1 Escola Politecnica / USP, Sao Paulo / SP / Brazil 18 th April 2006 Rupture Disks, Explosion Panels...

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Escola Politecnica / USP, Sao Paulo / SP / Brazil

18th April 2006

Rupture Disks,

Explosion Panels

& Industrial Applications

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Rupture Disks & Explosion Panels

Rupture Disks & Explosion Panels use the same calibrated membrane technology.

Opening pressure controls:

-Material thickness

-Size; open area

-Manufactured features to achieve low pressure with thicker material

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Rupture Disks are typically;

-Round shape

-Applied with custom machined holders

-Designed for burst pressures from 0.1 to 1000 Bar

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Explosion Vents are typically:

-Rectangular or round shape

-Applied with simple fabricated frames

-Designed for burst pressures from 0.05 to 0.5 Bar

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Codes & Standards:

Rupture Disks

-EN / ISO 4126 part 2,3,6 “CE” marking

-ASME Section VIII “UD” stamping

Explosion Vents

-ATEX directive 99/92/EC

-VDI 3673: 2000 revision

-NFPA 68: 2002 guideline

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Codes & Standards:

Explosion Vents

-ATEX directive 99/92/EC

- new ‘harmonized standards’ under development that will replace use of VDI 3673

-NFPA 68: 2007 revision becomes a ‘standard’

Both ATEX harmonized standards and new NFPA 68 standard set requirements for sizing & performance

of explosion panels.

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The Cost of Explosions

Explosions account for 4% of industrial damage in North America.

Overall Cost of Damages per Incident

$0 $500,000 $1,000,000$1,500,000$2,000,000$2,500,000$3,000,000

Explosion

Fire $168,000

$2.8 Million

Data from FM Global review of 2004.

Explosion cost per incident 1,600% of typical fire incident.

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Reminder of Potential Hazards

GrainPlasticPesticides & FertilizersInk, Dye and TonerPharmaceuticals

WoodSugarStarchMilk PowderCoal

Dusts, powders, pellets, grains, gases, vapors or mists

Mixed with Air:> 2 gm/m3

Dry:Low Moisture Content

Fine Particle Size:< 420 microns(or equivalent)

When the following conditions arise:

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What does it take to cause an Explosion?

Dust & Air Mixture

OxidantIgnition

ConfinementProcess Vessel

Limits gas expansion and results in pressure rise

Dust in Air

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The Task of Explosion Panels

Prevent the development of high pressure within a process enclosure.

Achieve a reduced explosion pressure, Pred within safe pressure limits.

Unvented explosion; may develop more than 10 Bar.

Vented Explosion reduces explosion pressure

Pressure

Time

Response to explosion followed by venting

Pred

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Explosion Panels: How to Achieve Acceptable Reduced Explosion

Pressure?

Combination of:

•Low opening pressure

•Fast dynamic performance

•Correct vent area / size and quantity of explosion panels

•Correct location of explosion panels

Unvented explosion; may develop more than 10 Bar.

Vented Explosion reduces explosion pressure

Pressure

Time

Response to explosion followed by venting

Pred

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Pressure?

Low opening pressure: To protect light metal enclosures, typical Pred is 0.2 Bar. Explosion Panel set pressure influences required vent area.

VDI 3673 & NFPA 68 provide method to calculate the influence of explosion panel opening pressure on vent area.

Example: Kst 200 for Cornstarch

Protection of 10 m3 outdoor cyclone, Pred 0.2 Bar

Pstat (panel opens) 0.1 Bar, required vent area is 1.32 m2

Pstat 0.15 Bar, required vent area is 1.61 m2

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Pressure?

Low opening pressure:

A lower explosion panel set pressure will result in a lower required vent area.

- this is not a linear relationship

- the explosion panel set pressure must be selected to ensure a proper margin between Pstat and normal operating pressure conditions.

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Pressure?

Fast Dynamic Performance:

Light weight explosion panels open fastest.

Codes & Standards set a target for mass to be below 10Kg per square meter.

Heavier explosion panels will have poor ‘vent efficiency’ and must be assessed a penalty = higher vent area.

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Pressure?


Weight is not the only factor.

Compare the performance of 0.1 Bar Pstat devices;

Metal Explosion Panel = 6 Kg / m2

Plastic Explosion Panel = 3 Kg / m2

Using the same Kst = 200 Cornstarch explosion in a 2.8m3 test vessel…

Pred for Metal Explosion Panel = 0.2 Bar

Pred for Plastic Explosion Panel = 0.33 Bar

The plastic explosion panel cannot behave in an elastic manner under explosion conditions & therefore its material shock strength is higher under dynamic load.

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Pressure?


Weight is not the only factor.

Explosion Panel design and material selection must be optimized for the best dynamic performance.

This is why ATEX and NFPA standards require validation of Explosion Panel design.

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Pressure?


Typical Pressure / Time response curve…

-0.02

0

0.02

0.04

0.06

0.08

0.1

0.12

-0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1

Ignition of explosion 420 msec. after injection of dust.

Vent Opens at 470 msec.

Peak pressure occurs after 491 msec.

From ignition to protection takes only 71 milliseconds in this example.

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Pressure?

Correct Vent Area / Size & Quantity of Explosion Panels:

Area calculation following VDI 3673 / NFPA 68 / ATEX harmonized standard or other method proven by testing must be followed.

Expert assistance may be required:NFPA 68 - 2002 Chapter 7 Av=(8.535 x 10-5)(1+1.75Pstat)KstV

.75(((Pmax/Pred)-1).5)

Av= Vent area (m2) - operating pressure < .2 bar (3 psi)

Pmax= Maximum pressure reached in a closed (unvented)

enclosureKst = Dust deflagration index

Pred = Maximum pressure reached in a vented enclosure

Pstat = Panel burst pressure

V=Hazard volume (m2)

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Pressure?

Correct Vent Area / Size & Quantity of Explosion Panels:

Area calculation following VDI 3673 / NFPA 68 / ATEX harmonized standard or other method proven by testing must be followed.

Expert assistance may be required:

Basic calculations will require modification in case of

- vent ducting

- elongated vessel (L/D)

- vent efficiency < 100%

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Explosion Panel Design

Select Panel Design According to the Requirements of the Application:

Metal Vents

-Good mechanical & corrosion resistance; typically Stainless Steel

-Light weight / good dynamic response

-Simple Installation using angle steel frames

-Provided with integral gaskets, ready to use

-Set pressures from 0.03 to 0.5 Bar

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Select Panel Design According to the Requirements of the Application:

Plastic Vents

-Light weight / good dynamic response must be confirmed by testing

-Supplied with integral Steel or Aluminum frame & gaskets, ready to use

-Translucent; can replace building windows

-Very Low set pressures from 0.01 to 0.1 Bar

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Factors influencing Explosion Panel selection:

The most significant application factors influencing Explosion Panel design selection are…

•Temperature

•Vacuum

•Vibration

•Cleanliness

•Control of Fragmentation

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Temperature related issues…

-Reduction in Heat Loss / Energy Efficiency

-Prevention of Condensation

-Resistance to High Temperature

Solution:

Use of Thermal InsulationIn this example, foam insulation is applied directly to the outlet side of the Explosion Panel to provide a thermal barrier.

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Vacuum related issues…

-Resistance to vacuum pulsations

-Resistance to strong vacuum

Solution:

Use of Domed Panel TechnologyThe structure developed by a dome is very strong, able to resist aggressive vacuum pulsation. The dome shape is varied to meet the level of vacuum resistance required. Not all domed vents are the same.

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Vibration related issues…

-Resistance to pulsations

Solution:

Use of Domed Panel TechnologyThe structure developed by a dome is very strong, able to resist pulsations. The dome shape is varied to meet the level of resistance required. This example shows a 2 stage dome. (Patent Pending.)

Not all domed vents are the same.

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Cleanliness related issues…

-Crevice free construction

-Control of contamination

Solution:

Use of Single Section TechnologyThis rectangular vent opens on 3 sides due to slots in the metal construction. These slots are sealed by process compatible gasket material.

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Control of Fragmentation…

-Prevent risk to discharge area

Solution:

Use of Explosion Panels Dynamically Tested to be Non FragmentingThis rectangular vent opens on 3 sides. The 4th side holds the rectangular vent material when it opens.

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Explosion Panel Application: Allowance for Fireball

Fireball can be estimated at 7 times protected volume.

New NFPA standards include an equation for estimation of Fireball impact;

D = 3.1(V/n)0.402

V = protected volume n = number of vents D = distance fireball

reaches in front of vent D/2 = estimated width of

fireball

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Explosion Panel Application: What else should be considered?

Protection of Connected Equipment

Zone A

Zone C

Zone B

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Isolation of Connected Equipment

Example of Isolation of dirty air inlet duct by injection of flame quenching agent into duct, triggered by sensor fitted to explosion panel.

This technique is called ‘Chemical Isolation”.

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Isolation of Connected Equipment

Other techniques include Mechanical Isolation, such as:

-Pinch Valve

-Screw conveyor

-Rotary valve

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Explosion Panel Application

Typical examples of industrial equipment protected by Explosion Panels:

Dust collectors CrushersGrinders Dust arrestersSilos ConveyorsPulverizers ElevatorsConveyor ducts DryersSieves OvensScrews FurnacesBlenders ShreddersMixers BinsFilters Hoppers

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Explosion Panel Application

As Codes & Standards become more detailed in their Engineering requirements, increased care is required in the selection of the best explosion panel. These changes are designed to introduce:

•Increased safety•Improved economy where risk permits

Be careful to consider the proper protection of connected equipment.

Vented dust collector showing flame exiting 150mm diameter inlet

duct.

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Sao Paulo, Brazil, 18th April 2006

Thank YouGeof Brazier, Director of Development,

BS&B Safety Systems, LLC&

Carlos Garcia, General Manager,BS&B Safety Systems, Brazil

1 Escola Politecnica / USP, Sao Paulo / SP / Brazil 18 th April 2006 Rupture Disks, Explosion Panels...

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