Explosion hazard of whey powder mixed with air

Introduction. In many countries, regulations consider combustible dust with a particle size of more than 500 μm as dispersed material non-explosive if mixed with air. The explosiveness of mixtures of air and some substance arouses researchers’ interest. In particular, the explosiveness of whey powder specimens (hereinafter referred to as whey powder) with an average particle size of 41, 162 and 750 μm, was identified in the process of their testing in a 1 m3 chamber. The task is to find out the maximum particle size of whey powder dcr using the earlier developed procedure and to demonstrate its failure to conform to the rule specified above.

Method to process experimental data. Continuous functions F of particle size distribution d were constructed for three whey powder specimens having the following values of the lower explosive limit (LEL1 = 250 g/m3, LEL2 = 250 g/m3 and LEL3 = 500 g/m3, respectively). Resulting functions F1(d), F2(d) and F3(d) were presented using Rosin – Rammler distributions that filled the gaps between the discrete data obtained as a result of the sieve analysis.

dcr evaluation. We used information about the first and third whey powder specimens in compliance with the well-known procedure (Poletaev, 2014). dcr values were identified using equation F1(dcr)/F3(dcr) = LEL3/LEL1. Having solved the equation, we found that dcr = 750 μm.

Discussion. The obtained evaluation of dcr is much higher than the limit value of the parameter proposed in the regulations. This evaluation is of objective origin, and it cannot be explained by the grinding of large particles during the spraying process. The latter statement is supported by a characteristic decrease in the explosibility index of whey powder and an increase in the average particle size (for explosive fractions) of the three specimens in question.

Conclusions. The maximum particle size of the explosive whey fraction is about 750 µm.

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