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Is Warm-up Considered in Condesate Pipe Sizing?

Is Warm-up Considered in Condesate Pipe Sizing?

Is Warm-up Considered in Condesate Pipe Sizing?

(OP)
When sizing steam condensate return lines, do we need to consider warm-up?  I understand the need to do so for steam traps, but I have never seen it for condensate piping.  I am guessing that although there is more mass flow, the condensate will probably be subcooled enough to reduce the percentage of flash.  And since the flash steam is the governing factor in condensate pipe sizing, I am guessing that there is no need to consider additional liquid flow during warm-up.  In other words, if the pipe is correctly sized for the full-load flash percentage, then it will be large enough for warm-up.

Agree?  

RE: Is Warm-up Considered in Condesate Pipe Sizing?

My refinery experience is that warm up is not considered even in steam trap sizing.

The length of time between warm-up situations does not justify the additional expense to capture the condinsate. No use spending dollars to save pennies.

During warm-up drain valves in the steam line are cracked open to release the additional condensate.

NozzleTwister
Houston, Texas

RE: Is Warm-up Considered in Condesate Pipe Sizing?

Nozzletwister, your experience is undoubtedly true for an industrial system with trained operators.  The typical HVAC or light process system is not constantly attended and warm-up drains are rarely used.  Warm-up load is an important consideration on such systems because if condensate is left to pool in the piping, it could lead to hammer.  But I agree, the full load case undoubtedly provides enough piping capacity, it's just the traps that need consideration.

RE: Is Warm-up Considered in Condesate Pipe Sizing?

It's a bit pointless sizing the trap for start-up loads if the piping can't get the condensate to and away from the trap. I suspect that if you do the detailed calcs for the low-end systems referred to by RossABQ, you will find that the loads are so light that the piping is oversized anyway just to make them self-supporting. A heater supplied with a 1 ot 2" steam line probably only needs a 1/4" condensate line, but you will find a 3/4" or 1" line installed for practical reasons.

On an industrial or refinery application you should size the piping for at least double the average load anyway because there will be flow fluctuations around the average.  This will help with the start-up situation.

NozzleTwister raises a valid point over the time between start-ups.  If this is a once-a-year thing then maybe you can live with it, but with smaller factories that start up every week or fortnight a few hours lost in start-up can be significant. My personal feeling is that it is worth spending another $500 on piping to ensure that a 2 million dollar distillation column runs smoothly.

Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com

RE: Is Warm-up Considered in Condesate Pipe Sizing?

If the condensate piping is sized correctly for the hot two-phase flow of steam trap discharge, the warm-up load will be no problem because it will be all water.  The very low or atmospheric pressure steam of flashed condensate has VERY large volume compared to even the much larger flow rate of the all liquid start-up flow.

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