Page 313 - Dust Explosions in the Process Industries

282 Dust Explosions in the Process Industries

- 0 ..\A0 0 0
I
I
I QUENCHING
l
I 0 NO QUENCHING
I
-
- 20 .qoo 00 0 0 0 0
I
E .ro,o B w 0 0 0 0 0
I a *\am0 m 0 0 0 0
n \
W u m ..qoo 0 0
z \
c4 e *.goo 0 0
2 10- * e .e ' q\ 0 0 0 0
2 e.... e30 0 0 0 0
W ['- ----- ---
aD a. n e.
w

Figure 4.1 8 The quenching distance of laminar flames of maize starch/air mixtures as a function of
the dust concentration (From Proust and Veyssiere, 1988).
stoichiometricconcentrationof 235 g/m3.For higher dust concentrations,up to 550 g/m3,
the quenching distance remains unchanged at the minimum value of 7 mm.
The lowest value of about 7 mm for the quenching distance for maize starch/airmix-
ture is in close agreement with the lowest value of about 6 mm found by Jarosinski et
al. (1987) in a similar experimental configuration. However, these workers found their
lowest value in the concentration range 500-1 100g/m3,whereas the values in the range
400 g/m3increased with decreasing concentration,being about 10 mm at 400 g/m3.
Proust and Veyssiere (1988) also determinedthe thickness of the laminar starch dudair
flame, using the criterion for laminar gas flames proposed by Jarosinski (1984).

Flame thickness = 2(T, -q)/(dT/dx),,, (4.21)

Fuel Maize starch Methane
Laminar burningvelocity (mk) 0.27 0.45
Quenching distance (mm) 7 2
Flame thickness (mm) 3-4 1