Resource Magazine September/October 2013 : Page 14

Table 1. Ash analysis of the three dusts tested with the CAAQES method. The average ash content of the cotton gin dust (CGD) was 87%, and only 13% of the CGD was volatile. Dust Corn starch “Dust X” CGD Ash (±95% CI) 0.98% (±0.02) 61.6% (±0.01) 87.2% (±1.13) Table 2. Particle size distributions of the three test dusts, including mass median diameter (MMD) and geometric standard deviation (GSD). Dust Corn starch “Dust X” CGD MMD (±95% CI) 15.5 ␮ m (±0.29) 13.7 ␮ m (±0.06) 23.7 ␮ m (±0.88) GSD (±95% CI) 1.6 (±0.08) 2.1 (±0.03) 1.9 (±0.01) Figure 3. Characteristic pressure vs. time curves for corn starch at 100 g m -3 . forming and then contacting the stationary ignition source. Note that only a small fraction of the chamber volume is occupied by the dust cloud. The third frame shows the self-propagating flame consuming the corn starch particles. The fourth frame shows the ruptured diaphragm and the flame leaving the chamber. Figure 3 shows pressure vs. time curves for corn starch for three tests at a dust concentration of 100 g m -3 . In each test, the self-propagating flame increased the pressure inside the CAAQES chamber. When the diaphragm burst, the pres-sure rapidly decreased, creating a vacuum. This is consistent with reports following an explosion at a grain handling facil-ity that piping leading from the primary explosion site col-lapsed as a consequence of vacuum. Figure 4 shows typical pressure vs. time curves for tests of corn starch at a concen-Figure 4. Characteristic pressure vs. time curves for corn tration near its MEC (43 g m -3 ). Note that two of the tests did starch at its MEC (43 g m -3 ). not result in bursting of the diaphragm. Figure 5 contains three video frames of a CGD test at a cluded that gin dust did not have an MEC, and therefore it is concentration of 1000 g m -3 in the CAAQES chamber. The not an explosible dust. first frame shows the gin dust being dispersed in the air. The For comparison with corn starch and CGD, figure 7 con-second frame shows the dust cloud contacting the hot coil and tains three video frames of “dust X” test at a concentration of igniting. The third frame shows that there was insufficient pres-sure to burst the diaphragm, as the flame did not self-propagate through the cloud. Figure 6 shows characteristic pressure vs. time curves for CGD at a concentra-tion of 1000 g m -3 . No deflagra-tions were observed for any of the tests. The flat lines in the graph show that there was a small rise in pressure, but it was insufficient to burst the diaphragm. It was con-Figure 5. Cotton gin dust (CGD) being tested in the CAAQES chamber at 1000 g m -3 . 14 September/October 2013 RESOURCE

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