PB-224 582
RECOMMENDED METHODS OF REDUCTION, NEUTRALIZATION,
RECOVERY, OR DISPOSAL OF HAZARDOUS WASTE
VOLUME III', DISPOSAL PROCESS DESCRIPTIONS,
ULTIMATE DISPOSAL, INCINERATION, AND PYROLYSIS
PROCESSES
TRW SYSTEMS GROUP
PREPARED FOR
ENVIRONMENTAL PROTECTION AGENCY
AUGUST 1973
DISTRIBUTED BY:
National Technical Information Service
U. S. DEPARTMENT OF COMMERCE
-------
BIBLIOGRAPHIC DATA
SHEET
4. I ii1- .in.)
I. Kcport No.
EPA-670/2-73-053-C
""|L Recommended Methods of Reduction, Neutralization,
Recovery, or Disposal of Hazardous Waste. Volume III, Disposal
Process Descriptions - Ultimate Disposal, Incineration, and
Pyrolysis Processes
PB 224 582
5. Kcport Date
Issuing date - Aug. 1973
6.
7. AU.I,O,(S) R. s. Ottinger, J. L. Blumenthal, D. F. Dal Porto,
G. I. Gruber. M. J. Santy. and C. C. Shih
9. Pcrfommif, Organization Nome and Adders-;
TRW Systems Group, One Space Park
Redondo Beach, California 90278
8. Performing Orjtniuzation Kept.
N°'21485-6013-RU-QQ
10. Projcct/'I ask/Work Unit No.
II. Contract/Gram No.
68-03-0089
12, Rponbomifl OiŁuni7ntinn N.uni- and
National Environmental Research Center
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
13. Type of Kcporr & Period
Covered
Final
14.
15. Supplcinfnia--y Notes
Volume III of 16 volumes.
16. Absuacts
This volume provides descriptions of ultimate disposal processes, incineration, and
pyrolysis processes currently utilized for the treatment or disposal of hazardous
wastes. These descriptions detail the important features of each process and discuss
their applicability to the various classes of waste materials. The ultimate disposal
processes described in this volume include deep well disposal, land burial, landfill
disposal, and ocean dumping.
17. Key Words and Document Analysis. I7o. Descriptors
Ultimate Disposal Processes
Incineration
Pyrolysis
Deep Well Disposal
Land Burial
Landfill Disposal
Ocean Dumping
I7b. Identifiers/Open-Ended Terms
I7c. COSAT1 F.e Id/Group
] gg
18. Availability Statement
Release to public.
19. Security Class (thus
Report)
UNCLASSIFIED
20. Security Class ('1 his
Page
UNCLASSIFIED
21. Mo. of Pages
22. Price
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EPA-670/2-73-053-C
August 1973
RECOMMENDED METHODS OF
REDUCTION, NEUTRALIZATION, RECOVERY
OR DISPOSAL OF HAZARDOUS WASTE
Volume III. Disposal Process Descriptions -
Ultimate Disposal, Incineration,
and Pyrolysis Processes
By
R. S. Ottinger, 0. L. Blumenthal, D. F. Dal Porto,
G. I. Gruber, M. J. Santy, and C. C. Shih
TRW Systems Group
One Space Park
Redondo Beach, California 90278
Contract No. 68-03-0089
Program Element No. 1D2311
Project Officers
Norbert B. Schomaker
Henry Johnson
Solid and Hazardous Waste Research Laboratory
National Environmental Research Center
Cincinnati, Ohio 45268
Prepared for
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
-------
REVIEW NOTICE
The Solid Waste Research Laboratory of the National Environmental
Research Center - Cincinnati, U.S. Environmental Protection Agency has
reviewed this report andi approved its publication. Approval does not
signify that the contents necessarily reflect the views-and policies of
this Laboratory or of the U.S. Environmental Protection Agency, nor does
mention of trade names of commercial products constitute endorsement or
recommendation for use.
The text of this- report is reproduced by the National Environmental
Research Center - Cincinnati in the form received from the Grantee; new
preliminary pages and new page-numbers have, been supplied.
ii
-------
FOREWORD
Man and his environment must be protected from the adverse
effects of pesticides, radiation, noise and other- forms of pollu-
tion, and the unwise management of solid waste. Efforts to protect
the environment require a focus that recognizes the interplay between
the components of our physical environment-air, water, and land.
The National Environmental Research Centers provide this multidisci-
plinary focus through programs engaged in:
• studies on the effects of environmental
contaminants on man and the biosphere, and
a search for ways to prevent contamination
and to recycle valuable resources.
Under Section 212 of Public Law 91-512, the Resource Recovery
Act of 1970, the U.S. Environmental Protection Agency is charged
with preparing a comprehensive report and plan for the creation of
a system of National Disposal Sites for the storage and disposal of
hazardous wastes. The overall program is being directed jointly by
the Solid and Hazardous Waste Research Laboratory, Office of Research
and Development, National Environmental Research Center, Cincinnati,
and the Office of Solid Waste Management Programs, Office of Hazard-
ous Materials Control. Section 212 mandates, in part, that recom-
mended methods of reduction, neutralization, recovery, or disposal
of the materials be determined. This determination effort has been
completed and prepared into this 16-volume study. The 16 volumes
consist of profile reports summarizing the definition of adequate
waste management and evaluation of waste management practices for
over 500 hazardous materials. In addition to summarizing the defini-
tion and evaluation efforts, these reports also serve to designate a
material as a candidate for a National Disposal Site, ifJ^e material
meets criteria based on quantity, degree of hazard, and difficulty of
disposal. Those materials which are hazardous but not designated as
candidates for National Disposal Sites, are then designated as candi-
dates for the industrial or municipal disposal sites.
A. W. Breidenbach, Ph.D., Director
National Environmental Research Center
Cincinnati, Ohio
i i i
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TABLE OF CONTENTS
VOLUME III
DISPOSAL PROCESS DESCRIPTIONS
v
ULTIMATE DISPOSAL, INCINERATION, AND PYROLYSIS PROCESSES
Page
Ultimate Disposal Processes
Deep Well Disposal !
Land Burial 17
Landfill Disposal 37
Ocean Dumping 59
Incineration and Pyrolysis Processes
Incineration 83
Pyrolysis 239
Preceding page blank
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DEEP HELL DISPOSAL
1. INTRODUCTION
Deep well disposal is a system of disposing of raw or treated,
filtered hazardous wastes by pumping the wastes into deep wells where
they are contained in the pores of the permeable subsurface rock,
separated from other groundwater supplies by impermeable layers of rock
or clay. A generalized flow sheet is shown as Figure 1.
HASTE TREATMENT
PLANT
INJECTION
PUNP
HASTE
PRODUCING
PLANT
' *."•
-•*"*•*• MATER TABLE'
- r - IMPERVIOUS STRATA
POROUS RESERVOIR
STRATA
Figure 1. Deep Well Disposal
Because adequate surface disposal of wastes is usually quite expensive,
the disposal of wastes in deep wells has been selected in many cases as
being a practical and economical alternative for limiting pollution
hazards.
Subsurface injection has been extensively and successfully used in
the disposal of oil field brines ... there are now somewhere between 10,000
and 40,000 brine injection wells in the United States. The same principles
can also be utilized in the design and installation of industrial waste
disposal well systems.
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Partly because of more stringent pollution legislation, the number of
industrial waste injection wells competed in the United States has increased
considerably over the recent past. From 1950 to 1963, 36 wells were com-
pleted; in the following 3 years, 39 more veils were installed; and by 1968,
there were some 100 disposal wells in operation.
Injection wells can be used by virtually any type of industry which is
located in the proper geologic environment and which has a waste product
amenable to this method. A number of industries presently using the deep
well injection method are shown below. The largest users of deep well disposal
systems are the chemical and pharmaceutical industries.
Percent
Chemical and pharmaceutical plants 50
Refineries 22
Steel and metal plants 7
Other, including paper mill, coke
plants, etc. 21
The following discussion provides an overview of the various factors
considered in the selection, design, construction, and operation of a deep
well waste disposal facility. Much of the technical and procedural infor-
1523
mation presented below was obtained from an article by Mr. John Heckard
1622
of Dames and Moore, Consulting Engineers, from personal communications
with Mr. Heckard, and from the report on deep well disposal by the National
Industrial Pollution Control Council. The discussion of the various factors
is followed by an assessment of the application of deep well disposal to
hazardous wastes.
2. OPERATION PRINCIPLE
Deep well injection is actually a storage system, since the waste materials
injected into the subsurface formations remain there indefinitely. The question
of major importance is, therefore, "Under what conditions can deep sub-
surface strata be utilized for the storage of liquid wastes?"
To serve as an adequate liquid storage reservoir, an injection
stratum must have sufficiently high porosity and permeability. Although
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under certain conditions all types of rocks are capable of storing
injected fluids, porous sedimentary rocks (such as sandstone, limestone,
and dolomite) are most likely to have the proper geologic characteristics
required for waste injection.
An injection horizon must be separated from fresh water aquifers 0"
any other usable natural resources by impervious confining strata such
as clay or shale. The selection of a site, therefore, must provide for
the protection of developed and undeveloped mineral resources, including
ground water.
3. DESIGN
The design of an injection well is based on the depth of the well,
the anticipated injection pressures, and the anticipated future main-
tenance requirements. In addition, state regulatory agencies often
maintain specific requirements concerning the construction of waste
injection wells; and, in all cases, the final design of the well must
be approved by the appropriate state agency.
The construction details of a typical injection well are shown in
Figure 2. In most cases, two or more well casings are used in the
injection well. The customary procedure is to drill a large diameter
hole through all fresh water aquifers. Casing is then inserted in the
well, and the annular space is filled with cement.
If the formation to be used for injection is known in advance,
drilling proceeds to the top of that formation, where a second string of
smaller pipe is cemented in the hole from top to bottom. Then a smaller
hole -- usually about eight inches in diameter — is drilled through the
injection formation. Injection tubing is placed in the casing and
sealed at the top and bottom with packers. The well is then ready for
testing.
If several rock zones need to be tested, the appropriate tests are
performed in each zone as the hole is being drilled. Once the hole
reaches the planned total depth, casing is installed and the annular
space is grouted with cement. The well is then completed by perforating
the casing and the cement at the appropriate zones.
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CEMENT
DIESEL FUEL
"jrjwrv.v vvv*
CASING
INJECTION TUBING
PACKERS
Figure 2. Typical Injection Well
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The annular space between the Injection tubing and the casing may be
filled with an inert fluid such as diesel fuel. A pressure recording
gauge is installed to measure changes in pressure in the annular space.
Should either the tubing or the casing develop a leak, a pressure change
would be recorded. In some instances, the fluid in the annular space
is maintained under a pressure higher than that in the injection tubing.
Then, if a break in the tubing occurs, the effluent will not leak into
the annular space.
Wells presently in use range from about 300 feet to more than 12,000
feet in depth; the depths of a sample of 75 wells now in use are as follows:
Depths of Well Percent of Total Wells
0-1000 feet 7
1000-2000 feet 29
2000-4000 feet 22
4000-6000 feet 31
6000-12,000 feet 9
greater than 12,000 feet 2
Effluent Treatment
Often it is necessary to treat the liquid waste to avoid detrimental
reactions during the injection process. The required treatment depends
on the amount and size of the solids suspended in the waste, the pore
sizes of the formation to be injected, the chemical compatibility of the
effluent and the formation fluids, and the corrosiveness of the effluent.
The removal of suspended solids may not be necessary if the injection
zones are composed of limestone or dolomite, since these rocks have
rather large pores.
Surface storage facilities are usually included in the design of
deep well disposal systems. Commonly, cement-lined sumps or steel tanks
-------
are used. An oil layer is frequently used to prevent contact of -the
effluent with the air. However, if there is oil in the effluent, it is
generally removed before injection because it tends to plug the injection
zone. Oil may be removed by first passing the waste through a settling
tank equipped with internal baffles and then through a clarifier or a
sedimentation tank designed to remove the suspended solids. The sedimen-
tation process.can be accelerated by using a flocculation or coagulation
agent such as aluminum sulphate or ferric sulphate.
Coagulation and sedimentation may not adequately prepare the effluent
for injection. Where sand-and sandstone injection zones are susceptible
to plugging, filtration is included as a part of waste treatment. The
filters may consist of a series of metal screens coated with diatomaceous
earth. If the waste contains microorganisms, some chemical treatment
may also be required. Generally, five types of microorganisms can inter-
fere with the subsurface injection system: slime formers, algae, iron
bacteria, sulphate-reducing bacteria, and fungi.
Often the cost of the effluent treatment facilities exceeds the cost
of drilling, testing, and -constructing the injection well; but nevertheless
this treatment is less expensive than the treatment which .would be
required to render the effluent acceptable for discharge into streams.
Operation of Injection Wells
Three critical factors which control the operation of an injection
well are: (1) the compatibility of the effluent with the formation and
the formation fluids; (2),the injection pressure; and (3) the injection
rate.
Effluent Compatibility. The physical and chemical properties of the
effluent are extremely important. The pores of the injection horizon can
be plugged by suspended splids or dissolved gas contained in the effluent.
Plugging can also be caused by chemical reactions between the effluent
and the aquifer materials, or between the effluent and the,.native water
in the injection zone. Plugging of the pores results in a'decrease in
-------
porosity of the storage formations which, in turn, causes a reduction in
well capacity.
Precautions to minimize the possibility of chemical reactions between
the effluent and the aquifer materials were discussed in the preceding
section. The various chemical reactions between injected and native water
have been studied in some detail by various researchers. Although the
exact influence of such reactions on aquifer permeability is uncertain,
they will often cause undesirable results.
Sometimes when chemical reactions between injected and intersticial
fluids are anticipated, the injection of a neutral fluid such as treated
water has been successful in forming a buffer zone between the injected
wastes and the interstitial fluids. Mathematical calculations substan-
tiated by laboratory experiments have shown that longitudinal effluent
dispersion will increase with the square root of the time or distance of
flow. The size of the neutral buffer zone necessary to prevent reaction
can be related to the undiluted width of the buffer zone by taking into
account the total pore space in the buffer zone. Generally, preventing a
chemical reaction from occurring within 100 feet of the well bore is suf-
ficient. For more critical conditions it may be necessary to consider
the dispersion coefficient and the viscosities of the fluids. It is
important, however, that the two injected fluids do not bypass each other
in the formation.
Injection Pressure. The injection pressure of a well consists of
the sum of the injection zone pressure and the friction head losses due
to the flow of the fluid through the well and into the injection zone.
Proper injection well design can minimize such head losses. For example,
they can be held at a minimum if the formation porosity is not reduced by
sedimentation or flocculation within the injection formation. Also,
artificial stimulation of the aquifier can sometimes increase the porosity
of the formation in the vicinity of the well.
-------
Generally, injection pressures vary with the depth of the well,
but most injection pressures are less than 200 psi. The range of injection
pressures for wells presently in use is shown below. High injection
pressures are usually undesirable
Injection Pressure, psi Percent of Total Wells
partial vacuum 14
0-150 29
150-300 27
300-600 9
600-1500 20
greater than 1500 1
not only because they restrict the rate of effluent injection but also
because they require considerably more expensive equipment. The well
itself must then be designed to withstand higher pressures.
Injection Rate. Most of the problems that arise during the operation
of an injection well are related to the rate of injection. Usually, an
optimum injection rate can be established for each well; to exceed this
rate might result in operational problems. Data regarding the Injection
rates of wells presently in use is as follows:
Injection Rate, GPM Percent of Total Wells
0-50 27
50-100 17
100-200 25
200-400 26
400-800 4
greater than 800 1
Sometimes it is necessary to increase the porosity and .permeability
of the injection formation to produce an increase in the injection rate.
This can be achieved by acid-lzing or fracturing the injection zone.
Acidizing increases the effective permeability of limestone and dolomite
8
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formations in the vicinity of the well bore by dissolving certain
minerals such as calcium carbonate. Fracturing increases the permeability
by breaking up the rock or by enlarging pre-existing fractures by hydraulic
or detonation methods. It is important, however, that fractures created
by this process do not extend vertically through confining layers, since
ground water contamination might then occur.
4. PROCESS ECONOMICS
In 1963, the cost of complete deep well disposal installations ranged
from $30,000 to $1,400,000. In the least expensive system, no surface
equipment was required for treating the waste; and the well was only 1,800
feet deep. The most expensive system included a treatment plant with a
clarifier, dual filters, and four positive displacement pumps for Injection
into a 12,000-foot-deep well.
Currently, the cost of deep well disposal ranges from 50 cents to
$2.00 per thousand gallons Injected. This cost depends upon many
variables including the depth of the well, the type of well completion,
injection pressure, and treatment equipment required.
Cost analysis for a typical well -- about 3,000 feet deep --
indicates that drilling, completing, and testing would cost less than
$150,000. The cost of necessary treatment facilities would be additional
expenses and dependent on the particular requirements of the wastes and
the site.
5. OTHER FACTORS TO BE CONSIDERED
Legal Requirements
Before starting a deep well disposal project, it is essential to
discuss the plan with the appropriate regulatory agency and to obtain
the necessary approvals. In about 34 states the construction of waste
injection wells is subject to certain requirements. Only 3 states,
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Missouri, Ohio and Texas, "have laws specifically governing wells for the
disposal of industrial wastes. Most other states do not rule out the use
of injection wells, but they often lack favorable geologic conditions
and, therefore, do not have suitable sites for injection wells. Some
states do not allow the use of deep well injection. If the geology is
suitable and if the plans for well construction are adequate, authori-
zation to proceed is generally given; but if a reasonable doubt exists
in the minds of regulatory officials, subsequent hearing may be required.
In some cases, conditional permits are issued. For example, a permit
may limit the maximum injection pressure which may be used, or it may
stipulate that one or more formation pressure monitoring wells must be
included in the project.
Regional Considerations
The specific location of a waste injection well must be evaluated
by a detailed geologic subsurface investigation. However, regional
geologic conditions can be used to evaluate whether certain areas are
generally suitable for injection wells.
j
The regional favorability map (Figure 3) indicates that
certain areas of the continental United States such as the Rocky
Mountains are generally unsuitable for waste Injection wells because
igenous or metamorphic rocks lie near the ground surface (gray areas in
the figure). Such rocks do not have sufficiently high porosity to warrant
their use as a disposal formation. Areas underlain by extensive layers
of volcanic rock (triangles on map) generally are not suitable for waste
disposal wells. Even though these rocks have porous zones, they
generally contain fresh water. The waste disposal potential of the
Basin and^Range Provinces (see angled lines on map) is largely unknown
owing to complex geologic conditions.
10
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While the central valley of California is geologically well suited
for the installation of disposal wells, several factors discourage their
use. Thick sequences of sandstone in the region provide suitable injection
horizons; but discontinuities in pervious strata, earthquake hazards,
and presence of extensive oil and gas accumulations are negative factors.
Although the geology of the West Coast is complex, coastal areas north of
Los Angeles may contain satisfactory potential sites for injection wells.
The Atlantic and Gulf coastal plains are underlain by thick sequences
of sedimentary rock which, except in oil and gas producing areas, are
generally suitable for deep well injection. The midcontinent and much of
the Midwest are underlain by rather thick sequences of sedimentary rocks.
Most of the injection wells in use today are located in these areas.
Geologic Investigations and Field Tests
The final appraisal of a disposal well site is usually determined by
a two-phased geologic investigation. The first phase includes an
evaluation of potential sites on the basis of available data. The second
phase consists of a more detailed evaluation of subsurface conditions
based on information obtained from drilling a pilot hole or the injection
well.
Information sought during the first phase of the investigation and
prior to the installation of an injection well includes the extent,
thickness, depth, porosity, permeability, temperature, water quality, and
hydrostatic pressure of potential injection zones. The presence of imper-
meable confining beds, lateral changes in rock properties, the existence
of faults or joints, and the occurrence of any mineral resource in the
area must also be evaluated. Existing wells in the area which may
penetrate the potential injection zones must be located since, if not
properly plugged, liquid wastes could escape through these wells.
11
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GENERALLY UNFAVORABLE
GENERALLY FAVORABLE
^I GENERALLY UNFAVORABLE
GENERAL FAVORABILITY
UNKNOWN
Figure 3. Deep Well Disposal Sites
-------
Injection.
different requirements relating to their extent of
may
system of zone classification has been proposed as follows.
this zone is normally precluded.
successfully with suitable monitoring.
F1ow. in this subzone the native liquid is
potential storage of the more concentrated wastes
13
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Stagnant Subzones. These subzones are, with few exceptions, several
thousand-feet below land surface, and the fluid is hydrodynamically trapped';
This zone would seem ideal for injection of very toxic waste. However, thef
capability,to accept and retain injected fluids needs to be assessed with
extreme caution.
Dry Subzones. A common type of dry subzone would be a salt bed or
dome in which free water is virtually nonexistent, and'which may be imper-
meable in a finite sense. Waste injected in such a zone would be wholly
isolated from natural hydrbdynamic circulation. However, since movement
could occur through hydrofractures, performance of a dry subzone under
injection should be assessed cautiously.
It is recommended that research be done to coordinate the limits of
the various zones mentioned and to associate such zones with the various
categories of wastes. In this manner, further information can be gathere'd.
6. RECOMMENDATION ON THE APPLICATION OF DEEP WELL DISPOSAL
In the past, there has not been enough attention given to the moni-
toring of deep well disposal systems. It' is desirable to monitor injection
wells to determine the extent of travel of injected waste permitting the
detection of well casing'or cement failures, the escape of waste-through
fractured or faulted cap rocks, or through other abandoned or operating
wells, and the loss of permeability in the injection horizon during injection.
Monitoring is also'required to determine the pressure-heeded to
maintain a constant injection rate, since this increases with time. An
increase in pressure probably indicates decreased permeability. A \
sudden increase in the intake rate of the injection well might indicate
the opening of horizontal or vertical fractures in the injection horizon
and possibly in the confining beds, or the failure of such well facilities
as the casing, cement, or packers.
Such monitoring activities need to be documented and be made require-
ments of State and Federal laws relating-to deep well disposal.
14
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Related to monitoring requirements is the necessity for developing
adequate planned methods and procedures to be followed to rapidly insti-
tute corrective actions in the event of a system failure. It is recom-
mended that research be done to establish a list of the proper monitoring
methods and implementation methods associated with deep well disposal and
to develop procedures for instituting corrective actions in the event of
a system failure.
In addition, complete operating records are required to denote
quantities and types of waste injected into a particular stratum. Require-
ments for such records need to be part of State and Federal legislation.
The use of deep well disposal techniques should be limited at the
present state-of-the-art to those waste stream constituents which have
low toxicity in themselves and which also do not have breakdown or expected
reaction products demonstrating high toxicity. This recommendation is
based primarily on the apparent lack of control over wastes following
injection. Without proper and adequate monitoring techniques the
migration of hazardous materials from the "storage" area may not be
detected until there is an effect on the non-storage area (ground water
contamination, etc.) when it might be too late. Furthermore, given that
an unexpected migration is detected there are currently no tested proce-
dures which will reverse the migration or allow total recovery of the
materials, or seal the periphera to insure halting the migration.
In summary, deep well disposal methods can be utilized subject to
detailed geological investigations and selection, rational selection of
wastes to be so disposed and proper monitoring of the sites so that
disposal can be stopped at the proper time without fear of migration.
15
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7. REFERENCES
0844. National Industrial Pollution Control Council. Waste disposal in
deep wells. Government Publication 55-95. Feb. 1971. 34 p.
1573. Heckard, John. Deep well injection of liquid wastes. Engineering
Bulletin No. 35. Los Angeles, Dames & Moore, 1970. 6 p.
1622. Personal communication. G. Melickian, Dames & Moore, to A. Lee,
TRW Systems, Apr.. 19, 1972.
16
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LAND BURIAL DISPOSAL
1. INTRODUCTION
Land burial is adaptable to those hazardous materials that require
permanent disposal. Disposal is accomplished by either near-surface or
deep burial. In near-surface burial the material is deposited either
directly into the ground or is deposited in stainless steel tanks or
concrete lined pits beneath the ground. The standard procedures for deep
burial are disposal in salt mines or hard bedrock, or in shale formations
by using hydraulic fracturing. Hydraulic fracturing is not covered here
but is covered under deep well disposal.
' In land burial the waste is transported to the selected site, where
it is prepared for final burial. Transportation of the wastes to the
burial site can be accomplished in three ways: by common carriers with
the waste packaged along with ordinary shipments of wastes, by contract
carriers that handle only the hazardous materials to be buried but collect
from various sources, or by private carriers that transport their own
wastes from the point of origin to the burial site.
Either solid or liquid wastes can be received at the burial site.
To reduce the mobility of the wastes before burial all liquid wastes
should be converted to a solid form. This requires that special solidifi-
cation equipment be located at the burial site. Coupled with this special
solidification equipment heavy equipment for excavation and lifting and
special monitoring instruments and stations will also be required.
^
At the present time near-surface burial of both radioactive and
chemical wastes are being conducted at several Atomic Energy Commission
(AEC) and commercially operated burial sites.1423 These wastes are buried
in unlined trenches approximately 20 ft in depth. The trenches are
filled to within 2 to 5 ft of the surface and are covered with either
17
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asphalt or soil and vegetation to reduce Infiltration of water. Radio-
active wastes are stored in either liquid or solid form in steel tanks
enclosed 1n concrete.0705'0710
Pilot plant studies have been conducted for deep burial in salt
formations °696' °957 and hard bedrock.0738 These wastes would be
buried approximately 1,000 to 1,500 ft beneath the ground in unlined
tunnels. The wastes are lowered into these tunnels by means of a
central access shaft. After the filling operation is complete in a
tunnel, it is sealed off by backfilling with salt and using a positive
seal (e.g.,concrete).
2. OPERATION PRINCIPLES
Land burial operates on the principle of permanent confinement and
isolation from the biosphere. The wastes can be disposed of near the
surface in specially constructed trenches or pits that are designed to
retain the wastes and prevent infiltration into the soil. They can also
be buried deep beneath the ground where better Isolation from the
biosphere is afforded. For either method the form of the waste, type
of container, and site geology are of utmost importance in determining
the suitability of any land burial disposal process.
3. DESIGN
This section describes the factors related to site selection and
type of monitoring system required. In addition, the design of current
land burial disposal operations is discussed.
Site Selection
The selection of a site for the disposal of hazardous materials is
dependent upbn several factors. These include physical characteristics
of the wastes to be buried, environmental characteristics of the area,
operating equipment and waste handling procedures required, and the
18
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geographic characteristics of the surrounding area.
The types of hazardous wastes to be buried at a particular disposal
site are important in determining whether the site is owned and operated
by a private concern or by the government. If only short-lived materials
are to be disposed of then private ownership and operation with state or
federal licensing and regulation can be considered. For long-lived
materials it is imperative that the disposal site be located on state
or federally owned land to ensure that perpetual monitoring and care
can be maintained. Even though government ownership of the site is
required, on-site operation can be performed by a private concern.
o
In selecting the location of a disposal site the environmental
characteristics of the area are important. The environmental factors of
principal concern are meteorology, geology, hydrology, and geoseismology.
Detailed meteorological data are required since if a particle or gas
escapes to the outside environment, its fate is determined by the
prevailing meteorological conditions. The frequency of wind direction
toward any given sector determines the degree of possible risk to the
population within that sector from material emitted upwind. Besides
wind direction, wind speed affects the dilution rate of the material.
The amount and rate of rainfall are significant factors in determining
the amount of material that can be leached from the wastes.
The geology and hydrology of the area determine whether waste is
dispersed or confined. The factors which influence the movement of
the waste are: main formations in the area, such as gravel, clay,
sand, and shale; permeability and ion exchange capacity of the soil;
and depth of the water table.
Since water represents the main vehicle of transporting any
significant quantities of wastes from the burial site, the site should
be as far as possible from any important ground water sources. Since
the ground water can convey the wastes to the surface streams, it is
19
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necessary to determine the possible movement of ground water from the
burial site into the streams, springs, and water sources. The points
of ground water discharge must be established and the dilution capacity
of the surface streams determined.
In near-surface burial the trenches or concrete and stainless steel
lined pits should be constructed to hold the wastes above the water table.
This is to prevent leaching of the waste by the ground .water. The wastes
should also be buried as far .as possible from any surface stream or water
wells in order to maximize the retention time in the soil if leaching
of the wastes does occur. In this way the waste can be retained by
the natural processes of absorption, filtration, and ion exchange. The
trenches or pits should be covered with an impermeable material to
prevent infiltration of rainfall. Infiltration of rain can be prevented
by covering with cement or by covering with clay or shale and capping
with asphalt. Also, infiltration of rain can be reduced by covering
with grass or other vegetatipn. This latter method is less desirable
than the other two since some infiltration of water can occur especially
during periods of heavy rainfall.
The geoseismology data such as faults, vibrations, and tsunamis are
the major earthquake phenomena that must be considered. Since there is
a general lack of knowledge about earthquakes, it is necessary to make
conservative estimates and evaluations of the critical geoseismological
data. A seismic probability map of the United States is shown in Figure 1
depicting zones of no, moderate, and major damage. The largest zone of
possible major seismic damage lies along the west coast of the United States
In locating the disposal site it is necessary to provide sufficient
distance between the site and the surrounding population to minimize
the danger to the general public by either normal operation or accidental
releases. For nuclear reactor plants federal regulations (10CFR100)
specify that'the reactor plant be surrounded by a zone of low population.
This same regulation should also apply to a disposal site of hazardous
materials. A population density map of the United States is shown in
-------
Legend
zone of no or minor damage
zone of moderate damage
zone of major damage
Figure 1. Seismic Probability Map.
0705
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Figure 2. The major areas with a population density of less than 30
persons per square mile are located in the midwest, southwest, and
northwest regions of the United States. In addition to selecting an
area of low population density the site should be located to minimize
the distance required to transport the hazardous materials to the site.
Monitoring System
For each waste received at the burial site inventory records should
be kept identifying the type of waste received, its activity and toxicity,
and the source and quantity of the waste. Also the form (liquid or
solid), type of container and date received should be recorded. A coding
or permanent marking system should be devised to record the location of
all buried wastes. These data should then be recorded on a map. A
monitoring system is also required to measure the amount and location of
any discharged wastes. This should include direct monitoring of the wastes
in each burial site and monitoring of test wells, surfaces, streams, and
lakes in the general area of the burial site.
In deep burial in either salt mines or hard bedrock a waste retrieval
pi in should be devised. This plan should call for the development of
systems capable of retrieving the wastes. This plan should also be
coupled with a worst case hazards analysis to determine what happens if
the integrity of the site is destroyed or the waste retrieval system
does not perform according t.o design. A continuous monitoring system
is not only needed to measure the discharge of any wastes but to also
measure any changes in the geology of the area and in the location of
the buried wastes.
Present Design
At the present time most hazardous materials are disposed of by
near-surface burial. These materials are either buried directly in
the ground or in stainless steel tanks or concrete lined pits beneath
the ground. Research and pilot plant studies are being conducted for
deep burial in salt mines or hard bedrock.
22
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Legend
<30 persons per sq. mi.
>30 persons per sq. ml.
Figure 2. Population Density in the United States.
0705
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Near-surface burial of radioactive wastes is being conducted at
several AEC sites and also at six commercial burial sites. The locations
of these sites are included in this report (Tables 1 and 2). In addition
to radioactive wastes some commercial burial sites also handle certain
chemical wastes. These commercial burial sites are regulated by the
AEC or by an AEC agreement state.
A complete description of the operation and facilities at several of
the commercial burial sites is provided by R. J. Morton, AEC. A
brief description of five of these sites is included (Table 3). At each
of these sites the wastes are buried in trenches approximately 20 ft in
depth. These trenches vary in width from 25 to 60 ft and vary in length
from 300 to 700 ft. The design of the trenches at each site is fairly
similar. The trenches are designed not to intercept the ground water
table and are constructed with a bottom drain and sump for water monitoring.
The trenches are unlined, so that the extent of leaching is dependent on the
permeability of the soil. At each site liquid wastes are solidified by.
mixing with various additiyss, such as concrete, which absorb and solidify
the wastes. These commercial facilities also offer packaging and
transportation services.
Radioactive wastes haye also been stored as liquids in stainless
steel encased in concrete and buried underground. These tanks range in
size from 0,33 to 1.3 million gal. The tanks are equipped with devices
for measuring temperatures, liquid levels, leaks, and for agitating the
contents. At the present time these tanks are considered as an interim
storage technique due to a-general lack of confidence in their long-term
integrity.
Stainless steel bins buried beneath the ground have also been used at
the Idaho Chemical Processing Plant, Idaho Falls, for solid radioactive
wastes The life of these bins has been estimated at 500 yr. The bins
are constructed of 1/4-in.-thick stainless steel and each bin is 12 ft in
diameter and 42 ft high. Six bins are enclosed in a concrete vault The
vault is constructed of two-ft-thick reinforced con.crete and is 46 ft in
diameter and 69 ft high. The vault is 45 ft below ground level and rests
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TABLE 1
AEC BURIAL SITES
Site Designation
Contractors
Location
Hanford
Savannah River
National Reactor
Testing Station
Los Alamos
Oak Ridge National
Lab.
Feed Materials
Production Center
Sandia Laboratories
Pantex Plant
Nevada Test Site
Paducah Gaseous
Diffusion Plant
Portsmouth Gaseous
Diffusion Plant
Atlantic Richfield; Douglas
E.I. duPont de Nemours & Co.
Argonne National Lab.; General
Electric; Idaho Nuclear Corp.;
Westinghouse
University of California
Union Carbide Corp.
National Lead Co. of Ohio
Sandia Corporation
Mason and Hanger-Silas
Mason Co.
Reynolds Electric and
Engineering Co.
Union Carbide Corp.
Goodyear Atomic Corp.
Richland,
Washington
Aiken,
S. Carolina
Idaho Falls,
Idaho
Los Alamos,
New Mexico
Oak Ridge,
Tennessee
Fernald, Ohio
Albuquerque,
New Mexico
Amarillo,
Texas
Mercury,
Nevada
Paducah,
Kentucky
Piketon,
Ohio
25
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TABLE 2
COMMERCIAL BURIAL SITES
iLocation Operator
West Valley, New'York Nuclear Fuel Services
Barnwell, South Carolina Chemical Nuclear Service, Inc.
Beatty, Nevada . Nuclear Engineering Co.
Richland, Washington Nuclear Engineering Co.
Sheffield, Illinois Nuclear Engineering Co.
Morehead, Kentucky Nuclear Engineering Co.
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TABLE 3
COMMERCIAL RADIOACTIVE WASTE BURIAL SITE CHARACTERISTICS1423
Characteristics
Site
Background
Ownership of site
Population - density in area
Location re towns and cities
Area of (1) site; (2) control (acres)
Communications
Precipitation (in.)
Beatty. Nevada
State of Nevada, leased to NECO
Desert, virtually uninhabited
About 12 mi southeast of Beatty
(1) 80; (2) desert, not controlled
Good; hwy U.S. 95
2.5-5.0/yr
Site Characteristics
Drainage
Bedrock depth and materials (est)
Surflcial material - depth; types
Ground water - depth; slope
Land and water use downstream
General soil characteristics
Adequate
575+ ft; various sedimentary and
metamorphic
-v-575 ft (?); alluvial clay, sand,
etc.
275-300 ft; SE-v-30 ft/mi
Very little, desert conditions
Semi-arid desert; deep soil
Operation - Equipment and Methods
Monitoring instruments and devices
Waste handling machinery
Trenches - (1) dimensions; (2) design;
(3) water pumped?
Waste handling - (1) transport by
company; (2) processing; (3)
burial procedures
14 survey instrs; film, air
monitors; etc.
Tank truck; trailer trucks; dozer;
35-T crane
(1) 650 x 50 x depth 20 ft; (2)
usual design, I.e., drain to
sumn, 4 ft backfill; (3) no water
collected
(1) yes; (2) liquids solidified;
(3) sp. nu. mat. spaced at
bottom, slit tr. for high-
activity materials
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TABLE'S
COMMERCIAL RADIOACTIVE WASTE BURIAL SITE CHARACTERISTICS1423 Cont'd.
Characteristics
Site
BackfjroumJ
Ownership of site
Population - ily in area.
Location re towns iind cities
Area of (1) site; (2) control (ncroi.)
Communications
Precipitation (in.)
West Valley, New York
NYASDA, leased to NFS
Rural, less than 50/sq mi
About 30 mi $W of Buffalo
(1) 10+; (2) 3345 state owned
Good; U.S. hwy and rwy
40/yr
Site Characteristies
Drainage
Bedrock depth and materials (est)
Surficial material - depth; types
Ground water - depth; slope-
Land and water use downstream
General soil characteristics
Several creeks
50-75 ft; type bedrock not
stated
25-35 ft glacial till; 25-35 -
ft silty till
Variable; slopes with surface'
drainage
Farming; no domestic surface -
supply
Slow water movement; good
sorption
Operation - Equipment and Methods
Monitoring instruments. andtdcvi.crs
Waste handling machinery
Trenches - (1) dimensions;*(2) design;
(3) water pumped?
Variety, types, and numbers -
as licensed
Usual - crane, shovel, dozer,
lifts, etc.
(1) 700 x 35 x depth 20 ft;
(2) usual design; bottom
slope 2: 100; (3) yes
Waste handling - (1) transport by
company; (2) processing;'(3)
burial procedures
(1) no; (2) no low-level
processing; (3) usual,
trenches filled, mounded
cover
28
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TABLE 3
COMMERCIAL RADIOACTIVE WASTE BURIAL SITE CHARACTERISTICS
1423
Cont'd.
Characteristics
Background
Ownership of site
Population - density in area
Location re towns and cities
Area of (1) site; (2) control (acres)
Communications
Precipitation (in.)
Morebead. Kentucky
State of Kentucky, leased to NECO
Rural, sparse (Maxey Flats)
10 mi northwest of Morehead
(1) 200 (est); (2) 1000 (est)
Fair; state hwy N and S
46/yr (heavy storms)
Site Characteristics
Drainage
Bedrock depth and materials (est)
Surficlal material - depth; types
Ground water - depth; slope
Land and water use downstream
General soil characteristics
Well drained
50-75 ft (?); shale, sandstone,
siltstone
50-75 ft (?) shale, clay, siltstone
>320 ft ("perched" none);
erratic
Very little nearby, distant (no
data)
Very Impermeable; good soil
sorption
Operation - Equipment and Methods
Monitoring instruments and devices
Waste handling machinery
Trenches - (1) dimensions; (2) design;
(3) water pumped?
Essentially same as at Beatty
Usual - crane; dozer; forkllfts;
etc.
(1) 300 x 50 x depth 20 ft; (2)
usual design, sump; (3) Yes
Waste handling - (1) transport by
company; (2) processing; (3)
burial procedures
(1) and (2) same as Beatty (both
NECO); (3) per "Radiation Safety
Plan" (NECO)
29
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TABLE 3
COMMERCIAL RADIOACTIVE-WASTE BURIAL SITE CHARACTERISTICS
1423
Cont'd.
Characteristic;
Site
Background
Ownership of site
Population - density in area
Location re towns and cities
Area of (1) site; (2) Control (acres)
Communications
Precipitation (in.)
Richland, Washington
State of Wash., leased to NECO
No residents, inside AEC plant
25 mi N of Richland
(1) 100; (2) 1000 state owned
Good; AEC Hanford reservation
6-8/yr
Site Characteristics
Drainage
Bedrock depth and materials (est)
Surficial material - depth; types
Ground water - depth; slope
Land and water use downstream
General soil characteristics
Well drained
250-450 ft; basalt
150-350 ft; silty sand, gravel,
clay
240 ft; N and E -x. 15-35 ft/mi.
Columbia River - all uses
Little-precipitation;.deep dry
soil
Operation - Equipment arid Methods
Monitoring instruments and devices
Waste handling machinery
Trenches - (1) dimensions; (2) design;
(3) water pumped?
AE licensed - survey instrs, film,
counters
Usual -crane, shovel, dozer, lifts,
etc.
(1) 300 x 60 x.depth 25 ft; (2)
usual design; (3) no water
collects in sump
Waste handling - (l) transport by
company; (2) processing; (3)
burial procedures
(1) yes, 95%; (2) liquids solidified;
(3) sp. nu. mat. spaced, separate
trench for ion-exchange resins
30
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TABLE 3
COMMERCIAL RADIOACTIVE WASTE BURIAL SITE CHARACTERISTICS
1423
Characteristics
Site
Background
Ownership of Site
Populatimi - density in area
Location re towns and cities
Area of (1) site; (2) control (acros)
Communications
Precipitation (in.)
Sheffield. Illinois
State of Illinois, leased to NECO
Rural, sparse
3 mi SW of Sheffield; others 3-7 mi
(1) 27; (2) isolated, not controlled
Excellent, expressways and 2-lane hwy
35/yr
Site Characteristics
Drainage
Bedrock depth and materials (est)
Surficial material - depth; types*
Ground water - depth; slope
Land and water use downstream
General soil characteristics
Intermittent drainage
40-60 ft; shale and clay, deeper
is sandstone
50-60 ft; glacial - silty clay, loess
40-60 ft (SW), 15-25 ft (N); N -u 100-
150 ft/mi
No specific information; probably
limited
Low permeabilities; some shallow
soil cover
Operation - Equipment and Methods
Monitoring instruments and devices
Waste handling machinery
Trenches - (1) dimensions; (2) design;
(3) water pumped?
Waste handling - (1) transport by
company; (2) processing; (3)
burial procedures
Survey instrs; mon.itoring system
and lab
Usual - lifts, dozer, crane, etc.;
medium cap
(1) 500 x 40 x depth 20 ft; (2) usual,
drain and sump; (3) no
(1) yes; (2) liquids solidified -
vermiculite and cement; (3)
usual, per regulation
31
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on bedrock. .The vauU is provided with a cooling air system to provide
convective cooling of the bins. A detailed design of these storage
facilities is available. 071°
Pilot plant studies have been conducted for deep burial in salt
mines. Detailed designs of a salt mine disposal facility for solid
radioactive wastes0696 and for solid chemical wastes0957 have been
prepared. At the salt disposal facility the wastes would be received
at a surface facility and lowered down a steel-lined shaft into the
working area of the mine. The working area would be located approximately
1,000 ft below the surface.. The wastes would then be transported to the
disposal area in the mine by either a specially designed underground
waste transporter or by a conveyor belt. After the waste disposal
operations are complete in a particular area, this area is then shut,
off by backfilling with salt.
Studies have been conducted at the Savannah River Plant near
Aiken, South Carolina for the disposal of radioactive wastes in-vaults
excavated in crystalline rock 1,500 ft beneath the surface. Access to
the vault would be provided, by a 15-ft-diameter shaft. The wastes would
be stored in tunnels extending from the central shaft. These tunnels
would be approximately 30 ft wide and 18 ft high. Each tunnel is
provided with a 2-ft-diameter service shaft. For the disposal of liquid
wastes the tunnel is isolated from the main shaft by two concrete Bulk-
heads, each 10 ft thick. The tunnel is then filled via the main shaft
with the service shaft serving as an air vent. After the tunnel is
filled, it is sealed by two concrete bulkheads.
4. PROCESS ECONOMICS
"f
Typical rates charged at the six commercial burial sites for near-
surface burial of radioactive or chemical wastes are included (Table 4). The
wastes received at each burial site must be enclosed within containers
that are in accordance with AEC, U. S. Department of Transportation (DOT),.
or U. S. Bureau of Explosives regulations. The minimum rate charged for
unloading,and burying these containers is $0.75 per cubic foot. Special
surcharges are also made for containers weighing in excess of 15 tons
32
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TABLE 4
1423
TYPICAL RATES CHARGED AT COMMERCIAL BURIAL SITES
Basic rate for containers less than 15 tons total weight: $0.70 per
cubic foot plus state charge of $0.05 per cubic foot.
Surcharge for containers in excess of 15 tons:
Surcharges ($)
Height . Tons, Per Shipnent Per Container
0 . 15 0.00 plus 0.00
15 _ 30 130.00 plus 200.00
30 . 50 260.00 plus 330.00
50 - 60 520-°° Plus 475*°°
60.80 1,600.00 plus 1,200.00
80 _ 130 3,200.00 plus 2,500.00
Surcharge for special handling of containers consisting of two or more parts.
This is for removing and burying inner containers which have been shipped inside
a shielded coffin, cask or container:
Primary Containers with shipment * Per Hour*
Surface Dose Rates j_pgrj>mpmcnt *_ - _
0.2tolOr/hr $25.00 Plus $26'°°
.
10to50r/hr 50.00 plus 26.00
50 to 100 r/hr 100.00 plus 26.00
100 to 500 r/hr 250.00 plus 26.00
*The $26.00 per hour referred to includes consulting and preparation of
proper procedures.
Minimum charga for any shipment is $L'0.00.
33
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and for containers that require special handling.
Cost studies have been conducted^5 for tank storage of radioactive
wastes. The waste management and storage costs were based on an economics
model using a discounted cash flow technique. This type of model requires
that the income received must provide for the recovery of investment, the
desired return on investment, all cash expenses, and the establishment of
a reserve account to pay all waste management operations that remain to
be completed after all income has ceased.. Using this model, costs were
determined0705 for perpetual tank storage of high-level liquid radioactive
wastes. For a 50-yr tank life and a 1,000,000 gal. capacity the costs
varied from $4,100 to $8,200 per ton of fuel depending on the type of
waste (acid or alkaline) and type of ownership (government or private-).
Costs for interim solid storage of radioactive wastes in water-filled
canals were presented as a function of age of the waste. The costs range
from $1,275 per ton of fuel for 1 yr storage of 30-yr-old waste in
6-in.-diameter pots to $4,100 per ton of fuel for 30 yr storage of 1-yr-old
waste. Costs were also presented for solidifying these wastes using the
pot calcination technique. For calcination in 6-in.-diameter pots these
costs ranged from $4,200 per ton of fuel for 1-yr-old waste to $800 per
ton of fuel for 30-yr-old waste.
For deep burial of hazardous materials in salt mines cost studies '
for radioactive wastes and ifor chemical wastes are included. For -
radioactive wastes the costs were based on the same economic model described
above. The wastes were assumed to be buried in vertical holes in the
floor of the salt mine at a depth of 1,000 ft. The burial costs vary with
the heat generation rate and age of the waste at burial. For burial in
6-in.-diameter pots the disposal costs range from $2,800 per ton of fuel
for 1-yr-old waste to $260 :per ton of fuel for 30-yr-old waste.
Detailed cost estimates for constructing and operating a chemical
waste storage facility in bedded salt have been derived. The facility
was located in Boco County, Colorado and had a storage space of 43.6 million
cubic ft mined in bedded salt at a depth of 1,330 ft. The total cost of
_=™S
34
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the facility was estimated at $41 million which gives an average cost of
$0.96 per cubic foot of waste stored. Cost for disposal in a solution
mined facility were also presented. This facility would consist of four
caverns having an average diameter of 67 ft and a height of 4,000 ft. The
total volume of the four caverns would be 43.6 million cubic ft and the
average cost of disposal was estimated at $0.32 per cubic foot of waste
stored.
5. PROCESS APPLICABILITY
Land burial is a possible choice for those hazardous materials that
require complete containment and permanent disposal. This includes
radioactive wastes as well as highly toxic chemical wastes. Disposal can
be accomplished by either near-surface or deep burial. Deep burial is
more applicable to the highly toxic or dangerous materials since better
isolation from the biosphere is afforded. The important criterion In
evaluating a particular land burial process is determining the integrity
of the site. Sites with a life expectancy of a few hundred years are
not applicable to wastes with a life expectancy of a few thousand years.
In addition, before any land disposal methods can be selected, it must
be determined if eventual retrieval of the wastes is required. This
could be required if new reprocessing techniques are devised or under
emergency conditions.
At the present time only near-surface burial is used for the
disposal of most wastes. Low-level radioactive wastes and some chemical
wastes are buried in unlined trenches 20 ft in depth. High-level radio-
active wastes are stored as liquid in steel tanks located near the ground
surface. For deep burial in salt formations or hard bedrock only pilot
plant studies are being conducted at the present time.
35
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6. REFERENCES
nfiQfi Bradshaw R L. et al. Evaluation of ultimate disposal methods for
0696. Bradshaw R. L. et^ padioactive wastes v; ?i , of solid wastes
in salt formations. Oak Ridge National Laboratory, ORNL-3358.
Mar. 1969.
0705. Staff of the Oak Ridge National Laboratory Siting of fuel
reprocessing plants and waste management facilities. Oak
Ridge National Laboratory, ORNL-4451, July 1970.
0710. Bendixsen, C. L. Storage facilities for radi.oacjj^tca1^
waste solids at the Idaho Chemical Processing Plant. Idaho
Nuclear Corp., Idaho Falls, IN-1155. July 1968.
0738 Proceedings of the Symposium on the Solidification and Long-Term
0738. ^«JJ;^f°H1 hl Ldioactive Wastes sponsored by Atomic Energy
Commission, Richland, Washington, Feb. 14-18, 1966. CONF-660208.
0957 Dunn, C. S. et al. Feasibility of permanent storage of solid
chemical waste in subsurface salt deposits. Femx and Scission,
Inc., Tulsa, Oklahoma, F&S-196, Oct. 1971.
1423. Morton, R. J. Land burial of solid radioactive fstes: study of
commercial operations and facilities. Atomic Energy Commission,
Washington, WASH-1143, 1968.
36
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LANDFILL DISPOSAL
1. INTRODUCTION
Wastes received at a hazardous waste disposal facility or generated
as the residue from other neutralization/detoxification processes can be
solids, liquids, sludges or slurries, or combinations thereof. Common
landfill disposal methods for these materials Include the following:
(1) mixing with soil, (2) evaporation and infiltration, and/or (3) shallow
burial.
Combinations of these methods can be involved in a disposal process.
For example, in the spreading of a slurry on land, the liquid content may
either evaporate or infiltrate into the subsoil. Solid wastes will nor-
mally be incorporated in a landfill and buried. Liquids, slurries, and
sludges might also be incorporated into a landfill; however, due to the
large quantity of moisture contained in these wastes, disposal practices
usually involve spreading them on land or placing them in ponds to maximize
evaporation or infiltration.
2. OPERATION PRINCIPLES
Landfills operate on two principles: (1) utilization of the absorptive
capacity of the soil and, perhaps, some biological degradation of the wastes
by soil microorganisms; and (2) storage of wastes such that they are isolated
from direct contact with man and the surface environment, t*'Some liquid wastes
are currently discharged to infiltrate and percolate into the underlying
porous sediments where there is no possibility of ground waste impairment.
In other cases simple, shallow burial of solid wastes in a geologically
"dead" area is the ultimate method of disposal. It must 'be stressed that
the usability of any landfill site is1 basically determined by the site's
characteristics and that their investigation is of utmost importance to
site selection.
37
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3. DESIGN
Climatological, Demographic, and Geological Investigations
As part of the selection investigations of a proposed hazardous waste
disposal site the basic meteorology of the site must be investigated. The
two primary elements of this investigation are the determination of the
average rainfall in the area and the construction (from available historical
data) of a wind rose for the site.
Demographic data for the area consists of a plot of the population
distribution-within a 25-mile radius of the site which can be compared
with the direction of the prevailing winds.
The geological and ground water conditions should be investigated
through a program of field inspection and testing that involve soil and
rock examination and the boring of test holes. The investigation
should study the depth and occurrence of ground water, its natural quality.
and the existence of natural impervious barriers. The soil types< perme-
ability, depth and thickness of impervious layers, extensiveness of their
lateral continuity, and occurrence of dip and strike of the layers should
also be determined. The investigation should indicate either that geologic
and hyrologic conditions will prevent migration of hazardous material onto
adjacent properties or that appropriate design features are feasible to
preclude such migration. Hydrogeologic conditions of the disposal facility
should be described in the report.
The number of test holes required to indicate underlying geologic
conditions should be related to the adequacy of detailed Information from
other sources. Information should be provided on underlying geology to
confirm rock types and ground water conditions (absence of ground water
and/or its occurrence and quality). Shallow zone exploration should In-
volve drilling a minimum of three test holes on the site to a depth deter-
mined by the geologist In charge of the investigation. More test holes
38
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may be necessary depending on the size of the property and the potential
for variable geologjc conditions. A rough guideline is one test hole per
each five acres of th« actual area to be used for waste disposal. Drilling
logs should be included in the report for the test holes and any wells
constructed.
The area used for any hazardous waste disposal facility should be
free from potential geological hazards, such as known earthquake faults
and land slippage or slide zones. In areas of major subsidence, this
hazard should also be evaluated. Land slippage or settlement can result
in rupture of levees surrounding industrial waste ponds, exposure of buried
hazardous materials, or slippage of earth masses into large ponds which
can result in liquids breeching or overtopping pond walls. The effect of
waste liquids percolating through soils on slope or levee stability of
other zones of weakness must be considered in the design of waste disposal
areas.
If the method of operation relies on the infiltration of large quan-
tities of liquids, the natural soils on the property should be relatively
permeable to allow infiltration to occur, and sufficient subsurface storage
capacity for the liquids should exist. Conversely, if impervious basins
are desired and the native soils are not suitable for that purpose, imper-
meable materials may have to be imported or artificial linings installed.
Soil and rock types should also be suitable for the type of excavation
work anticipated. Excavations made to allow location of the disposal facil-
ity should not create hazards of slope instability or problems of erosion.
The degree of slopes should be consistent with good engineering practice
for the particular soil or rock type. Erosive soils should be protected
such as by use of mulches or hydroseed applications.
Finally, if artificial barriers are to be installed, a report should
be submitted indicating the long-term competence of such a barrier. Re-
sponse to seismic activity and possibility of destruction through shrinking
39
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and cracking due to drying or action of the hazardous wastes should be
evaluated. Pre-tests should 'be made on all prospective liners to determine
compatibility with the material being disposed.
Qualitative Evaluation of Landfills
The parameters resulting from the investigation of potential sites
outlined above must be compared against standards designed to protect man
and the environment from the.hazards associated with the various wastes.
In California a set of standards for selecting landfill sites which is
based on contamination of usable water supplies has been defined and used
by the State Department of Public Health, the Department of Water-Resources,
and the various California Regional Water Quality Control Boards. According
to a paper by Lawrence A. Burch of the State Department of Health three
classes of wastes are recognized as requiring distinct levels of control
of site effluents (surface or subsurface): (1) water soluble materials
that constitute hazards of high toxici-ty or special water pollution poten-
tial; (2) decomposable orgaaic materials; and (3) relatively inert, non-
decomposable materials. Correspondingly, three classes of landfills dis-
posal sites are recognized and are described by Burch as follows:
"Class 1 sites are those sites located over nonwater-bearing sediments
or with only unusable ground water underlying them. The site location must
provide complete protection from flooding, surface runoff or drainage, and
waste materials and all internal drainage must be restricted to the site.
In essence, a Class 1 site is a large container providing safe, ultimate
storage of toxic or hazardous materials; a secondary function of the site
might be the processing of the waste such as evaporation to reduce the
volume of the material to be disposed of. These sites can accept almost
any type of materials, liquid or solid. These are the only sites where
the first group of wastes, such as toxic materials, oily sludges and soluble
'iA'-
industrial chemicals may be,, placed.'it''should be noted that possible public
health hazards must be recognized at the Class 1 sites in addition to water
quality protection. Certain very toxic chemicals such as pesticides or
tetraethyl lead may require- special handling techniques to protect site
personnel and to provide long-term protection of public health and the
environment.
4U
-------
"Class 2 sites are underlain by usable ground water and may be located
adjacent to streams. To protect the underlying ground water quality, a
distance Of separation must be maintained between the bottpm of the fill
and the water table. Any surface water must also be restricted from the
site to preclude water from contacting the wastes. The second group of
wastes (decomposable materials such as refuse) is the acceptable material
at this class of site, along with the third group materials.
"Class 3 sites are those sites which intercept ground water or where
wastes will be dumped directly into water. Examples are deep gravel pits
with- ground water ponded in the bottom and swampy areas where filling
operations commence without construction of levees and removal of the water.
Only the third group of wastes is allowed to be disposed of in this class
of site. These nonwater soluble, nondecomposable inert materials such as
concrete and bricks will not adversely affect the quality of water that
they may contact."
This type of classification together with geologic consideration such
as faults location, etc., described earlier is necessary for proper manage-
ment of wastes.
Quantitative Evaluation of Landfills
The procedures outlined above are all necessary to the proper selection
of a site utilizing Landfill Disposal. The data provided by the various
procedures includes both quantitative and qualitative information, but the
evaluation of these parameters is currently handled on a totally subjective
basis such as that outlined above. This subjeŁt&ve evaluation does not
t ** *
provide the necessary methodology for comparing one site with another or
for determining absolute suitability of a site for a particular waste
material. A methodology providing the framework for quantitative evaluation
0230
has been proposed by Pavoni, Hagerty, and Lee and is described in the
Appendix. Considerable research is required to test and revise the quan-
tification, but such methodology is necessary to ensuring that factors
other than economics will receive consideration in site selection.
41
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4. PROCESS ECONOMICS
The operating cost of a sanitary landfill depends of the cost of labor
and equipment, the method of operation, and the efficiency of the operation.
0772
The principal items in operating cost are:
(1) Personnel
(2) Equipment
Operating expenses - gas, oil, etc.
Maintenance and repair
Rental, depreciation, or amortization
(3) Cover material - material and haul costs
(4) Administration and overhead
(5) Miscellaneous tools, utilities, insurance, maintenance to
roads, fences, facilities, drainage, features, etc.
Wages ordinarily make up about 40 to 50 percent; cover material, admin-
istration, overhead, and miscellaneous amount to about 20 percent.
The operating costs per ton versus the amount of solid wastes handled
in tons and the population equivalent may be charted (Figure 1).
The operating cost of a small operation handling less than 50,000 tons
per year varies from $1.25 to approximately $5.00 per ton. This wide range
is primarily due to the low efficiency of the smaller operations which are
usually operated on a part-time basis.
Full-time personnel, full-time use of equipment, specialized equipment,
better management, and other factors that lead to high efficiency are pos-
sible at large sanitary landfill operations. The increased efficiency
results in lower unit cost of disposal. The unit cost of a large landfill
handling more than 50,000 tons per year will generally fall between $0'.75
to $2.00 per ton.
-------
4.00
3.00
o
l/l
o
2.00
TONS PER YEAR 0
TONS PER DAY * 0
POPULATION t 0
100,000
320
122,000
200,000
640
244,000
300,000
960
366,000
400,000
1280
488,000
500,000
1600
610,000
* BASED ON 6-DAY WORK WEEK.
ABASED ON NATIONAL AVERAGE OF 4.5 LBS PER PERSON PER CALENDAR DAY.
Figure 1. Sanitary Landfill Operating Costs
43
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5. APPLICABILITY OF PROCESS
The utilization of landfill procedures for the disposal of certain
hazardous waste materials at a National Disposal Site, in an industrial
environment, or in municipal application will undoubtably be required in
the future. In order to ensure that no damage to man or the environment
results from this technique it is recommended that all sites currently used
or proposed for the landfill disposal of hazardous wastes be subjected to
the design procedures specified in Section 3. It is further recommended
that any site considered as a National Disposal Site be subjected to the
analyses whether it is expected that landfill will be a primary disposal
mode at that site or not since account must also be taken of possible
accidental spillage of materials which represents an unintentional but
direct application of the landfill technique.
Tne waste stream constituents considered in the context of this pro-
gram are primarily in the category described in Section 3 as Class 1. It
is therefore recommended that any disposal facility handling these materials
be required to meet the Class 1 site criteria as specified in the Section 3
discussion. Finally, it is recommended that the landfill disposal model
described by Pavoni, Hagerty, and Lee, and presented in the Appendix to
this Process Description be'tested, modified, and applied to provide the
best possible sites for all types of landfill disposal.
44
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APPENDIX
Landfill Site Numerical Evaluation
In order to evaluate the potential danger of depositing any hazardous
material in a particular landfill site it is necessary to critically exam-
ine three general characteristics of that site: (1) the potential for
precipitated surface waters to infiltrate the deposited waste material;
(2) the potential for the waste material to be transported through fluid
transmission from its deposit location through underlying bottom soils
to groundwater systems; and (3) other mechanisms for the removal of haz-
ardous materials from the site and their transport to other areas. te
A number of factors have been included quantitatively in the
site rating procedure originally presented by Pavoni, Hagerty, and Lee
which follows:
Soil Parameters
"Infiltration Potential - The potential for water to enter a waste
deposit may be quantitatively expressed as the ratio of the amount of
water which may enter the top surface of the cover soil divided by the
amount of water necessary within the cover soil to produce a full passage
of moisture from the top of the layer to the bottom of the layer and out
into the contained refuse. The amount of water (i) which could theoret-
ically enter the site or enter the cover soil at the site may be estimated
as the total area under all of the rainfall intensity graphs for the site,
beneath a horizontal line representing the infiltration rate of the cover
soil (see Figure 2). The infiltration rate of the cover soil may be ex-
pected to vary from 0.01 in/hr for bare heavy clay soils to approximately
3 in/hr for loose sands. The probable range of (i) will be from 1 to 64 in.
45
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\ QUANTITY OF tli
|INFILTRATION §
TIME
AVERAGE
"iNTlLtRlfTON
RATE, IN/HR
Figure 2. Precipitation/Infiltration Chart
16
-------
The amounts of water necessary for passage of moisture through the
cover soil layer may be related to the volumetric field capacity of the
cover soil layer. In other words, whereas the field capacity refers to
the amount of water as a percentage of the dry unit weight of the soil
required for passage of water through a unit volume, the volumetric field
capacity in this instance would refer to the product of the thickness of
the cover soil layer times the field capacity of the soil. Thus, let
FC(H) be the denominator of the infiltration potential term.
where FC = field capacity of the soil expressed as a
decimal
and H = thickness of cover soil layers (inches)
The field capacity will vary from .05 for a clean sand to .40 for a clay,
whereas H will vary from approximately 30 inches to 72 inches. The in-
filtration potential may be finally quantitated as:
Tn 2i_
lp " (FC) H
having a practical range of 0.02 to 20. This infiltration potential may
be thought of as one of the most significant factors in determining the
site potential for waste transmission.
Bottom Leakage Potential - In addition to the problem of water entering
the refuse cells and removing the contained hazardous material^ consideration
must be given to the action of a waste in suspension or solution in water,
or in liquid form, passing through the bottom soil layer from its original
location and entering the groundwater system.
The potential hazard for a waste to travel through a bottom soil from
the bottom of the refuse cell through the containing soil layer and into a
groundwater flow system may be evaluated in terms of the permeability of
the bottom soil layer and its thickness. Since all natural geological
materials possess some finite permeability it is fatuous to think in terms
of an impermeable bottom in a landfill. Even in the situation where an
artificial lining material has been applied to the bottom of a refuse cell,
it is quite probable that the artificial liner is in truth not impermeable.
47
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For example, thin sheets of impervious polyvinyl chloride or polyethylene
lining may easily be pierced and penetrated during placement or after place-
ment by sharp-edged equipment or refuse items. Asphaltic liners likewise
may crack because of distortions experienced when the bottom soils settle
as a result of the applied loads of the landfill. Thus, in all cases, a
certain finite permeability of the bottom confining layer must be antic-
ipated. Therefore, in a true sense, the migration of materials from the
landfill site into the substrate must always be anticipated and the only
variable to consider is the time which will be required for such migration;
in other words, the migration time for a hazardous substance through a bot-
tom soil layer consisting of clay minerals may be sufficiently long so that
the substance's half life is greatly exceeded. In such a case the. virulence
and hazardous nature of these substances will be diminished.
For this reason this bottom leakage factor has been quite simply ex-
pressed in the form shown below to give a measure of the time factor'for
migration of a hazardous material in terms of permeability and thickness
of the bottom soils.
Bottom Leakage Potential (Lp) = y
where K = bottom soil permeability (cm/sec)
T = bottom soil thickness (ft)
The approximate range for K for all practical problems will be about 10"'
to 10 cm/sec, whereas T will vary from 5 to 50 feet. The overall
range of Lp will therefore be from approximately 0.02 to 20.
Filtering Capacity - A less important characteristic of the bottom
soils will be their ability to remove solid particles traveling downward
(through the bottom soil layer) in a fluid suspension. In general, this
filtering capacity is dependent upon the sizes of the pore spaces between
individual soil grains. In other words, the physical filtering ability
of the bottom soil will depend upon void-space size in that soil and may
therefore be related to the size of the soil particles themselves. The
48
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physical filtering capacity may be considered proportional to the inverse
of the average grain size in the soil stratum. Therefore, the filtering
capacity of the bottom soil layer may be easily expressed as shown below.
Filtering capacity (Fc) =
where 0 = average particle diameter (inches)
The average particle diameter of various soils will vary from about
to 2.5 x 10 inches. Therefoi
between approximately 2.1 and 15.0.
0.25 to 2.5 x 10"5 inches. Therefore the "filtering capacity" will vary
Adsorptive Capacities - In addition to the removal of solid particles
through physical filtering within the bottom soil layer, certain materials
will be removed from suspension and solution in a migrating fluid by the
physical-chemical attraction of the mineral constituents within the soils.
Adsorption of materials both organic and inorganic in the migrating fluids
will take place principally on colloidal-size particles consisting of clay
minerals which describe the attracting of such minerals for the migrating
particles. A general measure of such attraction is the cation exchange
capacity of the clay mineral. In this rating system the greater the danger
of transmission of a hazardous material from a landfill site the greater the
rating factor; therefore, the greater the ability of the bottom soil layer
to adsorb migrating materials the smaller should be the adsorption factor.
The ability of the soil is evaluated as an inverse quantity and a factor is
obtained by dividing a numerator by cation exchange capacity in the denom-
inator. The cation exchange capacity alone will not reflect the potential
for adsorption of a material on the minerals present in the soil. If the
available adsorption positions on the soil mineral are already occupied
then no further adsorption can occur. The occupancy of the adsorption sites
in the soil are already occupied by organic compounds and complex organic
ions. Therefore, the complete adsorptive capacity factor will consist of
the organic content as the numerator and the cation exchange capacity as
the denominator as follows:
49
-------
Adsorptive capacity (Ac) = EC) + 1
where o = organic. content expressed as a decimal
CEC = cation exchange capacity, me/100g
The range In the numerator will therefore be from 0 to 10, whereas the log
CEC will range between about 0.6 to 2.2. The adsorptive capacity (Ac) will
therefore vary between approximately 0 and 16.
Groundwater Parameters
Organit Content - Transmutations of a hazardous material following
contact with groundwater m,ust also be evaluated. Assuming that a hazardous
waste has reached the groundwater after disposal in a landfill, probably
the most important single ^water parameter to be considered would be that
of organic carbon content. The organic content of the groundwater may' be
quantitated in terms of the biochemical oxygen demand or BOD. The higher
the organic content (BOD) of a groundwater, the higher the substrate po-
tential, and consequently the higher the potential it may afford pathogenic
organisms.
Groundwater organic cpntent was assigned a third order of priority
with regard to landfill ranking factors so that its range of values was
fixed between 0 and 10 dependent upon. BOD values as follows:
Oc = .2 BOD
where Oc = organic content rating (.maximum value of 10)
BOD = biochemical oxygen demand of groundwater (mg/1)
Buffering Capacity - The buffering capacity of a groundwater is another
important parameter when cpnsidering transmutations of hazardous wastes in
groundwater systems. Any waste material having acidic or alkaline charac-
teristics would be less hazardous to the groundwater ecosystem if the water
it is entering possesses a high buffering capacity. In other words acidic
or basic waste characteristics would be neutralized or moderated upon con-
tact with a high buffering capacity water system.
50
-------
Groundwater buffering capacity was assigned a third order of priority
and was quantitated in relation to pH, acidity, and alkalinity. For the
purposes of this study the buffering capacity ranking (Be) will be equal
to ten minus the smallest number of mi Hi equivalents (maximum of ten) of
either an acid or base required to displace the original groundwater pH
below 4.5 or above 8.5. The buffering capacity ranking will therefore
vary from 0 for a strong buffer to 10 for a weak buffer.
Potential Travel Distance - The potential for travel of a hazardous
waste once it enters a groundwater system will determine how much of the
immediate landfill environment it may affect. This potential travel dis-
tance was assigned a fourth order of priority and varied in value from
0 to 5 depending upon the greatest possible distance a molecule of water
could travel from a point directly beneath the landfill through the
groundwater system and surface water systems, and thence to the sea.
Potential Travel Distance Travel Distance Ranking (Td)
0 to 500 ft -0
500 to 4000 ft !
4000 ft to 2 miles 2
2 miles to 20 miles 3
20 miles to 50 miles 4
Greater than 50 miles 5
Ground Mater Velocity - The groundwater velocity will determine how
fast a hazardous material may spread into the environment. A groundwater
system having a high velocity should therefore be assigned a higher ranking
since the time of waste transmission would be reduced.
The groundwater velocity, having a fourth order of priority, may be
defined as:
v = kS
51
-------
where V = velocity
k = permeability
S = gradient
Values of k will vary between 10"1 and 10"9 cm/sec whereas values of S will
usually range between 0 and 20 ft/mile. Groundwater velocities were ranked
according to the following formulation:
S
Gv =
log (f + 1)
where Gv = groundwater velocity rank
k = permeability (cm/sec)
S = gradient (ft/mile)
The groundwater velocity rank will .approximately r.an,ge between 0 and.
20.
Air Parameters
Prevailing Wind Direction - The third major site characteristic to
be investigated is air. The hazardous .potential of any toxin or pathogen
escaping through the atmosphere from the landfill would depend upon the
prevailing wind direction "in relation to the distribution of population
surrounding the site. Obviously the worst situation would be one in
which a strong prevailing wind blew from the site to the center of .a very.
dense population.
The following procedure was therefore developed to quantitatively
evaluate the potential ofthe prevailing wind direction. Initially, a
twenty-five mile radius circle was constructed-with the landfill site
as its center (see Figure 1). This circle was then divided into four
quadrants by drawing two -lines - one north-south, and one east-west. The
population of each quadraVit was determined (Pi) and-a point representing
the center of population (population node) was located in all 'four quad-
rants (PNi). A radius was then drawn from the site to each quadrant's
population node. The prevailing wind direction was determined and a
-------
PREVAILING
WIND
DIRECTION
Figure 3. Prevailing Wind Rose
0230
53
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radius drawn In this direction from the site (center of circle). The
angles from the prevailing wind direction to each site-population node
radius were determined (a, B, y. 6) and incorporated in the following
prevailing wind potential formula:
log
where Wp = prevailing wind potential rank
Ai = the angle from the prevailing wind direction to each
site-populatton node
Pi = the population of each quadrant
Wp quantitatively interrelates the prevailing wind direction, site
location, and population nodes of each quadrant. Wp has a practical range
of 0 to 5.
Population Factor - The population immediately surrounding the land-
fill site will determine how many persons could be adversely affected by
escaping hazardous materials. The higher the population within a specified
radius of the landfill site the higher the population factor ranking as
shown:
Pf = log p
i'
where Pf = population factor rank
p = population within a twenty-five mile radius of the
landfill site
The population factor rank will range between 0 and 7.
The total landfill site ranking formula may not be assembled by
uniting the various soil, water, and air parameters as follows:
Landfill Site Rank = Ip+Lp+Fc+Ac+Oc+Bc+Td+Gv+Wp+Pf
where Ip = Infiltration Potential
Lp = Bottom Leakage Potential
Fc = Filtering Capacity
54
-------
Ac = Absorptive Capacity
Oc = Organic Content
Be = Buffering Capacity
Td = Potential Travel Distance
Gv = Groundwater Velocity
Up = Prevailing Wind Direction
Pf = Population Factor
The first four parameters (Ip.Lp.Fc, and Ac) describe the soil system,
the next four factors (Oc.Bc.Td, and Gv) delineate the groundwater charac-
teristics, and the last two terms (Wp and Pf) depict air parameters. The
total landfill rank may assume values from approximately 0 to 110, the
lower the rank the better the landfill for hazardous waste disposal.
i
The following data has been accumulated concerning two existing land-
fill sites in Louisville, Kentucky so that a ranking comparison can be
developed.
Site fl Site #2
Yearly rainfall 43 in. 43 in.
Soil type clean sand heavy clay
Infiltration rate (% of rainfall) 75 10
Field capacity -05 .40
Permeability 10-3 iQ'8
Soil cover (inches) 60 24
Bottom thickness (feet) 20 15
Average particle diameter (mm.) 0.25 0.002
Organic content of soil 0.5 0
Groundwater BOD 10 10
Cation exchange capacity 0 80
Buffering capacity (meg) 7 4
Groundwater travel distance (miles) 750 750
Gradient (ft/mile) 5 5
Population within 25 mile radius 106 106
Prevailing wind direction WNW WNW
55
-------
Site #1 ranking-parameters - I.p=11.5, Lp=5, Fc=14.5, Ac=5, Oc=l, Bc=7,
Td=5, Gv-1.66, Wp=4.05, and Pf=6
Total landfill rank (Site #1) = 60.71
Site #2 ranking parameters = Ijp=1.03, Lp=0.145, Fc=3.2, Ac-0, Oc-1,
Bc=4, Td=5, Gv=0.625, Wp=2.9, and Pf=6
Total landfill rank (Site #2) = 23.9
Landfill #2 having a mucji smaller rank than landfill #1 would obviously
be more condusive to land disposal of hazardous wastes."
-------
REFERENCES
0230. Pavoni, J. L., D. J. Hagerty, and R. E. Lee. State of the art of
land disposal of hazardous wastes. Paper presented at the Seventh
American Water Resources Conference, Washington, D. C. Oct. 24-28,
0772. Sorg, T. J. and H. L. Hickman, Jr. Sanitary landfill facts.
Washington, U. S. Department of Health, Education, and Welfare,
1970. 30 p.
1509. California State Department of Public Health. Tentative guidelines
for hazardous waste land disposal facilities. Jan. 1972. 42 p.
57
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OCEAN DUMPING OF HAZARDOUS WASTE MATERIALS
1. INTRODUCTION
The oceans have always served both man and nature as the ultimate
disposal sink for all of the waterborne waste material carried by the
natural and man-made streams discharging at their shores, and for all of
the atmospheric pollutants scrubbed from the air by the rain that falls
on their surfaces. In addition, with increasing frequency in this century,
hazardous waste materials have been deliberately shipped out to sea and
dumped as either an expedient or an economically attractive disposal tech-
nique^ The hazardous waste materials thus disposed of have varied widely
in type, in quantity, and in frequency of disposal. Three examples of
this diversity may be cited as typical:
(1) "Spent" sulfuric acid (7 to 10% H2SO., and up to 30% FeSOJ
wastes from steel pickling and titanium oxide pigment manu-
facture processes are shipped daily to sea in specially n
designed barges, at the rate of 2.7 million tons per year.
(2) • The U. S. Army program for deep sea disposal of obsolete
chemical munitions was terminated in 1970 with the scuttling
in the Atlantic of a stripped cargo vessel laden with 418
concrete vaults which contained a total of 135,432 Ib of
GB chemical warfare agent (non-persistent "nerve gas") and
32,605 Ib of explosives.0353
(3) Individual 55-gal. drums filled with sodium metal sludge
(75% Na, 25% Ca) are pierced and dropped from the decks of
merchant vessels iptgcthe Gulf of Mexico on an intermittent,
unscheduled basis.0056
The three examples cited above illustrate the three basic techniques
for ocean disposal of hazardous waste materials. The first basic technique
is bulk disposal of liquid or slurry-type wastes. The waste materials are
loaded into barging equipment—generally, specially designed tank barges.
The barges are towed to sea, and emptied while underway at off-shore
distances that range from 10 to 125 miles.
59 Preceding page blank
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In the past, the U.S. Army and U.S. Navy have stripped obsolete or
surplus World War II cargo ships, and loaded the ships with obsolete
munitions of all types. The "explosive waste" laden bulks were towed out
to the pelagic depths beyond-the Atlantic and Pacific continental shelves,
and scuttled in pre-designated sites.
The third basic technique employed for deep sea disposal of hazardous
materials is the sinking at sea of containerized hazardous/toxic wastes.
The individual"containers, generally 55-gal. drums, are carried as deck
cargo on merchant vessels, and are discharged overboard at distances from
shore that, dependent upon the contents, may be well over 300 miles.
2. OPERATING PRINCIPLE
The operating principles involved in the three basic techniques
employed for deep sea dispos.al differ in their use of the ocean. Sea water is
used as a reacting, neutralizing medium and/or a diluent in the bulk disposal
of industrial wastes from tank barges. By contrast, obsolete munitions
detonated in the deep sea employ the ocean as a cushioning, isolating medium,
to protect the "on-shore" environment from the effects of the detonation.
Similarly, disposal of concrete-encased obsolete chemical munitions and
(undetonated) obsolete conventional ordnance items by "burial" in several
thousand feet of water use the ocean as a means of isolation, to minimize
or prevent both potential and actual impact upon the on-shore ecosphere.
The deep-sea disposal of containerized hazardous wastes is based upon
the principles cited above. Where the drums are deliberately ruptured at
the surface, the ocean is used as reactant and/or a diluent. Those ;drums
that are weighted and sunk tntact beyond the continental shelf employ the
thousands of feet of water for protective isolation of the barrels and their
contents.
The District Offices of the U.S. Army Corps of Engineers have handled
all applications for permission to engage in ocean disposal of hazardous
(and other) waste materials. If the other Federal (and State) agencies to whom
the Corps circulates the application are "reasonably agreeable," the Corps
issues a "letter of no objection" to the applicant tantamount to an
authorization to proceed. °056 The Corps may, in addition, specify
60
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TABLET.0056
MARINE DISPOSAL AREAS FOR HAZARDOUS WASTES
(BY REGION AND WASTE TYPE)
Waste Type
Industrial waste
Radioactive waste
Explosive and chemical
Pacific
9*
10*
19*
Atlantic
15*
25*
19*
Gulf
16
2
11
Total
40
37
49
munitions
Total 38 59 29 126
(No duplicates)
*Areas used for two or more types of wastes.
61
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2. Irreversibility of the impact of dumping.
t
3. Volume and concentration of materials involved.
4. Location of disposal, i.e., depth and potential impact
of one location relative to others."UJ/4
(7) Give high priority to protecting the estuaries and shallow,
near shore areas. Specifically, the Council made the fol-
lowing recommendati,o,ns to discontinue, prohibit, or phase
out the ocean dumping of the various categories of hazardous
wastes:
1. Continue prohibiting the ocean disposal of high-level
radioactive wastes.
2. Prohibit the ocean disposal of all other radioactive
wastes, excepting only the federally regulated discharge
from vessels and land-based nuclear facilities of low-
level liquid wastes, or such other low-level radioactive
wastes as have no alternative offering less harm to man
and the environment.
3. Prohibit further ocean disposal of chemical warfare
materials.
4. Continue prohibiting the ocean disposal of biological
warfare ma ten a-] s.
5. Terminate as sopn as possible ocean dumping of explosive
munitions.
6. Terminate immediately dumping of toxic industrial wastes,
excepting only those which have no alternative offering
less harm to man and the environment.
7. Phase out ocean dumping of all industrial wastes.
A number of studies have been made of the environmental effects of
ocean dumping of hazardous materials. Due to the (unique) requirement by
the Galveston District of the Corps of Engineers, that laboratory and field
studies of the effects of the wastes be filed in support of disposal appli-
cations, the majority of these studies have been carried out in the Gulf of
Mexico.0056 Inspection of the results of the various studies performed
(see Table 2 for a summary of the key findings) indicates that the toxic
effects of the hazardous chemical and pesticide wastes are generally limited
to short time periods and areas in immediate proximity to the discharge or
62
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regulatory procedures to be followed in connection with the disposal pro-
cesses.
There were 281 ocean areas designated for the disposal of wastes of
all types in 1969. Of these areas, 117 were employed for the disposal of
hazardous wastes. The regional distribution of these locations is summarized
by Smith and Brown (Table i).0056
The report to the President on ocean dumping by the Council on
Environmental Quality makes a number of strong, broad-based recommen-
dations "to ban unregulated ocean dumping of all materials, and strictly
limit ocean disposal of any materials harmful to the marine environment."
Specifically, legislation is recommended to:
(1) Require a permit from the Administrator of the Environmental
Protection Agency (EPA) for ocean, estuary, or Great Lake
disposal of any waste.
(2) Authorize the EPA Administrator to ban specific materials
and specify safe sites.
(3) Provide for Coast Guard enforcement, and establish penalties
for violations.
The Council recommended the use of the following principles in regu-
lating ocean disposal:
(4) Stop ocean dumping materials clearly identified as harmful
to the marine environment or.man.
(5) Phase out ocean disposal where existing information on
effects is inconclusive but where "best indicators" are
that the materials dumped could create adverse conditions.
If and when conclusive proof is obtained that disposal of
the materials in question produces no damage to the environ-
ment (short term, cumulative, and long-term), permit dumping
under regulation.
(6) Include in the criteria for setting disposal standards and
for urgency in stopping disposal operations:
1. "Present and future impact on the marine environment,
human health, welfare and amenities.
-------
TABLE 2.
SUMMARY OF ENVIRONMENTAL STUDIES ON INDUSTRIAL WASTES DISCHARGED AT SEA
,0056
Industrial
s-*ent sul
phur.h
acid
( hlor *u'
S'fdiurr
Slu^gt i*u
tai trued*
Pe ,i . des
Jisposal
P.aacVlr»«fcV
ORI ihoK depth
(miles) i (feet)
3 from ! 80
New |
Jeries
toast !
JS Si of 2400
r.alseston .
Texas
l
:: SE 01, 2-iou
Ca'seston
Texas
IWlSoi 2760
Freepoit
Texas
70 S of i 960
Frccpon |
Texas
i
IZSSEof ' 2400
Galveston.
Texas
i
HOSof ' 2«t»
Calvnton.,
Texas '
9SSSEof 720
Galscscon.
Texas
|
"" i
Barging Characteristics
of ssasie/
trip
3200 tons
5000 tons
1 2UO ton--
13OO luns
I7UU ions
240O tons
of do discharge ipced
charge tons/mm ; < trials)
15 feel 18 6
7U 7
i
1 2 (eel 5 6
lu(«l 5 ' 6 J
i
1 i
7 4
!
' 524 ! 6
i
1
i
1400 tors 13 25 5
< proposed I (return (rciom
mendeJi (mended*
15 55-gal
drums (500
570 pounds
per drum1
5055-gaI
dnms per
trip
Surface Va-iabie Id
•1200ft; ! barrel '2 \ 3
, ''mins '600 i
( i intenals \
on botfon '
!
Waste Characteristics
Gisen description
Fe.SO, llO'.l
l.SO, (R 5S)
3eta chloiopropslene (22"b)
tr ihloropropane (S1^) iso
props Khloridc |J8"»> allvl
chloride (1 l°i I misw chlor
des (3J«.I hiai-s cnji(3%l
pM 98 spenfi>. grants
-0 9 1 34
Pipe- " rmir 'ssastcs ** 47«J
wlid> BOO, 100.01X1 ppm
Nj.CO,. Sj,SO. NaOII
tn.' PH u
SpculK gravit) 1 27 at
60°C
Ammonium sulfatc (23%).
nitrogen ( 8°«) carbon (I2S),
organus (29°.) (alcohols
esters amides) IOD 9O
MC/L BOD, 57 (KX) ppm
pH 4 1 S C, 1 23
Sl.S (N. S,l (6°b)(NJ:S,l
SaHS \*° S (total) (6%).
NaCI iZIM organic 2%.
solids (dissolved and sus-
pended) specif K gravity
(Urganu UIMC) t-hlonnated
urginici ilO 15°.) inorganic
salts IM.SO.) (5-6%l
(acij> chlorinated organics
(l%i kulfuni and (10-15°.cl
mini. »uJ (0 1%)
Metallic sodium (75%) cil-
>.ium 1 24°!,) barium magnes
mm potassium ( 1 Si
Anilines (chloroanilme mo-
nochlorolienzene). liquid or-
ganns Imeihanol. p xylene
chloiobenunci dry chemi-
cals-insoluble (r/jrram thi
tam-E ihiontx ttneb fer
tarn mifluron Larbon disul-
(.^)
Field
Observations
Observed rffecu
Vsatir 'liscoloration plankton
tempor^rili immobile iron
allied rapidh from s irtacc
a\ei no appreciable ac^uni'ila
tion of iron found in hoftoin
Wjtri JiMiilnratini li^h
planklun kilkd nr direct
cuntaii nf ^xstr rut harmful
efledv seen atur J 4 hrs Bulk
of waste sink 1 *m diffusion ot
ssaste at Jipth
Slight ssattr disiiiioratui- Sn
morlahl) to marmi lift Bulk of
waste sank
No fish mortahts So floating
oil Bulk of uiste sank Maxi
mum ssastL sontentration at
depth
s?ci csidence of subsurface maxi-
mum ssaste Concentration
So mortalits to fish Flsin;
Jcbns hazardous lu disposal per
son nil 3OV mortality, to plank
ton clue to LOlliciion methods.
Misinif LharaeteristiLs
Initial
ddution
1-5000
1 10000-
1 100000
in 2 his
100 1
coefficient
cm" /sec
29 s 10'
2 Sx I"1
(isYrapel
(asciagcl
0002 x IOJ
Gmcral srud> i.u,rulu»ion»
Mixing and diffusion of wutc* ociur« rapidlx in the
wake of the Large So cxidffutr IP induatc .adveiw
ffffCIS
Disposal of toxiL wiNics u sea *.*n be ac..nmplished
with onl\ a slight cflcii nn organ sms in the hiomus
within a limited mrJim arc-
be a<.Lomplishcd vtuhnut >li.icrniinable -.ffct-is on
manne bioia L lutnaic disposal is ex(Us.tnl 10 be
aLLOfnplishedltx tuLtena Xdnsabk 10 monitor ea».h
separate load uf \%astr in determine toxicir> m
Uhnrator\
grc.it enough to ensure good dispersion to minimize
harmful effects to biota
Disposal should produce no significant mortal it) m
the biota nor an> prolonged eiiecu
disposal of dm uastr in the open ocean
Explosions caused b\ rejktinn of sodium with
sea water had no significant effects on targatsum and
zooplankion population*. Absence of fish kiln was
probably due lu barrenness ot disposal area
Consideration of available toxicitx and diffusion
data from literature sources indicate that Un zone of
water containing toxic concentrations of waste
surrounding each disposal drum will be limited in
extent and duration and will not endanger motile
aquatic life m the disposal area to a significant
-------
dump. The rate of dilution is, in general, so high that, after 12
hours, it is impossible to detect analytically chemical differences between
"contaminated" and uncontaminated sea areas. The toxic effects of waste
acid discharged from tank barges at sea are minimal; the zooplankton
from samples in the immediate discharge zone were immobilized temporarily,
but recovered rapidly in unpolluted water. Chlorinated hydrocarbon wastes
discharged in Gulf waters killed fish and plankton in direct contact with
the undiluted waste. In contrast, due to dilution, there was no effect
observed on marine life at the surface two to four hours after discharge.
The general ocean surface and upper level effects of chlorinated hydro-
carbon discharge range downward from the upper extreme noted above - fish
and plankton kill - through laboratory-study-detected inhibition of photo-
1783
synthesis and respiration to total absence of observable effect. The
possible effects of the discharged chlorinated hydrocarbons at deeper
levels, and on the bottom, have not been determined.
Smith and Brown report that unpierced barrels loaded with sodium
sludge (75 percent metallic sodium, 24 percent metallic calcium) have on
two occasions been retrieved in the Gulf of Mexico by fishermen. These
barrels were not pierced prior to dumping as prescribed, nor were they
dumped in the prescribed area. Pierced barrels of the sodium sludge
exploded when dropped overboard, produced no significant effects on the
nicrobiota, and, due to the probable barrenness of the area, produced no
visible fish kill.
The probable effects of deep-sea disposal in the Gulf of Mexico of
weighted steel drums, designed to rupture on the sea floor, and containing
herbicide and fungicide wastes (chloraniline, aniline, monochlorbenzene,
methanol, p-xylene, theram, theram-E, Thionex, Zmeb, Ferbam, and carbon
disulfide) were studied on a theoretical basis.0056 No field (at-sea)
confirmation of the study findings - that dilution due to eddy diffusion
and chemical degradation would reduce concentrations to below the median
tolerance limits --have been reported. On the contrary, pesticides
at sublethal dosages have been shown to reduce the size and strength of
mollusk shells, and to reduce growth rate and reproduction activity in
fish.0374
65
-------
The National Academy, of Sciences - National Research Council (NAS-NRC)
Committee of Oceanography, on the basis that the understanding of most of
the physical and biological processes in the ocean was too poor "to permit
precise predictions of the results of the introduction of a given quantity
of radioactive materials at a particular location in the sea," proposed
attacks upon several basic problem areas. These were all oriented towards
the potential hazards associated with deep sea disposal of radioactive
wastes. The most critical of these is the possibility of return of the
radioactivity to humans. Second in criticality was marine organism damage
due to exposure to radioactive waste. The two avenues cited for occur-
rence of such damage are (1) transport of the radioactive wastes from the'
disposal sites to the coastal zone, and (2) uptake of the radioactive
^
wastes by one or more of Ithe trophic levels in the marine biota, with pos*-
sible return to man via commercially important fish and shellfish.
The NAS-NRC studies produced reports2612'2613'2614 which covered the
key factors to be considered in disposal of low level radioactive wastes
at sea—both containerized., and liquid wastes from vessels and outfalls—-
and the disposal sites selections. Relatively little of the further re-
search recommended in the NAS-NRC reports to fill in the wide gaps in
factual data has been carried out. As of 19690056 only 'three off-shore
sites employed for disposal of low-leve.l containerized radioactive wastes'
had been resurveyed for the Atomic Energy Commission.0056
(1) The site near the Farallon Islands, off San Francisco.
(2) The Santa Cruz basin site, west-of Los Angeles (70 miles)
(3) The site 130 miles east-southeast of Cape May, New Jersey.
The first two sites, based.on beta-gamma counting of sediment samples, had
no apparent radioactive waste leakage. There were some indications in 1961,
based on similar counts, of possible leakage from the containers at the site
off Cape May. There are no reports of further investigations. As noted
earlier, low-level radioactivity liquids discharged from vessels and nuclear
facilities, if as per federal regulations and international standards, have
66
-------
not been recommended for termination; the ocean dumping of other radio-
active wastes was.
The President's Council on Environmental Quality, in the report on
ocean-dumping cited earlier, recommended termination of the disposal
of chemical warfare materiel and explosive munitions by dumping at sea.
As support for this recommendation, a Department of Defense calculation
was cited which indicated that the 1,000 tons of explosives detonated in
Deep Water Dump in the Pacific off Washington on September 4, 1970 was
capable of generating a shock wave that would "kill most marine animals
within 1 mile of the explosion and will probably kill those fish with swim
bladders out to 4 miles from the explosion." It should be noted that,
of 15 explosive ordnance laden bulks scuttled, 12 detonated during
scuttling.0471
President Nixon, in response to the above recommendation and the others
cited earlier, stated on October 7, 1970 that he would recommend legislation
to stop ocean dumping. The Secretary of the Navy immediately placed a
moratorium on Deep Water Disposal (DWD) operations. Subsequently, the
Chief of Naval Operations directed that an investigative program for con-
ventional explosives, be instituted to prepare a comprehensive environmental
condition report on representative past explosive ordnance DWD Sites;
develop criteria for selection of future DWD sites; and determine the
monitoring required at future DWD sites. This program was started in
the late spring of 1971. The representative sites selected were: an area
off Cape Flattery in the Pacific, where five ships were sunk and exploded
in 8,400 ft of water and an area 175 miles southeast of Charleston where
one ship was sunk and did not explode, in 6,300 ft of water. The pro-
gram will be completed early in 1972. Results to date show no evidence of
cratering of the sea floor in the Pacific. "A substantial number of or-
ganisms typical to the general region are apparently residing within the
debris area."0471
-------
There has been some fear that the ocean disposal of chemical warfare
munitions by techniques similar to those used in CHASE involved the
possibility that the explosive portions of the munitions would detonate
after sinking, and release the chemical warfare agent. In this
context, the chemical warfare material encased in concrete vaults that
were disposed of in 7,000 ft of water by scuttling the laden bulks off.
New Jersey in 1967 and 1968 did not explode and rupture the vaults.
It was also stated that sea water, because of its alkalinity, will both
i i 0353l
hydrolyze and dilute any chemical warfare aqent that is released.
3. OPERATING DESIGN
Deep sea disposal bulk transport systems vary from modern, specialized
tank barges to obsolete hulks.0482 The majority of bulk liquid and
slurry hazardous wastes dumped at sea are transported in specially designed
tank barges, from 1000 to 5000 short tons in capacity. The tank barges
are of double-skinned bottom construction, and must be certified for ocean
waters by the U.S. Coast Guard. The barge cargo is under U.S. Coast Guard
regulations covering the bulk shipment of chemicals from the U.S.
Industrial waste-laden barges are transported to the^industrial waste
disposal areas designated in Figures 1, 2, and 3 for the Pacific, Atlantic,
and Gulf of Mexico coasts, at off-shore distances that depend upon the type
of waste and the regulatory procedures. Typical distances are, for acid
wastes, 15 miles from New York City; for toxic chemical wastes, 125 miles
into the Atlantic; for Gulf of Mexico operations, 125 miles from the coast
(at the 2,400 ft depth line). In the disposal area, typical barge speeds
from 3 to 6 knots are used; typical discharge is at 6 to 15 ft submergence,
at rates that vary between 4 and 20 tons per minute. A characteristic
prediction rate for chlorinated hydrocarbon concentration in the disposal
area is C = PumP™9 rate where C is concentration in parts per million
U.Ubot
(p.p.m.); pumping rate is in grams per centimeter and t is time in minutes
1783
after pumping.
-------
LEGEND
E EXPLOSIVES AND TOXIC CHEMICAL AMMUNITION
EXPLOSIVES AND TOXIC CHEMICAL AMMUNITION,
INACTIVE SITE
I INDUSTRIAL WASTE
R RADIOACTIVE WASTE
/
SANDIEGO-
Figure 1. Pacific Coast Disposal Areas0056
69
-------
LEGEND
E EXPLOSIVES AND TOXIC CHEMICAL AMMUNITION / ME
(E) EXPLOSIVES AND TOXIC CHEMICAL AMMUNITION,
INACTIVE SITE
I INDUSTRIAL WASTE
R RADIOACTIVE WASTE \VT'.
BOSTON.
N.Y.W
NEW YORK
PHILADELPHIA
BALTIMORE
Figure 2. Atlantic Coast Disposal Areas
70
.0056
-------
LEGEND
E EXPLOSIVES AND TOXIC CHEMICAL AMMUNITION
© EXPLOSIVES AND TOXIC CHEMICAL AMMUNITION,
INACTIVE SITE
I INDUSTRIAL WASTE
R RADIOACTIVE WASTE
ALA.
TEXAS
HOUSTON
ST. PETERSBURG
Figure 3. Gulf of Mexico Disposal Areas
0056
-------
The last practice employed in deep water disposal of obsolete explosive
and chemical warfare ordnance was that of the U.S. Navy CHASE (Cut Holes And
Sink 'Em) disposal program. The Navy, which handled deep water dumping of
munitions for all of the services, obtained merchant hulks for this purpose
from the U.S. Maritime Administration Reserve of surplus World War II merchant-
men. The ship was stripped of anything readily removable or loose. The fuel
tanks were cleaned to eliminate oil contamination and scuttling valves were
installed to allow water to eoter the ship. To permit the water to spread
evenly, soft patches were installed in the bulkheads between the holds. The
material for dumping was made negatively buoyant (bulk density higher than
sea water), to prevent it from floating to the surface, and loaded into the
bulk at one of two Naval Depots (Earle, New Jersey, or the former Naval
Ammunition Deppt at Bangor, Washington.
After the operation had been cleared with all responsible authorities,
the munition-laden hulk was towed to the selected dumping site under naval
escort, and scuttled. The selected sites have been at least 10 miles from
any shore, and in waters at least 3,000 ft deep. The majority of sites
employed before the moratorium on DWD were at sea depths in excess of 6,000
ft.0056 Of the 15 explosive Jaden hulks scuttled, four were detonated
deliberately (two at 1,000 ft depth, two at 4,000 ft depth)0374 and eight
detonated unintentionally. '
Low level radioactive wastes have in the past been encased in concrete
contained in 55-gal.-steel drums, which were required by AEC regulations to
be of a minimum gross weight of 550 Ib, to ensure sinking. Another packaging
technique has been to encase 55-gal.-drums, loaded with liquid low level
radioactive wastes, in a concrete block. The concrete packages wastes were
then taken to designated disposal sites, and dropped overboard. Most'of
the wastes disposed of in the Pacific were dumped at two sites. Disposal
in the Atlantic, with one exception, has been at depths greater than 6,000
ft. The exception (in the area of Massachusetts Bay, about 12 to 15 miles
offshore) was in 300 ft of water.0374
-------
Low level radioactive liquid wastes, resulting from the operation of
U.S. Navy nuclear submarines, are discharged at sea in accordance with
regulations on depth and rate of pumping. As of 1970, one commercial
organization, two government agencies, and one university were the only
entities authorized to dispose of radioactive wastes in the ocean.
Containerized toxic industrial wastes, as noted earlier, are dumped at
sea after transport as deck cargo on either merchant vessels or contract
disposal vessels. The individual containers are either ruptured at the
surface, or weighted for sinking. These is no single "operating design"
or operating practice that covers the wide variety of materials thus
disposed of.
4. ECONOMICS
The average cost for ocean disposal of all types of wastes in 1968
(Table 3) was slightly over $0.60 per ton.0056 The 1968 average cost for
disposal of bulk industrial wastes was $1.70 per ton. Average ocean dis-
posal costs for explosives in 1968 were $15 per ton. Since the quantity of
containerized low-leve-1 radioactive wastes dumped at sea in 1968 was zero,
and only 4.2 tons per year were dumped in 1969 and 1970, costs were not
calculated for this category. The ocean disposal costs cited for industrial
wastes and miscellaneous wastes represent transportation and dumping costs
only, and do not include other costs incurred for treatment, storage and
loading of the wastes. The costs reported for explosives include hull
preparation, towing and loading costs, and are given as dollars per ton of
total waste cargo.
The costs for ocean dumping of industrial wastes are significantly
lower than those of other disposal techniques currently employed. The costs
of minimum environmental impact disposal techniques for the bulk industrial
wastes are very much higher than the costs of ocean dumping. As an example,
material (lime) costs for neutralization of the waste acid from Ti02 pigment
manufacture are estimated at roughly $1.00 per ton; operating costs and
73
-------
TABLE 3.
1968 COSTS PER TON FOR MARINE DISPOSAL OF HAZARDOUS WASTES
IN THE UNITED STATES COASTAL WATERS0056
Type
of
Waste
Industrial Wastes
Bulk
Containerized
Explosives
Miscellaneous*
Total United States
Average Cost
$1.707 ton
$24/ton
$157 ton
$15/ton
Reported Range
$0.60-9. 507 ton
$5- 130/ ton
$15-90/ton
$5-600/ton
Pacific Coast
Average Cost
$1.007 ton
$53/ton
-
$157 ton
Reported Range
$0.60-9. 507 ton
$50- 1307 ton
-
$5-6007 ton
Atlantic Coast
Average Cost
$1 .80/ton
$7.73/ton
-
"
Reported Range
$n.60-7.007ton
$5-17/ton
-
"
Gulf Coast •
Average Cost
$2. 307 ton
$28/ton
-
"
Reported Range
$0.75-3. 507 ton
$10-407 ton
-
'
Note: Although Reference 0056 quotes costs as "on the basis of the weight of the volume of water In which the wastes were
contained", marine costs are generally quoted on the basis of the weight of the volume of water displaced. It .Is
believed that the costs cited 1n this table are so based.
Includes barreled chemicals and sludges
-------
equipment amortization would add at least an equal amount, and land burial
with its attendant costs would still be required for the solid calcium
sulfate-iron hydrate produced as a product of neutralization, after recovery
by lagooning or filtration.
In general, the predominant factors which have given rise to ocean
disposal of hazardous wastes have been economic - avoidance of capital out-
lay, and/or a cheaper operating cost than the costs of other techniques.
This economic incentive will be increased as federal and local regulations
increase the requirements for the use of minimum impact disposal techniques,
with their attendant higher costs. Few of the hazardous waste materials
currently disposed of by ocean dumping present an economically attractive
recycle or by-product recovery picture. Recycling and reprocessing of
"waste add" (generally, waste sul f uric acid) which constituted 58 percent
of the bulk industrial wastes dumped at sea, has been the. objective of
many economically fruitless steel and pigment company research and develop-
ment projects. In fact, the major reason for the changeover from sulfuric
add to hydrochloric acid as the preferred material for pickling of steel
was the virtual impossibility of economic recycle via regeneration of the
spent sul f uric add.
5. PROCESS APPLICATIONS
The 11st of hazardous waste materials dumped in the ocean is almost
endless. The broad classes of hazardous waste materials have been categorized
as follows:0056 Industrial wastes; obsolete, surplus, and nonserviceable
conventional explosive ordnance and chemical warfare material; radioactive
wastes; miscellaneous hazardous wastes. The major types of Industrial
waste dumped at sea which are considered hazardous are: Spent adds; refinery
wastes; pesticide wastes; and "chemical wastes." Other, lower hazard Industrial
waste types disposed of at sea are: Pulp and paper mill wastes; oil drilling
wastes; and waste oil. Conventional explosive ordnance and chemical warfare
material which has received deep water disposal Includes nonserviceable or
obsolete shells, mines, solid rocket fuels, propellents, small arms ammunition,
rockets, pyrotechnics, and mines and rockets containing HS, GB and VX lethal
75
-------
chemical warfare agents. ' The "miscellaneous waste" category covers, for the
most part, materials disposed of in small lots, without sanction by any
regulatory authority. Hazardous wastes covered under this catch-all heading
include pesticides' and complex chemical solutions.
There were 4.7 million tons of all types (hazardous and nonrhazardous,
bulk and containerized) of industrial waste dumped at sea in 1968 (Tabled).
Conventional and chemical-warfare munitions subjected to ocean disposal in
1968 totaled 15,200 tons. No containerized radioactive materials were
ocean dumped in 1968 (average for 1969-1970 was 4.2 tons per year). "Mis-
celaneous" wastes amounted in 1968 to an estimated 200 tons.
The hazardous industrial-wastes which consitiute by far the largest
class of hazardous waste'materials dumped at sea are waste products of
pigment processing, steel production, petroleum refining, petrochemicals
manufacture, insecticideAherbicide-fungicide.manufacture, chemical manu-
facture, and metal finishing-cleaning-plating processes, amongst many
others. Some of the specific hazardous1 industrial wastes dumped at s'ea:are:
Spent Acids
Sulfuric acid is used in large quantities by the steel mills to pickle
(remove surface rust and mill scale from) steel stock (rod, bar, sheet,
plate, and the like) prior to fabrication or other manufacturing'processes.
The acid ("pickle liq-uor") is usually removed from further process-use when
between one-half and two-thirds of the free acid has been converted to fer-
rous sulfate by reaction with the steel and iron oxides. The spent acid
sent to disposal contains up to 7 percent free H2S04 and up to 30 percent
FeS04. -.
In some steel plants, hydrochloric acid is used for all or part of the
picklinq, and the spent-acid wastes contain free hydrochloric acid and
ferrous chloride instead of, or in addition to, the sulfuric acid and ferrous
sulfate resulting from the use of sulfuric acid for pickling.
-------
TABLE 4.
SUMMARY OF QUANTITIES OF HAZARDOUS WASTES DISPOSED OF
IN UNITED STATES COAST WATERS - 19680056
Waste Type
Industrial Wastes
Bulk
Containerized
Munitions
Radioactive Wastes
Miscellaneous*
Total, All
"Hazardous" Wastes1"
Pacific Coast
Annual Tonnage
981,300
981 ,000
300
—
—
200
981 ,500
Atlantic Coast
Annual Tonnage
3,013,200
3,011,000
2,200
15,200
—
—
3,028,400
Gulf Coast
Annual Tonnage
696,000
690,000
6,000
--
—
—
696,000
Total
«
Annual Tonnage
4,690,500
4,682,000
8,500
15,200
—
200
4,705,900
*Rough Estimate
'Includes all categories of industrial wastes dumped at sea
-------
Sulfuric acid is also used in large quantities by titanium pigment
plants, which digest the ore (whose principle impurity is iron), with H2S04-
The process, wastes are in the form of a liquor which contains 7 to 9 percent
free H2Sp4> 8-to 10 percent FeS04, and-a mud-slurry with 15 to 20 percent
inert solids.
i
Spent acid.wastes dumpedjat sea comprise 58 percent of all industrial
wastes so disposed, of, or about 2,700,000, tons.0056
Refinery. Wastes
Petroleum processing operations produced about 12 percent (about-'560,000,
tons)0056 of the total industrial wastes dumped in the ocean in 1968. Re-
finery wastes include spent caustic soda solutions, sulfuric acid sludges,
dilute process water solutions, spent catalysts, waste petrochemicals, and
chemical cleaning wastes. The solid wastes (spent catalysts and sludges)
are frequently slu.rried with the .liquid, wastes prior to shipment to sea for
disposal. Varying amounts of-sulfides, phenolates, naptheriates, cyanides,
heavy metals, mercaptides and.-chlorinated or brominated hydrocarbons are
among the hazardous minor contaminants of the -refinery wastes.
Chemical Wastes
A wide variety of waste chemicals dumped at sea is produced, by chemical
manufacturing, chemical laboratory, metal cleaningr.f-i-n.ishing-electrbp'?.attng,
.and other industrial operations. These include mercury and arsenic compounds",
chlorinated hydrocarbons, alkalies, anilines, cyanides and other highly toxic
substances. There is no valid estimate of the .tonnage of these wastes for
1968.
Pesticide Wastes
Pesticide (insecticide, herbicide, and fungicide) manufacturing oper-
ations produced about 7 percent (290,000 tons) of the total industrial
78
-------
wastes disposed of at sea in 1968. Of this amount, about 170,000 tons
were barged down the Mississippi from the Memphis/upriver area and dumped
100 miles offshore from Beaumont, Texas into 1,200 ft of water.
6. RECOMMENDATIONS
It is believed that the recommendations of the President's Council on
Environmental Quality should be reconsidered in the following specific areas
after the prerequisite research has been performed:
(1) Termination of the ocean dumping of explosive munitions
(2) Phase-out cf ocean dumping of spent sulfuric and/or hydrochloric
acid wastes from steel pickling, and from titanium pigment
manufacture
On the basis of data presented by Captain Reed? the dumping in the
ocean of conventional explosive munition at selected, pre-designated charted
sites where depths are in excess of 6,000 ft presents no apparent hazard if
the munitions are not detonated, and a minimal impact where the munitions
detonate at the lower depths. Similarly, the evidence presented by Smith
and Brown0056 if verified by additional laboratory and field test findings
in the Atlantic, indicates a minimal acceptable impact on the ecosphere if
proper current practice is followed for acid unloading at prescribed depths
and rates while underway at usual tow speeds in designated deep sea disposal
areas. Further research with these specific wastes and with other selected
materials is necessary to determine the necessary additional information on
the effects of the selected materials on the ocean environment. Additionally,
the effects of the ocean environment on the wastes to be dumped must also
be determined to ensure that toxic materials are not formed as the result
of reaction and interaction. Finally, research is necessary to develop
waste forms stabilized to ensure compatibility with the ocean environment
on both short and long term bases.
-------
7. REFERENCES
0055. Gunnerson, C. G., D. D. Smith, and R. P. Brown. An apprals.al of
marine disposal of solid wastes off the west coast: a preliminary
review and results of a survey.. 15th Annual Meeting, Institute of
Environmental Sciences, Anaheim, California, Apr. 23, 1969.
0056. Smith, D. D., and R. P. Brown. Ocean disposal of barge-delivered
liquid and solid wastes from U. S. coastal cities. (Dlllingham
Corporation, La Jol.la, Cal.ifornia). Contract No. PH 86-68-203,
U. S. Environmental, Protection Agency, Solid Waste Management
Office, 1971.
0057. Smith D. D., and R. P: Brown. Deep sea disposal of liquid and solid
wastes. Industrial. Water Engineering, Environmental-Protection
Agency, Sept. 1970.
0353. Ocean disposal of unserviceable chemical munitions. Hearings,
Subcommittee on Oceanography, Committee on Merchant Marine and
Fisheries, House of| Representatives, 91st Congress, Aug. 1970.
Serial No. 91-31.
0374. Ocean dumping; a national policy. Council on Environmental Quality,
Report to the President, Oct. 1970. 45 p.
0471. Reed, Jr., W. F., Captain, U.S.N. Assessment of the environmental
effects of past deep water dumping operations. Thirteenth Annual
Explosives Safety Seminar, Minutes, Armed Forces Explosives Safety
Board, San Diego, California, Sept. 1971. 257 p.
0582. Witt, Jr., P. A. Disposal of solid wastes. Chemical Engineering.
78(22):62-78, Oct. 4, 1971.
•• »
0857. Dumping of waste material. Hearings, Subcommittee On Fisheries and
Wildlife Conservation, Committee on Merchant Marine and Fisheries,
House of Representatives, 91st Congress, July 27, 28, Sept. 30, 1970.
Serial No. 91-39.
1783. Hood, D. W., B. Stevenson, and L. M. Jeffrey. Deep sea disposal of
industrial wastes. Industrial and Engineering Chemistry, 50(6);
.885-888, June 1958;
2612. National Research Council Committee on Oceanography. Radioactive
waste disposal Into Atlantic and Gulf coastal waters; a report
from a working group of the Committee on Oceanography of the
National Academy of Sciences - National Research Council. National
Research Council Publication No. 655, Washington, National Academy
of Sciences, 1959.
-------
REFERENCES (CONTINUED)
2613. National Academy of Sciences Committee on Effects of Atomic Radiation
on Oceanography and Fisheries. Considerations of the disposal of
radioactive wastes from nuclear-powered ships into the marine
environment. National Research Council Publication 568, Washington,
National Academy of Sciences-National Research Council, 1959. 52 p.
2614. National Research Council Committee on Oceanography. Disposal of
low-level radioactive waste into Pacific coastal waters. National
Research Council Publication 985, Washington, National Academy
of Sciences - National Research Council, 1962. 87 p.
81
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INCINERATION
1. INTRODUCTION
The purpose of this process evaluation is to discuss the various types
of incineration processes and their applicability to the 'disposal of waste
materials. The report format will be to initially discuss the variables
effecting waste combustion such as waste combustibility and combustion
temperature, time, and turbulence. A discussion of the variables affecting
proper incineration selection such as waste toxicity, disposal rates,
corrosiveness, secondary abatement requirements, steam plume generation
and waste form will then follow. The remainder of the report will present
the particulars on the individual processing units.
/
j
Incineration is a controlled process that uses combustion to convert
a waste to a less bulky, less toxic, or less noxious material. The
principal products of incineration from a volume standpoint are carbon
dioxide, water and ash while the products of primary concern,due to their
environmental effects are compounds containing sulfur, nitrogen and halogens.
When the combustion products from an incineration process contain undesirable
compounds, a secondary treatment such as afterburning, scrubbing or filtration
is required to lower concentrations to acceptable levels prior to atmospheric
release. The solid and liquid effluents from the secondary treatment processes
will occasionally require treatment prior to ultimate disposal.
Variables Effecting Proper Waste Combustion
Incinerators are generally classified by the form of waste that
they burn—gas, liquid or solid. However, most incinerator systems,
regardless of waste type, contain four basic components; namely, a waste
storage facility, a burner and combustion chamber, an effluent purification
device when warranted, and a vent or stack. It is the oxidation which
occurs in the combustion chamber of the system which is of primary importance
for proper hazardous waste disposal. It is here that the feed waste is
converted to a less hazardous compound and that secondary pollutants which
83 Preceding page blank
-------
must be removed by further treatment are formed. The variables which have
the greatest effect on the completion of the oxidation of the wastes are
waste combustibility, dwell time in the combustor, flame temperature, and
the turbulence present in the reaction zone of the incinerator.
Waste Combustibility. Combustibility is a measure of the ease at
which a material can be oxidize'd in a combustion environment. A materials
combustibility is'characterized by its upper and lower flammability limits,
its flash point, ignition temperature and autoignition temperature. In
general materials with a low fl-ammability limit, low flash point, and low
ignition and autoignition temperatures may be combusted in a less severe
oxidation environment (lower temperature and less excess oxygen) than those
-materials with a high flammability limit, high flash point and high igni-
tion and autoignition temperatures. The flash point and upper and lower
flammability limits of some of the pure compounds found on the hazardous
waste listing are presented (Table I).1456 The autoignition temperature
of some of the common organic compounds are also presented (Table 2).
Combustion Temperature. Of the "three T's" of good combustion, time,
temperature and turbulence, only the temperature may be readily controlled
after the incinerator unit is constructed. This can be done by varying
the air/fuel ratio. If solid carbonaceous waste is to be burned without
smoke, a minimum temperature of 1,400 F must be maintained in the combustion
chamber. Upper temperature limits in the incinerator are dictated by the
refractory materials available. Whenever a temperature of 2,400 F is
exceeded, special refractories are required. A design range of 1,800 to
2,000 F is usually desirable, unless thermodynamic equilibrium consider-
ations dictate "some other temperature requirement. The rates of most
combustion reactions increase rapidly with increases in temperature, while
a few peak at relatively low values. The latter are rare but must not be
0304
overlooked when unusual fuels are burned.
84
-------
TABLE 1
COMBUSTIBILITY CHARACTERISTICS OF PURE GASES
AND VAPORS IN AIR1456
•i
Gas or Vapor
Acetal dehyde
Acetone
Acetylene
Allyl alcohol
Ammonia
Amyl acetate
Amylene
Benzene (benzol )
Benzyl chloride
Butane
Butyl acetate
Butyl alcohol
' Butyl cellosolve
Carbon disulfide
Carbon monoxide
Chlorobenzene
Cottonseed oil
Cresol m or p
Crotonal dehyde
Cyclohexane
Cyclohexanone
Cycl opropane
Cymene
Di chlorobenzene
Dichloroethylene (1,2)
Diethyl selenide
Dimethyl formamide
Dioxane
Ethane
Ether (diethyl)
Ethyl acetate
Ethyl alcohol
Ethyl bromide
Ethyl cellosolve
Ethyl chloride
Ethyl ether
Ethyl lactate
Ethyl ene
Ethylene di chloride
Ethyl formate
Ethyl nitrite
Ethylene oxide
Furfural
Lower
Limit
Percent
by
Volume
4.0
2.5
2.5
2.5
15.5
1.0
1.6
1.3
1.1
1.8
1.4
1.7
-
1.2
12.5
1.3
-
1.1
2.1
1.3
1.1
2.4
0.7
2.2
9.7 •
2.5
2.2
2.0
3.1
1.8
2.2
3.3
6.7
2.6 -
4.0
1.9
1.5
2.7
6.2
2.7
3.0
3.0
2.1
Upper
Limit
Percent
by
Vol ume
57
12.8
BO
-
26.6
7.5
7.7
6.8
-
8.4
15.0
-
-
50
74.2
7.1
-
-
15.5
8.4
-
10.5
-
9.2
12.8
-
-
22.2
12.5
36.5
11.5
19.0
11.3
15.7
14.8
48
-
28.6
15.9
16.5
50
80
-
Closed
Cup
Flash
Point
Fahrenheit
- 17
0
-
70
_
77
-
12
140
_
84
-
141
- 22
_
90
486
202
55
1
111
-
117
151
57
57
136
54
_
- 49
28
54
-
104
- 58
- 49
115
-
56
- 4
- 31
-
140
85
-------
TABLE 1
COMBUSTIBILITY CHARACTERISTICS OF PURE GASES
AND VAPORS IN AIR1456 - CONTINUED
Gas or Vapor
Gasoline (variable)
Heptane
Hexane
Hydrogen cyanide
Hydrogen
Hydrogen sulfide
Illuminating gas (coal gas)
Isobutyl alcohol
Isopentane
Isopropyl acetate
Isopropyl alcohol
Kerosene •
Linseed oil
Methane
Methyl acetate
Methyl alcohol
Methyl bromide
Methyl butyl ketone
Methyl chloride
Methyl cyclohexane
Methyl ether
Methyl ethyl ether
Methyl ethyl ketone
Methyl formate
Methyl propyl ketone
Mineral spirits #10
Naphthalene
Nitrobenzene
Nitroe thane
Nitrome thane
Nonane .
Octane -
Paraldehyde
Paraffin oil
Pentane
Propane
Propyl acetate
Propyl alcohol
Propylene
Propyl ene di chloride
Propylene oxide
Pyridine:
Rosin oil
Lower
Limit
Percent
by
Volume
1.4 - 1.5
1.0
1.2
5.6
4.0
4.3
5.3
1.7
1.3
1.8
2.0
0.7
-
5.0
3.1
6.7
13.5
1.2
8.2
1.1
3.4
2.0
1.8
5.0
1.5
0.8
0.9
1.8
4.0
7.3
0.83
0.95
1.3
-
1.4
2.1
1.8
2.1
2.0
3.4
2.0
1.8
-
Upper
Limit
Percent
by
Vol ume
7.4 - 7.6
6.0
6.9
40.0
74.2
45.5
33.0
-
-
7.8
-
5
-
15.0
15.5
36.5
14.5
8.0
18.7
-
18
10.1
9.5
22.7
8.2
-
-
-
-
-
2.9
3.2
-
-
7.8
10.1
8.0
13.5
11.1
14.5
22.0
12.4
-
Closed
Cup
Flash
Point
Fahrenheit
- 50
25
- 15
-
-
-
-
82
-
43
53
100
432
-
14
52
-
-
-
25
-
- 35
30
- 2
-
104
176
190
87
95
88
•56
-
444
-
-
58
59
- '•
60
—
74
266
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TABLE 1
COMBUSTIBILITY CHARACTERISTICS OF PURE GASES
AND VAPORS IN AIR1456 - CONTINUED
Gas or Vapor
Toluene (toluol)
Turpentine
Vinyl ether
Vinyl chloride
Water gas (variable)
Xylene (xylol)
Lower
Limit
Percent
by
Volume
1.3
0.8
1.7
4.0
6.0
1.0
Upper
Limit
Percent
by
Volume
7.0
27.0
21.7
70
6.0
Closed
Cup
Flash
Point
Fahrenheit
40
95
63
-------
There are four basic methods of controlling the combustion temperature:
(1) Excess air control. The adiabatic flame temperature is a function
of both the type of fuel and the amount of air (oxygen) used. For
example, the adiabatic combustion temperatures* of a cellulose waste
that occur with variations in the amount of excess air very dramatically
(Figure 1), clearly indicating the importance of maintaining the
proper air/fuel ratio when the maintenance of a specific temperature
is required. Control is obtained through automatically controlled
or strenuously supervised operation. The designer can provide
limiting orifices, nozzles, or pumps to prevent overfirinq during
continuous feeding of liquids and gases. For liquid fuels the
problem is aggravated as the volatility of the fuel increases. If
an incinerator is fed with discrete amounts at intervals, the hourly
sum of these amounts must not exceed the rated capacity, and the
intervals between feeding must be regulated. The greater the
volatility of the waste, the smaller these discrete amounts must
be and the more frequent the feed intervals. To illustrate, one
may toss a teaspoon of gasoline every minute on the backyard grill
without creating havoc, but a pint of gasoline tossed at once can
have disastrous effects. All too often, this simple fact is over-
looked in incinerator operation.0304
(2) Radiant heat transfer. Most combustion processes exist for the
purpose of heat transfer,however, this is not usually the case
for incinerators. Some large municipal waste incinerators use
heat transfer surface as a means to control temperature and this
design practice is growing although it is seldom economically
feasible for industrial incinerators. It should be considred,
however, when economics might make it attractive. Radiation
to the sky is feasible, and several designs are capable of
doing this, wiiere either heat transfer surface or radiation
to the sky is used, surface area relationships liable 3) can
be used to estimate the combustion temperature. U4
(3) Two-stage combustion. When the combustion is divided into two
distinct steps and the first stage is supplied with a deficiency
of air, the first stage can act as a gasifier for certain fuels
while burning incompletely at reduced temperatures. A second
stage is necessary to burn the combustible products produced
in the first stage, and its temperature must be limited by
either the first method discussed (excess air control) or by
heat transfer. Incinerators of this type must be carefully
engineered to assure proper ignition and complete burning in
the second stage. Additionally, feed rates must be carefully
In practice, the actual temperatures will be less because of
thermal conduction losses through the furnace walls, thermal
radiation to cold surfaces and possible incomplete combustion
of the waste.
89
-------
3200
3000
2800
2600
2400
2200^0'
CELLULOSE
ADIABATIC TEMPERATURE VARIATION WITH
AIR SUPPLY
CURVES ARE THEORETICAL FOR CELLULOSE
AND WILL BE LOWERED BY HEAT LOSSES
IN PRACTICE
2000
1800
1600
1400
1200
\
x
u
10001
-40
+40 +80 +120 +160
EXCESS AIR %
+200 +240 +280
Figure 1. Adiabatic Temperature o
Fuel Versus Excess Air.
Cellulose
90
-------
TABLE 3
FURNACE TEMPERATURE VERSUS FIRING RATE0304
* r.--c K-ifiT furnace Ttmperottire ( AQT
Fraction Biu/l.r
Cold (f/'ft KI //
0 Any
10,000
10 4U.OOO
80,000
120.0J3
10,000
20 40,000
so.rioo
120,000
10,000
>0 40,OOCi
80,000
120,000
10,000
40 40,0'JU
80,000
123,000
10,000
50 40,000
80,000
120,000
10,000
60 40,000
sn.noo
i:>o,fii>n
1 0,000
8.'l 10.0-')')
&0.f/ )
I20.!WI
10 fill '
100 'It)/ '•>
8'. !."•..)
0%
LxctfS Air
?6V7
:o2i
2680
299?
3137
1709
2349
2680
2866
J518
2156
?-!87
?6SO
1422
20? 1
2349
2544
1336
1918
2243
2437
12(,S
1836
2156
23-19
1165
1709
20?. 1
2212
io;-y
1613
1918
2106
50%
Excess Air
279D
1839
2.v"3
2482
2563
1587
2083
2303
2413
1442
19-42
?178
2303
1342
1839
20S3
2216
1266
175S
200-1
2144
1206
1C9I
194?
208',
1114
1587
1SV)
198-J-
KU5
1507
175S
1904
700%
Excess Air
2230
1668
1984
2083
2124
1470
1844
1984
2047
1350
1745
1907
1984
1265
1668
1844
1930
1199
1606
1791
1884
1146
1554
1745
1844
1064
1470
166S
177S
1001
1-104
1606
1717
*- Fraction Cold is the ratio of the surface of the furnace enclosure
that receives heat divided by the total furnace surface.
f- Firing Rate is the ratio of the heat release in Btu/hr divided by the
sum of all enclosing surfaces.
+- Table is theoretical for conditions given and is computed with No. 6
fuel oil.
91
-------
controlled since a decrease in the waste feed rate without a
corresponding decrease in the air feed rate would result in
the first stage progressively moving toward complete.combustion
with progressively higher comDustion temperatures.
(4) Direct heat transfer. When heat-absorbing materials or other
fuels are added to the waste fuel the temperature of combustion
can be controlled. The most common method of achieving lower
temperatures is to add water to the fuel since each pound of
water added absorbs approximately 1000 Btu for evaporation and
1/2 Btu for every degree F of temperature rise as sensible heat
content. The water may be added with the fuel or sprayed into
the combustion zone if carefully controlled to avoid quenching
the fire or damaging the refractory. Temperature "layn^fiJ'11-
creased by burning other fuels with the waste stream.
Recommended minimum temperature requirements for complete combustion
of those candidate waste stre'am constituents applicable to incineration and
requiring National Disposal Site treatment are presented in the profile
reports discussing the individual constituents.
Combustion Zone Turbulen'ce. The degree of turbulence (intimate mixing)
of the air for oxidation with the waste fuel will affect the -incinerator
performance significantly. In general, either mechanical or aerodynamic
means are utilized to achieve1 the intimate scrubbing and mixing of the air
and fuel. The completeness of combustion and the time required for complete
combustion are significantly affected by the amount and the effectiveness of
the flame turbulence. There is no accepted parameter that will qua'riti-ta-
tively define an amount of turbulence, therefore it is judged by the com-
bustion results that are produced.
Turbulence may be created in the combustion zone mechanically and
aerodynamically. Turbulence c'an be induced mechanically through the use
of fixed and moving grates, rotary kilns, mechanical pokers and hand pokers.
There are two design factors which must be considered before applying
mechanical turbulence producers. First, they depend principally upon natural
factors to clear away gaseous combustion products and bring in fresh oxygen.
The primary function of mechanical turbulence producers is the removal of
noncombustible coverings (ash) to expose unburned material. Second, if
mechanical devices are metal, they must be protected from elevated combustion
temperatures. This protective cooling can usually be achieved by circulating
* 0304
either air or water through the device.
92
-------
Aerodynamic turbulence can be defined as; the creation of turbulence
by gases in motion. High velocity jets of forced air can create a degree
of turbulence that approaches perfection. The turbulence may be produced
with convergent nozzles using air or steam, or it may be produced by air
registers. Air registers are vane arrangements, usually circular, that
surround a fuel injection nozzle. They serve as multiple nozzles both to
increase the incoming air velocity and to create a forced vortex around the
fuel nozzle. It should be pointed out that for fixed nozzle and vanes, and
sometimes for variable ones, the degree of turbulence is almost always at
its maximum with the maximum air flow. For this reason best results are
often obtained if the incinerator is fired at its maximum rating. Shorter
firing periods at maximum rate may produce better results than continued
operation at low firing rates.
Another form of aerodynamic turbulence is achieved in the fluidized
bed. Air is forced vertically through a bed of solids (usually cylindrical)
at a rate that expands the bed without excessive solids carry-over. If the
bed container is lined with refractory and the bed material is: (1) uniform
and (2) does not fuse at the operating temperatures, excellent turbulence
is created. Uniformity can be helped by utilizing a permanent bed of sand.
By injecting new material at the rate of consumption, the bed is held level
and the air-flow resistance held constant. Since solid fuels without
appreciable ash (coke) can be added, the fluidized bed has found some
application with waste solids that require auxiliary fuel.0304
Residence Time in the Combustion Zone. The third major requirement
for good combustion is time. Sufficient time must be provided to the com-
bustion process to allow slow-burning particles or droplets to completely
burn before they are chilled by contact with cold surfaces or the atmosphere.
The amount of time required depends on the temperature-, fuel size and degree
of turbulence achieved. Although it is customary to specify certain furnace
volumes for heat releases in an attempt to obtain proper combustion times,
this method is now generally recognized as inadequate. In the absence of
specific data, combustion chambers with heat releases of 20,000 to 60,000
Btu/cu ft-hr are common. These values are very conservative for high per-
93
-------
fonnance burners, and the use of small compact incinerators means lower
investment and lower maintenance. The evaluation of the factor of time can
be made only by tests of individual burners and furnaces. Important infor-
mation on this subject can be obtained directly from burner manufacturers.
When slow-burning items are present, such as carbon particles or carbon
monoxide, additional chambers (secondary combustion chambers) may be needed
0304
to allow time for complete combustion.
Recommended minimum residence time requirements for complete combustion
of those candidate waste stream constituents applicable to incineration and
requiring National Disposal Site treatment are presented in the profile
reports discussing those individual constituents.
Incinerator System Selection
In order to determine the proper type of incinerator system (i.e.,
storage facility, incinerator, and effluent purification equipment) for
use in a particular waste disposal situation, certain basic information
about the waste material must? be known (Table 4.).
waste Toxicity. The toxicity of the waste material and its combustion
products dictates the safety procedures, safety equipment and monitoring
equipment required for personnel safety. For instance, an extremely toxic
material might require remote operation of all processing units and the
wearing of protective clothing, masks and self-contained breathing appara-
tuses by all operators in the vicinity of the incineration unit. Equipment
to monitor combustion temperature and/or effluent compound concentration
might be utilized in series with feed regulating equipment to ensure total
combustion of the toxic material. The overall ability of the disposal
system (storage facilities, transport equipment, incinerator, secondary
abatement equipment and.stack) to maintain low toxic contaminant concen-
trations at ground level could be determined through periodic or constant
monitoring in and around the disposal facility.
94
-------
TABLE 4
BASIC DATA CONSIDERATIONS WHEN CHOOSING A WASTE DISPOSAL SYSTEM
,0304
Typer (s) of waste
Liquid, solid, gas, or mixtures.
Utlimate analysis
Metals
Halogens
Heating Value
Solids
Liquids
Gases
Special characteristics
Disposal rates
Carbon, hydrogen, oxygen and nitrogen,
water, sulfur, and ash on an "as-
recc'ved" basis.
Calcium, sodium, copper, vanadium,
etc.
Bromides, chlorides, fluorides.
BTU/lb on an "as-received" basis.
Size, form and quantity to be
received.
Viscosity as a function of
temperature, specific gravity
and impurities.
Density and impurities-
Toxicity and corrosiveness,
other unusual features.
Peak, average,minimum (present
and future).
95
-------
Disposal Rate and Waste Corrosiveness. Regardless of the type of
waste to be incinerated, the disposal rate determines the size and number
of incinerators (as well as storage equipment) needed to combust a given
waste stream. The waste stream's corrosiveness determines the materials of
construction required in both,the incineration unit and materials handling
equipment. Incineration systems may be fabricated from a wide variety of
construction materials. The selection of construction materials depends
upon several factors: (1) corrosion, (2) strength, and (3) temperature.
Most incinerators are constructed of carbon steel material and are lined
with appropriate alumina refractory to withstand the temperatures of the
incineration process. Some catalytic units, however, as well as some thermal,
incinerators are fabricated without refractory, using only high-temperature
stainless steel. The advantage of this approach is the elimination of the
refractory, which will eventually need refurbishing or replacement. More
costly materials such as Inconel, Incoloy, or Hastelloy are normally util-
ized only when the waste is corrosive to other materials.
Refractories used in incineration systems are generally of the alumina
type. Standard or super duty firebrick backed up by insulting brick is
suitable in most cases. Castable refractories are also widely used. In
short, the refractories, which are used for most incineration applications
are equivalent to those which would be used for high-temperature furnaces.
Secondary Abatement Requirements. Many wastes which lend themselves
to incineration cannot be incinerated without some secondary form of treat-
ment, due to the production of compounds which might be toxic in nature
therefore cannot be released to the atmosphere. Normally these wastes can
be divided into three categories:
(1) waste which contains inorganic salts;
(2) waste which contains halogen compounds;
(3) waste which contains sulfur compounds.
96
-------
Those which contain inorganic salts will produce the oxide of the
metal ion of that salt upon combustion. The commonest inorganic metal
ion is sodium, although potassium, or for that matter any other metal
ion, may be found in the waste. The oxide which is formed in the combustion
reaction usually will be in a finely divided form and will require sub-
sequent removal by either mechanical methods or wet scrubbing. This type
of product usually requires a high-energy scrubber of the venturi type.
The halogen ions most commonly found in wastes are generally chlorine
and fluorine, which are often part of halogenated hydrocarbons. Complete
combution of the organic portion of the waste may result in the production
of chlorine or fluorine in the products of combustion. These are relatively
insoluble in water and therefore cannot be removed by wet scrubbing as long
as they are in this form. This type of waste should first be analyzed to
determine the amount of hydrogen present, since the hydrogen will react
with the halogen forming the halogen acid, if there is not sufficient
hydrogen in the waste material to accomplish complete conversion of the
halogen to the halogen acid, the conversion must be accomplished by
injection of additional hydrogen in the form of natural gas or other
combustible. Once the halogen has been converted to the acid gas, it
may be satisfactorily removed in a wet scrubber. Here the low-energy
or packed tower type of scrubber is satisfactory. For example, if
trichloroethylene is a major component in a waste effluent, it can be
incinerated in accordance with the following reaction:
CHC1CC12
While the hydrogen chloride which is formed in this reaction can be
removed by scrubbing with water, the chlorine, which is relatively in-
soluble, will pass through the water and into the atmosphere. By the
addition of natural gas or another hydrocarbon fuel, all the chlorine
can be converted to hydrogen chloride as follows:
CHC1CC12 + 7/2 02 + CH4—*3 C02 + 3HC1 + H20
97
-------
The hydrogen chloride formed in this reaction can be removed in a
wet scrubber. In this particular case, natural gas or other auxiliary
fuel would be required for combustion because of the low calorific value
npQK
of the trichloroethylene.
Sulfur compounds are often found in wastes either as part of a
sulfonated organic molecule or in the form of sulfates or sulfides.
Complete combustion of these wastes with air results in S02 formation.
Complete removal of S02 can be handled by caustic scrubbing or a number
of more complicated processes designed ultimately to recover sulfur.
One pollutant, NO, is common to all incineration processes which
utilize air as the oxidant source (as opposed to pure oxygen or some other
oxidant which contains no nitrogen). The NO formation is the result of
the oxygen and nitrogen from the air reacting at the elevated flame
temperature present in incinerators. The thermodynamic equilibrium con-
centrations of NO present in combustion effluent streams as a function
of flame temperature and excess air have been determined and are pre-
sented graphically (Figure 2). Generally industrial incineration operations
do not abate NO emissions. There are currently abatement techniques avail-
able but they involve catalytic or thermal reduction (requiring a reductant
such as CH. or H2) of NO to N? followed by thermal oxidation of excess
reductant. 5 These processes are capable of reducing NO concentrations
1 A 1C
in the stack effluent to the 50 ppm level. '*•" It is the reductant cost
plus the catalyst cost (when a catalyst is used) which makes application
of this type of abatement process economically unattractive in most situ-
ations.
The specific types of abatement equipment are discussed in detail in
the Appendix of this report. Their operating principles, characteristics
and general applications are delineated. It should be noted that when ap-
plied to treatment processes handling hazardous waste constituents, a high
degree of efficiency is of primary concern as opposed to economic consider-
ations. Therefore, the types of equipment most likely to be utilized in
conjunction with incineration facilities at National Disposal Sites are
packed bed scrubbers (both fixed and floating bed types), venturi scrubbers,
electrostatic precipitators, and fabric filters.
98
-------
500
10 15
EXCESS AIR (%)
20
Figure 2. Equilibrium Nitric Oxide Concentrations
4n r/Mnkiic + inn Ffflliontc UJU4
in Combustion Effluents.
99
-------
Steam Plume Generation. Another problem common to most incineration
processes is that of steam plume generation. The appearance of a steam
plume has a very important psychological implication which must be considered.
An incinerator process effluent may contain no harmful pollutants, however,
the presence of combustion product water plus any moisture picked up in
scrubbing operations will cause the stack effluent to show a steam discharge
plume upon becoming saturated with moisture. Although the steam will have
no deleterious effects on the surrounding area, its appearance may cause
concern with the public that the air cleaning equipment is inadequate or
malfunctioning.
Steam plumes are the result of rapid cooling of moisture containing
gases to below their saturation temperature. Gases from wet scrubbers will
quickly show a steam plume at the stack discharge. During the cold winter
months, the gases are subjected to a colder atmosphere and are thus air-
condensed sooner and have shorter plume trails compared with equivalent
gases cooled by the summer atmosphere.
As a guide, saturated gases which discharge from the stack below 105 F
will have a negligible appearance and will not create a questionable steam
plume. At 105 F the volume of moisture content is less than 7 percent,
whereas at higher saturation temperatures, the percentage of moisture by
volume is as follows: 130 F, 15.0 percent; 160 F, 32.5 percent; 180 F,
0285
51.0 percent.
In addition to appearance, steam plumes have other side effects
which include:
(1) SOo (or other corrosive gases) may be absorbed by the newly
forfoed droplets, forming sulfurous acid.and then fall on homes
and industrial sites.
(2) In some cases odoriferous constituents may be entrapped by
falling droplets to increase odor at ground elevation.
100
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... ... 0285
There are three basic methods for steam plume minimization.
(1) Indirect Cooling of Hot Gases
Cooling is effected within a continuous S shaped duct with
surface exposure for radiation and cooling by atmospheric
air surrounding the ducts. Often the ducts may be arranged
essentially vertically with U bends and should be furnished
with cleanout doors and hoppers to permit intermittent dust
removal. The addition of fans, handling large quantities of
atmospheric air, blowing or inducing air across banks of
ducts which transport the uncleansed gas, has recently been
introduced.
(2) Sensible or Direct Cooling of Saturated Gases
This technique cools already 100 percent saturated gases with
cool water. Sufficient coolness is required to dehumidify or
condense water vapor down to the desirable lower saturation.
By using a standard spray tower cooling water at 70 to 85 F
may be introduced at 25 psig. Droplets will fall counterflow
to the gas passage and carry away latent heat of the water
vapor and sensible heat of the dry gas. As a general rule,
the cool water leaving a properly designed tower will approach
within 10 or 15 F of the entrance gas temperature. Therefore,
pounds of 80 F water needed equals 3.51 Ib water/1b dry gas
or 0.42 gal/lb dry gas. Use of a tower filled with drip-point
grid tiles offers a method to obtain benefit of maximum heat
transfer with an approach of approximately 5 F or less (between
the gas and liquid discharging).
(3) Cooling by Mixing with Atmospheric Air
In some special cases sensible cooling may be obtained by the
addition of atmospheric air having a low dew point temperature.
However, this method becomes impractical where already large
saturated volumes of gas having high saturation temperatures
are involved.
Gaseous Waste Incineration. The type and form of waste will dictate
the type of combustion unit required. A number of control methods have
been successfully developed for applications where the pollutants are in
the form of fume or gas. If the waste gas contains organic materials which
are combustible, then incineration should be considered as a final method
of disposal. Direct flame, thermal, or catalytic oxidation of such wastes
can produce an effluent of carbon dioxide, nitrogen, and water vapor
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which can be vented se-fely to the atmosphere. Economic considerations
are paramount in the selection of incineration systems because of the
high fuel costs when concentrations of organic constituents are low.
Direct flame incineration is used normally with materials which
are at or near their lower combustibility limit. In a well-designed
commercial combustor or burner, gases having heating values as low as
100 Btu/cu ft can be burned without auxiliary fuel. Gases having even
lower heating values, which are preheated to 600 or 700 F, often will
sustain combustion without help from auxiliary fuel. Hydrogen cyanide,
which is an extremely toxic,gas, may be burned in air; carbon monoxide,
which is also a deadly gas and a by-product of many partial combustion
reactions, can be burned in this manner. Solvent vapors mixed in high
quantities wi.th air may produce a combustible mixture which can be -burned
in a conventional forced draft combustion system.
When the amount of combustible material in the mixture is below
the lower flammable limit, it may be necessary to add small quantities
of natural gas or other auxiliary fuel to sustain combustion in the burner.
But in either case, whether the material burns with or without the
assistance of auxiliary fuel, combustion occurs at high temperatures (about
2,500 F), good mixing is achieved with the oxygen in the air, and the resultant
products of combustion generally are carbon dioxide, nitrogen, and water
vapor. Here the contaminant, whether it is a solvent vapor or pure gas,
is serving as a part of the fuel. It is contributing a significant.portion
of the total heat released to the system and can be burned with a minimum
of auxiliary fuel and therefore a minimum of operating cost. Direct flame
combustion should be employed only where the amount of auxiliary fuel needed
to sustain combustion is low and where the contaminant supplies at least
50 percent of the fuel value of the mixture.
Equipment for direct flame incineration may be a conventional in-
dustrial burner or combustor and combustion chamber (either forced or
induced draft),or it may be a flare type burner as found in many petroleum
refineries and petrochemical plants. A detailed discussion of the
102
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individual processing units will be presented in Section 2 of this
process evaluation.
Most waste gas incineration problems involve mixtures of organic
material and air in which the amount of organic material is very small.
This means that if it were injected directly through a burner, along with
auxiliary fuel such as natural gas, the amo-jnt of natural gas required
to achieve complete combustion would be quite high. Most conventional
industrial burners require temperatures of 2,200 F or greater to sustain
combustion, whereas thermal incineration can be carried out at much lower
temperatures, sometimes as low as 900 F, but generally between 1,000 and 1,500 F.
Weak mixtures of organic material and air will usually have very low
heating values, on the order of 1 to 20 Btu/cu ft. Some of the most common
applications may be found in drying ovens which drive off a solvent or
plasticizer in low concentrations in air, or form lithographing ovens or
other process drying operations. Here it is more economical to heat a
combustion chamber, using a conventional fuel in an industrial burner, and
inject the contaminated air into this chamber just downstream from the burner
flame, or even into the burner flame. Usually the waste gas is essentially
air and therefore contains enough oxygen to complete combustion of the organic
contaminant. But in some cases, where sufficient oxygen is not present
in the fume, it can be added by means of a fan or blower, either by premixing
with the fume or by injecting into the secondary combustion chamber along
... .. . 0285
with the fume.
Incineration systems for thermal oxidation of gaseous wastes are of
many different types and forms. Some utilize "line" burners when the fume
contains sufficient oxygen for its own combustion. Here the waste gas
passes over and through the flame of the "line" burner in a refractory
lined duct. Other systems utilize an external burner, either natural,
forced draft, or aspirating type. In this system the flame passes into
the duct from the burner mounted in the duct wall, causing turbulence in
the chamber, and the contaminated air passes through and around the flame
and is heated to the reaction temperature. Such units may be vertical or
horizontal and may be induced or forced draft, depending upon the physical
opor
arrangement most desirable for the system.ut03
103
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Catalytic incineration is applied to gaseous wastes containing low
concentrations of combustible materials and air. Usually noble metals
such as platinum and palladium are the catalytic agents. A catalyst is
defined as a material which promotes a chemical reaction without taking a
part in it. The catalyst does not change nor is it used up.
These catalysts must be supported in the hot waste gas stream in a
manner that will expose the- greatest surface area to the waste gas so that
the combustion reaction can. occur on the surface, producing nontoxic ef-
fluent gases of carbon dioxide, nitrogen, and water vapor. Since most
waste gases from ordinary industrial processes are at low temperatures up
to 300 F, a preheat burner is required to bring these gases up to the
npoc
reaction temperature.
The advantage of the catalyst is that the reaction temperature in catalytic
systems is lower than it is-in thermal systems because the catalyst promotes
the reaction at a lower temperature. Most catalytic reactions can be carried
out at preheat temperatures.between 600 and 1,000 F. This of course results
in a fuel saving when compared with thermal systems but involves a much
higher initial investment because of the catalyst cost. Catalytic incinerators
usually operate at or below 25 percent of the LEL (lower explosive limit) of
the material in the waste gas and below the normal oxidation temperature of
the contaminant. Care should be taken, however, when analyzing the waste for
catalytic combustion, that the waste gas .contains a low enough concentration
of the contaminant to prohibit burnout of the catalyst. Most catalysts are
suitable for maximum operating temperatures of 1,500 to 1,600 F. A high con-
centration of contaminant in the waste gas, even with minimal preheat, may
release enough heat on the .surface of the catalyst to cause catalyst burnout.
Therefore, catalytic systems are most applicable t6 low concentrations of
contaminants where the temperature rise across the catalyst will be on the
0285
order of several hundred degrees.
104
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Catalytic systems have been used widely in the oxidation of paint
solvents, odors arising from cnemical manufacture, food preparation, wire
enameling ovens, lithographing ovens, and similar applications.
Catalyst systems are susceptible to poisoning agents, activity
suppressants and fouling agents. These compounds appear as contaminants
in the waste gas stream and are specific for different types of catalysts.
Catalyst manufacturers can usually state which compounds are detrimental
to the operation of specific catalysts. It is therefore necessary to
know what contaminants are present in a waste gas stream^prior to the
selection of an efficient catalytic combustion system.
Liquid Waste Incineration. Incineration is one possibility for the
destruction of liquid wastes. Liquid wastes may be classified into two
types from a combustion standpoint: (1) combustible liquids, and (2) par-
tially combustible liquids. Noncombustible liquids cannot be treated or
disposed of by incineration. The first category would contain all materials
having sufficient calorific value to support combustion in a conventional
combustor or burner. The second category would include materials that
would not support combustion without the addition of auxiliary fuel and
would have a high percentage of noncombustible constituents such as water.
A partially combustible waste may also contain material dissolved in the
liquid phase which, if inorganic in nature, will form an inorganic oxide
upon combustion and require secondary collection prior to atmospheric release,
Assuming that either of these types of wastes is primarily organic in
nature, even though the quantity of the organic material may be small, in-
cineration of such materials becomes essentially a straightforward com-
bustion problem in which air must be mixed with the combustible at some
temperature above its ignition temperature. When starting with a waste in
liquid form, it is necessary to supply sufficient heat for vaporization in
addition to raising it to its ignition temperature.
105
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liquids vaporize and react more rapidly when finely divided in the form of a
spray, atomizing nozzles are dsually employed to inject waste liquids into
incineration equipment whenever the viscosity of the waste permits atomization.
There are many wastes which might be classified liquid which are hardly liquid
in nature. Slurries, sludges, and other materials of high viscosity can be
0285
handled only in special types-of incineration systems.
In order that a liquid waste may be considered combustible, there are
several rules of thumb which should be used. The waste should be pumpable
at ambient temperatures or capable of being pumped after heating to some
reasonable temperature level. The liquid must be capable of being atomized
under these conditions. If it cannot be pumped or atomized, it cannot be
burned as a liquid but must be handled as a sludge or solid. Liquid waste
incineration generally involves liquids having viscosities up to approximately
1,000 SSU, although lower viscosities are desirable.
In order to be considered a combustible liquid waste, the material must
sustain or support combustion in air without the assistance of an auxiliary
fuel. This means that the waste will generally have a calorific value of
8,000 to 10,000 Btu/lb or higher. Below this calorific value, the material
would not exhibit properties which would enable it to maintain a stable .
flame in a commercial combustor or burner. Materials which fall into this
category (>8,000 Btu/lb) are light solvents(such as toluene, benzene, acetone,
ethyl alcohol) and heavy organic tars and still bottoms similar to residual
fuel oil. The wastes may be^combinations of both, which would give a mixture
having an intermediate viscosity and heating value. These wastes come from
cleaning operations in chemical plants and refineries or are the-residues
from distillation processes and are usually not recovered for economic
0285
reasons.
The equipment which is used to incinerate combustible liquid waste
can also vary from manufacturer, but its basic form will be that of a
combustor or burner designed to handle a liquid waste through a steam,
air, or mechanical atomizing nozzle. High heat release combustors require
minimal secondary incineration chambers, but usually incineration is
106
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carried out in combustion chambers having volumes which provide for a heat
release of 25,000 Btu/hr-cu ft of combustion volume. Residence times
within an incinerator burning liquid waste will vary from 0.5 to 1 sec.
The combustion chamber is usually cylindrical in shape and may be used in
a vertical or horizontal arrangement. The vertical chamber has the advan-
tage that the incinerator acts as its own stack, but obviously it is not
well adapted to a tall stack arrangement. Horizontal incinerators can be
0285
more easily connected to tall chimneys or stacks. Some specially
designed rotary kilns have been applied to the disposal of liquid chemical
warfare agents. Highly explosive wastes (wet machining wastes from munitions
manufacturing) are currently disposed of by ooen burning. A detailed de-
scription of these systems will be provided later in the report.
Many combustible liquid wastes can be utilized as fuel for a boiler,
air preheater, or other heat recovery device which can turn the waste heat
energy from the incineration system into profit. Heat recovery devices,
however, are advisable only when the amount of heat recovered and the cost
of the recovery equipment can be economically justified. If the waste
liquid should contain noncombustibles such as inorganic salts, or materials
which would be converted into corrosive compounds in the combustion reaction,
such as chlorides or fluorides, then heat recovery is usually incompatible
and should not be considered.
Liquid wastes having a heating value of below 8,000 Btu/lb can be con-
sidered in the partially combustible category. It must again be emphasized
that this is a rule of thumb and that some materials as high as 10,000 or
11,000 Btu/lb will not sustain combustion by themselves. It is also
important with this type of waste that the material handling method be
compatible with the equipment selected. Viscosities should be reduced
to the point where the material is pumpable and atomizable at either
ambient or slightly elevated temperatures.
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Waste material in this classification is often aqueous in nature,
consisting of organic compounds miscible with water. Such waste may also
contain sulfur.compounds, phosphorus compounds, or combinations of organic
and noncombustible inorganics. These materials may have enough organic con-
tent to exhibit visible combustion in a high temperature furnace, or they
may be so low in combustible material that no visible combustion is apparent.
There are several basic considerations in the design of an incinerator
for a partially combustible waste. First, the waste material must be
atomized as finely as possible to present the greatest surface area for
mixing with combustion air. Second, adequate combustion air to supply
all the oxygen required for oxidation or incineration of the organics
present should be provided in accordance with carefully calculated
requirements. Third, the heat from the auxiliary fuel must be sufficient
to raise the temperature of the waste and the combustion air to a point
above the ignition temperature of the organic material in the waste. Un-
like the combustible waste, which sustains combustion by itself, this
waste may not always be injected through the combustor or burner but may
rather be atomized into the secondary chamber. If the waste material is
marginal in combustibility, it may be fed directly through the burner or
combustor along with the auxiliary fuel. Temperatures of 2,200 to 2,700 F
will result, complete combustion of the organic in the waste will occur,
and the products of combustign can be vented to the atmosphere.
1O8
-------
The equipment for handling this type of waste is usually a horizontal
or vertical refractory lined cylindrical furnace with an auxiliary fuel
burner firing at one end or tangential to the cylindrical shell. The size
of the incinerator depends upon the heat release in the system and the amount
of combustion air to be used. Mixing is accomplished by baffles or a checker
wall, and the temperature of the incinerator should vary, depending on the
type and the amount of the waste. In most cases, it is possible to incin-
erate most organic aqueous mixtures below 1,800 F and many in the range of
1,200 to 1,500 F. As with gaseous wastes, the autoignition temperature of
the waste should first be determined, and the incinerator should be operated
nppc
at a controlled temperature several hundred degrees above this point.
Incineration of wastes which are not pure liquids but which might be
considered sludges or slurries is also an important waste disposal problem.
Because sewage is handled in sludge form, many of the processes and equipment
previously applied to handling sewage sludge have found application in the
industrial disposal field. The combustion principles are the same, but the
manner of achieving the combustion is different. Some of the types of in-
cinerators which are applicable to this type of disposal problem are rotary
kilns, multiple hearth furnaces and fluidized bed incinerators. A detailed
discussion of the individual processing units will be presented in Section 2
of this process evaluation. Some of the various liquid waste materials
which are currently incinerated are discussed by Jones (Table 5).
Solids Incineration. Solids incineration is not a total disposal method,
because most solid materials contain noncombustibles and have residual ash.
Municipal and industrial incinerators probably account for 30 to 50 percent
of the total trash disposal within the United States at the present time.
The object of any incinerator is to provide complete combustion of the mate-
rial fed into it. The complications are, however, the wide variety of mate-
rials which must be burned. There is everything from wet garbage with a
heating value of approximately 2,000 Btu/lb to such plastics as polystyrene,
which have a heating value of approximately 19,000 Btu/lb. Controlling the
proper amount of air to give good combustion of both materials is difficult,
and with most currently available incinerator designs it is impossible.
109
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TABLE. 5
DESTRUCTION OF WASTES BY.INCINERATION1
,0534
Waste .
liquid wastes from manuf. of ammonia, Wastes concentrated to 5W organic
urea, nylon intermediates, ethylene content-no auxiliary fuel required.
glycol.methylamines, methacrylates Steam atomized burners
Organic tars, catalyst complexes
Liquid Wastes containing hydrocarbons,
high-boiling degradation products,
tars from nylon intermediate manuf.
Liquid from aerylonitrile manuf. con-
taining acetonitrile and cyanides +
slop oils + phenolic resin wastes (in-
organic)
Two soot streams from acetylene
manuf.; still residues from acrylo-
nitrile and vinyl chloride processing
stripping steam with acrylonitrile.
Heavy sludge acid, sulforiated tars
from benzene plant. General refuse,
scrap plastic.
Styrene still residues.
Organic acids, salts, anhydrides,
hydrocarbons and chlorinated hydro-
carbons from manuf acture'.of chlo-
rinated organics.
Sludges containing oil, solids from
separators, clarifiers, tank bottoms
Biological sludges
Vent gases - H2S, mercaptans
Spent caustic-50% phenols
High-and low-boiling organics from
nylon manuf.
Metals must be collected when
catalysts are burned.
Nitrile wastes have high fuel value.
Provision for auxiliary fueV gas
was made, 1600 F.
Natural gas used as auxiliary fuel.
Flow and organic content of waste
fluctuates greatly, 1500 F
Solid wastes fed first, then liquid.
Mixed with fuel oil and used in
heating furnaces.
Natural gas fuel used in a vortex
burner. Wastes neutralized with
ammonia prior to incineration to
prevent corrosion.
Fluidized-bed furnace, 800-900 F
Fuel oil used as auxiliary fuel
110
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Certain basic principles for complete combustion of solid waste with
a subsequent low particulate emission from the combustion zone are as
folios:0285
m Excess air: Air quantities should usually be kept on the order
of 50 to 150 percent above the stoichiometric requirements.
(2) Minimum use of underfire air: This maintains low velocities and
therefore reduces the particulate emission from the incinerator
because it keeps small particles out of the gas stream.
(3) Proper use of overfire air: This provides ample oxygen and tur-
bulence in the combustion space above the fuel bed. The overfire
air injected into the system may be as high as 50 percent of the
total required.
(4) Temperature: Temperature in the furnace space should be between
1400 and 1800 F to reduce the rate of smoke formation and odor.
Temperatures below 1400 F will produce smoke and allow odor to
escape from the incinerator. Above 1800 F there may be sintering
or fusing of the ash with the furnace refractories. Excess air is
used to control the furnace temperature.
(5) Sufficient combustion volume: The incinerator should have enough
combustion volume to provide sufficient residence time for the
burnout of all flying particulate matter. The average heat re-
""ease per cubic foot of furnace volume should not exceed 25,000
Btu/cu ft-hr.
(6) Secondary chamber: A secondary chamber zone should be provided
in every incinerator and, in fact, is required in most municipal
and state codes now being adopted.
(7) Residence time: The residence time in the incinerator should be
between 1 and 2 seconds.
(8) Reasonable loading rates: Low loading rates per square foot of
grate surface should be adhered to, even in forced draft in-
cinerators. They should be no more than 60 Ib of waste/sq ft/hr.
Ill
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Early sol'id waste incinerators were charged by a crane from a storage
pit onto stationary grates. Some furnaces were hand stoked. Ash handling
was arranged through undergrate hoppers in which the ash was water quenched
and dumped into trucks and hauled away. Today, because of the awareness
of air pollution problems, more modern designs have been developed. A variety
of modern stokers (each best suited for a particular size and form of solid
waste), which provide uniform and regular agitation of the feed, are used
to feed the waste material onto the surface of the grate. The grate may
be a fixed grate or a traveling grate system. Where the traveling grate is
used, it is also considered part of the stoking apparatus.
The types of incinerators which are applicable to solid wastes are open-
pit incinerators (when no secondary pollution problem exists) and closed
incinerators such as retort and inline multiple chamber units, rotary kilns
r*coo
and multiple hearth incinerators. A detailed discussion of these units
will be presented in Section 2 of this process evaluation.
The incinerator design does not have to be limited to a single com-
bustible or partially combustible waste. Often it is both economical and
feasible to utilize a combustible waste, either liquid or gas, as the heat
source for the incineration of a partially combustible .waste which may be
either liquid or gas. Multiple or dual fuel burners for combustible wastes
can be utilized in a single incineration chamber. Combination systems can
often reduce the operating, cost in terms of auxiliary fuel and should be
carefully evaluated in the-overall waste treatment program of any process
plant. Heat recovery in these systems is applicable on an individual basis.
112
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2. PROCESS DESCRIPTION
The following sections of this report will discuss in detail the
operating principles, process applicability, process design, and process
economics of each of the various types of incineration systems. As
mentioned in the introduction of this evaluation, incinerators are generally
classified by the form of waste which they burn. There are ten basic types
of incinerator units, open pit incinerators, open burning, multiple chamber
incinerators, multiple hearth incinerators, rotary kiln incinerators,
fluizided bed incinerators, liquid combustors, catalytic combustors, gas
combustors and stack flares. The type of waste for which each of these
incineration units is best suited is detailed diagrarrmatically (Figure 3).
The types of incinerator systems which are amenable to secondary abatement
equipment application are also shown.
Fluidized Bed Incineration
Fluidized bed incinerators are versatile devices which can be used to
dispose of solid, liquid and gaseous combustible wastes. The technique is
a relatively new method for ultimate disposal of waste materials. It was
first used'commercially in the United States in 1962 and has found
limited use in the petroleum industry, paper industry and for processing
nuclear wastes.0582 In addition, applications of fluldized bed combustion
.• I'tObjIloO
to the disposal of sanitary sludge have been reported.
Operating Principle. A typical fluidized bed incinerator is shown
schematically (Figure 4). Air driven by a blower enters a plenum at the
bottom of the combustor and rises vertically through a distributor plate
into a vessel containing a bed of inert granular particles. Sand is
typically used as the bed material. The upward flow of air through the
sand bed results in a dense turbulent mass which behaves similar to a
liquid. Waste material to be incinerated is injected into the bed where
combustion occurs within the fluidizing media.
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JO'EN PIT
INCINERATORS
OFEN
INCINERATION
MULTIPLE
CnAMBfR
INCINERATORS
MULTIPLE
HEARTH
INCINERATORS
ROTARY KILN
INCINERATORS
FLUIDiZcD BED
INCINERATORS
LIQUID
COMBUSTORS
CATALYTIC
COMBUSTORS
GAS
COvbjSTORS
FLARES
Figure 3. Types of Incinerators and Their Applications
-------
FLUE GAS
MAKEUP SAND
ACCESS DOOR
AUXILIARY
BURNER (OIL OR GAS)
WASTE INJECTION
FLUIDIZ1NG AIR
ASH REMOVAL
Figure
4. Schematic of a Fluidized Bed Combustor
115
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Air passage through the bed produces strong agitation of the bed particles.
This promotes rapid and relatively uniform mixing of the injected waste
material within the fluidized bed.
The mass of the fluidized bed is large in relation to the injected material.
Bed temperatures are quite uniform and typically in the 1,400 to 1,600 F range:
At these temperatures, heat content of the fluidized bed is approximately
16,000 Btu/ft thus providing a large heat reservoir. By comparison, the
heat capacity of flue gases at similar temperatures is three orders of
magnitude less than a fluidized sand bed.
Heat is transferred from the bed into the injected waste materials to
be incinerated. • Upon reaching ignition temperature (which takes place
rapidly) the material combusts and transfers heat back into the bed. Con-
tinued bed agitation by the fjuidizing air allows larger waste particles
to remain suspended until combustion is completed. Residual fines (ash)
are carried off the bed by the exhausting flue gases at the top of the
combustor. These gases are subsequently processed and/or scrubbed before
atmospheric discharge.
Process Design. In specifying or designing a fluidized bed combustor,
t
primary factors to be considered are: gas velocity; bed diameter; bed
temperature; and, the type and composition of waste to be incinerated.
f
Gas velocities are typically low, in the order of 5 to 7 ft/sec.
Maximum gas velocity is constrained by the terminal velocity of the bed
particles and is therefore a function of particle size. Higher velocities
result in bed attrition and an increased particulate load on downstream
air correction equipment. Relatively low velocity reduces pressure drop
and therefore lowers power requirements.
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Present fluidized bed design technology limits the bed diameter to 50
ft or less. At nominal values of gas velocity and temperature, the
maximum volumetric flow would be approximately 2.5X10 acfm.
Bed depths range from about 15 inches to several feet. Variations in
bed depth affect waste particle residence time and system pressure drop.
One therefore desires to minimize bed depth consistant with complete
combustion and minimum excess air.
Bed temperatures are restricted Dy the softening point of the bed
material. If sand is used, temperatures should be maintained below 2UOU F
to avoid softening and consequent agglomeration of the particles.
The type and composition of the waste is a significant design parameter
in that it will impact storage, processing and transport operations (prior
to incineration), as well as the combustion. If the waste is a hetrogeneous
mixture such as municipal refuse and has a relatively low (<8,000 Btu/lb)
heating value, processing (shredding, sorting, drying, etc.) operations
will be more complex and auxiliary fuel addition to the combustor will be
required. Homogeneous wastes which can be injected and uniformly dispersed
in the bed should facilitate overall system design and minimize the bed
volume.
Process Economics. Installation and operating costs will vary signif-
icantly depending upon the type of waste to be processed and the quantity
and sophistication of water and air correction equipment required. Lund0285
indicates that investment costs and operating costs are approximately $20
and $5 per ton respectively.
Process Modifications. The fluidized bed combustor will noramlly be
incorporated in an overall material handling, processing and disposal system
to simultaneously cope with solid, liquid and gaseous waste or by-products.
This is illustrated schematically in a block diagram (Figure 5) which has
the following elements:
117
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OTHER _
USES
RECYCLE
WASTE
INPUT
WATER CONDITIONING
FOR RECYCLE OR
DISPOSAL
MAKEUP
W^STE MATERIAL
RECEIVING AND
STORAGE
DISCHARGE
WASTE PRE - PROCESSING
o DE - WATERING
o DISINTEGRATION
o SEPARATION
INERT ASH
FLUIDIZED BED
INCINERATION
DISPOSAL
I
AIR PREHEAT
1 I
I I
J !
L—
WASTE HEAT
UTILIZATION
ELECTRICAL
POWER GENERATION
AIR CORRECTION
EQUIPMENT
ATMOSPHERIC
DISCHARGE
Figure 5. Functional Diagram for Fluidized Bed Incineration Disposal of
Combustible Wa'ste Material
118
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(1) Receipt and storage of waste materials.
(2) Processing or conditioning waste materials prior to incineration.
(3) Waste material transport and handling.
(4) Waste incineration.
(5) Air correction of off gases from combustion.
(6) Disposal and/or recovery of residual solid and liquid by-products.
Incineration systems incorporating fluidized bed combustors vary
depending upon the application and economic desire to utilize waste heat.
Usually, systems will incorporate most if not all of the functional
activities illustrated (Figure 5).
Most of the fluidized bed incineration application reported in the
literature involve the disposal of sludges or slurried wastes. This may
necessitate a dewatering step in processing the waste prior to incineration
if comuustion gases are to be used for steam-electric or gas turbine
power generation. If power generation is a desired by-product of the
incineration process, then waste moisture content values less than approxi-
mately 60 percent are required. Moisture values in excess of this
value, or heavy concentrations of inert matter will require auxiliary fuel
burners to preheat the waste and ensure sufficient heat content in the
flue gases. Pre-drying of the sludge may be accomplished by aeration or
more sophisticated mechanical systems involving the addition of heat.
Waste material is pneumatically, mechanically or gravity fed into the
fluidized bed. Normally, inhomogeneous waste material must be reduced in
size (shredded, pulverized, etc.) to facilitate the feed system operation
and permit injection, distribution and combustion within the fluidized bed.
119
-------
In addition to reducing moisture content and waste material size,
separation of non-combustible material such as ferrous and non-ferrous
metals may be required. The former may be removed using magnetic separators.
Non-ferrous metals are commonly removed using ballistic-type separators.
The tasks of receiving,LStoring, processing and transport of more
hazardous wastes may often .require a completely closed system. In this
case, aeration in the conventional manner will be unacceptable. Enclosed
hot air dryers using recycled combustion gases may be considered; however,
the addition of gas or oil fuel burners to the incinerator (to accomplish
waste drying) will probably result in higher Initial equipment costs.
An auxiliary burner system will be required in any event for startup and
bed temperature conditioning.
Combustion of any waste.which results in particulate, odors or gaseous
stack emissions (other than water vapor and C02) may require air correction
equipment to meet emission standards. Particulate emissions may be controlled
using one or more of the following general categories of collectors; dry
collectors, wet scrubbers, electrostatic precipitators and fabric filters.
Auxiliary air correction equipment for odor control should not be required
with the fluidized bed incinerator process. In this instance, odors will
be eliminated by oxidation in the combustor. The operating temperature of
the fluidized bed combustor is 1400 to 1500 F which is adequate for most
0285
odor producing compounds. If odor control is a problem with certain
hazardous wastes, then an afterburner can be added to the incineration
process as a means of control.
Control of gaseous pollutants will depend upon the waste and its com-
uustion products. Because of its relativately low and controlled temperature
environment, fluidized bed incinerators should produce little or no nitric
oxide, a distinct advantage for this type of equipment.
120
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A rather Interesting and unique technique for scrubbing sulfur oxides
with fluidized beds is the utilization of calcined limestone particles in
place of sand as the bed material. ' Scrubbing efficiencies up to
90 percent have been obtained in experimental applications involving fossil
fuel combustion gases. In this work, the fluidized bed was utilized
purely as a desulfurization device, and not as a combustor. However, it is
conceivable that a limestone bed or a sand-limestone mixture could be used
in place of pure sand in an incinerator application to scrub a significant
portion of the sulfur oxides produced by the waste combustion. The remaining
sulfur oxides would be removed by conventional wet scrubbing equipment. It
should again be emphasized that this is a conceptual approach and has not
been reduced to practice.
Process Applicability. The fluidized bed incinerator is generally
applicable to the ultimate disposal of combustible solid, liquid and gaseous
wastes; a significant advantage over most other incineration methods. For
that reason, it is probable that this type of Incineration unit would find
application at a National Disposal Site, especially considering its suit-
ability to the disposal of sludges generated in any biological treatment
facilities which would be present at the site. It has the following ad-
vantages and limitations:
Advantages
(1) The combustor design concept is simple and does not require
moving parts in the elevated temperature regions of combustion.
(2) Designs are compact due to high volumetric heating rates
(100,000 to 200,000 Btu/hr-ft3) resulting in lower capital
investment.
(3) Comparatively low gas temperatures and excess air require-
ments* minimize formation of nitric oxide.
*For example, excess air requirements as low as 5 percent have been
reported in the combustion of coal in fluidized bed reactions. Low excess
air requirements reduce the size and cost of gas handling equipment.
121
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Limitations
(!) Bed diameters are limited with present design technology;
therefore, maximum volumetric flow rates per unit are
limited.
(2) Removal of inert residual material from the bed is a potential
problem area.
pa+aiyHc Incineration
catalytic incinerators are devices which are
—: r n riir^r :. .«
c oration, has ,een successful use, In the cH.Ua, process
1n
-------
Operating Principle. There are five steps in any solid catalyzed
vapor phase reaction. These five basic steps are:
(1) Diffusion of the reactants through the stagnant fluid around
the surface of the catalyst.
(2) Adsorption of the reactants on the catalytic surface.
(3) Reaction of the adsorbed reactants to form products.
(4) Desorption of the products from the catalytic surface.
(5) Diffusion of the products through the pores and surface
film to the bulk- vapor phase outside the catalyst.
Therefore, given the identical support, the rate of steps (1) and
(5) would be approximately equal regardless of the dispersed catalytic
metal which is present. The criteria which govern the effectiveness of
operation for various catalytic metals must therefore fall into
steps (2), (3) or (4). These criteria include reaction temperature,
waste material concentration, excess oxygen available, the chemical
composition of the catalyst and the geometric configuration of the
individual catalysts.
The operating efficiency (percent of the waste organic combusted to
carbon dioxide and water) of a catalytic system is strongly dependent
upon the catalyst temperature. Increased catalyst temperatures generally
result in increased removal efficiencies. A tabulation of removal effi-
ciencies of various solvents as a function of catalyst temperature is pre-
nflfi?
sented (Table 6). The data summarizes the type and quantity of coating
applied, the type and quantity of solvent evolved, the oven temperature,
the catalyst temperature and the removal efficiency for a coating oven
during tests with a catalytic incinerator.
The waste compound concentration as well as the oxygen concentration
in the gas stream have narked effects upon catalytic combustion efficiency.
The combustible waste concentration in the gas stream have marked effects
upon catalytic combustion efficiency. The combustible waste concentration
123
-------
TABLE 6
CATALYTIC OXIDATION OF SOLVENT VAPORS EVOLVED FROM A COATING OVEN*
.0862
Coating Quantity of Coating Evolved ^ved^nr"
V1nyl 19 Xylol and Isophorone 120
V1nyi 43 Methyl/isobutyl 271
He tone
FBO,V IB 6 Xylol and Butyl Cello- 86
*"* solve
Phenolic 18 5 Mineral Spirits 88
Oleoreslnous 1' 5 Mineral Spirits 77
Altyd 8 Mineral Spirits 30
Avenge Oven Catalyst Ten*).
350 800
920
1050
1200
340 840
890
930
990
350 800
900
414 730
425 800
920
1050
1200
290 690
700
800
920
1050
1200
! Solvent
Removal
28
54
77
93
77
79
BS
88
79
81
65
80
89
94
95
41
52
80
89
94
95
The catalysts discharge temperature -as held constant for each test and superficial gas velocities Mere constant
•Ithln - IS percent for all data points
-------
in the stream to be treated should never exceed the lower flammability
limit in order to guard against explosion and fire. However, it is
desirable to operate with as high a concentration of combustible (below the
lower flammability limit) as possible since conversion efficiencies
are generally proportional to combustible compound concentrations when
other operating variables are held constant. The conversion efficiency
of catalytic combustors is also effected by the oxygen concentration
present in the feed gas stream. It has been found that increased oxygen
concentration results in increased efficiency when other parameters are
held constant. There is, however, a trade-off, as oxygen concentration is
increased in a gas stream (through air injection), the contaminant con-
centration is decreased. That is, the efficiency of the system will be
increased by oxygen addition while simultaneously being decreased by con-
taminant dilution. There is generally an optimum which must be determined
for individual disposal systems. The normal effective range for catalytic
oxidation extends from a very few parts per million of combustible up to
a heating value of 20 Btu/std cu ft.
The chemical composition of a catalyst affects conversion efficiencies.
The various noble metals such as platinum, palladium, rhodium, etc., as
well as copper chromite and the oxides of copper, chromimum, manganese, nickel,
and cobalt, in varying concentrations have been applied successfully to the
catalytic oxidation of various combustible compounds. However, in air
pollution control it has not been practical to undertake research programs
to develop specific catalysts for each problem. Therefore, the goal
of commercial manufacturers has been to make available universal catalysts
which are effective in oxidizing the entire range of organic materials
over an extended period of exposure time with minimum maintenance and
replacement.0304'0862
When selecting a catalyst material care must be taken to make sure that
there are no poisoning agents, activity suppressants or fouling agents present
which inhibit the catalysts' effectiveness. With platinum family catalysts,
contaminants to look out for are:
125
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Poisons: Heavy metals
Phosphates
Arsenic compounds
Suppressants: Halogens (elemental and compounds)
Sulfur compounds
Fouling Agents: Alumina and silica dusts
Iron oxides
Silicones
Other materials that may reduce catalytic effectiveness in general are the
vapors of metals such as mercury, zinc and lead. ' Catalyst manu--
facturers can generally specify which materials are detrimental to catalysts
which they market.
The geometric configuration of tne individual catalysts can also in-
fluence the extent of the oxidation of a gaseous waste. There are many
commercial catalysts available in pellet, spherical or ring form. However",
in air pollution work, which is generally operated at or near atmospheYic
pressure, usually the pressure drop through catalyst beds of these types
is so large that the horsepower of the waste gas fan becomes too great for
economical operation. Therefore, three general commercial1 catalysts with-
a very low pressure drop (1/4 to 1/2 in.W.C.) have been developed (Figure 6).
The first ,is a mat type catalyst similar to an air filter. It consists
of a ribbion type "Nichrome" or stainless steel wire to which the catalytfc
material has been applied, randomly packed between screens and mounted in
a stainless steel frame. The second is a porcelain assembly consisting
of two end plates which are secured by a center post and a number of tear-
drop-shaped rods to which'the catalyst is applied. In this case the carrier
is procelain which is first coated with activated alumina and then with an
active metal coating. The third is honeycomb type ceramic material to which
the catalytic material is applied.0304 The geometric configuration best
suited for specific applications can usually be suggested by the catalyst-
manufacturer.
-------
MAT SUPPORTED CATALYST
PORCELAIN SUPPORTED CATALYST
HONEYCOMB SUPPORTED CATALYST
Figure 6. Commercially Used Catalyst Configurations0304
1*7
-------
Process Design. There are certain prerequisites required for an ef-
ficient catalytic operation. The basic requirements include intimate
mixing of the combustibles in the stream to be treated. The stream must
be brought up to the catalytic ignition temperature for the combustible
to be burned, and good temperature distribution through the catalyst bed
is essential. Sufficient oxygen must be present in the waste effluent or
must be added to it to ensure oxidation of the materials. The system must
be designed so that proper velocities and retention times through and with-
in the catalyst bed are maintained.
The influent gas stream should be free of particulate in order to ensure
against catalyst fouling. Therefore, if the stream contains high particulate
loadings, a pretreatment of filtration or electrostatic precipitation would
be required prior to catalytic oxidation. In such cases, it is generally
more economical to treat the waste gas stream with thermal incineration.
Basically, a catalytic .incinerator consists of an afterburner housing
containing a preheating section (if one is necessary) and a catalyst section.
A gas burner preheats the contaminated gases before they flow to the
catalyst section. Drawings of two catalytic incinerator installations are
presented (Figures 7 and 8). An arrangement for the recovery of heat from
the incinerator gases is illustrated (Figure 8).
Frequently, the contaminated gases are delivered to the afterburner
by the fan exhausting process equipment. In one type of catalytic in-
cinerator, the exhaust fan is located within the afterburner housing
between the preheat burner.and the catalyst bed. This *an also mixes
the gases and attributes them evenly over the catalyst. Cohdensates
do not occur in the fan since? it operates above condensation temperature.
Of course, the fan must be constructed of materials that can withstand
the maximum temperature of the gases being handled.
128
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DISCHARGE TO
ATMOSPHERE
CATALYST
PREHEAT
BURNERS
o o o o o o
fi
GASEOUS
INFLUENT
CONTAINING
COMBUSTIBLE
MATERIAL
Figure 7. Catalytic Incineration Without Heat Recovery
,0862
129
-------
HEAT
EXCHANGER
CATALYST
PERFORATED
PLATE
PREHEAT
BURNERS"
I
DISCHARGE
TO ATMOSPHERE
GASEOUS INFLUENT
CONTAINING COMBUSTIBLE
MATERIAL
Figure 8-. Catalytic Incineration- wi-th Heat Recovery
0862
-------
The interior chamber of the afterburner may be constructed of 11 to Ifa
gage black iron, heat-resisting steel, stainless steel, or refractory
materials. Heat-resisting steel should be used for operating temperatures
between 750 and 1,100 F; stainless steel is recommended for operating
temperatures exceeding 1,100 F. Refractory materials are recommended for
temperatures exceeding 1,300 F. A thickness of 4 to 6 inches of similar
thermal insulation is required unless refractory materials are used. The
exterior sheet is usually fabricated from 16 to 20 gage mild steel. The
framework is usually fabricated from standard structural steel. Gas
rtOCO
velocities througn the chamber of about 20 fps have been found satisfactory.
The contaminated gases are preheated to the reaction temperature by a
gas burner before passing thorugh the catalyst. When the preheat burner is
on the discharge side of a fan, a premix gas 'burner is normally used because
of the positive pressure in the combustion chamber. When the fan is between
the preheat burner and the catalyst bed, an atmospheric burner may be used
since a negative pressure exists in the preheat section of the combustor.
Sizing the preheat burner to increase the temperatue of the contaminated
gases to the required catalyst discharge temperature without regard to the
heating value of the combustible materials is advisable especially if considerable
variation in concentration occurs. The concentration of combustibles from
process equipment is normally 25 percent of the lower explosive limit or
less to meet the requirements of the National Board of Fire Underwriters.
Experience indicates that the preheat burner should have sufficient capacity
to heat the contaminated gas stream to 950 F minimum to obtain adequate
rtQ/TO
catalytic combustion of the compounds that are more difficult to burn.
some burning of contaminants usually occurs in the preheating zone. The
preheated gases then flow through the catalyst bed where the remaining
combustible contaminants are burned by catalysis.
131
-------
A direct relationship is believed to exist between the autoignition
temperature of an organic vapor and the temperature at which catalytic
oxidation will occur. In other words, the higher the autoignition
temperature of a compound, the higher the expected temperature required
nOCO
for catalytic oxidation.
Catalytic incinerators possess an inherent maintenance factor not
present in other types of incinerators; namely, that usage of the catalyst
produces a gradual loss of activity through fouling and erosion of the
catalyst surface. Occasional cleaning and eventual replacement of the
catalyst are therefore required.
Modulating controls on the burner regulated by the catalyst discharge
gas temperature are usually used. This allows the fuel gas input to the
preheat burner to be reduced as the rate of heat released in the catalyst
bed increases as a result of larger concentrations of combustible vapors.
<
The sensing instrument commonly used is a type employing a fluid-filled
oulb for detecting gas temperature with capillary and bellows. Movement
of the bellows is amplified and transmitted to the preheat burner gas valve
and combustion air blower blast gate. Electronic instruments are used less
f\ QC O
frequently because of considerably greater cost.
When operating conditions do not vary greatly, an improved means of
ensuring maximum combustion efficiency seems to be the firing of the preheat
burner at a fixed input capable of heating the contaminated gases-to the
temperature required for complete oxidation at the maximum rate of influx.
Installation of a high-temperature-limiting control on the downstream side
of the catalyst may be necessary to prevent overheating of the catalyst
.. 0862
section.
Finally, the burned gases are discharged through a stack to the atmosphere,
to a process that may use the sensible heat of the exhaust gases, such as
a bake oven or dryoff oven, or they may be passed through an exchanger for
heating the gases entering the combustor, which thereby reduces the amount
of fuel required by the preheat burners.
132
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Process Economics. The installed capital investment cost of a cata-
lytic incineration system is a function of the difficulty of the combustion
reaction, inclusion of auxiliary equipment, materials of construction and
the extent of heat recovery. Operating costs generally reflect fuel con-
sumption in the preheater (and are therefore a function of influent gas
temperature, catalyst temperature, and heat recovery) as well as periodic
catalyst replacement of activation. Estimates from various literature
sources of both capital and operating costs are presented (Table 7).
Process Modifications. Basically, the only process modifications
utilized in catalytic incineration is waste heat recovery through heat
exchange with or recirculation of the hot effluent gas exiting the catalyst
bed. Where the combustible concentration is relatively high, i.e., where
the temperature rise through the bed approaches 400 F or more, it is often
desirable to take a portion of the hot gases after passage through the
catalyst and recirculate them, combining them with relatively low temper-
ature influent prior to introducing them into the catalytic system. In
this way, a stream at approximately 300 F could be combined with a portion
of the effluent from the catalyst at 700 F, bringing the inlet temperature
up to 500 F, thereby reducing the preheat to a minimum. Another method of
reducing the preheat required, even when the combustible content is rela-
tively low, is to incorporate a heat exchanger. The influent to the pro-
cess is passed through the "cold" side of the heat exchanger, then passed
over the preheat burner and through the catalyst bed. The effluent from
the catalyst is passed through the "hot" side of the heat exchanger, there-
by increasing the temperature of the influent up to the approximate ignition
temperature of the catalyst. These two alternatives along with that of not
utilizing heat recovery are presented (Figure 9).
133
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TABLE 7
PROCESS ECONOMICS FOR CATALYTIC INCINERATION
CJ
uata from Reference No. 1533
Basic Catalytic Unit
Catalytic Unit with Heat
Exchanger
Data from Reference No. 0285
Basic Catalytic Unit
Catalytic Jnit With Heat
Amount of
Gas Treated
scfm(a)
10,000
10,000
10,000
10,000
Influent
Gas Temp.
F
350
550
350
550
300
300
Capital
Cost
S/scfm
2.30
2.30
2.85
3.39
2.00 - 2.50
- 3.50 - 4.50
Annual
fuel Lost
S/Year
14,600
4,800
7.100
(0
(o)
(»)
Exchanger
Data From Reference No. 1461
Basic Catalytic Unit
5,000
400
3.00
3.800
a Contaminants are at less than 25S of L.E.L.
(b) No data available
^ No fuel Is required. The preheat exchanger saves $14,600 annually in fuel costs.
-------
INFLUENT
PREHEAT
BURNERS
c
FAN
CATALYST
EFFLUENT TO
ATMOSPHERE
PREHEAT
BURNERS
C
FAN
CATALYST
INFLUENT
EFFLUENT TO
ATMOSPHERE
RECIRCULATED HOT GAS
PREHEAT
BURNERS
FAN
CATALYST
HEAT
EXCHANGER
EFFLUENT TO
ATMOSPHERE
INFLUENT
Figure 9. Heat Recovery Options
0304
135
-------
Process Applicability. Due to the form of the waste material to be
treated (dilute and in the gaseous state) catalytic incineration is best
suited for use at the processing site where the waste material is generated.
A listing of some of the typical industrial applications of catalytic in-
cineration systems is presented (Table 8).
Catalytic incineration would find use at a National Disposal Site
only as a secondary treatment (i.e., afterburner) on primary'treatment
processes evolving varying amounts of miscellaneous hydrocarbons, alcohols,
amines, acids, esters, aldehydes and many other contaminants which are
basically hydrocarbon in nature. These materials have varying degrees of
toxicity and different odor-levels; however, they all lend themselves to
catalytic oxidation. Generally, the commercial catalysts available for
installation in operations which emit compounds of this kind are not specific.
That is, they tend to oxidize all combustible? organic compounds in the stream
regardless of their type and concentration. Catalysts are also effective in
the reduction of oxides of nitrogen and in burning sulfur bearing compounds.
such as hydrogen sulfide and carbon bisulfide.
136
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TABLE 8
TYPICAL INDUSTRIAL APPLICATIONS OF
CATALYTIC INCINERATION SYSTEMS1580
Automotive paint baking
Coil & strip coating
Metal parts finishing
Metal decorating
Wire enameling
Hardboard coating & curing
Resin manufacture
Oil bodying
Varnish cooking
Oil sulfurization
Acrylate polymerization
Oil hydrogenation
Oil quenching
Asphalt blowing
Tar & asphalt coating & saturating
Phthalic and maleic anhydride manufacture
Nitric acid plants
Etching & dissolving metals with nitric acid
Fungicide manufacture
Pharmaceutical manufacture
Vitamin manufacturing
Rice browning
Corn popping
Nut roasting
Coffee roasting
Smoke houses
Potato chip cooking
Rendering of animal by-products
Carbon baking
Metal chip drying
Foundry core baking
Brake shoe bonding and burn-off
Paper coating
Printing
Fabric finishing & curing
Paper mill digesters
Fertilizer processing
Waste water stripping incinerators
Investment casting & mold burnout
Synthetic rubber manufacture
Sewage treatment
137
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Rotary Kiln Incinerators
Rotary kiln incinerators are versatile units which can be used to dispose
of solid, liquid and gaseous combustible wastes. They have been utilized
in both industrial and municipal installations. 0167,1002,1672,0053 Ip
addition, applications of rotary kiln incineration to the disposal of ob-
solete chemical warfare agents and munitions have been reported.0958'1688'1689
Operation Principle. The rotary kiln incinerator is a cylindrical
shell lined with firebrick or other refractory and mounted with its axis
at a slight s.lope from the horizontal. It is a highly efficient unit whe'n
applied to solids, liquids, sludges and tars because of its ability to
attain excellent mixing of unburned waste and oxygen as it revolves. Its
use as a concentrated waste gas combustor is considered a secondary appli-
cation. This is due to the fact that although proper conditions are present
for efficient gas combustion (i.e., long residence time at elevated temper-
atures) there is no need for .the cylinder to be rotating. Therefore rotary
kiln incinerators are used for gaseous waste combustion only in conjunction
with solid or liquid waste incineration.
Rotary kiln incinerators used in municipal applications are generally
designed to handle large volumes of solid combustible waste (refuse) along
with any entrained liquid. In this type of facility, the kiln actually
serves as a secondary combustion unit since the waste material is ignited
on traveling grates prior to entering the kiln (Figure 10). In this instance,
the kiln serves mainly as an efficient mixer of the burning waste with com-
bustion air.0053
Rotary kiln incinerators when applied to industrial (includes military)
applications are generally designed to accept both solid and liquid feed.
A typical major industrial installation is operated by the Dow Chemical
Company at Midland, Michigan (Figure II)1002. This particular unit consists
of a 65 million Btu/hr kiln that is used for the incineration of solid
chemical refuse, liquid residues, paper, wood and other solids of varying
Btu/content. A pack-feed mechanism is used to feed packs and drums of
solid waste chemicals into the incinerator.
138
-------
CHARGING
CHUTE
TO EXPANSION CHAMBER
AND GAS SCRUBBER
RESIDUE CONVEYORS
Figure 10. Municipal Rotary Kiln Incineration Facility
,0053
-------
a TAR PUMPING
PACK STORAGE AND
FEEDING FACILITY
SCRAP METAL
FLY ASH
RESIDUE
Figure 11. Typical Major Industrial Rotary Kiln Incineration Facility
1002
-------
Liquid wastes transported to the incinerator are transferred to designated
receiving tanks that contain compatible wastes. All drums of liquid wastes
are also transferred to the receiving tank by the way of a drum-dumping dock.
The waste is strained as it is pumped from the receiving tank into a burning
tank, where it is blended for optimum burning characteristics. All liquid
residues are burned in suspension by atomization with steam or air.
Drum quantities of solid tars are destroyed by feeding them into the
rotary-kiln incinerator via a hydraulically operated drum and pack-feeding
mechanism. All refuse, except full arums and packs of material, is dumped
into the refuse pit. An overhead crane is used to mix the refuse and raise
it to the charging hopper of the rotary kiln (see Figure 11).
While the solid refuse is being fed, liquid tars are fired horizontally
into the rotary kiln. As the refuse moves down the kiln, organic matter
is destroyed, leaving an inorganic ash. This ash is made up primarily
of slag, and other nonburnables such as drums and other metallic material.
The ash discharges from the end of the kiln into a conveyor trough that
contains water. Afer quenching, the material is conveyed into a dumping
trailer, and then to a landfill.
After leaving the kiln, the products of combustion enter the secondary
combustion chamber and impinge on refractory surfaces that cause a swirling
action. No secondary fuel or afterburners are used. Downstream of the
secondary combustion chamber, the gases pass through several banks of
water sprays in which the flyash is knocked down and sluiced onto the
ash-conveyor floor. Cooled gases pass under a stack damper and then to
a 200-ft. stack.
There are a variety of small relatively portable and inexpensive
rotary kiln incinerators currently marketed. These units usually are
not as versatile as large installations because they generally lack
the auxiliary equipment utilized in pretreatment of heterogeneous feeds.
141
-------
An example of this type of unit is the completely packaged compact THUMBLE-
BURNER, designed by Bartlett-Snow (Figure 12). 1672 These units have capacity
ranging from 100 pounds to 2 tons per nour with corresponding overall system
dimensions ranging from 5X5X15 feet to 14X15X34 feet. This type of system
will efficiently incinerate properly sized solid waste material with heat
content ranging from 1000 to 15,000 Btu per pound. It is also capable of
burning gaseous and liquid wastes when they are injected through the aux-
iliary burner which is used for incinerator temperature control.
The rotary kiln has been successfully applied to the Inclneritfon of
obsolete or excess chemical warfare agents (GB. VX and mustard) .
In this case, the waste is carefully fed to the unit at a relatively slow
flow rate and supplemented by fuel oil flame. The liquid chemical warfare
agents are fed cocurrent to the fuel oil flame. All incineration con-
trols are fail-safe and the agent feed is equipped with a fast acting
cutoff valve in the event of loss of flame.
sent to ultimate disposal.
Rotary kilns have also been used to incinerate explosives such as
obsolete munitions. In this case, the explosive is fed countercurrent
to a fuel oil flame. The kiln is equipped with an internal spiral to convey
materials. through the furnace. Feed and discharge is accomplished with
metal conveyers. The effluent fume scrubbing system consists of a packed
bed scrubber, utilizing a sodium carbonate solution, followed by a hydro-
clone or venturi scrubber. The scrubber liquor containing fly ash and
a sodium nitrate-nitrite mixture is then dried and sent to ultimate
, 0958,1688
disposal.
142
-------
1 WASTE TO INCINERATOR
2 AUTO-CYCLE FEEDING SYSTEM:
FEED HOPPER, PNEUMATIC FEEDER, SLIDE GATES
3 COMBUSTION AIR IN
4 REFRACTORY-LINED, ROTATING CYLINDER
5 TUMBLE-BURNING ACTION
6 INCOMBUSTIBLE ASH
7 ASH BIN
8 AUTO-CONTROL PACKAGE:
PROGRAMMED PILOT BURNER
9 SELF-COMPENSATING INSTRUMENTATION-CONTROLS
10 WET-SCRUBBER PACKAGE:
STAINLESS STEEL, CORROSION-FREE WET SCRUBBER; GAS QUENCH
11 EXHAUST FAN AND STACK
12 RECYCLE WATER, FLY-ASH SLUDGE COLLECTOR
13 SUPPORT FRAME
14 SUPPORT PIERS
15 AFTERBURNER CHAMBER
16 PRECOOLER
Figure 12. Portable Rotary Kiln Incineration Units
1672
-------
Process Design. Specific data on rotary kiln incinerator design para-
meters are scarce. This is due to the fact that incineration is a relatively
new application for rotary kilns. Additionally, information of this type
is generally considered proprietary by manufacturers.
Information sources indicate that rotary kiln incinerators generally
have a length to diameter ratio (L/D) between 2 and 10. Smaller L/D ratios
result in less particulate carry over. Rotational speeds of the kiln are
usually much slower than those for kilns which are utilized as calciners
or dryers and are on the order of 1 to 5 feet per minute measured at the
kiln periphery. Both the L/D ratio and the rotational speed are strongly
dependent upon the type of waste being combusted. In general, larger L/D
ratios along with slower rotational speeds are used when the waste material
requires longer residence times in the kiln for complete combustion.
The residence time and combustion temperature required for proper in-
cineration is totally dependent upon the waste materials combustion char-
acteristics. Combustion temperatures usually range from 1,600 F to 3,000 F.
Required residence times vary from seconds to hours. For instance, a
finely divided propellant may require 0.5 seconds while wooden boxes,
municipal refuse, and railroad ties may require 5, 15 and 60 minutes res-
pectively.1701
When it is desired to increase the capacity of an existing kiln in-
cinerator, consideration should be given to the following changes:
(1) Increase charge to the kiln.
(2) Increase temperature and quantity of combustion gases.
(3) Decrease quantity of air in excess of combustion needs.
(4) Increase speed of rotation of kiln.
(5) Increase capacity of feeding and discharge mechanisms.
(6) Decrease moisture content of feed material.
(7) Increase temperature "of feed material.
144
-------
(8) Preheat all combustion air.
(9) Reduce leakage of cold air into kiln.
(10) Increase stack draft by increasing height or by use of jets.
(11) Install instrumentation to control the kiln at maximum-capacity
conditions.
Efficient air seals are essential for the controlled and economical
operation of kiln incinerators. They reduce outside air entrance; certain
types effectively prevent entrance of all outside air. The inflow of air is
the result of the kiln incinerator operating under reduced pressures which
are caused by downstream induced draft fans and thermal lift from the stack.
This reduced pressure is necessary to ensure against any leakage of undesir-
able material to the surroundings.1673'1701
The simplest type of air seal is a floating T-section ring mounted on
a wearing pad around the feed end of the kiln shell. The web of the T-ring
is confined within circular retainer plates (Figure 13). The floating-type
discharge-end air seal consists of a circular bar which floats on a wearing
pad and which can be moved to provide the desired operating clearance bet-
ween air seal and support. The floating ring and the fixed portion of these
seals can be furnished with renewable wearing surfaces. Air infiltration
through this type of seal is usually less than 10 percent. For further re-
duction of air infiltration, lantern-ring-type floating seals, pressurized
with inert gas or stack gases, are employed.1673*1701
Process Economics. Capital and operating cost data on rotary kiln
incineration systems are scarce. The installed capital investment will
vary significantly depending upon the type and quantity of waste being
incinerated, the quantity and sophistication of water and air correction
equipment, waste pretreatment equipment, materials of construction and the
extent of heat recovery equipment. Operating costs are mostly dependent
upon the amount of secondary fuel required, replacement of refractory
linings (usually about once per year), heat recovery and labor.
145
-------
(a)
T RING
WEARING PAD
RETAINER PLATES
(b)
(a) SINGLE - FLOATING - TYPE - FEED- END AIR SEAL
(b) SINGLE - FLOATING - TYPE AIR SEAL ON AIR - COOLED TAPERED-FEED END
Figure 13. Kiln Seal Arrangements
1673,1701
146
-------
Uninstalled costs of the rotary kiln itself are reported to run between
$30 and $60 per cubic foot of kiln.1674*1701 Installation Is generally about
200 percent of the purchased cost.1674 Kiln maintenance averages 5 to 10
percent of the total installed cost per year but is dependent largely on the
life of the refractory lining.1673 These costs do not take into account
secondary combustion chambers, heat recovery equipment or air correction
equipment.
Installed costs for large municipal type rotary kiln incineration systems
(as discussed in the section on Operation Principle) are on the order of
$10,000 per daily ton of feed capacity.0582 This cost includes waste heat
broilers utilized for steam generation. The installed cost of relatively
small industrial type rotary kiln incinerator systems (as presented in
Figure 13) range from $2,500 to $5,000 per daily-ton of feed capacity,
depending on the specific application.
Process Modifications.°053'0582»1701 Basically, the only process mod-
ification utilized in rotary kiln incineration is waste heat recovery
(Figure 14). This practice is seldom followed in industrial and military
applications due to the expense of heat recovery equipment and the fluctu-
ations incurred in both waste feed quantity and composition. There have
been instances however, when waste heat boilers have been used to recover
heat from gaseous effluents where there is need for steam elsewhere on the
industrial site. In these cases, the incinerators also function as boilers
and constant heat output must be maintained through the use of auxiliary
fuels.
Large municipal installations generally utilize heat recovery either
for power generation or preheating of combustion air. In the latter case,
a significant increase in incineration capacity can be realized. These
alternatives are generally economically attractive because of the large
volumes of waste(refuse) and the relatively constant heat content of the
waste (usually 4800 to 6500 Btu/pound).
347
-------
SOLID WASTE
SECONDARY FUEL
AND/OR GASEOUS
OR LIQUID WASTES
ROTARY KILN
INCINERATOR
COMBUSTION
AIR
(A) NO HEAT RECOVERY
SOLID WASTE,.,
SECONDARY FUEL
AND OR GASEOUS
OR LIQUID WASTFi
SOLID RESIDUES
TO ULTIMATE
DISPOSAL
EFFLUENT
TO SCRUBBERS
AND STACK
STEAM TO POWER
GENERATOR OR OTHER
INPLANT USE
ROTARY KILN
INCINERATOR
EFFLUENT
TO SCRUBBERS
AND STACK
COMBUSTION
AIR
(B) WITH A WASTE HEAT BOILER
BOILER
SOLID
RESIDUES TO
ULTIMATE
DISPOSAL
WATER
COMBUSTION
AIR
SOLID WASTE.
SECONDARY FUEL
AND-OR GASEOUS
OR LIQUID WASTES
COMBUSTION
AIR
ROTARY KILN
INCINERATOR
SOLID
RESIDUES TO
ULTIMATE
DISPOSAL
EFFLUENT
TO SCRUBBERS
AND STACK.
RECUPERATOR
(C) WITH COMBUSTION AIR PREHEATING
Figure 14. Heat Recovery Options
148
-------
Process Applicability. The rotary kiln incinerator is generally ap-
plicable to the ultimate disposal of any form of combustible waste material
and represents proven technology. It can incinerate combustible solids
(including explosives), liquids (including chemical warfare agents), gases,
sludges and tars. For that reason, it is very likely that a National
Disposal Site would contain a large industrial type rotary kiln incinerator
installation such as the one operated by the Dow Chemical Company at Midland,
Michigan (discussed in the Section on Operation Principle). The National
Disposal Site facility would require the addition of highly efficient
secondary abatement equipment such as scrubbers and precipitators.
Liquid Waste Combustors
Liquid waste combustors are versatile units which can be used to dispose
of virtually any combustible liquid waste with a viscosity less than 10,000
SSU. There are a wide variety of liquid waste combustors presently market-
ed, however they are generally classified as being either horizontal or
vertical incineration units. These units have found wide usage throughout
the manufacturing industries.
Operation Principle. Before a liquid waste can be combusted, it
must be converted to the gaseous state. This change from a liquid to a
gas occurs inside the combustion chamber and requires heat transfer from
the hot combustion product gases to the injected liquid. In order to effect
a rapid vaporization (i.e., increase heat transfer), it is desirable to
increase the exposed liquid surface area. Most commonly the amount of
surface exposed to heat is increased by finely atomizing the liquid to
small droplets of 40u size or smaller. This atomization can be achieved
mechanically, by two phase flow, or by a combination of both methods. It
is usually achieved in the liquid burner directly at the point of fuel and
air mixing.
149
-------
Atomization is the heart of any good liquid incinerator. Mechanical
means of atomization include rotary cup and pressure atomization. The
rotary cup consists of an open cup mounted on a hollow shaft. The cup is
spun rapidly and liquid admitted through the hollow shaft. A thin film
of the liquid to be atomized is centrifugally torn from the lip of the cup
and surface tension reforms it into droplets. To achieve conical shaped
flames an annular high velocity jet of air (primary air) must be directed
axially around the cup. If too little primary air isvadmitted the fuel
will impinge on the sides of the incinerator. If too much primary air
is admitted the flame will not be stable, and will be-blown off the cup.
For fixed firing rates, the proper adjustment can be found and the unit
operated long periods of time without cleaning.
Pressure atomizing may take many forms. The familiar garden hose
nozzle is one example. 'Most commonly the liquid is given a direction by
internal tangential guide slots to the center of the nozzle and then re-
leased axially through an orifice. Good atomization can be achieved "at
moderate pressures (100 to 150 psi). Disadvantages include a limited -
variable flow range at low pressures and, especially in the smaller sizes,
a tendency to plug with foreign matter. Large sizes are reasonably free
from this problem.
Two-fluid nozzles may be used to impinge a compressible gas on a
liquid to tear it into small particles. The compressible gas may be air,
nitrogen, steam, etc. Steam is quite commonly used as a low cost source
of compressed gas. These nozzles may take three forms: internal mix,
external mix or sonic.
As the name implies, internal mix nozzles impinge the gas and liquid
before it is sprayed from the nozzle. External mix nozzles impinge jets of
gas and liquid together;outside of the nozzle body. Sonic nozzles (Fig"ure
15) use the compressed gas to create high frequency sound waves which are
directed on the liquid streams. The liquid passage is -large in diameter
and requires little pressure drop. It can handle slurries or large particles
without pluggage. Most two-phase nozzles can operate long periods without
150
-------
BODY
ATOMIZING
WASTE
FEED
REVERSERAND
FEED PASSAGE
\
RESONATOR
i
Figure 15. Typical Sonic Nozzle
0304
151
-------
difficulty and without cleaning. A commor consumption figure is 1/2 scfm
of compressed gas per gph of fluid atomized.
Liquid burners require considerably more turbulence and time to com-
plete combustion than do gas burners. To complete combustion violent
turbulence of the droplets is desirable, and the larger the particles, the
greater distance they will go before being completely vaporized and burned.
For this reason, forced draft units, if well designed, will have better com-
bustion characteristics than natural draft units. Burners must also be
located to prevent flame impingement on walls and, in the case of multi-
burner units, interference with one another. While multiple atomizers
can be located within a single air register, the performance will suffer,
and combustion volume must be added to offset this characteristic. When-
ever possible, the number of liquid streams should be minimized.
Liquid streams can carry impurities of every sort. Futhermore, they
may be highly viscous, which makes handling and atomizing difficult.
Liquids should generally have a viscosity of 10,000 SSU or less to be
satisfactorily pumped and handled in pipes. For atomization, they should
have a maximum viscosity of 750 SSU. If the viscosity exceeds this value
the atomization may not be fine enough, and the resultant droplets of un-
burned liquid may cause smoke or other unburned particles to leave the
unit. Viscosity can usually be controlled by heating with tank coils or
in-line heaters. Should gases be evolved in any quantity before the desired
viscosity is reached, they may cause unstable fuel feed and burning. If
this occurs, the gases should be trapped and vented safely, either to the
incinerator or elsewhere. If preheating is not feasible, a lower viscosity
and miscible liquid may be added to reduce the viscosity of the mixture.
Prior to heating a liquid waste stream, a check should be made to
insure that undesirable preliminary chemical reactions such as polymerization,
nitration, oxidation, etc., will not occur. Should these occur, it may be
more desirable to fill disposable containers with the liquid and treat
them as solids. Other preparatory steps may include filtration, degassing,
pressurizing, neutralizing, storage, mixing, etc. In every one of these
steps care must be employed to see that undesired and harmful results do not
152
-------
occur. Pump and piping materials of construction must be suitable for the
liquids encountered. Heated liquids that can solidify or become too viscous
should have jacketed or traced piping. Provision should be made to clean
out the piping and equipment when long shutdowns occur. This is usually
done by purging with steam. Certain atomizing nozzles should always be
blown clear with steam whenever flow is stepped. If not, the residual
heat in the incinerator may cause thermal cracking of the liquid remaining
in the nozzles, resulting in partial or complete pluggage.
Process Design. There are basically two forms of liquid waste incin-
erators; vertically and horizontally fired units. Units, regardless of
form, usually operate at temperatures ranging from 1,200 F to 3,000 F
(most units operate around 1,600 F) and residence times ranging from 0.5
to 1.0 second. Most units have combustion chamber volumes which provide
for a heat release of approximately 25,000 Btu/hr-ft3, however, the vortex
type liquid combustor has an unusually high heat release of about 100,000
Btu/hr-ft3.
A typical horizontally fired liquid waste incineration system is pre-
sented (Figure 16). This particular system is the one operated by the Dow
Chemical Company at their Midland, Michigan facility. The unit is a 81
million Btu/hr incinerator which has a combustion chamber 35 ft. long and
10 ft square in cross section. Residue are fed to the unit through a com-
bination of four dual-fired nozzles. Combustion gases are quenched in a
spray chamber, followed by a high-pressure-drop venturi scrubber, and a
cooler/mist-eliminator. About 1000 gpm of water is recycled from the
primary tanks to the wastewater treatment facilities to furnish scrubbing
water. This water flows back to the wastewater plant for treatment.
About 1,100 hp. is required for this unit.1002
The majority of the liquid wastes treated in the Dow unit are solids
at room temperature and must be kept hot in order to remain liquid. Many
residues are chlorinated and can contain as high as 50 percent chlorine, plus
several percent of ash in the form of Fe, Ca, Mg, Na, oxides and chlorides J002
153
-------
LIQUID WASTES FROM PLANT
V
T
[Of
a
[AGE
o 1 olo
1
MEI
ST
SEPARATE TANKS FOR
HIGH AND LOW
MELTING-POINT LIQUIDS
STRAINER
STACK 100 FT. HIGH
6 FT. 6 IN. 1.0.
4 FT. 6 IN. I. D. OUTLET
LINED WITH ACID-RESISTING
PLASTIC
ran
Ui
VENTURI SCRUBBER LINED WITH
ACID RESISTING PLASTIC
RECYCLED
WASTE
WATER
BURNING
TANK
WASTE-TAR
FEED
NATURAL
GAS
ATOMIZING
BLOWER
RELIEF
STACK
(CLOSED
DURING
OPERATION)
TEMPERING
AIR BLOWER
>•>. 10,000
I OJ CU FT /MIN.
lr»"
WATER
300 GPM.
\
RECYCLED
WASTE
WAfER
1,000 GPM
SPRAY
CHAMBER
COMBUSTION AIR BLOV/ER
13,000 CU. FT./MIN.
. 75 HP.
TOTAL AIR, 26 LB./LB WASTE
TEMPERING
AIR BLOV/ER
10,000
CU. FT MIN.
25 HP.
WATER
2,300GPM.
pH 1 0
INDUCED-DRAFT FAN
2,600 LB./MIN.
45,000 CU. FT./MIN.
600 HP.
WATER
240 GPM.
pH 1.0
WASTE TAR FEED AVG. 10GPM.
13,00 BTU. 'LB.
TEMPERATURE 80-1000C
VISCOSITY 150 SSU
5 PSI FEED
4 BURNERS, COMBUSTION
GAS AND TAR NOZZLES
5/16 - IN ORIFICE
Figure 16. Horizontally Fired Liquid Waste Incineration
-------
A typical vertically fired liquid waste incinerator is presented
(Figure 17). This particular unit is designed and marketed by the Prenco
Division of Pickands Mather and Company. It is a versatile system in that
it can be brought up to operating temperature (1,600 to 3,000 F, depending
on type of waste material to be destroyed) in one to two hours with minimal
fuel requirements. This quick warm-up permits periodic rather than con-
tinual operation.
The Prenco vertical combustor operates in the following manner. A
mixture of auxiliary fuel (usually natural gas) and high pressure air
are first fed into the vertical retort to bring it up to proper waste de-
composition temperature. When the retort reaches the correct temperature,
as determined by the temperature measuring instruments, fuel flow is mod-
ulated and waste is admitted to the air-waste entrainment compartment.
From there the aerated waste is fed into a turbulence compartment where
it is mixed with more high pressure air and injected into the high-tem-
perature vertical retort. Here the process breaks down the waste by
molecular dissociation, oxidation, and ionization. The gases and any
inert particles produced flow vertically through the air cone and out of
the top of the retort.0976
Decomposition efficiency is greatly increased through the injection of
pressurized air at a point near the top ot the retort through ports
in a specially designed refractory module. The air cone, which serves as
a fuel saver, increases decomposition efficiency by increasing heat re-
tention. It also provides additional air for an after-burner effect.
In addition, the air cone reduces the temperature of the decomposed
effluent to about650 F. As a result, scrubbers and effluent test equipment
can be utilized if desired.0976
The Prenco unit utilizes air pretreatment. Intake of air from the
top of the upper nacelle causes it to be pre-heated as it travels down
the outer wall of the decomposition chamber to both the turbo-blower and
after-burner fans. The use of preheated air significantly increases de-
composition efficiency and economy of operation.
155
-------
EFFLUENT DIRECTLY TO ATMOSPHERE
OR TO'SCRUBBERS AND STACK
FREE STANDING
INTERLOCKING REFRACTORY
MODULES
TEMPERATURE MEASURING
INSTRUMENTS ,
UPPER NACELLE
TURBO-BLOWER
IGNITION CHAMBER
HIGH VELOCITY
AIR SUPPLY
AIR-WASTE ENTRAINMENT
COMPARTMENT
WASTE LINE
FRESH AIR INTAKE
FOR TURBO-BLOWER
AND AFTERBURBER FAN
AIR CONE
DECOMPOSITION CHAMBER
DECOMPOSITION STREAM
AFTER-BURNER FAN
FLAME SENSITIZER
TURBULENCE COMPARTMENT
LOWER NACELLE
AUXILIARY FUEL LINE
TUBULAR SUPPORT COLUMNS
ELECTRICAL POWER LINE
Figure 17. Typical Vertically Fired Liquid
Waste Incinerator^976
156
-------
A fairly unique form of liquid waste incinerator is the vortex com-
bustor (Figure 18). Its unusual characteristic is its high heat release
capability (about 100,000 Btu/hr-ft ). The vortex combustor is a cylindrical
furnace which is tangentially fired with a modified oil burner. In operation,
the furnace is preheated for 1 hr. to a temperature of 800 to 1000 F.
Operating temperature is 1,200 to 1,600 F, with 20% excess air. Liquid
wastes, fuel gas and primary air pass through a hot ignition tunnel. Tan-
gential firing creates a vortex of hot gas and primary air that flow upward
through the hot combustion chamber. As the gases rise, preheated high-
velocity secondary air is Introduced from tangential tuyeres, maintaining
the vortex. The high heat release of this unit has resulted in some slagg-
ing and erosion of the refractory. '
Process Economics. Installation and operating costs will vary signif-
icantly depending upon the type and quantity of waste to be processed, the
amount and the sophistication of any water and/or air correction equipment
required, waste pretreatment requirements, materials of construction and
the extent of heat recovery. Liquid waste incineration costs are reported
to range between $1- and $100 per 1,000 gal. of waste incinerated depending
upon system complexity.0534'1661
Process Modification. The primary process modifications utilized in
liquid waste incineration are waste heat recovery options and burner design
options. The principle heat recovery options are primary combustion air
preheat through heat exchange with the hot gaseous effluent and waste heat
boiler utilization (Figure 19). Waste heat boilers are generally used only
when there is a demand for steam elsewhere on the industrial site and further-
more, heat recovery is any form is usually only considered economical for
large installations.1460'1703
157
-------
ANNULAR SPACE FILLED
WITH AIR UNDER
PRESSURE FOR TUYERES
BAFFLE SHELL
AIR TUYERES
EFFLUENT TO SCRUBBERS
AND STACK
REFRACTORY WALL
TUYERE AIR SHELL
AND PLENUM
REFRACTORY WALL
COOLING AIR PORTS
CAST IN REFRACTORY SLAB
AIR TUYERES
COMBUSTION AIR
TO TUYERES
REFRACTORY
COOLING AIR
COMBUSTION
AIR
BURNER
NOZZLE
GAS BURNER
RING
COOLING AIR
(FORCED DRAFT)
TUYERE AIR SHELL
BAFFLE SHELL
Figure 18. Vortex Liquid Waste Incinerators0285'05
158
-------
AUXILIARY
FUEL
LIQUID
WASTE
PREHEATED AIR
LIQUID EXCHANGER]
COMBUSTOR
AIR
(A) COMBUSTION AIR PREHEAT
STACK
STEAM
AIR
AUXILIARY
FUEL
LIQUID
WASTE
LIQUID
COMBUSTOR
WATER
STACK
WASTE HEAT BOILER
(B) WASTE HEAT BOILER UTILIZATION
Figure 19. Heat Recovery Options
1703
159
-------
The other major process modification is that of utilizing various
types of burners for specific applications. Some liquid incineration units
utilize very simple burners which are no more than a set of pipes; one
injecting the combustible liquid waste under pressure and the other inject-
ing air. This configuration is generally not very efficient and is usually
very specific in application (i.e., designed for a specific waste material
with specific characteristics and feed rate). More sophisticated burners
such as the John Zink Series DB-0 liquid waste burner, are designed for
combination firing of auxiliary fuel gas with waste liquid and waste gas
or waste liquid only. This type of burner uses steam to atomize the waste
liquid and can handle liquids and slurries with viscosities up to 1,000 SSU.
Inlet liquid pressures are variable (40 to 300 psi) as are atomizing steam
requirements (.15 Ib to .4 Ib of steam per pound of waste) depending upon
the characteristics of the waste liquid. These burners may be equipped
_, , ^ . . .„ 1456,1460,1702
with pilot burners and electric igmtors.
Another type of complex burner is the TRW Combustor, designed and
marketed by TRW Systems. It utilizes a central element injection technique
which was first developed for rocket engines and has subsequently been
adapated to the disposal of hazardous liquid wastes on a pilot scale.
The burner has been used to combust a wide range of materials- including
solid waste, liquids and gaseous fuels. Some of the reactants which have
been combusted in this type burner are presented (Table 9).
The basic injector design is a single central element configuration
wherein air is injected as a continuous cylindrical sheet which impinges
with fuel jets injected radially outward. The air and fuel mixture is
then further mixed by means of a deflector on the control element. This
deflector serves both to complete the mixing process and as a flame holder.
This burner design produces an externally premixed flame with a short
reaction zone.
Due to the premixed flame and short reaction zone, the TRW burner
has the added feature of reducing NO formation. It has been demonstrated
160
-------
TABLE 9
TRW BURNER APPLICATIONS
Reactants
Indonesian Crude
Oil /Air
Kerosene/Ai r
LPG/LF2/L02
N2H4/C1F3,C1F5
UDMH/N-0.
State
Liquid-gas
Liquid-gas
Gas-liquid
Liquid-liquid
Liquid-liquid
Combustor
Pressure
(psia)
14.7
14.7
100 to 50
300
50' to 300
Supply
Temperature
(F)
70
70
-300 to 70
70 Fuel/-300 Ox
40 to 90
161
-------
while using fuel oil as a fuel, that KOX concentrations are'cut by as much
as 75 percent when the proper amount of excess air Is used (Figure 20).
Process Applicability. Liquid waste Incinerators are generally ap-
plicable to the ultimate disposal of most forms (including dilute) of com-
bustible liquid waste materials and represent proven technology. Some of
the materials currently being disposed with this type incinerator are
presented (Table 10).
Because of their versatility, It is likely that some form of liquid
waste Incinerator (as discussed 1n the Section on Process Design) would be
an Intergal part of a National Disposal Site.
Open-Pit Incineration0582'0285
Open pit incinerators have been used to dispose of high heat content
solids and liquids. These incinerators solve the problem of high heat flux
by eliminating enclosure. Their chief drawbacks are the lack of confinement
of combustion product effluents and relatively high participate emissions.
Operation Principle. Open-pit incinerators vary from the pedestal-
mounted oil burner used by Union Carbide to the Du Pont pit (Figure 21).
The Union Carbide installation burns organic liquids containing, up to 25
percent water without visible smoke. The installation consists of burners
firing horizontally and mounted about 5 1/2 ft. above grade. The firing
area is surrounded by earthworks for personnel protection. Heat Is dis-
sipated by direct convection and radiation. By the very nature of the
design, there is always excess air.
The open-pit incinerator was orginally developed at Du Pont for the
safe destruction of nitrocellulose that presents an explosion hazard in
a conventional closed incinerator. The incinerator has an open top and
an array of closely spaced nozzles that create a rolling action of high-
velocity air. over the burning zone (Figure 21). Very high burning rates,
long residence times leading to complete combustion, and high flame
temperatures are achieved. Visible smoke is readily eliminated and smuts
1G2
-------
u
O
Z
400
_ 200
Q.
Q.
z
g
1
UJ
u TOO
O
80
60
40
rw»
COMMERCIAL BURNER
No. 2 OIL
2 X 106 BTU/HR
COMMERCIAL BURNER
No. 2 OIL, 10% FLUE GAS RECYCLE
105 BTU/HR
TRW OIL FIRED BURNER
No. 2 OIL
2 X 106 BTU/HR
10
20 30 40
EXCESS AIR (PERCENT)
50
60
70
Figure 20. NOX Concentration as a Function of Excess Air
-------
LOADING
RAMP
\
AIR
SPACE-
RAMP RETAINING-
WALL
PROVIDE COOLING
AIR ADMISSION
AT CORNERS
AIR
NOZZLE
;>
s/
COOLING AIR
EXIT PORTS
rq
\
\
\
\
\
\
y
\
\
\
\
\
\
\
\
9 IN WALL
9IN.X36IN.
REFRACTORY
STEP
TILE FLOOR
— 8FT-OIN.
AIR
HEADER
NOTE:
NOMINAL CAPACITY
IS3.4(10)6BTU/HR
PER FOOT OF LENGTH
FAN
FAN
DRIVE
EXISTING GRADE
18 IN. WALL
FOOTINGS5
Figure 21. Du Pont Open-Pit Incinerator
0235
-------
TABLE 10
LIQUID WASTES CURRENTLY BURNED IN LIQUID WASTE INCINERATION
Separator Sludges
Skimmer Refuse
Oily Waste
Detergent Sludges
Digester Sludges
Cutting Oils
Coolants
Strippers
Phenols
Wine Wastes
Potato Starch
Vegetable Oils
Washer Liquids
Still & Reactor Bottoms
Soap & Detergent Cleaners
Animal Oils & Rendering Fats
Cyanide & Chrome Plating Wastes
Lube Oils
Soluble Oils
Polyester Paint
PVC Paint
Latex Paint
Thinners
Solvents
Polymers
Resins
Cheese Wastes
Dyes
Inks
165
-------
are contained by proper screening. Oversized wastes and plastics that
create problems in conventional Incinerators are easily destroyed in the
open-pit incinerator. It should be noted that the concentration of partic-
ipates is slightly higher than conventional incinerators, and there is no
way to clean the exit gases. Although these pit incinerators are used,.for
liquid wastes, they are more efficient for solid wastes, especially rubber
and plastic.
Process Design. The incinerator consists of a rigid shell of either
reinforced-concrete or steel, lined with refractory on the floor and walls.
Empirical and theoretical calculations indicate the optimum width to be
8 ft. between refractory walls. The capacity is determined by length-
usual ly between 8 and 16 ft. The pit is about 10 ft. with cleanout doors
located at either end. Normally, a screened enclosure is placed over the
pit to contain large airborne particles and for insect and rodent control
when burning garbage.
The over-fire air is supplied from a manifold running along one edge
of the pit, with alternating 2- and 3-inch nozzles directed downward at an
angle of 25 to 35 deg. across the incinerator. Charging is from' the oppo-
site side of the nozzles from a leading ramp. The pit should be oriented
so that the loading ramp is located upwind. The high-velocity air jets
create turbulence in the burning zone, and the excess air aids complete
combustion. When the equipment is properly operated, the air pattern
creates a sheet of fTame under the air manifold on the back wall, rolling
the flame across the top of the pit. Parti oilates and unburned gases are
largely returned to the burning-zone more or less eliminating smoke. Smoke
intensity rarely exceeds Ringelmann #1 when properly operated.
Operating capacity of the pit depends on the lower heating value of the
feed, combustion character!" si tics, quantity of overfire air, size and con-
figuration of the pit, and method of charging. Not less than 100 percent
excess air is required, and 300 percent is usual. Du Font's criteri are:
166
-------
850 cu.ft./min. of overfire air at 11 in. of water column per foot of length
for standard trash (5,000 Btu/lb).
The incinerators are charged intermittently by dump trucks, although
hydraulic rams and skip hoists have been used. The rate of charge depends
on the material being burned, in order to meet the heat-release capability
of the pit. High-heating-value materials such as plastics are fed in small
quantities at frequent intervals. The operator's skill is the major factor
in minimizing emissions while maintaining a high burning rate.
Process Economics. Direct operating costs are low. Two men can
operate two pits. The only other costs are for energy to drive the blower
and operate the loader and any cleanout device. No auxiliary fuel is used,
as lighting off a small amount of combustible material will ignite the pit.
Maintenance is slight and largely consists of repair of the refractory.
Capital cost is low. An average price for a commercial unit 16 ft
long, 8 ft wide by 10 ft deep, completely installed, including a covered
storage building for the waste and a screened enclosure for the pit is
about $65,000. The capacity is 5,000 Ib/hr of low heat-release material,
and about half that for high heat-release material.
Process Applicability. A variety of wastes have been burned in the
pit incinerator. It readily accepts heavy timbers, cable reels and con-
struction wastes. It burns plastics and similar high heat-release materials
that might detonate, or erode the refractory in a closed unit. It effectively
handles numerous types of manufacturing and process wastes both liquid and
solid, plant trash and rubber wastes.
Although the open-pit incinerator is currently used industrially, it
Is not recommended for use at a National Disposal Site because of the
associated lack of effluent control. This lack of control might result
in emissions to the surroundings of harmful combustion products such as
167
-------
chlorides, fluorides, cyanides, sulfur compounds, carbon monoxide, or any
parti ally"combusted waste material.
Open Incineration1688'1689
Open Incineration Is the burning of waste materials on open land
without the use of combustion equipment. This form of Incineration Is
utilized mainly for the disposal of waste or excess high explosives. It
Is generally unacceptable for the disposal of other forms of waste because
of the associated lack of combustion product effluent control.
Process Description. A current disposal technique utilized for many
high explosive wastes such as TNT, Comp B-3, LX-09, as well as wet explosive
machining waste Is open burning. A typical open burning operation (conducted
at the rate of about 2,000 1b per week) Is to place the waste explosive and
explosive contaminated waste on an asbestos pad covering a flat gravel base
In a remote open area of the plant grounds. The wastes are thoroughly wet
down with fuel oil and Ignited from a safe distance by the use of a bridge-
wire and lead. Considerable black smoke along with NOX> CO and HF are
evolved (Table 11) during operation and are emitted directly to the atmo-
sphere. These emissions are the result of uncontrolled combustion temper-
ature, Incomplete combustion due to the Inability of oxygen to efficiently
mix with the waste, and the Inability to effect sufficient residence time
of the generated particulate at elevated temperature. Because of the emis-
sion problem, there Is currently an effort to develop combustion units which
are applicable to explosives and Incorporate effluent scrubbers.
Process Applicability. Open burning is not considered to be an adequate
form of waste disposal because of the associated loss of gaseous effluent
control. Although open burning Is currently utilized for the disposal of
explosives and explosive wastes, It 1s anticipated that this practice will
cease when new technology 1s developed for this application.
168
-------
TABLE 11
POLLUTION EMANATING FROM THE BURNING OF TNT, COMP B-3 AND LX-09
Emitted from
Burning 3.8
Pollutant Tons of TNT
Hydrocarbons
Carbon Monoxide
Oxides of Nitr-
ogen
Hydrogen Fluoride
Soot
4 Ib
213 Ib
570 Ib
0
684 Ib
Emitted from
Burning 3.8
Tons of Comp B-3
0
19 Ib
141 Ib
0
0
Emitted from
Burning 3.8
Tons of LX-09
0
4 Ib
110 Ib
23 Ib
0
169
-------
Multiple Chamber Incinerators0582'°862
The multiple chamber incinerator has been employed by both municipal
and industrial facilities for solid waste disposal.
, «
The configuration of modern multiple chamber incinerators falls into
two general types (Figures 22 and 23). These are the retort type, named
for the return flow of gases through the "U" arrangement of component
chambers, and the in-line type, so-called because the component chambers
follow one after the other in a line. Essential features that distinguish
the retort type of design are as follows:
(1) The arrangement of the chambers causes the combustion gases to
flow through 90-degree turns in both lateral and vertical
directions.
(2) The return flow of the gases permits the use of a common wall
between the primary and secondary combustion stages.
(3) Mixing chambers, flame ports, and curtain wall ports have
length-to-width ratios in the range of 1:1 to 2.4:1.
(4) Bridge wall thickness under the flame port is a function of
dimensional requirements in the mixing and combustion chambers.
This results in construction that is somewhat unwielding in the
size range above 500 pounds per hour.
Distinguishing features of the in-line-type design are as.follows.
(1) Flow of the combustion gases is straight through the in-
cinerator with 90-degree turns only in the vertical
direction.
(2) The in-line arrangement is readily adaptable to in-
stallations that require separated spacing of the
chambers for operating, maintenance, or other reasons.
(3) All ports and chambers extend across the full width
of the incinerator and are as wide as the ignition
chamber. Length-to-width ratios of the flame port,
mixing chamber, and curtain wall port cross
sections range from 2:1 to 5:1.
Each style has certain characteristics with regard to performance and
construction,that limit its application.
170
-------
SECONDARY
AIR PORTS
SECONDARY
COMBUSTION
CHAMBER
MIXING
CHAMBER
FLAME PORT
CURTAIN
WALL PORT
IGNITION
CHAMBER
CHARGING DOOR
WITH OVERFIRE
AIR PORT
CLEANOUT
DOOR
GRATES
CLEANOUT DOOR
WITH UNDERGRATE
AIR PORT
Figure 22. Retort Multiple Chamber Incinerator
.0862
-------
IGNITION
CHAMBER
CHARGING DOOR
WITH OVERFIRE
AIR PORT
FLAME
PORT
SECONDARY
AIR PORT
.CURTAIN WALL
GRATES
SECONDARY
COMBUSTION
CHAMBER
CLEANOUT DOORS WITH
UNDERGRATE AIR PORTS
LOCATION OF
SECONDARY
BURNER
MIXING
CHAMBER
CLEANOUT
DOORS
CURTAIN
WALL PORT
Figure 23. In-Line Multiple Chamber Incinerator
.0862,
-------
Operation Principle. The combustion process in a multiple chamber
incinerator proceeds in two stages-primary or solid fuel combustion in the
ignition chamber, followed by secondary or gaseous-phase combustion. The
secondary combustion zone is composed of two parts, a downdraft or mixing
chamber and an up-pass expansion or combustion chamber.
The two-stage multiple chamber incineration process begins in the
ignition chamber and includes the drying, ignition, and combustion of the
solid refuse. As the burning proceeds, the moisture and volatile components
of the fuel are vaporized and partially oxidized in passing from the ignition
chamber through the flame port connecting the ignition chamber with the mix-
ing chamber. From the flame port, the volatile components of the waste
material and the products of combustion flow down through the mixing chamber
into which secondary air is introduced. The combination of adequate temper-
ature and additional air, augmented by mixing chamber or secondary burners
as necessary, assists in initiating the second stage of the combustion pro-
cess. Turbulent mixing, resulting from the restricted flow areas and
abrupt changes in flow direction, furthers the gaseous-phase reaction.
In passing through the curtain wall port from the mixing chamber to the
final combustion chamber, the gases undergo additional changes in direction
accompanied by expansion and final oxidation of combustible components.
Fly ash and other solid particulate matter are collected in the combustion
chamber by wall impingement and simple settling. The gases finally dis-
charge through a stack or a combination of a gas cooler (for example, a
water spray chamber) and induced-draft system. Either draft system must
limit combustion air to the quantity required at the nominal capacity rating
of the incinerator.
The basic factors that tend to cause a difference in performance in
the two incinerators are (1) proportioning of the flame port and mixing
chamber to maintain adequate gas velocities within dimensional limitations
imposed by the particular type involved, (2) maintenance of proper flame
distribution over the flame port and across the mixing chamber, and
173
-------
(3) flame travel through the mixing chamber, into the combustion chamber.
A retort incinerator in its optimum size range offers the advantage's
of compactness and structural economy because of its cubic shape and re-
duced exterior wall length. It performs more efficiently .than its in-line
counterpart in the capacity range from 50 to 750 Ib per hour. In these
small sizes, the nearly square across sections of the ports and chambers
function well because of the abrupt turns in this design. In retort in-
cinerators with a capacity of 1,000 Ib per hour or greater, the in-
creased size of the flow cross section reduces the effective turbulence
in the mixing chamber and results in inadequate flame distribution and
penetration and in poor secondary air mixing.
No outstanding factors favor either the retort or the in-line con-
figurations in the capacity range of 750 to 1,000 ib per hour. The
choice of retort or in-line configuration in this range is influenced by
personal preference, space limitations, the nature of the refuse, and
charging conditions.
The in-line incinerator is well suited to high-capacity operation but
is not very satisfactory for service in small sizes. The smaller in-line
incinerators are somewhat less efficient with regard to secondary stage
combustion than the retort type is. In in-line incinerators with a capacity
of less than 750 Ib per hour, the shortness of the grate length tends
to inhibit flame propagation across the width of the ignition chamber.
This, coupled with thin flame distribution over the bridge wall, may
result in the passage of smoke from smoldering grate sections straight
through the incinerator and out of the stack without adequate mixing'and
secondary combustion. In-line models in sizes of 750 Ib per hour
or larger have grates long enough to maintain burning across their width,
resulting in satisfactory flame distribution in the flame port and
mixing chamber. The shorter grates on the smaller in-line incinerators
also create a maintenance problem. The bridge wall is very susceptible
to mechanical abuse since it is usually not provided with a structural
174
-------
can
break down the bridge wall in . short time.
hour may
Inc1ner,tors of larger capacity, hoever.
r s
readily standardized
„
r=
«
dnerators as
-*
to the design of smaller units.
Control of the combustion reaction, and reduction In
« irs: •
.«.. «»••
. -
...
— -
ignition chamber burners.
175
-------
TABLE
.
MULTIPLE CHAMBER INCINE>*ATORDESIGN FACTORS
Primary combustion zone:
Grate loading, LQ
Grate area, Afi
Average arch height, H^
Length-to-width ratio
(approx):
Retort
In-line
Recommended value
10 log Rc: Ib/hr-ft where
Rr equals the refuse com-
bustion rate in Ib/hr (refer
to Figure 24.)
R i L • ft2
l\i~ /* *
4/3 (AQ) 4/11; ft (refer to
Figure 25)
Up to 500 Ib/hr, 2:1
over 500 Ib/hr. 1.75:1
Diminishing from about 1.7:1
for 750 Ib/hr to about 1:2
for 2,000 Ib/hr capacity.
Over-square acceptable in
units of more than 11 ft
ignition chamber length.
Secondary combustion zone;
Gas velocities:
Flame port at 1,000 F
Mixing chamber at 1,000 F 25 ft/sec
Curtain wall port at
950 F
55 ft/sec
about 0.7 of mixing chamber
velocity
- 10%
- 20%
- 20%
Combustion chamber at
900 F
Mixing chamber downpass
length, from top of
ignition chamber arch to
top of curtain wall port.
Length-to-width ratios of
flow cross sections:
Retort, mixing chamber,
and combustion chamber
In-line
5 to 6 ft/sec; always less
than 10 ft/sec
Average arch height, ft
Range - 1.3:1 to 1.5:1
Fixed by gas velocities due
to constant incinerator width
- 20%
176
-------
TABLE'12
0862
MULTIPLE CHAMBER INCINERATOR DESIGN FACTORS"0"^ - CONTINUED
Item and symbol
itecommended value
Allowable
deviation
Combustion air:
Air requirement batch-charg-
ing operation
Combustion air distribution:
Overfire air ports
Underfire air ports
Mixing chamber air ports
Port sizing, nominal inlet
velocity pressure
Air inlet ports oversize
factors:
Primary air inlet
Underfire air inlet
Secondary air inlet
Basis: 300% excess air. 50% air
requirement admitted through
adjustable ports: 50% air re-
quirements met by open charge
door and leakage.
70% of total air required
10% of total air required
20% of total air required
0.1 inch water gage
1.2
1.5 for over 500 Ib/hr to
2.5 for 50 Ib/hr.
2.0 for over 500 Ib/hr to
5.0 for 50 Ib/hr
Furnace temperature:
Average temperature,
combustion products
1000 F
- 20 F
Auxiliary burners:
Normal duty requirements:
Primary burner
Secondary burner
3,000 to 10.000J Btu per Ib
A nnn +• 19 nnnl of moisture
4,000 to 12,000\
Draft requirements:
Theoretical stack draft
Available primary air in-
duction draft (Assume
equivalent to inlet ve-
locity pressure.)
Natural draft stack
velocity
0.15 to 0.35 inch water gage
0.1 inch water gage.
Less than 30 ft/sec at 900 F
177
-------
QD
1
z
o
8
0,000
4,000
3.000
2,000
1,000
500
400
300
200
100
50
40
30
20
10
•
1 T-/-
' / •
• / '
///
///
V//
w
x
//
?' — ~r
• /
! /
; / f
* f •
* m •
* m *
* m *
r7
^
FOR DRY REFU
VALUES, USE <
FOR MOIST RE
VALUES, USE •
• g
/
/ 1
/ / /
///
LG = 10 LOG
>E AND HIGH HI
H 10% CURVE (>9
FUSE AND LOW
• 10% CURVE « 1
,f—s
RC
lAI IINv^
000 BTU/LB).
HEATING —
'500 BTU/LB).
10 20 30
GRATE LOADING (Lg) , LB/FT2- HR
40
50
Figure 24. Relationship of Grate Loading to Combustion Rate for Multiple
Thamhar* Tnrinoratnr-c 0862
Chamber Incinerators.
-------
o
u
of
10
6
5
4
3
i
•*!^^«**
*
#
*
..•
IX
F
\
$
Ol
^A
S
([
LU
.*
/
)R
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»
Y(
>, I
^ffi
$Q
V
tEFUSE Ar
JSE + 10%
Ł
n ,
sIDH
CUR
e *
..•'
^
IGh
VE
/
4
3
\\\
c
••'
7
E/
>9
^
.•
(*
-------
The design and construction of multiple chamber incinerators are
regulated in several ways. Ordinances and statutes that set forth basic
building requirements have been established by most, if not all,
i
municipalities. Air pollution control authorities have also set some
limitations in material and construction that must be met, and manufacturers'
associations have established recommended minimum standards to be followed.
The most important element in construction of multiple chamber in-
cinerators, other than the design, is the proper installation and use of
refractories. High-quality materials are absolutely necessary if a reason-
able and satisfactory service life is to be expected. Manufacturers must
use suitable materials of construction since faulty construction may well
offset the benefits of good design. In the choice of one of the many
available materials, maximum service conditions should dictate the type of
lining for any incinerator. Minimum specifications of materials in normal
refuse should include high-heat-duty firebrick or 120 Ib per cubic foot
castable refractory. These materials, when properly installed, have proved
capable of resisting the abrasion, spalling, slagging, and erosion result-
ing from high-temperature incineration.
As the incinerator's capacity and severity of duty increase, superior
refractory materials such as super duty firebrick and plastic firebrick
should be employed. A recent improvement in standard construction has been
the lining of all stacks with 2,000 F refractory of 2-inch minimum thickness.
The grates commonly used in multiple chamber incinerators are made of
cast iron in "Tee" or channel cross section. As the size of the incinerator
increases, the length of the ignition chamber also increases. In the larger
hand-charged incinerators, keeping the rear section of the grates completely
covered is difficult because of the greater length of the ignition chamber.
The substitution of a hearth at the rear of the ignition chamber in these
units has been accepted as good practice. Since surface combustion is the
primary combustion principle, the use of a hearth has little effect upon
conbustion rate.
180
-------
Installation of a sloping grate, which slants down from the front
to the rear of the ignition chamber, facilitates charging. A grate such
as this also increases the distance from the arch to the grates at the
rear of the chamber and reduces the possibility of fly ash entrainment.
Stacks for incinerators with a capacity of 500 pounds or less per
hour are usually constructed of a steel shell lined with refractory and
mounted over the combustion chamber. A refractory-lined reinforced, red
brick stack is an alternative method of construction when appearance is
deemed important. Stacks for incinerators with a capacity of more than
500 pounds per hour are normally constructed in the same manner as those
for smaller units but are often free standing for structural stability.
Stack linings should be increased in thickness as the incinerator becomes
larger in size.
Process Economics. Capital and operating cost data on multiple chamber
incineration units are scarce. The installed capital investment will vary
depending upon the type and quantity of waste being incinerated, the quantity
and sophistication of air correction equipment, and materials of construction.
The relative costs (as of 1968) of incinerator and air pollution control
equipment of various capacities, exclusive of foundations are presented
(Table 13).
Operating costs are mainly a function of labor, power, fuel and
refractory repair and replacement. Multiple chamber units generally can
be operated by one to two men. As of 1968, overall processing costs were
reported as being $15 to $16 per ton of waste incinerated.
Process Applicability. Multiple chamber incinerators are generally
applicable to the ultimate disposal of most forms of combustible solid waste
and represent proven technology. Some of the materials currently disposed
of in this type of unit are general refuse, paper, garbage, wood, phenolic
resins, rubber, wire coatings, acrylic resins, epoxy resins, and polyvinyl
chloride. Although the multiple chamber incinerator is capable of handling
various types of solid wastes, its inability to process liquids, gases, sludges
181
-------
TABLE 13
APPROXIMATE COSTS OF MULTIPLE CHAMBER INCINERATORS*
Capacity Incinerator Wet Scrubber
Lb /Hr Cost. $ Cost. S
100 1,700 3,000
150 2,000 3,600
250 2,700 4,400
500 5,000 6,200
750 9,500 7,600
1,000 12,500 8,800
1,500 20,000 11,200
2,000 25,000 13,200
*Based on 1968 costs.
182
-------
and tars limits the application. Since there are other types of incineration
units available which are much more diverse in application (i.e., rotary kiln
fluidized bed and multiple hearth incinerators), it is doubtful that the
multiple chamber incinerator would be a primary candidate for National
Disposal Site utilization.
Multiple Hearth Incinerators0285'°582•]761
The multiple hearth incinerator (commonly called a Herreshoff furnace)
Is a versalite unit which has been utilized to dispose of sewage, sludges,
tars, solids, gases, and liquid combustible wastes. This type of unit was
Tnitally designed to incinerate sewage plant sludges in 1934. In 1968,
there were over 125 installations in operation with a total capacity of
17,000 tons per day (wet basis) for this application alone. There are
currently numerous industrial installations in operation which are primarily
utilized for chemical sludge and tar incineration as well as activated
carbon regeneration.
Operation Principle. The multiple hearth furnace consists of a refrac-
tory-lined circular steel shell with refractory hearths located one above
the other (Figure 26). Sludge and/or granulated solid combustible waste
feeds through the furnace roof by a screw feeder or belt and flapgate. A
rotating air-cooled central shaft with air-cooled rabble arms and teeth
plows the waste material across the top hearth to drop holes. It falls to
the next hearth and then the next until ash discharged at the bottom. The
waste is agitated as it moves across the hearths to make sure maximum sur-
face is exposed to hot gases. Waste grease and tars are generally fed into
the furnace through side ports.
Liquid and gaseous combustible wastes may be injected into the unit
through auxilliary burner nozzles. This utilization of liquid and gaseous
waste represents an economic advantage since the secondary fuel (e.g.,
natural gas, fuel oil) requirements will be reduced thus lowering operating
costs.
183
-------
QD
WASTE AIR TO
ATMOSPHERE
CLEAN GASES TO
ATMOSPHERE
VACUUM
FILTERS
SLUDGES-
FILTRATE
GREASE AND TARS
BURNERS
(FUEL OIL, GAS,
LIQUID AND GASEOUS WASTE)
AIR
INDUCED
DRAFT FAN
SCRUBBERS
WATER
BLOWER
ASH TO
DISPOSAL
ASH SLURRY TO FILTRATION AND
ASH DISPOSAL
Figure 26. Multiple Hearth Incineration System
1761
-------
The system has three operating zones: the top hearths where feed is
dried to about 48 percent moisture; the incineration/deodorization zone,
which has a temperature of 1,400 to 1,800 F; and the cooling zone, where
the hot ash gives up heat to incoming combustion air. Exhaust gases exit
at 500 to 1,100 F.
Incinerator ash is sterile and inert. Volume discharged from the
bottom hearth is about 10 percent of the furnace feed, based on sludge cake
with 75 percent moisture and 70 percent volatile content in the solids. The
ash usually has less than 1 percent combustible matter, which is normally
fixed carbon. Discharge can be moved hydraulically, mechanically, or
pneumatically, and used as landfill or roadfill.
Current systems include gas cleaning devices on exhaust air. A
number of multiple hearth incinerators are operating without difficulty
in areas with strict air pollution codes. Although the exhuast does not
violate opacity codes, existence of steam plumes has on occasion caused
adverse public reaction.
Process Design. Most multiple hearth incinerators are primarily designed
for sludge disposal. The other forms of waste which are simultaneously fed
to the system are usually considered a heat source to be utilized during
sludge incineration. A heat balance across a multiple hearth furnace must
consider the heat absorbed by: latent heat in free moisture and combustion
moisture, sensible heat in combustion gases, excess air, ash, radiation and
shaft cooling. These quantities are balanced against the heat evolved from
the combustibles in sludge solids and the fuel. Below is a typical analysis
of sludge combustibles.
C 59.8 percent
H2 8.5
02 27.5
N2 4.2
100.0 percent
Calorific value of this sludge is 10,000 Btu/lb.
185
-------
Sludge parameters that have the most influence over Incineration
are moisture content, percent volatiles and inerts, and calorific value.
Moisture is the principal one over which the plant operator has some
control. Minimum moisture is important because of its thermal load on the
incinerator.
Volatiles and inerts, which affect the Btu value of the sludge,
can be controlled to some extent by treatment processes such as degritting,
mechanical dewatering and sludge digestion. Almost all combustibles are
present as volatiles, much in the form of grease. Volatile percentage can
vary a great deal, so equipment must be designed to handle a range of values.
The sizing of a multiple hearth incinerator is dependent upon waste
combustion characteristics (Table 14) and water content. Incinerator
2
burning rates vary from 7 to 12 Ib/ft -hr for sewage plant sludges with
2
the value 7.5 Ib/ft -hr generally accepted as typical. The area referred
to in the burning rate is the total hearth area of the unit. Standard
2
multiple hearth incinerator sizes range from 85 ft of hearth to greater
than 3000 ft of hearth (Table 15). The secondary fuel requirement is
dependent upon the water content of the waste being incinerated. For
instance, a waste sludge with a heating value of 10,000 Btu/lb of volatile
solids which is composed of 60 percent volatile solids,will require about
•3
100 ft of natural gas per ton of wet feed when the moisture content of
3
the sludge is 75 percent. This same sludge will require about 1,200 ft
of gas per ton of wet sludge when the moisture content is 82.5 percent
(Figure 27).
The multiple hearth incinerator is usually operated so that the top
hearth temperature is in the 600 to 1,000 F range, the combustion hearths
are in the 1,400 to 1,800 F range, while the cooling hearths are maintained
in the 400 to 600 F range.
186
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TABLE 14
TYPICAL COMBUSTION VALUES OF WASTE MATERIALS
Material Combustible.% Ash.% Btu/lb.
Grease & scum 88.5 11.5 16,750
Fresh sewage solids 74.0 26.0 10,285
Fine screenings 86.4 13.6 8,990
Ground garbage 84.8 15.2 8,245
Rags 97.5 2.5 8,050
Digested sewage and garbage
solids 49.6 50.4 8,020
Digested sludge 59.6 40.4 5,290
Grit 33.2 69.8 4,000
Note: Where organic polymers can be utilized to condition sludges, rather
than ferric chlorides and lime, the heat value of the sludge cake
can be increased 1,500 Btu/lb to 4,000 Btu/lb of dry solids. The
ash from the furnace will also be reduced by 5 to 20 percent.
187
-------
TABLE 15
STANDARD MULTIPLE HEARTH FURNACE SIZE
1761
Outside
Diameter
4.5 ft
(ID)
7.0 ft
8.5 ft
10.0 ft
13.5 ft
16.0 ft
18.0 ft
19.5 ft
21.5 ft
Hearth area.sq ft
Column height, ft-in.
Shell height, ft-in.
Overall height, ft-in.
Hearth area, sq ft
Column height, ft-in.
Shell height, ft-in.
Overall height, ft-in.
Hearth area, sq ft
Column height, ft-in.
Shell heignt, ft-in.
Overall heignt, ft-in.
Heartn area, sq ft
Column height, ft-in.
Shell height, ft-in.
Overall height, ft-in.
Hearth area, sq ft
Column height, ft-in.
Shell height, ft-in.
Overall height, ft-in.
Hearth area, sq ft
Column height, ft-in.
Snell height, ft-in.
Overall height, ft-in.
Hearth area, sq ft
Column height, ft-in.
Stfell height, ft-in.
Overall height, ft-1n
Heartn area, sq ft
Column heignt, ft-in.
Shell height, ft-in.
Overall neight, ft-in.
Hearth area, sq ft
Column height, ft-in.
Shell height, ft-in.
Overall height, ft-in.
4
Hearth
130
5-0
10-10
16-7
188
6-6
10-8
18-8
390
6-6
11-8
20-8
b73
7-0
13-2
22-11
727
7-0
14-3
24-3
863
8-0
14-4
25-8
1077
8-0
16-1
27-9
6
Hearth
85
4-0
10-6
15-7
125
4-0
11-10
16-1
193
5-0
15-5
21-2
276
6-6
15-1
23-0
575
6-6
16-7
25-6
845
7-0
18-7
28-4
1068
7-0
20-2
30-1
1268
8-0
20-2
31-7
1580
8-0
22-9
34-6
8
Hearth
112
4-0
13-8
18-9
166
4-0
15-5
20-6
256
5-0
20-0
25-9
364
6-6
19-5
27-5
760
6-6
21-5
30-5
1117
7-0
24-1
33-10
1410
7-0
26-0
36-0
1660
8-0
26-1
37-5
2084
8-0
29-6
41-2
10 12
Hearth Hearth
140
4-0
16-10
21-11
208
4-0
19-0
24-1
319
5-0
24-7
30-4
452
6-6
23-10
31-9
944
6-6
26-4
35-3
1305 .
7-0
29-6
39-3
1752
7-0
31-11
41-10
2060
8-0
31-11
43-4
2570
8-0
36-2
47-11
1128
6-6
31-2
40-2
1550
7-0
35-0
44-9
2090
7-0
37-9
47-9
2464
8-0
37-10
49-2
3046
8-0
42-11
54T7
188
-------
Q 1,600
SLUDGE HEAT CONTENT - 10,000 BTU/LB.
VOLATILE SOLIDS
L, 1,400
2 1,200
V.S. = VOLATILE SOLIDS
75 76
77 78 79 80 81 82 83
MOISTURE CONTENT OF FEED, %
Figure 27. Fuel Requirement Variation with Feed Moisture
1761
189
-------
Process Economics. Capital and operating costs for multiple hearth
incinerators will vary significantly depending upon the type and quantity
of waste being incinerated, the sophistication of water and air correction
equipment, waste pretreatment requirements, materials of construction,
secondary fuel requirements, and labor. Total disposal cost per ton of
dry solids fed are reported to range between $8 and $15 while operating
costs generally run between $0.50 and $5.00 per ton of dry solids (Table 16)
depending on the size of the unit.
Process Applicability. The multiple hearth incinerator is generally
applicable to the ultimate disposal of most forms of combustible wastes
and represents proven technology. It can incinerate combustible sludges,
tars, granulated solids, liquids and gases and is especially well suited
to the disposal of spent biological treatment facility sludges. For that
reason, it is very likely that a National Disposal Site, especially one
which contained biological treatment facilities, would contain a multiple
hearth unit.
Flares0285
The fiare type burner has been utilized in many petroleum refineries and
petrochemical plants to incinerate relatively large volumes of combustible
gases and aerosols. Flare burners are of two basic types: the ground flare
and the elevated or tower flare. The ground flare, as its name implies, is
used at ground level where there is sufficient space around the flare 'for
safety purposes to burn waste gas from an oil field operation or similar
source. The tower flare, usually found in refineries, is elevated to keep
the flame well above the level of surrounding process equipment protecting
the refinery against possible fires. Flares are basically open pipes which
discharge a combustible gas directly to atmosphere with the end of the pipe
containing a flame device and a continuous pilot or pilots to ignite the waste
gas. Air for combustion is supplied by the surrounding atmosphere. Steam
injection is often supplied to the flame of the flare to prevent smoking when
190
-------
TABLE 16
--JLTIPLE HEARTH INCINERATION COSTS1761
Sludge incinerated, tons/wk.
(wet basis)
Sludge incinerated tons/wk.
(dry basis)
Operating schedule, hr/wk.
Furnace feed, Ib/hr
Furnace required 10
5
Installed Cost, $ 120,
Weekly fuel cost, S
Weekly power cost, S
Total utility cost, S
Operating cost-5>/ton dry solids
Filtration cost-S/ton dry solids
Maintenance cost-$/ton dry solids
Total disposal cost-t/ton dry solids
28.0
7.0
35
1,600
ft-9 in. OD
Hearth
000.00
27.50
9.00
36.50
5.20
8.00
.70
13.90
56.0
14.0
35
3,200
14 ft-3 in. OD
5 Hearth
185,000.00
45.00
12.00
57.00
4.06
8.00
.60
12.66
139.0
34.75
70
3,960
14 ft-3 in.
6 Hearth
200,000.00
30.00
13.00
43.00
1.24
8.00
.60
9.84
278.0
69.5
70
7,920
OD 18 ft-9 in OD
6 Hearth
310,000.00
45.00
25.00
70.00
1.01
8.00
.50
9.51
2,780.0
695.0
168
33,000
Two- 22 ft-3 in. OD
8 Hearth
750,000.00
50.00
165.00
215.00
0.31
8.00
.40
8.71
Cake moisture
Volatile content
Solids removal
75%
65%, 10,000 Btu/lb volatile solids
90%
-------
burning waste hydrocarbon gases which have more than two carbon atoms.
Flares are affected by atmospheric conditions, especially high winds.
They cannot be considered an infallible method of waste gas disposal be-
cause unburned waste gases often escape from a flare system, but they
are expedient and economical for high-volume discharges of combustible
waste gases.
Operation Principle.0862'1456'1460 From a pollution viewpoint, the
ideal flare is a combustion device that burns waste gases completely and
smokelessly. But, in actual practice, flare utilization introduces the
possibility of smoke and other objectionable gases such as carbon monoxide,
sulfur dioxide, and nitrogen oxides. Some types of flares have been de-
veloped that ensure that combustion is smokeless and in some cases non-
luminous. Luminosity, while not an air pollution problem, does attract
attention to the operation and in certain cases can cause bad public re-
lations. There is also the consideration of military security which non-
luminous emergency gas flares would be desirable.
Smoke, when present, is the result of incomplete combustion. Smokeless
combustion can be achieved by: (1) adequate heat values to obtain the
minimum theoretical combustion temperatures, (2) adequate combustion air,
and (3) adequate mixing of the air and fuel. An insufficient supply of
air results in a smoky flame. Combustion begins around the periphery of
the gas stream where the air and fuel mix, and within this flame envelope
the supply of air is limited. Hydrocarbon side reactions occur with the
production of smoke. In this reducing atmosphere, hydrocarbons crack to
elemental hydrogen and carbon, or polymerize to form hydrocarbons. Since
the carbon particles are difficult to burn, large volumes of carbon parti-
cles appear as smoke upon cooling. Side reactions become more pronounced
as molecular weight and unsaturation of the fuel gas increase. Olefins,
diolefins, and aromatics characteristically burn with smoky, sooty flames
as compared with paraffins and naphthenes. A smokeless flame can be obtained
vlien an adequate amount of combustion air is mixed sufficiently with the
fuel so that it burns completely and rapidly before any side reactions can
192
-------
giving good turbulence at the same time.
rr
weight and fraction of unsaturates in the waste gas.
incineration of hydrocarbons in a typical steam-in-spirated-type
elev t flare results in incomplete combustion of the feed gases. The
results of a field test on a flare unit were reported in tne form of
ratios as follows:
CO • hydrocarbons 2,100.1
C02: CO 243:
These results indicate that the hydrocarbons and carbon monoxide emissions
from a flare can be much greater than those from properly operated boilers
or furnaces.
Other contaminants that can be emitted from flares depend upon the
composition of the gases burned. The most commonly detected emission
is sulfur dioxide, resulting from the combustion of various sulfur com-
pounds (usually hydrogen sulfide) in the flared gas. Toxicity, combined
with low odor threshold, make venting of hydrogen sulfide to a flare an
unsuitable and sometimes dangerous method of disposal. Materials that tend
to cause health hazards or nuisances should not be disposed of in flares.
Compounds such as mercaptans or chlorinated hydrocarbons require special
combustion devices with chemical treatment of the gas or its products of
combustion.
193
-------
Process Design. There are, in general, two types of flares for the
disposal of waste gases: elevated flares and ground-level flares. The
essential parts of a flare are the burner, stack, seal, liquid trap, con-
trols, pilot burner, and ignition system.
Smokeless combustion may be attained through the use of elevated stack
flares which utilize steam injection to provide turbulence and inspirate
air. Three main types of steam-injected elevated flares are in use. These
types vary in the manner in which the steam is injected into the Combustion
zone.
In the first type, there is a commercially available multiple nozzle
which consists of an alloy steel tip mounted on th» top of an elevated
stack (Figure 28). Steam injection is accomplished by several small jets
placed concentrically around the flare tip. These jets are installed at
an angle, causing the steam to discharge in a converging pattern immediately
above the flare tip.
A typical refinery waste gas flare system utilizing a multiple steam
jet burner is-presented (Figure 29). Al.l relief headers from process units
combine into a common header that conducts the hydrocarbon gases and vapors
to a large knockout drum. Any entrained liquid is dropped out and pumped
to storage. Tne gases then flow in one of two ways. For emergency gas
releases that are smaller than or equal to the design rate, the flow is
directed to the main flare stack. Hydrocarbons are ignited by continuous
pilot burners, and steam is injected by means of small jet fingers placed
concentrically about the stack tip. The steam is injected in proportion
to the gas flow. The steam control system consists of a pressure controller,
naving a range of 0 to 20 inches water column, that senses the pressure in
the vent line and sends an air signal to a control valve in the steam line.
If the emergency yas flow exceeds the designed capacity of the main flare,
oackpressure ir the vent line increases, displacing the water seal and
permitting gas flow to the auxiliary flare. Steam consumption of the burner
at a peak flow is auout 0.2 to 0.5 Ib of steam per Ib of gas, depending upon
194
-------
LB
FUEL
STEAM
STACK
GASEOUS
WASTE
PILOT BURNERS
(USUALLY 3, 120° APART)
COMMERCIALLY
AVAILABLE
NOZZLE
STEAM
HEADER
era
FUEL
STEAM
Figure 28. Stack Flare Equipped with Mixing Nozzle
0862
195
-------
CD
STEAM
3 - IN.
STEAM RING
PILOT
MAIN
COLLECTION SYSTEM
HYDROGEN
REACTOR
DROPOUT ^
PETROCHEMICAL
SYSTEM
C
DRIP
TANK
12-FT
WATER
SEAL
CONDENSATE
BLINDS
BY-PASS
5 - IN. WATER^N
SEAL TANK J
CATALYTIC CRACKING COMPRESSORS
20-IN.X
40-FT
MAIN
FLARE
3-IN. NOZZLE v DRAIN
STEAM
PILOT
CZh
*
DRAIN
14-IN. X
15-FT
AUXILIARY
FLARE
Figure 29. Waste Gas Flare System Using a Multiple Steam Jet Burner
-------
the amount and composition of hydrocarbon gases being vented.
A small amount of steam (300 to 400 Ib per hour) is allowed to flow
through the jet fingers at all times. This steam not only permits smoke-
less combustion of gas flows too small to actuate the steam control valves
but also keeps the jet fingers cooled and open.
A second type of elevated flare has a flare tip with no obstruction to
flow, that is, the flare tip is the same diameter as the stack. The steam
is injected by a single nozzle located concentrically within the burner
tip. In this type of flare, the steam is premixed with the gas before
Ignition and discharge. This configuration flare is generally referred
to as an Esso type flare (Figure 30).
A typical flare system serving a petrochemical plant using this type
burner is shown (Figure 31). The type of hydrocarbon gases vented can
range from a saturated to a completely unsaturated material. The in-
jection of steam is not only proportioned by the pressure in the blowdown
lines but is also regulated according to the type of material being flared.
This is accomplished by the use of a ratio relay that is manually controlled,
The relay is located in a central control room where the operator has an
unobstructed view of the flare tip. In normal operation the relay is set
to handle feed gas which is most common to this installation.
In this installation, a blowdown header conducts the gases to a water
seal drum and the end of the blowdown line is equipped with two slotted
orifices. The flow transmitter senses the pressure differential across
the seal drum and transmits an air signal to the ratio relay. The signal
to this relay is either amplified or attenuated, depending upon its
setting. An air signal is then transmitted to a flow controller that
operates two parallel steam valves. The 1-inch steam valve begins to
open at an air pressure of 3 psig and is fully open at 5 psig. The 3-inch
valve starts to open at 5 psig and is fully open at 15 psig air pressure.
As the gas flow increases, the water level in the pipe becomes lower than
the water level in the drum, and more of the slot is uncovered. Thus,
197
-------
3 2-IN.
PILOT BURNERS
(120° APART)
3 IGNITORS
(TYPICAL 3 PLACES)
18 IN.
STEAM-
r
STACK
Figure 30. Esso Type Flare
0862
198
-------
STEAM
LARGE FLOW
—J
FLOW
CONTROLLER
SMALL FLOW
PURGE GAS
PRESSURE SENSOR
INSTRUMENT AIR
o
RATIO
RELAY
WASTE GAS
PRESSURE TAPS
HIGH LOW -»
WATER
FLAME ARRESTOR
D
STACK
SLOTTED
ORIFICE
LOOP
SEAL
Figure 31. Waste-Gas Flare System Using Esso Type Burner
.0862
-------
the difference in pressure between the line and the seal drum increases.
This information is transmitted as an air signal to actuate the steam
valves. The slotted orifice senses flows that are too small to be in-
dicated by a pi tot-tube-type flow meter. The water level is maintained
1-1/2 inches above the top of the orifice to take care of sudden surges
of gas to the sytem.
A 3-inch steam nozzle is so positioned within the stack so that the
expansion of the steam just fills the stack and mixes with the gas to
provide smokeless combustion. This type of flare is probably less
efficient in the use of steam than some of the commercially available
flares but is desiraole from the standpoints of simpler construction
and lower maintenance costs.
A third type of flare, the Sinclair elevated flare (Figure 32)
is equipped with a flare tip constructed to cause the gases to flow
through several tangential openings to promote turbukfce. A steam ring
at the top of the stack ha-; numerous equally spaced holes about 1/8
inch in diameter for discharging steam into the gas stream.
The injection of steam in this latter flare may be automatically or
manually controlled. In most cases, the steam is proportioned automatically
to the rate of gas> flow: however, in some installations, the steam is auto-
matically supplied at maximum rates, and manual throttling of a steam valve
is required for adjusting the steam flow to the particular gas flow rate.
There are many variations of instrumentation among various flares, some
designs being more desirable than others. For economic reasons, all de-
signs attempt to proportion steam flow to the gas flow rate.
There are four principal types of ground level flare: horizontal
vc,»turi, water injection, multijet, and vertical venturi. A typical
horizontal venturi-type ground flare system is shown (Figure 33).
200
-------
2 IN. OD
STEAM RING
GUSSET.^
PLATE \
SEaiON A-A
GAS PILOT
.COVER PLATE
SUPPORT
STRIPS
STEEL
SHROUD
PLASTIC
INSULATION
GAS STANDPIPE
PROTECTING SHROUD
STEAM SUPPLY PIPES
FLAME ARRESTER
Figure 32. Sinclair Type Flare
0862
201
-------
s
STEEL, CEMENT, OR
REFRACTORY WALL
GAS TO PILOT BURNERS
REFINERY
FLARE HEADER _
LIQUID
KNOCKOUT
TANK
f
CONDENSATE
TO SUMP OR
RECOVERY
PILOT BURNERS
v
AUTOMATIC SNAP ACTION VALVES
EMERGENCY OR BYPASS LINE
LIQUID SEAL
Figure 33. Typical Venturi Ground Flare
0862
-------
In this system, the refinery flare header discharges to a knockout drum
where any entrained liquid is separated and pumped to storage. The gas
flows.to the burner header, which is connected to three separate banks
of standard gas burners through automatic valves of the snap-action type
that open at predetermined pressures. If any or all of the pressure
valves fail, a bypass line with a liquid seal is provided (with no valves
in the circuit), which discharges to the largest bank of burners.
Another type of ground flare useJ in petroleum refineries has a water
spray to inspirate air and provide water vapor for the smokeless combustion
of gases (Figure 34). This flare requires an adequate supply of water
(Table 17) and a reasonable amount of open space.
The structure of the flare consists of three concentric stacks. The
combustion chamber contains the burner, the pilot burner, the end of the
ignitor tube, and the water spray distributor ring. The primary purpose
of the intermediate stack is to confine the water spray so that It will
be mixed intimately with burning gases. The outer stack confines the
flame and directs it upward.
Water is not as effective as steam for controlling smoke with high
gas flow rates, unsaturated materials, or wet gases. The water spray flare'
is economical when venting rates are not too high and slight smoking can
be tolerated.
A recent type of flare developed by the refining industry is known as
a multijet . This type of flare was designed to burn excess hydrocarbons
without smoke, noise, or visible flame.
A sketch of a multijet flare installation is shown (Figure 35}. The
flare uses two sets of burners; the smaller group handles normal gas
leakage and small gas releases, while both burner groups are used at
higher flaring rates. This sequential operation is controlled by two
water-sealed drums set to release at different pressures. In extreme
emergencies, the multijet burners are by-passed by means of a water
203
-------
WATER SPRAY
DISTRIBUTOR RING
•MXJ
cbHxi—
AFLAME AR
EIGHT 1-IN.
HOLES
FLARE HEADER
E?
§-•
WATER
SUPPLY
WATER
Y STRAINERS
Figure 34. Typical Water Spray Type Ground Flare
0862
-------
TABLE 17
WATER SPRAY PRESSURES REQUIRED FOR SMOKELESS BURNING*0862
Gas rate,
scfh
200,000
150,000
125,000
Unsaturates,
% by vol
0 to 20
30
40
Molecular
weight
28
33
37
Water pressure,
Dsig
30 to 40
80
120
Water
rate, gpm
31 to 35
45
51
* The data in this table were obtained with a 1-1/2 inch-diameter
spray nozzle in a ground flare with the following dimensions:
Height, ft Diameter, ft
Outer stack 30 14
Intermediate stack 12 6
Inner stack 4 2.5
205
-------
JETS
WASTE GASES
FLOW BALANCING
VALVE
J-
SEAL WATER
STACK SHELL
\
FIRST-STAGE BURNERS\
Y
FIRST-STAGE
SEAL DRUM
OVER
CAPACITY
SEAL
SECOND-STAGE
SEAL DRUM
SEAL WATER
VENT
-*- TO SEWER
Figure 35. Multiject Flare System
.0862
-------
seal that directs the gases to the center of the stack. This seal blows
at flaring rates higher than the design capacity of the flare. At such
an excessive rate, the combustion is\both luminous and smoky, but the
unit is usually sized so that an overcapacity flow would be a rare occurrence.
The overcapacity line may also be designed to discharge through a water
seal to a nearby elevated flare rather than to tne center of a multijet
stack. Similar staging could be accomplished with automatic valves or
backpressure regulators; however, in'this case, the water seal drums are
used because of reliability and ease:of maintenance. The staging system
is balanced by adjusting the hand control butterfly valve leading to the
first-stage drum. After its initial, setting, this valve is locked into
position. '. :
V
ll
The fourth type of flare,based1.upon the use of commercial-type venturi
burners,is presented (Figure 36). This type of flare has been used to
t
handle vapors from gas-blanketed tanks, and vapors displaced from the depres-
suring of butane and propane tank trucks. Since the commercial venturi
burner requires a certain minimum pressure to operate efficiently, a gas
blower must be provided. Generally; burners operate at a pressure of
1/2 to 8 psig.
. i
This type of flare is suitable -for relatively small flows of gas of
a constant rate (Table 18). Its main application is in situations where
other means of disposing of gases and vapors are not available.
Most refineries and petrochemical plants have a fixed schedule for
inspection and maintenance of processing units and their auxiliaries.
The flare system should not be exempted from this practice. Removal of
a flare from service for maintenance requires some type of standby equip-
ment to disperse emergency gas vents during the shutdown. A simple stack
with pilot burner should suffice for a standby. Coordinating this
inspection to take place at the time when the major processing units are
also shut down is good practice.
207
-------
IGNITOR
COMMERCIAL VENTURI
BURNERS
STEEL SHELL
REFRACTORY
3 FT DIAMETER X 10 FT HIGH
PiLOT BURNER
PILOT GAS
WASTE GAS
Figure 36. Vertical Venturi Type Flare
0862
208
-------
TABLE 18
VENTURI BURNER CAPACITIES, FT3/HR0862
Gas pressure,
in. H00
2
4
6
8
10
1/2 p-;ig
1 psig
2 psig
3 psig
4 psig
5 psig
6 psig
7 psig
8 Psig
3/16-in. orifice
70
100
123
142
160
210
273
385
7/16-in. orifice
1,042
1,488
2,157
2,654
3,065
3,407
3,742
4,040
4,320
1/2-in. orifice
1,360
1,900
2,640
3,200
3,680
4,080
4,480
4,800
5,160
Basis: 1,000 Btu/ft3 natural gas.
209
-------
Flare instrumentation requires schediled maintenance to ensure proper
operation. Most of the costs and problems of flare maintenance arise from
this instrumentation • Maintenance expenses for flare burners can be reduced
by constructing them of chrome-nickel alloy. Because of-the inaccessibility
of elevated flares, the use of alloy construction is recommended.
Process Economics.0862'1456'1460'1533 Capital and operating costs for
flare installations are scarce. The capital investment will vary signifi-
cantly depending upon the complexity of the overall system, the type and
quantity of waste gas being combusted and the materials of construction.
Capital costs of flare systems have been reported to range from $1 to $100
per 1,000 SCFH of capacity. Operating costs are mainly a function of steam,
water and pilot fuel requirements, maintenance and labor.
Process Applicability. Flares are generally applicable to the ultimate
disposal of large volumes of combustible gases and aerosols. They have
found application in most petroleum refineries and petrochemical plants.
However, flares are not recommended for use at National Disposal Sites
because of the associated lack of effluent control. This lack of control
might result in emissions to the surroundings of harmful conbustion pro-
ducts such as chlorides, fluorides, cyanides, sulfur compounds, carbon
monoxide and any partially combusted or uncombusted waste material.
Additionally, the form of waste handled by industrial flares (con-
centrated gases in large volumes) suggests that flares are best suited
for use at the processing sites where the waste gas is generated.
ic-j-a 1534
Gas Combustors'"'*''5'™
Gas combustors, or as they are more commonly called, direct-flame thermal
i
incinerators, are utilized to dispose of low concentration (usually less
than 25 percent of the lower flammability limit) combustible gaseous waste.
They have found wide application in the chemical and food processing
industries.
210
-------
In direct-flame incineration combustible emissions are destroyed by
exposure,under the proper conditions, to temperatures of 900 to 1,500 F.
in the presence of a flame. The actual temperature required to do an
effective job depends on the specific pollutants involved and the design
of the combustion chamber.
Operation Principle.0862'1533'1534 The basic components of a direct-
flame thermal incinerator are presented schematically (Figure 37). They
are the combustion chamber, gas burner, burner controls, and temperature
indicator. Operation of the unit is relatively simple. The contaminated
gases are delivered to the combustor from the process equipment by an
exhaust system. The combustion chamber must be designed for complete mixing
of the contaminated gases with the flames and burner combustion gases. The
presence of a flame is important for contaminant removal. Evidence indicates
that when using electric heat energy, much higher temperatures are required--
1,500 to 1,800 F-to obtain the same efficiency achieved with a direct-flame
system at 1,000 to 1,400 F. One satisfactory method of achieving proper
mixing is the admission of the contaminated gases into a throat where the
burner is located. Sufficiently high velocities may be obtained here for
thorough mixing of the gases with the burner combustion products in the
region of highest temperature.
Next, the gases pass into the main section of the combustor where velocity
is reduced somewhat by the larger cross-sectional area. Here the combustion
reactions are completed and the incinerated air contaminants and combustion
gases are discharged to either heat recovery equipment, scrubbers or direct-
ly to the stack.
Direct-flame incineration can be highly effective. Experience has shown
that direct-flame incineration systems L
-------
COMBUSTION
CHAMBER
BURNER
THROAT
CONTAMINATED
AIR STREAM
Q
FAN
BURNER
CONTROL
VALVE
EFFLUENT TO STACK
THERMOCOUPLE
TEMPERATURE
CONTROLLER
AND RECORDER
BURNER
FUEL
Figure 37. Direct-Flame Thermal Incinerator
.0862
-------
installation of modulating gas burner controls. These controls may effect
considerable savings in fuel where the volume of gases or the amount of
combustible material delivered to the combustor varies appreciably during
the process cycle, or where both vary. A constant temperature in the
afterburner chamber can be maintained through a gas temperature sensing
element that actuates the burner input control. When, however, the volume
of contaminated gases and the amount of combustible materials remain re-
latively constant, the firing of the burner at a fixed rate is preferable.
An indicating—or recording-type temperature-measuring device is usually
installed to show the combustors operating temperature at all times. A
bare thermocouple is normally used because of low cost and rapid response
to temperature changes. The thermocouple should be located near the end
of the combustion chamber to avoid large errors produced by direct radia-
tions from the burner flames. The thermocouples may be installed in a
thermocouple well for protection.
A safety pilot is usually provided to shut off the burner gas supply
if the main burner malfunctions or the flow of contaminated gases to the
combustor is interrupted. It may also be advisable to install a high-temp-
erature-limiting control to shutoff the gas burner fuel supply when com-
bustion temperatures exceed safe operating levels.
Process Design.0862'1533'1534'1792 in order to properly design an
effective direct-flame fume incineration system, the following information
is required: flow to be handled (scfm); temperature and pressure of gases
to be handled; list of contaminants involved--type and concentration; de-
posit problem, if any; fuel available—natural gas or oil; cost of fuel;
number of hours of plant operations; and an indication if heat energy can
be used elsewhere in the plant.
There are basically two basic configurations of direct-flame thermal
combustors; vertical and horizontal units (Figures 38 and 39). The type
of unit utilized is usually dictated by heat recovery requirements. That
is, vertical units are usually used when no heat recovery is desired while
horizontal units are well suited for this application.
213
-------
EFFLUENT TO SCRUBBERS
AND/OR STACK
GAS BURNER
PIPING
REFRACTORY LINED
STEEL SHELL
REFRACTORY RING BAFFLE
INLET FOR CONTAMINATED
AIRSTREAM
BURNER
BLOCK
Figure 38. Vertical Direct-Flame Combustor Without Heat Recovery
.0862
214
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MIXING
THROAT
RAW GAS
BURNER
REACTION
CHAMBER
cXHAUST
OUTLET
7 OUTER STEEL
/ JACKET
INSULATION
HEAT
EXCHANGER
STRUCTURAL
BASE
FUME
W INLET
A
ACCESS
PLATE
Figure 39. Horizontal Direct-Flame Combustor with Heat Recovery
1792
-------
Direct-flame combustors, regardless of form, usually operate with throat
velocities ranging from 15 to 25 fps, and combustion chamber residence times
between 0.3 and 0.5 seconds. Operating temperatures are usually between
850 and 1500 F depending upon the waste being combusted. Standard industrial
units are available with capacities ranging from 2,000 to 30,000 scfm of
contaminated waste gas.
Most direct-flame incinerators are constructed of firebrick or castable
refractory with a sheet iron shell. Several types of gas burners have
been successfully utilized in direct-flame combustors. Among these are:
atmospheric, nozzle mixing, pressure mixing, premixing, and multijet
gas burners.
Process Economics.0285'0862'1461'1533 The installed capital cost of
a function of the difficulty of the combustion reaction, materials of
construction and the extent of heat recovery operating costs generally
reflect fuel consumption and are therefore dependent, upon inlet gas tem-
peratures and the required combustion temperature. They also reflect
maintenance and labor. Estimates from various literature sources of both
capital and'operating costs are presented (Table 19).
Process Modifications.1459'1460'1461 The primary process modifications
utilized in direct-flame thermal combustion are waste heat recovery options.
The principle heat recovery options are influent preheat through heat ex-
change with the hot gaseous effluent and effluent heat exchange with other
process streams (Figure 40).
Additionally, secondary scrubbers may be utilized to further decrease
concentrations of pollutants such as chlorides, fluorides, sulfur contain-
ing compounds and nitrogen oxides when they are present. This practice
is usually very expensive since the contaminant levels in the combustor
effluent stream are usually very low.
216
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B
TABLE 19.
PROCESS ECONOMICS FOR DIRECT-FLAME INCINERATION
Amount of Gas
Treated, scfm*
Data from Reference No. 1533
Basic Unit 10,000
Basic Unit with Heat Exchanger 10,000
Data from Reference No. 1461
Basic Unit with Heat Exchanger 5,000
25,000
Data from Reference No. 0285
Basic Unit 10,000
Basic Unit with Heat Exchanger 10,000
Data from Reference No. 0862
Basic Unit t
Influent Gas
Temp F
350
550
350
550
400
150
300
300
t
Capital Cost
$/scfm
2.00
1.95
2.40
2.39
2.60
3.20
1.50-2.00
3.00-4.50
5.00-10.00*
Annual Fuel
Cost $/Year
48,000
30,700
33,500
12,200
8,600
35,400
t
t
t
Contaminants are at less than 25% of L.E.L.
No data available
^Installed capital cost
-------
TO ATMOSPHERE
PREHEATED INFLUENT
DIRECT -FLAME
COMBUSTOR
HEAT
EXCHANGER
V
•/
1
STACK
BURNER
FUEL
CONTAMINATED
INFLUENT
00
TO ATMOSPHERE
PROCESS STREAM
(HOT)
CONTAMINATED
INFLUENT
FUEL
HEAT
EXCHANGER
NER
DIRECT -FLAME
COMBUSTOR
V
1
STACK
PROCESS
STREAM
(COLD)
Figure 40. Heat Recovery Options
-------
Process Applicability. Due to the form of the waste material being
treated (dilute and in the gaseous state) direct-flame combustors are best
suited for use at the processing site where the waste is generated. A
listing of some of the typical industrial applications of direct-flame
1792
combustion systems is presented (Table 20).
Direct-flame combustors would find use at a National Disposal Site as
a secondary treatment (i.e., afterburner) on primary treatment processes
evolving varying amounts of combustible contaminants. They are also well
suited to the purification of ventilation air or any air which is moni-
tored for pollutant control.
219
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TABLE 20
TYPICAL DIRECT FLAME INCINERATION APPLICATIONS1792
Resin Manufacturing
Paint and Varnish Cooking
Wire Enameling
Metal Decorating
Coil and Strip Coating
Carbon Baking Ovens
Tar and Asphalt Blowing
Fish Meal Processing
Printing Press Ink Drying
Prithalic and Maleic Anhydride Manufacture
Food Processing
Rendering of Fats
Bonding and Burn-off
Grain Dryers
Plastic Curing
Sewage Treatment
Air Sterilization
220
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APPENDIX
AIR CORRECTION EQUIPMENT
1. INTRODUCTION
The following is a discussion of the general types of air correction
equipment currently employed for the control of gaseous and/or particulate
pollutants in process effluent streams. There are currently two general
categories of abatement equipment in use--wet collection equipment and
dry collection equipment. This report will summarize the general operating
principles, operational characteristics, and applications of the common
types of pollution control equipment.
2. WET COLLECTION EQUIPMENT2188'1673'2189
In the collection of gaseous pollutants, the primary removal mechanism
in wet collection systems is the absorption of the gaseous pollutant into
water or other suitable solvents. The basic operation consists of the
diffusion of the gas molecules to the water surface. Concentration
differentials near the liquid/gas interface serve as the driving force.
Control equipment which applies this principle is characterized by
high interfacial surface areas, turbulence in the gas phase, and high
diffusion coefficients. Fortunately, in the area of gaseous emission
control, a great number of the most common gaseous chemical species
have high solubility in water.
Particulate collection liquid scrubbers depend upon a somewhat
different set of physical processes. The primary collection mechanism
is the impaction of solid particulate material on liquid droplets generated
in the scrubber. The function of the liquid scrubber is to generate
and place in contact with the exhaust gas stream a sufficient number of
liquid droplets in the appropriate droplet size range. Additional
physical mechanisms by which particulate dispersoids are collected in
wet scrubbers are Brownian diffusion, condensation of liquid on the
particulate material, and agglomeration. In each case, the relative
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effective size of the participate rnateria is increased in the scrubber,
thus facilitating its ultimate collection and disposal.
It should be noted that the mechanisms of gaseous and particulate
collection in liquid collectors are somewhat different and that a liquid
scrubber designed to maximize gaseous pollutant removal may be significantly
less effective in the collection of particulate material. Application of
scrubbers to specific industrial effluent cleaning tasks should be made
only on the basis of careful consideration of the relative importance
of the gaseous and particulate emissions and analysis of the particle size
distribution in the effluent gas stream to be cleaned.
Spray Towers/Chambers
A chamber scrubber consists of a chamber into which the water or an
aqueous solution is introduced tnrougn spray nozzles. The gas stream may
make a single direct pass through the chamber, or the path may be controlled
by a series of baffles. Several such chambers or scrubbers are often used
sequentially to produce the desired degree of pollutant removal. These
devices are characterized by a very low pressure drop for the gas phase
(0.1 to 0.5 in. of water). Water pressure required for spray operation
ranges from 20 to 100 Ib per square in. Water consumption is usually in
2188
the range of 1/2 to 2 gal per 1,000 cu!>ic feet of gas treated.
v
Spray chambers are used for the removal of both particulate and
gaseous pollutants. The efficiencies of these devices are generally
rather low for particulate materials and are suitable only for the removal
of particulate materials 10 microns in size or larger. For the collection
of smaller particulate material, very high water pressures have been
successfully used. Water pressures on the order of 300 to 450 Ib per
square in. (psi) produce a fog spray which will achieve collection
efficiencies of the order of 90 percent for particles in the 1 to 2
micron size range. The larger water pressure drops required to acheive
'-•igh efficiency fog spray result in a proportionally higher pump
horsepower and operating cost. Baffled spray chambers require higher
qas velocities and result in greater gas pressure drops which, in turn,
222
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require greater fan horsepower to recover the lost pressure head
and more expensive ductwork.
The simple spray chamber is often used effectively for gaseous
pollution control, especially when treating some of the relatively more
soluble pollutants. Surface contact area, an important consideration in
gaseous absorption, is relatively low in spray chambers compared with
other types of liquid scrubbers. For this reason, simple spray chambers
must be very large to produce efficiencies equivalent to more sophisticated
liquid collection systems. The overall efficiencies reported for multiple
spray chamber installations are greater than 90 percent. There are no
limitations on gas throughput volume other than those imposed by equipment
2
size limits. However, gas flow rates of approximately 800 Ib/hr-ft have
been demonstrated as the upper limit, to prevent excessive liquid entrap-
ment.1673
Spray chambers or towers, because of their simple design, represent one
of the most economical control devices to purchase and install. The
operating and maintenance expenses associated with this type of device are
also low because of the mechanical simplicity. Primary maintenance
problems are caused by the use of small, high-pressure nozzles which may
tend to clog under prolonged usage. The low pressure drops (generally
less than 1 in. of water) allow the use of inexpensive ductwork and
fans to convey the effluent gas stream to the collector.
Packed Bed Scrubbers
The packed bed scrubber is similar to the spray chamber described
above in that the effluent gas stream to be cleaned is directed through
a chamber or tower in which it makes contact with the scrubbing liquid.
The high liquid surface area exposed to the gas stream is produced by
interaction with the packed bed. The packed bed may be in the form
of a fixed packing or loose material which is supported by the action
of the gas stream passing through it. This latter type is called a
floating bed scrubber. Scrubbing liquid is generally passed through
this type of scrubber in a direction crosscurrent or countercurrent
to the gas flow.
223
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The fixed bed scrubber is not often used strictly for particulate
pollutant collection. Operating problems have been encountered when
this type of collector is utilized to clean a gas stream containing
an excessively high concentration of pan.iculate material. Therefore,
in conjunction with this type of equipment, some form of dry collection
equipment is used that eliminates much of the particulate load on the wet
scrubber and helps prevent clogging.
The floating bed units, in which the packing is supported by the upward
motion of the exhaust gas stream, are reported to be more resistant to
clogging caused by particulate collection than the fixed packed bed units.
' This reported increased ability to handle particulate contaminant
is attributed to the relative motion between the packing materials which
produces a self-cleaning action and allows the collected particulate material
to be removed by the liquid flow. High particulate removal efficiencies
(95 to 98 percent) have been reported for floating bed scrubbing units.
A condition known as flooding occurs when the upward cas velocity in
the packed tower reaches a point at which there is a hold-up of liquid
phase on the packing. In this condition, the liquid held in the packing
builds up and eventually increases the pressure drop across the packed
tower unit to the point where liquid will be entrained and carried out
with the exhaust stream. Care must be taken in the design and operation
of tower equipment to ensure that this flooding condition is avoided and
a reasonable pressure drop is maintained. Properly designed packing
materials allow a high liquid surface area to be maintained within the
scrubber. Operation at proper liquid-to-gas flow ratios can achieve high
gaseous pollutant removal at relatively low gas flow resistances. Packing
materials commonly used are plastic materials of various shapes, including
rings, spiral rings, berl saddles, and other shapes which allow a high
ratio of surface area to volume.
T
Utility consumption for the packed bed scrubber depends on the
design of the bed, the packing material used and the collection efficiency
desired. Typical water consumption for the packed bed scrubber ranges from
224
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5 to 10 gpm per 1,000 CFM. Normal packed scrubber design dictates a
pressure drop of from 1 to 10 in. of water with a total horsepower
requirement of 0.3 to 2.8 for fan and pumping costs. Efficiencies of
95 to 98 percent have been realized for both particulate and gaseous control,
although not necessarily concurrently.
The choice between crossflow and countercurrent scrubber design is
dependent on the particular application. However, generally the crossflow
scrubber is applied to situations w'lere the bed depth is less than 6 ft
and countercurrent design is applied at bed depths of 6 ft or more. These
applications are based'on the lowest combination of installed capital cost
and operating cost.
Met Cyclone Scrubbers
Wet cyclones are characterized by tangential entry of the air stream
to be cleaned. The air stream passes through the collector iri a spiral
path. The liquid stream is directed outward from the center of the circular
collection chamber. The cyclonic scrubber thus possesses some of the
characteristics of both the simple dry cyclone collector and the spray
chamber.
Particulate collection is accomplished by combining centrifugal
acceleration of the particles toward the chamber wall with the action of
the spray droplets in contacting and removing the particle. Particulate
collection efficiences are generally in excess of 90 percent for particles
5 microns or larger. Gaseous pollutant capture is produced by the
intimate turbulent contact between the exhaust gas stream and the liquid
particles generated by spray nozzles and air stream shear forces within
the scrubbing unit. Liquid requirements are generally on the order of
2 to 10 gal. of water per 1,000 cubic feet of gas treated. Gaseous
collection efficiencies range up to 99 percent with pressure drops of 1 to 8
in. of water. Total fan and pump horsepower vary from 1 to 2 per 1,000 CFM.
Wet cyclones have been designed to treat up to 100,000 CFM.
225
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In summary, the wet cyclone has desirable characteristics when the
gas stream to be cleaned contains both ^articulate and gaseous materials.
The wet cyclone has an adequate capacity for handling high input dust
loadings and produces acceptable collection efficiencies for both
medium sized (>5 microns) particulate and gaseous pollutants. Where
extremely high particulate collection efficiencies are required, however,
the wet cyclone is used in conjunction with higher efficiency collection
units. The purchase, installation and operating costs associated with
cyclonic scrubbers are comparable with those of packed bed units for
situations where the exhaust gas stream to be cleaned represents a high
gas flow rate; however, the cyclonic scrubber requires less maintenance,
Self-Induced Spray Scrubbers
In this type of scrubber, the gas liquid contact is created as a
result of impingement of the carrier gas upon a liquid. The performance
characteristics are thus dependent upon the gas flow rate through the
collector. The effluent gas stream to be cleaned is impinged upon the
surface of the scrubbing liquid; the scrubbing liquid is fragmented and
broken into droplet-sized particles by the kinetic energy in the gas
stream. The liquid droplets formed are entrained, and the effluent gas
stream is passed through further sections in which turbulent contact
between the liquid and gas phases occur.
Particulate collection efficiency approaches 90 percent for particles
2 microns and larger. For medium efficiency collection units of this
type, pressure drops range between 3 and 6 in. of water. The entrained
water droplets and the collected particulate material are removed in the
01 Q~J
final demisting stage of the induced spray scrubber. This type of
equipment is particularly applicable to gas streams with high dust
loadings since continuous removal of sludge can be accomplished with the
installation of a screw convenyor. No pumping horsepower is required
since the water remains at essentially atmospheric pressure and is
atomized by the gas stream.
226
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Another advantage of the induced spray collector lies in the fact
that construction does not involve close clearances or small orifices.
Clogging, which often represents the bulk of the maintenance problems in
wet collectors, would not be expected under normal operating conditions.
Gaseous collection efficiency in the self-induced spray scrubber has
been reported to be greater than 99 percent removal. The control system
reported in these observations was a two-stage scrubbing operation with
sequential induced spray collectors. Liquid-to-gas requirements are
generally lower for this type unit than for most other wet collectors.
Liquid requirements range between 1/4 to 3 gal of liquid per 1,000
cubic feet of gas. Fan horsepower for head recovery is from 0.7 to 1.4
per 1,000 CFM of treated gas.
Orifice Plate Bubblers
The orifice plate buubler is a class of wet impingement scrubber.
The gas stream to be cleaned is passed through a perforated plate and
impinged on baffles where the gas jets attain maximum velocity. The
impingement baffles are covered by a layer of scrubbing liquid during
operation. The gas stream passing through the baffle plate prevents
the flow of liquid through the perforated plate. Intimate mixing of the
gas streams and the liquid occurs facilitating both gas transfer to the
liquid phase and particulate collection by the scrubbing liquid.
Particulate collection efficiencies from 90 to 95 percent have been
reported for 2-micron diameter dust particles. Several stages of perforated
plate and impingement baffle may be assembled into a single collector unit.
The particulate removal efficiency is directly related to the number of
plates used in the scrubber. As is usual in the design of wet collectors,
a mist eliminator is used following the last baffle plate section. Pressure
drop through the impingement baffle system has been reported between 1 to
10 in. of water depending upon the size and number of perforations used,
2188
and the number of impingement plates in the collector.
227
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Gaseous pollutant removal efficiencies between 99 and 99.5 percent
have been reported for orifice plate bubblers. High collection efficiencies
for both particulate and gaseous pollutants make this unit applicable in
a wide range of control situations. Water usage runs from 1 to 5 gpm per
1,000 CFM and the total (fan and pump) horsepower requirements range from
0.5 to 3 per 1,000 CFM.
Clogging has not proved to be a problem in this equipment even though
the perforations in the plate are typically only 1/4 in. or less in
diameter. Clogging is prevented by high (75 ft/sec or more) gas velocities
through these orifices which agitate the liquid on the surface of the plate
and keep the dust particles in suspension.
Venturi Scrubbers
The basic distinguishing design feature of the venturi scrubber is
the passage of the exhaust gas stream through a venturi-type constriction.
In this constriction, high linear gas velocities 0^1 the order of 12,000
to 42,000 ft per minute are attained. The scrubbing liquid is usually
introduced normal to the gas flow at or near the minimum flow area of the
venturi. The high gas velocity at this point atomizes the scrubbing
liquid into fine droplets that are maintained in turbulent contact with
the gas stream.
Particulate collection efficiencies in the venturi scrubber are
directly related to the gas phase energy input. Gas pressure drops of
10 to 100 in. of water are common in this type unit with particulate
collection efficiency for submicron particles approaching 99 percent
at the higher pressure drops. The freedom from clogging afforded by
the relatively simple liquid distribution system of this type unit makes
possible the treatment of exhaust streams containing high dust loads.
The high particulate removal efficiency further makes the venturi scrubber
most applicable when particulate removal is of primary importance.
228
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The intimate gas-liquid contact obtained in this type unit allows
the efficient removal of gaseous as well as particulate pollutants.
Gaseous pollutant removal efficiencies from 80 to 99 percent have been
reported. The venturi pressure drops associated with these reported
efficiencies ranged from 15 to 50 in. of water.2188 Scrubber liquid
requirements for this type of control equipment range from 3 to over 8
gal per 1,000 cubic feet of gas.
Jet Scrubber
Another type of scrubber open-ted on the venturi principle is the
jet scrubber or ejector venturi design. As in the case of the standard
venturi scrubber, the basic operating principle consists of passage of the
exhaust gas flow through a restrictive orifice. In the ejector venturi
design, the energy impelling the gas stream through the orifice comes
from a high pressure liquid spray rather than from the gas phase pressure
drop across the collecting unit i.e., water is used to aspirate the dust-
laden gas through the ejector. The ejector provides the head for the gas,
although large induced drafts (above several inches of water) are usually
avoided to maintain a high entrapment ratio since larger entrapment
ratios require less water for a qiven qas flow rate. Typical water
usage ranges from 50 to 100 gpm per 1,000 CFM with a pressure drop of 50
to 100 psi for the water across the ejector. This amounts to 1 to 5 pump
hp per 1,000 CFM. Particulate and gaseous collection efficiencies
experienced with the ejector venturi design are comparable with those attained
In conventional venturi scrubbing. In both devices, the air stream is
brought into intimate and turbulent contact with a fine droplet spray.
The jet scrubber is usually followed by a baffled or settling chamber
to capture the water treated particulate matter and water droplets. The
main use for this type of equipment is in situations where it is not
economical to add a fan to the system. A wide range of sizes is available
in this type of collection unit and multiple banks of ejector Venturis
have been used to control large process emission sources.
229
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Dynamic Met Scrubbers
In the dynamic wet scrubber, liquid is mechanically sheared into
fine droplets and then contacted with the dust laden gas stream. The
shearing usually is accomplished by injecting the water into fan blades
which simultaneously mix the water and dust streams and recover the lost
pressure head of the effluent stream. The wetted impeller and a housing
hold the collected dust particles and prevent re-entrainment. The dust
j
collection efficiency is approximately 95 percent for 1 micron particles.
Although no pressure drop is incurred by the process stream, there is a
3 to 20 hp/1,000 CFM requirement for the fan to disperse the water and recover
the head. Many of the higher horsepower dynamic units are being displaced
with venturi scrubbers. Typical water consumption varies from 3 to 5 gpm
per 1,000 CFM. Good gaseous collection efficiencies can be expected from
the dynamic wet scrubber because of an intimate mixing of the water and
the process stream.
3. DRY REMOVAL SYSTEMS2188'1673'218
Dry removal systems are generally used as primary treatment systems and
have little effect on gaseous pollutants. Under certain conditions, dry
collection systems have been applied to effluent streams either to decrease
the particulate load on subsequent control equipment or to collect a solid
adsorbant that has been used to reduce the stream's gaseous pollutant
content. In either case, the dry collection equipment is usually followed
by secondary or even tertiary treatment. Three main classes of dry collection
equipment are available'-mechanical collection equipment, electrostatic
precipitation, and fabric filtration.
Mechanical Collectors
Mechanical collectors (inertial separators) have proven to be reliable
collectors of dry particulate material in a number of air pollution control
applications. These devices collect particulate material by the use of
centrifugal force, gravitational force, or by rapid changes in the direction
of the dust laden stream. Mechanical devices are simple to construct,
relatively inexpensive, and operate at moderate pressure drops. Generally,
230-
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the efficiency of the mechanical collector will increase markedly with
increased dust loadings, thus, it is often used as a precollector for more
efficient control equipment which is susceptible to overload. Common types
of dry mechanical collectors employed in industry include the settling
chamber, the louver type collector, the cyclone, the impingement collector,
and the dynamic collector.
Settling Chamber. The settling chamber directs the dust laden gas into
an oversized duct where the gas velocity drops to a point where the entrained
particles drop out because of the rorce of gravity. This type of equipment
o
is used in relatively high particulate concentrations (above 5 grains/ft )
witn particles sizes of 50 microns or larger. Dust collection efficiencies
range from 50 to 90 percent depending on dust particle size distribution.
The pressure drop through the settling chamber ranges from 0.2 to 0.5 in.
water gage (wg) resulting in a low fan horsepower requirement of 0.04 to
0.12 per 1,000 CFM of treated gas. Since the efficiency of the settling
chamber is relatively low for dispersoid particulates and has no effect
on gaseous pollutants, this type of equipment is generally used for
pretreatment of a gaseous stream that is to be fed to some more efficient
type of collection device. The volume of gas that is treated by this type
of equipment is limited only by the space available for the unit designed
to treat that volume. The typical gas velocity through the chamber ranges
from 5 to 10 ft per second.
71RQ
Baffle Chamber. In the baffle chamber, settling is aided by
using the momentum of the heavy particulate matter to separate it from the
carrier gas. The dust laden gas enters the baffle chamber and is directed
downward around a baffle and out tne top of the chamber. The heavy dust
particles tend to continue moving downward and are separated from the gas
stream. They drop out a small opening in the bottom of the chamber and
are collected. The baffle chamber is used for the same type of conditions
as is the settling chamber with the advantage of a smaller space requirement.
Gas velocities of 20 to 40 ft per second are typical in the baffle chamber
with a pressure drop of 0.1 to 0.5 in. of water. The fan horsepower requirement
needed to compensate for this pressure drop is 0.02 to 0.12 per 1,000 CFM
of treated gas. The baffle chamber has a collection efficiency of from 50to
231
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90 percent depending on the dust particles to be removed (usually above
50-micron diameter).
Skimming Chamber.2189 The skimming chamber is similar to the baffle
chamber in that it uses the greater momentum of the dust particles to
separate them from the gas stream. The dirty gas stream enters an enclosed
metal scroll tangentially and the dust is carried to the edge by inertia.
A concentrated dust stream is skimmed from the edge of the scroll and sent
to a secondary chamber. Gas velocities of 35 to 70 ft per second are typical
for this type of equipment. Efficiencies of 70 percent are obtainable with
particles 20 microns in diameter. Pressure drops of up to 1 in. of water
can be expected with a resulting horsepower requirement of from 0.02 to 0.24
per 1,000 CFM. The limiting size for this type of equipment is 50,000 CFM.
Louver Type Collectors2189 This type of equipment also employs the
difference in momentum between the dust particles and the carrier gas tc
separate out the dust. The incoming gas must nake a sharp bend in order
to escape through the IOUVC.T (slots) in the wall. Tne heavier dust
particles are carried to the end of the apparatus where they are carried
out by a small portion of tne original gas stream in a concentrated stream.
Efficiency of 80 percent can be obtained on 20-micron particles at gas
velocities of 35 to 70 ft per second. Flow rates are limited to 30,000 CFM
for this type of equipment. A pressure drop of 0.5 to 2 in. of water can be
expected through this type of equipment requiring from 0.12 to 0.48 fan
hp per 1,000 CFM to return the yas stream to pretreatment pressure conditions,
Ury_Cyc1ones.2189 In a cyclone, the dust laden gas enters the top of
the apparatus tangentially, forming a vortex that extends downward toward
the oottoin of the cone-shaped base. At this point the gas then reverses
its direction and moves up the center of the outer vortex in a vortex core.
The separation of the dust occurs during the downward flow of gas when the
inertia of tne particles forces them out of the gas stream toward the wall
of the cyclone. At the bottom of the cone, the particles continue to move
downwards because of their momentum in that direction and are collected
through a hole at the base of the cone.
232
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The simple cyclone is typically applied to streams up to 50,000 CFM
and can obtain 50 percent efficiency on 20-micron particles. Pressure
drops of 0.5 to 3 in. of water are typical with gas velocities of 35 to 70
ft per second. Fan horsepower requirements are from 0.12 to 0.74 per
1,000 CFM to recover the lost pressure head.
There are several modifications of the simple cyclone also employed
as dust collection equipment. The high efficiency cyclone employs a
relatively small diameter and higher gas velocities in order to obtain a
greater efficiency. Efficiencies of 80 percent have been obtained on 10-
nncron particles. Flow rates in this type of cyclone are limited to 12,000
CFM with an increased pressure drop of 3 to 5 in. of water because of the
increased gas velocities. The larger pressure drop dictated by this
equipment requires a proportionally larger fan horsepower requirement in
order to recover the lost pressure head. Another common variation on the
simple cyclone is the multiple cyclone in which many small diameter cyclones
are employed to treat the same amount of gas as a conventional cyclone. The
effect of this approach is to decrease the effective diameter and increase
the efficiency. An efficiency of 90 percent is nominal for 7.5-micron
particles. The pressure drop and fan horsepower for the multiple cyclone
is similar to the high efficiency cyclone.
Impingement Collector.2189 The impingement collector also uses the
higher momentum of the dust particles to separate them from the carrier
gas. The dirty gas is accelerated by a venturi and the particle momentum
carries the dust particles through a slot in a facing metal plate where they
impinge on another plate and are collected. The carrier gas tends to
diffuse away from the path of the dust particles. It strikes the first
metal plate and is carried away rather than going through the slot. This
type of equipment can produce 90 percent efficiency on 10-micron particles
with a pressure drop of from 1 to 2 in. of water. Almost unlimited flow
rates are handled by impingement equipment with gas velocities of from 50
to 100 ft per second. Fan horsepower requirements for head recovery are
from 0.24. to 0.48 per 1,000 CFM.
233
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pi OQ
Dry Dynamic Collector. The dry dynamic collector is unique in
that it uses a specially designed fan to separate the dust particles from
the carrier gas and thus has no effective pressure drop. The gas stream
is drawn into the collector and accelerated by the impellers of the fan
causing the heavy dust particles to be thrown to the outside of the fan
chamber. Here they are collected as a concentrated stream and sent to a
hopper where they settle out. Since the dynamic collector employs a fan,
there is no pressure drop through the equipment and the only utility
required for this equipment is the horsepower for the collector itself.
Tho horsepower required for a dynamic collector is slightly greater than
that for a fan utilized for the same duty, since the mechanical efficiency
is somewhat smaller for the collector. Normally the dynamic collector can
handle up to 17,000 CFM of dirty gas with efficiencies of 80 percent on
15-micron particles.
21R8
Electrostatic Precipitation '°°
Electrostatic precipitators use an electrical field for charging the
particles in the incoming, pollutant-laden gas causing the charged particles
to migrate to a collecting electrode because of the electrical field.
Particles are collected on the opposite-polarity electrode and transferred
to storage for disposal. Control equipment of this type has had extensive
application in many fields of pollution control. A primary advantage of
electrostatic precipitators is the relatively low operating costs of these
units. Power requirements are low with the gas pressure drop rarely exceeding
1/2 to 1 in. of water. Additional power must, of course, be supplied in the
form of electric energy required to ionize and collect the particulate
material. The total power requirements for electrostatic precipitator
units, however, are low compared with power requirements to attain
equivalent efficiencies with other collecting mechanisms; they range between
0.1 and 0.6 kw per 1000 CFM. Electrostatic precipitation units are
cownonly designed to operate at greater than 90 percent particulate removal
efficiencies on particles of 2 microns or less with gas flow rates from
10,000 to 2,000,000 CFM. The initial cost (purchase and installation)
of electrostatic precipitation equipment is high relative to initial costs
for mechanical collectors or wet scrubbing systems.
234
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Fabric Filtration2188
The third class of dry collection equipment which must be considered
is fabric filters. In this type of unit, tne exhaust gas stream to be
treated is passed through a fabric filter bag which collects the particulate
material in the exhaust gases while allowing the gases to pass through
to the stack for emission. Very large areas of fabric are used to filter
gas streams. The pressure drop or resistance to air flow in fabric filter
units increases as the dust loading builds up on the fabric. In general,
the pressure drop for this type of unit is between 5 and 10 in. of water.
Various cleaning mechanisms are used periodically to remove collected
particulate material from the fabric filters.
Paniculate collection efficiency for this type of unit often exceeds
99.5 percent. Fabric filter units are relatively unaffected by dust loading
or gas throughput up to their design capacity. For this reason they
represent one of the most positive and efficient particulate control
devices available. When used in conjunction with a solid adsorbent
substance, fabric filtration can achieve a high degree of gaseous pollutant
removal.
Fabric filtration suffers from two major limitations. Humid gas
streams cause problems because of caking and binding of the collected
particulate material on the fabric surface. This causes greatly
increased pressure drop and, in some cases, prevents air flow through
the filter installation. The second major limitation is in the cleaning
of high temperature exhaust gases. Certain fabric filter materials,
such as glass fibers and aromatic polyimide fabrics, have the ability
to withstand exhaust gas streams up to 550 F. For gas temperatures
above this level, or when it is desirable to use less expensive filtering
materials such as nylon, cotton or wool, the gas stream must be cooled
prior to entry into the fabric filter unit.
235
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REFERENCES
0053. DeMarco, 0., D. J. Keller, J. Leckman, and J L. Newton. Incinerator
guidelines 1969. Public Health fervice Publication No. 2012.
Rockville, Maryland, Bureau of Solid Waste Management, 1969. 105 p.
0167 IIT Research Institute. Utilization of red-mud wastes for lightweight
structural building-products. Final report prepared for the U. S.
Department of the Interior, Bureau of Mines under Contract No. 14-
09-0070-382, May 1968. 41 p.
0285. Lund, H. F. Industrial pollution control handbook. 1 v. New York,
McGraw-Hill Book Company, 1971.
0304. Ross, R. D. Industrial waste disposal. New York, Van Nostrand
Reinhold Book Corporation, 1968. 340 p.
0534 Jones. H. R. Environmental control in the organic and petrochemical
industries. 'Park Ridge, New Jersey, Noyes Data Corporation, 1971.
264 p.
0582 Witt, Jr. , P. A. Disposal of solid wastes. Chemical Engineering.
78(22):62-78, Oct. 4, 1971.
°862-
.
by Air Pollution Control District, County of Los Angeles. Washington,
U. S. Government Printing Office, 1967. 892 p.
0958. Department of the Army, Edgewood Arsenal. Transportable disposal
systems, environmental statement. Special publication, EASP 200-11,
July 1971. 297 p.
0976 Prenco. Prenco brochure; the modern approach to liquid pollution
control. Detroit, Michigan, Pickands Mather and Company. 7 p.
1002 Novak, R. G. Eliminating or disposing of industrial solid wastes.
Chemical Engineering, 77(21) :79-82, Oct. 5, 1970.
1435. John Zink Company. NOX destructor. Tulsa, Oklahoma.
1456. Personal communication. J. Feldstine, Hirt Combustion Engineers, to
M. Santy, TRW Systems, Mar. 21, 1972.
1459. Personal communication. R. Stattenbenz, Air Preheater, to M. Santy,
TRW Systems, Mar. 21, 1972.
1460. Personal communi cation. C. Cantrel , John Zink Company, to M. Santy,
TRW Systems, Mar. 21, 1972.
1461. Personal communication. J. Brewer, UOP, Air Correction Division, to
M. Santy, TRW Systems, Mar. 21, 1972.
236
-------
REFERENCES (CONTINUED)
1465. Dorr-Oliver. The Dorr-Oliver FS disposal system. Bulletin No. 6051.
1466. Alford, J. M. Sludge disposal experiences at North Little Rock,
Arkansas. Journal of the Hater Pollution Control Federation.
41(2):175-183, Feb. 1969."
1533. Brewer, G. L. Fume incineration. Chemical Engineering, Oct. 14, 1968.
1534. Pauletta, C. Incineration. Jji Pollution Engineering, Mar./Apr.
1970. p. 1.
1574. Lewis, F. M. Discussions of papers presented at the 1968 National
Incinerator Conference, New York, May 5-8, 1968. American Society
of Mechanical Engineers, p. 1.
1575. Bertrand, R. R., J. T. Sears, and A. Skopp. Fluid bed studies of
the limestone based flue gas desulfurization process. Interim
Report Oct. 15, 1967-Feb. 15, 1969 prepared for National Air
Pollution Control Administration by Esso Research and Engineering
Company, Linden, New Jersey under Contract No. PH 86-67-130.
Washington, U. S. Government Printing Office, 1969.
1576. Bertrand, R. R., A. C. Frost, and A. Skopp. Fluid bed studies of
the limestone based flue gas desulfurization process. Interim
Report Oct. 31, 1968 prepared for National Air Pollution Control
Administration by Esso Research and Engineering Company, Linden
New Jersey under Contract No. PH 86-67-130. Washington, U. S.
Government Printing Office, 1969.
1580. Airpollutionomics UOP catalytic incineration systems. Bulletin
No. 602. Darien, Connecticut, May 1971. 12 p.
1661. PCB retreats again. Chemical Week. 110(5):14-15. Feb. 2, 1972.
1672. Bartlett-Snow Company. Tumble-burner, advertising brochure. Bulletin
205B. Cleveland, Ohio, 1970. 6 p.
1673. Perry, R. H. Chemical engineers handbook. 3d ed. New York, McGraw-
Hill Book Company, 1969.
1688. Honea, F. I., J. Wichmann, and W. A. Bullerdick. Disposal of waste
or excess high explosives. Progress Report, Jan.-Mar. 1972,
prepared for U. S. Atomic Energy Commission, Albuquerque Operations
Office by Mason & Hanger - Silas Mason Company, Inc.
1689. TFW internal correspondence. G. I. Gruber to R. S. Ottinger,
Apr. 7, 1972. Trip report Mar. 22-24, 1972 (Mason and Hanger;
Olin Company: Army Materiel Command)--Hazardous Waste Disposal.
237
-------
REFERENCES (CONTINUED)
1701. Personal communication. E. Dolsak, Bartlett-Snow Company, to
M. Santy, TRW Systems, May 11, 1972.
1702. John Zink Company. Waste liquid burner. Tulsa, Oklahoma. Bulletin
DB 0267.
1703. John Zink Company. Information on pollution control. lr\_ Chemical
Processing. Jan. 1972.
1761. Sebastian, F. P., and P. J. Cardinal. Solid waste disposal. Chemical
' Engineering. Oct. 14, 1968. p. 112-117.
1792. Airpollutionomics UPO thermal incineration systems. Bulletin No. 607.
Darien, Connecticut. 8 p.
2186. Kiflback. A. W. The development of floating bed scrubbers. Chemical
Engineering Progress, 57(35):51-54, 1961.
2187. Doyle, H. The Doyle scrubber. Industrial and Engineering Chemistry.
49(12):57-62, Dec. 1957.
2188. Caplaa, K. J. Wet collectors and adsorption of gases. Air Pollution
Manual, Part 2-Control Equipment. Detroit, Michigan, American
Industrial Hygiene Association, 1968. p. 1-110.
2189. Sargent, G. D. Dust collection equipment. Chemical Engineering.
72(2):130-150, Jan. 27, 1969.
238
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PYROLYSIS
1. INTROUUCTION
Pyrolysis is generally defined as the thermal decomposition of a
compound. With respect to waste carbonaceous materials, pyrolysis repre-
sents a means of converting the unwanted waste into a usable commodity
with economic value. That is, most municipal and industrial wastes which
are basically organic in nature can be converted to coke or activated
charcoal and gaseous mixtures which may approach natural gas in heating
values through the utilization of pyrolysis.1011* 1433
Pyrolysis has only recently (1968) been applied to the conversion of
organic wastes. The process has traditionally been used to convert low
economic value homogeneous materials, such as wood chips and heavy hydro-
carbon still bottoms, to compounds with higher overall economic value,
such as fuel gas, pitch, creosote, acetic acid, crude methanol and char-
coal (as in the case with wood chips), and coke, fuel gas and gas oil
(as in the case with still bottoms). ' For purposes of this report,
only the methods associated with waste conversion will be discussed.
2. OPERATION PRINCIPLE0145'1009
The heart of the pyrolytic waste conversion process is the pyrolytic
converter (Figure 1). The unit consists of a sealed, airtight retort
cylinder inside a heavy insulating jacket. The gas-fired retort revolves
slowly on a slight decline from infeed to outfeed. Wastes are injected
through a seal area that intermittently opens (the flapper valve seal is
designed to minimize entry of oxygen).
Inside the retort, ground-up wastes are subjected to temperatures of
about 1,200 F - plus or minus 300 F, depending upon the nature of the wastes,
in an essentially-oxygen-free atmosphere. Without oxygen, the.wastes
cannot burn and are broken down (pyrolyzed) into steam, carbon oxides,
volatile vapors and charcoal..
239
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SOLID-WASTE CONVEYOR
— —
1
J3F\
— — -
Itl
PAPER-
BOARD
• -»-
IN
METAL
m
ill
HI
GLASS
,";
« RECEIVING
AREA
O^=;^B(O)
SALVAGE BINS
CHARCOAL
COOLING
UNIT
PYROLYTIC CONVERTER
SELF - SUSTAINING
FUEL
EXCESS GAS
PYROLIGNEOUS - ACIDS
(CRESOTARE)
. 1009
Figure 1. Pyrolytic waste conversion
240
-------
Steam, carbon dioxide and carbon monoxide are the first gases to
emerge. They are trapped and then: (1) vented after flaring; (2) used to
dry incoming feed; or (3) the steam can be condensed and the effluent gas
burned for fuel value.
As the wastes are heated further, volatile gases are distilled.
Typically, these gases will include hydrogen, methane, ethylene and
ethane. About 25 cubic ft of combustible gases are recovered fromm
every pound of industrial and municipal refuse. Energy value per cubic
foot is usually between 400 and 500 Blu.
The crude, combustible gas is drawn off and used in part (30 to 40
percent) to fuel the converter while the remainder may be utilized to
fuel other aquipment or to make steam for such uses as heating and power
generation.
In fact,a 100-ton per day municipal waste conversion facility will
produce enough excess gas to create 400,000 kilowatts of electricity per
day. At a quarter-cent per KW, that amounts to $1,000 of electrical energy
per day. Thus, recovery of combustible gas usually offsets the total
operating costs of a waste-conversion facility.
The surplus gas cannot be piped over any great distance and retain
its original heat value. Nor can it be stored. For, allowed to cool,
pyroligneous acids begin to condense, reducing heat value per cubic foot
to around 350 Btu and reducing volume by as much as 80 percent.
However, the liquid condensate is of economic value. It constitutes
a form of cresotar which is used for, among other things, dust control on
unpaved roads. Moreover, the liquid represents a potentially valuable
source of organic compounds. Chemical analyses have identified such
constituents as methanol, ethanol, isobutanol, n-pentanol, tert. pentanol,
1,3-propanedial, 1-hexanol, acetic acid and various other alcohols, ketones
and tars.
241
-------
The last by-product is charcoal. Generally 30 to 35 percent of
input by weight is recovered in this form, and each pound of charcoal has
an approximate heat value of 12,000 Btu. Used as fuel, it can create
about half the electricity expected from the recovered gas.
Other major pieces of equipment required for a municipal or indus-
trial waste-conversion facility are a hogger/grinder, a magnetic separator,
conveyors, and storage facilities. A hogger/grinder is necessary because
converters generally operate best when solid waste materials are reduced
to no more than a few inches in size. Since pyrolysis units do not
usually vent any products to the atmosphere, they do not require any air
pollution control equipment.
3. PROCESS DESIGN0145' 1009
Pyrolytic conversion processes are generally custom-engineered
according to input volumes and types of waste being treated. For this
reason, there is not a great deal of specific design information available.
Converters have been made with capacities ranging from 1/4 ton to 12 tons
per hour. Units can be installed in batteries to handle more than 12 tons
per hour. For instance, one municipal pyrolytic process utilizes four
4-ton per hour converters.
Intake-to-discharge cycles vary with heat intensity, the converters
length, and its rotational speed. The average for industrial and municipal
refuse is 12 to 15 minutes. Such hard to pyrolyze materials as coal
(which is converted into coke) and rubber may take as long as 30 minutes.
Operational temperatures will vary with waste type and desired
products. Operating temperatures are usually in the 1,200 F - 300 F
range with the lower operating temperature generally resulting in greater
residue (coke), tar and light oil yields and lower gas yields (Tables 1
and 2).
242
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TABLE 1.
YIELDS OF PRODUCTS FROM PYROLYSIS OF MUNICIPAL AND INDUSTRIAL REFUSE
0145
Refuse
Raw municipal
Processed municipal
containing plastic
film
Indus trial-Samole A
Industrial-Sample B
Pyrolvsis
temp,
F
930-lbiC
1380
1650
930-165C
1380
1650
930-165C
1380
1650
930-165C
1380
1650
Yields, we Lent -percent of refuse
Resi- Light Free Liq-
due Gas Tar oil ammo- uor Total
in gas nia
9.3 26.7 2.2 0.5 0.05 55.8 94.6
11.5 23.7 1.2 .9 .03 55.0 92.3
7.7 39.5 .2 - .03 47.8 95.2
21.2 27.7 2.3 1.3 .05 40.6 93.2
19.5 18.3 1.0 .9 .02 51.5 91.2
19.1 40.1 .6 .2 .04 35.3 95.3
36.1 23.7 1.9 .5 .05 31.6 93.9
37.5 22.8 .7 .9 .03 30.6 92.5
38.8 29.4 .2 .6 .04 21.8 90.8
41.9 21.8 .8 .6 .03 29.5 94.6
31.4 25.5 .8 .8 .03 31.5 90.0
30 9 31.5 .1 .5 .03 29.0 92.0
Yields per ton of refuse
Gas, Tar, Light oil Liquor, Ammonium
cubic gal- in gas, gallons sulfate,
feet Ions gallons pounds
11,509 4.8 1.5 133.4 17.9
9,628 2.6 2.5 131.6 23.7
17,741 .5 - 113.9 25.1
11,545 5.6 3.7 96.7 16.2
7,380 2.2 2.6 122.6 28.4
18,058 1.4 .6 97.4 31.5
9,563 4.1 1.4 75.2 12.5
9,760 1.5 2.6 73.0 19.5
12,318 .5 1.6 51.1 21.7
9,270 1.7 1.6 70.2 20.4
10,952 1.8 2.2 74.9 21.2
14.065 .02 1.4 68.5 22.9
CO
TABLE 2.
CHEMICAL ANALYSES* OF SOLID RESIDUES FROM PYROLYSIS OF MUNIClPiJ, AND INDUSTRIAL REFUSE
Refuse
Raw municipal
Processed municipal
containing plastic
film
Industrial - Sample A
Industrial - Sample B
Pyrolysis
temp,
F
930-1651
1380
1650
930-165(
'1380
1650
930-165C
1380
1650
930-165C
1380
1650
Proximate,
Mois-
ture
2.6
2.2
1.0
1.7
1.3
1.2
.9
1.2
.1
.3
1.0
.2
Volatile
matter
4.4
7.4
4.7
4.8
13.4
3.3
2.6
5.1
2.5
3.0
3.6
6.4
percent
Fixed
29.6
51.4
31.7
56.7
34.6
53.5
15.2
17.0
12.9
9.7
16.6
16.2
I Ultimate
Ash
66.0
41.2
63.6
38.5
52.0
43.2
82.2
77.9
84.6
37.3
/9.8
77.4
Hydro-
Ken
0.4
.8
.3
.6
.8
.5
.3
.5
.3
.2
.3
.4
Car-
bon
32.4
54.9
36.1
57.7
41.9
53.4
17.0
19.4
14.8
11.8
19.5
19.3
. percent
Nitro- Oxy-
gen gen
0.5 0.5
1.1 1.8
.5 .0
.8 2.1
.8 4.4
.7 1.8
.1 .2
.2 1.8
.2 .0
.1 .4
.2 .0
.3 2.4
Sul-
fur
0.2
.2
.2
.3
.1
.4
.2
.2
.2
.2
.2
.2
Heating
value,
Btu/lb
5,020
8,020
5,260
8,800
6,080
8,090
2,520
2,900
2,180
1,660
2,680
2,810
Heating value,
million Btu/ton
10.040
16.040
10.520
17.700
12.160
16.180
5.040
5.800
4.360
3.320
5.360
5.620
Moisture on as-received basis; all other data on dry basis.
-------
4. PROCESS ECONOMICS0582' 101°
The primary factors determining the capital cost of pyrolysis systems
include waste flow rate, waste composition, secondary effluent treatment
for product recovery, and materials of construction. Operating costs are
determined by labor rates, maintenance requirements, and conversion
product values.
An exhaustive economic analysis of a commercial size (5,000 tens/day)
municipal refuse pyrolysis plant was made in 1970 by Cities Service Oil
Company.1010 The study indicated that a total investment including working
capital) of 32.6 million dollars was required and that the associated
operating cost would be $2.14 per ton of refuse pyrolyzed (Table 3).
There is no economic data available with respect to industrial waste
pyrolysis processes.
5. PROCESS MODIFICATIONS0582'1010
Modifications to the pyrolysis process generally involve treatment
of converter effluents (Figure 2). The pyrolysis oils may be sent through
a hydrotreating unit and converted to industrial fuel oil. The pyrolysis
effluent gas may be cooled and the resultant condensate separated into its
components, namely acetic acid, methanol, furfural, acetone, butyric acid,
propionic acid, methyl ethyl ketone.light fuel oil, and other water
soluble volatile organics, through the use of conventional separation
techniques. The cooled wet gas may be dried and utilized as fuel gas.
The char-like pyrolysis residue can be further treated and converted
into activated carbon.
6. PROCESS APPLICABILITY
The utilization of pyrolytic processes to convert waste into useful
materials is a relatively hew concept. For this reason, there are few
processes in operation today. Those processes which are in operation
244
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• TABLE 3
INVESTMENT AND OPERATING COSTS FOR A 1010
5000 TON/DAY MUNICIPAL PYROLYSIS PLANT
Capital Investment
Investment $ Million
Inside battery limits 16.0
Offsites 6.4
Total 22.4
Additional Costs
Contingency (25%) 5.6
Construction interest, first year
(8% x 33%) o.7
Construction interest, second year
(8% x 67%) 1.5
Startup extraordinary (assumed
8% x 100%) 2.4
Total additional costs 10.2
Total investment (includes working
capital) 32.6
Operating Costs
Fixed Costs
Labor
Supervision
Overhead
Maintenance, onsite
Maintenance, off site
Taxes and Insurance
Total fixed costs
Variable Costs
Water and power
Fuel
Total Variable Costs
Total Operating Costs
$ Million
0.49
0.15
0.64
1.00
0.24
0.49
3.01
0.20
0.70
0790
3.91
(per year)
\ r ^ »• «• • /
$1.65/ton
$0.49/ton
$2.14/ton
245
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ORGANIC LIGHT
CHEMICALS FUll OIL
* I
SALABLE
FUEL GAS
ACTIVATED
CARBON
LIQUIDS
SEPARATION
GAS DRYING
AND TREATING
CLIAN
FLUE
GAr.
FIRED
PLANT PRFHEATER
FLUl GAS
PYROLYTIC
CONVERTER
L FEED DRYER/
FLUE GAS FILTER
INDUSTRIAL
FUEL OIL
NONCOMBUSTIBLES
SEPARATION
LAND FILL
UNDERGROUND
STORAGE
CHAR RESIDUE
SEPARATION
AND
ACTIVATION
PYROLYSIS
OIL
LAND FILL
SCRAP METAL
SALVAGE
SCRAP SALES
Figure 2. Secondary Treatment Alternatives
0582
-------
convert municipal refuse, industrial refuse, paint sludges, tires,
plastics and other organic polymers into materials with economic value.1009'1011
Although the pyrolytic converter is a versatile piece of equipment that
can be operated under varying conditions with various feed materials, its
auxiliary equipment tends to be specific for various feeds and desired end
products. For that reason, the overall pyrolytic process tends to lack
versatility.
At a National Disposal Site, a pyrolysis unit would probably find
little direct application as a hazardous waste conversion unit. However,
if sufficient refuse was generated at the site, a pyrolysis unit could be
utilized to convert it into fuel gas for use in other operations (furnaces,
incinerators, reboilers, boilers for steam production and possible subse-
quent conversion to electricity, etc.) and coke which could be utilized
for its heat content or converted to activated carbon for use in water
treatment facilities.
2-17
-------
REFERENCES
0145. Sanner, W.S,., C. Ortuglio, J. G. Walters, and D. E. Wolfson.
Conversion of municipal and industrial refuse into useful
materials by pyrolysis. U.S. Department of the Interior,
Bureau of Mines, Report of Investigations 7428. Washington,
U.S. Government Printing Office, Aug. 1970. 14p.
0582. Witt, P.A., Jr. Disposal of solid wastes. Chemical Engineering.
78(22):62-78, Oct. 4, 1971. a
1009. Pyrolytic decomposition of solid wastes. Public Works, p.82,83
160, Aug. 1968.
1010. Rosen, B.H., R.G. Evans, P. Carabelli, and R.B. Zaborowski.
Economic evaluation of a commercial size refuse pyrolysis
Plant. Cities Service Oil Company. Cranbury, New Jersey,
Mar. 1970. 40 p.
1011. Chementator. Chemical Engineering. 75(26):53. Dec. 2, 1968.
1433. Kirk-Othmer encyclopedia of chemical technology. 2d ed. 22v. and
suppl. New York, Interscience Publishers, 1963.
1662. Shreve, R.N. Wood chemicals. Ir^ Chemical process industries.
3rd ed. New York, McGraw-Hill Book Company, p.617-621, 1967.
246
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