United States Office of Air Quality EPA-340/1 -88-007
Environmental Protection Planning and Standards July 1988
Agency Washington DC 20460
Stationary Source Compliance Series
vvEPA Municipal Waste
Incinerator
Field Inspection
Notebook
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EPA 340/1-88-007
Municipal Waste Incinerator
Field Inspection Notebook
Prepared by:
Richards Engineering
Durham, North Carolina 27705
and
Entropy Environmentalists, Inc.
Research Triangle Park, North Carolina 27709
Under Contract No. 68-02-4462
Work Assignment No. 15
Prepared for:
EPA Project Officer: Aaron Martin
EPA Work Assignment Manager: Pamela Saunders
U.S. ENVIRONMENTAL PROTECTION AGENCY
Stationary Source Compliance Division
Office of Air Quality Planning and Standards
Washington, DC 20460
July 1988
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DISCLAIMER
This manual was prepared by Richards Engineer-
ing and Entropy Environmentalists, Inc. for the
Stationary Source Compliance Division of the U.S.
Environmental Protection Agency. It has been com-
pleted in accordance with EPA Contract No. 68-02-
4462, Work Assignment No. 15. The contents of this
report are reproduced herein as received from the
contractor. The opinions, findings, and conclu-
sions expressed are those of the authors and not
necessarily those of the U.S. Environmental Protec-
tion Agency. Any mention of product names does not
constitute endorsement by the U.S. Environmental
Protection Agency.
The safety precautions set forth in this manual
and presented at any training or orientation session,
seminar, or other presentation using this manual
are general in nature. The precise safety precau-
tions required for any given situation depend upon
and must be tailored to the specific circumstances.
Richards Engineering and Entropy Environmentalists,
Inc. expressly disclaim any liability for any per-
sonal 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.
111
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TABLE OF CONTENTS
Page
Disclaimer iii
Safety Guidelines v
REFERENCE SECTION 1
1. Inspection Manual Introduction 3
1.1 Background Information 3
1.2 Purpose 5
1.3 Organization and Scope of the Notebook 6
1.3.1 Organization 6
1.3.2 Scope 7
1.4 Limitations of This Manual 8
2. Inspection of Waste Combustion Sources 10
2.1 Background Information 10
2.1.1 Diversity and Variability of
Municipal Waste Incineration 10
2.1.2 Pollutant Formation and Destruction
Mechanisms 15
2.2 General Incinerator Plant Components 27
2.2.1 Waste Storage and Handling 27
2.2.2 Energy Conversion and Utilization 28
2.2.3 Residual Disposal 29
2.2.4 Waste Combustion and Air Pollution
Control ' 30
2.3 Safety Considerations 42
2.3.1 Walking Hazards in Waste Receiving
and Handling Areas 42
2.3.2 Contact with Wastes and RDF Fuels 42
2.3.3 Eye Hazards Involved in Observing
Combustion Conditions 42
2.3.4 Internal Inspections Prohibited 43
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TABLE OF CONTENTS (Continued)
Page
3. Inspection of Dry Scrubbers 45
3.1 Components and Operating Principles of
Dry Scrubber Systems 45
3.1.1 Spray Dryer Absorbers 46
3.1.2 Dry Injection Adsorption Systems 50
3.1.3 Combination Spray Dryer and Dry
Injection Systems 51
3.2 General Comments 51
3.3 Safety Considerations 54
3.3.1 Inhalation Hazards Around Positive
Pressure System Components 54
3.3.2 Chemical Burns and Eye Hazards
Around the Pebble Lime and/or
Calcium Hydroxide Preparation Area 55
3.3.3 Internal Inspections Prohibited 55
4. Inspection of Electrostatic Precipitators 57
4.1 Components of Electrostatic Precipitators 57
4.2 Operating Principles 59
4.3 Safety Considerations 64
4.3.1 Inhalation Hazards 64
4.3.2 Use of Portable Instruments 65
4.3.3 Internal Inspections Prohibited 65
5. Inspection of Fabric Filters 67
5.1 Components and Operating Principles of
Pulse Jet Fabric Filters 67
5.2 Components and Operating Principles of
Reverse Air Fabric Filters 73
5.3 Safety Considerations 78
5.3.1 Hot Surfaces 78
5.3.2 Inhalation Hazards 78
5.3.3 Internal Inspections Prohibited 79
VI
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TABLE OF CONTENTS (Continued)
Page
6. Inspection of Wet Scrubbers 81
6.1 Components and Types of Wet Scrubbers 81
6.1.1 Spray Tower Scrubbers 82
6.1.2 Packed Bed Scrubbers 82
6.1.3 Venturi Scrubbers 83
6.2 Wet Scrubber Operating Principles 83
6.3 Safety Considerations 86
References 89
FIELD INSPECTION PROCEDURES SECTION 93
1. Inspection Procedures 95
1.1 Inspection Purpose and Scope 95
1.2 Levels of Inspection 97
2. Inspection of Combustion Equipment 99
2.1 Inspection Summaries 99
2.1.1 Inspection Overview 99
2.1.2 Inspection Checklists 101
2.2 Level 2 Inspection Procedures 104
2.2.1 Basic Level 2 Inspection Procedures 104
2.2.2 Follow-up Level 2 Inspection
Procedures 113
2.3 Level 3 Inspection Procedures 119
2.4 Level 4 Inspection Procedures 122
3. Inspection of Dry Scrubber Systems 125
3.1 Inspection Summaries 125
3.1.1 Inspection Overview 125
3.1.2 Inspection Checklists 127
3.2 Level 2 Inspection Procedures 130
3.2.1 Basic Level 2 Inspection Procedures 130
3.2.2 Follow-up Level 2 Inspection
Procedures 136
3.3 Level 3 Inspection Procedures 139
3.4 Level 4 Inspection Procedures 140
vn
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TABLE OF CONTENTS (Continued)
Page
143
143
143
145
147
4.2.1 Basic Level 2 Inspection Procedures 147
4.2.2 Follow-up Level 2 Inspection
Procedures 152
4.3 Level 3 Inspection Procedures 155
4.4 Level 4 Inspection Procedures 156
4. Inspection of Electrostatic Precipitators
4.1 Inspection Summaries
4.1.1 Inspection Overview
4.1.2 Inspection Checklists
4.2 Level 2 Inspection Procedures
5. Inspection of Fabric Filters
5.1 Inspection Summaries
5.1.1 Inspection Overview
5.1.2 Inspection Checklists
5.2 Level 2 Inspection Procedures
159
159
159
161
163
5.2.1 Basic Level 2 Inspection Procedures 163
5.2.2 Follow-up Level 2 Inspection
Procedures 167
.3 Level 3 Inspection Procedures 171
.4 Level 4 Inspection Procedures 174
6. Inspection of Wet Scrubbers
6.1 Inspection Summaries
6.1.1 Inspection Overview
6.1.2 Inspection Checklists
6.2 Level 2 Inspection Procedures
5.2.1
177
177
177
180
183
Basic Level 2 Inspection Procedures 183
5.2.2 Follow-up Level 2 Inspection
Procedures 189
6.3 Level 3 Inspection Procedures 193
6.4 Level 4 Inspection Procedures 195
Vlll
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TABLE OF CONTENTS (Continued)
Page
SUPPORT INFORMATION 197
Use of Portable Instruments 199
1. Temperature Monitors 199
1.1 Types and Operating Principles 199
1.2 Calibration and Routine Checks 202
2. Static Pressure Gauges 203
2.1 Types of Static Pressure Gauges 203
2.2 Calibration 203
3. Combustion Gas Analyzers 206
3.1 Types of Combustion Gas Analyzers 206
3.2 Calibration 206
3.3 Measurement Checks 207
Emission Test Method for Municipal Waste
Combustors 209
IX
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SAFETY GUIDELINES
1. DO NOT CONDUCT INTERNAL EQUIPMENT INSPECTIONS.
Offline equipment at incinerator facilities may have
a variety of significant hazards including but not
limited to: inhalation, asphyxiation, thermal burn,
chemical burn, eye, and falling hazards. Regulatory
agency inspectors should not enter equipment even
when it appears to be properly locked out and/or it
is occupied by plant maintenance personnel.
2. TAKE ALL PERSONAL SAFETY EQUIPMENT.
The minimum safety equipment for municipal incinera-
tors consists of a half face respirator with acid gas
cartridges, disposable dust/mist/fume masks, gloves,
safety glasses, safety shoes, sterile eye wash bottles,
and a hard hat. In some cases, more sophisticated
safety equipment is necessary. If all necessary
safety equipment is not available, avoid areas of
potential exposure.
3. AVOID AREAS OF SUSPECTED HIGH POLLUTANT CONCENTRATIONS.
Respirators provide only limited protection. Avoid
areas such as malfunctioning combustion equipment
operating at slight positive pressures, leaking ex-
pansion joints downstream of fans, fugitive emissions
from positive pressure equipment, and any area with
poor ventilation.
4. DO NOT DO ANYTHING WHICH APPEARS DANGEROUS.
If you think that it may be dangerous, it probably is!
Do not abdicate your safety judgement to plant per-
sonnel who may or may not be safety conscious.
5. NEVER HURRY DURING INSPECTIONS.
This causes careless walking and climbing accidents.
6. DO NOT ASK PLANT PERSONNEL TO TAKE UNREASONABLE RISKS.
Do not ask plant personnel to take risks to aid you
compile inspection data. Limit the inspection as
necessary to avoid health and safety hazards.
XI
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SAFETY GUIDELINES (Continued)
7. INTERRUPT THE INSPECTION IF,YOU FEEL SICK.
Interrupt the inspection immediately whenever you
have any of the following symptoms: headache, nausea,
dizziness, drowsiness, loss of coordination, chest
pains, shortness of breath, vomiting, and eye or nose
irritation. These symptoms may be caused by exposure
to toxic pollutants even though there is no odor.
8. FLUSH EYES CONTACTED BY ALKALINE MATERIALS.
It is important to flush eyes as soon as possible
after alkaline materials such as calcium hydroxide
or quick lime are contacted. Flush for 15 to 30
minutes. Get medical attention even if you think
the exposure was minor.
9. SHOWER IMMEDIATELY IF CONTACTED BY CHEMICALS.
In the unlikely event that you are splashed with
chemicals or waste materials, remove affected cloth-
ing and shower immediately for a period of at least
15 minutes.
10. USE PROTECTIVE CLOTHING AND GLOVES.
This equipment is needed when there is a risk of
contact with incinerator bottom ash, air pollution
control device solids, alkaline materials, or waste
sludges and solids. Gloves are also needed for
climbing abrasive and/or hot ladders. Contaminated
work clothes should either be discarded or washed
separately from personal clothes.
11. WEAR HEARING PROTECTION.
Hearing protection should be used whenever required
by the plant and whenever it is difficult to hear
another person speaking normally from a distance of
3 feet.
12. USE GROUNDING/BONDING CABLES ON PROBES.
This is especially important downstream of
electrostatic precipitators due to the possiblities
of injuries resulting from severe muscle spasms
caused by contact with high static voltages.
xn
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SAFETY GUIDELINES (Continued)
13. AVOID SEVERELY VIBRATING EQUIPMENT.
Equipment such as fans can disintegrate suddenly.
Notify plant personnel immediately of the condition
and leave the area.
14. PLANT PERSONNEL MUST BE PRESENT DURING THE INSPECTION,
Never conduct plant inspections alone. Plant per-
sonnel accompanying you must be knowledgeable in
plant operations, general safety procedures, and
emergency procedures.
15. FOLLOW ALL PLANT AND AGENCY SAFETY REQUIREMENTS.
Limit the inspection as necessary to ensure that
you completely adhere to all plant and agency
health and safety requirements.
Xlll
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REFERENCE SECTION
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1. INSPECTION MANUAL INTRODUCTION
1.1 Background Information
Municipal waste incinerators are not a new type of
air pollution source. They were included on the first
emission inventories that provided the basis for the
first set of comprehensive air pollution control regu-
lations between 1971 and 1975. They were one of the
first five sources for which New Source Performance
Standards were promulgated. Accordingly, municipal
waste incinerators have been inspected routinely for a
long time. In fact, one of the first source specific
inspection manuals prepared by EPA concerned municipal
waste incinerators [1]. Now fifteen years later, there
are numerous reasons why an updated inspection manual
is needed.
The limited availability of suitable landfill
space coupled with lessened public acceptance of land-
fills has created a very strong demand for thermal
incineration alternatives. Accordingly, there has been
a surge in the construction o.f municipal waste incinera-
tors. As of June 1987, there were 210 individual
facilities in the design or planning stages [2]. The
combined capacity of these facilities is estimated at
193,400 tons of waste per day which is four times the
total existing incinerator capacity. Obviously, muni-
cipal waste incineration will be an increasingly import-
ant source category as these new units come on-line
between 1987 and 1993. Furthermore, it is reasonable to
anticipate continued growth in the post-1993 period.
The characteristics of municipal waste incinera-
tion have changed dramatically since the 1970's. The
early facilities were intended primarily for the reduc-
tion of waste volume. New facilities now recover energy
in addition to reducing waste volume. Energy is general-
ly recovered in the form of steam, however, a few
larger facilities also generate electricity.
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The types of combustion systems have evolved sub-
stantially to allow energy recovery, improved combustion
efficiency, and reduced pollutant generation. It is
not surprising that many of the innovations and refine-
ments have come from Europe and Japan where the
economics and availability of direct landfill disposal
reached a critical stage long before the United States.
There have been substantial improvements in mass burn
technology which accounts for 59% of the planned new
capacity [2]. The refuse derived fuel (hereafter termed
RDF) systems that represent 20% of the new capacity
were only in the research stages at the time that the
previous inspection manual was prepared. There also
has been substantial growth in the smaller capacity
modular starved air and modular excess air type systems.
Accordingly, the scope of this inspection notebook is
much broader than the previous publication.
Inspection of municipal waste incinerators was pre-
viously oriented strictly toward particulate emissions
and opacity. Now, there is concern over additional
pollutants, especially hydrochloric acid, hydrofluoric
acid, metals, nitrogen oxides, and a variety of organic
pollutants such as dioxins and furans. To minimize
emission of these pollutants, many States and local
agencies have imposed specific permit restrictions
and/or have adopted strict emission limitations. These
requirements are in the form of equipment design stand-
ards, equipment performance standards, and pollutant
emission limits. Generally, the particulate emission
limitations are well below the NSPS requirement for
municipal waste incinerators which are currently being
revised. Accordingly, the on-site inspection conducted
by State and local agencies must address all of these
requirements that go beyond present Federal requirements,
The evolution and growth of the municipal waste
incinerator industry has been matched by changes in the
style and sophistication of the air pollution control
systems. Dry scrubbing systems for acid gas control
are now operating on a few existing sources and are
expected on many units in the planning stages. This
control technology did not exist in the early 1970's.
Several new approaches for nitrogen oxides control are
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presently in use and these also will find more applica-
tions especially in areas having difficulty achieving
photochemical oxidant ambient standards. Baghouses now
share the particulate control duties that were previously
performed mainly by electrostatic precipitators. There
have been substantial component design improvements in
both fabric filters and electrostatic precipitators.
Continuous emission monitors for opacity, sulfur dioxide,
nitrogen oxides, and hydrogen chloride are now commonly
used for the early identification of combustion system
and/or air pollution control system problems. All of
these changes obviously affect the scope of the air
pollution inspection.
There has also been refinements in air pollution
source inspection techniques. The Baseline Inspection
Technique [3] has been developed under the sponsorship
of EPA to improve the effectiveness of on-site inspec-
tions. The inspections have been categorized in four
separate levels ranging from simple surveillance activi-
ties to detailed engineering evaluations. The more
advanced inspections now may include the use of agency-
supplied portable instruments to provide certain impor-
tant data which is not otherwise available. The major
principles and practices included within the scope of
air pollution source inspections have been summarized
in an EPA general procedures manual titled, "Air Com-
pliance Inspection Manual [4]."
For all of the reasons discussed above, it is
necessary to revise and expand the previously published
inspection guidelines for this source category.
1.2 Purpose
The primary purpose of this manual is to assist
Federal, State, and local agency inspectors in conduct-
ing effective and safe Level 2 and Level 3 inspections
of municipal waste incinerators. A Level 2 inspection
is an on-site, walk through inspection that includes an
evaluation of present operating data as indicated by
plant instruments, an evaluation of operating records,
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and general observations of system condition and perform-
ance. A Level 3 inspection is a more comprehensive
evaluation of specific conditions of concern. Portable
instruments may be used in some Level 3 inspections.
These two types of inspections comprise the majority of
inspections conducted and are described in more detail
in Reference 4.
Checklists are not provided for Level 1 inspections
since these simply involve surveillance of visible
emissions from off-site locations. Level 4 inspections
are included but are not addressed in detail since they
are conducted only by senior inspectors and agency
management personnel. Furthermore, the types of activi-
ties included in the Level 4 inspection are not unique
to any one source category such as municipal waste
incineration. Information regarding Level 4 inspec-
tions is available in Reference 4 or in the U.S. EPA
Air Pollution Training Institute course #455 manual [5].
1.3 Organization and Scope of the Notebook
1.3.1 Organi zation
The notebook has been organized into the three
distinct parts listed below to address the differing
needs of field inspectors:
Reference information
Field inspection procedures
Support information
A reference section is presented first to provide
a brief overview of the numerous technical issues con-
cerning municipal waste incineration and air pollution
control. This section is needed due to the voluminious,
widely scattered literature concerning these subject
areas. It is also intended to help inspectors who
inspect many different types of air pollution sources
brush up on the characteristics of municipal waste
incinerators immediately before beginning the inspection,
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Inspectors who are already familiar with the types
of equipment in service and the common operating problems
may wish to go directly to the field inspection procedures.
This material has been divided three ways to make the
notebook as flexible and generally useful as possible.
The three inspection procedures formats are listed below.
oInspection overview
oInspection checklists
o step-by-step inspection procedure descriptions
An inspection overview summary has been presented
first in each of the six inspection procedures sections
to briefly summarize the fundamental approach being
used to evaluate the equipment compliance status.
Inspectors can apply these concepts to unique systems
not explicity covered in this manual.
Checklists have been prepared in a format that can
be quickly scanned during the field inspection. They
have been arranged in categories of Basic Level 2,
Follow-up Level 2, Level 3, and Level 4 inspections.
They serve as reminders of additional checks which
should be made before concluding the inspection and are
also helpful when discussing the inspection scope during
the preinspection meeting with the source personnel.
Detailed summaries of each inspection step are
presented following the checklists. To the maximum
extent possible, these provide specific information on
how to compile the necessary data and observations.
Inspectors should refer to one or more of the specific
discussions if questions arise during the inspection.
1.3.2 Scope
The scope of the manual includes many diverse
types of municipal waste combustion systems and air
pollution control systems. The combustion techniques
have been grouped into three categories listed below to
parallel the material presented in EPA's Municipal
Waste Combustion Study [6].
o Mass Burn Systems
o Refuse Derived Fuel Systems
o Modular Systems
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Despite the design variability of systems included
in any of these groups, the inspection steps within
each category are relatively similar. The remainder of
the inspection sections concern various types of air
pollution control systems. All of these sections are
modified and expanded versions of material previously
prepared by the author and included in the "Field
Inspection Notebook [7]." The format of this notebook
is similar to this predecessor document.
The dry scrubbing section addresses the three
separate types of systems listed below:
o Spray dryer absorber
o Dry injection
o Combined spray dryer and dry injection
It should be noted that there is no generally
accepted terminology for the types of dry scrubbers.
Accordingly, the terms used in this notebook may not be
consistent with other texts.
1.4 Limitations of This Manual
It is important to note that certain facilities
have unique design and/or operating procedures. It is
impossible for any reasonably sized notebook to address
all of these site specific items. Also, some inspec-
tion steps included in this notebook are not relevant
at certain facilities. Inspectors must tailor their
work to the specific site.
General inspection safety guidelines have been
included in this notebook. It is not possible to
anticipate all site specific hazards or combinations of
hazards. Accordingly, inspectors must exercise their
judgement in regard to what is included in the inspection.
Nothing should be done that endangers either the inspector
or source personnel.
The information provided in this notebook will
help inspectors to develop an independent and accurate
assessment of the source's compliance status. Much of
8
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the information will be of value in evaluating any
corrective actions proposed by the source personnel.
However, inspectors should not use the inspection data
and observations to demand or prescribe specific cor-
rective actions or operating procedures. Operation
and maintenance requirements of specific sources are
inherently complex and a one or two day inspection is
not designed to compile all of the information neces-
sary to prepare specific procedures. Furthermore,
there are numerous legal reasons why inspectors should
avoid prescribing specific actions.
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2. INSPECTION OF WASTE COMBUSTION SYSTEMS
The primary purpose of this section is to present
background information concerning waste combustion
systems and the generation of air pollutants. Later
introductory sections cover the various types of air
pollution control systems used on municipal waste
incinerators.
The information concerning combustion equipment
illustrates the purposes and limitations of the inspec-
tion steps presented in Section B of this notebook.
2.1 Background Information
2.1.1 Diversity and Variability of Municipal Waste
Incineration
One of the fundamental principles of the Baseline
Inspection Technique is that each plant and each operat-
ing system within a plant should be treated as unique.
Shifts in site specific operating conditions are used
to evaluate performance. This approach is especially
important in the case of municipal waste incinerators
due to the considerable diversity of the equipment
presently in service and the equipment being developed.
The capacities of the waste combustion units range
from very small (5 to 50 tons per day) to very large
(1000 to 3000 tons per day). Factory assembled modular
incinerators are generally used for the small plants.
Large plants utilize either mass-burn reciprocating
grate or rotary combustor incinerators, or refuse
derived fuel (RDF) production facilities in conjunction
with spreader stoker boilers. Combustion conditions
and pollutant generation/destruction mechanisms can be
quite different in these three substantially different
types of combustion systems. They also differ with
respect to their vulnerabilites to operating problems
and their maintenance requirements.
11
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The large majority of systems installed or planned
since 1980 incorporate energy recovery. This is general-
ly in the form of steam generation. However, some large
facilities also generate and sell electrical power. To
recover energy, it is necessary to install boiler tubes
in the main combustion chamber and to add steam super-
heater sections and feedwater economizers. These heat
exchangers effectively cool the gas stream down to
levels manageable in air pollution control systems.
Older municipal waste incinerators without heat
recovery have a water spray cooling section after the
combustion chamber in order to lower gas temperatures.
The presence of the heat exchange equipment in the newer
systems also affects the pollutant generation/destruction
mechanisms since it affects the diversity of localized
gas temperatures in the furnace area and since it pro-
vides metal surface area for possible catalytic reactions,
Waste composition varies from location to location.
Partially, due to this variability, it was necessary to
modify combustion equipment being installed in the U.S.
that was originally developed in Europe and Japan.
Also, it is difficult to compare the formation and
emission rates of certain pollutants in plants in the
United States with the European and Japanese plants.
The variability of waste composition at a given
site over time is even more of a problem than the
variability of waste from site to site. Sudden changes
in waste quality can upset combustion and lead to high
short term pollutant emission rates. Substantial equip-
ment damage and unscheduled outages also occur due to
problems with the waste feed characteristics.
It is interesting to compare fuel variability
problems of municipal waste incinerators (all types)
with the operations of pulverized coal-fired boilers
and stoker coal-fired boilers. General operating con-
ditions are provided in Table 2-1. A number of compar-
isons are useful to establish the proper perspective.
These are itemized below.
12
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(1) Heating Value - The heating values of the fuel
for municipal waste incinerators is 20 to 50%
of those of bituminous coal-fired boilers.
This means that the quantity of the fuel
necessary to produce a pound of steam is 2 to
5 times greater than it is in the case of the
coal boilers. Fuel handling is even a problem
for coal-fired systems!
(2) Fuel Sizing - The variability of coal sizing is
a major problem for both pulverized coal-fired
and stoker coal-fired boilers. However, munici-
pal waste has much greater fuel size variability.
(3) Maximum Fuel Size - Municipal waste includes
bulky, partially noncombustible materials such
as refrigerators, tires, car batteries, furni-
ture parts, rags, and cables. Failure to remove
these prior to firing leads to serious feed
mechanism and/or incinerator problems. Coal-
fired boilers are challenged only by small bits
of scrap metal.
(4) Ash Fusion Temperature - Due primarily to the
presence of glass, the temperature at which
the "ash" becomes fluid is much lower for
municipal waste incinerators than for coal-
fired boilers. Furthermore, the variability
of waste composition and the complexity of ash
chemistry makes it difficult to accurately
predict this temperature. Low ash fusion
temperatures lead to a variety of severe operat-
ing conditions including slagging of the furnace
walls, clinker formation, and pluggage of the
grates. Even coal-fired boilers have ash
fusion problems and they operate at the much
more forgiving fusion temperatures of 2100 to
2500°F.
13
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Table 2-1.
Fuel Differences Between Municipal Waste
Incinerators and Selected Types of
Coal-Fired Boilers
Heating Value (Btu/Lb as fired)
Municipal Waste Incinerators
Pulverized Coal (Bituminous)
Stoker Coal (Bituminous)
Maximum Fuel Size (as fired)
Municipal Waste Incinerators
Pulverized Coal (Bituminous)
Stoker Coal (Bituminous)
Normal Fuel Sizing
Municipal Waste Incinerators
Pulverized Coal (Bituminous)
Stoker Coal (Bituminous)
Fuel Sizing Variability
Municipal Waste Incinerators
Pulverized Coal (Bituminous)
Stoker Coal (Bituminous)
Sensitivity to Fuel Sizing
Municipal Waste Incinerators
Pulverized Coal (Bituminous)
Stoker Coal (Bituminous)
Ash Fusion Temperature (°F)
Municipal Waste Incinerators
Pulverized Coal (Bituminous)
Stoker Coal (Bituminous)
2,000 - 7,500
9,000 - 13,500
9,000 - 13,500
1 ft. - 2 ft.
1/16 in.
1/2 in.
1/32 in. - 2 ft.
95% past 200 mesh
1/32 in. - 1/2 in.
Extreme
Minimal
Moderate
Extreme
Moderate
Extreme
1300 - 1600
2100 - 2500
2100 - 2500
The purpose of Table 2-1 and the comparison with
coal-fired boilers is to illustrate one basic point:
garbage is not an especially good fuel. Occasional
problems at municipal waste incinerators should be
anticipated considering that even well designed and
operated coal-fired boilers sometimes have serious fuel
quality and fuel variability problems. Agency inspectors
14
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should exercise some patience and restraint when
inspecting municipal waste incinerators because of the
inherently lower fuel quality. The operating problems
are often more complex than they may seem. Furthermore,
there are no magic design formulas or special operating
procedures that ensure 100% reliability. Burning
garbage is not easy!
Inspection of municipal waste incinerators is
complicated by both the diversity of the industry and
the variability of equipment performance. The problem
is not going to get any easier in the next several
years since the municipal waste incineration industry
is relatively young and growing rapidly. A relatively
large number of individual equipment manufacturers are
developing innovative combustion equipment and air
pollution control devices to minimize operating problems
and to gain a substantial share of this growing market.
The diversity of the industry will increase until several
dominant equipment designs are established. The varia-
bility of performance will continue until plant personnel,
with the assistance of equipment manufacturers and
consultants, optimize performance of these relatively
new systems.
2.1.2 Pollutant Formation and Destruction Mechanism
Table 2-2 contains an extensive list of pollutants
of concern during most Level 2 or Level 3 inspections
of municipal waste incinerators. This is one of the
unique aspects of municipal waste incinerator inspections
since most other source categories involve only one or
two main pollutants.
As indicated in Table 2-2, the formation rates and
destruction rates of some of these are strongly influ-
enced by combustion conditions. In other cases, the
formation rates are a function primarily of the waste
composition. Obviously, the focus during the inspection
of the combustion equipment is on those factors that
significantly affect the formation/destruction mechanisms
of the pollutants of interest. Some of the important
combustion equipment parameters can be monitored. Others
involve very subtle and complex phenomenon which can
only be evaluated by indirect means.
15
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Table 2-2. Pollutant Formation/Destruction
Pollutant Influenced Strongly Influenced Strongly
by Combustion System by Waste Composition
Design/Operation
Particulate (total) Yes Yes
Particulate, metals Yes Yes
Hydrogen chloride No Yes
Hydrogen fluoride No Yes
Sulfur dioxide No Yes
Sulfuric acid Yes Yes
Nitrogen oxides Yes Yes
Organic compounds (total) Yes No
Dioxins and furans Yes Yes
2.1.2.1 Total Particulate Matter and Metals
Flyash is generated by three main mechanisms during
the incineration of municipal waste: (1) suspension of
noncombustible materials, (2) incomplete combustion of
organic material contained within small particles en-
trained in the flue gas, and (3) condensation of vapor-
ous material including both unburned organics and metals.
The flyash particles leaving the combustion equipment
are the chemical and physical sum of these three dif-
ferent generation mechanisms. The bulk of the particles
is composed of the noncombustible fraction along with
any partially oxidized organic particulate. The surfaces
of the particles have small quantities of the condensed
species. The average particle size is in the range of
1 to 5 microns which is similar to other combustion
sources. Particles in this size range are invisible
and as many as 50 could be lined up across the diameter
of a single human hair.
The total particulate quantities leaving the com-
bustion chamber are in the range of 2 to 10 grains per
actual cubic foot of gas (gr./ACF). The particulate
generation rates at any given site are a function of
the three factors listed below.
o Ash content of waste feed
o Adequacy of combustion
o Fraction of material removed as bottom ash
16
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Waste feeds to municipal waste incinerators have
ash contents in the range of 5 to 25% by weight. These
are high values considering the very low fuel heating
values discussed in the earlier section. The ash primar-
ily consists of glass, metal wastes (e.g. food cans and
household hardware), and any sand or clay accumulated
on vegetation. The ash content can be minimized by
the removal of any bulky, noncombustible items such as
batteries, cables, and small appliances. Shredding of
the wastes will also help lower ash content slightly.
The fraction of material removed as bottom ash
depends primarily on the method of introduction of the
waste into the combustion chamber and the size of the
waste at this point. In most mass-feed incinerators,
approximately 50 to 75% of the ash is removed as bottom
ash and 25 to 50% is present as flyash. There are
higher fractions of flyash in spreader stoker RDF-fired
boilers since the fuel is smaller and some particle
burning in suspension is intended. Smaller quantities
are generated in modular units, especially starved air
units. Design differences of the various types of
combustion equipment are discussed in a later subsection.
The adequacy of combustion determines the quantity
of organic char present along with the noncombustible
materials. As a general "rule-of-thumb", the flyash
removed from the particulate control device hoppers
should have a loss-on-ignition value in the range of 10
to 50%. The high organic char levels indicated by
higher than 50% loss-on-ignition levels suggest nonideal
combustion conditions.
It should be noted that there two other ash
streams generated during municipal waste incineration.
Relatively large particle, high loss-on-ignition ash is
collected in the hopper immediately downstream of the
feedwater economizer. In some plants this material is
reinjected back into the furnace. The pros and cons of
this practice will be discussed later. However, this
is not the ash stream that inspectors should evaluate
when checking the overall performance of the combustion
system. Another ash stream is the sittings removed
from the undergrate plenums. This very fine material
17
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seeps through the grate bars, stoker side rail seals,
and stoker front and rear air seals. The sittings are
a relatively insignificant ash stream and are generally
vacuumed out during each major outage.
There are a variety of common metals included in
the waste feed that can vaporize during combustion.
These metals include lead, zinc, cadmium, mercury, and
arsenic. Vapor pressure data illustrate that most of
the metals will condense back into a particulate form
by the time the gas stream reaches the particulate
control devices.
Due to the presence of a high concentration of
particles in the gas stream which can serve as conden-
sation nuclei, the metals probably condense heterogen-
eously rather than homogeneously. Since the very small
particles have greater surface area, the condensation
occurs preferentially here. Thus, there is some enrich-
ment of these small particles and unequal distribution
of the condensed materials as a function of the particle
size. This means simply that the small particles are
the most toxic. Unfortunately, small particles are
also the most difficult to remove in most air pollution
control systems.
2.1.2.2 Dioxins and Furans
For the purposes of this inspection notebook, the
terms dioxin and furan will refer collectively to the
210 isomers of these compounds. They are normally
grouped into two principal categories: (1) polychlor-
inated dibenzo-dioxins (acronym - PCDD), and (2) poly-
chlorinated dibenzo-furans (acronym - PCDF).
There are strong parallels between the formation
rates of organic pollutants such as dioxins and furans
and the formation rates of excessive particulate matter.
Both are believed to be created partially by nonuniform
and/or improper combustion system conditions. Further-
more, these organic compounds may condense on flyash
particles once the flue gas exits the high temperature
zones of the heat exchange equipment [8]. To illustrate
the extent to which combustion conditions potentially
influence dioxin/furan emissions, note that older
18
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plants designed simply for waste reduction have been
tested at PCDD emissions as high as 4000 nanograms per
normal cubic meter whereas state-of-the-art incinerators
incorporating improved designs and operational controls
have been tested as low as 12 nanograms per normal
cubic meter [ 9 ]. It should be noted that even the high
concentration indicated above is a relatively low con-
centration value when expressed in the conventional
form of ppm. The PCDD and PCDF concentrations are in
the range of 0.01 to 0.1 ppm.
There are a variety of theories concerning the
method of formation of the dioxins and furans which
have been detected in the outlet gas streams of municipal
waste incinerators. These are summarized in Table 2-3.
Table 2-3. Proposed Dioxin/Furan Formation Mechanisms
1. Vaporization of PCDD and PCDF compounds present
in waste feed to incinerator
2. Reactions between chlorinated organic precursors
such as chlorophenols and PCB
3. Chlorination of polyvinyl chloride or lignin in
waste feed by salt, HCl, or chlorine gas
4. Catalytic reactions between organic precursors
and trace metals adsorbed on flyash particles
and various chlorine compounds in the gas stream
The direct volatilization of dioxin/furan compounds
contained in the waste has been suggested by studies
done at several locations [10]. However, the quantities
of dioxin/furan found in the gas streams was much
greater than the feed quantities. Accordingly, some
formation mechanisms must also be active as the flue
gas passes through the boiler.
Despite the substantial chemical literature con-
cerning dioxin and furan formation/destruction there is
still considerable uncertainty regarding the chemical
19
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mechanisms involved in municipal waste combustion.
This is partially due to the analytical difficulties
involved with monitoring pollutants which exist in the
gas stream in parts per billion concentrations. The
problem is substantially complicated by the extreme
sampling problems involved in gaining "representative"
samples of pollutants which exist partially in the
vapor state and partially in a condensed form on the
surfaces of highly variable particles. Further
complicating the condition is the highly heterogeneous
nature of municipal waste incinerator feed composition
and combustion system operation.
Since the formation mechanisms are not fully under-
stood, there are no straight forward design procedures
or operating procedures than can prevent the formation
of PCDD and PCDF compounds. Instead reliance is placed
on the destruction of the pollutants created in the
combustion process and high efficiency collection of
the dioxin/furan containing flyash. Concerning the
combustion equipment, the EPA Municipal Waste Combustion
Study [6] presents three basic goals for controlling
the generation of dioxins/furans, namely:
o Mixing of fuel and air to minimize the
existence of long-lived, fuel-rich pockets
of combustion products
o Attainment of sufficiently high temperatures
in the presence of oxygen for the destruction
of hydrocarbon species
o Prevention of quench zones or low temperature
pathways that will allow partially reacted
fuel (solid or gaseous) from exiting the
combustion chamber
(Reference 6, Page 1-5)
There are no combustion system design or operating
parameters that can be related to the formation of
dioxin and furans. Instead, it is necessary to use a
set of indirect measurements that are logically related
to conditions conducive to dioxin and furan forma-
tion/destruction .
20
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One of the most obvious and important of these
indirect parameters is the furnace temperature itself.
A variety of laboratory research studies and field
measurement studies have indicated that gas temperatures
above 1800 °F yield very low dioxin/furan concentra-
tions [11]. In fact, the destruction efficiency-gas
temperature relationship shown in Figure 2-1, suggests
that these categories of organic pollutants are one of
the most easily destroyed during passage through the
incinerator as long as there is good vapor and oxygen
mixing.
100
10
HEXACHLORO-
' BENZENE
DIOXIN
FURANS
. 1
1COO 1100 1200 1300 1400 1500 1600
TEMPERATURE (°F)
Source: Seeker et al. [6, p. 4-6]
Figure 2-1. Temperature-Dioxin/Furan Destruction
21
-r
-------
The problem with the relationship illustrated in
Figure 2-1 is that substantial gas temperature nonuni-
formities may exist as the gas stream passes up through
the water tube lined furnace area and the other heat
exchange areas. All portions of the gas stream may not
be exposed to the same time-temperature "history."
Unfortunately, it is not possible to simply look in a
furnace/boiler and observe the "cold" zones.
Also it is somewhat difficult to accurately
monitor the gas temperature due to the temperature
nonuniformities and due to the extreme temperature
levels. Generally, thermocouples with water cooled
probes or pyrometers are used for temperature monitor-
ing and neither of these are especially discriminating
with respect to spatial temperature variability.
Accordingly, the gas temperature provides only a gross
indication of the potential for dioxin/furan survival.
The destruction temperature requirements for
dioxins and furans are also a function of the oxygen
concentrations throughout the furnace volume. The
average flue gas furnace temperatures necessary for
adequate dioxin and furan destruction are lower when
the oxygen levels increase [6]. Therefore, inspectors
should attempt to evaluate the temperature data in
conjunction with the oxygen analyzer.
Carbon monoxide monitoring data provides a useful
back-up check for evaluating potential dioxin/furan
emissions [12]. As in the case with furnace temperature,
this is an indirect indicator and it is not possible to
relate a certain concentration of CO to dioxin/furan
concentrations. However, increases in the CO levels
are indicative of combustion problems which in turn
could conceivably lead to increased pollutant emission
rates. The generally acceptable CO concentration curve
is presented in Figure 2-2. This indicates that CO
decreases rapidly as the average oxygen concentration
increases to 6 to 9% (volume basis, dry). At these
levels there is sufficient excess air to overcome major
nonuniformities in fuel-air mixing and the complex set
of combustion reactions is relatively complete. The
addition of more air than necessary results in some
22
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cooling of the furnace area since all of the oxygen,
nitrogen, and water vapor included in the air roust be
heated up to the exhaust gas temperatures. This cooling
action quenches the reactions responsible for oxidation
of carbon monoxide to carbon dioxide. Presumably, this
also quenches the reactions necessary to complete the
thermal destruction of the highly undesirable dioxins
and furans.
3 6 9 12
OXYGEN CONCENTRATION
A - Insufficient Air
B - Appropriate Operating Region
C - "Cold Burning"
Source: Seeker et al. [6, p.3-13]
Figure 2-2. Carbon Monoxide - Oxygen Profile
23
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As a general "rule-of-thumb" the carbon monoxide
concentrations should be maintained at levels below 100
ppm [12]. Excursions to1 levels in the range of 300 to
500 ppm certainly suggest possible combustion problems
and increased organic pollutant emissions. Inspectors
should ask plant personnel how they intend to respond
to increases in the monitored CO levels above 100 ppm.
Furthermore, CO records since the last inspection
should be reviewed to determine if chronic combustion
related problems exist.
2.1.2.3 Acid Gases
The sulfur dioxide emission rates from municipal
waste incinerators are directly related to the sulfur
content of the waste feed. The waste feed sulfur
contents of 0.05% to 0.25% are well below the levels of
coal-fired and No. 6 oil-fired boilers. Also, as much
as 50% of the feed sulfur is probably tied up in the
bottom ash [13]. Accordingly, sulfur dioxide concentra-
tions are typically in the range of 20 to 200 ppm with
an average value near 80 ppm [13].
The other acid gases of concern include hydro-
chloric acid, hydrofluoric acid, and sulfuric acid.
Hydrocloric acid formation is directly related to the
concentration of chlorine containing wastes being fed.
These could include polyvinyl chloride (PVC), other
chlorinated plastics, and sodium chloride. The fraction
of chlorine that is ultimately converted to hydrogen
chloride is not known. The tested concentrations
(uncorrected) of hydrogen chloride have ranged from 70
to more than 1000 ppm [13].
Hydrogen fluoride is also derived from the various
fluorinated wastes present in the feed. Tested concen-
trations are in the range of 3 to 20 ppm (uncorrected)
which is well below the levels of hydrogen chloride [13],
2.1.2.4 Nitrogen Oxides
Nitrogen oxides measurements at various existing
plants have indicated highly variable emission rates.
These have ranged from a low of 0.05 pounds per million
Btu to a high of almost 1.0 pound per million Btu [14].
Most of the measurements are in the range of 0.23 to
24
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0.63 pounds per million Btu [15], There has not been
any consistent relationship between the type of inciner-
ator and the emission rates.
The formation mechanisms are probably similar to
those involved in nitrogen oxides formation in coal-
fired boilers. These include thermal formation and fuel
nitrogen conversion [13]. In fact, the importance of
fuel nitrogen may be one of the reasons that it has
been difficult to develop correlations of nitrogen
oxides emissions and incinerator styles.
The thermal formation mechanism is highly dependent
on the furnace temperatures and oxygen concentrations.
The conditions which favor dioxin and furan destruction
are essentially identical to those that favor nitrogen
oxides formation. Accordingly, modern plants designed
to minimize the survival of the chlorinated organics
may suffer higher nitrogen oxides emissions than the
existing municipal waste incinerators.
The possible control options for reducing nitrogen
oxides emissions include (1) flue gas recirculation,
(2) Thermal DeNox (ammonia injection), (3) selective
catalytic reduction, and (4) reburning with natural gas.
Flue gas recirculation has been used successfully
on a variety of coal-fired boilers for nitrogen oxides
control. However, the potential nitrogen oxides reduc-
tions are only in the range of 20 to 50%. All of the
other control options have the capability of reducing
nitrogen oxides 50 to 70%.
The Thermal DeNox process was also developed for
coal-fired boilers. This process simply uses reactions
between ammonia and nitrogen oxides at high gas temper-
atures to yield molecular nitrogen. The ammonia is
injected through a series of nozzles immediately above
the furnace area of the incinerator as indicated in
Figure 2-3.
25
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Supcrtwater
' F.G. Exit [
/to Scrubber, '—I
' Baghouse
L«ft Hand SM* ChnMon
Source: Hurst and White [15, p.122]
Figure 2-3. Ammonia Injection Nozzle Locations for the
Thermal DeNox Process
In the Thermal DeNox process, the ammonia is
injected at an area of the furnace/boiler which is at
approximately 1800°F. This temperature range is critical.
If the gas temperatures at the injection location exceed
2200°F, the ammonia is oxidized and the resulting nitrogen
oxides emissions are actually increased rather than
being controlled. If the gas temperatures at the injec-
tion location are lower than 1600°F, unreacted ammonia
is emitted from the system [15].
26
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There are also some lingering concerns about the
possible formation of various ammonia compounds such as
ammonium sulfate, ammonium bisulfate, and ammonium
chloride. The main concerns are plume formation and
fouling of the heat exchange surfaces.
The selective catalytic technique is similar to
the Thermal DeNox process. A catalyst is added to
allow operation at much lower temperatures, to decrease
the potential for ammonia emissions from the system and
to increase the possible nitrogen oxides removal
efficiency [15]. The ammonia used for chemical reduction
of the nitrogen oxide is injected downstream from the
economizer where the temperature is in the range of 300
to 400°C (572 to 750°F). However, the catalyst is
vulnerable to poisoning due to the variety of metal and
acid compounds present in municipal waste that could
either poison or suppress the catalyst activity. Due
to the development work necessary for this process,
inspectors will not need to evaluate selective catalytic
systems in the immediate future.
Reburning techniques are also at a very early
stage of development and these also will be used on a
commercial scale for some time. Accordingly, it is not
discussed any further.
2.2 General Incinerator Plant Components
A complete municipal incinerator facility consists
of the following basic components:
Waste storage and handling
Energy conversion and utilization
Residual disposal
Waste combustion and air pollution control
2.2.1 Waste Storage and Handling
The waste storage and handling area generally
consists of a tipping floor or tipping pit for receiving
the waste from the trucks. This receiving and temporary
storage area is generally sized for several days proces-
sing rates to allow for short term plant outages. To
27
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the extent possible, the stored material should be mixed
to minimize fuel heating value and size variability [16].
As discussed in Section 2.1.1, fuel variability can
cause significant incinerator firing problems that in
turn lead to excessive particulate and organic pollutant
emissions. Therefore, the as-charged characteristics
of the fuel are the primary issue during the inspection
of this part of the facility. It is also necessary to
confirm that the operators are in fact attempting to
remove any bulky, noncombustible items which would
adversely affect the fuel-air ratios in the incinerator.
These bulky items could include large appliances, small
appliances, tires, automotive parts, and furniture.
Odor problems should also be noted while completing
the brief inspection of the waste storage area. Generally
the receiving area and incinerator charging area are
enclosed to prevent odors and to avoid wind problems in
the unloading area.
2.2.2 Energy Conversion and Utilization
The energy conversion and utilization consists
primarily of the heat exchange surfaces within the
boiler and, in a few cases, it also includes turbine
generators. The inspection of this part of the system
is generally limited to an evaluation of the steam
generation rate and the feed water rates. These two
important operating conditions are always monitored on
a continuous basis. They provide a clear indication of
the average incinerator loads and the variability of
the incinerator loads. This is a major issue with
incinerators since it is difficult to operate at low
loads without risking increased dioxin/furan and partic-
ulate emissions due to the low furnace gas temperatures.
The reason for looking at both feedwater and steam
rates is to ensure that accurate data is obtained.
Either one of the monitors could fail or provide
inaccurate readings. Since the two values should be
approximately equivalent at any given time, it is
possible to check the plant instruments.
28
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2.2.3 Residual Disposal
It is necessary to confirm that the incinerator
bottom ash and air pollution control device wastes are
disposed without creating fugitive particulate emissions.
Another issue is the possible classification as a hazard-
ous waste under RCRA regulations. If the waste material
has any one (or more) of the four characteristics
listed below, the material is labeled as hazardous.
oIgnitability,
o Reactivity,
o Corrosivity,
° EP Toxicity
The EP Toxicity test is simply an extraction type
test to determine if there are leachable components
(such as metals) in the ash which are considered toxic
(40 CFR 261.24). In the future, this test may be
replaced by the Toxicity Characteristic Leaching
Procedure [References 16 and 51 FR 21685, June 13, 1986].
Generally the bottom ash is nonhazardous. However,
the flyash can sometimes have sufficiently high concen-
trations of one or more metallic compounds to be labeled
as hazardous. This is partially due to the volatiliza-
tion of the metals in the furnace area and subsequent
condensation on flyash particles as the cooled flue
gases leave the heat exchange areas of the boiler (See
earlier discussion in section 2.2.1.). Since the gener-
ated flyash is much lower in quantity than the combustion
system bottom ash [20], there is the possibility that
mixing of the bottom ash and flyash will result in a
mixture that overall could be classified as nonhazardous.
This raises regulatory policy questions that are beyond
the scope of this notebook. Nevertheless, agency
inspectors should fully understand their agency's posi-
tion regarding mixing of bottom ash and fly ash.
If the bottom ash and/or flyash is hazardous waste
in accordance with the RCRA regulations, it must be sent
to a Subtitle C facility. These are specially designed
and operated landfills which can accept hazardous wastes.
The disposal costs are considerably higher than those
at conventional sanitary landfills.
29
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2.2.4 Waste Combustion and Air Pollution Control
The waste combustion equipment and its associated
air pollution control equipment obviously demand most
of the attention during the on-site inspection. Due to
the diversity of the various types of incinerator systems,
each of these must be discussed separately.
2.2.4.1 Mass Burn Systems
The waste feed materials receive very little pre-
treatment prior to charging to mass burn incinerators.
Obviously oversized material such as refrigerators are
often set aside. Also, any material which is potentially
explosive, including gas cylinders and paint cans, is
also removed if noticed by plant personnel. All other
materials are charged as received. The design of the
charge pit, the cranes, and entrance to the furnace
must be free of any obstacles which could be easily
blocked by oversized material being introduced to the
furnace. Furthermore, the ash pit entrance must be
sufficiently sized in the event that bulky noncombustible
material is inadvertently carried into the furnace.
There are two main styles of mass burn incinerators:
(1) the sloped, reciprocating grate design, and (2) the
rotary combustor design. The sloped, reciprocating
grate design is illustrated in Figure 2-4 and the
rotary combustor is illustrated in Figure 2-5.
The large reciprocating grate units have an arch
positioned over the waste feed entering the furnace.
This radiates heat to the fuel to dry and ignite the
material. This is analogous to the refractory arches
used in overfeed stokers designed for coal combustion.
The waste is rotated during passage through the
furnace to ensure that some waste is not partially
insulated from combustion. The rotating action created
by the grate bar movement also helps maintain a rela-
tively uniform fuel bed which is essential for proper
localized fuel-air ratios.
30
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REFUSE CHARGING
HOPPER 4 CHUTE
FURNACE WATER
TUBE PANEL
CAST IRON
BLOCK nVFRUY
REFRACTORIES
OVERLAY
FEEDER
HYDRAULIC
OIL CYLINDER
DRYING
GRATE
RIDDLING HOPPER
AND GRATE
AIR PLENUM
Cm'STIGN
GRATE
DOUBLE DUVPER
RIDDLING CONVEYOR
BURN-OUT GRATE
HYDRAULIC
OIL CYLINDER
ASH DISCHARGER
„ AUXILIARY
r FUEL BURNER
MAIN ASH
CHUTE
Source: Seeker et al. [6, p.5-39]
Figure 2-4. Cross Sectional Sketch of a Mass Burn
Incinerator
The normal variations in the fuel properties must
be handled by changes in the grate speed, the feed
rate, and the undergrate and overfire air supplies.
Accordingly, careful operator attention is necessary
since waste feed characteristics can change rapidly.
It is normally necessary to have at least two
undergrate plenums in the active burning area for dis-
tribution of air up through the grates. This is
31
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partially because the air flow through the waste fuel-
ash layer decreases as the combustion reactions reach
completion. The undergrate air pressures in the second
plenum are generally slightly lower since flow resistance
is lower and since there is now less combustible material.
Also, separate undergrate plenums are needed in the
initial drying zone and the ash zone burnout areas.
The pressures in these grates must be set in accordance
with the fuel characteristics and the ash quantities.
The undergrate and overfire air pressures can
generally be evaluated by inspectors, even during Level
2 inspections. The undergrate air pressures are almost
always monitored by means of on-site static pressure
gauges. Conventional pneumatic gauges have given way
to more modern differential pressure sensors/transmitters
which provide an electrical signal in the control room.
This data, along with the firing rate data and steam
rate data, should be routinely recorded on the furnace/
boiler operating log. Shifts in operating conditions
from baseline site specific levels should be evaluated.
Also, the data can be compared against the normal
operating conditions for each style of unit.
Due to differences in reciprocating grate design
philosophies among the various manufacturers, there are
substantial differences in the fuel-ash depths, the
grate air flow resistances, and the furnace configura-
tions. This obviously affects the normal operating
ranges of the underfire air pressures, the overfire air
pressures, and the fraction of total combustion air
used for overfire air. A summary of the manufacturer
specific operating conditions is provided in Reference
6 for inspectors who wish to compare plant values
against "typical" values for that specific style of
incinerator. However, it should be recognized that
most plants have made slight adjustments to these values
to achieve optimum operating conditions with their
waste fuel characteristics. Also, manufacturers may
modify their equipment slightly as additional experience
is gained with on-line systems. For these reasons,
comparisons with "typical" values are generally not as
meaningful as shifts in baseline site specific conditions.
32
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The uniformity of air-fuel ratios is primarily
dependent on the uniformity of the fuel-ash layers on
the grates and the adequacy of the undergrate air flows
for the fuel-ash beds. Inspectors can qualitatively
evaluate the fuel-ash beds by using observation
hatches on the sides of the furnace. However, extreme
caution is necessary since shrapnel from exploding
aerosol cans can cause severe injuries while looking
into the hatches. Eye protection is mandatory. Also,
the line of sight should be selected to avoid the
probable trajectories of high velocity objects. Addi-
tional information regarding the use of observation
hatches is included in Section 2.3.
The operating feedrate for a mass feed system is
based on an average design fuel heating value that is
often 4500 to 5000 Btu per pound. The stoker must be
sized for the expected variations in this heating value.
Very high heating value wastes could lead to excessive
Btu per square foot of grate area and this leads to
excessive furnace temperatures which damage the grates
and can lead to slagging. Plants which use preheated
undergrate air are especially prone to these problems.
Excessively low heating values can tax the capability
of the drying zone of the stoker to adequately prepare
the wastes for combustion.
A sketch of a rotary combustor is provided in
Figure 2-5. The waste feed techique is similar to that
of the reciprocating grate units with the exception of
the ram used for rotary combustor charging. There is a
series of undergrate air plenums in the rotary combustor
and in the afterburning grate. The air pressures and
flows in each of these plenums is set by a series of
dampers. A single forced draft fan supplies all of the
undergrate air. More turbulent mixing of the waste
with the combustion air is possible due to the rotation.
The Level 2 and Level 3 inspection is similar to the
sloped, reciprocating grates with the exception that
there is no attempt to maintain uniform fuel beds on
the grates in a rotary combustor.
33
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TVp CUUTTLTO
JJ I AIR/&AC. PLOW
?./ IO-M.'62. /J«J
CDRS?
-EOil_ER
Source: O'Connell, C.
1984 National Waste Processing
Conference, pp. 305-317
Figure 2-5. Rotary Combustor Type Mass Burn System
2.2.4.2 Refuse Derived Fuel Incinerator Systems
Processing of waste materials provides one means
to overcome the heterogeneous characteristics and low
heating value quality of the waste. Once prepared in a
more useable form, it can be fired either alone or in
combination with coal, wood chips, or other conventional
fuels having higher heating values.
One style of refuse preparation is the relatively
simple Mshred-and-burn." At this type of plant, the
34
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waste is deposited on the tipping floor and moved onto
conveyors by means of front-end loaders. As the
unprocessed waste moves toward the shredders, the solid
waste is examined visually by plant personnel for any
dangerous items that could cause explosions or other
problems [18]. The risk of explosions is very real.
Accordingly, regulatory agency inspectors should minimize
their time in this area and adhere to all facility
safety requirements. This will include staying behind
any personnel protective barriers and avoiding areas
adjacent to explosion vents.
Following the shredding operation, magnetic
separators are used to remove any tramp ferrous metals
that are included in the waste feed stream. This
material could damage the RDF fuel distribution equipment
and the stoker parts.
There are a variety of other RDF fuel preparation
techniques. These are summarized in a series of sketches
provided in Figure 2-6. The "shred-and-burn" arrangement
is shown in the top figure. In the next arrangement a
Trommel screen is added for the removal of some of the
small sized noncombustible material such as sand and
shattered glass. The oversized material from the Trommel
screen is recycled back to the hammermill for additional
size reduction.
The main problem with the arrangements shown in
Figures 2-6a and 2-6b is that the shredder is the first
unit to process the as-received wastes. Any undetected
containers of flammable liquids or compressed gases
could cause an explosion. RDF preparation tech-niques
shown in Figures 2-6c and 2-6d have been used to minimize
the very common and very serious explosion problems.
The flail shredder is a low energy unit designed simply
to rip open garbage bags and other containers so that
the waste can be screened. Small diameter noncombustible
material is separated prior to the hammermill. The
fourth arrangement, shown in Figure 2-6d includes a
screen after the hammermill and the magnetic separator
to further remove any improperly sized materials which
could damage the fuel transport equipment, the fuel
distribution equipment, or the stoker grates.
35
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4. Simpleit RDF preparation is shred and ferrous removal. Method is least expensive.
but causes boiler slagging problems from 5 ass content, plus high shredder wear
Figure 2-6a,
Figure 2-6b.
{. Addition of a trommel prevents many noncombusebles and glass from entering
better, but all material muv oass tftrougn snredder leading to heavy wear
Cyclone
(. Flail shredder before trommel eases matenals separation. Two-part screen ensures
IMS toss of comoustibie material to residue
Figure 2-6c.
Figure 2-6d.
7. Trommel placed before snreooer saves wear on tfw shredder ano reduces the
ttpKnan poiennu by aer»ernng out cans o< votanie tquKtt. etc
Source: Reason, J. [20, p.19]
Figure 2-6. Refuse Derived Fuel Preparation
36
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In all four cases, the RDF fuel is processed to
yield a fuel with a limited size distribution and
without any oversized material. The glass content is
reduced in some systems, thereby reducing the ash fusion
problems. Furthermore, there is some reduction in the
overall metals content of the waste feed. This has a
beneficial impact on the overall emissions of trace
metals from the combustion system. Basically, the
various RDF processing techniques produce a fuel which
is less variable and more desirable than those used in
mass burn plants.
Unfortunately, the operating problems at RDF
facilities are not limited to simply producing the RDF
fuel. One of the major problems with RDF systems is
the reliability and uniformity of the feed to the
stoker equipment [19]. The RDF materials are very
erosive due partially to the fuel size and due partially
to the metals content. Some of the problems include
erosion of the fuel transport lines and erosion of the
fuel distributors. The latter problem can lead to very
nonuniform fuel deposits on the grate which in turn
lead to nonuniform localized fuel-air ratios and high
pollutant generation rates.
Nonuniform fuel distribution on the grates can
generally be observed by looking in the front access
hatches of the spreader stoker unit (immediately above
the location of the person shown in Figure 2-7). It is
also possible to look at the back end of the grate
using the various side observation hatches (not shown
on Figure 2-7). The fuel-ash layers should appear to
be uniform from side-to-side and from front-to-back.
A partial list of the possible problems leading to
nonuniform distribution is provided below.
Poor front-to-back distribution
o Worn distributor plates
° Change in RDF particle sizing
oImproper matching of rotor blades
in coal feeders (if coal used)
o Frequent RDF fuel interruptions
37
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Poor side-to-side distribution
o Unbalanced RDF flows to each distributor
oImproper refractory angles near feeders
o Segregation of RDF fuels fed to each
distributor
Spreader stoker type RDF-fired boilers have only
one undergrate plenum as indicated in Figure 2-7. Non-
uniform fuel-ash layers on portions of the grate can
lead to serious thin spots as the high velocity combus-
tion air channels through the areas of minimum flow
resistance. The areas with high fuel-ash deposits have
insufficient air flow and operate fuel-rich.
Source: Daniel, P.L., Barna, J.L. & Blue, J.D.
1986 National Waste Processing
Conference, pp. 221-228
Figure 2-7. Spreader Stoker Boiler
38
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The thin spots also expose the grate parts and
support rails to the radiant heat of the combustion
chamber. This can lead to grate damage and clinkering.
The presence of the air preheater in Figure 2-7 renders
this unit even more vulnerable to this condition. The
importance of uniform fuel-ash deposits on the grates
of spreader stoker units should not be underestimated.
The undergrate air pressures and overfire air pres-
sures are as important for RDF-fired spreader stokers as
they are for the various types of mass burn incinerators.
The monitoring techniques are also similar. The large
majority of plants monitor these pressures continuously
using differential pressure transducers and transmitters.
This data should be available in the boiler control
room and should be recorded on a routine basis on the
daily operating logs for the boiler. There should also
be a series of 1/4" ports in the undergrate supply duct
and in the various overfire air manifolds for manually
checking these pressures.
The overfire air pressures are especially important
since the the furnace areas often have a greater cross
sectional area than the mass burn units. It is more
difficult for the overfire air to penetrate across this
area since the manifolds stretch across the front and
back walls. Therefore, each bank of nozzle must pene-
trate approximately one-half the length of the furnace
chamber. In the case of coal-fired boilers, there has
been a gradual trend from low overfire air pressures in
the range of 5 to 15 inches of water toward higher
overfire air pressures in the range of 25 to 40 inches
of water. A similar trend may occur in the case of
RDF-fired units.
Refractory linings over the lower boiler tubes
(not shown in Figure 2-7) have often been installed to
increase the furnace temperatures and thereby reduce
the formation of organic pollutants. In most plants,
the refractory has been effective. However, in certain
cases, slagging problems have occurred since the local-
ized temperatures have exceeded the ash fusion tempera-
tures of the particular waste being handled. Slagging
is an intolerable operating situation which leads dir-
39
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ectly to serious stoker equipment damage and excessive
pollutant (fly ash and organic pollutant) emissions.
In these cases, it has been necessary to remove the
refractory to avoid this severe problem.
Other problems with RDF feed systems include
fires, bridging, and jamming. Waste materials which
are especially troublesome include rags, wires, cables,
chains, and hose. All of these interrupt the flow of
RDF to the stoker.
Inspectors should avoid immediate contact with RDF
since it contains potentially irritating and toxic
chemicals in a finely divided form. It is the policy
of some plants that all personnel must cover all exposed
skin and wear respirators [18].
2.2.4.3 Modular Systems
Individual modular incinerator units typically
have a capacity of 5 to 100 tons per day [15]. Larger
modular facilities consist of multiple parallel systems
to allow flexibility of operation. These factory-
assembled units are often less expensive for small
communities to build and operate [16]. Energy recovery
in modular incinerators is less effective than for
larger, field erected mass burn systems and RDF systems.
One of the advantages of the modular units is that they
reduce the various problems involved in shipping wastes
long distances to a large centralized facility [20].
Modular systems consist of two combustion chambers
arranged in series. The waste material is feed in a
charging pit using a front end loader. A hydraulic ram
is used to move the material into the initial combustion
chamber which is called the primary chamber. The waste
is moved through the primary chamber by two additional
hydraulic rams which operate at the bottom of the
primary chamber. The average waste residence time in
the primary chamber is 6 to 12 hours (21), and this
helps to dampen out the normal variations in waste fuel
characteristics.
40
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The primary chamber is designed to gasify the
volatile fraction of the waste. Combustion of the
vaporous material is completed in the secondary chamber.
The operating temperatures are typically 1000 to 1200°F
in the primary chamber and 1600 to 2000°F in the second-
ary chamber. Auxiliary burners are used in the secondary
chamber when necessary to maintain desired outlet gas
temperatures.
There are two basic types of modular units: (1)
the excess air incinerators, and (2) the starved air
(sometimes termed controlled air) incinerators. In the
excess air units, the quantity of air supplied to the
primary combustion chamber is roughly equivalent to the
stoichiometric requirements. In other words, enough
air is provided to complete combustion. For these
types of systems, the secondary chamber simply provides
a polishing step to eliminate any uncombusted vapors
escaping the primary chamber.
In starved air units, the quantity of air supplied
to the primary chamber is reduced to approximately 40%
of the stoichiometric requirements. This reduces the
gas velocities in this chamber and thereby reduces the
quantities of particulate matter suspended in the flue
gas passing to the secondary chamber. The air necessary
to complete combustion is added to the secondary chamber
that normally operates at temperatures in the range of
1600 F to 2000°F. An auxiliary burner is present in the
secondary chamber to ensure proper exit gas temperatures.
Warping of dampers and charging doors in starved air
systems has been reported as a frequent problem. This
can lead to excessive combustion in the primary chamber
and is probably caused originally by excessive operating
temperatures.
41
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2.3 Safety Considerations
2.3.1 Walking Hazards in Waste Receiving/Handling Areas
There are a variety of walking and overhead equip-
ment hazards in the waste receiving area. Inspectors
should carefully select positions to observe waste
mixing operations, waste processing operations, and
general fugitive emissions.
2.3.2 Contact with Wastes and RDF Fuel
Direct skin contact with the wastes and RDF fuels
should be avoided. Gloves and protective clothing are
required when there is any possibility of contact.
2.3.3 Eye Hazards Involved in Observing Combustion
Conditions
The majority of municipal waste combustion systems
include a set of observation hatches to allow the
operators to periodically evaluate the distribution of
waste feed on the grates, the adequacy of undergrate
air flow, and the condition of overfire air nozzles.
Use of these hatches during the inspection involves
several hazards which include:
o Shrapnel from disintegrating aerosol cans
and paint cans
o Sudden high temperature puffs during
combustor pressure fluctuations
o Radiation from intense combustion
On units subject to pressure fluctuations, the
observation hatches should not be used since exposure
to the high temperature puffs (often flames 1 to 5 feet
in length which occur in fractions of a second) could
result in blindness, serious burns, and significant
pollutant inhalation hazards. Pressure fluctuations
are especially prevalent on the modular type incinerators,
Regardless of the type of unit, variations in the
combustion chamber static pressure should be reviewed
before using an observation hatch.
To minimize shrapnel hazards, inspectors should
avoid looking directly into the furnace area. The
observation hatch should be used as a partial shield
42
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while looking into the unit on an angle. Obviously,
this practice inhibits the inspector's view of the
combustion conditions. This is a necessary limitation
since aerosol can and paint can disintegration is a
relatively common occurrence and since the shrapnel can
cause blindness.
Proper eye protection must be used to shield the
eyes from the intense radiation generated during waste
combustion. Plant personnel can generally provide a
sight glass or full face shield for this purpose. It
should also be noted that observation hatches should
only be opened and closed by plant personnel. Regulatory
agency personnel should not touch any process equipment
during an inspection.
2.3.4 Internal Inspections Prohibited
Agency inspectors should not participate in internal
inspections of the combustion equipment under any circum-
stances. Sufficient time and safety equipment is not
available to ensure safety.
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3. INSPECTION OF DRY SCRUBBERS
Dry scrubbers utilize absorption and adsorption
for the removal of sulfur dioxide, hydrogen chloride,
hydrogen fluoride, and other acid gases. Some adsorption
of vapor state organic compounds and metallic compounds
also occurs in some dry scrubber applications. This
relatively new control technology is presently in use
on pulverized coal-fired boilers and municipal waste
incinerators. Much of the presently available informa-
tion applicable to municipal waste incinerators has
been drawn from European installations operating for
the last 3 to 5 years and U.S. installations operating
for the last 1 to 2 years. Changes and refinements in
municipal waste incinerator dry scrubbers should be
anticipated as more experience is gained.
3.1 Components and Operating Principles of Dry Scrubbers
There is considerable diversity in the variety of
processes which are collectively termed "dry scrubbing."
This is partially because the technology is relatively
new and is still evolving. The diversity also exists
because of the differing control requirements. For
purposes of this field inspection notebook, the various
dry scrubbing techniques have been grouped into three
major categories: (1) spray dryer absorbers, (2) dry
injection adsorption systems, and (3) combination spray
dryer and dry injection systems. Specific types 'of dry
scrubbing processes within each group are listed below.
Alternative terms for these categories used in some
publications are shown in parentheses.
Spray Dryer Absorption (Semi-wet)
o Rotary atomizer spray dryer systems
o Air atomizing nozzle spray dryer systems
Dry Injection Adsorption (Dry)
o Dry injection without recycle
o Dry injection with recycle
Combination Spray Dryer - Dry Injection (Semi-wet/dry)
45
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Simplified block diagrams of the three major types
of dry scrubbing systems are presented is Figures 3-1,
3-2 and 3-3. The main differences between the various
systems are the physical form of the alkaline reagent
and the design of the vessel used for contacting the
acid gas laden stream with the reagent. The alkaline
feed requirements are much higher for the dry injection
adsoption than the other two categories. Conversely,
the spray dryer absorption and combination systems are
much more complicated.
The pollutant removal efficiencies for all three
categories of dry scrubbing systems appear to be very
high. In most cases/ outlet gas stream continuous
emission monitors provide a direct indication of the
system performance. Agency inspections of all three
types of dry scrubbing systems are similar with respect
to the importance of reviewing the adequacy of these
continuous monitors and of reviewing data for selected
time periods since the last inspection. Subsequent
inspection steps vary substantially for the three types
of dry scrubbers due to different components and operat-
ing principles.
It should be noted that the particulate control
devices shown on the right hand side of the flowcharts
are generally fabric filters or electrostatic
precipitators. It is also possible that one and two
stage wet scrubbing systems will be used in certain
cases. However, the later discussions will primarily
focus on fabric filters and precipitators since these
dominate present and planned applications.
3.1.1 Spray Dryer Absorbers
In this type of dry scrubbing system, the alkaline
reagent is prepared as a slurry containing 5 to 20% by
weight solids [22,23,24]. This slurry is atomized in a
large absorber vessel having a residence time of 6 to
20 seconds [22,23].
There are two main ways of atomization: (1) rotary
atomizers, and (2) air atomizing nozzles. There is
generally only one rotary atomizer. However, a few
applications have as many as three rotary atomizers.
46
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Pump
Note: A - Motor current gauge
P - Pressure gauge
FI - Flow indicating gauge
TI - Temperature gauge
Figure 3-1.
Components of a Spray Dryer Absorber System
(Semi-wet Process)
47
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The shape of the scrubber vessel must be different
to take into account the differences in the slurry
spray pattern and the time required for droplet evapora-
tion. The length-to-diameter ratio for rotary atomizers
is much smaller than that for absorber vessels using air
atomizing nozzles.
It is important that all of the slurry droplets
evaporate to dryness prior to approaching the absorber
vessel side walls and prior to exiting the absorber
with the gas stream. Accumulations of material on the
side walls or at the bottom of the absorber would
necessitate an outage since these deposits would further
impede drying. Proper drying of the slurry is achieved
by the generation of small slurry droplets, by proper
flue gas contact, and by use of moderately hot flue
gases.
Drying that is too rapid can reduce pollutant
collection efficiency since the primary removal mechanism
is absorption into the droplets. There must be suffi-
cient contact time for the absorption. For this reason,
spray dryer absorbers are operated with exit gas tempera-
tures 90 to 180°F above the saturation temperature
[22,25,26]. The absorber exit gas temperatures are
monitsored to ensure proper "approach-to-saturation" and
therefore these values are an important inspection
point. It is simply the difference between the wet
bulb and dry bulb temperature monitors at the outlet of
the absorber vessel.
In rotary atomizers, a thin film of slurry is fed
to the top of the atomizer disk as it rotates at speeds
of 10,000 to 17,000 rpm. These atomizers generate very
small slurry droplets having diameters in the range of
100 microns. The spray pattern is inherently broad due
to the geometry of the disk.
High pressure air is used to provide the physical
energy required for droplet formation in nozzle type
atomizers. The typical air pressures are 70 to 90 psig.
Slurry droplets in the range of 70 to 200 microns are
generated. This type of atomizer can generally operate
over wider variations of the gas flow rate than can be
48
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used in a rotary atomizer. However, the nozzle atomizer
does not have the slurry feed turndown capability of
the rotary atomizer.
The alkaline material generally purchased for use
in a spray dryer absorber is pebble lime. This material
must be slaked in order to prepare a reactive slurry
for absorption of acid gases. Slaking is the addition
of water to convert calcium oxide to calcium hydroxide.
Proper slaking conditions are important to ensure that
the resulting calcium hydroxide slurry has the proper
particle size distribution and that no coating of the
particles has occurred due to the precipitation of
contaminants in the slaking water.
Some of the important operating parameters of the
lime slaker are the quality of the slaking water, the
feed rate of lime, and the slurry exit temperature.
However, it is difficult to relate present operating
conditions or shifts from baseline operating conditions
to possible changes in the absorption characteristics
of the dry scrubber system. A variety of subtle changes
in the slaker can affect the reactivity of the liquor
produced.
One of the problems which has been reported for
spray dryer absorber type systems is the pluggage of
the slurry feed line to the atomizer. Scaling of the
line can be severe due to the very high pH of this
liquor. The flow rate of the liquor to the atomizer is
usually monitored by a magnetic flow meter. However,
this instrument is also vulnerable to scaling since the
flow sensing elements are on the inside surface of the
pipe. To minimize the pluggage problems, the lines
must be well sloped and include the capability for
flushing of the lines immediately after outages. Also,
there should not be abrupt line changes, sharp bends,
or adjacent high temperature equipment. During the
inspection, it is essentially impossible to identify
emerging slurry line problems.
Recycle of the solids collected in the absorber
vessel is important in most systems. It increases the
solids content of the slurry fed to the atomizer and
49
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thereby improves the drying of the droplets. Recycle
also maximizes reagent utilization. The rate of solids
recycle is monitored on a continuous basis. The rest
of the spent absorbent is sent to a landfill.
3.1.2 Dry Injection Adsorption Systems
This type of dry scrubber uses finely divided
calcium hydroxide for the adsorption of acid gases.
The reagent feed has particle sizes which are 90% by
weight through 325 mesh screens [26]. This is approx-
imately the consistency of talcum powder. This size is
important to ensure that there is adequate calcium
hydroxide surface area for high efficiency pollutant
removal.
Proper particle sizes are maintained by transport-
ing the lime to the dry scrubber system by means of a
positive pressure pneumatic conveyor. This provides
the initial fluidization necessary to break up any
clumps of reagent which have formed during storage.
The air flow rate in the pneumatic conveyor is kept at
a constant level regardless of system load in order to
ensure proper particle sizes.
Fluidization is completed when the calcium
hydroxide is injected countercurrently into the gas
stream. A venturi section is used for the contactor
due to the turbulent action available for mixing the
gas stream and reagent. The gas stream containing the
entrained calcium hydroxide particles and fly ash is
then treated in a fabric filter.
Adsorption of acid gases and organic compounds (if
present) occurs primarily while the gas stream passes
through the dust cake composed of calcium hydroxide and
fly ash. Pollutant removal efficiency is dependent on
the reagent particle size range, on the adequacy of dust
cake formation, and on the quantity of reagent injected.
The calcium hydroxide feed rate for dry injection
systems is 3 to 4 times the stoichiometric quantities
needed [25,26]. This is much higher than the spray
dryer absorber type systems and it makes this approach
unattractive for very large systems.
50
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In one version of the dry injection system, solids
are recycled from the particulate control device back
into the flue gas contactor (sometimes termed "reactor").
The primary purpose of the recycle stream is to increase
reagent utilization and thereby reduce overall calcium
hydroxide costs.
3.1.3 Combination Spray Dryer and Dry Injection Systems
A flowchart for this system is shown in Figure 3-3.
The acid gas laden flue gas is first treated in an
upflow type spray dryer absorber. A series of calcium
hydroxide sprays near the bottom of the absorber
vessel are used for droplet generation.
After the upflow chamber, the partially treated
flue gas then passes through a venturi contactor section
where it is exposed to a calcium silicate and lime
suspension. The purpose of the second reagent material
is to improve the dust cake characteristics in the
downstream baghouse and to optimize acid gas removal in
this dust cake. The calcium silicate reportedly improves
dust cake porosity and serves as an adsorbant for the
acid gases.
Solids collected in the baghouse may be recycled
to the venturi contactor. This improves reagent utili-
zation and facilitates additional pollutant removal.
3.2 General Comments
Corrosion can present major problems for all types
of dry scrubbers used on applications with high hydrogen
chloride concentrations such as municipal waste inciner-
ators. The calcium chloride reaction product formed in
dry scrubbers and any uncollected hydrogen chloride are
both very corrosive and cause damage in any areas of the
absorber vessel or particulate control device where cool-
ing and water vapor condensation can occur. Two common
reasons for low localized gas temperatures include air
infiltration and improper insulation around support beams.
Due to the potential problems related to corrosion, the
inspections should include checks for air infiltration
and a visible evaluation of common corrosion sites.
51
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/ SETTLING /
'/, CHAMBER '
y.
Watte
Solids
Note: A - Motor current gauge
PI - Pressure gauge
TI - Temperature gauge
Figure 3-2.
Components of a Dry Injection Adsorption
System (Dry Process)
52
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Pump
Blower
Note: A - Motor current gauge
PI - Pressure gauge
TI (wet) - Wet bulb temperature gauge
TI (dry) - Dry Bulb temperature gauge
Figure 3-3.
Components of a Combination Spray Dryer and
Dry Injection Adsorption System
(Semi-wet/Dry Process)
53
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3.3 Safety Considerations
3.3.1 Inhalation Hazards Around Positive Pressure
System Components
Poorly ventilated areas in the vicinity of positive
pressure dry scrubber absorbers, particulate control
systems, and/or ductwork should be avoided. There are
a variety of inhalation hazards associated with municipal
waste incinerators, including but not limited to the
following:
o hydrogen chloride
o hydrogen fluoride
o sulfuric acid mist
o sulfur dioxide
o dioxins/furans
o carbon monoxide
o heavy metal enriched flyash.
Concentrations of these pollutants can conceivably
exceed the maximum allowable use levels of air-purifying
respirators. Furthermore, there is no single type of
air-purifying respirator which is appropriate for the
wide range of pollutant chemicals which are emitted
from municipal waste incinerators. Inspectors must be
able to recognize and avoid areas of potentially signi-
ficant exposure to fugitive emissions from the combus-
tion and dry scrubbing systems. A simple flowchart
which indicates the locations of all fans is a useful
starting point in identifying portions of the system
which operate at positive pressure.
54
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3.3.2 Chemical Burns and Eye Hazards Around the Pebble
Lime and/or Calcium Hydroxide Preparation Area
The strong alkalis used in dry scrubbing have the
potential to cause severe eye damage. While the proba-
bility of eye contact and skin contact is relatively
small for agency inspectors, it is nevertheless impor-
tant to keep in mind the general first aid procedures.
These are briefly summarized below.
o After eye contact, flushing should be started
immediately.
o Eyes should be flushed for 15 to 30 minutes.
o After skin contact, all affected clothing should
be removed and showering should be done for a
minimum of 15 minutes.
0 Medical attention should be obtained in all
situations.
During the routine inspection, agency personnel
should note the locations of all eye wash stations and
showers. These are generally located in the immediate
vicinities of chemical handling areas. After the firs*
aid procedures are completed, it is especially important
to get qualified medical attention regardless of the
presumed seriousness of the exposure. All inspectors
should have full first aid and safety training before
conducting field inspections of municipal waste incin-
erators or any other type of air pollution source.
3.3.3 Internal Inspections Prohibited
Inspectors should not enter dry scrubber absorber
vessels or air pollution control devices under any
circumstances. All of the necessary inspection steps
can be accomplished without internal inspections.
Proper isolation, lockout, and testing of confined
areas requires substantial time and safety equipment,
neither of which is available to the agency inspector.
Furthermore, serious accidents can and have happened to
agency inspectors while inside equipment with plant
personnel.
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4. INSPECTION OF ELECTROSTATIC PRECIPITATORS
Electrostatic precipitation is one of the main
particulate control techniques being used on municipal
waste incinerators installed during the last fifteen
years. Continued use of electrostatic precipitators
is expected both as a stand alone control device and as
part of dry scrubbing systems. The inspection of muni-
cipal waste incinerator precipitators is relatively
similar to the inspection of electrostatic precipita-
tors serving coal-fired boilers, cement kilns, and
kraft pulp mills.
4.1 Components of Electrostatic Precipitators
An electrostatic precipitator consists of a large
number of discharge electrodes and collection plates
arranged in parallel rows along the direction of gas
flow. The collection plates are grounded along with
the hoppers and shell of the precipitator. The dis-
charge electrodes are energized to negative voltages
ranging between 15,000 volts and 50,000 volts.
The gas velocity through the numerous parallel
passages of the precipitator ranges from 3 to 6 feet
per second. This represents an order of magnitude
decrease in the velocity that exists in the ductwork
leading to the precipitator. The deceleration is
accomplished in an inlet chamber at the front of the
precipitator. There are normally one or more perfor-
ated plates in the inlet chamber to achieve as uniform
gas distribution as possible. The high voltage for the
discharge electrodes is provided by a transformer-
rectifier set (hereafter termed T-R set). It converts
alternating current from a 480 volt supply to direct
current at very high voltages. Each T-R set energizes
an independent portion of the electrostatic precipitator
called a field. The T-R sets are always mounted on the
roof of the precipitator since it is difficult to run
the high voltage lines for long distances.
57
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In municipal waste applications there are normally
2 to 4 fields in series along the direction of gas
flow. Each field in series removes from 60 to 85% of
the incoming particulate matter to that field.
Some very large precipitators are also divided
into parallel chambers. Solid partitions between the
chambers prevents gas from passing from one chamber to
the other while passing through the precipitator. Each
of the chambers is evaluated separately during the
inspection.
Each of the T-R sets is connected to a control
cabinet. This controls the 480 volt alternating current
power supply to the T-R set. It contains all of the
electrical meters used to evaluate the operating condi-
tions inside each of the precipitator fields. A major
part of the inspection involves the interpretation of
this electrical data. One of the first steps in the
evaluation of the electrical data is to determine how
the T-R sets are laid out on the precipitator so that
the various control cabinets can be matched up with the
T-R sets they control. This is important since the
field-by-field trends in a chamber are used to evaluate
potential operating problems.
The types of meters present on the control cabinet
are listed below along with the usual range of the
gauge.
Primary voltage, 0 to 500 volts A.C.
Primary current, 0 to 200 amps A.C.
Secondary current, 0 to 2 amps D.C.
Secondary voltage, 0 to 50 kilovolts, D.C.
Spark Rate, 0 to 200 sparks/minute
The primary voltage and current data concerns the
480 volt alternating current power supply to the T-R
set. The secondary voltage is the voltage leaving the
T-R set and on the discharge electrodes within the
precipitator. The secondary current is the direct
current flow from the T-R set that passes through the
field. The spark rate is the number of short term arcs
that jump between the discharge electrodes and collec-
tion plates in the field.
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Electrical conditions can be evaluated using either
the primary meters or the secondary meters. Whenever
they are available, the secondary meters are generally
used since these provide information on the electrical
conditions within the precipitator fields. However,
many older precipitators were not equipped with secondary
voltage meters. For these units, the primary meters
can be used.
4.2 Operating Principles
Under normal operating conditions, the values of
the primary and secondary meters in each field can not
be set intentionally by the operators. Instead, the
electrical operating conditions are determined by the
characteristics of the particles passing through the
precipitator field and by the ability of the power
supply to respond to sparks within the field. Some of
the most important properties of the dust include the
total quantity of dust, the particle size distribution
of the dust, and the particle resistivity distribution.
The dust resistivity is a measure of the ability
of the electrons on the surface of the dust particles
to pass the grounded collection plate. If the electrons
can flow easily, the dust resistivity is low.
The electrons can flow around the outside surfaces
of particles that comprise the dust layer on the collec-
tion plate or they can pass directly through the dust
particles. Below 350°F, compounds such as sulfuric
acid and water condense on the particle surfaces to
facilitate electron flow around the outer surfaces.
Also, carbonaceous material due to incomplete combus-
tion in the incinerator can contribute to charge
dissipation. For these reasons, the ash resistivity
drops rapidly as the gas temperature drops below 350°F.
When the particle temperature is above 500°F, the
constitutents within the dust particles (other than
uncombusted material) generally provide a conductive
path. Therefore, the resistivity tends to decrease as
the gas temperatures increase above 500°F. This type
of charge dissipation is termed bulk conductivity. Due
59
-------
to the strong temperature dependence of these two
separate parts of charge dissipation, the particle
resistivity exhibits a peak when the temperature is
in the range of 350°F as illustrated in Figure 4-1.
Electrostatic precipitators serving municipal
incinerators generally have inlet gas temperatures
between 350°F and 450 °F which means that they operate
in the range having the least temperature sensitivity.
Precipitators operating on other types of sources with
gas temperatures in the range of 280 to 350°F can have
significantly more difficulty with resistivity varia-
tions caused by extreme gas temperature sensitivity.
Of course, municipal waste incinerator precipitators
can have similar problems if the gas temperature
decreases from 350°F.
As indicated in Figure 4-1, ash resistivities in
municipal waste incinerator precipitators are generally
in the moderate range of 1 x 109 ohm-cm to 5 x 1011
ohm-cm. This is range in which precipitators work
best. However, ash resistivities can become undesirably
low if the combustibles content of the ash increases or
if the gas temperature becomes very low in localized
parts of the precipitator.
Under low resistivity conditions, the precipitator
currents can be very high while the spark rates are
negligible. The operating voltages are low because the
power supplies reach the current limits at relatively
low voltages. In these areas, the dust layer on the
collection plates is not strongly bonded and even light
rapping can result in the reentrainment of the material
that had been collected. Conversely, the high resistiv-
ity zones in the precipitator generally have low currents,
low voltages, and high spark rates. Due to the poor
electrical operating conditions, overall particle collec-
tion can be guite low. Neither high or low resistivity
is desirable.
60
-------
10"
10"
§ 10"
10'
10'
t2XH,Obyvoturm
100 200 300 400 500 600 700
Temperature, °F
Source: Petersen, H.H.
1984 National Waste Processing Conference
pp. 377-384
Figure 4-1. Typical Resistivity Versus Temperature Relationship
The electrical operating conditions of an electro-
static precipitator can be summarized using graphs, and
power input totals. Figure 4-2 illustrates graphs of
the secondary voltage, secondary currents, and spark
rate for a one chamber, four field precipitator. Base-
line data for each parameter is provided in the graphs
to help identify shifts in these electrical conditions.
When all of the fields in a given chamber shift in
unison (there may be a time lag of several hours for
the outlet fields), there has normally been a change in
the dust characteristics due to process operating changes
or fuel changes. When only one of the fields shifts,
there is normally an internal mechanical problem.
61
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INSPECTION Of ELECTROSTATIC
30
20
10
IITI
BASUIHt
^1500:
Cmrtnl Limit
500-
— 40
I30
20'
10
FIELDS
Figure 4-3. Trends in the Voltages, Currents and Spark
Rates in a Precipitator Chamber
62
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The advantage of the graphs is that they allow for
rapid interpretation of the large quantity of data
obtained while observing the T-R set control cabinets.
Another way to summarize the electrical data is to
calculate the overall power input for a precipitator
chamber. This can be done using either the primary
meters using Equation 4-1 or the secondary meters using
Equation 4-2.
Primary Meters:
(Volts, A.C.) x (Amps A.C.) x 0.75 = (Watts)
Equation 4-1
Secondary Meters:
(Kilovolts, D.C.) x (Milliamps, D.C.) = (Watts)
Equation 4-2
The power input in watts for each field in the
chamber is then added to calculate the total power
input. If the actual gas flow rate is known, the power
input is often presented as total watts per thousand
actual cubic feet per minute of gas flow.
It should be noted, however, that the power input
is usually calculated only for precipitators that con-
sistently operate in either the moderate or high resis-
tivity range. In these ranges, an increase in the
power input generally corresponds with a decrease in
the particulate emission rate. In the low resistivity
range, there is no typical relationship between power
input and particulate emission rates.
The alignment between the parallel sets of collec-
tion plates and discharge electrodes is very important.
For units with high resistivity zones, the spacing
tolerances must be maintained within plus or minus a
quarter inch throughout the unit. Even for units with
moderate-to-low resistivity, the alignment must be
within plus or minus a half inch throughout the unit.
Considering that there are a large number of collection
plates and discharge electrodes, maintaining proper
alignment is not simple.
63
-------
Large quantities of dust are often handled by
electrostatic precipitators. The types of solids dis-
charge valves and solids handling systems are generally
selected based on the overall quantity of material to be
transported and on the characteristics of these solids.
The most common types of solids discharge systems used
on municipal waste incinerators include: (1) rotary
valves and screw conveyors, and (2) pneumatic systems.
The fan can be either located before or after the
electrostatic precipitator. When it is after the
precipitator (the normal location for MWCs), the gas
stream is "pulled" through and the static pressure
is less than atmospheric pressure (termed "negative
pressure"). As with other types of control devices,
negative pressure electrostatic precipitators are vul-
nerable to air infiltration. This can lead to a number
of significant operating problems considering the highly
corrosive nature of municipal waste incinerator exhaust
gas components.
When the fan is before the precipitator, the gas
stream is "pushed" through. This creates static pres-
sures inside the precipitator which are greater than
atmospheric pressure (termed "positive pressure").
Special care is warranted whenever inspecting these
units, since fugitive emissions from the unit can
result in very high levels of toxic pollutants in the
vicinity of the precipitator.
4.3 General Safety Considerations
4.3.1 Inhalation Hazards
Fugitive emissions from municipal waste incineration
systems can accumulate in poorly ventilated areas around
the precipitator such as the roof and hopper weather
enclosures, annular stack monitoring locations, and
areas adjacent to cracked breeching expansion joints.
The inhalation hazards can include chemical asphyxiants,
physical asphyxiants, toxic gases/vapors, and toxic
particulate.
64
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4.3.2 Use of Portable Instruments
Portable instruments should not be used on electro-
static precipitator systems. Very high static voltages
can accumulate on probes downstream of precipitators
due to the impaction of charged particles. Touching
improperly grounded and bonded probes can result in
involuntary muscle action that can result in a fall.
Furthermore, in some units, the probes could inadver-
tently approach the electrified zone of the precipitator
that operates at 15 to 50 kilovolts.
4.3.3 Internal Inspections Prohibited
Inspectors should not enter an electrostatic precip-
itator under any circumstances. All of the necessary
inspection steps can be accomplished without internal
inspections. Furthermore, the side access hatches and
penthouse/roof access hatches should not be opened under
any circumstances. The internal components can be at
high voltages even though the unit is out-of-service.
Also, the hopper hatches should not be opened during
the inspection since hot, free flowing dust can be
released and since the inrushing air can cause hopper
fires in some cases.
65
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5. INSPECTION OF FABRIC FILTERS
Pulse jet and reverse air fabric filters are
addressed in this section since these are the two most
common types of systems used on municipal waste inciner-
ators. The fabric filters are generally used as part
of the dry scrubbing system. However, they can also
serve as stand-alone particulate control devices.
5.1 Components and Operating Principles of Pulse Jet
Fabric Filters
Pulse jet fabric filters utilize compressed air
for routine bag cleaning. They are sometimes referred
to as "Reverse Jet" fabric filters.
The presence of a row of diaphragm valves along
the top of the baghouse indicates that the baghouse is
a pulse jet unit. These valves control the compressed
air flow into each row of bags which is used to routinely
clean the dust from the bags. On a few units, the
diaphragm valves can not be seen since they are in an
enclosed compartment on the top of the unit. In these
cases, the pulse jet baghouse can be recognized by the
distinctive, regularly occurring sound of the operating
diaphragm valves.
There are two major types of pulse jet baghouses:
(1) top access, and (2) side access. Figure 5-1 illus-
trates the top access design which includes a number of
large hatches across the top of the baghouse for bag
replacement and maintenance. Another major type has
one large hatch on the side for access to the bags.
The side access units often have a single small hatch
on the top of the shell for routine inspection of the
baghouse.
67
-------
TOP ACCESS HATCHES
GAS OUTLET
FAN
IAPHRAGM VALVES
AIR MANIFOLD
GAS INLET
HOPPERS
Figure 5-1. Top Access Pulse Jet Fabric Filter
68
-------
Like most small units, the pulse jet collector
depicted in Figure 5-1 is not divided into compartments.
These are not needed on small units that operate'inter-
mittantly since bags are cleaned row-by-row as the unit
continues to operate. A few of the large units are
divided into separate compartments so that it is possible
to perform maintenance work on part of the unit while
the other part continues to operate.
Another distinguishing characteristics of pulse
jet units is the use of a support cage for the bags.
The cage fits inside the cylindrical bags and prevents
the bags from collapsing during filtering. Bags and
cages are usually sold separately.
The fan shown in Figure 5-1 is after the baghouse.
This means that the particulate laden gas stream is
"pulled" through the baghouse and that the static
pressures throughout the unit are less than atmospheric
pressure. Outside air will leak into the baghouse if
the hatches are not secure, if the shell is corroded,
or if the hopper is not properly sealed. Air infiltra-
tion can result in a number of significant baghouse
maintenance problems.
Pulse jet units operate equally well when the fan
is ahead of the baghouse and the gas stream is "pushed"
through. In these units, the static pressures are
greater than atmospheric pressure and there are potential
safety problems with leakage of pollutant laden gas out
into the areas surrounding the baghouse.
A cross sectional drawing of a pulse jet fabric
filter is shown in Figure 5-2 on the next page. Refer
to this drawing while reading the following section
concerning the basic operating characteristics of pulse
jet baghouses.
The baghouse is divided into a "clean" side and a
"dirty" side by the tube sheet mounted near the top of
the unit. The dust laden gas stream enters below this
tube sheet and the filtered gas collects in a plenum
above the tube sheet. There are holes in the tube sheet
for each of the bags which are normally arranged in rows.
69
-------
BLOW TUB!
PILOT VALVE ENCLOSURE
DIAPHRAGM VALVE
*— AIR MANIFOLD _
PULSE TIMER
DIFFERENTIAL PRESSURE. SWITCH
IRTY GAS INLET
OTARY VALVE
Figure 5-2.
Cross Sectional Sketch of Pulse Jet
Fabric Filter
70
-------
The bags and cages hang from the tube sheet. The
dust laden inlet gas stream flows around the outside of
each bag and the dust gradually accumulates on the
outside surfaces of the bags during filtering. The
cleaned gas passes up the inside of the bag and out
into the "clean" gas plenum.
A pulse jet fabric filter uses bags which are
supported on cages. The cages hang from the tube sheet
near the top of the baghouse. Dust accumulates on the
outer surfaces of the bags as the gas stream passes
through the bags and into the center of the bags. The
filtered gas is collected in a plenum at the top of the
baghouse.
The dust must occasionaly be removed from the bags
in order to avoid excessively high gas flow resistances.
The bags are cleaned by introducing a high pressure
pulse of compressed air at the top of the bag. The
sudden pulse of compressed air generates a pressure
wave which travels down inside of the bag. The pres-
sure wave also induces some filtered gas to flow down-
ward into the bag. Due to the combined action of the
pressure wave and the reverse gas flow, the bags are
briefly deflected outward. This cracks the dust cake
on the outside of the bags and causes the dust to fall
into the hopper. Cleaning is normally done on a row-
by-row basis while the baghouse is operating.
The compressed air at pressures from 60 to 100
psig is generated by an air compressor and stored
temporarily in the compressed air manifold. When the
pilot valve (a standard solenoid valve) is opened by
the controller, the diaphragm valve suddenly opens to
let compressed air into the delivery tube which serves
a row of bags. There are holes in the delivery tube
above each bag for injection of the compressed air into
the top of each bag. The cleaning system controller
can either operate on the basis of a differential
pressure sensor as shown in Figure 5-2, or it can
simply operate as a timer. In either case, bags are
usually cleaned on a relatively frequent basis with
each row being cleaned from once every five minutes to
once every hour. Cleaning is usually done by starting
71
-------
with the first row of bags and proceeding through the
remaining rows in the order that they are mounted.
Bags used in pulse jet collectors are generally
less than 6 inches in diameter and range in length from
6 to 14 feet. Felted fabric is the most common type of
material.
One of the basic design parameters of a pulse jet
fabric filter is the gas-to-cloth ratio (sometimes
called the air-to-cloth ratio) which is simply the
number of cubic feet of gas at actual conditions passing
through the average square foot of cloth per unit of
time. The normal units are ft3/min/ft which can be
reduced to ft/min. Most new commercial pulse jet units
are designed for an average gas-to-cloth ratio between
3 and 8 depending on the characteristics of the fabric
selected, the particle size of the dust to be collected,
and the installation and operation costs. Some older
pulse jet units were designed for gas-to-cloth ratios
up to 15 ft/min.
Pulse jet units do not necessarily operate at the
design average gas-to-cloth ratio. When incinerator
operating rates are low, the prevailing average gas-to-
cloth ratio could be substantially below the design
value. Conversely, the average gas-to-cloth ratio
could be well above the design value if some of the
bags are inadequately cleaned or if sticky or wet
material blocks part of the fabric surface. Very high
gas-to-cloth ratio conditions can lead to high gas flow
resistance which in turn can result in both seepage of
dust through the bags and fugitive emissions from the
process equipment.
The difference between the gas stream pressures
before and after the baghouse is called the static
pressure drop. The actual static pressure drop depends
on the actual average gas-to-cloth ratio, the physical
characteristics of the dust, the type of fabric used in
the bags, and the adequacy of cleaning. A pulse jet
baghouse with new bags that have not yet been exposed
to dust would normally have a static pressure drop of
0.5 to 1.5 inches of water. During normal operation,
72
-------
the pulse jet baghouses generally have a static pressure
drop between 3 and 8 inches of water. The difference
between the static pressure drop across a clean, new
unit and one in normal service is due to the gas
flow resistance through the dust layer on each of the
bags. The dust layer (sometimes called the dust cake)
is important since it is responsible for much of the
particle filtering. Very low static pressure drops can
often indicate inadequate dust layers for proper filter-
ing. Very high static pressure drops often mean that a
substantial fraction of the available cloth area has
been inadequately cleaned or has been blocked by wet
and/or sticky material. High particulate emissions
also occur when the static pressure drop is very high.
The optimum overall efficiency of a pulse jet baghouse
system is generally in the moderate static pressure
drop range.
5.2 Components and Operating Principles of Reverse Air
Fabric Filters
In reverse air systems, the bags are suspended
from the top and are attached to a tube sheet which is
immediately above the hoppers. As shown in Figure 5-3,
the inlet gas enters from the hoppers and passes upward
into each of the bags. The dust cake builds up on the
inside surface of the bags and filtered gas passes into
the chamber surrounding the bags.
These baghouses are usually divided into 2 or more
compartments. The bags are cleaned by isolating the
compartment from the inlet gas stream. Filtered gas is
moved backward through the compartment to break up the
dust cake and discharge it to the hoppers below. The
cleaning gas from the compartment being cleaned is
recycled to the inlet gas duct. A set of dampers
(poppet valves in Figure 5-3) and activators are used.
Due to the relatively large size of many commercial
bags, a significant gas flow exists at the entrance to
the bags. The average gas velocity at this point can
be between 300 and 500 feet per minute, depending of
the actual gas-to-cloth ratio and the bag size. It is
73
-------
important that the particulate laden air enter the bag
in as straight a direction as possible in order to
minimize fabric abrasion. The inlet gas stream can
also cause fabric damage if the bags are slightly slack
and some of the fabric is folded over the bag inlet.
Because of these and other possible problems, the large
majority of the bag failures occur near the bottom of
the bags.
Bags used in reverse air baghouses generally range
in length from 10 to 30 feet. Reverse air bags utilize
a set of anti-collapse rings sewn around the bags at a
number of locations on the bag to prevent complete
closure of the bag during reverse air cleaning. Woven
fabrics are generally used. The bags are usually
attached to the tube sheet by using a thimble and clamp.
Firm bag attachments are important to prevent the flow
of unfiltered gas through any gaps.
Large quantities of dust are often handled by
reverse air and shaker baghouses. The types of solids
discharge valves and solids handling systems are gener-
ally selected based on the overall quantity of material
to be transported and on the characteristics of these
solids. The most common types of solids discharge
systems include (1) rotary valves and screw conveyors,
(2) pneumatic systems, and (3) pressurized systems.
An isometric drawing of a reverse air baghouse is
shown in Figure 5-4. This unit has the main fan down-
stream of the baghouse. This means that the particulate
laden gas stream is "pulled" through the baghouse and
that the static pressures throughout the unit are less
than atmospheric pressure (termed "negative pressure").
With this type of arrangement, outside air can leak
into the baghouse if the hatches are not secure, if the
shell is corroded, or if the hopper is not properly
sealed. Air infiltration can result in a number of
significant baghouse maintenance problems.
74
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RFVERSE AIR DUCTS
/<£
CLEAN GAS-
REVERSE AIR
_FAN-
u-
r
Ts-
W
ST —
r~'
•POPPET VALVES AND
.ACTUATORS
Mi! -\ iiKJ-fe
i I KJ^& T /=
WALKWAY
BAGS
TUBE SHEET
Figure 5-3. Cross Section of a Reverse Air Fabric Filter
75
-------
Reverse air and shaker units operate equally well
when the fan is ahead of the baghouse and the gas
stream is "pushed" through. In these units, the static
pressures are greater than atmospheric pressure (termed
"positive pressure") and there can be potential safety
problems with leakage of pollutant laden gas out into
the areas surrounding the baghouse. In most positive
pressure units, the filtered gas from each compartment
is released to the atmosphere through a large roof
monitor or through a set of short stacks.
One of the basic design parameters of reverse air
and shaker fabric filters is the gas-to-cloth ratio
(sometimes called the air-to-cloth ratio) which is
simply the number of cubic feet of gas at actual condi-
tions passing through the average square foot of cloth
per unit of time. The normal units are ft3/min/ft
which can be reduced to ft/min. Most new commercial
reverse air and shaker units are designed for an average
gas-to-cloth ratio between 1 and 3 ft/min depending on
the characteristics of the fabric selected, the particle
size of the dust to be collected, and the necessary
installation and operation costs.
Reverse air and shaker units do not necessarily
operate at the design average•gas-to-cloth ratio. When
production rates are low, the prevailing average gas-
to-cloth ratio could be substantially below the design
value. Conversely, the prevailing average gas-to-cloth
ratio could be well above the design value if some of
the bags are inadequately cleaned or if sticky or wet
material blocks part of the fabric surface. Very high
gas-to-cloth ratio conditions can lead to high gas flow
resistance which in turn can result in both the seepage
of dust through the bags and fugitive emissions from
the process equipment served by the baghouse.
The difference between the gas stream pressures
before and after the baghouse is called the static
pressure drop. The actual static pressure drop depends
on the actual average gas-to-cloth ratio, the physical
characteristics of the dust, the type of fabric used in
the bags, and the adequacy of cleaning. A reverse air
or shaker baghouse with new bags which have not yet
76
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_ COMPARTMENTS
BAGS
FAN
T GAS INLET
Figure 5-4. Isometric View of a Reverse Air Fabric Filter
77
-------
been exposed to dust would normally have a static
pressure drop of 0.5 to 1.5 inches of water. During
normal operation, the baghouses generally have a static
pressure drop between 3 and 8 inches of water. The
difference between the static pressure drop across a
clean, new unit and one in normal service is due to the
gas flow resistance through the dust layer on each of
the bags. The dust layer (sometimes called the dust
cake) is important since it is responsible for most of
the particle filtering. Very low static pressure drops
can often indicate inadequate dust layers for proper
filtering. Very high static pressure drops often mean
that a substantial fraction of the available cloth area
has been inadequately cleaned or has been blocked by
wet and/or sticky material. High particulate emissions
also occur when the static pressure drops are very
high. The optimum overall efficiency of a reverse air
or shaker baghouse system is generally in the moderate
static pressure drop range.
5.3 General Safety Considerations
5.3.1 Hot Surfaces
Pulse jet fabric filters serving municipal waste
incinerators operate at relatively high gas temperatures
of 250 to 350°F. Uninsulated baghouse roofs can be a
serious burn hazard. Unfortunately, it is important to
inspect this area due to the possible air infiltration
problems and due to the presence of the diaphragm
values and compressed air pressure gauge.
5.3.2 Inhalation Hazards
Fugitive emissions from positive pressure fabric
filter systems can accumulate in poorly ventilated areas
around the baghouse such as the walks between the rows
of compartments. The inhalation hazards can include
chemical asphyxiants, physical asphyxiants, toxic
gases/vapors, and toxic particulate.
78
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5.3.3 Internal Inspections Prohibited
Inspectors should not enter a fabric filter under
any circumstances. All of the necessary inspection
steps can be accomplished without internal inspections.
However, in some cases, it is helpful to open one or
more of the baghouse top and/or side access hatches in
order to observe internal conditions. In these situa-
tions, inspectors should request that plant personnel
open the hatches. The hopper hatches should not be
opened during the inspection since hot, free flowing
dust can be released.
79
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6. INSPECTION OF WET SCRUBBERS
The roost common types of wet scrubber systems used
on municipal waste incinerators are addressed in this
inspection notebook. These include the following:
o Spray tower
o Packed beds
o Venturi
Inspectors should modify these procedures as neces-
sary for types of scrubbers not specifically discussed
in this notebook. It should be noted that the wet
scrubbers presently in service are on relatively old
units. Most new incinerators use dry scrubbers or
electrostatic precipitators.
6.1 Components and Types of Wet Scrubbers
A scrubber is not an isolated piece of equipment.
It is a system composed of a large number of individual
components. A partial list of the major components of
commercial systems is provided below.
o Scrubber vessel
o Gas cooler and humidifier
o Liquor treatment equipment
o Gas stream demister
oLiquor recirculation tanks, pumps, and piping
o Alkaline addition equipment
o Fans, dampers, and bypass stacks
One of the first steps in the inspection of any
wet scrubber system is to prepare a flowchart which
includes the components listed directly above. This
will be invaluable in evaluating the on-site instrumen-
tation and in identifying system problems.
81
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6.1.1 Spray Tower Scrubbers
The gas stream enters near the bottom of the
scrubber and enters upward at velocities between 2 and
10 feet per second. The liquor enters at the top of the
unit through one or more spray headers. Nozzles are
oriented on the headers so that all of the gas stream is
exposed to the sprayed liquor. Careful scrubber design
is necessary to achieve proper liquor distribution
since this is a function of the type of nozzles used,
the spray angle of the nozzles, the nozzle placement,
and the liquor pressure. It is also important to design
the headers so that solid deposits do not accumulate.
A spray tower scrubber has a limited particulate
removal capability. For municipal waste incinerators,
it is used primarily for acid gas removal. A high
efficiency particulate control device must be upstream
of the scrubber to meet the particulate emission limit-
ations. Alkaline reagents are necessary to maintain
liquor pH during the absorption of hydrogen chloride,
hydrogen fluoride, and sulfur oxides.
6.1.2 Packed Bed Scrubbers
This type of scrubber is used strictly for acid
gas removal. The large liquor surface area created as
the liquor gradually passes over the packing material
favors gas diffusion and absorption. Packed bed scrub-
bers are not effective for collection of small particu-
late matter since the gas velocity through the bed(s)
is relatively slow.
Packed beds can be either vertical or horizontal.
Regardless of the orientation of the bed, the liquor is
sprayed from the top and flows downward across the bed.
Proper liquor distribution is important for efficient
removal of gases. This is one of the few types of
scrubbers in which the static pressure drop is not very
important.
One of the major problems with these scrubbers is
the accumulation of solids at the entry to the bed and
within the bed. The dissolved and suspended solids
levels in the liquor must be monitored carefully.
82
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6.1.3 Venturi Scrubbers
A conventional venturi scrubber is illustrated in
Figure 6-1. The gas stream enters the converging section
and is accelerated by approximately a factor of ten.
The liquor is injected just above the throat. Droplets
form due to the shearing action of the high velocity
gas. Impaction of particles occurs on the droplets
which are initially moving slower than the gas stream.
The high liquor surface area also allows for gas
absorption.
The gas stream is decelerated in the diverging
section. After the venturi section, the gas stream
turns 90° and passes into the demister chamber. The
venturi scrubbers are usually part of a large and
relatively complex scrubber system.
There are a large number of variations to the
standard venturi configuration. Figure 6-2 illustrates
one common throat design which incorporates internal
dampers to vary the gas velocity. These can be opened
or closed to maintain a constant static pressure drop
when the gas flow varies. The dampers can also be used
to- adjust the static pressure drop when the inlet
particle size distribution varies.
6.2 Wet Scrubber Operating Principles
Impaction is the primary means for collection of
particles in wet scrubbers. The effectiveness of impac-
tion is related to the square of the particle diameter
and the difference in velocities of the liquor droplets
and the particles.
The importance of particle size is emphasized in
Figure 6-3. For particles greater than 1 to 2 microns
in diameter, impaction is so effective that penetration
(emissions) are quite low. However, penetration of
smaller particles, such as the particles in the 0.1 to
0.5 micron range is very high. Unfortunately, munici-
pal waste incinerators can generate substantial quanti-
ties of particulate matter in this submicron range
due to the condensation of partially combusted organic
compounds and the condensation of metallic vapors.
83
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For constant particle size distribution, the over-
all particulate collection efficiency in a wet scrubber
system generally increases as the static pressure drop
increases. The static pressure drop is a measure of
the total amount of energy used in the scrubber to
accelerate the gas stream, to atomize the liquor drop-
lets, and to overcome friction. At high static pres-
sure drops, the difference in droplet and particles
velocities is high and a large number of small diameter
droplets are formed. Both of these conditions favor
particle impaction into water droplets.
Another important variable is the liquor surface
tension. If this is too high, some small particles
which impact on the water droplet will "bounce" off and
not be captured. High surface tension also has an
adverse impact on droplet formation.
Figure 6-1. Conventional Venturi Scrubber
84
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..-; INLET
INLET
THROAT DAMPERS
,iS OUTLET
Figure 6-2. Venturi Throat Dampers
1.0
09
08
07
06
OS
|
5 0.4
'e
| 0.3
02
0.1
345678910
Particle Diameter, .m
0
10
30
40
"I
60 «
=
UJ
TO »*
80
90
10O
Figure 6-3. Relationship Between Particle Penetration
(Emissions) and Particle size
85
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Unfortunately, the scrubber liquors having surface
tensions which provide optimum particle impaction may
have poor solids settling properties. Surfactants can
be added to reduce surface tension. Conversely, floc-
culants and anti-foaming agents generally increase the
surface tension.
6.3 General Safety Considerations
Venturi scrubbers may operate at much higher posi-
tive static pressures than other types of air pollution
control systems. Furthermore, there is a significant
potential for corrosion and erosion of the scrubber
vessel and ductwork. For these reasons, fugitive leaks
are a common problem. The inhalation hazards can
include chemical asphyxiants, physical asphyxiants,
toxic gases, and toxic particulate. Inspectors should
avoid all areas with obvious leaks and any areas with
poor ventilation. During Level 3 and Level 4 inspec-
tions, only small diameter ports should be used.
Extreme care is often necessary when walking
around the scrubber and when climbing access ladders.
Slip hazards can be created by the water droplets
reentrained in the exhaust gas, by the liquor draining
from the pumps, and by the liquor seeping from pipes
and tanks. These slip hazards are not always obvious.
Furthermore, freezing can occur in cold weather.
A few systems are subjected to fan imbalance
conditions due to the build-up of sludge on the fan
blades, due to the corrosion of the fan blades, due to
the erosion of the fan blades, and a variety of other
factors. The inspection should be terminated immedi-
ately whenever an inspector observes a severely vibra-
ting fan. A responsible plant representative should
be notified once the inspector reaches a safe location.
Severely vibrating fans can rapidly disintegrate.
All liquor samples necessary for Level 3 or Level
4 inspections should be taken by the plant personnel,
not the inspector. Furthermore, inspectors should only
ask responsible and experienced plant personnel to take
86
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the samples. Eye injuries and chemical burns (in some
cases) are possible if the samples are taken incorrectly.
Inspectors should not, under any circumstances,
enter a wet scrubber vessel or any tank or confined
area in the system. All of the necessary inspection
steps can be accomplished without internal inspections.
Access hatches or viewing ports should not be opened
during the inspection due to the risk of eye injuries.
87
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REFERENCES
1. Hopper, T., "Municipal Incinerator Enforcement Manual,"
U.S. Environmental Protection Agency Publication
No. 340/1-76-013, January 1977.
2. Radian Corporation, "Municipal Waste Combustion
Study: Characterization of the Municipal Waste
Combustion Industry," U.S. Environmental Protection
Agency Publication No. 530-SW-87-021b, June 1987.
3. Richards, J.R., and Segall, R.R., "Baseline Source
Inspection Techniques," U.S. Environmental Protection
Agency Publication No. 340/l-85-022a, June 1985.
4. U.S. EPA Stationary Source Compliance Division, "Air
Compliance Inspection Manual," U.S. Environmental
Protection Agency Publication No. 340/1-85-020,
September 1985.
5. Richards, J.; "Advanced Inspection Techniques for
Senior Inspectors and Managers, Instructor's Guide,"
U.S. Environmental Protection Agency, Air Pollution
Training Institute Course #455 Manual, November 1987.
6. Seeker, W.R., Lanier, W.S., and Heap, M.P., "Municipal
Waste Combustion Study: Combustion Control of MSW
Combustors to Minimize Emission of Trace Organics,"
U.S. Environmental Protection Agency Publication
No. 530-SW-87-021C, June 1987.
7. Richards, J., "Air Pollution Source Field Inspection
Notebook," U.S. Environmental Protection Agency
Publication No. 340-1-88-001, 1988.
8. Seeker, W.R., Lanier, W.S., and Heap, M.P.; "Municipal
Waste Combustion Study: Combustion Control of MSW
Combustors to Minimize Emission of Trace Organics,"
U.S. Environmental Protection Agency Publication
No. 530-SW-87-C, June 1987, page 4-6.
89
-------
9. Seeker, W.R., Lanier, W.S., and Heap, M.P.; "Municipal
Waste Combustion Study: Combustion Control of MSW
Combustors to Minimize Emission of Trace Organics,"
U.S. Environmental Protection Agency Publication
No. 530-SW-87-C, June 1987, page 2-4.
10. Ozvacic, V., Wong, G., Tosine, H., Clement, R.E.,
and Osborne, J.; "Emissions of Chlorinated Organics
from Two Municipal Incinerators in Ontario," J. of the
Air Pollution Control Association, Volume 35, No. 8,
pages 849-855, August 1985.
11. Fred C. Hart Associates, Inc., "Conclusions of New
York's Study of Dioxins and MSW Incineration," Waste
Age, pages 25-30, November 1984.
12. Hasselriis, F., "Minimizing Trace Organic Emissions
From Combustion of Municipal Solid Waste by the Use
of Carbon Monoxide Monitors," 1986 National Waste
Processing Conference, pages 129-144, June 1986.
13. O'Connell, W.L., Stotler, G.C., and Clark, R.,
"Emissions and Emission Control in Modern Municipal
Incinerators," 1982 National Waste Processing
Conference, pages 285-297, May 1982.
14. Seeker, W.R., Lanier, W.S., and Heap, M.P.; "Municipal
Waste Combustion Study: Combustion Control of MSW
Combustors to Minimize Emission of Trace Organics,"
U.S. Environmental Protection Agency Publication
No. 530-SW-87-C, June 1987, page 4-8.
15. Hurst, B.E., and White, C.M., "Thermal DeNOx: A
Commercial Selective Noncatalytic NOx REduction
Process for Waste-to-Energy Applications," 1986
National Waste Processing Conference, pages 119-127,
June 1986.
16. Cross, F., O'Leary, P., and Walsh, P.; "Waste-to-
Energy Systems: The Menu," Waste Age, pages 52-60,
February 1987.
90
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17. Walsh, P., O'Leary P., and Cross, F., "Residue
Disposal from Waste-to-Energy Facilities," Waste Age,
pages 57-62, May 1987.
18. Nollet, A.R., and Greeley, R.H., "New Concepts for
Explosion Alleviation in Shred-First Solid Waste
Plants,11 1982 National Waste Processing Conference,
pages 271-276, May 1982.
19. Barberis, J.L. and Lilly, R., "Shakedown Trials:
New York State RDF Steam Generating Plant - Albany,
New York," 1982 National Waste Processing Conference,
pages 277-283, May 1982.
20. Reason, J., "Next step for Waste-to-Energy: Better
Availability, Efficiency," Power, pages 17-24,
July 1986.
21. Seeker, W.R., Lanier, W.S., and Heap, M.P.; "Municipal
Waste Combustion Study: Combustion Control of MSW
Combustors to Minimize Emission of Trace Organics,"
U.S. Environmental Protection Agency Publication
No. 530-SW-87-C, June 1987, page 3-17.
22. Donnelly, J.R., Quach, M.T., and Moller, J.T.,
"Design Considerations for Resource Recovery Spray
Dryer Absorption Systems," Presented at the 79th
Annual Meeting of the Air Pollution Control
Association, Minneapolis Minnesota, June, 1986.
23. Ferguson, W.B. Jr., Borio, D.C., and Bump, D.L.,
"Equipment Design Considerations for the Control of
Emissions From Waste-to-Energy Facilities," Presented
at the 79th Annual Meeting of the Air Pollution
Control Association, Minneapolis Minnesota, June 1986.
24. Sedroan, C.B., and Brna, T.G., "Municipal Waste
Combustion Study Flue Gas Cleaning Technology, U.S.
Environmental Protection Agency Publication
No. 530-SW-87-021d, June 1987.
91
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25. Holler, J.T. and Christiansen, O.B.; "Dry Scrubbing
of MSW Incinerator Flue Gas by Spray Dryer Absorption:
New Developments in Europe," Presented at the 78th
Annual Meeting of the Air Pollution Control
Association, Detroit, Michigan, June, 1985.
26. Foster, J.T., Hochhauser, M.L., Petti, V.J.,
Sandell, M.A., and Porter, T.J., "Design and Start-up
of a Dry Scrubbing System for Solid Particulate and Acid
Gas Control on a Municipal Refuse-Fired Incinerator,"
Presented at the Air Pollution Control Association
Specialty Conference on Thermal Treatment of Municipal,
Industrial and Hospital Wastes, Pittsburgh, Pa.,
November 4-6, 1987.
92
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FIELD INSPECTION PROCEDURES
93
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1. INSPECTION PROCEDURES
1.1 Inspection Purpose and Scope
General
Objectives
Complete an independent, technically
defensible evaluation of the
compliance status.
Determine if stack tests or other
procedures are necessary to complete
the evaluation of compliance status.
Compile sufficient technically
defensible and legally sound data to
support any enforcement necessary.
Help plant personnel understand
regulatory requirements.
Do whatever possible within the
inspection authority to help sources
and agencies avoid costly and time
consuming litigation.
Specific
Objectives
Determine if there are any significant
baseline shifts in system operation
that are indirect indicators of non-
compliance with emission limitations.
Review continuous emission monitors
for direct indications of noncompli-
ance since the last inspection.
Review system operating logs for in-
direct indications of occasional
noncompliance since the last inspection.
Evaluate equipment operating practices
to qualitatively determine the potential
for near term equipment failures and
excess emission problems.
95
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INSPECTION PROCEDURES
Inspection Summaries
1.1 Inspection Purpose and Scope (Continued)
Inspection Do not prescribe or demand specific
Limitations operating practices, start-up and
shutdown practices, system operating
rate limits, or equipment
modifications.
Do not do anything which endangers
you or the plant personnel.
Do not enter equipment under any
circumstances.
Obey all agency and plant safety
policies.
Respect all company-union agreements.
Do not conduct the inspection alone.
An authorized plant representative
must be present at all times.
Do not attempt to reach conclusions
of law regarding the compliance status,
An inspection is limited to gathering
technical data.
96
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INSPECTION PROCEDURES
Inspection Summaries
1.2 Levels of Inspection
Level 1
Basic
Level 2
Follow-up
Level 2
Level 3
Level 4
Visible emissions observations and
odor surveys made from outside the
plant boundaries (not discussed in
this inspection notebook)
Walkthrough evaluation of the munici-
pal waste incinerator, the waste
preparation and handling equipment,
the residue disposal equipment, and
the air pollution control system
All data provided by on-site gauges
and records
The minimum inspection steps necessary
to determine compliance status and to
evaluate potential for violations
More comprehensive Level 2 inspection
made when there are indications of
noncompliance since the last inspection
or of emerging problems which could
cause noncompliance in the immediate
future
Comprehensive inspections made when
there is a need to negotiate compli-
ance programs with plant personnel or
to prepare enforcement cases
Certain data is obtained by inspector
supplied instruments
Initial inspection made by senior
inspector or agency managers to
acquire baseline data, to identify
potential inspection safety problems,
and to tailor the inspection check-
lists to the specific plant
97
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2. INSPECTION OF COMBUSTION EQUIPMENT
2.1 Inspection Summaries
2.1.1 Combustion Equipment Inspection Overview
Incinerator Evaluate adequacy of fuel-air ratios
since this can affect the emissions of
particulate, organic pollutants, and
dioxin/furans.
Evaluate adequacy of exit gas tempera-
tures since this is an indirect
indicator of dioxin/furan survival.
Gas temperature also affects nitrogen
oxides generation by thermal mechanisms.
Evaluate flue gas oxygen concentrations
since this affects particulate emissions,
dioxin/furan survival, and nitrogen
oxides formation. These also indicate
possible air infiltration.
Evaluate temporal variations in the waste
fuel quality and the methods used at the
plant to adjust combustion conditions.
Evaluate physical condition of
incinerator shell and waste feed
delivery equipment. Check for audible
air infiltration into incinerator and
for audible air losses from undergrate
plenums and forced draft supply ducts.
Review combustion equipment operating
load variations. These systems have
limited turndown capability and
operation at low loads can possibly
lead to high dioxin/furan emissions.
Review start-up, shutdown frequencies
and procedures since these can cause
short term emission problems and can
lead to rapid equipment deterioration.
99
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INSPECTION OF COMBUSTION EQUIPMENT
Inspection Summaries
2.1.1 Combustion Equipment Inspection Overview
Waste
Receiving,
Storage,
and
Handling
Steam
and
Electricity
Generation
Residue
Handling
and
Disposal
Evaluate efforts to mix wastes to
minimize the heterogeneous character-
istics and stabilize combustion.
Check for obvious changes in the types
of wastes being fired and/or in the
size range of the waste being fired.
Such changes could increase emissions
and/or require substantial operational
adjustments in the incinerator.
Evaluate efforts to remove bulky
items and explosive items which could
damage incinerator equipment.
Check for fugitive particulate
emissions and for windblown waste from
trucks and receiving area.
Check for odor emissions.
Review steam and/or electrical power
generation rates as one indicator of
load and the variability of load.
Rapid load swings and operation at
low loads can lead to high pollutant
emissions. However, note that energy
generation is also a function of fuel
heating value.
Check records concerning incinerator
bottom ash composition since this
could indicate combustion problems.
Observe bottom ash to determine
obvious combustion problems.
Check for RCRA Subtitle C compliance
and for fugitive emissions.
100
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INSPECTION OF COMBUSTION EQUIPMENT
Inspection Summaries
2.1.2 Inspection Checklists
2.1.2.1 Basic Level 2 Inspection Checklist
Mass Burn,
RDF-Fired,
and
Modular
Systems
RDF-Fired
Systems
Only
Modular
Incinerators
Only
oUniformity of ash beds on the grates
in the burnout zone
o Undergrate air pressures
o Overfire air pressures
oIncinerator draft
o Firing rates, last 8 hours
o Exit gas temperatures, last 8 hours
o Exit gas oxygen levels, last 8 hours
oExit gas carbon monoxide concentrations,
last 8 hours
oUltimate disposal of ash
o Fugitive emissions from waste receiving
and ash disposal operations
o Flowchart of system if not already
available
oQuantities of coal, wood, or other
supplemental fuels fired, last 8 hours
Primary and secondary chamber exit gas
temperatures, last 8 hours
Incinerator shell corrosion
Frequency of dump stack operation
101
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INSPECTION OF COMBUSTION EQUIPMENT
Inspection Summaries
2.1.2.2 Follow-up Level 2 Inspection Checklist
Mass Burn,
RDF-Fired,
and
Modular
Systems
RDF-Fired
Systems
Only
Modular
Incinerators
Only
o All elements of Basic Level 2 inspection
o Variability of wastes being charged
o General types and sizes of wastes fired
o Forced draft air leaks in undergrate
plenums and supply ducts
oIncinerator shell audible air
infiltration
o Audible air infiltration through
charging area
° Physical appearance of overfire air
nozzles (to the extent observable)
o Economizer ash reinjection (yes or no)
o Bottom ash appearance
o Exit gas temperature records, last 12
months
oExit gas oxygen level records, last 12
months
° Exit gas carbon monoxide concentration
records, last 12 months
o Forced draft and induced draft fan
currents
o Operating times of the auxiliary burner
° Physical appearance of RDF distributor
equipment (to the extent observable)
Quantities of waste placed in charge
pit for each charge
102
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INSPECTION OF COMBUSTION EQUIPMENT
Inspection Summaries
2.1.2.3 Combustion Equipment Level 3 Inspection Checklist
Mass Burn,
RDF-Fired,
and
Modular
Systems
o All elements of Basic and Follow-up
o Level 2 inspections
b Measured exit gas oxygen concentration
o Measured exit gas carbon monoxide
concentration
o Measured undergrate and overfire air
pressures (Mass Burn and RDF-Fired)
o Bottom ash samples
o Start-up and shutdown procedures
2.1.2.4 Combustion Equipment Level 4 Inspection Checklist
Mass Burn,
RDF-Fired,
and
Modular
Systems
o All elements of Level 2 follow-up
inspections and Level 3 inspections
o Flowchart of system
o Possible locations for additional
measurement ports and stack sampling ports
o Possible locations for ash sampling
0 Potential safety problems and necessary
inspector safety equipment
o Types of waste composition records and
incinerator operating records
o Necessary modifications to inspection
checklists due to site specific conditions
103
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INSPECTION OF COMBUSTION EQUIPMENT
Basic Level 2 Inspection Procedures
2.2 Level 2 Inspection Procedures
2.2.1 Basic Level 2 Inspection Procedures
Uniformity of ash bed on the grates in the burnout zone
(MASS BURN UNITS)
Nonunifona fuel-ash layers on the grates leads to
unequal fuel-air ratios and increased emissions of
particulate matter and partially combusted organic
compounds. The fuel-ash bed provides some of the air
flow resistance necessary to ensure uniform air
velocities upward through the grates. One reasonably
convenient location to observe the ash layer is the
burnout area since there is much lower flame brightness.
Also, the risk of shrapnel from exploding cans and
other waste is lower in this area. Nevertheless, extreme
caution is warranted whenever attempting to look inside
the incinerator. Eye and face protection is mandatory
and it is necessary to choose a viewing angle that is
protected from the trajectories of flying debris.
Perfectly even fuel distribution at the inlet of
the unit is never possible, therefore, some slight
variations in the ash layer at the burnout zone will
generally exist. However, there should be no substantial
side-to-side variations or variations along the line of
grate movement in the burnout zone. There should be no
extreme ash layer thin spots or exposed grate bars
since these indicate entrainment of partially combusted
ash due to the high localized undergrate velocities.
Also, there should be no very bulky noncombustible
waste in the ash deposits since this potentially damages
the ash handling equipment and since the items contribute
to nonuniform fuel distribution.
Uniformity of fuel beds on the grate (RDF-FIRED UNITS)
Nonuniform fuel-ash layers on the grates leads to
unequal fuel-air ratios and increased emissions of par-
ticulate matter and partially combusted organic compounds,
The fuel-ash bed provides some of the air flow resistance
necessary to ensure uniform air velocities upward through
104
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INSPECTION OF COMBUSTION EQUIPMENT
Basic Level 2 Inspection Procedures
Uniformity of fuel beds on the grate (RDF-FIRED UNITS)
the grates. The most convenient locations for observing
the fuel-ash beds are the front access hatches located
below the feeders on spreader stoker boilers. At this
location, the combustion is essentially completed and
only burned out ash and char remain. Therefore, the
flame luminosity is not a problem as long as you look
downward through the hatch rather than attempting to
look straight inwards. Eye and face protection is
mandatory due to the chance that small aerosol cans will
explode or the chance that there will be sudden inciner-
ator static pressure excursions. Neither of these pro-
blems is especially common with this type of incinerator.
From the front access hatches it is possible to
evaluate the adequacy of side-to-side variations in the
ash bed. Significant differences generally indicate a
feeder problem (Generally there are from two to four
separate feeders.), or fuel size segregation in the
fuel delivery equipment.
Uniformity of fuel beds on the grate (MODULAR UNITS)
This inspection step is not applicable to Modular
Incinerators. Do not attempt to look through the hatches
of this type of system.
Underqrate air pressures (MASS BURN UNITS)
Most modern mass burn incinerators have at least
four undergrate plenums at least two for the combustion
zone, one for initial drying of the waste feed, and one
for the burnout zone. The static pressures in each
zone are set by adjustable dampers located in the
supply lines to each plenum. The static pressures are
monitored in the main control room and most operators
record these pressures on a frequent basis.
The typical static pressure values depend primarily
on the grate design characteristics and there is consid-
erable variation among incinerator manufacturers. Values
are often between 1 to 5 inches of water and are rela-
tively stable during the inspection.
105
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INSPECTION OF COMBUSTION EQUIPMENT
Basic Level 2 Inspection Procedures
Undergrate air pressures (MASS BURN UNITS)
Actual undergrate air pressures depend on the fuel
bed depths being used, on the extent of pluggage of the
grates, and on the incinerator operating rate. Some
variations from baseline levels are normal. Extremely
low values could indicate thin spots in the fuel-ash
bed and possible incomplete burnout of the waste. High
values could indicate partial grate pluggage and non-
uniform air-fuel ratios on the grate.
Undergrate air pressure (RDF-FIRED UNITS)
Spreader stoker type incinerators have only one
undergrate plenum. The static pressure in this plenum
is generally controlled by the forced draft fan dampers.
The static pressure is monitored in the main control
room and most operators record this pressure on a
frequent basis.
The typical static pressure values depend primarily
on the grate design characterisitics and there are
moderate variations among stoker manufacturers. Values
are often in the range of 1 to 3 inches of water. The
indicated values should be relatively stable over the
time frame of the inspection.
Actual undergrate air pressure depend on the fuel
bed depths being used, the ash content of the waste,
the extent of pluggage of the grates, and the incinerator
operating rate. Some variations from baseline levels
are normal. Extremely low values could indicate thin
spots in the fuel-ash bed and possibly incomplete burnout
of the waste. High values could indicate partial grate
pluggage and nonuniform air-fuel ratios on the grate.
Undergrate air pressure (MODULAR UNITS)
This inspection step is not applicable to Modular
Units.
106
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INSPECTION OF COMBUSTION EQUIPMENT
Basic Level 2 Inspection Procedures
Overfire air pressures (MASS BURN UNITS)
Most mass burn units have from two to four overfire
air headers. Each of these headers supply an array of
nozzles within the incinerator. The air pressures in
each of the headers is controllable by means of dampers.
The pressures can be monitored either in the control
room or by static pressure gauges on the headers them-
selves (gauges not present in some older units). Typical
values are in the range of 15 to 50 inches of water.
These values should be relatively stable over the time
frame of the inspection.
Some variations from baseline levels are common
since these are changed slightly to optimize combustion
and since these are sometimes varied as a function of
the incinerator load. However,major shifts from the
baseline levels are very uncommon and should be ques-
tioned. Very low overfire air pressures suggest poor
mixing in the upper zones of the combustion chamber and
this could lead to poor combustion of volatile compounds
released from the grate and poor destruction of dioxin/
furan compounds. Much higher than baseline values
indicate either than plant personnel have installed
smaller diameter nozzles in the incinerator or that a
greater fraction of the total combustion air is now
being supplied by the overfire nozzles rather than the
undergrate plenums.
Overfire air pressures (RDF-FIRED UNITS)
Most RDF-fired spreader stokers have between two
and four separate overfire air headers. Generally
there are two parallel headers on the front wall, one
directly below the feeders and a second several feet
above the feeders. There is usually at least one
header across the back furnace wall, several feet above
the grates. The air pressures in each of the headers
is controllable by means of dampers. The pressures are
normally monitored either in the control room or by
static pressure gauges on the headers themselves.
Typical values are between 15 to 50 inches of water and
they are relatively stable during the inspection.
107
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INSPECTION OF COMBUSTION EQUIPMENT
Basic Level 2 Inspection Procedures
Overfire air pressures (RDF-FIRED UNITS)
Some variations from baseline levels are common
since these are changed slightly to optimize combustion
and since these are sometimes varied as a function of
the incinerator load. However, major shifts from the
baseline levels are very uncommon and should be ques-
tioned. Very low overfire air pressures suggest poor
mixing in the upper zones of the combustion chamber and
this could lead to poor combustion of volatile compounds
released from the grate and poor destruction of dioxin/
furan compounds. Much higher than baseline values
indicate either that plant personnel have installed
smaller diameter nozzles in the incinerator or that a
greater fraction of the total combustion air is now
being supplied by the overfire nozzles rather than the
undergrate plenums.
Overfire Air Pressure (MODULAR UNITS)
This inspection step is not applicable to Modular
Incinerators.
Incinerator draft (ALL TYPES OF INCINERATORS)
The static pressure of the incinerator in the main
combustion zone is typically a negative 0.05 to a
negative 0.15 inches of water regardless of equipment
manufacturer. This static pressure is monitored contin-
uously by an instrument located in the main control room.
The present value should be in this range and it should
be relatively stable. Incinerator drafts less than
negative 0.15 inches of water indicate problems with
the forced draft air supply and suggest severe air
infiltration. Both of these lead to less than ideal
combustion conditions. Incinerator drafts that are
0.0 inches of water or higher demonstrate that the
incinerator has gone positive pressure. This is a
severe combustion problem and a severe personnel
exposure problem. Under no circumstances should the
incinerator operate with positive pressures. This
indicates an induced draft fan problem or a gas flow
resistance problem either in the incinerator or the air
pollution system.
108
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INSPECTION OF COMBUSTION EQUIPMENT
Basic Level 2 Inspection Procedures
Exit gas temperatures for last 8 hours (All INCINERATORS)
The incinerator gas temperatures are generally kept
above 1800°F to ensure maximum destruction of dioxin/
furan compounds to complete oxidation of carbon monoxide
to carbon dioxide. This value is checked to confirm
that the plant has been able to maintain this minimum
temperature.
This temperature is monitored in the incinerator
control room along with other gas temperatures through-
out the system. In most plants, the temperature is
either recorded on a multi-pen chart recorder or moni-
tored by a data acquisition system. In either case,
it is possible to scan the temperature data for the
last 8 hours to determine the stability of this value.
Some variations in the exit gas temperature are normal
since it is a function of the incinerator load and the
waste fuel heating value. It can be depressed by wet
fuel such as leaves and it can be incresed when substan-
tial quantities of plastics and other high caloric
value wastes are added (Mass Burn and Modular Units).
The auxiliary burner (if present) should be operated if
the gas temperature falls substantially below 1800°F.
Exit gas oxygen levels for last 8 hours (ALL INCINERATORS)
There is usually a continuous oxygen analyzer
located downstream of the feedwater economizer (Mass
Burn or RDF-Fired) or the waste heat boiler (Modular).
As indicated in the reference section of this notebook,
the typical oxygen concentrations are generally in the
range of 6 to 12%. Values lower than 6% generally
indicate inadequate excess air rates and incomplete
combustion of volatile compounds. Values higher than
12% generally indicate severe air infiltration through
the charging area, the incinerator shell, or the ash
pit. The cold air infiltrating the unit could quench
the oxidation reactions and cause high concentrations
of partially combusted material to escape the incinerator.
These emissions could include dioxins and furans.
109
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INSPECTION OF COMBUSTION EQUIPMENT
Basic Level 2 Inspection Procedures
Exit gas carbon monoxide levels for last 8 hours (All
TYPES OF INCINERATORS
Carbon monoxide is used as one of the indirect
indicators of the adequacy of combustion. Typical
concentrations are in the range of 25 to 100 ppm
(uncorrected). Average values above 200 ppm suggest
significant combustion problems. Inspectors should
check the frequency and severity of short term CO
terms. Plant personnel should be asked about possible
corrective actions to improve combustion. Also, the
instrument calibration and routine maintenance records
should be briefly reviewed.
Flowchart of the system (ALL TYPES OF INCINERATORS)
A simple flowchart of the incinerator system com-
ponents and material streams should be prepared to aid
in the evaluation of the plant instruments and the
incinerator operating conditions. The flowchart should
include a block diagram of (1) the waste receiving,
storage, and handling operations, (2) the incinerator
chamber(s), the overfire air manifolds, the undergrate
plenums, the ash pits, the auxiliary burners, the econ-
omizer ash reinjection lines, (3) the air pollution
control system and solids handling equipment, and (4)
the stack and any effluent gas continuous emission
monitors. The main instruments used in the inspection
should be identified on this simple sketch.
Fugitive emissions (ALL TYPES OF INCINERATORS)
Visible emission observations should be performed
whenever there are apparent fugitive emissions from the
waste receiving area, the RDF processing equipment, or
the bottom ash handling equipment. There should not be
any uncovered outside storage of bottom ash or control
device ash. Furthermore, good plant housekeeping is
necessary to minimize fugitive emissions. Care is
necessary to avoid any skin contact with the waste
feed, the RDF fuel, or the ash. It is also necessary
to avoid overhead equipment and other moving equipment
in these areas.
110
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INSPECTION OF COMBUSTION EQUIPMENT
Basic Level 2 Inspection Procedures
Quantities of supplemental fuels for last B hours
(RDF-FIRED UNITS)
The combustion conditions are significantly depend-
ent on the mix of fuels being fired. The quantities of
coal or wood being fired can be determined approximately
by recording the scale readings. This information is
generally recorded on the daily operating logs. However,
it should be noted that fuel scale readings require
frequent calibration and these are often incorrect by
as much as 50% despite the best efforts of qualified
maintenance personnel. Therefore, this data provides
only a very rough indication of the supplemental fuel
feeding rates.
Primary and secondary chamber temperatures for last 8
hours (MODULAR UNITS)
The primary and secondary chamber exit gas temper-
atures are monitored by thermocouples in the outlet
ducts. This data can be obtained from the main inciner-
ator control panels. However, in some of the especially
small units, this is not recorded on a continuous
basis. In these cases, the temperature history over
the last 8 hours should be obtained .from the hour-by-
hour entries in the daily operating log sheets.
The primary chamber outlet temperatures are gener-
ally in the range of 1000 to 1200°F. For starved air
units, higher temperatures may indicate air infiltration
into the primary chamber and premature oxidation of the
volatile material released during waste combustion.
For excess air units, higher temperatures generally
indicate the charging of wastes with high caloric values
Low temperatures in the primary chamber indicate low
waste feed rates or low waste caloric value. Some
slight increases and decreases in the primary chamber
temperature are normal during the ram charging of fresh
wastes.
The secondary chamber outlet gas temperatures are
normally between 1800 and 2000°F. The secondary chamber
burner should on when necessary to maintain 1800°F.
Ill
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INSPECTION OF COMBUSTION EQUIPMENT
Basic Level 2 Inspection Procedures
Incinerator shell corrosion (MODULAR INCINERATORS)
Evaluate the exterior of both the primary and
secondary chambers for signs of corrosion. This can be
caused by the infiltration of cold air that in turn
results in the absorption of highly corrosive hydrogen
chloride into water droplets on the metal surfaces.
The air infiltration condition worsens as the corrosion
continues. This can lead to "cold" zones in the affected
chamber and thereby contribute to increased emissions
of partially combusted organic compounds.
Frequency of dump stack operation (MODULAR INCINERATORS)
There is generally a direct discharge dump stack
on the back of the secondary chamber. In some plants,
this is used when there is no need for the steam that
would be generated in the waste heat boiler or when the
waste heat boiler is down. For modular incinerators
requiring air pollution control equipment, the operation
of the dump stack results in the bypassing of this
device. The status of the dump stack can be determined
by observing the position of the stack seal (on the top
of stack) or by noting the dump stack status light on
the control panel.
112
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INSPECTION OF COMBUSTION EQUIPMENT
Follow-up Level 2 Inspection Procedures
2.2.2 Follow-up Level 2 Inspection Procedures
Variability of wastes being charged (All INCINERATORS)
From a safe vantage point, observe the variability
of the wastes being charged to the incinerator (Mass
Burn and Modular Incinerators). The operator should be
attempting to mix wastes with much different heating
values. Sudden shifts in the moisture content, density,
and heating value of the wastes being charged can upset
combustion within the incinerator and lead to excess
pollutant emissions.
The bulky, noncombustible items and the potentially
dangerous items should be removed prior to charging
(Mass Burn and Modular Incinerators) or prior to shred-
ding (RDF-Fired Incinerators). A partial list of
inappropriate materials for incineration is provided
below.
Red bag (infectious) wastes Gas cylinders
Paint and solvent cans Large appliances
Live ammunition boxes Small appliances
Metal furniture parts Mattresses
Automotive and bicycle parts Cables
Bagged asbestos waste Chemical drums
Tree stumps
Variability of RDF fuel (RDF-FIRED UNITS)
If there are indications of occasional combustion
system problems identified during the routine Level 2
inspection, the variability of the RDF fuel should be
briefly reviewed. RDF fuel proximate and ultimate
analyses provide one measure of the extent of variability.
Fuel samples must be sent to a testing laboratory for
the determination of proximate and ultimate analyses.
The reports consist of a single page. As part of these
analyses, it is also helpful to determine the ash
fusion temperature data.
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INSPECTION OF COMBUSTION EQUIPMENT
Follow-up Level 2 Inspection Procedures
Variability of RDF fuel (RDF-FIRED UNITS)
Low ash fusion values create possible slagging
problems and partial pluggage of the stoker grates.
These problems disrupt the fuel-air ratios in the boiler
and increase pollutant emissions. They also create
major maintenance problems for the plant.
Another very important fuel property is the size
distribution. This data is obtained by a relatively
simple gravimetric test using a set of screens. This
test can be conducted on-site. A relatively consistent
fuel size gradation is necessary to ensure proper fuel-
air ratios in the boiler. Excessive levels of very
fine material can result in large piles of fuel at the
front of the stoker immediately below the distributors.
Excessive quantities of large diameter material will
lead to fuel piles at the back end of the stoker.
Forced draft air leaks in undergrate plenums and supply
ducts (MASS BURN AND RDF-FIRED UNITS)
Possible leaks of forced draft air should be inves-
tigated if the undergrate air pressures are significantly
higher or significantly lower than the baseline levels
for a given incinerator load. While these leaks are
rarely the main reason for the change in undergrate
pressures, they can be serious problems since they
reduce the total quantity of undergrate air used for
combustion. The most likely leak sites, which can be
found during a Level 2 inspection, include the side
walls between the incinerator and the undergrate
plenums and any forced draft duct expansion joints.
Incinerator shell audible air infiltration (ALL TYPES
OF INCINERATORS)
This leads to cold zones within the incinerator
and increased emissions of partially combusted or reacted
organic compounds. Most of these leaks occur in the
refractory in inaccessible locations. However, they
are sometime noticeable around the charging area and
near the overfire air headers on both the front and
back of the incinerator.
114
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INSPECTION OF COMBUSTION EQUIPMENT
Follow-up Level 2 Inspection Procedures
Economizer ash reinjection (MASS BURN AND RDF-FIRED
UNITS)
If the unit has a chronic problem with excess
particulate emissons, inspectors should determine if
the plant is continuing to reinject economizer ash back
into the incinerator. In some cases, reinjection simply
recycles ash through the system until it is small enough
to escape both the economizer and the air pollution
control device. In other plants, reinjection can allow
very modest thermal efficiency improvements without
severe equipment wear and emission problems. The use
of reinjection can be visually determined by using the
site ports generally installed on the relatively short
pipes leading from the economizer hopper to the back of
the incinerator. In some cases, operators can also
safely obtain samples of the economizer ash. However,
this is rarely necessary.
Bottom ash appearance (ALL TYPES OF INCINERATORS)
The presence of substantial carbonaceous material
in the incinerator ash is a clear indication of combus-
tion problems. The ash characteristics can be observed
through observation hatches around the burnout zone of
the incinerator. In some cases, plant personnel may be
able to provide a small sample of ash which is being
sent to the landfill for disposal. However, inspectors
should not under any circumstances ask plant personnel
to take any personal risks to get a sample of the ash.
The sample should be sealed and handled properly since
it may contain hazardous materials.
Exit gas temperature records for last 12 months (ALL
TYPES OF INCINERATORS)
The gas temperature records since the last inspec-
tion should be reviewed to identify any problems in
maintaining a reasonable minimum exit gas temperature.
The generally accepted value is 1800°F. The auxiliary
burner (if present) is used to maintain minimum tempera-
ture during periods of waste feed interruption or during
periods when excessive quantities of wet or noncombus-
tible waste has been charged. For modern units, the
115
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INSPECTION OF COMBUSTION EQUIPMENT
Follow-up Level 2 Inspection Procedures
Exit gas temperature records for last 1^2 months (ALL
TYPES OF INCINERATORS)
gas temperature records and the status of the auxiliary
burner can be determined by scanning the daily operating
logs of the incinerator, by scanning some of the temper-
ature recorder strip charts, or by checking the output
reports from the data acquisition system.
Exit gas oxygen levels for last 12 months (ALL TYPES
OF INCINERATORS)
For modern units, the continuous oxygen analyzer
data for the past year should be scanned to determine
if the oxygen concentrations have remained in the normal
range. In most plants, this range is 6 to 12%. Values
higher or lower than this range can often indicate
combustion problems. This data is available on the
daily incinerator operating logs, on the analyzer strip
charts, or on the data sheets generated by the data
acquisition system.
Exit gas carbon monoxide levels for last 12 months
(ALL TYPES OF INCINERATORS)
Carbon monoxide concentration provides one indica-
tion of the adequacy of combustion (CO is not monitored
on all units). Values should generally be below 100 ppm
(uncorrected) except during periods of start-up and
shutdown. This data is available on the daily inciner-
ator operating logs, on the analyzer strip charts, or on
the data sheets generated by the data acquisition system.
Forced draft and induced draft fan motor currents
(ALL TYPES OF INCINERATORS)
These values are used as one indicator of the
overall operating rate of the incinerator system. The
steam generation rate data are not sufficient, due to
the variability of the waste feed characteristics and
the high potential moisture and noncombustibles levels
in this feed. These values should be compared against
baseline data sets as one means to confirm that the
system is operating at full load. It should be noted
that this data is not available in some facilities.
116
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INSPECTION OF COMBUSTION EQUIPMENT
Follow-up Level 2 Inspection Procedures
Ultimate disposal of ash and material removed prior to
charging (ALL TYPES OF INCINERATORS)
Waste handling and disposal practices should be
determined to confirm compliance with labeling, trans-
port, and disposal requirements of RCRA.
Forced draft air leaks in undergrate plenum and supply
duct (MASS BURN AND RDF-FIRED UNITS)
Possible leaks of forced draft air should be inves-
tigated if undergrate air pressure is significantly
higher or significantly lower than the baseline level
for a given boiler load. While these leaks are rarely
the main reason for the change in undergrate pressure,
they can be serious problems since they reduce the
total quantity of undergrate air used for combustion.
The most likely leak sites, which can be found during a
Level 2 inspection, include the side walls between the
incinerator and the undergrate plenum and any forced
draft duct expansion joints.
Physical condition of overfire air nozzles, (MASS BURN
AND RDF-FIRED UNITS)
On some units, side observation ports can be used
to see the upper rows of overfire air nozzles across
the front wall and back walls of the boiler. These
should not be plugged or slagged over. Eye and face
protection is mandatory when looking into the boiler.
Steam rates and feed water rates for last 12 months,
ALL TYPES OF INCINERATORS)
The variability of incinerator load can be evalua-
ted using steam rate and feedwater rate data available
from the daily logs or the strip chart recorders.
Periods of high opacity, high carbon monoxide concen-
tration, low exit gas temperatures, and/or unusual
oxygen levels should be compared with the incinerator
load data.
117
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INSPECTION OF COMBUSTION EQUIPMENT
Follow-up Level 2 Inspection Procedures
Audible air infiltration into incinerator shell and
charging door (MODULAR UNITS)
Air infiltration through warped charging doors or
corroded areas of the shell can lead to localized
"cold" zones in the primary chamber. They can also
cause some undesirable particle reentrainment and carry-
over into the secondary chamber. Care must be exercised
in attempting to find audible leaks, since there is
moving equipment around the charge pit and since there
can be fugitive pollutant emissions accumulating in the
poorly ventilated areas around the primary chambers.
118
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INSPECTION OF COMBUSTION EQUIPMENT
Level 3 Inspection Procedures
2.3 Level 3 Inspection Procedures
Economizer/waste heat boiler exit gas temperature
(ALL TYPES OF INCINERATORS)
The economizer or waste heat boiler exit gas temper-
ature should be used as an indirect measurement of the
average gas temperature entering the superheater section
of the boiler/incinerator. Direct measurement of the
gas temperature entering the superheater or waste heat
boiler is very difficult using portable instruments
since the gas temperature is very hot ( >1800°F hope-
fully) and since relatively long probes are necessary
to reach representative measurement locations. Also,
most systems do not have safe and convenient measure-
ment ports in this area of the incinerator.
The measured economizer or waste heat boiler exit
gas temperature can be compared against baseline values
for similar boiler load conditions. It can also be
compared against the economizer exit gas temperature
monitored continuously by the on-site instruments.
Lower gas temperature observed at this location suggest
low gas temperature readings from the on-site temperature
monitors located upstream of the superheater.
Exit gas oxygen concentration (ALL TYPES OF INCINERATORS)
The exit gas oxygen concentration should be measured
when there are indications of combustion related emis-
sion problems and when the on-site oxygen analyzer is
either inoperative or nonexistent. The types of in-
struments available include multi-gas combustion gas
analyzers, ORSATs, and manual single-gas absorbers.
Sampling locations having extreme high gas tempera-
tures should be avoided since this will destroy the
probe and create a safety problem. In the case of mass
burn units and RDF-fired boilers, the measurements
should be taken downstream of the feedwater economizer.
119
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INSPECTION OF COMBUSTION EQUIPMENT
Level 3 Inspection Procedures
The oxygen concentration should be measured at
several locations along the duct diameter. Stratifica-
tion of the gas stream can result in nonuniform oxygen
concentrations across the duct diameter. Also, the
measurements should be repeated several times over a
reasonable time span to account for short term fluc-
tuations in the oxygen levels. This is especially
important for the modular units since ram charging and
dump stack operation create frequent short term oxygen
concentration changes.
The oxygen measurements should be checked using
carbon dioxide measurements (if carbon dioxide data is
also provided by the instrument being used). The sum
of the oxygen and carbon dioxide measurements should be
in the range of 18 and 22%, e.g. 10% oxygen plus 9%
carbon dioxide equals 19%.
Carbon monoxide concentrations (ALL INCINERATORS)
This measurement should be made when there are
indications of combustion problems and there is no
carbon monoxide analyzer. Values greater than 200 ppm
(uncorrected for CO2 concentration) suggest nonideal
conditions and the emission of partially combusted
organic compounds. To ensure representative results,
the measurements should be made at several locations in
the duct and should be made several times over a reason-
able time span.
Undergrate and overfire pressures (MASS BURN AND RDF-
FIRED UNITS)
These pressures should be measured if there are
indications of significant combustion problems and the
on-site instruments are either unreliable or inopera-
tive. Manometers or diaphragm gauges having measure-
ment ranges of 0 to 10 inches of water and 0 to 40
inches of water are usually sufficient.
120
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INSPECTION OF COMBUSTION EQUIPMENT
Level 3 Inspection Procedures
Underqrate and overfire air pressures (MASS BURN AND
RDF-FIRED UNITS)
It should be noted that some systems do not have
measurement ports in the undergrate and overfire air
plenums. If these are not available, the measurements
cannot be performed during the present inspection.
Ports should be requested for future inspections.
Although the undergrate supply ducts and overfire air
headers are relatively safe, plant personnel should
never be asked to install measurement ports on opera-
ting systems.
Start-up and shutdown procedures (ALL TYPES OF
INCINERATORS)
If the facility has frequent start-ups, the
start-up and shutdown procedures should be evaluated.
The emphasis should be on techniques used to maintain
minimum furnace exit gas temperatures and on the
criteria for beginning waste charging to the unit.
Continuous monitoring data for carbon monoxide and
oxygen should be checked to determine the duration of
nonideal combustion conditions after waste charging has
begun (data not available on all units).
Also, the efforts to minimize the number of
start-up/shut-down cycles should be discussed since
this is generally the best means of minimizing both
equipment deterioration and pollutant emissions. The
equipment damage is primarily due to the thermal expan-
sion and contraction. Corrosion due to condensation of
acid vapors that are incompletely purged from the
furnace area is also a significant problem.
121
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INSPECTION OF COMBUSTION EQUIPMENT
Level 4 Inspection Procedures
System flowchart (ALL TYPES OF INCINERATORS)
A relatively simple flowchart is very helpful in
conducting a complete and effective Level 2/Level 3
inspection. This should be prepared by agency manage-
ment personnel or senior inspectors during a Level 4
inspection. It should consist of a simple diagram that
includes the following elements:
° Incinerator chamber(s), undergrate plenums,
and overfire air header locations
oLocation(s) of forced draft fans for under-
grate air and overfire air. Location of
induced draft fan for effluent gas movement.
o Charging pits, chutes, and rams
o Locations of major instruments and monitoring
locations on the equipment (static pressure
gauges, temperature monitors, oxygen
analyzers, and carbon monoxide analyzers)
o Waste receiving, storage,.and processing
o Ash handling and storage
Locations for measurement ports (ALL TYPES OF
INCINERATORS)
Many existing incinerators do not have convenient
and safe ports that can be" used for static pressure,
gas temperature, oxygen, and carbon monoxide measure-
ments. One purpose of the Level 4 inspection is to
select (with the assistance of plant personnel)
•locations for ports to be installed at a later date
to facilitate Level 3 inspections. Ports may be neces-
sary in the overfire air headers, the undergrate plenum
supply ducts, and the economizer gas outlet duct.
Information regarding possible sample port locations is
provided in the U.S. EPA Publication titled, " Prefer-
red Measurement Ports for Air Pollution Control
Systems," EPA 340/1-86-034.
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INSPECTION OF COMBUSTION EQUIPMENT
Level 4 Inspection Procedures
Potential safety problems (ALL TYPES OF INCINERATORS )
Agency management personnel and/or senior inspec-
tors should identify potential safety problems involved
in standard Level 2/Level 3 inspections at this site.
To the extent possible, the system owner/operators
should eliminate these hazards. For those hazards
which cannot be eliminated, agency personnel should
prepare notes on how future inspections should be
limited and should prepare a list of the necessary
personnel safety equipment. A partial list of common
health and safety hazards include the following:
° Eye injuries while observing combustion
conditions through observation hatches
° Skin contact with RDF fuels
o Thermal burns
° Moving equipment hazards
Records (ALL TYPES OF INCINERATORS )
A summary of the normal operating records and
routine laboratory analyses should be compiled. If
possible, example photocopies of these forms should be
included in the inspection file so that new personnel
assigned inspection responsibilities will know what
data and information is available on these forms.
Inspection checklists
Senior inspectors and/or agency management person-
nel should modify the checklists presented in this
notebook to match the specific conditions at the
facility being inspected. Inspection points which are
irrelevant and unnecessarily time consuming should be
omitted to reduce the inspection time requirements and
lessen the disruption of the plant personnel's schedule
Also, any inspection steps which involve unreasonable
risks to the inspector, the plant personnel, or the
equipment should be deleted. In some cases, it may be
necessary to add other inspection points not discussed
in this notebook. The modified checklist should be
included in the inspection file.
123
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3. INSPECTION OF DRY SCRUBBERS
3.1 Inspection Summaries
3.1.1 Dry Scrubber System Inspection Overview
Stack
Continuous
Emission
Monitors
Particulate
Control
Device
(see also
Sections 4-6)
Evaluate average opacities and puffing
conditions as direct indications of
particulate device operating problems.
The presence of a secondary plume is an
direct indication of severe combustion
problems or dry scrubber problems.
Evaluate frequency and severity of excess
emissions of particulate matter, hydrogen
chloride, sulfur dioxide, and nitrogen
oxides.
Evaluate inlet and outlet gas temper-
atures as one indication of air
infiltration. Listen for obvious
infiltration around the hoppers, access
hatches and expansion joints.
Evaluate adequacy of routine cleaning
system operation.
Evaluate operating parameters that are
indirectly related to particulate col-
lection efficiency (e.g. ESPs - power
data, wet scrubbers - pressure drop).
Compare present operating levels to
baseline values.
Evaluate corrosion problems.
Check for fugitive emissions from the
hopper solids handling equipment.
Evaluate operating logs and maintenance
records with respect to attempts to
prevent repeat failures of the same
components.
125
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INSPECTION OF DRY SCRUBBERS
Inspection Summaries
3.1.1 Dry Scrubber System Inspection Overview
Dry Scrubber
Vessel
Alkaline
Reagent
Preparation
Evaluate operating conditions which are
indirectly related to the acid gas removal
efficiency. One of the most important of
these is the outlet dry bulb and wet bulb
temperatures. Compare the present opera-
ting levels with baseline values.
Evaluate inlet gas temperatures at present
and variations of this value since the
last inspection. Low inlet temperatures
could lead to solids build-up problems in
spray dryer type systems.
Determine if solids recycle from the
absorber vessel and/or the particulate
control device is being used.
Review records to evaluate frequency and
severity of deviations from normal
operating conditions.
Evaluate corrosion problems which could
lead to future excess emission problems.
Review maintenance records to evaluate
efforts to maintain slurry feed and
density instruments.
Evaluate slaker (if present) liquor outlet
temperature as an indirect indication of
the adequacy of calcium hydroxide slurry
preparation.
Evaluate procedures used to adjust dry
scrubber operation to various incinerator
loads and inlet pollutant concentrations.
126
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INSPECTION OF DRY SCRUBBERS
Inspection Summaries
3.1.2 Level 2 Inspection Checklists
3.1.2.1 Basic Level 2 Inspection Points
Stack o visible emissions for 6 to 30 minutes
for each stack or discharge vent
o Presence of condensing plume
Continuous Monitors for Opacity, Sulfur Dioxide, Hydrogen
Chloride, and Nitrogen Oxides
o Double pass transmissometer condition
o Double pass transmissometer opacity data
for at least the last 8 hours
o Sulfur dioxide, hydrogen chloride, and
nitrogen oxides emissions for at least
the last 8 hours
Dry Scrubber - General
o System flowchart
o General physical condition
Dry Scrubber - Spray Dryer Absorbers and Combination
Systems
o Absorber vessel approach-to-saturation for
for at least the last 8 hours
o Make-up reagent feed rates and absorber
recycle rates for at least the last 8 hours
oNozzle air and slurry pressures (if present)
Dry Scrubber - Dry Injection System and Combination
Systems
o Calcium hydroxide feed rate for at least
the last 8 hours
o Calcium silicate/calcium hydroxide feed
rates for at least the last 8 hours
(if calcium silicate used)
oSolids recycle rates (if recycle used)
Dry Scrubber - Fabric Filters, Electrostatic Precipitators,
and Wet Scrubbers
See Sections 4, 5, and 6
127
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INSPECTION OP DRY SCRUBBERS ' '
Inspection Summaries
3.1.2.2 Follow-up Level 2 Inspections
Stack o All elements of a Basic Level 2
inspection
o Sulfur dioxide and hydrogen chloride
continuous monitoring data for previous
12 months
Dry Scrubber - Spray Dryer Absorber and Combination
Systems
o Absorber vessel approach-to-saturation
values during past previous 12 months
o Reagent feed rates during last 12 months
o Absorber vessel inlet gas temperatures
during past 12 months
o Slaker slurry outlet temperatures during
past 12 months (if slaker present)
o Slurry density monitor data and slurry
flow monitor maintenance information
during past 12 months
o Absorber gas flow rates (if monitored)
Dry Scrubber -
Dry Scrubber -
Dry Injection System and Combination
Systems
Reagent feed rates during past 12 months
Calcium silicate/calcium hydroxide feed
rates during past 12 months
Solids recycle rates during past 12
months (if recycle used)
Fabric Filters, Electrostatic Precipita-
tors , and Wet Scrubbers
See Sections 4, 5, and 6
128
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INSPECTION OF DRY SCRUBBERS
Inspection Summaries
3.1.2.3 Level 3 Inspection Checklist
Stack o All elements of a basic Level 2
inspection
Continuous Monitors for Opacity, Sulfur Dioxide,
Hydrogen Chloride, and Nitrogen Oxides
o All elements of a follow-up Level 2
inspection
Dry Scrubber o All Level 2 follow-up inspection elements
o Spray dryer absorber wet bulb and dry
bulb temperatures
o Absorber or contactor inlet gas
temperature
Dry Scrubber - Fabric Filters, Electrostatic Precipita-
tors, and Wet Scrubbers
See Sections 4, 5, and 6
3.1.2.4 Level 4 Inspection Checklist
Stack o All elements of a basic Level 2
inspection
Continuous Emission Monitors for Opacity, Sulfur Dioxide,
Hydrogen Chloride, and Nitrogen Oxides
o All elements of a follow-up Level 2
inspection
Dry Scrubber o Level 3 inspection elements
o Flowchart of system
o Locations of possible measurement ports
o start-up/shut-down procedures
o Potential inspection safety problems
129
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INSPECTION OF DRY SCRUBBERS
Basic Level 2 Inspection Procedures
3.2 Level 2 Inspection Procedures
3.2.1 Basic Level 2 Inspection Procedures
Dry scrubber system visible emissions
If weather conditions permit, determine the stack
effluent average opacity in accordance with U.S. EPA
Method 9 procedures (or other required procedures).
The observation should be conducted during routine
process operation and should last 6 to 30 minutes for
each stack and bypass vents. The majority of units
operate with effluent opacities less than 10% on a
continuous basis. Higher opacities indicate emission
problems.
The timing and duration of all significant spikes
should be noted after the visible emissions observation.
This information will be useful in determining some of
the possible causes of the spiking condition. Signifi-
cant puffs on either a regular frequency or on a random
basis are not normal. However, in some cases, light
puffing can occur even during optimal conditions.
If weather conditions are poor, an attempt should
still be made to determine if there are any visible
emissions. The presence of a significant plume indi-
cates emission problems. Do not attempt to determine
the "average opacity" at such times.
Condensing plume conditions
Condensing plume conditions in dry scrubber systems
are highly unusual since most vapor state species which
could cause such plumes are partially removed. The
presence of a condensing plume would indicate a major
malfunction of the dry scrubber system.
The principal characteristics of a condensing
plume include a bluish-white color, opacities which are
higher when the weather is cold or very humid, a low
opacity at the stack discharge, and increasing opaci-
ties in the first few seconds of plume travel.
130
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INSPECTION OF DRY SCRUBBERS
Basic Level 2 Inspection Procedures
System flowchart
A simple flowchart of the entire dry scrubber
system and the associated process equipment should be
prepared if one is not already available in the agency
files. This should consist of a block diagram which
includes the absorber or gas contactor, the reagent
preparation equipment, the particulate control device,
the combustion source, and all instruments relevant to
the inspection.
Double-pass transmissometer physical conditions
Most dry scrubbers have a transmissometer for the
continuous monitoring of visible emissions. If a unit
is present, and if it is in an accessible location,
check the light source and retroreflector modules to
confirm that these are in good workingorder. Check
that the main fan is working and that there is at least
one dust filter for the fan. On many commercial models,
it is also possible to check the instrument alignment
without adjusting the instrument. Note: On some models,
moving the dial to the alignment check position will
cause an alarm in the control room. This is to be
moved only by plant personnel and only when it will not
disrupt plant operations.
Double-pass transmissometer data
If the transmissometer appears to be working prop-
erly, evaluate the average opacity data for at least
the previous 8 hours prior to the inspection. If
possible, the average opacity data for selected days
since the last inspection should also be reviewed.
This evaluation is helpful in confirming that the units
being inspected are operating in a representative fashion.
If the unit is working better during the inspection than
during other periods, it may be advisable to conduct
an unscheduled inspection in the future.
As part of the review of average opacity, scan the
data to determine the frequency of emission problems
and to evaluate how rapidly the operators are able to
recognize and eliminate the condition.
131
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INSPECTION OF DRY SCRUBBERS
Basic Level 2 Inspection Procedures
Sulfur dioxide, nitrogen oxides,' and hydrogen chloride
monitor physical conditions
If the monitors are in an accessible location,
confirm that the instruments are in good mechanical
operating condition and that any sample lines are intact.
Check calibration and zero check records for all instru-
ments. Whenever working in the areas around the contin-
uous emissions monitors, inspectors should be cautious
about positive pressure fugitive leaks of effluent gas.
Sulfur dioxide, nitrogen oxides, and hydrogen chloride
emission data
If the gas monitors appear to be working properly,
evaluate the average emission concentrations for at
least the previous 8 hours prior to the inspection. If
possible, the average emissions for selected days since
the last inspection should also be reviewed. This
evaluation is helpful in confirming that the units
being inspected are operating in a representative fashion,
High emission rates of either sulfur dioxide or
hydrogen chloride indicate significant problems with ^
the dry scrubber system. The general classes of problems
include but are not limited to poor alkaline reagent
reactivity, inadequate approach-to-saturation (wet-dry
systems), low reagent stoichiometric ratios, low inlet
gas temperatures, and make-up reagent supply problems.
Follow-up Level 2 inspection procedures or Level 3
inspection procedures will be necessary if high emission
rates of either sulfur dioxide or hydrogen chloride are
observed.
High nitrogen oxides concentrations indicates a
problem with the combustion equipment operation, an
increase in the waste nitrogen content, or a problem
with the nitrogen oxides control system.
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INSPECTION OF DRY SCRUBBERS
Basic Level 2 Inspection Procedures
Spray Dryer Absorber "Approach-to-Saturation"
One of the most important operating parameters
affecting the efficiency of a wet-dry type dry scrubber
is the approach-to-saturation. This is simply the
difference between the wet bulb and dry bulb temperature
monitors at the exit of the spray dryer vessel. The
normal approach-to-saturation varies between 90 and
180°F. Very high values suggest lower acid gas removal
efficiencies since the baseline period.
The approach-to-saturation is monitored continuously
by a set of dry bulb and wet bulb monitors. An change
in this value is sensed by the automatic control system
which either increases or decreases the slurry feed
rate to the atomizer.
Due to the vulnerability of these temperature
monitors to scaling and blinding, inspectors should not
be surprised to find that some plants must occasionally
bypass the automatic process control system and operate
manually for limited time periods. This generally
means slightly worse approach-to-saturation values so
that operators have a margin for error in the event of
sudden process changes such as load changes. Gradually
plants should be able to increase the reliability of
the temperature monitors by relocation of the sensors
and by improved operation of the dryer.
Spray dryer absorber reagent feed rates
The calcium hydroxide (or other alkali) feed rates
are important since they partially determine the stoichi-
ometric ratio between the moles of reagent and the
moles of acid gas. Low stoichiometric ratios result in
reduced collection efficiencies. Higher than needed
stoichiometric ratios use excessive reagent and may
result in poor drying of the sorbent.
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INSPECTION OF DRY SCRUBBERS
Basic Level 2 Inspection Procedures
Spray dryer absorber reagent feed rates
The reagent feed rate is generally determined
using a magnetic flow meter on the slurry supply line
to the atomizer feed tank. It is also necessary to
know the slurry density. This is monitored by a
nuclear-type density monitor. Typical slurry densities
are in the range of 5 to 20% by weight. It should be
noted that both the magnetic flow meter and the
nuclear density meter are vulnerable to scaling due to
the nature of the slurry.
Another way to determine the reagent feed rate is
to record the feed rates of new pebble lime and recycled
solids indicated by the weigh belt feeders. The weigh
belt for the pebble lime is between the lime storage
silo and the slaker. The weigh belt feeder for the
recycled solids is close to the spray dryer absorber
vessel.
Both the slurry feed rates and the solids rates
should be compared with baseline values at a similar
combustion system load to determine if the stoichiometric
ratio has dropped significantly.
Spray dryer absorber nozzle air and slurry pressures
For units equipped with nozzles rather than rotary
atomizers, the air pressures and slurry pressures
should be recorded and compared with baseline levels.
Some variation in the slurry pressures are necessary in
order to maintain proper approach-to-saturation values
during combustion system load variations.
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INSPECTION OF DRY SCRUBBERS
Basic Level 2 Inspection Procedures
Dry injection system feed rates
The feed rate of calcium hydroxide to the pressur-
ized pneumatic system is generally monitored by either
a weigh belt feeder or a volumetric screw-type feeder.
Both of these feeders are located close to the calcium
hydroxide storage silos, and the feed rates are generally
indicated on the main system control panel. These
values should be recorded for at least the past 8 hours
and compared against baseline values for similar combus-
tion load periods. Decreased reagent feed rates indicate
possible reductions in the stoichiometric ratio and
thereby a reduction in acid gas collection effectiveness.
The blower motor currents and the pneumatic line static
pressures should also be recorded and checked against
baseline data sets. Higher motor currents and higher
conveying line static pressures indicate increases in
the air flow rates.
Calcium silicate feed rates
The semi-wet/dry system, utilizes a calcium
silicate/calcium hydroxide dry injection system down-
stream from the calcium hydroxide spray dryer absorber.
The feed rate of calcium silicate/calcium hydroxide is
monitored by weigh belt feeders or volumetric screw
conveyors. Feed rates for the past 8 hours should be
recorded and compared with baseline values.
Control device solids recycle rates
The semi-wet/dry system utilizes a recycle
stream from the fabric filter in order to improve
overall reagent utilization. The solids recycle rate
during the inspection should be recorded and compared
to baseline values.
Dry scrubber system general physical conditions
While walking around the dry scrubber and its
inlet and outlet ductwork, check for obvious corrosion
around the potential "cold" spots such as the bottom of
the absorber vessel and the particulate control device
hoppers and around the access hatches. Check for audible
air infiltration.
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INSPECTION OF DRY SCRUBBERS
Follow-up Level 2 Inspection Procedures
3.2.2 Follow-up Inspection Points for Level 2 Inspections
Continuous monitoring data for the previous 12 months
Obtain the continuous monitoring records and quickly
scan the data for the previous 12 months to determine
time periods that had especially high and especially
low emission rates. Select the dry scrubber operating
logs and the process operating logs that correspond
with the times of the monitoring instruments charts/
records selected. Compare the dry scrubber operating
data and process operating data against baseline infor-
mation to identify the general category of problem(s)
causing the excess emission incidents. Evaluate the
source's proposed corrective actions to minimize this
problem(s) in the future.
Spray dryer absorber approach-to-saturation values during
the previous 12 months
The approach-to-saturation value is an important
parameter which relates directly to the pollutant removal
effectiveness. If there is significant question concern-
ing the ability of the dry scrubber system to maintain
proper operation on a long term basis, the approach-to-
saturation values indicated on the dry scrubber system
daily operating log sheets should be checked. Values
much higher than baseline values or permit stipulations
indicate chronic problems such as the following.
o Absorber vessel temperature instruments
o Absorber vessel atomizer
o Absorber gas dispersion equipment
o Low absorber vessel inlet gas temperatures
during low load periods
o Nozzle erosion or blockage
o Slurry supply line scaling
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INSPECTION OF DRY SCRUBBERS
Follow-up Level 2 Inspection Procedures
Spray dryer absorber reagent feed rate data during the
previous 12 months
The feed rates of make-up pebble lime and recycle
solids are generally indicated on the daily operating
logs of the dry scrubber system. Values for the last
12 months should be compared with the corresponding
combustion load data to determine if significant changes
in the overall reagent stoichiometric ratios have
occurred. Data concerning the system load must be
obtained from the combustion system daily operating log
sheets. If available, dry scrubber system inlet sulfur
dioxide concentrations should also be used in this
qualitative evaluation of reagent/acid gas stoichio-
metric ratios.
Slaker slurry outlet temperatures during the past 12
months
The slaker slurry outlet temperature provides a
rough indication of the adequacy of the conversion from
lime (calcium oxide) to calcium hydroxide. The tempera-
tures should be compared to baseline values. Improper
slaking can result in poor reagent reactivity and reduced
acid gas collection efficiency.
Spray dryer absorber slurry flow rate and density monitor
maintenance records
The calcium hydroxide slurry monitors generally
consist of a magnetic flow meter and a nuclear density
meter. Both of these are sensitive to scaling especially
when slurry densities are high. The plant should have
maintenance records for the monitors either in the form
of completed work orders, a computerized maintenance
record, an instrument maintenance log, or notes on the
daily dry scrubbing operations log. The records should
be reviewed for the previous 12 months whenever there
is concern that there are periods of low slurry supply
to the atomizer.
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INSPECTION OF DRY SCRUBBERS
Follow-up Level 2 Inspection Procedures
Spray dryer absorber inlet gas temperatures values
during the previous 12 months
Dry scrubbing systems have a limited turndown
capability due to the need for complete drying of the
atomized slurry. Low gas inlet temperatures during
periods of low combustion system load can cause poor
drying of the droplets. The process control system is
generally designed to block atomizer operation once
inlet temperature drops below a preset value. The
inlet gas temperature data should be reviewed to confirm
that the controller is working properly, since operation
under these conditions could lead to absorber vessel
deposits and nonideal operation once loads increase.
Dry injection system feed rates during the past 12
months
The long term performance of the calcium hydroxide
supply system should be checked if the emissions data
indicates occasional emission excursions. (See earlier
inspection step.) The feed rate data for the previous
12 months provided by the weigh belt feeder or the
volumetric screw feeder should be compared against the
combustion system loads and against the inlet acid gas
concentration monitors (when available). The automatic
control system should be able to vary calcium hydroxide
(or other alkali) addition rates with load variations
and inlet gas acid gas concentrations.
Calcium silicate/calcium hydroxide feed rates during the
previous 12 months
The variability and reliability of the calcium
silicate/calcium hydroxide dry injection system in
the systems should be evaluated by reviewing the
daily system operating logs. Some loss in acid gas
collection efficiency could occur at low feed rates.
Dry injection system control device solids recycle rates
The recycle rates used in the semi-wet/dry
type systems have some impact on the overall acid gas
collection efficiency. Low recycle rates indicate
slightly reduced acid gas collection efficiency.
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INSPECTION OF DRY SCRUBBERS
Level 3 Inspection Procedures
3.3 Level 3 Inspection Procedures
The Level 3 inspection includes many inspection
steps performed during Level 2 basic and Level 2
follow-up inspection procedures. These are described
in earlier sections. The unique inspection steps of
Level 3 inspections are described below.
Spray dryer absorber vessel dry bulb and wet bulb
outlet gas temperatures
These measurements are taken if there is a signifi-
cant question concerning the adequacy of the on-site
gauges and if there are safe and convenient measurement
ports between the absorber vessel and the particulate
control device. The measurements should be made at
several locations in the duct to ensure that the values
observed are representative of actual conditions. The
values should be averaged and compared with the value
indicated by the on-site instruments (if operational)
and with baseline data sets. It should be noted that
it is rarely necessary to make this measurement since
the on-site gauges are a critical part of the overall
process control system for the dry scrubber system.
Failure to maintain these instruments drastically in-
creases the potential for absorber vessel wall deposits
and increased emissions. These temperature monitors
are normally very well maintained.
Spray dryer absorber vessel or dry injection system
inlet gas temperature
This measurement is taken when the on-site gauge
is not available, is malfunctioning, or is in a poten-
tially nonrepresentative location. For spray dryers,
the measurement should be taken in the main duct leading
to the atomizer or in one or more of the ducts that
lead to the gas dispersion system within the vessel.
For dry injection systems, the measurement should be
taken upstream of the gas stream/reagent mixing point.
The measurements should be taken at several locations
in the duct and averaged. Locations near air infiltra-
tion sites should be avoided.
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INSPECTION OF DRY SCRUBBERS
Level 4 Inspection Procedures
3.4 Level 4 Inspection Procedures
The Level 4 inspection includes many inspection
steps performed during Level 2/Level 3 inspections.
These are described in earlier sections. The unique
inspection steps of Level 4 inspections are described
below.
Start-up and shut-down procedures
The start-up and shut-down procedures used at the
plant should be discussed to confirm the following.
The plant has taken reasonable precautions to
minimize the number of start-up/shut-down cycles.
The dry scrubber is operated in a reasonable
time after start-up of the process equipment.
Inspectors should remember that starting the
atomizer (in spray dryer type systems) when the
inlet gas temperatures are low can lead to
absorber vessel deposits.
Possible locations for measurement ports
If the system does not have the necessary measure-
ment ports to facilitate a Level 3 inspection, candidate
sites should be identified. These should be in safe
and convenient locations which do not disturb plant
instruments or operations.
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INSPECTION OF DRY SCRUBBERS
Level 4 Inspection Procedures
Potential dry scrubber system safety problems
Agency management personnel and/or senior inspectors
should identify potential safety problems involved in
standard Level 2/Level 3 inspections at this site. To
the extent possible, the system owner/operators should
eliminate these hazards. For those hazards which can
not be eliminated, agency personnel should prepare
notes on how future inspections should be limited and
should prepare a list of the necessary personnel safety
equipment. A partial list of common health and safety
hazards include the following.
oInhalation hazards due to fugitive leaks
o Corroded ductwork and particulate control devices
o Eye hazards due to alkali solids and slurries
o High voltage in control cabinets
Dry scrubber and process system flowchart
A relatively simple flowchart is very helpful in
conducting a complete and effective Level 2/Level 3
inspection. This should be prepared by agency management
personnel or senior inspectors during a Level 4 inspec-
tion. It should consist of a simple block diagram that
includes the following elements.
oSource(s) of emissions controlled the system
o Location(s) of any fans and blowers used for
gas movement and solids conveying
o Locations of any main stacks and bypass stacks
oAlkali preparation equipment, adsorber vessel
or contactor, and particulate control device.
o Locations of major process instruments and gas
stream continuous monitors
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4. INSPECTION OF ELECTROSTATIC PRECIPITATORS
4.1 Inspection Summaries
4.1.1 Electrostatic Precipitator Inspection Overview
Stack
Discharge
The average opacity and frequency of
puffing are observed since these are a
direct indications of particulate emis-
sions and precipitator performance
problems. Also, the visible emission
limitations are separately enforceable
regulatory limits.
Any symptoms of secondary plumes are
noted during the visible emission obser-
vation. This is an indication of combus-
tion problems and/or dry scrubbing system
problems.
Transmissometer
Electrostatic
Precipitator
Basic mechanical checks of the transmis-
someter are made prior to reviewing any
of the present data.
The average opacity at the present time
and immediately prior to the inspection
is noted since it provides one index of
the representativeness of the inspection.
Recorded data since the last inspection
are reviewed since they provide a direct
indication of the frequency and severity
of particulate emission problems.
The field-by-field electrical operating
conditions are carefully obtained and
reviewed. These data provide an indirect
indication of resistivity conditions and
a direct indication of internal mechan-
ical faults. The electrical conditions
are compared against baseline data for
the facility.
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INSPECTION OF ELECTROSTATIC PRECIPITATORS
Inspection Summaries
4.1.1 Electrostatic Precipitator Inspection Overview
Electrostatic Inlet and outlet gas temperature data are
Precipitators reviewed as one indicator of air infiltra-
tion into the system. Also, audible
signs of air infiltration around the
hoppers, access hatches, rapper seals,
and expansion joints are noted. Air
infiltration can lead to rapid and
severe corrosion due to the hydrogen
chloride, hydrogen fluoride, and cal-
cium chloride present in the gas stream.
The general physical condition of the
unit is observed during the inspection
since this also indicates possible
internal corrosion problems, solids
build-up problems, and collection
plate-wire frame misalignment problems.
The collection plate, discharge electrode
frame, and gas distribution screen
frame rappers are checked. Excessive
rapping intensities can lead to rapping
reentrainment due to the low-to-moderate
resistivity range which often exists in
the application. Rapper failures can
lead to suppressed secondary currents
and reduced particulate collection
efficiency. The freguency of rapping
in each field is compared with the
frequency of routine spiking observed by
the transmissometer.
The wire failure records are reviewed
since they provide symptoms of internal
problems and misguided maintenance.
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INSPECTION OF ELECTROSTATIC PRECIPITATORS
Basic Level 2 Inspection Procedures
4.1.2 Level 2 Inspection Procedures
4.1.2.1 Basic Level 2 Inspection Procedures
Stack o Visible emissions for 6 to 30 minutes
for each stack or discharge vent
o Duration and timing of puffing
o Presence of condensing plume
Transmissometer
o Double-pass transmissometer mechanical
operating conditions
o Average opacity for at least the last
24 hours
Electrostatic o Transformer-rectifier set electrical
Precipitator data for each field (recorded in order
from inlet field to outlet field)
o General physical condition
4.1.2.2 Follow-up Level 2 Inspection Procedures
Stack o All elements of a Basic Level 2
inspection
Transmissometer
o All elements of a Basic Level 2
inspection
Electrostatic o Opacity strip charts/records and trans-
Precipitator former rectifier set records (baseline
files) since the last inspection
o Rapping frequency and intensity
Inlet and outlet gas temperatures
o wire failure rate and location records
4.1.2.3 Level 3 Inspections (Identical to Follow-up
Level 2 Inspections)
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INSPECTION OF ELECTROSTATIC PRECIPITATORS
Inspection Summaries
4.1.2.4 Level 4 Inspections
Stack o All elements of a Level 3 inspection
Transmissometer
o Adequacy of location
Electrostatic o All elements of a Level 2/Level 3
Precipitator inspection
o start-up/shut-down procedures
o Potential inspection safety problems
o System flowchart
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INSPECTION OF ELECTROSTATIC PRECIPITATORS
Basic Level 2 Inspection Procedures
4.2 Basic Level 2 Inspection Procedures
Electrostatic precipitator visible emissions
If weather conditions permit, determine the preci-
pitator effluent average opacity in accordance with U.S.
EPA Method 9 procedures (or other required procedure).
The observation should be conducted during routine
process operation and should last 6 to 30 minutes for
each stack and bypass. The majority of units operate
with effluent average opacities less than 10% on a
continuous basis. Higher opacities indicate emission
problems.
The timing and duration of all significant spikes
should be noted after the visible emission observation.
This information will be useful in determining some of
the possible causes of the spiking condition. Signifi-
cant puffs at either a regular frequency or on a random
basis are not normal. However, in some cases, light
puffing can occur even when the operating conditions
are optimal.
If weather conditions are poor, an attempt should
still be made to determine if there are any visible
emissions. The presence of a significant plume indi-
cates emission problems. Do not attempt determine the
"average opacity" at such times.
Condensing plume conditions
Condensing plume conditions in electrostatic pre-
cipitator systems serving municipal incinerators could
be caused by sulfuric acid vapors, partially combusted
organic vapors, and ammonium compounds (from NOx control
systems).
The vaporous material condenses once the gas enters
the cold ambient air. Condensing plumes usually have a
bluish-white color. In some cases, the plume forms 5
to 10 feet after leaving the stack. Condensing plumes
are more prevalent during cold weather or during periods
of high ambient relative humidity.
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INSPECTION OF ELECTROSTATIC PRECIPITATORS
Basic Level 2 Inspection Procedures
Double-pass transmissometer physical conditions
Most precipitators have a transmissometer for the
continuous monitoring of visible emissions. If a unit
is present, and if it is in an accessible location,
check the light source and retroreflector modules to
confirm that these are in good working order. Check
that the main fan is working and that there is a least
one dust filter for the fan. On many commercial models
it is also possible to check the instrument alignment
without adjusting the instrument. Note; On some models,
moving the dial to the alignment check position will
cause an alarm in the control room. This is to be
moved only by plant personnel and only when it will not
disrupt plant operations.
Double-pass transmissometer data
If the transmissometer appears to be working pro-
perly, evaluate the average opacity data for at least
the previous 24 hours prior to the inspection. If
possible, the average opacity data for selected days
since the last inspection should also be reviewed.
This evaluation is helpful in confirming that the units
being inspected are operating in a representative
fashion. If a unit is working better during the inspec-
tion than during other periods, it may be advisable to
conduct an unscheduled inspection in the future.
As part of the review of average opacity, scan the
data to determine the frequency of emission problems
and to evaluate how rapidly the operators are able to
recognize and eliminate the condition.
Transformer-rectifier set electrical data
The first step in evaluating the transformer-
rectifier (T-R) set electrical data is to obtain or
prepare a sketch that indicates the arrangement of the
T-R sets on the precipitator. This drawing should
indicate the number of chambers in the precipitator and
the number of T-R sets in series in each chamber.
The T-R set numbers should be included on the sketch.
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INSPECTION OF ELECTROSTATIC PRECIPITATORS
Basic Level 2 Inspection Procedures
Transformer-rectifier set electrical data
For each chamber, the T-R set electrical data are
recorded starting with the inlet field and proceeding to
the outlet field. In some cases, the control cabinets
are scrambled. The following data should be recorded.
Primary Primary Secondary Secondary Spark Rate
Voltage Current Voltage Current
(Volts) (Amps) (Kilovolts) (Millamps) (No./Min.)
Inlet
Field
Second
Field
nth
Field
The voltages and currents should be recorded when
the appropriate gauge reaches the highest stable value
for approximately one second or more.
If there is any question about the adequacy of the
spark rate meter, the spark rate should be determined
by counting the number of fluctuations of the primary
voltage and/or secondary voltage meters.
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INSPECTION OF ELECTROSTATIC PRECIPITATORS
Basic Level 2 Inspection Procedures
Transformer-rectifier set electrical data
Compare the secondary and/or primary voltages
against baseline levels for this unit and against
typical values. Generally, the primary voltages are
above 250 volts and they are usually in the range of
250 to 380 volts (A.C.)- The secondary voltages are
normally in the range of 20 to 45 kilovolts (D.C). A
drop in the primary voltage of 30 volts (A.C.) or a
drop in the secondary voltage of 5 kilovolts (D.C.) in
a given field indicates significantly reduced particu-
late control capability for that field.
To check the particle resistivity conditions, plot
the voltages, currents, and spark rates for each of the
chambers (Figure 4-3). Compare these drawings with
similar drawings prepared from baseline data. There
has probably been a significant shift in the particle
resistivity if all or most of the fields in a chamber
have shifted in the the same direction at approximately
the same time (outlet fields often lag several hours
behind). The symptoms of resistivity shifts are
summarized below.
Higher resistivity
o Reduced primary or secondary voltages
o Reduced primary or secondary currents
o Increased spark rates
Lower resistivity
o Reduced primary or secondary voltages
o Increased primary or secondary currents
o Decreased spark rates
In some units, the resistivity conditions in one
chamber are quite different from the resistivity condi-
tions in other adjacent chambers. In these types of
units, the changes in the secondary voltages and cur-
rents are much greater in some of the chambers. This
condition is often caused by slight differences in the
flue gas temperatures entering the various chambers.
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INSPECTION OF ELECTROSTATIC PRECIPITATORS
Basic Level 2 Inspection Procedures
Precipitator general physical condition
While walking around the precipitator and its
inlet and outlet ductwork, check for obvious corrosion
around the potential "cold" spots such as the corners
of the hoppers, near the solids discharge valve, and
the access hatches. On negative pressure units, check
for audible air infiltration through the corroded areas,
warped access hatches, eroded solids discharge valves,
or other sites. On positive pressure units, check for
fugitive emissions of dust from any corroded areas of
the system.
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INSPECTION OF ELECTROSTATIC PRECIPITATORS
Follow-up Level 2/Level 3 Inspection Procedures
Rapper systems
The collection plate, discharge electrode, and gas
distribution screen rapping systems are evaluated when
low power inputs are observed in one or more fields or
when there is puffing.
Note any rappers that do not appear to be working
or that do not sound proper when activating. A sketch
is often a useful way to summarize this information.
Request that plant personnel, if they are qualified,
open the rapper control cabinets. Compare the present
rapper system intensities with the baseline values.
° If the intensities are now higher, the unit may
have high resistivity dusts, binding or broken
rapper shaft connections, or poor start-up
procedures. It should be noted that it is rarely
possible to minimize high resistivity dust prob-
lems simply by increasing rapper intensities and
that some rapper shaft and/or collection plate
alignment problems can occur at high intensities.
°If the intensities are now much lower, the unit
may have low resistivity dusts, or the rappers
may have been temporarily turned down to minimize
obvious puffing.
Determine the activition frequency of the various
groups of rappers. This can often be done by watching
selected groups of rappers for a period of 10 to 60
minutes. It can also be determined by checking the
timers in the control cabinets. However, the indicated
rapper frequencies on the timers are not always reliable.
Compare the activation frequencies with the observed
frequency of puffing.
oIf the activation frequency is high, the unit
may be having problems with high resistivity
dust. It is rarely possible to minimize this
condition simply by increasing rapper frequency.
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INSPECTION OF ELECTROSTATIC PRECIPITATORS
Follow-up Level 2/Level 3 Inspection Procedures
Rapper systems
oIf the activation frequency is low, the unit may
have lower resistivity dust than during the
baseline period. As long as the electrical
conditions and the opacity are acceptable, low
frequency is desirable.
o Puffing is often related to the activation
frequency of the outlet field collection plate
rappers.
o Note any occasions when more than one rapper is
activated simultaneously or when two or more
rappers are activated within a period of several
seconds.
Opacity strip charts/records and the transformer-
rectifier set records (baseline files)
This is a time consuming portion of the inspection.
It should be done only when the plant is experiencing
frequent and significant excess emission problems and
there is some question concerning the proposed correc-
tive actions.
Obtain the opacity records and quickly scan the
data for the previous 1 to 12 months to determine time
periods that had especially high and especially low
average opacities. Time periods with and without severe
spiking are also of interest. Select the precipitator
operating logs and the process operating logs that
correspond with the times of the opacity strip charts/
records selected. Compare the precipitator operating
data and process operating data against baseline infor-
mation to identify the general category of problem(s)
causing the excess emission incidents. Evaluate the
source's proposed corrective actions to minimize the
problem(s) in the future.
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INSPECTION OF ELECTROSTATIC PRECIPITATORS
Follow-up Level 2/Level 3 Inspection Procedures
Wire failure and location records
Request the discharge wire failure records from
the operators if it appears that wire failures have
caused temporary outages of one or more fields since
the last inspection. If specific wire failure records
are not maintained, attempt to determine how many wires
have failed since the last inspection. Most electro-
static precipitors operate with wire failure rates
that are much less than l per month. Higher failure
rates may indicate plate-wire misalignment, clearance
problems, improper rapping operation, inadequate wire
tension, and/or corrosion. Wire failure is often a
symptom of other more substantial problems.
Evaluate the owner/operators' plan for minimizing
excess emission incidents caused by wire failure. It
is generally necessary to fix the underlying cause of
the failures rather than simply reinstalling wires.
Inlet and outlet gas temperatures
The locations of inlet and outlet gas temperature
monitors should first be identified. Data from these
instruments is normally available in the main control
room for the incinerator. The data during the inspec-
tion should be obtained. Furthermore, temperture rec-
ords since the last inspection should be reviewed.
There should not be a significant drop in gas
temperature while passing through the unit. Typical
temperature drops are in the range of 25 to 50°F
depending on the adequacy of the precipitator insula-
tion, the ambient temperature, and the ambient wind
speed. Increases in the temperature drop as compared
to baseline data provide a strong indication of possible
air infiltration and future problems with corrosion,
wire failure, insulator leakage, hopper overflow, and
collection plate misalignment.
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INSPECTION OF ELECTROSTATIC PRECIPITATORS
Follow-up Level 2/Level 3 Inspection Procedures
Evaluate inlet and outlet gas temperatures.
The inlet temperature data should be reviewed to
determine if there have been any high temperature excur-
sions. These may have exceeded the thermal expansion
capability of the precipitator electrodes and caused
severe misalignment of the collection plates. This
causes a significant decrease in the operating voltages
and a major increase in particulate emissions.
4.3 Level 3 Inspection Procedures
These are identical to Level 2 inspection procedures
since portable inspection instruments are not used for
precipitators.
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INSPECTION OF ELECTROSTATIC PRECIPITATORS
Level 4 Inspection Procedures
4.4 Level 4 Inspection Procedures
The Level 4 inspection includes all the inspection
steps performed during Level 2/Level 3 inspections.
These are described in earlier sections. The inspection
steps unique to Level 4 inspections are described below.
Start-up and shut-down procedures
The start-up and shut-down procedures used at the
plant should be discussed to confirm the following.
The plant has taken reasonable precautions to
minimize the number of start-up/shut-down cycles.
The precipitator is energized in a reasonable
time after start-up of the process equipment.
Inspectors should remember that energizing too
early in the start-up process can lead to
precipitator explosions or to deposits on the
collection plates that reduce performance.
Potential safety problems
Agency management personnel and/or senior inspectors
should identify potential safety problems involved in
standard Level 2/Level 3 inspections at this site.
For those hazards which can not be eliminated, agency
personnel should prepare notes on how future inspec-
tions should be limited and should prepare a list of
the necessary personnel safety equipment. A partial
list of common health and safety hazards include the
following:
Inhalation hazards due to fugitive leaks from
inlet breechings, access hatches, hoppers, the
outlet contraction section, and fans
Corroded precipitator roofs and ladder supports
Ungrounded rappers
High voltage in control cabinets
156
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INSPECTION OF ELECTROSTATIC PRECIPITATORS
Level 4 Inspection Procedures
System flowchart
A relatively simple flowchart is very helpful in
conducting a complete and effective Level 2/Level 3
inspection. This should be prepared by agency manage-
ment personnel or senior inspectors during a Level 4
inspection. It should consist of a simple block diagram
that includes the following elements.
Source(s) of emissions controlled by a single
precipitator
Location(s) of any fans used for gas movement
through the system (used to evaluate inhalation
problems due to positive static pressures and air
infiltration problems)
Locations of any main stacks and bypass stacks
Layout and identification numbers of transformer-
rectifier sets used in all chambers
Locations of major instruments (transmissometers,
thermocouples)
157
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5. INSPECTION OF FABRIC FILTERS
5.1 Inspection Summaries
5.1.1 Fabric Filter Inspection Overview
Stack
Fabric
Filter
Observe the average opacity and puffing
conditions as a direct indication of
fabric filter performance.
Observe any secondary plume conditions
since these indicate a serious combustion
problem and/or dry scrubbing problem.
Transmissometer
Evaluate transmissometer physical condi-
tion prior to reviewing opacity data.
Observe average opacity (transmissometer
data) at the present time and for the
last 8 hours to determine the represent-
ativeness of the inspection period.
Review average opacity records since
the last inspection to determine the
frequency and severity of excess
emission problems.
Evaluate baghouse pressure drop as an
indirect indication of bag blinding
problems, bag cleaning problems, and
gas flow changes.
Observe baghouse physical condition as
an indirect indication of corrosion and
air infiltration.
Evaluate present inlet gas temperature
to confirm that it does not exceed the
high temperature limitations of the
fabric being used. Review inlet gas
temperature records since the last
inspection to determine frequency and
severity of gas temperature excursions.
159
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INSPECTION OF FABRIC FILTERS
Inspection Summaries
Fabric Evaluate fabric filter outlet gas tern-
Filter peratures as an indication of air
infiltration and possible fabric chemical
attack. The outlet temperature should be
at least 20°F above the acid dewpoint.
The gas temperature drop across the bag-
house should be only 20 to 50 °F depend
ing OB ambient temperature, ambient wind
speed, and the adequacy of insulation.
Listen for audible air infiltration
around access hatches, hoppers, and
expansion joints.
Evaluate cleaning system operation to con-
firm that the bags are being cleaned at a
regular frequency and to identify any bag
problems possible due to nonideal cleaning,
Observe clean side conditions on units in
which one or more compartments can be
isolated. Solids deposits are an indica-
tion of emission problems. Physical con-
dition of the bags and other components
are also observed to the extent possible
without entering the baghouse.
Review bag failure rate and location
records as a indirect indication of bag-
house excess emission problems.
Perform or observe "rip" tests as a rough
indicator of the reasons for frequent bag
failures.
Observe cage conditions (pulse jet only)
to evaluate bag failures.
Determine number of start-up/shut-down
cycles and the number of hours that the
baghouse bypass was necessary.
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INSPECTION OF FABRIC FILTERS
Inspection Summaries
5.1.2 Inspection Checklists
5.1.2.1 Basic Level 2 Inspection Points
Stack
Trans-
mi ssometer
Pulse Jet
Baghouses
Reverse Air
Baghouses
5.1.2.2
Stack
o Visible emissions for 6 to 30 minutes
for each stack or discharge vent
o Presence of condensing plume
o Double-pass transmissometer conditions
o Double-pass transmissometer data
o Static pressure drop
o clean side conditions
o General physical condition
o Static pressure drop
o Compartment static pressure drops, during
cleaning
o clean side conditions
o General physical condition
Follow-up Level 2 Inspections
o All elements of a Basic Level 2 inspection
Transmissometer
Pulse Jet
Baghouses
Reverse Air
Baghouses
o All elements of a Basic Level 2 inspection
o Compressed air cleaning system operation
o Bag failure rate and location records
o Present baghouse inlet gas temperature
o Baghouse inlet gas temperature records
o Bag "rip" tests and laboratory analyses
o Cage characteristics
o Reverse air fan operation
o cleaning system equipment controller
o Bag failure rate and location records
o Present baghouse inlet gas temperature
o Baghouse inlet gas temperature records
o Bag "rip" tests and laboratory analyses
161
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INSPECTION OF FABRIC FILTERS
Inspection Summaries
5.1.2.3 Level 3 Inspection Checklist
Stack ° All elements of a Basic Level 2 inspection
Transmissometer
o All elements of a Basic Level 2 inspection
Pulse Jet o All elements of a Follow-up Level 2
Baghouses inspection
o Measure baghouse static pressure drop
o Measure inlet and outlet gas temperatures
o Measure inlet and outlet gas oxygen content
Reverse Air o All elements of a Follow-up Level 2
inspection
o Measure static pressure drop
o Measure compartment static pressure drops
during cleaning
o Measure inlet and outlet gas temperatures
o Measure inlet and outlet gas oxygen
content
5.1.2.4 Level 4 Inspection Checklist
Stack o All elements of a Basic Level 2 inspection
Transmissometer
o All elements of a Basic Level 2 inspection
Baghouse oAll elements of a Follow-up Level 2
(Both Types) inspection
o Flowchart of compressed air supply
(Pulse jet fabric filters only)
o Start-up/shut-down procedures
o Locations for measurement ports
o Potential inspection safety problems
o System flowchart
162
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INSPECTION OF FABRIC FILTERS
Basic Level 2 Inspection Procedures
5.2 Level 2 Inspections
5.2.1 Basic Level 2 Inspection Procedures
Baqhouse visible emissions
If weather conditions permit, determine baghouse
effluent average opacity in accordance with U.S. EPA
Method 9 procedures (or other required procedure). The
observation should be conducted during routine process
operation and should last 6 to 30 minutes. Fabric
filters generally operate with an average opacity less
than 5%. Higher opacities indicate baghouse emission
problems.
Some large, multi-compartment pulse jet baghouses
have separate stacks for each compartment. Long term
visible emission observations on each of these stacks
should be made only when the baghouse is suffering
major emission problems.
If weather conditions are poor, an attempt should
still be made to determine whether there are any visible
emissions. Do not attempt to determine "average opacity"
during adverse weather conditions. The presence of a
noticeable plume generally indicates baghouse operating
problems.
Puffing conditions (PULSE JET UNITS ONLY)
Evaluate the frequency and severity of puffs.
These are often caused by small holes in one or more
rows of bags.
163
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INSPECTION OF FABRIC FILTERS
Basic Level 2 Inspection Procedures
Condensing plume conditions
Condensing plume conditions in fabric filter systems
serving municipal incinerators could conceivably be
caused by partially combusted organic vapors, sulfuric
acid vapors, or ammonium compounds. The vaporous
material condenses once the gas enters the cold ambient
air. Condensing plumes usually have a bluish-white
color. In some cases, the plume forms 5 to 10 feet
after leaving the stack. If the baghouse operating
temperature drops substantially, this material can
condense inside the baghouse and cause fabric blinding
problems. Corrective actions must focus on the
incinerator or dry scrubber system.
Double-pass transmissometer physical conditions
If a transmissometer is present, and if it is in
an accessible location, check the light source and
retroreflector modules to confirm that these are in
good working order. Check that the main fan is working
and that there is a least one dust filter for the fan.
On many commercial models, it is also possible to check
the instrument alignment without adjusting the instrument,
Note; On some models, moving the dial to the alignment
check position will cause an alarm in the control room.
This JLS to be moved only by plant personnel and only
when it will not disrupt plant operations.
Some fabric filters have one or more single pass
transmissometers on outlet ducts. While these can
provide some useful information to the system operators,
these instruments do not provide data relevant to the
inspection.
Double-pass transmissometer data
Evaluate the average opacity data for selected
days since the last inspection, if the transmissometer
appears to be working properly. Determine the frequency
of emission problems and evaluate how rapidly the bag-
house operators are able to recognize and eliminate the
conditions.
164
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INSPECTION OF FABRIC FILTERS
Basic Level 2 Inspection Procedures
Baqhouse static pressure drop
The baghouse static pressure drop should be
recorded if the gauge appears to be working properly.
The gauge "face" should be clear of obvious water and
deposits. The gauge should fluctuate slightly each
time one of the diaphragm valves activates. These
valves can be heard easily when close to the pulse jet
baghouse. If there is any question about the gauge, ask
plant personnel to disconnect each line one at a time
to check if the gauge responds. If it does not move
when a line is disconnected, the line may be plugged.
Fabric filters operate with a wide range of static
pressure drops (2 to 12 inches W.C.). It is preferable
to compare the present readings with the baseline values
for this specific source. Increased static pressure
drops generally indicate high gas flow rates, and/or
fabric blinding, and/or system cleaning problems. Lower
static pressure drops are generally due to reduced gas
flow rates, excessive cleaning intensities/frequencies,
or reduced inlet particulate loadings.
Baqhouse general physical conditions
While walking around the baghouse and its inlet
and outlet ductwork, check for obvious corrosion around
the potential "cold" spots such as the corners of the
hoppers, near the solids discharge valve, and the access
hatches. On negative pressure baghouses, check for any
audible air infiltration through the corroded areas,
warped access hatches, eroded solids discharge valves,
or other sites. On positive pressure baghouses, check
for fugitive emissions of dust from any corroded areas
of the system.
165
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INSPECTION OF FABRIC FILTERS
Basic Level 2 Inspection Procedures
Clean side conditions
If there is any question about the performance of
the baghouse, request that plant personnel open one or
more hatches on the clean side (not available on some
commercial models). Note the presence of any fresh
dust deposits more than 1/8" deep since this indicates
particulate emission problems.
In the case of pulse jet fabric filters, also
observe the conditions of the bags, cages, and compressed
air delivery tubes. The compressed air delivery tubes
should be oriented directly into the bags so that the
sides of the bags are not subjected to the blast of
cleaning air. The cages and bags should be securely
sealed to the tube sheet in units where the bag comes
up through the tube sheet. There should be no oily or
crusty deposits at the top of the bags due to oil in
the compressed air line.
In reverse air units, also observe the bag tension
and condition of the bag attachments at the tube sheet.
The bags should have noticeable tension in the vertical
direction (some inward deflection of the bags is normal
when a compartment is isolated). The majority of bag
problems generally occur within the bottom 1 to 2 feet
of the bags in both types of baghouses. Regulatory
agency inspectors should observe conditions from the
access hatches and should not enter the compartments
under any circumstances.
In some cases, operators will be unable to isolate
any compartments without causing major gas flow problems
with the incinerator and/or the dry scrubber. Obviously,
the request to check clean side conditions should be
withdrawn under such circumstances.
166
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INSPECTION OF FABRIC FILTERS
Follow-up Level 2 Inspections Procedures
5.2.2 Follow-up Inspection Points for Level 2
Inspections
Compressed air cleaning system (PULSE JET BAGHOUSES)
The purpose of checking the compressed air cleaning
system is to determine if this contributes to a signifi-
cant shift in the baghouse static pressure drop and/or
if this contributes to an excess emission problem. The
inspection procedures for the compressed air cleaning
system can include one or more of the following.
Record the compressed air pressure if the gauge
appears to be working properly. It should fluc-
tuate slightly each time a diaphragm valve is
activated. Do not remove this gauge since the
compressed air lines and manifold have high
pressure air inside.
Listen for operating diaphragm valves. If none
are heard over a 10 to 30 minute time period, the
cleaning system controller may not be operating.
Check the compressed air shutoff valve to confirm
that the line is open.
Count the number of diaphragm valves that do not
activate during a cleaning sequence. This can be
done by simply listening for diaphragm valve oper-
ation. Alternatively, the puff of compressed air
released from the trigger lines can sometimes be
felt at the solenoid valve (pilot valve) outlet.
Check for the presence of a compressed air drier.
This removes water which can freeze at the inlet
of the diaphragm valves. Also check for com-
pressed air oil filter.
Check for a drain on the compressed air supply
pipe or on the air manifold. This is helpful for
routinely draining the condensed water and oil in
the manifold.
167
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INSPECTION OF FABRIC FILTERS
Follow-up Level 2 Inspection Procedures
Operation of reverse air fan (REVERSE AIR BAGHOUSES)
Confirm that the reverse air fan is operating by
noting that the fan shaft is rotating. This fan is
usually located near the top of the baghouse.
Operation of cleaning equipment controllers
(REVERSE AIR AND SOME MULTI-COMPARTMENT PULSE JET UNITS)
Observe the baghouse control panel during cleaning
of one or more compartments to confirm that the control-
ler is operating properly. Each compartment should be
isolated for cleaning before the static pressure drop
increases to very high levels that preclude adequate
gas flow. Also, cleaning should not be so frequent
that the bags do not build-up an adequate dust cake to
ensure high efficiency filtration.
Operation of cleaning equipment controllers
(REVERSE AIR AND SOME MULTI-COMPARTMENT PULSE JET UNITS)
It is generally good practice to allow a short
"null" period of between 5 and 30 seconds between the
time a compartment is isolated and the time that reverse
air flow begins. This reduces the flexing wear on the
fabric. It is also good practice to have a "null"
period of 15 to 60 seconds following cleaning to allow
fine dust to settle out of the bags prior to returning
to filtering mode.
Present baqhouse inlet gas temperature
The primary purpose of determining the present gas
inlet temperature is to evaluate possible excess emission
problems and/or high bag failure rate conditions that
can be caused by very high or very low gas inlet temper-
atures. Locate any on-site thermocouples mounted on
the inlet to the baghouse. If this instrument appears
to be in a representative position, record the tempera-
ture value displayed in the control room.
168
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INSPECTION OF FABRIC FILTERS
Follow-up Level 2 Inspection Procedures
Present baqhouse inlet gas temperature
The average inlet gas temperature should be 25 to
50°F below the maximum rated temperature limit of the
fabric. Fifteen to thirty minute spikes of less than
25°F above the maximum rated limit can usually be
tolerated without fabric damage.
The average inlet gas temperature should be 25 to
50°F above the acid gas dewpoint temperature. For
most commercial combustion processes, the acid dewpoint
is usually between 225 to 300°F. The inlet gas temper-
ature should also be above the water vapor dewpoint.
Baqhouse gas temperature records
The purpose of reviewing continuous temperature
recorder data is to determine, if temperature excursions
contribute to excess emission problems and/or high bag
failure rates. Review selected strip charts to determine
if the gas inlet temperatures have been above the
maximum rated fabric temperature or below the acid
vapor or water vapor dewpoints.
Fabric "rip" test and fabric laboratory analyses
The purpose of evaluating fabric condition is to
determine if any corrective actions planned by the
owner/operators have a reasonable probability of reducing
frequent excess emissions.
To perform a "rip" test, ask the plant personnel
for a bag that has been recently removed from the
baghouse. Attempt to rip the bag near the site of the
bag hole or tear. If the bag can not be ripped easily,
then the probable cause of the failure is abrasion
and/or flex damage. These bags can usually be patched
and reinstalled. If the bag can be ripped easily, then
the fabric has been weakened by chemical attack or high
temperature damage. Weakened bags should not be patched
and reinstalled. It may be necessary to install new
bags throughout the entire chamber if the bag failure
rates are high.
169
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INSPECTION OF FABRIC FILTERS
Follow-up Level 2 Inspection Procedures
Bag failure records
The purpose of reviewing bag failure records is to
determine the present bag failure rate and to determine
if the rate of failure is increasing. Plot the number
of bag failures per month for the last 6 to 24 months.
If there has been a sudden increase, the owner/operators
should consider replacing all of the bags in the compart-
ment(s) affected. If there is a distinct spatial pattern
to the failures, the owner/operators should consider
repair and/or modification of the internal conditions
causing the failures.
Bag cages (PULSE JET FABRIC FILTERS)
The bag cages are evaluated whenever there are
frequent abrasion/flex failures at the bottoms of the
bags or along the ribs of the cage. Ask the plant
personnel to provide a spare cage for examination.
There should be adequate support for the bag and there
should not be any sharp edges along the bottom cups of
the cage. Also check the cages for bows that would
cause rubbing between two bags at the bottom of the
baghouse.
170
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INSPECTION OF FABRIC FILTERS
Level 3 Inspection Procedures
5.3 Level 3 Inspection Procedures
Procedures for measurement of reverse fabric filter
system o ing conditions are described below. Other
observat ~o be completed as part of the Level 3
inspecti a identical to those included in the basic
and foil Level 2 inspection. See the Level 2
inspectic f >cedures section for a discussion of these
steps.
Baqhouse static pressure drop
The static pressure drop provides an indication of
gas flow rate changes (changes in actual gas-to-cloth
ratio), fabric blinding, and cleaning system problems.
The steps in measuring the static pressure drop are
described below.
Locate safe and convenient measurement ports on
the inlet and outlet ductwork or on the baghouse
shell. In some cases it may be possible to
temporarily disconnect the on-site gauge in
order to use the portable gauge. Under no cir-
cumstances should on-site plant instruments be
disconnected without the explicit approval of
responsible plant personnel. Also, instruments
connected to pressure transducers should not be
disconnected.
Clean any deposits out of the measurement ports.
If the inlet and outlet ports are close together,
connect both sides of the static pressure gauge
to the ports and observe the static pressure for
1 to 5 minutes.
If the ports are not close together, measure the
static pressure in one port for 10 to 30 seconds
and then proceed to the other port for 10 to 30
seconds. As long as the static pressure drop is
stable the two values can be subtracted to
determine the static pressure drop.
171
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INSPECTION OF FABRIC FILTERS
Level 3 Inspection Procedures
Inlet and outlet gas temperatures
These measurements are conducted whenever it is
necessary to determine if air infiltration is causing
fabric chemical attack due to reduced c 5 outlet temper-
atures. It is also helpful to measure ie inlet gas
temperature to evaluate the potential -. r high gas
temperature damage to the bags. The s- ps in measuring
the gas temperature are outlined below
Locate safe and convenient measurement ports on
the inlet and outlet ductwork of the collector.
Often small ports less than 1/4" diameter are
adequate. Measurements using ports on the bag-
house shell are often inadequate since moderately
cool gas is trapped against the shell.
Attach a grounding/bonding cable to the probe if
vapor, gas, and/or particulate levels are
potentially explosive.
Seal the temperature probe in the port to avoid
any air infiltration.
Measure the gas temperature at a position near
the middle of the duct, if possible. Conduct
the measurement for several minutes to ensure
a representative reading.
Measure the gas temperature at another port and
compare the values. On combustion sources, a gas
temperature drop of more than 20 to 40°F
indicates severe air infiltration.
Compare the inlet gas temperature with the maximum
rated temperature limit of the fabric present.
If the average gas temperature is within 25 to
50 °F of the maximum, short bag life and
frequent bag failures are possible. Also, if
there are short term excursions more than 25 to
50°F above the maximum temperature limits,
irreversible fabric damage may occur.
172
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INSPECTION OF FABRIC FILTERS
Level 3 Inspection Procedures
Inlet and outlet gas oxygen levels
These measurements are performed to further evaluate
the extent ~. air infiltration. An increase of more
than 1% ov n going from the inlet to the outlet
indicates /ere air infiltration (e.g. inlet oxygen at
6.5% and let oxygen at 7.5%). The steps involved in
measurinc :ie flue gas oxygen levels are itemized below.
Lc ite safe and convenient measurement ports.
Generally, the ports used for the temperature
measurements are adequate for the oxygen
measurements.
Attach a grounding/bonding cable to the probe if
there are potentially explosive vapors, gases,
and/or particulate.
Seal the port to prevent any ambient air
infiltration around the probe.
Measure the oxygen concentration at a position
near the center of the duct to avoid false
readings due to localized air infiltration.
The measurement should be repeated twice in the
case of gas absorption instruments. For contin-
uous monitoring instruments, the measurement
should be conducted for 1 to 5 minutes to ensure
a representative value.
If possible, measure the carbon dioxide concen-
tration at the same locations. The sum of the
oxygen and carbon dioxide concentrations should
be in the normal stoichiometric range for the
fuel being burned (a sum of 18 to 22%). If the
sum is not in this range, a measurement error
has occurred.
As soon as possible, complete the measurements at
the other port. Compare the oxygen readings
obtained. If the outlet values are substantially
higher, severe air infiltration is occurring.
173
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INSPECTION OF FABRIC FILTERS
Level 4 Inspection Procedures
5.4 Level 4 Inspection Procedures
The Level 4 inspection includes many inspection
steps performed during Level 2 and 3 inspections. These
are described in earlier sections. The unique inspection
steps of Level 4 inspections are described below.
Flowchart of the compressed air system (PULSE JET
FABRIC FILTERS)
The purpose of the flowchart is to indicate the
presence of compressed air system components that could
influence the vulnerability of the pulse jet baghouse
to bag cleaning problems. The flowchart should consist
of a simple block diagram showing the following components
o Source of compressed air (plant air or compressor)
oAir drier (if present)
oOil filter (if present)
oMain shutoff valve(s)
o Compressed air manifolds on baghouse
o Drains for manifolds and compressed air lines
o Heaters for compressed air lines and manifolds
o Controllers for pilot valves (timers or pneumatic
sensors)
Locations for measurement ports
Many existing fabric filters do not have convenient
and safe ports that can be used for static pressure, gas
temperature, and gas oxygen measurements. One purpose
of the Level 4 inspection is to select (with the assis-
tance of plant personnel) locations for ports to be
installed at a later date to facilitate Level 3 inspec-
tions. Information regarding possible sample port
locations is provided in the U.S. EPA Publication
titled, " Preferred Measurement Ports for Air Pollution
Control Systems", EPA 340/1-86-034.
174
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INSPECTION OF FABRIC FILTERS
Level 4 Inspection Procedures
Start-up and shut-down procedures
The start-up and shut-down procedures used at the
plant should be discussed to confirm the following.
o The plant has taken reasonable precautions to
minimize the number of start-up/shut-down cycles.
o The baghouse system bypass times have been
minimized.
o The baghouse system bypass times have not been
limited to the extent that irreversible damage has
not occurred.
Potential safety problems
Agency management personnel and/or senior inspectors
should identify any potential safety problems involved in
standard Level 2 or Level 3 inspections at this site. To
the extent possible, the system owner/operators should
eliminate these hazards. For those hazards that can not
be eliminated, agency personnel should prepare notes on
how future inspections should be limited and should
prepare a list of the necessary personal safety equipment.
A partial list of common health and safety hazards
includes the following.
o Inhalation hazards due to low stack discharge
points
o Weak catwalk and ladder supports
o Hot baghouse roof surfaces
o Compressed air gauges in close proximity to
rotating equipment or hot surfaces
o Fugitive emissions from baghouse system
oInhalation hazards from adjacent stacks and vents
Access to system components only available by
means of weak roofs or catwalks
175
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INSPECTION OF FABRIC FILTERS
Level 4 Inspection Procedures
System Flowchart
A relatively simple flowchart is very helpful in
conducting a complete and effective Level 2 or Level 3
inspection. This should be prepared by agency manage-
ment personnel or senior inspectors during a Level 4
inspection. It consists of a simple block diagram that
includes the following elements.
o Source(s) of emissions controlled by a single
baghouse
o Location(s) of any fans used for gas movement
through the system (used to evaluate inhalation
problems due to positive static pressures)
o Locations of any main stacks and bypass stacks
o Location of baghouse
o Locations of major instruments (transmissometers,
static pressure gauges, thermocouples)
176
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6. INSPECTION OF WET SCRUBBERS
6.1 Wet Scrubber Inspection Summaries
6.1.1 Wet Scrubber Inspection Overview
Stack
Induced
Draft Fan
Scrubber
Average opacity of the residual plume is
observed since this provides an indica-
tion of particulate matter penetration
and vapor condensation in the scrubber.
Short term variations in residual opacity
are an indication of variations in combus-
tion conditions.
Obvious mist reentrainment is a clear
indication of demister failure.
Inspectors must remain aware of severely
vibrating fans downstream from wet
scrubbers. The inspection is terminated
immediately when this is noticed.
Static pressure drop across the scrubber
is used as an indirect indicator of the
particulate removal effectiveness. The
present value is compared with baseline
values to determine if there has been a
significant pressure drop decrease.
Scrubber static pressure drop records for
the time since the last inspection are
reviewed to identify any operating periods
with low pressure drops.
Scrubber vessel general physical condi-
tion is observed during the walkaround
inspection to identify any obvious
physical conditions which could threaten
the compliance status of the unit in the
immediate future.
177
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INSPECTION OF WET SCRUBBERS
Inspection Summaries
6.1.2 Wet Scrubber Inspection Checklists
6.1.2.1 Basic Level 2 Inspection Checklist
Stack o visible emissions for 6 to 30 minutes
for each stack or discharge vent
o Minimum and maximum short term opacities
due to process cycles
o Droplet reentrainment
Induced
Draft Fan o obvious severe vibration
Scrubber Vessels
Spray Tower Scrubbers
oInlet liquor pressure
o General physical condition
Packed Bed Scrubbers
o Static pressure change
o Liquor turbidity
o General physical condition
Venturi Scrubbers
o static pressure change
o General physical condition
180
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INSPECTION OF WET SCRUBBERS
Inspection Summaries
6.1.2.2 Follow-up Level 2 Inspection Checklist
Stack o All elements of a Basic Level 2
inspection
Fan o Obvious severe vibration
Fan motor currents
Scrubber Vessels
Spray Tower Scrubbers
o Gas flow rate
o Liquor turbidity
o Liquor distribution from nozzles
o Demister condition
Packed Bed Scrubbers
o Liquor pH
o Liquor recirculation flow rate
o Scrubber gas flow rate
Venturi Scrubbers
o Liquor pH
o Liquor turbidity
o Liquor recirculation rate
o Scrubber gas flow rate
o Venturi scrubber adjustable throat
mechanism condition
o Demister condition
181
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INSPECTION OF WET SCRUBBERS
Level 3 Inspection Procedures
6.1.2.3 Level 3 Inspections
Stack o All elements of a Basic Level 2
inspection
Fan o obvious severe vibration
o Fan motor currents
Scrubber Vessels
Spray Tower Scrubbers
o Gas flow rate from scrubber
o Liquor pH
o Outlet gas temperature
Packed Bed Scrubbers
o static pressure change
o Gas flow rate from scrubber
o Outlet liquor pH
o Outlet gas temperature
Venturi Scrubbers
o Static pressure change
o Gas flow rate from scrubber
o Outlet liquor pH
o Outlet gas temperature
6.1.2.4 Level 4 Inspections
Stack o All elements of a Basic Level 2
inspection
Fan o obvious severe vibration
o Fan motor currents
Scrubber Vessel (All Types)
o All elements of a Level 3 inspection
o Locations for measurement ports
o Potential inspection safety problems
o System flowchart
182
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INSPECTION OF WET SCRUBBER SYSTEMS
Basic Level 2 Inspection Procedures
6.2 Level 2 Inspection Procedures
Wet scrubber visible emissions
If weather conditions permit, determine the wet
scrubber effluent average opacity in accordance with
U.S. EPA Method 9 procedures (or other required proce-
dure). The observation should be conducted during
routine process operation and should last 6 to 30 min-
utes for each stack and bypass vent. The observation
should be made after the water droplets contained in
the plume vaporize (where the steam plume "breaks") or
at the stack discharge if there is no steam plume
present. The presence of a particulate plume greater
than 10% opacity generally indicates a scrubber operating
problem, and/or the generation of high concentrations
of submicron particles in the process, and/or the pres-
ence of high concentrations of vaporous material in the
effluent gas stream.
In addition to evaluating the average opacity,
inspectors should scan the visible emission observation
to identify the maximum and minimum short term opacities.
This is especially useful information if there are
variations in the incinerator operating condition during
charging, soot blowing, or other cyclic activity. The
differences in the minimum and maximum opacities provides
an indication of changing particle size distributions.
If weather conditions are poor, an attempt should
still be made to determine if there are or are not any
visible emissions. Do not attempt to determine "average
opacity" during adverse weather conditions. The presence
of a noticeable plume indicates wet scrubber operating
problems.
183
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INSPECTION OF WET SCRUBBERS
Basic Level 2 Inspection Procedures
Induced Draft Fan Vibration
If the fan downstream of the scrubber vessel is
vibrating severely, the inspection should be terminated
at once and responsible plant personnel should be
advised of the condition. Fans can disintegrate due to
fan wheel corrosion, fan wheel solids build-up, bearing
failure, and operation in an unstable aerodynamic range.
All of these are possible downstream of a wet scrubber.
Shrapnel from the disintegrating fan can cause fatal
injuries.
Droplet reentrainment
Droplet reentrainment indicates a significant
demister problem which can create a local nuisance and
which can affect stack sampling results. The presence
of droplet reentrainment is indicated by the conditions
listed below.
Obvious rainout of droplets in the immediate
vicinity of the stack
Moisture and stains on adjacent support columns,
tanks, and stacks
Mud lip around the stack discharge
184
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INSPECTION OF WET SCRUBBERS
Basic Level 2 Inspection Procedures
Wet scrubber static pressure drop
The wet scrubber static pressure drop should be
recorded i the gauge appears to be working properly.
The follc. g items should be checked to confirm the
adequacy c zhe on-site gauge.
The gauge "face" should be clear of obvious water
and deposits.
The lines leading to the inlet and outlet of the
scrubber appear to be intact.
If there is any question concerning the gauge, ask
plant personnel to disconnect each line one at a time
to see if the gauge responds. If it does not move when
a line is disconnected, the line may be plugged or the
gauge is inoperable. Note: The lines should only be
disconnected by plant personnel and only when this will
not affect plant operations.
Wet scrubber systems operate with a wide range of
static pressure drops as indicated in the list below
(data not provided for spray tower scrubbers since
static pressure drop is not an useful inspection
parameter for this type of unit).
Packed bed 2 to 6 inches W.C.
Venturi 10 to 40 inches W.C.
185
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INSPECTION OF WET SCRUBBERS
Basic Level 2 Inspection Procedures
Wet scrubber static pressure drop
It should also be noted that there is a wide range
of required static pressure drops for identical wet
scrubbers operating on similar industrial processes due
to the differences in particle size distributions. For
these reasons, it is preferable to compare the present
readings with the baseline values for this specific
source.
Increased static pressure drops generally indicate
the following possible condition(s).
Packed bed scrubbers °High gas flow rates
° Partial bed pluggage
Venturi scrubbers o High gas flow rates
o High liquor flow rates
o Constricted venturi
throats
Decreased static pressure drops generally indicate
the following possible condition(s).
Packed bed scrubbers o Low gas flow rates
° Bed collapse
Venturi scrubbers o Low gas flow rates
o Low liquor flow rates
o Eroded venturi dampers
o Increased venturi throat
openings
186
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INSPECTION OF WET SCRUBBERS
Basic Level 2 Inspection Procedures
Liquor inlet pressure
The pressure of the header which supplies the
scrubber spray nozzle can provide an indirect indication
of the liquor flow rate and the nozzle condition. When
the present value is lower than the baseline value(s)
the liquor flow rate has increased and there is a
possibility of nozzle orifice erosion. Conversely, if
the present value is higher than the baseline value(s)
the liquor flow rate has decreased and nozzle and/or
header pluggage is possible.
Unfortunately, these pressure gauges are very
vulnerable to error due to solids deposits and due to
corrosion. It is also difficult to confirm that they
are working properly. For these reasons, other indica-
tors of low liquor flow such as the pump discharge
pressure and the outlet gas temperature should be
checked whenever low header or pipe pressures are
observed.
Wet scrubber system general physical conditions
While walking around the wet scrubber system and
its inlet and outlet ductwork, check for obvious
corrosion and erosion. If any material damage is
evident, check for fugitive emissions (positive pressure
systems) or air infiltration (negative pressure systems).
Avoid inhalation hazards and walking hazards while
checking the scrubber system general physical condition.
Prepare a sketch showing the locations of the corrosion
and/or erosion damage. In addition to corrosion and
erosion, inspectors should also check for any of the
conditions listed below.
o Cracked or worn ductwork expansion joints
o Obviously sagging piping
o Pipes which can not be drained and/or flushed
187
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INSPECTION OF WET SCRUBBERS
Basic Level 2 Inspection Procedures
Liquor turbidity
Ask a responsible and experienced plant representa-
tive to obtain a sample of the liquor entering the
scrubber vessel. This can usually be obtained at a
sample tap downstream from the main recirculation pump.
The agency inspector should provide a clear sample
bottle. Observe the turbidity of the liquor for a few
seconds immediately after the sample is taken. The
turbidity should be qualitatively evaluated as: clear,
very light, light, moderate, heavy, or very heavy.
188
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INSPECTION OF WET SCRUBBERS
Follow-up Level 2 Inspection Procedures
6.2.2 Follow-up Level 2 Inspection Procedures
Liquor p_H
Locate the on-site pH meter(s). Permanently mounted
units are generally in the recirculation tank or in the
liquor outlet lines from the scrubber vessel. Confirm
that the instrument is working properly by reviewing
the routine calibration records. In some cases, it is
possible to watch plant personnel calibrate these
instruments during the inspection.
If the pH meter(s) appears to be working properly,
review the pH data for at least the previous month. In
units with instruments on the outlet and the inlet, the
outlet values are often 0.5 to 2.0 pH units lower due
to the absorption of carbon dioxide, sulfur dioxide,
hydrogen chloride, and other acid gases. Generally,
all of the pH measurements should be within the range
from 5.5 to 10.0. Furthermore, any significant shifts
in the pH values from baseline conditions can indicate
acid gas removal problems and corrosion problems.
Corrosion can be severe in most systems when the
pH levels are less than 5.5. Also, high chloride
concentrations accelerate corrosion at low pH levels.
Precipitation of calcium and magnesium compounds at pH
levels above 10 can lead to severe scaling and gas-
liquor maldistribution.
189
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INSPECTION OF WET SCRUBBERS
Follow-up Level 2 Inspection Procedures
Scrubber liquor recirculation rate
One frequent cause of scrubber emission problems
is inadequate liquor recirculation rate. Unfortunately,
many commercial types of liquor flow monitors are subject
to frequent maintenance problems and many small systems
do not have any liquor flow meters at all. For these
reasons, a combination of factors are considered to
determine if the scrubber liquor recirculation rate is
much less than the baseline level(s). These factors
include the following:
o Liquor flow meter (if available, and if it appears
to be working properly)
o Pump discharge pressure (higher values indicate
lower flow)
o Pump motor current (lower values indicate lower
flow)
o Nozzle header pressure (higher values indicate
lower flow)
o Scrubber exit gas temperature (higher values
indicate lower flow)
o Quantity of liquor draining back into recircula-
tion tank or pond (lower flow rates indicate lower
recirculation rates)
190
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INSPECTION OF WET SCRUBBER SYSTEMS
Follow-up Level 2 Inspection Procedures
Fan motor currents
Changes in gas flow rate occur routinely in most
incinerators due to variations in charging rates and
waste heating values. Information concerning gas flow
rate changes is necessary when evaluating changes in
the scrubber static pressure drop.
Check the scrubber system fan motor current.
Correct the fan motor current to standard conditions
using the equation below.
Corrected Current =
Actual Current x (Gas Temp, in °F + 460)/520
An increase in the fan motor current indicates an
increase in the gas flow rate.
Demister conditions
The static pressure drop across the demister
should be noted and compared with the baseline values.
An increase in the pressure drop normally is due to
partially plugged demister vanes. The static pressure
drops of clean demisters are usually in the range of I
to 2 inches of water.
191
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INSPECTION OF WET SCRUBBER SYSTEMS
Follow-up Level 2 Inspection Procedures
Physical condition of scrubber packed beds and
and venturi throat dampers
This inspection step can be performed only when
the scrubber system is out-of-service. Locate a hatch
on the scrubber vessel shell which is either above or
below the internal component of interest. Look for the
problems listed below.
Packed bed scrubbers Corroded or collapsed bed
supports
Plugged or eroded liquor
Distribution nozzles
Venturi scrubbers Eroded throat dampers
Restricted throat damper
movement due to solids
deposits
Note: Safety conditions sometimes preclude observ-
ations of internal conditions. Respirators and other
personal protection equipment should be worn even if
the scrubber vessel has been purged out prior to the
observations.
Turbidity of presaturator/qas cooler liquor
On older incinerators without heat recovery, the
inlet gas temperature must be reduced prior to gas
entry to the scrubber. This may be done by means of a
presaturator immediately upstream of the scrubber vessel
Since some of the liquor droplets sprayed in this vessel
can evaporate to dryness, there is the potential for
small particle formation from the solids originally
present in the liquor. The turbidity of the liquor
used in the presaturator should be very low to avoid
this condition.
192
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INSPECTION OF WET SCRUBBERS
Level 3 Inspection Procedures
6.3 Level 3 Inspection Procedures
Procedures for measurement of wet scrubber system
operating conditions are described below. Other obser-
vations to be completed as part of the Level 3 inspection
are identical to those included in the basic and follow-
up Level 2 inspection.
Wet scrubber static pressure drop
The static pressure drop is directly related to the
effectiveness of particle impaction for particle capture.
Generally, the particulate removal efficiency increases
as the static pressure drop increases. The steps in
measuring the static pressure drop are described below.
o Locate safe and convenient measurement ports. In
some cases it may be possible to temporarily dis-
connect the on-site gauge in order to use the por-
table static pressure gauge. It also may be pos-
sible to find small ports in the ductwork ahead of
and after the scrubber vessel.
o Clean any deposits out of the measurement ports.
o If the inlet and outlet ports are close together,
connect both sides of the static pressure gauge to
the ports and observe the static pressure drop for
a period of 1 to 5 minutes.
o If the ports are not close together, measure the
static pressure in one port for 10 to 30 seconds
and then proceed to the other port for 10 to 30
seconds. As long as the static pressure drop is
reasonably stable then the two values can be
subtracted to determine the static pressure drop.
° Under no circumstances should on-site plant instru-
ments be disconnected without the explicit approval
of responsible plant personnel. Also, instruments
connected to differential pressure transducers
should not be disconnected.
193
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INSPECTION OF WET SCRUBBERS
Level 3 Inspection Procedures
Outlet gas temperatures
This measurement is conducted whenever it is neces-
sary to determine if poor liquor-gas distribution and/or
inadequate liquor flow rate is seriously reducing partic-
ulate collection efficiency. The steps in measuring
the gas temperature are outlined below.
o Locate safe and convenient measurement ports on
the outlet portion of the scrubber vessel shell or
on the outlet ductwork of the system. Often small
ports of 1/2" to 1/4" diameter are adequate.
oAttach a grounding/bonding cable to probe if vapor,
gas, and/or particulate are potentially explosive.
o Seal temperature probe in the port to avoid any air
infiltration which would result in a low reading.
o Measure the gas temperature at a position near
the middle of the duct, if possible. Conduct the
measurement for several minutes to ensure a
representative reading. Some fluctuation in the
readings is possible if the probe is occasionally
hit by a liquor droplet.
o Compare the outlet gas temperature with the base-
line value(s). If the present value is more than
10°F higher, then either gas-liquor maldistribu-
tion or inadequate liquor is possible.
Scrubber outlet liquor pH
Prior to obtaining a liquor sample, warm-up the
portable pH meter and check it using at least two
different fresh buffer solutions which bracket the
normal liquor pH range. Then request a responsible and
experienced plant representative to obtain a sample of
the scrubber outlet liquor. Measure the liquor pH as
soon as possible after obtaining the sample so that the
value does not change due to dissolution of alkaline
material or due to on-going reactions. Compare this to
the baseline value(s).
194
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INSPECTION OF WET SCRUBBER SYSTEMS
Level 4 Inspection Procedures
6.4 Level 4 Inspection Procedures
The Level 4 inspection includes many inspection
steps performed during Level 2 and 3 inspections.
These are described in earlier sections. The unique
inspection steps of Level 4 inspections are described
below.
Locations for measurement ports
Many existing wet scrubber systems do not have
safe and convenient ports which can be used for static
pressure, gas temperature, and gas oxygen measurements.
One purpose of the Level 4 inspection is to select
(with the assistance of plant personnel) locations for
ports to be installed at a later date to facilitate
Level 3 inspections. Information regarding possible
sample port locations is provided in the U.S. EPA
Publication titled, " Preferred Measurement Ports for
Air Pollution Control Systems", EPA 340/1-86-034.
Potential safety problems
Agency management personnel and/or senior inspectors
should identify any potential safety problems involved in
standard Level 2 or Level 3 inspections at this site. To
the extent possible, the system owner/operators should
eliminate these hazards. For those hazards which can not
be eliminated, agency personnel should prepare notes on
how future inspections should be limited and should
prepare a list of the necessary personnel safety equip-
ment. A partial list of common health and safety
hazards include the following:
o Inhalation hazards due to fugitive leaks from
high static pressure scrubber vessels and ducts
o Eye hazards during sampling of scrubber liquor
o Slippery walkways and ladders
o Fan disintegration
195
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INSPECTION OF WET SCRUBBER SYSTEMS
Level 4 Inspection Procedures
System flowchart
A relatively simple flowchart is very helpful in
conducting a complete and effective Level 2 or Level 3
inspection. This should be prepared by agency management
personnel or senior inspectors during a Level 4 inspec-
tion. This should consist of a simple block diagram
which includes the following elements:
o Source or sources of emissions controlled by a
single wet scrubber system
o Location(s) of any fans used for gas movement
through the system (used to evaluate inhalation
problems due to positive static pressures)
o Locations of any main stacks and bypass stacks
o Location of wet scrubber
o Locations of major instruments (pH meters, static
pressure gauges, thermocouples, liquor flow meters)
196
-------
SUPPORTING INFORMATION
197
-------
USE OF PORTABLE INSTRUMENTS - TEMPERATURE MONITORS
Types and Operating Principles
1. Temperature Monitors
Thermocouples and dial-type thermometers are used in
inspections of municipal waste incinerator sources.
The dial-type units are used primarily for low tem-
perature applications downstream of pollutant control
systems. The thermocouples may be used to check
incinerator outlet gas temperatures in some cases.
1.1 Types and Operating Principles
Thermocouples
The electromotive force generated by two dissimilar
metals is a function of the temperature. The thermo-
couple voltage is compared with a reference voltage
(equivalent to 32°F) and amplified by the thermometer.
There are a variety of thermocouple types, each des-
ignated by letters adopted originally by the Instru-
ment Society of America (ISA) and adopted as American
National Standard C96.1-1964. A summary of the
thermocouple properties is provided below:
Type K - This is the most common type of thermo-
couple due to the broad temperature range of
-400 F to + 2300°F. The thermoelectric
elements must be protected by a sheath since
both wires are readily attacked by sulfurous
compounds and most reducing agents. This
sheath must be selected carefully to ensure
that it also can take the maximum temperature
that the unit will be exposed to. The positive
wire is nickel with 10% chromium (trade name -
chromel) and the negative wire is nickel with
5% aluminum and silicon (trade name - alumel).
Type E - These generate the highest voltage of any
thermocouple, but are limited to a maximum
temperature of 1600°F. The positive wire is
nickel with 10% chromium (chromel) and the
negative wire is a copper-nickel alloy
(constantan).
199
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USE OF PORTABLE INSTRUMENTS - TEMPERATURE MONITORS
Types and Operating Principles
Type J - These have a positive wire composed of iron
and a negative wire composed of a copper-nickel
alloy (constantan). They can be used up to
1000°F in most atmospheres and up to 1400°F
if properly protected by a sheath. They are
subject to chemical attack in sulfurous
atmospheres.
Type T - These can be used under oxidizing and
reducing conditions. However, they have a very
low temperature limit of 700°F. They are
composed of copper positive wire and a copper-
nickel alloy (constantan) negative wire.
Type R and S - These can be used in oxidizing or
inert conditions to 2500°F when protected
by nonmetallic protection tubes. The Type R
thermocouples are composed of a positive wire
of platinum with 13% rhodium and a negative
wire of platinum. The Type S thermocouples
have a positive wire of platinum with 10%
rhodium. Both types can be subject to
calibration shifts to lower temperature
indications due to rhodium diffusion or
rhodium volatilization.
Type B - The positive wire is composed of platinum
with 30% rhodium and the negative wire is
platinum with 6% rhodium. These are less
sensitive to the calibration drift problems of
Type R and S thermocouples. They can be used
to a maximum temperature of 3100°F when
protected by nonmetallic protective tubes.
Thermocouple Sheaths
The maximum temperature that a thermocouple can
withstand is dependent on the wire compositions and
on the type of sheath wrapped around the thermocouple
junction. The temperature limits of common sheath
materials are indicated in Table 1-1.
200
-------
USE OF PORTABLE INSTRUMENTS - TEMPERATURE MONITORS
Types and Operating Principles
Table 1-1. Maximum Operating Temperatures for
Common Sheath Materials
Sheath Material Temperature Limit,°F
Aluminum 700
304 Stainless 1650
316 Stainless 1650
Inconel 2100
Hastelloy 2300
Nickel 2300
A hand-held potentiometer is used to convert the
thermocouple voltage to a temperature reading. This is
a battery powered unit which is generally not rated as
intrinsically safe. For this reason, thermocouples can
not be taken into hazardous locations.
Dial Type Thermometers
Temperature is sensed by the the movement of a
bimetallic coil composed of materials having dif-
ferent coefficients of thermal expansion. The coil
movement is transmitted mechanically to a dial on
the front of the thermometer.
One of the principle advantages of this type of
unit is that there are no batteries required and the
unit can be used safely in most areas.
The main disadvantage is the relatively short
probes of 6 to 12" which make it very difficult to
reach locations at representative gas temperatures.
Due to the short "reach", the dial-type instruments
often indicate lower than actual temperatures.
The dial-type units are best when there is very
little temperature variation in the measurement loca-
tion and when there is little or no insulation sur-
rounding the measurement ports. They are generally
used for low temperature applications.
201
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PORTABLE INSTRUMENTS - TEMPERATURE MONITORS
Calibration and Routine Checks
1.2 Calibration and Routine Checks
Ice and Boiling Water Temperature Measurements
Both the thermocouple based thermometers and the
dial-type thermometers should be checked prior to
leaving for the inspection site. The temperatures of
boiling water and finely crushed ice-water mixture
should be checked. The indicated temperature of the
boiling water should be 212°F or less depending on
elevation. The temperature of the ice-water mixture
should be between 32°F and 34°F depending on how well
the ice has been ground and how long the mixture has
had to reach thermal equilibrium.
Record the thermometer temperatures for boiling
water and ice-water in a notebook or file which is kept
at the agency lab. This simple two point check verifies
that the unit is operating satisfactorily.
Annual Calibration
The thermocouple should be calibrated on an annual
basis. This is often done by comparison of the voltage
developed by the thermocouple with the voltage develop-
ed by a NBS traceable thermocouple. A set of potentio-
meters is used to measure the voltages of the two
thermocouples placed together in a furnace.
Annual calibration of the dial type thermometers
is generally not required. The boiling point and ice
point measurements are sufficient for dial type thermo-
meters used in the temperature range of the 32°F to
212°F.
202
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USE OF PORTABLE INSTRUMENTS - STATIC PRESSURE GAUGES
Types, Operating Principles, and Calibration
2. Static Pressure Gauges
Static pressure gauges are used primarily to eval-
uate the static pressure across particulate control
devices and to evaluate overfire air pressures.
2.1 Types of Static Pressure Gauges
Slack tube manometers, inclined manometers, and
diaphragm gauges are used for measurement of static
pressure. The inclined manometer is the most accurate
instrument for low static pressures of less than 10
inches W.C. However, it is relatively bulky. Slack
tubes can be used up to static pressures of 36 inches
W.C. Larger slack tube manometers are cumbersome to
use. The diaphragm gauges come in various styles, most
of which are accurate to plus or minus 3% or 5% of the
instrument scale. These gauges are easy to carry. The
diaphragm gauges are composed of two chambers separated
by a flexible diaphragm. The diaphragm moves when
there are unequal pressures on each of the ports leading
to the two chambers. The diaphragm deflection is
mechanically transmitted to the dial on the front of
the unit. No batteries are required. Also, there is
no sample gas flow through the instrument.
2.2 Calibration
The slack tube manometer and the inclined manometer
do not need to be calibrated since these indicate a
static pressure directly. The diaphragm gauges are
calibrated by comparison with an inclined manometer or
a slack tube manometer.
The diaphragm gauges can be calibrated by connect-
ing both the manometer and the diaphragm gauge to a
source of pressure (one port of each gauge is left open
to the atmosphere). A squeeze bulb with check valves
on both sides provides a source of positive and nega-
tive pressure in the range of -40 inches w.c. to + 40
inches W.C.
203
-------
USE OF PORTABLE INSTRUMENTS - STATIC PRESSURE GAUGES
Calibration
Separate calibration curves should be prepared for
the positive and negative pressures. Each curve should
be comprised of a minimum of three points to indicate
any non-linearities in the gauge response. A sample
form for recording and plotting the calibration data is
provided in Figure 2-1.
Diaphragm gauge calibration should be performed
prior to each inspection day. Total time requirements
are less than 5 minutes when the manometers and squeeze
bulbs are kept in a convenient location.
204
-------
PORTABLE INSTRUMENTS - STATIC PRESSURE GAUGES
Calibration
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Figure 2-1. Possible Form for Diaphragm Gauge Calibration
205
-------
USE OF PORTABLE INSTRUMENTS - COMBUSTION GAS ANALYZERS
Types of Instruments/Calibration
3.1 Types of Combustion Analyzers
The three major types of portable combustion gas
analyzers that are used for the inspection of municipal
waste incinerators are listed below.
Multi-gas combustion analyzers
ORSAT analyzers
Manual gas absorption instruments
The multi-gas combustion analyzers have the cap-
ability to monitor oxygen, carbon dioxide, and carbon
monoxide. A sample is pumped continuously from the
measurement location and the gases are analyzed by a
variety of techniques including electroconductivity
cells and infrared absorption.
The ORSAT analyzers have similar capability, how-
ever, a manually pumped sample is used. Sequential
chemical absorption in a set of three solutions is used
to determine the combustion gas concentrations for
oxygen, carbon dioxide, and carbon monoxide. The main
advantage of this instrument is the ability to make
measurements without power.
The manual gas absorption kits are sold only for
oxygen and carbon dioxide. These are less expensive
than the ORSAT analyzers and they also use manually
pumped gas samples. They are slightly less accurate
and precise than the ORSAT instruments. However, they
are easy to use and provide adequate data for municipal
waste incinerator system evaluation.
3.2 Calibration
Consult the manufacturers literature concerning
the specific calibration procedures. Calibration gas
standards (compressed gas cylinders) are needed for the
multi-component gas combustion analyzers. Ambient air
is generally used for the ORSAT and manual instruments.
206
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USE OF PORTABLE INSTRUMENTS - COMBUSTION GAS ANALYZERS
Measurement Checks
3.3 Measurement Checks
Combustion systems such as incinerators operate
with a definite relationship between the carbon dioxide
and oxygen concentrations in the flue gas. The measure-
ment made by any of the techniques should be checked
using the information provided in the following table.
If the sum of the oxygen and carbon dioxide measure-
ments are not within the general ranges specified in
the table, it is probable that there are measurement
errors.
Table 3-1. Oxygen and Carbon Dioxide Totals
Fuel Sum of Oxygen and Carbon Dioxide
Concentrations, (% of Dry Gas)
Natural Gas 13 to 19
#2 Oil 15 to 20
#6 Oil 17 to 20
Bituminous Coal, Lignite,
and Sub-bituminous Coal 18 to 21
Anthracite Coal 19 to 21
Wood 18 to 22
Refuse 18 to 22
The ranges shown in Table 3-1 take into account
the stoichiometry of combustion and the gas concentra-
tion measurement errors. It should be noted that the
presence of extreme carbon monoxide concentrations
( >1% or 10,000 ppm) also affects the total.
207
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EMISSION TEST METHODS FOR MUNICIPAL WASTE COMBUSTORS
This section summarizes the sampling and analysis
procedures for those municipal waste incinerator air
pollutants most frequently regulated. These are:
o Particulate matter
oAcid gases (including sulfur dioxide)
o Carbon monoxide
o Metals
o Dioxins/furans
A document addressing the guidelines for emission
testing of MWCs is available from the U.S. EPA [1].
Particulate Matter
MWCs are sampled for particulate matter using EPA
Method 5 [2]. Although both the front and back halves
of the Method 5 train are generally used, the particu-
late is often considered only the material caught in
the probe or on the heated filter. However, to save
money, particulate sampling is often conducted in con-
junction with sampling for one or more other pollutants
using the same train or by making slight modifications
to the sampling train (e.g. different impinger reagents)
Sulfur oxides
EPA Method 8 is the reference test method for
combined sulfuric acid mist and sulfur dioxide and EPA
Method 6 is the reference method when only sulfur
dioxide is to be determined [2]. Both sampling methods
collect and separate the sulfuric acid mist. The
fractions are measured using the barium-thorin titra-
tion method.
209
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Hydrochloric and hydrofluoric acids
Currently, there is no EPA reference method for
measurement of HC1 emissions. Published methods for
HC1 [3, 4, and 5] use a dilute alkaline impinger
reagent (0.1 N NaOH or NaHCO3/Na2CO3) in a midget
impinger train for sample collection and dissolution to
chloride ion, followed either by chloride ion analysis
by mercuric nitrate titration or by ion chromatography
(1C). A slightly modified method currently being vali-
dated by EPA which eliminates potential interference
from diatomic chlorine (C12), utilizes two acidified
impingers (0.1 N H2S04) followed by two alkaline
impingers. The HC1 is caught in the first two
impingers while the C12 passes through and is collected
in the third and fourth impingers. The first method is
still routinely used at MWCs (sometimes being altered
to use distilled water in the first two impingers)
because diatomic chlorine is not typically an interferent
at these sources.
EPA Method 13B [2] for determination of total
fluoride emissions from stationary sources has been
used to measure HF emissions from MWCs. The fluoride
ion is collected in distilled water (and on a filter if
any particulate fluoride is present) and analyzed by
specific ion electrode (or HPLC). As a cost savings,
HC1 and HF testing can be combined by using the Method
13B train with 0.1 N NaOH as the impinger reagent
followed by chloride ion and fluoride ion analyses by
1C or chloride titration. NaOH causes a problem with a
direct specific ion electrode analysis for fluoride and
so this is not used.
The location of the filter in the backup position
for Method 13B, however, sometimes can present problems
because chloride salts (such as CaC12) from dry scrub-
bing) may reach the impingers causing a high bias in
the HC1 measurement. In this case, sampling can be
conducted nonisokinetically (for gaseous HC1 and HF),
using glass wool in the probe to filter the particulate
salts.
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HC1 sampling has also been combined with particu-
late matter sampling and dioxin/furan sampling. In
both cases, 0.1 N NaOH replaces the water in the back
half of the Method 5 or modified Method 5 sampling
train and an aliquot of the combined impinger reagent
is analyzed for chloride ion.
Carbon Monoxide
Carbon monoxide emissions from MWCs are measured
using EPA Method 10 [2]. An integrated or continuous
sample is extracted from the duct and analyzed using a
nondispersive infrared analyzer. The bias introduced
by carbon dioxide and water in the gas stream is elim-
inated by use of a drying tube and an Ascarite carbon
dioxide adsorption tube.
Metals
There are currently three EPA reference methods
for sampling metal emissions that are applicable to
MWCs. These are Method 12 for lead [2], Method 101A
for mercury [6], and Method 104 for beryllium [6].
During the last several years, modified Method 5 trains
have been used to collect various combinations of
metals. One method utilizing a modified Method 5 train
for sampling 16 metals (including: lead, zinc, cadmium,
arsenic, and mercury) is presently undergoing evalua-
tion by EPA. This train employs an all glass probe
including the nozzle and a glass or quartz fiber filter
with a low background level of the target metals. The
five impingers are charged as follows:
Impinger Contents
1 empty
2 and 3 5% HN03/10% H202
4 acidic KMnO4
5 silica gel
For analysis, inductively-coupled argon plasmography
(ICAP) is used to measure the concentrations of all
metals but mercury in (1) the digested front half
sample, and (2) the contents of the first three impingers.
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Lead and arsenic must be remeasured using atomic absorp-
tion spectrophotometry (AA) if found at levels less
than 2 ppm since aluminum and iron (which are commonly
found in MWC emissions) are principal interferents in
the ICAP analysis of lead and arsenic. The mercury
concentration in: (1) the fourth impinger, and in (2)
an aliquot of the first three impingers is measured
using cold vapor AA.
Particulate sampling may be combined with metals
sampling. A gravimetric analysis is performed on the
filter catch prior to digestion. The probe is rinsed
with acetone followed by a nitric acid solution. The
acetone rinse is dessicated and weighed and this weight
is added to the filter catch weight. The acetone rinse
residue is then resolubilized and added to the nitric
acid rinse to be taken through the analytical protocol
for metals analysis.
Dioxins/Furans
Dioxins/furans in stack gas emissions are typically
collected and quantified following the draft ASME/DOE/EPA
protocols [7]. Sampling involves using a modified
Method 5 train with a nickel-plated or glass nozzle,
borosilicate glass probe, glass filter holder, Teflon
or Teflon-coated frit, solvent extracted low background
level glass fiber filter, water-cooled condenser, XAD
sorbent trap for organics, and essentially organic-free
distilled water in the impingers. The train is pre-
pared, handled, and recovered according to a rigorous
scheme to prevent contamination in order to measure the
CDDs/CDFs at extremely low levels (ppt). Analysis of
the samples is generally performed using high resolution
gas chromatography/high resolution mass spectrometry
(HRSC/HRMS). Although there are 210 possible CDD/CDF
isomers, analyses are typically limited to quantifying
the isomers currently believed to be most toxic along
with total amounts in the various isomeric groups (e.g.
isomers chlorinated in the 2,3,7, and 8 positions).
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References - Emission Test Methods
1. Haile, C.L. and J.C. Harris, "Guidelines for Stack
Testing at Municipal Waste Combustion Facilities,"
U.S. EPA Publication 600/8-88-085, June 1988.
2. Code of Federal Regulations, Title 40, Part 60,
Appendix A, July 1, 1987.
3. Rollins, R., and J.B. Homolya, "Measurement of
Gaseous Hydrogen Chloride Emissions from Municipal
Refuse-to-Energy Recovery Systems in the United
States," Environmental Science and Technology,
13(11), pages 1380-1383, 1979.
4. Cheney, J.L., and C. R. Fortune, "Evaluation of a
Method for Measuring Hydrochloric Acid in Combustion
Source Emissions," The Science of the Total
Environment, 13, pages 9-16, 1979.
5. State of California, Air Resources Board, Method
421, "Determination of Hydrochloric Acid Emissions
from Stationary Sources," January 22, 1987.
6. Code of_ Federal Regulations, Title 40, Part 61,
Appendix A, July 1, 1987.
7. "Sampling for the Determination of Chlorinated
Organic Compounds in Stack Emissions" and
"Analytical Procedures to Assay Stack Effluent
Samples and Residual Combustion Products for
Polychlorinated Dibenzo-p-dioxins and
Dibenzofurans," prepared by Group C -
Environmental Standards Workshop, sponsored by
ASME/DOE/EPA, Revised Draft, December 31, 1984.
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