Utilization of Water Utility Lime Sludge for Flue Gas Desulfurization in Coal-Fired Power Plants: Part I. Supply–Demand Evaluation and Life Cycle Assessment

The feasibility of lime-softening sludge utilization for flue gas desulfurization in coal-fired power plants was evaluated through a supply–demand analysis and a life cycle assessment (LCA). To evaluate the demand and supply of lime sludge to replace limestone on a national scale, the annual amount of lime sludge generated by water treatment utilities in the United States was estimated and compared with the annual amount of limestone used by coal-fired power utilities. To evaluate the environmental sustainability of reusing lime sludge in power plants, an LCA study was performed in which the environmental impact and water footprint of the proposed approach were quantified, and these results were compared with the conventional approaches for limestone mining, grinding, and transportation to power plants and lime sludge disposal in landfills. Water utilities across the United States are currently generating approximately 3.2 million tons of lime sludge per year at an estimated disposal cost of approximately US$90 million, whereas power utilities are using approximately 6.3 million tons of limestone per year. The potential savings that would result from partial replacement of limestone with lime sludge was estimated to be approximately US$97 million per year. The LCA study showed that the environmental impact of lime sludge utilization in power plants under different scenarios was 2 orders of magnitude lower than that of the landfill disposal option. Furthermore, the water footprint for lime sludge reuse in power plants was almost negligible compared with that of the conventional approaches of disposing of lime sludge at water utilities or using limestone at power utilities.