Metering systems are used on pipelines to check the values of the gas/NGL parameters (Flow rate, Compositional Analysis& Heating value) when they are subject to change or when Gas/NGL is transferring from one company to another for sales purpose.
This system includes the integration of the flow computers that interconnect with the skid instrumentation (GC, Moisture analyzer, H2S analyzer) and with the Human Machine Interface (HMI), or Supervisory Control and Data Acquisition (SCADA) System which provides the platform for the information recorded by the flow computer to be presented in a clear and concise format for the custody transfer, operation and maintenance of the Metering System.
Metering System Features
Flow Computer
Flow Computer firmware has the capability to perform AGA3 orifice flow calculations or AGA7 pulse flow calculations using AGA8 compressibility. It also performs ISO 5167 flow calculations. It maintains API Chapter 21.1 compliant historical archives for measured and calculated values, as well as events and alarms. Other gas flow or properties calculations can be implemented using C programs. It has full capability to integrate with Telemetry, SCADA, DCS and PLC Systems. It monitors and records volumetric flow on an hourly, daily or monthly basis. The flow data is made available externally through an electronic interface so that other computers can download the information for the purposes of supervision, accounting or auditing.
Gas Chromatograph (GC)
Compositional analysis of pipeline gas C6+ application (C1- C6+, N2, and CO2) and C9+ application (C1- C6+, N2, and CO2) using GPA2172 ,GPA2145 ,ISO6976 & AGA-8 physical property data. It Calculates heating value (BTU), specific gravity, and compressibility can and Optionally calculate hydrocarbon Dew Point in English or Metric.
H2S Analyzer
H2S Analyzer does Compositional analysis of H2S for quality and process control. H2S level in the sales gas are strictly regulated and measured in regards to personal safety, corrosion control and contractual agreements. To comply with these demanding regulations a reliable, accurate and continuous analytical technique needs to be implemented which can continuously verify the hydrogen sulfide level in product gas.
Moisture Analyzer
The presence of moisture in high-pressure natural gas causes pipelines and associated valves to freeze. High moisture content also leads to the formation of hydrates of the liquid hydrocarbons present, thus causing further difficulties.
The moisture content of the gas also adversely affects the calorific value of the gas, thus lowering the quality and value of the product. Moisture is therefore measured at the point of extraction, at export stations, at gas storage locations and in the transmission grid .This requires Immediate, continuous and accurate moisture measurement for Gas, NGL and LNG.
Chart Recorder (optional)
Chart Recorder measures Process measurements such as as temperature, pressure and flow of natural Gas/ NGL with the Universal Probes and keeps graphical records of these variables. It might be used as a backup system for flow
computer at Metering Skid.
In order to know how much product is flowing and to report gas volumes a simple metering unit is used which measures a natural gas/NGL flow rate using a meter run and chart recorder.