The amount of flash steam generated depend on the steam pressure - the pressure in the condensate before it leaves the condensate trap - and the condensate pressure after the trap - the pressure in the condensate return pipe lines.
The table below indicates the ratio of flash steam generated at different pressures before and after the condensate trap.
A condensate system is vented to the surroundings and the pressure in the condensate system after the condensate traps is 101.33 kN/m2. The absolute steam pressure before the condensate trap is 1150 kN/m2.
According the table above 16.5% of the condensate will evaporate as flash steam after the trap.
Engineering ToolBox, (2003). Flash Steam Generation - SI-units. [online] Available at: https://www.engineeringtoolbox.com/flash-steam-generation-d_104.html [Accessed Day Mo. Year].