## 3 Results
### Release of Elements into the Atmosphere during Combustion
In recalculation on the element content of the input fuel, up to twice as many major elements (55 g/kg) were released from PB during combustion compared to WM (28 g/kg fuel for BEC2 and 19 g/kg for BEC3) and CB (BEC2 21 g/kg and BEC3 23 g/kg). Calcium (up to 37 g/kg of fuel) accounts for the major proportion of elements released when PB is burned (Figure 4). The concentration of emitted elements when burning PB decreasesin the following order: Si \(>\) Al \(>\) Ca \(>\) Ti \(>\) S \(>\) K = Fe \(>\) P, and for trace elements: Mn \(>\) Cl \(>\) Zn \(>\) Cu \(>\) Pb \(>\) Ni = Cr = As. The high sulphur emissions from burning PB are due to the presence of organically bound sulfur, which is part of lignin sulfonate, a by-product of the sulfite pulping process [74] used to glue cartons [75]. The thermal stability of sulfonic groups is rather weak, as indicated by the low-temperature evolution of SO\({}_{2}\). The decomposition is done in two stages at a temperature of between 120 and 360 \({}^{\circ}\)C, and the lignin component [76] decomposes from 360 to 700 \({}^{\circ}\)C. Cations (Na\({}^{+}\) and NH\({}_{4}\)\({}^{+}\)) bonded to the sulphonic groups strongly affect the decomposition of lignocellulosic. In the case of sodium sulfonate, sulphur is bound to Na\({}_{2}\)SO\({}_{3}\), or Na\({}_{2}\)SO\({}_{4}\) and sulfides are formed under reduction conditions. The sulfonic group with NH\({}_{4}\)\({}^{+}\) releases NH\({}_{3}\) at 270 \({}^{\circ}\)C, breaking down the sulfonate group into SO\({}_{2}\)[76]. The comparison of individual fuels shows that when burning PB, 1 kg of fuel releases the highest amount of trace elements 630-830 mg/kg (Figure 5). The value is affected by a high concentration of Mn. Other monitored elements (As, Cu, Cr, Ni, Pb, and Zn are emitted at a concentration of 121-128 mg/kg, which is lower than WM combustion emissions. In the case of printed cartons, the content of other elements of Sn and Sb is also increased in the blue gas [77]. The amounts of trace elements released when burning waste office paper and corrugated cardboard increases with temperature [78]. When burning waste paper at 750-950 \({}^{\circ}\)C, manganese (68-205 mg/kg of fuel) and lead (38-54 mg/kg of fuel) pass into blue gas [78]. In our case, the amount of Mn released into the air was about twice as high, with input paper briquettes containing Mn in concentrations up to 520 mg/kg. The combustion in the EC2 and EC3 boiler released Mn in amounts of 300 to 470 mg/kg of fuel and Pb in amounts of 18 to 20 mg/kg of fuel. Lead and zinc have a lower volatility of Zn during the combustion of waste paper at a lower rate of combustion. The behaviour of Cu is not affected by the rate of combustion [79]. When burning WM in BEC2 at the fuel ratios 2.5 kg/h and 4 kg fuel/h (BEC3), the differences in Cu, Pb, and Zn emitted were not significant. When burning WM, the series of released elements is P \(>\) Si \(>\) Ca \(>\) Al \(>\) Fe \(>\) K \(>\) S \(>\) Ti, and for trace elements: Mn \(>\) Cl \(>\) Zn \(>\) Cu \(>\) Ni \(>\) Pb \(>\) Ni = Cr = As. Phosphorus was released in the highest amounts; it can be completely released as gaseous phosphorus oxides during the combustion process when it is organically bound due to the high volatility of organic phosphorus compounds [80; 81]. Potassium release into the air from burning waste wood was studied by [PERSON] et al. [64], who found lower amounts of K release for waste wood (18.5 \(\pm\) 3.2%), hardwood chips (32.8 \(\pm\) 12.0%), and softwood chips (24.9 \(\pm\) 8.1%) than was demonstrated for the PB burning (54-56%). The contamination  
Figure 4: Major elements (Al, Si, Ti, Fe, Ca, S, K, and P) released from the burning of 1 kg of fuel in BEC2 and BEC3. caused by the presence of soil particles in biomass in the feedstock also affects potassium behaviour during the combustion process of compressed wood mass, where K is bound in silicate minerals, and thus the amount of produced K\({}_{2}\)SO\({}_{4}\) is decreased, resulting in an increase in SO\({}_{\rm x}\) emissions [54].