What is process shutdown (PSD) and emergency shutdown ( ESD)?

DCS
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Process shut down could be attributed to any planned shut down of the unit. It is an anticipated one and planned to attend the process issues during the favorable situation such as unit feed limited due to downstream unit issues, feed quality affects the unit throughput etc. Otherwise shut down time to be planned according to the severity of the issue.

Whereas emergency shutdown, as the terminology explains it is a forced situation on the process unit. One has to act according to the situation. Using the available resources, plan to go for safe shutdown of the unit as per the SOP of the unit.

Application of mind relating to the situation is the most important aspect as emergencies are always different and may be the type of emergency occurs also new. A very good knowledge about the process, plant and facilities available in the unit are the must to handle ESD safely.

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As the name suggest, the process shutdown originates from the unwanted process conditions and emergency shutdown originates from emergency related issues.

Process shutdown will be initiated if the control system capture any process abnormalities as defined in the control system design. This system will try to stop propagating the impacts of process abnormalities downstream.

Emergency shutdown will be mostly initiated originating from abnormalities leading to serious safety concerns such as Runaway reactions leading to excessive temperature.

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