To ensure air vents aid achieving higher process efficiencies and work satisfactorily, they should be installed above the condensate level.
When steam is first admitted to a pipe after a period of shutdown, the pipe is full of air. Further, small amounts of air and non-condensable gases will enter with the steam. When the steam condenses; these gases will accumulate in pipes and heat exchangers.
A film of air only 0.025 mm thick may resist as much heat transfer as a wall of copper 400 mm thick. It is therefore very important to eliminate air. Doing so allows optimum heat transfer to take place in the heat exchangers, allowing efficient operation and thus saving fuel.
Automatic air vents for steam systems should be fitted above the condensate level. This would ensure air reaches the vents and is discharged. The best location for air vents is at the end of the steam mains.
In addition to air venting at the end of steam mains, vents can also be installed
- In parallel with buckets trap as these traps are sometimes slow to vent air on start-up.
- Where there is large steam space (such as autoclave), and a steam/air mixture can affect process quality.