submerged return line in condensate drum 1

[amar122amar]

we have a LP condensate flash drum. The flashed steam passes through fin fan cooler, and return of fin fan cooler goes back in the drum as shown in the fig (attachment). The return line is submerged in the tank below the normal level. What is the purpose of submerged return line?can't it be above liquid level? Pressure in the drum is maintained by venting in the atmosphere or putting nitrogen in the fin fan outlet line (split range control valves).The condensate pump makes a lots of noise. Is it possible that N2 is entrained in the liquid and going to pump.

 

[katmar]

It is important that the return line from the condenser should discharge below the surface level of the condensate. If it were not done this way steam would be able to flow up the return line. Depending on the piping geometry, this could impede the flow of condensate back to the vessel. Also, if the fin fan condenser sub-cooled the condensate it could result in hammer in the return line.

The pump noise is much more likely the result of cavitation due to insufficient NPSH than being caused by dissolved or entrained N2.

Katmar Software
Engineering & Risk Analysis Software

http://katmarsoftware.com

 

[MortenA]

You write "steam" but do you mean vapour? Steam is normally H2O.

Your system seems like a solvens reflux system - do you have any significant amount of liquid condesing?

Re entrained/dissolved n2: I dont think this causes cavitation - because as the word implies something has to cavitate - and i doubt your pressure gets so high that the N2 does that - although it may be possible to dissolve some additional N2 at the increased pressure i doubt that you are excatcly at the line where all the N2 dissolve - and just that.

It seems more likely to me that the cavitation is because your liquid is near its boiling point. Either adding cooling to the vessel or icreasing the pressure could solve your cavitattion problem.

Best regards

Morten

 

[gerhardl]

I agree with both MortenA and Katmar. Look at it this way:

When hot condensate reches the condensate flash drum the flash drum does exactly that: flashes off steam (or vapour), while you maintain a certain pressure in the tank, balancing the level of condensate in the bottom with a certain level of vapour above (by coling off vapourization energy).

In this way the condensate will be at near the vapourization (boiling) point at that pressure.

If you lower the pressure, the boiling point will be lowered, and the condensate will flash again.

In all probability this is what happens in or near the pump, and then giving the cavitation noises and effects, as MortenA and katmar has pinpointed.

Your cure would be to ensure that the outlet layout and pump type is suitable for the purpose. Try to contact a company specialicing in steam/vapour condansate pumping and steam handling components.

It might also be an idea to let the pump be controlled by the condensate level inside the tank, to ensure you start with putting condensate into the pump, not already mixed with vapour.

Same goes for a look at internal layout and amounts to ensure that the return from the fin cooler is thorugly dissipated and not creating gas or vapour bubbels mixed in with what is drawn into the pump.

Would the control be easier with a standing tank?

 

[CJKruger]

amar122amar,

1) Check the NPSH available vs required, and ensure there is at least a 5ft or 25% margin. Water needs a bigger margin than hydrocarbon mixtures.

2) Ensure the water/N2 return is on the opposite end as the pump suction.