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Process Control Goes Green

Oil and natural gas operators can help reduce methane and other emissions—and increase revenue—by replacing traditional pneumatic devices with energy-responsible pneumatic pressure and level control devices.

 

An estimated $20 billion or more in revenue is lost each year globally due to methane emissions. Coupled with this lost revenue, global greenhouse gas emissions (GHG), of which methane comprises a substantial portion, have been gaining ever increasing visibility from a variety of agencies, special interest groups, national and international companies, politicians and the general public. It’s clear that a substantial problem exists. Many companies, however, are looking to alleviate that problem by changing their methods of operations and sharing best practices with each other.

THE METHANE FACTOR

Countless studies have analyzed the net effects greenhouse gases have on our environment and have resulted in a diverse range of views on the subject. However, one accepted fact is that methane is the most potent of the global greenhouse gas (GHG) emissions. Each year significant amounts of methane—the primary constituent of natural gas—are emitted into the atmosphere. These emissions cause concern because of the increasing negative effects on the environment as a whole, as well as the large amounts of revenue lost as a result. The importance of reducing methane emissions cannot be understated; but with innovative technology and implementation of best practices, the entire world’s industries can shift toward using more environmentally responsible products for process control functions. This shift in thinking will also result in cost savings and increased revenue.

Many owners and operators at oil and gas production, processing and transmission facilities have already taken initiatives to eliminate or reduce methane emissions. One shining example, which illustrates the widespread collaboration among companies, is the EPA Natural Gas STAR program. This program is a voluntary partnership between the U.S. Environmental Protection Agency and numerous natural gas companies, which provides a way to share best practices for reducing emissions among member companies. Currently, the program includes 23 of the top 25 natural gas producing companies which constitute 62% of the production, processing, transmission and distribution of natural gas. It also constitutes 62% of the production, processing, transmission and distribution of natural gas. As Figure 1 illustrates, in the 14 years since the program was established, more than 577 billion cubic feet of methane emissions, at a value of $3.4 billion, have been eliminated through voluntary initiatives by the member companies—initiatives that have also provided these companies cost savings and increased operational efficiency.(1)

This article provides examples of opportunities to reduce methane emissions in oil and natural gas applications, and highlights the significant cost savings that can be realized by implementing available technologies in the process control market. The primary methane emissions mitigation method discussed in this article is identification and replacement of high-bleed pneumatic pressure and level control devices.

PNEUMATIC CONTROL DEVICE BASICS

Continuous bleed pneumatic controllers are used in the oil and natural gas industry to regulate level, flow-rate, temperature or pressure. Given the infrastructure for installing these devices, natural gas may be the only option for a supply medium in places where it is not possible, economical or convenient for installing compressed air systems.
Nearly all pneumatic devices use the same basic design principle, which consists of a nozzle-flapper mechanism (Figure 2, left) that executes throttling control and exhibits continuous or intermittent bleed of the supply medium. Varying the separation between the flapper and nozzle alters the resistance to gas flow. Increasing the distance between the nozzle and the flapper reduces nozzle resistance and output pressure, while decreasing the distance has the opposite effect. In most pneumatic devices that use this concept, the inherent design of the nozzle flapper mechanism is the only reason the supply medium bleeds to the atmosphere.

Controllers that use a three-way valve for proportional band control also introduce another way for supply gas to bleed to the atmosphere (Figure 2, right). Some pneumatic controllers are designed to bleed only when the unit is in transient operation, or cycling, while others bleed both during steady-state conditions and transients. The steady-state bleed tends to dominate the emissions reduction focus; however, consumption during transients should not be underestimated because of the potentially significant effect on the total amount of gas consumed by the device.

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