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

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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

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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)

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            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.

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INSPECTION  OF ELECTROSTATIC  PRECIPITATORS
Components  and Operating Principles


                   INSPECTION Or ELECTROSTATIC HttCWUTORS
                                                     28
            20
            10
                                 man uu
                            MSUIKE
          •1500
         £1000
           500
          ••
            30
          *M 20
            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.

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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.
                               79

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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.


                               84

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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.
                               87

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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.
                               92

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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).
                               93

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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)
                               97

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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
                                99

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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.
                               106

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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.
                               115

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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.
                               118

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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.
                               122

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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
                               123

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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
                     •M-
                     •PO-
                                           -e»o-
                                                   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
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    »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.
                               134

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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.
                               135

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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
                              136

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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
                                137

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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
                               139

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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
                               140

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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.
                               141

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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
                               142

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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.
                               143

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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.

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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
                               145

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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.
                               146

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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
                               149

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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.
                               150

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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.
                               151

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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.
                              152

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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
                               153

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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.
                               154

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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

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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.

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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

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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
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M
MJ
B.I
•.I
M.I
                                       H.l
                                        ,1
                                        ,1
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                                          U.I
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                                             M
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                                                IM
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   •.4
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                                                    ,4
                                                  W.l
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         •••
         m.i
                      9.1
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                                                     •.*
     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

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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)
                               182

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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
                                183

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