-&EPA
Air Pollution Training Institute
MD20
Environmental Research Center
Research Triangle Park, NC 27711
EPA 450/2-82-005
April, 1982
Mir
APTI
Course Sl:412
Baghcuse Plan Review
Student Guidebook
-------
-------
United States
Environmental Protection
Agency
Air Pollution Training Institute
MD20
Environmental Research Center
Research Triangle Park, NC 27711
EPA 450/2-82-005
April, 1982
Air
APTI
Course Sl:412
Baghouse Plan Review
Student Guidebook
Written and designed by:
David S. Beachler
Marilyn Peterson
Northrop Services, Inc.
P.O. Box 12313
Research Triangle Park, NC 27709
Under Contract No.
68-02-3573
EPA Project Officer
R. E. Townsend
United States Environmental Protection Agency
Office of Air, Noise, and Radiation
Office of Air Quality Planning and Standards
Research Triangle Park, NC 27711
-------
Notice
This is not an official policy or standards document. The opinions and selections are those
of the authors and not necessarily those of the Environmental Protection Agency. Every
attempt has been made to represent the present state of the an as well as subject areas still
under evaluation. Any mention of products or organizations does not constitute endorse-
ment by the United States Environmental Protection Agency.
Availability
This document is issued by the Manpower and Technical Information Branch. Control
Programs Development Division, Office of Air Quality Planning and Standards. USEPA. It
was developed for use in training courses presented by the EP A Air Pollution Training
Institute and others receiving contractual or grant suppon from the Institute. Other
organizations are welcome to use the document.
This publication is available, free of charge. to schools or governmental air pollution
control agencies intending to conduct a training course on the subject covered. Submit a
written request to the Air Pollution Training Institute. USEPA. MD-20. Research Triangle
Park. NC 2771l.
Others may obtain copies. for a fee. from the National Technical Information Service
(NTIS). 5825 Pon Royal Road, Springfield. V A 2216l.
Sets of slides and films designed for use in the training course of which this publication is
a pan may be borrowed from the Air Pollution Training Institute upon written request.
The slides may be freely copied. Some films may be copied; others must be purchased from
the commercial distributor.
ii
-------
Table of Contents
Page
Lesson I. Course Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-1
Course Description. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... I-I
Course Goal and Objectives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. .............. I-I
Lesson Titles. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . I- 2
Requirements for Successful Completion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-2
Materials. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1- 2
Use of the Guidebook. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2
Instructions for Completing the Final Examination. . . . . . . . . . . . . . . . . . . . . . . . . . . . .1-3
Lesson 2. Fabric Filtration Operation and Baghouse Components. . . . . . . . . . . . . . . . . . .2-1
Lesson Goal and Objectives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-1
Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-1
Collection Mechanisms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 - 2
Bag Designs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4
Baghouses [[[ .2-5
Positive and Negative Pressure Baghouses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 - 7
Filtration Designs. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-8
Baghouse Components. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2-11
Lesson 3. Fabric Filter Material. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-1
Lesson Goal and Objectives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3.1
Filter Construction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1
Fibers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-4
Fabric Treatment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-6
Bag Failure Mechanisms. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-8
Gas Conditioning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-8
Lesson 4. Bag Cleaning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-1
Lesson Goal and Objectives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-1
Cleaning Sequences. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-1
Types of Bag Cleaning. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-2
Bag Cleaning Comparisons. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-10
Lesson 5. Baghouse Design Variables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-1
Lesson Goal and Objectives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5-1
Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1
Pressure Drop. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. ..........5-1
Filter Drag. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. ....... .......... 5-4
Filtration Velocity: Air-to-Cloth Ratio. . . . . . . . . . . . . . . . . . . . . . . . . . .. ...........5-6
Collection Efficiency. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 - 7
Lesson 6. Baghouse Design Review. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-1
Course Goal and Objectives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-1
Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1
Review of Design Criteria. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6-2
Typical Air-to.Cloth Ratios. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . " ........ .6-5
-------
....... .
Page
. . . ..7-1
.7-1
. . . . .7-1
. . . . . . . .7.2
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7-2
. . . . . .. .7-2
. . . . . . . . . . . . . . . . . . . . .7-8
.7-9
. . . . . .7-10
.. 7-11
. .7-13
. .7.14
. .7-16
.......... .
LesIOn 7. Baghowe Operation and Maintenance. . . . . . . . .
Lesson Goal and Objectives. . . . . . . .
Use of the Slide/Tape. . .
Suggested Readings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Baghouse Capacity.
Installation. . . . . . . .
Operation and Maintenance Training. . . . . . . . . . . . . .
Baghouse Stanup and Shutdown. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Routine Monitoring. . . . . . . . . . . . . . . . . . . . . . . . . . .
Routine Maintenance. . . . . . . . . . . . . . . . . . . .
Bag Maintenance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Troubleshooting. . . . .
Spare Pam......
........ .
............ .
....... .
...... .
............... .
....... .
....... .
........ .
....... .
...... .
........ .
...... .
....... .
........ .
....... .
...... .
......... .
......... .
........ .
. .8-1
. .8-1
.8.1
. .8-4
.8-8
LesIOn 8. Induatrial Applications of Baghouaes .........................
LesIOn Goal and Objectives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Dry Sulfur Dioxide (SOl) Control Systems. . . . . . . . . . . . . . . . . . . . . .
Capital and Operating Cost Estimations. . .
......... .
....... .
........... .
LesIOn 9. Design Criteria for Permit R.eview: Problem Set. ... . ... . . . . . . . . . . . . . .
Lesson Goal and Objectives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Example. . . . .
Solution. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Review Exercise. .
Solution. . . . . . .
............ .
........ .
....... .
.......... .
. . . .9-1
. .9-1
.9.1
. .9.1
.9.2
... . ..... ... . ..9-4
. . . . . . . . . . . .9-5
......... .
.......................... .
....... .
........ .
........ .
R.eferences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . R.-I
Appendix. Slide/Tape Program UBaghowe Operation and Maintenance" ... . . . . . . . . A-I
iv
-------
Lesson 1
Course Introduction
Course Description
This course is designed for engineers and other technical per-
sonnel responsible for reviewing plans for installations of fabric
filtration air cleaning devices. The course focuses on review
procedures for baghouse devices used to reduce particulate air
pollution from industrial sources. Major topics include:
General baghouse description
Bag cleaning methods
Fabric selection and filter types
Design parameters affecting collection efficiency
Operation and maintenance problems associated with
baghouses
Course Goal and Objectives
Goal
To familiarize you with the steps for evaluating a fabric
filter air pollution control device used to control particulate
emissions.
Objectives
Upon completion of this course, you will be able to:
1. recognize a baghouse and briefly describe its operation.
2. briefly describe the collection mechanisms for particle col-
lection by a bag.
3. name two types of filter construction used for bags.
4. recognize three ways to remove dust particles from the
bag.
5. recognize seven types of fibers used in making fabric filter
material.
6. identify the key design parameters influencing collection
efficiency.
7. recognize typical operation and maintenance problems
associated with baghouses.
1-1
Figure 1-1. Typical baghou.se.
-------
Lesson Titles
Lesson I:
Lesson 2:
Course Introduction
Fabric Filtration Operation and Baghouse
Components
Fabric Filter Material
Bag Cleaning
Baghouse Design Variables
Baghouse Design Review
Baghouse Operation and Maintenance
Industrial Applications of Baghouses
Design Criteria for Pennit Review: Problem Set
Lesson 3:
Lesson 4:
Lesson 5:
Lesson 6:
Lesson 7:
Lesson 8:
Lesson 9:
Requirements for Successful Completion
In order to receive 2.0 Continuing Education Units (CEUs) and
a cenificate of course completion. you must:
1. take one mail.in fmal examination.
2. achieve a final course grade of at least 70% (out of
100%) which is based on the final exam.
Materials
51:412
51:412
Guidebook "Baghouse Plan Review"
Lesson 7 slide/tape program, "Baghouse Operation and
Maintenance"
Final exam; approximately 50 questions
51:412
Use of the Guidebook
This guidebook directs your progress through the text material
and the slide/tape presentation for this course. This first lesson
introduces the rest of the course material and explains how to
use it. Lessons 2 through 8 are self. paced in a text fonnat that
provides review exercises for sections of each lesson. To com-
plete a review exercise, place a piece of paper across the page
covering the questions below the one you are answering. After
answering the question. slide the paper down to uncover the
next question. The answer for the first question will be given
on the right of the page separated by a line from the second
question (Figure 1-2). All answers for review questions will
appear below and to the right of their respective questions.
The answers will be numbered to match the questions. Please
do not write in this book. Since the answers you give are for
your information only, use the paper you cover the answers
1-2
Review Exercise
1. Question IClIIIII
1111. diu ~IIClIIIIIII
2. Questionll!. 11111
I. IIlIlUII~I( II
1. Answer
111111
3. Question 1 III lell 2. Answer
III 1111. diu ,,111111
Figure 1-2. Review exerciJe format.
-------
with or a scratch sheet to write on. Complete the review exer-
cise for each section in each lesson. If you are unsure about a
question or answer, review the lesson section preceding the
question. Then proceed to the next section.
Lesson 9 is a baghouse design problem. One example
problem will be described and the calculations necessary to
complete it will be covered. Then another problem will be
presented for you to complete. The solution to this problem
will be included. Lesson 7 contains a slide/ tape presentation
that will preview the major topics on baghouse operation and
maintenance presented in Lesson 7. You do not need to follow
the script as you view the slides; however, you can use it to
review the content. * The audiotape is designed to automa-
tically advance the slides at the correct place in the script if
your tape recorder has a mechanism for synchronizing
audiotape and slides. To use the slides and tape together,
ad vance the slides to slide 7 -1-1, a focusing slide . Focus this
slide and stan the tape. The tape recorder will advance the
slides for you.
*The script is included in the appendix.
Lesson Content
Lessons in this guidebook contain the following information:
. lesson goal
. lesson objectives
. text material
. use of audio-visual material (if applicable)
. review exercises and exercise answers
If supplementary reading material is available, it will be
recommended in the appropriate lessons, but this material is
not required for the course.
Instructions for Completing
the Final Examination
Contact the Air Pollution Training Institute if you have any
questions about the course or when you are ready to receive a
copy of the final examination.
After completing the final exam return it and the answer
sheet to the Air Pollution Training Institute. The final exam
grade and course grade will be mailed to you.
Air Pollution Training Institute
Environmental Research Center
MD 20
Research Triangle Park, NC 27711
1-3
-------
Lesson 2
Fabric Filtration Operation
and Baghouse Components
Lesson Goal and Objectives
Goal
To familiarize you with the operation of fabric filters and the
components of the baghouse.
Objectives
At the end of the lesson, you should be able to:
1. describe how a fabric filter operates to collect paniculate
matter.
2. briefly describe two filtration designs: interior and
exterior.
3. list five major components of a baghouse.
4. recognize how bags are attached in a baghouse.
Introduction
Fabric filtration is one of the most common techniques used to
collect particulate matter. Two basic types of filters are
disposable and nondisposable; Disposable filters are similar to
those used in a home heating or air conditioning system.
Disposable filters can be constructed as mats or as deep beds
(12 inches or more). Mat filters are usually made using
fiberglass bats with a thin metal plate on the outside of the
filter used for structural reinforcement. Depth filters are
generally constructed using fiberglass fibers, glass fiber paper
or some other inert material such as fine steel fibers to form a
deep mesh. The filters are very efficient (99.97%) for the col-
lection of 0.3 ",m particles but must be replaced when they
become loaded with particulate matter (when the pressure drop
across the filter exceeds design specifications). Depth filters are
widely useful for the collection of toxic dust materials.
Nondisposable fabric filters consist of a fabric material
(nylon, wool, or other). These filters are commonly used to
clean diny exhaust gas streams from industrial processes. The
panicles are retained on the fabric material, while the cleaned
gas passes through the material.
2-1
-------
The collected panicles are then removed from the filter by a
cleaning mechanism; by shaking or using blasts of air. The
removed particles are stored in a collection hopper until they
are disposed of or are reused in the process.
Collection Mechanisms
Particles are collected on a filter by a combination of several
mechanisms. The most imponant here are impaction. direct
interception and diffusion. In collection by impaction, the par-
ticles in the gas stream have too much inenia to follow the gas
streamlines around the fiber and are impacted on the fiber
surface (Figure 2-1).
In the case of direct interception the panicles have less
inenia and barely follow the gas streamlines around the fiber.
If the distance between the center of the panicle and the out-
side of the fiber is less than the panicle radius. the panicle will
graze or hit the fiber and be "intercepted" (Figure 2-2).
Impaction and direct interception mechanisms account for
99% collection of panicles greater than 1 p.m aerodynamic
diameter in fabric filter systems.
The third collection mechanism is that of diffwion. In diffu-
sion. small panicles are affected by collisions on a molecular
level. PaniCles less than 0.1 p.m aerodynamic diameter have
individual or random motion. The panicles do not necessarily
follow the gas streamlines. but move randomly throughout the
fluid. This is known as Brownian motion. The panicles may
have a different velocity than the fluid and at some point could
come in contact with the fiber and be collected (Figure 2-3).
Other collection mechanisms such as gravitational settling,
agglomeration, and elutrostatic attraction may contribute
slightly to panicle collection. Large panicles may be overcome
by the force of gravity and settle in the hopper. Panicles can
agglomerate or grow in size and then be more easily collected
by the fibers. Some panicles have a small electrostatic charge
and can be attracted to a material of opposite charge.
Electrostatic charges could. on the other hand. have a bad
affect if the charges of the panicles and fiber are the same.
Electrostatic charges can be panicularly useful for the capture
of panicles in the submicron range. The use of a selected fiber
material or a specially coated material may enhance panicle
capture (Frederick, 1974). Different materials will develop
2-2
~
Panicle ~
. .... ...~
-Gu streamlines~
Figure 2-1. ImpactioD
i'
. ...... .-
Panicle
-Gas streamlines~
Figure 2-2. Direct iDtereepCioD.
~8-
.. .
Panicle ~~. ... . Fiber
. ...y ~,
~GU stre'::nes~
Figure 2-3. DiffuaioD.
-------
electrostatic charges of varying degree and sign. A series of
these triboelectric effects or electrostatic charges for various
fabric materials was developed by Frederick and is shown in
Table 2-l.
Particles also are collected by gravitational settling. Rela-
tively large particles are overcome by the force of gravity and
fall into the baghouse hopper.
This force is particularly important when dust-laden gas
enters the baghouse through a hopper inlet.
Pooitive
charge
+25
Table 2-1. TriboelCCU'ic series for 50me
productioD fabrics.
-20
Negative
charge
Wool felt
+20
+ 15
Glass. mamem. heat cleaned and silicone
treated
Glass. spun. heat cleaned and silicone
treated
Wool. wov"" felt, T-2
Nylon 66, spun
Nylon 66, spun, heat set
Nylon 6, spun
Cotton 5at~
Orlon 81. mam""t
Orion 42. needled fabrics
Amel. mamem
Dacron. mam""t
Dacron, mament. silicone treated
Dacron, mamem. M-31
Dacron. combination mam""t and spun
Creslan, spun; Azaton. spun
Verel. regular. spun: Orion 81, spun
(55200)
Dynel. spun
Orion 81. spun
Orlon 42. spun
Dacron. needled
Dacron. spun; Orion 81, spun (79475)
Dacron. spun and heat set
Polypropylene 0 I. mam""t
Orion 39B, spun
Fibravyl. spun
Darvan. needled
Kodel
Polyethylene B, mamem and spun
+ 10
+ 5
o
5
-10
-15
Review Exercise
1. Disposable filters can be constructed as
or as
2. Nondisposable filters consist of some type of
1. mats
depth filters
3. Filters used to clean dirty exhaust gas streams from
industrial processes are
2. fabric material
4. The collection forces (mechanisms) responsible for 99% col-
lection of particles greater than 1 JLm aerodynamic dIameter
are and
3. non disposable filters
5.
charges can help capture particles in the sub-
micron range.
4. impaction
direct interception
5. Electrostatic
2-3
-------
Bag Designs
Nondisposable fabric filter systems are developed for industrial
application as baghouse systems. A baghouse consists of the
following components:
. filter medium and suppon
. filter cleaning device
. collection hopper
. shell
. fan
The panicle collection surface is composed of the filtering
material and a suppon structure. Most U.S. baghouse designs
employ long cylindrical tubes that contain felted fabric or
woven cloth as the filtering medium. The cloth can be sup-
poned at the top and bottom of the bag by metal rings or
clasps; or by an internal cage that completely suppons the
entire bag (Figure 2-4).
Dust is collected on either the inside or outside of the fabric
material depending on the baghouse design.
Some European baghouse designs employ an envelope filter
arrangement as shown in Figure 2-5. The envelope filter con-
sists of felted or woven fabric supponed by a metal retaining
cage. The metal cage keeps the fabric taut as the dust filters
through and collecu on the ouuide of the material. Clean air
passes out the open end of the envelope.
Recently, canridge filters have been used for filtering par-
ticulate matter from small industrial processes. The cartridge
filters are similar to truck filters and are approximately 2 ft
long (Figure 2-6). Dust is collected on the outside of the car-
tridge while clean air flows on through the center.
Figure 2-6. Canridp filter.
2-4
Metal cap
Anti-coUape
ring
Internal
suppon
cage
.....-
Clup
Figure 2-4. Sap and suppon.
. .
. .
.' .
.' .
Figure 2-5. Envelope filter.
-------
Baghouses
Baghouses are usually constructed using many cylindrical bags
that hang venically in the baghouse (Figure 2-7). The number
of bags can vary from a few hundred to a thousand or more
depending on the size of the baghouse. When dust layers have
built up to a sufficient thickness. the bag is cleaned, causing
the dust panicles to fall into a collection hopper. Bag cleaning
can be done by a number of methods. Panicles are stored in
the hopper and are usually removed by a pneumatic or screw
conveyer. The baghouse is enclosed by sheet metal to contain
the collected dust and to protect the bags from atmospheric
environmental conditions.
Bags
Figure 2-7. Typical baghoUle.
2-5
-------
The envelope baghouse consists of compartments that con-
tain envelopes of fabric mounted on frames and attached to
the walls of the collector (Figure 2-8).
'.
. ,"
. .
"". .
";'.' '.' '.
. ..
. ""
. ,',
. ,
Figure 2-8. EDYe!ope bagho_.
Canridge systems operate similarly to a baghouse that uses
bag tubes (Figure 2-9). Canridge baghouses are usually used
on smaller industrial processes handling exhaust flow rates less
than 50,000 cfm.
2-6
Figure 2-9. Canridge bagholUe.
-------
Positive and Negative Pressure Baghouses
Dirty gas is either pushed or pulled through the baghouse by a
fan. When the dust laden gas is pushed through the baghouse,
the collector is called a positive pessure baghouse (Figure 2 -1 0).
Vendors can construct positive pressure baghouses with weaker
support structure since the positive pressure will counterbalance
the atmospheric pressure on the baghouse shell. Limitations,
however, do exist since the fan is located on the dirty side of the
system. Premature deterioration of fan blades, bearings, and duct
work can occur in this configuration. This is very important in
terms of operation and maintenance of the baghouse. The fan is
an integral component; if it becomes worn out, it will cause a
shutdown of the entire baghouse.
Positive pressure baghouses usually have short stubby stacks or
outlets at the top of the baghouse called roof monitors. This is a
problem when stack testing for determining the compliance status
of the source. In this case a high volume sampler has been
inserted in the stack opening or into the baghouse compartment
for compliance testing. EPA is currently developing new testing
methods for these baghouses. Positive pressure systems are used
when filtering process streams containing low moisture content
and low dust concentration of nonabrasive dusts.
When the fan is on the downstream side of the baghouse, the
dirty gas is pulled through the baghouse and the collector is
called a negative pressure baghouse (Figure 2-11). The structure
of a negative pressure baghouse must be reinfotced because of the
suction on the baghouse shell. The construction costs will
therefore be higher than for positive pressure systems. Since the
baghouse housing is under negative pressure, there are no
pressure leaks, so general housekeeping in the immediate vicinity
is minimized. The wear and tear on the fan is much less than
with positive systems since the particulate matter is removed by
the bags before it can enter the fan. This may be the overriding
factor in selecting a negative pressure baghouse. Negative
pressure systems are used when filtering process streams con-
taining high moisture content, corrosive gases, and high concen-
trations of abrasive dusts.
. .
Figure 2-10. Positive pressure baghowe.
Fan
Figure 2-11. Negative pressure baghowe.
Review Exercise
1. The five major components of a baghouse are:
, and
2. Baghouses use either
as the filtering media.
, or
2-7
1. filter medium and support
filter cleaning device
collection hopper
shell
fan
-------
3. Most U.S. baghouse designs use many cylindrical bags that
in the baghouse.
4. Dust cleaned from the bags is collected in a
5. Baghouse systems can be grouped according to the place-
ment of the fan before or after the baghouse.
pressure baghouse systems have the fan before the
baghouse. pressure baghouse systems have the
fan after the baghouse.
2. bags
envelopes
cartridges
3. hang vertically
4. hopper
6. Fan blades. bearings. and ductwork can deteriorate when
the fan is located on the of the
baghouse .
7. Bag cloth is supported at the top and bottom of the bag by
or . or by an
that completely supports the entire bag.
5. Positive
Negative
6. dirty side
7. rings or clasps
internal cage
Filtration Designs
. Cell plate
There are two filtration designs used in baghouses: intenor
filtration and e:ctenor filtration. In baghouses using interior
filtration. particles are collected on the inside of the bag. The
dust laden gas enters through the bottom of the collector and
is directed inside the bag by diffuser vanes or baffles and a cell
plate. The cell plate is a thin metal sheet surrounding the bag
openings. The cell plate separates the clean gas section from
the baghouse inlet. The particles are filtered by the bag and
clean air exits through the outside of the bag (Figure 2-12).
Figure 2-12. Interior filtration
(partida coUected on the
imide of the bag).
2-8
-------
For interior filtration the bags are held at the top by a
spring and a metal cap (Figure 2-13). This arrangement is used
for reverse air cleaning baghouses.
Bags for shaker cleaning baghouses (also interior filtration)
are attached at the top by a hook (Figure 2-14). Shaker and
reverse air cleaning will be discussed in more detail in later
lessons.
In exterior filtration systems, dust is collected on the outside
of the bags. The filtering process goes from the outside of the
bag to the inside with clean gas exiting through the inside of
the bag (Figure 2-15). Consequently. some type of bag suppon
is necessary, such as an internal bag cage or rings sewn into the
bag fabric. Bags are attached at the top to a tube sheet and
are closed at the bottom by an end cap.
" '"
"',.'. , '
;;nrl>--; :i?'-.:!
,','.. .:. :. ... ~... .
. ','.' . ,,' .' .
:'>,\~).-- :::' l:ii:,
Figure 2-15. Exterior filtration (particles
collected on the ouuide of the
bag).
2-9
Figure 2-13. Bag anachment for
reverse air baghowes.
Figure 2-14. Bag attachment for shaker
cleaning baghouaes.
-------
The dust-laden gas inlet position for both filtration systems
often depends on the baghouse model and manufacturer. If
the gas enters the top of the unit. a downwash of gas occurs
which tends to clean the bags somewhat while the bags are
filtering. This usually allows slightly higher gas volumes to be
filtered through the baghouse before cleaning is required. If
the gas enters the bottom of the unit. the inlet is positioned at
the very top pan of the dust hopper (Figure 2-16). Bottom or
hopper inlets are easier to design and manufacture structurally
than are the top inlets. However. when using hopper inlets.
vendors must carefully design gas flows to avoid dust reentrain-
ment from the hopper.
"
'I
"I
-
Figure 2-16. Duac inlet to the baghowe.
Review Exercise
1. When dust is collected on the inside of the bag. the filtration
design is called . When dust is col-
lected on the outside of the bag. it is called
2. For interior filtration. dust enters the bottom of the bag
through a
1. interior filtration
exterior filtration
3. The bags are attached at the top in a reverse air cleaning
baghouse by a spring and a metal
2. cell plate
4. The bags are attached at the bottom to the cell plate by a
rubber gasket.
a. True
b. False
3. cap
5. For exterior filtration. bags are attached at the top to a
4. b. False
5. tube sheet
2.10
- '"
-------
6. Exterior filtration bags are supported by an internal cage.
a. True
b. False
7. Exterior filtration bags are closed at the bottom by a(an)
a. cell plate.
b. tube sheet.
c. end cap.
6. a. True
Baghouse Components
Bags
Tubular bags vary in length and diameter depending on
baghouse design and manufacturer. The length varies from 10
to 40 feet and the diameter is usually between 4 and 18 inches.
Bags are hung vertically in the baghouse (Figure 2-17). Reverse
air baghouses use long bags. 20 to 40 feet. with large
diameters. 12 to 18 inches. Pulse jet baghouses use smaller
bags. 8 to 12 feet with 4 to 6 inch diameters.
Howing
Baghouses are constructed as single or compartmental units.
The single unit is generally used on small processes that are not
in continuous operation such as grinding and paint spraying
processes. Compartmental units consist of more than one
baghouse compartment and are used in continuous operating
processes with large exhaust volumes such as electric melt steel
furnaces and industrial boilers. In both cases. the bags are
housed in a shell made of a rigid metal material. Occasionally
it is necessary to include insulation with the shell when treating
high temperature flue gas. This is done to prevent moisture or
acid mist from condensing in the unit. causing corrosion and
rapid deterioration of the baghouse.
Hoppers
Hoppers are used to store the collected dust temporarily before
it is disposed in a landfill or reused in the process. Dust should
be removed as soon as possible to avoid packing which would
make removal very difficult. They are usually designed with a
600 slope to allow dust to flow freely from the top of the hop-
per to the bottom discharge opening. Some manufacturers add
2-11
7. c. end cap.
Metal cap
S
8. - Anti-~ollapse
~ nng
~
t::)
o.--Clamp
Thimble
Cell plate
Figure 2-17. Bag construction (for a reverse
air baghou.se).
-------
devices to the hopper to promote easy and quick discharge.
These devices include strike plates. poke holes. vibrators. and
rappers. Strike plates are simply pieces of flat steel which are
bolted or welded to the center of the hopper wall. If dust
becomes stuck in the hopper. rapping the strike plate several
times with a mallet will free this material. Hopper designs also
usually include access doors or pons. Access pons provide for
easier cleaning, inspection. and maintenance of the hopper
(Figure 2-18).
Discharge Devices
A discharge device is necessary for emptying the hopper.
Discharge devices can be manual or automatic. The simplest
manual discharge device is the slide gate, a plate held in place
by a frame and sealed with gaskets (Figure 2-19). When the
hopper needs to be emptied. the plate is removed and the
material discharges. Other manual discharge devices include
hinged doors or drawers. The collector must be shut down
before opening any manual discharge device. Thus. manual
discharge devices are used on baghouses that operate on a
periodic basis.
Automatic continuous discharge devices are installed on
baghouses that are used in continuous operation. Some devices
include tn'd.le valves, rotary airlock valves, screw conveyors or
pneumatic conveyers. Trickle valves are shown in Figure 2-20.
As dust collects in the hopper. the weight of the dust pushes
down on the counterweight of the top flap and dust discharges
downward. The top flap then closes. the bottom flap opens,
and the material falls out. This type of valve is available in
gravity-operated and motorized versions.
Rotary airlock valves are used on medium or large sized
baghouses. The valve is designed with a paddle wheel which is
shaft-mounted and driven by a motor (Figure 2-21). The rotary
valve is similar to a revolving door: the paddles or blades fonn
an ainight seal with the housing: the motor slowly moves the
blades to allow the dust to discharge from the hopper.
Figure 2-21. Rotary airlock diJcha~ device.
2-12
Figure 2-18. Hopper.
'." ":f'~'.. ~~". -.....
Figure 2-19. Slide gate.
Figure 2-20. Triclr.1e valve discharge device.
-------
Other automatic dust discharge devices include screw and
pneumatic conveyers. Screw conveyers employ a revolving screw
feeder located at the bottom of the hopper to remove the dust
from the bin (Figure 2-22).
Pneumatic conveyers use compressed air to blow (remove)
dust from the hopper (Figure 2-23).
Blower or :
compressed.
air
Figure 2-23. Pneumatic conveyer.
Figure 2-22. Screw conveyor.
Review Exercise
1. The bags in a baghouse are housed in a
usually made of metal (steel).
that is
1. shell
2. Sometimes it is necessary to use with the shell to
prevent moisture or acid from condensing in the baghouse.
3.
units are used on small processes that aren't in
continuous use.
2. insulation
4.
units are used on large industrial processes.
3. Single
5. The dust is temporarily stored in a
4. Companmentalized
6. One continuous discharge device that uses the weight of col-
lected dust in the hopper to operate the flaps is a
6. trickle valve
2-13
5. hopper
-------
7. A
a revolving door.
discharge device works similar to
8. A uses a screw feeder located at
the bottom of the hopper to remove dust from the bin.
7. rotary airlock
9. A uses a blower or compressed air
to remove dust from the hopper.
8. screw conveyer
9. pneumatic conveyer
2-14
-------
Lesson 3
Fabric Filter Material
Lesson Goal and Objectives
Goal
To familiarize you with the construction of fabric filter
material, fibers used, and problems affecting fabric life.
Objectives
At the end of the lesson, you should be able to:
1. name two ways filters are constructed.
2. list at least five natural or synthetic fibers used to make
filters and recall the conditions under which they are
used.
3. name three failure mechanisms that reduce filter life.
Filter Construction
Woven and felted materials are used to make bag filters.
Woven filters are made of yam with a definite repeated pat-
tern. Felted filters are composed of randomly placed fibers
compressed into a mat and attached to some loosely woven
backing material. Woven filters are used with low energy
cleaning methods such as shaking and reverse air. Felted
fabrics are usually used with higher energy cleaning systems
such as pulse jet cleaning.
Woven Filters
Woven filters have open spaces around the fibers. The weave
design used will depend on the intended application of the
woven filter. The simplest weave is the plain weave. The yam
is woven over and under to form a checkerboard pattern
(Figure 3-1). This weave is usually the tightest, having the
smallest pore openings in the fabric. Consequently, it retains
particles very quickly. This weave is not frequently used.
Other weaves include the twill and sateen (satin). In the twill
weave (2/1), yam is woven over two and under one, but in one
direction only (Figure 3-2).
3.1
~
Figure 3-1. Plain weave or checkerboard.
~
Figure 3-2. Twill weave (2/1).
-------
The twill weave does not retain panicles as well as the plain
weave, but does not tend to blind as fast. It allows good flow
rates through the filter and high resistance to abrasion. The
satin weave goes one over and four under in both directions.
Sateen weave does not retain particles as well as the plain twill
weave, but has the best (easiest) cake release when the fabric is
cleaned (Figure 3-3).
Different weaving patterns increase or decrease the open
spaces between the fibers. This will affect both fabric strength
and permeability. Fabric permeability affects the amount of air
passing through the filter at a specified pressure drop. A tight
weave, for instance, has low permeability and is better for the
capture of small panicles at the cost of increased pressure
drop.
The true filtering surface for the woven filter is not the bag
itself, but the dust layer or filter cake. The bag simply provides
the surface for capture of larger panicles. Panicles are col.
lected by impaction or interception and the open areas in the
weave are closed. This process is referred to as sieving (Figure
3-4). Some particles escape through the filter until the cake is
formed. Once the cake builds up, effective filtering will occur
until the bag becomes plugged and cleaning is required. At
this point the pressure drop will be exceedingly high and file
tering will no longer be cost effective. The effective filtering
time will vary from a time of approximately 15 to 20 minutes
to as long as a number of hours, depending on the concentra.
tion of particulate matter in the gas stream.
3-2
Figure !-!. Sateen weave (saun weave).
Dust cake
I
, :.,. ~
.
. ....
. ~.":
.-
.:.
t
..
."
...
." ..-- ~-
.
r'
.-
.
.~
.. .-=--
, P'
."
.. ~ .
.... ...
..- tr.-- ~'-
.. ... ..
.. ....
.-. ....-
Figure !-4. Sienng (on a woven filter).
-------
Felted Filters
Felted filters are made by needle punching fibers onto a woven
backing called a scrim. The fibers are randomly placed as
opposed to the definite repeated pattern of the woven filter.
The felts are attached to the scrim by chemical. heat. resin.
and stitch-bonding methods.
To collect fine particles. the felted filters depend to a lesser
degree on the initial dust deposits than do woven filters. The
felted filters are generally 2 to 3 times thicker than woven
filters. Each individual randomly oriented fiber acts as a target
for particle capture by impaction and interception. Small
particles can be collected on the outer surface of the filter
(Figure 3.5).
Felted filters are usually used in pulse jet baghouses. A pulse
jet baghouse generally filters more air per cloth area (higher
air-to.cloth ratio) than a shaker or reverse air unit. Felted bags
should not be used in high humidity situations. especially if the
particles are hydroscopic. Clogging or blinding could result in
such situations.
.- .--
.- .-..
..
e. ... .-. ~
.= ....-
.-..
. .-
- .- .-
.- ..,.
.5-.- ..,
..
., ...-
.- :-.
...- .- ...-
.. .-
. ...
.- _. .
.:. . ..-
....- 8"-
.- ., ~-
.. -
'- Dust cake
Figure 3-5. Felted fabric filter.
Review Exercise
1. Bag filters (bags) are made from
materials.
or
2.
filters are made from yarn with a definite
repeated pattern.
1. woven
felted
weaves have better cake
3. The and
release than the simple weave.
4. In a woven filter. the woven material is not the true filtering
surface. The dust provides the surface for fil.
tering particles.
2. Woven
3. twill
sateen
5.
filters are made by needle punching fibers onto
a woven backing called a scrim.
4. cake
3-3
5. Felted
-------
Fibers
The fibers used for fabric filters vary depending on the
industrial application to be controlled. Some filters are made
from natural fibers such as cotton or wool. These fibers are
relatively inexpensive but have temperature limitations
« 212°F or lOOOC) and only average abrasion resistance. Cot-
ton is readily available making it very popular for low
temperature simple applications. Wool withstands moisture
very well and can be made into thick felts easily.
Synthetic fibers such as nylon. Orlon~ and polyester have
slightly higher temperature limitations and chemical
resistances. Synthetic fibers are more expensive than natural
fibers. Polypropylene is the most inexpensive synthetic fiber
and is used in many industrial applications such as foundries.
coal crushers and food industries. Nylon is the most abrasive
resistant synthetic fiber making it useful in applications fil-
tering abrasive dusts. Polyester or Dacron~ has good overall
qualities to resist acids. alkalines. and abrasion and is relatively
inexpensive. making it useful for many industrial processes
such as smelters. foundries. and other metal industries.
Nomex~ is a registered trademark of fibers made by
DuPont. DuPont makes the fibers. not the fabrics or bags.
Nomex is widely used because of its relatively high temperature
resistance and its resistance to abrasion. It is used for filtering
dusts from cement coolers. asphalt batch plants. ferroalloy
furnaces. and coal dryers.
Other fibers such as Teflon~ and Fiberglas~ or glass can be
used in very high temperature situations. Teflon has very good
resistance to acid attack (except fluorine) and can withstand
continuous temperatures up to 445°F (230°C). Fiberglas or
glass is often used in baghouses that handle very high
temperatures (up to 500°F or 260°C) for continuous operation.
Glass fibers are usually lubricated in some fashion so they will
slide over one another without breaking or cutting during the
cleaning cycle. Graphite is commonly used as a lubricant and
will help retain the upper service temperature limits. Glass
fibers are susceptible to breakage and require a very gentle
cleaning cycle. Both Teflon and glass have been used to
remove particulate emissions generated from industrial and
utility coal fired boilers.
Note: Orlon~, Dacronll, Teflon II , and Fiberglasll are registered with
the U.S. Patent Office. In this manual the name without the
registered symbol (II) will be used.
3-4
-------
Another material used to make bags is Gore-tex membrane
manufactured by W. G. Gore and Associates, Inc. Gore-tex
membrane is laminated with a variety of fibers such as
Fiberglas, polyester and Nomex to produce felt and woven
filters. Some repons have indicated very good emission reduction
(99.99+%), low pressure drops, increased bag life and higher
air-to-cloth ratios using this material in metal industries,
chemical industries, food industries, and coal fired boilers.
Table 3-1 lists a number of typical fibers used for fabric
filters. The properties of the listed fibers include temperature
limits, acid and alkali resistance. abrasion resistance, and
relative bag costs.
Table 3-1. Typical fabrio wed for bags.
Generic Masimum lemperature Acid Alkali Flex Relative
Fiber ContinuoUi Surges abruioD
name resUtaDce resistance em<
OF °C of °C resutance
Natural Couon 180 82 225 107 poor very good very good 2.0
fiber
cellulose
Polydefin Polypro. 190 88 200 95 good to very good ~xceUent 2.0
pylene excellent
Natural Wool 200.216 95.102 250 121 very good poor fair to good 5.0
fiber
protein
Polyamide Nylon 200.225 95.107 250 121 poor to good to excellent 2.5
fair excellent
Acrylic Orion 240 116 260 127 good to fair to good 2.75
excellent good
Polyester Dacron 275 155 325 165 good good very good 2.8
Aromatic Nomex 400 204 425 218 poor to good to excellent 8.0
polyamide good excellent
Fluoro. Teflon 400- 204- 500 260 excellent excellent fair 20.0
carbon 450 252 except except
poor to poor to
fluorine trifluoride.
chlorine
and
molten
alkaline
metals
Glass Fiberglas 500 260 550 288 fair to fair [0 fair 6.0
or glass good good
Sources: B"ethea, 1978: EPA, 1979: Theodore and Buonicore, 1976.
The cost (1982) of a polypropylene bag 12 feet long and
6 inches in diameter is approximately $10 to $12. From
Table 3-1 the price of a Teflon bag of the same size is approx-
imately $100 to $120.
3-5
-------
Review Exercise
1. Two natural fibers used for fabric filters are
and
2. Wool and cotton are inexpensive but are susceptible to
failure at
1. wool
cotton
3. Two fabrics that are good for use in high temperature
( > 200°C) industrial processes are
a. Teflon and Fiberglas
b. nylon and wool
c. cotton and Orlon
d. polypropylene and Dacron
2. high temperature
3. a. Teflon and Fiberglas
Fabric Treatment
Fabrics are usually pretreated to improve their mechanical and
dimensional stability. They can be treated with silicone to give
them better cake release propenies. Natural fabrics (wool and
cotton) are usually preshrunk to eliminate bag shrinkage
during operation. Both synthetic and natural fabrics usually
undergo processes such as calendering. napping. singeing.
glazing. or coating.
These processes increase fabric life and improve dimensional
stability and ease of bag cleaning.
. Calendering is the high pressure pressing of the fabric by
rollers to flatten. smooth. or decorate the material. Calen-
dering pushes the surface fibers down onto the body of the
filter medium. This is done to increase surface life. dimen-
sional stability and to give a more uniform surface to bag
fabric.
. Napping is the scraping of the filter surface across metal
points or burrs on a revolving cylinder. Napping raises the
surface fibers. creating a "fuzz". that provides a large
number of sites for panicle collection by interception and
diffusion. Fabrics used for collecting sticky or oily dusts
are occasionally napped to provide good collection and
bag cleaning ease.
. Singeing is done by passing the filter material over an
open flame. removing any straggly surface fibers. This
provides a more uniform surface.
. Glazing is the high pressure pressing of the fiber at
elevated temperatures. The fibers are fused to the body of
the filter medium. Glazing improves the mechanical
stability of the filter and helps reduce bag shrinkage that
occurs from prolonged use.
3-6
-------
. Coating, or resin treating. involves immersing the filter
material in natural or synthetic resin such as polyvinyl
chloride, cellulose acetate, or urea-phenol. This is done to
lubricate the woven fibers, or to provide high temperature
durability or chemical resistance for various fabric
material. For example. glass bags are occasionally coated
with Teflon or silicon graphite to prevent abrasion during
bag cleaning.
A summary of pretreatment processes for fabrics is presented
in Table 3-2.
Table 3-2. Summary of pretreatment processes.
Pretreatment Method Rault Rea.oon for use
Ciilendering High pre..ure flauens. smooths. Increases surface
pressing by roUers or decorates life
Incre...,. dimensioniil
stability
ProVIdes more uniform
fabric surface
Napping Scraping acro.. Raises surface Provides extra areas
metiil poinu fibers for inu~rc:q][ion
and diffwion
Singeing Pasaing over open Removes Straggly Provides uniform
flame surface fibers surface area
Glazing High pressure Fibers fused to Improves mechanlciil
pressing at filter medium Stability
elevated
temperatures
Coating Immersing in Lubricates woven Provides high
naturiil or synthetic fibers tempera[un~
resin durability
Provides chemiciil
resistance for
variow fabric
materiaJ
Review Exercise
1. Fabrics are pretreated to improve their mechanical and
dimensional stability.
a. True
b. False
2. The filter surface of fabric material is sometimes scraped
with metal points or burrs on a revolving cylinder to create
a "fuzz" on the material. This treatment is called
a. singeing.
b. glazing.
c. napping.
d. resin treating.
1. a. True
2. c. napping
3-7
-------
~. Glass bags are occasionally coated with Teflon or silicon
graphite to prevent abrasion during bag cleaning.
a. True
b. False
4. When fabric material is passed over an open flame to
remove straggly fibers. the treatment is called
~. a. True
4. singeing
Bag Failure Mechanisms
Three failure mechanisms can shonen the operating life of a
bag. They are related to abrasion. thermal durability and
chemical attack. The chief design variable is the upper
temperature limit of the fabric. The process exhaust
temperature will determine which fabric material should be
used for dust collection. Exhaust gas cooling may be feasible.
but one must be careful to keep the exhaust gas hot enough to
prevent moisture or acid from condensing on the bags.
Another problem frequently encountered in baghouse opera-
tion is that of abrasion. Bag abrasion can result from bags
rubbing against each other. or from the type of bag cleaning
employed in the baghouse or where dust enters the bag and
contacts the fabric material. For instance. in a shaker
baghouse. vigorous shaking may cause premature bag
deterioration. panicularly at the points where the bags are
attached. In pulse jet uniu. the continual. slight motion of the
bags against the supponing cages can also seriously affect bag
life. As a result. a 25% per year bag replacement rate is
usually encountered. This is the single biggest maintenance
problem associated with baghouses.
Bag failure can also occur by chemical attack to the fabric.
Changes in dust composition and ex.haust gas temperatures
from industrial processes can greatly affect the bag material. If
the exhaust gas stream is lowered to its dew point or a new
chemical species is created. the design of the baghouse (fabric
choice) may be completely inadequate. Proper fabric selection
and good process operating practices can help eliminate bag
deterioration caused by chemical attack.
Gas Conditioning
Occasionally it is necessary to cool the process gas stream
before the gas goes to the baghouse. Since there is an upper
temperature limit on the fabrics used for bags. gas cooling is
sometimes necessary to preserve bag life. This can be
accomplished by a number of cooling methods.
~-8
-------
Dz'lutz'on of the exhaust gas stream by air is the easiest and
cheapest method, especially at very high temperatures.
However, air dilution requires the use of a larger baghouse to
handle the increased volume of air. Other problems can arise
due to the difficulty of controlling the intake of ambient
moisture and other contaminants from the dilution air intake.
Radz'atz'on coolz"ng can also be used to lower the process
exhaust gas temperature. Radiation cooling involves the use of
long uninsulated ducts that allow the gas stream to cool as heat
radiates from the duct walls. Ducts can be designed in "U"
shapes to allow more duct surface area to be exposed for radia-
tion cooling (Figure 3-6). Radiation cooling would not
normally be very effective to cool gas temperatures below
572°F or 300°C. This would require substantial surface area,
lengthy duct runs, and increased fan horsepower. Precise
temperature control is difficult to maintain and there is a
possibility of the ducts becoming plugged due to particle
sedimentation.
Evaporatz've coolz'ng is also used to reduce exhaust gas stream
temperature. Evaporative cooling is accomplished by injecting
fine water droplets into the gas stream. The water droplets
absorb heat from the gas stream as they evaporate. Spray
nozzles are located in a quench chamber or somewhere in the
duct preceding the baghouse (Figure 3-7). Evaporative cooling
gives a great amount of controlled cooling at a relatively low
installation cost. Temperature control can be flexible and
accurate. However, this cooling method may increase the exhaust
volume to the baghouse. The biggest problem with evaporative
cooling is keeping the gas temperature above the dew point of
the gas (SOz, NOz, HC!. etc.). Otherwise, gases may condense
on the bags causing rapid bag deterioration. In addition, all
moisture injected into the gas must be evaporated to prevent
corrosion of metal parts and blinding or plugging of caked dust
on the bags.
3-9
..
- :
, ,
: !
",
1; ;
..>
--" I
! ~
, ,
~ i
I
!
'._-
., !
I
I
.I
...i
-...
Outlet
Figure 3-6. V-tube cooler
(radiation cooling).
Water
sprays
,;
Figure 3-7. Evaporative cooling using water
spra y',
-------
Review Exercise
1. Three failure mechanisms that shorten bag operating life
are . and
2. The chief design variable for prolonged bag life is the upper
temperature limit of the bag.
a. True
b. False
3. Cooling the process exhaust stream by dilution does not
increase the air volume to be handled by the baghouse.
a. True
b. False
1. abrasion
thermal durability
chemical attack
2. a. True
4. When long uninsulated ducts are used for cooling process
exhaust the cooling is called
a. radiation cooling.
b. evaporative cooling.
c. dilution cooling.
d. condensation.
3. b. False
4. a. radiation cooling.
5.
cooling is accomplished by spraying fine water
droplets into the process exhaust stream.
6. The biggest problem with evaporative cooling is
a. the long duct runs needed for cooling.
b. keeping the gas temperatur,e above the dew point.
c. the increased volume of air to handle as a result of
cooling.
5. Evaporative
6. b. keeping the gas temperature
above the dew point.
-------
Lesson 4
Bag Cleaning
Lesson Goal and Objectives
Goal
To familiarize you with mechanisms to clean collected dust from
the bags.
Objectives
At the end of the lesson. you should be able to:
1. name two bag cleaning sequences and briefly discuss the
conditions under which they are used.
2. list three major cleaning methods and briefly describe
how each method is used to remove dust from bags.
Cleaning Sequences
Two basic sequences are used for bag cleaning: intennittent. or
periodic cleaning; and continuous filter cleaning.
Intennittently cleaned baghouses consist of a number of
compartments or sections. One compartment at a time is
removed from service and cleaned on a regular rotation basis.
The dirty gas stream is diverted from the compartment being
cleaned to the other compartments in the baghouse. so it is not
necessary to shut down the process. Occasionally, the baghouse
is very small and consists of a single compartment. The flow of
dirty air into the baghouse is stopped during bag cleaning.
These small single compartment baghouses are used on batch
processes that can be shut down for bag cleaning.
Continuously cleaned baghouses are fully automatic and can
constantly remain on-line for filtering. The filtering process is
momentarily interrupted by a blast of compressed air that
cleans the bag, called pulse jet cleaning. In continuous
cleaning, a row of bags is always being cleaned somewhere in
the baghouse. The advantage of continuous cleaning is that it
is not necessary to take the baghouse out of service. Large con-
tinuous cleaning baghouses are built with compartments to
help prevent total baghouse shutdown for bag maintenance
and failures to the compressed air cleaning system or hopper
conveyers. This allows the baghouse operator to take one com.
partment off. line to perfonn necessary maintenance.
4-1
-------
Types of Bag Cleaning
A number of cleaning mechanisms are used to remove caked
particles from bags. The three most common are shaking,
reverse air, and pulse jet, Another mechanism called blow n'ng
or reverse jet is normally not used in modem bag cleaning
systems.
Shaking
Shaking can be done manually, but is usually performed
mechanically in industrial-scale baghouses. Small baghouses
handling exhaust streams less than 500 cfm (14.2 m'/min) are
frequently cleaned by hand levers. However, thorough cleaning is
rarely achieved since a great amount of effort must be used for
several minutes to remove dust cakes from the bags. In addition,
these small units do not usually have a manometer installed on
them to give pressure drop readings across the baghouse. These
readings are used to determine when bag cleaning is necessary.
Therefore, manual shaker baghouses are not recommended for
use in controlling paniculate emissions.
Mechanical shaking is accomplished by using a motor that drives
a shaft to move a rod connected to the bags. It is a low energy proc.
ess that gendy shakes the bags to remove deposited panicles. The
shaking motion and speed depends upon the vendors' design and the
composition of dust deposited on the bag, The shaking motion can
be either in a horizontal or venical direction, with the horizontal
being the most often used. The tops of the bags in shaker baghouses
are sealed or closed and supponed by a hook or clasp. Bags are
open at the bottom and attached to a cell plate. The bags are
shaken at the bottom by moving the cell plate or at the top by
moving the frame where the bags are attached. This causes the bags
to ripple and release the dust (Figure 4.1). The flow of diny gas is
stopped during the cleaning process. Therefore the baghouse must
be compartmentalized to be useable on a continuous basis. Shaker
baghouses usually use interior f11tration (dust collected on the inside
of the bags).
Shaking should not be used when collecting sticky dusts. The
forces needed for removing sticky dust can cause the bag to be
tom or ripped.
Bag wear on the whole can be a problem at the bottom of the
bag which is attached to the cell plate; the greatest wear is
usually at the top of the bag where the suppon loop attaches to
the bag. Proper shaking frequency is therefore imponant to pre.
vent prematUre bag failure.
In a few systems, shaking is accomplished by sonic vibration
(Figure 4.2). A sound generator is used to produce a low fre.
quency sound that causes the bags to vibrate. The noise level pro-
duced by the generator is barely discemable outside the
baghouse. This type of cleaning, however. is not used on many
newer baghouse systems.
4-2
Horizontal
V mical
~-ll--
~'===4
]
I
"
I,
"
,-1,..-
<-'
....;::-=
\ ' ,
\ ",
\' '. \
\ . - \
\ ' .\
\ , ,.\
\' . . ',\
\ ' " \
I,', ... '"
~,~,.,~j
'S3 ~~.:
'.", ..
i~~J~
Jn1Ri:
, ,', "I.' ..
:::: ~ ~:~::!=:.::
Figure 4-1. Shaking.
~~f;\it
Figure 4-2. Sonic vibration..
-------
A typical shaker baghouse is shown in Figure 4-3. The bags
are attached to a shaft that is driven by an externally mounted
motor. The bags are shaken, and the dust falls into a hopper
located below the bags. The duration of the cleaning cycle is
usually from 30 seconds to a few minutes.
The frequency of the cleaning depends on the type of dust.
the concentration, and the pressure drop across the baghouse.
The baghouse usually has two or more compartments to allow
one compartment to be shut down for cleaning.
Figure 4-4 is a detailed view of the shaking mechanism. The
bags are attached in sets of two rows to mounting frames across
the width of the baghouse. A motor drives the shaking lever,
which in turn causes the frame to move and the bags to shake.
Typical design parameters for shaking cleaning are given in
Table 4-1.
Table 4-1. Shake cleaning-parameters.
Frequency
Motion
Peak acceleration
Amplitude
Mode
Duration
Common bag dimensions
Usually several cycles per second; adjustable
Simple harmonic or sinusoidal
1 to 10 g
Fraction of an inch to few inches
Off. stream
10 to 100 cycles, ~O see to few minutes
5, 8, 12 inch diameters; 8 to 10. 22, ~o foot lengths
Source: McKenna and Greiner, 1981.
Figure 4-3. Typical shaker baghowe.
Figure 4-4. Detail of a shaking lever.
Review Exercise
and
1. Two basic sequences for bag cleaning are
cleaning.
2. Intermittent baghouses consist of compartments that are all
cleaned simultaneously.
a. True
b. False
1. intermittent
continuous
3. It is not necessary to take a continuously cleaned baghouse
off. line for bag cleaning.
a. True
b. False
2. b. False
4.3
3. a. True
-------
4. Mechanical shaking is accomplished by using a
that drives a shaft to shake the dust-laden bags.
5. The flow of diny air into a companment is shut down for
bag cleaning in a shaker baghouse.
a. True
b. False
4. motor
6. Bags are not sealed or closed at the top in a shaker
baghouse .
a. True
b. False
7. The shaking motion causes the dust cake to break and fall
into the
5. a. True
6. b. False
7. hopper
8. Bag cleaning frequency depends on dust type. dust concen-
tration. and the across the
baghouse.
Reverse Air
Reverse air. the simplest cleaning mechanism. is accomplished
by stopping the flow of diny gas into the comp'anment and
backwashing the companment with a low pressure flow of air.
Dust is removed by merely allowing the bags to collapse. thus
causing the dust cake to break and fall into the hopper. The
cleaning action is very gentle. allowing the use of less abrasion
resistant fabrics such as Fiberglas (Figure 4-5). Reverse air
cleaning is generally used for cleaning woven fabrics. Cleaning
frequency varies from 30 minutes to several hours, depending
on the inlet dust concentration. The cleaning duration is
approximately 10 to 30 seconds; the total time is 1 to 2 minutes
for valve opening and closing. and dust settling.
Reverse air cleaning baghouses are usually compan-
mentalized to permit a section to be off-line for cleaning. Dust
can be collected on either the inside or outside of the bag.
Normally dust is collected on the inside of the bag. the bag
being open at the bottom and sealed by a metal cap at the
top. The bag contains rings to keep it from completely col-
lapsing during the cleaning cycle. Complete collapse of the bag
would prevent the dust from falling into the hopper. Bags are
supponed by small steel rings sewn to the inside of the bag.
The rings are placed every 4 to 18 inches throughout the bag
length depending on the length and diameter of the bag.
Reverse air baghouses use very large bags (as compared to
shaker or pulse jet baghouses) ranging from 8 to 18 inches in
diameter and from 20 to 40 feet in length.
4-4
8. pressure drop
Backwash air
Figure 4-5. R.everle air cleaning.
-------
Cleaning air is supplied by a separate fan which is normally
much smaller than the main system fan, since only one com-
panmem is cleaned at a time. A typical reverse air cleaning
baghouse is shown in Figure 4-6. Typical design parameters for
reverse air cleaning are given in Table 4-2.
Companmmts filtering
Compamnent
being
cleaned
~: .':: ,',' . .. .: ~~
. ":... '. ..'
. . "",~' '., ~
t
Reverse air fan
Figure 4-6. Typical reverse air baghowe.
Table 4-2. Reverse air cleaning-parameters.
Frequency
Cleaned one compartment at a time, sequencing one compartment
after another: can be continuous or initiated by a maximum-
pressure-drop .witch
Gentle collapse of bag (concave inward) upon deflation; .Iowly
repressurize a compartment after completion of a back-flwh
Off. stream
I to 2 min. including valve opening and closing and dwt settling
periods; reverse air flow itself normally 10 to 30 see
8. 12. 18 inch diameten; 22. 30, 40 foot lengths
50 to 75 lb. typical. optimum varies; adjwted after on-stream
Motion
Mode
Duradon
Common bag dimensions
Bag tension
Source: McKenna and Greiner, 1981.
4-5
Main fan
-------
Review Exercise
1. Reverse air cleaning is accomplished by a blast of air into
each bag.
a. True
b. False
2. Reverse air cleaning is very gentle allowing the use of less 1. b. False
abrasion resistant fabrics such as woven (or
).
3. Cleaning duration is approximately 2. glass (or Fiberglas)
a. 1 to 2 hours.
b. 10 to 20 minutes.
c. 10 to 30 seconds.
d. less than 1 second.
4. Cleaning air in reverse air baghouses is usually supplied by 3. c. 10 to 30 seconds.
a
5. Reverse air baghouses use large bags whose lengths range 4. separate fan
from
a. 3 to 5 feet.
b. 20 to 40 feet.
c. 5 to 10 feet.
d. 75 to 100 feet.
6. During reverse air cleaning the flow of diny air into the 5. b. 20 to 40 feet.
companment is stopped.
a. True
b. False
7. The bag in a reverse air baghouse usually has rings sewn 6. a. True
into the inside of the bag every
a. 10 to 15 inches.
b. 1 to 2 inches.
c. 4 to 6 inches.
7. c. 4 to 6 inches.
Pulse Jet
The third bag cleaning mechanism most commonly used is the
pulse jet or pressure jet cleaning. Baghouses using pulse jet
cleaning make up approximately 40 to 50 percent of the new
baghouse installations in the U.S. today. The pulse jet cleaning
mechanism uses a high pressure jet of air to remove the dust
from the bag. Bags in the baghouse companment are
supponed internally by rings or cages. Bags are held firmly in
place at the top by clasps and have an enclosed bottom
(usually a metal cap). Dust.laden gas is filtered through the
4-6
-------
bag. depositing dust on the outSide surface of the bag. Pulse
jet cleaning is used for cleaning bags in an exterior filtration
system.
The dust cake is removed from the bag by a blast of com-
pressed air injected into the top of the bag tube. The blast of
high pressure air stops the normal flow of air through the
filter. The air blast develops into a standing or shock wave that
causes the bag to flex or expand as the shock wave travels
down the bag tube. As the bag flexes. the cake fractures and
deposited particles are discharged from the bag (Figure 4-7).
The shock wave travels down and back up the tube in approx-
imately 0.5 seconds.
The blast of compressed air must be strong enough for the
shock wave to travel the length of the bag and shatter or crack
the dust cake. Pulse jet units use air supplies from a common
header which feeds into a nozzle located above each bag
(Figure 4-8). In most baghouse designs. a venturi sealed at the
top of each bag is used to create a large enough pulse to travel
down and up the bag. This occurs in approximately 0.3 to
0.5 sec. The pressures involved are commonly between 60 and
100 psig (414 kPa and 689 kPa). The importance of the venturi
is being questioned by some pulse jet baghouse vendors. Some
baghouses operate with only the compressed air manifold above
each bag.
,
Shock wav~
,
, J,
. "."
. or. '..
. .~~. .' . . .
, '
, '
. ,""
"
,
. ~'.
",
,'"
, "
'..
" '
"
. . , .,. . .
. -. "
Figure 4-7. Pulse jet cleaning.
Compressed air supply
Blow pipe
Venturi
Figure 4-8. Typical pulse jet baghowe with air supply.
4-7
-------
Most pulse jet baghouses use bag tubes that are 4 to 6 in.
(10.2 to 15.2 cm) in diameter. The length of the bag is usually
around 10 to 12 ft (3.05 to 3.66 m), but can be as long as 25 ft
(7.6 m). The shaker and reverse air baghouses use larger bags
than the pulse jet units. The bags in these units are 6 to 18 in.
(15.2 to 45.7 em) in diameter and up to 40 ft (12.2 m) in
length. Typical design parameters for pulse jet cleaning are
given in Table 4-3.
Table 4-5. Pube jet cleaning-parameters.
Frrquency
Duration
UlUalJy. a row of bap at a time. sequenced one row after
anOther; can sequence such that no adjacent rows clean one after
anather; initiation of cleaning can br trigerrd by maximum.
pl'rllUl'l!.drop switch or may br continuo...
Shock wave pa8n down bag; bag distends from cage momentarily
On.scream; in difficult .to.clean applications such as coal fired boilers.
off. scream companment cleaning bring studied
Comprr8rd.air (100 poi) pu!lr duration 0.1 see; bag row effectively
off .line
S to 6 inch diamrcrn; 8 to 20 fOOt lengchs
Motion
Mode
Common bag dimeftl10ns
Source: McKenna and Greiner. 1981.
Compartmentalized Pulse Jet Baghowes
Pulse jet baghouses can also be compartmentalized. In this case
it is possible to stop the flow of dirty air into the compartment
by using poppet valves located in the clean air plenum. Each
compartment is equipped with a single pulse valve that supplies
compressed air to the group of bags. During the cleaning cycle
the poppet valve closes, stopping the air flow through the com-
partment. The pulse valve opens for about 0.1 see, supplying a
burst of air into the bags for cleaning. The poppet valve then
automatically reopens, bringing the compartment back on
stream. Alternate compartments are cleaned successively until
all the bags in the baghouse have been cleaned (Figure 4-9).
The cleaning cycle in each compartment lasts about 4.0 sec.
4-8
-------
Burst of cl~aning air
Poppet
valv~
Comparun~nt
b~ing cl~aned
Figur~ 4-9. Companmentalized pube jet baghowe (plenum pube baghowe).
Review Exercise
1. Pulse jet cleaning is accomplished by
a. shaking each bag in the companment while the damper
is closed.
b. a blast of compressed air into each bag.
c. reversing the flow of air into the baghouse compartment
and gently shaking the bags.
2. In a pulse jet baghouse dust is removed from the
of the bag when the bag is cleaned.
1. b. a blast of compressed air
into each bag.
2. outside
3. The dust collects on the outside of the bag. therefore the
bag must be supponed. usually by a
3. metal cage.
4-9
-------
4. The shock wave travels down and then back up the bag
tube in approximately
a. 1 to 2 minutes.
b. 10 to 30 seconds.
c. 0.5 seconds.
5. Pulse jet air is supplied from a common header which feeds
into a nozzle located above each bag.
a. True
b. False
4. c. 0.5 seconds.
6. Pulse jet baghouses use bags that are usually
a. 12 to 16 inches in diameter and 20 to 40 feet long.
b. 4 to 6 inches in diameter and 10 to 12 feet long.
c. 16 to 24 inches in diameter and 15 to 25 feet long.
7. In pulse jet cleaning. the flow of diny air into the compan-
ment mwt be stopped before cleaning is initiated.
a. True
b. False
5. a. True
6. b. 4 to 6 inches in diameter and
10 to 12 feet long.
Reverse Jet or Blow Ring
Another bag cleaning mechanism is reverse jet cleaning using a
blow ring. Some older baghouse designs employed this method.
but it has lost popularity due to the great number of moving
parts inside the baghouse. Blow ring cleaning involves reversing
the air flow on each bag. This cleaning method does not
depend on the collapse of each bag to crack the cake as in the
reverse air baghouse. A traveling blow ring carriage moves up
and down the bag companment (Figure 4-10). Each ring has a
number of slots where high velocity air jets penetrate the bag
tube and dislodge the accumulated dust layer (Figure 4-11).
The expense and complication of the blow ring mechanism
(motors. drives. and switches for both ring and fan) limits the
applicability of this equipment for air pollution control.
Bag Cleaning Comparisons
One way to compare bag cleaning mechanisms is by examining
air-to-cloth ratios. Air-to-cloth (A/C) ratios describe how much
dirty gas passes through a given surface area of filter in a given
time. A high air-to-cloth ratio means a large volume of air
passes through the fabric area. A low air-to-cloth ratio means a
small volume of air passes through the fabric. The A/C ratios
are usually expressed in units of (ftJ/min)/ftl of cloth
4-10
7. b. False
. .
Blow
ring
carriage
Figure 4-10. lle'9'ertc jet cleaning mog
blow rings.
-------
[(cm'/sec)/cmZ of cloth]. The A/C ratio can be used inter-
changeably with a term called filtration velocity. The units for
filtration velocity are ft/min (em/see). When using the A/C
ratios for comparison purposes one should use the units
(ft'/min)/ftZ or (cm'/sec)/cmz. Likewise, when using filtration
velocities one should use the units ft/min or em/sec. Air-to-
cloth ratios are also called gas-to-cloth ratios.
Reverse air cleaning baghouses generally have very low air-
to-cloth ratios.
For reverse air baghouses. the filtering velocity (filtration
velocity) range is usually between 1 and 4 ft/ min (0.51 and
2.04 em/see). For shaker baghouses, the filtering velocity
ranges between 2 and 6 ft/min (1.02 and 3.05 em/see). More
cloth is generally needed for a given flow rate in a reverse air
baghouse than in a shaker baghouse. Hence, reverse air
baghouses tend to be larger in size.
Occasionally, baghouse cleaning is accompli~hed by two
methods in combination. Many baghouses have been designed
with both reverse air and gentle shaking to remove the dust
cake from the bag.
Pulse jet baghouses are designed with filtering velocities
between 5 to 15 ft/min (2.5 to 7.5 em/see). Therefore, these
units usually use felted fabrics as bag material. Felted material
holds up very well under the high filtering rate and vigorous
pulse jet cleaning. Pulse jet cleaning methods have the advan-
tage of having no moving parts within the compartment. In
addition. pulse jet units can clean bags on a continuous basis
without isolating a compartment from service. The duration of
the cleaning time is short « 1.0 see) when compared to the
time length between cleaning intervals (approximately 20
minutes to several hours). The major disadvantage of high
pressure cleaning methods is that the bags are subjected to
more mechanical stress. Fabrics with higher dimensional
stability and high tensile strength are required for these units.
Air-to-cloth ratios for the various cleaning methods are given in
Table 4-4. Comparisons of the cleaning methods are given in
Table 4-5.
Table 4-4. Air-to-cloth ratio (filtration velocitY) comparisons
for three cleaning mechanuuu.
Cleaning Air-,o..do,h ra,io Filtration veloci,y
mechanism (cm'/oe<:)/cm' (f,'/min)/f,' cm/oec ftlmin
Shaking 1 to 3:1 2 to 6:1 1 to 3:1 2 to 6
R~v~ne air 0.5 to 2.0: 1 1 to 4.1 0.5 to 2.0: 1 1 to 4:1
Pulse je, 2.5 to 7.5:1 5 to 15:1 2.5 to 7.5:1 5 to 15:1
4-11
Cleaning
air.
Figure 4-11. Blow ring.
-------
Table 4-5. Comparison of bag cleaning parameten.
Parameter Shake cleaning Rever. air cleaning Pulse jet cleaning
Frt'qu~ncv l'suallv st'\'rral ClunPd one com. L'suallv. a row oC
cvelrs ~cond. panmt'nt it.( a bags at a ume.
adJu..abl. time. ~qutnclng ~quenced onr row
ont' companmrnc after another.
dle'r another; can ~quence such
can be continuous that no adjacent
or InUla(C~d bv rows clean onr
a maximum. aCI.. ano.h..:
pressure.drop mUliluon of cleaning
swuch can b. mg~red
bv maximum.
presoure.drop
switeh or may be
continuous
MOlion Simple harmonic ~nd. collapse oC Shock wave passes
or slnUlOldal bag (concave down bag; bag
inward) upon dis..nds Cram
deflallon. slowly ca~ momen.arily
reprnsurizr a
compartment aCer'r
complrtion of a
back. flush
Pt"ak ;tcef-lroratlao 1'0 10 g - -
Ampli.ud. Fracuon of an -
Inch 10 Crw
Inch"
Vlod. Off ..rum OCC'..ream On-Stream' an
difficult'lo.eI.an
applica.ions such
as coal firPd
boil.n. off... rum
compartment
elunlng b..ng
studied
Duration 10 10 100 cvcl.s. l [Q 2 man. Compresoed.alT
~O H'C 10 frw ancludlng valvr 1100 ps" pu~
minute'S openIng and dura.ion O. 1 see
closlftg and duSt bag row .CCec.ively
..."ling penods. oCC.lin.
reveDt aar now
"...IC normally
10.30...c
Common bag S, 8, 121ft. diam: 8.0 8. 12 in. diam: 22. S '0 6 in. diam:
dimenai0n8 10. 22, 30 Ct length 30. 40 Ct length 8 .0 20 Ct length
8~g tf'nSlon 50 [0 ;5 Ibs -
tvplcal. opumum
van... adJuSt.d
art~r on .SHe-am
Source VlcK.nna and Grein". 1981
4.12
-------
Review Exercise
1. Reverse jet or blow ring cleaning involves reversing the air
flow on each bag.
a. True
b. False
2. In reverse jet or blow ring cleaning 1. a. True
a. air jets enter the top of the bag fracturing the dust cake.
b. the air flow into the entire baghouse compartment is
reversed causing bags to deflate.
c. high velocity air jets penetrate the bag tube and dislodge
the accumulated dust layer.
3. Air-to-cloth ratios 2. c. high velocity air jets penetrate
a. describe how much dirty gas passes through a given sur- the bag tube and dislodge the
face area of filter in a given time. accumulated dust layer.
b. describe how efficiently bags are cleaned by a pulse of
reverse aIr.
c. indicate how fast the dirty air passes through a square
foot of cloth material.
4. The air-to-cloth ratio is frequently used interchangeably 3. a. describe how much dirty gas
with a term called filtration velocity. passes through a given surface
a. True area of filter in a given time.
b. False
5. Air-to-cloth ratios are usually expressed in units of 4. a. True
a. ft2/min.
b. (ft3/min)/ft2.
c. (ft/min)/ft2.
6. A high air-to-cloth ratio means that a volume 5. b. (ft3/min)/ft2.
of air passes through the fabric.
7. The baghouses that usually have the highest air-to-cloth 6. large
ratios are
a. pulse jet.
b . reverse air.
c. shaker.
7. a. pulse jet.
4-13
-------
Lesson 5
Baghouse Design Variables
Lesson Goal and Objectives
Goal
To familiarize you with the variables used by vendors to design
baghouse systems.
Objectives
At the end of the lesson you should be able to:
1. define pressure drop and recognize the equations used to
calculate pressure drop.
2. define filter drag.
3. define the tenns air-to-cloth ratio and filtration velocity,
and recall the typical air-to-cloth ratios for various
baghouse designs.
Introduction
Baghouses are designed by considering a number of variables:
pressure drop, filter drag, air-to-cloth ratz"o, and collection
efficiency. Although not always possible or practical, it is a
good idea to use a pilot scale baghouse during the initial stages
of the baghouse design. However, previous vendor experience
with the same or similar process to be controlled will generally
be adequate for design purposes. Careful design will reduce the
number of baghouse operating problems and possible air pollu-
tion violations.
Pressure Drop
Pressure drop (.1p), a very important baghouse design variable,
describes the resistance to air flow across the baghouse.
Pressure drop is usually expressed in mm of mercury or inches
of water. The pressure drop of a system (baghouse) is deter-
mined by measuring the difference in total pressure at two
points, usually the inlet and outlet. It can be related to the size
of the fan that would be necessary to either push or pull the
exhaust gas through the baghouse. A baghouse with a high
pressure drop would need a larger fan and more energy to
move the exhaust gas through the baghouse.
5-1
-------
Many different relationships have been used to estimate the
pressure drop across a fabric filter. In a baghouse the total
pressure drop is a function of the pressure drop across both the
filter and the deposited dust cake. Some minor pressure losses
due to friction also occur as the gas stream moves through the
baghouse.
The simplest equation used to predict pressure drop across a
filter is derived from Darcy's law governing the flow of fluids
through porous materials and given as:
(Eq. 5-1)
API = k\v,
Where:
ApI = pressure drop across the clean fabric,
in. HzO (cm HzO)
k\ = fabric resistance. in. HzO/(ft/min)
[cm HzO/(cm/sec)]
V, = filtration velocity. ft/ min (cm/ sec)
The term k\ is the fabric resistance and is a function of
exhaust gas viscosity and filter characteristics such as thickness
and porosity. Porosity describes the amount of void volume in
the filter.
The pressure drop across the deposited dust cake can be
estimated by using Equation 5.2 (Snyder and Pring. 1955).
This formula is also derived from Darcy's law and the
simplified form is given as:
(Eq. 5-2)
Ape = kzcjv,zt
Where:
Ape = pressure drop across the cake. in. HzO
(cm HzO)
kz = resistance of the cake. in. HzO/(lb/ftZeft/min)
[cm HzO/(g/cmzecm/sec)]
c; = dust concentration loading. Ib/ftJ (g/ cmJ)
v, = filtration velocity. ft/ min (cm/ sec)
t = filtration time, min (sec)
The term kz is the dust-fabric filter resistance coefficient and
is determined experimentally. This coefficient depends on
gas viscosity. particle density and dust porosity. The dust
porosity is the amount of void volume in the dust cake. The
porosity is related to the permeability. Permeability for the
fabric only is defined in ASTM standard D7S7.69 as the
volume of air which can be passed through one square foot of
filter medium with a pressure drop of no more than 0.5 inches
of water. The term kz is dependent on the size of panicles in
the gas stream. If the panicles are very small « 2 ,un) kz is
high. If kz is high, then the pressure drop will tend to increase
and the bags will have to be cleaned more frequently.
5-2
Pressure drop across the filter:
ApI = k\v,
Pressure drop across the deposited
dust cake:
Ape = kzc;v,zt
Dust-fabric filter resistance
coefficient:
kz
-------
The total pressure drop equals the pressure drop across the
filter plus the pressure drop across the cake and is given as:
(Eq. 5-3)
~PT = ~Pf + ~p.
~PT = k1 Vf + kZCiV/t
Equation 5.3 should be used as only an estimate of pressure
drop across shaker and reverse air cleaning baghouses. In the
industrial filtration process, complicated panicle-fabric inter-
actions are occurring just after the filtration cycle begins. In
addition, the filter resistance factor k1 can take on two values;
one value for the clean filter and another after the filter has
been cleaned. When the dust cake builds up to a significant
thickness the pressure drop will become exceedingly high (> 10
in. HzO or 30.5 cm HzO). At this time the filter must be
cleaned. Some dust will remain on the cloth even after
cleaning; therefore, the filter resistance level will be higher
than during original conditions. A baghouse is normally
operated with a pressure drop across the unit of 3 to 10 in.
HzO or less. Bag cleaning is usually initiated when the pressure
drop approaches this point.
Total pressure drop across a shaker
or reverse air baghouse:
~PT = k1 Vf + kzc. v/t
Review Exercise
1. The of a system is determined by
measuring the difference in total pressure at two points.
2. Compared to a baghouse with a high pressure drop, a
baghouse with a low pressure drop would need a large fan
and require more energy to move the gas through the
baghouse.
a. True
b. False
1. pressure drop
3. What is the formula used to estimate the pressure drop
across the clean fabric?
a. ~Pf= k1vf
b. ~p. = kZvf
C. ~Pf= V.ZCit
4. In the formula, ~p. = kZCiV/t, used to estimate the ~p across
the dust cake, the term kz is the dust-fabric filter resistance
coefficient. If the dust panicles are very small « 2 porn), kz
is large. In this case, the pressure drop will
a. generally decrease.
b. generally increase.
c. stay the same.
2. b. False
3. a. ~Pf= k1vf
5-3
4. b. generally increase.
-------
5. A baghouse is normally operated with a pressure drop
a. between 15 and 20 in. HtO.
b. greater than 20 in. HtO.
c. of approximately 3 to 10 in. HtO.
Filter Drag
Filter drag is the filter resistance across the fabric.dust layer.
The equation for filter drag essentially gives the pressure drop
occurring per unit velocity. It is a function of the quantity of
dust accumulated on the fabric and given as:
(Eq. 5-4)
s= ~p
VI
Where:
S = filter drag. in. HtO/(ft/min) [cm HtO/(cm/sec)]
~p = pressure drop across the fabric and dust cake.
in. HtO (em HtO)
V/= filtration velocity. ft/min (em/see)
As previously mentioned. the true filtering surface of a
woven filter is not the bag itself. but the dust layer. Dust
bridges the pores or openings in the weave. increasing the drag
rapidly.
Single Bag
A filter performance curve of a single bag of a fabric is shown
in Figure 5.1. The drag is plotted versus the dust mass
deposited on the filter.
The point c. on the graph is the residual drag of the clean
filter medium. The filter drag increases exponentially up to a
constant rate of increase. This is the period of cake repair and
initial cake buildup. Effective filtration takes place while the
filter drag increases at a constant rate. When the total pressure
drop reaches a value set by the system design. bag cleaning is
initiated. At this point. the pressure drop decreases (almost
venically on the performance curve) to the initial point. Cake
repair begins when the cleaning cycle stops and the cycle
repeats. Baghouses are designed to remove most of the dust
cake during the cleaning process. However. shaking or reverse
air baghouses are designed so that during the cleaning cycle
some dust will remain on the bags. Therefore. a dust layer will
not have to be built up again on the openings in the weave of
5.4
5. c. of approximately 3 to
10 in. HtO.
Filter drag:
s= ~p
VI
Cak~ ~ Effective filtration
repau
..
~
Ii:
l1li
"
..
~
Initiation of
cleaning cycle
Resistance of clean fa bric. .:.
Mau of dust deposited
Figure ~l. Performance curve for a lingle
woven bag.
-------
the fabric. If the fabric is cleaned too efficiently. the cake
repair cycle would be as long as the initial cake buildup.
lessening the overall effective filtration time of the baghouse.
Multicompartment Baghouse
In multicompartment baghouses where the various compart-
ments are cleaned one at a time. the perfonnance curve takes
on a different shape. In this case the change in the curve is less
pronounced than in Figure 5-1. The perfonnance curve has a
slight saw tooth shape for the net pressure drop across the
entire baghouse (Figure 5-2). Each of the minima points on the
curve represents the cleaning of an entire compartment. The
average pressure drop would be represented by the dotted line.
For optimum filtration rate and collection efficiency, the
baghouse should be designed to operate at a pressure drop that
approaches a constant value. This involves careful selection of
fabrics and cleaning mechanisms for the baghouse. The weave,
and any pretreatment of the fabric can affect the cake repair
time. Poor cleaning will increase the filter drag; therefore. it is
essential to thoroughly clean the bags to reduce the filter drag
effect. If cake repair time can be minimized, the pressure drop
will be lower. Consequently. the effective filtration rate will be
longer for optimum filtering use.
Pulse Jet Baghouse
In a pulse jet baghouse. felted filters are usually used as bag
material. Since there are no openings in the fabric material,
there is no initial cake buildup period. Effective filtration
begins immediately as the dust is filtered by the bag. The per-
fonnance curve of a pulse jet bag (or row of bags) is given in
Figure 5-3. The pressure drop across the bags is slightly higher
than with woven filters. The baghouse is usually operated with
pressure drops of 5 to 9 in. H20. In a pulse jet baghouse one
row of bags is cleaned at a time. Some of the dust is knocked
off the bags being cleaned while adjacent rows are still fil-
tering. Bag cleaning cycles are initiated to keep the overall
pressure drop across the baghouse within the designed range.
5-5
Cleaning initiated
, ,
Time
Figure 5-2. Overall pressure drop of a multi-
compartment baghowe.
Q.
o
..
...,
..
;
::I
..
~
Cleaning initiated
,
,
Mass of dust deposited
Figure 5-3. Performance curve of a pulse jet
bag or a row of bags.
-------
Review Exercise
1. The filter resistance across a fabric-dust layer is called
1. filter drag.
2. In a shaker baghouse using woven filters, effective filtration
begins as soon as the baghouse is turned on.
a. True
b. False
3. In a reverse air or shaker baghouse. bags are cleaned
a. to remove all dust completely.
b. to leave a small amount of dust on the bag.
c. to leave approximately 60% of the dust cake on the bag.
4. The pressure drop across a pulse jet baghouse is generally
higher than across a reverse air baghouse.
a. True
b. False
2. b. False
3. b. to leave a small amount of
dust on the bag.
Filtration Velocity:
Air-to-Cloth Ratio
The terms filtration velocity and air-to-cloth ratio can be used
interchangeably. The formula used to express filtration velocity
15:
(Eq. 5-5)
v,= Q
Ac
Where:
v, = filtration velocity. ftl min (cml sec)
Q = volumetric air flow rate. ftJ/min (cmJ/sec)
Ac = area of cloth filter, ftZ (cmZ)
Air-to-cloth ratio is defined as the ratio of gas f1Itered in
cubic feet per minute (dm) to the area of filtering media in
square feet. Typical units used to express the AIC ratio are:
(ftJ/min)/ftZ or (cmJ/sec)/cmZ
These AIC ratio units essentially reduce to velocity units.
The AIC ratio (filtration velocity) varies for various baghouse
designs (Table 5-1). Shaker and reverse air baghouses generally
have small AIC ratios. (Shaker units < 3:1 (cmJ/sec)/cmZ and
reverse air units <2.0:1 (cmJ/sec)/cmZ). On the other hand.
pulse jet units usually operate at AIC ratios between 2.5 and
5-6
4. a. True
Filtration velocity:
v,= Q
Ac
Table 5-1. Air-to
-------
7.5: 1 (cm' I sec)1 cmz For a given flow rate, pulse jet units can
be smaller in size (fewer bags) than the shaker and reverse air
baghouse.
The A/C ratio (filtering velocity) is a very important factor
used in the design and operation of a baghouse. Improper
ratios can contribute to inefficient operation of the baghouse.
Operating at an A/C ratio that is too high may lead to a
number of problems. Very high ratios can cause compaction of
dust on the bag resulting in excessive pressure drops. In addi-
tion. breakdown of the dust cake could also occur which in turn
results in reduced collection efficiency. The major problem of a
baghouse using a very low A/C ratio, is that the baghouse will
be larger in size.
Collection Efficiency
Extremely small particles can be efficiently collected in a
baghouse. Baghouse units designed with collection efficiencies
of 99.99% are common. Exhaust air from baghouses can even
be recirculated back into the plant for heating purposes, as
long as the gas stream is not toxic.
Baghouses are not normally designed with the use of frac-
tional efficiency curves as are some of the other particulate
emission control devices. Vendors design and size the units
strictly on experience. The baghouse units are designed to meet
particulate emission outlet loading and opacity regulations.
There is no one formula that can determine the collection effi-
ciency of a specific baghouse. Some theoretical formulas for
determining collection efficiency have been suggested. but
these formulas contain numerous (3 to 4) experimentally
determined coefficients in the equations. Therefore, these effi-
ciency equations give at best only an estimate of baghouse
performance.
Review Exercise
1. The terms filtration velocity, VI.
be used interchangeably.
a. True
b. False
2. Air-to-cloth ratio is defined as the ratio of gas filtered in
to the of
in square feet (ft2).
and air-to-cloth ratio can
1. a. True
2. cfm
area
filter media
5-7
-------
3. The air-to-cloth ratios for shaker baghouses are typically less
than (cm3/sec)/ cm2.
4. What are the usual air-to-cloth ratios for reverse air
baghouses?
a. less than 4: 1 (ft3/min)/ftZ
b. greater than 5: 1 (ft3/min)/ftZ
c. between 3: 1 and 8: 1 (ft3/min)/ftZ
3. 3:1
5. The air-to-cloth ratios for pulse jet baghouses are usually
less than reverse air and shaker baghouses.
a. True
b. False
4. a. less than 4:1 (ft3/min)/ft2
6. For a given exhaust flow rate, pulse jet baghouses are
usually smaller than reverse air baghouses.
a. True
b. False
5. b. False
7. Operating the baghouse at air-to-cloth ratios greater/less
than the designed values can cause problems in the
baghouse.
6. a. True
7. greater
5-8
-------
Lesson 6
Baghouse Design Review
Lesson Goal and Objectives
Goal
To familiarize you with the factors to be considered when
reviewing baghouse design plans for the permit process.
Objectives
At the end of the lesson you should be able to:
1. recall at least four factors important in good baghouse
design .
2. estimate the cloth area needed for a given gas process
flow rate.
Introduction
The design of an industrial baghouse involves consideration of
many factors including space restriction, cleaning method,
fabric construction, fiber, air-to-cloth ratio; and many con-
struction details such as inlet location, hopper design and dust
discharge devices. Air pollution control agency personnel who
review baghouse design plans should consider these factors
during the review process.
A given process might often dictate a specified type of
baghouse for particulate emission control. The manufacturers'
previous experience with a particular industry is sometimes the
key factor. For example, a pulse jet baghouse with its higher
filter rates would take up less space and would be easier to
maintain than a shaker or reverse air baghouse. But if the
baghouse was to be used in a high temperature application
(500°F or 260°C), a reverse air cleaning baghouse with woven
Fiberglas bags might be chosen. This would prevent the need
of exhaust gas cooling for the use of Nomex felt bags (on the
pulse jet unit) which are more expensive than Fiberglas bags.
All design factors must be weighed carefully in choosing the
most appropriate baghouse design.
6-1
-------
Review of Design Criteria
The principal design criterion is the gas flow rate to the
baghouse. measured in cubic meters (cubic feet) per minute.
The gas volume to be treated is set by the process exhaust. but
the ftltration velocity or air-to-cloth ratio is determined by the
baghouse vendor's design. The air-to-cloth ratio depends on a
number of variables. Figure 6.1 depicts a number of these
design variables. A thorough review of baghouse design plans
should consider the following factors.
Physical and chemical propenies:
type. shape, and density of dust; average and maximum
concentrations; chemical propenies such as abrasiveness.
explosiveness, electrostatic charge and agglomerating
tendencies. These are imponant for selecting the fabric
that will be used. For example. abrasive dusts will
deteriorate fabrics such as cotton or glass very quickly. If
the dust has an electrostatic charge. the fabric choice must
be compatible to provide maximum panicle collection yet
still be able to clean the bags without damaging them.
Gas flow rate:
average and maximum flow rate. temperature. moisture
content. chemical propenies such as dew point. cor-
rosiveness and combustibility. If the baghouse is going to
be installed on an existing source, a stack test should be
performed to determine the process gas stream propenies.
If the baghouse is being installed on a new source. data
from a similar plant or operation may be used. but the
baghouse should be designed conservatively. Once the gas
stream propenies are known. the designers will be able to
determine if the baghouse will require extras such as shell
insulation, special bag treatment. or corrosion-proof
coatings on structural components.
Fabric construction:
woven or felt filters. filter thickness. fiber size. fiber den-
sity. filter treatments such as napping. resin and heat
setting. and special coatings. Once dust and gas stream
propenies have been determined. filter choice and special
treatment of the filter can be properly made. For exam-
pIe. if the process exhaust from a coal fired boiler is 400 of
(204°C), with a fairly high sulfur oxide concentration. the
best choice might be to go with woven glass bags that are
coated with silicon graphite.
Fiber type:
natural, synthetic. Nomex. Teflon, etc. The design should
include e fiber choice dictated by any gas stream proper-
ties that would limit the life of the bag. (See Lesson 3 for
typical fabrics and fibers used for bags).
6-2
-------
Proper air-to-cloth (A/C) ratio:
reverse air lowest. shakers next,
the highest AI C ratio.
pulse jet baghouses allow
Diaphragm valve
Solenoid valve
Compressed air reservoir
.~...
J \
Top access
Clean air blow pipe
Vemuri
Inspection pan
Polyester felt bag
Access platfonn
Gas inlet
Figure 6-1. Design conaiderationa for a pube jet baghou.se.
6-3
-------
Cleaning methods:
low energy which are shaker and reverse air cleaning; high
energy which is pulse jet cleaning. The cost of the bag.
filter construction, and the normal operating pressure
drop across the baghouse help dictate which cleaning
method is most appropriate.
Cleaning time:
ratio of filtering time to cleaning time is the measure of
the percent of time the filters are performing; this should
be at least 10:1 or greater. For example. if the bags need
shaking for 2 minutes every 15 minutes they were on-line,
the baghouse should be enlarged to handle this heavy dust
concentration from the process.
Cleaning and filtering stress:
amount of flexing and creasing to the fabric; reverse air is
the gentlest. shaking and pulse jet have the most vigorous
stress on the fabric. For example, it would probably not
be advisable to use woven glass bags on a shaker or pulse
jet baghouse. These bags would normally not last very
long due to the great stress on them during the cleaning
cycle. However, some heavy woven glass bags (16 to 17 oz)
are being used on pulse jet units and shaker units.
Bag spacing:
bags must be properly spaced to eliminate rubbing against
each other; bags must be accessible for inspection and
maintenance service. The design should include access
ladders. walkways. and doors to get at bags for periodic
inspection and replacing.
Compartment design:
allowance for proper cleaning of bags; design should
include an extra companment to allow for reserve capacity
and inspection and maintenance of broken bags. Shaker
and reverse air cleaning baghouses that are used in con-
tinuous operation require an extra companment for
cleaning bags while the other companments are still on-
line filtering.
Space and cost requirements:
baghouses require a good deal of installation space; initial
costs, and operating and maintenance costs can be high.
Bag replacement will average between 25 and 50% of the
original number installed per year. This can be very
expensive if the bags are made of Teflon which are
approximately $100 for a 5-inch. 9-foot long bag.
Emission requirements:
efficiency in terms of opacity and grain-loading regula-
tions. Baghouses are very efficient. collection efficiency is
usually greater than 99+%.
6-4
-------
Typical Air-to-Cloth Ratios
During a permit review for baghouse installations the reviewer
should check the A/C ratio. Typical A/C ratios for shakers,
reverse air and pulse jet baghouses are listed in Table 6-1.
Baghouses should be operated within a reasonable design
A/C ratio range. For example, assume a permit was submitted
indicating the use of a reverse air cleaning baghouse using
woven Fiberglas bags for reducing particulate emissions from a
small foundry furnace. If the information supplied indicated
that the baghouse would operate with an A/C ratio of
6 (cm3/sec)/cm2 [12 (ft3/min)/ft2] of fabric material, one should
question this information. Reverse air units should be operated
with a much lower A/C ratio. The fabric would probably not
be able to withstand the stress from such high filtering rates
and could cause premature bag deterioration. Too high an
A/C ratio results in excessive pressure drops. reduced collection
efficiency, blinding. and rapid wear. In this case a better
design might include reducing the A/C ratio within the accep-
table range, thus adding more bags. Another alternative would
be to use a pulse jet baghouse with the original design A/C
ratio of 6 (cm3/sec)/cm2 [12 (ft3/min)/ft2] and use felted bags
made of Nomex fibers. However, Nomex is not very resistant to
acid attack and should not be used where a high concentration
of 502 or acids are in the exhaust gas. Either alternative would
be more acceptable to the original permit submission.
Typical air-to-cloth ratios for baghouses used in industrial
processes are listed in Tables 6-2 and 6-3. These values should
be used as a rule of thumb or guide only. Actual design
values may need to be reduced if the dust loading is high or
the panicle size is small. When companmental baghouses are
used. the design A/C ratio must be based upon having enough
filter cloth available for filtering while one or two compart-
ments are off-stream for cleaning.
6-5
Table ~l. Typical air-to-cloth ratios.
Baghowe
cleaning Air-to-<:Ioth ratios
method
Shaking 1.3 (ern"seel, em' 2.6Ift"nuoJ, ft'
Rev~rse au 0.5.2.0 lern' see), em' lA 1ft' rnmJ ft'
Pulse jet 2.5.7.5 (ern'/see)/em' 5.15 (ft" 1010)' ft'
Note: Alr-ro-cloth ratios are occasionally given as 2.0: 1
mst
-------
Table 6-2. Typical A/C ralios [(ft'/min)/fl') for !!elccled industrics..
I Fabric lilter
air"(CM:IOIh racio
, IndUSln
ReverK Pulse Mechanical
air jel .haker
8.J.slc Q,(\o~t'n fu.rnact's I j.;! 0 ,,~ I " 0 J 0
Bnck m~nufac(unng 1.0.20 9.10 :! ~. 3:! I
C.:Utablr ft'franortt's U 2.0 8.10 2.0.3.0
Clav rrfr3CtOrlt'5 I 5 :? () 8.10 ~ 5.3 2
Coal flr~d bOII~"
Conical LnclOrratOr5 I
COHon l(1nnm~ I
i Dt"u.n~'f"n( m.lnutanurmg I ~ I 0 5.tj :!.O.~ ~
! E(("([TlC uc lurnact'5 I 0.20 " ~ ~ 0 .I 0
i F..d mill. 10.10 3.0.0.0
Frrro.Jllov planu 2.0 9 2.0
GI.1u manufaCturing U
Get'\' Iron foundnrs I 0.2.0 7 8 2.5.30
Iron and su'rl t 5m(f~rlng) I 020 i.8 25.30
Korah rf'COvf'fV furnac~
Llmt' lulns 1.0.2.0 8.9 2.0.30
~1unlclpal InClnrralOf$
pf'crolrum cilcalvuc crackms
Pho'phal~ C~"ih,~r 1.8.2.0 8.9 30.3 :,
Pholphatt' rock crushing ;.10 3.0.3 ;
PolV\llOvl chlondr production 7
Ponland Cf'mf'm 1.2.1 :, 710 2.0.30
Pulp .nd p.~r t OUldlZ~d b~d
rr.J.Ctorl
St-condilrv ~Iumlnum smf'ltrn 6.8 2.0
St-cond..nr coppf'r smt'ltrrs 6.8
Stowage- sludgr m(lnC'racors
Surf.Jcr cOiltings 'prav boolh
8Hlgh dficumcv ~ sufficlt'nclv low gram loadlnlJ to t'xpt'C( a clrar stack.
Sourc~ EPA 1976 EP<\ ~;O 3-76-0\4.
Table 6-~. Typical AlC raliOi for fabric fillen UIed for conlrol
of paniculatc emillionl from industrial boilen.
Sile of boiler Tempera.ure Air-.o-cloch Cleaning Fabric
(10' Ib Heam (oF) ratio mechanism material
per hourI [ll'/minl/Il')
260 1 3 bollen) 400. ~ 4 I On. or orr.lin~ pulse Glass wuh 10~ T~Oon
or rrv~rx air coaling 124 011 yd')
170 t; boll~n) 000. ~ :, 1 Rl'vrI'W air with Gla.. wuh 10~ T~Oon
pul~ ]CI ...ISI coaung
14012 bollen! 360. 20 I Rnrnt' aar :-.10 0004 Fib~rglas wuh
"Iiconr.graphue.
T ~Oon finISh I
250 338. 2 3 I Shakr and defla.. Wovrn fibrrglas wuh
"Iiconr.graphi.. finish
200 13 bollen) 300. 36 I Shake and deOale Wo.en Fibergla. wuh
siliconr'graphitt' finish
~oo 12 bollen) Sloker. 285. 2.5 1 Re'VrfJr air GI... wuh T rOon finISh
10 300.:
pu\v~nled
coal. 350.
7; 150. 2.8:\ Rnt'nt' air Fibergla, wuh TrOon
coating
50 350. 3.0 1 On-line pul~ Glass wuh Trflon finISh
27012 boilen) 330. 3 7 1 On. line pulse Teflon Cell 123 0')
450 (4 bollen) 330. 3.7 1 On-line pulse T~Oon Cell (23 0"
380 :'IIA 2.0:1 Rrvt'rv ,..,. vibrator Glasa wuh 10~ TrOon
asaist coating
645 NA 2.0:\ Rrvrf'V air vibrator Glasa wuh 10~ T~flon
~IS[ coaung
1440 (3 boilen) 360. 341 Shake and deflale Woven Fiberglas wuh
"licone.graphur finish
Sourer: EPA. 1979
6-6
-------
Simple Cloth Size Check
Baghouse sizing is done by the manufacturer. A simple check
or estimate of the amount of baghouse cloth needed for a given
process flow rate can be computed by using Equation 6-1.
(Eq. 6-1)
VI = Q or A., = Q
A., vI
Where:
Ac = cloth area
Q = process exhaust rate
VI = filtration velocity
For example, the process gas exhaust rate is given as
4.72x 106 cm3/sec (10,000 ft3/min) and the filtration velocity is
4 em/see (A/C is 4:1 (cm3/sec)/cmz). Calculate the cloth area.
To determine the number of bags required in the baghouse,
one would simply use the formula:
Ab = 7I'dh
Where:
Ab = area of bag, m (ft)
71'=3.14
d = bag diameter, m (ft)
h = bag height, m (ft)
The bag diameter is 0.203 m (8 in.) and bag height is
3.66 m (12 ft). Calculate the area of each bag.
Calculate the number of bags in the baghouse.
A very imponant point to remember is that the bag length
may not be exactly that given in the published specifications.
For example, most 12-inch diameter bags are 11 5/8 inches in
diameter. The effective filtering area should be calculated
using the exact bag dimensions.
6-7
Example:
4.72x 106 cm3/sec
A., =
4 em/see
= 1,179,875 cm2 (cloth required)
= 117.98 m2 (cloth required)
Ab= 3.14x 0.203 mX 3.66 m
= 2.33 m2
117.98m2
Number of bags =
2.33
= 51 bags
-------
Review Exercise
1. From the baghouses listed below, which would take up less
space and be easier to maintain because of high filter rates?
a. Shaker
b . Pulse jet
c. Reverse air
2. The principal design criterion to consider is the:
a. bag length.
b. access to bag compartments.
c. gas flow rate.
d. bag diameter.
3. Gas and dust stream properties influence filter choice.
a. True
b. False
4. An appropriate ratio of filtering time to cleaning time
should be at least:
a. 3:1.
b. 1.5:1.
c. 5:1.
d. 10: 1.
5. An air-to-cloth ratio that is too high results in reduced
pressure drops.
a. True
b. False
6. Nomex is not very resistant to:
a. HtO.
b. COt.
c. SOt.
d. lead.
7. Calculate the area of a bag (A.) given a bag diameter of
15 inches and a bag height of 20 feet.
a. 942 feet
b. 70.5 inches
c. 78.5 feet
d. 25 feet
8. If the cloth area (A.,) is known to be 4050 ftt, how many
bags would be used in a baghouse with the bag area (A.)
given above?
a. 52 bags
b. 519 bags
c. 120 bags
d. 10 bags
6-8
1. b. Pulse jet
2. c. gas flow rate.
3. True
4. d. 10: 1.
5. b. False
6. c. SOt.
7. c. 78.5 feet
15
- x 20x 3.14= 78.5
12
8. a. 52 bags
4050 + 78.5 = 52
-------
Lesson 7
Baghouse Operation and
Maintenance
Lesson Goal and Objectives
Goal
To familiarize you with typical baghouse operation and
maintenance problems.
Objectives
At the end of the lesson you should be able to:
1. recall typical steps for baghouse inspection prior to
starting up.
2. recall typical factors to examine while operating the
baghouse.
3. recall typical maintenance steps for proper operation of
the baghouse.
Use of the Slide/Tape
This presentation will preview the major topics on baghouse
operation and maintenance presented in the text. You do not
need to follow the script as you view the slides; however. you
can use it to review the content. * The audiotape is designed to
automatically advance the slides at the correct place in the
script if your tape recorder has a mechanism for synchronizing
audiotape and slides. To use the slides and tape together.
advance the slides to slide 7-1-1. a focusing slide. Focus this
slide and start the tape. The tape recorder will advance the
slides for you.
*The script is included in the appendix.
7-1
-------
Suggested Readings
McKenna. J. D. and Greiner, G. P. 1981. "Baghouses". Air
Pollution Control EquiPment-Selection, Design, Operation
and Maintenance. Ed. by Theodore. L. and Buonicore. A. J.
Englewood Cliffs. N.].: Prentice Hall. Inc.
Reigel. S. A. and Applewhite. G. D. 1980. "Operation and
Maintenance of Fabric Filter Systems". Operation and
Maintenance for Air Particulate Control Equipment. Ed. by
Young, R. A. and Cross. F. L. Ann Arbor. MI: Ann Arbor
Science.
Baghouse Capacity
Baghouses can be grouped not only by the method used to
clean them, but also by the capacity of exhaust volume they
can handle. The three capacity ranges are low, medium, and
high. Low capacity baghouses are small off-the-shelf units that
normally handle 100 to 3000 cfm exhaust volume. These units
are prebagged and require little or no field assembly. Cleaning
methods used are pulse jet (canridge) or shaking.
Medium capacity units handle from approximately 3000 to
less than 100,000 cfm exhaust volume. These units are
generally prebagged and require little field assembly. Most
medium capacity baghouses use pulse jet cleaning with high
air-to-cloth ratios.
High capacity baghouses handle from 100,000 to 1.000.000
or more cfm exhaust volume. These units are usually field
assembled and bagged. Most high capacity baghouses use
reverse air or shake cleaning with low air-to-cloth ratios.
Installation
Depending on the baghouse chosen. installation and operation
stanup may take from a few days to a few months. In any
case, proper installation procedures will save time and money
and will also help in future operation and maintenance (O&M)
of the baghouse.
Good coordination between the baghouse designer and the
installation and maintenance personnel will help keep the
baghouse running smoothly for years. Occasionally this
coordination is overlooked. The baghouse is installed, turned
on. and forgotten about until it stops working completely. At
this point it may be too late to keep the unit going and the
7-2
-------
baghouse may have to be rebuilt or even scrapped. Some key
features to reevaluate during the installation period are listed
here:
Easy access to all potential maintenance areas: fans. motors,
conveyors. discharge valves, dampers, pressure and
temperature monitors. and bags.
Easy access to all inspection and test areas: stack testing
ports and continuous emission monitors (opacity monitors).
Weather conditions: the baghouse must be able to withstand
inclement weather such as rain or snow.
ETS Inc.. baghouse consultants, have suggested the fol-
lowing features for a properly designed and installed baghouse
(McKenna and Greiner, 1982):
1. Uniform air and dust distn'bu#on to all filters, Duct
design. turning vanes, and deflection plates all assist in
obtaining this. Often. they arrive loose and are field-installed.
If improperly installed, they can induce high airflow regions
that will abrade the duct or bag filters or cause reentrainment
and induce high-dust-concentration regions that can produce
uneven hopper loading and uneven filter bag dust cake.
2. Total seal of system from dust pickup to stack outlet,
Inleakage at flanges or collector access points either adds addi-
tional airflow to be processed or short-circuits the process gases.
Inleakage to a high-temperature system is extremely
damaging. as it creates cold spots and can lead to dew point
excursions and corrosion- If severe. it can cause the entire
process gas temperature to pass through the dew point and
result in condensate on the bags. Early bag failure and high
pressure drop will generally result. The best check for leaks is
to inspect the walls from inside the system during daylight.
Light penetration from outside isolates the problem areas. It is
particularly important to seal the dust discharge points in
negative systems. Inleakage here will result in incomplete or
no discharge, which can lead to reentrainment problems,
yielding high pressure drop and hopper fires.
3. Effectzve coatings and paint, Most systems are painted on
the exterior surfaces only. Take extra care to touch up
damaged areas with a good primer and if equipment is not
delivered finish-painted, apply it as soon as possible following
erection. Unprotected primers will soon allow corrosion and
require sandblasting plus many dollars to repair. If your system
has been internally protected with a coating, thoroughly
inspect for cracks or chips. particularly in comers, and repair
before operating. A poor interior coating can be worse than
none at all because it will trap corrosive elements between the
coating and the surface it was intended to protect.
7-3
-------
4. Properly installed fz'lter bags. The filter bags are the heart
of any fabric filter collection system. Improper installation can
result in early bag failure, loss of cleaning effectiveness, and
thus high pressure drop and operating costs or increased stack
emission. Each manufacturer provides instructions on the
proper filter bag installation and tensioning (where required).
These must be explicitly followed. Very often, early bag
failures can be traced to improper installation. Remember, it is
much easier to check and recheck bag connections, tensioning.
locations, and so on, in a clean. cool, dry collector than it will
be one day after startup. Bag maintenance usually accounts for
70% of annual maintenance time and money. Extra efforts in
this area during installation can have a significant effect.
5. Proper z'nsulatz'on installation. High-temperature collector
systems require special consideration in order to prevent O&M
problems. When handling high-temperature gases, it is impor-
tant to maintain the temperature of the gas and all collector
components coming in contact with it above the gas dew point.
Insulation is usually employed. Much of the time, all or a part
of the insulation is field-installed. Check to see that all surfaces
and areas of potential heat loss are adequately covered. In par.
ticular, check to see that field flashing also has insulation
beneath it. Cold spots cause local corrosion. Gross heat loss
may cause excessive warm-up time or lower the gas
temperature below the dew point.
6. Total seal between diTty side and clean sz'de of collector.
Remember, the primary purpose of the dust collector is to sepa-
rate the particulate matter from the gas by means of fabric filtra-
tion. This means that all the gas must pass through the fabric.
Any leaks bypassing the fabric filters will directly emit dust to
the stack and therefore reduce the collection efficiency of the
system. The time to inspect "bypass leaks" is before startup,
when everything is clean and accessible. The best technique is
to utilize a bright light on one side of the plenum and visually
observe for light penetration on the other. This is the most
effective in total darkness. Take that extra time to check this
important area. Tracking down stack emissions not associated
with bag failures can be extremely difficult after startup.
7. Properly l'nstalled and operating dampers. Most systems
employ several dampers to isolate areas of the system or control
the volume of air flow. Proper alignment is important both in
the case of internal blades and the operating linkage. In high-
temperature applications, special care must be taken to allow
for proper operation and sealing at the operating temperatures.
Some dampers may require readjusting after reaching high-
temperature operation. In modular systems, single modules are
normally isolated for bag cleaning and maintenance. Leakage
through these isolation dampers can cause improper bag
cleaning. It will also create a very poor ambient condition for
7-4
-------
maintenance workers to work in. This, in some applications,
can pose a health hazard, and in all applications results in
lower-quality workmanship or incomplete maintenance.
8. PToperly operating mechanical components. Most
mechanical components are designed with a normal operating
direction. Cylinder rod location, motor rotation, and so on,
must be checked. Remember, when hooking up an AC motor,
one has a 50% chance of being correct on the first try. Not
only will a backward-moving conveyor produce no discharge,
but it can pack material so that it bends the screw. Left uncor-
rected, a reversed screw conveyor will result in a full hopper.
The industry abounds with horror stories where full hoppers
have led to burned bags, or dust set up, requiring jack-
hammers to remove it.
9. Smoothly running fans. Fans must be checked for proper
rotation, drive component alignments, and vibration. Fans
should be securely mounted to sufficient mass to eliminate
excessive vibration.
10. Clean, dry compressed air. Most systems employ com-
pressed air to operate dampers, controls, instruments, and so
on. Probably more systems suffer shutdowns and maintenance
problems due to poor-quality compressed air than for any other
reason. Clean, dry air is necessary to maintain proper opera-
tion of the pneumatic components. In installations where the
ambient temperature drops below 32°F, a desiccant dryer
system is generally employed. Sometimes, insulation of air lines
and pneumatic components will be required. Often, these con-
siderations are not included in the dust collector system, with
"clean, dry compressed air to be supplied by owner."
Remember, the air must be clean and dry when it reaches the
pneumatic component.
7-5
-------
Each baghouse installation should have its own checklist
reflecting the unique construction components of the unit. The
installation crew should prepare a checklist before beginning
the final inspection and initial startup. ETS, Inc. has suggested
one typical inspection and startup checklist as shown in
Table 7.1.
Table 7-1. Inspection and stanup checklilt.
1. Visually IIUpec"
Slruaural connecllOns for ughlnlOll
Dua flanges for propn ",aI
Filler bap for proper seating in lUbe sheet
Dampen for opnauon and "'quence
Syaem fan. reverse air fan. and conYe"/On-check for propn rolallon
Electrical conttols for propn opnarion
Rolary valves or slide pIes for operation
2. Remove inspecrion door and check conveyor for lome ilems or obstructions
5. Adjult ductwOrk dampen-open or .1 propn "'lIing
4. Remove any lemporary baffles
5. Test horn alarm syaern. if included. by jumping conneaed seDlOn
6. SIan ~ conYe"/On and check for propn opnation
7. SIan reverse air fan. if included
8. SIan syaern fan
9. Log manometer and lempnalure (if appropriate) ~adinp al IS.minule
inlervals: log ~adinp
10. Check 10 - that reverse all dampen - cycling
11. Adjwt Ap swilch. if included
12. Determine syslem air volume and adjult dampen. u required
15. Check celb for dlUl leU.
14. Check to - Ihat dUll: .. being diJChuwed from hopper.
Source: McKenna and GrieDer. 1982.
7.6
-------
Installation errors can have a disastrous effect on the opera-
tion and maintenance of the baghouse. Typical installation
errors and their effect on O&M are given in Table 7-2.
Table 7-2. Typical installation enon and their effect on O&:M.
Item Immediate potential effeCt Long term
Baffle plates and turnmg vanes Uneven dust distribuuon: Bag wear. duct Wear.
improper installation or uneven hopper loading; hopper flfes
left out higher pressure loss
Poor seal of flanges and In leakage resulting in: Localized cold spotS resulting
access areas reduced inlet volume in:
higher fan volume component cOITosian
higher operating cosu bag degradauon
lower bal(house temperature
Poor seal at dust discharge Incomplete discharge. Reentrainment: creepmg ~p
flanges reentrainment: hopper fires
Cracked or chipped paint and Esthetics Corrosion
coatings
Improper bag te,,"ioning Ineffective cleaning; bag Bag wear: high .:1p
collapse
Improper bag seating Stack etnisoion Compliance failure:
bag wear: high .:1p
Incomplete insulation Cold spots Corrosion
Seal between dirty and clean Stack ernisoion: dirtying Compliance failure
air companmenu of clean side of plenum
Duct damper alignment Lou of flow control Poor maintenance ambient
Screw conveyor direction No discharge Bent screw: full hopper: fires
reversed
Fan mount Noise - vibration Broken c~mponents
Fan belt alignment Noise - improper fan volume Broken belts
Exposed compressed. air Freeze-up - condell5ation Damaged doW1Utream
line. without dryer components
Lack of i""pection aceess Lack of early warning sigm Major problet115
Lack of maintenance ace... Lack of regular preventauve Major breakdowns
maintenance
Source: McKenna and Greiner. 1982.
Review Exercise
1. Baghouses can be grouped by cleaning method or by
a. air pollutants for which they are designed.
b. length of bags.
c. capacity of exhaust volume handled.
d. number of bags.
2. Low capacity baghouses are usually field assembled and
bagged.
a. True
b. False
3. Inleakage at flanges or collector access' points can cause
on the bags which may result in early
and high
1. c. capacity of exhaust volume
handled.
2. False
7-7
3. con
-------
4. A poor interior coating is worse than none at all.
a. True
b. False
5. High capacity baghouses (> 100,000 dm) use reverse air or
shake cleaning and are usually field assembled.
a. True
b. False
4. True
6. Gas streams of high temperature should be maintained
a bove the
a. ignition temperature.
b. gas dew point.
c. concentration limit.
5. True
7. Cold spots in the baghouse can cause
a. local corrosion.
b. fires.
c. explosions.
8. Many systems suffer shutdown and maintenance problems
due to
a. low pressure drop.
b. low air-to-cloth ratio.
c. low dew point.
d. poor-quality compressed air.
9. Before the baghouse is staned up. the installation crew
should prepare and use a
6. b. gas dew point.
7. a. local corrosion.
8. d. poor-quality compressed air.
/'
9. checklist
Operation and Maintenance Training
Before the baghouse is staned up the plant engineer should
schedule training sessions for all plant employees that operate
and maintain the baghouse. In these training sessions the
following subjects should be covered: systems design. system
controls. critical limits of equipment, function of each
baghouse component. operating parameters that should be
monitored. good operating practices. preventive maintenance.
stanup and shutdown procedures, emergency shutdown pro-
cedures, and safety considerations.
O&M training !JeSSions should be attended by supervisors.
operators. and maintenance people. The training could be pro-
vided by the baghouse vendor or by a consulting company
specializing in baghouses. The length of training would vary
depending on the complexity of the system design. Average
training will ordinarily take at least 40 manhours for full-time
maintenance people.
7-8
-------
Baghouse Startup and Shutdown
A specific stanup and shutdown procedure should be supplied
by the baghouse vendor. Improper startup and shutdown can
damage the equipment. If hot moist gases are to be filtered.
the baghouse must be preheated to raise the interior
temperature in the baghouse above the dew point in order to
prevent condensation and potential corrosion problems. This
can be done by using heaters in each compartment or by
burning a clean fuel such as natural gas before filtering gases
from a coal fired boiler.
The baghouse must also be brought on line slowly to avoid
permanent damage to the fabric. Clean filters do not have a
protective dust cake on them and are sensitive to dust abrasion
and penetration by fine particles. Penetration can lead to per-
manent residual pressure drop. In some applications. bags are
precoated with a protective dust layer prior to bringing the
unit on-line. The filter velocity should always be kept low until
a sufficient dust cake is built up on the bags. This is indicated
by a pressure drop of 1 to 2 inches H20. The gas flow can then
be slowly increased to the designed rate (McKenna and
Greiner. 1982).
Some general rules for routine startup and shutdown sug-
gested by ETS. Inc. are:
Startup
Make sure all collector components are in working order and in
proper mode.
Do not allow higher-than-design filtering velocities or air
flow.
Avoid passing through (below) the dew point within the
baghouse when dirty gases are present. The system should be
preheated to above the dew point with clean. hot air before the
introduction of flue gas. During normal operation. maintain
the temperature above the dew point level.
Operate the bypass system to assure its readiness in an
emergency situation.
Check all indicating and monitoring devices for proper
operation.
Shutdown
Purge the collector with clean (hot when necessary) dry air
before allowing temperature to descend below the dew point.
When the collector cools at night it is possible that moisture will
condense on the bags once the dew point is reached.
7-9
-------
Do not store dust in the collector. Many maintenance
workers have resigned after spending a day with pick and
shovel inside a dust collector hopper.
Allow bags to clean down after dust flow ends. but do not
overclean.
Check to see that all componentS are in the proper shutdown
mode.
Routine Monitoring
The two indicators of the performance of a baghouse are col-
lection efficiency and pressure drop. If the pressure drop is
satisfactory. the proper amount of air is moving through the
baghouse. If the stack is clean. the baghouse- is doing the job it
was intended to do. Pressure drop is monitored by using a
manometer or magnehelic gage. Recorders can also be used to
give permanent pressure drop records. This can be useful for
determining maintenance needs and charting tendencies over
prolonged time periods. The opacity can be monitored by
visual observation or by using continuous monitors. Continuous
opacity monitors used in conjunction with a recorder will pro-
vide the data necessary for determining collector efficiency for
varying process conditions and for monitoring baghouse
malfunctions to determine maintenance needs. Typical
monitoring devices are listed in Table '.!S.
Table 7-5. Typical bagholl8C moairoriDg aad iad.icaciDg clnica.
lteal FlIDc:tioa
Piloclighu To show moron openoting. compamnenu on- or off. line. row of
bap being pulled
Opaci')' monitor To measure continuo... opaci')' of ..ack
Manometer or mapehelic To determine preooure drop at oario... poinu in the bapo...e.
gait!' Recorden are UJefui to gioe permanent prnaure drop rudinII'
Tempenoture indicaton To determine temperature at critical poinu in the bagh-
Cas now meten To measure actual gas flow rate through the bapUJe
Fan CUrTent. fan beanng To identify early warning signa indictating maintenance to the ran
temperature and ran
vibrator indicaton
'-10
-------
Review Exercise
1. Who should supply a specific startup and shutdown
procedure for baghouses?
a. The inspection team
b. The baghouse vendor
c. The process plant owner
d. The air pollution agency
2. Bringing a baghouse on-line quickly helps seal woven bags
and prevents damage to the fabric.
a. True
b. False
3. To operate properly. bags must be coated sufficiently with
a. paint.
b. condensate.
c. dust.
d. all of the above.
1. b. The baghouse vendor
2. b. False
4. Before allowing the collector temperature to descend below
the dew point. purge it with
a. clean dry air.
b. cool sprays.
c. an alcohol cleaner.
d. all of the above.
3. c. dust
5. The two indicators of the performance of a baghouse are
and
4. a. clean dry air
6. An opacity monitor is useful to baghouse maintenance
because
a. inspectors can monitor bag cleaning inside the baghouse.
b. inspectors can monitor the process stack gas plume.
c. inspectors can monitor operations of motors and on-and
off-line compartments.
5. collection efficiency
pressure drop
6. b. inspectors can monitor the
process stack gas plume.
Routine Maintenance
Good recordkeeping is the key to an effective maintenance pro-
gram. The logging of actual inspections. observations of the
collector. and preventive maintenance will help determine how
the baghouse is operating.
Inspection frequencies of all baghouse components should be
established. Vendors' recommendations of an inspection
schedule should be followed. A listing of typical periodic
maintenance follows.
7-11
-------
Daily Maintenance
1. Check pressure drop.
2. Monitor gas flow rate.
3. Observe stack outlet; visually or with a continuous monitor.
4. Monitor cleaning cycle; pilot lights or meters on control
panel.
5. Check compressed air on pulse jet baghouses.
6. Monitor discharge system; make sure dust is removed as
needed.
7. Walk through baghouse to check for nonnal or abnonnal
visual and audible conditions.
Weekly Maintenance
1. Check all moving parts on discharge system; screw-conveyor
bearings.
2. Check damper operation; bypass. isolation. etc.
3. Spot check bag tensioning; reverse air and shake bags.
4. Check compressed air lines including line oilers and filters.
5. Blowout manometer lines.
6. Verify temperature-indicating equipment.
7. Check bag-cleaning sequence to see that all valves are
seating properly.
8. Check drive components on fan.
Monthly Maintenance
1. Spot check bag-seating condition.
2. Check all moving pans on shaker baghouses.
3. Check fan for corrosion and blade wear.
4. Check all hoses and clamps.
5. Spot check for bag leaks and holes.
6. Inspect baghouse housing for corrosion.
Quarterly Maintenance
1. Thoroughly inspect bags.
2. Check duct for dust buildup.
3. Observe damper valves for proper seating.
4. Check gaskets on all doors.
5. Inspect paint on baghouse.
6. Calibrate opacity monitor.
7. Inspect baffle plate for wear.
Annual Maintenance
1. Check all welds and bolts.
2. Check hopper for wear.
3. Replace high-wear parts on cleaning system.
Sources: Reigel and Applewhite, 1980; McKenna and Greiner, 1981.
7.12
-------
Bag Maintenance
Inspecting and changing bags takes a long time and are the
highest maintenance costs in a baghouse. Bag failures occur at
varying times depending on the operation of the collector. The
longer the time before bag changeout, the lower the
maintenance cost to the owner. Typical bag life is from two to
five years.
Bag failures can be spotted through daily monitoring and
inspection. Stack opacity is a good indication of bag failure. If
the plume is diny. then some problem exists, either in a single
companment or throughout the baghouse. In a compartmen-
talized baghouse it is possible to monitor the stack while
isolating a companment. Stack emissions would be reduced if
the compartment with broken bags were taken off-line. In a
noncompanmentalized baghouse it may be necessary to check
the entire unit for broken bags.
Three ways to search for broken bags are (Reigel and
Applewhite. 1980):
1. hunt for the hole.
2. hunt for the accumulation of dust which can be
related. to a nearby hole.
3. use a detecting device.
In shaker and reverse air baghouses where dust is collected
on the inside of the bags, bag failures occur frequently at
the bottom of bags. Accumulation of dust on the cell plate is
sometimes visible, making it relatively easy to spot the failure.
It may be necessary to inspect the entire circumference and
length of the bag if the hole is higher up on the bag tube. In
reverse air baghouses, other bag failures can also occur near
the anti-collapse rings and at the top cuff where the bags were
attached. In shaker baghouses, bags tend to fail at the top
where they are attached to hooks or clamps.
In pulse jet baghouses it is normally very difficult to locate
bags that have failed. However, in many baghouses dust
accumulation on the top tube sheet or in the blow pipe above
the failed bag will be readily noticeable (Reigel and
Applewhite, 1980).
A recent technique for locating torn bags is to use fluores-
cent powder and a black light. Fluorescent powder is injected
in the inlet to the baghouse. An ultraviolet light is used to scan
the clean air side of the baghouse. Leaks can be detected by
the glow of the powder getting through a torn bag. This
technique is useful for spotting broken welds or leaks in the cell
plates, tube sheets or housing.
The imponance of detecting broken bags depends on the
baghouse design. In reverse air and shaker units, leaks in the
bags can cause air streams or jets of dust to abrade adjacent
bags. This causes what is known as the "domino effect". where
7-13
-------
one tom bag creates another tom bag. In pulse jet b agho uses ,
tom bags are not as great a problem since the dust leaves the
inside (clean side) of the bags. If opacity limits are exceeded.
the bag must be changed. It may take several broken b'ags to
cause an opacity violation. Maintenance can then be scheduled
for some other convenient time.
In the past. bags were usually replaced as they failed.
Recently. however. it has been found that a new bag in the
vicinity of old ones will be forced to take on more dust (air will
tend to follow the path of least resistance) and will become
worn-out quicker than the old "seasoned" bags (Reigel and
Applewhite. 1980). It has become accepted practice in reverse
air and shaker baghouses to simply tie off a tom bag and stuff
it into the cell plate. If the failure is close to the cell plate then
the hole should be plugged. This can be accomplished by steel
plate plugs with gaskets or sand bags to seal off the hole. In
pulse jet baghouses with top access. a plug is placed over the
tube sheet hole of the failed bag.
It is most imponant to keep track of the bag failure rate of
individual bags. This can be helpful to correct any conditions
that would cause premature bag failure. In addition. it is
helpful in scheduling complete changeout of bags at a con-
venient time.
Troubleshooting
When a baghouse begins to have problems. it is estremely
advisable to contact the vendor to identify and correct the
problem. A typical troubleshooting guide is listed in Table 7-4.
This table was prepared by ETS. Inc. and should be used only
as a general guide.
7-14
-------
Table 7-4. Troubleshoo[ing guide.
Symprom P.,..ible cause Remed.
High colleCtor '1alfunctlon of bag.cI~aning 5vst~m Check all cleamng.svstem
prt!S5ur~ drop compont'nts
Int!ffectlvt' cleanmg .\1OOif. cleanmg cvcle
Revlt'w with deslgneT
Rt't'ntramment of dust In colieccoT Check dIScharge valves
due (0 low-density matenal or Lower AI C raua
mleakage at discharge
Wetting of bags Control dew pOint excursions
Drv bags with clean air
Clean ba~ wnh vacuum or wet wash
Too high A, C ratio either through Verifv gas volume
added capacay or Improper Reduce mlet volume 1Ł possible I
oTlgJnal design Rev1t~w wnh designer
Change in inlet loading or particle Test
disaibulion Review with designer
Abnormallv low \tanometer line(s) plugged Blow back through lines
pres.sure drop Protect sensing pOint from dust
or water buildup
IncorpoTue autopurging system
In ~nsing linn
Manomett~r lint'(s) broken or Verify with local manomeu~r
uncoupled Inspect and repair
Overcleaning of bags Reduce cleamng energy and/ or
cycle time
Suck emiMlon Broken bag Set bag maintenance ~ctlon
Bag IXnn~abllity tncr~a~ Test bag
Check cleanmg .nergy' cycle
and reduce if possible
Clean.to.diny plenum leakage Inspect and repair
Chang~ of inl~t conditions T~t and r~vi~w
Puffing High pres.sure drop acros.s baghouse S.e a bOil
-------
Spare Parts
An inventory of spare pans suggested by the baghouse vendor
should be on hand for baghouse maintenance. A typical listing
as suggested by Reigel and Applewhite (1980), is given in
Table 7-5.
Table 7-5. SuggeICed span: para.-
Bags
BaS suppo" casa (pw.e jet and plenum pw.e)
BaS ciampi
5
-------
Lesson 8
Industrial Applications of Baghouses
Lesson Goal and Objectives
Goal
To familiarize you with the typical industrial uses and basic
cost estimates of baghouses.
Objectives
At the end of the lesson you should be able to:
1. recall four process industries that use baghouses to control
particulate emissions.
2. recognize the use of baghouses in industrial and utility
applications.
3. recall how to use charts and figures to estimate the cost of
baghouses.
Introduction
Fabric filters have been used for particulate emission reduction
for many industrial applications. Baghouses have been
designed to collect particles in the submicron range with
99.9+% control efficiency. They have occasionally been used to
remove particles and then recirculate the clean air back into
the plant to help supplement heating needs. Baghouses have
been used in the chemical, steel. cement. food, phar-
maceutical, metal working. aggregate, and carbon black
industries. Shaker. reverse air, and pulse jet baghouses have
been used in a number of industrial applications as shown in
Table 8-1.
Table 8-1. Typical indwtrial applications for baghouses.
Shaker Reverse air Pube jet
Screening. crushing. and Cement kilns Phannaceuticals
conveying of rock Lime kilns Food industry
producu Electric steel furnaces Woodworking
Low temperature steel Gypsum calcining Sinter plants
applications Ore smelters and roasters Metal working
Metal working Sintering plants Foundries
Mining operations Rock dryers Textiles
Textiles Foundries Chemical industry
Woodworking processes Carbon black Coal fired boilers
Chemical industry Magnesium oxide kilns Asphalt batch plants
Food industry Coal fired boilers
Coal fired boilers
8-1
-------
One recent baghouse application is filtering flyash in both
industrial and utility boilers. Here, baghouses are becoming as
popular as electrostatic precipitators for removing 99.7 to
99.9+% of the paniculate matter from the flue gas.
Table 8-2 lists some coal fired boilers that use a baghouse for
controlling paniculate emissions.
Table 8-2. Selected baghowes wed for fiy uh control from
coal fired boilen.
Boiler rize Temper- Air-co-
Plant Baghoue Fabrie atUre elotb ralio
(MW) (adm) (01') (elm/ft')
Pennsylvania Power
and Light
Sunbury Station 87 888.000 (4 total) GIUI coated 325 3.0:1
Rrvme air with Teflon
Holtwood Station 220.000 Combined GIUI coated 350 2.4:1
shake and with Teflon
rnene air
Brunner Island Revene aif GIUI coated 2.0:1
Station with Teflon
Nebrulta Public
Power District
Kramer Station 30120.000 (4 tOlal) GI- coated 325 2.0 to 2.4: I
10192.000 Rrvme air with Teflon
Southwestern Public
Service Company
Harrington Station 350 1.650.000 Revene air GI- coated "5 3.2 to 5.3:1
with silicon/
graphite
Source: JAPCA. 1979.
Examples of typical baghouse installations are given in Table
8-3. This table lists the industry, exhaust gas temperature, dust
concentration, baghouse cleaning method, fabrics. and air-to-
cloth ratios. This list is by no means inclusive of the industries
using baghouses for controlling paniculate emissions. Typical
air-to-cloth ratios of shaker, reverse air, and pulse jet
baghouses for various industries are also given in Tables 6-2
and 6-3.
8-2
-------
Table 8-3. Typical baghouse installations.
Process dust T emperarure Air-to-<: loth
Industry concentration Baghou,,", Fabrics rauo
(grift') (of) (cfm/ft')
Alummum
furnaces 6 co ~O Shak~r ;\lomex. Orlan 250 10 375 2.0102.5.1
scrap conveyor Puis< J~t Poly~S(~r 100 7.0<080.1
Asphalt batch plants Pu Is~ J~t ;\lomex 250 ~ 0 '0 6.0'1
Coal fir~d bOlI..s Reverse air Glass 350 <0 ~50 2.0.1
(1 5 ~ suJfur coal) Puis~ J~t T~non 300 10 450 4.0: I
Coal processing
pulvt"nzmg mill I PuLs~ J~I :-.10m.. fdt 240 ~ '0 6 I
drv~r Puls~ J~t :-;om~x f~lt ~OO 5 co 7 I
roll~r mIll Puis< J~t Polv
-------
Review Exercise
1. Baghouses cannot be used for the collection of flyash from
coal fired boilers since the flue gas deteriorates the bags.
a. True
b. False
2. For baghouses used on coal fired boilers, the bags are
usually made of
a. cotton
b. glass
c. wool
1. b. False
3. Baghouses with bags made of woven glass usually have air-
to-cloth ratios
a. greater than 6.0:1
b. approximately 7.5:1
c. less than 4.0:1
4. Pulse jet baghouses with polyester felt bags cannot be used
to collect iron oxide dusts from steel furnaces.
a. True
b. False
2. b. glass
3. c. less than 4.0: 1
5. Baghouses have been used for filtering dust-laden gas from
cement kilns, clinker coolers. and crushing operations.
a. True
b. False
4. b. False
5. a. True
Dry Sulfur Dioxide (SOl) Control Systems
One promising new technology for reducing sulfur dioxide
(501) emissions from combustion sources is using dry flue gas
desulfurization (FGD). In dry FGD, the flue gas containing 501
is contacted with an alkaline material to produce a dry waste
product for disposal. This technology includes:
. injection of an alkaline slurry in a spray dryer with col-
lection of dry particles in a baghouse or electrostatic
precipitator (ESP);
. dry injection of alkaline material into the flue gas stream
with collection of dry particles in a baghouse or ESP;
. addition of alkaline material to the fuel prior to
combustion.
These technologies are capable of 501 emission reduction
ranging from 60 to 90% depending on which system is used.
Table 8-4 summarizes the key features of each of these
technologies. These technologies have been used on boilers
8-4
-------
burning low sulfur coal (usually less than 2 %) and are attrac-
tive alternatives to wet scrub bing technology, particular! y in
the arid western V.S.
Table 8-4. Key features of dry flue gas desulfurizatioD SysteDU.
SO. Pamculate
emiuion emiJaion Development
Proceu Sorbentl removal removal
efficiency efficiency statUi
(%) (%)
Spray dryer with Sodium carbonate 60.90 99+ Th~ u,ili,y boilers
a baghouae or ES P Lime (400.500 MW) '0 be
Limes,one .,aned up 1981. 1982.
1985. Two indus,rial
boilers on-line.
Dry injection with a Sodium carbonate 60-90 99+ ~o commercial installations
baghouae or ESP Sodium bicarbonate planned as of 1980.
Nahcolite
Comb_ion of Limestone pellet 75-80 99+' EP A currendy funding
coall limestone Lilne pilot ,estS on small
mixture with a industrial boiler.
low NO. burner
'Note: a baghouae or ESP ;. used for paniculate emiasion control.
Source: EP A . February 1980.
spray Dryer with a Baghowe or ESP
The only commercial dry FGD installations in the V.S. at this
time use a spray dryer. Alkaline is injected into a spray dryer
with dry particle collection in a baghouse or ESP. Spray dryers
have been used in the chemical, food processing. and mineral
preparation industries over the past 40 years. Spray dryers are
vessels where hot flue gases are contacted with a finely
atomized wet alkaline spray. The high temperatures of the flue
gas, 250 to 400°F, evaporate the moisture from the wet
alkaline sprays, leaving a dry powdered product. The dry
product is collected in a baghouse or ESP (Figure 8-1).
Figure 8-1. Spray dryers with baghowe.
8-5
-------
Flue gas enters the top of the spray dryer and is swirled by a
fixed vane ring to cause intimate contact with the slurry spray
(Figure 8-2). The slurry is atomized into extremely fine droplets
by rotary atomizers. The turbulent mixing of the flue gas with
the fine droplets results in rapid SOz absorption and evapora-
tion of the moisture. A small portion of the hot flue gas is
added to the spray-dryer-discharge duct to maintain the
temperature of the gas above the dew point. Reheat prevents
condensation and corrosion in the duct. Reheat also prevents
bags in the baghouse from becoming plugged or caked with
moist particles.
Sodium carbonate solutions and lime slurries are the most
common absorbents used. A sodium carbonate solution will
generally achieve a higher level of SOz removal than lime slur-
ries (EPA. February 1980). When sodium carbonate is used.
SOz removal efficiencies are approximately 75 to 90%. lime
removal efficiencies are 70 to 85% (EPA. February 1980).
However. vendors of dry scrubbing systems claim that their
units are capable of achieving 90% SOz reduction using a lime
slurry in a spray dryer. Lime is very popular for two reasons:
lime is less expensive than sodium carbonate; sodium carbonate
and SOz form sodium sulfite and sodium sulfate which are very
soluble causing leaching problems when landfUled.
Some of the evaporated alkaline spray will fall into the
bottom of the spray dryer and be recycled. The majority of the
spray reacts with SOz in the flue gas to form powdered sulfates
and sulfites. These panicles. along with fly ash in the flue gas,
are then collected in a baghouse or electrostatic precipitator
(see 413 Student Manual. EPA 450/2-80-066). Baghouses have
an advantage because unreacted alkaline material collected on
the bags can react with any remaining SOz in the flue gas.
Some process developers have reported SOz removal on bag
surfaces on the order of 10% (Kaplan and Felsvang. 1979).
However. since bags are sensitive to wetting. a 35 to 50°F
margin above the saturation temperature of the flue gas must
be maintained (EPA, February 1980). ESPs have the advantage
of not being as sensitive to moisture as baghouses. However.
SOz removal is not quite as efficient using ESPs.
In a spray dryer. finely atomized alkaline droplets are con-
tacted with flue gas which is at air preheater outlet
temperatures (250 to 400°F). The flue gas is humidified to
within 50°F of its saturation temperature by the moisture
evaporating from the alkaline slurry. Reaction of the SOz with
the alkaline material proceeds both during and following the
drying process. although to what degree is not completely
understood. Since the flue gas temperature and humidity are
set by air preheater outlet conditions. the amount of moisture
that can be evaporated into the flue gas is also set. This means
that the amount of alkaline slurry that can be evaporated in
8-6
Spray nozzle
To
baghowe
Figure 8-2. Spray dryer.
-------
the dryer is limited by flue gas conditions. Alkaline slurry
sprayed into the dryer must be carefully controlled to avoid
moisture in the flue gas from condensing in the ducting, par-
ticulate emission control equipment, or the stack. SOz removal
efficiencies are generally < 85% (EPA, February 1980).
A number of spray dryer systems have been planned for or
installed on industrial and utility boilers. These are listed in
Table 8-5. Spray dryers will become more popular as
experience with existing units is funher documented. They will
be particularly useful in meeting NSPS regulations for utility
boilers burning low sulfur coal that require only 70% SOz
scrubbing.
Table 8-5. Commercial spray dryer FGD systems using a baghouse.
Coal .ulfur SO, emillion
Station or Size IDlUllation Syorem remoyal
plant (MW) date deocripaon Sorbent COnteDt efficiency
(%) (%)
OUer Tail Power 410 6/81 Rockwell/Wheelabracor. Soda ash 0.78 70
Company; Frye system: fo.... (sodium
Coyote Station spray towen in carbonate)
No. I. parallel with 5
Beulah, NO atomizen in each:
revene air - .haker
baghouae with
Dacron bap
Buin Electric: 500 Spring 1982 Babcock and Wilcox: Lime 0.54.0.81 85-90
Laramie River fo.... 'pray reacton with
Station No.5. 12 "y.jet" nozzles
Wheatland. Wy in each: electrostatic
precipitator
Strathmore Paper 14 12/79 Mikropul: spray dryer Lime 2-2.5 75
Co.: and p~ jet:
Woronco. MA baghouae
Celanese Corp.; 51 2/80 Rockwelll Wheelabrator- Lime 1-2 85
Cumberland, MD Frye; one spray tower
followed by a baghouae
Source: EPA. February 1980.
Dry Injection
In dry injection systems, a dry alkaline material is injected into a
flue gas stream. This is accomplished by pneumatically injecting the
dry sorbent into a flue gas duct, or by precoating or continuously
feeding sorbent onto a fabric filter surface. Most dry injection
systems use pneumatic injection of dry alkaline material in the
boiler furnace area or in the duct that precedes the ESP or
baghouse. Sodium-based sorbents are used more frequently than
lime. Many dry injection systems have used nahcolite, a naturally
occurring mineral which is 80% sodium bicarbonate found in large
reserves in Colorado. Sodium carbonate (soda ash) is also used but is
not as reactive as sodium bicarbonate (EPA, February 1980). The
major problem of using nahcolite is that it is not presently being
mined on a commercial scale. Large investments must be made
before it will be mined commercially. Other natural minerals such
as raw trona have been tested; trona contains sodium bicarbonate
and sodium carbonate.
8-7
-------
Dry injection systems have been tested at a number of power
stations throughout the U .5. Descriptions of these pilot systems
can be found in Survey of Dry S02 Control Systems (EPA,
February 1980). The major problems with dry injection systems
are the low sodium utilization in the process and the disposal of
leachable sodium-sulfur compounds. EPA reports that only 40
to 60% of the dry alkaline injected material is used at high
502 removal conditions (EPA, February 1980).
Review Exercise
1. One promising technology for reducing both 502 gas and
particulate emissions involves the injection of an
slurry in a spray with dry particle collection in
a baghouse.
2. In a spray dryer, moisture is from the wet
alkaline sprays, leaving a powdered product.
3. In dry sulfur dioxide control systems using a spray dryer.
the most common alkaline absorbents used are
a. sodium citrate and magnesium oxide.
b. sodium carbonate and lime.
c. sodium bisulfate and sodium hydroxide.
4. Dry FGD systems using lime injected in a spray dryer and a
baghouse for dry particle collection are capable of 70% 502
reduction and 99+% particulate matter removal efficiency.
a. True
b. False
1. alkaline
dryer
2. evaporated
dry
3. b. sodium carbonate and lime.
4. a. True
Capital and Operating Cost Estimations
This section contains generalized cost data for baghouse
systems described throughout this manual. These data should
be used only as an estimate to determine systems costs. In some
cases the cost of the control device may represent only a very
small portion « 20%) of the total installed cost; in other cases
it may represent the total cost. Variations in the total cost can
be attributed to a number of variable factors such as cost of
auxiliary equipment. new or retrofitted installation, local labor
costs, engineering overhead. location and accessibility of plant
site. and installation procedure (factory or field assembled).
This cost estimation data. included in this appendix, first
appeared in an EPA publication (EPA. 1976) and then in a
series of articles published in the Journal of the Air Pollution
8-8
-------
Control Association (JAPCA, 1978). The reader should refer to
these publications for additional information concerning this
subject. These estimations represent equipment costs based on
a reference date of December 1977 and are estimated to be
accurate to within :I: 20% on a component basis, except where
noted (JAPCA, 1978).
The cost data for fabric filters is based on the net cloth area.
The net cloth area is the total filter area available for on.
stream filtration. This would not include the isolated compart-
ment being cleaned in the case of an intermittently cleaned
baghouse. For intermittently cleaned baghouses requiring an
off. line compartment, the total cloth area must be calculated
as the gross cloth area. The gross cloth area is the net cloth
area of the baghouse plus the cloth area for an extra compart-
ment. The gross cloth area can be calculated for various values
of net cloth area from Table 8.6.
The cost for various baghouses - shaker, reverse air, or pulse
jet units - are listed in Figures 8- 3 through 8-7. These figures
include curves of additional prices for stainless steel construc.
tion, insulation, suction baghouses, and standard or custom
designed units. Suction baghouses are negative pressure systems
with the fan located on the clean side of the baghouse. Stan-
dard baghouses are predesigned and built as modules which
can be operated singly or combined to form units for larger
capacity. Custom baghouses are designed for a specific applica.
tion. are erected in the field, and are used most often for large
capacity applications. The cost of the baghouse units in Figures
8-3 through 8-7 are for the baghouse only (bags are not
included). The costs for bags using various fabrics can be
calculated from Table 8-7.
Table 8-7. Bag prices ($/ft'). Data valid for December 1977.
Cbao Type Dacron Orion Nylon Nomes Gbao Polypropylene Cotton
Mechanical shaker.
<'20,000 fl' 0.~6 0.62 o.n 1.14 0.47 0.62 0.4~
Mechanical shaker,
> 20.000 fl' O.~I 0.57 0.67 1.04 0.42 0.52 0.~8
Slandard Pulse jel 0.57 0.9~ - 1.30 - 0.67 -
Reverse air O.~I 0.57 0.67 1.04 0.42 0.52 0.~8
Mechanical shaker 0.21 O.~I 0.42 0.62 0.26 O.~I 0.~8
Cuslom R~erse air 0.21 O.~I 0.42 0.62 0.26 O.~I 0.~8
8-9
Table 8-6. Approximate guide 10 estimate
gross clotb area.
~ et cloth area G rou cloth area
(fl') (fI')
1 - 4000 \lultlplv bv ~
4401-12000 l.5
12001-NOOO 1.25
24001 - 36000 1 17
36001 - 48000 1 125
4800 1 - 60000 III
6000 I - 72000 1 10
72001 - 84000 1.09
8400 I - 96000 1.08
9600 I - 108000 I 07
108001- 1~2000 1.06
1~2001- 180000 1.04
-------
:55
:50
25
.;
.~ 15
:t:
5
140
120
...
Note: Baghouse price: $:5:551 + 1.84
times the net cloth area. All price
add.ons in Figures 8.3 through 8.7
are calculated in this manner.
2
4
Net cloth area.
Figure 8-5. IntermitteDt, p..-ure, mechanical shaker baghoUle priCei venUi
net cloth area. Data valid for December 1977.
Basic baghouse price:
5:570 + 7.6 x net cloth area
(bags not included)
Net cloth area. 1000 sq ft
Figure 8-4. ConbnUOUl, suction or pre5lure, pulle jet haghoUle priCei
venus net cloth area. Data valid for December 1977.
8-10
-------
...
<:>
<:>
::
oj
u
.;:
Q"
100
Net cloth area. 1000 sq ft
Figure 8-5. Continuous. pressure, mechanical shaker baghou.se prices
Verlua net cloth area. Data valid for December 1977.
...
<:>
<:>
<:>
1500
1200
oj
u
.;:
Q"
450
Net fabric area. 1000 sq ft
Figure 8-6. Cuatom PreslUn: or suction haghou.se prices
venua net cloth area. Data valid for December 1977.
8-11
-------
320
"
.=
::I:: 120
80
10
30
100
20
40
Net cloth area.
Figure 8-7. CoauauoUl, prellure, reYerIC air baghoUie prica
venUi aet cloth area. Dara valid for December 1977.
8-12
-------
Example:
A baghouse is used to clean the exhaust from an industrial
boiler with a flow rate of 50,000 cfm. The baghouse is a
reverse air unit, suction type, using glass bags and an air-to-
cloth ratio of 1.5. The baghouse should include an extra com-
partment for off-line cleaning.
Net cloth area =
gas volume
air-to-cloth ratio
Calculate the gross cloth area from Table 8-6.
Table 8-6. Approximate guide to estimate
gJ'OII cloth area.
Net cloch area G.... cloth area
(ft') 20,000 ft' O.~I 0.57 0.67 1.04 0.42 0.52 0.38
Standard Pulse jet 0.57 0.93 - 1.30 - 0.67 -
Reverse air O.~I 0.57 0.67 1.04 0.42 0.52 0.~8
Mechanical shaker 0.21 0.31 0.42 0.62 0.26 0.31 0.38
Custom Reverse au 0.21 0.31 0.42 0.62 0.26 0.31 0.38
8-13
50,000
Net cloth area =
1.5
= 33,333 ft2
Gross cloth area= 33,333 x 1.17
= 39,000 ft2
Baghouse
Suction
Insulation
Bags
Total
$142,680
14,170
75,940
16,380
$249,170
-------
Lesson 9
Design Criteria for Permit Review:
Problem Set
Lesson Goal and Objectives
Goal
To familiarize you with the review of baghouse plans by using
a problem set.
Objectives
At the end of the lesson you should be able to:
1. detennine the fabric filter material to use for a given set
of data.
2. detennine the bag cleaning method appropriate to a
given set of data.
Introduction
This lesson contains an example of the review of a typical
baghouse installation plan submitted to an air pollution control
agency for approval. This example is designed using the topics
covered in the previous seven lessons. The infonnation supplied
by the owner and/or operator of the air pollution source must
be sufficient in order for the review to be complete.
You should refer to various lessons in this course to complete
this review exercise.
Example
The Joe Magarac Steel Company is planning to install two
150-ton electric steel furnaces. The furnaces will be charged
with molten iron and cold scrap. The company is installing a
baghouse to control paniculate emissions. The peninent
process and baghouse data is given below. The main question
here is - should this plan for construction of this air pollution
source be approved by the State review engineer?
9-1
-------
Process Information
Process equipment:
Operating schedule:
Exhaust gas temperature:
Exhaust gas conditioning:
Exhaust gas volume
handled:
Inlet dust concentration
(to baghouse):
Panicle size data:
Baghowe Information
Positive pressure baghou.se
Reverse air cleaning:
Air-to-cloth ratio:
Pressure drop:
Bags:
Fabric:
Companments:
Bags/companment:
Dust/ outlet concentration:
Collection efficiency:
two 150-ton 3-phase electric arc
furnaces
24 hours/day. 7 days/week,
52 weeks/year
at canopy hood and furnace
tap = 27300F
water cooled by evaporation and
air dilution
2.290,000 acfm at 150 of (total
from both furnaces)
1.5 to 5.0 gr/ dscf
Size Percent
(#,m) (%)
>44 7
20-44 7
10-20 6
5-10 8
<5 72
from a separate fan 48.000 cfm at
15 in. HzO. 70°F
3:1
6 to 8 in. HzO
34.7 ft long. 11. 75 in. diameter
Dacron woven bags. silicon treated
34
228
0.0052 gr/dscf
99.77%
Solution
The panicle size data shows that the selection of baghouse is
very good since the majority of the panicles are very small
« 5 #'M) in diameter. The exhaust volume to the baghouse is
2,290.000 (total from both furnaces) at 150°F. The air-to-cloth
ratio is 3: 1.
1. To determine the cloth area needed. use the formula:
Ac= Q.
v,
9-2
A/C ratio = 3: 1
Ac = 2.290,000 ft'/min
3 ft/ min
= 763.334 ftZ
-------
2. To deteqnine the area of the bags required in the
baghouse, use the fonnula:
Ab = 1I"dh
Where:
Ab = area of bag. ft2
11"=3.14
d = bag diameter, ft
h = bag height, ft
3. To calculate the number of bags needed in the baghouse:
A.:
Number of bags = -
Ab
4. There are 228 bags per compartment. A good baghouse
design would include 2 extra compartments; 1 for bag
cleaning. and 1 for bag maintenance.
Number of bags
Number of compartments =
Number bagsl compartment
Since it is impossible to have a partial compartment, the
design should have 34 compartments; 32 for filtering. 1 for
cleaning. and 1 for maintenance.
5. From Tables 6-1 and 6-2, the air-to-cloth ratio of 3:1 seems
to be reasonable.
6. From Table 3.1. woven Dacron bags can withstand con-
tinuous temperatures up to 275°F or 135°C. Since the gas
temperature to the baghouse is less than 150°F, then the
use of Dacron bags is fine.
7. This baghouse is a positive pressure system and will
probably have roof vents at the top of the unit. This will
present some minor inconvenience in stack testing for source
compliance validation. The agency should require the
source operator to conduct compliance tests by using a high
volume filter in the top of the baghouse or some other
appropriate testing method.
8. The agency should require that the source owner submit an
operation and maintenance schedule that will help keep the
baghouse on-line.
9. It appears that this baghouse construction plan meets the
design criteria given in Lesson 6. This plan should be
approved.
9.3
11. 75
Ab=3.14X - ftX34.7 ft
12
= 106.7 ft2
N b f b 763,334 ft2
urn er 0 ags =
106.7 ft/bag
= 7154 bags
7154
Number of compartments = -
228
=31.3
A/C ratio = 3: 1
Dacron bags
Baghouse system = Positive pressure
Plan approved
-------
Review Exercise
The Cheeps Brewing Co. is planning to install a coal fired
industrial boiler for producing process steam and heat. The
boiler information and control equipment data are given
below. Should this plan be approved by the air pollution
control agency?
Boiler Information
1 pulverized coal fired boiler
Heat input: 152 X 10' Btu/hr
Coal: sulfur content 2%
ash content 10%
heat content 13,000 Btu/lb
24 hours/day, 7 days/week.
40 weeks/ year
48,000 acfm
360 to 390 of
10 gr/scf
Operating schedule:
Exhaust gas volume:
Exhaust gas temperature:
Inlet dust concentration
(to baghouse):
Particle size data:
Baghowe Information
Negative pressure baghouse
Pulse jet cleaning:
Air-to-cloth ratio:
Pressure drop:
Bags:
Fabric:
Number of compartments:
Number of
bags/ companment:
Size Percent
(/Lm) (%)
>60 5
20-60 7
10-20 20
5-10 30
<5 38
4 companments
4.5:1
6 in. HzO
12 ft long. 5 ~ in. diameter
23 oz Teflon felt
5
144
The baghouse is insulated to prevent condensation. Dust is
removed from the hopper by a pneumatic conveyor.
Stack height: 89 ft
Stack diameter: 4 ft 6 in.
Fan is induced draft:
100 hp and 580 rpm
9-4
-------
Sol ution
From examining the boiler and baghouse data a number of
points can be made.
1. The choice of fabric material used to make the bags can be
obtained from Figure 3-1. The logical choice can be the
following since the gas temperature is 360 to 390°F:
glass bags
Teflon bags
Nomex bags
Using Nomex bags would probably be ruled out because the
sulfur content is 2 % and the sulfur oxides and acids formed
destroy this material. Glass bags could be used for this unit.
Teflon bags would also be a good choice with the only deterrent
being their high cost.
2. The air-to-cloth ratio can be checked from Tables 6-1 and
6-3. For a pulse jet baghouse an air-to-cloth ratio of 4.5:1
(cfm/ftZ) is well within the limits of the typical range. The
use of a pulse jet baghouse will also enable the designer to
push the air-to-cloth ratio a little higher than if a reverse air
baghouse with woven glass bags were used.
3. The exhaust gas volume is 48.000 acfm at 360 to 390°F.
The air-to-cloth ratio is 4.5: 1. Calculate the cloth area:
Ac=Q
VI
4. Calculate the bag area:
Ab = 1I"dh
5. Calculate the number of bags needed:
Ac
Number of bags = -
Ab
6. There are 144 bags in each compartment. The design plan
calls for 5 compartments. which give a total of 720 bags.
This would be adequate in terms of filtering the fly ash. If
one compartment needed maintenance. the gas flow rate
into the other 4 would be higher. pushing up the air-to-
cloth ratio. Maintenance could also be performed during
scheduled boiler down time. or by reducing the steam load
to approximately 80%. An operation and maintenance
schedule should be included in the design plan.
9-5
Glass
Teflon
A/C ratio = 4.5: 1
48.000 ft3 I min
Ac = 4.5 ft/min
= 10.667 ftZ
Ab = 3.14 x 5.25 ft x 12 ft
12
= 16.49 ftZ
10.667 ftZ
Number of bags = 16.49 ftZ
= 647 bags
Number of compartments = 5
Number of bags
(from plan) = 720
-------
7. This baghouse is a negative pressure system with an induced
draft fan. 89-foot stack and 4.5-foot stack diameter. This
unit could easily be tested for compliance and the agency
should request a stack test before issuing an operating
permit.
8. This plan should be approved.
9-6
Plan approved
-------
References
Bethea, R. M. 1978. AŁr PollutŁon Control Technology: An EngŁneering Analysis PoŁnt of
VŁew. New York: Van Nostrand Reinhold Company.
Cheremisinoff, P. N. and Young, R. A., eds. 1977. Azr Pollutz'on Control and DesŁgn
Handbook, Part 1. New York: Marcel Dekker, Inc.
Cross, F. L. and Hesketh, H. E., eds. 1975. Handbook for the OperatŁon and MaŁntenance
of Azr PollutŁon Control EqUtpment. Westport, CN: Technomic Publishing Co., Inc.
Environmental Protection Agency (EPA). October, 1981. APTl Course 413, Control of
PartŁculate EmissŁons, Student Manual. EPA 450/2-80-066.
Environmental Protection Agency (EPA). February, 1980. Survey of Dry SOz Control
Systems. EPA 60017-80-030.
Environmental Protection Agency (EPA). 1979. PartŁculate Control by Fabn'c FŁltratz'on on
Coal-Ft'red lndustnal BoŁlers. EPA 625/2-79-021.
Environmental Protection Agency (EPA). 1976. CapŁtal and Operating Costs of Selected
Azr Pollutz'on Control Systems. EPA 450/3-76-014.
Environmental Protection Agency (EPA). 1973. Azr PollutŁon EngŁneen'ng Manual. 2nd ed.
AP-40.
Frederick, E. R. 1974. Some Effects of Electrostatic Charges in Fabric Filtration. j. Az'r
Pol. Control Assoc. 24: 1164-1168.
Hesketh, H. E. 1979. Azr PollutŁon Control. Ann Arbor: Ann Arbor Science Publishers Inc.
Kaplan, S. M. and Felsvang, K. 1979. Spray Dryer Absorption of SOz from Industrial
Boiler Flue Gas. 86th National AICHE Meeting Paper, Houston, Texas, April, 1979.
Kraus, M. N. 1979. Baghouses: separating and collecting industrial dusts. Chem. Eng,
86:94-106.
McKenna, J. D. and Greiner, G. P. 1981. "Baghouses". AŁr Pollutz'on Control
EqUtpment-Selection, Desz'gn, Operation and Maz'ntenance, ed. by Theodore, L. and
Buonicore, A. J. Englewood Cliffs, N.J.: Prentice Hall Inc.
Neveril, R. B., Price, J. U. and Engdahl, K. L. 1978. Capital and Operating Costs of
Selected Air Pollution Control Systems- I. j. Azr Poll. Control Assoc. 28:829-836.
Proceedings: Symposium on the use of fabric filters for the control of sub-micron par.
ticulates, April 8-10,1974, Boston, MA.j. AŁr Poll. Control Assoc. 24:1139-1197. 1974.
Proceedings: The User and Fabric Filtration Equipment III, October 1-3, 1978. Niagara
Falls, NY. Air Pollution Control Association Specialty Conference.
Reigel, S. A. and Applewhite, G. D. 1980. "Operation and Maintenance of Fabric Filter
Systems". Operation and Maz'ntenance for AŁr PartŁculate Control EqUtpment, ed. by
Young, R. A. and Cross, F. L. Ann Arbor, MI: Ann Arbor Science
Stem. A. C., ed. 1977. Azr Pollutz'on, 3rd ed. vol. IV. Engz'neen'ng Control of AŁr Pollu.
tz'on. New York: Academic Press.
Sittig. M. 1977. Partz'culates and Fz'ne Dust Removal Processes and Equzpment. New Jersey:
Noyes Data Corporation.
Theodore, L. and Buonicore. A. J. 1976. lndustnal AŁr PollutŁon Control EqUtpment for
Particulates. Cleveland: CRC Press.
R-l
-------
Appendix
Baghouse Operation and Maintenance
Slide
Script
Selected Visuals*
1.
2.
3.
4.
BAGHOUSE OPERATION
AND MAINTENANCE
5. Baghouse installation and operation stanup may take from a few
days to a few months. Using proper installation procedures will save
time and money and will reduce future operation and maintenance
expenses.
Inltanallon
6. Good coordination between the baghouse designer and the installa-
tion and m~intenance crews will help keep the baghouse running
smoothly for yean. Some key features should be reevaluated during
the installation period.
Is there easy access to all potential maintenance areas
7.
such as fans, moton, conveyon, discharge valves,
dampen, pressure and temperature moniton, and bags.
8.
Is there easy access to all inspection 'and test areas
such as stack testing pons and opacity moniton.
Will the baghouse be able to withstand inclement
weather such as rain or snow.
9. Each baghouse should have its own checklist reflecting its unique
construction components. The installation crew should prepare the
checklist before beginning the final inspection and initial stanup.
~~.
\}:;'"::-,_.~~'; I,',
, ,,-,' f I
,-.(f '-. ' ;
./' '
~
*illustrations included here, no live shots.
A-I
-------
Slide
Script
10. The installation crew should visually inspect the essential baghouse
components to ensure that they are properly installed.
Are the structural connections securely welded or bolted?
11.
12.
IS.
14.
15.
16.
Are duct flanges sealed?
Are fIlter bags seated properly on tube sheet or cell plate
thimbles?
Do all dampers operate, and do they operate in the
correct sequence?
Do all system fans. reverse air fans, and conveyors
rotate properly?
Are all electrical controls operating?
And. do the rotary or trickle valves discharge the
dust efficiently?
17. You should also perform other checklist functions.
Remove the inspection door to check conveyors for loose
itema or obstructions.
18.
19.
Stan screw conveyors to check rotation direction.
Stan the fans. Check to see if air is blowing in the
right direction and measure the air flow.
A-2
Selected Visuals
/,
I \
~~.n
I.'~:)~...j..
,)~( ..',
~{.,
I :
...1..,., ...-
-------
Slide
Script
20.
Log the pressure drop and temperature readings.
21.
And, check to see if dust is being discharged from the
hopper.
22. Before the baghouse is staned up. the plant engineer should
schedule training sessions for till plant employees who will operate
and maintain the baghouse.
23. These training sessions should cover systems design and controls;
maximum and minimum equipment limits; good operating prac-
tices; preventive maintenance; stanup. shutdown, and emergency
shutdown procedures; and safety considerations.
24. The baghouse vendor should always supply a specific stanup and
shutdown procedure.
A-3
Selected Visuals
-::
,~'\
====-
-fn: ~
~ I ' ';=:"d
If I I -----'
2'
"~i~'
~!.)
. - " ""'"'
-~!
" ,
f I
JJ
~,
A\
'_J
Q,
II ~c.::r
Equl- UmIt8
ap.8- Pr-
-?;~ ==:=....
;.1 '-- I 581.." ,
/' -,)
// 2:;.6
,.J
-------
Slide
Script
25.
If hot moist gases are to be filtered. the baghouse must be
preheated to raise the interior temperature in the baghouse above
the dew point. This will prevent condensation and potential
corrosion problems.
26. To avoid permanent damage to the fabric. bring the baghouse
on-line slowly. In some applications, bags are precoated with a
protective dust layer. Keep the filter velocity low until a sufficient
dust cake is built up on the bags.
27. To keep the baghouse in top operating condition, the entire
baghouse or individual compamnenu must be shut down for
periodic maintenance. Before allowing the internal baghouse
temperature to fall below the dew point, purge the baghouse with
clean, hot. dry air.
28. Clean the bags by initiating the cleaning cycle. Be careful not to
overclean, or the original dust cake on woven filters will be
destroyed. /'
29. And finally. empty the hopper of all dust.
SO. Once a baghouse is operating, it needs to be routinely monitored to
be sure it is operating efficiently.
S 1. The two primary indicators of baghouse performance are collection
efficiency and pressure drop. A clean stack indicates good collection
efficiency .
A-4
Selected Visuals
1.
',' ", V'I
I V 'f' 1~,
~~~:
-'----r--~
, ,I ,I
: r'\
, 1"11:' ,~
ii' I
" ''''~
I' -I t I
JI /,];, ,;ij~
(' ~rJ
i
,-'
~
~a
'J
RouU-
Monitoring
CoII- EffIcInc:y
~ Drop
-------
Slide
Script
32. Stack plume opacity can be monitored by visual observation or by
using continuous monitors.
33. Pressure drop is monitored by using a manometer or magnehelic
gauge. Stripchan recorders can also be used to give permanent
pressure drop records. They can be useful for determining
maintenance needs and for chaning tendencies over prolonged time
periods.
34. Good recordkeeping is the key to an effective maintenance program.
If you keep a log of actual inspections, observations, and preventive
maintenance. it should be easy to determine how the baghouse is
operating.
35. Establish a schedule for inspecting all baghouse components. It is
best to follow the vendor's recommendations. You will need to per-
form daily. weekly, monthly. quanerly. and annual inspections.
36. Perform the following inspections every day:
-walk through the baghouse to check for normal or abnormal
visual and audible conditions
37.
-check the pressure drop
-monitor the gas flow rate
-check the cleaning cycle
38.
-check compressed air on pulse jet baghouses
39.
-monitor the discharge system by making sure dust is removed
as needed,
-and observe the stack plume opacity
40. Once a week,
-spot check bag seating conditions
-spot check for bag leaks and holes
-check all moving parts on shaker baghouses
A-5
Selected Visuals
I r F-~=c.:,~l
EII=--===--: i
Recorda ! ::.::::.-::.: =. .
I ::'.-===;:'---=-": '
--..----.--
----.....-.
--------- ,
::.::::.-::.:::.:: I
i4«~~
~/~~
, ~~%~
! I I I!' I
! ~ ' 11: f ; If >
.
, ~! .
.f! f ~ .
2 !.
<'
uuuuW
Dally
Weeldy
-------
Slide
Selected Visuals
Script
41.
.check fans for corrosion and blade wear
.check all hoses and clamps
.inspect the baghouse housing for corrosion
42.
In addition to daily and weekly, other inspections must be made
once a month:
.spot check bag tensioning in reverse air and shaker
baghouses
.blow out the manometer lines
everify the working order of temperature-indicating equipment
Monthly
4~.
.check the compressed air lines. including line oilers and
filters
.check the bag cleaning sequence to see that all valves are
seating properly
44.
.check all moving parts on the discharge system and check
the screw conveyor bearings
.and, check the drive components on a fan.
45. At least once every three months,
.thoroughly inspect all bags
.calibrate the opacity monitor
Quarterly
46.
.check gaskets on all doors
.inspect the paint on the baghouse
A.6
-------
Slide
Script
47.
.inspect the baffle plate for wear.
.observe the dampers for proper seating.
.and, check the ducts for dust buildup.
48. And, once a year.
.check all welds and bolts
.check the hoppers for wear. and
.replace high-wear parts on the cleaning system.
49. Because of the time involved. the highest maintenance cost in a
baghouse involves inspecting and changing the bags. Failures can
occur in different places on the bag depending on the operation of
the dust collector.
50. Stack opacity is a good indication of bag failure. If the plume is
dirty. then some problem exists. either in a single compartment or
throughout the baghouse.
51. You can search for a broken bag in three ways:
.you can hunt for the hole,
52.
.you can hunt for the accumulation of dust that is often
associated with a nearby hole.
A.7
Selected Visuals
Annual
_,~
,.. ~ Bag Maintenance
~=-w~\
~ rn
- yy
.-
-
,..~~
/. .
!
I
I~ ~
'~ I
~----'- " ."
- -
:J'"'"- --
""'- -
--..."I~"'---"'''--"'' .' -~~ ---...---...
I . j
I ~ ,
! ~~~..
---- ~ ""----" . . j --- ""--"" ""--'"
II ~'1' ..
-------
Slide
Script
53.
.or you can use a detecting device.
54. In shaker baghouses. where dust is collected on the inside of the
bags, failures occur frequently at the bottoms of bags and also at
the top where they are attached to hooks or clamps.
55.
In reverse air baghouses, failures occur most frequently at the
bottom of the bags. and also near the anti-collapse rings and top
cuffs where the bags are attached.
56. In both shaker and reverse air baghouses. an accumulation of dust
on the cell plate is sometimes visible, making it relatively easy to
spot the bag that failed. However, to find the actual hole, it may be
necessary to inspect the tmnNJ circumference and length of the bag.
A-8
Selected Visuals
-------
Slide
Script
57. In pulse jet baghouses, it is usually very difficult to locate bags that
have failed.
58. However, in many pulse jet units, dust accumulation on the top
tube sheet or in the blowpipe above the failed bag will be readily
noticeable.
59. Recently, a new and effective technique has been developed for
locating tom bags. Fluorescent powder and a black light are used to
search for tom bags.
60. Fluorescent powder is injected in the inlet to the baghouse. An
ultraviolet light scans the clean air side of the baghouse.
61. Leaks are detected by observing the glow of the powder that leaks
through a tom bag. This technique is useful for spotting broken
welds or leaks in the cell plates, tube sheets, or housing.
A-9
Selected Visuals
~ ~1tt -' - '....J ..JUI"IU
-------
Slide
Script
62. An inventory of spare pans suggested by the baghouse vendor
should be on hand for baghouse maintenance. After operating the
baghouse a few years, the maintenance crew will know which parts
fail most frequently.
65. Some parts can be easily replaced and save shutdown time. A
complete bag changeout is needed every three to four years.
64. The rings welded on the suppon cages for pulse jet bags may
separate after continual use.
65. Bag clamps may wear out or corrode.
66.
Baffle plates may wear out, particularly when they are used with
heavy dust concentrations.
67. In reverse air baghouses, bags must occasionally be realigned on
their thimbles. Tensioning springs must also be adjusted periodically
to prevent bags from sagging.
68. Fan belts. bearings, and gaskets for all mechanical components will
also wear and need to be replaced. Thus, a collection of spare parts
will save time and money and will encourage preventive
maintenance practices.
A-IO
Selected Visuals
1:~
-------
Slide
Script
69.
Preventive maintenance safeguards against baghouse problems that
may cause shutdowns by detecting them early. Once detected. many
problems can be eliminated before they become major.
70.
Routine maintenance will keep the baghouse functioning and
prevent total plant shutdown.
71.
If the baghouse remains operational on a continuing basis. the
process emissions are controlled and the plant can keep operating
within the emission limits specified by the standards for protecting
the environment.
72.
73.
74.
A-ll
Selected Visuals
~ ~/ 'c!/0
"':-<"~ ~M .. ,~~~
-.r- -"'::J..-. 1."'- ~I'
"'-1 ~ ~ '-, ~~. "'\ ,'<";
'~--~: ~~'Yo~~~
......-1 ~ 0 I
~ ~
- -J- -, \
J,t. I "H
'-' 10,.,.1 10,.,.1 ~~
Than'" to the following for
the u.. of photographa:
~ . _can PNdoIon (nd..-..
(I I . ETS. Inc.
. . Journal of Teflon
~ ~. Tho McC.I.... Corparo-
. Roya. WIN P1'odUct8
. lam Indu8Ut..
BAGHOUSE OPERATION
AND MAINTENANCE
T8Cludca1 eon-t: Oovtd 5. -
1----- DnI4ID: Mordyn M. P-
G..pbIco: .... Hubor
"'-""""1 AudIo: Dovtd Churchill
Nan.doII: RIck P.""
Developed and produced by:
Northrop Services ,Inc.
under
EPA Contract No. 68-02-3573
-------
TECHNICAL REPORT DATA
(Plellse Telld IlUUUcrions on rhe Tellerse before completinv
,. REPORT NO. 12. 3. RECIPIENT'S ACCESSIOH'NO.
EPA 450/2-82-005
4. TITLE AND SUBTITLE 5. REPORT DATE
APTI Course SI:412 April 1982
Baghouse Plan Review 6. PERFORMING ORGANIZATION CODE
Student Guidebook 8. PERFORMING ORGANIZATION REPORT NO.
7. AUTHORIS)
David S. Beachler
Marilyn Peterson 10. PRCIGRAM ELEMENT NO'
8. PERFORMING OR~ANIZATION NAME AND ADDRESS
Northrop Environmental Training 11. CONTRACT/GRANT NO.
Northrop Services Inc.
P.O. Box 12313 68-02-3573 .
Research Triangle Park, NC 27709
12. SPONSORING AGENCY NAME AND ADDRESS 13. TYPE OF REPORT AND PERIOD COVERED
U.S. Environmental Protection Agency Student Guidebook
Manpower and Technical Information Branch 14. SPONSORING AGENCY CODE
Research Triangle Park, NC 27711
15. SUPPLEMENTARY NOTES
EPA Project Officer for this Student Guidebook is R. E. Townsend, EPA-ERC, MD-20,
Research Triangle Park, NC 27711
16. ABSTRACT
This Student Guidebook is a self-instructional course, APTI Course SI:412 "Baghouse
Plan Review." This course is designed for engineers and other technical personnel
responsible for reviewing plans for installations of fabric filtration air cleaning
devices. The course focuses on review procedures for baghouse devices used to
reduce particulate air pollution from industrial sources. Major topics include:
general baghouse description, bag cleaning methods, fabric selection and filter
types, design parameters affecting collection efficiency. and operation and
maintenance problems associated with baghouses.
.
,
17. KEY WORDS AND DOCUMENT ANALYSIS
~. DESCRIPTORS b.IDENTIFIERS/OPEN ENDED TERMS C. COSA TI Field/Group
Air Pollution Control Self-Instructional 13 B
Particulate Emission Control Guidebook for a 5 I
Baghouses Baghouse Plan Review 68 A
Training Manual
, 8. DIST"" BUTION STATEMENT Un1:iJRited 18. SECURITY CLASS (TlJu Report) 21. NO. OF PAGES
National Audio Visual Center Unclassified 111
20. SECURITY CLASS (TIJu pille) 22. PRICE
National Archives and Records Service, GS Unclassified
Order Service HH
EPA ,iln)u.l.. .ŁU4U~
------- |