Steam is used throughout industry, usually either as a force to drive mechanical equipment or as a method of heating. Steam traps are used in these types of applications to ensure that steam is not wasted, helping to control costs and make the process more efficient. In order to establish the kinds of applications where a steam trap would be employed, it is helpful to first understand what they are and how they work.
What is a steam trap and how does it work?
Steam traps are a type of automatic, self-contained valve that separate out condensate and non-condensable gases from a
pressurised steam system. A steam trap allows the condensate (condensed steam) and non-condensable gases (such as air) escape from the system whilst keeping the steam – the critical gas – from escaping.
Steam Traps operate on the difference in physical properties between steam and condensate. Condensate is around 1500 times denser than steam, so will, therefore, collect at the lowest point of the trap. Steam properties also change with pressure; at different pressures, there are different boiling points.
Steam traps can be split into 3 varieties: thermodynamic, mechanical and thermostatic:
Thermodynamic steam traps operate on the dynamics of steam vs condensate and the use of Bernoulli’s principle. This means that when condensate is released through the intake nozzle, the speed increases and a pressure drop occurs. This will flash steam to create a higher pressure to close a valve, thereby slowing the condensate discharge speed of the trap.
Thermostatic steam traps remove condensate through the temperature differential. The valve is controlled through the uneven expansion and contraction of a bimetallic element. A temperature delta causes the element to open and drain the condensate.
Mechanical steam traps come in two main types: inverted bucket traps and float traps. Float traps employ a sealed spherical float, while inverted bucket traps utilise a cylindrical cup.
In float traps, the float is raised or lowered by the level of condensate in the trap. The float follows the condensate level, opening and closing the valve by occluding the intake, causing the valve to compensate accordingly. Float steam traps allow for continuous drainage.
In inverted bucket steam traps, the bucket within the trap is attached to an arm that opens and closes the trap valve. When steam flows into the underside of the inverted bucket it floats, causing the trap valve to close. There is a vent hole in the top of the bucket that allows a small amount of the vapour into the trap, where it is discharged downstream. As vapour escapes through the vent, condensate starts to fill the inside of the bucket, causing it to sink and allowing the trap valve to open. This will discharge condensate. Due to the type of design, this solution only provides intermittent drainage.
Why are steam traps critical?
The steam trap is an essential part of any steam system. It is a key driver in good steam and condensate management, retaining steam for maximum efficiency and retention of energy, but releasing condensate and non-condensable gases at the appropriate time. Without steam traps, over time any steam system would reach equilibrium, and therefore be unable to continue functioning.
Where are steam traps used?
It is clear from the explanation of how steam traps work that any process where steam is used as a prime mover - where the efficiencies gained through minimising energy loss are important - will require a steam trap in order to maintain optimum working rates. Some of the key applications for steam traps are:
Drip applications: When steam loses its heat energy it begins to condensate in steam lines. When this happens, a steam trap is used to remove the condensate.
Process applications: During a heat transfer process, such as would be used in a radiator or heat exchanger, both air and condensate can form and become trapped within the system, making it less effective. A steam trap is used in this case to remove both the condensate and the air.
Tracing applications: steam tracing is used to ensure that a product passing through pipelines at a temperature which is higher than the surrounding air remains at a constant temperature. The product pipeline has small bore steam pipes, or tracers, attached; the heat from the steam is used to maintain the temperature of the core product. Steam tracing applications require steam traps to remove the condensate formed in these pipes.
