# Effect of Paper Sludge and Dendromass on Properties of Phytomass Pellets
## 3 Experimental Research and Results
### The Analyses of Results  
The experimental measurements consisted of two tasks, in the first the boiler heat power was recorded, and in the second the concentrations of gaseous emissions and particulate matter (PM) were measured.  
The heat power of the boiler did not differ significantly during all three measurements of one sample, since the boiler operated under stable conditions. Figure 5 shows the average power values of the boiler, and the highest power was registered when burning a sample of 100% pure wood pellets. A slightly lower power of 11.82 kW was measured for the sample SSPS-45/45/10, but it was higher by more than 2 kW compare to pure straw. The lowest heat output of the boiler was 9.49 kW, which was caused by a 20% share of paper sludge in the sample SSPS-40/40/20. The standard deviation of the measured values was evaluated, and was in the range of 0.49-1.10 kW (see Figure 5).  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sample** & **DT (\({}^{\circ}\)C)** & **ST (\({}^{\circ}\)C)** & **HT (\({}^{\circ}\)C)** & **FT (\({}^{\circ}\)C)** \\ \hline
**S100** & 1025 & 1081 & 1121 & 1205 \\
**SD–100** & 1115 & 1254 & 1313 & 1500 \\
**SSPS—45/45/10** & 1328 & \textgreater{}1500 & \textgreater{}1500 & \textgreater{}1500 \\
**SSPS—40/40/20** & 1301 & \textgreater{}1500 & \textgreater{}1500 & \textgreater{}1500 \\
**PS100** [18] & 1305 & \textgreater{}1500 & \textgreater{}1500 & \textgreater{}1500 \\
**Standard deviation** & \(\pm\)0.23 & \(\pm\)0.15 & \(\pm\)0.13 & \(\pm\)0.08 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Melting temperatures of the pellet samples.  
Figure 4: Experimental setup: 1—p pellet boiler, 2—fuel tank, 3—heat exchanger station, 4—flue gas analyzers and data logger, 5—chimney.  
In Figure 6a are the average values of carbon monoxide emissions measured during the combustion of the four pellet samples. The CO is formed during the incomplete combustion as a by-product, and its concentration depends on the amount of oxygen supplied to the combustion process. According to the standard STN EN 303-5 2012, the maximum CO concentration is 3000 mg\(\cdot\)m\({}^{-3}\) for an automatic boiler with a rated heat power up to 50 kW. All the produced samples met this standard, and the sample SD-100 had the lowest concentration of CO, as expected.  
The highest CO\({}_{2}\) emissions were during the combustion of 100-SD, indicating complete combustion. Thus, most of the C contained in this sample had left the boiler in the form of CO\({}_{2}\). The results of sample S-100 showed the lowest concentration, as expected.  
Another monitored emission parameter was NOx, which is formed depending on high temperatures by nitrogen oxidation, and chemical composition of the fuel. The value of the NOx emission limit for the combustion of phytomass is at the level of 650 mg\(\cdot\)m\({}^{-3}\). This value was met by all the tested pellet samples. In Figure 7a it can be seen that the lowest NOx emission production was shown for a sample of pure wood pellets of 179 mg\(\cdot\)m\({}^{-3}\), followed by a sample of pure straw of 295 mg\(\cdot\)m\({}^{-3}\). The SSPS-45/45/10 and 40/40/20 samples reached approximately the same NOx values, of 330 mg\(\cdot\)m\({}^{-3}\).  
It is also important to control the concentration of particulate matters, mainly due to the inhalation of these particles and the harmful effect on the human body [15]. The concentrations of the total particulate matters measured for the produced samples can be seen in Figure 7b. It is clear from the results that the SD-100 sample produced the least amount of PM, and the highest amounts of PM were measured for pellets made from pure straw. According to the standard STN EN 303-5 2012, a limit of up to 150 mg\(\cdot\)m\({}^{-3}\) is set for particulate matters.  
Figure 5: Comparison of the average heat output of the boiler.  
Figure 6: (a) Comparison of the average CO emissions, and (b) comparison of average CO\({}_{2}\) emissions.