Intensified Flue Gas Desulfurization Water Treatment for Reuse, Solidification, and Discharge

Wet flu gas desulfurization (FGD) scrubbing systems are operated in the major coal-fired power generation plants to remove SOx from the flue gas while removing various metals, metalloids, and chlorides generated from the coal, limestone, and make-up water. To mitigate corrosion and retain SOx removal efficiency, a purge stream needs to be discharged from the FGD system for chloride removal. As a result, in addition to significant levels of chloride, the purge stream, termed FGD wastewater, typically contains 4,000-40,000 ppm total dissolved solids (TDS) and 1.4-17wt% total suspended solids (TSS). To effectively treat FGD wastewater, “Intensified Flue Gas Desulfurization Water Treatment for Reuse and Zero Liquid Discharge” is proposed, aimed at (1) removing government-regulated species and TSS in a combined electrocoagulation with flotation unit to avoid further Se treatments by a biological method, subsequently reducing the footprint by >20%, (2) reducing TDS in a nanofiltration unit to promote water recycle with 80% water recovery, (3) dewatering liquid waste for landfill disposal in a zeolite dewatering unit to produce >20 wt% of TDS, thereby pursuing a zero liquid discharge (ZLD) process, (4) polishing discharge in a continuous capacitive deionization (CDI) to meet the effluent limitation guidelines (ELG) limits if ZLD is not necessary or chosen by a utility. This process design has been recently presented, discussed, and encouraged with our utility partners, i.e., LGE&KU and Duke Energy, which provides a competitive alternative to the current biological process combined with several physical/chemical steps. Through the preliminary results performed at UKy-CAER and its teamed members, four objectives are identified to address the feasibility of the proposed process for FGD wastewater treatment, which includes (1) effectiveness of electrocoagulation combined with flotation, (2) performance degradation of membrane-based filtrations, (3) determination of the minimum salt concentration for fixation/stabilization, and (4) removal of the remaining regulated species using CDI. We believe that, along with the success of each objective, a multistage process at a sub-pilot scale will be assembled at the end of the project to prove the proposed process that is able to continuously treat FGD wastewater at 1 L hour-1. This project will be led by UKy-CAER with China University of Mining and Technology (CUMT) as a subcontractor responsible for a flotation design, South Research Institute (SRI) as a subcontractor responsible for a fixation/stabilization study, and Trimeric Cooperation as subcontractor responsible for a techno-economic assessment. Utility partners, LGE&KU and Duke Energy, will assist the DOE NETL to guide this project, as needed. Compared to the current biological treatments following from several physical/chemical steps, we believe that the proposed process will immediately result in two major benefits: (1) a reduction in the footprint of a physical/chemical treatment process and (2) a reduction in withdraws of fresh water at power generation plants.