Figure 5.24.7 shows a pressure-relief valve and rupture device to control fugitive emissions. This device does not allow any emissions until the pressure is large enough to rupture the disk. The pressure-relief valve opens at a set pressure and then reseats when the pressure returns to below the set value.
Reseating the pressure-relief device after a discharge is often a source of a fugitive emission. The source can vary from a single improper reseating to a continuous failure because of a degraded seating element. Like other valves, pressure-relief valves with emissions greater than 500 ppmv above background are considered leakers.
An alternative to rupture disks and other techniques that achieve less than 500 ppmv above background is for plants to vent pressure-relief devices to a closed-vent system connected to a control device.
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