Page 81 - Dust Explosions in the Process Industries

54 Dust Explosions in the Process Industries

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0
I

-
L " 0 0.5 1.0 1.5 2.0
CONTENT OF METHANE IN AIR 1~0l%l

Figure 1.63 The necessary mass percentage of incombustible solid material for clouds of dry coal
dust of38% volatiles and 10% ash in air containing various low percentages ofmethane (from Torrent
and Fuchs, 1989).
8

1 600 g/m3 COAL DUST
600 g/m3 COAL DUST IN AIR
IN AIR + 2 ~01% 0
METHANE
= 6 0
ol
I
L
m
z?.
x5
4
a= f 600 g/m3 COAL DUST IN AIR
4 + 2~01% METHANE
600
/%%\\AIR
DUST
IN
g/m3
COAL
0 I I I I I
10 20 30 0 10 20 30
DUST DISPERSION PRESSURE, DUST DISPERSION PRESSURE,
[ARBITRARY UNlTSl [ARBITRARY UNlTSl
Figure 1.64 Influence of 2 vol% methane in the air on maximum explosion pressure and maximum
rate of pressure rise of coal dust in a 28 liter closed vessel at various levels of initial turbulence (from
Nagy and Portman, 796 I).
was intensified.However, as the dust dispersionpressure was increased further,the dust
without methane started to burn less efficiently, probably due to quenching by intense
turbulence. In the presence of methane, this effect did not appear, presumably due to
faster combustion kinetics. The influence of the methane was even more apparent for
the maximum rate of pressure rise, which, for a dust dispersion pressure of 30 arbitrary
units, dropped to less than 100 bark without methane, whereas with 2% methane, it
increased further up to 500 bar/s. This comparatively simple experimentrevealed impor-
tant features of the kinetics of combustion of turbulent clouds of organic dusts. Ryzhik
and Makhin (1978) also investigated the systematic decrease of the induction time for