## 3 Result and Discussion  
Suppression Effect of Industrial Solid Waste-Based Composite Powder Explosion Inhibitors on Coal Dust Explosion  
It is very important to study the characteristics of the explosion suppression of coal dust in an enclosed space for the explosion protection parameters of explosion protection facilities (such as the key parameters of venting area and venting pressure). The variation of the maximum explosion pressure and maximum explosion pressure rising rate can reflect the inhibition effect of explosion inhibitor on coal dust explosion. According to the standard GB/T16425, the standard 20 L spherical explosion system was used for the explosion suppression experiment [26; 27; 28], as indicated in Figure 6. The test apparatus is composed of the following three parts: the main spherical tank, the control system and the data acquisition system. The main spherical tank is made of stainless steel, and a nozzle and ignition lead are built in the main spherical tank. In the experiment, a given weight of dust was placed in the dust vessel. A 10 KJ chemical igniter mounted at the center was connected to the ignition lead. The explosion vessel was safely closed. The explosion chamber was vacuumed to 0.06 MPa. The dispersion gas pressure was set to 2.0 MPa. When the solenoid valve between the dust vessel and the test chamber started automatically, air and dust were injected into the explosion chamber and ignited after a 60-millisecond time delay. The mixture of coal dust with the MCN-NaHCO\({}_{3}\) composite powder explosion inhibitor, the MCN-KH\({}_{2}\)PO\({}_{4}\) composite powder explosion inhibitor and the MCN-Al(OH)\({}_{3}\) composite powder explosion inhibitor was carried out. The explosion characteristics of the mixture of single powder (pure NaHCO\({}_{3}\), pure KH\({}_{2}\)PO\({}_{4}\), pure Al(OH)\({}_{3}\) and pure MCN) and coal dust were compared. Into the coal dust, 0, 10, 20, 30, 40, 50, 60, 70, 80, 90 and 100% of the explosion suppression powder were added. Figure 7 shows the explosion pressure curve of the explosion inhibitor for suppressing a coal dust explosion. The results show that the maximum explosion pressure (\(P\)max) and maximum rate of explosion pressure rise (\((dp/dt)\)max) of the coal dust decrease under the action of an explosion inhibitor. A 40% MCN-NaHCO\({}_{3}\) composite powder explosion inhibitor, an MCN-KH\({}_{2}\)PO\({}_{4}\) composite powder explosion inhibitor and a 50% MCN-Al(OH)\({}_{3}\) composite powder explosion inhibitor can completely inhibit the explosion of coal dust,  
Figure 6: 20 L spherical explosion system. (1) 20-liter spherical tank, (2) Testing system for explosive characteristics electrode, (3) Computer, (4) High-pressure air cylinder, (5) Vacuum pump, (6) Nozzle, (7) Powder storage bin, (8) Solenoid valve, (9) High pressure air storage vessel, (10) Pressure gauge, (11) Exhaust valve 1, (12) Air inlet valve, (13) Pressure relief valve, (14) Vacuum pump ventilation valve, (15) Pressure sensor, (16) Ignition lead, (17) Exhaust valve 2.  
and the inhibition effect of single powder is not as good as that of a red mud-based composite powder explosion inhibitor. The _P_max of coal dust is 0.64 MPa, and the \((dp/dt)\)max is 26.5 MPa/s. After the red mud composite powder explosion inhibitor is added, the maximum pressure reduction rate of the coal dust is 52.3% for a 30% MCN-NaHCO\({}_{3}\) composite powder explosion inhibitor, 49.9% for a 30% MCN-KH\({}_{2}\)PO\({}_{4}\) composite powder explosion inhibitor and 46.7% for a 40% MCN-Al(OH)\({}_{3}\) composite powder explosion inhibitor. By coal dust explosion suppression efficiency, the composite powder explosion inhibitors are sorted as MCN-NaHCO\({}_{3}\) composite powder explosion inhibitor > MCN-KH\({}_{2}\)PO\({}_{4}\) composite powder explosion inhibitor > MCN-Al(OH)\({}_{3}\) composite powder explosion inhibitor.