Steam Traps and Condensate Recovery

There are many varieties of steam traps and for each application they should be chosen with care. There are advantages and disadvantages for each type.

Thermostatic traps do not open until the condensate temperature has fallen below steam temperature. For this reason, it is common to see 1 to 3 M of bare line upstream of the trap - giving a continuous energy loss to atmosphere.

Thermodynamic traps rely for closure on discharging until all condensate is gone and steam enters the trap. There is therefore some steam leakage into the condensate system (if condensate recovery is installed) on every drainage cycle. This can give rise to water hammer. Ob the positive side, these traps can operate with up to 80% back pressure.

Mechanical traps such as the ball float type only discharge condensate. They are only suitable for large flows, such as steam reboilers. They are also relatively expensive.

There are trap manufacturers' web sites which give considerable detail on trap design, performance and selection.

Condensate recovery is always a challenge. If the condensate has to be pumped, then it should be recovered to an elevated drum giving adequate pump NPSH for return to the utility de-aerator. For condensate recovery from the HP steam system to operate satisfactorily, the drum pressure has to be below the HP steam system pressure and so the drum generates flash steam. In a well designed system, this flash steam simply passes into the MP steam header.

Low pressure condensate also loses flash steam at most sites, especially when fed from thermodynamic traps. Depending on the location of the collection drum, it may be worth adding cold water which would otherwise be used as part of the de-aerator make-up. This eliminates the flash steam, reduces the chance of water hammer and retains all the energy apart from insulation loss. An alternative is to install a long, bare, self-draining vent above the drum in order to condense the majority of the flash steam.

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