When the hot condensate at high pressure passes through the trap and reaches lower pressure, some of it spontaneously turns into steam. This is called flash steam. Flash steam can be collected in a flash tank and used in low-pressure heating; this is a significant energy saving.
Formula
Flash rate = (hf₁ − hf₂) ÷ hfg₂
hf₁: saturated water enthalpy at high pressure, hf₂ and hfg₂: saturated water enthalpy and latent heat of vaporization at low pressure.
Example
When 1,000 kg/h condensate at 10 bar(g) pressure drops to 0.5 bar(g) pressure, flash steam is formed at the rate of 14.08%, that is, approximately 141 kg/h.
We explained the savings provided by condensate return in this article.