Rob Lade - IEP TECHNOLOGIES, UK - Ignition location control as the key for barrier location

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Rob Lade delivered the presentation at the 2014 Dust Explosions Conference.

The 2014 Dust Explosions Conference examined industrial hazards, the means to control or eliminate dust and analysed the latest technology to ensure the maximum protection and safety of organizations. The event also featured recent industrial case studies and new safety recommendations.

For more information about the event, please visit: http://www.informa.com.au/dust14

Published in: Engineering, Technology, Business
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Rob Lade - IEP TECHNOLOGIES, UK - Ignition location control as the key for barrier location

  1. 1. Ignition Location – Key to Understanding Explosion Isolation 17th June 2014: Dr. Rob Lade
  2. 2. 2013 IEP Technologies, LLC. 2 Industrial Explosion Protection Designed to mitigate consequence of an explosion incidents
  3. 3. 2013 IEP Technologies, LLC. 3 Explosion Protection Means Vessel Protection Containment Pmax = Pred > 8bar Suppression Relieves pressure Extinguished flame Contains explosion Venting Relieves pressure Inexpensive Does not extinguish flame Fireball 8x vessel volume
  4. 4. 2013 IEP Technologies, LLC. 4 Pressure Time Ps –Plant Strength Pmax - unmitigated Pred - mitigated Pressure Time Characteristics
  5. 5. 2013 IEP Technologies, LLC. 5 All vessel protection means require explosion isolation to minimise the risk of explosion propagation Flame Transfer between connected plant leads to enhanced explosion severity – Flame Jet Ignition Explosion Isolation Explosion Isolation more complicated than Venting / Suppression!! Explosion Isolation
  6. 6. 2013 IEP Technologies, LLC. 6 Why Isolate? DN300 – 30m long Vent Area=0.5m2 Vent Area=0.26m2 Fan V1=9.6m3 V2=4.4m3 Air velocity ~16m/s Air in Air out DN300 – 30m long Vent Area=0.5m2 Vent Area=0.26m2 Fan V1=9.6m3 V2=4.4m3 Air velocity ~16m/s Air in Air out DN300 – 30m long Vent Area=0.5m2 Vent Area=0.26m2 V1=9.6m3 V2=4.4m3 Air velocity ~16m/s Control Panel DN300 – 30m long Vent Area=0.5m2 Vent Area=0.26m2 V1=9.6m3 V2=4.4m3 Air velocity ~16m/s Control Panel
  7. 7. 2013 IEP Technologies, LLC. 7 Explosion Isolation Trials at FSA
  8. 8. 2013 IEP Technologies, LLC. 8 No Isolation Isolation 1x2kg HRD
  9. 9. 2013 IEP Technologies, LLC. 9 No Isolation Isolation 1x2kg HRD
  10. 10. 2013 IEP Technologies, LLC. 10 No Isolation Isolation 1x2kg HRD
  11. 11. 2013 IEP Technologies, LLC. 11 No Isolation Isolation 1x2kg HRD
  12. 12. 2013 IEP Technologies, LLC. 12 No Isolation Isolation 1x2kg HRD
  13. 13. 2013 IEP Technologies, LLC. 13 No Isolation Isolation 1x2kg HRD
  14. 14. 2013 IEP Technologies, LLC. 14 No Isolation Isolation 1x2kg HRD
  15. 15. 2013 IEP Technologies, LLC. 15 15 No Isolation Isolation 1x2kg HRD
  16. 16. 2013 IEP Technologies, LLC. 16 16 No Isolation Isolation 1x2kg HRD
  17. 17. 2013 IEP Technologies, LLC. 17 17 No Isolation Isolation 1x2kg HRD
  18. 18. 2013 IEP Technologies, LLC. 18 No Isolation: Pressure vs. time 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 Time / s Pressure/bar(g) V1 V2 Flame Entry into Duct Flame Exit from Duct
  19. 19. 2013 IEP Technologies, LLC. 19 Isolation: Pressure vs. time 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 Time / s Pressure/bar(g) V1 V2 Flame Entry into Duct
  20. 20. 2013 IEP Technologies, LLC. 20 Explosion Isolation Schematic of an Explosion Isolation System Detector, ta Duct transit, td Duct entry, te Controlling Equation ta + tb < te + td d tb Detection, ta
  21. 21. 2013 IEP Technologies, LLC. 21 Explosion Isolation:- Fundamentals Thus a modelling tool must calculate a safe location, dmin, such that This is the MINIMUM safe distance, dmin ta + tb < te + td
  22. 22. 2013 IEP Technologies, LLC. 22 Explosion Isolation:- Fundamentals Controlling Equation; ta + tb < te + td ta Pressure Detection – Vessel shape and size – Fuel properties – calculate P(t) to get ta – Field of view te tb – Specific to barrier hardware – Vessel shape and size – Fuel properties – Ignition location Optical Detection td – Duct size – Flame velocities – Barrier location te=ta Optical Detection td ……… the difficult one!
  23. 23. 2013 IEP Technologies, LLC. 23 Explosion Isolation:- Fundamentals In order to calculate td; we need the flame front velocity, Vff   b P P aVp         5.01 Vff = Vair + Vp + Vf Bulk air velocity Pressure piling Instantaneous flame speed = ++ k D d jSfVf        1 Vff Empirical fitStandard fluid dynamics Integration of vff w.r.t time gives the transit distance, dmin, along the duct from the mouth to the barrier. This is the minimum barrier distance criterion.
  24. 24. 2013 IEP Technologies, LLC. 24 Validation - Maize Starch Explosions 0 50 100 150 200 0 50 100 150 200 experimental tff / ms modeltff/ms perfect fit 1 m3 data 4.25 m3 data 9.4 m3 data
  25. 25. 2013 IEP Technologies, LLC. 25 Validation - Propane Explosions 0 10 20 30 40 0 10 20 30 40 Experimental tff / ms Modeltff/ms 1 m3 data 4.25 m3 vessel perfect fit
  26. 26. 2013 IEP Technologies, LLC. 26 Importance of Ignition Location! ?
  27. 27. 2013 IEP Technologies, LLC. 27 Importance of Ignition Location
  28. 28. 2013 IEP Technologies, LLC. 28 Importance of Ignition Location CFD simulation - flame at 180ms from ignition as a function of ignition location
  29. 29. 2013 IEP Technologies, LLC. 29 Explosion Isolation Example P PLANT AIR IN AIR & DUST CYCLONE Vent Vent GRINDERGRINDER ISOLATION VALVE 3m 5m • In this example the isolation valve is not efficacious Te+d = 49ms, ta+b =79ms • For te+d = ta+b barrier needs to be 8m from the Grinder • Represents a real issue for isolation systems in the practice
  30. 30. 2013 IEP Technologies, LLC. 30 Pressure Detection Only The locus of Lpress defines a volume element in which if ignition were to occur, flame passage would be expected P 3m a Lpress For our example this volume element constitutes 7.2% of the Grinders volume – represents Risk of failure to isolate
  31. 31. 2013 IEP Technologies, LLC. 31 O 3m Lopt Optical Detection Only The locus of Lopt defines a volume element in which if ignition were to occur, efficacious explosion isolation expected In this example, optical detection is far worse than pressure detection, with 99.9% of ignition locations resulting in the isolation barrier failing its mission.
  32. 32. 2013 IEP Technologies, LLC. 32 P 3m a O Lopt Lpress Dual Detection (Pressure + Optical) The volume element in which ignition would results in flame passage is now defined by Lpress and Lopt Only 7.1% of ignition locations would result in flame passage
  33. 33. 2013 IEP Technologies, LLC. 33 0 1 2 3 4 5 6 7 8 9 10 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Distance of Ignition from Duct Mouth / m MinimumBarrierDistance(dmin)/m Pressure Detection dmin vs. Ignition location Lpress Installed Barrier Distance Pressure Detection 7.2% % Ignition locations Allow flame passage Lopt Optical Detection 99.9% Dual Detection 7.1%
  34. 34. 2013 IEP Technologies, LLC. 34 Importance of Ignition Location Replace fast-acting valve with a suppressant barrier Barrier establishment time much faster P PLANT AIR IN AIR & DUST CYCLONE Vent Vent GRINDER 3m 5m P PLANT AIR IN AIR & DUST CYCLONE Vent Vent GRINDERGRINDER 3m 5m
  35. 35. 2013 IEP Technologies, LLC. 35 dmin vs. Ignition location Installed Barrier Distance Pressure Detection Lpress Optical Detection 99.6% Lopt 0 1 2 3 4 5 6 7 8 9 10 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 Distance of Ignition from Duct Mouth / m MinimumBarrierDistance(dmin)/m Chemical Isolation Barrier Installed at 3m 1.8% Ignition locations Allow flame passage Dual Detection 0.0%
  36. 36. 2013 IEP Technologies, LLC. 36 Conclusion • Ignition location key in understand efficacy of explosion isolation • “Worst Case” ignition location should be used in Barrier Design – Pressure detection – close to the duct mouth – Optical detection – remote from the duct mouth • These concepts have been adopted by EN15089 / ATEX • Residual risk determination is critically dependent on the detail of the elected explosion protection system
  37. 37. 2013 IEP Technologies, LLC. 37 Thank You

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