Explosion characteristics of hybrid dust mixtures

The history of process safety is full of explosions from different chemicals including dusts, vapors and gases, and a combination of dusts and vapors/gases, which are called hybrid mixtures explosion. Soy oil plants have experienced some immense explosions before due to the co-presence of hexane as a solvent and soy flour, creating an inherently hazardous environment. Soybean oil takes around 50% of the vegetable oil resources, and soybean is increasing in importance year by year. As serious and hazardous, yet prevalent in the industry this hybrid mixture is, there has been no study before to determine its explosion characteristics. This study aims to find the pmax and (dp/dt)max of the above-mentioned mixture, and to find the minimum explosion concentration of soy flour through experiments in the 20-L Siwek explosion chamber and the MIKE3 apparatus. The results of this study show that soy flour alone is hard to ignite and the maximum explosion pressure of 7.7 bar g can only be reached with 10 kJ ignition energy. Hexane is highly explosible with a pmax value of 8.8 bar and a KG of 689 bar.m/s. As an example, adding hexane as much as one-third of its LEL (0.2 ml) to soy flour increases the severity of the explosions considerably: The overpressure increased from 0.3 bar to 5.2 bar for 500 g/m3 (moisture content of 2 weight%). Adding low amounts of soy flour to hexane increased its maximum overpressure slightly to 8.9 bar, while decreasing KH to 627 bar.m/s. Chemical igniters and exploding wires showed comparable results in general, especially for overpressure values. Lastly, the MEC of soy flour in the presence of an inductance is between 100 J and 300 J. Overall, the presence of hexane increases the severity of explosions for soy flour significantly, even in very small amounts. Soy flour/hexane hybrid mixtures show severe explosions and efforts to mitigate the explosion effects and to find a substitute solvent for hexane should be of utmost focus.