# Scenario-Based Techno-Economic Analysis of Steam Methane Reforming Process for Hydrogen Production
## 2 Methods
### Scenario Development  
To investigate the effect of process design and operating conditions on process economics, we developed six scenarios as shown in Table 2. We consider five different conditions, namely reformer pressure, number of WGS reactors, WGS reactor temperature, CO\({}_{2}\) emission allowances, and CO\({}_{2}\) capture and sales.  
In Sc 2, the temperature of the WGS reactor is 250 \({}^{\circ}\)C. The higher temperature of the WGS reactor increases the productivity of H\({}_{2}\) but increases utility requirements at the same time, leading to an increase in operating costs.  
In industrial SMR processes, two WGS reactors operating at different temperatures are usually introduced to increase the CO-to-H\({}_{2}\) conversion rate. However, the additional reactor leads to an increase in capital cost. To investigate this effect, Sc 3 with two WGS reactors is considered.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameters** & **Values** & **References** \\ \hline Area 100: Hydrogen production & & \\ Natural gas pressure (kPa) & 800 & [31] \\ Steam reformer temperature (\({}^{\circ}\)C) & 800 & [25] \\ GHSV of steam reformer (m\({}^{3}\)/h\(\cdot\)kg-cat.) & 2.0 & [32] \\ GHSV of high temperature of WGS reactor (m\({}^{3}\)/h\(\cdot\)kg-cat.) & 1.0 & [33] \\ GHSV of low temperature of WGS reactor (m\({}^{3}\)/h\(\cdot\)m\({}^{3}\)-cat.) & 6000 & [34] \\ Area 200: Steam production & & \\ Steam to CH\({}_{4}\) molar ratio & 3.0 & [25] \\ Area 300: Hydrogen purification & & \\ H\({}_{2}\) recovery & 75\% & [24] \\ H\({}_{2}\) purification & 99.99\% & [24] \\ Operating pressure range (kPa) & 2–800 & Assumed \\ Area 400: Feed intake & & \\ Temperature of exhaust gas (\({}^{\circ}\)C) & 900 & Assumed \\ \hline \hline \end{tabular}
\end{table}
Table 1: Design and operating conditions in each process area of the developed process.  
In this study, reformer pressures of 100 kPa and 800 kPa are considered. As the reformer pressure decreases, the conversion rate of CH4 to H2 increases, while the amount of fuel gas required for the reformer increases because of the decrease in the amount of unreacted CH4, thus leading to a decrease in the energy content of the tail gas. Moreover, when the reformer pressure is 100 kPa (Sc 4), an additional compression step is required between the reformer and the PSA process.  
The CO2 emission allowances is a cost to be paid and thus has a negative effect on the economics of the process. It is assumed that CO2 is released into the atmosphere without any restrictions when the CO2 emission allowances are not considered. In Sc 5, the CO2 emission allowances apply to 100% of the CO2 generated from the combustion of the tail gas.  
Sc 6 involves the capture and the sale of CO2 as a byproduct. 90% of the CO2 produced from the combustion of the tail gas is captured and 10% of the remaining CO2 is applied to the CO2 emission allowances. There is a large global market for CO2 and the demand for CO2 continues to grow in various industrial sectors including refrigeration, food & beverages, oil & gas, pharmaceuticals, rubber, and firefighting [35]. CO2 can also be used in CCU [36] and CCF [37] technologies in cleaner ways. If SMR is combined with CCF, the system is clean because no CO2 is released into the atmosphere. Detailed analysis on the use of CO2 in CCU and CCF appeared to be beyond the scope of this work, therefore we left it for later analysis.