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Saturday, August 30, 2014

Pneumatic Controllers for Natural Gas Wells Face Emissions Limits

Credit: Blue Source Inc.

Credit: Blue Source Inc.

U.S. natural gas production is on the rise. So are greenhouse gas emissions. To some extent, one trend is helping to offset the other, especially in the power generation industry, where gas boilers are replacing those previously fired by coal.

However, since methane has a much higher heat-trapping greenhouse gas effect than carbon dioxide, much of that benefit is squandered on releases of uncombusted natural gas.

One methane release mechanism can be found in remote natural gas production sites that might not have access to AC power. In these situations, pneumatically powered devices, such as liquid level controllers, transducers, pressure regulators, and valve actuators that are driven by the flow of gas coming up from the well, are often used. The devices are classified, depending on the amount of gas they release as part of their normal operation, as low-bleed or high-bleed units. Releases from some 400,000 of these devices in the production sector was estimated in 2006 at over 50 billion cubic feet (bcf) annually.

This problem caught the attention the U.S. Environmental Protection Agency, which has regulated these fugitive emission sources under provisions of the Clean Air Act, which are known as the New Source Performance Standards (NSPS) for volatile organic compounds and the National Emissions Standard for Hazardous Air Pollutants (NESHAP) for oil and natural gas production.

The EPA has been encouraging companies to take action by either installing bleed reduction retrofit kits or replacing high-bleed units with low-bleed units — a move that it claims could pay for itself in a year or less, depending on the price of gas.

Beginning on Jan. 1, 2015, all gas-driven controllers located between the wellhead and the point where gas enters the transmission pipeline will be restricted by the EPA to a maximum bleed limit of 6 standard cubic feet of gas per hour (SCFH).

Fisher i2p-100

Fisher i2P-100 from Emerson Process Management is a electro-pneumatic transducer for regulating operating natural gas supply to pneumatically driven valve/actuator assemblies at the wellhead.

Another option for addressing this challenge just came on the market, with the release of the Fisher i2P-100 electro-pneumatic transducer from Emerson Process Management. The supplier says its lower pneumatic supply consumption not only allows it to meet EPA’s latest standards but helps reduce operating cost. The transducer is CSA and FM approved for high output volume, corrosion resistance, and pipe-away vent capability.

The i2P-100 converts a milliamp input to a proportional pressure output. Both the input and output ranges are user-configurable in the field (output is between 2 and 33 psi). The converter module uses low-mass parts, which are balanced around the center of mass, which, in turn, results in lower sensitivity to vibration, producing an output shift of less than 1 percent of span when tested to ISA S75.13.

It is a single-seal device, tested in accordance with ANSI/ISA Standard 12.27.01.

The unit incorporates a high-capacity pneumatic relay to drive pneumatic control valve/actuator assemblies without additional boosters or positioners. It provides stable, accurate operation when its output is transmitted to small-volume chambers, such as pneumatic positioners. These properties, plus its first-order lag characteristics, make the i2P-100 transducer suitable for direct mounting on natural gas control valve/actuator combinations.

Another key feature of the device is its corrosion resistance. It utilizes separate housing compartments to isolate the electronics from the pneumatic process. The electronics are encased in a rugged plastic shell, while the printed wiring board assembly and dip switches, as well as all coils, are conformal coated to help prevent corrosion, and all flexures are gold plated to provide protection from hostile environments.

The unit is also designed to be tolerant of dirt supply media, with large internal air passages. The removable primary orifice and replaceable 5 micron filter enable service and maintenance.

 

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