Low-carbon hydrogen via integration of steam methane reforming with molten carbonate fuel cells at low fuel utilization

Abstract

Hydrogen production is critical to many modern chemical processes – ammonia synthesis, petroleum refining, direct reduction of iron, and more. Conventional approaches to hydrogen manufacture include steam methane reforming and autothermal reforming, which today account for the lion's share of hydrogen generation. Without CO2 capture, these processes emit about 8.7 kg of CO2 for each kg of H2 produced. In this study, a molten carbonate fuel cell system with CO2 capture is proposed to retrofit the flue gas stream of an existing Steam Methane Reforming plant rated at 100,000 Nm3 h−1 of 99.5% pure H2. The thermodynamic analysis shows direct CO2 emissions can be reduced by more than 95%, to 0.4 to 0.5 kg CO2/kg H2, while producing 17% more hydrogen (with an increase in natural gas input of approximately 37%). Because of the additional power and hydrogen generation of the carbonate fuel cell, the efficiency debit associated with CO2 capture is quite small, reducing the SMR efficiency from 76.6% without capture to 75.6% with capture. In comparison, the use of standard amine technology for CO2 capture reduces the efficiency below 70%. This demonstrates the synergistic nature of the carbonate fuel cells, which can reform natural gas to H2 while simultaneously capturing CO2 from the SMR flue gas and producing electricity, giving rise to a total system with very low emissions yet high efficiency.