Decarbonizing the energy supply chain: Ammonia as an energy carrier for renewable power systems

Abstract

Growing global awareness of global warming has led to a focus on reducing greenhouse gas emissions and promoting renewable energy. Energy storage is essential for ensuring a reliable power supply due to the intermittent nature of renewables. While green hydrogen (H2) is considered a clean energy carrier, it faces challenges such as high cost, safety concerns, and low volumetric energy density. In contrast, safer and cost-effective ammonia (NH3) offers higher volumetric energy density for storage. The study explores the Electricity-H2-NH3-H2-Electricity system, a promising low-carbon global renewable electricity transportation avenue. It involves an Aspen Plus process simulation, encompassing air separation, NH3 synthesis, and H2 generation from the NH3 decomposition process. We analyze renewable energy sources, NH3 transportation, process mass balance, and energy consumption and conduct economic and CO2 analyses. Three scenarios (current, near future, sustainable future) with varying technology levels and costs are presented. The findings reveal that 11.044–9.349 MWh of renewable electricity in exporting countries generates 1 tonne of NH3, then split, with 0.17 tonnes combusted to provide heat for the decomposition process and the remaining 0.83 tonnes converted to produce 0.145 tonnes of H2. This H2 is sent to fuel cells, yielding 1.711–2.436 MWh of imported electricity to the grid, with 575–141 USD/MWh cost. Additionally, the imported NH3 and H2 incur costs of 0.719–0.289 USD/kg and 5.993–2.362 USD/kg, respectively. Considering the heat integration of the fuel cells and NH3 decomposition process, an additional 23 % of H2 production is achieved (0.178 tonnes), and a 34 % increase in imported electricity is sent to the grid (2.370–3.259 MWh). This leads to a 27 % decrease in imported renewable energy costs (432–103 USD/MWh) and a 29 % reduction in H2 costs (4.087–1.666 USD/kg); the ultimate CO2 emission of the system is 318–36 kg/MWh.