Life Cycle Assessment of Hydrogen and Natural Gas Combustion in Aluminum Pusher Furnaces

In Europe, natural gas (NG) combustion has become a bidimensional problem from both political and environmental perspectives. Consequently, substituting hydrogen (H2) for NG as a CO2-free fuel is a promising decarbonization option. This study addresses this issue by conducting a “cradle-to-gate” Life Cycle Assessment (LCA), comparing NG/air and H2/air combustion for preheating a one-ton aluminum slab in the semi-finished aluminum industry. This evaluation is based on data from energy and mass balances and combustion calculations from the off-gas composition in an 11 MW pusher furnace. Three scenarios were simulated, each corresponding to a specific fuel type. The simulations were performed using Umberto 11® software, the ReCiPe 2016 (Hierarchist) life cycle impact assessment methodology, and the ecoinvent® 3.11 database. The results demonstrate the significant environmental impact that NG and H2 production and the German grid have in comparison to the furnace combustion process. Nevertheless, the use of gray H2 and H2 produced through electrolysis with the current electricity mix results in worse environmental impacts across 16 out of 17 impact indicators, with values between 1.25 and 13 times higher in comparison to those associated with NG.