## 2 Materials and Methods
### Combustion Test  
The combustion tests were carried out using a technical-scale combustion chamber (height of 3.4 m and internal diameter of 0.6 m), which was used in previous research [22]. The three main parts of the installation are the combustion chamber with burners, a high-temperature precipitator, and an exhaust gas cooling system. The schematic of the experimental setup is presented in Figure 1. The combustion chamber is equipped with four burners: (1) main burner (gaseous, liquid, or pulverized), (2) additional gaseous burner, (3) pilot burner (gaseous), and (4) radial burner. Burners (1)-(3) are situated at the top cover of the combustion chamber. The radial burner is situated in the cylindrical wall (close to the top zone) of the chamber. The maximum possible liquid fuel feed to the main burner is 14 kg/h. The system of liquid fuel consists of the fuel tank, fuel pipes, valves system, and pump. The temperature of liquid fuel was controlled using heating elements. The maximum possible temperature of liquid fuel is 250 \({}^{\circ}\)C. A dust separator (DS) is equipped with ceramic elements. The particles were removed from the DS using pressurized air impulses. The maximal admissible temperature of flue gas in the DS zone is 600 \({}^{\circ}\)C. The heating of the combustion chamber was performed using a natural gas burner and the burner was switched to liquid fuel burner. The average natural gas flow rate (during the heating period) was 6.5 m\({}^{3}\)/h (input power \(\sim\)65 kW). The flame structure was observed using an inspection hole (window) placed at the top part of the chamber. The temperature in the combustion zone was measured at three points of the chamber: 958 mm (top zone, TT), 1258 mm (central zone, TC), and 1508 mm (bottom zone, TB) from the top cover of the chamber. The flue gas was continuously analyzed for CO\({}_{2}\) (0-45 v.%), CO (0-6000 ppmv), H\({}_{2}\)O (0-30 v.%), NO (0-1000 ppmv), N\({}_{2}\)O (0-200 ppmv), NO\({}_{2}\) (0-200 ppmv), SO\({}_{2}\) (0-6000 ppmv), C\({}_{4}\)H\({}_{10}\) (butane; 0-500 ppmv), C\({}_{2}\)H\({}_{8}\) (toluene, 0-200 ppmv), CHOH (formaldehyde; 0-50 ppmv) using an FTIR analyzer (GASMET DX4000), and O\({}_{2}\) (inlet and outlet), which was measured using a paramagnetic analyzer (Oxymat 61) and a zirconium sensor analyzer (AMS Analysen). The measurement uncertainty of the presented analyzers was estimated at below 2% of the total measuring range.  
As in our previous research [23], PAHs were analyzed using the application of a measurement system, including an externally heated glass filter and a set of tubes, including XAD-2 resin and active carbon. The captured organic matter in the glass filter and tubes were processed using extraction (ASE 350 provided by DIONEX) in the presence of acetone and methylene chloride. Solvents were evaporated using RAPIDVAP apparatus provided by Labconco, and the next TOC was determined. Finally, the quantitativeanalysis of 16 PAHs was carried out using a gas chromatograph and a flame ionization detector (Trace-GC provided by Thermo Scientific, Waltham, MA, USA). A total of 16 PAH emissions included the following compounds: naphthalene, acennaphthene, diuorene, phenanthrene, anthracene, fluoranthene, pyrene, benzo(a)anthracene, chrysene, benzo (b + k) fluoranthene, benzo(e)pyrene, benzo(a)pyrene, beryline, bibenzo(a, h) anthracene + indeno (1, 2, 3) pyrene, and benzo(g, h, i) perylene.