- Improved controls bleed significantly less gas under steady state conditions.
- Increased accuracy over given control range.
- Safe, reliable and accurate pressure delivery under all conditions.
Natural gas custody transfer point.
Natural gas transportation and storage service company including grid transportation between other interstate and intrastate pipelines.
This transfer station is a critical natural gas feed into a major metropolitan area, and requires safe, reliable and accurate pressure delivery to the custody transfer metering equipment. This pressure is controlled through three parallel pipe runs, each containing a six-inch (NPS 6) Fisher control valve. Each valve is controlled by a Fisher® FIELDVUE™ digital valve controller that receives its pressure command from a local RTU. Because the control equipment is electronic in nature, it is critical that there be a local backup control source, should there be a power outage or lightning strike. Each valve was previously controlled by older, pneumatic equipment using nozzle-and-flapper technology with significant bleed gas to the atmosphere.
The previous backup control was provided through local pneumatic pressure controller that use natural gas as the supply pressure medium. It is critical that these controllers take over control accurately with minimal gas bleed to the atmosphere. The previous controllers allowed a constant bleed as part of their normal operation, and the internal linkages were subjected to wear and corrosion. There was also an unacceptable dead band when the valves were required to operate under pneumatic control. The controllers were replaced with new units manufactured by VRG Controls, which bleed zero gas under steady state conditions and minimal gas when moving, plus have more accuracy over a given control range. Now any bleed gas has been substantially reduced, helping the customer meet their environmental goals and also reduce lost and unaccounted-for natural gas. Better control accuracy and increased reliability helps them maintain good standing with the local distribution company whom they are supplying.
This Novaspect / Emerson solution included:
- VRG Controls Model VPC-700-SA-BV
- Fisher FIELDVUE digital valve controller
- Fisher NPS 6 EWT valve with 657 actuator.
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