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
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