Desalination of MSWI fly ash washing wastewater coupled with in-plant flue gas waste heat: Techno-economic analysis and carbon emission accounting

Achieving low-cost, energy-efficient, and sustainable fly ash (FA) washing wastewater (WWS) desalination is crucial for FA reutilization for building materials. This study develops a novel WWS desalination process that synergistically integrates in-plant low-temperature flue gas (LTFG) waste heat recovery and optimizes impurity removal. The process is evaluated through comprehensive simulations, techno-economic analysis (TEA), and life cycle carbon emission accounting. Results indicate LTFG waste heat recovery yields 3500–3600 kg/h of steam. The optimized Na₃PO₄-based impurity removal method decreases comprehensive costs to 34.2 CNY/m³. Combined with waste heat recovery, PT-H achieves a lowest cost of 39.4 CNY/m³—a 79.4 % reduction versus conventional methods—improving economic benefits by 59.3 % under benchmark conditions. Sensitivity analysis identifies that the Na₃PO₄-based and triple-effect evaporation exhibit superior economic competitiveness. Under optimal scenarios, the MVR demonstrates higher profit potential (19.4 CNY/m³) but carries greater economic risk, whereas the triple-effect evaporation offers superior stability (4.6 CNY/m³). Environmentally, the integrated process is highly effective, achieving negative carbon emissions when product carbon offsets are considered. Interestingly, the carbon emission factor of municipal solid waste incineration (MSWI) shows considerable volatility, leading to a minimum of −706.1 kg CO₂-eq/m³ for PM-H. This novel synergistic process provides an economically viable and potentially carbon-negative solution for WWS desalination, promoting the sustainable and cost-effective resourceful utilization of FA.