TECH TALK
provide a means to continuously monitor packing performance and alarm if problems are detected . Alternately , plant personnel can replace a valve style with a rotary actuator , which tends to leak less over time . In certain lethal-service applications , a zero-emission bellows seal design may be an excellent choice .
Another common source of fugitive emissions comes from relief valve seat leaks . These leaks can be very difficult to detect since each valve lacks any embedded sensors and often vents into a flare header , where a leak is not easily noticed . The preferred solution for this situation employs a WirelessHART ® acoustic sound and temperature monitor , which is simply strapped to the discharge of existing relief valves Figure 4 .
Figure 4 : A WirelessHART acoustic transmitter ( blue device in the upper left of the photo ), can be mounted on the discharge of a pressure safety valve , allowing it to detect the vibrations caused by any release .
and avoid leaks , while allowing the valve actuator to move freely . This can be quite challenging , particularly with a valve design where the valve stem moves up and down and cycles continuously . The combination of process pressure and temperature swings , along with thousands of valve cycles , presents a difficult design problem .
Recent advances in materials and engineering designs have yielded dramatic improvements in valve packing performance , shown in Figure 2 . The latest environmental 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 parts per million ( ppm ). Despite the low leak rate , they are developed to handle a wide range of process temperatures and pressures . The new packing designs also incorporate valve stems with special coatings and materials to provide long life , along with smooth and unimpeded movement .
Older valve styles do not usually incorporate this type of packing , so the first step for many plants is to evaluate the packing styles on existing valves and quantify their performance . If the existing valve components are well known and leakage
data is available , this evaluation is easily implemented . If the valve design data is not readily available , then the plant can perform a walk down of their facility , targeting valves that handle volatile organic products and other targeted and / or restricted process media . These walkdowns can be performed by plant personnel , or they can be outsourced to a third-party service provider if plant resources are constrained .
If a valve has a history of leaks , a simple and inexpensive packing upgrade to a more advanced design will typically yield dramatic reductions in emissions . Improved positioner diagnostics also
When a leak event is detected , the plant can immediately respond to eliminate the leak and avoid lost product . These solutions have yielded dramatic reductions in emissions , product loss , and reportable releases .
Solutions for Vented Emission Reduction
Vented emissions often result when a pressure relief device opens to protect the process from an overpressure event . While this does protect the equipment , the resulting environmental release must be documented and reported . The obvious solution to reducing vented emissions is to avoid the overpressure event in the first place , but these issues cannot be addressed until the plant has an easy way to detect and quantify pressure relief events .
www . valve-world-americas . net • September 2022 | Valve World Americas 19