Expander, Energy, enthalpy,

[cryotechnic]

Hi,
In our ASU we have a turbo expander/compressor. The expander is driving the compressor.

Now, we are thinking about the energy released at the expander.
The energy needed for the compression of a surten amount of gas must be released by the gas in the expander. (for this moment, we are talking about 100% efficiency, we know that's a theoretical case)

We want to calculate the energy released in the expander but at this moment the formula to calculate does not come in to our mind.

Gas inlet expander: 50 bar -80dgr C
Gas outlet expander: 5 bar -165 dgr C
Gas flow through expander: 24000Nm3/h Nitrogen

Gas inlet compressor: 40 bar 18dgr C
Gas outlet compressor: 50 bar 40dgr C
Gas flow through compressor: 30000Nm3/h Nitrogen

Hopefully someone can help us with the formula.
Thanks!
Cryotechnic

"Math is the ruler of your potential succes...."

 

[pmover]

gee whiz cryotechnic,

the equations you seek are located in your thermodynamic textbooks, perry's handbook, ME handbook, etc. the energy needed to drive the expander and to compress the gas is simply massflow x enthalpy difference (assuming 100% efficiency, but not the case) across the machine. if pure n2, then there are ample tables available to obtain enthalpy values. massflow is easily determined as well - hint 1 lb-mol occupies 379.5 cf at STP.

good luck!
-pmover

 

[cryotechnic]

Thanks pmover,

The equation of massflow x enthalpy difference I knew, the thing is, I couldn't find a equation with both the factors Pressure, and Temperature to calculate the enthalpy at the inlet and outlet (or enthalpy difference for that matter).

And yes, equation is a better word, I was looking for that, it didn't come to my head.

By the way... Whiz? Why? hahaha I just love my job....

Thanks again.
Cryotechnic

"Math is the ruler of your potential succes...."