Gary Blythe and Ben Bayer, URS Corporation John Grocki, Advantage Resources Consulting, LLC Casey Smith, Lower Colorado River Authority

Transcription

1 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 Background LCRA was considering technologies for MATS Hg control compliance at the Fayette Power Project station Three PRB-fired units, 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 2

3 Balance-of-Plant Impact Concerns for Bromine-based 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 3

4 Technical Issue How to Assess Increased Risk to FGD Alloys from Br-based Hg Controls Inventory of water at station and closed water loop on Units 1 and 2 FGD make testing for steadystate 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 4

5 Technical Approach FGD Water/Halide Mass Balance + Metallurgical Evaluation 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 5

6 Part 1: Developing Balance Cases 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 6

7 Example Water Balance Process Flow Diagram SUPPLY 0 LIMESTONE PREP PUMP & AGITATOR SEALS MIST ELIMINATORS UNIT #3 FGD SYSTEM EVAPORATION TO ATM. GYPSUM HYDRATION 88% closure 100% closure EVAPORATION TO ATM THICKENER ABSORBER WASHDOWN 15 4 DEING AREA 7 WASHDOWN RECIRC SUPPLY 0 TANK B 4 GYPSUM HYDRATION 100% UNIT #2 FGD 33 FILTER FEED FILTER FEED closure 0 SYSTEM TANK C TANK B % closure EVAP. EVAPORATION 100% closure 142 EVAPORATION 11 1 TO ATM TO ATM. VACUUM FILTER % closure RAIN SUPPLY GYPSUM TO COMBUSTION 0 36 SPRAY EVAPORATION TO ATM. 3 BYPRODUCTS LANDFILL GYPSUM 27 DUST HYDRATION U1 & U2 BOILER SUPPRESSION MISC. INFLOWS (COAL) 328 UNIT #1 FGD 38 SEAL SYSTEMS RECLAIM SYSTEM U3 BOILER 51 SYSTEM 12 ASH TRUCK WASHDOWN 31 SEAL SYSTEM / SUPPPRESSION (ASH) SEWAGE 95% closure FROM CBL TREATMENT 5 RAIN U3 BOILER SUPPLY SUMP 62 2 RAIN VIA U1 & U2 LS SYSTEM FLUSH FROM RECIRC C 0 U1 & U2 ASH AREA SUMPS ASH UNLOADING RAIN 2 LIMESTONE PREP WASHDOWN 3 U3 FLYASH TRANSPORT WASHDOWN RECIRC TANK C PLANT COOLING 7

8 Example Br Balance Process Flow Diagram SUPPLY PUMP & AGITATOR SEALS MIST ELIMINATORS EVAPORATION TO ATM. GYPSUM HYDRATION ABSORBER 0.2 WASHDOWN DEING 0 AREA 0.0 WASHDOWN UNIT #3 FGD SYSTEM THICKENER % closure 111% closure COAL PLANT COOLING EVAPORATION TO ATM COAL 1.2 RECIRC 0.0 TANK B 0.0 GYPSUM HYDRATION 101% UNIT #2 FGD 16.3 FILTER FEED FILTER FEED closure 0 SYSTEM TANK C TANK B LIMESTONE 0.2 PREP RECIRC 88% closure 34.1 TANK C EVAP. EVAPORATION 101% closure 17.6 EVAPORATION TO ATM TO ATM. 0.0 VACUUM FILTER 102% closure RAIN SUPPLY COAL COMBUSTION SPRAY EVAPORATION TO ATM. 0.0 GYPSUM BYPRODUCTS LANDFILL 0.2 DUST HYDRATION U1 & U2 BOILER SUPPRESSION MISC. INFLOWS (COAL) 0.4 UNIT #1 FGD 20.3 SEAL SYSTEMS RECLAIM SYSTEM U3 BOILER 0.4 SYSTEM 0.1 ASH TRUCK WASHDOWN 0.2 SEAL SYSTEM / SUPPPRESSION (ASH) SEWAGE FROM CBL TREATMENT 105% closure 0.0 RAIN U3 BOILER SUPPLY SUMP 0 RAIN VIA U1 & U2 0.0 U1 & U2 ASH AREA SUMPS 0.1 ASH UNLOADING RAIN 0.0 LIMESTONE PREP WASHDOWN U3 FLYASH TRANSPORT WASHDOWN SUPPLY 8

9 Part 2: Predicting Br - Impacts on FGD Materials 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) 9

10 Part 2: Predicting Br - Impacts on FGD Materials (continued) 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 10

11 Part 2: Predicting Br - Impacts on FGD Materials (continued) 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 11

12 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 12

13 Results 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 13

14 Recommendations 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 biweekly 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 14