Global fugitive emissions regulations are increasingly stringent, including monitoring of carbon emissions and pressure relief devices (PRDs). Historically, PRDs have been difficult to monitor because they aren’t typically connected to automation or monitoring systems.
In their article, Comply with environmental regulations and detect PRD malfunctions in the AFPM Show Daily, Marcio Donnangelo and Marcos Peluso of Emerson describe the issues with PRDs:
PRDs include pressure relief valves, pressure safety valves or rupture disks. They activate when pressure approaches the maximum allowable working pressure of the vessel or process component. Monitoring methods have included manual inspection for telltale signs, or the indication of a leak or release by a larger than-normal flare. In theory, PRD activation should occur only in exceptional circumstances. However, in practice, activation occurs more often due to small leaks when the PRD does not reseat fully.
Manual monitoring methods do not work well due to difficulty of access and other factors, so the answer is to use wireless instruments, as they explain:
A reliable, effective and economic way to monitor PRDs is WirelessHART acoustic transmitters. Process fluid flowing through valves and orifices generates acoustic waves in a wide and complex range of frequencies and magnitudes. Acoustic transmitters detect ultrasound acoustic waves in the pipe wall, as well as its temperature. These small, wireless, lightweight and non-intrusive devices can be easily clamped onto an exhaust pipe.
Using acoustic transmitters, PRD operating conditions can be determined. A noise level increase indicates the PRD has been activated. A high noise level indicates leakage due to the valve not closing completely. A continuous noise level above baseline indicates the valve may be simmering or chattering.
A PRD event is sometimes the only noticeable indicator of process upsets, so the sooner it can be detected the better, allowing operators to respond. But, as Marcio and Marcos note, it’s not only helpful to the plant, it’s becoming a requirement:
PRD monitoring is necessary for regulatory compliance. It also mitigates the risk of expensive fines (and potential process unit or plant shutdowns) and provides awareness when a PRD is leaking, prompting immediate action. WirelessHART acoustic transmitters are an effective, reliable and economic way to be compliant and mitigate losses to the flare.