Brine system refrigeration.... smashed compressor

We have a custom built brine refrigeration system installed servicing a commercial fishing vessel that has killed a compressor after 2 years, here are the system details. Any help would be appreciated in finding the cause of the problem?😁
brine system specs
compressor - bitzer 6je-33y (2 x cylinder unloaders) first unloaded set at -15c - -8c second unloaded -20c - -12c
condensor - bitzer 813hb water cooled condensor
refrigerant - r404a
brine evaporator - stainless steel spiral (flooded) x 6
tx valves - danfoss te5 no3 orifice
oil separtor - bitzer with temprite external oil float
brine tanks - 6 x 5tonne salt water entering at 26-29c pulldown time per tank 16hours
The issue we have is not with the operating parameters of the system once tank temperatures have been achieved but during the initial pull down phase upon start. For 6-8 hours we will have a suction temperature at the compressor service valve of 15-20c which causes the discharge temp to be around 83c would this temp be acceptable or should a liquid injection be used?

Have you had an autopsy done on the dead compressor to establish what caused the failure?

It does need a compressor investigation to find the reason for failure,it could be so many reasons but this needs to be done before replacement as another failure will occur,keep us posted.

Setrad,
All these compressors have a maximum suction superheat at compressor suction stop valve to stay in design limits. Not sure, but might be 20 deg C, check with Bitzer.
I found this looking for max superheat, looks interesting.

http://sporlanonline.com/literature/misc/10-207.pdf

https://www.bitzer.de/websoftware/Ca...180318&mod=HHK

As said above compressor & oil needs to be analyzed.
Also need all conditions when pulling brine down, suction, discharge pressures/temps, superheat, brine.
Also when down to to temp.

Does it have a suction trap?
Oil pressure, does protection work, as well as all other safeties?
Oil levels, is it always a good level?

Setrad
I agree with Ranger as I believe the compressor is running outside its operating envelope during the pull down period causeing the compressor and its lubricant to run too hot . Often the compressor capacity exceeds the Tevs combined capacity and the suction superheat is way too high during the pull down ,but at design conditions, under lower load the Tevs control as required with a few degrees of superheat
One other thing to check and I have experienced this many times, is the water cooled condenser . Make sure the water flow is IN the bottom and OUT the top of the condenser. If it is the other way around then the system is often overcharged and has elevated discharge pressures and temperatures , as the liquid waiting to exit the condenser is subjected to water that has been pre-heated by the highly superheated discharge gas. The liquid , as the hot water passes through the subcooling tubes in the bottom of the condenser starts to boil and causes flashing in the sight glass, so more charge is added which simply backs up into the condenser which starts to submerged the condensing tubes thereby reducing the condensers capacity as tubes submerged in liquid can no longer condense they simply become subcooling tubes, but the waters high temperature will still causes bubbles to appear until the condenser is so full of liquid that the sight glasss clears but at the same time the discharge pressures and temperatures have risen to dangerous levels . Which then causes excessive wear to the compressor and subsequent failure.
Incorrectly piped water cooled condensers will slowly kill compressors. Often the condenser is connected up by a sub contractor who may not appreciate what the function of a water cooled condenser is and what problems will arise by a simple error ,,or maybe it was easier to pipe it that way around !!!!!
A simple check that the condenser is piped correctly is to touch the condenser shell with your hand , the top of the condenser shell should be hot to the touch and as your hand slowly travels down the shell, the condenser temperature will drop and as you get approx to the 4-5 o'clock position on the shell you should feel a rapid drop in temperature as you detect the cold subcooled liquid level. Touching the water in and out tubes will also confirm which way the water is flowing , but checking the subcooled liquid level will with experience give a good onsite if the condenser is performing correctly and if the system charge is correct.

Hi Glenn,
thanks for your reply! The water cooled condenser is definitely piped correctly... the problem with the system is the lengthy time required during initial pull down of the brine tanks (5 tonne water x 6 tanks) once temps are achieved system is running flawless. The problem we have is balancing between pull down and normal operating conditions, we could have a bigger compressor to lower pull down times therefore reducing time of high super heat but then we have an oversized compressor once tanks are down to temp...and being a fishing boat it’s hard to watch the system over its multiple ranges as it’s out to sea for most of the time. All things considered this thing smashed it for 10 years with an open drive bitzer.... I seriously think the quality of bitzer has gone to **** and their compressor are ****ing weak!

Quote:

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Originally Posted by setrad7791

Hi Glenn,
thanks for your reply! The water cooled condenser is definitely piped correctly... the problem with the system is the lengthy time required during initial pull down of the brine tanks (5 tonne water x 6 tanks) once temps are achieved system is running flawless. The problem we have is balancing between pull down and normal operating conditions, we could have a bigger compressor to lower pull down times therefore reducing time of high super heat but then we have an oversized compressor once tanks are down to temp...and being a fishing boat it’s hard to watch the system over its multiple ranges as it’s out to sea for most of the time. All things considered this thing smashed it for 10 years with an open drive bitzer.... I seriously think the quality of bitzer has gone to **** and their compressor are ****ing weak!

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Have you found out what happened to compressor yet?

Is it in design range, ring Bitzer or Actrol.

Do all safeties work, as would have had a few extra than before.

Hi setrad
If the system runs during pull down with a very high superheat, have you thought about using electronic stepper expansion valves. The problem with the TE 5 valve is the small movement of the diaphragm with the corresponding small capacity band, so at pull down evap condition the compressor can do more duty than the expansion valves leading to high pull down superheat conditions and overheated compressor oil and componentry
Using an electronic stepper expansion valve the valve capacity matches the compressor capacity right across the range , so that the compressor is never subjected to damaging high superheat conditions also the pull down time is greatly reduced as the evaporator is utilised fully during the pull down as well as near set point. I will get the full Bitzer capacity chart and see how the TE5 no 3 orifice valves match from pull down to set point , I’ll also select an electronic valve and controller for you to think about

Attachment 15092

All fine.