TECHNO-ECONOMIC ANALYSIS OF THREE-STAGE CHEMICAL LOOPING FOR AMMONIA PRODUCTION (3CLAP)

Abstract

ABSTRACT Ammonia (NH3) is an essential chemical used in the agriculture industry as fertiliser. It also shows a promising trend as an energy carrier due to its high content of hydrogen (H2) and the ease of transportation and storage. However, the primary technology for ammonia synthesis, the Haber-Bosch method, is an energy- and resource-demanding process that emits CO2 emissions to the atmosphere. In this work, a sustainable ammonia production approach was suggested using a three-stage chemical looping process employing metal as a nitrogen carrier. The process operates at ambient pressure and relatively low temperature (200 – 500 °C). The chrome metal was selected as a nitrogen carrier based on various criteria such as Gibbs free energy, enthalpy, melting temperature and nitrogen capacity. The process consists of a nitrogen fixation reaction followed by metal nitride hydrolysis reaction that produces ammonia and metal oxide. Metal extraction with ionic liquid (IL) technology was developed as a new approach to regenerate the metal. The Aspen Plus software package was used to simulate the process and investigate the effect of several parameters on the ammonia yield. The results indicate that the process has high end-product flexibility as it is likely to produce more hydrogen than ammonia at elevated temperatures. Increasing the steam flow allows the total conversion of CrN to Cr2O3 and attains ammonia’s optimum production rate. The complete recovery of the metal is achieved using high-efficiency IL, namely, (1-Hexyl-3-methyl-imidazolium-hexafluorophosphate [HMIM+][PF6-]). The economic analysis of the system finds that the ionic liquid (IL) accounts for about 90% of the operating cost. Nevertheless, integrating the metal regeneration step into the process reduces the production cost of 1kg of ammonia by 11.5%. The levelized cost of ammonia (LCOA) produced by the suggested system is 106 £/GJ making it not competitive with other technologies. Extensive research around utilising different metals or low-cost ILs may lessen the overall cost of the process. These findings open a new avenue towards producing ammonia using an environmentally friendly method.