# Scenario-Based Techno-Economic Analysis of Steam Methane Reforming Process for Hydrogen Production
## 2 Methods  
### Process Description  
An SMR process model was developed using a commercial simulator, Aspen Plus, based on the experimental data obtained from the literature. Figure 2 shows the detailed process flow diagram of the SMR process developed in this study (see Figures S1-S3 in the Supplementary Materials for the process flow diagrams for Sc 2-4, respectively). The process consists of four areas: (1) hydrogen production, (2) steam production, (3) hydrogen purification, and (4) feed intake. A detailed description of each process area is given below.  
Area 100 Hydrogen production: The flow rate of CH4 is adjusted to produce H2 at 500 kg/d. Steam (stream 204) and CH4 (stream NG1) are combined and supplied to the steam methane reformer (R101) where CO and H2 are produced through a highly endothermic reaction, in the presence of a nickel-based catalyst (Ru-Ni/Al2O3) [24]. The steam to CH4 molar ratio is maintained at 3 to prevent coke deposition on the surface of the catalyst [25]. The heating requirement of the reformer is satisfied by the heat released from the combustion of the tail gas. The effluent from the reformer (stream 104) is then routed to the WGS reactor (R102) where CO and steam are converted to additional H2 and a coproduct of CO2. The WSG reaction occurs over a copper-promoted iron-chromium oxide catalyst (Cu/Fe3O4-Cr2O3) to increase the amount of H2  
Figure 2: Process flow diagram of steam methane reforming.  
content [24]. In the flash (F101), the water is separated as the bottom product (stream WAT) and the gaseous mixture (stream 301) is discharged from the top and sent to the hydrogen purification area for further treatment.  
Area 200 Steam production: Steam is produced from deionized water using two heat exchangers, E201 and E202. Approximately 46% of the demineralized water is supplied from recycled water (stream WAT) separated from the flash drum (F101) and the remaining 54% is replenished from external sources (stream DI). The steam produced in this area is used in reactors R101 and R102.  
Area 300 Hydrogen purification: The gaseous product of F101 is a mixture of H\({}_{2}\), H\({}_{2}\)O, CO\({}_{2}\), CO, and CH\({}_{4}\). To meet the specification of H\({}_{2}\) as the final product, the mixture is purified using a pressure swing adsorption (PSA) process, as is often used in industrial practice [26; 27; 28; 29]. H\({}_{2}\) (stream 303) is produced with 99.99% purity and 75% recovery. The tail gas (stream 302) separated from the PSA process (PSA301) is sent to the feed intake area and used for heat generation [30].  
Area 400 Feed intake: This area includes three heat exchangers (E402, E403, and E404) to preheat CH\({}_{4}\), steam, and tail gas (streams NG, 101, and 402, respectively) using the heat released from the flue gas (stream 404). The preheated streams 102 and 403 are then sent to the reformer (R101).  
See Tables S1-S4 in the Supplementary Materials for detailed process stream information for Sc 1-4, respectively. Table 1 summarizes the main design and operating conditions used in the four process areas of the proposed SMR process.