Dynamic Analysis of Flex-gNH3 – a Green Ammonia Synthesis Process


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The future of a decarbonised ammonia production is seen as the alignment of the intermittent production of renewable energy, energy demands and ammonia process features. The current Haber-Bosch ammonia synthesis process can indeed be altered to enable green and sustainable ammonia production primarily being driven by renewable electricity. However, this will require to enhance current commercial Haber-Bosch (H-B) process flexibility with modifications to redefine the conventional H–B process with a new optimised control.

The technical feasibility of green-ammonia (gNH3) process had been widely discussed and analysed focusing on its energy efficiency, the development of small-scale, distributed, modularised processes that can be turned into a commercially attractive solution aligned to the geographically isolated and intermittent renewable energy sources.

In this paper, we focus on dynamic behaviour of gNH3 synthesis that is seen as a key enabler for successful fast deployment of gNH3, and plays a paramount role to alter the current Haber-Bosch ammonia synthesis process. A typical conventional, “rigid”, ammonia synthesis at 60 metric tonnes per day (MTPD) is compared with a Casale’s optimised gNH3 process of the same capacity – called “flex-gNH3” – where a flexible ammonia synthesis loop operating with Clariant’s Amomax catalyst is combined with an optimised hydrogen storage to achieve lower levelized cost of green ammonia (LCOgA). The authors share the results of the dynamic modelling achieved using Casale’s gNH3 Dynamic Model – a dedicated tool that combines the features of ammonia synthesis loop with renewable electricity profile, dynamic performance of hydrogen and nitrogen generation and type and capacity of hydrogen storage. Pre-sizing of the “flex-gNH3” process is done with Casale’s gNH3 Optimiser, a tool that can serve customers with a tailored – to the customer’s renewable electricity profile – “flex-gNH3” process scheme, resulting in lowest LCOgA and highest electricity utilisation.

Four real and specific scenarios of renewable electricity production profiles of wind, solar and solar-wind mix were used to calculate the economic value of the new gNH3 process at an average electricity price of US$40/MWh. The dynamic analysis employs a peak backup power of 500 kW for the maximum backup time of 10 hr and a fruition factor of the power profile. We demonstrate that the “flex-gNH3” process enables process load ramps at ±100%/h that is combined and illustrated in the dynamic profiles of the hydrogen storage, the loop load and the power utilisation. When realised, the gNH3 allows achieving the LCOgA reduction by 35% (on average) at the minimum and maximum load at 10 and 110% accordingly. Moreover, the flex-gNH3 process incorporate a patented plantwide control philosophy that combines the process profitability and the plant safety suited for a variety of plant scales of production, location, nature and price of renewable electricity production profiles.

Authors present the arguments that such novel flex-gNH3 process will open the door to flexible and innovative deployment of Low-Carbon Ammonia Production worldwide.