Sheila Glesmann / December 5, 2016 / SVP, ADA Carbon Solutions, LLC

Transcription

1 Sheila Glesmann / December 5, 2016 / SVP, ADA Carbon Solutions, LLC

2 Mercury Control Applications under MATS Optimization of Mercury Controls Intersections with Pending ELG and CCR Requirements Implications

3 Activated Carbon Injection Over 70 GW documented by DOE s Energy Information Agency from 2014-April 2016; understates magnitude Many coal-fired plants were already using ACI under state rules, permits, and consent decrees EPA s Air Markets Program Database (AMPD) as of June 30 (downloaded 11/30/16) shows 183 units reporting ACI as part of strategy

4 Additives In EPA s AMPD there is no distinction between coal additives (e.g. halogens on coal) and/or scrubber additives (e.g. sulfides or PAC) Scrubber additives require oxidation of mercury upstream of scrubber, this can be accomplished through native halogens in coal or halide additives, or through SCR 82 units list additives as part of strategy

5 Other technologies listed include: Catalyst for Hg oxidation 10 units Non-PAC sorbents 5 units Sodium-based 4 units Regenerative Activated Carbon 2 units Many units list multiple technologies In total 239 units of 879 coal units subject to MATS list some Hg control strategy (27%)

6 Plants have found ways to reduce reagent use or do intermittent injection distribution and synergies Suppliers have advanced the technology to reduce sorbent consumption and address morechallenging applications: SO 3 tolerant PACs or DSI for SO 3 management Higher temperature PACs Sodium reagent interferences Still addressing and troubleshooting startup/shutdown and corresponding temperature excursions

7 Primary Input Hg in coal Key Influences on Oxidation (Conversion) Native coal halogens Added halogens Process temps, metallurgy SCR APH Key Influences on Contact Fly ash Added acid gas sorbents Added activated carbon ESP vs baghouse Dry scrubber Wet scrubber Mercury inputs in combination with the Conversion, Contact and Capture determine the Outputs

8 Key Influences on Capture Capture media surface chemistry and pore structure Oxidation of mercury Effectiveness of contact with Hg Primary Hg, Se, As-containing output streams Fly ash Scrubber byproduct Scrubber effluent Flue gas Of all these output streams, only one is continuously monitored under MATS: Flue gas Hg

9 Mercury can be partitioned in the gas, liquid, or solid phase and subsequently concentrated and sequestered by control technologies, but not destroyed; similar to Se and As, all key ELG and CCR (RCRA) metals Philosophy of active control (a control knob ) Mechanistic approach to ensure completion of conversion, contact, capture CaBr 2 injection on coal has been shown to increase the scrubber liquor Se content, increasing ELG treatment system loading Secure capture needed to ensure ash and effluent streams are not adversely affected CCRs have value and utilization is increasing ELG potential for zero discharge Reference Power Engineering article for further information: 11/features/mats-and-beyond-the-role-of-technologychoices-in-present-and-future-coal-plant-compliance.html

10 Example of native control with SCR, ESP and wet scrubber Pros: no reagent use except SCR ammonia or urea SCR provides oxidation Wet scrubber captures oxidized mercury Cons: SCR oxidation/conversion of Hg may be inconsistent as catalyst ages; no control knob to turn/passive control Insufficient oxidation results in pass-through of elemental Hg Wet scrubber is a large sink for mercury but may not be stable as process conditions vary : re-emission risk Cycling up scrubber concentrations to reduce effluent flow is limited by halogen content Ash and unburned carbon have a loose hold on mercury captured in ESP; is it stable? Management: May be able to manage ORP and ph of scrubber liquor to minimize reemissions Challenge is understanding fate of emissions in each individual system; RCRA metals fate Stability of stream flow and concentration into effluent treatment/bio system is crucial

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12 Remember scientific principles for conversion, contact and capture and obtain accurate mass balances where achievable to confirm fate of trace species Assess the stability of those species and the process streams Engage active rather than passive controls Revisit compliance strategies as appropriate when new requirements or operating conditions develop (ELG, new coal, etc) Always evaluate Balance-of-Plant impacts such as ash utilization, corrosion, scrubber chemistry Testing is critical to demonstrate effects

13 ADA Carbon Solutions, LLC Institute of Clean Air Companies