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What is flash steam?
What is flash steam?

What is flash steam? 

You often see plumes of flash steam being vented from plants and factories, which is both unsightly and uneconomical.

Many people wrongly think that flash steam is a waste product but really it’s no less valuable than live steam and is an equally useful source of heat.

Flash steam is the name given to the steam formed from hot condensate when the pressure is reduced.

No different from, ‘normal,’ or ‘live,’ steam that is produced at a boiler, steam generator, or waste heat recovery generator, it occurs when high pressure / high-temperature condensate is exposed to a large pressure drop, for example when exiting a steam trap.

High-temperature condensate contains an excess of energy, which prevents it from remaining in liquid form at lower pressure. 

This excess energy causes a percentage of the condensate to flash and it happens because the saturation point of water varies according to pressure.

The saturation point of water is 100 °C at atmospheric pressure but at 10 bar g it is 184 °C. 

So what happens when condensate kept under pressure at 184 °C is released to the atmosphere?

The condensate contains too much energy (enthalpy) to remain entirely liquid and a portion of it evaporates, causing the temperature of the remaining condensate to drop to the saturation temperature (i.e. 100 ° if discharging to atmosphere).

This phenomenon is known as flash evaporation.

When hot condensate is discharged into a lower pressure environment, its enthalpy (total energy) remains the same, but its saturation point drops (the temperature at which condensate can exist in both the liquid and gaseous state).

To compensate for the excess amount of energy, part of the water molecules absorb the excess energy as latent heat and evaporate to form steam.


Download our eBook to read more about where you can find flash steam and why and how you should recover it.