AGA8 & AGA3 - tuning the Controlstar® into a powerful flow measurement device

Both the AGA8 and AGA3 function blocks form part of the library of blocks available within the Controlstar’s® visual programming and ‘live’ control algorithm environment. Multiple AGA8 and AGA3 function blocks can be used on the same Controlstar® system and the flow calculations can be integrated within the process control algorithms. Multiple AGA8 function blocks have also been used to calculate gas velocity and provide warnings of potential erosion conditions at critical positions in a process. The provides accurate erosion prediction using the reliable primary flow monitoring element, and saving the costs of a separate erosion monitoring system,(link to Wits etc)

The Controlstar Systems Ltd AGA8 Function block uses the ‘Detailed characterization method’ and fully realises the AGA committee report No.8 November1992 i.e. ‘The calculation of compressibility factors of natural gas and other related Hydrocarbon gases’ second edition. The resultant calculation provides the compressibility factors for the gas phase of methane, ethane, nitrogen, carbon dioxide, hydrogen, and hydrogen sulphide and gas mixtures of up to twenty-one compounds. The calculations are valid for temperatures from –130 to 400 degrees C at pressures up to 280Mpa (40,000 psia). The function block has been validated against the standard.
Multiple AGA8 and AGA3 function blocks can be used on the same Controlstar® system and the flow calculations can be integrated within the process control algorithms.
Example of on of our AGA3 / AGA8 function blocks.

[ Click image to enlarge ]
The user can manually enter the gas fractions through the SCADA, alternatively the system collects ‘live’ measurements of the gas fractions directly from an associated Gas Chromatograph, at present a Modbus RTU interface is available, the system supports the range of Daniel Chromatographs. The Gas Chromatograph interface includes provision for automatic fallback to manually entered variables and alarming on the failure of the communications with the Chromatograph.
The AGA3 Function block is according to the AGA report no. 3 ‘Orifice metering of natural gas and other related hydrocarbon fluid’. The AGA3 block has been extended to support the Rosemount Annubar flow element, these devices cover a high turn down ratio and so provide accurate measurement of flow in less than ideal conditions.