Suction pressure of centrifugal compressor to be lowered

[GasOilEng]

Hi
We have centrifugal compressor of 8.0barg suction pressure (15.0barg discharge pressure), we want to change its suction pressure to 5.0barg (New operating pressure), What are the guidlines to follow in order to know if it's possible or no? please give me help.

Many Thanks

 

[EmmanuelTop]

Centrifugal compressors are fixed head, variable flow machines. Reducing suction pressure as much as 30% or more and increasing compression ratio from 1.8 to 2.7 does not look even theoretically possible.
Without knowing any other detail, I can advise to get in touch with the OEM (original equipment manufacturer) and seek their advice.

Dejan IVANOVIC
Process Engineer, MSChE

 

[GasOilEng]

Hi EmmanuelTop

We are not going to change compression ratio, but theoretically what about flow, I mean, sizing : suction line, impellers of compressor and so on.

Many thanks for your replying

 

[LittleInch]

GasOilEng,

Not enough data, but clearly at lower pressure, your density decreases and hence overall flow capacity will almost certainly suffer as velocities inside the compressor increase.

However if compressor speed is variable / able to be changed, you might not suffer as much flow reduction as you would for a fixed speed unit, but max flow will reduce.

your compression ratio may well change as well for the worse.

on the other hand power decreases....

what are the guidelines? - Contact the vendor.


Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[EdStainless]

Why is your discharge 15barg? What can you do to lower it?

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P.E. Metallurgy, Plymouth Tube

 

[rotw]

I think the guideline is to contact the OEM (or an upgrade specialist) and ask for feasibility study.

 

[MortenA]

@OP,
With regards to compression ratio - bear in mind that if you lower your discharge pressure the same as you inlet pressure - then you still change your compression ratio:

R1= 16/9=1.8 (have to use abs no.)
R2= 13/6=2.2

That may or may not be feasible but for a fixed speed compressor you should expect a serios reduction in capacity. Since you also have an increase in absolute flow rate (assuming that your mass/molar flow is kept constant this just makes it worse.

I gues that what you will have to do is to set up a simulation. Review the data with the compressor curve, feed the data to your manufactor and make them tell you if its possible. Perhaps some internal modification can make it fly.

Best regards, Morten