What Is A Flow Computer?
Frequently referred to as the "cash register" of the petroleum industry, a flow computer is a scientific instrument that is typically used for custody or fiscal transfer between contracting parties. Flow computers monitor and calculate the volume and mass flows in gathering and transportation pipeline systems for natural gas, crude oils, refined products, LPGs, and NGLs.
A flow computer is an electronic computational and totalizing device that implements a wide selection of complex density algorithms and equations of state for single-phase hydrocarbon fluids and petrochemicals with known physical properties. Gas density calculations for natural gas, steam, oxygen, hydrogen, nitrogen, and ethylene are also selectable. Using these specific algorithms and equations of state, the flow computer converts a volume at flowing conditions to a volume at industry-defined base contract conditions.
OMNI flow computers are pre-programmed, configurable devices that use OMNI's proprietary configuration software packages to set up connections to flow meters, transmitters, liquid provers, flow control valves, and samplers in dynamic metering systems, communication interfaces to gas chromatographs, programmable controllers (PLCs), and distributed control systems (DCSs). OMNI flow computers can be safely networked to industry-recognized supervisory systems (SCADAs) with the latest security safeguards.
An OMNI flow computer averages and records all digital signals received from various types of flow meters, and analog or digital signals from temperature, pressure, and density transmitters. Every 500 milliseconds, a new incremental volume and mass calculation is performed. A continuously running total of the cumulative volume and mass is maintained for each flow meter that the flow computer monitors. An OMNI flow computer can monitor and record data for up to six independent meters.
A key component in custody transfer systems, OMNI flow computers are approved to international metrological and quality standards, including OIML R 117‑2 for liquids, EN 12405 for gas, WELMEC 7.2 and OIML D31 for software development, and ISO 9001:2008 for quality.
A transactional record of this volume and mass can be created by the OMNI flow computer on a fifteen-minute, hourly, batch, daily, and monthly basis. The flow data are made available externally by providing digital or text interval and archive reports through multiple serial and Ethernet connections to process or pipeline control networks. The information can then be accessed for supervisory control of the pipeline, hydrocarbon accounting, contractual billing, and auditing.
An OMNI flow computer also records changes that have been made to any of the parameters that can influence the conversion of the flow meter and transmitter signals into an accurate measurement of volume or mass. In addition, it records, archives, and reports events and alarms that can influence accurate measurement. These include changes in fluid types and properties, calibration factors, and flow rate, as well as changes or failures of electrical signals from transmitters, or when these electrical signals are near or exceed their upper or lower range limits.