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fold67
29-09-2016, 03:58 AM
Hi all,

Taking a break from designing and doing some troubleshooting. Over the last couple of weeks we've been having problems in our engine room with our inter cooler going to high level and shutting down our high stage compressors which then takes out our low stage compressors due to high discharge pressure saftey cutout (cut out @45psig, normal operating pressure ~25psig). This started after we enlarged the feed line to the inter cooler coil from 1" to 2" because we were constantly low on NH3 in the vessel. I don't think we should have gone to a 2" feed line but rather either a 1-1/4 or 1-1/2" feed line. We have four "small" (30-50TR) evaporaters we run off the "intermediate" pressure / HSS with BPR's to maintain ~40degF in our cold rooms. The intercooler seems to only go to high level while we have no real heat load for the system, less than 300 ton on a 1200 ton system.

Any thoughts on what might be causing it?
Brian

Magoo
29-09-2016, 04:53 AM
Hello Brian,
what is controlling the liquid level in the inter cooler vessel?.

Grizzly
29-09-2016, 06:25 AM
Hi Brian.
Magoo's reply makes me think.
He is thinking along the same lines as I am reading your post.
Increasing the pipe sizes will increase the potential for surged volumes of liquid.
These can create large fluctuations in the level of the working level in the Intercooler.
Check your level control and try reducing the working level away from the High level.
Or try reducing the fill rate!
Etc.Etc.

RANGER1
29-09-2016, 09:10 AM
Assuming you have a solenoid & hand expansion valve, suggest new solenoid if not already replaced.
Hand expansion valve would have been open to far with previous smaller line.
Under high load liquid feed should be roughly 70% on 30%off.
Seasonal changes may need adjustment to suit loads.
Level control column LLC float switch faulty (If new type Parker extremely likely) contacts.
Oil fouling control column another possibility.
Probe faulty, oil on probe.
Recommend modulating control valve for best plant control.

Just guessing everything really!

fold67
29-09-2016, 11:29 AM
Thank you for the replies, yes the vessel is controlled by three floats on a sight column, low(on) mid level(off) high level cutout, that modulate the on/off of a new solenoid valve train. We have the hand expansion valve open half to three quarters of a turn. Floats and valves are all Parker made and brand new as of labor day. Possible small internal coil leak not being noticed under full load? The vessel was manufactured in 1972, I know were running on some old equipment, have a howden compressor with well over 20 years on it, can't remember off the top of my head right now. But for now we've resorted to turning the solenoid control off an hour before the load goes down, if we are told enough time in advance, to flash off the ammonia so we don't go to high level.

Brian

RANGER1
29-09-2016, 08:43 PM
Brian,
We have found serious problems with Parker LLC switch with new style magnet, especially on frequent use like liquid make up, Hansen seem OK.
Test with ohm meter multiple times slowly inserting screw driver or similar to test switching mechanism.
Maybe need to observe level under low load to see what's going on first hand if nothing obvious.
Oil can dampen reading in column, try to drain anyway, might have built up when you did modifications.

Magoo
30-09-2016, 12:14 AM
Hi Brian,
is there any chance the side load freezers are flooding after low stage booster load stops and system capacity drops.

Josip
30-09-2016, 08:38 PM
Hi, fold67 :)

welcome to RE forums ...


Thank you for the replies, yes the vessel is controlled by three floats on a sight column, low(on) mid level(off) high level cutout, that modulate the on/off of a new solenoid valve train. We have the hand expansion valve open half to three quarters of a turn. Floats and valves are all Parker made and brand new as of labor day. Possible small internal coil leak not being noticed under full load? The vessel was manufactured in 1972, I know were running on some old equipment, have a howden compressor with well over 20 years on it, can't remember off the top of my head right now. But for now we've resorted to turning the solenoid control off an hour before the load goes down, if we are told enough time in advance, to flash off the ammonia so we don't go to high level.

Brian

a lot of informations, but (at least for me) some of them missing .... hand made sketch of your system in question ...

regarding feeding line ...you can put even 3"+ pipe (bigger pipes with bigger valves can cause hamering what can be estremely dangerous), but volume of liquid entering into your intercooler depend on the size and opening of your hand regulating valve (valve flow factor Kv ..must be calculated - https://en.wikipedia.org/wiki/Flow_coefficient#Kv_.28flow_factor.29) and of course condensing pressure (assuming) your liquid is coming from receiver ....

You need to adjust your hand regulating valve during maximum load ... you liquid level would be at mid level between low and mid float ... i.e. during normal run with full load your feeding solenoid valve would be constantly open ... don't worry it will not affect compressor ... anyhow you need to remove expansion gasses from feeding liquid ... if you have feeding line open at reduced amount of liquid entering into intercooler (enough liquid to cover feeding coil for low temperature system) expansion gasses will be also reduced ...

I think you have some problem with floats on a sight column ... if they are arranged well by levels the mid float must cut off solenoid valve and feeding into vessel should stop and liquid level cannot act to upper float i.e. trip high stage compressors ... this function you must check ...

..... what is the size of your sight column (3" pipe or less) ... is that pipe isolated!?! probably with ice .... if not try to put some isolation around to reduce heating from environment

.... do you have hand valves on the top and bottom of your sight column? if yes ... try to close upper valve and then open again for one turn or less .. this will reduce boiling of liquid in sight column and probably the top float will not be affected by boiling liquid ... we are using special orifices on the top side to reduce affect of boiling liquid within sight column or side pipe for level transmitters i.e. floats ... there are so many level control systems in use

of course as said before ... we are discussing technical matter without any sketch ... for me that is very hard ... plus we are "speaking in language which is not my mother tongue" ... but sketch can override a lot of "lost in translation" problems ....

If your internal coil is leaking I believe you can prove that ... unfortunately cannot be done a lot ... just take care about until you replace that vessel ... it is enough old to be retired;)

This is my "thinking out loud" ... anyhow I do hope it will be of some help to you...

Then again maybe your floats are faulty;) ... as per RANGER1 explanation ...


Best regards, Josip :)

RANGER1
15-10-2016, 01:53 AM
Just a few extra thoughts with system.
pipework design could have traps or risers that could fill up & return liquid in a surge.
Also compressor loading to quickly causing surge.
The best tool to help is level probe with trend, they are worth their weight in gold as long as they work correctly.

Magoo
16-10-2016, 12:34 AM
Or if a sub cooler circuit internally fracture from high turbulence, leaking HP liquid int inter cooler under low low load conditions.