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

Abstract

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.

Utilization of Water Utility Lime Sludge for Flue Gas Desulfurization in Coal-Fired Power Plants: Part II. Lime Sludge Characterization and Mercury Re-emission

“…Based on the results presented in Part I of this article, the reuse of lime sludge generated at water utilities to capture acid gases at power utilities can be a sustainable and cost-effective solution benefiting both the water and energy sectors. 1 The laboratory-scale results presented in this work confirmed the high reactivity of various tested lime sludge samples without negatively affecting mercury reemission or undesirable elements leaching into the scrubber slurry. More testing at a pilot scale is needed to further evaluate possible operational issues before consideration for potential large-scale implementation.…”

“…Overall, lime sludge can be used as a potential replacement to limestone for the removal of acid gases from power plant flue gas. On the basis of the results presented in Part I of this article, the reuse of lime sludge generated at water utilities to capture acid gases at power utilities can be a sustainable and cost-effective solution benefiting both the water and energy sectors . The laboratory-scale results presented in this work confirmed the high reactivity of various tested lime sludge samples without negatively affecting mercury re-emission or undesirable elements leaching into the scrubber slurry.…”

“…As discussed in Part I of this article, based on the reported physicochemical properties of lime sludge and limestone samples and reactivity data, lime sludge could be a suitable replacement for limestone in FGD systems. 1 Mercury reemission from FGD scrubbers needs to be investigated further if power plants switch from limestone to lime sludge for the scrubbing process. We were unable to identify any research investigating the impact of lime sludge use on mercury reemission from FGD scrubbers.…”

Utilization of Water Utility Lime Sludge for Flue Gas Desulfurization in Coal-Fired Power Plants: Part III. Testing at a Higher Scale and Assessment of Selected Potential Operational Issues

“…Wet scrubbers are widely used for removal of SO 2 from flue gas through reaction with limestone slurries . A supply–demand evaluation and a life cycle assessment performed in Part I of this investigation demonstrated that switching from limestone to lime-softening sludge can be highly beneficial to water treatment and power generation industries, both economically and environmentally …”

“…1 A supply−demand evaluation and a life cycle assessment performed in Part I of this investigation demonstrated that switching from limestone to lime-softening sludge can be highly beneficial to water treatment and power generation industries, both economically and environmentally. 2 In Part II of this work, the feasibility of lime sludge utilization in the flue gas desulfurization (FGD) process was evaluated by conducting laboratory-scale tests with a simulated flue gas at a flow rate of 0.5 L/min (LPM). 3 Eight lime sludge samples and a baseline limestone sample were evaluated for their performance capability to remove SO 2 from a simulated flue gas, while monitoring Hg re-emission from the scrubber.…”