Efficient co-production of power and ammonia from black liquor

Abstract

Black liquor (BL) is a by-product in the paper and pulp industry. Although it has good potential for providing energy as an industrial waste, BL's high moisture content limits its usability. In this study, an integrated system to effectively co-produce power and ammonia (NH3) from BL is modeled and evaluated. The modeling and integration are conducted using the principles of exergy recovery and process integration to effectively circulate the energy/heat throughout the whole system. The developed system involves BL evaporation, gasification, syngas chemical looping (SCL), and NH3 synthesis. During SCL process, H2, CO2, and N2-rich gas are produced consecutively in the oxidation, reduction, and combustion reactors, respectively. The designed system can achieve the total energy efficiency of ~50%. The result also suggests that N2-rich gas and pure H2 produced during SCL can be used directly for NH3 synthesis without any additional energy penalty. The additional step for CO2 separation can also be avoided, affording a cleaner and more efficient system that provides complete carbon capture.