© 2010 Chevron

Pyrophoric Ignition Hazards in

Typical Refinery Operations

CAER Safety Summit Meeting December 2010. Doug Jeffries Chief Fire Protection Engineer

© 2010 Chevron

Agenda

Definitions and chemistry of pyrophorics

Conditions required to form pyrophoric iron sulfide

Where pyrophorics have been known to form in refinery equipment

Possible methods to mitigate and prevent pyrophoric related incidents

A couple example pyrophoric related incidents

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Definitions

A pyrophoric material is a liquid or solid that, even in small quantities and

without an external ignition source, can ignite within 5 minutes after

coming in contact with air1

In oil and petrochemical industry, this only partially defines the concern.

We also need to be concerned with the fact the pyrophoric material can

create heat which can ignite residual hydrocarbons associated with the

equipment containing the pyrophoric material.

Example pyrophoric materials include alkali metals and many

organometallic compounds such as alkylmagnesiums, alkylzincs, and

of course pyrophoric iron sulfide. Nickle carbonyl in some catalysts

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Chemistry of Pyrophorics

Pyrophoric compound + oxygen (typically air) Oxide of the

compound + heat

Sometimes with several intermediate reaction steps

Can be very reactive or very slow to react

Can vary with conditions, humidity, temperature, particle size, degree of

disbursement in air, etc.

Bottom line: pyrophorics can be a very elusive and tricky animal to

recognize and capture until it bites you

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Conditions required to form pyrophoric iron sulfide

H2S concentration > 1% (can form at lower concentrations but

typically not in concentrations that are a concern)

Iron scale or rust (FeS)

Less than a 1:1 ratio of oxygen to H2S (some oxygen is required to

form the rust but if insufficient oxygen is present the reaction with H2S

cannot go to completion)

Fe2O3 + 3H2S = 2FeS + 3H2O + S

4FeS + 3O2 = 2Fe2O3 + 4S + heat

4FeS + 7O2 = 2Fe2O3 + 4SO2 + heat

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Where pyrophorics have been known to form in refinery equipment

Crude oil tanks

Asphalt tanks

Sour water tanks

Vessels in sour service such as coke drums, distillation columns, inlet

separators, pig receiver / launchers

Reactors

API Separators

Marine tankers and barges

Portable tanks and tote bins

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Pyrophorics and the Fire Triangle

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FUEL

IGNITION OXYGEN

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Example 1

Marine tanker cargo hold.

Cargo was light crude with low, sufficient vapors to reduce oxygen

levels to near zero

High humidity accelerated rust and formation of pyrophoric iron

sulfide

As crude cargo was off loaded, the normal inerting with engine

exhaust was halted

Air was allowed to enter causing the pyrophoric iron sulfide to react,

heat up, and ignite

Fortunately, the vapor space was relatively small so the damages

were slight and there were no injuries

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Example 2

Filter cake deposits ignite.

Powdered filter cake is added to a mix tank to assist filtration after

mixing

Powder accumulates in the vapor space of the tank, particularly near

the baffles

Reaction begins to occur but is disrupted when product and more

filter cake dust covers the deposits

Vibration from turning on the tank mixers or disturbance while

cleaning the tank exposes the unreacted layers in the deposits

The reaction generates heat igniting vapors in the tank

The tank is severely damaged but thankfully there were no injuries

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Example 3

Reactor catalyst ignites in drums.

Reactor is normally flooded with water prior to dumping catalyst

In a trial to recover more precious metal and reuse the catalyst, it is

decided to dry dump

Process stream contains hydrogen sulfide and nickle carbonyl and

possibly other pyrophoric compounds are formed in the catalyst

Reactor is purged with nitrogen while dumping catalyst and

removing internals

Upon exposure to air catalyst heats up, igniting residual hydrocarbon

in the catalyst

Fortunately, drums are moved away from the reactor so no damage

and no injuries

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Example 4

Sour water tank roof blown off.

Sour water is high in H2S and is a wet environment

Odor complaints cause operators to alter the tank vent and

pressure / vacuum valve

Normal ventilation of the tank vapor space is changed resulting in

formation of pyrophoric iron sulfide

When the tank vent and P/V valve are returned to normal service,

oxygen is allowed to enter

Pyrophoric iron sulfide reaction occurs, sufficient heat is generated

to ignite the vapor space blowing the roof off the tank

A similar incident occurred when the tank was opened for cleaning

and inspection

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Example 5

API Separator explosion.

An API Separator in an upstream producing facility is in operation in

a sour producing area

The separator is gas blanketed to prevent oxygen from getting inside

Pyrophoric iron sulfide forms inside the separator

The separator is taken out of service for maintenance

No washing or chemical neutralization is performed prior to opening

the separator

Air enters, a pyrophoric reaction takes place, igniting residual

hydrocarbon inside the separator

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Example 6

Hot oil tank fire.

A refinery has a hot oil tank and hot oil system for heating process streams and storage tanks

The synthetic hot oil compound is replaced with medium cycle oil from the catalytic cracker (which happens to contain H2S and a high level of particulates)

The particulates accumulate in the horizontal hot oil tank, mandating a clean out.

The oil is drained and the decision is made to put a man inside to soften the deposits with diesel

The manway and vent are opened, the man enters

Air sweeping across the top of the tank produces a pyrophoric reaction which heats and ignites hydrocarbon

The man inside the tank receive fatal burns

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Mitigation methods

Most effective method is chemical neutralization before opening the

equipment; potassium permanganate solution (typically around a 1%

solution, circulate and check for color)

Keeping the deposits and scale wet until it can be safely removed to

a remote area and allowed to dry

Maintain a constant air ventilation to ensure there is plenty of oxygen

to allow the reaction to go to completion, preventing the formation of

the pyrophoric intermediates

Replace components that contain sulfur compounds

Use nitrogen or other inert gases to keep oxygen out (obviously

difficult and adds hazards of its own)

Quickly move scale and potential pyrophoric deposits to a remote

area and monitor in case ignition does occur

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