## 3 Results and Discussion
Figure 9: _Cont._  
Figure 9 shows the analysis results of carbon oxide formation during pyrolysis of T grade coal, wood, and the mixtures based on them with an increase in the proportion of the wood component in the mixture from 10% to 50%. Analysis of Figure 9 showed an increase in the carbon monoxide concentration. The increase in the maximum peak concentration was 51%, which is only 10% less compared to the calculated area under the same curve. The results of calculating the areas under the gas curves for lean coal are presented in Table 3.  
Figure 9: Changes in the concentration of carbon oxide in the gaseous products of the thermal decomposition of mixed fuels based on T-grade coal and wood with a change in the proportion of the latter in the mixture from 10% to 50%: (**a**) lean coal 100%; (**b**) lean coal 90%/wood waste 10%; (**c**) lean coal 75%/wood waste 25%; (**d**) lean coal 50%/wood waste 50%. Analysis of the areas under the gas curves for T-grade coal made it possible to reliably state a significant 80.24% decrease in sulfur oxides in the thermal decomposition products of mixed fuels with an increase in the biomass fraction in the mixture. The difference between the maximum concentration of sulfur oxides and the area under the curve was no more than 10.02%. The results of the experiments allow us to conclude that addition of wood to coals of different grades (for example, D, T) does not lead to an identical process of formation of sulfur, nitrogen, and carbon oxides. An increase in the concentration of pine sawdust in the mixed fuel up to 50% leads to a significant increase in the yield of carbon oxides for D-grade coal. The concentration of CO\({}_{2}\) in the pyrolysis products of a mixture of T-grade coal with wood is significantly reduced in comparison with homogeneous T-grade coal. A smaller discrepancy in the concentrations of nitrogen oxides was found after experiments with mixtures of wood with D- and T-grade coal. A stable and significant decrease in concentrations was found only for sulfur oxides in pyrolysis products of mixtures of D- and T-grade coals with wood. According to the results of similar experiments [51], a hypothesis was formulated that products of thermal decomposition interact during the joint combustion of mixtures of crushed wood with dispersed coals, which results in formation of calcium and aluminum sulfates in the ash of the studied fuel mixtures. Introduction of wood (in the form of pine sawdust) in a mixture with T-grade coal leads [55] to an increase in the concentration of sulfur, calcium, and aluminum in the ash residue of the mixture compared to the ash of homogeneous coal. However, analysis of the total elemental composition shows that the formation intensity of such salts can differ quite significantly for different coals (depending on the mineral composition of the fuel). Analysis of the total elemental composition of the ash of T- and D-grade coals and wood obtained at a medium temperature of 1073 K was performed to substantiate the hypothesis formulated in [50]. The analysis was performed using iCAP Duo, Thermo Scientific instrument, Santa Clara, United States. This optical emission spectrometer with inductively coupled plasma allows for qualitative, semi-quantitative, and quantitative elemental analysis. The results of the study are shown in Figure 6:0  
Analysis of Figure 10 allows us to conclude that wood ash contains significantly more calcium in comparison with homogeneous coals. However, the presence of calcium in wood can enhance the synergistic effect of calcium sulfates formation in the ash of mixed fuels. The content of aluminum in T grade coal was 23%, and in the D grade coal--27%. The high concentration of this metal in comparison with other elements contained in the ash of the initial components suggests that it has a significant effect on reducing the yield of sulfur oxides; for example, in the gaseous products of the thermal decomposition of mixtures of the studied coals and wood.