Control Valve Sizing for Amine Service 2

[cwood3]

#1, I am mechanical, not process/chemical/instrumentation. Heck, actually right now I am just hiring myself out to do some CAD work for various entities. I got interested in control valves (Fisher D-body style) and what makes the able to do what they are supposed to do. So naturally I start reading up on sizing parameters and such and I run across an issue that I am struggling with. If I wanted to size a control valve for amine service (methyldiethanolamine/MDEA) and the steps involve utilizing Pc (critical pressure) at a given temperauture, how do I find that ?

I'm just curious because I always thought I was a good instruction follower.....then I hit a wall.

Thanks!

 

[PaoloPemi]

I am mechanical, too, and my point of view is that valves (as well as many other process equipments) are mainly mechanical stuff
The critical pressure of liquids (not temperature dependendt) in original Masoneilan formulation (now ISA/ISO standard) is a empirical parameter used (with pure fluids) to estimate a critical pressure drop (choking condition), note that the formulation is not suitable for mixtures as it may produce wrong results. If you do not know the critical pressure you may assume there is no flashing, to be reasonably sure you should know at least the saturation pressure of liquid (at operating temperature) , if the saturation pressure is well below the output pressure the assumption could be correct, differently you may need a process simulator to calculate the percentage of liquid vaporizing and adopt one method for two phases flow.

 

[PaoloPemi]

I forgot to mention (supposing you know the formulation) that pressure drop should be below about fl*fl*(pin-Cr*pv) where pin is inlet pressure, pv saturation pressure anc cr (crtical factor) about 0.9 (if you can't calculate it)

 

[ChEMatt]

If you're working with an amine, you may be dealing with hydrogen sulfide. Make sure your instrumentation is up to NACE spec.

Onwards,

Matt

 

[dcasto]

if the valves are the level control valves on the contactor or flash gas sep, you'll need to take into account flashing!!!!

 

[sheiko]

Try to google "Fisher Control Valves Handbook". It's very informative and free!

"We don't believe things because they are true, things are true because we believe them."