## 3 Results and Discussion
### Basic Technoeconomical Study  
3.4.1. Comparison between Electrochemical and Thermal Regeneration with a Model Case from the Middle East  
The comparative study of energy costs between a typical large natural gas treatment facility in the Middle East with and without electrochemical regeneration served to assess the industrial interest of this new technology. Electrochemical regeneration replaced the desorption column of the first AGRU as well as the entire downstream sulfur removal unit (Claus + TGTU) (see Figure 1). Fuel and steam consumption were evaluated for units replaced by electrochemical regeneration and were compared with the energy consumption of the latter. The unit chosen to compare these two systems was the energy contained in the methane required to produce steam or electricity.  
Base Case AGRU/SRU  
To be conservative, a gas treatment facility with optimal thermal integration was considered (lower energy consumption of the thermal reference case). The burners in the thermal part of the Claus unit produce 126 MW. They consume 12,600 kghr\({}^{-1}\) of fuel gas at 5 bar(g) with a lower heating value (LHV) of 45 MJkg\({}^{-1}\) with an efficiency of 80%. Combining these figures gives 126 MW. In addition, the SRU has a surplus of low and high-pressure steam. The SRU supplies 45 thr\({}^{-1}\) of high-pressure steam at 41 bar(g) and 685 K. Under these conditions, 1 thr\({}^{-1}\) is equivalent to 0.5 MW. The SRU therefore produces 22.5 MW. The SRU supplies 46 thr\({}^{-1}\) of low-pressure steam at 5.5 bar(g) and 440 K. Under these conditions, 1 thr\({}^{-1}\) is equivalent to 0.6 MW. The SRU therefore produces 27.6 MW. The AGRU consumes 177 thr\({}^{-1}\) of low-pressure steam in the reboiler of the regenerator, which is equivalent to 106.2 MW. Therefore, the AGRU-SRU consumes 182.1 MW. This is summarized in Table 4.  
Two model case configurations were studied, namely the base case without CO\({}_{2}\) capture and the case with CO\({}_{2}\) capture at the SRU outlet with a standard aqueous amine. CO\({}_{2}\) capture for storage or reuse increases the energy consumption by 75% (one needs an entire extra AGRU unit with thermal regeneration). This is summarized in Table 5.  
Electrochemical Regeneration  
Electrochemical energy is defined by the following equation: \(E=nF\Delta V\), where \(n\) is the number of electrons exchanged, \(F\) is the Faraday constant, and \(\Delta V\) is the voltage across the electrochemical cell. One electron is consumed to regenerate CO\({}_{2}\), while two electrons are consumed to oxidize H\({}_{2}\)S to S. The applied voltage is estimated at 1 V,  
\begin{table}
\begin{tabular}{l c c c} \hline \hline
**(In MW)** & **SRU** & **AGRU** & **Total** \\ \hline Fuel & 126 & - & - \\ HP steam & \(-\)22.5 & - & - \\ LP steam & \(-\)27.6 & 106.2 & - \\ \hline Total & 75.9 & 106.2 & 182.1 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Energy consumption of thermal SRU-AGRU.  
\begin{table}
\begin{tabular}{l l l l} \hline \hline  & **Without CO\({}_{2}\) Recovery** & **With CO\({}_{2}\) Recovery** & **Electrochemical Regeneration** \\ \hline Energy OPEX (MW) & 182 & 319 & 122 \\ Efficiency & 85\% & 85\% & 60\% \\ Fuel equivalent (MW) & 214 & 375 & 203 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Comparison between the two base cases and electrochemical regeneration.  
which gives an electrical energy of 100 kJmol\({}^{-1}\) of CO\({}_{2}\) and 200 kJmol\({}^{-1}\) of H\({}_{2}\)S. To be able to compare with a typical installation in the Middle East, these molar energies were multiplied by the molar flow rate of H\({}_{2}\)S and CO\({}_{2}\) of the model case. \(D_{H_{2}S}\), the flow rate of H\({}_{2}\)S and \(D_{CO_{2}}\), the flow rate of CO\({}_{2}\), were 450 and 316 mols\({}^{-1}\), respectively. With \(E_{electrochemical\ regeneration}=D_{CO_{2}}\times E_{CO_{2}}+D_{H_{2}S}\times E_{H_{2}S}\) an energy consumption of 122 MW was obtained.