A combined gasification-chemical looping approach for valorizing waste tires into ammonia: Techno-economic analysis

The worldwide accumulation of scrap tires presents a significant waste management challenge with major environmental and health implications, where, the stockpiles of waste serve as breeding grounds for disease-carrying insects. Meanwhile, the rapid rise in energy demand brings mounting pressure to develop renewable and sustainable fuel options. One strategy is to produce hydrogen based fuel via waste thermochemcial recycling but transporting and storing hydrogen remains difficult due to its physical properties. Ammonia, on the other hand, is a hydrogen-rich compound that exists in liquid form at moderate pressures, making it promising for use as an efficient hydrogen carrier. This study presents an integrated process design to valorize waste tires into ammonia through chemical looping gasification and Haber-Bosch synthesis. Two cases were modeled and evaluated: Case 1 utilized conventional gasification and air separation for nitrogen, while Case 2 integrated chemical looping technology. In Case 2, chemical looping was employed to supply the nitrogen necessary for the Haber-Bosch process and to enhance syngas production in the initial reactor by utilizing partial oxidation step. Technical analyses found Case 2 achieved 16-17% greater process efficiency and 4% higher exergy efficiency compared to Case 1. An economic assessment revealed Case 2 reduced total investment costs by 13.5% and levelized ammonia production costs by 12%. The results demonstrate the potential for the proposed chemical looping approach to sustainably address the growing scrap tire problem worldwide, while simultaneously producing ammonia, which is an efficient mean of storing and transporting hydrogen. Overall, the concept merits further development and scale-up testing as a viable pathway satisfying future energy needs while achieving circular economy principles through full tire valorization.