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


2/20


3/20


Theodore &

Buonicore,

Air Pollution

Control

Equipment,

CRC Press,

1988.


4/20


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?


5/20


Reverse-Air

Q: Pros and Cons?Cleaning dust on baghouse

walls by traditional sledge-

hammering
http://www.bha.com/SuccessStories/K6MK1035.pdf


6/20


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


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?



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?



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



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)


11/20



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?



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



Parallel

FlowOperation

Q: How do you determine when to clean?



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.



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?



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



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



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


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