Steam boilers are integral in manufacturing and processing units to generate steam utilized for heating, drying, and sterilizing purposes. Steam is essential for process operations as it has high energy holding capacity, it is safe to use, easily transportable, and economical to generate. However, steam boilers face various phenomena that need to be addressed or prevented. One such occurrence is known as flash steam. The steam that is formed by the hot condensate with reduced pressure is termed flash steam. Flash steam is no different than ordinary steam except that it is produced as the stream is exiting the boiler system and there is a pressure drop at the boiler’s outlet, which is the exit of the steam trap.
What is Flash Steam?
Flash steam is generated when the high-pressure condensate is released to lower pressure. The term flash indicates the way it is formed. Water boils at 100°C at atmospheric pressure. Steam is usually utilized at a pressure above the atmospheric pressure inside the steam piping. As the steam loses its heat by transporting it for the process operations or radiation loses, it results in the condensate. The condensate formed is of the same pressure and temperature as that of the steam.
The pressurized condensate is introduced to the atmospheric pressure with more energy than it could be contained in atmospheric pressure. The excess energy is utilized for converting the condensate. The occurrence is known as flashing and the steam generated is known as flash steam.
Due to flash steam, steel and copper piping connected to the outlet or steam traps are more exposed to internal corrosion. The steam trap becoming clogged leads to high stresses at the internal piping system. It removes the internal corrosion resistance coating that results in the thinning of the internal metal surface. The steam carries the impurities and further damages the pipe.
The formula to calculate the flash steam generated is as follows,
Flash % = (Hf1-Hf2)/Hfg2
Where,
Hf1 = Sensible heat in the condensate at higher pressure
Hf2 = Sensible heat in the condensate at lower pressure
Hfg2 = Latent heat of the steam formed at lower pressure
The volume of Flash Steam Generated:
Steam is denser compared to water, resulting in a small increase in the percentage of flash steam generated to appear as a large volume increase of generated steam. To understand it in-depth, the condensate volume at 100°C (212°F) is 0.00104 m3/kg, and the volume of atmospheric steam is 1.67 m3/kg. As high-temperature condensate at 1.0 MPaG (145 psig) is released to lower pressure like atmosphere, 16.1% by mass of that condensate flashes into steam.
Utilizing Flash Steam:
The vapor cloud is formed by flash steam as the aftermath of condensate discharge. Since the quality of flash steam and live steam is the same, many process units utilize a considerable amount of flash steam whenever possible.
Reusing flash steam in a lower pressure system generated by the high-pressure system leads to significant energy savings, along with reducing vapor clouds. The waste heat management system assesses the condensate recovery system and the flash steam recovery system as pairs.
Flash Steam Recovery:
A Flash steam recovery system releases flash steam into a vessel instead of the atmosphere. It is reintroduced in the steam boiler system or for feeding low-pressure applications. Condensate that is flashing while leaving steam traps enters the flash vessel. It reaches halfway with the steam and condensate separating to the top and bottom of the vessel, respectively.
Effective flash steam recovery system requires various factors:
- It requires adequate high-pressure condensate for releasing sufficient flash steam to result in cost-effective recovery
- Appropriate low-pressure application for the recovered flash steam. It is necessary to ensure that the demand for the flash steam is in accordance with its availability
- The application for the flash steam should be approximate to the high-pressure condensate source
- The steam trap and equipment should properly function against the backpressure applied by the flash system
- The steam pressure reaching below the determined flash steam pressure reduces the overall amount of flash steam formed
Advantages of Flash Steam Recovery:
- Improvement of process operation by recovering heat energy from the condensate boosts the overall efficiency of the steam boiler.
- Increase in the steam boiler capacity by reducing lost steam as flash steam, which is utilized for other operational purposes
- Reduction in Carbon emission
Conclusion:
Flash steam is an effective method to reuse steam and save energy and production costs of the manufacturing facilities.
Since our inception in 1983 as a boiler manufacturer in Pune, Rakhoh Boilers have emerged as a leading steam boiler and thermal solution provider globally. With more than 3000 successful installations of boilers in over 26 countries, Rakhoh ensures efficiency and reliability with their steam boilers, waste heat recovery system, thermic fluid heaters, boiler accessories, and boiler services.
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