## 3 Investigation of Adhesive Clogging Characteristics in Underground Coal Bunkers
### Analysis of Adhesive Clogging Characteristics of the Coal Bunker
#### 3.3.2 Influence of Raw Coal Moisture Content on Adhesive Clogging in Coal Bunker  
(1) Coal flow characteristics  
This study conducted simulations under conditions of a coal storage height of 5 m and a Bunker hopper angle of 60\({}^{\circ}\), with varying raw coal moisture contents of \(w=0\%\), 1%, 3%, and 5%. Figure 19 presents the characteristics of coal discharge flow velocity under different moisture content conditions. Figure 19: Coal flow velocity distribution under different raw coal moisture content conditions: (a) \(w=0\%\); (b) \(w=1\%\); (c) \(w=3\%\); (d) \(w=5\%\). Figure 18: Dynamic wall pressure changes during the discharge process at different coal Bunker convergence angles. From this figure, it can be observed that the raw coal moisture content has a significant impact on the coal flow characteristics. When \(w=0\%\), except for a small amount of coal adhering to the wall, the overall flow velocity of the coal is relatively high, exhibiting mass flow characteristics. When \(w=1\%\) and \(3\%\), the coal flow velocity decreases, and low-velocity adhered coal appears near the bunker wall, with a high-velocity channel forming in the center of the bunker. The coal flow pattern transitions from mass flow to central flow, which is due to the increased moisture content enhancing the adhesion of the coal, leading to a higher flow velocity in the center as the coal in the center is less affected than the coal near the bunker wall. When \(w=5\%\), only the coal at the discharge outlet loses support and flows out of the coal bunker, while the flow velocity of the remaining coal is close to zero, resulting in an arching blockage. Figure 20 illustrates the adhesive clogging situation of the coal bunker at different raw coal moisture contents. When \(w=0\%\), the adhered coal in the coal bunker is distinctly layered, conforming to the mass flow characteristic. When \(w=1\%\), a small portion of the upper layer of adhered coal mixes with the bottom layer, causing the coal flow pattern to transition to central flow. When \(w=3\%\), a substantial amount of mixed adhered coal is observed, which is more consistent with the characteristics of central flow. The simulation test results of coal bunker adhesive clogging can be correlated with the coal bunker flow pattern characteristics depicted in Figure 20.  
Figure 21 depicts the curve of the mass fraction of adhered coal in the coal bunker as a function of raw coal moisture content. It can be observed that as the moisture content \(w\) increases, the fraction of adhered coal in the coal bunker exhibits an exponential growth trend. When \(w=0\%\), \(1\%\), there is only a small amount of adhered coal in the coal bunker, with mass fractions of \(5.76\%\) and \(6.31\%\), respectively. When \(w=3\%\), the amount of adhered coal in the coal bunker increases significantly, with the mass fraction increasing to \(17.97\%\), more than triple the value at lower moisture contents, and a substantial amount of coal agglomeration occurs inside the bunker. When \(w=5\%\), an arching blockage occurs in the coal bunker, and the mass fraction of adhered coal reaches \(98.26\%\). These findings demonstrate that the raw coal moisture content has a significant impact on the coal flow, and coal with higher moisture content is more prone to causing adhesion and increasing the risk of blockage in the coal bunker. Figure 20: Adhesive clogging situation of coal bunker under different raw coal moisture content conditions: (**a**) \(w=0\%\); (**b**) \(w=1\%\); (**c**) \(w=3\%\); (**d**) \(w=5\%\). Pressure distribution on the coal bunker wall  
The dynamic wall pressure variation curves in Figure 22 show that wall pressure changes with moisture content correspond to the bunker's adhesive clogging conditions. When \(w\) = 0% and 1%, the wall pressure curves of the coal are similar, with closely related adhesive clogging situations. When \(w\) = 3%, the peak wall pressure is relatively high, facilitating coal adhesion to the wall, and thus the amount of adhered coal increases significantly.