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Chemical Process Technology

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Monday, May 11, 2009

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Liquid product like Chemical, condensate, etc is commonly stored in fixed roof vertical cylindrical tank. Inert gas blanketing system is provided to avoid air and moisture contact and contaminate liquid product. Liquid movement by content filling (pump-in) or emptying (pump out) and weather changes (ambient heating or cooling) will results internal pressure increase (overpressure) or decrease (vacuum) in the tank. Thus, a protecting system providing inbreathing or outbreathing gas is provided to maintain a constant pressure in the tank.

Inbreathing
Emptying (pump-out) and ambient cooling will lead to normal inbreathing. Siddhartha (2006) proposed a general equation to determine inbreathing flow :

If Vtank less than or equal to 3500 m3,

Qin,air = Qoutflow + 0.178 x Vtank

If Vtank more than 3500 m3,

Qin,air = Qoutflow + 3.2 x Vtank0.651

where
Qin,air = Total inbreathing in Sm3/h (Air)
Qoutflow = Pump-out or emptying in m3/h
Vtank = Tank capacity in m3

Outbreathing
Filling (pump-out) and ambient heating will lead to normal outbreathing. Siddhartha (2006) proposed a general equation to determine outbreathing flow :

Liquids with a flash point (FP) greater than 37.8°C or Normal Boiling Point (NBP) above 149°C

If Vtank less than or equal to 3500 m3,

Qout,air = 1.069 x Qinflow + 0.107 x Vtank

If Vtank more than 3500 m3,

QOut,air = 1.069 x Qinflow + 1.92 x Vtank0.651

Liquids with a flash point less than 37.8°C or Normal Boiling Point (NBP) below 149°C

If Vtank less than or equal to 3500 m3,

Qout,air = 2.138 x Qinflow + 0.178x Vtank

If Vtank more than 3500 m3,

Qout,air = 2.138 x Qinflow + 3.2 x Vtank0.651

where
Qout,air = Total outbreathing in Sm3/h (Air)
Qinflow = Pump-in or filling in m3/h
Vtank = Tank capacity in m3

To convert Sm3/h to Nm3/h, divide inbreathing / outbreathing flow with a factor of 1.055. Refer "Relate NORMAL to STANDARD Volumetric Flow"

Note:
Sm3/h indicates volume flow at standard conditions of 101.325 kPa(a) and 15 degC

Nm3/h indicates volume flow at standard conditions of 101.325 kPa(a) and 0 degC


Ref : "Understanding Atmospheric Storage Tanks" by Siddhartha Mukherjee, Chemical Engineering, April 2006

**********************************

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posted by Webworm, 12:04 PM

1 Comments:

Blogger laharia said...

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October 1, 2010 at 3:55 AM  

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