Steam Reforming. Currently, 95% of the hydrogen produced in the US is obtained using SMR . After over 80 years of development, SMR has become the dominant industrial route to produce hydrogen and synthesis gas (mix of hydrogen and carbon monoxide) . The following reaction takes place in a steam reformer, where high-temperature steam (700-1000°C) reacts with methane at 3-25 bar to produce hydrogen and carbon monoxide . Figure provides a simplified flowsheet diagram of SMR. The SMR unit simulated in this work is a two-step reforming process where a fired tubular reactor (primary reformer) is followed by an oxygen-fired adiabatic reformer (secondary reformer). The advantage of combing two reforming technologies is that the composition of the produced syngas can be adjusted to the most suitable condition for methanol synthesis. After removing sulfur, purified methane is compressed and mixed with steam. The high-pressure steam is obtained by heating the high-pressure water in the vaporizer. Natural gas and steam mixture is sent to a fired tubular reactor. The mixture of natural gas and steam passes through catalyst-filled tubes, where it is converted into syngas. Because this reaction is highly endothermic, a portion of natural gas is combusted in a direct-fired furnace to provide the necessary heat for the primary reactor. To control the heat flow and the temperature of the reformer, several burners are arranged inside the furnace. Nearly 50% of the energy obtained from combustion of natural gas is used in the reforming reaction; the rest of the energy embedded in flue gas is typically utilized for pre-heating feedstocks or for generating steam. Typically, 35-40% of the natural gas is converted in this primary reactor at 800°C and 20 bar . After leaving the primary reformer at 800°C 29 , the unreacted natural gas and syngas are fed to the secondary reformer, where the rest of the reaction is completed. The secondary reactor is an autothermal reforming (ATR) unit that consists of a burner, a combustion zone, and a catalyst bed. The feed stream is a mix of unreacted natural gas and steam with oxygen; the stream passes through the combustion zone, where partial oxidation takes place at 1000°C 27 . The stream then passes through the catalyst bed, where the final reaction takes place. Importantly, this adiabatic reformer enables the adjustment of the hydrogen/CO ratio of the synthesis gas, by tuning the amount of oxygen or the reaction temperature .