Module 12 · Efficiency and Audits3 min read
Condensate and Flash Recovery: Counting the Savings
Returning condensate saves three things at once — fuel, water, and the treatment and blowdown that water would have needed. Recovering flash steam saves fuel. Counting them separately, and not twice, is what makes a recovery proposal credible.
You'll learn
- Value returned condensate in fuel and water
- Value captured flash steam
- Avoid double-counting
- Know the hidden benefit: feed tank temperature
Before this: What condensate is worth, Flash vessels, Cost of Steam
BeginnerThe idea in plain words, and where you meet it. No maths.
Three savings in one pipe
- Fuel: hot condensate replaces cold make-up, so the boiler adds less heat.
- Water: every kilogram returned is a kilogram not bought, softened or dosed.
- Blowdown: condensate is nearly free of dissolved solids, so the boiler needs less blowdown.
Flash steam, captured and used, saves fuel only. It is not water back in the tank unless it is condensed somewhere else and returned.
IntermediateThe formula, its units, and a worked example on real plant numbers.
A worked example
Worked example
Recovering 3,000 kg/h of condensate
Given
- 3,000 kg/h of condensate leaving traps at 8 kg/cm²(g), returned through a flash vessel at 0.5 kg/cm²(g); 70% recovered; make-up at 30 °C; 20 h/day, 25 days/month; coal-fired.
- Flash at the vessel: 12.2%, leaving 2,633 kg/h of liquid at 111.4 °C.
- Liquid returned: 1,843 kg/h, carrying 1,50,330 kcal/h above make-up.
- Fuel saved: 45.8 kg/h of coal, 275 t a year.
- Water saved: 11,058 m³ a year.
- Capturing the flash as well adds 257 kg/h of steam, taking the coal saving to 93.9 kg/h — and the water saving stays the same.
Answer: Feed tank temperature rises to about 80 °C, from 30 °C.
ExpertThe fine print: where the simple model breaks, and what it costs.
Making the numbers hold
- Use measured condensate, not steam flow: some steam is used directly, lost in leaks or contaminated.
- Use a realistic recovery fraction; the last few percent are the most expensive to collect.
- Check the feed pump can handle hotter water: above about 90 °C, net positive suction head becomes a design issue.
- Contamination risk decides what can be returned; fit conductivity monitoring where product could leak in.
Key takeaways
- Condensate return saves fuel, water and blowdown; flash recovery saves fuel only.
- Count each saving once; feed tank temperature is a consequence, not an extra saving.
- Base the figures on measured condensate and a realistic recovery fraction.
- Hotter feedwater needs a feed pump suited to it.