1. Minimum cloud and layer ignition temperatures of mixtures of combustible and inert dusts
Enrico Danzi, Luca Marmo, Giuseppe Liotta, Daniela Riccio & Giuseppe Scicchitano
Tenth International Symposium on Hazards, Prevention, and Mitigation of Industrial Explosions
10-14, June, 2014, Bergen, NORWAY

2. Work summary
Experimental campaign on Minimum Ignition Temperature of dust disposed in layers or clouds (MITL, MITC)
Combustible – inert dusts mixtures
Combustible – combustible dust mixtures
Influence of PSD and other properties on ignition
Evaluation of Statistical Ignition Temperature

3. Hot plate device according to CEI EN 50281:2-1
Experimental setup
Hot plate device according to CEI EN 50281:2-1
Godbert-Greenwald furnace

4. Combustible dusts Dust d10 d50 d90 Flour “OO” type 12 57 148
Glucose (Ardet) 42
156
358
Lactose (Milei) 6 33
101
Sucrose (PaneAngeli) 4 20
129
Sulphur 3 10 46

5. According to granulometric sieve requested (500/250, 250/125, 75/32)
Inerts
Material
d10 [mm]
d50 [mm]
d90 [mm]
Extinguishing powder, ABC 93 5 58
199
Extinguishing powder, ABC40 7 61
196
Extinguishing powder, ABC 2010 10 72
249
Limestone
According to granulometric sieve requested (500/250, 250/125, 75/32)
Silica sand

6. Sample preparation Conditioning treatment: 3 h @ 65°C
Silica-gel dryer preservation: Max 48 h
Mechanical 75 μm: MITC measurements (combustible dusts)
Grinding with shredding mill: Inert coarse matrix to several granulometric sieves (Limestone and Silica sand)

7. Mixtures preparation
Conditioning treatment: 3 65°C (combustible & inert) 1
Weighting conditioned samples with analytical balance 2
Mechanical blending and rotation to avoid segregation 3

8. Extinguishing powders
Tests overview (c/i)
Specifications
Flour
Extinguishing powders
ABC93
ABC40
ABC 2010
Silica sand
PSD 75/32 um
Limestone
PSD 250/125 um
PSD 500/250 um
Combustible dust
Inert dust

9. Tests overview (c/c) Flour – Lactose Flour – Sucrose Flour- Glucose
MIT test
SIT test
Flour – Lactose
Flour – Sucrose
Flour- Glucose
Flour - Sulphur
Sucrose – Lactose
Lactose – Glucose

10. Measurements
Minimum ignition Temperature in layer (MITL): according to CEI EN 50281:2-1
Minimum Ignition Temperature in cloud (MITC): according to CEI EN 50281:2-1

11. Operating methods Setting T plate T plate variation ± 50 K then ± 10 K
MITL evaluation
MITC evaluation
Setting T plate
T plate variation ± 50 K then ± 10 K
MITL: Minimum T plate to ignite the sample
T setpoint = 500°C
p = 1.1 bar
Investigating for optimal ignition conditions
Decreasing Tsp -20 K until 10 NI
MITC: Minimum furnace temperature to ignite the sample

12. Statistical Ignition Temperature, SIT
According to and deriving from UNI EN 13821: 2004
T2 : lower T with at least ONE ignition
T1 : T with NO ignition after 10 tests
I[T2]: tests with T2
N[T2]: T2

13. Results (c/i mixture, MITC)
Chemical inertia
Physical inertia

14. Results (c/c mixture, MITC)
Harmonic model

15. Results (flour/i mixture, MITL)
Flour, pure

16. Results (MITL measurements)
Flour 80% w.- Limestone 20% w.
Tset 350°C
5 mm ring
ASTM ignition

17. Flour 80% w.- Limestone 20% w. Tset 350°C 5 mm ring CEI ignition
ASTM ignition

18. Flour 80% w.- Limestone 20% w. Tset 370°C 5 mm ring CEI ignition
ASTM ignition

19. Results (MITL resume) Inert (size, um) Mixture composition (% weight)
Flour - Inert
Limestone (75/32)
Limestone (250/125)
Limestone (500/250)
Silica sand (75/32)
ABC 40
90-10
350
>400
380
80-20 -
70-30
340
60-40
330
50-50

20. Conclusions
MITC
The MITC of combustible dust – inert mixtures has been proved to decrease with % mass weight of inert
Inert which undergo chemical decomposition have greater inertial effect on mixtures
Limestone particle size distribution has no significant effects on MITC
Limited accuracy of MITC measurements (small influcence of variables)

21. Conclusions
MITC
Adopting the Statistical Ignition Temperature method to describe mixtures with similar MITC
No significant correspondance btw harmonic model and SIT measurements
Steep decrease of SIT with adding small amount of component (Lactose-Flour/Sucrose, Flour- Sulphur)

22. Conclusions
MITL
MITL showed strong dependance on PSD of inert in mixtures
Drop of MITL with increasing inert (Limestone/ABC40-Flour): different combustion evolution respect to pure Flour
Coarser inerts do not provoke a MITC decrease (Flour-Limestone)

23. Perspectives
Investigation and validation of SIT method with further experimentations
Focusing on Flour-like behaviour dusts with respect to MITL decreasing with inert increasing

24. Thanks for your attention!
…any questions?