## 5 Results and Discussion
### Mass Balance
#### 5.4.1 Energy Flow Analysis  
The control of energy consumption is one of the most pivotal aspects in the HDRSF process, which is directly related to the production cost of DRI. The energy flow of the HDRSF process without or with waste heat recovery are shown in Figures 6 and 7, respectively.  
As observed in Figure 6, the sole source of heat that keeps the shaft furnace's heat consumption stable is the heat brought in by the high-temperature reduction gas. In the absence of waste heat recovery, 2083 m\({}^{3}\) of reducing gas is needed to manufacture one ton of DRI at process parameters of 900 \({}^{\circ}\)C and H\({}_{2}\):CO = 1:1. The energy of reducing gas entering the furnace is 2.62 \(\times\) 10\({}^{7}\) kJ. The electric heating furnace provides the energy needed to heat up the reducing gas. Given the electric heating furnace's conversion efficiency, the amount of external energy required to be input in the absence of waste heat recovery is 2.75 \(\times\) 10\({}^{7}\) kJ, which is comparable with the calculation result of Zhang  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multicolumn{3}{c}{**Input**} & \multicolumn{3}{c}{**Output**} \\ \hline
**Item** & **Mass/kg** & **Percentage/\%** & **Item** & **Mass/kg** & **Percentage/\%** \\ \hline Iron ore & 1623.05 & 29.45 & DRI & 1000 & 18.14 \\ Reducing gas & 1042.2 & 18.91 & Top gas & 1611.04 & 29.23 \\ Cooling gas in & 2846.25 & 51.64 & Cooling gas out & 2846.25 & 51.64 \\  & & & Gangue & 54.21 & 0.99 \\ Total & 5511.5 & 100 & Total & 5511.5 & 100 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Mass balance of the HDRSF with waste heat recovery.  
Figure 6: Energy flow analysis of the HDRSF process without waste heat recovery.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multicolumn{3}{c}{**Input**} & \multicolumn{3}{c}{**Output**} \\ \hline
**Item** & **Mass/kg** & **Percentage/\%** & **Item** & **Mass/kg** & **Percentage/\%** \\ \hline Iron ore & 1623.05 & 27.68 & DRI & 1000 & 17.05 \\ Reducing gas & 1394.7 & 23.78 & Top gas & 1963.54 & 33.48 \\ Cooling gas in & 2846.25 & 48.54 & Cooling gas out & 2846.25 & 48.54 \\  & & & Gangue & 54.21 & 0.93 \\ Total & 5864 & 100 & Total & 5864 & 100 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Mass balance of the HDRSF without waste heat recovery.  
et al. [30]. Furthermore, the primary energy-consuming components of the shaft furnace are the cooling gas heat and the top gas heat, excluding the required energy consumption of reduction reaction heat absorption and furnace body heat dissipation. Figure 7 depicts the HDRSF process's energy flow following the top gas recovery and high-temperature cooling gas residual heat. Because of the extra energy income from preheating the iron ore, the amount of gas required to produce one ton of DRI decreases to 1557 m\({}^{3}\), and the amount of gas energy entering the shaft furnace decreases to 1.96 \(\times\) 10\({}^{7}\) kJ. In addition, heating gas in the electric heating furnace uses less energy when the reduction gas is preheated using top gas. Following waste heat recovery, the energy needed is lowered to 1.70 \(\times\) 10\({}^{7}\) kJ.