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Function Blocks
3.2.6 AG8 - AGA 8 Compressibility Factors of Natural Gas
AG8 function blocks, which can be used on a one per
loop basis, are available in firmware 1.30 and higher. This
block calculates the compressibility factors of natural gas
in accordance with AGA 8 Report No. 8, July 1994 (AGA
Catalog No. XQ9212). It computes various
compressibility factors and the specific gravity (relative
density) using the detailed characterization method
described in the report. The mole percentage of the gas
components and the base temperature and pressure are
entered in the configuration and the flowing temperature
and pressure are provided as block inputs. Parameter
MOL% SUM provides a read only value that is the total
of all the gas compounds that have been entered. The
AGA8 computation is time consuming and is calculated
over a total of 100 scan cycles so as not to have any
significant effect on the controller cycle time.
Z s (compressibility at standard conditions) is calculated
after a power-up or after a configuration change is made.
Z b and Z f are calculated on a periodic basis with the
actual update time dependent on the number of gas
components and the scan cycle of the controller.
3-14
AGA 8
AG8
ESN = 000
Pf
Input Pf
AGA 8
Input Tf
Tf
P b
base Pressure (psia)
T b
base Temperature (deg F)
M E
T
H
A N
E
METHANE
% composition
N I
T
R
O G
E
N
NITROGEN
% composition
C
D I
O
X
D
Carbon DIOXiDe
E
T
H A
N
E
ETHANE
% composition
P
R
O
P A
E
N
PROPANE
% composition
W
A T
E
R
WATER
% composition
H
Y
S
U L
D
F
HYdrogen SULFiDe
H Y
D
R
O G
E
N
HYDROGEN
% composition
C
M
O
N
O
X
D
Carbon MONOXiDe
O
X
Y G
E
N
OXYGEN
% composition
U
T A
i
-
B
N
E
i-BUTANE
% composition
n
-
B
U
T A
E
N
n-BUTANE
% composition
i
-
P
N
T A
N
E
i-PeNTANE
% composition
n
-
P
N
T A
E
N
n-PeNTANE
% composition
n
-
H
E
X A
N
E
n-HEXANE
% composition
n
-
H
P
T A
N
E
n-HePTANE
% composition
n
-
O
C
T A
N
E
n-OCTANE
% composition
O
N A
n
-
N
N
E
n-NONANE
% composition
n
-
D
E
C A
E
N
n-DECANE
% composition
H
E
L I
U
M
HELIUM
% composition
A
R G
N
O
ARGON
% composition
M O L
%
S U M
MOL% SUM
(read total % composition)
I
N
P
U
T
P f
INPUT Pf ...............
N
P
U
T
T
f
I
INPUT Tf ...............
E
S
N
Exec. Seq. No. ...................... 000 to 250
UM353-1
Gr
Output Gr
Zs
Output Zs
Zf
Output Zf
Zb
Output Zb
(14.73)
................................ Real
..................... Real
(60.0)
...................
Real
(96.5222)
..................
Real
(.2595)
.........
% composition
Real
(.5956)
......................
Real
(1.8186)
...................
Real
(.4596)
........................
Real
(0.0)
....
% composition
Real
(0.0)
................
Real
(0.0)
.....
% composition
Real
(0.0)
.....................
Real
(0.0)
...................
Real
(.0977)
..................
Real
(.1007)
..................
Real
(.0473)
.................
Real
(.0324)
..................
Real
(.0664)
.................
Real
(0.0)
..................
Real
(0.0)
..................
Real
(0.0)
..................
Real
(0.0)
.......................
Real
(0.0)
.......................
Real
(0.0)
..........
Real
(100.0)
loop tag.block tag.output
(null)
loop tag.block tag.output
(null)
(000)
March 2003
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