Flue Gas Particle Characterization at Different Parts of the Power PlantVille Niemelä, Erkki LamminenDekati Ltd., Tampere, Finland

A&WMA International Specialty Conference: Leapfrogging Opportunities for Air Quality Improvement May 10-14, 2010, Xi’an, China

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Introduction

• Power plants and coal combustion are major sources for fine particles

• This work focuses on particle measurements at power plant

• Particle characterization at plant allows – Understanding particle formation and transformation

– Optimization of combustion process

– Optimization and control of cleaning systems

In this work we present:

• Sampling system for power plant flue gas PM measurements– Sample dilution in different locations of the plant

– Controlled sample cooling and VOC control

• Measurement system for power plant PM measurements– Particle concentration and size measurement at power plant

environment

• Results for– Particle concentration and size distribution in the flame, after heat

exchangers and after baghouse filter

• Size distribution change

• Effect of baghouse filter cleaning system

• Discussion– About PM transformation

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Method 1: Sampling

• Temperature controlled probe– Heated and cooled with pressurised

air, 200 C

– Austenitic stainless steel for high

temp measurement

• P and T measurement after probe

• Heated sampling line, 200 C

• DEED – Two-stage dilution system

– Control / removal of VOC and water

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Dilution air

heater and

temperature

controller,

200°C

Heated SS sampling

line 200°c

ELPI DEED

T P

STACK

PA

Method 2: Dilution with DEED

• Three-stage dilution:– Heated dilution stage 1:10

reduces gaseous VOC

concentration without condensation

– Evaporation tube at 350°C evaporates already condensed VOCs

– Cold dilution stage 1:10 cools down the sample without condensation

– (Extra 1:10 dilution stage on/off)

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Outlet (sample to ELPI)

First dilution stage (PND 1)

with dilution ratio of 10

Dilution at 150°C

Second dilution stage

(PND 2) with dilution

ratio of 10

Dilution at ambient

temperature

Evaporation tube (ET) 350°C

Inlet

(sample from CVS) 2.5 micron cyclone (optional)

Pre-diluter with dilution ratio

of 1 or 10 (OFF or ON)

DEED Offers

• Two or three dilution stages plus evaporation tube

• High dilution ratios: 1:100 and 1:1000

• Controlled sample cooling with low losses

• Heated 1st stage and evaporation tube prevent VOC and other volatile material condensation

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Method 3: PM characterization with ELPI

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ELPI offers

• Real-time particle size distribution 0.007/0.030 – 10 µm

• Real-time number concentration, estimation for mass

• Wide dynamic range - from ambient concentrations up to power plant levels

• Particles are collected - option for size-selected chemical /physical analysis

• Option for particle charge level measurements (ESP studies)

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Measurements:

• 4 MW pilot power plant in Finland

• Circulating Fluidised Bed combustion

• Wood pellets

• Baghouse filter

• Measurement locations:– Right after the flame, T=800 °C

– After heat exchangers, T=200 °C

– After baghouse filter

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Measurements

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Results 1: PM concentration

• Flame (hot location) has lower number concentration

• Mass concentration is the same

• Effect of soot blowing – decrease number, increase in mass (fine particle washout)

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0.0E+00

5.0E+06

1.0E+07

1.5E+07

2.0E+07

2.5E+07

3.0E+07

3.5E+07

4.0E+07

0 100 200 300 400

Nu

mb

er

con

cen

tra

tio

n [

1/

cm3

]

Time [s]

Number concentration

Hot

Cool

0

200

400

600

800

1000

1200

0 100 200 300 400 500

Ma

ss c

on

cen

tra

tio

n [

mg

/m

3]

Time [s]

Mass concentration

Hot

Cool

Results 2: PM size distribution

• Increase in number-based size (and concentration) when T decreases – dominated by small particles

• Mass distribution (coarse particles) remains the same except during soot blowing

• Bi-modal distribution (seen in surface area)

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0.0E+00

5.0E+06

1.0E+07

1.5E+07

2.0E+07

2.5E+07

3.0E+07

3.5E+07

4.0E+07

0.01 0.1 1 10

dN

/dLo

gDp

[1

/cm

3]

dp [um]

Number

Hot

Cool

Soot

blowing

0

50

100

150

200

250

300

350

400

0.01 0.1 1 10

dM

/d

Lo

gD

p [

mg

/m

3]

dp [um]

Mass

Hot

Cool

Soot blowing

0.0E+00

2.0E+05

4.0E+05

6.0E+05

8.0E+05

1.0E+06

1.2E+06

0.01 0.1 1 10

dA

/d

Lo

gD

p [

µm

²/cm

³]

dp [um]

Surface areaHot

Cool

Soot

blowing

Results 3: Baghouse filter

• Efficiency 90% for number, 92% for mass

• Drop in efficiency at about 100 nm

• Concentration after the filter 10.8 mg/m3

© Dekati Ltd.

0

20

40

60

80

100

120

0.01 0.1 1 10

Fil

trat

ion

eff

icie

ncy

[%

]

dP [um]

Filtration efficiency

Filtration

efficiency

0.0E+00

5.0E+06

1.0E+07

1.5E+07

2.0E+07

2.5E+07

3.0E+07

3.5E+07

4.0E+07

0.01 0.1 1 10

dN

/d

LogD

p [

1/

cm3

]

dP [um]

Baghouse filter

Before filter

After filter

Discussion

• Reason for small particle size change– Condensation? Agglomeration?

– Further chemical and SEM / TEM analysis possible

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Conclusions

• A system capable of measuring PM size distribution and concentration in real time at different parts of the power plant – anywhere from the flame to the flue gas exit

• Measurement shows clear change in particle size distribution when flue gas temperature decreases

• Size-resolved filtration efficiency for flue gas cleaning system

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Thank you for your attention!