## 3 Results and Discussion
Notably, the ratio of masses of fuel compositions from three groups (FC; FC + 10% polymer particle, impregnated with a combustible liquid; FC + 30% wood sawdust), identical in the calorific value, is 1: 0.92: 1.12. According to the ultimate analysis (Table 2), wood contains 10 times less nitrogen and sulfur. Therefore, adding wood sawdust to FC significantly reduces the NOx and SOx concentrations from the combustion of these fuel compositions of identical mass. However, the heat of combustion of wood is 35% lower than that of FC (Table 2). Therefore, the mass of the fuel composition based on FC with 30% of wood sawdust has to be 1.12 times bigger to generate the same amount of heat, as the combustion of FC does. Thus, the difference in the NOx and SOx concentrations for composition No. 1 and compositions No. 5-No. 8 (per a unit of heat, released from the fuel pellet combustion) is 30% and 25% (Figure 7), respectively. Moreover, the ash content of wood is an order of magnitude lower than that of FC, so, the combustion of a larger mass of fuel pellets with it will not increase the amount of non-combustible solid residue, but will, on the contrary, somewhat decrease it. In its turn, adding a porous polymer particle, impregnated with a combustible liquid, to the fuel pellet composition, has a positive effect on its calorific value, since the heat of combustion of oil is almost twice as high as that of FC (Tables 2 and 3). Therefore, the mass of the fuel composition based on FC with 10% of porous polymer, impregnated with a combustible liquid, has to be 1.09 times smaller to generate identical amount of heat. Under such conditions, the difference in the NOx and SOx concentrations of the corresponding composition and FC without any components is 30% and 20% (Figure 7), respectively. The co-firing of dry coal with used oil increases the concentrations of the oxides of nitrogen and sulfur in flue gases. This is explained by a higher combustion temperature  
Figure 7: NOx (**a**) and SOx (**b**) concentrations in flue gases per a unit of heat released from fuel pellet combustion at \(T_{g}\) = 1000 \({}^{\circ}\)C.  
of such fuel compositions. It was established that [5], adding used oils to composite fuels increases the combustion temperature by 100-200 \({}^{\circ}\)C. For fuel compositions containing municipal solid waste, higher combustion temperature reduces the concentration of carcinogens, e.g., PCDD/Fs, despite higher NOx and SOx concentrations [5]. Apart from the effect of adding combustible components with lower content of nitrogen and sulfur or with greater calorific value to FC, the concentration of anthropogenic emissions in flue gases also depends on the chemical interaction of a large group of substances and compounds in the gas medium at relatively high temperatures [4]. The temperature of gases in the flame can reach 1100-1400 \({}^{\circ}\)C [5]. Under such conditions, the water vapors, as well as oxides of alkaline and alkaline-earth metals, [4] can significantly reduce the anthropogenic emissions [42]. However, a detailed mechanism of chemical reactions, explaining the content of anthropogenic emissions in flue gases from the combustion of different fuel compositions based on hydrocarbons, has not been established yet. We did not consider solving this task in our study, since it requires independent research. The analysis of anthropogenic emissions has shown that adding some biomass (from several percent to several-dozen percent) to FC significantly reduces the concentrations of sulfur and nitrogen oxides. This reduction in anthropogenic emissions is attributed to the following groups of factors. First, replacing some part of coal with components that contain much less sulfur and nitrogen (Table 2) reduces the NOx and SOx concentrations in flue gases, since solid fossil fuels are the main sources of the respective oxides [43], forming from the oxidation of volatiles and fuel coke during combustion.