Sunday, February 1, 2009

Relate NORMAL to STANDARD Volumetric Flow

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In gas processing industry, gas flow has been referred to STANDARD (i.e. Sm3/hr, MMSCFD, etc) and NORMAL condition (i.e. Nm3/h). Vendor catalog in many event can be in Sm3/h or Nm3/h.

What is the useful factor to convert Nm3/h to Sm3/h or vice versa ?

Definition
As discussed in "Avoid Confusion In "Standard" Flow Definition", definition is one of the most important factors to avoid discrepancies. First far most important task is to provide a correct definition of STANDARD and NORMAL condition. In "general",

NORMAL condition : 1.01325 bara @ 0 degC

STANDARD condition : 1.01325 bara @ 15 degC

Conversion
From this post,

Q2 = (z2/z1) x (T2/T1) x (P1/P2) x Q1 .....[1]

where
Q1 & Q2 are Volumetric Flow in m3/h for condition 1 & 2
P1 & P2 are Pressure in bar abs for condition 1 & 2
T1 & T2 are Temperature in K for condition 1 & 2
z1 & z2 are compressibility factor for condition 1 & 2

Condition 1 : 1.01325 bara @ 0 degC (NORMAL Contractor manual)
Condition 2 : 1.01325 bara @ 15 degC (STANDARD)
Assume
z1 = z2 = 1
Q1 = 1 Nm3/h

From [1],
==>
Q2 = (z2/z1) x (T2/T1) x (P1/P2) x Q1
==> Q2 = (288.15 / 273.15) x 1
==> Q2 = 1.055 Sm3/h

Therefore,
1 Nm3 = 1.055 Sm3
when
NORMAL condition : 1.01325 bara @ 0 degC
STANDARD condition : 1.01325 bara @ 15 degC

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