how to perform energy balance across centrifugal compessor

[engahmedbahgat]

hello,
this my first participation in this helpful forum, so I need some one to help me performing energy balance across centrifugal compressor working on natural gas by answering following questions :

1- what is exactly rated power of compressor driver ( for example gas turbine) is that the net power ready to be received by compressor shaft or it is the gross power produced by driver before any efficiency values applied ?? for example if I say that rated power of driver (gas turbine) is 27 mw is that mean compressor can take all this value ( when needed) or the actual quantity of power compressor can take is (27 * efficiency )

2 - how I can calculate energy added to gas inside compressor (by speed of rotation) and energy lossed by recycling the flow from discharge to suction (when opnening surgeline) and also how to convert between pressure and energy

thank you in advance for any help

ahmed bahgat

 

[MortenA]

try to google polytropic or adiabatic efficiency

 

[25362]

You may as well, use the "search posts" fixture at the top of this page, by just writing, for example, centrifugal compressors, i/o to get additional information.

 

[jorvas]

1. Rated power - that is shaft (mechanical) power. During factory tests could be measured with dynometter or electrical generator. On side - easiest way is to calculate the power, consumed from compressor. The termopower is that before efficiency applied.
2. The easiest way is to take your compressor map and to see at current speed, pressure ratio and flow how much is power consumed. If you don't have it (wich would be strange) you should calculate it as isentropic power.
About the power losses through recycle line: discover the flow, you know inlet and outlet pressure and temperature of the line, you should know the molecular weigth of the gas - no problem to calculate the power losses.
You can not convert pressure to energy becаuse the pressure is force to area but energy is power for time.

 

[engahmedbahgat]

first thank you for every one for honest help.then I don't want to convert pressure to energy Mr.jorvas, I want to calculate energy due to this pressure.
thank you again

 

[jorvas]

Energy - this is enthalpy. The diference between enthalpies at inlet and discharge = energy added by the compressor.