Start up for a recycle gas centrifugal compressor 1

[MechanicalGraduate]

Hi All,

I am a graduate mechanical engineer and I as wondering if any of you can help me on this question that I have on Centrifugal compressors.

"An electric motor driven 8 megawatt recycle gas centrifugal compressor circulates a stream composed primarily of hydrogen but at startup the circuit must be dried out by circulating nitrogen with the same compressor".

What is the porpoise of doing this and how can this be done?. Is this something related to the Surge system?.

Thank you very much.

 

[sshep]

The dry-out must surely be due to down stream equipment- i.e. you are circulating back to a reactor or something.

Of more interest is the control to use a single centrifugal compressor in such different services. H2 MW=2, N2 MW=28. At the same speed, the developed pressure with N2 be many times higher. Since the drive is electric, it is not obvious that the compressor will be variable speed. We wonder what sort of pressure control is used- i.e. suction throttling.

 

[RaRo]

This would also avoid having hydrogen within the compressor during its heat-up phase, although it may very well not be relevant.

 

[MechanicalGraduate]

Hi sshep and Raro,

I appreciate yours comments, I think your comments are really important from the process point of view.

I agree with sshep that the gas molecular weight of H2 and N2 is 2g/mol and 28g/mol this will generate higher discharge pressure and temperature. However, I was wondering if there is any other concern from the Mechanical point of view.

thanks,

Mechgraduate.