Control valve fugitive emissions
February 2013
Valves, Actuators & Pump Control
Process plant managers have a host of good reasons to minimise fugitive emissions from their facilities and reduce the amount of process fluid released into the atmosphere and surrounding environment. Those reasons include keeping employees and neighbours safe, lessening the facility’s environmental impact, complying with increasingly stringent air-quality regulations, optimising the plant’s energy consumption and maximising plant operating efficiency.
Industrial valves are a leading source of leakage from typical process plants. In fact, studies of refineries have shown that valves and relief valves account for about 75% of fugitive emissions. Because of this reality, monitoring, controlling and reducing valve leakage can make a significant impact on overall plant fugitive emissions. Of particular concern are control valves, which pose a greater challenge than other industrial valves because of their typical operating mode and potential leak paths. There are, however, techniques, technologies and strategies that plant owners and managers can implement to manage fugitive emissions from the control valves in their facilities. This article highlights some of these options for typical control valve features, characteristics and options.
Implementing methods of adjusting the packing tightness to compensate for changes in operating conditions can minimise leakage, though some level of fugitive emissions will still exist. Zero leakage designs, such as a bellows seal, should be used when a process involves extremely harmful or potentially lethal process fluids. But implementing these solutions throughout an entire plant would be extremely cost-prohibitive. To balance safety and economic realities, plant personnel should employ the best low-emissions sealing solution possible and support it with an effective emissions monitoring system.
The monitoring process can be automated, however, using a concept similar to the diagnostics capabilities offered by digital valve positioners. A series of sensors can be mounted on the valve assembly, which monitors fugitive emissions from the various leak paths and communicates the data directly to the digital positioner. The fugitive emissions limits or parameters for the specific plant or application can be compared by the positioner, which can then communicate any status reports or warnings back to the control system. As with any diagnostics tool, the accuracy of the sensors is critical, as is the ability of the positioner to convert the data collected into clear and easily understood actions for the plant operator.
Readers wanting to learn more about the subject can visit http://instrumentation.co.za/+C17435
For more information contact Piet Botha, GE Energy, +27 (0)11 452 1550, [email protected], www.dresser.co.za
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