Reciprocating Compressor Application

[EEBubba]

We are trying to size a motor for a Recip. Compressor. There is some information that is not making much sense to us. The customer wants a 500 hp motor, the compressor vendors data sheets show a BHP of 1200 hp, and an calculated HP of 500.

The torque effort curve indicated something in the 10,000-12,000 ft-lb max effort for the combined load. This works out to something like 600% of the motors rated torque.

Can this be right or is this a misapplication? Is there something specifically about recip. compressors that allows for this sizing to be correct?

Any information or advice would be greatly appreciated.

 

[waross]

Have you considered starting unloaded and flywheel effect?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[EEBubba]

We have considered it, however the customer data shows a very low ineria, low enough that I feel it reflects the driven equipment alone, without any flywheel attached.

The information we are getting is that the motor should be sufficent without any sort of flywheel assistance. I am questioning this, but I do not have much experience with reciprocating compressors.

Thanks for pointing me in the right direction at least, this truly is a helpful place. Please feel free to give any more advice, as I feel totally lost on this one.

 

[Compositepro]

There must be a gearbox or pulley between the motor and compressor to get the torque required. At the lower speed the motor horspower should be enough for the compressor. But it seems that you have a much bigger compressor than you need or there is some other reason to run it at lower than rated speed.

 

[itsmoked]

Usually recips have a large flywheel that represents a large gear reduction. 5:1 to 10:1. I wonder if that is not the missing info. 600% 6:1?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[EEBubba]

I went and pulled the file, I was hoping you guys were right and I had overlooked a gearbox. The customer is wanting to do this direct coupled.

I am worried now that I might have been correct with my first impression and this motor is grossly undersized.

 

[macmckim]

What is the brand of compressor?
I have supplied number of motors for various gas compressors and the mfg data sheets show the maximum BHP that compressor "XX" model can handle, where the HP required by the client is always much lower. There was no gear boxes between the motor and the compressor, just direct drive. Sometimes there is a flywheel, about 10% of the time. Your motor supplier will need the, inertia, ST curve and crank effort curve based on the pressure and volume you need from the compressor.

 

[jraef]

Direct drive on a recip? Seems unlikely; 1800RPM (assuming 4 pole 60Hz) on a recip that big is very very fast.

But be that as it may, as I understand it, the BHP rating of a driven machine such as that compressor is saying that this is the MAXIMUM HP you can safely apply to the compressor shaft without worry of mechanical damage. It is NOT directly related to the actual input (shaft) HP requirement, other than the shaft HP from the driver (motor or engine) needs to be something less. The actual drive HP you couple to it has to do with the delivery you want out of it: air volume, pressure differential, piston stroke, speed, duty cycle etc. So you need to use the "calculated HP" rating given to you, in this case, 500HP.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376