Evaporator Steam Economy Calculator
Estimate the live steam a multi-effect evaporator needs, using a practical steam economy of about 0.85 kg water per kg steam per effect. Used to evaluate and compare the energy demand of industrial evaporators.
Last updated: September 2026
Formula below · 2 sources (aiche.org, Wikipedia) · Updated Sep 2026
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About this calculator
Steam economy is a key performance metric for evaporators, defined as the mass of water evaporated divided by the mass of steam consumed. In a single-effect evaporator, economy ≈ 0.85 kg water/kg steam (accounting for heat losses). Each additional effect reuses the vapour from the previous stage, roughly multiplying economy by the number of effects. The calculator first finds the water to evaporate from a solids balance, W = F × (1 − C_i / C_f), where F is the feed flow rate (kg/h) and C_i and C_f are the initial and final concentrations (% w/w). It then applies a practical economy E ≈ 0.85 × N (N = number of effects) and returns the live steam required, S = W / E. More effects raise the economy and cut steam roughly in proportion.
How to use
Example: Feed flow rate F = 1000 kg/h, initial concentration C_i = 5% w/w, final concentration C_f = 20% w/w, and N = 3 effects. Step 1: water evaporated W = 1000 × (1 − 5/20) = 750 kg/h. Step 2: steam economy E = 0.85 × 3 = 2.55 kg water per kg steam. Step 3: live steam S = 750 / 2.55 = 294 kg/h. A single effect would need 750 / 0.85 = 882 kg/h, three times as much. With the defaults (10,000 kg/h, 10 → 50%, triple effect) W = 8,000 kg/h and S = 3,137 kg/h.
Frequently asked questions
What is steam economy in an evaporator and why does it matter?
Steam economy is the ratio of kilograms of water evaporated to kilograms of live steam consumed. It directly measures energy efficiency: a steam economy of 2.5 means 2.5 kg of water is removed for every kilogram of steam purchased. Higher economy reduces operating costs significantly, since steam is typically the largest energy cost in evaporation. In large-scale food, pharmaceutical, or chemical plants running continuously, even a 0.1 improvement in steam economy can translate to hundreds of thousands of dollars in annual savings.
How does the number of effects improve steam economy in multi-effect evaporation?
In a multi-effect evaporator, the secondary vapour produced in the first effect is used as the heating steam in the second effect, and so on. This cascade reuse of latent heat means that one kilogram of live steam evaporates approximately N × 0.85 kg of water across N effects, compared to just 0.85 kg in a single effect. Each additional effect improves economy proportionally but also increases capital cost and complexity. The optimal number of effects is determined by balancing the annual steam cost savings against the additional capital investment for each extra effect.
What factors reduce actual steam economy below the theoretical value in industrial evaporators?
Several factors cause actual steam economy to fall short of the theoretical N × 0.85 benchmark. Boiling point elevation (BPE) — where dissolved solutes raise the boiling point above pure water — reduces the effective temperature driving force available for heat transfer in downstream effects. Heat losses through insulation, non-condensable gases in steam, and throttling losses between effects also reduce economy. Fouling on heat transfer surfaces raises thermal resistance over time, requiring more steam for the same evaporation duty. Proper design with BPE corrections, good insulation, and regular cleaning are essential to maintaining high steam economy.