Revision 2
June, 1988
AIR POLLUTION SOURCE
FIELD INSPECTION NOTEBOOK
Prepared by:
Richards Engineering
Durham, North Carolina
Prepared for:
U.S. Environmental Protection Agency
Air Pollution Training Institute
Purchase Order 6D3843NASA
June 16, 1988
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DISCLAIMER
This manual was prepared by Richards Engineering for the Air
Pollution Training Institute of the U.S Environmental Protection
Agency in partial fulfillment of Purchase Order 6D3843NASA. The
contents of this report are reproduced herein as received from the
contractor. The opinions, findings, and conclusions expressed are
those of the author and not necessarily those of the U.S. Environ-
mental Protection Agency. Any mention of product names does not
constitute endorsement by the U.S. Environmental Protection Agency.
The safety precautions set forth in this manual and presented at
any training or orientation session, seminar, or other presentation
using this manual are general in nature. The precise safety precau-
tions required for any given situation depend upon and must be tail-
ored to the specific circumstances. Richards Engineering expressly
disclaims any liability for any personal injuries, death, property
damage, or economic loss arising from any actions taken in reliance
upon this manual or any training or orientation session, seminar, or
other presentations based upon this manual.
iii
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TABLE OF CONTENTS
Page
Safety Guidelines see cover
1. Inspection of Fabric Filters 1
1.1 Components and operating principles 1
1.2 General safety considerations 14
1.3 Inspection summaries 15
1.4 Inspection procedures 18
2. Inspection of Mechanical Collectors 33
2.1 Components and operating principles 33
2.2 General safety considerations 36
2.3 Inspection summaries 37
2.4 Inspection procedures 39
3. Inspection of Electrostatic Precipitators 49
3.1 Components and operating principles 49
3.2 General safety considerations 56
3.3 Inspection summaries 57
3.4 Inspection procedures 59
4. Inspection of Wet Scrubbers 69
4.1 Components and operating principles 69
4.2 General safety considerations 79
4.3 Inspection summaries • 80
4.4 Inspection procedures ' 83
5. Inspection of Dry Scrubbers 97
5.1 Components and..operating principles 97
5.2 General safety considerations 106
5.3 Inspection summaries 108
5.4 Inspection procedures 112
6. Inspection of Carbon Bed Adsorbers ~3f (?••?
6.1 Components and operating principles 125
6.2 General safety considerations 130
6.3 Inspection summaries 131
6.4 Inspection procedures 133
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Table of Contents (Continued)
Inspection of Thermal and Catalytic Incinerators 139
7.1 Components and operating principles 139
7.2 General safety considerations 146
7.3 Inspection summaries 147
7.4 Inspection procedures 149
Use of Portable Instruments 155
6.1 VOC detectors 155
6.2 Temperature monitors 170
6.3 Static pressure gauges 174
8.4 Pitot tubes I77
VI
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1. INSPECTION OF FABRIC FILTERS
The three most common categories of fabric filter systems are
addressed in this inspection notebook. The inspection procedures
discussed in this section have been tailored to the specific design
characteristics and operating problems of these fabric filters.
0 Pulse jet
0 Reverse air
c Shaker
Inspectors and their supervisors should modify these procedures as
necessary for types of fabric filters not specifically discussed in
this notebook.
1.1 Components and Operating Principles
1.1.1 Components of Pulse Jet Fabric Filters
Pulse jet fabric filters utilize compressed air for routine bag
cleaning. This type of fabric filter is used in a wide variety of
applications including asphalt batch plants, material transfer
operations, and industrial boilers. They are sometimes referred to
as "Reverse Jet" fabric filters.
The presence of a row of diaphragm valves along the top of the
baghouse similar to those shown in Figure 1-1 indicates that the
baghouse is a pulse jet unit. These valves control the compressed
air flow into each row of bags which is used to routinely clean the
dust from the bags. On a few units, the diaphragm valves can not be
seen since they are in an enclosed compartment on the top of the unit.
In these cases, the pulse jet baghouse can be recognized by the dis-
tinctive, regularly occurring sound of the operating diaphragm valves.
The shells of pulse jet units are usually small. This is because
it is possible to put a relatively high gas flow rate through the
types of fabric generally used in pulse jet units. Also, pulse jet
units are usually more economical than other types of fabric filters
for very small particulate sources.
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INSPECTION OF FABRIC FILTERS
Components and Operating Principles
Figure 1-1. Row of diaphragm valves along the top of a
pulse jet fabric filter
There are two major types of pulse jet baghouses: (1) top access,
and (2) side access. Figure 1-2 illustrates the top access design
which includes a number of large hatches across the top of the bag-
house for bag replacement and maintenance. Another major type has one
large hatch on the side for access to the bags. The side access units
often have a single small hatch on the top of the shell for routine
inspection of the baghbuse.
Like most small units, the pulse jet collector depicted in
Figure 1-2 is not divided into compartments. These are not needed on
small units that operate intermittently since bags are cleaned row-
by-row as the unit continues to operate. A few of the large units are
divided into separate compartments so that it is possible to perform
maintenance work on part of the unit while the other part continues to
operate.
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INSPECTION OF FABRIC FILTERS
Components and Operating Principles
TOP ACCESS MATCHES
. GAS OUTLET
FAN
IAPHRAGM VALVES
AIR MANIFOLD
GAS INLET
HOPPERS
Figure 1-2. Top access pulse jet fabric filter
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INSPECTION OF FABRIC FILTERS
Components and Operating Principles
Another distinguishing characteristics of pulse jet units is the
use of a support cage for the bags. The cage fits inside the cylin-
drical bags and prevents the bags from collasping during filtering.
Bags and cages are usually sold separately.
The fan shown in Figure 1-2 is after the baghouse. This means
that the particulate laden gas stream is "pulled" through the bag-
house and that the static pressures throughout the unit are less
than atmospheric pressure. Outside air will leak into the baghouse
if the hatches are not secure, if the shell is corroded, or if the
hopper is not properly sealed. Air infiltration can result in a
number of significant baghouse maintenance problems.
Pulse jet units operate equally well when the fan is ahead of
the baghouse and the gas stream is "pushed" through. In these units,
the static pressures are greater than atmospheric pressure and there
are potential safety problems with leakage of pollutant laden gas out
into the areas surrounding the baghouse.
1.1.2 Pulse Jet Fabric Filter Operating Principles
A cross sectional drawing of a pulse jet fabric filter is shown
in Figure 1-3 on the next page. Refer to this drawing while reading
the following section concerning the basic operating characteristics
of pulse jet baghouses.
The baghouse is divided into a "clean" side and a "dirty" side
by the tube sheet which is mounted near the top of the unit. The
dust laden gas stream enters below this tube sheet and the filtered
gas collects in a plenum above the tube sheet. There are holes in
the tube sheet for each of the bags. The bags are normally arranged
in rows.
The bags and cages hang from the tube sheet. The dust laden
inlet gas stream flows around the outside of each bag and the dust
gradually accumulates on the outside surfaces of the bags during
filtering. The cleaned gas passes up the inside of the bag and out
into the "clean" gas plenum.
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INSPECTION OF FABRIC FILTERS
Components and Operating Principles
•LOW TU
PILOT VALVE ENCLOSURE
DIAPHRAGM VALVE
'.PULSE TIMER
DIFFERENTIAL PRESSURE. SWITCH
IRTY CAS INLET
OTARY VALVE
Figure 1-3. Cross sectional sketch of pulse jet fabric filter
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INSPECTION OF FABRIC FILTERS
Components and Operating Principles
A pulse jet fabric filter uses bags which are supported on
cages. The cages hang from the tube sheet near the top of the bag-
house. Dust accumulates on the outer surfaces of the bags as the gas
stream passes through the bags and into the center of the bags. The
filtered gas is collected in a plenum at the top of the baghouse.
The dust must occassionaly be removed from the bags in order
to avoid exessively high gas flow resistances. The bags are cleaned
by introducing a high pressure pulse of compressed air at the top of
the bag. The sudden pulse of compressed air generates a pressure
wave which travels down inside of the bag. The pressure wave also
induces some filtered gas to flow downward into the bag. Due to the
combined action of the pressure wave and the reverse gas flow, the
bags are briefly deflected outward. This cracks the dust cake on
the outside of the bags and causes the dust to fall into the hopper.
Cleaning is normally done on a row-by-row basis while the baghouse
is operating.
The compressed air at pressures from 60 to 90 psig is generated
by an air compressor and stored temporarily in the compressed air
manifold. When the pilot valve (a standard solenoid valve) is
opened by the controller, the diaphragm valve suddenly opens to let
compressed air into the delivery tube which serves a row of bags.
There are holes in the delivery tube above each bag for injection of
the compressed air into the top of each bag. The cleaning system
controller can either operate on the basis of a differential pressure
sensor as shown in Figure 1-3, or it can simply operate as a timer.
In either case, bags are usually cleaned on a relatively frequent
basis with each row being cleaned from once every five minutes to
once every hour. Cleaning is usually done by starting with the first
row of bags and proceeding through the remaining rows in the order
that they are mounted."
Bags used in pulse jet collectors are generally less than 6
inches in diameter and range in length from 6 to 14 feet. Felted
fabric is the most common type of material.
One of the basic design parameters of a pulse jet fabric filter
is the gas-to-cloth ratio (sometimes called the air-to-cloth ratio)
which is simply the number of cubic feet of gas at actual conditions
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INSPECTION OF FABRIC FILTERS —^ T
Components and Operating Principles /"/
passing through the average square/root of cloth per unit of time.
The normal units are ft3/min/ft "which can be reduced to ft/min.
Most new commercial pulse jet units are designed for an average gas-
to-cloth ratio between 3 and 8 depending on the characteristics of
the fabric selected, the particle size of the dust to be collected,
and the installation and operation costs. Some older pulse jet
units were designed for gas-to-cloth ratios up to 15 ft/min.
Pulse jet units do not necessarily operate at the design average
gas-to-cloth ratio. When production rates are low, the prevailing
average gas-to-cloth ratio could be substantially below the design
value. Conversely, the average gas-to-cloth ratio could be well
above the design value if some of the bags are inadequately cleaned
or if sticky or wet material blocks part of the fabric surface.
Very high gas-to-cloth ratio conditions can lead to high gas flow
resistance which in turn can result in both seepage of dust through
the bags and fugitive emissions from the process equipment.
The difference between the gas stream pressures before and after
the baghouse is called the static pressure drop. The actual static
pressure drop depends on the actual average gas-to-cloth ratio, the
physical characteristics of the dust, the type of fabric used in the
bags, and the adequacy of cleaning. A pulse jet baghouse with new
bags that have not yet been exposed to dust would normally have a
static pressure drop of 0.5 to 1.5 inches of water. During normal
operation, the pulse jet baghouses generally have a static pressure
drop between 3 and 8 inches of water. The difference between the
static pressure drop across a clean, new unit and one in normal
service is due to the gas flow resistance through the dust layer on
each of the bags. The dust layer (sometimes called the dust cake)
is important since it .is responsible for much of the particle filter-
ing. Very low static pressure drops can often indicate inadequate
dust layers for proper filtering. Very high static pressure drops
often mean that a substantial fraction of the available cloth area
has been inadequately cleaned or has been blocked by wet and/or
sticky material. High particulate emissions also occur when the
static pressure drop is very high. The optimum overall efficiency
of a pulse jet baghouse system is generally in the moderate static
pressure drop range.
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INSPECTION OF FABRIC FILTERS
Components and Operating Principles
1.1.3 Components of Reverse Air and Shaker Fabric Filters
In reverse air and shaker fabric filter systems, the bags are
suspended from the top and are attached to a tube sheet which is
immediately above the hoppers. As shown in Figure 1-4, the inlet
gas enters from the hoppers and passes upward into each of the bags.
The dust cake builds up on the inside surface of the bags and
filtered gas passes into the chamber surrounding the bags.
These baghouses are usually divided into 2 or more compartments.
Cleaning of the bags is done by isolating the compartment from the
inlet gas stream. In the case of reverse air bags, filterd gas is
moved backward through the compartment to break up the dust cake and
discharge it to the hoppers below. The cleaning gas from the compart-
ment being cleaned is recycled to the inlet gas duct. In the case of
shaker baghouses, the compartment is entirely isolated and the top
hanger assembly is oscillated to physically dislodge the dust on the
bags. In both types of fabric filters, a set of dampers (poppet
valves in Figure 1-4) and activators are used.
Due to the relatively large size of many commercial bags, a
significant gas flow exists at the entrance to the bags. The
average gas velocity at this point can be between 300 and 500 feet
per minute, depending of the actual gas-to-cloth ratio and the bag
size. It is important that the particulate laden air enter the bag
in as straight a direction as possible in order to minimize fabric
abrasion. The inlet gas stream can also cause fabric damage if the
bags are slightly slack and some .of the fabric is folded over the
bag inlet. Because of these and other possible problems, the large
majority of the bag failures occur near the bottom of the bags.
Bags used in reverse air and shaker baghouses generally range
in length from 10 to 30 feet. Reverse air bags utilize a set of
anti-collaspe rings sewn around the bags at a number of locations
on the bag to prevent complete closure of the bag during reverse
air cleaning. Woven fabrics are generally used for these types of
baghouses.
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INSPECTION OF FABRIC FILTERS
Components and Operating Principles
•RFVERSE AIR DUCTS
CLEAN GAS
AEVERSE AIR
-FAN
POPPET VALVES AND
ACTUATORS
WALKWAY
'BAGS
TUBE SHEET
Figure 1-4. Cross section of a reverse air fabric filter
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INSPECTION OF FABRIC FILTERS
Components and Operating Principles
The bags are attached to the tube sheet either by using a snap
ring sewn into the bag or by using a thimble and clamp. Figures 1-5
and 1-6 illustrate both of these approaches. Firm bag attachments
are important in order to minimize the flow of unfiltered gas through
any gaps.
Large quantities of dust are often handled by reverse air and
shaker baghouses. The types of solids discharge valves and solids
handling systems are generally selected based on the overall quantity
of material to be transported and on the characteristics of these
solids. The most common types of solids discharge systems include
(1) rotary valves and screw conveyors, (2) pneumatic systems, and
(3) pressurized systems.
An isometric drawing of a reverse air baghouse is shown in
Figure 1-7. This unit has the main fan downstream of the baghouse.
This means that the particulate laden gas stream is "pulled" through
the baghouse and that the static pressures throughout the unit are
less than atmospheric pressure (termed "negative pressure"). With
this type of arrangement, outside air can leak into the baghouse if
the hatches are not secure, if the shell is corroded, or if the
hopper is not properly sealed. Air infiltration can result in a
number of significant baghouse maintenance problems.
Reverse air and shaker units operate equally well when the fan
is ahead of the baghouse and the gas stream is "pushed" through. In
these units, the static pressures are greater than atmospheric
pressure (termed "positive pressure") and there can be potential
safety problems with leakage of pollutant laden gas out into the
areas surrounding the baghouse. In most positive pressure units,
the filtered gas from each compartment is released to the atmosphere
through a large roof monitor or through a set of short stacks.
10
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INSPECTION OF FABRIC FILTERS
Components and Operating Principles
BAG
SNAP RING SEWN
INTO BAG
TUBE SHEET
Figure 1-5. Snap ring attachment for reverse air and shaker bags
• BAG
.WORM DRIVE CLAMP
TUBE SHEET
Figure 1-6. Thimble and clamp arrangement for reverse air and
shaker bags
11
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INSPECTION OF FABRIC FILTERS
Components and Operating Principles
_ COMPARTMENTS
FAN
BAGS
*T GAS INLET
Figure 1-7. Isometric view of reverse air fabric filter
12
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INSPECTION OF FABRIC FILTERS
Components and Operating Principles
1.1.4 Reverse Air and Shaker Baghouse Operating Principles
One of the basic design parameters of reverse air and shaker
fabric filters is the gas-to-cloth ratio (sometimes called the air-
to-cloth ratio) which is simply the number of cubic feet of gas at
actual conditions passing through the average square foot of cloth
per unit of time. The normal units are ft3/min/ft which can be
reduced to ft/min. Most new commercial reverse air and shaker units
are designed for an average gas-to-cloth ratio between 1 and 3 ft/min
depending on the characteristics of the fabric selected, the particle
size of the dust to be collected, and the necessary installation and
operation costs.
Reverse air and shaker units do not necessarily operate at the
design average gas-to-cloth ratio. When production rates are low,
the prevailing average gas-to-cloth ratio could be substantially
below the design value. Conversely, the prevailing average gas-to-
cloth ratio could be well above the design value if some of the bags
are inadequately cleaned or if sticky or wet material blocks part of
the fabric surface. Very high gas-to-cloth ratio conditions can lead
to high gas flow resistance which in turn can result in both the
seepage of dust through the bags and fugitive emissions from the
process equipment served by the baghouse.
The difference between the gas stream pressures before and after
the baghouse is called the static pressure drop. The actual static
pressure drop depends on the actual average gas-to-cloth ratio, the
physical characteristics of the dust, the type of fabric used in the
bags, and the adequacy of cleaning. A reverse air or shaker baghouse
with new bags which have not yet been exposed to dust would normally
have a static pressure drop of 0.5 to 1.5 inches of water. During
normal operation, the baghouses generally have a static pressure drop
between 3 and 6 inches of water. The difference between the static
pressure drop across a clean, new unit and one in normal service is
due to the gas flow resistance through the dust layer on each of the
bags. The dust layer (sometimes called the dust cake) is important
since it is responsible for most of the particle filtering. Very low
static pressure drops can often indicate inadequate dust layers for
proper filtering. Very high static pressure drops often mean that a
substantial fraction of the available cloth area has been inadequately
cleaned or has been blocked by wet and/or sticky material. High
13
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INSPECTION OF FABRIC FILTERS
Components and Operating Principles
particulate emissions also occur when the static pressure drops are
very high. The optium overall efficiency of a reverse air or shaker
baghouse system is generally in the moderate static pressure drop
range.
i.2 general Safety Considerations
Pulse jet fabric filters often serve relatively hot industrial
processes such as asphalt plant driers, clinker coolers, and lime
kilns. Uninsulated units can be hot, especially on the baghouse
roof.
Reverse air and shaker fabric filters often serve combustion
sources such as cement kilns, lime kilns, coal-fired boilers, and
glass furnaces. Fugitive emissions from positive pressure fabric
filter systems can accumulate in poorly ventilated areas around
the baghouse such as the walkways between the rows of compartments.
The inhalation hazards can include chemical asphyxiants, physical
asphyxiants, toxic gases/vapors, and toxic particulate.
Inspectors should not enter a fabric filter under any circum-
stances. All of the necessary inspection steps can be accomplished
without internal inspections. However, in some cases, it is helpful
to open one or more of the baghouse top and/or side access hatches in
order to observe internal conditions. In these situations, inspectors
should request that plant personnel open the hatches. The hopper
hatches should not be opened during the inspection since hot, free
flowing dust can be released.
14
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INSPECTION OF FABRIC FILTERS
Inspection Summaries
1.3 Inspection Summaries
1.3.1 Level 1 Inspections
Stack ° Visible emissions for 6 to 30 minutes for
each stack or discharge vent
0 Presence of condensing plume
Baghouse Not applicable
Process ° Presence or absence of fugitive emissions
1.3.2 Level 2 Inspections
Basic Inspection Points
Stack ° Visible emissions for 6 to 30 minutes for
each stack or discharge vent
0 Presence of condensing plume
0 Double-pass transmissometer conditions
0 Double-pass transmissometer data
Pulse Jet Fabric Filters
0 Static pressure.drop
0 Clean side conditions
0 General physical condition
Reverse Air and Shaker Fabric Filters
0 Static pressure drop
0 Compartment static pressure drops during
'cleaning
0 Clean side conditions
0 General physical condition
Process e Process operating rate
0 Process operating conditions
e Presence or absence of fugitive emissions
15
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INSPECTION OF PULSE JET FABRIC FILTERS
Inspection Summaries
1.3.2 Level 2 Inspections (Continued)
Follow-up
Pulse Jet Fabric Filters
Compressed air cleaning system operation
Bag failure rate and location records
Present baghouse inlet gas temperature
Baghouse inlet gas temperature records
Bag "rip" tests and fabric laboratory analyses
0 Cage characteristics
Reverse Air and Shaker Fabric Filters
Reverse air fan operation
Shaker assembly operation
Cleaning system equipment controller
Bag failure rate and location records
° Present baghouse inlet gas temperature
Baghouse inlet gas temperature records
Bag "rip" tests and fabric laboratory analyses
Process ° Fugitive emissions
1.3.3 Level 3 Inspections
Stack c Visible emissions for 6 to 30 minutes for
each stack or discharge vent*
0 Presence or absence of condensing plume*
Double-pass transmissometer condition*
0 Double-pass transmissometer data*
Pulse Jet Fabric Filters
0 Static pressure drop
"-.Inlet and outlet gas temperature
0 Inlet and outlet gas oxygen content
0 Compressed air system operation*
0 General physical condition*
0 Bag failure rate and location records*
Baghouse inlet gas temperature records*
Bag "rip" tests and fabric laboratory analyses*
8 Cage characteristics*
* See Basic Level 2 Inspection Procedures
16
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INSPECTION OF FABRIC FILTERS
Inspection Summaries
1.3.3 Level 3 Inspections (Continued)
Reverse Air and Shaker Fabric Filters
0 Static pressure drop
0 Compartment static pressure drops during
cleaning
Inlet and outlet gas temperature
Inlet and outlet gas oxygen content
General physical condition*
Bag failure rate and location records*
Baghouse inlet gas temperature records*
Bag "rip" tests and fabric laboratory analyses*
Process
Process operating rate*
Process operating conditions*
Presence or absence of fugitive emissions*
1.3.4 Level 4 Inspections
Stack
Baghouse
Process
0 All elements of a Level 3 inspection
0 All elements of a Level 3 inspection
0 Flowchart of compressed air supply
(Pulse jet fabric filters only)
0 Start-up/shut down procedures
0 Locations for measurement ports
e Potential inspection safety problems
0 All elements of a Level 3 inspection
0 Basic flowchart of process
0 'Potential inspection safety problems
* See Level 2 basic and follow-up inspection procedures.
17
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INSPECTION OF FABRIC FILTERS
Basic Level 2 Inspection Procedures
1.4 Inspection Procedures
Techniques for the inspection of fabric filter systems can
be classified as Level 1, 2, 3, or A. The Level 1 inspection
consists of a visible emissions observation from outside the
plant. This is not discussed in this manual. The Level 2
inspection primarily involves a walkthrough evaluation of the
baghouse system and process equipment. All data are provided by
on-site gauges. The Level 3 inspection includes all inspection
points of the Level 2 inspection and includes independent
measurements of baghouse operating conditions when the on-site
gauges are not adequate. The Level A inspection is performed by
agency supervisors or senior inspectors to acquire baseline data.
The scope of the Level A inspection is identical to the Level 3
inspection.
I.A.I Level 2 Inspections
Evaluate the baghouse visible emissions.
If weather conditions permit, determine baghouse effluent
average opacity in accordance with U.S. EPA Method 9 procedures
(or other required procedure). The observation should be con-
ducted during routine process operation and should last 6 to
30 minutes. Fabric filters generally operate with an average
opacity less than 5%. Higher opacities indicate baghouse emis-
sion problems.
Some large, multi-compartment pulse jet baghouses have
separate stacks for each compartment. Long term visible emission
observations on each of these stacks should be made only when the
baghouse is suffering major emission problems.
If weather conditions are poor, an attempt should still be
made to determine whether there are any visible emissions. Do
not attempt to determine "average opacity" during adverse weather
conditions. The presence of a noticeable plume generally
indicates baghouse operating problems.
18
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INSPECTION OF PULSE JET FABRIC FILTERS
Basic Level 2 Inspection Procedures
Evaluate puffing conditions (PULSE JET UNITS ONLY).
Evaluate the frequency and severity of puffs. These are
often caused by small holes in one or more rows of bags.
Evaluate condensing plume conditions.
Condensing plume conditions in fabric filter systems are
usually caused by organic vapors generated in the process equip-
ment. The vaporous material condenses once the gas enters the
cold ambient air. Condensing plumes usually have a bluish-white
color. In some cases, the plume forms 5 to 10 feet after leaving
the stack. If the baghouse operating temperature drops substan-
tially, this material can condense inside the baghouse and cause
fabric blinding problems. Corrective actions must focus on the
process equipment that is the source of the vaporous material.
Evaluate double-pass transmissometer physical conditions.
Most fabric filter systems _do not have a transmissometer
for the continuous monitoring of visible emissions. If a unit
is present, and if it is in an accessible location, check the
light source and retroreflector modules to confirm that these
are in good working order. Check that the main fan is working
and that there is a least one dust filter for the fan. On many
commercial models, it is also possible to check the instrument
alignment without adjusting the instrument. Note; On some
models, moving the dial t£ the alignment check position will
cause an alarm in the control room. This is to be moved only
by plant personnel and only when it will not disrupt plant
operations.
Some fabric filters have one or more single pass trans-
missometers on outlet ducts. While these can provide some
useful information to the system operators, these instruments
do not provide data relevant to the inspection.
Evaluate double-pass transmissometer data.
Evaluate the average opacity data for selected days since
the last inspection, if the transmissometer appears to be working
properly. Determine the frequency of emission problems and
evaluate how rapidly the baghouse operators are able to recognize
and eliminate the conditions.
19
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INSPECTION OF FABRIC FILTERS
Basic Level 2 Inspection Procedures
Evaluate the baghouse static pressure drop.
The baghouse static pressure drop should be recorded if the
gauge appears to be working properly. The gauge "face" should
be clear of obvious water and deposits. The gauge should fluc-
tuate slightly each time one of the diaphragm valves activates.
These valves can be heard easily close to the pulse jet
baghouse. If there is any question about the gauge, ask plant
personnel to disconnect each line one at a time to see if the
gauge responds. If it does not move when a line is disconnected,
the line may be plugged.
Fabric filters operate with a wide range of static pressure
drops (2 to 12 inches W.C.). It is preferable to compare the
present readings with the baseline values for this specific
source. Increased static pressure drops generally indicate high
gas flow rates, and/or fabric blinding, and/or system cleaning
problems. Lower static pressure drops are generally due to re-
duced gas flow rates, excessive cleaning intensities/frequencies,
or reduced inlet particulate loadings.
Evaluate baghouse general physical conditions.
While walking around the baghouse and its inlet and outlet
ductwork, check for obvious corrosion around the potential "cold"
spots such as the corners of the hoppers, near the solids dis-
charge valve, and the access hatches. On negative pressure bag-
houses, check for any audible air infiltration through the cor-
roded areas, warped access hatches, eroded solids discharge val-
ves, or other sites. On positive pressure baghouses, check for
fugitive emissions of dust from any corroded areas of the system.
Evaluate the clean side conditions (when possible).
If there is-eny question about the performance of the bag-
house, request that plant personnel open one or more hatches on
the clean side (not available on some commercial models). Note
the presence of any fresh dust deposits more than 1/8" deep since
this indicates particulate emission problems.
In the case of pulse jet fabric filters, also observe the
conditions of the bags, cages, and compressed air delivery tubes.
The compressed air delivery tubes should be oriented directly
20
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INSPECTION OF FABRIC FILTERS
Basic Level 2 Inspection Procedures
Evaluate the clean side conditions (continued).
into the bags so that the sides of the bags are not subjected
to the blast of cleaning air. The cages and bags should be
securely sealed to the tube sheet in units where the bag comes
up through the tube sheet. There should be no oily or crusty
deposits at the top of the bags due to oil in the compressed
air line.
In reverse air and shaker units, also observe the bag
tension and status of the bag attachments at the tube sheet.
In reverse air baghouses, the bags should have noticeable
tension in the vertical direction (some inward deflection of
the bags is normal when a compartment is isolated). In shaker
units, the bags should not be under any tension and should not
be slack. The majority of bag problems generally occur within
the bottom 1 to 2 feet of the bags in both types of baghouses.
Regulatory agency inspectors should observe conditions from the
access hatches and should not enter the compartments under any
circumstances.
In some cases, operators will be unable to open the access
hatches during the inspection. In one compartment units, the
entire baghouse must be shut down and locked out before a hatch
can be opened. Shutting down the unit may cause significant in-
plant inhalation hazards and safety problems. Similar problems
can occur on multi-compartment baghouses having only the minimum
capacity necessary to handle process gas flow requirements. In
a few cases, safety problems near the baghouse preclude clean
side checks.
Evaluate the process operating rate.
Record one or more process operating rate parameters that
document that the source conditions are representative of normal
operation.
21
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INSPECTION OF FABRIC FILTERS
Basic Level 2 Inspection Procedures
Evaluate process operating conditions.
Record any process operating parameters that have an impact
on the characteristics and/or quantities of pollutants generated.
Some of the important variables are listed below.
8 Gas stream temperatures
0 Gas stream static pressures
0 Gas stream oxygen levels
0 Raw material characteristics
Evaluate process fugitive emissions.
Perform complete visible emission observations on any
major process fugitive emissions. If the conditions preclude
a complete observation, note the presence and timing of any
fugitive releases.
1.4.2 Follow-up Inspection Points for Level 2 Inspections
Evaluate compressed air cleaning system (PULSE JET BAGHOUSES).
The purpose of checking the compressed air cleaning system
is to determine if this contributes to a significant shift in
the baghouse static pressure drop and/or if this contributes to
an excess emission problem. The.inspection procedures for the
compressed air cleaning system can include one or more of the
following.
0 Record the compressed air pressure if the gauge appears
to be working properly. It should fluctuate slightly
each time a diaphragm valve is activated. Do not remove
this valve since the compressed air lines and manifold
have high pressure air inside.
0 Listen for operating diaphragm valves. If none are heard
over a 10 to 30 minute time period, the cleaning system
controller may not be operating.
0 Check the compressed air shutoff valve to confirm that
the line is open.
22
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INSPECTION OF FABRIC FILTERS
Follow-up Level 2 Inspection Procedures
Evaluate compressed air cleaning system (PULSE JET FABRIC
FILTERS).
0 Count the number of diaphragm valves that do not activate
during a cleaning sequence. This can be done by simply
listening for diaphragm valve operation. Alternatively,
the puff of compressed air released from the trigger
lines can sometimes be felt at the solenoid valve (pilot
valve) outlet.
0 Check for the presence of a compressed air drier. This
removes water which can freeze at the inlet of the
diaphragm valves. Also check for compressed air oil
filter.
0 Check for a drain on the compressed air supply pipe or
on the air manifold. This is helpful for routinely
draining the condensed water and oil in the manifold.
Confirm operation of reverse air fan (REVERSE AIR BAGHOUSES)
Confirm that the reverse air fan is operating by noting
that the fan shaft is rotating. This fan is usually located
near the top of the baghouse.
Confirm operation of shaker assemblies (SHAKER BAGHOUSES)
Confirm that each of the shaker assemblies is working by
observing the movement of the shaker linkages on the outside
of each compartment.
Confirm operation of_ cleaning equipment controllers.
(REVERSE AIR. SHAKER. AND SOME MULTI-COMPARTMENT PULSE JET
FABRIC FILTERS)
Observe the baghouse control panel during cleaning of one
or more compartments to confirm that the controller is operating
properly. Each compartment should be isolated for cleaning
before the static pressure drop increases to very high levels
that preclude adequate gas flow. Also, cleaning should not be
so frequent that the bags do not build-up an adequate dust cake
to ensure high efficiency filtration.
23
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INSPECTION OF FABRIC FILTERS
Follow-up Level 2 Inspection Procedures
Confirm operation of cleaning equipment controllers.
(REVERSE AIR. SHAKER. AND SOME MULTI-COMPARTMENT PULSE JET
FABRIC FILTERS)
It is generally good practice to allow a short "null" per-
iod of between 5 and 30 seconds between the time a compartment
is isolated and the time that reverse air flow or shaking begins.
This reduces the flexing wear on the fabric. It is also good
practice to have a "null" period of 15 to 60 seconds following
cleaning to allow fine dust to settle out of the bags prior to
returning to filtering mode.
Determine present baghouse inlet gas temperature.
The primary purpose of determining the present gas inlet
temperature is to evaluate possible excess emission problems
and/or high bag failure rate conditions that can be caused
by very high or very low gas inlet temperatures. Locate any
on-site thermocouples mounted on the inlet to the baghouse.
If this instrument appears to be in a representative position,
record the temperature value displayed in the control room.
The average inlet gas temperature should be 25 to 50 °F
below the maximum rated temperature limit of the fabric.
Fifteen to thirty minute spikes of less than 25 °F above the
maximum rated limit can usually be tolerated without fabric
damage.
The average inlet gas temperature should be 25 to 50°F
above the acid gas dewpoint temperature. For most commercial
combustion processes, the acid dewpoint is usually between 225
to 300 °F. The inlet gas temperature should also be above the
water vapor dewpoint.
Evaluate the baghouse gas temperature records.
The purpose of reviewing continuous temperature recorder
data is to determine if temperature excursions contribute to
excess emission problems and/or high bag failure rates. Review
selected strip charts to determine if the gas inlet temperatures
have been above the maximum rated fabric temperature or below
the acid vapor or water vapor dewpoints.
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INSPECTION OF FABRIC FILTERS
Follow-up Level 2 Inspection Procedures
Perform fabric "rip" test and review fabric laboratory
analyses.
The purpose of evaluating fabric condition is to determine
if any corrective actions planned by the owner/operators have a
reasonable probability of reducing frequent excess emissions.
To perform a "rip" test, ask the plant personnel for a bag
that has been recently removed from the baghouse. Attempt to
rip the bag near the site of the bag hole or tear. If the bag
can not be ripped easily, then the probable cause of the failure
is abrasion and/or flex damage. These bags can usually be
patched and reinstalled. If the bag can be ripped easily, then
the fabric has been weakened by chemical attack or high tempera-
ture damage. Weakened bags should not be patched and reinstalled.
It may be necessary to install new bags throughout the entire
chamber if the bag failure rates are high.
Evaluate bag failure records.
The purpose of reviewing bag failure records is to deter-
mine the present bag failure rate and to determine if the rate
of failure is increasing. Plot the number of bag failures per
month for the last 6 to 24 months. If there has been a sudden
increase, the owner/operators should consider replacing all of
the bags in the compartment(s) affected. . If there is a distinct
spatial pattern to the failures,.the owner/operators should
consider repair and/or modification of the internal conditions
causing the failures.
Evaluate the bag cages (PULSE JET FABRIC FILTERS).
The bag cages are evaluated whenever there are frequent
abrasion/flex failures at the bottoms of the bags or along the
ribs of the cage*. Ask the plant personnel to provide a spare
cage for examination. There should be adequate support for the
bag and there should not be any sharp edges along the bottom
cups of the cage. Also check the cages for bows that would
cause rubbing between two bags at the bottom of the baghouse.
Process equipment fugitive emissions.
A careful check for process fugitive emissions is necessary
whenever the baghouse static pressure drop is substantially
higher than the baseline value or when air infiltration is
25
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INSPECTION OF FABRIC FILTERS
Follow-up Level 2 Inspection Procedures
Process equipment fugitive emissions (continued).
severe. In both cases, poor capture of the dust at the process
equipment is possible. Walk around the process sources to the
extent safely possible to evaluate pollutant capture.
1.4.3 Level 3 Inspection Points
Procedures for measurement of reverse fabric filter system
operating conditions are described below. Other observations
to be completed as part of the Level 3 inspection are identical
to those included in the basic and follow-up Level 2 inspection.
See the Level 2 inspection procedures section for a discussion
of these steps.
Measure the baghouse static pressure drop.
The static pressure drop provides an indication of gas flow
rate changes (changes in actual gas-to-cloth ratio), fabric
blinding, and cleaning system problems. The steps in measuring
the static pressure drop are described below.
0 Locate safe and convenient measurement ports on the inlet
and outlet ductwork or on the baghouse shell. In some
cases it may be possible to temporarily disconnect the
on-site gauge in order to use the portable gauge.
0 Clean any deposits out of the measurement ports.
0 If the inlet and outlet ports are close together, connect
both sides of the static pressure gauge to the ports and
observe the static pressure for 1 to 5 minutes.
0 If the ports are not close together, measure the static
pressure in one port for 10 to 30 seconds and then proceed
to the other port for 10 to 30 seconds. As long as the
static pressure drop is stable the two values can be sub-
tracted to determine the static pressure drop.
0 Under no circumstances should on-site plant instruments
be disconnected without the explicit approval of
responsible plant personnel. Also, instruments connected
to pressure transducers should not be disconnected.
26
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INSPECTION OF FABRIC FILTERS
Level 3 Inspection Procedures
Evaluate inlet and outlet gas temperatures.
These measurements are conducted whenever it is necessary
to determine if air infiltration is causing fabric chemical
attack due to reduced gas outlet temperatures. It is also
helpful to measure the inlet gas temperature to evaluate the
potential for high gas temperature damage to the bags. The
steps in measuring the gas temperature are outlined below.
0 Locate safe and convenient measurement ports on the
inlet and outlet ductwork of the collector. Often small
ports less than 1/4" diameter are adequate. Measurements
using ports on the baghouse shell are often inadequate
since moderately cool gas is trapped against the shell.
0 Attach a grounding/bonding cable to the probe if vapor,
gas, and/or particulate levels are potentially explosive
(a relatively common situation).
0 Seal the temperature probe in the port to avoid any air
infiltration that would result in a low reading.
0 Measure the gas temperature at a position near the
middle of the duct if possible. Conduct the measurement
for several minutes to ensure a representative reading.
0 Measure the gas temperature at another port and compare
the values. On combustion sources, a gas temperature
drop of more than 20 to 40 °F indicates severe air
infiltration.
0 Compare the inlet gas temperature with the maximum rated
temperature limit of the fabric present. If the average
gas temperature is within 25 to 50 °F of the maximum,
short bag life and frequent bag failures are possible.
Also, if there are short term excursions more than 25 to
50 °F above the maximum temperature limits, irreversible
fabric damage may occur.
27
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INSPECTION OF FABRIC FILTERS
Level 3 Inspection Procedures
Evaluate the inlet and outlet gas oxygen levels.
These measurements are performed to further evaluate the
extent of air infiltration. However, these tests are limited to
combustion sources since they are the only sources with oxygen
concentrations in the effluent gas that are less than ambient
levels. An increase of more than 1% oxygen going from the inlet
to the outlet indicates severe air infiltration (e.g. inlet
oxygen at 6.5% and outlet oxygen at 7.5%). The steps involved
in measuring the flue gas oxygen levels are itemized below.
0 Locate safe and convenient measurement ports.
Generally, the ports used for the temperature measure-
ments are adequate for the oxygen measurements.
0 Attach a grounding/bonding cable to the probe if there
are potentially explosive vapors, gases, and/or
particulate (a relatively common situation).
8 Seal the probe to prevent any ambient air infiltration
around the probe.
0 Measure the oxygen concentration at a position near the
center of the duct to avoid false readings due to
localized air infiltration. The measurement should be
repeated twice in the case of gas absorption instruments.
For continuous monitoring instruments, the measurement
should be conducted for 1 to 5 minutes to ensure a
representative value.
0 If possible, measure the carbon dioxide concentration at
the same locations. The sum of the oxygen and carbon
dioxide concentrations should be in the normal stoichi-
ometric range for the fuel being burned. If the sum
is not in this range, a measurement error has occurred.
0 As soon as possible, complete the measurements at the
other port. Compare the oxygen readings obtained. If
the outlet values are substantially higher, severe air
infiltration is occurring.
28
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INSPECTION OF FABRIC FILTERS
Level 4 Inspection Procedures
1.4.4 Level 4 Inspection Procedures
The Level 4 inspection includes many inspection steps
performed during Level 2 and 3 inspections. These are described
in earlier sections. The unique inspection steps of Level 4
inspections are described below.
Prepare £ flowchart .of the compressed air system (PULSE JET
FABRIC FILTERS). '
The purpose of the flowchart is to indicate the presence
of compressed air system components that could influence the
vulnerability of the pulse jet baghouse to bag cleaning problems.
The flowchart should consist of a simple block diagram showing
the following components.
0 Source of compressed air (plant air or compressor)
e Air drier (if present)
0 Oil filter (if present)
0 Main shutoff valve(s)
0 Compressed air manifolds on baghouse
0 Drains for manifolds and compressed air lines
0 Heaters for compressed air lines and manifolds
0 Controllers for pilot valves (timers or pneumatic sensors)
Evaluate locations for measurement ports.
Many existing fabric filters do not have convenient and
safe ports that can be used for static pressure, gas tempera-
ture, and gas oxygen measurements. One purpose of the Level 4
inspection is to select (with the assistance of plant personnel)
locations for ports to be installed at a later date to facili-
tate Level 3 inspections. Information regarding possible sample
port locations is provided in the U.S. EPA Publication titled,
" Preferred Measurement Ports for Air Pollution Control Systems",
EPA 340/1-86-034.
29
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INSPECTION OF FABRIC FILTERS
Level A Inspection Procedures
Evaluate start-up and shutdown procedures.
The start-up and shutdown procedures used at the plant
should be discussed to confirm the following.
The plant has taken reasonable precautions to minimize
the number of start-up/shutdown cycles.
The baghouse system bypass times have been minimized.
The baghouse system bypass times have not limited to
the extent that irreversible damage which will lead to
excess emission problems in the near future.
Evaluate potential safety problems.
Agency management personnel and/or senior inspectors should
identify any potential safety problems involved in standard
Level 2 or Level 3 inspections at this site. To the extent pos-
sible, the system owner/operators should eliminate these hazards.
For those hazards that can not be eliminated, agency personnel
should prepare notes on how future inspections should be limited
and should prepare a list of the necessary personal safety
equipment. A partial list of common health and safety hazards
includes the following.
0 Inhalation hazards due to.low stack discharge points
0 Weak catwalk and ladder supports
0 Hot baghouse roof surfaces
0 Compressed air gauges in close proximity to rotating
equipment-or hot surfaces
0 Fugitive emissions from baghouse system
0 Inhalation hazards from adjacent stacks and vents
0 Access to system components only available by means of
weak roofs or catwalks
30
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INSPECTION OF FABRIC FILTERS
Level 4 Inspection Procedures
Prepare a. system flowchart.
A relatively simple flowchart is very helpful in conducting
a complete and effective Level 2 or Level 3 inspection. This
should be prepared by agency management personnel or senior
inspectors during a Level A inspection. It consists of a simple
block diagram that includes the following elements.
0 Source(s) of emissions controlled by a single
baghouse
0 Location(s) of any fans used for gas movement
through the system (used to evaluate inhalation
problems due to positive static pressures)
0 Locations of any main stacks and bypass stacks
0 Location of baghouse
0 Locations of major instruments (transmissometers,
static pressure gauges, thermocouples)
Evaluate potential safety problems in the process area.
The agency management personnel and/or senior inspectors
should evaluate potential safety,problems in the areas that may
be visited by agency inspectors during Level 2 and/or Level 3
inspections. They should prepare a list of the activities which
should not be performed and locations to which an inspector
should not go as part of these inspections. The purpose of this
review is to minimize inspector risk and to minimize liability
concerns of plant personnel.
31
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32
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2. INSPECTION OF MECHANICAL COLLECTORS
2.1 Components and Operating Principles
2.1.1 Components of Mechanical Collectors
The simple cyclone consists of an inlet, a cylindrical section,
a conical section, a gas outlet tube, and a dust outlet tube. On
some units, there is a solids discharge valve such as a rotary valve
or a flapper valve. A typical tangential inlet, axial outlet cyclone
is shown in Figure 2-1.
PLAN VIEW
GAS
INLET
GAS
IN"1
^^m
CY1
I
• • ••
^^•i
•^M
.INORICAL
SECTION
SECTIONAL VIEW
OUTLET TUBE
OUST DISCHARGE
TUBE
Figure 2-1. Typical cyclone collector
33
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INSPECTION OF MECHANICAL COLLECTORS
Components and Operating Principles
Medium efficiency single cyclones are usually less than 6 feet
in diameter and operate at static pressure drops of 1 to 6 inches
of water. Overall collection efficiency is a function of the inlet
particle size distribution and the gas flow rate.
A multiple cyclone consists of numerous small diameter cyclones
operating in a parallel fashion. The high efficiency advantage of
small diameter tubes is obtained without sacrificing the ability to
treat large effluent volumes.
The individual cyclones, with diameters ranging from 3 to 12
inches, operate at pressure drops from 2 to 6 inches of water. The
inlet to the collection tubes is axial, and a common inlet and outlet
manifold is used to direct the gas flow to a number of parallel tubes.
The number of tubes per collector may range from 9 to 200 and is
limited only by the space available and the ability to provide equal
distribution of the gas stream to each tube. Properly designed units
can be constructed and operated with a collection efficiency of 90
percent for particles in the 5 to 10 micron range.
2.1.2 Mechanical Collector Operating Principles
In a cyclone or a cyclone tube, a vortex is created within the
cylindrical section by either injecting the gas stream tangentially
or by passing the gas stream through a set of spinner vanes. Due to
particle inertia, the particles migrate across the vortex gas stream
lines and concentrate near the cyclone wall. Near the bottom of the
cyclone cylinder, the gas stream makes a 180 degree turn and the
particulate matter is discharged either downward or tangentially into
hoppers below. The treated gas passes out of the opposite end of the
cyclone.
Particle separation is a function of the gas flow throughout
the cyclone. At high gas flow rates and small cylinder diameters,
the inertial force is high and particle collection efficiency is
optimized. However, there is an upper limit to gas flow rate beyond
which the increased gas turbulence leads to slightly reduced
particle collection efficiency.
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INSPECTION OF MECHANICAL COLLECTORS
Components and Operating Principles
The importance of particle size is illustrated in the collection
efficiency curves shown in Figure 2-2. For any given particle size,
the collection efficiency is also a strong function of the gas flow
rate. Multiple cyclones are less efficient at low flow rates.
LARGE DIAMETER TUBES
MEDIUM DIAMETER TUBES
SMALL DIAMETER TUBES
1C
20
30 40 50 60 70 80
AERODYNAMIC PARTICLE DIAMETER, umA
90 100
Figure 2-2. Particulate collection as a function of particle size
It is important that the inlet duct to the multiple collector
be properly oriented so there is no induced gas maldistribution
among the cyclone tubes. There must also be allowances for the
expansion of the ductwork and collector as the equipment heats up
to normal operating temperatures.
35
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INSPECTION OF MECHANICAL COLLECTORS
General Safety Considerations
2.2 General Safety Considerations
Mechanical collectors often serve combustion sources such as
cement kilns, lime kilns, coal-fired boilers, and glass furnaces.
Fugitive emissions from positive pressure systems can accumulate in
poorly ventilated areas around the collector such as the walkways
between the rows of compartments. The inhalation hazards can include
chemical asphyxiants, physical asphyxiants, toxic gases/vapors, and
toxic particulate. Furthermore, the collectors generally operate at
high gas temperatures. Burns can occur while attempting to walk
around constricted areas adjacent to the mechanical collector. Poor
ventilation can also create potential heat stress problems.
Inspectors should not enter a mechanical collector under any
circumstances. All of the necessary inspection steps can be accom-
plished without internal inspections. Unlike the inspection proce-
dures for other types of air pollution control systems, even access
hatch observations are not performed for mechanical collectors.
This is because the collector access hatches are rarely in a conven-
ient location to observe internal problems and because of additional
safety hazards in opening the hatches of these units.
36
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INSPECTION OF MECHANICAL COLLECTORS
Inspection Summaries
2.3 Inspection Summaries
2.3.1 Level 1 Inspections
Stack ° Visible emissions for 6 to 30 minutes for
each stack or discharge vent
0 Presence of condensing plume
Collector ° Not applicable
Process ° Presence or absence of fugitive emissions
2.3.2 Level 2 Inspections
Basic Inspection Points
Stack ° Visible emissions for 6 to 30 minutes for
each stack or discharge vent
0 Presence of condensing plume
9 Double-pass transmissometer conditions
0 Double-pass transmissometer data
Collector * Static pressure drop
0 General physical condition
0 Solids discharge valve operation
Process * Process operating rate
0 Process operating conditions
0 Presence or absence of fugitive emissions
Follow-up
Collector e Air infiltration indicators
37
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INSPECTION OF REVERSE AIR AND SHAKER FABRIC FILTERS
Inspection Summaries
2.3.3 Level 3 Inspections
Stack
Collector
Process
0 Visible emissions for 6 to 30 minutes for
each stack or discharge vent*
Presence or absence of condensing plume*
Double-pass transmissometer condition*
Double-pass transmissometer data*
Static pressure drop
Inlet and outlet gas temperature
Inlet and outlet gas oxygen content
General physical condition*
0 Process operating rate*
e Process operating conditions*
0 Presence or absence of fugitive emissions*
2.3.4 Level 4 Inspections
Stack ° All elements of a Level 3 inspection
Collector
Process
All elements of a Level 3 inspection
Locations for measurement ports
Potential inspection safety problems
All elements of a Level 3 inspection
Basic flowchart of process
Potential inspection safety problems
* See Level 2 basic and follow-up inspection procedures,
38
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INSPECTION OF MECHANICAL COLLECTORS
Basic Level 2 Inspection Procedures
2.4 Inspection Procedures
Techniques for the inspection of mechanical collectors can
be classified as Level 1, 2, 3, or 4. The Level 1 inspection
consists of a visible emissions observation from outside the
plant. This is not discussed in this manual. The Level 2
inspection primarily involves a walkthrough evaluation of the
collector system and process equipment. All data are provided
by on-site gauges. The Level 3 inspection includes all inspec-
tion points of the Level 2 inspection and includes independent
meassurements of collector operating conditions when the on-site
gauges are not adequate. The Level 4 inspection is performed by
agency supervisors or senior inspectors to acquire baseline data.
The scope of the Level 4 inspection is identical to the Level 3
inspection.
2.4.1 Level 2 Inspections
Evaluate the collector visible emissions.
If weather conditions permit, determine baghouse effluent
average opacity in accordance with U.S. EPA Method 9 procedures
(or other required procedure). The observation should be made
during routine process operation and should last 6 to 30 minutes
for each stack and bypass vent. The majority of mechanical col-
lectors operate with an average opacity less than 20%.
If weather conditions are poor, an attempt should still be
made to determine if there are any visible emissions. Do not
attempt to determine "average opacity" during adverse weather
conditions. The presence of a very noticeable, dark plume
generally indicates collector operating problems.
*-«•
Evaluate condensing plume conditions.
Condensing plume conditions in mechanical collector systems
are usually caused by partially combusted material generated in
the process equipment. The vaporous material condenses once the
gas enters the cold ambient air. Condensing plumes usually have
a bluish-white color. In some cases, the plume forms 5 to 10
feet after leaving the stack.
39
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INSPECTION OF MECHANICAL COLLECTORS
Basic Level 2 Inspection Procedures
Evaluate double-pass transmissometer physical conditions.
Most mechanical collector systems do not have a trans-
missometer for the continuous monitoring of visible emissions.
If a unit is present, and if it is in an accessible location,
check the light source and retroreflector modules to confirm
that they are in good working order. Check that the main fan
is working and that there is a least one dust filter for the
fan. On many commercial models, it is also possible to check
the instrument alignment without adjusting the instrument.
Note; On some models, moving the dial to the alignment check
position will cause an alarm in the control room. This is to
be moved only by_ plant personnel and only when It will not
disrupt plant operations.
Many mechanical collectors serving coal-fired boilers have
one or more single pass transmissometers on outlet ducts. While
they can provide some useful information to the system operators,
these instruments do not provide relevant data.
Evaluate double-pass transmissometer data.
Evaluate the average opacity data for selected days since
the last inspection if the transmissometer appears to be working
properly. Determine the frequency of emission problems and
evaluate how rapidly the baghouse operators are able to recognize
and eliminate the condition.
40
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INSPECTION OF MECHANICAL COLLECTORS
Basic Level 2 Inspection Procedures
Evaluate the mechanical collector static pressure drop.
The collector static pressure drop should be recorded if
the gauge appears to be working properly. The following items
should be checked to confirm the adequacy of the on-site gauge.
0 The gauge "face" should be clear of water and deposits.
0 The gauge value should respond to process operating
rate changes.
0 The lines leading to the inlet and outlet of the
collector should be intact.
If there is any question concerning the gauge, ask plant
personnel to disconnect each line one at a time to check if the
gauge responds. If it does not move when a line is disconnected,
the line may be plugged or the gauge is inoperable. Note; the
lines should only be disconnected by_ plant personnel and only
when this will not affect plant operations.
If the on-site gauge appears to be working properly, record
the indicated value. The time that the data was obtained should
also be noted if the process operating rates change frequently.
The observed static pressure should be corrected for the
present operating rate by using the equation* listed below. The
corrected value should then be compared with baseline value(s).
Csp - Osp (X2/B2)
Where: Csp « corrected static pressure drop, inches W.C.
Osp'« observed static pressure drop, inches W.C.
X • present process operating rate
B « baseline process operating rate
If the corrected static pressure drop is significantly
different from the baseline value(s), then the gas flow resist-
ance has changed and particulate emissions have probably
increased.
*Note: This equation ignores gas density changes
41
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INSPECTION OF MECHANICAL COLLECTORS
Basic Level 2 Inspection Procedures
Evaluate the mechanical collector static pressure drop (cont.)
Increased static pressure drops generally indicate solids
build-up in the collector, most commonly on the inlet spinner
vanes of small diameter multi-cyclone tubes. This causes poor
vortex formation and reduced collection efficiency in the
affected tubes. Low static pressure drops are generally due to
erosion of the outlet extension tubes, corrosion of the clean
side tube sheet, or failure of the tube gaskets. These prob-
lems allow some of the particulate laden flue gas to "short
circuit" the collector.
Evaluate mechanical collector general physical conditions.
While walking around the mechanical collector and its
inlet and outlet ductwork, check for obvious corrosion around
the potential "cold" spots such as in the corners of the hoppers,
near the solids discharge valve, and on the access hatches. On
negative pressure units, check for any audible air infiltration
through the corroded areas, warped access hatches, eroded solids
discharge valves, or other sites. On positive pressure units,
check for fugitive emissions of dust from any corroded areas of
the system.
Evaluate solids discharge valves and solids discharge rates.
For multi-cyclone collectors using rotary discharge valves
or flapper valves, check for continuous movement of the valve
and for continuous discharge of solids into the screw conveyor
or into the disposal container (if safely possible). For multi-
cyclone collectors using pneumatic or pressurized hopper dis-
charge systems, check for the sound of discharge valve operation
at a frequency ranging from once per hour to once per 8 hours.
Note; Only plant personnel should open observation hatches on_
screw conveyors gr dust storage/disposal containers and protec-
tive goggles and respirators may be needed in some cases.
Evaluate the process operating rate.
Record one or more process operating rate parameters that
document that the source conditions are representative of normal
operation.
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INSPECTION OF MECHANICAL COLLECTORS
Basic Level 2 Inspection Procedures
Evaluate process operating conditions.
Record any process operating parameters which have an
impact on the characteristics and/or quantities of pollutants
generated. Some of the important variables are listed below.
0 Gas stream temperatures
0 Gas stream static pressures
0 Gas stream oxygen levels
0 Raw material characteristics
Evaluate process fugitive emissions.
Perform complete visible emission observations on any
major process fugitive emissions. If the conditions preclude
a complete observation, note the presence and timing of any
fugitive releases.
2.4.2 Follow-up Inspection Points for Level 2 Inspections
Evaluate air infiltration indicators.
Locate any permanently mounted temperature gauges on the
inlet and outlet ducts of the mechanical collector. The pres-
ence of a thermocouple is indicated by the presence of a thermo-
couple "head" connection in the ductwork. If the instrument(s)
appears to be in representative locations, check the indicated
temperatures at the control room. Compare the inlet and outlet
values. In most mechanical collectors serving combustion pro-
cesses, the gas temperature drop across the collector is 20 to
40 °F depending primarily on the gas flow rate and the adequacy
of insulation. Gas temperature drops that are higher than base-
line values suggest significant air infiltration and reduced
particulate matter collection efficiency.
Also compare the inlet gas temperatures to the baseline
levels. If there is a significant difference, check the process
operating rate and the process operating conditions.
On units having oxygen monitors, check for the increase
in flue gas oxygen concentration across the collector. In most
cases, it should be less than 1% 02 increase (e.g. 7% inlet,
82 outlet).
A3
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INSPECTION OF MECHANICAL COLLECTORS
Level 3 Inspection Procedures
2.4.3 Level 3 Inspection Points
Procedures for measurement of mechanical collector system
operating conditions are described below. Other observations
to be completed as part of the Level 3 inspection are identical
to those included in the basic and follow-up Level 2 inspection.
See the Level 2 inspection procedures section for a discussion
of these steps.
Measure the collector static pressure drop.
The static pressure drop provides an indication of gas flow
resistance passing through the mechanical collector. The steps
in measuring the static pressure drop are described below.
0 Locate safe and convenient measurement ports. In some
cases it may be possible to temporarily disconnect the
on-site gauge in order to use the portable static pressure
gauge. It also may be possible to find small ports in the
ductwork ahead of and after the collector.
0 Clean any deposits out of the measurement ports.
0 If the inlet and outlet ports are close together, connect
both sides of the static pressure gauge to the ports and
observe the static pressure for 1 to 5 minutes.
0 If the ports are not close together, measure the static
pressure in one port for 10 to 30 seconds and then proceed
to the other port for 10 to 30 seconds. As long as the
static pressure drop is reasonably stable (the typical
condition), the two values can be subtracted to determine
the static pressure drop.
0 Under no circumstances should on-site plant instruments
be disconnected without the explicit approval of respon-
sible plant personnel. Instruments connected to differ-
ential pressure transducers should not be disconnected.
The static pressure data should be adjusted to the baseline
process operating rate in order to evaluate shifts in gas
resistance since the baseline period. The equation presented
in section 2.5.1 can be used for this calculation.
44
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INSPECTION OF MECHANICAL COLLECTORS
Level 3 Inspection Procedures
Evaluate inlet and outlet gas temperatures.
These measurements are conducted whenever it is necessary
to determine if air infiltration is causing reduced particulate
matter collection efficiency and/or collector corrosion. The
steps in measuring the gas temperature are outlined below.
0 Locate safe and convenient measurement ports on the
inlet and outlet ductwork of the collector. Often small
ports less than 1/4" diameter are adequate. Measurements
using ports on the baghouse shell are often inadequate
since moderately cool gas is trapped against the inside
wall of the shell.
0 Attach a grounding/bonding cable to the probe if vapor,
gas, and/or particulate levels are potentially explosive.
0 Seal the temperature probe in the port to avoid any air
infiltration that would result in a low reading.
0 Measure the gas temperature at a position near the middle
of the duct if possible. Conduct the measurement for
several minutes to ensure a representative reading.
0 Measure the gas temperature at another port and compare
the values. On combustion sources, a gas temperature
drop of more than 20 to 40 °F indicates severe air
infiltration.
45
-------
INSPECTION OF MECHANICAL COLLECTORS
Level 3 Inspection Procedures
Evaluate the inlet and outlet gas oxygen levels.
These measurements are performed to further evaluate the
extent of air infiltration. However, these tests are limited
to combustion sources since they are the only sources with
oxygen concentrations in the effluent gas that are less than
ambient levels. An increase of more than 1% oxygen going from
the inlet to the outlet indicates severe air infiltration (e.g.
inlet oxygen at 6.5% and outlet oxygen at 7.5%). The steps
involved in measuring the flue gas oxygen levels are itemized
below.
0 Locate safe and convenient measurement ports.
Generally, the ports used for the temperature measure-
ments are adequate for the oxygen measurements.
e
Attach a grounding/bonding cable to the probe if there
are potentially explosive vapors, gases, and/or
particulate.
0 Seal the probe to prevent any ambient air infiltration
around the probe.
0 Measure the oxygen concentration at a position near the
center of the duct to avoid false readings due to
localized air infiltration. The measurement should be
repeated twice in the case of gas absorption instruments.
For continuous instruments, the measurement should be
conducted for 1 to 5 minutes to ensure a representative
value.
0 If possible, measure the carbon dioxide concentration at
the same locations. The sum of the oxygen and carbon
dioxide concentrations should be in the normal stoich-
iometric range for the fuel being burned. If the sum
is not in this range, a measurement error has occurred.
0 As soon as possible, complete the measurements at another
port. Compare the oxygen readings obtained. If the out-
let values are substantially higher, severe air infiltra-
tion is occurring.
46
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INSPECTION OF MECHANICAL COLLECTORS
Level A Inspection Procedures
2.A.4 Level A Inspection Procedures
The Level A inspection includes many inspection steps per-
formed during Level 2 and 3 inspections. These are described
in earlier sections. The unique inspection steps of Level A
inspections are described below.
Evaluate locations for measurement ports.
Many existing mechanical collectors do not have safe and
convenient ports that can be used for static pressure, gas
temperature, and gas oxygen measurements. One purpose of the
level A inspection is to select (with the assistance of plant
personnel) locations for ports to be installed at a later date
to facilitate Level 3 inspections. Information on possible
sample port locations is provided in the U.S. EPA Publication
titled, " Preferred Measurement Ports for Air Pollution Control
Systems", EPA 3AO/1-86-03A.
Evaluate potential safety problems.
Agency management personnel and/or senior inspectors
should identify any potential safety problems involved in
standard Level 2 or Level 3 inspections at this site. To the
extent possible, the system owner/operators should eliminate
these hazards. For those hazards that can not be eliminated,
agency personnel should prepare notes on how future inspections
should be limited and should prepare a list of the necessary
personnel safety equipment. A partial list of common health
and safety hazards includes the following.
0 Inhalation hazards due to fugitive leaks into
walkways near the collector
0 Inhalation hazards due to exposed friable asbestos
insulation on the mechanical collector and hoppers
0 Burn hazards on incompletely insulated surfaces
0 Weak catwalk and ladder supports
0 Heat stress in vicinity of hot collectors
A7
-------
INSPECTION OF MECHANICAL COLLECTORS
Level 4 Inspection Procedures
Evaluate potential safety problems i.n the process area.
The agency management personnel and/or senior inspectors
should evaluate potential safety problems in the areas which
may be visited by agency inspectors during Level 2 and/or Level
3 inspections. They should prepare a list of the activities
that should not be performed and locations to which an inspector
should not go as part of these inspections. The purpose of
this review is to minimize inspector risk and to minimize the
liability concerns of plant personnel.
Prepare _a system flowchart.
A relatively simple flowchart is very helpful in conducting
a complete and effective Level 2 or Level 3 inspection. This
should be prepared by agency management personnel or senior
inspectors during a Level A inspection. It should consist of a
simple block diagram that includes the following elements.
0 Source(s) of emissions controlled by a single
mechanical collector
0 Location(s) of any fans used for gas movement
through the system (used to evaluate inhalation
problems due to positive static pressures)
4 Locations of any main stacks and bypass stacks
0 Location of mechanical collector
0 Locations of major instruments (static pressure
guages, transmissometers, thermocouples)
-------
3. INSPECTION OF ELECTROSTATIC PRECIPITATORS
3.1 Components and Operating Principles
3.1.1 Components of Electrostatic Precipitators
An electrostatic precipitator consists of a large number of
discharge electrodes and collection plates arranged in parallel rows
along the direction of gas flow. The collection plates are normally
grounded along with the hoppers and shell of the precipitator. The
discharge electrodes are energized to negative voltages ranging
between 15,000 volts and 50,000 volts.
The gas velocity through the numerous parallel passages of the
precipitator ranges from 3 to 8 feet per second. This represents an
order of magnitude decrease in the velocity that exists in the duct-
work leading to the precipitator. The deceleration is accomplished
in an inlet nozzle at the front of the precipitator. There are
normally one or more perforated plates to achieve as uniform gas
distribution as possible.
The high voltage for the discharge electrodes is provided by a
transformer-rectifier set (hereafter termed T-R set). It converts
alternating current from a 480 volt supply to direct current at very
high voltages. Each T-R set energizes an independent portion of the
electrostatic precipitator called a field. The T-R sets are always
mounted on the roof of the precipitator since it is difficult to run
the high voltage lines for long distances.
There are normally 2 to 5 fields in series along the direction
of gas flow. However, in some units handling difficult to collect
dust and subject to very stringent emission requirements, there can
be as many as 14 fields in series. Each field in series removes
from 50 to 852 of the incoming particulate matter.
Most large precipitators are also divided into parallel
chambers. Solid partitions between the chambers prevents gas from
passing from one chamber to the other while passing through the
precipitator. Each of the chambers is evaluated separately during
the inspection.
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INSPECTION OF ELECTROSTATIC PRECIPITATORS
Components and Operating Principles
Each of the T-R sets is connected to a control cabinet. This
controls the 480 volt alternating current power supply to the T-R
set. It contains all of the electrical meters used to evaluate the
operating conditions inside each of the precipitator fields. A
major part of the inspection involves the interpretation of this
electrical data. One of the first steps in the evaluation of the
electrical data is to determine how the T-R sets are laid out on the
precipitator so that the various control cabinets can be matched up
with the T-R sets they control. This is important since the field-
by-field trends in a chamber are used to evaluate potential
operating problems.
The types of meters present on the control cabinet are listed
below along with the usual range of the gauge.
* Primary voltage, 0 to 500 volts A.C.
0 Primary current, 0 to 200 amps. A.C.
e Secondary current, 0 to 2 amps D.C.
0 Secondary voltage, 0 to 50 kilovolts, D.C.
0 Spark Rate, 0 to 200 sparks/minute
The primary voltage and current data concerns the ABO volt
alternating current power supply to the T-R set. The secondary
voltage is the voltage leaving the T-R set and on the discharge
electrodes within the precipitator. The secondary current is the
direct current flow from the T-R set that passes through the field.
The spark rate is the number of short tern arcs that jump between
the discharge electrodes and collection plates in the field.
3.2 Operating Principles
Electrical conditions can be evaluated using either the primary
meters or the secondary meters. Whenever they are available, the
secondary meters are generally used since these provide information
on the electrical conditions within the precipitator fields. However,
many older precipitators were not equipped with secondary voltage
meters. For these units, the primary meters can be used.
50
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INSPECTION OF ELECTROSTATIC PRECIPITATORS
Components and Operating Principles
Under normal operating conditions, the values of the primary and
secondary meters in each field can not be set intentionally by the
operators. Instead, the electrical operating conditions are deter-
mined by the characteristics of the particles passing through the
precipitator field and by the ability of the power supply to respond
to sparks within the field. Some of the most important properties of
the dust include the total quantity of dust, the particle size distri-
bution of the oust, and the particle resistivity distribution.
The dust resistivity is a measure of the ability of the electrons
on the surface of the dust particles to pass to the grounded collection
plate. If the electrons can flow easily, the dust resistivity is low.
As illustrated in Figure 3-1, the electrons can flow around the
outside surfaces of particles that comprise the dust layer on the
collection plate or they can pass directly through the dust particles.
When the particle temperature is above 500 °F, the constitutents
within the dust particles generally provide a conductive path. There-
fore, the resistivity tends to decrease as the particle temperatures
increase above 500 °F. This type of charge dissipation is termed
"bulk conductivity". Below 350 °F, compounds such as sulfuric acid
and water condense on the particle surfaces to facilitate electron
flow around the outer surfaces. Generally the resistivity drops
rapidly as the particle temperature drops below 350 °F. Due to the
strong temperature dependence of these two separate parts of charge
dissipation, the particle resistivity exhibits a peak when the temper-
ature is in the range of 350 to 500 °F as illustrated in Figure 3-2.
For precipitators designed to operate in the less than 350 °F
temperature range, slight changes in the flue gas temperature can
have a dramatic impact on the resistivity. Changes of 20 to 25 °F
can result in more than a factor of 10 difference in the observed
resistivity. This is significant since many commercial precipitators
operate on gas streams in which inlet temperature on one side is more
than 30 °F different than the inlet temperature on the other side.
In these cases, significant differences in the resistivity can exist.
51
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INSPECTION OF ELECTROSTATIC PRECIPITATORS
Components and Operating Principles
Smile Particle
lulk
CinJuctmty
Surface
Conductivity
firtienlate
layer
Ctlltction.
Plate
Figure 3-1. Alternative paths for electron flow through
dust layers on collection plates
10
,12
f ID11
10
= 10
' ,„•
20C 300 400 WO 600
GAS
Figure 3-2. Typical resistivity versus temperature relationship
52
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INSPECTION OF ELECTROSTATIC PRECIPITATORS
Components and Operating Principles
The high resistivity zones in the precipitator generally have
low currents, low voltages, and high spark rates. Due to the poor
electrical operating conditions, overall particle collection can be
quite low. In the low resistivity zones, the currents can be very
high while the spark rates are negligible. In these areas, the dust
layer on the collection plates is not strongly bonded and even light
rapping can result in the reentrainment of the material that had
been collected. It is desirable to maintain a precipitator in the
moderate resistivity range.
The electrical operating conditions of an electrostatic
precipitator can be summarized using graphs, and power input totals.
Figure 3-3 illustrates graphs of the secondary voltage, secondary
currents, and spark rate for a one chamber, four field precipitator.
Baseline data for each parameter is provided in the graphs to help
identify shifts in these electrical conditions. When all of the
fields in a given chamber shift in unison (sometimes there is a
several hour time lag for the outlet fields), there has normally been
a change in the dust characteristics due to process operating changes
or fuel changes. When only one of the fields shifts, there is normal-
ly an internal mechanical problem. The advantage of the graphs is
that they allow for rapid intrepretation of the large quantity of data
obtained while observing the T-R set control cabinets.
Another way to summarize the electrical data is to calculate
the overall power input for a precipitator chamber. This can be
done using either the primary meters using Equation 3-1 or the
secondary meters using Equation 3-2.
Primary Meters:
(Volts, A.C.) x (Amps. A.C.) x 0.75 • (Watts) Equation 3-1
Secondary Meters:
(Kilovolts, D.C.) x (Milliamps, D.C.) « (Watts) Equation 3-2
The power input in watts for each field in the chamber is then
added to calculate the total power input. If the actual gas flow
rate is known, the power input is often presented as total watts per
thousand actual cubic feet per minute of gas flow.
53
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INSPECTION OF ELECTROSTATIC PRECIPITATORS
Components and Operating Principles
It should be noted, however, that the power input is usually
calculated only for precipitators that consistently operate in either
the moderate or high resistivity range. In these ranges, an increase
in the power input generally corresponds with a decrease in the
particulate emission rate. In the low resistivity range, there is no
typical relationship between power input and particulate emission
rates.
The alignment between the parallel sets of collection plates
and discharge electrodes is very important. For units with high
resistivity zones, the spacing tolerances must be maintained within
plus or minus a quarter inch throughout the unit. Even for units
with moderate-to-low resistivity, the alignment must be within plus
or minus a half inch throughout the unit. Considering that there
are a large number of collection plates and discharge electrodes,
maintaining proper alignment is not simple.
Large quantities of dust are often handled by electrostatic
precipitators. The types of solids discharge valves and solids
handling systems are generally selected based on the overall quantity
of material to be transported and on the characteristics of these
solids. The most common types of solids discharge systems include
(1) rotary valves and screw conveyors, (2) pneumatic systems, and
(3) pressurized systems.
The fan can be either located before or after the electrostatic
precipitator. When it is after the precipitator, the gas stream is
pulled" through and the static pressure is less than atmospheric
pressure (termed "negative pressure")* As with other types of
control devices, negative pressure electrostatic precipitators are
vulnerable to air infiltration. This can lead to a number of
significant operating problems.
When the fan is before the precipitator, the gas stream is
"pushed" through. This creates static pressures inside the precipi-
tator which are greater than atmospheric pressure (termed "positive
pressure"). Special care is warranted whenever inspecting these
units, since fugitive emissions from the unit can result in very high
levels of toxic pollutants in the vicinity of the precipitator.
-------
INSPECTION OF ELECTROSTATIC PRECIPITATORS
Components and Operating Principles
INSPECTION Or ELECTROSTATIC HttCWUTORS
28
20
10
man uu
MSUIKE
•1500
£1000
500
••
30
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1O
UTA
'FIELDS •
Figure 3-3. Trends in the voltages, currents and spark rates in
a precipitator chamber
55
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INSPECTION OF ELECTROSTATIC PRECIPITATORS
General Safety Considerations
3.2 General Safety Considerations
Electrostatic precipitators often serve combustion sources such
as cement kilns, lime kilns, coal-fired boilers, and glass furnaces.
Fugitive emissions from systems can accumulate in poorly ventilated
areas around the precipitator such as the roof and hopper weather
enclosures, annular stack monitoring locations, and areas adjacent
to cracked breeching expansion joints. The inhalation hazards can
include chemical asphyxiants, physical asphyxiants, toxic gases/
vapors, and toxic particulate.
Portable instruments should not be used on electrostatic
precipitator systems. Very high static voltages can accumulate on
probes downstream of precipitators due to the impaction of charged
particles. Touching improperly grounded and bonded probes can
result in involuntary muscle action that can results in a fall.
Furthermore, in some units, the probes could inadvertently approach
the electrified zone of the precipitator that operates at 25 to 45 kV.
Inspectors should not enter an electrostatic precipitator under
any circumstances. All of the necessary inspection steps can be
accomplished without internal inspections. Furthermore, the side
access hatches and penthouse/roof access hatches should not be
opened under any circumstances. The internal components can be at
high voltages even though the unit is out-of-service. Also, the
hopper hatches should not be opened during the inspection since hot,
free flowing dust can be released and since the inrushing air can
cause hopper fires in some cases..
56
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INSPECTION OF ELECTROSTATIC PRECIPITATORS
Inspection Summaries
3.3 Inspection Summaries
3.3.1 Level 1 Inspections
Stack ° Visible emissions for 6 to 30 minutes for
each stack or discharge vent
0 Presence of condensing plume
Electrostatic Precipitator
0 Not applicable
Process ° Presence or absence of fugitive emissions
3.3.2 Level 2 Inspections
Basic Inspection Points
Stack e Visible emissions for 6 to 30 minutes for
each stack or discharge vent
0 Duration and timing of puffing
0 Presence of condensing plume
Transmissometer
0 Double-pass transmissometer conditions
0 Average opacity.for at least the last 24 hours
Electrostatic Precipitator
* Transformer-rectifier set electrical data
0 General physical condition
Process "Process operating rate
0 'Process operating conditions
Follow-up
Electrostatic Precipitator
0 Opacity strip charts/records and transformer-
rectifier set records (baseline files)
0 Rapper frequency and intensity
0 Wire failure rate and location records
57
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INSPECTION OF ELECTROSTATIC PRECIPITATORS
Inspection Summaries
3.3.3 Level 3 Inspections (Identical to Level 2 Inspections)
3.3.4 Level 4 Inspections
Stack ° All elements of a Level 3 inspection
Transmissometer
0 Location
0 Quality assurance procedures
Electrostatic Precipitator
0 All elements of a Level 2/Level 3 inspection
0 Flowchart of compressed air supply
0 Start-up/shut down procedures
0 Potential inspection safety problems
Process ° All elements of a Level 3 inspection
0 Basic flowchart of process
0 Potential inspection safety problems
58
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INSPECTION OF ELECTROSTATIC PRECIPITATORS
Basic Level 2 Inspection Procedures
3. A Inspection Procedures
Techniques for the inspection of electrostatic precipi-
tators can be classified as Level 1, 2, 3, or A. The Level 1
inspection consists of a visible emission observation from
outside the plant. This is not discussed in this manual. The
Level 2 inspection primarily involves a walkthrough evaluation
of the electrostatic precipitator system and process equipment.
All data are provided by on-site gauges. The Level 3 inspection
is identical to the Level 2 inspection since it is impractical
to use portable instruments to evaluate large electrostatic
precipitator systems. Furthermore, there are a number of unique
and significant hazards involved in the use of the portable
instruments on precipitator systems. The Level 4 inspection
is performed by agency supervisors or senior inspectors to
acquire baseline data. The scope of the Level A inspection is
identical to the Level 2/Level 3 inspection.
3.A.I Level 2 Inspections
Evaluate the electrostatic precipitator visible emissions.
If weather conditions permit, determine the baghouse
effluent average opacity in accordance with U.S. EPA Method 9
procedures (or other required procedure). The observation
should be conducted during routine process operation and should
last 6 to 30 minutes for each stack and bypass. The majority
of units operate with effuent opacities less than 10% on a
continuous basis. Higher opacities indicate emission problems.
The timing and duration of all significant spikes should be
noted after the visible emission observation. This information
will be useful in determining some of the possible causes of
the spiking condition. Significant puffs on either a regular
frequency or on a random basis are not normal. However, in
some cases, light puffing can occur even when the operating
conditions are optimal.
If weather conditions are poor, an attempt should still be
made to determine if there are any visible emissions. The pres-
ence of a significant plume indicates emission problems. Do not
attempt determine the "average opacity" at such times.
59
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INSPECTION OF ELECTROSTATIC PRECIPITATORS
Basic Level 2 Inspection Procedures
Evaluate condensing plume conditions.
Condensing plume conditions in electrostatic precipitator
systems are usually caused by sulfuric acid vapors, ammonium
chloride vapors, and/or ammonium sulfate vapors generated in
the process equipment. They can also be caused by improper
operation of a flue gas conditioning system (present on some
systems).
The vaporous material condenses once the gas enters, the
cold ambient air. Condensing plumes usually have a bluish-
white color. In some cases, the plume forms 5 to 10 feet after
leaving the stack.
Evaluate double-pass transmissometer physical conditions.
Most precipitators have a transmissometer for the continu-
ous monitoring of visible emissions. If a unit is present, and
if it is in an accessible location, check the light source and
retroreflector modules to confirm that these are in good work-
ing order. Check that the main fan is working and that there
is a least one dust filter for the fan. On many commercial
models it is also possible to check the instrument alignment
without adjusting the instrument. Note; On some models, moving
the dial to the alignment check position will cause an alarm in
the control room. This is to be moved only by plant personnel
and only when It will not disrupt plant operations.
Evaluate double-pass transmissometer data.
If the transmissometer appears to be working properly,
evaluate the average opacity data for at least the previous 24
hours prior to the inspection. If possible, the average opacity
data for selected days since the last inspection should also be
reviewed. This evaluation is helpful in confirming that the
units being inspected are operating in a representative fashion.
If the unit is working better during the inspection than during
other periods, it may be advisable to conduct an unscheduled
inspection in the future.
As part of the review of average opacity, scan the data to
determine the frequency of emission problems and to evaluate how
rapidly the operators are able to recognize and eliminate the
condition.
60
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INSPECTION OF ELECTROSTATIC PRECIPITATORS
Basic Level 2 Inspection Procedures
Evaluate the transformer-rectifier set electrical data.
The first step in evaluating the transformer-rectifier
(T-R) set electrical data is to obtain or prepare a sketch that
indicates the arrangement of the T-R sets on the precipitator.
This drawing should indicate the number of chambers in the pre-
cipitator and the number of T-R sets in series in each chamber.
The T-R set numbers should be included on the sketch.
For each chamber, the T-R set electrical data is recorded
starting with the inlet field and proceeding to the outlet field.
In some cases, the control cabinets are scrambled. The follow-
ing data should be recorded.
Primary Primary Secondary Secondary Spark Rate
Voltage Current Voltage Current
(Volts) (Amps) (Kilovolts) (Millamps) (Number/Min.)
Inlet
Field
Second
Field
nth
Field
The voltages and currents should be recorded when the gauge
reaches the highest stable value for approximately one second or
more.
If there is any question about the adequacy of the spark
rate meter, the spark rate should be determined by counting the
number of flucuations of the primary voltage and/or secondary
voltage meters.
61
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INSPECTION OF ELECTROSTATIC PRECIPITATORS
Basic Level 2 Inspection Procedures
Evaluate the transformer-rectifier set electrical data.
Compare the secondary and/or primary voltages against base-
line levels for this unit and against typical values. Generally,
the primary voltages are above 250 volts and they are usually in
the range of 250 to 380 volts (A.C.). The secondary voltages
are normally in the range of 20 to 45 kilovolts (D.C). A drop
in the primary voltage of 30 volts (A.C.) or a drop in the sec-
ondary voltage of 5 kilovolts (D.C.) in a given field indicates
significantly reduced particulate control capability for that
field.
To check the particle resistivity conditions, plot the
voltages, currents, and spark rates for each of the chambers
(Figure 3-3). Compare these drawings with similar drawings
prepared from baseline data. There has probably been a signi-
ficant shift in the particle resistivity if all or most of the
fields in a chamber have shifted in the the same direction at
approximately the same tine (outlet fields often lag several
hours). The symptoms of resistivity shifts are summarized
below.
0 Higher resistivity
Reduced primary or secondary voltages
Reduced primary or secondary currents
Increased spark rates .
0 Lower resistivity
Reduced primary or secondary voltages
Increased primary or secondary currents
Decreased spary rates
In some units, the resistivity conditions in one chamber
are quite different from the resistivity conditions in other
adjacent chambers. In these types of units, the changes in the
secondary voltages and currents are much greater in some of the
chambers. This condition is often caused by slight differences
in the flue gas temperatures entering the various chambers
and/or by maldistribution of resistivity conditioning materials
injected into the system.
62
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INSPECTION OF ELECTROSTATIC PRECIPITATORS
Basic Level 2 Inspection Procedures
Evaluate precipitator general physical conditions.
While walking around the precipitator and its inlet and out-
let ductwork, check for obvious corrosion around the potential
"cold" spots such as the corners of the hoppers, near the solids
discharge valve, and the access hatches. On negative pressure
units, check for audible air infiltration through the corroded
areas, warped access hatches, eroded solids discharge valves, or
other sites. On positive pressure units, check for fugitive
emissions of dust from any corroded areas of the system.
Evaluate the process operating rate.
Record one or more process operating rate parameters that
document that the source conditions are representative of normal
operation.
Evaluate process operating conditions.
Record any process operating parameters that have an impact
on the characteristics and/or quantities of pollutants generated.
Some of the important variables are listed below.
0 Gas stream temperatures and static pressures
0 Gas stream oxygen levels
0 Raw material characteristics
Evaluate process fugitive emissions.
Perform complete visible emission observations on any major
process fugitive emissions. If the conditions preclude a com-
plete observation, note the presence and timing of any fugitive
releases.
3.4.2 Follow-up Inspection Points for Level 2 Inspections
Evaluate rapper systems.
The collection plate, discharge electrode, and gas distri-
bution screen rapping systems are evaluated when low power inputs
are observed in one or more fields or when there is puffing.
Note any rappers that do not appear to be working or that
do not sound proper when activating. A sketch is often a useful
way to summarize this information
63
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INSPECTION OF ELECTROSTATIC PRECIPITATORS
Follow-up Level 2 Inspection Procedures
Request that plant personnel open the rapper control
cabinets (if they are qualified). Compare the present rapper
system intensities with the baseline values.
If the intensities are now higher, the unit may have
high resistivity dusts, binding or broken rapper shaft
connections, or poor start-up procedures. It should
be noted that it is rarely possible to minimize high
resistivity dust problems simply by increasing rapper
intensities and that some rapper shaft and/or collection
plate alignment problems can occur at high intensities.
0 If the intensities are now much lower, the unit may have
low resistivity dusts, or the rappers may have been
temporarily turned down to minimize obvious puffing.
Determine the activition frequency of the various groups
of rappers. This can often be done by watching selected groups
of rappers for a period of 10 to 60 minutes. It can also be
determined by checking the timers in the control cabinets.
However, the indicated rapper frequencies on the timers are not
always reliable. Compare the activation frequencies with the
observed frequency of puffing.
c If the activation frequency is high, the unit may
be having problems with high resistivity dust. It
is rarely possible to minimize this condition simply
by increasing rapper frequency.
0 If the activation frequency is low, the unit may
have lower resistivity dust than during the baseline
period. As long as the electrical conditions and the
opacity are acceptable, low frequency is desirable.
0 Puffing is often related to the activation frequency
of the outlet field collection plate rappers.
0 Note any occasions when more than one rapper is
activated simultaneously or when two or more rappers
are activated within a period of several seconds.
-------
INSPECTION OF ELECTROSTATIC PRECIPITATORS
Follow-up Level 2 Inspection Procedures
Evaluate the opacity strip charts/records and the
transformer-rectifier set records (baseline files).
This is a time consuming portion of the inspection. It
should be done only when the plant is experiencing frequent and
significant excess emission problems and there is some question
concerning the proposed corrective actions.
Obtain the opacity records and quickly scan the data for
the previous 1 to 12 months to determine time periods that had
especially high and especially low average opacities. Time
periods with and without severe spiking are also of interest.
Select the precipitator operating logs and the process opera-
ting logs that correspond with the times of the opacity strip
charts/records selected. Compare the precipitator operating
data and process operating data against baseline information
to identify the general category of problem(s) causing the
excess emission incidents. Evaluate the source's proposed
corrective actions to minimize this problem(s) in the future.
Evaluate wire failure and location records.
Request the discharge wire failure records from the opera-
tors if it appears that wire failures have caused temporary
outages of one or more fields since the last inspection. If
specific wire failure records are not maintained, attempt to
determine how many wires have failed since the last inspection.
Most electrostatic precipitors operate with wire failure rates
that are much less than 1 per month. Higher failure rates may
indicate plate-wire misalignment, clearance problems, improper
rapping operation, inadequate wire tension, and/or corrosion.
Wire failure is often a symptom of other more substantial
problems.
Evaluate the owner/operators' plan for minimizing excess
emission incidents caused by wire failure. It is generally
necessary to fix the underlying cause of the failure rather
than simply reinstalling the wire.
3.4.3 Level 3 Inspection Procedures
These are identical to Level 2 inspection procedures since
portable inspection instruments are not used for precipitators.
65
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INSPECTION OF ELECTROSTATIC PRECIPITATORS
Level 4 Inspection Procedures
3.4.4 Level 4 Inspection Procedures
The Level 4 inspection includes many inspection steps per-
formed during Level 2/Level 3 inspections. These are described
in earlier sections. The unique inspection steps of Level 4
inspections are described below.
Evaluate start-up and shutdown procedures.
The start-up and shutdown procedures used at the plant
should be discussed to confirm the following.
The plant has taken reasonable precautions to minimize
the number of start-up/shutdown cycles.
The precipitator is energized in a reasonable time after
start-up of the process equipment. Inspectors should
remember that energizing too early in the start-up
process can lead to precipitator explosions or to deposits
on the collection plates that reduce the performance
capability of the unit.
Evaluate potential safety problems.
Agency management personnel and/or senior inspectors should
identify potential safety problems involved in standard Level 21
Level 3 inspections at this site. To the extent possible, the
system owner/operators should eliminate these hazards. For those
hazards which can not be eliminated, agency personnel should
prepare notes on how future Inspections should be limited and
should prepare a list of the necessary personnel safety equipment.
A partial list of common health and safety hazards include the
following.
0 Inhalation hazards due to fugitive leaks from inlet breech-
ings, inlet expansion section, access hatches, hoppers,
outlet contraction section, expansion joints, and fans
0 Corroded percipitator roofs ladder supports
0 Ungrounded rappers
0 High voltage in control cabinets
66
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INSPECTION OF ELECTROSTATIC PRECIPITATORS
Level 4 Inspection Procedures
Prepare a_ system flowchart.
A relatively simple flowchart is very helpful in conducting
a complete and effective level 2/level 3 inspection. This should
be prepared by agency management personnel or senior inspectors
during a level A inspection. This should consist of a simple
block diagram that includes the following elements.
0 Source(s) of emissions controlled by a single
precipitator
0 Location(s) of any fans used for gas movement
through the system (used to evaluate inhalation
problems due to positive static pressures)
0 Locations of any main stacks and bypass stacks
0 Layout and identification numbers of transformer-
rectifier sets used in all chambers
0 Locations of major instruments (transmissometers,
thermocouples)
Evaluate potential safety problems in the process area.
The agency management personnel and/or senior inspectors
should evaluate potential safety problems in the areas that
may be visited by agency inspectors during Level 2/Level 3
inspections. They should prepare a list of the activities
that should not be performed and locations that an inspector
should not go as part of these inspections. The purpose of
this review is to minimize inspector risk and to minimize the
liability concerns of plant personnel.
67
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A. INSPECTION OF WET SCRUBBERS
The most common types of wet scrubber systems are addressed in
this inspection notebook. The inspection procedures discussed in
this section have been tailored to the specific design characteristics
and operating problems of these scrubbers.
Spray tower
Packed beds
Tray tower
Mechanically aided
Orifice
Rod deck
Venturi
Inspectors and their supervisors should modify these procedures
as necessary for types of scrubbers not specifically discussed in
this notebook.
4.1 Scrubber system components and operating principles
A scrubber is not an isolated piece of equipment. It is a sys-
tem composed of a large number of individual components. A partial
list of the major components of commercial systems is provided below.
Scrubber vessel
Gas cooler and humidifier
Liquor treatment equipment
Gas stream demister .
Liquor recirculation tanks, pumps, and piping
Alkaline addition equipment
Fans, dampers, and bypass stacks
One of the first steps in the inspection of any wet scrubber
system is to prepare a flowchart that includes any of the components
listed directly above. This will be invaluable in evaluating the
on-site instrumentation and in identifying system operating problems.
69
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INSPECTION OF WET SCRUBBER SYSTEMS
Components and Operating Principles
4.1.1 Characteristics of spray tower scrubbers
A simplified sketch of a spray tower scrubber is illustrated
in Figure 4-1. The gas stream enters near the bottom of the scrubber
and goes upward at velocities between 2 and 10 feet per second.
The liquor enters at the top of the unit through one or more spray
headers. Nozzles are oriented on the headers so that all of the gas
stream is exposed to the sprayed liquor. Careful scrubber design is
necessary to achieve proper liquor distribution since this is a
function of the type of nozzle used, the spray angle of the nozzles,
the nozzle placements, and the liquor pressure. It is also important
to design the headers so that solids deposits do not accumulate.
A spray tower scrubber has only a limited particulate removal
capability. It is selected for applications where there is very
little particulate matter smaller than 5 microns. These scrubbers
can be effective gas absorbers in addition to particulate collectors.
Most of these systems are relatively simple and have only
limited instrumentation. However, alkaline addition equipment and
liquor treatment systems are often necessary when the units are used
for gas absorption. Such units can be quite complicated.
(tor.. *n
Source: APTI
Figure 4-1. Spray towei scrubbers
Source: APTI
70
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INSPECTION OF WET SCRUBBER SYSTEMS
Components and Operating Principles
4.1.2 Characteristics of Packed Tower Scrubbers
This type of scrubber is used primarily for gas absorption.
The large liquor surface area created as the liquor gradually passes
over the packing material favors gas diffusion and absorption.
Packed bed scrubbers are not effective for collection of small
particulate matter since the gas velocity through the bed(s) is
relatively slow.
Packed beds can be either vertical (as shown in Figure 4-2) or
horizontal. Regardless of the orientation of the bed, the liquor is
sprayed from the top and flows downward across the bed. Proper
liquor distribution is important for efficient removal of gases.
This is one of the few types of scrubbers in which the static
pressure drop is not very important.
One of the major problems with these scrubbers is the accumula-
tion of solids at the entry to the bed and within the bed. The
dissolved and suspended solids levels in the liquor must be monitored
carefully.
Source: A?" I
Figure 4-2. Packed bed scrubber
71
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INSPECTION OF WET SCRUBBER SYSTEMS
Components and Operating Principles
4.1.3 Characteristics of Tray Tower Scrubbers
A tray tower scrubber (Figure 4-3a) can be used for both
particulate and gaseous removal. It consists of a series of trays
with holes. The gas stream enters from the bottom and passes upward
through the holes. Liquor enters from the top and passes across
each tray as it goes downward. Downcomers are used for moving the
liquor from one tray to another.
Two of the major tray designs are shown in Figure 4-3b. The
sieve plate has relatively large holes compared with the impingement
tray. The latter has high velocities through the holes and a target
directly above the holes.
One of the main advantages of this style of scrubber vessel is
that there are several opportunities to collect pollutants. Slight
gas-liquor maldistribution on one tray can be tolerated since the
material can be caught on subsequent trays. The liquor suspended and
dissolved solids concentrations are important since it is easy for
the holes to plug.
Source:
Figure 4-3a. Tray tower scrubber Figure A-3b. Common tray designs
72
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INSPECTION OF WET SCRUBBER SYSTEMS
Components and Operating Principles
A.1.4 Characteristics of Mechanically Aided Scrubbers
One common type of mechanically aided scrubber is illustrated
in Figure 4-4. The gas stream enters axially and is spun outward
due to the rapid rotation of the scrubber fan blade. Liquor is
sprayed in the inlet duct. Impaction of particles occurs on the
initially slow moving droplets.
Unlike all other types of scrubbers, this particular design
does not have a "pressure drop". The mechanical energy provided by
the shaft achieves the scrubbing action and moves the gas stream
through the ductwork. There is a static pressure rise across this
type of unit.
These scrubbers are used only for relatively small systems
having gas flows less than 10,000 ACFM. The scrubber systems are
relatively simple. However, it is important to have high quality
liquor so that erosion and build-up on the fan blades is minimized.
Obviously, no fans are necessary with this type of system.
Source: APTI
Figure 4-4. Mechanically aided scrubber
73
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INSPECTION OF WET SCRUBBER SYSTEMS
Components and Operating Principles
A.1.5 Characteristics of Orifice Scrubbers
The orifice scrubber is one of a large number of units which are
classified as a gas atomized scrubber. This means that the droplets
which serve as impaction targets are formed in high velocity gas
streams.
A sketch of an orifice scrubber is shown in Figure 4-5. In this
unit, the gas enters the vertical tube and makes a 180° turn just
above the surface of the liquor. The action of the gas stream atom-
izes the liquor that was entrained by the passing gas stream. Baffles
included in the scrubber vessel knock down any drops which remain
suspended in the gas.
Orifice scrubbers are often very small and very simple scrubbers.
In some units, there is no recirculation pump and piping system. The
inspection of these small orifice scrubbers is often complicated by
the almost complete lack of instrumentation.
Soi rce: APTT
Figure 4-6. Orifice scrubber
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INSPECTION OF WET SCRUBBER SYSTEMS
Components and Operating Principles
A.1.7 Characteristics of Venturi Scrubbers
A conventional venturi scrubber is shown in Figure 4-7a. The
gas stream enters the converging section and is accelerated approx-
imately a factor of ten. The liquor is injected just above the
throat. Droplets form due to the shearing action of the high gas
velocities. Impaction of particles occurs on the droplets which are
initially moving slower than the gas stream. The high liquor surface
area also allows for gas absorption.
The gas stream is decelerated in the diverging section. After
the venturi section, the gas stream turns 90° and passes into the
demister chamber. The venturi scrubbers are usually part of a large
and relatively complex scrubber system.
There are a large number of variations to the standard venturi
configuration. Figure 4-7b illustrates one common throat design
which incorporates internal dampers to vary the gas velocity. These
can be opened or closed to maintain a constant static pressure drop
when gas flow varies, or the dampers can be used to adjust the static
pressure drop when the inlet particle size distribution varies.
GAS INLET
LIQUOR INLET
THROAT DAMPERS
GAS OUTLET-
Figure 4-7a. Venturi scrubber Figure 4-7b. Throat dampers
75
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INSPECTION OF WET SCRUBBER SYSTEMS
Components and Operating Principles
4.1.8 Characteristics of Rod Deck Scrubber
This type of unit is similar to a venturi scrubber. However, a
horizontal deck of rods is used to accelerate the gas stream rather
than a conventional venturi. The restricted area between the rods
provides for liquor atomization and particle impaction. The numbers
of rods and the diameters of the rods can be varied as necessary to
achieve the desired gas velocities and static pressure drops.
The inspection procedures for this style of scrubber is very
similar to that for classical venturi units. The only difference
is that there is concern with rod erosion and corrosion in this
design.
Unlike conventional venturi scrubbers, these units can have
several decks in series. The multiple deck arrangement is used
primarily for gas absorption rather than particulate control.
Source: APTI
Figure 4-8. Rod deck scrubbers
76
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INSPECTION OF WET SCRUBBER SYSTEMS
Components and Operating Principles
A.1.9 Operating Principles
Impaction is the primary means for collection of particles in
wet scrubbers. The effectiveness of impaction is related to the
square of the particle diameter and the difference in velocities of
the liquor droplets and the particles.
The importance of particle size is emphasized in Figure 4-8.
For particles greater than 1 to 2 microns, impaction is so effective
that penetration (emissions) is quite low. However, penetration of
smaller particles, such as the particles in the 0.1 to 0.5 micron
range is very high. Unfortunately, some commercial processes can
generate substantial quantities of particulate in this submicron
range. Most aerosols in this size range are formed from vaporous
material that condenses as the gas stream leaves the process equip-
ment or as the gas stream enters the relatively cold scrubber.
For a constant particle size distribution, the overall particu-
late collection efficiency generally increases as the static pressure
drop increases. The static pressure drop is a measure of the total
amount of energy used in the scrubber to accelerate the gas stream,
to atomize the liquor droplets, and to overcome friction. At high
static pressure drops, the difference in droplet velocities and
particle velocities is high and a large number of small diameter
droplets are formed. Both of these conditions favor particle
impaction into water droplets.
Another important variable is the liquor surface tension. If
this is too high, some small particles that impact on the water
droplet will "bounce" off and not be captured. High surface tension
also has an adverse impact on droplet formation. Unfortunately, the
scrubber liquors having surface tensions that provide optimum parti-
cle impaction may have poor solids settling properties. Surfactants
can be added to reduce surface tension. Conversely, flocculants and
anti-foaming agents generally increase the surface tension.
77
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INSPECTION OF WET SCRUBBERS
Components and Operating Principles
4 S • 7 •
Particte Diameter. »m
10
Figure 4-9.
Relationship between particle penetration (emissions)
and particle size
78
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INSPECTION OF WET SCRUBBER SYSTEMS
General Safety Considerations
A. 2 General Safety Considerations
Some wet scrubbers systems operate at much higher positive
static pressures that other types of air pollution control systems.
Furthermore, there is a significant potential for corrosion and
erosion of the scrubber vessel and ductwork. For these reasons,
fugitive leaks are a common problem. The inhalation hazards can
include chemical asphyxiants, physical asphyxiants, toxic gases, and
toxic particulate. Inspectors should avoid all areas with obvious
leaks and any areas with poor ventilation. During Level 3 and
Level A inspections, only small diameter ports should be used.
Extreme care is often necessary when walking around the scrubber
and when climbing access ladders. Slip hazards can be created by
water droplets reentrained in the exhaust gas, by liquor draining
from the pumps, and by liquor seeping from pipes and tanks. These
slip hazards are not always obvious. Furthermore, freezing can occur
in cold weather.
A few systems are subjected to fan imbalance conditions due to
the build-up of sludge on the fan blades, the corrosion of the fan
blades, the erosion of the fan blades, and a variety of other factors,
The inspection should be terminated immediately whenever an inspector
observes a severely vibrating fan. A responsible plant representa-
tive should be notified once the inspector reaches a safe location.
Severely vibrating fans can disintigrate.
All liquor samples necessary .for Level 3 or Level A inspections
should be taken by the plant personnel, not the inspector. Further-
more, the inspectors should only ask responsible and experienced
plant personnel to take the samples. Eye injuries and chemical
burns (in some cases) ire possible if the samples are taken incor-
ectly. Inspectors should not under any circumstances enter a wet
scrubber vessel or any tank or confined area used in the system.
All of the necessary inspection steps can be accomplished without
internal inspections. Access hatches or viewing ports should not
be opened during the inspection due to the risk of eye injuries.
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INSPECTION OF WET SCRUBBERS
Inspection Summaries
4.3 Inspection Summaries
A.3.1 Level 1 Inspections (All types of scrubbers)
Stack ° Visible emissions for 6 to 30 minutes for
each stack or discharge vent
0 Mist reentrainment
Wet Scrubber
e Not applicable
Process ° Presence or absence of fugitive emissions
A.3.2 Level 2 Inspections
Basic Inspection Points
Stack ° Visible emissions for 6 to 30 minutes for
each stack or discharge vent
c Minimum and maximum stort term opacities
due to process cycles
0 Droplet reentrainment
Scrubber Vessels
Spray Tower Scrubbers
0 Inlet liquor pressure
0 General physical condition
Packed Bed, Tray Tower, and Mechanically Aided Scrubbers
0 Static pressure change
0 Liquor turbidity and settling rate
0 General physical condition
Venturi, Rod Deck and Orifice Scrubbers
Static pressure change
General physical condition
Process
Process operating rate
Process operating conditions
Presence or absence of fugitive emissions
80
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INSPECTION OF WET SCRUBBER SYSTEMS
Inspection Summaries
A.3.2 Level 2 Inspections (Continued)
Follow-up
Scruber Vessels
Spray Tower Scrubbers
0 Scrubber gas flow rate
0 Liquor turbidity and settling rate
0 Liquor distribution from nozzles
0 Demister condition
Packed Bed, Tray Tower, and Mechanically Aided Scrubbers
0 Liquor pH
0 Liquor recirculation flow rate
0 Scrubber gas flow rate
0 Tray, bed, and demister condition
0 Mechanically aided scrubber rotational speed
Venturi, Rod Deck, and Orifice Scrubbers
0 Liquor pH
0 Liquor turbidity and settling rate
0 Liquor recirculation rate
0 Scrubber gas flow rate
6 Venturi scrubber adjustable throat
mechanism condition .
0 Demister condition
A.3.3 Level 3 Inspections
Stack ° Visible emissions for 6 to 30 minutes for
each stack or discharge vent*
0 Maximum and minimum short term opacities
during process cycles*
0 Droplet reentrainment*
Scrubber Vessels
Spray Tower Scrubbers
0 Gas flow rate from scrubber
0 Liquor pH
0 Outlet gas temperature
81
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INSPECTION OF WET SCRUBBER SYSTEMS
Inspection Summaries
4.3.3 Level 3 Inspections (continued)
Packed Bed, Tray Tower, and Mechanically Aided Scrubbers
0 Static pressure change
0 Gas flow rate from scrubber
0 Outlet liquor pH
0 Outlet gas temperature
Venturi, Rod Deck, and Orifice Scrubbers
Static pressure change
Gas flow rate from scrubber
Outlet liquor pH
Outlet gas temperature
Process
Process operating rate*
Process operating conditions*
Presence or absence of fugitive emissions*
A.3.4 Level A Inspections
Stack e All elements of a Level 3 inspection
Wet Scrubber
0 All elements of.a Level 3 inspection
0 Locations for measurement ports
e Potential inspection safety problems
Process e All elements of a Level 3 inspection
* Basic flowchart of process
",Potential inspection safety problems
* See Level 2 basic and follow-up inspection procedures.
82
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INSPECTION OF WET SCRUBBER SYSTEMS
Basic Level 2 Inspection Procedures
4.4 Inspection Procedures
Techniques for the inspection of wet scrubber systems can
be classified as Level 1, 2, 3, or 4. The Level 1 inspection
consists of a visible emission observation from outside the
plant. This is not discussed in this manual. The Level 2
inspection primarily involves a walkthrough evaluation of the
wet scrubber system and process equipment. All data are provided
by on-site gauges. The Level 3 inspection includes all inspec-
tion points of the Level 2 inspection and includes independent
measurements of wet scrubber operating conditions when the on-
site gauges are not adequate. The Level 4 inspection is per-
formed by agency supervisors or senior inspectors to acquire
baseline data. The scope of the Level 4 inspection is
identical to the Level 3 inspection.
4.4.1 Level 2 Inspections
Evaluate the wet scrubber visible emissions.
If weather conditions permit, determine the baghouse
effluent average opacity in accordance with U.S. EPA Method 9
procedures (or other required procedures). The observation
should be conducted during routine process operation and
should last 6 to 30 minutes for each stack and bypass vent.
The observation should be made after the water droplets
contained in the plume vaporize (where the steam plume
"breaks")' The presence of a particulate plume greater than
10% generally indicates a scrubber operating problem, and/or
the generation of high concentrations of submicron particles
in the process, and/or the presence of high concentrations of
vaporous material in the effluent gas stream.
In addition to evaluating the average opacity, inspectors
should scan the visible emissions observation to identify the
maximum and minimum short term opacities. This is especially
useful information if there are variations in the process
operating conditions. For processes such as grey iron cupolas
and drum mix asphalt plants, the difference in the minimum and
maximum opacities provides an indication of changing particle
size distributions.
B3
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INSPECTION OF WET SCRUBBER SYSTEMS
Basic Level 2 Inspection Procedures
Evaluate the vet scrubber visible emissions, (continued)
If weather conditions are poor, an attempt should still be
made to determine if there are any visible emissions. Do not
attempt to determine "average opacity" during adverse weather
conditions. The presence of a noticeable plume generally
indicates wet scrubber operating problems.
Evaluate droplet reentrainment.
Droplet reentrainment indicates a significant demister
problem that can create a local nuisance and that can affect
stack sampling results. The presence of droplet reentrainment
is indicated by the conditions listed below.
0 Obvious rainout of droplets in the immediate
vicinity of the stack
0 Moisture and stains on adjacent equipment
0 Mud lip around the stack discharge
Evaluate the wet scrubber static pressure change.
The wet scrubber static pressure drop* should be recorded
if the gauge appears to be working properly. The following
items should be checked to confirm the adequacy of the on-site
gauge.
0 The gauge "face" should be clear of obvious water
and deposits.
0 The lines leading to the inlet and outlet of the
baghouse s'hould be intact.
If there is any question concerning the gauge, ask plant
personnel to disconnect each line one at a time to see if the
gauge responds. If it does not move when a line is disconnected,
the line may be plugged or the gauge is inoperable. Note: The
lines should only be disconnected _by_ plant personnel and only
when this will not affect plant operations.
* For mechanically aided scrubbers it is a static pressure rise.
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INSPECTION OF WET SCRUBBER SYSTEMS
Basic Level 2 Inspection Procedures
Evaluate the wet scrubber static pressure change fcont.).
Wet scrubber systems operate with a wide range of static
pressure drops as indicated in the list below. Data is not
provided for spray tower scrubbers since static pressure drop
is not a useful inspection parameter for this type unit.
Packed bed 2 to 6 inches W.C.
Tray tower 2 to 12 inches W.C.
Mechanically Aided 2 to 12 inches W.C.
Orifice A to 25 inches W.C.
Rod deck 10 to 120 inches W.C.
Venturi 10 to 120 inches W.C.
It should also be noted that there is a wide range of
required static pressure drops for identical wet scrubbers
operating on similar industrial processes due to the differ-
ences in particle size distributions. For these reasons, it is
preferable to compare the present readings with the baseline
values for this specific source.
Increased static pressure drops* generally indicate the
following possible condition(s).
Packed bed scrubbers ° High gas flow rates
0 Partial bed pluggage
Tray tower scrubbers * High gas flow rate
Partial pluggage of trays
Mechanically aided ° High rotational speed
scrubbers
Orifice scrubbers
Venturi and Rod deck
scrubbers
High gas flow rate
High liquor levels
High gas flow rate
High liquor flow rates
Reduced rod spacings or
constricted venturi throats
* Static pressure rise for mechanically aided scrubbers
85
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INSPECTION OF WET SCRUBBER SYSTEMS
Basic Level 2 Inspection Procedures
Evaluate the wet scrubber static pressure change (cont.).
Decreased static pressure drops* generally indicate the
following possible condition(s).
Packed bed scrubbers
Tray tower scrubbers
Mechanically aided
scrubbers
Orifice scrubbers
0 Low gas flow rates
0 Bed collaspe
0 High gas flow rate
0 Collaspe of tray(s)
e Low liquor flow
0 Low rotational speed
Venturi and Rod deck
scrubbers
Low gas flow rate
Low liquor levels
Low gas flow rate
Low liquor flow rates
Eroded rods or venturi dampers
Increased rod spacings or
increased venturi throat openings
Evaluate the liquor inlet pressure.
The pressure of the header that supplies the scrubber
spray nozzle can provide an indirect indication of the liquor
flow rate and the nozzle condition. When the present value is
lower than the baseline value(s), the liquor flow rate has
increased and there is a possibility of nozzle orifice erosion.
Conversely, if the present value is higher than the baseline
value(s) the liquor flow rate has decreased and nozzle and/or
header pluggage Is possible.
Unfortunately, these pressure gauges are very vulnerable
to error due to solids deposits and due to corrosion. It is
difficult to confirm that they are working properly. For
these reasons, other indicators of low liquor flow such as the
pump discharge pressure and the outlet gas temperature should be
checked whenever low header or pipe pressures are observed.
* Static pressure rise for mechanically aided scrubbers
86
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INSPECTION OF WET SCRUBBER SYSTEMS
Basic Level 2 Inspection Procedures
Evaluate the vet scrubber system general physical conditions.
While walking around the wet scrubber system and its inlet
and outlet ductwork, check for obvious corrosion and erosion.
If any material damage is evident, check for fugitive emissions
(positive pressure systems) or air infiltration (negative pres-
sure systems). Avoid inhalation hazards and walking hazards
while checking the scrubber system general physical condition.
Prepare a sketch showing the locations of the corrosion and/or
erosion damage.
In addition to corrosion and erosion, inspectors should also
check for any of the conditions listed below.
c Severely vibrating fans (Leave area immediately!)
0 Cracked or worn ductwork expansion joints
0 Obviously sagging piping
0 Pipes that can not be drained and/or flushed
Evaluate the liquor turbidity and solids settling rate.
Ask a responsible and experienced plant representative to
obtain a sample of the liquor entering the scrubber vessel.
This can usually be obtained at a sample tap downstream from
the main recirculation pump. The agency inspector should
provide a clear sample bottle.
Observe the turbidity of the liquor for a few seconds
immediately after the sample is taken. The turbidity should be
qualitatively evaluated as clear, very light, light, moderate,
heavy, or very heavy. After allowing the sample to settle for
five minutes, repeat the evaluation of the liquor turbidity and
describe the thickness of the settled solids.
Evaluate the process operating rate.
Record one or more process operating rate parameters that
document that the source conditions are representative of normal
operation.
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INSPECTION OF WET SCRUBBER SYSTEMS
Basic Level 2 Inspection Procedures
Evaluate process operating conditions.
Record any process operating parameters that have an impact
on the characteristics and/or quantities of pollutants generated.
Some of the important variables are listed below.
0 Gas stream temperatures
0 Gas stream static pressures
0 Gas stream oxygen levels
0 Raw material characteristics
Evaluate process fugitive emissions.
Perform complete visible emission observations on any major
process fugitive emissions. If the conditions preclude a com-
plete observation, note the presence and timing of any fugitive
releases.
4.4.2 Follow-up Inspection Points for Level 2 Inspections
Check liquor pH.
Locate the on-site pH meter(s). Permanently mounted units
are generally in the recirculation tank or in the liquor outlet
lines from the scrubber vessel. Confirm that the instrument is
working properly by reviewing the routine calibration records.
In some cases, it is possible to watch plant personnel calibrate
these instruments during the inspection.
If the pH meter(s) appears to be working properly, review
the pH data for at least the previous month. In units with
instruments on the outlet and the inlet, the outlet values are
often 0.5 to 2.0 pH units lower due to the absorption of carbon
dioxide, sulfur dioxide, or other acid gases. Generally, all
of the pH measurements should be within the range from 5.5 to
10.0. Furthermore, any significant shifts in the pH values
from baseline conditions can indicate scrubber system operating
problems.
Corrosion can be severe in most systems when the pH levels
are less than 5.5. Also, high chloride concentrations accelerate
corrosion at low pH levels. Precipitation of calcium and
magnesium compounds at pH levels above 10 can lead to severe
scaling and gas-liquor maldistribution.
88
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INSPECTION OF WET SCRUBBER SYSTEMS
Follow-up Level 2 Inspection Procedures
Evaluate the scrubber liquor recirculation rate.
One frequent cause of scrubber emission problems is inade-
quate liquor recirculation rate. Unfortunately, many commercial
types of liquor flow monitors are subject to frequent maintenance
problems and many small systems do not have any liquor flow
meters at all. For these reasons, a combination of factors are
considered to determine if the scrubber liquor recirculation
rate is much less than the baseline level(s). These factors
include the following:
0 Liquor flow meter (if available, and if it appears
to be working properly)
0 Pump discharge pressure (Higher values indicate
lower flow.)
0 Pump motor current (Lower values indicate lower flow.)
0 Nozzle header pressure (Higher values indicate
lower flow.)
0 Scrubber exit gas temperature (Higher values indicate
lower flow.)
0 Quantity of liquor draining back into recirculation
tank or pond (Lower flow rates indicate lower
recirculation rates.)
Evaluate gas flow rate.
Changes in gas flow rate occur routinely in most processes
due to variations in process operating rates and conditions.
Information concerning gas flow rate changes is necessary when
evaluating changes in the scrubber static pressure drop.
Check the scrubber system fan motor current. Correct fan
motor current to standard conditions using the equation below.
Corrected current - Actual Current x (Gas Temp.+ 460)/520
An increase in the fan motor current indicates an increase
in the gas flow rate.
89
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INSPECTION OF WET SCRUBBER SYSTEMS
Follow-up Level 2 Inspection Procedures
Evaluate demister conditions.
The demister physical condition should be evaluated if
substantial liquor reentrainment has occurred recently. It
should be noted, however, that there oust be safe and convenient
access hatches and that there must not be any process gas in
the scrubber at the time of the inspection.
Note any deposits on the bottom or the top of the demister.
This can lead to localized high gas velocity areas which lead
to liquor reentrainment. The appearance of any spray nozzles
used for the routine cleaning of the demister should also be
noted.
Evaluate liquor distribution from spray nozzles (SPRAY TOWER
SCRUBBERS ONLY).
This inspection step can be performed when the scrubber
system is out-of-service. Locate a hatch on the scrubber
vessel shell that is above the elevation of the spray nozzles
and that has a good view of the spray pattern from the nozzles.
Observe the spray pattern from each of the nozzles when there
is no process gas being handled by the scrubber and when no
moving ambient air is in the scrubber vessel. The spray pattern
should appear to be uniform and should completely cover the
area of gas flow. Nonuniform spray patterns indicate that the
nozzle is partially plugged. If none of the nozzles on a
single header are operating, the entrance to the header may be
plugged.
If a safe and convenient hatch can not be located, do not
attempt to perform this inspection step. Also, only the plant
personnel should open and close the access hatches.
Evaluate mechanically aided scrubber rotational speed.
Request that a responsible and experienced plant repre-
sentative measure the rotational speed of the scrubber (if this
can be done safely). Compare the present speed with the baseline
value(s). A higher speed indicates higher gas flow rates and
higher static pressure rises across the scrubber.
90
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INSPECTION OF WET SCRUBBER SYSTEMS
Follow-up Level 2 Inspection Procedures
Evaluate physical condition of scrubber packed beds, trays.
and venturi throat dampers.
This inspection step can be performed only when the scrub-
ber system is out-of-service. Locate a hatch on the scrubber
vessel shell that is either above or below the internal compon-
ent of interest. Look for the problems listed below.
Packed bed scrubbers
Tray tower scrubber
Orifice scrubbers
Rod deck scrubbers
Venturi scrubbers
0 Corroded or collapsed bed supports
0 Plugged or eroded distribution
nozzles
e Bowed or sagging trays
e Corroded or broken downcomers
Plugged tray holes
0 Solids deposits in liquor containers
0 Solids deposits at gas inlet to
orifice section
* Plugged spray nozzles at gas inlet
to orifice section
0 Eroded gas stream baffle at gas
inlet to orifice section
0 Solids deposits in demister section
0 Eroded or corroded rods
0 Plugged or eroded liquor nozzles
0 Eroded throat dampers
0 Restricted throat damper movement
due to solids deposits
Process equipment fugitive emissions.
A careful check for process fugitive emissions is necessary
whenever the scrubber system static pressure drop is substan-
tially higher than the baseline value or when air infiltration
is severe. In both cases, poor capture of the dust at the
process equipment is possible. Walk around the process sources
to the extent safely possible to determine if pollutant capture
is adequate.
91
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INSPECTION OF WET SCRUBBER SYSTEMS
Level 3 Inspection Procedures
4.4.3 Level 3 Inspection Points
Procedures for measuring wet scrubber system operating
conditions are described below. Other observations to be
completed as part of the Level 3 inspection are identical to
those included in the basic and follow-up Level 2 inspection.
See the Level 2 inspection procedures section for a discussion
of these steps.
Measure the wet scrubber static pressure drop.
The static pressure drop is directly related to the
effectiveness of particle impaction for particle capture.
Generally, the particulate removal efficiency increases as the
static pressure drop increases. The steps in measuring the
static pressure drop are described below.
0 Locate safe and convenient measurement ports. In some
cases it may be possible to temporarily disconnect the
on-site gauge in order to use the portable static pres-
sure gauge. It also may be possible to find small ports
in the ductwork ahead of and after the scrubber vessel.
0 Clean any deposits out of the measurement ports.
0 If the inlet and outlet ports are close together,
connect both sides of the static pressure gauge to the
ports and observe the static pressure for a period of
1 to 5 minutes.
0 If the ports are not close together, measure the static
pressure in one port for 10 to 30 seconds and then
proceed to the other port for 10 to 30 seconds. As long
as the static pressure drop is reasonably stable (the
typical condition), the two values can be subtracted
to determine the static pressure drop.
e
Under no circumstances should on-site plant instruments
be disconnected without the explicit approval of
responsible plant personnel. Also, instruments connected
to differential pressure transducers should not be
disconnected.
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INSPECTION OF WET SCRUBBER SYSTEMS
Level 3 Inspection Procedures
Evaluate the outlet gas temperatures.
This measurement is conducted whenever it is necessary to
determine if poor liquor-gas distribution and/or inadequate
liquor flow rate is seriously reducing particulate collection
efficiency. The steps in measureing the gas temperature are
outlined below.
o
Locate safe and convenient measurement ports on the
outlet portion of the scrubber vessel shell or on the
outlet ductwork of the system. Often small ports less
than 1/4" diameter are adequate.
0 Attach a grounding/bonding cable to the probe if vapor,
gas, and/or particulate levels are potentially explosive
0 Seal the temperature probe in the port to avoid any air
infiltration which would result in a low reading.
0 Measure the gas temperature at a position near the
middle of the duct if possible. Conduct the measurement
for several minutes to ensure a representative reading.
Some flucuation in the readings is possible if the probe
is occassionally hit by a liquor droplet.
0 Compare the outlet gas temperature with the baseline
value(s). If the present value is more than 10 °F higher,
then either gas-liquor maldistribution or inadequate
liquor is possible.
Measure the scrubber outlet liquor pH.
Prior to obtaining a liquor sample warm-up, the portable
pH meter and chec~k it using at least two different fresh buffer
solutions that bracket the normal liquor pH range. Then request
that a responsible and experienced plant representative obtain a
sample of the scrubber outlet liquor. Measure the liquor pH as
soon as possible after obtaining the sample so that the value
does not change due to dissolution of alkaline material or due
to on-going reactions. Compare this to the baseline value(s).
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INSPECTION OF WET SCRUBBER SYSTEMS
Level 3 Inspection Procedures
Evaluate the scrubber outlet gas flow rate.
The gas flow rate is measured using an S-type pitot
and U.S. EPA Reference Methods 1 and 2. The necessary charts
are provided in section 7 of this notebook.
It is especially important to check for cyclonic flow
before making the pitot traverse. This is a common condition
in wet scrubbers since many types of demisters impart cyclonic
action in order to reduce the quantity of reentrained liquor
droplets in the outlet gas stream.
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INSPECTION OF WET SCRUBBER SYSTEMS
Level 4 Inspection Procedures
4.4.4 Level 4 Inspection Procedures
The Level 4 inspection includes many inspection steps per-
formed during Level 2 and 3 inspections. These are described in
earlier sections. The unique inspection steps of Level 4 inspec-
tions are described below.
Evaluate locations for measurement ports.
Many existing wet scrubber systems do not have safe and
convenient ports that can be used for static pressure, gas
temperature, and gas oxygen measurements. One purpose of the
Level 4 inspection is to select (with the assistance of plant
personnel) locations for ports to be installed at a later date
to facilitate Level 3 inspections. Information regarding
possible sample port locations is provided in the U.S. EPA
Publication titled, " Preferred Measurement Ports for Air
Pollution Control Systems", EPA 340/1-86-034.
Evaluate potential safety problems.
Agency management personnel and/or senior inspectors should
identify potential safety problems involved in standard Level 2
or Level 3 inspections at this site. To the extent possible,
the system owner/operators should eliminate these hazards. For
those hazards that can not be eliminated, agency personnel should
prepare notes on how future inspections should be limited and
should prepare a list of the necessary personnel safety equipment.
A partial list of common health and safety hazards include the
following.
0 Inhalation hazards due to fugitive leaks from
high static pressure scrubber vessels and ducts
•V-
0 Eye hazards during sampling of scrubber liquor
0 Slippery walkways and ladders
e Fan disintegration
95
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INSPECTION OF WET SCRUBBER SYSTEMS
Level 4 Inspection Procedures
Prepare &_ system flowchart.
A relatively simple flowchart is very helpful in conduct-
ing a complete and effective Level 2 or Level 3 inspection.
This should be prepared by agency management personnel or senior
inspectors during a Level A inspection. It should consist of a
simple block diagram which includes the following elements:
0 Sources(s) of emissions controlled by a single
wet scrubber system
0 Location(s) of any fans used for gas movement
through the system (used to evaluate inhalation
problems due to positive static pressures)
0 Locations of any main stacks and bypass stacks
0 Location of wet scrubber
0 Locations of major instruments (pH meters, static
pressure gauges, thermocouples, liquor flow meters)
Evaluate potential safety problems in the process area.
The agency management personnel and/or senior inspectors
should evaluate potential safety.problems in the areas that may
be visited by agency inspectors during Level 2 and/or Level 3
inspections. They should prepare a list of the activities that
should not be performed and locations to which an inspector
should not go as part of these inspections. The purpose of this
review is to minimize inspector risk and to minimize the liabil-
ity concerns of plant personnel.
96
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5. INSPECTION OF DRY SCRUBBERS
Dry scrubbers utilize absorption and adsorption for the removal
of sulfur dioxide, hydrogen chloride, hydrogen fluoride, and other
acid gases. Some adsorption of vapor state organic compounds and
metallic compounds also occurs in some dry scrubber applications.
This relatively new control technology is presently in use on
pulverized coal-fired boilers and municipal waste incinerators.
Potential future applications could include municipal waste inciner-
ators and hospital waste incinerators.
5.1 Components and Operating Principles
There is considerable diversity in the variety of processes
which are collectively termed "dry scrubbing." This is partially
because the technology is relatively new and is still evolving. The
diversity also exists because of the differing control requirements
of the types of sources being treated. For purposes of this field
inspection notebook, the various dry scrubbing techniques have been
grouped into three major categories: (1) spray dryer absorbers,
(2) dry injection adsorption systems, and (3) combination spray
dryer and dry injection systems. Specific types of dry scrubbing
processes within each group are listed below. Alternative terms for
these categories used in some publications are shown in parentheses.
Spray Dryer Absorption (Semi-wet)
0 Rotary atomizer spray dryer systems
0 Air atomizing nozzle spray dryer systems
Dry Injection Adsorption (Dry)
0 Dry injection without recycle
0 Dry injection with recycle
(sometimes termed "circulating fluid bed adsorption")
Combination Spray Dryer and Dry Injection (Semi-wet/dry)
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INSPECTION OF DRY SCRUBBERS
Components and Operating Principles
Simplified block diagrams of the three major types of dry
scrubbing systems are presented is Figures 5-1, 5-2 and 5-3. The
main differences between the various systems are the physical form
of the alkaline reagent and the design of the vessel used for con-
tacting the acid gas laden stream with the reagent. The alkaline
feed requirements are much higher for the dry injection adsoption
than the other two categories. Conversely, the spray dryer absorp-
tion and combination systems are much more complicated.
The pollutant removal efficiencies for all three categories of
dry scrubbing systems appear to be very high. In most cases, outlet
gas stream continuous monitors emissions provide a direct indication
of the system performance. Agency inspections of all three types of
dry scrubbing systems are similar with respect to the importance of
reviewing the adequacy of these continuous monitors and of reviewing
data for selected time periods since the last inspection. Subsequent
inspection steps vary substantially for the three types of dry
scrubbers due to the difference in the components and operating
principles of the systems.
It should be noted that the particulate control devices shown
on the right hand side of the flowcharts are generally fabric
filters or electrostatic precipitators. It is also possible that
one and two stage wet scrubbing systems will be used in certain
cases. However, the later discussions will primarily focus on
fabric filters and precipitators since these dominate present and
planned applications.
5.1.1 Spray Dryer Absorbers
In this type of dry scrubbing system, the alkaline reagent is
prepared as a slurry^containing 5 to 20% by weight solids. This
slurry is atomized in a large absorber vessel having a residence
time of 6 to 15 seconds.
There are two main ways of atomization: (1) rotary atomizers,
and (2) air atomizing nozzles. There is generally only one rotary
atomizer per scrubber vessel. However, a few facilities have as
many as three rotary atomizers. There can be a number of air
atomizing nozzles in each scrubbing vessel.
98
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INSPECTION OF DRY SCRUBBERS
Components and Operating Principles
Cump
Note: A - Motor current gauge
FI - Flowrate gauge
TI - Temperature gauge
- Density gauge
Figure 3-1. Components of a Spray Dryer Absorber System
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INSPECTION OF DRY SCRUBBERS
Components and Operating Principles
The shape of the scrubber vessel oust be different to take into
account the differences in the slurry spray pattern and the time
required for droplet evaporation. The length-to-diaraeter ratio for
rotary atomizers is much smaller than that for absorber vessels
using air atomizing nozzles.
It is important that all of the slurry droplets evaporate to
dryness prior to approaching the absorber vessel side walls and
prior to exiting the absorber with the gas stream. Accumulations of
material on the side walls or at the bottom of the absorber would
necessitate an outage of the system since these deposits would
further impede drying. Proper drying of the slurry is achieved by
the generation of small slurry droplets, by proper flue gas contact,
and by use of moderately hot flue gases.
Drying that is too rapid can reduce pollutant collection
efficiency since the primary removal mechanism is absorption into
the droplets. There must be sufficient contact time for the
absorption. For this reason, spray dryer absorbers on coal-fired
boilers are operated with exit gas temperatures only 20 to 30°F
above the saturation temperature. The approach-to-saturation for
municipal waste incinerators is 90 to 180 °F. The absorber exit
gas temperatures are monitored to ensure proper "approach-to-
saturation" and therefore these values are an important inspection
point. It is simply the difference between the wet bulb and dry
bulb temperature monitors at the outlet of the absorber vessel.
In rotary atomizers, a thin film of slurry is fed to the top
of the atomizer disk as it rotates at speeds of 10,000 to 17,000
rpm. The disk speeds remain at a constant level regardless of
system load. These atomizers generate very small slurry droplets
having diameters in the range of 100 microns. The spray pattern is
inherently broad due to the geometry of the disk.
High pressure air is used to provide the physical energy
required for droplet formation in nozzle type atomizers. The typical
air pressures are 70 to 90 psig. Slurry droplets in the range of 70
to 200 microns are generated. This type of atomizer can generally
operate over wider variations of the gas flow rate than can be used
in a rotary atomizer. However, the nozzle atomizer does not have
100
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INSPECTION OF DRY SCRUBBERS
Components and Operating Principles
the slurry feed turndown capability of the rotary atomizer. For
these reasons, different approaches must be taken when operating at
varying system loads.
The alkaline material generally used in a spray dryer absorber
is pebble lime. This material must be slaked in order to prepare a
reactive slurry for absorption of acid gases. Slaking is the addi-
tion of water to convert calcium oxide to calcium hydroxide. While
this may appear simple, proper slaking conditions are important to
ensure that the resulting calcium hydroxide slurry has the proper
particle size distribution and that no coating of the particles has
occurred due to the precipitation of contaminants in the slaking
water.
Some of the important operating parameters of the lime slaker
are the quality of the slaking water, the feed rate of lime, and the
slurry exit temperature. However, it is difficult to relate present
operating conditions or shifts from baseline operating conditions to
possible changes in the absorption characteristics of the dry
scrubber system. A variety of subtle changes in the slaker can
affect the reactivity of the liquor produced.
One of the problems which has been reported for spray dryer
absorber type systems is the pluggage of the slurry feed line to the
atomizer. Scaling of the line can be severe due to the very high pH
of this liquor. The flow rate of the liquor to the atomizer is
usually monitored by a magnetic flow meter. However, this instrument
is also vulnerable to scaling since the flow sensing elements are on
the inside surface of the pipe. To minimize the pluggage problems,
the lines must be well sloped and include the capability for flushing
of the lines immediately after outages. During the inspection, it is
essentially impossible to identify emerging slurry line problems.
Recycle of the solids collected in the absorber vessel is
important in most systems. It increases the solids content of the
slurry fed to the atomizer and thereby improves the drying of the
droplets. Recycle also maximizes reagent utilization. The rate of
solids recycle is monitored on a continuous basis using conventional
slurry flowrate monitors.
101
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INSPECTION OF DRY SCRUBBERS
Components and Operating Principles
5.1.2 Dry Injection Adsorption System
This type of dry scrubber uses finely divided calcium hydroxide
for the adsorption of acid gases. The reagent feed has particle
sizes which are 90% by weight through 325 mesh screens. This is
approximately the consistency of talcum powder. This size is
important to ensure that there is adequate calcium hydroxide surface
area for high efficiency pollutant removal.
Proper particle sizes are maintained by transporting the lime
to the dry scrubber system by means of a positive pressure pneumatic
conveyor. This provides the initial fluidization necessary to break
up any clumps of reagent which have formed during storage. The air
flow rate in the pneumatic conveyor is kept at a constant level
regardless of system load in order to ensure proper particle sizes.
Fluidization (mixing unagglomerated particles with the gas
stream) is completed when the calcium hydroxide is injected counter-
currently into the gas stream. A venturi section is used for the
contactor due to the turbulent action available for mixing the gas
stream and reagent. The gas stream containing the entrained calcium
hydroxide particles and fly ash is then treated in a fabric filter.
Adsorption of acid gases and organic compounds (if present)
occurs primarily while the gas stream passes through the dust cake
composed of calcium hydroxide and fly ash. Pollutant removal
efficiency is dependent on the reagent particle size range, on the
adequacy of dust cake formation,.and on the quantity of reagent
injected.
The calcium hydroxide feed rate for dry injection systems is 3
to A times the stoichlpmetric quantities needed. This is much
higher than the spray dryer absorber type systems and it makes this
approach unattractive for very large systems.
In one version of the dry injection system, solids are recycled
from the particulate control device back into the flue gas contactor
(sometimes termed "reactor"). The primary purpose of the recycle
stream is to increase reagent utilization and thereby reduce overall
calcium hydroxide costs.
102
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INSPECTION OF DRY SCRUBBERS
Components and Operating Principles
Note: A - Motor current gauge
PI - Pressure gauge
TI - Temperature gauge
Figure 5-2. Components of a Dry Injection Adsorption System
103
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INSPECTION OF DRY SCRUBBERS
Components and Operating Principles
5.1.3 Combination Spray Dryer and Dry Injection System
A flowchart for this system is provided in Figure 5-3. The
acid gas laden flue gas is first treated in an upflow type spray
dryer absorber. A series of calcium hydroxide sprays near the
bottom of the absorber vessel are used for droplet generation.
After the upflow chamber, the partially treated flue gas then
passes through a venturi contactor section where it is exposed to a
calcium silicate and lime suspension. The purpose of the second
reagent material is to improve the'dust cake characteristics in the
downstream baghouse and to optimize acid gas removal in this dust
cake. The calcium silicate reportedly improves dust cake porosity
and serves as an adsorbant for the acid gases.
Solids collected in the baghouse may be recycled to the venturi
contactor. This improves reagent utilization and facilitates
additional pollutant removal.
5.1.4 General Comments
Corrosion can present major problems for all types of dry
scrubbers used on applications with high hydrogen chloride concen-
trations such as municipal waste incinerators and hazardous waste
incinerators. The calcium chloride reaction product formed in the
dry scrubbers and any uncorrected hydrogen chloride are both very
corrosive and cause damage in any areas of the absorber vessel or
particulate control device where cooling and water vapor conden-
sation can occur. Two common reasons for cold localized gas temper-
atures include air infiltration and improper insulation around
support beams. Due to the potential problems related to corrosion,
the inspections should include checks for air infiltration and a
visible evaluation of"common corrosion sites.
104
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INSPECTION OF DRY SCRUBBERS
Components and Operating Principles
Pirnip
Note:
A - Motor current gauge
PI - Pressure gauge
TI (dry) - Dry bulb temperature gauge
TI (wet) - Wet bulb temperature gauge
Figure 5-3.
Components of a Combination Spray Dryer and
Dry Injection Adsorption System
105
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INSPECTION OF DRY SCRUBBERS
General Safety Considerations
5.2 General Safety Considerations
5.2.1 Inhalation Hazards Around Positive Pressure System Components
Poorly ventilated areas in the vicinity of positive pressure
dry scrubber absorbers, particulate control systems, and/or ductwork
should be avoided. There are a variety of inhalation hazards
associated with municipal waste incinerators and coal-fired boilers,
including but not limited to the following:
0 hydrogen chloride
0 hydrogen fluoride
0 sulfuric acid mist
0 sulfur dioxide
0 dioxins/furans
0 carbon monoxide
0 heavy metal enriched flyash.
Concentrations of these pollutants can conceivably exceed the
maximum allowable use levels of air-purifying respirators. Further-
more, there is no single type of air-purifying respirator which is
appropriate for the wide range of pollutants which are emitted from
municipal waste incinerators and coal-fired boilers. Inspectors
must be able to recognize and avoid areas of potentially significant
exposure to fugitive emissions from the combustion and dry scrubbing
systems. A simple flowchart which indicates the locations of all
fans is a useful starting point in identifying portions of the
system which operate at positive pressure.
5.2.2 Chemical Burns, and Eye Hazards Around the Pebble Lime and/or
Calcium Hydroxide Preparation Area
The strong alkalis used in dry scrubbing have the potential to
cause severe eye damage. While the probability of eye contact and
skin contact is relatively small for agency inspectors, it is never-
theless important to keep in mind the general first aid procedures.
These are briefly summarized below.
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INSPECTION OF DRY SCRUBBERS
General Safety Considerations
0 After eye contact, flushing should be started immediately.
0 Eyes should be flushed for 15 to 30 minutes.
0 After skin contact, all affected clothing should be removed
and showering should be done for a minimum of 15 minutes.
0 Medical attention should be obtained in all situations.
During the routine inspection, agency personnel should note the
locations of all eye wash stations and showers. These are generally
located in the immediate vicinities of chemical handling areas.
After the first aid procedures are completed, it is especially
important to get qualified medical attention regardless of the
presumed seriousness of the exposure. All inspectors should have
full first aid and safety training before conducting field inspec-
tions.
5.2.3 Internal Inspections Prohibited
Inspectors should not enter dry scrubber absorber vessels or
air pollution control devices under any circumstances. All of the
necessary inspection steps can be accomplished without internal
inspections. Proper isolation, lockout, and testing of confined
areas requires substantial time and safety equipment, neither of
which is available to the agency inspector. Furthermore, serious
accidents can and have happened to agency inspectors while inside
equipment with plant personnel. •
107
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INSPECTION OF DRY SCRUBBERS
Inspection Summaries
5.3 Inspection Summaries
5.3.1 Level 1 Inspections
Stack ° Visible emissions for 6 to 30 minutes for
each stack or discharge vent
Presence of condensing plume
0
Process ° Presence or absence of fugitive emissions
5.3.2 Level 2 Inspections
Basic Inspection Points
Stack ° Visible emissions for 6 to 30 minutes for
each stack or discharge vent
0 Presence of condensing plume
Continuous Monitors for Opacity, Sulfur Dioxide, Hydrogen
Chloride, and Nitrogen Oxides
0 Double pass transmissometer physical condition
0 Double pass transmissometer .opacity data for
at least the last 3 hours
0 Sulfur dioxide, hydrogen chloride, and
nitrogen oxides emissions for at least the
last 8 hours
Dry Scrubber - General
0 System flowchart
0 General physical condition
Dry Scrubber..- Spray Dryer Absorbers and Combination Systems
0 Absorber vessel approach-to-saturation for
at least the last 8 hours
9 Make-up reagent feed rates and absorber vessel
recycle rates for at least the last 8 hours
0 Nozzle air and slurry pressures (if nozzles
present)
0 System flowchart
Process e Presence or absence of fugitive emissions
108
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INSPECTION OF DRY SCRUBBERS
Inspection Summaries
5.3.2 Level 2 Inspection, Basic Inspection Points (Continued)
Dry Scrubber - Dry Injection System and Combination Systems
0 Calcium hydroxide feed rate for at least the
last 3 hours
0 Calcium silicate/calcium hydroxide feed rates
for at least the last 8 hours
(if calcium silicate used)
0 Solids recycle rates (if recycle used)
Dry Scrubber - Fabric Filter
See Sections 1 and 2
Dry Scrubber - Electrostatic Precipitator
See Section 3
Process
0 Process operating rate
0 Process operating conditions
Follow-up Level 2 Inspection
Continuous Monitors for Opacity, Sulfur Dioxide,
Hydrogen Chloride, and Nitrogen Oxides
- ° Continuous monitoring data for previous
6 to 12 months.
Dry Scrubber - Spray Dryer Absorber and Combination Systems
G Absorber vessel approach-to-saturation values
during past previous 6 to 12 months
0 Reagent feed rates during previous 6 to 12
•; months
0 Absorber vessel inlet gas temperatures during
past 6 to 12 months
0 Slaker slurry outlet temperatures during
past 6 to 12 months (if slaker present)
0 Slurry density monitor data and slurry flow
monitor maintenance information during
previous 6 to 12 months
0 Absorber gas flow rates (if monitored)
109
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INSPECTION OF DRY SCRUBBERS
Inspection Summaries
5.3.2 Level 2 Inspections, Follow-up Inspection Points (Continued)
Dry Scrubber - Dry Injection System and Combination Systems
8 Reagent feed rates during previous 6 to 12
months.
0 Calcium silicate/ calcium hydroxide feed rates
during previous 6 to 12 months
0 Solids recycle rates during previous 6 to 12
months (if recycle used)
Dry Scrubber - Fabric Filters
See Sections 1 and 2
Dry Scrubber - Electrostatic Precipitator
See Section 3
5.3.3 Level 3 Inspections
Dry Scrubber
0 Level 2 follow-up inspection elements
0 Spray dryer absorber wet bulb and dry bulb
temperatures
0 Absorber or contactor inlet gas temperature
Dry Scrubber - Fabric Filters
See Sections 1 or 2
Dry Scrubber - Electrostatic Precipitator
See Section 3
5.3.A Level A Inspections
Stack
0 All elements of a Level 3 inspection
Continuous Emission Monitors for Opacity, Sulfur Dioxide,
Hydrogen Chloride, and Nitrogen Oxides
0 All elements of a Level 3 inspection
110
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INSPECTION OF DRY SCRUBBERS
Level A Inspection Procedures
5.3.4 Level A Inspections (Continued)
Dry Scrubber
0 Level 3 inspection elements
0 Flowchart of system
0 Locations of possible measurement ports
0 Start-up/shut down procedures
0 Potential inspection safety problems
Process ° All elements of a Level 3 inspection
0 Potential inspection safety problems
111
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INSPECTION OF DRY SCRUBBERS
Basic Level 2 Inspection Procedures
5. A Inspection Procedures
Techniques for the inspection of dry scrubbers can be
classified as Level 1, 2, 3, or A. The Level 1 inspection
consists of a visible emissions observation from outside the
plant. This is not discussed in this manual. The Level 2
inspection primarily involves a walkthrough evaluation of the
dry scrubber system and the associated process equipment. All
data are provided by on-site gauges. The Level 3 inspection
is similar to the Level 2 inspection with the exception that
several key dry scrubbing operating parameters are measured
using portable instruments supplied by the inspectors. These
instruments are used when the on-site gauges are either not
present or not reliable. The Level A inspection is performed
by agency supervisors or senior inspectors to acquire baseline
data. The scope of the Level 4 inspection is identical to the
Level 2/Level 3 inspection.
5.A.I Level 2 Inspections
Dry scrubber system visible emissions
If weather conditions permit, determine the stack effluent
average opacity in accordance with U.S. EPA Method 9 procedures
(or other required procedures). The observation should be con-
ducted during routine process operation and should last 6 to 30
minutes for each stack and bypass vents. The majority of units
operate with effluent opacities less than 10% on a continuous
basis. Higher opacities indicate emission problems.
The timing and duration of all significant spikes should be
noted after the visible emissions observation. This will be
useful in determining some of the possible causes of the spiking
condition. Significant puffs on either a regular frequency or on
a random basis are not normal. However, in some cases, light
puffing can occur even during optimal operating conditions.
If weather conditions are poor, an attempt should still be
made to determine if there are any visible emissions. The pres-
ence of a significant plume indicates emission problems. Do not
attempt to determine the "average opacity" when conformance with
U.S. EPA Method 9 is not possible.
112
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INSPECTION OF DRY SCRUBBERS
Basic Level 2 Inspection Procedures
Condensing plume conditions
Condensing plume conditions in dry scrubber systems are
highly unusual since most vapor state species which could cause
such plumes are partially removed. The presence of a condensing
plume would indicate a major malfunction of the dry scrubber
system.
The four principal characteristics of a condensing plume
are a bluish-white color, opacities which are higher during
cold or humid weather, low opacity at the stack, and increasing
opacities in the first few seconds of plume travel.
System flowchart
A simple flowchart of the entire dry scrubber system and
the associated process equipment should be prepared if one is
not already available in the agency files. This should consist
of a block diagram which includes the absorber or gas
contactor, the reagent preparation equipment, the particulate
control device, the combustion source, and all instruments
relevant to the inspection.
Double-pass transmissometer physical conditions
Most dry scrubbers have a transmissometer for the continu-
ous monitoring of visible emissions. If a unit is present, and
if it is in an accessible location, check the light source and
retroreflector modules to confirm that these are in good working-
order. Check that the main fan is working and that there is at
least one dust filter for the fan. On many commercial models,
it is also possible to check the instrument alignment without
adjusting the instrument. Note; On some models, moving the
dial t.o the alignment check position will cause an alarm iji the
control room. This is £o be moved only Jjy_ plant personnel and
only when it will not disrupt plant operations.
Sulfur dioxide, nitrogen oxides, and hydrogen chloride
monitor physical conditions
If the monitors are in an accessible location, confirm
that the instruments are in good mechanical operating condition
and that any sample lines are intact. Check calibration and
zero check records for all instruments.
113
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INSPECTION OF DRY SCRUBBERS
Basic Level 2 Inspection Procedures
Double-pass transmissometer data
If the transmissometer appears to be working properly,
evaluate the average opacity data for at least the previous 8
hours prior to the inspection. If possible, the average opacity
data for selected days since the last inspection should also be
reviewed. This evaluation is helpful in confirming that the
units being inspected are operating in a representative fashion.
If the unit is working better during the inspection than during
other periods, it may be advisable to conduct an unscheduled
inspection in the future.
As part of the review of average opacity, scan the data to
determine the frequency of emission problems and to evaluate how
rapidly the operators are able to recognize and eliminate the
condition.
Sulfur dioxide, nitrogen oxides, and hydrogen chloride
emission data
If the gas monitors appear to be working properly,
evaluate the average emission concentrations for at least the
previous 8 hours prior to the inspection. If possible, the
average emissions for selected days since the last inspection
should also be reviewed. This evaluation is helpful in
confirming that the units being inspected are operating in a
representative fashion.
High emission rates of either sulfur dioxide or hydrogen
chloride indicate significant problems with the dry scrubber
system. The general classes, of problems include but are not
limited to poor alkaline reagent reactivity, inadequate
approach-to-saturation (wet-dry systems), low reagent stoichio-
metric ratios, low inlet gas temperatures, and make-up reagent
supply problems.'" Follow-up Level 2 inspection procedures or
Level 3 inspection procedures will be necessary if high
emission rates of either sulfur dioxide or hydrogen chloride
are observed.
High nitrogen oxides concentrations indicates a problem
with the combustion equipment operation, an increase in the
waste nitrogen content, or a problem with the nitrogen oxides
control equipment.
114
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INSPECTION OF DRY SCRUBBERS
Basic Level 2 Inspection Procedures
Spray Dryer Absorber "Approach-to-Saturation"
One of the roost important operating parameters affecting
the efficiency of a wet-dry type dry scrubber is the approach-
to-saturation. This is simply the difference between the wet
bulb and dry bulb temperature monitors at the exit of the spray
dryer vessel. The normal approach-to-saturation for coal-fired
boiler systems varies between 15 and 50 °F with most systems
attempting to maintain a 20 to 25 °F value. Very high differ-
ences indicate lower acid gas removal efficiencies since the
baseline period. Municipal waste incinerator systems operate
with an "approach-to-saturation" range of 90 to 180°F.
The approach-to-saturation is monitored continuously by a
set of dry bulb and wet bulb monitors. An increase in this
value is sensed by the automatic control system which quickly
reduces the slurry feed rate to the atomizer.
Due to the vulnerability of these temperature monitors to
scaling and blinding, inspectors should not be surprised to find
that some plants must occasionally bypass the automatic process
control system and operate manually for limited time periods.
This generally means slightly worse approach-to-saturation values
so that operators have a margin for error in the event of sudden
process changes such as load changes. Gradually plants should be
able to increase the reliability of the temperature monitors by
relocation of the sensors and by improved operation of the dryer.
Spray dryer absorber reagent feed rates
The calcium hydroxide (or other alkali) feed rates are
important since they partially determine the stoichiometric
ratio between the moles of reagent and the moles of acid gas.
Low stoichiometric ratios result in reduced efficiencies.
The reagent feed rate is generally determined using a
magnetic flow meter on the slurry supply line to the atomizer
feed tank. It is also necessary to know the slurry density.
This is monitored by a nuclear-type density monitor. Typical
slurry densities are in the range of 5 to 20% by weight. It
should be noted that both the magnetic flow meter and the
nuclear density meter are vulnerable to scaling due to the
nature of the slurry.
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INSPECTION OF DRY SCRUBBERS
Basic Level 2 Inspection Procedures
Spray dryer absorber reagent feed rates (continued)
Another way to determine the reagent feed rate is to
record the feed rates of new pebble lime and recycled solids
indicated by the weigh belt feeders. The weigh belt for the
pebble lime is between the lime storage silo and the slaker.
The weigh belt feeder for the recycled solids is close to the
spray dryer absorber vessel.
Both the slurry feed rates and the solids rates should be
compared with baseline values at a similar combustion system
load to determine if the stoichiometric ratio has dropped
significantly.
Spray dryer absorber nozzle air and slurry pressures
For units equipped with nozzles rather than rotary
atomizers, the air pressures and slurry pressures should be
recorded and compared with baseline levels. Some variation in
the slurry pressures are necessary in order to maintain proper
approach-to-saturation values during combustion system load
variations.
Dry in lection system feed rates
The feed rate of calcium hydroxide to the pressurized
pneumatic system is generally monitored by either a weigh belt
feeder or a volumetric screw-type feeder. Both of these
feeders are located close to the calcium hydroxide storage
silos, and the feed rates are generally indicated on the main
system control panel. These values should be recorded for at
least the past 8 hours and compared against baseline values for
similar combustion load periods. Decreased reagent feed rates
indicate possible reductions in the stoichiometric ratio and
thereby a reduction in acid gas collection effectiveness. The
blower motor currents and the pneumatic line static pressures
should also be recorded and checked against baseline data sets.
Higher motor currents and higher conveying line static pres-
sures indicate increases in the air flow rates.
116
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INSPECTION7 OF DRY SCRUBBERS
Basic Level 2 Inspection Procedures
Calcium silicate feed rates
The Spray absorber/dry injection system utilizes a calcium
silicate/calcium hydroxide dry injection system downstream from
the calcium hydroxide spray dryer absorber. The feed rate of
calcium silicate/calcium hydroxide is monitored by weigh belt
feeders or volumetric screw conveyors. Feed rates for the past
8 hours should be recorded and compared with baseline values.
Control device solids recycle rates
The Spray absorber/dry injection system utilizes a recycle
stream from the fabric filter in order to improve overall
reagent utilization. The solids recycle rate during the
inspection should be recorded and compared to baseline values.
Dry scrubber system general physical conditions
While walking around the dry scrubber and its inlet and out-
let ductwork, check for obvious corrosion around the potential
"cold" spots such as the bottom of the absorber vessel and the
particulate control device hoppers and around the access hatches.
Check for audible air infiltration through the corroded areas,
warped access hatches, and eroded solids discharge valves.
Process operating rate
Record one or more combustion system operating rate para-
meters that document that the source conditions are representa-
tive of normal operation. For coal-fired boilers, these
parameters include the electrical generation rate, the steam
generation rate and the coal ultimate analyses. For municipal
waste incinerators, the main, process operating parameters
include the steam generation rate and the waste charging rate
(where monitored).
117
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INSPECTION OF DRY SCRUBBERS
Basic Level 2 Inspection Procedures
Process operating conditions
Record any process operating parameters that have an impact
on the characteristics and/or quantities of pollutants generated.
Some of the important variables for coal-fired boilers are
listed below.
0 Air preheater exit gas temperatures and static pressures
0 Economizer exit gas oxygen concentrations
For municipal waste incinerators the important process
operating parameters may include the following items.
0 Overfire air pressures
0 Undergrate air pressures
0 Uniformity of waste and ash on grates
0 Furnace (or secondary chamber) exit gas oxygen and
carbon monoxide concentrations
0 Quantity and type of fuel being fired with refuse
derived fuels
0 Extent of supplemental burner operation
5.4.2 Follow-up Inspection Points for Level 2 Inspections
Continuous monitoring data for the previous £ £o ^2_ months
Obtain the continuous monitoring records and quickly scan
the data for the previous 6 to 12 months to determine time
periods that had especially high and especially low emission
rates. Select the dry scrubber operating logs and the process
operating logs that correspond with the times of the monitoring
instruments charts/records selected. Compare the dry scrubber
operating data and process operating data against baseline
information to identify the general category of problem(s)
causing the excess emission incidents. Evaluate the source's
proposed corrective actions to minimize this problem(s) in the
future.
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INSPECTION OF DRY SCRUBBERS
Follow-up Level 2 Inspection Procedures
Spray dryer absorber approach-to-saturation values during
the previous £ to 12 months
The approach-to-saturation value is an important parameter
which relates directly to the pollutant removal effectiveness.
If there is significant question concerning the ability of the
dry scrubber system to maintain proper operation on a long term
basis, the approach-to-saturation values indicated on the dry
scrubber system daily operating log sheets should be checked.
Values much higher than baseline values or permit stipulations
indicate chronic problems such as the following.
0 Absorber vessel temperature instruments
0 Absorber vessel atomizer
0 Absorber gas- dispersion equipment
0 Low absorber vessel inlet gas temperatures
during low load periods
8 Nozzle erosion or blockage
0 Slurry supply line scaling
Spray dryer absorber reagent feed rate data during the
previous J5 to jj months
The feed rates of make-up pebble lime and recycle solids
are generally indicated on the daily operating logs of the dry
scrubber system. Values for the last 6 to 12 months should be
compared with the corresponding combustion load data to deter-
mine if significant changes in the overall reagent stoichio-
metric ratios have occurred. Data concerning the system load
must be obtained from the combustion system daily operating log
sheets. If available, dry scrubber system inlet sulfur dioxide
concentrations should also be used in this qualitative
evaluation of reagent/acid gas stoichiometric ratios.
Slaker slurry outlet temperatures during the previous 6 to 12
months
The slaker slurry outlet temperature provides a rough
indication of the adequacy of the conversion from lime (calcium
oxide) to calcium hydroxide. The temperatures should be compared
to baseline values. Improper slaking can result in poor reagent
reactivity and reduced acid gas collection efficiency.
119
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INSPECTION OF DRY SCRUBBERS
Follow-up Level 2 Inspection Procedures
Spray dryer absorber slurry flow rate and density monitor
maintenance records
The calcium hydroxide slurry monitors generally consist of
a magnetic flow meter and a nuclear density meter. Both of
these are sensitive to scaling especially when slurry densities
are high. The plant should have maintenance records for the
monitors either in the form of completed work orders, a computer-
ized maintenance record, an instrument maintenance log, or notes
on the daily dry scrubbing operations log. The records, should
be reviewed for the previous 6 months to 2 years whenever there
is concern that there are periods of low slurry supply to the
atomizer.
Spray dryer absorber inlet gas temperatures values during the
previous £ £o _12 months
Dry scrubbing systems have a limited turndown capability
due to the need for complete drying of the atomized slurry.
Low gas inlet temperatures during periods of low combustion
system load can cause poor drying of the droplets. The process
control system is generally designed to block atomizer operation
once inlet temperature drops below a preset value. The inlet
gas temperature data should be reviewed to confirm that the
controller is working properly, since operation under these
conditions could lead to absorber vessel deposits and nonideal
operation once loads increase. The inlet temperature data may
be available on the dry scrubber system daily operating logs,
the archived continuous strip charts, or on the computerized
data acquistion file.
Dry injection system feed rates during the previous _6
_to _12 months
The long term performance of the calcium hydroxide supply
system should be "checked if the emissions data indicates
occasional emission excursions. (See earlier inspection step.)
The feed rate data for the previous 6 to 12 months provided by
the weigh belt feeder or the volumetric screw feeder should be
compared against the combustion system loads and against the
inlet acid gas concentration monitors (when available). The
automatic control system should be able to vary calcium
hydroxide (or other alkali) addition rates with load variations
and inlet gas acid gas concentrations.
120
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INSPECTION OF DRY SCRUBBERS
Follow-up Level 2 Inspection Procedures
Calcium silicate/calcium hydroxide feed rates during the
previous J3 t£ _12_ months
The variability and reliability of the calcium silicate/
calcium hydroxide dry injection system in the spray absorber/dry
injection systems should be evaluated by reviewing the daily
system operating logs. Some loss in acid gas collection
efficiency could occur if feed rates were low.
Dry injection system control device solids recycle rates.
The recycle rates used in the spray absorber/dry injection
systems have some impact on the overall acid gas collection
efficiency. Low recycle rates indicate slightly reduced acid
gas collection efficiency.
5.4.3 Level 3 Inspection Procedures
The Level 3 inspection includes many inspection steps per-
formed during Level 2 basic and Level 2 follow-up inspection
procedures. These are described in earlier sections. The
unique inspection steps of Level 3 inspections are described
below.
Spray dryer absorber vessel dry bulb and wet bulb
outlet gas temperatures.
These measurements are taken if there is a significant
question concerning the adequacy of the on-site gauges and if
there are safe and convenient measurement ports between the
absorber vessel and the particulate control device. The
measurements should be made at several locations in the duct to
ensure that the values observed are representative of actual
conditions. The'values should be averaged and compared with
the value indicated by the on-site instruments (if operational)
and with baseline data sets. It should be noted that it is
rarely necessary to make this measurement since the on-site
gauges are a critical part of the overall process control
system for the dry scrubber system. Failure to maintain these
instruments drastically increases the potential for absorber
vessel wall deposits and increased emissions. These temper-
ature monitors are normally very well maintained.
121
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INSPECTION OF DRY SCRUBBERS
Level 3 Inspection Procedures
Spray dryer absorber vessel or dry injection system
inlet gas temperature
This measurement is taken when the on-site gauge is not
available, is malfunctioning, or is in a potentially nonrepre-
sentative location. For spray dryers, the measurement should be
taken in the main duct leading to the atomizer or in one or more
of the ducts that lead to the gas dispersion system within the
vessel. For dry injection systems, the measurement should be
taken upstream of the gas stream/reagent mixing point (such as
the venturi contactor). The measurements should be taken at
several locations in the duct and averaged. Locations near air
infiltration sites should be avoided. Procedures for the temp-
erature measurements are included in the Appendix.
5.A.4 Level 4 Inspection Procedures
The Level 4 inspection includes many inspection steps per-
formed during Level 2/Level 3 inspections. These are described
in earlier sections. The unique inspection steps of Level 4
inspections are described below.
Start-up and shutdown procedures
The start-up and shutdown procedures used at the plant
should be discussed to confirm the following.
0 The plant has taken reasonable precautions to minimize
the number of start-up/shutdown cycles.
0 The dry scrubber is operated in a reasonable time after
start-up of the process equipment. Inspectors should
remember that starting the atomizer (in spray dryer type
systems) when the inlet gas temperatures are low can
lead to absorber vessel deposits.
Possible locations for measurement ports
If the system does not have the necessary measurement
ports to facilitate a Level 3 inspection, candidate sites should
be identified. These should be in safe and convenient locations
which do not disturb plant instruments or operations.
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INSPECTION OF DRY SCRUBBERS
Level 4 Inspection Procedures
Potential dry scrubber system safety problems
Agency management personnel and/or senior inspectors should
identify potential safety problems involved in standard Level 2/
Level 3 inspections at this site. To the extent possible, the
system owner/operators should eliminate these hazards. For those
hazards which can not be eliminated, agency personnel should
prepare notes on how future inspections should be limited and
should prepare a list of the necessary personnel safety equipment.
A partial list of common health and safety hazards include the
following.
0 Inhalation hazards due to fugitive leaks from inlet breech-
ings, absorber vessels, particulate control systems, and
alkaline reagent storage/preparation/supply equipment
0 Corroded ductwork and particulate control devices
0 Eye hazards due to alkali solids and slurries
0 High voltage in control cabinets
Dry scrubber and process system flowchart
A relatively simple flowchart is very helpful in conducting
a complete and effective Level 2/Level 3 inspection. This should
be prepared by agency management personnel or senior inspectors
during a Level A inspection. It should consist of a simple block
diagram that includes the following elements.
0 Source(s) of emissions controlled the system
0 Location(s) of any fans and blowers used for gas
movement and solids conveying
0 Locations of any main stacks and bypass stacks
0 Alkali preparation equipment, adsorber vessel or
contactor, particulate control device, and recycle
streams
0 Locations of major process instruments and gas
• stream continuous monitors
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INSPECTION OF DRY SCRUBBERS
Level 4 Inspection Procedures
Potential safety problems in the process area
The agency management personnel and/or senior inspectors
should evaluate potential safety problems in the areas that
may be visited by agency inspectors during Level 2/Level 3
inspections. They should prepare a list of the activities
that should not be performed and locations that an inspector
should not go to as part of these inspections. The purpose
of this review is to minimize inspector risk and to minimize
the liability concerns of plant personnel.
124
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6. INSPECTION OF CARBON BED ADSORBERS
This section concerns regenerable and nonregenerable carbon bed
adsorbers used for the removal of solvent vapors. This type of
control system is often used when the gas stream contains one or more
valuable organic compounds that can be economically recovered for
reuse. It is also ideal for very small systems for which other VOC
control techniques are impractical.
6.1 Components and Operating Principles
Organic vapors are removed by adsorption as the gas stream
passes through a bed of specially "activated" carbon. This material
has a very large surface area for adsorption due to the presence of a
large number of pores throughout the carbon. The organic vapors
diffuse into these pores and are retained on the carbon surfaces due
to both chemical and physical forces.
There is a fixed quantity of organic vapor that can be adsorbed
on the carbon. This limit is a function of (1) the amount of carbon
in the bed, (2) the carbon characteristics, (3) the gas stream temper-
ature, (4) the organic vapor concentration, and, (5) the chemical
characteristics of the organic compound(s) present. The capacity of
the bed decreases as the temperature of the organic vapor/air stream
increases. A change of only 15 to 20°F can have a significant impact
on the organic vapor capacity of a carbon bed system. A change in
the chemical characteristics can also affect performance. Generally,
high molecular weight organic compounds are retained more effectively
than low molecular weight compounds. With all organic vapor compounds,
the maximum capacity increases as the vapor concentration increases.
Commercial carbon bed systems are designed to operate well below
the maximum organic vapor capacity. Equipment designers use a value
called the Working Capacity which takes into account losses of carbon
adsorption area due to a variety of common operating conditions. The
working capacity is generally 25 to 50% of the maximum capacity.
125
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INSPECTION OF CARBON BED ADSORBERS
Components and Operating Principles
GUAM
MUWtN
MUTlCUATI
HI Ik*
•UTU9
•00
r
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•PO-
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WATIM
MCANTin
> NATIM
•TfAM
Figure 6-1. Flowchart of a two-bed carbon adsorber system
126
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INSPECTION OF CARBON BED ADSORBERS
Components and Operating Principles
Once the working capacity of organic vapor has been adsorbed,
the organic compounds must either be removed, or the carbon must be
discarded. Very small systems, such as those used in dry cleaning,
usually discard the carbon since the cost of the desorption equip-
ment is high. In the case of large systems, the quantities of
solvent recovered are large enough to justify the the cost of
desorption. The term "regeneration" is often used for the process
of desorbing organic vapors from carbon beds.
In regenerable systems, the carbon bed is isolated from the
gas stream and heated with steam to remove the organic compounds
from the carbon. The high gas temperature overcomes the physical
and chemical forces binding the organic vapor to the carbon. Once
the organic vapors have been removed from the carbon bed, the bed
is cooled so that it will be ready when it is placed back into
service.
The organic vapors released during desorption are condensed
along with the steam used in the desorption step. The organic
compounds are usually insoluble in the water and float on the
surface. The organic compounds can therefore be removed by means
of a decanter.
A simple flowchart for a two-bed carbon adsorption system is
shown in Figure 6-1. The solvent laden air is drawn from the
process equipment by a fan. On the discharge side of this fan, the
static pressure in the ductwork is positive. Therefore, there is
a possibility that some fugitive leaks can occur. The contaminated
gas stream is directed to the on-line bed by means of isolation
dampers. The cleaned gas stream is then exhausted directly from
the carbon bed to the atmosphere. There is usually a VOC detector
on the outlet of each- bed. The VOC detector is a very important
instrument since it indicates if high VOC concentrations exist in
the gas stream that is leaving the carbon bed and entering the
ambient air.
Initially, the adsorption of organic vapor on the activated
carbon is both rapid and efficient. However, as the capacity of
the carbon is approached, the efficiency of removal decreases and
127
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INSPECTION OF CARBON BED ADSORBERS
Components and Operating Principles
the effluent VOC concentration begins to rise. The concentration
suddenly increases from the normal levels of 100 to 500 ppm (v/v)
to levels that ultimately approach the inlet VOC concentration. The
beginning point of the concentration rise is called the breakthrough
point. Carbon bed systems should be operated so that any one bed of
the total system never reaches the breakthrough point, the organic
vapor detectors used on many large carbon bed adsorber systems are
intended to prevent breakthrough conditions by increasing the fre-
quency of bed desorption whenever high concentrations exist.
The organic vapor concentration versus time curve shown in
Figure 6-2 is a typical "breakthrough" curve. It illustrates the
potential organic vapor emissions if a carbon bed is not taken off-
line for desorption before it reaches it working capacity. One of
the primary functions of the inspector is to confirm that all beds
in a system are being desorbed before they reach the breakthrough
threshold indicated by the arrow in Figure 6-2.
The working capacity of a carbon bed can decrease over time due
to the adsorption of compounds which can not be removed by normal
desorption procedures. These compounds are held very tightly to the
activated carbon and are riot released under the normally mild desorp-
tion temperatures. Activity of the carbon bed can also be reduced by
the deposition of fine particles which block access to the pores.
Due to these problems, carbon beds can suffer breakthrough much
sooner than anticipated by the operator.
The static pressure drop through the carbon bed is a valuable
performance indicator. The pressure drop is proportional to the gas
flow rate through a bed that remains in good physical condition.
Changes in gas flow rate can be confirmed by comparing the measured
static pressures in the inlet ducts with the base-line values. If
the gas flow rate has not changed dramatically, the change in ob-
served carbon bed pressure drop is probably due to deterioration of
the carbon pellets. The physical breakdown of the carbon pellets is
usually accompanied by a reduction in VOC removal effectiveness.
128
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INSPECTION OF CARBON BED ADSORBERS
Components and Operating Principles
Nett: This curvt 1s in txMplt.
Actual tlM will vtry for
application.
MO
coo
I
e
«00
»0
100
M
1 2 3
OB-St
30
Ttai
40
45
Figure 6-2. Typical breakthrough curve
129
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INSPECTION OF CARBON BED ADSORBERS
General Safety Considerations
6.2 General Safety Considerations
No internal inspections should be conducted. Regulatory agency
inspectors should not attempt to enter off-line carbon bed systems
for any reason. There are a number of significant hazards, including
but not limited to the following.
0 Low oxygen levels due to adsorption of oxygen
on the surfaces of wet carbon
0 Hydrogen sulfide gas, hydrochloric acid vapor and
other toxic compounds formed on the carbon
Only intrinsically safe portable instruments should be used.
All portable VOC detectors, temperature monitors, flashlights, and
other electrically powered equipment should be rated as intrinsically
safe.
Respirators should be available for use. Portions of the carbon
bed system usually operate under positive static pressure. Leaks
from ductwork or the adsorber shell can lead to localized high VOC
levels. Inspectors should be fitted and trained in the use of the
necessary respirators and should be medically certified as capable of
wearing the units.
130
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INSPECTION OF CARBON BED ADSORBERS
Inspection Summaries
6.3 Inspection Summaries
6.3.1 Level 1 Inspections - No Inspection Steps
6.3.2 Level 2 Inspections
Basic Level 2 Inspection Steps
Stack/Exhaust
0 Exhaust VOC concentration for 10 - 15 minutes
near the end of the adsorption cycle*
Carbon Bed Adsorber
e Obvious corrosion on the adsorber shell
0 Adsorption/desorption cycle times
9 Steam pressure and temperature during
desorption
Process Equipment
0 Obvious fugitive emissions*
Follow-up Level 2 Inspection Steps
Carbon Bed Adsorber
0 Inlet gas temperature
0 Inlet and outlet static pressures
0 Outlet detector calibration and maintenance
0 Quantity of .solvent in recovered solvent
tank
Process Equipment
0 Maximum production rate during the last
6 months
0 Average production rate during the
last 12 months
0 Types of solvents used
0 Quantities of solvents purchased
0 Quantities of solvents sold/discarded
131
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INSPECTION OF CARBON BED ADSORBERS
Inspection Summaries
6.3.3 Level 3 Inspections
Stack/Exhaust
c Exhaust VOC concentration for 10 - 15 minutes
near the end of the adsorption cycle*
0 Outlet gas temperature*
Carbon Bed Adsorber
0 Inlet gas temperature *
0 Obvious corrosion on the adsorber shell*
0 Adsorption/desorption cycle times*
0 Inlet and outlet static pressures*
0 Outlet detector calibration and maintenance*
0 Quantity of solvent in recovered solvent tank*
0 Measure the outlet VOC concentration
0 Measure the inlet gas temperature
0 Measure the static pressure drop
Process Equipment
0 Obvious fugitive emissions*
0 Maximum production rate for last 6 months*
0 Average production rate for last 12 months*
0 Types of solvents used*
0 Quantities of solvents purchased*
0 Quantities of solvents sold/discarded*
0 Hood static pressure
6.3.4 Level 4 Inspection Procedures
Exhaust Stack
0 All elements. of a Level 3 inspection
Carbon Adsorber
8 -All elements of a Level 3 inspection
e Locations for measurement ports
Potential inspection safety problems
0
Process Equipment
0 All elements of a Level 3 inspection
0 Basic flowchart of process
0 Potential inspection safety problems
* Refer to Level 2 Inspection Procedures
132
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INSPECTION OF CARBON BED ADSORBERS
Basic Level 2 Inspection Procedures
6.4 Inspection Procedures
Techniques for the inspection of carbon bed adsorbers can
be classified as Level 2 or Level 3. The Level 2 inspections
primarily involve a walkthrough evaluation of the carbon bed
adsorber system and process equipment using on-site gauges.
The Level 3 inspection incorporates all of the inspection
points of the Level 2 inspection and includes independent
measurements of the adsorber operating conditions.
6.A.I Basic Level 2 Inspections
Evaluate the VOC outlet detector.
The VOC detectors often used at the outlet of the carbon
bed systems are relatively sophisticated instruments which
require frequent maintenance. Confirm that they are working
properly by reviewing the calibration records since the previous
inspection. Maintenance work orders should also be briefly
reviewed to determine if the instruments have been operational
most of the time.
Check carbon bed shell for obvious corrosion.
Some organic compounds collected in carbon bed systems can
react during steam regeneration. This leads to severe corrosion
of the screens retaining the carbon beds and of the unit shell.
Observe the adsorption/desorption cycles.
Determine the time interval between bed regenerations and
compare this with previously-observed values. An increase in
this time interval could mean that breakthrough is occurring if
the quantities of organic vapor entering the carbon bed have
remained unchanged. Systems in which the cycle frequency is
controlled by a timer rather than an outlet organic vapor detec-
tor are especially prone to emission problems due to longer than
desirable cycle times.
Check the regeneration steam line pressure.
Any decrease in the steam line pressure from previously
recorded levels could indicate less than necessary steam flow
for regeneration of the carbon beds.
133
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INSPECTION OF CARBON BED ADSORBERS
Follow-up Level 2 Inspection Procedures
6.4.2 Follow-up Level 2 Inspection Procedures
Evaluate carbon bed system static pressure drop.
If there are on-site gauges, evaluate any changes in the
static pressure drop. A decrease could mean deterioration of
the carbon bed to the point that channeling of the gas stream
is affecting gas-solid contact. Higher than normal static
pressure could mean partial pluggage of the carbon bed due to
fines formation or due to material entering with the gas stream.
However, gas flow changes could also be responsible for changes
in the static pressure drop.
Prepare solvent material balances.
For some processes, the effectiveness of the carbon bed
system can be evaluated by preparing a solvent material balance
around the facility for a period of several weeks to a month.
The information needed for the calculations includes solvent
quantities purchased, changes in solvent storage tank levels,
and solvent quantities transferred from the system.
Evaluate ventilation system.
To the extent safely possible, gas flow rates from process
equipment to the carbon bed system should be evaluated. Record
hood static pressures (if monitored) and look for any holes or
gaps in the ductwork.
6.A.3 Level 3 Inspections
Measure the VOC outlet concentrations.
The effluent concentration from each bed should be measured
if^ there is safe and convenient access to the effluent ductwork.
The measurements .should be made with an organic vapor analyzer
that is calibrated for 50 to 2000 ppm.
The instrument (and its portable recorder, if any) should
be certified as intrinsically safe for Class I, Group C and D
locations. This means simply that the instrument is incapable
of initiating an explosion when used properly. A small port is
adequate to draw a 0.5 to 3.0 liter per minute sample into the
instrument. An observed VOC concentration greater than 500 ppm
(v/v) is a sign that the bed is not performing properly.
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INSPECTION OF CARBON BED ADSORBERS
Level 3 Inspection Procedures
Measure the VOC outlet concentration (continued).
It is important to determine the approximate desorption
cycle of multi-bed systems. Outlet VOC measurements conducted
earlier in the adsorption cycle of a bed may appear adequate
even when the bed activity is severely reduced. Breakthrough
usually does not occur until late in the operating cycle unless
the condition of the carbon is extremely poor. Therefore, an
effort should be made to measure the outlet VOC concentration
of each bed at a time when it is approaching the end of the
adsorption mode. The adsorption/desorption cycle is normally
controlled by a timer and this can be used to determine the
approximate status of each bed.
In some commercial multi-bed units there is only poor acces-
sibility to the effluent ducts from each unit. In this case,
the VOC concentration in the combined duct should be measured
at the exhaust point. Obviously, this measurement should be
attempted only when there is safe and convenient access to the
exhaust. It is especially important to avoid areas where high
VOC concentrations could accumulate.
Measure the inlet gas temperature.
Adsorption is inversely related to the gas temperature
entering the carbon bed adsorbers. An increase in the gas
temperature from the baseline period could result in a decreased
capacity for organic vapors. The gas temperature should be
measured in the inlet ductwork, immediately ahead of the carbon
bed.
Measure the static pressure drop.
A change in the static pressure drop since the baseline
period is usually due to either a change in the gas flow rate
through the carbon bed or due to the physical deterioration of
the bed itself.
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INSPECTION OF CARBON BED ADSORBERS
Level 3 Inspection Procedures
Measure the static pressure drop (continued).
Measurement taps on the adsorber shell should be used,
if available. Alternatively, the static pressure drop can be
measured using ports in the inlet ductwork to the adsorber
system and the outlet duct from the adsorber. Obviously, the
static pressure drop should be determined while the adsorber
is on-line.
Check/measure the hood static pressure.
At the hood, the gas stream is accelerated to the velocity
of 1200 to 2000 feet per minute. The static pressure in the
hood is a useful indicator of the total gas flow rate. A drop
in the hood static pressure from previously recorded levels
means that the gas flow has decreased.
The relationship between gas flow rate and hood static
pressure is indicated below. The equation simply illustrates
that the gas flow rate is proportional to the square root of
the hood static pressure. If the hood static pressure decreases
by a factor of 2, the gas flow rate has decreased by approxi-
mately a factor of 1.41.
G «
Where: G » Gas flow rate, ACFM
C • Proportionality constant, ACFM/(Inches W.C.)
Sph « Hood static pressure
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INSPECTION OF CARBON BED ADSORBERS
Level 4 Inspection Procedures
6.4.4 Level 4 Inspection Procedures
The Level 4 inspection includes many inspection steps
performed during Level 2 and Level 3 inspections. These are
described in earlier sections. The unique inspection steps of
Level 4 inspections are described below.
Evaluate locations for measurement ports.
Many existing carbon bed adsorbers do not have safe and
convenient ports that can be used for volatile organic compound
concentration, static pressure, and gas temperature measurements.
One purpose of the Level 4 inspection is to select (with the
assistance of plant personnel) locations for ports to be
installed at a later date to facilitate Level 3 inspections.
Evaluate potential safety problems.
Agency management personnel and/or senior inspectors should
identify any potential safety problems involved in standard
Level 2 or Level 3 inspections at this site. To the extent
possible, the system owner/operators should eliminate these
hazards. For those hazards that can not be eliminated, agency
personnel should prepare notes on how future inspections should
be limited and should prepare a list of the necessary personnel
safety equipment. A partial list of common health and safety
hazards includes the following.
0 Inhalation hazards due to low stack discharge points
0 Fugitive emissions from process equipment system
0 Inhalation hazards from adjacent stacks and vents
0 Access to system components only available by means
of weak roofs or catwalks
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INSPECTION OF CARBON BED ADSORBERS
Level 4 Inspection Procedures
Prepare £ system flowchart.
A relatively simple flowchart is very helpful in conducting
a complete and effective Level 2 or Level 3 inspection. This
should be prepared by agency management personnel or senior
inspectors during a Level 4 inspection. It should consist of a
simple block diagram that includes the following elements.
Source(s) of emissions controlled by a single
carbon bed adsorber
0 Location(s) of any fans used for gas movement
through the system (used to evaluate inhalation
problems due to positive static pressures)
0 Locations of any main stacks and bypass stacks
0 Location of any prefilters for particulate removal
0 Location of carbon bed adsorbers
0 Locations of major instruments (VOC concentration,
static pressure gauges, thermocouples)
Evaluate potential safety problems ±n the process area.
The agency management personnel and/or senior inspectors
should evaluate potential safety problems in the areas that may
be visited by agency inspectors during Level 2 and/or Level 3
inspections. They should prepare a list of the activities that
should not be performed and locations to which an inspector
should not go as part of these inspections. The purpose of
this review is to minimize inspector risk and to minimize the
liability concerns of plant personnel.
138
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7. INSPECTION OF THERMAL AND CATALYTIC INCINERATORS
This section concerns incinerators that are generally used on
curing ovens, driers, and other common process sources. They are
used whenever it is uneconomical to recover the organic vapors, and
whenever compliance can not be achieved by use of low solvent
coatings or inks. In some cases, these control devices have been
installed to allow compliance with regulatory requirements until
low-solvent coatings and inks can be developed without sacrificing
product quality.
7.1 Components and Operating Principles
The basic purpose of any incinerator is to raise the temperature
of the VOC containing gas stream to a sufficient temperature to allow
complete oxidation of the organic compounds. Thermal incinerators
utilize a burner flame mounted in the main chamber of the incinerator
to generate the necessary quantity of hot combustion gas. This gas
then heats the relatively cool VOC containing gas stream to a level
several hundred degrees Fahrenheit above the autoignition temperature
for the specific organic compound. The autoignition temperature is
generally in the range of 800 to 1400 degrees Fahrenheit. In the
case of catalytic incinerators, a preheater burner (or burners) is
used to raise the gas stream temperature to the level necessary to
complete oxidation on the surface of the catalyst bed. Catalytic
incinerators generally operate several hundred degrees below thermal
incinerators for the same organic compounds since the catalyst pro-
motes oxidation reactions. It should be noted that in both thermal
and catalytic incinerators, the VOC compounds are not oxidized within
the burner flame itself. The burner (or burners) simply provides the
turbulent mixing and the hot gas -that is necessary to accomplish VOC
oxidation.
Thermal and catalytic incinerator inlet gas stream VOC
concentrations are usually limited to between 500 ppm and 7,500 ppm
for safety reasons. It is generally necessary to maintain VOC
concentrations lower than 25% of the Lower Explosive Limit (L.E.L)
so that the incinerator flame does not flashback to the process
equipment. The 25% L.E.L. value is a widely accepted.upper concen-
tration limit which allows for some nonuniformity and variablity in
the gas stream VOC levels. The concentrations corresponding to 25%
of the L.E.L. are provided in Table 7-1 for a number of common
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THERMAL AND CATALYTIC INCINERATORS
Components and Operating Principles
organic chemicals. When mixtures of organic compounds are present
in the inlet gas stream, the total concentration is generally
limited to 25% of the lowest L.E.L. for the various compounds.
Incinerators having VOC concentrations up to 50" of the L.E.L.
have recently been installed on systems having continuous inlet VOC
concentration monitors. Incinerators on these sources may have
higher inlet VOC concentrations than those indicated in Table 7-1.
Table 7-1. VOC Concentrations Corresponding
to 25% of Lover Explosive Limits
Contaminant Concentration, ppm
Butane A,750
Ethane 7,500
Ethylene 7,750
Propylene 6,000
Styrene 2,750
Benzene 3,500
Xylene 2.500
Toluene 3,500
Methyl alcohol 18,250
Isopropyl alcohol 5,000
Acetone 7,500
Methyl ethyl ketone A,500
Methyl acetate 7,750
Cellosolve acetate 4,250
Acrolein 7,000
Cyc.lohexanone 2,750
Acetaldehyde 10,000
Furfural 5,250
Source: L.E.L. Data from EPA
Publication 600/2-84-118a
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THERMAL AND CATALYTIC INCINERATORS
Components and Operating Principles
7.1.1 Thermal Incinerators
The major components of a thermal incinerator include a burner,
a refractory lined combustion chamber, and a stack. The burner
includes a combustion air supply controller, a fuel rate controller,
a flashback arrestor, and a burner assembly. A thermocouple on the
discharge of the incinerator is often used to operate the controller
which maintains proper air/fuel ratio. In some systems, heat recovery
equipment is used on the incinerator discharge to reduce the operating
costs.
Burners in thermal incinerators generally operate whenever the
incinerator is on line since the concentration of the VOC containing
waste stream is too low to support combustion. The burners supply
the additional heat necessary to achieve oxidation temperatures. Gas
streams having a low VOC concentration obviously require slightly
less fuel than those with concentrations approaching 25* of the L.E.L.
Most operation and maintenance problems associated with thermal
incinerators concern the burner since this is the component subjected
to the extreme gas velocities and gas temperatures. These problems
include poor fuel atomization (oil-fired units), deposits within the
burner that cause poor air-fuel mixing, inadequate air supply, and
quenching of the flame on refractory surfaces. Routine maintenance
on at least a quarterly basis is necessary to clean and readjust the
burners for proper operation. Symptoms of poor burner performance
include black smoke generation, lower than normal outlet tempera-
tures, and higher than normal VOC outlet concentrations.
Thermal incinerators are also subject to problems caused by
rapidly varying VOC concentrations and gas flow rates. These change
the fuel requirements necessary to maintain a stable outlet tempera-
ture. A sudden decrease in the VOC concentrations coupled with an
increase in the gas flow rate can lead to short term periods with
lower than desirable operating temperatures. A sharp increase in the
VOC concentration with a decreased gas flow rate can lead to short
term excursions above the maximum temperature limits of the combus-
tion chamber.
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THERMAL AND CATALYTIC INCINERATORS
Components and Operating Principles
7.1.2 Catalytic Incinerators
The basic components of a catalytic incinerator include a preheat
burner, a nixing chamber, a catalyst bed, a heat recovery system, and
a stack. The preheat burner is used whenever supplemental fuel is
needed to achieve the necessary operating temperature. In many cases,
the VX contaminants have sufficient heat value to achieve the rela-
tively low combustion temperatures without preheat burners. Therefore,
inspectors should not conclude that the unit is not operating correctly
simply because the preheat burner is not operating at the time of the
inspection. It is quite possible that the preheat burner is used only
during start-up or during periods of low VOC concentration.
The temperatures required for high efficiency oxidation depend
on the type of catalyst, the incinerator design, and the type of
organic compound. Some typical operating temperatures for common
compounds are provided in Table 7-2.
Table 7-2. Typical Operating Temperatures for 90% Conversion
in Catalytic Incinerator
Compound Operating Temperature,
Acetylene 200
Propyne 240
Propylene 260
Ethylene 290
n-Heptane . 300
Benzene 300
Toluene 300
Xylene 300
Etha'n'ol 315
Methyl ethyl ketone 370
Methyl isobutyl ketone 370
Propane 410
Ethyl acetone 415
Ethane 430
Cyclopropane 455
Methane 490
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THERMAL AND CATALYTIC INCINERATORS
Components and Operating Principles
Catalytic incinerators are vulnerable to a number of operating
problems due to the participation of the catalyst in the oxidation
reactions. These problems include the following.
o
Catalyst thermal aging
Catalyst burnout due to high temperature fluctuations
Catalyst scouring from catalyst bed
Soot masking of catalyst due to upset combustion
conditions in preheat (oil-fired) burners
Particulate masking of catalyst
Poisoning of the catalyst by non-VOC contaminants
entrained in the gas stream
Thermal aging is the inevitable result of gradual recrystalliz-
ation of the noble metal catalyst materials due to exposure to the
hot combustion products. The catalyst simply becomes less effective
in promoting oxidation of VOC compounds. Because of this problem,
all noble metal catalysts must eventually be replaced with fresh
catalysts.
Thermal burnout is the sudden volatilization of the catalytic
compounds from the support matrix that comprises the catalyst bed.
The temperature excursions that cause catalyst losses are often
due to an undesirable increase in the VX concentration in the
waste gas stream. The catalyst bed must be replaced once signifi-
cant burnout has occurred.
Masking inhibits catalyst activity by preventing contact
between the vapor phase organic compounds and the surface of the
catalyst material. This can be caused by deposition of particulate
material in the catalyst bed or by soot formation in the preheat
burner. Removal of water soluble materials from the catalyst
surface can be accomplished simply by washing with a detergent
solution. Non-water soluble materials can sometimes be removed by
solvent washing and/or physical scrubbing of the catalyst materials.
There is no permanent damage to the catalyst unless the cleaning
process results in physical attrition of the catalyst from the
surface of the substrate.
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THERMAL AND CATALYTIC INCINERATORS
Components and Operating Principles
Poisoning of catalyst involves irreversible chemical reactions
between gas stream contaminants and the catalyst materials. There
can be significant reductions in VOC oxidation efficiency since the
affected catalyst is no longer effective in the oxidation reactions.
Therefore, the catalyst bed must be replaced after a significant
fraction of the catalyst has been affected.
A partial list of common catalyst poisons and masking materials
is presented in Table 7-3. It should be noted that the severity of
the impact depends on the specific type of catalyst, the gas stream
temperatures, and the concentration of the catalyst inhibitor.
One indication of catalyst inhibition is a lower than "normal"
gas temperature increase across the catalyst bed. Since the
oxidation reactions occurring on the catalyst bed are exothermic,
there should be a significant temperature increase if the catalyst
material is in good condition. Unfortunately, variations in the
inlet VOC concentration can also affect the gas temperature rise
across the bed. Low VOC concentrations result in a relatively
small temperature increase. Therefore, the inspector must attempt
to determine if a small temperature increase is due to catalyst
inhibition or to a short term decrease in the VOC concentration.
-------
THERMAL AND CATALYTIC INCINERATORS
Components and Operating Principles
Table 7-3. Catalyst Inhibitors
Type of Inhibitor
Fast Acting Poisons
Phosphorus, Bismuth, Lead,
Arsenic, Antimony, Mercury
Slow Acting Poisons
Iron, Tin, Silicon
Reversible Inhibitors
Sulfur, Halogens, Zinc
Surface Maskers
Organic solids
Effect
Irreversible reduction of
catalyst activity at a rate
dependent on concentration
and temperature
Irreversible reduction of
catalyst activity. Higher
concentrations than those of
fast activity catalyst
inhibitors can be tolerated
Reversible surface coating of
catalyst active area at a rate
dependent on concentration
and temperature
Reversible surface coating
of catalyst active area.
Removed by increasing
catalyst temperature
Surface Eroders and Maskers
Surface coating of catalyst
active area. Also, erosion of
catalyst surface at a rate
dependent on particle size,
grain loading, and gas stream
velocity
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THERMAL AND CATALYTIC INCINERATORS
General Safety Considerations
7.2 General Safety Considerations
Areas of potential VOC exposure should be avoided. Thermal
and catalytic incinerators are often located on building roofs
near numerous uncontrolled process vents. High concentrations
of organic compounds and other pollutants can exist in localized
areas downwind of these vents. There can also be leaks of the
contaminated gas stream from the inlet ductwork and the inciner-
ator shell. Inspectors must remain upwind of these vents and
leak sites. If this is not possible, the inspection should be
terminated.
Inspectors should have the appropriate respirator available
for use in case there is unexpected exposure to organic compounds,
chlorine, or hydrogen chloride. (Chlorine and hydrogen chloride
result from oxidation of chlorinated hydrocarbons). Inspectors
should be fitted and trained in the use of the specific respirator
and be medically certified as capable of wearing the unit.
Only intrinsically safe portable instruments should be used.
All portable VOC detectors, temperature monitors, flashlights, and
other electrically powered equipment should be rated as intrinsically
safe for the specific type of hazardous locations that exist in the
inspection area.
Walking on roofs must be done carefully. Inspectors should
avoid roofs that may be structurally weak. Furthermore, they should
walk behind plant personnel in order to avoid obscured skylights and
weak spots in the roof.
No internal inspections should be conducted. Regulatory agency
inspectors should not-attempt to enter off-line incinerator systems
for any reason. There could be low oxygen levels and high contamin-
ant concentrations even though the unit is off-line.
Inspectors must avoid hot surfaces. The inlet ductwork, outlet
ductwork, and incinerator shell are generally at elevated tempera-
tures. Inspectors should avoid leaning on or touching these surfaces.
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THERMAL AND CATALYTIC INCINERATORS
Inspection Summaries
7.3 Inspection Summaries
7.3.1 Level 1 Inspections - Not Applicable
7.3.2 Level 2 Inspections
Basic Inspection Points
Stack ° Visible emissions
Bypass Stack
0 Vapor refraction lines
Incinerator
Heat recovery outlet gas temperature
Incinerator outlet temperature
Temperature rise across catalyst bed
Audible air infiltration
Obvious corrosion
Process Equipment
0 Process operating rate
Follow-up
Incinerator
0 Fan motor current
0 Hood static pressure
7.3.3 Level 3 Inspections
Stack °- All elements of a Level 2 Inspection
Incinerator
0 All elements of a Level 2 Inspection
0 Inlet gas temperature
0 Inlet VOC concentration
0 Outlet VOC concentration
Process * All elements of a Level 2 Inspection
0 Coatings compositions
147
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INSPECTION OF THERMAL AND CATALYTIC INCINERATORS
Inspection Summaries
7.3.4 Level 4 Inspections
Stack
0 All elements of a Level 3 inspection
Incinerator
0 All elements of a Level 3 inspection
0 Locations for measurement ports
0 Potential inspection safety problems
Process Equipment
0 All elements of a Level 3 inspection
0 Basic flowchart of process
0 Potential inspection safety problems
148
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THERMAL AND CATALYTIC INCINERATORS
Inspection Procedures
7.4. Inspection Procedures
The inspection procedures for incinerators can be classi-
fied as Level 2 and Level 3 inspections. The Level 2 inspec-
tion is a detailed walkthrough inspection utilizing the on-site
incinerator and process instrumentation. The Level 3 inspec-
tion includes all of the Level 2 steps and also includes the
limited use of portable instruments to verify incinerator per-
formance. The instruments generally used are the portable VOC
detectors and portable thermocouple thermometers. Instrument
measurement procedures and safety considerations are discussed
in another section of this notebook.
7.4.1 Basic Level 2 Inspections
Observe the Incinerator Exhaust.
There should be no visible soot or particulate emissions
from the exhaust. Visible emissions are generally due to
improper burner operation or condensation of unburned organic
compounds.
Observe the incinerator bypass stack.
Incinerators generally must have bypass stacks so that the
process equipment can be safely vented in the event of inciner-
ator malfunction. However, during routine operation, there
should be no significant leakage of VOC contaminated gas
through the bypass stack dampers. The leakage of high VOC
concentration gas can often be identified by the wavy light
refraction lines at the stack mouth.
Record the incinerator operating temperature.
For thermal,incinerators, the combustion chamber exhaust
gas temperature should be recorded. This is generally monitored
by a thermocouple that is used to adjust the main burner firing
rate. A reduction in the operating temperature could result in
a reduced VOC oxidation efficiency.
For catalytic incinerators, the inlet and outlet gas tem-
peratures to the catalyst bed should be recorded. The inlet gas
temperature is the temperature after the preheat burner and
immediately ahead of the catalyst bed. The bed
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INSPECTION OF THERMAL AND CATALYTIC INCINERATORS
Basic Level 2 Inspection Procedures
Record the incinerator operating temperature.(Continued)
outlet temperature is the temperature before the gas stream
enters any of the heat recovery equipment. Smaller than normal
temperature increases across the catalyst bed are due to either
catalyst inhibition or to a reduced VOC concentration in the
inlet gas stream.
Listen for air infiltration into the incinerator system.
Air infiltration into incinerators under negative pressure
(fan downstream of the incinerator) can lead to localized
cooling of the gas stream. Incomplete VOC oxidation can occur
in these areas. Severe air infiltration into the inlet duct
could prevent proper incinerator operating temperatures since
this reduces the sensible heat and the heating value of the
inlet gas stream. Infiltration also reduces the VOC capture
effectiveness at the process source.
Check the incinerator shell, outlet ductwork, and stack for
obvious corrosion.
Hydrochloric acid vapor can be formed in incinerators due
to the oxidation of chlorinated hydrocarbons. This can lead to
corrosion of the incinerator shell and downstream gas handling
equipment.
Review the process operating records.
Confirm that the incinerator was operated whenever high-
solvent materials were being used.
7.4.2 Follow-up Level 2 Inspection Steps
Evaluate the fan motor current.
A decrease -in the fan motor current as compared to the
baseline levels indicates a decrease in the total gas flow from
the process equipment. A flow rate decrease could be due to a
decrease in the process operating rate or a change in the process
operating conditions. Fugitive emissions should be evaluated to
the extent possible when there has been a significant decrease in
the fan motor currents without process operating changes.
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INSPECTION OF THERMAL AND CATALYTIC INCINERATORS
Follow-up Level 2 Inspection Procedures
Measure the hood static pressure.
The hood static pressure provides a general indication of
the gas flow rate from the process equipment. This data is
useful to confirm that there are no significant fugitive VOC
emissions.
7.4.3 Level 3 Inspections
Measure the VOC outlet concentration.
The effluent gas concentration should be measured if there
is safe and convenient access to the effluent gas duct. The port
should be located downstream of the heat recovery equipment so
that the gas temperature is as low as possible. A glass-lined
probe is usually advisable to minimize losses of organic vapor to
the surfaces of the probe. If the gas temperature is greater
than 300 °F, it will probably be necessary to include a condenser
and knock-out trap in the sample line in order to protect the VOC
detectors.
The VOC detector (and its portable recorder, if any) should
be certified as intrinsically safe for the type of hazardous
location prevailing in the vicinity of the incinerator. No
electrically powered equipment should be used that could ignite
fugitive VOC vapors.
The observed concentration should be less than 5 to 10% of
the inlet concentration if the incinerator is operating properly.
Measure the inlet VOC concentration.
The inlet gas stream VOC concentration can usually be
measured using the same VOC instrument used for the outlet port.
A dilution probe will often be necessary for photoionization
instruments and flame ionization instruments limited to 1000 to
2000 ppm. The condenser and knock-out trap are rarely necessary
since the gas stream temperatures are normally less than 250 °F.
As in the case with the outlet measurements, the measurement of
the inlet concentration should be done only when all safety
requirements are satisfied.
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INSPECTION OF THERMAL AND CATALYTIC INCINERATORS
Level 3 Inspection Procedures
Measure the incinerator outlet temperature.
The measurement of the incinerator outlet temperature is
attempted whenever the on-site gauge does not appear to be
providing accurate data. However, measurement of the outlet
temperature using portable gauges is subject to a number of
significant possible errors. These include the following.
0 Higher than actual values due to exposure of
the probe to radiant energy from the burner.
0 Lower than actual values due to shielding of
the probe behind refractory baffles in the
combustion chamber.
0 Non-representative values due to spatial
variations of gas temperature immediately
downstream of the incinerator.
For these reasons, the independent measurement of the
incinerator outlet temperature is rarely done by regulatory
agency inspectors. Also, battery powered thermocouple ther-
mometers are not intrinsically safe and can therefore not be
used in certain areas.
Measure the hood static pressure.
The hood static pressure provides a general indication
of the gas flow rate from the process equipment. This data
is useful to confirm that there are no significant fugitive
VOC emissions.
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INSPECTION OF THERMAL AND CATALYTIC INCINERATORS
Level 4 Inspection Procedures
7.4.A Level 4 Inspection Procedures
The Level 4 inspection includes many inspection steps per-
formed during Level 2 and 3 inspections. These are described
in earlier sections. The unique inspection steps of Level 4
inspections are described below.
Evaluate locations for measurement ports.
Many existing fabric filters do not have convenient and
safe ports that can be used for static pressure, gas temperature,
and gas oxygen measurements. One purpose of Level 4 inspections
is to select (with the assistance of plant personnel) locations
for ports to be installed at a later date to facilitate Level 3
inspections.
Evaluate potential safety problems.
Agency management personnel and/or senior inspectors should
identify any potential safety problems involved in standard Level
2 or Level 3 inspections at this site. To the extent possible,
the system owner/operators should eliminate these hazards. For
those hazards that can not be eliminated, agency personnel should
prepare notes on how future inspections should be limited and
should prepare a list of the necessary personal safety equipment.
A partial list of common health and safety hazards includes the
following.
6 Hot exhaust duct surfaces
0 Inhalation hazards due to low stack discharge points
6 Weak catwalk and ladder supports
0 Fugitive emissions from process equipment
0 Inhalation hazards from adjacent stacks and vents
0 Weak roofs or catwalks
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INSPECTION OF THERMAL AND CATALYTIC INCINERATORS
Level 4 Inspection Procedures
Prepare a_ system flowchart.
A relatively simple flowchart is very helpful in conducting
a complete and effective Level 2 or Level 3 inspection. This
should be prepared by agency management personnel or senior
inspectors during a Level 4 inspection. This should consist of
a simple block diagram that includes the following elements.
c Source(s) of emissions controlled by a single
incinerator
0 Location(s) of any fans used for gas movement
through the system (used to evaluate inhalation
problems due to positive static pressures)
0 Locations of any main stacks and bypass stacks
0 Location of incinerator
0 Locations of major instruments (static pressure
gauges, thermocouples)
Evaluate potential safety problems in the process area.
The agency management personnel and/or senior inspectors
should evaluate potential safety problems in the areas which
may be visited by agency inspectors during Level 2 and/or Level
3 inspections. They should prepare a list of the activities
that should not be performed and locations to which an inspec-
tor should not go as part of.these inspections. The purpose of
this review is to minimize inspector risk and to minimize the
liability concerns of plant personnel.
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8. USE OF PORTABLE INSTRUMENTS
8.1. VOC Detectors
6.1.1 Types of Instruments
There are five basic types of instruments in common use for the
measurement of organic vapor concentration. Since each of these uses
a different measurement principle, there are substantial differences
in the abilities of the instruments to monitor various types of
organic compounds. Each of these types of instruments can meet the
performance specifications of EPA Reference Method 21. For this
reason, the instruments must be chosen for each specific application.
8.1.1.1. Flame lonization Detectors - A gas sample containing the
organic vapor is fed into a hydrogen flame. Partial combustion of
the organic compounds produces ions which are measured with an
electrometer.
Common applications - Responds to most organic compounds,
including methane, aliphatic hydro-
carbons, and aromatic hydrocarbons.
Operating limits - Reduced response for oxygenated and
chlorinated organic compounds. Does
not respond significantly to carbon
monoxide, carbon dioxide and water
vapor.
The portable instruments are different from flame ionization
detectors often used on laboratory gas chromatographs. In the
portable instruments, the oxygen necessary for hydrogen combustion
is supplied by the sample gas stream.
Due to the need for oxygen, the instrument flame can be extin-
guished if the organic vapor concentration entering the instrument is
above the upper explosive limit.
155
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USE OF PORTABLE INSTRUMENTS - VOC DETECTORS
Types and Operating Principles
8.1.1.2. Photoionization Detectors - High energy ultraviolet light
emitted by the instrument lamp is used to ionize a portion of the
organic vapor contained in the gas stream. The measured current
flow is proportional to the organic vapor concentration.
The instrument is generally used for compounds having ionization
potentials less than the ratings of the ultraviolet lamps. The lamp
intensities range from 10 electron volts (abbreviated e.v.) to more
than 11 electron volts.
Common applications - Most chlorinated and oxygenated hydro-
carbons, aromatic compounds, and high
molecular weight aliphatic compounds.
Operating limits - Insensitive for methane, ethane, propane,
butane, carbon monoxide, carbon dioxide,
and water vapor.
The electron volt rating applies specifically to the wavelength
of the most intense emission line of the lamp's output spectrum.
Some compounds with ionization potentials above the lamp rating can
still be detected due to the presence of small quantities of more
intense light.
6.1.1.3. Catalytic Combustion Detectors - The principle used to de-
tect organic vapors is the electrical resistance change in a filament
coated with catalyst used to ignite the organic vapors. The filament
is part of a Wheatstone bridge circuit so that the resistance change
in the coated filament causes a current flow that is proportional to
organic vapor concentration.
Common application - Most hydrocarbons that can be oxidized.
Operating limits - Some chlorinated compounds and lead com-
pounds can poison the catalyst. Response
to chlorinated and oxygenated compounds
is poor.
156
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USE OF PORTABLE INSTRUMENTS - VOC DETECTORS
Types and Operating Principles
8.1.1.4. Dispersive Infrared Detectors - Absorbance of infrared light
occurs in a variable path gas sample cell. Monochromatic light is
generated by a spectrometer so that monitoring can be done at a wave-
length where the compound of interest absorbs strongly.
Common applications - Most hydrocarbons
Operating limits - Water vapor absorption will interfere with
measurements of many compounds.
The response of dispersive infrared units is highly dependent on
the specific chemical.
8.1.1.5 Nondispersive Infrared Detectors - Detection of organic vapor
is performed by absorption of infrared light. The sample gas contain-
ing the organic vapor is passed through one cell and a reference gas
is sealed in a second cell. The ultraviolet light is split between
the two cells and the differential pressure resulting from the unequal
heating is detected. The pressure is proportional to the organic
vapor concentration.
Common applications - Most hydrocarbons
Operating limits - Water vapor and carbon dioxide can absorb
infrared energy.
157
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USE OF PORTABLE INSTRUMENTS - -VOC DETECTORS
Types and Operating Principles
8.1.2 Initial Instrument Checks
Prior to leaving for the inspection site and/or conducting
calibrations, the instrument should be carefully checked. If the
instrument does not pass these routine checks, it should be
repaired before it is taken to the inspection site.
Leak Checks
To leak check the probes on units with flow meters, the,probe
outlet should be plugged for one to two seconds while the sample pump
is running. If the sample flow rate drops to zero, there are no
significant leaks in the entire sampling line. If there is any detec-
table sample flow rate, further leak checks will be necessary to
prevent dilution of the VOC sample gas during screening tests. The
leak checks involve a step-by-step disassembly of the probe/sample
line starting at the probe inlet and working backwards toward the
instrument.
At each step, the probe/sample line is briefly plugged to deter-
mine if there is still inleakage at an upstream location. After the
problem has been corrected, the probe/sample line is reassembled and
rechecked.
Units without flow monitors are calibrated in a similar manner.
The sound of the pump during temporary blockage of the probe provides
an indication that the flow has been stopped and that air infiltration
is insignificant.
Check Probe Condition
The physical condition of the instrument probe should be visual-
ly checked before use. These checks include:
0 Presence of any organic deposits on the inside surfaces
0 Presence of a clean particulate filter in the probe and the
presence of a glass wool "prefilter".
0 Condition of orifice used to control dilution air flow into
probe (dilution probes only).
0 Condition of sealing "0" rings or other seals.
158
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USE OF PORTABLE INSTRUMENTS - VOC DETECTORS
Initial Instrument Checks
Check Probe Condition (Continued)
If organic deposits are found on the inside surfaces, they can
usually be removed using either acetone or methanol (check instrument
manufacturer's recommendations). The cleaned probes must be purged
of solvent vapors before reassembly.
Check Battery Pack Status
The battery pack condition is normally checked simply by switch-
ing the instrument to the "Battery Check" position and observing the
dial setting. If the battery pack is weak, a new battery pack should
be installed. Battery life is especially limited in cold weather.
Check Detector
The detectors used in each type of instrument are vulnerable to
operating problems. The following steps are useful to confirm that
the detectors are functioning:
0 Photoionization - Clean the windows and then turn the unit on.
It should be possible to obtain a zero reading.
0 Flame lonization - Attempt to ignite the burner. If this can
not be done, then there are problems with the batteries, the
ignitor, or the hydrogen supply.
0 Catalytic Combustor - Attempt to zero instrument. If this can
not be done, the detector has failed.
159
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PORTABLE INSTRUMENTS - VOC DETECTORS
Calibration Procedures
8.1.3 Calibration Procedures and Requirements
Calibration requirements for VOC instruments are specified in
EPA Method 21 and in the specific NSPS and NESHAPS regulations
applicable to sources of fugitive VOC emissions. A brief summary of
the calibration requirements is provided below.
0 The instruments should be calibrated daily.
0 The gas concentration used for calibration should be close
to the leak definition concentration.
0 The calibrant gas should be either methane or hexane.
0 A calibration precision test should be conducted every month.
0 If gas blending is used to prepare gas standards, it should
provide a known concentration with an accuracy of plus or
minus 2%.
Calibration Type
The NSPS and NESHAPS regulations do not specify the type of
calibration to be performed on a daily basis. The inspector should
determine whether single point or multi-point calibrations are
necessary.
All calibrations should be performed with the type of probe and
prefilters that will be used in the screening tests. This is impor-
tant since these affect response time and the sample flow rate.
Calibrant Gases
Calibrations can'be performed using either commercially prepared
gas mixtures or blended gas mixtures. Disposable cylinders are most
convenient when the calibrations are done at the inspection site.
The types of calibrant gases normally recommended by the instrument
manufacturers are listed in Table 8-1.
160
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USE OF PORTABLE INSTRUMENTS - VOC DETECTORS
Calibration Procedures
Table 8-1. Calibrant Gases and Concentrations
Type of Instrument Calibrant Gas and Concentration
Flame lonization 10,000 ppm Methane in Air
500 ppm Hexane in Air
Photoionization 250 ppm 1,3 Butadiene in Air
250 ppm Benzene in Air
Catalytic Combustion 500 ppm Hexane in Air
20,000 ppm Methane in Air
Infrared Varies depending on application
Consult the instrument operating manual and the manufacturer's
representative to obtain more information concerning the types of
Calibrant gases and the expected instrument response.
Calibration Location
The NSPS and NESHAPS regulations do not specify where the cali-
brations should be performed. The author recommends that an initial
calibration be done at the agency lab before leaving for the inspec-
tion site. Calibrations can be performed under more controlled sample
flow rate and sample temperature conditions when done in the agency
lab. Both factors can influence instrument response. Furthermore,
this calibration clearly demonstrates that the unit is operating
satisfactorily and can., be taken to the inspection site.
161
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USE OF PORTABLE INSTRUMENTS - VOC DETECTORS
Calibration Procedures
Calibration Apparatus
One possible means to calibrate VOC detectors is illustrated in
Figure 8-1. A calibrant gas mixture from a disposable cylinder is
used to fill a 20 liter Tedlar bag having several Roberts valves.
The sample is drawn from the bag into the instrument at a controlled
flow rate. The steps involved in calibration using disposable
cylinders and Tedlar bags are listed below. This list is based on
the assumption that the battery packs, probes, and detectors have
been already checked (see Section 8.2).
0 Warm up instrument and assemble calibration apparatus.
0 Flush sample bags with hydrocarbon free air.
0 Confirm that sample flow is within normal range.
0 Reset instrument span and zero.
0 Reflush Tedlar bag and inject different calibrant gas
concentration (for multi-point calibration).
0 Record results in lab notebook.
Another technique for calibration of VOC instruments is shown
in Figure 8-2. This is a relatively simple approach which can be
used on instruments which are only slightly flow sensitive, such as
the photoionization instruments. The flow meter should be set at a
flow rate large enough to ensure that there is an excess of calibra-
tion gas for the instrument.
Calibration Records
The records should be kept in an organized file so that it is
possible to demonstrate that the unit was calibrated properly if the
agency data are ever challenged.-
162
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USE OF PORTABLE INSTRUMENTS - VOC DETECTORS
Calibration Procedures
Cal. Gas Bag Sample
Instrument
Figure 8-1. Calibration Apparatus Using Tedlar Bag-
Excess
Rotameter
Instrument
Cal. Gas
Figure 5-2. Calibration Apparatus Having Flow 'Directly to Instrument
163
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USE OF PORTABLE INSTRUMENTS - VOC DETECTORS
Field Check Procedures
8.1.A Field Check Procedures
There are several routine instrument performance checks which
should be conducted during the field work. These demonstrate that
the instrument is continuing to perform in a proper manner.
Instrument Zero
The instrument zero should be rechecked whenever it has been
exposed to very high organic vapor concentrations or whenever organic
liquids may have been inadvertently sucked into the probe. Even if
these situations have not occurred, the zero should be checked several
times per day.
The instrument zero can be checked by sampling background air
upwind of any possible VOC sources. Alternatively, sone hydrocarbon
free air can be supplied using a charcoal filter. If the instrument
zero has drifted significantly, the probe particulate filter and the
prefilter (if used) should be replaced. Also, the probe should be
cleaned using acetone or a similar solvent to remove the condensed
organics. The instrument should be recalibrated (single point) after
changing the filters and cleaning the probe.
Instrument Response
Confirm that the instrument is responding by sampling a source
of VOC emissions. This could be leaking sources at the plant, the
calibration gas in the Tedlar bag, or a small portable source of
organic vapor.
Routine response checks are especially important for flame
ionization and catalytic combustion units. The FIDs can flame out
above 70,000 ppm of organic vapor due to insufficient oxygen. The
catalytic units can suffer catalyst volatilization if exposed to high
concentrations of organic vapor over an extended time period. The
catalytic units are also subject to catalyst poisoning and catalyst
coating in certain sources.
Automobile exhaust should NOT be used as a source of organic
vapor when checking instrument response. There are large quantities
of condensible vapor and particulate that can harm the instrument's
detectors and accumulate in the probes.
164
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USE OF PORTABLE INSTRUMENTS - VOC DETECTORS
Field Check Procedures
Battery Condition
In the case of some flame ionization detectors, weak batteries
will not have enough power to operate the ignitor, even though a
proper reading was obtained during the battery check. This can be a
problem after the FID has been operated for several hours and after
a number of flameouts have occurred. For this reason, the battery
condition should be checked several times during the screening tests.
Probe/Sampling Line Leakage
The probe and sampling line integrity should be checked several
times per day by simply plugging the probe inlet. The continual
movement of these probes and lines can loosen the connections and
allow significant air infiltration. This reduces the ability to
identify fugitive VOC sources.
165
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USE OF PORTABLE INSTRUMENTS - VOC DETECTORS
Special Tests
8.1.5 Special Tests
The NSPS and NESHAPS regulations (primarily Method 21) require
several instrument tests on an infrequent basis. These include
determination of the response time and calibration precision.
Response Time
The response time of the instrument must be measured prior to
using the unit on inspections. It must also be performed whenever
there are changes in the probe, sample flow lines, or pump that could
conceivably influence the response time.
The test is conducted in accordance with paragraph 4.A.3 of
Method 21. Hydrocarbon free sample gas is introduced into the instru-
ment until a stable zero reading has been obtained. Then a supply of
calibration gas of known concentration is quickly substituted for the
hydrocarbon free gas. The time required for the instrument to indi-
cate 90% of the calibration gas concentration is recorded as the
response time. The test sequence is performed three times, and the
response time values are averaged. A possible form for recording the
response time tests is provided in Figure 8-3.
The response time for instruments required in Method 21 tests is
30 seconds. A reduction in the response time of an instrument is
generally due to severely reduced sample gas flow rates.
Calibration Precision
This test must be performed for instruments being used in Method
21 type inspections. The tests must be done before the instruments
are used on inspections and at three month intervals during routine
use.
The test is performed by alternating sampling hydrocarbon free
sample gas and a calibration gas. The observed organic vapor concen-
trations when sampling the calibration gas are algebraically averaged,
divided by the calibration gas concentation, and multiplied by 100.
The calibration precision must be equal to or less than 102. A sample
form for calibration precision tests is presented in Figure 8-4.
166
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USE OF PORTABLE INSTRUMENTS - VOC DETECTORS
Special Tests
Instrument ID
Calibration Gas Concentration
90S Response Time:
1. _____ Seconds
2. _____ Seconds
3. _____ Seconds
Mean Response Time Seconds
Figure 8-3. Sample Form for Response Time Tests
167
-------
USE OF PORTABLE INSTRUMENTS - VOC DETECTORS
Special Tests
C*Ubratlo« Precision
ID
Calibration CM Niitwri Out
ligh
IM CBlibratloa CM ZBftruwnt Motor Dtfftrtnct.(l)
No. CbKMtratioa. ffm
1.
2.
3.
4.
3.
6.
U» fash
«M£ Olfr.
Mm Mffmw* (2)
Ctl Error • OlikratloB CM Ceacntrttloa « 100
(1)
(2) Akselar* TK!M
Figure 8—4. Sample Form for Calibration Precision Tests
168
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USE OF PORTABLE INSTRUMENTS - VOC DETECTORS
Spare Parts
8.1.6 Spare Parts
A minimum number of spare parts are generally advisable to ensure
that the VOC detectors can be repaired and maintained during field
inspections. A list of recommended spare parts which should be taken
to the inspection site is provided in the lists below. The instrument
manufacturer should also be consulted regarding the need for spare
parts.
All Instruments
0 Battery pack
0 Particulate filters
e Flexible tubing (l"-2")
0 Glass wool
Flame lonization Detectors
0 Flame arrestor
0 Probe
Photoionization Detectors
0 Window cleaning kit
0 Lamp
0 Rotameter
Catalytic Detectors
0 Detector cell
Infrared Detectors
0 Rotameter
169
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USE OF PORTABLE INSTRUMENTS - TEMPERATURE MONITORS
Types and Operating Principles
8.2 Temperature Monitors
Thermocouples and dial-type thermometers are used in inspections
of VOC sources. The dial-type units are used primarily for low temp-
erature applications such as carbon bed adsorbers. The thermocouples
are used to check incinerator outlet gas temperatures.
3.2.1 Types and Operating Principles
Thermocouples
The electromotive force generated by two dissimilar metals is
a function of the temperature. The thermocouple voltage is compared
with a reference voltage (equivalent to 32 °F) and amplified by the
thermometer.
There are a variety of thermocouple types, each designated by
letters adopted originally by the Instrument Society of America
(ISA) and adopted as American National Standard C96.1-1964. A brief
summary of the thermocouple properties and composition is provided
below.
Type K - This is the most common type of thermocouple used
for VOC inspections due to the broad temperature
range of -400 °F to + 2300 °F. The thermoelectric
elements must be protected by a sheath since both
wires are readily attacked by sulfurous compounds
and most reducing agents. This sheath must be
selected carefully to ensure that it also can take
the maximum temperature that the unit will be
exposed to. The positive wire is nickel with 10%
chromium (trade name - chromel) and the negative
wire is nickel with 5 % aluminum and silicon (trade
name - alumel).
Type E - These generate the highest voltage of any thermo-
couple but are limited to a maximum temperature
of 1600 °F. The positive wire is nickel with 10%
chromium (chromel) and the negative wire is a
copper-nickel alloy (constantan).
170
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USE OF PORTABLE INSTRUMENTS - TEMPERATURE MONITORS
Types and Operating Principles
Type J - These have a positive wire composed of iron and a
negative wire composed of a copper-nickel alloy
(constantan). They can be used up to 1000 °F in
most atmospheres and up to 1400 °F if properly
protected by a sheath. They are subject to
chemical attack in sulfurous atmospheres.
Type T - These can be used under oxidizing and reducing
conditions. However, they have a very low
temperature limit of 700 °F. They are composed
of copper positive wire and a copper-nickel alloy
(constantan) negative wire.
Type R and S - These can be used in oxidizing or inert
conditions to 2500 °F when protected by nonmetallic
protection tubes. The Type R thermocouples are
composed of a positive wire of platinum with 13 %
rhodium and a negative wire of platinum. The Type
S thermocouples have a positive wire of platinum
with 10% rhodium. Both types can be subject to
calibration shifts to lower temperature
indications due to rhodium diffusion or rhodium
volatilization.
Type B - The positive wire is composed of platinum with 30%
rhodium and the negative wire is platinum with 6%
rhodium. These are less sensitive to the calibra-
tion drift problems of Type R and S thermocouples.
They can be used to a maximum temperature of 3100 °F
when protected by nonmetallic protective tubes.
171
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USE OF PORTABLE INSTRUMENTS - TEMPERATURE MONITORS
Types and Operating Principles
Thermocouple Sheaths
The maximum temperature that a thermocouple can withstand is
dependent on the wire compositions and on the type of sheath wrapped
around the thermocouple junction. The temperature limits of common
sheath materials are indicated in Table 8-2.
Table 8-2. Maximum Operating Temperatures for
Common Sheath Materials
Sheath Material Temperature Limit, °F
Aluminum 700
304 Stainless 1650
316 Stainless 1650
Inconel 2100
Hastelloy 2300
Nickel 2300
Thermocouple Thermometer Limits
A hand-held potentiometer is used to convert the thermocouple
voltage to a temperature reading. This is a battery powered unit
which is generally not rated as intrinsically safe. For this reason,
thermocouples can not be taken into hazardous locations.
Dial Type Thermometers
Temperature is sensed by the the movement of a bimetallic coil
composed of materials having different coefficients of thermal
expansion. The coil movement is transmitted mechanically to a dial
on the front of the thermometer.
One of the principle advantages of this type of unit is that
no are batteries required and it can be used safely in most areas.
The main disadvantage is the relatively short probes of 6 to 12"
which make it very difficult to reach locations at representative gas
temperatures. Due to the short "reach", the dial-type instruments
often indicate lower than actual temperatures.
The dial-type units are best when there is very little tempera-
ture variation in the measurement location and when there is little
or no insulation surrounding the measurement ports. They are gener-
ally used for low temperature applications.
172
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PORTABLE INSTRUMENTS - TEMPERATURE MONITORS
Calibration and Routine Checks
8.2.2 Calibration and Routine Checks
Ice and Boiling Water Temperature Measurements
Both the thermocouple based thermometers and the dial-type
thermometers should be checked prior to leaving for the inspection
site. The temperatures of boiling water and a finely crushed ice
water mixture should be checked. The indicated temperature of the
boiling water should be 212 °F or less depending on elevation. The
temperature of the ice water mixture should be between 32 °F and
34 °F depending on how well the ice has been ground and how long the
mixture has had to reach thermal equilibrium.
Record the thermometer temperatures for boiling water and ice
water in a notebook or file which is kept at the agency lab. This
simple two point check verifies that the unit is operating
satisfactorily.
Annual Calibration
The thermocouple should be calibrated on an annual basis. This
is often done by comparison of the voltage developed by the thermo-
couple with the voltage developed by a NBS traceable thermocouple.
A set of potentiometers is used to measure the voltages of the two
thermocouples placed together in a furnace.
Annual calibration of the dial type thermometers is generally
not required. The' boiling point and ice point measurements are
sufficient for dial type thermometers used in the temperature range
of 32 °F to 212 °F.
173
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USE OF PORTABLE INSTRUMENTS - STATIC PRESSURE GAUGES
Types and Operating Principles
8.3 Static Pressure Gauges
Static pressure gauges are used primarily to evaluate the static
pressure across carbon bed adsorbers and to evaluate ventilation
systems leading to VOC control devices.
8.3.1 Types of Static Pressure Gauges
Slack tube manometers, inclined manometers, and diaphragm gauges
are used for measurement of static pressure. The inclined manometer
is the most accurate instrument for low static pressures of less than
10 inches W.C. However, it is relatively bulky. Slack tubes can be
used up to static pressures of 36 inches W.C. Larger slack tube
manometers are cumbersome to use. The diaphragm gauges come in
various styles, most of which are accurate to plus or minus 3% or 5%
of the instrument scale. These gauges are easy to carry.
The diaphragm gauges are composed of two chambers separated by
a flexible diaphragm. The diaphragm moves when there are unequal
pressures on each of the ports leading to the two chambers. The
diaphragm deflection is mechanically transmitted to the dial on the
front of the unit. No batteries are required. Also, there is no
sample gas flow through the instrument.
-------
USE OF PORTABLE INSTRUMENTS - STATIC PRESSURE GAUGES
Calibration
8.3.2 Calibration
The slack tube manometer and the inclined manometer do not need
to be calibrated since these indicate static pressure directly. The
diaphragm gauges are calibrated by comparison with an inclined man-
ometer or a slack tube manometer depending on the static pressure
range of interest.
The diaphragm gauges can be calibrated by connecting both the
manometer and the diaphragm gauge to a source of pressure. One port
of each gauge is left open to the atmosphere. A squeeze bulb with
check valves on both sides provides a source of positive and negative
pressure in the range of -40 inches W.C. to + 40 inches V.C. A hose
clamp is necessary to maintain the pressure while both static pressure
gauges are being checked.
Separate calibration curves should be prepared for the positive
and negative pressures. Each curve should be comprised of a minimum
of three points to indicate any non-linearities in the gauge response.
A sample form for recording and plotting the calibration data is
provided in Figure 8-5.
Diaphragm gauge calibration should be performed prior to each
inspection day. Total time requirements are less than 5 minutes when
the manometers and squeeze bulbs are kept in a convenient location.
175
-------
PORTABLE INSTRUMENTS - STATIC PRESSURE GAUGES
Calibration
PrMaur* Gauge CaBbntton
JNCHOWC,
MVCMTOHY NUMKA.
CAUVUTON DATE _
CALWATMN ITAWAMCL
.TIMI.
\
WC
ions.
Figure 8-5. Possible Form for Diaphragm Gauge Calibration
176
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USE OF PORTABLE INSTRUMENTS - PITOT TUBES
Gas Flow Measurement Procedures
8.4 Pitot Tubes
Both S-Type and standard pitot tubes can be used in VX inspec-
tions to measure the gas flow rates. The standard pitot tube is most
convenient since there is no need to calibrate the unit. However, it
should not be used when there is some particulate in the gas stream
that could plug the static pressure holes around the circumference of
the outer tube. The S-type unit should be used when particulate is
present.
8.4.1 Gas Flow Measurement Procedures
Selection Measurement Site
The measurement port used for the pitot traverse should conform
to the minimum distances upstream and downstream of flow disturbances
specified in Table 8-3. Preferred measurement site locations are
also listed in this table. For rectangular ducts, the equivalent
"diameter" of the duct is calculated as follows.
Equivalent "Diameter" « 2 x L x W/(L + W)
of Rectangular Duct
Table 8-3. Measurement Site Characteristics
Minimum Distances to Flow Disturbances
0 At least 2 diameters downstream
0 At least 0.5 diamters upstream
Preferred Distances to Flow Disturbances
0 At Least 8 diameters downstream
0 At least 2 diameters upstream
177
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USE OF PORTABLE INSTRUMENTS - PITOT TUBES
Measurement Procedures
The minimum number of. traverse points should _be_ determined
Figure 8-6.
• POU
fTACM Oft DUCTS
!
j "^kmvmtMCt
;• wt
It
Figure 8-6. Minimum Number of Traverse Points Necessary
Locations of. Traverse Points
For circular stacks, the traverse points should be located on
two perpendicular diameters of the stack at locations such as shown
in Figure 8-7. The traverse point locations are specified in
Table 8-4.
For stacks with diameters less than 24 inches, do not locate
a traverse point within 0.5 inches of the stack wall. For stacks
larger than 24 inches, do not locate a traverse point within 1.0
inches of the stack wall. Move the last point away from the wall at
least one nozzle diameter. If the adjusted point overlaps with the
adjacent traverse point, treat the observed velocity pressure as two
points when making the calculations.
178
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USE OF PORTABLE INSTRUMENTS - PITOT TUBES
Gas Flow Measurement Procedures
•
I
Figure 5-7. Traverse Point Locations
TMU t. mean or swa ow*cm nm mm MKL TO runuc
POWT rat CIIQIUW mcu
IU
•.I
N.4
M.I
•J
mj
M
MJ
B.I
•.I
M.I
H.l
,1
,1
t.1
U.I
W.I
M
H.4
M.I
•.I
U
IM
HJ
•.4
IM
M.I
•J
•.I
ii .1
,4
W.l
I.I
M
kl
l.t
M.I
U.I
H.I
lt.4
•••
m.i
9.1
IM
JI.I
•.I
m.%
•.*
Table 8-4. Locations for Traverse Point for Circular Stacks
179
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USE OF PORTABLE INSTRUMENTS - PITOT TUBES
Gas Flow Measurement Procedures
Locations of_ Traverse Points (Continued)
For rectangular stacks determine the grid configuration from
Figure 8-8. Notice that the minimum number of traverse points for
a rectangular stack is 9.
TJ::--
—-,--._ i_
• 1 •
1
1
• 1 *
1
* 1 *
— 1
• ! •
Figure 8-8. Rectangular Stack Grid Configuration
Divide the stack into the grid configuration as determined from
Table 8-5. Locate a traverse point at the centroid of each grid. An
example is shown in Figure 7-8.
Table 8-5. Example Traverse Point Locations - Rectangular Stacks
Number of Traverse
Points
9
12
16
20
25
30
36
42
Grid
Configuration
3x3
4x3
4x4
5x4
5x5
6x5
6x6
7x6
7x7
180
-------
USE OF PORTABLE INSTRUMENTS - PITOT TUBES
Gas Flow Measurement Procedures
Verification of Absence of Cyclonic Flow
The presence or absence of cyclonic flow at the traverse location
must be verified if there are any tangential inlets or other duct
configurations which tend to introduce gas swirling. Cyclonic flow is
evaluated using the following procedure.
e Level and zero the manometer.
0 Connect a Type S pitot tube to the manometer.
0 Place the pitot tube at each traverse point so that the face
openings of the pitot tube are perpendicular to the stack
cross-sectional plane. At this position, the pitot tube is
at 0° reference.
0 If the differential pressure is null (zero) at each point,
an acceptable flow condition exists.
0 If the differential pressure is not zero at 0° reference,
rotate the pitot tube until a zero reading is obtained.
0 Note the angle of the null reading.
0 Calculate the average of the absolute values of the angles.
Include those angles of 0°.
0 If the average is greater than 20°, the flow conditions of
the sample location are unacceptable.
Measure the stack gas velocity and gas flow rate.
If the measurement location does not have cyclonic flow, the gas
velocity and flow rate are measured using the procedure outlined
below. A standard pitot is generally used if the particulate loadings
are low.
0 Conduct a pretest leak check of the apparatus.
0 Level and zero the manometer.
e Measure the velocity head at each of the traverse points and
record the data..on the form presented in Figure 6-9.
e Measure the gas temperature at each traverse point.
0 Conduct a post test leak check.
0 Calculate the average stack gas velocity and volumetric flow
rate using the simplified equations presented on the next page.
181
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USE OF PORTABLE INSTRUMENTS - PITOT TUBES
Gas Flow Measurement Procedures
Measure the gas velocity and flow rate (continued) .
The equation for the gas velocity is based on air at standard
pressure. This is generally a valid approximation for VOC sources.
Vs « 2.9 Cp (p ) avg. ^(Ts) avg.
where: Vs « Average stack gas velocity (ft/sec)
Cp « Pitot tube coefficient (dimensionless)
Usually 0.99 for standard pitot tubes
Usually 0.83 to 0.87 for S-Type pitot tubes
Ap * Velocity head measured by pitot tube
(inches of water)
Ts « Absolute stack temperature (°R) equals stack
temperature in °F + 460
The gas flow rate in actual cubic feet per minute is calculated
by multiplying the average gas velocity by the stack cross sectional
area.
Qs - 3600 Vs A
where: Vs - Average stack gas velocity, (ft/sec)
A « Cross sectional area of stack (ft squared)
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USE OF PORTABLE INSTRUMENTS - PITOT TUBES
Gas Flow Measurement Procedures
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V«1w1* TrmrM 0«U (Proa n. V«l. 42. Ni. 1M. ?fl. 417U.
An«. U. W77). ~
Figure 8-9. Velocity Traverse Data Form
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