Abstract
The U.S. produces 10 million metric tons (MMT) of hydrogen annually, emitting about 41 MMT of carbon dioxide equivalents ( \(\hbox {CO}_2\) -eqs). With rising hydrogen demand and new emission regulations, integrating conventional and novel hydrogen production systems is crucial. This study presents an integrated optimization framework to model diversified hydrogen economies as mixed integer linear programs (MILPs). Moreover, the accounting of emissions extends to the system exterior (scope 3), thus providing a comprehensive sustainability assessment. The primary focus of the presented computational example is to analyze the impact of scope 3 emissions, particularly material emissions during the construction phase, on process system optimization while complying with stringent environmental constraints such as carbon limits. By evaluating emission reduction scenarios the model highlights the role of power purchase agreements (PPAs) from renewable sources and the trade-offs between conventional and novel hydrogen production technologies. The key findings indicate that while electrolyzer-based systems (PEM and AWE) offer potential for emission reduction, their high energy demand and significant scope 3 material emissions pose challenges for a complete transition in the near term. The study identified two optimal design configurations: one utilizing PPAs as the primary energy source coupled with the conventional SMR-CCS process, and another that combines both conventional (SMR-CCS) and novel hydrogen production technologies under a hybrid purview. Ultimately, the findings contribute toward the ongoing efforts to achieve true net-carbon neutrality.
Graphical abstract
