Large Scale Tests for Explosion Pressure Resistant Design in Combination with Explosion Venting. Folie 1

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1 Explosion Protection in Bucket Elevators: Large Scale Tests for Explosion Pressure Resistant Design in Combination with Explosion Venting Folie 1

2 Explosion Tests Folie 2

3 Objective Optimization of the layout of explosion pressure resistant design in combination with explosion venting Execution of the explosion tests t taking into concideration practical operating conditions Explosion tests with typical types of dusts which are clearly different regarding to the explosion characteristics Introduction of results into technical rules (CEN) Folie 3

4 Execution of the Tests Two different test methods were used: 1. Dispersion of the dust layers ( no-load running ) 2. Dust injection system Systematic variation of the vent configurations Venting area of each vent opening = cross section area of the elevator leg Static activation pressure of the venting device p stat = 01b 0.1 bar Folie 4

5 Execution of the Tests Explosion Characteristics of the Used Dusts Bulk P max K St LEL MIE MIT S N Material [bar] [bar m s -1 ] [g/m³] [mj] [ C] Wheaten flour Malt dust Corn starch S N Dusting number as per VDI 2263-Part 9 Folie 5

6 Execution of the Tests Explosion Venting of a Twin Leg Elevator -Malt Dust - Ignition in the boot - Flame propagation into a pressure vented cyclone of the dedusting system Folie 6

7 Venting Boot and Head Folie 7

8 Results 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) Folie 8

9 Results Maximum Explosion Pressure Depending on Measuring Location pressure e [bar] explosi ion over 0,75 0,5 0,25 0 Wheaten flour (K St = 109 bar m s -1 ) Tests without dust injection Weizenmehl (K St = 109 bar m s -1 ) Versuche ohne Staubeinblasung Venting head Venting head + legs boot elevator leg L [m] head Folie 9

10 Results Maximum Explosion Pressure Depending on Measuring Location pressure e [bar] explosi ion over 0,75 0,5 0,25 0 Wheaten flour (K St = 109 bar m s -1 ) Tests without dust injection Weizenmehl (K St = 109 bar m s -1 ) Versuche ohne Staubeinblasung without Venting Venting head Venting head + legs boot elevator leg L [m] head Folie 10

11 Results Maximum Explosion Pressure Depending on Measuring Location explos ion overp pressure [b bar] 0,75 0,5 0,25 0 Wheaten Weizenmehl flour (K St (K = 109 bar m s -1 ) St = 109 bar m s -1 ) Versuche mit Staubeinblasung Dust injection system without Venting Venting head Venting head + legs boot elevator leg L [m] head Folie 11

12 Results 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 the location of ignition or between location of ignition and next vent opening The maximum peak explosion pressure was p max 0.6 bar without vent opening Folie 12

13 Results 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 could be found Folie 13

14 Results Maximum Explosion Pressure Depending on Measuring Location 1,5 Malt dust (K St = 143 bar m s -1 ) exp plosion pressur re [bar] 1,0 0,5 Venting head+legs Venting head Venting boot+head+legs 0, boot elevator leg L[m] head A1, DE Kopf + Schacht + Fuß, ohne Staubeinblasung F1, DE Kopf + Schacht + Fuß, mit Staubeinblasung No-load running Dust Injection System A19, DE Kopf + Schacht, ohne Staubeinblasung F15, DE Kopf + Schacht, mit Staubeinblasung A24, DE Kopf, ohne Staubeinblasung F14, DE Kopf, mit Staubeinblasung Folie 14

15 Results of the Explosion Tests Malt Dust Maximum explosion pressures were achieved nearby the location of ignition or between location of ignition and next vent opening Maximum explosion pressures were produced d 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) No correlation between flame speed and pressure could be found Folie 15

16 Results of the Explosion Tests Maximum Explosion Pressure Depending on Measuring Location ex xplosion pr ressure [bar] 2,5 20 2,0 1,5 1,0 Corn starch (K St = 203 bar m s - 1 ) Dust Injection System 0,5 0, boot elevator leg L [m] head Venting boot+head+legs Venting head+legs Venting head C1, DE Kopf + Schacht + Fuß, ohne Staubeinblasung F11, DE Kopf + Schacht + Fuß, mit Staubeinblasung C6, DE Kopf + Schacht, ohne Staubeinblasung F16, DE Kopf + Schacht, mit Staubeinblasung C32, DE Kopf, ohne Staubeinblasung Venting boot+head+legs Venting head+legs Folie 16

17 Results of the Explosion Tests Corn Starch Induced turbulence due to the dust injection system (Method B) produced a strong increase of the peak explosion pressures Induced turbulence is relevant in case of dust with high K St -value Results using the dust injection system in combination with high K St -values may overestimate the explosion course under practical operating conditions Folie 17

18 Results Pressure Venting of Twin-Leg Bucket Elevators The 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 - Free area in relation to the cross section area of the elevator legs < 60 % - Bucket spacing 280 mm if K St 150 [bar m s -1 ] - Bucket spacing 140 mm if 150 < K -1 St 210 [bar m s ] - Venting area of each vent opening cross section area of the elevator leg - Static activation pressure of the venting device p stat 0.1 bar Folie 18

19 Results Explosion Venting of Twin-Leg Bucket Elevators K St 100 bar m s -1 K St 150 bar m s -1 explosion vent vent pressure resistance 1) boot head spacing legs 2) boot head spacing legs 2) p [bar] L [m] L [m] 0.5 no yes 6 yes yes no no no yes yes no no no no yes no no no no yes no 1) overpressure 2) maximum vent spacing Folie 19

20 Results Explosion Venting of Twin-Leg Bucket Elevators K St 100 bar m s -1 K St 150 bar m s -1 explosion pressure resistance 1) boot head p [bar] vent spacing legs 2) boot head L [m] vent spacing legs 2) L [m] 0.5 no yes 6 yes yes no no no yes yes no no no no yes no no no no yes no 1) overpressure 2) maximum vent spacing Folie 20

21 Results Explosion Venting of Twin-Leg Bucket Elevators K St 100 bar m s -1 K St 150 bar m s -1 explosion pressure resistance 1) boot head p [bar] vent spacing legs 2) Boot head L [m] vent spacing legs 2) L [m] 0.5 no yes 6 yes yes no no no yes yes no no no no yes no no no no yes no 1) overpressure 2) maximum vent spacing Folie 21

22 Results Explosion Venting of Twin-Leg Bucket Elevators explosion pressure boot head p [bar] K St 210 bar m s -1 vent spacing legs 2) L [m] yes yes yes yes no yes 6 1) overpressure 2) maximum vent spacing Folie 22

23 Introduction Bucket Elevator for Vertical Conveying of Bulk Materials Folie 23

24 Experimental Set-up Sketch and Technical Data of the Bucket Elevator Ignition location Ignition location Vent Vent Conveying capacity ~ 150 t/h Conveying velocity m/s Cross-section area (leg) m² Bucket spacing 130 mm Wall clearance a ce front ~ 60 mm Wall clearance side ~ 55 mm Wall clearance rear ~ 45 mm Vent Ignition location Pressure-shock- 3 bar resistance Pressure vent area m² Folie 24

25 Experimental Set-up Twin Leg Bucket Elevator at the Test Site Measuring Technique Piezoelectric pressure transducers Infrared sensitive indicators Transient recorder Ignition Pyrotechnical igniters with ignition energie of 2 kj Ignition location: Elevator boot, head or leg Folie 25