Two Restricive Orifices in Series 2

[blbrooks]

Hello,

Are there any guidelines for the distance required between two restrictive orifices in series used for staged pressure drop? I have a mixture of isobutene and ammonia at 200 barg that I am trying to depressure to 30 barg. Any help is appreciated. Thanks!

 

[JLSeagull]

Use a choke.

 

[EmmanuelTop]

Hello,

If the purpose of having two-stage pressure drop is to avoid minimum temperature encountered in single-stage depressuring calculations, than it will have no effects. Temperature drop is governed 99% by initial pressure differential, and even 10 restriction orifices will not help. In both cases, you will have to design your you 1st orifice in the way as there are no choking elements downstream.

Reagards,

http://antwrp.gsfc.nasa.gov/apod/astropix.html

 

[blbrooks]

Thanks for the responses.

JLSeagull, what do you mean a "choke"?

EmmanuelTop, the purpose of the two orifice configuration is to depressure the liquid stream from 200 barg to 30 barg while maintaining the current flowrates through the line. To do this with one orifice would require a very small bore diameter.

Thanks again.

 

[sshep]

EmmanualTop,
Interesting that you would say that two orifices wouldn't have an effect on outlet temp after the extensive discussion in thread124-202829. It was pointed out that once the critical pressure drop was reached (gas depressuring), excess energy was released as an irreversable process (i.e. noise) resulting in a lower outlet temp than if all the energy were conserved in process. Therefore, a multistaged pressure drop (avoiding critical pressure drop) would allow more energy to be dissipated in the outlet stream giving a higher outlet temp than a single orifice. In most cases the difference might be minor, but I felt sort of silly after that discussion for thinking only in terms of a reversible process. Anyway multiple restriction orifi in blbrooks case could have a significant benifit of reducing noise when letting down vapor across such large dP's.

blbrooks,
A think a choke in this case reffers to an orifice tube- i.e. like drilled out barstock placed in a pipe. The pressure drop is then taken across some distance rather than at a single point. If this reasoning holds then there is little reason to seperate the orifice plates by significant distance. A few pipe diameters seems sufficient seperation between plates if indeed there is really any concern at all. That's my opinion anyway.

best wishes,
sshep

 

[JLSeagull]

Choices include fixed chokes and adjustible choke valves.

The fixed chokes include an angle body with a bean (an orifice tube like drilled out barstock). Beans are available from oil-patch supply houses drilled in increments of 1/64 inches. Several standard patterns exist based upon the models available before WWII. Special bean removal tools or wrenches permit changing the bean size.

The adjustible chokes are throttling valves based upon the fixed choke body patterns.

 

[EmmanuelTop]

Hi sshep,

Thank you for your observations. Some time ago, while I was working in refinery operations, I remember you've been of a lot help to me in solving naphtha stabilizer reboiler problems and Alkylation refrigerant compressor operational issues (together with reena1957) - you pointed out at some really interesting inter-relationships which would otherwise go unnoticed. So i really enjoy your inputs in this forum.

My comment in this thread was governed by the fact that - thermodinamically speaking - there can be no significant difference in final fluid parameters, regardless of the path that is being choosen for changing the initial fluid state and bringing the fluid down to desired parameters. I did so many calculations related to this particular issue, that I feel some questions being more academical than practical. Of course, every case under consideration has some unique drawbacks and resulting conditions will never be the same in each case, but the difference is so small that can be neglected in design and operational calculations.

http://antwrp.gsfc.nasa.gov/apod/astropix.html

 

[EGT01]

blbrooks,

As a relatively new member to the forum, be sure to read
Eng-Tips.com Forum Policies
faq731-376
to get the most out of your experience here.

To address your original post, here are a couple of links to past discussions...
thread124-119130
thread378-125921
There are others you may also want to see as well.

I'm including a copy of the old Chemical Engineering article that was posted previously. The second thread above indicates the Tung and Mikasinovic article is from Chemical Engineering, December 12, 1983, pgs 69-71.

In reference to JLSeagull's suggestion, here's a few links to choke equipment you might find interesting...

http://www.glossary.oilfield.slb.com/Display.cfm?Term=bean choke

http://www.houmavalve.com/html/cameron.html

http://www.wellheadinc.com/Products/chokes.htm

 

[sshep]

Hey EmmanualTop,

Thanks for your kind comments. You get two kinds of knowledgable people in these forums- those taking an engineering model approach, and those taking a scientific approach. I appreciate you to be more of the practical engineering type as well, but at times I really enjoy the scientific posts that get me thinking outside of my box.

In this post anyway, its pretty practical stuff, but the poster doesn't give much data (flowrate, phase, etc). The observations of small bore (and noise) come up frequently in these situations. My own preference is often a small valve and orifice combination, but there are many solutions to this problem as JLSeagull's suggestion proves.

anyway, best wishes as always,
sshep

p.s. Nice link to the double cluster on 7Dec. I really felt like I missed out on comet Holmes (and these familiar sky sights) as a result of being now located so far in the Southern Hemisphere. I read this morning in Sky&Tele it has renewed visiabilty- it must be nice to see it so high in the sky!