overpressure protection

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Design forOverp ressure and

UnderpressureProtect ion

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SLIDE PRESENTATION

Design for

Overp ressu re andUnderpressure

Protect ion

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Outline• Introduction

• Causes of Overpressure andUnderpressure

• Reliefs• Effluent Handling Systems for

Reliefs

• Runaway Reactions

• Overpressure Protection forInternal Fires and Explosions

Introduction

Reliefs

Runaways

Safeguards



For Further Information:Refer to the Appendix

Supplied with this Presentation

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Causes of Overpressure

• Operating Problem

• Equipment Failure

• Process Upset

• External Fire

• Utility Failures

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Causes of Underpressures



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Presentation 1 of 3: Reliefs

Causes of

Overpressure/Underpressure

Presentation 1: Reliefs

Presentation 2: Runaways

Presentation 3: Safeguards Home

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Pressure Relief Devices

• Spring-Loaded Pressure Relief Valve

• Rupture Disc

• Buckling Pin

• Miscellaneous Mechanical

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Spring-LoadedPressure Relief Valve

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Rupture Disc

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Buckling Pin Relief Valve

ClosedPressure Below

Set Pressure

Full OpenPressure at or Above

Set Pressure(Buckles in Milliseconds at a Precise Set Pressure)

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Simple Mechanical

Pressure Relief

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Types of Spring-Loaded

Pressure Reliefs• Safety Valves for Gases and Vapors

• Relief Valves for Liquids

• Safety Relief Valves for Liquids

and/or Gases

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Types of Safety Valves

• Conventional

• Balanced Bellows, and• Pilot-Operated

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Conventional Safety Valve

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Balanced Bellows Safety Valve

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Pilot-Operated Safety Valve

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Types of Relief Valves

• Conventional

• Balanced Bellows

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Types of Rupture Discs

• Metal

• Graphite

• Composite

• Others

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Rupture Disc and PressureRelief Valve Combination

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Vacuum Relief Devices

• Vacuum Relief Valves

• Rupture Discs

• Conservation Vents

• Manhole Lids

• Pressure Control

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Conservation Vent

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Pressure or Vacuum Control

• Add Air or Nitrogen

• Maintain Appropriately

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Relief Servicing

• Inspection

• Testing

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Relief Discharges

• To Atmosphere

• Prevented

• Effluent System

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Effluent Systems

• Knock-Out Drum

• Catch Tank

• Cyclone Separator

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Effluent System (continued)

• Condenser

• Quench Tank

• Scrubber

• Flares/Incinerators

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Effluent Handling System

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Presentation 2 of 3: Runaways

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Causes of




Presentation 3: Safeguards



Runaway Reaction

• Temperature Increases

• Reaction Rate Increases

• Pressure Increases

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Causes of Runaway Reactions

• Self-Heating• Sleeper

• Tempered

• Gassy

• Hybrid

Characteristics of Runaway

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Self-Heating Reaction

• Loss of Cooling

• Unexpected Addition of Heat

• Too Much Catalyst or Reactant

• Operator Mistakes

• Too Fast Addition of Catalyst or Reactant

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Sleeper Reactions

• Reactants Added But Not Mixed

(Error)

• Reactants Accumulate

• Agitation Started .. Too Late

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Tempered Reaction

• Heat Removed by Evaporation

• Heat Removal Maintains a Constant

Temperature

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Gassy System

• No Volatile Solvents

• Gas is Reaction Product

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Hybrid System

• Tempered

• Gassy

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Reliefs for Runaway Reactions

• Two Phase (or Three Phases:

Liquid, Vapor, and Solid) Flow

• Relief Area: 2 to 10 Times theArea of a Single Gaseous Phase

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Two Phase Flow

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Relief Valve Sizing

Methodology• Special Calorimeter Data

• Special Calculation Methods

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Characterization of

Runaway Reactions• ARC

• VSP• RSST

• APTAC

• PHI-TEC• Dewars

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Presentation 3 of 3:Safeguards

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Causes of







Safeguards

• Safety Interlocks

• Safeguard Maintenance System

• Short-Stopping

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Safety Interlocks

• Agitator Not Working: Stop Monomer

Feed and Add Full Cooling

• Abnormal Temperature: StopMonomer Feed and Add Full Cooling

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Safety Interlocks

(continued)• Abnormal Pressure: Stop Monomer Feed

and Add Full Cooling

• Abnormal Heat Balance: Stop MonomerFeed and Add Full Cooling

• Abnormal Conditions: Add Short-Stop

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Safeguard Maintenance

System• Routine Maintenance

• Management of Change

• Mechanical Integrity Checks

• Records

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Short-Stops to Stop Reaction

• Add Reaction Stopper

• Add Agitation with No Electrical

Power

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Protection for Internal

Fires and Explosions

• Deflagrations

• Detonations

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Protection Methods for

Internal Fires and Explosions

• Deflagration Venting

• Deflagration Suppression

• Containment

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Internal Fires and Explosions(continued)

• Reduction of Oxidant

• Reduction of Combustible

• Flame Front Isolation

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Internal Fires and Explosions(continued)

• Spark Detection and Extinguishing

• Flame Detection and Extinguishing

• Water Spray and Deluge Systems

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Deflagration Venting

• Vent Area via NFPA 68

• Vent Safely

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Vent of Gas Deflagration

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Vent of Dust Deflagration

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Deflagration SuppressionSystem

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Containment

• Prevent Rupture and Vessel

Deformation

• Prevent Rupture but Deform

Vessel

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Reduction of Oxidant

• Vacuum Purging

• Pressure Purging

• Sweep-Through Purging

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Reduction of Combustible

• Dilution with Air

• NFPA 69

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Flame Front Isolation

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S k/Fl D t ti



Spark/Flame Detectionand Extinguishing

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Water Spray orDeluge Systems

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Conclusion

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End of Slide Presentation

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SLIDES WITH TEXT



This presentation includes technical information

concerning the design for overpressure and

underpressure protection. The presentation is designed

to help students and engineers to: Slide



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• Understand the root causes of overpressure and

underpressure incidents, and

• Design plants with the appropriate features to protect

against overpressure and underpressure incidents. Slide



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Six Sections

1. Introduction2. Causes of Overpressure and

Underpressure

3. Reliefs

4. Effluent Handling Systems for Reliefs

5. Runaway Reactions, and

6. Overpressure Protection for Internal Fires

and Explosions

This presentation is divided into six sections:

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Six Sections


Underpressure

3. Reliefs




and Explosions

The “Introduction” button on your left will lead you to this

introduction and an explaination of the Causes of

Overpressure and Underpressure

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Six Sections


Underpressure

3. Reliefs




and Explosions

The “Reliefs” Button sends you to Sections 3 and 4,

covering Reliefs and Effluent Handling Systems for

Reliefs

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Six Sections


Underpressure

3. Reliefs




and Explosions

The “Runaways” Button leads to a discussion on

Runaway Reactions, and . . .

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Underpressure

3. Reliefs




and Explosions

The “Safeguards” Button will take you to a section on

Overpressure Protection fot Internal Fires and

Explosions

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Appendix ContainsDetailed Information

This design package includes an appendix with detailed

information for each of the sections of this presentation.

The appendix also includes an extensive list of relevant

references. Slide



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The major causes of overpressure include:• Operating problems or mistakes such as an operator mistakenly

opening or closing a valve to cause the vessel or system pressure toincrease. An operator, for example, may adjust a steam regulator togive pressures exceeding the maximum allowable working pressure

(MAWP) of a steam jacket. Slide



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Although the set pressure is usually at the MAWP, the design safety

factors should protect the vessel for higher pressures; a vessel fails when

the pressure is typically several times the MAWP.

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• Equipment failures; for example a heat exchanger tube rupture that

increases the shell side pressure beyond the MAWP. Although the set

pressure is usually the MAWP, the design safety factors should protect

the vessel for higher pressures; a vessel fails when the pressure is

typically several times the MAWP. Slide



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• Process Upset

• External Fire

• Utility Failures• Process upset; for example a runaway reaction causing high

temperatures and pressures.

• External heating, such as, a fire that heats the contents of a vesselgiving high vapor pressures, and

• Utility failures, such as the loss of cooling or the loss of agitation

causing a runaway reaction. Slide



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The causes of underpressure or the inadvertent creation of avacuum are usually due to operating problems or equipmentfailures.

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• Operating problems include mistakes such as pumping liquidout of a closed system, or cooling and condensing vapors in aclosed system.

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• Equipment failures include an instrument malfunction (e.g.vacuum gage) or the loss of the heat input of a system thatcontains a material with a low vapor pressure.

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Part 1 of 3: Reliefs

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Pressure relief devices are added to process equipment toprevent the pressures from significantly exceeding the MAWP(pressures are allowed to go slightly above the MAWP duringemergency reliefs).

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• Spring-Loaded Pressure Relief Valve

• Rupture Disc

• Buckling Pin

• Miscellaneous Mechanical

The pressure relief devices include spring-loaded pressure reliefvalves, rupture discs, buckling pins, and miscellaneousmechanical devices.

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Spring Loaded



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Spring-LoadedPressure Relief Valve

This is a sketch of a spring-loaded pressure relief valve. As thepressure in the vessel or pipeline at point A exceeds thepressure created by the spring, the valve opens. The reliefbegins to open at the set pressure which is usually at or belowthe MAWP; this pressure is usually set at the MAWP.

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Rupture Disc

This is a sketch of a rupture disc. In this case the disc ruptureswhen the pressure at A exceeds the set pressure. Recognize,however, that it is actually the differential pressure (A-B), thatruptures the disc.

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Set Pressure


Set Pressure

(Buckles in Milliseconds at a Precise Set Pressure)

This sketch shows a buckling pin pressure relief valve. Asshown, when the pressure exceeds the set pressure, the pinbuckles and the vessel contents exit through the open valve.

The rupture disc and the buckling pin relief valves stay open

after they are opened. Slide



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Set Pressure


Set Pressure

(Buckles in Milliseconds at a Precise Set Pressure)

The spring operated valves close as the pressure decreases

below the “blowdown” pressure. The blowdown pressure is the

difference between the set pressure and closing pressure.

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Si l M h i l



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Simple MechanicalPressure Relief

A simple mechanical pressure relief is a weighted man-waycover as shown in this sketch. Another mechanical relief is a U-tube filled with water (or equivalent).

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T f S i L d d



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Types of Spring-Loaded

Pressure Reliefs

• Safety Valves for Gases and Vapors

• Relief Valves for Liquids

• Safety Relief Valves for Liquids

and/or Gases

There are three types of spring-loaded pressure relief valves:

• Safety valves are specifically designed for gases.

• Relief valves are designed for liquids, and

• Safety relief valves are designed for liquids and/or gases.

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Conventional Safety Valve

A conventional safety valve is designed to provide full opening

with minimum overpressure. The disc is specially shaped to

give a “pop” action as the valve begins to open.

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A balanced bellows safety valve is specially designed to reducethe effect of the back pressure on the opening pressure. Asillustrated in this sketch the differential pressure that is requiredto open the valve is the pressure inside the vessel minus theatmospheric pressure.

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The bellows design allows the outside air and pressure to be onthe downstream side of the valve seal. Once the relief is open,then the flow is a function of the differential pressure A-B.

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A pilot-operated safety valve is a spring-loaded valve. Asillustrated, the vessel pressure helps to keep the valve closed.When the pressure exceeds the set pressure (or the springpressure), the pressure on top of the valve is vented and thevalve opens.

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The set pressure of this type of valve can be closer to theoperating pressure compared to conventional and balancedbellows valves. The disadvantages, however, are (a) theprocess fluid needs to be clean, (b) the seals must be resistantto the fluids, and (c) the seals and valves must be appropriately

maintained. Slide



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These disadvantages are also true for spring operated reliefs.Pilot-operated valves are not used in liquid service; they arenormally used in very clean and low pressure applications.

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Types of Relief Valves

• Conventional

• Balanced Bellows

Relief valves (for liquid service) are either the conventional or

the balanced bellows types.

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• Metal

• Graphite

• Composite

• Others

As illustrated, there are many different types of rupture discs.

They are especially applicable for very corrosive environments;

for example: discs made of carbon or Teflon coating are used

for corrosive service.

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• Metal

• Graphite

• Composite

• Others

A rupture disc that is used for pressure reliefs may need a

specially designed mechanical support if it is also used in

vacuum service.

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Rupture Disc and Pressure



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Rupture discs, as illustrated, are sometimes used incombination with a spring operated relief device. In this casethe disc gives a positive seal compared to the disc-to-sealdesign of a spring operated valve.

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This is useful when handling very toxic materials where even avery small release (through the seal) may be hazardous, orwhen handling materials that polymerize.

The spring operated relief following the rupture disc reseatswhen the pressure drops below the blow-down pressure.

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This design, therefore, stops the discharge from the vessel.The discharge is not stopped if only a rupture disc is used. Thisdesign (rupture disc followed by a spring-operated relief) isdiscouraged by some practitioners.

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In this design, as illustrated, a pressure detection device (per ASME Code), e.g., a pressure indicator, needs to be placedbetween the disc and the spring-operated valve. This pressurereading is checked periodically to be sure the rupture disc hasits mechanical integrity.

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A pin-hole leak in the rupture disc could increase the pressureon the discharge side of the disc. This is a major problembecause it increases the relief pressure, that is: the differentialpressure across the disc is the rupturing mechanism.

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Another major problem with this design is the possibility that apiece of the rupture disc could plug the discharge orifice of thespring operated relief. This problem is prevented by specifyinga rupture disc that will maintain its integrity when it is ruptured;that is, non-fragmenting.

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Vacuum Relief Devices

• Vacuum Relief Valves

• Rupture Discs

• Conservation Vents

• Manhole Lids

• Pressure ControlVacuum relief devices are: vacuum relief valves, rupture discs,

conservation vents, manhole lids designed for vacuum relief,

and pressure control.

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Conservation Vent

A conservation vent is illustrated in this sketch. As shown, it isdesigned to relieve a pressure usually for pressures in theregion of 6 inches of water. It is also designed to let air into thevessel to prevent a vacuum, usually a vacuum no more than 4inches of water.

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Pressure or Vacuum Control

• Add Air or Nitrogen

• Maintain Appropriately

Sometimes pressure or vacuum control systems are used to add air or

nitrogen to the vessel to maintain a slight pressure. In this case, the

system needs to be appropriately maintained because a malfunction

could result in an overpressure or underpressure. In either case the

consequence could be a ruptured vessel.Slide



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Relief Servicing

• Inspection

• Testing

Every relief device needs to be inspected and tested beforeinstallation and then at predetermined intervals during itslifetime. The interval depends on the service history, vendorrecommendations, and regulatory requirements, but it is usuallyonce a year.

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Relief Servicing

• Inspection

• Testing

Operating results and experience may indicate shorter or longerintervals.

Records must be carefully maintained for every inspection andtest, and for the entire life of the plant.

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Relief Discharges

• To Atmosphere

• Prevented

An additional option is to prevent releases by (a) designing

vessels with high MAWPs to contain all overpressure scenarios,

or (b) add a sufficient number of safeguards and/or controls to

make overpressure scenarios essentially impossible.

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Effluent System (continued)

• Condenser

• Quench Tank

• Scrubber

• Flares/Incinerators

• Condenser• Quench tank• Scrubber, and/or• Flares or incinerators

An effluent handling system may have any combination of the above unit

operations. Slide

Effl t H dli S t



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One effluent handling system is illustrated in this sketch. Everyelement of an effluent system needs to be designed verycarefully. The design requires detailed physical and chemicalproperties, and the correct design methodology for each unitoperation.

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Effl t H dli S t



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It should also be recognized that it is important to size the reliefappropriately, because the size of the entire effluent system isbased on this discharge rate. The design methodology is in thereferences noted in the Appendix of this package.

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Part 2 of 3: Runaways

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R R i



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Runaway Reaction

• Temperature Increases

• Reaction Rate Increases

• Pressure Increases

A runaway reaction is an especially important overpressure scenario. Arunaway reaction has an accelerating rate of temperature increase, rateof reaction increase, and usually rate of pressure increase. Thepressure, of course, increases if the reaction mass has a volatilesubstance, such as, a solvent or a monomer; or if one of the reaction

products is a gas. Slide



Causes of Runaway Reactions



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Causes of Runaway Reactions• Self-Heating

• Sleeper

• Tempered

• Gassy

• Hybrid

Characteristics of Runaway

When protecting a system for overpressures due to runaway reactions

the engineer needs to know the type of runaway and needs to

characterize the behavior of the specific runaway with a special

calorimeter. This specific methodology is described in this section of this

presentation.

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S lf H ti R ti



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Self-Heating Reaction

• Loss of Cooling

• Unexpected Addition of Heat

• Too Much Catalyst or Reactant

• Operator Mistakes

• Too Fast Addition of Catalyst or Reactant

One self-heating scenario occurs when the reaction is

exothermic and a loss of cooling gives an uncontrolled

temperature rise. A few causes of self-heating scenarios are

shown.

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Sleeper Reactions


(Error)

• Reactants Accumulate• Agitation Started .. Too Late

Sleeper reactions are usually the result of an operator error. Two

examples include: (a) the addition of two immiscible reactants when the

agitator is mistakenly in the off position, and (b) the addition of a reactant

to the reaction mass when the temperature is mistakenly lower than that

required to initiate the reaction.

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Sleeper Reactions


(Error)

• Reactants Accumulate• Agitation Started .. Too Late

In these cases the runaway is initiated by starting the agitatorand adding heat respectively.

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T d R ti



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Tempered Reaction

• Heat Removed by Evaporation

• Heat Removal Maintains a Constant

Temperature

Tempered runaway reactions maintain their temperature when the energyexiting the relief device is equal to the energy generated in the reactordue to the exothermic reaction. The reaction heat is absorbed by theevaporation of the volatile components. The vapor pressure in atempered system can typically be characterized by an Antoine type

equation. Slide

G S t



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Gassy System

• No Volatile Solvents

• Gas is Reaction Product

A system that is characterized as “gassy” has no volatile

solvents or reactants. The pressure build-up is due to the

generation of noncondensible gas such as N2 or CO2.

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Under runaway conditions, when the relief device opens, the

relief discharge is a foam; that is, the gases are entrained with

the liquid.

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To maintain a constant temperature in the reactor (i.e. control the

runaway reaction), the relief valve is sized to remove all the heat

generated from the exothermic reaction via the heat removed with the

discharged mass, which is typically a foam. Detailed information on

runaway reactions is found in the appendix.

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Two Phase Flow



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Two Phase Flow

This is a picture that illustrates the two-phase flowcharacteristics of a relief discharge due to a runaway reaction.

As illustrated, the discharge is similar to the release of foamfrom a freshly opened bottle of pop after being shakened. If therelief is not designed for two-phase flow, the pressures would

increase rapidly and the vessel could rupture. Slide

Relief Valve Sizing



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g

Methodology

• Special Calorimeter Data

• Special Calculation Methods

The relief valve sizing methodology for runaway reactions isvery complex. It requires the characterization of the runawayreaction using a specially designed calorimeter.

Relief valve sizing, additionally, requires special calculationmethods that are described in the Appendix of this package.

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Characterization of



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Runaway Reactions

The characterization of runaway reactions includes thedetermination of the rates of rise of the temperature andpressure under adiabatic conditions. The test results alsocharacterize the reaction type, that is, tempered, gassy, and/ora hybrid system.

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Characterization of



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Runaway Reactions

• ARC

• VSP

• RSST

Various calorimeters are used for this characterization:

• The accelerating rate calorimeter (ARC)

• The vent sizing package (VSP)

• The reactive system screening tool (RSST)

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Characterization of



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Runaway Reactions

• ARC

• VSP

• RSST

• APTAC

• PHI-TEC

• Dewars

• The automated pressure-tracking adiabatic calorimeter (APTAC)

• The Phi-Tec, and

• Dewars.

Each of these calorimeters have advantages and disadvantagesthat need to be understood when studying a specific system.

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Part 3 of 3: Safeguards

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Safeguards



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Safeguards

This section of the presentation covers safeguards. Safeguardsinclude the methods and controls used to prevent runaways. Asillustrated previously, a containment system (a safeguard), canbe very complex and expensive. Alternatively, a series ofsafeguards may be justified.

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Safeguards



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Safeguards

• Safety Interlocks

• Safeguard Maintenance System

• Short-Stopping

Safeguards include safety interlocks, safeguard maintenancesystem, and/or short-stopping.

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Safety Interlocks



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Safety Interlocks

• Agitator Not Working: Stop Monomer

Feed and Add Full Cooling

• Abnormal Temperature: StopMonomer Feed and Add Full Cooling

The list of alternative interlocks is fairly extensive. Usually more than one

interlock and some redundancy and diversity is required for each

runaway scenario. As the number of interlocks increases, the reliability of

the system increases. These are examples of safety interlocks for a

semibatch polymerization reactor.

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System

• Routine Maintenance



• Records

A safeguard maintenance system includes routine maintenance,management of change, mechanical integrity checks, and theappropriate records. These are the steps that are required tobe sure the safeguards and interlocks perform appropriatelyunder emergency conditions and/or potential runaway reactionscenarios.

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System

• Routine Maintenance



• Records

The maintenance of safeguard systems is especially important, because:• Safeguards and interlocks do not operate on a day-to-day basis, but• When they are required to operate (emergency conditions) they need

to operate flawlessly.See ISA SP 84.01 for details for the design of safety instrumentedsystems.

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Power

A short-stopping system, stops a runaway reaction by adding areaction stopper solution to the reacting mass. The reaction-stopperstops the reaction in time to short-circuit the progress of thereaction. A reaction stopper needs to be added when the reactionmass is relatively cold. If the mass is too hot, a short-stopper willnot work.

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Power

Good agitation, of course, is required to adequately mix the reactionmass with the inhibitor. Since a power failure is often the initiatingevent of a runaway, an alternative method of agitation needs to beincluded in the design. A compressed nitrogen system together witha sparge ring is one alternative.

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• Deflagrations

• Detonations

This section of the presentation covers protection methods forinternal fires and explosions.

Overpressure protection is needed for process equipment thatcan potentially explode due to an internal deflagration ordetonation.

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• Deflagrations

• Detonations

A deflagration is defined as the propagation of a combustionzone at a velocity in the unreacted medium that is less than thespeed of sound. A detonation has a velocity greater than thespeed of sound in the unreacted medium.

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• Deflagrations

• Detonations

The burning material can be a combustible gas, a combustibledust, a combustible mist, or a hybrid mixture (a mixture of acombustible gas with either a combustible dust or combustiblemist). The reaction actually occurs in the vapor phase betweenthe fuel and the air or some other oxidant.

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• Deflagration Venting

• Deflagration Suppression• Containment

The protection methods used for fires or explosions include

• Deflagration venting

• Deflagration suppression

• Containment

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(continued)

• Reduction of Oxidant

• Reduction of Combustible• Flame Front Isolation

• Reduction of the oxidant

• Reduction of the combustible

• Flame front isolation

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(continued)

• Spark Detection and Extinguishing

• Flame Detection and Extinguishing

• Water Spray and Deluge Systems

• Spark detection and extinguishing

• Flame detection and extinguishing

• Water or foam spray deluge systems

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The technology required for venting deflagrations is given in

NFPA 68. Deflagration venting is usually the simplest and least

costly means of protecting process equipment against damage

due to the internal pressure rise from deflagrations.Slide




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• Vent Safely

If equipment is located inside a building, the vents must bedischarged through a vent duct system to a safe locationoutside of the building. The design of the vent duct system iscritical to avoid excessive pressures developed during theventing process. See NFPA 68 for details.

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• Vent Safely

A safe location will avoid injury to personnel and minimizedamage to equipment outside of the building. The next twopictures illustrate that the “safe venting” may not be trivial.

Slide




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This is a picture of the venting of a gas deflagration. As illustrated,the flame propagates a significant distance from the vessel. Thelength of the flame is estimated using an equation found in NFPA68. The main purpose of venting is to protect the mechanicalintegrity of the equipment. As illustrated, even when it is ventedsafely, this is a major event. Slide



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System

One alternative to venting a deflagration is suppression. This

sketch illustrates a deflagration suppression system that

includes (a) a flame or pressure detector, (b) a quick opening

valve, and (c) the addition of a flame suppressant.Slide




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System

The commonly used suppression agents include water,

potassium acid phosphate, sodium bicarbonate, and Halon

substitutes. The technology for deflagration suppression is

described in NFPA 69.Slide

Containment



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Containment

• Prevent Rupture and Vessel

Deformation

• Prevent Rupture but DeformVessel

The thickness of vessel walls may be increased to contain thepressure of a deflagration.

• The wall thickness can be large enough to prevent thedeformation of the vessel, or

• The wall thickness may be large enough to prevent a rupture, butallow the vessel to deform. Slide




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• Vacuum Purging



Protection for overpressures is also provided with an inert gasblanket to prevent the occurrence of a deflagration. Beforeintroducing a flammable substance to a vessel, the vessel mustalso be purged with an inert gas to reduce the oxidantconcentration sufficiently so that the gas mixture cannot burn.

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• Vacuum Purging



The purging methods include vacuum purging, pressurepurging, and sweep-through purging. See NFPA 69 and thebook by Crowl and Louvar for more details.

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Reduction of Combustible



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educt o o Co bust b e

• Dilution with Air

• NFPA 69

A deflagration can also be prevented by reducing the concentration

of the combustible material so that the concentration is below the

lower flammability limit (LFL). This is usually accomplished by

dilution with nitrogen. The specifications for this type system are

given in NFPA 69. Slide

Flame Front Isolation



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As illustrated, isolation devices are used in piping systems to prevent the

propagation of a flame front. The method illustrated has a fast-acting

block valve.

This isolation system prevents the propagation of the flame front; more

importantly it prevents deflagration transitions to detonations.Slide

Spark/Flame Detectionand Extinguishing



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g g

Another method of preventing the propagation of deflagrations inpipelines is the early detection and extinguishment of sparks or flames.In this type system, a detector activates an automatic extinguishingsystem that sprays water or other extinguishing agents into the fire. Thissystem is similar to the deflagration suppression system discussedpreviously.

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Water Spray orDeluge Systems

Process equipment and structures are very effectively protected against

fire by water spray or deluge systems. They can be activated manually

or automatically. They are designed to cool the equipment or structural

members so that the heat from a fire will not weaken them.

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Deluge System



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g y

This picture shows a typical deluge system in operation. In this

example, the deluge system is automatically activated when the

concentration of the flammable gas below the vessel is detected

to be at or over 25% of the lower flammability limit.Slide



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Conclusion

This concludes our technology package covering overpressure and

underpressure protection. The appendix of this package contains

more detailed information. The enclosed references contain the

state-of-the-art technology to assist engineers and students with

their detailed designs. Slide



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