EPA/625/6-89/024
                                              January 1990
                 Handbook


    Operation and  Maintenance of
Hospital  Medical Waste  Incinerators
         Office of Air Quality Planning and Standards
                       and
       Air and Energy Engineering Research Laboratory
           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 45268
                                        Printed on Recycled Paper

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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.
                                      11

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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
from the manufacturer which provide  specific O&M instructions 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
Disclaimer	 ii
Preface  	  iii
Figures  	  viii
Tables  	 ix
Acknowledgments	 x

1    Introduction  	 1

2    Hospital Incineration Systems  	 3
     2.1    Introduction 	 3
     2.2    Fundamental Concepts Related to Hospital Waste Incineration	  3
           2.2.1 Pathogen Destruction  	 4
           2.2.2 Principles of Combustion  	 4
     2.3    Hospital Waste Characteristics	 9
     2.4    Types of Hospital Waste Incinerator Systems	   10
           2.4.1   Introduction  	   10
           2.4.2   Multiple-Chamber Incinerators  	   11
           2.4.3   Controlled-Air Incinerators	   14
           2.4.4   Rotary Kilns  	   18
           2.4.5   ^Auxiliary Equipment  	   20
     2.5    References for Chapter 2	   20

3    Air Pollution Control 	   23
     3.1    Introduction 	   23
     3.2    Pollutant Formation and Generation  	   23
     3.3    Control Strategies	   24
           3.3.1   Controlling Feed Material  	   24
           3.3.2   Combustion Control  	   24
           3.3.3   Add-On Air Pollution Control Systems 	   24
     3.4    References for Chapter 3  	   32
4    Operation  	   35
     4.1    General Objectives	   35
     4.2    Incinerator Key Operating Parameters  	   36
           4.2.1   Introduction  	   36
           4.2.2   Controlled-Air Incinerators	   36
           4.2.3   Multiple-Chamber Incinerators  	   39
           4.2.4   Rotary Kiln Incinerators  	   40
     4.3    Waste Feed Handling  	   41
           4.3.1   Proper Waste Handling  	   41
           4.3.2   Restricted Wastes  	   43
     4.4    Incinerator Operation, Control, and Monitoring	   43
           4.4.1   Batch Feed Controlled-Air Incinerator 	   43
           4.4.2   Intermittent-Duty, Controlled-Air Incinerators  	   48

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                                      Table of Contents (continued)
                            4.4.3   Continuous-Duty, Controlled-Air Incinerators	  50
                            4.4.4   Multiple-Chamber Incinerators 	  51
                      4.5   Add-On Air Pollution Control Systems  	  52
                            4.5.1   Wet Scrubbers	  53
                            4.5.2   Fabric Filters  	''.'.'.'.'.'.  55
                            4.5.3   Spray Dryers 	  57
                            4.5.4   Dry Injection	  53
                      4.6   References for Chapter 4	  59
                 5    Maintenance 	  61
                      5.1   Hospital Waste Incinerators  	  61
                            5.1.1   Hourly/Daily Maintenance  	  61
                            5.1.2   Weekly/Biweekly Maintenance  	  63
                            5.1.3   Monthly/Semiannual Maintenance 	  63
                      5.2   Wet Scrubbers	  64
                            5.2.1   Daily/Weekly Maintenance  	  64
                            5.2.2   Monthly/Semiannual Maintenance 	'.	  64
                      5.3   Maintenance of Fabric Filters  	  65
                            5.3.1   Daily Inspection/Maintenance  	  66
                            5.3.2   Weekly Inspection/Maintenance  	  66
                            5.3.3   Monthly/Quarterly Inspection/Maintenance  	  66
                            5.3.4   Semiannual/Annual Inspection/Maintenance   	  67
                      5.4   References for Chapter 5  	  67

                 6    Control and Monitoring Instrumentation 	  69
                      6.1   Operating Parameters that Should be Monitored  	  69
                      6.2   Typical Instrumentation	  69
                            6.2.1   Temperature Sensors  	  69
                            6.2.2   Pressure	  70
                            6.2.3   Oxygen Concentration  	  71
                            6.2.4   Carbon Monoxide 	  72
                            6.2.5   Opacity  	'.. "  73
                            6.2.6   Charge Rate	  74
                            6.2.7   Scrubber Liquor pH  	  75
                      6.3   References for Chapter 6  	  75
                 7    Operational Problems and Solutions  	  77
                      7.1   Operational Problems and Solutions Associated with
                              Hospital Waste Incinerators  	  77
                            7.1.1  Excessive Stack Emissions - Controlled-Air Units  	   77
                            7.1.2  Excessive Stack Emissions - Multiple-Chamber Units  	   78
                            7.1.3  Leakage of Smoke From Primary Chamber  	   78
                            7.1.4   Excessive Auxiliary Fuel Usage  	  79
                            7.1.5   Incomplete Burnout-Poor Ash Quality   	   79
                      7.2   Operational Problems and Solutions Associated with
                              Wet Scrubbers	  80
                            7.2.1  Corrosion 	  80
                            7.2.2  Scaling	'  80
                            7.2.3  Erosion 	  81
                      7.3    Operational Problems and Solutions Associated with
                              Fabric Filters  	  81
_
                                                       VI

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                   Table of Contents (continued)
          7.3.1   Opacity	  81
          7.3.2   Pressure Drop 	  82
    7.4   References for Chapter 7	  83
8   Recordkeeping	  85
    8.1   Manufacturer's Specifications and Literature 	  85
    8.2   Compliance Emission Test Records 	  85
    8.3   Operating Records 	  85
    8.4   Maintenance Records  	  86
          8.4.1   Retrieval of Records	  87
    8.5   References for Chapter 8	  87

9   Safety Guidelines  	.•	  89
    9.1   Prevention of Infection During Waste Handling	  89
    9.2   Equipment Safety Procedures  	  89
    9.3   Fire Safety  	  90
    9.4   References for Chapter 9	  91

10  Glossary  	  93
    10.1  References for Chapter 10	  97
                                      VII

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                                   Figures
2-1.    Major components of an incineration system	  4
2-2.    Relationship of temperature to excess air	  7
2-3.    In-line multiple-chamber incinerator with grate	  12
2-4.    Retort multiple-chamber incinerator for pathological wastes	  13
2-5.    Schematic of a controlled-air incinerator	  15
2-6.    Schematic of a single batch controlled-air incinerator	  15
2-7.    Example intermittent-duty, controlled-air incinerator	  16
2-8.    Hopper/ram mechanical waste feed system	  17
2-9.    Incinerator with step hearths and automatic ash removal	  18
2-10.   Rotary kiln with auger feed	  19
2-11.   Incinerator with waste heat boiler and bypass stack	  19
3-1.    Impaction	  25
3-2.    Spray venturi with circular throat	  26
3-3.    Spray venturi with rectangular throat	  26
3-4.    Countercurrent packed tower absorber	  27
3-5.    Countercurrent-flow spray tower	  28
3-6.    Pulse jet baghouse	  29
3-7.    Components of a spray dryer absorber system (semiwet process)	  31
3-8.    Components of a dry injection absorption system (dry process)	  31
6-1.    Schematic of an extractive monitoring system	  73
6-2.    Typical transmissometer installation for measuring opacity	  74
                                      Vlll

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                                   Tables
2-1.    Stoichiometric Oxygen Requirements and Combustion Product Yields  	  6
2-2.    Examples of Infectious Waste  	.'	  9
2-3.    Characterization of Hospital Waste	  H
2-4.    Characterization of Hospital Waste  	  H
2-5.    Classification of Hospital Incinerators 	  12
3-1.    Control Strategies for Air Pollutants from Hospital Waste Incineration  	  25
4-1.    Key Incinerator Operating Parameters and Recommended
         Operating Range: Controlled-Air Incinerator	  37
4-2.    Key Incinerator Operating Parameters and Recommended
         Operating Range: Multiple-Chamber Incinerator 		  40
4-3.    Example Timed Control Cycle for Batch Mode Incinerator 	  47
4-4.    Wet Scrubber Performance Parameters for Hospital Waste Incinerators  ...  54
4-5.    Key Operating Parameters for Fabric Filter Control Systems	  55
5-1.    Typical Maintenance Inspection/Cleaning/Lubrication Schedule
         for a Hospital Waste Incinerator	  62
5-2.    Typical Maintenance Inspection/Cleaning/Lubrication Schedule
         for a Wet Scrubber  	•	  65
5-3.    Typical Maintenance Inspection/Cleaning/Lubrication Schedule
         for a Fabric Filter System	  67
6-1.    Thermocouple Types	  70
6-2.    Performance Specifications for Opacity Monitors  	  74
8-1.    Recommended Operating Parameters that Should be Included in
         Operating Logs for Incinerators, Wet Scrubbers, Fabric Filters,
         and Continuous Emission Monitors 	  86
                                        IX

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                            Acknowledgments
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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                                           Chapter 1
                                         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
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 affect 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

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 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.

 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.

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                                          Chapter 2
                             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.
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

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             Control and
             Monitoring
                Waste
                          Waste
                          Charge
                          System
                               Incinerator
                                                    To Atmosphere
                                                                   Stack
                                                                                       To Atmosphere
                                                                                            I
                                                                                              Stack
Ash
Removal
System
                                                                      1  Waste  '
                                                                     "!  Heat  f
                                                                      j_ Boiler J
                                      Air   |
                                    Pollution i--
                                    Control  [
                                    System  i
           Figure 2-1.   Major components of an incineration system.

       remainder of this document; they do not provide
       complete coverage of the subject areas.

       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 & susceptible host  could result in an  infectious
disease."1 Some examples of hospital wastes which
may be considered to be infectious are: i
       1.
       2.

       3.
       4.
       5.

       6.
   Microbiological laboratory wastes including
   cultures and equipment which has  come in
   contact with cultures of infectious agents;
   Blood and  blood products (such as serum,
   plasma);
   Sharps,  including needles, laboratory  glass
   wastes, and glass pipets;
   Surgical, autopsy, and obstetrical wastes which
   have had contact with patient blood or body
   fluids;
   Wastes  which   have  had  contact  with
   communicable disease isolation wastes;
   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
_
                                                                  Ash
     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 microorganisms from the
     incinerator could be  attributed  to insufficient
     retention time and temperature  as a result of the
     following conditions:

     1.   Initial  charging of the  incinerator before
         operating temperatures are  achieved;
     2.   Failure to preheat the refractory lining;
     3.   Temperature fluctuations caused by intermittent
                                                          4.
                                                              use;
        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 microorganisms in
    the incinerator ash also depends on temperature and
    time exposure.


    2.2.2    Principles of Combustion^

    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

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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
(O). 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.

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 + O2-»CO2 + Heat           (2-1)

            2H2 + O2 -> 2H2O + Heat       (2-2)

When complete combustion occurs, carbon  and
hydrogen combine with the oxygen of the combustion
air to form carbon dioxide  (CC>2) and water vapor
(H2O), 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  (SO2) at a
rate directly proportional to the sulfur content of the
waste. Some  SO2 may react with alkaline reagents
also present in the waste or ash. However,  the
amount of SO2 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 SO2, HC1
will react more quickly  with available alkaline
compounds  than SO2 and will tie up the alkaline
compounds  before they have a chance to  react with
SO2. Consequently, essentially  all organic sulfur
present in  the  waste will leave the combustion
chamber as vapor phase SO2.

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 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 NOX"
results from the oxidation of nitrogen 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.9


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:


    Qo = M0 x K                           (2-3)

where:
Q0   = volumetric flow of O2 (scm/h)

M0  = Mass flow of O2(kg/h)

K   = 0.2404 scm O2/kg O2 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
combustion. These calculations permit determination

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  Tabla 2-1.   Stoichlometrfc Oxygen Requirements and
            Combustion Product Yields10
Elemental
Waste
Component
C
H2
02
N2
H20
CI2

F2

Br2
k
S
P
Air N2
Stoichiometric
Oxygen
Requirement
2.67 Ib/Ib C
8.0 Ib/Ib H2
-1.0lb/lb O2
-
-
-0.23 Ib/Ib CI2

-0.42lb/lb F2

-
-
1.0lb/lbS
1.29 Ib/Ib P
-
Combustion Product Yield
3.67 Ib C02/lb C
9.0 Ib H2O/lb H2

1.0 Ib N2/lb N2
1.0 Ib H2O/lb H2O
1.03 lbHCI/lbCI2
-0.25 Ib H2O/lbCI2
1.05lbHF/lb F2
-0.47 Ib H20/lb F2
1.0lbBr2/Ib Br2
I.0lbl2/lbl2
2.0 Ib SO2/lb S
2.29 Ib P2O5/lb P
3.31 Ib N2/lb ( 02)sloioh
 Stotchtometric air requirement = 4.3ix(O2)stoich.

 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
 COg  and H2O (and SO2) as the end  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 - HVc 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/m3 (Btu/lb or Btu/scf).

 Net or lower heating value - HVff 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). Alternatively, 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."

 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 combustion chamber temper-
 ature. 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 tem-
 perature 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 combus-
 tion 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

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            Temperature
                               Deficient Air
                                     Percent Excess Air
 Figure 2-2.  Relationship of temperature to excess air.7
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 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:
         60V                             (2-5)
 where:

 t      = residence time, s
V


Qgas



Qair



QH2O
= combustion chamber volume, m3

=  combustion gas flow rate at combustion
   chamber conditions, m3/min

=  combustion airflow rate  at  combustion
   chamber conditions, m3/min

=  release rate of free moisture from the
   waste at combustion chamber conditions,
   m3/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:
                M.                        (2-7)
     V. = 24.04-   l
                                                                 MW.
                                                   where:
        =  volume of compound i at  standard
           conditions, scm

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  MJ     =  mass of compound i, kg

  MW,   =  molecular weight of compound i, g/g mole

  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)
                                           (2-9)
T P
Ar
     Q2 =
 where:
 V{  =  volume at condition i, m3

 Tf  =  temperature at condition i, K
        (where K = 273+°C)

 Pf  =  absolute pressure at condition i, atm

 Qi  =  volumetric flow at condition i, m3/min

 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 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 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

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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 characteristics
and the physical characteristics of the metals,
particularly the solid/vapor distribution and the size
distribution of the metals that are entrained as
particles.

2.3 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 pharmaceutical
 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.1 Examples of wastes defined as infectious
are presented in Table 2-2.1  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.

Table 2-2.   Examples of Infectious Waste1
    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 intentionally exposed to
  pathogens
 a These materials are examples of wastes covered by each category.
  The categories are not limited to these materials.
 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  characteristics,
 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

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        presented in Table 2-3  (SI units)  and Table 2-4
        (English units).2

        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
        polyethylene). Because of the potential  for a wide
        range in waste characteristics 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.

        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 um 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.

       2.4 Types of Hospital Waste  Incinerator
           Systems

       2.4.1    Introduct!on7,ii,i2

       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 - "multiple-chamber," "controlled-
       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
 controlled-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" combustion, "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
 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.11

 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
_
                                                      10

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     Table 2-3.   Characterization of Hospital Waste2 (Metric)
Component description
Human anatomical
Plastics
Swabs, absorbants
Alcohol, disinfectants
Animal infected anatomical
Glass
Beddings, shavings, paper, fecal
matter
Gauze, pads, swabs, garments,
paper, cellulose
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/m3
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 %
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
     Table 2-4.    Characterization of Hospital Waste2 (English)
Component description
Human anatomical
Plastics
Swabs, absorbants
Alcohol, disinfectants
Animal infected anatomical
Glass
Beddings, shavings, paper, fecal
matter
Gauze, pads, swabs, garments,
paper, cellulose
Plastics, PVC, syringes
Sharps, needles
Fluids, residuals
HHV dry basis,
Btu/lb
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 density as
fired, Ibffis
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 %
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,
Btu/lb
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
operation can be single batch, intermittent duty, or
continuous duty. Ash is  removed on a batch or a
semicontinuous basis. Characteristics of the  major
types of incinerators that are likely to be found at
U.S. hospitals with respect to  these three factors
described  above  are listed in Table 2-5. The
remainder of this section describes the types of
incinerators as classified in Table 2-5.

2.4.2    Multiple-Chamber Incinerators™

Two traditional designs that are used for multiple
chamber incinerators are the "in-line hearth" and
"retort" hearth. The in-line hearth design is depicted
in Figure 2-3. 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). Depicted in
Figure 2-4 is  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 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
                                                 11

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                Table 2-5.   Classification of Hospital Incinerators

                      Type of incinerator	Air supply3
                  Waste feed
                                                                                              Ash removal
                Multiple chamber                  Excess

                Batch/controlled air                Starved

                Intermittent duty controlled air         Starved

                Continuous duty controlled air         Starved


                Rotary kiln                       Excess
       Manual or mechanical batch feed; single  Batch at end of
       or multiple batches per burn            burn
       Batch (manual or mechanical); 1 batch    Batch at end of
       per burn                           burn
       Manual or mechanical batch feed;       Batch at end of
       multiple batches per burn              burn
       Mechanical continuous or multiple batch   Intermittently or
       fee^                              continuously during
                                       burn
       Mechanical semicontinuous or continuous  Continuous
       feed
               a Indicates whether primary chamber operates at below (starved) or above (excess) stoichiometric air levels.
                                Grates
                                        Charging Door
                                         with Overfire
                                             Air Port
   Ignition
  Chamber/Flame
          Port
Curtain Wall
   Secondary
   Combustion
   Chamber
Secondary
 Air Port
                                   Cleanout Doors with-
                                   Undergrate Air Port
Location of
Secondary
Burner
                                                           Mixing
                                                          Chamber
                           Curtain
                           Wall Port
          Figure 2-3.  In-line multiple-chamber incinerator with grate.14

       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
_
                                                          12

-------
     Charging
     Door
                      Stack
Ignition Chamber
         Hearth
Secondary
Combustion
Chamber
                                       Flame
                                     , Port
                                     Secondary
                                       Air Ports

                                     Secondary
                                       Burner
                                       Port

                                       Mixing
                                       Chamber
                           First
                           Underhearth
                           Port
        Mixing Chamber
                     Flame Port
               Cleanout
               Doors
                                        Charging
                                        Door
                                        Hearth
                                       Primary
                                       Burner
                                       Port
                                     Second
                                     Underhearth
                                     Port
Figure 2-4.
Retort multiple-chamber incinerator for
pathological wastes.14
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.

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.14 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.15


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. 15 (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 redbag wastes  has several
drawbacks. First, operating  in  the surface-
combustion excess-air mode in the primary chamber
results in entrainment  of flyash 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
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
                                                13

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 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 next section. 15


 2.4.3   Controlled-Air Incinerators

 2.4.3,1  Principle of Controlled-Air Incinerations

 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 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
automatically  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).H 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, 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   Batchi'Controlled-Air Incinerators"

 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. 17 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.
                                               14

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                         Combustion Gases
                  rt
 Waste Feed
  Auxiliary
  Ignition
  Burner
                                  Secondary Chamber
                              Volatile Content is Burned Under
                                  Excess Air Conditions
                                      Primary Chamber
                                    (Starved Air Condition)


                                    Volatiles and Moisture
                                      I,    i i
Main Burner for Maintaining Minimum
     Combustion Temperature
                                                                                         Main Flameport Air
                                                                                   Ash and Non-combustibles
                                                                                    Controlled Undertire Air for
                                                                                      Burning "Fixed Carbon"
Figure 2-5.   Schematic of a controlled-air incinerator.16
  Waste
  Charge
  Door
                                                        I  i
                                                 OfanL-  I  T*
                                                 Stackl  J
                                      Barometric     yf
                                        Damper     	1   i
  Oxygen
': Control
                                                               Primary
                                                               Blower
 Figure 2-6.   Schematic of a single batch controlled-air incinerator.17
                	Air
           "Secondary Blower
                                                         15

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 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 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
   1.  Cleanout of ash
      from previous day
      15 to 30 minutes
   2.  Preheat of
      incinerator 15 to
      60 minutes

   3.  Burndown

   4,  Cooldown
   Typical duration
15 to 30 minutes


15 to 60 minutes


2 to 4 hours

5 to 8 hours
For jintermittent-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
                             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.18
 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.

 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.11

 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.
                                                16

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                                               Hydraulic Fire 	*j
                                               Door Actuator     | |
                                    Hopper Cover
                  Hydraulic
                  Ram
                  Actuator
Charging  ~Ram Fac8
Ram      Quench
         Spray
                                 Waste
                                 Charging
                                 Hopper
                                 Primary
                                 Combustion
                                 Chamber

                                 Fire Door
                                 Enclosure
Furnace
Opening
    Figure 2-8.  Hopper/ram mechanical waste feed system.2
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 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. A continuous-duty, controlled-air
 incinerator with a  stepped hearth and multiple ash
 transfer rams is depicted in Figure 2-9.21 The use of
 the stepped hearth  promotes "mixing" the ash bed as
 the ash is moved from hearth to hearth and, conse-
 quently, promotes improved solid-phase combustion.
 Typically, when the ash  reaches the end of the
 hearth, it drops off ibhe 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
                                                 17

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                               To Boiler
                                                                     Fossil Fuel Burner


                                                                        r— Primary Chamber
                  Feed Ram
                                                                                 Ash Sump
                          Ash Transfer Rams
                                              Air Tube

                                              Ash Discharge Ram
                                                              Ash Chute

                                                                   Ash Quench
     Figure 2-9.  Incinerator with step hearths and automatic ash removal.2°
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 2-10.
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 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 substoichiometrically
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
semicontinuous  or continuous waste  feed  input.
Consequently, a rotary kiln typically has a mechan-
ical waste feed system and  a system for continuous
ash removal.
                                                 18

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                          Rotating Primary
                         Oxidation Chamber
                                   High Temp. Secondary
                                   1 Oxidation Chamber
                                                                             ,Baghouse
                                                             Waste Heat
                                                                Boiler
 Auger-Sizer
Stack
, -A,

'
<\sh
*,'
^
\
N
By-Pass Gate
Hot Water /
—
I 	 1
)
\


'.'
^ *
V

—
jC\
X
                                                                                    1   A
                                                                                                                  Stack
                                                                                                           Exhaust Fan
Figure 2-10. Rotary kiln with auger feed.21
             Bypass
             Shutoff
              Valve
                                     Bypass
                                      Stack
                                                                Gas Flow
                                                            Waste Heat
                                                              Boiler
                             Incinerator

     Figure 2-11.  Incinerator with waste heat boiler and bypass stack.
Stack
                                                                                              ID
                                                                                              Fan
                                                                              Damper
                                                            19

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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
continuously 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  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.T  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, incin-
erators 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

I.  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.

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.
                                               20

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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.

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.
                                                21

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                                          Chapter 3
                                    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 (SO2), 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, will describe The factors
affecting pollutant  formation and generation,
including the effects  of waste feed composition, are
described in Section 3.2. Air pollution control
strategies are discussed in Section 3.3. Electrostatic
precipitators are not discussed in  this chapter
because they are not commonly used for air pollution
control on "local" hospital incinerators.  They are
more  likely  to be used for large  regional-type
facilities, possibly  in conjunction  with a dry-
scrubbing system. Information on their operation and
maintenance can be found in reference 2 of Chapter 8.

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 organics.  Organic material found in the waste
feed material  theoretically can be completely
combusted to form water (H^O) and carbon dioxide
(CO2). 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 H2O and CO2- 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.
                                                23

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 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 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 SO-2 during combustion regardless 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., polyethylene) for PVC,
 where possible, would reduce the chlorine input to
 the incinerator. Materials that could be segregated
 from waste to be incinerated 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.

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 SO2. In both cases, most of the chlorine
 and  sulfur will be converted to HC1 and SO2 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 SO2J fabric filters are used
 to remove particulate matter; dry scrubbers are used
 to remove HC1 and SO2-


 3.3.3.1   Wet Sceubbers
 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
 particulate matter. These units are not effective for
 controlling particulate 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>4 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
                                                24

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            Table 3-1.   Control Strategies for Air Pollutants from Hospital Waste Incinerators
                             	Control strategy	Add-on pollution control equipment
                 Pollutants
 Controlling   Combustion   Venturi   Packed-bed              Dry
feed material    control    scrubber3   scrubber15   Fabric filter  scrubber
Particulate matter
Toxic metals
Toxic organics
Carbon monoxide
Hydrogen chloride
Sulfur dioxide
Nitrous oxides
X
X


X
X
X
X

X
X


X
X
X
c

c
C

c
C
c

X
X

X
X
c

X
X

            aVenturi scrubber with water as the scrubbing media.
            bPacked-bed scrubber utilizing an alkaline sorbent
            cWill achieve some limited control but not designed for high-efficiency collection.
information for these units controlling hospital waste
incinerators is not readily available, and they will
not be discussed in this document.

Wet scrubbing principles? 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 meters per second (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 (um)
are collected by this mechanism.

Very small particles (less than 0.1 um 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, 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
                                 Gas Streamlines
                            Particle
Droplet
                       Figure 3-1.  lmpaction.5

                       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.
                                                   25

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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. 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 um 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 um range is very
high. Unfortunately, small particle size distribution
is typical for fuel combustion sources including
hospital waste incinerators and results from the
                             — Converging Section
                             — Throat
                             — Diverging Section
Figure 3-2.   Spray venturi with circular throat.6
                                                    Figure 3-3.   Spray venturi with rectangular throat.7
                                                 26

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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 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 = (5x10-5) V2(L/G)
                                    (3-1)
where

AP =
v   •—
pressure  drop,  in. w.c. (inches of water
column)

the gas velocity in the venturi throat, ft/s
(feet per second), and
L/G = the liquid-to-gas ratio, gal/Macf (gallons per
       thousand actual cubic feet).

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,
an inadequate liquid supply to cover the venturi
throat completely has resulted from L/G ratios less
than 3 gal/Macf.

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 follows:

 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
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 um) 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.
                                                                                 Mist Eliminator
                                                                                 Liquid Sprays
                                                                                 Packing
                                             Figure 3-4.  Countercurrent packed tower absorbed
                                             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.
                                                  27

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  Gas absorption is affected by the extensive liquid
  surface contacted by the gas stream as the liquid
  flows downward over the packing material. A 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 (NaaCOa), 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  SOz collected in the scrubber
 react with NaOH to produce sodium chloride (NaCl)
 and sodium sulfite (Na2SO3) in an aqueous solution.

 One of the major problems with these scrubbers is the
 accumulation of solids at the entry to the bed and
 within the bed. The  dissolved and suspended solids
 levels in the liquor must be monitored carefully to
 maintain performance.

 Spray Towers.2 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
 countercurrent 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 um 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.
       Liquid
       Sprays
 Figure 3-5.  Counterourrent-flow spray towerJ"
 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 um in  diameter, although with
 increased liquid inlet nozzle pressures, particles with
 diameters of 2.0 um 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.
                                                28

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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. U 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 impaction, 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 um
 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.
     Clean Air
      Plenum •
 Plenum Access H
 Blow Pipe •
    Induced -
      Flow
    Bag Cup &
       Venturi
                  Tube Sheet
 Bag Retainer -
To Clean Air
Outlet and Exhauster
                                     /*•
                1
                                          Housing
                 Filter
                 Tube
 Dirty Air Inlet & Diffuser
              .  -
                                     Rotary
                                    Air Lock
 Figure 3-6.  Pulse jet baghouse.12


 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
 approximately 0.5 seconds.11
                      in
 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
                                                  29

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 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  (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. n

 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).H 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/ft2. 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 m3/s/m2  (5 to
 10 acfm/ft2) of bag area. 13

 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
 HCl (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.

 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 (a) 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 alkaline 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.*

 Components and operating principles of dry scrubber
 systems.1-3,14: 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.

 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 fluid 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
and the design of the vessel  used for contacting the
acid gas-laden  stream.  The  alkaline  feed
 1 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).
                                                 30

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    Lime
   Storage
Lime
Slaker
1
Slurry
Mixing
Tank



Slurry
Feed
Tank

,
              Combustion
                 Gases
Figure 3-7.   Components of a spray dryer absorber system (semiwet process).
   Feeder
 Combustion
 Gases from
 Incinerator
 Figure 3-8.   Components of a dry injection absorption system (dry process).
                                                      31

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  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 containing 5 to 20 percent by
  weight solids. This reagent must be slaked in order to
  prepare the reactive slurry for  absorption of acid
  gases. Slaking is the  addition of water to convert
  calcium oxide to calcium hydroxide. Proper slaking
  conditions are important to ensure that the resulting
  calcium hydroxide slurry has the proper particle size
  distribution and  that no coating of the particles has
  occurred due to the precipitation of contaminants in
  the slaking water. 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 per 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 for droplet formation in nozzle type
 atomizers. The  typical air  pressures are 70 to
 90 pounds per square inch, gage (psig). Slurry drop-
 lets in the range of 70 to 200 microns are 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.

 All of the slurry droplets must 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 lime) 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
 size is approximately the consistency of talcum
 powder. This size is important to ensure an 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. Environ-
   mental Protection Agency. March 1984.
                                                32

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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, O. L., and Means, J. D. Utilization of
   Hydro-Sonic® Scrubbers for the Abatement of
   Emissions from Hazardous, Industrial, Municipal
   and Biomedieal 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. Environ-
   mental 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 (NTISPB87-
    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.
                                               33

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                                          Chapter 4
                                          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  malfunc-
tions 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 in 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 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:

l.Bateh/controlled-air incinerators;
2.1ntermittent-duty, controlled-air incinerators;
3.Continuous-duty, controlled-air incinerators;
4. Multiple-chamber incinerators; and
S.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 regulations. However, a growing number of
States have promulgated  or will soon promulgate
more stringent regulations governing hospital waste
incinerators 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 specific manufacturer's
                                                 35

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 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.

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).l.2 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 microorganisms 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 microorganisms
 into the atmosphere. His research indicated that the
 destruction of the microorganisms 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
 (1400°F).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  chamber
 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 a 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 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. 5

 At the same time, the primary chamber temperature
 must be maintained below the point that will result
 in refractory damage. Modern incinerators commonly
 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.2
Another, perhaps more important, limiting factor for
                                               36

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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/hr

Ignition chamber combustion air (percent of stoichiometric)
Total combustion air (percent excess air)
Combustion gas oxygen concentration, percent
Ignition chamber draft, in w.c.
Burndown 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°
1 0 to 25 percent of
rated capacity at 5 to
1 5 min intervals
30 to 80
140 to 200
12 to 14
-0.05 to -0.1
Not applicable
the upper operating temperature of the primary
chamber is 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).2,6
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 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
precursors (e.g., hexachlorobenzene) is near 930°C
(1700°F)J

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 recommended a minimum secondary
combustion chamber temperature of 980°C (1800°F).l
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
                                                37

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 under conditions of a constant thermal input.  For
 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. Manufacturers 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
 assembly are blocked.9  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
 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.u The charging frequency
 may need to  be adjusted 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/combus-
tion 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. 1.2 Typically,  about
20 percent of the total air requirement to the
incinerator is supplied as underfire air to the ignition
chamber. 2 The remainder of the air is supplied to the
secondary mixing chamber.
                                               38

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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.
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) + (6 x 20 minutes)
= 3 hours. A typical burndown period for batch and
intermittent units is in the range of 2 to 4 hours.11.14
4.2.2.4  Combustion Chamber Pressure (Draft)
A typical draft for controlled-air incinerators is in the
range of-0.05 to -0.1 in. water column (w.c.). Exces-
sive draft is not desirable because increased carry-
over 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 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.14

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, io 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
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
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 controlled-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 controlled-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 Sec-
tion 4.2.2.1  for controlled-air  incinerators, a min-
imum  temperature to  prevent the discharge of
potentially toxic products of incomplete combustion
is  required; a minimum secondary combustion
                                               39

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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,
  Charging rate
   1600 to 1800
   1800 to 2200
Single layer on hearth
      1000to 1400
      1800 to 2200
10 to 25% of rated capacity at
   5- to 15-min  intervals
Ignitkxi chamber combustion air (percent excess air)
Total combustion air (percent excess air)
Combustion gas oxygen concentration, percent
Ignitkxi chamber draft, in. w.c.
80
120 to 200
10 to 14
-0.05 to -0.1
150
250 to 300
15 to 16
-0.05 to -0.1
chamber temperature of 980°C (1800°F) is recom-
mended 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. Accordingly, the controlling factor
for the combustion rate is essentially 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. Therefore,  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 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. Accordingly,  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. Overall excess-air  levels for multiple-
  chamber  incinerators  are typically  250 to
  300 percent.15 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
  controlled at a lower level than for a typical multiple-
  chamber incinerator.
  4.2.3.4  Chamber Pressures
  A negative draft is maintained in the combustion
  chambers. A typical range for the ignition chamber
  draft is -0.05 to -0.1 in. w.c. 15
  4.2.4    Rotary Kiln Incinerators
  Currently,  there are relatively  few rotary kiln
  incinerator installations at hospitals for incinerating
  hospital medical waste.  Consequently,  little
  information is available on the application of rotary
  kilns to this waste type. However, rotary kilns are a
  proven technology and have been used for a wide
  variety of industrial  applications  including
  hazardous  waste incineration. The operating
  parameters identified below are based mainly on the
  application of rotary kilns to the incineration of
  hazardous waste because  of the availability of
  information in this area.
                                                40

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4.2.4.1  Ignition and Combustion Chamber
        Temperatures
As discussed in Chapter 2, a rotary kiln incineration
system consists of an inclined rotary  kiln which
serves to volatilize the waste  and a secondary
combustion chamber  which completes  the
combustion process by burning the volatiles in the
kiln off-gas. Temperatures in rotary kiln incinerators
usually range from about 760° to 1670°C (1400° to
3000°F) depending on the types of waste being burned
and on the location in the kiln.

In evaluating the  application of rotary  kiln
incineration to hospital medical waste,  it is likely
that the  kiln (primary  chamber)  and secondary
chamber  operating temperatures will be similar to
those identified for other hospital medical waste
incineration systems,  i.e., a primary chamber
temperature of 760°C (1400°F)  and a secondary
chamber temperature of 980°C(1800°F).


4.2.4.2  Charging Rate
Rotary  kiln  incinerators  may  be batch or
continuously fed and have a feed capacity that ranges
from 600 to 2,000 kg/h (1,300 to 4,400 Ib/h).

The waste throughput of a rotary kiln is determined
both by the speed of rotation and by the incline angle
(rake). Typically, rotary  kilns rotate at a speed that
ranges from 0.25 to 1.5 revolutions per  minute and
are oriented at a rake of less than 3 percent (i.e.,
around  11° from  horizontal). Both of these
parameters may be  adjusted depending on the
throughput desired. However, once the rake is set, it
is usually not altered.  Assuming that all  other
operating parameters  are in the  normal operating
ranges, incompletely burned material in the ash is an
indication that waste is  traveling through the  kiln
too quickly. The waste throughput may be reduced by
reducing  the speed of rotation of the  kiln which in
turn must include a corresponding decrease in the
charging  rate. Some experimentation with charge
rates and speed of rotation may be required to obtain
optimum ash quality and throughput.


4.2.4.3  Ignition and Combustion Chamber Air
        Levels
Based on information available on hazardous waste
rotary kiln incinerators, the rotary kiln excess-air
level ranges from 140 to 210 percent  or greater,
depending on the desired operating temperature and
the heating value of the waste. When high aqueous
wastes are being burned, lower excess-air rates may
be needed to maintain adequate  temperature.
Secondary  chamber  excess-air levels  are
approximately 80 percent of the rotary kiln excess-air
levels. For example, in a typical system operating at
820°C (1500°F) in the kiln and 980°C (1800°F) in the
secondary  chamber,  approximately 160 to
170 percent excess air would be maintained  in the
secondary chamber compared to about 210 percent in
the kiln. Manufacturers are now  designing  rotary
kilns utilizing special kiln seals and air injection that
operate with substoichiometric air levels in the kiln.
Operating the kiln at substoichiometric air levels
decreases the kiln size and reduces auxiliary fuel
usage.4
4.3  Waste Feed Handling

The physical and chemical properties of wastes and
the effects of these properties on the incineration
process were presented in Chapter 2. Furthermore,
typical characteristics of hospital infectious wastes
were presented and discussed. In most cases, the
operator of an incinerator does not have control over
the quantity or types of wastes which are transported
to the incinerator for disposal. However, the operator
does have control over two of the most important
parameters - how 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.
                                                41

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 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.3 For
 example, Massachusetts specifies a minimum  bag
 thickness while California requires use of the ASTM
 dart test.3  Even if appropriate bag materials are
 used, overloading of bags, placement of sharp objects
 within the bags, or mishandling can result in tearing.
 "Sharps" (e.g., needles, broken  glass) should be
 placed in special rigid sealed containers; these
 containers  can then be  placed in  the  red bag. The
 options that can be used if bag tearing is a problem
 include  double  bagging and the  use  of rigid
 containers to contain the bags. Rigid containers such
 as reusable metal/plastic drums or disposable
 cardboard drums or boxes can be used to contain the
 individual plastic bags.  If reusable containers are
 used, the plastic bag would be placed as a liner in the
 container (much like one might do at home for
 household garbage). When  filled, the bag is  sealed,
 and a lid is placed on the container. The container is
 then transported to the  incineration area. Reusable
 containers  have some disadvantages in that they
 require additional  handling and  will need to be
 disinfected after each use.1 Because the waste is to be
 incinerated, disposable cardboard cartons that can be
 loaded directly into the incinerator and disposed with
 the waste  is a  reasonable  alternative.  Use of
 disposable  containers with mechanical charging
 systems also minimizes  the potential for spillage in
 and contamination of the charging equipment during
 operation of the incinerator.

 Another approach to enhancing integrity of the red
 bags is to use rigid carts,  usually made of rigid plastic
 or of metal, to collect and  transport the red bags.
 These rigid  carts  protect the waste bags from
 bumping, tears, etc.; the  integrity of the bags is more
 easily maintained. Also, should a bag tear or break,
 the waste is contained, even if liquids are involved.
 Finally, handling of the  waste can be minimized by
 the use of rigid carts. Once the red bags are placed in
 the cart, they need not be handled again until they
 are loaded directly into  the incinerator or into the
 mechanical charging system for  the incinerator.
 Since waste handling is  minimized, the approach of
 keeping the wastes in the transport cart up until the
 time it is charged to the incinerator is preferred over
 the approach of unloading the waste to a storage area
or charging pile on  the  floor. When rigid transport
carts are used for  large automated  incineration
systems, the waste may never need to be handled
manually after collection.  Charging  systems are
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  (lb/ft3) 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

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.
                                                42

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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.
4.4.1     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.
4.3.2    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
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.
4.4.1.1  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
    8h.

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.
                                                43

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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.
Plastic items are an example of materials with high
heating values. Large quantities of plastic, which
may contain poly vinyl 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, the operator
may 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), and  trash) are being charged to the
incinerator, charging the incinerator with some of
each waste type is better than charging it with all of
one waste type. 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 manufac-
turers' 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
igniter. When the pilot 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  loaded
manually. 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
chamber reaches a preset temperature (i.e., the
                                               44

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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 burners, like the
combustion air, is typically automated. A barometric
damper on the stack is used to  maintain draft. The
incinerator chambers should both be maintained
under negative draft.

4.4.1.1.4  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 indicating
combustion is complete. 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.14 When combustion is complete, the 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
cycle.9.11  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. 14

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 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;
3. Primary and secondary burner operation;
4. Temperature; and
5. Combustion, burndown, and cooldown 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
                                               45

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 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
 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 thermocouples. 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.4

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 units.9.11 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.

 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.,
 temperature), 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.
 An example timed control cycle for a batch operated
 incinerator is presented in Table 4-3.


 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
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 Table 4-3.   Example Timed Control Cycle for Batch Mode Incinerator
           Cycle
           Controlling Parameter/Level
    Resulting Automatic Control Action
  1.   Secondary combustion
      chamber preheat

  2.   Ignition
  3.   Combustion
  4.   Burndown
  5.   Cooldown
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 temperature override

1 hour after override activated

8 hours from ignition

16 hours from ignition; cycle completed
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

Primary air switched to high level

Secondary burner shuts off

Combustion air blowers shut off
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.

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 arp 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
                                                  47

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 value in the waste will need to be considered in
 determining charge size.

 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 impingement
 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.

 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 per-
 formance. 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.

 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.21 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.
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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.

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.10'1! 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 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.14

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 manufacturer'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
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  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 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.

 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.
                                               50

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4.4.3.3  Monitoring

The operating parameters that can be monitored for
continuous-duty incinerators are the same as those
parameters  discussed in  Section 4.4.2.3 for
intermittent-duty incinerators.  The use  of auto-
matic/mechanical feed systems simplifies the mon-
itoring 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 Sec-
tion 4.4.1.1.1  for batch mode controlled-air incin-
erators.

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 tem-
perature. 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.

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.

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.
                                                51

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 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 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
 ceased. *5

 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. 15


 4.4.4.3  Monitoring
 The same  operating parameters that are monitored
 on controlled-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 (APCS) to a hospital waste incinerator
 increases the number of operating parameters the
operator  must  control,  monitor,  and adjust.
 Furthermore, addition of an APCS to an incinerator
 significantly modifies how at least one important
incinerator operating parameter is controlled; this
parameter is the incinerator draft. Operation of the
APCS will require use of an induced draft (ID) fan to
provide the necessary airflow through the system.
                                               52

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Natural draft control will no longer be applicable; gas
flow through the system will be controlled by the ID
fan.

4.5.1    Wet Scrubbers22-24

4.5.1.1  Key Operating Parameters
All wet scrubbers utilize a liquid scrubbing media to
remove pollutants from the incinerator exhaust gas
stream. Actual  collection of the pollutant in the
liquid is primarily through impaction for particulates
and absorption for acid gases. The liquid/gas (L/G)
ratio is an important parameter for all wet scrubbers.
The appropriate  L/G ratio varies with scrubber type.
Venturi scrubbers require a relatively low L/G ratio
with 7 to 10 gallons per thousand actual cubic feet
(gal/Macf) recommended.22 This low L/G ratio is
acceptable because  venturi scrubbers rely  on high
energy pressure drops to create  high gas velocities,
turbulence, and  lots of small water droplets for the
collection of fine particulate matter by impaction.
Therefore, pressure drop (AP) and L/G ratio are the
two  key  performance parameters for  venturi
scrubbers. Packed-bed scrubbers, however, rely on
creating large surface areas of gas to liquid interface
for collection  of  gaseous pollutants  through
absorption. Large pressure drops are not required by
packed-bed scrubbers. However, relatively large L/G
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
recommended.22 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 plugging 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.

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.
                                                 53

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               Table 4-4.   Wet Scrubber Performance Parameters for Hospital Waste Incinerators2*-**

                     Parameter         Typical range*        units of measure      Operating range*"
Ventur! scrubbers
Pressure drop
Liquid feed rate0
Liquid-to-gas ratio
Liquid feed pressure
Liquid feed turbidity
Gas flow ratec
Liquid feed pH
Packed-bed scrubbers
Pressure drop
Liquid feed rate0
Liquid feed pH
Liquid-to-gas ratio
Liquid feed pressure
Gas flow rate3
Liquid feed turbidity
Spray towers
Pressure drop
Liquid-to-gas rate
Mist eliminator
Pressure drop
Liquid feed rate0
Liquid feed pressure
Liquid-to-gas ratio
Liquid turbidity
Gas flow rate0
Liquid feed pH

15-60
>35
4-10
20-60
1-10
> 5,000
5-10

1-5
>5
5.5-7.0
10-30
20-60
> 5,000
1-10

0.5-3.0
5-20

1-3
>5
20-60
1-6
0-3
> 5,000
5-10

in. w.c.
gal/min
gal/Macf
psi
Percent suspended solids
acfm
PH

in. w.c.
gal/min
PH
gal/Macf
psi
acfm
Percent suspended solids

in. w.c.
gal/Macf

in. w.c.
gal/min
psi
gal/Macf
Percent suspended solids
acfm
pH

20-50

7-10
20-60
0-3

5.5-7.0



5.5-7.0
15-25
30-60

1-3

1-3
5-20

1-3

30-60
2-3
0-0.5

7
               • The typical range is the range of operating parameters that can exist on a broad range of source
                categories,
               bThe operating range is the range of operating parameters specified by manufacturers for combustion
                sources similar to hospital waste incinerators.
               c Values, or range of values, are dependent on the size of the scrubber system.
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 manu-
    facturer'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 build up  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 suggested
    that the dissolved solids not exceed 10 percent
    (weight).22 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 an
    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
                                                  54

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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  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.
 Table 4-5.   Key Operating Parameters for Fabric Filter
            Control Systems
         Parameter
    Operating range26
  Upper gas temperature, °F
  Lower gas temperature, °F
  Pressure drop, in. w.c.
  Cleaning air pressure, psig
Below upper limit for fabric3
Above dewpointb
5-9
60-100
  a The upper temperature limit will be dependent on fabric type.
   Consult manufacturer.
  b The gas temperature usually is maintained above 300 °F.
The pressure drop across the system for pulse jet
baghouses typically is maintained within a range of 5
to 9 in. w.c.25 Pressure drop gives an indication  of
filter  cake formation.  Filter cake  formation  is
dependent 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.
                                                 55

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 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) precoating 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 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 combus-
 tion, 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
parfciculate. 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 Section4.5.2.4.  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.

 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
 plugging.

 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 tem-
 porary 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.
                                               56

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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.


4.5.2.4  Monitoring
A well-designed and maintained fabric  filter should
provide adequate 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.

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.

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
                                                 57

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 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 CaC^. 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.
4.5.3.4  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 SOz 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.2'''
 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  at the manu-
facturer'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.
                                                58

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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 SOz outlet gas concentrations.
4.6 References for Chapter 4

1.  Ontario Ministry of the Environment. Incin-
    erator Design and Operating Criteria, Volume II
    - Biomedical Waste Incinerators. October 1986.

2.  McRee, R. Operation and Maintenance  of
    Controlled-Air Incinerators. Ecolaire Combus-
    tion 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.  Letter from Ken Wright, John Zink Company, to
    J. Eddinger, U. S. EPA. January 25,1989.

5.  Personal conversation between R. Neulicht, Mid-
    west 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 D1709-75.  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.

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)
                                                59

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23. Joseph, J. and D. Beachler. APTI Course SI:412C,
    Wet Scrubber Plan Review - Self Instructional
    Guidebook.  EPA 450/2-82-020. U. S.  Environ-
    mental 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.
                                             60

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                                          Chapter 5
                                        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 the  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.1

Because of the diversity in both size and design of
hospital waste incinerators,  specific recommenda-
tions 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  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 main-
tenance, 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 incinerator.2 The operator
must routinely replenish the water in the quench pit
because water is constantly removed by evaporation
and by the ash removal system.2,3 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
proper range. If not, maintenance personnel should
be informed. An additional check for the opacity
 monitor is  to observe the  stack emissions and
                                                61

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Tabla 5-1.    Typical Maintenance Inspection/Cleaning/Lubrication Schedule for a Hospital Waste Incinerator4
 Activity frequency                 Incinerator component                                    Procedure
 Hourly

 Daily
 Weekly
Biweekly
Monthly
Semiannually
 Ash removal conveyor
 Water quench pit
 Opacity monitor

 Oxygen monitor
 Thermocouples
 Underfire air ports
 Limit switches

 Door seals
 Ash pit/internal dropout sump

 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

 Hydraulic systems

 Ash removal conveyor bearings
 Fuel trains and burners

 Control panels

 External surface of incinerator and stack

 Refractory

 Internal rarn 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   Lubricate.
all moving components
Burner pilots
Hot external surfaces
 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 leakage.
 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.  Investigate sources of
 fuel leakage as required.
 Inspect and clean as required.  Keep panel securely
 closed and free of dirt to prevent electrical
 malfunction.
 Inspect external "hot" surfaces. White spots or
 discoloration may indicate loss of refractory.
 Inspect and repair minor wear areas with plastic
 refractory material.
 Inspect for wear. These skinless steel faces may
 wear out and may require replacement in 1 to 5
years depending on service.
 Inspect and vacuum any particulate matter that has
 accumulated on the chamber floor.
 Lubricate.
                   Ambient external surfaces
                   Chains
Inspect and adjust as required.
Inspect and paint with high-temperature paint as
required.
Inspect and paint with equipment enamel as required.
Inspect and brush clean as required. Lubricate.
                                                          62

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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.4 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.2 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.4 Also, a
noticeable  change in response time  of the
thermocouple is an indication of problems. Unfortu-
nately, 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.4 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).2
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 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 Maintenance4
 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) should 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
conveyor bearings on large incinerators  should be
lubricated biweekly.


5.1.3    Monthly/Semiannual Maintenance4
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 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 effec-
tively 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
                                                 63

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 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 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 Scrubberss-7

 A typical maintenance inspection, cleaning, and
 lubrication schedule for a wet scrubber is presented
 in Table 5-2. 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.

 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. There-
 fore, 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
                                               64

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   Table 5-2.    Typical Maintenance Inspection/Cleaning/Lubrication Schedule for a Wet Scrubber

                            Component        	Procedure
Inspection
frequency
    Daily        Scrubber liquid pump

                Variable throat activator
                Scrubber liquid lines
                Mist eliminator pressure lines
                Reagent feed system
                Fan
                Fan bearings
                Fan belt8
    Weekly      Fan
                Scrubber liquid pump
                Damper air purge system
    Monthly      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

    Semiannually Fan, pump, motor, and drag chain
                bearings and gear reducers
                Flowmeters
                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 temperature, and lubricate.
                                            Check oil level and lubricate pump motor bearings.
                                            Check for proper operation.
                                            Inspect for leakage.
                                            Inspect for leaks, cracks, and loose fittings.
                                            Inspect for material buildup and clean as required. Inspect for abrasion
                                            and corrosion and repair as required.
                                            Check chain tension, sprocket wear and alignment, and oil level.
                                            Inspect for plugging/leaking 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.                           	
    a Check fan belt tension whenever fan is out of service.

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.

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 recommendations,
                                                  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
                                                     65

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 the manufacturer's recommendations. A typical
 maintenance inspection, cleaning, and lubrication
 schedule for a fabric filter is presented in Table 5-3.


 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 (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, plugging,  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  invaluable  for
 identifying recurrent prob'^ms 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 rebagging, 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
                                                66

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    Table 5-3.   Typical Maintenance Inspection/Cleaning/Lubrication Schedule for a Fabric Filter System*^

                                      Component                                    Procedure
Inspection
frequency
     Daily
     Weekly
     Monthly
     Quarterly
     Semiannually

     Annually
             Stack
             Manometer

             Compressed air system
             Collector

             Damper valves

             Rotating equipment and drives

             Dust removal system

             Filter bags


             Cleaning system



             Hoppers

             Shaker mechanism
             Fan(s)

             Monitor(s)
             Inlet plenum

             Access doors
             Shaker mechanisms
             Motors, fans, etc.

             Collector
Check exhaust for visible dust.
Check and record fabric pressure loss and fan static
pressure. Watch for trends.
Check for air leakage (low pressure). Check valves.
Observe all indicators on control panel and listen to
system for properly operating subsystems.
Check all isolation, bypass, and cleaning damper
valves for synchronization and proper operation
Check for signs of jamming, leakage, broken parts,
wear, etc.
Check to ensure that dust is being removed from the
system.
Check for tears, holes, abrasion, proper fastening,
bag tension, dust accumulation on surface or creases
and folds.
Check cleaning sequence and cycle times for proper
valve and timer operations. Check compressed air
lines including oilers and filters. Inspect shaker
mechanisms for proper operation.
Check for bridging or plugging. Inspect screw
conveyor for proper operation and lubrication.
Inspect for loose bolts.
Check for corrosion and material buildup 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 ail 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 tile
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.
more  than  half a bag's "normal" life  expectancy
remains.
                                                  filter. Additionally, the unit  should be cleaned  and
                                                  painted as appropriate.
5.3.4    Semiannual/Annual
         Inspection/Maintenance
Some motors and packaged blowers are supplied with
sealed bearings and,  therefore,  require  no
lubrication. Semiannual fabric filter system main-
tenance 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^nd welds on the fabric
                                                  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
                                                        67

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   Maintenance Study.  EPA-340/1-87-002.
   June 1987.

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, D., 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, D. APTI Course SI:412, Baghouse Plan
   Review. U. S. Environmental Protection Agency.
   EPA 450/2-82-005. April 1982.
                                            68

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                                         Chapter 6
                      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 param-
eters listed are sometimes monitored on larger incin-
erators 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. 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 Venturis
and packed beds, the scrubber liquid flow  is usually
established at a constant rate and is not auto-
matically controlled 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 automat-
ically. 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 dew-
point 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 thermo-
couple  wires and the critical thermocouple junction
from direct exposure to the combustion gases and
entrained dust particles,  among other vagaries.
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
                                               69

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slag buildup, which can slow response to temperature
changes. Generally, 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 thermo-
couple. 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.


  Table 6-1.   Thermocouple Types
Type
J
E
K
S
R
B
Materials
Iron/Constantan
Chromel/Constantan
Chromel/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
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
thermocouple 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 conditions; 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 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.

A differential pressure  transmitter  contains  a  dia-
phragm  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
                                                70

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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  plugging 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 plugging, 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 Concentration^
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 combustion gases, so long as the characteristics of
the waste feed are the  same. However, if the
composition of the feed changes (i.e., its heating  value
changes), more or less air will 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  tem-
perature.

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 nonrepresen-
tative 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 the monitor's design. High  tem-
peratures, particulate 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 plugging or in-
leakage of air), the conditioning system (if one  is
present) is operating properly, and the instrument is
calibrated.  Eleetrocatalytic 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 plugging in the
system, or small air in-leaks, etc. The  extractive
systems should be checked daily by the operators, and
                                                71

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        maintained and calibrated on a weekly basis by the
        incinerator instrument personnel.


        6,2.3.7  In-S'rtu 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 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, semipermeable membrane and react at an
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 concentration (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
.
                                                       72

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J

Y 1
Secondary
Combustion
Chamber f—
\
r

Sample Probe
f
"T — Filter —
N
* <
r1!
                                                                                         Vent
                                                                              Analyzer
   Back Flush
   Purge Air
                                                              Sample Pump
                                             Drain
              Zero
Figure 6-1.  Schematic of an extractive monitoring system.

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, calib-
ration 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.

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    Opacityi,2
Like CO monitors, opacity monitors (or transmis-
someters) 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. A typical transmissometer  is depicted in
Figure 6-2.
                                                 73

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                    Transceiver
                    Assembly
                                                                                     Retroreflector
                                                                                       Assembly
                   Preseparator Air Inlet
                             Ambient Air
                                       Blower
     Figure 6-2.  Typical transmissometer installation for measuring opacity. 1
                                                                             Blower
 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 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 promulgatedS performance specifica-
 tions  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
  Table 6-2.
Performance Specifications for Opacity
Monitors^
           Parameter
                    Specifications
   Calibration error3
   Response time
   Conditioning periodb
   Operational test period13
   Zero drift (24-hour)a
   Calibration drift (24-hour)a
   Data recorder resolution
               s 3 percent opacity
               <10 seconds
               <168 hours
               <168 hours
               s 2 percent opacity
               <2 percent opacity
               50.5 percent opacity
  a Expressed as the sum of the absolute value of the mean and
   the absolute value of the confidence coefficient.
  b During the conditioning and operational test periods, the CEMS
   must not require any corrective maintenance, repair,
   replacement, or adjustment other than that clearly specified as
   routine and required in the operation and maintenance
   manuals.


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
                                                   74

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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.

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 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 the 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 Main-
    tenance, an Advanced Course. EPA 450/2-84-004.
    U.S. Environmental Protection Agency, Research
    Triangle Park, N.C. September 1984. p. 6-9.

 3.  Code of Federal Regulations, Title 40 Part 60
    (40CFR60), Appendix B, Performance Specifica-
    tion 1.  Specifications and Test Procedures for
    Opacity Continuous  Emission Monitoring
    Systems in Stationary Sources.
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                                          Chapter 7
                         Operational  Problems and Solutions
Potential operational problems associated with
hospital waste incinerators, wet scrubbers, and fabric
filters are described in this chapter. The cause of the
problems and possible solutions to them are discussed
also. Unfortunately, some operational problems are
the result of deficiencies in design, fabrication, and/or
installation of the equipment. Deficiencies  in
incinerator design are  usually the  result  of
insufficient information on the waste characteristics
and/or quantity. The assumption is made in  the
following paragraphs that the incinerator and its air
pollution control  system have been properly
designed, fabricated, and installed. Therefore,  no
deficiencies in these areas are addressed. Purchasers
of hospital waste incinerators and air pollution
control systems should 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.
 7.1.1    Excessive Stack Emissions - Controlled-
         Air Units'! .2
 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:
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 combus-
tion 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
2.
    air;
   Check/decrease underfire air (if necessary); an
   air decrease  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.
                                                77

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 Operating the primary chamber at too high a
 temperature can cause the plastics to rapidly
 volatilize.
 5.  Inadequate secondary combustion air; and
 6.  Operating at too high a  primary chamber
    temperature.
 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 causes 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.


 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;
 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.
 7.7.2.2   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.


 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;
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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 setpoints,
then the unit will supply its own heat in the form of
auxiliary  fuel,  i.e., natural gas or oil. Consistent
charging of waste 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.
          f
          v
 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;
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.

7.7.5.2  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 manufacturers 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.
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 Two conditions  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 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 Scrubbers4,5
 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 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.

 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.
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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.

 7.3 Operational Problems and Solutions
      Associated with Fabric Filters^
 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 condensable 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.

 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
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  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;
 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 arrestor 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
 (10tol4in.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  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 systems
 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 Con-
   trolled-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 In-
   structional 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). Sep-
   tember 1983.

6.  U.  S. Environmental Protection  Agency.
   Operation and Maintenance Manual for Fabric
   Filters, EPA/625/1-86/020. June 1986.
                                               83

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                                          Chapter 8
                                       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) operating 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 manufacturers' 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,  performance
 guarantee, piping and  instrumentation diagram,
process flowsheet, material balance information for
normal and maximum design conditions, and an
instruction manual for O&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 Records*
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 Records*-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 that it operates, and the availability of
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  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.

  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.   Pnmary combustion chamber temperature
      3.   Secondary combustion chamber temperature
      4.   Incinerator draft
      5.   Exhaust gas O2 concentration
      6.   Auxiliary fuel feed rate
  B.  Wet Scrubber Operating Parameters
      i.  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 Fiitor 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
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 Records*
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
 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.
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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.

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 Protection 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.
                                                 87

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                                          Chapter 9
                                     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
     Handlingi

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;
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 continued problems with bag integrity occur;
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.
9.2  Equipment Safety Procedures*^

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;
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  8.  Avoid direct contact with the hot surfaces of the
     incinerator chamber,  heat recovery equipment,
     ductwork, and stack;
  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 and 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.
  9.3 Fire Safety^

  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 arid
 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 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.
                                               90

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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. 1986
                                               91

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                                        Chapter 10
                                         Glossary
ABSORPTIONS

ACID GASES*
ACTUAL CUBIC
FEET PER MINUTE
(acfm)3

AERODYNAMIC
DIAMETER*
                      The process by which gas molecules are transferred to (dissolved in) a liquid phase.

                      Corrosive gases formed during combustion of chlorinated or halogenated
                      compounds and sulfur-containing compounds, e.g., hydrogen chloride (HC1), or
                      sulfur oxides (SOX).

                      A gas flow rate expressed with respect to temperature and pressure conditions.
                      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:
                      where:
                       ipa
                      p
                      C
                           =  aerodynamic diameter
                           =  physical diameter
                           =  particle density
                           =  Cunningham correction factor
                      Air containing no water vapor.

                      The noncombustible inorganic residue remaining after the ignition of combustible
                      substances.

                      The reduction of liquid to a fine spray.

                      The loading, or accumulation, of filter cake on the bag fabric to the point where
                      capacity air flow 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.
AIR, DRY*

ASH5


ATOMIZATION*

BAG BLINDING
BOTTOM ASH5
 BURN RATE*
                      The solid material that remains on a hearth or falls through the grate after
                      incineration is completed.

                      The total quantity of waste that is burned per unit of time that is usually
                      expressed in pounds of waste per hour.
 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.
 GEMS
                      Continuous Emission Monitoring System (CEMS). The total equipment required
                      for the determination of opacity or an emission rate for stack gases.
                                              93

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 CHARGE RATE4

 CLINKERS5


 COCURRENTOR
 CONCURRENT4

 COLLECTION
 EFFICIENCY!

 COMBUSTION*


 CONDENSATION*

 CONTROLLED AIR
 INCINERATIONS


 COOLDOWN PERIOD


 CROSSFLOW4

 CYCLONE4

 DAMPER2

 DEHUMIDIFYl
 DEMISTER4

 DENSITY2

 DIFFUSION
 (AEROSOL)4

 DRAFT!
DUST2


DUST LOADING2
 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.

 Hard, sintered, or fused pieces of residue formed in an incinerator by the
 agglomeration of ash, metals, glass, and ceramics.

 Flow of scrubbing liquid in the same direction as the gas stream.


 The ratio of the weight of pollutant collected to the total weight of pollutant entering
 the collector.

 A thermal process in which organic compounds are broken down into carbon dioxide
 (CO2) and water (H2O).

 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.

 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.

 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.

 Flow of scrubbing liquid normal (perpendicular) to the gas stream.

 A device in which the velocity of an inlet gas stream is transformed into a confined
 vortex from which inertial forces tend to drive particles to the wall.

 An adjustable plate installed in a duct to regulate gas flow.

 To remove water vapor from a gas stream.

 A mechanical device used to remove entrained water droplets from a scrubbed gas
 stream.

 The ratio of the mass of an object to the volume of the object.

 Random motion of particles caused by repeated collisions of gas molecules.


 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.

 Solid particles less than 100 micrometers created by the breakdown of larger
 particles.

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.
                                              94

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ENDOTHERMIC*

ENTRAINMENT3
EXOTHERMIC*

FEEDBACK
CONTROLS
FIXED CARBON*
GRID1
HEADERi
HEAT RELEASE
RATE*

HEATING VALUE*
HUMIDITY,
ABSOLUTE2
HUMIDITY,
RELATIVE2
INCINERATOR*
INDUCED DRAFT
FAN3
INERTIA*
 LIQUID-TO-GAS
 RATIO3
 LIQUOR*
 MAKEUP WATERS

 MIST ELIMINATORS
 OPACITY*
 PACKED-BED
 SCRUBBERS
 PARTICLE*
 PARTICLE SIZE*
A chemical reaction that absorbs heat from its surroundings. For example:
C + H2O + heat -» CO+H2.
The suspension of solids, liquid droplets, or mist in a gas stream.
A chemical reaction that liberates heat to its surroundings. Combustion is an
exothermic reaction. For example: C + O2 -» CO2 + heat
An automatic control system in which information about the controlled parameter is
fed back and used for control of another parameter.
The nonvolatile organic portion of waste.
A stationary support or retainer for a bed of packing in a packed bed scrubber.
A pipe used to supply and distribute liquid to downstream outlets.
The energy released over a unit of time during combustion. Calculated as the
heating value (Btu/pound) X burn rate (pound/hour). Usually expressed as Btu/hour
(Btu/h).
The amount of heat that is released when a material is combusted, usually expressed
as Btu/lb.
The weight of water vapor carried by a unit weight of dry air or gas.

The ratio of the absolute humidity in a gas to the absolute humidity of a saturated
gas at the same temperature.
A thermal device which combusts organic compounds using heat and oxygen.
A fan used to move a gas stream by creating a negative pressure.

Tendency of a particle to remain in a fixed direction, proportional to mass and
velocity.
The ratio of the liquid (in gallons per minute) to the inlet gas flow rate (in acfm).

A solution of dissolved substance in a liquid (as opposed to a slurry, in which the
materials are insoluble).
Water added to compensate for water losses resulting from evaporation and water
disposal.
Equipment that removes entrained water droplets downstream from a scrubber.
Measure of the fraction of light attenuated by suspended particulate.
 Equipment using small plastic or ceramic pieces, with high surface area to volume
 ratios for intimate gas/liquid contact for mass transfer.
 Small discrete mass of solid or liquid matter.
 An expression for the size of a liquid or solid particle, usually expressed in microns
 (or micrometers).
                                               95

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 PARTICULATE
 EMISSION*
 PARTICULATE
 MATTER*
 PATHOGENIC

 PATHOLOGICAL
 WASTE

 PENETRATION*

 pHl

 PRESSURE DROPS


 PRESSURE, STATIC*


 PROXIMATE
 ANALYSIS*


 PYROLYSIS


 QUENCHi

 REAGENT3

 RED BAG WASTE
RESIDENCE TIME


SATURATED GAS*


SIZE DISTRIBUTION*


SLURRYl

SMOKE*



SPECIFIC GRAVITY!


SPRAY NOZZLEl
 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 CO2 or 7% oxygen.

 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.

 Waste material capable of causing disease.

 Waste material consisting of anatomical parts.


 Fraction of suspended particulate that passes through a collection device.

 A measure of acidity-alkalinity of a solution.

 The difference in static pressure between two points due to energy losses in a gas
 stream.

 The pressure exerted in all directions by a fluid; measured in a direction normal
 (perpendicular) to the direction of flow.

 The determination of the amounts of volatile matter, fixed carbon, moisture, and
 noncombustible (ash) matter in any given waste material, usually expressed in
 percentages by weight.

 The chemical destruction of organic materials in the presence of heat and the
 absence ofoxygen.

 Cooling of hot gases by rapid evaporation of water.

 The material used in a scrubbing system to react with the gaseous pollutants.

 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.

 Amount of time the combustion gases are exposed to mixing, temperature, and
 excess air for final combustion.

 A mixture of gas and vapor to which no additional vapor can be added at specified
 conditions.

 Distribution of particles of different sizes within a matrix of aerosols; numbers of
 particles of specified sizes or size ranges, usually in micrometers (um).

 A mixture of liquid and finely divided insoluble solid materials.

 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.

 The ratio between the density of a substance at a given temperature and the density
of water at 4°C.

A device used for the controlled introduction of scrubbing liquid at predetermined
rates, distribution patterns, pressures, and droplet sizes.
                                              96

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STANDARD CUBIC
FEET PER MINUTE
(scfm)3

STARVED-AIR
INCINERATION

STOICHIOMETRIC
AIR

STUFF AND BURN
ULTIMATE
ANALYSIS


VAPOR*
VOLATILE MATTER
A gas flow rate expressed with respect to standard temperature and pressure
conditions (20°C [68°F] and 29.92 in. Hg [760 mm]).


Controlled air incineration in which the primary chamber is maintained at less than
stoichiometric air conditions.

The theoretical amount of air required for complete combustion of waste to CO2 and
H2O vapor.

A situation in which the charging rate is greater than the burning rate of the
incinerator.

A determination of the quantities of the various elements (i.e., carbon, hydrogen,
sulfur, nitrogen, and oxygen) and ash of which a substance is composed, usually
expressed in percentages by weight.

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.

That portion of waste material which can be liberated with the application of heat
only.
10.1  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.

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.
                                                         • U.S. GOVERNMENT PRUNING OFFICE:! 993 .750 .002/ 6016K
                                                97

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