229502079-Filter (1).ppt

Aerosol & Particulate Research Lab 110/03/2002

FILTRATION

Packing density/solidity

Fiber filter

Reading: Chap 6

porosity - 1 volumetotal

mefiber volu

For fiber filter, < 0.1For woven filter, ~ 0.3

Q: Do filters function simply as sieves (to collect particles larger than the sieve spacing)?


Theodore & Buonicore, Air Pollution Control Equipment, CRC Press, 1988.


Shaker Baghouse

Theodore & Buonicore, Air Pollution Control Equipment, CRC Press, 1988.

Frequency Several cycles/sMotion type Simple harmonic

or sinusoidalPeakacceleration

1-10 gravity

Amplitude Fraction to a fewinches

Mode Off-streamDuration 10-100 cycles, 30

s to a few minutesCommonbag diameter

5, 8, 12 in

Shaker Cleaning Parameters

Q: What are the common problems encountered?


Reverse-Air

Q: Pros and Cons?Cleaning dust on baghouse walls by traditional sledge-hammering

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


Reverse-Air Cleaning Parameters

Reverse-Jet


Pulse-Jet

Q: How can the blown-away particles by the on-line cleaning process be collected?Q: Felted fabric or woven fabric?


Air/Cloth Ratio

AQV

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)

EKu

Pe

Ped U

D

Ku

D

f

2 581

12

34 4

2 3

0

2

.

ln

/

Peclet number

Kuwabara hydrodynamic factor

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.html


• Impaction (Yeh & Liu, 1974)

EStk JKu

StkUd

d C Ud

J R R R

I

f

p p c

f

( )

( . ) . .. .

2

18

29 6 28 27 5 0 4

2

02

0

0 62 2 2 8

for f

p

dd

R

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)


• Interception (Krish & Stechkina, 1978)

2

2

)1(2

)2

1(1

11)1ln(221 R

RR

KuRER

Krish, A. A. & Stechkina, I. B., “The theory of Aerosol Filtration with Fibrous Filters”, in Fundamentals of Aerosol Science, Ed. Shaw, D. T., Wiley, 1978.

Q: How to increase interception efficiency?

Fat Man’s Misery, Mammoth Cave NP

http://www.geocities.com/wrique2002/ParentsVisit/FatmansMisery2.jpg


• Gravitational Settling

• Total Single Fiber Efficiency

• Total Filter Efficiency

E G R

GVU

d C gU

G

TS p p c

( )1

180

2

0

for U and V in the same direction0 TS

GRID

GRID

EEEEEEEEE

)1)(1)(1)(1(1

ESdHE

PE ff

exp1)1(

4exp11

Sf: Solidarity factor

Q: How does the filter efficiency change wrt particle size?


H = 1mm = 0.05df = 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?


• ProblemFilter is made of fibers with diameter of 10 um, density of

2.35 g/m3 and solidity of 5%Filter must collect 0.5 um particles with 90% eff.Air velocity is 10 ft/min

Question: How thick must the filter be?


Parallel Flow

Operation

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 empiricallyPf: fabric pressure dropPf: particle layer pressure dropPs: structure pressure drop

Time (min) P, Pa0 1505 380

10 50520 61030 69060 990

Q: What is the pressure drop after 100 minutes of operation? L = 5 g/m3 and V = 0.9 m/min.


Time to clean

ccrf tttNt )(

NQQN

Flow rate

11 N

QQN

Filtering velocity

CC

NN NA

QAQV

CC

NN AN

QA

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 VVf3 0 . 8 74 0 . 85 0 . 7 67 0 . 7 1

1 0 0 . 6 71 2 0 . 6 51 5 0 . 6 42 0 0 . 6 2

2 0


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.

Other factors to be considered for selecting a filter?• Temperature & Humidity• Chemical nature of gas• Fire/Explosion• Bag/arrangement• Dust handling• Fan location


• Advantages:

• Disadvantages:

Advantages & Disadvantages of a Baghouse

229502079-Filter (1).ppt

Documents

Transcript of 229502079-Filter (1).ppt