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SAFETY IN NAPHTHA CRACKER

By

Kushal chaudhuri

ETHYLENE CRACKERS IN INDIA

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Plant/location Capacity in 000’TPA.

HAZIRA/RIL 750

BARODA/RIL(ex-IPCL) 170

HALDIA/HPL 550

PANIPAT/IOCL 800

Naphtha Crackers

Gas Crackers Plant/location Capacity in 000’TPA.

NAGOTHANE/RIL(ex-IPCL) 400

GANDHAR/RIL(ex-IPCL) 400

PATA/GAIL 400

Upcoming Dual Crackers Plant/location Capacity in 000’TPA.

OPAL(ONGC Petro Additions Ltd.) 1100

BCPL(Brahmaputra Valleys Cracker

Petrochemical Ltd.) 220

IOCL NAPHTHA CRACKER & ASSOCIATED UNITS

Plant Capacity,

TMTPA Mode

Technology /

Licensor

NCU & AU 800 Steam Cracking CBI Lummus,

USA

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TMTPA Licensor

C4HU 142 CBI Lummus,

PGHU 541 CBI Lummus

BEU 168 GTC,USA

TYPICAL FLOW DIAGRAM OF NAPHTHA

CRACKER UNIT

Recycle

furnace

GENERIC PROCESS SAFETY DESIGN ISSUES

IN NAPHTHA CRACKER UNIT

Emergency Remote Isolation of Flammable Inventories

Emergency Remote Equipment Depressurization

267 class-6 remote isolation valve ( XV ) provided through out NCU & AU

Heat Exchanger Overpressure Protection external fire, thermal expansion, blocked outlet, and tube rupture

provision of safety interlock Systems with suitable redundancy

To prevent major process operating upsets from threatening the physical integrity of process equipment usually by mitigating the extent of pressure and/or temperature deviations.

To protect against temperature excursions outside of the mechanical design envelope of process equipment

SIL-3 interlock system provided for flare load mitigation

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GENERIC PROCESS SAFETY DESIGN ISSUES

IN NAPHTHA CRACKER UNIT

Two independent effluent relief systems have been provided for handling

effluent relief vapors:

cold dry flare system for handling liquid /vapor below 4C

wet flare system for handling liquid /vapor above 4C

Separate liquid vaporiser & superheater provided in the dry flare system

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CASE STUDY OF FLARE HEADER FAILURE

A low temperature alarm sounded as

the overhead line temperature fell to 0

F, and the thermocouple went bad. at

a value of -13 F

With the cold flare drum overhead line

running below its minimum design

temperature of -10 F, the pipe

ruptured resulting in loss of

hydrocarbon containment

The hydrocarbon released found an

ignition source, resulting in an

explosion and fire

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PROCESS HAZARDS AND SAFETY

SYSTEMS 8

Firebox explosions during lighting of burners

Light up procedures must be followed

Over temperature in furnace convection & radiation section

Excessive firing rate – Partial trip provided at loss of feed

Low or no flow rate in selected coils –

Minimum lock provided in dilution steam supply

direct injection of medium pressure steam provided

Over temperature protection in TLE / steam superheat coil

Minimum lock provided at BFW feed C/V

Furnace trip provided at low flow of BFW / Low level at steam drum

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PROCESS HAZARDS AND SAFETY SYSTEMS IN

PYROLYSIS FURNACE

Switch to backup fuel can cause a rapid

increase in firing causing over heating of

the coil

Wobbe Meter provided in fuel gas

system to cater the situation

Fire from coil outlet due to thermowell

erosion

Rotation of thermowell after 3

decoking cycle is recommended

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PROCESS HAZARDS AND SAFETY SYSTEMS IN

PYROLYSIS FURNACE

Position where thermowell broke

TLV/DV system provided along with

mechanical link

To prevent hydrocarbon backup to

firebox by maintaining sufficient

back pressure

allows the heater to be isolated in

the unlikely event of a heater

radiant coil rupture

To protect the overpressurization

of radian coils & TLE tubes

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PROCESS HAZARDS AND SAFETY SYSTEMS IN

PYROLYSIS FURNACE

Hazard for runway reaction due

to excess hydrogenation &

polymerization reaction

Emergency shut down valve

provided for immediate

hydrogen cutoff & releasing

the inventory to flare

Provision for immediate

nitrogen purge in all the

reactors to cool down the

reactors

Auto cutting provision

provided in liquid recycle

standby pumps in case of

liquid /Mixed phase

hydrogenation rectors

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PROCESS HAZARDS AND SAFETY SYSTEMS IN

HYDROGENATION REACTORS

Lowest temperature handled in cold box is -165 C

Piping and vessels in Coldbox are made of aluminum

Internally insulated with loose“Perlite” (very high insulating value)

Over chilling of the cold box outlet piping due to loss of heating media

interlocks are provided to isolate the subject piping with two out of three voting logic for protecting possible embrittlement

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PROCESS HAZARDS AND SAFETY SYSTEMS IN

CHILLING TRAIN

Cold box under slight positive nitrogen

pressure

Keeps air and moisture out of cold

box

Nitrogen minimizes hydrocarbon

accumulation if a small leak

Nitrogen vent monitored for

hydrocarbon presence

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PROCESS HAZARDS AND SAFETY SYSTEMS IN

CHILLING TRAIN

TYPICAL SAFETY ISSUES IN COLD BOX

Potential Acetylene Freezing

Potential Nitrogen Oxides Freezing

Potential Benzene Freezing

Potential Mercury Embrittlement

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PROCESS HAZARDS AND SAFETY SYSTEMS IN

COLD SERVICE LIQUID VALVE

One side of the seat is drilled to relieve

pressure as liquid vaporizes.

Typically and arrow on body showing

direction of relief.

CAUTION

Must be installed correctly

Arrow is NOT direction of flow

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Drill Gate

Arrow is in the

direction of vent

Arrow is in

the direction

of vent

PROCESS HAZARDS AND SAFETY SYSTEMS IN

GASOLINE FRACTIONATOR

Low pressure rating

Not designed for TLE outlet temperatures

Furnaces trip provided at high if Quench fittings outlet temperature

Pyrophoric material deposits on Trays & Packing's

Special precautions required for man entry during shut down

Pool Fire potential if a leak

Caution: No PSV for overpressure protection

When items are off line and isolated administrative

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SAFETY CONCERN IN DEPROPANISER &

PROPYLENE SPLITTER

Potential concentration of MAPD above 70% is

dangerous forms explosive mixture

Avoid excessively good fractionation In

DePropaniser

Likely if design reflux flow is maintained at

reduced plant capacity.

Reflux should always be reduced in

proportion to the tower feeds.

C4s in overhead is evidence that MAPD is

not conc

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GENERAL SAFETY ISSUES IN EHTYLENE

PLANT

Injuries

Hot Water

Steam

Catastrophic Failures

Furnace light off

Over chilling Equipment due to

Adding liquid before pressuring

Depressuring before removing liquid

Inadequate vent capacity

Non engineered changes

Not following good operating practices/procedures

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THANK YOU

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