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Deaerator Vent Sizing

vent sizing in deaerator

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#1 Phanendra

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Posted 03 April 2012 - 03:26 AM

Hi,
Working as process engineer and i have done standardisation of deaerator where i got stuck up with Deaerator vent sizing.
Generally deaerators will have two types of vents one is used only in startup of deaerator and after stabilization of deaerator this vent will be closed and in general we mention this vent size as 1".
The other vent is to release the air which contains oxygen and other noncondensible gases which is more crucial for deaerator. my question is how to size the vent. Deaerator vent steam quantity is around 400 Kg/hr, Pressure is 0.232 Kg/cm2(g) and temperature is 105 Deg.C.
Please anyone give me a solution for the same.

#2 ankur2061

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Posted 03 April 2012 - 01:23 PM

Phanindra,

Is your vent connection open to atmosphere and is a gooseneck connection? If yes, then you can size the gooseneck vent as follows:

Minor loss in head or pressure takes the form of the equation:

h = K*v2 / 2g

where:

h = head loss in meters

K = head loss coefficient (consider 1.5 for your case of gooseneck)

v = velocity in m/s from the goose neck (= Flow rate in m3/h (Q) / C/S area of the goose neck pipe in m2 (A)

g =acceleration due to gravity, 9.81 m/s2

Once you have calculated the head loss in meters you can calculate it in terms of pressure drop using the equation"

P = rho*g*h

where:

P = pressure drop in Pa (N/m2) (1 Pa = 0.00001 bar)

rho = density of steam/air mixture @operating temperature, kg/m3

g, h are described above

Once you have calculated the pressure drop from your vent, you need to ensure that this value is below the design pressure of the deaerator. Suppose if your design pressure of the deaerator is say 0.14 barg then you need to ensure that the pressure drop is well below this value, say 0.07 bar or less. If your pressure drop through gooseneck is close to the deaerator design pressure or exceeds it then you have to select a bigger gooseneck size and re-calculate the pressure drop. This exercise may have to be repeated many times till you are satisfied that the pressure drop from the gooseneck is below the design pressure and there is enough margin between the pressure drop from the vent and the deaerarator design pressure so as to ensure a safe deaerator design.

Hope this helps.

Regards,
Ankur

#3 kkala

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Posted 03 April 2012 - 01:55 PM

Topic has been discussed at http://www.cheresou...team-vent-flow , which can help you. According to it vent pipe diameter is oversized, but flow is controlled through a manual valve or orifice.

Edited by kkala, 03 April 2012 - 02:12 PM.


#4 Phanendra

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Posted 07 May 2012 - 04:29 AM

Thank you Mr.Ankur, My apology for taking this much gap for my reply.
I was Outstationed on a project work
In our case the vent is 40 NB with two orifice plates inserted in the vent.
The orifice hole is 10 mm in diameter and were placed opposite to each other at 40 mm in the vent pipe.
We generally take the flow of steam through vents as 5% of steam required for deaerator charging.
Thankyou for your guidance.




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