Increase pressure in a compressor

[Abualnassr]

Hi.

What are the consequences if we need to increase the current parameters in an over-hung centrifugal compressor as the following :

P1 = 0.15 Bar -> 0.5 Bar
P2 = 0.60 Bar -> 0.8 Bar

These changes will be done by installing some constrains in the lines. So, what do you think, will these changes will effect the compressor's health ?

 

[TPL]

Depending on wether you are using BarG or BarA the compression ratio of the modifed system is less than that of the original but, what you really want to know is how the flow will be changed so that you don't run into surge issues

At the very least, I suggest you will have to consider having the surge line remapped.

 

[Abualnassr]

Thanks TPL for replying.

Well, the pressure mention is in BarG.

My main concern is that, will this modification effect the mechanical components of the compressor (carbon seal, journal brg, thrust brg, gearbox, motor, etc.) ??

 

[dcasto]

the mass flow rate will increase by 39% and the head will decrease by 57% and energy will decrease by 40%. If yo slow the the compressor to 72% speed, the head will be at 52%, just a little more than required.

 

[Abualnassr]

But, do you think that will effect the internal mechanical parts ?

 

[wimple]

is the compressor API compliant or ISO compliant?

 

[pmover]

your questions need to be forwarded to the compressor manufacturer. without knowing the design of the compressor, nor its components, it is difficult for anyone in this forum to reliably assist you.
as far as mechanical internal parts, there are numerous internal parts to refer to.

good luck!
-pmover

 

[wimple]

dcasto

how can you guess such figures without knowing the shape of perf curves?

thks

 

[dcasto]

fan laws

 

[Abualnassr]

dcasto, can you please give us more details ?

 

[wimple]

dcasto

I guess it is not fully correct. At least Pin, Tin and MW are required figures. For example with High Mol. weight application for instance, the shape Head vs. Flow drastically change then it is for low mol. weight. Small % increase in flow will drastically reduce the head. Turndown is lower.

 

[dcasto]

OK, I assumed it was the same gas so rho was consistant. The other thing that changes is efficency, but again, it typically follows linearlly.

 

[Abualnassr]

Gas is the same and dp is the same. But the only changes were inlet and discharge pressures. Well, i assume increasing the suction pressure might increase the thrust load. What do u think guys ?!

 

[dcasto]

Yes the thrust would change, but most machines today have a thrust balancing sytem.

 

[wimple]

Hi

Basically with the changes, you run with quite lower head and therefore lower speed (less 70 % ??).

Very generally speaking, you need to check new operating speed versus the Critical ones (speration margin) versus code (API if applicable?)

There are other points to check...you need to revert to compressor Mfg (even I would doubt of feasibility...but just w/o tecnical details this still just a feeling..)

Regards
Wimple

 

[Abualnassr]

dcasto, this compressor doesn't have thrust balancing system.
Is there any way that I can make sure that the increase in pressure won't effect the internal components of the compressor ?!

wimple, "lower speed" do you mean flow speed ?!
Can you please elaborate more ?

I really appreciate your help guys

 

[wimple]

you did not advise wether your comppressor is API compliant or not. Lower speed means lower then your acual rated speed.

 

[Abualnassr]

Well, the speed will not be changed(if you mean compressor speed).

Do you think the increased pressure will increase the probability of thrust bearing failure ?!

 

[dcasto]

you should be able to recalculate thrurst from your original data or from some pressures taken while the machine is running.

Thrust = inlet pessure * effective area of inlet - outlet pressure * Effective area of outlet.

You should be able either measure values like pressures and the thrust forces which is will be a pressure on the thrust bearing and derive the effective areas or find those areas in a job book.

 

[Abualnassr]

Do you mean by effective inlet area = impeller area - center bolt ?

And effective discharge area = discharge spool area ?

Thanks for your help.