reciprocating air compressor 1

[somacast]

hi,

We do have a very old piston air compressor double (2 cylinders) of capacity 800 Nm3/hr , and for modernization and due to issues with availability of cooling water for this compressor, we were exploring the possibility of replacing it with a new oil-free screw type air compressor of the same size.

so I do have a few questions to help me in this comparison:

1- if both of them are rated as 100 KW, are we going to save anything in terms of electricity? the old compressor is driven by fixed speed induction motor with 50% & 100% loading by unloading valves, and the proposed screw type compressor is also of 100 kw fixed speed motor.

2- how do I calculate the efficiency of the existing compressor?

Thank you very much

 

[LittleInch]

1) Maybe but is dependant on efficiency of each

2) Efficiency is work (energy) out divided by energy in.

Work out is actual volumetric flow per second x pressure rise from inlet to outlet.

Work in is electrical power.

note efficiency changes with flow so more than one flow rate would be required unless you have a fixed flow rate.

see

https://www.eng-tips.com/viewthread.cfm?qid=163620

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[somacast]

thanks for your reply , I will go through the link before I ask again ..

 

[somacast]

@LittleInch

Hi again, to be honest I could not make much use of the link and did not go through it fully because there are many formulas and I just need a certain way to follow.

regarding the flow its fixed , but which flow do I use? as the inlet flow to the compressor is more than the discharge as per the data sheet, also what is the basis behind the formula you mentioned for work done (volumetric flow x pressure change)?

and I have noticed that there is a (volumetric efficiency) for the first cylinder, so what is that basically? and does it account over here? and also please note that I don't have the efficiency of the motor of the compressor, so do I just use the rated 100 KW as power in ?

Sorry that I have many questions but I do need them to get this done.

Thanks alot