Role of Hydrogen in Industrial Decarbonization: A Case for Ammonia Industry in the United States
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Ammonia production contributes more than 1% of the global greenhouse gas emissions (GHG) while being used to serve a majority of the demand for nitrogen-containing fertilizer for agricultural use. While the predominant route for ammonia production today relies on natural gas as a source of energy and hydrogen for thermochemical Haber-Bosch (HB) synthesis, there is growing interest in electrically-driven routes that can reduce carbon-footprint of ammonia production, by relying on low-carbon electricity supply from variable renewable energy (VRE) sources. This electrically-driven ammonia route could not only serve existing uses for fertilizer production, but also be deployed to service energy needs for other end-use sectors where ammonia use is being contemplated (e.g. marine transport). Here, we evaluate the spatial variations in cost of the above electrically-driven ammonia process across the U.S. predominantly, for different scenarios of electricity supply as well as technology cost scenarios for 2030. Our approach goes beyond prior techno-economic assessments of electricity-driven ammonia production by explicitly accounting for variability in electricity supply and its implications on plant design, cost and emissions. This is achieved by using a least-cost integrated design and operations modeling framework that treats as variables the relative sizing of various units (e.g. electrolyzer, Air Separation Unit, renewables capacity), including deployment of alternative forms of on-site storage (battery energy storage, gaseous 𝐻2 and liquid 𝑁2). The overall mixed-integer linear programming (MILP) model is able to optimize for the minimum annualized cost of providing round-the-clock ammonia under the required system emission and flexibility constraints. We also evaluate dedicated grid connected VRE-based ammonia production for locations in close proximity to existing 𝑁𝐻3 production facilities and agricultural hubs in the US, to identify the cost-optimal VRE mix and storage requirements for future projections of grid scenarios in the US. Based on this framework, we are able to develop optimal sizing requirements for the facility in terms of VRE and capital investments in equipment to be able to sustain round-the-clock production. Our analysis shows that a standalone renewable ammonia production facility makes use of storage of intermediate products (𝑁2, 𝐻2) in the production process so as to be able to dispatch them during non-availability of renewable electricity. To meet the minimum power input necessary to operate the thermochemical HB process, electrochemical storage (e.g. Li-ion) is also needed. However, if the thermochemical HB process can be operated at less than nameplate feed flow rates, the need for Li-ion battery storage is minimized, allowing for more cost-effective production options.
DepartmentTechnology and Policy Program
Massachusetts Institute of Technology