# Techno-Economic Analysis of Flare Gas to Hydrogen: A Lean and Green Sustainability Approach
## 2 Method
### Hydrogen Simulation Set up  
The process simulation of the steam methane reforming for the production of hydrogen from flare gas was performed using the Aspen HYSYS V14 [54] in a steady state and then optimized in terms of thermodynamic parameters to maximize hydrogen production and reduce pollutant gas. The main process in the simulation consists of the flare-steam stream intake, the reformer, water gas shift, and lastly, hydrogen purification, which consists of the separator and Pressure Swing Adsorption (PSA). The process flow diagram is shown in Figure 6, and the following simulation steps were followed. **Define Component**:  
In setting up the simulation, the components of the natural gas were first specified. The composition of the natural gas used for this simulation, as shown in Table 2, was obtained from an existing gas plant located in the Niger Delta region of Nigeria [55]. Water (H\({}_{2}\)O) was also used in this simulation. \begin{table}
\begin{tabular}{l l l} \hline
**Component** & **Chemical Formula** & **Volume Fraction** \\ \hline Methane & CH\({}_{4}\) & 0.88748 \\ Ethane & C\({}_{2}\)H\({}_{6}\) & 0.04402 \\ Propane & C\({}_{3}\)H\({}_{8}\) & 0.02572 \\ i-Butane & C\({}_{4}\)H\({}_{10}\) & 0.00553 \\ n-Butane & C\({}_{4}\)H\({}_{10}\) & 0.00843 \\ i-Pentane & C\({}_{5}\)H\({}_{12}\) & 0.00265 \\ n-Pentane & C\({}_{5}\)H\({}_{12}\) & 0.00195 \\ N-Hexane & C\({}_{6}\)H\({}_{14}\) & 0.00174 \\ N-Heptane+ & C\({}_{7}\)H\({}_{16}\) & 0.00178 \\ Nitrogen & N\({}_{2}\) & 0.00113 \\ Carbon Dioxide & CO\({}_{2}\) & 0.01957 \\ \hline \end{tabular}
\end{table} 
Table 2: Natural gas composition. Figure 6: The process flow diagram of the hydrogen production simulation. **Select the Thermodynamic Package:**  
Once the component has been defined, the next step involves selecting an appropriate thermodynamic package. Packages such as the Peng-Robinson or Soave-Redlich-Kwong are commonly employed for hydrocarbon processing [56]. In this study, the Peng-Robinson equation of state was selected due to its widespread acceptance in hydrocarbon simulation and its capability to accurately predict the pressure and temperature of gases [57]. Following the selection of the fluid package, the subsequent step is to construct the flow sheet by transitioning to the simulation environment in HYSYS. **Feed stream:**  
The model has two feed streams: The flare stream and the steam stream. Both streams were passed into a mixer and then into a compressor. During the industrial SMR process with CCS, natural gas reacts with steam to produce high-quality hydrogen as shown in Equation (4) [57; 58]. \[\mathrm{C_{n}H_{m}+nH_{2}O\rightleftarrows nCO+(0.5m+n)H_{2}} \tag{4}\]  
The natural gas and steam mixture was heated before being moved to the reformer reactor. **Reformer reactor:**  
In the reformer reactor, methane combines with steam to generate hydrogen and carbon monoxide, which are then cooled before being directed to the water gas shift reactor, as shown in Equation (5). The reactor operates as a conversion reactor, and the reaction conditions were modified accordingly. \[\mathrm{CH_{4}+H_{2}O\to CO+3H_{2}} \tag{5}\]  
The CO and CO2 methanation pathways [59], though thermodynamically linked to this system, are not considered here because the reactor is designed for the SMR process, which is not conducive to methanation, and the study focuses on hydrogen production via SMR. **Water Gas Shift Reactor:**  
A second reactor, known as the water gas shift reactor, was added to convert CO and H2O into additional hydrogen and CO2, as shown in Equation (6). A second cooler was also used to cool the product before it was sent to the absorber and the Pressure Swing Adsorption for separation and purification. To maximize hydrogen production, the temperatures of the reformer and WGS were set at 263 \({}^{\circ}\)C and 203 \({}^{\circ}\)C, respectively.