What is a gas metering system?

A gas metering system is defined as a transfer in which a fluid or gas is measured and sold from one direction to another. In the process of trade handover, accuracy is crucial for both the company delivering the materials and the ultimate recipient when transmitting them. CTM is defined as an instrument designed, installed, and operated to meet the requirements of trade handover measurement. Trade handover requires a complete metering system designed and manufactured for measuring product gas applications, not just flow meters.

The trade handover measurement sled is an integrated pipeline system supported on a structural foundation. It is suitable for all major measuring instruments, including ultrasonic flow meters, pressure transmitters, temperature transmitters, and MOVs, with a linear length that complies with AGA 9. The design, manufacturing, and testing of flow profiling instruments, pipelines, and structures comply with project specifications and applicable codes and standards, taking into account functional requirements.

The analyzer analyzes the gas composition and provides input to the flow computer for energy calculation. The analyzer room is designed to be located in the hazardous area of Zonal Gr-HB T3, with HVAC equipment and fire and gas sensors with safety PLC provided inside the enclosure. Provide sample probes (installed on the measuring sled) and analyzer sample processing systems to ensure sample representativeness.

The measuring cabinet is located in the control room of the safe area. This panel is equipped with a flow computer, workstation computer, GC controller, PLC, HMI, and Ethernet switch with DCS interface. All flow and energy calculations are completed by flow computers, which collect various signal data from pry blocks and analyzer houses. Compile station values on the station computer and generate reports.

The components of a gas metering system (also known as CTM) typically include:

1. Ultrasonic flowmeter

2. Gas chromatograph

3. Traffic computer

4. Operating at a speed of over meters per meter

5. Support automation

6. Analyzer (moisture, dew point, CO2, H2S)

7. Pressure and temperature transmitters

Two ultrasonic transducers installed at a certain angle to the airflow are alternately used as transmitters and receivers. The signal transmitted through gas accelerates in the direction of flow and decelerates in the direction of reverse flow.

The resulting propagation (transmission) time difference is used to determine the average gas velocity. Then use the cross-sectional area to calculate the volumetric flow rate.

In order to improve measurement accuracy, gas velocity is measured through multiple chordal paths. Uncorrected measurements are not affected by pressure, temperature, or gas composition.

Gas chromatograph (GC) is used for the entire natural gas pipeline network, providing analysis of flowing gases and calculating physical properties for flow calculation and trade handover.

A gas chromatograph (GC) is an analytical instrument used to measure the content of various components in samples. The sample solution injected into the instrument enters the airflow and is transported to a separation tube called a "chromatographic column". (Helium or nitrogen is used as the so-called carrier gas.) Various components are separated in the chromatographic column.

The detector measures the quantity of components leaving the chromatographic column. To measure samples of unknown concentration, a standard sample of known concentration is injected into the instrument. Compare the peak retention time (appearance time) and area of the standard sample with the test sample, and calculate the concentrations of various gas components.

The flow computer is designed specifically for measuring hydrocarbon liquids and gases, with versatility and accuracy being of utmost importance. Flow computers allow for the configuration of multiple flow, multi station applications to simultaneously measure liquids and gases.

The main function of a flow computer is to collect gas flow data from instrument operation, instrument or transmitter connectors, and calculate the volumetric flow rate and energy flow rate under reference conditions. Traffic is calculated based on hourly, daily, and overall volume. All data generated by the traffic computer is genuine billing data, which has been stored and processed.

The volume of gas consumed is calculated separately for each instrument by their respective flow calculators. The flow calculator is designed to calculate the flow rate of energy and gas volume, taking into account signals from the corresponding instrument operation metering device, temperature, pressure, and overall chemical analysis using a gas chromatograph.

More specifically, the traffic calculator can:

1. Calculate the gas volume (m) and volumetric flow rate (m/h) under the operating pressure and temperature of the instrument.

2. Calculate the gas volume (m) and volumetric flow rate (m/h) by applying the error correction equation of the corresponding instrument (ultrasonic flowmeter) to the operating pressure and temperature of the instrument.

3. Calculate the gas volume (μ m) and volumetric flow rate (μ m/h) under normal pressure and temperature conditions (reference conditions).

4. Calculate the gas compression rate under the operating temperature and pressure conditions of the instrument, as well as the components detected by the chromatograph.

5. Calculate the energy (MJ) and energy flow rate (MJ/h) of the gas based on its total calorific value and volume.

Source: Instrument and Tool Network