Explosion Protection in Bucket Elevators: Explosion Protection in Bucket Elevators: Large Scale Tests for Explosion Pressure Resistant Designgin Combination with Explosion VentingInternational Symposium on Process and Explosion Protection, Nrnberg 2008 Folie 1Explosion TestsInternational Symposium on Process and Explosion Protection, Nrnberg 2008 Folie 2Objective Optimization of the layout of explosion pressure resistant Optimization of the layout of explosion pressure resistant design in combination with explosion venting E ti f th l i t t t ki i t id tiExecution of the explosion tests taking into concideration practical operating conditions Explosion tests with typical types of dusts which are clearly different regarding to the explosion characteristics clearly different regarding to the explosion characteristics Introduction of results into technical rules (CEN)International Symposium on Process and Explosion Protection, Nrnberg 2008 Folie 3Execution of the Tests Two different test methods were used:1. Dispersion of the dust layers (no-load running)2 Dust injection system 2. Dust injection system Systematic variation of the vent configurations Venting area of each vent opening = cross section area of the elevator leg g Static activation pressure of the venting device0 1 b pstat= 0.1 bar International Symposium on Process and Explosion Protection, Nrnberg 2008 Folie 4Execution of the TestsExplosion Characteristics of the Used DustsBulkPmaxKSt1LEL MIE MIT SNMaterial [bar] [barms-1] [g/m] [mJ] [C]Wheaten 6 8 109 60 30 400 0 6 Wheaten flour6.8 109 60 30400 0.6Malt dust 7 4 143 60 10 370 20 1 Malt dust 7.4 143 60 10370 20.1Corn starch 9 0 203 60 5 370 10 2 Corn starch 9.0 203 60 5 370 10.2SN Dusting number as per VDI 2263-Part 9International Symposium on Process and Explosion Protection, Nrnberg 2008 Folie 5Execution of the TestsExplosion Venting of a Twin Leg Elevator- Malt Dust- Ignition in the boot- Flame propagation into a pressuref vented cyclone of thededusting systemInternational Symposium on Process and Explosion Protection, Nrnberg 2008 Folie 6Venting Boot and HeadInternational Symposium on Process and Explosion Protection, Nrnberg 2008 Folie 7ResultsThe following diagrams show: The following diagrams show: Maximum explosion overpressure over measuring location depending on the vent opening arrangement Results of the most violent explosion tests (worst case)Results of the most violent explosion tests (worst case)International Symposium on Process and Explosion Protection, Nrnberg 2008 Folie 8ResultsMaximum Explosion Pressure Depending on Measuring LocationWeizenmehl (KSt= 109 barms-1)Versuche ohne Staubeinblasung0,75e [bar]Wheaten flour (KSt= 109 barms-1)Tests without dust injection Versuche ohne Staubeinblasung0,5rpressureTests without dust injection0,25ion overVenting head0explosiVenting head + legs0 5 10 15elevator leg L [m] boot headInternational Symposium on Process and Explosion Protection, Nrnberg 2008 Folie 9ResultsMaximum Explosion Pressure Depending on Measuring LocationWeizenmehl (KSt= 109 barms-1)Versuche ohne Staubeinblasung0,75e [bar]Wheaten flour (KSt= 109 barms-1)Tests without dust injection Versuche ohne Staubeinblasung0,5rpressureTests without dust injectionwithout Venting0,25ion overVenting head0explosiVenting head + legs0 5 10 15elevator leg L [m] boot headInternational Symposium on Process and Explosion Protection, Nrnberg 2008 Folie 10ResultsMaximum Explosion Pressure Depending on Measuring LocationWeizenmehl (KSt= 109 barms-1)Versuche mit Staubeinblasung0,75bar]Wheaten flour (KSt= 109 barms-1)Dust injection system0,5pressure [bDust injection systemwithout Venting0,25ion overpVenting head0explosVenting head + legs00 5 10 15elevator leg L [m]boot headInternational Symposium on Process and Explosion Protection, Nrnberg 2008 Folie 11Results of the Explosion Tests Wheaten Flour (1) Independent on the type of dust: maximum pressures were produced when ignition took place at the boot Maximum explosion pressures were achieved nearby thep p ylocation of ignition or between location of ignition and next vent opening next vent opening The maximum peak explosion pressure was pmax 0.6 bar without vent opening International Symposium on Process and Explosion Protection, Nrnberg 2008 Folie 12Results of the Explosion Tests Wheaten Flour (2) The maximum explosion pressures were in the same order of magnitude according both test methods No correlation between flame speed and pressure couldNo correlation between flame speed and pressure could be foundInternational Symposium on Process and Explosion Protection, Nrnberg 2008 Folie 13ResultsMaximum Explosion Pressure Depending on Measuring Location1,5Malt dust (KSt= 143 barms-1)1,0re [bar]Venting headplosion pressurVenting head+legs0,5expVenting boot+head+legs0,00 5 10 15elevator leg L[m]boot headA1, DE Kopf + Schacht + Fu, ohne Staubeinblasung F1, DE Kopf + Schacht + Fu, mit StaubeinblasungA19, DE Kopf + Schacht, ohne Staubeinblasung F15, DE Kopf + Schacht, mit StaubeinblasungA24, DE Kopf, ohne Staubeinblasung F14, DE Kopf, mit StaubeinblasungNo-load running Dust Injection SystemInternational Symposium on Process and Explosion Protection, Nrnberg 2008 Folie 14Results of the Explosion Tests Malt Dust Maximum explosion pressures were achieved nearby the location of ignition or between location of ignition the location of ignition or between location of ignition and next vent openingM i l i d d hMaximum explosion pressures wereproduced when ignition took place under no-load running (Method A) Observed behaviour of malt dust can be explained by the very high dusting number (excellent dispersion) the very high dusting number (excellent dispersion) No correlation between flame speed and pressure could be foundInternational Symposium on Process and Explosion Protection, Nrnberg 2008 Folie 15Results of the Explosion TestsMaximum Explosion Pressure Depending on Measuring Location2 02,5Corn starch (KSt= 203 barms-1)1,52,0ressure)Dust Injection System1,0xplosion pr [bar]0,5ex0,00 5 10 15elevator leg L [m]bootheadC1, DE Kopf + Schacht + Fu, ohne Staubeinblasung F11, DE Kopf + Schacht + Fu, mit StaubeinblasungC6, DE Kopf + Schacht, ohne Staubeinblasung F16, DE Kopf + Schacht, mit StaubeinblasungC32, DE Kopf, ohne StaubeinblasungVenting boot+head+legsVenting head+legsVenting head Venting boot+head+legsVenting head+legsInternational Symposium on Process and Explosion Protection, Nrnberg 2008 Folie 16Results of the Explosion Tests Corn Starch Induced turbulence due to the dust injection system (Method B) prod ced a strong increase of the peak (Method B) produced a strong increase of the peak explosion pressures Induced turbulence is relevant in case of dust with high KSt-value high KStvalue Results using the dust injection system in combination i h hi h K l i h l i with high KSt-values may overestimate the explosion course under practical operating conditionsInternational Symposium on Process and Explosion Protection, Nrnberg 2008 Folie 17ResultsPressure Venting of Twin-Leg Bucket Elevators Th lt b d f th l t f l iThe results can be used for the layout of explosion pressure resitant design in combination with explosion venting The recommendations are valid under the following conditions:- Rectangular cross section of the elevator legs g g- Free area in relation to the cross section area of the elevator legs < 60 %g- Bucket spacing 280 mm if KSt 150 [barms-1]Bucket spacing 140 mm if 150 < K 210 [barms-1] - Bucket spacing 140 mm if 150 < KSt 210 [barms1]- Venting area of each vent opening cross section area of the elevator leg the elevator leg- Static activation pressure of the venting device pstat 0.1 barInternational Symposium on Process and Explosion Protection, Nrnberg 2008 Folie 18ResultsExplosion Venting of Twin-Leg Bucket ElevatorsKSt 100 barms-1KSt 150 barms-1 explosion vent vent explosion pressureresistance 1)boot headvent spacinglegs 2)boot headvent spacinglegs 2)p [bar]L [m] L [m]0.5 no yes 6 yes yes 31.0 no no no yes yes 61.5 no no no no yes 62 0 no no no no yes no 2.0 no no no no yes no1) overpressure 2) maximum vent spacingInternational Symposium on Process and Explosion Protection, Nrnberg 2008 Folie 19ResultsExplosion Venting of Twin-Leg Bucket ElevatorsKSt 100 barms-1KSt 150 barms-1 explosion pressureresistance1)boot headvent spacing legs2)boot headvent spacing legs2)resistance p [bar]legs 2)L [m]legs L [m]0.5 no yes 6 yes yes 3 0.5 no yes 6 yes yes 31.0 no no no yes yes 61.5 no no no no yes 62.0 no no no no yes no1) overpressure 2) maximum vent spacingInternational Symposium on Process and Explosion Protection, Nrnberg 2008 Folie 20ResultsExplosion Venting of Twin-Leg Bucket ElevatorsKSt 100 barms-1KSt 150 barms-1 explosion pressureresistance1)boot headvent spacing legs2)Boot headvent spacing legs2)resistance p [bar]legs L [m]legs L [m]0.5 no yes 6 yes yes 3 y y y1.0 no no no yes yes 61.5 no no no no yes 62.0 no no no no yes no1) overpressure 2) maximum vent spacingInternational Symposium on Process and Explosion Protection, Nrnberg 2008 Folie 21ResultsExplosion Venting of Twin-Leg Bucket ElevatorsKSt 210 barms-1explosionventexplosion pressureresistance 1)boot headvent spacing legs 2)p [bar]L [m]0.5 - - -1.0 yes yes 31 5 6 1.5 yes yes 62.0 no yes 61) overpressure 2) maximum vent spacingInternational Symposium on Process and Explosion Protection, Nrnberg 2008 Folie 22IntroductionBucket Elevator for Vertical Conveying of Bulk MaterialsInternational Symposium on Process and Explosion Protection, Nrnberg 2008 Folie 23Experimental Set-upSketch and Technical Data of the Bucket ElevatorV tConveying capacity ~ 150 t/h C i l it 3 5 /VentIgnition locationConveying velocity 3.5 m/sCross-section area (leg) 0.105 mBucket spacing 130 mmWall clearance front ~ 60 mmIgnition locationa c ea a ce o t 60Wall clearance side ~ 55 mmW ll l 4VentWall clearance rear ~ 45 mmPressure-shock-i t3 bar VentresistancePressure vent area 0.105 mIgnition locationInternational Symposium on Process and Explosion Protection, Nrnberg 2008 Folie 24Experimental Set-upTwin Leg Bucket Elevator at the Test SiteMeasuring Technique Piezoelectric pressureptransducers Infrared sensitive indicators Transient recorderI iti Ignition Pyrotechnical igniters with ignition energie of 2 kJ Ignition location: Elevator boot, head or leg International Symposium on Process and Explosion Protection, Nrnberg 2008 Folie 25