XCEL ENERGY MERCURY MONITORING EXPERIENCES. David Hillesheim November 11, 2015

Transcription

1 XCEL ENERGY MERCURY MONITORING EXPERIENCES David Hillesheim November 11, 2015

2 PRESENTATION TOPICS History of Mercury monitoring at Xcel Energy Facilities Overview - Northern States Power Region (NSP) Monitor Selection Process Hg Monitoring Approach Hg Monitoring Challenges Monitoring Enhancements Made Technological Changes Lessons Learned 2

3 HISTORY OF MERCURY MONITORING MN Hg Reduction Act Required (2006): Monitors installed and operational on qualifying Units Qualifying Unit? Monitors installed and operational by July 1, 2007 Begin gathering 6 months of baseline data Mercury Reduction Plan Dry scrubbed Units by December 31, 2007 Wet Scrubbed Units by December 31, % Reduction Controls implemented on dry scrubbed Units by December 31, 2009 Controls Implemented on wet scrubbed Units by December 31,

4 OTHER REGULATORY DRIVERS Consent Decree with the State of Colorado Clean Air Mercury Rule State Permit for Allen S. King Plant Effective May day rolling average limit of 1.0 lb/tbtu Includes all hours of operation Incorporated MATS QAQC Requirements Mercury and Air Toxic Standards 4

5 FACILITY OVERVIEW (NSP) Sherburne County Generating Plant, located in Becker MN 45 minutes NW of Minneapolis Allen S. King Generating Plant, located in Bayport MN 30 minutes East of Minneapolis 5

6 FACILITY OVERVIEW (NSP) Sherburne County Generating Plant, located in Becker, MN Three Units Unit 1 and 2 Babcock and Wilcox tangentially fired boilers discharging out a 650 ft common stack Each boiler combusts 420 tons per hour of PRB sub-bituminous coal at full load (750 MW each) 24 wet scrubber modules with wet ESP Scrubbers remove over 95% of SO2, and 99% of PM Low NOx burner technology Activated carbon injection system for Hg control Fuel oil start-up fuel Unit 3 Carolina style Babcock and Wilcox Boiler discharging out a 650 ft stack Combusts 500 tph of PRB sub-bituminous coal at fulll load (980MW) Spray Dry absorbers (SDA s) for SO2 control, and fabric filter baghouse Low-NOx burner technology Activated carbon injection system for Hg control Fuel oil start-up fuel 6

7 SHERBURNE COUNTY GENERATING PLANT 7

8 FACILITY OVERVIEW (NSP) Allen S. King Generating Plant, located in Bayport, MN Single Unit Babcock and Wilcox cyclone boiler Selective Catalytic Reduction (SCR) for NOx control Dry lime flue gas desulfurization (DLFGD) Electro-static Precipitator (ESP) and Baghouse for PM control Activated Carbon Injection (ACI) System for Hg control 595 MW maximum load firing on PRB sub-bituminous coal Discharges through a 784 foot stack 8

9 ALLEN S. KING GENERATING PLANT 9

10 HG MONITOR SELECTION PROCESS Hg CEMS Evaluation Thermo Fisher Scientific Mercury Freedom System and Tekran Instruments Evaluated Installed monitors on Units 1 and 2 at Comanche Plant in Pueblo Colorado in 2006 Provided opportunity for head to head comparison Evaluated performance of both instruments for 6 months In-house vendor presentation Goal of corporate standardization Thermo Fisher Scientific Selected 10

11 HG MONITORING APPROACH Hg CEMS Thermo Fisher Scientific Mercury Freedom System Currently Installed 3 systems in NSP region, (5 in SPS, 5 in PSCo) Black Dog Unit 3/4 retired in April 2015 Voluntary install for TMDL Hg data gathering purposes Additional Inlet Hg CEMS monitors at King and Sherco Originally configured with the GameCube Probe Probe design initially selected due to size and weight (1 of 2 design options available) Compact design Operates at high temps Issues with System Integrity Check performance Difficult to perform maintenance and troubleshoot Extensive downtime during maintenance activities Upgraded to Nitrogen Generator dilution air supply 11

12 HG MONITORING APPROACH Thermo Fisher Scientific Hg Freedom System 12

13 HG MONITORING APPROACH Stack level monitoring Compete CEMS enclosure built on each stack at platform level Decision made to go with stack mounted installation Shorten response time avoid sample transport Keep probe in close proximity to analyzer for troubleshooting and maintenance purposes Dedicated data logger for each system 13

14 HG MONITORING APPROACH Began controlling for Hg at Sherco Unit 3 in December 2009 Following installation of ACI, achieving excellent removal Carbon usage lower than expected Is the data believable?? Times when little, to no carbon being injected required Purchased Apex Method 30B Sampler Allowed opportunity to spot-check stack emissions data Portable device Small compact unit that can be used as a 30B device, or for compliance (proportional sampling) Initial thought was to use as a backup instrument Used at multiple emission sources Verify inlet Hg concentrations 14

15 HG MONITORING APPROACH Apex MercSampler XC-6000EM 15

16 HG MONITORING APPROACH Findings?? Sorbent trap comparison agreed well with Hg CEMS Getting a lot of removal from residual carbon in pollution control system Annual RATA results confirmed CEMS accuracy 16

17 HG MONITORING CHALLENGES Have faced, and continue to face, several Hg Monitoring Challenges: Sherco Unit 3 Hg spiking issue Weekly System Integrity Checks Sherco Unit 1/2 Common Stack Hg scrubbing?? 17

18 SHERCO 3 HG SPIKING ISSUE Startup spikes significantly impacted 30-day rolling average Problem not a lot of startup opportunities to test theories Hg spike an analyzer interferent? Apex STS device used to confirm actual stack Hg emissions Off-gassing from stack and duct walls during unit startup? Stack testers brought in to measure duct Hg concentrations along flue gas path during unit startup Measured baghouse inlet and outlet concentrations, and points downstream from baghouse SH3 Startup Hg lb/tbtu Hg lb/tbtu 8:00 12:00 4:00 8:00 12:00 4:00 8:00 12:00 4:00 8:00 12:00 4:00 8:00 12:00 4:00 8:00 12:00 4:00 8:00 12:00 18

19 SHERCO 3 HG SPIKING ISSUE Findings: Found elevated Hg concentrations exiting baghouse Elevated Hg concentrations correlated to elevated flue gas temperatures Once SDA s brought into service, flue gas cooled, Hg concentrations dropped Implemented new startup procedure to lower SDA outlet temperatures to around 175ºF Successful in decreasing impact of startup spike Also using MATS startup option 2 4 hour startup window Believe we have mitigated this issue. 19

20 Weekly System Integrity Checks Performance of Weekly System Integrity Check Required once every 7 Unit Operating Days May be conducted at High or Mid level calibration point Labor intensive procedure issue from day 1 with Thermo Gamecube Baseline value determination Introduction of Chlorine gas Compare baseline with reported HgT Failure? Data invalid until completed passing test Significant monitor downtime 20

21 Weekly System Integrity Checks Thermo Recommend SIC Procedure Perform System zero and System span in speciated mode, calibrate if required. Use the following Oxidizer schedule a. Hg Baseline 15 min b. Cl2 Duration 20 min c. Post Condition 10 min Start oxidizer test. After the Cl2 is turned on via the probe valve (15 minutes after the start) record Cl2 pressure and flow. psi ccm After recording the Cl2 flow, adjust the regulator such hat the flow is at least 400 sccm. Record corresponding pressure psi. Download lrecs and calculate total efficiency. Allow system to run in Sample mode for at least 20 minutes If the Total Efficiency is below 90%, repeat the System Integrity test. This time, spike the oxidizer with twice the Hg span concentration for the first 90 seconds of the Chlorine duration cycle to accelerate the equilibrium period. 21

22 Weekly System Integrity Checks Thermo Recommend SIC Procedure 22

23 Weekly System Integrity Checks Not just total only mode... Must show at least 50% oxidation Chart weekly checks showing all three parameters 23

24 WEEKLY SYSTEM INTEGRITY CHECK SOLUTION? Needed to resolve issue prior to King Permit effective date in May 2013 Conversations with M&C indicate good repeatability with weekly SIC performance using new probe design Only a few of these retrofits running in the field M&C still working out contractual issues with Thermo at the time. Required use of existing converter/oxidizer certified by Thermo. 24

25 M&C SP2006 HG PROBE Introduced in 2013 Larger footprint Two-piece design; cold and hot Easier to access key components (routine maintenance) Excellent history with the repeatability of System Integrity Checks 25

26 M&C SP2006 HG PROBE 26

27 M&C SP2006 HG PROBE 27

28 WEEKLY SYSTEM INTEGRITY CHECK SOLUTION? Purchased new probe at King Plant in Feb Tested while unit was offline during outage good performance Ultimate test when unit came back online in May Fully certified Hg CEMS system with new probe To date no issues outside of routine CEMS maintenance activities, i.e. filter, lamp, pump Problem solved..at King Plant 28

29 SHERCO PROBE UPGRADE Early 2014 upgraded to M&C probe design at Sherco Initial performance similar to that experienced with King CEMS upgrade Gradual degradation of performance on Units 1 and 2, coincided with SO2 controls upgrade Flue chemistry changes appeared to lead to Hg probe fouling and Hg scrubbing 29

30 SHERCO PROBE UPGRADE Poor performance in weekly SIC s on Unit 1/2 Common Stack Total Hg Elemental Hg Ionic Hg 30

31 SHERCO PROBE UPGRADE I&C/Probe vendor troubleshooting Filter replacement 20-plus hours per week in maintenance Probe cleaning and trouble shooting/parts change-out Changed timing sequence of chlorine phase of integrity check Modified probe with wingtip design to deflect particulate Blowback frequency and timing modifications Solenoid vibration fix Initially thought to be an integrity check issue Data was still thought to be representative elemental Hg converting to oxidized, total Hg measured was accurate 31

32 SHERCO PROBE UPGRADE Sorbent trap samples taken on December 11, 2014 ACI installed Wanted to confirm readings from CEMS Results were surprising. Confirmed that System Integrity Check results were reflecting a loss of Hg in the monitoring system More significant at lower Hg concentrations 32

33 POSSIBLE SOLUTIONS? Replace Probe Filter Would need to replace probe filter every 2 days in order to pass integrity check Not feasible due to extensive amount (14 hours) of downtime incurred maintenance and recovery time Costly ~$500 per replacement Calls to question validity of data previously reported SIC failure is real. Reflects monitors inability to accurately measure total Hg. Change monitoring approach Time is up End of 2014 MATS deadline fast approaching Exhausted CEMS options which are compliant with existing regulations Sorbent trap 33

34 SHERCO CS1 MONITORING METHODOLOGY CHANGE Evaluation sorbent trap monitoring technologies/vendors Clean Air Apex M&C M&C Sorbent trap monitoring system chosen Good rapport with vendor I&C liked system Installed in May, intending to be certified in June in order to meet the MATS October 13 th 2015 compliance demonstration date Steep learning curve Not without issues: Sample pump issues Replaced entire sampling panel Short sample runs before trap pluggage Dual unit stacks have wide range of operation (unit trip) Flow proportional sampling becomes an issue Certification test delayed till August to work out bugs 34

35 SHERCO CS1 SORBENT TRAP MONITORING Delay pushes testing into 3 rd Quarter Buys us more time to learn and work out the bugs Additional time to work through DAHS configuration issues SV 4.7 and 4.7 r1 update contained several MATS Sorbent Trap related updates ECMPS schema upgrades associated with sorbent trap systems M&C Sorbent trap monitor certified on 8/11/15 Excellent agreement with RM Finally demonstrating compliance on all units! Well. 35

36 SHERCO CS1 SORBENT TRAP MONITORING Early October started hearing rumblings of Mass Flow Meter calibration issue Contacted M&C directly to verify M&C confirmed, waiting on formal letter from EPA to determine course of action Followed up with Alexis Cain at USEPA Region 5 Alexis confirmed, issuing sent by Ned Shappley at OAQPS 36

37 SORBENT TRAP MASS FLOW METER ISSUE 37

38 SORBENT TRAP MASS FLOW METER ISSUE Mass Flow Meter Calibration Issue Alicat MFM audit device deemed unsuitable for calibration checks by EPA Alicat MFM laminar flow device, not a displaced volume based device M&C proposes to use Mesa Labs BIOS Definer Dry-Cal device (Dry-Cal) as a replacement M&C contracted RMB Consulting to assist with completion of alternate method 38

39 SORBENT TRAP MASS FLOW METER ISSUE RMB worked with EPA to develop procedure to validate data Procedure needs to be performed with an approved NIST traceable device 3-level audit (0.5, 1.0, and 1.5 lpm) 10 minutes for each level Both A and B side EPA determined procedure adequately challenged the MFM for the purpose of validating data collected to date M&C provided MesaLab mass flow meter, and onsite oversight of audit Second Issue identified by EPA: Gas composition settings in MFM s editable unlocked Gas composition must be fixed (81%N2, 12%CO2, and 7%O2 for coal fired EGU application) M&C will upgrade firmware to password protect MFM 39

40 SHERCO CS1 SORBENT TRAP MONITORING Sorbent Trap Monitoring Lessons learned: Petition EPA for site specific moisture value MATS doesn t allow for coal default Default value of 8% too low = over-reporting Hg Xcel petitioned for 10 th percentile value of 13.3% Lag-time of results biggest concern Start out with short trap runs 3 to 4 days Purchases Ohio Lumex for onsite analysis of traps Trap plugging issue Working with Ohio Lumex on different trap designs Changing sample flow rates to achieve longer trap runs Continue to investigate Hg CEMS Beneficial for use in process control Experimented with adding a filter on the probe tip M&C has been onsite twice testing new probe designs Dilution/inertial filter hybrid design 40

41 QUESTIONS/ISSUES REMAIN Permeation source procedure Correct way to perform weekly SIC s? Humidification of Calibration gas Reference Values? Upcoming changes to RA requirements? What happens when RATA RM values are above limit? Need DAHS to track QA operating time, i.e alarm when 7 day system integrity check is due 41

42 PERMEATION SOURCE PROCEDURE Following EPA s Interim Traceability Protocol for Elemental Hg Gas Generators: Thermo Fisher Scientific 84i Permeation Source Currently perform checks approximately every week (required monthly) 42

43 PERMEATION SOURCE PROCEDURE Ratio s repeatable gradual drift? 43

44 PERMEATION SOURCE PROCEDURE Permeation source repeatability? Issue with loss of power to permeation source Subsequent shift in perm source ratio what now? Documented event in logbook Started new baseline 44

45 PERMEATION SOURCE PROCEDURE Calibrator re-certification Once every 8 calendar quarters if not required for any other reason Currently are re-certifying annually Will continue to do so until comfort level established with permeation source checks What is the requirement for spare calibrators? 45

46 WEEKLY SYSTEM INTEGRITY CHECK PROCEDURE What is the correct procedure? Thermo procedure calls for: Span gas through oxidizer (no chlorine) minutes Last 2 minutes averaged for baseline reference value Chlorine gas enabled minutes Baseline reference value compared to oxidized RMB contends that the calibrator certified reference value should be what the calibration response is compared to. Baseline value can be quite a bit different than reference value 46

47 HG CALIBRATOR REFERENCE VALUES As required in MATS - need to account for addition of moisture and chlorine 47

48 HG CALIBRATOR REFERENCE VALUES Humidification of calibration gas Thermo indicates that calibration gas humidified with 1.2% moisture Reference value corrected with multiplier What happens when moisture corrected reference values fall outside of % s( low 20-30%, mid 50-60%, high %)? 48

49 HG CALIBRATOR REFERENCE VALUES Need to account for chlorine used in SIC DAHS is accounting for chlorine flow in weekly SIC calculation 49

50 QUESTIONS/ISSUES REMAIN Permeation source procedure Correct way to perform weekly SIC s? Humidification of Calibration gas Reference Values? Upcoming changes to RA requirements? What happens when RATA RM values are above limit? Need DAHS to track QA operating time, i.e alarm when 7 day system integrity check is due 50

51 Thank you. Questions??? 51