## 3 Results and Discussion
The basic parameters characterizing the combustion process are presented in Table 3 and the content in exhaust gas, as well as CO, NO, SO\({}_{2}\), CO\({}_{2}\) emission, are presented in Table 4.  
Interpretation of the obtained results regarding the content of CO, NO and SO\({}_{2}\) in the exhaust gas refers to the adopted combustion criteria, the characteristic feature of which was the use of a grate combustion system with fuel ignition from below and air distribution under the grate. The obtained values of these compounds were diversified due to the periodicity of fuel feeding to the boiler and the phase of the combustion process. Immediately after 1 kg of fuel was placed on the stabilized embers layer, the temperature increased and the volatiles evaporated from the fuel, mainly represented by the maximum values of CO, NO and SO\({}_{2}\). Under the test conditions, burning of crushed hemp straw occurred most rapidly with significant CO, NO and SO\({}_{2}\) emissions. Its compaction to type A briquettes led to a 60% reduction in CO emissions, 25% NO emissions and 20% SO\({}_{2}\) emissions during combustion. On the other hand, combustion of type B briquettes made of additionally crushed hemp biomass in relation to crushed straw led to further stabilization of the combustion process and reduction of emissions of the analysed compounds in the flue gas by 80%, 40% and 25%, respectively (Table 4). The difference of parameters (Table 3) could have resulted from better contact of type A briquettes with hot gases, due to their greater \"external \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Assortment**} & \multirow{2}{*}{\begin{tabular}{c} **Combustion Speed** \\ **(kg-h-1)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Excess Air Coefficient** \\ **(-)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Exhaust Gas Temperature** \\ **(\({}^{\circ}\)C)** \\ \end{tabular} } \\ \hline \begin{tabular}{c} Hemp straw \\ Type A briquettes \\ \end{tabular} & \(5.14\pm 0.10\) & \(2.06\pm 3.23\) & \(354.0\pm 153.7\) \\ \
\begin{tabular}{c} Type B briquettes \\ \end{tabular} & \(4.30\pm 0.08\) & \(4.16\pm 3.74\) & \(297.2\pm 104.8\) \\
\begin{tabular}{c} Type B briquettes \\ \end{tabular} & \(3.93\pm 0.07\) & \(5.48\pm 4.44\) & \(234.9\pm 82.4\) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Parameters of the combustion process. roughness\" (Figure 1c) caused by the less fragmented raw material fraction. Similar results were obtained by [PERSON] et al. [48] comparing the combustion rate and weight loss during the development of ignition for different sized wood particles. For larger particles, the ignition front speed was higher than for smaller particles. In addition, [PERSON] and his team [49] noted that smaller particle sizes result in high CO emissions. Statistical analysis carried out in terms of combustion parameters showed significant differences between the tested biofuel assortments. The obtained values were comparable with data presented by other researchers analysing the emission of hemp biomass biofuels [10], and they were close to the literature values for wood biomass and energy plants [50; 51; 52; 53]. At the same time, it is worth noting that, while briquetting, CO emissions were acceptable for this type of boiler, falling into class 3 according to PN-EN 303-5:2012 [54]; however, they did not meet the requirements of the ecodesign requirements for solid fuel boilers [55].