Investigation of a novel integrated system for zero liquid discharge wastewater treatment utilizing flue gas waste heat

Coal-fired power plants face dual challenges of high-salinity wastewater discharge and significant underutilization of low-grade flue gas heat, both of which hinder sustainable water-energy management. To address these issues in a synergistic manner, this study proposes an integrated treatment system that combines ammonia-water absorption refrigeration (AAR), freeze crystallization (FC), and humidification-dehumidification desalination (HDH). The system is driven entirely by flue gas waste heat and designed to achieve zero liquid discharge while improving thermal energy utilization. A steady-state simulation model is developed using Aspen Plus, incorporating mass and energy balance equations to characterize thermodynamic interactions across the subsystems. Under representative conditions, the system achieves a freshwater recovery rate of 44.5%, a total salt removal rate of nearly 100% in the product-water stream, and an energy efficiency ratio of 0.43. Thermal utilization efficiency reaches 28.62%, and the cooling energy released from ice melting is partially recovered for auxiliary use. The economic assessment reveals a levelized cost of water (LCW) of 5.54$/m3. These findings support the proposed AAR-FC-HDH system as a technically viable and economically attractive pathway for achieving sustainable saline wastewater management, by harnessing low-grade waste heat to facilitate zero liquid discharge in power industry scenarios characterized by high thermal intensity and stringent regulatory demands.