Summary

Prism Systems was hired to build, program, and install RTUs to measure gas flow into a power plant in Texas. Two separate gas companies with their own pipelines could supply natural gas to the facility. The power company wanted to perform their own gas calculations to verify the charges from the gas companies. They also wanted to be able to monitor each pipeline interconnect with their plant DCS system.

Solutions

Prism Systems built three enclosures using Emerson ROC 829 RTUs. To properly perform AGA flow calculations, the gas composition must be obtained from a gas chromatograph (GC). The gas supply companies provided the GCs without enough communication ports for the Prism-provided RTUs to obtain the data. Instead, the gas companies provided a MODBUS port from their RTUs to the Prism RTUs. Due to terrain challenges, Prism Systems worked with a satellite communication contractor to provide a data path from each gas interconnect back to the power plant's main facility. The facility's DCS contractor was then able to poll all registers from the ROCs via Modbus/TCP.

Customer Benefits

• Real-time flow rates from each gas flow company can be monitored from the plant DCS
• Hourly, daily, and monthly flow totals can be monitored and archived from the plant DCS
• Interconnect operating conditions such as power failure, UPS failure, and intrusion detection can be monitored from the plant DCS
• Plant personnel are aware of any discrepancies between plant-calculated energy totals and gas provider-calculated energy totals

Technologies

• Emerson ROC 829
• DataCom/Blackhawk Satellite Communications
• MODBUS/TCP
• Emerson Bristol ControlWave
• Daniels Gas Chromatographs and Ultrasonic Flowmeters