## 3 Results and Discussion
### TGA of Individual Fuels
The second DTG  
\begin{table}
\begin{tabular}{l c c c c c c} \hline \hline \multicolumn{1}{c}{**Characteristics**} & \multicolumn{6}{c}{**Fuels**} \\ \cline{2-7}  & **C-1** & **C-2** & **B-1** & **B-2** & **CB-1** & **CB-2** \\ \hline \(DTG_{\text{max1}}\), \%/min & 0.69 & 0.49 & 0.77 & 0.84 & 0.60 & 0.50 \\ \hline \(T_{\text{DTGI}}\), \({}^{\circ}\)C & 93 & 98 & 92 & 102 & 87 & 82 \\ \hline \(DTG_{\text{max2}}\), \%/min & - & - & 5.19 & 4.56 & 3.16 & 2.52 \\ \hline  
extremum for the third stage, which includes the combustion of the main part of the coke residue, is observed in the temperature range 382-542 \({}^{\circ}\)C for B-1 with a maximum mass loss rate of 2.7 %/min and 400-642 \({}^{\circ}\)C for B-2 with a maximum mass loss rate 1.9 %/min (Figure 3b). Mass loss during coke residue combustion was 39% for B-1 and B-2. The process of burning needles is completed at a temperature of 542 \({}^{\circ}\)C for B-1 and 642 \({}^{\circ}\)C for B-2. For needle particles B-1, the combustion index was 5.02 \(\times\) 10\({}^{-8}\) min\({}^{-2}\)\({}^{\circ}\)C\({}^{-3}\), and for larger particles B-2, it was 4.01 \(\times\) 10\({}^{-8}\) min\({}^{-2}\)\({}^{\circ}\)C\({}^{-3}\) (Table 2). In general, the combustion index of biomass is several times higher than for coal due to the high content of flammable volatiles in biomass. A comparison of the heating process of cedar needles with different particle sizes showed that for large B-2 particles, the main stages at which the combustion of volatiles and coke residue occurs also shifted (as for coal) to higher temperatures compared to fine B-1 particles. The maximum mass loss rate of B-2 was reduced by 14%, and the combustion index was reduced by 25% compared to coal. The mass loss for both particle sizes did not change during the combustion of the cedar needle coke residue, in contrast to coal, where with an increase in particle size, the mass loss of C-2 decreased by 5% compared to C-1 (Figure 3a). The characteristics of the coal combustion process are lower compared to those obtained from studying the combustion characteristics of biomass (Table 2). This pattern was also noted by [PERSON] et al. [34], who conducted a study of the co-combustion of coal and pine sawdust. When heating coal and biomass particles, distinct differences in the profiles of TG and DTG curves are observed for particles of different sizes (Figure 3), especially in the second and third combustion stages. An increase in particle size negatively affects the combustion characteristics of coal and biomass, which may be attributed to the formation of a significant temperature gradient in large particles. When burning coal with a larger particle size, the mass loss rate decreases, as does a shift to higher temperatures in the value of the maximum temperature corresponding to the maximum mass loss rate (Table 2). These main characteristics influence the reduction of the coal combustion index. The decrease in the combustion index is also affected by a decrease in the temperature at which ignition of the coke residue occurs, the temperature of which increased with the increase in coal particles. When comparing the combustion of biomass with different particle sizes, similar processes occur as with coal.