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Methodology for Assessing FGD Corrosion Risk for Bromine-based Mercury Control Technologies
Gary Blythe and Ben Bayer, URS Corporation
John Grocki, Advantage Resources Consulting, LLC
Casey Smith, Lower Colorado River Authority
2
Methodology for Assessing FGD Corrosion Risk for Bromine-based Mercury Control Technologies
• LCRA was considering technologies for MATS Hg control
compliance at the Fayette Power Project station
–Three PRB-fired units, 450-610
gross MW, C-ESP, wet FGD
–Native Hg oxidation ~50%
• Candidate technologies were
tested at full scale in 2011:
–Br addition with coal
–Injection of brominated powdered activated carbon (PAC)
–Br addition with coal plus injection of non-Br PAC
Background
3
Methodology for Assessing FGD Corrosion Risk for Bromine-based Mercury Control Technologies
• Potential corrosion in bunkers, coal feeders
• Air heater basket corrosion
• Increased pitting and/or crevice corrosion of wet FGD alloys of construction
–Station operates with zero liquid discharge
–Units 1 and 2 FGD use mostly Stebbins Tile and C-276; some lesser alloys in wetted areas
○ Closed-loop water balance
–Unit 3 FGD uses 316L with Potential Adjustment Protection, 317 LM, Alloy 2205
○ Relatively open-loop water balance
–Large reclaim water system ties the FGD systems together
○ Cl- purge water from Unit 3 used as makeup for Units 1 and 2
Balance-of-Plant Impact Concerns for Bromine-based Technologies
4
Methodology for Assessing FGD Corrosion Risk for Bromine-based Mercury Control Technologies
• Inventory of water at station and closed water loop
on Units 1 and 2 FGD make testing for steady-
state Br concentrations impractical
–Months of testing would be required
• Substantial industry experience with Cl- and FGD
alloys, but little experience
with Cl-/Br- mixtures to
determine safe limits
Technical Issue – How to Assess Increased Risk to FGD Alloys from Br-based Hg Controls
5
Methodology for Assessing FGD Corrosion Risk for Bromine-based Mercury Control Technologies
• Developed spreadsheet-based mass balance tool
–Process flow diagrams, water balance, Cl and Br balances
• LCRA data available to develop tool:
–Multiple years of coal data
–Existing station-wide water balance
○ But represented annual averages; not tied to specific coal, or unit operating conditions
–Measurements of Br in FGD inlet flue gas during 2011 Hg control option testing
–Process water Cl- and Br- concentration data collected over several months (summertime drought conditions)
–However, did not have Br in coal or makeup water
Technical Approach – FGD Water/Halide Mass Balance + Metallurgical Evaluation
6
Methodology for Assessing FGD Corrosion Risk for Bromine-based Mercury Control Technologies
• Established baseline:
–Adapted station water balance to spreadsheet
–Converted average flows to process-based rates where possible (based on unit load, coal S, etc.)
–Used plant process water halide data to develop Cl-, Br- balances (educated guess on coal, makeup water Br-)
–Adjusted process flow diagram, flow rates to achieve good closures
• Developed predictive balances for Hg control conditions
–Used 2011 Hg control test data for future Br- input to FGD
–Let mass balance spreadsheets predict steady-state Cl-, Br- in FGD systems
Part 1: Developing Balance Cases
7
Methodology for Assessing FGD Corrosion Risk for Bromine-based Mercury Control Technologies
Example Water Balance Process Flow Diagram
173 0
143
2
70
4 7
2
173 310
3
15
109 2
146
22 81
22 3
0
88% closure 100% closure
3
28 0
122
451 229 0
0
4
100% 170 86
321 33 closure 0
33
100% closure 108
136
100% closure
142 11 1 0
86 98
100% closure 58
432 0
11
0 36
3 27
54 76
328 38
51 12
31
43 41
95% closure
5 63 57
62 2
LS SYSTEM FLUSH FROM RECIRC C 0
WATER SUPPLY
MISTELIMINATORS
ABSORBERWASHDOWN
LIMESTONE PREP
PUMP & AGITATORSEALS
UNIT #3 FGDSYSTEM
UNIT #2 FGDSYSTEM
UNIT #1 FGDSYSTEM
THICKENER
EVAPORATIONTO ATM.
FILTER FEED TANK C
FILTER FEED TANK B
VACUUM FILTER
RECIRC WATER TANK B
RECIRC WATER TANK C
RECLAIM WATER SYSTEM
MISC. INFLOWS
GYPSUMHYDRATION
EVAPORATIONTO ATM.
EVAPORATIONTO ATM.
GYPSUMHYDRATION
GYPSUMHYDRATION
GYPSUM TO COMBUSTION
BYPRODUCTS LANDFILL
FROM CBL
EVAPORATIONTO ATM.
SPRAY EVAPORATION TO ATM.
SEWAGETREATMENT
ASH TRUCK WASHDOWN/ SUPPPRESSION (ASH)
RAIN
RAIN
EVAP.
WATER SUPPLY
PLANT COOLINGWATER
LIMESTONE PREP
WASHDOWN
DEWATERING AREA
WASHDOWN
RAIN VIA U1 & U2 ASH UNLOADING
RAIN
U3 FLYASHTRANSPORT WASHDOWN
U3 BOILERSEAL SYSTEM
U3 BOILERSUMP
U1 & U2 BOILERSEAL SYSTEMS
U1 & U2 ASH AREA SUMPS
DUST SUPPRESSION
(COAL)
WATER SUPPLY
WATER SUPPLY
8
Methodology for Assessing FGD Corrosion Risk for Bromine-based Mercury Control Technologies
Example Br Balance Process Flow Diagram
0.2 0.0
1.0
0.01
0.1
0 0.0
0.0
0.2 0.0
0.0
0.2 0.1
0.1 0.0
2.1
0.2 2.0
0.3 0.0
0.0
88% closure 111% closure
COAL 0.8 0.0
9.7 0.0
46.6
0.0 1.6 0.0
COAL 1.2
0.0
0.0
101% 0.0
0.4 16.3 closure 0
0.2
88% closure 34.1 0.6
16.8
101% closure
17.6 0.0 34.0 0.0
0.6 0.0
102% closure 0.0
0.0 0.0
COAL 1.1 3.9
0 0.0
0.0 0.2
0.4 0.1
0.4 20.3
0.4 0.1
0.2
0.1 0.0
105% closure
0.0 0.0 0.1
0
0.0 0.1
WATER SUPPLY
MISTELIMINATORS
ABSORBERWASHDOWN
LIMESTONE PREP
PUMP & AGITATORSEALS
UNIT #3 FGDSYSTEM
UNIT #2 FGDSYSTEM
UNIT #1 FGDSYSTEM
THICKENER
EVAPORATIONTO ATM.
FILTER FEED TANK C
FILTER FEED TANK B
VACUUM FILTER
RECIRC WATER TANK B
RECIRC WATER TANK C
RECLAIM WATER SYSTEM
MISC. INFLOWS
GYPSUMHYDRATION
EVAPORATIONTO ATM.
EVAPORATIONTO ATM.
GYPSUMHYDRATION
GYPSUMHYDRATION
COMBUSTION BYPRODUCTS LANDFILL
FROM CBL
EVAPORATIONTO ATM.
SPRAY EVAPORATION TO ATM.
SEWAGETREATMENT
+
ASH TRUCK WASHDOWN/ SUPPPRESSION (ASH)
RAIN
RAIN
EVAP.
WATER SUPPLY
LIMESTONE PREP
WASHDOWN
DEWATERING AREA
WASHDOWN
RAIN VIA U1 & U2 ASH UNLOADING
RAIN
U3 FLYASHTRANSPORT WASHDOWN
U3 BOILERSEAL SYSTEM
U3 BOILERSUMP
U1 & U2 BOILERSEAL SYSTEMS
U1 & U2 ASH AREA SUMPS
DUST SUPPRESSION
(COAL)
PLANT COOLINGWATER
WATER SUPPLY
WATER SUPPLY
9
Methodology for Assessing FGD Corrosion Risk for Bromine-based Mercury Control Technologies
• Established baseline
–Materials of construction of all FGD components
–Operating history (pH, Cl- conc., etc.)
–Current condition
○ Schedule did not allow for assessment inspections
–Develop Cl- limits for existing materials
• Estimated Br- effects on materials
–Limited data available for FGD conditions
–Relative effects of Br- vs. Cl- are alloy specific
○ Steen, et al. (short-term pitting potential measurements)
○ Sherlyn (defined a critical temperature which impacts relative Br-
vs. Cl- corrosivity, and which correlates with PREN values)
Part 2: Predicting Br- Impacts on FGD Materials
10
Methodology for Assessing FGD Corrosion Risk for Bromine-based Mercury Control Technologies
• Developed alloy-specific halide relationships:
[Total Halide] = [Cl-] + X * [Br-]
–X establishes the relative weighting of Br- versus Cl-
concentrations on potential for pitting and crevice
corrosion
–X can vary from alloy to alloy
–Total Halide limits are then set using industry experience
with Cl- for each alloy
–With limited data available, considerable professional
judgment was required to establish X values
Part 2: Predicting Br- Impacts on FGD Materials (continued)
11
Methodology for Assessing FGD Corrosion Risk for Bromine-based Mercury Control Technologies
• Total Halide limits not represented by single values
–pH, temperature, presence of scale and duration of
exposure all must be considered
–All of these variables impact recommended time between
component inspections
–Must consider the probability of simultaneous excursions
of multiple variables outside of “normal” range (e.g., high
Total Halides and low pH)
• Total Halide limits must consider lowest alloy installed
in FGD systems
Part 2: Predicting Br- Impacts on FGD Materials (continued)
12
Methodology for Assessing FGD Corrosion Risk for Bromine-based Mercury Control Technologies
Example pH, Temperature, Scaling and Total Halide Relationship
• All parameters in blue - minimal halide
corrosion risk
• One parameter in yellow range –
moderate halide corrosion risk
• One parameter in red or two or more in
yellow – high risk of halide corrosion;
inspect soon
13
Methodology for Assessing FGD Corrosion Risk for Bromine-based Mercury Control Technologies
• Units 1 and 2 FGD systems are more sensitive to Hg
control system selection in spite of higher alloys of
construction
–Closed-loop operation leads to elevated Total Halide
concentrations (outside of “blue box”)
• Based on 2011 test data, brominated PAC poses less of a
materials risk than Br addition with coal + non-Br PAC
(@2011 addition rates)
–Future testing with state-of-the-art PAC, optimized addition
rates may change these results
–Mass balances can predict steady-state Total Halogens at
future addition rates
Results
14
Methodology for Assessing FGD Corrosion Risk for Bromine-based Mercury Control Technologies
• Implement brominated PAC injection as a near-term MATS compliance technology
–Determine optimal injection rates
–Consider Br with coal plus non-Br PAC later
• Monitor halide concentrations in FGD systems on a bi-weekly frequency, use Cl- and Br- specific analytical methods to apply “X” factor
• Update FGD component inspection frequencies as needed
–Use alloy-specific relationships, and
–Actual experience for Total Halide concentration, pH, temperature, scaling and duration of exposure
Recommendations