H
VTIL1ZATJON OF
MUNICIPAL SOLID WASTE
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Sculpture made of bumpers, Le Roi Soleil,
by Professor Jason Seley, Cornell University
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RECOVERY AND
UTILIZATION OF
MUNICIPAL SOLID WASTE
summary of available cost
and performance characteristics
of unit processes and systems
This report (SW-lOc) was prepared for the Solid Waste Management Office
by N. L. DROBNY, H. E. HULL, and R. F. TESTIN
Battelle Memorial Institute, Columbus Laboratories
under Contract No. PH 86-67-265
Environmental Protection Agency
librar. , V -. j. ,n V
1 HV/.L'I,I: 'v.aoiur Drive
Chicago, Illinois fiQfiCH
U.S. ENVIRONMENTAL PROTECTION AGENCY
Solid Waste Management Office
1971
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2d printing
1972
ENVIRONMENTAL PROTECTION AGHR*
This is an Environmental Protection Publication
This publication is also in the Public Health Service numbered series as Public Health Service Publi-
cation No. 1908. Its entry in two government publication series is the result of a publishing interface re-
flecting the transfer of the Federal solid waste management program from the U.S. Public Health Service
to the U.S. Environmental Protection Agency.
Library of Congress Catalog Card No. 70-611464
FOR SALE BY THE SUPERINTENDENT OF DOCUMENTS, U.S. GOVERNMENT PRINTING OFFICE, WASHINGTON, D.C. 20402
PRICE $1.75
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Foreword
DIRECTED BY CONGRESS, J the emphasis of the
national solid waste management research program should be
shifted from disposal toward recycling and reuse. This
is perhaps part of a recent national turning from over-afflu-
ence and conspicuous consumption towards values encom-
passing a quality environment. Resource recovery would be
part of a national return to the prudent Yankee temperament.
And none too soon.
According to the feedback now coming from all parts of our
ecosystem, the self-regulating controls of nature's economy
are signaling that the system is dangerously overloaded and
may become inoperative. Thus, traditional Yankee prudence
combined with soaring American imagination, are very much
needed in solving the Nation's ecologic crisis. This document,
which continues the work begun by our survey of the state of
the art of solid waste processing, 2 can contribute its specifics
to that national effort.
i The Solid Waste Disposal Act. Sec. 202, Title II of Public Law 89-272, 89th Cong. S.306, October
20, 1965, as amended, 91st Cong., 1970.
2 Engdahl, R. B. Solid waste processing; a state-of-the-art report on unit operations and processes.
Public Health Service Publication No. 1856. Washington, U.S. Government Printing Office, 1969. 72 p.
iii
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Contents
PAGE
I. Summary 1
II. Introduction 3
III. Recovery Potential of Solid Waste 5
IV. Size Reduction 7
PRINCIPLES OF SIZE REDUCTION 7
Tension forces 7
Compression forces 7
Shear forces 8
Theoretical power requirements 8
CURRENT EQUIPMENT DESIGNS 8
Crushers 8
Cage disintegrators 8
Shears 9
Shredders, cutters, and chippers 9
Rasp mills 9
Drum pulverisers 10
Disk mills 10
Wet pulpers 10
Hammermills 11
MAJOR APPLICATIONS IN SOLID WASTE PROCESSING AND RELATED INDUSTRIES. 11
EXISTING AND ESTIMATED PERFORMANCE DATA 12
EXISTING AND ESTIMATED COST DATA 14
FINDINGS 18
Principles of size reduction 18
Current applications, performance, and costs 18
Requirements for additional data 20
New equipment designs 21
V. Separation 23
UNIT PROCESSES FOR SOLID WASTE SEPARATION 25
Magnetic separation 25
Eddy-current separation 28
Size classification 31
Vibrating screens
Spiral classifiers
Gravity separation 36
Flotation
Dense media
Stoners
Wilfley tables
Mineral jigs
Osbome dry separator
Fluidized bed separator
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PAGE
Optical sorting 47
Inertial separation 49
FINDINGS 5^
Data gaps 50
Synergistic and antagonistic effects 52
VI. Recovery and Utilization 55
COMPOSTING CONVERSION PROCESSES 55
Recent and current applications of composting 56
Metropolitan Waste Conversion Corporation (METRO) 56
International Disposal Corporation (IDC) 58
Fair field-Hardy Process 58
JohnR. Snell Process 61
Gruendler Crusher and Pulverizer Company 62
The U.S. Public Health Service-Tennessee Valley Authority 62
Summary of composting costs and operational requirements 63
HEAT RECOVERY 66
Refuse incineration and steam generation in Europe 66
Refuse incineration and steam generation in the United States 66
Atlanta, Georgia
Chicago, Illinois
Miami, Florida
Hempstead, Long Island, New York
U.S. Naval Station, Norfolk, Virginia
Houston, Texas
Operating characteristics and costs of selected incinerator systems., 67
Capital costs of incinerators with or without heat recovery
Economics of waste-heat recovery
Refuse-fired gas turbines 73
CHEMICAL CONVERSION 74
Prolysis 74
Current applications of pyrolysis to solid waste 75
Paper evaluation of pyrolysis
Retort research on the pyrolysis of municipal waste
Operating pyrolysis units for waste disposal
Summary of progress and research needs
Hydrolysis 80
Production of Ethyl Alcohol from Municipal Refuse 81
Madison Wood Sugar Process 81
Production of alcohol from municipal refuse—a paper evaluation 81
Summary of progress and research needs
Production of protein from solid waste 82
Conversion of waste paper to protein
Evaluation of a process to culture yeast on solid waste: a report
of the work of Ionics, Inc.
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PAGE
General chemical methods of solid waste conversion 82
Partial oxidation of solid organic wastes
Chemical transformation of solid waste
FLY-ASH UTILIZATION 83
Utilisation of coal fly ash 83
Concrete additive
Soil stabilization
Asphalt paving mixes
Soil conditioner
Water and waste water treatment
Lightweight aggregate
Fly-ash based bricks
Economics
Prospects for the utilization of refuse incinerator fly ash 85
SALVAGE OF MUNICIPAL SOLID WASTE 86
Tin cans 86
Utilization technology
Existing salvage operations
Paper 87
Recovery of paper stock from municipal solid waste
Processing systems
Deinking
Bulk fiber recovery
Glass 90
Plastics , 91
Rubber , 91
Rags 92
Incinerator residues 92
FINDINGS 92
Salvage versus by-product recovery 92
Data gaps 93
Synergistic and antagonistic effects 94
VII. Conclusions 95
UNIT PROCESSES AND RELATED COST AND PERFORMANCE DATA 95
BY-PRODUCT RECOVERY VERSUS SALVAGE 95
ECONOMICS OF SOLID WASTE RECOVERY AND UTILIZATION 96
VIII. Potentially Attractive Process Combinations 97
Appendix A. Summary of Contacts Established 101
Appendix B. New Size-Reduction Equipment Designs _ __ 109
Appendix C. Other Separation Patent Art 117
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/. Summary
SOLID WASTE constitutes a resource
disguised as a nuisance. This is the
underlying philosophy that has moti-
vated this study. The study has
resulted in this sourcebook of all
available cost and performance char-
acteristics of unit processes that are,
or might be, employed in solid waste
recovery and utilization. The study
covers three main areas: size reduc-
tion, separation, and recovery. Re-
covery includes both direct salvage
and the manufacture of new by-
products.
The cost and performance informa-
tion presented herein provides a basis
for preliminary technical and eco-
nomic evaluations of equipment and
processes for recovery and utilization
of solid waste. The primary informa-
tion sources for the study were the
operators of existing processing sys-
tems, equipment manufacturers, and
selected experts. Over 200 such con-
tacts were established. A previous
study conducted by Battelle had indi-
cated that the information needed
could not be found in the published
literature.1 Because existing applica-
tions of equipment and processes to
the recovery and utilization of solid
waste are not well documented in
quantitative terms, potential uses of
industrial processes were also investi-
gated. Examples include the minerals
beneflciation, pulp and paper, and
chemical processing industries. Pri-
mary problems encountered in the
study were the lack of existing opera-
tional data, questionable reliability
of available data, and proprietary
constraints that made it impossible to
obtain some data. Where warranted,
engineering estimates were employed
to fill data gaps.
It is essential for the separation and
eventual recovery of solid waste that
the components to be processed be
physically free from one another.
This, in turn, often implies a need for
size reduction to precede salvage or
by-product manufacture.
Size-reduction equipment employs
three basic forces—compression, ten-
sion, and shear—in various combina-
tions. Available cost and performance
data were collected for nine types of
equipment which differ principally in
their application of the above three
forces; these are crushers, cage disin-
tegrators, shears, shredders, rasp
mills, drum pulverizers, disk mills, wet
pulpers, and hammermills. Based
upon data obtained from the various
sources, relationships were generated
indicating power requirements and
product cost as a function of through-
put. Estimates were developed for
product cost and power requirements
as a function of product size and pro-
duction rate. Power requirements
were also related to theoretical
equipment efficiencies.
Existing applications of size-reduc-
tion equipment to solid waste proces-
sing merely adapt standard equipment
designed for other functions. Conse-
quently, serious problems have been
reported by solid waste processors.
Based upon operational difficulties
and engineering design considera-
tions, new concepts were generated
during the study for improved solid
waste size-reduction equipment.
Due to the heterogeneity of typical
solid waste and diversity of recovery
operations which can be conceived,
separation is a second important step
in the recovery and utilization of solid
waste. The efficiency with which sep-
aration is effected and the degree to
which the desirable materials can be
segregated are significant factors con-
tributing to cost and marketability of
recovered products. Consequently, sig-
nificant effort was devoted to the col-
lection of technical data for equip-
ment and processes that could be used
in the separation of solid waste.
As of 1968 the most widely em-
ployed means for separating solid
waste is handpicking and sorting from
conveyors. Handsorting is employed,
almost without exception, at nearly
all U.S. and European compost
plants, and at some municipal incin-
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2 SUMMARY
erators, to remove such items as clean
newsprint and cardboard, rags, met-
als, glass, and plastic. These materials
are removed for salvage purposes and
in the case of composting to upgrade
the quality of the final product. Hand-
sorting is unsatisfactory for large-
scale recovery and utilization for
several reasons including: (1) low
salvage prices that limit the economic
attractiveness of such operations; (2)
the limited degree of separation that
can be effected since a nominal size
work force can be concerned only with
removing more bulky pieces; (3)
human fallibility.
In recognition of the need for a va-
riety of improved separation tech-
niques, and in view of the extremely
limited number of existing applica-
tions of advanced technology to solid
waste processing, the entire field of
industrial separation technology was
surveyed in detail for potentially
adaptable techniques and related per-
formance and cost characteristics. As
indicated, only a small number of the
more sophisticated separation tech-
niques have been applied to solid
waste processing, and the historical
experience of these applications is ex-
tremely limited. Consequently, much
of the collected cost and performance
data relate to industrial applications
significantly different from solid
waste processing and must be em-
ployed and interpreted with extreme
care. Such data, therefore, cannot be
used for design purposes, but rather
are intended to be used to indicate
the general types of separations
which are possible, general feed re-
quirements, and order-of-magnitude
costs. This type of information is es-
sential in making preliminary judg-
ments as to potentially desirable proc-
ess and equipment combinations for
solid waste recovery.
All of the separation techniques
studied are designed to detect and to
operate selectively on (and to a large
extent automatically) differences in
various properties of the materials
being separated. Primary properties
employed in the separation techniques
investigated in this study include
magnetic properties, particle size, spe-
cific gravity, and light-reflectance
properties of the surfaces.
Specific separation processes stud-
The mention of commercial products
within this report does not imply endorse-
ment by the U S. Government.
ied included magnetic separation,
eddy-current separation, flotation,
dense-media separation, screening,
vibrating tables (wet and dry), opti-
cal sorting, and ballistic separation.
In principle each of these processes
has potential application to process-
ing. However, with the exception of
magnetic separation, the degree to
which these techniques can be
adapted in practice is not well estab-
lished because of the lack of suitable
cost and performance data upon
which to base evaluations. The pri-
mary technical obstacle in the appli-
cation of these techniques to the sep-
aration and recovery of solid waste is
that its components generally do not
exhibit one unique property that per-
mits straightforward separation.
The ultimate objective of both size
reduction and separation is the re-
covery of solid waste, either in the
form of new manufactured by-prod-
ucts or by direct salvage. Existing
techniques, practices, and market sit-
uations for salvage of tin cans, pa-
per, glass, plastics, rubber, rags, and
incinerator residues from solid waste
were investigated. Although a salvage
market does exist and is being used in
a few instances to recover selected
fractions of solid waste, the long-term
potential of direct salvage is not
large. The primary problem relates to
technical difficulties and the relatively
high cost of obtaining sufficiently
pure fractions to comply with salvage
specifications and the relatively lower
cost of raw materials which the sal-
vaged products are supposed to re-
place. It is concluded, therefore, that
the major potential for solid waste re-
covery is in the manufacture of new
by-products.
Available cost and performance data
were collected for four general areas
of by-product recovery: composting,
heat recovery, chemical recovery in-
cluding biochemical processes, and
fly-ash utilization. Composting along
with its auxiliary salvage operations
is the recovery process which is being
employed most widely and for which
most data are consequently available.
Data have been collected on capital
and operating costs, power require-
ments, and labor requirements for
both U.S. and European compost
plants. Data on municipal incinerators
employing waste heat recovery are
scarce. Actual experience in the
United States is limited to installa-
tions in Chicago, Atlanta, Norfolk,
Long Island, and Miami. Operational
data were difficult to obtain, although
sufficient data were available to de-
velop preliminary relationships for
capital costs. Chemical conversion of
solid waste has not been practiced on
a large scale, and available informa-
tion is limited to laboratory data and
process estimates. Studies conducted
by others have indicated potential
economic merit in the hydrolysis of
solid waste containing 60 percent pa-
per, and in the fermentation of mixed
refuse to produce protein. Available
cost estimates have not yet been sub
stantiated by large operations. De-
tailed laboratory data have been made
available by various researchers, for
the pyrolysis of solid waste to produce
fuel gases, carbon, and organic acids,
but cost estimates have not yet been
developed. A potential for the utiliza-
tion of incinerator fly ash was also
identified. This application may be
limited, however, by the wide availa-
bility of coal fly ash which is a higher-
quality, more uniform product.
Based upon the quantitative and
qualitative data collected during the
study, potential processes and equip-
ment combinations are defined which
appear sufficiently promising to war-
rant either additional development
through research or further opera-
tional study at the demonstration level
to obtain detailed performance and
cost data of the type required for use
in the design of future systems.
Based upon information collected,
it is considered that solid waste recov-
ery may never become economic in the
engineering sense, but that the exter-
nal diseconomies and social costs
associated with the disposal-oriented
methods of solid waste management
may provide a strong motivation for
continued development of solid waste
recovery techniques. It is also con-
cluded that meaningful and reliable
cost data are not available from exist-
ing operations and that the Bureau
of Solid Waste Management will need
to collect such data from demonstra-
tion projects and similar activities
conducted under its own auspices. A
final major conclusion is that by-
product manufacture from mixed
refuse offers more economic potential
for solid waste recovery than does
material salvage.
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II. Introduction
WHAT TO DO with the more than
300 billion Ib of municipal solid waste
generated annually in the United
States is a question receiving exten-
sive attention at all levels of tech-
nology ranging from research to facil-
ity construction. Most current activity
can be traced to authority delegated
and financial resources made available
by passage of the Solid Waste Disposal
Act, PL 89-272, in October 1965. Fur-
thermore, much of the recent activity
has centered both on disposal of this
great quantity of material and its uti-
lization. This latter aspect of solid
waste disposal, or more properly solid
waste management, is the subject of
this study. Specifically, the objective
of this study was to prepare a hand-
book of equipment and process tech-
nology and associated costs that could
be used in solid waste recovery and
utilization. Studies focused on three
main areas—size reduction, separa-
tion, and recovery. For purposes of
this study, recovery includes both
direct salvage and the manufacture
of new by-products.
The current emphasis on the re-
covery and utilization of solid waste
is the result of many factors. Perhaps
most important is the growing inade-
quacy of traditional methods of dis-
posal. Land areas suitable for landfill
near urban centers where the bulk of
the solid waste is generated are be-
coming increasingly scarce and more
costly to obtain. Open burning has
been outlawed in most major urban
centers because of its contribution to
air pollution.
Open dumping has also been
stopped in most areas for a variety of
reasons including health hazards,
aesthetic considerations, and con-
ditions that lead to insect and rodent
proliferation and water pollution. In-
cineration, as traditionally practiced,
is becoming increasingly less attrac-
tive due to expensive air pollution con-
trol equipment required to meet ac-
ceptable air-quality standards.
Another reason for investing con-
siderable effort in the recovery and
utilization of solid waste is that much
of this material is, in effect, a re-
source disguised as a nuisance. For
example, approximately 12 million
tons of steel, mostly in the form of
tin cans, are being lost every year in
landfills as a result of our current
waste disposal practices.* It makes
sense from both economic and re-
source conservation viewpoints that
better use be made of such materials.
An analysis of the recovery and utili-
zation potential of solid waste is
deferred to the next section of this
report.
Within the context of these con-
siderations, this study was undertaken
to define the technology, economics,
and future potential for the recovery
and utilization of municipal solid
waste. Since these factors hinge large-
ly upon costs and performance capa-
bilities, emphasis was placed upon
obtaining cost and performance data
from literature, patent files, equip-
ment manufacturers, and currently
operating refuse reclamation and dis-
posal plants. A previous study con-
ducted by Battelle indicated that the
published literature is not an ade-
* 0.825 tons refuse
X200X10" personsX
persons years
0.075 Ib ferrous material _
Ib refuse
12.375 tons ferrous material
year
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4 INTRODUCTION
quate source of the cost performance
data desired.1 Consequently, heavy
reliance was placed, as information
sources, upon manufacturers and
operators of equipment and processes
that could be used in various aspects
of solid waste recovery. During the
study, over 200 such contacts were
established. These are summarized in
detail in Appendix A.
Based upon equipment and process
capabilities (and associated capital
and operating costs) and expected
ranges in solid waste characteristics,
possible synergistic and antagonistic
effects of one process upon another
have been identified, and potentially
promising process combinations have
been suggested.
Problems encountered during the
study related primarily to the lack of
available data. Wherever possible,
engineering estimating procedures
were employed to fill data gaps.
Where the generated estimates are
not sufficiently reliable or could not
be developed, recommendations are
provided for specific programs de-
signed to generate missing data either
through research or demonstration
study programs.
The work summarized in this report
was supported by the Bureau of Solid
Waste Management,* U.S. Depart-
ment of Health, Education, and Wel-
fare under contract Ph-86-67-265.
Considerable assistance in the collec-
tion of information was also rendered
by various manufacturers and opera-
tors of existing systems. Specific
acknowledgements are indicated in
the text and are summarized in Ap-
pendix A.
*The Bureau is now the Solid Waste Man-
agement Office o! the U.S. Environmental
Protection Agency.
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777. Recovery potential
of solid waste
THE UNDERLYING PHILOSOPHY that
has motivated this study is that solid
waste is a resource. This philosophy
is, however, meaningful only to the
extent that techniques and processes
can be developed to exploit this re-
source through the recovery of solid
waste materials in an economically vi-
able operation. The assessment of
economic viability is by no means a
simple task; however, one must not
only consider processing costs in
light of income and market potential
of recovered materials, but must also
consider social costs and, perhaps
TABLE 1
EXPECTED RANGES IN MIXED MUNICIPAL REFUSE COMPOSITION*
Percent composition as received
(dry weight basis)
Component
Anticipated
range
Nominalf
Paper.
Newsprint-
Cardboard.
Other
Metallics.
37-60
7-15
4-18
26-37
7-10
55
12
11
32
Ferrous
Nonferrous.
Food
Yard
Wood
Glass
Plastic
Miscellaneous. _-
6-8
1-2
12 18
4-10
1-4
6-12
1-3
<5
7. 5
1. 5
14
5
4
9
1
3
Moisture content:
Range (percent) 20-40
Nominal (percent) 30
100
more important, social benefits asso-
ciated with the alleviation of pollu-
tion, health hazards, and other prob-
lems associated with traditional dis-
posal techniques. These latter consid-
erations relating to the socioeconomic
aspects of solid waste recovery are
outside the scope of this study which
has concentrated on technical per-
formance of selected processes and
direct processing costs.
To provide a basis for evaluating
the technical aspects and the en-
gineering economics, it was necessary
to establish guidelines regarding the
typical composition of mixed munic-
ipal refuse.*
Recent studies have shown this to
be highly variable according to geo-
graphic location, climate, season, and
socioeconomie characteristics of the
contributing population.2'3 Sampling
difficulties also contribute to the diffi-
culties in obtaining precise composi-
tion data.
Data collected from several sources
on solid waste characteristics are con-
sidered to be a reasonable representa-
tion of available data (Tables 1 and
2).
*Based upon data contained in References 2 to 8.
fBattelle estimate.
*In the broadest sense, municipal refuse
is defined to include all waste materials that
are not handled by air or waterborne car-
riers. Within this category fall aai of the
solid waste materials generated by domestic,
commercial, institutional, and industrial
operations as well as solid materials result-
ing from air pollution control (e.g., flyash),
water pollution (sewer sludge), and miscel-
laneous material such as junk cars. In this
handbook, the term "mixed municipal
refuse" Is used to cover the mixed solid ma-
terials resulting from household, commer-
cial, and Institutional garbage and trash
collections, but excluding special industrial
wastes, the larger demolition wastes, and
specialty loads of like items (e.g., loads of
rubber tires, junk cars, and sewage sludge).
The mixed municipal refuse will be used as
a basis for evaluating the technical and
englneerng aspects of solid waste recovery
since it provides the greatest challenge In
terms of nonhomogeneity of constituents
and difficulty in separation.
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6 RECOVERY POTENTIAL OF SOLID WASTE
TABLE 2
DEFINITIONS OF MIXED MUNICIPAL REFUSE COMPONENTS'
Newsprint Newspapers. Does not include magazines, handbills,
etc.
Cardboard Corrugated boxboard and the heavier paperboard
used in cartons. Light cardboard in food packages
and the backing of paper pads are included with
"miscellaneous mixed paper."
Miscellaneous mixed paper. All other paper not included above.
Metallics Tinned and aluminum cans, hardware, bottle caps,
utensils, wire, and other ferrous and nonferrous
metal articles.
Food (garbage) waste Wastes, from the handling, preparation, cooking, and
serving of foods. Does not include packaging ma-
terials or paper discarded with garbage.
Yard waste Lawn, garden, and shrubbery clippings, sod and
small yard debris other than branches.
Wood waste Branches, scrap lumber, and other wooden articles.
Glass Glass and ceramic materials.
Plastic Film plastics and molded plastic articles.
Miscellaneous Stones, metal oxides, articles made of natural and
synthetic fibers, rubber products, and leather goods.
* Kaiser, E. R., and C. D. Zeit. The composition and analysis of domestic refuse at the Oceanside plant.
Personal communication to N. I. Drobny, Aug. 1966.
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IV, Size reduction
SIZE REDUCTION is becoming an in-
creasingly important operation in
municipal solid waste processing. Size
reduction is of primary interest here
because it permits more efficient sep-
aration and recovery processes. Of
more general interest is the fact that
reduction of material bulk often fa-
cilitates handling. Examples of the
effects of particle size on the efficien-
cy of separation is given in a later
section on material separation. The
Stoner, for example, a gravity separa-
tion device, requires closely controlled
particle size to effect good separation.
Similarly, the Osborne separator can
tolerate organic particles no larger
than 1 in. or inorganic particles no
greater than A in.
For many years, recovery from
municipal solid waste was accom-
plished entirely by handsorting, and
size reduction was applied only to
such materials as oversize burnable
waste and compostable material. In
recent years, however, the combina-
tion of greater waste generation and
increased costs from handsorting has
resulted in the need for more mech-
anization to provide for recovery
that is economical. This, in turn, has
Tension
Interrelated
forces
Compression
FIGURE 1. The application of
forces in size-reduction operations.
Shear
created a need for size-reduction
equipment suitable for use on solid
municipal waste.
PRINCIPLES OF SIZE
REDUCTION
Size reduction of municipal solid
waste is the mechanical separation of
bodies of material into smaller pieces.
Some minor biodegradation and
water-dissolving effects are helpful in
composting and wet-pulping proc-
esses, but size reduction by the appli-
cation of mechanical forces is the
focus of this discussion. These mech-
anical forces are categorized as fol-
lows: tension forces, compression
forces, and shear forces (Figure 1).
TENSION FORCES
The application of tension to a
body is usually accompanied by com-
pression and shear forces as a result
of gripping forces and the internal
transfer of energy. The energy in-
volved in the separation of a body into
smaller pieces by tension forces is the
force applied multiplied by the dis-
tance through which it moves. To sep-
arate a ductile body by tension forces,
the energy required is theoretically
greater when the length of the yield-
ing member between the points of
application of the forces is greater.
Therefore, the closer together the
opposing tension forces, the lower
will be the breaking energy. Ham-
mermills in which a hammer impacts
a mass and breaks off a section are
one example where tension forces de-
velop at points separated by relatively
small distances.
COMPRESSION FORCES
The fracture of a body by compres-
sion is usually caused by internal ten-
sion and shear forces that are a result
of the compression force. Here again,
the energy used is the force applied
multiplied by the distance traveled.
Strong, brittle materials—e.g., glass—
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8 SIZE REDUCTION
may require high forces for fracture
such as those obtained by impact. The
distance through which the force
travels to bring the material up to the
yield point may be very short, how-
ever, and this may result in relatively
low theoretical power requirements.
SHEAR FORCES
Shear forces in a body are usually
accompanied by both tension and
compression forces (Figure 1). Com-
pression forces are applied to a body
in offset planes to produce a shearing
action. Tension forces can result in
the body due to the distance between
the offset planes during the shearing
operation.
The energy required to shear a body
into smaller pieces is also the force
applied times the distance through
which the force is applied. The shear-
ing of flat material (even if it is
ductile) may be accomplished with a
minimum of work because of the rel-
atively short distance that the force
travels. This suggests that emphasis
on the use of shearing forces in munic-
ipal solid waste size reduction could
lead to increased efficiency.
THEORETICAL POWER
REQUIREMENTS
The power requirements for size
reduction of ductile material by ten-
sion are, in general, higher than for
brittle material because of the long
stretching travel required to produce
separation. Thus, in order to consider
the more difficult task for comparison
purposes, theoretical requirements
were computed for reducing large
sheets of 0.050-in. ductile steel to 6-
and 3-in. squares.
The following simplifying assump-
tions were made: (1) 1-ton grip force
to produce a 1-in. deep corrugation;
(2) yield strength of 50,000 psi; (3)
elongation of 20 percent; and (4)
yield occurring for 3 in. on each side
of the fracture line. The computations
are as follows: force requirements to
bring two sides of a square to the
yield point are:
The force required for 6-in. pieces = 50,000X0.050X
6X2 =30,000 Ib
The force required for 3-in. pieces = 50,OOOX0.050X
3X2 =15,000 Ib
Travel =0.2X6 =1.2 in. or 0.1 ft
Clamping energy=2,OOOX;7, = 167 ft-lb or 0.1 ft
12
Breaking energy for 6-in. pieces=30,000X0.1 = 3,000
ft-lb
and
Breaking energy for 3-in. pieces = 15,000X0.1 = 1,500
ft-lb
Now, 0.050-in. steel sheet weighs about 2 lb/ft2
Pieces/ton = ' 0 lu,t,f—— =4,000, 6-in. pieces/ton
and
2 lb/fti
2,000X16
= 16,000, 3-in. pieces/ton
Power requirements per ton are:
4 000X3 167
Power for 6-in. pieces= ^ nnri Jan =6.4 hp-hr/ton
and
Power for 3-in. pieces =
33,000X80
16,000X1,667
33,000X60
= 13.5 hp-hr/ton
The tearing of wood, as an example
of a more easily reduced component of
solid waste, may be compared to the
tearing of steel by applying density,
strength, and yield factors, and as-
suming the same piece sizes. Assum-
ing relative densities of 0.28 lb/in3 for
steel and 0.023 for wood, a strength
ratio of 50,000 to 4,000 psi and a yield
ratio of 20 to 10, theoretical power re-
quirements for the size reduction of
thin wood sheets to 6- and 3-in.
squares would be as follows:
no i flfln 10
Power required =6.4 X X X =3.1 hp-hr/
ton (6-in. wood)
a 1
Power required =13.5X^7 =6.3 hp-hr/ton (3-in.
wood)
As expected, the actual power re-
quirements discussed later under the
heading "Existing and Estimated Per-
formance Data" were found to be con-
siderably higher than the theoretical
values.
CURRENT EQUIPMENT
DESIGNS
In the course of the program, 68
companies identified as manufacturers
of size reduction equipment were con-
tacted; these company contacts are
summarized in Appendix A. Basic
equipment types available from these
manufacturers include: crushers; cage
disintegrators; shears; shredders, cut-
ters, and chippers; rasp mills; drum
pulverizers; disk mills; wet pulpers;
and hammermills.
All except cage disintegrators, cut-
ters, and disk mills have direct poten-
tial applications in municipal waste
size reduction, with hammermills
being used in about 90 percent of the
existing systems.
CRUSHERS
Pour types of crushers are used in
industry (Figure 2). These are jaw,
FIGURE 2. Crushers.
roll, gyrating, and impact types. All
four of these have potential uses in
the solid waste program; however, the
impact crusher, a form of hammer-
mill, has the most universal appli-
cation.
The jaw, roll, and gyrating crushers
use the relatively slow efficient appli-
cation of compression to friable ma-
terials such as coal and rock. General
usage is in mines and quarries, and a
wide range of product size, V2 to 10 in.,
may be obtained. Power may range as
widely as 25 hp in the small units to
2,000 hp in huge mine installations.
CAGE DISINTEGRATORS
Cage disintegrators are high-speed
machines which use single or multiple
contrarotating cages to produce im-
pact on material (Figure 3). Some-
what selective input is introduced at
the center, and material is fractured
on natural cleavage planes by the
repeated action of the heavy cage bars
as it escapes radially. This action pro-
duces rapid, efficient application of
compression; but, as in the case of
most of the crushers, it is limited to
brittle materials such as glass and
rock salt. Cage disintegrators are used
primarily in chemical industries with
a product ranging from fine powder to
1/2-in. pieces. The usual range of power
is from 2 to 1,000 hp. The most suita-
ble application of cage disintegrators
-------
Input
Single or
multiple
contrarotatmg
cages
* }
FIGURE 3. Cage disintegrators.
o
Single alligator-type
FIGURE 4. Shears.
Cutting type
FIGURE 5. Shredders, cutters,
and chippers.
to solid waste size reduction would
be in secondary size reduction of sep-
arated, friable materials.
SHEARS
The single-blade shear is an illus-
tration of a class of size-reduction
equipment which is directly applica-
ble to solid waste (Figure 4). Shears
may range from the small, single-
blade, alligator type to the large, mul-
tiple-blade hopper type. As the name
implies, shears employ the slow appli-
cation of shear forces. Use of shears
is somewhat limited to bulky materials
such as wood timbers found in demoli-
tion and harbor waste and metal auto-
mobile bodies.
Single-blade shears are often found
in scrap-metal yards where they are
used on a wide range of materials
from drive shafts and I-beams to au-
tomobile bodies. Multiple-blade shears
are often used for automatic reduc-
tion of trees and other oversize items.
The product normally ranges from
1-ft cubes to auto bodies cut into
thirds. Applications to municipal solid
waste would, in general, be primary
size reduction operations.
SHREDDERS, CUTTERS, AND
CHIPPERS
Shredders, cutters, and chippers
utilize both tension and shear. In this
class of equipment, two general types
are of interest—the pierce-and-tear
type and the cutting type (Figure 5).
Although the cutting type is more
widely used in industry, it is not well
suited to the reduction of municipal
solid waste. Its blades properly sharp-
ened for good efficiency are exces-
sively vulnerable to damage by un-
sorted solid waste.
The pierce-and-tear type of shred-
Rasp Mills 9
der uses overlapping fingers operating
at various speeds—slow, medium,
fast—to pierce, tear, and shear. This
machine uses the interaction of rela-
tively dull members to apply a tear-
ing action.
In general, the application of ten-
sion and shear by piercing and tearing
is best suited to fibrous or ductile ma-
terials as found in the paper and box-
board industries. Of more direct use
on municipal solid waste, however, are
the more familiar mobile yard-waste
chippers and the large auto-body
shredders.
Power inputs to shredders of inter-
est in municipal solid waste process-
ing range from 100 hp on the small
units to 2,000 hp on the large ham-
mermills.
RASP MILLS
Rasp mills are massive cylindrical
machines, 20 ft or so in diameter,
which employ the slow application of
all three forces—tension, shear, and
compression (Figure 6).
The input to the rasp mill is flexible.
Through a large opening, a wide
range of solid waste can be
introduced.
An internal rotor, traveling at 5 to 6
rpm, swings heavy arms which push
the waste around and around over
rasping pins and down through holes
to produce about 2-in. product.
Thus, the mill is self-limiting; and,
after a reasonable length of time,
durable bulky items which have not
been properly reduced are turned out
through a reject chute.
Rasp mills, like drum pulverizers,
are used primarily in composting
plants. The only rasp mill found in
the United States during this study
was the one in the joint U.S. Public
Input
Reject
FIGURE 6. Rasp mills.
-------
10 SIZE REDUCTION
Health Service-Tennessee Valley Au-
thority composting project at Johnson
City, Tennessee. However, it is re-
ported that several are being used in
Europe" and one in Tel Aviv, Israel."
DRUM PULVERIZERS
Drum pulverizers have an action
similar to the rasp mill (Figure 7).
The input is flexible, again accepting
a wide range of materials. These ma-
terials pass through a rotating drum
about 10 ft in diameter. The drum
may be circular, octagonal, or hexag-
onal in design and may rotate at
speeds up to 11 rpm. Drum pulverizers
may have added churning effects by
the action of stationary or contraro-
tating beaters or baffles. Reducible
material is torn and pushed through
the holes which may be the same size
or graduated. As the material passes
through the drum longitudinally, a
rough size separation may be provided.
DISK MILLS
Disk mills are a class of precise
machines with very high-speed single
or contrarotating disks between which
selected material is passed (Figure 8).
The material is literally torn to bits.
Disk mills are best suited to pulpable
materials, although other materials
such as flour and sugar are processed
in them.
Their applications are limited to
relatively small input sizes—perhaps
2-in. maximum. They are used exten-
sively in the paper, boxboard, and
food production industries. Their
product is usually a refined pulp or
fine grain.
Possible applications of disk mills
to municipal solid waste could be con-
sidered as a secondary size-reduction
operation on pulpable materials.
Power up to 4,000 hp on these ma-
chines is not unusual in large paper
mills. Smaller models of these ma-
chines appear to be more applicable
to municipal solid waste.
WET PULPERS
Wet pulpers are similar to single-
disk mills except they have vertical
axes (Figure 9). In operation, a slurry
of about 90 percent water and some-
what selected waste produces a toroid
in which the solids are subject to
repeated impact by hardened high-
speed members. These members nor-
mally operate at a speed of about 5,000
ft per min. Thus, the rapid application
of all three forces is attained. Wet
pulpers are best suited to fibrous ma-
terial, although a wide range of mate-
rial including occasional cans and
Input
^o. Rejects
Perforated inner drum :
circular .octagon or hexagon
II rpm
FIGURE 7. Drum pulverizers.
Output
Single or contrarotating
FIGURE 8. Disk mills.
Hard member
Rejects
Product
FIGURE 9. Wet pulper.
-------
Major applications in solid waste processing and related industries 11
Shredder teeth
FIGURE 10. Hammermills.
000°
Grate
bars
rocks can be tolerated. Unpulpable
material, such as rubber tires, is re-
jected. Barbed wire type of conveying
devices called raggers are often used
for automatic extraction of rope and
fabric; but to date, they are somewhat
limited to more selective input. Bar
screens in the output stream also have
been used, but tend to clog with gen-
eral solid waste input. As a result of
the buildup problem, conveyor-type
screens have been considered. Appli-
cations to municipal solid waste proc-
essing are primarily in composting
plants; however, the characteristics of
the product have been cited as readily
adaptable to separation, recovery, and
landfill operation.
HAMMERMILLS
Hammermills, as mentioned before,
represent the largest percentage of
municipal waste size-reduction equip-
ment (Figure 10).
There are two general types of ham-
mermills—the swing-hammer type
and rigid-hammer type. Pivoted swing
hammers may vary considerably in
design from the rectangular block
type, to sharp choppers and flexible
flails, to the ring-hammer with multi-
ple wearing corners. Rigid hammers
fixed to the rotor also have a wide
range of designs from thin, sharp
choppers to the wide, blunt impact-
crusher type. Clearance adjustment of
the impact surfaces and swinging
tramp-metal traps are often provided.
On some hammermills, plate-con-
veyor-type impact surfaces are added
to provide extended wearing surfaces
plus an antijamming effect.
Another variation is the combina-
tion of standard hammermill action
with the use of shredding members
meshing with the hammers. These
may be stationary or moving (Figure
10). Usually grate bars determine the
Shredder
teeth
Moving
product size, but some designs use
the clearance of the hammers with
impact surfaces or shredder teeth and
machine speed to determine the prod-
uct size.
Hammermills make use of rapid ap-
plication of tension, compression, and
shear forces. A ballistic presorting or
rejecting effect can be obtained by
upswinging hammers. In this mode of
operation, durable bulky items are
bounced by the hammers into the re-
ject bins or chutes. Another design,
which uses a unique vertical axis
rotor, rejects unwanted material by
flinging it up a conical surface into
a reject area.
Hammermills have, perhaps, the
widest range of feed in regard to ma-
terial composition; but the adjustment
of feed rate is critical for efficient
operation. Information obtained on
size reduction of municipal solid waste
by the hammermill is quite variable
because of wide variations in operat-
ing conditions.
MAJOR APPLICATIONS IN
SOLID WASTE
PROCESSING AND
RELATED INDUSTRIES
Of primary concern in this project
is the universal processing of mixed
municipal refuse; useful information
was also obtained, however, on the
size reduction of selected materials
such as wood and steel car bodies.
Twenty-one of the 68 companies
contacted provided performance data
on equipment currently applied to
some portion of solid waste size re-
duction.* The equipment discussed
here are hammermills, 14 companies;
*Full address, contacts, and types of
data are presented in Appendix A.
shredders, two companies; drum pul-
verizers, two companies; wet pulpers,
two companies; and rasp mills, one
company. Other types of equipment
such as chippers and cage disintegra-
tors may be applied to a minor portion
of solid waste size reduction, but the
more universal types were emphasized
in this program. The specific compa-
nies contacted regarding size-reduc-
tion equipment are listed below.
Hammermills
American Pulverizer Company
St. Louis, Missouri
Buffalo Hammermill Corporation
Buffalo, New York
Buhler Brothers (Swiss)
Ontario, Canada
Perrox Corporation
Scott, Louisiana
Hell Company (Gondard, French)
Milwaukee, Wisconsin
Gruendler
St. Louis, Missouri
Hammermills, Inc.
Cedar Rapids, Iowa
Hazemag U.S.A. (German)
New York City
Jeffrey Manufacturing Company
Columbus, Ohio
Newell Manufacturnig Company
San Antonio, Texas
Pennsylvania Crushers
Broomall, Pennsylvania
Stedman Foundry and Machine
Aurora, Indiana
Tollemache, Ltd.
London, England
Williams Patent Crusher and Pulverizer
Company
St. Louis, Missouri
Shredders
Centriblast Corporation
Subdivision of Joy Manufacturing Company
Pittsburgh, Pennsylvania
Logemann Brothers
Fond du Lac, Wisconsin
Drum Pulverizers
John Thompson Company
England
Vickers Company
England
Wet Pulpers
French Oil Mill Company
Piqua, Ohio
Black Clawson Company
Middletown, Ohio
Rasp Mills
Dorr-Oliver Company
Netherlands
-------
12 SIZE REDUCTION
TABLE 3
SOLID WASTE SIZE-REDUCTION EQUIPMENT IDENTIFIED
Capital
Identifi- investment
cation* (thousands
of dollars)
®
®
(D
A
© - -
• --{
®
0
@ ____
m
m ----
m
35. 0
8. 5
33
80
130
50
30
60
86
160
17. 5
150
200 \
59. 5
14.2
53.0
,0 {
15.0
69. 5
Horse-
power
800
300
200
3501
1, 500/
80
1,000
150
350
800
300
800
150
2,000
500]
1, 000 1
1, 500 f
4, OOOj
800
300
50
150
60
150
4,000
150
350
Average
Material handled t capacity
(tons/hr)
MSW . __
Dry to wet
fibers.
Picked MSW
MSW j
Picked MSW
Car bodies
Picked MSW
Picked MSW
Car bodies
MSW
Harbor waste
Wood waste
Presheared car
bodies.
Car bodies \
MSW
Wood waste
Picked MSW
Picked MSW
Picked MSW
Picked MSW
Car bodies
Picked MSW
Picked MSW
17
40
10
30
70
9
20
10
20
25
30
140
30
50
10
16
20
50
40
24
7
10
8
10
100
12
60
Hp-hr
per ton
47
7. 5
20
12
21
8.9
50
15
18
32
10
5. 7
5.0
40
50 ]
62 1
75 1
80 J
20
12
7
15
7. 5
15
40
12
6
Weight
(tons)
25
10
19
33
35
52
100
75
^
45
15
Inlet opening
(in.)
55 x 60
50 x 50
38 x 79
48 x 60
48 x 72
48 x 48
40 x 80
Estimate.
40 x 40
42 x 60
60 x 120
96 x 150
42 x 48
40 x 60
60 x 80
Estimate.
60 x 80
36 x 72
Special features, installations
Ring hammers, Erie, Tampa.
Ring hammers, no bulky items.
Double rotor, Europe.
Crushing feeder, 4-in. product,
Meshing hammer/anvil,
Gainesville.
Rasp mill, 2-in. product,
Johnson City, Tennessee.
Flattened car, Scott, Louisiana.
Ballistic reject, Madison,
Wisconsin.
Plate-conveyer impact area,
Mobile, Alabama.
Car bodies, Toledo, Ohio.
Rigid hammers,
Impact crusher, New York City.
Semiblunt hammers.
V-shaped hammers meshing with
rotating grate ; gripping feed to
12-in. from hammers, Fond du
Lac, Wisconsin.
Feed rollers flatten the car bodies,
San Antonio, Texas.
6-in. product (2 stages required
for IK-in. product).
Semiblunt hammers.
Drum pulverizers, 2-in. product,
England.
Vertical shaft, ballistic reject,
England.
Drum pulverizer, 2-in. product,
England.
Johnson City, Tenn., Los Angeles,
and Cleveland.
Wet pulper, 6-in. input 1-in.
product, Altoona, Pa.
1-in. product, 6-in. input, wet
pulper.
"'Manufacturer's code. See Table 4.
tMSW, Municipal solid waste.
EXISTING AND ESTIMATED
PERFORMANCE DATA
Performance data have been col-
lected on 27 size-reduction machines
manufactured by the 21 companies
(Tables 3 and 4). The data presented
are mostly from manufacturers' rat-
ings, to a limited extent from exist-
ing installations, and theoretical
calculations outlined earlier (Figure
11 and Table 3). Users' data are avail-
able on some of the equipment and
give general trend information.
The upper shaded area on Figure
11 includes size-reduction equipment
applied to metal automobile-body
size reduction. The lower shaded area
includes equipment processing typi-
cal of mixed municipal refuse. Be-
tween these two areas falls equipment
processing other bulky material such
as harbor waste. Below both cross-
hatched areas fall machines operat-
ing on selected solid waste or on wood
products. Comparing the performance
of Machines 12 and 13 having power
requirements of 40 and 80 hp-hr per
ton with the theoretical requirement
of 6.4 hp-hr per ton for reducing steel
to 6-in. pieces, the theoretical effi-
ciencies of Machines 12 and 13 are
only 8 and 16 percent. The size reduc-
tion of wood, in contrast, indicates
relatively high efficiencies. For exam-
ple, Hammermllls 2 and 11, requir-
ing 7.5 and 5 hp-hr per ton, respec-
tively, would have efficiencies of 41
and 62 percent based on theoretical
power requirements of 3.1 hp-hr per
ton.
Direct comparisons of individual
equipment items are impractical be-
cause of the wide range of materials,
machine size, and product size repre-
sented (Table 3 and Figure 11). Nev-
ertheless, higher unit power require-
ments (hp-hr per ton) of the larger
-------
Existing and estimated performance data 13
TABLE 4
MANUFACTURERS' CODE NUMBEKS
O Hammermills
D Drum Pulverizers and Wet Pulpers
A Rasp Mill
© American Pulverizer Company, St.
Louis, Missouri.
(D Buffalo Hammermill Corporation,
Buffalo, New York.
(D Buhler Brothers (Swiss), Ontario,
Canada.
-------
14 SIZE REDUCTION
TABLE 5
ADJUSTED PERFORMANCE AND COST DATA
Capital
Horsepower investment
(thousands
of dollars)
©
©
©
A
© ---
®
®
©
r~.
©
©
[8]
©
on
(19)
n
OD
800 35. 0
300 8. 5
200 33
350 80
1, 500 130
80 50
1, 000
150 30
350
800 60
300 86
800 160
150 17. 5
2, 000 150
500
1, 000 200
1, 500
4,000
800 59. 5
300 14. 2
50
150 53. 0
60
150 10
[ 4, 000
150+(12X15)=330 15.0
350+ (60X15) = !, 250 69.5
Adjusted capacity (tons per hr)
17X1 = 17
40X0.43=17
10X0.65 = 6.5
30X1.39 = 42
70X1.39 = 97
9X0.65X1.64=10
20X2.8=56
10X0.65 = 6.5
20X0.65=13
25X 2.8 = 70
30X1 = 30
140X1 = 140
30X0.43=13
50X2.8=140
10X2.8 = 28
16X2.8 = 45
20X2.8=56
50X2.8=140
40X1 = 40
24X0.43=10
7X0.65X1.64 = 7.5
10X1 = 10
8X065X1.64=8.5
10X0.65 = 6.5
100X2.8 = 280
12X2.38 = 28.56
60X2.38=143
Adjusted power Adjusted unit
requirements capital investments
(hp-hr per ton)* (dollars per ton-per-
hr capacity)
47
19
31
8. 3
15. 5
8.0
17. 8
23
27
11. 4
10
5. 7
11. 5
14. 3
17. 9
22
27
29
20
30
6
15
7
23
14
11. 8
8. 8
2, 060
500
5,080
1,900
1,340
5,000
4, 620
857
2,870
1, 140
1,310
1,070
7, 150
4, 450
3,570
1,430
1,490
1, 420
5, 300
1,540
536
485
•Primary size-reduction power added.
Approximate purchase prices were
obtained on 19 of the machines and
unit machine costs were calculated
(Table 5). The wide spread of ad-
justed unit machine costs, from $500
to over $7,000 per ton per hr is at-
tributed to the variety of pricing
methods and machine designs. For
example, Machine 2 is a light-duty
unit for wood only; Machine 13 is a
heavy-duty machine for steel. The
graph of these unit machine costs
versus the adjusted capacity indicates
the general trend of the unit cost of
size-reduction equipment (Figure 12).
When performance data are plot-
ted (Table 5 and Figure 13), the
data scattering is much less than that
of the theoretical data (Figure 11),
indicating that the rough correction
factors provide a means of making
the data more useful. The large group-
ing of machines near the origin on
Figure 13 includes many small
machines of different types.
EXISTING AND ESTIMATED
COST DATA
Twelve of the companies contacted
provided cost data applicable to size
reduction of municipal solid waste.
Two Demonstration Grant Projects
sponsored in part by the Bureau of
Solid Waste Management provided
complementary data on two types of
size-reduction equipment—the rasp
mill at Johnson City, Tennessee, and
a hammermill at Madison, Wisconsin.
The combined data in four cate-
gories, based on potential yearly pro-
duction, have been summarized (Table
6). The production is computed by
assuming single 8-hr shifts for 5V2
days per week, 52 weeks per yr (tons
per hr x 8 x 286). The following were
also assumed: maintenance, manu-
facturers' data modified by users'
information and estimates from aver-
ages of similar equipment; equivalent
annual cost, 6 percent, 10 yr; power,
1 cent/hp-hr; and labor, $10,000/yr.
Total costs from Table 3 can be re-
-------
g
- 3
0
Existing and estimated cost data 15
0
20
40
120
60 80 100
Adjusted Tons per Hour
FIGURE 12. Unit machine price versus adjusted production rate.
140
160
180
5000
4000
3OOO
2000
IOOO
f MSW
I Picked MSW
00
Input material factors <^ £ CR«a M=w. j X2*
p ] Wood and fibers only — 045
Automobile bodies 282
Primary size reduction adds
15 hp per ton per hour
MSW = Municipal Solid Waste
17 15
19 H6
FIGURE 13. Adjusted power requirements.
60 80 100
Production, tons per hour
120
140
-------
16 SIZE REDUCTION
TABLE 6
APPROXIMATE SIZE-REDUCTION COSTS'
N
Capacity! (tons per hr.) p
®
®
A -'-'-'-'-' ~~
(w)
%
0
(io)
a -
©
gg
m
17
40
10
30
9
10
7.2
6. 1
25
30
50
40
12
60
ominal
size
(in.)
6
6
6
4
2
6
4
2
6
6
6
6
1
1
Costs (dollars per ton)
Mainte- Equivalent
nance annual cost
0. 22
0. 05
0.27
0. 27
0.06
0. 18
0. 25
0. 28
0. 55
0. 55
1. 10
0. 55
0. 11
0. 11
0. 12
0. 22
0. 19
0. 20
0.33
0. 18
0. 25
0. 29
0. 14
0. 17
0. 18
0. 09
0.08
0.08
Power
0. 45
0. 08
0. 19
0. 18
0.09
0. 15
0. 21
0. 25
0. 32
0. 10
0. 40
0. 20
0. 13
0. 06
labor
0. 25
0. 11
0.41
0. 17
0. 48
0.43
0. 61
0. 72
0. 18
0. 14
0. 09
0. 11
0. 36
0.08
Total
1. 04
0.46
1.06
0. 82
0.96
0. 94
1.32
1. 54
1. 19
0. 96
1. 77
0. 95
0. 68
0.33
Variations from packer-truck input
Bulky waste included.
Wood only (nonbulky).
Twelve percent prepicked.
Some bulky extras ; 4-in. product.
Thirty percent durable bulky items rejected.
Ten percent reject of durable items.
Bulky waste included.
Harbor waste.
Auto bodies.
Bulky waste included.
Premilled input.
Premilled input.
'These costs are based on manufacturers' data modified by users' data and do not include site costs, crane costs, or other handling costs
tTons per year=average tons per hrx 8x 286.
•2-in. product
O
o
•o
8
1
a.
Auto bodies
50 tons per
hour
50 ton/hr
8l.77/ton
4-in.
product
2-in. product
I-in. product
60 ton/hr
Selected / $.33/ton
pulpable
l-in. product
Product size: Nominal 6- inch pieces
except as noted
Wood only
10
20
30
40
Production Rate , tons per hour
FIGURE 14. Cost of size reduction versus production rate.
-------
Existing and estimated cost data 17
C
o
0)
Q.
^
"o
(ft
O
O
O
O
^.
0_
0
Auto bodies
Madison,Wisconsin
demonstration project
data
20 and 21 with
primary size
reduction cost
added
-30% of input
rejected
6-in. input
Manufacturer's data
Dotted figures were computed
0
I
234
Nominal Product Size, inches
FIGURE 15. Size-reduction cost versus nominal produce size.
lated to production, rate in tons per
hr (Figure 14). As with the power
data, the cost data show considerable
scattering. The shaded area includes
equipment for processing the range
of materials from selected waste
through bulky waste which may be
found in municipal solid waste. The
boundaries of the shaded area derived
from the "six-tenths" factor for capi-
tal costs as follows:
Cost;_ /CapacityA0 6
Costi~\Capacityi/
Unit cost;_Cost2/Capacity2_ /CapacityzN-"'
Unit costi ~ Costi/Capacityi ~~ \ Capacityi /
The data plotted exhibit the general
trend indicated by this relationship.
Product costs from Table 5 versus
product size may be plotted (Figure
15). Here again, the increasing cost
trend with smaller product size
roughly follows the 0.6 exponent rela-
tionship. An extra cost of $1.20 per ton
is added to the 1-in. wet pulper prod-
uct cost to account for a preliminary
size-reduction operation. The dotted
figures give theoretical costs for prod-
uct sizes other than reported and
were computed using the above
equation.
To acquire comparable data on
product costs from the various types
-------
18 SIZE REDUCTION
TABLE 7
ADJUSTED SIZE-REDUCTION COSTS'
©
®
®
©
A
7*r
®
13
a
Nominal
size
(in.)
6
6
6
4
2
6
4
2
6
6
6
6
1
1
material
Mf
W
P
M
P
P
P
P
A
M
A
M
PG
PG
(tons/hr)
17
40
10
30
9
10
7. 2
6. 1
25
30
50
40
12
60
Combined
material
factors
1. 00
0. 43
0. 65
1. 39
1. 07
0. 65
0 90
1. 07
2. 82
1.00
2. 82
1. 00
1. 41
1. 41
(tons/hr)
17
17
6. 5
42
10
6. 5
6. 5
6.5
70
30
140
40
28
143
capital (cost
X $1,000)
35
8. 5
33
80
50
30
30
30
60
86
150
60
15
87
Mainte-
nance
0. 22
0. 05
0. 27
0. 27
0. 06
0. 18
0. 25
0. 28
0. 55
0. 55
1. 10
0. 55
0. 11
0. 11
Power
0. 47
0. 18
0. 31
0. 13
0. 08
0. 23
0. 23
0. 24
0. 11
0. 10
0. 14
0. 20
0. 06
0. 03
Costs (do!
1
Labor
0. 25
0. 26
0. 64
0. 12
0. 45
0. 67
0. 67
0. 67
0. 07
0. 14
0. 04
0. 11
0. 16
0. 05
liars per ton)
Maintenance,
power, and
labor costs
0. 94
0. 49
1. 22
0. 52
0. 59
1. 08
1. 15
1. 19
0. 73
0. 79
1. 28
0. 86
0. 33
0. 19
Amorti-
zation
0. 12
0. 03
0. 30
. 14
0. 31
0. 27
0. 27
0. 27
0. 06
0. 17
0. 07
0. 09
0. 04
0. 04
Total
of all
costs
1. 06
0. 52
1. 52
0. 66
0. 90
1. 35
1. 42
1. 46
0. 79
0.96
1. 35
0. 95
1. 57t
1. 23J
'These costs are based on those from Table 3 and adjusted to unsorted municipal solid waste reduced to a nominal 6-in. product by the application of the combined
size and material factors.
t M=municipal solid waste, W=wood or fibers, P = picked municipal solid waste, A-autombile bodies, and PG = picked municipal solid waste preground to 6-in.
size.
{Includes $1.20 for cost of primary grinding.
of equipment while operating under
more comparable conditions, the cost
data were adjusted to bring all ma-
chines to municipal-solid-waste and
6-in.-product levels. Table 7 presents
the adjusted size-reduction costs, ap-
plying the input-material and size
factors.
Approximate capital costs of the
basic size-reduction units with capac-
ities adjusted to the theoretical value
for unsorted municipal solid waste in-
put and a 6-in. product have been
plotted (Figure 16). Although the
data are still scattered, the trend in-
dicates that the capital cost of size-
reduction equipment in general does
not increase linearly with capacity,
but follows the classical 0.6 exponent
relationship.
Maintenance, power, and labor
costs per adjusted ton capacity as to-
taled in Table 7 have also been sum-
marized (Figure 17).
As pointed out in previous sections
of this report, the municipal solid
waste size-reduction cost figures pre-
sented are widely variable because of
the wide variation in machines, mate-
rial, and product size.
FINDINGS
Two trends are apparent from the
investigations conducted during this
study. (1) The demand on the ton-
nage or throughput capabilities of in-
dividual equipment items is increas-
ing; (2) The capability of equipment
is being increasingly challenged by
the heterogeneity of the diverse ma-
terials to be processed.
These trends are attributed to both
the population increase and the ele-
vated standard of living. Both factors
contribute to increased waste genera-
tion, and the latter results in a greater
variety of material in municipal solid
waste. Higher living standards con-
tribute to demands for more efficient
waste management, but in decreasing
the incentive for manual presorting
of municipal refuse.
PRINCIPLES OF SIZE REDUCTION
In summarizing the principles in-
volved in size reduction, the forces
utilized and the distances these forces
must move are of prime consideration.
The theoretical minimum energy re-
quirements for size reduction of most
of the components in municipal solid
waste is considerably lower than the
actual energy required by existing
equipment. This indicates the pres-
ence of a great deal of friction in the
processes and considerable overload
capacity to handle the input varia-
tions. Much can be done in process
and equipment improvement.
Evidence of synergistic effects with
the use of combinations of principles
indicates the efficacy of some ap-
proaches: (1) Automatic presorting
followed by separate size reduction;
(2) Automatic preshearing followed
by a secondary size-reduction opera-
tion in the same line; (3) Automatic
precrushing followed by subsequent
size-reduction operations better suited
to ductile material; (4) Multiple-stage
size reduction in combinations of
parallel and tandem operations (such
as precrushing and separation into
parallel lines having ductile and non-
ductile material, followed by further
size reduction as required).
Current equipment. A review of
current size-reduction equipment in-
dicated that more than two-thirds of
this equipment is used primarily on
uniform material in industry and is
not recommended for direct use on
municipal solid waste.
Potential usage, however, does exist
for all types of size-reduction equip-
ment. There exist eight general types
of size-reduction equipment with
variations and potential applications
in municipal solid waste size reduction
(Table 8).
CURRENT APPLICATIONS, PER-
FORMANCE, AND COSTS
The survey has shown that current
size-reduction equipment, as applied
to municipal solid waste, is undergoing
growing pains. The trend seems to be
toward larger and larger machines.
-------
Current applications, performance, and costs 19
150
FIGURE 16. Capital cost versus
adjusted capacity.
Cost of 60 ton/hr primary
grinder added
of » ' 20 Per ton for
preliminary grinder added
60 80 100
Adjusted Tons per Hour
120
140 160
FIGURE 17. Adjusted maintenance,
power, and labor costs of size reduction.
20
40
60 80 100
Capacity, tons per hour
120 140
160
-------
20 SIZE REDUCTION
TABLE 8
CURRENT SIZE-REDUCTION EQUIPMENT AND POTENTIAL APPLICATIONS TO MUNICIPAL SOLID
WASTE
Basic types
Variations
Potential application to municipal solid waste
Crushers Impact.
Cage disintegrators.
Shears
Shredders, cutters,
and chippers.
Rasp mills and drum
pulverizers.
Disk mills
Jaw, roll, and
gyrating.
Multi-cage or
single-cage.
Multi-blade or
single-blade.
Pierce-and-tear
type.
Cutting type
Wet pulpers__
Hammermills_
Single or multiple
disk.
Single or multiple
disk.
Direct application as a form of
hammermill.
As a primary or parallel operation
on brittle or friable material.
As a parallel operation on brittle
or friable material.
As a primary operation on wood
or ductile materials.
Direct as hammermill with meshing
shredding members, or parallel
operation on paper and boxboard.
Parallel on yard waste, paper,
boxboard, wood, or plastics.
Direct on moistened municipal
solid waste; also as bulky item
sorter for parallel line operations.
Parallel operation on certain
municipal solid waste fractions
for special recovery treatment.
Second operation on pulpable
material.
Direct application or in tandem
with other types.
This trend will probably continue as
an expediency to keep up with the
fast-growing rate of solid waste gen-
eration. Methods to improve efficiency
of size-reduction equipment are also
being sought, but, as pointed out ear-
lier, this is leading to technical ineffi-
ciency. Approaches to greater effi-
ciency have been cited in such
combinations as preshearing or pre-
crushing bulky items prior to ham-
mermill action.
The performance and cost data on
the wide variety of input material and
product size were adjusted to levels
corresponding to the size reduction
of average municipal solid waste to a
nominal 6-in. product. Before adjust-
ment, the power and cost values
ranged from 5 hp-hr and $0.46 per
ton to 80 hp-hr and $1.77 per ton.
After adjustment, the ranges closed
from 6 hp-hr and $0.52 per ton to 30
hp-hr and $1.52 per ton, roughly a 3
to 1 decrease in power and cost ratios.
The adjusted performance and cost
spreads of approximately 4 to 1 are,
however, still very high, indicating
the need for more closely controlled
test conditions or perhaps a better
model.
REQUIREMENTS FOR ADDITIONAL
DATA
There are obvious gaps in the data
coming directly from size-reduction
operations on municipal solid waste.
Data from the.processing of material
similar to certain fractions of munici-
pal solid waste, fortunately, have pro-
vided usable performance and cost in-
formation. This was accomplished by
the application of factors derived from
the more limited solid waste size-re-
duction data. Whereas a fair general
picture of solid waste size reduction
has been obtained, additional data are
required in more specific areas. For
example, this study has leaned heavily
on a single source of data (the Madi-
son, Wisconsin, Demonstration Grant
Project) for hammer-wear data and
product-size effects. Other demonstra-
tion projects will provide data that
will permit more information on
operations.
Refinements in the collection and
processing of data from municipal
solid waste size reduction also appear
to be desirable. These could be in the
nature of a series of closely controlled
experiments performed on representa-
tive size-reduction units. In these ex-
periments, controlled input and thor-
ough instrumentation should be con-
sidered. Standardized containers of
selected materials might be one form
of controlled input. Using recording
instruments, short runs with con-
trolled input could be used to corre-
late data from the current runs of
municipal solid waste. The instru-
-------
Requirements for additional data 21
TABIE 9
EFFECTS OF NEW EQUIPMENT DESIGNS IN COMBINATION
Design combination
Possible effects
Advantages
Disadvantages
Bottle breaker on municipal
solid waste conveyor
leading to hammermill.
Wet pulpers, single- or
multiple-abrasive-disk
radial axis with hammer-
mill.
Lump-breaker feed on
refuse cutting machine.
Axial feed on preliminary
disintegrating machine.
Drum pulverizer feeding
hammermill.
Ultrasonic apparatus after
primary separation opera-
tion.
Screw driers on wet pulpers.
Individually removable
hammers on hammermill.
Oblique cornered hammers
on hammermill.
Shear-type feed of hammer-
mill.
Crushing-type hammermill
feed.
Shredding action with
hammermill.
Combination of shear, crush,
and shred.
Friable material reduced
by lower wearing-rate
members.
Finer product better
suited to some separa-
tion and recovery
operations.
Crushing action tends to
homogenize the refuse.
Homogenizing and prelimi-
nary size reduction.
Fine material can bypass
the final stages.
Minimum wear.
Minimum cost.
Minimum downtime,
staggered hammers,
reduced vibration.
Greater shearing action,
more wearing volume,
higher impact.
Less slugging.
Less slugging, less wear
(especially if crushed
friables bypass ham-
mers).
Closer grip on material
during fracture precludes
grate plugging.
Homogenization plus semi-
primary size reduction,
minimum wear.
More complicated
conveyor.
Higher investment.
More complicated
conveyor.
Higher investment.
Material limitation.
Input material
limited.
Higher investment.
More vulnerable to
damage.
Higher investment.
Higher investment.
More vulnerability.
Higher investment.
mentation could be so complete as to
record such data as motor loads,
speeds, strains, temperatures, and
noise level. Part wear could even be
monitored by scintillator readings of
tracer elements worn from specially
prepared wearing members.
The data that should be obtained in
a controlled test are summarized in
the following list of possible re-
quirements :
(1) Motor current
(2) Voltage
(3) Kilowatts
(4) Speed
(5) Bearing load (strain gage)
(6) Temperatures
(a) Bearing
(b) Product
(7) Noise level
(8) Wear monitoring by tracer element
check
(9) Standard test materials
(a) Unsorted, packaged in oil drums
(b) Precrushed, in boxes along with
flattened oil drums
(c) Presheared, in smaller cans.
Instrumentation to record the
above-listed data would probably be
too costly and complex for continuous
use on one installation, so a portable
package unit is recommended for spot
checking several municipal solid waste
size-reduction installations.
NEW EQUIPMENT DESIGNS
Summaries of new equipment de-
signs as applied to municipal solid
waste are slanted mainly toward pos-
sible synergistic effects, although
some antagonistic effects result and
are pointed out.
The patents and Battelle-generated
concepts discussed in Appendix B dis-
close various features having possible
Application to municipal solid waste
size reduction. These designs and
some of the more likely combinations
along with possible advantages and
disadvantages are listed (Table 9).
-------
-------
V. Separation
FOLLOWING SIZE REDUCTION, separa-
tion is sequentially the second critical
step in the recovery and utilization of
mixed municipal solid waste.
Due to the heterogeneity of typical
solid waste and the diversity of recov-
ery operations which can be conceived,
separation is a second important step
in the recovery and utilization of solid
waste. The efficiency with which sep-
aration is effected and the degree to
which the desirable materials can be
segregated are significant factors con-
tributing to cost and marketability of
recovered products. Consequently, sig-
nificant effort was devoted to the col-
lection of technical data for equip-
ment and processes that could be used
in the separation of solid waste.
As of 1968, the most widely em-
ployed means for separating solid
waste is handpicking and sorting from
conveyors. Handsorting is employed,
almost without exception, at nearly
all U.S. and European compost plants,
and at some municipal incinerators,
to remove such items as clean news-
print and cardboard, rags, metals,
glass, and plastic (Figure 18). These
materials are removed for salvage
purposes and, in the case of compost-
ing, to upgrade the quality of the final
product. Handsorting is unsatisfac-
tory for large-scale recovery and util-
ization for several reasons including:
(1) low salvage prices that limit the
economic attractiveness of such op-
erations; (2) limited degree of sepa-
ration that can be effected since a
nominal size work force can be con-
cerned only with removing more bulky
pieces; and (3) human fallibility. It
FIGURE 18. Handsorting at Lone
Star Organics, Inc., compost plant,
Houston, Texas.
23
-------
24 SEPARATION
FIGURE 19. Eriez suspended-type permanent magnetic separator.
has been reported that approximately
Yz to % ton of newsprint and card-
board can be handpicked from mixed
waste by one man in an hour.11 This
corresponds to 1%- to 2-man hr per
ton. Separation costs, therefore,
ranges on the order of $3.50 to $5.00
per ton assuming low cost labor.
The need was recognized for a
variety of improved separation tech-
niques owing to the extremely limited
existing applications of more advanced
technology to solid waste processing.
The entire field of industrial sep-
aration technology was surveyed in
detail for potentially adaptable tech-
niques and related performance char-
acteristics and costs. As indicated
below, very few of the more sophisti-
cated separation techniques have been
applied to solid waste processing, and
the historical experience of these
applications is extremely limited.
Therefore, much of the cost and per-
formance data available relates to
industrial applications significantly
different from solid waste processing
and must be employed and interpreted
with extreme care. These data should
not be used for design purposes, but
rather should be employed to indicate
the general types of separation possi-
ble, general feed requirements, and
order-of-magnitude costs. This type
of information is essential in making
preliminary judgments as to poten-
tially attractive process combinations
for investigation on both pilot and
demonstration scale. Several such
combinations are discussed in a later
section.
As indicated, this study has at-
tempted to cover a largely uncharted
domain of technology. Two ap-
proaches were possible. One would
have been to decide a priori what com-
ponents and mixtures were desirable
to separate and then to limit the in-
vestigation to a search for equipment
which would effect the separation. Al-
ternatively one could ask the question,
what can be separated using existing
and potential equipment designs. The
former approach was not suitable to
the task at hand, since the decision
as to what one would like to separate
depends to a large extent upon what
can be separated, what degree of sep-
aration can be effected, and other un-
defined factors relating to markets,
and the processing and recovery of
by-products. Consequently the second
approach was elected; and the general
overall task was to determine what
types of separations are, or might be,
possible using existing technology,
with or without suitable modifications.
This information is presented below
to the extent that it is available.
Separation techniques are designed
to detect and to operate selectively on
differences in various properties of the
materials being separated. Primary
properties employed in the separation
techniques investigated in this study
-------
Unit processes /or solid waste separation 25
FIGURE 20. £Yte£ pulley-type permanent magnetic separator.
include magnetic properties, particle
size, specific gravity, and light reflec-
tance properties of the surfaces. The
primary obstacle in the application of
these techniques to the separation and
recovery of solid waste is that the com-
ponents which one might wish to sep-
arate are generally not sufficiently
unique in any single property such
that the separation is rendered
straightforward. Consequently, the
best one can imagine is a combination
of processes and somewhat less than
100 percent separation.
Technical information and avail-
able data on specific processes and
separation techniques are outlined be-
low. Generally speaking, there is al-
most a universal lack of data related
to the mechanical separation of solid
waste. Most of the performance and
cost statements in this report are
based on qualitative extrapolations of
data for specialized industrial applica-
tions. Experimental data need to be
collected for nearly all applications
discussed to determine interrelation-
ships among such properties as par-
ticle size and distribution in the mixed
feed, separation efficiency, capacity,
moisture content, and material type.
Three general sources of informa-
tion were employed in this phase of
the study. These are existing plants
and operations, equipment manu-
facturers, and patent literature. As
indicated below, several potentially
promising separation techniques are
available; but additional experimental
work is required to establish perform-
ance criteria and cost relationships
suitable for design purposes.
UNIT PROCESSES FOR SOLID
WASTE SEPARATION
MAGNETIC SEPARATION
The removal of ferrous materials
from heterogeneous industrial mix-
tures and from municipal solid waste
is practiced quite widely. Prevalent in-
dustrial applications include minerals
beneficiation, the recovery of scrap in
metal fabrication plants, and automo-
bile salvage operations. Compost
plants in Houston, Texas; Gainesville,
Florida; and Johnson City, Tennessee;
and other municipal incinerators in
Atlanta, Georgia; Chicago, Illinois;
and other localities use magnetic sep-
arators to remove tin cans. Tin cans
are removed for salvage and, at the
compost plants, to upgrade the quality
of the final product.
In general, two types of separators
are adaptable to the removal of fer-
rous materials from mixed refuse and
are used extensively in solid waste
processing plants (i.e., compost plants
and municipal incinerators) which
are removing tin cans from mixed
refuse. These may be broadly classed
as suspended-type and pulley-type
separators (Figures 19 and 20). Sus-
pended-type separators are used to
-------
26 SEPARATION
4000
o
"5
o
o
Q.
O
O
3000
2000
1000
Enez P-T ( pulley-type) permanent
magnetic separator (12" head pulley)
Enez suspended permanent magnetic separator ( Model 510)
1000
2000
30OO
4000
5OOO
6000
7000
8000
9000 10,000 11,000 12,000
Capacity , ftvhr
I
25 50 75 100 125
Capacity , Ions per hr ( assuming bulk density of 25 Ib per ft3 )
FIGURE 21. Capital cost of magnetic separators. (Data supplied by Eriez Manufacturing Company.)
150
make a "first cut" to remove ferrous
materials from refuse which may or
may not have been subjected to size
reduction. The pulley-type separators
are employed as a second-stage
cleanup to remove ferrous materials
after removal by a suspended-type
separator and processing through a
hammerhill.
Efficient magnetic separation is
affected mostly by the degree of size
reduction provided and the extent to
which ferrous materials are physi-
cally liberated from other types of
materials. Hammermilling, and per-
haps even crushing, of raw waste is
considered to be satisfactory prepara-
tion for efficient magnetic separation
of ferrous materials from solid waste.
The particle size in the feed material
to the magnetic separator is not crit-
ical, since existing equipment can ac-
commodate nearly all ferrous objects
ranging from large tin cans on down.
The occasional large items such as
appliances need to be reduced in size
to pieces about 8 in. or smaller. In any
event, the primary requisite for effi-
cient magnetic separation is that the
materials be physically freed from one
another. Magnetic separation is not
likely to be affected by, or to have
major effects upon, other upstream or
downstream separations, except per-
haps in the sense that inefficient re-
moval of ferrous material may result
in an unexpected contaminant or
component to be reckoned with at
later processing or recovery stages.
Equipment employed in the re-
moval of tin cans from solid waste are
adaptations of equipment designed
primarily for large industrial opera-
tions such as the automobile macer-
ators and salvagers. Consequently,
the capacities of existing equipment,
ranging from 25 to 100 tons-per-hr,
are considerably higher than required
in solid waste processing plants where
the ferrous content of the throughput
is relatively small. For example, fer-
rous throughput rates for various
nominal plant sizes and ferrous con-
tent are as follows (Table 10).
TABLE 10
FEKROUS THROUGHPUT RATES AS A FUNCTION
OF CONTENT AND PLANT SIZE
Total solid waste throughput Ferrous Ferrous
content throughput
(tons/10-hr day) (tons/hr) (percent) (tons/hr)
150
300
15
30
5
6
7
8
5
6
7
8
0. 75
0.90
1. 05
1.20
1. 50
1. 80
2. 10
2.40
Data provided by Eriez Manufac-
turing Company, a large supplier of
magnetic separators, indicating capi-
tal cost as a function of size and ca-
pacities of the two main types of
-------
Unit processes for solid waste separation 27
1000
20
40
30
Belt Width, inches
FIGURE 22. Capital cost of magnetic separators. (Data supplied by Eriez Manufacturing Company.)
50
magnetic separators are provided
(Figures 21 and 22). Equipment is
rated by the manufacturer in terms
of cu ft per hr; and the tonnage
capacities given are based upon the
bulk density of the ferrous material
as 25 Ib/cu ft. Operating costs for
magnetic separators are minimal and
result primarily from power consump-
tion. Small magnetic separators, more
than adequate for use in solid waste
recovery, require at most about 1 hp,
and so power costs for magnetic sep-
aration are expected to be an insig-
nificant fraction of total power
consumption in a solid waste recovery
plant. Consequently, the major cost
of magnetic separation is the cost of
equipment, especially the auxiliary
equipment for handling influent and
effluent streams. Cost data for tin
can recovery facilities discussed in a
later section indicate that the major
cost item is not the magnetic separa-
tor, but, rather, the auxiliary facili-
ties.12 The total cost of a can recovery
facility at an 800-ton/day incinerator
was estimated at $400,000, with the
major fraction of the capital cost
being attributable to site preparation,
structures, and auxiliary equipment
such as a shredder, conveyors, and
railroad siding. Similarly only a frac-
tion of the estimated operating costs
are attributable to the magnetic sep-
aration process. In fact, less than 25
percent of the total cost for all equip-
ment was attributable to power and
maintenance. The remaining 75 per-
cent resulted from labor (system
operators and inspectors). Total cost
of can recovery including amortiza-
tion and operating cost was estimated
to be $13.60 per ton recovered.
The above analysis of magnetic sep-
arator costs indicates something
which one must keep in mind when
interpreting the various unit process
costs quoted throughout this report.
The point is that the unit process
itself may constitute only a small frac-
tion of the cost required to put this
process in operation. As in the above
example, the major cost item may be
the supporting and auxiliary materi-
als handling equipment needed to
synthesize a complete system. A sim-
ilar trend is noted in a later section
on composting where it is seen that
actual digester costs are only about
25 to 40 percent of the total capital
investment required.
In addition to the standard mag-
netic separation equipment discussed
above, one additional rather unique
application is worthy of mention. The
Los Angeles By-Products Company
operates several machines at various
landfills in the San Francisco area
which remove tin cans from loads of
refuse dumped at the landfill sites.
The salvaged products eventually find
their way to the copper smelters. Cur-
rent design as well as operational de-
tails of these machines, including
costs, are considered to be proprie-
tary information by Los Angeles By-
products Company13 A patent search
-------
28 SEPARATION
led to the discovery of a patent relat-
ing to an early design of this
machine."
EDDY-CURRENT SEPARATION
The separation of nonmagnetic,
conductive materials (copper, alum-
inum, zinc) in solid waste based upon
eddy-current phenomena has been
proposed on several occasions. How-
ever, limited experimental studies
conducted to date have indicated sub-
stantial problems in the application
of this phenomena not only to the
separation of materials from munici-
pal solid waste, but also to the seg-
regation of much less heterogeneous
industrial waste. Eriez Manufacturing
Company, for example, has investi-
gated these applications rather exten-
sively and has been quite cooperative
in providing information on its re-
search in this area.15 The following
discussion is based largely upon in-
formation provided by Eriez.
Since the principles of eddy-cur-
rent separation are not well docu-
mented in the solid waste literature,
they are outlined briefly below.
When an electric current is passed
through a coil surrounding a core
made of a conducting material, a
magnetic flux develops (Figure 23).
By varying the current, one may cause
the magnetic flux to change. This
changing magnetic flux is the key to
eddy-current phenomena. It should be
noted that the arrangement shown is
only one means of producing a chang-
ing flux and is selected for illustra-
tion because the arrangement simpli-
fies explanation of the phenomena
under consideration. Another tech-
nique for creating a changing flux,
more suitable to the concept of an
eddy-current separator, is discussed
later. As indicated, the changing mag-
netic flux is the key to eddy-current
phenemona. This is true because when
a magnetic field in a conducting me-
dium changes with time, an electro-
motive force is generated in the plane
of the medium which is perpendicular
to the direction in which the flux is
changing. As a result of the electro-
motive force, eddy currents develop
within the material. Associated with
these eddy currents is an eddy-current
flux which is opposite in direction to
the initially imposed magnetic flux.
The eddy-current flux may be em-
ployed to effect a separation (Figure
24). As previously mentioned, the
eddy-current flux always opposes the
flux that produced it. These two op-
posing magnetic fields create a repel-
N
Eddy current
Eddy -current
Current
Conducting material
Changing magnetic flux
Coil
FIGURE 23. Principles of eddy-current phenomena.
-------
Eddy-current
Eddy-current flux
Repulsive force
Conducting material
Changing magnetic flux
Current
FIGURE 24. Application of eddy-current phenomena.
Eddy-current separation 29
ling force, and if the core consists of
two parts, separation will occur.
In principle, the phenomena dis-
cussed above could be employed to
separate various nonmagnetic con-
ductive materials since the magnitude
of the repulsive force depends in part
upon characteristics of the material
such as its resistivity and permeabil-
ity. Other factors, unrelated to mate-
rial characteristics, are the magnitude
and the rate of change of flux density.
One attempt by Eriez to apply these
principles involved the use of a mag-
netic pulley (Figure 25). In this case,
a drum is equipped with a series of
magnets installed around its interior
circumference which in turn cause a
magnetic field to develop outside the
drum or pulley; and by rotating the
pulley, a constantly changing flux is
produced. When a nonmagnetic con-
ductive material is placed in this
changing field, eddy currents develop
in the material and a repulsive force
is generated. If this force is sufficiently
strong, it will deflect the material and
effect a separation.
In addition to the pulley arrange-
ment, other configurations have been
investigated in an effort to develop a
suitable eddy-current separator. Eriez
has reported serious limitations with
all techniques studied to date. The
basic difficulty is that the magnitude
of the repulsive force generated de-
pends largely upon the geometry of
the materials to be separated. The
size, shape, and surface irregularities
play a key role. Since the technique
has not been perfected, an optimum
particle size cannot be defined. It
should be noted, however, that in the
Eriez experimental work, Y2 -in.-diam-
eter disks, ys-in. thick, were used. In
genuine waste mixtures, particles ex-
hibit a wide degree of variation in size,
shape, and surface irregularities. A
piece of aluminum, for example, may
be subjected to the same repulsive
force as a piece of copper due to dif-
ferences in particle geometry even
though significant differences exist
in material characteristics. Conse-
quently, meaningful separations do
not result when using a typical waste
feed. To date a suitable technique for
overcoming these limitations has not
been discovered, and prospects that
one will be discovered in the near fu-
ture are not great. At present, eddy-
current separation does not constitute
a technically promising method of
separating the various nonmagnetic,
conductive materials in municipal
solid waste.
-------
30 SEPARATION
Net repulsive force
Magnetic
pulley
Permanent
magnets
Material
Changing
magnetic flux
Rotation
Material feed
Deflected
materials
Rotation
FIGURE 25. Concept of pulley-type eddy-current separator.
-------
Size classification 31
TABLE 11
VARYING DEGREES OF SIZE REDUCTION FOR GLASS, TIN CANS, AND WOOD WASTE "
Glass
Tin cans
Wood
Size range
(in.)
Material
occurring
in stated
size range
(percent)
Size range
(in.)
Material
occurring
in stated
size range
(percent)
Size range
(in.)
Material
occurring
in stated
size range
(percent)
>3 15. 7
; to 8 x
\Vi x 1.
40
~>l/ <^1i
>V 2, <3
<2
30. 5 0 to \%
58. 8
60
* From Stirrup, F. L. Public cleansing refuse disposal. Oxford, England, Pergamon Press, 1965. p. I
SIZE CLASSIFICATION
Vibrating screens. Screening is a
technique for separating materials
based upon particle size and involves
the separation of a mixture of vari-
ous size particles into two fractions,
or more if multiple deck screens are
used, each of which is more uniform
in particle size than is the original
mixture. Screening may be wet or
dry. Dry screening implies the treat-
ment of a material containing a nat-
ural amount of moisture or a material
that has been dried before screening;
whereas wet screening refers to an op-
eration in which water is added to the
material being treated for the purpose
of washing the fine material through
the screen. Another application of wet
screening is the dewatering of slur-
ries containing relatively hard solids
which will not blind (clog) the
screen.
Within the context of solid waste
processing, it appears that only dry
screening has major potential appli-
cation. The small quantity of fine ma-
terials (fines) in solid waste would
not merit wet screening because of the
auxiliary problems of water handling,
material drying, and their tendency
to become quite soft in an aqueous
environment, thus blinding the screen.
As is the case for many separation
processes discussed in this report, the
selection of screening equipment re-
quires empirical studies to determine
the effect of the several variables. The
critical variables are so interrelated
that no satisfactory analytical method
of correlating them has been devel-
oped. Therefore, no specific recom-
mendations can be made as to type of
screen material to be selected, or ca-
pacity and efficiency to be obtained.
Manufacturers suggest that proces-
sors submit samples for testing prior
to selection of equipment. Critical fac-
tors include particle-size distribution,
density, and undefined interactions
among particle size, shape, and mois-
ture content. All available published
data on screen capacities relate to
minerals-oriented processes, and this
experience is not directly applicable
to solid waste processing.
The only reported experience with
the use of screens in the processing of
solid waste is at two compost plants;
one in Houston, Texas, and the other
in Altoona, Pennsylvania, where
screens are used to size the compost
before a stoning operation to remove
glass as described in a later section.
Performance data from these applica-
tions were not available at the time of
this study.
The sizing of waste product streams
for further separation and processing
appears to be one of two major po-
tential applications for screening in
the recovery and utilization of solid
waste. The other relates to a possible,
but as yet quantitatively undefined,
synergistic effect in conjunction with
size reduction. Specifically it seems
reasonable to expect that during size
reduction, brittle materials such as
glass, metals, and thermosetting plas-
tics might end up in smaller pieces
due to their relatively lower resistance
to impact than materials such as
paper and food wastes. If this phe-
nomena does occur to an appreciable
extent, a basis would exist for making
a separation in a two-stage size-re-
duction screening operation. A small
amount of published data is available
which would cause one to expect these
effects.18 The results of studies con-
ducted in England indicate varying
degrees of size reduction for glass,
tin cans, and wood (Table 11).
Costs of screening are related al-
most entirely to equipment costs and
only in a small way to operating costs
which are, in turn, dictated princi-
pally by power consumption. Capital
costs of screening equipment are gen-
erally given in terms of square feet of
screen area. Required area is, in
turn, determined by screening rates.
A fair amount of data is available
for estimating screen sizes required
for conventional minerals applica-
tions. However, as previously indi-
cated, applications to solid waste
processing are extremely limited and
performance data are not available.
Nevertheless, the data on minerals
separation can be employed to deter-
mine approximate performance char-
acteristics for other potential solid
waste processing.
Denver Equipment Company has
supplied a technique for estimating
screen size requirements (Table 12).
Values are given for various factors
related to key design variables. Note
that Factor A, which is directly pro-
portional to screen openings and
which is also related to material type,
is provided only for conventional
minerals processing. Depending on
the type of material, Factor A ranges
between a low of 1.08 to a maximum
of 4.90. Thus for materials listed, re-
quired screen area could vary by a
factor of about five. This range of
variation would be expected to be
even more pronounced, perhaps as
great as a factor of ten, for applica-
tion to solid waste. Thus the proce-
dure given is satisfactory only for de-
termining order-of-magnitude screen
area requirements. It also serves,
however, to indicate the type of ex-
perimental studies required, the vari-
-------
32
A
o
S
8*
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CA
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•asSsa.-
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S.2IS5S.
oj o
II
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5
I
SS
H-O
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HwK
OOOOOQO
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oododdooo
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P
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StgxS
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HHHC4t
-------
Size classification 33
ables that need to be monitored to
gather data to determine screen ca-
pacity requirements for given appli-
cations, and the relative effects of the
key properties.
Data were provided by two manu-
facturers* indicating screen capaci-
ties for selected industrial applica-
tions (Figures 26 and 27). It is seen
that throughputs range from, about
1 to 8 tons/hr per sq ft of screen.
Nominal particles size range for dry
screening is V8 to 3 in. Still needed
are data that concern the relation-
ships between particle size, capacity,
and efficiency of separation for proc-
essing solid waste and various compo-
nent and by-product streams.
As indicated, the primary reason for
concern with screen capacities at this
stage is to provide a means for esti-
mating cost. Cost data were provided
by the two manufacturers for single
and double deck screens (Figures 28
and 29).
Spiral classifiers. Spiral classifica-
tion is a minerals beneflciation tech-
nique developed specifically for wet
sizing high-density materials. Most
common applications relate to remov-
ing fine solids from coarse solids of
approximately the same specific grav-
ity. By controlling design and operat-
ing conditions, cuts can be made on
mixed materials containing particles
in the size range 200 mesh to Va in.
In addition, the basic equipment is
also adaptable to separation of light
materials from heavy materials of ap-
proximately the same size.
The spiral classifier consists of an
inclined tank containing one or more
inclined revolving spirals. A slurry
containing the materials to be sep-
arated is fed into the lower end of the
unit where it collects in a pool. The
•Syntron Company and Denver Equip-
ment Company.
Assume 10% loss in screen area for second decks
Based on oversize in feed < 65% (undersize > 35%)
Based on 50% of undersize smaller than 1/2 screen
opening
Assumes dry materials
1/4
I 1/4
1/2 3/4 I
Size of Square Screen Openings, inches
FIGURE 26. Capacity of Denver vibrating screens. (Data supplied by Denver Equipment Company.)
I 1/2
-------
34 SEPARATION
Assume dry materials , 75 % of feed passing screen
and at least 50% undersize < 1/2 screen opening
For multiple decks, assume 10% loss of screen area
for second deck, and 20 % for third deck
When used with water, capacities may be 50-100 %
higher
For shaded capacities 9 , use dual or high thrust
vibration
1/8 3/16 1/4 5/16 3/8 T/te 1/2 3/4 I
Size of Square Openings,inches
FIGURE 27. Capacity of Syntron vibrating screens. (Data supplied by Syntron Company.)
1-1/2
8
O Syntron Company
8 Denver Equipment Company
40 50 60
Screen Area, ft
FIGURE 28. Capital costs of single-deck vibrating screens. (Data
supplied by Syntron Company and Denver Equipment Company.)
-------
Size classification 35
Q
/
/
°x
r^
j
* «
I/' o
)
X
/
(
^ «
O Syntr
® Derive
O .,
'
on Compa
r Equipm
X
^x
jnt Compc
ny
D 10 20 30 40 50 60 70 80 90 10
Screen Area per Deck, ft
FIGURE 29. Capital costs of double-deck vibrating screens. (Data supplied
by Syntr on Company and Denver Equipment Company.)
water is removed by permitting flow
over a weir. The overflow contains the
fines to be separated. The larger ma-
terials, termed sands, settle and are
collected and removed by means of
the revolving spiral. As indicated, the
sand-making mechanism may be ei-
ther a double or single spiral. In the
single-spiral assembly, the sands are
conveyed up one side of a tank, leav-
ing a drainage channel between the
spiral and the tank on the opposite
side. In the double-spiral machines,
the spirals rotate in such a manner
that the sands are conveyed up the
center of the tank between the spirals.
Feed enters through an opening on
one or both sides of the tank. Overflow
is discharged at the lower end over
an adjustable weir. Potential applica-
tions in solid waste processing to ef-
fect separations based on differences
in specific gravity should be evident
from the equipment descriptions out-
lined above, although no known ap-
plications have been encountered.
A typical spiral classifier is shown
(Figure 30). The selection of equip-
ment and the design of classification
systems hinge on several variables.
These include: (1) tonnage of fine
and coarse materials to be processed;
(2) mesh size at which separation is
to be made; (3) settling rates of ma-
terials to be processed; (4) solids con-
centration and particle-size distribu-
tion in the slurry; (5) moisture/solids
content of sands and overflows; (6)
specific gravity of materials being
processed; (7) spiral revolution rate;
(8) weir width and depth (and hence
pool size); (9) tank slope; (10) pool
-------
36 SEPARATION
Sand (separated solids)
Liquid
surface
Overflow
weir
Influent
Effluent
FIGURE 30. Denver spiral classifier. (Source: Denver Equipment Company.)
TABLE 13
CAPACITY OF SPIRAL CLASSIFIERS*
Spiral diameter (in.) Tons of sands per hr
(approximately)
24
36
48
54
72
1-3
3-10
9-26
10-31
28-85
•Source: Denver Equipment Company.
area (I.e., percent of spiral surface
submerged); (11) spiral length.
Spiral sizes are related in terms of
spiral diameter. Capacities are nor-
mally given in terms of tons of sand
per hr. Capacities of equipment vary
for typical minerals beneflciatlon ap-
plications (Table 13).
Capital costs of spiral classifiers are
a function of spiral size (Figure 31).
Operating costs are mainly related to
power consumption; power require-
ments for these spiral classifiers
range from 2 to 15 horsepower.
GRAVITY SEPARATION
Flotation. Flotation is basically a
gravity separation process; although,
as seen from the brief discussion of
the process mechanisms outlined be-
low, other than pure gravity-related
phenomena are employed. Flotation
effects the separation of dissimilar
solids through the selective affinity of
their surfaces, properly modified by
reagents, if necessary, for air and
water. Detailed process mechanisms
are discussed elsewhere and will not
be repeated here." The first step in
flotation is size reduction to physically
free from one another the materials
to be separated. An aqueous slurry or
pulp is then created and air bubbles
are introduced into the bottom of a
tank containing the mixture. By the
selection of flotation agents, the ma-
terial which one desires to remove is
made selectively hydrophobic impart-
ing to it a greater affinity for air than
water. As the bubbles rise in the
slurry, the fraction to be separated is
carried to the surface along with the
bubbles and is then collected in a
suitable fashion.
Flotation equipment and processing
systems were developed initially for
minerals beneficiation, and this is
still the major application of flota-
tion technology. Nevertheless, the
operation is being extended into other
fields such as the separation of wheat
hulls from kernels and the deinking
of newspaper.
Existing flotation technology is con-
cerned almost entirely with the sep-
aration of finely divided material,
usually varying in size from 20 to
under 200 mesh. Mineral solids re-
quire fine grinding to physically free
mineral crystals from other portions
of the ore. Surface conditions are
important, and it is necessary that the
air bubbles support the solid in the
slurry. As indicated, flotation agents
are employed to impart hydrophobic
properties to materials to be sepa-
rated. At least 60 flotation agents are
-------
Gravity separation 37
24
36
60
72
Spiral Diameter, inches
FIGURE 31. Capital cost of Denver spiral classifiers. (Data supplied, by Denver Equipment Company.)
-------
38 SEPARATION
TABLE 14
FLOTATION AGENTS COMMONLY USED IN MINERALS BENEFICIATION*
1. Acintol FA-1 tall oil fatty acid 31.
2. Acintol FA-2 tall oil fatty acid 32.
3. Aero Depressant 610 33.
4. Aero Depressant 633 34,
5. Aerofloc 550 35.
6. Aerofloat 15 36.
7. Aerofloat 25 37.
8. Aerofloat 31 38.
9. Aerofloat 208 39.
10. Aerofloat 238 40.
11. Aero Promoter 404 41.
12. Aero Promoter 710 42.
13. Aero Promoter 801 43.
14. Aero Promoter 825 44.
15. Aerosol GFG 45.
16. Amine D acetate 46.
17. Armac C 47.
18. Armac T 48.
19. Armac TD 49.
20. Armacflote P 50.
21. Barrett No. 4 Creosote 51.
22. Barrett No. 634 Creosote 52.
23. Beneflte 89 53.
24. Caustic soda (NaOH) 54.
25. Copper 55.
26. Cresylic acid 56.
27. Duomac T 57.
28. Dowfroth 250 58.
29. Formonyte 602 59.
30. Formonyte 616 60.
Lime
Merasperse CB
Methyl isobutyl carbinol
Minerec B
Orzan S
Pamak 1
Pamak 4
Pearl starch
Pine oil, Yarmor F
Quebracho
Sepa an MGL
Soda ash
Sodium Aerofloat
Sodium dichromate
Sodium silicate
Sodium sulfide
Sodium sulflte
Stadex Dextrin 120
Superfloc 16
Superfloc 20
Thiocarbanilide 130
Z-3, potassium ethyl xanthate
Z-4, sodium ethyl xanthate
Z-5, potassium sec-amyl xanthate
Z-6, potassium amyl xanthate
Z-ll, sodium isopropyl xanthate
Z-12, sodium sec-butyl xanthate
Z-14, sodium isobutyl xanthate
Z-200
Zinc sulfate
*Source: Denver Equipment Company.
known to be used in minerals bene-
flciation (Table 14).
The selection of notation equipment
and the design of flotation systems
are highly empirical in that most de-
sign variables need to be selected upon
the basis of experimental data. Fac-
tors which need to be determined
before notation capacity for a given
application can be determined are
specific gravity of the solids being
treated, optimum percent solids in the
aqueous slurry, particle size, reten-
tion time, aeration rates, and flota-
tion agents. The degree of separation
obtained in a given application is a
function of complex interrelation-
ships between each of these factors
and the surface properties of the
material being separated. Conse-
quently, process design usually in-
volves extensive laboratory-scale
experimental work to find the opti-
mum combination of the several vari-
ables involved. This is true even for
applications within the minerals
beneflciation field for which a fair
amount of operational experience is
documented. For the reasons indi-
cated above, and because no
laboratory or operational experience
exists, very little can be said about
expected performance and costs for
separating various components in
solid waste by flotation. Possible ap-
plications which come to mind include
the cleaning of compost; separation of
glass and/or nonferrous metals from
mixed refuse or from by-products
such as compost; and the separation
of paper from mixed refuse, as well as
various undefined separations which
may be required in the manufacture
of selected by-products.
The only indication of experimental
studies related to the application of
flotation to municipal solid waste re-
covery is work being done by the U.S.
Bureau of Mines in College Park,
Maryland, which is discussed in a
later section. These studies are con-
cerned with the recovery of metals
and other materials from municipal
incinerator residues. Although this is
a very specialized form of solid waste,
the experimental data generated by
these studies should provide valuable
guidelines as to the merits of this as
well as other potential applications of
flotation technology to solid waste
recovery.
A related application is reportedly
being studied by Luria Brothers, auto-
mobile salvagers, for the removal and
separation of nonferrous metals and
also for the cleaning of ferrous and
nonferrous products." Details of this
work are proprietary, and it was not
possible to obtain additional infor-
mation during the course of this
study.
Capital costs of flotation are mainly
for tankage and aeration equipment;
operating costs are mainly for power
to provide aeration. Before one can
determine tankage, and hence capital
costs, many of the design variables
mentioned above must be determined.
Once one knows the throughput rates,
retention times, and percent solids, it
is rather straightforward to calculate
capacities on the basis of a mass
balance as follows:
Letting:
C =required flotation capacity (cu ft)
9 = material throughput rate (tons of solids/8-hr
day)
•y = specific gravity of solids
s = percent solids-^ 100
t =retention time (min)
one may derive the relationship:
C=0.0688
["-
L y
+— 1 Qt.
j
Based upon experience with min-
erals beneflciation, one manufacturer
estimated that retention times in
processing solid waste could vary from
5 to 20 min. and optimum solids con-
tent from 5 to 20 percent. All of these
variables affect required flotation
capacity (Figure 32). It is seen that
-------
Gravity separation 39
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S
£
o
a
o
8
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I
-------
40 SEPARATION
an extremely wide range in required
capacity is indicated, further demon-
strating the need for experimental
data before even order-of-magnitude
cost estimates can be generated. The
capital cost of Denver flotation equip-
ment may be related to capacity (Fig-
ure 33).
As previously indicated, operating
costs consist almost entirely of power
costs. Power requirements to operate
pumps, mixers, and compressors are
functions of flotation capacity (Fig-
ure 34).
Dense media. Dense media separa-
tion, sometimes referred to as the
sink-float process, is a gravity sepa-
ration technique for separating ma-
terials having a specific gravity higher
than that of the medium employed
from those having a specific gravity
lower than that of the medium em-
ployed. Particle sizes in the feed for
minerals beneflciation applications
range from 3 in. down to 10 mesh
(0.066 in.). It is generally true that
differences in the specific gravity of
the materials to be separated can be
less than that required for efficient
separations by jigging or tabling.
Dense media have been used exten-
sively in laboratory separations and
for industrial applications such as ore
beneficiation.
There are two types of heavy media
used for separation: (1) solids-water
systems, and (2) organic liquids. Sus-
pensions of solids in water usually
consist of ferrosilicon, magnetite, or
galena. When ground to suitable fine-
ness and mixed with water in correct
proportion, these high specific grav-
ity solids provide a medium that
closely duplicates the fluid character-
istics of a true heavy liquid. Recent
trends have favored the use of mag-
netite and ferrosilicon since these ma-
terials can be more easily reclaimed
and are lower in initial cost. Specific
gravities of dense media attainable
with suspensions of these materials
range from 1.25 to 3.4. Magnetite
alone is used to obtain specific gravi-
ties in the 1.25 to 2.20 range; magne-
tite and ferrosilicon mixtures are used
to obtain specific gravities in the 2.20
to 2.85 range; and ferrosilicon alone
is used for specific gravities >2.85.
Process details are available in the
literature.10
Applications of dense media sep-
aration are not sufficiently wide-
spread that typical industrial per-
formance and cost data are available.
Applications to solid waste processing
are nonexistent, but various potential
applications exist. The work being
conducted by the Bureau of Mines at
College Park, Maryland, includes
plans for some experimental studies
to be conducted at an unspecified
time in the future to investigate the
recovery of incinerator residues by
heavy media techniques. Similarly,
research mentioned earlier may also
develop information in this technical
area, as related to the cleaning of
automobile scrap and the recovery of
nonferrous metals."
In order for dense media separation
to be economical, the suspension
solids must be recovered. Magnetite
and ferrosilicon are recovered by mag-
netic means, and galena is recovered
by froth flotation.
Ferrosilicon is the most widely used
material. In order to maintain mag-
netic properties essential to recovery
and to prevent rusting, a 15 percent
silicon content having a specific grav-
ity of approximately 6.8 has been
found most suitable. Where the sepa-
ration is between 2.6 and 2.9, the fer-
rosilicon is ground to <100 mesh
(0.0059 in.), and for separation at
higher specific gravities ~3.2), <65
mesh (0.0083 in.) is employed.
Organic liquids (primarily chlori-
nated and brominated hydrocarbons)
are true heavy media; but their in-
dustrial use has many drawbacks, in-
cluding health hazards from inhala-
tion of fumes, danger of contact with
an operator's skin, losses by splash
and evaporation, corrosive action,
chemical breakdown, and the high
cost of materials. Typical heavy media
liquids and their properties have been
tabulated (Table 15). Again, in the
interest of economy, it is necessary to
recover as much of the material as
possible. Typical losses for minerals
beneficiation on pilot and in small mill
operations run about 1 Ib per ton of
material processed.
Stoners. Stoners are devices for
separating material primarily on the
basis of differences in specific gravity.
Only one manufacturer is in the
United States at present.* As indi-
cated below, particle size and shape
also contribute to the basic separa-
tion phenomena employed. Stoners
have been applied only recently (late
1967) to solid waste processing with
reasonable success. Applications to
date have been limited to the removal
of glass and nonmetallics from com-
post. As of this writing, two compost
plants, one in Altoona, Pennsylvania,
and one in Houston, Texas, are em-
ploying stoners in their processing
systems.
Stoners were originally developed,
TABLE 15
PROPERTIES OF HEAVY ORGANIC LIQUIDS USED
IN HEAVY MEDIA SEPARATION
Compound
Specific Approximate
gravity cost* (dollars
per Ib)
Tetra-bromo- ethane
(acetylene tetra-
bromide) 2. 96 0. 53
Bromoform 2. 89
Methyl bromide 2.48 0.57-0.64
Ethylene dibromide__ 2. 17 0. 285
Pentachloroethane
(pentalin) 1.67
Tetrachloro-methane
(carbontetra-
chloride) 1.50 0.1075
Trichloroethylene 1.46 0.0925
'From Oil, Paint, and Drug Reporter, May 6 and
13,1967.
•Button, Steele, and Steele, Dallas,
Texas.
-------
Gravity separation 41
4500
c
"o 3000
O
O
O
1500
O
50
100 150
Flotation Capacity , ft3 / cell
200
250
FIGURE 33. Flotation capacity capital costs. (Data supplied by Denver Equipment Company.)
14
12
= 10
a>
o
50
100
150
200
Flotation Capacity , ft3/cell
FIGURE 34. Flotation power requirements. (Data supplied by Denver Equipment Company.)
-------
42 SEPARATION
FEED^
SLOW IMPULSE'
RAPID RETURN!
SCHEMATIC REPRESENTATION OF VIBRATING TABLE
FIGURE 35. Schematic representation of dry vibrating table.
-------
TABLE 16
SUMMARY OF PATENTS RELATED TO STONERS
Patent No.
Title
797, 239 Dry concentrating table.
898, 020 Separating table.
979, 046 Process of concentrating
comminuted material.
1, 073, 644 Separating table and
process of separation.
1, 133, 760 Process of and apparatus
for separating and
grading seeds.
1, 315, 881 Process of and apparatus
for separating and
grading material.
1, 574, 637 Air baffle.
1, 632, 520 Process of and apparatus
for separating, cleaning,
and grading all kinds
of nuts, cereals, and
legumes.
2, 137, 678 Apparatus for separating
a mass of seeds of
varied characteristics.
2, 137, 679 Process for separating a
mass of seeds of varied
characteristics.
and are traditionally employed, for
the removal of stones, shells, and
other heavy materials from nuts,
seeds, grains, and other similar light
products. A stoner is basically a dry
vibrating table that operates by pass-
ing a stream of air upward through
an inclined screen or perforated
table (Figure 35). Feed enters near
the top of the inclined screen. Lighter
particles are buoyed up by the air
passing through the screen and flow
downward to the lower end where
they are discharged. The inclined
screen vibrates in an oscillating mo-
tion which causes the dense particles
to migrate upward along the screen
surface and discharge over the higher
end of the table. By proper installa-
tion of baffles and the selection of the
point where feed material enters, a
feed stream containing materials with
different specific gravities can be
separated into several product
streams. In order to effect good sepa-
ration, particle size must be con-
trolled rather closely. Otherwise,
large less dense particles may end up
in the heavy fraction and small
heavy particles may end up in the
light fraction. Size control is nor-
mally accomplished by screening. De-
pending on the material, particle sizes
in the range l/16 to 2 in. can be
accommodated.
Basic patents upon which stoner
designs are based have been sum-
marized (Table 16). As indicated, ex-
isting applications of stoners to the
solid waste processing field are lim-
ited to the separation of glass from
compost. At the Altoona FAM Plant
in Altoona, Pennsylvania, a small
laboratory scale unit is employed to
process 2 to 3 tons/hr. Prior to
processing in the stoner, the compost
is pelletized and screened through
a vibrating screen having s/16-in.-
diameter openings. Material passing
through the screen is fed to the stoner.
The heavy fraction from the stoner,
amounting to about 5 percent of the
feed, has a bulk, density of about 1.2
Ib/cu ft, whereas the light compost
product has a bulk density of 0.6 lb/
cuft.
A second similar application is at
the Lone Star Organics, Inc., compost
plant in Houston, Texas. Although the
system is still under development, a
flow sheet indicating approximate
operating conditions is provided (Fig-
ure 36). The compost feed to the sys-
tem is not pelletized, but is taken
directly from the digesters and sub-
jected to a final size reduction. Be-
cause the application is so new,
operating conditions are continually
being modified and the process flow
sheet cannot be interpreted as firm.
For example, inputs to the system as
high as 25 tons per hr have been tried,
and screen size openings on the lower
screen have been varied from 5/i6 to
% in. In addition, the extent of re-
grinding and recycling depends on the
market for the coarse compost. One
market which has consumed a major
portion of the coarse product is high-
way landscaping.
The stoner used at the Houston
plant is the Mark IV model manufac-
tured by Sutton, Steele, and Steele
(Figure 37).
Capital costs for the major equip-
ment items at the Houston plant are
as follows:
Screening equipment $8,000
Two Mark IV stoners at $10,000
each 20,000
$28, 000
Assuming 10-yr life and 6 percent in-
terest, amortized capital costs amount
to $0.10-0.15 per ton of compost (feed)
processed. Power requirements are
very low—on the order of 1 hp (0.75
kw) per ton per hr—and so operating
costs are also very low.
Capital costs of various size stoners
manufactured by Sutton, Steele, and
Steele do not exhibit normal econo-
mies of scale (Figure 38); this is
presumably due to the more flexible
Gravity separation 43
capabilities of the larger production-
scale units and limitations on the
smaller ones which are intended for
laboratory use.
Wilfley tables. Wilfley tables are
similar to stoners in many ways and
effect separations of solids mainly
upon differences in specific gravity
and to a lesser extent upon shape and
size of the particles being processed
(Figure 39). The main difference be-
tween Wilfley tables and stoners is
that water instead of air is used as the
buoying medium. Wilfley tables are
used mostly in minerals beneflciation
to concentrate metallic ores in the size
range from 6 mesh (0.132 in.) to 150
mesh (0.0041 in.) but can be used to
separate lighter materials such as
coal (and presumably solid waste) of
considerably larger size.
Separation is effected by flowing a
pulp across a riffled plane surface,
which is inclined slightly (2 to 5 de-
grees) from the horizontal in the di-
rection perpendicular to the riffles.
The table is vibrated in the direction
of the long axis (along the riffles) and
washed by water flowing at right an-
gles to the direction of vibration.
Lighter materials buoyed by the water
wash over the riffles and travel to the
low side of the table. The heavier par-
ticles are collected in the riffles. The
vibrating motion employs a slow stroke
and rapid return, thereby causing the
heavy particles in the riffles to migrate
toward the end of the table (Figure
39).
During operation several "bands"
of materials of varying specific gravi-
ties will develop on the surface of the
table, and each may be collected sep-
arately by the proper placing of baffles.
It is seldom possible to achieve a
sharp separation, and materials at the
boundaries of the various bands are
mixtures termed "middlings." To
achieve high degrees of separation,
these middlings must be recycled to
the feed. Tables are usually surfaced
with hard linoleum or rubber. Rif-
fles may be wooden or rubber strips.
Although the potential exists, Wil-
fley tables have not been applied to
the processing of solid waste. One ex-
ception to this statement is work re-
cently initiated by the Bureau of
Mines on municipal incinerator resi-
due recovery. However, at the time of
the writing no data were available
concerning this work.
The cost of tabling ores is very low.
Tables with relatively large capacities
are not expensive and power require-
ments are minimal. A comparison of
selected information on the two tables
manufactured by Denver Equipment
456-7% O - 72 - 4
-------
44 SEPARATION
Preliminary Performance Indicators
for
Sutton, Steele, fi Steele Air-float Stoners
Digested compost throughput
M5 tons/hr
(30 - 50% moisture)
(70-90% compost)
r~
FIGURE 36. Approximate process flows sheet
for Lone Star Organics, Inc., compost plant,
Houston, Texas.
TVr7'B"^g^r7en^
_!l_J^°meter openings
6-8 tons/hr
Reject
+ IT'
2-3 tons/hr
6-8 tons/hr
1
Compost (80-90%)
Nonferrous metallics
Ceramics •
Temporary
1 storage
5-8 tons/hr
t
| Mark IV stoner
Compost (80-90%)
Nonferrous metallics
Ceramics
Rubber
Plastics
Temporary
| storage j
4-6 tons/hr
t
Mark IV stoner J
I ^^\ *-oa
! I ^or
Compost (99%) Nonferrous metallics
Ceramics
Regrind [-«
rse \,
ipost f
Nonferrous metallics
Ceramics
Rubber
Plastics
Direct sale
product
FIGURE 37. Sutton, Steele, and Steele Mark IV
stoner.
-------
10
Gravity separation 45
Mark IV Model
o
TJ
0 6
o
O
o
O
5-40-60 model
^S-30-G model
0
I
234
Capacity for+'/4 - % Compost ( Tons / Hour) ± 25 %
FIGURE 38. Capital cost of Button, Steele, and Steele stoners.
horizontal
Flow of eoorse,heavy
Power art vibrator
mechanism
fine, light material
FIGURE 39. Wilfley table. (Source: Denver Equipment Company.)
-------
46 SEPARATION
Company indicates significant econo-
mies of scale (Table 17).
Mineral jigs. A jig is a mechanical
device for separating presized materi-
als of different specific gravities by
the pulsation of a stream of liquid
through a bed of the material. The
liquid on the screen pulsates or jigs
up and down, causing repeated ex-
pansion and contraction of the bed,
thereby causing the heavy material
to work to the bottom of the bed and
the lighter material to the top. Jigging
thus results in the stratification of
particles into layers of different den-
sities. Jigging is widely used in min-
erals beneficiation, but has not been
applied to solid waste processing. It
is mentioned primarily in the interest
of completeness, since the method
may be applicable to the recovery of
special types of solid waste such as
incinerator residues.
A jig consists primarily of a rec-
tangular tank fitted with a horizontal
screen slightly below an overflow. The
screen may be given a pulsating or
jigging motion which causes an al-
ternate upward and downward motion
through the suspension. Alternatively
the screen may be fixed and the sus-
pension forced upward through the
screen by means of a plunger. In
either model, solids are lifted free
from the screen and allowed to settle
for a short period. The material is
stratified vertically on the screen and,
after a suitable number of cycles, is
removed through properly installed
baffles and spigots. Particles passing
through the screen are fed to a second
jig in series for similar processing. Up
to six compartments in series are not
uncommon in minerals beneficiation.
The feed is introduced over the
screen at one side and subjected to a
series of short settling periods as it
moves across the screen to the over-
flow. Screen openings are about twice
the diameter of the largest particle in-
tended to pass through the screen. A
bedding of large, dense particles builds
up on the screen. Less dense particles
collect on the top of the bed and are
washed into the next compartment,
if one is provided. If the feed is a
size such that only stratification on
the screen and no particle passage
through the screen are desired, a bed
of steel balls is placed upon the
screen.
Several jig designs are available
and depart in minor ways from the
devices and operation described
above. Particle sizes capable of being
accommodated for minerals beneficia-
tion applications range from fines
to iy2-in. Specifications are given
Plunger-
Wafer service
Plunger
compartment —
£> o o a
^—Screen
Concentrate
discharge
777777/
CONCENTRATES
FIGURE 40. Denver plunger jigs. (Source: Denver Equipment Company.)
-------
Optical sorting 47
TABLE 17
CHARACTERISTICS OF WILFIEY TABLES*
Model
No. 6
No. 12
Capacity (tons/24 hr). 15-150 5-20
Wash water (gpm).._ 5-20 3-15
Deck size (approx.)__ 6' x 15' 3}£' x 7'
Horsepower, motor.. 1J4 1
Capital cost ($) 2,250 1,550
'Source: Denver Equipment Company.
TABLE 18
SPECIFICATIONS FOR DENVER PLUNGER JIGS"
Compartment size
(horizontal cross
section, in.)
18 x 32 _.
24x36 __.
30 x 36 .- _
Average
capacity
(tons/24hr)
t,l
40
60
75
Horse-
power
1
1^
1^
Capital
cost
(dol-
lars)!
1,630
2,150
2,590
* Source: Denver Equipment Company.
t Capacity based on 10 tons of material per 24 hr.
Actual capacities for selected minerals are chromite,
4 to 8; pyrite, 8 to 12; galena, 8 to 16; sphalerite, 4 to 8;
manganese, 5 to 10; and fluorspar, 1J6 to 2.
J Water requirements vary from 3 to 10 tons per ton
of material treated for ore beneficiation.
§ Multicompartment units can be employed to
effect economies of scale.
FIGURE 41. Osborne dry separator. (Source: Raymond G. Osborne
Laboratories, Inc.)
TABLE 19
CHARACTERISTICS OF THE OSBORNE DRY
SEPARATOR'
(Table 18) for Denver plunger jigs
(Figure 40).
Osborne dry separator. In principle
the Osborne Dry Separator is designed
to separate high density materials
from low density materials (Figure
41).20 It was used and was reported
successful for removing glass and
other similar fractions from compost
produced at the General Conversion
Systems compost plant during its op-
eration in San Fernando, California,
during the period 1963 to 1964 (Figure
41). Successful applications are also
claimed for the separation of gold,
tungsten, and other minerals.
In concept the device is a jig or
pulsed, hindered settling separator.
It is very similar to the wet mineral
jig, with the exception that air is
used as the working medium instead
of water.
Cost and performance data are
available for the unit used in San
Fernando (Table 19).
Fluidized bed separator. Another in-
teresting gravity separation technique
developed in England, which has re-
ceived brief mention in the literature,
is a process which employs a fluidized
bed of dry materials as a working
medium.21 Materials heavier than the
powder medium sink, while lighter
materials are carried along. The de-
vice was developed specifically for sal-
vaging copper from used cables after
grinding. Efforts during the course of
this study to obtain additional infor-
mation were not successful.
OPTICAL SORTING
Optical sorting machines, which
separate particles on the basis of color
(surface light-reflectional proper-
Size :
Length—7 ft, 7 in.
Width—5 ft, 0 in.
Height—7 ft, 3 in.
Feed rate—based on composed munic-
ipal solid waste:
V/i tons per hr
Particle size:
Maximum:
Inorganic fraction—Me in.
Organic fraction—1 in.
Minimum:
Inorganic—%* in. Battelle es-
timates
Organic—jKo in. Battelle esti-
mates
Separation:
90 to 95 percent of the glass, sand,
metals, and other heavy frac-
tions are removed from the fin-
ished composts
Cost:
$25,000.00 approximately
•Source: Raymond G. Osborne Laboratories, Inc.,
Los Angeles, California.
-------
48 SEPARATION
Photocell-Hlb
High-speed
grooved feed
belt
o
o
o
o
8
Product Product
No. 2 No. I
/
o
o
o
o
o
/
Dividing edge
FIGURE 42. Diagram illustrating
the operating principle of the
Sortex unit. (From Mining and
Minerals Engineering, 1(6) :221,
Feb. 1965.)
ties), have been used quite success-
fully in the agricultural and food
processing industries and more re-
cently in minerals beneficiation.
Typical applications have included
the cleaning and grading of peas,
beans, nuts, and seeds and the bene-
ficiation of rock salt and gypsum.
Color sorting machines encountered
during this study are manufactured
by Sortex Company of North Amer-
ica, Lowell, Michigan. The outlined
operating principles (Figure 42) are
documented in the literature.22 The
material to be separated is fed into
a hopper and delivered by a pair of
vibrating chutes to a grooved, endless
feed belt moving at high speed. This
belt projects the pieces in a contin-
uous stream so that they fall freely
through an optical box. Around the
sides of this box, four photomulti-
pliers are arranged and suitable il-
lumination is provided. Each photocell
head is aimed through the viewing
area at a background on the opposite
side of the box. These backgrounds
match the reflectivity of the particles
to be separated. Background slides of
varying shades are readily exchange-
able to give different selectivity for
any reauired separation. As the parti-
cles fall through the optical box as-
sembly, each passes through the cen-
ter of a four-lens, wide-angle viewing
system and receives a complete sur-
face inspection on all sides. Any
pieces whose color or shade differs
from the set standard for one reason
or another (too little or too much color
content, stains, rock inclusions) cause
a change in output voltage in at least
one of the photomultipliers. This sig-
nal is amplified by an electronic cir-
cuit and is used to trigger a short-
blast compressed air jet that deflects
the unwanted fragment into a reject
chute. To ensure that the rejection
air blast does not blow dust on the
lens system, the ejection does not
operate until the product has cleared
the optical zone (i.e., a free fall of
3 in.). All the light sources and optical
components are kept clear of dust
particles by a low pressure air
curtain.
Sortex manufactures three models
of optical sorters having capacities up
to 50 tons per hr. Particle sizes that
can be accommodated range from Vi
to 6 in. It is required that close control
of sizing be exercised to maximize
separating efficiency. Major charac-
teristics and capital costs have been
summarized (Table 20).
TABLE 20
CHARACTERISTICS AND CAPITAL COSTS OF
SORTEX SEPARATORS
Typical
Model throughput
(tons/hi)
621 M 1-2^
711 M 2-8
811 M 30-50
Particle Capital
size cost
(in.)
Y±-%, 812, 460
%-2 27, 900
2-6 60, 800
Performance characteristic curves
for the Model 621 M separators apply
to a fully liberated material having a
specific gravity of 2.7 (Figure 43). It
is reported that these curves were
obtained by separating dark particles
from a feed mixture consisting of
light and dark colored granite.
-------
O -C
CL 21
it
O 3
co -o
5T 2
cc CL
c
o
o
CL
c <-
— c
(/> CO
0) O
la
If
CD CU
Z *
® -§
o> o
O T3
c £
o o
-
O CO
Q. -O
O C
^- O
CL -Z.
c. c
~ cu
in o
-?> £
O Q.
o> 5
-Q
2 O
O !3
Q) "O
•* 2
cc Q.
o-
18
"*" H—
If
£ §
QL -Z-
10
9
8
7
6
5
4
3
2
I
0
10
9
8
7
6
5
4
3
2
I
Particle size- f +y
(- I9mm + I2.7mm )
10 15 20 25 30 35 40 45 50
Feed Rate ,tons / 24 hours
Particle size- -}-+ -f-
— 28
(-12 7mm + 96mm)
Feed composition
50% dark rejectable
30% dark
rejectable
20% dark
rejectable
10% dark
Tejectable
I I
10 15 20 20 30 35 40 45 50
Feed Rate,tons / 24 hours
10
9
8
7
6
5
4
3
2
I
Feed composition
•50 % dark rejectable
-96 mm +6.4mm)
20 % dark
rejectable
10% dark
rejectable
I
I
I
I
Inerttal separation 49
Curves of total processing costs for
optical sorting, based upon data pro-
vided by Sortex, are presented (Fig-
ure 44).
Optical sorting has not been applied
to solid waste processing, but poten-
tial applications such as the separa-
tion of dirt from glass may have merit
because of the relatively low overall
processing cost.
Another form of optical sorting was
developed by Battelle for the removal
of dark impurities from rock salt and
combines a thermoadhesive process
with optical phenomena.23 24 The proc-
ess effects a separation by selective
radiant heating of the impurities on
a heat-sensitive surface such that the
dark impurities become warmer and
adhere preferentially to the surface
thereby effecting a separation. The
process worked satisfactorily for the
beneflciation of rock salt, and poten-
tial applications in solid waste proc-
essing might be for the recovery of
rubber and plastics.
INERTIAL SEPARATION
The use of inertial forces to effect
the separation of solid waste ma-
terials is a concept that has received
much discussion, but has not been im-
plemented successfully. There are
three conceptual types of inertial
separators—ballistic, secator, and in-
clined conveyor (Figure 45). The bal-
listic separator effects a separation
based upon size (i.e., air resistance)
and density (i.e., gravity effects). The
secator depends on the elastic prop-
erties of the materials being sepa-
rated. The inclined conveyor depends
on both density and elastic properties.
Although it has been reported that
inertial separators are used in Euro-
pean compost systems, attempts to
locate installations and operating ex-
periences were not successful during
this study.25 The first known attempt
in the United States to employ inertial
type separation in the recovery of
solid waste is at the Gainesville,
Florida, demonstration project com-
post plant. The device, a "jet slinger,"
cost approximately $16,000 to fabri-
cate, including motors, drives, etc.28 As
of this writing, serious operational
problems had been encountered dur-
ing initial shakedown trials of the
plant, and further use of the jet
10 15 20 25 30 35 40 45
Feed Rate, tons 724 hours
50
FIGURE 43. Performance of Model 621M
Sortex optical separator. (Source: Sortex
Company of North America.)
-------
50 SEPARATION
i.tu
i ^n
1 20
1.10
1 100
<+~
*4—
° 0.90
o
\
£ 0.8O
J3
-8 0.70
In
° 0.60
o>
^ 0.50
en
NN
TJ
31621 M
\
\
r
i
c
k
^N
T.
^
<^
0—0
o--a
A — A
MnHnl
**0^
^A~
Total cos
Amortize
Vlaintenc
71 1 M
k
^^"-^.
• • -
* +
>d capitc
mce and
' -^
— t
il cost, 5 y€
operating c
>
,
ars,6%
ost
j^Model 8
IIM
| A ^«^§Ssgj
V
567
Feed Rate , tons / hour
30
40
5O
FIGURE 44. Total processing cost for Sortex optical separators. Specific gravity of material=2.7. (Data
provided by Sortex Company of North America.)
slinger has been discontinued.27
Inertial separation therefore has not
been successfully applied to the sep-
aration of solid waste.
FINDINGS
This study not only collected and
analyzed cost and performance data
for the various recovery processes, but
also sought to identify potentially at-
tractive process combinations. In
order to determine these combina-
tions, it is necessary to have informa-
tion not only on the cost and perform-
ance of individual processes, but also
on their effects upon one another.
Unit process characteristics and
costs for various mechanical separa-
tion methods have been discussed in
preceding sections. This section will
concentrate upon data gaps related to
cost and performance characteristics
and the synergistic and antagonistic
effects among various size-reduction
and separation processes.
DATA GAPS
Preceding discussions have indi-
cated a considerable lack of reliable
data concerning performance and cost
of mechanical separation techniques
for the processing and recovery of
solid waste. As indicated, applications
of mechanical separation of solid
waste processing and recovery are
currently limited and involve only the
use of magnetic separation for tin can
recovery, vibrating screens for size
clarification, and gravity separation
by air-flotation stoners to remove
glass from compost. This study
demonstrated that none of the exist-
ing installations had reliable per-
formance and cost data, nor were
they collecting it.
Magnetic separation data is needed
on performance and on the efficiency
of removing ferrous materials from
mixed solid waste. Relationships that
need to be investigated include the
effect of particle size and ferrous con-
tent of the mixed waste on removal
efficiency and separator capacity.
No eddy current separation data are
available other than that reported by
one company whose experience seems
to indicate little potential for appli-
cations of eddy phenomena to the
separation of nonmagnetic, conduc-
tive materials from solid waste.*
Controlling the particle size of the
input to an eddy-current separator by
use of screening might eliminate some
problems, but would not do much for
the control of shape and other fac-
*Eriez Manufacturing Company, Asbury
Road at Airport, Erie, Pennsylvania.
-------
tors. It may be worth investigating,
however, since the relative effects of
these variables have not been defined.
Because of this high sensitivity of
gravity separation devices to particle
size in solid waste recovery systems,
size classification will be an essential
element. Dry size classification is ac-
complished in various industrial ap-
plications by vibrating screens. Dry
size classification in the processing
and recovery of solid waste can be
effected by similar systems. However,
performance data are available only
for specialized industrial applications
such as in minerals beneflciation. Cur-
rent applications of screening in solid
waste processing are limited to the
preparation of compost for processing
in stoners to remove glass. However,
it is not considered likely that data
will become available from these ap-
plications. The addition of screening
and stoning operations to the Bureau
of Solid Waste Management demon-
stration compost planting in Gaines-
ville, Florida, would provide an excel-
lent opportunity to collect some basic
process data, not only on glass re-
moval, but also on the removal of
plastic, nonferrous metals, and other
materials.
In the area of wet processing, and
specifically wet classification, spiral
Ballistic Separator
Organic particles
Inorganic
particles
Secator
Bounce
plate
Pulley
Inclined-Conveyor Separator
Inclined-plate
conveyor-
Heavy and
resilient
particles
Light and
inelastic
particles
Heavy and
resilient
particles
Light and
inelastic
particles
FIGURE 45. Types of inertial separators. (From Wiley, John S. Some
specialized equipment used in European compost systems. Compost Science,
4(1).-10, Spring 1963.)
Data gaps 51
classifiers need to be investigated for
the recovery of relatively dense, small
particles such as those found in
incinerator residues. Investigators of
this area should be aware of studies
being conducted by the U.S. Bureau
of Mines in connection with their
work on the salvage of municipal
incinerator residues.
Perhaps one of the largest unknown
areas and one with several potential
applications to solid waste recovery is
flotation and its companion process,
dense media separation. As indicated
in earlier discussions, the variables
determining process cost and per-
formance for flotation range over
several orders of magnitude. Experi-
mental studies should be conducted to
establish critical factors for making
several cuts on mixed solid waste and
component cleanup. The studies being
conducted by the U.S. Bureau of
Mines should generate flotation and
dense media separation data for the
recovery of incinerator residues. Ad-
ditional work is needed, however, to
explore the possibility of separating
organics, cellulosic components, non-
ferrous metals, glass and other suit-
able input materials for the by-prod-
uct recovery processes. But it must be
emphasized that the first requirement
is to determine the feasibility of these
separations and then to obtain cost
and performance measurements.
There is a universal lack of unit
process cost and performance data for
the application of mechanical sepa-
ration techniques to solid waste re-
covery. The specific data of interest
concerns the interrelationship be-
tween particle size and distribution in
the feed stream, throughput or capac-
ity, processing cost, and separation
efficiency. The lack of data stems from
a lack of application of the techniques
and from the failure to collect data in
the few applications that do exist. De-
termining which data voids are the
most critical requires an assessment
of the attractiveness of various over-
all process combinations. This will be
discussed following a review of recov-
ery and utilization process technology.
In addition to unit process cost and
performance data, there is also a need
for acceptable standardized cost allo-
cation procedures so that unit process
costs can be established and compared
on a meaningful basis. A significant
fraction of total product cost is re-
lated to auxiliary items (i.e., materials
handling equipment, structures, etc.).
Therefore, the sum of the unit costs of
the functional equipment items may
not adequately represent the entire
-------
52 SEPARATION
TABLE 21
SYNERGISTIC AND ANTAGONISTIC EFFECTS RELATIVE TO PARTICLE SIZE FOR SIZE-REDUCTION
AND SEPARATION PROCESSES
DRY PROCESSING
Size reduction Nominal output particle size
capability—range
Crushers }£-10 in.
Cage disintegrators Powder-% in.
Shears 1-4 ft
Shredders 4-6 in.
Rasp mills <2 in.
Drum pulverizers <2 in.
Disk mills Fine powder
Hammermills 1-6 in.
Separation Approximate nominal input particle
size required—range
Magnetic separation <8 in.
Vibrating screens J4-3 in.
Stoners >16-2 in.
Osborne separator J^HKe in. (organic fraction)
jKs-1 in. (inorganic fraction)
Optical sorting J4-6 in.
WET PROCESSING
Size reduction Nominal output particle size
capability—range
Disk mills Pulp
Wet pulpers Fine Fibers-1 in.
Separation Approximate nomimal input particle
size required—range
Spiral classifiers 200 mesh (0.0024)~Kin.
Flotation 100 mesh (0.0059)-Ke in.
Dense media 10 mesh (0.066)-3 in.
Wilfley tables 6 mesh (0.132 in.)-150 mesh
Mineral jigs
cost. An example of this was pro-
vided in the discussions of magnetic
separation. Similar problems are en-
countered in the cost analyses for the
recovery systems, but are less pro-
nounced since the data on total recov-
ery systems include the costs of
auxiliary equipment. In the area of
separation equipment, however, aux-
iliary cost items must be defined and
allocated to the respective process so
that meaningful overall unit process
costs can be developed.
SYNERGISTIC AND ANTAGONISTIC
EFFECTS
Key factor in the selection of at-
tractive process combinations is the
synergistic and antagonistic effects
between performance characteristics
and operating features of the various
unit processes. These effects may be
discussed in terms of trade-offs be-
tween those size-reduction and sepa-
ration processes which are principally
related to particle size output-input
compatibility. These trade-offs are
discussed in qualitative terms since
sufficient information is not available,
especially as relating cost and per-
formance characteristics of separa-
tion processes as a function of
particle size.
In terms of compatibility with sepa-
ration processes, two general categor-
ies of size-reduction equipment may
be denned—wet and dry systems. Dry
size-reduction systems are more flex-
ible, permitting either wet or dry op-
erations downstream. Once a wet size-
reduction system is selected, one is
limited to consideration of wet sepa-
ration systems unless drying is pro-
vided. On the basis of existing expe-
rience with solid waste recovery, it is
difficult to justify the high drying
costs which would be incurred.
In a wet system, sizing would prob-
ably be accomplished best in spiral
classifiers, even though these have not
as yet been applied to solid waste proc-
essing. Potential applications would
be in preparing feed material for Wil-
fley tables, mineral jigs, and flotation
operations; all these require a rela-
tively small particle size. Wet screen-
ing, as previously mentioned, does not
hold much promise for solid waste
processing because the generally soft
nature of mixed solid waste would
tend to promote screen clogging.
Except for the wet versus dry con-
siderations, sufficient information is
not available to determine the best
type of size-reduction equipment for
preparing feed to a given separator.
Nevertheless, some general observa-
tions can be made relating size-
reduction equipment output capabil-
ities to separator input requirements
(Table 21 and Figure 46). Particle size
output-input compatibility, however,
is not the only factor in determining
overall process combinations. Other
critical factors are the type of mate-
rial being processed and the freedom
of the individual components. It
should also be noticed that reduction
to small particle sizes would be accom-
plished in several stages because of
the constraints on the size of input to
the various size-reduction equipment.
In addition, manufacturers' experi-
ence indicates that most efficient par-
ticle size reduction is accomplished in
stages.
Another type of synergistic effect
relates to a possible phenomenon con-
cerning different degrees of particle
size reduction for different materials.
Certain observations indicate that dif-
ferent materials in mixed solid waste
are reduced to different sizes when
processed in a hammermill (Figure
10). Thus, size reduction followed by
screening might constitute a basis for
effecting a separation of different
materials.
Synergistic and antagonistic effects
may also be defined among the vari-
ous separation processes themselves.
These definitions are of interest since
any complete solid waste recovery sys-
tem is likely to contain several parallel
and sequential separation processes,
and compatible outputs of one process
and input requirements of another
are essential. This is especially true
for the various gravity separation
methods that require close control of
particle size input to effect efficient
gravity separation. Input particle size
control may also be one technique for
achieving improved performance of
eddy current separation techniques.
Data do not exist for defining cost-
benefit trade-offs between increased
costs associated with screening and
size reduction to yield a fine particle
stream and benefits in terms of in-
creased performance of the separation
process which would be associated
with the finer particles.
-------
Synergistic and antagonistic effects 53
Dry Size Reduction Followed by Dry and/or Wet Separation
Dry
Size
Reduction
Crushers
Cage Disintegrators
Shears
Shredders
Rasp Mills
Drum Pulverizers
Disk Mills
Hammer Mills
+
4-
-
+
+
+
-
+
+
4
-
+/-
+
+
-
+
_
+
-
-
+
+
-
+
-
+
-
-
+/-
4
-
+
4
+
-
-
+
+
-
+
-
+
-
-
+/-
+
+
-
-
+
-
-
+/-
+
+
-
-
+
-
-
+/-
+
+
-
-
+
-
-
-
-
+
-
+/-
+
-
-
+
+
+
+/-
Wet Size Reduction - Wet Separation
Size
Reduction
Disk Mills
-Wet Pulpers
+
+
+
+
+
+
+
+/-
+
+/-
LEGEND
Generally compatible
Marginal due to considerations
regarding materials and
physical liberation or other
factors
Incompatible
FIGURE 46. Summary of compatibility of size-reduction output, particle-size capabilities, and separation
process particle-size requirements.
-------
-------
VI. Recovery and utilization
RECOVERY AND UTILIZATION of solid
waste encompass two general con-
cepts: recovery by conversion and re-
covery by salvage. Conversion involves
the chemical, biological, or physical
processing of waste components to
produce new by-products. Salvage
connotes recovery of waste compo-
nents in their original form, i.e., re-
covery of tin cans to produce steel,
or recovery of newsprint for manu-
facture into other paper products.
Conversion processes investigated
during this study were composting,
incineration and waste heat recovery,
pyrolysis, hydrolysis, and fermenta-
tion. Within the general context of
separation and salvage the following
materials were investigated: tin cans,
paper, plastics, glass, fly ash, and in-
cinerator residues.
The ultimate motivation for size re-
duction and separation of solid waste
is to make possible various recovery
schemes. Each technique requires a
different degree and type of preproc-
essing in terms of size reduction and
separation. The extent to which these
requirements can be established based
upon existing operating experience is
discussed below.
As has been indicated, this study
emphasized the collection of cost and
performance data. Since recovery
processes are, for the most part, more
related to the end product, and, hence,
the economics of solid waste recovery,
proprietary limitations constrained
availability of data more than was the
case for size-reduction or separation
equipment. This constraint was fur-
ther compounded by the marketing
philosophy of many companies cur-
rently engaged in solid waste recovery,
in that they do not wish to sell equip-
ment or processes, but, rather, are
interested only in selling a disposal
service to municipalities. Conse-
quently, equipment and process costs
and system capabilities are closely
guarded as proprietary secrets.
COMPOSTING CONVERSION
PROCESSES
Composting is the solid waste re-
covery technique for which the great-
est amount of data are available. This
information pertains primarily to
complete plants and covers size re-
duction, separation, and salvage as
well as the compost process itself.
Compost is a humus-like material
which results from the aerobic bio-
logical stabilization or digestion (at
temperatures of 150 to 170 F) of the
biodegradable (organic) materials in
solid waste. Aerobic conditions are
essential in order to minimize odor
problems and to ensure sufficiently
rapid, and hence economic, processing
times. Because of the difficulty of
separation, a considerable amount of
nonbiodegradable material is typically
passed through the digestion process
and emerges essentially unchanged.
The primary attributes of compost
are those of a soil conditioner. In this
role, compost will: (1) improve soil
structure, (2) increase moisture hold-
ing capacity, (3) reduce leaching of
soluble inorganic nitrogen, (4) in-
crease the phosphorus availability to
growing plants, and (5) increase
buffering capacity of the soil. It
should be emphasized that compost
is not a fertilizer. It contains only
1 percent or less of each of the major
fertilizer nutrients—nitrogen, phos-
phorus, and potassium. Thus, only a
limited market exists for compost and
the economics of a given operation
are highly sensitive to market limi-
tations. It is clear that the future for
compost as a soil conditioner alone is
not bright. Peat moss is the major
form of soil conditioner utilized in
the United States today. In 1966,
slightly in excess of 600,000 tons were
consumed.28 The solid waste from a
city with a population of about
55
-------
56 RECOVERY AND UTILIZATION
*tft ^W*
FIGURE 47. Basic Metro process as indicated in the schematic flow diagram of the Lone Star Organics, Inc.,
compost plant, Houston, Texas. (From Chemical Engineering, Nov. 6,1967. Reprinted with permission.)
800,000 could produce this much com-
post in a year's time. The merits and
economics of compost should be eval-
uated in new terms, for example, as
an organic base for the manufacture
of chemical fertilizer. Failure to un-
derstand this point has contrib-
uted to rather unsuccessful manage-
ment and promotion of several com-
posting operations during the last
several years in the United States.
Recently there has been much doc-
umentation of composting technology
and its successes and failure.28'30 This
information is not repeated here;
only enough background information
is provided to render the cost and
performance data meaningful.
In addition to manufacturing, com-
post plants have traditionally engaged
in salvage operations. Most systems
employ various types of size reduc-
tion, and separation of materials such
as tin cans, newsprint, rags, and glass,
which are removed for their salvage
value and to upgrade the quality
of the compost produced. Most exist-
ing plants operate under contract with
municipalities served with service
charges of $3 to $4 per ton of refuse
accepted.
Major U.S. composting systems are
of two types, depending on the type
of digestion employed. The first and
most common type involves mechani-
cal digestion with retention of the
material in a bin, tank, or other simi-
lar type of digester for about 5 days.
During this period, the waste is agi-
tated and air is introduced to main-
tain aerobic conditions. The second
type, adapted largely from European
practice, involves piling the compost
out-of-doors for several weeks in
windrows several hundred ft long,
about 6 to 10 ft wide at the base,
and 3 to 5 ft high. During this
period the material in the windrows
is turned or otherwise agitated once
or twice per week. After digestion in
windrows and sometimes even after
mechanical digestion, the compost is
"cured" in windrows for an additional
2 to 3 weeks. Actual curing mecha-
nisms are not well established, but it
is believed that the more resistant
cellulosic materials are broken down
at this time. Some other change also
occurs, for it has been observed that
cured compost does not seem to in-
hibit plant growth, whereas uncured
compost usually does. This effect is
unlikely to be dependent on cellulose
breakdown alone.
Of the two methods, mechanical
digestion appears to hold the most
promise, especially for large compost-
ing systems in urban centers where
the bulk of the solid waste is gen-
erated. In agricultural and rural
areas where land is available and
where odor problems are not critical,
the windrow system may have ad-
vantages. Odor problems are a definite
consideration since it is somewhat
more difficult to maintain aerobic
conditions in the windrow system
than in mechanical systems.
RECENT AND CURRENT APPLICA-
TIONS OF COMPOSTING
In 1967 and 1968, six companies
or organizations had experience in
large-scale composting of municipal
solid waste; each employing a some-
what different system. They are as
follows: (1) Metropolitan Waste Con-
version Corporation, Wheaton, Illi-
nois; (2) International Disposal
Corporation, St. Petersburg, Florida;
(3) Fairneld Engineering Company,
Marion, Ohio; (4) United Compost
Services, Inc., Houston, Texas; (5)
Gruendler Crusher and Pulverizer
Company, St. Louis, Missouri; and
(6) Tennessee Valley Authority Com-
posting Plant, Johnson City, Tennes-
see (joint venture with U.S. Public
Health Service). The systems and
operations of each of these organiza-
tions are discussed below with cost
data, to the extent they were avail-
able.
METROPOLITAN WASTE CONVER-
SION CORPORATION (METRO)
Metro entered the composting field
in 1963 with a small 50-ton-per-day
pilot plant in Largo, Florida. Based
upon experience at Largo, a 360-ton-
-------
Metropolitan Waste Conversion Corporation 57
-TRUCK UNLOADING PLATFORM
RECEIVING CONVEYOR
FIGURE 48. Schematic flow diagram
of the Gainesville Municipal
Waste Conversion Authority, Inc.,
compost plant, Gainesville, Florida.
(From Harding, C. I. Recycling and
utilisation. In Proceedings; the
Surgeon General's Conference on
Solid Waste Management for
Metropolitan Washington, July 19-20,
1967. Public Health Service
Publication No. 1729. Washington,
U.S. Government Printing Office, 1967.
p. 105-119.)
-SORTING AREA PLATFORM
- SALVAGE COLLECTOR CONVEYOR
-BAILER
VIBRATOR
PRIMARY GRINDER
STORAGE HOPPER
SEWAGE SLUDGE THICKENER
MIXING SCREW CONVEYOR
TRIPPER CONVEYOR
AGITATOR
UNLOADING CONVEYOR
CONVEYOR -
BAGGER-
per-day plant was built in Houston,
Texas, and has been operating suc-
cessfully since January 1967, under
the name of Lone Star Organics, Inc.
The Metro system is also being em-
ployed in a 150-ton-per-day Bureau
of Solid Waste Management dem-
onstration project in Gainesville,
Florida, which began operation early
in 1968.
The basic Metro process, as in-
stalled in Houston and Gainesville,
involves sorting and salvage, two
stages of size reduction, sewage
sludge addition, digestion, and final
product preparation (Figures 47 to
50).
As indicated previously, the major
difference in composting schemes is
in the digestion process. Material de-
livered to the digesters by a conveyor
is moved longitudinally by an agitator
on which a track mixes the compost
about once a day. Digester retention
time is about 5 days, after which the
compost is conveyed to the final
processing.
Another unique feature and recent
addition to the Houston plant, as men-
tioned previously, is the use of a Mark
IV, Button, Steele, and Steele air-float
stoner to remove glass from the final
compost product.
Capital costs for the Houston and
Gainesville plants were $1.7 and $1.25
million, respectively, somewhat higher
than the general trends exhibited by
FIGURE 49. Digesters at Lone Star Organics, Inc., compost
Houston, Texas.
-------
58 RECOVERY AND UTILIZATION
the other date because of the experi-
mental and prototype nature of these
plants (Table 22).
INTERNATIONAL DISPOSAL COR-
PORATION (IDC)
In July 1966, IDC began operation
of a 105-ton-per-day compost plant
employing the Naturizer process in St.
Petersburg, Florida. The system de-
sign is based upon pilot tests con-
ducted by Salvage and Conversion
Systems Corporation (SACS) in the
early 1960's at San Fernando, Cali-
fornia, and Norman, Oklahoma. IDC
was formed from a recapitalization of
SACS, the All State Insurance Com-
pany, and the Westinghouse Electric
Corp. Size reduction, handsorting, and
magnetic separation is accomplished
in a fashion similar to that employed
by the Metro system (Figure 51).
The unique feature of the Naturizer
system is the digestion process con-
sisting of five stacked conveyors. After
size reduction, separation, and addi-
tion of water to raise the moisture
content, the material is delivered to
the digester where it is stacked to a
depth of about 6 ft on the continuous
conveyors. These conveyors are about
9 ft wide and about 150 ft long. On the
average of once a day, material is
dumped or transferred to a lower con-
veyor where a fan supplies air to the
compost. Early in 1968, the St. Peters-
burg plant was reported temporarily
closed due to odor problems.31 These
conditions may have been due largely
to the limited amount of air supplied
by the aeration system which would in
turn lead to the development of
anaerobic conditions and associated
odors.
Capital cost of the St. Petersburg
plant was $1.5 million. Capital costs
for other capacities of the system de-
sign were estimated and summarized
(Table 23).
FAIRFIELD-HARDY PROCESS
The Fairfield Engineering Com-
pany uses the Fairfield-Hardy com-
posting system (Figure 52). Opera-
tional experience with this system is
limited to a 25-ton-per-day plant in
Altoona, Pennsylvania. Waste ma-
terial processed by the plant is a por-
tion of the garbage collected by the
city; Altoona has separate garbage
and rubbish collection. As of this writ-
ing, construction is underway for a
300-ton-per-day Fairfield-Hardy sys-
tem in San Juan, Puerto Rico.
In the Fairfield-Hardy digester, ma-
terial is fed through the top center
and is distributed to the outer cir-
FIGURE 50. Mixing of compost in digesters at Lone Star Organics, Inc.,
compost plant, Houston, Texas.
TABLE 22
ESTIMATES OF CAPITAL COSTS, ENERGY, AND LABOR REQUIREMENTS FOR METRO COMPOST
SYSTEMS
Capacity (tons/day)
Capital cost
(dollars)
Power require- Labor require-
ments (hp) ments (men)
100 *900,000 *1, 250
150 (Gainesville) H, 250, 000 fl, 100
200 H, 200, 000 *1, 700
300 _ .__ *1, 500, 000 *1, 900
360 (Houston) 11,700,000
400 *1, 600, 000 *2, 000
*12
*17
*25
*30
*Harding, C. I. Recycling and utilization. In Proceedings; the Surgeon General's Conference on solid waste
management for Metropolitan Washington, July 19-20, 1967. Public Health Service Publication No. 1729. Wash-
ington, U.S. Government Printing Office, 1967. p. 115.
fPersonal communication from H. W. Houston, Project Director, Gainesville Municipal Waste Conversion
Authority, Inc., Aug.8,1967.
^Personal communication from G. Vaughn, Plant Manager, Lone Star Organics, Inc., Aug. 8, 1967.
TABLE 23
ESTIMATES OF CAPITAL COSTS, ENERGY, AND LABOR REQUIREMENTS FOR IDC-NATURIZER COM-
POST SYSTEMS
Capacity (tons/day)
Capital cost
(dollars)
Power require- Labor require-
ments (hp) ments (men)
100
105
200
300
400 . __
*1, 400, 000
fl, 500, 000
*2, 100, 000
*2, 700, 000
*3, 200, 000
*600
*800
*950
*1, 100
*20
*28
*36
*45
•Harding, C. I. Recycling and utilization. In Proceedings; the Surgeon General's Conference on Solid
Waste Management for Metropolitan Washington, July 19-20, 1967. Public Health Service Publication No. 1729.
Washington, U.S. Government Printing Office, 1967. p. 105-119.
fPersonal Communication from R. Lynn, Plant Manager, IDC, St. Petersburg, Florida, Aug. 1967.
-------
Fair field-Hardy process 59
MAGNETIC
OVERAGE RETURN S'x*-' SEPARATOR
TO RECEIVING AREA
DIVERTER ^GRINDER
CONVEYOR
MASTER
CONTROL
FIGURE 51. Schematic flow diagram—IDC-Naturizer Compost Plant, St. Petersburg, Florida. (Source:
International Disposal Corporation.)
-------
60 RECOVERY AND UTILIZATION
ALTERNATE DRY GRINDING PROCESS
NON ORGAMC
MATERIAL TO
SALVAGE OR
LANDFILL
CONTROL PANEL
FAIRFIELD-HARDY DIGESTER
PAN
TO STORAGE
CURING
PELLETIZING
BAGGING
BAGGING
FIGURE 52. Schematic flow diagram for Fair field-Hardy compost system. (Source: Fairfleld Engineering Company.)
cumference of the tank by a rotating
distributor bridge. Attached to the ro-
tating bridge are nine augers that
periodically agitate the material in
the digester, gradually working it to-
ward the center where it is discharged
through the bottom of the digester
(Figure 53). Retention time in the di-
gester is about 5 days.
Another unique feature of the Fair-
fleld-Hardy system is the size reduc-
tion process. Wet pulping followed by
dewatering is employed, as opposed
to dry grinding in a hammermill.
There is a dry grinder at the Altoona
plant, but its use is largely experi-
mental. Although the cost figures in-
dicate this to be a rather expensive
process (Tables 24 and 25), an ex-
tremely high-quality product results.
An air-float stoner has been added
Legend
(I) and (2) feed conveyors
(3) rotating bridge with augers
(4) standpipe for discharge
(5) discharge conveyor
FIGURE 53. Fairfield-Hardy digester. (Sources: Fair field Engineering
Company.)
-------
John R. Sne//process 61
TABLE 24
ESTIMATES OF CAPITAL COSTS, ENERGY, AND LABOR REQUIREMENTS FOR FAIRFIELD-HARDY
COMPOST SYSTEMS
Capacity (tons/day) Capital cost Power require- Labor require-
(dollars) ments (hp) ments (men)
100
200
300
400
1, 370, 000
2, 000, 000
... 2,510,000
. 3,210,000
930
1,590
1, 830
2,560
11
18
25
30
Source: Fairfield Engineering Company.
TABLE 25
ESTIMATES OF PROCESSING COSTS FOR FAIRFIELD-HARDY COMPOST SYSTEMS
Operating costs
Capacity
(tons/day)
100
200
300
400
(tons/yr)
28, 600
57, 200
85, 800
114, 400
Payroll
(S/yr)
81, 000
126, 400
172, 400
204, 800
(*/ton)
2. 83
2.21
2.01
1.79
Utilities and
(S/yr)
74, 400
141, 700
189, 000
262, 000
. supplies
($/ton)
2. 60
2.48
2.21
2.29
Administration including
interest
(S/yr)
145, 800
214, 630
270, 435
336, 750
(S/ton)
5. 11
3. 76
3.20
3.02
Total
(I/ton)
10. 54
8.45
7.42
7. 10
Amortized
(excluding ing cost
land) and
interest
($/ton)
2.41
1.75
1.46
1.40
($/ton)
12.95
10.20
8. 88
8.50
Source: Fairfield Engineering Company.
•Assuming 20-yr life.
recently to the Altoona plant.* Due
to the low capacity of the Altoona
plant (3 to 4 tons per hr), a labora-
tory model stoner was found ade-
quate. The heavy fraction from the
stoner which is mostly glass has a
bulk density of about 73 Ib per cu ft.
The light compost product has a bulk
density of about 39 Ib per cu ft.
Estimates of capital costs, energy
and labor requirements (Table 24),
and of overall processing costs (Table
25) were determined for the Fairfield -
Hardy system.
An analysis of the capital costs
shows that approximately 30-40 per-
cent of the costs is attributable to the
digestion process, and the remainder
*Manufactured by Button, Steele, and
Steele.
to auxiliary support facilities (Figure
54).
JOHN R. SNELL PROCESS
In January 1967, United Compost
Services in Houston, Texas, put into
operation a 300-ton-per-day plant
employing a design developed by John
R. Snell Engineers, Lansing, Michi-
gan. The system design is a hybrid
of the Metro and Pairfleld-Hardy
systems, with the digester consisting
of a large open rectangular concrete
tank. After sorting and grinding, the
refuse is fortified with sewage sludge
and is conveyed to the digester, where
oxygen is supplied by pulling air down
through the material with large ex-
haust fans. The material is agitated
by means of rotating augers mounted
on a bar suspended across the width
of the tank, which traverses the tank
longitudinally. The rotation of the
augers is adjusted so that material is
moved across the width of the tank
in about 5 days and is discharged at
the opposite side.
The United Compost Services Plant
operated until April 1967 when a con-
tractual dispute with the city resulted
in termination of the operation. As
of this writing, the dispute has not
been resolved and operation has not
resumed.
The Houston plant, which has a ca-
pacity of 300 tons per day, cost $1.6
million. Power requirements amount
to about 1,700 hp. Attempts to obtain
process flow sheets and photographs
of the system were unsuccessful, but
costs for other plant capacities em-
ploying SnelFs design range from $2.69
to $3.44 per ton (Table 26).M
-------
62 RECOVERY AND UTILIZATION
3.5
3.0
S
c
o
1 20
c
D
c
13
€ '-5
x
LU
^~
(0
O
O
I i.o
0.5
^x -Preparation
H -Digestion
V\ -Drying and pelletizing
/2 -Receiving
EE -Storage
JJl-Site development
^-Mobile equipment
1- Administration
"
$3,208,200
27.4% I
<
$2,511,000
-Scale
8 1,996,900
&
15%
l.l%\
368.C
XXXS
5o
88
1
ys.
I
'/
s// /
IJIlll]
)00
35.6%
27.5%
10.8%
10.0%
6.1%
37%0.8%
>O<
I
^
xx
8?
?$<
Rx
XX
XX
ftr
\\
H
m
34 3%
8.3%
10.5%
73%
,,4.0%
^3.4%
1.2% 0.6%
m
xSoo
^
^
SrSAA
1
§
|
i
jji
K
OR | o/
406%
J396% E
7.6%
106%
10.0%
8.2%
4.2%
2.7%_c:o.
10% ub/2
wv
>oo<
xSo<
XXV
XXX
>w
XSo$x
>vv<
v9<
V$8
>$N/\y
p
1
ij^l
X
X
><
s
<
<
\
^ 6.6%
\
/
/
/
/
/
- 73%
39%
it 21%
• 1.0%
100
200 300
Plant Capacity,tons/day
400
FIGURE 54. Cost breakdown 1or Fairfteld-Hardy compost systems.
(Source: Fair field Engineering Company.)
TABLE 26
ESTIMATED CAPITAI AND PROCESSING COSTS FOR COMPOST PLANTS USING
THE JOHN R. SNEI1 COMPOSTING PROCESS
Capacity (tons/day)
Capital cost
Amortization of Operation and
fixed charges maintenance Total
100 *540, 000 *1. 52 *1. 92
200 *960, 000 *1. 35 *1. 68
300 *1,350,000 *1.27 *1. 56
300 (Houston) fl, 600, 000 _ _^_ _ _ _. .._ _
400 .. *1, 776, 000 *1. 25 *1. 44
*3. 44
*3. 03
*2. 93
*2. 69
GRUENDLER CRUSHER A1SD PUL-
VERIZER COMPANY
Gruendler offers a composting sys-
tem employing the windrow method
of digestion. To date the only plant
built is a 300-ton-per-day plant in
Mobile, Alabama. This plant cost $1.6
million to build and began operation
in 1966. Since that time, the plant has
operated only intermittently for a va-
riety of undetermined reasons. It was
not possible during the course of this
study to obtain estimated cost and
performance data on any aspect of the
operation either from the City of Mo-
bile or from the Gruendler Company.
THE U.S. PUBLIC HEALTH
SERVICE-TENNESSEE VALLEY
AUTHORITY
In June 1967, PHS and TVA began
operation of a 50-ton-per-day joint
composting plant in Johnson City,
Tennessee (Figure 55). This plant, fi-
nanced by the Public Health Service,
employs windrow digestion and rep-
resents the first attempt in the United
States to obtain scientific data on this
method of composting on a large
scale.
Material is delivered to the plant
and conveyed to a picking area where
handsorters remove such items as
rags, bottles, cardboard, magazines,
and other noncompostables. These
materials are not removed for salvage
but rather to upgrade the quality of
the compost. Tin cans are removed
magnetically for the same purpose.
The remaining waste material is
ground in a Dorr-Oliver rasp, sewage
sludge is added, and the material is
then piled in windrows about 100 ft
long, 9 ft wide, and 4 ft high. Total
time in the windrow is about 35 days,
during which period the compost is
turned mechanically once or twice per
week using a Cobey Windrow Turner.*
Problems have been reported with
odors and with the control of fly pop-
ulations. Another drawback of the
windrow method, especially for urban
centers, is the amount of land re-
quired. It has been estimated for ex-
ample that 30 acres are required to
serve a population of 100,000, com-
pared to 5 acres for a typical mechani-
cal digestion system.33
The Johnson City plant has not
been in operation long enough to gen-
erate cost data for this system. Capi-
tal cost of the plant was $750,000,
•From Snell, J. R. On the basis of a dumping fee only. Compost Science, 8(1): 17, Spring-Summer 1967.
fPersonal communication from J. George, President, United Compost Services, Houston, Texas, to N. L.
Drobny, Aug. 9, 1967.
*Manufactured by General Products of
Ohio, Crestline, Ohio.
-------
Summary of composting costs and operational requirements 63
(T) RECEIVING HOPPER
©DECEIVING HOPPER CONVEYOR
(D LEVELING ^METERING GATE
® ELEVATING BELT CONVEYOR
©REJECTS HOPPER
§ MAGNETIC SEPARATOR
RASPER
©GRINDER
® MIXER
® BUCKET ELEVATOR
©GROUND REFUSE STORAGE SIM
® SLUDGE THICKENER
S SLUDGE COACULATINS TANK
SLUDGE HOLDING TANK
@ CHEMICALS MIXING TANK.
INCOMING RCfUSE
REJCCTS TO LAMOnu. |
GROUND REFUSE TO WINDROWS
TUHNIHG- SHBtDDINC A. SCREtNlNtt
COMPOSTING
STORAGES SHIPPING
FIGURE 55. Schematic flow diagram for USPHS-TVA Compost Plant,
Johnson City, Tennessee. (From Wiley, John S., et al. Concept and design
of a 3-way composting project. Compost Science, 7(2) :11-14, Autumn 1966.)
including experimental facilities
which would normally not be included
in a purely operational plant. As in-
dicated in a previous section, the
Johnson City plant affords an ideal
opportunity to collect extensive and
reliable data on the Dorr-Oliver rasp.
SUMMARY OF COMPOSTING
COSTS AND OPERATIONAL
REQUIREMENTS
Data in the preceding section sum-
marize available information for
composting operations in the United
States. Because economic conditions
differ significantly between countries,
an attempt to correlate these data
with that published for European
compost plantsM was unsuccessful,
even upon adjustment of all Euro-
pean data to 1968 U.S. conditions.
Capital costs for both the IDC-
Naturizer and the Fairfield-Hardy
process are about 1.5 to 2 times that
for the Metro and Snell system de-
signs (Figure 56). Precise judgments
cannot be made as to the exact rea-
sons for these differences. The high
cost of the IDC plants is probably re-
lated to the large digester building
required. The high cost of the Fair-
field-Hardy systems may be related
to the pulping and dewatering equip-
ment costs, the net cost of which
would be expected to be greater than
that for a hammermill for dry size re-
duction. These factors alone would not
explain the total cost differences indi-
cated above. In addition, it must be
kept in mind that the data given were
estimates for the most part and are
based on limited operational experi-
ence. Estimates of total processing
cost were available only for the Fair-
field-Hardy and the John R. Snell
systems (Figure 57). Extreme care
must be exercised in the interpreta-
tion of these data since they are based
upon estimates only. In addition, it
has not been possible to determine
the basis for the data for the Snell
system in that detailed cost break-
down is not available. Detailed break-
downs for the Fairfield-Hardy sys-
tem were available, and these data are
considered to be much more reliable.
Data were obtained for the esti-
mated labor and power requirements
for various systems. Extremely close
correlation was noted between the re-
quirements for the Metro and Fair-
field-Hardy systems. Requirements
for the IDC-Naturizer system were
significantly higher. Sufficient details
on this system were not available to
determine the reasons for the dis-
crepancy (Figures 58 and 59).
-------
64 RECOVERY AND UTILIZATION
o
o
XD Fairfield-Hardy system
Metro waste system
John R Snell system
j>Q IDC-Natunzer system
Existing Plants
a Gainesville Demonstration Project
b Lone Star Organics, Houston, Texas
c United Compost Services, Houston, Texas
d St Petersburg, Florida
e City of Mobile, Alabama
f TVA/PHS Demonstration Plant,
Johnson City, Tenn.
100 200
Plant Capacity, tons/day
FIGURE 56. Capital costs of composting systems.
300
400
13
12
§ II
S. 10
VI -,
o 7
O
? 6
a- 4
~a
John R Snell system
100
200 300
Plant Capacity, tons/day
400
FIGURE 57. Estimated total processing costs for Fairfleld-Hardy and John R. Snell composting
systems.
-------
Summary of composting costs and operational requirements 65
45
36
o>
=; 27
cr
01
\8
O O Fairf ield - Hardy systems
•—• Metro system
D—DIDC-Natunzer system
o 100 200
Plant Capacity, tons/day
FIGURE 58. Estimated labor requirements for composting systems.
300
400
3000
- 2000
0.
X
1000
O—O Faimeld-Hardy system
•—• Metro system
D—D I DC-Naturizer system
Existing Plants
a. Gamsville Demonstration Project
b United Compost Services, Houston, Texas
100
200
Plant Capacity, tons/day
300
400
FIGURE 59. Energy requirements for composting systems.
-------
66 RECOVERY AND UTILIZATION
HEAT RECOVERY
The recovery of waste heat in con-
junction with incineration of munici-
pal refuse has recently received special
emphasis because of success in Europe,
especially in Germany, with combined
municipal incinerator steam power
generating stations.
Waste-heat recovery systems for
steam production may involve one of
two general designs. The first em-
ploys a conventional refractory fur-
nace followed by a waste-heat boiler.
The second, and the one which is used
widely in Germany and throughout
Europe, employs a waterwall furnace.
One advantage of a waterwall furnace
is its increased heat transfer efficiency.
This permits furnace temperature to
be held within reasonable limits
which would be exceeded in a refrac-
tory furnace without large quantities
of excess air. Thus, the waterwall
furnace will help alleviate air pollu-
tion control problems. Conventional
refractory furnaces are normally de-
signed for about 150 to 200 percent
excess air, whereas there is some indi-
cation that waterwalled furnaces may
operate satisfactorily on only 50 to 60
percent excess air. The smaller quan-
tity of excess in waterwall systems re-
sults in smaller volumes of combustion
products and, in turn, permits the use
of smaller gas handling equipment.
The disadvantages of a waterwall
furnace are slightly higher capital
and operating costs. Only one appli-
cation of a waterwall furnace for
waste-heat recovery exists in the
United States.
Another general feature of waste-
heat recovery systems for steam pro-
duction is the need for auxiliary fuel
to insure that constant steam produc-
tion can be maintained despite mois-
ture content and other variables that
govern the heating value of refuse.
European practice employs pulverized
coal for this purpose whereas gas or oil
would be more suitable for U.S.
facilities.
Another form of waste-heat recov-
ery, being studied by researchers in
Connecticut and California, envisages
power production through the use of
gas fired turbines driven by effluent
gases from municipal incinerators.35^8
REFUSE INCINERATION AND
STEAM GENERATION IN EUROPE
The largest and most familiar Euro-
pean combined incineration/power
generation facility is located in Mu-
nich, West Germany.37 Two separate
power generating facilities have been
built: a 60-MW plant burning a com-
TABIE 27
SUMMARY OF OPERATING COSTS FOR CHICAGO SOUTHWEST MTJNICIPAI INCINERATOR «
Operating cost
Cost item: ($/ton)
labor (62 men) $1. 92
Repairs 0. 73
Electrical 0. 19
Supplies 0. 60
Residue hauling 1. 05
Steam production (4,000 Ib at $0.50/1,000 Ib) 2. 00
6.49
Income item:
Sales of steam (4,000 Ib at $0.625/1,000 Ib) 2. 70
Profit from salvage 0. 14
2.84
Net operating cost 3. 65
Amortization of capital cost *1. 26
Total operation and maintenance cost f4. 91
Source: Reference 41 plus Battelle estimates.
'"These calculations assume 100 percent steam utilization. Reference 41 states that actual operating cost is
$3.98 per ton implying that only 86 percent ( —^ - --— 1 percent steam utilization is practiced.
tReference 41 gives $5.24 per ton, again reflecting less than 100 percent steam utilization.
bination of refuse and pulverized coal
(with 40 percent of the power output
supplied by refuse) and a 112-MW
plant with 20 percent of the power
output from refuse and 80 percent
from pulverized coal. The reason for
the "poorer" refuse to coal ratio for
the larger plant is that the Munich
refuse has a heating value of only
2,500 Btu per Ib so that the bulk
refuse throughput in terms of tons
per day fed is the limiting factor on
the larger design. A third plant iden-
tical to the second is now being con-
structed. With the three plants in
operation, the city of Munich will be
obtaining almost 70 MW of electricity
from the combustion of 108 tons per
hour of mixed municipal refuse.
These operations are technically
and economically sound for Europe,
but may not apply directly to condi-
tions in the United States.38 Fuel costs
are relatively higher in Germany and
the economic environment is more
favorable for waste-heat utilization.
In addition, the higher population
density of West Germany (eight times
that of the United States) has moti-
vated strict air pollution control for
a number of years. One technique for
cooling effluent gases and hence con-
trolling emissions is by heat transfer
to produce steam. In addition, the
Europeans have a greater concern for
conservation and resource manage-
ment. This also has contributed to
the acceptance and success of waste-
heat recovery in European refuse
incinerators.
Finally, the difference in institu-
tional arrangements must be consid-
ered. In Germany, power and utility
services, as well as all waste collec-
tion and disposal services, are the re-
sponsibility of local governments.
Consequently, the organizational and
administrative aspects are consider-
ably more simplified than they would
be in the United States.
REFUSE INCINERATION AND
STEAM GENERATION IN THE
UNITED STATES
Waste-heat recovery from munici-
pal solid waste incineration has been
quite limited to date in the United
States. In the past, it has been prac-
ticed to varying degrees in Boston,
Massachusetts; Oyster Bay, New
York; Providence, Rhode Island; and
Hempstead, Long Island, New York
(Merrick Plant). Waste-heat recov-
ery is currently practiced in Atlanta,
Georgia; Chicago, Illinois; Miami,
Florida; Hempstead, Long Island, New
York (Oceanside plant); and U.S.
Naval Station, Norfolk, Virginia. All
but the Norfolk plant employ conven-
tional refractory furnaces followed by
waste-heat boilers. The Norfolk plant
is the first U.S. application of water-
wall furnaces employing waste-heat
recovery. Current U.S. applications
are discussed below.
-------
Atlanta, Georgia. The city of At-
lanta operates two incinerators and
several landfills. Tin cans are salvaged
at both incinerators. At the Mayson
incinerator, which has a design
capacity of 700 tons per day, waste-
heat recovery and steam generation
are practiced.30-40
Four 175-ton-per-day combined
grate and rotary kiln furnaces are
installed at the Mayson plant. Two
were installed in 1942 at a cost of
$800,000, and two in 1952 at a cost of
$1,250,000. Total cost in 1968 dollars
has been calculated to be $4,567,000.
Steam produced at the Mayson plant
is 175 psig saturated and is sold at
$0.20 per 1,000 Ita to the Georgia Power
Company to heat buildings in down-
town Atlanta.
Chicago, Illinois. The city of Chi-
cago generates steam at its South-
west Incinerator.39'" The Southwest
plant has four 300-ton-per-day com-
bined grate and rotary kiln furnaces.
Metal salvage in addition to waste-
heat generation is practiced at the
Southwest plant. The incinerator was
constructed in 1963 at a cost of
$6,825,000. Of the total cost, $1,625,000
was for the steam plant and distribu-
tion system.41
Steam generated at the Southwest
plant is produced for about $0.50 per
1,000 Ib and is sold to a private con-
tractor for $0.625 per 1,000 Ib. It is
used mostly in the stockyard area of
Chicago. Since demand is low in the
summer, the full steam capacity is not
utilized during this period.
The Southwest incinerator is op-
erated 24 hr per day, 7 days per week
(Table 27). Waste heat is supplied to
four boilers, each capable of generat-
ing 50,000 Ib of steam per hr. Based on
1,200 tons per day of refuse, this
amounts to a design capacity of 2.0 Ib
of steam per Ib of refuse incinerated.
Miami, Florida. Steam is recovered
from a 900-ton-per-day municipal in-
cinerator in Miami, Florida.42 The
incinerator, constructed in 1954, cost
$3 million. Steam produced at 250
psig and 406 F is sold to the Jackson
Memorial Hospital for $0.70 per 1,000
Ib. Approximately three Ib of refuse
are required to produce one Ib of
steam. This appears to be somewhat
less efficient than the other installa-
tions discussed in this section.
Hempstead, Long Island, New York.
A 750-ton-per-day municipal owned
incinerator employing waste-heat re-
covery both for steam generation and
water desalination was recently put
into operation at Hempstead's Ocean-
side plant at a total cost of $6 mil-
Operating characteristics and costs of selected incinerator systems 67
Feed to the system includes large
quantities of crates and packing mate-
rials, in addition to the normal rub-
bish. The system is designed for refuse
having a heating value of 5,000 Btu
per Ib and a moisture content of 25
percent (Table 28). Two 180-ton-per-
day furnaces are used, each capable of
generating 50,000 Ib of 275 psig dry
saturated steam per hr. This corre-
sponds to about 3.33 Ib of steam per
Ib of waste. An auxiliary oil burner is
also capable of supplying 50,000 Ib of
275 psig dry saturated steam per hr.
The steam produced saves over 5 mil-
lion gal of fuel oil per year.
Houston, Texas. A facility is planned
for Houston, Texas, which will incin-
erate 10,000 tons per month (about
330 tons per day) of industrial solid
waste and produce 100,000 Ib of steam
per hr.50 This corresponds to a steam
production rate of 3.57 Ib of steam per
Ib of waste. Steam will be sold for in-
dustrial consumption. The plant is a
joint venture of several local indus-
tries utilizing one disposal agency,
Consolidated Oxidation Process En-
terprises. The plant will be designed
by Foster Wheeler Corp. and Nichols
Engineering Research Corp., and will
employ a waterwall furnace. The
plant is expected to cost $5 million
and is scheduled for completion in
1969.
TABLE 28
SPECIFICATIONS FOB BOILER-FURNACE UNITS
AT U.S. NAVAL STATION, NORFOLK, VIRGINIA*
Mixed refuse (tons per day) _ 180
Heating value as fired
(Btu/lb) 5,000
Moisture (percent) 25
Noncombustible (per-
cent) 12. 5
Steam production
With refuse at 5,000
Btu/lb (Ib/hr) 50, 000
With drier refuse or
with refuse plus oil
(Ib/hr) 60,000
With oil only (Ib/hr) 50, 000
Design stoker loading
Ib refuse/sq ft/hr of
effective grate sur-
face 65
Heat release
Btu/hr/sq ft effective
grate surface 325,000
Btu/cu ft primary fur-
nace volume (max)__ 25, 000
Minimum gas temperature
leaving primary furnace
at 50 percent of rated
load (degree F) 1,400
Steam pressure (psig) 275
Steam quality Saturated
Feedwater temperature
(degree F) 288
Exit gas temperature from
boiler at design refuse
capacity (degree F) 580
*From Moore, H. C. Refuse fired steam generator
at navy base, Norfolk, Va. In Incineration of Solid
Wastes; proceedings, MECAR Symposium New York
Mar. 21, 1967. p. 10-21.
lion.43'4" Steam is produced in two boil-
ers, each having a capacity of 85,000
Ib of steam per hr (462 F and 460
psig), and is used to produce 2,500 KW
power to operate the plant. Exhaust
steam from the power plant is used to
produce about 500,000 gal per day of
fresh water for cooling, boiler makeup
water, and fly-ash scrubbing within
the plant.
The plant design employs two
300-ton-per-day refractory furnaces
which burn mixed solid waste, and one
150-ton-per-day unit for bulk rubbish.
The gases from the two large furnaces
discharge through boilers for heat re-
covery. Heat is not recovered from the
bulk rubbish unit. Based upon steam
production of 170,000 Ib per hr and
solid waste throughput of 600 tons
per day, approximately 3.4 Ib of steam
are produced per Ib of refuse.
U.S. Naval Station, Norfolk, Vir-
ginia. Recently the U.S. Naval Station
at Norfolk, Virginia, put into opera-
tion the nation's first waterwall solid
waste incinerator.4^4" Capital cost of
the system was $2.2 million.
OPERATING CHARACTERISTICS
AND COSTS OF SELECTED
INCINERATOR SYSTEMS
Large scale systems for heat recov-
ery and solid waste incineration have
not been in operation long enough to
generate operating data. Certain re-
lationships which governed recent de-
signs have been published. It must be
emphasized, however, that this infor-
mation has not been confirmed on an
operational scale.
A recent paper describing the Nor-
folk plant reported anticipated steam
production as a function of the heat-
ing value of the refuse, refuse
throughput, and percent excess air
(Figures 60 to 62) .4° The curves are
based upon the design specifications
for the Norfolk plant (Table 28).
Similar but less complete data have
recently been presented in a paper
summarizing European experience
with emphasis on potential applica-
tions of waste heat recovery in the
United States.'1 Assuming 88 percent
excess air, the refuse heating value
was used to compute steam produc-
tion. These values can be compared
to those of the Norfolk plant using 50
percent excess air (Figure 63). As
expected, a slightly higher specific
-------
68 RECOVERY AND UTILIZATION
5000
Btu per Lb Refuse as Fired
FIGURE 60. Estimated steam production at
Norfolk from refuse having various heat capacities.
Assume 180 tons/day and 50 percent excess air.
(Based upon: Moore, H. C. Refuse fired steam
generator at navy base, Norfolk, Va. In Incineration
of Solid Wastes; Proceedings, MECAR Symposium,
New York, Mar. 21,1967. p. 10-21.)
LB 275-psig Dry Saturated Steam Per Hour, I03 Ib
FIGURE 61. Estimated steam production at
Norfolk from refuse at various loads. Refuse
of 5,000 Btu/lb and 50 percent excess air is
assumed. (Based upon: Moore, H. C. Refuse
fired steam generator at navy base, Norfolk,
Va. In Incineration of Solid Wastes; Proceedings
MECAR Symposium, New York, Mar. 21,1967.
p. 10-21.)
LB 275-psig Dry Saturated Steam Per Lb Refuse
-------
Operating characteristics and costs of selected incinerator systems 69
60i-
Q.
E
50
40
20
40
Percent Excess Air
FIGURE 62. Estimated steam production at Norfolk
from refuse as a function of excess air. Assume
180 tons/day—5,000 Btu/lb. (From Moore, H. C.
Refuse fired steam generator at navy base, Norfolk,
Va. In Incineration of Solid Wastes; Proceedings,
MECAR Symposium, New York, Mar. 21,1967.
p. 10-21.)
FIGURE 63. Estimated steam production from refuse
having various heat capacities. Assume 88 percent
excess air. (Based upon: Stabenow, G. Performance
and design data for large European refuse incinerators
with heat recovery. In Proceedings; 1968 National
Incinerator Conference, New York, May 5-8,1968.
New York, American Society of Mechanical Engineers.
p. 278-286.)
5000 6000
Btu Per Lb Refuse as Fired
7000
-------
70 RECOVERY AND UTILIZATION
2! 3.0
3
«*-
tr
.0
t 25
0)
CL
I
«5 2.0
T3
O>
O
0 . c
co 1 5
Q
CP
H
o? '-°
CM
CM
5 0.5
n
^^^«.
-
1 — ^
^\
^^^
I^Water-c
.^^ Refractc
ooled furna
^-^, 1
jry furnace
^^^
ce
h-^.
•\_
^
^^^^
^^
50 100 150 200
Percent Excess Air at Boiler Outlet
250
300
FIGURE 64. Estimated effect of excess air
on steam generating capacity of 800-ton-per-
day refuse incinerator. Assume 20 percent
moisture in refuse. (From Day &
Zimmermann, Engineers & Architects.
Heat recovery. In Special studies for incin-
erators ; for the Government of the
District of Columbia, Department of
Sanitary Engineering. Public Health
Service Publication No. 1748.
Washington, U.S. Government Printing
Office, 1968. p. 55-73.)
FIGURE 65. Estimated effect of refuse
moisture content on steam generating
capacity of 800 ton per day refuse generator.
(From Day & Zimmermann, Associates.
Heat recovery. In Special studies for
incinerators; for the Government of the
District of Columbia, Department of
Sanitary Engineering. Public Health Service
Publication No. 1748. Washington, U.S.
Government Printing Office, 1968.
p. 55-73.)
8.
E
o
a>
CO
o
CO
CO
a_
in
CM
PJ
4.0
3.5
3.0
2.5
20
1.5
10
0.5
Water wall unit
at 60% excess air
Refractory furnace
at 200% excessair
10 20 30 40
Percent of Moisture in Refuse
50
60
-------
Operating characteristics and costs of selected incinerator systems 71
TABLE 29
CAPITA1 COSTS OF U.S. INCINERATION EMPLOYING WASTE-HEAT RECOVERY
Yfiar hutlt
Capacity
ftnnaMavt
Capital cost
(Actual)
(1968)'
Atlanta, Georgia _________ 1942 and 1952 __ 700 82,050,000 $4,567,000
Chicago, Illinois _________ 1963 ___________ 1,200
Miami, Florida ___________ 1954 ___________ 900
Hempstead, L.I., New 1964 ___________ 750
York (Oceanside plant).
U.S. Naval Station, 1966 ___________ 360
Norfolk, Virginia.
6,825,000
3,000,000
6,000,000
8,300,000
4,880,000
6,500,000
2, 200, 000 2, 540, 000
•Calculated using "Engineering News Record" Building Cost Index.
TABLE 30
ESTIMATED CAPITAL COSTS FOR 800-TON-PER-DAY MUNICIPAL INCINERATOR EMPLOYING WASTE-
HEAT RECOVERY
System description
Variable
capital cost*
Constant
capital costt
Total
capital cost
Conventional refractory furnace with
spray cooling of flue gas $3, 583, 000
Conventional refractory furnace with
spray cooling boiler in by-pass flue 5, 737, 000
Waterwall furnace with convection boiler. 4, 297, 000
Waterwall furnace with spray cooling of
flue gas 4, 303, 000
S150, 000 $3, 733, 000
150, 000
150, 000
5, 887, 000
4, 447, 000
150, 000 4, 453, 000
TABLE 31
CAPITAL COSTS OF CONVENTIONAL REFRACTORY MUNICIPAL INCINERATORS*
Installation
Capacity
(tons/day)
Capital cost
ENR building 1968 ENR building
cost index=580 cost index=700
Alexandria, Virginia
Lexington, Kentucky
Evanston, Illinois
Wauwatosa, Wisconsin-
Portsmouth, Virginia. _.
200
200
180
165
300
$922, 000
750, 000
881, 000
835, 000
1, 068, 000
$1, 100, 000
900, 000
1, 060, 000
1, 000, 000
1, 170, 000
•From Clarke, S. M. Incinerating plant costs. Public Works, 93(9): 122-83, Sept. 1962.
TABLE 32
CAPITAL COSTS OF CONVENTIONAL REFRACTORY FURNACE MUNICIPAL INCINERATORS*
Installation
Buffalo, New York
Baltimore, Maryland
Cincinnati, Ohio.
Hartford, Connecticut _ -
Rochester, New York
Year
constructed
1953
1955
1954
1954
1956
Capacity
(tons/day)
400
800
500
600
600
Capital cost
(Actual)
$1, 500, 000
2, 153, 000
1, 494, 000
1, 434, 000
2, 110, 000
(1968)
$2, 400, 000
3, 350, 000
2, 330, 000
2, 240, 000
3, 100, 000
•Source: Michaels, A. Incineration. In Public Works Engineers Handbook, Chicago, American Public
Works Association, 1957.
steam production rate results for the
lower percentage of excess air.
In addition, Day & Zimmermann
Associates, Philadelphia, have pre-
pared estimates on waste-heat re-
covery for an 800-ton-per-day incin-
erator for the District of Columbia.5"
These studies evaluated the following:
conventional refractory furnace with
spray cooling of flue gas; conventional
refractory furnace with spray cooling
of flue gas and boiler in by-pass flue;
waterwall furnace with convection
boiler; and waterwall furnace with
spray cooling of flue gas. Estimates of
steam-generating capacity as a func-
tion of excess air and as a function of
refuse moisture content were pre-
sented (Figures 64 and 65).
All of the data in this section rep-
resent engineering estimates 'and are
not the results of direct operational
experience. The potential pitfalls in
the use of such data must be
emphasized.
Capital costs of incinerators with or
without heat recovery. The following
section summarizes actual and esti-
mated costs of incinerators with and
without waste-heat recovery. The
previously presented cost data on U.S.
waste-heat recovery has been ad-
justed to 1968 conditions using the
Engineering News Record Building
Cost Index (Table 29).
In their report to the District of
Columbia, Day & Zimmermann pro-
vided partial capital cost estimates for
the systems investigated.62 The costs
covered only those items expected to
vary from one design to another. The
constant cost items listed below were
not included in the estimates: dump-
ing floor, plant enclosure, cranes with
crane bay steel and enclosure, offices,
locker rooms, stair towers, elevators,
storage room, machine shop, heating
and ventilating, plumbing and sani-
tary waste, electricity for above items,
site development, roads, paving, land,
scale house, and scales. The total cost
of the above items, excluding land and
site developments, were estimated by
Battelle to ranges between $100,000
and $200,000, averaging $150,000. The
capital cost estimates for the systems
studied by Day & Zimmermann were
summarized (Table 30) and may be
compared with published data on con-
ventional refractory furnaces without
heat recovery (Tables 31 and 32) .ra' "
The Day & Zimmermann cost esti-
mates may be used to generate cost
functions based on a conventional en-
gineering estimating factor which
states that cost is proportional to the
six-tenths power of capacity (Figure
66). Data presented earlier show that
-------
72 RECOVERY AND UTILIZATION
n Long Island (Oceanside
— Day and Zimmerman data
extrapolated using six-tenths factor
O Conventional refractory-no waste -
heat recovery
Water wall with waste heat recovery
Conventional refractory with waste
heat recovery
200
300
400
500 600 700
Capacity , tons /day
FIGURE 66. Capital costs of municipal incinerators.
800
900
1000
1100
1200
reasonable correlation exists for the
waterwall designs. The Day & Zim-
mermann extrapolated cost data for
the conventional refractory without
heat recovery indicate a trend some-
what higher than the adjusted costs
for existing installations. This may be
attributed to the more costly air pol-
lution control equipment required on
today's incinerators.
Economics of Waste-Heat Recovery.
Data on cost of steam production in
conjunction with municipal solid
waste incineration in the United
States are very limited. It has been
noted that the additional cost to pro-
duce steam at the 1,200-ton-per-day
Chicago Southwest Refractory Fur-
nace Incinerator was about $0.50 per
1,000 Ib. Estimates on the additional
cost of steam production in the Day &
Zimmermann systems were $1.06 and
$0.49 per 1,000 Ib for 800-ton-per-day
refractory and waterwall systems,
respectively.
To evaluate the implication of these
costs assumes a conservative produc-
tion of 2 Ib of steam per Ib of refuse
and an additional cost of $0.50 per
1,000 Ib to produce steam. Since this
cost is additional to that of waste
incineration, to break even, the steam
produced must be sold for at least
$0.50 per 1,000 Ib. To justify waste-
heat recovery, it must be sold at a
profit unless there are economic justi-
fications for its production. If steam
can be sold for $0.60 per 1,000 Ib, this
results in recovery of $0.10 per 1,000
Ib of the costs of incineration. Pro-
duction of 2 Ib of steam per Ib of
refuse corresponds to 4,000 Ib of
steam per ton of refuse, or an incin-
eration cost recovery of $0.40 per ton
of refuse. The Chicago costs, where
steam sold at $0.625 per 1,000 Ib, re-
sulted in a net income of $0.50 per
ton of refuse (Table 27).
On the basis of existing data, it ap-
pears that only about 10 percent of
incineration cost could be saved by
employing waste heat recovery, if
there is a customer willing to buy the
steam. This is not always the case.
For instance, Day & Zimmermann
concluded that waste-heat recovery
could not be justified. This was due to
-------
Refuse-fired gas turbines 73
EXHAUST
1&&Q YW \
eef/eeAToe I
etecTeic
SWITCH
C6AB
WK9O
FIGURE 67. CPU-400 Refuse-
fired gas turbine. (.From
Aerospace Commercial
Corporation. CPU-400 Technical
description and economics
study, TR 6702; report on
Contract PH 86-67-259. Palo
Alto, California, Sept. 1967.
p. 2-3.)
the lack of a customer within the
vicinity of the incinerator who could
justify a demand for an interruptable
supply of steam.
Control of air pollution is an addi-
tional factor that cannot be evaluated
on the basis of existing data. More
stringent controls may lower the ad-
ditional cost of steam production
through assignment of a portion of
the equipment and operating costs to
pollution control rather than to
steam production. For example, as-
suming (1) additional heat-recovery
equipment cost to equal air pollution
control equipment costs and (2)
steam to be sold at $0.60 per 1,000 Ib,
the net profit per ton of refuse would
be $2.40 per ton or less than half the
cost of incineration. Thus, cost alloca-
tion techniques are significant in
evaluating waste-heat recovery econ-
omy. Sufficient data are not available
to determine the true net cost of
waste-heat recovery.
REFUSE-FIRED GAS TURBINES
Two research investigations are
studying the possibility of using ref-
use-fired gas turbines for power
production. One system, the CPU-400,
is being investigated by Aerospace
Commercial Corporation (Figure
67) .M A Pratt & Whitney FT4A-8 sta-
tionary jet engine gas turbine or a
General Electric Series 5000 industrial
gas turbine-generator supplies high-
pressure air for the refuse combustion
and to electric power generation. It is
claimed that the CPU-400 burns
refuse at 7 to 12 times atmospheric
pressure. Three alternative combus-
tion systems have been identified;
direct combustion, fluidized bed, and
pyrolysis (Figure 68).
Based upon selected assumptions
and theoretical calculations, the sys-
tem should generate power at a cost
of 1.7 mills per kwh. However, the
technical validity of the basic assump-
tions remains to be established. Po-
tential problem areas may be:
(1) Electrostatic collectors are re-
quired to operate at 1,500 F. (Battelle
is aware of two attempts to develop
such a system, neither of which was
successful.)
(2) No provision is made to guard
against air bleeds from the compres-
sor, although leakage of a few percent
of the air would eliminate all power
capability.
(3) Considerable expense (perhaps
several million dollars) would be re-
quired to adapt the Pratt & Whitney
unit by providing remote ducting for
an outside combustor. (The General
Electric turbine, however, has already
been altered.)
(4) The estimates for additional
maintenance due to fly-ash erosion
assume no more than that normally
expected from burning No. 6 fuel oil.
(However, in high velocity turbines
any ash content would create exten-
sive erosion. It is not likely that zero
ash content could be attained with ex-
isting technology.)
These comments are not intended as
criticism of the research, since most
research programs are aimed at over-
coming technical obstacles. The com-
ments should put the apparently at-
tractive power costs in the proper
perspective.
Studies at the University of Hart-
ford have explored a system similar
in concept to the CPU-400 unit.38 The
system involves both the production
of electric power in a high-tempera-
ture and pressure combustion process
and the manufacture of a ceramic-
metal composite. The system consists
of three main components: a Pratt &
Whitney FT-4 gas turbine, a large
hammermill, and the materials proc-
essing system. As in the CPU-400, sig-
nificant erosion problems would be ex-
pected from the extremely high ve-
locities characteristic of aircraft tur-
bines. This and other substantial
problems appear to be unduly dis-
counted in the preliminary feasibility
study. Estimated net power-generat-
ing costs were in the range of 0.4 to
3.3 mills per kwh, depending upon the
income from recovering metal scrap
-------
74 RECOVERY AND UTILIZATION
JET et/ewe
COM8U9TOR
TO
.
fcj CW00N (CO)
COMBUSTION
FLU 10
pyeouzee
FIGURE 68. Alternative combustor types. (From Aerospace Commercial Corporation. CPU-400
Technical description and economics study, TR 6702; report on Contract PH 86-67-259. Palo Alto,
California, Sept. 1967. p. 2-16.)
and manufacturing the ceramic ma-
terial. In addition, significant prob-
lems could arise in developing suffi-
ciently strong bonds between silicates
and the metal scrap. Problems would
be similar to those in enameling op-
erations where process variables must
be closely controlled.
The above investigations discount
previous unsuccessful attempts to use
solid fuel containing ash to generate
power in gas turbines. To date, the
high degree of ash removal needed to
protect the turbine blades from ero-
sion is not possible. Mr. P. G. LaHaye,
the General Electric Company, in dis-
cussing the closed-cycle coal-fired tur-
bine stated:
"Over the past two decades, sev-
eral investigations have been under-
taken in the United States and abroad,
directed at developing a practical
commercial coal-fired gas turbine.
The best known programs originated
in the United States and Canada were
the exhaust-fired cycle program of
Professor D. L. Mordell and associates
at McGill University, Toronto, Can-
ada; the direct-fired locomotive gas
turbine development program by the
Locomotive Development Committee
of the Bituminous Coal Institute at
Dunkirk, New York; and the coal
gasification studies jointly undertaken
by the Babcock & Wilcox Company
and the General Electric Company.
To date, none of these programs
have sufficiently reduced first costs
of capital equipment or improved
cycle performance to warrant their
commercial exploitation." M
The potential of the refuse-fired
gas turbines cannot be evaluated
meaningfully without regard to the
experiences mentioned above. Since
the major obstacle is blade erosion,
cleaning of the gases should be at-
tacked first.
CHEMICAL CONVERSION
A great many processes for con-
verting solid waste into usable prod-
ucts can be grouped loosely under the
term "chemical conversion." In this
report, chemical recovery includes
thermal, chemical, and biological
processes for the treatment of mixed
municipal solid waste. Chemical proc-
esses directed toward recovery of a
specific fraction of solid waste such
as tin can reutilization, secondary-
fibers production, glass reforming,
etc., are covered in later sections.
Specific processes presented here are
pyrolysis, the application of heat in
the absence of oxygen; hydrolysis, the
conversion of cellulosic materials to
sugars by acids or bases; and bio-
chemical processes, which include the
manufacture of yeast or alcohols.
PYROLYSIS
Pyrolysis, often termed "destructive
distillation," is a process in which or-
ganic material is heated to a high
temperature (1,000 F to 2,000 P) in
either an oxygen-free or low-oxygen
atmosphere. Unlike combustion in an
excess of air, which is highly exother-
mic and primarily produces heat and
carbon dioxide, pyrolysis of organic
material is analogous to a distillation
process and is endothermic. The high
temperatures and lack of oxygen in
the pyrolysis of solid waste result in
a chemical breakdown of the organic
materials into three component
streams: (1) a gas consisting pri-
marily of hydrogen, methane, carbon
monoxide, and carbon dioxide; (2) a
"tar" or "oil" that is liquid at room
temperature and includes organic
-------
chemicals such as acetic acid, acetone,
methanol; and (3) a "char" consist-
ing of almost pure carbon plus any
inerts (glass, metals, rock) that enter
the process. Kaiser suggests a reac-
tion for decomposition of cellulose
(CaHioOs) undergoing pyrolysis as
follows:
3(C«HioOj)->8HjO +"CiHiO"
+2CO +2COi +CH, +H2 +7C
where "C6H8O" represents the family
of liquid products obtained in pyroly-
sis.58 While cellulose is the major
reactant in pyrolysis of solid wastes,
other organic materials will also
pyrolyze. The relative fractions of the
various organic constituents would, of
course, affect the yield of products.
Batch retort experiments conducted
at San Diego indicate that product
breakdown is strongly dependent upon
temperature." This suggests that a
great many parallel reactions are
occurring.
CURRENT APPLICATIONS OF PY-
ROLYSIS TO SOLID WASTE
Pyrolysis is an advanced waste
treatment technique, and, conse-
quently, applications to solid waste
are extremely limited. References to
pyrolysis of solid waste illustrate the
state of this very interesting process.
A paper by Porteous discusses pyroly-
sis of solid waste to make acetone, ace-
tic acid, charcoal, and salable tars
and oils.68 Laboratory scale experi-
ments on the pyrolysis of solid waste
are being conducted at New York Uni-
versity and by the Utilities Depart-
ment of the City of San Diego."'69 Two
pilot scale devices are also in opera-
tion. The first of these is operated by
Cameron-Yakima, Inc., at Yakima,
Washington,60 and the second by the
Waste Conversion Systems Division of
Pan American Resources, Inc., located
in Albuquerque, New Mexico. As re-
ported in Chemical Engineering and
from personal contact, the Cameron-
Yakima unit has been tested on a va-
riety of specific wastes, but not on mu-
nicipal refuse per se.60'61 The Lantz
Converter of Pan American Resources,
on the other hand, is apparently the
only pyrolysis system designed for and
tested upon mixed municipal refuse,
although it has been applied to a va-
riety of specialty wastes as well.
An attempt has been made above to
list the more interesting ongoing
pyrolysis work in order of chronologi-
cal distance from actual application
to municipal solid waste. As with any
new technology, there is a large dis-
parity in the results, ranging from ex-
tremely unfavorable (Porteous) to
Current applications of pyrolysis to solid waste 75
Refuse
Store
Predry
Char
Vacuum Distill
Condense
Tars
Heavy
oils
Settle
Boil
Strip
Boil
Rectify
Recycle of
high boiling
solvent
Condense
FIGURE 69. Flow diagram, acetic acid from refuse*
extremely favorable (Lantz Con-
verter) . Since the Lantz Converter is
being marketed as a potential waste
disposal system in which only the
service is sold, detailed data on feed
and product analysis, performance,
and equipment design are not avail-
able for publication. Some limited cost
data have, however, been obtained.
Detailed analytical data are available
from the San Diego pyrolysis work,
but these are from small-scale batch
retorts and the data may not be di-
rectly applicable to larger continuous
units. Specific information from on-
going pyrolysis work is discussed in
the following sections.
Paper Evaluation of Pyrolysis. A
cost analysis of pyrolysis as a process
for municipal solid waste disposal is
given by Porteous.58 Since this effort
was a paper study only, equipment for
the process was designed and cost esti-
mates made in consultation with a
leading manufacturer in the field. The
refuse is compressed into bales 3 ft
in diameter by 5 ft in length with a
dry density of 30 Ib per cu ft. These
bales are predried and destructively
distilled in vacuum retorts, 3V2 ft in
diameter by 30 ft in length, producing
noncondensable gases, condensed
liquids, and char. The noncondensable
gases are burned for process heating,
and the char is quenched, briquetted,
and sold. The condensate is separated
into heavy and light fractions. The
heavy fraction is sent to a tar still
to yield creosote and a phenolic ag-
glomeration, or is burned for process
heat. The acetic acid is stripped from
the oils in the vapor phase of the
lighter fraction using a suitable high-
boiling solvent. The acetic acid is
then separated from the solvent by
vacuum distillation to yield commer-
cial-grade acetic acid (Figure 69).
The cost breakdown was estimated
-------
76 RECOVERY AND UTILIZATION
TABLE 33
REVENUE ESTIMATE FOR PYR01YSIS «
Item
Acetone
Acetic acid
Tars - -
Oils
Charcoal
Yield
(percent)
0.3
3. 1
7
- - - 5
. _ 25
Ton per
day
0.45
4. 65
10. 5\
7. 5/
37. 5
Price
6.5f!/lb
9fi/lb
10/1 D
$7/ton
Revenue
(per diem)
$57
835
3bl)
260
$1,512
based on 1967 prices and the process
appeared to be a highly unprofitable
operation costing about $5.70 for each
ton of raw refuse (Tables 33 and 34).
This process is, by design, directly
analogous to destructive distillation of
wood even to the extent that refuse is
compressed into large blocks before
processing. Much of the processing
cost is tied up transporting heat and
mass to and from this large com-
pressed block; a retort residence time
of 23 hr is required to effect destruc-
tive distillation.68 While design of a
better pyrolysis process is beyond the
scope of this report, it seems likely
that greater efficiency would be pos-
sible if the process was designed ex-
clusively for the treatment of solid
wastes.
Retort Research on the Pyrolysis of
Municipal Waste. Two experimental
programs on the pyrolysis of solid
waste are being conducted under re-
search grants of the Bureau of Solid
Waste Management. The first of these
(Grant No. SW 00043-03) is being di-
rected by Kaiser at New York Uni-
versity." This work has included
measurement and analysis of pyrolysis
gases obtained from various organic
components of municipal refuse in-
cluding paper, wood, grass, leaves, and
food wastes.68'69 Work has also been
initiated on pyrolyzing mixed refuse
and operating a continuous pilot-scale
TABLE 35
SAN DIEGO SANITARY FILL MATERIAL SURVEY"
(Started July 30, 1966—Completed March 85, 1966)
Total material
(percent)
As received Range during survey
Combustibles. .
Incombustibles
Combustible portion
Constituent
Paper
Yard trimmings..
Wood
Rags _
Rubber
Plastic
Garbage
Metal
Glass..
Moisture
Total
As re-
ceived
46. 16
21. 14
7. 48
3. 46
4. 73
0. 27
0. 81
7. 64
8. 31
. 100. 00 .
Range during
survey
50. 55-40. 99
26. 65-20. 78
8. 10-4. 41
4. 07-0. 32
4. 76-3. 60
0. 52-0. 25
0. 92-0. 77
9. 68-6. 30
10. 38-7. 67
(percent)
Moisture
ASTM
D271-88
8.23
51.30
10. 50
7.40
9.74
0.06
57.80
0
0
50.27
49.73
55.51-43.72
56.28-46.33
Dry basis
With metal
and glass
42.36
10.30
6.69
3.20
4.27
0. 27
0.34
7. 64
8. 31
16. 62
100. 00
Without metal
and glass
50.40
12.25
7.96
3. 82
5.08
0.32
0.40
0
0
19.77
100. 00
TABLE 34
COST ESTIMATE FOR PYROIYSIS "
Plant cost
18,000,000
Fixed charges at 0.1030*... 824, 000
Labor, 12 men at 87, 000 84, 000
4 men at $9,000 36, 000
Maintenance (2% retort in-
vestment)f 190,000
Disposal 149T residual ref-
use/day at $4.50/ton 245, 000
Total cost 1,065,000
Revenue at $l,521/day 550, 000
Net annual cost 515,000
Disposal cost/ton $5. 66
•Original paper assured 20-year plant life at 4
percent interest. These figures were changed to 1C
years and 6 percent, respectively.
tData obtained on hammermill operation indi-
cated maintenance costs of the order of il.OO/ton
processed could be expected. Approximately 190,000
was, therefore, added to Porteous* maintenance
figure.
-------
Current applications of pyrolysis to solid waste 77
TABLE 36
PYROLYSIS PRODUCT YIELD «
Temp
(F)
900
1200
1500
1700
Refuse
(lb*)
100
100
100
100
Gases
(lb)
12.33
18. 64
23. 69
24.36
Pyroligneous acids
and tars (Ibt)
61.08
18. 64
59.67
58.70
Char
(lb)
24.71
59. 18
17.24
17.67
Mass accounted
for (lb)
98. 12
99. 62
100. 59
100. 73
*0n an as-received basis, except that metals and glass have been removed.
fThis column includes all condensables and the figures cited include 70 to 80 percent water.
TABLE 37
PROXIMATE ANALYSIS OF PYROLYSIS CHAR «
Percent
Volatile matter (percent)
Fixed carbon (percent) __
Ash (percent)
Btu per lb.
Pyrolyzing temperatures (F)
900
21. 81
70. 48
7. 71
12, 120
1,200
15.05
70. 67
14. 28
12, 280
1,500
8. 13
79.05
12. 82
11, 540
1,700
8.30
77.23
14.47
11,400
Pennsylvania
anthracite
7.66
82. 02
10.32
13, 880
TABLE 38
GASES EVOLVED BY PYROLYSIS »'
Constituent
Percent by volume at indicated temperatures (F)
900
1,200
1,500
1,700
H2
CH4
CO
C02
5. 56
12 43
33 50
44. 77
0. 45
3. 03
16. 58
15 91
30. 49
31. 78
2. 18
3. 06
28. 55
13 73
34 12
20 59
2. 24
0. 77
32. 48
10 45
35. 25
18. 31
2. 43
1. 07
Accountability 99. 74 100. 00 100. 00
99.99
refuse gaslfler. Data are not yet avail-
able from these portions of the
program.
The city of San Diego, California,
has been conducting small-scale re-
search on pyrolysis of solid waste. The
work, partially funded under a grant
from the Bureau of Solid Waste
Management (Grant No. SW 00036-
02), has resulted in significant ad-
vances in the analysis of the prod-
ucts from pyrolysis of municipal
solid waste as well as information on
process heat balances. Typical San
Diego municipal waste was fed to a
retort in which pyrolysis was con-
ducted (Table 35). The glass and
metal were removed before the start
of the pyrolysis experiments. These
experiments were conducted in a
retort containing approximately 0.4 lb
of refuse. The condensable liquids
were captured in a series of cooled
traps and the gaseous products in a
gas balloon. Pyrolysis experiments on
the typical San Diego waste were run
at temperatures from 900 to 1,700 F.
The amount of char and condensables
were determined gravimetrically, and
the pyrolysis gases were measured by
volume (Table 36). Qualitative
analyses were made on the condens-
able fraction to identify the organic
compounds present. A proximate
analysis of the char portion was ob-
tained, and the gas phase was an-
alyzed quantitatively by means of a
gas chromatograph (Tables 37 and
38).
As pointed out, no quantitative
analyses have yet been made of the
"Pyroligneous acid" (i.e., condensa-
ble) phase. Qualitatively, in addition
to water, the condensable phase in-
cludes methanol, ethanol, isobutanol,
n-pentanol, tert-pentanol, 1,3-pro-
panediol, 1-hexanol, and ascetic acid.
There are a number of alternative
paths that can be considered in at-
tempting to employ pyrolysis as a
process for the recovery of solid waste.
As discussed earlier, Porteous directed
his paper evaluation toward the man-
ufacture of acetic acid from the
condensable phase.68 Another, and per-
haps more direct, approach is to uti-
lize the products of pyrolysis to pro-
vide the thermal energy required for
the process. One of the most signifi-
cant results of the San Diego pyrolysis
-------
78 RECOVERY AND UTILIZATION
8
5
CD
o:
3
l-
co
6000
5500
5000
4500
4000
3500
3000
2500
2000
1500
1000
500
O
Gas H
Pyroligneous acids U
and tars
Thermal efficiency:
/
/
/
/
/
/
/ /
/
50%
x-
x--
.^— ---
,,^-^"'
~~
900
1200
Degrees Fahrenheit
1500
1700
FIGURE 70. Pyrolysis per tt> o/ typical refuse."
Measured energy of products is plotted against
energy required to sustain process.
experiments was measurement of the
heat content of the products of py-
rolysis and evaluation of these in
terms of the heat required to sustain
the process (Figure 70). For a realis-
tic thermal efficiency of 50 percent,
only pyrolysis at 900 F is self-sustain-
ing unless the energy content of the
char is also employed to provide addi-
tional heat to the process. It should
be noted that the San Diego pyrolysis
work is now moving out of batch
processes and into a continuous device.
Preliminary unpublished data indi-
cate that the self-sustaining potential
of a continuous pyrolysis unit is much
greater than one would conclude from
batch work. These fragmentary data,
if verified, would confirm the claims
for privately operated pyrolysis units*
in which the gas and condensable
product are reported to be more than
sufficient to sustain the process.
Operating Pyrolysis Units for Waste
Disposal. E. C. Cameron of Yakima,
Washington, has applied for a patent
on a device that pyrolyzes organic
wastes at 2,000 F in a low-pressure (4
to 7 psig) steam environment.61 The
unit has been used to demonstrate
processing of various organic wastes
including wood, rubber tires, photo-
graphic film, etc. A variety of carbon
products are recoverable including
coke, lampblack, or charcoal, depend-
ing on the nature of the feed material.
Specialty items such as silver (from
the processing of photographic film)
have also been recovered. The system
is designed so that the condensable
overloads can be recovered and used
to fire the retort. No mention was
made of the noncondensable gases,
but these are apparently lost with this
process. Although pilot-scale units
have been employed to convert a
variety of wastes to carbon, little data
are available on the system. Published
information is limited to a brief news
item in Chemical Engineering and a
patent application.60 The above in-
formation is based on these sources
and supplemented by letter and per-
sonal contact with the inventor of
the device.61
The most completely developed de-
vice for pyrolyzing municipal waste is
the Lantz Converter. This device was
patented in 1961 by a private inventor,
is on the market,6^ and represents
the most advanced application of the
principle of pyrolysis to the processing
of municipal waste. Lantz Converters
have been quoted with input ranging
from Vi, to 12 tons per hr, although
the largest unit constructed to date
is rated at 2 tons per hr.
The Lantz Converter is basically a
pyrolysis unit in which mixed munic-
ipal refuse is fed continuously
through a hammermill to a revolving
stainless steel drum. The process is
initiated using natural gas to bring
the equilibrium temperature up to
2,000 F in the absence of air. As
pyrolysis takes place, the "off-gases"
(condensable and noncondensable)
are fed back into the gas burners in
a self-sustaining process. According
to Pan American Resources, Inc., only
about 70 percent of the off-gases are
required to maintain the pyrolysis
temperatures. At this time, the excess
off-gases are flared and only charcoal
recovery has been explored. Eventual
usage of the off-gases not required to
sustain combustion is contemplated.
However, since the Lantz Converters
are not sold as equipment per se, little
specific data on cost of operation are
available. Company brochures fur-
nished the only basis for cost esti-
mates and these were overall capital
equipment costs for units of 54 and 12
-------
Summary of progress and research needs 79
I 234567
Capacity, tons/hour
FIGURE 71. Estimated range in capital cost of Lantz converters.
10
12
•See the following section for a discus-
sion or the "Lantz Converter."
tLantz Converter Division of Pan Ameri-
can Resources, Inc., of Albuquerque, New
Mexico.
tons per hour. A range of capital costs
can be generated from these two data
points using the "six-tenths factor"
(Figure 71).
Summary of Progress and Research
Needs. Information on pyrolysis of
cellulose has been accumulated by the
charcoal and wood chemical indus-
tries. With the exception of charcoal,
production of other materials from
pyrolysis of wood has proved to be
only marginally successful. However,
coupling the concept of pyrolysis
with a true waste product that has no
present market value may prove to be
economically attractive. Progress to
date on the pyrolysis of refuse has
proceeded down two parallel, but
widely separated, paths: laboratory
batch processes (in which detailed
scientific data are taken, but from
which little information is directly ap-
plicable to a scaled-up, continuous
pyrolysis unit), and full-scale devices
operated privately (from which no
data are available). Research needs
are apparent since the Federal
Bureau of Solid Waste Management
sponsored laboratory tests have indi-
cated a promising potential for this
method. The primary research need
at this point is for a pilot or full-scale
pyrolysis system (l/2- to 1-ton per hr)
including associated gas, condensable,
and charcoal recovery systems; ap-
propriate feed preparation devices
(size reduction, drying, etc.) should
also be provided. To ensure that heat
and mass balances as well as reaction
rates are closely monitored as the
system operates, continuous chemical
and thermal data should be taken.
-------
80 RECOVERY AND UTILIZATION
Dense
refuse
Crude refuse
249 tons per day
~ 79 tons per day
Bypass: to assist
slurry flow
244 C
Storage, pulverization, and
separation section
20 C, 170 tons per day
Shredding and cellulose slurry
pumping section
22,500 GPH
Make-up
water
20 C, 170 tons per day
1,500 GPH
Reactor 0.4% H2S04
480 gal, 230 C, 420 psia
Storage, 5,000 G
550psia, 244 C
244 C
Feed healer
210 C
12 x 106 btu/hr
9.6 tons per day
H2S04
24,000 GPH
230 C
0.4% H2S04
9 stage flash cooling
Filter cake
97 tons per day
(dry wt)
Neutralize!
CaCO
9.6 tons per day
100 C
Liquor pump and pressure
filters
4 Stage flash cooling
20 C
Fermenting vats
700,000 gal.
22,500 GPD
15 x 106 BTU/tu
Yeast
Bubble cap column reflux
ratio 4:1
nutrients
5,000 BOD
24,000 GPH
Ethanol 10,780 GPD
} 100 BOD .refuse.'
FIGURE 72. Process flow sheet,
continuous ethanol production from
In summary, the concept of pyroly-
sis applied to solid waste is new, but
can, on the basis of available infor-
mation, be considered one of the
more promising advanced techniques
for waste management because (1)
laboratory results indicate that a wide
variety of valuable products (includ-
ing producer gas, acetic acid, meth-
anol, and charcoal) can be simul-
taneously produced; (2) relatively
large pyrolysis units have been built
privately and operated with reported
success; and (3) the process has the
potential of being self-sustaining.
HYDROLYSIS
Of the many possible chemical re-
actions that can be considered for
solid waste utilization, one of the most
interesting is the hydrolysis of cellu-
lose, the major chemical constituent
of municipal refuse. As in pyrolysis,
the historic background is in the hy-
drolysis of wood, specifically the
"Madison Wood Sugar Process" that
was developed at the U.S. Forest
Products Laboratory at Madison, Wis-
consin during World War II.63-"5
The specific reaction involved in
cellulose hydrolysis is:
H;SO,
CjHioOi+HjO » C.HnOo
(cellulose) (glucose)
where the dilute (0.5%) sulfuric acid
acts only as a catalyst. Various other
sugars and sugar products also are
formed as by-products and much ef-
fort has been expended to minimize
-------
these side reactions. Sugar is no
longer produced from wood in this
country because it can be obtained
more economically and conveniently
from other sources. However, as with
pyrolysis, when the source of cellulose
is municipal refuse, hydrolysis may
have a more favorable economic basis
because of the "negative value" of the
major raw material.
Hydrolysis of cellulose resulting in
a dilute glucose solution is of little
value unless it is considered in con-
junction with other processes. The
Madison Wood Sugar process, for ex-
ample, includes neutralization of the
sugar-bearing acid solution followed
by fermentation to produce ethyl
alcohol. Another approach is to initi-
ate biological activity in the sugar
solution under aerobic conditions to
promote digestion of the sugar with a
resultant large increase in the yeast
population. This latter process is di-
rected toward producing protein for
animal feeds. Consequently, the costs
and flow charts for the hydrolysis
step are discussed in conjunction with
the overall processes for solid waste
utilization.
PRODUCTION OF ETHYL ALCOHOL
FROM MUNICIPAL REFUSE
Ethyl alcohol may be manufactured
from four general types of raw mate-
rial: (1) sugar-bearing materials
(sugar cane, etc.), (2) starchy ma-
terials (grains, etc.), (3) hydrocarbon
gases (e.g., ethylene), and (4) cellu-
losic materials'" Traditionally, most
ethyl alcohol for both beverage and
industrial use has been manufactured
by fermentation of natural materials
in the sugar-bearing and starch cate-
gories. In recent years, however, syn-
thetic ethyl alcohol manufactured by
the esterification of ethylene has dis-
placed ethyl alcohol from fermenta-
tion as the major source of industrial
alcohol. Such synthetics, by law
and/or custom, cannot be used to
manufacture alcohol for beverage use
or for certain solvent uses. Ethyl
alcohol manufactured from cellulose
would be similarly restricted.
The manufacture of ethyl alcohol
from cellulose, the fourth raw-ma-
terial source listed above, is predicated
upon the hydrolysis of cellulose to
sugar (glucose) as discussed earlier.
Fermentation of the glucose to ethyl
alcohol is written as follows:
yeast
CjHuOi > SCjHsOH +2COz
(glucose) (ethyl alcohol)
As in the case of hydrolysis, trouble-
some side reactions should be mini-
Production of alcohol from municipal refuse—a paper evalua tion 81
TABLE 39
ECONOMIC ANALYSIS OF ETHANOL PRODUCTION FROM MUNICIPAL REFUSE CONTAININO 60
PERCENT CELLULOSE «
Plant cost $2, 262, 000
Annual costs:
Fixed charges at 0.1030* 233,000
Maintenance (2 % equipment cost) f 110, 000
Material cost, including power 305, 000
Labor 156,000
Disposal of 176 tons/day of residual refuse 280, 000
Reduction of 23,500 Ib/day BOD 258, 000
Total cost per yr $1, 340, 000
Annual revenue:
3.93 X 108 gal ethyl alcohol at 40(
-------
82 RECOVERY AND UTILIZATION
TABLE 40
PRODUCTION COST IN CENTS PER IB SUGAR FOR VARIOUS RAW WASTE COMMODITIES AND
VARIOUS PLANT CAPACITIES'
Raw material type
No. 1 mixed wastepaper
Bacasse
Organic urban refuse
Mixed urban refuse f
Price
(per ton)
4.
12.
.- 5.
15.
2.
4.
2.
4.
00
00
00
00
50
50
50
50
Cr
Cr
Cr
Cr
Plant capacities (tons
4.
5.
4.
5.
3.
3.
4.
3.
80
39
42
53
81
56
30
19
94
150
3. 76
4. 80
3. 90
5. 18
2. 93
2.68
3.39
3. 13
300
3.
4.
3.
4.
2.
2.
2.
2.
20
22
33
60
36
11
69
44
per day)
500
2.
3.
3.
4.
2.
1.
2.
2.
91
93
03
32
07
81
34
08
1,000
2. 59
3. 62
2. 73
4.01
1. 76
1. 51
1.96
1.71
•Basis: three-stage continuous plant.
flncludes hydrapulper operation.
the cost figures are preliminary and
should be viewed with caution. Serious
questions must be raised regarding
the costs of the process. Specifically, it
was noted that the cost estimate for
size reduction appeared to be low. Of
even more 'Concern is the apparent dis-
crepancy in costs estimated by Por-
teous and by Ionics, Inc.68 Cursory ex-
amination of capital and operating
costs for similar portions of the two
processes (both employ hydrolysis)
indicates an almost two-fold differ-
ence. The Porteous process was on the
low side, despite the fact that many
conservative features were built into
the cost estimates. Among these are:
data from wood hydrolysis were used
in the calculation (whereas paper and
refuse may react more quickly), and
the break-even point for alcohol pro-
duction is taken at $0.40 per gal
(whereas the market price has re-
mained around $0.52 per gal for the
past several years).
The production of ethyl alcohol
from wood proved to be at least mar-
ginally economic, and first estimates
of the process applied to municipal
solid waste appear favorable. It is rec-
ommended that research be con-
ducted : to evaluate In detail the eco-
nomics of the process, using as a basis
ongoing data from the Federal Office
of Solid Waste Management spon-
sored work68; and, if these results
still indicate favorable economics, to
proceed with a pilot-scale demonstra-
tion of the manufacture of ethyl al-
cohol from mixed municipal solid
waste.
PRODUCTION OF PROTEIN FROM
SOLID WASTE
Conversion of waste paper to pro-
tein. The Denver Research Institute,
Denver, Colorado, is attempting to
convert waste paper to protein using
a fast-growing hydrocarbon-cellulose-
digesting organism having a high
chemical or protein score (PHS Grant
No. UI00565-01). The process includes
fermentation of waste paper in water
enriched with hydrocarbons, oxygen,
and nitrogen. The resultant protein
product would be utilized for livestock
feed. Little information is available on
this project which is in its first year,
but following microbe selection, future
work will include optimization of the
process, pilot-scale testing, and feed-
ing studies.
Evaluation of a process to culture
yeast on solid waste: a report of the
work of Ionics, Inc. The most detailed
cost evaluation of any of the advanced
chemical conversion methods for solid
waste is in a report by Ionics, Inc., to
the Public Health Service (Contract
No. PH 86-67-204). In this study, de-
tailed costs estimates and limited
process optimizations were prepared
for a hydrolysis-fermentation plant
producing yeast.08
The hydrolysis portion of this proc-
ess includes four processing steps: hy-
drolysis, flash vaporization, neutrali-
zation, and centrifugation. The rec-
ommended plant utilized the hydroly-
sis reactors in series and was assumed
to operate on a continuous basis.
Four possible feed materials were
considered for the hydrolysis plant:
No. 1 mixed wastepaper, bagasse, or-
ganic urban refuse (i.e., no cans, bot-
tles, etc.), and mixed urban refuse.
In the cost analyses, a range of
commodity prices was considered for
the No. 1 mixed wastepaper and the
bagasse, whereas a dumping credit
was taken for both organic and mixed
urban refuse. For the mixed urban
refuse, moreover, a feed-preparation
penalty was imposed in the form of
an additional equipment item (a
Black Clawson hydropulper). The
cost to produce sugar in the hydrolysis
operation was determined as a func-
tion of plant input and raw materials
(Table 40).
The neutralized sugar solution from
the hydrolysis process is fed into a
fermenting process where, under
aerobic conditions, the organism
Candida utilis is cultured. Costs for
the fermentation process were calcu-
lated on two bases: (1) maximum-
cost plant, utilizing a metal f ermentor
and a refrigeration-cooling tower sys-
tem; and (2) minimum-cost plant,
using wooden construction for the
fermentor and a local surface water
source for cooling. The cost of produc-
ing yeast was determined for feed
rates ranging from 80 to 1,000 tons
per day (Table 41).
TABLE 41
YEAST PRODUCT COSTS VERSUS PLANT SIZE «»
Product cost for yeast
Plant size* (cents per lb)t
80
150
300
500
1000
Maximum
cost plant
9.22
7. 78
6. 60
5. 70
5.00
Minimum
cost plant
5.96
3.96
* Basis: feed to hydrolysis plant.
t These figures do not include the cost of the
hydrolyzate sugars.
On the basis of the sugar production
costs (Table 40), the yeast costs
(Table 41), and the percent protein
in the C. utilis yeast, the cost of pro-
tein production can be calculated for
any size plant. These costs can then
be compared with protein prices from
other sources. For a 500-ton-per-day
plant, assuming a 50 percent sugar to
yeast utilization factor, the cost of
producing protein from urban refuse
appears competitive (Table 42).
It is expected that research on the
process will now proceed from the
current paper study to an experi-
mental program.
GENERAL CHEMICAL METHODS OF
SOLID WASTE CONVERSION
The potential for chemical conver-
sion of solid waste is almost unlimited,
at least in terms of the processes that
can be considered. Pyrolysis and hy-
drolysis-fermentation represent proc-
esses that have been demonstrated at
least on a pilot scale, or have a wood-
chemical counterpart, or have had
-------
TABLE 42
SUMMARY PROTEIN COSTS VERSUS ALTERNATE ANIMAL FEEDS««
Protein source
Percent
protein
Cost/lb
protein
Soy bean meal
Animal meal
Fish meal
Torula yeast (Candida utilis):
Sulflte waste liquor
Bagasse
Wastepaper
Mixed urban refuse
Organic urban refuse
44
50
60
55
8. 0-14. 8
8. 2-12. 6
10. 5-14. 2
'"27-29""
18. 2-26
17. 8-24. 7
14. 7-18. 9
13. 8-17. 8
extensive economic evaluations. None
of the other work in chemical con-
version has progressed beyond paper
or preliminary laboratory studies. Two
additional approaches for chemical
conversion of solid waste are
suggested.
Partial oxidation of solid organic
wastes. Research is being conducted
at Rensselaer Polytechnic Institute,
Troy, New York, on the partial oxida-
tion of organic wastes in a heated
fluidized bed.™ The process closely re-
sembles the pyrolysis processes dis-
cussed earlier, except that oxygen is
controlled rather than eliminated and
the reaction takes place in a fluidized
bed. As in pyrolysis, partial oxidation
produces a variety of organic gases
and condensables that can be captured
in a series of traps and analyzed. To
date, only wastepaper has been pro-
cessed in laboratory scale experi-
ments; evidence indicates that
methane, acetic acid, formaldehyde,
and formic acid have been produced.
Work on this project is continuing
at Rensselaer under PHS Grant No.
UI 00552-02 and will be extended to
include materials other than paper.
The goal of the program is, of course,
to develop this technique to produce
economically salable organic products.
Because of the basic nature of the
work to date, no cost information is
available.
Chemical transformation of solid
waste. A literature and laboratory
program being conducted at Oregon
State University under PHS Grant No.
UI 00510-02 includes almost all pos-
sible chemical reactions applicable to
solid waste conversion. Thus far,
chemical reactions with straw, dust
bark, and transformed municipal solid
waste (compost); the markets and
uses for cellulose and solid waste; and
the hydrogenation of cellulose have
been studied. Recent experimental
work in this project has included in-
creasing the nitrogen, phosphorus,
and sulfur content of cellulosic mate-
rials to enhance their values as solid
amendments or as feeds for rumin-
ants. Results of the investigations to
date provide an almost complete cata-
log of possible chemical reactions for
the cellulosic materials in solid waste.
FLY-ASH UTILIZATION
This discussion outlines recent
trends in the technical and economic
aspects of coal fly-ash utilization and
assesses the utility of incinerator fly
ash in similar applications. A wide
range of potential uses exists, but
many technical and economic obsta-
cles must be overcome before wide-
spread use becomes a reality.
Since there is no experience with the
utilization of fly ash from municipal
incinerators in the United States, any
discussion must rely heavily upon ex-
perience with utilization of coal fly
ash. A short discussion will put the
subject into perspective, but for addi-
tional details, the reader is referred to
the proceedings of a conference spon-
sored jointly by the Edison Electric
Institute, the National Coal Associa-
tion, and the U.S. Bureau of Mines.™
When pulverized coal is burned, fly
ash is formed from the noncombusti-
ble components of the coal and un-
burned particles of coal that result
from incomplete combustion. The con-
siderable variation in fly-ash proper-
ties is a contributing factor to its lim-
ited reutilization. Average particle size
ranges from 1 to 80 microns. A sim-
ilarly wide range occurs with respect
to particle shape, density, color, and
chemical properties. The chemical
composition of most fly ash is more
than 85 percent alumina, silica, iron
Utilization of coal fly ash 83
oxide, lime, and magnesia, with the
percentage of any one component
varying widely (Table 43).
Traditional uses for fly ash have
been as an additive to replace another,
presumably more costly, material in
a given application. Most of these ap-
plications require a fly-ash conform-
ing to established specifications. The
cost of processing fly ash to meet
these specifications is a significant
factor governing the economics of re-
utilization. However, a new brick-
making process being developed by the
Coal Research Bureau may tolerate
loosely specified fly ash and may elim-
inate this limitation.
Electric utilities produce about 20
million tons of coal fly ash each year,
but only an estimated 1.5 million tons
are reused.71 This limited use is a re-
sult of (1) a lack of basic knowledge
concerning the factors that govern
fly-ash performance in a given appli-
cation; and (2) economic factors (fly
ash must compete with other readily
available, rather low-cost, high-quali-
ty products).
UTILIZATION OF COAL FLY ASH
Concrete additive. Perhaps the
greatest single application of fly ash
is in concrete and concrete products.
An example is the Hungry Horse Dam
on the Flathead River in Montana,
which required 3,086,000 cu yd of con-
crete and contained 126,000 tons of
fly ash, at an estimated savings of
$1,500,000 in material cost.72
Mixed with concrete, fly ash serves
two primary purposes. First, it may
serve as a filler to balance aggregate
particle size distributions. Second, as
a pozzolanic material it reacts chemi-
cally with lime to form a cementitious
material which increases the strength
of the concrete. The mechanisms
whereby fly ash effects changes in
concrete properties, such as strength,
TABLE 43
RANGES OF CHEMICAL COMPOSITION OF U.S.
FLY ASH »
Constituent
Range (percent
by weight)
Silica (SiO,) 34-48
Alumina (A1203) 17-31
Iron oxide (Fe203) 6-26
Calcium oxide (CaO) 1-10
Magnesium oxide (MgO) 0. 5-2
Sulfur trioxide (S03) 0. 2-4
Unburned material 1.5-20
-------
84 RECOVERY AND UTILIZATION
CVCLOt A* CLEANER
WO
PROCESS WATER AND
SOCHUM SILICATE
55 GALLON DRUMS
WITH IMPELLER MKERS
(BATCH MIXING)
TL
MANUAL LCAONG
ONTO KILN CARS
^_ _^
TWO GAS OPERATED
FIRED
TOTE
AND SI
BRICK
3 TNG
WAGE
GREEN BRICK
TO STORAGE
FIGURE 73. Schematic flaw diagram—continuous test plant OCR-WVU fly-ash based brick manufacturing
process.™
durability, workability, finish, chem-
ical resistance, and volume change,
are not well understood. Such un-
knowns in the applications of fly ash
in concrete require considerable ex-
perience on the part of the designer.
These limitations plus economic con-
siderations have prohibited more
wide-scale utilization of fly ash as a
concrete constituent.
Soil stabilization. Pure lime has
been used for purposes of soil stabili-
zation in construction for centuries,
but even the Romans noted that mix-
tures of lime and pozzolanic materials
were superior to lime alone. Ply ash is
used advantageously with lime today
for soil stabilization in the construc-
tion of roads, parking areas, airport
runways, embankments, and founda-
tions. Interest in the use of lime fly-
ash mixtures for these purposes dates
back to the 1940's. Lime fly-ash sta-
bilization as practiced today includes
the use of lime fly-ash mixtures with
both sized aggregates and soils. Since
soil characteristics and properties
vary greatly, the selection of stabiliza-
tion agents, including fly ash, must
be based upon tests and studies of the
soil being treated.
Asphalt paving mixes. Fly ash has
also been used to a limited degree as
a fine mineral filler for asphalt paving
mixes.
Primary factors determining the
suitability of fly ash for this applica-
tion are particle size and carbon con-
tent. This application is most often
limited by the availability of other
low-cost fillers such as limestone dust.
Soil conditioner. The U.S. Bureau
of Mines is sponsoring research at
Virginia Polytechnic Institute to in-
vestigate the use of fly ash as a soil
conditioner and fertilizer. Fly ash con-
tains elements essential to plant nu-
trition, and preliminary studies have
indicated increased crop yield after
fly ash addition. Basic chemical and
physical reactions between soils and
fly ash will be determined and evalu-
ated in terms of crop yield.
Water and waste water treatment.
Studies conducted by the Bureau of
Mines indicate that fly ash may be an
effective adsorbent for removing or-
ganic contaminants from secondary
sewage treatment plant effluents.73 A
similar application relates to sludge
dewatering.74 Studies have indicated
that coal fly ash facilitates sludge de-
watering and thus might prove to be
an effective filter aid.
Lightweight aggregate. Lightweight
aggregates can be made by sintering
coal fly ash. Sintering refers to the
process of heating a loose material
to a temperature at which it softens
and agglomerates, but does not melt
into a solid mass. Bulk densities at-
tained through laboratory and pilot
studies compared favorably with those
of available lightweight aggregates
manufactured from clay shale or blast
furnace slag.
Fly-ash based bricks. Studies con-
ducted by the Coal Research Bureau
at West Virginia University (OCR-
WVU) have indicated the possibility
of producing dry-pressed fly-ash
based brick without close controls on
the physical and chemical properties
of the ash.75"" Experiments have indi-
-------
TABLE 44
COMPARISON BETWEEN THE PHYSICAL PROPERTIES OF CLAY BASED BRICK AND FLY-ASH BASED
BRICK "
ASTM standard specifications
ASTM
grade NW
clay brick
ASTM
grade MW
clay brick
ASTM
grade SW
clay brick
Fly-ash'
based brick
Compressive breaking
strength (psi).
Saturation coefficient..
Water absorption (per-
cent after 5-hr boil).
1,500 min__ 2,500 min__ 3,000 min.. 3,000-20,000
No limit 0.88 max 0.78 max
No limit 22.0 max 17.0 max
0.72-0.86
12-22
Other properties
Apparent porosity
(percent)
Linear shrinkage on
firing
Suction (em H20/30 .
in.2/min)
Bulk density-
Color range
Clay brick
Probably less than fly-ash
brick.
Probably greater than fly-
ash brick.
Generally 130-160
Whites to buffs to deep
reds.
Fly-ash brick
22-35.
0-8.
. 75-300.
90-120.
Same color range as
brick.
clay
'Properties vary within the indicated range depending on fly-ash, slag, sodium silicate, and manufactur-
ing conditions used.
TABLE 45
ESTIMATED ECONOMICS OF PRODUCING FLY-ASH BASED BRICKS USING THE WVU-OCR* PROCESS
Capacity (bricks/hr)
3,000
9, 000
Fly-ash consumption
(tons/hr)
5
15
Capital cost
($)
1, 074, 000
2, 293, 000
Estimated gross profit
($/1000 brick)
19.23
24. 48
•WVU-OCR: West Virginia University, Office of Coal Research.
TABLE 46
SPECIFIC CAPITAL COSTS OF COAL FLY-ASH UTILIZATION PLANTS IN THE FEDERAL REPUBLIC
OF GERMANY n
Product
Cewilith (aggregate).
Corson-Lite sinter
Lime*bonded bricks
Cellular concrete
Production Ash used Capital cost
(cu yd/day) (tons/day) (I/ton ash per day)
460
750
360
460
500
400
500
180
0. 10
2.20
1.25
9.70
Prospects for the utilization of refuse incinerator fiy ash 85
cated that a fly-ash content of 74 per-
cent combined with about 23 percent
coarser aggregate and 3 percent so-
dium silicate binder, on a dry basis,
yielded a suitable product. Tests indi-
cate that the coarse aggregate can be
eliminated if a fairly coarse fly ash is
used resulting in a product containing
about 97 percent coal fly ash. The fly-
ash bricks have structural properties
similar to clay bricks (Table 44). The
Coal Research Bureau has suggested a
configuration for a full-scale plant
(Figure 73). An economic analysis
has been made for two plant sizes,
3,000 and 9,000 bricks per hr (Table
45). Gross profits are based upon a
selling price of $55 per thousand, a
common price for clay brick. The per-
centage of fly ash upon which profits
are based is not clearly defined in the
analysis.
Economics. Except for the studies
conducted by the Coal Research Bu-
reau on the manufacture of bricks
from fly ash, cost data for U.S. fly-ash
products is not generally available.
Presumably this is the result of the
limited production of these materials
in the United States. Cost data Is
available for fly-ash utilization plants
in the Federal Republic of Germany
(Table 46). Of particular interest is
the relatively large plant capacity (in
terms of fly-ash consumption) that
appears to be required for economical
operation.
PROSPECTS FOR THE UTILIZATION
OF REFUSE INCINERATOR FLY
ASH
The utilization of fly ash from
municipal refuse incinerators has not
been practiced in the United States,
and there has been only limited ex-
perience in this practice in Europe.
However, fly ash and incinerator resi-
dues from a refuse incinerator in
Berlin are recovered for sintering
and the production of lightweight
aggregate.
The extent to which incinerator fly
ash can be employed in applications
similar to coal fly ash has not been
established. Presumably, the compo-
sitions of the two ashes are different
since they result from burning entirely
different materials. The long-range
potential for fly-ash recovery does not
appear to be great unless recovery is
included in the salvage process for in-
cinerator residues and ashes (dis-
cussed in a later section). The limited
market for fly-ash products, the
cost of producing a usable ash, and
the large quantities that must be
processed to render a plant econom-
-------
86 RECOVERY AND UTILIZATION
ically sustaining are the main rea-
sons for this low potential. It is
possible, however, for the situation to
change, especially if new and highly
economical processes and products
can be developed such as the OCR-
WVU brick manufacturing process.
SALVAGE OF MUNICIPAL
SOLID WASTE
TIN CA1VS
Tin cans are removed from munic-
ipal solid waste for salvage purposes
at several localities throughout the
United States. Tin cans are salvaged
at several municipal incinerators and
at nearly all compost plants. Until
1961, Los Angeles had separate col-
lection and salvage of tin cans, which
resulted in an income to the city of
approximately $500,000/year. Munici-
palities do not sell salvaged cans
directly, but rather deal through a
scrap broker. Two brokers handle al-
most all the can salvage in the United
States: Proler Steel Company, Hous-
ton, Texas, and Los Angeles By-Prod-
ucts Company, Los Angeles, California.
In addition, the Los Angeles By-
Products Company salvages tin cans
at landfills in the San Francisco area.
Utilisation technology. Three po-
tential uses of salvaged tin cans are
known—as precipitation iron in a
leaching process for the beneflciation
of copper ore, as a source of tin
through chemical detinning opera-
tions, and as a source of steel scrap
for reuse in steelmaking. By far the
largest use of salvaged cans today is
for precipitation iron, since salvaged
cans do not readily meet the high-
quality scrap requirements in either
the detinning or steelmaking proc-
esses. In addition, the use of recovered
tin cans at copper mines is con-
strained by high shipping costs and
limited demand. Nevertheless, the
largest use of tin cans is in refining
copper ore. Copper bearing ores en-
compass a diverse range of materials
and require a wide range of tech-
niques for beneficiation. For ores rich
in oxides, a leaching process based on
a copper-iron ion-exchange process is
used, with detinned cans as a source
of iron. Ore is dumped on large piles
of tin cans and a 5 to 10 percent solu-
tion of sulfuric acid is percolated
through the pile.
The ore reacts with the sulfuric
acid, and copper sulfate is formed.
When the copper sulfate reaches the
tin cans, ferrous sulfate is formed and
copper precipitates on the cans.79'80
The precipitated copper (cement cop-
per) is washed off, decanted, and sent
to the smelting operation. Theoreti-
cally only 0.878 Ib iron is required to
precipitate 1 Ib copper, but in practice
this often reaches 2 Ib iron per Ib
copper.
Incinerated and shredded tin cans
having a bulk density of 20 to 25 Ib
per cu ft are an excellent source of
precipitation iron because of their
high surface-to-volume ratio.38'81 In-
cineration is required to burn off trash
and other contaminants, including
tin. It has been reported, however,
that the increasing aluminum content
of cans causes problems in the pre-
cipitation process. In addition, the
requirement for low bulk density
materials increases shipping costs
considerably. The cost of shipping
shredded cans by rail from Washing-
ton, D.C., to copper mines in Arizona
or Utah has been estimated at over
$80 per ton. Since most copper mines
can buy shredded cans for $50 to $65
per ton, with an upper limit of $75 per
ton,38'81 shipping cost is a critical fac-
tor. At the $75 limit, the feeling is that
the copper companies would find it
more economical to make sponge iron
from slag or other material. Proler
Steel Company has facilities at at
least one copper mine for onsite
shredding.39
Although the copper industry is the
largest consumer of scrap tin cans, it
does not constitute an infinite mar-
ket, since less than 4 percent of the
copper ore in the United States is
refined by the leaching/cementation
process.80 In 1966, approximately
250,000 tons of tin cans were em-
ployed for this purpose. This consti-
tutes only about 2.5 percent of all the
cans available in municipal refuse.
Furthermore, it has been estimated
that the maximum potential con-
sumption is only about 5 percent of
the cans available in refuse.39 Conse-
quently, before truly large-scale re-
utilization of tin cans becomes a
reality, another market must be devel-
oped. One potential market for tin
cans is the detinning industry where
tin from industrial tin-plate scrap is
recovered.
The common industrial technique
used for tin recovery is the alkaline
chemical process.'2 Scrap is treated
with a hot solution of caustic soda in
the presence of an oxidizing agent,
usually sodium nitrate or nitrite, and
tin is dissolved as sodium stannate.
The tin is then recovered from solu-
tion as sodium stannate crystals, as
metal by electrolysis, or as tin oxide
by neutralization of the solution with
sulfuric acid or carbon dioxide. How-
ever, lacquer coatings on tin plate
interfere with the detinning solution;
fats, waxes, and greases also create
problems. Thus, the potential use of
salvaged tin cans hinges on the capa-
bility to get the cans clean. Once this
is accomplished, there should be no
reason why used tin cans cannot be
an excellent source of tin-plate scrap.
Even though the current supply of
tin scrap is not great, detinners have
not been motivated to increase the
supply by cleaning cans. It has been
estimated that 90 percent of the tin
plate produced is lost through the dis-
posal of tin cans.39
Steelmaking, especially in conjunc-
tion with tin recovery, is another po-
tential use of tin cans. Since the
detinning process does not affect the
steel, detinned steel scrap is often
used in steelmaking. The steel-scrap
industry, however, is faced with many
difficulties. Steel has been manufac-
tured conventionally by processing
iron ore in a blast furnace to produce
pig iron. Pig iron is then further re-
fined in the open hearth furnace to
produce steel. Retention time in the
open hearth is on the order of 6 to 8
hr. Recently the basic oxygen furnace,
with processing times on the order of
15 min, has begun to replace the open
hearth. Because of the short process-
ing times, only a very limited amount
of scrap can be tolerated in the basic
oxygen furnace. Consequently, the
market for scrap has decreased in
recent years. This may be offset, how-
ever, by the advent of the electric
furnace, which can produce steel from
a charge of 100 percent scrap. This
change will not occur overnight since
a steelmaker is not likely to switch to
electric furnaces until the supply of
ore becomes short. In addition, the
price of scrap is volatile compared to
that of ore which is predictable, if not
stable. The subtle details of the steel-
scrap industry have been the subject
of recent articles.'3'8*
There are other problems in recov-
ering steel from tin cans. The tin and
zinc content foul refractory linings
in steel furnaces. However, tin-
removal problems may be reduced
somewhat during incineration.
Studies conducted by the U.S. Bureau
of Mines indicates that the tin content
of cans ranges from 0.3 to 0.4 percent
and that incineration will reduce this
to 0.25 to 0.35 percent. A maximum of
approximately 0.04 percent can be
tolerated in steelmaking.81 As previ-
ously indicated, a more economical
process combination might be that of
detinning followed by recovery for
steelmaking. Both the technology and
-------
TABLE 47
THIKTEEN MUNICIPAL INCINERATORS PRACTICING METAI SALVAGE IN 1988
Paper 87
Location
Plant
Year built
Capacity
Type furnace (tons/day)
Income from cans
Capital cost*
($/ton)
($ total)
Total ($)
Metal
salvage
equipment
Atlanta, Georgia Mayson 1939 and Rotary kiln 1#700 #17. 58 #150, 000 12, 050, 000
1952.1
. Hartsfield 1963 Rotary kiln t#500 #17.58 #3,338,000 #200,000
. 1957 Rotary kiln #1,000 f#15. 82
Atlanta, Georgia. -
Louisville, Ken-
tucky
Chicago, Illinois__
Chicago, Illinois__
1963 Rotary kiln #**!, 200 #11.23 **6, 825, 000
1958 Rotary kiln
Chicago, Illinois__
Chicago, Illinois_-
Chicago, Illinois. _
Broward County,
Florida:):
Broward County,
FloridaJ
Tampa, Florida-
Dayton, Ohio...
DeKalb County,
Georgia
_ Southwest
. _ Stickney
(private).
Boda (pri- Rotary kiln
vate).
Medill 1956 Batch, rocking #780 #11.23
grate.
Calumet - 1959__ Rotary kiln #1,200 #11.23
No. 1 1964 Continuous re- #150 #1,200,666 #40,666
ciprocating
grate.
No. 2 1964 Continuous re- #150 #1,200,000 #40,000
ciprocating
grate.
1967 Rotary kiln
. Montgomery 1967 Rotary kiln
County.
1967 Rotary kiln
Based upon: Day & Zimmermann, Engineers and Architects. Can-metal recovery. In Special Studies for Incinerators; for Government of the District of Columbia,
Department of Sanitary Engineering. Public Health Service Publication No. 1748. Washington, U.S. Government Printing Office, 1968. p. 75-80. Except as noted in the
last three items below.
•Not adjusted to 1968 conditions.
tNet profit of $7.40 per ton of cans has also been quoted.
{Currently metal salvage not being practiced due to lack of market for product; no provision at these plants for washing or shredding of cans.
SNot completed at time of survey—planned metal salvage facilities.
^Personal communication from D. Speer, Public Works Department, City of Atlanta, Georgia, to N. L. Drobny, April 22, 1968.
fSullivan, M., U.S. Bureau of Mines, Department of Interior, College Park, Maryland.
"ASME Incinerator Committee, Midwest Section, Minutes of Meeting, June 3, 1966, Chicago, Illinois.
economies of using this combination
on tin cans remains to be investigated.
Existing salvage operations. As indi-
cated, most compost plants employ
magnetic separation to salvage tin
cans. In addition, tin cans are re-
ported to be salvaged at 11 municipal
and two private incinerators (Table
47).
Most incinerators sell their cans to
Proler Steel Company at a price
varying from $10 to $20 per ton. Indi-
cations are that most of the cans end
up at copper mines in the West, al-
though there is some indication that
a small fraction is sent to South
America.
A recent study examined the possi-
bility of incorporating tin can salvage
facilities at the proposed Incinerator
No. 5 in the District of Columbia (Fig-
ure 74) .S1 Estimated cost to include a
can-metal recovery system in con-
junction with the 800-ton-per-day
incinerator was $400,000. It was cal-
culated that the total cost of recover-
ing can metal would be $13.60 per ton
including operating and amortization
charges. It was further estimated that
shipping costs from Washington to
copper mines in Utah or Arizona
would be $83 per ton, and that the
can-metal operation would therefore
be impractical.
PAPER
This discussion is concerned with
the recovery of wastepaper (or paper
stock as it is termed in the industry)
from municipal solid waste for reuse
in the manufacture of paper-oriented
products. The use of wastepaper in
various chemical and biochemical
conversion processes for the manu-
facture of entirely new by-products
was discussed earlier.
In 1966, approximately 10 million
tons of paper stock were recovered for
reuse. This represented about 21 per-
cent of the total fiber utilized in the
manufacture of paper and paperboard
products in the United States.
Although many grades of paper
stock exist, three basic categories may
be defined. The pulp substitute cate-
gory includes bleached foodboard side
runs and various other white cuttings
which require very little preprocessing
other than defibering. The deinking
category primarily includes heavy
books and ledgers. The use of maga-
zines, once a major deinking item,
has declined due to the increasing
amounts of adhesives, fillers, and
other contaminants, which make de-
inking uneconomical with existing
technology. A new, more economical
process for deinking clean salvaged
newsprint has been developed by Gar-
den State Paper Company of Oarfield,
New Jersey.86"87 Deinking grades con-
stitute only about 15 to 20 percent of
the total paper stock utilization in the
United States.88 The third major cate-
gory of paper stock, and one which
accounts for 70 percent of the paper
stock consumed, is bulk grade.8" This
category consists mostly of mixed
news and corrugated, and is used prin-
cipally in the manufacture of fiber-
board containers and boxboard,
molded pulp products such as egg car-
tons and flower pots, and felt roofing
-------
88 RECOVERY AND UTILIZATION
materials and building board.
Recent market prices for paper
stock vary from $8 to $16 per ton de-
pending on the grade (Table 48). The
motivation for paper stock recovery
is economics. Recovery is practiced
only when manufacturing costs using
paper stock are lower than those using
virgin pulp. Prices are by no means
stable and vary both geographically
and temporally. The relatively low
market prices reflect both the diffi-
culties and costs associated with the
use of paper stock as a raw material
and the readily available supply of vir-
gin pulpwood at moderately low cost.
Recovery of paper stock from mu-
nicipal solid waste. As recovery of the
high quality material required for
even bulk grades of paper stock Is not
economical, the major potential for
the recovery of paper stock from mu-
nicipal solid waste lies in salvaging
clean newsprint and corrugated. The
other major forms of paper in mixed
refuse are magazines and packaging
materials. As indicated, the recovery
of magazines is becoming less at-
tractive economically, because of the
increase in the amounts of inks, lac-
quers, and adhesives used. The situa-
tion with packaging materials is sim-
ilar; generally, the function of these
materials dictates that considerable
quantities of coating and other pro-
tective materials be employed. In ad-
dition, packaging materials are often
contaminated by the product they
contained, which interferes with fiber
recovery.
The National Committee for Paper
Stock Conservation is interested in
promoting the recovery of newsprint
and cardboard from solid waste, but
emphasize that only high quality ma-
terial can be tolerated in the recovery
process, and that responsibility for
providing high quality material rests
with the supplier. The committee fur-
ther believes that household separa-
tion of newsprint and cardboard from
other wastepapers is essential to in-
sure the supply of contaminant-free
material.™
Recovery of paper stock from mu-
nicipal refuse is currently practiced
to a small extent. As previously indi-
cated, most compost plants remove
clean newsprint and corrugated by
hand at the plant both for salvage and
to upgrade the quality of the compost
produced. Approximately % to %
tons per hr can be handsorted by one
man, corresponding to 1.3 to 2 man-hr
per ton or a separation cost on the
order of $3.50 to $5 per ton, assuming
very low-cost labor. These plants sell
the paper stock on the open market
-------
Paper 89
TABLE 48
SELECTED SECONDARY FIBER USAGE, PAPER STOCK GRADES, SPECIFICATIONS, AND RECENT
MARKET PRICES«»,«
Grade description and specifications *,x>
Market price Jan. 20, 1967 «
(I/ton)
No. 2—Mixed paper:
Consists of a mixture of various qualities of paper
not limited as to type of packing or soft stock
content
Prohibitive materials may not exceed
Total outthrows may not exceed
No. 1—Mixed paper
Consists of a mixture of various qualities of paper,
packed in bales weighing not less than 500 Ib
and containing less than 25 percent of soft stocks
such as news
Prohibitive materials may not exceed
Percent
2
10
Total outthrows may not exceed
Super mixed paper
Consists of a clean sorted mixture of various quali-
ties of papers, packed in machine-compressed
bales not less than 60 in. in length and containing
less than 10 percent of soft stocks such as
newspapers
Prohibitive materials may not exceed
1 $8. 00-S9. 00
(New York)
5
Total outthrows may not exceed
Boxboard cuttings
Consists of baled new cuttings of paperboard such
as are used in the manufacture of folding paper
cartons, setup boxes and similar boxboard
products
Prohibitive materials may not exceed
Total outthrows may not exceed
No. 1—News:
Consists of newspapers packed in bales of not less
than 54 in. in length, containing less than 5 per-
cent of other papers
Prohibitive materials may not exceed
0. 5 $11. 00-813. 00
(Chicago)
3
0. 5
Total outthrows may not exceed
Super news:
Consists of sorted fresh newspapers, not sunburned,
packed in bales of not less than 60 in. in length,
free from papers other than news, and containing
not more than the normal percentage of roto-
gravure and colored sections
Prohibitive materials None permitted
Total outthrows may not exceed
0. 5 $15. 00-816. 00
(New York)
2
$18. 00-$20. 00
Over-issue news:
Consists of unused overrun regular newspapers
printed on newsprint, baled or securely tied in
bundles, and shall contain not more than the
normal percentage of rotogravure and colored
sections
Prohibitive materials None permitted
Corrugated containers:
Consists of corrugated containers having liners of
either jute or kraft, packed in bales of not less
than 54 in. in length
Prohibitive materials may not exceed
Total outthrows may not exceed.
$22. 00-823. 00
(New York)
$16. 00-818. 00
(New York)
•Grade definitions: The definitions described are
intended to define grades as they should be packed
and graded. Consideration should be given to the fact
that paper stock, as such, is a secondary material
produced manually and may not be technically
perfect.
Outthrows: The term "outthrows" as used
throughout this section is defined as "all papers that
are so manufactured or treated or are in such a form as
to be unsuitable for consumption as the grade
specified." The maiimum quantity of "outthrows"
indicated in connection with the above grade defi-
nitions is understood to be the total of "outthrows"
and "prohibitive materials."
Prohibitive materials: The term "prohibitive ma-
terials" is defined as
(1) any material which by their presence in a
packing of paper stock, in excess of the amount
allowed, will make the packing unusable as
the grade specified
(2) any materials that may be damaging to equip-
ment.
-------
90 RECOVERY AND UTILIZATION
to various brokers for unspecified
end-uses, although most of it would
be expected to be used in processing
various bulk grades of paper. If paper
stock recovered from municipal solid
waste is classified in the bulk cate-
gory, the maximum potential market
for these materials may be estimated.
The bulk category accounts for 70
percent of total secondary fiber usage
or about 7 million tons per year. If
22 percent of typical municipal solid
waste is newsprint and corrugated,
the total potential supply is about 35
million tons per year, about five times
existing national demand. Wide-
spread recovery for bulk paper stock
has limited potential.
Processing systems. Deinking: The
technology of deinking is well docu-
mented and has been described re-
cently by the Technical Association
of the Pulp and Paper Industry
(TAPPI) .'3 The description will not be
repeated here since deinking tech-
nology is confined, for the most part,
to higher quality paper stock than
that which can be salvaged from solid
waste.
The development of a satisfactory
deinking process for the recovery of
paper stock in mixed refuse, especially
newsprint, could pave the way to
large-scale recovery and utilization of
this major form of paper stock from
municipal solid waste. A recent study
of conventional deinking practices has
indicated that, while deinked stock
can aid in economic and quality pro-
duction, rising contaminant content is
a major problem.94 As previously indi-
cated, the Garden State Paper Com-
pany, Garfleld, New Jersey, has made
significant contributions in the deink-
ing of newsprints. Although details of
this process are proprietary, basically
they manufacture high quality news-
print from a supply of 100 percent sal-
vaged newsprint, which includes a
substantial fraction of overissue news.
The quality requirements are high and
can be satisfied only with presorted
newsprint (i.e., newsprint which has
not been soiled with mixed refuse).
The success of Garden State's process
has resulted in new plants now under
construction in Pomona, California,
and Alsip, Illinois.
Bulk fiber recovery: Black Clawson
Company, Middletown, Ohio, has been
active in the development of pulping
systems for the recovery of mixed
paper stock for use as bulk secondary
fiber. A Black Clawson system in-
stalled in England has been described
as processing 80 percent mixed waste
and 20 percent container waste, pack-
aging, etc. (Figure 75) .m Daily
Freshwater,
r
[*-*] White water tank
{"TrfFlote purge
|1 attachment
Dilution
Hydrapulper with
Selectifier
screen
Liquid
junk remover and ] cyclone
ragger. I
1/8 in. dia. extraction T.. .
holes ' ' Thickener
Drubber
FIGURE 75. Black Clawson fiber recovery system.™
Vibrating White
screen water
tank
throughput is about 200 long tons per
day with rejects accounting for about
5,800 Ib per day. At normal running
conditions, the pulper requires 350 hp,
but 500 hp is required to overcome
starting torque. Efforts to obtain more
information on this and similar sys-
tems were unsuccessful.
GLASS
The percentage of glass in municipal
solid waste has grown significantly
in recent years, primarily because of
the advent of the nonreturnable
bottle."
Average returnable bottle life 10 yr
ago was 35 to 40 round trips; today
it is as low as eight. Nonreturnable
bottles, of course, make only one trip.
The waste problem is further com-
pounded by the fact that many retail-
ers prefer to discard returnable bottles
rather than handle them for only a
$0.01 to $0.02 refund.
The recovery of glass from munic-
ipal solid waste is limited due to both
technical and economic considera-
tions. Technical aspects of separating
glass from compost have been men-
tioned in earlier discussions of the
Osborne separator and the Button,
Steele, and Steele stoners. Another
potential technique, especially for seg-
regating various colors of glass, is
the Sortex optical sorter.
There are two major categories of
salvaged scrap glass (properly re-
ferred to as cullet in the industry)—
bottle glass, and sheet and plate glass.
The type of glass cullet for which the
major market exists is sheet and plate
glass trimmings produced in various
industrial operations including the
manufacture of window sashes, doors,
and automobile plate. This material
is used to manufacture powdered glass
which has a variety of industrial ap-
plications including reflective highway
paints, abrasives, match heads and
strikers, ammunition, refractory ma-
terials, and for the cleaning and tum-
bling of castings. Industrial sheet and
plate cullet is ideally suited for these
applications since it requires only
minimal cleaning and fine grinding to
use.
The major form of glass in munici-
pal solid waste is bottles, and the
market for bottle cullet is diminish-
ing. Thirty to forty years ago, al-
most all of the glass cullet marketed
was bottle cullet used to remanufac-
ture bottles. Bottle cullet melts faster
than raw materials; thus, older fur-
naces can be operated at greater ca-
pacity. The importance of this, how-
-------
Rubber 91
ever, has declined owing to increased
costs (largely labor) of cleaning and
processing bottle cullet; low-cost raw
materials; and new glassmaking
systems, which have accelerated
processing.
A glass cullet dealer in Cleveland,
Ohio, indicated that the only form of
bottle cullet for which a Cleveland
market exists is the discarded broken
and defective bottles from bottling
plants.*7 Market prices generally pro-
hibit considerations of glass salvage
from municipal refuse. In Cleveland,
the maximum price brokers will pay
for cullet is about $5 to $6 per ton.
Prices received for crushed and
cleaned cullet is proprietary informa-
tion. Existing markets for such cullet
are decreasing and will continue to
shrink; the market is mostly com-
posed of manufacturers with older
equipment that needs the fast melting
rates of cullet.
There is no technical reason why
bottle cullet cannot be used in the
manufacture of powdered glass, which
is the major market for glass cullet.
The problem, however, is the abun-
dant supply of scrap plate and sheet
glass which exceeds the demand for
cullet for this purpose.
Another use identified for glass
cullet salvaged from municipal solid
waste is in the manufacture of foam
glass. A Polish process is claimed to
manufacture foam glass from 100
percent unsorted waste cullet.08 Al-
though no data on product character-
istics or production costs are provided,
the potential is extremely limited
because the overall growth potential
of the foam glass market is not
significant.
PLASTICS
Plastics constitute only about 1
percent of typical mixed refuse.
Studies conducted by Battelle have in-
dicated that the percentage composi-
tion should increase to slightly over
3 percent by 1976, for a total of about
11 billion Ib of plastic waste annual-
'y.w This three-fold increase is at-
tributed almost entirely to expected
increases in the use of convenient
packaging materials, which are ex-
pected to constitute about 6,600 mil-
lion Ib by 1976 (Table 49).
Generally speaking, plastics are
one of two types—thermoplastic and
thermosetting. Thermoplastic ma-
terials are readily recovered by re-
nelting and this is often done within
a manufacturing facility. Thermo-
setting materials, on the other hand,
cannot be reworked. Thermoset plas-
tics are composed of cross-linked net-
works with the molecular chains
bonded to one another where they
cross. The strength of these bonds
makes the thermosetting materials
more resistant to heat and chemical
solvents and causes them to retain
their shape until decomposition
temperature is reached. Major types
of thermoplastics in solid waste have
been estimated by Battelle as fol-
lows ": polyethylene (38%), poly vinyl-
chloride (32%), and polystyrene
(21%).
The recovery of plastics from solid
waste is complicated by manufactur-
ing requirements for high quality
scrap, which is expensive. Virgin raw
materials are readily available at
costs ranging from $0.10 to $0.20 per
Ib. This leaves very little margin for
salvage and separation costs; clean
and baled plastic milk bottles, for
example, bring only $0.03 to $0.04 per
Ib. Another problem, again related to
quality considerations, is the pre-
dominance of plastic laminates con-
taining both thermoplastic and
thermosetting plastics, whose molec-
ular structures are incompatible.
Fabrication of products from scrap
containing mixtures of these ma-
terials is impossible. In addition,
several constraints exist with regard
to potential uses of plastics. POT ex-
ample, regulations prohibit the reuse
of plastic waste material in the pack-
aging of food products.
There are also many technical prob-
lems in separating plastics from
mixed refuse. The first attempt in this
country to separate film plastics from
mixed refuse is at the Gainesville com-
post plant in Florida, where a ballistic
type separator was used experi-
mentally in conjunction with an air
stream that functioned as a giant
vacuum cleaner. The plastic film was
not separated for salvage, but to up-
grade the compost and to reduce blow-
ing film plastic, a problem at most
compost plants. At present, the sal-
vage of plastic from mixed refuse does
not have much promise. No tech-
niques exist for processing mixed
plastic in the manufacture of new
products, although it has been sug-
gested that short-chain polymers
might be recovered from thermoset-
ting plastics by pyrolytic distillation.100
RUBBER
In the salvage and recovery of rub-
ber are found two factors not asso-
ciated with the recovery of other solid
waste materials: (1) a practical
method exists for recovery, and (2)
TABLE 49
ESTIMATES OF MASTICS USE IN PACKAGING
IN 1866 AND 1976 >>
Components
Plastic bottles .
Other rigid plastic con-
tainers (closures,
flexible tubes, etc.)..
Plastic film and sheet. .
Plastic coatings and
adhesives
Amount (millions
oflb)
1966
900
1,000
1,600
750
4,250
1976
1,800
1,500
2,300
1,000
6,600
scrap quality (mixes of natural and
synthetic rubber) is not a severe con-
straint. The availability of reclaimed
rubber for use in the rubber goods in-
dustry has been instrumental in mini-
mizing excessive and sustained rises
in the cost of crude rubber.100 Re-
claimed rubber also has technological
advantages over synthetic and crude
rubber. It can be mechanically masti-
cated more rapidly than most syn-
thetic or crude rubber and is well
adapted to the absorption of fillers.
In addition to the recycle of re-
claimed rubber in the rubber industry,
some promising experimental work
has been done with the pyrolysis of
scrap automobile tires to produce
carbon.101
The rubber content of mixed mu-
nicipal solid waste is considered to be
very low (0.5 to 1.5%) although no
extensive studies have been conducted
to establish composition ranges. Do-
mestic rubber waste consists of items
such as hot water bottles, shoes, rain-
wear, and the variety of other house-
hold items that contain rubber pads,
gaskets, washers, and occasionally
rubber tires.
Rubber tires, most frequently dis-
posed of in service stations, constitute
the major source of scrap rubber, ac-
counting for 16 percent (360,000 tons)
of the total U.S. rubber usage in
1962.1"2 About 60 percent of the reproc-
essed rubber is used in the manufac-
ture of new tires. Other uses include
the manufacture of automobile floor
mats, windshield mounting strips,
rubber hose, rubber inner soles, heels,
and motor mounts.
The price of salvage rubber varies
with demand and locale. A processor
in St. Louis, a high demand area, is
reported to pay $14 per ton delivered,
4if>-796 O - 72 - 7
-------
92 RECOVERY AND UTILIZATION
SCREENING!-
35m«h O
ll.oth, gl«t nonf«froui mctol
_J HK>H-,NTENSITYI
["I MAGNETIC SEPARATIONr]
Nonmogntf-C (Oil Mogn*tic concwitroU
t f
HYDRAULIC IRON OXIDE PRODUCT
I CLASSIFICATION | TO SMELTING
apigor NO f
• 1 TABLING | 1
Nonfwrout wwtol
conctnirott
— *i
1 O. A
MELTING AND CHEMICAL
L
CARBONACEOUS
PRODUCT
,
REFINING PLANT
Gloi», mint'oif and oih
TO FURTHER PHYSICAL AND CHEMICAL PROCESSING
FOR RECOVERY OF GLASS AND MM4OR MINERAL AND
METALLIC CONSTITUENTS
FIGURE 76. Bureau of Mines experimental procedure for physical benefldation of metal and mineral values
in incinerator residues.1"
whereas, In Los Angeles, a low-
demand area, the market price is only
about $7,50 per ton delivered.100
RAGS
Rags are salvaged by industrial
brokers for use in the manufacture
of fine writing paper and roofing pa-
per. In general, the removal or sepa-
ration of rags from mixed solid waste
is not practical because of the pres-
ence of contaminants and the diffi-
culty of discriminating between
natural and synthetic fibers. Syn-
thetic fibers cannot be used by the
paper industry, and so the salvage
of rags from municipal solid waste is
generally uneconomical. Nevertheless,
two compost plants have reportedly
elected to salvage clean rags when the
market price reaches $40 per ton.103'1W
Handsortlng is expensive, but is the
only means of obtaining a satisfactory
clean product. Salvage is further com-
pounded by relative scarcity of brok-
ers interested in dealing in this rather
marginal product.
INCINERATOR RESIDUES
As mentioned earlier, the Bureau of
Mines is conducting extensive studies
on the salvage of incinerator resi-
dues.39' 1
-------
Data gaps 93
Thus, the greatest economic poten-
tial for the future large-scale recovery
and utilization of municipal solid
waste lies in the manufacture of by-
products. The reasons for this are:
the small probability of developing
new separation technology capable of
extracting salvageable (high quality)
materials; and the undersirable con-
sequences associated with household
separation. It is emphasized that this
is true only in sense of classical
engineering economics. It is quite pos-
sible that considerations related to
external diseconomies (such as re-
source depletion) and social costs
(such as pollution of the environ-
ment) might provide strong motiva-
tion for turning from conventional
disposal-oriented to recovery-oriented
methods of solid waste management.
DATA GAPS
Several needs may be defined for
additional information and future re-
search on salvage and by-product
recovery. Salvage techniques need to
be explored for the detinning and
cleaning of tin cans so that they can
be reused in the steelmaking process.
Both chemical and thermal detin-
ning possibilities should be explored.
In the area of by-product recovery,
which appears to hold the largest po-
tential for solid waste recovery, a
general need is for new by-products
and new uses. It can be seen that, al-
though a large number of potential
combinations and permutations of
present equipment and processes
exist, there are only a few basic re-
covery schemes and the number of
potential by-products is limited. In
addition to this rather general need,
several specific needs related to proc-
ess cost and performance data can
also be defined.
With respect to composting, either
new markets must be developed or
processing costs must be decreased by
process modifications, thereby im-
proving the market situation of
compost. One possible application
which needs to be explored is the
large-scale recovery of desert lands
and abandoned mines. In order to
close cost data gaps for existing com-
posting systems, it seems essential
that the true cost be established for
manufacturing compost from solid
waste. The wide range of cost esti-
mates quoted in this report indicates
the lack of agreement on this matter.
If these costs can be established, al-
lowing for adjustment due to differ-
ences in local markets, so that cities
can evaluate the financial viability of
a proposed composting contract, then
the merits of this technique as com-
pared to another alternative can be
assessed. City officials do not have
satisfactory guidelines at present for
evaluating a proposed contract; and
this information must be developed to
prevent uneconomical attempts at
solid waste recovery.
With regard to process modifica-
tions in composting, a significant de-
crease in processing time, and hence,
cost might be possible using aerobic
digestion of pulped solid waste in an
aqueous slurry. Such a system would
provide for more efficient oxygen-
food-organism contact and would
provide a greater reservoir of dis-
solved oxygen to guard against the
development of local (and overall)
anaerobic conditions.
For waste-heat recovery, available
data on steam-production efficiency,
optimum excess-air requirements, and
optimum refuse: auxiliary fuel ratio
must be investigated. Sensitivity to
ranges in characteristics and compo-
sition of solid waste and their effect
on the overall economies of waste-
heat recovery must be determined.
This needs to be done both for water-
wall and waste-heat boiler systems.
These studies then need to be ex-
panded to a refined analysis of the
economies of waste-heat recovery
considering potential savings in terms
of air pollution control equipment. In
turn, this will require the develop-
ment of sound cost-allocation proce-
dures for determining the true
incremental cost of waste-heat recov-
ery and, hence, associated net savings.
In the related area of power produc-
tion using refuse-fired turbines, the
concept needs to be evaluated in light
of previous unsuccessful experiments
to use solid fuels in gas turbines. Be-
cause of the high research costs asso-
ciated with the development of these
systems, the potentials for success
need to be established, and the as-
sumptions upon which expected per-
formance are based need to be re-
viewed in detail.
The utilization of and possible re-
covery techniques for incinerator fly
ash and residues should be explored in
investigations such as those being con-
ducted for coal fly-ash utilization. For
example, the manufacture of bricks
and other structural shapes in a proc-
ess similar to the one developed at
West Virginia University for coal fly-
ash utilization needs to be explored.
This will, in all likelihood, require ex-
perimental studies to determine the
effect of refuse ash characteristics and
TABLE 50
COMPOSITION OF GRATE-TYPE INCINERATOR
RESIDUES ""
Component
Average.
percent-
age-
Tin cans
Mill scale and small iron
Iron wire
Massive iron
Nonferrous metals
Stone and bricks
Ceramics
Unburned paper and chemical.
Partially burned organics
Ash
44. 1
17. 2
6. 8
0. 7
3.5
1.4
1.3
0.9
8.3
0.7
15.4
Total 100.3
•Dry weight basis.
TABLE 51
COMPOSITION OF ROTARY-KILN INCINERATOR
RESIDUES i"
Component
Average
percent-
age*
Fines, minus 8-mesh (ash, slag,
glass)f 35. 8
Glass and slag, plus S-meshJ 21. 2
Shredded tin cans 19. 3
Mill scale and small iron 10. 7
Nonmetallics from shredded tin
cans 6. 5
Charcoal 3. 4
Massive iron 1. 9
Iron wire 0. 5
Ceramics 0. 2
Handpicked nonferrous metals __ 0. 1
Total.
99. 6
* Dry weight basis.
t Of the total weight of this fraction, 1.8 percent ii
recoverable nonferrous metal.
t Of the total weight of this fraction, 1.4 percent it
recoverable nonferrous metal.
-------
94 RECOVERY AND UTILIZATION
composition on processing and to de-
termine related economies. In addi-
tion, techniques should be explored
and economies established as a basis
of encouragement for municipalities
to use the structural and soil condi-
tioner properties of incinerator ash
in municipal construction and land
improvement projects.
SYNERGISTIC AND ANTAGONISTIC
EFFECTS
The synthesis of new process com-
binations for solid waste recovery re-
quires that the interactions among
the available size reduction, separa-
tion, and recovery techniques be op-
timized as nearly as possible. This, in
turn, requires a delineation of poten-
tial synergistic and antagonistic ef-
fects between the various unit
processes. Relationships between the
various size-reduction and separation
processes have been discussed previ-
ously. Interactions between size-
reduction and separation processes
and the salvage and by-product recov-
ery systems are discussed below.
The major potential for salvage
from mixed solid waste is tin can re-
covery for steel scrap and to a limited
extent for use by the copper industry.
For efficient recovery of tin cans,
some degree of size reduction is essen-
tial to free the cans as much as pos-
sible from entrapped and attached
materials. Magnetic separation is in-
dicated for separation; burnout and
cleaning is also likely to be required.
When waste incineration is to be pro-
vided at some point within the system,
it may be desirable to defer magnetic
separation until after incineration.
This would provide a burnout of at-
tached and entrapped material and a
limited degree of detinning, perhaps
eliminating an additional clean-
ing process.
In the area of by-product recovery
and specifically compost production,
several potentially unexplored syner-
gistic effects exist. These basically re-
late to the potential advantages of
producing compost in an aqueous
slurry as opposed to the conventional
mulch form. Conventional chemical
engineering technology suggests that
significantly increased mass transfer
rates and, hence, reduced digestion
time might be possible in an aqueous
slurry system. In addition, it appears
that the smaller particle sizes achiev-
able in a wet pulping system would
contribute significantly to increased
mass transfer in an aqueous environ-
ment. Wet processing also opens other
avenues of opportunities in that it
may be possible to separate the or-
ganic biodegradable materials from
the remaining noncompostables by
flotation techniques prior to digestion.
Compost production is an excellent
example of a by-product recovery
process in which salvage may hold
considerable merit, since high-quality
compost can only be produced after
the removal of impurities such as fer-
rous and nonferrous metals, glass, and
plastic. Ferrous materials are conven-
tionally and properly removed by
magnetic separation. Nonferrous ma-
terials can be removed, in principle,
either before or after biological di-
gestion by a wet process such as flo-
tation or by a dry process such as the
stoners. In a slurry composting proc-
ess, wet separation would most likely
be indicated to avoid the need for dry-
ing and size reduction beyond the
degree required for the final product.
With respect to incineration and
waste-heat recovery, some degree of
size reduction may be desirable to
achieve increased burning rates. How-
ever, a lower size limit would exist be-
low which fly-ash control and air-
resistance problems would become
excessive. Another critical factor is the
economic trade-offs related to in-
creased cost of producing smaller par-
ticle sizes versus the undefined eco-
nomic advantages of increased per-
formance of the incineration process.
In addition to considering waste-heat
recovery for potential sale, incinera-
tion may be considered in combination
with one of the other recovery proc-
esses requiring drying of a product
such as compost or protein.
In the area of chemical recovery, an-
tagonistic and synergistic phenomena
have not yet been identified be-
cause the processes are still under
development. An exception perhaps
exists in the area of pyrolysis, where-
in it has been reported that an opti-
mal particle size may exist. A rather
general and perhaps obvious consid-
eration is the selection of wet versus
dry processing. Pyrolysis should be
preceded only by dry-size-reduction
and separation processes whereas hy-
drolysis, basically a wet process, could
be proceeded by wet size reduction
and separation.
At present, specific antagonistic and
synergistic effects cannot be defined
in the area of fly-ash recovery, al-
though certain phenomena might be
described. Once desirable fly-ash
properties have been determined for
various end uses, however, the varia-
tion of the critical factors as a func-
tion of feed composition, operating
schedule, an incinerator design can
be tested experimentally. At that time,
potentially antagonistic and synergis-
tic effects may be explored, and this
may provide a means for product
quality control.
-------
VII. Conclusions
UNIT PROCESSES AND RE-
LATED COST AND PER-
FORMANCE DATA
RELIABLE AND MEANINGFUL cost and
performance data on unit processes
for the recovery and utilization of
mixed municipal solid waste are not
generally available from existing op-
erations owing to: the limited applica-
tion of many equipment designs and
processing techniques, the failure to
collect meaningful data on the
applications that do exist, and the
proprietary nature of much of the
available cost and performance data.
The only way for the Bureau of
Solid Waste Management to obtain
reliable and meaningful data on unit
processes for the recovery and utili-
zation of solid waste is to sponsor ex-
perimental studies and full-scale
operations and to collect basic data
in conjunction with such studies.
Consequently, opportunities should be
exercised at all existing solid wastes
demonstration projects to collect cost
and performance data on the various
unit processes employed, and to ex-
periment with other equipment types
not originally provided in the plant
designs. Uniform cost-allocation
standards and procedures should be
developed so that data collected from
various installations can be compared.
The analytical design of size-reduc-
tion and separation equipment for
processing industrial materials is gen-
erally not possible due to the non-
homogeneity of materials processed.
Consequently, empirical studies are
usually required to select equipment
and operating conditions. The non-
homogeneity of solid waste dictates
a need for even greater reliance on
experimental studies; extrapolation
of cost and performance data collect-
ed for selected industrial applications
cannot be expected to yield reliable
information for the design or evalua-
tion of solid waste processing systems.
Although several wet and dry size-
reduction equipment designs are suit-
able for processing solid waste for
separation and recovery, the most
versatile, in terms of material and
particle size capability, is the ham-
mermill. For processing waste streams
not containing bulky materials, the
rasp mill and drum pulverizer offer
advantages. For high degree of size
reduction (from very large to very
small particles), a series of two or
more stages of size reduction is more
efficient than a single stage.
Except for handsorting and mag-
netic separation of tin cans and other
ferrous materials, performance char-
acteristics and associated costs for
solid waste separation techniques are
not well established.
BY-PRODUCT RECOVERY
VERSUS SALVAGE
In the area of recovery and utiliza-
tion of mixed solid waste, by-product
recovery appears to have significantly
greater economic potential in the
classical sense than does salvage and
should be given priority for research
and development. There are three rea-
sons for this: (1) The immediate and
long-range market potential for the
salvage of materials from solid waste
appears to be unpromising, except
perhaps for tin cans. The preliminary
indications uncovered in this study,
however, need to be explored in
greater detail before a firm judgment
can be made. (2) The high quality
requirements for salvaged materials
for reuse in manufacturing processes
are beyond the economic and techni-
cal capabilities of existing and fore-
seeable separation technology. (3)
By-product recovery systems do not
require a high degree of feed prep-
aration, and it is anticipated that
95
-------
96 CONCLUSIONS
processing requirements can, for the
most part, be met by reasonably fore-
seeable extensions of existing separa-
tion technology.
The primary role of salvage in solid
waste recovery should be an adjunct
to a by-product recovery system if, for
example, it is desirable to extract a
given material in conjunction with
manufacture or upgrading of a given
by-product. For reasons outlined
above, salvage should not be made the
primary function of a mixed solid
waste processing and recovery system.
Technically, the most promising
technique for increasing the overall
salvage potential of solid waste is
household separation of clean news-
print and other paper, by far the larg-
est single component in solid waste.
Recovered paper has a definite mar-
ket, and the long-range reuse and sal-
vage potential is attractive, if a steady
supply of clean materials can be guar-
anteed. It is likely, however, that ad-
vantages attributable to household
separation will not be sufficient to jus-
tify disadvantages related to attempts
to secure the public's cooperation.
This is true because cellulose is not a
critical resource; that is, modern for-
est management practices are capable
of adequate replacement so that acute
shortages of cellulose are not likely to
develop.
ECONOMICS OF SOLID
WASTE RECOVERY
AND UTILIZATION
Throughout this report reference
has been made to the economics of
solid waste recovery. Based upon the
information collected and the general
trends observed during this study (and
despite the fact that recovery of spe-
cialty items from municipal solid
waste and the manufacture of specific
products may prove to be economic for
certain geographic areas or certain
situations), it is concluded that the
recovery and utilization of municipal
solid waste may never become gener-
ally economic in the classical sense.
This is because transportation and
processing costs are likely to be so
high that products recovered or
manufactured from solid waste will
cost more than their conventionally
manufactured counterpart or, alter-
natively, the process must operate at a
loss to compete in an open market.
Even if the above situation should
prove to be the case, development of
techniques directed toward the recov-
ery of material from solid waste must
continue to be explored. This is be-
cause motivation for solid waste re-
covery may be provided by the growing
awareness and concern about the ex-
ternal diseconomies and social costs
associated with the classical disposal-
oriented methods of solid waste man-
agement. We are rapidly moving into
a society in this country where, in
areas such as pollution control, di-
rect dollar costs are no longer the sole
consideration. For example, the full
costs of air pollution from burning
refuse whether in dumps or in most
modern incinerators have not yet been
accurately measured. Similarly, the
social costs of a landfill operation
(which can be positive or negative) or
of an incinerator operation cannot be
readily determined. Still more im-
portant, perhaps, is consideration of
external diseconomies such as re-
source depletion. Although some ma-
terials, such as cellulose, are converted
by disposal-oriented practices to basic
constituents (such as carbon dioxide
and water) and thus enter a natural
cycle culminating in the growth of
timber, other materials, such as
metals and their oxides, can be lost
irretrievably to future generations
through present solid waste disposal
practices.
Battelle believes that all the "costs"
of solid waste disposal, including the
social as well as economic costs of
pollution and considerations regard-
ing resources management, must be
evaluated before comprehensive deci-
sions regarding recovery and reutiliz-
ation of solid waste can be made.
Thus, it is quite possible that landfill
and conventional incineration (i.e.,
without by-product recovery) may be-
come unattractive for solid waste
management, not from the develop-
ment of an economic (in the 'direct
dollar cost sense) recovery process,
but rather through increased dissatis-
faction with associated undesirable
side effects in the form of aesthetic
offenses to the environment, resource
depletion, and objectionable or harm-
ful pollution of the land, air, and
water resources.
Further evaluation of recovery and
reuse of solid waste should include a
systems analysis approach to the
standard engineering costs potential
of solid waste recovery. This approach
would establish a priority of best, next
best, etc., processes in a classical eco-
nomic sense. One or more of the "best"
processes (which may still prove to be
uneconomical in the classical sense)
could lead to a broader program,
taking into account the less tangible
costs associated with solid waste dis-
posal in an attempt to justify recov-
ery and reutilization of material.
Although it is not difficult to be-
lieve that social-cost considerations
rather than classical economics will
determine future directions in solid
waste management, implementation
of these considerations will be diffi-
cult. The major problem is the defini-
tion and measurement of the various
social costs, once they have been iden-
tified. This is essential in order to
provide decision criteria to municipal
and other government officials who
are committed, to a large extent, to
least-cost alternatives (in terms of
direct dollar expenses) in the dis-
bursement of public funds. Conse-
quently, it appears that significant
technical and public relations effort
is required, aimed at defining the mag-
nitude and long-term effects of dis-
posal-oriented solid waste manage-
ment practices.
-------
VIII. Potentially attractive
process combinations
BASED UPON THE DATA COLLECTED and
the trends observed during this study,
several potentially attractive process
combinations have been conceived.
Before the technical and economic
merits of these possibilities can be
evaluated, however, several kinds of
additional information are required.
One, of course, is the unit process cost
and performance data that has been
the main subject of this study. But
it is also necessary to explore in some
detail the immediate and long-range
market potential in various sections of
the country for salvage material and
the several manufactured by-products
which can, in principle, be produced
in solid waste recovery systems. Be-
cause of differences in local econo-
mies, markets would be expected to
vary from one region to another. It
is also true that in a given locality,
the market for any single product is
not likely to be so great that a solid
waste recovery system producing only
one product would be economically
attractive. This indicates that a mul-
tiple-product system would be de-
sirable. However, as the number of
product streams increases, the magni-
tude of each decreases and higher
costs associated with small-scale
processing are incurred. The volume
of individual product streams can
be increased by increasing the
input to the plant, but this ap-
proach may cause increased waste
collection costs since a greater area
must be served by a given plant.
Notwithstanding these considerations
and the general lack of data upon
which to base quantitative process
evaluations, several potentially at-
tractive process combinations have
been developed and are outlined be-
low. In accord with the conclusions
outlined previously, a common fea-
ture of the proposed combinations is
that they are all centered about by-
product recovery with auxiliary sal-
vage streams.
Four major recovery schemes can
be identified—composting, conven-
tional waste-heat recovery, pyrolysis,
and hydrolysis followed by biochemi-
cal production of alcohols or protein.
It is not surprising that three of the
above four schemes (all except com-
posting) are directed toward the uti-
lization of the cellulosic fraction of
solid waste, the largest single compo-
nent in mixed municipal solid waste.
In fact composting is also capable of
recovering some cellulosic materials
since a limited amount of paper and
related materials are desirable in
compost.
Of the systems judged to be most
promising for solid waste processing,
each is directed toward a specific
major objective, but also includes
auxiliary salvage operations. Their
common salvage objectives include
reclaiming of steel and tin, precipi-
tation iron for use at copper mines,
materials for the manufacture of
structural shapes, and residual mate-
rial that can be used for landfill.
97
-------
98 POTENTIALLY ATTRACTIVE PROCESS COMBINATIONS
Steam
(for in-plant use or sale)
I I
Steel Tin
FIGURE 77. Solid waste processing system: waste-heat recovery and auxiliary salvage.
Tin cans and
other ferrous
Land fill/reclamation
material
Waste heat
Final processing
size reduction
and/or separation
Sewage
sludge
Land fill/
reclamation
material
FIGURE 78. Solid waste processing system: biochemical conversion and auxiliary salvage.
-------
Potentially attractive process combinations 99
Steel Tin
r-«- Carbon
Activated carbon
Briquettes
r— Ash
Structural shapes
Fill material
FIGURE 79. Solid waste processing system: pyrolysis and auxiliary salvage.
The major objectives of the system
are: waste-heat recovery-—steam
(Figure 77); biochemical conver-
sion—alcohol, protein (Figure 78) ;
and pyrolysis—carbon (Figure 79).
Conventional composting and waste-
heat recovery were not outlined
separately since each has been cov-
ered in detail in previous sections.
Flow diagrams of the three schemes
suggest that several minor variations
related to equipment and unit-proc-
ess permutations and combinations
are possible. The merits of such com-
binations need to be evaluated in
terms of total processing costs, which
cannot be provided with the current
state of knowledge, and local market
opportunities for the various by-prod-
ucts and salvage materials. Selected
elements of the proposed processes
(Figures 77 to 79) could be combined
to synthesize a processing system
capable of producing a multitude of
products.
-------
-------
Appendix A
Summary of Contacts Established
Information furnished
Company/organization
Contact(s)
Vehicle
Response
rec'd
General
Technical
data
Technical area
Tele-
letter phone Visit Yes No Yes
Size Sepa- Eecovery
No Yes No reduc- ration and
tion utilization
Aerojet General Corporation Mr. Robert Mitchell.— X XXXX X
Building 160, Dept. 3401
Azusa, California 91702
Aerospace Commercial Corp... ... ._ Mr. Richard D. Smith, President _ X X X X X
2502 Ash Street
Palo Alto, California 94306
Allis Chalmers Mr. A. J. Mestier, Manager Planning X X XXXX
846 S. 70th Street & New Products.
Milwaukee, U isconsin 53201
Altoona FAM Company Mr. Carlos McCleave, Plant Supervi- X XX X XXX
Altoona, Pennsylvania 16601 sor.
American Can Company Mr. D. J. Lohuis X X XXX
100 Park Avenue
New York, New York 10017
American Public Health Association.. Dr. George J. Kupchik, Director of X XXX
1740 Broadway Environmental Health.
New York, New York 10019
American Design & Development Mr. A. Dean Tomlinson, Vice Presi- X XXX
Corporation. dent.
200 Essex Street
Whitman, Massachusetts 02382
American Pulverizer Company Mr. Don Graveman, Sales Manager.. X XXXX
1249 Macklind Avenue
St. Louis, Missouri 63110
Asplundh Chipper Company Mr. Harold E. Gentile, Manager X XXXX
Chalfont, Pennsylvania 18914
Atkins Saw Division, Nicholson File Mr. M. M. Krebs, Jr X XXX
Company.
1825 North Theobold St.
Greenville, Missouri 38701
Baldwin Lima Hamilton Corp Mr. Robert Wheeler X XX XX
Lima Division
Lima, Ohio 45802
Barber-Greene Company Mr. Carl H. Ulm, Sales Engineer X XXXX
400 N. Highland Avenue
Aurora, Illinois 60507
Barnes Drill Company X X XXX
818 Chestnut
Rockford, Illinois 61102
Bassichis Glass Company Mr. Erwin Stern. XXXX X X X
2323 W. 3rd Street
Cleveland, Ohio 44113
Bauer Brothers Company, The Mr. R. M. Ginaven, Ind. Division X XXX X XX
1718 Sheridan Avenue
Springfield, Ohio 45501
Blark Clawson Company Mr. Joe Baxter XX XXX X
606 Clark Street
Middletown, Ohio 45042
Blaw Knox Company Mr. Roscoe Warner X X XX
Food & Chemical Equipment Divi-
sion
1325 S. Cicero
Chicago, Illinois 60660
Blaw Knox Company. XX X
Food & Chemical Equipment Divi-
sion
43 Winchester Avenue
Buffalo, New York 14211
X
X
X
X
101
-------
Information furnished
Vehicle Response General Technical Technical area
Company/organization Contact(s) rec'd data
Tele- Size Sep_a- Recovery
Letter phone Visit Yes No Yes No Yes No reduc- ration and
lion utilization
Blower Application Company X X
7259 N. 51st Street
Milwaukee, Wisconsin 53223
Borg-Warner Company X X
Mechanical Sales Division
Vernon Avenue at Thomas
Los Angeles, California
Boxboard Research & Development Mr. A. T. Luey, Manager X X
Association.
350 S. Burdick Mall
Kalamazoo. Michigan 49006
Branford Vibrator Company Mr. G. W. Cartier, General Manager.. X X
New Britian, Connecticut 06050
BSP Corporation Mr. Paul J. Cardinal, Manager Sani- X X
6205 Harvard Avenue tary Division.
Cleveland, Ohio 44105
Buffalo Forge Company Mr. Gunnar Hurtig, Jr., Export X X
495 Broadway Manager.
Buffalo, New York 14240
Buffalo Hammer Mill Company Mr. D. F. Ruff XX X
1245 McKinley Parkway
Buffalo, New York 14218
Buffalo Pattern Corporation X X
828 Hertel Avenue
Buffalo, New York 14216
Buhler Brothers (Canada) Ltd Mr. E. Rimensberger X X
1925 Leslie Street
Don Mills, Ontario
Bux-Shrader Magnetic Products Mr. K. L. Gille, General Manager X X
11623 South Broadway
Los Angeles, California 90061
Cameron-Yakima, Inc. - Mr. E. C. Cameron, President X X X X
P.O. Box 1554
Yakima.Washington 98901
Carter-Day Company X X
665 19th Avenue, N.E.
Minneapolis, Minnesota 55418
Centriblast Corporation Mr. Paul Daria, Vice President X X X X
Vista Industrial Park
Campbells Run Road
Pittsburgh, Pennsylvania 15205
City of Atlanta Mr. S. W. Grayson, Director of Sam- X X
Department of Public Works tation; Mr. Robert D.Speer.
Atlanta, Georgia
City of Chesterfield Mr. A. E. Higgison, Superintendent X X
Department of Public Cleansing of Public Cleansing.
Chesterfield, N.E.
Derby, England
City of Cleveland Mr. Herbert Wicks, Civil Engineer... X X
Division of Engineering & Construc-
tion
Department of Public Service
Cleveland, Ohio
City of Madison Mr. John Reinhardt, Project Director. X X X X
City-County Building
210 Monona Avenue
Madison, Wisconsin 53709
City of Memphis Mr. Steve Warren, Director of Public X X
Memphis Light, Gas, & Water Divi- Relations.
sion
P.O. Box 388
Memphis, Tennessee 38101
CityofMiami Mr. J. Grady Phelps XX X
Department of Public Works
1950 N.W. 12th Avenue
Miami, Florida 33136
CityofMobile Mr. Lambert C. Mims, Public Works X XX
City Hall Commissioner; Mr. Meyers, Pub-
109 S. Royal lie Works Superintendent.
Mobile, Alabama 36602
City of New York Mr. Maurice Feldman, Acting Com- XXX
Department of Sanitation missioner.
125 Worth Street
New York, New York 10013
City of San Diego Mr. D. A. Hoffman X X
Utilities Department
7100 Colorado Avenue
La Mesa, California 92041
Combustion Engineering, Inc X X
Raymond Division
427 Randolph
Chicago, Illinois 60606
Continental Can Company • X X
633 Third Avenue
New York, New York 10017
Crobaugh Laboratories Mr. Henry R. Friedberg, Vice Presi- X X
3800 Perkins Avenue dent.
Cleveland, Ohio 44114
102
-------
Information furnished
Vehicle Response General Technical Technical area
Company/organization Contact(s) rec'd data
Tele- Size Sepa- Recovery
Letter phone Visit Yes No Yes No Yes No reduc- ration and
tion utilization
D & J Press Company X XXX
605 Main Street
Tonawanda, New York 14150
Dan B. Vincent, Inc _ Mr. Daniel B. Vincent, President X XXX
3015 Third Avenue
Tampa, Florida 33605
Day & Zimmermann Associates Mr. W. D. Brown X X
1700 Sansom Street
Philadelphia, Pennsylvania 19103
Denver Equipment Company Mr.J. E. Carr, Central Sales Manager. XXXX X XXX
1400 17th Street
Denver, Colorado 80217
Derrick Manuiacturing Co Mr. H. Wm. Derrick, Jr., President.. X XXX
590 Duke Bead
Buffalo, New York 14235
Dings Machine Separator Co X XXX
4740 W. Electric Avenue
Milwaukee, Witconsin 53219
District of Columbia Mr, Robert Perry, Deputy Chief X XX XX
Sanitation Department
District Building
14th & E Streets
Washington, D.C.
Dorr-Oliver Company, Inc Mr, W. E. Budd, Director of Water XX X XX XX
77 Havemeyer lane Management Systems; Mr. Mike
Stamford, Connecticut 06904 lewis.
Duplex Mill and Manufacturing Com- X XXX
pany.
400 Sigler
Springfield, Ohio 45506
Environmental Engineering, Inc Dr. Charles I. Harding, President XXXX X
2324 S.W. 34th Street
Gainsville, Florida 32601
Entoleter, Inc Mr. Franklin R. Farrow, Sales Ap- X XX XX
P.O. Box 1919 plication Engineer.
251 WeltonStreet
New Haven, Connecticut 06509
Eriez Manufacturing Co Mr. Robert F. Merwin, President; XXXX X X
Asburg Road at Airport Mr. Frederick D. Buggie, Manager
Erie, Pennsylvania Technical Contracts/Systems.
Esco Corporation Mr.MaxGowing X XXX
2141 N.W. 25th Street
Portland, Oregon 97210
Exebec Corporation X X
P.9- Box 4175
Bridgeport, Connecticut 06607
Exolon Company Mr. R. R. Harty, President X XXX
950 East Niagara
Tonawanda, New York 14150
Fairfield Engineering Co Mr. John Houser, Director of Re- X X X X X X
Marion, Ohio 5B466 search; Mr. James Coulson, Sales
Manager.
Farrel Corporation Mr. A. H. Trerorrow, Jr X XX XX
148 Maple Street
Ansonia, Connecticut 06401
FateKoote Heath Company X X
607 Bell Street
Plymouth, Ohio 44865
S. 6. Frantz Company, Inc X X
60 E. Darrah lane
Trenton, New Jersey 08638
French Oil Mill Machinery Company.. Mr. John L.Dillon XX XXX X
1088 Green Street
Piqua, Ohio 45356
Fuller Company _X X
124 Bridge Street
Catasauqua, Pennsylvania 18032
Fuller Company Mr. E. J. Roll X XXX
Infilco Division
P.O. Box 5033
Tucson, Arizona 85703
Gainesville Municipal Waste Conver- Mr, H. W. Houston XXXX X X
sion Authority.
P.O. Box 1152
Gainesville, Florida 32601
Garden State Paper Company Mr. Frank Lorey, Corporate Research XXXX X
River Road Director.
Garfield, New Jersey 07026
General Products of Ohio Mr. Herbert!. Cobey, President... X XX XX
West Bucyrus Street
Crestline, Ohio 44827
Glasgow University Dr. Andrew Porteous, Lecturer in X XXX
DepartmentofMechanicalEngineer- Mechanical Engineering.
ing.
Glasgow University
Glasgow, Scotland
103
-------
Information furnished
Vehicle Response General Technical Technical area
Company/organization Contact (s) rec'd data
Tele- Size Sepa- Recovery
Letter phone Visit Yes No Yes No Yes No reduc- ration and
tion utilization
Glass Container Manufacturers Insti- Mr. John H. Abrahams, Manager of X XXX
tute, Inc. Environmental Pollution Control
1625 K Street, NW. Programs.
Washington, D.C. 20008
Glenn King Company Mr. Michael Gummond XX X
Houston, Texas.
Westinghouse Air Brake Mr. Carl E. Hanson,Sales Manager.. X XX
Goodman Division
4834 S. Halsted Street
Chicago, Illinois 60609
Gruendler Crusher & Pulverizer Mr. Wm. P. Gruendler, President X X X X
2800 N. Market Street
St. Louis, Missouri 63103
Gundlach,T.J.,MachineCompany Mr. J. D. Frazer, Sales Engineer X X X X
Division of JMJ Industries, Inc.
P.O. Box 385
Belleville, Illinois 62220
Hammermills, Inc Mr. Wm. D. Robinson, Manager of X X X X X
625 C Avenue Solid Waste Systems.
Cedar Rapids, Iowa 52405
azemag U.S.A., Inc Richard E. Kleinhaus, Vice President. XX XXX
60 E. 42nd Street
New York, New York 10017
Heil Company, The Mr. Arnold F. Meyer X X X X X X
3000 W. Montana Street
Milwaukee, Wisconsin 53201
Ir. J. A. Hendricks XX
Oud Loosdr Dyk 239
Oud Loosdrecht, The Netherlands
C. B. Hobbs Company Mr. Ronald Guard, Plant Superin- XX XX
Milpitas, California 95035 tendent.
Hoffman Industries Mr. James J. Joseph, Field Engineer, X X X
P.O. Box 214
Syracuse, New York
Hugo Neu-Proler ... Mr. Richard Neu, General Manager.. XXX X
901 New Dock Street
Terminal Island, California 90731
Hutchinson Manufacturing Company... Mr. W. C. Philipp, Manager of In- X XX
P.O. Box 9335 dustrial Development.
Houston, Texas 77011
Indiana General Corp Mr. W. A. Bronkala, Sales Manager._ X XX
6001 S. General Avenue
Cndahy, Wisconsin 53110 T ™ » •* * *, v
International Disposal Corp Mr. Roger Lynn, Plant Manager; XX X X
280122nd Street Mr. Frank Rigo, Maintenance
St. Petersburg, Florida 33712 Superintendent.
Ionics Corporation
85 Grove Street
Watertown, Massachusetts 02172
Iowa Manufacturing Company Mr. Kenneth Lindsay, Sales Manager. X XX
916 16th Street, N.E.
Cedar Rapids, Iowa 52402
Jeffrey Manufacturing Co X X
956 N. 4th Street
Columbus, Ohio 43201
J.H. Day Company XX
4900 Beech Street
Cincinnati, Ohio 45212
Kennametal, Inc Mr. Gail P. McCleary, Project Engi- X XX
700 Lloyd Avenue neer.
Latrobe, Pennsylvania 15650
Kennedy Van Saun Corp Mr. Lester R. Ferguson, Vice Presi- X XX
405 Park Avenue dent.
New York, New York 10022
Lawden Manufacturing Company, Ltd. Mr. A. S. Pittwood, Managing Di- X XX
Spring Road rector.
Ettingshall, Wolverhamptom, Eng-
land
Link Belt Company x
138 E. Court Street
Cincinnati, Ohio 45202
Link Belt Company X X
Department TR^67
Prudential Plaza
Chicago, Illinois
Lippman Products Operations XX
Hewitt Robins Division
Litton Industries
666 Glenbrook Road
Stamford, Connecticut 06906
Lippman Products XX
4603 W. Mitchell
Milwaukee, Wisconsin 53214
Logemann Brothers Company Mr. R. J. Smiltneek, Director XX XXX
3150 W. Burleigh Street
Milwaukee, Wisconsin 53245
104
-------
Information furnished
Vehicle Response General Technical Technical area
Company/organization Contact (s) rec'd data
Tele- Size Sepa- Recovery
Letter phone Visit Yes No Yes No Yes No reduc- ration and
tion utilization
lone Star Organics Corp Mr. Gerald Vaughn, Plant Manager; XXXX X X XXX
9225 Lawndale Avenue Mr. Wages, Assistant Plant Man-
Houston, Texas 77012 ager.
Los Angeles By-Products Company Mr. C. C. Sexton, President; Mr. Ben XXXX X XXXX
1810 E. 25th Street Litchfield, Manager Sacramento
los Angeles, California 90058 Division.
Los Angeles County Sanitation District.. Mr. Walter E. Garrison, Chief Engi- XXXX X X
2020 Beverly Boulevard neer; Mr. Frank Dair, Division
los Angeles, California 90057 Engineer.
luria Brothers Mr. Mort Seiden, Manager; Mr. XXXX XX X
5850 Boyle Avenue Andrew DeVries, Operating Engi-
Vernon, California 90058 neer.
luria Brothers Mr. William Magnes, Director of XXX X XXXX
Five Points Road Research; Mr. Curtis Dudda,
Cleveland, Ohio Plant Manager.
Machinery and Equipment Company XX X
514 Bryant
San Francisco, California 94107
Manufacturers Equipment Co X X XXX
218 Madeira Avenue
Dayton, Ohio 45404
Metropolitan Washington Council Mr. John J. lentz X XXX X
of Government.
1250 Connecticut Ave., N.W.
Washington, D.C. 20036
Metropolitan Waste Conversion Cor- Mr. Victor Brown, President; Mr. I. XXXX X X XXX
poration. Anderson, Manager, Plant Engi-
P.O. Box 1028 neering Dept.
Wheaton, Illinois 60187
Franklin P. Miller & Son, Inc Mr. Harold Galanty X XX XX
36 Meadow Street
E. Orange, New Jersey 07017
Mitts & Merrill Mr. J. W. Ranous, Sales Manager; X XX XX
109 McKoskry Street Mr. Goddard.
Saginaw, Michigan 48601
Munson Alhert D. Matthai, Jr X XX XX
210 Seward Avenue
Utica, New York 13503
Mclanahan Corporation Michael W. McLanahan, Assistant X XXXX
200 Wall Street Sales Manager.
Hollidaysburg, Pennsylvania 16648
McNally Pittsburg Manufacturing Mr. R. F. Wesner, President X XX XX
Company.
Drawer D
Pittsburg, Kansas 66762
NV Vuilafvoer Maatschappij (VAM) __. Dr. Ir. Stolp, Director XX X
Jacob Obrechstraat 67
Amsterdam-Z, The Netherlands
National Canners Assn Mr. Walter Rose, Head of Water and XXXX X X X
1950 6thStreet Waste Engineering Section.
Berkeley, California 94710
National Committee for Paper Stock Mr. Wm. M. Russell, Special Con- X XXX X XX
Conservation. sultant.
The Chase Bldg.
212 N. Kingshighway
St. Louis, Missouri 63108
National Engineering Company Mr. A. J. Dumcins, Sales Manager.-- X X XXX
549 W. Washington Blvd.
Chicago, Illinois 60606
National Organic Corporation Mr. Stanley Spiegel X XXX X
904 First Federal Building
Atlanta, Georgia 30303
National Waste Conversion Systems Mr. Stephen Varro XX X
Corporation.
425 East 51st Street
New York, New York 10022
Naval Facilities Engineering Com- Mr. R. E. Short, LCDR, CEL, USN XXX X
mand. Acquisition Coordination Officer.
Atlantic Division
Norfolk, Virginia
New YorkState Health Dept
Office of local Governments
Albany, New York
Newaygo Engineering Co Mr. Ray Sweitzer, Sales Manager XX X
Newaygo, Michigan 49337
Newell Manufacturing Co Mr. Scott Newell, Vice President X XXXX
726 Probandt Street
San Antonio, Texas 78204
New York University Dr. Elmer K. Kaiser X XXX X
West 177th Street and Cedar Avenue
Bronx, New York 10493
Nordburg Manufacturing Co XX X
Box 383
Milwaukee, Wisconsin 53201
Noro Industrial Corporation XX X
S. Cottage Grove Avenue
Chicago, Illinois
105
-------
Information furnished
Vehicle Response General Technical Technical area
Company/organization Contact (s) rec'd data
Tele- Size Sena- Recovery
Letter phone Visit Yes No Yes No Yes No reduc- ration and
tion utilization
Ohio Magnetics XX X
142-A East Pearl Avenue
Lima, Ohio 45801
W. W. Oliver Manufacturing Company XX X
10 Beard Avenue
Buffalo, New York 14214
Oregon State University Dr. Virgil H. Freed; Mr. Robert R. X XXX
Agricultural Engineering Depart- Groner.
ment
CorvalHs, Oregon 97330
Orville Simpson Company Mr. Norman L, Zundt, Sales Engi- X X XXX
1230 Knowlton Street neer.
Cincinnati, Ohio 45223
Pan American Resources, Inc Mr. Robert Buckbinder, Vice Presi- X X X X X X
5443 San Fernando Rd., W. dent; Mr. Charles Fink, Marketing
Los Angeles, California 90039 Manager.
Pennsylvania Crushers Mr. D. F. Webb, Sales Engineer X X X X X
P.O. Box 100
Broomall, Pennsylvania 19008
Prater Industrial Products Inc Mr. P. E. McKamy, Vice President-- X XX XX
1515 S. 55th Street
Chicago, Illinois 60650
Arthur G. McKee & Company Mr. J. J. Davey X XX XX
Process Machinery Div.
650 5th Street
San Francisco, California 94107
Proler Steel Corporation Mr. Samuel Proler, President; Mr. XXXX X XXX
7501 Wallisville Road Herman Proler, Executive Vice
Houston, Texas 77020 President.
PHS-TVA Compost Plant Mr. John Wiley, Research Director; XXX X X XX
RFD 4 Dr. Carl Sova, Microbiologist.
Johnson City, Tennessee 37601
Quad-City Solid Waste Mr. W. T. Ingram X XXXX
Room 53—City Hall
Patterson, New Jersey
Raymond G. Osborne Laboratories Mr. Phillip S. Osborne, Vice Presi- X XXX X
2636 S. Grand Avenue dent.
Los Angeles, California 90007
Reed Paper Group, Ltd Mr. James Peddie, Project Engineer-. X
Aylesford Paper Mills
Lakefield
Maidstone, Kent
England
Rensselaer Polytechnic Institute Dr. Wm. A. Shuster X X
Department of Civil Engineering
Troy, New York
Rietz Manufacturing Co Mr. Warren S. Enochian X X XXX
182 Rodd Road
Santa Rosa, California 95402
A. J. Sackett & Sons Co- - Mr. Walter Sackett, Jr., Vice Presi- X XX XX
1702 S. Highland Ave. dent.
Baltimore, Maryland 21224
San Diego State University Dr. R. A. Fitz XX XXX
School of Engineering
San Diego, California
Segredyne Corporation X X XXX
23 Charles Street
Cambridge, Massachusetts 02141
Slick Industrial Company Mr. Dennis Reekers, Representative- X XX XX
Pulverizing Machinery
100 Chatham Road
Summit, New Jersey 45103
Smith Engineering Works Mr. J R. Smith, Vice President X XX XX
532 E. Capital Drive
Milwaukee, Wisconsin 53201
John R. Snell Engineers, Inc Dr. John R. Snell, President X XXX
221 N. Cedar Street
Lansing, Michigan 48933
Sortex Company of North America Mr. T. G. Gilbert, Vice President X XXX X
P.O. Box 160
Lowell, Michigan 49331
Sprout Waldron & Company, Inc Mr. Howard D. Egli, Jr X X XX XXX
Muncy, Pennsylvania 17756
Stanford Research Institute Mr. R. A. Boettcher, Research Engi- X X XXX
820 Mission Street neer.
South Pasadena, California 91108
Stedman Foundry & Machine Com- Mr. Ronald L. Bradford, Factory X XX XX
pany, Inc. Sales Engineer.
Aurora, Indiana 47001
J. C.Steele&Sons .. .- Mr. J. C.Steele, Jr X XX XX
P.O. Box 951
Statesville, North Carolina 28677
Stephens-Adamson Manufacturing Mr. R. H. Humm, Vice President X XXX
Company.
19 Ridgeway Avenue
Aurora, Illinois 60507
106
-------
Information furnished
Vehicle Response General Technical Technical area
Company/organization Contact(s) rec'd data
Tele- Size Sepa- Recovery
Letter phone Visit Yes No Yes No Yes No reduc- ration and
tion utilization
StrongScott Manufacturing Company... Mr. George H. Paulson X XX
Minneapolis, Minnesota 55413
Sturdevant Mill Company Mr. A. T. Glynn, Engineer X X X X X
Park & Clayton Streets
Dorchester, Boston, Massachusetts
02122
Sumitomo Shojo Chicago, Inc Mr. N. Murakami X XXX X
208 S. La Salle Street
Chicago, Illinois
Sundstrand Corporation Mr. Mario Calvagna, Chief Proposal X X XXX
Sundstrand Machine Tool Division Engineer.
2531 llth Street
Sockford, Illinois 61101
Button, Steele, and Steele, Inc Mr. Eodgers Hill XX XXX X
1029S.Haskell
Dallas, Texas 75223
SWECO Dr. Albert M.Soldale, Vice President- X XXX X X
6111 E. Bandini Blvd.
los Angeles, California 90022
Syntron Company Mr. L. R. Morgan, Advertising Man- X X X X X X
Homer City, Pennsylvania 15748 ager.
TAPPI Mr. H. O. Teeple X XX XXX
360 Lexington Avenue
New York, New York 11216
Tennessee Valley Authority Mr. Earl E. Elliott, Chief, Fertilizer X XXX X
F202 National Fertilizer Development Distribution & Marketing Staff.
Center.
Muscle Shoals, Alabama
Testing Machines, Inc XX X
72 Jerico Turnpike
Mineola, Long Island, New York
11501
Tezuka-Kosan Company, Ltd N.Murakami X XXX X
7-Chome, Ojima
Tokyo, Japan
Thomas Foundries, Inc XX X
P.O. Box 1111
3800 Tenth Avenue
N. Birmingham, Alabama 35234
John Thompson, Ltd X X
Taristock House East
Weburn Walk
Taristock Square
London W.C.I., England
Tollemache Composting Systems, Ltd.. Mr. D. H. G. Tollemache X X X X X X X
25 Berkeley Square
London W.I., England
W.S. Tyler Company Mr. S. J. Janovac, Application Engi- X XX XX
8200 Tyler Boulevard neer.
Mentor, Ohio 44060
Union Carbide X XX XX
Paper Chemicals
270 Park Avenue
New York, New York 10017
United Compost Service Mr. Jeffrey George, President XXXX X XX X
3701 Kirby Drive
Houston, Texas 77006
United Conveyor Corp X XXX
6505 N. Ridge Blvd.
Chicago, Illinois 60626
Universal Road Machinery Company X XX XX
Emrick Street
Kingston, New York 12401
Universal Vibrating Screen Company XX X
P.O. Box 942
Racine, Wisconsin 53405
University of California Dr. Clarence J. Golueke, Research X XXXX X
Sanitary Engineering Research Lab- Biologist.
oratory
1301 E 46th Street
Berkeley, California
University of California Dr. Samuel A. Hart X X X X X X X
Davis Campus
Agricultural Engineering Depart-
ment
Davis, California
University of Florida Mr. Dennis Falgorit XXXX X
Gainesville, Florida 32601
University of Hartford Mr. Alfred Eggen X X X X X X
Department of Mechanical Engineer-
ing
Hartford, Connecticut
University of Louisville. Mr. J. E. Heer X XXX XX
Department of Civil Engineering
Louisville, Kentucky
107
456-796 O - 72 - 9
-------
Information furnished
Vehicle Response General Technical Technical area
Company/organization Contact(s) rec'd data
Tele- Size Sepa- Recovery
letter phone Visit Yes No Yes No Yes No reduc- ration and
tion utilization
U.S. Bureau of Mines Mr. Carl Rampacek, Research Di- X
Metallurgy Research Center rector; Mr. Paul Sullivan, Super-
College Park, Maryland visor, Chemical Engineer.
U.S. Bureau of Mines Mr. Prank Cservenyak, Manager, X
Washington, B.C. Solid Waste Projects.
U.S. Industries, Inc., Engineering _ „. X
ltd.
Burtonwood
Warrington, Lancashire
England
U.S. NavalStation ENS Ralph Hesler, CEC, USN
Department of Public Works
Norfolk, Virginia 23511
USPHS-TVA Compost Plant Dr. John S. Wiley Research Director... X
Johnson City, Tennessee 37801
U.S. Plywood Champion Papers, Inc X
777 Third Avenue
New York, New York 10017
Virginia Polytechnic Institute Mr. D. C. Martins, Assistant Pro- X
College of Agriculture fessor.
Blacksburg, Virginia
Vortec Products X
1414 W. 190th Street
Torrence, California 90504
West Virginia University Mr.HarryE. Shafer, Jr., Supervising X
School of Mines Research Technologist.
Morgantown, West Virginia 26505
WEMCO Mr. D. W. Jenkinson, Consulting X
Division of Arthur G. McKee Engineer.
P.O. Box 15619
Sacramento, California 95813
Williams Patent Crusher & Pulverizer. Mr. J. H. Herb, Regional Sales Man- X
Company. ager.
807 Montgomery
St. Louis, Missouri 63102
Wascon Systems, Inc.. Mr. James, Sattelle Marketing As- X
Hatboro,Pennsylvania 19040 sistant.
Wheelabrator Corporation Mr. Robert L. Orth X
454 S. Byrkit
Mishawaka, Indiana 46544
Ir. W. A. G. Westrate X
Stationkade 70
Amsterdam-Z
The Netherlands
108
-------
Appendix B
New Size-Reduction
Equipment Designs
PATENT ART
The patents that were selected
(from a review of U.S. patents col-
lected by the Bureau of Solid Waste
Management, Solid Waste Informa-
tion Retrieval System *) for study by
Battelle were the ones more closely
related to solid waste size reduction.
Most of these were improvement pa-
tents on standard size-reduction
equipment. The following patents
were selected because they disclose
elements showing promise for future
application to municipal solid waste
size reduction.
Patent Number 2,248,108—Bottle
Breaking Machine
The gravity-actuated member dis-
closed may have use in a preliminary
operation on municipal solid waste.
Automatic action of hammers on
municipal solid waste as it is conveyed
could be in the nature of a series of
shattering blows. These blows could
be continuous or be initiated by a
bulky item, in a manner similar to
electric typewriter action.
Patent Number 2,641,165—Multiple
Disk, Radial Axis Wet Pulper
The multiple abrasive disks shown
may have some advantage over the
single disk in a wet pulper, with, per-
haps, added action if the axis were
canted to allow disks to overlap and
promote the formation of a slurry
toroid.
Patent Number 2,708,552—Refuse
Cutting Machine
The lump-breaker, feather-compacter
feeder disclosed is similar to crushing-
type feeders used on some hammer-
mills and suggests a possible modifica-
tion to "homogenize" bagged garbage.
Patent Number 2,738,932—Prelimi-
nary Disintegrating Machine
The meshing stationary blades (called
breaker anvils in the patent) and
breaker arms (helically inclined mem-
bers) have action similar to impact
crushers with shredder teeth and
added axial conveying action. On se-
lected material, such as municipal
solid waste with bulky items excluded,
a machine such as this might be use-
ful in an automatic preliminary
operation.
Patent Number 2,980,345—Ultrasonic
Apparatus and Method of Com-
minution
The ultrasonic siren used appears to
be best suited to friable materials; a
heterogeneous mixture such as munic-
ipal solid waste would attenuate the
energy severely. The absence of mov-
ing parts in contact with the material,
however, would minimize wear and
allow free passage of material. This
would appear to be useful in a system
using automatic presorting.
Patent Numbers 3,188,942 and
3,191,872
These are wet pulpers with screw-
type extrusion dewatering devices.
Screening of unpulpable material is
also disclosed. The separation of ma-
terials found in municipal solid waste
is partially successful, but the need
for a conveyor-type, self-cleaning
screen for automatic sorting is indi-
cated.
109
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HO APPENDIX B
FIGURE B-l. Improved hammer and hammer-mounting means for hammermill.
BATTELLE'S CONCEPTS OF
IMPROVEMENTS
In the course of the solid waste
size-reduction studies, improvements
for machine components and in ma-
chine combinations became apparent.
Improvements for Machine Compo-
nents
Hammermill hammers, hammermill
feeders, and moving shredder mem-
bers were considered candidates for
improvements in their components.
Hammermill Hammers. Prevalent
uneven hammer wear and long down-
time for hammer change or resurfac-
ing indicate the need for improved
hammers and means for faster ham-
mer changing.
Threaded pivots to permit quick
removal or rotation of individual
hammermill hammers and a hammer
designed to improve efficiency are
conceived (Figure B-l). This arrange-
ment also staggers the hammers to
minimize the number of simultaneous
blows, thus reducing vibration and
noise. A rake angle, bi, will promote
a piercing action and reduce wedging
of the material between the hammers
and the grate bars. Wear area to a
given radius, r, is also increased as
shown by comparing a± on the ham-
mer with rake angle bi and a2 on the
square hammer with a negative rake
angle &. The center of percussion is
also nearer the hammer tip on this de-
sign, which would reduce the ratio of
weight-to-impact.
Hammermill Feeders. The feed
waste into hammermills was observed
to be a critical operation. Even when
fairly selective material is handled,
where such bulky items as oil drums
and refrigerators have been presepa-
rated, operations near rated capacity
require close control to prevent over-
loading. Automatic conveyor speed
control based on hammermill power
demand has been used, but rather
large power input excursions due to
nonuniform material and slow sys-
tem response were observed. This
wide swing in power input dictates
a somewhat conservative average
power setting and indicates the need
for improved hammermill feeding.
Homogenizing feeds has been con-
-------
Battelle's concepts of improvements 111
Multiple throw cranks K
Moving shredding
members
FIGURE B-2. Improved hammermill feeder.
sidered, ranging from the wiping ac-
tion of a gate in a conveyor system to
a crushing-tearing concept (Figure
B-2). This type could be in the form
of a hopper to accommodate surges in
input and variations in feed rate. Au-
tomatic speed control could be per-
formed with minimum backlash by
monitoring the crushing and tearing
action to produce uniform semimac-
erated ribbons. The feeding and tear-
ing would be done by the piercing and
pulling action of hard teeth on con-
verging walking beams driven in a
variety of orbits by multiple-throw
cranks.
Moving Shredder Members. Some
of the hammermills studied utilize
shredding members which mesh with
the hammers to provide additional
tearing action. Product size can be
determined by the clearance of the
hammers and the shredding mem-
bers. Free recirculation in the ham-
mermill is prevented in these, and
jamming and buildup on stationary
shredding members may occur. One
set of the walking-beam members
could be used as moving shredding
members (Figure B-2). In operation,
buildup of material on the shredding
members would be periodically re-
leased by the retracting action.
Combination Improvements
Combinations of existing size-
reduction equipment offer some ad-
vantages when applied to solid waste.
Among these are the combined shear-
ing and hammermilling and combined
crushing and hammermilling, which
prompted the composite configura-
tion (Figure B-2). In this concept,
close clearance of passing teeth could
also be provided for a shearing action.
Conceivably, a combination such as
this could accommodate an extremely
wide range of unsorted materials.
Combinations of hammermills and
wet pulpers were also studied, and it
is indicated that a primary size reduc-
tion may use more horsepower than
the final size reduction. This could
also be the case with a crushing and
tearing feeding unit combined with
the hammermill. Either of these com-
binations appears to promote syner-
gistic effects.
-------
-------
Appendix C
Other Separation Patent Art
In addition to the separation tech-
nology discussed in preceding sections,
other potentially applicable tech-
niques have been extracted from the
review of U.S. patents collected by the
Bureau of Solid Waste Management,
Solid Waste Information Retrieval
System.107 The information summa-
rized below has been abstracted from
the respective patents. Information is
not available regarding current ap-
plications.
Patent No. 2,422,203—Specific Gravity
Separation of Solids in Liquid
Suspension—(June 17,1947)
The invention relates to the re-
covery of solids from liquids by sink-
float methods. Separation according
to size or specific gravity is claimed.
The invention claims an arrangement
whereby the requirement to employ
heavy media is eliminated. Specifi-
cally, a controlled centrifugal move-
ment of a body of mixed solids in a
liquid is claimed to permit clean and
distinct separation between solids of
different sizes and/or specific gravities
in an aqueous pulp. The process was
developed as an improved ore-bene-
flciation technique, although potential
uses in coal-washery applications and
the treatment of potash ores are
claimed. Performance data on ores
in the size range 6-200 mesh are
provided. Performance attainable on
various forms of solid waste cannot
be established without experimental
studies, except that it should be noted
that potential applications are
limited to relatively fine fractions.
Patent No. 2,474,695—Collecting and
Separating Apparatus—(June 28,
1949)
This device was designed to sepa-
rate particles from a fluid medium,
to separate heavier fluids from lighter
ores, and to remove dust, sand par-
ticles, and chips from castings and
other items produced in foundries,
mills, etc. A mixed fluid stream is ac-
celerated in a duct connected to an
elbow or bend. As the stream enters
the elbow, heavier materials are sepa-
rated from lighter ones because of
differential centrifugal forces. A com-
plex baffle arrangement is provided
in the elbow to collect the separated
material streams. No data indicating
performance of the device are pro-
vided in the patent.
Patent No. 2,561,665—Continuous
Classifier for Solids—(July 24,
1951)
This device was developed as an
improved technique for separating
solids of various specific gravities
from a fluid medium, provided that
all solids to be separated have a spe-
cific gravity greater than the fluid. A
series of tanks are provided such that
the cross-sectional area of flow path
increases, tank-by-tank, in the direc-
tion of flow. A liquid suspension is
introduced in a tank in a downward
and upward path thereby inducing
the settling of solids in each tank. Be-
cause the flow path of each subse-
quent tank is of larger cross-sectional
area, the upward velocity of flow de-
creases, thus permitting the deposi-
tion of lighter solids in each stage. An
adjustable baffle is provided in each
tank which is claimed as a novel
means for controlling flow and mini-
mizing turbulence.
Patent No. 2,689,646—Fluid Flotation
Separator and Method for Sep-
arating Pulverized Materials—
(September 21, 1954)
This device relates to a method for
separating fines from pulverized ma-
113
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114 APPENDIX C
terials using gas flotation. Problems
with previous state-of-the-art are
reported to be (1) difficulty in dis-
lodging and rendering buoyant an ef-
ficient quantity of fines, which are
distributed throughout the pulverized
material; and (2) a tendency of fines
to agglomerate and form heavy nod-
ules which are not rendered buoyant
and consequently not separated.
The new method involves conveying
a pulverized material over an inclined
porous surface at an appreciable
speed. A stream of gas under pressure
is passed through the porous surface
from below and then through the pul-
verized material. As the pulverized
material is conveyed over the porous
surface, small portions of the moving
material are agitated by the gas to
break down the nodules. Simultane-
ously, small portions of the material
adjacent to the upper surface of the
material stream are elevated above
the material and thereafter are per-
mitted to fall in a cascading effect
through the flotation gas flowing up-
wardly from the surface of the mate-
rial stream. The fine particles of ma-
terial in the cascading portion are
rendered buoyant and become en-
trained in the flotation gas. The agi-
tation and elevation of the pulverized
material are produced by several de-
flector members positioned above the
porous plate. After the flotation gas
and the fine particles of material en-
trained therein have been conducted
to a collector, the velocity of the flota-
tion gas is reduced to permit the fine
particles of material to settle and be
collected.
Patent No. 2,689,648—Separation of
Metallic from Nonmetallic Parti-
cles—(September 21,1954)
This invention provides a method
for separating metallic from non-
metallic particles. The method is based
on the phenomena that nonmetallic
particles may become electrostatically
charged and thereby caused to react
to forces created by an electrostatic
field. The mixture to be separated is
transported along a horizontal plane
by means of a conveyor through an
electrostatic field of alternating po-
tential. Alternating forces created by
this field impart sufficient vibration to
the nonmetallic particles resulting in a
stratification and concentration of
metallic particles which do not so re-
spond. Separation of the resultant
layers of the two types of particles
is accomplished mechanically. This
device is an extension of long-estab-
lished minerals-beneficiation technol-
ogy whereby stratification and con-
centration of ores is accomplished by
vibratory means alone. Performance
data and feed requirements are not
outlined in the patent, although it is
expected that small particle size and
low moisture content would be essen-
tial. Potential applications to solid
waste recovery are judged to be mini-
mal and would probably be limited to
the removal of nonferrous metals from
other nonmetallic components. The
cleaning of compost may be one such
potential application.
Patent No. 2,707,554—Grain Separa-
tors—Way 3,1955)
This invention is claimed to be an
improved machine for the removal of
weed seeds from cereal grains (wheat,
oats, barley, rye, etc.). The device is
also claimed to segregate various
grains from one another. The device
provides a three-stage separation em-
ploying in combination a variable
transverse diameter-dividing assem-
bly, a weight-dividing (specific grav-
ity) assembly, 'and a selective length-
dividing assembly operating on a given
mass of grain in the order listed above.
Width separation is accomplished by
one or more cylindrical screens with
adjustable circumferential longitu-
dinal openings which permit the divi-
sion of the mixture into two fractions
according to transverse diameter.
Density separation is accomplished by
classification in an air separator.
Length separation is accomplished by
means of a complex arrangement of
rotating disks, the operation of which
is difficult to describe in narrative
form.
Patent No. 2,806,600—Separator for
Separating Granular Poultry
Feed from Poultry Bedding—
(September 17, 1957)
This device is a very simple applica-
tion of screening and consists es-
sentially of a perforated cylinder
mounted to rotate about a horizontal
axis. Immediately below the cylindri-
cal screen in a semicircular trough. A
means is provided to deliver feed con-
taminated with bedding material to
the rotating and tumbling screen; for
collecting, in the trough, clean feed
passing through the screen; and for
collecting and discharging from the
screen the bedding material separated
from the mixture.
Patent No. 2,820,705—Method of
Recovering Metals from Non-
ferrous Metallurgical Slags—
(January 21, 1958)
Generally stated, the process is de-
signed for recovering metals from
nonferrous metallurgical slags con-
taining reducible compounds of the
metals and involves establishing a re-
duction zone in a furnace containing
a matrix of carbon or other reducing
materials for the reducible com-
pounds. This zone is maintained at a
temperature between the melting
point of the slag and 1450 C. Also, an
atmosphere of carbon monoxide and
carbon dioxide is established in such
proportions that log CO/Co2 is,
broadly, from —4 to +2.
The molten slag is contacted with
the reducing material in the re-
duction zone by percolating it down-
wardly. This requires but a few
seconds. However, during this short
time under the conditions present in
the reduction zone, the. reducible
compounds of the valuable metals to
be recovered are converted to the free
metals, while the iron content of the
slag is substantially unaffected.
Accordingly, there is produced a
treated slag product which contains
the valuable metals in the reduced or
free state. The treated slag contain-
ing these metals is then withdrawn
from the reduction zone almost im-
mediately, to prevent reduction of
any iron compounds which might be
present and concomitant contamina-
tion of the desired metal products.
The treated slag then may be proc-
essed for separation of the metal frac-
tion from the residual slag.
Potential applications in solid waste
processing would relate to the recov-
ery of high-temperature incinerator
slags.
Patent No. 2,868,376—Heavy Media
Separator—(January 13, 1959)
This device is an adaptation or
modification of a spiral classifier. In
general, classifiers of this type con-
sist of a tank having an inclined bot-
tom, an overflow for fines or "float,"
an elevated discharge for the "sink"
or coarse rake products, and a spiral
conveyor for agitating the pulp and
raking the sink out of the tank. Three
classifiers are used to separate a mass
of grains of mixed sizes and/or dif-
ferent specific gravities into various
grades or sizes.
This patent claims a modification of
the spiral classifier to utilize heavy
media, which in turn permits the seg-
regation of mineral ores into a sink
fraction, a middling fraction, and a
float fraction. This device appears to
be very similar to units manufactured
by Denver Equipment Company and
discussed in an earlier section of this
report.
-------
Patent No. 2,986,277—Method and
Means for Treating and Sort-
ing Comminuted Substances—
(May 30, 1961)
The invention relates to an appa-
ratus for sorting comminuted par-
ticles on the basis of density, by
means of a whirling motion. However,
unlike a cyclone where particles move
concurrently with air flow, this inven-
tion provides for a portion of the par-
ticles to move counter to the flowing
gases.
The device is adaptable to particle
size ranges on the order of 50 microns,
and so would have extremely limited
application for solid waste recovery.
Patent No. 3,064,806—Apparatus for
Wet Sizing of Solid Materials—
(November 20, 1962)
This invention relates to a means
for wet sizing of finely ground (35-
200 mesh) solid particles. The process
combines hydraulic classification and
wet screening and is claimed to be su-
perior to either technique used alone.
The invention consists of a stationary
container equipped with an impeller
to impart rotary motion to the mixed
slurry, which is fed constantly to the
unit; an inclined screen; and means
for directing the upper portion of the
slurry against the screen. Coarser ma-
terials are retained in the container
and are removed after settling. Finer
particles passing the screen are col-
lected along with the overflow as a
separate product. Because of the small
particle sizes, direct application to
solid waste processing will probably be
extremely limited.
Patent No. 3,127,016—Sorting of Ar-
ticles—(March 31, 1964)
This device employs the mechanics
of partially elastic collision to effect
separation. Particles or articles to be
sorted are impinged one by one onto a
stationary target element of desired
elastic properties. Elastic properties of
the colliding materials determine the
amount of energy transfer and, hence
the subsequent movement of the im-
pinged particle. Provision is made to
Appendix C 115
sort the particles into two fractions,
depending on whether or not the re-
sulting trajectory deflects the particles
a certain degree.
Patent No. 3,327,857—Object Count-
ing and Discrimnating Device—
(June 27, 1967)
This device is designed to auto-
matically sort broken tablets from
whole tablets, although extension of
the principles involved to other appli-
cations is possible. A method is pro-
vided for comparing by photometric
means every tablet to be sorted with
a standard, i.e., integral tablet. Tab-
lets which are smaller than the stand-
ard, because of being broken or other
defects, are rejected. Those which
compare favorably to the standard
are retained. It is claimed that, with
modification, the basic invention may
be constructed to distinguish shape,
color, or other physical characteris-
tics. Operating principles are very
similar to the Sortex optical separator
discussed in a previous section.
-------
-------
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72-2-0019S
U.S. GOVERNMENT PRINTING OFFICE: 1972 O—456-796
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