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10
FabricFilters
IO.I NTRODUCTION
Fabric
iltration is a widely acceptedmethod
or
particulate
emissions
ontrol. In fabric
filtration, the
particle-laden as
lows through a
number of filter bags
placed n
parallel, eaving
the dust
retainedby the tabric. Extendedoperationof a
fabric filter, or baghouse,
equires hat
the
dust be
periodically
cleaned
off the cloth surfaceand removed rom
the baghouse.
After a new
fabric
goes
hrough a f'ew cycles of use and cleaning,
t retains a residualcake
of dust that
becomes he filter medium.
This
phenomenon
s responsible or the
highly efficient
filtering of
small
particles
hat characterizes
aghouses.
The type of cloth fabric limits the temperature f
operationof baghouses. otton
fabric
has he least esistanceo
high
temperature
about
355
K), while fiberglass
has he most
(530
K).
In many cases his
requires ha t the waste
gas
streambe
precooled
before entering he
baghouse.
The cooling system hen
becomesan integral
part
of the design.Conversely,
he temperature
f
the exhaust
gas
streammust be well above he dew
point of
any
of its condensable
onstituents s
liquid
particlesplug
the fabric
poresquickly.
Most of the energy requirements f the systemare
to overcome he
gas pressure
drop
across he bags,dustcake, nd associated'ductwork.
ypical valuesof
pressure rop range
rom I
to 5 kPa. The most mportantdesign
parameters the ratio of the
gas
volumetric
'low
rate o fab-
ric area,known as he ga.r-lo-clothatio. Other mportantprocess ariables ncludeparticlechar-
acteristics
such
as sizedistributionand stickiness),
as
characteristics
temperature
nd corrosivi-
ty), and abric
properties.
Electric
utilities have made significant
progress n recent
years
n designing
and operat-
ing baghouses
br the collectionof coal fly ash.
nterest n
baghouses
an be expected
o continue
increasing s air emissionstandards ecome
more stringentand concernsover
inhalable
particles
and air toxic emissions ncrease.
n many
cases.
he relative nsensitivityof
baghouses
o changes
in
fly ash
properties
make hem more attractive han ESPs
The oldest fly-ash baghousewas commissioned
n 1973. By 1990, here were close to
100
baghouses
n
operationon
utility boilers, representingmore than 21,000
MW of
generating
capacity
Cushing
et al. 1990).
414
Se
r
0
thc'
n te t
r
0 ,
l i - -
t - l L ' .
( ) \ s l .
l e i t .
l I a : . :
l C ] .
I I L
l 1 J - -
rc.1 .
e r .
10
ed ,
inr f
c l a .
i l l l d :
s - : - :
] ] ' :
'
. ; :
S)
',
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Sec.
10.2 Types f
Fabric
ilters
415
IO.2
ryPESOF
FABRIC
ILTERS
Your objectiven studying hissections to
Describe he operational
haracteristics
f the three
nost common
baghouse
esigns:
I
)
shaker;
2)
reverse ir:
and
3)
pulse
et.
The most
mportant istinction
etween
abric ilters
designs
s the
methodused
o clean
the dust
f iom the
bags between
iltration
cycles.
The distinguishi ng
'eatures
f each
cleaning
method redescribed
ubsequently,
ollowing
Turneret al
(1987a).
10.2.1 hoker
leoning
For
any type of cleaning.
enougl.r
nergy
niust be
imparted
o the
fabric to
overcome
he
adhesion
brcesholcling
he dust
o the bags.
n shaker
leaning.
sed
with inside-to-outside
as
flow. this
is accornplished
y
suspending
he bag
from a
motor-driven
ook
or fiamework
ha t
oscillates.
he
motion creates
sine
wave along
he fabric,
which
dislodges
he
previously
ol-
lectedclust.Chunks
of
agglomerated
ust all
into a hopper
below
the compartment.
he cclmpart-
mentsoperate
n sequence
o hat
onecompartment
t
a t ime
s cleaned.
igure
0.l is a
schenrat-
ic diagramof
a shakerbaghouse.
Parameters
hat affect
cleaning
nclude the
amplitude
and
fiequency
of the
shaking
motion and he
tension
of the mounted
bag.
Typical values
of the
first two
parameters re
4 Hz for
frequencyand 50
to 7-5
urm fbr
antplitude.
The vigorous
oscillations
end
to
stress he
bags and
require
heavier
and more
durable
abrics.
n the United
States,
woven
fabricsare used
almost
exclusively
or shaker leaning,
whereas
n Europe
elted abrics
are used.
| 0.2.2Reverse-Air leoning
When fiberglass
'abrics
were ntroduced,
gentler
means
of cleaning
he bags
was
need-
ed
o
prevent
remature ag
ailure.Reverse-air
leaning
wasdeveloped
s
a less ntensive
a)' o
impart energy
o the
bags.Gas
-low o
the bags
s stopped
n the compaftment
eing
cleaned.
and
a reverse
low of
air is directed
hrough
he bags.
This
reversal
f flow
gentlycollapses
he
ba-ss
and the
shear
orces developed
emove he dust
from
the surface
of the
bags.
The
reverse
air tilr'
cleaning
omes rom
a separate
an capable
f supplying
lean,dry
air
for one
or t\\
o compart-
ments t a
gas-to-clothirtiosimilar
o that
of the orrva rd
as
low.
Many
reverse-air
achouses
re nstalling
onic
horns
t-rntprove
hc
performance
f the
cleaning
tep.
Sonic
nergv
sins
horns ur ing
he
everse
lou concent l r te\
l lore
leuning
ner-
gy
at
the bag-dust
ake
nterface.
he
esulting eciuction
n residual
ustcake
density
educes
he
pressureropb1 50. i to 60.r rCur landSmith 9Slbr Sonic orns perate)n ompressedirat
,t
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416 Chap.
0 Fabric
ilters
Figure
10.1Schematic iagram of a shaker
baghouse
pressures
of about 400 to 900 kPa. It appears hat
reverse-air
cleaning
with sonic assistance
s the
cleaningmethodof choice
or
baghouses n
pulverized
coal-fired
boilers
Cushing
et
al. 1990).
|
0.2.3
Pulse-Jel
leoning
This form of cleaning orces
a
burst of compressed ir down through he bag
expanding
it violently. As with shaker
baghouses,
he fabric reachests extension
imit
and
he dust separates
from the bag. n
pulse
ets,
however, iltering flows are opposite n direction
when compared
with
shakeror reverse-air esigns,
with
the outside-to-inside
as
low.
Bagsare mountedon
wire
cages
to
prevent
collapse
while the dusty
gas
lows through hem.The top of the bag and
cageassembly
is attached o the baghouse tructure,whereas he bottom end
is loose and tends o
move in the
turbulent
gas
low.
Most
pulse-jet
baghousesare not compartmented.Bags are cleaned
by rows
when a
timer initiates he burst of
cleaning
air through a
quick-opening alve.
Usually
lOToof the
collec-
tor is pulsed at a time by zones.A pipe aboveeach row of bags carries the compressedair. The
Sec
l : I a
. .
:
_ f i
r e
n : : : .
L.rs'
P. '
' r0,3
F
n n t i n r ' - -
Althous
desi
ne;
10 ,3 ,
\ o
u n l I i . ' ' ;
i t ; i < r . - : : ' .
. : - .
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Sec.
10.3 Fabric iltrationheory
417
pipe
s
pierced
aboveeachbag so that cleaningair exits directly downward
nto the bag.The
pulse
opposesand
interrupts forward
gas
flow for
only
fractions of a second.
However. the
quick
resumptionof
forward
flow redeposits
most
of the dust back
on the
"clean"
bag or on
adjacent
bags.Pulsejetsnormally operate t about wice the
gas-to-cloth atio
ofreverse-air
baghouses.
IO.3FABRICITTRATIONHEORY
Your
objectives
n
studying his section re
o
1. Describe, n
qualitative
erms, he mechanisms f
particle
penetration
througha
fabric filter.
2. Estimate he tubesheet
ressure
rop n baghouses.
The key
to designinga
baghouse s to
determine
he
gas-to-cloth atio
that
produces
he
optimum balancebetween
pressure
drop
(operating
cost) and baghouse
ize
(capital
cost).
Although collection efficiency is another mportant measureof
baghouse
erformance,
roperly
designed nd well-run baghouses re
highly
efficient
I0.3..| enetrotion
Design overall efficiencies
or fabric filters range from
98Va
o more
than
99.97o.
Most
units currently
n
operationmeet or exceed
heir design efficiencies
Cushing
et al. 1990).Two
basic mechanisms ccount or the
particles
hat
pass
hrough he baghouse.
Particlescan escape
collection through
leaks in the ducting, tubesheet,or bag clamps,
or through holes, tears,
or
improperly sewn seams n the bags hemselves. he second
mechanism or emissions
s
particle
movement hrough the dustcakeand the fabric, also
known as bleed-through.Bleed-through s
primarily
a
function
of baghouse esign
and
particle
morphology.Smooth,
spherical
particles
are
less
cohesive, nd can seep
hrough he dustcake nd abric easily,
ncreasing missions.
Well-developedequationsexist in aerosol
physics
o
calculate he fractional
penetration
of
particles
on various structures y filtration
forces
(Crawford
1976;Flagan
and Seinfeld 1988).
However, each requiresdetailedknowledge of the
geometry
of the collection
medium.
Because
the structureof dust cakes
s not
defined-and,
in fact, appears o be
systemdependent
n ways
that are now not
understood-none
can be used o
predict ractional
penetration.
Figure 10.2 shows actualbaghouse
enetration
ata reported
by Ensor et al.
(1981).
Considering
he dominantcollectionmechanisms, iffusion
(which
decreases
ith increasing
ar-
ticle size).and mpaction and nterception
which
increase
with particlesize), he classic heoreti-
cal
penetration
urve exhibits
a singlemaximum n the 0.
-
to 0.3-pm
range.
Thus, additional
mechanismsmust act to create he bimodal curve of Figure 10.2.A reasonable xplanation s to
attribute
he arge-particle
enetration
mode o bleed-through
Can
and Smith
1984a).
t
li
.-t
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418
Chap. 0
Fabric
ilters
Figure
10.2
Measured
baghouse
ractional
penetration
From
Carr,
R.
C.,
and
Smith,
W. B.
IAPCA,34:79,7984;
reprinted
with
permis-
sion from
IAPCA)
Sec.1
Exampl
wh
Th
kg/
an
Soluti
S
Th
re
ti m
0.
0.0
\c
. 2
a
=
'5
?
LL
0.1
I
Particle
iameter;rm)
Dennis
and Klemm
(1979)
proposed
he
following
semiempirical
verall penetration
equation
based
on
the observations
hat penetration
ncreased
with
increasinggas-to-cloth
atio
and
decreased
s
he
dust cake
on
the fabric
grew:
Pt= Pt.\
+
(116
pt,\e-,,w
+
pt1,,
(
1 . 1 )
where
P/
=
overall penetration
Pl.
=
low-level
penetration
ue o pinholes
n
the
cake-fabric
tructure;
ncreases
with
the
gas-to-cloth
atio
P/0= penetrationhroughajust-cleanedhbricarea,
Prl,r
=
penetration
ue
o bleed-through;
function
of parlicle
morphology
w
=
dust
massper
unit
bag surface
area,
also
known
as areal
densitv,
ks/m2
r,r
=
cakepenetration
ecay
ate
Viner
et al.
(198'1)
ound
that Eq.
(10.1)
overpredicts
enetration
ust
after
a compart-
ment
hasbeen
cleaned:
ut.
as
he dust
cake
on
the ilter grows,
he
discrepancy
etween redict-
ed
and measured
alues
diminishes.
ll the
terms
n Eq.
(10.
)
must
be determined
rnpir ically
for
a
given
fabric-dust
ake
combination.
he
following
example
llustrates
ypical
con<Jitions
n
a reverse-air
ilter.
\ l
"6
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Sec.
10.3 Fabric
iltration
heory
419
Example
10.1 Time
Dependency
of Penetration
in Baghouse
The
waste
gases rom a coal-fired
boiler
flow through
a reverse-air
aghouse
or
111'-ash
removal.
he bllowing
empirical
quation
or overall
penetration s a function
of operation
time between leaning ycleswasdeveloped:
p l
=
t60y r ' l
+ 0 . 0
t60y r ' ' r
exp { - t80c ;v r ) *
: . l u
where
V
-
gas-to-clothatio,
m/s
Ci
=
inlet dust
oading,
g/m3
I
=
operation
ime since
astcleaning
The baghouse
perates
t an air-to-cloth
atio
of 0.0
m/s and he
nlet
dust oading
s 0.004
kg/m3.
Eachcompartment
s
cleaned
everl'
20 min.
Plot
penetration
s a function of time.
andcalculatehe average verallpenetrationor thecycle.
Solution
Substituting
he
valuesof V
and C;
n the
penetration quation:
P/
=
0.0038
0.0963
xp
-0.432r ' )
where
' is the
ime n
minutes.
igure10.3
hows he
variation
n
penetration
ith t ime.
Most of the
particle
emissions
ake
place
shortly
after
he bags
arecleaned.
To calculate
he
average
enetration.ntegrate
ver a cycle
and divide
by the
ength
of the cycle.
20
i
o.oo:s
0.0963
"^p
o.+:zt
ai
)
Vrtnn
Bush
t al t1989)der ived
n
expression
o
quant i ty he
exture
r sur face
r lorphol-
..
:
1r.l\ .r.h
lntflr ':.
Their
morphology
actor
,41)
s a dimer.rsionless
uantitl based
n
rolu-
' - : : : - . . . ' r - , l l , t n l i r : t , , r ' r J . r t . L nt e a . L r r e d u i t h a C o u l t e r C o u n t er ( a d e v i c e t h a t m e a \ u r e \ p a n i c l e s i z e
- . : i
:
: i . i , . : , , . ' : r -
: . . i \ l r \ l t r
r .
pec i f i c
u r l ' ace
rea
A) .
and
hc
fue
den \ i t \o t ' t he
ash
' '
.
-
:
0.0
49
t
i
I
i
:
I
:
t
q{ffi&s,,
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420
Chap."
0
Fabric
ilters
Figure
10.3
Penetration
ersus
time
in
a
reverse-air
baghouse.
(r0.2)
Sec.1
reglons,
a
tubesheet
and
the m
constant
F
tion
throu
continuo
mal ly
use
is cake
il t
the actual
to-cloth
r
tion
betu
pressure
T
maximur
designer
sure
drop
where
surface
u
i're:;
L
,,i
::
x
()
0.01
8 1 2
Time
min)
n;
D];
ln Dpi
u
=1"*v
n;D];
where
ni
=
the
otal
number
f
particles
ounted
n Coulter
hannel
Doi= thegeometricmean iameter
f
Coulter
channel
,
pm
A
low
value
of
M
indicates
hat
he
particles esemble
mooth
pheres,
hile
a
high
value
ndicates
hat
he
particles
ave
very
rregular
hapes
nd
surfaces.
or
perfect
spheres,
=
1.0.
Field experience
hows
hat
ashes
ith
ow values
f
M
(2.0
o
2.7)seep
hrough
he
abric,
increasing
missions
Felix
and
Menitt
1986;
Milleret
al.
1985)'
The
mechanism
fbleed-through
s not
well understood
et
and here
s
no
general heo-
retical
model o
predict
ts
effect
on
particle
penetrationhrough
baghouses'
t
is
fortunate hat
fabric
filters
properly
designed
ased
n
pressure
rop
considerations
enerally
xhibit
penetra-
tions
well below
he
applicable
SPS.
10.3.2
ressure
roP
There are
several
contributions
to
the total
pressure
drop
across
a baghouse
ncluding
the
pressure
drop
from the
flow through
the
inlet and
outlet
ducts,
from
flow through
the hopper
; - t
,l|
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Sec.
10.3
Fabric
iltration
heory
421
regions,
and
from flow
through
he
bags.The
pressure rop
across
he bags
(also
called
he
tubesheet
ressuredrop)
is a complex
function of
the
physical
propertiesof the
dust
and
fabric
and
the manner
n
which the
baghouse
s designed
and
operated.
he duct
and
hopper
ossesare
constant
nd
can be
minimized
effectively
hrough
properdesign'
Fabric
filtration
is inherently
a batch
process hat has
been
adapted
o
continuous
opera-
tion
through
clever
engineering.
he dust collected
on the
bags
must be
removed
periodically
br
continuous
operation.
Shaker
and
reverse-air
esigns
are
similar
in the
sense
hat they
both
nor-
mally
use
woven
fabric bags
un at
relatively
ow
gas-to-cloth
atios,
and
he filtration
mechanism
is cake
iltration.
The
fabric merely
serves
as a support
or the
formation
of
a dust
cake.
which
is
the
actual
iltering
medium.
Pulse-jet
aghouses
enerallyuse
elt fabrics
and
run
with a high
gas-
to-cloth
ratio.
The f'elt
abric
plays a much
more
active
role in
the flltration
process.
The distinc-
tion
between
cake
filtration
and
fabric
filtration
has important
implications
for calculating
he
pressure rop across
he
filter bags.
The design
of a
fabric filter
begins
with a
set of specifications
ncluding
average
and
maximum
pressure rop, otal
gas 1ow,and
other
requirements.
asedon
these
equirements,
he
designer
pecifies
he
maximum
face
velocity
allowed.
The standard
way
to relate
ubesheet
res-
suredrop
o
cas-to-cloth
atio
s
^P( r )=(dY
(
1 0 . 3 )
where
AP(r
)
=
the
pressure rop through
he
filter, a
function
of time,
t
S(r
)
=
the
drag hrough
he fabric
and cake,
Pa-s/m
V
=
the average
r design
gas-to-cloth atio,
m/s
The
drag across
he
fabric and
cake
s a function
of
the amount
of
dust
collected
on
the
surface
f the
bags.
Assuming hat
he
filter drag
s a
linear
unction
of the dust
oad,
s(r)=
.
+ <zw(t)
(
10 .4)
ri
here
S"
=
the drag
of a
dust-free
freshly
cleaned)
ilter
bag
Kz.= the
dust
cake low
resistance,
-l
The dust
mass
as a function
of
time
is W
=
C;Vf,
where C;
is the
inlet dust
concentratlon
,kg/m3).
Substituting
his expression
n Eqs.
10.3)
and
10.4):
A P ( r )
S " V
+ K ; C ; V 2
(
1 0 . 5
The constants
,
and
K; depend
n the
fabric and
he
nature
and size
of
the dust'
Th e
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422
Fabric
ilters
relationship
between heseconstantsand the dust and fabric
properties
are not understood
well
enough o
permit
accurate
redictions
and so must be determined mpirically.
Example 10.2Estimation
of
Parameters n Filter
Drag Model
(a)
Estimate he
parameters
n Eq.
(
10.4)
basedon the following data or a freshly cleaned
fabric. The
gas-to-cloth
atio is
0.0167
m/s and he nlet
dust concentration
s
0.005
kg/m:.
(b)
Estimate he
pressure
rop for
the sameconditionsafter 70 min of continuous peration.
Test Data
Time
(min)
AP
(Pa)
9.00
22.80
30.30
36.60
41.40
-59.40
0
0.025
0.050
0. r00
0.150
0.030
Sec
l
Exam
Solut i
Chap.
0
0
5
l 0
20
30
60
r50
380
50 5
6 1 0
69 0
990
Solution
(a)
Basedon the testdata,
generate
plot
of filter drag versusarealdensity.The
following
table llustrates
he data o be
plotted.
S = LP/V kPa-s/m) W =CiVt (kg/rn2)
\
:
Figure 10.4showsan nitial characteristic urvature ollowed by a linear dependency f fil-
ter
drag on
areal
dust density.The nonlinear
portion
of the curve s due o a
non-uniform
initial flow
through he
fabric. The previous
cleaningcycle usuallydislodges he
cake n
,'
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Sec.
10.3
Fabric
iltration
heory
S = 2 . 1 . 5 6 8 +
l 5 . 7 1 W
423
60
30
l 0
a
-o
l t
Figure
10.4
Filter
drag
versus
dust
areal
density
or
Example
10.2
|
. | |
|
|
| r I
r
I
l:
lT_rr_rt_rrrT,T-r1
0 .05
0 .
0 . l . s
0 .2
0 .25
0 .3
0 .3 -5
Areal usr cnsiry'(W.g/ml
irregular
hunks.
earing
someparts
ofthe
bagvery
clean
and
others
ti l l quite
dusty,
resulting
n
spatial
ariations
n
the
nit ial
gas
low.
A least-squares
it
of
the inear
portion
of
the
curveyields:
S"
=
21.51
Pa-s/m,
nd
K2
=
I 15.7
pa_s_m/kg
l. l6 x
l0s
s
r.
(b)
Equation
10.-5)
ives
he pressure
rop
after
70
min
of
continuous
peration:
p
=
24,510(0.0167)
( l . tU
t
1gs;(0.00-5)(0.0167)r(70X60)
1.090
a.
Example
10.3
Cycle
ime
for
Reverse-Air
Fabric
Filter.
A reverse-air
abric
llter
has
1,000
ml of
f i l ter in-s
rea
and reats
0 m3/s
f
air
carrying
dust
concentration
f
0.005
kg/m3.
Assume
S,, lg.g
kpa-s/m
nd
K2
=
I
.0
x
l0s
s
l.
I f the
filter
must
be
cleaned
hen
hepressure
rop
eaches
.0kPa,
after
what
period
must
he
c leun ing
ccur?
Solution
Thegas-to-cloth
at io
s
11
1971.000
0.01
m/s.
Solving
q.
10.-5)
br
the
irne
f
opera-
t ion
befbre
he
pressure
L'op
rceecls
.000
Pa.
=
[2.000
(20.000)(0.01) l / t (105)(0.005)
(0 .01 ) r l
36 .000
=
l [ )
h
sjffiknr
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424
Chap.
0 Fabric ilters
Pulse-jetbaghouses ave been designed o operate n
a
variety
of modes.Some
remain
on line at all times and are cleaned iequently.
Othersare aken off line for cleaningat relatively
long intervals.A
complete
model
of
pulse-jet
iltration
therefbremust account or the composite
dust-fabric iltration occun'ingon a relatively clean bag. the cake filtration that result fiom
pro-
longedperiods n ine.and he ransition eriodbetweenhe wo regimes.
If a cornpartments takenofl ' l ine fclr
cleaning. he dust hat s removed rom the bags
falls into the hopperbefbre orward
gas
low resumes. f
a comparlment s cleanedwhile on
line,
only a small fi-actionof the dust removed iom the bag falls
to the
hopper.The remainderof the
dislodged ustwill be redeposited
i.e.,
recycled")
n the bagby the brward
gas
low. The
rede-
posited
dust layer has clifl 'crent
ressure
rop characteristic shan the freshly deposited ust.
Dennis
and Klemm
(
1979) roposed
he bllowingmodelof
dragacross
pulse-jet i l ter:
s
=
s,,
(xr),w,.
K2w11
(
10.6)
where
(K1),=
specif ic ust esistancefthe recycling
ust
W.
=
arealdensityof the recycling
dust
K2
=
specif ic ust esistancef
the
ieshly
deposited ust
Ws
=
arealdensityof the freshly deposited
ust
Th is
mode l can eas i l y accoun t o r
a l l t h ree eg imeso f f i l t r a t i on n a
pu lse - je t
baghouse.The
ressure
rop can thus be expressed s the sum
of a
relatively
constant
erm and a
term hat ncreas es ith dustbuilduo.
Sec.
10
Eranrp l
1 -
Solut ion
E r a m p l c
and
RifT
\
- . :
.:
-
' . :
:
where
(
0.7)
(
10 .8)
a p = ( p g ) r "
+ K 2 w o v
(pst,,
is"
+
xz),.w,lv
The
disadvantagefthe model epresen ted
y Eqs.
10.7)
and
10.8)
s that he constants
S",
K2,
and W, cannotbe
predicted
at this
time. Consequently, orrelations f laboratorydata
must
be used o determine he value
of
(PE)1,,
For one fabric-dus tcombinationof Dacron felt and
coal ly ash.DennisandKlemm
(
1980)
evelopedhe ollowingcorrelation:
(f'f)o,,
=
1,045
r,
n ot
(PE)r",
is in kPa
P;
-
gaugepressure
f the cleaning
pulse,
n kPa
Y = gas-to-clothatio, n m./s
(
0.9)
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Sec.
10.3
Fabric
iltration
heory
425
Example
10.4
Tubesheet
Pressure
Drop in Pulse-Jet
Baghouse
A
pulse-jetbaghouse
sesDacron
elt bags
or the control
of fly-ash
emissions.
he
gas-to-
cloth
atio s 0.02,1
m/s and he
nletdust
oading s 0.01
kg/m3.
The bagsare
cleaned
t l0-
min ntervals
with
pulses f air at 650
kPa
gauge' f K:
= l'5 x 105 l' estimatehe maxi-
mum ubesheet
ressure
rop.
Solution
The conditions
resimilar
o those
or whichEq.
(
10.9)wasdeveloped.
hen,
PE)a"
-
(
1,045)(0.024)(65Ofo
:
=
0.372
Pa.At the
endof the
l0-min cycle,
4ze
(0.01X0.024)
(600)
=
0.144
g/m2.
Equation
10.7)
gives
he ubesheet
ressure rop:
AP
=
0.312
+
(
L5
x
1
05)(0.
44)(.0.024)
t.000
=
0.89
kPa.
Example
10.5
Effect of
Filter
Inhomogeneities
n
Filter
Drag Model(Cooper
and
Riff
1983)
Knowing
the mean
of a
property,suchas
dust arealdensity,
may be misleading
br
predict-
ing
the effect of
that
property.
When
estimating
he
specific
dust resistance
or a filter cake
(Kz)
fiom
pressure
rop
data,Eq.
(
10.7)
predicts hatK2
n
W
|
. However,
n a typical
bag-
house he
arealdensity
s not
homogeneous,
ut changes
rom
bag o bag.
For example,
Ellenbecker
.1919)
measured
realdensities
n a
pulse-jet
baghouse
nd ound
that he
data
could
be fitted
by a log-normal
distribution
with a median
of 0.64
kg/m2and
a
geometric
standard
eviat ion, * ,
of
1.15.
In the
presence
f
inhomogeneities,
he
average
alue of l{
shouldbe
used
br estimating
K2.
The
proper
average
o use
s the harmonic
nrcon.not he arithmeticmean.For a log-nor-
mal distribution.
he
ratio of the
harmonic
o the
reciprocalof
the arithmetic
mean
s
=
exp
(h206')
(
10 .0 )
where he
harmonic
verage
br a og-normal
istribution
s:
g
l
=
I i /<11
xp
{-0 . :
tn
o .
)
l
r 1 0 , I I t
W :
- l
w
^b
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Sec.
10.4
Practical
esign
onsiderations
Toble
0.l
Gos-to-Cloth
Rotioso
cm/s)
427
Shaker/Woven
Reverse-AirAVoven
Pulse-Jet/Felt
Alumina
Asbestos
Cocoa,chocolate
Cement
Coal
Enamel
frit
Feeds, rain
Fertilizer
Flour
Fly
ash
Graphite
Gypsum
Iron
ore
Iron
oxide
Iron
sulfate
Leather
dust
Lime
Limestone
Paint pigments
Paper
Rock
dust
Sand
Sawdust
Sil ica
Soap,detergents
Starch
Sugar
Talc
Tobacco
Zinc
oxide
1 . 2 7
t . 5 2
1.42
1.02
l .2 l
1 . 2 7
1 . 7 8
t . 5 2
t . 5 2
1.02
1.02
1 . 0 2
t . 5 2
1.21
1.02
1.78
1.21
1 . 3 1
t .27
r . 7 8
1 . 5 2
1 . 2 1
1 . 7 8
1.21
1 . 0 2
1 . 5 2
1.02
t .2 l
t . 7 8
r . 0 2
4.01
5.08
6 . 1 0
4.07
4.01
4.51
' 7 . 1 1
4.01
6 . 1 0
',
<A
2.54
5.08
5.59
3.56
3.05
6 . 1 0
5.08
4.01
3.56
5.08
4.51
5.08
6 . 1 0
3.56
2.54
4.01
3.56
5.08
6.61
r 5 J
a Generally
afe
design
alues.
Source: rom
Turner
J
Reprinted 'ith permissionrom JAPCA.
H. e t a l .JAPCA.
i7 :7-19987)
t
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Chap:
0
Fabric
ilters
Sec.
Solutio
Tab
clor
l \
1 -
Co
\ , .
j e : :
10.4.2
of che :-.
chent i ; . .
k n i | .
r .
. .
Oh
pL l : t
; r
membr ' :
act ion :
th is r
r r '
_
Cott tn : - ,
t he
n r . . . : :
t a b r i c : : .
428
Solution
Table
10.
1
gives
v
=
Q/A,
=
2.5,1
m/s
br
filtration
of
fly-ash
n
pulse-jet
ilters'
Then,
he
netcloth
area
s
A,
=
(13
6)/(0'0254)
930
m2 '
For
conttnuouslv
operated
shaker
and
reverse-gas
leaned
ilters,
the
area
must
be
increased
o allow
tor
snuitin_l
lown
of one
or
more
compartments
or
cleaning
and
maintenance'
A typical
compartmenrr-,r.,
*.gr
0.3
m
in
diameter
nd
10.7
m
long,
with
the
number
of
bags
per
compartment
anging
rom'10
L O+S.
able
10.2
provides
a
guide
or adjusting
he
net
area
o
the
grossarea
br
these
\\
o t)'pes
of
baghouses.
ecause
ulse-jet
ilters
are
cleaned
on
line'
no addi-
tional
flltratron
area
s required,
and
he
net
and
gross
cloth
areas
re
equal'
t . 5
t .25
t . 1 1
1 . 1 2 5
1 . i l
1 . 1 0
1.09
1.08
1.01
1.06
1.05
1.04
Toble
10.2
Guide
o
Eslimofe
hqker
And
Reverse-Air
oghouse
Gross
Cloth
Areo
Net Cloth
Area
(m2)
Multiply
Net
Area
by
I
-170
z
3 7 1 - 1 , 1 1 5
t,16-2,230
) ) ? r - 1 1 5 0
3,351-4,460
4,461-5,580
5,58
-6690
6691-7 ,810
7,811*8,920
8921-10,040
t0,041-12.210
t2,211*16,130
> 16,730
ted
with
Permission
rom
JAPCA
Example
10.7
Gross
Cloth
Area
of
Reverse'Air
Baghouse
Estimate he grosscloth area equired or the conditionsof Example10'6 f a reverse-atr
baghouse
s
sPecified.
Exanrpl
l - .
: -_
So lu t io
T l -
-
l : - :
c u . ;
\ I ; : -
-
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Sec.
10.4 Practical esign onsiderations
429
Solution
Table 10.
gives
V
=
I .02cm/s
or fly-ash iltra tion n reverse-air aghouses.
hen. he
ne t
clotharea
equireds A,
=
(23.6X0.0102)
2,314
m2.From Table 10.2, he
sross
lotharea
i s
2 , 3 1 4 ) ( 1 . 1 7 ) =
. 7 1 0 r .
Comment
Notice that he reverse-air aghouse
equiresalmost hree imes as
much areaas he
pulse-
jet
to
process
he same
lue
gas
low rate.
10.4.2 iltermediq
The ypeof filter material sed n baghousesepends n the specific pplicationn terms
of chemical
composition f the
gas,
operating emperature.
ust oading,
and the
physical
an d
chemical
haracteristicsf the
particulate. varietyof fabrics. ither
eltedor woven
sometimes
kni|,
is
available.
he selection f a specif icmaterial.
weave. inish,or weight
s based
rirnarily
on
past
experience.
or somedilficult applications, ore-Tex.
polytetraf'luoroethylene
PTFE)
membrane aminated o a substrate abric
(f'elt
or woven) may be used.
Becauseof the
violent
action of mechanical hakers,
pun or heavy weight staple
yarn
fabrics are commonly
r.rsed.r th
this ypeof cleaning. ighter-weight
lament
arn
abricsareused
with reverse-airleaning.
The ypeof
materialwill limit the maximumoperating
as
emperature
br the baghouse.
Cotton abric s among he
east esistanto high em peratures
about
355
K) while
f iberglass s
the most esistant
about
530
K). Table 10.3
gives
he
maximum emperature
imits of the
eading
fabric materials.
Example 10.8 Fabric Filter for
Open-Hearth
Steel
Plant
(Licht
1980).
The flue
gases
rom an open-hearth
teel
plant
low at the
rate of I l0 m3/s
at 1,000K and
l0l .3 kPa with an ron oxides
articulateoadingof 0.0026
g/m3.The
watercontent f the
gases
s
87c.
Designa tabric i l ter
system o reduce he
particulateoading
f the -l lre
a'es
to thecorresponding
SPS.
Solution
The SPS 1'or
l r t iculate
r l is: ions
ronrsteel
lants
s 50
mg/dscm
:ec' . ih, le .1r .
t r
c l l -
;u l . i te heoreral l err t , r l . ' f ic iencr er lu i led.( ) l lectheactual ar t icLr l r teo.rJinStrdr 'y.
. i . r nJ .L rJ . , r n . i i t r i . r : .
1 .6 (
r
l . i l t
t r 0
t ) l r r l - - l r ]=
10 .3 - i l
t s /d \ c l l t
I t c , r e r r i l l i i i e
enc r
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430
Chap.
0
Fabric
ilters
Toble
10.3
Properties
f
Leoding
Bqghouse
Fobric
Moteriols
Fabric
Temp.u
K)
Acid
resistance
Base
resistance
Sec .1
that
dias
.\
ca1
( l l t t
a t I '
l 0 t
/ { . r .
n i h : :
l l f i . :
T; -
i .
i .
: '
n'.-
-
{ r j ' -
r -.:
Cotton
355
Creslanb
395
Dacronc
41 0
Dynel'
Fiberglasd
Filtron'
Gore-Text
Nomexc
,165
Nylonc
36 5
Orlon'
400
Polypropylene
36 5
Teflon' 505
Depends
n backing
Depends
n backing
3,15
-530
-105
Dependsn
backing
Poor
Good
Good
Excellent
Fair-good
Excellent
Fair
Fair
Excellent
Excellent
Excellent
Very
good
Very good
Very
good
Fair
Fair-good
Very
good
Excellent
Excellent
Fair-good
Excellent
Excellent
Wool
365
Very
good
Poor
"
Maximum
continuous
operating
emperature.
b
American
Cyanamid
egistered
rademark.
c
Du Pont
registered
rademark.
d
Owens-Corning
iberglass
egistered rademark'
e
W.
W. Criswell
Division of
Wheelabrator-Fry
nc.
r
W
L. Gore
and Co.
registered
rademark.
Source:
From
Turner J.
H. et
al.JAPCA,
37
749
(1987).
Reprinted
with
permission
rom
JAPCA.
is 11,
=
(10,352
50y10,352
0.9952
99.52E;).
his eff iciency
s within
the imits
achiev-
able
by a
properly designed
abric
filter. However,
he
temperature
f the
gases s well
above
he operating
imits of available
abric
materials.
A
precoolingsystem
s required,
ut
a fabric
to
operate s
hot as
possibleshould
be
sought.
Table
10.3shows
hat
iberglass
agscan
operate
ontinuously
at temperatures
p
to 530
K. Previous
experience
hows
hat
iberglass
ilters
can remove
ron oxides
dust with
effi-
ciencies
higher
han 99.67o
n sonic-assisted,
everse-air
aghouses
at
an
air-to-cloth
atio
of
| .21 cm/s
(Licht
1980).Choose
iberglass
agsat
an operating
emperature
f
530
K.
There
are,
basically,
hreealternatives
or cooling
he
gases o 530
K:
(l)
dilution
with
ambient
alr;
2)
evaporation
f a water
spray
nto
the
gas and
(3)
cooling
n
a waste
heat
boiler.
Dilution
with ambient
air will
more
han riple
the
filter area
equired,
while
evapo-
rative cooling
will increase
t by
about30Vo
see
Problem
10.
0). They
both
waste
he
pre-
cious
hermal
energy
contained
n the
gases.A waste
heatboiler
recovers
lose
o 507o
of
t : :
l i
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Sec.
10.4
Practical
esign
onsiderations
431
that
energy
with
no penalty
n
terms
of
filtering
area
equired.
igure
10.5
s
a schematic
diagram
of
the proposed
ystem.
Assume
hat
he
waste ases
ehave
ike
air
(p
=
it.:S2+
kg/m3,
Cp
=
l.0g
kj,/kg_K)
nd
calculate
he
enthalpy
hange
hey
experience
n going
iorn 1,000K to 530 K: AH* =
( l l 0 ) (0 .3524) (1 .08 ) (530-
1 .000)
-19 ,671kJ .Theenrha lpychangeo f
l kgo f
l i qu idwa te r
at
298
K
that
s
convertecl
o saturated
ream
t 445
K
(g30
kpa)
s Z,1AS.+
J.
Assurning
10Vo
nerf,y
osses,
he
amount
f sleam
roducecl
n
rhe
vaste
eat
boiler
s
(0.9t(19.677i
l(2'665'4)
=
6.64
kg/s
or 23,900
g/h.
To
estimate
he
heat-transfer
rea,
alculare
he
oga-
rithmic
mean
emperature
lifference:
LMTD
=
[(
1.000
4.15)
(-530
2gL]/1n(55-5/23t)
370
K.
Assume
hat he
overall
heat-transfer
oefTicient
s
300
Wm2-K.
The
heat-transfer
area
s
(19,677) l [ (0.3)( .310))
t ] t
mz.
The
gas
low
rate
entering
he
baghouse
s
(110X530/1.000)
-5g.3
m3/s;
he dust
oading
is
(0.0026)(
l0/58.3)
=
0.005
kg/m:.
For
a
gas-to-cloth
atio
of l .2l
cm/s,
hener
clorh
area
is
58'3/0 '0121
4.590
m2.
From
Table
10.2.
hegross
loth
area s
(
. l l
) (4,590)
5.
00
m2.
A
reasonable
esign
might
use 0 compartments.\'ith50 bags ercompartment ac h
0.3
m
diameter
nd
10.7
m long.
The
length
of the
filtration
time
depends
n the
nraximum
allowable
pressure
rop
through
he abric-dustcake.
ssume
hat.
or
thrs
case.
he
maximum
s
2.,5
pa
For
ro n
oxides
dust
on
fiberglass.
he paramcters
n
the firter
drag
moder-
Eq.
(10.5)-are
s"
-
142
Pa-s/m
nd
K2
=
l.2l
x
t06
s
I
(Lichr
9g0).
Then,
.5
=
(142)(0.012j)
(1.21
106X0.005X0.0121
21/1,000.
Solving,
='713
s
=
l2
minutes.
Saturated
team
.1'15
K
Water
298
K
Iron
oxides
dust
Figure
10.5
Vaste-heat
oi ler
of
Example
0.E
Waste
gases
1.000
K
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432
Chap.
0
Fabric
ilters
IO.5
COSTS
F
FABRIC
ILTRATION
Yourobjectivesn studying hissection re to
1.
Estimate
he
equipment
ost
of
the
most
common
baghouse
ypes'
2. Estimate
he
corresponding
CI .
3.
Estimate
he
TAC
associated
ith
fabric
filtration'
The
annualizecl
ost
of owning
and
operating
a
baghouse
an
be
very
high.
The
capital
cost
fbr
a fabric
f i l ter
system
can
be estimated
based
on the
gross
cloth
area'
The
cost
also
depends
n
the
type
of
baghouse,
whether
t is
made
of
stainless
r
mild
steel,
and
whether
or
not
it is
insulated.
Furthermore,
tandardized
modular
baghouses
re
ess
expensive
han
custom-built
units.
10.5.1
EquiPment
osf
Baghouse
equipment
costs
consist
of
two
components:
he
baghouse
unit
and
the
bags'
Both
costs
are
unctions
of the
gross
cloth
area,
Ac.
The
baghouse
nit
cost
s'
in turn'
comprised
of
the
basic
baghouse
ost
and
he
costs
of
"add-ons"
or stainless
teel
and
nsulation.
The
prices
for the
basic
unit
or
add-ons
are
inear
unctions
of
the
grosscloth
area
Vatavuk 1990),
E C
=
a +
b A ,
i l 0 . 1 2 )
where
a
and
b are
regression
onstants
isted
in
Table
10'4.
Notice
that
the
parameters
n Table
10.4
apply
only to certaingrosscloth area anges'
Table
10.5
gives selected
ag
prices
(in
$/m2)
br
pulse-jet,
shaker,
and
reverse-air
ag-
houses.
The
pulse-jet
bag
prices
n
Tabie
10.5
do
not
include
he
prices
of
protective
cages'
Mild
steel
cages
will
add
approximately
$13/mz
of
filter
area
June
1990
dollars).
Stainless
teel
cages
will
cost
about
$32lm2.
Example
10.9
Equipment
Cost
of
Reverse-Air
Baghouse
Estimate
he
cost
of the
reverse-air
aghouse
f
Example
10.8.
The baghouse
hell
material
can
be
mild
steel.
nsulation
s
required.
The
bags
should
be
0.3-m
diameter
with
sewn-in
snap ings.
Sec.
10 .
Toble
0
Baghouse
Shaker-inl
Shaker-:.,
Pulse-1et
Pulse-jet-
Reverse-
Custom-b
u
Prices
Reprinte
Solutio
For
me
Ba
Inr
Fo r
B a
,f
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Sec.
10.5
Costs
f Fabric iltration
Tqble 0.4 Porometers
or FobricFilterEquipment
Cosfso
433
BaghouseType Area Range m2
Component
a
Shaker-intermittent
370-1.-500
Shaker-continuous 370-5,600
Pulse-jet-common-housing
370-
500
Pulse-jet-modular 370-
I
,500
Reverse-air
930-7,500
Custom-built-alltypes
9,300-37,200
Basic ni t
stainless teel
Insulat ion
Basicunit
Stainless
teel
Insulation
Basic
n i t
Stainless teel
Insulat ion
Basic
n i t
Stainless teel
Insulation
Basicunit
Stainless
teel
Insulation
Basic ni t
Stainless
teel
Insulat ion
4,t20
14,000
2,200
43,800
29,100
0
l l ,280
t2 ,100
1.610
55.
40
29,300
3,500
34.200
r6.500
1,320
263,000
108,400
70.200
8+.6
l l . 9
.5.7
9 3 . 8
6 l . l
1 r 1
69.8
59.
n .1
92.0
81.1
2 6 . 1
88.i)
68 .5
r 0 . 0
69.3
28.1
8.0
o
Prices pdatedo June1990. ource:
rom
Turner .
H.
et al .JAPCA,37:1
05 1987).
Reprintedwith
permission
iom JAPCA.
Solution
For a reverse-airaghouse i th 930
<A,.<
,-500
2,Table 10.4
gives
he
bllor.ing equip-
ment costs:
Basic
unit: 34,200
(8UX5.100)
$483,000
Insulat ion dd-on:
.320
(
10X5.100)
S-52.320
For 0.3-mdiameter
iberglass ags
.r
th rings.Table
10.-5
sir
s
B a s s o s t :
1 2 . 2 ) ( 5 . 1 0 0 i =6 l . l l 0
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434
Chap.
0
Fabric ilters
Sec.
Tobfe10.5
SelectedBoq Prices
$
in
June l99o/mz)
Pulse et
Shaker
Reverse
Air
Material"
TRb
BBR.
Strapd Loop.
w/Ringsr
w/o Rings
PE
PP
NO
FG
TF
CO
5.1-13
5.5-7.-5
19.2-23.1
13.3--5 .9
83.8-
l
1
NA
-+.0-4.6
.1 .1J .9
r4.6-
.9
r
1 . 7 - 1 5 . 3
82.7-108
NA
5.7-5.8
NA C
20.1-21.2
9.3-12.2
NA
NA
4.0
NA
14.3-14.8
6.5-8.s
NA
NA
Solut i
T
l i
B
l n
r )
Il.l
10 .5
\ \ \ : .
-
Eram
So lu t i
5.6
5.9
15.7
NA
NA
5.5
5.1
s.6
14.5
NA
NA
4.8
a
Materials:
PE
=
polyester;
PP
=
polypropylene;
NO
=
Nomex; FG
=
Fiberglass
with
10%
Teflon; TF
=
Teflon
felt;
CO
=
cotton.
u,.
Bag removal
method:TR
=
top bag
removal;
BBR
=
bottom
bag removal.
d'"
Bag top
design. Prices
are
given
for
bagswith
and without sewn-in snap rings. c
Not applicable.
Ranges
shown reflect
different bag
diameters. ulse-jet
ag
diameters:
.1-0.2 m; reverse
air:0.2-0.3
m; shaker:
.13 m.
Source:
rom Turner
J. H.
et al . JAPCA,37:1105
1987).
Reprinted
with
permission
from
JAPCA.
Example
10.9
Continuation
The
equipment
ost s EC
=
483,000
52,320
62,220
$598,000
n
June 990.
Example
10.10
Cost of
Pulse-Jet
Baghouse
or Municipal
Solid Waste
(MSW)
Incinerator
The air
pollution
control
systemof
a
MSW
incinerator
onsists
f a spraydryer ollowed
by
a
pulse-jet
abric filter
(Frame
1988).The
flue
gas
entering
he baghouse
lows at the rate
of
35 m3/s
at 500 K and
1 atm and
contains ignificant
amounts
of HCl. A design
gas-to-cloth
ratio
of
0.025 m/s s specified
when
usingTeflon f'elt
bags,which are
extremely esistant
o
the harsh
environment revailing
n
the baghouse.
stimate
he
fabric
filter equipment
ost.
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Sec.10.5
Costs f Fabric iltration
435
Solution
The net
iltrationarea s
(35)/(0.025)
1,400
m2.Assuming hat hecleaning s done
on -
line, the
gross
iltration
area s also 1,400
m2 and a commonhousing
design s appropriate
Because f
the corrosiveconditions
and high temperature, tainless
teelconstruction nd
insulationare required.
The diameterof
the bags s 0. m, and hey
are of the top removal
type. Stainless teel
cagesare also equired.
The following table summarizes
he disburse-
ments hat comprise
he equipment
ost
or
this system.
Item
Cost
$
n June1990)
Basic
unit
Stainless
teel
add-on
Insulation
dd-on
Teflon f-elt
bags
Stainless teel ages
Equipment
ost
108,580
95,140
18,050
111,320
44,800
384.190
r0.5.2 CI
The total
capital nvestment s
estimated rom a series f factors
applied o the
purchased
equiprnent
ost o obtaindirect
and
ndirect
ostsof installatio n.
he TCI is the sumof these hree
costs. able 10.6 ives
he requiredactors.
Example
10.11 TCI for Reverse-Air
Baghouse
Estimate
he otalcapital nvestment
or thebaghouse
f Examples 0.8 and 10.9.Assume
that no
specialsite
preparation
r buildingsare needed. he
cost of auxiliary equipment,
excluding
hewasteheatboiler, s
$150,000.
Solution
From
Example10.9, he
equipment ost or thebaghouse-includ ing hebags is
Sr98.000. he
costof thewaste eatboiler
o
produce
3,900 g/h
of steam aturated t
r-+-5
(830
kPa)mustbe estimated. ased
n data
published
y Peters nd
Timmerhaus
199) . thecos to f
hebo i le r fb r s teampressuresup to.800kPacanbees t i r na ted f rom:
-
-
l
I
l \
l r
t \
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436
Toble10.6
Copitol Cost
Foclors or Fobric
Filters.
Chap.
0 Fabric ilters
Sec.1
Costs
Factor
Direct
costs
Purchased quipment ost
Fabric ilter,
plus
bags.
lus
auxil iary
equipment
Instruments ndcontrols
Taxesand ieight
Total
purchased
quipment ost
(B)
Installation irectcosts
Total direct costs
Indirect
costs
Totalcapital nvestment
A
0 . 1 0 4
0.08A
1 . 1 8
0 . 1 2 8 + S P o + B l d g b
1 . 1 2 8 + S P + B l d g
0.45
B
2 . 1 1 + S P + B l d g
shiti. \1.r
andNer. '
i n q l r i e , r '
1987b.
drop
thrrr
work
an.l
appro\rn
drag
coei
number
.
gas-to- .
is
abour
a shaker
w
here
boi ler e;
k P a .
r : .
recr ie;
ther r l :
.
r e p l a c r l
i l D C C . . : l - .
t h e u i r : .
Eramp
" l
* #
u
SP
=
sitepreparation.. Bldg
=
buildings.Source:From TurnerJ. H. et al.JAPCA,
37:l105
(1987).
Reprinted
with
permission
rom
JAPCA.
nc
=
qo(,;r)o
a
l,4oo< ,it,
ksh
<
18o,ooo
( 1 0 . 1 3 )
where
EC
=
cost
of
the
boiler,
n
June
1990
m
=
rate of steam
generation,
g/h
The costcalculatedwith Eq.
(
10. 3) is for
a complete
package
oiler
plant,
which includes
feed-water eaerator, oiler f-eed umps,chemical njection system,and stack.For a rateof
steam
roduction
f 23,900 g/h ,Eq.
(10.13)
ives
a boilercost
of
$190,500.
rom Table
10.6,
=
598,000
190,500
150,000
$938,500.
he
purchased
quipment ost s B
=
I 18A
=
$1.107,400.
CI
=
2.11B
=
$2,403,000
in
June1990).
r0.5.3
AC
Direct annual costs nclude operatingand supervisory
abor, replacement ags,
mainte-
nance abor and materials,
utilities, and dust disposal. Indirect annualcosts nclude capital ecov-
ery,
property
ax, nsurance, dministrative osts,and overhead.
Typical operating abor requirements re 2to 4h
per
shift
for
a wide
rangeof filter sizes.
Supervisory
abor s
taken as
157o
of operating abor. Maintenance abor varies rom I to 2 h
per
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Sec.10.5
Costs f Fabric il tration
437
shift.Maintenance
materials
ostsare
assumedo be
equal o maintenanceabor
costs
Vatavuk
and
Neveril
1980). he rr-rajor
eplacenent aft
tems
are ilter
bags,
which
have
a typicaloperat-
ing life
of
2
yr.
The bag replacement
abor s
approximately
2.00/m:
of bag area
Turner
et al.
r
987b).
Electricpower is required o operatesystem 'ansand cleaningequipment.The pressure
drop through
he system s
the sum of the
pressure
rop
through he baghouse
tructllreand
duct-
work
and he
tubesheet
ressure
rop. The
contribution
of the baghouse
tructureand ductwork rs
approximately
kPa. The
tubesheet ressure
rop is estimatedwith
Eq.
(10.3)
when
the f l l ter
drag
coefficients
are
known.
Cleaning
energy or
reverse-air ystems
an be calculated iorri
the
number
of compartments
o be
cleaned t one
ime
(usually
ne.sometimeswo),
and he re\ierse
gas-to-cloth
atio
(tiom
one o two times
he forward
gas-to-cloth
atio). Reverse-air ressure
rop
is
about1.7kPa.The
reverse-airfan enerally
uns
continuously.
ypicalenergy
onsumptionor
a shaker
leaning
ystem anbe
estimatediom
(Turner
t al. 198.1b):
l A /
- A
( z t A - 5 , r
r r
\
-
u . J
-
t v n l
( r0 . r4 )
wnere
lV.
=
power.
n kW
A.
=
grosS
loth area. n ml
Cooling
process
-sases
o acceptable
emperatures y water
evaporation r in
a
waste
heat
boiler require
plant
water. Pulse-jet
ilters
use compressed
ir at
pressures
f about -500 o 800
kPa.
Typical
consumptions
about2 standard
3/1,000
ctualm3. f the collected
ustcan not be
recl 'cled
r sold, he
costs br final
disposalmust
be ncluded.Disposal
ostsaresirespecific.
ut
they are ypically
about
$30 to
$50/metric
on including
ranspofiation.
Capital recovery
costsare basedon
the total depreciablenvestment
ess he
cost of
replacing
he
bags.The if'etime
f the abri c ilter
system s typically20
yr.
Property
axes. nsur-
.rncc.
ord administrative
hargesare about 4c/c
f the TCl. The
overhead s calculated
as 60% of
ihe sumof al l laborand he maintenance aterials.
Example
10.12TAC for Reverse-Air
Baghouse
Estimate
he TAC for the baghouse f Example
10. 1. The systemoperates ,640h/;-r.The
operatingaborrate
s
$12lh,
he maintenance
aborrate s
$15/h.
The costof electricitl s
$0.06/kW-h,
process
water
costs
$0.26lmetric
on. The
dust
recovered
an
be returned o
the
process
t
no
additional ost.The recovery
redit
br
the
waste-heat
team
s
Sl/nretlic on
The
pressure
rop hrough
he
uasteheat
boiler s 2 kPa.The minimumattracti\e ateof
return s lZc/clyr',
he sr:tenr
it'etine
s l0
vears.
he rnechanical
fficiencroi
the ans s
65%.
ilhrffrid',
A
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438
Chap.
0 Fabric ilters
Solution
Table 10.7
gives
he direct
and
ndirect
annualcostsas calculated rom factors
given previ-
ously.To calculatehe annualized
ostof
replacing
heba-es,
he otal
cost
of
replacement,
including abor, axes,and reightmust be estimated. he cost of purchasinghe bags s
multiplied by a factor ol 1.08
o account
or
taxesand reight. The
cost
of replacementabor
is
estimated t a
rate
of
$2/mr
of filtering area.The
capital ecovery actor for a 2-yr
life-
t imeand
=
O.l2lyr s 0.592.
To
calculate
he
electricitycost o operate he main fan,
the total
pressure
rop through
the system
must
be estirnated.rornExample10.8,
he maximum ubesheet
ressure
rop s
2.5 kPa.The otal
pressure
rop
ncluding
he waste eatboiler, s
6.5
kPa.Assuming
ha t
the fan is locatedat the entrance
fthe baghouse,he
gas
low rate
hrough he
fan is 58.3
m3/s. herefore,he
power
o opelate t is
(58.3)(6.5X0.65)
583 kW. A reverse-air-a n
will
operate ontinuouslyo cleanone
out
of
10)
compartment t a time.The reverse
as-
to-cloth atio is equal
o the
forward
gas-to-cloth
atio: 0.0127m/s.The reverse
ir
f-low s
(5,100)(0.1X0.0127)
6.48mr/s.The
corresponding
ressure
rop s 1.7kPa, herefore,he
power o operatehe everse-airan s (6.18)(1.7X0.65) 17 ryy.
The capital ecovery actor
(0.
34)
for
the depreciablenvestment orrespondso a life-
t ime
of 20
yr
anda minimumattractiveate
of
return
of 12 Volyr. s usualwhencalculating
the capital ecoverycost,
he otal cost ofreplacing the bags s
subtracted
rom the total
depreciable
nvestment
o avoid
doubleaccounting.Because he recovered ust can be
returned o the
process
t no additionalcost. here s no
cost associated
ith final
disposi-
tion
of the solid
residue.
There s a substantial ecovery
credit br the wasteheatsteam,
which
helps o
partially
offset he annualcosts.The total
annual
cost br
the
system s
$504,800.
he
otalamount f
particulate
emoved
s
(0.0026)(
l0)(3,600)
8,640X
,000)
=
8,900
metric
ton/yr. Therefbre, he cost
efTectivenessf the system s
$56.7/metric
on of
dustcollected.
r
0.6coNcLUStoN
Fabric filtration
s rapidly becomingan
accepted nd frequently
preferredparticulate
mattercontrol echnology. nterest
n baghouses
ill
continue
ncreasing
s air crniss ions
tan-
dardsbecomemore stringent
and concernsover fine
particulates
ncrease. hey
are
gaining
acceptance
or
usedownstream f dry FGD s),stems
nd
'luidized
edboilers. he baghouse
ro-
vides additionalSO2 emoval.
and
particulate
ollection s not
affectedby the
high
alkali
content
of the
products
of dry SO2 emoval.The relative nsensitivity
of f'abric ilters to
variations
n dust
electric resistivity makes hem more
attractive han ESPs n many applications.ElectricuLly
enhancetl
fabric ilters,
an
emerging echnology, perate t higher
gas-to-cloth
atios han conven-
tional baghouses, nd at greatly educedpressure rops.
Sec.
Toble
DAC
Oper
Supe
- \ t a tn l
L"
Repl
U t i l i r
r '
f , - -
P r
Total
D
\
IAC
Or
e : :
Prope:
Capr i . .
> -
Total
\ [
Recor
: ,
T.{C
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Sec.
10.5 Costs
f
Fabric
iltration
439
Toble
10.7
AnnuolCosts
or he
Fqbric
Filter f
Exomple
0' 2
DAC
Operating
abor:6
x
360
x
$12
=
Supervisoryabor:0.15 25,900=
Maintenance
L a b o r : 3 x 3 6 0 x $ 1 5 =
Materials
Replacement
arts,
ags:
$62,200
1.08
+
$2
x 5,100)
0.592
=
Utilities
Electr icity:
583
+ 17)
x
8,640 $0.06
=
Process
water
or boiler:
23.9
x
8,640
x
$0.26
=
Total
DAC
IA C
Overhead:
25,900
3,900
+ 2
x 16,200) 0.60
=
Property ax,
nsurance,
dministration:
.04
x
$2,403,000
Capital
ecoverycost
($2,403,000
$2
x
5,100
$62,200
1.08)
0'134
=
Total
IAC
Recovery
credit
or
wasteheatsteam:
23.9
x 8,640
x
$2
=
TAC
Sl-\ .900
-r.900
16.100
16.100
4 5 . 8 r 0
31
,000
53,70t)
$412,100
37,300
96,120
3
1,6,10
$44s,100
$413.000
$s04.800
r)
,'
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442
Chap.
10
Fabric
ilters
PROBLEMS
The
problems
at
the end of each
chapter
have been
grouped into
four classes
designated
by a superscript
after the
problem
num-
ber)
Class
a: Illustrates
direct
numerical
application
of the
formulas
n the
text.
Class
b:
Requires lementary
nalysis
f
physical
situations,
ased
on
the subject
material
n the chapter.
Class :
Requires
omewhat
more
matureanalysis.
Classd:
Requires omputer
olution.
10.lu. Effect
of the
gas-to-clothatio
on
penetration
If the
gas-to-clothatioof
Example
0.1ncreaseso 0.015
m/s, alculate
he
aver-
age verall
enetrationor
a
20-min ycle.
Artsu;er:
.65Vo
10.2b. Effect of
operation cycle
ength
on
penetration
Determine
he operation
ycle
ength hat
reduces he
average
verall
penetration f
Example
0. to
| 07
Answer:
36 min
10.3c.
Penetration and
pressure
drop
through
a fabric
filter
The filter drag
parametersbr the
fly-ash and
abric combination
of
Example
10.1
are,S"
100kPa-s/m
nd
K2 106 -I. Choose
gas-to-clothatioandoperation
im e
such hat the
average verall
penetrationor
the
cycle does
not exceed
1.IVa
and he
pres-
suredroo does
not exceed
.5
kPa.
Prob l
10..1.
( e
(
0 . l
r
r
where
.r, I
\ { r
- \ l \ .
( b
Teras
U
compa
than-er
sonabl i
operati
was
me
1 9 8 9 ) .
Dpi
r
*m
F
0.05
0.08
0 .10
0.20
0.30
0.40
0.60
Est
whether
morphol
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Problems
10.4c.Alternative
form
of the
morphology factor
(a)Show
hat an alternative xpression
or the morphology actor definedby'
Eq.
(10.2)
s
443
,=+ ,
o'l'= vtco
where
;r; s the mass raction collected
n
chanel
MGD
=
mass-weighted
eometric
meandiameter
(b)The
Monticello GeneratingStation
s
a coal-fired
power plant
operated y
the
TexasUtilities GeneratingCompany
Felix
et al. 1986).Part of the
flue
gases o
to a 36-
compartment
hakerbaghouseor
particle
emoval.The baghouse xperienced
igher-
than-expected
ressure
ropsand
arge
penetration
pikes,even hough
t
operated
t rea-
sonably low gas-to-clothatios. n an effort to find an explanationo theseunexpected
operational
roblems,
samples f the fly ashwere analyzed.
he specificsurface
area
was measured t 0.85
m2lg and he true
particle
density at2,420
kg/m3
Vann
Bush et al.
1989).The ollowing able
gives
a typicalsize
distribution nalysis.
Dpi
(pm)
MassFraction
DpiQtm)
Mass Fraction
0.02
0.05
0.08
0 .10
0.20
0.30
0.40
0.60
5x10 :
2x l } t
1 .6 10+
0.0010
0.0008
0 .0010
0.0070
0.0100
0.80
2.00
5.00
7.00
10 .0
20.0
50.0
70.0
0.0503
0.0600
0 .1500
0.3540
0.2640
0.1020
0.0010
8x10s
Estimate he value of the morphology actor
or
the
Monticello
fly-ash and discuss
whether he operational
roblems
experienced
an be explained
n termsof the
particle's
morphology.
Answer:
M
=
2.22
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444
Chap.
0
Fabric
i l ters
10.5a.Morphology
of
particles
from
atmospheric fluidized-bed
combustor
(AFBC)
The
TVA atmosphericluidized-bed
ombustor s
a 20 MW
power plant,
which
burns
eastern ituminous
coal.
The
flue
gases
low
througha reverse-air
aghouse
or
particle emoval.The f1y-ash as he following properties: rue density,2,620 g/m3;spe-
cific surfacearea,11.44
ml/g; mass
geometric
meandiameter,
.0
pm.
Estimate he mor-
phology
actor or
this f1y-ash
see
Problem
10.4).Do
you
expect
penetration roblems
owing
o bleed-through?
Answer : L5
10.6b.Filter
drag model
parameters
estimation
Estimate he
parameters
n Eq.
(10.4)
based n
the ollowing estdata.
Gas-to-clothatio
=
0.013m/s
Inlet
dust
oading
=
0.005kg/ml
10.9b.
A
l q r - I
:
0
I
I
:
l
Probl
Sh
geometr
( b t l
mean.
( c t I
Time
min)
5 10
15
20 25
AP
(kPa)
0.33
0.49
0.55
0.60 0.64
Ansvyer:Kt
=
I .96 x 105 s-1
10.7a.Maximum
and
average ubesheet
pressure
drops
The fabric
filter
of
Problem
10.6
operateswith an nlet
dust oading of 0.01 kg/m3.
The filtration
time is I h. Estimate
he maximum
and average
ubesheet
ressure
rops
during the filtration
time.
10.g"
Tirbesheet
pressure
drop
in
a
pulse-jet
baghouse
Ansvver: P'"*
=
1'58
Pa
A
pulse-jet
baghouse
sesDacron elt
bags
or
the control
of
fly
ashemissions. he
gas-to-cloth
atio
s
0.030
m/s
and he nlet
dust oa ding s
0.02
kg/m3.
The bagsar e
cleaned
t lO-min ntervals
with
pulses
f air at 690 kPa
gauge.
f
K2
=
2.0
x
l0: s
r,
esti-
mate
he
maximum
ubesheet
ressure
rop.
Answer:2.61kPa
0.70
10.10b.
( a t l
298
K. e
the mean
effectof I
( b r
cooled
r
10.11b.
Th .
into
a
r
a: '
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Problems
10.9b.
Areal density
distribution
in
a baghouse
(a)The
ollowine areal
densitv istribution ataweremeasuredn a bashouse:
Areal
density
{2,
g/m2)
Cumulat ive
ercent
ess han
l
445
0.56
0.11
l . l 0
1 .60
2.40
4 .10
I
-5
20
,5 0
80
98
Show hat thesedata ollow
a
log-normal
distributionand estimate he medianand
geometric
landard
eviat ion
(b)
Estimate he ratio
of the harmonicmean o the reciprocalof the arithmetic
mean.
(c)
Estimate hearithmeticmeanof the distribution
Answer:
L
l8
Answ'er: .71 kg/tn2
10.10b.Precooling of waste
gases
upstream of
fabric
filters
(a)
f the waste
gases
f Example10.8
are
precooled
y dilution
with
ambient
ir at
298 K,
estimatehe
volumetric
low rateof the
gases
t the baghouse
nlet.Assume hat
the
mean
heatcapacity f air n the ange298 o
530
K is 1.02 J/kg-K.Neglect he
effectof heat osses.
Attsv'er: 83 f/.s
(b)
Estimate he flow rate
of
the waste
gases
t the baghouse
nlet if they are
pre-
cooledby evaporation f waterat 298 K.
Art: t et ' ; 74.8
tt t l / . t
10.11b.Baghouse eat
exchanger
The
J.
E. BakerCompany f York,Pennsylvania
rocesses
olomitrc
imestone
into a varietyof agricultural nd ndustrial
roducts
Krout,
B.. and
Kilheffer.
. JAPCA.
r)
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446
Chap.
0
Fabric
ilters
3l:293,1984).
They operate
wo
rorary
coal
and coke-fired
kilns.
In 1978,
hey fined
Numer
One
kiln
with
a fiberglass
everse-air
aghouse
or
particulate
matter
control.
The
system ncluded
a heat
exchanger
o lower
the
exhaust
as
emperature
rom
756 K to
533
K before
entering
he baghouse.
he cooling
luid
is ambient
air
which enters
he
heatexchanger t 300 K and eaves t 590K. Theunit hasa heat-transferreaof1,374
m2 or
an nlet
flow rate
of 56.7m3/s.
Estimate
he overall
heat-transfer
oefficient
or
the unit.
Assume
hat the
exhaust
gases
ehave ike
air.
Answer:23
W/m2-K
10.12".
Gross
cloth area for
a
reverse-air
fabric
filter
Estimate
he
gross
cloth
area or
the reverse-air
aghouse
f Problem
10.11.The
particles
coming
out
of the kiln
are
a mixture
of lime
dust
and ly-ash.
Answer: ,400
m2
10.13a.
Cloth area for
a
pulse-jet
baghouse
The
exhaust
ases
rom
a cement
plant
flow
at
the rate
of 130m3/s
at 500 K.
Calculate
he net
cloth
area or
a
pulse-jet
baghouse
o remove
he cement
dust.
Assume
on-line
cleaning
f
the bags.
Answer:
,190
m2
10.14u.
Reverse-air
baghouse
or
a coal-fired power
plant
Consider
he
coal-fired ower
plant
of Example
5.1.The plant
will
consist
f two,
150-MW
boilers.
Design
a
reverse-air
abric
filter
for
eachboiler
to remove
at least
99
percent
of the fly
ash n
the flue gases.
he
bagsare
0.3 m in
diameter
and 10.7m
long.
There
are 120
bags
per
compartment.
pecify
he
gross
cloth
area
and he number
of
compartments
or
eachbaghouse.
Answe 22
compartments/unit
Probl
10.15b.
Ac
tion
with
and mat
where
T/
T
(-
N,I
C
0.1 6
Flour
Tobacctr
Grain
Sari ust
E : t
open-h
1 9 8 0
.
l0 . l6h .
T l -
-
I t - -
dn' ing
L
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448
Cha p. 0 Fabric il ters
fuel savings
are approximately
100,000/yr.
he annual
operationand maintenance
expenses
f the
heat
exchanger
re
$20,000/yr.
Estimate
he
profitability
ndex for
the
capital nvested
n the heatexchanger.
ssume hat
he useful ife
of the unit
is 15
yr
with
no salvage alue.The
following equation
an be
used o estimate he cost of heat
exchangersVatavuk,W. M. andNeveril,R. B. Chemical ngineering,p)2g,July 12,
1982):
rc= r4.84A-o' ' '
"*p[o.oozz(ni lz)
where
EC
=
cost n 1978
dollars
A
=
heat-transfer
rea,m2
Assume
hatTCI
=2.34
EC.
10.17^.
TCI for
a
fabric
filter system
Estimate
he total capital
nvestment or
the
fabric
filter
systemof Problem 10.14.
Because he fabric
filters will
be
ocated
upstream
f the FGD
system, he flue
gases
re
acidic
at this
point,
which mandates
tainless
teel abrication.
At the temperaure f
oper-
ation
(530
K)
insulation s required
and he
bagsmust be made
of
Fiberglass.
he cost
of
auxiliary
equipment or
eachbaghouses
$300,000.
Answer:TCI
=
$19.9
millions n
June
1990
10.18b.
TAC
of a
reverse-gas
aghouse
Estimate he total
annual
costsand he cost effectiveness
$/metric
on)
for
the bag-
housesystemof Problem10.17.The systemoperates ,640Wyr.The operatingabor rate
is
$25lh,
he maintenance
abor rate
s
$28lh.
The
cost of
electricity
s
$0.06/kW-h;
he
total
pressure
rop through he
system s
5
kPa. The
cost of final fly-ash
disposal
s
$20lmetric
on. The minimum
attractive ate
of return s
lT%alyr; he system ifetime is
20
yr.
The mechanical
fficiencyof the fans s
65
percent.
Answer:
$77/metric
on
10.194.
CI for
a MSW incinerator
pulse-jet
aghouse
Estimate
he otal
capitalnvestmentor
thebaghousef
Example
0.10.
ssume
Probl
that he
t ion s
n
10.20"
I n
control
o
conside
is capa
Proble
tubeshe
s-l and
a
20 r'r. e:
$
15,4r
n
process
$7.00/
t
( a t
( b t
( c
Ch
merit.
C
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Problems
449
that he
cost of the
auxiliary
equipment s
$90,000.
No
buildingsor specialsite
prepara-
tion s
needed.
Answer:
$1,214,000
n
June1990
10.20c
Design
of a
pulse-jet
filter
for
a
Portland
cement kiln
In Problem
8.17,a multiple
cyclone system
was
designed s a
precleaner
or the
;ontrol
of
particulate
missions rom
a Portland
cementkiln.
For each
of
the alternatives
:onsidered
n
that
problem,
design
a
pulse-jet
abric
filter
such hat he combined
system
rr
capable
f satisfying
he
particulate
NSPS or
the source.
Use the correlation
of
Problem
10.15
o estimate
he
gas-to-cloth-ratio
or
eachalternative.Assume
hat he
:.-ibesheetressure
ropcan
be calculated
rom Eqs.
10.7)
o
(10.9),
with
K2
=
1.5
x
105
.-
and
a
cleaning
nterval
of 10
min. The lifetimes
of the bagsand system
are2
yr
and
it) r r. respectively, ith no salvage alue.Operatingand maintenanceabor ratesare
>1,s,tr
nd
$20lh,
respectively.
he dust
collected n
both devices
can be
recycled
o
the
::ocess
at no additional
cost.
Compressed
air
(dried
and iltered)
is availableat
)-.00/1,000
standardm3.
For each
aTtemative,
pecify he ollowing:
(a)
Total iltration
area
lb)
Filter
media,
numberand
dimensions
f the
bags
tc) TCI
and TAC
of the combined
multiple
cyclone-fabric ilter
system.
Choose
between he
threealternatives
uggested
asedon the EUAC measure
f
-
::rI.
Compare
our
results o
those f Problem
.22.
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