Comparative assessment and multi-objective optimization for the gray and blue ammonia synthesis processes: Energy, Economic and Environmental (3E) analysis

Abstract

A blue ammonia process was designed by incorporating the carbon capture and storage process into the gray ammonia process. A natural-gas-based ammonia synthesis process involved steam methane reforming, water gas shift reaction, acid gas removal, methanation, and ammonia synthesis. Energy analysis (specific energy consumption, SEC), economic analysis (levelized cost of ammonia, LCOA), and environmental analysis (global warming potential, GWP), denoted as 3E analysis, were executed for the gray and blue ammonia processes. Key process variables exhibiting a trade-off relationship for the 3E features were extracted via the local sensitivity analysis (LSA) and the global sensitivity analysis (GSA). Then, both processes were optimized by genetic algorithm (GA) based multi-objective optimization (MOO) technique for the 3E features, SEC, LCOA, and GWP. Three scenarios were selected on the Pareto front obtained through MOO, and the optimized results of the 3E analysis were compared. Through the MOO for 3E in the blue ammonia process, the minimum SEC, LCOA, and GWP were 31.03 GJ/tNH3, $415.15/tNH3, and 0.3172 tCO2eq/tNH3, respectively, compared to the gray ammonia process, +8.01%, +23.7%, and −81.47% increased or decreased.