Biomass Based Sustainable Ammonia Production: Digestion vs Gasification

The synthesis of ammonia is one of the most important chemical processes in the world. The Haber–Bosch process has predominantly been used to synthesize ammonia over the last decades. However, it uses coal or natural gas as raw materials. In this work, the path to produce ammonia from biomass has been evaluated and optimized. Thermochemical and biochemical routes have been compared. Three alternative gasification technologies have been considered together with anaerobic digestion. For the reforming stage, two alternatives have been compared: autothermal and steam reforming. Finally, ammonia is synthesized in a multibed reactor with two different configurations: direct or indirect cooling. The problem is formulated as a mixed integer nonlinear program but solved as a set of 14 nonlinear programs. Indirect gasifier followed by steam methane reforming and direct cooling ammonia reactor is the path that presents the best performance with an ammonia production cost of about 380 €/t. The biochemical route shows worse results to ammonia due to the low yield to biogas and, therefore, to ammonia.