PB87-167086
Combustion Technologies for Hazardous Waste
(U.S.) Environmental Protection Agency
Cincinnati, OH
Mar 87
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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
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HAZARDOUS WASTE ENGINEERING RESEARCH LABORATORY
same OFF ICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OH 45268
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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.
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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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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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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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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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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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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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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 150°C to 270°C. 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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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 800°C to 1200°C.
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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or of the catalytic type which Incorporate a catalytic surface to accelerate
the oxidation of uncombusted gas constituents. Temperatures ranging from
650°C to 1300°C 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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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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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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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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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 1650°C.
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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18
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 UICIi«Et
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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
, •
•_ ~mmm—ml NO A fUEL OIL
^^^^^^^mm
CEMENT
CLINKER
FIGURE 5. SCHEMATIC OF CEMENT KILN FIRING WASTE
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