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...."

 

[bogos]

I, need help. i'have choose to take a

turboexpander in a heavy hydrocarbon recovery plant instead of a compression refrigeration system.the problem is the choice of the expander : our gas flow rate is about 72.9 MSCF and for 3 pressure drop and finally the efficiency should be about 70% . i need help for the types i should use.

 

[cryotechnic]

bogos,
your post is al "little" confusing... Can you please give us more information?

What is the inlet pressure? What is the outlet pressure? what product are you using?

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

 

[dcasto]

Th math for an expander is the same as a compressor. You'll have to iterate to find effiency. At 100% effiency the outlet would be about -200C and at 0% (work = 0), it would be about -105C. Use a Mollier chart for methane and calculate work off of it. Just plot the two points draw a line, then plot a line at constant s and see the differnce.