Emergency Shut Down System
The process unit is classified into two levels of Shutdown dependent upon the reliability and risk analysis studies. The reason for this choice that the plate shall segregation of plant, which is sensible to maintain for purpose of ESD levels. This evaluation will be incorporate into the reliability for two analysis document.
The definitions for two levels of are presents are:
Level 1: A shut down which trips outputs for more than one operation group associated with single ESD panel.
Level 2: localized shutdown relevant one operating group.
The shutdown system shall employ a triplicate isolated, parallel control system and extensive diagnoses integrated into one system (TMR). A two out of three voting shall be provided for high integrity, error tree, uninterrupted process operation with no signal point of failure online programming feature shall be implemented limit switches shall not be used as implemented limit switches shall not be used as interlocks for ESD input but to report DCS status only, all ESD input signals that require line monitoring are digital field inputs and manual shutdown buttons but the normally closed contact signal is not required.
Sequence of Events Recorder (SER) shall be provided as part of the ESD system.
The following design principles of the ESD system incorporate the following:’
• ESD resets
• Maintenance bypass key switches
• Operational bypass key switches
• Output override key switches
Wiring and devices such as trip initiators, switch related ESD functions shall be required to be hard wired power supply system:
- ESD valves shall basically be of ball type, which has the best flow co-efficient and sealing for minimum leakage during maximum differential pressure in the closed position.
- ESD valves shall close in fail position on loss of external signal and external power. The actual closure time for the valves shall be 30 sec. Maximum.
- Globe type control valves shall be generally be specified and sized nominal flow at no more than 70% of capacity.
- Butterfly valves shall be sized for a maximum flow @60% angular opening or for a “fish fail” characterized valve @900.
- Displacement type level instrument to be selected for normal applications up to a range of 1200 mm unless the liquid is viscous, corrosive or where flashing may occur.
- Preferred ranges for displacement type level instrument 350, 800, 1200 mm.
- D.P. instrument 1500, 1800, 2100,2400,2700,3000 mm.
- Orifices shall be sized with normal flow rate at approx seven and minimum flow rate not less than three on a 0~10 square root chart.