Effectiveness and mechanism of carbamide/fly ash cenosphere with bilayer spherical shell structure as explosion suppressant of coal dust

[Display omitted] •Carbamide decreases (dP/dt)max in 0∼τ1 stage.•Fly ash cenosphere acts on τ1∼τ2 stage and reduces Pmax.•The loaded carbamide was of nanoscale.•Explosion suppression mechanisms of the composite suppressant are proposed. This study aims to eliminate or suppress explosion accidents in powder preparation and storage systems of coal dust. The modified fly ash cenosphere (FAC) was used as an inner spherical shell carrier with carbamide impregnated. Carbamide/FAC composite suppressant with bilayer spherical shell was prepared by vacuum freeze-drying. The flame propagation and explosion performances of coal were tested, respectively. The results showed that the surface-loaded carbamide particles had a particle size of ∼4 nm. With the increasing content of carbamide/FAC composite suppressant, the maximum flame length gradually decreased, and the explosion suppression effect was gradually improved. Nearly complete explosion suppression of coal could be achieved with an added amount of 40 wt% carbamide/FAC composite suppressant. The carbamide loaded in carbamide/FAC composite suppressant mainly acted in the 0−τ1 stage to weaken (dP/dt)max. FAC mainly but not solely acted on the stage of τ1−τ2 to decrease Pmax. Carbamide particles were highly efficient and responsive. The suppression mechanism of carbamide/FAC composite suppressant was proposed, which was micro-nano multiscale complementary effect and deceleration-depressurization coupling effect.