Enhanced process integration of black liquor evaporation, gasification, and combined cycle

Energy recovery from black liquor (BL) can be performed through gasification at temperatures above the melting point of inorganic chemicals. Complementarily to BL gasification experimental research, this study is conducted to simulate the thermodynamic modeling of an integrated system for BL evaporation, gasification, and combined cycle for power generation. For BL evaporation, a novel system is proposed based on the concept of exergy recovery to minimize exergy loss, and thus, lower the required energy input for evaporation. From the process design and calculations, higher target solid content leads to lower total required energy for BL evaporation. The lowest required total energy for evaporation can be achieved at a target solid content of 75 wt% wb. Furthermore, an integrated power generation system adopting gasification and combined cycle is modeled, and an application of different BL evaporation technologies is also evaluated in terms of net energy efficiency. The integrated system with exergy recovery-based evaporation can achieve a net energy efficiency of 34.5%, which is significantly higher than those of multi-effect evaporators (24.5%) and conventional boiler-based evaporation (14.7%).