PB87-167086
      Combustion Technologies  for  Hazardous Waste
      (U.S.)  Environmental Protection Agency
      Cincinnati, OH
      Mar 87
L
J

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                                      EPA/600/D-87/066
                                      March 1987
COMBUSTION TECHNOLOGIES FOR HAZARDOUS HASTE
                      By

              Robert A. Olexsey
      Chief, Treatment Technology Staff
          Thermal Destruction Branch
      Alternative Technologies Division
 HAZARDOUS HASTE ENGINEERING RESEARCH LABORATORY
       OFFICE OF RESEARCH AND DEVELOPMENT
      U.S. ENVIRONMENTAL PROTECTION AGENCY
              CINCINNATI, OH 45268

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COMBUSTION TECHNOLOGIES FOR HAZARDOUS WAS

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Robert A. Olexsey
U.S. Environmental Protection Agency, Hazardous
Waste Engineering Research Laboratory, Alternative
Technologies Division, Thermal Destruction Branch,
Cincinnati, Ohio 45268
11. S*OrtOlNG AOf NC KAMI AND ADOMSS
HAZARDOUS WASTE ENGINEERING RESEARCH LABORATORY
same OFF ICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OH 45268
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March 1987
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Encyclopedia Article
EPA/600/12
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This article describes basic Incineration technology. Terminology 1s defined
and EPA's regulations stated. The universe of Incinerated and 1nc1nerab1e
waste 1s described. Technology descriptions are provided for liquid Injection
Incineration, rotary kiln Incineration, at-sea Incineration. Industrial boiler
disposal, and cement kiln combustion advantages and disadvantages of each approach
are given.
19. V*0*MAPe
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Release to Public
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Unclassified

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28


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                      NOTICE

This document has been reviewed in accordance with
U.S. Environmental Protection Agency policy and
approved for publication.  Mention of trade names
or commercial products does not constitute endorse-
ment or recommendation for use.

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                 COMBUSTION TECHNOLOGIES FOR  HAZARDOUS  WASTE
                              Robert A.  Olexsey
                      Chief, Treatment Technology  Staff
                          Thermal  Destruction Branch
                      Alternative Technologies Division
               Hazardous Waste Engineering Research Laboratory
                     U.S. Environmental  Protection Agency
                           Cincinnati. Ohio  45268
INTRODUCTION
    The U.S. Environmental Protection Agency (EPA)  estimates  that,  in 1981,
there were 260 million metric tonnes (MKT)  of hazardous  waste generated in
the United States.  From Table 1, we can see that this waste  1s managed in a
variety of fashions.  The numbers are based on notifications  received by the
Agency under the Resource Conservation and  Recovery Act  of 1976 (RCRA) and
contain some double accounting. -For instance, some wastes may be stored,
then treated, and the residues subjected to disposal.  Some wastes  may go
directly to disposal facilities.  Under RCRA, EPA has  promulgated separate
regulations for treatment, storage,  and disposal  facilities (TSDFs).  The
principal disposal operations are underground Injection  (60 percent) and
landfill (5.5 percent).  Under RCRA, Incineration 1s classified as  a treatment
technique.  Table 2 describes the waste treatment technologies employed 1n
1981 (1).
    As can be seen from Table 2, RCRA regulated Incineration  currently accounts
for a small amount of total  hazardous waste management 1n  the United States.
EPA estimate*, that 25 MMT of hazardous waste 1s capable  of being Incinerated.
Therefore, there 1s significant potential for Increased  use of Indne^fion
as a hazardous waste disposal practice 1n the United States.   In addition to

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                                      2
the 1.70 HMT of hazardous waste Incinerated under RCRA,  3.50 MHT of Industrial
wastes are burned 1n about 1300 Industrial  boilers and 0.35 MMT are burned 1n
other Industrial processes such as cement kilns.   Under  RCRA, the wastes
currently disposed of In boilers and Industrial processes  are considered
fuels and not subject t.o existing RCRA regulations.  Incineration and combustion
1n boilers and Industrial processes will  be discussed 1n later sections of
this paper (2).
TERMINOLOGY
     EPA defines what constitutes hazardous waste and what 1s acceptable waste
management technology.  EPA's regulations have led, Invariably, to the use
of acronyns to describe laws, regulations, and technical terms within the
context of discussion of hazardous waste  combustion. Definition of some of
these terms 1s 1n order here to acquaint  the uninitiated reader with the specific
vernacular used 1n the field of hazardous waste Incineration.
     RCRA - The Resource Conservation and Recovery Act  of 1976.  This act
            required EPA to promulgate regulations to control the generation
            and management of hazardous wastes.  This act has been amended  .
            and extended a number of times, most  recently 1n 1984.
     TSDF - A treatment, storage, and/or  disposal facility.  The facilities
            can be commercial or on-s1te  (at the  point of generation) and are
            facilities that manage hazardous wastes. These facilities are
            subject to RCRA regulations.   These regulations apply to the
            treatment, storage and/or disposal components of the waste manage-
            ment process.  A given TSDF may merely be a  storage facility or
            1t may store, treat, and dispose of wastes.   Incinerators, whether

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                                3
       they are located at  a  commercial or on site facility, are
       subject to the RCRA  TSDF  regulations that govern Incineration.
ORE -  Destruction and Removal Efficiency.  The performance benchmark
       against which RCRA Incinerators  are measured.  The RCRA Incinerator
       regulations limit the  amount of  hazardous waste material that can
       be emitted to the air. Specifically, the regulations require that
       a total of 99.99 percent  of  a particular waste compound that 1s fed
       Into an Incinerator  must  be  either destroyed  (0) 1n the combustor.
       or removed (R) by the  air pollution control equipment.  Conversely,
       taking the Incinerator and the scrubber as a  system, no more then
       0.01 percent of an Input  waste compound may be emitted from the
       system.
POHC - Principal Organic Hazardous  Constituent.  The target compound to
       be destroyed and/or  removed  1n the Incineration system.  It Is
       a hazardous organic  waste compound designated by the permit writer
       to be the subject of sampling and analyses to determine 1f the ORE
       requirement has been met.
PIC -  Product of Incomplete  Combustion.  Hazardous  organic compounds
       that are not present 1n detectable quantities In the feed to an
       Incinerator but are  emitted  from the Incinerator 1n the exhaust
       gas.
TSCA - The Toxic Substances Control Act.  The act that regulates production,
       distribution, transport and  use  of toxic materials.  The treatment,
       disposal, and Incineration of PCBs are regulated under the authority
       of TSCA.

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     PCS -  PolychloHnated Blphenyls.  Persistent organic  chemical formulations
            that have been used predominantly as  coola'ts 1n electric utility
            transformers and lubricants 1n Industrial  applications.
EPA REGULATIONS
    On January 23, 1981, EPA promulgated regulations for the Incineration
of RCRA hazardous wastes.  These regulations  state:
    *  A destruction and removal efficiency (ORE) of 99.99  percent must  be
       achieved for each principal  organic hazardous constituent  (POHC)
       designated 1n the waste stream.
     TABLE 1.  HAZARDOUS WASTE GENERATION AND MANAGEMENT (1981)
    GENERATION
    MANAGEMENT
       STORAGE
       DISPOSAL
       TREATMENT
QUANTITY
(MMT)
260
134
54
176
VOLUME
(BILLION GALLONS)
71
36.5
14.7
47.5
NUMBER OF
FACILITIES
4818
4299
430
1494
             TABLE 2.  HAZARDOUS HASTE TREATMENT (1981)
  SURFACE IMPOUNDMENTS
  TANKS
  INCINERATORS
  OTHERS
QUANTITY
(MMT)
62
32
1.7
17
VOLUME
{BILLION GALLONS)
16.6
8.73
0.45
4.48
NUMBER OF
FACILITIES
410
609
240
372

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                                     5
    0  Partlculate emissions may not exceed 180 mg/dscm  (0.08 gralns/dscf)
       for a stack gas that contains 7 percent  oxygen or  1s corrected to 7
       percent oxygen.
    0  Stack emissions of hydrogen chloride (HC1)  must be no greater than the
       larger of either 1.8 Kg per hour (4 Ib/hr)  or 1 percent  of  the HC1 1n
       the stack gas prior to entering any air  pollution  control equipment
       (3).
    A POHC 1s 2, substance which 1s listed by EPA as a hazardous waste in
Appendix VI11 of the Federal Register (40 CFR Part 261.  May 19, 1980) or a
waste which Is determined to be hazardous because  1t falls one  or  more  of
EPA's waste characteristic tests (1gn1t1b1et toxic, corrosive,  reactive).
For wastes which are made up of only one hazardous component, the  single
compound 1s the POHC.  For mixtures of compounds,  EPA provides  guidance that
recommends selecting as POHCs those compounds which are  present in the  waste
in the highest concentration and a'iso those compounds which are the most
difficult to destroy through incineration.  For cases where data on "1ncin-
erabillty" (degree of difficulty of achieving the  99.99  percent ORE) 1s
lacking, EPA recommends using the compound unit heat of  combustion ( HC per
molecular weight) as an 1nc1nerabil1ty ranking  procedure  (the higher the
HC/MW, the easier the compound 1s to destroy) (4).
     EPA's regulations provide for certain exceptions to  the Incineration
standard.  Hastes that are hazardous solely due to the characteristic of
1gn1t1b1l1ty are exempt from the regulations.  Certain military reactive
waste that possess no toxlcity characteristics  are also exempt  from the
regulations.  Finally, as stated previously, wastes that  are burned in  any

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                                      6
device that functions primarily to produce energy are  considered fuels, not
RCRA hazardous wastes, and are exempt from the Incinerator requirements.   EPA
1s considering regulations for these boilers and Industrial  thermal  processes.
The Agency has Issued guidelines that will help permitting officials determine
1f a given thermal operation 1s, Indeed, a legitimate  energy production
process, or merely a "sham" to evade the regulations.   These guidelines  deal
with fuel value of the waste, the disposition of the energy produced, and  the
ratio of waste to primary fuel 1n the combustor.
    EPA has proposed a regulation for limitation of hazardous combustion by
products, or products of Incomplete combustion (PICs)  but the proposal has
not been finalized.  In addition, RCRA regulations require minimum operating
controls such as preheating the combustion chamber with fossil fuel  before
waste 1s Introduced, automatic waste cut-off in the case of combustor "upset",
and continuous monitoring of carbon monoxide, flame activity, and  combustion
gas temperature.  Exact control parameters for each Individual facility  are
determined during the permitting process and most often established through a
trial burn.
    Incineration of polychlorinated biphenyls (PCBs) 1s regulated  under  the
Toxic Substances Control Act (TSCA).  These regulations require a  destruction
efficiency of 99.9999 percent.  In addition, design specifications for burner
operation are Imposed.  A combustion temperature of 1200*C and a gas residence
time of 2 seconds are required (5).
    Burning of wastes at sea in ocean-going incinerator ships is regulated
per international agreement (6).  Current requirements are for a 99.9 percent
destruction efficiency but any permits that may be granted most likely will

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require performance equivalent to RCRA provisions  for POHC destruction.  The
ships do not have air pollution devices and could  not operate  1f  requirements
are Imposed for HC1 control.
U.S. INCINERATION PROFILE
    Incinerator facilities 1n the United States are predoninantly privately
owned with a few facilities operated by the military and  very  few publicly
owned and operated hazardous waste Incineration plants.  Seventy-seven  percent
of the operating facilities handle only wastes that are generated on-sHe.
Such Incinerators are located at manufacturing or  processing facilities and
are dedicated to handling only wastes generated by the  facility.   The bulk of
the remainder are commercial facilities that accept, for  a disposal  fee,
wastes from a variety of generators.  All  Incinerators, whether commercial,
private, off-site, or on-s1te, must comply with the Incinerator regulations
that were described 1n the preceding section of this paper.
    Seventy-nine percent of the Incinerators handle liquids  only  while  11
percent are designed for bulk wastes and can accommodate  both  solids and
liquids.  Ten percent of the units are special purpose  Incinerators  dedicated
to radioactive, military, biological, or other type wastes.
     Table 3 describes the major waste streams incinerated 1n  the United
States 1n 1981.  The Waste I.D. Numbers are derived from  EPA'* system which
categorizes wastes by characteristics and/or Industrial process source  (7).
Hastes considered ideal  for Incineration are ignitible, nonhalogenated,
nonaqeous liquids which have low ignition temperature and little  propensity
to form hazardous combustion byproducts.  Alcohols and  spent nonhalogenated
solvents are examples of wastes which are excellent incineration  candidates.

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                                      8
    The Incineration Industry 1s fairly well  established  1n  the United States.
In 1982, there were 57 companies actively marketing  Incinerators, with 28
companies actually having sold units.  In addition to the 240 Incinerators
operating 1n the United States 1n 1982 there  were  40 units under construction.
About one-half of the operating unlcs and almost all  the  units under  construction
have air pollution control  systems.  Almost one-quarter of the operating
systems practice heat recovery of some type.   Of the total number of  Incinerators
1n operation, 64 percent were of the liquid Injection type,  17 percent were
fixed hearth, 12 percent were rotary kiln, 3  percent were fluldlzed bed, and
2 percent were multiple chamber hea^h.  Almost all  the facilities under
construction were liquid Injection, rotary kiln, or  combination  liquid/kiln
facilities (8).
INCINERATION TECHNOLOGIES
    The five hazardous waste combustion approaches which  have the most sig-
nificance from a current and/or potential application perspective will be
discussed here.  The five technologies are those presented 1n Table 4, namely
liquid Injection, rotary kiln, at-sea, Industrial  boilers, and cement kilns.
There are many other combustion approaches that appear to have the ability to
achieve acceptable waste destruction, but, at least  in the short run, are
likely to have less applicability than those  described in Table 4.  Technologies
that have promise for hazardous waste application, either generally or for
                                     ^            '                    
specialized wastes, Include the fluldlzed bed, starved air or pyrclytlc approaches,
and other industrial processes such as 11 me kiln and brick making furnaces.
Some or all of these approaches have been tested (or will  be tested)  by EPA
and have been found capable of destroying wastes.

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                                      9
LIQUID INJECTION
    Figure lisa block diagram for a liquid  Injection Incineration system.
The most common type of combustion  units marketed today are the horizontally
and vertically-fired units as depicted 1n  Figures 2  (9) and 3.  The two con-
figurations are basically similar 1n operating  conditions.
    The liquid Injection Incinerator 1s confined to  hazardous liquids, slurries,
and sludges that have kinematic viscosity  of  770 SSU or less.  The liquid
waste must be converted to a gas prior to  combustion and  this change  1s
brought about by changing the waste surface area through  atomlzatlon.  If the
kinematic viscosity exceeds 750 SSU, the atomlzatlon may  not be fine  enough
and droplets of unburned liquid may leave  the Incinerator.  An Ideal  size
droplet 1s about 40 micrometers or  less and Is  attainable mechanically by
using rotary cup or pressure atomlzatlon or via gas-fluid nozzles and high
pressure air or steam.
    The combustion chamber Is a refractory lined cylinder.  Burners are
normally located in the chambers In such a manner that the flames do  not
Impinge on the refractory walls. The combustion chamber  wall can be  actively
cooled by process air prior to Its  entry Into the combustion zone, thus
preheating the air to 150C to 270C.  Afterburners  may be used on the flue
gas but are generally not required  when the wastes have a sufficiently high
heating value*  In the case where a number of wastes are  burned, conventional
practice 1s to blend wastes prior to Introduction Into the combustion chamber
to maintain a relatively constant feed Into the chamber.
    The key to efficient destruction of liquid  hazardous  wastes lies in
minimi ring unevaporated droplets and unreacted  vapors.  As in any combination

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operation, the optimization of temperature,  residence time, and turbulence 1s
critical.  Liquid Injection Incinerators are variable dlmenslonally and have
feed rates of up to 5600 L/hr.
    Application of air pollution control processes  depends  on  operating
characteristics of the components or devices, the physical/chemical charac-
teristics of the waste to be treated, and the emission  standards  Imposed by
regulations.  For clean spent nonhalogenated solvents,  1t 1s possible that
minimal or no air pollution control  may be required.  For materials that
contain chlorine or dissolved solids, removal of HC1 and particulate emissions
may be achieved through use of high  energy venturl  scrubbers,  ionizing wet
scrubbers or, 1f HC1  has been removed or 1s not present, electrostatic precip-
itators (ESPs).  Particularly in add gas situations, corrosion and erosion
are problems and the use of add resistant tile liners, polymeric liners, and
Inconel 625 are commonplace.  Caustic solutions are used to reduce the acidity
of the gas and liquid in the air pollution control  system.
    The advantages of liquid Injection incineration are that it is capable of
accepting a wide range of liquid hazardous wastes;  it requires no continuous.
ash removal system other than for air pollution control; it possesses a fast
temperature response to changes in the waste fuel flowrate; it has virtually
no moving parts; and has relatively  low maintenance costs.  Its limitations
are that it can only accept wastes that can be atomized through a burner
nozzle; supplemental  fuel must be provided if heat  content of  the waste is
Insufficient to maintain Ignition temperature; and  the  burners are suscept-
ible to pluggage (10).

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                                      11
               TABLE 3.  MAJOR WASTE STREAMS INCINERATED  (1981)
HASTE TYPE
IgnUlble Organic Liquids
Contaminated Water
Corrosive, Reactive
Spent Halogenated Solvents
Spent Nonhalogenated Solvents
Acrylon1tr11e Bottoms
Hydrocyanic Add
39 Other Waste Streams
WASTE
I.D. NO.
D001
D001
D002, D003
F001, F002
F003
K011
P063

NUMBER OF
INCINERATORS
69
19
32
18
22
3
6
..
QUANTITY
INCINERATED
(THOUSAND
MT/YEAR)
36
127
175
16
212
109
123
107
   TABLE 4.  OPERATING RANGES OF HAZARDOUS WASTE COMBUSTION PROCESSES
PROCESS
Liquid Injection
Rotary K11n
At-Sea
Industrial Boilers
Cement Kilns
TEMPERATURE
RANGE (C)
650 to 1600~
820 to 1600
1350 to 1470
870 to 1430
1400 to 1650
RESIDENCE
TIME
0.1 to 2 seconds
Liquids and gases, seconds; solids,
hours
0.1 to 2 seconds
0.1 to 3 seconds
Liquids and gases, seconds; solids,
hours
     The U.S. EPA has conducted a number of field tests  of operating liquid
Injection facilities and has found that, generally, the  units  have achieved
the ORE required by the RCRA regulations.  Particulate emission reductions.

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especially 1n jurisdictions that have  lower  standards than the Federal require-
ment, have been more difficult to achieve.
ROTARY KILN
    Rotary kiln Incinerators are generally  refractory-lined  cylindrical
shells mounted at a slight 1ncl1ne~from the  horizontal  plane.  Rotary kiln
systems are used to degrade solid and  liquid combustible wastes, but combustible
gases may also be oxidized.  Figure 4  1s schematic of a rotary kiln system.
     Solid wastes, sometimes packed 1n fiber drums, are fed  Into the kiln,
generally being strained, then burned  1n suspension by  atomlzatlon with steam
or air.  The kiln and liquid burner are equipped with gas or oil burners  for
1nt1t1al refractory heating, flame stability, and supplemental heat if necessary.
Rotary kilns currently manufactured in the  United States Include both concurrent
(burner at the front end with the waste feed) and countercurrent (burner  at the
back end) types.  Optimal length-to-diameter (L/D) ratios range from 2 to 10 and
rotational speeds of 0.3 to 1/5 m/min  are common, depending  on the nature of
the waste.  Residence times vary from  a few seconds for a highly combustible
gas to a few hours for a low combustible solid waste.   A typical feed capacity
range 1s 600 kg/hr to 2000 kg/hr for solids, and 630 L/hr to 2250 L/hr for
liquids at tempertures ranging from 800C to 1200C.
     After leaving the kiln, the flue  gas enters a secondary combustion chamber
that contains an afterburner.  Gaseous or liquid fuels  are used to generate
a high-temperature oxidizing environment 1n  order to ensure  a complete destruction
of organic vapors.  Afterburners are generally of the direct flame type which
pass the fuel gas directly through a flame  zone.  However, afterburners may be
of the thermal type in which the flue  gas flows through a high temperature zone,

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                                      13
or of the catalytic type which Incorporate a  catalytic  surface to  accelerate
the oxidation of uncombusted gas constituents.  Temperatures ranging  from
650C to 1300C are generally required for successful operation  of afterburners.
Depending on the type of pollutant 1n the gas stream, residence  times may  range
from 0.2 to 2.0 seconds.  To ensure good mixing, afterburners are  operated at
high velocity gas flows, ranging from 8 to 15 m/s.  A typical afterburner  will
be 10 m long, 4 m high, and 4 m wide.
     Due to the nature of the feed material,  air pollution control requirements
are more severe for rotary kilns than for liquid Injection units.   High  energy
venturl scrubbers, Ionizing wet scrubbers, or wet ESPs  are required to  reduce
particulate emissions to acceptable levels (11).
     EPA has conducted field tests of operating rotary  kiln Incinerators and
found them capable of achieving the required  destruction and removal  efficiency
for organlcs.  Particulate emissions have presented a problem and  some  facilities
were not 1n compliance with the Federal  standard.
     A common configuration for large commercial Incineration facilities is
to have separate rotary kiln and liquid injection units firing Into a common
afterburner.  In this case, the afterburner 1s of the unfired thermal type
with the heat supplied by the liquid injection Incinerator.
   The main advantage of the rota"*y kiln is Its feed flexibility.   The main
disadvantage of the rotary kiln 1s its relatively low thermal efficiency.
AT-SEA
    Incineration at sea 1s a commercially viable process.  There are  currently
two ships operating 1n Europe.  Ships have operated  intermittently off the
United States Gulf Coast burning specialized  wastes. One ship has applied  for

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                                      14
a  permit for continuous operation  off the  United  States coast and at least
two United States ships are under construction.
    Incinerator ships are, In essence, large  floating liquid Injection Incin-
erators.  The ships consist of crews'  quarters,  storage tanks, and Incinerators.
The ships generally have two or three  Incinerators.  Unit Incinerator sizes
can be as much as 50 percent larger than  the  largest land based liquid Injection
Incinerators.  A single ship can handle as  much  as 6000 metric tons of liquid
hazardous wastes per voyage.
    The Incinerator ships do not use flue gas scrubbers, even for highly
halogenated wastes.  The premise behind the absence of scrubber 1s that the
plume will touch down 1n the ocean  and the  sea water will serve as a buffer
for the add gas.  If the Incinerator  ships were required to Incorporate
scrubbers, the cost advantage they  accrue due to their larger capacities than
land based units would be diminished.   Incinerator ships require, of course,
shore based facilities for collecting, storing,  and loading the wastes.
    The U.S. EPA has conducted performance  tests during a number of waste
burns.  Haste destruction efficiencies (DEs)  were  found to be equivalent to.
those achieved by land based Incinerators.
    The main advantages of at sea Incineration are fie large waste handling
capacities, low unit disposal  costs, and  the  alleviation of Incinerator
siting problems by removal of the burn site from land.  Disadvantages Include
the Inability to handle solids and  sludges, the  need for the shore facilities,
and the lack of HC1 control.

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                                 15
INDUSTRIAL BOILERS
     There are over 240,000 Industrial  boilers  1n  the  United States.  Under
current U.S. EPA RCRA regulations, hazardous  materials could be burned 1n
any of these boilers without being subject to the  Incinerator  performance
standards.  More likely to be used for  waste  disposal  are the  over 5,500
boilers that have heat production capacities  of 1.0 x  1010  joules/hr  (107
Btu/hr) or greater 1n the chemicals, petroleum  refining, and paper Industries.
    Boilers that have been or could be  used for hazardous Industrial  waste
disposal Include small flretube gas- or oil-fired  units 1n  the 1.0 to 5.3 x
1010 joule/hr (10 to 50 million Btu/hr) range,  package gas- or oil-fired watertube
units 1n the 5.3 to 15.8 x 10 joule/hr range  (SO to  150 million Btu/hr), and
large field erected oil or coal boilers larger  x::*n 15.8 x  10l joules/hr (150
million Btu/hr).  Hastes that are fired generally  are  liquid wastes that are
generated on the site of the facility (or plant) that  contains the boiler.
Hastes that are burned Include alcohols, spent  nonhalogenated  solvents, and
highly volatile by-products which may be gaseous when  Introduced Into the
boiler.
    For the smaller boilers with only one burner,  conventional practice 1s to
premlx the primary fuel (oil) and the waste material 1n a tank prior  to
Introduction Into the firebox.  For larger boilers with multiple burners, one
                                                                   *
or more burner 1s dedicated to waste Introduction  with the  remaining  burners
fired with primary fuel and used for leveling.
    Waste may constitute over 50 percent of the fuel to the boiler for partic-
ularly clean, high energy value wastes.  However,  generally, the waste feed

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                                 16
rate Is below 20 percent of the total  fuel  to the boiler.   For difficult to
burn wastes and, particularly for corrosive halogenated wastes, feed con-
centrations below 5 percent (on a volume basis)  are most common.
    Small Industrial boilers (less than 15.8 x 100 joules/hr) 1n the United
States are not currently subject to Federal air  pollution  control  regulations.
Therefore, most Industrial gas- or oil-fired boilers do not have air pollution
control devices.  Larger pulverized coal-fired boilers do  generally have ESPs
for paniculate control.  Smaller stoker-coal boilers may  have mechanical
cyclone collectors for large particles.  Some boilers which are specifically
designed to fire halogenated wastes may have wet scrubbers but there are very
few, 1f any. Industrial  boilers which  fire  waste on a retrofit basis that
have such control devices.
    As part of Its process to determine if  a Federal regulation Is required
for boiler disposal  of hazardous wastes, EPA has conducted field tests of
several operating facilities.  Generally, the tested boilers have  achieved
performance in the vicinity of 99.99 pecent ORE, not quite as good as incin-
erators, but not as bad as the Agency  feared at  the outside of the test
program.  Emissions of products of incomplete combustion from boilers, as
might be expected due to the reaction  product quenching in the superheaters
and through the steam tubes, have been 5 to 20 times higher than emissions of
principal organic hazardous constituents from the boilers  (12).
     The greatest advantage of boiler  disposal  is Its reduced cost to the
waste generator over either onsite or  offsite incineration. Besides realizing
the fuel value of the waste, the generator  appreciates waste material in a
RCRA regulated process.  Also, the waste material  does not have to be transportated,

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                                      17
at some environmental risk, to a waste disposal  site,  which,  under RCRA,
prolongs the waste generator's liability for the waste material.
     The biggest disadvantage of boiler disposal  1s  the fact  that the process
1s not regulated and may be prone to abuse by operators.  It  also deprives
Incinerator operators of a prime fuel  material  and may contribute to an
Increase 1n the cost of commercial Incineration of RCRA hazardous wastes.
CEMENT KILNS
      Figure 5 1s a schematic of a cement kiln operation that describes how
waste material may be burned along with a primary fuel.  In this arrangement,
which 1s a wet process kiln, the cement making raw materials  are fed Into the
top (left) of the kiln and exit at the bottom (right)  as cement clinker.  The
burner 1s located at the lower end of the kiln.  The fuel  and the waste are
Ignited.  The hot gases travel up the kiln, thereby  heating the cement raw
materials, exit the kiln, and are then cleaned in a  baghouse  before being
exhausted through a stack.  When waste 1s fired,  any ash that is produced
becomes part of the cement product.
     Kiln lengths range from 18.3 to 231 meters (60  to 760 ft) with diameters
from 1.8 to 7.6 meters (6 to 25 ft).  Charge retention time in the kiln
ranges from 1 to 4 hours.  Gas retention time 1s  approximately 10 seconds.
Gas temperatures will typically reach a maximum of 1650C.
     There 1s ample opportunity to employ cement  kilns as disposal vehicles
in the United States.  The United States cement Industry has  158 plants and
342 operating kilns.  Plant capacities range from 50,000 to 2,200,000 tonnes
per year of cement product.  Plants tend to be  located near large population
centers and, therefore, close to the sources of waste  generation.  Unlike

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boilers, however, cement kilns are not located  on the premises of the waste
generator and the waste must be transported off site for  disposal.  There 1s
significant economic Incentive for a kiln operator  to accept wastes for
disposal.  Besides obtaining a fee for disposal of  the  wastes, the operator
can offset some of the 33 to 40 percent of the  total cost of cement manu-
facture that 1s attributed to energy demand.
    Cement kilns generally have efficient e1r pollution control devices to
control partlculate emissions that are generated 1n the kiln.  These devices
are generally baghouses or ESPs.  Very few wet  scrubbers  are used 1n the
Industry today.  However, like boilers, kilns are extremely sensitive to high
chlorine contents which must be kept below 3 percent for  the sake of kiln and
product Integrity.
     EPA has conducted several tests of operating kilns that burn hazardous
waste materials.  While more sensitive to adherence to  proper operating
conditions than first believed, the kilns were  found to perform at least as
well as boilers.  A key factor that serves to police kiln disposal 1s the
fact that temperatures in the kiln must be adequate to  produce the cement   *
product.
    The advantages of kiln disposal are similar to  those  for boiler disposal.
However, while the combustion process, Itself,  1s not regulated at the Federal
level, the transport and storage processes are  subject  to EPA RCRA regulations.
Due to their numbers and their capacities, cement kilns have tremendous
potential for contributing to solution of the hazardous waste problem (13).

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                                      19

CONCLUSIONS
    Less than one percent of the hazardous wastes generated 1n the United
States are managed by Incineration.  Nearly IS times more wastes  could be
Incinerated than 1s currently managed through Incineration.  Approximately
three times more wastes are burned 1n unregulated Industrial  processes than
are managed 1n RCRA regulated Incinerators.
     Combustible hazardous wastes are amenable to destruction 1n  a wide
variety of combustion processes.  Most combustion processes have  been found
capable of performing 1n compliance with the EPA performance regulation  for
Incinerators.  At-Sea Incineration and cement kiln Incineration have considerable
potential to handle large volumes of hazardous wastes.
    The trend will be toward Increased utilization of combustion  as  a waste
management technique as more wastes-are prohibited from landfills.   The  trend
will be accelerated by recently enacted Federal legislation which bans specific
wastes from landfills altogether.

REFERENCES

1.   Uestat, Inc., "National Survey of Hazardous Waste Generators and Treatment,
     Storage, and Disposal Facilities Regulated Under RCRA 1n 1981," Report
     to U.S. Environmental Protection Agency, 1984.
2.   Oppelt, E. T. and Oberacker, D. A., "Comparative Assessment  of  Land
     Based and Ocean Incineration Systems."  Presented at the 1984 Summer
     National Meeting, Amerdan Institute of Chemical  Engineers,  Philadelphia,
     Pennsylvania, August 1984.
3.   U.S. Federal Register, 40 CFR, Parts 264 and 265, Volume 46, No. 15,
     January 23, 1981.
4.   "Guidance Manual for Hazardous Waste Incinerator Permits," USEPA and
     Nitre Corporation, September 1982.

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                                      20

 5.  U.S. Federal Register, 40 CFR Part  761.40.  Volume 44. No. 106. May 31.
     1979.

 6.  Convention on the Prevention of Marine Pollution by Dumping of Wastes
     and Other Matter (1972 London Dumping Convention). Intergovernmental
     Maritime Consultative Organization  (IMCO),  Lorjon. U.K., November 1972.

 7.  U.S. Federal Register, 40 CFR. Part 261,  Volume 45, No. 98. May 19, 1980.

 8.  Keltz, et al., "A Profile of Existing Hazardous Waste Incineration
     Facilities and Manufacturers 1n the United  States," Draft Report to U.S.
     Environmental Protection Agency by  Mitre  Corporation, 1984.

 9.  "Alternative Technology for Recycling and Treatment of Hazardous Wastes,"
     Second Biennial Report, State of California,  July 1984.

10.  Bonner, T. A., et al., "Engineering Handbook  for Hazardous Waste
     Incineration," Report to U.S. Environmental Protection Agency by
     Monsanto Research Corporation (SW-889), September 1981.

11.  Ackerman, D., et al., "Destroying Chemical  Waste 1n Commercial Scale  In-
     cinerators, Facility Report No. 6." Report  to U.S. Environmental Protection
     Agency by TRW Corporation (PB-270-897), June  1977.

12.  Castaldlnl, C., et al., "Engineering Assessment Report:  Hazardous Waste
     Cof1r1ng 1n Industrial Boilers," Report to  U.S. Environmental Protection
     Agency by Acurex Corporation, June  1984.

13.  Olexsey, R. A., "Alternative Thermal Destruction Processes for Hazardous
     Wastes," 1n Proceedings 1982 National Waste Processing Conference. American
     Society of Mechanical Engineers. NfYork,  New York. May 1984.

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   AULILIARY FUEL   WASTE
                                                                                        CLEAN
COMBUSTION
 AIR
MAKEUP
QUENCH
 WATER
              THERMAL
              OXIDIZER
                                   AOJUSTAPLE
                                     VENTURI
                                    SCRUBBER
SEPARATOR
                              NEUTRALIZING
                                SOLUTION .
                                                                              MIST
                                                                           ELIMINATOR
WATER SPRAY


    I
                                                                                          VtNT-
                                                                                          STACK
                                            FIG.IKE 1.   L10U1U lilCIHEKATIUII SYSTE.1

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         LIQUID WASTE
                                                          SCRUBBED
                                                           GASES
 STORAGE
   WASTE
CONDITIONING
      SUPPORT FUEL
       IF REQUIRED
      ATOMIZING GAS
 COMBUSTION
          AIR
                         FUMES
                                                             PRECOOLER
                                                                     COOLING
                                                                     SCRUBBER
                  COMBUSTION CHAMBER
                           VENTURI SCRUBBER
                                                        MAKEUP WATER
                                                  X
                                      WATER TREATMENT
                                                                              RESIDUE
FIG.'WF 2.  miUZIKJTAL
                                          U1ECTION UICIiEt
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    WASTE
AUXILIARY
  FUEL
   KILN
EXIT OUCT
                                        AFTERBURNER
                                                                        WATER
                                                                  EXIT GAS
                                                                    i
                                                       WATER
                                       ASH
                                                                QUENCH
                                                               'CHAMBER
                                                                             AA/\
                                                       WATER
                                                        ASH
                                                                                          INDUCED
                                                                                        DRAFT FANS
                                                                   STACK
                                                               VENTURI
                                                                THROAT
                                            L.
  NIST
SEPARATOR
                                                                             WATER
                                                                              ASH
                  FIGURE 4.   SCHEMATIC OF  A ROTARY  KILN TYPE  INCINERATION SYSTEM

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PROCESS
 WATER
RAW
                                                    VAPORS
1



















1
J
STACK



v
^v^^^
^^^
"O-^
10
FAN
MATERIALS ^



BAGHOUSE
FILTER



1
BAGHOUSE
OUST

SLURRY
FEED

CASES!
* H

L





j

KILN




..
TWASTE j^CS

, 
_ ~mmmml NO A fUEL OIL


^^^^^^^mm

CEMENT
CLINKER
       FIGURE 5.  SCHEMATIC OF CEMENT KILN FIRING WASTE

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