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AGA8Detail American Gas Association Report No. 8 Detail Calculation Module ACCOL II Reference Manual Page AGA8Detail-1 The AGA8Detail Module uses gas component mole percent informa- tion to compute the base compressibility (Zb), flowing compress- ibility (Z), and supercompressibility (Fpv= Zb/Z ) for natural gas mixtures according to the Detail Characterization method explained in American Gas Association Report Number 8 (AGA-8), 2nd edition of November, 1992. Up to 21 gas components can be processed by the module. For best results, the gas component information should come from a chromatograph. 8DETAIL Z_FLOWING Z_BASE FPV ERROR STATUS BASE_TEMP BASE_PRESS ENABLE PRIORITY FLOW_TEMP STAT_PRESS ARRAY COLUMN LIST The components in the signal list or data array must be in the fixed order defined under Component Order in this section. 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 AGA8Detail Module, the STATUS terminal is updated to indicate the progress of the calculations. The AGA8Detail Module’s output terminals (Z_FLOWING, Z_BASE, and FPV) are updated only when calculations have been completed. AGA8Detail ACCOL II Reference Manual Page AGA8Detail-2 AGA8Detail American Gas Association Report No. 8 Detail Calculation Module AGA8Detail 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 calcula- tions 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 AGA8Detail calculations will run. (System tasks are discussed in the section 'Task', later in this manual.) Values lower than 1 or larger than 64 on this terminal 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. FLOW_TEMP Default: None, entry required Format: Analog signal Input/Output: Input is the flowing gas temperature in degrees Fahrenheit. AGA8Detail American Gas Association Report No. 8 Detail Calculation Module ACCOL II Reference Manual Page AGA8Detail-3 STAT_PRESS Default: None, entry required Format: Analog signal Input/Output: Input is the 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 gas base temperature in degrees Fahrenheit. BASE_PRESS Default: 14.73 psia Format: Analog signal Input/Output: Input is the gas base pressure in psia. If the terminal has a negative value no computations are performed. LIST Default: None, entry required if ARRAY terminal is not wired Format: Analog signal Input/Output: Input is the number of a list containing the gas component information. The gas components MUST be placed in the order specified in the Compo- nent Order portion of this section. If both the LIST and ARRAY terminals are wired, only the LIST terminal will be used. ACCOL II Reference Manual Page AGA8Detail-4 AGA8Detail American Gas Association Report No. 8 Detail Calculation Module ARRAY Default: None, entry required if LIST terminal is not wired Format: Analog signal Input/Output: Input is the number of an analog array containing the gas component information. The gas components must be placed in the order specified in the Component Order portion of this section. One dimensional arrays must be 1 column by N rows, where N can be 1 to 21. For cases where the array contains components from multiple gas streams, more columns can be added. If both the LIST and ARRAY terminals are wired, the ARRAY termi- nal is ignored. COLUMN Default: None, entry required if LIST terminal is unwired Format: Analog signal Input/Output: Input is the array column containing up to 21 gas components to be used in the calculation. This signal can be used to perform successive AGA8Detail calculations on multiple gas streams by indexing through the array columns. Invalid column values produce an error and no computation is performed. 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. AGA8Detail American Gas Association Report No. 8 Detail Calculation Module ACCOL II Reference Manual Page AGA8Detail-5 Code Message 0 No errors -1 Missing ENABLE signal -3 Missing input terminals: FLOW_TEMP or STAT_PRESS or both ARRAY and LIST missing. -4 Signal in list is not an analog signal -5 Not a valid list -6 Not a valid array -7 Not a valid array column -8 Missing FPV output terminal -9 Invalid PRIORITY (less than 1 or larger than 64) -10 Negative pressure 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 -2 No positive inputs in the component list or array -3 Floating point error detected -11 No convergence -12 Root not bounded -13 Negative square root -14 Pressure has a negative density derivative -15 Maximum number of iterations exceeded ACCOL II Reference Manual Page AGA8Detail-6 AGA8Detail American Gas Association Report No. 8 Detail 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 AGA8Detail 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 AGA8Detail 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 AGA8Detail Module is executing, and if the value on the STATUS terminal is 10; i.e. calculations are complete. ❏ Component Order Gas components in lists or array columns must be in the following order. The number of components can vary from 1 to 21, but the order is important and must be followed. If the list or array is short; i.e., less than 21 components, the remaining undefined components will be given a default value of 0. AGA8Detail American Gas Association Report No. 8 Detail Calculation Module ACCOL II Reference Manual Page AGA8Detail-7 Component Name Component Name 1 Methane 11 i-Butane 2 Nitrogen 12 n-Butane 3 Carbon Dioxide 13 i-Pentane 4 Ethane 14 n-Pentane 5 Propane 15 n-Hexane 6 Water 16 n-Heptane 7 Hydrogen Sulfide 17 n-Octane 8 Hydrogen 18 n-Nonane 9 Carbon Monoxide 19 n-Decane 10 Oxygen 20 Helium 21 Argon ❏ Using the Module Place the AGA8Detail 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 should also be as low as possible. When the AGA8DetailModule 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 AGA8Detail 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 AGA8Detail ACCOL II Reference Manual Page AGA8Detail-8 AGA8Detail American Gas Association Report No. 8 Detail Calculation Module 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 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 AGA8Detail 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. Return to the Table of Contents Return to the List of Manuals
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