## 6 Discussion of Results
The \(A_{n}\) values corresponded to the range of 0.03-0.907. The maximum efficiency of most fuels was achieved when the combustion chamber temperature was about 800 \({}^{\circ}\)C. The highest \(A_{n}\) belonged to coal processing waste (fuel 1) and waste-derived slurry with turbine oil (fuel 3) when calculated using AHP. When making the transition from the WSM and the WPM to the AHP, the integral efficiency indicator changed substantially (the difference reached 90% with some types of fuels; see Figure 5a). Coal had the lowest efficiency indicator of all the fuels under study. Coal-water slurry (fuel 2) was closest to coal in terms of the integral efficiency indicator. Thus, we can conclude that the country under consideration could be interested in using the combustion technologies of coal processing waste (filter cake in a wet state) and slurries with a combustible liquid to achieve the maximum effect in the environment, energy performance, economy, social life, and enterprise safety. Figure 4: Influence of the temperature on the integral efficiency indicator of waste-derived slurry (the indicator was calculated for Japan using the WSM, the WPM, and the AHP). Figure 5: The integral efficiency indicator calculated using three multi-criteria decision analysis (MCDA) methods at 700 \({}^{\circ}\)C, 800 \({}^{\circ}\)C, and 900 \({}^{\circ}\)C (results for China). By generalizing the research findings, we can conclude that it makes sense to use MCDA methods to evaluate and compare several fuel alternatives. Without them, it seems impossible to identify the best options when the number of contributing factors increases. The final MCDA result does not give the full picture to understand the specific advantages and disadvantages of fuel alternatives. It is necessary to apply the comparison matrices of absolute and normalized parameter values. Nevertheless, multi-criteria analysis methods can be exploited as a tool for the planning, designing, and use of combustible waste disposal technologies to produce thermal and electrical energy. Thus, for example, it was found that the waste-derived slurries under study had the lowest efficiency indicators in Japan. However, on the whole, such fuels have great potential in different spheres, since their generalized efficiency indicator exceeds that of coal 20-50 times. In earlier works (for example, [PERSON] and colleagues [35; 36]) that dealt with atypical fuel mixtures from wastes, specific multi-criteria analysis methods were not used. The dimensionless ratios of several parameters when compared with coal or fuel oil were used in these studies. However, the fact of interest is that despite the difference in the calculation procedures in the present work and previous studies, the total efficiency indicator for fuel waste-derived slurries was still higher than for coal or close to it. Of course, the methods used in [PERSON] and colleagues [35; 36] were more limited since they did not explicitly present the variability of priorities and all the assessments were performed without any reference to the region or enterprises. In contrast, this study aimed to apply the MCDA tools to the assessment of waste-based fuels for different countries by taking into account different economic, social, and environmental priorities. The modern energy sector needs diversification, which is due to several economic and environmental problems (high energy rates, environmental degradation, fuel deficit, and others). This need can be satisfied by developing alternative energy sources. Renewable power generation can be viable and efficient under certain conditions, but its development is limited by the lack of investment, geographical, and climate opportunities of particular regions. On the other hand, waste, considered as a fuel slurry component, is available even where it is difficult or impossible to put in place the production of energy from renewable energy sources. When taken critically, each of the fuels under consideration has both benefits and disadvantages.