Aga8gros - Cesar Delgado

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ACCOL II Reference Manual
Page AGA8Gross-1
AGA8Gross
American Gas Association Report No. 8 Gross Calculation Module
The AGA8Gross Module uses heating value, relative density, and
nitrogen and carbon dioxide mole percent information to compute the
base compressibility (Zb), flowing compressibility (Z), and
supercompressibility (Fpv= Zb/Z ) for natural gas mixtures accord-
ing to the Gross Characterization method explained in American Gas
Association Report Number 8 (AGA-8), 2nd edition, of November,
1992.
BASE_TEMP
BASE_PRESS
ENABLE
PRIORITY
8GROSS
FLOW_TEMP
MODE
STAT_PRESS
Z_FLOWING
Z_BASE
FPV
ERROR
STATUS
REF_P_HV
REL_DENS
HEAT_VALUE
REF_T_HV
MOLE_%_N2
MOLE_%_CO2
REF_T_RD
REF_P_RD
MOLE_%_H2
MOLE_%_CO
If the ENABLE signal is ON, the module checks the entries on its
terminals. Incorrect conditions will be indicated via the ERROR
terminal signal and computations will not occur. If all conditions are
correct, then calculations are initiated.
On subsequent executions of the AGA8Gross Module, the STATUS
terminal is updated to indicate the progress of the calculations. The
AGA8Gross Module’s output terminals (Z_FLOWING, Z_BASE, and
FPV) are updated only when calculations have been completed.
AGA8Gross
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AGA8Gross
American Gas Association Report No. 8 Gross Calculation Module
AGA8Gross calculations require significant amounts of memory and
computation resources, and could result in other ACCOL tasks 'slip-
ping' from their normal execution rate (see PRIORITY terminal
below).
❏ Module Terminals
ENABLE Default: None, entry required
Format: Logical signal
Input/Output: Input
allows calculations to proceed if ON and no calculations are already in
progress. This signal will be set OFF automatically when calculations
begin.
PRIORITY Default: ACCOL task priority 1; (This cor-
responds to system task priority
55.)
Format: Analog signal
Input/Output: Input
is the priority at which the system task which performs the
AGA8Gross calculations will run. (System tasks are discussed in the
section 'Task', later in this manual.) Values lower than 1 or larger
than 64 will produce an error. Priority will affect system performance
if it is so high that other tasks cannot run. The priority should be kept
as low as possible.
MODE Default: 1
Format: Analog signal
Input/Output: Input
selects one of two Gross calculation methods. If 1 is entered on this
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AGA8Gross
American Gas Association Report No. 8 Gross Calculation Module
terminal, the module calculates using the inputs of volumetric gross
heating value, relative density, and the mole fraction of carbon diox-
ide. If 2 is entered on the MODE terminal, the module calculates
using inputs of relative density, and the mole fractions of nitrogen and
carbon dioxide. If the MODE terminal value is anything other than 2,
it will default to mode 1.
FLOW_TEMP Default: None, entry required
Format: Analog signal
Input/Output: Input
is the flowing gas temperature in degrees Fahrenheit.
STAT_PRESS Default: None, entry required
Format: Analog signal
Input/Output: Input
is the gas static pressure in psia. If this terminal has a negative value,
computations will not be performed.
BASE_TEMP Default: 600 F
Format: Analog signal
Input/Output: Input
is the base temperature in degrees Fahrenheit.
BASE_PRESS Default: 14.73 psia
Format: Analog signal
Input/Output: Input
is the base pressure in psia. If the terminal has a negative value no
computations are performed.
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American Gas Association Report No. 8 Gross Calculation Module
HEAT_VALUE Default: None, entry required (MODE 1
only)
Format: Analog signal
Input/Output: Input
is the volumetric gross heating value in BTU/FT3.
REF_T_HV Default: 600 F (MODE 1 only)
Format: Analog signal
Input/Output: Input
is the reference temperature of the volumetric heating value in de-
grees Fahrenheit.
REF_P_HV Default: 14.73 psia (MODE 1 only)
Format: Analog signal
Input/Output: Input
is the reference pressure of the volumetric heating value in psia.
REL_DENS Default: None, entry required
Format: Analog signal
Input/Output: Input
is the relative density of gas (specific gravity).
REF_T_RD Default: 600 F (MODE 1 only)
Format: Analog signal
Input/Output: Input
is the reference temperature of the relative density in degrees Fahren-
heit.
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American Gas Association Report No. 8 Gross Calculation Module
REF_P_RD Default: 14.73 psia
Format: Analog signal
Input/Output: Input
is the reference pressure of the relative density in psia.
MOLE_%_N2 Default: 0 (MODE 2 only)
Format: Analog signal
Input/Output: Input
is the nitrogen mole fraction composition. This terminal is optional.
MOLE_%_CO2 Default: 0
Format: Analog signal
Input/Output: Input
is the carbon dioxide mole fraction composition. This terminal is
optional.
MOLE_%_H2 Default: 0
Format: Analog signal
Input/Output: Input
is the hydrogen mole fraction composition. This terminal is optional.
MOLE_%_CO Default: 0
Format: Analog signal
Input/Output: Input
is the carbon monoxide mole fraction composition. This terminal is
optional.
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American Gas Association Report No. 8 Gross Calculation Module
ERROR Default: None
Format: Analog signal
Input/Output: Output
displays one of the following codes. Errors are detected by the module
prior to the start of calculations.
Code Message
 0 No errors
 -1 Missing ENABLE signal
 -3 Missing input terminals
 -8 Missing FPV output terminal
 -9 Invalid PRIORITY (less than 1 or larger than 64)
-10 Negative pressure values detected for STAT_PRESS or
BASE_PRESS
STATUS Default: None
Format: Analog signal
Input/Output: Output
contains one of the following status codes:
Code Message
10 Calculation complete
 4 Calculating compressibility at flow conditions
 3 Calculating density at flow conditions
 2 Calculating gas characterization
 1 Calculating compressibility at base conditions
 0 Not running, check error terminal for errors
 -1 No memory available
 -3 Floating point error detected
-11 No convergence
-12 Root not bounded
-13 Negative square root
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American Gas Association Report No. 8 Gross Calculation Module
 Z_FLOWING Default: None, entry is optional
Format: Analog signal
Input/Output: Output
is the compressibility at flowing conditions. This terminal will only be
updated if the AGA8Gross Module is executing, and if the value on the
STATUS terminal is 10; i.e. calculations are complete.
Z_BASE Default: None, entry is optional
Format: Analog signal
Input/Output: Output
is the compressibility at base conditions. This terminal will only be
updated if the AGA8Gross Module is executing, and if the value on the
STATUS terminal is 10; i.e. calculations are complete.
FPV Default: None, entry required
Format: Analog signal
Input/Output: Output
is the supercompressibility ratio ( Zb/Z ). This terminal will only be
updated if the AGA8Gross Module is executing, and if the value on the
STATUS terminal is 10; i.e. calculations are complete.
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AGA8Gross
American Gas Association Report No. 8 Gross Calculation Module
CAUTION
The AGA8Gross Module, as implemented in the AH.00
PROM set, has a small discrepancy between the module's
Z_FLOWING output value, and the tables (B.6-3 and B.6-
4) in the 1992 American Gas Association (AGA-8) Report.
Users with this PROM set revision level should upgrade
their PROMs to version AH.01 (or later revision) which
corrects this known discrepancy.
❏ Using the Module
Place the AGA8Gross Module in an ACCOL task which has a task
priority of 32 or less. A task rate of 1 second is recommended for
efficient monitoring of the calculations and update of the STATUS and
output signals. The value on the PRIORITY terminal of the module
shouldalso be as low as possible.
When the AGA8Gross Module executes, if the ENABLE signal is ON
and no previous calculation is active, the input terminals are auto-
matically checked for errors. If none are detected, calculations are
initiated and the ENABLE signal is set to OFF.
Setting the ENABLE signal to ON should be controlled by logic in the
ACCOL program to limit calculation activity to a reasonable level
based on potential changes of the input information. For example, if a
chromatograph is used to provide the gas component information, the
AGA8Gross Module ENABLE should be turned on when new compo-
nent information is available from the chromatograph. A Timer
Module might also be used to enable execution of the AGA8Gross
calculations at some frequency, e.g. once per minute. It is recom-
mended that the ENABLE signal not be set to ON while a previous
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AGA8Gross
American Gas Association Report No. 8 Gross Calculation Module
calculation is active, i.e. before the STATUS terminal value indicates
completion. In this case, a new calculation cycle will be started as soon
as the current cycle completes and the output signals are updated,
therefore the STATUS terminal completion status value will not be
visible because it will immediately change to one of the active status
values.
When the AGA8Gross Module executes, the STATUS terminal is
updated. If calculations are active, the STATUS value will show the
progress of the calculations (values 1 through 4). All of these interme-
diate values may not be seen, depending on the ACCOL task rate and
other activities in the system.
When calculations are complete as indicated by the STATUS value,
the output signals Z_FLOWING, Z_BASE, and FPV are updated with
the results.
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