Inhibitory effect and mechanism of urea on wheat starch explosion

This paper aimed to determine the inhibitory effect of urea on wheat starch explosion and reveal its chemical inhibition mechanism. Dust explosion pressure tests and flame propagation experiments were conducted using 20 L Siwek spheres and modified Hartmann tubes. The inhibitory mechanism of urea on wheat starch explosion was investigated using the chemical kinetic model Gri3.0. Results demonstrated that urea can significantly reduce the starch explosion pressure and decrease the probability of explosion. Urea also effectively reduced the flame size (projected area, height) of starch combustion, slowed down flame propagation velocity, and suppressed reburning. When the inerting ratio of urea in starch reached 0.2, the reburning phenomenon disappeared. When the inerting ratio of urea reached 0.4, flame propagation was effectively controlled, and the flame projected area was reduced by 95 %. Analysis of the inhibitory mechanism of urea on starch explosions revealed that after capturing H and OH radicals in the combustion reaction, the pyrolysis products of urea, NH3 and HNCO, generated NH2, NH, HNO, and NCO. These intermediates further captured H, O, and OH and formed a reaction chain that consumed key free radicals, which slowed down the reaction rate of important elementary reactions in the combustion process and thus inhibited combustion.