Setting up a mass balance and knowing when it does not close

Worked example

The figures below were produced by running the Plant Mass Balance with the same inputs .

These figures are worked by the published method rather than executed at build time, because this tool is a self-contained page calculator without a programmatic engine.

1. Total mass in equals total mass out; only the species balance moves.
2. The closing stream is calculated, not measured — and it absorbs every error upstream.
3. A closing stream outside its plausible range means the measurement, not the model, is at fault.

Tools for this problem

These are the EngiMetric calculators that compute the numbers in this topic. Each one shows its formula, its units and its limits rather than returning a bare result.

• Plant Mass Balance Assemble the whole plant as an ordered chain of unit operations: raw intake to product and waste, stage-to-stage product flow, external make-up, derived concentrate TDS by salt conservation, and plant-wide water and salt balance checks.
• RO Mass Balance Calculator Simplified TDS-based dissolved-solids balance for RO feed, permeate, and concentrate flow and quality checks.

References & standards

• Felder, Rousseau & Bullard — Elementary Principles of Chemical Processes
• ISO 45012 — water balance

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