Condensate load on a steam main

[McCormick93]

Hello,
I'm sizing traps for a long straight 8" pipe carrying 50 psi saturated steam, with 0F ambient.
Using the tables in steam equipment catalogs, they produce an answer in the neighborhood of 50 lb/hr condensate per 100 ft insulated pipe.

Typically I like to check the tables against my own calculations. In this case, my calcs gave me around 1.2 lb/hr condensate per 100 ft insulated pipe.

At first glance, it looks like the catalog tables assume crummy insulation or they incorporate a generous safety factor. Has anyone else encountered this problem with the tables in Armstrong or Spirax Sarco books?

 

[katmar]

The trap suppliers' recommendations will probably be based on start-up conditions, during which the large mass of cold pipe has to be heated. The steam consumption during this stage is much higher than the steady state consumption once the pipe is hot.

The choice depends mainly on how often you start up that line. If it is once a year, then you can proabably afford to decrease the rating on the traps, and open the bypasses during start-up. If you shut down every week-end, you may prefer to have the traps handle the start-up load automatically.

Remember also that a larger trap will waste a lot more steam than a small one if they are stuck open. How often are your traps checked and maintained?

 

[CRG]

A rough calculation of mine yields 17 lb/hr per 100 feet for 2” CalciumSilicate ins on 8” 50 psi line. Note that Spirax Sarco table is based on 80% efficiency for insulation, or around ½” CalciumSilicate insulation.

Double check your calculations and look carefully at the units.

 

[TBP]

Depending on how long this line is, and how far apart the drip traps are, you'll likely wind up using a load that will take you into a range that's the smallest of the 1/2" trap capacities anyway. Remember that on start-up, the very first thing you have to kick out of the line, is the air. Then it's the steam it takes to heat the cold line, which gives you the highest condensate load combined with the lowest pressure differential to move it across the orifice in the trap. The trap selection needs to condsider these conditions.