2 replies to this topic

[HKk]

Sir

We are opearting a 2 stage N2 compressor to pressurize N2 from 40 kg/cm2 to 120 kg/cm2 . however due to certain changes in the system N2 is available at 6 kg/cm2 only . Is it possible to use the same compressor with same pressure ratio.if same pressure ratio is achieved , the discharge pr. would be around 18kg/cm2. What parameters are to be kept in mind while changing suction from 40 to 6 kg/cm2.

Regards

HKK

[akslzf]

To repeat what has been said a few hundred times in the past, state your case in as much a detailed manner as possible. I presume you are talking about a reciprocating compressor. Or is it a screw compressor?
First of all, all positive displacement compressors, deliver a constant volume of gas and work towards matching the discharge header pressure, irrespective of the suction pressure.
Assuming this to be a reciprocating compressor, for whatever reason, if your suction header pressure has dropped from 40 to 6 barG, but the discharge header pressure continues to be at 120 barG, the compressor will strive to achieve a discharge pressure of slightly above 120 barG so as to force the gas into the discharge header. This is, provided, the DRIVER IS ABLE TO DELIVER ADEQUATE POWER TO ACHIEVE THIS.
A drop in suction pressure will therefore cause a corresponding increase in load on the piston rod and reduce the rod load reversal & lubrication to the cross head.
Due to the tremendous drop in suction pressure in your case, the rod load is bound to be excessively high, load reversal absent and driver power inadequate, in your case. Check the rod load before proceeding. Consult the O&M manual or the OEM. Or come back with details of the compressor and rod.

[mech_eng]

Hello, Hkk!
N2 compressor is the enough safety thing and you can try to change operation conditions without any fear. Simple run it and keep your eyes opened!
Keep in mind that the pressure difference between discharge and suction must be less than (120-40)=80 kg/cm2.
During the trial start-up you can get data to order new valves.