Recovering flash steam returns almost 50% of the energy in condensate but care must be taken to ensure the back pressure created does not affect the process.
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.
If full use is to be made of flash steam, the first essential is to have a sufficient supply of condensate, from loads at sufficiently higher pressures. This is to ensure that enough flash steam will be released to make recovery economically effective. The steam traps and the equipment from which they are draining the condensate must be able to function satisfactorily while accepting the back pressure applied to them by the recovery system.
In particular care is needed when recovering flash steam from condensate leaving temperature controlled equipment. At less than full loads, the steam pressure will be lowered by the action of the control valve. If the steam pressure approaches or even falls below the flash steam pressure, the back pressure will be higher than the steam pressure and as a result condensate evacuation will be restricted. Thus flash steam recovery from in such situations becomes impractical.
Thus care must be taken while designing flash recovery system to ensure the back pressure created does not affect the process. The quantity of flash steam generated depends on the amount of heat that can be held in condensate. Typically, 10% - 15% of the condensate is converted to flash steam with an energy content equal to 50% of the energy in condensate. Thus flash steam recovery can deliver quantum savings to the plant but the system should be well engineered.