Week 10-Safety Design Philosophy

OSE571 Ocean Plant Design

Safety Design Philosophy

Korea Advanced Institute ofScience and Technology

Daejun CHANG ([email protected])

Division of Ocean System Engineering

Design Procedure and Key deliverablesDesign Procedure and Key deliverables

Design Basis (Philosophy)

Concept Consolidation

Process Flow DiagramProcess Simulation

Equipment SpecificationEquipment Design

System Description

Production Availability ?

-1- Ocean Systems EngineeringOcean Systems Engineering

Process Operation and Control Philosophy

P&ID

Layout

HAZOPRisk AssessmentSafety Studies

Caution: Not universally applicable

Hazards and Safety SystemsHazards and Safety Systems

Accident Controlling Protection(F&G Detection, ESD, Depressurization, Alarm)

Accident Mitigating Protection(Active/Passive Fire Protection, Fire/Blast Walls)

Emergency Response(Escape Route, TR, Evacuation Means, Rescue Equipment, Emergency Power)

Potential Accident:

Accident:Fire/Explosion


Inherent Safety Design(Layout, Inventory, Leak, Ignition)

Basic Process Control(P, T, F, Surge, Back Pressure)

Preventive Protection(Structural & Machinery Integrity, Relief, PSV)

Potential Accident:Gas Leak

Layered Structure of Safety Systems against Fire and Explosion

Principles of Safety DesignPrinciples of Safety Design

Segmentation

Depressurization (Blowdown)

Pressure Protection

Preventive Measures


Preventive Measures

Mitigating Measures

Shutdown Logic

Segmentation Segmentation

What if there is a leak? All the inventory (gas) will get out of the process! Segmentation

- Divide the whole plant into several segments(Divide and defeat!)


(Divide and defeat!)- Boundary of the segments: block valves- The valves are closed if there is a leak. The inventory within the segment will get out.

Depressurization (Depressurization (BlowdownBlowdown))

Do we have to wait until all the inventory gets out. Venting of the inventory into a safe area. How? Depressurization (Blowdown)

- Install a vent line from each segment.- The vent line is normally blocked by blowdown valves.


- The vent line is normally blocked by blowdown valves.- In case of fire, the valve is open to guide the inventory to the

flare stack. Reduce the leaked inventory by the amount vented to flare

Pressure ProtectionPressure Protection

What if the internal pressure of a segment increases? Cause

- Too much incoming feed flow- Outlets blocked- Fire thermal explosion


- Fire thermal explosion- Leak due to internal rupture (tube rupture of exchanger)

Double-layer pressure protection- Layer 1: PSV, rupture disc- Layer 2: depressurization

Pressure ProtectionPressure Protection

Flare Open

BDV

PSV


Closed

Closed Drain

Closed

Open

ESDV ESDV

PSDVPSV: Pressure Safety ValveBDV: Blowdown ValveESDV: Emergency Shutdown ValvePSDV: Pressure Shutdown Valve

Preventive MeasuresPreventive Measures

Prevent an accident from happening (or to decrease the frequency) Detection: Fire and Gas (F&G System) Ventilation


Mitigating MeasuresMitigating Measures

Once an accident happens, mitigate the consequence. Water spray (deluge) Fire and blast walls


Overview of Safety SystemsOverview of Safety Systems


An Real Example: ESDV & PSDVAn Real Example: ESDV & PSDV

-11- Ocean Systems Engineering

An Real Example: PSV and BDVAn Real Example: PSV and BDV


Shutdown LogicShutdown Logic

Shut down the system partially or entirely. To what degree depending on the seriousness

Low seriousness partial shutdown High seriousness total shutdown Extreme seriousness Just escape and abandon the facility


Extreme seriousness Just escape and abandon the facility

Level 1 APS Abandon platform

Level 2 ESD I Emergency shutdown (total)

Level 3 ESD II Emergency shutdown (partial)

Shutdown LogicShutdown Logic


Level 3 ESD II Emergency shutdown (partial)

Level 4 PSD Process shutdown (total)

Level 5 PSD Process shutdown (partial)

Shut DHSVAuto Depressurisation

Timer-based disconnectionFire&gas detectionPA, ESD/PSD, radioEmergency generator/UPS

DisconnectionMain generatorNon-critical non-EXequipment

APS

ESD I

Manual

Manual

Input

Gas detection Non hazardous area

Fire&gas detectionHazardous area

Standardizing


Start Emergency generator

equipment

Shut fuel gas supply

Activation of DHSV (fire in riser/ well area)Riser ESDVDepressurisation

ESD II

PSD

Manual

Low pressurehydraulic system

Low pressure Instrument air

High lev flare k.o drum

Tube rupture in cooler

Hazardous area

Cause

Effect

Cause and Effect ChartCause and Effect Chart


X

Design and Maximum Operating PressureDesign and Maximum Operating Pressure

Design Pressure The maximum allowable pressure for equipment and piping

under pressure Used for equipment design (with some margin)

Maximum Operating Pressure (or Maximum Allowable Working Pressure)


(or Maximum Allowable Working Pressure) The maximum of all the pressure fluctuations over the all the

conceivable operation mode. start-up/shutdown, process flexibility, control requirements and

process upsets Shut-off (discharge blocked) cases for rotating machineries For unknown cases, the rules of thumbs are

- Pump: 1.25 times the discharge pressure- Compressor: 1.3 times the discharge pressure

Design PressureDesign Pressure

PSV (pressure safety valve) to vent out the internal gas Segment with a PSV

Maximum operating pressure (MOP), barg

Design pressure, barg

0 23 MOP + 3.5 bar


0 23 MOP + 3.5 bar

35 70 1.1 MOP

70 200 Max (1.085 MOP, MOP + 7 bar)

200 + 1.05 MOP

Design TemperatureDesign Temperature

Maximum design temperature When the maximum operating temperature is clear, take it for the

design temperature Otherwise, design temperature = MOT + 30 oC

Minimum design temperature Material selection may be affected.


Material selection may be affected. The minimum operating temperature 5 oC Operating conditions considered

- Air temperature (winter condition)- Normal- start-up, shutdown, process upsets- Cooldown due to depressuriization

Week 10-Safety Design Philosophy

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