Boiler Blowdown Percent
Worked example: 100 ppm feedwater, 3000 ppm limit → 3.33% blowdown — press Try an example to run it live, then adjust anything.
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UniversityProcess & Water Chemistry
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Boiler Blowdown Percent explained
Blowdown percentage is the reciprocal of cycles wearing a different hat: if the drum may hold 3000 ppm and the feedwater carries 100 ppm, you must dump 100/3000 = 3.3% of the feedwater to keep the solids in balance. It is the number a plant engineer actually budgets, because blowdown leaves at saturation temperature and takes its enthalpy with it — every percent of continuous blowdown on a 100 psig boiler costs roughly 0.2–0.3% of fuel.
The lever that pays is the feedwater, and the biggest single term in feedwater TDS is usually makeup rather than condensate. Raise condensate return from 50% to 80% and the feedwater TDS falls by more than half, and the blowdown percentage falls with it — fuel, water, chemical and sewer savings all at once. Two field cautions: measure boiler TDS on a cooled, depressurised sample or the flashing will concentrate it and read high, and do not confuse continuous surface blowdown, which controls TDS, with the bottom blowdown that clears sludge from the mud drum. Only the surface blowdown belongs in this equation.
Boiler Blowdown Percent formula
- = Blowdown percent of feedwater (%)
- = Feedwater TDS (%)
- = Boiler water TDS limit (%)
Missing one of these? Work it out first, then come back
- Blowdown percent of feedwater — Percent Blowdown, Percent Yield
- Feedwater TDS — Boiler Cycles of Concentration, Percent Yield
- Boiler water TDS limit — Boiler Cycles of Concentration, Cycles of Concentration from Chloride