Download - Filter Ppt Vvi
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7/31/2019 Filter Ppt Vvi
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Aerosol & Particulate Research Lab 109/22/2008
Fabric Filters
Filtration
Fabric Selection
Fabric Cleaning
Air/Cloth Ratio, Filtration Velocity
Filtration Mechanisms
Pressure Drop and Design Consideration
Nanofiber Filter
Reading: Chap. 6
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Aerosol & Particulate Research Lab 309/22/2008
Theodore &
Buonicore,
Air Pollution
Control
Equipment,
CRC Press,
1988.
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7/31/2019 Filter Ppt Vvi
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Aerosol & Particulate Research Lab 409/22/2008
Shaker Baghouse
Theodore & Buonicore,
Air Pollution Control Equipment,
CRC Press, 1988.
Frequency Several cycles/s
Motion type Simple harmonic
or sinusoidal
Peak
acceleration
1-10 gravity
Amplitude Fraction to a few
inches
Mode Off-stream
Duration 10-100 cycles, 30s to a few minutes
Common
bag diameter
5, 8, 12 in
Shaker Cleaning Parameters
Q: What are the common
problems encountered?
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Aerosol & Particulate Research Lab 509/22/2008
Reverse-Air
Q: Pros and Cons?Cleaning dust on baghouse
walls by traditional sledge-
hammering
http://www.bha.com/SuccessStories/K6MK1035.pdf -
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Aerosol & Particulate Research Lab 609/22/2008
Frequency Clean a compartment at a time,
sequencing 1 compartment
after another; continuous orinitiated by a max.-pressure-
drop switch
Motion Gentle collapse of bag
(concave inward) upon
deflation; slowly repressurize acompartment after completion
of a backflush
Mode Off stream
Duration 1-2 min, incl. valve opening,
closing & dust settling periods;reverse-air flow itself normally
10-30 s
Bag diameter 8, 12 inch; length 22, 30 ft
Bag tension 50-75 lb
Reverse-Air Cleaning Parameters
Reverse-Jet
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7/31/2019 Filter Ppt Vvi
7/20Aerosol & Particulate Research Lab 709/22/2008
Pulse-Jet Frequency A row of bags at a time;sequenced 1 row afteranother; can sequence such
that no adjacent rows clean
one after another; initiation of
cleaning can be triggered bymax-pressure-drop switch or
may be continuous
Motion Shock wave passes down bag;
bag distends from cage
momentarily
Mode On-stream; in difficult-to-clean applications such as
coal-fired boilers, off-stream
compartment cleaning being
studied
Duration Compressed air (100 psi)
pulse duration 0.1 s; bag roweffectively off-line
Bag
diameter
5-6 in
Q: How can the blown-away particles by the on-line cleaning process be collected?
Q: Felted fabric or woven fabric?
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Air/Cloth Ratio
A
QV
Filtration velocity
(average velocity)
Q: If thicker fabric is needed
to sustain the high force, is
its operating cost higher?
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Filtration Mechanisms Diffusion(Lee & Liu, 1982)
factorichydrodynamKuwabara44
3ln
2
1
numberPeclet
158.2
2
0
3/2
Ku
D
UdPe
Pe
Kuf
D
Lee, K.W. & Liu, B.Y.H.,Aerosol Sci. Technol.,
1:47-61, 1982
Q: How does efficiency change wrt dp?
Q: How to increase efficiency by diffusion?
http://aerosol.ees.ufl.edu/respiratory/section04.html
http://aerosol.ees.ufl.edu/respiratory/section04.htmlhttp://aerosol.ees.ufl.edu/respiratory/section04.html -
7/31/2019 Filter Ppt Vvi
10/20Aerosol & Particulate Research Lab 1009/22/2008
Impaction (Yeh & Liu, 1974)
4.0for5.27)286.29(
18
2
)(
8.2262.0
0
2
0
2
RRRJ
d
UCd
d
UStk
Ku
JStk
f
cpp
f
I
f
p
d
dR
Yeh. H.C. & Liu, B.Y.H.,J. Aerosol Sci.,
5:191-217, 1974
Q: How to increase impaction efficiency?
Q: How does efficiency change wrt dp?
(J= 2 for
R > 0.4)
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7/31/2019 Filter Ppt Vvi
12/20Aerosol & Particulate Research Lab 1209/22/2008
Gravitational Settling
Total Single Fiber Efficiency
Total Filter Efficiency
0
2
0
TS0
18
directionsamein theVandfor U)1(
U
gCd
U
VG
RG
cppTS
G
GRID
GRID
)1)(1)(1)(1(1
f
f
SdHP exp1)1(
4exp11
Sf: Solidarity factor
Q: How does the filter efficiency change wrt particle size?
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7/31/2019 Filter Ppt Vvi
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H= 1mm
= 0.05
df= 2m
U0=10 cm/s
Q: Should we increase or decrease flow velocity in order to increase
collection efficiency for (a) tobacco smoke, (b) cement dust?
Filter efficiency for individual mechanismand combined mechanisms
dp (m)0.01 0.1 1 10
Effic
iency
0.0
0.2
0.4
0.6
0.8
1.0
Interception
ImpactionDiffusion
Gravitation
Total
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7/31/2019 Filter Ppt Vvi
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Parallel
FlowOperation
Q: How do you determine when to clean?
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Pressure Drop (Filter Drag Model)
spf PPPP
VLVtKVK 21 Areal Dust Density LVtW
Filter drag
VPS WKKS 21
K2
K1
K1 & K2 to be determined empirically
(resistance factor)
Pf: fabric pressure drop
Pf: particle layer pressure drop
Ps: structure pressure drop
Time (min) P, Pa
0 150
5 380
10 505
20 610
30 690
60 990
Q: What is the pressure drop after 100 minutes of operation?
L = 5 g/m3 and V = 0.9 m/min.
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7/31/2019 Filter Ppt Vvi
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tr
tc
tftj
Time
Pressure
pm
Time to clean
ccrf tttNt )(N
QQN
Flow rate
11
N
QQN
Filtering velocity
CC
NN
NA
Q
A
QV
CC
NN
AN
Q
A
QV
)1(
11
Q: What are the parameters that affect our decision on the
number of compartments to be used?
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Areal dust density
))(1( 1 cNrNj LtVLtVNW
Filter drag
jj WKKS 21
Actual filtering velocity
1 NNj VfVPressure drop
jjmj VSPP
N 1/ NfN VVf
3 0.874 0.8
5 0.76
7 0.7110 0.6712 0.65
15 0.64
20 0.6220
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Ex. Calculate the max pressure drop that must be supplied
for the following baghouse for a filtration time of 60
minutes: K1 = 1 inch H2O-min/ft, K2 = 0.003 inch H2O-min-ft/grain, tc = 4 min, 5 compartments, L = 10
grain/ft3, Q = 40000 ft3/min, Ac = 4000 ft2/compartment.
Nanofiber FilterNano-alumina on microglass
Argonide
E-spun PAN nanofiber
Dr. Wolfgang Sigmund, MSE. UF
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19/20Aerosol & Particulate Research Lab 1909/22/2008
Minimum Efficiency Reporting Value (MERV) for HVAC(Heating, Ventilating and Air Conditioning) Filters
http://www.mechreps.com/P
DF/Merv_Rating_Chart.pdf
http://www.mechreps.com/PDF/Merv_Rating_Chart.pdfhttp://www.mechreps.com/PDF/Merv_Rating_Chart.pdfhttp://www.mechreps.com/PDF/Merv_Rating_Chart.pdfhttp://www.mechreps.com/PDF/Merv_Rating_Chart.pdf -
7/31/2019 Filter Ppt Vvi
20/20A l & P ti l t R h L b 2009/22/2008
Quick Reflection