Reciprocating compressors

[macabihaifa]

Hello all,

A compressor with a total of 4 stages, the first two with a common motor and the last two stages also with a common separate motor. Can I use another stand by compressor with two stages to operate as the two first stages and if needed also to operate as the last stages?

Regards,
Moshe

 

[LittleInch]

I doubt it. Look at the sizes of the cylinders, stoke length and rpm and I doubt the second two stages are the same as the first two.

 

[pmover]

no process data to work with . . .

theoretically possible with motor shafts extending from both ends of motor. 1st 2 stages at one end and 2nd 2 stage on other end using clutches.

but i doubt you will find a manufacturer or packager to build one. most likely a specialized case.

i have seen centrifugal compressors for different gases installed on both ends of an electrical motor; a rather unique installation.

 

[georgeverghese]

"Another recip compressor" is very vague - you've got to do better than that talking to other engineers asking for advice.

 

[FMJalink]

Hi macabihaifa,
As mentioned above, in theory possible and a nice cost reduction investigation, but give it low change of success.

Just a simple indicative approach:
Per stage you have a pressure increase with a pressure ratio r = p_out/ p1_in.
The volumetric flow rate decreases inversely (assuming full inter cooling between each stage and at the last stage discharge.) Phi_vol_out = (1/r)^2 * Phi_vol_in. You can see here that the volumetric flow rate decreases fast per stage and therefor a smaller stage is required with the same revolutions per minute.
Such a spare 2 stage recip should be suitable for suction flowrate of the first compressor and have the pressure rating of the second compressor.
You can play than with a cooled recirculation over that spare 2 stage compressor and its rotational speed.
Will be a nice study, which will be compressor manufacturer dependant and where piping and control complexity should not be under estimated in cost comparisons.
Success

 

[goutam_freelance]

If the additional standby compressor has dimensions and power rating matching with first two stages then it can operate as standby for the first two stages.

But as indicated above the last two stages will have a lower size than the first two stages and possibly motor power requirement will also be different. So depending on the size and power ratings either first two or last two stages can have a standby, given that there is only one standby compressor.