Driven by the need to reduce the destructive and irreversible effects of global warming caused by greenhouse gas emissions, the world is transitioning away from fossil fuels towards renewable alternatives. This transition brings the growing challenge of intermittency, as the availability of renewable energy from wind and solar fluctuates. This creates a big challenge for the chemical industry, which still relies on a continuous supply of energy and materials. Therefore, the chemical industry must adapt by using flexible processes capable of handling these fluctuations.

One application of flexible chemical processes is blue hydrogen production. Hydrogen is essential for decarbonizing hard-to-abate sectors such as heavy transport, steel, and chemical industries. While green hydrogen, produced from renewable electricity, offers a zero-emission solution, its supply is typically variable due to the intermittency of renewables. Flexible blue hydrogen production, made from natural gas with carbon capture and storage, can provide a reliable back-up supply, ensuring a stable supply of hydrogen for industrial processes with steady demand. By integrating flexibility into blue hydrogen production, the chemical industry can enhance system stability and support the transition to a sustainable hydrogen economy.

The aim of this research is to evaluate the potential of flexible natural gas reforming with carbon capture and storage to stabilize the intermittent supply of green hydrogen, ensuring a stable supply of hydrogen for downstream processes. This is done through a case study where blue hydrogen production compensates for fluctuations in green hydrogen generated from offshore wind energy, with limited hydrogen storage capacity. Using a hypothetical large scale ammonia synthesis plant in the port of Rotterdam as the downstream process. This research identifies process uncertainties, uses strategies to enhance flexibility, and quantifies their effects on process efficiency, costs and emissions.

To evaluate the potential of flexible blue hydrogen production, three case studies were simulated using Aspen Plus V12. The first case modeled a blue hydrogen plant operating continuously at maximum capacity (22.9 tons/h). This was used to clearly define the process steps needed for blue hydrogen production, serving as a benchmark for comparing continuous and flexible operations. In the second case study, an uncertainty is introduced to which the plant needs to adapt to. This uncertainty is modeled using hourly data from the Hollandse Kust Noord offshore wind farm, which supplies electricity to electrolysers with limited hydrogen storage capacity. The fluctuating green hydrogen output (0-11.3 tons/h) and steady hydrogen demand for ammonia synthesis (22.9 tons/h) determined the hourly blue hydrogen production. Multiple steady-state simulations were made in Aspen to model the plant at varying throughputs. In the last case, increased wind power output required the blue hydrogen plant to adapt with higher volume flexibility. An operating envelope of the blue hydrogen plant was developed to find the bottlenecks, and design strategies were applied to increase volume flexibility.

Results show that flexible blue hydrogen, using autothermal reforming with a gas heated pre-reformer, can effectively stabilize fluctuating green hydrogen production. The plants volume flexibility can be increased through design strategies such as selecting inherently flexible equipment, storage for intermediate production and using techniques like inert gas for load regulation. But there is a trade-off between flexibility and cost. The plant produces hydrogen at the lowest cost when operating continuously at maximum capacity, with a levelised cost of hydrogen (LCOH) at 3.19 €/kg. Increasing the volume flexibility of the blue hydrogen plant too much resulted in a LCOH of at least 4.02 €/kg, making alternatives like hydrogen storage a cheaper option for balancing out the intermittent supply of green hydrogen. However, when operating flexibly within its base volume flexibility the LCOH is cost effective compared to some alternatives as it increases only slightly to 3.47-3.57 €/kg. Mainly due to underused CAPEX, but also because of transient state losses and reduced efficiency at lower capacities.

This research shows the potential of flexibility in natural gas reforming processes and how it can play a key role in future energy systems. While there is still much to learn, integrating flexibility into the chemical industry enables it to adapt to the ever growing intermittently available feedstock and energy.