Loosing liquid out of receiver1

[Chevy 383]

Hi guys am a greenhorn at this so go easy. Have an ongoing very annoying issue with a 3 stage NH3 plant! Theres 2x 465kw 250 VLD Mycom screws taking care of IP load (180kpa), 2x 265kw 320 VMD-B Mycom screws doing LP duties (-10kpa) and 1x 465kw 250 VLD Mycom screw doing ULP duties (-40kpa) can also do IP load! This is a liquid recirculated plant with all hand expansion valves set to between 1 and 1.5 turns open on all coils and PHE's The main LP compressor is the only one with a VSD. Theres 4 BAC evaporative condenser and the fans are all on VSD's and ramp up and down together, the pumps are all fixed speed! The issue am having is liquid getting held up out in the field then not returning and the compressors going out on hi discharge temps or oil temps (oil coolers are liquid thermosyphon coolers). Most of the time i find a coil (large) iced up so defrost it and returns. Also seems if plant does shut down alot of liquid returns to the pots and plant can re start and run. Any advice/info would be much appreciated and. Realise very hard to get a real handle of problem with the limited info so can answer any questions. Cheers.

[RANGER1]

Chevy 383,
Sounds like multiple problems so can only start with most basic issues.
Thermosyphon oil cooler should have preference of liquid above all else.
This can achieved by vessel design so level can not go down below X % mechanically
with a float/probe, or piped internally so liquid level has to be above say 25% or whatever
for liquid dip tube to pick it up.
As long as it works when there is a level then above should eliminate that problem.

As far as liquid in vessels there are a few reasons why it can get overfilled.
You named one with defrosting of large air cooler.
If compressors shut down on high oil/discharge temps because of low liquid levels in reciever or whatever
then liquid makeup solonoids should be interlocked with compressor control .
If for example low side compressors shut down on a fault then liquid makeup solenoid to low side vessel should be turned off until fault is rectified & reset.
This prevents overfilling of vessel as liquid pump sends it away but comes back when compressor/s are restarted possibly causing high levels.

Maybe this is relevant to you?

If you have a probe on liquid reciever maybe you can instal minimum liquid level in your liquid reciever.

Do your liquid pump cavitate at all

[zeh0085]

What is the outside temperature? Have you explored your condensers to see if your logging liquid in them?

[Chevy 383]

Hey guys thanks for the heads up, I have since put in 1.6 tonnes of ammonia in the system and this has settled it down alot , still believe its short as this raised the receiver from approx 35% average to approx 37% and if there's an ice up on a coil it does'nt drain the receiver and shut down system. Am unsure how the receiver vessel is piped internally so the float you are talking about sounds interesting, could you give me a bit more info please?

[Magoo]

Hi Chevy.
Sounds alot like the TipTop site. did some work there recently.

[RANGER1]

Hey guys thanks for the heads up, I have since put in 1.6 tonnes of ammonia in the system and this has settled it down alot , still believe its short as this raised the receiver from approx 35% average to approx 37% and if there's an ice up on a coil it does'nt drain the receiver and shut down system. Am unsure how the receiver vessel is piped internally so the float you are talking about sounds interesting, could you give me a bit more info please?


If you have a level probe on liquid reciever you can have it programmed in PLC or in series with float switch on reciever ,so as liquid makeup solonoids cannot be energized below a certain level.
If you do not have anything then possibly instal a liquid level control float or a probe & programme in as above (level set point is in series with level control/solenoid).
These have to be installed on level control column on liquid reciever.

Probes could be Hansen or Danfoss
LLC float control usually Parker,Hansen or Danfoss

[Josip]

Hi, Chevy 383 :)


Hi guys am a greenhorn at this so go easy. Have an ongoing very annoying issue with a 3 stage NH3 plant! Theres 2x 465kw 250 VLD Mycom screws taking care of IP load (180kpa), 2x 265kw 320 VMD-B Mycom screws doing LP duties (-10kpa) and 1x 465kw 250 VLD Mycom screw doing ULP duties (-40kpa) can also do IP load! This is a liquid recirculated plant with all hand expansion valves set to between 1 and 1.5 turns open on all coils and PHE's The main LP compressor is the only one with a VSD. Theres 4 BAC evaporative condenser and the fans are all on VSD's and ramp up and down together, the pumps are all fixed speed! The issue am having is liquid getting held up out in the field then not returning and the compressors going out on hi discharge temps or oil temps (oil coolers are liquid thermosyphon coolers). Most of the time i find a coil (large) iced up so defrost it and returns. Also seems if plant does shut down alot of liquid returns to the pots and plant can re start and run. Any advice/info would be much appreciated and. Realise very hard to get a real handle of problem with the limited info so can answer any questions. Cheers.


Hey guys thanks for the heads up, I have since put in 1.6 tonnes of ammonia in the system and this has settled it down alot , still believe its short as this raised the receiver from approx 35% average to approx 37% and if there's an ice up on a coil it does'nt drain the receiver and shut down system. Am unsure how the receiver vessel is piped internally so the float you are talking about sounds interesting, could you give me a bit more info please?

welcome to RE forums .... don't worry we do not bait .... ;), maybe sometimes....

assume this is an older plant which was running well some time ago ... and now something went wrong ...

... try to observe liquid level within receiver when complete plant is running "normally", also try to defrost some evaporators manually to observe liquid level, check liquid level setup for each separator .... maybe you have some air within system due to LP system (ingress of air) make purging ....

if possible attach a schematic drawing of your plant ...

According to minimum/maximum liquid level within separators and receiver you can make some decision about further charging amount .... if you recharge from cylinders it is not a problem ... adding one by one cylinder you can charge your system very accurate ...

Of course if you running that plant with help of PLC then you can observe status of your plant in many points in the same time and act accordingly .... we do not know too much about your plant but maybe can help if you inform us with as much as possible data....

Anyhow whenever you need some help, revert to RE forums ...

Hope this will help a little...


Best regards, Josip :)

[aham]

I agree Josip, sounds like system may be contaminated with air or other non-condensables. May even have hydration built up on low side. Water has a large affinity for Ammonia and will migrate to low side of system and can cause problems.

[aham]

a good system purge may help out tremendously.

[Mark Selby]

All good info above but have you addressed why the coils are freezing up in the 1st place???