Turnkey PLC/RTU Solution for Gas Pipeline Metering

Yokogawa’s gas flow calculation APPF (application portfolios) can be used for gas flow measurement. APPFs consist of various software components in which an autonomous controller can perform control functions without writing custom code – a true turnkey solution.
 

Introduction

In the gas metering skid of a pipeline, gas compensation equations are used to execute the correction for compressibility and super compressibility and to get compensated flow at normal, standard, or reference pressure and temperature. Yokogawa provides an embedded controller flow calculation library based on American Gas Association (AGA) reports.

Fig. 1. Pipeline skid measuring station

Fig. 2. Gas reduction plant

Challenges

Operators must monitor several critical measurements and need fast calculation results. The APPF flow equations are based on the following standards: 

• AGA Report No. 3: Orifice metering of natural gas and other related hydrocarbon fluids (Also ISO 5167). 
• AGA Report No. 7: Turbine metering of natural gas is required.  This portfolio uses the pulse train from the turbine meter and some parameters as inputs to perform natural gas flow calculations.
• AGA Report No. 8: Compressibility factors of natural gas and other related hydrocarbon gases.

Fig. 3. Gas metering skid of pipeline with STARDOM flow computer function - AGA3 calculation

Solutions

Yokogawa offers the flow calculation for a metering solution as an APPF (application portfolio) on the STARDOM autonomous controller, FCN-500/FCN-RTU.

Fig. 4. FCN-RTU: Low Power Consumption Autonomous Controller
 

Combining the IEC 61131-3 language with hot-swappable modules including CPU and I/O modules ensures processes continue without interruption even when a damaged module is replaced. STARDOM can provide the same functions as a flow computer with quicker response to I/O and calculation results.

Furthermore, due to the high memory capacity of FCN-500/FCN-RTU Meter APPF will store 35 days of daily average data (Pressure, Differential Pressure, Temperature, Flow, and 2 user-defined variables), and the history of the last 70 parameter changes. The Meter APPF calculates the flow accuracy in real-time, considering the uncertainty of all measures involved. Data settings regarding natural gas composition can be made manually or automatically by online chromatograph connection (MODBUS, OPC, etc.). 
The interface for manual data composition inputs is provided as part of Meter APPF this interface provides historian and parameters data visualization.

Fig. 5. FCN-500: Dual redundant configurable PLC/RTU

Meter APPF provides:

• AGA3 flow calculations: The orifice plate (flange taps or pipe taps) metering of natural gas is required. The application portfolio uses pressure, differential pressure, temperature, and some parameters as inputs to perform the natural gas flow calculation.
• AGA7 flow calculations: This is where turbine metering of natural gas is required. The application portfolio uses the pulse train from the turbine meter and some parameters as inputs to perform the natural gas flow calculation.
• AGA8 super-compressibility: This application portfolio uses pressure, natural gas composition, and temperature as inputs to perform the compressibility gas factor calculations.
• AGACOM: This makes all interfaces of AGA blocks with physical inputs, making unit conversion and ensuring data consistency. 
• AGAHIST: This prepares data for recording to flash memory (SD card). It stores 35 days of daily average data (Pressure, Differential Pressure, Temperature, Flow, 2 user-defined variables), and the history of the last 70 parameter changes.

Key Advantages

Yokogawa’s gas flow calculation APPF (application portfolios) for Yokogawa’s PLC (Process Control)/RTU: STARDOM can be used for gas flow measurement. Which allows operators to:

• Eliminate cost for a flow computer 
• Access fast response to I/O and calculation results 
• Store daily data on non-volatile flash memory (SD card) for 35 days 
• Easily integrate with SCADA or local display