Waste heat utilization from boiler exhaust gases for zero liquid discharge of desulphurization wastewater in coal-fired power plants: Thermodynamic and economic analysis

Abstract

Zero liquid discharge (ZLD) of wet flue gas desulphurization (WFGD) wastewater in coal-fired power plants (CFPPs) would contribute to sustainable development of fossil electricity generation. In the present work, improved flue gas-driven forced-circulation multi-effect distillation and crystallization (FCMEDC) systems were proposed for achieving low-cost ZLD of WFGD wastewater. Different types of integration scenarios were investigated, including FCMEDC systems driven by waste heat recovered from boiler and economizer exhaust gases, and incorporated with low-pressure economizer and flue gas bypass high-pressure economizer systems. Thermodynamic and techno-economic analysis models were developed for comprehensive evaluation of the technical and economic feasibility of the integrated ZLD schemes. The levelized cost of wastewater (LCOW) and operating expenditure (OPEX) were found to be significantly reduced by 41.5% and 53.6%, respectively, when plant auxiliary steam was substituted by boiler exhaust gas as the heat source in a 600 MW unit. A parametric study was further conducted to investigate the impact of wastewater salinity and flow ratio on the process design. The flue gas-driven FCMEDC system demonstrated favorable adaptability to variations in wastewater quality. Moreover, sensitivity analysis suggested that the LCOWs of the proposed ZLD systems were explicitly subject to the expected lifetime, brine disposal options, and brine pre-concentration. The methodology and results could provide insights into the process development of WFGD wastewater ZLD systems based on the FCMEDC technology.