1 reply to this topic

[GSaikrishn]

Sirs,

at platforming unit we have a centrifugal compressor which recycles hydrogen rich gases (6.6 mw)(hydrogen mol % of ~87%). The discharge of the compressor is used to maintain the reactor pressure as well as to lift the fresh liquid naphtha. Now the centrifugal compressor has following operating points.

Im unable to generate a sketch right now, please bear with me.

Flow path is as follows:

Liquid feed + Recycle gas -----> Combined feed exchanger -----> Furnace -----> Reactors -----> Combined feed excahnger -----> Condenser ------> Separator -----> Recycle gas compressor ----> Liquid feed + Recycle gas (closed loop)

a) Suction temperature: 45 Deg C
suction pressure before suction valve: 5.8 kg/cm2(g).
c) Suction pressure after suction valve: 4.55 kg/cm2(g). Effectively this is the suction pressure.
d) Discharge pressure: 10.5 Kg/cm2(g).
e) Discharge temperature: 91 Deg C.
f) Volumetric flow: 38000 m3/hr (suction)

Now on account of change in the reactor operation, the recycle gas mw changes from 6.5 to as high as 9.5.

The compressor controls maintains the compressor discharge flow by manipulating or controlling the suction HV while keeping a limit on the compressor motor amps. Normal is 365 amps and the controls unload the compressor at 375 amps.

Now my query is how can i prevent the suction pressure loss across the HV. Increasing the suction pressure straight away will reduce my volumetric flow and indirectly reduce my compressor power consumption.

I have tried searching on the topic in the forums and i did find some useful topics related to compressor systems. Based on what i have learnt in these topics i have posted this query.

Regards
Saikrishna

[sheiko]

Hi,
I believe your problem description is not clear enough. Namely, the control philosophy should be clarified. Try also to upload the PID or PFD showing the compressor, its source and destination.
As for a reference, I would suggest you to buy the book " A Working Guide to Process Equipment" by Norman Lieberman.

Edited by sheiko, 02 September 2012 - 06:06 AM.