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luissandoval
16-10-2008, 09:49 PM
hi Guys:

I have a problem, i'm checking a installation of liquid overfeed system of ammonia, and I found that the vertical recirculator is more small of the symtem need. what is the better solution for this problem?
I hope you may help me.

Best regards.
US Iceman
16-10-2008, 10:12 PM
What do you mean the vessel is too small?

What problems do you see?
luissandoval
17-10-2008, 12:20 AM
US ICEMAN:

I think the vessel is too small because when the sytem is in defrost ( hot gas defrosting ) the system stop for high level of liquid and the pump begin and cavitate, i attach the sketch of vessel, the operating contions are:

LOAD: 73 700 Kcal/h
Circulate rate: 4
Refrigerant: R 717
there are 4 evaporators ( the hot gas defrosting consider 2 evaporator at the same time)
Evaporating temperature: -25ºC
Pump: Q = 1.37^3/h
rP = 38.5m

what do you suggest me?
luissandoval
17-10-2008, 12:23 AM
Sorry¡¡¡¡

I forget attach drawing of vessel.
US Iceman
17-10-2008, 12:25 AM
...the system stop for high level of liquid and the pump begin and cavitate.


If the liquid level is high, then what causes the pumps to cavitate? Normally, the higher the liquid level is above the pump suction the less problems you have with cavitation.

Are the compressors shutting off when high level is reached?
luissandoval
17-10-2008, 12:37 AM
For this system we used a compressor frick (screw compressor) because the compresor exists in the plant this compressor have a capacity of 145 000 Kcal/h and the compressor shutting off when high level is reached. the suction pump is of 1 1/2" of diameter.
US Iceman
17-10-2008, 01:42 AM
When does the pump cavitate?
smpsmp45
17-10-2008, 06:07 AM
What is the defrosting circuit? Since there is enough liquid in the vessel, it should not give any problems for the pumps.
nh3wizard
17-10-2008, 04:42 PM
How many evaps are you defrosting at once? How long has this been going on? What has changed in the system to start this problem? So many questions, not enough information.
RANGER1
17-10-2008, 11:30 PM
Maybe to much load is taken off compressor to quickly at time of defrost and compressor cannot unload quick enough ?
Could try a long pump down on evaporator eg 15-20 mins.
Also check compressor can unload fast enough so as pressure does not
drop to fast causing possible cavitation.
Evaporators not on defrost have to be running and LLSV must be energized to circulate liquid all the time .
It looks like compressor is a bit bigger than required so it may need to be loaded up pretty slow so as not to over shoot .