3 replies to this topic

[Bodhisatya]

Hello All

 

Am currently working in an Air Separation unit,where we have two 3 stage Motor Driven Centrifugal Air Compressors.

 

In design case both Main Air Compressors are supposed to run with a discharge pressure of 9.7 bar A and flow of 5000 Nm3/hr from each Compressor .But currently both the Compressor are running on unequal load ,while one Compressor is running in max  load with full IGV opening and flow of 6300 Nm3/hr,the other Compressor is running in Min load with minimum IGV and antisurge valve being opened.Although at downstream we are maintaing steady flow as per design.

 

My first question is Why is this happening.

 

Secondly on consulting the Vendor they have installed a energy saving module which resulted in BOV closing of both machines,but still IGVs of both machines are not at nearly equal opened.So obviously  power consumption is also varying.At Compressor discharge we have flow of 5100 Nm3/hr and 5300 Nm3/r respectively as against 5000 Nm3/hr.So the power consumption of each machine is 624 KW and 690 KW(As against the Guarantee Figure of 600 KW for each).On interrogation vendor says the additional flow of 100 Nm3/h and 300 Nm3/hr is resulting in an enhanced Power Consumption of 24 KW and 90 KW respectively.I was not satisfied with this reply.

 

Would Like to know is there any thumb rule or detailed calculation on what is the ratio of Power increase per 100 Nm3/hr extra withdrawal

 

Regards

Bodhisatya.

[Bobby Strain]

For load balancing, you need a controller to do this. You give little information, but it seems you are not controlling flow from each machine, but the combined flow. You control vendor didn't do a very good job; or else you took the lowest priced bid. You get what you pay for, sometimes, but no more.

 

Bobby

[Bodhisatya]

Bobby Strain:

 

Please let me know what more details do you need to get a proper insight..

[Art Montemayor]

Bodhisatya:

 

I’m going to try to interpret what you have written.  First, in order to stop using undefined acronyms, do you mean blow off valve (same as blow down valve) by BOV and Inlet Guide Vanes by IGV?

 

Presumably you (or your company) bought two, identical centrifugal air compressors to feed the same air separation column.  Each compressor is identical in drivers and is design to deliver 50% of the feed air to the air separation column (a total of 10,000 Nm³/hr).  That would be a normal plan for feeding the air column.  Is this correct?

 

If so, then why are you operating one compressor at 26% more capacity than the other?  Since you don’t explain this obvious anomaly, Bobby Strain’s guess that you are trying to control the total output from both machines after the merge of both outputs must be correct.  I would not try to control the performance of each machine that way.  Please explain if this is true or if you are using another method to control each machine’s output.

 

After telling us one machine is delivering 6,300 Nm3/hr, you tell us that one machine is delivering 5,100 and the other 5,300 Nm3/hr.  Which is real case?

 

The bottom line is that the machines are not performing as guaranteed.  Am I also correct here?  If so, this will probably end up in litigation unless the compressor supplier can mitigate what is happening and resolve the situation to your satisfaction.  There is no way we could tell from here what is happening in your air separation plant.