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Reduce Emissions with Advanced Controls Reduce Emissions with Advanced Controls
NATURAL GAS TRANSMISSION
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

Application

Natural gas custody transfer point

Customer

Natural gas transportation and storage service company including grid transportation between other interstate and intrastate pipelines
Challenge

Challenge

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.

One of three parallel natural gas lines within the transfer station installation is shown to the right with the six-inch Fisher control valve and Fisher FIELDVUE™ digital valve controller at center.

Digital valve controllers feature low bleed relays that limit unwanted leakage into the atmosphere plus provide more accuracy within the control range.

Solution

The previous backup control was provided through local pneumatic pressure controllers that used 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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