# Development of a Novel Shaft Dryer for Coal-Based Green Needle Coke Drying Process
## 4 Results and Discussions  
Figure 6 shows three kinds of green coke with different size at the initial moisture content of 22%. As the moisture content relates to the granulation properties [41], the lump, fine, and mixed green coke particles with the median size of 35.0, 1.0, and 21.4 mm, respectively, were selected in this experiment. For mixed green coke, the lump green coke accounts for 60%. Figure 7 shows the relationship between moisture content and gas temperature. With the increase in gas temperature, the moisture content reduces remarkably. For drying gas at 350 \({}^{\circ}\)C, the moisture content of lump green coke was 6.82%, while that of fine and mixed green cokes could be as low as 1.38% and 0.40%, respectively. Though lump green coke can be dried by using this shaft dryer, it may consume more energy. It can be found that the mixed green coke has the lowest moisture content because this plan has the best gas flow and heat transfer effect. Thus, mixed green coke is a good option in the real drying process. Table 3 lists the measurement data and results of the vertex angle of the pile of green cokes of five reduplicative experiments. The vertex angle of the pile is another key property of coke besides the particle size distribution and strength [42]. It is shown that the average vertex angle of pile of green cokes is 109.2\({}^{\circ}\), which is very important to design the structure of the distributor. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**No.** & **Vertical Height (mm)** & **Hypotenuse (mm)** & **Vertex Angle (\({}^{\circ}\))** \\ \hline
1 & 314 & 556 & 112 \\
2 & 283 & 477 & 108 \\
3 & 287 & 495 & 110 \\
4 & 283 & 470 & 106 \\
5 & 284 & 495 & 110 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Results of vertex angle of the pile of green cokes. Figure 6: Three different green cokes used in the experiment. Figure 7: Relationship between moisture content and gas temperature. To investigate the pressure drop characteristics of green cokes, a fixed bed experiment was conducted. Four sets of green cokes as shown in Table 2 were used in this experiment. The relationship between the pressure drop and bed height is shown in Figure 8. An approximately linear relationship is shown and the pressure drop increases with the increase in bed height. The pressure characteristics vary with the particle sizes [43]. The green coke with larger size has a less pressure drop, because of its relatively large void ratio and good gas flow behavior. When the bed height is 1250 mm, the total pressure drops of the four test sets with median green coke size of 26.85, 29.00, 30.45, and 31.80 mm are 6104, 5944, 5744, and 5504 Pa, respectively. It can be found from Figure 9 that the specific pressure drops of the four test sets are 5714, 5554, 5354, and 5114 Pa/m, respectively. Figure 10 shows the relationship between the mass of green coke leakage and tooth spacing based on the results of five repeated experiments. It can be seen that the green coke leakage increases with the increase in tooth spacing. Given that the rolls may experience a horizontal movement because of the axial compression among green cokes when discharging, the initial green coke leakage should be  
Figure 8: Relationship between pressure drop and bed height. Test no. refers to that listed in Table 2.  
Figure 9: Relationship between specific pressure drop and green coke size. small and adjusted to its reasonable leakage tardily. The optimal tooth spacing can be determined according to the requirement of production yield. The optimal rotary speed can be determined as follows. The mixed green cokes with the maximum particle size as 70 mm were filled in the drying tank. The rolls horizontally set in the shaft dryer were rotated by 180\({}^{\circ}\) at a constantly rotary speed. After discharging, the green coke leakage was weighed. Then, the rotary speed of the rollers can be obtained by the mass of leakage and the required leakage per minute in real production.