Abstract
Cost reduction of green ammonia production is critical to advancing the hydrogen-ammonia economy, as ammonia capable of cost-effective storage and transportation is a promising hydrogen carrier and energy carrier to alleviate the intermittency and geographical limitations of renewables. Optimisation and techno-economic assessment based on rigorous model are essential to accurately investigate techno-economic feasibility and fully explore optimisation potential. This work estimates the levelized cost of ammonia (LCOA) of an integrated system including a hydrogen generation process employing Proton Exchange Membrane (PEM) water electrolysis, a nitrogen generation process from flue gas recovery, and an ammonia synthesis process based on Haber-Bosch Process. To enhance the reliability of LCOA, detailed equipment sizing and costing is conducted according to stream data from rigorous modelling in Aspen Plus. A novel optimisation strategy is proposed to enhance the computational robustness by sequentially largening the group of optimised variables and improving the quality of initial points. Homotopy-continuation (HC) method is employed to ease the convergence difficulties for solving the flowsheet with multiple recycle streams and scaling up the plant capacities between 100 tNH3 d-1 and 600 tNH3 d-1 from an initially feasible point. Heat integration is also considered to realise the combined supply of heat and power by introducing a steam turbine power cycle and utilising the waste heat from exothermic ammonia synthesis.