# Study on the Ash Deposition Characteristics for Co-Combustion of Zhundong Coal with Cotton Stalk
## 3 Results and Discussion
### Effect of Cotton Stalk Blending Ratio on Ash Deposition Characteristics  
Ash deposition distribution under different blending ratios is shown in Figure 3. It can be seen that the distribution of the ash deposition in the furnace was relatively concentrated. Among these, the most severe slagging occurred on the four walls at the height of the main combustion zone. When the blending ratio was 0, the ash deposition rate in the main combustion zone was the highest, reaching 0.22 kg/(m\({}^{2}\cdot\)s), while the deposition rates in other areas predominantly ranged from 0.008-0.1 kg/(m\({}^{2}\cdot\)s). The deposited ash formed band-shaped, horizontally distributed layers, and the deposition rate decreased gradually along the flue-gas flow direction. In addition, it can be seen that the distribution of the ash deposits on each wall was not uniform, which was mainly due to the uneven distribution of the flow field in the furnace. The formation of ash deposition on the wall surfaces involved two essential processes: the melting of the ash particles under high temperatures and subsequent impingement onto heating surfaces. Therefore, the temperature and flow field distribution in the furnace were the primary factors influencing the ash deposition behavior. To further explore the reasons for the differences in the ash deposition distribution under different blending ratios, the temperature and flow field distribution in the furnace were analyzed. By comparing the ash deposition conditions in different areas, it can be seen that the ash deposition on the lower wall was light. This is because the temperature of the bottom area of the boiler was low, and therefore the adhesion probability of the ash particles was low. As the furnace height increased, the temperature and proportion of the molten ash increased, resulting in significant ash deposition on the furnace wall. The ash deposition status on the wall surface under different blending ratios is shown in Figure 3b-e; it can be seen that with the increase in the blending ratio, the deposition rate and deposition area also increased gradually. This is mainly because at the same temperature, the ash melting ratio gradually increased with the increase in the blending ratio. In order to reveal the cause of the uneven ash distribution, the temperature distribution at the height of the area with more serious ash deposition was further analyzed, as shown in Figure 4. The four sections are the lower, middle, and upper burner, and the middle of the SOFA. The temperature distribution of the different sections shows that the near-wall temperature exceeded 1700 K, creating favorable conditions for slagging. With the increase in the furnace height, the effect of tangential combustion decreased gradually. At furnace heights of 13.92 m, 18.92 m, and 22.16 m, the near-wall region maintained a high temperature of 1700-1850 K, corresponding to 0.37-0.40 molten ash in the mixed fuel. At  
Figure 3: Ash deposition distribution under different blending ratios: (**a**) 0%, (**b**) 10%, (**c**) 15%, (**d**) 20%, and (**e**) 25%. the height of 27.60 m, the SOFA obviously adhered to the wall, causing a large number of molten ash particles to impact and deposit on the wall. To further analyze the differences in ash deposition characteristics under different mixing ratios, the average ash deposition rate on the wall of the main combustion zone was calculated, and the results are shown in Figure 5. It can be seen that the average deposition rate increased gradually with the increase in the blending ratio. This may be due to the increase in alkali metal content in the ash after the addition of cotton stalks; the mass fraction of the molten phase in the ash increased, thus aggravating slagging. When the mixture ratio was 20% and 25%, the average ash deposition rate was 39.4% and 77.6%, which is higher than the deposition rate when the mixture ratio was 0%.