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Aga3iter - Cesar Delgado

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ACCOL II Reference Manual
Page AGA3Iter-1
AGA3Iter
American Gas Association Report No. 3 - Iterative Module
The AGA3Iter Module computes natural gas volume flow rate in
MSCF/h for orifice plates, with flange taps ONLY, according to the
factors method explained in the American Gas Association (AGA)
Report #3 of August, 1992, 3rd Edition (Part 3, Equations 3-B-2 and 3-
7). This method retains factors such as Fpb , Fpv , Ext, and others
described in the American Gas Association (AGA) Report #3 of 1985,
but provides greater accuracy by using a new equation to calculate the
coefficient of discharge.
PIPE_DIAM
TAP_LOC
POINT
ORIF_DIAM
OUTPUT
TRACK
3ITER
ADJ _PRESS
STAT_ PRESS
FLOW_TEMP
SPEC_GRAV
THERM_COEF1
BASE _TEMP
BASE _PRESS
INPUT_1
LIST
THERM_COEF2
VISCOSITY
ISEN_COEF
INPUT_2
INPUT_3
Z_BASE
Z_FLOWING
DIFF_ PRESS
AGA3Iter
ACCOL II Reference Manual
Page AGA3Iter-2
AGA3Iter
American Gas Association Report No. 3 - Iterative Module
The paragraphs below outline the rules under which the AGA3Iter
performs its computations:
The output volume flow rate is computed in thousands of standard
cubic feet per hour (MSCF/h), at base conditions, according to tech-
niques described in the 1992 AGA Report #3, Part 3, Equations 3-B-2
and 3-7.
The orifice coefficient and slope coefficient are calculated by
iteration using the Reader-Harris equation shown in the 1992 AGA
Report #3, Part 3. These two factors are combined into a coefficient of
discharge, CD.
Internal factors used in the calculations can be stored in an ACCOL
signal list for examination. Input terminals to the AGA3Iter Module
allow the user to substitute factors for CP and Ext, and to specify a
standard compressibility, Z
s
.
A standard cubic foot is one which exists at the standard pres-
sure of 14.73 psia, and a temperature of 60 degrees Fahrenheit. When
contract base conditions are not standard conditions, the module
BASE_PRESS (base pressure) and BASE_TEMP (base temperature)
terminals should be changed so that flow rate will be computed at
base conditions.
The base compressibility, Zb , is input to the module via the Z_BASE
terminal. Zb must come from one of the AGA8 Modules (AGA8Gross,
or AGA8Detail) and must have been computed at the same base
conditions specified by the BASE_PRESS and BASE_TEMP terminals
of the AGA3Iter Module.
❏ Module Equation
The equation given in the 1992 American Gas Association (AGA)
Report #3, Part 3, Equation 3-B-2 is as follows:
ACCOL II Reference Manual
Page AGA3Iter-3
AGA3Iter
American Gas Association Report No. 3 - Iterative Module
Qv = Fn (Fc + Fsl) Y Fpb Ftb Ftf Fgr Fpv . hw Pf1
Equation 3-B-2 calculates flow rate at standard conditions (14.73 psia
and 600 F).
The AGA3Iter Module calculates flow rate at base conditions, as
follows:
Q
b
 = CP Ext BCF F
m
where Q
b
= Flow rate at base conditions
CP = F
n
 CD Y F
pb
 F
tb
 F
tf
 F
gr
 F
pv
Ext = h
w
 P
f1
 F
m
= additional correction factor on the
 POINT terminal.
BCF = Base correction (Zb/Zs) for Zb other than
 AGA report Zs value.
where
Fn = A numeric conversion factor which
includes Ev the velocity of ap-
proach factor.
CD = Orifice coefficient of discharge,
which is the sum of the orifice
calculation factor, Fc and the
orifice slope factor Fsl.
Y = Expansion factor.
ACCOL II Reference Manual
Page AGA3Iter-4
AGA3Iter
American Gas Association Report No. 3 - Iterative Module
Fpb = Pressure base factor.
Ftb = Temperature base factor.
Ftf = Flowing temperature factor.
Fgr = Specific gravity factor.
Fpv = Supercompressibility factor,
computed as Z
b
 / Z
f 
. The Z
b
and Zf values MUST come from an
AGA8Detail or AGA8Gross calcu-
lation.
hw = Differential pressure, in inches of
H
2
O.
P
f1
 = Absolute static pressure, in psia.
NOTE
This equation is for flange tapped orifice plates
ONLY. If pipe taps are being used, the
AGA3TERM Module must be used.
❏ Module Terminals
DIFF_PRESS Default: None, entry required
Format: Analog signal or constant
Input/Output: Input
is the differential pressure, hw , in inches of water across the orifice
ACCOL II Reference Manual
Page AGA3Iter-5
AGA3Iter
American Gas Association Report No. 3 - Iterative Module
plate. Negative input values are clamped at zero, and zero produces a
zero flow rate.
STAT_PRESS Default: None, entry required
Format: Analog signal or constant
Input/Output: Input
is the Upstream or Downstream static pressure, specified in psig.
Negative input values are clamped at zero, and zero produces a zero
flow rate. When it is a Downstream pressure, the TAP_LOC terminal
should be non-zero.
TAP_LOC Default: 0
Format: Analog signal
Input/Output: Input
indicates the pressure tap location for flange taps. A value of 0 on this
terminal indicates that the tap location is Upstream, and a non-zero
value indicates that the tap location is Downstream.
When Downstream is specified, the differential pressure is converted
to psi and added to the Downstream static pressure to obtain an
Upstream value for use in calculations. See 'Module Usage Notes.'
ADJ_PRESS Default: 14.73 psia
Format: Analog signal or constant
Input/Output: Input
is the site barometric pressure in psia. This value is added to the
value on the STAT_PRESS terminal to obtain absolute pressure.
ACCOL II Reference Manual
Page AGA3Iter-6
AGA3Iter
American Gas Association Report No. 3 - Iterative Module
ORIF_DIAM Default: None, entry required
Format: Analog signal or constant
Input/Output: Input
is the orifice bore diameter in inches at 68 degrees Fahrenheit. Output
of the module will be zero if this terminal is unwired, or if the value
entered is zero, negative, or larger than 80% of the value on the
PIPE_DIAM terminal.
PIPE_DIAM Default: None, entry required
Format: Analog signal or constant
Input/Output: Input
is the inside diameter of the pipe in inches at 68 degrees Fahrenheit.
Output of the module will be zero if this terminal is unwired, or if the
value on the terminal is zero or negative.
THERM_COEF1 Default: 0.00000925 (stainless
steel)
Format: Analog signal or constant
Input/Output: Input
is the orifice coefficient of thermal expansion in inches per inch-degree
Fahrenheit.
THERM_COEF2 Default: 0.0000062 (carbon steel)
Format: Analog signal or constant
Input/Output: Input
is the pipe coefficient of thermal expansion in inches per inch-degree
Fahrenheit.
ACCOL II Reference Manual
Page AGA3Iter-7
AGA3Iter
American Gas Association Report No. 3 - Iterative Module
BASE_PRESS Default: 14.73 psia
Format: Analog signal or constant
Input/Output: Input
is the base pressure Pb in psia. This value is used to calculate the
factor Fpb.
BASE_TEMP Default: 60o Fahrenheit
Format: Analog signal or constant
Input/Output: Input
is the base temperature, Tb , of the gas in degrees Fahrenheit. This
value is used to calculate the factor Ftb .
FLOW_TEMP Default: 60o Fahrenheit
Format: Analog signal or constant
Input/Output: Input
is the temperature, Tf , in degrees Fahrenheit. This value is used to
calculate the factor Ftf .
VISCOSITY Default: 0.0000069 lbm/foot-second
Format: Analog signal or constant
Input/Output: Input
is the dynamic viscosity of the gas at flowing conditions in pound mass
per foot-second. Viscosity is used to calculate the Reynolds number.
This terminal should normally be left unwired unless the gas viscosity
is known to be outside the range of .0000059 to .0000079 given in the
1992 American Gas Association (AGA-3) Report, Part 3, page 11.
ACCOL II Reference Manual
Page AGA3Iter-8
AGA3Iter
American Gas Association Report No. 3 - Iterative Module
SPEC_GRAV Default: 0.6
Format: Analog signal or constant
Input/Output: Input
is the specific gravity, Gr, of the gas at standard conditions. This value
is used to calculate the factor Fgr.
ISEN_COEF Default: 1.3
Format: Analog signal or constant
Input/Output: Input
is the gas Isentropic exponent. This value is used in the calculation of
the expansion factor, Y. This terminalshould be left unwired unless
the gas isentropic exponent is known to be other than the 1.3 value
given in the 1992 American Gas Association (AGA-3) Report.
Z_FLOWING Default: 1.0
Format: Analog signal or constant
Input/Output: Input
is the flowing compressibility factor, Zf , generated from an AGA8
calculation referenced to the Upstream conditions.
NOTE
When TAP_LOC is non-zero, this module internal-
ly adds the DIFF_PRESS (in psia) to the
STAT_PRESS value to calculate Upstream pres-
sure for ALL calculations. Any AGA8Detail module
calculating Zf MUST use an equivalent Upstream
pressure.
ACCOL II Reference Manual
Page AGA3Iter-9
AGA3Iter
American Gas Association Report No. 3 - Iterative Module
Z_BASE Default: 1.0
Format: Analog signal or constant
Input/Output: Input
is the base compressibility factor, Zb , from an AGA8 calculation.
POINT Default: 1.0
Format: Analog signal or constant
Input/Output: Input
is used internally as the meter correction factor, Fm , to compensate
for external equipment calibration error or local variations in condi-
tions such as gravity, or Downstream tap compressibility.
TRACK Default: 1.0 or ON
Format: Analog or logical signal
Input/Output: Input
is used to force the module output to zero. When a logical signal is
wired to this terminal, ON enables calculation, and OFF forces the
output of the module to zero. If an analog signal is wired to this
terminal, it is used as a differential pressure threshold value or 'cutoff'
level; calculations cease and the output of the module is forced to zero
when the DIFF_PRESS terminal value is less than the TRACK value.
OUTPUT Default: None
Format: Analog signal
Input/Output: Output
is the gas flow rate, Qb , at base conditions in MSCF per hour.
ACCOL II Reference Manual
Page AGA3Iter-10
AGA3Iter
American Gas Association Report No. 3 - Iterative Module
LIST Default: None
Format: Analog Signal or constant
Input/Output: Input
is the number of a signal list into which the factors used in the equa-
tion are to be moved. Factors are moved to the list in the following
order: CP, Fn , CD, E, Y, Fpb , Ftb , Ftf , Fgr , Fpv , Fm , Ext, Reyn, and
BCF, where Reyn is the pipe Reynolds number computed by iteration
as part of the CD calculation. The output list is not written to when
the CP value factor comes from an input.
INPUT_1 Default: None
Format: Analog signal or constant
Input/Output: Input
allows the substitution of an alternate value for CP in situations
where the factor is required to be different and internal calculation of
that factor is not desired. If this terminal is wired, and its signal value
is not less than zero, the value will be substituted for CP in the equa-
tion, and the internal calculation of that factor will not be done. If the
terminal is unwired, or has a negative value on it, the factor will be
calculated internally.
INPUT_2 Default: None
Format: Analog signal or constant
Input/Output: Input
allows the substitution of an alternate value for Ext in situations
where the factor is required to be different and internal calculation of
that factor is not desired. If this terminal is wired, and its signal value
is not less than zero, the value will be substituted for Ext in the
equation, and the internal calculation of that factor will not be done. If
the terminal is unwired, or has a negative value on it, the factor will
be calculated internally.
ACCOL II Reference Manual
Page AGA3Iter-11
AGA3Iter
American Gas Association Report No. 3 - Iterative Module
INPUT_3 Default: 0.997971
Format: Analog signal or constant
Input/Output: Input
is the standard compressibility Zs for the gas composition in use. Zs is
used in the calculation of the flow rate correction factor BCF (the ratio
of Zb to Zs). A default value of 0.997971 is supplied which corresponds
to the set of conditions defined in Appendix 3-C, Section 3-C.2 of
American Gas Association (AGA) Report #3 of August, 1992, 3rd
Edition. If this terminal is wired, and its signal value is not less than
zero, the value will be substituted for Zs in the equation, and the
internal default value of that factor will not be used. If the terminal is
unwired, it is set to its default value of 0.997971. If the terminal has a
negative value on it, the factor is set to 1.0. For most uses, this termi-
nal will be wired with a Zs signal.
❏ Module Usage Notes
Conditions Which Cause Zero Flow Rate to be output by the Module:
The following conditions can force the flow rate output of the
AGA3Iter Module to zero. These are:
a. Negative or zero differential pressure.
b. Negative or zero static pressure.
c. Negative or zero orifice diameter.
d. Negative or zero pipe diameter.
e. Orifice diameter larger than 80% of pipe diameter.
f. Track terminal conditions are satisfied.
Bounded Inputs:
The isentropic exponent value used internally will be forced to 1.3 if
the input value is less than 1.0 or larger than 2.0. The viscosity value
used internally will be forced to .0000069 if the input value is zero or
negative, or larger than 1.0.
ACCOL II Reference Manual
Page AGA3Iter-12
AGA3Iter
American Gas Association Report No. 3 - Iterative Module
Compressibility:
In cases where both the AGA8Detail and AGA3Iter Modules use
standard conditions (14.73 psia, 600 F) on the BASE_PRESS and
BASE_TEMP terminals, only one AGA8Detail module is needed
because Zb is the same as Zs, and the Zb signal will be wired to the
Z_BASE and INPUT_3 terminals.
Where base conditions are other than standard, then an AGA8Detail
module is used to obtain Z_FLOWING (Zf) and Z_BASE (Zb) signal
values at base conditions. Another AGA8Detail module will be needed
to compute a Zs at standard conditions. This Zs is to be wired to
INPUT_3. This Zs comes from the AGA8Detail module Zb output, but it
is the same as Zs because the BASE_PRESS and BASE_TEMP termi-
nals are set at 14.73 and 600 F.
Static Pressure Tap Location:
If the static pressure is from a downstream tap, the TAP_LOC should
be non-zero, in which case the DIFF_PRESS is converted to psia and
added to the STAT_PRESS to obtain an upstream pressure. Users
must ensure that the static pressure used for the AGA8Detail and
AGA8Gross module is the sum of the downstream pressure and the
differential pressure (in psia) or the Z factors will be incorrect.
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