Process development of flue gas desulphurization wastewater treatment in coal-fired power plants towards zero liquid discharge: Energetic, economic and environmental analyses

Abstract

Zero emission of wastewater from coal-fired power plants (CFPPs) is one of the pathways for cleaner electricity production. It is expected that low-cost and reliable zero liquid discharge (ZLD) of flue gas desulphurization (FGD) wastewater will be achieved by applying the forced circulation multi-effect distillation and crystallization (FC-MEDC) technology. In the present work, different FGD wastewater ZLD processes were compared in terms of energy consumption, economic cost and environmental impact. The results suggest that the levelized cost of water (LCOW) could be reduced by the integration of pre-concentration and waste heat utilization with FC-MEDC. Typically, the LCOW could be reduced by 9.5% and 28.8% in reverse osmosis (RO) and flue evaporation (FE) incorporation scenarios, respectively. The implementation of crystal seed technology in the FE-assisted FC-MEDC system significantly decreased the LCOW by 45.4% for chemical pretreatment cost reduction. A further parametric study was performed to examine the influence of key variables on the LCOW. Overall, a comprehensive investigation of FC-MEDC treatment of FGD wastewater was performed, resulting in cost-effective design of a thermal ZLD process with a minimum LCOW of 5.60 $/m3. Sensitivity analysis was conducted, revealing the influence of market factors on the economic viability of different schemes. In addition, environmental analysis indicates that the greenhouse gas (GHG) emissions from the FGD wastewater ZLD processes ranged from 38.1 to 86.8 kg CO2-eq/m3 in different scenarios and representative regions, and could be notably reduced by 51.7%. The methodology and results are useful for wastewater ZLD process screening to minimize costs and environmental impacts.