## 3 Results and Discussion
### Efficiency Indicators of Combustion of Slurry Fuels with Biomass
Using the method from [17], the preparation, storage, and combustion costs were calculated for coal (main fuel) and slurry fuels based on coal flotation waste at a thermal power plant. When switching from traditional fuel to slurries, the amount of the necessary equipment for the systems listed above decreases significantly, hence the costs are reduced as well. Costly equipment (unloader, belt conveyor, crusher, pulverizer, raw coal and coal dust bunker, sizer, cyclone, etc.) for coal storage, pulverization, and transportation is no longer needed. The fuel system, when using composite fuels based on coal processing waste, includes much fewer elements and consists of tanks for storing separate components and ready-to-use slurries with a homogenizer and fuel feeding system. When using filter cake, no equipment for fuel pulverization and transportation on the conveyor is needed, since coal particles are already 80-140 \(\upmu\)m in size. Using Equation (1), it was calculated the relative efficiency indicator for all the fuels. The results are presented in Table 6. Figure 5 presents an angle diagram to illustrate the regions of minor and, on the contrary, great differences in the integral characteristics, studied for the six compositions vs. coal. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c} \hline \hline \multirow{3}{*}{**Criteria**} & \multicolumn{10}{c}{**Fuel \({}^{*}\)**} \\ \cline{2-13}  & \multicolumn{3}{c}{**1**} & \multicolumn{3}{c}{**2**} & \multicolumn{3}{c}{**3**} & \multicolumn{3}{c}{**4**} & \multicolumn{3}{c}{**5**} & \multicolumn{3}{c}{**6**} & \multicolumn{3}{c}{**7**} \\ \cline{3-13}  & **abs** & **norm** & **abs** & **norm** & **abs** & **norm** & **abs** & **norm** & **abs** & **norm** & **abs** & **norm** & **abs** & **norm** \\ \hline \multirow{3}{*}{\(\tau_{\text{d}}\), s} & at 700 \({}^{\circ}\)C & 8.3 & 1 & 10.97 & 0.76 & 23 & 0.36 & 12.9 & 0.64 & 11.3 & 0.74 & 12 & 0.69 & 12.2 & 0.68 \\ \cline{2-13}  & at 800 \({}^{\circ}\)C & 6.7 & 1 & 8.87 & 0.76 & 14 & 0.48 & 10 & 0.67 & 8.97 & 0.75 & 9.5 & 0.71 & 11.3 & 0.59 \\ \cline{2-13}  & at 900 \({}^{\circ}\)C & 2.5 & 1 & 8.33 & 0.30 & 11.5 & 0.22 & 7.5 & 0.33 & 7.36 & 0.34 & 8 & 0.31 & 9.5 & 0.26 \\ \hline \multirow{3}{*}{\(T_{\text{g}}\), \({}^{\text{max}}\), \({}^{\circ}\)C} & 1350 & 1 & 987 & 0.73 & 1020 & 0.76 & 930 & 0.69 & 885 & 0.66 & 896 & 0.66 & 1025 & 0.76 \\ \hline \multirow{3}{*}{\(T_{\text{g}}\), \({}^{\text{min}}\), \({}^{\circ}\)C} & 530 & 0.84 & 445 & 1 & 475 & 0.94 & 461 & 0.96 & 449 & 0.99 & 454 & 0.98 & 448 & 0.99 \\ \cline{2-13}  & \(Q^{\prime}\), M/kg & 29.76 & 1 & 14.55 & 0.49 & 18.96 & 0.64 & 14.44 & 0.49 & 14.4 & 0.34 & 14.51 & 0.49 & 14.15 & 0.47 \\ \hline \multirow{3}{*}{NO\({}_{\
u}\), ppm} & at 700 \({}^{\circ}\)C & 140 & 0.41 & 80 & 0.71 & 57 & 1 & 78 & 0.73 & 84 & 0.68 & 104 & 0.55 & 80 & 0.71 \\ \cline{2-13}  & at 800 \({}^{\circ}\)C & 179 & 0.45 & 100 & 0.8 & 80 & 1 & 130 & 0.53 & 108 & 0.74 & 122 & 0.66 & 157 & 0.51 \\ \cline{2-13}  & at 900 \({}  
The findings (Table 6, Figure 5) show that all the slurries are characterized by a higher complex efficiency indicator than coal (green region in Figure 5). Obtained results show that replacing conventional coal with slurries will make it possible to increase the fuel efficiency by 10%-24%, depending on the combustion conditions and type of biomass used in the mixture. The composition with 90% filter cake and 10% leaves features the maximum An. This fuel has quite good indicators in all the criteria, which leads to the highest An. Considering these criteria separately (Table 5), the composition with 90% filter cake and 10% rapeseed oil was the best in the group in most of the criteria, however the high cost of rapeseed oil and its low ignition indicator led to a lower overall efficiency An. Therefore, it is reasonable to choose the type and concentration of biomass in the fuel composition, evaluating a complex of environmental, economic, and energy performance indicators.