Evaluating Metals Sequestration in Ash by Powdered Activated Carbon

摘要

Activated Carbon Injection(ACI)using Powdered Activated Carbon(PAC)is commonly used for control of mercury in coal-fired flue gases.It has become the dominant technology for compliance with the EPA’s Mercury and Air Toxics Standard(MATS)rule and is used on many coal types and unit configurations.The ash often can be sold for beneficial use in concrete or as road base,with common PAC-fly ash blends of <0.5 to 1 wt% PAC in ash.New requirements for treatment of scrubber discharge under the Effluent Limit Guidelines(ELG)rule drive increased concern at power plants about the fate of metals in the power plant.Intersecting requirements for air pollution control,effluent limits and coal combustion residuals under the Coal Combustion Residuals(CCR)rule underscore the importance of understanding the fate of metals including mercury,selenium and arsenic in the power plant system.Mercury has been demonstrated as stable once collected with PAC in the power plant flue gas train,and other metals have had variable results.This study analyzes the stability of these metals in ash and with the use of PAC injection for mercury control and describes the implications regarding the ELG and CCR rules.New PAC sorbents are being developed to improve metals uptake and stability.