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Increase pressure in a compressor

Increase pressure in a compressor

Increase pressure in a compressor

(OP)
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 ?

RE: Increase pressure in a compressor

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.

RE: Increase pressure in a compressor

(OP)
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.) ??

RE: Increase pressure in a compressor

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.

RE: Increase pressure in a compressor

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

RE: Increase pressure in a compressor

is the compressor API compliant or ISO compliant?

RE: Increase pressure in a compressor

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

RE: Increase pressure in a compressor

dcasto

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

thks

RE: Increase pressure in a compressor

fan laws

RE: Increase pressure in a compressor

(OP)
dcasto, can you please give us more details ?

RE: Increase pressure in a compressor

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.




 

RE: Increase pressure in a compressor

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.

RE: Increase pressure in a compressor

(OP)
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 ?!

RE: Increase pressure in a compressor

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

RE: Increase pressure in a compressor

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

RE: Increase pressure in a compressor

(OP)
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

RE: Increase pressure in a compressor

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

RE: Increase pressure in a compressor

(OP)
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 ?!

RE: Increase pressure in a compressor

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.

RE: Increase pressure in a compressor

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

And effective discharge area = discharge spool area ?

Thanks for your help.

RE: Increase pressure in a compressor

I am sorry, but you do not provide any consistant details for compressor to let us help you
To estimate the axial thrust of overhung compressor is serious matter. going with such crude rule of thumb you are at risk that what you expect is one order of magnitude of actual.
please attach a description of compressor, stages, seal description, gear etc to let us help you in better way.

Regards
Wimple
 

RE: Increase pressure in a compressor

(OP)
Wimple, the compressor is 1 stage over-hung centrifugal compressor driven by a motor through a 1 stage speed increaser.

Here are the design specs :

Volume Flow Rate = 7060 Nm3/hr
Mass Flow Rate = 21655.4 Kg/hr
Suction Pressure = 0.15 Barg
Suction Temperature = 138 ◦C
Inlet Volume = 10620 m3/hr
Discharge Pressure = 0.593 Barg
Discharge Temperature = 208 ◦C
Polytropic Head = 2528 m
Brake Horsepower = 234 HP
Compressor Speed = 5813 RPM
Motor Speed = 1800 RPM

The compressor is supported with 2 tilting pad journal bearings and 1 double pivoted shoes thrust bearing.

Production guys want to increase suction pressure to be around 0.4 Barg. What other parameter will change due to suction pressure increment? And how that will effect the bearings ?

Please, let me know if more info are required.
Appreciate your help man.

 

RE: Increase pressure in a compressor

(OP)
dcasto,

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

And effective discharge area = discharge spool area ?

Regards,

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