# Study on the Combustion Behavior and Kinetic Characteristics of Semi-Coke from Oil Shale
## 3 Results and Discussion  
### Combustion Characteristics of Oil Shale Semi-Coke  
#### 3.1.1 Thermogravimetric Analysis (TGA) Results  
The thermogravimetric analysis (TGA) experiment was conducted to obtain the TG and DTG curves of oil shale semi-coke at different heating rates (5 \({}^{\circ}\)C/min, 10 \({}^{\circ}\)C/min, 15 \({}^{\circ}\)C/min, 20 \({}^{\circ}\)C/min, and 25 \({}^{\circ}\)C/min). The results are shown in Figure 2.  
As shown in Figure 2, the combustion process of the sample can be divided into three stages. The first stage is the low-temperature stage (50-310 \({}^{\circ}\)C). According to the TG curve, the mass loss during this stage is relatively small (about 10%). A minor loss peak appears on the DTG curve, with a peak temperature around 80-110 \({}^{\circ}\)C. At higher heating rates, the peak temperature shifts to a higher value. This stage mainly involves the volatilization of volatile components. The second stage is the medium-temperature stage (310-670 \({}^{\circ}\)C), which is the main stage of mass loss, accounting for about 28-37% of the total. A significant  
Figure 2: TG and DTG curves of oil shale semi-coke.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Function** & **Mechanism** & **Differential Form \(f(\alpha)\)** & **Integral Form \(G(\alpha)\)** \\ \hline \multicolumn{4}{c}{Nucleation Models} \\ \hline [PERSON]\(-\)[PERSON] & Random nucleation and nuclei growth & \(1/2(1-\alpha)[-\ln(1-\alpha)]^{-1}\) & \([-\ln(1-\alpha)]^{2}\) \\  & A2, 2D, \(n=2\) & & \\ [PERSON]\(-\)[PERSON] & Random nucleation and nuclei growth & \(1/3(1-\alpha)[-\ln(1-\alpha)]^{-2}\) & \([-\ln(1-\alpha)]^{3}\) \\  & A3, 3D, \(n=3\) & & \\  & \(n=1/4\) & \(4\alpha^{3/4}\) & \(\alpha^{1/4}\) \\  & \(n=1/3\) & \(3\alpha^{2/3}\) & \(\alpha^{1/3}\) \\  & \(n=1/2\) & \(2\alpha^{1/2}\) & \(\alpha^{1/2}\) \\  & \(n=2\) & \(1/2\alpha^{-1}\) & \(\alpha^{2}\) \\ \hline \hline \end{tabular}
\end{table}
Table 3: _Cont._loss peak is observed on the DTG curve. During this stage, the carbonaceous components in oil shale semi-coke (mainly fixed carbon and a small amount of residual volatiles) undergo oxidation reactions. The peak temperature also shifts to higher values with the increasing heating rate. The third stage is the high-temperature stage (670-950 \({}^{\circ}\)C), mainly caused by the decomposition of carbonate minerals and oxidation of residuals, with a mass loss of about 43-62%. A more prominent mass loss peak appears on the DTG curve, with a peak temperature at around 770-820 \({}^{\circ}\)C. However, the reaction rate in this stage is relatively low and is significantly affected by the mineral composition [21].  
The combustion process of oil shale semi-coke was found to consist of three distinct stages, with the main mass loss occurring in the medium-temperature zone (310-670 \({}^{\circ}\)C). This observation is consistent with the findings of [PERSON] et al. [22], who reported a similar multi-stage combustion pattern in thermogravimetric analysis of semi-coke samples. However, the onset temperature of the main combustion stage in this study (\(\sim\)310 \({}^{\circ}\)C) is slightly lower than that reported by [PERSON] et al. [23], which may be attributed to differences in sample composition and particle size.