## 5 Analysis of the Implementation of Energy Efficiency Measures from the 2018 Audit
### Recovery of the Final Cooling Air from the Tunnel Kiln to the Air Dryer  
When the kiln was shut down in August 2021, a system was installed to recover the final cooling air from the continuous kiln and send it to the air dryer. The thermodynamic system of the continuous furnace before the implementation of the measure is represented in Figure 10.  
The heat from the final cooling air that did not escape to the outside was recovered in the existing pre-furnace. The heat was not fully utilized. There was waste from the use of this heat by the chimney (Figure 10), both in the outgoing cooling air and also in the recovery for the pre-furnace. The solution was to install a valve to prevent the passage of air to the outside and install fans so that some of this heat could be used in the air dryer. The thermodynamic system after implementing this measure is represented in Figure 11. Figure 12 shows the ducts used to recover the cooling air from the continuous kiln to the air dryer.  
In April 2022, the researcher accompanied the auditor to carry out some measurements. The ducts had three holes placed at strategic points that allowed obtaining the necessary values for the effective calculation of recovered heat. Using a data logger, a pitot tube, and a thermocouple, the values of velocity and temperature of the air inside the ducts were collected. To determine the volumetric flow rate of the oven's cooling air, it was necessary to measure the perimeter of the pipes. From this value, its diameter was obtained. The formula used to calculate the recovered heat, Q (kJ/h), for the air dryer and pre-furnace was shown in Equation (5) [25].  
\[\mathrm{Q=V\times\rho\times Cp\times\Delta T} \tag{5}\]  
where V is the volumetric flow of the furnace cooling air (m\({}^{3}\)/h) and \(\rho\) is the specific mass of air (kg/m\({}^{3}\)). Moreover, \(\Delta T\) is the temperature difference between the initial and final temperatures of the recovery air (\({}^{\circ}\)C), and Cp is the specific heat of the air (kJ/kg \({}^{\circ}\)C).  
According to the energy audit manual used [13], the value of the specific mass of air is \(\rho\) =1.292 kg/m\({}^{3}\), and the specific heat of air is Cp = 1.0 kJ/kg \({}^{\circ}\)C. The area of the duct without insulation is 0.1942 m\({}^{2}\). The measurements taken are shown in Table 14.  
Figure 10: Thermodynamic system of the continuous furnace before the implementation of the measure.  
As the temperature measured in the orifice directed to the outside is 36 \({}^{\circ}\)C, and a valve was installed in the duct, can be inferred that nearly all of the cooling air is being effectively used. According to the calculations made using equation 4, the effective heat used for the air dryer was 206,781 kJ/h and 2,628,695 kJ/h for the pre-furnace.  
As the heat from the cooling air is completely used for the air dryer and the pre-furnace and there is no final cooling air going outside, it can be said that the final cooling air recovery measure from the tunnel kil to the air dryer was successfully implemented.  
Figure 11: Thermodynamic system of the continuous furnace after the implementation of the measure.  
Figure 12: Conducts in link from the oven continuous to the air dryer.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{3}{c}{**Measurements Taken**} \\ \cline{2-4}  & **Outwards Hole** & **Aerial Dryer Hole** & **Rear Hole to the Aerial Dryer** \\ \hline Average speed (m/s) & 1.55 & 4.7 & 3.05 \\ \hline Temperature (\({}^{\circ}\)C) & 36 & 384 & 335 \\ \hline Pipe diameter without isolation (m) & 0.491 & 0.497 & 0.497 \\ \hline \hline \end{tabular}
\end{table}
Table 14: Measurements were carried out in the holes of the continuous furnace ducts.