Process modeling and integration of hydrogen and synthetic natural gas production in a kraft pulp mill via black liquor gasification

The black liquor gasification integrated to chemical plants has shown potential for reducing the process irreversibility and promoting the decarbonization of this industrial sector. In the integrated chemical plants proposed in this work, the purpose is co-producing pulp and gaseous fuels, either hydrogen or synthetic natural gas, in order to expand the biorefinery product portfolio and, consequently, increase the plant revenues. However, due to additional equipment and utility demands, along with the uncertainty about the prices of the commodities; the benefits of the integrated setups must be thoroughly weighed by considering thermodynamic, economic and environmental indicators before the retrofit of the existing configuration is implemented. The exergy method is used along with the energy integration technique and other financial indicators to determine whether and in which scenarios the integrated biorefineries would be more attractive. The average exergy efficiency of the integrated chemical production plants is 44%, which is higher than that of the conventional case (40%). The balance of the overall CO2 emissions vary from 1.97 to -0.56 tCO2/tPulp, for the conventional and integrated setups, respectively. An incremental financial analysis under uncertainty also shows that the hydrogen production route with partial import of electricity and carbon taxations above 60 EUR/tCO2 outperforms the other scenarios. Therefore, the import of electricity from low-carbon grids and the upgrade of biorefinery residues arise as key factors for ensuring the sustainable production of traditionally fossil-based chemicals under more stringent environmental regulations.