EPA-450/3-89-002
OPERATION AND MAINTENANCE OF
HOSPITAL MEDICAL WASTE INCINERATORS
CONTROL TECHNOLOGY CENTER
SPONSORED BY:
Emission Standards Division
Office of Air Quality Planning and Standards
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
Air and Energy Engineering Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
Center for Environmental Research Information
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, OH 46268 ,Qtv
<°
March 1989 .S. ^* Sl" "
6060^
230
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EPA-450/3-89-002
March 1989
OPERATION AND MAINTENANCE OF
HOSPITAL MEDICAL WASTE INCINERATORS
EPA Contracts No. 68-02-4395
Work Assignment 16
Prepared by:
Midwest Research Institute
Suite 350
401 Harrison Oaks Boulevard
Gary, North Carolina 27513
Prepared for:
James A. Eddinger
Office of Air Quality Planning and Standards
U. S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
Control Technology Center
U. S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
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DISCLAIMER
This document generally describes the proper operation of a hospital
waste incinerator. It is based on EPA's review and assessment of various
scientific and technical sources. The EPA does not represent that this
document comprehensively sets forth procedures for incinerator operation,
or that it describes applicable legal requirements, which vary according
to an incinerator's location. Proper operation of an incinerator is the
responsibility of the owner and operator.
Mention of trade names or commercial products does not constitute
endorsement or recommendation for use.
n
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ACKNOWLEDGEMENT
This document was prepared by Midwest Research Institute located in
Gary, North Carolina. Principal authors were Roy Neulicht, Mark Turner,
Dennis Wallace, and Stacy Smith. Participating on the project team for
EPA were Ken Durkee and James Eddinger of the Office of Air Quality
Planning and Standards, Charles Masser of the Air and Energy Engineering
Research Laboratory, James Topsale of Region III, Charles Pratt of the Air
Pollution Training Institute, and Justice Manning of the Center for
Environmental Research Information. Also participating on the project
team were Carl York and William Paul of the Maryland Air Management
Administration.
The review of this document by representatives of the National Solid
Waste Management Association Waste Combustion Equipment Council (NSWMA—
WCEC) and the Ontario Ministry of the Environment is acknowledged and
appreciated.
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PREFACE
The hospital medical waste incinerator program was funded as a
project of EPA's Control Technology Center (CTC).
The CTC was established by EPA's Office of Research and Development
(ORD) and Office of Air Quality Planning and Standards (OAQPS) to provide
technical assistance to State and local air pollution control agencies.
Three levels of assistance can be accessed through the CTC. First, a CTC
HOTLINE has been established to provide telephone assistance on matters
related to air pollution control technology. Second, more in-depth
engineering assistance can be provided when appropriate. Third, the CTC
can provide technical guidance through publication of technical guidance
documents, development of personal computer software, and presentation of
workshops on control technology matters.
The technical guidance projects, such as this one, focus on topics of
.national or regional interest that are identified through contact wth
State and local agencies. In this case, the CTC became interested in
developing a training course for operators of hospital waste incinerators
through a request by the State of Maryland. This document was prepared to
be used as the basis for development of the training materials. The
document also is intended as a technical guide for use by Federal, State,
and local agency personnel, hospital waste management personnel, and
hospital incinerator operators.
This document provides information on the operation and maintenance
(O&M) procedures that should be practiced on hospital waste incinerators
and associated air pollution control equipment to minimize air
emissions. This document provides only a general overview of proper O&M
procedures with the intention of identifying good operating practices.
Operators of hospital waste incinerators should have O&M manuals for the
manufacturer which provide specific O&M instruction for their equipment.
This document should be viewed as a supplement to the manufacturer's O&M
recommendations.
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TABLE OF CONTENTS
Page
LIST OF FIGURES vii
LIST OF TABLES vi 11
SECTION 1.0 INTRODUCTION 1-1
SECTION 2.0 HOSPITAL INCINERATION SYSTEMS 2-1
2.1 INTRODUCTION 2-1
2.2 FUNDAMENTAL CONCEPTS RELATED TO HOSPITAL WASTE
INCINERATION 2-2
2.2.1 Pathogen Destruction 2-4
2.2.2 Principles of Combustion 2-5
2.3 HOSPITAL WASTE CHARACTERISTICS 2-16
2.4 TYPES OF HOSPITAL WASTE INCINERATOR SYSTEMS 2-20
2.4.1 Introduction 2-20
2.4.2 Multiple-Chamber Incinerators 2-21
2.4.3 Controlled-Air Incinerators 2-27
2.4.4 Rotary Kilns 2-36
2.4.5 Auxiliary Equipment 2-41
2.5 REFERENCES FOR CHAPTER 2 2-41
SECTION 3.0 AIR POLLUTION CONTROL 3-1
3.1 INTRODUCTION 3-1
3.2 POLLUTANT FORMATION AND GENERATION 3-1
3.3 CONTROL STRATEGIES 3-3
3.3.1 Controlling Feed Material 3-3
3.3.2 Combustion Control 3-5
3.3.3 Add-On Air Pollution Control Systems 3-5
3.4 REFERENCES FOR CHAPTER 3 3-26
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TABLE OF CONTENTS (continued)
Page
SECTION 4.0 OPERATION 4-1
4.1 GENERAL OBJECTIVES 4-1
4.2 INCINERATOR KEY OPERATING PARAMETERS 4-3
4.2.1 Introduction 4-3
4.2.2 Controlled-Air Incinerators 4-3
4.2.3 Multiple-Chamber Incinerators 4-11
4.2.4 Rotary Kiln Incinerators 4-15
4.3 WASTE FEED HANDLING 4-16
4.3.1 Proper Waste Handling 4-17
4.3.2 Restricted Wastes 4-20
4.4 INCINERATOR OPERATION, CONTROL, AND MONITORING.. 4-21
4.4.1 Batch Feed Controlled-Air Incinerator.... 4-21
4.4.2 Intermittent-Duty, Controlled-Air
Inci nerators 4-34
4.4.3 Continuous-Duty, Controlled-Air
Incinerators 4-37
4.4.4 Multiple-Chamber Incinerators 4-39
4.5 ADD-ON AIR POLLUTION CONTROL SYSTEMS 4-43
4.5.1 Wet Scrubbers 4-43
4.5.2 Fabric Filters 4-48
4.5.3 Spray Dryers 4-54
4.5.4 Dry Injection 4-56
4.6 REFERENCES FOR CHAPTER 4 4-57
SECTION 5.0 MAINTENANCE 5-1
5.1 HOSPITAL WASTE INCINERATORS 5-1
5.1.1 Hourly/Daily Maintenance 5-2
5.1.2 Weekly/Biweekly Maintenance 5-6
5.1.3 Monthly/Semiannual Maintenance 5-6
5.2 WET SCRUBBERS 5-8
5.2.1 Daily/Weekly Maintenance 5-8
5.2.2 Monthly/Semiannual Maintenance 5-10
VI 1
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TABLE OF CONTENTS (continued)
Page
5.3 MAINTENANCE OF FABRIC FILTERS ................... 5-11
5.3.1 Daily Inspection/Maintenance ............. 5-13
5.3.2 Weekly Inspection/Maintenance ............ 5-13
5.3.3 Monthly/Quarterly Inspection/Maintenance 5-14
5.3.4 Semi annual /Annual Inspection/Maintenance 5-15
5.4 REFERENCES FOR CHAPTER 5 ........................ 5-15
SECTION 6.0 CONTROL AND MONITORING INSTRUMENTATION ............... 6-1
6.1 OPERATING PARAMETERS THAT SHOULD BE MONITORED... 6-1
6.2 TYPICAL INSTRUMENTATION ......................... 6-2
6.2.1 Temperature .............................. 6-2
6.2.2 Pressure ................................. 6-5
6.2.3 Oxygen Concentration ..................... 6-6
6.2.4 Carbon Monoxide .......................... 6-11
6.2.5 Opacity .................................. 6-12
6.2.6 Charge Rate .............................. 6-14
6.2.7 Scrubber Liquor pH ....................... 6-16
6.3 REFERENCES FOR CHAPTER 6 ........................ 6-17
SECTION 7.0 OPERATIONAL PROBLEMS AND SOLUTIONS ................... 7-1
7.1 OPERATIONAL PROBLEMS AND SOLUTIONS ASSOCIATED
WITH HOSPITAL WASTE INCINERATORS .............. 7-1
7.1.1 Excessive Stack Emissions—
Controlled-Air Units ................... 7-1
7.1.2 Excessive Stack Emissions—
Multiple-Chamber Units ................. 7-4
7.1.3 Leakage of Smoke From Primary Chamber.... 7-5
7.1.4 Excessive Auxiliary Fuel Usage ........... 7-5
7.1.5 Incomplete Burnout—Poor Ash Quality ..... 7-6
7.2 OPERATIONAL PROBLEMS AND SOLUTIONS ASSOCIATED
WITH WET SCRUBBERS ............................ 7-8
7.2.1 Corrosion ................................ 7-8
7.2.2 Scaling .................................. 7-9
7.2.3 Erosion .................................. 7-9
VII 1
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TABLE OF CONTENTS (continued)
Page
7.3 OPERATIONAL PROBLEMS AND SOLUTIONS ASSOCIATED
WITH FABRIC FILTERS 7-11
7.3.1 Opacity 7-11
7.3.2 Pressure Drop 7-13
7.4 REFERENCES FOR CHAPTER 7 7-15
SECTION 8.0 RECORDKEEPING 8-1
8.1 MANUFACTURER'S SPECIFICATIONS AND LITERATURE.... 8-1
8.2 COMPLIANCE EMISSION TEST RECORDS 8-2
8.3 OPERATING RECORDS 8-2
8.4 MAINTENANCE RECORDS 8-4
8.4.1 Retrieval of Records 8-5
8.5 REFERENCES FOR CHAPTER 8 8-6
SECTION 9.0 SAFETY GUIDELINES 9-1
9.1 PREVENTION OF INFECTION DURING WASTE HANDLING... 9-1
9.2 EQUIPMENT SAFETY PROCEDURES 9-2
9.3 FIRE SAFETY 9-4
9.4 REFERENCES FOR CHAPTER 9 9-5
SECTION 10.0 GLOSSARY 10-1
REFERENCES FOR CHAPTER 10 10-6
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LIST OF FIGURES
Figure 2-1
Figure 2-2
Figure 2-3
Figure 2-4
Figure 2-5
Figure 2-6
Figure 2-7
Figure 2-8
Figure 2-9
Figure 2-10
Figure 2-11
Figure 3-1
Figure 3-2
Figure 3-3
Figure 3-4
Figure 3-5
Figure 3-6
Figure 3-7
Figure 3-8
Figure 6-1
Figure 6-2
Major components of an incineration system
Relationship of temperature to excess air
In-line multiple-chamber incinerator with grate
Retort multiple-chamber incinerator for
pathological wastes
Schematic of a control led-air incinerator
Schematic of a single batch control led-air
i nci nerator
Example intermittent-duty, control led-air incineraor..
Hopper/ram mechanical waste feed system
Incinerator with step hearths and automatic ash
removal ...._.
Rotary kiln with auger feed
Incinerator with waste heat boiler and bypass stack...
Impaction
Spray venturi with circular throat
Spray venturi with rectangular throat
Countercurrent packed tower absorber
Countercurrent-flow spray tower
Pulse jet baghouse
Components of a spray dryer absorber system
(semiwet process)
Components of a dry injection absorption system
(dry process)
Schematic of an extractive monitoring system
Typical transmissometer installation of measuring
ooacitv
Page
2-3
2-11
2-23
2-24
2-28
-31
2-33
2-34
2-37
2-38
2-39
3-7
3-10
3-11
3-14
3-16
3-19
3-23
3-24
6-10
6-13
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LIST OF TABLES
TABLE 2-1 STOICHIOMETRIC OXYGEN REQUIREMENTS AND COMBUSTION
TABLE 2-2
TABLE 2-3
TABLE 2-4
TABLE 2-5
TABLE 3-1
TABLE 4-1
TABLE 4-2
TABLE 4-3
TABLE 4-4
TABLE 4-5
TABLE 5-1
TABLE 5-2
TABLE 5-3
TABLE 6-1
TABLE 6-2
TABLE 8-1
PRODUCTS YIELDS
EXAMPLES OF INFECTIOUS WASTE
CHARACTERIZATION OF HOSPITAL WASTE
CHARACTERIZATION OF HOSPITAL WASTE
CLASSIFICATION OF HOSPITAL INCINERATORS
CONTROL STRATEGIES FOR AIR POLLUTANTS FROM HOSPITAL
WASTE INCINERATORS
KEY INCINERATOR OPERATING PARAMETERS AND RECOMMENDED
OPERATING RANGE: CONTROLLED-AIR INCINERATOR
KEY INCINERATOR OPERATING PARAMETERS AND RECOMMENDED
OPERATING RANGE: MULTIPLE-CHAMBER INCINERATOR
EXAMPLE TIMED CONTROL CYCLE FOR BATCH MODE INCINERATOR
WET SCRUBBER PERFORMANCE PARAMETERS FOR HOSPITAL
WASTE INCINERATORS
KEY OPERATING PARAMETERS FOR FABRIC FILTER CONTROL
SYSTEMS
TYPICAL MAINTENANCE INSPECTION/CLEANING/LUBRICATION
SCHEDULE FOR A HOSPITAL WASTE INCINERATOR
TYPICAL MAINTENANCE INSPECTION/CLEANING/LUBRICATION
SCHEDULE FOR A WET SCRUBBER
TYPICAL MAINTENANCE INSPECTION/CLEANING/LUBRICATION
SCHEDULE FOR A FABRIC FILTER SYSTEM
THERMOCOUPLE TYPES
PERFORMANCE SPECIFICATIONS FOR OPACITY MONITORS
RECOMMENDED OPERATING PARAMETERS THAT SHOULD BE
INCLUDED IN OPERATING LOGS FOR INCINERATORS, WET
SCRUBBERS, FABRIC FILTERS, AND CONTINUOUS
EMISSION MONITORS
2-8
2-17
2-18
2-18
2-22
3-4
4-4
4-13
4-30
4-45
4-49
5-3
5-4
5-12
6-4
6-15
8-3
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1.0 INTRODUCTION
The main objective of this document is to identify the operation and
maintenance (O&M) procedures that should be practiced on hospital waste
incinerators and associated air pollution control equipment to minimize
air emissions. Proper O&M, in addition to reducing air emissions,
improves equipment reliability and performance, prolongs equipment life,
and helps to ensure proper ash burnout. This document provides only
general guidance on proper O&M procedures with the intention of
identifying good operating practices. The operator of a hospital waste
incinerator should have O&M manuals from the manufacturer which provide
specific O&M instructions for their equipment. This document does not
provide such specific instructions, and is not intended to do so. The
document is intended as a technical guide for use by Federal, State, and
local agency personnel, hospital waste management personnel, and hospital
incinerator operators.
The concern about disposal of infectious wastes generated by
hospitals is increasing rapidly due to the fear of the spread of viruses
such as acquired immune deficiency syndrome (AIDS) and hepatitis B, as
well as the concern about exposure to toxic metals and organics.
Incineration continues to be an attractive infectious waste disposal
option for hospitals encountering high disposal costs, refusal of their
waste at treatment and disposal facilities, and tighter regulation.
Proper incineration sterilizes pathogenic waste, reduces waste volumes by
over 90 percent, and, in some cases, may provide economic benefits through
waste heat recovery. Onsite incineration is an attractive option because
it reduces handling and transportation of the wastes and because waste
heat recovery can have economic advantages for the facility. The need for
disposal of infectious wastes and problems associated with such disposal
also has spurred the interest in special commercial incineration
facilities. In either case, the operating facility must address the
problems of air emissions and ash disposal from the incinerator.
Hospital waste incinerators may emit a number of pollutants depending
on the waste being incinerated. These pollutants include: particulate
matter, acid gases, toxic metals, toxic organic compounds, carbon
1-1
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monoxide, sulfur oxides, nitrogen oxides, and pathogens and viruses.
Proper operation of the incinerator will reduce the emissions of most of
these pollutants. Air pollution control devices are available to further
control these pollutants.
In response to public concern about hospital incineration, several
States recently have enacted or are in the process of enacting regulations
which govern the incineration of general hospital wastes and infectious
wastes, specifically. These regulations specify emission limits for
hospital incinerators, and frequently they also address operating
practices related to waste handling and charging, combustor operations,
ash characteristics, and ash handling practices. Some of the operating
practices that have been specified in these regulations include:
1. Limits on characteristics of wastes charged to the incinerator;
2. Specific requirements for waste packaging and waste charging
practices;
3. Combustor temperature limits;
4. Ash burnout levels; and
5. Ash handling and disposal practices.
The combustion efficiency of a hospital waste incinerator and the
pollutant removal efficiency of its associated air pollution control
equipment ultimately is affected by equipment O&M. Regardless of how well
the equipment is designed, poor O&M practices will lead to the
deterioration of components and a resultant decrease in both combustion
quality and pollutant removal efficiency. In addition, O&M practices
impact equipment reliability, on-line availability, continuous compliance
with emission limits and operating practice standards, and regulatory
agency/source relations. Lack of timely and proper O&M leads to a gradual
deterioration in the equipment, which in turn increases the probability of
equipment failure and decreases both the reliability and on-line
availability of the equipment. Frequent violations of emission limits or
operating the facility outside the limits of operating practices
established by regulations can result in public complaints, increased
frequency of inspection, potential fines for noncompliance, and in some
cases, mandatory shutdown until emission problems are solved. Good O&M
practices are essential to safe, reliable operation of the facility.
1-2
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This document summarizes technical information related to the proper
operation and maintenance of hospital waste incinerators and associated
air pollution control systems. Chapter 2 presents background information
on hospital waste incineration systems including a summary of combustion
principles and descriptions of the types of incinerators typically used
for hospital waste. Chapter 3 presents background information on add-on
air pollution control systems for hospital waste incinerators. Chapter 4
identifies key operating parameters and good operating practices for
hospital waste incineration and air pollution control systems. Operating
parameters which can be monitored and/or automatically controlled also are
discussed in Chapter 4. Chapter 5 provides general guidance on the
maintenance of incinerators and air pollution control systems. Chapter 6
describes instrumentation which can be used for the control and monitoring
of the key operating parameters. Chapter 7 identifies some common
operational problems associated with hospital waste incinerators and air
pollution control systems; the possible causes and solutions to the
problems are discussed. Chapter 8 discusses recordkeeping procedures
which can assist in operating and maintaining an incineration system.
Chapter 9 provides general safety guidelines, and Chapter 10 presents a
glossary of terms.
1-3
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2.0 HOSPITAL INCINERATION SYSTEMS
2.1 INTRODUCTION
Incineration is the process by which combustible materials are
burned, producing combustion gases and noncombustible residue and ash.
The product combustion gases are vented directly to the atmosphere or to
the atmosphere after treatment in an air pollution control device. The
noncombustible ash residue is removed from the incinerator system and is
disposed of in a landfill. Incineration provides the advantage of greatly
reducing the mass and volume of the waste. This reduction substantially
reduces transportation and disposal costs. For infectious hospital
wastes, another major objective of the incineration process is the
destruction of infectious organisms (pathogens) that may exist in the
waste. The destruction of the pathogens is caused by their exposure to
the high temperatures which exist within the incinerator. Incineration of
hospital wastes also is attractive aesthetically because it destroys
organic components of the waste that the community often finds
objectionable when wastes are disposed, of in landfills.
Two additional objectives achievable through proper operation of
hospital waste incinerators are minimizing organic content in the solid
residue and controlling atmospheric emissions to acceptable levels.
Generally, tight control on organics in the ash, i.e., good burnout,
promotes waste reduction and pathogen destruction. Reduction of
atmospheric emissions of constituents that are potentially harmful to
human health and the environment is a prerequisite to acceptance of
hospital incineration as a feasible disposal alternative by the community.
The overall purpose of this technical document is to present
information on the operation of hospital waste incineration systems that
can contribute to achieving these objectives. This chapter provides
background information on the incineration process that will enhance the
usefulness of the remainder of the document. It presents information on
basic incineration principles and processes and integrates this
information to promote an understanding of hospital waste incineration as
an overall system.
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The hospital waste Incineration process can be separated into the
following steps:
1. Waste preparation;
2. Waste charging;
3. Waste combustion;
4. Treatment of the combustion gases, (i.e., add-on air pollution
control); and
5. Residue ash handling.
Waste heat recovery also may be included as a part of the incinerator
system. The incineration process and the major subsystems of an
incineration system are depicted in Figure 2-1. An incinerator operates
as a system in which all of the process steps mentioned above are
interrelated. For example, the charging procedures implemented by the
operator will affect how well the wastes burn in the combustion chamber
and, consequently, the ash quality. Proper operation of a system requires
an understanding of the principles of operation of each of the components
and of the interrelationship of those components for a particular system
configuration.
The remainder of this chapter presents background information on
hospital incineration processes in three parts. Section 2.2 presents
fundamental concepts on pathogen destruction and combustion principles.
Section 2.3 describes hospital waste characteristics and briefly addresses
how these characteristics affect incineration. Section 2.4 describes
incineration system components and the different incinerator systems that
are used to treat hospital wastes.
2.2 FUNDAMENTAL CONCEPTS RELATED TO HOSPITAL WASTE INCINERATION
An understanding of how an incinerator operates as a system requires
familiarity with some basic scientific and engineering principles. This
section provides a brief discussion of the key principles related to two
basic areas—pathogen destruction and combustion chemistry/physics. The
discussions are quite abbreviated and are designed to provide the reader
with the basic information needed to understand the remainder of this
document; they do not provide complete coverage of the subject areas.
2-2
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To
Atmosphere
Stack
To
Atmosphere
t
Stack
r Waste ~!
i Heat
L Boiler _]
Air i
Pollution '
Control J"
System i
Ash
Figure 2-1. Major components of an incineration system.
2-3
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Those readers desiring more information on these subjects should consult
References 1 through 3 on pathogen destruction and References 4 through 8
on combustion.
2.2.1 Pathogen Destruction
The primary objective of hospital waste incineration is the
destruction of pathogens in infectious wastes. The U. S. Environmental
Protection Agency (EPA) has defined infectious waste as "waste capable of
producing an infectious disease .... For a waste to be infectious, it
must contain pathogens with sufficient virulence and quantity so that
exposure to the waste by a susceptible host could result in an infectious
disease."1 Some examples of hospital wastes which may be considered to be
infectious are:
1. Microbiological laboratory wastes including cultures and
equipment which has come -in contact with cultures of infectious agents;
2. Blood and blood products (such as serum, plasma);
3. Sharps, including needles, laboratory glass wastes, and glass
pipets;
4. Surgical, autopsy, and obstetrical wastes which have had contact
with patient blood or body fluids;
5. Wastes which have had contact with communicable disease isolation
wastes;
6. Human and animal tissue containing pathogens with sufficient
virulence and quantity so that exposure to the waste by a susceptible
human host could result in an infectious disease; and
7. Dialysis unit wastes; i.e., wastes that were in contact with the
blood of patients undergoing hemodialysis.
The pathogens in infectious waste can be destroyed by the high
temperatures achieved in hospital incinerators. Data on the incinerator
conditions required to destroy the universe of pathogens that are present
in infectious waste are quite limited, but they do indicate that
temperature and time of exposure are important. Emissions of micro-
organisms from the incinerator could be attributed to insufficient
retention time and temperature as a result of the following conditions:
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1. Initial charging of the incinerator before operating temperatures
are achieved;
2. Failure to preheat the refractory lining;
3. Temperature fluctuations caused by intermittent use;
4. Exceeding design airflow rates, thereby reducing the retention
time;
5. Charging beyond incinerator capacity; and
6. Excessive moisture content of the waste.
Other factors such as the type of refractory lining, the positioning
and number of burners, and the precision of temperature controlling
devices also can have a significant bearing on the effectiveness of
sterilization.2'3 The destruction of micro-organi;
ash also depends on temperature and time exposure.
sterilization. ' The destruction of micro-organisms in the incinerator
2.2.2 Principles of Combustion**"9
In principle, combustion of hospital waste is a chemical process that
is equivalent to combustion of fossil fuels for energy recovery. It is a
chemical reaction that involves rapid oxidation of the organic substances
in the waste and auxiliary fuels. This violent reaction releases energy
in the form of heat and light and converts the organic materials to an
oxidized form. Some of the basic principles related to the combustion
process are discussed in the following subsections. Specifically, the
basic chemical reactions, stoichiometric air requirements, thermochemical
relations, and volumetric flows are discussed in the first four
subsections. In the last subsection, the combustion process is discussed
in general terms, and the role of waste characteristics in that process is
outlined.
2.2.2.1 Chemical Reactions. The organic portion of hospital waste
consists primarily of carbon (C), hydrogen (H), and oxygen (0). These
elements are involved in the reactions that generate most of the energy
and the bulk of the combustion gas products that are released during
incineration. Other elements found to a lesser degree are metals, sulfur
(S), nitrogen (N), and chlorine (Cl). Although these elements are of
lesser importance to the main "combustion reaction," they play an
important role in potential air pollution problems.
2-5
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The reaction chemistry in the combustion zone is quite complex and
involves a wide variety of organic compounds and free radical species.
However, a general understanding of combustion can be achieved by treating
these reactions simply as a combination of carbon and hydrogen in the
organic material with the oxygen in the combustion air and organic
material. These simplified reactions can be represented by the chemical
equations:
C+02 - C02 + Heat (2-1)
2H2+02 * 2H20 + Heat (2-2)
When complete combustion occurs, carbon and hydrogen combine with the
oxygen of the combustion air to form carbon dioxide (C02) and water vapor
(H20), respectively, as shown above. If incomplete combustion occurs,
carbon monoxide (CO) also will be formed.
Available thermodynamic equilibrium data and bench-scale test data
indicate that organic chlorine which enters the combustion chamber reacts
almost completely to form hydrogen chloride (HC1) and elemental chlorine
(C12). Unless the system has very low H:C1 ratios in the feed, almost no
C12 is formed.8 The HC1 and any C12 that is formed leave the combustion
chamber in vapor phase.
Sulfur that is chemically bound in organic materials making up the
hospital waste is oxidized during the combustion process to form sulfur
dioxide (S02) at a rate directly proportional to the sulfur content of the
waste. Some S02 may react with alkaline reagents also present in the
waste or ash. However, the amount of S02 involved in such reactions is
expected to be negligible due to the high HC1 content of the flue gas.
Because it is a stronger acid than S02, HC1 will react more quickly with
available alkaline compounds than S02 and will tie up the alkaline
compounds before they have a chance to react with S02. Consequently,
essentially all organic sulfur present in the waste will leave the
combustion chamber as vapor phase S02.
Nitrogen enters the combustion chamber as a component of the waste
and in the combustion air. It can react in the combustion chamber to
produce nitrogen oxides (NOX). The NOX is formed by one of two general
2-6
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mechanisms. "Thermal NOX" is the result of the reaction between molecular
nitrogen and molecular oxygen, both of which enter the combustion zone in
the combustion air. "Fuel NO'1 results from the oxidation of nitrogen
A
which enters the combustion zone chemically bound within the fuel
structure. The rate of thermal NOX formation is sensitive to the flame
temperature. The detailed mechanisms of fuel NOx formation are not well
understood, but the formation is not extremely sensitive to temperature.
2.2.2.2 Stoichiometric Combustion Air. The theoretical amount of
oxygen required for complete combustion is known as the Stoichiometric or
theoretical oxygen and is determined by the nature and the quantity of the
combustible material to be burned. Combustion oxygen is usually obtained
from atmospheric air. The additional oxygen (or air) over and above the
Stoichiometric amount is called "excess air."
The overall chemical composition (ultimate analysis) of the waste/
fuel mixture can be used to calculate the mass-based Stoichiometric oxygen
requirements with the factors in Table 2-1. Volumetric oxygen require-
ments can be estimated with the following equation:
Q0 - MQ • K (2-3)
•
Q = volumetric flow of 02 (scm/h)
MQ = Mass flow of 02 (kg/h)
K = 0.2404 son 02/kg 02 at 20°C and 1 atm.
Total volumetric air requirements can be estimated by multiplying
volumetric oxygen requirements by 5.
2.2.2.3 Thermochemical Relations. Thermochemical calculations are
used to estimate heat release and heat transfer associated with combus-
tion. These calculations permit determination of the energy released by
the combustion process and assessment of the transfer of the energy to the
environment. Thermochemical calculations involve determination of fuel
(or waste) heating values, heat contents of entering and leaving streams,
and any other heat losses. A definition of terms that will be helpful for
understanding these calculations is presented below.
Heat of combustion. Heat energy evolved from the union of a
combustible substance with oxygen to form C02 and H20 (and S02) as the end
2-7
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TABLE 2-1. STOICHIOMETRIC OXYGEN REQUIREMENTS AND COMBUSTION
PRODUCTS YIELDS
Elemental Stoichiometric
waste component oxygen requirement Combustion product yield
C
H2
02
N2
H20
C12
F2
Br2
I2
S
P
Air N2
2.67 Ib/lb C
8.0 Ib/lb H2
-1.0 Ib/lb 02
—
—
-0.23 Ib/lb C12
-0.42 Ib/lb F2
—
—
.1.0 Ib/ Ib S
1.29 Ib/lb P
—
3.67 Ib C02/lb C
9.0 Ib H20/lb H2
1.0 Ib N2/lb N2
1.0 Ib H20/lb H20
1.03 Ib HCl/lb C12
-0.25 Ib H20/lb C12
1.05 Ib HF/lb F2
-0.47 Ib H20/lb F2
1.0 Ib Br2/lb Br2
1.0 Ib I2/lb I2
2.0 Ib S02/lb S
2.29 Ib P20s/lb P
3.31 Ib N2/lb (02)stoich
Stoichiometric air requirement = 4.31x(02)S|-0jc:.n
2-3
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products, with both the reactants starting and the products ending at the
same conditions, usually 20°C (68°F) and 1 atm (29.92 in Hg).
Gross or higher heating value—HVg or HHV. The quantity of heat
evolved as determined by a calorimeter where the combustion products are
cooled to 16°C (60°F) and all water vapor is condensed to liquid. Usually
expressed in terms of kcal/g or kcal/m (Btu/lb or Btu/scf).
Net or lower heating value—HVN or LHV. Similar to the higher
heating value except that the water produced by the combustion is not
condensed but is retained as vapor at 18°C (60°F). Expressed in the same
units as the gross heating value.
Enthalpy or heat content. Total heat content, expressed in kcal/g
(Btu/lb), above a standard reference condition.
Sensible heat. Heat, the addition or removal of which results in a
change of temperature.
Latent heat. Heat associated with a change of phase, e.g., from
liquid to vapor (vaporization) or from liquid to solid (fusion), without a
change in temperature. Usually expressed as kcal/g (Btu/lb)."
Available heat. The quantity of heat available for intended (useful)
purposes. The difference between the gross heat input to a combustion
chamber and all the losses.
For steady-state operations:
Heat in (sensible + HHV) = Heat out (sensible + latent + available) (2-4)
Heat is liberated in the combustion process at the rate of 7.8 kcal/g
of carbon burned and 34 kcal/g of hydrogen burned (14,100 Btu per pound of
carbon burned and 61,000 Btu per pound of hydrogen burned). Alterna-
tively, heat is liberated from the combustion process at a rate that is
equal to the product of the mass flow rate of the waste (and auxiliary
fuel) and the higher heating value of waste (and fuel). A major latent
"heat loss" is the energy required to evaporate moisture in the waste and
vaporize organic constituents. The energy required to raise the
temperature of the evaporated moisture and any excess air to combustion
chamber temperatures is a part of the sensible "heat loss."
2-9
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Maximum combustion temperatures are attained at stoichiometric
conditions. As the amount of excess air is increased above the
stoichiometric point, the combustion temperature is lowered because energy
is used to heat the combustion air from ambient temperature to the combus-
tion chamber temperature. The greater the volume of the excess air, the
greater the "heat loss" due to raising the air temperature. As the amount
of excess air is decreased, the combustion temperature increases until it
becomes maximum at the stoichiometric point. Below the stoichiometric
point, the temperature decreases because complete combustion has not
occurred. Since the complete combustion reaction (which is exothermic)
has not occurred, the maximum heat is not generated. A graphical
representation of the relationship between combustion temperature and
excess air level is shown in Figure 2-2.
As the excess-air level increases, the volume of oxygen supplied to
the incinerator that is not reacted increases, resulting in a higher
oxygen concentration in the effluent gas stream. Since the total amount
by weight (kg) of carbon dioxide generated during combustion is based on
stoichiometric ratios, it remains constant for a specific quantity of
carbon in the waste. However, as the excess-air level increases, the
concentration of carbon dioxide in the total combustion gas stream
decreases due to dilution from the excess air (oxygen and nitrogen). The
oxygen concentration and carbon dioxide concentration of the effluent gas
stream are useful indicators of the combustion excess air levels and are
useful for monitoring the combustion process.
2.2.2.4 Volumetric Gas Flows. Gas flows through a combustion system
and air pollution control system are a major consideration in the design
and operation of those systems. Three key principles that are important
to understanding the operation of those systems are the relationship of
volumetric flow to gas residence time, the volume occupied by compounds
(either organic constituents or water) vaporized in the combustion
chamber, and the relationship of gas volume to temperature and pressure.
Complete destruction of pathogens and complete combustion of organic
constituents require exposure of the materials to high temperatures for
minimum residence times. Some State regulations now require a minimum
residence time in the secondary combustion chambers, and operators must
2-10
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TEMPERATURE
MAXIMUM
TEMPERATURE
DEFICIENT AIR
EXCESS AIR
PERCENT EXCESS AIR
Figure 2-2. Relationship of temperature to excess air.
2-11
-------
comply with these requirements. The residence time is a function of
chamber volume and volumetric flow rate and can be estimated (plug flow
assumed) with the following equations:
t _ 60 V . ,.
t - * (2-5)
s 'air + V ('
where:
t = residence time, s
V = combustion chamber volume, m
Qgas = combustion gas flow rate at combustion chamber conditions,
m /min
r = combustion airflow rate at combustion chamber conditions,
m /min
Q = release rate of free moisture from the waste at combustion
chamber conditions, m /min
These equations assume complete turbulent flow in the combustion chamber
and that the volume of combustion gas is approximately equal to the volume
of combustion air.
As waste is exposed to high temperatures in the combustion chamber,
some materials in that waste are volatilized into the vapor or gas
phase. Two issues of particular concern are the volume of water vapor
produced by the moisture in the waste and the volume of gas produced by
highly volatile organic materials such as solvents that evaporate almost
instantly as they are exposed to high temperatures. The volume of gas
produced from a given mass of material can be calculated from the
equation:
Mi
V. = 24.04 ^ (2-7)
where:
V.j = volume of compound i at standard conditions, son
M.J = mass of compound i, kg
MW.J = molecular weight of compound i, g/g mole
2-12
-------
This equation estimates volumes at standard conditions, which are defined
to be 20°C (68°F) and 1 atm (29.92 in. Hg). The paragraphs below describe
how volumes can be estimated for different temperatures and pressures.
The volume that a gas occupies, or the volumetric flow rate of a gas,
is dependent on the temperature and pressure of the gas. Estimates of gas
volume or gas volumetric flow can be modified to reflect different
temperatures or pressures with the equations:
(2-8)
where:
Vj = volume at condition i, m
T.J = temperature at condition i, K (where K = 273+°C)
PJ = absolute pressure at condition i, atm
Q.J = volumetric flow at condition i, m3/nnn
2.2.2.5 The Combustion Process. The goal of the combustion process
is complete combustion of the organic constituents in the waste feed.
Complete combustion requires sufficient air in the combustion chamber,
sufficient temperatures in the combustion bed and combustion gas,
sufficient time over which materials are exposed to a temperature profile,
and mixing that assures good contact of the waste/fuel with the combustion
air.
Each organic substance in hospital waste has a characteristic minimum
ignition temperature that must be attained or exceeded, in the presence of
oxygen, for combustion to occur. Above the ignition temperature, heat is
generated at a higher rate than it is lost to the surroundings, and the
elevated temperatures necessary for sustained combustion are maintained.
The residence time of a constituent in the high-temperature region
should exceed the time required for the combustion of that constituent to
2-13
-------
take place. Residence time requirements establish constraints on the size
and shape of the furnace for a desired firing rate. Because the reaction
rate increases with increasing temperature, a shorter residence time will
be required for combustion at higher temperatures if good combustion
conditions are present.
Adequate oxygen supplies and turbulence and the resultant mixing of
organic materials and oxygen are also essential for efficient
combustion. Inadequate mixing of combustible gases and air in the furnace
can lead to emissions of incomplete combustion products, even from an
otherwise properly sized unit with sufficient oxygen. Turbulence will
speed up the evaporation of liquid fuels for combustion in the vapor
phase. In the combustion of waste solids, turbulence will help to break
up the layer of combustion products formed around a burning particle of
waste. Under nonturbulent conditions, the combustion rate is slowed
because this layer of combustion products decreases the amount of oxygen
that contacts the surface of the particle.
For hospital waste incinerators, the distribution of combustion air
between the primary and secondary chambers and the methods used to inject
that air to the chamber are key operating considerations. The
distribution of air between the two chambers affects the amount of oxygen
that is available for reaction in each chamber. (See the discussion of
stoichiometry above.) The method of injection of the air to the two
chambers is one of the factors that controls turbulence and mixing.
The chemical and physical characteristics of the waste stream also
have significant effects on the combustion process and on the composition
of the effluents from the process. Generally, wastes can be characterized
by a "proximate analysis," which is a laboratory determination of four
waste characteristics—volatile matter, fixed carbon, moisture, and ash or
noncombustibles. The paragraphs below define these four parameters and
describe their effects on the combustion process.
Volatile matter is that portion of the waste which can be liberated
(i.e., vaporized) with the application of heat only (i.e., no chemical
reaction occurs). Actual combustion of volatile matter is a gas-phase
reaction (i.e., the combustion occurs after the material has been
vaporized). Key factors that must be considered when volatile matter is
2-14
-------
introduced to the combustor are the rate at which the material is
vaporized and the ability of the combustor to provide adequate volume and
airflow for that release.
Fixed carbon is the nonvolatile carbon portion of the waste and must
be burned at higher temperatures and at increased duration of exposure to
the combustion air. The combustion of fixed carbon is a solid-phase
reaction. An incinerator should be operated with a solids residence time
that is sufficient for fixed carbon combustion.
Moisture, which is evaporated from the waste as temperatures of the
waste are raised in the combustion chamber, passes through the
incinerator, unchanged, as water vapor. Two major impacts that this
moisture has on the combustion system are increasing volumetric flow and
reducing residence time of the combustion gases. It also absorbs energy
and reduces the temperature in the combustor.
Unlike organic constituents, inorganic constituents, specifically
metals, are not "destroyed" during the combustion process. Rather, they
are distributed or partitioned among the incinerator effluent streams.
Metals constituents can leave the combustion chamber as bottom ash or in
the combustion gas. The relative distribution of the metals between these
streams is based on such factors as the chemical form of the metals
charged to the combustor, the localized reaction atmosphere in the
combustion chamber, localized chamber temperatures, and localized chamber
airflows. Metals that leave the chamber as bottom ash ultimately can
reach a land disposal site or can be lost to the atmosphere as fugitive
emissions. Metals can leave the combustion chamber in the gas stream
either as entrained particulate matter or as a metal vapor. If the metals
emissions from an incinerator are of concern, they can be reduced by using
an add-on air pollution control system. The efficiency of such a control
system will depend on the control system design and operating character-
istics and the physical characteristics of the metals, particularly the
solid/vapor distribution and the size distribution of the metals that are
entrained as particles.
2-15
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2.3 HOSPITAL WASTE CHARACTERISTICS
Hospital wastes are heterogeneous mixtures of general refuse,
laboratory and pharmaceutical chemicals and containers, and pathological
wastes. All of these wastes may contain potentially infectious wastes.
In some cases, the wastes fired to hospital incinerators also may contain
wastes classified as hazardous under the Resource Conservation and
Recovery Act (RCRA) or low-level radioactive waste.
General refuse from hospitals is similar to generic wastes from
residences and institutions and includes artificial linens, paper,
flowers, food, cans, diapers, and plastic cups. Laboratory and pharmaceu-
tical chemicals can include alcohols; disinfectants; antineoplastic
agents; and heavy metals, such as mercury. Infectious wastes include
isolation wastes (refuse associated with isolation patients); cultures and
stocks of infectious agents and associated biologicals; human blood and
blood products; pathological wastes; contaminated sharps; and contaminated
animal carcasses, body parts, and bedding. Examples of wastes defined as
infectious are presented in Table 2-2. In the U.S., infectious wastes are
required to be discarded in orange or red plastic bags or containers.
Often these "red bag" wastes may contain noncontaminated general refuse
discarded along with the infectious waste.
Incinerators are thermal systems; they are designed to operate at a
certain heat input (kcal/h or Btu/h). Under the most efficient operating
conditions, the heat input rate would be constant at or near the maximum
design rate. Furthermore, all of the heat input would come from the
waste, with little or no need for auxiliary fuel. The waste character-
istics, i.e., heat content and moisture content of the waste being charged
to the incinerator, will affect the operator's ability to maintain good
combustion conditions in the incinerator without the use of auxiliary
fuel.
The chemical and physical characteristics of the different waste
materials that are fired to hospital waste incinerators vary widely. A
study of hospitals in Ontario provided information on the heating value,
bulk density, and moisture content of different waste materials. The
results from this study are presented in Table 2-3 (SI units)" and
Table 2-4 (English units).2
2-16
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TABLE 2-2. EXAMPLES OF INFECTIOUS WASTE
Waste category
Examples3
Isolation wastes
Cultures and stocks of
infectious agents and
associated biologicals
Human blood and blood
products
Pathological waste
Contaminated sharps
Contaminated animal
carcasses, body parts,
and bedding
• Wastes from patients with diseases
considered communicable and requiring
isolation
• Refer to Centers for Disease Control,
Guidelines for Isolation Precautions in
Hospitals, July 1983
• Specimens from medical and pathology
laboratories
• Cultures and stocks of infectious agents
from clinical, research, and industrial
laboratories; disposable culture dishes,
and devices used to transfer, inoculate
and mix cultures
• Wastes from production of biologicals
• Discarded live and attenuated vaccines
• Waste blood, serum, plasma, and blood
products
• Tissues, organs, body parts, blood, and
body fluids removed during surgery,
autopsy, and biopsy
• Contaminated hypodermic needles, syringes,
scalpel blades, pasteur pipettes, and
broken glass
• Contaminated animal carcasses, body parts,
and bedding of animals that were inten-
tionally exposed to pathogens
These materials are examples of wastes covered by each category. The
categories are not limited to these materials.
2-17
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TABLE 2-3. CHARACTERIZATION OF HOSPITAL WASTE'
Component description
Human anatomical
Plastics
Swabs, absorbants
Alcohol, disinfectants
Animal infected anatomical
Glass
Beddings, shavings, paper,
fecal natter
Gauze, pads, swabs, gar-
ments , paper , ce 1 1 u 1 ose
Plastics, PVC, syringes
Sharps, needles
Fluids, res i dua 1 s
TABLE 2-4.
Component description
Human anatomical
Plastics
Swabs, absorbants
Alcohol, disinfectants
Animal infected anatomical
Glass
Beddings, shavings, paper,
fecal aatter
Gauze, pads, swabs, gar-
ments , paper , ce 1 1 u 1 ose
Plastics, PVC, syringes
Sharps, needles
Fluids, residuals
HHV
dry basis,
kJ/kg
18,600-27,900
32,500-46,500
18,600-27,900
25,500-32,500
20,900-37,100
0
18,600-20,900
18,600-27,900
22,500-46,500
140
0-23,200
Bulk
density as..
fired, kg/irr5
800-1 ,200
80-2,300
80-1 ,000
800-1 ,000
500-1 ,300
2,800-3,600
320-730
80-1 ,000
80-2,300
7,200-8,000
990-1 ,010
Moisture
content of
component,
weight 2
70-90
0-1
0-30
0-0.2
60-90
0
10-50
0-30
0-1
0-1
80-100
Heat
value as
fired, kj/g
1,860-8,370
32,300-46,500
13,000-27,900
25,500-32,500
2,090-14,900
0
9,300-18,800
13,000-27,900
22,300-46,500
140
0-4,640
CHARACTERIZATION OF HOSPITAL WASTE2
HHV
dry basis,
Btu/ 1 b
8,000-12,000
14,000-20,000
8,000-12,000
11,000-14,000
9,000-16,000
0
8,000-9,000
8,000-12,000
9,700-20,000
60
0-10,000
Bulk
dens i ty
as fired,
Ib/ft-5
50-75
5-144
5-62
48-62
30-80
175-225
20-45
5-62
5-144
450-500
62-63
Moisture
content of
component,
weight i
70-90
0-1
0-30
0-0.2
60-90
0
10-50
0-30
0-1
0-1
80-100
Heat va 1 ue
as f i red ,
Btu/ 1 b
800-3,600
13,900-20,000
5,600-12,000
11,000-14,000
900-6,400
0
4,000-8,100
5,600-12,000
9,600-20,000
60
0-2,000
2-18
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Hospital waste can vary considerably in composition and consequently
in heat content, moisture content, and bulk density. Hospital waste can
vary in Btu content from a low value of about 3,400 kj/kg (1,500 Btu/lb)
(primarily low-Btu, high-moisture anatomical waste) to 45,000 kJ/kg
(20,000 Btu/lb) (low-moisture, high-heat content plastics such as poly-
ethylene). Because of the potential for a wide range in waste character-
istics and the impact of varying waste characteristics on incinerator
performance, large volumes of wastes with unusually high or low Btu or
moisture contents should be identified so that charging procedures and
rates to the incinerator can be adjusted accordingly as described in
Chapter 4.0.
The chemical composition of the waste materials also may affect
pollutant emissions. Wastes containing metals and plastics are of
particular concern. Metals which vaporize at the primary combustion
chamber temperature (e.g., mercury) may become metal oxides with particle
size distributions primarily in the size range of 1 ym or less. These
small particles may become easily entrained and exhausted with the
combustion gases with limited capture by conventional air pollution
control equipment. Halogenated plastics, such as polyvinyl chloride, will
produce acid gases such as HC1. The presence of the chlorinated waste
also may contribute to the formation of toxic polycyclic organic material
such as dioxins and furans under poor operating conditions.
Some plastics such as polyethylene and polystyrene do not contain
significant amounts of halogens and can be incinerated efficiently without
major concern for acid gas or toxic pollutant formation. However, the
high heating value of these and other plastic materials can cause
excessively high temperatures in the primary combustion chamber. The
potential for refractory damage, slagging, and clinker formation increases
unless charging rates are adjusted or the plastics are mixed with other
wastes of lower heat content.
2-19
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2.4 TYPES OF HOSPITAL WASTE INCINERATOR SYSTEMS
2.4.1 Introduction7'11'12
The terminology used to describe hospital waste incinerators that has
evolved over the years is quite varied. Multiple names have been used for
the same basic types of incinerators, and much of the terminology does not
enhance precise definitions that can be used to define good O&M practices.
However, most incinerators have been grouped historically into one of
three types--"muHipie-chamber," "control! ed-air," and "rotary kiln."
Most incineration systems installed before the early 1960's were
"multiple-chamber" systems designed and constructed according to
Incinerator Institute of America (IIA) standards. The multiple-chamber
incinerator has two or more combustion chambers. These "multiple-chamber"
systems are designed to operate at high excess-air levels and, hence, are
often referred to as "excess-air" incinerators. Multiple-chamber, excess-
air incinerators are still found at many hospitals. Many of the multiple-
chamber incinerators were designed specifically for pathological wastes
and are still being used for that purpose. Note that although the term
"multiple-chamber" incinerator typically is used to describe this type of
excess-air incinerator, the typical control 1ed-air and rotary kiln units
also contain multiple chambers.
The incineration technology that has been installed most extensively
for hospital wastes over the last 15 years generally has been "controlled-
air" incineration. This technology is also called "starved-air" combus-
tion, "modular" combustion, and "pyrolytic" combustion. The systems are
called "controlled air" or "starved air" because they operate with two
chambers in series and the first chamber operates at substoichiometric
conditions. Similar modular "controlled-air" units which operate with
excess-air levels in the primary chamber are also manufactured and sold
for combustion of municipal solid waste (MSW); however, these units
apparently are not widely used for hospital waste incineration.
Rotary kiln-type incineration systems have been widely used for
hazardous waste incineration in the U.S. The rotary kiln has two
combustion chambers. The primary chamber is a horizontal rotating kiln
2-20
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that typically operates with excess air. However, some manufacturers now
have rotary kilns designed to operate with a substoichiometric atmosphere
in the kiln; these kilns use special seals and air injection schemes.13
The exhaust gases exit the kiln to a fixed secondary chamber. Rotary kiln
incineration technology is being applied to hospital waste incineration at
a few locations in the U.S. and Canada.
This historical grouping of incineration types is of some assistance
in characterizing how hospital waste incinerators operate, but it is
limited because it does not address the complete combustion "system" and
how the incinerator is operated. Three important factors which help to
characterize the hospital waste incinerator system and its operation are
(1) the air distribution to the combustion chambers, (2) the mode of
operation and method of moving waste through the system, and (3) the
method of ash removal. For hospital waste incinerators, air distribution
can be classified based on whether the primary chamber operates under
substoichiometric (starved) or excess-air conditions. The mode of
operation can be single batch, intermittent duty, or continuous duty. Ash
is removed on a batch or a semicontinuous basis. Table 2-5 characterizes
the major types of incinerators that are likely to be found at U.S.
hospitals with respect to these three factors described above. The
remainder of this section describes the types of incinerators as
classified in Table 2-5.
2.4.2 Multiple-Chamber Incinerators1"
Two traditional designs that are used for multiple chamber
incinerators are the "in-line hearth" and "retort" hearth. Figure 2-3
depicts the in-line hearth design. For in-line hearth incinerators,
combustion gases flow straight through the incinerator, with turns in the
vertical direction only (as depicted by the arrows in Figure 2-3).
Figure 2-4 depicts the retort hearth multiple-chamber incinerator. In the
retort hearth design, the combustion gases turn in the vertical direction
(upward and downward) as in the in-line incinerator, but also turn
sideways-as they flow through the incinerator. Because the secondary
chamber is adjacent .to the primary chamber (they share a wall) and the
2-21
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TABLE 2-5. CLASSIFICATION OF HOSPITAL INCINERATORS
Type of Incinerator
A1r supply
a
Waste feed
Ash removal
ro
i
ro
ro
Multiple chamber
Intermittent duty
controlled air
Continuous duty
controlled air
Rotary kiln
Excess
Batch/controlled air Starved
Starved
Starved
Excess
Manual or mechanical batch
feed; single or multiple
batches per burn
Batch (manual or mechanical);
1 batch per burn
Manual or mechanical batch
feed; multiple batches per
burn
Mechanical continuous or
multiple batch feed
Mechanical semi continuous
or continuous feed
Batch at end of burn
Batch at end of burn
Batch at end of burn
Intermittently or continuously
during burn
Continuous
Indicates whether primary chamber operates at below (starved) or above (excess) stolchlometrlc air
levels.
-------
GralM
Figure 2-3. In-line multiple-chamber incinerator with grate.
1 5
2-23
-------
Charging
Door
Stack
Ignition Chamber
Hearth
Secondary
Air Ports
Secondary
Burner Port
Mixing
Chamber
First
Underhearth
Port
Secondary
Combustion
Chamber
Mixing Chamber
RamePort
Charging
Door
Hearth
Primary
Burner Port
Second
Underhearth
Port
Figure 2-4. Retort multiple-chamber^incinerator for
pathological wastes.
2-24
-------
gases turn in the shape of a U, the design of the incinerator is more
compact. In-line incinerators perform better at capacities greater than
750 Ib/h. The retort design performs more efficiently than the in-line
design at capacities less than 750 Ib/h. The retort design is the most
common design used in hospital waste applications.
Multiple-chamber incinerators may have fixed hearths or grates or a
combination of the two in the primary chamber. The use of grates for a
system incinerating infectious waste is not recommended because liquids,
sharps, and small, partially combusted items can fall through the grates
prior to complete combustion or sterilization.
Multiple-chamber incinerators frequently are designed and used
specifically for incinerating pathological ("Type 4" anatomical) wastes.
Pathological waste has a high moisture content and may contain liquids;
consequently, a pathological incinerator always will be designed with a
fixed hearth. A raised "lip" at the door often is designed into the
hearth to prevent liquids from spilling out the door during charging.
Because the heating value of pathological waste is low and is not
sufficient to sustain combustion, the auxiliary burner(s) provided in the
primary chamber of pathological incinerators are designed for continuous
operation and with sufficient capacity to provide the total heat input
required.
2.4.2.1 Principle of Combustion and Air Distribution. Combustion in
the multiple-chamber incinerator occurs in two (or more) combustion
chambers. Both chambers are operated with excess air (thus these units
often are referred to as "excess-air" incinerators). Ignition of the
waste, volatilization of moisture, vaporization of volatile matter, and
combustion of the fixed carbon (solid-phase combustion) occur in the
primary chamber. The combustion gases containing the volatiles exit the
primary chamber through a flame port into a mixing chamber and then pass
into the secondary combustion chamber. Secondary air is added into the
flame port and is mixed with the combustion gas in the mixing chamber. A
secondary burner is provided in the mixing chamber to maintain adequate
temperatures for complete combustion as the gases pass into and through
the secondary combustion chamber.
2-25
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The incinerator is designed for surface combustion of the waste which
is achieved by predominant use of overfire combustion air and limiting the
amount of underfire air in the primary chamber. Multiple-chamber, excess-
air incinerators operate with an overall excess-air range of 300 to
600 percent.llf In older units, combustion air typically was provided by
natural draft via manually adjusted dampers and air in-leakage through
doors. Newer multiple-chamber incinerators often use forced-draft
combustion air blowers to provide the combustion air to the combustion
chambers.
2.4.2.2 Mode of Operation. Multiple-chamber incinerators typically
are designed for single batch or intermittent-duty operation. That is,
this type of incinerator typically does not have an automatic, continuous
ash removal system which would make continuous operation possible.
Consequently, the incinerator must be shut down at routine intervals (for
example, daily) for ash removal, and the incinerator is operated
"intermittently."
2.4.2.3 Waste Feed Charging Systems. Waste feed charging to
multiple-chamber units is typically done manually. The waste is loaded
into the primary chamber through the open charging door. Mechanical
charging systems, such as hopper/ram-feed systems also may be used.
(Hopper/ram-feed systems are discussed in the next section.)
2.4.2.4 Ash Removal Systems. For the typical multiple-chamber
incinerator, ash is removed manually after the incinerator is shut down.
The charging and/or ash cleanout doors are opened, and either a rake or
shovel is used to remove the ash.
2.4.2.5 Use of Multiple-Chamber Incinerators for Incinerating
Hospital Wastes. The use of multiple-chamber, excess-air incinerators for
incineration of red-bag wastes has several drawbacks. First, operating in
the surface-combustion excess-air mode in the primary chamber results in
entrainment of fly-ash which can cause excessive particulate matter
emissions. Second, since the incinerator is designed to operate with the
primary chamber in an excess-air mode, the combustion air levels and the
combustion rate within the primary chamber are not easily controlled.
Consequently, the incinerator control system may not provide a sufficient
level of control to assure complete combustion when waste composition and
2-26
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volatile content of the waste fluctuates over a wide range. Red bag
wastes are not homogeneous and may vary widely in volatile content and
moisture content. Third, operating with high levels of excess air is less
energy efficient because it requires auxiliary fuel usage to maintain
secondary combustion chamber temperatures.
Multiple-chamber, excess-air incinerators are better suited to
incineration of pathological wastes than red bag wastes because the
consequences of the above-mentioned drawbacks are not as severe for
pathological wastes.2 The volatile content of pathological waste is low,
and in general, the waste composition is not highly variable. The primary
burner provides most of the heat input and the incinerator operates in a
steady, constant mode with a steady, consistent combustion air input and
excess-air level.
In some cases, older multiple-chamber incinerators may be upgraded to
include more modern technology. Recently, some older multiple-chamber
units have been retrofitted so that the incinerator operates with
substoichiometric air levels in the primary chamber; in essence, these
units have been converted into the controlled-air units discussed in the
. . . 15
next section.
2.4.3 Controlled-Air Incinerators
2.4.3.1 Principle of Controlled-Air Incineration.16 The principle
of controlled-air incineration involves sequential combustion operations
carried out in two separate chambers. Figure 2-5 is a simplified
schematic of an incinerator that operates on the controlled-air
principle. The primary chamber (sometimes referred to as the ignition
chamber) accepts the waste, and the combustion process is begun in a below
stoichiometric oxygen atmosphere. The amount of combustion air to the
primary chamber is strictly regulated ("controlled"). The combustion air
usually is fed to the system as underfire air. Three processes occur in
the primary chamber. First, the moisture in the waste is volatilized.
Second, the volatile fraction of the waste is vaporized, and the volatile
gases are directed to the secondary chamber. Third, the fixed carbon
remaining in the waste is combusted. The combustion gases containing the
2-27
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AUXILARY
IGNITION
BURNER
COMBUSTION GASES
SECONDARY CHAMBER
Volatile Content is Burned
Under Excess Air Conditions
MAIN BURNER
FOR MAINTAINING
MINIMUM COMBUSTION
TEMPERATURE
MAIN FLAMEPORT AIR
ASH AND
NON-COMBUSTIBLES
CONTROLLED UNDERFIRE
AIR FOR BURNING
"FIXED CARBON"
Figure 2-5. Schematic of a controlled-air incinerator.
1 6
2-28
-------
volatile combustible materials from the primary chamber are directed to
the secondary chamber (sometimes referred to as the "combustion
chamber"). There, the combustion air is regulated to provide an excess-
air combustion condition and is introduced to the chamber in such a manner
as to produce turbulence and promote good mixing of the combustion gases
and combustion air. This gas/air mixture is burned, usually at high
temperatures. The burning of the combustion gases under conditions of
high temperature, excess oxygen, and turbulence promotes complete
combustion.
Combustion control for a controlled-air incinerator is usually based
on the temperature of the primary (ignition) and secondary (combustion)
chambers. Thermocouples within each chamber are used to monitor
temperatures continuously; the combustion air rate to each chamber is
adjusted to maintain the desired temperatures. Systems operating under
controlled-air principles have varied degrees of combustion air control.
In many systems, the primary and secondary combustion air systems are
aufomatically and continuously regulated or "modulated" to maintain the
desired combustion chamber temperatures despite varying waste composition
and characteristics (e.g., moisture content, volatile content, Btu
value). In other systems (particularly batch or intermittent-duty
systems), the combustion air level control is simplified and consists of
switching the combustion air rate from a "high" to a "low" level setting
when temperature setpoints are reached or at preset time intervals.
The controlled-air technique has several advantages. Limiting air in
the primary chamber to below stoichiometric conditions prevents rapid
combustion and allows a quiescent condition to exist within the chamber.
This quiescent condition minimizes the entrainment of particulate matter
in the combustion gases, which ultimately are emitted to the atmosphere.
High temperatures can be maintained in a turbulent condition with excess
oxygen in the secondary chamber to assure complete combustion of the
volatilized gases emitted from the primary chamber. The temperature of
the secondary chamber can be maintained in the desired range (hot enough
for complete combustion but not hot enough to cause refractory damage) by
separately controlling the excess-air level in the secondary chamber; as
the excess-air level is increased, the temperature decreases. Second,
2-29
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control of the primary chamber combustion air to below stoichiometric
levels maintains primary chamber temperatures below the melting and fusion
temperatures of most metals, glass, and other noncombustibles, thereby
minimizing slagging and clinker formation.
For the controlled-air incinerator, the capacity of the secondary
combustion chamber dictates (i.e., limits) the burning rate; the
combustion chamber must have adequate volume to accept and completely
oxidize all the volatile gases generated in the primary chamber and to
maintain sufficient combustion air so that excess oxygen is available.
2.4.3.2 Batch/Controlled-Air Incinerators.11 In this type of unit,
the incinerator is charged with a single "batch" of waste, the waste is
incinerated, the incinerator is cooled, and the ash residue is removed;
the cycle is then repeated. Incinerators designed for this type of
operation range in capacity from about 50 to 500 Ib/h. In the smaller
sizes, the combustion chambers are often vertically oriented with the
primary and secondary chambers combined within a single casing.
Figure 2-6 is a schematic of a controlled-air incinerator intended for
batch operation. This unit's combustion chambers are rectangular in
design and are contained within the same casing.
Batch/controlled-air units can be loaded manually or mechanically.
For the smaller units up to about 300 Ib/h, manual waste feed charging
typically is used. Manual loading involves having the operator load the
waste directly to the primary chamber without any mechanical assistance.
For a batch-type unit, one loading cycle per day is used. The incinerator
is manually loaded; the incinerator is sealed; and the incineration cycle
is then continued through burndown, cooldown, and ash removal without any
additional charging. Ash is removed manually at the end of the cycle by
raking or shoveling the ash from the primary chamber.
2.4.3.3 Intermittent-Duty, Controlled-Air Incinerators. The
charging procedures of an incinerator that could operate in single batch
mode often are varied to include multiple charges (batches) during the 12-
to 14-hour operating period before final burndown is initiated. These
intermittent-duty units typically operate in the 50 to 1,000 Ib/h range.
The intermittent charging procedure allows the daily charge to the
incinerator to be divided into a number of smaller charges that can be
2-30
-------
Waste
Charge
Door
Oxygen
Control
Primary
Blower
Secondary Burner
Figure 2-6. Schematic of a single batch controlled-air incinerator.
1 7
2-31
-------
introduced over the combustion cycle. Consequently, a more uniform gas
stream is fed to the secondary chamber. Figure 2-7 is a schematic of a
controlled-air incinerator which is intended for intermittent-duty
operation. This unit has a vertically oriented primary chamber followed
by a horizontal combustion chamber. This unit, although not shown with a
mechanical feeder, can be fitted with a hopper/ram assembly.
A typical daily operating cycle for a controlled-air, intermittent-
duty- type incinerator is as follows:
Operating step Typical duration
1. Cleanout of ash from previous day 15 to 30 minutes
2. Preheat of incinerator 15 to 60 minutes
3. Burndown 2 to 4 hours
4. Cooldown 5 to 8 hours
For intermittent-duty operation, the daily waste loading cycle of the
incinerator is limited to about an 8- to 14-hour period. The waste
loading period is limited by the amount of ash the primary chamber can
physically hold prior to shutting down the unit for ash removal. The
remainder of the 24-hour period is required for burndown of the ash,
cooldown, ash cleanout, and preheat.
For smaller units, the waste often is fed manually. For units in the
300 to 500 Ib/h range, mechanical waste feed systems often are employed,
and for units above 500 Ib/h, mechanical waste feed systems typically are
employed. The typical mechanical waste feed system is a hopper ram
assembly. Figure 2-8 is a schematic of a typical hopper ram assembly.20
In a mechanical hopper/ram feed system, waste is manually placed into a
charging hopper, and the hopper cover is closed. A fire door isolating
the hopper from the incinerator opens, and the ram moves forward to push
the waste into the incinerator. The ram reverses to a location behind the
fire door. After the fire door closes, the ram retracts to the starting
position and is ready to accept another charge. A water spray to quench -
the ram face as it retracts typically is provided. The entire charging
sequence normally is timed and controlled by an automatic sequence. The
cycle can be started manually by the operator or, in some systems, the
cycle is automatically started on a predetermined basis.
2-32
-------
STACK
CHARGING
DOOR
SECONDARY CHAMBER
SECONDARY BURNER
PRIMARY AND SECONDARY
COMBUSTION BLOWER
PRIMARY CHAMBER
IGNITION BURNER
Figure 2-7. Example intermittent-duty, controlled-air incinerator .
L 3
2-33
-------
Hydraulic Fire W
Door Actuator I I
Hopper Cover
Hydraulic -
Ram
Actuator
Waste
Charging
Hopper
Primary
Combustion
Chamoer
Fire Door
Enclosure
• Charging -am Face
Ram Quench
Spray
Furnace
Opening
Figure 2-8. Hopper/ram mechanical waste feed system.
20
2-34
-------
Mechanical loading systems have several advantages. First, they
provide added safety to the operating personnel by preventing heat,
flames, and combustion products from escaping the incinerator during
charging. Second, they limit ambient air infiltration into the
incinerator. This assists in controlling the combustion rate by strictly
controlling the quantity of available combustion air. Third, they
facilitate charging the incinerator with smaller batches of waste at
regulated time intervals.
With intermittent-duty incinerators, ash removal is a limiting factor
for the incinerator operations. As with the single batch-operated units,
the ash is removed at regular intervals (typically daily) after the
incinerator has gone through a cooldown cycle. The ash usually is
manually removed by raking and/or shoveling from the primary chamber.
2.4.3.4 Continuous-Duty, Controlled-Air Incinerators. Controlled-
air units intended for continuous operation are available in the 500 to
3,000 Ib/h operating range. Continuous-duty, controlled-air units operate
according to the controlled-air principles of the systems described
earlier. However, continuous operation requires a mechanism for
automatically removing ash from the incinerator hearth. The ash must be
moved across the hearth, collected, and removed from the combustion
chamber.
Continuous-duty units typically have mechanical waste feeding
systems. For large continuous-duty units, the charging sequence may be
fully automatic. The incinerator can be automatically charged with
relatively small batches (in relation to the primary chamber capacity) at
frequent, regulated time intervals. The use of frequent, small charges
promotes relatively stable combustion conditions and approximates steady-
state operation. For large systems, the mechanical charging system may
include waste loading devices such as cart dumpers, which automatically
lift and dump the contents of carts that are used to collect and contain
the waste, into the charge hoppers. Use of these loading devices reduces
the operator's need to handle infectious waste and, consequently, further
improves worker safety.
For smaller units, the mechanical waste feed charging ram is
sometimes used to move the ash across the hearth. As a new load is pushed
2-35
-------
into the incinerator, the previous load is pushed forward. Each
subsequent load has the same effect of moving the waste across the
hearth. The waste should be fully reduced to ash by the time it reaches
the end of the hearth. For larger systems, one or more special transfer
rams are provided to move the waste across the hearth. Figure 2-9 depicts
a continuous-duty, controlled-air incinerator with a stepped hearth and
multiple ash transfer rams.21 The use of the stepped hearth promotes
"mixing" the ash bed as the ash is moved from hearth to hearth and,
consequently, promotes improved solid-phase combustion.
Typically, when the ash reaches the end of the hearth, it drops off
the end of the hearth into a discharge chute. One of two methods for
collecting ash is usually used. The ash can discharge directly into an
ash container positioned within an air-sealed chamber or sealed directly
to the discharge chute. When the container is full, it is removed from
the chamber and replaced with an empty ash container. The second method
is for the ash to discharge into a water pit. The water bath quenches the
ash, and it also forms an air seal with the incinerator. A mechanical
device, either a rake or a conveyor, is used to remove the ash from the
quench pit intermittently or continuously. The excess water is allowed to
drain from the ash as it is removed from the pit, and the wetted ash is
discharged into a collection container.11
2.4.4 Rotary Kilns
A rotary kiln also utilizes two-stage combustion and has two
combustion chambers. Figure 2-10 is a simplified schematic of a rotary
kiln. The primary combustion chamber is a rotating cylindrical chamber
which is slightly inclined from the horizontal plane; hence, the name
"rotary kiln." The secondary chamber often is cylindrical in shape and
oriented horizontally much like the secondary chambers described for
controlled-air incinerators, or it may be box-like as depicted in
Figure 2-11.
2.4.4.1 Principle of Operation. The rotating kiln is inclined at
an angle determined during design of the system. Waste is fed to the
higher end of the kiln by a mechanical feed system. Typically, combustion
2-36
-------
TO BOILER
FEED RAM -^
ASH TRANSFER RAMS
.AIR TUBE
ASH DISCHARGE RAM •
FOSSIL FUEL BURNER
PRIMARY CHAMBER
ASH SUMP
ASH CHUTE -/
ASH QUENCH —
Figure 2-9. Incinerator with step hearths and automatic ash removal.2i
2-37
-------
EXHAUST FAN
Figure 2-10. Rotary kiln with auger feed.
22
2-38
-------
n
Bypass
Shutoff
Valve
Bypass
Stack
Incinerator
Gas Flow
Damper
Waste Heat
Boiler
Stack
ID
Fan
Figure 2-11. Incinerator with waste heat boiler and bypass stack.
2-39
-------
air is provided to the kiln such that an excess-air atmosphere exists.
However, some manufacturers now have rotary kilns designed to operate with
a substoichiometric atmosphere in the kiln; these kilns use special seals
and air injection schemes. Running the kiln substoichiometric decreases
kiln sizes required and reduces auxiliary fuel usage in the secondary
chamber. Inside the kiln, moisture and volatiles are vaporized from the
waste, and the waste is ignited. An auxiliary burner provided in the kiln
maintains the desired combustion temperature if sufficient heat input is
not available from the waste. As the kiln rotates, the solids are tumbled
within the kiln and slowly move down the incline toward the discharge
end. The turbulence of the waste within the kiln provides exposure of the
solid waste to the combustion air. Combustion of the solids occurs within
the kiln, and the residue ash is discharged from the end of the kiln into
an ash removal system.
The volatile gases pass into the secondary chamber where combustion
of the gases is completed. A secondary burner is used to maintain the
secondary chamber temperature, and secondary combustion air is added to
the chamber as necessary to maintain the desired excess-air level.
2.4.4.2 Mode of Operation. Since the solid waste continuously moves
down the length of the rotating kiln, the incineration system is designed
to operate in a continuous mode with a semi continuous or continuous waste
feed input. Consequently, a rotary kiln typically has a mechanical waste
feed system and a system for continuous ash removal.
2.4.4.3 Charging System. The waste feed system must provide waste
to the kiln in a continuous or semicontinuous manner. One manufacturer
that provides rotary kiln incinerators for hospital waste applications
uses an auger-feeder system to feed the waste continuously to the
kiln.22 Waste is fed to the feed hopper, and the auger-feeder continu-
ously discharges the waste from the bottom of the hopper to the kiln.
The hopper/ram feed system of the type previously described also has
been used for feeding rotary kilns (particularly in hazardous waste
incineration applications).
2.4.4.4 Ash Removal. As the kiln rotates, the ash is continuously
discharged from the end of the kiln. A system for collecting the ash and
continuously or semicontinuously removing the ash is required. Automated
2-40
-------
ash removal systems such as those previously described for the continuous-
duty, controlled-air incinerators are used.
2.4.5 Auxiliary Equipment
2.4.5.1 Waste Heat Boilers. Incinerator manufacturers often provide
waste heat boilers as an option to their incineration units. Waste heat
boilers are used in conjunction with a hospital waste incinerator to
generate steam or hot water for use in the hospital. The combustion gases
from the incinerator pass through the waste heat boiler prior to being
emitted to the atmosphere via the stack. Use of a waste heat boiler
requires that an induced draft fan be added to the system. Furthermore,
incinerators equipped with waste heat boilers have a system for diverting
the combustion gases directly to the atmosphere and bypassing the
boiler. This bypass system is required for safety (for example, to avoid
excessive pressures in the incinerator should the fan cease operation) and
for normal operation if demand for waste heat is low (so the boiler can be
taken off line). Typical systems include either a second "bypass" stack
before the waste heat boiler or a breeching directly connecting the
incinerator to the stack and bypassing the boiler. Figure 2-11 is a
schematic of a controlled-air unit with waste heat recovery.16
2.4.5.2 Auxiliary Waste Liquid Injection. Incinerators also may
include the capability to inject liquid wastes into the primary chamber.
Generally liquid waste incineration is accomplished through either an
atomizing nozzle or burner assembly in the primary chamber. Wastes such
as used solvents can be readily incinerated via liquid injection.
2.5 REFERENCES FOR CHAPTER 2
1. U. S. Environmental Protection Agency. EPA Guide for Infectious
Waste Management, EPA/530-SW-86-014. (NTIS PB86-199130). U. S. EPA
Office of Solid Waste. May 1986.
2. Ontario Ministry of the Environment. Incinerator Design and
Operating Criteria, Volume II-Biomedical Waste Incineration.
October 1986.
2-41
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3. Barbeito, M. S. and M. Shapiro. Microbiological Safety Evaluation of
a Solid and Liquid Pathological Incinerator. Journal of Medical
Primatology. pp. 264-273. 1977.
4. Beard, J. T., F. A. lachetta, and L. V. Lillelehet. APTI Course 427,
Combustion Evaluation, Student Manual, EPA 450/2-80-063. U. S. EPA
Air Pollution Training Institute. February 1980.
5. Beachler, D. S. APTI Course SI:428A, Introduction to Boiler
Operation, Self Instructional Guidebook, EPA 450/2-84-010. U. S.
EPA. December 1984.
6. Brunner, C. R. Incineration Systems. Van Nostrand Reinhold. 1984.
7. McRee, R. "Operation and Maintenance of Controlled Air
Incinerators." Undated.
8. Chang, D., R. Mournighan, and G. Hoffman. Thermodynamic Analysis of
Post Flame Reactions Applied to Waste Combustion. Land Disposal,
Remedial Action, Incineration, and Treatment of Hazardous Waste:
Proceedings of the Thirteenth Annual Research Symposium.
EPA/600-9-87-015. (NTIS PB87-233151).
9. U. S. Environmental Protection Agency. Municipal Waste Combustion
Study: Combustion Control. EPA 530-SW-87-021C. (NTIS PB 87-206090).
June 1987. pp. 4-8 - 4-11.
10. Bonner, T., B. Desai, J. Fullenkamp, T. Huges, E. Kennedy,
R. McCormick, J. Peters, and D. Zanders. Draft Engineering Handbook
for Hazardous Waste Incineration. EPA Contract No. 68-03-2550.
November 1980.
11. Doucet, L. C. Controlled Air Incineration: Design, Procurement and
Operational Considerations. Prepared for the American Society of
Hospital Engineering, Technical Document No. 55872. January 1986.
12. U. S. Environmental Protection Agency. Hospital Waste Combustion
Study: Data Gathering Phase. EPA 450/3-88-017. December 1988.
13. Letter from K. Wright, John Zink Company, to J. Eddinger, EPA.
January 25, 1989.
14. Air Pollution Control District of Los Angeles County. Air Pollution
Engineering Manual, 2nd Edition AP-40. (NTIS PB 225132) U. S.
EPA. May 1973.
15. Personal conversation with Larry Doucet, Doucet & Mainka Consulting
Engineers. November 28, 1988.
16. Ecolaire Combustion Products, Inc., Technical Article: Principles of
Controlled Air Incineration. Undated.
2-42
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17. Ashworth R. Batch Incinerators—Count Them In; Technical Paper
Prepared for the National Symposium of Infectious Waste.
Washington, D.C. May 1988.
18. Ecolaire Combustion Products, Inc., Technical Data Sheet for E Series
Incinerator. Undated.
19. Doucet, L. Fire Prevention Handbook, National Fire Protection
Association, Waste Handling Systems and Equipment. Chapter 12,
p. 116.
20. Source Category Survey: Industrial Incinerators. EPA 450/3-80-013
(NTIS PB 80-193303). U. S. Environmental Protection Agency. May
1980.
21. Technical Data Form: Consertherm Systems, Industronics, Inc.
Undated.
2-43
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3.0 AIR POLLUTION CONTROL
3.1 INTRODUCTION
Hospital incinerators are potentially significant sources of air
pollutants. Pollutants of concern from hospital incinerators include
particulate matter; toxic metals; toxic organics; carbon monoxide (CO);
and the acid gases, hydrogen chloride (HC1), sulfur dioxide (S02), and
nitrous oxides (NOX). Emission rates of these pollutants can be limited
by removing pollutant generating materials from the waste feed material,
proper operation of the incinerator, and add-on pollution control
equipment. The objectives of this Chapter are to describe the factors
affecting formation and generation of the pollutants and to identify and
discuss control strategies that can be used to control the pollutant.
Section 3.2 will describe the factors affecting pollutant formation and.
generation including the effects of waste feed composition. Section 3.3
will discuss air pollution control strategies.
3.2 POLLUTANT FORMATION AND GENERATION
The pollutants of concern from hospital incinerators either exist in
the waste feed material or are formed in the combustion process.
Particulate matter. Particulate matter emissions from the combustion
of hospital wastes are determined by three factors: (1) suspension of
noncombustible materials, (2) incomplete combustion of combustible
materials, and (3) condensation of vaporous materials. The ash content of
the waste feed material is a measure of the noncombustible portion of the
waste feed and represents those materials which will not burn under any
conditions in the incinerator. Emissions of noncombustible materials
result from the suspension or entrainment of ash by the combustion air
added to the primary chamber of the incinerator. The more air added, the
more likely that noncombustibles will become entrained. Particulate
emissions from incomplete combustion of combustible materials result from
improper combustion control of the incinerator. Condensation of vaporous
materials results from noncombustible substances that volatilize at
-------
primary combustion chamber temperatures with subsequent cooling in the
flue gas. These materials usually condense on the surface of other fine
particles.
Toxic metals. Particulate metal emissions are dependent on the
metals content of the feed material. Metals may exist in the waste as
parts of discarded instruments or utensils, in plastics, paper, pigments,
and inks, or as discarded heavy metals used in laboratories. Many metals
are converted to oxides during combustion and are emitted primarily as
submicron to micron size particles. Metals that volatilize at primary
combustion chamber temperatures may selectively condense on small,
difficult to control particles in the incinerator flue gas. Metals
generally thought to exhibit fine-particle enrichment are arsenic (As),
cadmium (Cd), chromium (Cr), manganese (Mn), nickel (Ni), molybdenum (Mo),
lead (Pb), antimony (Sb), selenium (Se), vanadium (V), and zinc (Zn).1
Toxic orqanlcs. Organic material found in'the waste feed material
theoretically can be completely combusted to form water (H20) and carbon
dioxide (C02). However, incomplete combustion will result in emissions of
organics found in the waste feed and in the generation of new organic
species from complex chemical reactions occurring in the combustion
process. When chlorine is available in the form of PVC plastic materials,
these organics can include highly toxic chlorinated organics, such as
dioxins and furans. Combustion conditions that favor increased
particulate matter emissions due to incomplete combustion also favor
increased organic emissions.
Carbon monoxide (CO). As noted above, complete combustion of organic
material will result in the formation of H20 and C02. The concentration
of CO in the incinerator exhaust gas stream is an indicator of the
combustion efficiency of the unit. The formation of CO is dictated by the
oxygen concentration in the incinerator, the degree of mixing of the fuel
and air, and the temperature of the gases. Carbon monoxide is an
intermediate product of the reaction between carbonaceous fuels and
oxygen. Combustion conditions that result in incomplete combustion will
produce CO as well as particulate matter and organics.
Acid gases. The principal acid gas of concern from hospital
incinerators is HC1. The determining factor in HC1 formation and emission
3-2
-------
is the availability of chlorine in the feed material. In the presence of
available hydrogen, as would exist in highly organic hospital wastes, most
of the available chlorine will be converted to HC1. Sulfur dioxide
generation is similar to HC1; most of the sulfur in the wastes will be
converted to S02 during combustion irregardless of incinerator design or
operation.
Nitrogen enters the combustion chamber as a component of the waste
and in the combustion air. It can react in the combustion chamber to
produce NOX.
3.3 CONTROL STRATEGIES
Formation and generation of all of the pollutants discussed above are
dependent on either the availability of certain materials in the waste
feed or on the efficiency of the combustion process. Removing problem
materials from the waste feed and improving combustion efficiency are,
therefore, two control strategies for reducing pollutant emissions. If
pollutants are formed and generated, add-on pollution control equipment
represents a third control strategy for emissions reduction. Table 3-1
presents the control strategies that can be effective for each of the
pollutants of concern.
3.3.1 Controlling Feed Material
Controlling feed material consists of either establishing procedures
that eliminate the use of certain materials, specifying segregation of
certain wastes at the point of origin, or removing problem materials from
the waste material prior to incineration. Obviously, eliminating the use
of certain materials or establishing segregation procedures are more
feasible. The substitution of nonchlorinated plastics (e.g., poly-
ethylene) for PVC, where possible, would reduce the chlorine input to the
incinerator. Materials that could be segregated from waste to be inciner-
ated include noncombustible fine dust and powders that could contribute to
particulate matter emissions, heavy metals from dental clinics or
laboratories, PVC plastics that contribute to HC1 formation, and other
chlorine- or sulfur-containing materials.
-------
TABLE 3-1. CONTROL STRATEGIES FOR AIR POLLUTANTS FROM HOSPITAL WASTE INCINERATORS
Control strategy
Pollutants
Particulate matter
Toxic metals
Toxic organlcs
Carbon monoxide
Hydrogen chloride
Sulfur dioxide
Nitrous oxides
Controlling
feed material
X
X
X
X
X
Combustion
control
X
X
X
X
Add-on pollution control equipment
Venturl
scrubber8
X
X
c
c
c
Packed-bed
scrubber0
c
c
c
X
X
Fabric Dry
filter scrubber
X
X
c
X
X
*Venturi scrubber with water as the scrubbing media.
°Packed-bed scrubber utilizing an alkaline sorbent.
Will achieve some limited control but not designed for high-efficiency collection.
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3.3.2 Combustion Control
Complete combustion of combustible material requires adequate
temperatures, excess air, turbulence, mixing, and retention time. Because
of the variability in hospital waste with respect to heating values,
moisture contents, etc., incinerator operating parameters should be varied
with the variations in the waste to maximize combustion. In general,
higher temperatures, excess air rates, mixing, and retention time result
in improved combustion and lower emissions of particulate matter,
organics, and CO. However, as these factors are increased there is an
economic penalty in auxiliary fuel costs and energy loss. In addition,
combustion control has little or no effect on emissions of HC1 and S02.
In both cases, most of the chlorine and sulfur will be converted to HC1
and S02 under the entire range of combustion conditions which normally
occur in a hospital incinerator. As opposed to the other pollutants, both
NOX and toxic metal emissions can actually be increased by combustion
adjustments that increase temperatures and excess air rates. Therefore,
the waste feed composition should be considered before making adjustments
to control combustion.
3.3.3 Add-On Air Pollution Control Systems
Add-on air pollution control systems (APC's) used on hospital
incinerators are usually wet scrubbers, fabric filters, or dry
scrubbers. Wet scrubbers, in their various designs, are used to remove
particulate matter as well as HC1 and S02; fabric filters are used to
remove particulate matter; dry scrubbers are used to remove HC1 and S02.
3.3.3.1 Wet Scrubbers. Venturi, spray tower, and packed-bed
scrubbers are the most common types of wet scrubber systems used on
hospital incinerators. Venturi scrubbers are used primarily for
particulate matter control and packed-bed scrubbers are used primarily for
acid gas control. However, both types of systems achieve some degree of
control for both particulate matter and acid gases. A third scrubber type
is spray towers. Spray towers are used to remove particulate matter;
however, they are relatively inefficient for the removal of fine
3-5
-------
particulate matter. These units are not effective for controlling
participate emissions from controlled-air incinerators and are used
exclusively on multiple-chamber units which can emit significant
quantities of large particles. There are other scrubber types with
potential application to hospital waste incinerators including (but not
limited to) the wet ionizing scrubber, the collision scrubber, and the
Hydro-sonic® steam ejector scrubber.3'1* Hydro-sonic® scrubber uses
supersonic steam ejector drives to accelerate the injected water droplets
and provide mixing. The Hydro-sonic® scrubbers are reported to offer high
efficiency on fine particulate emissions at relatively low energy costs
where there is a source of waste heat for steam production. Use of these
scrubbers is not widespread on hospital waste incinerators. Detailed
operation and maintenance information for these units controlling hospital
waste incinerators is not readily available, and they will not be
discussed in this document.
Wet scrubbing principles.2 Wet scrubbers capture relatively small
dust particles with large liquid droplets. Droplets are produced by
injecting liquid at high pressure through specially designed nozzles, by
aspirating the particle-laden gas stream through a liquid pool, or by
submerging a whirling rotor in a liquid pool. These droplets collect
particles by using two primary collection mechanisms--impaction and
diffusion.
In a wet scrubbing system, dust particles will tend to follow the
streamlines of the exhaust stream. However, when liquid droplets are
introduced into the exhaust stream, particles cannot always follow these
streamlines as they diverge around the droplet (Figure 3-1). The
particle's mass causes it to break away from the streamlines and impact on
the droplet. Impaction .is the predominant collection mechanism for
scrubbers having gas stream velocities greater than 0.3 m/s (1 ft/s).
Most scrubbers operate with gas stream velocities well above 0.3 m/s.
Therefore, at these velocities, particles having diameters greater than
1.0 micrometer (pin) are collected by this mechanism.
Very small particles (less than 0.1 urn in diameter) experience random
movement in an exhaust stream. These particles are so tiny that they are
bumped by gas molecules as they move in the exhaust stream. This bumping,
3-6
-------
Gas streamlines
•*•
-»•
•*•
Droplet
Particle
-*•
-»••
-a*
•^
Figure 3-1. Impaction.
3-7
-------
or bombardment, causes them to move first one way and then another in a
random manner, i.e., diffuse, through the gas. This irregular motion can
cause the particles to collide with a droplet and be collected.
The rate of diffusion depends on relative velocity, particle
diameter, and liquid-droplet diameter. As with impaction, collection due
to diffusion increases with an increase in relative velocity (liquid- or
gas-phase input) and a decrease in liquid-droplet size. However,
collection by diffusion increases as particle size decreases. This
mechanism enables certain scrubbers to remove the very tiny particles
effectively.
The process of dissolving gaseous pollutants in a liquid is referred
to as absorption. Absorption is a mass-transfer operation in which mass
is transferred as a result of a concentration difference. Absorption
continues as long as a concentration differential exists between the
liquid and the gas from which the contaminant is being removed. In
absorption, equilibrium depends on the solubility of the pollutant in the
liquid.
To remove a gaseous pollutant by absorption, the exhaust stream must
be passed through (brought in contact with) a liquid. Three steps are
involved in absorption. In the first step, the gaseous pollutant diffuses
from the bulk area of the gas phase to the gas-liquid interface. In the
second step, the gas moves (transfers) across the interface to the liquid
phase. This step occurs extremely rapidly once the gas molecules
(pollutant) arrive at the interface area. In the third step, the gas
molecule(s) diffuses into the bulk area of the liquid, thus making room
for additional gas molecules to be absorbed. The rate of absorption (mass
transfer of the pollutant from the gas phase to the liquid phase) depends
on the diffusion rates of the pollutant in the gas phase (first step) and
in the liquid phase (third step).
To enhance gas diffusion, and, therefore, absorption:
1. Provide a large interfacial contact area between the gas and
liquid phases;
2. Provide good mixing of the gas and liquid phases (turbulence);
and
3-8
-------
3. Allow sufficient residence, or contact, time between the phases
for absorption to occur.
Venturi scrubbers. A venturi scrubber consists of a liquid sprayed
upstream from a vessel containing a converging and diverging cross-
sectional area as illustrated in Figure 3-2. The portion of the venturi
which has the minimal cross-sectional area and consequently the maximum
gas velocity is commonly referred to as the throat. The throat can be
circular as shown in Figure 3-2 or rectangular as shown in Figure 3-3. As
the gas stream approaches the venturi throat, the gas velocity and
turbulence increases. Liquid droplets serve as the collection media and
can be created by two different methods. The most common method is to
allow the shearing action of the high gas velocity in the throat to
atomize the liquid into droplets. The other method is to use spray
nozzles to atomize the liquid by supplying high pressure liquid through
small orifices.
To attain a high collection efficiency, venturi scrubbers need to
achieve gas velocities in the throat in the range of 10,000 to 40,000 feet
per. minute. These high gas velocities atomize the water droplets and
create the relative velocity differential between the gas and the droplets
to effect particle-droplet collision. The effectiveness of a venturi
scrubber is related to the square of the particle diameter and the
difference in velocities of the liquor droplets and the particles.
The performance of a venturi scrubber is strongly affected by the
size distribution of the particulate matter. For particles greater than 1
to 2 ym in diameter, impaction is so effective that penetration is quite
low. However, penetration of smaller particles, such as the particles in
the 0.1 to 0.5 ym range is very high. Unfortunately, small particle size
distribution is typical for fuel combustion sources including hospital
waste incinerators and results from the condensation of partially
combusted organic compounds and metallic vapors.
The particulate matter collection efficiency in a venturi scrubber
system 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 and to atomize the liquor
droplets. The pressure drop across the venturi is a function of the gas
-------
Converging
section
— Throat
_ Diverging
section
Figure 3-2. Spray venturi with circular throat.
3-10
-------
Liquid inlet
Figure 3-3. Spray venturi with rectangular throat.7
3-11
-------
velocity and liquid/gas ratio and in practice acts as a surrogate measure
for gas velocity. The Calvert equation can be used to predict the
pressure drop for a given throat velocity. The Calvert equation is:8
AP = (5xlQ-5) v2 (L/G) (3-1)
where
AP = pressure drop, in. w.c.
v = the gas velocity in the venturi throat, ft/s, and
L/G = the liquid-to-gas ratio, gal/Macf.
The equation implies that pressure drop is equal to the power required to
accelerate the liquid to the gas velocity. The Calvert equation predicts
pressure drop reasonably well for the range of L/G ratios from 5 to
12 gal/Macf. At L/G ratios above 12, measured pressure drops are normally
about 80 percent of the value predicted by the Calvert equation. In
practice it has been found that at L/G ratios less than 3 gal/Macf, there
is an inadequate liquid supply available to completely cover the venturi
throat.
Other variables that are important to venturi scrubber performance
are the liquid surface tension and liquid turbidity. If surface tension
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 effect on droplet formation. High liquid turbidity, or high
suspended solids content, will cause erosion and abrasion of the venturi
section and ultimately lead to reduced performance of the system.
A list of the major components of commercial scrubber systems is
provided below.
1. Venturi section;
2. Spray nozzles;
3. Liquor treatment equipment;
4. Gas stream demister;
5. Liquor recirculation tanks, pumps, and piping;
6. Alkaline addition equipment;
7. Fans, dampers, and bypass stacks; and
3-12
-------
8. Controllers for venturi throat area, caustic feed, makeup water,
and emergency water quench for temperature excursions.
Packed-bed scrubbers. A packed-bed scrubber generally is used for
acid gas removal. The large liquor-to-gas surface area created as the
liquor gradually passes over the packing material favors gas diffusion and
absorption. Packed-bed scrubbers are not effective as stand-alone
scrubbers for collection of fine particulate matter (less than 2.5 urn)
since the gas velocity through the bed(s) is relatively low. However,
packed beds are effective for the removal of particle-laden droplets or
charged particles when used as a downstream collector behind a venturi or
electrostatically-enhanced wet scrubber.
Packed beds can be either vertical or horizontal. Figure 3-4
illustrates a vertically oriented scrubber. 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.
Absorption is the primary means of collection of acid gases in
packed-bed scrubbers. The effectiveness of absorption in packed beds is
related to the uniformity of the gas velocity distribution, the surface
area of the packing material, the amount and uniform distribution of
scrubber liquid, and the pH and turbidity of the scrubbing liquid.
Gas absorption is affected by the extensive liquid surface contacted
by the gas stream as the liquid flows downward over the packing material.
variety of available packing materials offer a large exposed surface area
to facilitate contact with and absorption of acid gases. The packing
materials range in size from 0.5 to 3 in. and are randomly oriented in the
bed.
Typically, sodium hydroxide (NaOH) or occasionally sodium carbonate
(Na2C03) is used with water to neutralize the absorbed acid gases in a
packed-bed scrubber. These two soluble alkali materials are preferred
because they minimize the possibility of scale formation in the nozzles,
pump, and piping. For the typical case of using NaOH as the neutralizing
agent, the HC1 and S02 collected in the scrubber react with NaOH to
produce sodium chloride (NaCl) and sodium sulfite (Na2S03) in an aqueous
solution.
-------
Mist eliminator
Liquid sprays
Packing
Figure 3-4. Countercurrent packed tower absorber.
3-14
-------
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 sus-
pended solids levels in the liquor must be monitored carefully to maintain
performance.
Spray Towers. Spray towers are relatively simple scrubbers. Most
units consist of an empty cylindrical steel vessel containing nozzles that
spray the liquid scrubbing media into the vessel. Most units use counter-
current flow with the exhaust gas stream entering the bottom of the vessel
and moving upward, while the liquid is sprayed downward. Figure 3-5 shows
a typical countercurrent flow spray tower. Countercurrent flow exposes
the exhaust gas with the lowest pollutant concentration to the freshest
scrubbing liquid.
Many nozzles are placed across the tower at different heights to
spray all of the exhaust gas as it moves up through the tower. The major
purpose of using many nozzles is to form a tremendous amount of fine
droplets for impacting particles and to provide a large surface area for
absorbing gas. Theoretically, the smaller the droplets formed, the higher
the collection efficiency achieved for both gaseous and particulate
pollutants. However, the liquid droplets must be large enough to not be
carried out of the scrubber by the exhaust stream. Therefore, spray
towers use nozzles to produce droplets that are usually 500 to 1000 urn in
diameter. The exhaust gas velocity is kept low, from 0.3 to 1.2 m/s (1 to
4 ft/s) to prevent excess droplets from being carried out of the tower.
Because of this low exhaust velocity, spray towers must be larger than
other scrubbers that handle similar exhaust stream flow rates. Another
problem occurring in spray towers is that after the droplets fall short
distances, they tend to agglomerate or hit the walls of the tower.
Consequently, the total liquid surface area for contact is reduced, thus
reducing the collection efficiency of the scrubber.
Spray towers are low-energy scrubbers. Contacting power is much
lower than in venturi scrubbers, and the pressure drops across such
systems are generally less than 2.5 cm (1 in.) of water. The collection
efficiency for small particles is correspondingly lower than in more
energy-intensive devices. They are adequate for the collection of coarse
particles larger than 10 to 25 urn in diameter, although with increased
3-15
-------
Liquid
sprays
Figure 3-5. Countercurrent-flow spray tower.
10
3-15
-------
liquid inlet nozzle pressures, particles with diameters of 2.0 pm can be
collected. Smaller droplets can be formed by higher liquid pressures at
the nozzle. The highest collection efficiencies are achieved when small
droplets are produced and the difference between the velocity of the
droplet and the velocity of the upward-moving particles is high. Small
droplets, however, have small settling velocities, so there is an optimum
range of droplet sizes for scrubbers that work by this mechanism.
Because of their inherent design, particulate matter emissions from
controlled-air incinerators are usually composed of relatively fine
particulate matter. Therefore, spray towers are not commonly applied to
controlled-air units. Multiple-chamber incinerators, however, can emit
large quantities of relatively large particle particulate matter and are
often controlled by spray towers.
3.3.3.2 Fabric Filters. Fabric filters (i.e., baghouses) are used
on a limited number of hospital incinerators for control of particulate
matter emissions. They have some advantages over wet scrubbers in that
they are highly efficient at removing fine particles if they are properly
operated and maintained. However, poor operation and maintenance (O&M)
can result in bag blinding, bag corrosion, or bag erosion.
Filtration principles. Fabric filtration is one of the most common
techniques used to collect particulate matter. A fabric filter is a
collection of bags constructed of a fabric material (nylon, wool, or
other) hung inside a housing. The combustion gases are drawn into the
housing, pass through the bags, and are exhausted from the housing through
a stack to the atmosphere. When the exhaust stream from the incinerator
is drawn through the fabric, the particles are retained on the fabric
material, while the cleaned gas passes through the material. The
collected particles are then removed from the filter by a cleaning
mechanism typically by using blasts of air. The removed particles are
stored in a collection hopper until they are disposed.
With a new filter, the open areas in the fabric are of sufficient
size that particles easily penetrate the bag. Over time, a cake builds on
the bag surface, and this cake acts as the primary collection medium.
Particles are collected on a filter and cake by a combination of several
mechanisms. The most important are impaction and direct interception.
-------
In collection by impact!on, the particles in the gas stream have too
much inertia to follow the gas streamlines around the fiber and are
impacted on the fiber surface. In the case of direct interception, the
particles have less inertia and barely follow the gas streamlines around
the fiber. If the distance between the center of the particle and the
outside of the fiber is less than the particle radius, the particle will
graze or hit the fiber and be "intercepted". Impaction and direct
interception mechanisms account for 99 percent collection of particles
greater than 1 ym aerodynamic diameter in fabric filter systems.
Fabric filter performance. Generally, fabric filters are classified
by the type of cleaning mechanism that is used to remove the dust from the
bags. The three types of units are mechanical shakers, reverse air, and
pulse jet. To date, the only hospital incinerators that have been
identified as having fabric filters use pulse jet units. The paragraphs
below briefly describe the design and operating characteristics of pulse
jet filters and identify key design parameters.
A schematic of a pulse jet baghouse is shown in Figure 3-6. Bags are
supported internally by rings or cages. Bags are held firmly in place at
the top by clasps and have an enclosed bottom (usually a metal cap).
Dust-laden gas is filtered through the bag, depositing dust on the outside
surface of the bag. Pulse jet cleaning is used for cleaning bags in an
exterior filtration system.
The dust cake is removed from the bag by a blast of compressed air
injected into the top of the bag tube. The blast of high pressure air
stops the normal flow of air through the filter. The air blast develops
into a standing or shock wave that causes the bag to flex or expand as the
shock wave travels down the bag tube. As the bag flexes, the cake
fractures and deposited particles are discharged from the bag. The shock
wave travels down and back up the tube in approximately 0.5 seconds.
The blast of compressed air must be strong enough for the shock wave
to travel the length of the bag and shatter or crack the dust cake. Pulse
jet units use air supplies from a common header which feeds into a nozzle
located above each bag. In most baghouse designs, a venturi sealed at the
top of each bag is used to create a large enough pulse to travel down and
up the bag. The pressures involved are commonly between 414 and 689 kPa
-------
TUBE SHEET
CLEAN AIR PLENUM
PLENUM ACCESS—
BLOW PIPE
INDUCED FLOW
TO CLEAN AIR OUTLET
AND EXHAUSTER
DIRTY AIR INLET & OIFFUSER
Figure 3-6. Pulse jet baghouse.
12
3-19
-------
(60 and 100 psig). The importance of the venturi is being questioned by
some pulse jet baghouse vendors. Some baghouses operate with only the
compressed air manifold above each bag.
Most pulse jet filters use bag tubes that are 10 to 15 cm (4 to
6 in.) in diameter. Typically the bags are 3.0 to 3.7 m (10 to 12 ft)
long, but they can be as long as 7.6 m (25 ft). Generally, these bags
are arranged in rows, and the bags are cleaned one row at a time in
sequence. Cleaning can be initiated by a pressure drop switch, or it may
occur on a timed sequence.
The key design and operating parameters for a pulse jet filter are
the air-to-cloth ratio (or the filtration velocity), the bag material,
operating temperature, and operating pressure drop.
The air-to-cloth ratio is actually a measure of the superficial gas
velocity through the filter medium. It is a ratio of the flow rate of gas
through the fabric filter (at actual conditions) to the area of the bags
and is usually measured in units of acfm/ft . No operating data were
obtained for hospital incinerators, but generally, the air-to-cloth ratio
on waste combustion units is in the range of 0.025 to 0.05 m /s/m (5 to
10 acfm/ft ) of bag area.
Generally, bag material is specified based on prior experience of the
vendor. Key factors that generally are considered are: cleaning method,
abrasiveness of the particulate matter and abrasion resistance of the
material, expected operating temperature, potential chemical degradation
problems, and cost. To date, no information has been obtained on types of
material typically used for hospital incinerator applications.
The operating temperature of the fabric filter is of critical
importance. Since the exhaust gas from a hospital incinerator can contain
HC1, the unit should be operated at sufficiently high temperatures to
assure that no surfaces drop below the acid dewpoint. Otherwise,
condensation of HC1 will result in corrosion of the housing or bags. The
boiling point of HC1 (aqueous hydrochloric acid) is 110°C (230°F); gas
temperatures should be maintained at 150°C (300°F) to ensure that no
surfaces are cooled-below the dewpoint. Above a maximum temperature that
is dependent on filter type, bags will degrade or in some cases fail
completely. Gas temperatures should be kept safely below the allowed
maximum.
3-20
-------
Pressure drop in fabric filters generally is maintained within a
narrow range. Pressure drops below the minimum indicate that either
(1) leaks have developed, or (2) excessive cleaning is removing the base
cake from the bags. Either condition results in reduced performance.
Pressure drops greater than the maximum indicate that either (1) bags are
"blinding", or (b) excessive cake is building on the bags because of
insufficient cleaning. The primary problem that results from excessive
pressure drop is reduced flow through the system and positive pressure at
the combustor. Over time, high pressure drops also lead to bag erosion
and degradation.
3.3.3.3 Dry Scrubbers. Dry scrubbers use absorption 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. Basically, dry
scrubbers use an alkajine sorbent to react with and neutralize the acid
gas. The reaction product is a dry solid which can be collected by a
particulate control device. Dry scrubbers usually are followed by either
fabric filters or electrostatic precipitators (ESP's) for collection of
the reaction products and the unreacted sorbent. Currently, there are not
any hospital incinerators known to be using spray dryer absorption
systems. There are at least three hospital waste incinerators which are
known to be using dry injection control systems.3
Components and operating principles of dry scrubber systems. 13»llt
There is considerable diversity in the variety of processes which are
collectively termed dry scrubbing. Dry scrubbing techniques that could be
applied to hospital incinerators can be grouped into two major
categories: (1) spray dryer absorbers, and (2) dry injection absorption
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.
Southland Exchange Joint Ventures, Hampton, South Carolina (dry
injection/ESP); Fairfax County Hospital, Falls Church, Virginia (dry
injection/baghouse); Borgess Medical Center, Kalamazoo, Michigan (dry
injection/baghouse).
-------
1. Spray dryer absorption (semiwet)
• Rotary atomizer spray dryer systems
• Air atomizing nozzle spray dryer systems
2. Dry injection absorption (dry)
• Dry injection without recycle
• Dry injection with recycle (sometimes termed circulating flu d
bed absorption)
Simplified block diagrams of the two major types of dry scrubbing
systems are presented in Figures 3-7 and 3-8. The main differences
between the two systems are the physical form of the alkaline reagent an
the design of the vessel used for contacting the acid gas-laden stream.
The alkaline feed requirements are much higher for the dry injection
system. Conversely, the spray dryer system is much more complicated.
Spray dryer absorbers. In this type of dry scrubbing system, the
alkaline reagent, usually pebble lime, is prepared as a slurry containin
5 to 20 percent by weight solids. This reagent must be slaked in order n
prepare the reactive slurry for absorption of acid gases. Slaking is th
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. The prepared slurry is atomized in a
large absorber vessel having a residence time of 6 to 20 seconds.
Atomization of the slurry is achieved through the use of: (1) rotary
atomizers or (2) air atomizing nozzles. Generally, only one rotary
atomizer is included in a spray dryer absorber. However, a few
applications have as many as three rotary atomizers.
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 revolutions pe
minute. 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 f< •
droplet formation in nozzle type atomizers. The typical air pressures a :
70 to 90 psig. Slurry droplets in the range of 70 to 200 microns are
-------
Lime
Storage
Slurry
Mixing
Tank
Slurry
Feed
Tank
1
Combustion
Gases
Stack
Figure 3-7.
Components of a spray dry.er absorber system
(semiwet process). 15
3-23
-------
So r bent
Storage
Blower
Feeder
Combustion
Gases from <
Incinerator
Pneumatic
Line
Stack
Waste
Heat
Boiler
•••••
Combustion
Air Dnrt
Expansion/
Reaction
Chamber
Solid
Residue
Figure 3-8. Components of a dry injection absorption system
(dry process).16
3-24
-------
generated. This type of atomizer generally can operate over wider
variations of the gas flow rate than can be used in a rotary atomizer.
However, the nozzle atomizer does not have the slurry feed turndown
capability of the rotary atomizer. For these reasons, different
approaches must be taken when operating at varying system loads.
The shape of the scrubber vessel must be designed to take into
account the differences in the slurry spray pattern and the time required
for droplet evaporation for the two types of slurry atomizers. 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
requires generation of small slurry droplets and adequate mixing with the
hot flue gases.
Drying that is too rapid can reduce pollutant collection efficiency
since the primary removal mechanism is absorption into the droplets.
There must be sufficient contact time for the absorption. For this
reason, spray dryer absorbers are operated with exit gas temperatures 90°
to 180°F above the saturation temperature.
Dry injection absorption systems. This type of dry scrubber uses
injection of a finely divided alkaline sorbent such as calcium hydroxide
(hydrated line) or sodium bicarbonate for the absorption of acid gases.
The reagent feed has particle sizes which are 90 percent by weight through
325 mesh screens. This is approximately the consistency of talcum
powder. This size is important to ensure that there is adequate alkaline
sorbent surface area for high efficiency pollutant removal.
Proper particle sizes are maintained by transporting the sorbent 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 to ensure proper particle sizes.
-------
Fluidization is completed when the alkaline sorbent is injected
countercurrently into the gas stream. The alkaline sorbent may be
injected directly into a reaction vessel or may be injected directly into
the ducting with a reaction vessel (expansion chamber) located downstream
to increase residence time. The gas stream containing the entrained
sorbent particles and fly ash is then ducted to a fabric filter or ESP.
When a fabric filter is used for particulate control, acid gas removal may
be further enhanced by the reaction with the sorbent in the filter cake.
In one version of the dry injection system, solids are recycled from
the particulate matter control device back into the flue gas contactor.
The primary purpose of the recycle stream is to increase reagent
utilization and thereby reduce overall calcium hydroxide costs.
3.4 REFERENCES FOR CHAPTER 3
1. U. S. Environmental Protection Agency. Hospital Waste Combustion
Study: Data Gathering Phase, EPA-450/3-88-017. December 1988.
2. Joseph, J. and D. Beachler. APTI Course SI:412C, Wet Scrubber Plan
Review - Self Instructional Guidebook. EPA 450/2-82-020. U. S.
Environmental Protection Agency. March 1984.
3. Schifftner, K. and Patterson, R. Engineering Efficient Pathological
Waste Incinerator Scrubbers. Paper presented at First National
Symposium on Incineration of Infectious Waste. Calvert, Inc.
May 1988.
4. Holland, 0. L., and Means, J. D., Utilization of Hydro-Sonic®
Scrubbers for the Abatement of Emissions from Hazardous, Industrial,
Municipal and Biomedical Wastes; Technical Paper No. 7802, John Zink
and Company, 1988.
5. Reference 2. p. 1-4.
6. Reference 2. p. 3-2.
7. Reference 2. p. 3-4.
8. U. S. Environmental Protection Agency. Wet Scrubber System Study:
Volume I—Scrubber Handbook. EPA-R2-72-118a, PB 213016.
August 1972. p. 5-122.
9. Reference 2. p. 5-3.
10. Reference 2. p. 3-4.
-------
11. Beachler, D. and M. Peterson. APTI Course SI:412A, Baghouse Plan
Review - Student Guidebook. EPA 450/2-82-005. U. S. Environmental
Protection Agency. April 1982.
12. U. S. Environmental Protection Agency. Control Techniques for
Particulate Emissions from Stationary Sources, Volumes 1 and 2.
EPA 450/3-81-005a,b. (PB83-127498). U. S. Environmental Protection
Agency. September 1982.
13. Sedman, C. and T. Brna. Municipal Waste Combustion Study: Flue Gas
Cleaning Technology. EPA/530-SW-87-021d (NTIS PB 87-206108)
U. S. Environmental Protection Agency. June 1987.
14. Richards Engineering. Air Pollution Source Field Inspection
Notebook; Revision 2. Prepared for the U. S. Environmental
Protection Agency, Air Pollution Training Institute. June 1988.
-------
4.0 OPERATION
The success of incineration as a technique for treating hospital
waste depends on the proper operation of the incinerator and its air
pollution control devices. Proper operating techniques can affect
equipment reliability, on-line availability, combustion efficiency, and
compliance with air pollution regulations. The operator is in control of
many of the factors that affect the performance of a hospital incinerator
including: (1) waste charging procedures, (2) incinerator startup and
shutdown, (3) air pollution control device startup and shutdown,
(4) monitoring and adjusting operating parameters for the incinerator and
air pollution control system, and (5) ash handling. This section
identifies key operating parameters, identifies operating ranges for key
parameters, and discusses general operating procedures that can minimize
unexpected malfunctions and improve the performance of the incinerator and
air pollution control devices. Appropriate monitoring procedures also are
discussed in this section.
4.1 GENERAL OBJECTIVES
The primary objectives associated with the proper operation of a
hospital waste incineration system are to operate the system in a manner
so that infectious materials in the waste are rendered harmless, waste
volume is reduced, good ash quality (from an aesthetic standpoint) is
ensured, and air pollution emissions of particulate matter, organic
compounds, carbon monoxide, and acid gas are minimized. The operator is
responsible for knowing key operating parameters and the proper operating
ranges for these parameters to assure that the system is operated at its
design efficiency. The operator also should know the operating procedures
and monitoring techniques which will assist fn maintaining those
parameters within the acceptable operating range.
Because each incinerator model is designed differently, design
criteria, operating parameters, and operating procedures will vary.
Nonetheless, recommended operating ranges can be established for some
general key parameters to assist in meeting the objectives of the
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incineration process—destruction of pathogens and reduction of waste
volume—while minimizing air pollution and maintaining good ash quality.
To identify these key parameters and discuss proper operating procedures,
incineration systems have been categorized as follows:
1. Batch/controlled-air incinerators;
2. Intermittent-duty, controlled-air incinerators;
3. Continuous-duty, controlled-air incinerators;
4. Multiple-chamber incinerators; and
5. Rotary kilns.
The operation of air pollution control systems is addressed later in this
chapter.
Currently, most hospital waste incineration systems do not include an
air pollution control device mainly because with proper combustion control
through proper operation, the systems can meet current emission regula-
tions. However, a growing number of States have promulgated or will soon
promulgate more stringent regulations governing hospital waste inciner-
ators that will increase the numbers of incinerators requiring add-on air
pollution control devices to meet the regulations. When an air pollution
control system is included as part of the incineration system, the
operation of the incinerator and the control device are interrelated.
Therefore, the optimum approach to describing the proper operation of
incineration systems (including air pollution control devices) would be to
discuss the operation of each of the possible combinations of incinerators
and control devices. However, because of the large number of combinations
of equipment types that may constitute an incineration system, the proper
operation of incinerators and air pollution devices will be discussed
separately.
This document provides a discussion of operating ranges for the key
operating parameters and presents an overview of proper operating
procedures and monitoring techniques. This information will provide the
reader with a basic understanding of what constitutes good operating
practice. However, it does not substitute for manufacturers' operating
procedures. Specific steps and operating procedures for equipment will be
specified by each manufacturer; furthermore, the control and monitoring
systems used by each manufacturer may be different. Consequently, a
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specific manufacturer's recommended and detailed operating procedures
should be followed.
4.2 INCINERATOR KEY OPERATING PARAMETERS
4.2.1 Introduction
The interrelationship among an incinerator's thermal capacity, waste
feed characteristics, heat input rate from the waste feed, and combustion
air was discussed in Chapter 2. This section identifies the operating
parameters and presents recommended operating ranges for these
parameters. The majority of the key parameters and the recommended
operating ranges remain the same for the different incinerator systems,
but because they do differ somewhat for different types of incinerators,
the parameters are presented for each type system that was described in
Chapter 2. Controlled-air incinerators, multiple-chamber incinerators,
and rotary kilns are discussed in order.
4.2.2 Controlled-Air Incinerators
Table 4-1 summarizes the key incinerator operating parameters and the
operating range for each parameter. These parameters assume the waste is
primarily a heterogeneous mixture of hospital infectious waste with a Btu
content that will sustain combustion (i.e., greater than 6,000 Btu/lb).
For "pathological" incinerators, burning pathological wastes, the
recommended operating ranges are slightly different because waste
characteristics differ significantly. An explanation of why each key
operating parameter in Table 4-1 is important and a discussion of each
operating range is presented below.
4.2.2.1 Primary and Secondary Combustion Chamber Temperatures.
Maintaining the desired operating temperatures within each combustion
chamber is critical to proper operation of a controlled-air incinerator.
Both upper and lower limits on the temperature range for each chamber are
of interest. The desired range of operation is different for the ignition
(primary) and combustion (secondary) chambers because the functions of
these chambers differ.
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TABLE 4-1. KEY INCINERATOR OPERATING PARAMETERS AND RECOMMENDED
OPERATING RANGE: CONTROLLED-AIR INCINERATOR
Parameter
Ignition chamber temperature, *F
Combustion (secondary) chamber
temperature, °F
Charging rate, Ib/h
Ignition chamber combustion air
(percent of stoichiometric)
Total combustion air
(percent excess air)
Combustion gas oxygen
concentration, percent
Ignition chamber draft, in w.c.
Burn down period, h
Batch feed
1000° to 1800°
1800' to 2200'
Fill 'chamber once at beginning
of cycle
30 to 80
140 to 200
12 to 14
-0.05 to -0.1
2 to 5
Incinerator type
Intermittent feed
1000° to 1800°
1800° to 2200"
10 to 25 percent of rated
capacity at 5 to 15 min
intervals
30 to 80
140 to 200
12 to 14
-0.05 to -0.1
2 to 5
Continuous duty
1400° to 1800°
1800* to 2200"
10 to 25 percent of rated
capacity at 5 to 15 min
intervals
30 to 80
140 to 200
12 to 14
-0.05 to -0.1
Not appt i cable
-------
The literature indicates that typical operating ranges for the
ignition chamber of controlled-air incinerators range from 400° to 980°C
(750° to 1800°F). ' The ignition chamber must be maintained at a minimum
temperature sufficient to sustain combustion, combust the fixed carbon in
the ash bed, and kill any micro-organisms in the waste bed so that the
remaining ash is sterile. The temperature also must be maintained below a
level that will damage the refractory and result in slagging of the waste.
Few studies have been conducted to determine the conditions necessary
to achieve complete pathogen kill in incinerators. Barbeito et al.,
conducted a study on a multiple-chamber, industrial-refuse incinerator to
determine the minimum operating temperatures required to prevent release
of viable micro-organisms into the atmosphere. His research indicated
that the destruction of the micro-organisms within the incinerator depends
on the temperature and time of exposure. These parameters are affected by
many factors, including charging beyond incinerator capacity and exceeding
design linear velocities, which reduces retention time. Barbeito
recommended a minimum primary chamber temperature of 760°C (14000F).1>3
From an operational (operating efficiency) standpoint, it is
desirable to operate the primary or ignition chamber at a temperature high
enough to sustain combustion in the chamber and to generate sufficient
volatile combustion gases and heat to maintain the desired secondary
combustion temperature without the use of auxiliary fuel. Consequently,
the desired primary temperature will depend somewhat on the waste
composition. Furthermore, a sufficiently high temperature to effectively
combust the fixed carbon in the waste bed is desired. One manufacturer's
experience indicates that this temperature is in the 760° to 870°C (1400°
to 1600°F) range for continuous-duty incinerators.2 This temperature may
be as low as 540°C (1000°F) for batch feed and intermittent-duty units
because the burnout time can be extended in these units.2 Operating batch
feed incinerators at a low primary chamber temperature (relative to
continuous-duty incinerators) helps assure that volatiles are not
generated at an excessive rate which cannot be handled by the secondary
chamber.
When the waste stream contains a significant amount of plastics,
"cracking" of light hydrocarbons can be significant and can affect the
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combustion gas. volume in the secondary chamber. Operating the primary
chamber at lower temperatures (540° to 650°C [1000° to 1200°F]) may help
to minimize rapid increases in flue gas volume.4 Some incinerator
manufacturers use water quenching in the primary chamber to maintain gas
temperatures below the 930° to 980°C (1700° to 1800°F) range and minimize
cracking.
At the same time, the primary chamber temperature must be maintained
below the point that will result in refractory damage. It is common for
modern incinerators to use nominal 1540° to 1650°C (2800° to 3000°F)
quality refractory. Although this refractory is rated at 1540° to 1650°C
(2800° to 3000°F), reactions can occur with contaminants in the combustion
gas, making it desirable to expose this refractory to no higher than
1200°C (2200°F) on a continual basis. Another, perhaps more important,
limiting factor for the upper operating temperature of the primary chamber
Ts slagging of the waste. Most ash residues begin to become soft at
temperatures in the range of 1200° to 1370°C (2200° to 2500°F).2 While
thermocouples in the primary chamber indicate the temperature of the
combustion gas exiting the primary chamber, the temperature in the ash bed
at the hearth adjacent to the underfire air ports can be consistently
higher. Consequently, although the combustion gas temperature can
indicate that clinker (fused slag) formation should not be a problem, the
ash bed can be hot enough to form clinkers. Experience has shown that a
control temperature of 980°C (1800°F) can be used in most cases with
acceptable performance with regard to clinker formation and carbon
burnout, but the performance problems due to slagging may begin to occur
at primary chamber temperatures as low as 760°C (1400°F). '
The secondary chamber serves to complete the combustion process
initiated in the primary chamber. As with the primary chamber, it is
desirable to operate within a lower and upper range. At temperatures that
are too low, complete combustion may not occur. At temperatures that are
too high, refractory damage may occur, residence time may be decreased,
and auxiliary fuel may be unnecessarily wasted.
A minimum temperature is needed to prevent the discharge of
potentially toxic products of incomplete combustion. Experimental work
conducted at the University of Dayton Research Institute (UDRI) indicates
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that temperature is the primary factor that affects these emissions.7 The
experimental data for thermal decomposition indicate that the destruction
of a species depends predominantly on the temperature, and effectively a
threshold temperature exists above which the compound will rapidly
combust. The threshold temperature found for polychlorinated dibenzo-p-
dioxin (PCDD) and polychlorinated dibenzofurans (PCDF) and potential
precursers (e.g., hexachlorobenzene) is near 930°C (170CTF).7
Sufficient temperature in the secondary chamber is necessary to kill
microorganisms entrained in the gas stream from the primary chamber.
Again, little information on the required temperature is available, and
data from studies conducted on specific incinerators are specific to those
incinerators and the experimental operating conditions, e.g., residence
time and turbulence. Based upon his incineration study, Barbeito recom-
mended a minimum secondary combustion chamber temperature of 980°C
(1800°F). The limiting factor for the secondary combustion chamber
temperature upper operating range is refractory damage. The upper limit
will depend on the refractory used, but a typical limit is 1200°C (2200°F)
on a continual basis.2
In summary, temperatures in both chambers should be maintained at
high enough levels to ensure complete combustion of the waste but not so
high that refractory damage or slagging of the ash occurs. A minimum
temperature for the primary chamber in the range of 540° to 760°C (1000°
to 1400°F) should be maintained to ensure pathogen kill, sterile ash, and
good ash quality, The minimum temperature required for proper operation
will depend on waste characteristics as well as the retention time of the
ash in the primary chamber and consequently the incinerator design. To
prevent clinker formation, the recommended upper bound primary chamber
temperature is 980°C (1800°F). To assure complete combustion, yet
conserve auxiliary fuel and prevent refractory damage, an operating range
of 980° to 1200°C (1800° to 2200°F) is recommended for the secondary
combustion chamber.
4.2.2.2 Charging Rate. An incinerator system is designed for a
particular thermal input rate. The thermal input comes from the waste
and, as necessary, the auxiliary fuel. Under ideal conditions, the
incinerator operates under conditions of a constant thermal input. For
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controlled-air incinerators, the thermal release from the "fuel" (the
waste in the chamber) is controlled, to the extent possible, by
controlling the available combustion air (the typical ranges for
combustion air will be discussed in the next section). Additional control
of the thermal input is obtained by controlling the quantity and frequency
of waste charges to the incinerator. The charging process, thermal input,
and combustion approaches a steady state condition as the waste
homogeneity increases, the charge loads decrease in size, and the
frequency of charges increase. Therefore, a charging scenario of more
frequent charges of smaller volume is more desirable than one of a single
large charge.8
4-2.2.2.1 Batch feed incinerators. By nature of their design, batch
feed incinerators are intended to accept a single load of waste at the
beginning of their incineration cycle; the heat release rate is controlled
solely by controlling the size of the initial charge and the available air
for combustion. The primary chamber acts as a fuel storage area. Manu-
facturers of batch operated incinerators recommend that the primary
chamber be filled to capacity, but not overfilled or stuffed so full that
the flame port to the secondary chamber or the ignition burner port
Q
assembly are blocked. If wastes containing an unusually high volatile
content are charged to the unit, a full load may contain enough volatiles
that, even if the primary air is controlled, the capacity of the secondary
combustion chamber will be exceeded. Therefore, it may be necessary to
decrease the size of the charge to the incinerator. That is, volume of
waste is an imperfect method for determining the thermal input to the
incinerator. The incinerator chamber size is designed for a particular
volume of waste with a particular Btu content. If the waste being charged
is significantly higher in Btu content, even though the volume capacity of
the chamber is not exceeded, the thermal capacity of the incinerator may
be exceeded. Consequently, it will be necessary to decrease the thermal
input of the batch charge by decreasing the volume input.
Regardless of the type, incinerators should never be overcharged
above the manufacturer's specifications. In the case of batch feed
incinerators where all charging occurs at the beginning of the
incineration cycle, there may be a tendency to stuff that last bag of
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waste into the. incinerator so that no waste is left over for the next
burn. This practice can lead to excessive emissions, incomplete
combustion, and damage to the incinerator. Overcharging with waste adds
more fuel to the incinerator than it can handle, may block the incinerator
air ports, and damage the primary burner. Excessive fuel combined with an
inadequate air supply causes excessive amounts of volatile material to be
passed to the secondary chamber which cannot be handled effectively in the
secondary chamber and results in high particulate matter emissions.
Additionally if a large quantity of plastic material is charged, the
excessive temperatures produced can cause refractory damage and clinker
formation. Higher primary chamber temperatures also cause higher gas
volumes and velocities which effectively reduces the secondary chamber
retention time.
4.2.2.2.2 Intermittent-feed and continuous-duty incinerators.
Intermittent- and continuous-duty, controlled-air incinerators are
designed to accommodate semicontinuous charging. The primary design
change for this type unit is that the charging system is set up with some
type of a mechanical device (either manually or automatically operated)
which allows the operator to safely add charges while the system is
operating. The mechanical device is designed to protect the operator from
exposure to the flame and heat of the primary combustion chamber.
Additionally, the mechanical charging device may be designed to limit air
in-leakage to the incinerator during charging to maintain control of the
combustion air level. The primary difference between the "intermittent"
and "continuous" duty units is not in the charging rate or operation, per
se, but that the continuous-duty system has a means for continuously
removing the ash generated by the waste. Consequently, this type unit can
maintain continuous "steady state" operation. The intermittent unit can
maintain continuous "steady-state" operation only for a limited time; once
the ash in the incinerator builds up to an unacceptable level, the unit
must be shutdown and the ash removed.
To approach a steady thermal input, manufacturers recommend that
multiple charges be made at equally timed intervals. The recommended
charge size is 10 to 25 percent of the rated capacity charged at 5 to
15 minute intervals.10'11 The charging frequency may need to be adjusted
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based upon variations in moisture content, volatile content, and overall
Btu value. The procedures that the operator can use to monitor the
charging rate and to make appropriate decisions is discussed in
Section 4.4.
4.2.2.3 Primary and Secondary Combustion Air Rate and Combustion Gas
Oxygen Concentration. For controlled-air units, the volatilization/
combustion rate in the primary chamber is controlled by using combustion
airflow rate to control the chamber temperature. The typical combustion
air operating range for the ignition chamber is 30 to 80 percent of
stoichiometric conditions. * Typically, about 20 percent of the total
air requirement to the incinerator is supplied as underfire air to the
ignition chamber. The remainder of the air is supplied to the secondary
mixing chamber.
Approximately 80 percent of the total combustion air required during
incineration is supplied to the secondary combustion chamber. Typically,
the total combustion air level is 140 to 200 percent excess air.12'13
Measurement of the oxygen concentration provides a convenient way of
determining and monitoring the excess-air level. Operating the
incinerator at a total excess-air level in the range of 140 to 200 percent
will result in stack gas oxygen concentrations in the range of 12 to
14 percent.
4.2.2.4 Combustion Chamber Pressure (Draft). A typical draft for
control!ed-air incinerators is in the range of -0.05 to -0.1 in. water
column (w.c.). Excessive draft is not desirable because increased
carryover of particulate matter to the secondary chamber can occur.
4.2.2.5 Burndown Period. After volatilization diminishes,
sufficient time must be provided for the fixed carbon in the waste bed to
combust.
For continuous-duty incinerators, there is no .distinct burndown
period since the burndown occurs continuously as the waste moves through
the system during the "steady state" operation. However, on some
continuous-duty incinerators with internal transfer rams, once the last
load of waste is charged, each ram may go into a burndown mode
sequentially where the rams' strokes are increased to push the waste from
one hearth to the next. For example, the ram on the first or drying
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hearth will stroke at the same time intervals but will stroke several
inches more on each stroke. During this period, the ash underfire air to
this part of the hearth is shut off. On the last stroke, the ram is at
the edge of the hearth, and all of the waste falls to the next hearth
which then goes into its burndown mode, and so on. This burndown sequence
is usually preset at the factory but can be changed by the manufacturer if
ash quality is poor. On these units, the burndown sequence is normally in
the range of 4 to 6 hours.llf
For batch and intermittent-duty operations, there is a distinct
burndown period associated with the operating cycle. During this period,
the volatiles have been combusted, and the fuel remaining in the waste bed
is slowly diminishing. In order to combust the fixed carbon remaining in
the waste, a higher temperature is required and, therefore, more underfire
air is introduced into the primary chamber.10 As the burndown proceeds
and the fuel is further diminished, the temperature slowly decreases.
During burndown, a minimum temperature level (e.g., 1400°F) is maintained
for a predetermined time period; auxiliary fuel may be required to
maintain this temperature. It is difficult to recommend a required
burndown period because it is somewhat experimental and will vary
depending upon the waste composition and combustion air rate. According
to one manufacturer, a rule of thumb for a trial burndown setting for an
intermittent-duty, small capacity incinerator is 1 hour plus an additional
20 minutes for each hour of operation.10 Therefore, a trial burndown
setting for a unit that operated 6 hours would be (1 hour)+(6x20 minutes)=
3 hours. A typical burndown period for batch and intermittent units is in
the range of 2 to 4 hours.llfllf
4-2.3 Multiple-Chamber Incinerators
Traditionally, multiple-chamber units were designed specifically to
burn pathological waste and contained a fixed (solid) hearth. Other
multiple-chamber incinerators use a grate type of hearth. Combustion of
medical waste containing significant quantities of fluids and/or
infectious material is not recommended in multiple-chamber units with
grates. Both type units employ large quantities of excess air for
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combustion and will operate at similar temperature ranges. The operating
parameters and ranges for a multiple-chamber incinerator are summarized in
Table 4-2 and are briefly discussed below.
4-2.3.1 Primary and Secondary Chamber Temperatures. As discussed
for control!ed-air incinerators, the temperature in the primary chamber
must be maintained at such a level as to assure pathogen kill. Most
multiple-chamber incinerators operate on a batch or intermittent-duty
basis. An extended burndown period is available to assure adequate ash
burnout and sterilization of the waste. A minimum primary chamber
temperature in the range of 540° to 760°C (1000° to 1400°F) is
recommended. The upper operating range for the primary chamber should be
established to prevent refractory damage. As previously mentioned for
contro11ed-air units, sustained operation above 2200°F is generally not
desirable.
Pathological wastes have a high moisture content and low volatile and
fixed carbon content. For pathological wastes, continuous operation of an
auxiliary burner is required to maintain the primary chamber temperature.
To facilitate burndown of the pathological wastes, a minimum primary
combustion chamber temperature of 1600°F is recommended.15
A minimum secondary chamber temperature of 1600°F for pathological
incinerators is recommended in the Air Pollution Engineering Manual to
assure complete combustion.15 As discussed in Section 4.2.2.1 for
controlled-air incinerators, a minimum temperature to prevent the
discharge of potentially toxic products of incomplete combustion is
required; a minimum secondary combustion chamber temperature of 980°C
(1800°F) is recommended for multiple-chamber incinerators.
4.2.3.2 Charging Rate. Whether a multiple-chamber unit is
incinerating red bag waste or pathological waste affects the charging rate
and procedures because the volatile content, moisture content, and Btu
value of these wastes are so different. An incinerator system is designed
and sized for a particular thermal input rate. The thermal input comes
from the waste and, as necessary, the auxiliary fuel. Unlike a
controlled-air unit, the combustion rate in a multiple-chamber unit cannot
be controlled by controlling the combustion air to the primary chamber.
Therefore, the controlling factor for the combustion rate is essentially
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TABLE 4-2. KEY INCINERATOR OPERATING PARAMETERS AND RECOMMENDED
OPERATING RANGE: MULTIPLE-CHAMBER INCINERATOR
Parameter
Pathological
waste
General refuse
Ignition chamber temperature, °F
Combustion (secondary) chamber
temperature, °F
Charging rate
Ignition chamber combustion air
(percent excess air)
Total combustion air (percent
excess air)
Combustion gas oxygen concentration,
percent
Ignition chamber draft, in. w.c.
1600 to 1800 1000 to 1400
1800 to 2200 1800 to 2200
Single layer
on hearth
80
120 to 200
10 to 14
10 to 25% of
rated capacity
at 5- to 15-min
intervals
150
250 to 300
15 to 16
-0.05 to -0.1 -0.05 to -0.1
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the availability of fuel; i.e., the amount of waste charged when general
refuse/red bag waste is being incinerated. The thermal input to the
incinerator and the combustion approaches a steady-state condition as the
waste homogeneity increases, the charge loads decrease in size, and the
frequency of charges increase. Therefore, charging procedures using more
frequent charges of smaller volume are more desirable than one single
large charge. A charge rate of 10 to 15 percent of the rated capacity at
regular intervals is recommended. Note that if a mechanical feeder is not
used, the more frequently the charging door is opened, the greater the
risk to the operator. Consequently, safety considerations make less
frequent charging desirable, which contradicts the more frequent charging
procedures desired from a thermal input standpoint. Thus, the objective
should be to assure that the individual charges to the incinerator are not
so large and infrequent that the capacity of the incinerator is exceeded
by rapid volatilization of combustibles resulting in excess emissions.
Consequently, charging frequency and load size will depend on waste
characteristics and incinerator design.
Pathological wastes have a low Btu content and a low volatiles
content. Consequently, rapid volatilization and rapid changes in heat
release to the primary chamber are not a concern when charging
pathological wastes. The primary chamber burner(s) provides(e) a steady
heat input to the incinerator. Because of the high moisture and low
volatile carbon content of pathological waste, the burner flame must
impinge on or near the waste for efficient combustion to occur.
Consequently, fresh pathological waste should not be charged into the
incinerator until the previous waste charge has burned down almost
completely. Completeness of burndown can be determined by inspection
through a view port and examining the waste bed.
4.2.3.3 Primary and Secondary Chamber Combustion Air Levels. For
multiple-chamber incinerators the primary chamber excess-air level is
typically 150 percent or greater excess air. Overall excess-air levels
for multiple-chamber incinerators are typically 250 to 300 percent.1
This roughly corresponds to a combustion gas oxygen concentration of 15 to
16 percent. When incinerating pathological wastes, since the primary heat
release is coming from the auxiliary burner, the combustion air can be
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c°ntroHed at a lower level th.» ,
incinerator. than '«• - typica, ™,tip,e.chanDer
4-2-3-4 aHSber
waste throughput of a rotarv H, .
on an, by the incline " '« "termined
by the
speed
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*re oriented at a rake of ]ess th ,
H°n-zonta]). Both of these 1 P6rCent (7''e" 'round 11° f
*«» 'n y redUCln9 ^ =eed
*«» 'n turn utt fnclude y redUCln9 ^ =Peed of rotation
«- So ''nS ^
.,
~
4-3 WASTE FEED
HANDLING
I JIG Dhvsi^ai a .j
cind ^OOnii ^* » 1
»ft i Dl*onov*^* T ** >•
and the effects of
process
4-16
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the waste is charged and at what rate. Waste charging procedures are
specific to the type incinerator and the incinerator's mode of operation;
proper charging procedures will be discussed in Section 4.4. In this
section, some general concepts with regard to types of waste and handling
of the wastes are discussed. Although the operator does not have control
(or has very little control) over the waste which is to be incinerated,
the operator must understand how waste composition affects operation of
the incinerator and must learn to recognize problems related to waste
composition or to identify significant changes in waste composition. The
operator then can modify charging procedures, modify incinerator
combustion parameters (if properly trained to make such adjustments),
and/or notify the appropriate hospital administrators of continued waste
related problems which are severely affecting incinerator operation. The
remainder of this section addresses the following concerns:
1. Safe waste handling procedures; and
2. Wastes that should not be incinerated.
4.3.1 Proper Waste Handling
Infectious waste will be delivered to the incinerator area in "red
bags." The primary concern is to avoid exposure to pathogens;
consequently red bag wastes should be handled in a manner which maintains
the integrity of the container. Proper procedures dictate that:
1. Sturdy containers are used;
2. Waste handling is minimized;
3. The waste storage area is secure if wastes are to be stored; and
4. Mechanical handling/loading systems are properly operated and
maintained.
Plastic bags are the typical containers used for infectious waste.
Tear-resistant bags that will maintain their integrity during the
handling/transporting process should be used. The two main criteria used
to evaluate bag durability are bag thickness and the ASTM dart test.3'16
Some State regulations specify minimum bag requirements based on one of
these two criteria. For example, Massachusetts specifies a minimum bag
thickness while California requires use of the ASTM dart test.3 Even if
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appropriate bag mater1a,s
objects w,th,n the
conta,ners
and „,„ need tQ
°f
of
. ~.
containers are used the 'nd1V''dUa' p'««c bags
*euseab,e
they requfre ^
. A,so, shoul<( . b {e
VM, are Involved Flln ' ***
b> the use of r,g d c ^ ""'^T"1* °f
cart they need not be h,nd,ed agan unt " ? "«
nc,nerator or ,nto tta ^chanca c ' ^ "
. since waste ' 9 Systei" for '"e
easny
1s "«.»ned
can be
P'«ed ,„ the
tt
'nc.nerator „ preferre<( aon ' tlme '« charged to the
storage area or charging p, e on thef7 " Un'°adin9 ^ ««• to a
for urge automated Ind °"' *" "*"
"rts
4-18
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available which will automatically lift and dump the contents of the
collection transport carts into the charging hopper without handling of
the waste by the operator.8'17 Consequently, use of rigid type transport
carts can be effective in minimizing waste handling.
To assure the integrity of the red bags, mechanical means of
transporting the waste should not be used, except for final charging into
the incinerator. For example, dumb-waiters, chutes or conveyors should
not be used to transport the waste.3 The mechanical charging systems for
the incinerator should be designed and operated to minimize bag-breakage,
spillage, and possible contamination. For example, trash compactors
should not be used since when the bags are compacted, they will likely
break open. Furthermore, compaction will affect the wastes' bulk/density
(Ib/ft ) which will consequently affect the combustion process.3
The treatment of infectious waste as soon as possible after
generation is preferable. However, because same-day treatment is not
always possible, the incinerator operator may be responsible for waste
storage. If the waste must be stored prior to incineration, four factors
should be considered:
1. Maintaining container integrity and minimizing handling;
2. Storage temperature;
3. Storage duration; and
4. Location of the storage area.
The waste storage area should be a "secure" area, out of the way from
normal hospital traffic and should have restricted access. Certainly, the
area should be secure from public access. The storage area and/or the
containers should be secure from rodents and vermin which can contract and
transmit disease.
As temperature and storage time increases, decay occurs and
unpleasant odors result. There is no unanimous opinion on acceptable
storage temperature or times. The EPA Office of Solid Waste simply
recommends that storage times be kept as short as possible.3 Some States
do regulate storage times. For example, Massachusetts allows infectious
waste to be stored for 24 hours (1 day) at room temperature or for
72 hours (3 days) at refrigerated temperatures (34° to 45°F).3
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Obviously, the level of control that the incinerator operator has
over the items just discussed will vary with the situation and with the
particular waste handling issue. That is, the operator may have little
control over what strength red bag is used, but may have a great deal of
control over whether red bags are removed from transport carts to a
"charging floor" or whether the bags are simply loaded into the
incinerator directly from the cart—thus eliminating handling each bag two
more times.
The operator does, however, have control of personal protection items
used. It is prudent that when handling infectious waste, an operator
should always wear hard-soled shoes to avoid the potential for punctures
and thick rubber gloves to resist cuts and punctures and to prevent direct
contact with fluids. Safety precautions are discussed further in
Chapter 9. The operator must remember that his/her safety is at stake and
should bring deficiencies in waste handling practices (e.g., consistent
tearing of bags due to poor bag quality) to the hospital administrator's
attention.
4.3.2 Restricted Wastes
It is inappropriate to dispose of some wastes in a hospital waste
incinerator unless special permits are obtained. Wastes which should not
be incinerated, unless special permits are obtained include:
(1) radioactive wastes, and (2) hazardous wastes regulated under the
Resource Conservation and Recovery Act (RCRA).
Some State regulations or specific operating permits may dictate
charging limits for certain types of wastes. For example, an operating
permit may allow only up to 5 percent of the hourly charging rate to be
human or animal parts (i.e., "pathological waste"). Obviously, the
operator cannot tell whether the waste contains 4 percent or 5 percent of
pathological wastes; nor should the operator ever open red bag wastes to
examine the contents. Nonetheless, the operator must be aware of the
regulations and must be attuned to spotting problem wastes, either by the
obvious (e.g., gallon jugs of liquids, containers marked "radioactive") or
by more subtle means (i.e., identifying large quantities of human/animal
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anatomical parts in the incinerator waste bed, while viewing the bed
through a glass covered viewport.)
4.4 INCINERATOR OPERATION, CONTROL, AND MONITORING
The key operating parameters for incinerators were presented in
Section 4.2. This section provides a summary of the operating procedures,
parameters which can be automatically controlled, and monitoring
techniques for incineration systems. The operation, monitoring, and
control of these four "typical" systems are discussed:
1. Batch feed controlled air;
2. Intermittent-duty controlled air;
3. Continuous-duty controlled air; and
4. Multiple chamber.
The operation, control, and monitoring of rotary kilns is not presented
here because very few units are used to incinerate hospital waste and
detailed information regarding their operation was not available.
4.4.1 Batch Feed Controlled-Air Incinerator
This type incinerator typically is a small unit, up to 500 Ib/h, but
more typically less than 200 Ib/h capacity. The incinerator is operated
in a "batch mode" over a 12- to 24-h period which entails a single charge
at the beginning of the cycle, followed by combustion, ash burnout,
cooldown, and ash removal. The operating cycle from startup to shutdown
is discussed in the following sections. Parameters which can be
automatically controlled and monitoring techniques also are discussed.
4.4.1.1 Incinerator Operating Procedures. .
4.4.1.1.1 Ash removal. Startup of the .incinerator actually begins
with removal of the ash generated from the previous operating cycle. The
following are guidelines for good operating practice:10
1. In general, allowing the incinerator to cool overnight is
sufficient for the operator to remove the ash safely. This cooling can
take as long as 8 h.
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2. The operator should open the ash cleanout door slowly both to
minimize the possibility of damage to the door stop and seal gasket and to
prevent ash from becoming entrained.
3. The operator should exercise caution since the refractory may
still be hot and the ash may contain local hot spots, as well as sharp
objects.
4. The ash and combustion chamber should not be sprayed with water
to cool the chamber because rapid cooling from water sprays can adversely
affect the refractory.
5. A flat blunt shovel, not sharp objects that can damage the
refractory material, should be used for cleanup.
6. Avoid pushing ash into the underfire air ports.
7. Place the ash into a noncombustible heat resistant container,
i.e., metal. Dampen the ash with water to cool and minimize fugitive
emissions.
8. Once the ash has been removed and prior to closing the ash
cleanout door, the operator should inspect the door seal gasket for frayed
or worn sections. Worn seal gaskets should be replaced.
9. To prevent damage to the door seal gasket, the operator should
close the ash cleanout door slowly and should not overtighten the door
clamps. Overtightened door clamps may cause the seal gasket to
permanently set and allow infiltration of outside air around the door
face.
4.4.1.1.2 Waste charging. The operator may have the option of
selecting which items are included in a particular charge. Waste
properties which should be considered when the waste is segregated into
charges include: (1) the heating value, (2) the moisture content, (3) the
plastics content, and (4) the amount of pathological wastes. The heating
value and moisture content of waste affects the performance of an
incinerator. A charge of waste with a very high heating value may exceed
the thermal capacity of the incinerator. The result is high combustion
temperature, which can damage the refractory of the incinerator and can
result in excessive emissions. Similarly, a charge of waste with a very
high moisture content will not provide sufficient thermal input, and the
charge will require the use of more auxiliary fuel than usual.
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Plastic items are an example of materials with high heating values.
Large quantities of plastic, which may contain polyvinyl chloride, should
be distributed through many waste charges, not concentrated in one charge,
if possible. When sorting loads of waste to be incinerated, the operator
should try to create a mixture of low, medium, and high heating value
wastes in each charge, if possible, to match the design heat release rate
of the incinerator. In general, lighter bags and boxes will contain high
levels of low density plastics which burn very fast and very hot. Heavier
containers may contain liquids (e.g., blood, urine, dialysis fluids) and
surgical and operating room materials which will burn slowly. As a
general rule for segregating waste into charges, it is best for the
operator to mix light bags and heavy bags to balance the heating value of
each charge. If several different types of waste, i.e., red-bag, garbage
(cafeteria wastes), trash, are being charged to the incinerator, it is
generally better to charge the incinerator with some of each waste, rather
than all one type of waste. Special care should be taken to avoid
overcharging the incinerator (beyond its intended use) with anatomical
wastes.
Prior to initiating charging, operation of the combustion air blowers
and ignition and secondary burners should be checked. Follow the
manufacturers' recommendations. The proper operation of the primary and
secondary burners is best achieved by observing the burner flame pattern
through the viewports in the incinerator wall or in the burner itself.
Some burners are equipped with one observation point to view the main
flame and another to view the pilot flame. The flame pattern will likely
vary with the type of burner. However, the length of the flame should be
such that the flame touches the waste but does not impinge directly on the
refractory floor or wall. Obviously, the absence of a flame indicates a
problem with the burner or the system that controls the burner.
Most burners are equipped with a flame safeguard system that includes
a flame detector that effectively cuts off the fuel (gas or oil) supply to
the burner if a flame is not detected. When the burner is first started,
the burner blower starts and when it reaches full speed, a purge timer
starts. When the purge timer times out, the flame safeguard energizes the
pilot relay that opens the pilot fuel supply and ignitor. When the pilot
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lights, a flame detector (either an ultraviolet scanner [gas or oil] or
flame rod circuit [gas only]) detects the flame and causes the main flame
relay to activate the fuel supply to the main burner. The pilot then
ignites the main burner. The flame detector continues to operate and
shuts the burner down if the main burner fails. Additionally, if the air
supply is lost both pilot and flame relays shut off the fuel supply. The
pilot usually is ignited for no more than 15 seconds (interrupted
pilot). If the main burner does not ignite during the period, the flame
safeguard system shuts the entire system down.18
The incinerator is charged cold. Because these units generally are
small, they are usually manually loaded. The waste is loaded into the
ignition chamber, which is filled to the capacity recommended by the
manufacturer. Typically, the manufacturer will recommend filling the
incinerator completely, but not overstuffing the chamber. Overstuffing
can result in blockage of the air port to the combustion chamber and in
premature ignition of the waste and poor performance (i.e., excess
emissions) during startup. Overstuffing also can result in blockage of
the ignition burner port and damage to the burner. After charging is
completed, the charge door seal gasket is visually checked for
irregularities. The door is then slowly closed and locked. The charge
door seal gasket should then be inspected for any gaps that would allow
air infiltration into the primary chamber. Once operation is initiated,
no further charges will be made until the next operating cycle is
initiated, i.e., after cooldown and ash removal.
4.4.1.1.3 Waste ignition. Prior to ignition of the waste, the
secondary combustion chamber is preheated to a predetermined temperature
by igniting the secondary burner. A minimum secondary chamber temperature
of 980°C (1800°F) is recommended prior to ignition of the waste. The
manufacturer should be consulted regarding proper preheat procedures;
improper preheat can result in refractory damage.
After the secondary chamber is preheated, the secondary combustion
air blower is turned on to provide excess air for mixing with the
combustion gases from the primary chamber.
The primary chamber combustion air blower is activated and the
primary burner is ignited to initiate waste combustion. When the primary
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chamber reaches a preset temperature (i.e., the minimum operating
temperature for the primary chamber, see Table 4-1) and the waste
combustion is self-sustaining, the primary burner is shutdown.
The primary combustion air and secondary combustion air are adjusted
to maintain the desired primary and secondary chamber temperatures.
(Typically this adjustment is automatic and can encompass switching from
high to low settings or complete modulation over an operating range.)
During operation, the primary burner is reignited if the ignition
chamber temperature falls below a preset temperature. Similarly, the
secondary burner is reduced to its lowest firing level if the secondary
chamber rises above a preset high temperature setting. Again, control of
the burr—s, like the combustion air, is typically automated. A
baromet damper on the stack is used to maintain draft. The incinerator
chamber ould both be maintained under negative draft.
4.H. .1.4 Burndown. After the waste burns down and all volatiles have
been released, the primary chamber combustion air level is increased to
facilitate complete combustion of the fixed carbon remaining in the ash.
The temperature in the primary chamber will continue to decrease. During
the burndown period, the primary burner is used to maintain the primary
chamber temperature at the predetermined minimum level of the operating
range. The length of time required for the burndown period depends on the
incinerator design, waste characteristics, and degree of burnout
desired. A typical burndown period is 2 to 4 h.1* When combustion is
complete :he primary and secondary burners are shutdown.
Shutdown of the secondary burner which initiates the cooldown period
usually is automatically determined by a preset length of time into the
9 11
cycle. * The combustion air blowers are left operating to cool the
chambers prior to subsequent ash removal. The blowers are shutdown when
the chambers are completely cooled or prior to opening the ash door for
ash removal. Cooldown typically lasts 5 to 8 h.llf
The final step in the cycle is examination of ash burnout quality.
Inspection of the ash is one tool the operator has for evaluating
incinerator performance. The operator should look for fine gray ash with
the consistency of ash found in the fireplace at home or in the barbeque
grill. Ash containing large pieces of unburned material (other than
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materials which are not combustible, such as cans) shows that incinerator
performance is poor. It may be necessary to return these large pieces of
material to the incinerator to be reburned because poor quality ash may be
refused at landfills for disposal. Ash color also is an indicator of ash
quality. White or gray ash indicates that a low percentage of carbon
remains in the ash. Black ash indicates higher carbon percentages
remaining. Although carbon remaining in the ash indicates that available
fuel has not been used and combustion has not been complete, the fact that
carbon remains in the ash is not in itself an environmental concern or an
indicator that the ash is not sterile. Nonetheless, ash color can be used
to assist the operator in evaluating burnout and incinerator performance.
4.4.1.1.5 Special considerations. If pathological waste is being
burned, the ignition burner should be set to remain on until the waste is
completely burned. Further, the volume of waste charged likely will need
to be significantly reduced. The time required to burn an equivalent
volume of Type 4 waste will be extended, since the waste contains high
moisture and low volatile content. To destroy pathological waste
efficiently, the waste must be directly exposed to the burner flame;
consequently piling pathological waste in a deep pile (e.g., filling the
entire chamber) will result in inefficient combustion.15 If large volumes
of pathological wastes are to be incinerated, an incinerator which is
especially designed for pathological waste should be used.
4.4.1.2 Automatic Controls. Various levels of automatic controls
are available for hospital incinerators, even for the smallest units
sold. The smallest batch type units can be designed to use the same
automatic control concepts and hardware for the key combustion control
parameters (e.g., temperature and combustion air) as the larger
continuous-duty incinerators.19 The use of control systems allows key
combustion parameters to be adjusted automatically based on data (e.g.,
temperature) from the incineration system. These automatic controls
permit the combustion process to be more closely controlled.
For batch feed systems, parameters that can be automatically
controlled include:
1. Charging frequency;
2. Combustion air rate;
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3. Primary and secondary burner operation;
4. Temperature; and
5. Combustion, burndown, and cool down cycle times.
4.4.1.2.1 Charging frequency. The charging frequency can be
automatically controlled by providing an interlock system on the charging
door. The interlock will prevent the charging door from being opened
after the primary burner is ignited and will prevent additional charges to
the batch system until after burndown and cooldown have been completed.
The operation of the interlock can be set up in one of two ways. The
interlock can be activated by a timer so that the door cannot be opened
until after a preset time has elapsed (e.g., 24 hours). Alternatively,
operation of the interlock can be based on temperature; the interlock is
set to deactivate only after the proper temperature in the cool down cycle
is attained. The latter approach truly controls operation of the unit in
a manner that assures the incinerator will run through the complete
charge, combustion, burnout, and cooldown cycle.
4.4.1.2.2 Combustion air rate. Combustion air rate can be
automatically controlled by on/off settings, low/high settings, and full
modulation of the flow over an entire operating range. The control
settings can be activated based upon the value of a monitored parameter
(e.g., temperature) or by a specified time in a cycle. Some manufacturers
are now using different types of more advanced combustion air controls
that sense parameters such as gas flow, opacity, oxygen concentration, and
loading cycles to assure that adequate combustion air is available in the
secondary chamber."*
4.4.1.2.3 Primary and secondary burner operation. Like the combustion
air, the ignition and main combustion (secondary chamber) burners can be
controlled over an entire operating range (i.e., modulated), at low/high
levels, or in the on/off position. The settings can be based upon a
monitored value (e.g., temperature) or as part of a timed sequence. The
use of such settings in a control system is discussed in the following
sections.
4.4.1.2.4 Temperature. Both the primary ignition and secondary
combustion chamber temperatures can be automatically controlled. At least
two levels of control are available. The first control approach is
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designed to control temperature in each chamber by modulating the
available combustion air to each chamber. In this type system, the
temperature in each chamber is monitored, and the combustion air to each
chamber is separately controlled based on feedback from the thermo-
couples. The combustion air is modulated continuously over a wide range
in order to maintain the set point temperatures. Auxiliary burners are
used as necessary to maintain minimum temperatures. Since instantaneous
peaks in the combustion gases generated in the primary chamber can occur,
some manufacturers recommend operating the secondary burner at all times
(in a low fire position if heat is not required) to assure complete
combustion of primary chamber gases."*
This type control system effectively controls the waste combustion
rate in the primary chamber by controlling the combustion air.
Controlling the combustion rate in the primary chamber subsequently limits
the combustion rate in the secondary chamber. Controlling the secondary
chamber combustion air controls that chamber's temperature by increasing
or decreasing the excess-air level. The firing rate of the main
combustion burner (secondary chamber) may be modulated upward or downward
if low and high temperature set points are reached in the secondary
chamber. Similarly, the ignition burner can be activated automatically if
the primary chamber temperature falls below the minimum set point. This
type system provides a true control of the key parameter, combustion
temperature, by modulating the combustion air.
One manufacturer controls the combustion rate in the primary chamber
and the temperature in the secondary chamber by monitoring the oxygen
concentrations in each combustion chamber and using these data to
control/adjust the combustion air levels.20
Review of manufacturers' information indicate that a second approach
to automatically controlling the combustion process is used for batch type
9 11
units. ' In this approach, a series of timers are used to establish a
timed sequence of events and the key process equipment (i.e., burners and
combustion air) have high/low or on/off settings. The switching of the
burners and combustion air from one setting to another is controlled by
the timed sequence. Overrides for the timed sequence are typically
provided to assure that minimum or maximum set point temperatures are not
exceeded.
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This type control system does not offer the same level of combustion
control as the modulated system previously described. Instead of
continuously modulating to achieve a specific set point (i.e., tempera-
ture), this type system utilizes on/off or low/high settings to maintain
control between two set points.
4.4.1.2.5 Combustion, burndown, and cooldown cycle times. An
automatic control sequence operating on a timer cycle typically is used to
initiate and control the length of burndown and cooldown cycles.
Table 4-3 presents an example timed control cycle for a batch operated
incinerator.
4-4.1.3 Monitoring Operations. The monitoring of key operating
parameters provides several benefits. First, monitoring provides the
operator with information needed to make decisions on necessary combustion
control adjustments. For example, continuous monitoring of the
temperature and carbon monoxide level of the secondary combustion chamber
effluent gas stream allows the operator to determine whether optimum
combustion conditions are being maintained. Indications of an abnormally
high CO level and low temperature can immediately be used to adjust the
secondary burner rate to raise the combustion chamber temperature.
Second, properly maintained monitoring records can provide useful
information for identifying operating trends and potential maintenance
problems. This historical information can be used to make decisions with
respect to modifying standard operating procedures or control set
points. For example, careful visual inspection of ash quality each day
complemented by comments in a daily operator's log book can be used to
track ash burnout patterns. If a gradual trend towards poor ash burnout
becomes evident, identification of possible reasons and corrective actions
can be initiated. Finally, monitoring generally is needed to satisfy
regulatory requirements.
Monitoring can be divided into three broad categories:
1. Continuous monitoring—involves continuous instrumental
measurement with continuous data recording; e.g., use of a temperature
sensor with a strip chart recorder.
2. Continuous measurement—involves continuous instrumental
measurement but requires the operator to monitor the data output manually;
e.g., use of a temperature sensor with a digital meter display.
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TABLE 4-3. EXAMPLE TIMED CONTROL CYCLE FOR BATCH MODE INCINERATOR
Cycle
Controlling
parameter/level
Resulting automatic
control action
Secondary
combustion chamber
preheat
Ignition
3. Combustion
4. Burndown
Manual start
Combustion chamber
temperature reaches
1100°F
Primary chamber
temperature reaches
1000°F
Secondary temperature
reaches high set
point, 2000°F_
Secondary temperature
reaches low set point,
1800°F
(Burner will cycle as
high/low set-points
are reached)
5 hours from ignition
High primary temper-
ature override
Secondary burner--
High fire
Secondary combustion
air-high level
Primary combustion
air—high level
Primary burner on
Primary burner off
Secondary burner
switches to low fire
Secondary burner
switches back to high
fire
Primary air switched
to high
Primary air switched
back to low
Cooldown
1 hour after override
activated
8 hours from ignition
16 hours from igni-
tion; cycle completed
Primary air switched
to high level
Secondary burner shuts
off
Combustion air blowers
shut off
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3. Manual monitoring—involves inspection by the operator on a
noncontinuous basis, e.g., visual stack gas opacity readings.
All of these techniques can be used to monitor the operation of batch type
incinerators. Continuous monitoring of operating parameters will, in most
cases, provide more information than manual monitoring. For example,
continuous opacity monitoring of stack gas opacity will provide opacity
data for the entire operating period and will provide a permanent record
of changes in opacity over the operating cycle and trends over time. On
the other hand, visual inspection of the stack gas opacity will provide
limited data, and a record will be available only if the observer records
the result.
The following operating parameters can be monitored:
1. Charge rate;
2. Combustion gas temperature;
3. Condition of the waste bed and burner flame;
4. Combustion gas oxygen level;
5. Combustion gas carbon monoxide level;
6. Combustion gas opacity;
7. Auxiliary fuel usage; and
8. Ash quality.
The techniques for monitoring each of these parameters are briefly
described in the following paragraphs.
Note that this section is not intended to recommend specific
monitoring requirements, but is intended to present the key parameters
which can be monitored and provide a brief description of how the
parameters can be monitored and what useful information monitoring can
provide. Chapter 6 further discusses actual instrumental monitoring
methods.
4.4.1.3.1 Charge rate. The weight of each charge can be recorded in
a log book. This procedure will help to indicate whether the rated
capacity of the incinerator is being exceeded. Note that incinerators are
designed for a specific thermal input. Since the heat value (Btu/lb) of
wastes will vary, the weight of a charge is not a true indicator of
whether the rated capacity is being exceeded. Variations in heating value
in the waste will need to be considered in determining charge size.
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Nonetheless, monitoring the weight of the charge will provide historical
data which can be used to make systematic modifications to operating
procedures, i.e., reduction of the charge rate by 20 percent to evaluate
the effect on resolving poor burnout problems. Monitoring this parameter
will require a scale or weigh bin which can be used to weigh individual
waste bags or transport carts.
4.4.1.3.2 Combustion gas temperature. The combustion gas
temperatures (primary and secondary) are critical operating parameters.
These parameters typically are monitored continuously using
thermocouples. Permanent strip chart (or data logger records) may be
kept; for small units only meters without permanent recordkeeping
typically are provided.
4.4.1.3.3 Condition of waste bed and burner flame. If viewports are
provided in each chamber, the operator can view the flame pattern and the
waste bed. Visual observation of the combustion process provides useful
information on the burner operation (i.e., potential problems such as
flame impingment on the refractory, or smoking of the secondary burner
flame can be identified) and on the combustion process in general (i.e.,
quantity and condition of remaining waste charge can be identified).
Viewports should be sealed glass covered by blastgates. "Inspection
doors" which open the chamber to atmosphere should not be used for viewing
the combustion process because these pose safety problems and affect the
combustion air control.
4.4.1.3.4 Combustion gas oxygen level. The combustion gas oxygen
concentration is a direct measure of the excess-air level. Although this
measurement is not essential, it provides real-time information about
changing conditions in the combustion chamber. Typically, the oxygen
level of the combustion gas exiting the secondary chamber is used to
assure that excess air is always available for complete combustion. A
continuous oxygen monitoring system typically is used (see Chapter 6).
However, a portable instrumental measurement system also can be used
occasionally for monitoring oxygen levels to confirm proper operation or
to provide information necessary for adjusting combustion air dampers.
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4.4.1.3.5 Combustion gas carbon monoxide level. Carbon monoxide is
a product of incomplete combustion; excessive levels indicate that a poor
combustion condition exists. The CO concentration of the combustion
chamber effluent can be monitored continuously to alert the operator to
poor combustion conditions. An instrumental CO monitoring system
generally is used for this procedure (see Chapter 6). Alternatively, a
portable instrumental measurement system can be used to make occasional
measurements of CO to monitor performance. As with the oxygen
measurements, this approach often is used to check performance in
conjunction with maintenance or adjustment of combustion control level
settings.
4.4.1.3.6 Combustion gas opacity. Combustion gas opacity provides an
indirect measurement of particulate matter concentration in the stack gas;
hence opacity is an indicator of incinerator performance. As particulate
concentration increases, so does the opacity. Continuous emission
monitoring systems (CEMS) for measuring opacity (referred to as
"transmissometers") are available (see Chapter 6). An alternative, and
simpler monitoring technique, is visual observation of the stack
emissions. The opacity of the stack gas can be determined accurately by a
trained observer. Even an untrained observer can detect gross changes in
stack gas opacity and can use visual observations to note combustion
problems.
4.4.1.3.7 Fuel usage. Monitoring fuel usage provides historical
data for identifying maintenance problems and for identifying the need for
adjustments to control system settings to increase efficiency. Fuel usage
can be monitored with a simple metering system. Fuel usage can than be
determined by logging meter readings or continuously recording the
metering system's output.
4.4.1.3.8 Ash quality. Ash quality is one indication of combustion
performance. Visual inspection is the simplest means of determining ash
quality and incinerator performance. For example, large pieces of
uncombusted materials (e.g., paper) indicate very poor ash quality. The
operator should inspect the ash visually and record comments on ash
quality in a log book routinely.
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For a more technical determination of ash quality, a chemical
analysis of a sample of the ash can be conducted. The amount of
combustible materials remaining in the ash can be determined by a
laboratory test which subjects a sample of the ash to a combustion
atmosphere and then determines the weight loss. This procedure measures
the ash's "burnout" quality. A 100 percent "burnout" means no volatile or
combustible materials remain in the ash; some incinerators are capable of
90 percent burnout. Occasional checks of ash burnout are useful for
monitoring performance of the incinerator.
4.4.2 Intermittent-Duty. Controlled-Air Incinerators
Intermittent-duty, controlled-air incinerators typically are used for
"shift" type operation. The incinerator must be routinely shutdown for
ash removal. Hence, there is a distinct operating cycle. The main
feature which distinguishes this type incinerator from the batch
incinerator is the charging procedures which are used. The charging
system is designed to accommodate multiple charges safely throughout the
operating cycle rather than rely on a single batch charge at the beginning
of the operating cycle. Either manual or automated charging systems can
be used.
4.4.2.1 Operation.
4.4.2.1.1 Ash removal. The residual ash from the previous
operating cycle must be removed before a cycle can be initiated. Ash
removal procedures are essentially the same as those described in
Section 4.3 for batch mode incinerators.
4.4.2.1.2 Startup. Before the operator initiates startup, proper
operation of the primary and secondary burners and combustion air blowers
should be checked according to manufacturer's instructions. The following
steps are conducted during startup:
1. The primary and secondary burner(s) are ignited, and preheat of
the combustion chambers is initiated. The manufacturer should be
consulted regarding proper preheat procedures, since improper preheat can
damage the refractory.
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2. The secondary chamber must reach a predetermined temperature
(e.g., 1800°F) before the incinerator is ready for charging; and
3. After the predetermined secondary chamber temperature is
attained, the primary and secondary combustion air blowers are
activated. The incinerator is ready to be charged.
4.4.2.1.3 Waste charging. Stable combustion can be maintained most
readily with a constant thermal input to the incinerator. Feeding too
much waste in a charge causes the incinerator to overload. These
overloads can result in poor burndown (because of waste pile buildup on
the hearth) or can cause excessive emissions because the rapid generation
of volatiles overloads the capacity of the secondary chamber. Feeding too
little waste results in inadequate thermal input and consequent excessive
auxiliary fuel use.10 A charge frequency and quantity recommended by two
manufacturers is 15 to 25 percent of the rated capacity (Ib/h) at 10 to
15 minute intervals.10'11 Another rule of thumb is to recharge the
incinerator after the previous charge has been reduced by 50 to 75 percent
in volume, determined by observation of the waste through the view ports
or operating experience.11 Charging volume and frequency will vary with
waste composition, and the operator must use some judgment to determine
appropriate rates.
The temperature profile of a combustion chamber is a picture of how
the temperature in the chamber fluctuates during the course of the
incineration process. The variations in temperature are shown on the
strip or circular chart recorder that records the temperatures measured by
the thermocouples in the combustion chambers. The temperature
fluctuations are affected by the frequency of waste charging and the size
of the charge. Insufficient or infrequent charging may cause the
temperature to become too low and necessitates the use of auxiliary fuel
to help maintain the desired set point temperature. Charging too much
waste may cause a rapid increase in secondary combustion chamber
temperature if the waste has a high volatile content. On the other hand,
if the waste has a low Btu content or contains a lot of moisture,
overcharging may have the effect of first decreasing the primary
combustion chamber temperature (while the moisture is being volatilized)
before a temperature increase is noted. Charging on a regular basis with
4-35
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the same volume of waste in each charge helps to "flatten" the temperature
variation and allow proper combustion while preventing refractory damage
and excessive auxiliary fuel consumption. Monitoring the temperature
profile of the combustion chambers will assist in determining the proper
charging rates.
After the last charge of the day is completed, the incinerator is set
to initiate the burndown cycle. The limiting factor on how long the
charging period can be sustained without initiating the burndown cycle is
the degree of ash buildup on the hearth. Typically the charging period is
limited to 12 to 14 hours.^
4.4.2.1.4 Burndown. The burndown cycle is essentially the same as
described for batch incinerators and is initiated after the last charge of
the day is made. For intermittent-duty incinerators the burndown sequence
can be initiated manually or may be initiated automatically. One manufac-
turer's control system is designed to include a control timer which is
activated by the charging door.11 Whenever the charging door is opened
and then closed, the burndown timing cycle is initiated by resetting the
burndown timer to a preset time-period, e.g., 5 hours (the actual length
of the burndown time is determined by experience with waste stream).
4.4.2.1.5 Cooldown. The cooldown period is the same as for batch
incinerators.
4.4.2.2 Automatic Controls. The parameters which can be controlled
automatically for intermittent-duty controlled-air incinerators are
essentially the same as those already discussed for the batch-operated
incinerators. The automatic control techniques used also are essentially
the same. Either timed sequences with high/low burner and air settings or
control systems which have fully modulated burner and air controls that
are continually adjusted based on control feedback (e.g., temperature) can
be used. For intermittent-duty units, the charging rate can be controlled
automatically if an automatic mechanical charging system is provided with
the unit. Automatic control for a ram feed charger consists of a timing
sequence which will initiate the charging sequence at regularly timed
intervals. The size of the charge is controlled by the volume of the feed
hopper. An override on the automatic feeder can be provided so that the
control system will not allow a charge to be fed at the regular interval
4-36
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if certain conditions are not met. For example, if the primary chamber
temperature exceeds a high level set point, the incinerator is not yet
ready for another "fuel" charge and the charging cycle will not initiate.
4.4.2.3 Monitoring. The operating parameters that can be monitored
for intermittent-duty incinerators are the same as those parameters
discussed in Section 4.4.1.3 for batch incinerators. The same monitoring
techniques generally apply. However, continuous monitoring and recording
of the ignition and combustion chamber temperatures have added importance
for intermittent-duty incinerators. The trends in these measured values
are useful to the operator in determining the appropriate charging
frequency and in adjusting the charging frequency as waste characteristics
change. Similarly, the use of appropriate viewports has added
significance in making decisions on charging frequency based upon
appearance of the waste bed.
4.4.3 Continuous-duty. Controlled-Air Incinerators
Continuous-duty incinerators have the capability of continuously
removing the ash from the incinerator hearth. Consequently, the
incinerator can be operated at a near-steady-state condition by
continuously charging the unit at regularly timed intervals and similarly
by removing the ash at regularly timed intervals.
4.4.3.1 Operation.
4.4.3.1.1 Startup. Startup procedures for continuous-duty
incinerators are essentially the same as for the intermittent-duty
incinerators. The chambers are first preheated before the initial charge
is loaded to the incinerator. The manufacturer should be consulted
regarding proper preheat procedures, since improper preheat can damage the
refractory.
4.4.3.1.2 Charging. To approach steady state operation, consistently
sized charges should be fed at regularly timed intervals. Practically
speaking, continuous-duty incinerators are likely to be more automated
than the types of units previously discussed. Continuous-duty
incinerators will include a mechanical feed system, which may be fully
automated so that charges are automatically fed at regularly timed
intervals.
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During operation, the waste bed/ash bed is typically moved through
the incinerator by one of two methods. In the first method, the waste bed
is continually pushed towards the back end of the chamber when each new
waste charge is pushed into the incinerator by the feed ram. In the
second method, where the incinerator hearth is exceptionally long, the
hearth is built in a stepped fashion, and special ash rams are provided
for pushing the ash from one step to the next step. Ultimately, in both
systems, the ash is pushed off the hearth into an ash discharge chute.
During operation, the operator must assure that the ash is being
removed from the system. For manual ash removal systems, an ash bin must
be emptied routinely. The ash bin is located inside a sealed chamber at
the end of the ash discharge chute or is directly sealed to the combustion
chamber ash discharge chute. For fully automated ash systems, the ash is
mechanically removed by a rake or conveyor from a water quench pit located
at the end of the ash discharge chute. For these systems, the operator
need only monitor the ash discharge system to assure that no mechanical
problems have developed and to assure that the quench pit water level is
maintained.
4.4.3.1.3 Shutdown. Shutdown of the incinerator involves stopping the
charging process and maintaining temperatures in the combustion chamber
until the remaining waste burns down to ash and is finally discharged from
the system in the normal manner.
4.4.3.2 Automatic Controls. The parameters which can be controlled
automatically for this type unit are essentially the same as those for the
intermittent duty unit. However, when separate ash transfer rams are a
part of the system, ash removal may also be automatically controlled. If
the waste feed system is on an automatically timed sequence, the ash
removal system likely will be integrated into the timed sequence.
The operating controls for the parameters discussed in Section 4.2.2
are more likely to be fully automated for continuous-duty incinerators
than for batch units, simply because of the size and frequency of use of
the units. Automated controls relieve the operator from the burden of
continuously making adjustments.
4.4.3.3 Monitoring. The operating parameters that can be monitored
for continuous-duty incinerators are the same as those parameters
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discussed in Section 4.4.2.3 for intermittent-duty incinerators. The use
of automatic/mechanical feed systems simplifies the monitoring of waste
feed charge frequency (and consequently volume). A recording indicator
can be installed that indicates how frequently the waste feed charge
system is activated. This information can be used to provide a rough
estimate of the charging rate (Ib/h) for the unit and also may be helpful
in diagnosing other operational problems, such as reasons for temperature
excursions.
4.4.4 Multiple-Chamber Incinerators
Typically, multiple-chamber incinerators are used to burn
pathological waste. However, other medical waste including red bag waste
are sometimes burned in these units; when burning red bag waste special
precautions should be taken during charging to assure the incinerator's
capacity is not exceeded. Typical applications of multiple-chamber
incinerators include batch or intermittent operation; continuous-duty
operation automatic ash removal is atypical. Operation of these units is
discussed briefly below.
4.4.4.1 Operation.
4.4.4.1.1 Ash removal. The residual ash from the previous operating
cycle must be removed before a cycle can be initiated. Ash removal
procedures are essentially the same as those described in
Section 4.4.1.1.1 for batch mode controlled-air incinerators.
4.4.4.1.2 Startup. Startup of the excess-air incinerator is similar
to startup for the batch-mode, controlled-air incinerators. The secondary
chamber is first preheated to a predetermined chamber temperature. The
incinerator is then charged with the waste.
4.4.4.1.3 Charging. Multiple-chamber incinerators may be either batch
or intermittent duty and may be charged manually or with a mechanical
loading device. Because of the significant difference in heat contents
between pathological waste and red bag waste and because incinerators are
designed to burn a waste with a specific heat input, the proper charging
(addition of fuel) procedures are different for different wastes.
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Pathological waste has a low heat content, a high moisture content,
and a low percentage of volatiles. Consequently, it must be constantly
exposed to the auxiliary burner(s') flame(s) to be combusted. The
following proper pathological waste charging procedures are recommended:
1. The waste should be placed on the hearth in an even layer that
provides maximum exposure to the burner(s) flame(s). The waste should not
be deeply piled.
2. Recharging the incinerator should not be done until considerable
reduction in volume (greater than 75 percent) of the previous charge has
occurred.
3. When recharging the incinerator:
a. Turn off the primary burner (some units may have an interlock
system that automatically turns the burner off when the charge door is
opened);
b. Place the fresh charge in a single, layer on the hearth so that
the burner(s) impinge on the waste; and
c. Close the charge door before restarting the primary burner.
The heat content of red bag waste will be variable depending on the
contents of the bag. Proper operation of the incinerator dictates that:
(1) sufficient waste should be charged to the unit to sustain the desired
temperature without excessive use of the primary burner; and (2) to
maintain the primary chamber temperature below the upper limit and to
prevent emissions, the charge rate should not exceed the capacity of the
incinerator at any time. Obviously, if the incinerator was designed for
pathological waste, then a significantly smaller red bag waste charge
should be made than is typically made of pathological waste. The
following guidelines are recommended for charging red bag waste into a
multiple-chamber incinerator:
1. Use of frequent, small batches rather than one large batch. The
objective is to avoid causing a rapid release of volatile compounds that
exceeds the combustion capacity of the incinerator. The frequency and
size of each charge will be determined by the incinerator being operated
and the type of waste. A recommended procedure is to charge about 1/10
the rated capacity (Ib/h) every 6 minutes.
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2. Keep a fairly consistent waste bed in the incinerator. The
incinerator should not be jammed full, nor should it be empty.
3. Avoid "stuffing and burning" in the incinerator; that is, do not
fill the incinerator chamber to full capacity, floor to ceiling, ignite
the waste, and allow the incinerator to operate unattended.
4. When recharging the incinerator:
a. Turn the primary burner off (some units may have an interlock
system that automatically turns the burner off when the charge door is
opened);
b. The partially burned waste from the previous charges should be
pushed towards the back of the hearth with a rake; and
c. The new waste charge should be fed to the front end of the hearth
(near the charge door). This procedure allows good exposure of the
partially combusted waste to the overfire air and allows a good flame from
the waste bed to be maintained. On the other hand, if cold, newly charged
waste is thrown on top of the existing waste bed it partially smothers the
burning bed which can result in increased emissions.
5. If the incinerator has a grate, it is important that the entire
grate be covered with a waste bed.
4.4.4.1.4 Operation. When burning pathological waste, the primary
burner is operated throughout the combustion cycle and thermal output
should be relatively constant without rapid fluctuations. The primary
chamber combustion air is preset to maintain a constant excess-air level,
and primary chamber temperature is controlled by modulating the primary
burner. Since the pathological waste does not contain large amounts of
combustible volatiles, secondary chamber combustion settings also will
remain relatively constant. The combustion air damper settings and burner
settings necessary to attain the desired secondary chamber temperature and
excess-air levels are set and normally do not need to be adjusted.
Temperature control normally is achieved only by modulating the primary
burner settings.15
Modulating the primary burner does not offer the same degree of
control over temperature as the adjustment of air supply. If a multiple-
chamber incinerator was overcharged with red bag waste, modulation of the
primary burner (or even shutdown of the burner) would not reduce the
4-41
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temperature because once ignited, the red bag waste will continue to burn
out of control with the large excess-air level carrying excessive unburned
material to the secondary chamber. In such a scenario, the secondary
chamber would be unable to respond to such a high carryover of
volatiles. Therefore, while red bag waste may be burned in a multiple-
chamber incinerator, the potential exists for high temperatures that may
damage the unit and for high emissions if the unit is overcharged. Some
multiple-chamber units may have an automatically modulated air supply
system that adds air if the temperature rises (cools the combustion
process) or restricts air if the temperature falls. However, the large
excess-air level in the primary chamber will still produce carryover of
particulate matter to the secondary chamber. Therefore, multiple-chamber
incinerators are better suited to burn pathological waste than they are to
burn red bag waste because of the relatively stable and constant heat
output of pathological waste and the fact that pathological waste
combustion is controlled entirely by the firing of the primary burner
(i.e., pathological waste cannot sustain combustion without the primary
burner and will not burn out of control as the red bag waste can).
4.4.4.1.5 Burndown. There is no burndown period in the operation of
multiple-chamber incinerators. The degree of burnout achieved is dictated
by the length of time that the primary burner is left in operation after
the last charge. After complete destruction of the waste has been
achieved (as noted by visual observation through a viewport), the primary
burner is shut down. The secondary burner is not shut off until all
smoldering from residual material on the hearth in the primary chamber has
. 1 5
ceased.
4.4.4.1.6 Cooldown. After all smoldering in the ignition chamber has
ceased, the secondary burner is shut down, and the incinerator allowed to
cool.
4.4.4.2 Automatic Controls. The primary operating parameters which
are automatically controlled are the primary and secondary chamber
temperatures. Control of the temperatures is achieved by modulating the
burner rates. The primary and secondary combustion air levels typically
are not automatically controlled, but are preset. Incinerator draft
typically is controlled by a barometric damper. Charging rate also is not
likely to be controlled automatically in this application.
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4.4.4.3 .Monitoring. The same operating parameters that are
monitored on control!ed-air incinerators can be manually or continuously
monitored during operation of the multiple-chamber unit.
4.5 ADD-ON AIR POLLUTION CONTROL SYSTEMS
Key operating parameters and procedures for wet scrubbers, fabric
filters, and dry scrubbers are discussed in this section. Addition of an
air pollution control system (ARCS) to a hospital waste incinerator
increases the number of operating parameters the operator must control,
monitor, and adjust. Furthermore, addition of an ARCS to an incinerator
significantly modifies how at least one important incinerator operating
parameter is controlled; this parameter is the incinerator draft.
Operation of the ARCS will require use of an induced draft (ID) fan to
provide the necessary airflow through the system. Natural draft control
will no longer be applicable; gas flow through the system will be
controlled by the ID fan.
4.5.1 Wet Scrubbers
22_2i»
4'5-1-1
-------
packed-bed scrubbers. However, relatively large L/6 ratios are required
to adequately cover the packing media and create a large wetted surface.
The L/G ratio is the key performance parameter for packed-bed scrubbers
used for acid gas control with 10 to 15 gal/Macf recommended.23 Spray
towers also require a L/G ratio of 5 to 20 gal/Macf.23 While these are
the most important key performance parameters, there are several key
parameters for each scrubber type that can be monitored and adjusted by
the operator to achieve the desired performance of the unit. Table 4-4
lists the key parameters and identifies typical operating ranges for
venturi scrubbers, packed-bed scrubbers, spray towers, and mist
eliminators for application to hospital waste incineration systems.
Control of scrubber liquor pH is important to minimize corrosion from
acid or alkaline conditions. A scrubber liquor pH range of 5.5 to 7.0 is
22
recommended. A pH in this range represents neutral water. A lower pH
indicates acidic water which can cause corrosion. Higher pH values may
result in scaling.
Turbidity of the scrubber liquor feed also is an important operating
parameter with regard to maintaining particulate matter control
efficiencies. High turbidity (a measure of the dissolved and suspended
solids in the liquid) can result in increased particulate matter emissions
and pluggage of nozzles.
Proper design and operation of the mist eliminator system is
necessary for maintaining particulate matter control efficiencies.
Scrubber system design sometimes includes a clean water spray for rinsing
mesh pad eliminators and maintaining performance.
4.5.1.2 Scrubber Operation. Proper operation of a scrubber requires
that the operator (1) establish a fixed liquid flow rate to the scrubbing
section, (2) initiate gas flow through the system by starting a fan, and
(3) set up the liquid recirculation system so that suspended and dissolved
solids buildup does not create operating problems. Once the system has
been started and operation has stabilized, little additional operator
attention will be needed. Operators should refer to the instruction
manual provided by the scrubber manufacturer for adjustment of site-
specific operating conditions.
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TABLE 4-4. WET SCRUBBER PERFORMANCE PARAMETERS FOR
HOSPITAL WASTE INCINERATORS '
Parameter
Typical
rangea
Units of
measure
— — — — ^— _^_
Operating
range13
Venturl scrubbers
Pressure drop 15-60
Liquid feed ratec >35
Liquid-to-gas ratio 4-10
Liquid feed pressure 20-60
Liquid feed turbidity 1-10
Gas flow ratec >5,000
Liquid feed pH 5-10
Packed-bed scrubbers
Pressure drop 1-5
Liquid feed ratec >5
Liquid feed pH 5.5-7.0
Liquid-to-gas ratio 10-30
Liquid feed pressure 20-60
Gas flow rate3 >5,000
Liquid feed turbidity 1-10
Spray towers
Pressure drop 0.5-3.0
Liquid-to-gas rate 5-20
Mist eliminator
Pressure drop 1-3
Liquid feed ratec >5
Liquid feed pressure 20-60
Liquid-to-gas ratio 1-6
Liquid turbidity 0-3
in. w.c.
gal/min
gal/Macf
Percent suspended
solids
acfm
in. w.c.
gal/min
PH
gal/Macf
acfm
Percent suspended
solids
in. w.c.
gal/macf
in. w.c.
gal/min
gal/Macf
Percent suspended
20-50
7.10
20-60
0-3
5.5-7.0
5.5-7.0
15.25
30-60
1-3
i_3
5.20
i_3
30-60
2-3
0-0.5
Gas flow rate0
Liquid feed pH
>5,000
5-10
3U 1 1 US
acfm
PH
7
The typical range is the range of operating parameters that can exist on
ba broad range of source categories.
The operating range is the range of operating parameters specified by
manufacturers for combustion sources similar to hospital waste
incinerators.
Values, or range of values, are dependent on the size of the scrubber
system.
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4.5.1.2.1 Scrubber Startup. The scrubber should be started prior to
charging waste feed to the incinerator but not necessarily prior to
preheat. The specific manufacturer's startup instructions should be
followed. The following procedures in sequence are typical during startup
of a scrubbing system to insure proper operation:
1. Turn on the liquid recirculation system or liquid supply(s) to
the scrubber(s) and mist eliminator.
2. Adjust the liquid flow rates to those specified in the
instructions supplied by the scrubber manufacturer.
3. If the induced draft or forced draft fan feeding the scrubbing
system has a damper installed at its inlet or outlet, close the damper.
4. Start the induced draft or forced draft fan.
5. If the system is equipped with a damper, gradually open the
damper until the proper gas flow rate is established.
6. Again recheck the liquid flow rate(s) and adjust as necessary.
7. Check the differential pressure across the scrubber and compare
with the design pressure drop specified in the operating manual. If the
differential pressure is too low across the scrubber, either the liquid
rate is too low or the gas flow rate is too low. To correct this
condition, either increase the gas flow rate by opening a damper, or
increase the liquid flow rate to the scrubber. If the scrubber is a
venturi unit with an adjustable throat, the pressure can be increased by
decreasing the throat area.
8. Initiate the liquid bleed to treatment or disposal as specified
in the manufacturer's manual. If the bleed is taken by an overflow from
the recirculation tank, the flow rate at this point is established by the
rate at which makeup water is introduced to the recirculation tank. The
manufacturer's manual should show the anticipated water evaporation rate
in the scrubbing system. If, as an example, the evaporation rate is
1 gallon per minute, and if you wish to establish a bleed rate of 1 gallon
per minute, it will be necessary to feed 2 gallons per minute of total
water to the recirculation tank. The bleed rate is determined by the rate
at which the solids buildup in the scrubbing system. These solids can be
either suspended or dissolved solids or both. A scrubber is capable of
handling a maximum of 3 percent (weight) suspended solids, and it is
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22
suggested that the dissolved solids not exceed 10 percent (weight).2
Based on design data, a recommended bleed rate from the system should be
provided by the manufacturer. The operator should combine this figure
with the evaporation figures to give a total recommended makeup water rate
to the recirculation tank if an overflow type bleed system is used. If a
bleed system is provided from a slip stream off the pump feeding the
venturi scrubber, liquid makeup is normally provided by a level control
device in the recirculation tank. The flow rate required will be the same
as the flow rate required for the overflow bleed system. However, it is
only necessary to insure that adequate water supply is available to the
level control device on a continuous basis.
4.5.1.2.2 Scrubber shutdown. To shut the system down without
overloading the fan or causing any damage to the scrubbing equipment, the
following procedures in sequence are typical:
1. Shut off the induced draft or forced draft fan feeding the
scrubbing system.
2. Wait until the fan impeller has stopped rotation and then shut
off the scrubbing water recirculation pump.
3. Shut off the makeup water supply system.
4.5.1.3 Automatic Control. Key operating parameters which may be
automatically controlled for a scrubber system include:
1. Venturi pressure drop;
2. Scrubber liquid flow rate;
3. Scrubber liquid pH; and
4. Gas flow rate.
The venturi pressure drop is the key performance parameter for
venturi scrubbers and the scrubber system can be designed to monitor this
parameter and provide automatic control based on adjustment of the venturi
throat.
For Venturis, packed beds, and spray towers, the scrubber liquid flow
rate is a key parameter. This parameter usually remains constant during
operation but, nonetheless, can be designed for automatic flow rate
control.
When caustic materials are added to the scrubber liquid, control of
scrubber liquid pH is necessary to prevent damage to the scrubber
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equipment. A pH meter is used to monitor the pH of the liquid. The
output of the meter is used to control the amount of caustic material
added to the scrubber sump.
Gas flow rate through the system can be controlled automatically by
monitoring and adjusting fan rpm for a variable speed fan, or by
monitoring and controlling fan static pressure using a damper for a
constant rpm fan. Gas flow rate is controlled to maintain the desired
draft in the incinerator combustion chambers, as well as the desired
pressure drop across the scrubber.
4.5.1.4 Monitoring. Scrubber parameters which can be monitored by
the operator include:
1. Venturi pressure drop;
2. Scrubber liquid flow rate;
3. Scrubber liquid pH;
4. Fan static pressure, rpm, or amperage; and
5. Gas inlet temperature.
The first four items listed were discussed in the section above with
regard to using these parameters for automatic system control. Gas inlet
temperature is of interest to the operator because excessive temperatures
can damage the pollution control equipment, especially in systems where
fiber reinforced plastic materials are used. A thermocouple is used to
monitor the gas inlet temperature.
4.5.2 Fabric Filters25"27
4.5.2.1 Key Operating Parameters. The key operating parameters for
fabric filter control systems are summarized in Table 4-5. To prevent
damage to the system the gas temperature must be maintained in a range
between the dewpoint of the gas and the upper temperature limit of the
fabric. The upper operating temperature of the fabric will depend on the
fabric type; the manufacturer should be consulted regarding the upper
temperature limit.
The pressure drop across the system for pulse jet baghouses typically
is maintained within a range of 5 to 9 in. w.c. Pressure drop gives an
indication of filter cake formation. Filter cake formation is dependent
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TABLE 4-5. KEY OPERATING PARAMETERS FOR FABRIC FILTER CONTROL SYSTEMS
Parameter Operating range26
Upper gas temperature, °F Below upper limit for fabric4
Lower gas temperature, °F Above dewpointb
Pressure drop, in. w.c. 5-9
Cleaning air pressure, psig 60-100
aThe upper temperature limit will be dependent on fabric type. Consult
.manufacturer.
The gas temperature usually is maintained above 300°F.
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on the effectiveness of the bag cleaning cycle. The frequency and dwell
of bag cleaning must be set to maintain the desired pressure drop. The
cleaning pressure must be maintained at sufficient pressure to properly
clean the bags; the desired range is 60 to 100 psig.25
4.5.2.2 Operation of Fabric Filters. While the performance of a fabric
filter is dependent on proper design and the timely detection of upset
conditions, proper operation and preventive maintenance procedures dictate
satisfactory long-term performance. This section discusses general
operating procedures that can minimize unexpected malfunctions and improve
the performance of the fabric filter. Preventive maintenance practices
are discussed in Chapter 5. Proper operating procedures are important
during startup, normal operation, shutdown, and emergency conditions.
4.5.2.2.1 Startup Procedures. Prior to operation of new fabric
filters, a complete check of all components is recommended including the
cleaning system, the dust-discharge system, and the isolation dampers and
fans. Clean, ambient air should be passed through the system to confirm
that all bags are properly installed. New bags are prone to abrasion if
subjected to high dust loadings and full-load gas flows, particularly
during the initial startup before new bags have the benefit of a dust
buildup cake to protect the fibers from abrasion or to increase their
resistance to gas flow. Full gas flow at high dust loadings can allow the
particulate matter to impinge on the fabric at high velocity and result in
abrasion that may shorten bag life. In addition, the dust may penetrate
so deeply into the fabric that the cleaning system cannot remove it, and a
"permanent" pressure drop results. Bag abrasion may be prevented by
either (1) initially operating the incinerator at a low throughput and
reduced gas volume to allow the dust cake to build gradually or (2) pre-
coating the bags to provide a protective cake before the incinerator
exhaust is introduced. The baghouse manufacturer should be consulted
regarding proper startup procedures and acceptable precoat materials.
The fabric filter should not be operated at temperatures approaching
the dewpoint of water and/or the hydrochloric acid formed by the
combustion of chlorinated plastics because if the dewpoint is reached,
serious operating problems may arise. Warm moist gas that is introduced
into a cool or cold fabric filter will cause condensation on the bags or
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on the fabric filter shell. Condensation can cause a condition known as
"mudded" bags where the bags are blinded by dust and moisture. The acid
dewpoint depends on the amount of moisture and acidic material in the gas
stream. Condensation of acid can cause corrosion of the fabric filter
components, sticky particulate and cake-release problems, and acid attack
on some fabrics. Preheating the fabric filter to a temperature above the
acid dewpoint will prevent condensation and enhance fabric filter
performance. Since the incinerator goes through a warmup period using
natural gas or fuel oil burners prior to waste combustion, the problems
associated with condensation of water or hydrochloric acid are unlikely to
occur.
Unstable combustion during startup can cause some carbon carryover,
which may result in a sticky particulate. This situation creates the
potential for fires in the fabric filter when a combustion source and an
adequate oxygen supply are available. Therefore, during startup, the
fabric filter hoppers that collect the particulate should be emptied
continually. More importantly, unstable combustion conditions during
startup should be minimized by going through proper incinerator startup
procedures.
4.5.2.2.2 Normal operating procedures. Under normal conditions,
operation of the fabric filter is straightforward. The operator has to do
very little other than monitor the key parameters, as discussed later in
Section 4.5.2.4. Combustion gas flow rate through the system must be
maintained at the level necessary to maintain negative draft in the
combustion chambers.
4.5.2.2.3 Shutdown procedures. The top priority during shutdown of a
fabric filter is avoiding dewpoint conditions. Bag cleaning and hopper
emptying are lower-priority items.
When processes operate on a daily cycle, the last operation of the
day should be to purge moisture and acidic materials from the fabric
filter without passing through the dewpoint. In the case of a hospital
waste incinerator, the operator should leave the secondary chamber burner
on for a few minutes after combustion is completed to remove moisture from
the fabric filter. Ambient air could then be drawn through the system to
purge the remaining combustion products.
4-51
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After shutdown, the fabric filter should be allowed to go through a
complete bag cleaning cycle. This procedure will help prevent blinding of
the bags. Additionally, continuing to operate the hopper discharge system
while the cleaning system is in operation will minimize the potential of
hopper pluggage.
When emergency conditions are encountered such as high temperatures,
spark detection, or other process upsets, the fabric filter is usually
bypassed to prevent damage to the system. If a fire occurs in the hopper,
the addition of water under oxygen-starved conditions is not advisable
because the water will hydrolyze forming hydrogen and causing the
potential for an explosion inside the fabric filter. Both the fabric
filter manufacturer and insurance carrier should be contacted whenever a
known potential for fires/explosions exists.
Other process failures may necessitate only temporary bypassing of
the fabric filter, and operation can be restored in a matter of minutes.
In these cases, the fabric filter generally does not have to be shut down
completely and purged. If the upset cannot be corrected within a
reasonable amount of time, however, shutdown and the subsequent startup of
the fabric filter may then be necessary to prevent dewpoint problems.
It is important to note that bypassing the fabric filter during
startup, soot blowing, or an emergency may not be acceptable to the
applicable regulatory agency. Such occurrences should be investigated and
addressed during the design stages of development.
4.5.2.3 Automatic Controls. Operating parameters which are
controlled automatically for fabric filter control systems include the bag
cleaning cycle and the ash removal system.
The combustion gas flow rate through the system also can be
controlled automatically. Control is achieved by adjusting fan rpm's
(variable speed fans) or fan static pressure by way of a damper. Proper
gas flow through the system must be maintained to assure sufficient
negative draft in the combustion chambers. Reduction of the gas stream
temperature to the fabric filter typically is achieved by passing the
combustion gases through a waste heat boiler. Temperature monitoring
systems are available that will cause automatic bypass of the fabric
filter under high temperature conditions.
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4-5.2.4 Monitoring. A well-designed and maintained fabric filter
should provide adeguate control of particulate matter emissions.
Parameters that can be monitored to maintain optimum performance include
opacity, pressure drop, fan motor amperage, and temperature.
Opacity readings can help to determine the presence of pinholes and
tears in bags and, in some cases, the general location of the bag
failure. These visible emissions are usually the first indicator of poor
fabric filter performance. The failed bags should be replaced as
necessary.
The pressure drop across the fabric filter is another indicator of
poor performance. A high pressure drop outside the normal operating range
may indicate inadequate cleaning of the fabric, bag blinding, or excessive
gas volume through the system. In some cases, the pressure drop before
and after cleaning increases steadily as the bags age. Excessively low
pressure drop may indicate inadequate filter cake formation resulting from
too frequent cleaning.
When used in conjunction with the pressure drop across the fabric
filter, measurement of fan motor amperage also can provide an indication
of the gas flow rate. In general, an increase in current combined with an
increase in pressure drop indicates an increase in gas volume, and a
decrease in amperage reflects a decrease in gas volume. These changes,
however, must be normalized for temperature (density) changes because
temperature influences the energy required to move the gas through the
system.
High-temperature operations such as hospital waste incinerators
should be equipped with continuous strip chart recorders and high-
temperature alarms. The high-temperature alarms should provide some
margin for corrective action, i.e., set points of 50° to 75°F below the
high temperature limit of the fabric. The temperature alarm/recorder also
may be connected to an automatic damper system to control the temperature
or to bypass the fabric filter. Although some differential between the
maximum temperature and the alarm activation must be provided, the
temperature set point should not be so low that the alarm is continually
activated. The temperature indicator also will monitor against
excessively low temperatures and dewpoint problems.
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4.5.3 Spray Dryers7*
28
4.5.3.1 Key Operating Parameters. The key parameters that are
necessary for effective operation of a spray dryer are slurry feed rate,
slurry sorbent content, and the outlet gas wet and dry bulb
temperatures. Effective operation of a spray dryer system requires that
adequate sorbent is provided in the slurry for reaction with the acid
gases and that all slurry moisture is evaporated in a time frame that
allows for reaction with the acid gases. Drying that is too rapid can
reduce acid gas collection efficiency. Drying that is too slow will
result in solids buildup on the sides of the reaction vessel that will
further impede drying. The liquid slurry feed rate and sorbent content
should be balanced with the hot flue gas volume and acid gas content to
ensure the desired removal of acid gases and the timely evaporation of all
water. The recommended slurry sorbent content is 5 to 20 percent by
weight solids. The slurry moisture added to the flue gas serves to cool
and increase the moisture content of the gas stream. The difference
between the wet bulb and dry bulb temperatures gives an indication of the
saturation of the gas stream and the potential for evaporation of the
slurry moisture. As the slurry feed rate is increased, the wet bulb and
dry bulb temperature difference will decrease. The recommended wet
bulb/dry bulb outlet gas temperature difference (for Municipal Solid Waste
Systems) is 30° to 80°C (90° to 180°F).28
4-5.3.2 Spray Dryer Operation. The design specifications for the
dry scrubber should identify the sorbent-to-water ratio for the mix
tank. The sorbent content should be set at a level that will provide
ample sorbent for the range of acid gas concentration expected to occur.
Proper operation of the dry scrubber requires that the operator adjust the
slurry flow rate to the atomizer in the reaction vessel to maintain an
acceptable wet bulb/dry bulb temperature difference. If the wet bulb/dry
bulb temperature difference is too low, the slurry feed should be
decreased.
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4.5.3.2.1 Spray dryer startup. Startup of a spray dryer should
follow procedures that ensure evaporation of all slurry moisture in the
reaction vessel and that prevent condensation of moisture in the fabric
filter. One method of ensuring evaporation and prevention of condensation
in the fabric filter is to use auxiliary fuel firing in the incinerator to
bring the exhaust gas temperature up to the normal operating range before
injecting the slurry. Slurry injection should be initiated before
charging the incinerator with waste feed material. An alternative method
would be to gradually increase the slurry feed rate during startup to
maintain a 90° to 180°F wet bulb/dry bulb temperature differential.
4.5.3.2.2 Spray dryer shutdown. Proper shutdown procedures for spray
dryers should ensure that no liquid moisture remains in the spray dryer or
that condensation in the fabric filter does not cause bag blinding or
corrosion. Slurry remaining in the system after shutdown can cause solids
buildup. Also, the reaction products resulting from the neutralization of
the acid gases include highly corrosive salts such as NaCl and CaCl2.
After the waste material in the incinerator has been combusted, auxiliary
fuel firing should be used to maintain temperatures above saturation until
all sorbent is purged from the system. To prevent bag blinding and
reaction product salt corrosion that could occur in the presence of
condensation, the fabric filter should go through a complete cleaning
cycle to remove the filter cake after shutdown of the incinerator and
spray dryer.
4.5.3.3 Automatic Control. The most important key parameter from a
control standpoint is the slurry feed rate. The slurry feed rate
determines the amount of sorbent available for acid gas collection (along
with the sorbent content of the slurry) and the outlet gas wet bulb/dry
bulb temperatures. Slurry feed rate can be automatically controlled in
response to monitoring of HC1 outlet gas concentration or wet bulb/dry
bulb temperature. In less complex systems, the slurry sorbent content is
fixed and the slurry feed is automatically increased or decreased in
response to the outlet gas temperatures. Under conditions of low inlet
HC1 concentrations these systems will use excessive amounts of sorbent.
More complex systems are available that automatically adjust the sorbent
feed to the slurry mix tank in response to HC1 concentration and slurry
feed rate to the atomizer in response to outlet gas temperatures.
4-55
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4-5.3.4 Monitoring. Spray dryer parameters which can be monitored
by the operator include:
1. Sorbent feed to the mix tank;
2. Slurry feed rate to the atomizer;
3. Gas inlet temperature;
4. Gas outlet wet bulb and dry bulb temperature; and
5. HC1 and S02 outlet gas concentrations.
The most important parameters are the outlet gas HC1 concentration which
indicates the performance of the unit and the outlet gas wet bulb/dry bulb
temperatures which determine evaporation rate. As explained earlier, the
evaporation rate is important to ensure that adequate absorption time is
available for acid gas removal and that all moisture is evaporated prior
to leaving the reaction vessel.
4.5.4 Dry Injection
4.5.4.1 Key Operating Parameters. The key operating parameters for
a dry injection system are the sorbent injection rate and the particle
size of the sorbent. The sorbent injection rate should provide adequate
sorbent for neutralization of the acid gases and is dependent on the acid
gas content of the flue gas. The sorbent feed rate for dry injection
systems is usually three to four times the stoichiometric requirements.27
The acid gas/sorbent reaction requires that the acid gas come in
physical contact with the surface of the solid sorbent particles. To
maximize the efficiency of the collection process it is necessary to
maximize the surface area of the sorbent material. Because the surface
area-to-volume ratio increases with decreasing particle size, acid gas
removal efficiency increases with the decreasing particle size of the
sorbent. Generally, the sorbent feed should have a particle size where
90 percent by weight will pass through a 325 mesh screen.28
4.5.4.2 Dry Injection Operation. Dry injection systems are
relatively simple to operate compared to spray drying systems. The
particle size of the sorbent should be specified to the supplier. To
ensure that the particles do not agglomerate prior to injection, the
airflow rate in the pneumatic transfer line should be set and maintained
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at the manufacturer's specified rate. Proper airflow in the pneumatic
line will fluidize the sorbent particles and prevent agglomeration.
Sorbent injection rates for dry injection systems, as stated above, are
usually three to four times stoichiometric requirements. The large amount
of extra sorbent can handle moderate variations in inlet acid gas
concentrations. For systems that are not equipped with outlet acid gas
continuous monitors, the sorbent injection rate can be set at a constant
level or varied with flue gas flow rate. If the system is equipped with
an outlet monitor for HC1, the sorbent injection can be varied as needed.
4.5.4.2.1 Dry injection startup. There are no special considerations
for dry injection startup. At startup of the incinerator, sorbent
injection can be initiated.
4.5.4.2.2 Dry injection shutdown. The only special concern for
shutdown of a dry injection system is to put the fabric filter through a
cleaning cycle after sorbent injection is stopped. This prevents possible
blinding from condensation and reaction product salt damage to the fabric
filter components.
4.5.4.3 Automatic control. Dry injection systems can be equipped
with outlet gas HC1 continuous monitors. The sorbent injection rate can
be controlled automatically based on the outlet HC1 concentration.
4.5.4.4 Monitoring. Dry injection system parameters which can be
monitored by the operator include:
1. Sorbent injection rate;
2. Pneumatic transfer line airflow rate;
3. Flue gas flow rate; and
4. HC1 and S02 outlet gas concentrations.
4.6 REFERENCES FOR CHAPTER 4
1. Ontario Ministry of the Environment. Incinerator Design and
Operating Criteria, Volume II - Biomedical Waste Incinerators.
October 1986.
2. McRee, R. Operation and Maintenance of Controlled-Air
Incinerators. Ecolaire Combustion Products. (Undated)
3. U. S. Environmental Protection Agency Office of Solid Waste. EPA
Guide for Infectious Waste Management, EPA/530-SW-86-014 (NTIS
PB 86-199130). May 1986. *
4-57
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4. Letter from Ken Wright, John Zink Company, to J. Eddinqer
U. S. EPA. January 25, 1989. '
5. Personal conversation between R. Neulicht, Midwest Research
Institute, and J. Kidd, Cleaver-Brooks. February 22, 1989.
6. Personal conversation with representatives of the National Solid
Waste Management Association. December 15, 1988.
7. U. S. Environmental Protection Agency. Municipal Waste Combustion
Study: Combustion Control of Organic Emissions, EPA/530-SW-87-021C
(NTIS PB87-206090). June 1987.
8. Ecolaire Combustion Products, Inc. Technical Paper: Controlled Air
Incineration. (Undated)
9. Simonds Incinerators. Operation and Maintenance Manual for Models
751B, 1121B, and 2151B. January 1985.
10. Ecolaire Combustion Products, Inc. Equipment Operating Manual for
Model No. 480E.
11. John Zink Company. Standard Instruction Manual: John Zink/Comtro
A-22G General Incinerator and One-Half Cubic Yard Loader.
12. Brunner, C. Incineration Systems Selection and Design. Van Nostrand
Reinhold. p. 22. 1984.
13. Personal conversation between Roy Neulicht, Midwest Research
Institute and Larry Doucet, Doucet and Mainka Consulting Engineers.
November 29, 1989.
14. Doucet, L. C. Controlled-Air Incineration: Design, Procurement, and
Operational Considerations. American Hospital Association Technical
Series, Document No. 055872. January 1986.
15. Air Pollution Control District of Los Angeles County. Air Pollution
Engineering Manual, AP-40. (NTIS PB 225132). U. S. Environmental
Protection Agency. May 1973.
16. American Society for Testing and Materials. ASTM Standard
01709-75. Philadelphia, Pennsylvania. 1975.
17. Consumat Systems, Inc. Technical Data Sheet. (Undated)
18. Ecolaire Combustion Products, Inc. Equipment Operating Manual for
Model No. 2000TES.
19. Personal conversation between Roy Neulicht, Midwest Research
Institute, and Steve Shuler, Ecolaire Combustion Products.
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20. Ashworth, R. Batch Incinerators—Count Them In. Technical paper
prepared for the National Symposium of Infectious Wastes
Washington, D.C. May 1988.
21. Cross, F. and J. Tessitoire. Incineration of Hospital Infectious
Waste. Pollution Engineering. November 1988.
22. Engineering Manual With Operation and Maintenance Instructions
Anderson 2000, Inc. Peachtree City, Georgia. (Undated)
23. Joseph, J. and 0. Beachler. APTI Course SI:412C, Wet Scrubber Plan
Review - Self Instructional Guidebook. EPA 450/2-82-020. U S
Environmental Protection Agency. March 1984.
24. U. S. Environmental Protection Agency. Wet Scrubber Inspection and
Evaluation Manual. EPA 340/1-83-022. (NTIS PB85-149375)
September 1983.
25. U. S. Environmental Protection Agency. Fabric Filter Inspection and
Evaluation Manual. EPA 340/1-84-002. (NTIS PB86-237716)
February 1984. '*
26. Beachler, D.S. APTI Course SI:412, Baghouse Plan Review. U. S
Environmental Protection Agency, EPA-450/2-82-005. April 1982.
27. U. S. Environmental Protection Agency, Operation and Maintenance
Manual for Fabric Filters, EPA/625/1-86/020. June 1986.
28. Richards Engineering, Air Pollution Source Field Inspection Notebook:
Revision 2. Prepared for the U. S. Environmental Protection Agency,
Air Pollution Training Institute. June 1988.
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5.0 MAINTENANCE
Efficient operation of a hospital waste incinerator and any
associated air pollution control device requires an aggressive preventive
maintenance (PM) program. Effective maintenance will prolong the service
life of the equipment, reduce the frequency of upset conditions and air
pollution episodes, and save the hospital money by avoiding costly
repairs. Information on the types and frequency of equipment inspections
and maintenance procedures for incinerators, wet scrubbers, and fabric
filters-is provided in this chapter. The information provided represents
only general guidance and should not be substituted for tne equipment
manufacturer's recommended maintenance schedule. Recordkeeping, which is
an important part of a PM program is mentioned briefly below and is
discussed more fully in Chapter 8. Records of maintenance activities can
help pinpoint problems and show trends in maintenance activities that may
increase the life of the equipment and minimize emissions.
5.1 HOSPITAL WASTE INCINERATORS
Typically, the incinerator operator does not perform PM but makes
hourly and daily inspections to ensure proper operation of the incinerator
and its air pollution control device and the identification of potential
problems. The hospital's maintenance.department performs PM on the
incinerator on a set schedule and corrects any potential problems
identified by the operator. At some hospitals, the maintenance department
performs PM on a work order system.1 In practice, minimizing the number
of PM items per work order ensures that PM is performed properly and with
less downtime.L
Because of the diversity in both size and design of hospital waste
incinerators, specific recommendations on PM practices and frequency that
would be applicable to all units are impossible to make. Also, as noted
above, the manufacturer's or vendor's recommended PM schedule for a
particular unit should be followed, and the information presented here
should only be used to supplement, not replace, that schedule. In
general, however, PM activities for any hospital waste incinerator involve
5-1
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inspection, cleaning, and lubrication of incinerator components on a
regular basis. Table 5-1 presents a typical PM program for a hospital
waste incinerator. Note that both the components listed on the table for
maintenance and the maintenance frequency will vary depending on the type
and amount of waste being incinerated and the type of incinerator used.
The sections below discuss the items on Table 5-1 in greater detail and
are organized according to hourly/daily maintenance, weekly/biweekly
maintenance, and monthly/semiannual maintenance.
5.1.1 Hourly/Daily Maintenance
The hourly maintenance activities described in Table 5-1 are simple
inspections that are applicable to large, continuous-feed incinerators.
These large units may be equipped with a water quench pit and an ash
removal conveyor system that continuously removes ash from the
2
incinerator. The operator must routinely replenish the water in the
quench pit because water is constantly removed by evaporation and by the
ash removal system. » The water quench pit is used to quench or
extinguish the hot ash as it is removed from the incinerator and to
provide an air seal for the ash removal conveyor.3 Therefore, it is
essential that sufficient water be available. In addition, the operator
should check the ash removal conveyor system frequently to remove any
debris that could cause it to jam.3 Small, batch-feed incinerators will
likely have neither a water quench pit nor an automatic ash removal
conveyor system.
Daily maintenance activities involve checking the operation of any
opacity, oxygen, and CO monitors. These monitors indicate whether the
operating/combustion conditions of the incinerator are within an
acceptable range; for some units, the oxygen monitor may also be used to
control the combustion air rate. Before the incinerator is started up,
the opacity monitor and the CO monitor should read 0 percent opacity and
0 parts per million (ppm), respectively. The oxygen monitor should read
about 21 percent oxygen (ambient air). If these monitors are equipped to
conduct for daily calibration checks, the calibration checks should be
conducted and the calibration values noted to assure that they are in the
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TABLE 5-1. TYPICAL MAINTENANCE INSPECTION/CLEANING/LUBRICATION
SCHEDULE FOR A HOSPITAL WASTE INCINERATOR^
Activity
frequency
Incinerator component
Procedure
Hourly Ash removal conveyor
Water quench pit
Da i I y Opac i ty mon i tor
Oxygen monitor
ThermocoupIes
Underfire air ports
Limit switches
Door seals
Ash pit/internal dropout sump
Weekly Heat recovery boiler tubes
Blower intakes
Burner flame rods (gas-fired
units)
U.V. scanner flame sensors
Swing latches and hinges
Hopper door support pins
Ram feeder carriage wheels
Heat recovery induced-draft
fans
BiweeKly HydrauIic systems
Ash removal conveyor bearings
Fuel trains and burners
Control panels
Monthly External surface of
incinerator and stack
Inspect and clean as required
Inspect water level and fill as required
Check operation of the opacity monitor and
check exhaust for visible emissions
Check operation of the oxygen monitor
Check operation of the thermocouples
Inspect and clean as required
Inspect for freedom of operation and
potential obstructing debris
Inspect for wear, closeness of fit, and
air Ieakage
Clean after each shift on batch units that
do not have continuous ash conveyor
cleaning system
Inspect and clean as required. (Clean
weekly for 6 weeks to determine optimum
cleaning schedule.)
Inspect for accumulations of lint, debris;
clean as required
Inspect and clean as required
Inspect and clean as required
Lubricate
Lubricate
Lubricate
Inspect and clean fan housing as required.
Check for corrosion and V-belt drives
and chains for tension and wear
Check hydraulic fluid level and add the
proper replacement fluid as required.
Investigate sources of fluid leakage
Lubricate
Inspect and clean as required. Investi-
gate sources of fuel leakage as required
Inspect and clean as required. Keep panel
securely closed and free of dirt to pre-
vent electrical malfunction
Inspect external "hot" surfaces. White
spots or discoloration may indicate loss
of refractory
(continued)
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TABLE 5-1. (continued)
Activity
frequency Incinerator component
Procedure
y
continued
Semi-
annual ly
Refractory
Internal ram faces
Upper/secondary combustion
chamber
Large combustion air blowers
and heat recovery induced
draft fans (those fans whose
bearings are not sealed)
Hydraulic cylinder clevis and
trunnion attachments to all
moving components
Burner pi lots
Hot external surfaces
Ambient external surfaces
Chains
Inspect and repair minor wear areas with
plastic refractory material
Inspect for wear. These stainless steel
faces may wear out and may require
replacement in 1 to 5 years depending on
serv i ce
Inspect and vacuum any particulate matter
that has accumulated on the chamber
floor
Lubricate
Lubricate
Inspect and adjust as required
Inspect and paint with high-temperature
paint as required
Inspect and paint with equipment enamel as
requ i red
Inspect and brush clean as required.
Lubricate
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proper range. If not, maintenance personnel should be informed. An
additional check for the opacity monitor is to observe the stack emissions
and compare the observation to the opacity monitor reading. For example,
if the opacity monitor, which normally reads below 5 percent, reads
25 percent, and a simple check of the exhaust stack shows an opacity of
0 percent, then something is wrong with the opacity monitor.
The thermocouples that indicate the temperature of the primary and
secondary chambers should also be checked daily/ It is essential that
these thermocouples be operating properly because the temperature
monitored by these thermocouples typically is the parameter that controls
the combustion airflow into the incinerator (controlled-air units) and
burner operation. The temperature readings should be ambient prior to
incinerator startup. A thermocouple problem may be indicated if the
operator notices a significant change in startup conditions, i.e., if
significantly more auxiliary fuel is required than normal, or if it takes
significantly longer to heat the incinerator than normal/ Also, a
noticeable change in response time of the thermocouple is an indication of
problems. Unfortunately, there is no simple way to check the accuracy of
a thermocouple; either the thermocouple must be removed and tested or a
second thermocouple must be inserted in a second thermocouple port, if
available.
The remaining daily maintenance activities involve inspection for
slagging and plugging (underfire air ports); inspection for obstructing
debris (e.g., limit switches on charging doors, charging rams, hopper
doors, etc.); inspection of door seals for wear, closeness of fit, and air
leakage; and cleaning the ash from the hearth on batch and intermittent-
duty incinerators.1* The underfire air ports must be kept clean so that
the proper amount of underfire air can reach the burning waste in a well
distributed manner. Limit switches must be kept clear of debris because
they control the proper adjustment of the charging door and the ram feeder
(if installed). Proper functioning of charging door and hopper/ram limit
switches is essential because these switches ensure that the doors are
fully opened/closed at the proper times and help prevent excessive air in-
leakage to the incinerator during charging and operation.2 Improperly
sealed doors, which result in excessive air leakage, will not only affect
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incinerator operation, but also may result in more severe maintenance
requirements (damage to seals or warpage due to excessive heat), as well
as causing a fire/safety hazard. Finally, the ash typically is allowed to
cool overnight and is removed from the hearth on batch and intermittent-
duty incinerators the day after the burn.1
5.1.2 Weekly/Biweekly Maintenance"
Some of the large hospital waste incinerators (20 to 25 tons waste/d)
may employ a waste heat recovery boiler to produce steam for use in the
hospital. When first installed, the heat recovery boiler tubes should be
cleaned weekly. The first indication of fouled tubes on the gas side will
be the gradual increase of boiler outlet gas temperature. All blower
intakes and the heat recovery induced-draft fan housing should be
inspected weekly and cleaned as required. The burner flame rods (gas-
fired units) or ultraviolet scanner flame sensors (other units) sjiould
also be inspected weekly and cleaned as required. The swing latches and
hinges, the hopper door support pins, and the ram feed carriage wheels
should all be lubricated weekly.
The biweekly maintenance items include the inspection of the fuel
trains, burners, and control panels. These pieces of equipment should
also be cleaned as required. Any sources of fuel leakage should be
investigated. The hydraulic fluid level should be checked on all
hydraulic systems, and the appropriate replacement fluid should be added
as needed. Only the fluid recommended by the manufacturer should be used
because other fluids may damage the hydraulic seals. The ash removal con-
veyor bearings on large incinerators should be lubricated biweekly.
5.1.3 Monthly/Semiannual Maintenance"
On a monthly basis, the incinerator operator should inspect the
external hot surfaces of both the incinerator vessels and stack for white
spots or other discoloration that may indicate a loss of refractory
inside. Additionally, whether white spots are evident or not, the
refractory lining inside the incinerator should be inspected for wear
5-6
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areas and any buildup of ash or metal oxides such as calcium, potassium,
and sodium. Any minor wear areas in the refractory should be repaired
using plastic refractory material. The metal oxides can cause a marked
decrease in the softening temperature of the refractory that effectively
reduces the operating temperature range. Any ash and metal oxide buildup
should be washed off only after the incinerator has cooled to avoid
damaging the refractory if the temperature of the wash water is
significantly different from that of the refractory.
Large incinerators may be equipped with internal ash rams that push
burning waste from one hearth to the next. The rams typically are made of
refractory material with the exception of the front face of the ram, which
is made of stainless steel. These stainless steel ram faces should be
inspected for wear and damage each month initially until an optimum
inspection schedule can be established. The ram faces may last from
1 year to 5 years depending upon the type of service in which they are
used.
In controlled-air incinerators, the primary chamber is operated at
less than stoichiometric air (starved-air) conditions, which minimizes the
amount of fly ash carryover to the secondary (excess-air) chamber.
However, in multiple-chamber (excess-air) designs, carryover of fly ash to
the secondary chamber should be expected; the carryout of carryover will
depend on the amount of excess air at which the primary chamber is
operating. Therefore, a monthly inspection and cleaning schedule for the
secondary chamber is appropriate for multiple-chamber units but may be
unnecessary for controlled-air units. Manufacturers of controlled-air
units specify vacuuming ash from the secondary chamber at least every
6 months. Therefore, an effective cleaning schedule for these units may
be every 3 to 4 months until an optimum cleaning schedule can be
established.
Large fans (those that do not have sealed bearings) and the hydraulic
cylinder clevis and trunnion attachments should be lubricated monthly.
Lastly, the burner pilots should be inspected and adjusted as required.
The semiannual maintenance activities include the inspection of all
hot external surfaces, all ambient external surfaces, and any conveyor
chains. All external surfaces should be cleaned; high-temperature paint
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should be applied to hot surfaces, and equipment enamel should be applied
to ambient surfaces as required. The chains should be brushed clean if
necessary and lubricated.
5.2 WET SCRUBBERS5'7
Table 5-2 presents a typical maintenance inspection, cleaning, and
lubrication schedule for a wet scrubber. As with incinerators, the
frequency with which these activities take place will depend on a number
of variables including the size and complexity of the scrubber, the number
of hours per day it operates, and the volume and pollutant concentration
of the exhaust gas it handles. In addition, not all of the maintenance
activities listed in Table 5-2 will be required at each scrubber
installation. The type and frequency of maintenance activities will
depend in large part on the scrubber vendor's recommendations and the
experience of personnel with the unit.
5.2.1 Daily/Weekly Maintenance
The daily maintenance activities described in Table 5-2 are simple
inspections that are applicable to all scrubbers. Most of these
inspections involve checking various components for proper operation and
fluid leakage. These inspections should be carried out after the scrubber
has been started up and prior to startup of batch-feed incinerators so
that any necessary repairs can be made before the scrubber has to control
emissions. Scrubbers controlling continuous-feed incinerators should be
inspected while both units are in operation.
Failure of components such as the scrubber liquid pump and variable
throat activator (on venturi scrubbers) will cause the scrubber to be
ineffective in controlling emissions from the incinerator. In such cases,
the incinerator may have to be shut down depending on both the severity of
the problem and any State regulations concerning operation of the
incinerator without its attendant air pollution control device. Liquid
leakage from these components also can have a detrimental effect on the
performance of wet scrubbers. The sources of such leaks should be
investigated and repaired as required.
5-8
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TABLE 5-2. TYPICAL MAINTENANCE INSPECTION/CLEANING/LUBRICATION SCHEDULE
FOR A WET SCRUBBER
Inspec-
tion
frequency
Component
Procedure
Daily
Weekly
Monthly
Semi-
annual ly
Scrubber liquid pump
Variable throat activator
Scrubber liquid lines
Mist eliminator pressure lines
Reagent feed system
Fan
Fan bearings
Fan belt3
Fan
Scrubber liquid pump
Damper air purge system
Duct work
Fan and motor bearings
Fan blades and internal
housing
Drain chain drive mechanism
Pipes and manifolds
Dampers
Spray bars
Pressure gauges
Main body of scrubber
Fan, pump, motor, and drag
chain bearings and gear
reducers
FIowmeters
Damper drive mechanism
Damper seals, bearings,
blades, blowers
Check for proper operation and leakage.
Investigate sources of fluid leakage and
repair as required.
Check for proper operation and leakage.
Check for leakage. Repair as required.
Check for leakage. Repair as required.
Check for leakage. Repair as required.
Check for vibration and proper operation.
Check for abnormal noise.
Check for abnormal noise.
Check oil level, oil color, oil tempera-
ture, and lubricate.
Check oil level and lubricate pump motor
bearings.
Check for proper operation.
Inspect for leakage.
Inspect for leaks, cracks, and loose
f ittings.
Inspect for material buildup and clean as
required. Inspect for abrasion and cor-
rosion and repair as required.
Check chain tension, sprocket wear and
alignment, and oil level.
Inspect for piugging/leak ing and
clean/repair as required.
Check for leakage.
Inspect for nozzle wear and plugging and
clean as required.
Check for accuracy.
Inspect for material buildup and clean as
required. Inspect for abrasion and
corrosion and repair as required.
Inspect clearances and wear, pitting, and
scoring. Inspect for leaks, cracks, and
loose fittings.
Check for accuracy.
Check for proper operation and alignment.
Check for wear and leakage.
Check fan belt tension whenever fan is out of
service.
5-9
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Fans in wet scrubber service operate under substantially more severe
conditions than those serving dry systems because humid conditions enhance
the possibility of condensation of acids on the fan and fan housing. In
the case of hospital waste incinerators, scrubbers and fans are likely to
experience hydrochloric acid mist as a result of the combustion of
chlorinated plastic material. Therefore, acid-resistant materials should
be used in the construction of the scrubber interior and more frequent
cleaning of the fan system serving the scrubber should be practiced.
Unusual noise or vibration from any part of the fan system, including the
bearings or belt, may indicate that replacement is necessary.
The weekly maintenance items include more inspections of components.
The fan and the scrubber liquid pump oil levels should be checked and
adjusted as appropriate. Additionally, the fan oil temperature and color
should be checked. Temperature or color readings that are outside of the
manufacturer's recommended ranges may indicate excessive wear and/or
contamination of the oil. Both the fan and scrubber liquid pump bearings
should be lubricated weekly.
5.2.2 Monthly/Semiannual Maintenance
The monthly maintenance activities consist of additional inspections
and appropriate corrective actions as required. Clogged pipes, manifolds,
and spray nozzles can hinder the proper operation of the scrubber. The
pressure drop of the scrubber will be lower than normal if plugging is
experienced. The pressure drop is a critical indicator of scrubber
performance in removing particulate from the incinerator exhaust, and the
pressure gauges should be checked and calibrated for accuracy. Some
regulations may require a minimum pressure drop to be achieved across the
venturi to assure a minimum pollutant removal efficiency. Therefore, it
is important that the pressure gauges operate properly.
The main body of the scrubber, fan blades, and internal fan housing
are subject to buildup of particulate matter that can adversely affect
both scrubber and fan performance. These components should be inspected
and cleaned monthly. In addition, these components should be inspected
for any abrasion caused by particulate matter or corrosion caused by
hydrochloric acid mist that might adversely affect performance.
5-10
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Fan and motor bearings should be inspected for leaks, cracks, and
loose fittings. Dampers and ductwork should be checked for any air
leakage. Leakage of air can cause condensation of moisture and acid gases
due to the introduction of cool ambient air. Also, a large number of
leaks in the ductwork will cause the induced-draft fan to pull more air,
and the incinerator operator will have less control over the air
introduced into the incinerator. The drag chain drive mechanism used on
some automatic ash removal systems should be inspected for wear, chain
tension, and sprocket alignment. The oil level also should be checked on
this component and adjusted as required.
The semiannual maintenance activities include inspections of all
bearings on fans, pumps, motors, and gear reducers for leaks, cracks, and
loose fittings. Additionally, the clearances and any wear, pitting, or
scoring should be checked on these components. The flow meters on the
scrubber should be checked for accuracy. State regulations, in addition
to requiring a pressure drop, also may require a specific water flow
rate. Therefore, the flow meters should operate properly. The damper
drive mechanism should be checked for proper operation and alignment; and
the damper seals, bearings, blades, and blowers should be inspected for
wear and leakage.
5.3 MAINTENANCE OF FABRIC FILTERS8'9
Although the frequency and components of a PM program for a fabric
filter system will depend on the type of system and the vendor's recom-
mendations, the major components should be inspected on a routine basis,
and any needed maintenance should be performed. The following sections
describe the daily, weekly, monthly/quarterly, and semiannual/annual
inspections/maintenance that are recommended. A specific PM program
should be established based on the manufacturer's recommendations.
Table 5-3 presents a typical maintenance inspection, cleaning, and
lubrication schedule for a fabric filter.
5-11
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TABLE 5-3. TYPICAL MAINTENANCE INSPECTION/CLEANING/LUBRICATION SCHEDULE
FOR A FABRIC FILTER SYSTEM8**
I nspection
frequency
Component
Procedure
Daily
Week Iy
Monthly
Quarter Iy
Semiannually
Annually
Stack
Manometer
Compressed air system
Col lector
Damper valves
Rotating equipment and drives
Dust removal system
FiIter bags
Cleaning system
Hoppers
Shaker mechanism
Fans(s)
Monitor(s)
Inlet plenum
Access doors
Shaker mechanisms
Motors, fans, etc.
Co 11ector
Check exhaust for visible dust.
Check and record fabric pressure loss
and fan static pressure. Watch for
trends.
Observe all indicators on control panel
and listen to system for properly
operating subsystems.
Check all isolation, bypass, and
c I ean i ng damper valves for
synchronization and proper operation.
Check for signs of jamming, leakage,
broken parts, wear, etc.
Check to ensure that dust is beinq
removed from the system.
Check for tears, holes, abrasion,
proper fastening, bag tension, dust
accumulation on surface or increases
and folds.
Check cleaning sequence and cycle times
for proper valve and timer
operations. Check compressed air
lines including oi lers and filters.
Inspect shaker mechanisms for proper
operation.
Check for bridging or plugging.
I nspect screw conveyor tor proper
operation and lubrication.
Inspect for loose bolts.
Check for corrosion and material
buijdup and check V-belt drives and
chains for tension and wear.
Check accuracy of all indicating
equipment.
Check baffle plate for wear; if
appreciable wear is evident.
replace. Check for dust deposits.
Check a 1 1 gaskets.
Tube type— (tube hooks suspended from a
tubular assembly): inspect nylon
bushings in shaker bars and clevis
(hanger) assembly for wear.
Channel shakers — (tube hooks suspended
from a channel bar assembly):
inspect drill bushings in tie bars,
shaker bars, and connecting rods for
wear.
Lubricate all electric motors, speed
reducers, exhaust and reverse-air
fans, and similar equipment.
Check all bolts and welds. Inspect
entire collector thoroughly, clean,
and touch up paint where necessary.
5-12
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5.3.1 Daily Inspection/Maintenance
At least twice per shift (and perhaps as often as every 2 hours),
plume opacity (visual inspection of stack outlet) and pressure drop should
be checked. Sudden changes in these values along with those of
temperature and gas volume may indicate a problem. For example, the
failure or partial failure of the cleaning system generally will cause a
relatively rapid increase in pressure drop in most systems. Timely
identification, location, and correction of this problem can minimize
operating problems and long-term effects on bag life. Although
identification and subsequent correction of relatively minor problems have
little effect on fabric life, some minor problems tend to turn into major
failures. The ability to perform on-line maintenance depends on the
design of the control equipment.
Routine checks of the fabric filter include pressure drop (and
patterns if a AP indicator and recorder are used), plume opacity at the
outlet, dust discharge operation, and external checks (i.e., visual
inspection) of the cleaning system operation. Other factors that can be
checked include temperature (range) and fan motor current. If a check of
these factors reveals a sudden change, maintenance should be scheduled as
soon as possible.
5.3.2 Weekly Inspection/Maintenance
The extent of the weekly maintenance program depends greatly on
access and design of the fabric filter. Where possible, quick visual
inspections should be conducted; however, not all systems or processes are
amenable to this type of review. A weekly lubrication schedule should be
established for most moving parts. Manometer lines should be blown clear,
and temperature monitors should be checked for proper operation.
When a fabric filter is the air pollution control device of choice
for a hospital waste incinerator, it is almost always a pulse-jet fabric
filter. The following items should be checked weekly. On the dirty side
of the tubesheet, bags should be checked for relatively thin and uniform
exterior deposits. Bags also should be checked for bag-to-bag contact
5-13
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(points of potential bag wear). On the clean side of the tubesheet, each
row of bags should be examined for leakage or holes. Deposits on the
underside of the blowpipes and on the tubesheet may indicate a bag
failure. The cleaning system should be activated (the inspector should
use hearing protection), and each row of bags should fire with a
resounding "thud." The blowpipes should remain secured, and there should
be no evidence of oil or water in the compressed air supply. The surge
tank or oil/water separator blowdown valve should be opened to drain any
accumulated water. Misaligned blowpipes should be adjusted to prevent
damage to the upper portion of the bag. The compressed air reservoir
should be maintained at about 90 to 120 psi.
On a weekly basis, the dust removal system including hopper and screw
conveyor should be inspected to make sure that dust is being removed from
the system by checking the conveyor for jamming, pluggage, wear and broken
parts, etc. Problems with the conveyor system are indicated when the
conveyor appears to be moving but no, dust is dropping into the dust
storage container, when the conveyor does not move, or when the conveyor
makes unusual sounds.
5.3.3 Monthly/Quarterly Inspection/Maintenance
Requirements for monthly or quarterly maintenance and inspection for
fabric filters are very site specific. Clear-cut schedules cannot be
established for such items as bag replacement and general maintenance of
the fabric filter. Some items, however, may warrant quarterly or monthly
inspections, depending on site-specific factors. Items to be checked
include door gaskets and airlock integrity to prevent excessive in-leakage
(both air and water) into the enclosure. Any defective seals should be
replaced. Baffles or blast plates should be checked for wear and replaced
as necessary, as abrasion can destroy the baffles. Some facilities prefer
to use fluorescent dye to check the integrity of the bags and bag seals.
Any defective bags should be replaced, and leaking seals should be
corrected.
Bag failures tend to occur shortly after installation and near the
end of a bag's useful life. A record of bag failures and replacements is
5-14
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invaluable for identifying recurrent problems and indicating when the end
of bag life has been reached. Initial bag failures usually occur because
of installation errors or bag manufacturing defects. When new bags are
installed, a period with few or no bag failures is normally expected
unless serious design or operation problems exist. As the bags near the
end of their useful life, however, the number of bag failures may increase
dramatically. When weighed against factors such as downtime for
rebagglng, the cost of new bags, and the risk of limited incinerator
operating time as the result of keeping the old bags in service, the most
economical approach may be to replace all the bags at one time to
eliminate or minimize failure rate.
In some cases, bags can be washed or drycleaned and reused, e.g.,
when dewpoint limits are approached or the bags are blinded in some
manner. Although cleaning may shorten bag life somewhat, cleaning may
still be more economical than replacement if more than half a bag's
"normal" life expectancy remains.
5.3.4 Semi annual/Annual Inspection/Maintenance
Some motors and packaged blowers are supplied with sealed bearings
and, therefore, require no lubrication. Semiannual fabric filter system
maintenance activities include the lubrication of the following components
having nonsealed bearings: all electric motors, speed reducers, exhaust
and reverse air fans, and similar equipment.
Annual maintenance activities include checking the tightness and fit
of all bolts and welds on the fabric filter. Additionally, the unit
should be cleaned and painted as appropriate.
5.4 REFERENCES FOR CHAPTER 5
1. Personal Conversation between Mark Turner, MRI, and William Tice, Rex
Hospital, Raleigh, North Carolina. August 16, 1988.
2. Murphy, P., and Turner, M. Report of Site Visit to Ecolaire
Combustion Products, Charlotte, North Carolina. July 20, 1988.
3. Allen Consulting and Engineering, Municipal Waste Combustion Systems
Operation and Maintenance Study. EPA-340/1-87-002. June 1987.
5-15
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4. Ecolaire Combustion Products, Inc. Equipment Operating Manual for
Model No. 2000TES; Equipment operating manual for Model No. 480E.
5. U. S. Environmental Protection Agency. Wet Scrubber Inspection and
Evaluation Manual, EPA 340/1-83-022. (NTIS PB 85-149375).
September 1983.
6. Joseph, J. and Beachler, 0., APTI Course SI:412C, Wet Scrubber Plan
Review, Self-Instructional Guidebook. U. S. Environmental Protection
Agency. EPA 450/2-82-020. March 1984.
7. Engineering Manual with Operation and Maintenance Instructions.
Anderson 2000, Inc. Peachtree City, Georgia. (Undated).
8. U. S. Environmental Protection Agency. Operation and Maintenance
Manual for Fabric Filters. EPA/625/1-86/020. June 1986.
9. Beachler, 0. APTI Course SI:412, Baghouse Plan Review. U. S.
Environmental Protection Agency. EPA 450/2-82-005. April 1982.
5-16
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6.0 CONTROL AND MONITORING INSTRUMENTATION
6.1 OPERATING PARAMETERS THAT SHOULD BE MONITORED
Proper operation of incinerators depends to a large extent on certain
operating parameters that are commonly monitored to provide necessary
information to properly control the process. These usually consist of:
1. Temperature;
2. Pressure;
3. Oxygen;
4. CO;
5. Opacity; and
6. Charge rate.
Although all of the above parameters provide useful information, many
hospital incinerators monitor only temperature and pressure. The other
parameters listed are sometimes monitored on larger incinerators or if
regulatory agencies require that monitoring be conducted (e.g., opacity).
The temperature and oxygen level are key parameters, and incinerators are
normally designed to monitor one or both of these parameters to provide
the necessary information for automatic control of combustion air input
and auxiliary fuel rates. In order to maintain the desired draft in the
incinerator, control loops may be used to adjust incinerator draft by
means of barometric dampers or the induced draft fan. The other
parameters provide additional information that operators can use to
maintain proper operation (e.g., charge rate, oxygen levels).
Proper operation of wet scrubber systems is dependent on several
operating parameters that are commonly monitored, usually consisting of:
1. Pressure and pressure drop;
2. Scrubber liquid flow;
3. Scrubber liquid pH;
4. Temperature.
For venturi scrubbers, pressure drop is normally monitored and
automatically controlled to a fixed level by adjusting the venturi
throat. For venturi's and packed beds, the scrubber liquid flow is
usually established at a constant rate and is not automatically controlled
6-1
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during operation. For both types of scrubbers, control of pH is necessary
to prevent damage to the scrubber equipment. Most scrubbers are designed
to monitor and control pH automatically. Gas flow and temperature are
often monitored to provide operators with additional information useful in
maintaining proper operation by indicating potential problems and the need
to make manual adjustments. Other instrumentation and control often
includes an automatic liquid level control for the scrubber liquid sump,
and a temperature switch/solenoid valve to activate an emergency quench
spray and/or an emergency bypass stack.
For fabric filters, the key operating parameter which typically is
monitored is pressure drop across the bags. Temperature also is monitored
to assure that the temperature does not decrease below the dewpoint or
increase to a level which will cause bag damage.
The next section describes the typical instrumentation used to
monitor/control these key parameters and briefly discusses its proper use
and operation.
6.2 TYPICAL INSTRUMENTATION
6.2.1 Temperature Sensors
Thermocouples are used to monitor temperatures in the combustion
chambers and the air pollution control system. The thermocouples are
always enclosed in a thermowell to protect the small thermocouple wires
and the critical thermocouple junction from direct exposure to the
combustion gases and entrained dust particles, etc. Thermocouples are
usually located near the exit of the combustion chamber to provide a
representative temperature reading away from the flame zone, which can
otherwise cause erratic temperature readings as well as damage to the
thermocouple. Thermowells may extend several inches past the inner wall
of the refractory into the gas stream, or may extend only to the depth of
the refractory. Thermowells that extend past the refractory provide a
more accurate measure of the gas temperature and respond more quickly to
temperature changes; however, this type also may be subject to dust and
slag buildup, which can slow response to temperature changes. Generally,
6-2
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thermocouples also are located upstream of the air pollution control
system to provide a warning or control mechanism for high temperature
excursions that could damage control equipment.
The different types of thermocouples are identified by the metal used
for the thermocouple junction wires. The most common types are listed in
Table 6-1. Replacement thermocouples must always be the same type as the
original because the receiver to which a thermocouple is connected is
designed to receive the signal from a specific type of thermocouple.
Thermocouples generate a small millivolt signal that increases with
increasing temperature, but the amount of voltage for a given temperature
is different for each type of thermocouple. It is important to realize
that thermocouples operate on the basis of a junction between two
different metals that generates only a small millivolt signal.
Consequently, any wiring connections from the thermocouple to the receiver
or any interfering electrical signals can affect the resulting temperature
reading. This sensitivity necessitates the special shielding of the wire
in electrical conduit.
Although thermocouples typically are very reliable, they can fail or
give erroneous readings. For example, the thermocouple junction or wire
may break after long exposure to high temperatures. However, a thermo-
couple can give erroneous readings for reasons that are not as obvious as
a broken junction or wire. For example, if mechanical vibration abrades
the insulation and one of the thermocouple wires comes into contact with
the metal wall of the thermowell or other grounded metal surface, an
erroneous temperature reading will likely result. As noted earlier,
faulty thermocouple readings may also be the result of external condi-
tions; for example, excessive dust buildups around a thermowell can
insulate it from the gas stream and result in erroneously low temperature
readings. To have the ability to compare readings to identify a faulty
thermocouple, dual thermocouples are often used at nearby locations in the
incinerator chamber. The second thermocouple enables continued monitoring
of temperatures while the faulty thermocouple is being checked or
replaced.
Periodic replacement of thermocouples, and checking the physical
integrity of the thermowell and any outer dust buildup, is probably the
6-3
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TABLE 6-1. THERMOCOUPLE TYPES
Type
J
E
K
S
R
B
Materials
Iron/Constantan
Chrome! /Constantan
Chrome 1/Alumel
Pt 10% Rhodium/Pure Pt
Pt 13% Rhodium/Pure Pt
Pt 30% Rhodium/Pt 6% Rhodium
Upper
temp. ,
°F
1400
1650
2300
2650
2650
3100
6-4
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best maintenance procedure. Because it is not practical to perform a high
temperature calibration of the thermocouple, only periodic replacement
ensures that a properly operating thermocouple is in place. The receiver
should be checked periodically using calibrated equipment that produces a
known millivolt signal equivalent to a specific temperature reading for a
particular type of thermocouple. The generated signal can be applied to
the thermocouple leads to check that the receiver's output produces the
correct "temperature" reading.
Close monitoring of temperatures is essential to good incinerator
operation. It is essential, therefore, to identify possible thermocouple
problems because the temperature signal is usually the primary measurement
used for the automatic control of auxiliary fuel burners and combustion
air input. Any problem with the thermocouple temperature reading can
cause the automatic control system to make inappropriate changes in the
controlled variable in an attempt to maintain the desired (setpoint)
temperature.
6.2.2 Pressure
The incinerator draft is measured in units of gauge static pressure,
but it is actually a measure of the differential pressure (aP) between the
inside of the chamber and the outside air. Monitoring of AP can be done
with a common U-tube manometer, but for incineration systems, a
differential pressure gauge (e.g., Magnehelic®) or a differential pressure
transmitter typically is used. All of these instruments use the same
basic method to monitor incinerator draft. One side (the high-pressure
side) of the instrument is always open to the ambient air; the other (low-
pressure) side is connected by tubing or piping to the incinerator.
These types of pressure monitors also are used to measure
differential pressure across an air pollution control system (e.g.,
venturi scrubber throat or fabric filter baghouse). For this application,
the low-pressure side is connected to a pressure tap in the ductwork
downstream from the control device and the high-pressure side is connected
upstream from the control device.
6-5
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A differential pressure transmitter contains a diaphragm with two
tubes connected on each side of the diaphragm; the diaphragm moves or
deflects as a result of changes in pressure. The transmitter is designed
so that any change or deflection causes a change in an electrical output
signal from the transmitter. The electrical signal is sent to the monitor
in the control room that indicates the incinerator draft or the pressure
differential across the air pollution control system.
Several problems can cause faulty incinerator draft readings.
Transmitters used to measure AP are sensitive devices that can be damaged
by excessive vibration or sudden shocks. The severe hot and dirty
conditions in the incinerator may also cause problems such as pluggage in
the tubing and its connections. When faulty incinerator pressure readings
are suspected, several procedures for correcting them can be used. Air
can be blown through the tubing to clear any pluggage, and a known AP can
be applied to the transmitter to check its response and span.
Disconnecting any instrumentation should be done by experienced
instrumentation personnel and must be coordinated with the operator so
that the appropriate instrument can be put on manual control. For
example, if the incinerator's automatic control system maintains
incinerator draft via a damper on the ID fan inlet duct, disconnecting the
pressure tap would probably cause the ID fan to increase flow in an effort
to maintain the draft setpoint, thereby upsetting the temperature and
other process operating parameters.
6.2.3 Oxygen Concentration1
Some incinerators may be equipped with oxygen analyzers to monitor
the oxygen concentration in the combustion gases from the secondary
combustion chamber to help ensure that adequate oxygen is available for
proper combustion (i.e., that the excess-air level is sufficient). In
some incinerators, the oxygen levels measured by the monitor are used to
control air feed rates for control of the combustion process. In essence,
lower waste feed rates require lower air feed rates in order to maintain
essentially constant temperature and constant percent oxygen in the com-
bustion gases, so long as the characteristics of the waste feed are the
6-6
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same. However, if the composition of the feed changes (i.e., its heating
value changes), more or less air win be needed to maintain the same
temperature and oxygen content in the combustion gases. Thus, the oxygen
content is a useful parameter to monitor and is an important control
parameter if the incinerator is set up to control based on oxygen level
rather than temperature.
Oxygen monitors may be of two types: in situ or extractive. In situ
merely means that the analyzer's sensor is mounted in direct contact with
the gas stream. In an extractive system, the gas sample is continuously
withdrawn (extracted) from the gas stream and directed to the analyzer
which may be located several feet or several hundred feet away.
Extractive analyzers include a conditioning system to remove dust and
moisture from the gas sample; thus, the oxygen concentration measurement
is on a dry basis. In situ analyzers, on the other hand, do not include a
conditioning system, and the oxygen concentration measurement is on a "wet
basis." For the same gas stream, the oxygen measurement obtained with an
in situ analyzer will be slightly lower than that obtained with an
extractive analyzer. For example, a typical combustion gas stream that
contains 10 percent water vapor will yield a reading of 8 percent oxygen
using an in situ analyzer and a reading of 10 percent oxygen using an
extractive analyzer.
Regardless of the type of analyzer, the location of the sampling
point is very important to ensure that a representative sample is
obtained. The monitoring point may be in the stack, the combustion
chamber exit, or other locations within the process (e.g., duct between
air pollution control system and the stack). In most cases, the intent is
to monitor the combustion gases at the exit of the combustion chamber and
that, in fact, is where the sampling point is often located. One of the
main problems related to sampling location that can occur is obtaining a
nonrepresentative sample due to in-leakage of air. For example,
substantial air in-leakage can occur through emergency stack dampers. Any
such in-leakage affects the analyzer reading if the sample point is
downstream of the in-leakage. However, there are practical limitations
with regard to locating oxygen monitors. The in situ sensor or probe for
extracting the sample must be located in an environment consistent with
6-7
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the monitor's design. High temperatures, participate concentrations, and
acid gas concentrations can have adverse effects on the monitoring system
resulting in operational and/or maintenance problems.
Oxygen analyzers are capable of good accuracy (±1 percent of full
scale) as long as the actual gas to be sampled reaches the analyzer (no
pluggage or in-leakage of air), the conditioning system (if one is
present) is operating properly, and the instrument is calibrated.
Electrocatalytic in situ monitors have rapid response times (i.e.,
seconds). The response times for polarographic and paramagnetic
extractive analyzers are slower (several seconds to a minute). Extractive
systems inherently involve longer response times, usually on the order of
1 to 2 minutes, depending on the sampling rate and the volume of the
sampling line and conditioning system.
Problems with oxygen analyzer systems may be difficult to discern
since they commonly are associated with slowly developing pluggage in the
system, or small air in-leaks, etc. The extractive systems should be
checked daily by the operators, and maintained and calibrated on a weekly
basis by the incinerator instrument personnel.
6.2.3.1 In Situ Oxygen Analyzers. In situ analyzers provide rapid
response to changes in the oxygen content of the gas because the sensor is
in direct contact with the gas stream. In most cases, the sensing element
is enclosed in a sintered stainless steel tube, which allows the gas to
permeate through the tube but prevents particles in the gas stream from
entering. Most in situ oxygen analyzers are equipped with connections so
that zero gas (nitrogen) or calibration gas (air) can be flushed through
the permeable tube and in contact with the sensing element. Flushing
provides a means of zeroing and spanning the analyzer, and also creates
reverse flow of gas through the permeable tube that helps to remove dust
particles that eventually will clog the tube and slow the detector's
response time. Even so, the tube periodically must be removed for
cleaning or replaced if warranted.
Most in situ oxygen analyzers are of the electrocatalytic type,
sometimes referred to as fuel-cell analyzers. Operation of these
analyzers is based upon an electron flow created by reaction of oxygen
with a solid zirconium oxide electrolyte. Consequently, manufacturers
6-8
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recommend that.the sensing element be replaced after several months of
service.
6.2.3.2 Extractive Oxygen Analyzers.
Extractive analyzers always involve a "conditioning system" for
removal of water, dust, and sometimes other constituents that would
interfere with operation of the analyzer. An example extractive system is
illustrated in Figure 6-1. The moisture knockout for removal of water
vapor and the normal connections for zeroing and calibrating the analyzer
are shown.
The integrity of the sample line and the conditioning system is
crucial to obtaining a representative sample and accurate results. Any
in-leakage of air can drastically distort the reading. As shown in
Figure 6-1, the extractive system requires a pump to draw the sample gas
continuously through the sample line, conditioning system, and analyzer.
Most systems include a small rotameter (flowmeter) which shows that sample
gas is flowing through the system. This flowmeter is always one of the
first items that should be checked if any problem is suspected because
loss of flow will occur if the pump fails or the system is plugged.
However, even if the flow rate is correct, the measured gas concentration
will not be correct if there is any problem with in-leakage of air.
Two types of extractive oxygen analyzers, paramagnetic and
polarographic analyzers, are available in addition to the electrocatalytic
type described previously for in situ analyzers. Paramagnetic analyzers
measure the oxygen concentration as the strength of a magnetic field in
which oxygen molecules are present. Oxygen molecules are somewhat unique
in displaying a permanent magnetic moment (paramagnetism), allowing oxygen
concentration to be differentiated from the stack gas sample. Calibration
is performed by monitoring an inert gas such as nitrogen (zero) and a gas
of known oxygen concentration (span). A potential problem with this type
of analyzer is its susceptibility to paramagnetic molecules other than
oxygen. Nitrogen oxide and nitrogen dioxide in particular display a high
degree of paramagnetism (about one-half that of oxygen), but their concen-
tration is usually low compared to that of oxygen.
Polarographic analyzers monitor oxygen concentration by allowing
oxygen to pass through a selective, semi permeable membrane and react at an
6-9
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f
J
r
J
SECONDARY
COMBUSTION
CHAMBER
Y ^
r
i
r
SAMPLE
-\
r PHUBt J~ " 1
1- FILTER -fl
BACK FLUSH
PURGE AIR
DRAIN
ZERO
SPAN
LOW
/
MID
LEVEL LEVEL
CAL CAL.
VENT
SAMPLE
PUMP
Figure 6-1. Schematic of an extractive monitoring system.
6-10
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electrode in an oxidation-reduction reaction. Measuring the current
produced by the reaction indicates the oxygen concentration. Improper
conditioning of the sample gas is a potential problem with these
analyzers, since moisture and particles will hinder performance of the
semipermeable membrane. Calibration is performed by zeroing with an
oxygen-free gas (nitrogen) and spanning with a gas of known oxygen con-
centration (e.g., air). Furthermore, these monitors contain a liquid
electrolyte that has a limited life span and must be replaced at regular
intervals.
6.2.4 Carbon Monoxide1
Carbon monoxide (CO) analyzers are used to measure emissions of CO
and indicate whether proper combustion conditions are being maintained.
Carbon monoxide analyzers typically are not part of the automatic process
control system. In general, a problem with CO levels (i.e., high level)
indicates some other problem in the process and its control system (e.g.,
feed rate or temperature).
Location of the CO sampling point may vary, although it is most
commonly in the stack or at the exit of the combustion chamber. As with
oxygen monitors, CO analyzers can be affected by upstream in-leakage of
air, but usually not as dramatically as oxygen monitors.
Carbon monoxide analyzers also may be in situ or extractive, but by
far the most common type is extractive. Both types are based on the
principle that CO will absorb specific wavelengths of light in the
infrared region. They are therefore referred to as nondispersive infrared
(NDIR) analyses.
In situ CO monitors involve an infrared signal that is transmitted
across the duct or stack to a receiver or reflector on the opposite
side. The change in the signal, due to absorbence by CO, is processed by
the analyzer system and output as an equivalent CO concentration. In situ
CO monitors are difficult to calibrate directly because the duct cannot be
filled with a gas of known concentration. Therefore, calibration is
performed using an optical filter that can be moved into the signal path,
or a calibration gas that can be put through a separate cell through which
the infrared signal can be sent.
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In most cases, in situ systems are installed at a location in a stack
after pollution control devices have removed most of the particulate
matter because solid particles also absorb the IR signal. Water vapor and
carbon dioxide also may interfere with the signal. Because all these
interferences can be removed by a sample conditioning system, the
extractive systems are more commonly used.
Much of the previous discussion on extractive oxygen systems applies
to extractive CO systems. In fact, the same extraction/conditioning
system often is used for both monitors. Daily checks of the system should
be made by the operator, with weekly maintenance and calibration by the
instrument personnel.
Currently, there are no specific EPA performance requirements for CO
analyzers on hospital incinerators. However, EPA is developing guidelines
for CO monitors that are required on hazardous waste incinerators
permitted under the Resource Conservation and Recovery Act (RCRA).
6.2.5 Opacity1*2
Like CO monitors, opacity monitors or transmissometers are used as
indicators of proper operation rather than as a part of the automatic
control system and almost always are located in the stack or in the
ducting to the stack downstream of air pollution control devices. The
operating principle for these transmissometers involves measurement of the
absorbence of a light beam across the stack or duct. Consequently, they
are not applicable in saturated wet streams downstream of wet scrubbers
unless the gas has been reheated to vaporize any water droplets.
Transmissometers involve a light source directed across the stack and
a detector, or reflector, on the opposite side. The amount of light
absorbed or scattered is a function of the particles in the light path,
path length (duct diameter), and several other variables that are
considered in the design and installation. Figure 6-2 depicts a typical
transmissometer.
The lenses on the light source and the detector must be kept clean of
any buildup of dust. For this reason, the systems often include air
blowers and filters that continuously blow clean air past the lenses to
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Transceiver
assembly
Preseparator air inlet
Ambient
air
Retroreflector
assembly
Blower
Blower
Figure 6-2. Typical transmissometer installation for measuring opacity.1
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prevent contact with the gas and dust in the stack (see Figure 6-2).
These blowers and filters should be checked and cleaned regularly but
often are neglected because of their location on the stack.
The EPA has promulgated performance specifications for opacity
monitoring systems that are required at some types of plants as summarized
in Table 6-2. The calibration procedure for this performance
specification, or normal checking of the instrument, is based on filters
having known light absorbence that can be placed in the light path. Some
systems automatically calibrate on a regular schedule that is evident to
the operator because it usually activates a high opacity alarm or a spike
on the opacity recorder.
6.2.6 Charge Rate
The amount of waste charged into the incinerator and the charging
frequency are important operating variables for an incinerator. Some
incinerators may be equipped with systems that weigh the amount of each
charge and automatically record this weight, but, at most facilities, the
amount charged is based on operator experience and hopper charge size and
is not closely monitored. Thus, operator experience is relied upon to
avoid overcharging (stuffing), which may decrease temperature, increase
emissions (CO), and cause poor burnout. Undercharging will require
excessive auxiliary fuel usage.
For mechanically charged systems, the charging frequency is often
automatically set by the system at preselected time intervals. As long as
the loader fills the charging hopper to a certain level within this time
interval, the charging rate will be maintained constant by the control
system, unless the charging frequency is changed by the operator.
Altering the charging frequency is sometimes necessary when the
characteristics or composition of the waste has changed. For example, if
a charge contains large amounts of plastic or other high heating value
material, temperatures may rise rapidly. Thus, the operator may decide to
delay the next charge until the system can again handle another charge.
For mechanical systems, a recorder can be set up to indicate the frequency
of changes automatically, i.e., when a charge is fed to the incinerator.
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TABLE 6-2. PERFORMANCE SPECIFICATIONS FOR
OPACITY MONITORS
Parameter Specifications
Calibration errora <3 percent opacity
Response time
-------
Having a charging record available is useful for monitoring and
troubleshooting problems and for determining whether adjustments to the
charging procedures are necessary.
Operator judgment and experience are usually key to proper control of
charging rate; pressure on the operator to increase the charging rate when
the amount of accumulated waste has increased cannot be allowed to
compromise proper incinerator operating conditions.
6.2.7 Scrubber Liquor pH
There are two types of pH sensors: immersion (dip-type) and flow-
through. The immersion sensor is merely inserted into a tank and can be
removed for maintenance and calibration. A flow-through sensor depends
upon a continuous flow in the sample line. Both have advantages and
disadvantages. The immersion sensor is easier to operate and maintain.
Performance can also be improved by locating the sensor in a special
sampling tank, by using redundant sensors, and by frequent cleaning and
calibration. The flow-through pH sensor is prone to wear and abrasion.
Redundant sensors are also desirable for the flow-through type but are not
easy to provide.
The pH measurement probe consists of a pH measuring electrode, a
reference electrode, and a high input impedance meter. The voltage of the
pH electrode varies with the pH of the solution it is in contact with,
while the reference electrode delivers a constant voltage. The difference
between the two voltages is measured by the impedance meter, allowing pH
of the system to be monitored. Such a system is susceptible to signal
loss and noise, making it desirable to locate the preamp, controller, or
signal conditioning unit as close to the electrodes as possible.
Calibration of a pH monitoring system is performed through the use of
known pH buffer solutions. Typically, pH 7 is used for calibration,
although pH 4 and pH 10 may also be used, depending upon the expected
ranges of scrubber operation. For greatest accuracy, buffer solutions
should be selected that are close to expected pH values.
The pH monitoring system electrodes may become fouled over time by
dirt, particulate matter, and bacteria. This fouling can damage or
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inhibit correct electrode operation, introducing drift and inaccuracy in
the unit's calibration. To maintain reliability, electrodes can be boiled
in a solvent or cleaned with a built-in ultrasonic device. Calibration
checks usually are necessary every few weeks.
Control systems for pH meters range in complexity from simple ON/OFF
types to more sophisticated proportional controllers. In an ON/OFF type,
as pH goes out of range, a valve opens and neutralizing reagent is added
until the pH is corrected. Proportional controllers add an amount of
neutralizing reagent in proportion to deviation of pH from the setpoint,
which provides much smoother control. The exact type of controller
necessary for the system is based upon individual needs, but typically a
proportional controller is used.
The pH measurement probe should be placed at a representative
location within the system. Turbulent flow is needed to ensure a well-
mixed solution and to limit dead time (reaction time of the controller) to
30 seconds or less. Excessive dead time will cause the system to
overshoot fhe pH setpoint continually as the controller is unable to react
quickly enough and continues to add neutralizing reagent beyond the
desired pH. Dead time can be reduced by locating the pH probe a short
distance downstream from where the reagent is added.
6.3 REFERENCES FOR CHAPTER 6
1. U. S. EPA. Continuous Air Pollution Source Monitoring Systems
Handbook, EPA 625/6-79-005. June 1979.
2. Jahnke, J. APTI Course SI:476A, Transmissometer Systems Operation and
Maintenance, an Advanced Course. EPA 450/2-84-004. U. S. Environ-
mental Protection Agency, Research Triangle Park, N.C. September
1984. p. 6-9.
3. Code of Federal Regulations, Title 40 Part 60 (40 CFR 60), Appendix B,
Performance Specification 1. Specifications and Test Procedures for
Opacity Continuous Emission Monitoring Systems in Stationary Sources.
6-17
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7.0 OPERATIONAL PROBLEMS AND SOLUTIONS
This section describes potential operational problems associated with
hospital waste incinerators, wet scrubbers, and fabric filters; discusses
the cause of the problems; and discusses possible solutions to the
problems. Unfortunately, some operational problems are the result of
deficiencies in design, fabrication, and/or installation of the equip-
ment. Deficiencies in incinerator design are usually the result of
insufficient information on the waste characteristics and/or quantity.
The following paragraphs assume that the incinerator and its air pollution
control system have been properly designed, fabricated, and installed and
do not address any deficiencies in these areas. It is recommended that
purchasers of hospital waste incinerators and air pollution control
systems consult with reputable manufacturers. In many cases, these
companies can provide complete turnkey service that includes evaluation of
the purchaser's needs, proper design of the incinerator based on waste
characteristics, proper design of the air pollution control device based
on expected combustion exhaust gas characteristics, fabrication of the
incinerator with appropriate quality control, installation and shakedown
of the entire system, and operator training.
7.1 OPERATIONAL PROBLEMS AND SOLUTIONS ASSOCIATED WITH HOSPITAL WASTE
INCINERATORS
Incinerator operational problems include excessive stack emissions in
the form of white or black smoke, smoke leakage from the charging door or
other openings, excessive auxiliary fuel usage, and incomplete burnout of
the waste. These operational problems can be minimized through proper
operation of the incinerator together with an effective preventive
maintenance program.
I 2
7.1.1 Excessive Stack Emissions—Controlled-Air Units1'
The proper operation of controlled air incinerators results in
relatively low emission rates. Excessive emission rates can usually be
attributed to one of the following causes:
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1. High setpoint for the secondary burner temperature is not high
enough;
2. Excessive negative draft in the primary chamber;
3. Excessive infiltration air (from charging door);
4. Excessive underfire air in the primary chamber;
5. Operating at too high a primary chamber temperature;
6. Overcharging;
7. Problem wastes; and
8. Inadequate secondary combustion air.
7.1.1.1 Black Smoke. The appearance of black smoke indicates the
presence of unburned carbonaceous material. Dense black smoke is caused
because incomplete combustion is occurring. Incomplete combustion is due
to insufficient amounts of combustion air for the quantity of volatiles/
soot present and is usually the result of overcharging the unit charging
of a highly volatile material or operating the primary chamber at too high
a temperature. The following steps may assist in eliminating black smoke:
1. Check/increase secondary chamber combustion air;
2. Check/decrease underfire air (if necessary); this should result
in reducing the primary chamber operating temperature;
3. Check/increase secondary chamber temperature.
Should these steps fail to eliminate the black smoke, evaluate the
composition of the material remaining to be charged. Highly combustible
materials (i.e., rubber, plastics, etc.) that are charged in too great a
proportion to the other refuse will result in a combustion rate which is
too rapid for the incinerator to handle. These materials may be charged
in very small quantities and in relatively small pieces along with general
refuse. If such materials must be burned frequently, experimentation as
to the quantity that may be charged along with other materials may be
necessary. Generally, highly combustible materials must be charged at
less than 10 percent by weight of the total charge. If the waste contains
a significant amount of plastics, then reducing the primary chamber
temperature (to the 540° to 650°C [1000° to 1200°F] range) may assist in
reducing emissions. Operating the primary chamber at too high a
temperature can cause the plastics to rapidly volatilize.
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7.1.1.2 White Smoke. The appearance of a steady stream of white
smoke from the stack indicates the presence of small aerosols in the
effluent gas. There are several causes for this problem. Either excess
air is entering the incinerator causing entrainment of micron-sized
particles or the secondary chamber is operating at too low a temperature
(i.e., too much air) causing premature cooling of the combustion gases.
The following steps may assist in eliminating white smoke:
1. Check to see that the secondary burner is operating and that
secondary chamber temperature is above 1200°F.
2. Check/decrease underfire air.
3. Decrease secondary air.
4. If all the secondary burner capacity is not being used, gradually
increase the operating rate of the burner until full capacity is reached.
If adjustment of the combustion parameters fail to stop the issuance
of white smoke, examine the material to be charged. Possibly the white
smoke is the result of finely divided noncombustible mineral material
present in the waste charge which is being carried out the stack. Paper
sacks that contain pigments or other metallic oxides, and minerals such as
calcium chloride, generate fine inorganic particulate which cause white
smoke.
The appearance of a white plume (other than a condensing water vapor
plume) a short distance away from the stack probably indicates that
hydrogen chloride is condensing. Unfortunately, there is no incinerator
adjustment that will solve this problem. One solution is to reduce the
amount of chlorinated waste incinerated in each load. This option is
often impractical because the waste is mixed together in packages and,
therefore, cannot be separated. Probably the best solution is to
eliminate chlorinated plastics from use in the hospital or to install an
acid gas scrubbing system.
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7.1.2 Excessive Stack Emissions—Multiple-Chamber Units
Excessive emission rates from multiple-chamber units can usually be
attributed to one of the following causes:
1. High setpoint for the secondary burner temperature is not high
enough;
2. Excessive draft in the primary chamber;
3. Overcharging;
4. Problem wastes;
5. Inadequate secondary combustion air; and
6. Operating at too high a primary chamber temperature.
7.1.2.1 Black Smoke. The appearance of black smoke indicates the
presence of unburned carbonaceous material. Dense black smoke is caused
by incomplete combustion as a result of insufficient amounts of combustion
air for the quantity of volatiles/soot present. Black smoke is often the
result of overcharging of the incinerator or of too large an amount of
highly volatile materials in the waste charged.
Steps which can be taken to eliminate black smoke include:
1. Decrease the charging rate;
2. Increase the secondary combustion air; and
3. Reduce the percentage of highly volatile materials in the waste
feed; and
4. Reduce the primary chamber operating temperature.
7.1.2.2 White Smoke. The appearance of a steady stream of white
smoke from the stack indicates the presence of small aerosols in the
effluent gas. Steps which can be taken to eliminate white smoke include:
1. Check to see that the secondary burner is operating. If all the
secondary burner capacity is not being used, increase the operating rate
of the burner to full capacity; and
2. Decrease the secondary and/or primary air in order to increase
the secondary temperature.
The appearance of a white plume (other than a condensing water vapor
plume) a short distance away from the stack probably indicates that
hydrogen chloride is condensing. No incinerator adjustment will solve
this problem.
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7.1.3 Leakage of Smoke From Primary Chamber
The leakage of smoke through charging doors or other openings
indicates that a positive pressure differential exists in the primary
chamber. Positive pressure can be caused by excessive combustion air, by
excessive charging of a highly volatile material, by too high a primary
chamber operating temperature, or by too much hot ash being discharged to
a wet sump all at one time. The following steps may help eliminate
leakage of smoke:
1. Check/decrease underfire air (controlled-air units);
2. Decrease feed rate;
3. Adjust ash discharge ram cycle; and
4. Adjust draft control (damper or ID fan) setpoints.
If a positive pressure persists, operation of the incinerator draft
control system (draft monitor, barometric damper, induced draft fan)
should be checked.
7.1.4 Excessive Auxiliary Fuel Usage1
For controlled-air units, improper underfire air distribution,
excessive air infiltration, or improper setting of the underfire and
secondary combustion air levels can result in excessive fuel usage. If
the underfire air distribution in the primary chamber is incorrect or if
there is excessive air inleakage, even a substoichiometric air/fuel
mixture, which generates combustible gases for maintaining the secondary
combustion chamber temperature, will not exist in the primary chamber.
Instead, the waste bed will completely burn in some areas and not burn at
all in other areas. The gases conveyed to the secondary chamber will
already be fully oxidized, and auxiliary fuel will be necessary to
maintain the secondary chamber temperature.2
Another cause of excessive auxiliary fuel usage is that the
incinerator is not consistently charged. If the incinerator is not
receiving enough heat input in the form of waste to maintain its
temperature set-points, then the unit will supply its own heat in the form
of auxiliary fuel, i.e., natural gas or oil. Consistent charging of waste
7-5
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at regular timed intervals at a rate near 100 percent of the incinerator's
design capacity will reduce the amount of auxiliary fuel required and will
enhance the incinerator's performance. It is best to charge waste in
batches which are 10 to 15 percent of rated capacity. Therefore, if a
unit is rated at 500 pounds of waste per hour, then the unit should be
charged at 6-minute intervals with charges of approximately 50 pounds
each. The following actions may assist in reducing auxiliary fuel usage:
1. Charge waste at regularly timed intervals at a rate consistent
with 100 percent of the design (thermal input) capacity;
2. Check/reduce secondary combustion air levels;
3. Check primary combustion air levels and distribution;
4. Check charging door seals and other seals for air leakage
(controlled-air units); and
5. Check the fuel trains and burners for fuel leakage.
7.1.5 Incomplete Burnout—Poor Ash Quality
The causes of incomplete burnout include primary burner malfunction,
insufficient primary chamber combustion air or poor underfire air
distribution, overcharging the incinerator with waste, and charging too
much wet waste. As with other operational problems, the causes of
incomplete burnout can be minimized by proper operation of the incinerator
and an effective preventive maintenance program.
7.1.5.1 Primary Burner Malfunction. Primary burner malfunction
causes incomplete burnout because the primary chamber temperature will not
be maintained and because the flame is insufficient to ignite the waste
and keep it burning. Primary burner malfunction may arise due to burner
power loss, burner pluggage, failure of the flame safeguard, or leaking
fuel trains. Each of these problems can be eliminated by preventive
maintenance performed on a regular basis as outlined in Section 5.1. If
the primary burner should fail, the following steps are recommended:
1. Check power supply to the primary burner;
2. If power is available, check burners for pluggage and clean as
required;
7-6
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3. Check the operation of the burner safeguard system as outlined in
the owner's manual; and
4. Check fuel trains and burner assembly for fuel leakage and repair
as required.
7.1.5.2 Insufficient Underfire Air (Controlled-Air Units). In a
controlled-air incinerator, insufficient underfire air can cause the
combustion process to stop completely. Primary causes of the lack of
combustion air are an improper underfire air setting, clinker buildup
around the underfire air ports, and air ports clogged with ash or slag
from previous charges. Clinker buildup around primary chamber air ports
is usually the result of too much air, resulting in local hot spots that
cause the ash to soften, agglomerate, and then harden as clinker during
the cool down cycle. Some manufacturer utilize steam injection into the
ash bed to facilitate burnout of fixed carbon in the ash bed and at the
same time help prevent hot spots and clinker formation.3 Maintaining
proper air levels and air distribution through all underfire air ports is
important. Proper operation and preventive maintenance can prevent these
problems. If poor burnout occurs, the following items should be checked:
1. Check underfire air ports for ash pluggage and rod out as
required;
2. Check around the underfire air ports for clinker buildup and
clean as required; and
3. Check underfire air setting and adjust to the proper setting
(increase) as required.
7.1.5.3 Waste Charging. Charging of waste into the incinerator
should be performed as described in the vendor's literature. Two condi-
tions to be avoided that can cause incomplete burnout are overcharging the
incinerator and charging too much wet waste as part of a charge.
These problems may be encountered with the so called "stuff-and-burn"
type batch units operating on a timed-cycle. When the incinerator is
overcharged and tightly packed with waste, the combustion air cannot
circulate freely through the compacted waste, thereby inhibiting
combustion. When incinerating wet waste, the waste must first be dried by
evaporating the moisture in the waste; if the batch contains a large
fraction of wet waste, insufficient time for complete combustion may be a
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problem. Both of these conditions should be prevented by not overcharging
the incinerator or by increasing the burnout cycle time.
For intermittent-duty, controlled-air, and multiple-chamber
incinerators, reduction of the charge rate may improve the ash burnout
quality. The burndown period also can be increased in an attempt to
improve burnout.
For continuous-duty incinerators, reducing the waste feed charge rate
will increase the residence time of the solids in the primary chamber and
may help to improve ash burnout quality.
7.2 OPERATIONAL PROBLEMS AND SOLUTIONS ASSOCIATED WITH WET SCRUBBERS"'5
The performance of a wet scrubber system is dependent on the key
operating parameters discussed in Chapter 4, on effective preventive
maintenance, and on the integrity of the scrubber components. Premature
failure of these components will lead to increased costs, extended
downtime of the system, and/or operation in temporary noncompliance. The
main problems experienced by wet scrubber systems include corrosion,
scaling, and erosion. An effective preventive maintenance program can
minimize these problems by correcting malfunctions, observing trends in
maintenance activities and making modifications to prolong equipment life,
and correcting minor problems before they become costly, time consuming
repairs. The following sections describe the problems, identify affected
equipment, and recommend solutions.
7.2.1 Corrosion
Corrosion of wet scrubber components is the result of absorption of
sulfur dioxide, sulfur trioxide, or hydrochloric acid gas from the dirty
gas to the scrubbing liquid. The resulting acidic conditions cause
corrosion of the wet scrubber system if it is made of carbon steel. Wet
scrubbers controlling hospital waste incinerators are likely to experience
corrosion from hydrochloric acid as a result of combustion of chlorinated
plastics. The types of equipment that are likely to be subject to
corrosion include scrubbers, absorbers, fans, dampers, ductwork, and
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exhaust stack. If the scrubbing liquid is recirculated (i.e., the system
does not use once-through water), the importance of maintaining the pH of
the scrubbing liquid above the level at which carbon steel is attacked
cannot be stressed enough. An appropriate pH of 6 or greater is usually
maintained through additions of alkaline reagents such as soda ash, lime,
or limestone. The operation of the pH monitor used to control the rate of
alkaline addition should be checked on at least a daily basis to minimize
short-term low pH excursions.
Corrosion also can be a problem in the pumps, pipes, valves, tanks,
and feed preparation areas in slurry service. Slurry tanks and associated
feed preparation equipment should be checked daily for leaks. Equipment
temporarily removed from slurry service should be thoroughly flushed.
Typically, slurry pumps are disassembled at least annually to verify
lining integrity and to detect wear and corrosion or other signs of
potential failure. Bearings and seals are checked but not necessarily
replaced. Pipelines also must be periodically disassembled or tested in
other ways (e.g., hand-held nuclear and ultrasonic devices) both for
solids deposition and for wear. Valves must be serviced routinely,
especially control valves.
The solution to corrosion problems in wet scrubber systems is to
maintain the pH of the scrubbing liquid by the following:
1. Check the proper operation of the pH monitor that controls
alkaline additions daily;
2. Check the alkaline addition system for leaks daily and repair as
required; and
3. Perform regular preventive maintenance on pumps, pipes, valves,
and tanks to minimize and correct corrosion problems.
7.2.2 Scaling
Scaling is a common problem that arises in scrubber components in wet
service such as mist eliminators, fans, dampers, and ductwork. Scale
deposits in mist eliminators can cause nonuniform flow and plugging. Fans
in wet service can develop vibrations as a result of scale deposition on
the fan blades. Dampers may become stuck in place.
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The best solution to scaling and/or plugging is an effective
preventive maintenance program. Observation of the differential pressure
across the mist eliminator can alert personnel to scaling problems.
Periodic cleaning of equipment can minimize scaling problems.
7.2.3 Erosion
Erosion is a common problem associated with scrubber components in
dry service such as fans, dampers, and ductwork. Erosion is also a
problem for scrubber spray nozzles due to the suspended solids recovered
in the scrubbing liquid from the dirty gas. For fans in dry service, fan
vibration may be caused by erosion of fan blades. In such cases, the fan
blades may have to be replaced. Erosion may cause holes in the
ductwork. These holes must be repaired to prevent air in-leakage.
Scrubber spray nozzles are extremely susceptible to erosion and
pluggage problems due to the high velocities of the liquid stream and the
suspended solids within the stream. Pluggage and erosion in the spray
nozzles can be determined by observing the spray angle. If the spray
angle has become enlarged, then the nozzle orifice probably has been
enlarged by erosion. Conversely, if the spray angle has decreased or if a
distinct spray pattern is no longer achieved, then the nozzle orifice
probably is partially or completely plugged. The potential for erosion of
the scrubber components is directly related to the percent suspended
solids. The greater the recirculation flow rate relative to the makeup
and purge (blowdown) flow rates, the greater the potential for buildup of
solids. Infrequent purging also can cause high solids buildup.
Erosion in dry service components is to be expected. Effective
preventive maintenance and equipment replacement when required are the
best solutions.
Erosion in scrubber spray nozzles and'other scrubber components may
be prevented by proper operation and maintenance as follows:
1. Rod out spray nozzles on a regular basis to prevent plugging;
2. Purge the system frequently to prevent solids buildup; and
3. Adjust the recirculation rate as appropriate.
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7.3 OPERATIONAL PROBLEMS AND SOLUTIONS ASSOCIATED WITH FABRIC FILTERS6
The two main operational problems associated with fabric filters are
high opacity and high pressure drop. Well designed, operated, and
maintained fabric filters will generally have a very low opacity (between
0 to 5 percent), and the pressure drop will fall within a general
operating range for the particular fabric filter type (5 to 9 in. w.c. for
pulse-jet fabric filters). Opacity and/or pressure drop deviations from
the baseline values are good indicators of fabric filter performance
deterioration. Higher or lower than normal inlet temperatures can cause
opacity and pressure drop problems. The inlet temperature should be
monitored continuously. The following sections describe each operational
problem, the cause, and possible solutions.
7.3.1 Opacity
Large fabric filter installations may have an opacity monitor coupled
with a strip-chart recorder. Typically, smaller installations have no
opacity monitor and must rely on visible emission observations. In any
event, opacity measurements are useful in determining trends in the
performance of the fabric filter. Typically, the opacity plume of a
properly operated and maintained filter will be very low, except when a
condensible plume is present (even in this case the condensing plume
should be detached). In general, high opacity is a good indicator of
fabric failure. A consistently elevated opacity level relative to the
baseline level is an indication of major leaks and tears in the filter
bags. A puffing, intermittent opacity observed after cleaning that is
higher than the baseline opacity level is a good indication of pinhole
leaks in the filter bags. The factors that cause fabric failure include
improper filter bag installation, high temperature, chemical degradation,
and bag abrasion.
Improper installation of filter bags can result in leaks around
seals, improper bag tensioning, and damage to the bags. Lack of training
of maintenance personnel in filter bag replacement and poor access to the
fabric filter housing are contributing factors to improper installation.
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High temperatures are the result of process malfunction(s) upstream
of the fabric filter. Therefore, in the fabric filter design phase, a
fabric must be chosen on the basis of expected temperature range with an
adequate margin for error. High temperature breaks the polymer chains in
most commercially available fabrics causing loss of strength and reduced
bag life. High temperature attacks the finish on fiberglass bags causing
increased bag abrasions. In general, high temperatures shorten bag life
considerably. High enough temperatures can cause filter bags to ignite.
Some installations may have an alarm system to warn of high temperature
excursions and a bypass system to prevent damage to the filter bags. Such
a system may be appropriate should the cooling system prior to the fabric
filter fail. Sparks may also be a problem with a combustion source such
as a hospital waste incinerator. A spark arrestor can help eliminate the
potential for sparks in the fabric filter.
Chemical degradation of the filter bags occurs as the result of acid
gas condensation. In addition to specification of a temperature range for
filter bags, a chemical resistance rating must also be specified for the
fabric. In the case of hospital waste incinerators, fabric should have
good chemical resistance to hydrochloric acid due to combustion of
chlorinated plastics. Additionally, operation at a high enough
temperature to prevent acid gas condensation will reduce chemical
degradation.
Filter bag abrasion can be caused by contact between a bag and
another surface (e.g., another bag or the walls of the fabric filter) or
by the impact of higher-than-average gas volumes and particulate loading
on the bags. Bag abrasion can also be a problem when the fabric filter
experiences a high pressure drop. Usually, when bag abrasion is a
problem, the greatest abrasion occurs within 18 to 24 inches from the
bottom of the bags. A blast plate or diffuser will redirect the larger
particles away from the bags and reduce bag abrasion.
While the only solution to the problem of high opacity is replacement
of the failed filter bags, it can be prevented by the following:
1. Train maintenance personnel in the proper installation of
replacement filter bags;
2. Design fabric filters for ease in bag replacement;
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3. Choose filter bag fabric with an appropriate operating
temperature range and chemical resistance rating;
4. Blast plates or diffusers are recommended for those facilities
experiencing severe bag abrasion;
5. Monitor inlet temperature—an alarm and bypass system may be
installed to prevent filter bag damage from high temperature excursions;
6. Install a spark arrester to prevent sparks and fire inside the
fabric filter; and
7. Install a bypass/alarm system to prevent damage to filter bags
during high temperature excursions.
7.3.2 Pressure Drop
The pressure drop across a fabric filter is an important indicator of
performance. An increase in pressure drop indicates greater resistance to
flow and can be a symptom of a high air-to-cloth ratio or an increase in
dust cake thickness due to condensation or cleaning system failure.
The air-to-cloth ratio is a design parameter that is determined
during the fabric filter design phase. In the pulse-jet baghouses used to
control emissions from hospital waste incinerators, the air-to-cloth ratio
and therefore pressure drop are relatively high (5 to 9 in. w.c.). Bag
abrasion and/or fugitive emissions may result if the pressure drop is too
high (10 to 14 in. w.c.).
Condensation of moisture on filter bags is caused by temperatures in
the fabric filter below the dewpoint. "Mudding" or blinding of the bags
increases the resistance to flow and occurs because the cleaning system
cannot remove the dust. Condensation can be prevented by preheating the
fabric filter during the startup operation and by purging moist gases from
the unit prior to shutdown. During operation it is critical to maintain
the operating temperature above the dewpoint of the gas stream at all
times.
Cleaning system failures in pulse-jet systems are usually the result
of worn or undersized compressors, and failed solenoids and/or timers.
Compressor problems are indicated by a low compressed-air pressure.
Because of the low pressure the system cannot clean the bags properly and
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an increased pressure drop across the fabric filter results due to dust
cake buildup. Compressor capacity may be a problem and should be checked
against the needs of other systems the compressor serves. Routine
preventive maintenance can prevent premature failure of the compressor and
can prevent worn compressor seals from passing oil into the fabric filter
and blinding the filter bags. Both reduced compressed-air pressure and
bag blinding can cause an increase in pressure drop.
Failure of solenoids and or timers can prevent the filter bags from
being cleaned at all. These sytems require clean, dry mountings to
operate properly. Solenoid failures affect the only row of filter bags
that the solenoid services, while timer failures tend to affect most, if
not all, of the fabric filter system.
An additional problem is that associated with the pulse pipe that
discharges the compressed air into the bags. Pulse pipes may sometimes be
damaged by the force of the compressed air causing ineffective cleaning
and pressure drop increase, improper pipe alignment that may blow holes in
the filter bags, or a loose pipe that may damage the interior of the
fabric filter. The sound of a loose pulse pipe is unmistakable because it
moves whenever compressed air is fired into the pipe.
An increase in pressure drop may indicate operation and maintenance
problems that may be corrected. However, blinded bags resulting from
condensation or the accidental discharge of compressor oil into the fabric
filter will likely have to be replaced. An increase in pressure drop can
be prevented by the following:
1. Preheat the fabric filter prior to process operation;
2. Purge the fabric filter of moist air prior to shutdown;
3. Always maintain the temperature of the gas entering the fabric
filter above its dewpoint;
4. Perform preventive maintenance of the compressor system and
solenoid/timer system;
5. Make necessary repairs to pulse pipes as required; and
6. Adjust the cleaning cycle to shorten the cycle between cleanings.
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7.4 REFERENCES FOR CHAPTER 7
1. McRee, R. Operation and Maintenance of Controlled-Air Incinerators
Ecolaire Environmental Control Products. Undated.
2. Letter from K. Wright, John Zink Company to J. Eddinger, U. S EPA
January 25, 1989.
3. Personal conversation between R. Neulicht, MRI, and G. Swan, Ecolaire
Combustion Products and J. Kidd, Cleaver Brooks. February 22, 1989.
4. Joseph, J., and D. Beachler. APTI Course SI:412C, Wet Scrubber Plan
Review—Self Instructional Guidebook. EPA 450/2-82-020.
U. S. Environmental Protection Agency. March 1984.
5. U. S. Environmental Protection Agency. Wet Scrubber Inspection and
Evaluation Manual. EPA-340/1-83-022. (NTIS PB85-149375)
September 1983.
6. U. S. Environmental Protection Agency. Operation and Maintenance
Manual for Fabric Filters, EPA/625/1-86/020. June 1986.
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8.0 RECORDKEEPING
Recordkeeping is an integral part of an equipment operation and
maintenance (O&M) program. The purpose of recordkeeping is to document
major O&M events and to collect historical data on key operating
parameters. The objective of recordkeeping is to prevent premature
failure of equipment, increase the life of the equipment, and to minimize
emissions. Recordkeeping allows facility and regulatory agency personnel
to track performance, to evaluate trends, to identify potential problem
areas, and to determine appropriate solutions. The magnitude and scope of
recordkeeping activities will depend on a combination of factors,
including personnel availability and training, size and sophistication of
the equipment, and the level of maintenance required. Only records of key
performance parameters and activities should be maintained to avoid
accumulation of unnecessary information.
The following information should be readily available to O&M
personnel: (1) the manufacturer's equipment specification and instruction
manuals, (2) compliance emission tests, (3) operating permits, (4) operat-
ing logs, and (5) maintenance activities log. The operating history
provided by this information is useful in evaluating current and future
performance, maintenance trends, and operating characteristics. A spare
parts inventory also should be maintained with periodic updates so that
parts can be obtained and installed in a timely manner. A recommended
spare parts inventory typically is supplied with the equipment manufac-
turers' O&M manuals. Whether a facility maintains an extensive or minimal
parts inventory is dependent on the available space for parts storage and
whether the facility has a service agreement with the equipment vendor.
8.1 MANUFACTURER'S SPECIFICATIONS AND LITERATURE
The manufacturer's information is the foundation of a recordkeeping
program. A copy of the information and literature supplied by the
incinerator and air pollution control device manufacturers should be
easily accessible for use and review by personnel responsible for O&M.
This literature includes the manufacturer's design specifications,
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performance guarantee, piping and instrumentation diagram, process
flowsheet, material balance information for normal and maximum design
conditions, and an instruction manual for Q&M.
The O&M manuals discuss the theory and design of the equipment;
operating procedures for startup, shutdown, normal operation, and
troubleshooting; maintenance procedures; and a recommended spare parts
list. The guarantee or warranty provisions in the contract are
conditioned on the proper care and treatment of the equipment as specified
in the O&M instruction manual.
8.2 COMPLIANCE EMISSION TEST RECORDS1
Records of initial compliance test results and records of incinerator
process and air pollution control device operating conditions during the
compliance test form the baseline information against which subsequent
operating data are compared. The baseline period normally occurs soon
after shakedown of new equipment and represents conditions when the
control device is operating in compliance with applicable regulations.
Comprehensive baseline test results and equipment operating data establish
the relationship between operating conditions and emission levels for a
specific process/air pollution control device combination. Once this
relationship exists, operating personnel and regulatory groups can use
subsequent measurements of the same parameters to compare against baseline
conditions and thereby identify excursions from acceptable performance.
8.3 OPERATING RECORDS1"3
There is a practical limit to the operating parameters that should be
routinely checked and to the frequency with which the data are logged.
Table 8-1 presents a list of recommended operating parameters for
incinerators, wet scrubbers, fabric filters, and continuous emission
monitors that should be monitored and logged on a regular basis. However,
the decision on which operating parameters will be monitored and recorded
and with what frequency is largely site-specific. This decision depends
on the size and complexity of the equipment, the number of hours per day
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TABLE 8-1. RECOMMENDED OPERATING PARAMETERS THAT SHOULD BE INCLUDED IN
OPERATING LOGS FOR INCINERATORS, WET SCRUBBERS, FABRIC FILTERS,
AND CONTINUOUS EMISSION MONITORS
A. Incinerator Operating Parameters
1. Charging rate/frequency
2. Primary combustion chamber temperature
3. Secondary combustion chamber temperature
4. Incinerator draft
5. Exhaust gas 02 concentration
6. Auxiliary fuel feed rate
B. Wet Scrubber Operating Parameters
1. Gas temperature, inlet and outlet
2. Static pressure drop, total
3. Static pressure drop, mist eliminator
4. Liquor feed rate
5. Liquor pH
6. Water makeup rate
7. Fan(s) current, rpm
8. Nozzle pressure
9. Solids content of liquor
C. Fabric Filter Operating Parameters
1. Gas temperature, inlet and outlet
2. Static pressure drop, total
3. Cleaning cycle frequency
D. Continuous Emission Monitors
1. CO emission concentration, ppm
2. Opacity of emissions, percent
8-3
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that it operates, and the availability of personnel. The greater the
frequency of data gathering, the more sensitive the operators will be to
equipment operational problems. However, as the amount of data increases,
the effort required to collect and manipulate the data also increases.
The optimal frequency of data gathering may be every 4 hours (twice per
shift). If sudden and dramatic changes in performance occur, if the
source is highly variable (such as an incinerator), or if the air
pollution control device operation is extremely sensitive, shorter
monitoring intervals, such as once per hour, are required.
In addition to the numerical values of the operating parameters, a
checklist should be included to confirm operation of fans, limit switches,
burners, ram feeders, pumps, nozzles, and the other general physical
considerations that can adversely influence performance.
8.4 MAINTENANCE RECORDS2
Maintenance records provide an operating history of equipment. They
can indicate what equipment has failed, where, when, and how often; what
kinds of problems are typical; what actions were taken; and, over time,
the efficacy of the remedial actions. These records can be used in
conjunction with a spare parts inventory to maintain and update a current
list of available parts and the costs of these parts.
The work order system is one way to keep useful maintenance
records. This system would be administered by the engineer in charge of
the proper O&M of the incinerator. Whenever maintenance is required, the
engineer will issue a work order to the appropriate department (e.g.,
maintenance) detailing the work to be performed. Additionally, the work
order form should include the following information to assure both good
communication between departments and prompt completion of the work: a
work order number, the date of the work request, the name of the person
requesting the work and his/her department, the department to which the
work order is sent, any special equipment required, any special
precautions that should be taken, a signature block for the person
performing the work, and the date of completion of the work. The format
of the work order form is variable as long as it fits the needs of the
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particular hospital. The engineer, upon return of the completed work
order, may check the satisfactory performance of the work requested. When
properly designed and used, this system provides information on the
suspected problem, the problem actually found, the corrective action
taken, time and parts required, and any additional pertinent information.
Additionally, such a system can also be used to ensure that the monthly,
quarterly, and semiannual routine preventive maintenance is performed. In
developing a work order maintenance log system, facility personnel should
consult both the schedules in Chapter 5.0 and the manufacturer's
recommended maintenance schedule. The work order system may involve the
use of triplicate carbon forms or it may be computerized. Triplicate
carbons provide a copy of the work order to the engineer (requestor), the
department performing the work, and the hospital administration. These
copies would become part of the O&M log. Daily and weekly preventive
maintenance activities should be included as part of the routine operation
of the incinerator and associated air pollution control device.
Preventive maintenance activities and schedules for incinerators, wet
scrubbers, and fabric filters are discussed more fully in Chapter 5.0.
Another approach is to use a log book in which a summary of
maintenance activities is recorded. Although not as flexible as a work
order system (e.g., copies of individual work orders can be sent to
appropriate departments), it does provide a centralized record and is
probably better suited for the small facility.
8.4.1 Retrieval of Records2
A computerized storage and retrieval system is ideal for
recordkeeping. A computer can manipulate and retrieve data in a variety
of forms and also may be useful in identifying trends. A computerized
system is not for everyone, however. The larger the data set to be
handled, the more likely it is that a computer can help to analyze and
sort data. Sorts might include a history of maintenance activities and
identification of recurring operating problems that might indicate a need
for more frequent maintenance or inspections. For a small source that
presents few problems and that has a manageable set of operating
parameters to be monitored, a computer system may not be cost effective.
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Retention time is also a site-specific variable. If records are
maintained only to meet a regulatory requirement and are not used or
evaluated, they can probably be disposed of at the end of the statutory
limitation (typically 2 years). It can be argued that these records
should not be destroyed because if the equipment fails prematurely, the
data preserved in the records could be used to troubleshoot the problem.
In some cases, records going back 10 to 12 years have been kept to track
the performance, cost, and system response to various situations and the
most effective ways to accomplish remedial actions. These records serve
as a learning tool to optimize performance and minimize emissions, which
is the underlying purpose of recordkeeping. Some of these records may be
kept throughout the life of the equipment. After several years, however,
summaries of O&M activities are more desirable than the actual records
themselves. These can be created concurrently with the daily O&M records
for future use. If needed, actual data can then be retrieved for further
evaluation.
8.5 REFERENCES FOR CHAPTER 8
1. U. S. Environmental Projection Agency. Wet Scrubber Inspection and
Evaluation Manual. EPA-340/1-83-022. (NTIS PB85-149375).
September 1983.
2. U. S. Environmental Protection Agency. Operation and Maintenance
Manual for Electrostatic Precipitators. EPA 625/1-85-017. September
1985.
3. U. S. Environmental Protection Agency. Operation and Maintenance
Manual for Fabric Filters. EPA/625/1-86/020. June 1986.
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9.0 SAFETY GUIDELINES
This section provides general safety guidelines in the O&M of
hospital incinerators and associated air pollution control devices. The
information presented here is intended to supplement safety information
provided by manufacturers and/or safety standards established by
individual hospitals. There are two primary concerns with respect to the
operator's safety. The first concern is the potential for exposure to
pathogens during handling of infectious waste. The second concern is the
prevention of injury due to the general hazards normally associated with
industrial equipment such as incinerators and air pollution control
devices.
9.1 PREVENTION OF INFECTION DURING WASTE HANDLING1
The major risk of infection to an operator is from puncture wounds
caused by contaminated objects such as surgical instruments, needles, and
broken glass. Most, if not all, hospitals are using special rigid, secure
containers to prevent injury from infected sharp objects. Nonetheless, to
prevent possible injury which could result in infection, safety rules
which should be followed include:
1. Minimize the handling of red bag waste;
2. Keep red bag wastes in a secure location prior to incineration;
3. Never open red bags to inspect the contents; and
4. Follow procedures which maintain the integrity of the red bag
waste. If breakage/spillage of red bag waste occurs, then handling
procedures must be changed. The use of double bags, stronger bags, rigid
carts, or cardboard containers to contain the red bag waste should be
instituted. The hospital administration should be contacted if there are
continued problems with bag integrity;
5. Wear thick rubber gloves when handling red bag wastes;
6. Wear hard-soled rubber shoes when handling waste and working in
the area around the incinerator; and
7. Wear safety glasses.
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9.2 EQUIPMENT SAFETY PROCEDURES
2_5
General safety procedures to prevent injury when working around the
incinerator and air pollution control equipment include:
1. Containers of flammable liquids or explosives should never be
fed into the incinerator;
2. The incinerator charging door should not be opened if the
incinerator is under positive pressure, if the ignition burner is on, or
if other conditions recommended by the manufacturer are not met (i.e.,
minimum time between charges). Always exercise caution when opening the
charging door. Wearing safety glasses, the operator should stand behind
the door, open the door several inches and pause, then open the door
fully;
3. Never open cleanout ports to view into the incinerator during
operation;
4. Never enter the chambers of mechanical ram feeders, ash
conveyors, or the incinerator without first turning off all power sources
and assuring that the units are "locked out." If a chamber must be
entered, after locking the unit out, make sure a second person is standing
by;
5. Observe caution around all moving belts, hydraulic cylinders,
and doors;
6. For systems requiring manual ash removal, exercise extreme
caution when removing the ash. Do not enter the incineration chamber to
remove the ash. Instead, use the mechanical ash ram or conveyor (if
available) or rakes or shovels with handles of sufficient length to reach
the back of the incinerator ash compartment. When using rakes or shovels,
use caution so as not to damage the incinerator refractory;
7. Wear proper personal safety equipment when operating the
incinerator and removing/handling the ash to prevent burns, cuts,
punctures, or eye injury. Proper safety equipment includes gloves, hard-
soled rubber shoes, and safety glasses;
8. Avoid direct contact with the hot surfaces of the incinerator
chamber, heat recovery equipment, ductwork, and stack;
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9. The scrubber liquor from wet scrubbers likely will be caustic.
Avoid contact with the liquid and wear eye protection near and around the
scrubber;
10. Venturi scrubbers operate at high positive pressures. Be
cautious of leaks in the scrubber vessel, ductwork, or piping;
11. Entry into fabric filters other than for maintenance should be
avoided. Only persons who have been properly trained should enter fabric
filters, and they should be alert to the following hazards ad necessary
precautions.
(a) Before personnel enter the unit, the filter bags should be
thoroughly cleaned and dust dislodged and discharged from the hopper by
mechanical vibration to prevent fugitive emissions and dust inhalation.
Hopper doors should only be opened when the unit (including fan and hopper
evacuation systems such as screws and drag chains) has been shut down.
(b) Oxygen deficiency as is common in incinerator combustion gases
makes fabric filter entry especially dangerous. Purging of the unit does
not always replace the exhaust gases with ambient air. Inspectors should
know the dangers associated with oxygen deficiency.
(c) Explosion is possible in a confined space such as a fabric
filter. Ventilation/purging prior to entry is recommended.
(d) Exposure to toxic chemicals in the collected dust is another
danger of fabric filter entry. A quantitative assessment of the expected
compounds in the dust and threshold dose levels should be made prior to
entry. Proper personnel protection equipment such as respirators should
be worn.
12. Eye protection, hearing protection, long sleeved shirts, and
gloves should be worn during fabric filter inspection. Inspectors also
should be cognizant of heat/thermal stress associated with the length of
time required for inspection/repairs. Because of the dusty, humid
conditions and limited access, thermal effects may be severe.
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9.3 FIRE SAFETY6
Fire safety is particularly important when working around
incinerators due to the nature of the high temperature combustion
process. The areas in which the operator should exercise caution
include: waste storage, waste charging to the incinerator, and ash
removal.
The location of the waste storage area relative to the incinerator is
an important consideration regarding fire safety. Waste should be stored
away from the incinerator and ash storage areas such that access to the
unit is not blocked and premature ignition of the stored waste from stray
sparks or burning flyash is eliminated.
Charging of the waste into the incinerator has a particularly high
fire hazard associated with it because of the potential exposure of high
temperature and flaming conditions to the operator and surrounding
building areas. When charging manually charged incinerators, the operator
should exercise extreme caution. A fire safety feature that should be
included on manually loaded incinerators is an interlock system that shuts
off the primary chamber burner(s) when the charging door is opened. Some
systems shut off the underfire air when the charge door opens. The charge
door should operate freely and be free of any sharp edges or projections
that could catch or hang up waste materials and cause spillage. When
charging automatically charged incinerators, a potential fire hazard
exists when waste material (particularly plastics) adheres to the hot
charging ram. If these materials do not drop from the ram during its
loading cycle, they may ignite and be carried back into the charging
hopper where the remaining waste will become ignited. Automatic loading
systems usually have automatic safety systems activated by a flame scanner
that spray water to quench the hot ram face and any flames and/or
automatic systems that reinitiate a loading sequence to charge the burning
waste into the incinerator.
Handling of ash is another area where the operator should exercise
extreme caution regarding fire safety. Manual ash removal involves
removing ash with rakes and shovels followed by a water quench. Because
the ash may contain hot spots, the operator should wear proper personal
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safety equipment including gloves, hard-soled rubber shoes, and safety
glasses. Water quenching should occur only after removing the ash from
the incinerator to prevent damage to the incinerator refractory.
Automatic ash removal systems quench the ash as it is removed from the
incinerator and dump the quenched ash into ash carts. Quenched ash should
be stored in a fire rated area in a location isolated from stored waste
materials.
9.4 REFERENCES FOR CHAPTER 9
1. U. S. Environmental Protection Agency. EPA Guide for Infectious Waste
Management. EPA/530-SW-86-014. (NTIS PB86-199130). U. S. EPA Office
of Solid Waste. May 1986.
2. U. S. Environmental Protection Agency. Operation and Maintenance
Manual for Fabric Filters. EPA/625/1-86/020. June 1986.
3. U. S. Environmental Protection Agency. Wet Scrubber Inspection and
Evaluation Manual. EPA 340/1-83-022. (NTIS PB85-149375).
September 1983. '
4. Richards Engineering. Air Pollution Source Field Inspection Notebook'
Revision 2. Prepared for the U. S. Environmental Protection Agency
Air Pollution Training Institute. June 1988.
5. U. S. Environmental Protection Agency. Air Pollution Source
Inspection Safety Procedures: Student Manual, EPA-340/l-85-002a
September 1985.
6. Doucet, L. Fire Protection Handbook, National Fire Protection
Association Waste Handling Systems and Equipment. Chapter 12.
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10.0 GLOSSARY
ABSORPTION. The process by which gas molecules are transferred to
(dissolved in) a liquid phase.
ACID GASES. Corrosive gases formed during combustion of chlorinated or
halogenated compounds, e.g., hydrogen chloride (HC1).
ACTUAL CUBIC FEET PER MINUTE (acfm).3 A gas flow rate expressed with
respect to temperature and pressure conditions.
AERODYNAMIC DIAMETER/ The diameter of a unit density sphere having the
same aerodynamic properties as an actual particle. It is related to
the physical diameter according to the equation below:
where:
dpa = aerodynamic diameter
dp * physical diameter
P » particle density
C = Cunningham correction factor
AIR, DRY. Air containing no water vapor.
ASH. The noncombustible inorganic residue remaining after the ignitionof
combustible substances.
ATOMIZATION." The reduction of liquid to a fine spray.
BAG BLINDING. The loading, or accumulation, of filter cake to the point
where capacity rate is diminished.
BAROMETRIC SEAL. A column of liquid used to hydraulically seal a
scrubber, or any component thereof, from the atmosphere or any other
part of the system.
BOTTOM ASH. The solid material that remains on a hearth or falls through
the grate after incineration is completed.
(4.
BURN RATE. The total quantity of waste that is burned per unit of time
that is usually expressed in pounds of waste per hour.
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BURNDOWN PERIOD. The period of time in an incinerator's operating cycle
during which no additional waste is charged to the incinerator and
the primary combustion chamber temperature is maintained above a
minimum temperature (using auxiliary burners as necessary) to
facilitate the solid phase combustion of the waste bed.
i+
CHARGE RATE. Quantity of waste material loaded into an incinerator over
a unit of time but which is not necessarily burned. Usually
expressed in pounds of waste per hour.
CLINKERS. Hard, sintered, or fused pieces of residue formed in an
incinerator by the agglomeration of ash, metals, glass, and ceramics.
COCURRENT OR CONCURRENT/ Flow of scrubbing liquid in the same direction
as the gas stream.
COLLECTION EFFICIENCY.1 The ratio of the weight of pollutant collected to
the total weight of pollutant entering the collector.
COMBUSTION. A thermal process in which organic compounds are broken down
into carbon dioxide (C02) and water (H20).
CONDENSATION.1 The physical process of converting a substance from the
gaseous phase to the liquid phase via the removal of heat and/or the
application of pressure.
CONTROLLED AIR INCINERATION.5 Incineration utilizing two or more
combustion chambers in which the amounts and distribution of air to
each chamber are controlled. Partial combustion takes place in the
first zone (chamber) and subsequent zones are used to complete
combustion of the volatilization gases.
COOLDOWN PERIOD. The period of time at the end of an incinerator's
operating cycle during which the incinerator is allowed to cool
down. The cooldown period follows the burndown period.
CROSSFLOW. Flow of scrubbing liquid normal (perpendicular) to the gas
stream.
CYCLONE.** A device in which the velocity of an inlet gas stream is
transformed into a confined vortex from which inertia! forces tend to
drive particles to the wall.
DAMPER.2 An adjustable plate installed in a duct to regulate gas flow.
DEHUMIDIFY. To remove water vapor from a gas stream.
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tl
OEMISTER. A mechanical device used to remove entrained water droplets
from a scrubbed gas stream.
2
DENSITY. The ratio of the mass of an object to the volume of the
object.
DIFFUSION (AEROSOL)/ Random motion of particles caused by repeated
collisions of gas molecules.
DRAFT. A gas flow resulting from pressure difference; for example, the
pressure difference between an incinerator and the atmosphere, which
moves the products of combustion from the incinerator to the
atmosphere. (1) Natural draft: the negative pressure created by the
difference in density between the hot flue gases and the
atmosphere. (2) Induced draft: the negative pressure created by the
vacuum action of a fan or blower between the incinerator and the
stack. (3) Forced draft: the positive pressure created by the fan
or blower, which supplies the primary or secondary air.
DUST. Solid particles less than 100 micrometers created by the breakdown
of larger particles.
DUST LOADING. The weight of solid particulate suspended in an airstream
(gas). Usually expressed in terms of grains per cubic foot, grams
per cubic meter, or pounds per thousand pounds of gas.
ENDOTHERMIC." A chemical reaction that absorbs heat from its
surroundings. For example: C+H20+heat --> CO+H2
ENTRAPMENT.3 The suspension of solids, liquid droplets, or mist in a gas
stream.
EXOTHERMIC/ A chemical reaction that liberates heat to its
surroundings. Combustion is an exothermic reaction. For example:
C+02 --> C02+heat
FEEDBACK CONTROL.3 An automatic control system in which information about
the controlled parameter is fed back and used for control of another
parameter.
FIXED CARBON.** The nonvolatile organic portion of waste.
GRID. A stationary support or retainer for a bed of packing in a packed
bed scrubber.
HEADER. A pipe used to supply and distribute liquid to downstream
outlets.
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HEAT RELEASE RATE."* The energy released over a unit of time during
combustion. Calculated as the heating value (Btu/pound)xburn rate
(pound/hour). Usually expressed as Btu/hour (Btu/h).
HEATING VALUE/ The amount of heat that is released when a material is
combusted usually expressed as Btu/lb.
HUMIDITY, ABSOLUTE.2 The weight of water vapor carried by a unit weight
of dry air or gas.
HUMIDITY, RELATIVE.2 The ratio of the absolute humidity in a gas to the
absolute humidity of a saturated gas at the same temperature.
INCINERATOR. A thermal device which combusts organic compounds using
heat and oxygen.
INDUCED DRAFT FAN. A fan used to move a gas stream by creating a
negative pressure.
INERTIA. Tendency of a particle to remain in a fixed direction,
proportional to mass and velocity.
LIQUID-TO-GAS RATIO.3 The ratio of the liquid (in gallons per minute) to
the inlet gas flow rate (in acfm).
LIQUOR.1 A solution of dissolved substance in a liquid (as opposed to a
slurry, in which the materials are insoluble).
MAKEUP WATER. Water added to compensate for water losses resulting from
evaporation and water disposal.
ELIMINATOR.3 Equipment thai
downstream from a scrubber.
[TY/ Measun
particu late.
MIST ELIMINATOR.3 Equipment that removes entrained water droplets
m<
OPACITY/ Measure of the fraction of light attenuated by suspended
PACKED-BED SCRUBBER.3 Equipment using small plastic or ceramic pieces,
with high surface area to volume ratios for intimate gas/liquid
contact for mass transfer.
PARTICLE/ Small discrete mass of solid or liquid matter.
PARTICLE SIZE/ An expression for the size of liquid or solid particle
usually expressed in microns.
PARTICULATE EMISSION/ Fine solid matter suspended in combustion gases
carried to the atmosphere. The emission rate is usually expressed as
a concentration such as grains per dry standard cubic feet (gr/dscf)
corrected to a common base, usually 12 percent C02.
10-4
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PARTICULATE MATTER/ As related to control technology, any material
except uncombined water that exists as a solid or liquid in the
atmosphere or in a gas stream as measured by a standard (reference)
method at specified conditions. The standard method of measurement
and the specified conditions should be implied in or included with
the particulate matter definition.
PATHOGENIC. Waste material capable of causing disease.
PATHOLOGICAL WASTE. Waste material consisting of anatomical parts.
PENETRATION. Fraction of suspended particulate that passes through a
collection device.
pH. A measure of acidity-alkalinity of a solution.
PRESSURE DROP. The difference in static pressure between two points due
to energy losses in a gas stream.
(.
PRESSURE, STATIC. The pressure exerted in all directions by a fluid;
measured in a direction normal (perpendicular) to the direction of
flow.
PROXIMATE ANALYSIS." The determination of the amounts of volatile matter,
fixed carbon, moisture, and noncombustible (ash) matter in any given
waste material.
PYROLYSIS. The chemical destruction of organic materials in the presence
of heat and the absence of oxygen.
QUENCH. Cooling of hot gases by rapid evaporation of water.
REAGENT. The material used in a scrubbing system to react with the
gaseous pollutants.
RED BAG WASTE. As used in this document, red bag waste refers to
infectious waste; the name comes from the use of red plastic bags to
contain the waste and to clearly identify that the waste should be
handled as infectious.
RESIDENCE TIME. Amount of time the combustion gases are exposed to
mixing, temperature, and excess air for final combustion.
SATURATED GAS. A mixture of gas and vapor to which no additional vapor
can be added, at specified conditions.
SIZE DISTRIBUTION/ Distribution of particles of different sizes within a
matrix of aerosols; numbers of particles of specified sizes or size
ranges, usually in micrometers.
10-5
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SLURRY.1 A mixture of liquid and finely divided insoluble solid
materials.
SMOKE. Small gasborne particles resulting from incomplete combustion;
particles consist predominantly of carbon and other combustible
material; present in sufficient quantity to be observable
independently of other solids.
SPECIFIC GRAVITY.1 The ratio between the density of a substance at a
given temperature and the density of water at 4°C.
SPRAY NOZZLE. A device used for the controlled introduction of scrubbing
liquid at predetermined rates, distribution patterns, pressures, and
droplet sizes.
STANDARD CUBIC FEET PER MINUTE (scfm).3 A gas flow rate expressed with
respect to standard temperature and pressure conditions.
STARVED-AIR INCINERATION. Controlled air incineration in which the
primary chamber is maintained at less than stoichiometric air
conditions.
STOICHIOMETRIC AIR. The theoretical amount of air required for complete
combustion of waste to C02 and H20 vapor.
STUFF AND BURN. A situation in which the charging rate is greater than
burning rate of the incinerator.
VAPOR.* The gaseous form of substances that are normally in the solid or
liquid state and whose states can be changed either by increasing the
pressure or by decreasing the temperature.
VOLATILE MATTER. That portion of waste material which can be liberated
with the application of heat only.
REFERENCES FOR CHAPTER 10
1. Industrial Gas Cleaning Institute. Wet Scrubber Technology.
Publication WS-1,-July 1985.
2. Industrial Gas Cleaning Institute. Fundamentals of Fabric Collectors
and Glossary of Terms. Publication F-2, August 1972.
3. Flue Gas Desulfurization Inspection and Performance Evaluation.
EPA/625/1-85-019. October 1985.
10-6
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4. U. S. Environmental Protection Agency, Control Techniques for
Particulate Emissions from Stationary Sources. Volume I.
EPA-450/3-81-005a. September 1982.
5. Brunner, C. R. Incineration Systems Selection and Design. Van
Nostrand Reinhold Company, 1984.
10-7
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»-,i protection Agency.
U.S. Environmental > roiecuw o
Region V, Library
U.S. Environmental Protection Agency ?3* SoJth Dearborn Street
Region V. ' :' - -/ Chicago, Illinois 60604
230 So ' "' 'ct
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TECHNICAL REPORT DATA
'Please read instructions on the reverse oelore comnlennei
1. REPORT NO. 2.
EPA 450/3-89-002
4. TITLE AND SUBTITLE
Operation and Maintenance of Hospital Medical Uaste
Incinerators
7. AUTHOH(S)
Neulicht, R.M.; Turner, M.B.; Chaput, L.S.;
Wallace, D.D.; Smith, S.G.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Midwest Research Institute
401 Harrison Oaks Boulevard, Suite 350
Cary, North Carolina 27513
12. SPONSORING AGENCY NAME AND ADDRESS
U. S. Environmental Protection Agency
Control Technology Center
Research Triangle Park, N,C, 27711
3. RECIPIENT'S ACCESSION NO.
5. REPORT DATE
March 1989
6. PERFORMING ORGANIZATION CODE
8. PERFORMING ORGANIZATION REPORT NO.
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
68-02-4395
63-C8-G011
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
is. SUPPLEMENTARY NOTES Work Assignment Managers:
James Eddinger, Office of Air Quality Planning and Standards
Justice Manning, Center for Environmental Research
The primary objective of this document is to identify the operation and
maintenance (O&M) procedures that should be practiced on hospital medical waste
lfl/"Trtov*a^rtv*c An/4 accrt/»Ta4»«*J a 4 n« M^lln^^A.— — ^ i • ^_ *_ • • • •
— 3.1 r*
emissions. Proper O&M, in addition to reducing air^emissions, improves equipment
reliability and performance, prolongs equipment life, and helps to ensure proper ash
burnout. This document provides general guidance on proper O&M procedures with the
intention of identifying good operating practices. The document is intended as a
technical guide for use by Federal, State, and local agency personnel, hospital
waste management personnel, and hospital incinerator operators.
The document presents background information on hospital medical waste
incineration systems including a summary of combustion principles and descriptions
of the types of incinerators typically used for hospital medical wastes. Background
information on add-on air pollution control systems also is presented. Key
operating parameters and good operating practices for the incineration and air
pollution systems are identified and discussed. General guidance on maintenance of
the systems also is provided. Common operating problems, their possible causes, and
possible solutions to the problems are presented. Other topics discussed include
control and monitoring instrumentation, recordkeeping procedures, and safety.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b-IDENTIFIERS/OPEN ENDED TERMS
COSATI f'leld/Group
Medical Uaste Incineration
Hospital Waste Incineration
Air Pollution Control Technology
Incineration
Medical Waste
Hospital Waste
Air Pollution Control
i. DISTRIBUTION STATEMENT
Release unlimited
I 19. SECURITY CLASS (This Report I
21. NO. OF PAGES
'20. SECURITY CLASS
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