Process plant shutdown systems

SIL applies to both hardware and software requirements such as cards, processors redundancy and voting functions.

Inputs include for example manual activation and signals from the fire and gas system (FGS).

Equipment such as pressure vessels exposed to fire could undergo catastrophic failure leading to an uncontrolled loss of containment.

A process plant is typically divided into isolatable sections by emergency shutdown valves (ESDVs).

Each section may be designated as belonging to a fire zone that is depressurized by a dedicated blowdown valve (BDV) or set of BDVs.

Blowdown may be strategically delayed by fire zone to shave peak flow and allow the flare to deal with the incoming gas.

A restriction orifice (RO) downstream of the BDV is sized to achieve the desired blowdown rate.