Fabric Filters

1
Fabric Filters
Reading Chap. 6

• Filtration
• Fabric Selection
• Fabric Cleaning
• Air/Cloth Ratio, Filtration Velocity
• Filtration Mechanisms
• Pressure Drop and Design Consideration
• Nanofiber Filter

2
Filtration
Fiber filter
Q Do filters function simply as sieves (to
collect particles larger than the sieve spacing)?
Packing density/solidity
For fiber filter, a lt 0.1 For woven filter, a
0.3
3
Theodore Buonicore, Air Pollution Control
Equipment, CRC Press, 1988.
4
Shaker Baghouse
Shaker Cleaning Parameters
Q What are the common problems encountered?
Theodore Buonicore, Air Pollution Control
Equipment, CRC Press, 1988.
5
Reverse-Air
Q Pros and Cons?
Cleaning dust on baghouse walls by traditional
sledge-hammering
6
Reverse-Air Cleaning Parameters
Reverse-Jet
7
Pulse-Jet
Q How can the blown-away particles by the
on-line cleaning process be collected? Q Felted
fabric or woven fabric?
8
Air/Cloth Ratio
Filtration velocity (average velocity)
Q If thicker fabric is needed to sustain the
high force, is its operating cost higher?
9
Filtration Mechanisms

• Diffusion (Lee Liu, 1982)

http//aerosol.ees.ufl.edu/respiratory/section04.h
tml
Q How does efficiency change wrt dp? Q How to
increase efficiency by diffusion?
Lee, K.W. Liu, B.Y.H., Aerosol Sci.
Technol., 147-61, 1982
10

• Impaction (Yeh Liu, 1974)

Q How to increase impaction efficiency? Q How
does efficiency change wrt dp?
(J 2 for R gt 0.4)
Yeh. H.C. Liu, B.Y.H., J. Aerosol Sci.,
5191-217, 1974
11

• Interception (Krish Stechkina, 1978)

Fat Mans Misery, Mammoth Cave NP
Q How to increase interception efficiency?
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.
12

• Gravitational Settling
• Total Single Fiber Efficiency
• Total Filter Efficiency

Sf Solidarity factor
Q How does the filter efficiency change wrt
particle size?
13

• H 1mm
• 0.05
• df 2mm
• U010 cm/s

Q Should we increase or decrease flow velocity
in order to increase collection efficiency
for (a) tobacco smoke, (b) cement dust?
14
Parallel Flow Operation
Q How do you determine when to clean?
15
Pressure Drop (Filter Drag Model)
Areal Dust Density
Filter drag
K1 K2 to be determined empirically (resistance
factor) DPf fabric pressure drop DPf particle
layer pressure drop DPs structure pressure drop
Q What is the pressure drop after 100 minutes of
operation? L 5 g/m3 and V 0.9 m/min.
16
Time to clean
Filtering velocity
Flow rate
Q What are the parameters that affect our
decision on the number of compartments to be used?
17
Filter drag
Areal dust density
Pressure drop
Actual filtering velocity
18
Nanofiber Filter

• 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.

Nano-alumina on microglass
E-spun PAN nanofiber
Dr. Wolfgang Sigmund, MSE. UF
Argonide
19
Quick Reflection