Energy Conversion and Management 229 (2021) 113735 0196-8904/© 2020 Elsevier Ltd. All rights reserved. Sustainable three-stage chemical looping ammonia production (3CLAP) process M.M. Sarafraz * , F.C. Christo School of Engineering, Deakin University, Waurn Ponds, Geelong, Victoria, Australia A R T I C L E INFO Keywords: Three-stage ammonia production Thermal plasma Chemical looping Metal nitride, green process ABSTRACT In the present paper, a new CO 2 -neutral thermodynamic process is developed based on a chemical looping principle that circulates nitrogen carrier between reactors for producing ammonia and/or hydrogen via a ni- trogen fxation reaction. This study advances the knowledge on selecting plausible nitrogen carrier candidates from a wide range of metals including rare and transient elements. The proposed three-stage chemical looping ammonia production (3CLAP) system consists of two exothermic reactors: nitridation and ammoniation reactors to drive the nitrogen fxation reactions, and an endothermic thermal plasma reactor to handle dissociation of metal oxides back into a pure metal that is re-circulated in the process. The heat released in the nitridation and ammoniation reactors is recovered to generate electricity, which partially meets the energy demand of the thermal plasma unit. Several key criteria were used in the thermochemical analysis for selecting suitable metals for the 3CLAP process; the spontaneity of the reactions, melting temperature of the metals, availability of metals, energetic performance of heat recovery unit, and the nitrogen and steam economy. It was identifed that chrome (Cr), magnesium (Mg), aluminium (Al), calcium (Ca), and manganese (Mn) were the best nitrogen carrier metals amongst all candidates. Chrome yielded the highest nitrogen economy of molar ratio (NH 3 /N 2 ) of ~ 1.97 and the highest steam economy (NH 3 /H 2 O) of ~ 0.98. However, the lowest performance of nitrogen and steam economy was for Mn of ~0.96, and ~0.3, respectively. With chrome, the power block effciency was ~ 32.3%, which is a competitive value to the current state-of-the-art effciencies reported in the literature. The highest self-sustaining factor (SSF) was ~ 0.33, meaning that one-third of the total energy demand of thermal plasma reactor could be delivered via a heat recovery system. 1. Introduction Ammonia is one of the most promising chemicals for storing and transporting hydrogen safely [1]. The current global ammonia produc- tion is around 162 million metric tons per annum, which is partitioned to produce agricultural nitrogen-based fertiliser and nitric components for supporting >50% of global food production [2]. Commercialised pathway for ammonia production is predominantly through the Haber- Bosch (H-B) process, which requires high pressure (~200 bar), high temperature (200 to 300 ◦ C), and expensive catalysts such as rhodium, nickel [3] or iron [4]. The spent catalysts require cyclic regeneration and re-activation, which adds to the complexity and cost of the process. Required hydrogen for the Haber-Bosch process is usually supplied from methane reforming process [5], which utilises several reforming re- actors that are energy-intensive and contributes to global warming by releasing CO 2 and NO x to the environment [6]. Despite these disadvantages, ammonia is still produced commercially through the H-B process because there is no other economically viable and cleaner pathway for synthesis of ammonia. As mentioned earlier, the H-B pro- cess is an energy-intensive process [7], and process-wise is based on centralised nitrogen fxation production plant with limited effciency and high energy consumption of 1 MJ/mol of N 2 [8]. Chemical looping gasifcation and chemical looping hydrogen pro- duction are two viable pathways for effcient conversion of fossil fuels into clean hydrogen or ammonia. Hence, signifcant effort has been made to improve the chemical performance and effciency of these systems to reach competitive level to existing reforming systems for hydrogen production. Recently, Pereira et al. [9] assessed a chemical looping process for producing 500 kt/y of ammonia from methane in- tegrated with a CO 2 separator unit. They chose packed bed as a plausible confguration for the reactors and yielded 1.54–1.63 kg NH 3 per kg methane. Together with this, the system consumed up to 2.32 MJ/kg CO 2 to separate carbon dioxide from ammonia. They concluded that the * Corresponding author. E-mail address: mohsen.sarafraz@deakin.edu.au (M.M. Sarafraz). Contents lists available at ScienceDirect Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman https://doi.org/10.1016/j.enconman.2020.113735 Received 26 October 2020; Received in revised form 22 November 2020; Accepted 1 December 2020