Nozzle Velocity Separator

[oillio]

Good Afternoon,

I would like to know how to calculate the velocity of the gaz in outlet nozzle of separator.
It is a 2 phases separator. I have the flow, the density, the viscosity of the gas.

Thank you for your help

 

[tickle]

When I was at school it was

flow / nozzle area = velocity

 

[oillio]

Thank you tickle for your response.

Actually I thought also about this formula but as it seems too easy I was not sure...

The problem is when I do the calculation flow / nozzle area = velocity I found 180 m/s....

too huge I think...

 

[PaoloPemi]

I examined several gas condensate separators designs and found values in the range 30-50 m/s for velocity in inlet/outlet lines at operating consitions, however these should have a limited influence in separation process, the efficency being determined mainly by the vertical velocity, the turbolence etc. etc. inside the separator...
In my experience the value you mentioned (180 m/s) seems a bit too high for a natural gas line (but could be acceptable for different purposes), I would check the values of gas density and flow, then calculate the speed of sound and compare values with the velocity at maximum flow.

 

[oillio]

Hello PaoloPemi,

Thank you for your response.

The flow rate is 10 MMscfd, the diameter of the nozzle is 6 inch...maybe I did a mistake in my formula.

The density of the gas is 33kg/m3 and viscosity 0.0129 cp.

I will try to see is the flow is correct.

Thanks again

Regards,

 

[PaoloPemi]

assuming MMscfd as million standard cubic feet per day and
presuming natural gas with a density of 0.75 Kg/M3 (at std. cond.)
10 MMscfd -> 10 * 1000000 MMscfd / 35.31 / 3600 -> SM3/s * 0.75 Kg/M3 -> 58.95 kg/s
58.95kg/s -> 58.95Kg/s / 33Kg/M3 -> 1.78 M3/s (at operating conditions)
internal area (6 inches) -> 0.017 M2
1.78 M3/s / 0.017M2
should be something about 100 M/s
(hoping there are not too much errors in my conversion...)
you can calculate the speed of sound with a process simulator or some free tool as for example

http://www.prode.com/en/properties.htm

then compare the values.

 

[PaoloPemi]

assuming MMscfd as million standard cubic feet per day and
presuming natural gas with a density of 0.75 Kg/M3 (at std. cond.)
10 MMscfd -> 10 * 1000000 MMscfd / 35.31 / 86400 -> SM3/s * 0.75 Kg/M3 -> 2.45 kg/s
2.45kg/s -> 2.45Kg/s / 33Kg/M3 -> 0.075 M3/s (at operating conditions)
internal area (6 inches) -> 0.017 M2
0.075 M3/s / 0.017M2
should be something about 5 M/s
(sorry, out of office and doing conversions by hand...)

 

[oillio]

Good Morning,

Thank you PaoloPemi for your explanation. I have another question why do we consider natural gas?

Thank you

Best Regards,

 

[PaoloPemi]

you haven't specified composition so I presumed a gas with a density (at standard conditions) of 0.75 Kg/M3, change this value if you have a different gas composition.

 

[oillio]

PaoloPemi ,

Thank you a lot for all your explanation. I get the composition of the gas and I calculated the velocity.

Merci again

Best Regards,