7 replies to this topic

Hello! I am currently designing a pressure vessel. My feed is a vapour-liquid mixture that will then get separated. My question is, how do you calculate for the nozzle size for both the inlet and outlet streams? I was wondering if there are basic rules of thumb when it comes to sizing it properly. Thanks!

[Zauberberg]

The momentum of fluid passing through the nozzle is normally the criterion we apply for sizing nozzles.
Here is one design standard for sizing gas-liquid separators, and is available online: http://www.mop.ir/st...pr/e-pr-880.pdf

Cheers,

[Zauberberg]

These are interesting as well:

http://www.mop.ir/st...pr/e-pr-850.pdf
http://www.mop.ir/st...pr/e-pr-440.pdf

thank you so much! This is exactly what i needed! This brightened up my day!

[Zauberberg]

It's good that you are happy with Design standards. Also grab the first opportunity in your career to walk into the real plant, and everything will be much more clear afterwards.

Apart from IPS, the NORSOK standards can also be downloaded for free and there are some really good materials in there. Visit: http://www.standard....tors/Petroleum/

Process Design: http://www.standard....Process/P-0012/
Process Systems: http://www.standard....Process/P-1002/
Field Instrumentation: http://www.standard....ntation/I-0011/
Safety and Automation Systems: http://www.standard....entation/I-002/
Piping and Valves: http://www.standard....-Layout/L-0012/
Materials Selection: http://www.standard....aterial/M-0012/
Mechanical Equipment: http://www.standard....chanical/R-001/

Happy reading,

[ankur2061]

Hello! I am currently designing a pressure vessel. My feed is a vapour-liquid mixture that will then get separated. My question is, how do you calculate for the nozzle size for both the inlet and outlet streams? I was wondering if there are basic rules of thumb when it comes to sizing it properly. Thanks!

A standard I had written for a middle east O&G gives the following guidelines for momentum criteria for the inlet & outlet (gas/liquid) nozzles for separators:

Feed Inlet

The function of the inlet device is to initiate gas/liquid separation and distribute the gas flow evenly in the gas compartment of the vessel

It comprises of the inlet nozzle & inlet device, if any.

The diameter of the inlet nozzle is the function of the feed flow rate & the pressure.

The criterion for nozzle sizing is that the momentum of the feed shall not exceed prescribed levels. The maximum allowable inlet momentum can be increased by fitting inlet devices.



The nozzle internal diameter may be taken equal to that of the feed pipe but also momentum criteria shall be satisfied, as per the table given below:



Inlet Device

Momentum

None

r_mV²_m,in <=1400 kg/m.s²

Half Open Pipe

r_mV²_m,in <= 2100 kg/m.s²

Schoepentoeter

r_mV²_m,in <= 8000 kg/m.s² (Note-1)

Cyclone (conventional)

r_mV²_m,in <= 10,000 kg/m.s² (Note-1)

Multi-cyclone

r_mV²_m,in <= 35,000 kg/m.s² (Note-1)

Where r_m is the mean density of the mixture in the feed pipe in kg/m³

& V_m,in is the velocity of the mixture in the inlet nozzle in m/s



Note 1: Vendor to confirm the values

Gas and Liquid Outlets

After the separation of the gas & liquid phases, the two phases will exit the separator via their respective nozzles.



The nozzle sizing criteria is as below:

Gas

The internal diameter of the gas outlet nozzle should normally be taken equal to that of the gas outlet pipe but additionally the following criterion shall be satisfied.

r_GV²_G,out <= 3750 kg/m.s²

where;

r_G = the density of the outlet gas from the separator

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

Liquids

For new installations the liquid outlet nozzle shall be sized considering velocity below 2 m/s.

Hope this helps.

Regards,
Ankur.

[theleftcoast]

Why are the limits for sizing dictated by momentum? Just curious.

[Zauberberg]

Good question. I can't give you an explanation from mechanical point of view, but what I know from process point of view is that the excessive momentum causes two things:

- Intensive dispersion of liquid phase into a fine mist (speaking about the feed nozzle) which adversely affects separation efficiency,
- A so-called "sucking effect" in the gas outlet nozzle which can cause upset/dislogding of vessel internals

Hope to hear some more opinions on the subject, especially from mechanical point of view.