screw compressor high discharge temp

[daredevil]

we have an oil flooded screw compressor for propylene refrigeration service that trips frequently on high discharge temperature(78 deg c, ) (usually when the plant is running at turndown)what changes do u guys think can be made to lower the discharge temperatures(lowering suction pressure,increasing economizer duty etc). I have also noticed that propylene coming to the compressor from the evaporators is sometimes highly superheated at the suction conditions. what could be the possible reason?

[yorkman_gr]

1) can you define what is oil flooded screw compressor? in my +30 years on the refrigeration systems i never heard of it, so please if your be so kind can you expand my knowledge by explain to me what compressor is that?
and who is the maker of this compressor?
2) you said that propylene entering the oil flooded screw compressor from the evaporator in a very high superheated conditions and you ask the cause of this?
Botom line according to your question you have one refrigeration system with one oil flooded screw compressor that is compressing propylene in gas form, the condenser liquified the propylene, you have expansion valve that expands the propylene, and evaporator that using propylene to absorb the heat.
Do i got it correct ?

[goshen]

Hi
we indeed need some info on type of unit ,type of refregirant,and so on .
good luck

[daredevil]

yes you are right. An oil flooded screw compressor is a screw compressor where oil is injected to lubricate the internals and remove partly the heat of compression and the oil is removed in a downstream separator

[daredevil]

propylene is the refrigerent and Mr yorkman is spot on.

[yorkman_gr]

i am not gonna argue with no one on this forums but slowly i will forget the basics about refrigeration here its time some others gonna help you good luck with your flooded screw and your propylene refrigerant

[RANGER1]

we have an oil flooded screw compressor for propylene refrigeration service that trips frequently on high discharge temperature(78 deg c, ) (usually when the plant is running at turndown)what changes do u guys think can be made to lower the discharge temperatures(lowering suction pressure,increasing economizer duty etc). I have also noticed that propylene coming to the compressor from the evaporators is sometimes highly superheated at the suction conditions. what could be the possible reason?

daredevil

I think discharge temp safety cut out could easily be increased to minimum of 90 deg C.
Most compressors like Howden can go to 100 deg C.

What is the oil tempreture when discharge temp goes up to cutout point (78 C)
& is this its normaloil temp?

Is the oil injection line into rotors always on ie no solonoid or automatic shut off valve?

Have you an adjustment or metering valve on oil injection you could open a little to
reduce discharge temp?

Where are you measuring suction superheat as if compressor is unloaded etc maybe no gas flow in suction line?

What pressures/temps is system running at?

[daredevil]

The oil temperaure is roughly always the same as the discharge temperature.
Yes the oil injection is always on
We cannot alter the oil flow rate
P,T (3.5 bara,-12 to 0 deg C)suction
discharge(16 bara 70-78 degC)

[Magoo]

Hi daredevil.
what is the oil temp., entering compressor injectors and bearings. Should be approximately +45'C./ leaving the oil cooler. The oil temp in separator will always being same or close to discharge.

[daredevil]

Yes its between 45 to 50 deg C.

[RANGER1]

daredevil,
Is this a new plant or a plant that has been running OK until now?

Is oil pressure differential oil pressure feed or with an oil pump?

Maybe oil filters need changing.

By saying brand of compressor it might help a bit as well.

Your not giving much information to work on!