Condensate Lines - Flash Steam

Flash steam produced in condensate pipe lines

In general condensate lines should be designed to handle start-up conditions with huge amounts of condensate generated from cold steam pipes and cold heating equipment. As a rule of thumb - the maximum condensate load at start up is often twice the maximum steam load during operation.

Sometimes, especially in high pressure steam systems with heavy load heat exchangers, generated flash steam may be the limitation of the condensate lines.

Flash steam generated  can be calculated as

w% = 100 (hil - hfl) / hfe                                      (1)


w% = ratio of flash steam generated (%)

hil = initial liquid enthalpy (kJ/kg)

hfl = final liquid enthalpy (kJ/kg)

hfe = enthalpy of evaporation (kJ/kg)

The condensate load can be calculated as

wc = ws w% / 100                                          (2)


wc = condensate load (kg/h)

ws = steam flow rate (kg/h)

Related Topics

  • Flash Steam - Flash steam generation - thermodynamic fundamentals, heat loss, energy recovery and more
  • Pipe Sizing - Sizing steam and condensate pipes - pressure loss, recommended velocity, capacity and more

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