experience with mercury compliance - o2 groupexperience with mercury compliance gary blythe,...
TRANSCRIPT
Experience with Mercury Compliance
Gary Blythe, Katherine Dombrowski, Gwen Eklund, Mandi Richardson
1
Presentation Outline
• Overview of the MATS rule • Lessons learned from Mercury compliance/testing
– Bromine addition – FGD co-benefit capture/re-emissions control – PAC injection – Other issues (startup/shutdown, target control levels, coal
variability) • Overview of other relevant rules
– Draft Effluent Limitations Guidelines (ELGs) – Coal Combustion Residues (CCR) rule
• How MATS compliance can impact compliance with these other rules 2
MATS Rule Overview
Emission Limits for Hg, FPM, Acid Gases
Work Practice Standards for
Organics
Notification, Recordkeeping, and
Reporting
Initial and Continuous Compliance
April 16, 2015-April 16, 2016
40 CFR Part 63 Subpart UUUUU (5U) Citations: 63.9980 through 63.10042
3
MATS Emission Standards Existing Coal Units, >8,300 Btu/lb
4
Pollutant Compliance Options Heat Input Standard Output Standard
Hg Hg 1.2 lb/TBtu 0.013 lb/GWh
Acid Gas HCI or
Acid Gases*
0.002 lb/MMBtu 0.2 lb/MMBtu
0.02 lb/MWh 1.5 lb/MWh
Particulate FPM or
Total Metals ** or
Individual Metals **
0.03 lb/MMBtu 50 lb/TBtu Good Luck!
0.3 lb/MWh 0.5 lb/GWh
*Unit must have FGD and SO2 CEMS **Sb, As, Be, Cd, Cr, Co, Pb, Mn, Ni, Se
LESSONS LEARNED FROM MERCURY CONTROL IMPLEMENTATION
5
Hg Emissions (mainly Hg0)
Hg in Coal
Volatilized Hg (mainly Hg0)
Hg Oxidation Across SCR Hg0 Hg+2
Bromide Addition
ACI Hg Oxidation and
Hg Removal Across AH Hg0 Hg+2
Hg in Fly Ash Hg in Gypsum and Wastewater
Hg Removal Across PCD
Removal of Hg+2 Across FGD
Hg0 = Elemental Hg (insoluble in water) Hg+2 = Oxidized Hg (soluble in water)
Hg Oxidation Across SCR, AH, PCD
Hg+2 Removal by FGD
/ACI
6
Bromide addition enhances mercury removal of ACI, fly ash, and wFGD by converting Hg0 to Hg+2
Corrosion is most frequently observed bromine balance-of-plant (BOP) effect EPRI Bromine BOP Study – 71 units participating • Fly ash sales - no effects observed • Opacity - increase at one plant with SCR/FF/FGD • FGD effluent - potential areas of concern
– Increase in Hg, Se, Br, brominated organics
• Corrosion – 36 units reported corrosion
7
Bromide Addition
36 of 71 surveyed units had corrosion: All fired low-sulfur coals; all but two had air heater corrosion
Location of Corrosion # of Units Reported Corrosion Coal Handling 3 Boiler Tube 1 Air Heater 34 Air Heater Outlet Duct 3 ESP 2 ID Fan 4 FGD 2
8
Air heater parts – constructed from carbon steel
9
Rotor (axle) Diaphragm (spokes) Two Baskets
Seal
Elements
Diaphragm plate
Cold-end baskets most likely AH part to corrode Air Heater Part # Units Reporting Corrosion Cold-end baskets (plane outlined) 32 Cold-end basket bars 4 Diaphragm plate 2 Cold-end radial seal (attached to each diaphragm plate) 8
Courtesy Alstom Power
Hot-end radial seals
Cold-end radial seals
10
Corrosion most likely in coldest parts of air heater; Estimate cold-end metal temperature
11
Estimated Average Cold-End Metal Temperature =
Average of Air Inlet and Flue Gas Outlet Temperature
Minimum metal temperatures can be 50°F lower than average → closer to HBr condensation temp
12
HBr Condensation Temperature
Some PRB units with low Br have corrosion; Bituminous units not corroding, despite higher Br
13
PRB Units Bituminous Units
Units with Corrosion Units with No Corrosion
Minimizing risk of corrosion
• Enamel coating of AH • Minimize bromine released for Hg control • Operational changes to AH
– Monitor air heater temperatures – Pre-heat air – Soot blowing – Move carbon injection downstream of AH
14
Measuring Hg oxidation upstream of FGD is important for diagnosing Hg emissions excursions
15
Wet FGD Flue gas
Hg2+ = 3
Hg0 = 3
HgT = 3 (nearly all as Hg0)
Flue gas
Hg2+ re-emitted as Hg0
HgT = 6 Hg2+ = 5
Hg0 = 1 Hg2+ captured
Insufficient Hg oxidation by Br
Bromide Addition
Measurements may over-predict Hg oxidation • Methods not validated for use in the presence of Br in flue gas.
– CEMs, App K, 30B traps, speciated sorbent traps, Ontario Hydro
• Upstream of FGD, Hg measurement susceptible to bias – Measure artificially high Hg oxidation, low total Hg – Observed with the commercial Hg CEMS, speciated sorbent traps
• Downstream of FGD, measurement bias less likely – Br is scrubbed by FGD
• Common observations in bromide test programs – High Hg oxidation measured at FGD inlet – Yet, Hg emissions measured at FGD outlet remain high – Plants assume Hg re-emissions, but measurement bias is more likely
16
FGD Co-benefit Capture of Hg
• Oxidized mercury (Hg2+) is scrubbed at high efficiency, elemental mercury (Hg0) is insoluble and generally not scrubbed
• Once scrubbed by the flue gas, oxidized mercury can be chemically reduced in the scrubber back to the elemental form – Elemental mercury formed is released into the stack flue gas
• The Oxidation-Reduction Potential (ORP) at which the FGD absorber operates has a major role in whether re-emissions occur – ORP represents a new parameter that should be monitored in
scrubbers used for co-benefit mercury capture
17
Effect of ORP on Percent of Hg in Absorber Slurry Remaining in Liquor
• Forced oxidation, low ORP – little Hg remains in liquor – Re-emission typically
minimal or none
• Forced oxidation, high ORP – most of Hg remains in liquor – Significant re-
emission levels likely
18
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
-100 0 100 200 300 400 500 600 700
% o
f Mer
cury
in S
lurr
y Li
quor
ORP, mV
Forced Oxidation Systems Inhibited/Low Oxidation Systems
Effects of Load Cycling on ORP, Re-emissions
High Load
• Sulfur input to scrubber is near design level
• O2 in flue gas low • Operating near design levels
for L/G ratio, forced oxidation air O:SO2 ratio
• ORP should be in the low range
• Re-emissions are hopefully minimal
Low Load • Sulfur input to scrubber is
much lower than design level
• O2 in flue gas is high • L/G ratio is much higher
than design level – Increased O2 pickup from flue
gas • O:SO2 ratio is higher than
design level • ORP increases • Re-emissions occur
19
How to Deal with Re-emissions
• Tune scrubber operation to lower ORP into ideal range – Decrease oxidation air rate, particularly at low load – Run fewer recycle pumps, particularly at low load – Increase pH set point slightly, if possible
• Use re-emission additives – Additives that contain reduced sulfur (organic or inorganic
base) • Work by producing an insoluble mercuric sulfide precipitate • Are only effective at lower ORP • Additives themselves can lower ORP
– PAC addition to scrubber slurry • Work by adsorbing Hg from FGD slurry liquor • Do not impact ORP, performance not affected by ORP
20
Powdered Activated Carbon Injection Startup Issues • Equipment corrosion
– In silo – Feeder hoppers and valves – Transport headers
• Poor activated carbon distribution – Vendors should model gas/particle flow through entire
injection system, not just at lance injection point • Model should be rigorous enough to model powdered
carbon as a second, solid phase instead of as a gas – Particulate control device hopper sampling may be
required to determine carbon distribution 21
Coal Hg Variation Impacts on Hg Concentrations in Flue Gas – Example Data
Effects of Coal Hg Variation Case Study
• Two large coal-fired units on East Coast; equipped with SCR, ESP, wet scrubbers
• Plant tested a low Hg Columbian coal, among others, to see which would bring units into Hg compliance with co-benefit capture – When firing Columbian coal (0.05 ppm Hg) stack Hg emissions were
<1 lb/Tbtu – Plant signed multi-year contract for supply of this coal as a MATS
compliance strategy • Later shipments of Columbian coal contain up to 0.08 ppm
Hg – Units cannot achieve MATS compliance with the higher Hg coal – Plant now has a large stockpile of high Hg coal they cannot fire and
maintain compliance – Plans to test Br addition and/or re-emission additives
23
Coal Hg Variation Case Study (cont’d)
• This is a good example of how coal Hg variations can cause MATS compliance issues
• It’s an even better example of the risk of taking an “empirical” approach to achieving MATS compliance: – Tried control approaches for short periods (~1 week each in
this case) – Only measured stack mercury concentrations, picked whatever
worked • Did not conduct upstream measurements to determine Hg removal
with fly ash, to measure Hg oxidation at FGD inlet, or to detect if re-emissions were occurring
• Now having to test additional approaches while trying to maintain compliance
24
Unit Startup Impacts on Mercury Measurement
• Mercury emissions can spike during startup • Utilities have concerns about how these spikes impact
the 30-day rolling average • Separate trap monitoring systems have been installed at
many plants to supplement the compliance traps (which may be weekly runs) – Measure the impact of spikes in mercury emissions during
startup
25
What Level to Control Stack Hg to Ensure MATS Compliance?
Normal Stack Hg Control Level, lb/TBtu
Uncontrolled Hg at Stack, lb/TBtu
Hours of Upset (no Hg Control) allowed to stay below 1.2 lb/Tbtu in 30-day Average
1.1 8.0 10
1.0 8.0 20
0.9 8.0 30
0.8 8.0 40
0.7 8.0 49
0.6 8.0 58
0.5 8.0 67
26
OTHER RELEVANT REGULATIONS/DRAFT REGULATIONS
27
COMPANY CONFIDENTIAL
Draft Effluent Limitation Guidelines – History
28
New Final Action Date: September 2015, Permit Implementation beginning ~ late 2018
COMPANY CONFIDENTIAL
Consider all the Options (Existing) – EPA Preferred
29
Current Conditions
Option 3a Option 3b Option 3 Option 4a
FGD Wastewater (including gypsum wash water)
Included as Low Volume Wastes T = Impoundment L: TSS & Oil and Grease
BPJ determination (technology and limits)
T: Chemical Precipitation(CP) a and Biological Treatment (BT) for facilities ≥ 2000 MW scrubbed capacity; BPJ determination <2000 MW L: Hg, As, Se and nitrate-nitrite ≥ 2000 MW scrubbed capacity; BPJ determination <2000 MW
T: CPa and BT L: Hg, As, Se and nitrate-nitrite
Fly Ash Transport Water
T: Impoundment L: TSS & Oil and Grease
T: Dry handling b L: Zero discharge
Bottom Ash Transport Water
T: Impoundment L: TSS & Oil and Grease
T: Impoundment L: Equal to BPT (no change from current rule)
T: Dry handling/ closed loop c for units >400 MW; Impoundment ≤ 400 MW L: Zero discharge for units >400 MW; Equal to BPT ≤ 400 MW
Increasing Pollutant Reduction
Must meet the limits established, do not need to use the preferred technology
COMPANY CONFIDENTIAL
Consider all the Options (Existing) – EPA Preferred
30
Current Conditions Option 3a Option 3b Option 3 Option 4a
Coal Combustion Residual Leachate
Included as Low Volume Wastes T = Impoundment L: TSS & Oil and Grease
T: Impoundment L: Equal to BPT
(no change from current rule)
FGMC Wastewater (Activated Carbon Injection)
Included as Low Volume Wastes but common practice is no discharge
T: Dry handling b L: Zero discharge (current practice)
Nonchemical Metal Cleaning Wastes*
Included in Metal Cleaning Wastes BPT for Cu and Fe
T: CP L: Cu, Fe
Increasing Pollutant Reduction
*Nonchemical metal cleaning wastes exemption: if previously permitted as LVW without copper and iron limits (up to 27% of plants)
Activated carbon injection upstream of FGD should not be subject to FGMC Wastewater limits
COMPANY CONFIDENTIAL
Comparison of Proposed Limits to Existing Limits
31
FGD Wastewater (all dischargers; approximately 311 plants) 1982 - Daily Max 1982 - Monthly
Average Daily Max Monthly Average
Arsenic, total 8 µg/l 6 µg/l
Mercury, total 242 ng/l 119 ng/l
Selenium, total 16 µg/l 10 µg/l
Nitrate/Nitrite as N 0.17 mg/l 0.13 mg/l
Total Suspended Solids
100.0 mg/l 30.0 mg/l 100.0 mg/l 30.0 mg/l
Oil and Grease 20.0 mg/l 15.0 mg/l 20.0 mg/l 15.0 mg/l
Combustion Residual Leachate (“new” leachate only) 1982 - Daily Max 1982 - Monthly
Average Daily Max Monthly Average
Arsenic, total 8 µg/l 6 µg/l
Mercury, total 242 ng/l 119 ng/l
Total Suspended Solids
100.0 mg/l 30.0 mg/l 100.0 mg/l 30.0 mg/l
Oil and Grease 20.0 mg/l 15.0 mg/l 20.0 mg/l 15.0 mg/l
Previously only limited for BPT as Low Volume
Wastes
Previously only limited for BPT as Low Volume Wastes
Final CCR Rule – Preamble: Pages 1 (21302) to 167 (21467) – Final Rule: Pages 167 (21467) to 201 (21501)
Perspective from the EPA on the Preamble “The final definition makes extremely clear the impoundments that are covered by the rule, so an owner or operator will be able to easily discern whether a particular unit is a CCR surface impoundment.” [Final CCR Rule, Page 57 (21357)]
EPA’s CCR Rule
• Comprehensive set of requirements for the safe disposal of coal combustion residuals (CCRs) in landfills and surface impoundments under subtitle D of RCRA, based on environment and public health studies; the rule also addresses beneficial use.
• These regulations address the risks from coal ash disposal -- leaking of contaminants into ground water, airborne fugitive dust, and failures of coal ash surface impoundments.
• The CCR rule sets out recordkeeping and reporting requirements as well as the requirement for each facility to establish and post specific information to a publicly-accessible website.
CCR Rule Compliance – Potential Requirement Elements to Consider Increased Hg in Impoundments, Landfills & Use
Requirement Deadline to Comply Description of Requirement
Air Criteria (257.80) October 19, 2015 - Prepare a fugitive dust control plan
Run-on & Run-off Controls (257.82)
October 17, 2016 - Prepare an initial run-on and run-off control plan
Groundwater Monitoring and Corrective Action (257.90-257.98)
October 17, 2017 - Install the groundwater monitoring system; develop the groundwater sampling & analysis program; initiate the detection monitoring program; and begin evaluating the groundwater monitoring data for statistically significant increases
Closure and Post-Closure Care (257.103-257.104)
October 17, 2016 - Prepare written closure and post-closure plans
Beneficial Use - keep records to show that that environmental releases to groundwater, surface water, soil and air will be at or below relevant regulatory and health-based benchmarks for human and ecological receptors during use.
Groundwater Monitoring and Corrective Action
Applicability • All CCR landfills (except inactive landfills that are not subject to the CCR Rule)
• All surface impoundments and lateral expansions (except inactive surface impoundments that will close within 36 months of the Rule)
Overview • Within 30 months of publication
- Install groundwater monitoring system - Conduct 8 monitoring events (must account for seasonal and spatial variability)
• Semiannual detection monitoring can trigger assessment monitoring (one statistical failure of Appendix III)
• If Assessment monitoring identifies presence of Appendix IV constituent above Groundwater Protection Standards (GWPS), then an Assessment of Corrective Measure is triggered.
• Leads to Implementation of Corrective Action Program
Install GW Monitoring
System
Detection Monitoring
Assessment Monitoring
Corrective Measures
Corrective Action Program Appendix III Constituents
Boron
Calcium
Chloride
Fluoride
pH
Sulfate
Total dissolved solids (TDS)
Appendix IV Constituents Antimony Arsenic Barium Beryllium Cadmium Chromium Cobalt Fluoride Lead Lithium Mercury Molybdenum Selenium Thallium Radium 226 and 228 combined
Effects of MATS Compliance on ELG Compliance
• Br Addition – – Additional Br in wastewater may trigger tri-halomethane concerns for
downstream municipal water supplies – Possible increase in Se in FGD wastewater
• PAC Injection upstream of Particulate Control Device – – No significant impacts, particularly if handling fly ash dry
• Re-emission additives – reduced sulfur additives – – For high ORP FGD systems, lower ORP w/additive can benefit Se oxidation,
additive can lower liquor-phase Hg – For low ORP FGD systems, very low liquor-phase Hg may be achieved, but
possible increases in liquor-phase Se and As • PAC injection to slurry for re-emission control –
– Lower Hg in FGD liquor (not as low as with reduced-sulfur additives) and lower peroxodisulfate concentrations (affects nitrate and Se removal)
– No impact on ORP, liquor Se or As
36
Possible CCR Rule Risks from MATS Compliance
• Higher mercury concentrations in CCR impoundments, CCR landfills or CCRs for beneficial uses
• If EPA’s regulatory limits for mercury in groundwater, surface water, soil or air emissions are exceeded, closure and corrective action may be triggered (not likely based on AECOM experience)
• Higher mercury concentrations of mercury or the additional constituents added by mercury control technology (e.g., bromine or carbon) may affect relevant byproduct specifications, regulatory standards or design standards – The only evidence of this to date for AECOM has been Hg
concentration limits for FGD gypsum used for wallboard production