## 3 Results and Discussion
### Experimental Results
The presence of water and additional plant component significantly affects the concentrations of sulfur and nitrogen oxides, produced from combustion. Replacing coal with neutral (in terms of sulfur and nitrogen) components has a direct effect on the amount of fuel sulfur and nitrogen [49; 50]. They are the main sources of the corresponding oxides, formed in the oxidation of volatiles and coke of the fuel during combustion, which is why the lowest emissions were recorded for the composition with rapeseed oil, which has the lowest amount of sulfur and nitrogen (Table 2). Metal-containing components in the ash part of dry plant components and filter cake (ash analysis (wt %) biomass and filter cake are presented in [10; 20]) can also react with sulfur and nitrogen oxides (CaO+SO\({}_{2}\)+1/2O\({}_{2}\)\(\rightarrow\)CaSO\({}_{4}\); 3 SO\({}_{2}\)+2 Fe(OH)\({}_{3}\)\(\rightarrow\)Fe\({}_{2}\)(SO\({}_{3}\))\({}_{3}\)+H\({}_{2}\)O; 2 Fe+3 NO\(\rightarrow\)3/2N\({}_{2}\)+Fe\({}_{2}\)O\({}_{3}\)) [10; 49; 50; 51]. Figure 2: Frames of slurry fuel (90% filter cake, 10% straw) combustion. at certain temperatures (over 800 \({}^{\circ}\)C). This produces new substances, which either become ash residue or take part in further chemical transformations, without NO\({}_{\rm x}\) or SO\({}_{\rm x}\) formation [49,51]. Based on the data [10,20] about the composition of fuel components, biomass contains a greater amount of metal compounds (e.g., calcium, magnesium), capable of reacting with sulfur and nitrogen oxides, than filter cake does. We can assume that sulfur and nitrogen oxides interact with metal compounds during the combustion in a gas medium, even when 10% of biomass is added to filter cake. This hypothesis is also confirmed by the results of other authors [49,52,53]. In particular, in the combustion of straw, the reactions between metal-containing compounds in the ash part of biomass and gaseous emissions can compensate for a higher content of nitrogen (as compared with filter cake) (Table 2). Additionally, the final NO\({}_{\rm x}\) emissions are affected by the type of nitrogen-containing compounds in the fuel. In biomass, most of the nitrogen is in volatile components, which are released and burn out at the initial stage of ignition and combustion as compounds, some of which do not produce nitrogen oxides [54]. In the case of coal and coal processing waste, nitrogen oxides are usually formed at the stage of the oxidation of the coke part at relatively high temperatures [49]. Figure 4: Concentration of nitrogen (**a**) and sulfur oxides (**b**) emissions of slurry fuels with biomass and coal vs. combustion chamber temperatures: 1%– 00% coal; 2%–90% filter cake and 10% sawdust; 3%–90% filter cake and 10% rapeseed oil; 4%–90% filter cake and 10% leaves; 5%–90% filter cake and 10% sunflower cake; 6%–90% filter cake and 10% straw; 7%–100% filter cake. Figure 3: Ignition delay times of slurry droplets with biomass and coal vs. combustion chamber temperatures (**a**); threshold (minimum) ignition temperatures and maximum combustion temperatures of slurry droplets (**b**): 1%–100% coal; 2%–90% filter cake and 10% sawdust; 3%–90% filter cake and 10% rapeseed oil; 4%–90% filter cake and 10% leaves; 5%–90% filter cake and 10% sunflower cake; 6%–90% filter cake and 10% straw; 7%–100% filter cake. The Y-axis represents the fuel number. The caption to the figure shows these numbers and the corresponding fuel. Different color in (**b**) correspond to color in (**a**) that characterized different fuel compositions. In addition to anthropogenic emissions during the co-combustion of fossil fuels with some additives, carcinogenic substances are also formed.