3 replies to this topic

[rajee7]

Hi ,
I have to design an hydrocyclone for gaz-liquid separation for cryogenic application LNG (gaz liquid cylindric cyclone- GLCC)
First, is there any one know why the gaz flow inverse his axial direction at the bottom of a cyclone?

Then, can you please help me to design this type of separator? how we calculate equilibruim level between 2 phases? did any one have an excell sheet to deal with kind of problem.

Thanks a lot

[kkala]

I dare say an opinion, despite my limited experience on the subject. Comments are welcomed for a better interpretation.
- Mentioned apparatus is usually called cyclone, hydrocyclone is called when feed is liquid (not gas).
-The gas inverses its direction near the base of cyclone because it collides with the concentric cylindrical walls. Look at http://www.google.gr...QEwBg&dur=17434.
Note: As having seen in the plant, solids from cyclone bottom are continuously discharged into a hopper. The hopper is periodically discharged from its bottom, e.g. through a level dumper at the exit pipe. So there is normally no air passing the cyclone from bottom upwards, which could disturb its operation. Numerous cyclones can be connected to one hopper.
- As previous posts indicate, design of cyclones separating liquid droplets from gas can be similar to those separating solids from gas. Look at http://www.cheresour...h__1#entry49822.http://www.progepi.f...ion-cyclone.pdf. Of course liquid droplet size distribution should be specified somehow.
- Probably it is practical to assume as operating pressure the average between inlet and outlet cyclone pressure (specify liquid phase at this condition). Pressure drop through cyclone is usually small compared to gas inlet pressure.

Edited by kkala, 22 July 2011 - 12:12 PM.

[rajee7]

I'm sorry I didn't specify the application.
It’s an hydrocyclone since I try to separate liquid –gas before injecting the liquid phase to the LNG Tank…
The conical cyclone is suitable only to separate particles (solid) from other phase liquid or gas, Particule loose it tangential velocity due to the friction which reduce the centrifugal action… To keep this velocity cst we use this conical shape …

For my case, I can’t use conical shape because the LNG will reduce his static pressure following Bernouilli Equation to increase his velocity. So, the idea is to use cylindrical cylone. And this is more suitable for saturated liquid. http://www.osti.gov/...tive/819517.pdf

For the gas aspiration, I don’t understand why the gas phase change from free vortex to forced vortex … and thus I’m not really sure that the gas changes his axis direction due to the cylindrical-collides, the liquid will do the same thing in this case ????

Thanks

[kkala]

Thanks for the link about cylindrical cyclone separators, which I did not know. It is difficult to "feel" that static pressure inside a conical cyclone falls so considerably; we estimate global pressure drop through cyclone, without knowing pressure levels inside it.
In a conical (*) cyclone, gas really change direction from downwards to upwards, irrespective of interpretation, together with some re-entrainment of solid particles (small portion of the whole in a well designed cyclone). Probably it is the higher specific gravity of solids (having been already settled) that neglects more re-entrainment; besides settled material cannot be easy re-suspended (saltation velocity).
Hope of being successful in your task, being something new (to many of us) in liquid gas separation.

Note (*) 8-8-11: "conical" has replaced "cylindrical", to correct the apparent error

Edited by kkala, 08 August 2011 - 08:58 AM.