mercury speciation in flue gas from coal-fired power ... · PDF fileMercury Speciation in Flue...

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Mercury Speciation in Flue Gas from Coal-fired Power Stations

Matthew A Dexter, Warren T Corns and Peter B Stockwell

P S Analytical Arthur House

Crayfields Industrial EstateMain Road

Orpington BR5 3HP

www.psanalytical.com

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Overview

• Hg in stack gas measurements– Why?– Offline analysis

• Continuous Emission Monitors– Sample collection – Sample transport– Sample pre-treatment– Analysis– Calibration

• Typical Data• Summary

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Why Measure Power Station Hg Emissions?

• Public concern about Hg emissions– Environmental accumulation of toxic metals

• Major sources of emissions:– coal fired power plants– waste incinerators

• Transport strongly dependent on speciation• Regulatory compliance

– US EPA Clean Air Mercury Rule (March 2005)

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Offline Analysis

Reference methodsEPA Methods 29 and 101a (Total Mercury)Impinger based – HNO3/H2O2 or H2SO4/KMnO4

Ontario Hydro Method (Speciation)ASTM Method D6784-02Impingers with KCl & H2SO4/KMnO4

Monitoring methodsQuickSEMTM (Total Mercury)40 CFR Part 75 Appendix KCarbon trap based

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Offline Analysis

Reference methods•Average data over 1+ hours•Labour intensive•Delay for results from lab.

Monitoring methods•Average data over hours or days•Delay for results from lab.

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Online AnalysisContinuous Emissions Monitor (CEM)

Stack

PROBE

Computer

Sir Galahad

Stream Selector

Calibration Device

Speciation Module

Heated Sample Line

Hg0

HgT

Sample collection Sample transportSample pre-treatmentAnalysisCalibration

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Sample Collection - The Probe

Stack

PROBE

Computer

Sir Galahad

Stream Selector

Calibration Device

Speciation Module

Heated Sample Line

Hg0

HgT

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Inertial Probe Schematic

VenturiEductor

Flange

PumpCal Gas Port

Gas Sampleto Analyser

Gas Outlet

Gas Inlet

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Sample Transport – Heated Lines

Stack

PROBE

Computer

Sir Galahad

Stream Selector

Calibration Device

Speciation Module

Heated Sample Line

Hg0

HgT

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Sample transport

• Inert materials– Durinert (glass) coatings– PFA/PTFE components

• Temperature– Raw sample– Ash-free sample

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Sample Pre-treatment –The Speciation Module

Stack

PROBE

Computer

Sir Galahad

Stream Selector

Calibration Device

Speciation Module

Heated Sample Line

Hg0

HgT

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Primary Vent

Hot Flue Gas

HgCl2 adsorbent

Thermolytic convertor

Drain Pump

Drain Pump

Optional Reagent Feed

Optional Reagent Feed

Hg

Hg

Peltier Cooler

Peltier Cooler

Total

0

Heated Oven

The Speciation Module

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Typical Data Using Bench Scale Apparatus

Dry Base Speciation Unit, HgT channel Effect of different flue gas components

05000

100001500020000250003000035000

00:00 01:12 02:24 03:36 04:48 06:00 07:12 08:24time/hh:mm

conc

/ng

m-3

air water, HCl water, HCl, SO2, NO2 water, HCl, SO2, NO2, NO

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Analysis – The Sir Galahad

Stack

PROBE

Computer

Sir Galahad

Stream Selector

Calibration Device

Speciation Module

Heated Sample Line

Hg0

HgT

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Sir GalahadAmalgamation – Atomic Fluorescence Spectroscopy

• Why AFS?SensitivitySelectivitySimplicity

• Why amalgamation?Sample pre-treatment –selectivitySample preconcentration

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Schematic Flow Diagram of theSir Galahad

Argon

Waste

MFC

PUMP Waste

AFS

Sample Argon

MFC

PUMP Waste

AFS

Sample

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Calibration

Stack

PROBE

Computer

Sir Galahad

Stream Selector

Calibration Device

Speciation Module

Heated Sample Line

Hg0

HgT

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On-Line Calibration System

MFC 1

MFC 2

Hg Reservoir

Span

Oven

Blank

Air

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A Power Station in Kentucky

• 120MW unit• Fuel: bituminous coal

– Kentuckian

• Environmental controls– Electrostatic Precipitator (ESP)– No Flue Gas Desulfurisation (FGD)– No DeNOx

• (low NOx burners)

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A Power station in KentuckyStack monitoring

Inertial probe & wet/dry speciation

• Wet and Dry HgT show good agreement

0

2

4

6

8

10

12

14

16

23/10/200412:00

24/10/200412:00

25/10/200412:00

26/10/200412:00

27/10/200412:00

28/10/200412:00

29/10/200412:00

30/10/200412:00

date/time

Hg/

ug m

-3

HgT dry HgT wet Hg0 dry

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A Power Station in SE England

• 500MW unit• Fuel: bituminous coal

– Russian– Colombian– South African– <10% biomass (cereal pellets)

• Environmental controls– Electrostatic Precipitator (ESP)– No Flue Gas Desulfurisation (FGD)– No DeNOx

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A Power station in SE EnglandStack monitoring

Heated filter blowback probe & dry speciationUnattended operation

• Hg levels trend with unit load

0

2

4

6

8

10

12

14

16

08/1107:00

09/1107:00

10/1107:00

11/1107:00

12/1107:00

13/1107:00

14/1107:00

15/1107:00

16/1107:00

17/1107:00

18/1107:00

19/1107:00

date & time

conc

/ug

m-3

-200

-100

0

100

200

300

400

500

load

/MW

Stack Hg0 Stack HgT Load/MW

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A Power station in SE EnglandStack monitoring

Heated filter blowback probe & dry speciationUnattended operation

• SO2 trending – shows variation in fuel

0

2

4

6

8

10

12

14

16

18

20

08/1107:00

09/1107:00

10/1107:00

11/1107:00

12/1107:00

13/1107:00

14/1107:00

15/1107:00

16/1107:00

17/1107:00

18/1107:00

19/1107:00

date & time

Hg

conc

/ug

m-3

-500

-400

-300

-200

-100

0

100

200

300

400

500

SO2 c

onc/

ppm

Stack Hg0 Stack HgT SO2/ppm

B

AHg in coal

A 30 ppb

B 100 ppb

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Conclusion

CEM developed to measure mercury in power station stack gases

Difficult sampling, transport and pretreatment issues have been addressed

Successfully operated unattended on numerous power station stacks