Power-to-hydrogen-ammonia coordination and planning for integrated energy systems with ammonia co-firing and waste heat recovery

With the continuously increasing penetration of renewable generation into integrated energy systems (IES), the limited capacity for renewable energy integration has emerged as a critical bottleneck, resulting in significant renewable curtailments and suboptimal operation. An alternative to putting renewable generation onto electrical grids is to produce ammonia from surplus renewables, which can be transported and co-fired with coal at thermal power plants, reducing carbon emissions and enhancing operational flexibility of IES. To promote the co-development of renewables and green ammonia within IES, the paper proposes a bi-level optimisation model for IES coordination and planning with power-to-hydrogen (P2H) and power-to-ammonia (P2A) systems. The lower-level model schedules daily multi-energy flows and their mutual conversion within an electricity-gas-heat IES to minimise overall operating costs on each typical day. Capital and operating expenses of P2H and P2A systems together with the carbon trading revenue and IES operating cost savings achieved by coal-ammonia co-firing and waste heat recovery are translated into a net present value, which is then maximised to suggest the best production and storage capacities of P2H and P2A components in the upper level. The proposed bi-level model is tested in the context of a modified IEEE 39-node electrical grid combined with 20-node gas and 6-node heat networks based on 2019, 2030 and 2050 techno-economic parameters, respectively. In addition to the power-to-hydrogen-ammonia technologies, the joint use of P2H and hydrogen electrification for spatio-temporal shift of renewables is evaluated in terms of their capacities and resulting economics as comparison. Furthermore, the sensitivity of P2H-P2A sizing results and system economics to coal unit costs, carbon trading prices and electrolyser unit costs is explored, respectively, offering insights into feasible pathways for deployment of P2H-P2A technologies alongside renewables in future IES.