less than the 25,000 kg/h feed flow.
MVR illustration: at an assumed compressor consumption of 12 kWh/t evaporated water, power is 18.75 × 12 = 225 kW. Enter any additional steam separately. This is not a complete plant energy total.
Need help applying this calculation to your specific plant or process?

Calculations on paper are one thing; real plant operation, validation, and commercial decisions need expert review. Schedule a call with Watson Dairy Consulting →

Interactive Calculator

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Frequently Asked Questions

What steam economy should be used?

Use measured or supplier data at the relevant feed temperature, concentration, throughput and duty boundary. The calculator presets are illustrative. Number of effects alone does not establish consumption; thermal vapour recompression and heat recovery change the result. MVR electricity and additional steam are entered separately.

When does MVR make sense over multi-effect?

MVR makes sense when electricity is cheap relative to steam, when product is heat-sensitive (low temperatures throughout), or when steam supply is constrained. Multi-effect favours cheap steam and high throughput.

Why is the calculated steam demand approximate?

The result inherits the assumptions entered. Feed heating, fouling, heat losses, condensate recovery and operating conditions can change demand. There is no substantiated universal ±20% accuracy band for this model. Establish performance from reconciled measurements at comparable conditions.

What's the difference between feed solids and concentrate solids?

Feed solids (XF) is the % total solids in the raw feed entering the first effect. Concentrate solids (XC) is the % total solids in the final concentrate leaving the last effect. The concentration ratio is XC/XF.

Need expert support on evaporator mass & steam balance? Watson Dairy Consulting provides independent support including process design, plant audit, and troubleshooting. Contact Watson Dairy Consulting.

Reference and further reading

University of Guelph: Evaporation and Dehydration explains evaporation, vapour recompression and drying. The calculator's 12 kWh/t MVR starting value is an illustrative input, not a guaranteed plant performance figure; replace it with the actual duty and account for other loads.

Further reading: John Watson publishes articles on dairy industry topics on LinkedIn. Browse all articles by John Watson on LinkedIn →

Disclaimer: This calculator and the calculations on this page are provided for educational and indicative purposes only. Real plant performance depends on many factors not captured by simple models. Always verify against your specific plant data, ingredient specifications, regulatory requirements and safety procedures. Watson Dairy Consulting accepts no liability for production, regulatory, safety or commercial decisions made on the basis of this calculator alone. For project-specific support, please contact Watson Dairy Consulting.

See related calculators: Evaporator Operator Training, Spray Drying, or browse all consultancy services.




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