Presentation on theme: "Susan Thorneloe US EPA National Risk Management Research Laboratory Research Triangle Park, North Carolina September 13, 2006 Susan Thorneloe US EPA National."— Presentation transcript:
Susan Thorneloe US EPA National Risk Management Research Laboratory Research Triangle Park, North Carolina September 13, 2006 Susan Thorneloe US EPA National Risk Management Research Laboratory Research Triangle Park, North Carolina September 13, 2006 Evaluating Life-Cycle Environmental Trade-Offs from Use of FGD Gypsum
Research Objective Evaluate impact of air pollution control on coal combustion residues (CCRs) Identify potential cross-media transfers of mercury and other metals from CCR management which includes FGD gypsum and fly ash Compare life-cycle environmental tradeoffs from use of CCR and non- CCR materials
Background In March 2005, EPA announced a multipollutant approach to reduce power plant air emissions through the Clean Air Interstate Rule (CAIR) and the Clean Air Mercury Rule (CAMR) through cap and trade approach. Air pollution control (APC) results in transferring metals from the flue gas to fly ash and other APC residues. Anticipate that wet scrubber usage and production of FGD gypsum will double or triple in response to CAIR. Primary focus on mercury but also interest in arsenic, selenium, and other constituents of concern. Key release route for land-managed CCRs is leaching to groundwater. Concern also for release to surface waters, re-emission of mercury (e.g., cement kilns), and bioaccumulation.
Importance of Coal - Electricity Production by Fuel for 1980 – 2030 (Billion kilowatt hours) Source: DOE/EIA 2006
CCR Production and Utilization Production 122 million tons Source: ACAA 2004 CCR Survey; DOE, % Utilization 49 million tons Cement/ Concrete 36% Construction 25% Mining 5% Wallboard 17% Waste Stabilization 8% Other 9% Fly Ash 57% Bottom Ash 15% Boiler Slag 2% FGD Material 25% FBC Ash 1%
Calculating Hg Mass Balance in Response to CAIR and CAMR Implementation Source: Thorneloe, 2006
Projection of Scrubber Use at Existing Units
COAL SUPPLY BOILER SUPERHEATER SCR AMMONIA INJECTION SORBENT INJECTION ESP OR FF ASH + SORBENT REMOVAL WET FLUE GAS DESULFURIZATION (FGD) SCRUBBER FGD GYPSUM OR SCRUBBER SLUDGE REMOVAL FLUE GAS STACK
9 Tracking Fate of Hg and Other Metals Through Life-Cycle Analysis In 2004, 31 million tons of wet scrubber residues were produced. –12 million tons (or 40%) used to make gypsum. –90% of the 12 million tons used to make wall board. –Expect increased interest in other uses of FGD gypsum such as use as soil amendment (collaboration with China). Comparing life-cycle environmental tradeoffs for production of wallboard with and without use of FGD gypsum. This is also being done for the production of cement and asphalt. –Considering potential pathways of environmental release (includes used of leaching and thermal stability studies) –Need to understand stability of Hg and track fate of Hg and other metals on a life-cycle basis. –Information will help with ensuring if intended mercury reductions are achieved in mercury cap and trade program.
Series of 4 Reports Documenting Findings 1.Enhanced sorbents for mercury capture (Jan, 2006) 2.FGD gypsum and other scrubber residues (2007) 3.Residues from other air pollution control strategies (2008). 4.Probabilistic assessment of mass release rate for a range of management scenarios, including disposal and beneficial use (2008).
Leach Testing Protocol ORD adopted OSW’s recommended approach to evaluating the leaching potential of coal combustion residues (CCRs) anticipated to be generated as a result of CAIR & CAMR OSW recommended the use of a leach testing framework developed by Kosson et.al, from Vanderbilt University. The detailed protocol is published at: Kosson, D.S., van der Sloot, H.A., Sanchez, F. and Garrabrants, A.C., An Integrated Framework for Evaluating Leaching in Waste management and Utilization of Secondary Materials. Environmental Engineering Science 19(3): An additional publication on using the data in probabalistic modeling is: Sanchez, F., Kosson, D.S., Probabilistic approach for estimating the release of contaminants under field management scenarios. Waste Management, 25(5), OSW’s recommendation was based on the fact that this approach: Most fully considers the key conditions affecting leaching for a range of CCRs and their plausible management; Is appropriate for evaluating a broader range of materials, beyond fly ash; and Addresses previous concerns raised by Science Advisory Board.
Leach Testing Protocol Considers range of values for key parameters that both affect leaching and vary with disposal and reuse: pH: The solubility of constituents of concern vary with pH. Liquid to Solid ratio (L/S): Reflects rainfall infiltration Lower L/S ratio can result in different pH and contaminant concentration Waste form – Fine particles (equilibrium test) Stabilized and solid materials (mass transfer effects) A single set of test results can be used to evaluate leaching potential for a range of management scenarios including disposal and reuse.
Data Can Support Environmental Assessment Modelling for Different Scenarios…….. Drinking water well Landfill Road base Plant Agriculture Coastal protection Contaminated soil Drinking water pipes Mining Construction sewer Drinking water well
NAS Concern for Providing Full Characterization of reuse materials …. Historically, CCRs are given special consideration because of their wide range of beneficial use applications Since 1991, CCR utilization increased from 31 to 40%. RCC goal is to increase CCR utilization to 50% by Recent National Academy of Science (NAS) report on CCR use in mine filling stated that full characterization should not be cut short “in the name of beneficial use”.
Arsenic Leaching as a Function of pH for Coal Fly Ash Facility LFacility CBrayton Point
Coal Fly Ash Results For Facilities Using Sorbents for Enhanced Hg Capture Mercury: Low totals and leach Total: mg/kg Leach: Most 0.1 ug/L or lower MCL=2 ug/L TC= 200 ug/l Low leach variability relative to pH Results do not include modeling of transport from landfill site to drinking water well (i.e, no DAF applied)
Ranges of Hg Leachate Concentrations (From Report 1 on Use of Enhanced Sorbents)
Coal Fly Ash Results For Facilities Using Sorbents for Enhanced Hg Capture Arsenic: Totals and leach high/variable Total: mg/kg Leach: ug/L MCL=10 ug/L TC=5000 ug/L Leach variability is moderately to highly pH dependent Results will be used in modeling of transport from disposal or management site to drinking water well
Ranges of As Leachate Concentrations (From Report 1 on Use of Enhanced Sorbents)
Coal Fly Ash Results For Facilities Using Sorbents for Enhanced Hg Capture Selenium: Totals moderate; leach high/variable Total: mg/kg Leach: 1-10,000 ug/L MCL=50 ug/L TC=1000 ug/L) Leach variability moderately pH dependent Results will be used in modeling of transport from disposal or management site to drinking water well
Ranges of Se Leachate Concentrations (From Report 1 on Use of Enhanced Sorbents)
What do the CCR Leach Test Results Mean for CCRs Evaluated to Date? For CCRs evaluated in Report 1, found apparent low release potential for Hg from CCRs that are land applied or landfilled Current emphasis is on wet scrubber residues including FGD gypsum Arsenic and Selenium showed higher potential for release by leaching: Highest As leach values at 20% of TC Highest Se leach value is 10 x TC Arsenic was identified as a concern in the 1999 Report to Congress on coal combustion wastes Indicate importance of evaluating full range of CCRs and use of results in risk assessment modeling.
How Is This Information To be Used? Beneficial use programs to help clarify appropriate practices and quantify potential benefits RCC program for coal combustion products State, Federal (DOE, DOT, DOI), and industry programs that promote beneficial use Regulatory efforts including Effluent guidelines (OW), RCRA Subtitle D for coal combustion waste (OSW), Cap and trade programs through implementation of CAIR and CAMR (OAR) Identifying potential cross media transfers Helping to ensure that intended reductions are achieved Cement kilns (MACT) – issue raised regarding use of CCRs (OAR) Helping to quantify life-cycle environmental tradeoffs
Development of a CCR Management Decision Support Tool LeachXS is a set of integrated software tools under development to provide: Guidance on the selection of test methods to answer specific management option questions Database of leaching characteristics, lysimeter and field data for wide range of materials for performance comparison Database of management scenarios (disposal, beneficial use), case studies and prior experience Data management, evaluation and presentation to communicate scenarios and results Geochemcial speciation and coupled reaction - mass transfer models to estimate long-term release for specific combinations of CCR material and use or disposal scenario Quality control for materials production and use – tracking CCR material conformance with use criteria
FGD Gypsum is Under Evaluation for these Scrubber Facilities Facility Code Coal Rank Scrubber Type Oxidation Type SCRParticulate Control O,NBitWetForcedYesESP-CS O,NBitWetForcedNoESP-CS B,KSub-BitWetNaturalYesESP-CS BSub-BitWetNaturalNoESP-CS MBitWetInhibitedYesESP-CS MBitWetInhibitedNoESP-CS ABitWetNaturalSNCR -On Fabric Filter
Conclusions Working to develop information that will provide understanding of impact of air pollution control on FGD gypsum and coal fly ash; current emphasis is on FGD gypsum Conducting life-cycle analysis that allows comparison of environmental tradeoffs from use of CCR and non-CCR materials Providing information to help determine if intended reductions of CAMR cap and trade programs are being achieved Developing leach testing protocol into official EPA method in SW846 Identifying potential CCR management practices of concern resulting from application of new air pollution control technology at coal-fired power plants