Hydrogen production and storage as ammonia by supercritical water gasification of biomass

Abstract

A new energy self-sufficient process is designed, developed, and evaluated to produce hydrogen by supercritical water gasification from wet biomass or organic waste and store it as ammonia, produced by the Haber-Bosch process, using energy integration to establish an upper limit for the application of both technologies with improved overall energy efficiency. The assessment of the process is carried out with the aid of Aspen Plus. For an aqueous feed of 10 t/h with 32 wt% biomass, 745 kg/h of almost pure ammonia (equivalent to 132 kg/h of hydrogen) are produced, sequestrating 3 t/h of carbon dioxide and generating 1.8 MW of net electrical power. Exergy efficiencies are between 33.6 % and 35.4 %, and energy efficiencies are between 37.0 % and 40.0 %. The distribution of lost exergy flow for sets of process units, so the main lost work occurs in reactors (about 51 %) and heat exchangers (about 26 %). In addition, a techno-economic analysis of the process is carried out, concluding that the feed should be ten times higher (100 t/h) to achieve competitiveness with minimum selling prices for ammonia and hydrogen of 0.70 $/kg and 3.90 €/kg, respectively.