Boiler blowdown and heat recovery
Continuous blowdown rate from feedwater and boiler water TDS, cycles of concentration, and the heat and money a flash vessel and heat exchanger recover.
Inputs
Results
Steam and Energy Excel kit — coming soon
Boiler efficiency and fuel cost, steam trap losses, flash steam and condensate recovery, insulation thickness and payback — with print-ready reports, any units and visible formulas.
Join PlantCalcKit — free
Be first to hear about new calculators, Excel tools and field guides — one short email when something new is ready. The calculators stay free with or without an account.
By joining you agree to our privacy policy. Unsubscribe or delete your details any time.
You are a PlantCalcKit member
Signed in as . We will email you when new tools and guides are ready.
How this calculator works
Dissolved solids enter a boiler with the feedwater and stay behind when the water turns to steam, so some boiler water must be blown down to hold the TDS below the limit. A solids balance gives the continuous blowdown: blowdown = steam × F/(B − F), where F is the feedwater TDS and B the boiler water limit; the cycles of concentration are B/F. Blowdown leaves at the boiler's saturation temperature, so it carries heat. A flash vessel recovers part of it as low-pressure steam (flash fraction from IAPWS-IF97 saturation enthalpies), and a heat exchanger on the remaining water can preheat the makeup. The calculator prices the heat still lost, the recovery and the water, and shows what a higher TDS limit would save.
Example: a boiler raising 10,000 kg/h of steam at 10 bar g, with feedwater at 150 ppm and the boiler water held at 3,000 ppm: blowdown 526 kg/h, 5.0 % of the feedwater and 20 cycles; it carries 102 kW above 20 °C makeup. A flash vessel at 0.5 bar g recovers 74 kg/h of steam (14.1 %, 54 kW), and an exchanger cooling the rest to 35 °C another 40 kW — 94 kW recovered, worth about USD 25,500 a year at USD 8/GJ, 85 % efficiency and 8,000 h; 8 kW (USD 2,100) is still lost. Raising the limit to 3,500 ppm cuts the blowdown to 448 kg/h. Checked against an independent mass and energy balance with the iapws steam tables.
Limits: continuous (surface) blowdown on a TDS basis; bottom blowdown for sludge is extra. Silica, alkalinity or suspended solids can set a tighter limit than TDS. Set the limit with your water treatment supplier and boiler maker — for example ABMA guidance for water-tube boilers falls from about 3,500 ppm at low pressure as the pressure rises. References: US DOE, Improving Steam System Performance: A Sourcebook for Industry (2012); Spirax Sarco, The Steam and Condensate Loop; IAPWS-IF97.