otfvp00-1111cen_flare & vent

Handbook

presents

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Flaring, Venting, and Purging

OTFVP00-1111CEN

Flaring, Venting, and Purging OTFVP00-1111CEN

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CONTENTS

INTrOduCTION..............................................................................................3GENEral CONSIdEraTIONS...........................................................................4

Waste.Gas.Handling.Considerations............................................................4Waste.Gas.Removal....................................................................................4Challenge.Questions..................................................................................7

VENTING........................................................................................................8Conditions.That.Require.Venting..................................................................8

Filling.a.Tank.........................................................................................8Draining.a.Tank.....................................................................................9Steam.Cleaning.a.Tank........................................................................10

Types.of.Vents..........................................................................................10Safe.Work.Practices..................................................................................13Challenge.Questions................................................................................14

PurGING.....................................................................................................15Materials.Used.for.Purging........................................................................15Purging.Methods......................................................................................16

Continuous.Purge.Method...................................................................16Fixed.Volume.Purge.Method................................................................16

Inerting....................................................................................................17Safety......................................................................................................18Operator.Responsibilities.........................................................................19Challenge.Questions................................................................................21

FlarE SySTEm.............................................................................................22Safety.Considerations...............................................................................22Components.and.Operation......................................................................22Challenge.Questions................................................................................26

FlarE OPEraTIONS, ParT 1.........................................................................27Startup.Preparations................................................................................27Startup....................................................................................................28Control.Room.Operator.Responsibilities....................................................30Challenge.Questions................................................................................31

FlarE OPEraTIONS, ParT 2.........................................................................32Outside.Operator.Responsibilities.............................................................32Abnormal.Conditions................................................................................33

Loss.of.Flare.Stack.Gas.Purge...............................................................33Loss.of.Pilot.Flames.............................................................................34Abnormal.Steam.Flow..........................................................................34Abnormal.Water.Seal.Level..................................................................34

Flare.Shutdown........................................................................................35Challenge.Questions................................................................................36

aNSWErS TO CHallENGE QuESTIONS..........................................................37GlOSSary...................................................................................................40

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INTrOduCTION

Industrial.process.operations.produce.many.different.types.of.useful.products.. In.many.cases,.however,.these.operations.also.produce.waste.materials.that.must.either.be.recovered.for.reuse.or.safely.discarded..Although.waste.materials.may.be.solids,.liquids,.or.gases,.this.course.focuses.on.waste.gases..Specific.attention.is.directed.to.how.waste.gases.are.removed.from.process.systems.and.safely.disposed.of.


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GENEral CONSIdEraTIONS

This.section.describes.some.general.considerations.for.handling.waste.gases.and.uses.an.example.to.show.how.a.relief.and.flaring.system.can.remove.waste.gas.

Objectives•. Describe.some.considerations.for.handling.waste.gases.•. Explain.how.a.relief.system.can.remove.waste.gas.

Waste Gas Handling ConsiderationsWaste.gases.are.formed.during.certain.types.of.process.operations..For.example,.

they. are. often. formed. when. materials. are. heated. during. processing.. In. some. pro-cesses,.reactions.occur.that.give.off.heat.and.gases.as.by-products..The.evaporation.of.liquids.also.produces.gases.or.vapors.

The.main.consideration.that.makes.it.important.to.handle.waste.gases.properly.is.safety..When.waste.gases.are.formed.in.vessels.and.equipment,.the.gases.increase.the.pressure.inside.the.vessels.and.equipment..If.the.gases.are.not.removed,.the.pres-sure.can.exceed.the.pressure.rating.for.the.vessel.or.piece.of.equipment..The.result.of.the.overpressurization.can.be.personal.injuries,.equipment.damage,.and,.in.extreme.cases,.explosions.and.fires.

Another.consideration.is.health.protection..Although.waste.gases.must.be.removed.from.equipment,.gases.that.are.potentially.hazardous.cannot.be.simply.released.to.the.atmosphere..The.release.of.potential.pollutants.can.cause.health.problems.for.plant.workers.and.for.people.in.surrounding.communities..In.many.cases,.it.is.a.violation.of.clean.air.regulations.to.release.certain.types.and.amounts.of.gases.or.vapors.to.the.at-mosphere..Violations.of.federal,.state,.or.local.clean.air.regulations.can.result.in.fines,.plant.closings,.and.imprisonment.for.some.personnel.

A.third.consideration.is.cost..Since.waste.gases.cost.companies.money,.companies.have.procedures.and.work.practices.that.must.be.followed.to.minimize.the.creation.of.waste.gases..When.waste.gases.are.generated,.as.much.as.possible.is.recovered.and.ultimately.reused.in.processes.to.reduce.costs.

Waste Gas removalWaste.gases.are.generally.removed.from.vessels.and.equipment.by.releasing.them.

through.openings,.or.vents..This.process.is.called.venting..

In.some.cases,.hazardous.gases.and.other.materials.are.removed.from.vessels.and.equipment.through.vents.by.purging..Purging.is.the.removal.of.hazardous.materials.from.piping.and.equipment.with.a.gas.or.vapor.to.prevent.the.formation.of.explosive.mixtures.

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The. basic. purpose. of. venting. is. to. release. waste. gases. and. purge. gases,. which.collectively.can.be.called. relief.gases..The.vents. through.which. these.gases.are. re-leased.are.typically.pipes.located.on.top.of.equipment..Some.vents.discharge.to.the.atmosphere,.but.this.is.done.only.when.the.gas.is.relatively.harmless.and.does.not.contribute.to.pollution..When.hazardous.gases.are.involved,.vents.usually.discharge.into.piping..

Vents.and.the.piping.they.discharge.into.are.part.of.what.is.called.a.relief.system..For.the.purposes.of.this.training.unit,.a.relief.system.is.considered.to.be.a.collection.of.vessels,.piping,.and.equipment.designed.to.handle,.recover,.or.dispose.of.gases.released.from.process.equipment..For.other.applications,.relief.systems.may.also.be.designed.to.handle.liquids.

Figure.1.is.an.illustration.of.a.relief.system..The.example.system.includes.the.vents.and.piping.from.a.unit’s.vessels.and.equipment,.a.relief.header,.a.knockout.drum.with.a.pump,.a.vapor.recovery.unit,.and.a.flare.

Figure 1. relief System

Gas.that.is.released.through.the.vents.flows.through.the.piping.to.the.relief.header..The.relief.header.is.the.main.pipeline.to.the.rest.of.the.system..Its.primary.purpose.is.to.collect.gases.and.vapors.from.the.vents.of.vessels.and.equipment..A.relief.system.may.include.more.than.one.header.

From.the.header,.the.waste.gas.flows.to.the.knockout.drum,.where.any.liquid.en-trained.in.the.gas.is.removed..The.knockout.drum.represented.in.Figure.2.contains.a.gas.inlet,.baffles,.a.liquid.outlet.line,.a.pump,.and.a.gas.outlet.


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Figure 2. Knockout drum

Gas.that.enters.the.knockout.drum.strikes.the.baffles.and.changes.direction..Any.liq-uid.contained.in.the.gas.is.knocked.out.by.the.baffles..The.pump.is.used.to.maintain.a.certain.level.in.the.drum.by.removing.liquid.when.necessary..In.some.cases,.the.liquid.is.oily.water..When.the.liquid.is.removed,.it.is.sent.elsewhere.so.that.the.oil.and.water.can.be.separated.for.reuse.

The.waste.gas.flows.out.of.the.knockout.drum.and.on.to.the.vapor.recovery.unit..The.purpose.of.the.vapor.recovery.unit.is.to.recover.relief.gases.that.would.otherwise.be.wasted..The.vapor.recovery.unit.includes.another.knockout.drum.that.removes.any.liq-uid.remaining.in.the.gas..The.gas.flows.next.to.compressors,.where.it.is.compressed,.and.it.is.then.sent.on.for.storage.or.reuse.

Any.portion.of.the.waste.gas.that.exceeds.the.handling.capacity.of.the.vapor.recovery.unit.is.sent.to.the.flare.Figure.3..When.the.flare.is.operated.properly,.it.safely.disposes.of.combustible.gases.by.burning.them..All.that.remains.after.combustion.are.harmless.amounts.of.carbon.dioxide.and.water.vapor..If.a.flare.is.not.operated.properly.or.if.a.mal-function.occurs,.smoke,.odorous.gases,.and.excessive.light.and.noise.may.be.generated.

Figure 3. Flare

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Flares.are.generally.used.to.handle.waste.gases.resulting.from.unusual.conditions.such.as.unit.upsets.or.unscheduled.shutdowns..During.such.times,.more.waste.gas.is.relieved.than.the.vapor.recovery.unit.can.handle..

General Considerations—Challenge Questions

1. Namethreeconsiderationsassociatedwithhandlingwastegases.

2. ____________istheremovalofhazardousmaterialsfrompipingandequip-mentwithagasorvaportopreventtheformationofexplosivemixtures.

3. Thebasicpurposeofventingisto:a. Eliminatepollutionb. Increaseplantefficiencyc. Releasewastegasesandpurgegasesd. Alloftheabove

4. Hazardousgasescreatedduringprocessoperationsareusuallydischargedintoareliefsystem.

a. Trueb. False

5. Wastegases thatexceedthehandlingcapacityofa reliefsystem’svaporrecoveryunitaregenerallysenttoa:

a. Knockoutdrumb. Flarec. Secondaryreliefsystemd. Holdingtank

Please refer to the end of the handbook for answers.


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VENTING

Venting.helps.to.prevent.damage.to.equipment.and.vessels.from.overpressurization.or.other.hazards..This.section.describes.some.of.the.conditions.that.require.venting,.identifies.several. types.of.vents,.and.describes.safe.work.practices.associated.with.venting.

Objectives•. Describe.conditions.that.require.venting.•. Describe.various.types.of.vents.•. Describe.work.practices.that.help.ensure.the.safe.venting.of.equipment.and.ves-

sels.

Conditions That require VentingSeveral. routine. tasks.associated.with.vessels.and.equipment. require. the.vessels.

and.equipment.to.be.vented..These.tasks.include.filling,.draining,.and.steam.cleaning..Venting.is.also.necessary.when.conditions.such.as.high.fluid.levels.and.excessive.tem-peratures.result.in.equipment.or.system.upsets.that.may.involve.excessive.pressures.

Filling a TankThe.tank.represented.in.Figure.4.has.a.pump.on.the.feed.inlet.and.a.pump.on.the.liq-

uid.outlet..The.tank.also.has.a.vent.on.top,.which.is.closed..Although.the.tank.is.empty.of.liquid,.it.contains.air,.because.it.was.recently.open.to.the.atmosphere.

Figure 4. Empty Tank With Vent Closed

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When.liquid.is.pumped.into.the.tank,.the.air.in.the.tank.is.displaced.to.make.room.for.the.liquid..Without.venting,.as.the.level.of.the.liquid.rises,.the.air.is.compressed.at. the. top. of. the. tank. (Figure. 5).. Eventually,. the. compressed. air. will. prevent. liquid.from.completely.filling.the.tank..It.also.increases.the.pressure.in.the.tank..In.extreme.situations,.the.pressure.could.increase.so.much.that.the.tank.could.be.damaged.from.overpressurization.

Figure 5. Tank Filling—Vent Closed

If.the.vent.is.open.during.filling.(Figure.6),.overpressurization.does.not.occur..When.liquid.is.pumped.into.the.tank,.the.displaced.air.is.forced.out.of.the.vent..The.open.vent.helps.equalize.the.pressure.inside.the.tank.with.the.pressure.outside.the.tank.

Figure 6. Tank Filling—Vent Open

Draining a TankEqualizing.pressure.is.also.important.when.a.tank.is.drained..If.the.vent.is.closed.

(Figure.7).as.the.pump.removes.liquid.from.the.tank,.a.vacuum.is.pulled.above.the.liq-uid..This.occurs.because.air.cannot.enter.through.the.vent.to.equalize.the.pressure..If.the.tank.is.not.rated.to.withstand.a.vacuum,.it.could.eventually.collapse.


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Figure 7. Tank draining—Vent Closed

Steam Cleaning a TankWithout.venting,.a.tank.or.other.vessel.may.collapse.after.it.has.been.steam.cleaned..

For.example,.to.steam.clean.a.distillation.column.Figure.8,.steam.is.sent.into.the.col-umn.until.a.certain.pressure.is.reached..After.the.steam.supply.is.shut.off,.the.vessel.begins.to.cool,.and.the.steam.condenses,.which.causes.the.pressure.to.drop.inside.the.column..As.the.column.becomes.cooler,.and.more.condensate.forms,.the.pressure.can.drop.below.atmospheric.pressure,.creating.a.vacuum..To.prevent.the.creation.of.a.vacuum.that.could.collapse.the.column,.vents.are.normally.opened.after.the.steaming.is.complete.

Figure 8. distillation Column after Steaming

Types of VentsOne.simple.method.of.venting.is.through.an.open.pipe.connected.to.equipment..This.

type.of.vent.is.always.open..Because.open.vents.release.gases.directly.to.the.atmo-sphere,.they.are.not.generally.used.on.equipment.that.handles.hazardous.materials.

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A.variation.on.the.open.vent.is.a.type.of.vent.that.can.be.called.a.pipeaway.vent..In.a.pipeaway.vent,.the.vent.line.typically.contains.a.valve.to.relieve.pressure..If.the.pressure.gets.too.high,.the.valve.is.opened.to.allow.vapor.to.leave.through.piping.for.treatment.or.disposal.

Another.type.of.vent.that.is.commonly.used.on.piping.and.equipment.is.a.manually.operated.valved.vent.(Figure.9)..This.kind.of.vent.can.be.opened.by.hand.to.release.gas.and.vapor.from.a.system.

Figure 9. manually Operated Valved Vents

A.valved.vent.may.also.be.opened.and.closed.by.a.pressure.control.valve..In.this.type.of.arrangement,.a.controller.is.used.to.position.the.valve.so.that.internal.equipment.pressure.does.not.exceed.a.preset.value..For.example,.when.the.pressure.in.a.vessel.exceeds.an.established.set.point,.the.controller.detects.the.high.pressure.and.opens.the.valve.to.release.gas.or.vapor.through.the.vent.and.relieve.the.pressure..The.control-ler.closes.the.valve.again.when.the.pressure.drops.below.the.set.point.

Conservation.vents.(Figure.10).are.often.used.on.storage.tanks.to.reduce.the.evapo-ration.of.tank.contents..This.is.done.by.means.of.a.valve.that.is.weighted.to.relieve.pressure.at.a.preset.value..The.conservation.vent.reduces.evaporation.by.allowing.the.vapor.to.accumulate.within.a.safe.pressure.range..This.accumulation.keeps.more.vapor.from.forming.


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Figure 10. Conservation Vents

In.some.situations,.such.as.equipment.upsets.that.may.involve.sudden.and.exces-sive.pressure.increases,.emergency.venting.is.necessary..Emergency.vents.allow.the.relief.of.relatively.large.amounts.of.material.to.quickly.reduce.pressure.

Included.in.(Figure.11).are.hatch-type.emergency.vents..This.type.of.vent.typically.uses.a.spring.or.a.weighted.pallet.to.open.the.vent.when.tank.pressure.gets.too.high.

Figure 11. Hatch-Type Emergency Vents

Another.type.of.emergency.vent.is.commonly.called.a.relief.valve,.but.it.may.also.be.called.a.safety.valve..When.pressure.overcomes.the.force.of.an.internal.spring,.this.type.of.valve.opens.and.vents.the.gas.

A.rupture.disc.is.another.type.of.emergency.vent..There.are.various.types.of.rupture.discs,. but. they. all. operate. in. essentially. the. same. way.. The. rupture. disc. shown. in.Figure.12.contains.small.cuts,.or.scores..When.a.certain.pressure.is.reached,.the.disc.splits.at.the.scores.to.vent.the.gas.and.relieve.the.pressure..After.a.rupture.disc.has.burst,.it.must.be.replaced.with.a.new.one.

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Figure 12. rupture disc

Safe Work PracticesOperators.must.follow.all.applicable.company.procedures.to.ensure.that.vessels.and.

equipment.are.safely.vented..In.addition,.operators.must.know.the.pressure.ratings.of.the.equipment.in.their.area..This.information.is.often.stamped.on.equipment.name-plates.or.included.in.company.procedures.

It.is.also.important.for.operators.to.know.the.pressures.at.which.pressure.controlled.vent.valves.and.emergency.vent.valves.open..These.valves.are.usually.marked.or.have.tags.that.provide.the.relief.pressure.and.other.information..A.rupture.disc.also.typically.has.a.tag.indicating.the.disc’s.relief.pressure.

In.some.cases,.to.make.sure.that.open.vents.remain.open,.an.operator.may.be.re-quired.to.lock.valves.in.their.open.positions..This.ensures.that.the.vents.are.not.mis-takenly.blocked.off.

Operators.may.also.be.required.to.keep.track.of.vent.problems,.such.as.sticky.valves..This.type.of.information.can.be.used.to.determine.when.to.repair.or.replace.a.vent.


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Venting—Challenge Questions

1. Whichofthefollowingtaskstypicallyrequire(s)ventingtoavoiddamagingequipment?

a. Fillingatankb. Steamcleaningatankc. Drainingatankd. Alloftheabovee. Onlyaandc

2. Ventingissometimesneededwhenconditionssuchashighfluidlevelsandexcessivetemperaturesresultinequipmentorsystemupsets.

a. Trueb. False

3. Openvents(are/arenot)generallyusedonequipmentthathandleshazard-ousmaterials.

4. Tohelpensurethatequipmentissafelyvented,operatorsshoulda. Knowthepressureratingsoftheequipmentintheirareab. Knowthepressuresatwhichpressure-controlledventvalvesand

emergencyventvalvesoperatec. Keeptrackofventproblemsd. Alloftheabovee. Onlyaandb


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PurGING

Purging.is.the.process.of.removing.hazardous.materials.from.equipment.using.a.gas.or.vapor..Purging.is.also.used.to.remove.oxygen.from.process.equipment.or.to.keep.oxygen.from.entering.process.equipment..

Oxygen.alone.is.not.necessarily.a.hazardous.material..However,.when.it.combines.with.a.material.that.is.flammable,.a.mixture.is.formed.that.will.readily.ignite..Oxygen.can.enter.equipment.any.time.the.equipment.is.open.to.the.atmosphere,.such.as.dur-ing.cleaning.and.repairs..Oxygen.can.also.enter.equipment.through.leaky.components.

This.section.describes.purging.materials.and.purging.methods..Safety.concerns.and.operator.responsibilities.associated.with.purging.are.also.covered.

Objectives•. Explain.why.nitrogen.and.fuel.gas.are.used.for.purging.•. Describe.two.methods.used.to.purge.vessels.and.equipment.•. Explain.what.inerting.is.and.why.and.how.it.is.done.•. Describe.safety.concerns.and.operator.responsibilities.associated.with.purging.

materials used for PurgingOne.material.that.is.often.used.for.purging.is.nitrogen..The.main.reason.for.using.

nitrogen.is.that.it.is.inert,.that.is,.it.does.not.react.easily.with.other.materials.

Steam.may.also.be.used.to.purge.hazardous.materials.from.equipment..However,.some.equipment.parts,.such.as.seals.and.instrumentation.components,.cannot.with-stand.steam.temperatures,.and.they.may.be.damaged.

Another.material.that.may.be.used.for.purging.is.natural.gas,.or.fuel.gas..Fuel.gas.is.generally.used.for.purging.when.it.is.readily.available,.economical.to.use,.and.compat-ible.with.the.products.being.produced.

When.fuel.gas.is.used.for.purging,.it.must.not.be.combined.with.oxygen.in.propor-tions.that.will.allow.combustion.to.occur..In.order.for.combustion.to.occur,.a.certain.amount.of.oxygen.is.needed.for.a.given.amount.of.fuel..However,.a.mixture.of.fuel.and.oxygen.will.not.burn.if.there.is.either.too.little.fuel.or.too.much.fuel.in.proportion.to.the.amount.of.oxygen..When.fuel.gas.is.used.to.purge.equipment.that.contains.com-bustible.vapor,.which.is.basically.a.fuel,.the.total.amount.of.fuel.in.the.equipment.is.increased..As.a.result,.if.proportionately.smaller.amounts.of.oxygen.mix.with.the.fuel,.the.fuel-rich.mixture.will.not.burn.


16

Purging methodsTwo.methods.that.are.commonly.used.to.purge.equipment.are.the.continuous.purge,.

or.sweep,.method.and.the.fixed.volume,.or.“pop.and.purge,”.method.

Continuous Purge MethodFigure.13.is.a.simplified.illustration.of.a.mixer.that.contains.air..The.air.is.removed.

by.continuously.purging.the.mixer.with.nitrogen..The.nitrogen.is.sent.into.the.mixer,.and.the.oxygen.in.the.air.is.diluted.and.swept.out.of.the.mixer.through.a.vent..Nitrogen.is.continuously.supplied.until.testing.indicates.that.the.atmosphere.inside.the.mixer.is.free.of.oxygen.

Figure 13. Continuous Purging

Fixed Volume Purge MethodWhen.the.fixed.volume.purge.method.is.used.to.purge.oxygen.from.a.vessel.such.as.

a.mixer,.the.vent.on.the.mixer.is.initially.closed..To.begin.the.purge,.nitrogen.is.sent.to.the.mixer.until.a.certain.pressure.is.reached.(Figure.14)..The.pressure.is.held.for.a.designated.period.of.time.while.the.nitrogen.mixes.with.any.oxygen.that.is.present.

Figure 14. Fixed Volume Purging; Vent Closed

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The.vent.on.the.mixer. is. then.opened.(Figure.15),.which.releases,.or.“pops,”.the.contents.out.of. the.mixer,. thereby. reducing. the.amount.of.oxygen. in. the.vessel..To.prevent.oxygen.from.entering.the.mixer.again,.the.vent.is.closed.before.the.pressure.in.the.mixer.drops.to.atmospheric.pressure.

Figure 15. Fixed Volume Purging; Vent Open

With.the.fixed.volume.method.of.purging,.the.steps.required.to.reduce.the.level.of.oxygen.are.usually.repeated.a.number.of.times..With.each.repetition,.less.oxygen.is.left.in.the.vessel.

InertingIn.many.cases,.after.equipment.has.been.purged.of.undesirable.materials,.nitrogen.

may.be.used.to.maintain.an.inert,.or.nonreactive,.atmosphere.in.the.equipment..This.process.is.called.inerting,.or.blanketing.

Inerting.may.be.done.for.a.number.of.reasons..For.example,.the.mixer.represented.in.Figure.16.is.supplied.with.nitrogen.to.form.a.blanket,.or.pad,.at.the.top.of.the.mixer..When.a.liquid.flows.into.the.mixer,.it.can.build.up.a.static.charge,.which.could.ignite.flammable.materials..The.nitrogen.blanket.makes. the.mixer’s.atmosphere.nonreac-tive,.which.prevents.any.combustion.reaction.from.occurring.

Figure 16. Nitrogen Blanket in a mixer


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In.some.cases,.a.nitrogen.blanket.is.kept.on.a.vessel.while.the.vessel.is.in.opera-tion..A.positive.nitrogen.pressure.maintains.a.nonreactive.atmosphere.and.prevents.air.from.entering.the.vessel.and.mixing.with.its.contents..The.nitrogen.also.prevents.combustion.reactions.with.static.charges.generated.by.moving.parts.

When.a.nitrogen.blanket. is.applied.to.equipment,. the.nitrogen.pressure.must.be.controlled..This. is. especially. important. for. situations. in. which. changes. in. pressure.might.create.an.undesired.vacuum.in.the.equipment..Such.pressure.changes.might.be.caused.by.weather-related.temperature.changes,.or.they.might.be.caused.by.process.reactions.

One.way.to.control.nitrogen.pressure.is.to.use.an.automatic.control.system..For.ex-ample,.Figure.16.is.a.simplified.illustration.of.a.tank.that.contains.liquid.and.a.blanket.of.nitrogen..The.tank.has.a.pressure.gauge;.a.vent.that.branches.into.a.nitrogen.supply,.or.vacuum.relief,.line;.and.a.pressure.relief.line..Each.line.contains.a.motor-operated.control.valve..

Figure 16. Tank With Nitrogen Supply Control System

If.the.pressure.in.the.tank.drops.below.a.predetermined.set.point,.a.controller.sends.a.signal.to.the.nitrogen.supply.control.valve..The.valve.then.opens.to.supply.nitrogen.to.the.tank..When.the.desired.pressure.is.reached,.the.valve.closes.

If.the.pressure.in.the.tank.increases.above.its.set.point,.the.control.valve.in.the.pres-sure.relief.line.opens,.and.nitrogen.is.bled.off..When.the.desired.pressure.is.reached,.the.valve.closes.

SafetyAlthough.nitrogen.is.nonflammable,.there.are.some.safety.concerns.associated.with.

its.use..For.example,.exposure.to.high.concentrations.of.nitrogen.should.be.avoided..Nitrogen.can.dilute.oxygen.in.the.air.below.the.point.at.which.air.can.support.life.

19


Nitrogen.is.often.stored.as.a.liquid.in.a.pressurized.tank..Liquid.nitrogen.is.extreme-ly.cold,.so.personnel.who.handle.it.must.be.careful.to.avoid.frostbite.

Operators.must.always.follow.company.procedures.and.take.the.required.precau-tions.when.they.open.equipment.that.has.been.purged.or.blanketed.with.nitrogen.

Operator responsibilitiesOne. important. operator. responsibility. associated. with. purging. is. ensuring. that.

valves. are. properly. lined. up.. Company. procedures. should. be. followed. carefully. to.ensure.that.the.purge.gas.will.be.supplied.to.and.vented.from.all.the.required.points.

Operators.are.also.responsible.for.making.sure.that.equipment.is.properly.isolated..To.do.this,.an.operator.may.have.to.close.block.valves.and.install.blinds..Blinds.are.solid.discs.that.are.inserted.into.pipelines.to.block.flow..When.blinds.are.used,.the.correct.size.blinds.must.be.installed..Improper.equipment.isolation.can.result.in.over-pressurizing.equipment.and.can.cause.relief.valves.to.lift.

Before.lines.are.opened.to.install.blinds,.operators.must.obtain.any.necessary.per-mits.and.notify.appropriate.areas.of.the.plant,.such.as.those.downwind.of.the.work.area..Company.procedures.applicable.to.the.use.of.respirators.and.standby.operators.during.blinding.should.always.be.followed..Purging.may.be.required.when.a.line.or.a.piece.of.equipment.is.opened.

In.some.cases,.operators.may.have.to.make.nitrogen.supply.connections.with.tem-porary.lines.from.bleeders,.drains,.and.other.parts.of.a.process.system.to.the.relief.system..These. lines.must.be. installed.according.to.procedures,.and.all.connections.must.be.tight.

To.avoid.subjecting.equipment.to. inappropriate.pressures.during.purging,.opera-tors.must.know.the.pressure.and.vacuum.ratings.of.equipment..They.should.also.know.the.lifting.pressures.of.relief.valves.

To.start.purging,.the.nitrogen.supply.valve.is.opened.slowly.to.avoid.surges.of.nitro-gen.flow.and.pressure,.which.could.put.unnecessary.stress.on.the.system..Pressure.gauges.on.the.purged.equipment.and.lines.are.checked.to.make.sure.that.the.equip-ment.pressure.stays.within.a.safe.range.

Equipment. is.often.checked.for. leaks.during.purging..After.equipment. is.pressur-ized.with.nitrogen,.any.large.leaks.can.be.heard.or.felt.by.operators..Small.leaks.are.detected.by.squirting.a.leak-detecting.liquid.solution.onto.likely.areas,.such.as.around.flanges.or.valve.packing..If.leaks.are.present,.the.solution.will.bubble.


20

When.steam.is.used.to.leak-test.equipment,.operators.can.see.the.sources.of.any.leaks..When.a.leak.is.found,.it.should.be.reported.so.that.it.can.be.repaired.

After. all. detected. leaks. have. been. repaired,. the. equipment. can. be. pressurized.again..While.this.is.being.done,.the.pressure.on.the.equipment.must.be.monitored..If.there.is.any.drop.in.pressure,.additional.leaks.may.be.present..Those.leaks.must.then.be.found.and.repaired..

Leaks.can.also.be.a.problem.when.nitrogen.is.used.for.blanketing..In.some.applica-tions,.nitrogen.is.supplied.to.equipment.for.blanketing.and.then.turned.off..If.the.pres-sure.starts.to.drop.in.the.blanketed.equipment,.a.possible.cause.is.nitrogen.leaking.by.the.isolation.valves.

When.a.vessel.or.a.piece.of.equipment.containing.flammable.material.is.under.a.gas.purge.or.a.blanket,.an.interruption.of.the.gas.flow.can.pose.an.immediate.danger..If.this.happens,.the.equipment.must.be.blocked.in.to.trap.the.purge.gas.inside..Blocking.in.the.equipment.also.keeps.air.from.entering.and.mixing.with.the.flammable.material.until.the.problem.can.be.corrected.

Finally,.to.make.sure.that.equipment.has.been.properly.purged,.operators.may.use.a.portable.gas.analyzer.to.test.the.atmosphere.inside.the.equipment.

21


Purging—Challenge Questions

1. Nitrogenisoftenusedforpurgingbecauseitiswhat?a. Inertb. Highlyreactive

2. Nametwomethodsthatarecommonlyusedtopurgeequipment.

3. ___________istheprocessofmaintaininganonreactiveatmosphereinsideequipmentaftertheequipmenthasbeenpurgedofundesirablematerials.

4. WhichofthefollowingisNOTasafetyconcernrelatedtotheuseofnitrogenforpurging?

a. Potentialforfrostbitefromliquidnitrogenb. Dilutionofoxygenbelowthepointnecessarytosupportlifec. Dangerofexplosiond. Bothaandc

5. Operatorresponsibilitiesassociatedwithpurgingtypicallyinclude:a. Installingblindsb. Performingvalvelineupsc. Checkingforleaksd. Alloftheabovee. Onlybandc



22

FlarE SySTEm

Relief.gases.that.cannot.be.processed.by.a.relief.system’s.vapor.recovery.unit.are.of-ten.sent.to.a.flare.to.be.safely.burned.off..This.section.identifies.safety.considerations.associated.with.flaring.and.describes.the.basic.operation.of.a.flare.

Objectives•. Describe.safety.considerations.associated.with.flaring.•. Describe.the.main.components.and.the.basic.operation.of.a.flare.

Safety ConsiderationsThe.function.of.a.flare.is.to.dispose.of.combustible.gases.by.safely.burning.them..

Safety.is.particularly.important.when.a.flare.is.operating.because.two.of.the.elements.required.for.combustion.are.always.present:.fuel,.in.the.form.of.combustible.gases,.and.an.ignition.source,.in.the.form.of.flames..The.only.element.that.is.needed.to.start.a.fire.or.an.explosion.is.oxygen.

Pressure.fluctuations.in.the.system.that.feeds.relief.gas.to.the.flare.can.cause.pres-sure.in.the.flare.to.become.less.than.atmospheric..This.condition.can.result.in.air.being.drawn.back.down.into.the.flare.and.the.relief.header,.which.can.lead.to.fire.and.explo-sion.hazards..Extreme.care.must.be.taken.to.ensure.that.the.flare.and.the.rest.of.the.relief.system.are.protected.from.air.entry.

Components and OperationFigure.17.is.a.simplified.illustration.of.a.flare..The.flare’s.main.components.are.a.

flare.stack,.or.riser;.a.stack.inlet;.a.stack.seal,.or.molecular.seal;.a.water.seal.at.the.base.of.the.stack;.and.a.flare.tip.

Figure 17. Flare Components

23


The.function.of.the.stack.is.to.route.gases.entering.through.the.inlet.to.the.flare.tip,.where.they.can.be.burned..Because.it.is.critical.to.keep.air.from.backflowing.into.the.flare.stack,.the.flare.has.a.number.of.safeguards..These.safeguards.include.the.stack.seal,.the.water.seal,.and.purge.gas.

The.function.of.the.stack.seal.is.to.keep.air.from.backflowing.down.the.stack..The.stack.seal.contains.a.complex.network.of.baffles.(Figure.18).that.make.it.difficult.for.oxygen.to.penetrate.

Figure 18. Baffles in Stack Seal

The.water.seal.is.the.next.line.of.defense.against.the.backflow.of.air..If.a.mixture.of.flammable.gases.and.air.is.ignited.in.the.stack,.the.water.seal.is.designed.to.quench.the.flame..In.this.way,.the.water.seal.protects.the.relief.system.and.plant.equipment.from.flashback.fires.or.explosions.by.stopping.the.flame.before.it.can.leave.the.stack.

A.typical.water.seal.is.represented.in.Figure.19..Basically,.the.water.seal.is.a.reser-voir.that.contains.water..The.example.water.seal.has.a.makeup.water.line,.an.overflow.line,.and.a.distributor,.which.is.basically.a.plate.with.holes.submerged.in.the.water.

Figure 19. Water Seal


24

Water.is.sent.in.through.the.makeup.water.line.to.replace.seal.water.that.is.evapo-rated.by.the.relatively.hot.relief.gases.that.pass.through.it..To.control.the.water.seal.level,.water.is.continuously.added.through.the.makeup.water.line,.and.excess.water.leaves.through.the.overflow.line..

When.relief.gas.enters.the.stack,.it.passes.through.the.distributor..The.holes.in.the.distributor.spread.out.the.gas,.which.bubbles.up.through.the.water.and.then.flows.up.the.stack.

Purge.gas.is.also.sent.in.through.the.stack.inlet.to.the.flare.tip..The.purge.gas.helps.maintain.a.positive.pressure.at.the.flare.tip.to.prevent.the.backflow.of.air.into.the.stack..Purge.gas.used.in.this.way.may.be.called.a.gas.seal.

The. purge. gas. used. in. a. flare. may. be. fuel. gas. that. is. introduced. near. the. relief.header’s.point.of.origin,.so.that.the.entire.relief.system.is.swept.with.purge.gas..In.addition. to.preventing.air. from.entering. the.stack,. fuel.gas.used.as.purge.gas.also.performs.other.functions..It.maintains.a.fuel-rich.mixture.that.prevents.air.from.pro-ducing.a.combustible.or.explosive.mixture.within.the.stack..It.also.helps.maintain.the.flare.flame.during.periods.of.low.relief.gas.flow,.when.there.is.not.enough.relief.gas.to.support.combustion.

The.function.of.the.flare.tip.is.to.mix.air.with.the.relief.gas.in.order.to.promote.com-plete.and.smokeless.gas.burning..The.flare.tip.represented.in.Figure.20.includes.an.opening.for.the.relief.gas;.pilot.gas.burners,.or.pilots;.steam.nozzles;.a.steam.line;.a.pilot.gas.line;.and.ignitor.lines..(Only.one.ignitor.line.is.represented.in.Figure.20.)

Figure 20. Flare Tip

25


During.operation,.a.mixture.of.natural.gas.and.air.is.constantly.supplied.to.the.pi-lots..A.flame.is.sent.to.the.pilots.to.ignite.the.gas.mixture..The.pilot.flames.are.kept.on.as.long.as.the.flare.is.in.operation.

As.the.relief.gas.flows.through.the.flare.tip,.air.is.drawn.into.the.relief.gas..When.the.air.mixes.with.the.gas,.the.flames.from.the.pilots.ignite.the.mixture.and.burn.it.

During.normal.operation,.the.relief.gas.should.burn.cleanly.and.completely..In.some.cases,.however,.because.of.factors.such.as.the.kinds.of.gases.being.burned.and.unit.upsets,.combustion.may.be.incomplete..One.sign.of.incomplete.combustion.is.smoke..Smoke.indicates.that.unburned.hydrocarbons.are.being.released.to.the.atmosphere..

In.order.to.achieve.the.smokeless.burning.expected.of.a.flare,.steam.is.injected.from.the.steam.nozzles.into.the.flame.(Figure.21)..The.steam.reduces.smoking.by.creating.turbulence.and.pulling.in.air.to.mix.with.the.relief.gas..The.thorough.mixing.of.relief.gas.and.air.helps.to.produce.complete.combustion..When.complete.combustion.occurs,.the.only.emissions.from.the.flare.tip.are.water.vapor.and.carbon.dioxide.

Figure 21. Steam Injected into Flame

In. some. cases,. a. steam. flow. control. system. is. used. to. automatically. adjust. the.amount.of.steam.needed.to.prevent.the.flare.from.smoking..Various.types.of.steam.control.systems.may.be.used,.and.they.all.work.similarly..One.type.of.steam.control.system.uses.an.infrared.monitor.that.is.pointed.at.the.flare..The.monitor.senses.the.infrared.radiation.of.the.unburned.carbon.at.the.flare.tip.and.generates.a.correspond-ing.signal.

The.signal.from.the.infrared.monitor.is.sent.to.a.steam.flow.converter.that.converts.the.signal.into.a.steam.flow.set.point.for.a.controller..The.controller.is.connected.to.a.valve.in.the.steam.supply.line..As.the.amount.of.unburned.carbon.changes,.the.control-ler.sends.a.signal.that.adjusts.the.valve.until.the.steam.flow.rate.equals.the.set.point.established.by.the.converter.


26

Flare System—Challenge Questions

1. Ingeneral,thebackflowofcombustiblegasesintoaflareorareliefheaderisnotaproblem.

a. Trueb. False

2. A__________________isbasicallyareservoirofwaterthatquenchesanyflamethatmayresultfromtheignitionofamixtureofflammablegasesandairinaflarestack.

a. Flarestackb. Watersealc. Stackseald. Flareinlet

3. WhichofthefollowingstatementsisFALSEregardingfuelgasusedasthepurgegasinaflaresystem?

a. Promotesthebackflowofairintothestackb. Maintainsafuel-richmixturethatreducescombustionhazardsc. Helpstomaintaintheflareflameduringperiodsoflowreliefgasflow

4. Thefunctionofthe___________istomixairwiththereliefgasinordertopromotecompleteandsmokelessgasburning.

a. Flamejetb. Flaretip

5. Whenreliefgasisburnedcleanlyandcompletelyataflare,theonlyemis-sionsfromtheflaretiparewatervaporandsmoke.

a. Trueb. False


27


FlarE OPEraTIONS, ParT 1

Operators.who.work.with.flares.must.know.how.flares.work.and.how.they.should.be.operated..This.section.describes.some.basic.operator.responsibilities.related.to.the.startup.and.normal.operation.of.flares.

Objectives•. Describe.typical.operator.responsibilities.associated.with.a.flare.system.startup.•. Describe. some. typical. control. room. operator. responsibilities. associated. with.

normal.flare.operation.

Startup PreparationsFlares.are.generally.kept.in.operation.most.of.the.time..Even.when.there.is.little.or.

no.relief.gas.being.sent.to.them,.the.pilots.usually.remain.lit..However,.there.are.occa-sions.when.a.flare.is.shut.down.for.repairs.and.must.then.be.returned.to.service.

The.preparations.for.a.flare.startup.begin.upstream.of.the.flare..The.first.major.step.in.preparing.for.the.startup.is.purging.a.portion.of.the.relief.header.and.the.knockout.drum..Purging.is.typically.done.first.with.steam.and.then.with.gas,.but.in.some.cases,.only.a.gas.is.used.

In. the. online. course,. the. operator. began. by. lining. up. valves. to. purge. the. relief.header,.the.knockout.drum,.and.the.lines.between.them.with.steam..The.steam.purge.would. clean. lines. and. equipment,. and. enable. the. operator. to. check. for. leaks.. The.steam.would.also.help.to.purge.oxygen.from.the.system.

After. the. appropriate. equipment. was. properly. isolated,. the. operator. opened. the.necessary.drains,.bleeders,.and.vents.to.prevent.pulling.a.vacuum.on.the.knockout.drum.and.other.parts.of.the.relief.system..The.operator.then.connected.steam.supply.lines.at.various.points.between.the.relief.header.and.the.knockout.drum..This.helps.minimize.condensation.and.the.time.needed.to.heat.up.and/or.dry.out.the.system..Finally,.he.opened.steam.line.valves.to.start.the.steam.purge.

During.the.purge,.the.operator.checked.bleeders.for.constant.steam.flow.(Figure.22).to.ensure.that.steam.was.reaching.everywhere.it.should..When.the.steam.becomes.dry,.it.means.that.most.of.the.air.has.been.removed.and.any.condensate.from.the.steam.has.been.blown.out..A.constant.flow.of.dry.steam.indicates.that.the.purge.is.complete.


28

Figure 22. Checking a Bleeder for Steam Flow

When. the. operator. was. satisfied. that. the. steam. purge. was. complete,. he. closed.vents,.bleeders,.and.drains.to.pressurize.the.system.for.leak.testing..As.the.pressure.built.up,.the.operator.watched.a.pressure.gauge.on.the.knockout.drum.to.make.sure.that.the.pressure.did.not.get.too.high..He.then.checked.the.knockout.drum.for.visible.or.audible.signs.of.leaks..All.flanges.in.the.relief.system.that.was.under.purge.were.also.checked.for.leaks.

Next,.a.nitrogen.purge.was.started.at.the.relief.header.to.completely.remove.any.air.left.in.the.system.and.keep.it.out..After.connecting.nitrogen.supply.lines.to.bleeders,.the.operator.gradually.opened.valves.to.start.the.nitrogen.purge..When.a.nitrogen.sup-ply.line.had.been.connected.at.all.the.necessary.locations.in.the.system,.the.operator.shut.off.the.steam.purge..These.steps.prevented.a.vacuum.from.being.created.by.con-densing.steam..Then.the.steam.line.was.disconnected.

Next,.the.operator.lined.up.valves.to.send.the.nitrogen.purge.gas.from.the.knockout.drum.to.the.flare..While.the.relief.system.was.under.the.nitrogen.purge,.the.operator.made.sure.that.the.knockout.drum.pump.was.ready.for.operation,.so.that.it.could.be.started. when. needed. to. remove. liquid. from. the. drum. to. maintain. the. proper. level..The.operator.also.checked.the.relief.system.at.several.locations.with.a.gas.analyzer.to.make.sure.that.the.oxygen.content.was.at.a.safe.level.

StartupA.typical.flare.startup.procedure.includes.establishing.the.water.seal,.establishing.

steam.flow,.purging.the.flare.stack,.and.lighting.the.pilots..

To.establish.the.water.seal,.the.operator.in.the.online.course.lined.up.valves.to.fill.the.seal.until.the.water.level.neared.the.overflow.pipe.

To.begin.establishing.steam.flow,. the.operator.opened.drain.valves. in. the.steam.supply.for.the.flare.tip.to.make.sure.that.there.was.no.water.or.condensate.present..Condensate.that.collects.in.the.steam.lines.to.the.flare.can.interfere.with.the.flow.of.steam..If.the.condensate.is.not.removed,.the.steam.will.not.reach.the.flare.tip.

29


Steam.traps.are.used.to.remove.the.condensate.without.losing.steam..As.part.of.the.startup.procedure,.the.operator.checked.the.steam.traps.to.make.sure.that.they.were.functioning.properly..After.the.flare.is.in.service,.the.traps.are.checked.periodically.

Steam.flow.to.the.flare.tip.was.established.by.opening.block.valves.upstream.and.downstream.of.the.two.steam.control.valves.

After.testing.showed.that.the.flare.stack.was.free.of.oxygen,.the.operator.positioned.valves.to.start.continuous.purging.of.the.relief.system,.including.the.flare,.with.fuel.gas..Once.the.continuous.purge.was.started,.the.nitrogen.supply.was.blocked.in.

In.the.online.course.example,.the.flare.stack.was.purged.with.a.separate.source.of.natural.gas..This.additional.purge.gas.was.used.so.that.the.flare.would.not.have.to.be.shut.down.if.the.relief.system.had.to.be.isolated.from.the.flare.

With. the. purge. gas. flow. is. established,. the. next. step. in. a. typical. flare. startup. is.lighting.the.pilots..In.the.example,.the.pilots.were.lit.using.a.flame.front.generator,.or.ignitor.station..Basically,.an.ignitor.station.consists.of.air.and.gas.supply.lines.and.an.air/gas.mixer.fitted.with.a.spark.plug,.or.ignitor,.that.provides.a.source.of.ignition..Lines.called.ignitor.lines.connect.the.air/gas.mixer.to.the.pilots.

Before.the.pilots.are.actually.lit,.several.additional.preparations.are.needed..First,.at.the.base.of.the.flare,.the.operator.drained.the.ignitor.lines.of.any.condensate..This.is.important.because.condensate.can.snuff.out.a.flame.in.an.ignitor.line.before.the.flame.reaches.the.pilot..Next,.the.operator.opened.valves.to.supply.natural.gas.to.the.pilots.

At.the.ignitor.station,.the.operator.opened.valves.to.blow.down.the.air.and.gas.lines.to.make.sure.that.they.were.free.of.moisture..To.make.sure.that.the.ignitor.was.working.properly,.the.operator.pressed.the.ignitor.button.and.checked.a.sight.glass.to.verify.that.the.ignitor.produced.a.spark.

To.begin.lighting.the.pilots,.the.operator.opened.a.valve.on.a.mixer.line.to.supply.the.first.pilot.with.an.air/gas.mixture..

Then.he.set. the.air.pressure.and.the.gas.pressure..The.correct.settings.send.the.proper.amounts.of.air.and.gas.to.the.mixer.

Next,.the.operator.pressed.the.ignitor.button.to.produce.a.spark,.which.ignited.the.air/gas.mixture.and.produced.a.flame..The.flame.left.the.mixer.and.traveled.through.the.ignitor.line.to.the.first.pilot.

The.lighting.of.the.pilots.is.verified.by.checking.the.pilot.temperatures.in.the.control.room..After.the.first.pilot.is.lit,.valves.are.lined.up.to.mix.air.and.gas.and.direct.a.flame.to.another.pilot..The.steps.are.repeated.to.light.the.remaining.pilots..After.all.the.pilots.are.lit,.the.air.and.gas.valves.to.the.ignitor.are.closed,.and.the.flare.is.ready.to.receive.relief.gases.


30

Control room Operator responsibilitiesOnce.the.gases.are.flowing.to.the.flare,.there.are.a.number.of.duties.that.operators.

have.to.perform.to.ensure.that.the.flare.operates.safely..For.example,.several.variables.must. be. monitored..Some. of. these. variables. may. be. monitored. only. in. the. control.room,.while.others.may.be.monitored.both.inside.and.outside.of.the.control.room.

One.variable.that.must.be.monitored.is.the.flare.flame..It.is.especially.important.for.control.room.operators.to.observe.the.flame.during.unit.shutdowns.and.emergency.situations,.when.flare.activity.is.greatest..During.such.times,.operators.need.to.know.that.the.steam.control.system.is.reacting.properly.to.continue.to.provide.smokeless.burning.

The.flow.rate.of.steam.to.the.steam.nozzles.is.also.monitored,.so.that.any.problems.with.steam.flow.can.be.detected..In.addition,.the.temperature.of.the.flare.tip.is.checked.to.make.sure.that.it.does.not.get.too.hot..In.some.systems,.if.the.flare.tip.gets.too.hot,.steam.can.be.supplied.to.a.ring.inside.the.flare.tip,.or.throat,.to.cool.it.

.The.temperatures.of.the.pilots.are.also.monitored..If.the.temperature.of.a.pilot.is.too.

low,.it.can.mean.that.the.pilot.has.gone.out.and.must.be.relit..Control.room.operators.also.monitor.the.flow.rates.of.relief.gas.from.various.locations..Any.unusual.flow.could.indicate.problems..For.instance,.an.abnormal.increase.in.relief.gas.flow.could.mean.that.a.relief.valve.is.leaking.by.

During.periods.of.unusually.high.relief.gas.flow,.samples.of.the.relief.gas.may.be.taken.at.the.flare.stack.and.analyzed.in.a.lab..The.lab.tests.determine.the.makeup.of.the.gas.that.is.being.burned,.which.can.affect.the.environment.

Information.about.the.purge.gas.is.also.available.in.the.control.room..An.operator.can.check.on.which.kind.of.purge.gas.is.used.in.the.flare.stack,.and.he.can.check.the.purge.gas.flow.rate.and.the.water.seal.flow.rate.and.level.over.a.24-hour.period.to.see.if.there.are.any.unusual.trends.

31


Flare Operations, Part 1—Challenge Questions

1. Whyissteamlikelytobeusedtopurgeaflarebeforestartup?a. Tocleanlinesandequipmentb. Toestablishawatersealc. Toenablepersonneltocheckforsystemleaksd. Bothaandce. Bothbandc

2. When both steam and nitrogen are used to purge a flare system beforestartup,the___________purgeisperformedlast.

a. Nitrogenb. Steam

3. WhichofthefollowingisNOTastepinatypicalflarestartupprocedure?a. Pullingavacuumb. Establishingthewatersealc. Establishingsteamflowd. Lightingthepilots

4. Basically,an____________consistsofairandgassupplylinesandanair/gasmixerfittedwithasparkplugthatprovidesasourceofignition.

5. Afteraflareisstarted,operatorstypicallymonitor:a. Theflareflameb. Theflowrateofsteamtothesteamnozzlesc. Theflowratesofreliefgasfromvariouslocationsd. Thetemperatureoftheflaretipe. Alloftheabove



32

FlarE OPEraTIONS, ParT 2

In.addition.to.knowing.how.to.start.a.flare.and.monitor.normal.flare.operations,.op-erators.must.also.know.how.to.handle.abnormal.flare.conditions.and.how.to.shut.down.a.flare,.if.necessary..This.section.describes.typical.operator.duties.that.are.performed.outside.of.the.control.room,.abnormal.flare.conditions.and.how.to.handle.them,.and.basic.operator.responsibilities.associated.with.a.flare.shutdown.

Objectives•. Describe.typical.outside.operator.responsibilities.associated.with.normal.flare.

operation.•. Identify.some.abnormal.flare.operating.conditions.and.describe.typical.operator.

responsibilities.for.handling.them.•. Describe.basic.operator.responsibilities.associated.with.a.flare.shutdown.

Outside Operator responsibilitiesDuring.normal.flare.operation,.outside.operators.routinely.check.the.relief.system.

purge.gas.flow.rate..This.flow.rate.is.typically.indicated.on.a.flow.meter.at.the.relief.header..If.the.proper.flow.rate.is.not.maintained,.air.could.leak.into.the.system..In.ad-dition.to.the.purge.gas.flow.rate,.the.flow.rate.of.natural.gas.to.the.pilots.should.also.be.checked.

The.level.and.pressure.in.the.knockout.drum.should.also.be.checked.during.flare.operation..These.checks.are.especially.important.when.a.unit.is.upset.and.when.equip-ment.is.washed.or.steamed,.which.increases.the.amount.of.liquid.sent.to.the.knockout.drum..If.the.knockout.drum.pressure.or.level.gets.too.high,.liquid.will.remain.entrained.in.the.relief.gases.and.be.carried.over.to.the.water.seal..This.would.add.liquid.that.may.contain.oil.and.other.contaminants.to.the.water.seal.

Operators.should.check.the.lubricating.oil.level.for.the.knockout.drum.pump,.and.they.should.check.the.pump.for.abnormal.conditions.such.as.leaks.and.for.unusual.noises.and.vibration.

Another.check.that.operators.must.make.is.at.the.water.seal..A.sight.glass.is.typically.used.to.check.the.seal.level..A.normal.operating.level.will.ensure.that.air.will.not.enter.the.relief.system.

In.the.online.course,.the.operator.double-checked.the.operation.of.the.level.instru-mentation. by. touching. the. stack. where. the. appropriate. water. level. should. be.. The.stack.should.be.relatively.cool.up.to.the.water.seal.level..Above.the.water.level,.it.will.be.relatively.warmer..The.physical.location.of.the.water.level.can.then.be.compared.to.the.sight.glass.reading..A.flow.meter.at.the.water.seal.may.be.checked.to.see.if.the.makeup.water.flow.is.at.the.proper.rate..If.there.is.not.enough.makeup.water,.the.seal.

33


level.will.drop,.and. its.effectiveness.will.be.reduced..A. level. that. is. too. low.will.not.quench.a.flame..Too.much.makeup.water.generates.excess.water.that.is.usually.con-taminated.by.relief.gases.and.must.be.treated.

Accumulations. of. scale,. other. solids,. and. liquid. hydrocarbons. in. the. water. seal.can.also.obstruct.various.lines,.such.as.connections.for.level.instrumentation.and.the.overflow.line..To.prevent.this.problem,.the.water.seal.lines.are.periodically.steamed.to.remove.any.accumulations..

The.operator. in. the.online.course.was.able. to. look. into.a.“bull’s-eye”. to.observe.signs.of.water.contamination..At.the.seal.outlet,.the.water.may.be.sampled.(Figure.23).and.tested.periodically.to.determine.the.degree.of.contamination.it.contains.

Figure 23. Sampling the Water Seal

If.testing.indicates.too.much.seal.water.contamination,.an.operator.may.be.able.to.correct.the.problem.by.increasing.the.fresh.water.flow.to.the.seal..When.this.is.done,.the.seal.is.allowed.to.overflow.until.the.fresh.water.displaces.the.contaminated.water.

The.buildup.of.solids.and.oil.can.also.be.a.problem.for.the.stack.seal..Such.accumu-lations.can.interfere.with.the.flow.of.gas.to.the.flare.tip..In.some.cases,.the.stack.seal.is.steamed.regularly.to.keep.it.clean.

abnormal ConditionsMost. of. an. operator’s. responsibilities. are. routine. ones.. In. some. cases,. however,.

unusual.conditions.require.actions.that.are.not.routine..Operators.must.be.prepared.to.deal.with.these.unanticipated.occurrences.quickly.and.safely.

Loss of Flare Stack Gas PurgeOne.abnormal.condition.that.may.occur.is.the.loss.of.the.flare.stack.gas.purge..Usu-

ally,.nitrogen.and.natural.gas.are.both.available.to.purge.the.stack..As.soon.as.the.purge.loss.is.detected,.valves.must.be.lined.up.to.switch.to.another.available.purge.gas..The.failed.purge.gas.line.should.be.blocked.in,.and.the.problem.should.be.found.and.corrected.as.soon.as.possible.


34

Loss of Pilot FlamesThe.loss.of.pilot.flames.is.another.problem.that.demands.immediate.attention..Sev-

eral.conditions.can.cause.a.pilot.flame.to.go.out..For.example,.if.the.pilot.gas.flow.is.too.high,.the.pilot.flames.can.lift.off.of.the.pilot.tips.and.blowout..If.the.gas.flow.to.the.pilots.is.too.low,.the.flames.can.burn.down.inside.the.pilot.tips,.where.they.would.be.extinguished.

If.all.of. the.pilots.go.out.during.operation,. the.units.venting. to. the.flare.must.be.notified,.and.environmental.personnel.must.be.contacted..An.emergency.alarm.may.have.to.be.sounded.to.notify.other.plant.personnel,.depending.on.factors.such.as.the.amount.of.material. that.can. leave.the.flare.unburned,. the.speed.with.which.the.af-fected.unit.can.stop.venting,.and.how.quickly.the.pilots.can.be.relit.

In.general,.chances.are.good.that.if.one.or.more.pilots.go.out,.quickly.troubleshoot-ing.the.cause.of.the.problem.will.avoid.an.emergency.situation..The.pilot.gas.pressure.and.flow.rate.should.be.checked,.and.it.may.also.be.necessary.to.check.the.pressure.and.flow.rate.of.the.natural.gas.used.to.purge.the.flare.stack.

Abnormal Steam FlowAbnormal.steam.flow.to.the.flare.can.also.create.problems..If.too.little.steam.is.sent.

to.the.flare,.unburned.materials.can.be.released.into.the.atmosphere..Too.much.steam.can.put.out.the.pilots,.with.the.same.results..

An.interruption.in.steam.flow.could.indicate.problems.with.the.steam.supply,.such.as.a.down.or.malfunctioning.boiler..If.the.steam.supply.is.normal,.then.the.positions.of.the.steam.line.block.valves.and.the.operation.of.the.control.valves.should.be.checked..Steam.traps.may.also.be.checked.for.proper.operation..If.the.problem.is.not.found,.ap-propriate.personnel.may.have.to.clean.the.steam.flow.monitor.lens.and.adjust.or.align.the.steam.control.system.

Abnormal Water Seal LevelAt.the.flare,.another.abnormal.condition.that.may.be.encountered.is.an.abnormally.

high.or.low.water.seal.level..A.low.level.can.easily.be.corrected.by.simply.increasing.the.makeup.water.rate.

A.high.water.seal.level.may.be.caused.by.a.blocked.outlet.line.or.by.excessive.liquid.carryover.from.the.knockout.drum..The.high.level.can.cause.excessive.backpressure.in.the.relief.system.and.create.resistance.to.gas.flow.through.the.system..In.extreme.circumstances,.the.water.level.can.eventually.reach.the.flare.tip..If.the.water.contains.hydrocarbons,.it.can.be.ignited.and.then.spew.from.the.flare.tip.

If.the.water.seal. level. is.too.high,.the.makeup.water.flow.rate.should.be.verified..If.necessary,.the.flow.rate.should.be.reduced.or.shut.off..Valves.can.be.positioned.to.supply.steam.to.the.outlet.line.to.remove.any.blockages.

35


Flare ShutdownTo.handle.certain.abnormal.conditions.or. to.allow. for. repairs. to.be.made,.opera-

tors.may.be.required.to.shut.down.a.flare..In.some.cases,.the.unit.relief.systems.that.use.the.flare.can.be.rerouted.to.a.second.flare.that.is.isolated.from.the.first.one,.and.then.the.first.flare.can.be.shut.down..If.a.second.flare.is.not.available.or.rerouting.is.not.possible,.the.units.whose.relief.systems.use.the.flare.have.to.be.shut.down.and.depressurized.before.the.flare.is.shut.down.

After. the.flare.has.been. isolated. from.the.relief.systems.and.the.knockout.drum,.the.natural.gas.pilots.must.be.isolated..The.purge.gas.at.the.base.of.the.flare.must.be.stopped,.the.water.to.the.water.seal.must.be.isolated,.and.the.steam.to.the.flare.tip.must.be.isolated..Additional.cleanup.steps.may.be.necessary.to.complete.the.shut-down.according.to.company.procedures.


36

Flare Operations, Part 2—Challenge Questions

1. Typicaloutsideoperatorresponsibilitiesduringnormalflareoperationin-cludechecking:

a. Thereliefsystempurgegasflowrateb. Theknockoutdrumlevelandpressurec. Theknockoutdrumpumplubricatingoilleveld. Thewaterseale. Alloftheabove

2. Ifallofthepilotflamesgooutduringflareoperation:a. Theunitsventingtotheflaremustbenotifiedb. Environmentalpersonnelmustbecontactedc. Anemergencyalarmmayhavetobesoundedtonotifyotherplant

personneld. Alloftheabove

3. Iftoolittlesteamissenttoaflare,unburnedmaterialscanbereleasedintotheatmosphere.

a. Trueb. False

4. An abnormally low water seal level can be corrected by increasing the____________flowrate.

5. WhichofthefollowingstepsistypicallyNOTpartofaflareshutdownproce-dure?

a. Reroutingsystemsthatventtotheaffectedflareb. Establishingawatersealc. Isolatingtheflarefromthereliefsystemsandtheknockoutdrumd. Isolatingthenaturalgaspilotse. Stoppingthepurgegasatthebaseoftheflaref. Isolatingthesteamtotheflaretip


37


aNSWErS TO CHallENGE QuESTIONS

General Considerations

1.. Three.considerations.associated.with.handling.waste.gases.are.safety,.health.protection,.and.cost.

2.. Purging.is.the.removal.of.hazardous.materials.from.piping.and.equipment.with.a.gas.or.vapor.to.prevent.the.formation.of.explosive.mixtures.

3.. c. The.basic.purpose.of.venting.is.to.release.waste.gases.and.purge.gases.

4.. a.(True)

5.. b. Waste.gases.that.exceed.the.handling.capacity.of.a.relief.system’s.vapor.recov-

ery.unit.are.generally.sent.to.a.flare.

Venting

1.. d. Tasks.that.typically.require.venting.to.avoid.damaging.equipment.include.filling.

a.tank,.steam.cleaning.a.tank,.and.draining.a.tank

2.. a.(True)

3.. Open.vents.are not.generally.used.on.equipment.that.handles.hazardous.ma-terials.

4.. d. To. help. ensure. that. equipment. is. safely. vented,. operators. should. know. the.

pressure. ratings.of. the.equipment. in. their.area,.know.the.pressures.at.which.pressure-controlled.vent.valves.and.emergency.vent.valves.operate,.and.keep.track.of.vent.problems.

Purging

1.. a. Nitrogen.is.often.used.for.purging.because.it.is.inert.

2.. Two.methods.that.are.commonly.used.to.purge.equipment.are.the.continuous.purge.(sweep).method.and.the.fixed.volume.(pop.and.purge).method.


38

3.. Inerting, or blanketing,.is.the.process.of.maintaining.a.nonreactive.atmosphere.inside.equipment.after.the.equipment.has.been.purged.of.undesirable.materials.

4.. c. Danger.of.explosion. is.not.a.safety.concern. related. to. the.use.of.nitrogen. for.

purging.

5.. d. Operator. responsibilities. associated. with. purging. typically. include. installing.

blinds,.performing.valve.lineups,.and.checking.for.leaks.

Flare System

1.. b.(False)

2.. b. A.water seal.is.basically.a.reservoir.of.water.that.quenches.any.flame.that.may.

result.from.the.ignition.of.a.mixture.of.flammable.gases.and.air.in.a.flare.stack.

3.. a. When.fuel.gas.is.used.as.the.purge.gas.in.a.flare.system,.it.maintains.a.fuel-rich.

mixture.that.reduces.combustion.hazards.and.helps.to.maintain.the.flare.flame.during.periods.of.low.relief.gas.flow..It.does.not.promote.the.backflow.of.air.into.the.stack.

4.. b. The.function.of.the.flare.tip.is.to.mix.air.with.the.relief.gas.in.order.to.promote.

complete.and.smokeless.gas.burning.

5.. b.(False)

Flare Operations, Part 1

1.. d. Steam.is.likely.to.be.used.to.purge.a.flare.before.startup.to.clean.lines.and.equip-

ment.and.to.enable.personnel.to.check.for.system.leaks.

2.. a. When.both.steam.and.nitrogen.are.used.to.purge.a.flare.system.before.startup,.

the.nitrogen.purge.is.performed.last.

3.. a. Pulling.a.vacuum.is.NOT.a.step.in.a.typical.flare.startup.procedure.

4.. Basically,.an.ignitor station.consists.of.air.and.gas.supply.lines.and.an.air/gas.mixer.fitted.with.a.spark.plug.that.provides.a.source.of.ignition.

39


5.. d. After.a.flare.is.started,.operators.typically.monitor.the.flare.flame,.flow.rate.of.

steam.to.the.steam.nozzles,.flow.rates.of.relief.gas.from.various.locations,.and..temperature.of.the.flare.tip

Flare Operations, Part 2

1.. e. Typical.outside.operator.responsibilities.during.normal.flare.operation.include.

checking.the.relief.system.purge.gas.flow.rate,.knockout.drum.level.and.pres-sure,.knockout.drum.pump.lubricating.oil.level,.and.water.seal.

2.. d. If.all.of.the.pilot.flames.go.out.during.flare.operation,.the.units.venting.to.the.

flare. must. be. notified,. environmental. personnel. must. be. contacted,. and. an.emergency.alarm.may.have.to.be.sounded.to.notify.other.plant.personnel.

3.. a.(True)

4.. An.abnormally.low.water.seal.level.can.be.corrected.by.increasing.the.makeup water.flow.rate.

5.. b. Establishing.a.water.seal.is.typically.NOT.part.of.a.flare.shutdown.procedure.


40

GlOSSary

This.glossary.contains.terms.pertinent.to.the.study.of.flaring,.venting,.and.purging..The.meanings.of.the.terms.are.given.in.that.context.

Blanketing.–.See.Inerting.

Conservation vent.–.A.valved.vent.that.is.weighted.to.relieve.pressure.at.a.preset.value.after.allowing.vapor.to.accumulate.within.a.safe.pressure.range.

Continuous purge method. –. A. purging. method. in. which. the. purging. material. is.continuously.supplied.to.a.piece.of.equipment.until. testing. indicates.that. the.equipment’s.atmosphere.is.free.of.undesirable.materials..Also.called.the.sweep.method.

Fixed volume method.–.A.purging.method.in.which.the.purging.material.is.sent.to.a.piece.of.equipment.until.a.certain.pressure.is.reached..After.the.pressure.is.held.for.a.designated.period.of.time,.a.vent.on.the.equipment.is.opened.to.release,.or.pop,.the.contents.out.of.the.equipment..The.vent.is.closed.before.pressure.in.the.equipment.drops.to.atmospheric.pressure..The.steps.are.repeated.until.the.amount.of.undesirable.material. in. the.equipment.has.been.reduced. to.a.safe.level..Also.called.the.pop.and.purge.method.

Flame front generator.–.See.Ignitor.station.

Flare. –. A. flame. that,. when. operated. properly,. will. safely. dispose. of. combustible.gases.by.burning.them.

Flaring.–.The.process.of.disposing.of.combustible.gases.by.burning.them.

Hatch-type emergency vent.–.A.type.of.vent.that.typically.uses.a.spring.or.a.weight-ed.pallet.to.open.the.vent.when.the.pressure.in.a.tank.gets.too.high.

Ignitor station.–.A.device.used.to.light.the.pilots.for.a.flare.

Inerting.–.The.process.of.using.nitrogen.or.another.inert.gas.to.maintain.a.nonreac-tive.atmosphere.in.a.piece.of.equipment.after.purging..Also.called.blanketing.

Knockout drum.–.A.piece.of.equipment.that.removes.liquid.entrained.in.gas.

Pipeaway vent.–.A.type.of.vent.that.opens.to.allow.vapor.to.leave.through.piping.for.treatment.or.disposal.

41


Pop and purge method –.See.Fixed.volume.method.

Purging.–.The.removal.of.hazardous.materials.from.piping.and.equipment.with.a.gas.or.vapor.to.prevent.the.formation.of.explosive.mixtures.

relief system.–.A.collection.of.vessels,.piping,.and.equipment.designed.to.handle,.recover,.or.dispose.of.gas.released.from.process.equipment.

relief valve.–.A.type.of.emergency.vent.valve.that.opens.when.pressure.overcomes.the.force.of.an.internal.spring.

rupture disc.–.A.type.of.emergency.vent.that.bursts.open.to.vent.gas.and.relieve.excess.pressure.

Sweep method.–.See.Continuous.purge.method

Venting.–.The.process.of.removing.waste.gases.from.vessels.and.equipment.by.re-leasing.them.through.openings,.or.vents.

otfvp00-1111cen_flare & vent

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