air pollution control techniques for aerosol- and … · department of mechanical process...

Department of Mechanical Process Engineering

Vienna University of Technology Institute of Chemical Engineering

Air Pollution Control Techniques for Aerosol- and Dust emissions

Wilhelm HoeflingerVienna University of Technology, Institute of Chemical Engineering,

Vienna, AUSTRIA

Presentation at the Novi Sad University

July 2010



2

Content• Dust, Aerosol:

Definitions,

European concentration regulations,

Particle size measurement techniques

• Dust SeparatorsDifferent kinds of dust separators

Bag house filters,

Filter media characterisation by microscopical image analysis,

Standard test facilities for comparing different filter media

Electrostatic enhancement of bag house filtration, hybrid filters



3

Definitions

• Technically, dust or an aerosol are suspensions of fine particles in a gas.

• Dust: all suspended particles in a gas below appr. 100 micrometer

• Aerosol: all suspended particles in a gas below 10 micrometer

• Solid aerosol, liquid aerosol

• Smoke, haze: aerosol with high concentration

http://en.wikipedia.org/wiki/Suspension_%28chemistry%29

http://en.wikipedia.org/wiki/Gas



4

Environmental Air Quality RegulationsEU- Council Directive 2008/50EC, PM10 PM2.5 for Aerosol-immissions

Definition: Emission - Immission



5

• EU- Council Directive 99/30/EC valid since 1.1. 2005, sets limit values for:

PM10 (Particle dust concentr. below an aerodynamic diameter of 10 micrometer)

24 hour mean: 50µg/m3, 35 exceedences per year, from 1.1.2010 7 exceed.

Annual mean: 40µg/m3, from 1.1.2010: 20µg/m3

EU- Council Directive 2008/50/EC since 11.6. 2008

PM2.5 Annual mean:25µg/m3 target value from 1.1.2010 – 1.1.2015

ab 2015: limit value

PM2,5 Annual mean 20µg/m3 from 1.1.2020Up till now many EU- countries could not reach these limiting values for PM10

extension of the fullfilling deadline: June 2011

→ calls for more intensive separation actionsfor particle emissions



6

Staubdeposition im menschlichen Atmungstrakt

A-Dustalveolengängig 50% smaller than 4 µm

Thorax-

gängiger

Dust 50% smaller than10 µm

E-Dustinhalable50% smallerthan 100 µm

Working place regulationsRespirable particle size

EN 481, ISO 778 Workplace (indoor)Inhalable dust fraction: E-dust < 100µmThoracic dust fraction: < 10µmAlveolic dust fraction: A-dust < 4µm



7



8

Often used particle size measurement techniquesHigh Volume sampler:(PM10, PM2.5 PM1) with discontinouus filter sampling, particle mass

1 stage impactor with beta radiation:(PM10, PM2.5 PM1) with continous filter sampling, particle mass

Cascade impactor:particle size distribution 0.1 to 20µm, discontinous, particle mass,

Scattered light sensor:particle size distribution 0.25 to 40µm, continous particle number

Scanning mobility sizer: particle size distribution 0.02 to 1µm, continous, particle number



9

High Volume sampler:Measurement of PM10, PM2.5 discontinous measurement

24 hour measuringdevice



10

1 stage impactor with beta radiation:Measurement of PM10, PM2.5, continous measurement

PM10 or PM2.5 impactor

Moving filterbandBeta radiation



11

Cascade impactor: mass sized particle size distributionbetween 0,1 and 20 µm, discontinous measurement

Aerosol flow In

Clean air out



12

Scattered light sensor: number sized particle sizedistribution 0.25 – 40 µm, continous measurement

•



13

Scanning mobility sizer SMPS: number sized particlesize distribution 0.02 – 1 µm, continous measuring

DMA (Differential mobilityanalyser)

CPC (Condensationparticle counter)



14

Dust separatorsSettling chamber

Cyclone

Electrostatic separator

Filtering separator

Wet scrubber



15

Improvement of the cyclone separation efficiency

Multi cyclone Rotary flowdust collector

Pocket cyclone

Cooled wall cyclone

Application preferably forhot gas cleaning



16

Electrostatic separator

Plate type

Tube type

Wet electr. separator

Electric dustresistance

→ problem forseparationefficiency



17

Wet scrubber

Venturi scrubber

Vortex scrubber

Centrifugal scrubber

Nozzle scrubber

Separation efficiencyPollution is shifted into the liquid

Spra tower



18

Filtering separator, 2 kinds:Depth filter: low raw gas dust concentrations (mg/m3)Cleanable filter: high raw gas dust concentrations(g/m3)

Depth filter Cleanablefilter

Excellent separation efficiency



19

Characterisation of dust separators- Fractional separation efficiency T(x)

E: Total separation efficiency

qf: Particle size distribution clean gas

qe: Particle size distribution raw gas

( ))(

)(11)(

xqxqE

xTe

f⋅−−=⇒

- Pressure drop, energy consumption

→ Filtering separator: best separation efficiency

High pressure drop

Goal of furtherinvestigations



20

Operation behaviour of cleanable filters

Clean gas concentration

Pressure drop

Time

Important part of the cleanable filter:

FILTER MEDIUM



21

Filter medium for cleanable filters: mostly Needle feltsdifferent materials, surface treated (calandered, singed, laminated) to prevent the particle penetration into the depth and to reduce theresidual pressure drop



22

Surface treated area raw gas side

Clean gas side

hp50,

0

hpi

hp

3

hp

2

hp

1

At

otsurface area of

all sample

s

A1A2A3

Ai

O1

O2O3

Oi

hp

i

PF-layer

.

.

.

.

.

.

.

.

.

Microscopical (transmitting light) and image analysisEvaluation of the porous situation at the surface treated raw gas side and method to optimise the surface treatment of the filter medium



23

Image analysis: Conversion of a coloured image into a binary black/white image and elliptic pore approximation

Threshold 130

Threshold: 160to high

Threshold: 115

to low

Elliptic pore approximation

Ap,totOp,totE0dh



24

sharp

Determination of the pore depth distribution by an reflecting light microscope

1,0

0,5

0,0hp50,0 hpmax hphp=h2-h1

Q0(hp)

h1

h2

sharp

Pore depth distribution



25

Pore depth distribution together with surface porosity E0→

model pore

Q0(hp)0,0 0,5 1,0

hp50,0

hpmax

hp

0,500 * phEH =H: measure for the dust holding capacity



26

Model pores of different needle felts

0

200

400

600

800

1000

1200

1400

1600

-0,5 -0,4 -0,3 -0,2 -0,1 0 0,1 0,2 0,3 0,4 0,5

surface porosity E0 [-]

dept

h of

por

e (h

P) [µ

m]

870

FM7

FM6FM5

FM3

FM1FM2

FM4

FM5

FM6

FM7

FM3FM1FM4

FM2

0

50

100

150

200

250

300

350

0 50 100 150 200 250 300 350 400 450

pore volume equivalent H=E0*hp50,0 [µm]

resi

dual

dus

t mas

s mre

s af

ter

100

cycl

es [g

/m²]

mattached

φ tgφ=kacc

mres=mwithin + mattached = kacc * H + mattaches

Calibration line IResidual dust mass after 100 cycles

FM7

FM6

FM5

FM3

FM4

FM2FM1

y = 0.0462xR2 = 0.9473

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0 1 2 3 4 5 6 7 8

clean gas concentration c [mg/Nm³]

effe

ktiv

e su

rfac

e po

rosi

ty ε

eff [

-]

εeff = tg φ * c φ

Calibration line IIMean clean gas concentr. After 100cycles



27

Investigation of the operation behaviour of cleanable filter media

Tested by standard lab test equipment

Test parameter:

-Residual pressure drop

-Average clean gas concentration

-Dust load of the filter mediumMeasurement of these parameters not at thebeginning, but after a so called aged period.

Aging of the filter medium: should bring the filter medium with the test equipmentin a short time into a state, which iscomparable to a long industrial operationtime



28

Different national standard test regulations

Dust feeder

Blow tube

Pressure tankFilter sampleRaw gas channel

Absolute filter

Dust loaded carrier gas

Dust feeder

Blow tube

Pressure tankFilter sampleRaw gas channel

Absolute filter


Absolute filter

Photometer

Raw gas channel

Dust feeder

Back-up filter

Discharge tube

Vakuum pump

Filter sample

Cleaning system

Dust

Absolute filter

Photometer

Raw gas channel

Dust feeder

Back-up filter

Discharge tube

Vakuum pump

Filter sample

Cleaning system

Dust

USA ASTM German VDI3926 Typ I

German VDI 3926 Typ2



29

Different national standard test regulations

Dust container

Air inlet

Control valveVakuum

pump

Clean gas ductPressure transducerAbsolut filter

Mass-flowcontroller

Raw gas channelFilter sample

Photometric concentrationmonitor


Pressure tank

Baseplate

Inspection glass

Dust container

Air inlet

Control valveVakuum

pump

Clean gas ductPressure transducerAbsolut filter

Mass-flowcontroller

Raw gas channelFilter sample

Photometric concentrationmonitor


Pressure tank

Baseplate

Inspection glass

German VDI3926 Typ III

JIS Z 8909-1 Japan



30

Development of an international ISO standard (Draft)Test procedure

Measuring phasesVDI 3926 (1994) VDI 3926 (2004) ISO/CD 11057

Phase 1: Conditioning no30 loading cycles with differential pressure controlled pulse-jet cleaning (1000 Pa)

30 loading cycles with differential pressure controlled pulse-jet cleaning (1000 Pa)

Phase 2: Aging no 10000 pulse-jet cleaning cycles at an interval of 5 s each

2500 pulse-jet cleaning cycles at an interval of 20 s each

Phase 3: Stabilizing no10 loading cycles with differential pressure controlled pulse-jet cleaning

10 loading cycles with differential pressure controlled pulse-jet cleaning

Phase 4: Measuring

Type 1: 100 loading cycles (1000 Pa) Type 2: 10 loading cycles (1200 Pa)

30 loading cycles minimum with differential pressure controlled pulse-jet cleaning, but at least 2 h

2 hour loading cycle with differential pressure controlled pulse-jet cleaning (1000 Pa; 1800 Pa)

Conditions

Round Robin test which compares different standards shows large differences

One of the problems: aging behaviour unclear

Aging: key issueFilter media are usually several years in operation and comparing filter tests should focus also on the filtration behaviorafter long operation time.That means the filter media should be aged in a short time which is comparable to a situation after a long operation time. Tests with very short cycle times (5 – 100 seconds, many cycles up to 10.000)



31

Investigation of the clogging behavior during the agingtime

pressurised air

vacuum pump

test filter holder

dust feeder

dust collection box

∆P

FIC

exhaust air

∆P

secondary pressurised air

pulsjet cleaning

analytical filter

Aging chamber

-Development of an aging Chamber

-Aging tests with different parameter values



32

0

5

10

15

20

25

30

35

40

0 5 10 15 20 25

time [h]

filte

r med

ium

pre

ssur

e dr

op [h

Pa]

32

New characteristic value for characterising the clogging behaviour of filter media (characteristic aging value)

The characteristic aging value contains information about the residual pressure drop development and the cake pressure drop development (cycle time 100s).

characteristic aging value

Def.: The time period until the progressive pressure drop increase is used as a characteristic aging value.



3333

Characteristic aging lines of different filter media

By means of the characteristic aging value the different clogging behaviour of filter media can be characterised

0

20

40

60

80

100

120

1,9 2,1 2,3 2,5 2,7 2,9 3,1filtration velocity [m/min]

time

for r

each

ing

the

extre

me

pres

sure

dro

p in

crea

se [h

]

P84 hydroentangled

P84 filter media 2(needle felt)P84/PPS mixture(needle felt)P84 filter media 1(needle felt)

raw gas concentration / [g/m3]: 5.5cycle time / [s]: 100tank pressure / [MPa]: 0.5valve opening time / [ms]: 60test dust: Sasol Pural NF



34

Comparative characterisation of filter media

On the basis of the VDI characterisation values the following values are used for the filtration behaviour assesment:

•Characteristic aging value•Mean clean gas concentration•Residual dust mass per filtered gas volume

The characteristic aging value has the advantage that the influence of the cycle duration and the residual pressure drop are unified in one characteristic value.

34



35

Combination of electrostatic charging or an electrostatic separator with a bag housefilter- Electrostatic enhanced filtration

- Hybrid filter: Electrostatic filter (ESP) with downstreambag house filter

- Electrostatic particle agglomeration upstream of a baghouse filter

Reason: due to the more stricter air quality regulations for particulates, electrostatic filters can not fulfill these requirements any more

Baghouse filter can fulfill it, but disadvantagous is high pressure drop and premature clogging

Combination can fulfill high separation efficiency also with low pressure drop



36

Electrostatic enhancementCharged dust particles produce lower dust cake resistance

ESFF/MAX9 ConceptualDesign



37

Hybrid Filter Combination of ESP and bag house filter

Large dust masses ar separatedin the ESP (90%) which works notvery efficiently but cheaply

Remaining dust masses (low conc.) are separated down stream in thebag house filter

-longer cycle and operation times

-Lower pressure drop and pressurised air consumption

-Overall: cost-efficient solutionespecially by retrofitting an ESP



38

Hybrid filter designRetrofit already existingE-filter with a down stream bag filter

Redesign a hybrid filter in onehousing



39

Hybrid filter

Pre collection in the precipitator section of the filter reduces the dust load and wearon the filter bags.

Less dust on the filter bags results in lower pressure drop, fewer cleaningcycles, and significant compressed airsavings.

Reduced pressure loss compared to a traditional fabric filter solution.

Reduced energy consumption comparedto a traditional fabric filter solution.

Constant low emissions in spite of varying operational conditions.

Use of existing ESP structure and footprint makes the Hybrid solution costeffective.



40

Electrostatic agglomeration upstream the bag house filter

Indigo Agglomerator

Australia



41

Thank you very much for yourattention



42

Electrostatic enhancement of cleanable dust filter

Longer cycle times

Lower pressure drop

Lower particle penetration

Riebl et al: TU Cottbus



4343

Difference between time controlled and pressure controlled cleaning

pressure controlled (phase 1,3,4)time controlled (aging)

time

Δp

Δpmax

ΔpR

time

ΔpΔpmax

ΔpR

=>A different clogging behaviour results for time controlled cleaning in comparison to pressure controlled cleaning

∆pmax increasing ∆pmax constant∆pR……..residual pressure drop ∆pmax.......maximal pressure drop

-20

-10

0

10

20

30

40

0 5 10 15 20 25 30 35

test time [h]

filte

r med

ium

pre

ssur

e dr

op [h

Pa]

overpressure

pressure pulse propagation time [ms]

pressure pulse propagationtime [ms]

pressure pulse propagation time [ms]

maximal pressure drop



44

PM10, PM2.5: Definition

• PM-10, PM2.5 - Particulate with an aerodynamic diameter smallerthan or equal to 10, (2.5) micrometers.

da,d. = (ρ/1)1/2 . de

Aerodynamic Diameter (da.d.): is the diameter of a sperical particlewith density 1 g/m3 and the same terminal settling velocity as theirregularly shaped particle



45

Air pollution substances can be divided into 5 main harmful substances

• Sulfur oxide (SO2, SO3, H2SO4)

• Nitrogen oxide (NOx)

• Carbon monoxid (CO)

• Volatile organic compounds

• Dust, Aerosol

air pollution control techniques for aerosol- and … · department of mechanical process...

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