EPA REGION VII IRC
8 160317 EPA-340/1-84-019a
"k_
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EPA-340/1-84-019a
Wet Scrubber Inspection
Procedures Workshop
Prepared by:
JACA Corporation
550 Pinetown Road
Fort Washington, Pennsylvania 19034
and
Richards Engineering
2605 Tanglewood Road
Durham, North Carolina 27705
Contract No: 68-02-3962
EPA Project Officer: John Busik
EPA Task Manager: Kirk Foster
Submitted to:
U.S. ENVIRONMENTAL PROTECTION AGENCY
Stationary Source Compliance Division
Office of Air Quality Planning and Standards
401 M Street, S.W.
Washington, D.C. 20460
September 1984
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DISCLAIMER
This manual was prepared by JACA Corporation and Richards Engineering for
the Stationary Source Compliance Division of the U.S. Environmental Protection
Agency in partial fulfillment of Contract No. 68-02-3962, Task 1-14. The con-
tents of this report are reproduced herein as received from the contractors.
The opinions, findings and conclusions expressed are those of the authors and
not necessarily those of the U.S. Environmental 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 precautions required for any
given situation depend upon and must be tailored to the specific circumstances.
JACA Corporation and Richards Engineering expressly disclaim 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.
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ACKNOWLEDGMENTS
JACA Corporation and Richards Engineering would like to thank Mr. Kirk
Foster of the U.S. Environmental Protection Agency for his assistance during
this project. Subcontractors assisting with this project included Mr. Kenneth
Schifftner, P.E. of Schifftner & Associates, Mr. Raymond Richards, P.E. of
Richards Technical Services and Mr. Larry Hill, P.E. of EST Corporation. The
technical information and assistance they provided is gratefully achknowledged.
The project director was Mr. Uday Patankar, P.E. of JACA Corporation. He was
assisted by Mr. Robert Schlosser, P.E. The project manager at Richards
Engineering was Mr. John Richards, Ph.D., P.E.
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VI
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TABLE OF CONTENTS
Page
Introduction to the Use of the Manual 1
Lecture 1. Introduction to Wet Scrubber Systems 11
Lecture 2. Baseline Inspection Technique 51
Lecture 3. Visible Emission Observation of Wet Scrubber
Systems 73
Lecture 4. Evaluation of On-Site Gauges and Use of
Portable Instruments 83
Lecture 5. Evaluation of Wet Scrubber System Components 135
Lecture 6. Liquor Analyses 213
Lecture 7. Evaluation of Particulate Wet Scrubbers 227
Lecture 8. Evaluation of Gaseous Absorbers 271
Lecture 9. Inspection Safety 301
Appendix A Bibliography 339
Appendix B Workshop Forms 351
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INTRODUCTION
The Stationary Source Compliance Division of the U.S. Environmental Pro-
tection Agency has sponsored the development of this manual which is intended
to assist regulatory agencies in performing detailed inspections of wet scrubber
systems. These inspections are conducted to determine if the air pollution
control equipment is operating in compliance with applicable regulations and to
determine if the corrective actions proposed by source owners have a reasonable
chance to successfully rectify chronic excess emission problems. The technical
information will also help equipment operators to monitor the performance of
their scrubber systems. The evaluation procedures are intended to identify
operating problems at an early stage so that excess emission problems can be
avoided and so that any necessary equipment repairs can be made quickly and
economically.
The workshop program addresses both particulate and gaseous scrubbers.
Common modes of failure of these systems are discussed to illustrate the
importance of the various inspection activities. Emphasis is placed on the
evaluation of wet scrubber components such as pumps, nozzles, demisters, and
piping. There is also considerable information concerning the critical eval-
uation of on-site gauges and the use of portable instruments when necessary.
Inspection safety is also emphasized.
1.0 Use of This Manual
The materials have been prepared so that it is possible to use the manuals
either in workshops or as self instructional guides. Both the Lecturer's Manual
and the General Manual are used for workshops. The General Manual includes black
and white reproductions of all the visual aids used in the workshop program.
Detailed lecture notes are included with each of the slides so that all of the
attendees can review the technical information at a later date. The presence
of the lecture notes also allows the attendees to concentrate on listening to the
workshop coordinator rather than attempting to compile a complete set of notes.
The general manual also includes a set of review problems and questions at the
end of each lecture. These can be answered either individually or in small
working groups.
The Lecturer's Manual is identical to the General Manual with the addition
of suggestions of various options for presenting the technical material. This
is very important since most audiences are comprised of attendees with very
diverse backgrounds with respect to wet scrubber systems. It is common to have
persons with no experience at all in the same audience with engineers having
more than 10 years of practical field experience. The program must be adjusted
to the attendees' level of experience. The Lecturer's Manual also includes a
detailed discussion of each review problem and question. The additional
material in the Lecturer's Manual is arranged so that the workshop coordinator
is always on the same page as the attendees who are using the General Manual.
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The Lecturer's Manual can be used as a self-instruction manual by persons
who want to review material discussed during a previous workshop or by persons
who were unable to attend a full workshop. The lecturer's notes will be help-
ful in determining what material should be studied. The answers to the review
problems and questions will be helpful in reviewing the lectures.
2.0 Presentation of Workshops
Workshops are intended to be valuable learning experiences for all of the
participants, including the workshop coordinator. To achieve this goal, a con-
siderable amount of preparation work is necessary. This section addresses some
of this initial effort required to structure a successful program
2.1 Know Your Audience - This is the most important step in preparing for
a workshop program. The range of experience with wet scrubber systems should
be determined since it is important to orient the technical information to the
backgrounds of the participants. It is easy to bore the highly experienced
individuals and to overwhelm those with no prior experience with wet scrubbers.
If the range of experience is very large, it may be wise to split the group
into more homogeneous groups so that the material of interest to each can be
properly presented.
People learn in different ways. Some can effectively learn during formal
lectures while others retain more when solving problems or discussing questions
in small groups. Others retain the concepts only after they have had an oppor-
tunity to try them in the field. To the extent possible, the workshop should
include all three major elements: (1) formal lecture, (2) problem sessions, and
(3) field demonstrations. Obviously, this manual can only address the first
two. Nevertheless, the value of field demonstrations should not be underesti-
mated. They should be conducted soon after the workshop program. The mix of
lecture material and problem sessions used in the workshop must be chosen by
the workshop coordinator based on the perceived interests of the participants.
Within the time frame allowed by the typical workshop agenda, there is insuffi-
cient time for both as presented in this manual. This means that the workshop
coordinator must carefully review this manual and decide what technical inform-
ation is relevant and what portion of the time should be devoted to the problem
sessions.
It is equally important to know the types of wet scrubbers of concern.
The workshop materials are intended for an entirely different purpose than
college level engineering courses and the U.S. Environmental Protection Agency
Air Pollution Training Institute courses. These formalized educational programs
are designed to provide a sound foundation in fundamental principles and calcu-
lation techniques. As such they are invaluable pre-requistes to the material
presented in this workshop. Here the primary objective is to present very
practical information on what the field inspector should do "tomorrow" on the
specific scrubber systems within his or her jurisdication. For this reason, it
is necessary to emphasize the material concerning the specific scrubbers that
are of concern to the participants. Regulatory agency inspectors are usually
too busy to enjoy discussing topics which do not appear to have a practical
application in their areas.
If the interests and background of the participants are not known prior to
the workshop, the coordinator should make a survey at the very beginning of the
program. The material should then be adjusted to the extent possible. It is
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better to preregister all participants so that there is more lead time to
tailor the program to the group. Appendix B includes a sample card that can
be distributed in advance or used at the beginning of the workshop. This card
provides the necessary information on the backgrounds of the attendees and
also provides a permanent record of their participation.
2.2 Use an Adequate Meeting Room - Most of the participants attending the
program will be accustomed to field work. They are especially intolerate of
inadequate meeting rooms. The room should have the following features:
0 The chairs should be comfortable.
0 The room should be large enough to accomodate the group without taxing
the heating and air conditioning system.
0 There should be tables for all participants to facilitate note taking
and problem solving.
0 There should be a way to show the 35 mm slides without darkening the
entire meeting room.
0 The room should be reasonably quiet.
0 There should be an area to display portable inspection equipment
and safety equipment.
Overall, the room must be conducive to an intense learning exercise.
It is unfortunate that many of the meeting rooms available in agency office
buildings are not good for workshops. Hard chairs are common since the rooms
were intended only for short meetings, not two or three day programs. It is
often impossible to dim the lights without incurring the wrath of other agency
personnel in adjacent offices. Also, the rooms are often so small that it is
difficult to use the visual aids without the attendees feeling the hot exhaust
of the projector. Long programs in inadequate meeting rooms are a form of
cruel and unusual punishment. It should be remembered that the cost of a good
meeting room is often a small fraction of the transportation costs incurred in
bringing field inspectors in to a central location from the various district
offices.
2.3 Prepare for the Program - There are a number of preliminary activities
which are necessary to ensure that the program runs smoothly. The most impor-
tant of these is for the workshop coordinator to read the manual thoroughly and
decide what portions are relevant. It is also helpful to distribute copies of
the general manual to the preregistered attendees so they have an opportunity to
review the material before the program. More detailed and interesting questions
are asked when the manuals are distributed before program.
The room should be completely set up prior to the arrival of the
attendees. The visual aid equipment should be set up and checked out so that
there is no question that it is working properly. It is almost always wise to
have spare projection bulbs for the visual aid equipment. The slides should be
tried on the screen to confirm that the screen is placed properly and that the
entire slide is visible. If not, the projector and/or the screen should be
repositioned. All of the slides should be loaded and checked on the screen.
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One of the most embarrasing and distracting events in a workshop is the
occassional backwards and upside down slide. This is entirely avoidable!
The tables should be arranged so that there are enough seats and that
everyone has an adequate view of the screen. Handouts and forms should be
distributed to each seat to save time at the beginning of the workshop and
to ensure that there is no question that there are sufficent copies for
everyone.
The locations of rest rooms and fire escapes should be noted so that the
attendees can be advised at the beginning of the workshop. It is also helpful
to identify a phone which can be used for messages.
2.4 Conducting the Workshop - The workshop coordinator sets the tone for
the workshop in the initial remarks. The participation of all the attendees
should be encouraged since often they have valuable experience with is relevant
to the specific plants in the area. Their comments liven up the program and
supplement the technical material in this manual. An informal attitude is gen-
erally effective in encouraging active participation.
Under no circumstances should the information simply be read from the
manual. This defeats the basic objective of this manual which is to free both
the speaker and the attendees from having to cover each detailed point. Any
attendee who is truly interested in the topic can read the manual carefully
after (or before) the program. This manual simply provides a skeleton over
which the speaker and attendees can discuss issues relevent to their area.
Occassional breaks are built into the program. These are necessary to
allow everyone to stretch and to allow the speaker's voice to rest briefly.
Also, these periods provide some of the most useful informal discussions
concerning the lecture material.
At the end of the workshop, a critique form should be handed out to all of
the participants (including the coordinator). It should be filled out before
everyone leaves since few will ever return it otherwise. The coordinator should
carefully review the comments to determine ways to improve future programs and
ways to assist the participants in getting the resources necessary to implement
the techniques discussed. The latter point is especially important since the
workshop is intended to be of DIRECT AND IMMEDIATE BENEFIT TO FIELD INSPECTORS.
In many cases, they will not have the time or equipment necessary to perform
these inspections. Presumably, they will be receiving these soon or there was
no sense in presenting the program in the first place! The critiques help to
determine just what is necessary to begin implementing the program. A sample
critique form is included in Appendix B.
One conunon misunderstanding regarding critiques is that they are intended
to rate the capability of the speaker or to rate the value of the program.
Actually, the value of the program can not be judged until the participants
have had an opportunity to try the techniques in the field for six months to a
year. The speaker's performance should be just one element of a successful
workshop. The very successful workshops are those in which the speaker simply
guides the discussion. The attendees should do most of the talking. Remember,
this is not a training course! A workshop is a meeting of professionals
discussing and refining their technical procedures.
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3.0 Typical Agenda
A typical agenda for a two-day program is presented on the next two pages.
As discussed above, this should be used as a starting point in the development
of a program for the specific audience. A copy of the program agenda to be
used should be given to all participants before the start of the program.
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WET SCRUBBER SYSTEM INSPECTION WORKSHOP
Sample Agenda
Time Lecture
8:30 a.m. Welcome and Introduction
8:45 a.m. 1. Introduction to Wet Scrubber Systems
A. System Components
B. Flowcharting Techniques
C. Review Problems and Questions
10:15 Break
10:30 2. Baseline Inspection Techniques
A. Basic Principles
B. Comparison of Baseline Data with Inspection Data
C. Review Problems and Questions
12:00 Lunch
1:00 3. Visible Emission Observation
A. Expanded Method 9 Procedures
B. Reentrainment
C. Odor Surveys
D. Review Problems and Questions
1:45 4. Evaluation of On-Site Instruments and Use of Portable Gauges
A. Static Pressure Gauges
, B. Temperature Monitors
2:30 Break
2:45 4. (Continued)
C. Oxygen and Carbon Dioxide Analyzers
D. pH Meters and Indicator Paper
E. Gas Flow Measurement
F. Fan Speed and Motor Currents
G. Pump Motor Currents
H. Liquid Pressures
I. Liquid Flow Rates
J. Other Instruments
K. Recommended Port Designs
4:30 Adjourn
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WET SCRUBBER SYSTEM INSPECTION WORKSHOP
Sample Agenda (Continued)
Day 2
Time Lecture
8:30 5. Evaluation of Wet Scrubber System Components
A. Demisters
B. Pumps
C. Piping
D. Nozzles
E. Fans
F. Materials of Construction
G. Review Problems and Questions
10:30 Break
10:45 6. Liquor Analyses
11:15 7. Particulate Wet Scrubbers
A. Particle Size
B. Pressure Drop
12:00 Lunch
1:00 7. (Continued)
C. Spray Tower Scrubbers
D. Packed Tower Scrubbers
E. Moving Bed Scrubbers
F. Tray Scrubbers
G. Mechanically Aided Scrubbers
H. Venturi and Other Gas-Atomized Scrubbers
I. Review Problems and Questions
2:00 . Break
2:15 8. Gas and Odor Scrubbers
A. HC1 and Chlorine Scrubbers
B. Fluoride and SiF4 Scrubbers
C. Hypochorite and Permanganate Odor Scrubbers
3:15 9. Inspection Safety
A. Walking and Climbing Hazards
B. Explosion Hazards
C. Burn Hazards
D. Eye Hazards
E. Heat and Cold Stress
F. Inhalation Hazards
G. Review Problems and Questions
4:15 Summary and Critique
4:30 Adjourn
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INTRODUCTION
TO
WET SCRUBER SYSTEM
INSPECTION
SLIDE 1-1
INSPECTION OF
WET SCRUBBER SYSTEMS
This workshop concerns particulate and
gaseous scrubbers. The program begins
with a summary of the major differences
between wet scrubber systems and other
types of control devices. Some of the
common components are introduced and all
major definitions are presented.
The lecture which follows concerns the
Baseline Inspection Technique. The
approach for wet scrubber systems is
conceptually similar to that for other
control devices. However, there are
some important differences in emphasis.
There are certain inspection procedures common to all types of scrubber
systems. These common operations are grouped together in one major lecture
which includes: the use of portable instrumentation, the evaluation of visible
emissions, the evaluation of reentrainment, the inspection of pumps, nozzle
inspection, and the evaluation of the piping system.
Specific inspection procedures are presented for each major class of
particulate and gaseous scrubbers. This material emphasizes the problems which
are most common for these types of units.
Lecturer's Notes
This slide and written material is intended to provide a brief overview
of the workshop. It is important at this stage of the program to survey the
experience of the audience and adjust the level of the technical discussions
accordingly. The initial lecture is for persons with only limited experience
with scrubber systems. Some of the material concerning portable instrumenta-
tion and scrubber evaluations is intended primarily for experienced personnel.
The safety considerations are very important for all attendees, and should not
be abbreviated under any circumstances.
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SLIDE 1-2
COMPONENTS
Fan
Filter
Clarifier
Demister
Gas Cooler
Scrubber Vessel
Recirculation Tank
Recirculation Pump
Bypass Ducts and Dampers
Alkaline Additive System
Purge and Make-up Systems
Scrubber Instruments
A scrubber is not an isolated piece of
equipment. It is a SYSTEM comprised of
a large number of individual components.
This single point is the most important
fact to be presented in this first
lecture. It distinguishes scrubbers
from other types of air pollution con-
trol devices.
Many of the scrubber performance prob-
lems originate with deficiencies with
the components rather than errors in the
design and operation of the scrubber
vessel itself. This means that the
operation of each system component must
be understood and that each inspection
will involve a number of inspection
points.
union *nnc ntEsaxc • o'
SLIDE 1-3
A logical starting, point in the
evaluation of a wet scrubber SYSTEM
is to determine the orientation of
the scrubber vessel with respect to
the fan which moves the gas stream.
If the fan is downstream from the
scrubber vessel, the ductwork leading
to the scrubber and the scrubber vessel
itself are under negative pressure.
This simply means that the gas pressure
inside is lower than the atmospheric
pressure. The small circles contain
typical static pressures at the scrubber
outlet and the beginning of the duct-
work. The static pressures become more
negative as the gas approaches the fan.
Wet scrubber systems operate at much greater negative pressures than any
other type of air pollution control system. It is common for the scrubber
outlet static pressure to be in the range of -25 to -60 inches of water. There
are a few units operating in the range of -100 to -150 inches of water.
Lecturer's Notes
The term "static pressure" may be unfamiliar to some of the attendees. If
so, it should be stated that this is simply the pressure of the gas at rest or
measured in a direction normal to the flow direction. It may also be necessary
to compare "inches of water" to "pounds per square inch". One pound per square
inch (psi) equals approximately 27.7 inches of water.
The concept of "negative pressure" is very difficult for some who see this
as a contradiction in terms. It should be stressed that negative pressures are
lower than ambient pressure but nevertheless real gas pressures.
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SLIDE 1-4
COLD STACK
REcmc.
PUMPS TANR
FAN
When the static pressure in the scrubber
system is negative, there is a tendency
for air to infiltrate the system. This
can reduce the amount of gas pulled from
the process source and can cause local-
ized gas-liquor distribution problems in
the scrubber. Both conditions can lead
to significantly increased emissions
from the system.
Points of entry are shown on this slide.
Since the static pressures are more
negative on the discharge side of the
scrubber and at the fan inlet, these
areas are common sites of infiltration.
It is also important to maintain a
water seal at the scrubber sump equal
to or greater than the static pressure
to prevent air infiltration here.
SLIDE 1-5
The fan can be located upstream of the
scrubber vessel, thereby placing the
entire scrubber and connecting ductwork
under positive pressure. Typical
static pressure values are shown on
this slide. Note that the static
pressures become progressively smaller
as the gas passes through the scrubber
vessel and out the ductwork to the
stack.
( Since the gas pressures inside are
higher than ambient pressures, there is
a tendency for gas to leak out. These
gases can be quite dangerous if there
are poorly ventilated areas around the
scrubber and ductwork.
The health hazards which can exist around positive pressure scrubber
systems should not be underestimated. Wet scrubber systems tend to operate at
higher positive pressures than any other type of control system. This combined
with corrosion and erosion problems makes gas leakage very possible. Often
wet scrubbers are placed indoors to minimize freezing problems, and this con-
tainment structure reduces natural ventilation. Field inspectors should have
proper safety equipment and should not enter areas with anticipated high
pollutant concentrations.
Lecturer's Notes
The gas leakage problem should be stressed here and be reiterated during
the safety lecture. It may be useful to point out that some scrubbers handling
toxic gases can operate as high as +200 inches of water!
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SLIDE 1-6
TO
STACK
PROCESS
SOURCE
FAN
SCRUBBER
VESSEL
FAN
Another gas flow arrangement has fans
both before and after the scrubber
vessel. This is termed a "push-pull"
arrangement.
This type of system usually results
from the upgrading of a scrubber
beyond the capability of an existing
fan. The additional fan provides
greater static pressures for the
modified system.
As before, the static pressures decrease
progressively from the discharge of the
one fan to the inlet of the other. This
arrangement has no adverse impact on the
scrubber performance.
SLIDE 1-7
It is common to include a bypass stack
ahead of the scrubber vessel. This can
be opened in the event of a sudden
process upset or the need for scrubber
maintenance while the process remains
in operation.
The draft created by the stack is
usually sufficient to exhaust the
process equipment during the interim.
Therefore, it is rare to have a fan on
the bypass stack.
Corrosion of the bypass damper can lead
to some unintentional leakage of un-
treated gas out the bypass stack. This
will not have the characteristic steam
plume since the water vapor content at
this point of the system is low.
On negative pressure systems as shown here, there can be some infiltration
of ambient air down the bypass stack if (1) the negative pressure in the duct
is lower than the draft created by the stack, and (2) there is leakage of the
bypass damper. Methods of checking for both untreated gas release and air
infiltration are included in the inspection procedures discussed later.
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I
PftCSATURATOft
UQWO ftCQItCULATOM
SLIDE 1-8
Many sources served by wet scrubbers
have very hot gas temperatures. It
is not prudent to expose the scrubber
vessel itself to these temperatures
since this could damage the protective
liners on the scrubber walls. The evap-
oration of droplets exposed to high
temperature also makes the droplet less
likely to capture a particle. Therefore,
scrubber performance is reduced.
Cooling of high temperature gas streams
is done almost exclusively by spraying
water into the gas stream. Unlike
fabric filters, dilution and radiant
cooling tubes are not common.
The gas cooling can be done in a specially designed evaporative cooler or
in a small presaturator attached to the scrubber vessel. This slide shows a
small presaturator ahead of the scrubber. Note that separate liquor lines are
shown for the scrubber and the presaturator since the source of liquor is often
different.
SLIDE 1-9 An evaporative cooler is shown in this
slide. It can be a simple spray cham-
ber with low pressure nozzles or a
large cylindrical chamber having a set
of high pressure nozzles near the top.
Some of the water sprayed into the cham-
ber evaporates, thereby cooling the gas
stream. The remainder of the water
drains from the bottom. Specially de-
signed evaporative coolers with high
pressure nozzles often achieve 70 to 95%
water evaporation.
The quality of water used in gas coolers
is critical to both the evaporative
cooler and to the overall scrubber sys-
tem. This is an important inspection
step.
Once the gas stream temperature has been reduced, material which has been
in the vapor state begins to condense to form particulate matter. The particle
size range of the resulting material depends on the quantity of material con-
densed and on the manner of condensation. The water vapor injected into the
gas stream may also begin to condense on the surfaces of particles in the gas
stream. Both of these phenomenon favor improved collection efficiency.
Lecturer's Notes
One of the major differences between wet scrubber systems and other types
of air pollution control systems is that the particulate matter characteristics
can change drastically while passing through the system. Such changes have a
large effect on pollutant removal efficiencies.
(aft
cw
TT*
©-
PROCESS
SOURCE
gVAPORATIve
COOLER
OMAIN
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SLIDE 1-10
Centrifugal fans are used to move the
gas stream through the wet scrubber
system. There are two major types in
service: (1) radial blade fans, and
(2) backward curved fans. The latter
are more prone to build-up of solids on
the blades and, therefore, require more
maintenance.
The inspection procedures will use some
of the fan operating data such as the
fan motor currents. For this reason, it
will be important to have a general
understanding of fan curves and system
resistance curves. It will become
apparent that fan curves have similar-
ites with centrifugal pump curves.
The gas flow rate delivered by the fan is primarily controlled by the
dampers before or after the fan. During start-up it is common practice to keep
the dampers partially closed to minimize the initial fan motor load.
DAMPCR
SLIDE 1-11
The last major component of the gas
handling equipment is the stack. Unlike
large fabric filter and electrostatic
precipitator systems, there are no
transmissometers used on wet scrubber
stacks. This is because the water
droplets which invariably condense in
the gas stream scatter light very
effectively. Transmissometers can not
distinguish between the scattering due
to particles and that due to droplets.
The only visible emissions data which
can be used in the inspection technique
is that which is obtained by stack ob-
servation. No continuously recorded
data is available.
The water droplets which preclude the use of transmissometers also can
complicate the manual observations. Field inspectors must be trained in the
proper procedures for observing wet scrubber plumes. Some of the important
points are summarized in a later lecture.
Lecturer's Notes
The frequent lack of adequate visible emissions data forces greater
emphasis on measurable scrubber operating parameters. This is one of the major
differences between wet scrubber inspections and the inspection of other air
pollution control systems.
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f MS, 50,000 ACFM
9,,OV
SAS-
SLIDE 1-12
The next set of slides concerns the
liquor recirculation system. There are
two basic arrangements: (1) the once
9invi ^^^ through system, and (2) the recircula-
tion system. Obviously, the once
through system is easier to inspect due
to the relative simplicity of the flow
pattern.
This slide illustrates the once through
flow arrangement. The scrubber liquor
is drawn from a process water source or
municipal supply. It is drained into a
sewer or other treatment unit for final
disposal.
The main advantage of this approach is that solids and corrosive materials
do not gradually accumulate to harmful levels. This reduces the pump, nozzle
and scrubber vessel erosion and corrosion problems. Absorption of some gases
is also favored. However, the large majority of these systems have been con-
verted to recirculation systems to reduce water useage and to reduce waste-
water treatment costs.
LIOUOH TO
TRC«TU€NT AND
DISPOSAL
SAS f '
30,000 ACFM
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.'he heart of the recirculation system
.3 the recirculation pump. Centrifugal
pumps are used exclusively for this
service because they are capable of
of supplying high liquor flow rates at
moderate to high pressures. The pump
must not only provide the necessary
liquor pressures at the scrubber inlet;
it must also lift the liquor back up to
the elevation of the inlet.
The pump must be carefully chosen to
provide desired flow rates and pressures
for the actual system present.
During the inspection, the pump operating data will provide indirect
indications of the liquor flow rate. This is important since the flow rate
monitors are rarely present. The operating condition of the pump should be
observed briefly to confirm that there are no emerging problems.
SLIDE 1-15
There is more to the wet scrubber
piping system than simply connecting
point A to point B. The pipe must be
sized properly to get the desired system
resistance. The materials of construc-
tion should be selected so that the
pipes will withstand the corrosive,
erosive and settling characteristics of
the liquor.
The piping arrangement must allow for
complete draining of the lines during
off-line winter conditions. There must
also be provisions for the flushing of
solids from the pipes on a routine
basis.
The pipes must be supported in a manner that places no loads on the
recirculation pump. The valves should be selected so that water hammer is
also not transmitted back to the pump. The pump suction line should be sloped
to prevent gas pockets and to provide adequate suction head at the pump. In
short, the piping should not be an afterthought in the design and installation
of a scrubber system.
-------
SLIDE 1-16
Any scrubber composed of carbon steel
must operate at pH levels above 5 and
preferably above 5.5. Scrubbers being
used for odor control often operate
between ph levels of 8 to 10 in order to
maximize absorption.
To maintain the pH in the desired range,
it is necessary to add a neutralizing
agent. Materials in common use include
soda ash, lime, and limestone. These
can be added either on an intermittant
basis by dumping bags into the recircu-
lation tank, or on a continuous basis as
shown in the slide.
The continuous addition systems are more complicated. However, they do
not suffer the frequent large swings in pH common to those with intermittant
addition. The rate of addition is generally controlled by a pH meter located
in the recirculation tank or similar location.
Lecturer's Notes
Obviously when evaluating the liquor pH, it is important to know both
where the sample was taken and when it was taken. The pH can be a highly
variable parameter in wet scrubber systems. The importance of documenting
time and location will be a common theme of later discussions of wet scrubber
operating parameters.
SLIDE 1-17
,.-e nozzles and liquor distribution
headers are critical to all scrubber
designs. Pluggage of even a small
fraction of the nozzles leads to very
poor gas-liquor distribution.
There are a wide variety of commercially
available nozzles. The nozzle model
must first match the suspended solids
levels expected in the scrubber system.
Certain types are appropriate only for
clean liquors.
""*' The arrangement of nozzles must take
Into account the spray angle and spray
uattern of the specific nozzle.
While the nozzles are the sme.ll.-=" individual component used in a wet
scrubber system, they are normally responsible for a large share of the
unscheduled maintenance effort. The small clearances through many nozzle
designs makes then especially prone to pluggage even at solids levels which
do not affect control valves and pipes. The high velocities at the nozzle
orifice can result in rapid erosion.
19
-------
LIQUOR TREATMENT SYSTEMS
Clarifiers with Vacuum Filters
Settling Ponds
SLIDE 1-18
Wastewater treatment facilities range
from very simple ponds to elaborate
clarifier-vacumn filtration plants.
Obviously, only the very large scrubber
systems have the latter type of fac-
ilities. All of these, however, share
the common purpose of reduction in the
liquor solids content.
The clarifier (sometimes called a sed-
imentation tank) is simply a large tank
where the suspended solids can settle
to the bottom. The accumulated sludge
is continuously removed from the bottom.
A rotary vacuum filter is used to remove
the suspended solids from the calrifer
underflow. The clarified effluent is
removed from the top of the clarifier.
Often the settling characteristics of the suspended solids can be improv-
ed by the addition of flocculation agents. These cause the fine particles to
agglomerate together and thus increase the settling rate. Unfortunately, the
flocculants may have an adverse impact on the liquor surface tension.
Lecturer's Notes
It is an unfortunate fact that steps taken to optimize the performance
of one of the wet scrubber system components can have an harmful affect on
another component. In this case, the increased surface tension with certain
flocculants can change spray droplet size and decrease particle capture for a
given size droplet. Both changes can affect particulate removal. A number of
trade-offs must be made by a well informed operator in order to achieve
optimum performance of the overall system.
SLIDE 1-19
Ponds are the simplest type of liquor
treatment system. They can range from
very small, single zone ponds to quite
large, multi-zoned settling basins.
The test of pond performance is the
ability to deliver relatively clean
liquor back to the scrubber system over
a long time period. One means to im-
prove performance is the use of several
zones each separated by an overflow
weir. There should also be an easy way
to remove the solids from the first and
second zones on a regular basis.
20
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INSTRUMENTATION
GAS STREAM MONITORS
A. Thermocouples
B. Pressure Drop Gauges
C. Fan Motor Current
LIQUID STREAM MONITORS
A. pH Meters
B. Pump Discharge Pressure
C. Pump Motor Current
D. Pipe Pressures
E. Flow Rate Monitors
SLIDE 1-20 This slide lists the types of instrumen-
tation available on wet scrubber systems.
Some of these are used to control system
operation and some are intended to pro-
vide general indications of performance
for the operator.
All instruments used on wet scrubber
systems are subject to pluggage,
2. LIQUID STREAM MONITORS erosion and corrosion. Conscientious
maintenance is often not sufficient to
keep all instruments in proper working
order. Therefore, the process control
instruments should always be included
on an initial list of possible culprits
responsible for performance problems.
Also, the indicated data for scrubber
instruments always deserves scrutiny.
The more advanced forms of the inspection procedures will utilize some
portable instruments. They are necessary to overcome the limitations of the
permanently mounted instruments and they are also helpful when the necessary
gauges are not available. Measurement ports are necessary.
Lecturer's Notes
The attendees need to understand that it is very difficult to keep wet
scrubber instrumentation working and they should not be too quick in accusing
plant operators of inadequate maintenance of the instruments. While this may
sometimes be the case, more often it is due simply to the tendencies for
pluggage, erosion and corrosion. In other words, field inspectors need to be
sympathetic to occassional instrument malfunctions. Material presented later
will address some of the steps which can be taken to minimize failure.
SLIDE 1-21
Source: Air Pollution
Training Institute
There are several distinct types of
demisters in common service. All of
these are intended to remove the very
large (100 to 800 micron diameter)
droplets formed in the scrubber.
The type shown in this slide can be
placed in the upper sections of
cylindrical scrubbers. The gas stream
passes through the demister at super-
ficial velocities in the range of 5 to
20 feet per second. The droplets which
impact on the demisters simply drain
back into the scrubber.
The chevron demisters force the gas stream to make several quick turns
which the large droplets can not negotiate. These come in numerous blade
designs and with 2, 3, and 4 passes. Mesh pads (not shown) operate in the same
manner as household furnace filters with the fibers serving as impaction targets.
Both styles of demisters must be cleaned regularily to prevent the accumulation
of solids on the surfaces.
21
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SLIDE 1-22
Other styles of demisters are shown in
this slide. Both of these take advan-
SIOE ELEVATION =_ ^^ PLAN VIEW tage of a spinning gas stream which
x \ x—~~"\ results in the impaction of the large
'ouacr droplets on the demister wall. These
types of units are commonly included
with venturi scrubbers.
On positive pressure units, the stack
sampling ports are directly above this
demister. Provisions must be made to
eliminate the cyclonic flow in the
stack so that pitot traverses and stack
sampling procedures can be conducted.
Generally the type of demister used is determined by the configuration of
the scrubber vessel. The demisters shown in the last two slides serve differ-
ent applications and are not competitive approaches.
Lecturer's Notes
The removal of 100 to 800 micron droplets may seem simple. However, this
is one of the most common sources of trouble in some systems. The consequences
of improper demister performance include rainout of particulate laden droplets
close to the stack and the accumulation of material on downstream fans.
SLIDE 1-23
The most common scrubber designs will
be addressed in the program. It is
important to be able to recognize the
TYPE OF SCRUBBER VESSELS advantages and limitations of each
during the inspection. Specific in-
p' DA^I7^/ERS spection procedures have been prepared
D. HACKED BEOS j_ £ . ._i_ ._ j r
C MOVING BEDS ocus in on the most common modes of
D. MECHANICALLY AIDED failure of each type.
E. ORIFICE
F. VENTURI The list provided is far from complete.
G. TRAY TOWER There are a number of innovative
designs which have been commercially
introduced in the last five years.
There are also a number of variations
of the listed types, each having unique
design features. The inspection techni-
ques for these modified and new designs
will have to be developed by each in-
spector based partially on the proced-
ures presented in this program.
Lecturer's Notes
The terminology in the wet scrubber industry is not standardized. These
titles could differ from those familiar to some of the attendees. Also, the
manner in which scrubbers are grouped can vary. These categories are conven-
ient for this program since the inspection procedures are distinctly different
for each of the categories listed.
22
-------
Clean gas
SLIDE 1-24
A spray tower scrubber is illustrated
in this slide. This is the simplest
type of unit and it has only a limited
particulate removal capability. It is
selected for applications where there is
not much particulate matter smaller than
5 microns. It can also be used in some
gas absorption systems.
The gas stream enters near the bottom
and flows upward at velocities between
2 and 5 feet per second. The liquor
enters at the top. Therefore, the flow
is in the countercurrent direction
relative to the gas stream. Liquor
distribution is entirely controlled by
the types of nozzles, the nozzle spray
angle, the nozzle placements and the
liquor pressure.
Most of these systems are relatively simple. However, alkaline addition
equipment is sometimes necessary. The instrumentation is usually very limited
and this complicates the inspection procedures.
MiK eliminator
SLIDE 1-25
Packed bed scrubbers are primarily in-
tended for gas absorption. The large
liquor surface area created as the
liquor gradually passes over the pack-
ing material favors gas diffusion and
absorption. These are not effective
for particulate removal since the low
gas velocities do not result in much
paticulate impaction on water droplets.
The gas stream again enters from the
bottom and passes upward through one or
more beds. The liquor is sprayed on
the top and flows downward. Liquor
distribution is important for high
efficiency removal of gases.
One of the major problems with these scrubbers is the accumulation of
solids at the entry to the bottom bed and within the beds. The dissolved
soilds and suspended solids levels in the liquor must be monitored carefully.
It is difficult to routinely remove these solids due to the characteristics of
the packing materials.
!•'.*• Dirty gu
23
-------
SLIBF 1-26
Clean ga*
Mist eliminator
Dirty gu
Moving beds have entirely different
characteristics than packed beds.
They have moderate to high particulate
removal capability due to the formation
of fine droplets within each bed and
the relatively high gas velocities.
Both of these factors favor particle
impaction. The high liquor surface
area created also makes these units
acceptable for gas absorption. The
turbulent action of the packing pro-
vides a self cleaning characteristic.
Therefore, pluggage is not an issue.
These were originally developed by the
primary aluminum industry which needed
to remove sticky organic particles and
hydrogen fluoride gas.
The most common version of moving bed scrubbers has several "beds" partially
full of hollow balls which closely resemble ping pong balls. The packing
moves violently due to the combined action of the rising gas stream and the
falling liquid. Water droplets formed in the turbulent bed serve as the
particle impaction targets and as the gas absorption surface.
Lecturer's Notes
One common trade name for this style of scrubber is the Turbulent Contact
Absorber, or TCA for short. It is also called simply a "Ping Pong Ball Scrub-
ber." Marble bed scrubbers are sometimes classified as a moving bed since the
packing is free to move. However, the performance characteristics are more
like the packed bed than the TCA shown above.
SLIDE 1-27
Source: Air Pollution
Training Institut
One common type of mechanically aided
scrubber is illustrated in this slide.
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.
24
-------
Liquid
MUt eliminator
Liquid inlet
Plate or tr»y
SLIDE 1-28
A tray tower scrubber can be used for
both particulate and gaseous removal.
However, the most common applications
are for particulate control. It con-
sists 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.
A chevron or mesh pad demister is placed
above the elevation of the liquor inlet.
This collects any droplets entrained
from the top tray of the scrubber.
Two of the major tray designs are
shown in this slide. 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 is that there are several opport-
unities to collect pollutants. Slight gas-liquor distribution problems on one
tray can be tolerated since the material can be caught on subsequent trays.
The liquor quality is again important since it is easy for the holes to plug.
BLIDE 1-29
The orifice scrubber is one of a large
number of units which is classified as a
gas atomized scrubber. This means that
the droplets which serve as impaction
targets are formed in high velocity gas
streams.
In this case, the gas enters the vert-
ical tube and makes a 180° turn just
above the surface of the liquor. The
action of the gas stream atomizes the
liquor which was entrained by the
passing gas stream. Baffles included in
the scrubber "box" knock down any drops
which remain suspended in the gas.
They are usually very small scrubbers. The system can be exceedingly
simple since it is not absolutely necessary to have a recirculation pump and
piping system. In a sense, everything is self contained in the scrubber vessel.
The inspection of these units is often complicated by the almost complete lack
of instrumentation.
25
-------
SLIDE 1-30 A classic style of a venturi scrubber
is shown here. The gas stream enters
the converging section and is acceler-
ated by approximately a factor of ten
above normal duct velocities. 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
some gas absorption.
The gas stream is decelerated in the diverging section. In early designs,
the diverging section was long and had a small angle in order to reconvert some
of the gas stream kinetic energy back to potential energy (pressure recovery).
Most of the units in present use have a very short diverging section and angles
approaching 25°. There is only limited pressure recovery with these units.
After the venturi section, the gas stream turns 90° and passes into the
demister chamber. The venturi scrubbers usually are part of a large and
relatively complex scrubber system. Waste water treatment systems, alkaline
addition equipment and presaturators are common.
Lecturer's Notes
The feature which makes the venturi so effective is also its Achilles
Heel. The very high gas velocities of 20,000 to 40,000 feet per minute at the
throat entry provide excellent impaction conditions. However, the gas stream
quickly exits the throat and decelerates. Very little particle removal occurs
after the gas stream leaves the throat. If the gas-liquor distribution is not
proper at the throat entry, the scrubber effectiveness will be compromised.
SLIDE 1-31
LIQUOR INLET
THROAT DAMPERS
There are a large number of variations
to the standard venturi configuration.
This slide shows dampers mounted on both
sides of a rectangular throat. These
can be partially closed to reduce the
throat area. At a constant gas flow
rate, the reduced throat area results in
higher gas velocities. The improved
particulate removal efficiency is
obtained at the expense of higher static
pressure drops across the throat.
The position and physical condition of
the dampers can not generally be con-
firmed by external checks and there is
no way to see inside while the unit is
operating. These must be checked when
the unit is down, however, since the
dampers are subject to extreme abrasion.
26
-------
Source: Air Pollution
Training Institute
Another common style of venturi scrubber
is shown in this slide. Instead of a
"venturi" assembly, this scrubber uses a
horizontal deck of rods. The restricted
area between the rods accelerates the
gas stream and provides a zone for drop-
let atomization. The "throat" has
almost negligible length. The numbers
or diameters of the rods can be varied
as necessary to achieve the desired gas
velocities.
The inspection procedure for this style
of scrubber is very similar to that for
the classical venturi units. The only
difference is that there is concern with
rod erosion and corrosion in this design.
Unlike classicl venturi scrubbers, these units can be arranged to have
several decks in series. This multiple deck arrangement is used most commonly
when the scrubber's primary purpose is gas absorption rather than particulate
control. In gas absorption units, the gas velocities between the rods is lower
than it is in particulate scrubbers.
Lecturer's Notes
These "Rod Deck" scrubbers are mentioned because of the growing use for
both particulate and gaseous control applications. Some of the particulate
systems can be quite small and serve applications in which historically the
"venturi" has not been competitive. Large units are used for utility scale
flue gas desulfurization.
SLIDE 1-33 The first portion of this lecture has
concerned the typical components of a
wet scrubber system and a brief intro-
duction to the most common types of
TERMS AND DEFINITIONS scrubber vessels. Basic functions of
each of these must be understood before
proceeding with this program.
It is equally important that all of
major terms used in the program are
defined. Unfortunately, there is some
inconsistency in the wet scrubber lit-
erature terminology. The next set of
slides discusses these terms.
Lecturer's Notes
Up to this point, the material has been introductory in nature and could
be skipped when the attendees are experienced with scrubber systems. It is
advisable, however, to go over the next few slides so that everyone will under-
stand the meaning of the terms used later in the program manual. It should be
noted that the definitions used here are not represented as being the best or
most commonly used definitions. They are simply the meanings intended by the
author of this manual.
27
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SLIDE 1-34
STATIC PRESSURE DROP
Pressure drop is sometimes used as a
measure of the amount of energy consumed
in the scrubber. This is supposedly
related to the overall effectiveness of
the scrubber for particulate removal.
The fact that the correlation seems to make sense sometimes does not alter
the fact that pressure drop versus collection efficiency alone is not a measure
of energy use. In fact, the energy consumption is related to the TOTAL PRESSURE
DROP divided by the AVERAGE GAS DENSITY. The STATIC PRESSURE DROP (which is
what is implicitly meant by "pressure drop") is just one component of the TOTAL
PRESSURE. The other is the VELOCITY PRESSURE. It is also important to specify
the locations between which the pressure drop is measured. In this report the
term "pressure drop" will mean the difference in static pressures measured at
two specified locations.
Lecturer's Notes
The sloppy use of the term "pressure drop" can be a serious problem. If
there is some confusion on the part of the attendees, the definitions of static,
velocity, and total pressure should be provided. It may also be helpful to
introduce Bernoulli's Equation at this time for the more experienced groups.
This will be used later in the program.
SLIDE 1-35
A term as simple as particle diameter
can be confusing. The meaning of the
PARTICLE SIZE term depends on the way in which the
material was obtained and anaylzed.
, In this manual, the diameter specified
is the aerodynamic diameter. This is
the diameter of a unit density (same
specific gravity as water) sphere having
the same aerodynamic properties as an
actual particle.
What this means is that the actual particle behaved in a sampling device
in a manner which is identical to a known size test aerosol. The factors which
affect the motion of a particle in a gas stream also affect the aerodynamic
diameter. They include actual diameter, actual density, and particle shape.
Lecturer's Notes
It should be noted that the particle size distribution that would be
derived from microscopic analyses may differ from that determined from a
cascade impactor. Since almost all size data is obtained by cascade
impactors, and since this directly yields an aerodynamic diameter, this term is
the easiest to use despite the cumbersome units.
23
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SLIDE 1-36
INLET LIQUOR
A, 6PM
LIQUIO-TO-GAS
RATIO
A/(Y/IOOO)
OUTLET LIQUOR
B, GPM
The liquid-to gas ratio is illustrated
here. In this manual, the term means
the total gas flow rate in actual cubic
feet per minute divided by the liquor
flow rate introduced at the scrubber
vessel only. It does not include liquor
or make up water sprayed in evaporative
coolers, or water use to flush
demisters.
The outlet gas flow rate is used as the
basis for the definition since this is
the easiest to measure. Stack sampling
ports are usually available for this
purpose. Also, the outlet gas flow rate
is less subject to change due to temp-
erature fluctuations.
SLIDE 1-37
Erosion is the physical removal of a
surface caused by impacting particles.
Corrosion is the chemical and electro-
__„ chemical removal of surfaces.
EROSION/CORROSION
While these are distinctly different
phenomenon, there is some interaction
between the two. Surfaces which have
been eroded are more susceptible to
corrosion. Surfaces which have corrod-
ed are more susceptible to erosion. The
term "erosion/corrosion" is used fre-
quently to refer to the combined action
of both. This is a logical approach
since it is often impossible to deter-
mine which is most significant or which
occurred first.
Erosion and corrosion present more problems for wet scrubber systems than
for any other type of air pollution control system. One of the reasons is that
there are a number of localized areas in the wet scrubber system which have
high liquor and gas velocities. The suspended particulate in both streams
becomes highly erosive at high velocities. Corrosion is promoted by the moist
surfaces.
29
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30
-------
cw V
EVAPORATIVE
COOLER
INLET—-
GAS
OUTLET
GAS
VENTURI SCRUBBER
WITH CYCLONIC
DEMISTER
CAUSTIC
STORAGE
PURGE—
RECIRCULATION
PUMP
RECIRCULATION
TANK
SLIDE 1-38
PREPARATION OF FLOWCHARTS
FOR
WET SCRUBBER SYSTEMS
Flowcharts are absolutely necessary for
a detailed and effective inspection of
a wet scrubber system.
The locations of all measurement ports
and instruments should be shown along
with the sources of all liquid streams.
Bypass vents and stacks should also be
marked.
The flowchart should not be cluttered with unnecessary detail. Also, it
should be remembered that a flowchart is not judged on the basis of artistic
merit, but rather the insight it provides to an inspector trying to evaluate a
change in system operating conditions.
Symbols and drawing conventions presented in the next set of slides have
been taken from the Chemical Engineering literature and from standards pre-
sented by the Instrument Society of America. However, some license has been
taken in order to compile a set of symbols specifically for inspectors of air
pollution control equipment. Each field inspector is invited to make further
changes as they see fit.
31
-------
FIXED THROAT
VENTURI
i
FLOODED DISK
ADJUSTABLE
THFtoAT
VENTURI
CYCLONIC
DEMISTER
i
QQQQQ
\
ROD DECK
MESH PAD DEMISTER
CHEVRON DEMISTER
32
-------
SLIDE 1-39
The first step in the procedure is to
••" adopt a convention for liquid and
gaseous streams. The line types shown
in this slide have been arbitrarily
chosen for this purpose.
Note that the pipe sizes can be easily
shown on the solid lines. The size
data shown is the actual diameter
(approximate data is sufficient) rather
than the specific pipe size. The dotted
lines for the pollutant laden gas
streams can also be interrupted to show
the approximate size of the ducts. This
data helps to identify ducts and pipes
while comparing the flowchart to the
actual system.
It is usually best not to show steam lines and other material transfer
lines not directly related to the scrubber operation. It is difficult enough
simply trying to understand some of the complicated and often modified
systems. Extraneous material is not helpful.
SLIDE 1-40
The type of scrubber vessel and
^_ demister should be indicated using the
figures on the opposite and next pages.
Note that these provide just enough
information to indicate the type of unit
but do not require extensive drawing.
The points at which the various gas and
liquid streams enter and exit the unit
should be shown. The directions of
flow are indicated by arrows.
With this part of" the flowchart, it
should be possible to get a conceptual
idea of how the unit is working.
With the number of innovative systems now entering the v/et scrubber
market, there will soon be a need to develop additional symbols. Remember that
consistency and logic are necessary when it comes to flowcharts.
VPINGEMENT
33
-------
SPRAY
CHAMBER
I-
SIEVE
PLATE
PACKED
BED ,
IMPINGEMENT
PLATE
0° O
MOVING
BED
MECHANICALLY
AIDED
34
-------
SLIDE 1-41
This is an example of a wet scrubber
system based on the symbols presented.
The scrubber vessel is an impingment
type tray scrubber and there is a
chevron demister at the top of the unit.
The liquor enters from the top and flows
down to a sump at the bottom of the unit.
While most of the liquor is recirculated,
a purge stream (number 3) is drawn off
for treatment. Fresh water is used for
occassional cleaning of the demister.
The fan is upstream of the scrubber.
Therefore the scrubber vessel and
ductwork from the source are under
positive pressure.
Note that the stack is numbered. It is best to have a consistent number-
ing scheme for each stack and vent rather than relying on the identification
system used at the plant. These are subject to change over time. When making
visible emission observations, the number of the stack specified on this flow-
chart should be recorded along with other identification information.
FROM WASTEWATER
TREATMENT
•TO WASTEWATER
TREATMENT
SLIDE 1-42
I — GAS STF
RECIRCULATED
LIQUOR
INLET GAS
(EXIT
LIQUID
The symbols for process water, city
water, compressed air and other system
utilities are shown in the list below.
The figure to the left shows how these
can be used in a flowchart. Use of
these symbols helps to unclutter the
flowchart.
A - Plant compressed air
IA - Plant instrument quality air
CW - City water
PW - Water from process equipment
BW - Boiler feed water
DW - Distilled water
FG - Fuel gas
FO - Oil
FC - Coal
FW - Wood fuel
HM - Heating medium
HS - High pressure steam
LS - Low pressure steam
SC - Steam condensate
E - Electrically controlled
It should be noted that some of these symbols differ from conventional
flowchart practice. The symbol CW, for example, often stands for cooling
water rather than for city water.
35
-------
SLIDE 1-43
r-
i
STATIC PRESSURE -5*
TEMPERATURE 360-F
T
STATIC PRESSURE -17'
TEMPERATURE 134-F
FLOW RATE 32.OOO ACFM
In some cases, it may be helpful to put
some of the typical operating data on
the flowchart itself. There are two
ways this can be done easily.
The figure to the left shows the data
contained in blocks. A thin indicator
line is used to connect this block to
the appropriate stream line.
This is an adequate approach as long as
the system is relatively simple and the
amount of data listed in small. For
large scrubber systems, this can become
cumbersome and confusing. The approach
shown on the next slide is appropriate
for such systems.
IDE 1-44
V
STREAM
1
2
STATIC PRESSURE
IN. W.C.
-9
-17
TEMPERATURE
•F
360
134
FLOW RATE
ACFM
NO DATA
32.000
The liquid and gas streams in this
flowchart have been assigned numbers
which are enclosed in diamond shaped
boxes. These are connected to the
appropriate streams by thin indicator
lines.
The applicable data for the stream num-
ber is shown below the flowchart in a
tabular format. Considerably more data
can fit into this table than could be
put into the individual data boxes
shown in the previous slide.
36
-------
SLIDE 1-45
Notation for the process and wet
scrubber system instrumentation has
been patterned after standard chemical
enginering symbols. Several additions
and changes were necessary to include
features of importance to scrubber
systems.
The presence of an instrument or an
accessible measurement tap are shown
as a circle. A thin indicator line is
used to connect this symbol to the
appropriate location of the system.
The notation inside presents informa-
tion on the type of instrument.
There are 3 distinct types of codes: those ending in "I" specify that
the unit is an indicating gauge only, those ending in "R" are equipped with
a recorder, and those ending in "T" are simply accessible measurement ports.
The recommended symbols are listed on the opposite page.
The operating range of the instrument can be specified in the indicator
circle along with the instrument symbol. For ports, the inside diameter is
useful information since it determines the type of equipment which is necessary
to seal the port during measurements.
SLIDE 1-46
DP!
a
The use of a line across the diameter of
the instrumentation circle indicates
that the instrument is panel mounted.
The slide to the left has three differ-
ent symbols to illustrate how the line
can be helpful. The first (l-46a) means
that there is a differential pressure
indicator on the the system itself. The
second (l-46b) means that a differential
pressure indicator gauge is on a control
panel somewhere. The third (l-49c) is
more explicit in that the location of
the gauge is stated to be the control
room symbol. CR is a useful symbol for
this.
37
-------
INSTRUMENTATION SYMBOLS
1. TI - Temperature indicator
2. TR - Temperature recorder
3. DPI - Gas stream static pressure drop indicator
4. DRP - Gas stream static pressure drop recorder
(Both upstream and downstream measurement
locations must be indicated for differential
pressure instruments)
5. SPI - Gas stream static pressure indicator
6. SPR - Gas stream static pressure recorder
7. GFI - Gas flow rate indicator
8. GFR - Gas flow rate recorder
9. LFI - Liquid flow rate indicator
10. LFR - Liquid flow rate recorder
11. PI - Liquid pressure indicator
12. PR - Liquid pressure recorder
13. LCI - Liquid level control indicator
14. pH - pH meter
15. RHO - Liquid density meter
16. PWI - Power on indicator liqht
17. MCI - Motor'current indicator
18. MWI - Motor wattage indicator
19. VI - Voltage indicator
20. AI - Current indicator
21. PVI - Primary voltage
22. PCI - Primary current
23. SVI - Secondary voltage
2'4. SCI - Secondary current
25. SPI - Spark rate
26. 02R - Gas stream oxygen recorder
27. COR - Gas stream carbon monoxide recorder
28. GBR - Gas stream combustibles recorder
29. S02R - Gas stream sulfur dioxide recorder
30. OPR - Gas stream opacity recorder
31. AT - Accessible measurement tap
32. ST - Stack sampling ports
33. API - Compressed air pressure indicator
34. IAPI - Instrument air pressure indicator
38
-------
SLIDE 1-47
GAS STREAM
IN SITU INSTRUMENT
[] EXTRATIVE INSTRUMENT
For the few wet scrubber systems having
continuous emission monitors, it is
useful to specify the general type of
instrument. Extractive instruments are
shown as a box removed from the gas
stream and connected by a short dotted
line. The in-situ instruments are
shown straddling the gas stream line.
SLIDE 1-48
4 C5-40
UNLINED
-4- C5-IO-RUBBER
CS-40-RUBBER
Some of the main causes of wet scrubber
system failure are corrosion and ero-
sion. If these problems are likely,
the materials of construction can be
noted on the flowchart.
A four part coding system is proposed
here for identification of the materials
of construction. The first part is the
pipe or duct size in inches. The second
is the basic material. The third is the
thickness (or schedule number in the
case of pipes) and the fourth i,s the
type of coating or liner. Material
codes are presented below and use of
the entire code is illustrated in the
adjacent figure.
CS - Carbon steel (Specify AISI number if known)
SS - Stainless steel (Specify AISI number if known)
FRP - Fiberglass reinforced plastic
PVC - Polyvinyl chloride (Specify type if known)
NAS - Nickel alloy stainless steel (Specify trade name or AISI number)
W - Wood
There are no abbreviations suggested for the liner. The type should
simply be spelled out. The material codes listed above are similar to the
standard chemical engineering symbols. However, some changes have been made,
39
-------
-------
SLIDE 1-49
4*9CH40-CS —
A complete flowchart for a wet scrubber
system is shown in this slide.
It incorporates every major feature
discussed in this section.
Flowcharts similar to that shown are
invaluable when attempting to diagnose
operating problems with a system.
They also help to determine the most
appropriate measurement locations.
Measurement errors and system gauges
which are indicating incorrectly can
often be identified using the
flowchart.
41
-------
LECTURE 1. REVIEW PROBLEMS AND QUESTIONS
It should be clear that the figure represents a tray type scrubber with
a chevron demister. The liquor is recirculated. For simplicity, the
entire scrubber system has not been shown.
1-1. The correct answer to this problem is that the static pressure drop can
not be calculated from the present set of data which is obviously in
error. There is no way the static pressure at point #3 could be higher
than the static pressure at point #2.
If a number of the attendees answered either 3 inches (point 3 minus
point 2) or 12 inches (point 3 minus point 1), that indicates a lack of
understanding about the way static pressures vary while gas streams pass
through control devices. It increases only when going past a fan.
1-2. Now that we have what appears to be sensible data, the scrubber pressure
drop can be calculated as the value at point 3 minus the value at point
2, which is simply 7 inches. PLEASE STRESS THAT THE LOCATIONS OF THE
MEASUREMENT SHOULD BE INCLUDED WITH THE DATA. THEREFORE, THE PROPER
ANSWER IS: 7 INCHES FROM POINTS 2 TO 3. Note that this now includes the
demister's contribution to the overall scrubber pressure drop. It would
have been preferable to use data from point 4 had this been available.
1-3. In this particular case there is sufficient information about the
liquor flow rates and it possible to calculate the purge stream flow rate
from a simple material balance. The answer is 15 gallons per minute.
There are times when an approximate material -balance can be very useful
and the attendees will occassionally be reminded of these in the program.
Usually, it is easier to do this with the gas streams than the liquor
streams because in the large majority of cases, the flow rates of most
streams will not be known. We can measure the flow rates of the gas
streams easily. To answer this question correctly, the attendees will
also haye to be able to recognize which stream is the purge stream.
1-4. The concepts of positive and negative pressure are reviewed in this
question. Since the hole in the scrubber wall is downstream of the fan,
the chances are very high that there will be gas flow out rather than
air infiltration inward. If the gas is highly toxic and ventilation in
the area of the hole is poor, this could represent a dangerous situation.
One of the first steps in any inspection is the recognition of areas
where gas leakage and accumulation is possible.
-------
LECTURE 1. REVIEW QUESTIONS AND PROBLEMS
r
r\
TO STACK 101
FROM WASTEWATER
TREATMENT
WASTEWATER
TREATMENT
Sample Flowchart #1
1-1. What is the scrubber pressure drop when the static pressures are as
follows: SPI 1 = -6 inches, SPI 2 = + 3 inches, and SPI 3 = + 6 inches.
1-2. What is the scrubber pressure drop and the demister pressure drop when
the following static pressures are measured: SPI 1= -3 inches,
SPI 2 = +8 inches, and SPI 3 = +1 inches.
1-3. What is the approximate purge stream flow rate if the liquid flow rates
are as follows: Stream #1 - unknown, Stream #2 - 210 gpm, Stream #3 -
unknown, Stream 14 - 50 gpm, Stream #5-0 gpm, Stream #6 - 175 gpm.
1-4. There is a small hole in the scrubber vessel wall, directly below one of
the trays. Is air infiltration likely?
43
-------
LECTURE 1. REVIEW QUESTIONS AND PROBLEMS
This is again a tray tower scrubber. However, this time the unit is
under negative pressure. None of the liquid flow lines have been shown
since none of the questions involve this part of the system.
1-5. Assuming that the static pressure measurements at points #1 and #3 have
been made carefully, the on-site gauge is definitely wrong. Based on
the measurements, the maximum static pressure drop is 8 inches and this
includes the demister which normally contributes about 1 inch. The
preferred locations for the static pressure drop measurements would be
locations AT #1 and AT #2.
1-6. There is no reason to believe that a measurement error has occurred
based only on the data provided. It is very possible that some of the
oxygen has been absorbed in the scrubber, therefore, reducing the levels
in stream. Some air infiltration is always possible, especially at the
fan itself, and this could increase the oxygen levels in stream #3. The
fact that both streams #1 and #3 are at 8% is a coincidence presented
here to confuse the unwary. The point of this question is that oxygen
changes before and after a scrubber are not very useful in attempting to
diagnose and quantify air infiltration.
1-7. The liquid-to-gas ratio is approximately 11.45 gallons per thousand ACF.
1-8. This is probably not a measurement error. There is some temperature
gain across most fans due to the conversion of some mechanical energy
to heat. This was not discussed as yet in the program. Through out the
workshop program these questions and problems will be used not just for
review but also to introduce some useful information which can not be
conveniently discussed in the slide-lecture note format. This is the
first of these points.
44
-------
LECTURE 1. REVIEW PROBLEMS AND QUESTIONS
Example Flowchart #2
1-5. The static pressure drop gauge on this system is indicating 12 inches
of water. The static pressures measured at points AT #1 is -12 inches
and at point AT #3 is -20 inches. Is there any reason to suspect the
accuracy of the permanently mounted static pressure drop gauge?
1-6. The measured flue gas oxygen content in stream #1 is 8%, in stream #2 is
5% and in stream #3 is 8%. Does this show that the inspector has made
incorrect oxygen measurements?
1-7. What is the liquid-to-gas ratio for this system if the total liquor flow
rate is 200 gpm, the gas flow rate of stream #1 is 20,500 ACFM, and the
gas flow rate of stream #2 is 17,500 acfm?
1-8. The gas temperature in stream #2 is measured at 109 °F and the tempera-
ture in stream #3 is measured at 118 °F. Has a measurement error been
made?
-------
LECTURE 1. REVIEW PROBLEMS AND QUESTIONS
This system has a rod deck type gas-atomized scrubber and a cyclonic
demister. A calcium hydroxide solution is being added to the recirc-
ulation tank to maintain the liquor pH in an acceptable range. Not
shown in the figure is a clarifier and vacumn filter system which are
necessary to maintain an acceptable solids content in the liquor. A
bypass stack with butterfly dampers is included. The damper on the
stack is normally closed and the one on the gas stream to the scrubber
is normally open. The scrubber and demister are rubber lined carbon
steel. Everyone should have been able to describe this system using
the flowchart symbols.
1-11. Yes, there is a slight possibility that untreated gas could be going up
the bypass stack. Note that the static pressure in stream #3 is more
negative than it is in stream #2 due to the draft created by the stack above
point #3. If the damper is not seated properly this will cause some
leakage.
1-12. It is clear from the flowchart that the liquor sample has been withdrawn
from the area which should have the highest ph since it is downstream
from the location of the calcium hydroxide addition. The liquor pH will
be lower after the scrubber throat and in the scrubber sump due to the
absorption of acidic gases such as S02 and C02.
1-13. If things work as they should, the bypass damper should open quickly
to vent the hot, untreated gas directly to the atmosphere. If the
dampers don't work properly, hot gas will destroy the rubber liner,
leading to major damage and perhaps a prolonged outage. This question
is intended to illustrate the usefulness of placing materials informtion
on the flowchart. If this information were not here, it would be easy to
forget that the scrubber is extremely vulnerable to temperature spikes.
1-14. Air infiltration is most likely in areas of the maximum negative static
pressure. This means any area downstream of the rod deck in this case.
Upstream, the static pressures would be quite low.
46
-------
LECTURE 1. REVIEW PROBLEMS AND QUESTIONS
4"SCH40-CS —
FROM LIME
SLAKER
TO CLARIFIER
.FROM
CLARIFIER
Example Flowchart #3
1-9. The static pressures in stream #1 is -1 inch, in stream #2 is -1 inch,
and in stream #3 is -2 inches. Is there any possibility for loss of
untreated gas up through the bypass duct?
1-10. The pH of the recirculation liquor is measured using a sample obtained
at the recirculation pump discharge. If the measured pH is 7 and
corrosion is only a problem when the pH is below 5.5, is there any
reason to worry about corrosion?
1-11. Due to a sudden failure of the recirculation pump, all liquor flow to
the inlet of the scrubber is lost for a period of 20 minutes. What
will be the result this problem?
1-12. If air infiltration is suspected due to very poor capture of
particulate at the process hoods, where are the logical places to begin
searching for the infiltration points?
47
-------
-------
LECTURE 2
BASELINE INSPECTION PROCEDURES
FOR
WET SCRUBBER SYSTEM EVALUATION
SLIDE 2-1 This lecture concerns the application
of the Baseline Inspection Technique
to wet scrubber systems. The procedure
BASELINE INSPECTION PROCEDURES is designed to help regulatory agency
FOR inspectors and source operators to
•vET SCRUBBER SYSTEM EVALUATION identify performance problems at the
earliest possible stage. Determination
of the possible causes of observed
problems is another important aspect
of the Baseline Technique.
The inspection procedure is limited to the full identification and eval-
uation of problems and does not address specific correction actions. The
latter would infringe on the perogatives of the source management. The role
of the inspector is limited to determining if the actions proposed by the
source have a reasonable possibility of success and would abate the excessive
emission conditions in a timely manner. The data and observations made during
the baseline inspection enable the regulatory agency to evaluate these pro-
posed actions very effectively. If the plant management actions appear to be
unsatisfactory, the baseline inspection data can also be used to support
enforcement actions.
The slides which follow present some of the basic principles of the Base-
line Inspection Technique. The concept of inspection levels is also defined.
The latter is intended to provide flexibility to regulatory agencies in the
amount of time invested in each wet scrubber system inspection.
49
-------
USE SITE SPECIFIC DATA
TO EVALUATE
WET SCRUBBER SYSTEMS
SLIDE 2-2
EACH WET SCRUBBER SYSTEM SHOULD BE
APPROACHED INITIALLY AS IF IT PERFORMS
IN A DIFFERENT MANNER THAN ALL OTHER
SIMILAR WET SCRUBBERS ON SUPPOSEDLY
SIMILAR SOURCES. In other words, the
performance of one unit should not be
compared with the performance of an-
other, unless data gathered over a long
time period shows these two to be
similar. In the case of wet scrubber
systems, there are numerous reasons why
significant performance differences occur
in two systems which appear similar.
Unlike some control systems, the particle size distributions in the gas
streams entering and leaving wet scrubbers are subject to subtle but signifi-
cant changes. Some of the phenomenon which can affect particle size include
heterogenous condensation, agglomerate shattering, and particulate regenera-
tion. Since performance is highly sensitive to particle size, these affect the
overall performance. Another major reason for unit to unit differences is the
gas-liquor distribution. Subtle changes in this distribution have a major
impact on the overall particulate and gaseous control efficiencies. The varia-
tion in system components also contribute to the site-to-site differences.
SLIDE 2-3
BASELINE EVALUATION
Normal Value
of Parameter
for This Unit
Present Value
of Parameter
for This Unit
COMPARISON
Instead of using literature data or the
performance data from other systems as
the yardstick of performance, the Base-
line Inspection Technique uses data from
the specific unit. This data is more
easily accessible and is more accurate
since there is no question about its
representiveness.
During the inspection of wet scrubbers,
the present operating conditions are
compared with conditions some time in
the past when the unit was believed to
be working properly. A shift in the
a parameter is a symptom of a problem.
Lecturer's Notes
The importance of evaluating scrubbers using unit-specific data can not be
overemphasized. One cupola venturi scrubber operating at a 25 inch static
pressure drop can have better performance than an adjacent unit operating at 50
inches. Inspectors must avoid the simplistic conclusions which can result
from comparing one unit to another. Such comparisons can only be done after
it has been demonstrated that the units are in fact similar.
The acquistion of baseline data is discussed in later slides. Questions
concerning baseline data should be reserved for later.
50
-------
SLIDE 2-4
USE AS MUCH DATA
AND INFORMATION
AS POSSIBLE
Sometimes it is possible to identify
a wet scrubber performance problem by
examining the shift in one parameter.
For example, a 50% drop in liquor flow
rate indicates serious trouble for
almost all types of scrubbers.
In most cases, however, it necessary to
look at as much data as possible in
order to figure out the likely fundamen-
tal problem. Small shifts in a number
of parameters are also useful for the
early identification of problems. For
these reasons, the inspection procedures
used in this workshop deal with sets of
symptoms.
SLIDE 2-5
ON-SITE INSTRUMENTS
ARE OFTEN
UNAVAILABLE OR UNRELIABLE
It is not easy to maintain instruments
on wet scrubbers systems. The probes
are subject to pluggage, corrosion, and
erosion. Even well maintained instru-
ments can be incorrect some of time.
There is a general correlation between
the level of performance of the wet
scrubber system and the accuracy and
availability of the instruments. Those
units which seem to be performing very
well usually have monitoring instruments
which work at least most of the time.
The units with chronic compliance pro-
blems frequently seem to have instru-
ments out of service or no instruments
at all. It is obviously the latter
group which is of most interest to regu-
latory agency inspectors. Therefore, it
is good practice to question the accur-
acy of the gauges.
51
-------
SLIDE 2-6
RECOMMENDED INSTRUMENTS
Primary 1. Safety Equipment
Equipment 2. Static Pressure Gauge
3. Temperature
4. Oj/COj Analyzer
5. Flashlight
6. pH Meter or pH Paper
Secondary 1. PitotTube _
Equipment 2. Tachometer
3. Velorneter
The types of portable instrumentation
used in the inspection of wet scrubbers
are listed in this slide. The list is
divided into a primary set which is used
very frequently and a secondary set
which is rarely used.
All of this equipment is relatively
inexpensive and easy to use. The gauges
needed for a given inspection can usual-
ly be carried in a tool pouch or small
tool case. Instrument calibrations are
simple except for thermocouples.
There are several approaches to the use of portable instruments. In
plants which have union agreements regarding instrumentation, the gauges should
be given to the appropriate plant personnel to conduct the measurements while
the inspector observes. In other cases, the plant management may perfer that
the agency inspector make the measurements. If the regulatory agency does not
presently have the necessary instruments, the inspector can request that plant
personnel conduct the measurements using their own gauges (most plants have the
items listed above). In any case, the objective is to make sure that accurate
and complete data has been gathered during the inspection.
Lecturer_' s Notes
It should be noted that portable instruments are used only on detailed
inspections. On most occassions, the accuracy of on-site gauges will be eval-
uated visually with no attempt to measure any operating conditions. Anyone
using portable instruments must adhere to the general safety procedures covered
later in the workshop and any specific policies at the plant being inspected.
COUNTERFLOW APPROACH
STACK
Field inspections should be conducted in
a methodical order. The initial data
should be reviewed during the inspection
so that the remainder of the effort can
be focused on any suspected problems.
If the initial data suggests that system
performance is similar to baseline per-
iods then the inspection is terminated.
The approach recommended in the program
is termed the "Counterflow" procedure.
The inspection starts with a careful
evaluation of stack visible emissions
and then proceeds in a countercurrent
direction relative to the gas stream.
Emphasis is given to evaluation of scrubber vessel and liquor recircula-
tion system operating parameters. The process equipment is evaluated only
when (1) there are indications of an emissions problem, and (2) the data and
observations made of the stack and wet scrubber system suggests that the fun-
damental cause of the condition is a change in process operation. This does
not mean that process conditions are not important, but this time consuming
part of the inspection should be done only when there is a clear need to do so.
52
-------
SLIDE 2-8 Two key words necessary in wet scrubber
system inspections are flexibility and
judgement.
FLEXIBILITY Due to the extreme diversity of system
JUDGEMENT designs, it is difficult to develop an
inspection scheme which is appropriate
for each one. In some cases, it will be
necessary to go beyond the observations
and data discussed in the workshop in
order to evaluate conditions. In other
cases, strict adherence to all the steps
mentioned would represent overkill. Each
field inspector must understand the in-
spection procedures and control system
operating principles well enough to
tailor the inspection to the system. In
other words, the inspection procedure
must be moderately flexible.
The field inspection, in conjunction with his or her supervisor must make
certain judgements regarding the amount of effort warranted for the specific
inspection. The material presented for each scrubber type is divided into
several distinct levels. The most detailed inspections are done on sources
with chronic compliance problems or on those at which a problem is now suspect-
ted. There must also be some judgements regarding any potential health and
safety problems. Obviously, a field inspector should not do anything that in
his or her judgement would present a safety problem or which could harm the
plant equipment.
SLIDE 2-9 The inspection procedures are divided
into distinct levels. Level 1 inspec-
tions are done mainly from the plant
boundry and consist of an observation of
the visible emissions and any fugitive
BEVELS OF emissions from plant facilities.
'NSPECTION
\Level 2 inspections are walk through
inspections of the control system and
the process equipment. These are
routine inspections which are conducted
on sources believed to be in compliance.
The emphasis here is on identification of
any problems which could lead to excess
emissions in the near future.
The most detailed form of the inspection procedure is Level 3. This
involves the use of portable instruments so that all possible parameters
relevant to the suspected problem(s) are measured and evaluated. The data and
observations are shared with plant personnel to see if agreement can be reach-
ed concerning the types of problems which exist. The actions proposed by plant
personnel to correct or prevent the problem should be evaluated by the field
inspector and supervisory agency personnel.
53
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LECTURE 2. EXAMPLE BASELINE ANALYSES
Stream 1 Static Pressure
Stream 2 Static Pressure
Stream 1 Gas Temperature
Stream 2 Gas Temperature
Stream 4 Liquor Flow
310
Inspection Number
295
303
308
Present
-5
-51
452
136
-5
-49
436
134
-4
-47
445
134
-4
-50
441
131
-3
-46
447
129
306
Comparison of Present Data with
Inspection 1 Data Only
AP(present)
AP(insp 1)
43 inches
46 inches
T2(present) = 129
T2(insp 1) = 136
Conclusion: Minor Variation
Comparison of Present Data with
All Four Previous Inspections
AP(present) = 43 inches
A.P(mean, 1-4) = 45 inches
AP(
1-4) =
T2(present) = 129 °F
T2(mean, 1-4) = 134 °F
T2U , 1-4) =
Conclusion: Student's t Test
indicates >95% probability that
present pressure drop is low and
a >98% probability that the gas
temperature of stream 2 is low.
Air infiltration likely.
54
-------
SLIDE 2-10
The baseline data should not be regarded
as some mystical, unchanging yardstick
with which scrubber performance can
always be measured. It should, instead,
be a constantly growing data set which
is supplemented by the results of each
inspection.
For example, The inspection data from
plant A is a hypothetical level 3
inspection. Inspections B and C are
level 2 inspections during which the
plant instruments appeared to be
working. A comparison of the present
data with the range of data in all three
previous inspections clearly shows that
there has been a change in the operating
conditions. If only the data from in-
spection A were available, it would have
been hard to determine if the differ-
ences were due to a change or just to
normal variability. When combining data
from several inspections it is neces-
sary to confirm that there have been no
major process changes.
55
-------
LECTURE 2. EXAMPLE 2
0.30
t
CD
0.20
CO
g
CO
CO
LU
0.10
TEST
1
2
3
4
5
DATA
AP
900
1300
600
2000
1000
Lbs/MMBTU
0.14
0.05
0.27
0.02
0.12
Regulatory Limit
400 800 1200 1600 2000
CORRECTED PRESSURE DROP, (Lbf.-Ft/Lbm)
To calculate corrected pressure drop from
data in units of inches of water,
Inches W.G.* (5.2 Lbf/ft2/inch WG) =
M(Lbf-ft2)
M/(Gas Density, Lbm/ft3) =
C, (Lbf-Ft/Lbm)
56
-------
SLIDE 2-11 In most cases, scrubber performance is
evaluated by comparing present condi-
itions to the general operating range.
-—.T-.^T-,^... »»,AI w*»ir«-» This was illustrated in the previous
STATISTICAL ANALYSES slide In some cases> however, it is
useful to apply some basic statistical
tests to gain some insight regarding the
significance of shifts in the operating
parameters. The example on the oppos-
ite page provides the data used here.
With only one inspection serving as the baseline, the shifts in static
pressure drop and gas temperature are difficult to evaluate. With data from
several inspections, the normal variability can be reviewed and the Student's
t test can be used to evaluate the significance of the shifts. Both the gas
temperature and the pressure drop have apparently changed substantially. In
this case, it is very possible that the scrubber vessel is experiencing some
air infiltration and this is reducing the quantity of gas pulled from the
process source. The remainder of the present inspection concentrates on air
infiltration issues. The sites of air infiltration are be checked and pitot
traverses are conducted before and after the scrubber vessel.
Lecturer's Notes
The purpose of this example is to show how the baseline data expands over
time and how the basic statistic analyses can be applied. This procedure is
one step beyond simple comparison of conditions against a range of values as
illustrated in the previous example. . The next step goes one step further by
using a performance correlation.
57
-------
SLIDE 2-12
TRANSFORMED TEST DATA
Test P "x" Emissions "y"
9
13
6
20
11
2.64
1.61
3.30
0.69
2.48
A useful correlation for certain wet
scrubber systems can sometimes be pre-
pared when several stack tests have
been conducted at different operating
conditions.
The hypothetical set of data provided
on the opposite page has been used to
illustrate how the confidence interval
on the correlation changes as more
data is obtained. The 90% confidence
interval using tests 1 and 2 can be
compared with the interval using all
five tests.
As a starting point, it is helpful to transform this data to a form which
is easier to use. The data taken from the opposite page has been converted in
the form shown in this slide. The natural log of the emissions data has been
used since the "eyeball" curve seems to be exponential in nature. Multiplica-
tion of the number by 100 avoids the necessity of handling negative logarithms.
The pressure data has been converted from the familar inches of water format to
the corrected pressure drop form. The general procedures are illustrated at
the bottom of the opposite page (the corrected pressure drop term will be
introduced later). The corrected pressure drops have then been divided by 100
so it will not be necessary to manipulate large numbers.
SLIDE 2-13
« 030
= 020
£ 0 IS
g 0.05
7, 004
I 0.03
0.02
0.01 >-
20
10 15
P, INCHES.wc.
The statistical procedures summarized
at the end of this lecture have been
applied to the data shown in the above
slide. The curve shown in this slide is
the result of including all five of the
tests.
The solid line in the middle is the
linear regression line. The curved
lines above and below this are the 90%
confidence intervals.
If the measured pressure drop is so low
that the lower confidence interval is
above the regulatory limit, then there
is a 90% probability, based on this one
correlation, that the unit is now out
of compliance.
The circle on the right indicates the average corrected pressure drop
which is necessary to remain below the regulatory limit. If there is a correc-
ted pressure drop of 11 inches of water (see circle to the left), then there
is a good possibility that emissions are now greater than the 0.10 pounds per
million BTU imput.
58
-------
SLIDE 2-14
This is a graph of the correlation using
only tests 1, 3 and 4. The confidence
interval now looks much larger. This
indicates that less is known about the
variability of the emissions-corrected
pressure drop data.
In this case, the corrected pressure
drop must decrease below 9 inches before
there is reasonable confidence that
excess emissions are occurring. In the
earlier example, a decrease to 11 inches
would have indicated this clearly.
These curves are intended to illustrate simply that the more data
available, the more sensitive the baseline analyses can be. Each set of data
helps to further define the normal variability so that abnormal conditions are
easier to spot. It should be noted that the data used in this hypothetical
example was specifically chosen so that there would be very little variability.
This inherently reduces the width of the two confidence intervals. In some
cases, the plotted confidence intervals with just three data points could be
so large as to render the entire procedure meaningless. The factor which
determines the number of data points necessary for a good correlation is the
variability of the system itself and the choice of an operating parameter used
in the correlation.
59
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SLIDE 2-15
For some wet scrubber systems, the
performance correlations using the
baseline data can be very useful in
SUMMARY estimating the potential for excess
PERFORMANCE CORRELATIONS emissions. It should be remembered,
however, that these are not sufficient-
ly accurate to serve as a basis for a
notice of violation. That can only be
done by a reference method test speci-
fied in the applicable regulations.
These correlations are only intended as
an aid to the agency inspector or source
operator attempting to determine if a
shift in conditions is significant.
One common problem with wet scrubber correlations is that there are a
number of conditions which can invalidate a usually accurate relationship. The
most common of these are sudden shifts in the inlet gas stream particle size
distribution. These changes will be examined in some detail in later sections
of the workshop.
Lecturer's Notes
The use of correlations should not be overemphasized. The simple com-
parisons of present conditions to several previous sets of inspection data are
usually more than sufficient. It is conceivable that some of the attendees
will spend too much time compiling performance correlations. Sometimes these
are worthwhile, sometimes they are not.
SLIDE 2-16 One way to compile a baseline data set
is to extract data from wet scrubber
system operating logs. The main risk
with this approach is that data from
OPERATING LOGS AND RECORDS *alfunctionin§ instrumentation will be
used. Nevertheless, this is the only
approach possible when the unit has not
been stack tested and detailed inspec-
tions have never been conducted. Once
better data becomes available, the in-
formation retrived from old files can be
retired.
The data which is most useful includes gas temperatures, static pressure
drops, liquor flow rates, liquor pH levels, and nozzle header pressures. Only
rarely will data other than that listed above be found.
As much information as possible on the process operating rate and condi-
tions should also be pulled from the files. This information is almost always
recorded on other operating logs. Therefore, additional "digging" is in order.
Unfortunately, some plants discard operating records after 3 months. This
practice may preclude any access to data which predates the apparent problems
with the wet scrubber system.
60
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SLIDE 2-17
EXAMPLE DATA EVALUATION
There are several ways to evaluate the
present data against a set of data
retrived from the files. This slide
presents data showing how the Student's
t test can be applied to several sets
of scrubber system operating data.
In this case, all three parameters
appear to be significantly different
from the data taken from the records.
The manner in which the present data
deviates from the recorded values
indicates a sudden drop in liquor flow
rate to the inlet of the scrubber. The
diagnosis of problems is discussed in
some detail later in the program.
The Student's t test indicates that there is a 90% probability that the
pressure drop is lower than normal, there is an 80% probability that the outlet
gas temperature is higher, and a 95% probability that the nozzle header pres-
sure has decreased. All of these indicate a reduction in the liquor flow to
the scrubber. One possible explanation is a change in the recirculation pump
impeller. It is often the simultaneous changes in several parameters that are
most useful for pinpointing possible problem areas. The use of several para-
meters is especially important when using data from operating logs where the
accuracy of the data can not be easily confirmed.
Date
5/24/80
7/13/81
6/30/82
9/20/83
Present
22
24
21
25
18
Outlet
Gas Temp
286
276
281
264
293
Nozzle
Pressure
76
80
74
77
71
SUMMARY
SLIDE 2-18
In summary, the baseline data provides
a means to measure present operating
conditions. Shifts in the values of
key operating parameters can be
evaluated simply by inspection or
through basic statistical techniques.
There are distinct levels of effort
used for different circumstances.
Plant boundry inspections consist only
of visible emission observation. The
regularily scheduled walk through
inspecton involves both visible
emissions observations and the eval-
uation of operating conditions indic-
ated by on-site gauges
When a wet scrubber system has a history of excess emission problems or
the data gained in the level 1 or 2 inspections suggests potential scrubber
performance problems, a detailed inspection is conducted. This involves the
use of portable instruments as necessary and a more comprehensive check of
system conditions. Regardless of the level of the inspection, the performance
is always evaluated by the comparison of present conditions against site-
specific baseline data.
ol
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LECTURE 2. REVIEW PROBLEMS AND QUESTIONS
2-1. Yes, a more detailed inspection is necessary as soon as possible to
determine if the unit is now or soon will be out of compliance. An
increase of this magnitude is a very bad sign even though the unit is
not out of compliance based on the visible emission observation.
2-2. No, each field inspector, with the assistance of his or her supervisor,
decides what is the most effective and safe procedure for conducting an
inspection of a given facility. A certain amount of professional judge-
ment is required for all field inspections.
2-3. The answer is simple, the inspector should NOT enter the unit under any
circumstances. While most plant personnel are well trained and aware of
safety hazards, there are always a few that are not. There could be
pockets of toxic gas and inadequate oxygen inside a unit that is out-of-
service. It is also possible that the unit is not properly locked off
line. Everything a regulatory agency inspector needs to see can be seen
very well from an acces hatch. There is NEVER ANY REASON TO ENTER.
2-4. The only correct answer is c, a general assessment of the performance
of the wet scrubber. It is very presumptous to think that anyone can
go into a plant and in a matter of several hours completely judge the
adequacy of their maintenance procedures. Furthermore, no inspection
procedure can ever substitute for a reference stack test method, which is
the only way to determine compliance with mass emission requirements.
To compile and present a list of demanded repairs and modifications is
both unwise and wrong. First of all, the agency takes on some of the
liability for systems specifically demanded. Furthermore, this approach
preempts their ligitimate options for running the plant. The inspection
simply results in a list of probable problems so that the inspector can
determine if the corrective actions planned by the source have a reason-
able chance of minimizing the problem in a timely manner. If there is
disagreement between the plant and the agency, legal action is the
appropriate next step.
2-5. There is no reason to stack test either unit based on the information
presented. Answer c is correct. The fact that two identical scrubbers
on two supposedly identical asphalt plants are running at different
pressure drops is not significant. What would be significant is a
decrease in the pressure drop for the specific unit. It should also be
noted that supposedly identical plants can have remarkably different
particle size distributions and therefore require different pressure
drops. In this case, slight movement of the asphalt injection pipe or
a slight change in the mix temperature could create drastic differences
in the particle size distributions from the two "identical" plants.
62
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LECTURE 2. REVIEW PROBLEMS AND QUESTIONS
2-1. During a routine plant boundry observation of the visible emissions from
a cupola wet scrubber system, the inspector notices that the residual
opacity has increased from the normal 5% to a level between 10 and 15%.
The regulatory limit is 20%. Is a more detailed inspection of the
system necessary at this time?
a. Yes
b. No
c. Maybe
2-2. Is it mandatory to conduct the inspection in a counterflow manner when
performing a Baseline Inspection?
a. Yes
b. No
c. Sometimes
2-3. During a level 3 inspection, the plant personnel invite the agency
inspector to enter the cyclonic demister to observe a scaling problem
which has developed recently. What safety procedures are appropriate
in this situation?
2-4. Which of the following is achieved during a Baseline Inspection of
a wet scrubber system?
a. An accurate and complete determination of compliance with the
regulatory requirements
b. A general evaluation of control system performance
c. An assessment of the adequacy of the plant maintenance procedures
d. Compilation of a list of needed modifications and repairs
e. All of the above
2-5. There are two Model SX-68-7 fixed throat venturi scrubbers serving two
identical drum mix asphalt plants. One of these is operating at a
pressure drop of 19 inches W.C. and an inlet gas temperature of 264 °F.
The other is operating at 14 inches W.C with an inlet gas temperture of
270 °F. Does this data demonstrate the need to stack test either one or
both of the scrubbers?
a. The one with the low pressure drop should be tested
b. Both should be tested
c. None of the above
o3
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LECTURE 2. REVIEW PROBLEMS AND QUESTIONS
2-6. No, it is not significant at the 90% level. Those who feel it is
significant have probably used the wrong degrees of freedom when using
the t Tables.
2-7. Comparison of conditions at one unit with data from others should be
done only as a last resort and only if it can be demonstrated that the
process and control systems are very similar. No statistical test is
appropriate at this time.
2-8. The correct answer is that the inspector should recommend that the
agency conduct a stack test based on whatever observations and data
could be obtained. Concerning the plant's refusal to install ports,
they could well have valid legal, technical and/or safety reasons for
taking this position. The agency can not demand measurement ports.
It is equally inappropriate to wait until a level three inspection can
be done. Again, the main purpose of inspections is to minimize air
pollution and not to complete some arbitrary sequence of inspections.
In other words, it is not necessary to complete a level 3 inspection
before requesting a stack test or before discussing the potential
problems with source management personnel.
2-9. "Maybe" is the best answer. The point of this question is that inspectors
should not let themselves be boxed in by any statistical analyses. Just
because the changes are not significant at the 90% level does not mean
that they are not real. In fact, excess emissions may have already
resulted. The inspection should continue until all of the potentially
relevant information regarding possible problems has been obtained. The
inspector should base his or her conclusion on all the data and observa-
tions made and not just on the few items for which the statistical tests
can be applied. Subjective judgements also have a legitimate role in
reaching a position regarding the source's compliance status.
2-10 The correct answer is "b", the measurement should be forgotten. In many
cases, "all reasonable precautions" may not be enough and the inspector
can be overcome. Now plant personnel may be tempted to place themselves
at risk to remove the inspector from a location where he or she should
not have gone in the first place. The other three answers listed are
also poor. Guesses should never be used just because a measurement was
not possible. Sometimes no information is better than incorrect inform-
ation. Calling supervisory personnel for advice may sound good, but how
can this individual fully appreciate the exact conditions facing the
inspector? It is also possible that during the call, the inspector will
not completely describe the situation. Requesting the plant personnel to
enter an area that you are not willing to enter is not appropriate. It
is the inspector's job to perform the inspection and plant personnel (no
matter how willing) should not have to take unreasonable risks to obtain
necessary data. Forget the measurement!
-------
LECTURE 2. REVIEW PROBLEMS AND QUESTIONS
2-6. During the previous three inspections the gas outlet temperature from
the scrubber demister has been 126 °F, 134 °F, and 132 °F. Now the
demister outlet temperature is 137 °F. Using the Student's t Test, is
the increase significant at the 90% level?
2-7. Data concerning three venturi scrubbers on grey iron cupolas has been
published in a recent publication of the U.S. Environmental Protection
Agency. This indicates that these operate at pressure drops of 36, 42,
and 43 inches W.C. A similar cupola venturi scrubber being inspected
has a pressure drop of 34 inches W.C. What statistical test should be
used to determine if there is a potential scrubber operating problem?
2-9. During a level 2 inspection, the data and observations made by the
inspector strongly indicate that the unit is out of compliance with
the mass emission limits. There are no presently available ports to
confirm the on-site instrumentation and the plant management refuses
to install these ports so that a more detailed inspection can be
conducted in the near future. What course of action should the
inspector take?
a. Issue a Notice of Violation to the plant due to the
lack of measurement ports.
b. Recommend that the agency request a stack test under the
conditions representive of present performance.
c. Wait until a level 3 inspection can be completed, and then
determine if enforcement action is necessary.
2-9. The comparison of present scrubber conditions against the available
baseline data indicates decreases in the static pressure drop and the
liquor flow rate, but an increase in the nozzle header pressure. The
statistical evaluations indicate that none of the changes are signifi-
cant at the 90% level. Does this demonstrate that the unit is working
property?
a. Yes
b. No
c. Maybe
2-10. During a level 3 inspection, it is noticed that there is only limited
ventilation around one measurement port of a positive pressure unit.
If the measurement is not obtained, it may be impossible to fully
evaluate the operating conditions. What should the inspector do?
a. Using all possible precautions, make the measurement.
b. Forget the measurement.
c. Make a reasonable estimate.
d. Call supervisory personnel back at the office for advice.
e. Ask plant personnel to make the measurement.
o5
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Ot)
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LECTURE 3
PLANT BOUNDRY LINE INSPECTIONS
SLIDE 3-1
A Level 1 inspection of any wet
scrubber system consists simply of an
evaluation of the scrubber plume and
PLANT BOUNDRY LINE INSPECTIONS any bypass stacks plumes. ^ese in_
1. Visible Emissions Observations spections are normally conducted from
2. Scrubber Reentrainment the plant boundry .
3. Odor Surveys
The primary purpose is to determine if
the unit is in compliance with visible
emission regulations (particulate wet
scrubbers) or with odor requirements
(gaseous scrubbers). More detailed
Level 2 or Level 3 inspections are con-
ducted if symptoms of problems exist.
This lecture briefly reviews important points concerning visible emission
and odor observations conducted from plant boundries. This material goes be-
yond simply determining that there is a problem. A number of observations are
discussed which help determine the nature of the problem and which aid in the
preparations for the more detailed inspections.
Lecturer's Notes
The plant boundry inspection can be quite beneficial if a modest amount
of time is invested by the inspector. It will become obvious that this mat-
erial is not a rehash of lectures presented in the "smoke schools" or other
similar programs.
67
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SLIDE 3-2
Before leaving for a Level 1 inspection
of a wet scrubber system, the general
weather conditions should be noted.
Days similar to the one shown in this
slide are obviously not conducive to
visible emissions observations. It may
be possible to conduct a meaningful
odor survey. However, even this is
doubtful under the conditions shown.
In these circumstances, it may be more
appropriate to conduct a Level 2 inspec-
tion of the wet scrubber system. On
the other hand there is always some
paper work to catch up on.
O
SLIDE 3-3
The initial task during a boundry line
inspection is to make a presurvey of
available observation sites. The
hypothetical plant layout shown in this
slide is used as an example of such a
presurvey.
The purpose of the initial survey is to
determine the optimum location for a
visible emission observation for the
stack or stacks of interest. This goes
beyond just concern over sun angle and
the direct of plume travel. The in-
spector should note any activity which
could lead to multiple plumes along the
line of sight. This could be caused by
several stacks grouped closely together
or due to fugitive emissons close to
the stack of interest. The reasons for
selecting the observation point should
be briefly documented in the inspection
notes.
During the presurvey, the inspector should make both upwind and downwind
odor surveys. This should be done before any visible emission observations,
since olefactory fatigue can reduce the sensitivity to odors after prolonged
periods of time. The wind direction at times that odors are apparent should be
observed and noted. Trees, flags, and plume travel directions usually provide
sufficient indicators of wind direction.
63
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SLIDE 3-4
ODOR CHARACTERISTICS
Cool
Mint
Perfume
Sweet
Floral
Etherish
Sharp
Cltral
Fruity
Sour
Spicy
Musty
Putrid
Fecal
Rancid
Nutty
Oily
Heavy
Greasy
Rubbery
Burnt
Woody
Methanol
Warm
If odors are detected, the "character"
of the odor should be described using
some accepted descriptive terms. The
list provided in this slide can be used
as is or can be modified for common
odors near the source. In any case, it
is helpful if the regulatory agency
inspector, the plant personnel and the
residents of community agree on a rea-
sonably concise set of terms. This
will facilitate comparison of the
records kept by everyone concerned.
The time of day that any odors are noticed should be carefully recorded
in the inspection notes. The meteorological conditions are also of interest.
This data will be helpful later in tracking down the source(s) of odors and in
comparing the inspector's observations with those of the residents and plant
employees.
SLIDE 3-5
One of the main questions faced in the
visible emissions observations of wet
scrubber systems is whether or not the
observed plume is composed of real
particulate or just condensed water
droplets. It is a legitimate question
since water droplets scatter light as
well as particles.
There are several ways to distinguish
the condensed water droplets (sometimes
called the "steam" plume) from the true
particulate matter in the plume.
This photograph shows the plume from a
series of spray scrubbers serving
fiberglass forming lines. The point at
which the condensed water droplets re-
vaporize is marked with arrow #1. It
is not difficult to identify this point
of the plume and to see that there is
considerable residual aerosol left in
the plume after the water droplets
cease to exist.
69
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SLIDE 3-6
The residual plume from this scrubber
stack is apparent downwind from the
point marked as arrow #1. This has a
distinct bluish white color (which is
not readily apparent in the black and
white reproduction). This color is the
result of the scattering of blue light
by submicron aerosols. Particles in
this very small size range scatter blue
light efficiently since the particle
diameter is close to the wavelength of
blue light.
Any time that a bluish white color is
noted, it is clear that significant
quantities of particulate matter is
present.
The color of the plume should be carefully described in the inspection
notes. The location in the plume at which it becomes visible and the color
itself should be described. The bluish white plumes often indicated inade-
quate collection of fine particulate (less than 2 microns), condensation of
vapors in the scrubber, or regeneration of particles due to droplet evapor-
ation. Brownish-white plumes often indicate poor collection of moderate and
large size particulate. Combustion problems in fossil-fuel fired sources can
generate a black residual plume.
SLIDE 3-7
OBSERVE STEAM VENTS
IN THE VICINITY
OF EMISSION SOURCE
In addition, inspectors should observe
any steam vents in the general vicinity
of the scrubber system or adjacent
plants. The time it takes for these
to disperse should be noted.
There should be a noticeable difference
between the steam plume dissipation and
the persistence of the scrubber plume.
There should also be a very distinctive
color difference.
In a sense, the use of known steam vent
plume descriptions provides an "inter-
nal standard" regarding the behavior
of condensed water droplets under the
present meteorological conditions.
70
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SLIDE 3-8
For compliance determinations, the
visible emissions must be observed at
the point of maximum opacity either
before the water droplets begin to
condense (see arrow #1) or at a point
after they have re-vaporized (see arrow
#2). Since a baseline inspection in-
cludes a reference method stack test,
such an observation should be made.
However, for diagnostic purposes, the
opacity should be observed directly
above the stack whenever conditions
permit (no water droplets). At the
stack there is a constant path length
and the opacity readings can be com-
pared with baseline levels.
The path length through the residual plume varies with the weather
conditons. Due to this factor it is difficult to compare present conditions
against baseline conditions. Also, the residual plume is generally highly
diluted and is not a very sensitive indicator of scrubber performance. There
could be substantally increased emissions without a noticeable increase in the
residual plume.
SLIDE 3-9
1200'
The elevation angle of the visible
emission observation is illustrated in
this slide. Stack observations made
strictly for diagnostic purposes should
be corrected for the difference in the
path length between the actual line of
sight versus the actual plume diameter.
The equation for correcting the opacity
value is shown at the bottom of the
slide. The angle of observation can be
calculated by knowing the stack height
(check file data) and by estimating the
distance to the stack. The latter can
be accurately estimated from a plot plan
of the facility. If the plot plan is
not available, a range finder can be
used to estimate distance accurately.
120OT
71
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\
\
SLIDE 3-10 During the visible emission observation,
the presence of a condensing plume or
reacting plume should be noted. As
shown in this slide, the plume has a
gradually increasing opacity as it
travels downwind.
This characteristic is opposite to what
is normally expected. It is caused by
the formation of particulate from gases
reacting in the plume. In some cases,
it could be caused by the condensation
of vapor phase material in the plume.
However, the latter mechanism would
probably be completed in the scrubber
vessel and would not be noticed in the
plume .
The presence of a plume of increasing opacity is generally caused by
material which passes through the scrubber system as a gas or a vapor. This
may indicate inadquate collection efficiency for these materials, improper
conditioning of the gas stream before scrubber entry, or a change in the
process operation which results in the generation of pollutants which can not
be properly treated in this scrubber system. In any case, a more detailed
inspection is necessary.
SLIDE 3-11 The presence of a layer of mud at the
stack discharge is an indication of
iroplet reentrainment. Another common
symptom is a discolored area caused by
; che drainage of scrubber liquor down
: the outside of the stack. When these
• are noticed, there is often rainout of
small liquor droplets in the general
• vicinity of the stack.
If these small droplets are falling
k outside the plant boundry line, local
* residents may complain of damage to car
, finishes, house paints and gardens.
» During the follow-up level 2 or level 3
inspection, the operation of the scrub-
ber demister should be checked in some
detail. Such problems are almost always
correctable in a short amount of time.
To determine if the reentrainment conditions still persist, a general
survey of the area outside the plant boundry should be made. Obvious spotting
of car finishes usually provides a good indication of recent droplet carry-
over into neighborhood areas. Spotting and discoloration of house finishes
are less reliable indicators since this could have occurred some time in the
past and the owners have just not had the opportunity to repaint.
72
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SLIDE 3-12 After completing the scrubber stack
visible emission observation, a second
trip around the facility should be
made. During this survey, anything
which may have interferred with the
stack observation should be noted.
Possible situations include fugitive
emissions from vehicle movement or from
storage piles, and the start-up of an-
other source along the line of site.
The absence of any of these conditions
confirms that only the scrubber stack
was observed.
Steam vent dissipation characteristics
should also be described. This helps to
demonstrate that the material observed
was in fact particulate and not steam.
The second survey around the facility also provides a good time to select
the best observation point for checking bypass stack emissions and fugitive
emissions from the process equipment served by the scrubber. Standard Method
9 procedures should be used in observing these possible emission sources.
During the second survey, any odors should again be noted. The intensity
and characteristics should be described so that the source(s) can eventually
be identified.
73
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LECTURE 3. REVIEW PROBLEMS AND QUESTIONS
3-1. There is reason for concern. Two 20% opacity plumes in series would
result in an opacity of approximately 36%. The observed value is in
excess of this level. Attendees who were incorrect probably assumed
that opacities are additive. A review of the basic principles of
transmittance quickly indicates that opacity is an exponential
function.
3-2. The observations should be repeated for each stack.
3-3. Answer c is the correct answer, assuming that the inspector is
qualified to conduct level 2 or level 3 inspections of scrubber
systems. The key point is that there is a very significant excess
emissions problem at the present time which can not be ignored.
The unit is definitely out of compliance with the visible emissions
regulations.
3-4 Yes, the 45° angle results in a true 20% opacity plume equivalent
27% opacity.
3-5. Answer b is correct. In this case, it is probable that there is severe
air infiltration into the unit or a similar problem which reduces the
capture of pollutants at the process area.
74
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LECTURE 3. REVIEW PROBLEMS AND QUESTIONS
3-1. During the second survey of the facility, it is discovered that a second
scrubber system has started since the beginning of the visible emission
observation. The plume from this second system is in the same line of
sight as the observed plume. If the average opacity of the observation
just completed was 39%, is there any reason to believe that either of the
scrubber systems is out of compliance with a 20% opacity regulation?
(Additional Notes: It lasted more than 6 minutes, and the observation
point did not include steam from either scrubber).
3-2. In the situation described in problem 3-1, a second source along the line
of site starts operating at sometime during the observation. This is not
discovered until after the observation is concluded. What should be done?
3-3. During a properly conducted observation of a scrubber stack, the opacity
pattern has regularly occurring spikes of 70 to 90% opacity lasting from
30 seconds to 90 seconds. These occur approximately every 4 minutes.
The reminder of the time the opacity is in the range of 10 to 15% opacity.
The baseline opacity data for this facility indicates an average of 10 to
15% without any spiking. The visible emissions limit is 20%. What should
be done?
a. Nothing, there has been no shift in the baseline opacity levels
and the unit is in compliance with the 20% regulation.
b. The next regularly scheduled inspection of this facility should
be either a Level 2 or Level 3 inspection rather than a Level 1
inspection.
c. A Level 2 or Level 3 inspection should be conducted immediately
to determine the cause of the spiking and to determine the
corrective actions that the source intends to take.
3-4. During a presurvey of a plant, the best observation point is a small hill
overlooking the scrubber stack. The angle down through the plume is 45°.
If the observed opacity is 27%, is the unit in compliance with a 20%
opacity standard?
3-5. The residual plume from a scrubber system has an average opacity of less
than 5%. There are fugitive emissions from the roof monitor above the
process equipment served by the scrubber. However, these fugitive
emissions are not noticeable at the plant boundry line. What should be
done?
a. Nothing
b. A Level 2 or Level 3 inspection should be performed as soon as
possible.
c. The observations should be repeated during some period when
there are no condensed water droplets anywhere in the plume.
75
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76
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LECTURE 4
EVALUATION OF SYSTEM INSTRUMENTS
AND
USE OF PORTABLE INSTRUMENTATION
SLIDE 4-1
WET SCRUBBER DATA
A. GAS STREAM DATA
Static Pressures
Flow Rates
Temperatures
Oxygen Concentrations
B. LIQUID STREAM DATA
Pressures
Flow Rates
PH
This lecture concerns data. The para-
meters which are important in most wet
scrubber system inspections are listed
in the adjacent slide.
In level 2 inspections it is important
to confirm that the permanently mounted
on-site instruments are working proper-
ly. Some of the common symptoms of
gauge malfunction are discussed. While
it will not be possible to make a com-
prehensive evaluation of instrument
performance, these procedures will at
least help identify gauges suffering
from the most common failures.
In level 3 and 4 inspections, both the on-site gauges and some portable
instruments may be used. Procedures for using the portable instrumets to
evaluate wet scrubber systems are discussed in this lecture. They include
basic calibration checks and ways to avoid measurement errors. Safety consid-
erations are an important part of this material.
Measurement ports are necessary for the portable instruments. The proper
sizes and locations of measurement ports on common types of wet scrubbers are
discussed in this lecture.
77
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SLIDE 4-2
SELECTION AND USE
OF MEASUREMENT PORTS
1. Ports should be >V4" and <2" diameter.
2. There should be safe access to the port
to facilitate rod out prior to the measure-
ment
3. Never use ports connected to D/P
transmitters.
4. Never have measurement ports installed
while the system is running.
Before beginning the discussions of
each type of instrument, basic common
sense facts deserve some attention.
There are a large number of on-site
gauges and measurement ports located in
strange and obscure locations around
wet scrubber systems. HEROIC MEASURES
SHOULD NOT BE TAKEN TO REACH THESE
IMPROPERLY LOCATED GAUGES OR PORTS.
This means that the inspection will not
be as thorough as it might otherwise be,
However, this is preferable to an
accident.
Only the data necessary to confirm compliance or to determine the general
types of problems which exist should be obtained. Extensive time should not
be devoted to the inspection just so that the inspection is "complete" or so
some inspection report form can be filled out. The art of field inspection is
determining which measurements are relevant for the particular system at the
specific time. Anything beyond these measurements is a waste of the inspect-
or's time and an inconvenience to source personnel who must accompany the
inspector.
Lecturer's Notes
There is a tendency of some inspectors to try to become the "consultant"
of the source. This is not an appropriate use of time. The job of the in-
spector is only to determine if there is a problem and if the source has made a
reasonable response to correct and minimize this condition in the near future.
It is the job of the plant personnel to make whatever supplemental measure-
ments and observations necessary to evaluate the exact nature of the problem
and to recommend the design and/or operational changes.
SLIDE 4-3.
MEASUREMENT OF STATIC PRESSURE
1. Manometers
2. Diaphragm Gauges
There are two main options available
for the measurement of static pressure:
manometers, (2) diaphragm gauges.
The manometer wnich can be filled with
. _, . , ' , ,
either oil or water, does not need to
be calibrated. It is a relatively
simple instrument and is not very vul-
nerable to malfunctions. Low range
manometers can be mounted on the
scrubber vessel permanently and slack
tube manometers can be used as a
portable instrument.
The diaphragm gauge can also be used as a permanently mounted unit or as a
portable instrument. These are made in a number of ranges from 0 to 2 inches
W.C. to as high as 0 to 150 inches. At the higher static pressures ( >36
inches W.C.) these diaphragm gauges are the only practical approach since the
manometers would be too long.
78
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SLIDE 4-4
A manometer is simply a U-shaped tube
filled with a fluid. When unequal
pressures exist at the tops of the two
ends, the fluid moves to equalize the
pressure difference.
The difference in the heights of fluid
in the two sides is a measure of the
pressure difference. In the sketch
shown here there is a difference of 20
inches. Therefore, the pressure is 20
inches of water.
It should be noted that the specific
gravity of the fluid is important. For
example, if mercury was placed in the
manometer shown to the left, it would
show a difference of only 1.5 inches
since it has a specific gravity of
13.6. Most scales used on manometers
assume a specific gravity of 1 (for
water).
SLIDE 4-5
The diaphragm gauge is shown in this
photograph. Near the back of the instru-
ment are two chambers separated by a
flexible diaphragm. This moves when
unequal pressures exist in the two
chambers. The degree of movement is
proportional to the static pressure
difference.
Diaphragm movement is sensed by a helic
coil. The move of this coil is trans-
mitted mechanically to the indicator
needle on the face plate. The unit
does not need electrical power
There is no gas flow through the two chambers. These actually are like
dead end streets to the lines coming from the scrubber to the instrument.
This feature minimizes the accumulation of material in the chambers and the
chemical attack of the diaphragm. As with any resilent synthetic material,
the diaphragm does have temperature sensitivities. Due to these limits, the
gauge is subject to problems when the diaphragm temperature is lower than 20
°F and higher than 140 °F.
79
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SLIDE 4-6
A small water filled manometer is shown
on the downstream side of a rod deck
gas-atomized scrubber. While this is a
relatively cold location, the gas temp-
erature going through this part of the
scrubber vessel is still 125 °F. This
is a very typical temperature for ex-
haust streams from wet scrubbers.
Since the manometer is in direct con-
tact with the wall, the manometer fluid
is constantly heated. The vaporization
will gradually reduce the amount of
fluid in the manometer. If the fluid
level is so low that a measurement can
not be obtained, plant personnel can be
asked to refill the manometer during
the inspection.
It should be noted that there is nothing to stop fluid vaporization from
a manometer regardless of how it is connected. When it is being used to
measure static pressure, one side is open to the atmosphere. When it is being
used to measure static pressure drop, both sides are open to areas with moving
gas streams.
SLIDE A-
Pluggage of a portion of the manometer
can occur due to the gradual diffusion
of particulate matter down one of the
lines. The accumulated material blocks
the movement of the fluid and can lead
to erroneous readings. Occassionally
there may be a need to remove the mano-
meter and clean it out.
These deposits are easy to spot. Plant
personnel should be able to correct
this during the inspection.
80
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SLIDE 4-8
A .T.cre common site of pluggage is at
the port itself. Solids or sludge can
quickly accumulate in the fitting used
to connect the manometer (or diaphragm
gauge) lines to the port. This is more
difficult to identify.
On negative pressure units, the lines
can be disconnected at the instrument
(by plant personnel) and a very small
scrap of paper placed against the line
opening. If the line is open the scrap
will be held firmly on the line. This
works even when the static pressure is
as low as -1 inch W.C. On positive
pressure lines, it should be possible
to feel slight flow out of the dis-
connected line onto the back of the
hand. This is not quite as sensitive
as the negative pressure test.
Some people attempt to feel the slight gas flows by placing the line
against their face. While this may be more sensitive for low positive pres-
sure conditions, it places the potentially toxic gas stream near the nose.
SLIDE 4-9
A manometer or diaphragm gauge used for
static pressure measurements should in-
dicate zero when the single line is
disconnected. This is indicated in the
slide to the left.
If a manometer fails to indicate zero
there is probably an obstruction in one
or both of the lines. Another possible
explanation is freezing of the fluid.
An attempt should be made to re-zero
diaphragm gauges which do not return to
zero when the static pressure line is
disconnected. If it can not be zeroed
it is definitely bad. Even if it can
be zeroed there still remains the
chance that it is defective.
A small section of 1/4" O.D. tubing can be connected to the instrument
(.with the plant representative's approval) and the response of the diaphragm
checked by applying slight positive and negative pressures. A squeeze bulb
with two check valves is useful for this purpose (one of these is present with
the oxygen analyzer to be discussed later). If the gauge responds in the
proper directions, it probably is operational.
dl
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SLIDE 4-10
"luggage of the port and/or the line
leading to the static pressure gauges
can be expected whenever a situation as
shown here exists. These are 1/4" O.D.
copper tubes leading from a number of
ports down to static pressure gauges in
the control room. It doesn't take much
solids to close off a tube this small.
The lines should be as short as possi-
ble and as large as possible. It is
not unusual to find plants which have
ripped out lines like this and put in
1/2" to 2" lines in order to minimize
the pluggage problem,
SLIDE 4-11
Another feature which is prone to
pluggage is the use of an elbow fitting
close to the port. This is an ideal
site for solids build-up. As a com-
plicating matter, the small pipe ahead
of the elbow fitting is horizontal and
fluid may not flow out easily.
62
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SLIDE 4-i;
One way to minimize pluggage problems
is to use a differential pressure
transmitter close to the port. This
converts the static pressure to an
electrical value which is then
displayed on a control room gauge.
Note that the pipe coming from the
scrubber wall is a 1" pipe. This will
plug less frequently than 1/4" ports
which are commonly used.
SLIDE 4-13
Liaphragm gauges which are attached
iirectly to the scrubber vessel wall
_^r. be adversely affected by the
internal gas temperatures. The exit
gas temperatures of the scrubber are
often quite close to the maximum
allowable temperature of the diaphragm
between the two chambers. Due to the
ease of heat conduct between the wall
of the scrubber and the gauge body, the
diaphragm could exceed recommended
temperatures. It should be remembered
"hat the diaphragm is in the back of
the instrument and therefore is quite
-lose to the scrubber wall.
One way to minimize this problem is to mount the gauge on a small
stand-off so that there is an inch of more of clearance between the back of
the gauge and the scrubber wall. This reduces heat transfer by direct con-
duction to relatively low rates.
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SLIDE 4-14
On-site gauges which are partially or
completely full of liquid are probably
not working properly. It is easy for
this liquid to accumulate even though
there is no gas flow through the in-
strument. Diffusion of moisture (and
some corrosive materials) can occur
down one or both of the connecting
lines. Condensation can occur in the
gauge itself or in the connecting
tubing. The orientation of many gauges
ensures that any condensation in the
tubing drains down to the gauge itself.
SLIDE 4-15
PROBLEMS WITH PLASTIC TUBING
1. 8RITTLENESS CAUSED BY
PROLONGED EXPOSURE TO
SUNGLIGHT AND COLD
2. COLLAPSE CAUSED BY
HOT ADJACENT SURFACES
Prior to accepting data from the on-
site gauges, the condition of the
connecting lines should be briefly
checked.
Tubing composed of polypropylene and
polyethylene can be common brittle and
break. This means that the part of the
gauge is actually sensing atmospheric
pressure rather than the scrubber sys-
tem static pressure. The error will
not always be apparent from the gauge
reading.
Tubing composed of a soft plastic (e.g. Tygon) can be inadvertently
crimped. If it drapes over a hot surface part of the tube may have collasped.
If problems with the guage connecting lines are chronic or severe, it may
be advisable to replace these with copper tubing. This is less susceptible to
crimping and can withstand surface temperatures up to 800 °F. It is the most
rigorous material for small diameter gauge connection lines.
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SLIDE 4-16
During level 3 inspections of wet
scrubber systems, portable instruments
should be used when there are questions
regarding the performance of the on-
site gauges. The portable instruments
for measuring static pressure are the
same as those used for on-site gauges.
This slide shows a slack tube manomet-
er. It rolls up to facilitate moving
from place to place. Magnets at the
top and bottom (see arrows #1 and #2)
are used to hang the instrument. Screw
in caps (see arrows #3 and #4) seal the
instrument when not in use.
It is obviously important to remember to close the end caps before
rolling up the unit and moving on. The fluid will run all over the careless
inspector. The manometer should not be used at locations which exceed the
limits of the unit. For example connecting a 36" slack tube to a port where
the static pressure is -50 inches will result in the quick loss of some of the
fluid into the duct.
SLIDE 4-17 Both the standard size and minature
size diaphragm gauges are shown in this
photograph. The small sized unit fits
in a pocket and is therefore easy to
carry around. It has an accuracy of
plus or minus 5% while the standard
sized unit is plus or minus 3% accuracy.
Both instruments are relatively insen-
sitive to vibration and shock. If the
static pressures measured are above or
below the range of the instrument, it
simply pegs. This does not hurt the
unit or throw it out of calibration.
Before use, the instrument is zeroed using the small set screws at the
front of each gauge. When used to measure static pressure one of the taps is
connected to the wet scrubber system and the other is left open to the atmos-
phere. When used to measure static pressure drop directly, both taps are
connected to ports on the scrubber system.
They are obviously subject to the same temperature limitations as gauges
mounted permanently on control systems. When used as portable instruments,
however, it is unlikely that they will be exposed to the extreme temperatures
for more than several minutes at a time before being put back into a protected
area. There is also little time available for diffusion of corrosive gases
down into the chambers. In other words, these work better when used as
portable instruments than when used into full time service as permanently
mounted gauges.
85
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SLIDE 4-18 Prior to starting the field work, the
diaphragm gauges should be calibrated
against a manometer. The apparatus for
doing this calibration is simple as
illustrated in the adjacent sketch.
Both the diaphragm gauge and a mano-
meter are connected to a tee fitting,
which in turn leads to some source of
positive and negative pressure. The
squeeze bulb with check valves is a
convenient source of positive or neg-
ative pressure since it is possible to
hold the pressure for a few moments.
The squeeze bulb supplied with the oxygen/carbon dioxide analyzer can be
used for this service. This has a range of -40 inches W.C. to + 40 inches
W.C. which is adequate for most situations. The complete calibration takes
about 5 minutes as long as the slack tube manometer can be left set up in some
out of the way location.
One of the basic requirements involved in the use of any portable instru-
ment is that the unit should be checked out and calibrated before leaving
the office for field work.
SLIDE 4-19
The diaphragm gauge calibration curve
^ should look like the graph shown here.
The data should fall close to a 45°
line. If the unit fails to remain
within the error band or if the plotted
data is non-linear, then the gauge
should be repaired or replaced.
The calibration data should be main-
tained in a convenient file at the
"i office and should not be taken to the
field. This data can be used later to
demonstrate that the measurements taken
in the field were accurate.
The same procedure discussed in the last two slides can be used to
calibrate a permanently mounted diaphragm gauge at the plant being inspected.
The connecting tubes are simply disconnected, and a slack tube manometer used
as the primary standard. It is not unusual to find that the various insults
suffered by the permanently mounted gauge has thrown it well out of
calibration.
86
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SLIDE 4-20 jr One of the wet scrubber operating para-
meters of most interest is the static
pressure drop. It is usually not
advisable to try to measure this dir-
ectly even though this can be done by
connecting the "hi" and "low" ports to
different parts of the system as shown
in the top portion of this slide.
With this approach, a large quantity of
flexible tubing is required and this
can become crimped during the measure-
ment. There is also a chance that one
of the ports will plug during the
measurement.
It is preferable to make the static pressure measurements one at a time.
The pressure drop is then calculated by subtracting one value from the other.
This approach is easier and less subject to measurement error. Less tubing is
also required since a maximum of 3 feet is normally required for static pres-
sure measurements.
SLIDE 4-21
-20
For locations which have high negative
static pressures, it is very important
to completely seal the port to prevent
aspiration effect error. With the
condition shown in this slide, the
localized static pressure at the tip of
the copper probe can be more negative
than the true negative static pres-
sure. This is due to the additional
suction effect caused by the high
velocity ambient air rushing in around
the probe. The threshold of this
effect is around -10 inches W.C. and it
becomes progressively more significant
as the pressures decrease (at -50 inches
it is worse than at -10 inches W.C.).
For example, it is possible to "measure" a static pressure of -25 inches
W.C. when the true static pressure is -20 inches W.C. At higher negative
static pressures, it is possible to "measure" a static pressure of -150 inches
W.C. when the true static pressure is -100 inches W.C. Sealing the port
tightly eliminates the problem immediately. Movement of the probe well into
the gas stream and away from the area of the infiltration also totally elimi-
nates the problem.
Lecturer's Notes
In practically every measurement discussed in the workshop, it will be
possible to enhance measurement accuracy by moving the probe into the gas
stream and away from the duct wall.
This problem is not unique to portable gauges. A permanently mounted
gauge with a crack in the weld of the port will suffer the same effect.
87
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PORT SEALING TECHNIQUES
1. Hand
2. Glove or Fabric Piece
3. Rubber Stopper
4. Sanding Disk with Rubber Stopper
SLIDE 4-22
Options for sealing of ports are listed
in this slide. The hand is never a
good choice since a tight seal is
almost impossible to achieve. Also,
the metal surfaces are usually hot and
may be covered with deposits of toxic
dusts.
A glove is also not appropriate. At
very high static pressures there can be
5 to 10 pound of force across the small
open areas of ports. The unwary person
will lose the glove to the equipment.
Inside, the glove will not be benefic-
ial for the system, regardless of where
it comes to rest.
The rubber stopper or the sanding disk with rubber stopper are more use-
ful since it is possible to get a good seal. The rubber stoppers main func-
tion is to maintain a tight hold on the probe so it is not lost. These two
approaches are useful as long as the port surface temperature is not too high.
SLIDE 4-23
SANDING DISK
COPPER TUBE
RUBBER STOPPER
The sanding disk with rubber stopper
approach is illustrated here. The
sanding disk must be a least 1" larger
in diameter than the outer diameter of
the port. It is the sanding disk which
provides the main seal against air in-
filtration. The rubber stopper behind
the sanding disk is drilled slightly
small so that the 1/4" copper tube is
firmly held. This apparatus is extreme-
ly cheap to assemble and is easy to use.
-DUCT WALL
88
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SLIDE 4-25
SLIDE 4-24 Another problem that can occur during
static pressure measurement does not
affect the accuracy but instead in-
volves a potential safety hazard. As
illustrated in this slide, any probe in
a rapidly moving gas stream will have
particles frequently colliding with the
probe surface. The rubbing action will
cause static electrical charges to
accumulate on the probe surface. It is
conceivable in certain situations that
the charges could reach a high enough
voltage to cause an arc from the probe
to the grounded duct wall. This would
initiate a primary explosion in the
duct with the possibility for more vio-
lent secondary explosions as the duct
ruptures. The factors which favor this
condition include: (1) an electrically
isolated probe, (2) low relative
humidity in the duct, and (3) high
particulate mass concentration.
One way to avoid any static charge
build-up on the probe is to use a
grounding/bonding cable similar to that
shown in this slide. On one end is a
standard household type clamp which can
be firmly attached to the metallic probe,
The other end is a jaw type clamp which
attaches to any grounded item outside of
the port. Since the cable does not have
any insulation, it is easy to confirm
that there are no breaks.
The grounding/bonding cable should be
visually inspected prior to use and all
connections should be made before the
probe is inserted into the gas stream.
The grounding/bonding cable allows the continual dissipation of the
electrical charges. The duct wall and the probe remain at the same voltage
potential. Therefore an arc can not occur.
If there is any question at all concerning the need for a grounding/bond-
ing cabe, it should be used. Obviously the clamp should not be attached to
any electrical line or conduit in the vicinity of the port.
One of the reasons this subject is emphasized in this workshop is that
wet scrubbers are often used to remove pollutants from gas streams which are
potentially explosive. All other particulate control systems have components
which could detonate the gases components, thus leaving wet scrubbers as the
only alternative. It is particularly important at the inlet of scrubbers to
avoid any possibility of static arcs. Downstream there usually (but not
always) is enough moisture to dissipate the static without the cable.
89
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SLIDE 4-26
Static pressure data is an important
part of all level 2 and level 3 wet
scrubber system inspections.
SUMMARY
STATIC PRESSURE MEASUREMENTS In the level 2 inspections, the on-site
guages should be checked to the extent
possible before the data is recorded in
the inspection notes. With the plant
management's permission, the lines to
gauge should be disconnected to check
the meter response and to determine if
the lines are plugged.
Obvious problems should also be noted, such as freezing of manometer
fluid, use of improper fluid for manometer scale, excessive temperatures on
diaphragm gauges, and water in diaphragm gauges.
The portable gauges used in level 3 inspections should be checked and
calibrated before use. Air infiltration around the port should be prevented
during the measurement by a seal which can not be sucked into the duct. The
probes should be grounded to prevent static accumulation.
SLIDE 4-27
The four types of instruments that can
be used to measure gas stream and
TECHNIQUES liquid stream temperatures are listed
FOR THE ^n this slide. Of these, the mercury
MEASUREMENT OF TEMPERATURE thermometer is definitely not desirable
1. Mercury Thermometer since it is easily broken.
2. Dial-Type Thermometer
3. Thermistor The thermister is often readily avail-
able from the control agency lab. This
however, is limited to a maximum temp-
erature of approximately 150 °F. It is
useful primarily for the measurement of
liquid temperatures and possibly the
measurement of pipe skin temperatures.
The dial type thermometer is attractive to control agencies since it is
relatively inexpensive. The limited reach of this instrument can lead to
measurement errors.
The most versatile instrument is the thermocouple. It operates over the
widest temperature range of any temperature monitor and the probes are easier
to use. The main disadvantage is the relatively high cost. Like all battery
powered instruments, the thermocouple should not be taken into potentially
hazardous locations.
90
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SLIDE 4-28
I
361
DIAL TYPE
THERMOMETER
HEAD
DUCT WALL
One disadvantage of the dial-type
thermometers is the very limited reach
possible with the 9 to 12 inch stems.
As shown in the adjacent sketch, the
temperatures of the gas streams close to
the wall may be lower than those out in
the main part of the duct.
In some common ports, the pipe nipple
extends out from the duct wall 4 to 8
inches. With these ports, the sensor
part of the instrument may only barely
be in the gas stream at all.
It is not wise to attempt to use the dial-type thermometers in any duct
in which there is a strong gas temperature gradiant. This situation should be
suspected whenever the port is close to flow disturbances such as elbows,
and access hatches.
This same problem can affect the accuracy of thermocouple mounted in
permanent thermowells. If they do not extend far enough into the gas stream,
they may also indicate lower than actual gas temperatures. There is no way
to tell from the outside of the thermowell just how far it does extend inward.
However, the plant instrumentation group should be able to supply this inform-
ation and explain the rationale for the specific thermowell length and
location.
SLIDE 4-29
If condensed water (or any other fluid)
is visible in the dial-type thermometer
the gauge is no longer working. It is
supposed to be a totally enclosed gauge,
so the presence of liquids demonstrates
that part of the stem has corroded or
eroded away.
91
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This is a photograph showing the
connection heads for two thermocouples.
Just by locating these heads it is
possible to determine the locations of
any thermocouples along the gas stream
path.
There is very little that happens to
these instruments that does not com-
pletely shut them down. If the unit
is providing a read-out at all, it is
probably working adequately. Of,
course it is always prudent to check
if the indicated temperature is logical,
All thermocouple data must be obtained in the control room for the
process or wet scrubber system. One of the most common errors in recording
this data is misassigned location I.D.s on the strip chart recorder or plant
data acquistion system. The best way to screen out these inadvertent errors
is to check the changes in temperature as the gas stream passes through the
wet scrubber system. Usually it gets colder until it reaches a gas reheater
(if used in the system). This is one of the reasons that it is helpful to
have a flowchart handy so the locations of the thermocouples can be clearly
marked.
SLIDE 4-31
THERMOCOUPLES
1. Calibrate probe and meter against a NBS
traceable thermocouple.
2. Check ice point and boiling point values
prior to each day.
When conducting level 3 inspections,
there is often the need to supplement
the available temperature data supplied
by on-site monitors. The instruments
commonly used for this purpose include
the dial-type thermometer and the
thermocouple.
Before starting any field work each
day, both should be checked in boiling
water and in finely crushed ice. This
two point check is not a full calibra-
tion but it does increase confidence in
the performance of either instrument.
On a regular basis, the units should be calibrated at a certified lab.
In the case of the thermocouple, it should be compared against an NBS
traceable probe and instrument. The cost for these semi-annual or annual
calibrations is nominal.
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SLIDE 4-32
TEMPERATURE MEASUREMENT ERRORS
1. Unrepresentative Measurement
Location
2. Cooling of the Probe Due to Air
Infiltration Through the Port
3. Impaction of Water Droplets
This list summarizes the three most
common errors in the measurement of gas
stream temperatures with portable
monitors.
To avoid the problems of unrepresent-
ative measurement locations, the port
location should be carefully chosen.
Again ports downstream of large access
hatches, or in bends in the duct work
are not the optimal locations. Also,
it is important to measure the gas
streams in the main flow of the duct
and not just at the wall.
The problem with air infiltration should be solved with the same basic
approach discussed with respect to the aspiration error in static pressure
measurements. The port should be completely sealed using a rubber stopper or
a sanding disk and rubber stopper.
SLIDE 4-33
Two ways to position the thermocouple
probe at the desired location well
inside a duct are shown in the photo-
graph to the left. The one on the left
of the slide is the tip of a S-Type
pitot tube. A flexible thermocouple
probe without a protective sheath has
been attached to the pitot tube. The
thermocouple bead is approximately 1"
behind the end of the pitot.
The equipment to the right of the slide
is a standard 1/4" O.D. copper tube
through the sanding disk seal. The
flexible thermocouple probe has been
threaded through the copper tube and
terminates at the end of the copper
tube.
93
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SLID? 4-34
Erratic temperature measurements can
occur immediately downstream from wet
scrubbers and evaporative coolers.
Liquor droplets in the gas stream
impact on the temperature probe and
briefly reduce the temperature from the
dry bulb to the wet bulb levels. The
observed temperature is characterized
by sudden drops in the values followed
by slow climbs back to steady state
values. This, of course, is only a
problem when the gas stream is not
fully saturated and there is a differ-
ence between the wet bulb and dry bulb
temperatures.
In some cases, it is possible to shield the thermocouple probe so that
there is no impaction on the probe itself. Also, a sample can be extracted
through a trap to remove the droplets prior to the monitor. The latter is
done at the risk of cooling the gas stream as it passes through the trap and
sample delivery lines. The preferred approach is to find another location
where the dry bulb temperature can be measured accurately.
When evaluating gas-liquor maldistribution, it is sometimes useful to use
ports where some liquor droplet entrainment remains. Gas streams from wet
scrubbers should usually be saturated and the presence of this measurement
problem is a sign of poor distribution. Wet bulb measurements can also be
made by wetting a sleeve around the thermocouple probe.
SLIDE 4-35
The liquor temperatures can be measured
by obtaining a small sample and then
using a dial-type thermometer, a therm-
ister, or a thermocouple. The probe
should be washed and dried after each
measurement to remove corrosive materials,
Frequently, it is necessary to estimate
the liquor temperatures at locations
where it is inconvenient to obtain a
sample. One example is the various
headers leading to nozzles on the inlet
of a venturi scrubber. For these sit-
uations, the pipe skin temperature can
be measured using either a thermocouple
or a thermister.
The pipe skin temperature is always slightly lower than the actual liquor
temperatures. However, it is proportional to the liquor temperatures. One of
the advantages of the baseline approach is that a shift in the pipe skin
temperatures becomes a meaningful parameter. It is not absolutely necessary
to know the actual values.
94
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SLIDE 4-36
When making temperature measurements
one of the main requirements is to
ensure that a representative location
is chosen. This applies to both on-
SUMMARY site instruments and to portable units.
GAS TEMPERATURE MEASUREMENT „.,,., , ,, . . «.-,..
With the portable instruments it is
possible to locate the probe well
inside the duct or even to perform a
complete traverse. This is useful when
a strong temperature gradient exists
across the duct.
Before using any portable instruments,
a two point (zero and 100 °C) calibration
should be made. The units,should be sent
out for calibration every six to twelve
months.
For liquid stream lines, the temperature of a small sample is measured.
In locations where it is impractical to get a sample, the pipe skin tempera-
ture should be measured.
SLIDE 4-37
The oxygen concentration of the inlet
gas stream is useful for evaluating the
combustion conditions at the boiler and
OXYGEN MEASUREMENT INSTRUMENTS for evaluating air infiltration up-
stream of the wet scrubber system.
1. ORSAT Analyzer
3. S^SSU *« instruments generally used for this
purpose are listed in the adjacent
slide. All permanently mounted units
are electroconductivity sensors. These
extract a small gas sample continuously.
They are normally installed directly
behind the boiler and next to any
continuous monitors for sulfur dioxide.
The ORSAT is a manual, wet chemical method which simultaneously yields
data concerning oxygen, carbon dioxide and carbon monoxide. The ORSAT
apparatus is relatively inexpensive. However, the measurement is time consum-
ing. The gas absorption instruments utilize the same techniques as the ORSAT.
The main difference is that each unit will only measure one compound. Also,
there is no gas absorption unit for carbon monoxide. The gas absorption units
are easy to carry around during an inspection.
95
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SLIDE 4-38
PROBLEMS WITH ELECTROCONDUCTIVITY
ANALYZERS
1. Unrepresentative Measurement Location
2. Air Infiltration into Sample Line
3. Defective Electroconductivity Cell
4. Pump Failure
The most frequent problems with the
electroconductivity instruments are
listed in this slide.
Unrepresentative locations can be
avoided by pulling the sample from well
inside the gas stream. It should not
be extracted close to the duct wall.
All of the other problems can be identi-
fied by the attempted calibration. All
permanently mounted units should have a
calibration cylinder having a known
oxygen concentration close to the con-
centration expected in the duct.
The calibration gas should be connected to the sample line through a
three-way valve which shuts off the duct line when the cal gas line is open.
The cal gas should enter the line very close to the duct wall so that leaks
along the sample line to the instrument can be found. Air infiltration along
the line leads to higher than expected oxygen concentrations while electrocon-
ductivity cell problems usually gives low readings.
SLIDE 4-39
The ORSAT analyzer is shown here. It
consists of three liquid reserviors
and a sample reservior. A gas sample
is drawn into the instruments and
sequentially mixed with all three
liquids, each of which removes one of
the gas sample components. The oxygen,
carbon dioxide and carbon monoxide
concentrations are determined by the
height of a column of liquid displaced
by the gas sample. This decreases as
each component is removed. The unit
has an accuracy of plus or minus 1/2%
for each gas compound.
The gas sample is drawn from the measurement port using a pump and a
Mylar or Tedlar sample bag. A portion of this sample is then pumped into the
ORSAT instrument. Care is necessary to avoid dilution of the sample during
pumping from the duct, during storage in the bag, and during pumping to the
instrument. This will obviously lead to high oxygen levels and lower than
actual carbon dioxide and carbon monoxide values. Another potential error
results from the use of exhausted absorption chemicals.
96
-------
SLIDE 4-40
A common type of gas absorption unit is
shown in this photograph. The absorb-
ing solution is similar to that used in
the ORSAT with the exception that there
are separate units for oxygen and car-
bon dioxide.
The types of solutions used in the car-
bon dioxide unit is potassium hydroxide
and in the oxygen unit is a combination
of zinc chloride, cuprous chloride and
hyrdochloric acid. Both solutions are
highly corrosive and should be handled
with care. If used improperly, it is
possible to get these materials on the
hands.
As with the ORSATs, it is necessary to change the fluids on a regular
basis. The oxygen solutions last for 50 to 100 measurements while the carbon
dioxide solutions last for 200 to 400 measurements. The actual fluid life
depends partially on the concentrations of gases measured.
SLIDE 4-41
DOUBLE
SEALED
PLUNGER
VALVE
FIN—^
ABSORBING
FLUID
This slide presents a cutaway sketch of
the Fyrite analyzer. The gas sample
is pumped into the top reservior using
a squeeze bulb (not shown). The double
seated plunger valve is manually closed
when sampling is done. The entire unit
is then inverted several times (between
two and four times) to completely mix
the gas sample and the fluid. The ab-
sorption of the specific gas compound
reduces the overall gas pressure inside
the unit, thereby causing the flexible
diaphragm at the bottom to rise. This
lifts the column of fluid up the small
center tube. The rise in the height of
the fluid is proportional to the amount
of gas absorbed.
The absorption of any gas is a temperature dependent process. If the
fluid is too hot, the indicated reading can be low and if the fluid is chilled
(during winter inspections) the indicated readings can be high.
Pumping gas through the reservior too long before closing the top valve
can give lower than actual readings. This is due to slow diffusion of the gas
down to the fluid surface resulting in depletion of part absorbable component
in the gas sample.
TOP
RESERVOIR
ADJUSTABLE
SCALE
FLEXIBLE
DIAPHRAGM
97
-------
SLIDE 4-42
GAS ANALYSIS ERRORS
1. Unrepresentative Location
2. Air Infiltration Through
Measurement Port
3. Air Infiltration Into
Sampling Line
4. Exhausted Chemicals
The four most common errors in the
use of gas absorption instruments and
ORSAT instruments are listed in this
slide.
In selecting a location to make the
measurement, it is wise to avoid the
areas adjacent to potential air in-
filtration sources. These include
access hatches, expansion joints, duct
flanges, and dust drop out hoppers.
If stratification of the gases in the
flowing gas are anticipated, it will be
necessary to make the measurements at a
number of locations across'the duct.
The pitot tube provides a convenient
means to "traverse" the gas stream for
this purpose.
SLIDE 4-43
TO GAUGE
When using a 1/4" O.D. copper tube as
the sampling line, it should extend a
foot or two into the gas stream. It
should also be bent in an upstream
direction so that any air infiltrating
through the port is not pulled into the
instrument sample line.
As with all metallic probes in rapidly
moving gas streams, a grounding/bond-
ing rod should be attached to the tube
before it is used.
98
-------
SLIDE 4-44
A typical sampling line for the gas
absorber is shown here. Item #1 is a
humidification tube which is needed only
during the calibration. The friction
seals on either side of the tube can
leak and it is helpful to use a line
without one of these for the field
measurements.
The items marked as #2 and #3 are the
inlet and outlet check valves. Air
infiltration can occur on the inlet
check valve if it does not seat
properly in the squeeze bulb or if the
check valve has cracked. Both problems
are common. Before using the sampling
line, its integrity should'be checked.
This is done by crimping the flexible tubing near the metallic probe and
squeezing the bulb. It should not reinflate while this line is crimped. If
it does, one of the check valves is not adequate. The fitting on the end of
the sampling line (marked with arrow #4) should then be blocked with a thumb.
It should be impossible to pump the squeeze bulb if the check valves are in
good shape. If the sampling line does not pass these two tests, then it
should be replaced before attempting any measurements.
SLIDE 4-45
CHECKING 02 AND C02
MEASUREMENTS
FUEL
Natural Gas
#2 Oil
#6 Oil
Bituminous Coal
Lignite
Anthracite Coal
Refuse
Wood
SUM OF 02 AND CO2
CONCENTRATIONS, %
13-19
15-20
17-20
18-21
18-21
19-21
18-22
18-22
To check the accuracy of either the gas
absorber instruments or the ORSAT the
sum of the oxygen and carbon dioxide
measurements should be checked against
the ranges shown in this slide.
If the sum of the two measurements does
not fall within this range, then there
has been a measurement mistake or the
chemicals are exhausted. In either
case the data is not good and should
not be used. These ranges take normal
instrument error into account.
Lecturer's Notes
A demonstration of the gas absorbers (or ORSAT) is often useful to
further explain how to check the accuracy of the measurements. A small mylar
bag should be filled with your exhausted breath to be used as "typical flue
gas" Measurements of the oxygen concentration should be approximately 15 to
16% and the carbon dioxide concentration should be approximately 4 to 5%. The
sum falls into the range for bituminous coal and for wood.
99
-------
SLIDF 4-46
GAS ABSORPTION INSTRUMENT
CALIBRATION TECHNIQUES
1. Gas Cylinders containing known
concentrations of oxygen and
carbon dioxide
2. Ambient Air for 02 instrument;
Exhaled Breath for CO: instrument
The two options for calibrating any
oxygen analyzer are listed in this
slide. Obviously the gas cylinders
containing known concentrations of
oxygen and carbon dioxide are the
preferred approach. This is the way
the electroconductivity instruments
should be calibrated. Records con-
cerning the frequency and method of
calibration should be on file at the
plant.
Agency inspectors using the ORSATs and
the gas absorption units should also
use gas cylinders if they are afford-
able. Alternatively, these can be
calibrated using ambient air and ex-
haled breath.
SLIDE 4-47
SUMMARY
During level 2 inspections it is useful
to mark the locations of any oxygen
analyzers on the system flowchart and
OXV6EN ANO
electroconductivity instruments should
be checked briefly. The condition of
the sample delivery line should be
checked for possible leaks. If there
are any questions about the data, the
plant personnel should be asked to
repeat the calibration (single point is
adequate) during the inspection.
If plant personnel are using the ORSAT
or the gas absorbers, the inspector
should confirm that the sum of the
values makes sense and that the probe
or bag is not leaking.
The gas sample should always be taken at a location well within the duct
to avoid ambient air infiltration. In some cases, multiple measurements
across the duct may be necessary if the gas stream is stratified.
As with any probe used in the rapidly moving gas stream, it is important
to use the grounding/bonding cable to prevent static accumulation. Both the
ORSAT and the gas absorption instruments use highly corrosive liquids and care
in handling is necessary. If some is spilled it is important to wash it off
the skin prompty and keep the liquid away from the eyes.
100
-------
TECHNIQUES
FOR THE
MEASUREMENT OF SCRUBBER LIQUOR pH
1. Indicator Paper
2. pH Meter (Battery Powered)
SLIDE 4-48 pH instruments are used in wet scrubber
systems to control the addition rate of
alkaline materials. They enhance the
absorption of some gases, ensure that
oxidizing chemicals are in the active
chemical form, and reduce the chances
of corrosion.
The only way to check the on-site pH
meter accuracy is to obtain a liquor
sample FROM THE SAME LOCATION AS THE
METER PROBE and repeat the measurement
with another meter. On level 2 in-
spections this is not possible since a
meter is not brought to the plant. It
would be possible to take a sample back
to the agency lab. However, there is
always a question about the stability of
the pH as the sample ages.
On level 3 inspections, it is possible to use either indicator paper or a
battery powered pH meter. The measurement should be made soon after the sample
has been obtained.
LIMITATIONS OF pH PAPER
2. Oxidizing Solutions
3. High Suspended Solids Levels
SLIDE 4-49 The inherent limitations of pH indica-
tor paper are listed here. These are
most common when inspecting odor con-
trol scrubbers using hypochlorite
solutions or permanganate solutions.
As long as the listed conditions are
not present, the pH paper has an accur-
acy in the range of plus or minus one
full pH unit. This may not seem to be
very accurate, but highly accurate pH
data is not needed in all inspections.
In many situations, it is only necessary to know that the pH is not much
below 6 or much above 11. The pH paper provides sufficient accuracy to
support this conclusion. Therefore, it is acceptable for a large portion of
the particulate wet scrubbers.
101
-------
rr .use
CALIBRATION TECHNIQUE
FOR pH MEASUREMENT
Use Fresh Buffer Solutions to
Calibrate Battery Powered pH
Meter or to Check Indicator
Paper.
Prior to any pH measurement, the meter
should be checked against buffer
solutions of approximately 4, 7 and 10
pH units. Reasonably fresh buffers
should be used since they have a ten-
dency to age.
Although it is not usually done, it is
also a good practice to check the
indicator paper against a least one of
the buffers within the measurement range
of the paper. If the paper has aged, it
will not indicate properly.
Lecturer's Notes
If there are any questions concerning how to use a pH meter,'it should be
demonstrated using the coffee, soft drink and limestone slurry solutions. The
latter is used to illustrate how the pH can change over time as alkaline mat-
erial slowly dissolves. Most of the attendees are experienced with these in-
struments. Therefore, these demonstrations can often be skipped
SLIDE 4-51
PITOT TRAVERSES
TO
MEASURE GAS FLOW RATE
The pitot traverse is conducted when
there is a need to determine the gas
flow rate. These is done (1) to eval-
uate the amount of gas pulled from
process hoods and equipment, (2) to
evaluate increases in static pressure
drop across scrubbers, and (3) to quan-
tify air infiltration into scrubbers.
This is a time consuming measurement
that is not done routinely by plant
personnel or agency inspectors. For
these reasons, this is not part of a
normal level 2 inspection. It is
necessary in only a fraction of the
level 3 inspections.
102
-------
SLIDE 4-52 There are two types of pitot tubes: the
standard pitot and the S-type pitot.
The standard pitot is two concentric
tubes shaped like an "L". The center
tube is open to the gas flow and
measures the total pressure of the gas
stream (velocity pressure plus the
static pressure). The outer tube has
a number of small holes around the
circumference. When the standard pitot
tube is in the proper orientation,
these small holes are pointed normal to
the gas flow direction. They measure
only the static pressure. When both
pitot tubes are connected across the
differential pressure gauge, the vel-
ocity pressure is read directly.
t
The S-type pitot tube is shown on the left center of the photograph.
It consists of two parallel tubes bent in opposite directions. The one
facing the gas stream measures the total pressure and the one pointed away
from the gas stream measures the static pressure. The velocity pressure is
measured as the difference between these two pressures.
The S-type pitot tube is preferred for equipment inspection since it is
less prone to pluggage when used in areas with high particulate mass levels or
with entrained water droplets. The main disadvantage of the S-type is that it
must be calibrated.
Lecturer's Notes
Both types of pitot tubes should be on display during breaks during the
lecture. It is also helpful to have an inclined manometer or a low range
diaphragm gauge available to illustrate how the velocity pressure is measured.
It is not wise to pass the large 6 foot long pitot tubes around the room
during the lecture for obvious reasons.
SLIDE 4-53
VELOCITY PRESSURE GAUGES
0-10" Inclined Manometer
O-2" Differential Pressure Gauge
The two instruments available for the
measurement of velocity pressure are
listed in this slide The type used in
stack tests is the inclined manometer
(either 0 to 5 inch or 0 to 10 inch
units are available). It provides high
accuracy in the 0 to 1 inch velocity
pressure range which is the most commonly
encountered range. It is somewhat bulky
to carry around and difficult to level.
As an alternative to the inclined man-
ometer, the low range diaphragm gauge
can be used. This one has a "D" ring
taped to the top so it can be hung from
a magnet. It is slightly less
accurate but easier to use.
103
-------
4-54
CHECKING FOR CYCLONIC FLOW
Port
K^£
Por^f
xC
1 Pitot-/
Tub*
Flow
PLAN VIEW
(Gal flow upword
"out of pog«")
Duct Wall
SIDE VIEW
A check for cyclonic flow should be made
before beginning the pitot traverse or
any of the preliminary work in deter-
mining the number of traverse points
required. Cyclonic flow is very common
down stream of wet scrubber denisters
and certain fans.
As shown in the adjacent slide, the
pitot tube is inserted with the nozzles
oriented perpendicular to the direc-
tion of gas flow. Since both nozzles
should be sensing the static pressure,
the differential pressure indicated on
the gauge should be zero.
The pitot tube should be rotated 10 to 20° in both directions in an
attempt to "null" the readings. If measurable velocity pressures persist even
with this slight twist, then the flow has too much cyclonic character to con-
duct a pitot travers.
Lecturer's Notes
It is important that this check be done first. There is no sense making
all the traverse point calculations and marking the probe if the location is
not acceptable due to cyclonic flow. Inspectors should not ignore this test
even though cyclonic flow appears unlikely. The angular momentum of cyclonic
flow can persist for long distances. Therefore, the origin of the gas spin
may not be so obvious.
SLIDE 4-55
a:
to
CO
UJ
a:
a.
>-
o
3
LJ
PARABOLIC
/DISTRIBUTION
PLUG FLOW
DISTRIBUTION
DISTANCE FROM PORT, *.
Conducting a pitot traver in accordance
with EPA Reference Method 2 can be very
time consuming. In some cases, the
inspector may be able to make a single
point velocity pressure measurement
rather than a full traverse. This is
appropriate when only an approximate
estimate of flow rate is sufficient.
A quick check of the velocity pressures
across the duct should be made to deter-
mine if a single point traverse is
possible. If the distributions are
similar to either of those shown on this
slide, a single point measurement is
possible.
In the case of the parabolic distribution, the velocity pressure should
be measured at the peak of the curve. The average velocity is related to the
peak velocity multiplied by 0.81. In the case of the plug flow distribution,
the average velocity is equal to the measured value near the center.
104
-------
SLIDE 4-56
If a complete traverse is necessary, the
procedures stated in EPA Method 2 should
be followed. The distances to the
upstream and downstream flow disturb-
ances are measured and the number of
traverse points are determined from the
Method 2 figure.. The next step is to
measure the diameter of the stack or
duct. The diameter can be measured by
placing the pitot tube across the duct.
However, this risks damage to the sensor
tips of the pitot. It is also possible
to jam solids into the pitot tube if the
opposite wall has thick deposits. A
better approach for measuring the dia-
meter is to measure the circumference
and divide by 3.14 (assuming it is
cylindrical).
SLIDE 4-57
Source: Air Pollution
Training Institute
One of the most common errors made
during a pitot traverse is the rotation
of the tube away from the direction of
the flow. When this occurs in the manner
shown in this slide, it is termed the
"Yaw" error.
With slight rotation, there tends to be
higher than actual velocity pressures
measured. Additional rotation results
in readings far below the actual values.
This type of error is generally due to
lack of concentration on the part of the
inspector. It is important to keep the
two parallel tubes which comprise a
S-type pitot tube constantly lined up
in the direction of gas flow.
105
-------
SLIDE 4-58
Source: Air Pollution
Training Institute
j.'he second form of alignment error is
the "Pitch" angle. As the pitot tube
moves at an angle to the gas flow
direction, the value of the observed
velocity pressure drops rapidly.
This error is particularity difficult
to prevent on large ducts when the
pitot tube may be extended as much as 6
feet into the gas stream. The inspect-
or is then holding only a small portion
of the pitot and has very little lever-
age. Compounding the problem is the
tendency for the pitot tube to "sail"
in high velocity gas streams.
Every attempt should be made to minimize this error by watching the
angle of the pitot tube relative to the duct or stack. The measurements
should be repeated several times if there is any question concerning the
quality of the data.
As with any probe in a moving gas stream, a grounding/bonding cable
should be attached to the pitot tube prior to conducting the measurement. It
is also important to seal the port to prevent air infitration related errors
on points close to the port and to prevent exposure to toxic particulate and
gases coming out of the duct.
Lecturer's Notes
Several of the.port designs shown later in this lecture have been
specifically designed to minimize yaw and pitch error while conducting pitot
traverses. These designs also seal the port so there is less chance of
exposure to toxic gases and particulate during the measurement.
SLIDE 4-59
SUMMARY
GAS FLOW MEASUREMENTS
In summary, an S-type pitot tube is
normally used for gas flow measurements
since it is less prone to pluggage
than the standard pitot tube. Before
conducting the full traverse, it is
necessary to check for cyclonic flow.
A pitot traverse should not be done in
any location where cyclonic flow is
significant. The velocity pressure
distribution should also be checked
before beginning the calculations for
the traverse. If it is parabolic or
very uniform, a single point traverse
may be possible.
Whenever conducting a pitot traverse
the grounding/bonding cable should be
attached. The port should be sealed
to prevent exposure to toxic pollutants
and to prevent measurement errors.
106
-------
FACTORS AFFECTING GAS FLOW
Rotational Speed
System Resistance
Dampers
SLIDE 4-60
The gas flow rate through a wet scrub-
ber system is partially controlled by
the fan rotational speed and the fan
damper settings. The fan operation
should be checked whenever gas flow
changes have been shown by pitot trav-
erses or are suspected based on the
scrubber operating conditions.
One of the best indicators of fan op-
erating conditions is the fan motor
current. AN INCREASE IN THE CURRENT
MEANS AN INCREASE IN THE TOTAL MASS OF
GAS MOVED BY THE FAN. By adjusting for
changes in gas density, it is possible
to QUALITATIVELY evaluate changes in
the gas flow rate.
There is no practical means to check the accuracy of on-site fan current
meters using inspector supplied portable instruments. Inspectors should re-
quest that the plant representative arrange for the current to be measured
using an inductance ammeter if there is any question concerning the indicated
value. This can also be done if the fan motor current is not monitored. Under
no circumstances should the inspector attempt to make this measurement! Only a
qualified electrician should open electrical cabinets and make current mea-
surements.
SLIDE 4-61
MEASUREMENT OF FAN SPEED
1. Manual Tachometer
2. Phototachometer
3. Strobetachometer
4. Sheeve Ratio Calculation
The gas flow through an air pollution
control system is proportional to the
fan rotational speed. In a sense, the
fan works like a shovel and the faster
it moves, the more gas is moved.
On direct drive fans, the speed can be
changed only by changing the motor.
The speed can be read directly from the
nameplate of the motor. On belt driven
fans, the most common type on wet
scrubber systems, it is easy to modify
the fan speed simply be changing the
sheaves.
There are rarely monitors for the fan speed. Whenever the fan speed data
is needed, it is measured by plant personnel using one of the instruments listed
above. The same instruments can be used by agency inspectors. The manual
tachometer is inexpensive and easy to use. There must be good access to the
end of the fan shaft, but this is often blocked by belt guards. Phototachometers
and strobotachometers do not require direct access to the rotating equipment.
However, these are more expensive and difficult to use. In the case of the
phototachometer, a piece of reflective tape must be placed on the fan shaft
(when the unit is down) to serve as a light reflector.
107
-------
SLIDE 4-62
One way to estimate the fan speed is to
::easure the fan sheaves. The fan speed
is the ratio of the fan sheaves times
the fan motor rotational speed. The
latter can read directly from the name-
plate of the motor.
This photograph illustrates the mea-
surement of the sheave on the fan. In
this case, it is easy to see the sheave
and to make a reasonable measurement of
the diamter. Some fans come with a
sheet metal belt cover rather than the
expanded metal cover shown here. With
the sheet metal covers, it is impossible
to estimate the sheave diameter and this
approach is not possible. 'THE BELT COVER
SHOULD NEVER BE REMOVED. ALSO, THE FAN
SHOULD NOT BE OPERATING WHEN THE SHEAVE
DIMETER IS BEING MEASURED.
Fan RPM = (MRPM)[MD/FD]
Where:
MRPM = Motor Speed
MD = Motor Sheave Diameter
FD = Fan Sheave Diameter
It could be argued that this is not an
accurate enough measurement. However,
it clearly indicates when an inten-
tional change in fan speed has been
made. This fact is more important than
the actual fan rotational speed value
at the present time.
OBSERVATION OF FAN
OPERATING CONDITIONS
1. Severe Vibration
2. Belt Squeal
SLIDE 4-63
The presence of fan vibration and/or
belt squeal should be noted.Severe fan
vibration can occur due to build-up of
material on the fan wheel or due to
erosion of the fan wheel. Bearing wear
is another common cause of this conditions,
IF THERE IS SEVERE VIBRATION, THE
INSPECTOR SHOULD LEAVE THE AREA
IMMEDIATELY! THE FAN CAN DISINTEGRATE
SUDDENLY! It can occur during start-up
and during sudden changes in routine
operation.
Belt squeal is due to the slippage of the drive belts in the fan and/or
motor sheaves. This results in a modest fan rotational speed reduction, often
in the range of 100 to 200 rpm. It is hard not to notice the highly irritat-
ing belt squeal.
108
-------
FAN EVALUATION LIMITS
1. Damper Settings
2. Gas Flow Rates
SLIDE 4-64 There are two things that can not be
determined by evaluating fan operating
parameters or by checking fan condi-
tions . These practical limits to fan
evaluation are listed in this slide.
It is usually impossible for an agency
inspector to check the damper position
from the position of damper activators
outside the duct. A change in the gas
flow rate can be made by changing the
damper position without any change in
the rotational speed. The only in-
dication of this is a change in the
motor current and the latter is af-
fected by a number of conditions, not
just damper position.
It is also extremely difficult to estimate the gas flow rate through the
fan based on fan operating parameters such as static pressure rise, motor
current, rotational speed and gas temperature. The fan performance curves are
expressed in terms of the brake horsepower which is related to the motor
current. Unfortunately the brake horsepower is also affected by the motor
load factor for common three phase motors as indicated in the equation below.
B.H.P.
-yr
Where: B.H.P. =• Brake Horsepower, Watts
A = Motor Current, Amps A.C.
V = Motor Voltage, Volts A.C.
L = Motor Load Factor, dimensionless
The load factor is the difference in the phase angles of the voltages and
currents in the alternating current line. This is not a constant value at a
given site over time. For example, this will vary significantly as the over
load of the motor is varied. Also, other electrical equipment at the plant
can influence the load factor for the motor serving the wet scrubber fan. The
only way to measure this value is to place wattmeters on two of the three lines
of the three phase motor. This degree of effort goes beyond that reasonable
for field inspectors especially considering that the pitot traverse is both
easier and more accurate.
SLIDE 4-65
SUMMARY
FAN EVALUATION
During level 2 inspections the fan
motor current should be noted from the
on-site meters. If there is any question
about the data, the inspector should
request that plant personnel remeasure
the motor currents using an inductance
meter. In some cases, the fan speed can
be estimated by using the sheave ratio
method. The nameplate rpm ratings of
the fan motors should be noted in every
case. During level 3 inspections, the
fan speed should be measured when gas
flow changes are suspected.
109
-------
PUMP OPERATING PARAMETERS
1. MOTOR CURRENT
2. DISCHARGE PRESSURE
SLIDE 4-66 The data concerning pump performance is
similar to that for analyzing fan op-
eration. The pump motor current is
proportional to the quantity of liquid
delivered. If this is not measured
continuosly, it can be measured during
the inspection by plant personnel using
an inductance ammeter. Like the fan
gas flow rates, it is not possible to
quantify the liquid flow rate using the
motor currents.
The second operating parameter of in-
terest is the pump discharge pressure.
This is normally monitored by a gauge
mounted immediately downstream of the
main control valve on the discharge
line.
It should be obvious that there are no "portable" gauges which can be
used to measure the pressure in a pipe. If there is no gauge or not a fitting
which would accept a gauge, it is impossible to determine the pressure. When
there is some question concerning an existing gauge, it is sometimes possible
to temporarily substitute a new unit for the present gauge. There must be a
valve isolating the gauge if this is done while the pump is operating. It is
conceivable that a regulatory agency inspector could bring a gauge for this
purpose. However, a pipe fitter would be needed to connect the gauge to the
specific valve fittings.
SLIDE 4-67 The most common type of liquid pressure
gauge is a bourdon tube. This has a
metallic element which bends slighlty
when exposed to pressure. The movement
of the bourdon tube in response to the
pressure is transmitted mechanically to
the indicator needle.
Pressure gauges of this type are vul-
nerable to pluggage within the tube
itself and in the gauge inlet. The
indicated value on the gauge is no
longer valid when it is plugged. As
with all pressure gauges, there is no
flow through the gauge to purge it of
accumulated solids. To minimize the
problem, the gauges should be mounted
above the pipe to facilitate drainage.
Excessive vibration can also lead to the early demise of bourdon gauge.
Constant vibration, especially on the pump discharge, leads to the eventual
failure of the mechanical linkage between the bourdon tube and the indicator
needle. Vibration can be minimized by mounting the pressure gauge on a short
coil of pipe or tubing which dampens the vibration intensity.
110
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TYPES OF LIQUID FLOW MONITORS
1. Rotameters
2. Orifice Plates
3. Paddle Wheel Gauges
4 Vane Type Gauges
5. Magnetic Flow Meters
6. Doppler Gauges
SLIDE 4-68 There are a number of instruments in
use for measuring the liquid flow
rates. All but one of these must be
permanently installed on the pipe.
While the doppler instrument could be
used as a portable inspection tool, its
use has been limited due to its high
cost. This means that there is no
portable instrument available to check
the accuracy of the on-site permanent
instruments. This fact increases the
importance of checking the meter op-
eration to the extent possible.
All of the liquid flow meters can suffer performance problems when
exposed to high suspended solids liquor streams and to corrosive liquids The
degree of vulnerability varies roughly with the cost and sophistication of the
instrument .
Lecturer's Notes
large majority of wet scrubber systems do not have flow meters This
is especially common on the medium to small systems. Due to the lack of port-
able instruments, there is no way to estimate liquid flow rate in such
systems. This is particularly unfortunate since a number of scrubber
problems include a reduction in liquid flow and the availability of this data
would aid in the early detection of the problems. Some inspectors have at-
temped to overcome this deficiency of data by attempting to measure the flow
from the scrubber sump using a bucket and stopwatch. This is not advisable
since many of the scrubber effluent liquors have irritant characteristics and
a few have pathogenic organisms.
SLIDE 4-69
This is a photograph of an orifice
meter on a sewage sludge incinerator
scrubber. The orifice plate is in the
middle of the flange. Taps before and
after the flange are connected to a
mercury filled manometer to measure the
differential pressure across the plate.
This pressure is proportional to the
liquid flow rate through the orifice.
Gradual erosion and corrosion of the
sharp edge orifice plate will cause the
gauge to read less than the actual flow
rate. Unfortunately, there is no easy
way to confirm that the orifice plate
has been damaged until the pipe can be
isolated or the system shut down.
These must be inspected frequently due
to the susceptibility to v/ear.
Ill
-------
I Venturi
Meter
SLIDE 4-70
A venturi meter works in a similar manner
to the orifice plate. Here, the liquid
is accelerated as it enters the converg-
ing section and it decelerates as it
&f leaves through the diverging section.
^ Pressure lines before and after the
venturi throat are connected to a mer-
cury filled manometer. The liquor flow
is proportional to the differential
pressure. Unlike the orifice plate,
this instrument does not have a compon-
ent in the direct path of the abrasive
liquid stream.
The main disadvantage of the venturi
meter is the space requirement. It is
also much more expensive than the
orifice plate.
One of the few problems which can affect the accuracy of this type of
flow monitor is pluggage of one or both of the manometer leads. It may be
possible to see these deposits.
SLIDE 4-71
Swinging
Vane
A sketch of a swinging vane liquid
flow meter is shown in this slide.
This instrument is mounted in line with
the piping. The deflection of the vane
is proportional to the liquid velocity.
This deflection can be seen through
the transparent portion of the unit.
Like most other styles of flow meters,
these are vulnerable to error when used
in high suspended solids streams. The
accumulation of solids on the vane
changes the weight and therefore
affects the amount of vane movement at
a given liquid velocity. The solids
can accumulate to the point that the
vane is unmoveable.
112
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SLIDE 4-72
Magnetic Flowmeter
A magnetic flowmeter is less susceptible
to measurements problems in liquid
streams with high solids levels. It is
considerably more expensive than other
flow monitors discussed so far.
A magnetic field is established at right
angles to the flow through the instrument,
Since water is an electrical conducter,
a current is induced as the water cuts
the magnetic field lines. The inducted
current is measured by electrodes on both
sides of the instrument. This current is
proportional to the liquid velocity. The
flow rate is calculated as the cross
sectional area of the pipe times the
average velocity.
i
Since the sensor portion of the instrument is not in the direct path of
the liquid, there is only minimal abrasion. The only components which are
vulnerable are the two electrodes and the lining of the flow tube. The latter
is normally lined with an abrasion resistant material such as polyurethane.
The instrument can be calibrated using actual liquid streams in a cal-
ibration rig. A simplier and more common technique is an electronic calibra-
tion of the instrument circuits. The latter is normally adquate for use
with wet scrubber systems.
SLIDE 4-73 The doppler liquid flow monitors use
ultrasonic noise to sense the velocity
of solids and bubbles entrained in the
liquid stream. These can be installed
as permanent instruments or used as
small portable gauges. The permanent
instruments generally have a sensor
that is exposed to the liquid stream
while the portable units simply clamp to
the outside of the pipes.
The transmitting element sends an ultra-
sonic sound wave diagonally into the
liquid stream. The rapidly moving par-
ticles or bubbles reflect this wave back
at a frequency slightly higher than the
transmission signal. The difference in
frequencies is proportional to the
velocity of the liquid stream.
To use this portable instrument, it is necessary to carefully clamp the
sensor to the pipe wall. An acoustic pad supports the sensor and special
petroleum is used on the pipe wall. This is necessary to optimize the
transmission of the sound waves in and out of the pipes. The "wetted" sensor
used for permanent installations is more sensitive since there is no pipe wall
to attenuate the signal and to cause "ringing" of the sound.
113
Source MAPCO Controls Co.
-------
DOPPLER METER LIMITATIONS
1. Bubbles or Paniculate Necessary
2. Velocities Must Be Greater Than
One Foot Per Second
3. Pluggage of Element Port Possible
SLIDE 4-74 The major limitation of this approach
is the need for an adequate concentra-
tion of bubbles and/or particles in the
liquid stream. This technique will not
work for clean liquids.
As with any sensor exposed to the
liquid stream there is always the
potential for pluggage over the sensor.
This could act to reduce the sensit-
ivity of the instrument. Corrosion of
the ultrasonic elements is also
possible in some cases.
This can not be used at all below liquid velocities of 1 foot per second
and has limited sensitivity below 3 and 1/2 feet per second. Neither of these
limits presents serious problems, however, since most liquid streams are in
the range of 5 to 12 feet per second.
OTHER POTENTIALLY USEFUL INSTRUMENTS
1. BuMMLml
2. FitMTKOP*
3. Sling Psychromettr
4. Nvptil4onMlflr
6. ExotMion Proof Flashlight
7. Range Finoef
SLIDE 4_75 Other instruments potentially useful
for wet scrubber system inspection are
listed here.
A small level is used to determine if
the piping is sloped properly. The
suction line should be sloped as least
1° to prevent the accumulation of air
pockets. The recirculation lines
should be sloped to faciliate draining
and to faciliate solids flushing.
Fiberscopes have the potential to allow
close-up inspection of nozzles mounted
inside hard-to-reach scrubber internal
areas. Commercially available models
include a battery powered light source
and a 6 foot long rigid probe which
rotates. The probes are normally 1/4"
diameter. Therefore, these would fit
through common static pressure measure-
ment ports.
The sling psychrometer is often useful for measuring the ambient relative
humidity during visible emission observations. The wet bulb and dry bulb
temperatures are measured simultaneously with this instrument and the relative
humidity is determined by plotting the data on a psychometric chart.
Nephleometers have been suggested for use as portable opacity monitors
for wet scrubber systems. These are not vulnerable to water droplet inter-
ference problems which to date have precluded use of transmissometers. They
operate as extractive instruments. Therefore, only a small port is
needed.
114
-------
The next set of slides concerns
measurement ports. It is important
to select the appropriately sized and
SELECTION OF located ports in order to avoid the
MEASUREMENT PORTS measurement problems discussed so far
in this lecture.
Unfortunatly, a large number of exist-
ing wet scrubber systems have no ports
at all or have ports in inaccessible
locations. HEROIC EFFORTS SHOULD NOT
BE MADE TO REACH IMPROPERLY LOCATED
PORTS
Hopefully, in the next several years, regulatory agencies will encourage
source operators to install the proper ports so that both the operators and the
inspectors can adequately evaluate performance of wet scrubber systems. Some
port designs are recommended in this section. Locations for measurement ports
are discussed in the lecture concerning each specific type of scrubber vessel.
SLIDE 4-77
The only ports available on some units
are the stack sampling ports downstream
of the scrubber. These are usually
four inches in diameter.
If the gas stream is slightly positive,
the pollutant laden gas will flow out
rapidly and accumulate in the breathing
zone of the person making the measure-
ment. If the port is under negative
pressure, ambient air will rush through
the port and cause errors. These ports
are difficult to work with.
An additional problem with large ports is the removal of the pipe caps or
plugs used to seal the ports when not in use. This can take several hours.
115
-------
SLIDE 4-73
This photograph illustrates the ideal
size for a measurement port on a wet
scrubber vessel. It should be in the
range of 1/4" diameter to 1" diameter.
This minimizes the potential for
fumigation in positive pressure systems
and reduces the ambient air infiltration
problems in negative pressure units.
The small plug is also much easier to
remove than large ports.
On gas handling ducts, a larger port is
necessary to permit the use of an S-type
pitot tube. It should be at least 1 and
1/2" in diameter but smaller than
2" diameter.
SLIDE 4-79
There must be convenient and safe
access to the port itself. Running
small diameter tubing down from an
inaccessible ports is not sufficient.
It is difficult to clean out a plugged
port with this arrangement. It is
impossible to measure the gas tempera-
ture even if a pump were used to pull a
gas sample. The temperature would drop
close to ambient levels while passing
down the tubing. Even the measurement
of gas stream oxygen and carbon dioxide
concentrations is difficult under these
circumstances.
116
-------
4-80
This is a photograph of a clean out
port (marked as arrow #1) with a dif-
ferential pressure transducer (marked
as arrow #2). The purpose of this port
is to permit removal of accumulated
solids from the port while the D/P
transducer is off-line. OPENING THIS
PORT WHILE THE INSTRUMENT IS OPERATING
WILL RESULT IN AN ERRONEOUS SIGNAL
BEING SENT TO THE PLANT PROCESS CONTROL
SYSTEM. THE PROCESS WILL BE TRIPPED
OFF-LINE. Do not open these clean out
ports!
A small inspection port installed at
least several feet from the instrument
port could be opened without causing
this problem.
Lecturer's Notes
This is a good time in the lecture to make the point that specific ports
are needed to faciliate wet scrubber inspection. Ports installed for stack
sampling or for routine system monitors are rarely the correct size or at the
correct location. Specific ports should be installed to faciliate the use of
portable inspection instruments!
SLTDE 4-81
~i
INSTRUMENT
S»iGEU» PLUG • SS-«00-»,
WRKER 0-RING
SIZE 2-202
MttGELOK NUT
• SS-602-1
SVHAGELDK "ALE CONNECTOR
-
Fi|ur. 3-3b. I/A" Port With
SuMt'd Flu|
OUTSIDE
INSIDE
55 FLAT HEAD RIVET
!/«• X 1 S/«'
StUGELOK NUT -SS-«02-I
-SWAGELOK TO MALE
HRE WELD CONNECTOR
»SS-«00-l-«Mfw
Fiturt 3-Jt. 1/A" Pen wi
S««l hi! O
SWAGELOK MALE CONNECTOR
J-Jc. 1M* fort With
Sut Typ. Up
A sketch of a 1/4" inspection port is
shown in this slide. This port is made
from a standard Swagelock fitting which
is welded to the side of the duct or wet
scrubber wall. An 0-ring seal prevents
any gas leakage outward or ambient air
infiltration.
For areas where accumulation of solids
or sludge is likely, the port can be
inclined 30° to permit drainage.
The port is sealed with a cap with a
small rod attached. This fills the port
recess when not in use. A simple cap
plug could be used in situations where
rodding out the port is not difficult.
117
-------
S'.JDE 4-82
0-fiir.G '• n/16 CC * ' 5/16 1C X 3/)t DIA
/-l/4"-20 THUMB SCREW X !'LG
1 S/1«' WOBE SHELL
SCORE CO_A«
"I
JJrH
LD UJ—I
M
-S5P1PE-1 1/4-|« I
.MO WALL
(2) 3/8 HEX HS BOLT X 1' LG
WITH HEX NUT
A Dort useful for ductwork ahead of and
following the wet scrubber vessel is
shown here. This consists of a 1 and
5/16 inch diameter pipe welded to a
flange. There is also a gas tight weld
to the side of the duct.
This port serves as a support and
alignment mechanism for a pitot tube.
An outer flange allows rotation 10 to
20° in either direction to correct for
minor cyclonic flow. An 0-ring on the
shoulder of the inner flange fits
around the pitot tube to provide a gas
tight seal. This again protects the
inspector during the measurements and
also prevents air infiltration on
negative systems.
It should be noted that the hole in the duct v/all is only 1 and 1/4
inches which is considerably smaller than the 4 inch holes common to stack
sampling ports. While opening the port to put the pitot tube in or to pull it
out, the inspector is subject to fumigation in positive pressure ports. With
the smaller ports, the flow is only appoximately 10% that of the large ports.
xi ^1
I
i
.;
t? i =
LJj
.^U BAR-I S/lCDiA X 4 1/2' LG
¥
\
ii-'SASTlOHT
"^k *^Lt
PITC- *
uss POS" WITH PLUS
BULKHEADS
lA'OROX 3 Ot)
, '-BULKHEAD
(WELCGiS
TlGHTl
NOTE: vi6 » i s/n SLEEVES
ADO I LB/FT OFLGTn
SS TUBE !/!«' 0.0 X .Oil' WALL'
SS TUBE I US' 0.0 X 0<9* WALI
APWOX
1/4'DRILL
SLIDE 4-83
The pitot tube must have some minor
modifications for use in the port
T described in the previous slide. These
modifications are inexpensive and can be
^ made to existing pitot tubes.
As shown here, the pitot tube has been
encased in a 1" tube with gas tight
seals at either end. There is also a
bulkhead support at the middle of the
tube. This converts the pitot tube into
a round assembly which can be easily
sealed with an 0-ring.
The tube and seals add only about 4 to
5 pounds to the total weight of the
pitot tube. This is a small price to
pay for improved security against toxic
gas and particulate fumigation. It
also prevents yaw and pitch error.
Static grounding occurs inherently due to the direct contact between the
pitot tube assembly and the port on the duct wall. Nevertheless, the grounding
cable should be attached.
VltW I-I SECTION a-g »UL»HtAD DETAIL
MODIFICATION OF 3/B" STANDARD S-TYPE PITOT TUBE
E: s/is" a i s/ie" O.D. SLEEVES ADD LESS THAN i»/rr OF »ITO-
TUSE LENGTH
118
-------
SLIDE 4-84
inspection ports of the type shown
or any other type can only be
installed when the system is off-line
and the immediate area has been purged
af explosive dusts or vapors.
INSPECTORS SHOULD NEVER REQUEST THAT
THESE PORTS BE INSTALLED WHILE THE
EQUIPMENT IS OPERATING OR BEFORE THE
AREA HAS BEEN PROPERLY PREPARED.
Drilling or cutting could easily result
in an explosion. In particulate control
systems, a light layer of dust is common
on the bottom of the ducts. Even a 1/16"
layer can lead to a devastating explosion,
Many of the gaseous control systems can have pockets of explosive gases
including but not limited to ammonia and carbon monoxide. The unit must be
purged of these gases before hot work is begun.
SLIDE 4-85
SELECTION AND USE
OF MEASUREMENT PORTS
i Ports should be >V4" and <2" diameter.
2. There should be safe access to the port
to facilitate rod out prior to the measure-
ment.
3. Never use ports connected to D/P
transmitters.
i Never have measurement ports instance
wnile the system is running.
This slide summarizes some of the
important points regarding the use of
measurement ports in level 3 and level
4 inspections. Safety is the prime
consideration. If significant climbing
or inhalation risks are involved in
making the measurement, it should not
be attempted. All probes inserted into
rapidly moving gas streams should be
bonded to the duct using the grounding
and bonding cable.
The port must be sealed well enough to
prevent air infiltration related errors
and to preclude loss of the probe into
the duct.
When making measurements in ductwork, it is important to choose a repre-
sentative location. Whenever possible, the measurements should be repeated at
several locations as the probe traverses the gas stream. Single point measure-
ments taken close to the wall should to be avoided to the extent possible.
In the slow moving gas streams found on the walls of scrubber vessels and
demisters, the measurements must inherently be taken close to the wall surface.
This is not a serious problem since there are lower temperature and static
pressure gradiants across these areas.
Lecturer's Notes
The safety guidelines should be emphasized in the summary of this lecture.
It should be noted that attendees should avoid the level 3 and 4 inspections
until they are fully qualified. There is no need to rush into the use of
portable instruments. However, once the use of these has been mastered and
they are able to easily evaluate on-site instrumentation data, the speed and
accuracy of their inspections will improve significantly.
119
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LECTURE 4 REVIEW PROBLEMS AND QUESTIONS
4-1. Any or all of the first three (a,b,and c) could cause this increase in
the measured oxygen concentration. Answer d is very improbable since
there would not be enough dissolved oxygen in the liquor to cause this
increase in gas stream oxygen levels. The point of this question is
that the oxygen concentration of the effluent gas stream is influenced
by both infiltration and absorption. Therefore, it is rarely measured.
4-2 Answers c and d are correct. The fan calculations are theoretically
possible but prohibitively difficult due to the need to know the motor
load factor. Also, the accuracy of the published fan curves for a
specific unit can always be questioned. Answer b is for those who had a
stack sampling course 6 years ago and forget that they talked about F
Factors for estimating gas flow rates from combustion sources. Some may
cry foul concerning tracer tests. These were not discussed. However,
they are very effective for determining the gas flow rates in low
velocity gas streams. As they should remember, a pitot tube is not
effective below 600 feet per minute. You should point out that some new
material is intentional being introduced in these sets of review
problems and questions.
4-3. The gauge is certainly not in the best of shape and should be discarded
if others are available. However, if this is the only one available, it
is possible to struggle through by calibrating immediately before and
after the inspection. As long as the two calibrations are similar, the
curves can be used to correct the data. If there is a shift in the
curves, the static pressure measurements are not good.
Attendees who are alert may question why the static pressure gauge should
be used at all. The slack tube manometer must be available, otherwise
how could this curve be generated? Good point! However, the slack tubes
are miserable when some climbing is involved in reaching the various
static pressure measurement ports.
4-4. Answers c and d are correct. The measurements should be taken. However,
the calibration should be rechecked at the earliest opportunity. Those
who have mastered the art of multiple choice questions should have been
able to guess this just from problem 4-3.
120
-------
LECTURE 4 REVIEW PROBLEMS AND QUESTIONS
4-1. The oxygen concentration in the scrubber inlet is 8.5% and at the outlet
• is 10.8%. What are the possible explanations for this increase?
a. Severe air infiltration into the scrubber vessel
b. Absorption of some of the gas stream components
c. Measurement error
d. Stripping of oxygen from the liquor
e. None of the above
4-2. Gas flow rate can be accurately measured using which of the following
techniques?
a. Fan calculations based on published fan curves
b. E factors
c. Pitot traverses
d. Tracer tests
4-3. During a routine calibration of a diaphragm valve the data plotted below
is obtained. Is it possible to conduct an inspection using this gauge?
o
MANOMETER STATIC PRESSURE
4-4. During an inspection, a diaphragm gauge is accidently dropped about ten
feet to a hard surface. Upon reaching the unit it is noticed that the
zero is no longer correct. However, it can be reset using the set screw
on the front of the gauge. What should be done now?
a. The guage should be discarded.
b. The gauge should be used in the reminder of the inspection if
no other operational gauge is available.
c. The gauge should be calibrated at the site, if possible. If this
is not possible, it should be calibrated immediatly on return to the
office.
d. The gauge is resistant to vibration and shock. Therefore it is
not affected by this accident.
121
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LECTURE 4 REVIEW PROBLEMS AND QUESTIONS
4-5. The static pressure drop across the scrubber vessel and the demister can
not be determined from the data shown. It is necessary to know the
static pressure in stream #3 and in stream #2 to calculate the static
pressure drop.
4-6. The most likely explanation is aspiration effect error during the mea-
surement in stream #1. Another explanation would be an increase in the
liquor flow rate which was not indicated properly by the liquid flow
monitor.
4-7. No. Actually all of the data seems to be indicating a flow rate increase.
Also, these instruments have a tendency to give a low reading if the
suspended solids and/or low pH conditions have damaged the orifice plate.
One way to check the liquor flow rate data is to determine if there has
been an increase in the scrubber static pressure drop. Most, but not all,
scrubbers have an increase in static pressure drop if the liquor flow
rate increases while the gas flow rate remains constant. The latter is
indirectly indicated by stable fan motor currents.
4-8. No. The data could be correct. This answer may catch those who try to
answer to quickly. Without any information concerning the gas handling
system preceeding the portion shown on the flowchart, there is no way to
tell if there is also a fan ahead of the scrubber. It is not uncommon
to find just such a "push-pull" arrangement with fans ahead of and fol-
lowing the scrubber vessel.
Opening a large port on stream #1 on the assumption that the port is at
negative pressure could lead to fumigation of the inspector. The
complete system flowchart should be reviewed and a check should be made
of the actual gas handling system. All fans must be located so that a
reasonable estimate of the static pressure drop at any location can be
made before opening the port. This question again illustrates the value
of system flowcharts during the inspection.
122
-------
LECTURE 4 REVIEW PROBLEMS AND QUESTIONS
4-5. In the wet scrubber system above, what is the pressure drop across
the scrubber vessel and demister if the static pressure in stream #1
is -16 inches and the static pressure in line #4 is -1/2 inch?
4-6. During an inspection of the scrubber system above, the static pressure in
stream #1 is measured at -34 inches and the static pressure in stream #3
is measured at -5 inches. The fan motor current is close to typical
values and the liquid flow rate monitor on stream 2 indicates close to
baseline flow rates. What is one logical explanation for the increase
in static pressure drop from baseline levels of 24 inches to the present
29 inches?
4-7. There is an orifice plate liquor flow meter in stream 2, downstream from
the recirculation pump. The liquor has a suspended solids concentration
of approximately 5% (by weight) and the pH is 5.1. The pump discharge
pressure is lower but the motor current is slightly higher. The nozzle
pressure has increased slightly. The liquid flow meter is indicating
15% higher liquid flows than normal. Can this liquid flow rate data be
dismissed as being obviously in error? What can be done to check it
further?
4-8. A static pressure measurement made at in stream #1 indicated a value of
+4 inches W.C. Can this be dismissed as being obviously in error?
123
-------
LECTURE 4 REVIEW PROBLEMS AND QUESTIONS
4-9. The correct answers are a and c. The entrained water droplets cause the
meter to flucuate between the wet bulb and dry bulb temperatures. A
short in the thermocouple probe would cause a similar problem. However,
the flucuations would be even more intense and rapid. Answer b is very
improbable. There may be a rapid step change in the gas temperature but
there is rarely a series of rapid flucuations. The scrubber would tend
to dampen any such flucuations thereby making these even less plausible.
The inner surface of the duct wall would be slighly cooler than the gas
stream but occassional touching of this wall with the probe would not
cause rapid flucuations.
4-10. Only the battery powered pH meter should be used. The hypochlorite
solution would attack the dye in the pH indicator paper.
4-11. Only answer e is correct. Answer d may make sense. However, it is hard
to find a rubber stopper that large. Answer f has some elements of truth.
However, sometimes it is necessary to use less than optimum ports.
Answer f would be correct only if there were significant safety problems
with the port also.
4-12. Nothing can be done except to go back to get it before starting any
measurements. A grounding/bonding cable is necessary whenever a
probe is used in any duct where static accumulation is conceivable.
Inlet gas streams of scrubbers could have static accumulation.
4-13. Answer b is correct, the oxygen concentration remains 20.9%. Anyone
answering c has a nasty habit of guessing and is very weak in
geography.
4-14. Of the answers listed, only b makes sense. Answers a and c are done
at the risk of a serious explosion.
124
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LECTURE 4 REVIEW PROBLEMS AND QUESTIONS
4-9. An erratic reading is noted while making a temperature measurement
downstream from a scrubber. Why?
a. The gas stream is not saturated and there are entrained droplets.
b. There are very rapid flucuations in the inlet gas temperature
to the scrubber.
c. The probe is damaged.
d. The probe is occassionally touching the inner wall of the duct.
4-10. There is some apparent corrosion in a recirculation tank in a odor
scrubber. The suspended solids level is less than 3% and the liquor
temperature is 105 °F. The liquor being used is a hypochlorite sol-
ution. What should be done to evaluate the liquor pH.
a. Measure the pH using a battery powered pH meter.
b. Measure the pH using pH indicator paper.
c. Either a or b
4-11. A 4 inch diameter stack sampling port is to used to measure the gas
stream temperature and static pressure. The static pressure is
believed to be between -2 inches and -5 inches W.C. What can be used
to seal the port at these static pressure levels?
a. Nothing is necessary at these low static pressures.
b. A hand
c. A glove
d. A rubber stopper having a diameter greater than 4 inches
e. A sanding disk having a diameter greater than 5 inches with
a rubber stopper behind the sanding disk
f. A port this large should never be used under any circumstances.
4-12. During an inspection it is necessary to conduct a pitot traverse ahead
of the scrubber to confirm a severe inleakage problem with the scrubber
vessel. What can be done if you forgot to bring the grounding/bonding
cable?
4-13. When calibrating the gas absorber type oxygen instrument, what oxygen
value should the unit indicate when using ambient air?
a. 21.9% in the winter, 20.9% in the summer.
b. 20.9% in the summer, 20.9% in the winter
c. 19.9% north of the 20° longitude, 19.7% south of 20° longitude
d. 21.9% everywhere, all the time
4-14. A wet scrubber is strongly suspected to be out of compliance due to
a large residual plume from the stack. There are no instruments on
the unit and no measurement taps safely available. What should be done?
a. Demand ports be installed immediately so the inspection can be done.
b. Recommend to agency supervisors that the operators be requested
to perform a stack test as soon as possible.
c. Offer to drill a 1/4" hole to facilitate the present inspection and
request permanent ports for future inspections.
125
-------
126
-------
LECTURE 5
INSPECTION OF WET SCRUBBER SYSTEM
COMPONENTS
SLIDE 5-1
INSPECTION OF WET SCRUBBER
SYSTEMS COMPONENTS
1. Demisters
2. Pumps
3. Piping
4. Nozzles
5. Fans and
Ventilation
Systems
This lecture addresses some of the
components used in most wet scrubbers.
Evaluation of these compontents is a
necessary part of most level 2 and
level 3 inspections.
Demisters remove large droplets formed
during the passage of the gas stream
through the wet scrubber vessel. The
removal of the droplets is necessary to
protect the downstream fans. Failure
of the demisters can also result in
localized nuisance problems due to
droplet rainout.
Pumps and fan problems can have a
severe impact on the overall perform-
ance of the scrubber. The purpose of
the inspection is to qualitatively
estimate changes in liquid and gas
stream flow rates.
Proper liquid-gas distribution can be achieved only when the proper
nozzles are selected and when they are operating properly. Unfortunately,
they are very susceptible to pluggage and erosion problems when there are
high suspended solids in the recirculation liquor.
System piping is inspected to evaluate the potential for pluggage of
lines and freezing of lines in the vicinity of the scrubber vessel. Problems
with the pumps can also occur due to improper piping.
127
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DEMISTERS
1. Prevent Stack Rainout
2. Protect Downstream Equipment
a. Fans
b. In-Line Reheaters
c. Stack Liners
d. Ductwork
SLIDE 5-2 One of the main functions of demisters
is to prevent the rainout of liquor
droplets from the scrubber system
plume. At the very least, the deposited
droplets are a nuisance to the general
community near the plant boundry line.
In some cases, damage to automobile
finishes and house paints can occur.
An equally important function of de-
misters is to protect the downstream
scrubber components listed in this
slide. The gradual accumulation of
solids on fan blades can result in
corrosion or fan balance problems. The
bypass stack for the system may have to
be used while repairs to the fan are
made.
The demisters are not part of the routine scrubber system inspection
agenda. They are added only when the symptoms of demister problems are ob-
served during initial phases of the inspection. Some of these include obvious
rainout of droplets close to the stack, the presence of a mud "lip" at the
stack discharge, the presence of a discolored area near the stack discharge,
and/or moderate fan vibration. During level 2 inspections, the demister
evaluation is limited to a review of demister cleaning system characteris-
tics. Measurements can be performed in a level 3 inspection to isolate some
of the common demister problems.
SLICE 5-3 The droplets which must be removed from
the gas stream by demisters are large
in comparison to typical particles. It
is common for these droplets to be in
the 100 to 500 micron range. The largest
of these has a mass which is more than
100,000 times that of a 1 micron duct
particle. The projected areas shown
in this slide illustrate the typical
t size distribution of entrained droplets.
Due to the large droplet sizes, all
commercially available demisters use
impaction to separate entrained droplets
from the gas stream. The effectiveness
of impaction is proportional to the gas
stream velocity and to the square of of
the droplet diameter.
Considering the large size of the droplets, they should be easy to
collect. In fact, most demisters have very high removal efficiencies unless
the gas velocities drop far below normal design ranges. The problems which
are most common have nothing to do with initial capture of the droplets, but
rather with what happens afterwards to the liquid on the demister.
•
1
o
0. O
1
2&O
^_^
i Microns
0
128
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SLIDE 5-4
Excessive gas velocities through the
• •'. '• demister can lead to formation of
droplets from the surfaces of the
demisters. A common mechanism for
droplet formation is shown on this
slide.
While gas velocity is the dominant
factor, the configuration of the
demister obviously plays a role in the
tendency for reentrainment. Sharp
edges on the downstream side of the
demister favor droplet formation. The
surface tension of the liquid is also
important. As this decreases, the
tendency for reentrainment increases.
Lecturer's Notes
This is one of the first times that the surface tension is mentioned as
an important operating variable. It will be discussed later in the section
concerning spray tower scrubbers and venturi scrubbers. It is also discussed
with respect to nozzle performance. Unfortunately, there is rarely any data
on surface tension.
If any of the attendees do not understand the meaning of surface tension,
it should be discussed at this time.
?LIDE 5-5
High gas velocities can occur on
\ . ' • <' ' .' • demisters due to pluggage and scaling.
'. * , . • '•. Pluggage is the accumulation of
suspended solids on the demister
elements. Scaling is the precipitation
of soluble materials out of solution
onto the demister elements.
Regardless of the mechanism of solids
accumulation, the area available for
gas passage is drastically reduced.
This leads to increased gas velocities
through at least a portion of the de-
mister. Reentrainment occurs in these
areas due to the mechanisms presented
in the previous slide.
In the previous slide, the reentrainment problem is due to the excessive
design gas velocities for the demister. The solids accumulation related pro-
blems are due to inadequate demister cleaning, to excessive solids in the
liquor droplets or to improper demister location.
129
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SLIDE 5-6
DEMISTER TYPES
1. Cyclonic Demisters
a. Standard Flow
b. Reverse Flow
c. Rotary Vane
2. Impaction Target Demisters
a. Chevrons
b. Baffles
c. Mesh Pads
d. Tube Banks
3. Dry Stages
a. Trays
b. Moving Beds
These are the most common types of
demisters. They differ with regard to
the tendency to plug and the velocities
at which reentrainment becomes serious.
The standard flow and reverse flow
cyclonic demisters are used primarily
behind gas-atomized scrubbers, such as
venturi scrubbers. All of the other
styles primarily serve scrubbers having
vertical cylindrical scrubber vessels.
The latter includes tray towers, packed
beds, moving beds and spray towers.
Many of these can be installed in either
a vertical or horizontal orientation.
The latter has better liquid drainage
and is less prone to reentrainment.
The dry stages can be used on moving bed and tray tower scrubbers which
can achieve the necessary pollutant removal efficiencies without using all of
the stages. The liquor inlet is moved to one of the lower stages and the top
stage is operated dry. The droplets which are captured simply drain back
down into the scrubber. This type of demister is rarely used on a new system.
It has been used infrequently for some existing systems.
SLIDE 5-7
Source: Air Pollution
Training Institute
This is a sketch of a standard cyclonic
demister. Its most common application
is downstream of a venturi or rod deck
scrubber. Its effectiveness improves
with increasing gas velocities due to
the improved centrifugal forces on the
droplets.
There is obviously nothing in this unit
which can plug. Scaling can occur in
the lower areas (the sump), but this
does not lead directly to droplet re-
entrainment.
There is very little to inspect on one
of these units. They either work or
they don't work. On level 3 inspec-
tions, it may be helpful to measure the
outlet gas flow.
Lecturer's Notes
The measurement of gas flow is often complicated by the persistence of
cyclonic flow in the stack. This is especially common on positive pressure
units in which the cyclonic chamber outlet duct serves as the stack.
130
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SLIDE 5-8
SIDE ELEVATION
PLAN VIEW
OUTLET
DRAIN
At high gas flow rates, the liquid
which impacts on the inner wall of the
cyclonic demister can spiral up the
side and enter the stack area. This
path is illustrated in this slide using
a heavy dotted line. The point of
reentrainment is the outlet of the
demister (arrow #1).
Reentrainment can also occur as the
spiraling liquid stream returns to the
upper portion of the inlet gas duct.
Here the liquid is sheared off the sharp
edge by the high velocity gas stream.
The location where most of the reentrain-
occurs is shown by arrow #2.
SLIDE 5-9
One simple procedure for eliminating
reentrainment on the gas inlet duct
(arrow #2, Slide 5-8) has been suc-
cessfully demonstrated at a grey iron
frtoundry. As shown in this slide, a
small section of angle iron was been
welded along the gas inlet duct. This
serves as a scalper for the liquid
spiraling around the demister. The
liquid is directed down to the sump and
away from the high velocity gas stream.
A similar approach may help reduce the
spiraling stream passing up to the de-
mister outlet duct. However, a long
section of angle iron or similar mat-
erial may also disrupt the vortex
necessary for proper droplet capture.
131
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SLKE 5-10
SIDE ELEVATION
DRAIN
INLET
OUTLET
This is a reverse flow type cyclonic
demister. The gas stream enters near
the bottom and flows upward in the
outer annular area. A 180° turn is
made as the gas stream enters the down-
ward point outlet duct. The bottom of
the demister is sloped to facilitate
drainage.
Removal of entrained droplets occurs
due to both the cyclonic action and the
sharp gas stream turn. These units are
not prone to reentrainment. However,
it is still possible to have some drop-
let formation at the lip of the inlet
duct. With this style, it is especially
important to keep the drain open so
that the liquid level does not rise.
Lecturer's Notes
Inspectors who are not experienced with wet scrubbers may not be able to
identify these initially during an inspection. There is a natural expectation
to have the gas stream exit from the top of scrubbers and demisters and this
leads to the confusion.
SLIDE 5-11
Source: Air Pollution
Training Institute
This is a sketch of a mesh pad demist-
er . Collection of droplets occurs due
to impaction on the filaments of the
mesh pad. These are oriented horizon-
tally and the liquid simply drains back
down into the scrubber.
To prevent flooding (excessive liquid
hold-up), some units are inclined
slightly to improve the drainage.
Also, it is possible to install a
standpipe and trap to drain the liquid
above the pad.
It is important that the mesh pads be
installed tightly against the wall.
There should be no obvious voids which
gas could pass through. All of the
individual sections should be wired
together and to the retainer supports.
It should not be possible to manually
move the mesh pad sections if they are
installed properly.
132
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SLIDE 5-12
U
max =
Mesh pad pluggage and reentrainment
are minimized by properly gas vel-
ocities. As a general guideline, the
velocity should not exceed the value
indicated by the equation in the slide.
The face velocity is simply the actual
gas flow rate (ACFM) divided by the
total open area of the demister. The
latter is calculated by subtracting the
area of supports, grids and retainers
from the demister total area.
The empirical "K" factor for metallic meshes having densities of 5 to 9
pounds per cubic feet is 0.4, and for metallic meshes having densities of more
than 9 but less than 12 pounds per cubic feet is 0.35. For mesh pads composed
of Teflon, Polypropylene or Kynar use a "K" factor of 0.3. The equation yields
velocity in feet per second.
Lecturer's Notes
For a rough approximation, the density of the liquor can be taken as 62.4
pound per cubic foot and the density of the gas can be taken as 0.06 pounds
per cubic foot (-10 inches static pressure, 130 °F). This makes the square
root term equal to 32.25.
SLIDE 5-13
CHRONIC PLUGGAGE
PROBLEMS WITH MESH PADS
1. Use Coarser Mesh
2. Flush With Clean
Water
For mesh pads having chronic pluggage
conditions, the alternatives listed
here may be of use.
Mesh pads are especially prone to plug-
gage due to the low open area and the
difficult drainage path. A coarser
mesh partially alleviates these
problems. This will also lead to a
slightly lower pressure drop. However,
this is done at the risk of lower drop-
let capture effectiveness in the
coarser mesh pad.
Sprays should generally be used whenever there is appreciable solids
levels in the scrubber liquor. With mesh pads, it is important that these
sprays be pointed downward. Upward sprays can drive the solids deeply into
the mesh pad and partially blind the demister. Demisters with high solids
deposits can suffer reentrainment and high static pressure drop. If the
conditions are sufficiently severe, the entire demister can be ripped from its
supports and sucked into downstream I.D. Fans. For example a completed
blinded demister 8 feet in diameter with a 10 inches W.C. static pressure on
the downstream side is subjected to a force of over 2500 pounds!
The initial sign of mesh pad pluggage is an increase in the static
pressure drop at a given gas flow rate. Baseline data is helpful for
identifying the onset of pluggage. In any case, a static pressure drop over
0.5 inches W.C. is a sign of trouble.
133
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SLIDE 5-1A
2 PASS
Source: Electric Power
Research Institute
This is a side view of a two pass
chevron demister. The gas stream enters
from the bottom and must pass up through
the twisted passages. Droplets impact
on the blades and drain down.
These are available in two, three and
four pass designs with the capture im-
proving with the number of passes. The
inside angles of the chevrons vary from
a low of 60° to maximum of 120°. Drop-
let collection improves with increasing
angles.
Various blade designs are available to reduce reentrainment tendencies.
These involve small channels and scalpers to aid the liquid drain downward
without any wave action which could result in droplet formation. 'These also
prevent liquid from reaching the downstream edge of the blades where the
liquid could be sheared off by the gas stream passing out of the demister.
The main disadvantage of these pockets and channels is the tendency to plug
when high suspended solids are collected. This can accelerate pluggage of the
entire demister since washing is inhibited. These special blade designs are
used most frequently on demisters in which the chevrons are mounted vertically
and the gas flow is horizontal. These demisters have inherently improved
drainage so the pluggage is less of a problem.
GENERAL GAS VELOCITY LIMITS
FOR CHEVRONS
Vertical Gas Flow
5 to 15 Feet Per Second
Horizontal Gas Flow
7 to 25 Feet Per Second
SLIDE 5-15
Chevron demisters are subject to drop-
let reentrainment at high gas velocities
as indicated in the equation shown in
slide 5-12. The "K" factors for a
typical 3 pass chevron with vertical gas
flow is 0.2 to 0.5. The value of the
constant for the same 3 pass unit having
horizontal gas flow is 0.2 to 0.8. The
large range is needed due to differences
in the blade angles, blade geometry, and
liquor surface tension. At typical
liquid and gas stream densities, this
equation indicates that the superficial
velocities should be between the values
shown in this slide.
Most chevrons are designed for a gas velocity between 10 and 20 feet per
second, depending on the specific characteristics of the application. The
accumulation of solids can result in an unintentional increase in the gas vel-
ocities and increased reentrainment. To minimize solids build-up, it is common
practice to spray the demister sections on a regular basis. The sprays can be
either above or below the demisters.
134
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SLIDE 5-16
To facilitate early identification of
the solids accumulation on. chevron de-
mister sections, there should be static
pressure measurement taps before and
after the demister . An increase in the
pressure drop at a constant flow rate is
a clear sign of emerging pluggage (and
reentrainment) . The static pressure
drop should be measured during the
baseline period to serve as a compar-
ison when problems are suspected later.
There should also be a viewing port or
hatch in the demister area so that the
conditions can be evaluated when the
scrubber is down for service.
When comparing against baseline pressure drops, it is necessary to correct
for differences in the gas flow rates. The equation shown below can be used
to make this correction. This is intended only as a rough approximation and
is based on the fact that pressure drop is related to the square of the gas
flow rate. Production data can sometimes be used as a rough indicator of the
gas flow rate.
AP = AP
Where: AP
AP
Q
Q
Corrected Pressure Drop
Observed Pressure Drop
Baseline Gas Flow Rate
Present Gas Flow Rate
SLIDE 5-17
Source: Air Pollution
Training Institute
A radial vane type demister is shown
here. There are curved baffle vanes
which are attached to the hub and to
the outer spool. As the gas stream
passes around the curved vanes, it is
accelerated and spun. Droplets impact
the wall of the scrubber vessel due to
centrifugal force. The accumulated
liquid is continuously drained from the
annular area between the scrubber wall
and the radial vane demister.
For adequate performance, it is import-
ant that there is some clearance above
the demister for the spinning gas
stream. A minimum clearance of one-half
the scrubber diameter is necessary to
complete droplet removal.
As with any demister, solids accumulation must be removed frequently.
This can be done with sprays either above or below the demister. It is also
necessary to keep the drain line open. It can plug at the entry point or at
the discharge point
135
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SLIDE 5-18
This is the downstream side of a radial
vane demister. Note the heavy deposits
on the blades and the restricted gas
passages between the blades. A unit in
this condition is prone to reentrain-
ment. The solids accumulated on this
demister primarily because it had to be
cleaned manually and this was done on a
once per week basis.
SLIDE 5-19
EVALUATION OF
RADIAL BLADE DEMISTERS
During Level 3 inspections of the radial
vane demisters, the static pressure drop
should be checked. Increases over base-
line levels (after correction for gas
flow rate changes) indicate the accumu-
lation of solids. Any pressure drop in
excess of 2 inches W.C. is a possible
indication of pluggage.
136
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DEMISTER CLEANING SYSTEM
INSPECTION
1. Liquor Turbidity
2. Liquor pH
3. Liquor Pressure
4. Operating Frequency
5. On-Time
SLIDE 5-20
During all inspections of demisters, the
washing system layout and operation
should be checked. Some of the import-
ant points are listed on this slide.
However, some of this operating data is
often unavailable.
The cleaning system must be run often
enough and at high enough pressure to
remove the solids which accumulate. The
nozzle type and spray angle must ensure
complete coverage of the demister.
If possible, a sample of the liquid used
as demister wash should be checked.
This should be low in total solids so
that the wash water does nbt contribute
to a scaling and/or pluggage condition.
The pH should also not be so high that
scaling is inevitable.
In some scrubber systems, the demister wash system is used as the scrubber
system make-up water line. This is a good practice since the make-up water
supply is normally clean and close to a neutral pH.
SLIDE 5-21
UoU. p^ta.
Another factor of importance is the
distance between the top stage of the
scrubber and the and the bottom of the
demister (see distance from #1 to #2).
This is termed the "freeboard" distance.
The demister must be high enough above
the last scrubber tray so that it is
not subject to the very high liquor
loadings close to the trays (or beds).
There must be a sufficient distance for
large settleable drops and liquid jets
to fall back to the tray without hit-
ting the demister.
Excessive freeboard distance does not
affect demister performance. However,
this does add to the scrubber vessel
height and cost.
137
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SUMMARY
DEMISTER INSPECTION
1. Wash Water Quality
2. Cleaning Operating Times
3. Liquid Pressures
4. Static Pressure Drop
5. Gas Flow Rate
This is a brief summary of the common
inspection points for suspected de-
mister problems. The presence of a
water wash system and the quality of
wash water should be checked during all
inspections. The distance of the de-
mister from the top of active trays or
beds should also be checked, especially
when gas velocities through the unit
are high.
On Level 3 inspections, the pressure
drop should be compared against the
baseline values. Even slight shifts
after correction for gas flow changes
indicates the onset of pluggage. The
ceiling value pressure drop's listed
earlier should generally not be ex-
ceeded. The gas flow rate can be
measured to determine if the capacity
of the demister has been exceeded.
On scrubber systems that are down, an internal check should be made for
deposits on the demister and for the condition of the washing system spray
nozzles. Under no circumstances should the inspector enter the scrubber
vessel since there could be toxic gases trapped in portions of the off-line
scrubber system. It is also possible to crush fragile chevron blades and
rotary spin vanes which are often made of plastic.
SLIDE 5-23
1/2 Tube —,
-4'
Source: Shifftner
When symptoms of demister problems are
noted during Level 3 inspections, the
probe shown in this sketch can help to
determine the source of the liquor
droplets observed. This is a section
of 1/2 inch O.B. copper tube with a
slot cut out near the top. The tube is
sealed with an end cap and the other
end includes fitting which reduce down
to a nipple. A flexible piece of
tubing leads from the probe nipple down
to a sample bottle.
The probe is inserted into the stack to
determine if there are droplets in the
gas stream. Checks are also made to
determine if liquor is moving up or down
the scrubber stack.
138
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SLIDE 5-24
A ° A
The rate of liquor capture should be
noted when the probe is placed near the
center of the stack. Droplets in this
portion of the stack clearly indicate
that there is excessive liquid carry-
over from the scrubber vessel. The
demister should be inspected in detail.
Anything that would contribute to drop-
let reentraimnent should be removed
from the stack and placed elsewhere in
the system, if possible.
SLIDE 5-25
When the probe is placed in the
position shown here, the presence of
ascending wall flow can be determined.
The liquor moving up the interior wall
can be due to demister failure or
simply to the condensation of water
vapor in the cold stack. The latter is
possible when ambient temperatures are
low. Normally, the stack velocity must
be more than 35 feet per second to push
the liquor up the wall.
This is one possible explanation for
slight rainout conditions in the
absence of any demister malfunctions.
139
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SLIDE 5-26
PLUME OBSERVATIONS
#1
BYPASS_ T
DAMPERS5^
PLUME OBSERVATIONS
* 1
COLD STACK
-iDn
SJgg UME
TRUCK
This flowchart shows the typical locations of pumps in a wet scrubber
system. The recirculation pump is the one that most directly affects the
performance of the wet scrubber and is, therefore, the one of most interest to
control agency inspectors. This pump must be capable of delivering the liquor
at the design flow rates and pressures at the inlet to the scrubber. It
must be able to withstand the suspended solids and corrosive materials which
accumulate in the recirculation liquor.
To maintain the suspended solids and corrosive materials at an acceptable
maximum concentration, some of the liquor is either purged from the system or
sent to a liquor treatment circuit. This purge line pump handles only 5 to 20%
of the capacity of the recirculation pump. However, it is subject to the same
liquor quality. The make-up pump delivers relatively clean process water or
liquor to replace that lost due to evaporation, lost in the sludge removed, and
lost as stack reentrainment. This pump usually has a capacity similar to the
purge pump.
Other pumps are used for alkaline supply and for metering in additives
for foam suppression, odor control, surface tension control, and solids
settling. Sludge pumps may be used under clarifers for removal of high solids
liquid streams.
140
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SLIDE 5-27
PUMP REQUIREMENTS
1. Continuous Delivery
of Liquor at Desired
Flow Rate
2. Delivery of Liquor at
Necessary Pressure
A failure of any one of the main pumps
could result in temporary outage of the
scrubber and the bypassing of the ef-
fluent gas stream. The recirculation
pumps and the purge line pumps are most
susceptible to these sudden problems due
to the characteristics of the liquor
often handled. However, the loss of the
alkaline supply pump or additive supply
pump could lead to serious corrosion
conditions which demand immediate correc-
tive actions.
The recirculation pump operating data can provide a useful, indirect
measurement of the liquor flow rate. Comparison of the discharge pressures and
pump motor currents with baseline values can indicate if the liquor flow rate
has probably increased or decreased significantly since the baseline period.
The pump discharge pressure and the general operating conditions can help
determine if the pump is the cause for decreases in either the liquor flow
rates or the pressures at the scrubber inlet.
TYPES OF PUMPS
1. Centrifugal
2. Positive Displacement
3. Progressing Cavity
SLIDE 5-28
There are numerous pump designs. How-
ever, for wet scrubber applications the
pump types listed in this slide are the
most common. The centrifugal pumps are
used most frequently for liquor recir-
culation and liquor purge since they can
handle large quantities of liquor which
are abrasive and corrosive. The centrif-
ugal pumps usually operate at 400 to 900
rpm and deliver liquor at 40 to 200 psig.
These are relatively modest demands com-
pared to the requirements for centrifugal
pumps in other applications.
The types of centrifugal pumps can be further divided into a number of
individual categories which are primarily based on the pump impeller design.
These different types are discussed in more detail in later slides.
The diaphragm pump is a type of positive displacement pump (one of the
major categories of pumps) which is used almost exclusively for the movement
of very high solids content slurries. These are most common on the clarifier
and thickener underflows. The progressing cavity pumps are useful for the
movement of high solids, large suspended particles and/or potentially clogging
type solids.
141
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SLIDE 5-29
•Casing
Radial force
RADIAL CENTRIFUGAL
PUMP
Source: Chemical Engineering
June, 1972
The radial flow centrifugal pump is the
most common type of pump used for wet
scrubbers. The liquor enters the pump
axially and is accelerated by the
rotating impeller. The flow from the
impeller into the casing area is radial
with respect to the impeller.
As the liquor leaves the impeller, it
decelerates somewhat which results in
the conversion of some of the velocity
head to pressure head. The general
relationship between the two is pro-
vided in the equation below:
=>£ x (GH)
Velocity, V,is in feet per second, G
gravitation acceleration in feet per
second squared, and pressure head, H,
in feet.
is
is
SLIDE 5-30
The centrifugal pumps can either be
oriented in the vertical or horizonal
directions. The most common is the
horizontal arrangement shown in the top
portion of the slide.
A vertical arrangement is useful to
obtain greater suction head (a very
important operating requirement to be
discussed later) and to minimize the
required floor space.
The pump body configurations in the
vertical and horizontal orientations
are somewhat different. However, the
differences do not change the way in
which pump performance is analyzed, and
it does not significantly change the
types of problems which are most
common.
142
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COMPONENT OF A
PUMPING SYSTEM
SLIDE 5-31 The components of a pumping system in-
clude the suction pipe, strainer,
suction side check valve (termed foot
valve in slide), discharge check valve,
and discharge valve. The latter is
termed a gate valve (a specific type of
control valve). Not all of these are
necessary for each system.
The strainer removes tramp iron and
large particulate which would damage
the pump impeller and/or liner. The
strainer is usually used on all new
systems but is sometimes removed when
there is a tendency for the liquor to
blind the strainer. This would cause
serious pump damage.
The foot valve (or check valve) prevents air infiltration into the suction
side of the pump during outages. If air enters the pump it must be primed and
there is a risk of cavitation (a serious operating problem). The eccentric
reducer on the suction line allows connection of the suction line to the pump
flange without the creation of air pockets which can also cause cavitation
under some operating conditions. The suction line is angled downward to also
prevent air pockets.
The flow of liquid out of the pump is controlled by the discharge line
valve. This is normally a gate valve (valve designs are discussed in a later
part of the lecture). Although not shown, there is often a discharge line
pressure gauge on the line before the discharge valve.
SLIDE 5-32
(il ara IWELUBS
Several examples of the large number of
available impeller designs are shown in
this slide. The open and semi-open
impellers are often used on heavy
slurries and other abrasive liquors.
The nonclogging impeller is useful for
heavy slurries including stringy
materials.
The closed impeller design is suitable
for relatively clean liquors with
little or no solids. This design
provides higher efficiency.
: SEM1WEM IMPELLER
The quantity of liquor and the pressure of the liquor supplied by the
pump depend on the impeller configuration and the impeller iameter. When
impellers are replaced, identical units should be reinstalled. The use of
smaller diameter impellers with or without the identical configuration can
result in less than the desired pump performance.
143
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SLIDE 5-33
200
180
50
fcj 40
LL! 20
§100
g 80
50
200 400 600 800 1000
200 400 600 800
CAPACITY, GPM—*-
1000
The characteristic curve of a centri-
fugal pump is shown. As the quantity
of liquid delivered increases, the head
developed decreases slightly.
The position and shape of this curve is
determined by a number of design
factorsincluding: (1) impeller shape,
(2) impeller diameter, (3) casing
shape, and (4) pump rotational speed.
Under normal conditions, the pump will
perform on this curve at a position
determined by the piping system re-
sistance. However, problems such as
cavitation and impeller wear can cause
reductions in both flow rate and head.
Field inspectors and maintanence personnel will rarely have these curves
for use in evaluating pump performance. The curves are used simply to
illustrate the meanings of the pump instrumentation such as the discharge
pressure gauge and the pump motor ammeter.
SLIDE 5-34
200
180
160
u 140
u.
o" 120
£ 100
80
60
200 400 600 800 1000
The system resistance curve is shown in
this graph along with the pump curve
introduced in the previous slide. At
the origin, the system resistance is
equal to the discharge head, which is
equivalent to the vertical distance that
the liquor is being lifted. The system
resistance increases with the square of
the flow rate due to frictional losses
in the pipes and valves.
The system resistance curve is cal-
culated for a new system based on the
IOOO piping layout, liquor velocities and
the pipe characteristics. The intersec-
tion of the pump curve with the system
curve defines the intended operating
point (point A on this graph) of the
overall system.
Unfortunately, several factors can lead to a change in the position of
the system resistance curve. Some designers may assume higher estimated
resistances than actually exist in order to provide a "safety factor". This
can lead to lower resistance than intended. There can also be pluggage of
control valves, nozzles and piping which leads to higher resistance than
desired. In either case, the pump selected may not be appropriate for the
actual conditions which exist.
200 400 600
CAPACITY, GPM
800
144
-------
SLIDE 5-35
200
ISO
ZOO 4OO 60O 80O K5OO
u 160
o 140
u 120
100
40
2O
0
40
30
20
IOO
80
SO
40
40
SO
20
Hp =
200 4OO 60O 800 IOOO
CAPACITY. 6PM —
x V x C x P.F.
The brake horsepower curve is now added
to the pump and system curves discussed
in the last two slides. The horsepower
rises as the quantity of liquor pumped
increases.
The brake horsepower is the total
energy being used by the pump motor.
It includes the energy imparted to the
liquid stream and the portion of the
energy which is wasted and dissipated
as heat in the pump motor. It is
related to the motor current by the
relationship shown in the equation
below.
Where
Hp = Total Horsepower
V = Volts, A.C.
C = Current, A.C.
P.F.= Power Factor, dimensionless
While there is obviously a direct proportionality between the motor
current and the horsepower, it is not possible to calculate the present horse-
power from the motor current and operating voltages. The power factor is not
generally known, is not generally constant, and is difficult to measure. For
this reason, it is not possible to use a pump curve to calculate the flow rate
from the motor currents and voltages. Variable liquor characteristics and
pump impeller wear also make this impossible. However, a decrease in the motor
current usually means that the liquor flow rate has decreased from baseline
levels.
The total pressure head (see vertical axis) is the total of the liquor
velocity pressure and the absolute liquid pressure. These two components of
the total pressure head are convertible from one form to the other and are
related by the equation shown below. Application of this equation for typical
pipe velocities will illustrate that the velocity head is much smaller than
the absolute pressure component.
x G x H
Where: V = velocity of liquor in feet per second
G = gravitational acceleration, in feet per second squared
H = liquid pressure, in feet
While the measured pressure will depend on the velocity of the liquor at
the point of measurement, the discharge pressure does provide a general
indicator of the overall pressure head being supplied by the pump. Many pump
operating problems result in a significant reduction in the pressure head.
One complicating factor in the use of the discharge pressure, is the
pluggage of downstream valves and nozzles. This can increase the measured
discharge pressure slightly, while reducing the flow.
145
-------
SLIDE 5-36
There are many common operating problems
of wet scrubber system pumps. Most of
these have a direct impact on the per-
PUMP OPERATING PROBLEMS quantity" of
pressure of the liquor.
In the slides that follow, some of the
possible reasons for these problems will
be presented to help inspectors determine
if the corrective actions planned have a
reasonable chance of success. However,
it is usually not possible for an
inspector to determine the exact cause
of the problem
There are more than 90 commonly reported causes of pump failure due to
both mechanical and hydraulic factors. Some of these can be identified by
observing pump operation and some can be identified when the pump is torn down
for maintenance. The reasons for repeat failures of certain components,
however, can be a complicated issue best left to pump specialists.
The inspector's role is to confirm: (1) that the operators are aware of
a change in pump performance which may be an emerging scrubber problem, that
(2) the operator's corrective actions will probably prevent or minimize the
condition, and that (3) the operator is not tolerating frequent pump problems
without attacking the fundamental cause(s).
SLIDE 5-37
The lack of liquor flow can be due to a
number of pump problems, all major.
Most of these listed on the slide result
LOW LIQUOR FLOW RATE in burnout of the PumP motor-
1. CAVITATION Other possible causes for the lack of
a PLUGGEDPSTE^.NER lic*uor flow include a closed discharge
4. IMPELLER EROSION line valve and pluggage along the
s: PLUGGED PIPES OR NOZZLES discharge line and/or nozzles.
6. PARTIALLY CLOSED DISCHARGE VALVE
7. SOLIDS ACCUMULATION IN CASING j^ SQUrce of the problem can rapidly
be identified by checking the pump
operation. If the drive shaft is still
spinning, the problem is in the
discharge valve or piping. The pump
should be shut down immediately.
If the shaft is not spinning, the pump is either already shut off or has
bound up. Before starting up the pump again or starting up a spare pump, the
condition of the nozzles and other potential areas for line pluggage should be
checked. Loads placed on the pump by the piping should also be visually
evaluated.
146
-------
SLIDE 5-3S
One cause of the no flow condition is
the freezing of exposed piping from the
pump discharge to the top portion of
the scrubber vessel. Ways to minimize
line freezing include:
1. Maintaining flow through lines
even when scrubber is down.
2. Insulating lines.
3. Draining and flushing lines
during outages.
4. Placing pumps in heated and/or
sheltered pump house
The last two steps are common during operation in cold climates. Main-
taining flow during all periods can also help prevent the settling of solids
in the piping. Insulation of lines will be of help for short periods but will
not prevent freezing when systems are shut down for weekends or other extended
periods.
SLIDE 5-39
This is a view of a recirculation pump
within the pump house. The heated area
protects the pump from freezing
conditions during extreme weather and
during outages.
The suction line of a pump must be kept
full of liquid so that the pump will
not cavitate (problem defined in a
later slide) during start-up. Since
the line can not be drained, the pump
must be kept in a heated area.
Freezing of the seal water line or the
packing material could also lead to
pump damage.
147
-------
PUMP IMPELLER WEAR
1. CORROSION DUE TO LOW pH
2. EROSION DUE TO CAVITATION
3. EROSION DUE TO SUSPENDED SOLIDS
4. EROSION DUE TO TRAMP METAL
5. CORROSION DUE TO CHLORIDES
SLIDE 5-40
Impeller wear and damage can be caused
by the problems listed in this slide.
Corrosion occurs when the liquor com-
position and/or pH is not compatible
with the impeller materials of con-
struction. The pH measurement provides
one indication of impending corrosion
problems. The condition of the casing
can also provide some warning.
Cavitation conditions usually result in
pump vibration and high noise levels.
Rapid corrective action is necessary in
this case.
Abrasion occurs due to high suspended
solids levels and large particle sizes
of the suspended materials. Low pump
speeds can minimize this problem.
The consequences of impeller wear include reduced liquor flow rate and
reduced discharge line pressures. The pressure gauge will provide one
indication of this problem. However, there are a number of conditions which
can reduce the pressures.
SLIDE 5-41
Rotation
Impeller Vane
Shaft with
Key Insert
Source: Plant Engineering
October 3, 1974
Cavitation is a serious operating
problem which occurs when a portion of
the liquor being handled in the pump
vaporizes while passing over the
impeller blades. This slide illus-
trates the location of the bubble
formation on the impeller surfaces.
As the liquor proceeds outward, the
pressures increase and the bubble
implodes. The energy released during
this action can destroy protective
liners on the impeller and can even
remove metal from the impeller itself.
The imploding bubbles also result in
noise and pump vibration.
Due to the rapid damage to the impeller and the casing liners (if
present), cavitating pumps should be shut down as soon as possible. The
source of the cavitation should be corrected before returning the pump to
service. Some of the most common causes of this condition include, air
infiltration, inadequate net positive suction head, and gas pockets in the
suction line. These problems are discussed in the next set of slides.
148
-------
SLIDE 5-42
(NPSH)a = (H - Pv)/« - hf - he
Where:
H = Absolute suction pressure
at the pump inlet
Pv = Vapor pressure of the liquid
at the given temperature
8 = Specific weight of liquor
hf = Frictional lossed in suction
he = Entry losses
The available net positive suction head
is the difference between the existing
absolute suction head and the vapor
pressure of the liquor at the operating
temperature of the pump. This is a
characteristic of the system in that it
is determined by: (1) the liquor com-
position, (2) the elevation of the
suction point relative to the pump, and
(3) the frictional losses in the suction
line. The procedure for calculating the
available net positive suction head
(NSPH)a is shown in the equation.
It is apparent that the available net positive suction head depends on the
elevation of the reservoir supplying the pump (or the depth of the suction line
in a pond). Another important factor is the flow rate of the liquor since this
determines the magnitudes of both the frictional losses and the suction pipe
entry losses.
The required net positive suction head is a function of both the pump
design and the liquor flow rate. It must be specified by the manufacturer of
the pump. Selecting the appropriate pump for the system available net
positive suction head is the responsibility of the system operator.
Inadequate net positive suction head is reported to be one of the most
common reasons for inadequate pump performance.
SLIDE 5-43
, zoo
!r I8°
w 160
o I4O
u 120
100
40
200 400 coo aoo 1000
yj Ul C
o
40
20
100
eo
eo
4O
40
30
20
The net positive suction head required
for a given pump, along with the system
resistance curve and the pump character-
istic curve are shown in this slide.
This data is always presented for liquid
liquid at standard temperatures and
specific weights. It should be corrected
for temperature and solids content for
the actual system before the pump is
selected.
20O 400 60O 800 IOOC
CAPACITY. 6PM——
Plant Engineering
August 8, 1974
149
-------
SLIDE 5-44
REDUCING CAVITATION PROBLEMS
1. INCREASE HEIGHT OF INTAKE
2. DECREASE ELEVATION OF PUMP
3. ELIMINATE AIR INFILTRATION
ON INTAKE PIPE
4. ELIMINATE GAS POCKETS ON
INTAKE PIPE
5. MODIFY INTAKE CONFIGURATION
6. INSTALL FOOT VALVE ON INTAKE
If the pump is subject to cavitation,
problems, one or more of the following
steps could be taken to prevent the
condition.
Raising the height of the recirculation
tank and/or the scrubber sump is often
uneconomical. Lowering the intake
point of the suction line is more
practical. Converting to a vertical
pump can also be done with a minimum of
system modification.
Operation at lower flows can have some
beneficial impact for the pump, but
adversely affect scrubber operation.
Also, the required net positive suction
head increases slightly at very low
flows, as indicated on the earlier slide.
SLIDE 5-45
PUMP
PUMP
Another source of cavitation is the
presense of gas pockets in the suction
line of the pump. Three ways to avoid
gas pockets are shown in the slides
which follow.
The suction pipe leading to the pump
slopes upward a minimum of 1° so that
gas pockets can not occur in a high
point of this piping.
Source: Machine Design
May 8, 1980
150
-------
SLIDE 5-46
Bleed valve permits
air removal
Discharge
Hole allows air to escape
from pump casing
-Tongue blocks air escape
through discharge port
asing
The volute casing of the pump may
accumulate some air at a high point of
the casing behind the tongue. A vent
at this point allows bleeding off of
any air trapped in this area during
start-up of the pump.
Source: Machine Design
May 8, 1980
SLIDE 5-47
Trapped Standard
Reducer
Pump-
Straight section
realigns flow—-j
Eccentric Reducer—j f
Pump-
Eccentric reducers should be used to
connect the suction line to the pump
itself. In this way, gas pockets can
not develop.
Any flange gaskets should be cut with
an oversize opening so that a portion
of the flange does not extend into the
liquid stream as shown.
Source: Machine Design
May 8, 1980
151
-------
SLIDE 5-48
DISCHARGE
LINE
A foot valve is advisable when the
suction line is drawing liquor up out
of a tank or pond. This acts as a float
type check valve which closes off the
suction line if the liquid level drops.
This type of check valve is not necessary
when there is a flooded suction line.
Systems in which the pump pulls from the
scrubber sump generally have flooded
suction. It is important to fill the
sump (necessary as a water seal anyway)
before starting the pump.
Source: Plant Engineering
July 6, 1978
SLIDE 5-49
PUMf INTAKE
LIQUOR
CIRCULATION
When the pump pulls from a tank, it is
important to place the intake line(s) at
the proper position to avoid vortices.
Air can be drawn into the line if the
pick up point is too close to these vor-
tices.
There are published guidelines .on the
minimum depth of the suction line for
the size of the suction pipes. Also,
information is available to design the
tank to prevent air pick-up.
152
-------
SLIDE 5-50
PUMP MATERIALS OF CONSTRUCTION
1. CARBON STEELS
2. STAINLESS STEEL
3. NICKEL ALLOY STEELS
4. RUBBER LINED CARBON STEELS
5. FIBERGLASS REINFORCED PLASTICS
Typical materials used in pumps are
listed here. The carbon steels are
adequate for general service. However,
life will be very limited when the pH
is below 6 and/or there is high solids
content.
The stainless steels provide greater
corrosion resistance except for liquors
having high chloride and fluoride levels
When the concentrations of the halogen
materials exceeds 500 ppm, pitting of
the stainless is rapid.
The nickel alloys provide generally excellent corrosion resistance, but
at a substantial cost penalty. These materials also have moderate to
excellent abrasion resistance.
SLIDE 5-51
This is a summary of the inspection
points for recirculation pumps of wet
SUMMARY scrubber systems.
PUMP EVALUATION - .. . ..
The discharge pressure provides a
useful index of the flow rate. An
increase from the baseline level
generally means a decrease in the
liquor flow rate.
An increase in the pump motor current is another flow indicator. As it
increases, the flow increases unless the viscosity has changed dramatically
(which is unlikely in most air pollution control systems). A major increase
in the solids content can also affect the pump currents.
An increase in the pump noise and/or vibration is a possible indication
of cavitation. This is often accompanied by a decrease (possibly slight) in
the discharge pressure and a decrease in the liquor flow. Whenever cavitation
is suspected, the suction line should be examined carefully for sites of gas
pockets, sites of air infiltration, the elevation of the suction line intake,
and the configuration of the intake.
For pumps using water seals, there should be a small quantity of seal
water continually draining from the stuffing box. The lack of visible drain-
age is a sign of inadequate seal water supply and this can lead to premature
failure of bearings and corrosion of the shaft.
Another factor which should be checked is possible pump misalignment
conditions due to forces imposed on the pump by the discharge piping. The
provisions for flushing out any pumps handling slurries (total solids contents
greater than 3% by weight) during outages and the provisions to prevent
freezing during system outages should be checked.
153
-------
SLIDE 5-52
EVALUATION OF LIQUOR FLOW RATE
AND FiriNG SYSTEMS
The objectives of this section include:
(1) the evaluation of liquor flow rates
in systems without flow monitors, and
(2) the evaluation of operation and
maintenance problems due to piping and
valve related conditions.
The principal problems associated with
the piping included pluggage or erosion
in systems handling slurries. Improper
piping supports can place undesirable
loads on the pump and the nozzle
headers. If the piping system is not
designed properly, it is difficult to
flush out settled material, it is
difficult to drain lines during cold
period outages, and it is difficult to
replace worn or corroded segments.
SLIDE 5-53
In order to make a rough estimate of
the flow in a pipe, it is necessary to
know the pipe dimensions. The pipe
1 ~ I PS - 40 ~ CS sizes are often specified as shown in
the example on the slide.
The first number is the nominal pipe
size. This may be followed by an
alphabetic code which denotes the type
of pipe, such as IPS for standard pipe.
The next code specifices the schedule
which is an indication of the pipe's
ability to withstand internal pressures
The letter directly following the
schedule codes represents the types of
materials used for the pipe. Any letters
following the hyphen present information
concerning liners or other special
design requirements.
If it is impossible to get the piping data from drawings or other plant
records, the dimensions should be measured. Either the outside diamter
(termed the O.D.) or the pipe circumference should be measured. These values
can then be used with standard pipe dimension tables and flow rate guidelines
to estimate the flow rate.
154
-------
SLIDE 5-54
PIPING INSPECTION
PIPE SIZES
Nominal Sin
pnchM)
ScMdute
NumMr
40
go
40
80
10S
40
80
Iraki*
OKnwur.
(Inch**)
1.185
1.049
0.957
3.260
3.068
2.900
5.345
5.047
4.813
Outlid*
Dlamur.
(menu)
1.315
1.315
1.315
3.500
3.500
3.500
5.563
5.563
5.563
This slide presents the pipe inside and
outside diameters for certain common
nominal pipe sizes. It should be re-
membered that the nominal diameters used
in standard piping handbooks (and est-
ablished in ASTM standards) do not
exactly match the measured diameter.
The table value is actually closer to
the inside pipe diameter (termed the
I.D.) for most of the pipes. In the
case of very small pipes, there are
substantial differences between the
nominal value and both the inside and
outside diameters.
This data has been excerpted from tables applicable to steel pipes. The
values are different for each major class of pipe including polyvinyl chloride
pipe (PVC), iron pipe, fiberglass reinforced plastic (FRP), and copper pipe.
SLIDE 5-55
SCH. No. = 1OOO P/S
P = Pressure, Ibf/in2
S = Allowable
Stress, Ibf /in2
The next task is to estimate the pipe
inside area which is related to the
pipe schedule. The schedule number
represents the ability of the pipe to
withstand the actual internal pressures
It is approximated by the equation
shown here.
As the schedule number goes up, the
pipe can take higher pressures.
The most common schedule pipe used in
wet scrubber systems is the schedule 40
which is approximately equivalent to
pipe which was characterized as "stan-
dard strength" before the schedule
designation was common. If no other
information is available, it should be
assumed that the pipe of interest is a
schedule 40.
Other typical pipes include schedule 80 and 160. There are schedule
numbers ranging from 5 to 160. The wall thickness increases as the schedule
number increases.
155
-------
SLIDE 5-56 Once the pipe inside dimensions are
identified in the applicable table, it
is necessary only to use a standard
pipe velocity factor to calculate the
TYPICAL LIQUID VELOCITIES flow rate. Unfortunately, there is a
IN PIPES substantial range in the design flow
Type of Liquid Average Velocities rates based Partially on. engineering
(Feet Per Second) perogatives and partially on the
_. ... „ f characteristics of the materials.
Clear Water 8 to 15
Light Slurries 6 to 12
Heavy Slurries 5 to 8 A range of typical values for pipes
handling water, light slurries and
heavy slurries are shown in this
figure. Note that flow rates in the
suction lines of pumps are consid-
erably lower than those specified in
the slide. Also, lines with only
gravity flow are much lower.
For a pipe with a nominal size of 2 inches (circumference 7 and three
quarters inches), the capacity at an assumed rate of 5 feet per second would
be 52.25 gallons per minute. At an assumed rate of 15 feet per minute, the
capacity would be 156.75 gallons per minute.
High liquor velocities can be used whenever there are no abrasive mater-
ials in the stream which would erode the piping and/or pipe liners. Low
liquor velocities are used for slurries. However, they must not be so low
that settling of the liquor is facilitated.
Once a pipe is installed, the actual inside dimensions may vary from
those specified in the table. Erosion will result in some enlargement of the
pipe while settling can reduce the area open for flow. Nevertheless, use of
this approach allows calculation of "ballpark" liquor flows and thereby aids
in the evaluation of the overall system conditions.
SLIDE 5-57
REDUCING PIPE EROSION Possible ways to minimize pipe erosion
1. REDUCE SUSPENDED SOLIDS LEVELS are listed on this slide. By far the
2. INCREASE TURN RADII most effective is to reduce the sus-
3. DECREASE LIQUOR VELOCITIES pended solids level and solids particle
I'. S^SaiSSKooNCEMmATioN sizes ^rou8h P*™* S-eatment <* the
6. INCREASE PIPE WALL THICKNESS recirculation liquor. This has other
7. INSTALL WEAR PLATES ON ELBOWS obvious benefits for the pump and
nozzles.
The liquor velocities can be decreased by use of a slightly larger pipe
size. Evaluation of the tables presented in the Appendix will demonstrate
that major reductions in the velocity will occur by increasing the pipe dia-
meter by 1 inch.
A higher schedule pipe can be used to increase the time necessary before
replacement of pipe segments. This simply provides more metal to be lost
before the pipe is seriously weakened.
156
-------
DECREASING PLUGGING OF PIPES
1. REDUCE SUSPENDED SOLIDS LEVELS
2. FLUSH OUT DEPOSITS ON A
REGULAR BASIS
3. SELECT PROPER CONTROL VALVES
4. ELIMINATE SAGGING PIPES AND
OTHER LOW SPOTS IN SYSTEM
5. SLOPE ALL PIPES
SLIDE 5-58
Pluggage is also best reduced by
lowering the suspended solids content
of the liquor. This is accomplished
by (1) increasing the purge rate,
(2) improving solids settling and/or
filtering, and (3) decreasing the liquor
pK. The latter would reduce the quan-
tity of calcium and magnesium compounds
which are precipitating from solution.
The pipe sizes should be selected to
provide sufficient velocity to con-
tinually cleanse the pipes. If this is
not possible due to erosion conditions,
then provisions for routine clean-out
should be included.
The lines are flushed by connecting a clean water source to Tee fittings
located at every major turn of the piping. All the piping should be sloped
slightly downward and have drains at low points so that the solids can be
easily removed. The sloped pipe with drain connections also aids in draining
the system during cold weather periods to avoid freezing.
Piping systems with chronic problems should have flanged pipe connections
so it is possible to easily remove and clean out a section. This also helps
when replacing worn or corroded piping.
Scrubber
SLIDE 5-59
The piping system should be rigidly
supported so that loads are not
transmitted to either the pump or the
scrubber. The vertical pipe run
illustrated in this slide needs a pipe
support either at the base or a hanger
near the top to carry the load. It
should be remembered that the weight
consists of both the pipe and the
liquor within - and this can be con-
siderable. For a 50 foot vertical run
of 4 inch Schedule 40 steel pipe, the
contained liquor weighs approximately
275 pounds and the pipe itself weighs
540 pounds.
The weight of the full pipe combined with normal vibration and shock can
cause misalignment of the pump and/or leakage at pipe fittings and flanges.
157
-------
SLIDE 5-60
Sagging Pipe
Pump
The weight of the pipe can cause
sagging in long unsupported horizontal
runs. As shown in this sketch, the
sagging places undesirable loads on the
pipe fitting at each end. It also
allows a low spot in the line which
complicates draining of the line for
freeze protection and the removal of
solids during flushing.
Pipe supports should be provided at
regular intervals to reduce deflections
and the line should be intentionally
sloped to facilitate drainage.
SLIDE 5-61
Bleed valves should be placed at points
of the line where air is likely to
accumuluate. This slide shows a pipe
leading to a header around the scrubber
throat. The high point next to the
shut-off valve is one common point of
air accumulation.
Another common area of accumulation is
the nozzle header itself. The nozzles
should be oriented at a point which has
a lower elevation than the top portion
of the header.
While the air will often be carried away
harmlessly, it could damage the control
valve and the nozzles. It should be
bleed off after start-up of the scrubber
system.
158
-------
SLIDE 5-62
TYPES OF VALVES
1. GATE
2. GLOBE
3. CHECK
4. BALL
There are a number of valve designs,
each having different applications and
service limits. The major categories
are listed on the adjacent slide.
The main considerations are the
usefulness for shut-off service versus
the usefulness for flow control. Also,
the vulnerability of the materials with
respect to slurry abrasion and pluggage
and with respect to corrosion must be
considered when selecting valves.
The next set of slides presents the
basic design features plus the
advantages and disadvantages of each
type. The drawings presented will
demonstrate that many of these appear
similar from an external view.
SLIDE 5-63
A globe valve is shown in this slide.
All globe valves have a disc or plug on
the valve stem which rests against a
metallic seat to provide the seal. The
name for these valves was derived from
an earlier design which used a globe on
the valve stem rather than the disc or
plugs now common.
All of these have high pressure drop due
to contorted path through the valve.
These are used for both throttling and
shut-off.
Due to the partition in the lower half of the valve body, this type of
valve impedes line drainage. Also, solids can accumulate on the metallic seat
and prevent an adequate seal. These valves are rarely used on slurry carrying
lines.
159
-------
Source: Air Pollution
Training Institute
The gate valve shown here is intended
for shut-off service rather than flow
control. While it is theoretically
possible to control flow with this
design, the high liquor velocities at
the bottom of the disc would cause
damage.
Since the disc on the valve stem moves
entirely out of the path of the liquid,
there is very low pressure drop through
the valve.
Deposition of solids within the valve
body could prevent closure of the valve
Therefore, this style is not used for
heavy slurries.
Due to the straight through flow
conditions of a gate valve, there is no
restriction to drainage of the line.
This also minimizes the accumulation of
solids within the valve.
The quick closing action of gate valves can cause water hammer down the
piping system. This can damage both the pipe connections and the pump.
SLIDE 5-65
A ball valve is shown in this slide.
The control element is a ball having a
large open area. When closed, the flow
passage is oriented normal to the pipe
direction and the ball is pressed against
plastic xseat rings. These valves are used
both shut-off and throttling.
Source: Air Pollution
Training Institute
160
-------
SLIDE 5-66
SWING CHECK
VALVES '
Source: Air Pollution
Training Institute
Swing check valve are designed to prevent
flow of liquid in a reverse direction.
These may be used to prevent the drainage
of liquid down out of an elevated pipe
back through the pump.
Modest liquid pressure in the forward
direction easily opens the valve. The
pressure drop to flow in the forward
direction is very low since there is no
flow obstacle.
Under no flow conditions, the force of
gravity causes the valve element to drop
into the closed position. The flow of
liquid in a reverse direction forces the
valve element against a seal and thereby
prevents leakage.
These valves must be installed in a
horizontal position to allow for the
movement of the check valve element.
SLIDE 5-67
EVALUATION OF
SPRAY NOZZLES
Nozzles disperse a liquor stream into a
gas stream. The important factors to be
considered when selecting a nozzle type
include:
1. Droplet Size Distribution
2. Spray Angle
3. Spray Pattern
4. Droplet Initial Velocity
There are a large number of nozzle
designs to provide different spraying
requirements.
Improper nozzle selection can prevent adequate performance of a wet
scrubber system due both to poor liquor-gas contact and to weak particle
capture conditions. Nozzles are also subject to operating problems due to
high liquor velocities. Liquors with high suspended solids levels can erode
critical nozzle components and can plug the nozzles. There are substantial
differences with respect to the abilities to handle erosive and corrosive
liquids.
161
-------
GENERAL TYPES OF NOZZLES
1. PRESSURE
2. TWO FLUID
3. ROTARY
SLIDE 5-68
The are three main categories of spray
nozzles. Most nozzles are the pressure
type in which the energy is supplied by
the pressure of the liquid stream. There
is limited use of the two fluid nozzles.
These are only used when very small
liquid droplets are necessary. In two
fluid nozzles, the energy for atomization
and dispersion is primarily supplied by
an air or steam line under high pressure.
The rotary nozzles are not used for air
pollution control applications.
The pressure nozzles can be further subdivided into the full cone, hollow
cone, fan, and jet type units. The jet nozzles are used for surfaces cleaning
and other applications where the energy of droplet impact can be used. The
other three types are all used extensively in particulate and gaseous wet
scrubber systems.
SLIDE 5-69
The spray pattern for the full cone
type of pressure nozzles is shown in
this slide.
The full cone spray has relatively even
distribution of drops across the entire
circular cross section of the spray. In
some nozzles types, there can be a small
center area which is dry. Nozzles are
available which develop either the
circular or square patterns.
The uniformity of the distribution is
affected by extremes in the liquid
pressure. Under very low pressures, the
cone can deteoriate to a weak "jet"
which resembles a household kitchen
faucet.
The spray angles usually range from 30° to 90°. Typical operating
pressures range from 20 psig to 120 psig in air pollution control systems.
162
-------
SLIDE 5-70
This is a typical hollow cone spray.
As the name implies, the droplets are
released in a narrow band. On a cross
section, the liquor appears as an outer
ring around a dry circular area inside.
This type of nozzle operates with design
spray angles from 30° to 90° and these
angles are relatively constant under
differing liquor conditions.
Operating pressures are similar to the
full cone nozzles. However, the flow
rates are often slightly smaller at a
given pressure.
SLIDE 5-71
Nozzles generating a jet type spray
pattern are less common than the other
two types of pressure nozzles. These
are used primarily to provide a screen
of liquid droplets across an inlet duct
to a control device.
The spray forms a fan-like pattern. The
spray angles range from almost 0°(jet
sprays) to up to 100°.
Due to this pattern, nozzles of this
type are inappropriate for the distri-
bution of liquor across circular and
rectangular areas.
163
-------
Liquid
Liquid
SLIDE 5-72 Several example full cone type pressure
nozzles are shown in this slide. The
top nozzle includes an internal spinner
vane for distribution of the liquor
leaving the nozzle. The lower unit is
termed a "helix" nozzle. The flow of
liquid past the helix results in a
modified full cone spray. There is
usually a small dry circular area in the
middle of the spray pattern due to the
nozzle tip.
The nozzles with the internal spinner
vanes are very difficult to rod out
after they become plugged. They must
be removed for cleaning. Care is
necessary for the helix type nozzles
when rodding out since it is possible
to damage the metal tip.
The droplet size distribution is normally finer for the spinner type full
cone nozzles. They operate at higher liquid pressures than the helix nozzles.
These nozzles are usually not directly interchangable.
DEFINITION OF DROPLET SIZE
1. VOLUME MEAN DIAMETER
2. SAUTER MEAN DIAMETER
SLIDE 5-73 The droplet size distribution is one of
the more important characteristics of
an operating nozzle. Unfortunately, it
is difficult to measure and difficult
to even define droplet sizes. The most
common definition is the volume mean
diameter which is simply the diameter
in which 50% of the liquid collected is
less than the specified value as shown
on the following graph.
Another common definition is the Sauter
mean diameter whih is the droplet
diameter having a volume-to-surface
ratio equal to the overall droplet
population. This definition is used
in most of the theoretical scrubber
models.
Other water droplet definitions include the surface median diameter and
the number median diameter. The definition of "droplet size" must be specified
along with the value.
The measurement of water droplet sizes is more difficult than solid
particulate since cascade impactor and diffusion battery techniques can not be
used. Most of the data is based on photography and light scattering. These
tests are expensive and can not be performed well under field conditions.
Therefore, little droplet size data is available.
164
-------
SLIDE 5-74
1000
500
200
100
O
cc
o
ui
UJ
1 50
ui
0.
o
or
o
20
10 20 50 100 200 500 1000 5000
The general relationship between the
nozzle operating pressure and the mass
average droplet diameter (another term
for the volume mean diameter) is shown
in this figure. As the pressure rises,
the droplet size decreases.
Since the majority of wet scrubber
systems operate between 20 and 120 psig,
it is apparent that the droplets are
relatively large. This can have some
effect on the tendency to become
reentrained and on the efficiency of
collecting particles.
The two fluid nozzles have droplet sizes below that shown for typical
pressure nozzles. Nevertheless, the spray droplets are usually above 25
microns and usually in the range of 50 to 100 microns. Generally, as the
capacity of a nozzle increases, the droplet sizes produced increases (at
constant pressures).
SLIDE 5-75
DROPLET SIZE
HIGH SURFACE TENSION O
LOW SURFACE TENSION %
COLLISION
—-cT
—-©
The physical characteristics of the
liquor have an influence on the droplet
sizes generated in the nozzle. As the
surface tension decreases, the droplet
sizes also decrease. A decrease in the
liquor viscosity has a similar effect.
A decrease in the liquid density, which
is related to the solids content, has
an opposite effect in that the size
range increases.
The surface tension of scrubber liquor could be altered by the additon of
either surfactants (reduction in surface tension) and of flocculants (increase
in surface tension usually). The liquid density is a function of the solids
content of the recirculation liquor. Changes in the liquor temperature and
the solids content could influence the viscosity. Because of these factors,
it is unlikely that the droplet size distribution is constant in many wet
scrubber systems.
165
-------
GPMi
GPM2 VPSI2
SLIDE 5-76
This equation shows the relationship
between the nozzle liquor flow rate and
various operating conditions.
For a nozzle in good condition and
handling liquor of consistent surface
tension and density, the flow rate is
related to the square root of the
nozzle manifold pressure. A decrease
in this pressure since the baseline
period would supposedly provide an
indicator of decreased liquor flow.
Unfortunately, the flow rate through the nozzle is also a function of the
liquor density. Another complicating factor is that nozzle condition can rarely
be verified. Pluggage of the nozzle will increase manifold pressure while
decreasing flow. Erosion of the nozzle orifice will decrease manifold pressure
while increasing flow. The erosion and pluggage effect factors have the
opposite effect on manifold pressure than normal changes in flow rate for a
nozzle in good condition.
SLIDE 5-77
COMMON NOZZLE PROBLEMS
1. COMPLETE PLUGGAGE
'2. PARTIAL PLUGGAGE
3. ORIFICE EROSION
4. ORIFICE CORROSION
5. MISALIGNMENT
6. LOW LIQUID PRESSURE
7. IMBALANCED FLOW TO
MULTIPLE HEADERS
This list includes the most common
nozzle problems for wet scrubber systems.
As a consequence of the nozzle problems,
there can be: (1) inadequate gas-liquor
contact, (2) low liquor flow rate, and
(3) poor particle capture. All of these
can singly or collectively have a severe
impact on the scrubber performance.
The inspection steps outlined in the
next set of slides will be helpful in
identifying any problems that exist.
166
-------
SLIDE 5-78
Pluggage of nozzles can occur due to
high suspended solids levels in the
liquor and due to scale from ductwork
and scrubber walls which is entrained in
the liquor stream. Nozzles with small
orifices and internal spinner vanes are
most susceptible.
The nozzle shown in this slide is a
typical full cone unit. This was taken
from a unit in which pluggage of all
nozzles occurred on almost a daily
basis.
SLIDE 5-79
When the nozzle begins to plug, the
spray angle is distorted. Less than
adequate gas-liquor contact results
for those units in which the main
dispersion technique is the nozzle.
After the nozzle is completely blocked,
the liquor flow reaches zero for this
nozzle.
Symptoms of nozzle pluggage include (1)
high suspended solids levels, (2) high
pH liquor, (3) increased nozzle dis-
charge pressures, and (4) increased
effluent residual opacity. If a number
of the nozzles are plugged, the liquor
flow rate monitor may indicate reduced
liquor flow.
167
-------
SLIDF 5-80
One means of reducing the severity of
pluggage problems is to use a nozzle
with manual or hydraulic rod-out
capaability. The nozzle shown in this
slide is equipped with a small rod which
can move through the nozzle orifice.
Obviously, only nozzle types in which
there is no spinner vane or distributor
can have this type of rod-out apparatus.
The whirl type hollow cone nozzles (which
are inherently non-plugging) are the most
appropriate nozzle type to be equipped
with the mechanical rod-outs.
.In order to use the mechanical rod-out, the nozzle must be mounted on the
wall of the scrubber. This is often possible in the case of venturi scrubbers,
but is impractical for both the packed tower and tray-type scrubbers.
The hydraulic rod out systems are composed of a clean liquor supply at
moderate to high pressures which is connected to the nozzle manifold through
an isolation valve. On regular intervals, the high suspended solids liquor
flow is discontinued and the fresh water is briefly supplied to flush out both
the manifold and the nozzles.
SLIDE 5-81
Y-TYPE STRAINER
Source: Spraying Systems, Inc.
Another means of reducing pluggage is
to use strainers in the recirculation
line. They can either be placed before
the recirculation pump or before entry
to the nozzle headers. The latter is
shown in this figure. For each header
at different elevations in the spray
tower scrubber, there should be a
strainer outside the scrubber shell.
This will prevent scale and other large
material from jamming in the small
passages of the nozzle.
The strainer is not effective for
solids which are precipitating out of
solution or other relatively small
particle size solids.
168
-------
SLIDE 5-S2
Source: Spraying Systems Inc.
The strainer can itself be a source
of pluggage. In fact, if it becomes
blinded, the entire nozzle header is
shut down. For this reason, it is
important that the strainer be cleaned
en a frequent basis.
To prevent scrubber outages during
cleaning of strainers, a double arrange-
ment, as shown in this slide, can be
used. One line at a time can be isolated
and the strainer cleaned while flow
continues through the other. There is
also a "double basket" unit which can be
shifted from one filter to the other
without interruping flow.
The strainer can also be placed before the recirculation pump. In this
location, it also provides some protection against erosion of the pump impeller.
SLIDE 5-83
SYMPTOMS OF NOZZLE EROSION
1. HIGH LIQUOR SUSPENDED SOLIDS
2. REDUCED NOZZLE HEADER PRESSURE
3. REDUCED PUMP DISCHARGE PRESSURE
4. CORROSIVE CONDITIONS
5. UNSATURATED CONDITIONS AT THE
SCRUBBER OUTLET
Erosion of nozzles is caused by the
mechanical action of suspended solids
passing through the nozzle orifice. As
the nozzle wears, the spray angle
gradually decreases, thereby affecting
the effectiveness of gas-liquid contact.
One symptom of erosion is a decrease in
the nozzle manifold pressure from base-
line values. This decrease is more
severe than the slight drop in the pump
discharge pressure which occurs at the
same time.
169
-------
SLIDE 5-S4
A sample of the recirculation liquor
should be obtained in a transparent
container as shown in this slide.
The presence of high suspended solids
in itself can demonstrate the potential
for nozzle erosion (and pump impeller
erosion). However, it is the settling
rate which is most indicative of this
problem. If the materials settle
rapidly, the particle sizes of this
suspended material are large. It is
this large material which has the most
erosive effect.
The pH of the sample should also be measured since this provides one
indication of the corrosive nature of the liquor. Obviously, a material which
is subject to corrosive attack will be more vulnerable to erosive action as
the surface layers of metal become corroded. If nozzle wear is severe and/or
frequent, the sample of liquor should be brought back to the lab for both
chloride and fluoride analyses.
Ways to minimize erosion are similar to those for reducing plugging of
nozzles. These include reductions in the suspended solids levels, the use of
strainers before the pump or before each nozzle header, and the use of the
proper nozzles for the service intended.
SLIDE 5-85
To check for nozzle erosion and/or plug-
gage in the absence of nozzle header
pressure gauges (and pump discharge
pressure gauges), it may be possible to
observe the nozzle spray patterns.
When the scrubber is OUT-OF-SERVICE AND
HAS BEEN PURGED OUT, the hatch above
the nozzles should be opened. Once the
main recirculation pump has been turned
on, the conical spray patterns should
be observed. If there is damage, both
full cone and hollow cone type nozzles
exhibit a severely distorted pattern.
Often a high powered flashlight is
necessary to see the sprays.
Under no circumstances should the inspector attempt to see the nozzles
from below the spray headers since the liquor pH levels are often below 4 and
above 9. Under both conditions, eye damage is possible if some of the liquor
splashes into the eye. Also, the scrubber vessel should not be entered.
Footing is difficult inside most scrubbers, the protective liners can be
damaged, and the vessel is poorly ventilated.
170
-------
SLIDE 5-86
NOZZLE MATERIALS OF CONSTRUCTION
1. BRASS
2. STAINLESS STEEL
3. CERAMIC
4. TEFLON
5. POLY VINYL CHLORIDE
6. POLYPROPYLENE
7. NICKEL ALLOY STEELS
The proper materials of construction
should be chosen for the nozzles. Most
suppliers have a very wide selection of
materials for various corrosive and
erosive conditions.
One option which is not available for
nozzles is the use of rubber linings.
While this approach is very useful for
the protection of pump impellers and
casing and for the protection of some
pipes, it is not applicaple to nozzles.
The velocities are too high and the
clearances to small to permit the use
of linings.
A partial list of nozzle materials is presented in this slide. Brass is
generally the least expensive material. However, it is subject to erosion,
corrosion and pluggage. Teflon is good for corrosive conditions. Stainless
steels are excellent for corrosive conditions with the exception of chloride
and fluoride containing liquors. Nickel alloy stainless steels and the silicon
carbide nozzles are excellent for abrasion resistance and corrosion resistance.
The price of the nozzle increases rapidly as the more resistant materials are
selected.
SLIDE 5-87
NOZZLE EVALUATION SUMMARY
1. NOZZLE HEADER PRESSURES
2. PUMP DISCHARGE PRESSURES
3. LIQUOR TURBIDITY
4. LIQUOR pH
5. PHYSICAL CONDITION OF NOZZLES
6. SPRAY PATTERNS
A summary of the inspection points for
nozzles is provided in this slide.
For operating systems, the inspection is
normally limited to the nozzle manifold
pressures, the pump discharge pressure,
the liquor turbidity, the rate of solids
settling and the pH.
For units out of service, the nozzles
can be visually inspected. However, it
is often not possible to clearly see
internal deposits and mild erosion
conditions.
A more accurate nozzle evaluation can be performed by observing the spray
patterns during the operation of the recirculation pump (when the scrubber is
out-of-service). With this approach it is possible to see the internal deposits
and to see the effects of slight erosion. However, a safe vantage point is
rarely available.
Scrubber performance deteoriation is usually significant with only one
nozzle plugged or eroded. For this reason, the evaluation of nozzle condition
is important.
171
-------
SLIDE 5-88
Many existing scrubber systems do not
have pressure gauges on the manifolds
leading to the nozzles. The arrow in
this slide illustrates one possible
location for a gauge.
There should be a separate gauge for
each header so that it is possible to
identify pluggage or erosion of a single
nozzle in the group served by the header
Also, a separate gauge is needed for
each level of spray bars since the liquid
pressures will be different by values
equivalent to the difference in head.
SLIDE 5-89
STATIC CHARGE GENERATION
DURING DROPLET FORMATION
There is very little known about the
generation of static electricity during
the spraying of liquor in wet scrubber
systems. The action of the liquor
passing over the nozzle orifice should
generate considerable static charges on
both the nozzle body and the droplets.
The static charges on the droplets
could conceivably affect both the drop-
let size distribution and the effect-
iveness of particle capture. The charges
on the nozzles are probably drained away
continuously down the grounded header
and piping.
172
-------
SLIDE 5-90
I I
GAS STREAM
The persistence of the spray pattern
when the nozzle is spraying against
the flow of the gas stream is not well
known. The spray angle will increase
as the gas velocity increases.
Since the gas flow inside scrubber
vessels and inside venturi throats is
not uniform, the effect on the sprays
is not equal throughout. This could
conceivably lead to areas within the
scrubber with poor gas-liquor contact.
Scrubbers with persistant compliance
problems may benefit from some trial
and error analyses of different nozzle
types and operating pressures.
Anything which increases the droplet velocity leaving the nozzle should
favor penetration across opposed gas streams. This includes the use of small
spray angle nozzles, the use of full cone nozzles, and decreased liquor
pressures. Also, nozzles which generate larger droplets should be considered,
If none of these are successful, then a redesigned nozzle pattern may be
necessary.
SLIDE 5-91
The fans, ductwork and hoods of air
pollution control systems are checked
on all level 2, 3 and 4 inspections.
EVALUATION OF FANS The effectiveness of pollutant capture
AND VENTILATION SYSTEMS at the point of generation is checked
by observing visible emissions from the
process equipment. The static pressure
at the hood also provides an indirect
indication of the capture velocities.
Leakage through the ductwork can lead to significant fugitive emissions,
regardless of whether the system is under positive or negative pressure. There
is no sense in fine tuning a scrubber system while tolerating massive fugitive
emissions from either the ducts or the process equipment.
The fans on wet scrubber systems are more vulnerable to operating problems
than those on other types of air pollution control systems. This is due to
build-up of entrained droplets and solids on the fan blades, the corrosion of
the fan blades, and the high static pressures which must be developed. During
the inspection, the potential for fan problems which could lead to wet scrubber
system outages is evaluated. Also, the fan performance data is used as an
indirect indication of the gas flow rate through the scrubber vessel.
173
-------
SLIDE 5-92
TYPES OF FANS
1. RADIAL BLADE
2. BACKWARD CURVED
3. FORWARD CURVED
Due to the high positive and negative
pressures which are required in wet
scrubber systems, the centrifugal fan
is the only type of fan which is suit-
able. The three main categories of
centrifugal fans are listed in the
adjacent slide. Only the radial blade
and backward curved blade types are
generally used on wet scrubbers.
The radial blade fan is slightly less
efficient than the backward curved
blade, but is less susceptible to solids
build-up on the fan blades.
EVALUATION OF FAN PERFORMANCE
1. CHANGES IN GAS FLOW RATE
2. CHANGES IN SYSTEM RESISTANCE
SLIDE 5-93
While approaching a wet scrubber
system, the vibration of the fan should
be noted. IF THE FAN IS VIBRATING
SEVERELY, THE AREA SHOULD BE LEFT
IMMEDIATELY. THE DISINTEGRATION OF THE
FAN AND HOUSING CAN SEND METAL PARTS
(LIKE SHRAPNEL) OVER A WIDE AREA.
This problem, although not common,
happens frequently enough that all
regulatory agency inspectors must res-
pect the seriousness of this condition.
Responsible plant personnel should be
notified of the severe vibration, if
they are not aware of it already.
To prevent this accident, it is necessary to shut down the fan immediately.
This means that the pollutant laden gases must be temporarily vented through the
bypass stack. Regulatory agency inspectors should not oppose the temporarily
bypassing of the scrubber while the plant personnel conduct an orderly shut-
down of the process equipment.
174
-------
SLIDE 5-94
CAUSES OF FAN VIBRATION
1. EXCESSIVE TIP SPEEDS
2. BEARING FAILURE
3. AERODYNAMIC INSTABILITY
Wet scrubber systems are especially
prone to fan vibration problems due to
the conditions listed in this slide.
Excessive tip speeds result when plant
operators change sheaves of belt driven
fans without consulting the fan manu-
facturers. They exceed the structural
capability of the fan wheel at the
higher than anticipated rotational
speed.
As with most maintenance problems,
severe fan vibration related outages
should not occur frequently at a given
plant. The fundamental problem should
be identified by plant personnel and
corrected before the unit is restarted.
All similar units at the plant should
also be fixed as soon as possible.
SLIDE 5-95
EVALUATION OF GAS FLOW CHANGES
The main reason for evaluating the fan
performance is to determine if the fan
can deliver the necessary gas flow rate
under the present conditions in the
scrubber vessel and the ductwork. No
attempt should be made to quantify the
flow rate. Instead, the objective is to
determine if the flow rate has changed
significantly since the baseline period.
The next set of slides concerns the
operating principles of centrifugal
fans. The performance curves are very
similar to those discussed earlier with
respect to centrifugal pumps.
175
-------
SLIDE 5-96
ui
tr
v>
v>
UJ
en
a.
u
I
FAN CHARACTERISTIC
GAS FLOW-
This is a typical fan performance
curve. The unit must operate at some
point along this line.
The "No Flow" point is the intersection
of the curve with the vertical axis.
This is the point at which the maximum
static pressure is provided by the fan.
The "Free Flow" point is the intersec-
tion of the curve with the horizontal
axis. The maximum gas flow is delivered
here, but at a negligible static pressure.
The fan normally operates in a middle
position, away from both extremes.
The position and shape of this curve depends on the type of fan blades,
the fan housing, and the inlet duct configuration. Each fan has a different
fan performance curve. The only factor which can change this curve for an
existing fan is a change in the rotational speed.
SLIDE 5-97
SYSTEM CHARACTERISTIC
OPERATING POINT
FAN CHARACTERISTIC
GAS FLOW •
The new curve added in this graph is
the system resistance curve. This is
the static pressure required to move
the specified quantity of gas against
the resistance of the ductwork, hoods,
and wet scrubber vessel. The system
flow resistance is proportional to the
square of the gas flow rate.
The point at which the system resistance
curve intersects the fan performance
curve is the system operating point.
The fan and system reach this automat-
ically as the unit is started.
176
-------
SLIDE 5-98
QUJ
Si
x«n
BACKWARD CURVED FAN
GAS FLOW-
The fan motor horsepower curve is shown
in this graph. It rises as the gas flow
increases in much the same way that the
pump motor horsepower increases with
liquor flow.
Since the fan motor current is propor-
tional to the brake horsepower, the motor
current serves as an indirect indication
of gas flow rate. Even slight changes
in the currents mean major changes in the
gas flow rates.
As with pump curves, no attempt is made to quantify the gas flow rate
based on the motor currents. The relationship between motor currents and brake
horsepower (the form in which characteristic fan curves are presented) involves
the load factor. This can not be measured easily during an inspection. There
is also some question concerning the accuracy of fan characteristic curves when
applied to existing systems. The geometry of the inlet and outlet ducts of the
fans can modify flow characteristics to the extent that the characteristic
curves are no longer strictly applicable.
177
-------
SLIDE 5-99
APinsp-
APbaseline
where
^baseline)
Q » flowrate, ACFM
d » density factor,
dimensionless
Before making the comparison of the
present motor currents to the baseline
! data, it is necessary to correct for the
> gas density. The equation shown in this
1 slide is used to correct the present data,
Obviously, it is necessary to know the
gas temperature in the fan to perform
this correction. If on-site tempera-
ture monitors are not available, it is
necessary to measure the temperature
(level 3 and 4 inspections only). For
fans downstream of the scrubbers the
gas temperature is normally in the range
of 120°F to 140 °F.
This correction is necessary since a fan it behaves like a shovel, moving
a certain volume of gas during each rotation. However, the density of the gas
being moved is a strong function of the temperature and is also influenced by
the local static pressures and humidities. The work being done by the fan
increases as the density increases (cold gas temperatures).
The correction factors which should be used are presented below for common
static pressures and temperatures. Since most fans are on the downstream side
of wet scrubber vessels, the data here is for saturated conditions. For fans
ahead of the wet scrubbers, psychrometric charts should be used to determine
the density at the specific gas temperatures and mois-ture level. This should
then be corrected for the fan inlet static pressure.
GAS DENSITY CORRECTION FACTORS
Gas Temperature, °F
120
130
140
150
160
170
180
190
-0
1.15
1.18
1.22
1.27
1.33
1.42
1.52
1.64
Static Pressure, Inches of Water
-20
1.20
1.25
1.29
1.35
1.40
1.49
1.60
1.73
-40
1.28
1.32
1.37
1.43
1.50
1.53
1.71
1.86
-60
1.35
1.40
1.46
1.50
1.60
1.70
1.83
2.00
-80
1.44
1.49
1.56
1.63
1.72
1.83
1.98
2.18
178
-------
INCREASED SYSTEM RESISTANCE
BASELINE SYSTEM CHARACTERISTIC
_IDE 5-100
The operating point of the system can
change if there has been a shift in the
system flow resistance. An increase in
the resistance lowers the curve in the
direction shown by arrow #1. Decreases
in resistance result in a shift to the
left as shown by arrow #2.
Air infiltration lowers flow resistance
since the gas stream travels a shorter
path through the system A decrease in
the liquid flow rate or a decrease in
the gas velocities through the scrub-
ber results in significantly lower gas
flow resistance.
An increase in the flow resistance is less common in wet scrubber systems.
It can occur due to pluggage of packed beds or demisters. Increased liquor flow-
rates can also have this effect. However, it is more common to have decreases
in the liquor flow rate due to nozzle pluggage, line freezing and pump impeller
wear.
GAS FLOW -
TYPES OF FAN DRIVES
1. DIRECT DRIVE
2. BELT DRIVES
3. VARIABLE SPEED DRIVES
SLIDE 5-101
There are three common fan drive arrange-
ments used on wet scrubber systems. In
direct drive units, the fan rotational
speed is fixed by the motor speed. On
alternating current motors this means
that the fan speed can not vary. The
speed of direct current motors can be
easily varied over a wide range. However
it is very rare to find a direct current
motor on a wet scrubber fan.
The most common arrangement is the belt
drive fan. This has small sheaves on
the motor and large sheaves on the fan.
A set of from two to six belts is used
to drive the fan. Fan rotational speed
can be changed by changing the sheaves.
Some of the large scrubber installations can use variable speed drives.
These have hydraulic couplings for transfer of the shaft energy from the motor
and the fan. The rotational speed of the fan can be easily and rapidly varied
over a wide range in response to process operating conditions.
179
-------
SLin 5-102
These curves illustrate the shifts in
the operating point when the rotational
speed of the fan changes. Even a slight
change in the fan speed can make a
noticeable change in the gas flow rates.
Increased fan speed allows higher gas
flow rates and better pollutant capture
at the process source. Fan speed is
sometimes increased when the capacity of
the process equipment is being increased,
All increases in fan speed are inten-
tional .
Decreases in fan speed are usually the result of a change in the sheaves
(on belt driven units). This may be done in an effort to reduce the energy
cost of the fan which is often the single largest operating cost of the wet
scrubber system. On direct drive (alternating current) fans, the fan speed
can only be decreased by replacing the motor.
Belt slippage can result in a 100 to 300 r.p.m. reduction in the fan
speed. This is usually accompanied by a very annoying and noticeable squeal.
6AS FIOW-
SLIDE 5-103
If there has been a significant change
in the fan motor current (after the gas
CAM CWAI iiATirtM density correction), but the fan rota-
FAN EVALUAHUN tional speed has not changed, then there
SUMMARY has been a change in the system resistance.
The most common explanations include air
infiltration and reduced liquor flow.
If there has been both a significant
change in the corrected fan current and
the fan speed, then the operators have
been making adjustments to the system.
This may have been done to increase gas
flow rate or to reduce energy consumption.
In the case of reduced gas flow rate, it
is advisable to check for fugitive
emissions from process equipment.
During the evaluation of fan operation, the condition of the fan housing
should be noted. Obvious corrosion here is often accompanied by corrosion of
the fan wheel and the ductwork leading to the fan.
180
-------
HOOD AND DUCTWORK PROBLEMS
1. Erosion due to Abrasive
Paniculate
2. Corrosion to Acidic Gases
and Moist Duct Surfaces
3. Severe Thermal Expansion
and Contraction
SLIDE 5-104
The physical condition of the ductwork
and hoods (if present) should be check-
ed whenever there are symptoms of gas
flow rate decreases or there are fug-
itive emissions. There is considerable
potential for trouble with these non-
moving parts of the wet scrubber system.
Some of the contributing factors are
listed on this slide.
Erosion is a common problem on wet scrub-
bers handling high concentrations of
large diameter particulate. Unlike most
air pollution control devices, the gases
accelerate when they enter scrubbers.
This aggravates the erosion potential.
Most wet scrubber systems handle gas streams with one or more corrosive
components. During start-up, absorption of these gases can occur on downstream
ductwork which has a light coating of moisture on the surfaces.
It is common for gases leaving process equipment to be at temperatures of
500 to 2000 °F. While passing to the scrubber vessel, these gases are cooled
to temperatures less than 300 °F. During start-up and shut-down of the system,
there can be major differences in the rates of expansion and contraction of
the ductwork. This can lead to air infiltration points.due to the ductwork
deterioration.
SLIDE 5-105
One of the most common sites of duct
erosion is at sharp turns. The inertia
of large diameter particles results in
severe erosion of a portion of the duct
as shown in the top part of the slide.
It is common practice to install wear
plates on the outer surfaces of the
elbow to minimize the frequency of duct
replacement.
Another approach is to reduce the duct
velocity by reducing the gas flow rate
or by increasing the radius of the turn.
Erosion may become a problem on systems in which the fan speed has been
increased to increase overall production capacity. The gas velocity will
increase in direct proportion to the increase in the actual cubic feet per
minute of gas flow. The normal gas transport velocities range from 3000 feet
per minute to 4500 feet per minute. However, erosion can occur even in this
range.
Idl
-------
GAS TEMPERATURE -F
4OO J-
20O
100 200 300 4OO 9OO 6OO 700
Equivalent Ltngth, fttl
SLIDE 5-106
Air infiltration sites are often hard
to find due to the inaccessibility of
the ductwork and due to the combined
effect of a large number of small
erosion and corrosion holes. A duct
temperature profile can be prepared to
determine if infiltration does exist
and to determine the most probable
areas for the problem.
The profile is constructed by measuring
the gas temperature in the duct at all
points with safe and convenient access.
The data is plotted as shown in this
slide. The graph starts with the
location of the process equipment and
proceeds along the ductwork to the
scrubber. The sudden drop near the
right of the graph shows is the effect
of the scrubber.
Although this approach can not be used on all wet scrubber systems, it is
convenient in many cases. It is necessary to have some baseline data so that
normal temperature decreases due to radiation and convection can be differen-
tiated from the cooling which results from the infiltration of ambient air.
EXAMPLE OXYGEN AND TEMPERATURE PROFILES
GAS TEMPERATURE T
OXYGEN CONTENTS, f
400
ZOO E
SLIDE 5-107
A similar duct profile can be prepared
using the oxygen concentrations in gas
streams from boilers and similar com-
bustion systems. The measured oxygen
data is plotted along the ductwork line
from the combustion chamber to the
scrubber.
The oxygen concentration should not
change much. There will usually be some
slight infiltration across the fan and
the scrubber vessel, but this is usually
slight.
This type of profile can only be prepared for combustion sources having
oxygen concentrations in the range of 2 to 12%. It is not very effective for
most driers since these often operate at 17 to 19% oxygen. These values are
too close to the ambient level of 20.9% to provide any reasonable sensitivity
in detecting air infiltration.
IOO 200 SOO 40O 90O COO TOO
E^traUn
182
-------
SLIDE 5-1OS
Another means to check the significance
I of air infiltration is to compare the
\y S £ Y St. hood static pressure with the baseline
•' values.
-rj , \7 I *t ^e h°°d static pressure is proportional
V "~ /Jtw£Tjg'? VelOCITy to the velocity pressure in the duct
leading from the hood. The constant "C"
is primarily determined by the geometry
C,— L. nod! Sk'QtlC °^ t'le h°°d' However, with the baseline
h comparison, it is not necessary to know
rTGSSUre "C" unless the hood configuration has
been modified significantly.
The hood static pressure is normally in the range of -0.5 inches W.C. to
-2.0 inches W.C. Therefore, it should be measured by an inclined manometer or
by a low-range diaphragm gauge. The measurement port should be in the duct
immediately after the hood. For maximum accuracy, there should be 4 ports
spaced 90° around circular ducts. Due to the potential for pollutant exposure
near the hoods, direct accessibility to the port location is usually not
desirable. Instead, the port should be connected by means to tubing to a safe
and convenient measurement location.
Lecturer's Notes
Some of the attendees may ask why a complete traverse should not be done
to get very accurage static pressure data across the entire duct. It should
be pointed out that the effort required for this is equivalent to simply doing
a complete velocity pressure traverse and calculating flow rate directly. The
static pressure measurement is meant to be a convenient short-cut. Also, it
is often unsafe directly adjacent to a hood and a pitot traverse can not be
conducted.
SLIDE 5-109
Even if the gas flow rate through the
hood has not changed since the base-
line period, it is possible to have
poor pollutant capture. This can be
caused by a damaged hood or by cross
drafts.
The hoods can be damaged by overhead
cranes. When the hood partially re-
stricts access to the process
equipment, the operators often move the
hood away permanently. Both of these
mean that the hood is not handling some
plant area and less of the pollutant
laden gases.
Source: Kational Audiovisuals Center
183
-------
SLIDE 5-11C
Two explanations for reduced gas flow
at the hood are the partial closure of
the blast gates in the downstream duct
and the accumulation of solids which
serve as a "damper" on the system.
A photograph of a blast gate is shown
here. It is simply a guillotine dam-
per which can close off all or part of
the duct when the process is not being
operated. Some operators can change
the positions of these on several of
the ducts without being aware that the
entire system is adversely affected.
In systems handling large quantities of large diameter particulate or
which have oversized ducts with low gas velocities, it is possible for solids
to accumulate. Initially this simply restricts gas flow. If the deposits
exceed the load bearing capability of the duct supports, the entire duct will
sag or fall. Clean-out ports can be used to remove accumulated materials when
the scubber system is out-ot-service.
SLIDE 5-111
MATERIALS OF CONSTRUCTION
FOR
WET SCRUBBER SYSTEMS
The next few slides address the wet
scrubber system materials of construc-
tion. The proper selection and main-
tenance is largely responsible for the
successful performance of the system.
As an inspector, it is important to
understand what can go wrong. The goal
is to minimize both the obvious and the
repeat mistakes.
The selection of materials of construction is not a single decision, but
a long series of judgements concerning each individual component of the system.
Rarely are the same materials appropriate in each portion of the unit. These
judgements must be based on reasonable estimates of the chemical and physical
conditions to which the materials will be exposed. It is important to consider
both the steady-state conditions and the exposures during process upset and
start-up.
184
-------
TYPES OF MATERIALS
1. METALS
2. ORGANIC COATINGS
AND LININGS
3. CERAMIC AND
INORGANIC
MATERIALS
The three basic categories of materials
are listed in this slide. The metals
commonly used include, but are not
limited to: carbon steels, austenitic,
ferritic and martensitic stainless
steels, and various types of high nickel
stainless steels.
There are a large variety of organic
liners for metal surfaces. These in-
clude polyester and epoxy materials.
The polyester materials can be pro-
vided with a flaked glass reinforce-
ment. Included in this category are
the natural rubber and neoprene sheet
materials.
The ceramic and inorganic materials include, but are not limited to pre-
fired brick, hydraulic bonded concretes and chemically bonded concretes.
These materials provide both corrosion and erosion resistance in especially
vulnerable areas of the wet scrubber system.
Lecturer's Notes
The selection of the specific materials to be used is a complicated task
and should remain the sole perogative of the plant operator and designers.
The regulatory agency should not encourage the use of certain materials simply
because these were used successfully elsewhere. There are too many site
specific factors which must be considered in the selection of materials.
SLIDE 5-113
IMPORTANT FACTORS WHICH
AFFECT
CORROSION RATES
1. Liquor pH
2. Chloride
Concentration
The areas subject to corrosion are all
the wetted parts of the scrubber system
These include the scrubber vessel, pumps,
piping, outlet ductwork, fans, and
recirculation tanks.
In these wetted areas, the most important
factors affecting the corrosion rate are
the pH and the chloride concentration.
Neither of these are constant in a
scrubber system. The pH is generally
lowest in the scrubber outlet. The
chloride concentration can be higher in
solids deposits than in the recirculating
liquor.
185
-------
SLIDE 5-11A
This graph illustrates the general re-
lationship between pH and chloride
concentration on the rates of pitting
and crevice corrosion (two common modes
of metal damage) for AISI 316L stain-
less steel. At the pH levels of 4 and
above which are common in wet scrubber
systems, the chloride concentrations
above 1000 ppm result in severe damage.
Even at levels as low as 100 ppm, there
can be damage. It is apparent that
higher chloride concentrations can be
tolerated at higher pH levels.
Source: Chemical Engineering
June 5, 1978, Page 163
PH
SLIDE 5-115
It is apparent from the slide provided
above that pH levels in the range of 1
to 4 are especially prone to corrosion,
even at very low chloride levels. It is
important that the unit always be main-
tained above this level. Problems often
occur when the scrubber system is shut-
down and not purged of acidic gases.
Also, the failure of an alkaline addition
system can lead to sudden drops in the pH.
A short term drop in the pH levels can
initiate corrosion of materials that
would not otherwise be damaged. Once
the pitting action has started, it can
continue under the conditions which were
previously acceptable.
Only the nickel alloys are relatively immune to the low pH related types
of corrosion damage. These are rarely used due to the very high cost of the
materials.
14
13
12
I l
10
9
8
7
6
5
4
3
2
I
186
-------
SLUT 1-116
CONDITIONS WHICH FAVOR
LOCALIZED CORROSION
1. CREVICES
2. SOLIDS DEPOSITS
3. HIGH CHLORIDES LEVELS
4. LOW pH
5. EROSIVE LIQUORS
Localized deposits of solids should be
avoided wherever possible. They can be
rich in chloride levels and create
oxygen depleted areas near the metal
surface. This can result in accelerated
corrosion in localized portions of the
scrubber.
Crevices should also avoided. These
provide sites for crevice corrosion.
SLIDE 5-117
ORGANIC LINER PROBLEMS
1. Blistering
2. Debonding
3. Chemical Attack by
Scrubber Liquor
4. Nonuniform Coating
5. Erosion of Liner
Organic linings are less costly than
corrosion resistant metals. However,
they are susceptible to the problems
listed here.
Temperature excursions are a common
factor in liner failure. They can lead
to both blistering and debonding of the
liner from the base metal it was intended
to protect. The loss of liquor flow can
lead to short term temperature spikes.
Proper surface preparation is critical to the success of the liner. The
metal surface must be cleaned and then coated with a primer. The coating must
be applied uniformly and at the proper thickness. There should be no voids or
pinholes in the liner. Surface preparation is also important when repairs are
being made to damaged portions of the liner.
Organic liners can have a limited life in the high liquid and gas stream
velocity areas of the scrubber. It does not take long to remove portions of a
liner which is typically 40 to 80 mils thick (0.04 to 0.08 inches) when highly
abrasive particulate is present.
187
-------
5-11S
TEMPERATURE LIMITS
OF
ORGANIC LINERS
1. Polyesters - 250 °F
2. Epoxy - 250 °F
3. Vinyl Esters - 360°F
4. Fluoropolymer
- 400 °F
The temperature limits of common types
of organic liners are presented in this
slide. Slightly higher short term
transient temperatures can usually be
tolerated, but continuous operating
conditions should be lower.
Th fluoropolymers have the highest
allowable temperature and a relatively
high cost. These material are used
mainly in areas where high temperatures
during shut-down or system upsets are
expected.
The temperatures listed above are for dry conditions.
wet conditions are lower.
The maximums for
The temperature limits for all of these materials could easily be exceed-
ed if the recirculation pump fails. Systems in which there is a presaturator
or evaporative cooler are obviously less susceptible to this type of damage
since two separate pumps must fail in order to have a sudden excursion.
Bypassing is necessary on any system when the gas exceeds normal tempera-
tures. On units where the bypass is controlled by manually activated dampers,
the damage to the liners may have already occurred before the hot gas is
directed up the bypass stack. In any case, the scrubber system should be
purged of hot and pollutant laden gas trapped inside.
SLIDE 5-119
RUBBER LINERS
1. MINIMIZE LIQUID PENETRATION
UNDERNEATH LAYERS
2. PREPARE SURFACE PROPERLY TO
ACCEPT ADHESIVES
3. MINIMIZE TEMPERATURES
EXURSIONS
The rubber liners are applied as sheets.
It is important that they be layered
properly so that scrubber liquor will
not be forced underneath the layers and
attack the adhesive.
As with the organic liners, it is
important to maintain the temperature
at low levels to prevent damage. It is
also necessary to prepare the surface
to accept the adhesive.
188
-------
SLIDE 5-120
For existing systems, there is sometimes
a need to evaluate changes in the mat-
erials of construction in order to mini-
TEST SPOOLS FOR mize system failures. One way of per-
EVALUATING MATERIALS OF CONSTRUCTION forming these tests is to use a test
1 WEIGHT LOSS spool containing samples of a number of
2 PITTING different metals with or without liners.
3. CREVICE FORMATION The spool is placed in the portion of
the scrubber system experiencing fre-
quent materials problems.
The materials are compared based on the
general rate of weight loss, the rate
of pitting and the depth of crevice
formation. This can be done on several
occasions so that the rates of corrosion
can be compared with present materials.
189
-------
LECTURE 5 - REVIEW PROBLEMS AND QUESTIONS
5-1. The correct answer is "b". Pluggage is not a likely explanation for the
observed rainout. The gas velocity through the demister is 29.03 feet
per second, assuming that the entire demister is open. This velocity is
above the normally accepted limits for chevron demisters. The rainout
is probably due to the reentrainment of droplets from the downstream
edges of the demister. The demister is undersized. Those who answered
"a" may protest that pluggage is also conceivable. While this is true,
it would only aggravate the situation with the obviously inadequate
demister. Their answer is wrong since correction of the pluggage con-
dition would not alleviate the rainout conditions, only improve it
slightly.
5-2. Answer "b" is correct. It takes much less energy for a fan to move a
cubic foot of gas at 325 °F than at 125 °F. The gas has a much lower
density at higher temperatures. As an analogy, relate the effort in-
volved in shoveling a light fluffy snow to that of shoveling a wet snow
If anyone is having trouble with this concept, go back and review the
section of motor current correction factors. It may also be helpful to
briefly review the ideal gas laws.
5-3. Those who have been answering "b" are on a hot streak. It is correct
again. However, answer "c" is equally correct. The squeal usually
indicates drive belt slippage. The reduction in the fan rotational
speed leads directly to a reduction in the gas flow rate. It would be
worthwhile to check the scrubber pressure drop since this is related to
the square of the gas flow rate. The presence or absence of fugitive
emissions should also be checked.
5-4. The correct answer is "b" again. Pipe sizes for different materials are
not identical. It is necessary to consult standard tabulations of sizes
to determine the actual inside and outside diameters denoted by the pipe
nominal size.
5-5. The correct answer is "d". The increase in the nozzle header pressure
and the decrease in the scrubber pressure drop both suggest a reduction
in the liquor flow rate due to nozzle pluggage. The high liquor
turbidity also suggests the potential for nozzle pluggage. Cavitation,
answer "a", would also lead to a reduction in the liquor flow rate and
a drop in the scrubber pressure drop. However, it would also decrease
the nozzle header pressure.
190
-------
LECTURE 5 - REVIEW PROBLEMS AND QUESTIONS
5-1. The gas flow rate measured downstream from a 3-pass chevron demister is
67,500 ACFM. The average gas temperature at the port used to measure
the gas flow rate is 126 °F. The demister static pressure drop is 1.2
inches of water and the diameter of the circular demister is 8 feet. Is
pluggage a likely explanation for the observed rainout from the stack?
a. Yes.
b. No.
c. Maybe.
5-2. Does it take more energy for a centrifugal fan to move a cubic foot of
gas at 325 °F than it does to move a cubic foot at 125 °F?
a. It takes more energy at 325 °F than at 125 °F.
b. It takes less energy, at 325 °F than at 125 °F.
c. There is no difference in the energy requirements.
5-3. During an inspection of a wet scrubber system, a squeal is heard in the
vicinity of the fan. Is this a symptom of an operating problem?
a. Yes, the gas velocity at the fan inlet is excessive.
b. Yes, the fan rotational speed has probably decreased.
c. Yes, the gas flow rate through the scrubber system has
probably decreased.
d. No, this is normal around fans.
5-4. Is a 1 inch PVC pipe the same size as a 1 inch steel pipe?
a. Yes.
b. No.
c. The outside diameters are the same, but the inside diameters differ.
d. The inside diameters are the same, but the outide diameters differ.
e. The hydraulic diameters are identical.
5-5. The recirculation liquor has a very high turbidity. The liquid pressure
at the nozzle header has increased from a baseline average of 45 psig to
62 psig. The scrubber pressure drop has decreased from a baseline
average of 17 inches W.C. to 14 inches W.C. The gas temperature of the
scrubber inlet stream has decreased from 350 °F to 334 °F. What
possible problems should be checked during the remainder of the
inspection?
a. Pump cavitation.
b. Erosion of the spray nozzles.
c. Process operating conditions.
d. Pluggage of the spray nozzles.
e. None of the above.
191
-------
LECTURE 5 - REVIEW PROBLEMS AND QUESTIONS
5-6. Only answers "c" and "e" are correct. All of the others listed, with
the exception of guillotine valves, are for shut-off type service.
There is no such thing as a guillotine valve for liquids.
5-7. No. Pump cavitation does not conclusively demonstrate air infiltration
into the suction line of the pump. Cavitation is the localized vapor-
ization of liquor components near the impeller due to low pressures in
this part of the pump. It can be caused by air infiltration or
anything which reduces the Net Positive Suction Head.
5-8. The seal water is meant to protect the bearings, therefore answer "a"
is correct. Following the bearing damage, excessive vibration and pump
failure will occur. Therefore, answers "c" and "d" are also correct.
Anyone having answers "b" and "e" needs to review the pump section.
5-9. The main objective of this question is to illustrate that there is a
lot which can be done during a level 2 inspection. In this case, the
following answers are correct - "b", "d", "f", "h", and "j". The
reason for checking the pH is to determine if there is potential for
scaling due to chemical precipitation on the demister blades. Answers
"d", "f", and "h" all help evaluate the effectiveness of the cleaning
action. Answer "j" is correct since it is possible that an increase
in overall gas flow rate due to production increases has resulted in
more carry-over of liquor from the top stage of the scrubber to the
demister. The latter is especially troublesome if the freeboard dis-
tance is small.
192
-------
LECTURE 5 - REVIEW PROBLEMS AND QUESTIONS
5-6. What types of valves are normally used for throttling liquid flow rates?
a. Check valves
b. Foot valves
c. Globe valves
d. Gate valves
e. Ball valves
f. Guillotine valves
g. All of the above
5-7. Does cavitation of a pump conclusively demonstrate that air is
infiltrating the suction line of the pump?
a. Yes.
b. No.
c. Maybe.
5-8. A recirculation pump is handling a liquor having a suspended solids
level of 2%. If the seal water is accidently stopped, what possible
problems can occur?
a. Bearing failure
b. Accelerated impeller wear
c. Excessive vibration
d. Pump failure
e. Reduced Net Positive Suction Head
f. All of the above
5-9. A demister is suffering chronic rainout problems and there have been a
large number of community complaints During a level 2 inspection, it is
determined that there is a demister cleaning system which is operated at
least once per shift. Is there anything else which should be checked
during this level 2 inspection?
a. No. A level 3 inspection should be conducted in the near future.
b. Yes. Plant personnel should be asked to measure the pH of the
demister wash liquor.
c. No. A stack test is obviously necessary.
d. Yes. The duration of the cleaning cycle should be determined.
e. No. Slight rainout is inevitable from demisters.
f. Yes. The pressure of the demister wash water line during cleaning
should be determined if possible.
g. No. Obviously cleaning should be discontinued to reduce the
quantity of water on the demister which can be reentrained into
the gas stream going up the stack.
h. Yes. The turbidity of the demister wash liquor should be
qualitatively evaluated.
i. No. Small gaps should be opened between demister sections to reduce
the gas velocity through the demister to more reasonable velocities.
j. Yes. The freeboard distance and production rates should be checked.
193
-------
LECTURE 5 - REVIEW PROBLEMS AND QUESTIONS
5-10. Answer "d" is correct, the inlet damper serves all of these functions.
This is a subject that was not addressed during the lecture. It is
included to illustrate that some useful information can be obtained
only by working the problems.
5-11. The correct answer is "b". The objective of the demister spray nozzles
is to clean off the entire demister surface. The hollow cone nozzles
would miss large areas directly below the nozzles.
5-12. The chloride concentration of 0.2% is equivalent to 2000 ppm which is a
very high level! The pH of the liquor should be determined (answer "a"),
if at all possible since there is a strong relationship between the rate
of corrosive attack and the pH. If the pH is less than 7, most metals
are vulnerable. The type of metal is important since there is a major
difference in susceptibilities. Those with higher molybdenum, chromium
and nickel are less vulnerable. The nickel alloys may experience no
problems under these conditions. Answer "d" is also correct for obvious
reasons.
There can be considerable room for disagreement on answer "e". The
plant should have the right to use whatever materials are most econ-
omical as long as they do not cause unnecessary excess emission con-
ditions. If they can shut down the system before violations occur, it
may be possible to use cheap sacrifical materials. On the other hand,
they should not claim that corrosion control is a "mysterious art" and
that frequent bypass conditions are inevitable.
5-13. The plant data is not reasonable. Answer "b" is correct. The pipe
velocity assuming Schedule 40 pipe is approximately 19 feet per second
which is about 50% higher than normally used maximum transport
velocities.
5-14. Answer "c" is correct. This is another one of those education questions
buried in the midst of the review problems and questions. Those who
answered "e" should get at least partial credit for recognizing a
question which is not central to the job of agency inspector. This is
just a "nice-to-know" fact.
5-15. The Austenitic stainless steels are not magnetic while the carbon steels
obviously are. A magnet is a convenient and quick way to determine the
difference.
194
-------
LECTURE 5 - REVIEW PROBLEMS AND QUESTIONS
5-10. What is the purpose of the damper on the inlet to the fan?
a. To improve gas stream loading into the fan wheel
b. To control the gas flow rate through the system
c. To protect the fan motor from overloads
d. All of the above
5-11. Would a hollow cone spray nozzle be appropriate for demister cleaning
service?
a. Yes.
b. No.
c. Maybe.
5-12. The measured chloride concentration in the effluent liquid stream of a
scrubber is 0.2%. What should be done to evaluate the potential for
serious corrosion?
a. Determine the pH of the scrubber liquor.
b. Nothing. The chloride concentration is below the threshold levels
necessary to contribute to corrosion.
c. Request information of the type of metals used in the scrubber.
d. Check for obvious corrosion.
e. Corrosion is strictly a plant economic consideration and not an
appropriate concern for regulatory agency inspectors.
5-13. During an inspection an attempt is made to calculate the present
liquid-to-gas ratio for a scrubber. However, there is no liquid flow
monitor. Plant personnel report that the 3" steel pipe supplying the
scrubber is handling 435 gallons per minute. Is this data reasonable?
a. Yes.
b. No.
c. Maybe.
5-14. Is AISI 316L stainless steel different from AISI 316 stainless steel?
a. No. They are just trying to confuse us.
b. Yes. The AISI 316L has less alloy materials and is cheaper and more
subject to corrosion.
c. Yes. The AISI 316L has less carbon. It is both easy to fabricate
parts and less subject to a certain type of corrosion.
d. I really don't think this is one of the better questions.
5-15. Is it possible to differentiate a carbon steel from a 300 series
stainless steel during a level 2 inspection?
a. Yes. But only on a good day.
b. Yes. I can also leap over tall scrubbers in a single bound.
c. Yes. With a magnet.
195
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961
-------
LECTURE 6
LIQUOR ANALYSES
SLIDE 6-1
This lecture concerns the analyses of
liquor samples obtained while inspect-
ing wet scrubber systems. These tests
help to identify the fundamental causes
of corrosion, erosion and pluggage of
the scrubber components.
The surface tension affects the rate of
solids settling, the spray droplet size,
and the ease of particle capture.
The conductivity and the oxidation/
reduction potential are of interest when
evaluating odor scrubbers. The alkalin-
ity and sulfates levels are important to
sulfur dioxide removal systems.
With the exception of the pH measurement, all of the analyses must be
conducted at the control agency laboratory. The type of instrumentation
required and the quantity of sample necessary are discussed in this section.
The importance of proper sample acquistion techniques are emphasized.
LIQUOR ANALYSES
1. Suspended Solids
2. Dissolved and Total Solids
3. Turbidity
4. pH
5. Sulfates
6. Alkalinity
7. Surface Tension
8. Conductivity
9. Oxidation-Reduction Potential
197
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SLIDE 6-:
SAMPLING PRINCIPLES
1. Take Representative Samples
2. Use Proper Sampling
Techniques
3. Protect the Samples
There is .very little sense in performing
highly accurate and demanding analyses
on samples that have been taken at the
wrong location or handled improperly.
These three sampling principles must be
satisfied and thisis not as easy as it
may seem.
The logical starting point in acquiring
samples is to review the scrubber flow
chart to determine the locations at
which samples should be taken. Sampling
times should be carefully chosen to pro-
vide the maximum diagnostic information.
The procedures used to acquire any samples should be briefly but completely
described in the field inspection notes. The names of plant persbnnel author-
izing sample acquistion should also be recorded in the notebook.
Obviously, all samples should be labeled with information such as location
of sample collection, date and time of collection, and notation of any informa-
tion that may change before analysis (temperature, pH, appearance). Also, if a
sample must be stored for any period of time, the general practice is to refrig
-erate it at 4 °C.
GRAP SAMPLES
VS.
COMPOSITE SAMPLES
SLIDE 6-3
One of the first questions faced in
sampling is whether to use a grap or a
composite sample.
A grap sample is one taken at one part-
icular time and indicates the condition
of the stream at that one time. A com-
posite sample is a mixture of smaller
grap samples taken over an extended
period of time and is representative of
the stream over that longer period of
time.
In the case of a liquor analysis, a number of grap samples taken at half
hour intervals and analyzed separately could be preferred over a composite
sample covering the same time period. This is because the composite could
average out any irregularities which, as an example, may have occurred because
of an increased gas flow to the scrubber. Also, these grap samples can be
taken as a set at the scrubber inlet and outlet, so a comparison can be made
and the performance of the scrubber determined.
198
-------
SLIEF c-4
SAFETY PRECAUTIONS
1. Open all Sample Valve
Slowly and Wear Eye
Protection at All
Times.
2. Avoid Rotating Mixers
in Tanks and Other
Moving Equipment.
3. Avoid Direct Contact
with Liquor.
4. Do Not Drop Objects
Into Tank of Vessel.
Safety procedures deserve special con-
sideration when discussing sampling.
The potential safety hazards listed in
this slide should be considered prior to
beginning any sampling work.
The most common problem is splashing
liquor from taps downstream of the
recirculation pump. With typical line
pressures in the range of 20 to 100
psig, it is possible to get an eyeful
if the valve is opened rapidly. Highly
alkaline liquors can cause severe eye
damage. This liquor is also almost
always hot.
Direct skin contact with the liquor being sampled is almost never wise.
Some of these may contain pathogenic bacteria and viruses and most contain
skin irritants.
When leaning over mixing and recirculation tanks, it is easy to drop
pens and other materials carried in shirt pockets into the tank. It is con-
ceivable that this will be carried into the pump suction line and damage the
pump impeller. The dropped material may also contribute to pluggage of the
pump suction line strainer.
SLIDE 6-5 The turbidity of the liquor is one of
the most important operating parameters
when anaylzing systems with chronic
nozzle plugging problems and/or bed
plugging problems.
Turbidity is the measure of the clarity
or cloudiness of the liquor. It is
caused by the presence of suspended
matter in a finely divided state.
Particulate matter, precipitates, and
organic matter all contribute to the
turbidity. The terms "suspended mat-
ter" and "turbidity" should not be con-
fused, although they are closely relat-
ed. Suspended matter is the amount of
material in a sample which can be
trapped by a filter. Turbidity is a
measurement of the optical scattering
and absorption of light through a
sample.
The turbidity should be evaluated qualitatively as soon as the sample is
obtained since it can change rapidly. If quantitative data is desired, the
analyses should be done the same day. In most cases, the sample can be stored
in the dark for up to twenty-four hours if it is wrapped in aluminum foil and
not exposed to extreme temperatures.
199
-------
SLIDE C-c
TURBIDITY
JTU - NTU
It is important to understand the test
methods for turbidity since some plants
measure this on a regular basis. In a
few cases, the inspector may also wish
to have the agency lab perform the
analysis.
The standard method for determining the
turbidity has been based on the use of
the Jackson candle turbidimeter. How-
ever, the lowest value that can be
measured on the instrument is 25 units.
With the need to measure samples in the range of zero to five units, an
alternative method is used incorporating nephelometers which measure the inten-
sity of light scattered at right angles to the incident beam. Since there is
no direct relationship between the optics of the two methods, turbidities
measured on a nephelometer are expressed in nephelometric turbidity units (NTU)
and those measured on the candle turbidimeter as Jackson turbidity units (JTU).
The nephelometer is preferred because of its greater precision, sensitivity,
and range.
SLIDE 6-7
A typical nephelometer is shown here.
This instrument must be calibrated
using standards in each turbidity range
anticipated.
The sample is shaken vigorously and
then poured into the turbidity tube
after air bubbles have been allowed to
escape. It is important that the tube
be scrupulously clean and have no flaws
or scratches. Fingerprints on the tube
and air bubbles clinging to the sides
will also cause erroneously readings.
For samples above 40 NTU, the sample should be diluted with one or more
volumes of distilled water until the turbidity falls into a measurable range.
The turbidity of the original sample is simply the turbidity of the diluted
sample multiplied by the dilution factor. For example, if two volumes of
distilled water were added to one volume of sample and a reading of 30 NTU
was obtained, the turbidity of the original sample would be 90 NTU.
Manufacturers of turbidimeters often use different optical designs in
their units and this can result in different turbidity reading of a particular
sample. Therefore, analyses performed by the agency lab may differ somewhat
from values routinely recorded by plant tests. Changes in the sample during
transport to the agency lab can also contribute to observed differences.
200
-------
SLIDE 0-6
The solids which quickly settle out of
solution should be removed before taking
the turbidity measurement.
The more material that settles to the
bottom of the sampling tube in a short
time, the greater the potential for
erosive wear of pump impellers, valves
and nozzles. This is because rapidly
settling solids have large diameters.
This large material is naturally erosive
in high velocity areas.
When taking the sample, the presence of
rapidly settling solids should be noted
since this is as important as the sample
turbidity.
SLIDE o-9
SUSPENDEDEO SOLIDS
DISSOLVED SOLIDS
TOTAL SOLIDS
The suspended solids are of interest
whenever the system being evaluated has
had erosion or pluggage problems. The
dissolved solids are important in any
system prone to scaling. Both the dis-
solved and suspended solids are important
when liquor is being sprayed into an
evaporative cooler or a presaturator for
gas cooling.
This is not an absolute distinction
between suspended and dissolved solids.
The nature of the filter used in sep-
arating the materials influencing the
results. Some of the important factors
include: (1) the nature of the material
in suspension, (2) the pore size of the
filter, (3) the area and thickness of the
filter, and (4) the amount of material on
the filter mat.
The temperature used to dry the sample has an important influence on the
results because weight losses due to the volatilization of organic mater,
mechanically occluded water, water of crystallization, and gases from chemical
decomposition are all dependent on the drying temperature. Most residuals are
dried at 103 to 105 °C (217 to 221 °F). At this temperature, some mechanically
occluded water and water of crystallization are retained. Volatilization of
organics will be inconsequential. The temperature used for drying the sample
should be specified along with the results.
201
-------
SLIDE 6-10
TECHNIQUES
FOR THE
MEASUREMENT OF SCRUBBER LIQUOR pH
1. Indicator Paper
2. pH Meter (Battery Powered)
The pH of both the scrubber inlet and
scrubber outlet liquors should be tested
In the majority of cases, the inlet
liquor has a higher pH than the outlet
liquor due to the absorption of acidic
gases such as sulfur dioxide and carbon
dioxide.
The same sample used for qualitatively
evaluting the turbidities can be used
for the pH tests.
The two available techniques for pH analysis are listed here. Indicator
paper should not be used whenever highly accurate data is necessary since it
is good to only plus or minus a full pH unit. As the paper ages, the accur-
acy decreases. The battery powered pH meters generally provide data good to
plus or minus 0.1 pH units. '
Solutions which chemically attack the pH paper dyes include, but are not
limited to hypochorite and permanganate. These units and those with highly
colored liquors should not be evaluated using pH paper.
SLIDE 6-11
CALIBRATION TECHNIQUE
FOR pH MEASUREMENT
Use Fresh Buffer Solutions to
Calibrate Battery Powered pH
Meter or to Check Indicator
Paper.
Liquor pH should be measured immediately
after obtaining the sample since it is
subject to change. Prior to each
measurement, the pH meter should be
adjusted using buffer solutions of
approximately 4, 7 and 10. Since these
buffers can age, fresh solutions should
be obtained on a regular basis.
If indicator paper is being used, it is
a good practice to occassionaly check
the response of this paper against buffer
solutions. This can be done at the agency
lab before leaving for any field work.
It is important to check all instruments prior to beginning the field
work. In the case of the battery powered pH meter, the battery should be
checked and the condition of the pH electrode checked. A spare battery is
usually advisable. A small quantity of deionized water is necessary for
washing the pH electrode during measurements.
202
-------
SLIDE 6-12
Tensionmeters are used to quantify the
surface tension of a liquor sample.
After centrifuging for removal of the
suspended solids, the sample is placed
in a holder having a large surface area,
The sample is raised into position so
that the platinum-iridium ring of the
tensiomenter is submerged approximately
3 mm.
After approximately 30 minutes, the
sample holder is slowly lowered until
the ring breaks through the surface.
The force involved in breaking the
surface is measured and converted to a
reading in dynes/cm. The evalution is
usually done several timesi
Unfortunately, there are no reliable field checks for changes in the
surface tension. This can change signficantly in day-to-day operation due to
the addition of surfactants and flocculants.
SLIDE 6-13
Alkalinity is the capacity of a liquor
to neutralize a strong acid to a
designated pH. The alkalinity of a
ALKALINITY = C03~ + HC03~ + OH~ fmPle is the combined effect of car-
bonate, bicarbonate and hydroxide ion
concentrations in the liquor. It is
usually expressed as the equivalent
concentration of calcium carbonate.
The analysis procedure involves the
titration of the sample with an acid
endpoint. First phenophtalein is put
into the liquor and the sample is
titrated until the phenolphtahlein
turns from red to colorless. This is
approximately a pH of 8.3. The quan-
tity of acid and its normality can be
used to calculate the "phenolphtahlein"
alkalinity.
Next a small quantity of methyl orange indicator is placed in the solution
and the titration is resumed. This has an endpoint at approximately 4.5 pH.
The total quantity of acid necessary to reach the methyl orange endpoint can be
used to calculate the "total" alkalinity.
The alkalinity is of most interest in the evaluation of sulfur dioxide
control systems. The removal of sulfur dioxide can be a function of the
alkalinity under some operation conditions.
203
-------
SLIDE 6-14
ANALYSES FOR SULFATES
1. GRAVIMETRIC
2. TURBIDIMETRIC
There are two general methods of test-
ing for sulfates in scrubber liquors:
gravimetric and turbidimetric. The
gravimetric is the most accurate. How-
ever there are a number of chemical
interferences in the analysis. The
turbidimetric procedures are subject
only to suspended solids and liquor
color problems. In most cases, the
turbidmetric procedure is satisfactory.
In this technique, the sulfate ion is
precipitated as barium sulfate after
the addition of barium chloride. The
resulting turbidity is determined by a
nephleometer, filter photometer or
spectrophotometer and compared to a
curve prepared from standard sulfate
solutions.
SLIDE 6-15
ANALYSES FOR CHLORIDES
1. SPECIFIC ION ELECTRODE
2. SILVER NITRATE TITRATION
The chlorides concentration is of
interest whenever corrosion is observed
or anticipated.
Due to the high solubility of chloride
compounds, there is very little which
can happen to a sample during transport
which would affect the chlorides con-
centration. For this reason, the
sample precautions which are discussed
earlier for other analyses, are not as
important for chlorides.
The chlorides can be determined using a specific chloride ion electrode
similar to that used for pH determinations. It can also be measured using a
silver nitrate titration. Potassium permanganate is used as the endpoint
indicator in this test. Both analytical approaches are accurate for the
concentrations of concern in wet scrubber systems.
-------
SLIDE 6-16
ANALYSES FOR FLUORIDES
1. SPECIFIC ION ELECTRODE
2. COLORIMETRIC TEST
Fluorides are of concern in particulate
wet scrubbers only because of the cor-
rosive action. The concentration of
fluroides in some gaseous scrubbers is
important since this potentially limits
the absorption of fluoride materials in
the gas stream.
The fluorides can be determined by a
specific fluoride electrode test. The
colorimetric test is more accurate. How-
ever, it is much more time consuming.
Due to the interferences caused by
chlorides, sulfates and carbonates, it
is necessary to distill the sample
before starting a fluoride colorimetric
test.
The fluoride concentration is determined photometrically at a specific
wavelength. The absorbance is compared against known concentrations of
fluoride prepared for known solutions.
SLIDE 6-17
HOW MUCH IS ENOUGH?
Test
Alkalinity
Chlorides
Fluorides
Solids
Suspended
Dissolved
Sulfates
Surface
Tension
Turbidity
Volume (ml)
100
100
200
1000
1000
1000
200
1000
The sample volumes necessary to conduct
the analyses discussed in the lecture
are provided in this slide. In all
cases, 1 liter (1000 ml) is sufficient
to conduct the specific test. It should
be noted, however, that more than this
amount will be needed if multiple tests
of a single parameter are needed or if
there is interest in several parameters.
Samples should be stored in bottles
which will not affect the material to be
tested. Polypropylene bottles are the
most common containers since these are
relatively inert and unbreakable.
The analyses should be performed as soon as possible. The maximum holding
times are generally considered to be 7 days for all of the tests except the
turbidity test which has a limit of 1 day. Of course, exposure to significant
temperature changes can result in changes in the samples.
205
-------
206
-------
SLIDE 6-16
TPQT MPTHnn^ This is a brief summary of the test
It&l witmuuo methods used for liquor analyses.
Parameter S.M. EPA ASTM These test numbers should be specified
Suspended & when discussing the test results so
Dissolved that there is no confusion regarding
Solids 208 160 D1888 the specific analytical procedures used.
Alkalinity 403 310 D 1067
The abbreviation S.M. stands for stand-
Chlorides 408 325 D 512 ^ methods ag published in Standard
Fluorides 414 340 D1179 Methods for the Examination of Water and
Surface Wastewater, 14th Edition.
Tension None None D 1590
_ ,. .OT ,,c n _... The EPA test procedures numbers are from
Suifates 427 375 D 516 publication EPA-600/4-79-020, dated
March, 1979.
The abbreviation ASTM stands for the
American Society of Testing Materials,
1984 Standards.
207
-------
LECTURE 6 - REVIEW PROBLEMS AND QUESTIONS
6-1. The correct answer is "c". The type of sample which is most represent-
ative of the conditions being evaluated should be used. Long term
averages are usually evaluated using composite samples. Short term
extreme conditions are usually evaluated using grap samples.
6-2. There is no direct relationship between the two different measures of
turbidity. The correct answer is "d".
6-3. The correct answers are "b", "c", and "d". All of these affect the
degree of light scattering within the instrument. The large diameter
particulate do not cause a "measurement error" since they contribute to
the sample turbidity.
6-4. The correct answer is "d". Higher temperatures can result in the
volatilization of organic compounds and other problems discussed in
the lecture.
6-5. There are no field instruments available for spot checking the liquor
surface tension. The tensionmeter is too susceptible to problems to
permit field use. The correct answer is "d".
208
-------
LECTURE 6 - REVIEW PROBLEMS AND QUESTIONS
6-1. Are composite samples more useful than grap samples?
a. Yes
b. No
c. It depends on the purpose of the liquor analyses
d. None of the above
6-2. If the measured turbidity is 34 JTUs, what is the value
of the turbidity expressed in NTUs?
a. 68 NTUs
b. 34 NTUs
c. 17 NTUs
d. It can not be determined from the information given.
6-3. Which of the conditions listed below can cause errors in
turbidity measurements?
a. The presence of large diameter suspended particles
b. Fingerprints on the sample tube
c. Scratches on the sample tube
d. Air bubbles
e. All of the above
6-4. What temperature is generally used for drying of solids samples?
a. 50 to 75°F
b. 100 to 105°F
c. 150 to 175°F
d. 215 to 220°F
e. 250 to 265°F
f. 295 to 305°F
g. 345 to 355°F
6-5. What field instruments are useful for spot checking the liquor
surface tension?
a. Tensionmeters
b. Bubbleometers
c. Nephleometers
d. None of the Above
209
-------
210
-------
LECTURE 7
INSPECTION AND EVALUATION
OF
PARTICULATE WET SCRUBBER SYSTEMS
SLIDE 7-1
The single most important factor which
affects the performance of participate
wet scrubber systems is the particle
INSPECTION AND EVALUATION size distribution. This lecture starts
OF with a discussion of particle size and
^ARTICULATE WET SCRUBBERS the changes in size which can occur in
the scrubber.
Scrubber static pressure drop has been
used extensively in the past to judge
the adequacy of scrubber operation.
The uses and limitations of pressure
drop are briefly examined.
Inspection procedures for each major
category of scrubber are addressed. The
purpose of these sections is to present
the data and observations which are most
useful for identifying commonly reported
problems.
211
-------
SLIDE 7-2
Gls
.Strti«lfncl
The two mechanisms .primarily responsi-
ble for particle capture in scrubbers
are impaction and diffusion.
Impaction occurs when the particle in-
ertia is so high that the particle can
not move around an obstacle in the
gas stream. As shown in the slide, the
inertia is proportional to the square
of the particle diameter. Impaction is
much higher for large particles than
for very small particles. This is one
of the reasons that particle size is
important to scrubber performance.
In addition to the particle size, im-
paction is related to the difference in
particle and obstacle velocites. This
is important since the relative veloci-
ties developed in scrubbers differ
substantially.
SLIDE 7-3
Trajectory
mttrOrople!
Diffusion is the random movement of
small particles due to collisions with
gas molecules. The rate of diffusion
is inversely proportional to the
particle diameter. It is significant
only for very small particles which have
very little total mass.
212
-------
SLIDE 7-4
IMPORTANCE OF
PARTICLE SIZE
ARBITRARY CURVE
T3 To.o 100.
PARTICLE DIAMETER MICRONS ^
The combined effect of impaction and
diffusion is a performance curve
similar to the one shown here. Impac-
tion is very effective for particles
which are larger than 10 microns, but
becomes less effective as the particle
size decreases to the 0.2 to 0.5 micron
range. Diffusion begins to exert some
influence in the 0.2 to 0.5 range and
becomes more effective as the particle
size decreases.
The peak of the curve represents the
particles in the range where neither
impaction nor diffusion are especially
effective.
Lecturer *s Notes
The left side of the curve is often not important when considering mass
emissions from the scrubber system. Particle size data for this range is also
more difficult to obtain.
SLIDE 7-5
FACTORS WHICH AFFECT
WET SCRUBBER PERFORMANCE
1. VARIATIONS IN PARTICLE SIZE
DISTRIBUTION
2. PARTICLE SURFACE CHARACTERISTICS
3. LIQUID SURFACE TENSION
4. GAS-LIQUID DISTRIBUTION
If the performance curve for a given
scrubber were known, and the particles
had a uniform size, it would be a simple
matter to design a wet scrubber. Unfor-
tunately, there are a number of very
important factors which make this imprac-
tical. These include: (1) the wide
variation in particle sizes, (2) the
influence of particle surface on impac-
tion, and (3) the influence of liquor
characteristics on impaction.
The most important of these is the
variation in the particle size distribu-
tion in the scrubber inlet gas stream.
213
-------
o .
SLIDE 7-6 The untreated gas stream never contains
particles with a uniform size. There
is a distribution of sizes as suggest-
ed in this slide.
The largest of the particles are in the
range of 50 to 100 microns. As a frame
of reference, this is approximately the
diameter of a human hair! The smallest
particles (of any significance to air
pollution emissions) are in the range
of 0.1 microns. A particle of this
size has approximately one millionth
the mass of a 100 micron particle.
One of the challenges in designing a scrubber system is determining the
type of scrubber vessel that is most appropriate for the size distribution
which exists. It is obviously easier to collect particles in the'10 to 100
micron range than it is to collect the particles in the 0.1 to 10 micron range.
In fact, all of the scrubber types perform very well on the 10 to 100 micron
particles. However, there are substantial differences in the capability to
remove the 0.1 to 10 micron material.
Lecturer's Notes
In addition to differences in physical size, there are also differences
in particle shape and in particle specific gravity. All of these have an
impact on the behavior of the particle In the scrubber.
Si.TP^ 7-7 Condensation of vapors can occur as the
gas stream cools while passing through
the scrubber vessel. These vapors could
result from a variety of causes including,
but not limited to incomplete combustion,
vaporization of raw material components,
and the generation of high concentration
of acidic compounds in the process
equipment.
If this material condenses on the surfaces
of existing particles, the overall size
distribution shifts slightly. If it con-
denses as a homogeneous particle, a large
number of very small particles are created.
These homogeneous particles often grow to
reach final particle sizes in the range
of 0.1 to 1.0 microns.
It is important to realize that the condensation and particle growth
processes require a finite amount of time. It starts as the gas stream enters
the scrubber and continues until the gas stream is no longer supersaturated
with the vaporous material. This means that some of the very small particles
may not exist as particles until the gas stream is partially through the
scrubber. Also, the particle size distribution is changing as the gas stream
passes through the scrubber. Scrubbers differ with respect to their capability
to handle this complicated situation.
CONDENSATION
VAPORS
'.•i'/ PARTICLE
GROWTH
214
-------
REGENERATION
o.
DROPLET
V
X. SHATTERED
.;/. DROPLET
•/•• PARTICLES
Very small particles can also be gen-
erated by the evaporation of droplets
containing solids. This can occur in
evaporative coolers or presaturators
handling gas-streams of high gas temp-
eratures. The total quantity of solids
put back into the gas stream can comprise
a significant fraction of the total mass
present in the small particle range.
SLIDE "-9
PARTICLE SHATTERING
t -*
•.«••*'
One additional mechanism for the develop-
ment of small particles is the shattering
of agglomerates as illustrated here. The
high gas velocities necessary to ensure
good impaction can result in the shatter-
ing of the agglomerates as they move in
the gas stream. The individual particles
are more difficult to capture than the
agglomerate since they have much lower
inertia.
215
-------
Diameter, Microns
Jue to the formation of very small
particulate matter, it is possible to
have a major fraction of the parti-
culate mass in a size range which is
beyond the capability of the scrubber.
Unfortunately, the fraction efficiency
curve, as shown on the slide is rarely
known for the specific scrubber being
inspected. Also, the particle size
data is never known during the period
of the inspection. There are no in-
struments with which the inspector can
:ake a quick sample and determine if
vhere has been a shift in the particle
size distribution.
Changes in the particle size distribution can be inferred from changes in
the process operating conditions and from the visible emissions levels. It is
apparant that the particle size of most concern in scrubber performance is also
the size range in which liqht scattering is most effective. A sudden increase
in the residual opacity without any. other obvious changes in scrubber opera-
ting conditions may indicate a change in particle size distribution character-
istics.
S^TDF. 7-11
USES AND LIMITATIONS
OF
STATIC PRESSURE DROP DATA
There is no question that the pressure
drop is a very important operating
parameter for most types of particulate
wet scrubber systems. However, there
are some very important limitations
which must be considered when using this
data. The next set of slides examines
the uses and limitations of the static
pressure data.
216
-------
SLIDE 7-12
"When compared at the same power con-
sumotion, all scrubbers give subsiantialiy
the same degree of collection of a given
dispersed dust, regardless of the mechanism
involved and regardless of whether the
pressure drop is obtained by high gas flow
rates or high water flow rates."
The use of static pressure drop data
has been based primarily on the Contact
Power Theory which is summarized in the
two equations to the left. The first
states that the penetration (which is a
way of expressing emissions) is propor-
tional to the energy consumed in the gas
phase plus the energy consumed in the
liquid phase.
The gas stream power input was always
considered to be the dominant factor.
In the late 70's EPA funded studies
indicated that the liquid stream power
input for certain types of scrubbers was
less important than indicated by the
equation. This reduced the Contact
Power Theory to a simple proportionality
between the emissions and the pressure
drop.
SLIDE 7-13
The generally assumed relationship
between static pressure drop and over-
all scrubber performance based on the
Contact Power Theory is shown in this
slide. In some cases, curves have been
compliled for "similar" scrubbers in a
certain industry category. These cor-
relations can suffer from large plant-
to-plant particle size variations.
Other variables which contribute to the
scatter in the data include variations
in the surface characteristics of the
particles, variations in the liquor
characteristics, and variations in the
degree of gas-liquor maldistribution.
The net result of the plant-to-plant differences and the variations over
time at any given plant render these correlations almost meaningless for the
purposes of the inspector. The scatter in the data is too great to draw mean-
ingful conclusions from an industry wide pressure drop-emissions correlation.
PRESSURE DROP -
217
-------
SLIDE 7-14
o
20 _ • ASPHALT PLANTS J
.10-
.02
l
10 20
PRESSURE DROP, Inches
This is one extreme example of the degree
of scatter which is possible when data
from more than one scrubber system is
used in a correlation. In this case, the
correlation attempts to relate emissions
from Hot Mix Asphaltic Concrete Plants
using mechanically aided scrubbers.
This degree of scatter should not exist
if the relationship between pressure
drop and emissions is strong and if the
particle sizes distributions are
consistent.
Lecturer's Notes
This is the first of several examples intended to illustrate that the
evaluation of particulate wet scrubber performance is more complex than simply
recording the static pressure drop.
SLIDE 7-15
.ot—
.04—
.05 i-
COAL HfPAKATION
PLANTS
This is another example of an industry
wide correlation of wet scrubber perfor-
mance. It is for venturi scrubbers on
coal preparation plant thermal driers.
There is no obvious correlation between
the pressure drop and particulate emis-
sions rate.
II
i I
20 30 40 SO 70
PftESSUKf DROP, ln
-------
SLIDE 7-16
T T
• Flint A
T Plant B
A Plant C
O punt 0
• Pilnt Plant
0.02 5.05 0.10
EMISSIONS, Gr/ttF
;j
This is published data for venturi
scrubbers serving 4 commercial lime
kilns and one pilot scale lime kiln.
There appears to be a relationship
between the pressure drop and the
particulate emissions. However, it
should be noted that the data is
plotted in log-log coordinates for
the convenience of the authors. The
degree of scatter may be much less
than the previous two slides, but it
is still too high for use by inspectors,
Lecturer's Notes
The main point of this slide is that there are a number of published
correlations of the type shown in this graph. The authors were simply
illustrating the general relationship between the pressure drop and the
emissions. They were not advocating that the performance can be evaluated by
use of the static pressure drop alone.
SLIDE 7-17
0.40
u.
< 0.20
I 0.10
-------
SLIDE 7-18
.04-
.03 -
:.02
Olh
m -ul
Q-BOP
I
60 62 64 66 68 70
PRESSURE DROP, Inch** (Minute* 5 -11)
One way to minimize the scatter in the
pressure drop - emissions correlations
is to limit it to a specific plant.
This slide presents a correlation for
three venturi scrubbers on three Q-BOP
units at the same plant. The reduced
variability is probably due to the fact
that the systems were identical and the
liquor quality was very similar.
For single site correlations, the
variability should be reduced to only
those conditions which change with time
at the site. This conceivably allows
for the preparation of a meaningful
correlation which could be'used during
an inspection.
There are never enough stack tests on a specific site to adequately
define this correlation. Furthermore, there is always the possibility that
there has been a sudden shift in the one or more of the particle generation
mechanisms. The pressure drop data must be used carefully.
SLIDE 7-19
• 001
ROSEBUD COAL
5 10 It 20 25
VCNTURI PRESSURE DROP, Incntl notor
The consequences of a shift in process
operating conditions is illustrated in
this slide. The two curves relate the
outlet particulate emissions to the
pressure drop of a pilot scale venturi
scrubber serving a coal-fired boiler.
The only major difference is the coal
characteristics. The emissions are 10
to 20 % higher with the McKay coal
supply. In other types of applica-
tions, there can be a much greater
shift in the site specific performance.
220
-------
SLIDE 7-20
Another potential source of error in the
use of the Contact Power type correlations
is the erroneous application of the
original equation.
The author of the original paper derived
the equation from Bernoulli's Law. The
0.158 constant which appears in slide
7-17 represents the inverse of the gas
density at 70 °F and 14.7 psia. Although
this was stated in the article, the
importance of gas density was forgotten
by some.
A rederivation of the Contact Power theory (see Wet Scrubber Performance
Evaluation Manual, EPA 340/1-83-022) indicates that the relationship should be
as shown in the above slide. The pressure drop divided by the average gas
density should be correlated with the total energy consumed by the scrubber.
The average gas density can vary substantially from scrubber to scrubber. It
is a function of the gas temperature and the static pressure as indicated in
the equation.
A check of the change in gas densities before and after some high pres-
sure drop scrubbers also indicates that there can be more than a 10% change.
This means that the incompressible flow assumption on which the Contact Power
Theory was based is also in.error.
Lecturer's Notes
The point regarding compressible flow is not very important for field
inspectors. They do need to understand, however, that the gas density is an
important variability. Gas temperature measurements are made during inspec-
tions to aid in estimating the densities before and after the unit.
221
-------
HIGH SURFACE TENSION
LOW SURFACE TENSION
DROPLET SIZE
O
COLLISION
—-cf'
..—©
SLIDE 7-21
Two other factors of importance to
particulate scrubber performance are
the surface tension of the liquid and
the surface characteristics of the
particle. As illustrated in this slide
(see middle column), the liquids with
high surface tension often yield large
droplets when sprayed from nozzles.
This decreases the number of impaction
targets for particles passing through
the scrubber. It is also more diffi-
cult for a particle to penetrate into
the droplet when the liquid surface
tension is high.
Particles composed primarily of hydrocarbons or coated with'an organic
material are less wettable. This also hinders the coalescence of the parti-
cle into the water drop. Unfortunately, the particles which result from the
condensation of incompletely burned fuels and other hydrocarbon materials can
be difficult to "wet" due to the surface characteristics and difficult to
impact due to the very small size range.
The chemicals added to the system at the pond, the clarifier, or the
recirculation tank can have a large influence on the surface tension of the
liquor going to the scrubber. This can conceivably have an impact on the
efficiency of the overall scrubber. Unfortunately, both the particle surface
characteristics and the liquor surface tension are difficult to evaluate
during the inspection.
SLIDE 7-22
INSPECTION TECHNIQUES
FOR MAJOR TYPES OF
PARTICULATE WET SCRUBBERS
The remainder of the lecture will
concern specific types of scrubbers.
The focus of this material is on the
relevant operating parameters for each
type to order to identify common prob-
lems. The inspection procedure is
"tailored" for each group.
Each of these categories is actually a
group of different designs which share
some basic similarities. The specific
inspection procedures must be adjusted
for these minor differences. It is the
responsibility of each field inspector
to make these changes in the inspection
procedure and to perform the inspection
in a safe manner.
222
-------
SLIDE 7-23
Source: Air Pollution
Training Institute
This is a sketch of a spray tower
scrubber. It is the simplest type of
wet scrubber and it has the lowest
overall particulate removal capability.
This is partially due to the low rel-
ative velocities between the liquor
droplets formed at the nozzles and the
particles moving with the gas stream.
Remember that impaction is proportional
to the relative velocity of the particle
to the droplet.
Due to the limited capability of the
unit, it should not be used at sources
for which a major fraction of the parti-
culate matter is in the 0.1 to 5 micron
range.
Another common version of a spray tower scrubber has the spray nozzles
arranged on a vertical header near the center of the cylindrical shell. The
gas enters tangentially so that there is some cyclonic action to aid particle
removal.
Lecturer's Notes
Another particle capture mechanism that could contribute to particle
removal in spray tower scrubbers is electrostatic attraction. Static charges
could conceivably occur on droplets sprayed from high pressure nozzles.
SLIDE 7-24
S=>RAY TOWER SCRUBBERS INSPECTION DATA
1. Average Opacity (Residual)
2. Minimum and Maximum Opacities
3. Droplet Reentrainment
4. Liquor Flow Rate
5. Nozzle Operating Pressures
6. Liquor pH
7. Liquor Turbidity
8. Nozzle Operating Condition
9. Shell Condition
This is a list of the operating data
and observations which should be made
during routine inspections of spray
tower scrubbers.
The emphasis is placed on nozzle per-
formance problems such as pluggage,
erosion, and corrosion. Since the
nozzles can rarely be observed, in-
direct symptoms of these problems must
be used. These include nozzle pres-
sure, liquor pH, and liquor turbidity.
One parameter not listed here is the static pressure drop. Performance
is not a strong function of the normally low static pressure drops in this
type of scrubber. While the liquor flow rate is listed explicity, it is
rarely measured by on-site instruments. In these cases, changes in the the
liquor flow must be determined from pump performance conditions and/or changes
in the nozzle operating conditions.
Evaluation of the ductwork and shell physical condition is especially
important since many of these scrubbers are made with unlined carbon steel.
Low pH excursions can lead to rapid and severe damage.
223
-------
SLIDE 7-25
This is a photograph of a simple spray
tower scrubber serving a Hot Mix
Asphaltic Concrete plant drier. The
fan is ahead of the scrubber vessel and
not shown here. The stack discharge is
directly above the frame of the
picture.
One of the first steps in any scrubber
system inspection is the evaluation of
the visible emissions. The residual
opacity should be observed, using the
established reference methods. Any
variations in the opacity are normally
due .to changes in process conditions.
The timing of these cycles'or spikes
should be noted so that the process
equipment performance can be checked
later in the inspection.
The physical condition of the shell and the ductwork should be checked
for signs of erosion and corrosion. Spray tower scrubbers are used on sources
of large particulate which can be very erosive. The absorption of carbon dio-
xide and sulfur dioxide can reduce the liquor pH to the corrosive range. Some
smaller systems do not have alkaline addition systems which add neutralizing
materials on a continuous basis.
SLIDE 7-26
These are potential symptoms of nozzle
pluggage. The increase in the nozzle
header pressure from baseline levels
occurs only when the flow rate is
increased or the nozzles have plugged.
If the pump motor currents have not
changed since the baseline period and
the pump discharge pressure is also
similar, it is unlikely that the flow
rate has increased.
The presence of high suspended solids
in the recirculation liquor is often
associated with nozzle pluggage. The
turbidity of the recirculation liquor
should be qualitatively evaluated. If
it appears to be high, the sample can
be taken for a suspended solids test.
For systems that are operating, the type of nozzle presently being used
should be determined. This should be compared with the type used previously
to see if the present nozzles are more susceptible to pluggage. The type of
spray and the spray angle should also be noted on any data sheets concerning
the nozzles.
NOZZLE PLUGGAGF
IN SPRAY TOWER
SCRUBBERS
1. Increased Quality
2. Increased Nozzle
Header Pressure
3. Unchanged Pump Motor
Currents
4. Unchanged Pump
Discharge Pressure
5. High Liquor Turbidity
6. Small Ponds
7. Low Pump Intake
8. Corroded Piping and
Shell
9. Scaling Conditions in
Scrubber Vessel
224
-------
SLIDE 7-27
Several of the items listed on the last
slide concern settling pond related
nozzle pluggage problems. This area
should be part of the inspection when-
ever nozzle pluggage problems are
suspected.
This is a photograph of a pond for a
small spray tower scrubber. The turbid-
ity of the pond water near the pump
intake should be checked. The sample
should be taken at a safe and convenient
location in the last zone of the pond.
If the turbidity is high, the settling
characteristics are not satisfactory.
The position of the pump intake should be carefully checked. It must be
deep enough to prevent cavitation of the pump, but not so deep that silt from
the bottom of the pond is carried into the suction line.
Lecturer's Notes
The performance of settling ponds can often be improved by the construc-
tion of several distinct settling zones separated by overflow weirs. It may
be necessary to occassionally remove the settled material in the first zone.
SLIDE 7-28
Whenever nozzles are removed for clean-
ing or replacement, the type of damage
should be briefly described in the
maintenance records.
The objective of the records is to pre-
vent repeat failures. Either the fund-
amental cause of the nozzle problem
should be rectified or a nozzle which
is less vulnerable should be used.
The field inspector should plan to
inspect the scrubber the first time
that it comes out of service and the
aozzles are being checked. In this
way, a first hand opinion can be formed
concerning the cause of the problem.
225
-------
SLIDE 7-29
Pluggage of a small number of nozzles
in the same general location within the
scrubber system can lead to poor gas-
liquor distribution. This may not have
a major effect on the nozzle header
pressure or the pump operating condi-
tions. The only way to identify these
problems is to observe nozzle perform-
ance at a time when the scrubber is out
of service.
From a vantage point above the nozzle
header, the spray angles of the nozzles
are observed when the recirculation
pump is turned on. Distorted spray
angles and completely plugged nozzles
can be seen with a bright flashlight.
Under no circumstances should an inspector enter the scrubber to check
the conditions of the nozzles or lean through the hatch to see the spray
angles. There can be oxygen deficient conditions and high concentrations of
toxic pollutants trapped in a scrubber which is out-of-service.
This is an especially effective way to find nozzle problems which are
causing excess emission conditions. However, it is rare to find a spray tower
scrubber with a safe and convenient access hatch to view the nozzles. This
should not be attempted unless the inspector can comply with all plant and
agency safety policies.
SLIDE 7-30
LEAKAGE AND INFILTRATION
IN
SPRAY TOWER SCRUBBERS
Leakage from Positive
Pressure Scrubbers
1. Reduced Gas Flow
2. Visible Leaks
3. Audible Leakage Points
Infiltration Into Negative
Pressure Scrubbers
1. Audible Infiltration
Points
2. Reduced Hood Static
3. Fugitive Emissions
Gas leakage can occur due to corrosion
of the ductwork and scrubber shell.
These can be identified as visible
leaks from the scrubber and as audible
leaks from ductwork. The drop in gas
flow through the scrubber can be quan-
tified by conducting a pitot traverse
at the stack.
Air infiltration into negative pressure
spray tower scrubber systems is diffi-
cult to identify. There is little
decrease in the fan inlet gas temperature
since the temperature is normally
120 °F to 140 °F at this point.
There is also very little change in the scrubber outlet static pressure
since the resistance to flow through these systems is normally low. A pitot
traverse at the stack outlet is not useful for quantifying the leakage since
gas flow rate does not change substantially. The best symptoms of air infil-
tration are increased fugitive emissions, reduced hood static pressure (see
Lecture #5), and audible leakage sites.
226
-------
Mist eliminator
Liquid tpriyi
Picking
This is a sketch of a packed bed scrub-
ber . These are used primarily for gas
absorption or for gas cooling, both of
which are facilitated by the large
liquid surface area on the packing.
They have only a very limited cap-
ability for removal of particulate.
However, there are applications where
both gases and particulate must be
removed.
Particle removal by impaction is limit-
ed due to the low velocities between
the particles in the gas stream and the
liquid on the packing. These scrubbers
are rarely effective for particles less
than 3 microns.
Source: Air Pollution
Training Institute
Another style of packed bed has horizontal gas flow through a vertical
packed bed. The liquor is introduced at the top and from the front of the
packing and flows in a cross current direction relative to the gas stream.
SLIDE 7-32
This photograph shows some of the most
common types of packing material used
in packed bed scrubbers. The one in
the upper left corner is a cross part-
ition ring, the ones in the lower left
are Intalox saddles. Tellerettes are
in the lower center of the slide. Pall
rings are in the lower right and a Ras-
chig ring in the uppper right. Gravel
is another material which is commonly
used.
All of the packing materials are avail-
able in various sizes, ranging from
1/2 inch to 3 inches. The materials of
construction include synthetic plastics,
ceramics, porcelain, and metal. The
packing size and configuration affects
the overall pressure drop and liquid
hold-up within the bed.
Source: Air Pollution
Training Institute
227
-------
SLIDE 7-33
This is a list of the inspection data
and observations which should be made
during a routine inspection of a packed
tower scrubber. The primary emphasis is
on any conditions which promote bed
pluggage, bed channeling, and poor
liquor distribution.
On level 3 inspections, it is necessary
to have accessible measurement ports at
the scrubber inlet and outlet. Ports
between beds in series are also helpful.
As with the spray tower scrubbers, these
systems are often small and lack any on-
site instrumentation. In these cases,
the liquor flow rate must be estimated
from the pump operating characteristics.
Reentrainment is less common with this type of scrubber since the gas
velocities up through the bed are low. The only opportunity for reentrainment
is while the gas stream passes around the nozzles at the top of the scrubber.
However, these nozzles should not be generating fine droplets which could be
carried upwards with the gas stream. The function of the nozzles is simply to
uniformly distribute the liquor on the top surface of the packing.
PACKED TOWER SCRUBBER
INSPECTION DATA
1. Average Opacity (Residual)
2. Minimum and Maximum Opacities
3. Presence or Absence of Detached Plume
4. Droplet Reentrainment
5. Inlet and Outlet Gas Temperatures
6. Shell Condition
7. Liquor Flow Rate
8. Nozzle Operating Pressures
9. Liquor pH
10. Liquor Turbidity
11. Rate of Addition of Alkaline Material
BED PLUGGAGE IN
PACKED TOWER SCRUBBERS
1. High Static Pressure
Drops Across Beds
2. High Liquor Turbidity
3. High Liquor pH
4. High Solids Content
in Inlet Gas Stream
SLIDE 7-34
Packed beds are prone to pluggage since
the liquid stream is not flowing rapidly
enough to continually remove accumulated
materials. The sources of the solids
include: (1) suspended solids in the
recirculation liquor, (2) precipitated
dissolved solids from the recirculation
liquor, and (3) impacted solids from the
gas stream on the first bed.
The symptoms which may indicate the
development of bed pluggage are listed
on this slide. An increase in the
static pressure drop across the entire
scrubber or any individual bed must be
due to either a gas flow increase or
pluggage. The gas flow rate can be
evaluated using the fan motor currents
or a pitot traverse. In the case of
severe pluggage, there could be a drop
in gas flow rate and increased fugitive
emissions.
The liquor turbidity should always be low at the inlet of a packed tower
scrubber. An increase in the pH may suggest that some precipitated solids are
scaling the packed bed.
228
-------
SLIDE 7-35
Channeling can occur whenever part of
the packing material is incompletely
wetted or when the gas stream flow up
the bed(s) is very nonuniform. The
latter can be caused by solids deposits
withing the bed.
Channeling is especially difficult to
avoid when the liquor flow rate is low.
For this reason, attempts should be made
to evaluate the liquor flow rate using
either the on-site gauges or the pump
operating conditions.
On large packed tower scrubbers with multiple beds.it is common practice
to have liquid redistributors between the beds. For all packed t6wer
scrubbers, the spray nozzles must have the proper spray angle and must be
located at the appropriate distance from the top of the bed.
CHANNELING IN PACKED
TOWER SCRUBBERS
1. Reduced Liquor
Flow Rate
2. High Turbidity Liquor
3. High Solids Content
of Inlet Gas Stream
SLIDE 7-36
SYMPTOMS OF CHANNELING
1. CHANGE IN NOZZLE HEADER
PRESSURE
2. MODERATE LIQUOR TURBIDITY
3. REDUCED LIQUOR FLOW RATE
Channeling can be especially severe in
the cross flow type of packed bed
scrubbers. There is a natural tendency
for the liquor to flow to the bottom of
the bed. Under low flow conditions, a
major fraction of the packing at the top
remains unwetted. This reduces the
amount of particulate captured and
significantly reduces gas absorption.
On units which have worked well
previously, the most useful symptoms of
this problem include a decrease in the
total liquor flow rate or a change in
the nozzle header pressure (indicating a
problem with the front spray nozzles).
For units which have suffered a chronic channeling problem, it may be
possible to substitute large capacity nozzles for the top header and reduce
flow to the lower header. The use of smaller diameter packing in the top
portion of the bed can lead to greater flow resistance, thereby shifting some
of the gas flow rate to the lower portion of the bed. The latter approach must
be done carefully so that the gas absorption is not hindered by the shorter
retention time in the bed.
229
-------
SLIDE 7-37
Sneakage can occur around the bottoms of
the cross flow packed beds. This is
normally prevented by internal weir
seals which maintain a head of liquor
greater than the static pressure of the
gas stream. However, some of the gas
stream will bypass the packed bed if the
weirs are improperly sized or corroded.
This is not a problem with the counter-
current flow (vertical flow) type pack-
ed bed. The packing extends from one
side of the scrubber vessel to the other
without any open areas which could
permit sneakage.
Source: Air Pollution
Training Institute
Sneakage is identified by measuring the static pressure drop across the
entire scrubber or the individual beds. A decrease in the pressure drop which
is not accompanied by a gas flow rate decrease is a clear sign of sneakage.
The gas flow rate can be measured using a pitot tube or estimated from the fan
operating conditions.
SLIDE 7-38
Mist eliminator
Liquid iprayt
This is a sketch of a single stage
moving bed scrubber. This unit has
hollow spheres as packing material which
are entrained by the gas stream.
Impaction of particulate occurs on the
droplets which are formed within the
turbulent bed. The liquor is introduced
from the top using a set of nozzles
similar to those used in packed bed
scrubbers. There can be a number of
beds in series.
These are used for both particulate
control and gas absorption. They are
especially effective for sources which
have sticky materials which would clog a
conventional packed bed scrubber.
Source: Air Pollution
Training Institute
230
-------
SLIDE 7-39
MOVING BED SCRUBBER INSPECTION DATA
1. Average Opacity (Residual)
2. Minimum and Maximum Opacities
3. Droplet Reentrainment
4. Presence or Absence of Detached Plume
5. Pressure Drop Across Each Stage
6. Inlet and Outlet Gas Temperature
7. Condition of Shell
8. Liquor Flow Rate
9. Nozzle Operating Pressures
10. Liquor pH
The routine inspection observations and
measurements for moving bed scrubbers
are listed in this slide.
Reentrainment is more of a problem with
these units than with the spray towers
and packed beds discussed previously.
This is due to the higher gas velocities
through the beds and the possible forma-
tion of fine droplets within the turbu-
lent bed.
Both the static pressure drop across the
scrubber and the liquor flow rate are
important operating parameters. Gas
absorption and particulate'removal are
favored at high liquor-to-gas flow
rates. Particulate removal is favored
at high static pressure drops.
The liquor turbidity is not very important since the moving bed scrubber
is inherently resistant to pluggage. The movement of the beds prevents the
accumulation of solids and the spray nozzles generally have pluggage resistant
large orifices. The liquor pH is important primarily when corrosion of the
scrubber vessel or the recirculation pump is possible. At very high pH
levels, scale deposits can occur in the scrubber sump and in portions of the
screens which retain and support the packing.
SLIDE 7-40
SYMPTOMS OF GAS-LIQUOR
MALDISTRIBUTION
1.
2.
REDUCED PRESSURE DROP
UNSATURATED GAS STREAM
AT SCRUBBER OUTLET
CHANGE IN NOZZLE HEADER
PRESSURE
LOW LIQUOR FLOW
HIGH LIQUOR TURBIDITY
Poor gas-liquor distribution can occur
due to improper inlet duct config-
uration, low liquor flow rate, the
presence of precipitated solids on the
support screens or nozzle problems.
One symptom of this condition is
a reduction in the pressure drop across
one of more of the stages. If this
occurs without any obvious changes in
the gas flow rate or the liquor flow
rate, poor distribution is likely.
On those few units with observation
windows (which remain partially trans-
parent) , it is possible to visually
identify severe maldistribution. The
hollow spheres will tend to rotate
across the bed away from the area of
highest gas velocity.
When the distribution is poor, the gas stream will not reach the adiabatic
saturation temperature. The temperature probe discussed in Lecture #2 (dev-
eloped by Shifftner) can be used in the outlet gas duct to evaluate the degree
of saturation.
231
-------
SLIDE 7-41
The performance of the moving bed scrub-
ber is partially dependent on the gas
flow rate through the scrubber. These
units have limited turndown capability
since the area of gas flow can not be
easily reduced. The droplet size pop-
ulation and size distribution are both
dependent on the gas velocity.
Changes in the gas flow rate can occur
due to: (1) gas leakage in positive
pressure units, (2) infiltration in
negative pressure units, and (3) re-
duced process operating rates in all
types of units.
The preferred method for estimating the gas flow rate is to perform a
pitot traverse at the outlet of the scrubber or at the stack. Alternatively,
changes in the gas flow can be identified from changes in the corrected fan
motor currents and fan speed (Lecture #5). Audible sites of gas leakage
and infiltration should be noted during the inspection.
DECREASED GAS FLOW RATE
IN MOVING BED SCRUBBERS
1. Reduced Static Pressure
Drop
2. Lower Fan Motor Currents
3. Decreased Fan Speed
4. Decreased Production Rate
5. Audible Gas Leakage or
Infiltration
6. Reduced Gas Flow Rate
Measurements
SLIDE 7-42
PACKING FAILURE
ON MOVING BED SCRUBBERS
1. Gradual Absorption of
Chemicals
2. Exposure to High Gas
Temperatures
3. Exposure to Low Gas
Pressure
Premature failure of the hollow sphere
packing materials can reduce the over-
all performance of the scrubber and
present a threat to the recirculation
pump.
The absorption of chemicals into the
packing material leads to gradual loss
of the'natural elasticity. Due to the
turbulent motion of the packing, it is
possible to shatter the brittle spheres.
Exposure to moderately high gas temp-
eratures due to temporary loss of liquor
flow can have the same effect.
Spheres exposed to low gas pressures during shipment can be seriously
weakened due to the difference between the internal pressure (basically sea
level pressure) and the external air pressure. After a short period of use,
they can have a high rate of failure.
The small fragments from the shattered spheres can be retained in the
recirculation system if the settling rates in the recirculation tank are poor.
These fragments can blind a strainer on the suction line or can accelerate
abrasion of the pump impeller and lining.
232
-------
SLIDE 7-43
DEMISTER PROBLEMS
IN MOVING BED SCRUBBERS
1. High Demister Static
Static Pressure Drop
2. High Turbidity Demister
Cleaning Water
3. Absence of Demister
Cleaning System
4. Rainout from Stack
5. Mud "Lip" at Stack
6. I.D. Fan Vibration
The demisters can be troublesome for
moving bed scrubbers when the liquor
used for cleaning the demister is the
same as the recirculated liquor. These
types of scrubbers often use a liquor
with moderate to high suspended solids
levels. Another cause of problems is
inadequate freeboard distance (see
Lecture #5 for definition). The liquor
carried from the top stage will drop
back down if the freeboard distance is
great enough.
The symptoms of demister problems are
listed in this slide. The pressure drop
across the cyclonic demisters or chevron
demisters is usually in the range of 0.5
to 2.0 inches. Higher static pressures
indicate partial pluggage.
SLIDE 7-44
Liquid intei
This is a sketch of a sieve plate scrub-
ber. As with all tray type scrubbers,
it consists of one or more horizontal
stages mounted in a vertical shell. The
liquor is introduced at the top through
a simple delivery pipe. The height of
the liquor on the stage is controlled by
the overflow weir on the opposite side
of the tray. The liquor passes from
tray to tray by means of downcomers.
The gas stream passes upward through the
holes in the tray. Atomized droplets
formed when the gas passes through the
liquid layer serve as the impaction
targets for capturing particles.
Source: Air Pollution
Training Institute
This type of scrubber is not as common as spray tower or venturi type
scrubbers. Its efficiency is moderate to good for small particles. The main
operating variables include the liquid flow rate, the gas flow rate, the height
of liquor on each tray, the number of trays in series and the suspended solids
content of the liquor. As with all scrubbers, the pH is also important.
233
-------
SLIDE 7-45
The impingement plant scrubber shown in
the sketch is similar to the sieve
plate scrubber shown in the previous
slide. The holes in the trays of
impingement tray units are much smaller
and more numerous. Due to the higher
gas velocities through the holes, the
particulate matter collection is more
efficient than the sieve plate units.
This advantage is gained at the expense
of increase sensitivity to pluggage of
the very small holes.
The operating parameters important to
impingement scrubbers are identical to
those which are important for the sieve
plate scrubbers. The inspection pro-
cedures are also similar.
Source: Air Pollution
Training Institute
SLIDE 7-46
TRAY-TYPE SCRUBBER INSPECTION DATA
1. Average Opacity (Residual)
2. Minimum and Maximum Opacities
3. Droplet Reentrainment
4. Presence or Absence of Detached Plume
5. Pressure Drop Across Each Stage
6. Liquor Flow Rate
7. Liquor Turbidity
8. Liquor pH
9. Condition of Shell
The inspection observations and
mesurements for tray type scrubbers are
summarized on the adjacent slide.
The liquor quality is extremely impor-
tant due to the susceptibility to plug-
gage of the trays. A sample of the
liquor should appear almost clear and
have a total suspended solids content of
less than 1% by weight.
The pressure drop across each stage can
be used to evaluate a variety of pro-
blems which affect particulate control.
Low pressure drop can be caused by low
gas flow rate, low liquor flow rate, low
liquor levels on the trays, or sneakage
of the gas around the trays.
The outlet gas temperature is useful for identifying severe maldistribu-
tion or inadequate liquor flow rates. The pH is especially important since
there are a number of wetted scrubber components which are vulnerable to
corrosion. These include the trays, impingement targets (if used), inlet weir
box, overflow weirs and downcomers.
234
-------
SLIDE 7-47
C:MERVs.
INLET WEIR SOX
-TRAY
END WEIR
MAINTAINS LEVEL ON
TRAY
— LIQUID
INLET
Weepir.
c
Reduced gas flow rate can lead to
reduced particulate removal in several
different ways. The lower velocity
through the holes and the liquor layer
reduces the effectiveness of impaction.
In severe situations, the gas velocity
can be so low that the liquor "weeps"
through the holes. In this case, the
gas-liquor distribution is very poor and
there are few small droplets to serve as
impaction targets.
Reduced gas velocity can be identified
by using the static pressure drop across
each of the stages. Decreases from the
baseline values indicate reduced gas
flow rate. Values less than 1.5 inches
W.C. indicate potential "weeping".
When low static pressure drops are observed, it is useful to estimate
changes in the gas flow rate since the baseline period. If possible, a pitot
traverse should be conducted on the outlet of the scrubber or in the stack.
The fan motor current and speed should also be noted.
Audible air infiltration points in the outlet duct or fan (negative pres-
sure systems) should be noted. Gas leakage (positive pressure systems) ahead
of the scrubber vessel should be noted.
SLIDE 7-48
DOWN-
COMER \
INLET WEIR BOX
•TRAY
eposit
s
Pluggage of trays has the opposite
effect of reduced gas flow rates. The
observed static pressure drop across the
trays increases. This increase may be
most severe for the bottom tray since
it handles the liquor with the highest
solids content and since it is the
tray exposed to the inlet gas stream.
Another symptom of pluggage problems is
the liquor turbidity. A sample of the
recirculation liquor should appear
relatively clean.
If there is an opportunity to view the trays while the scrubber is out-of-
service, the presence of solids on the trays can be confirmed. Under no cir-
cumstances should the inspector enter the scrubber vessel since there can be
oxygen deficient or toxic gases contained inside. Also, the corrosion resis-
tant liners can be easily damaged.
235
-------
SLIDE 7-49
f*
fe—
— LIOUID
INLET
>nocifccgo
Sneakage around the trays can occur when
the pressure drop across the trays ex-
ceed expected values. The downcomer
weir shown in this sketch must be high
enough so that the resistance to gas
flow up through the downcomer is too
high. If the designer did not antici-
pate the present high static pressure
drops across the tray, this weir may be
too short and gas may be sneaking around
the tray. The static pressure drop
across the tray will often exhibit rapid
variations when sneakage up the down-
comer is occurring.
Sneakage can also occur around the outer edges of each tray. These must
be secured and sealed completely around the tray. Even moderately small gaps
between the tray and the scrubber wall will allow significant gas sneakage and
a permanently reduced pressure drop across the tray.
SLIDE 7-50
CAUSES OF GAS-LIQUOR
MALDISTRIBUTION
1. SLOPED TRAY
2. PLUGGED HOLES
3. SOLIDS ACCUMULATION
ON TRAYS
4. CORROSION OF WIRES
5. EXCESSIVE GAS
VELOCITY
Nonuniform gas-liquor distribution can
occur due to a number of tray related
conditions. These are indicated on the
adjacent slide.
The tray must be level to ensure a
uniform layer of liquid across the top
of each tray. The lower resistance in
the areas with low liquid levels have
increased gas flow rates which only
aggravate the distribution problem.
Unfortunately, it is difficult to
identify the presence of non-level trays
since the pressure drop does not de-
crease substantially.
Non-level trays can occur due to poor installation, failure of tray sup-
ports, or bowed trays. The cause of the problem can be determined only by an
internal inspection by plant personnel.
Solids can accumulate adjacent to the tray overflow weir. This closes off
a portion of the tray to gas flow and increase gas flow elsewhere on the tray.
236
-------
SLIDE 7-51
INLET WEi," BOX
DOWN- .
COMER \
-TRAY
High gas flow rates can be another
source of gas-liquor maldistribution
problems. The high velocities can cause
pluggage of the holes in the middle of
the tray as shown in the sketch to the
left. This forces the gas stream to
pass up through the holes on the outer
edge of the tray.
Pluggage in one portion of the tray due
to either high gas flow rates or the
build-up adjacent to the overflow weir
will cause increased static pressure
drop. This is due to the higher
velocities necessary for the gas stream
to pass through the few open holes.
During the inspection, an attempt should be made to assess the changes in
the gas flow rate since the baseline period. The procedures used are identical
to those discussed in slide 7-52 regarding low gas flow rates (see also
Lecture #5).
SLIDE 7-52
A mechanically aided scrubber operates
quite differently from all other types
of particulate scrubbers. Due to the
shaft energy supplied to the gas stream,
there is a static pressure increase
rather than a pressure drop. The only
other type of scrubber which operates in
a similar manner is the ejector scrub-
ber which is rarely used for removal
of particulate.
The liquor quality is again critical
with the mechanically aided scrubbers.
High levels of suspended solids can lead
to erosion of the fan blades or solids
accumulation on the fan blades.
Source: Air Pollution
Training Institute
This type of unit is normally small, with gas flow rates in the range of
1,000 ACFM to 10,000 ACFM. Like most small systems, there are rarely measure-
ment ports for static pressure and gas temperature. Few systems have liquor
flow rate meters.
237
-------
SLIDE 7-53
MECHANICALLY AIDED SCRUBBER
INSPECTION DATA
1. Average Opacity (Residual)
2. Minimum and Maximum Opacities
3. Droplet Reentrainment
4. Scrubber Rotational Speed
5. Scrubber Static Pressure Rise
6. Liquor Flow Rate
7. Nozzle Operating Pressure
8. Liquor Turbidity
9 Liquor pH
10. Condition of Shell
This list summarizes the useful data and
observations for mechanically aided
scrubbers of the type depicted in the
previous slide. The emphasis is on the
static pressure increase across the
scrubber, since this is related to the
effectiveness of particle capture.
The liquor turbidity of the recircula-
tion liquor should be checked as an
indication of the total suspended solids
content of the liquor. The nozzle
operating pressures and the pump
discharge pressures can be evaluated to
determine changes in liquor flow rates
and possible pluggage problems in the
nozzle.
Decreased static pressure rise across the scrubber may indicate a change
in the scrubber rotational speed. Data concerning the speed should be request-
ed. During level 3 inspections, the speed can be measured if there is safe
access to the main shaft. It is also helpful to measure the gas flow rate
through the scrubber by means of a pitot traverse in the stack. Reduced gas
flow rates are usually due to decreased scrubber speeds.
If there is reduced gas flow, there is some potential for fugitive
emissions from the process equipment. The hood static pressure (if measured)
should be checked and visible emission observations should be conducted.
SLIDE 7-54
TYPES OF GAS ATOMIZED
SCRUBBERS
1. Fixed Throat Venturis
2. Variable Throat
Venturis
3. Flooded Disc Scrubbers
4. Rod Decks Scrubbers
5. Orifice Scrubbers
A number of different gas-atomized
scrubbers have been introduced in
Lecture #2. Each of these has unique
advantages and is susceptible to
different operating problems. While the
inspection procedure is basically the
same for all types, it is necessary to
"tailor" the inspection procedure to
each specific type. Some ares of
emphasis are presented in the next set
of slides.
233
-------
SLIDE 7-55
VENTURI SCRUBBER INSPECTION DATA
1. Average Opacity (Residual)
2. Minimum and Maximum Opacities
3. Presence or Absence of Detached
Plumes
4. Droplet Reentrainment
5. Inlet and Outlet Static Pressures
6. Inlet and Outlet Gas Temperatures
7. Inlet Oxygen and Carbon Dioxide
Levels
8. Recirculation Liquor Flow Rate
9. Nozzle Operating Pressures
10. Pipe Skin Temperature
11. Recirculation Liquor Turbidity
12. Recirculation Liquor pH
13. Evaporative Cooler or Presaturator
Liquor Turbidity
14. Condition of Shell and Ductwork
This a fairly complete list of the
inspection observations and measurements
for gas-atomized scrubbers. Not all of
these inspection points have to be per-
formed on each inspection.
The static pressure drop divided by the
average gas density is almost always im-
portant since this is related to the over-
all effectiveness of particulate removal
in most cases (see earlier portion of
Lecture #7).
The liquor suspended solids level is
critical when the recirculation liquor
is used for evaporative cooling ahead of
the scrubber. It is also important for
any units in which the liquor is sprayed
into the gas stream
The outlet gas temperature is measured to provide an indication of severe
gas-liquid maldistribution. These is tan especially serious problem with gas-
atomized scrubbers since there is only one very brief opportunity for particle
capture. Poor distribution at the location of maximum gas velocity results in
substantially reduced particulate removal. Most of the scrubbers discussed
previously are less susceptible to this problem since there are several
"collection zones" in series.
Gas-atomized scrubbers are more prone to erosion problems than other types
of particulate scrubbers. This is the result of the high gas velocities in the
restricted area (the "throat") and due to the sharp changes in flow direction
common in most designs.
SLIBE 7-56
This is a sketch of a simple fixed
throat venturi scrubber. A decrease in
the corrected pressure drop can be due
to a drop in the gas flow rate or a drop
in the liquid-to-gas ratio. As
indicated below, the pressure drop can
be adequately represented by these two
terms and a proportionality constant.
{Q, /Q
Source: Air Pollution
Where: P = Static Pressure Drop
C = Proportionality Constant
. -, ' V = Throat Velocity
QI /Qg = Liquid-to-Gas Ratio
Changes in the gas flow rate can be evaluated directly by means of a pitot
traverse or indirectly based on the fan operating conditions. The liquid flow
rate can be evaluated directly using on-site gauges or estimated based on the
pump operating conditions.
239
-------
SLIDE 7-57
LIQUOR INLET
THROAT DAMPERS
GAS OUTLET
Maldistribution of the gas and liquid
can result from improper nozzle
placement, improper throat design, or
partial pluggage of the nozzles. The
problem stems from the difficulty of
spraying liquid from the side wall into
a gas stream moving between 20,000 to
40,000 feet per minute. This is equi-
valent to spraying liquid out of a car
moving between 200 and 400 miles per
hour! As one may expect, much of the
liquor will be deflected and will not
penetrate far into the throat. It is
possible to incompletely irrigate the
middle of the throat.
One symptom of this problem is outlet gas temperatures which are above the
saturation temperature. This can be measured using the temperature probe dis-
cussed in Lecture #4. It is common practice to include manual rod out
capability on all side mounted nozzles so that plugging is minimized. The loss
of even one nozzle in some units can significantly reduce performance due to
incomplete liquor distribuition across the gas stream.
The reason that distribution is so important in venturi scrubbers is that
the point of maximum impaction is the entry to the throat. Here, the gas
velocity is high and the liquor velocity is near zero.
SLIDE 7-58
Erosion is common in the three areas
shaded in the fixed throat venturi
sketch. The high velocities within the
throat (arrow #1) are responsible for
the erosion in this area. The 90°turn
near the bottom of the diverging section
(arrow #2) are responsible for damage in
this area. There can also be some
erosion in the tangential entry to the
cyclonic demister (arrow #3).
The damage to the elbow and the demister
tangential entry can be easily seen
during a walk around inspection of the
unit. On negative pressure units, both
areas are under high negative pressures
and will have severe infiltration if
there is damage.
The problems can be minimized by maintaining the pH in a noncorrosive
range. In the case of the elbow, a shallow recession of 6 to 9 inches can be
made directly below the diverging section of the throat. This "flooded elbow"
blunts the abrasive action of the turning gas stream.
240
-------
SLIDE 7-59
6AS INLET
LIQUOR INLET
THROAT DAMPERS
GAS OUTLET
This is a side view of an adjustable
throat mechanism for a venturi scrubber.
A scrubber with these internal dampers
would look similar to that shown in the
previous slides. There is another com-
mon version which has a single damper
mounted on one side of the inlet. In
this case, the "throat" is often on the
tangential inlet duct to a cyclonic
demister.
Venturi scrubbers with these dampers can
suffer severe abrasion of the dampers due
to the high gas velocities in the
restricted area. The symptom of this
problem is reduced static pressure drop
'without any significant changes in the
gas flow rate or the liquor flow rate.
Due to the sensitivity of the pressure
drop to throat velocities, even a little
damper erosion can result in a static
pressure decrease from baseline levels.
The liquor inlet configuration of this particular design is quite different
from the array of side mounted nozzles depicted in the previous sketches.
While it obviously does not have spray penetration problems, this design is
also not immune to maldistribution problems. It is possible for the liquor
to incompletely wet the sloped sides of the section which leads to the throat.
This results in incomplete distribution of the liquor across the throat.
SLIDE 7-60
This is a photograph of the liquor inlet
and converging section of a venturi
scrubber. In this cases, the liquor
swirls down to the throat in a manner
which resembles a dentist bowl.
Maldistribution of the gas and liquor is
possible if one or more of the pipes
leading to the scrubber plugs. On
systems in which a warm liquor ( 90 to
140 °F) is recirculated, it is often
possible to identify these plugged
lines. There is a difference in- the
pipe skin temperatures with the plugged
line being several degrees colder than
the others.
The pipe skin temperature can be measured using either a battery powered
thermocouple or a thermister. The location for the measurement on each inlet
pipe is shown by the arrows in the photograph. In some cases, it is possible
to identify plugged lines simply by touch.
241
-------
242
-------
SLIDE 7-61
This is a cut-away sketch of a flooded
disc gas-atomized scrubber. In this
type of scrubber, the "throat" is the
concentric area between the disc and the
outer shell. The throat area is changed
by moving the disc assembly up or down
in the tapered section of the inlet
column. The liquor comes up the center
support of the disc and flows out over
the top. The liquor is atomized on the
outer edges by the high velocity gas
stream.
For proper gas-liquor distribution, it is very important to maintain the
disc level. If it is tipped slightly, the liquor will flow to one side and
only partially irrigate the annular area. The maldistribution problem will be
aggravated by the constricted passage on the side with liquor and the enlarged
opening next to the high side of the disc.
Due to its position facing the inlet gas stream,.the flooded disc must be
very abrasion resistant. Linings should be checked regularily and replaced
occassionally.
These scrubbers perform in basically the same manner as the venturi
scrubbers discussed earlier. .The inspection procedures for evaluating
decreased pressure drop and materials of construction problems are identical.
The flooded disc scrubbers are less susceptible to high suspended solids levels
in the liquor since nozzles are not used.
SLIDE 7-62
Source: Air Pollution
Training Institute
This is a sketch of a variable rod type
venturi scrubber. The "throat" of this
unit is the rectangular area between the
rods. This area can be varied by moving
the rods. Some versions of this design
have several rod decks in series. The
liquor is introduced through several
large nozzles above the rod deck.
"This unit is susceptible to erosion due
to the high velocity particulate laden
gas stream. The rods must be checked
routinely and replaced whenever the
erosion has progressed significantly.
Rod erosion can often be identified as
reduced pressure drop without a change
in gas or liquor flow rates.
Gas-liquor maldistribution problems can result from improper nozzle
selection, improper nozzle placement, and nozzle erosion. This can often be
detected by evaluation of the outlet gas temperature.
243
-------
LECTURE 7 - REVIEW PROBLEMS AND QUESTIONS
7-1. The best answers are "b" and "e". It is very possible that the asphalt
plant is presently operating at higher mix temperatures and this is
causing some additional volatilization of the components from the
asphalt binder used in the drum mixer. It is also possible that the
binder injection point has been moved forward toward the burner or that
the binder recently received has a lower smoke point. Any of these
process changes would result in large quantities of submicron organic
particles which condense while passing through the scrubber. These
particles would be difficult to capture and difficult to "wet". The
possibility of these process related problems could be evaluted by
observing the mix temperature monitored in the control room and by
reviewing records on the grade of asphalt binder and its smoke point.
Answer "b" remains a possible explanation since there are normally only
a few nozzles above the throat. Pluggage of one would leave a major
portion of the throat without any water droplets and zero particle
collection efficiency for this zone. The nozzle header pressure should
have increased slightly if one nozzle plugged. However, these gauges
are often not reliable due to solids accumulation in the inlet and
due to severe vibration. To check out the gauge, the pump discharge
pressure and the pump motor currents should be checked. Unfortunately,
these are rarely available on small systems such as drum mixers. The
point of this part of the question is that it is often wise to check
the condition of the spray nozzles. This can usually be done when
the asphalt plant is not operating.
Answer "a" is not correct since the decrease in pressure drop is not
very large. It would be unlikely that a drop of this magnitude would
result in an increase in opacity from 5% to 65%.
7-2. Only answers "c" and "d" are correct. The stem of the gauge has probably
corroded away since the system is not operating at the time. The latter
can be easily confirmed. Concerning answer "a", it is highly unlikely
that the system would operate this far below normal saturation
temperatures. It would require massive quantities of very cold liquor
to depress the gas temperature to this level. Answer "b" is totally
incorrect since liquor is not sprayed into a cyclonic demister.
244
-------
LECTURE 7 - REVIEW PROBLEMS AND QUESTIONS
7-1. A venturi scrubber with an adjustable throat damper is being used to
control the particulate emissions from a drum mix type asphaltic concrete
plant. The residual opacity has increased from 5% to 70% since the last
stack test. The pressure drop is now 17 inches W.C. and the baseline
values ranged from 18 to 19%. There is no liquor flow meter. However,
the nozzle header pressure has remained constant at 45 psig. The inlet
gas temperature now is 283 °F compared with baseline values ranging from
276 to 294 °F. What are some of the possible explanations for the
present high opacity?
a. Serious erosion of the throat damper has decreased the throat
velocity, thereby reducing impaction.
b. One or more of the liquor inlet nozzles is plugged.
c. The liquor flow rate has decreased substantially.
d. There is some oil scum on the surface of the settling pond.
e. The process operating conditions and/or raw materials have
changed.
7-2.
This is a slide of a dial type thermometer in the upper section of a
cyclonic demister. The indicated temperature is approximately 65 °F.
What can be concluded from this data?
a. Since the gas stream is below normal saturation temperatures, the
gas-liquor distribution is probably adequate.
b. The liquor sprayed into the cyclonic demister is too cold.
c. The gauge is not operating correctly.
d. The scrubber system is presently out-of-service
e. All of the Above
245
-------
LECTURE 7 - REVIEW PROBLEMS AND QUESTIONS
7-3. Answer "f" is the best. The increase in pressure drop across a packed
bed scrubber is usually due to either an increase in the gas flow rate
or to the accumulation of solids within the bed. While the liquor flow
rate has only a little impact on pressure drop, the decrease in liquor
flow rate may indicate other developing problems. For this reason, the
presence of audible pump cavitation should be checked. The process raw
materials and operating conditions should also be checked to determine if
the particulate loading in the inlet gas stream could have increased.
7-4. Answers "b" and ' c" could be correct. The depressed temperature of
line 3 suggests the potential for pluggage. Answer "c" has been
included only to caution the attendees that the pipe skin temperature
evaluation is not absolutely reliable. There is at least a slim
possibility that all the lines are open and in good condition.
7-5. This is a repeat of a question used in Lecture #5. The only correct
answers are "c" and "e". The consequences of fan disintegration should
not be underestimated.
7-6. The pressure drop will increase due to the higher gas velocities through
the throat. This question was included since venturi scrubbers with
throat inserts are common. These were not discussed in the lecture
portion since the inspection procedures are identical to those for fixed
throat Venturis.
246
-------
LECTURE 7 - REVIEW PROBLEMS AND QUESTIONS
7-3. The pressure drop across a packed bed scrubber has increased from 6 inches
of water to 11 inches of water. The liquor flow rate as indicated by an
on-site gauge has dropped slightly. The inlet gas temperature has dropped
from 164 °F to 145 °F. What are the logical follow-up inspection points?
a. The gas flow rate through the scrubber should be checked using
a pitot traverse and using the fan operating conditions.
b. The inlet liquor turbidity should be qualitatively evaluated.
c. The potential for pump cavitation should be checked.
d. Changes in process raw materials and fuels should be checked.
e. Answer s a,b,and c
i
f. Answers a,b,c, and d
7-4. A venturi scrubber being inspected has four tangential liquor inlets and
one center flush line above the throat. A check of the pipe skin temp-
eratures indicates the following: line 1 - 124 °F, line 2 - 123 °F,
line 3 - 120 °F, line 4 - 124 °F, and line 5 - 125 °F. What are the
possible explanations for these results?
a. Line 5 is partially or completely plugged.
b. Line 3 is partially or completely plugged.
c. All of the lines are open and in good condition.
7-5. A fan downstream of a cupola venturi scrubber is vibrating severly during
the inspection. What should be done next?
a. A pitot traverse should be done to determine if this condition
has adversely affected the gas flow rate,
b. The fan motor current and speed should be measured.
c. The inspection should be interrupted due to the potentially
dangerous situation.
d. This is strictly a maintenance problem and should be ignored.
e. A responsible plant employee should be advised of the situation.
7-6. An operator of a fixed throat venturi scrubber has proposed adding
a small plate across the throat to decrease the open throat area.
If the gas flow rate remains constant, will this increase or decrease
the static pressure drop?
a. Increase
b. Decrease
247
-------
LECTURE 7 - REVIEW PROBLEMS AND QUESTIONS
7-7. Answer "b is correct. The hollow cone nozzles do not provide good
gas-liquor distribution in spray tower scrubbers. Answer "a" is not
correct even though hollow cone nozzles are, in fact, less prone to
pluggage. In this case the operator is simply exchanging a maintenance
problem for a performance problem (which leads to excess emissions).
Answer "c" is logical. However, this may be expensive. In may be
possible to eliminate the problem simply by finding nozzles which are
not prone to pluggage at the prevailing solids levels at the plant.
7-8. Answer "c" is correct. It is possible it have a major fraction of
the particulate in the submicron range and still have the quoted
mass median particle size. Possible causes include vapor condensation
and particle regeneration. The object of this question is to emphasize
the importance of the size distribution.
7-9. The efficiency will decrease due to the lower gas velocities. Answer
"a" is correct. The residence time is not important in particulate
removal systems.
7-10. The only logical follow-up inspection point listed is the check for
fugitive emissions from the process equipment (Answer "d"). The position
of the adjustable throat dampers can not be determined externally. Also,
it is more likely that the observed decrease in pressure drop is due to
the downstream air infiltration problem than a change in the damper
position. The pitot traverse in the stack will not be very helpful since
in this position, both the gas and air flows will be measured together.
To evaluate the quantity of infiltrated air it would be necessary to
conduct a pitot traverse ahead of the scrubber in addition to the one in
the stack.
248
-------
LECTURE 7 - REVIEW PROBLEMS AND QUESTIONS
7-7. An operator of a spray tower scrubber has had chronic problems with
full cone spray nozzles. To minimize the problem, it is proposed that
all of these be replaced with hollow cone spray nozzles. Is this a
logical approach?
a. Yes. Hollow cone nozzles are less prone to pluggage.
b. No. Hollow cone nozzles have spray patterns which do not
provide good gas-liquor distribution in spray tower scrubbers.
c. No. The liquor suspended solids levels should also be reduced,
if possible.
7-8. The mass median particle size in the inlet gas stream to a spray tower
scrubber is 7.0 microns. Should it be possible to achieve an outlet
particulate concentration of 0.10 grains/ACF if the scrubber is in good
operating condition?
a. Yes. This is within the normal capability of spray tower scrubbers.
b. No. This is too small for spray tower scrubbers.
c. Maybe. It depends on the size distribution of the particulate matter.
7-9. The gas flow rate to an impingement plate scrubber has decreased 40% due
to a permanent drop in the production rate. Will this have a beneficial
or an adverse effect on the particulate removal efficiency of this unit?
a. Efficiency will decrease due to lower gas velocities through the
holes in the tray.
b. Efficiency will increase due to higher gas residence times.
c. Efficiency will not be affected by this change.
7-10. The static pressure drop across a venturi scrubber has dropped from a
baseline level of 28 inches W.C. to 21 inches W.C. The liquor flow rate
has not changed. However, the gas temperature to the scrubber has dropped
from a baseline level of 241 °F to 230 °F. Severe air infiltration is
noted in the cyclonic demister of the scrubber. What are the logical
follow-up inspection points?
a. The location of adjustable throat dampers should be checked.
b. The air infiltration rate should be quantified by means of a-
pitot traverse in the stack.
c. Process operating conditions should be checked to determine
the reason for the inlet gas temperature drop.
d. The hood static pressure should be checked and equipment served by
the scrubber should be checked for possible fugitive emissions.
249
-------
LECTURE 7 - REVIEW PROBLEMS AND QUESTIONS
7-11. Answers "b" and "c" are both correct. Obviously, it is possible to
climb the short stack and measure the static pressure (if conditions
on the platform are safe). However, the static pressure here will be
very close to ambient static pressure which is zero. Therefore, the
static pressure can be calculated as the difference between +9.8 inches
and either -1/2 or + 1/2 inches. The result is an estimated static
pressure of 9.3 inches to 10.3 inches. This approach saves the effort
of climbing the stack.
7-12. Answers "b", "c" and "d" could all be correct. The anti-fearning
solution would obviously have some beneficial impact on foaming in
the scrubber. It would also have some impact on the liquor surface
tension which in turn affects the droplet size distribution and the
effectiveness of impaction. It is difficult to determine without
stack tests whether the anti-foaming solution will have a beneficial
or adverse impact on performance. However, the inspector should note
the quantities and types of anti-foaming solutions presently being used,
250
-------
LECTURE 7 - REVIEW PROBLEMS AND QUESTIONS
7-11. During an inspection of a venturi scrubber, the static pressure ahead of
the scrubber is measured as + 9.8 inches W.C. The only port downstream of the
scrubber at which the static pressure could supposedly be measured is the stack
sampling port on the platform 75 feet above the ground. The stack terminates
approximately 4 feet above the sampling elevation. What should be done to
determine the static pressure drop across the scrubber?
a. The pressure drop can not be determined since the fan is between
the scrubber vessel and the stack.
b. Take a guess that the static pressure is between -1/2 inches to
+ 1/2 inches and calculate the pressure drop.
c. Go up and measure the static pressure at this port.
7-12. During an inspection of a scrubber system, the operator is observed
dumping a gallon of anti-foaming solution each hour into the recirculation
tank. What can happen to the system due to the addition of these chemicals?
a. Corrosion is dramatically accelerated.
b. There less foam flowing off the top of the recirculation tank and
within the scrubber. Therefore, scrubber performance is improved.
c. Particle i.mpaction effectiveness is probably affected.
d. Droplet formation in the scrubber is affected.
251
-------
252
-------
LECTURE 8
INSPECTION AND EVALUATION
OF
GAS ABSORBERS
INSPECTION AND EVALUATION
OF
GAS ABSORBERS
SLIDE 8-1
This lecture concerns wet scrubber sys-
tems used for the control of gaseous
compounds, acid vapors and odor-causing
organic vapors. It does not specifi-
cally address sulfur dioxide flue gas
desulfurizations systems since this is
covered in a separate U.S. EPA workshop
program. However, the principles for
gaseous scrubbers also apply to the
S02 control units.
The basic operating principles of this
category of wet scrubbers are intro-
duced. This is necessary to establish
the most important parameters and to
illustrate their differences from the
particulate scrubbers discussed in
Lecture 7.
The specific types of wet scrubber systems used for different applica-
tions are discussed. Inspection techniques for evaluating common modes of
failure are presented. This incorporates much of the previous material from
Lectures 3, 4, 5 and 6 into a complete inspection procedure.
253
-------
SLIDE 8-2
GASES AND VAPORS
ARE CAPTURED
BY DIFFUSION
PARTICULATE MATTER
IS CAPTURED
MAINLY BY IMPACTION
There are numerous differences between
gaseous absorbers and particulate wet
scrubbers. One of the most important
is listed in this slide.
Since most of the pollutants are cap-
tured by means of diffusion rather than
impaction, certain parameters are impor-
tant for absorbers which were not very
important for particulate scrubbers.
For example, the residence time in the
scrubber becomes important in gaseous
scrubbers since it takes time for the
molecules to diffuse to the surface of
the liquid and to transfer across the
gas and liquid films.
The gas temperature becomes important in gaseous scrubbers since diffu-
sion becomes more rapid as the temperature increases, while the solubility of
most gases increases as the liquid temperature decreases. The scrubber pres-
sure drop which is central to the performance of particulate scrubbers is less
inmportant with- the gaseous scrubbers. The liquor surface tension is also less
important.
SLIDE 8-3
LIQUOR CHARACTERISTICS
ARE CRITICAL
TO
PERFORMANCE
The characteristics of the liquor
stream are critical to the performance
of a gaseous scrubber. In the case of
the particulate scrubber, the liquor
characteristics are important only
with regard to maintenance problems
such as erosion, pluggage and corro-
sion.
With gaseous absorbers, the liquor
temperature, pH, and composition
can all influence the performance of
the air pollution control device.
254
-------
SLIDE 8-4
LIQUID-TO-GAS-RATIOS
ARE HIGHER
FOR
GASEOUS ABSORBERS
The quantity of liquor used in gaseous
scrubbers is much larger than that used
in particulate scrubbers. One of the
reasons is that the maximum possible
surface area for absorption is neces-
sary. More liquor normally favors
higher collection efficiencies. In the
case of the particulate scrubbers, there
is a broad range in which the liquid-to-
gas ratio is not very important. That
does not apply to the gaseous scrubbers.
SLIDE 8-5
Source: Air Pollution
Training Institute
The sketch shown in the circle on the
right of this slide illustrates the
microscopic process of absorption.
Some of the gas molecules are diffusing
across the interface between the gas
and liquid streams. The overall rate
of pollutant transfer from the gas
stream to the liquid stream is depen-
dent on the liquid surface area
available and on the concentrations of
the pollutant which exist in the liquid
and gas phases. Turbulent mixing of
both the gas and liquid streams favors
absorption by decreasing the time re-
quired to cross the interface between
the two phases.
Obviously, increased gas residence times favor the absorption of pollu-
tants in a scrubber by allowing more time for diffusion to be completed This
is an especially important difference between absorbers~and particulate'wet
scrubbers. With the latter, the impaction process occurs almost instanteously
as a discrete event, while absorption is the collective process of mass trans-
fer from the gas phase to the liquid phase. Absorption is time dependent. In
Lecture 7 only the effectiveness of impaction is discussed, not the "rate of
of diffusional
255
-------
SLIDE 8-6
Mass transfer occurs in both directions
until there are equilibrium concentra-
tions of the specific compound in the
liquid and gas streams. Once this
equilibrium condition has been reached,
there is no net transfer of pollutants
into the liquid stream and the rate of
pollutant collection is zero.
At this point, there are equal numbers
of the specific molecules crossing the
interface in each direction.
Source: Air Pollution
Training Institute
SLIDE 8-7
o
-
0.6
0.5
0.4
0.3
{£0.2
w o.i
0.002 0.006 0.010 0.014
MOLE FRACTION S02
IN WATER -
The equilibrium concentrations are an
important operating limit for the wet
scrubber systems. This slide shows one
equilibrium relationship for sulfur
dioxide in water at 50°C.
The units used in the graph are "mole
fraction". This is simply a ratio of
the number of molecules of the pollu-
tant versus the number of molecules of
the liquid. A 0.1 mole fraction S02
concentration is equivalent to 100,000
ppm (or .1% by volume). A useful
source for this data is the vapor pres-
sures of the pollutant over.the
specific liquid of interest.
256
-------
SLIDE 8-8
06
0.5
S 04
W2 0.3
§80.2
O.I
50'C
This is a repeat of the graph shown
above. The equilibrium lines for 30°C
and 70°C have been added to illustrate
the strong temperture dependence of the
equilibrium concentrations. Gases are
much more soluble in cold liquids than
in hot liquids.
0.002 0.006 0.010 0.014
MOLE FRACTION S02
IN WATER
SLIDE 8-9
MOLE FRACTION A, IN WATER
Pollutants, which release large quanti-
ties of energy when dissolved, can have
curved equilibrium lines. The graph
shown earlier illustrates the strong
effect that temperature has on the
equilibrium levels. At high tempera-
tures, gases are less soluble. When
energy is released to the solution the
temperature increases and the equili-
brium levels decrease. This result is
the curved line shown in this graph.
This type of curve can occur whenever
gases such as HF and HCL result in a
temperature gradiant across the scrub-
ber. A portion of the unit^ may have
very low rates of mass transfer under
these conditions.
257
-------
SLIDE 8-10
In some cases involving air pollution
control systems, the pollutant con-
5 H-.^!-. centrations are sufficiently low that
Q Q the equilibrium data can be adequately
represented by Henry's Law. This is
shown in the adjacent slide.
It simply states that there is a
straight line relationship between the
gas stream and liquid stream concentra-
tions of the specific compound. The
slope of the equilibrium relationship
is the Henry's Law Constant. In these
cases, the equilibrium can be obtained
from standard references.
Henry's Law is not followed whenever the molecule dissociates upon enter-
ing the liquid solution. Pollutants which dissociate include hydrochloric
acid and hydrofluoric acid. For all molecules which do react once dissolved,
the equilibrium relationship is normally curved, and it can only be obtained
empirically.
SLIDE 8-11
The primary objective of the last
FACTORS WHICH SHIFT THE several slides has been to demonstrate
EQUILIBRIUM CURVE that the equilibrium relationship in a
wet scrubber can change. Any of the
1. CHANGE IN GAS TEMPERATURE factors listed on this slide can cause
2. HEAT RELEASE DURING ABSORBTION h±f t ± th values
3. CHEMICAL REACTIONS IN LIQUID 3 Stlirt 1J1 tneS6 values •
The performance of an absorber is de-
pendent on the operating temperature
and the chemical reactions in the
liquid stream. High concentrations of
pollutants with high heats of dissolu-
tion can also cause an adverse shift in
the equilibrium line.
Due to the number of variables which affect the equilibrium conditions,
there is no one set of charts which can be universally applied to the wet
scrubber systems.
253
-------
SLIDE 8-12
!b •to!* in = lb mole out
G.(in) T U.(in)» G.(out) + L».(out)
The importance of the liquid to ga<
ratio is illustrated in the next
several set of slides. This slide
begins with a material balance aroi
the total system. The equation be]
the scrubber sketch states that wha
goes in also comes out!
The second equation is a material b
ance for the pollutant material. S
the concentrations of pollutants ar
small relative to the gas and liqui
streams, this equation reduces to t
third equation shown.
=(X,-X,)
SLIDE 8-13
<
o
u
EQUILIBRIUM
•LINE
The third equation shown in the slid
above defines a line with the slope
equal to the liquid-to-gas ratio.
Point number one is determined by th(
concentration of the pollutant in the
inlet gas stream and the outlet liquc
stream.
Point number two is determined by the
concentration of the pollutant going
the stack and by the inlet liquor
stream.
The straight line between these two
points is the operating line. This
defines the liquor and gas stream
concentrations of the pollutant at an;
point in the scrubber.
The difference between the equilibrium line and the operating line is t\
driving force for diffusion. The rate of mass transfer is proportional to
this driving force.
MOLE FRACTION IN LIQUID -
259
-------
SLIPS 8-14
OPERATING UNES-
EDUILIBRIUM
INE
As the liquid-to-gas ratio is
increased, the concentration of the
pollutant material in the effluent
stream decreases. Line number two has
a liquid-to-gas ratio which is approx-
imately twice that of line one. The
effluent liquid concentration is much
lower with higher liquid-to-gas ratios.
MOLE FRACTION IN LIQUID -
SLIDE 8-15
-------
SLIDE 8-16
ABSORBER OPERATING VARIABLES
1. INLET GAS TEMPERATURE
2. INLET LIQUOR TEMPERATURE
3. LIQUOR FLOW RATE
4. LIQUOR TO GAS RATIO
5. INLET POLLUTANT CONCENTRATION
6. ABSORBENT CONCENTRATION
7. pH
Some of the major absorber operating
parameters used during the inspection
are listed in this slide.
The inlet gas temperature and the inlet
liquor temperature are important since
they will largely determine the opera-
ting temperature of the absorber. High
temperatures adversely affect the total
performance.
The characteristics of the inlet liquor
stream, are -important since they define
the minimum stack concentration of the
pollutant. Factors such as the liquor
pH and the hypochlorite concentration
are important.
The liquid-to-gas ratio is important since it is a major factor in
determing the rate of absorption. It also can affect the degree of liquor-gas
maldistribution.
SLIDE 8-17
HCI SOURCES
1. High Concentration
Effluent from
Chlorination Reactors
2. Low Concentration
Effluent from
Waste Incinerators
The principal sources of HCI include
organic chlorination reactors and
chlorinated waste incinerators. These
two sources differ with respect to the
concentration of the HCI vapor in the
gas stream and with respect to the ef-
fluent gas stream temperature. The
control system designs must be different
to adquately handle these two different
situations.
In the high HCI concentration applica-
tions, recovery of the HCI as a 30 to
38% weight percent solution is econ-
omically possible. In the low concen-
tration applications, there*is too
little acid to justify recovery.
The heat of absorption must be taken into account for the high concentra-
tion HCI sources. It releases approximately 800 BTUs per pound of HCI upon
absorption. As discussed earlier, this heat release to the solution has an
adverse impact on the equilibrium concentrations.
261
-------
SLIDE 8-18
07»
051
026
0
m
LJL
3o22242628S032S4 36 WT %
. , J 1 u—b—
ooos 0.001 OKS 0130 aiss ais2 0210 MCX.E
The equilibrium curves for HC1 in water
at several temperatures are shown in
this slide. The right side of the
graph shows the relationship at high
concentrations of acid in water. The
left side of the graph is an extra-
polation to the origin. This was done
to illustrate a Henry's Law type rela-
tionships at low HC1 concentrations.
The strong effect of temperature is
evident in the equilibrium data.
Anything which increases the gas
temperature will lead to reduced HC1
removal.
SLIDE 8-19
A typical control system of a high con-
centration HC1 scrubber is shown here.
It consists of three ejector venturi
scrubbers in series with a tail end
packed tower scrubber.
Absorption water is brought to the last
stage and moves forward through the
system to the first stage. The heat of
absorption is removed in the first two
stages. The last ejector venturi and
the packed tower operate at cold
temperatures to maximize absorption.
There is also a heat exchanger on the
liquid stream inlet to the first
scrubber to minimize the operating
temperature in the first 'stage.
Due to the counter-current arrangement of the liquid and gas streams, the
HC1 concentration in the gas stream leaving the last ejector venturi is rela-
tively low. Nevertheless, this would not satisfy most regulatory limitations.
The packed tower is necessary as a polishing scrubber. This scrubber has rel-
atively clean liquor at the inlet so that the stack levels of HCL can be min-
imized.
262
-------
SLIDE 8-20
HCI SCRUBBER INSPECTION DATA
1. PACKED TOWER LIQUOR pH
2. PACKED TOWER PRESSURE DROP
3. PACKED TOWER LIQUOR FLOW RATE
4. PACKED TOWER OUTLET GAS
TEMPERATURE
5. PACKED TOWER DEMISTER
PRESSURE DROP
6. PACKED TOWER LIQUOR TURBIDITY
7. EJECTOR SCRUBBER STATIC
PRESSURE RISES
8. EJECTOR SCRUBBER OUTLET GAS
TEMPERATURES
9. EJECTOR SCRUBBER INLET LIQUOR
PRESSURES
The important inspection points for the
system shown in the last slide are
listed here. The pH of the inlet
liquor to the packed tower scrubber is
of interest since this determines the
minimum achievable outlet concentration
of HCI. The pH should be relatively
high, with normal conditions being in
the 7 to 10 range. The temperature of
this stream should also be kept to a
minimum. The outlet gas temperature is
the best indicator of an increase in
the operating temperature of the
scrubber. Increases from baseline
levels suggest reduced removal
efficiency.
The liquor recirculation rate to the packed tower scrubber is important
since this partially determines the rate of absorption. This is rarely mon-
itored directly. Indirect indications of flow include the pump discharge
pressure and packed tower scrubber inlet line pressure.
The packed tower scrubber can be overwhelmed by HCI if the ejector scrub-
bers do not perform properly. The data which should be obtained is the static
pressure rise across each ejector and the gas stream temperatures after each
ejector scrubber. Reduced liquor flow rates can be identified by increases in
the gas stream temperatures.
SLIDE 8-21
CAUSES OF REENTRAINMENT
1. PARTIAL PLUGGAGE OF
DEMISTER
2. EXCESSIVE GAS VELOCITY
3. INADEQUATE DEMISTER
CLEANING
Reentrainment from the packed tower is
especially objectionable due to the
potentially corrosive nature of the
effluent liquor. The most common
types of demisters are chevrons and
mesh pads.
Any reentrainment which does occur is
probably due to partial pluggage of
the demister. Excessive design vel-
ocities are rare, due to the inherently
low gas velocities necessary for the
packed bed. ~ —
263
-------
SLIDE 8-22
Low gas velocities through the scrub-
ber system can result from a number of
quite different problems. These are
indicated on the modified sketch to the
left.
Anything which reduces the liquid pres-
sure at the ejector nozzle will reduce
the gas flow rate. The operating con-
dition of the recirculation pumps
should be checked if the discharge
pressures are low or if the static
pressure increase across any of the
ejector units is lower than the base-
line levels.
Problems with the ejector scrubber nozzle can also reduce the gas flow
rate. These high pressure nozzles are especially prone to pluggage and
erosion. Obviously, the liquor quality is important in preserving these
vulnerable nozzles.
COOLER/
ABSORBER
GAS OUTLET
ABSORPTION
WATER
PACK ED TOWER
WEAK AGIO
SLIDE 8-23
This is a second type of high HC1 con-
centration scrubber system. Absorption
of HC1 takes place on the inside tube
surfaces of a vertical heat exchanger
with graphite tubes. The absorbing
water (with acid) flows downward as a
film along with the gas. This is a
co-current flow arrangement.
The heat of absorption is removed as
quickly as it is released, thereby
maintaining the equilibrium vapor
pressure of HC1 as low as possible.
This system yields high strength acid
(38% or greater), but the removal of HCL
is incomplete in the cooler/absorber.
This is due to the inherent- limitations
of a co-current scrubber.
To meet emission requirements, a packed bed tail gas scrubber is often
used. The inlet liquor to this scrubber is relatively clean so that the stack
concentration can be low. Automatic control of the entire system can be based
on either the packed bed exit liquor temperature or the cooler/absorber exit
liquor acid strength.
PUMP
STRONG
HYDROCHLORIC.
ACIO
264
-------
SLIDE 8-24
INSPECTION POINTS FOR
FALLING FILM ABSORBERS
PACKED TOWER
1. Exit Gas Temperature
2. Exit Liquor Temperature
3. Inlet Liquor Temperature
4. Inlet Liquor pH
5. Inlet Liquor HC1 Content
COOLER/ABSORBER
1. Static Pressure Drop
2. Cooling Water Temperature
3. Product Acid Rate
4. Product Acid Strength
The inspection points for the falling
film absorption system are very similar
to those for the ejector-packed bed
scrubber system discussed earlier.
These are listed on the adjacent slide.
All of these parameters are related
directly to the equilibrium concen-
tations or to the rate of absorption in
the scrubber system.
Note that there must be a fan with this
system. Changes in the gas flow rate
can be identified by the evaluation of
the fan motor currents and the fan
inlet gas temperatures.
The liquor flow rate to both the packed tower and the cooler/absorber are
approximately the same since the exit liquor from the packed tower flows to
the top of the cooler/absorber. While there may not be a flow monitor on this
line, it is possible to approximate the liquor flow rate from the flow of the
strong hydrochloric acid. It is necessary to account for the quantity of HCL
absorbed and the quantity of cooling water added near the bottom of the
cooler/absorber.
As with any scrubber, it is also necessary to check for apparent air
infiltration due to problems with the scrubber shells or the ductwork. Also,
the presence of reentrainment from the packed tower stack should be noted.
SLIDE 8-25
WOKCU.ATION
PUMP
•CCmCULATIOH
IUUC
This is an example of a low HC1 con-
centration wet scrubber system. It
is used on sources such as waste
incinerators where the concentration of
HC1 is less than 1000 ppm and the gas
stream temperature is very high.
The evaporative cooler ahead of the
scrubber is necessary to drop the gas
temperature down to a range in which
absorption is possible. HCJ. is removed
in a venturi scrubber which also' serves
as a particulate removal device.
The pressure drop across the venturi throat is governed more by the
particulate removal requirements than by the HC1 removal requirements. The
control of HC1 is primarily dependent on the pH of the liquor. It is main-
tained at alkaline levels by the addition of caustic (normally 5 to 10% by
weight). It takes 1.1 pounds of caustic for each pound of HC1 absorbed.
265
-------
SLIDE 8-26
F = C x V2 x (L/G)
P = Static Pressure Drop
C = Constant
V m Gas Velocity in Throat
L " Liquid Flow Rate
G = Gas Flow Rate
The equation shown here is the formula
which approximates the static pressure
drop in venturi scrubbers (presented
earlier in Lecture #7). It is possible
to achieve the same pressure drop at
numerous combinations of gas stream
velocities and liquid-to-gas ratios.
With a scrubber intended for both gas
and particulate removal, the correct
combination of gas velocities and
liquid-to-gas ratios are necessary.
The pressure drop is not a reliable
indicator of the performance of the unit
with respect to HC1 removal.
For this reason, the liquid flow rate should be obtained from plant
gauges or estimated from pump performance data. The temperature of the
recirculation liquor should also be determined. This can be measured directly
at the recirculation tank or measured indirectly using the skin temperatures of
the piping leading to the scrubber inlet.
VtMTUHI SOtUME*
WITH CYCLONIC
SLIDE 8-27
The pH of the liquor leaving the scrub-
ber sump should be determined. In this
co-current type of flow arrangement, it
is this value which determines the mini-
mum concentration of HCL which can exist
in the stack (due to equilibrium
considerations)
This pH also is important with regard
to the rate of corrosion of the scrub-
ber vessel. As discussed in Lecture
#5, the rate of corrosion is governed
by both the pH and the chloride con-
tent. At the high chloride levels
which are inherently involved in HC1
scrubbers, the pH must be relatively
high at all points in the system.
The scrubber sample should not be taken at the pump discharge since at
this point the recirculation liquor has been neutralized by the caustic added
to the recirculation system.
266
-------
SLIDE 8-28
Ejector-Venturi
Scrubbers
NoOH Solution
Clz Gas
Inlet
Solution
—Packed Tower
Spent Scrubbing
Solution
A chlorine absorption system appropri-
ate for control of emergency spills and
appropriate for small continuous sources
is shown in this slide. It consists of
an initial ejector venturi followed by
another ejector venturi and a packed
bed combination scrubber. The ejectors
are-generally used since they are ideal
scrubbers for applications requiring
high liquid-to-gas conditions and there
is no need for a separate fan to move
the gas stream.
In the first ejector venturi, there is
some liquid temperature rise due to the
heat of absorption which is over 600
BTUs per pound of chlorine'.
The solubility of chlorine in water is very small. Therefore, it is
necessary to use caustic to react with any dissolved chlorine to yield the
hypochlorite ion as indicated in the reaction shown below:
Cl +2 NaOH
NaCl + NaOCl + H 0
A once through liquor flow system is generally used due to the small
scale of the equipment.
SLIDE 8-29
INSPECTION POINTS FOR
SMALL CHLORINE SCRUBBER
1. Flow Rates of All Inlet
Liquor Streams
2. Gas Stream Exit
Temperature
3. Gas Flow Rate to
Scrubber
4. Static Pressure Rise
Across Ejector
5. Pump Discharge Pressure
and Motor Currents
The inspection of these scrubbers is
similar to that for any other gaseous
absorption system. The liquid-to-gas
ratio is important since this affects
the rate of absorption in all three of
the scrubber vessels arranged in series.
The gas flow rate and the capture of
the chlorine at the site of release are
obviously important. This is evaluated
by checking the static pressure rise
across the ejector Venturis. If this
appears low, the ejector nozzle pressure
or the pump discharge pressure should be
checked.
Since these are once-through flow systems, the quality of the liquor
coming into the last stage (the packed tower scrubber) is not usually a
problem. The pH of the inlet NaOH solution should be sufficiently high to
ensure very high efficiency chlorine removal. The temperature of the exit gas
stream should be measured to indicate any conditions which have increased
temperature and thereby reduced chlorine absorption.
267
-------
SLIDE 8-30
GAS OUTLET
GAS
IN_ETS -
DETECTOR
EJECTOfi-VENTUR;
DEMISTER
STORAGE
AND
RECIRCU-
LATION
TANK
This scrubber system is often used in
water treatment and sewage treatment
plants for the control of large
releases of chlorine.
The large NaOH storage and recircula-
tion tank contains sufficient caustic
(5 to 10 weight percent solution) to
neutralize one ton of chlorine. In the
event of a spill, a chlorine detector
activates a remote alarm system and
starts the scrubber recirculation pump.
At the same time, all openings and vents
in the room where the spill occurred
are closed. The ejector venturi draws
in the gas, neutralizes the chlorine,
and returns the scrubbed gas to the
room.
A single stage system is adequate because the efficiency per pass is not
an important consideration where there is no escape of gas to the surroundings.
A typical system will neutralize the chlorine to a 1 ppm.level in a matter of
hours.
The wet chlorine environments are highly corrosive. The common materials
of construction include titanium, PVC and special FRP fabrications. The in-
tegrity of the ductwork and scrubber vessel should be checked during all
inspections.
SLIDE 8-31
RECIRCULATION
PUMP
It is unusual to find these scrubbers
operating during any routinely sched-
uled inspection. Therefore, the in-
spection must be limited to an eval-
uation of the "capability to comply"
rather than the operating conditions.
The level detector on the caustic
storage and recirculation tank should
indicate a normal level of caustic.
The plant records should be checked to
confirm that there is, in fact, caustic
in the tank. The recirculation pump
and piping shoul'd appear ~tv be in good
working order.
The system should be checked on a routine basis to ensure that the
chlorine detector and the recirculation pump are operational. The ductwork
should also be in good condition.
EMERGENCY RELEASE CHLORINE SCRUBBEF
INSPECTION OBSERVATIONS
1. LEVEL OF CAUSTIC IN
RECIRCULATION TANK
2. SYSTEM COMPONENTS SHOULD
APPEAR IN GOOD CONDITION
3. RECORDS SHOULD INDICATE
THAT DETECTOR IS CHECKED
ON A REGULAR BASIS
268
-------
SLIDE 8-32
The principal sources of fluorine emis-
sions are the phosphate fertilizer
industry and the primary aluminum
industry. The specific sources in
these industries emit both gases and
particulate matter which must be remov-
ed by the control system.
To avoid contamination of natural
waters, fluoride systems usually
involve recycle streams from a pond.
The high flouride levels can present an
equilibrium problem under extreme con-
ditions and the quality of the recycle
liquor can adversely affect pumps,
nozzles and scrubber vessels.
The stringent regulatory requirements for fluorides means that it often
necessary to have several scrubber units is series to achieve the necessary
outlet gas stream concentration. As the system grows in complexity, the
static pressure drop requirements can become large.
FLUORIDE CONTROL SYSTEMS
1. Gas Streams Often Contain
Both Gases and Particulate
Forms of Fluoride
2. Liquor is Often High in
Fluoride Concentration and
in Suspended Solids Levels
3. Liquor is Highly Corrosive
4. Control Requirements are
Stringent
SLIDE 8-33
g 10
f
«
120 140 ICO 110 200
SATURATED GAS TEMP *F
FLUORINE SCRUBBING
HITH
HYOROFLUOSILIC ACID
M as
The problem with high fluoride content
recycle liquor streams is illustrated
in this graph. The lower line repre-
sents the conditions during a baseline
period when the liquor temperature is
low. An increase in the liquor temp-
erature alters the equilibrium concen-
trations as shown in the higher line.
With fluoride scrubbers, it is important
to maintain proper operating tempera-
tures to prevent low efficienty due to
equilibrium conditions.
ILIC A
zSlFe
269
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SLIDE 8-34
DESIGN PARAMETERS FOR
FLUORIDE WET SCRUBBER
SYSTEMS
1. Saturated Gas Temperature
2. Temperature of Scrubbing
Liquor
3. Fluoride Concentration of
Recycle Liquor
4. Inlet Fluoride Concentration
and Physical Form
5. Allowable Fluoride Emissions
6. Scrubber Effectiveness
7. Demister Effectiveness
The design parameters for all types of
fluoride scrubbers are listed in this
slide. They become the inspection
points for operating units.
This list starts with the saturated gas
temperature for the reasons discussed
in the previous slide. All of the
other parameters are similar to those
discussed with respect to other types
of gas absorbers.
SLIDE 8-35
One type of scrubber used for the
control of fluorides from wet process
phosphoric acid plants is shown here.
Due to the simultaneous presence of
gases and particulate, there are a
combination of control techniques
within a single scrubber vessel.
The initial device is a venturi throat
which is irrigated from a set of deluge
nozzles above the converging section.
The venturi is used for particulate
removal. The next stage is a large
cross flow packed bed for gas absorp-
tion. This is irrigated by front
sprays, a distributor at the top, and
the carry-over spray from the venturi.
All of this liquor- drains' -into the pond
water sump.
A mist eliminator is used to prevent the transfer of the high fluorides
liquor into the fresh water system downstream. A partition is used to keep
the two .liquor supplies separate. Within the fresh water portion of the
scrubber, the absorption is completed using a liquor with low fluoride content
and low liquor temperature. This fresh water section of the scrubber vessel,
in a sense, serves as a separate "tail gas" scrubber.
270
-------
SLIDE 8-36
FLUORIDE SCRUBBER INSPECTION DATA
1. VENTURI THROAT PRESSURE DROP
2. VENTURI THROAT LIQUOR FLOW RATE
3. CONTACT BED LIQUOR FLOW RATE
4. CONTACT BED LIQUOR TEMPERATURE
5. CONTACT BED LIQUOR TURBIDITY
6. CONTACT BED LIQUOR pH
7. POND WATER SUMP LEVEL
8. IRRIGATED BED LIQUOR FLOW RATE
9. IRRIGATED BED PRESSURE DROP
10. IRRIGATED BED LIQUOR TEMPERATURE
11. IRRIGATED BED LIQUOR TURBIDITY
12. IRRIGATED BED LIQUOR pH
13. CUTLET GAS TEMPERATURE
Inspection points for the fluoride
scrubber shown in the previous slide
are listed here.
The pressure drop across the venturi
scrubber is important since this in-
dicates the degree of particulate re-
moval in the venturi. Carry-over of
particulate into the contact bed could
lead to partial pluggage and channel-
ing. The total liquid flow in streams
5 and 8 are related to the absorption
rate in the scrubber. The fluoride
content of this liquor is important.
The temperature and fluoride content of the fresh water supply is import-
ant in determining the minimum fluoride concentration that can be present in
the effluent gas stream. The outlet gas temperature also indicates the pre-
vailing absorption temperature. The flow rate of stream 2 has a direct impact
on the rate of absorption in the fresh water section of the scrubber.
SLIDE 8-37
FACTORS WHICH CONTRIBUTE
TO MIXING OF POND AND
FRESH LIQUOR SUPPLIES
1. SUMP PARTITION CORROSION
2 DEMISTER REENTRAINMENT
* LEVEL CONTROLLER FAILURE
Anything which allows mixing of the
pond water sump liquor and the fresh
water sump liquor will reduce the
collection efficiency of the scrubber
system. The increase in the fluoride
content will reduce the absorption of
fluoride in the last stage.
This mixing of the two liquors can
occur due to failure of the demister
between the two compartments, due to
failure of the liquid level control-
lers, or due to failure of the part-
ition between the two sumps.
Due to the high fluoride levels often existing in the pond recycle'
liquor, it is necessary to neutralize with lime. If the pH becomes too high,
some precipitation of calcium fluoride can occur in the contact bed and other
portions of the scrubber system. This can have a very adverse effect on the
contact bed and the first mist eliminator. For this reason, the pH of the
liquor in line 1 (a portion of which becomes streams 5 and 8) should be
checked during the inspection.
271
-------
SLIDE 8-38
CORROSION IS A PROBLEM
FOR FLUORIDE SCRUBBERS
Due to the severely corrosive nature of
wet fluoride environments, the integrity
of the materials of construction in the
entire scrubber system should be visual-
ly checked. Areas of possible corrosion
and air infiltration include the hoods,
ductwork, fans, and pumps. The scrubber
vessel is normally constructed of
fluoride resistant materials.
Air infiltration into the scrubber
system will obviously increase the
quantity of untreated gas released to
the atmosphere.
SLIDE 8-39
In the production of ROP Triple Super-
phosphate, there are several sources of
silicon tetrafluoride. High concentra-
tions of SiF4 are evolved from .the
Acid/Rock Mixer, the Curing Den and the
Cutter. These sources are often vented
to a scrubber system similar to that
shown in this slide. The principal
purpose of the first two scrubber
vessels is the concentration and
recovery of the SiF4. The last scrub-
ber stage is necessary for compliance
with environmental requirements.
The first stage of absorption is done
with 16 to 20% by weight acid while the
second is done with 2 to 5% by weight
acid. The performance of both of these
are of interest to the inspector only
because problems..here could_ overload the
tail gas scrubber.
Recycled pond water is used for the final gas stream cleaning, since this
has minimum fluoride levels and minimum temperatures. The unit illustrated
here is a cyclonic spray tower scrubber.
272
-------
SLIDE 8-40
Common inspection points for the tail
gas scrubber shown in the previous
slide include those listed here. The
quality of the pond water is of central
importance. The fluoride levels should
be as low as possible and the liquor
should be in the range of 7 to 10 pH.
The recycle liquor flow rate affects
the removal efficiency of the scrubber.
This flow rate should be obtained from
on-site monitors or estimated from
recirculation pump operating
conditions.
v
The operating condition of the fan is important since this governs the
gas flow rate from the various SiF4 sources. This fan is vulnerable to
fluoride attack and carry-over liquor droplets from the second stage scrubber.
Fi_JORIDE SCRUBBER INSPECTION DATA
1. LIQUOR pH
2. RECIRCULATION LIQUOR
FLOW RATE
3. FAN OPERATING CONDITIONS
4. STATIC PRESSURE DROP
5. OUTLET GAS TEMPERATURE
6. INLET GAS TEMPERATURE
7. INLET LIQUOR TEMPERATURE
SLIDE 8-41
STOHASE
BU1UI1W
SiF4 continues to evolve in the curing
pile. These emissions are collected in
a building evacuation system and treat-
ed in a simple tail gas scrubber. The
concentration is too low to economi-
cally recover the material. The type
of scrubber illustrated here is a
cyclonic spray tower similar to the one
discussed in the previous two slides.
The inspection of this unit again em-
phasizes the recycle liquor quality and
flow rate. Corrosion and reentrain-
ment problems should also be evaluated.
273
-------
SLIDE 8-42 These are the primary -problems which
must be addressed in the design and
operation of odor scrubbers.
Like many fluorine scrubbers, the ef-
fluent gas often containds both parti-
culate matter and and vapors. Systems
must have a combination of scrubbing
techniques to handle both types of
pollutants.
Very high removal efficiencies are
necessary since odors can be detected
by some individuals at very low concen-
trations. Scrubbers having an inlet
concentration of 100,000 odor units
often must reduce this to less than a
100 odor units in the effluent.
Unlike the previous scrubber systems, there is more than one compound
which must be removed. In fact, it is highly probable that sources such as
food product driers and rendering plants have 10 to 25 major components in the
gas stream. The composition is rarely known. The various compounds all have
different solubilities and this complicates the use of the equilibrium rela-
tionships discussed earlier.
CHARACTERISTICS OF ODOR
CONTROL WET SCRUBBERS
1. Both Paritculate and
Vapors Must be
Removed.
2. Very Highly Removal
Efficiency of Vapors
Necessary
3. Numerous Compounds
of Varying Solubilities
Present
COMMON ABSORBERS FOR
ODOR SCRUBBER
1. HYPOCHLORITE
2. POTASSIUM PERMANGANATE
SLIDE 8-43 These are the most common absorbents
used in odor scrubbers. The concen-
trations of the solutions generally
vary between 0.5% to 5.0% by weight.
The removal efficiency is not as highly
dependent on the oxidant concentration
as might be expected. Most field tests
indicate that there is a certain
minimum concentration necessary to
react with the odorous compounds.
Higher concentrations of oxidant yield
only slightly additional odor removal.
The effectiveness of each of the com-
pounds varies for different chemical
species. However, there is very little
test data to aid in the selection of
the most effective oxidant for the com-
pounds identified in the gas stream.
The oxidant is selected based on vendor
experience in similar sources.
There are certain odor causing materials which are essentially unreactive
with these common oxidizing agents. The absorption of these unreactive mat-
erials (often termed "refractory" chemicals) is a function of the equilibrium
concentrations and the effectiveness of the scrubber. Unfortunately, in some
units the equilibrium concentrations can be quickly reached, thus limiting the
performance of the system.
274
-------
SLIDE 8-44
pH SHOULD BE
HIGHER THAN 10
HOC1
:OC1
In the case of hypochlorite scrubbers,
optimum odor reduction occurs when the
pH is above 10. Under these conditions
the chemical equilibrium shown in this
slide shifts to primarily hypochlorite
ion (OC1 ). This is the species which
reacts with the absorbed pollutant
compounds. The hypochlorous acid is
unreactive. The pH is adjusted using a
caustic solution
SLIDE 8-45
OPTIMUM pH FOR
PERMANGANATE SCRUBBERS
8 - 10
For permanganate scrubbers, the optimum
liquor pH is between 8 and 10. In this
range, the hydroxyl ion-(OH ) aids in
the chemical attack of some absorbed
pollutants.
275
-------
276
-------
SLIDE 8-46
iNSPECITON POINTS
FOR
ODOR SCRUBBERS
1, Liquor pH
2. Liquor Oxidant
Concentration
3. Liquor Flow Rate
4. Liquor Inlet
Temperature
5. Gas Exit Temperature
6. Venturi Pressure Drop
7. Packed Bed Pressure Drop
8. Condition of Scrubber
Shell, Fan and Ducts
9. Presence of Retrainment
10. Gas Flow Rate
These are the inspection points for
odor scrubbers. The liquor oxidant
concentration and pH are two of the
most important variables. The oxidant
concentration can not be measured
during the inspection. The on-site
conductivity monitor or oxidation-
reduction monitor is used to determine
if there has been a shift in the oxi-
dant concentration.
As with all. absorbers, the operating
temperature and the liquid-to-gas ratio
are important. The gas temperature
leaving the scrubber provides a good
indication of the operating
temperature. The flow rate can be
evaluated based on the recirculation
pump discharge pressure and motor
current.
The static pressure drop across the venturi provides a good indication of
the particulate removal effectiveness. The static pressure drop across the
packed tower is useful for identifying plugging problems within the bed.
The gas flow rate can be measured at the scrubber outlet using a pitot
tube or estimated from the fan operating parameters. The fan rotational
speed, inlet gas temperature and motor currents are necessary when evaluating
gas flow rate changes.
The condition of the scrubber vessel shell, the ductwork and fans should
be visually evaluated during the inspection. Any air infiltration can reduce
the quantity of odorous gas pulled from the process equipment. The stack area
should be checked for possible reentrainment from the packed tower stack.
This is especially objectionable in the case of odor scrubbers due 'to the
highly alkaline pH and the presence of the oxidant compounds.
277
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LECTURE 8 - REVIEW PROBLEMS AND QUESTIONS
8-1. The correct answer is "c", the mole fraction is 0.097. The molecular
weight of HCL is approximately 37.5. Therefore, 18 pounds is equivalent
to 0.4d pound moles. The molecular weight of water is 18. Therefore 80
pounds of water is equivalent to 4.44 pound moles. The mole fraction of
HCL is 0.48 divided by (0.48 + 4.44) or simply, 0.097.
8-2. Answers "a" and "c" are possible. At this pH, only a small fraction of
the hypochlorite ion exists in solution. Most of it is tied up as
hypochlorous acid. Since only a little hypochlorite ion is available to
react with dissolved pollutants, it is possible that some of these
pollutants are reaching the saturation concentration. After this is
reached, there will be no more net transfer of the pollutant to the
scrubber liquor. If the quantity of odorous material in the inlet gas
stream is small, there may be sufficient reactants to adquately remove
the odorous material. In this case, however, much of the hypochlorous
acid solution will be wasted in the purge stream of the scrubber.
8-3. Answers "a", "b" and "c" are all possible. There has probably been a
drop in the liquid-to-gas ratio of the scrubber. An increase in the
inlet fluoride concentration is possible, but less likely.
8-4. Gases are more soluble at cold temperatures. Therefore, the observed
increase in exit gas temperatures will have an adverse effect on the
fluoride removal efficiency.
278
-------
LECTURE 8 - REVIEW PROBLEMS AND QUESTIONS
8-1. What is the mole fraction of HC1 if there are 18 pounds of HC1 and 82
pounds of water? (0.095)
a. 18
b. 0.18
c. 0.097
d. 0.00457
e. It can not be determined from this data
8-2. An operator of a hypochlorite scrubber for a animal rendering plant is
not presently adding caustic to the solution. The pH measured in the
recirculation tank is 7.6. What statements could be true about the
system at the present time?
a. The unit is operating satisfactorily, but a large quantity of the
hypochlorite solution is being wasted.
b. Odor removal is not very effective since a pH in the range of 2 to 5
is necessary to initiate the oxidation reaction in the scrubber.
c. Some of the odorous materials are reaching equilibrium
concentrations in the recirculated liquor and are no longer being
removed effectively.
d. Plugging of the packed tower scrubber is probable under these
conditions.
e. All of the above
8-3. The effluent liquor concentration of fluoride ion has increased by 46%
since the baseline period. What does this possibly indicate?
a. The inlet concentration of HF has increased dramatically since
the baseline period.
b. The liquid flow rate to the scrubber has dropped significantly since
the baseline period.
c. The gas flow rate has increased substantially since the baseline
period..
d. Severe air infiltration is occurring near the top of the scrubber
vessel. ._
8-4. The exit gas temperature from a fluoride scrubber has increased 34 °F
since the baseline period. Will this increase or decrease the
fluoride removal efficiency?
a. Increase fluoride removal efficiency
b. Decrease fluoride removal efficiency
279
-------
LECTURE 8 - REVIEW PROBLEMS AND QUESTIONS
8-5. Answers "a", "c", "d", and "e" are all correct. In high concentration
sources of HC1 and HF, it is important to dissipate the heat of absorp-
tion in the first scrubber stage and then to complete the absorption in a
tail gas scrubber. This is also necessary when recovering high con-
centration HC1. A-particulate removal section is often used first to
prevent pluggage of the packed tower absorption sections. The concept
of transfer units was not discussed specifically.. This is related to
the required control efficiency.
8-6. Answers "b" and "c" are possible. The ambient air passing through the
unit will strip out fluoride compounds until the equilibrium concentra-
tion in the liquor is reached.
8-7. All of these favor absorption. Although not listed here, the liquid-to-
gas ratio is equally important.
8-8. There is no indication that the gas flow rate has increased. However,
the static pressure drop across the packed bed has increased substan-
tially. Answer "c" is very probable.
280
-------
LECTURE 8 - REVIEW PROBLEMS AND QUESTIONS
8-5. Why are several scrubbers often used in series on absorber systems?
a. To allow removal of the heat of absorption without adversely
affecting absorption efficiency.
b. To allow removal of corrosive gases before the gas stream
reaches the particulate removal section of the scrubber.
c. To allow for the concentration of a recoverable product
d. To allow removal of particulate before the gas stream reaches the
gas removal section of the scrubber.
e. To increase the number of Transfer Units of the scrubbing system.
8-6. What would happen to a fluoride scrubber using recycled pond water of
3% by weight fluorides, if the inlet duct coming to the scrubber were
handling only ambient air?
a. Absorption of fluorides would be high, due to the low gas
temperature.
b. A small quantity of fluorides would be stripped from solution.
c. The stack concentration of fluorides would be higher than the
inlet stream.
d. None of the above.
8-7. Which of the following conditions favor absorption
a. Turbulence
b. Time
c. Low temperature
d. High liquid surface areas
8-8. During an inspection of a packed tower absorber, it is noticed that the
pH has dropped from 10.6 to 10.4 The static pressure drop across the
bed has increased from 4 inches to 7 inches and the exit gas temperature
has remained relatively constant. The fan rotational speed is constant,
but the motor current is down slightly. What is probably occurring in
this unit. — . -—
a. The gas flow rate has decreased.
b. The gas flow rate has increased.
c. The bed is partially plugged.
281
-------
282
-------
LECTURE 9
INSPECTION SAFETY
SLIDE 9-1
POTENTIAL INSPECTION HEALTH
AND SAFETY HAZARDS
1. Inhalation of Toxic Gases
2. Inhalation of Toxic Particles
3. Inhalation of Asphyxiants
4. Burns on Hot Surfaces
5. Entrapment in Rotating Equipment
6. Falls off Ladders
7. Falls on Icy Surfaces
8. Falls from Weak Roofs and
Platforms
9. Electrical Shock
10. Static Electrical Shock
11. Eye Injuries
12. Noise
13. Cold Stress
14. Fan Disintegration
15. Steam Burns
16. Contact with Pathogenic
Organisms
17. Contact with Skin Absorbable
Chemicals
Inspection safety is the most important
topic in this workshop program. There
are a number of potential health and
safety hazards regardless of the level
of inspection. A partial list of the
types of hazards are provided in this
slide. The inspector must be constantly
alert so that these can be avoided.
The purpose of this lecture is to make
everyone involved in field activities
aware of the possible hazards near wet
scrubber systems. Most of these are
easily avoided as long as^ they are
recognized.
The information presented here is not
intended to replace or supersede any
safety guidelines adopted by the agency
of by the plant being inspected.
283
-------
SLIDE 9-2
There are a number of factors which make
FACTORS rnwTmmiTiMr- regulatory agency personnel potentially
™
TO PBLEMS *"*
1 . Lack of Familiarity with
Hazards at Specific Plant One of the most important of these is
2. Distractions Due to the lack of familiarity with the loc-
Conversations with Plant ations of the hazards at the specific
Personnel plant. It is easy to overlook trip
3. Attempts by Plant Personnel hazards such as valve stems and low
to Hurry Inspector support rods. High traffic
areas may be in the same general area as
the scrubber system. Also, some plants
have high voltage cables and tracks.
Even though these are marked, it is
possible for the unwary inspector to
contact the energized lines.
A contributing factor to the safety and health risk are the distractions
inherent in conducting an inspection. The field inspector spends much of the
time asking the plant representative questions about changes since the last
visit. Also, it is not uncommon for the inspector to have to patiently listen
to a long list of arguments and complaints from the plant personnel. Both
the routine questions and the occassional arguments distract the person con-
ducting the inspection.
An additional complicating factor is the tendency of a few plant repre-
sentatives to "hurry" the inspector through the plant. The combined effect of
a lack of familiarity and fairly rapid movement around the equipment creates
favorable conditions for a serious accident.
SLIDE 9-3
These are several other factors which
FACTORS CONTRIBUTING Can make a re§ulatory agency inspector
TO INSPECTION SAFETY PROBLEMS especially at risk.
1. Hypersensitivity to Specific Due to the large number of different
Pollutants facilities, it is possible for an
2. Lack of Acclimatization to inspector to encounter low levels of a
Specific Pollutants very iarge number of pollutants. There
3. Synergistic Interactions is a reasonable probability that an
inspector who is hypersensitive to a
certain chemical will encounter this
material at some time during his or her
career. ~
Unlike plant personnel, inspectors can rarely become acclimated to the
materials which are sometimes encountered when inspecting wet scrubber systems
and the associated process equipment. There is also the possibility for some
synergistic interactions between pollutants inhaled in different plants and
those retained in the lung. On plants with hot processes, it possible to have
very hot and/or humid conditions around the scrubber. The inspector rarely
spends the several days necessary to become acclimated to this heat stress.
284
-------
FACTORS CONTRIBUTING
TO INSPECTION SAFETY PROBLEMS
1. High Positive and Negative
Static Pressures
2. Wet Walking and Climbing
Surfaces
3. Icy Walking and Climbing
Surfaces
4. Fan Disintegration Due to
Solids Carry-over
5. Explosive Gases and
Paniculate in Gas Stream
SLIDE 9-4
The intrinsic nature of wet scrubber
systems makes them especially prone to
safety and health hazards!
They operate at higher pressure
extremes (both positive and negative)
than any other type of air pollution
control device. This means that the
potential for gas leakage out into the
breathing zone can be high.
Leaks of water or entrained water from
the stack can make all walking surfaces
around the equipment hazardous, espec-
ially in cold weather. There are a
number of sharp obstacles around the
scrubber that would make any fall
serious.
The wet and muddy conditions can also render fixed and portable ladders
dangerous to climb. The foot rungs can be either muddy or icy. It is often
difficult to secure portable ladders on the wet surfaces.
Wet scrubbers are often used on gas streams handling potentially explosive
dusts and gases. It is the only type of collector which can not inherently
ignite the mixture. However, the improper use of measurement probes and
power tools ahead of the scrubber systems can create explosive conditions.
Furthermore, there is potential for fan disintegration due to solids carry-over
from the scrubber vessel.
SLIDE 9-5 Due to the reasons presented in the
previous set of slides, it is important
that each agency have a routine safety
training program for all individuals
involved in wet scrubber system inspect-
ion (and all other field activities).
This should address recognition of the
problems and the agency policies
regarding proper safety procedures.
There should be a medical monitoring
program for all field personnel. This
involves an initial physical to confirm
that the individual is physically able
to conduct the inspection. This exam
then serves as the "baseline" for
evaluating the health of the inspector
in the future. This is important since
some problems take time to develop.
There should be written safety procedures which contain all of the agency
safety policies regarding personnel protective equipment and the performance of
inspections. They should include any specific safety requirements at the
plants to be inspected.
BASIC FEATURES OF AN
INSPECTION SAFETY PROGRAM
1. ROUTINE TRAINING
2. MEDICAL MONITORING
3. WRITTEN PROCEDURES
285
-------
SLIDE 9-6
PERSONNEL PROTECTION EQUIPMENT
USUALLY NECESSARY
1. Hard Hat
2. Gloves
3. Respirators
4. Safety Shoes
5. Hearing Protection
6. Eye Protection
The next set of slides presents the
general safety principles which should
be observed during the inspection of
any air pollution control system.
The inspector should bring all the
necessary personal protective equipment
and be throughly trained in the proper
use of the equipment. Sources have
often distributed respirators and
other protective equipment without
realizing that the individuals did not
know how to use them.
Hards hats are necessary primarily for
protection against head blows against
overhead obstacles. The safety shoes
provide a slip resistant sole
Respirators are necessary for the various inhalation hazards potentially
encountered at the specific plant. It should be remembered that each
respirator is effective only for a small number of specific pollutants.
The need for gloves should not be underestimated. These are necessary for
climbing ladders with rough foot rungs. Special gloves are also necesary when
handling liquors with skin absorbable components or with pathogenic organisms.
SLIDE 9-7
NON-SPECIFIC SYMPTOMS
OF EXPOSURE
1. Dizziness
2. Nausea
3. Lightheadedness
4. Drowsiness
5. Eye or Nose Irritation
6. Chest Pains
Whenever these non-specific symptoms are
felt, the inspection should be interrupt-
ed. The inspector should proceed to an
area with fresh air. The inspection
should not be resumed until the cause of
the ill feelings are identified. These
are the initial symptoms of exposure to
a large number of pollutants. Remaining
in the area can quickly lead to serious
health problems.
286
-------
SLIDE 9-8
BASIC SAFETY PRINCIPLES
Work at Controlled Pace
Do Not Place Absolute Trust
in Plant Personnel Regarding
Inspection Safety
The last two basic safety principles are
listed on this slide. The importance of
conducting the inspection at a control-
led pace can not be overemphasized. In
this way, the common walking and climbing
hazards can be avoided. There is also
less chance or becoming trapped in areas
with high pollutant concentrations.
Most field inspectors visit between 25
and 100 different facilities each year.
While most plant personnel are safety
conscious, it is inevitable that the
inspector will encounter a few plants
each year at which the personnel are
either not concerned or arfe not aware of
the potential problems. The inspector
must never fall into the bad habit of
abdicating judgment regarding inspection
safety to the plant personnel. Some-
times they fail to realize that the
inspector is not aware of potential
safety hazards.
SLIDE 9-9
The next set of slides concerns the
numerous walking and climbing hazards
which can exist in the vicinity of wet
scrubber systems.
Slippery areas are very common due to
leakage of water from pump seals,
rainout of scrubber liquor from the
stack, and the occassional overflow of
tanks. During cold weather periods
these wet areas freeze.
The large number of pipes and electrical
conduits provide a number of trip
hazards. _
Corrosion of the scrubber vessel walls and platform supports can make
elevated platforms dangerous. The ladder leading to and from the platform can
also present safety hazards.
287
-------
SLIDE 9-10
This photograph shows the area around a
centrifugal pump. The entire area is
covered with water and wet pulp fibers.
The water is due to the constant slight
leakage of pump seal water. The wet
pulp is due to an occassinonal overflow
of foam from the recirculation tank.
This makes the area around the pump very
slippery. A fall here could result in a
head injury on one of the footings shown
in the slide.
During the inspection there is a natural
tendency to look around or up at the
various system components. Inspectors
must be constantly aware of slip hazards
around pumps.
SLIDE 9-11
This slide is similar to the one above.
The only difference is that the wet area
has frozen. Obviously, care is neces-
sary when walking on the ice.
288
-------
SLIDE 9-12
This is a view of a railroad siding next
to a packed tower scrubber system. It
is apparent that there is some ice
approximately 15 feet ahead. What may
not be apparent is that there is another
patch of ice in the foreground. While
this area looks like dirt, it is
actually "black ice". It is simply
frozen water with a high suspended
solids content. This can form when the
ambient temperature is very low.
SLIDE 9-13
This is a view of a platform supporting
a small rod deck scrubber. A small
puddle of water has accumulated in a
depression and frozen.
It would be easy to overlook this patch
of ice since there are a number of
overhead obstacles (out of view of the
slide) which must be avoided while
walking around the scrubber. A fall
could result in a serious injury due to
the sharp objects in the general area.
During cold weather periods, it should be assumed t~hat almost"all elevated
platforms will have some frozen puddles or other slipper areas. Since some of
them do not have hand rails, it is particularly important to avoid these
slippery areas.
289
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SLIDE 9-U
This board has been placed on a snow
covered roof to improve the walking
surface from a flooded disc scrubber to
the access ladder (see in the upper
right hand corner of the photograph).
However, the board has become covered
with a thin layer of ice due to water
which has dripped off an adjacent roof
and refrozen. A fall on this plank
could result in a fall of 15 feet off
the roof. Note that the roof does not
have any railings to impede a fall.
SLIDE 9-15
This is a temporaty walkway over an
excavated area. These should be used
only when: (1) the ends are secured, (2)
the wood appears to be in good condi-
tion, and (3) there are hand rails.
Alternative routes are generally pre-
ferable to these temporary walkways.
Under no circumstances should inspectors
use single boards as planks between two
platforms, between two building roofs,
or over open tanks. The support beams
between two adjacent control systems or
around a single scrubber should never be
used for walking or climbing. Further-
more, ladders should not Tie" used, as
planks.
It is not unusual for the field inspector to be ridiculed by plant
personnel for refusing to walk across support beams or to use weak planks
between high platforms. Inspectors must develop the self discipline to ignore
this ridicule and to maintain safe inspection procedures at all time.
290
-------
SLIDE 9-16
This is a view of the settling pond for
a rod deck scrubber. It has a sloped
ground level entry to permit a front end
loader to occassionaly remove the solids
from the first two zones. The walking
area near the pond is very slippery.
The unwary inspector could easy end up
taking a swim in the pond. Due to the
heavy winter clothes and the sloped side
of the pond, this could result in a fatal
accident. Also, the liquid temperature
in the first zone can be as high as 140
°F and the pond can contain toxic sus-
pended solids.
While access to activated sludge ponds is usually restricted', these can be
especially dangerous. The specific gravity of the pond liquor can be so low
that swimming and floating is impossible.
The areas immediately around basins and ponds should be avoided by the
field inspector. Samples of the liquor should not be obtained at any location
where it is easy to fall into the pond.
SLIDE 9-17
There are many locations around wet
scrubber systems where steam clouds can
suddenly envelop localized areas. This
makes walking particularily hazardous.
This is a view of the same area shown in
the previous slide. It was taken 15
seconds after the previous slide. The
cloud is due to the contact of a cold
breeze across the warm pond liquor. The
inspector who fails to slow down as the
cloud passes could easily get too close
to the pond entry.
The inspector should not proceed until there is adequate visibility. Some
make the assumption that they are completely familar with the plant. This can
be a very bad assumption since plant personnel may have forgotten to replace a
grating, or have left some obstacle in the walking path. Many changes can
occur between inspections.
291
-------
SLIDE 9-iS
Several safety chechs should be made
before climbing up to the elevated
platforms around the wet scrubber
vessels or the stack sampling areas.
The supports should be visually inspec-
ted for obvious corrosion. Also, the
integrity of the ladder supports should
be observed. Rotted wooden plants or
gaps in the gratings should be checked.
The potential for entrapment in a
rising cloud of high temperature steam
or a toxic cloud of fugitive emissions
should be considered before going to the
platform. If there are intermittant
process operations which could create
these highly dangerous conditions, the
inspection should only be done when that
portion of the plant is not running.
Inspectors should never underestimate the potential problems resulting
from rising steam clouds and/or toxic clouds of pollutants. These can form
suddenly due to process upsets or intermittant process operations. It is
difficult to get off platforms when both visibility and breathing are impaired.
Respirators should be taken when going to elevated platforms.
SLIDE 9-19
There are some elevated surfaces which
may not be able to withstand any
additional load. An inspector who walks
across a roof, as shown in this slide,
may fall through. It is important to
stay within designated walking areas.
It is also prudent to walk behind the
plant personnel.
292
-------
SLIDE 9-20
This is a picture of the floor around a
packed bed wet scrubber. The entire
system is in a very dimly lit building.
While walking between the stockpiled
materials near the scrubber, it is easy
to miss the small raised portion of the
floor. The severity of the accident
depends on what is hit on the way down.
Whenever entering a building from the
outside, it is necessary to wait briefly
for the eyes to adjust to the low light
conditions. Many scrubbers are placed
in enclosed areas to protect piping from
freezing during winter off-line periods.
SLIDE 9-21
While walking around the scrubber sys-
tem, it is easy to become preoccupied
with inspection details. The valve stem
shown in this slide sticks out far into
the walkway at about the height of a
knee. It is very hard to see due to the
lack of light within the building (the
photograph was shot with 1000 speed film
and a 100 watt bulb approximately 2 feet
away). This is just one example of the
many trip hazards which can exist around
the wet scrubber system.
293
-------
SLIDE 9-22
This is a photograph of a small beam at
about head height which is close to an
access ladder. A painful and serious
injury could occur to those who fail to
wear a hard hat. It is surprising how
many plants do not require these hats.
It is also surprising how many overhead
beams, conduits, valve stems, pipes, and
other obstacles exist around a wet
scrubber system.
SLIDE 9-23
While walking around a wet scrubber sys-
tem it is easy to forget about rotating
equipment in the general area. This
slide shows a partially covered fan
sheave and drive belt. This was along a
very narrow path to a rod deck scrub-
ber. It is possible for loose clothing
to get caught between the rapidly moving
belt and sheave.
One way to minimize the risk of entrap-
• ment in rotating equipment is to avoid
wearing loose clothing. Ties should not
be worn during inspections.
The area immediately around the rotating equipment~should beTavoided to
the extent possible. If there is only one path to the control system and
there is a reasonalbe risk of entrapment even when caution is exercised, then
the inspection should not be done!
294
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SLIDE 9-2
This is a winch beside a narrow path to
the same system discussed in the last
slide. It is 4 feet above the walking
surface and the cable cuts over the path
that the inspector must take. The oper-
ation of the winch is controlled by
plant personnel who can not see the
scrubber from their work station. A
serious injury could occur if an inspec-
tor placed a hand on the winch while
trying to duck under the obstacles. It
should be assumed that equipment which
is designed to move will start suddenly!
SLIDE 9-25
Climbing ladders is a common part of wet
scrubber system inspections. There are
periods when these ladders can be very
treacherous.
This slide illustrates a common problem
with ladders around wet scrubber sys-
tems. The first person up the ladder
(normally the plant representative)
deposits a layer of mud or sludge on
the foot rungs. This makes the ladder
slippery
295
-------
SLIDE 9-26
**<
This slide illustrates one possible way to
a ladder. There is a temptation to hold
on to the side rails of the ladder to
avoid the mud or sludge shown on the
previous slide. However, it is easy for
a foot to slip off the foot rungs under
these conditions. With the hands on the
side rails, an inspector may not be able
to maintain a grasp on the ladder when
the foot slips.
The inspector in this slide is making
the mistake of trying to carry portable
instruments while climbing. These
significantly reduces the grip on the
ladder.
SLIDE 9-27
This slide illustrates another possible
way to climb a ladder. The hands are
placed on the foot rungs and the
inspector is wearing gloves which
improve his grip on the ladder. The
portable instruments are being carried
on a side pouch which does not impede
the climbing motion.
Any large instruments should be trans-
ported to the platform or roof by means
of a rope (with a bucket in some cases).
Obviously, it is important that nothing
falls during lifting and that the rope
is not used near power lines. The wind
speed should be Tow enough "to prevent
swinging of the rope.
296
-------
SLIDE 9-28
There should be at least 9 inches of
clearance between the foot rungs and any
obstacle behind l^he ladder. This is
necessary to ensure that the foot rests
securely and completely on the foot
rung. The person shown in this slide
should have been climbing by placing the
back of the heel against the foot rung.
While the large majority of ladders on
wet scrubbers have the necessary clear-
ance, occassionally there are pipes,
support beams or electrical conduits
placed too close to the ladder.
SLIDE 9-29
Repaired portable ladders such as shown
in this slide should not be used under
any circumstances. If it has been
necessary to fix one of the rungs, it is
possible that some of the other rungs
have also weakened.
All of the foot rungs should be inspec-
ted prior to use. The ladder should not
be used if any of the rungs appear to be
rotted or if a rung has separated from
the side rail.
297
-------
SLIDE 9-30
One of the basic requirements of a
portable ladder is that it be secure at
the bottom. It is often difficult to
find a location near wet scrubber sys-
tems "which is free of a coating of
sludge or mud.
This slide shown a portable ladder
sitting on a slippery layer of sludge
next to a rod deck scrubber. There is a
possibility that the ladder will slip at
the bottom as an inspector climbs this
ladd.-jr-.
In addition to locating a dry spot for the ladder, it is necessary to have
the right type of slip resistant protector on the bottom of the ladder. Two of
the most common slip protectors are spurs and pads.
SLIDE 9-31
This is the same ladder shown in the
previous slide. Another common problem
with the portable ladders involves weak
upper supports. Close examination of
the slide illustrates that the small
angle iron which is supporting this
ladder has be cut approximately 80% of
the way through. The load created on
this beam as the inspector climbs will
be enough to break the angle iron.
Ladders should not be resting on small
support beams, pipes or electrical con-
duit. These were not constructed to
withstand the 25 to 100 pounds of lat-
eral force which-can develop. Also the
ladder should not be placed against a
slippery wall.
The portable ladders should be inclined on an angle so that the ladder
will not tip over and so that the base will not slip out. As a general rule
the triangle defined by a sloped ladder should have a height which is 4 times
the base. The ladder should never be near high voltage power lines.
298
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SLIDE 9-32
CATEGORIES OF EYE HAZARDS
• Physical
• Chemical
• Thermal Radiation
• Other Radiation
Potential eye injuries which can occur
while inspecting wet scrubber systems
are listed on this slide. The most
common of these is chemical burn from
fumes or splashes. It is important to
wear eye protection while inspecting wet
scrubber systems.
SLIDE 9-33
This is a photograph of a valve on the
discharge line of a wet scrubber pump.
The liquor is under approximately 90
psig pressure and the pH is quite high.
If care is not taken in sampling the
liquor, it can splash into the unpro-
tected eye. This can result in a severe
burn and/or blindness. The valve must
be opened gradually and the receiving
container must not facilitate splashing.
The inspector should wear splash goggles
while this is being opened. Plant per-
sonnel should take a.ll liquor samples.
299
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SLIDE 9-34
$K
f \ *^^.
This slide shows three types of eye
protection in general use for wet
scrubber inspections. Most plants
require eye protection and inspectors
should be sure that theirs satisfies
plant requirements. It is suggested
that eye protection be used even if not
specifically required. At the very
least, it will prevent the introduction
of chemicals and foreign materials into
the eye by careless rubbing.
SLIDE 9-35
ON INDUSTRIAL JOBS . . .
DONT
WEAR CONTACT LENSES
It is recommended that field inspectors
avoid wearing contact lenses unless
these are specifically allowed by plant
and agency safety personnel. It is
conceivable that hard contacts can
increase the damage done to the eye by a
foreigh body which gets trapped behind
the lense. Soft contact lenses, parti-
cularily the gas permeable ones, may
make the eye more susceptible to
chemical damage.
Lecturer's Notes
, There are differing opinions regarding the potential advantages and dis-
advantages of contact lenses during work in industrial facilities. Until this
is settled satisfactorily, it is prudent to avoid the contact lenses. These
are also not allowed during the use of any full face mask respirator.
300
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SLIDE 9-36
HEARING PROTECTION
USE WHENEVER IT IS DIFFICULT
TO HEAR SOMEONE TALKING FROM
2 - 3 FEET AWAY.
USE WHENEVER REQUIRED BY PLANT
POLICIES.
USE WHENEVER IN THE VICINITY
OF IMPACT NOISE.
Noise exposure related hearing loss is
not a common problem in the inspection
of wet scrubbers. The most probable
sources of noise are the process equip-
ment served by the scrubber system. The
only significant source of noise on the
scrubber system is the fan. Units which
are operating a high tip speeds can have
an appreciable noise level.
The best way to minimize noise related
problems is to minimize the amount of
time spent in the proximity to the
noise source. Hearing protection should
also be used whenever it is difficult to
understand someone talking'in a normal
tone of voice from more than 2 feet
away.
SLIDE 9-37
EXPLOSIONS, ELECTRICAL SHOCK
AND BURNS
Some of the problems which seem the
least likely on wet scrubber systems are
the ones that can have the most serious
consequences. These include explosions,
burns, and electrical shock. -The next
set of slides briefly introduces ways to
minimize the risk due to these problems.
301
-------
SLIDE 9-38
This slide shows flames engulfing an
access ladder to a cupola wet scrubber
system. This occurs when the plant is
"dropping bottom". The inspector should
not go near the scrubber system when
this is about to occur.
Plant personnel are usually quite
careful about advising inspectors about
this operation. The problem occurs when
the cupola operator is unaware of the
presence of the inspector on the
platform of the scrubber. The inspector
must remain aware of plant operations
and must not assume that the operators
are always aware of his or-her presence.
After all, inspections occur only once
or twice a year and it is easy for the
operator to forget.
This is one of the many reasons why it is always advisable to perform the
inspection in the company of a plant representative. This individual will know
which operators must know about the inspector and will recognize when something
is about to occur at the plant which could endanger the inspector.
SLIDE 9-39
Most plants have areas where explosions
could be initiated by smoking. While
the plant personnel are warned repeat-
edly about such areas, the inspector may
not recognize the hazard. DO NOT TAKE
SMOKING MATERIALS ON INSPECTIONS OF WET
SCRUBBER SYSTEMS.
302
-------
SLIDE 9-40
This is one type of portable thermo-
couple used for measuring"gas, liquid,
and pipe skin temperatures. It should
not be taken into potentially explosive
areas since most battery powered inst-
ruments can initiate explosions. All
flashlights used should be explosion
proof.
Potential safety problems with battery
powered thermocouples, pH meters and
flashlights should be discussed with
plant personnel before use in the plant,
SLIDE 9-41
It is sometimes necessary to obtain a
sample of fuel oil or other material
stored in drums. When transferring the
liquid from a storage drum to a sample
bottle, is is possible to build up a
high static charge on the sample bottle
due to splashing. An explosion is
possible if the drum and sample bottle
are not properly grounded and bonded.
This slide shows a storage drum and a
small clip which is part of the bonding
line. This clip has so rusted that it
would not provide a good contact. Also,
the grounding line to the drum has been
disconnected.
Samples should not be taken under the circumstances shown in the slide.
A metallic sample bottle should be used and a grounding/bonding cable in good
condition should be connected between the bottle and the drum. Another cable
in good condition should connect the drum to the grounding rod. Plastic and
glass bottles should not be used since it is impossible to ground these
properly. Unfortunately, agency lab quality assurance personnel often are not
aware of the significant explosion hazards and that often request field inspec-
tors use plastic or glass bottles to prevent contamination.
303
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SLIDE 9-42
Several times during the previous
lectures the potential dangers of fan
disintegration have been mentioned.
This can occur on wet scrubber systems
due to the carry-over of liquor and
solids from the demister. The erosion
or solids accumulation on the fan blades
lead to unbalanced conditions. Due to
the high rotational speed the lack of
balance can ultimately lead to the
disintegration of the fan wheel and fan
housing.
Other causes of fan disintegration
include bearing failure and aerodynamic
forces (fan operating in unstable region
of fan curve).
The area around the scrubber should be left immediately if the vibration
appears to be excessive. A responsible plant representative should be notified
about the situation.
SLIDE 9-43
Static grounding/bonding cables should
be used whenever making measurements at
the inlet ducts of evaporative coolers
and scrubber vessels. Static electrical
charge accumulation can occur whenever
the relative humidity is low (high gas
temperatures) and the particulate mass
concentration is high. It is conceiv-
able that the charge will reach a suf-
ficient voltage to arc within the duct
and cause an explosion.
It should be noted that this problem has
not been reported or discussed in the
literature. However, the author has
been able to develop high voltages on a
pitot system which resembles the inlet
to a wet scrubber system.
The gas streams in the inlet duct usually have more than enough
particulate to sustain an explosion and many of these have the necessary oxygen
levels. Scrubbers are often used specifically becuase of the potentially ex-
plosive nature of the inlet gas stream. For all of these reason, the .probes
should be bonded to a grounded portion of the plant using the grounding/bond-
ing cables.
304
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SLIDE 9-44
COMMON AREAS WITH
INHALATION HAZARDS
Elevated Sampling Platforms
Areas Adjacent to Process Vents and Discharge Points
Partially Confined Areas
Fugitive Process Emissions
Fugitive Emissions from Solids Discharge Equipment
The next set of slides concerns the
large number of inhalation hazards which
can be encountered during inspection of
wet scrubber systems. One of the fund-
amental principles of industrial hygiene
is that inhalation exposures should be
minimized or eliminated through the
application of engineering controls. In
the case of the field inspector, this is
not a realistic possibility. Most ex-
posures occur because of fugitive leaks
of the pollutant-laden gas stream out
into the area immediately surrounding
the wet scrubber system.
These conditions occur by accident and often are not identified by plant
personnel. Other sources of exposure are contact with the downdraft from
nearby stacks or rising clouds of toxic pollutants released from intermittant
process operations. Both types of exposure can result when inspectors are
present on elevated platforms around the scrubber or on stack sampling plat-
forms .
Since the exposures can not be easily limited by engineering controls, the
inspector must substitute awareness of the potential problem areas and
awareness of the warning properties of all chemicals present in the general
area. The inspector must know when certain areas should be avoided and what
respirators and other protective clothing to use in the areas which must be
visited. The choice of respirators is complicated by the lack of monitoring
data for the types of materials present. The conditions are highly variable
and this makes monitoring data subject to error. Furthermore, there is rarely
any monitoring data in the specific Ipcations where the inspector may
experience the most significant exposures.
SLIDE 9-45
One common source of fugitive emissions
are the open 4 inch stack sampling ports
sometimes used when measuring scrubber
operating conditions. This is a photo-
graph of several inspectors attempting
to use an oxygen analyzer at a 4 inch
port having less than 1 inch W.C. pos-
itive pressure. Even at this low
pressure, a substantial quantity of the
gas can escape through the port into the
breathing zone of. the inspector.
These large diameter ports should be
avoided whenever possible. The ports
should be between 1/4 inch and 1 inch
diameter. Only ports in areas with good
natural ventilation should be used.
305
-------
SLIDE 9-46
There can be areas around scrubber sys-
tems which have poor ventilation. Any
fugitive leaks which occur in these area
result in high localized pollutant con-
centrations. These can exceed the cap-
abilities of some respirators.
This photograph shows a fan serving a
large venturi scrubber. The fan and
scrubber are enclosed on three sides by
building walls. A gap in the isolation
sleeve on the fan or corroded ductwork
could lead to very high concentrations
near the fan. All fan housings or
partially enclosed areas surrounding
fans must be approached carefully.
SLIDE 9-47
This is a close-up photograph of the
isolation sleeve on the discharge side
of the fan shown in the slide above.
There are a number of gaps which are
leaking pollutant laden gas into the
area around the scrubber.
306
-------
SLIDE 9-48
This is the scrubber control cabinet
which is located less than 3 feet from
the cracked isolation sleeve (see last
two photographs). An inspector trying
to determine the operating conditions of
the scrubber system could be fumigated
with toxic or oxygen deficient gases.
SLIDE 9-49
This is a view of a pump house. High
concentrations of vaporous material can
accumulate in this area. These must be
approached cautiously since ventilation
in pump houses can be limited.
307
-------
SLIDE 9-50
High concentrations of pollutants can
occur almost anywhere in wet scrubber
systems which operate at positive
pressures (fan ahead of the scrubber
vessel). This slide illustrates a
scrubber system under positive pres-
sure. Wet scrubber systems operate at
higher static pressures than all other
types of air pollution control devices.
All partially confined areas around
areas of possible fugitive leaks should
be avoided. The inspector must remain
constantly alert for symptoms of possi-
ble exposure.
SLIDE 9-51
MOST CONTAMINANTS
HAVE
POOR WARNING PROPERTIES
Avoiding hazards is the best way to
minimize risk. Many of the materials
inhaled during the inspection have poor
warning properties. In other words, the
person may have no physical sensation
that there are high levels of pollutants
in the air.
The inhalation of dust and fume rarely
causes any immediate physical discomfort
or impairment. For this reason, it is
possible for undesirable quantities of
toxic materials such as lead, arsenic
and asbestos to reach the lungs where
they can be slowly absorbed by the
blood.
The chemical and physical asphyxiants are another group of chemicals with
very poor warning properties. Chemical asphyxiants, such as carbon monoxide and
hydrogen sulfide, can occur at life threatening levels without any odor or taste
preception. The most common physical asphyxiant, carbon dioxide, also does not
have any odor. __
Most organic compounds and nitrogen dioxide are not very soluble and can
penetrate into the deep lung. The initial symptoms of exposure are non-
specific and may not be recognized by the inspector who is preoccupied with
conversations with plant personnel. These symptoms include dizziness,
headache, light-headedness, and nausea. Acute exposure can result in pul-
monary edema hours after the exposure. It should also be remembered that non-
soluble chemicals are not removed effectively in wet scrubbers. That means
that high concentrations can exist in both the inlet and outlet gas streams.
308
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SLIDE 9-52
Route of Entry
Symptoms
HYDROGEN SULFIDE
— Inhalation of Gas
— At High Concentrations There Is No Odor
Consequences — Chemical Pneumonia May Develop Several
Hours After Exposure
The next three slides illustrate the
differing characteristics of common air
pollutants which can be encounted while
inspecting wet scrubber systems.
At low concentrations, hydrogen sulfide
is an eye irritant and it has a very
disagreeable rotten eggs odor. If these
symptoms are noted, the inspector should
leave the area immediately. Exposure to
higher concentrations of hydrogen sul-
fide can occur in areas close to the
point where these symptoms were first
noted. At moderate to high concentra-
tioi s, hydrogen sulfide is an very
deadly chemical and there is no odor at
all! High concentrations of hydrogen
sulfide immediately overcome the
olefactory senses.
It is possible to walk into a confined or partially confined area with
toxic concentrations of hydrogen sulfide and not be aware of its presence at
all. Brief exposure to such conditions can lead to pulmonary edema and other
serious respiratory problems in 6 to 12 hours after the exposure. In other
words there is a delayed response during which the victim feels only slightly
ill. The exposure can also result in immediate death.
Due to the almost total lack of warning properties, respirators do not
provide an adequate defense. There are no commercially available respirators
rated for hydrogen sulfide.
SLIDE 9-53
NITROGEN OXIDES
Route of Entry — Inhalation of Gas
Symptoms — Initial Symptoms Include Cough, Chills,
Fever, Headache, Nausea
Consequences — Acute Pulmonary Edema May Follow Five
to Twelve Hours After Exposure
During the exposure to nitrogen oxides
only mild bronchial irritation may be
experienced. Concentrations of 100 to
150 ppm are dangerous for periods of 30
to 60 minutes.
Nitrogen oxides are generated in almost
all combustion processes. While they do
not have a distinctive odor, it is some-
times possible to see the orange color
of nitrogen oxides.
These gases are examples of the non-soluble chemicals which can be
treated in wet scrubber systems.' They are often accompanied by other combus-
tion related pollutants such as sulfur dioxide, ozone, carbon monoxide and
particulate matter. Any respirator used in areas of fugitive gas leakage must
be capable of handling all of these potentially dangerous gases.
309
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SLIDE 9-54
Route of Entry
Symptoms
Consequences
CHLORINE
Inhalation of Fibers
Intense Irritation of Eyes, Nose, and Throat
Respiratory Problems
Chlorine is one of a number of chemicals
which are partially soluble in mucous
membranes. The initial site of attack
includes the eyes, nose, and throat. It
has relatively good warning properties.
Exposure can occur due to an accidental
release from process equipment. Inspec-
tors must be aware of plant warning
sirens and know what to do if a cloud of
chlorine is approaching their location.
Chlorine is often stored for use in odor scrubbers. It is also a common
process chemical. Inspectors in areas vulnerable to sudden chlorine releases
should be equipped with emergency respirators.
SLlrfE 9-55
The wind socks and pennants on high •
places in the plants provide a good
indication of prevailing wind direction.
These should be observed whenever an
inspection is being performed in a plant
which could conceivably suffer an acci-
dental spill or process release. As soon
as the warning siren sounds or it is
apparent that a gas cloud is approach-
ing, all personnel should move to a safe
position. It is also helpful to call in
to a central location to report that
everyone has reached a safe location.
This call may prevent others from get-
ting hurt while attempting a "rescue" of
the inspection group. ~—
310
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SLIDE 9-56
SELECTION CRITERIA
• Concentration of Contaminants
• Forms of Contaminants
• Oxygen Levels
• Size and Shape of Head
The selection of the appropriate res-
pirator for each inspection is a very
important and complicated task. This
provides a very brief overview of some
important points. The readers are
strongly advised to get expert assist-
ance in the selection, fitting, main-
tenance and use of respirators.
The respirators must be selected based
on a number of factors, some of which
are listed on this slide.
One of the most important factors is the concentration of the material.
The respirator must satisfactorily perform at these concentrations. It is also
important to know if the concentration is in the range that is considered to be
Immediately Dangerous to Life and Health (IDLH) and if the concentration is in
the explosive range. These areas should not be entered by regulatory agency
field inspectors.
Unfortunately, the concentrations of the contaminants are rarely known
because the exposures are due to accidential and/or intermittent conditions.
Also, the inspector visits many different localized sites around the control
system and there is rarely any monitoring data available for all of these
locations.
It is very important to know what the oxygen level is at the various areas
to be visited. Many wet scrubber systems handle gas streams with very low
oxygen levels of 3 to 6%. Even some small leaks can lead to localized oxygen
concentrations below 19.5%, the point at which oxygen deficiency becomes a
problem.
The warning properties of the materials must be known. This is best done
by the file review before starting the inspection. If some of the chemicals
are irritants, a full face piece unit may be required, regardless of the
concentration. If the chemical(s) can be absorbed through the skin, protec-
tive clothing may be necessary in addition to a respirator.
The physical form of the material (gas, vapor, fume, dust) must be known
to the extent possible. This is not as obvious as it would seem since the form
of the contaminant can change in the wet scrubber or after release from the
stack. There can be condensation of vaporous material to form submicron
particles. There can also be stripping of dissolved compounds to form gases.
The moist conditions can also promote atmospheric reactions between several
pollutants. — —-
The size and shape of the individual's head should be considered in the
selection of respirators. There are usually several models of each type
available, and the unit chosen must be comfortable and fit tightly.
311
-------
SLIDE 9-57
There are a number of requirements con-
cerning the the use of respirators.
The material which follows has been
excerpted from OSHA Standard 1910.13A.
The full text of the OSHA Standard and
other material concerning the safe use
of respirators should be read.
The user should be instructed and train-
ed in the proper use and limitations of
the specific respirators.
Whenever practicable, the respirators
should be assigned to individual work-
ers for their exclusive use.
Respirators should be regularly cleaned and disinfected. Those issued for
the exclusinve use of one worker should be cleaned after each day's use, or
more often if necessary. Those used by more than one worker should be thoroug-
ly cleaned and disinfected after each use.
Respirators should be stored in a convenient, clean, and sanitary location
between uses. The trunk of a car is not adequate.
Respirator should be routinely inspected during cleaning. Worn or
deteriorated parts should be replaced. Respirators for emergency use such as
self-contained devices should be thorougly inspected at least once a month and
after each use.
Appropriate surveillance of work area conditions and the degree of ex-
posure or stress should be maintained.
Persons should not be assigned to tasks requiring use of respirators
unless it has been determined that they are physically able to perform the work
and to use the equipment. A local physician should determine what health and
physical conditions are pertinent. .The respirator user's medical status should
be reviewed periodically.
Written standard operating procedures governing the selection and use of
respirators should be established.
312
-------
SLIDE 9-58
SOURCES WITH POTENTIAL
BIOLOGICAL HAZARDS
Municipal Incinerators
Pathological Incinerators
Foodstuff Processors
Genetic Engineering Firms
The adjacent slide is a partial list
of the possible sources of biological
hazards. It is obviously important to
avoid direct contact with contaminated
materials. The appropriate respirators
should be selected based on agency and
plant industrial hygiene guidelines. Eye
protection should be worn in situations
where splashing or contaminated water is
possible. It is important to avoid any
rubbing of the eyes at any time since
this is an easy entry route for patho-
genic organisms. After the inspection
the work cloths should be washed and the
inspector should shower.
SLIDE 9-59
Here is one example of a commonly
encountered potential biological hazard.
This inspector is attempting to obtain a
scrubber liquor sample. Since it is
possible that the liquor contains
pathogenic organisms, the inspector
should avoid contamination of his skin
and clothing. THIS IS THE WRONG WAY TO
TAKE THE SAMPLE.
It is far better to sample in a area
where there is no direct contact with
the liquor and no possibility for
splashing of the liquor.
313
-------
314
-------
SLIDE 9-60
This is the most important safety
precaution that should be taken during
the inspection of wet scrubber systems.
UNDER NO CIRCUMSTANCES SHOULD AN AGENCY
INSPECTOR ENTER ANY PORTION OF THE WET
SCRUBBER SYSTEM. Oxygen deficiency
and/or high concentrations of highly
toxic pollutants can be trapped in
scrubber vessels, tanks, ductwork, and
other areas. The conditions can persist
even after the system has been off-line
for a period of time. It is often
difficult to detect the dangerous
conditions.
It takes special training and personal protective equipment to make safe
internal inspections of air pollution control systems. Regulatory agency
personnel do not have either this training or equipment. Furthermore, there
are certain safety procedures that must be observed at each plant.
Regardless of the possible encouragement by plant personnel or the natural
curiosity of the inspector, entry inside the equipment should not be done.
Everthing thing that must be done by an inspector can be done satisfactorily
and safely outside the equipment.
INTERNAL
INSPECTIONS
315
-------
LECTURE 9 - REVIEW PROBLEMS AND QUESTIONS
9-1. All of these are potential areas of high pollutant concentrations. They
should all be approached very carefully.
9-2. The correct answer is "d". It is important to use the grounding/bonding
cables whenever there is any possibility for static electricity. This is
most likely at the inlets to wet scrubber systems.
9-3. Answers "b", "c", and "d" are correct. Often the plant personnel are not
using hard hats, safety shoes, hearing protection and respirators. The
inspector should not abdicate his or her judgement to plant personnel
since there are a few who are not safety conscious and a few who are
totally oblivious to health and safety risks.
9-4. The correct answer if "e". The inspector should always be accompanied by
a plant representative who: (1) knows the warning siren codes and plant
evacuation procedures, (2) notifies process operators of the inspection
activities, and (3) knows the safe routes around process and scrubber
equipment.
9-5. The correct answer is obviously "b", most pollutants have very poor or
nonexistent warning properties.
9-6. The correct answer is "h", all of these are possible symptoms of ex-
posure. The inspector should proceed immediately to a well ventilated
area.
316
-------
LECTURE 9 - REVIEW PROBLEMS AND QUESTIONS
9-1. Areas around wet scrubber systems which have often have poor
ventilation and high pollutant concentrations include the
following:
a. Fan houses
b. Walkways between adjacent scrubbers
c. Walkways adjacent to duct expansion joints
d. Pump houses
9-2. Before inserting a probe into a gas stream it is important to check which
of the following items:
a. The grounding/bonding, cable is in good condition
b. The ground clamp does not interfere with the probe
c. The clamp has penetrated any paint or corrosion layer
d. All of the Above
9-3. When selecting personal safety equipment necessary for an inspection,
the inspector should be guided by which of the following:
a. What the plant representative and other plant personnel are using
b. Plant policies
c. Agency policies
d. Common sense
9-4. An inspector should not work alone during an inspection, unless the
following conditions exist:
a. Plant personnel are too busy to accompany the inspector.
b. The inspector is very familiar with the plant.
c. No entry into pratially confined or confined areas are anticipated.
d. The inspector has all of the necessary personal protection
equipment.
e. None of the above
9-5. Most gaseous contaminants have good "warning properties". Therefore the
inspector is usually aware they are present.
a. True
b. False
9-6. Which of following symptoms may indicate exposure to air contaminants?
a. Headache " ~~ -
b. Drowsiness
c. Shortness of breath
d. Nausea
e. Loss of coordination
f. Eye irritation
g. Answers a,b,c,d,f
h. All of the above
317
-------
LECTURE 9 - REVIEW PROBLEMS AND QUESTIONS
9-7. Hydrogen sulfide is especially dangerous since it has no odor at high
concentrations. Answer "d" is correct.
9-8. Answer "c" is correct. The equipment should not be entered even though
the plant personnel seem to be feeling fine inside the unit. It is
always possible that they will develop serious respiratory problems in
the next several hours due to high concentrations of pollutants having
no warning properties. Everything can usually be seen from an access
hatch. If it can not be seen just take their word for it.
318
-------
LECTURE 9 - REVIEW PROBLEMS AND QUESTIONS
9-7. At high concentrations what best describes the odor of hydrogen
sulfide?
a. Fragrant
b. Sewer
c. Rotten Eggs
d. No Odor
9-8. During the inspection of a rod deck scrubber, the operator states that
a chronic gas-liquor distribution problem has been solved by movement of
both the spray headers and the rod deck. He suggests that you follow
him into the scrubber to confirm that this has been done properly. What
should the inspector do to complete this inspection?
a. Review the drawings and do not waste time on the equipment
inspection.
b. Make sure the plant personnel enter first, and then follow
them inside to confirm the modifications have been completed.
c. Limit the inspection to what can been seen through an access
hatch without going inside.
319
-------
320
-------
APPENDIX A - BIBLIOGRAPHY
321
-------
322
-------
Bibliography: Scrubber Types and Operating Principles
1-1 Atkinson, D. S. F. and W. Strauss. Droplet Size and Surface
Tension in Venturi Scrubbers. Journal of the Air Pollution Control
Association, Volume 28: Pages 1114-18. November 1978."
1-2 Boll, R. H. Particle Collection and Pressure Drop in Venturi
Scrubbers. Presented at 69th National American Institute of
Chemical Engineers Meeting. Cincinnati, Ohio, 1971.
1-3 Buonicore, A. J., and L. Theodore. Industrial Control Equipment
for Gaseous Pollutants, Volume I. CRC Press, 1975.
1-4 Calvert, S., H. Barbarika and G. Monahan. American Air Filter
Kinpactor 10x56 Venturi Scrubber Evaluation. U.S. Environmental
Protection Agency, Research Triangle Park, N.C. Publication
EPA-600/277-209b. November 1977.
1-5 Calbert, S. Venturi and Other Atomizing Scrubbers: Efficiency
and Pressure Drop. American Institute of Chemical Engineers,
Chemical Enginnering Progress, Number 16, Pages 392-296. May
T97o~:
1-6 Calvert, S. "Engineering Design of Fine Particle Scrubbers."
Journal of the Air Pollution Control Association, Volume 24,
Number 10. Pages 929-934.
1-7 Calvert, S., S. C. Yung, H. F. Barbrika, and L. E. Sparks. Entrain-
ment Separators for Scrubbers. Second EPA Fine Particle Scrubber
Symposium. EPA-600/2-77-193, May 2-3, 1977.
1-8 Calvert, S., I. L. Jashnani, and S. Yung. Entrainment Separators
for Scrubbers. Journal of Air Pollution Control Association,
Volume 24, Number 19: Pages 971-975. October 1974.
1-9 Calvert, S., S. Yung, and J. Yung. Entrainment Separators for
Scrubbers - Final Report. EPA-650/2-74-119-b, August 1975.
1-10 Calvert, S.; Barbarika, H. F.; and Monahan, G. M. Evaluation
of Three Industrial Particulate Scrubbers. U.S. Environmental
Protection Agency, Research Triangle Park. Publication EPA-600/2-78-
-032, February 1978.
1-11 Calvert, S., H. F. Barbarika, and G. M. Monahan, G. M. Evaluation
of Three Industrial Particulate Scrubbers. EPA 600/2-78-032,
February 1978.
1-12 Calvert, S. Scrubber Performance for Particle Colleciton. Proceed-
ings of the Symposium on Control of Fine Particulate Emissions
from Industrial Sources. January 15-18, 1974. Pages 193-212.
1-13 Calvert, S., and N. C. Jhaveri. Flux Force/Condensation Scrubbing.
Journal of the Air Pollution Control Association, Volume 24,
Number 10: Pages 946-951. October 1974.
323
-------
Bibliography: Scrubber Types and Operating Principles
1-14 Calvert, S. J., Goldschmid, D. Leith, and D. Mehta. Wet Scrubber
System Study, Volume I: Scrubber Handbook. U.S. Environmental
Protection Agency, Research Triangle Park, N.C. Publication
EPA-R2-72-118a, Pages 5-89 to 5-93. August 1972.
1-15 Calvert, S., D. Lundgren, and D. S. Mehta. Venturi Scrubber
Performance. Journal of the Air Pollution Control Association,
Volume 22, Number 7: Pages 529-532. July 1972.
1-16 Calvert, S., S. C. Yung, H. Barbarika, G. Monahan, L. E. Sparks,
and D. L. Harmon. A.P.T. Field Evaluation of Fine Particle Scrub-
bers. Second EPA Fine Particle Scrubber Symposium. May 2-3,
1977. Pages 221-254.
1-17 Cole, R. M., T. M. Kelso, N. D. Moore, and R. F. Robards. "Evalua-
tion of 1-MW Horizontal Scrubber", EPRI FP-752, December 1978.
1-18 Engineering Science, Inc. Scrubber Emissions Correlation Final
Report to U.S. Environmental Protection Agency. Contract No.
68-01-4146, Task Order 49. May 1979.
1-19 Green, G. P. Operating Experience with Particulate Control Devices.
Presented at the American Society of Mechanical Engineers, Air
Pollution Control Division, National Symposium. Philadelphia,
April 1973.
1-20 Gurney, A., R. J. Chironna, "Condensible Organics Removal with
Wet Scrubbers". Paper 77-17.6 Presented at the 70th Annual Meeting
of the Air Pollution Control Association, Toronto, Ontario,
Canada, June 20-24, 1977.
1-21 Hesketh, H. E. Fine Particle Collection Efficiency Related to
Pressure Drop, Scrubbant, Particle Properties, and Contact Mecha-
nism. Journal of the Air Pollution Control Association, Volume
24, Number 10: Pages 933-942. October 1974.
1-22 Hesketh, H. "Atomization and Cloud Behavior in Wet Scrubbers."
Presented at the Symposium in Control of Fine Particulate Emissions
from Industrial Sources. San Francisco, California. January
15-18, 1974, Pages 455-478.
1-23 Hubbert, G. Wet Collector Design, Operation and Maintenance.
Presented at Specialty Conference on Design, Operation, and
Maintenance of High Efficiency Particulate Control Equipment.
St. Louis, May 29-30, 1973.
1-24 Javorsky, B. S. Gas Cleaning with Foam Scrubber. Fi1ibration
Separation (Purley) Volume 9, Number 2: Pages 173-175. March-April
1972.
1-25 Kalika, P. W. How Water Recirculation and Steam Plumes Influence
Scrubber Design. Chemical Engineering, July 28, 1969. Pages
.133-138.
324
-------
Bibliography: Scrubber Types and Operating Principles
1-26 Lancaster, B. W., and W.M. Strauss. Condensation Effects in
Scrubbers. Air Pollution Control, Part I. W. Strauss (editor).
Wiley-Interscience, New York, 1971. Pages 377-427.
1-27 Lapple, C. E. and H. J. Kemack. "Performance of Wet Dust-Scrubber".
Chemical Engineering Progress. Volume 51, Pages 110-121. 1955.
1-28 McCain, J. D. "CEA Variable Throat Venturi Scrubber Evaluation",
EPA-600/7-78-094, June 1978.
1-29 Muir, D. M., and Y. Miheisi. Comparison of the Performance of
A Single and Two-Stage Variable-Throat Venturi Scrubber. Atmospheric
Environment. Volume 13, Number 8: Pages 1187-1196. 1979.
1-30 Muir, D. M., and Y. Miheisi. Prediction of Collection Efficiency
and Pressure Drop in Venturi Scrubbers. Paper presented at the
Symposium on Dust Control. Manchester, England, March 21-22,
1978, sponsored by Institute of Chemical Engineering, London,
England. 1978. Pages 4.1 - 4.4.
1-31 Nguyen, X. T. On the Efficiency of a Centrifugal Fan Wet Scrubber.
Canadian Journal of Chemical Engineering Volume 57, Number 3:
Pages 263-267. June 1979.
1-32 Anon, "Power Factor and Conservation", Power, May 1973, Pages
43-45.
1-33 Ranade, M. B. and E. R. Kashdan. Second Symposium on the Transfer
and Utilization of Particulate Control Technology. U.S. Environ-
mental Protection Agency, Cincinnati, Ohio. Publication 600/9-80--
039a. September 1980. Pages 583-560.
1-34 Richards, J. R. and R. Segall. Wet Scrubber Performance Eval-
uation. EPA-340/1-83-022, September 1983.
1-35 Semrau. K. T., C. L. Witham, and W. W. Kerlin. Energy Utilization
by Wet Scrubbers. U. S. Environmental Protection Agency. Cincinnati,
Ohio. Publication No. EPA-600/2-77-234. November 1977.
1-36 Semrau, K. T. "Correlation of Dust Scrubber Efficiencies." Journal
of the Air Pollution Control. Volume 10: Pages 200-207. 196T^
1-37 Semrau, K. T. "Dust Scrubber Design - A Critique on the-State
of the Art." Journal of the Air Pollution Control Association'.
Volume 16: Pages 587-594. 1967.
1-38 U.S. Environmental Protection Agency, Wet Scrubbers, Section
4.5 in Control Techniques for Particulate Emissions from Stationary
Sources - Volume 1. Report No. EPA-450/3-81-005a, September
1982.
325
-------
Bibliography: Scrubber Types and Operating Principles
1-39 Walker, A. B. and R. M. Hall. "Operating Experience with a Flooded
Disc Scrubber. A New Variable Throat Orifice Contactor." Journal
of the Air Pollution Control Association, Volume 18: Pages 319-323.
1-40 Woffinden, C. J., Markawski, C. R. and D. S. Ensor. "Effects
of Surface Tension on Particle Removal." Symposium on the Transfer
and Utilization of Particulate Control Technology. U.S. Environ-
mental Protection Agency. Publication EPA 600/7-79-044C, Pages
179-192.
1-41 Yung, S., Calvert and H. F. Barbarika. Venturi Scrubber Performance
Model. U.S. Environmental Protection Agency. Publication 600/2-77-
172. August 1977.
1-42 Yung, S., S., Barbarika, H., and Sparks, L. "Venturi Scrubber
Performance Model" Environmental Science and Technology, Volume
12. Number 4: Page's 456-4by. April 1978.
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ance Model. U.S. Environmental Protection Agency, Cincinnati,
Ohio. Publication No. EPA-600/2-77-172. August 1977.
326
-------
Bibliography: Pumps
2-1 Biheller, J.H., "Check Your New Centrifugals Against This 16
Point List", Power, January 1974, Pages 60-61.
2-2 Bieheller, J.H., "What You Need To Know About Pump System Head
Curves", Power, March, 1982. Pages 53-56.
2-3 Birk, J. R., Peacock, J. H., "Pump Requirements for the Chemical
Process Industries", Chemical Engineering, February 18, 1974,
Pages 16-124.
2-4 Buse, F., "The Effects of Dimensional Variations on Centrifugal
Pumps", Chemical Engineering, September 26, 1977, Pages 93-100.
2-5 Cunningham, E. R., "Pumps Without Seals", Plant Engineering,
August 4, 1977, Pages 66-75.
2-6 Fraser, W. H., "Working with Centrifugal Pumps", Plant Engineering,
June 12, 1975, Pages 120-122.
2-7 Fraser, W. H., "Points to Weigh in Applying Centrifugal Pumps",
Plant Engineering, April 17, 1975, Pages 195-199.
2-8 Holmes, E., Et al, " Handbook of Industrial Pipework Engineer-
ing", John Wiley & Sons, New York, N.Y., 1973.
2-9 Huang, S. Y., "Preventing Cavitation Under Conditions of Partial
Flow in Centrifugal Pump Operation", Plant Engineering, August
20, 1981, Pages 71-73.
2-10 Karassik, I. J., "Are You Short on NPSH? Nine Ways to Improve
Unfavorable Suction Conditions", Combustion, July 1980, Pages
37-41.
2-11 King, R. C. and S. Crocker, "Piping Handbook", 1967, McGraw-Hill,
Inc. 1967.
2-12 Lobanoff, V., "Specific Speed is a Useful Index for Pump Design
and Selection", Power, June 1979.
2-13 Luley, R., "Selecting a Centrifugal Pump", Plant Engineering,
August 8, 1974, Pages 65-68.
2-14 Neerken, R. F., "Pump Selection for the Chemical Process Indus-
tries", Chemical Engineering, February 18, 1974, Pages 104-115.
2-15 Neerken, R. F., "Selecting the Right Pump". Chemical Engineering,
April 3, 1978, pages 87-98.
2-16 O'Keefe, W., "Pumps", Power. June 1972.
327
-------
Bibliography: Pumps
2-17 Reynolds, J. A., "Pump Installation and Maintenance", Chemical
Engineering, October 11, 1971, Pages 67-76.
2-18 Roche, R. H., "Mechanical Seals in Centrifugal Pumps", Plant
Engineering, February 19, 1981, Pages 100-103.
2-19 Rosenberg, H. S., Et al., "Construction Materials for Wet Scrub-
bers", Volume I, EPRI Final Report No. CS-1736, March 1981,
pages 3/59 - 3/64.
2-20 Stindt, W. H., "Pump Selection", Chemical Engineering, October
11, 1971, pages 43-49.
2-21 Whitmore, C. H., H. Wojda, and W. Marietta, "Reducing the Operating
Noise of Industrial Hydraulic Systems", Parker Hannifin Reprint
PC-1, October 1972.
2-22 Yedidiah, S., "Analyzing Suction Performance of Centrifugal
Pumps", Plant Engineering, October 3, 1974, Pages 69-71.
2-23 Yedidiah, S., "Avoiding Cavitation in Centrifugal Pumps", Machine
Design, March 6, 1980, Pages 265-269.
2-24 Yedidiah, S., "Faulty Piping Layout Can Ruin a Centrifugal Pump",
Machine Design, June 12, 1980, Pages 86-91.
2-25 Yedidiah, S., "Diagnosing Troubles of Centrifugal Pumps, Part
I", Chemical Engineering, October 24, 1977, Pages 124-128.
2-26 Yedidiah, S., "Diagnosing, Part II", Chemical Engineering, November
21, 1977, Pages 193-199.
2-27 Yedidiah, S., "Diagnosing, Part III", Chemcial Engineering,
December 5, 1977, Pages 141-143.
2-28 Yedidiah, S., "Methods for Preventing Water Hammer Damage to
Centrifugal Pump Systems", Plant Engineering, July 6, 1978,
Pages 85-88.
2-29 Yedidiah, S., "Performance Curves: Key to Centrifugal Pump Selec-
tion", Machine Design, April 10, 1980, Pages 117-122.
2-30 Anon, "Pipe Line Rules of Thumb Handbook", Gulf Publishing Co.
(Book Division), Houston, Texas.
2-31 Yedidiah, S., "Selection and Application of Nonclog Centrifugal
Pumps", Plant Engineering, August 3, 1978, Pages 95-97.
2-32 Yedidiah, S., "Tracking Down Problems in Centrifugal Pumps",
Machine Design, May 8, 1980, Pages 95-100.
2-33 Anon, "Troubleshooting a Pumping System", Waukesha Pump Engineering
Manual, Second Edition, 1976, Pages 68-71.
328
-------
Bibliography: Corrosion
3-1 Adams, A. B., Jr. Corrosion Problems with Wet Scrubbing Equipment.
Journal of the Air Pollution Control Association, Volume 26,
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3-2 Adams, A. B., Jr., "Corrosion Problems with Wet Scrubbing Equip-
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Equipment, National Association of Corrosion Engineers, Houston,
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3-3 Ashbaugh, W. G., "Materials Selection for Chemical Process Equip-
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3-5 Banks, J. H., "Corrosion Control with Fiberglass-Reinforced
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Engineering, Volume 79, Number 8: Pages 48-51, 1975.
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3-13 Crow, G. L., "Corrosion Tests Conducted in Prototype Scrubber
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Titanium's Usage in Gas Scrubbing Equipment for Refuse Incinera-
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Control and Design Handbook, Chapter" 41, Marcel Dekker, New
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Engineering, Volume 84, Number 23: Pages 145-48, 1977.
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in Air Pollution Control Equipment, National Association of
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tator Design," Resolving Corrosion Problems in Air Pollution
Control Equipment, National Association of Corrosion Engineers,
Houston, Texas, 1976. .._ __
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3-26 Handwerk, R. J., "Recycling Water Effectively," Foundry, Volume
100, Number 7: Pages 40-43, 1972.
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"The Chemistry of Scrubbers,'" Combustion, Volume 47, Number
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Preventing Scaling and Fouling in Gas Scrubbing Systems," Plant
Engineering, Volume 32, Number 2: Pages 155-57, 1978.
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Chemical Engineering, November 15, 1977, Pages 163-166.
3-30 Holt, W. H., "Fiberglass-Reinforced Plastic Construction in
Baghouses," Resolving Corrosion Problems in Air Pollution Control
Equipment, National Association of Corrosion Engineers, Houston,
Texas, 1976.
3-31 Hoxie, E. C., "Discussion of Materials of Construction for Wet
Scrubbers for Incinerator Applications," Resolving Corrosion
Problems in Air Pollution Control Equipment, National Association
of Corrosion Engineers, Houston, Texas, 1976.
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Tests in Power Plant Flue Gas Scrubbing Processes," Resolving
Corrosion Problems in Air Pollution Control Equipment, National
Association of Corrosion Engineers, Houston, Texas, 1976.
3-33 Hughson, R. V., "High-Nickel Alloys for Corrosion Resistance,"
Chemical Engineering, Volume 83, Number 24: Pages 125-36, 1976.
3-34 Javetski, J., "Solving Corrosion Problems in Air Pollution Control
Equipment - Part I," Power, Volume 122, Number 5: Page 72, 1978.
3-35 Javetski, J., "Solving Corrosion Problems in Air Pollution Control
Equipment - Part II," Power, Volume 122, Number 6: Page 80,
1978.
3-36 Kirchner, R. W., "Corrosion of Pollution Control Equipment,"
Chemical Engineering Progress. Volume 71, Number 3: Pages 58-63,
T975~:
3-37 Klodt, D. T., "Corrosion of Air Pollution Control Equipment
in the Mineral Industries," Mineral Industrie's Bu 11 ettn,-Volume
16, Number 1: Pages 1-14, 1973";
3-38 Lahr, P. T., "Pumping Corrosive Scrubbing Liquids," Resolving
Corrosion Problems in Air Pollution Control Equipment, National
Association of Corrosion Engineers, Houston, Texas, 1976.
331
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Bibliography: Corrosion
3-39 Landrum, R. J., "Designing for Corrosion Resistance of Air Pollu-
tion Control Equipment," Resolving Corrosion Problems in Air
Pollution Control Equipment, National Association of Corrosion
Engineers, Houston, Texas, 1976.
3-40 Lizlovs, E. A., "Laboratory Corrosion Test for Stainless Steels
for SCL Scrubber Service," Materials Performance, Volume 17,
Number^: Pages 36-37, 1978":
3-41 Lomasney, H. L., "Testing Wet Scrubber Lining Materials," Paper
No. 39 presented at the National Association of Corrosion Engi-
neers' Corrosion/79, Atlanta, Georgia, March 12-16, 1979.
3-42 Maier, J. H., "Analysis of Wet, Dirty and Corrosive Combustion
Gases," Proceedings of the 20th Annual ISA Analysis Instrument
Symposium, Pittsburgh, Pennsylvania, May 12-15, 1974.
3-43 Mappes, T. E. and R. D. Terns. An Investigation of Corrosion
in Particulate Control Equipment. EPA-340/1-81-002, February
1981.
3-44 McDowell, D. W. Jr., "Problems in Wet Gas Scrubbing Systems,"
Presented at the Air Pollution Control Associatin Seminar on
Corrosion Problems in Air Pollution Control Equipment, Atlanta,
Georgia, January 17-19, 1978.
3-45 Michaels, H. T., and E. C. Hoxie, "Some Insight into Corrosion
in SOp Exhaust Gas Scrubbers," Presented at the Air Pollution
Control Association Seminar on Corrosion Problems in Air Pollution
Control Equipment, Atlanta, Georgia, January 17-19, 1978.
3-46 Miller, P. D., "Corrosion Studies in Municipal Incinerators,"
Battelle Memorial Laboratories, Columbus, Ohio, 1972.
3-47 Mistry, N. T., "Material Selection for Gas Scrubbers," Materials
Performance. Volume 15, Number 4: Pages 27-33, 1976.
3-48 Mockbridge, P. C., and D. W. McDowell, Jr., "Materials and Corro-
sion Problems in a Fly Ash Scrubbing System," Materials Performance,
Volume 13, Number 4: Pages 13-17, 1974.
3-49 Moreland, P. J., and J. G. Mines, "The Concept and Developement
of Corrosion Monitoring," Materials Performance, Volume 18,
Number 2: Pages 65-70, 197?:~~,
3-50 Nowak, F., "Corrosion Problems in Incinerators," Combustion,
Volume 40, Number 5: Pages 32-40, 1968.
3-51 Paul, G., "Dealing with High Chloride Concentrations in Closed-Loop
Sulfur Dioxide Scrubbers," Industrial Water Engineering, Volume
15, Number 1: Pages 24-28, 1978.
332
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Bibliography: Corrosion
3-52 Sakol, S. L., and R. A. Schwartz. Construction Materials for
Wet Scrubbers. Chemical Engineering Progress, Volume 70, Number
8: Pages 63-68. August 1974.
3-53 Sheppard, W. L., "Uses of Chemically Resistant Masonry in Air
Pollution Control," Presented at the Air Pollution Control Associ-
ation Seminar on Corrosion in Air Pollution Control Equipment,
Atlanta, Georgia, January 17-19, 1978.
3-54 Shinskey, F. G., "pH Controls for SCL Scrubbers," Air Pollution
Control and Design Handbook, Chapter 37, Marcel Dekker, New
York, 1977.
3-55 Steel, C. J., "Corrosion Protection Strategy for Pollution Control
Equipment," Pollution Engineering, Volume 10, Number 3: Pages
49-50, March 1978.
3-56 Thaxton, L. A., and A. G. Zourides, "Corrosion Problems in Specific
Pollution Control Equipment," Paper No. 196, presented at the
5th International Pollution Engineering Exposition and Congress,
Anaheim, California, November 9-11, 1976.
3-57 Velzy, C. 0., "Materials of Construction for Wet Scrubbers for
Incinerator Applications," Resolving Corrosion Problems in Air
Pollution Control Equipment, National Association of Corrosion
Engineers, Houston,-Texas, 1976.
3-58 Zarfoss, J. R., "Clean Air from Paper Mill Recovery Boilers
Without Corrosion," Resolving Corrosion Problems in Air Pollution
Control Equipment, National Association of Corrosion Engineers,
Houston, Texas, 1976.
333
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334
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Bibliography: Demisters
4-1 Calvert, S. State-of-Art Survey of Mist Elimination in the U.S.A.
EPA-600/7-78-037, March 1978. Pages 180-193.
4-2 Conkle, H. N., H. S. Rosenberg, and S. T. DiNovo, "Guidelines
for the Design of Mist Eliminators for Lime/Limestone Scrubbing
Systems," EPRI FP-327, December 1976.
4-3 Hanf, E. B. Design Considerations for Venturi Entrainment Separa-
tors. Presented at the American Institute of Chemical Engineering
National Meeting. Cincinnati, Ohio, May 16-19, 1971.
4-4 Jashnani, I. L. and S. Calvert. Wet Scrubber Entrainment Separa-
tors. Presented at the Air Pollution Control Association Annual
Meeting, Denver, June 9-13, 1974. Paper 74-230.
4-5 Schifftner, K. C. How to Check Scrubber Entrainment. Pollution
Engineering, July 1982, pages 38-39.
335
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336
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Bibliography: Nozzles
5-1 Bete Fog Nozzle, Inc. Catalog 81A. 1981.
5-2 Bieber, D., and A. B. Buhl, "Spray Nozzles in Air Pollution •
Control", Spraying Systems Co. Pollution Abatement Manual, December
27, 1974.
5-3 Cox, R. K., "Spraying Droplets To Order,"Automation, Volume
21, August 1974.
5-4 Gleason, T. G., "Halt Corrosion in Particulate Scrubbers," Chemical
Engineering, October 24, 1977.
5-5 Rosenberg, H. S., Et. All, "Construction Materials For Wet Scrub-
bers," Volume I," EPRI Final Report No. CS-1736, March 1981.
5-6 Spraying Systems Co. Pollution Abatement Manual. No Date.
5-7 Tate, R. W., "Spray Nozzles for Pollution Control," Pollution
Engineering, April 1973.
337
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338
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Bibliography: Monitoring Instruments
6-1 Olszewski, Richard, "Conditioning Air For Pneumatic Systems."
Instruments Control Systems, Sept., 1976, Volume 49, Number
9, Pages 119-122.
6-2 Griffin, M. F. and J. H. Grzenda, "The Magnetic Flowmeter Operating
Principles Installation And Use," Advances in Instrumnetation,
Volume 36, Part 2, Proceedings of the ISA Conference and Exhibit,
Anaheim, California, October 6-8, 1981.
6-3 Grezenda, J. H., "Understanding Magnetic Flowmeters," Plant
Engineering, April 30, 1981, Volume 35, Number 9, Pages 67-70.
6-4 Hall, John, "Flowmeters-Matching Applications and Devices,"
Instruments & Control Systems, February, 1978, Volume 51, Number
2, Pages I/-22.
6-5 Harrison, Paul, "Flow Measurement-A State of the Art Review,"
Chemical Engineering, January 14, 1980, Pages 97-104.
6-6 Liptak, Bela G., "Magnetic Flowmeters," Instrument Engineers
Handbook, Volume I, Process Measurement, Pages 478-487.
6-7 Lomas, D. J., "Selecting the Right Flowmeter-Part I: The Six
Favorites," Instrumentation Technology, Volume 24, Number 5,
May, 1977, pages 55-62.
6-8 Lomas, D. J., "Selecting the Right Flowmeter-Part II: Comparing
Candidates," Instrumentation Technology, Volume 24, Number 6,
June, 1977, pages 71-77.
6-9 Mclntyre, Craig, "Nuclear Weight Scales in Hostile Environments,"
Advances in Instrumentation, Volume 36, Part 2, Proceedings
of the ISA Conference and Exhibit, Anaheim, California, October
6-8, 1981.
6-10 Olszewski, Richard, "Conditioning Air for Pneumatic Systems,"
Instruments & Control Systems, Sept., 1976, Volume 49, Number
9, Pages 119-123.
6-11 Sandford, Jim, "What You Should Know About Flow Monitoring De-
vices," Instruments Control Systems, Sept., 1976, Volume 49,
Number 9. Pages 25-32.
6-12 Watson, Bruce, "Magnetic Flowmetering: Problems and Solutions,"
Engineering and Mining Journal. Oct., 1973, Volume 174, Number
10. Pages 96-97.~ —
6-13 Wallace, Leonard M., "Sighting in on Level Instruments," Chemical
Engineering, February 16, 1976, Pages 95-104.
6-14 Webb, A. S., "Electromagnetic Flowmetering," Instrumentation
Technology, Journal of the Instrument Society of America7"Vo"lume
21, Number 3, March, 1974, pages 29-36.
339
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340
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Maintenance
7-1 Creason, S. C., Selection and Care of pH Electrodes. Chemical
Engineering. Octobe'r 23, 1978. pp. 161-163.
7-2 Cross, F. L., Jr. and H. E. Hesketh. Handbook for the Operation
and Maintenance of Air Pollution Control Equipment. Technomic
Publishing Co., 1975.
7-3 Czuchra, P. A., "Operation and Maintenance of a Particulate
Scrubber System's Ancillary Components." Presented at the U.S.
EPA Environmental Research Information Center Seminar on Operatin
and Maintenance of Air Pollution Equipment for Particul ate Control.
Atlanta, Georgia. April 1979.
7-4 Gilbert, W., "Troubleshooting Wet Scrubbers." Chemical Engineering,
October 24, 1977. pages 140-144. ;
7-5 Kelly, W. J. Maintaining Venturi - Tray Scrubbers. Chemical
Engineering, December 1978. pp. 133-137.
7-6 Schifftner, K. C. Venturi Scrubber Operation and Maintenance.
Presented at the U.S. EPA Environmental Research Information
Center Seminar on Operatin and Maintenance of Air Pollution
Equipment for Particulate Control. Atlanta, Georgia, April 1979.
341
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342
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Bibliography: Industrial Application
8-1 Carpenter, B. H., D. W. Van Osdell, D. W. Coy; and R. Jablin.
"Pollution Effects of Abnormal Operations in Iron and Steel
Making - Volume II. Sintering, Manual of Practice." U.S. Environ-
mental Protection Agency. Publication 600/2-78-1186. June 1978.
8-2 Ensor, D. S., B. S. Jackson, S. Calvert, C. Lake, D. V. Wallon,
R. E. Nilan, K. S. Campbell, T. A. Cahill, and R. G. FLocchini.
Evaluation of a Particulate Scrubber on a Coal-Fired Utility
Boiler. EPA Contract No. 68-02-1802, November 1982.
8-3 Ekono, Inc. Environmental Pollution Control, Pulp and Paper
Industries, Part I-Air. U.S. Environmental Protection Agency,
Research Triangle Park, N.C. Publication 625/7-76-01. October
1976.
8-4 Environmental Science and Engineering, Inc. Field Surveillance
and Enforcement Guide: Wood Pulping Industry. U.S. Environmental
Protection Agency, Research Triangle Park, N.C. Publication
450/3-75-027. March 1975.
8-5 JACA Corporation. Model Operation and Maintenance Guidelines
for Asphalt Concrete Plants. U. S. Environmental Protection
Agency, Washington, D.C. Final Report. Contract No. 68-01-4135,
Task 44.
8-6 Kemner, W. F. and R-. W. Mcllvaine. Review of Venturi Scrubber
Performance on Q-BOP. Vessel C at the Fairfield Work of the
United States Steel Corporation, Birmingham, Alabama. Final
Report to U.S. Environmental Protection Agency. Contract 68-01-4147
Task 03. Feburary 1979.
8-7 LaMantia, C. R., R. R. Lunt, I. L. Jashnani, R. G. Donnelly,
E. Interess, L. R. Woodland, and M. E. Adams, "Application of
Scrubbing Systems to Low Sulphur/Alkaline Ash Coals," EPRI FP-595,
December 1977.
8-8 Lemon, E. D. Wet Scrubbing Experience with Fine Borax Dust.
Journal of the Air Pollution Control Association, Volume 27,
Number 11: Pages 1020-1052. November 1977.
8-9 National Asphalt Paving Association. The Maintenance and Operation
of Exhaust Systems in the Hot Mix Plant. Information Series
52 (second edition) and 52A (combined volumes). 1975.
8-10 Lemon, E. "Wet Scrubbing Experience with Fine"Borax DiTstr." Second
EPA Fine Particle Scrubber Symposium. U.S. Environmental Protection
Agency, Research Triangle Park, N.C. Publication 600/2-77-193
pages 25-34. September 1977.
343
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Bibliography: Industrial Applications
8-11 Nixon, D., and C. Johnson. "Particulate Removal and Opacity
Using a Wet Venturi Scrubber - The Minnesota Power and Light
Experience." Second Symposium on the Transfer and Utilization
of Particulate Control Technology. U.S. Environmental Protection
Agency, Research Triangle Park, N.C. Publication EPA-600/9-80-
039a. September 1980.
8-12 Patankar, U., and K. E. Foster. "Evaluation of the Drum-Mix
Process for Asphalt Concrete Manufacturing." Presented at the
Seminar on Asphalt Industries Environmental Solutions. January
1978.
8-13 PEDCo Environmental, Inc. Operation and Maintenance of Particulate
Control Devices in Kraft Pulp Mill and Crushed Stone Industries.
Environmental Protection Agency, Research Trianlge Parkj N.C.
Publication 600/2-78-210. October 1978.
8-14 Scheroenan, J. A., and L. V. Binz. "Controlling Air Pollution
While Recycling Asphalt Pavements Through a Drum Mix Plant."
Presented at the Canadian Technical Asphalt Association Meeting.
November 1979.
8-15 Steiner, B. A. and Thompson, B. J. Wet Scrubbing Experience
for Steel Mill Applications. Second EPA Fine Particle Scrubber
Symposium. U.S. Environmental Protection Agency, Research Triangle
Park, N.C. Publication EPA 600/2-77-193. pages 5-24. September
1977.
8-16 Steiner, B. A., and R. J. Thompson. Wet Scrubbing Experience
for Steel Mill Applications. Journal of the Air Pollution Control
Association, Volume 27, Number 1: Pages 1069-1975. November
iy/7.
8-17 U.S. Environmental Protection Agency. Atmospheric Emission for
the Pulp and Paper Manufacturing Industry. Publication EPA-450/1-73-
002. September 1973.
344
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Liquor Analysis
9-1 American Society of Testing Methods. Annual Book of ASTM Standards,
Part 31. Water. "Standard Test Method for Surface Tension of
Water." 1982.
9-2 Franson, M. A., "Turbidity," Standard Methods for the Examination
of Water and Wastewater. Fourteenth Edition, Published by American
Public Health Association, 1976.
345
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346
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General
10-1 Beachler, D., and J. A. Jahnke. APTI Course 413. Control of
Participate Emissions. Student Manual. EPA 450/2-80-066, October
1981.
10-2 Calvert, S., J. Goldshihd, D. Leith, and D. Mehtor. Wet Scrubber
System Study, Volume I, Scrubber Handbook. EPA-R2-7s-118a (PB-213--
016), August 1972.
10-3 Dickerson, R. C., and B. N. Murthy. Study of Wet Scrubbers for
Odor Control. Preprint, EPA, RTP, N.C., National Environmental
Research Center, 1973.
10-4 Drockta, H., and R. L. Lucas. Information Required for the Selec-
tion and Performance Evalution of Wet Scrubbers. Journal of
the Air Pollution Control Association, Volume 22, Number 6:
Pages 459-462. June 1972.
10-5 Eckert, J. S. Wet Packed Gas Scrubbers. Australian Chemical
Process Engineering (Sydney), Volume 25, Number 9: Pages 13-18.
September 1972.
10-6 Ellison, W., and R. M. Mark. Designing Large Wet Scrubber Systems.
Power Volume 116, Number 2: Pages 67-69. February 1972.
10-7 Gardenier, H. E. A Manufacturer's View of Scrubber Collectors.
Presented at Specialty Conference on Design, Operation, and
Maintenance of High Efficiency Particulate Control Equipment.
St. Louis, March 29-30, 1973.
10-8 Mayinger, F., and M. Neumann. Dust Colleciton in Venturi-Scrubbers.
German Chemical Engineering, Volume 1, Number 5: Pages 289-293.
November 1978.
347
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348
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Bibliography: Alkaline Additions
11-1 Elder, H. W. and W. H. Thompson, "Removal of Sulfur Dioxide
from Stack Gases: Recent Developments in Lime-Limestone Wet
Scrubbing Technology," Transactions of the American Society
of Mechanical EngineersT July,1973, Pages 150-154.
11-2 Rosenbert, H. S., Et a!., "Construction Materials For Wet Scrub-
bers," Volume I, EPRI Final Report No. CS-1736, March 1981,
Pages 3/59 - 3/64.
11-3 Anonymous, "Lime for Water and Wastewater Treatment," BIF Engineer-
ing Data, June, 1969.
349
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350
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APPENDIX B - WORKSHOP FORMS
351
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352
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Sample Critique Form
Wet Scrubber Inspection Techniques
Location
Date
I. For each statement circle the one response that is the closest to your
opinion.
1. Overall, I think this program was:
a. excellent
b. good
c. fair
d. poor
2. The program content was geared to a level that was generally:
a. appropriate for my background
b. too elementary
c. too difficult
d. inappropriate for my background
3. I think the organization of the program material was:
a. completely clear and useful; excellent
b. for the most part, clear and useful; good
c. some topics were organized in a clear and useful manner, while others
were not; fair
d. there was little apparent organization in this course; poor
4. After reading the progarra handouts, I think they are:
a. well written and useful documents
b. fairly well written documents, but nevertheless useful
c. poorly written documents that ai*e of limited utility
d. neither well written nor useful documents
e. I have not been able to read the manuals yet
5. The amount of time allotted for this program was:
a. sufficient
b. too long
c. too short
d. this program should last number of days
6. For future programs, there should be: - — .... ~ .
a. no substantive changes
b. more practical application of the program material
c. more theory presented as a basis for the material taught
d. more of a "balance" provided between theory and practical application
353
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Sample Critique - Wet Scrubber Inspection Techniques
Location
Date
II. Please check the statement that represents the extent of your agreement
with each of the following statements. READ EACH ITEM CAREFULLY.
Strongly Agree Disagree Strongly No
Agree Disagree Opinion
11. The program content was
useful for my professional
growth.
12. The program content was
what I had expected.
13. The program content was too
complex.
14. The program content was too
simple.
15. The program content was
up to date.
16. During the program I felt
challenged to learn.
17. Generally, the program materials
were presented in an interesting
manner.
18. The program content was well
coordinated among the speakers
19. The speakers were well
prepared for most class sessions._
20. The speakers were quite
knowledgeable about their subject
areas.
354
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Sample Critique - Wet Scrubber Inspection Techniques
Location
Date
Strongly Agree Disagree Strongly No
Agree Disagree Opinion
21. The questions raised during the
lectures were usually answered
to my satisfaction.
22. The production quality of the
audio-visual materials was
technically adequate.
23. The audio-visual materials aided
my understanding of the topics
presented.
24. Overall, I was pleased with this
program.
25. I think my technical skills
and/or knowledge have been
strengthened was a result of
this program
26. I think I will be able to use
what I have learned from this
program in my current position.
III. Additional comments
27. The "best" part of this program was:
28. The "worst" part of this program was:
355
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Sample Critique - Wet Scrubber Inspection Techniques
Location
Date
29. I consider the most needed improvements in this program to be:
30. Other Comments:
V. General Information:
31. Years of air pollution experience:
a. less than 2 years
b. between 2 and 5 years
c. between 5 and 10 years
d. more than 10 years
32. Present responsibilities .(circle all which apply)
a. field inspection
b. permit review
c. stack sampling
d. management and supervision
e. ambient air monitoring
f. other
356
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Sample Registration Form
357
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United States
Environmental Protection
Agency
Office of Air and Radiation
Office of Afr Quality Planning and Standards
Research Triangle Park, NC 27711
Official Business
Penalty for Private Use
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If your address is incorrect, please change on the above label;
tear off; and return to the above address
If you do not desire to continue receiving this technical report
series, CHECK HERE D; tear off label; and return it to the
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