To completely realize the savings from flash steam recovery, flash steam should be utilized in an application closer to the source of high pressure condensate.
Flash steam is generated when the condensate is moved from a high to a lower pressure. In order to make up for the difference in sensible heat, the excess heat in condensate is used to boil a part of the condensate back to steam. This constitutes flash steam.
It is preferable to select an application for the flash steam which is reasonably close to the high pressure condensate source. This is because low pressure steam occupies more area and hence requires bigger piping. With an increase in the pipe size, the radiation losses increase, owing to the higher surface area. Thus, when flash steam is transported through long distances it may lose substantial heat through radiation losses and condense into water before it reaches the end point. So the heat loss from large diameter pipes reduces the benefits obtained from flash steam recovery.
Additionally, the larger piping required for transporting flash steam also increases the piping cost. Partially condensed flash steam also is very erosive and leads to pitting and erosion of the flash steam piping, leading to increased leakages.
Thus to ensure flash steam does not condense during transportation and for deriving the maximum benefit from flash steam recovery without high piping cost, flash steam should preferably be utilized at a point closer to the source of high pressure condensate.
Illustration: Relative volume occupied by condensate and flash steam in a condensate flow of 1000kg/hr at a pressure of 6bar.