Using TNT equivalence for dust explosion is not a good idea for 2 reasons (you are trying to use some correlations with VCE, for which TNT equivalence method widely applicable):
1) mechanism of burning of dust and vapor is very different - for dust explosion you may see up to 8 explosions for same mixture (coal, for example) - relay mechanism. As a result of this, dynamic of pressure generation and its max value for dust exp. and VCE are different.
2) you have no correlations for calculation of flammable mass of dust, because in different conditions the difference between flammable mass of dust in the same dust cloud may be up to 10 times.