5 replies to this topic

[singh ar]

Can anyone help me how to find out the efficiency of cryogenic turbines or cryogenic expanders ?

Edited by singh ar, 23 August 2010 - 03:11 AM.

[Zauberberg]

For actual efficiency of any machine, you should refer to the vendor performance/efficiency curves. Turboexpander efficiencies range from 60-85% (source: J.Campbell). For preliminary design purposes, a figure between 70-75% is a reasonable estimate.

If you are interested in the efficiency estimation/calculation procedure, please refer to the Campbell's "Gas Conditioning and Processing Vol.3 - Advanced Techniques and Applications", pages from 13-27 to 13-34.

[Zauberberg]

Attached below. Quite comprehensive. The book gives very illustrative description of what happens if the turbo-expander efficiency is under- or over-estimated.

Attached Files

•  Campbell - Turboexpander Efficiency.pdf   448.98KB   193 downloads

[singh ar]

dear Zauberberg,

thanks a lot for your quick response. It gave me some hope, but can i get the info regarding how to calculate the H_I, hp & Q which are in page 13-29 of 'campbell -turboexpander efficiency", hopefully this might be in previous pages of this book. By the by Zauberberg this efficiency estimation can be applied to turbines in which air is a medium, because in air seperation plants the Turbines are used for providing refrigeration to the sum total heat leak in the cryogenic plant.


er efficiency is under- or over-estimated.
[/quote]

Edited by singh ar, 23 August 2010 - 03:09 AM.

[Zauberberg]

For calculating enthalpy change (remember: at isentropic conditions S1 = S2), actual work/horsepower, and volumetric flow, please refer to any of the thermodynamic textbooks. You should be familiar with that already, especially if you are planning to work on detailed expander calculations.

[Zauberberg]

Here's another guideline from the Phillips engineering manual (I have uploaded it in the Forum some few weeks ago):

"For expander-compressor preliminary designs, limit the adiabatic efficiency to 72% for the expander and 65% for the compressor. Use a 95% mechanical efficiency for transferring horsepower from the expander to the compressor."

It's always better to underestimate expander-compressor efficiencies since you can easily combat against excessively low temperatures by using J-T valve in parallel, or by running the De-C2 tower at higher pressures. On the other hand, if you overestimate expander efficiency, there is no other way to obtain lower process temperatures and that can cost you a lot.