## 3 Investigation of Adhesive Clogging Characteristics in Underground Coal Bunkers
### Analysis of Adhesive Clogging Characteristics of the Coal Bunker
#### 3.3.3 Influence of Coal Storage Height on Adhesive Clogging of Coal Bunker  
1. Coal flow characteristics In this study, under the conditions of a hopper angle \(\alpha=60^{\circ}\) and a raw coal moisture content \(w=3\%\), we set coal storage heights \(h\) at 3 m, 5 m, 7 m, 10 m, and 20 m, with the numerical calculation model depicted in Figure 23.  
Simulation calculations provided insights into the distribution of coal discharge flow velocities at varying storage heights, as shown in Figure 24. At \(h=3\) m, the coal flow velocity within the bunker is relatively high, exhibiting characteristics of mass flow. Conversely, at \(h=5\) m and 7 m, the flow velocity decreases significantly, transitioning to funnel flow. At \(h=10\) m and beyond, the coal movement is negligible, leading to arching and blockage. It is evident that as storage height increases, the compaction force and adhesive interactions between coal particles intensify, affecting flow velocity and altering the flow state, which in turn increases the occurrence of adhesive coal and, in severe cases, results in arching blockages.
2. Adhesive clogging situation of coal bunker Figure 25 shows the adhesive blockage conditions in coal bunkers at various storage heights. At \(h=3\) m, the distribution of adhesive coal aligns with the storage sequence, and coal discharges in an orderly mass flow state. At \(h=5\) m and 7 m, adhesive coal forms layered mixed deposits, consistent with a \"last-in, first-out\" pattern. Thus, the storage height influences the flow state of coal, affecting the distribution of adhesive blockages within the bunker.  
Figure 23: Numerical calculation model of coal bunker with different coal storage heights: (**a**) \(h=3\) m; (**b**) \(h=5\) m; (**c**) \(h=7\) m; (**d**) \(h=10\) m; (**e**) \(h=20\) m.  
Figure 26 presents the variation curve of the adhesive coal mass fraction with storage height. It indicates that at \(h\) = 3 m, 5 m, and 7 m, the bunker experiences varying degrees of adhesive coal, with mass fractions of 9.78%, 16.97%, and 28.14%, respectively. At \(h\) = 10 m and 20 m, arching blockages occur, with mass fractions reaching 90.36% and 98.18%, respectively, severely affecting the bunker's functionality.  
Figure 24: Coal flow velocity distribution under different coal storage height conditions: (**a**) \(h\) = 3 m; (**b**) \(h\) = 5 m; (**c**) \(h\) = 7 m; (**d**) \(h\) = 10 m; (**e**) \(h\) = 20 m.  
Figure 25: Adhesive clogging situation of coal bunker under different coal storage height conditions: (**a**) \(h\) = 3 m; (**b**) \(h\) = 5 m; (**c**) \(h\) = 7 m; (**d**) \(h\) = 10 m; (**e**) \(h\) = 20 m.  
(3) Pressure distribution on the coal burker wall  
Given that severe arching blockages occur at \(h\geq 10\) m, resulting in minimal changes in wall pressure, this study focuses on bunkers with storage heights of 3 m, 5 m, and 7 m. Dynamic pressure changes on the walls during discharge are shown in Figure 27. As \(h\) increases, the initial static pressure on the burker wall increases significantly, the compaction force on the coal increases, the contact force between the coal particles increases, and the adhesion effect is enhanced. Simultaneously, the peak dynamic wall pressure during the discharge process increases significantly, prompting the coal to adhere to the burker wall more frequently and thus exacerbating the coal adhesion.  
In conclusion, the coal storage height in bunkers affects the degree of coal compaction and flow state, leading to adhesive blockages. Scientific planning of storage height can reduce contact forces between coal particles or between coal and burker walls, lowering the likelihood of blockages and ensuring efficient operation of underground coal bunkers.