Isolation valves are widely used throughout industrial plants and facilities worldwide. Though most perform well for their primary purpose of isolating one area of a process from another, many older models emit excess emissions. Regulations regarding these types of emissions are becoming much more stringent, as is pressure to improve upon corporate environmental, social, and governance (ESG) performance. In my March 2023 Valve World Americas article titled “Reducing Fugitive Emissions from Isolation Valves,” I describe the issues:
The global focus on fugitive and greenhouse gases has resulted in a host of new and more restrictive regulations. These mandates are also being enforced more strictly, with frequent inspections and large penalties being levied on those companies who fail to comply. Adding to the pressure are the demands of investors and stakeholders, who now insist that companies engage in environmental improvements and show their progress. In response to the latter point, the U.S. Security and Exchange Commission created reporting guidelines so companies can provide consistent and accurate accounts of their ESG programs.
Valves of all types are a major source of emissions in industrial plants and facilities.
Figure 1: Valve stems and joints account for a large percentage of fugitive emissions in a plant,
which is why so many government regulations specifically target these areas.
Costs from excess emissions are not limited to fines for violations, with escaping product adding to costs, along with increased maintenance expenses. One way to reduce maintenance expenses is by limiting the number of emitting devices.
Figure 2: Leak detection and repair (LDAR) inspections can be reduced from monthly to quarterly,
or even annually if the number of emitting devices is kept below 0.5%.
Manual testing of each valve to find leaks is impractical and expensive, leading to a search for a better approach.
Most valve emissions come from valve stem packing, as it tends to wear with each stroke, eventually allowing process media to escape. This issue can be addressed by selecting the right valve type, as explained by the author:
From a sealing perspective, a quarter turn valve has distinct design advantages. Since the valve stem makes a comparatively shorter 90-degree rotation, rather than reciprocating up and down, it tends to wear more slowly. Additionally, any scoring of the packing caused by particulate trapped against the stem occurs horizontally. In rising stem designs, this scoring occurs vertically through the packing rings, which can create a direct leak path to atmosphere, resulting in substantially more leakage.
Figure 3: Quarter turn valves tend to emit fewer emissions over time than rising stem valves. However, certain design
features allow some valve designs to leak far less, while requiring significantly reduced maintenance over their lifetime
The Offshore and Onshore Reliability Data Project has estimated that 90% of valve fugitive emissions can be eliminated by upgrading rising stem valves to a quarter turn design, with the packing design of these valves a critical issue.
Recent advances in materials and engineering designs have yielded dramatic improvements in emission reduction These packing designs utilize spring-loaded washers to continuously compress the packing seals, paired with a combination of different packing ring materials to achieve extremely low leak rates of less than 100 ppm. New packing designs also incorporate special coatings and special valve stem materials to provide long life and smooth movement.
Figure 4: Modern packing designs (Emerson’s KTMTM Series EB1 OM-2 Split Body Floating Ball Valve shown) use special springs
or compressed Belleville washers to maintain constant pressure on the packing rings. This minimizes fugitive emissions, even as the rings wear.
Actuators and positioners can also be significant source of fugitive emissions when natural gas is used as a motive force. In these situations, advanced low bleed or zero bleed actuators can be employed to minimize or eliminate leakage.
Plan of attack
To control costs and reduce risk, plant personnel should upgrade those valves providing the best payback. These valves are usually found in applications with frequent cycling and thermal variations. Valves in lethal or corrosive service should obviously be upgraded, along with those in critical service. Valves installed in remote or hazardous locations should be prioritized for upgrade to reduce the burden on maintenance teams tasked with their monitor and repair.
When facing fugitive emission challenges, end users should move beyond the typical response of increased monitoring and repair, and instead look carefully at the valve design. Often there are alternate designs that can resolve the emission problems and reduce operational costs.
Visit the Isolation and Shutoff Valves section on Emerson.com for more on the technologies and solutions to help you reduce emissions.
All figures courtesy of Emerson.