## 3 Results and Discussion
### Commissioning of Full-Scale Technology and Adjustment of Process Parameters
A series of experiments were conducted to adjust the process parameters of the dryer under different conditions for the temperature of the inlet hot air (t\({}_{\text{in}}\), \({}^{\circ}\)C) and exposure time (\(\tau\), min). At the end of the drying process, the granules were subjected to moisture content analyses (W\({}_{\text{gran}}\), wt. %), crushing tests at 2.5 kgf, and the determination of K\({}_{2}\)O and P\({}_{2}\)O\({}_{5}\) content in wt. %. The experimental conditions and the obtained results are listed in Table 4. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter** & **Regime 1** & **Regime 2** & **Regime 3** \\ \hline W\({}_{\text{in}}\) & 5–8 & 9–12 & 13–15 \\ wt. \% & & & \\ G\({}_{\text{tw}}\) & 18 & 8 & 2 \\ L/min & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Established working regimes of the humidifier based on the initial moisture. Figure 3: Delivered and constructed facilities by Green Circle Biotech Ltd. at the Polski Trambesh site: (**a**) drum granulator; (**b**) heater. As can be seen from the results obtained, the low drying temperature, even with a longer exposure time, cannot meet the criteria for the final moisture in the granules or the content of K\({}_{2}\)O and P\({}_{2}\)O\({}_{5}\). Other authors successfully performed low temperature drying that is more effectively in terms of energy consumption and production costs [37; 38; 39]. In our technological solution, the low temperature treatment is unsuccessful due to the previous stage of moisturizing in the humidifying mixer, which is a prerequisite for the self-granulation of SHA, eliminating the need of additives. At high temperatures, on the other hand, the desired material composition is obtained, but the crushing tests are unsuccessful due to the embrittlement of the granulate. The optimal conditions of the drying process in the drum heater are obtained for the inlet temperature range of 180-220 \({}^{\circ}\)C and an exposure time of 20 min. The lack of additional compounds in the granulation process compensate for the high-temperature drying regime in terms of economic and environmental effectiveness. The obtained relatively high temperature regimes should not have a negative impact on the nutrient properties of the final product due to its mineral composition unlike the negative effect obtained from other authors investigating organic fertilizers [40]. It is important to note that inorganic fertilizers are not used as single additives to soil for long periods because this may lead to a decline in the nutrient content in soil and make the crops more susceptible to various diseases [41]. In the next stage of the processes, the dried granules pass through cyclone filters for the separation of the remaining powder fraction that is redirected by elevator belt to the grinder before returning to the humidifying mixer for retreatment. The granules that pass through the cyclone filter enter a cooler vessel for 15 min to decrease their surface temperature of 55 \({}^{\circ}\)C to an ambient condition. The cooler is a closed rotary vessel with a diameter of 1.5 m, a length, of 16 m, and a constant speed of 6 rpm. The cooling process is based on convective heat exchange performed in an air environment ensured by a fan with a capacity of 15,000 m\({}^{3}\)/h. A conveyor belt moves the cooled granules to the screening machine for separation into differently sized fractions (Figure 4a). Granules with a diameter <2 mm are returned to the process in front of the humidifying mixer, those with diameter >5 mm are returned to the grinder, and the fraction with a diameter in the range of 2-5 mm is directed to the packing machine (Figure 4b). During the packaging process each batch is examined by crushing tests at 2.5 kgf and by IR analyses to confirm the presence of moisture of approx. 5 wt. %.