A general criterion for the design and operation of flexible hydrogen storage in Power-to-X processes

This paper introduces a general criterion for the optimal design and operation of hydrogen storage tanks. Specifically, the proposed procedure identifies the optimal delivery schedule that minimizes the capacity of material storage systems. Indeed, many manufacturing processes need some buffer storage to administer mass flows appropriately according to the operating needs (one class above all: Power-to-X processes) and have one of their highest expenditures right in those tanks when proving not sufficiently flexible. Hence, the novelty of the proposed method lies in a rigorous mathematical formulation that converts arbitrarily fluctuating inlet streams into optimally fluctuating outlet streams that minimize the storage volume and comply with different operating requirements. The criterion is validated by considering the techno-economic assessment of a chemical plant featuring a dedicated green hydrogen production facility that feeds the process. Specifically, the required capacity of the “ Flexible ” hydrogen buffer storage, which connects the green hydrogen generation system to the conversion process, significantly decreases by 91.31%–99.31% (depending on the flexibility ranges enabled by the downstream conversion process) compared to the “ Rigid ” storage alternative based on a constant outlet mass flow withdrawal, coinciding with the hydrogen consumption rate at nominal operating conditions. Correspondingly, the resulting levelized cost of hydrogen benefits accordingly, ranging from 4.19 to 6.03 USD/kg (California, 2023). • Without flexibility, Power-to-X processes demand large buffer storage capacities. • We introduce a criterion minimizing the size of dynamically operated storage tanks. • Optimally fluctuating outlet streams mitigate arbitrarily fluctuating inlet streams. • Full compliance with downstream processes' supply specifications is proven. • Our “ Flexible ” policy saves >90% in storage size compared to the “ Rigid ” one.