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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
Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
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
Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
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
Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
4
Environmental Air Quality RegulationsEU- Council Directive 2008/50EC, PM10 PM2.5 for Aerosol-immissions
Definition: Emission - Immission
Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
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• 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
Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
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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
Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
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Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
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
Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
9
High Volume sampler:Measurement of PM10, PM2.5 discontinous measurement
24 hour measuringdevice
Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
10
1 stage impactor with beta radiation:Measurement of PM10, PM2.5, continous measurement
PM10 or PM2.5 impactor
Moving filterbandBeta radiation
Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
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Cascade impactor: mass sized particle size distributionbetween 0,1 and 20 µm, discontinous measurement
Aerosol flow In
Clean air out
Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
12
Scattered light sensor: number sized particle sizedistribution 0.25 – 40 µm, continous measurement
•
Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
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Scanning mobility sizer SMPS: number sized particlesize distribution 0.02 – 1 µm, continous measuring
DMA (Differential mobilityanalyser)
CPC (Condensationparticle counter)
Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
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Dust separatorsSettling chamber
Cyclone
Electrostatic separator
Filtering separator
Wet scrubber
Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
15
Improvement of the cyclone separation efficiency
Multi cyclone Rotary flowdust collector
Pocket cyclone
Cooled wall cyclone
Application preferably forhot gas cleaning
Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
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Electrostatic separator
Plate type
Tube type
Wet electr. separator
Electric dustresistance
→ problem forseparationefficiency
Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
17
Wet scrubber
Venturi scrubber
Vortex scrubber
Centrifugal scrubber
Nozzle scrubber
Separation efficiencyPollution is shifted into the liquid
Spra tower
Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
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
Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
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
Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
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Operation behaviour of cleanable filters
Clean gas concentration
Pressure drop
Time
Important part of the cleanable filter:
FILTER MEDIUM
Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
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
Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
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
Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
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
Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
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
Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
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
Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
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
Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
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
Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
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
Dust loaded carrier gas
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
Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
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
Dust loaded carrier gas
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
Dust loaded carrier gas
Pressure tank
Baseplate
Inspection glass
German VDI3926 Typ III
JIS Z 8909-1 Japan
Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
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)
Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
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
Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
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.
Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
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
Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
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
Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
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
Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
36
Electrostatic enhancementCharged dust particles produce lower dust cake resistance
ESFF/MAX9 ConceptualDesign
Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
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
Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
38
Hybrid filter designRetrofit already existingE-filter with a down stream bag filter
Redesign a hybrid filter in onehousing
Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
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.
Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
40
Electrostatic agglomeration upstream the bag house filter
Indigo Agglomerator
Australia
Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
41
Thank you very much for yourattention
Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
42
Electrostatic enhancement of cleanable dust filter
Longer cycle times
Lower pressure drop
Lower particle penetration
Riebl et al: TU Cottbus
Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
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
Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
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
Department of Mechanical Process Engineering
Vienna University of Technology Institute of Chemical Engineering
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
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