14 replies to this topic

[silkroute]

Hi All,

 

What are the criteria for selection of inlet device(half open pipe,vane type,cyclone) and outlet device(mesh pad,vane type,cyclone) ? Is there any standards / guidelines? Please advice.

 

silkroute.

[ankur2061]

silkroute,

 

Refer the link below for an answer to your query:

 

http://www.cheresour...quid-separator/

 

Regards,

Ankur.

[Atttyub194]

Dear all
 
Good day!
 
Inlet design is one of the most commonly neglected aspects of a knockout drum/ separator design, thus  the cause of poor performance.
Improperly selected inlet device may result in :

• Gas jets to the back wall of the vessel.
• Without enough space to diffuse the jet, gas utilizes only part of the mist eliminator. Due to uneven velocity profile liquid carryover occurs.
• The gas jet agitates the accumulated liquid below, generating droplets.
• Turbulence spoils normal gravity settling of larger liquid droplets below the mist eliminator. Additional liquid load increases the likelihood of flooding the mist eliminator.

When a fluid stream strikes a solid surface, it reduces its momentum by exerting a force on that surface, and an equal but opposite force is exerted on itself. If this force is too great, liquid shatter can occur when the surface tension forces of the liquid are overcome. In order to avoid liquid shatter, different types of inlet devices have been developed which can reduce the momentum. The sizing of nozzles is normally judged by the maximum  ρv² value, which depends on the type of inlet device that is used or to be installed.
 
Commonly used values of ρv² throughout the industry for some of these types of inlet devices are as follows:

• No inlet device or simple baffle: ρv² ≤ 1,000 kg/ms²
• Half-open pipe inlet device: ρv² ≤ 1,500 kg/ms²
• V-baffle: ρv² ≤ 2,500 kg/ms²
• Vane-type inlet device: ρv² ≤ 15,000 kg/ms²

Half pipe or better to use perforated pipe
 
 

 
V-baffle  ( rarely used now )
 
 

Vane inlet device
 
Additionally, the best document, I have seen for sizing , selection is Shell DEP 31.22.05.11-Gen " GAS/LIQUID SEPARATORS - TYPE SELECTION AND DESIGN RULES".
 
Few year back I have seen an old version of the document  on an iranian official  site " fumblog.um.ac.ir" . I am not aware whether it is still available or not . However, you may find a similar document on " http://www.namdaran....Separators).pdf "
 
At the end, please do realize that you may suggest a device but the selection would finally be governed by the manufacturer of the device
 
Best regards and God Bless you
 

Edited by Attyub194, 29 April 2013 - 11:44 AM.

[silkroute]

^{Ankur / Attyub,}

 

^{Thanks for sharing good stuff however I think I have made a mistake. Actually I did not describ problem fully.Apology for my mistake.}

^{What you guys provided is more related to brownfield job for existing separator / vessel and existing piping around the vessel.}

^{My question was more related to Greenfield job. What are the criteria to select inlet/outlet devices for greenfield job where I can size inlet line as per my momentum requirement? I am pretty sure, it is not only about momentum only.}

^{Moreover, I am also expecting few comments for outlet device too.}

 

^Silkroute.

[ankur2061]

silkroute,

 

The same criteria are also to be applied for a new design.

 

For liquid outlet from a separator the outlet nozzle should be chosen such that the liquid velocity does not exceed 1 m/s. The minimum liquid nozzle size should be 2". The liquid nozzle outlet nozzle should be equipped with a vortex breaker.

 

For gas outlet from a separator the nozzle size should be at least equal to the outlet line but additionally the following criteria should be satisfied

 

ρ_Gv²_G,out ≤ 4500

 

where:

 

ρ_G = density of the outlet gas from the separator

v²_G,out = velocity of the gas in the outlet nozzle

 

Regards,

Ankur

[Atttyub194]

Dear silkroute

 

Good day!

 

For outlet nozzle the  recommendation by ankur should be followed. Similar guidelines are available in the referred documents

 

Please go through the documents and you will find all information either for sizing new separators or for retrofit existing separator

 

We will be in a better position, if you can share some more information regarding your application and intent.

 

For a new know out for a centrifugal compressor , I personally prefer to use gravity separator (if there are no layout constraints) with no vane pack and with  demister pad  only  when MOC is Carbon steel for the safety of the machine. You may find a few  incidents caused due to rust carry over resulting in high vibration in the machine or damage to rotor. Therefore, please  give due consideration while selecting internals for knockouts based on your application.

 

I have tried to paste an interesting image but unable to paste. so please download the following document for better understanding

 

http://www.sulzer.co..._Technology.pdf

 

Best regards and God Bless You

[silkroute]

Attyub/Ankur,

 

In greenfield projects, i got freedom to select pipe diameter and nozzle diameter in such a way that momentum can keep as I want.

Then , how can i select device based on momentum?

 

e.g. I will select inlet pipe diameter & nozzle diameter in such a way that momentum remains below 1000 kg/m s2. In this case I don't need inlet device.Am I correct ???

 

To Attyub: Thanks for sharing interesting material.

[Atttyub194]

Dear silkroute

 

Good day!

 

your understanding is correct

 

Best regards and God Bless you

[fallah]

e.g. I will select inlet pipe diameter & nozzle diameter in such a way that momentum remains below 1000 kg/m s2. In this case I don't need inlet device.Am I correct ???

 

Hi,

 

You can, but it might lead to very big sizes of inlet pipe and nozzle that in turn would need more space and supporting facilities along with higher installation cost...

[silkroute]

Thanks to all of you guys....

[LITchamp]

Dear members,

 

Does anyone has idea about Feed inlet / Gas outlet and liquid nozzle momentum criteria for 3 phase Test separator, Considering Test separator as intermittent service for around 12-15 hours of operation per month.

 

Can we go for higher momentum if separator function is intermittent, if yes how much it should be ?

 

One of our separator vendor has considered much lower nozzle size (Much higher momentum compare with Shell Dep) and deviated from Shell DEP requirement considering it as intermittent service.

 

 

 

 

[Bobby Strain]

Intermittent service has nothing to do with the design of a test separator. Its function is to separate phases. The physics don't change for intermittent service.

 

Bobby

[LITchamp]

Intermittent service has nothing to do with the design of a test separator. Its function is to separate phases. The physics don't change for intermittent service.

 

Bobby

Thanks Bobby.

[Butterfly]

Hello

 

sorry to insist on this topic. Which momentum shall I use for the inlet nozzle if I have an horizontal separator with an impact plate?

 

With the current design I am getting a value of 3800 kg/ms2

 

Thanks

[Butterfly]

It is actually a tilted deflector bafle.