PSA1

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

PSA2

Overview

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

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

• Typical Data• Summary

PSA3

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)

PSA4

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

PSA5

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.

PSA6

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

PSA7

Sample Collection - The Probe

Stack

PROBE

Computer

Sir Galahad

Stream Selector

Calibration Device

Speciation Module

Heated Sample Line

Hg0

HgT

PSA8

Inertial Probe Schematic

VenturiEductor

Flange

PumpCal Gas Port

Gas Sampleto Analyser

Gas Outlet

Gas Inlet

PSA9

Sample Transport – Heated Lines

Stack

PROBE

Computer

Sir Galahad

Stream Selector

Calibration Device

Speciation Module

Heated Sample Line

Hg0

HgT

PSA10

Sample transport

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

• Temperature– Raw sample– Ash-free sample

PSA11

Sample Pre-treatment –The Speciation Module

Stack

PROBE

Computer

Sir Galahad

Stream Selector

Calibration Device

Speciation Module

Heated Sample Line

Hg0

HgT

PSA12

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

PSA13

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

PSA14

Analysis – The Sir Galahad

Stack

PROBE

Computer

Sir Galahad

Stream Selector

Calibration Device

Speciation Module

Heated Sample Line

Hg0

HgT

PSA15

Sir GalahadAmalgamation – Atomic Fluorescence Spectroscopy

• Why AFS?SensitivitySelectivitySimplicity

• Why amalgamation?Sample pre-treatment –selectivitySample preconcentration

PSA16

Schematic Flow Diagram of theSir Galahad

Argon

Waste

MFC

PUMP Waste

AFS

Sample Argon

MFC

PUMP Waste

AFS

Sample

PSA17

Calibration

Stack

PROBE

Computer

Sir Galahad

Stream Selector

Calibration Device

Speciation Module

Heated Sample Line

Hg0

HgT

PSA18

On-Line Calibration System

MFC 1

MFC 2

Hg Reservoir

Span

Oven

Blank

Air

PSA19

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)

PSA20

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

PSA21

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

PSA22

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

PSA23

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

PSA24

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