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? is this the correct forum or should i be posting somewhere else?

[Sandro Baptista]

Daredevil,

Propylene (glycol?) superheated??

+78ºC is not a high discharge temperature. check the operating limits of the screw compressor and check the setpoints of the controller.

[daredevil]

no c3h6 propylene. the vendor of the refrigeration package has provided a trip on high compressor discharge temp 78 deg C.
what i meant was at the compressor inlet saturated propylene should have a temp of about -15 deg C at suction pressure of 3.5 bara according to our simulations...but weve found this is much higher upto 0 deg C

[Sandro Baptista]

no c3h6 propylene. the vendor of the refrigeration package has provided a trip on high compressor discharge temp 78 deg C.
what i meant was at the compressor inlet saturated propylene should have a temp of about -15 deg C at suction pressure of 3.5 bara according to our simulations...but weve found this is much higher upto 0 deg C

A high superheat could result on higher discharge temperatures...of course the magnitude depends on the refrigerant used. For example for ammonia this fact is very important.

Does the evaporator is been well fed? Also if there is a high pressure drop on the all suction line that would "help" to get higher superheated vapor at the compressor inlet.

[K.R.Iyer]

discharge temperature is a function of suction gas temp and the pressure ratio (discharge / suction pre). both these should be relatively lower if you want to lower the discharge gas temperature. not sure if this helps...

Is propylene a refrigerant in screw? I have not heard before. other forum people may be knowing better.

[Magoo]

I had never heard of it before, but Mr Google says its R1270 propene[ propylene] made by Linde.

[sterl]

Propylene not far off propane. Mixture of (2) called MAP gas....

What lubricant being used and how is it cooled? Many of the higher suction pressure hydrocarbons do not require very much cooling at peak loads but depending on the compressor and oil circulation will need considerable cooling at low loads....And the oil cooling determines your discharge temp; the 2-temperatures should track each other or even be nearly identical depending on how your are cooling the oil as well as how you are managing its flow...