Selection tables and advice on trap selection for different types of steam mains, headers and off-takes are included in this tutorial, together with process vats and pressure reducing valve stations.
Selecting Steam Traps - Steam Mains; Tanks and Vats; Pressure Reducing Valves
Process vats (rising discharge pipe)
Figure 11.11.5 is most important. A coil in a process liquor vat should have a fall, and finish in a ‘U’ seal if the outlet rises. The rising pipe must be of small diameter. By placing a small pipe down to the bottom of the seal, and closing the pipe at the top with a convenient coupling, steam locking is prevented. The steam trap can be a float-thermostatic, thermodynamic or a balanced pressure type. A thermodynamic trap can sometimes prove useful in the case of certain corrosive liquors if the coil leaks, because it is less affected by corrosion than the other types. Should there be fear of contamination of the condensate by the tank contents, allow the condensate to drain to waste. Any condensate from corrosive liquors should be carefully disposed of, particularly if there is a fear that the tank contents could contaminate the steam and condensate system. A vacuum breaker should be fitted on the steam inlet side of the coil if the tank content is corrosive, to remove the possibility of corrosive liquor being drawn back into the steam supply.
Process vats (discharge pipe at base)
If the coil has an outlet through the side of the vat, Figure 11.11.6 shows the recommended drain arrangement using a float-thermostatic trap. Thermodynamic and balanced pressure types can also be used. It is important to use an eccentric reducer on the end of a horizontal coil, not a concentric one. A concentric reducer could cause waterlogging of the bottom part of the coil, which would reduce heat transfer, and increase the risk of waterhammer.
The system will operate better if condensate from the trap is allowed to fall to a non-flooded return line or vented receiver for pumping.
Pressure Reducing Valves
Where there is a possibility that the pipework downstream of reducing valves could be shut off during normal operation, a trapping point should be provided to drain any condensate formed during this period. This keeps the downstream pipework free of water and protects the reducing valve from filling with water and 'locking-up'. Float traps discharge condensate continuously and do not disturb the pressure in the pipe when discharging.