Descarga la aplicación para disfrutar aún más
Vista previa del material en texto
AGA8 American Gas Association Report No. 8 Module ACCOL II Reference Manual Page AGA8-1 The AGA8 Module uses gas component mole percent information to compute the base compressibility (Zb), flowing compressibility (Z), and supercompressibility (Fpv= Zb/Z ) for natural gas mix- tures according to the method explained in American Gas Association Report Number 8 (AGA-8) of Dec 15, 1985.* Up to 20 gas components can be processed by the module, and these can come from a signal list or a data array. For best results, the gas component information should come from a chromatograph. This module does not perform the gas component estimation explained in the AGA-8 Report. Such estimated gas component information in accordance with the report can be generated by the ACCOL Charac- terize Module described later in this manual, under 'Characterize'. Alternately, component information can come from a signal list or data array containing the component percentages. The components in the list or array must be in the fixed order defined under Component Order and Percent Requirements in this section. If the Characterize Module generates the list or array, the components will automatically be in the proper order. 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 AGA8 Module, the STATUS terminal BASE_TEMP BASE_PRESS ENABLE PRIORITY 8 FLOW_TEMP ARRAY COLUMN LIST STAT_PRESS Z_FLOWING Z_BASE FPV ERROR STATUS * Users requiring the calculation method described in the Nov., 92 (2nd edition) of the AGA8 report should see 'AGA8Detail' or 'AGA8Gross', later in this manual. AGA8 ACCOL II Reference Manual Page AGA8-2 AGA8 American Gas Association Report No. 8 Module is updated to indicate the progress of the calculations. The AGA8 Module’s output terminals (Z_FLOWING, Z_BASE, and FPV) are updated only when calculations have been completed. The AGA8 Module should be used only where the ACCOL FPV Module (NX-19) will not suffice (see 'FPV', later in this manual). This is because the AGA8 calculations require signficant amounts of memory and computation resources, and could result in other ACCOL tasks 'slipping' 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 or constant Input/Output: Input is the priority at which the system task which performs the AGA8 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 perfor- mance if it is so high that other tasks cannot run. The priority should be kept as low as possible. AGA8 American Gas Association Report No. 8 Module ACCOL II Reference Manual Page AGA8-3 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: 600F 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 Component ACCOL II Reference Manual Page AGA8-4 AGA8 American Gas Association Report No. 8 Module Order and Percent Requirements, later in this section. If both the LIST and ARRAY terminals are wired, only the LIST terminal will be used. 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 Component Order and Percent Requirements, later in this section. One dimensional arrays must be 1 column by N rows, where N can be 1 to 20. 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, only the LIST terminal will be used. COLUMN Default: None, entry required if LIST terminal is unwired. Format: Analog signal Input/Output: Input is the array column containing up to 20 gas components to be used in the calculation. This signal can be used to perform successive AGA8 calculations on multiple gas streams by indexing through the array columns. Invalid column values produce an error and no computation is performed. AGA8 American Gas Association Report No. 8 Module ACCOL II Reference Manual Page AGA8-5 ERROR Default: None Format: Analog signal Input/Output: Output contains 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: FLOW_TEMP or STATIC_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 values detected for STATIC_PRESS or BASE_PRESS STATUS Default: None Format: Analog signal Input/Output: Output contains the following status codes: Code Message -3 Floating point error detected -2 All input components are zero ACCOL II Reference Manual Page AGA8-6 AGA8 American Gas Association Report No. 8 Module Code Message (continued): -1 No memory available 0 Not running, check error terminal for errors 1 Combining components 2 Mixing terms at flowing conditions 3 Calculating density at flowing conditions 4 Mixing at base conditions 5 Calculating density at base conditions 10-19 Calculation complete - final root (includes iteration count) 20-23 Calculation complete - approximate root (includes approxi- mation code) 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 AGA8 Module is executing, and the value on the STA- TUS terminal is at least 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 AGA8 Module is executing, and the value on the STA- TUS terminal is at least 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 AGA8 Module is executing, and the value on the STA- TUS terminal is at least 10, i.e., calculations are complete. AGA8 American Gas Association Report No. 8 Module ACCOL II Reference Manual Page AGA8-7 o Component Order and Percent Requirements Gas components in lists or array columns must be in the following order. The number of components can vary from 1 to 20, but the order is important and must be followed. The Characterize Module will produce 15 components in the proper order. You may supply up to 20 components.If the list or array is too short (i.e., not enough compo- nents,) the remaining components are assumed to have a value of 0. Component Name Component Name 1 Nitrogen 11 n-Pentane 2 Carbon Dioxide 12 i-Pentane 3 Hydrogen Sulphide 13 n-Hexane 4 Water 14 n-Heptane 5 Helium 15 n-Octane 6 Methane 16 n-Nonane 7 Ethane 17 n-Decane 8 Propane 18 Oxygen 9 n-Butane 19 Carbon Monoxide 10 i-Butane 20 Hydrogen The AGA-8 Report specifies the following mole percent ranges for results within the stated uncertainty limits: Methane 50 to 100% Nitrogen 0 to 50% Carbon Dioxide 0 to 50% Ethane 0 to 20% Propane 0 to 5% Butanes 0 to 3% Pentanes 0 to 2% Hexanes 0 to 1% (also heavier hydrocarbons) All others 0 to 1% In addition, the report also indicates what percentage uncertainties can be expected for gases with compositions in the above specified ACCOL II Reference Manual Page AGA8-8 AGA8 American Gas Association Report No. 8 Module ranges over various pressure and temperature regions. Region 1: -60 F to 180 F from 0 to 1500 psia 0.1% Region 2: -60 F to 180 F from 1500 to 2500 psia 0.3% -80 F to -60 F from 0 to 2500 psia 0.3% 180 F to 240 F from 0 to 2500 psia 0.3% Region 3: -80 F to 240 F from 2500 to 10000 psia 0.5% 240 F to 400 F from 0 to 10000 psia 0.5% -200 F to -80 F from 0 to 10000 psia 0.5% Region 4: -200 F to 400 F from 10000 to 20000 psia 1.0% ❏ Using the Module Place the AGA8 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 AGA8 Module executes, if the ENABLE signal is ON and no previous calculation is active, the input terminals are automatically 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 AGA8 Module ENABLE should be turned on when new component information is available from the chromatograph. A Timer Module AGA8 American Gas Association Report No. 8 Module ACCOL II Reference Manual Page AGA8-9 might also be used to enable execution of the AGA8 calculations at some frequency, e.g. once per minute. It is recommended 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 AGA8 Module executes, the STATUS terminal is updated. If calculations are active, the STATUS value will show the progress of the calculations (values 1 through 5). All of these intermediate values may not be seen, depending on the ACCOL task rate and other activi- ties in the system. In general, STATUS code 5 will not be seen unless the methane component is less than 80% or if the base pressure exceeds 16.0 psia because the Z b value requires a longer computation in those circumstances. When calculations are complete, the value of the STATUS terminal signal is updated, and the output signals Z_FLOWING, Z_BASE, and FPV are updated with the results. The STATUS value indicates if a final root (STATUS values 10-19) or approximate root (STATUS values 20-23) was obtained. If the STATUS value is 10-19, subtract 9 to obtain the iteration count; i.e. the number of passes required to determine the root. If the STATUS value is 20-23, subtract 10 to get the approximation code. The approximation codes are: 10 Minimum density used 11 Maximum density used 12 Root not found; last iteration used 13 No bisection convergence; last iteration used Return to the Table of Contents Return to the List of Manuals
Compartir