EPA/530/SW-140
MARCH 1975
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SOLID WASTE SHREDDING
and
SHREDDER SELECTION
This report (SW-140), which updates the Midwest Research
Institute 1972 contract report on this subject,
was prepared by Harvey W. Rogers and Steven J. Hitte,
Office of Solid Waste Management Programs
U.S. ENVIRONMENTAL PROTECTION AGENCY
November 1974
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Table of Contents
Preface v
Acknowledgment vi
Conclusions vii
Chapter I Introduction 1
Chapter II Size Reduction of Municipal Solid Waste 2
Chapter III Shredder Types and Power Requirements 7
Chapter IV Ancillary Provisions and Equipment 21
Chapter V Operating Considerations and Problems 31
Chapter VI Shredder Selection Criteria 37
Appendices
I. List of Shredder Installations 44
II. EPA Position Paper on Landfill ing of Shredded 46
Solid Waste
III. St. Louis Shredder Specification Example 51
IV- New Orleans Shredder Specification Example 72
List of Figures
Figure
1 Diagram of a Horizontal Hammermill 9
2 Cross Sectional View of the Swinq Hammer Type Rotor 10
3 Types of Hammers Used on Hammermills 12
4 Sizes and Shapes of Grate Bars 13
5 Common Types of Drive Motor Systems 15
11
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Figure
6 Block Diagram Flow Chart of a Size Reduction Facility 22
7 Example of a Size Reduction Facility Layout 23
8 Layout of a Size Reduction Facility With a Vibratory Feeder 27
9 Example of a Shredder Decision Matrix 43
List of Tables
Table
1 Solid Waste Categories for Shredding 17
2 Suggested Minimum Shredding Horsepower 18
3 Actual Size Reduction Installations 19
IV
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Preface
Within the past several years, one solid waste unit process
has seen an outstanding growth pattern. That unit process is solid
waste shredding.* In recognition of future potential importance
of this process, the Office of Solid Waste Management Programs con-
tracted with the Midwest Research Institute in 1972, to study
and report on the state-of-the-art of solid waste shredding and
develop an evaluation and comparison procedure for those considering
the purchase of shredding equipment. Since the completion of this
effort in January 1973, there have been unforeseen developments which
already outdate portions of the original final report. The purpose
of this document is to update the MRI document to reflect the latest
developments in this rapidly emerging field, as well as to compile
a comprehensive listing of those objective and subjective factors
which should go into the decision-making process for shredder selection.
Portions of the original MRI report have been deleted because
new data has tended to make obsolete some of the original material.
Also, the original version contained a decision-making algorithm
which has been omitted in this version. The decision-making
factors from that algorithm, however, have been included and expanded
in this document to acquaint the decision maker with the criteria
that should impact the shredder selection.
Because the field of shredding continues to evolve in technology
and application, OSWMP plans to periodically update this document as
the need arises and new data is brought to light. If the reader is
aware of significant developments not contained in this document,
this office would welcome being informed of such developments.
Since the MRI report has been completed, very little additional
documentation concerning solid waste shredding has emerged; consequently,
the evolution of this report has been based primarily on actual site
observations and discussions with shredder plant operators, consultants,
shredder manufacturers and others knowledgable in the area of shredding.
* Shredding is the-term recommended by Waste Equipment Manufacturer
Institute (WEMI) for the mechanical process of solid waste size
reduction and supersedes such terms as milling and grinding.
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Acknowledgment
Sincere appreciation is extended to the many people who reviewed
the original Midwest Research Institute's version of this report
and provided responsible suggestions for its revision.
Special recognition is warranted for the following groups and
individuals for volunteering exceptional effort in helping to make
this document as current and factual as possible.
in alphabetical order were: (1) Harvey Alter and
of the National Center for Resource Recovery, (2)
City of Madison, Wisconsin, (3) Harvey D. Funk of
Durham and Richardson, Inc., Omaha, Nebraska, and
Subcommittee of the Waste Equipment Manufacturers
the National Solid Waste Management Association.
are:
a. Allis Chalmers
b. Carborundum Company
c. Hammermills, Inc.
d. The Heil Company
e. Jeffrey Manufacturing Company
f. Newell Manufacturing Company
g. Saturn Manufacturing Company
h. Williams Patent Crusher
The contributors
Kenneth L. Woodruff
Gary Boley,
Henningson,
(4) Shredder
Institute of
These members
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CONCLUSIONS
The following paragraphs present a summary of the major
conclusions of this effort:
1. Size Reduction of municipal solid waste is an emerging
technology. There is, as yet, no comprehensive assembled body of
knowledge on the planning, design and fabrication of facilities and
equipment, or on the economics of purchasing and operating a facility,
although much work has been done by consultants in this area and
knowledge is emerging. Most manufacturers firmly believe that sales
of size reduction equipment for application in solid waste systems
will significantly increase in the next five years.
2. A major application of size reduction is in land
disposal systems. Size reduction is especially suited to land disposal
operations because it increases site life, reduces odors, blowing,
and strewing, eliminates voids and reduces vermin infestation, and
reduces the need for daily soil cover.
3. The future major application of solid waste size
reduction is in resource recovery systems. Size reduction produces
a manageable range of particle sizes, increases homogeneity, and
reduces the bulk of solid waste. All of these factors are necessary
for efficient operation of many of the currently proposed resource
recovery systems.
4. There are 11 basic types of size reduction equipment
and many of them can theoretically be used for shredding of solid waste,
However, only three types—the hammermill, the grinder, and the
wet pulper—are considered practical.
5. Hammermills and grinders are the principle type of
solid waste size reduction machines now being used or considered for
future installations in the United States.
6. The wet pulper is not usually considered a primary
machine for size reduction of solid waste. Although one installation
is in operation in the United States, most wet pulper installations
now being studied or proposed also include a shredder ahead of the
pulper.
7. Hammermills are either vertical or horizontal shaft
type designs. There are distinct differences in their technical
performance. Grinders are vertical shaft type designs.
VII
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8. Limited technical performance data for shredders
used in solid waste size reduction are available. Some equipment
manufacturers possess data on the performance of their machines,
but consider the data proprietary and confidential.
9. Economic performance data for shredders used in solid
waste size reduction are available but unreliable. The data are
usually reported in dollars per ton of waste and are not itemized
in categories, such as capital investment, amortization, power,
labor costs, and maintenance costs. Variations in the data are
often due to bookkeeping practices, management practices, and
inaccuracies in data collection techniques. EPA is currently
publishing a document to aid shredder operators in categorizing
and collecting these costs.*
* Hitte, Steven J. An Accounting System for Solid Waste
Shredder, (in press). January 1975.
vm
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Chapter I
INTRODUCTION
A. Background
The Solid Waste Disposal Act of 1965 as amended has
concentrated considerable interest on the question of what to do
with the huge quantities of municipal solid waste generated in the
United States each year.* Recent activity has centered on the utilization
of this great quantity of material as a national resource. Thus,
emphasis in solid waste management has changed in recent years from
disposal to recovery, recycling, or reuse. Many systems for the
recovery and reuse of solid waste require that the waste components
be physically separated from each other and that a reduction in
the particle size of the waste precede recovery operations. Even
in those geographic areas where disposal will continue to be the
only economic solution to the solid waste problem, size reduction
may increase the efficiency and life of the disposal system.
Size reduction is an operation that is common to many
solid waste management systems—reuse, recovery* or disposal. It
is also an operation that can be accomplished with off-the-shelf
commercially available equipment. This report presents the results
of a study to develop a rational procedure for the comparison and
evaluation of size reduction equipment.
B. Objective of the Study
The objective of this report is to provide a state-of-the-art
report describing shredder technology. This report is intended for
use by administrative personnel (or other equipment purchasers
without technical backgrounds) as an aid in the comparison, evalua-
tion, and selection of shredding equipment. A secondary objective
is to illustrate a method of organizing data for shredder selection.
* The Solia Waste Disposal Act; Title II of Public Law
89-272, 89th Cong. S.306, Oct. 20, 1965. '-'ashinqton, U.S.
Government Printing Office, 1966. 5 p.
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CHAPTER II
SIZE REDUCTION OF MUNICIPAL SOLID WASTE
A. Introduction
Size reduction is defined as operations or processes which
reduce the size of influent materials through division into two or more
subunits. For the purpose of this report, only size reduction by the
application of mechanical forces is considered. Size reduction of
municipal solid wastes (often called shredding, grinding, or pulverizing)
is a new concept, and much of the technology has been borrowed from the
mining and rock-crushing industry.* Because solid waste is a
heterogeneous mixture'(unlike rock), much of the technology is not directly
transferable; and size reduction of solid waste has not,always been
efficient; however, as more solid waste systems have been built,
the technology of solid waste size reduction has been significantly
advanced. (See Appendix 1 for a current state-by-state listing of
shredding facilities.)
B. Reasons for Size Reduction in Solid Haste Management
More than 125 million tons of municipal solid waste are
produced annually in the United States. Land areas suitable for
land disposal near urban areas where the bulk of the solid waste is
generated are becoming scarce and expensive. Open burning and open
dumping have been outlawed in many areas because of pollution and health
hazards. Incineration is becoming,increasingly more expensive because
of sophisticated pollution control equipment required to meet acceptable
air and water quality standards. Current emphasis in solid waste
management, therefore, has centered on both disposal of this great
quantity of material and its utilization as a national resource.
Because the quantities of solid waste produced each year are so great,
the relatively high capital costs of mechanical processing equipment
can be amortized over large tonnages, and consequently the cost of
processes such as shredding have become competitive with other
solid waste management options. This in turn has permitted shredding
to become an integral part of disposal and resource recovery systems
as will be explained in the following sections.
. * Waste Equipment Manufacturers Institute defines
equipment as "a mechamcal device used to break un solid
recoverable materials into smaller pieces." WEMI has desinnafprl
the term "shredder" to cover all such equipment that fulf lls
this definition. Shredding and size reduction can be considered
synonomous for purpose of this renort. wjnsiaerea
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C. Shredding as an Integral Part of a Disposal System
Municipal solid waste generally has a low, but nonuniform bulk
density. Size reduction increases the homogeneity and the bulk density.
The process of size reduction yields a smaller range of particle sizes
and thoroughly mixes the solid waste. The net result is that the waste
can be easily compacted to a uniform density, and voids formed by
bulky items are eliminated. The amount of reduction in bulk can vary
depending on the final processing of the waste; however, landfill
measurements have indicated that shredded waste placed in a landfill
and compacted in a manner similar to unshredded waste can have
the effective density increased 25 to 60 percent over that of unshredded
solid waste, depending on whether or not dailv cover is reqin>eH.*+
It is the bulk reduction and mixing of the waste that gives
size reduction its most promising potential for immediate application
in land disposal technology. Solid waste that has been shredded and
compacted has fewer voids than unshredded waste, has no objectionable
odor when properly compacted, does not attract vermin, and has been
used in landfill without a daily cover of soil. It is because of
these advantages that a milled solid waste disposal site tends to
be more saleable to the general public than a standard land disposal site
Shredding can also fit into another disposal system
variation, and that is, land disposal preceded by incineration.
Shredders are sometimes used to reduce bulky wastes so that they
may be fed into the incinerator combustion chamber and processed
along with the nonshredded waste. Additionally, there are new
incinerator combustion chamber designs, such as fluidized beds,
spreader stokers, and suspension burners, that require shredded solid
waste for certain feed characteristics, as well as, rapid combustion
characteristics.
Shredding has also been used in conjunction with solid waste
baling as in the San Diego, California, solid waste baling demonstration
project funded by EPA. The bales were found to maintain relatively
high density, after wire tying, with a relatively low compactive
-*Effective density = Weight refuse/(Volume refuse + volume
cover in landfill).
+Reinhard, J. J., and R. K. Ham. Solid waste milling and
disposal on land without cover. U.S. Environmental Protection
Agency, 1974. 2 v. (Distributed by National Technical Information
Service, Springfield, Va., as PB-234 930—PB-234 931.)
*EPA position on landfill of shredded solid waste can be
found in the Appendix II.
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effort as compared to a scrap metal type baler using nonprocessed
waste and no wire tying.* Should market conditions warrant,
fractions of the shredded waste (e.g. light combustibles, ferrous
material, etc.) can be separated out prior to baling for disposal.
D. Shredding as an Integral Part of a Resource Recovery System
As was indicated in the preceding paragraph, solid waste
disposal and resource recovery are neither mutually exclusive, nor
independent. An increasing number of communities are looking to
resource recovery to serve not only as a means of conservinn
resources, but also as a means of reducing the volume of solid waste
for disposal. Shredding is a processing step that serves both
resource recovery and disposal.
There are basically two forms of resource recovery being
instituted in communities today. The first form is recovery of materials
such as glass, paper or metals. The other is recovery of energy such
as by pyrolysis (heating with limited oxygen to produce chemical
by-products with fuel value) or by direct combustion of the light
combustible portion of solid waste in power plant boilers along with
fossil fuel. Many variations of both forms of resource recovery are
facilitated by or directly require shredded solid waste as an input
material. The reasons for this are:
1. Ease of handling: Compared to nonprocessed solid waste,
shredded solid waste has a smaller range of particle size, is more uniform
in density, and is a more homogeneous mixture, thus permitting it to
be easily handled and processed by mechanical equioment. The mechanical
and chemical processes used by most recovery systems require separation
of various components. This senaration is easier and more efficient
when particle size range is controlled. Sorting operations such as
screening, air classification and magnetic separation can be optimized
with respect to power requirements and efficiency of separation by shredding
waste to designated particle size ranges. Shredding should he con-
sidered a "service" component of the system--!.e., it does not
determine what the operating oarameters of the system are; it simply
adjusts the physical characteristics of the solid waste to optimize
efficiency of the system.
* Baling Solid Waste to Conserve Sanitary Landfill Space
San Diego California. Office of Solid Waste Management Programs,
1J74. (Unpublished report, Grant No. G06-EC-00061.)
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2. Improved burning characteristics: For energy recovery
systems such as the one employed by the Union Electric facility in
St. Louis, Missouri, shredding serves a twofold purpose. As stated
above, it improves handling and separation characteristics for sorting
into a light, fuel fraction and a heavy, chiefly inorganic fraction.
The heavy fraction, in turn, can be further separated into ferrous,
nonferrous metals, and glass fractions. The light, fuel fraction of
shredded material is amenable to pneumatic feeding of the tangentially
coal fired boilers employed by Union Electric. Once inside the boiler,
the solid waste particles are burned in suspension. Because these
particles are relatively small (typically 1.5 inches or smaller),
the chances of complete combustion of the waste are enhanced for the
relatively short time that the waste is in suspension. Similarly,
for some forms of heat recovery incinerators, such as fluidized
bed furnaces, or spreader stoker furnaces, small particle sizes
can increase the surface area of the solid waste for better heat
transfer characteristics. It should be pointed out, however, that
for many standard grate incinerators shredded waste is actually
detrimental to complete combustion, because too dense a fuel bed
is formed to allow for complete combustion and mixing with process
air.
E. Particle Size Specification
Output particle size is normally specified in terms of
the "nominal" particle size produced by a shredder. The nominal
particle size is usually designated as a minimum percentage by
weight of waste passing a given screen size, such as 80 or 90 percent
passing a three inch square mesh screen.
The single, most important step in designing a solid waste
size reduction facility is to determine what functions the facility
is expected to perform in the solid waste management system. This
involves determining what input the shredder will receive and what
output it is expected to deliver. Of the two—input and output—an
exact definition of the output requirements is the more critical,
for the output requirements determine the performance specifications
of the size reduction facility—capacity in tons per hour, output
particle size, composition, etc. The output particle size required
will depend on what the next step in the solid waste management system
is to be. For instance, if land disposal is the next step, a nominal
particle size of three or four inches might be specified as the required
output of the shredder. For the derivation of solid waste fuel for
power plant application, a nominal particle size of 1.5 inches might
be specified. For such an application,multi-stage shredding might
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be warranted, that is,the first stage shredding would produce a
nominal particle size of four inches for the purpose of Reparation
into a heavy fraction and a light fuel fraction. This light fuel
fraction would in turn go through a second stage shredder with an^
output nominal particle size of 1.5 inches for feeding into a boiler.
This multi-stage shredding would yield an overall shredding power and
maintenance savings by not reducing the heavy fraction smaller than
necessary. Similarly, other solid waste management systems will
define particle size requirements where shredding is to be used.
These particle size requirements should be carefully noted to avoid
too coarse a shred which could adversely affect the remainder of the
system or to avoid too fine of a shred which could adversely affect
the system and unnecessarily increase power, maintenance and other
operating costs.
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CHAPTER III
TYPES OF SHREDDING EQUIPMENT AND POWER REQUIREMENTS
There are 11 basic types of size reduction equipment
commercially available—crushers, cage disintegrators, shears,
shredders, grinders, cutters and chippers, rasp mills, drum pulverizers,
disk mills, wet pulpers, and hammermi11s. WEMI now designates all
of the pieces of equipment under the general term "shredder" with
the exception of wet pulpers. To date, hammermiUs, grinders, and
wet pulpers have been used in the United States for the size reduction
of municipal solid waste. The other forms of shredders have seen
considerably less application for large scale municipal waste shredding
and consequently will not be discussed further. *
A. Uet pulpers
A wet pulper is similar in design and operation to a common
household blender. In operation, a slurry of about 90 percent
water and 10 percent solid waste is placed in the pulper. The
interior of the pulper may be lined with protruding hardened impact
pins, but often the interior is a smooth surface. A central rotating
element (either a disk or a set of blades) spins at high speed
(peripheral speed of 5,000 ft/min) forming a vortex or whirlpool
in the slurry. Repeated impact of the solids with the rotating element
reduces the solid waste to a pulp. Unpulpable items, such as rubber
tires are ballistically rejected. Wet pulpers can operate as a
batch process or a continuous process. After pulping, the slurry
is removed from the pulper; and the majority of the water is removed
by squeezing and is reused.
Wet pulping as a means of solid waste reduction has had
limited application in the United States. To date, the operating
experience in this area has been limited to a plant in Franklin, Ohio,
funded partially under an EPA demonstration grant. The Franklin
plant is a small pilot plant having a capacity of six tons/hour.
Larger plants have been proposed; however, their plans may include
the use of a dry shredder ahead of the pulper to increase pulper
efficiency as well as reducing wear and damage to the pulper.
* Midwest Research Institute. Size reduction equipment for
municipal solid waste. Environmental Protection Publication SW-53c.
U.S. Environmental Protection Aqency, 1974. 126 p. (Distributed
by National Technical Information Service, Springfield, Va., as
PB 226 551.)
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The wet pulper and dry shredding system are not generally
interchangeable in application. The wet system requires extensive
auxiliary equipment for addition and removal of water and this
equipment is not needed for the dry system. Additionally, the wet
system is usually designated for a specific resource recovery
system such as fiber recovery, whereas dry shredders generally have
broader application. Because of its presently limited use, the wet
pulper will not be discussed further in this document.
B. Mammermills
A hammermill is a common type of equipment currently used
for size reduction of solid waste. A hammermill consists of a
central rotor or shaft with radial arms (hammers) protruding from
the rotor circumference. The rotor is enclosed in a heavy duty
housing, which may be lined with abrasion resistant steel members. Some
hammermills may also have stationary breaker plates or cutter bars
mounted inside the housing. Input material is reduced in size by
impact, attrition, and shearing forces induced by the hammers.
There are two basic types of hammermills--the horizontal
shaft type and vertical shaft type. The horizontal shaft hammermill
is the more common type (Figure 1). As the name implies, the rotor
or shaft is horizontal and supported on each end. Input is usually
at the top and material flows through the machine assisted by gravity.
Force feed at the side of the hammermill has also been used for solid
waste shredding. Most horizontal hammermills have a grate placed
across the output opening. Input material cannot pass through
this grate until it has been sufficiently reduced in size in at least
two dimensions. Output particle size is controlled primarily by
the size of openings in the grate. Some manufacturers also offer
reversible rotor horizontal hammermills.
The vertical shaft hammermills have the rotor placed in
a vertical position. The input material moves parallel to the shaft
axis and flow is assisted by gravity. The lower shaft bearing must
be a thrust bearing; that is, a bearing capable of supporting the
weight of the rotor. The machines may have a decreasing clearance
between the hammer tips and the stationary housing from top to bottom,
thus effecting progressively finer size reduction as the material
moves through the machine.
There are two basic variations of both the vertical or horizontal
shaft hammermills--the swing hammer type and the rigid hammer type.
The swing hammer type is the most common in solid waste processing and
has hammers mounted on pins and free to pivot (Figure 2). The
swing hammer concept reduces damage to the machine when it encounters
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INLET
MOTOR
INTAKE HOPPER
HEAVY DUTY HOUSING
CONVEYOR
10TPHTO 150TPH
Figure 1. Diagram of a horizontal
the various components. Source: Funk,
and Richard&on, Inc. Unpublished data,
hammermill identifying
H. D. Henningston, Durham,
1974.
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HAMMER
C SHAFT
HAMMER PIN
--
/
/
/
/
/
/ •
/,
>
LEI\
/
' 1.
__
IGTH40TO120 INCHES
1
t CIRCLE
HAMMEF
\
DIA 36" TO 96" " |
TOP VIEW - HORIZONTAL ROTOR
HAMMER
HAMMER PIN
SHAFT
ROTOR SPEED
400 TO 1200 RPM
TIP SPEED
12,000 TO 14,000 FEET PER MINUTE
END VIEW - HORIZONTAL ROTOR
Figure 2. Cross sectional views of the swing hammer type
rotor showing Its dimensions and rotation speeds. Source: Funk, H. D,
Henningson, Durham, and Richardson, Inc. Unpublished data, 1974
10
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a very hard piece of input material. However, the hammers can create
a severe imbalance problem if they become entangled with the input
material and are not allowed to swing freely. The rigid hamraer
type is more typical of smaller sized machines not specifically
designed for solid waste. For both the fixed- and rigid-hammer types,
hammer shapes vary from sharp choppers to blunt rectangular beaters.
(Figure 3). The latter are often used in machines for processing
solid waste materials.
C. Grinders
Another common type of equipment currently used for size
reduction of solid waste is the vertical shaft grinder. This machine
uses rolling star wheels, which look much like heavy gears or cog
wheels, protruding from the rotor circumference,which grind the
refuse by rolling it between the wheels and the housing side walls.
The material flows through the machine assisted by gravity.
D. Methods of Controlling Ouput Particle Size
As was mentioned in the preceding chapter, output particle
size is quite important to the effectiveness of the next step of the
solid waste management system, whether it be resource recovery or
disposal or a combination of the two. Once the particle
size requirements have been determined, the shredding system
must be capable of producing an output particle size to meet those
requirements. Each of the shredders described above have particle
size control provisions which will be briefly described.
1. Horizontal shaft iiammermill: This type of shredder
has a system of grates on the bottom or output side of the shredder
housing (Figure 4). The grate openings are usually rectangular in
shape, and by varying the size of these openings, the nominal particle
size may be controlled. Material cannot pass through the grates
until it is small enough in at least two dimensions to pass through
the grate openings. Minor changes in particle size occur with changes
of material feed rate, moisture content, and composition.
2. Vertical shaft hammermi11: This shredder has control
over particle size within the configuration of the shredder itself,
where the hammer tip distance to the housing wall is decreased from
the top to the bottom of the shredder. Average output particle size
has been found to change as the feed rate or material composition changes
11
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MULTIPLE EDGED
BLUNT EDGED
BELL
SHARP EDGED
2 EDGES
SHREDDER RING
SPLITTER
ROUND EDGED
4 EDGES
Figure 3. Types of hammers used on hammermills depicting their
shapes. The weight may vary from 15 to 500 pounds each. Source:
Funk, H. D. Henningston, Durham, and Richardson, Inc. Unpublished data, 1974.
12
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nnaaa
Dnnnaa
hDODCHZHDOOODDChDOCh
2X2 PANEL GRATE
n_-n
il
j lf '• \ : !
i"l n ]. d
x 14 PANEL GRATE
j I
fil H___
i i
^ - • . *• • ' * * • o •
1 H
in
1
H :-
1 i ^
i !! I
-•
H H H
! i ! i
»
h 'f
H
RECTANGULAR PANEL. GRATE
Figure 4. Sizes and shapes of grate bars located on the bottom
of the horizontal shaft hammermill. Source: Funk, H. D. Henningson,
Durham and Richardson, Inc. Unpublished data, 1974.
13
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and as the hammers and housing plates wear. Although this
factor would appear at first to be a disadvantage, for systems that
do not require accurate particle size control, it may be of minor
importance.
3. Vertical shaft grinder: This shredder uses an adjustable
choke ring plus internal arrangements to vary shredding clearances and
thus effect particle size control.
Besides the above provisions for particle size control,
other factors can effect the nominal output particle size. These
factors include wear of components within the shredder, moisture
content of solid waste, number of hammers used within the shredder,
and solid waste composition and feed rate.
E. Drive Motors (Figure 5)
Most size reduction equipment designed for shredding municipal
solid waste requires a main drive motor in the range of 200 to 1,500 hp.
The electric motor, such as the squirrel cage or wound rotor motor, is
the most common type of motor selected, although diesel drives and
steam turbines have been proposed and used for some installations.
Factors to consider in choosing a motor type include (1) type of power
available, (2) location of the facility; if remote, diesel power,
units may be more cost effective than having high capital cost of
providing adequate electrical service, (3) maintenance and dependability
characteristics of motor, (4) ability to handle surge requirements,
and (5) the overall operating cost efficiency of the motor which
relates to the above factors.
One procedure for connecting the drive motor to the
shredder is direct drive, i.e., the motor shaft is coupled directly
to the shredder rotor shaft. This procedure is generally the most
simple and least expensive connection method. Almost all
manufacturers of horizontal shaft hammermills recommend direct
drive. However, one manufacturer does use a belt drive from the
motor shaft to the rotor with a large flywheel mounted on the other
end of the rotor. There does not appear to be any significant
problems with the belt drive system, although it is slightly more complex
than the direct drive. The belt drive does allow some flexibility
in motor locations, and may be advantageous in locations where space
is at a premium.
14
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8EL.T DRIVE
DIRECT DRIVE
1=
i
M
•M
C J
t
M=
D
STEAM TURBINE
Figure 5. Common types of drive motor systems varying from
200 to 1,500 hp. The prime moves may be gas, steam, or electric.
Source: Funk, H. D. Henningson, Durham, and Richardson, Inc.
Unpublished data, 1974.
15
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The vertical shaft hammermills and grinders generally use
a gear or belt drive system. Direct coupling of the motor shaft
to the vertical rotor is not practical. Thus, for most vertical
shaft hammermills and grinders, the motor is located along side
the unit and a gear drive unit is utilized. One manufacturer uses
the gear box as an integral part of the shredder structure. Gear
units, depending on specific designs, will require additional support
equipment (such as lubricant pumps and temperature control devices;,
that are not required for direct or belt drives. They may also
increase the maintenance requirement of the shredder facility.
F. Motor_$i'ze Requirements^
The machine size and the power required for a solid waste
shredder are determined by the size and nature of the input material,
the processing rate (in tons per hour) desired, and the output
particle size required. The output particle size determines the
degree of size reduction and the minimum theoretical energy.
required. The size and nature of the input material determines the
minimum horsepower required to attain a level of performance
without frequent jams or damage to the machine. The processing
rate determines the physical size of the machine and the total
horsepower required.
The following paragraphs present general guidelines for the
selection of machine size and horsepower. The data presented in
these paragraphs were developed from analysis of existing solid
waste size reduction installations, contacts with shredder manufacturers
and users, and a review of the technical literature. The guidelines
necessarily represent averages and are therefore believed to be
conservative, i.e., use of the guidelines will yield specifications
for a shredder that are more than adequate for the desired performance.
(For listing of ongoing shredder installations see Appendix I.)
1. Input material: Determining the amount, size, and
nature of the input material is the first step in selecting a properly
sized shredder and motor.
a. Categories of solid waste: A characteristic
of solid waste is that it is of a mixture varying from automobiles
at one extreme to paper at the other. To simplify discussion of
the problem, three categories of solid waste have evolved from
common usage and are in general used throughout the industry.
The categories are shown in Table 1.
b. Municipal solid waste: Current per capita
solid waste production in the United States is about one ton/
year. Approximately 80% of this waste is medium waste and
about 20% is bulky waste. (Heavy waste has been excluded
16
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because it represents a form of waste that is generally not collected
and processed by government agencies and is not considered as a part
of municipal solid waste in the accepted understanding of the phrase.)
This 80% — 20% mixture can be expected to "show up" at th°
receiving area of a solid waste size reduction opera tfo~n "t'Ffat processe;
all municipal solid waste. This mixture will be referred to as
combined municipal solid waste. It is important to realize that
a size reduction facility may have to handle a significant variation
from this, "combined municipal solid waste mix," depending on
location; and seasonal fluctuations.
TABLE 1
SOLID WASTE CATEGORIES FOR SHREDDING*
Solid waste category Composition
Medium Packer truck wastes, such as—paper, cardboard,
bottles, cans, garbage, lawn trimmings,
small crating, small appliances, small
furniture, bicycles, tree trimmings, and
occasional auto tires.
Bulky Oversize and bulky items of the above plus—
stoves, refrigerators, washers, dryers,
doors, large furniture, springs, mattresses,
tree limbs, and truck tires.
Heavy Large and dense materials, all of the above
plus items such as—demolition rubble,
logs, stumps, and automobile parts.
* Midwest Research Institute. Size reduction equipment for
municipal solid waste. Environmental Protection Publication
SW-53c. U.S. EPA, 1974 p. 24. (Distributed by National Technical
Information Services, Springfield, Va., as PB 226 551.) Modified
because shredder manufacturers often desire that waste throughput
be specified only in terms of "normal" packer truck waste and
oversize bulky waste. Automobiles are usually handled separately.
17
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c. Minimum horsepower requirements: Experience
has indicated that there is a minimum horsepower that is required to
reliably and efficiently process municipal solid waste within a
reasonable time and with a minimum of trouble and delay. Of course,
this should be accomplished at a minimum net operating cost,
including capital cost, energy consumption, throughput at required
particle size and maintenance. The data shown in Table 2 represent
the suggested minimum shredder horsepower for each waste category.
These data are based on analysis of existing shredding operations.
It should be noted that 10 hp per ton/hour is often considered
to be a minimum power requirement. Some existing installations
approach this figure.
TABLE 2
SUGGESTED MINIMUM SHREDDING HORSEPOWER**
Category of waste Minimum horsepower1!1
Medium 200
Bulky 500
Heavy 1,000
Automobiles 1,500
* Source: Personal communication. Waste Equipment
Manufacturers Institute, NSWMA shredder subgroup, to H. W. Rogers,
Office of Solid Waste Management Programs, October 1974.
+ This table shown is a function of throughput, motor
type, particle size requirements etc. and should not be
considered as a rigid table. Shredder manufacturers can more
accurately determine the power needs for their equipment based
on particular user requirements.
£ Six inch nominal particle size.
2. Particle size: Very limited data are available on the
effects of particle size on power requirements. Some actual installation
power - particle size - throughput relationships are given in Table 3.
Generally, the nominal particle size of the output material directly
affects the power requirements of the shredder. The smaller the particle
size, the larger the motor that is required for a given capacity or
stated in other words, the capacity decreases for a given motor size
as particle size requirements become smaller in size.
18
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One other consideration must be made when considering the
power requirements for size reduction. The data indicate that power
requirements increase exponentially as particle size decreases. Thus,
for any given category of waste, there will be a particle size below
which it becomes more economical to use two stage size reduction
(i.e., a primary and secondary shredder operated in series) than to
use one large machine. Current practice in the industry indicates
that for the combined bulky and medium waste, the minimum particle
size economically feasible in single stage reduction is in the
range of two to four inches. However, there is almost no available
technical data (except manufacturers proprietary design data) on this
subject and no standard procedures have been developed. Each installation
must be examined individually, evaluating such factors as power costs,
wear, maintenance, labor costs, and capital investment.
3. Total throughput (tons per day and tons per hour): In
addition to the category of waste, the particle size, and the power
requirements, the total anticipated throughput must be known before
the shredder can be sized. In many instances, this is a trivial
question since the plant may be originally conceived and designed
for a certain capacity in tons oer day. This capacity is usually
based upon some input parameter (i.e., the tons per day is known
by previous collection data) or upon some output parameter (i.e.,
the size reduction plant is to supply shredded waste for a process
that requires a given tonnage per day).
TABLE 3
ACTUAL SIZE REDUCTION INSTALLATIONS*
City
Tens
per
hour
liorse
power
Rotor
speed
Discharge
opening
Honum.r
weight
No. of
h atone r*
Nominal
•Ire of
output
No. of
•hreddtr
unit*
A
B
c
D
E
F
G
H
35-75
40-50
20-25
8-17
15-25
22
100
40-50
1250
500
500
200
200
900
1000
900
900
850
1250
1350
1350
900
369
2k x 3<<
6'i x 11
box-type
15! m.
10 x 18
6 x 72
200 lb» 30
100 Ibs
96 Ibs
16 Ibs
14 Ibs
It Ibs
120 Ibs
22
33
6* Ibl.t 60"r
IV
3 "
5
3 "
3 "
3 f
I "
3 "
1
1
1
1
1
1
4+
1
* Courtesy of the Nation*! Crater for F««ourc« Meovny.
•f 4 unltl represent t«o llnee of tvo lt«f* ehreddlnf.
+ King grinders.
It is also necessary to establish the required capacity
of the machine in terms of tons per,hour. This requires an analysis
of such factors as number of operating days per week, number of shifts
per day and number of hours per shift, as well as, the working
schedules of the collection crews. There are several points that
must be considered when calculating capacity requirements of a
shredder: (1) twenty-four hours per day operation is not practical
19
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because of maintenance and downtime provisions which are both necessary
and unavoidable for shredding equipment, (2) there is a time lag
between the collection of waste and its delivery to the size reduction
facility. In order to provide multi-shift operation of the shredders,
increased storage provisions may be necessary, and (3) there are
practical limits on the capacity of a single processing line or
facility. These factors will be discussed in more detail in the
chapter entitled, "Operating Considerations."
4. Total horsepower: After considerations on waste
categories, particle size, power requirements, and macrnne
capacity have been determined, total machine horsepower is simply
the product of capacity in tons per hour and unit power required in
horsepower hours per ton. For example, a 50 ton/hour machine processing
waste with a unit power requirement of 20 hp hour/ton would need
a 1,000 hp motor.
20
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CHAPTER IV
ANCILLARY PROVISIONS AND EQUIPMENT
Thus far, the discussion of shredding equipment has centered
around the shredder and its accompanying motor. After sizing these
items, it is necessary to provide ancillary or support facilities
of compatible capacity to complete the size reduction facility.
These ancillary provisions can be grouped into two classifications:
1) those provisions that serve to store and handle the solid waste
and 2) those provisions that serve to make the shredding operation more
economically efficient, operationally efficient, safe, and environ-
mentally acceptable. The first classification will be discussed in
this chapter and the second will be incorporated into the following chapter
on operating considerations.
The functions of a typical facility are indicated in the block
diagram flow chart of Figure 6 and a facility layout is shown in
Figure 7. The installation includes the following basic operations:
1. Receiving and holding—receiving input waste, premixing,
sorting, separation of bulky items, temporary storage for processing;
2. Input conveying—material transfer, inspection,
sorting, separation;
3. Feed control—material flow rate control;
4. Size reduction—shredding of the solid waste;
(Chap. Ill)
5. Discharge conveying—material transfer, separation
of unwanted and marketable components; and further processing
6. Removal, storage or, disposition of shredded waste.
A. Receiving and Holding
The receiving and holding area of the size reduction facility
serves the function of accepting the input solid waste from the
collection system (usually packer trucks), and storing the
material prior to processing by the shredder. This function is
necessary because the input is usually in batches (i.e., individual
packer trucks) with varying quantities of waste at different times.
Maximum efficiency of the shredder usually requires continuous
feeding at a uniform rate. Thus, a buffer or temporary
21
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Input Receiving
and Holding
Input Conveying
And Feed Rate
Control
Size Reduction
' Pre-Mixing, .
1 Sorting,
J _Se_fia ration -I
i Sorting,
", Inspection,
Separation
_| Dust Control '
j _J
Discharge
Conveying
Sorting,
Inspect!on,
Separation
I.
J
Secondary
Size
Reduction
Dust Control
1 Discharge
1 Conveying
I
L
Sorting.
Inspection,
Separation
Storage/Removal
Figure 6. Block diagram flow chart of a size reduction
facility. The dashed lines indicate optional unit operation,
22
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Feed
Conveyor
System
Shredder
Receiving and Holding
Various Separation and Sorting Techniques
(Optional)
\
Di s charge
Conveyor
Figure 7. Example of a size reduction facility layout
identifying each operation.
23
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storage is needed between the waste collection and the shredding
operations. The number of shifts of operation will affect the
sizing of the receiving and holding area. It is quite important
that this portion of the facility be designed so that material can
be moved as needed into the input conveyor while at the same time
allowing collection vehicles to maneuver and unload with a minimum
of delay or confusion.
One procedure developed for receiving, holding, and handling
the solid waste material has been the open receiving pad. The
pad is simply an open, level and paved area adjacent to the waste
shredder. In some installations, the pad is enclosed so that operations
are not affected by inclement weather, and so that site aesthetics
can be maintained. Packer trucks deposit the waste on the pad at the
direction of an operator. The pad operator uses a bucket-equipped
hi-loader, or a typical front end loader, to pile and mix the waste,
and to place the waste on the input conveyor. The operator partially
controls the feed rate to the shredder by the amount of waste he
places on the conveyor. He can also increase the efficiency of the
shredder by distributing bulky and difficult-to-process items throughout
the waste. In some cases, the white goods (stoves, washers, etc.)
are not mixed but are processed together to effect a more efficient
magnetic separation where appropriate.
The open receiving pad has been proven to be a workable inout
system because it provides an easy and economical means of presorting
and mixing the input waste. Although municipal solid waste is
generally considered to be a heterogeneous material, it is not .a
thorough mixture as received, and it will contain occasional bulky
items, such as appliances or pieces of furniture. Also contained are
difficult-to-shred items such as tires, rolled-up rugs, tree
trunks, heavy metal pieces, etc. With an open receiving pad, the
operator can normally remove some of the items that he does not want
to enter the machine, distribute the remainder of the bulky items,
and mix the solid waste before feeding it to the shredder.
Other input receiving systems have also been used. One
frequently used procedure has been to have the packer trucks dis-
charge the waste directly into a feed hopper or storage bin. These
systems should be designed and operated to minimize bridging, or jams
and to assure uniform feeding from the storage pile. Another common
system is to discharge the waste from the packer trucks directly
onto the shredder input conveyor. This system subjects the input
conveyor to considerable abuse and causes uneven feeding of the
shredder—sometimes resulting in motor overloads, machine jammina and
shutdowns. The "push-pit" system has also been used as a method~of
shredder system feeding.
24
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In this system, the waste is discharged into a pit containing one
or more hydraulic rams which "push" the waste onto the incline
conveyor. Another receiving and handling method is the storage pit
and crane system where the waste is discharged into a large receiving
pit and loaded via crane onto the input or feed conveyor system.
This system can take advantage of existing storage and handling
provisions at incinerators that are being converted into shredding
facilities; however, this method of feeding can tend to result in
surge loadings.
B. Input Conveying
Input conveying consists of those components within the
facility which transfer the solid waste from the receiving and holding
area to the shredder. The conveying operations control material
flow rate will frequently consist of two or more conveyors--a
horizontal conveyor sometimes located in a pit that handles material
directly from the receiving pad, and an incline conveyor that transports
the material up and into the shredder.
1. Horizontal feed conveyors: Heavy duty metal pan-type
and piano hinge conveyors have proven to be a reliable type of input
conveyor. The horizontal conveyors receive considerable abuse,
mainly due to dropping and dumping of the solid waste onto the conveyor.
Operating life of flexible belt conveyors has, in general, not been
adequate in this application. Other conveyors such as vibratory
conveyors have also served in this capacity. The typical arrangement
places the conveyor in a horizontal position at the bottom of a
feed trench. The trench is often about five feet deep and has
vertical or diverging skirt boards reaching from the conveyor surface
up to the receiving pad. The solid waste is simply pushed from the
receiving pad onto the horizontal conveyors.
The horizontal conveyor often operates at a fixed speed,
and the waste feed rate to the shredder is adjusted by the depth of
waste the operator places in the trench. Several installations
have installed variable speed conveyors for additional feed control.
The horizontal conveyor should be electrically interlocked to the
incline conveyor; and they both should be electrically interlocked
to the shredder motor. These interlocks will stop the conveyors
if the shredder motor overloads. This gives the shredder an
opportunity to clear itself before receiving additional input that
could cause a jam.
25
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2. Incline conveyors: Flow into a shredder is generally
assisted by gravity. Therefore, it is necessary to raise the waste
to the feed opening of the shredder unless the shredder is located
in a pit rather than above grade. The incline conveyor may be a
flexible or rubber belt conveyor since this conveyor is not subject
to the same abuse that the horizontal conveyor receives, except
where significant amounts of oversized bulky waste is processed or
the belt would otherwise be subject to high impact or shock loading.
A common problem with some belt conveyors is the tendency of the
waste to slide back down the conveyor. This problem can be minimized
by using a shallow slope or a belt with a textured surface or with cleats
Another problem with rubber belt conveyors are that they cannot
take the abuse from the ricocheting waste if extended into the
shredder housing.
3. Sorting and separating: Some separation of the waste
can be done at the feed conveyor system. Separation at this point
is usually a protective measure designd to prevent undesirable
materials from entering the shredder. Due to the depth of material
on the conveyors, the presence of numerous closed bags and boxes,
and the tangled nature of the material before shredding, a thorough
separation is not practical. A metal detecting system can be used to
detect large pieces in the waste stream. However, the generally
accepted procedure is to visually monitor the feed conveyor and manually
remove any undesirable material.
C. Feed Control Techniques
Control of feed rate is probably the most important aspect
of daily operation of a size reduction facility. Feed control is of
major importance because it has a great affect upon the efficiency
and life of the shredder. It is also difficult to control the feed
rate accurately and reliably. Several techniques have been tried
with varying degrees of success. Some of the more common techniques
are discussed in the following paragraphs.
1. Oscillating and vibratory feeders: The vibratory
feeder has long been used in the ore and rockcrushing industry to
feed aggregate material of variable composition. It will agitate
the input and tend to distribute it evenly over the feeder surface.
It thus tends to "smooth out" variations in flow rate. A diagram of
a typical installation is shown in Figure 8. The vibratory feeder
is installed in the bottom of a trench with sloping sides. The
feeder is shorter than a normal input conveyor and can be fed from
three sides. The waste material is simply pushed off the pad and
onto the feeder which then feeds the inclined belt that raises the
solid waste to the shredder. Structural problems from the vibrations
can occur with this type of installation if there is inadequate
base support. »
26
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Trench with Vibrating
feeder in bottom
Shredder
Figure 8. Layout of a solid waste size reduction facility
utilizing a vibratory feeder.
27
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2. Leveling bars: Leveling bars, or "doctor" blades,
have been used with the feed conveyor system to control the depth
of waste on the conveyor. Often, these devices have not been successful
because of the tendency of the waste to jam, bridge, and hang up
on items caught on the bar or blade. One successful application has
a direct feed from the input conveyor to a shredder mounted in a pit.
A hydraulically operated blade is located over the input conveyor
just ahead of the shredder. An operator continuously monitors
the input and controls feed rate to the shredder by adjusting the
height of the blade. Minor jams at the blade are frequent, but
they are easily controlled by operator action.
3. Compression feeders: This device can be a crawler belt or
roller that compresses the input waste and literally "force feeds"
it into the machine. It usually has a hydraulic power drive with a
variable speed control. This device serves three functions:
a. It controls the rate of feed;
b. It physically holds the waste and slowly releases
it into the shredder thus minimizing severe surges and overloads to
the shredder. The waste is "nipped" off a little at a time as it
is being fed to the shredder.
c. It obstructs the input opening and reduces "backfire"
or ejection of material out the input opening.
D. Discharge Conveying
The discharge conveying elements of the shredding installation
serve the function of removing the processed waste from the shredder
and conveying it to a further processing or disposal area. There are
normally two elements to the discharge area; the discharge chute
or collector and the discharge conveyor.
1- Discharge chute: The material being discharged from
the shredder typically possesses considerable energy and moves at
high velocities. For horizontal shaft hammerrm'lls with bottom discharge,
a simple chute or deflection plate may be placed directly under
the discharge to absorb most of the energy from the waste. The waste
then slides down the chute or plate onto the discharge conveyor.
However, the waste can "stick" to the chute and cause a jam. To
avoid this potential problem, the chute or deflector plate can be
replaced by a vibrator conveyor. The vibratory conveyor can take
the_abuse and impacts from the discharged waste and still provide a
positive method of transporting the waste away from the shredder.
Steel apron and belt conveyors can also be used in this capacity.
28
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2. Discharge conveyor: The discharge conveyor transports
the waste from the discharge chute to further processing or disposal
operations. This conveyor is typically a flexible belt that moves
at a much faster speed than the input conveyor. A flexible belt
conveyor can be used in this application because the shredded waste
is relatively homogeneous and contains no bulky objects to subject
the conveyor to abnormal physical abuse. The conveyor moves at a
faster speed to assure that the discharge of the shredder is always
clear. The speed may cause displacement of the waste so conveyor
sides and covers are frequently used.
3. Further processing for resource recovery: If separation
or recovery of certain waste components is to be performed, it is
usually done at some location in the discharge conveyor system.
At this point, the waste has been shredded, has a narrow range of particle
size, should not be very deep on the conveyor, and has not been com-
pacted or compressed. A wide variety of separation devices including
magnetic, pneumatic, and vibratory may be employed. A discussion of
separation techniques is beyond the scope of this report.
E. Removal, Storage, and Disposal
The final operation of the size reduction facility is removal--
i.e., disposition or disposal of the shredded waste. Several removal
systems are now in use at various size reduction facilities in the
United States. The waste may be:
a. Directly conveyed (mechanically) to the next operation
in the solid waste management system; i.e. land disposal;
b. Loaded into transfer vehicles, either directly or
via stationary compactor, for bulk transport to the next operation; or
c. Placed in intermediate storage to await transfer
to the next operation.
Direct mechanical conveyance of the shredded waste to
the next operation is not frequently used. In fact, it is generally
only used when the next operation is landfill and the size reduction
facility is located at the landfill site. Even then, it is not
common because of the capital investment required for long conveyor
runs, and the fact that the waste will still have to be spread at
the conveyor end.
29
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Loading the shredded waste into transfer vehicles for bulk
transport to the next operation is a typical procedure, especially
in landfill systems. This procedure offers a direct cost savings
when the landfill is at a remote location. The size reduction
facility may be placed at a convenient location within the collection
system and serve as a shredding plant and a transfer station.
Placing the shredded waste in temporary storage prior to
transfer to the next operation is a common technique. The simple
reason for this is the difficulty of synchronizing operations at the
size reduction facility with the next operation in the system. Thus,
a storage or buffer zone is needed. However, problems can occur
in feeding the shredded waste out of the storage facility. The waste
is easily compacted, does not readily flow, bridges across openings
and is, in general, difficult to handle in bulk.
Provisions used for removing stored shredded waste including
live bottom bins, open pad storage, and bins with an arm installed
in the bottom, which "sweeps" material to a discharge opening.
30
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CHAPTER V
OPERATING CONSIDERATIONS
Once the shredder and motor have been selected and installed
along with complementary materials handling equipment the plant
would be, for all practical purposes, ready to operate. There are,
however, a number of additional considerations to make in designing
the plant to assure minimal downtime, employee safety, efficient plant
layout, good sanitation and so forth. This chapter discusses
some of these considerations.
A. Shredder Installation
Three concepts for physical location of the shredder are
in general use. They are: (1) below ground (in a pit); (2) at or
above ground level; and (3) on the side of a hill. All three concepts
have been used successfully and neither has a distinct advantage over
the others. Often, the choice of installation is det-finTn'nprl-by
site restrictions or topography rather than by technical or performance
factors.
Installation of the shredder at ground level is the simplest
and the most common type of installation. The shredder is usually
mounted on a concrete base and has easy access from all sides.
A drawback with this type of installation is that it requires
an inclined feed conveyor to lift the waste to the shredder input.
An approach to this problem is to put the input receiving pad
on the roof. The inclined conveyor would thus be eliminated and the
shredder feed would be directly from the input feed conveyor. This approach
has an obvious appeal for facilities located in congested urban areas
where space for a receiving pad is at a premium.
Installation of the shredder below ground level or in a
pit is a concept that has been used at several installations in order
to shorten input conveyor runs. Some reasons behind this choice
has been that noise is confined and plant personnel may be
protected from fires or explosions that may occur due to flammable
materials in the waste and also from flying debris from the shredder.
There is also the consideration that the inclined conveyor is moved
from the input to the output (to lift the waste out of the pit),
thus resulting in a minor cost savings because of the less complicated
equipment required for conveying the shredded waste. However, access
to the shredder for maintenance becomes limited. This can be accomp-
lished with an overhead crane or a yard crane.
31
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If the plant site has a hill or a pronounced slope, it
may be wise to install the unit on the side of the hill. The input
pad is then located at the top of the hill, and the discharge area
is located at the bottom. The incline conveyors are eliminated and
this concept has an obvious appeal in simplicity and equipment cost
savings; structural costs may be increased if the plant is to be
enclosed.
B. Power Assist Devices
Most manufacturers of shredders offer items that can aid
in the operation of the shredder. Any shredder that has a pressurized
bearing lubrication system can take advantage of the pressure producing
equipment to operate hydraulic power assist devices. Some manu-
facturers recommend a separate hydraulic power pac for these devices.
These devices include:
1. Hydraulically operated access doors: These items are
especially helpful on horizontal shaft hammermills where manufacturers
include these door openers as standard equipment for quick access to
the rotor and hammers.
2. Hammer pin extractors: These devices are used to
pull the hammer pivot pins from their mounting so that worn hammers
may be replaced. These devices are helpful as it is sometimes diffi-
cult to manually remove hammer pins after extensive use of the shredder.
3. External breaker and grate bar adjustments: Several
shredders have stationary breaker bars or cutter bars whose clearance
with the hammers can be adjusted from outside the shredder. Manual
adjusters are standard equipment, however, hydraulic adjusters are
available and have been well received by operators who have used them.
C. Motor Controls
In addition to the necessary motor switch gear, installation
of indicating and recording power meters, input and discharge conveyor
interlocks, as well as bearing and motor temperature interlocks are
typically included.
32
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Indicating ammeters are a standard item at most shredder
installations since observations of motor current draw is the
easiest way to determine overloads. The operator can watch the
ammeter and adjust the feed rate to obtain maximum efficiency
of the shredder. Many installations have warning devices connected
to the ammeter to signal the operator when overloads occur. Several
installations have recording amp or watt meters. These are not con-
sidered necessary and are only used when continuous records of power
consumption are desired. Such records can be quite useful in deter-
mining long-term motor power requirements and efficiencies.
Shredder motor interlocks to the input conveyor are becoming
the standard device for protecting the shredder and drive motor
from overloads. These devices stop the input conveyor when the
shredder drive motor overloads. This prevents further feeding of
material into the shredder, reduces the load, and gives the shredder
an opportunity to "clean out" a potential jam before it occurs.
Typical design is to have an automatic cutoff which stops the input
conveyor, with restart being manual or automatic, thereby requiring
operator attention to the cause of the stoppage. Many operators
of size reduction facilities consider the shredder motor conveyor
interlock the single, most important automatic control in the entire
facility. Even those installations not originally including the
interlock have now installed them because damage to the shredder and
motor has resulted from overfeeding.
The shredder bearing temperature sensor is another protective
device gaining wide acceptance. At most installations, it ils
designed to issue a warning if the shredder bearing overheats, and
will continue to give the warning until the temperature returns to the
safe range. The warning alerts the operator to stop the feed conveyor
thus reducing the load on the shredder (and bearings) until the
temperature drops. Some installations have included a bearing tempera-
ture interlock that will shut off the shredder and feed system if the
bearings continue to overheat or exceed a critical temperature.
D. Fire Control Systems
Due to the high percentage of flammable materials in municipal
solid wastes, fires in the shredder can occur. Normally, a fire can
be "snuffed out" by continued feeding of the shredder; however, fires
associated with jams or stoppages must be extinguished. Manually activated
carbon dioxide or water extinguisher systems are available., Additionally,
heat sensitive, or infrared detectors can be installed at the beginning
of the output conveyors. When a fire is visually detected in the input
conveyor, the shredder and the output conveyor can be immediately
stopped to keep from spreading the fire to other portions of the
facility.
33
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E. Dust Control Systems
Dust and small particle debris are a constant problem
around a solid waste shredder. Two techniques are used to control
and minimize the problem. The simplest is to use a continuous
water spray inside the shredder. Water reduces the amount of
dust generated and causes most debris to exit the shredder with the
discharge. However, water can accelerate leachate potentials for
landfills and decrease the apparent B.T.U. value of the combustibles.
Pneumatic dust collectors are the other form of dust
control technique used. Typically, they are used in systems where the
shredded waste is being used in an incinerator or boiler where addi-
tional water content is undesirable. The devices usually consist of
cyclones placed downstream of the shredder and are more efficient
than water sprays.
Litter control devices to minimize spillage of shredded
material consist of some form of cover, such as a wire mesh placed
over the output conveyors.
F. Explosion Provisions
It is almost inevitable in a shredder installation that
some potentially explosive materials will enter the facility. The
majority of these, such as aerosol cans, nearly empty gas cans
and so forth, may explode within the shredder with little or no
consequence. There are, however, some materials which may cause
extensive damage to the facility and more importantly cause danger
to the workers. Provisions such as separate, outdoor shredder place-
ment, special pressure relief devices and so forth, should be explored
to minimize explosion potentials. The manufacturers of shredding
equipment should be consulted for further information concerning these
provisions. Attempts should be made to screen input material, where
possible, to keep potentially explosive materials from entering the
shredder.
G. Other Operating Problems and Provisions
1. Shredding of difficult items: Because the horizontal
and vertical shaft hammermills have a restricted opening, they
may be subject to damage from difficult to process items. The
shredder will "try" to reduce the item to the output size or to
"extrude" it through the opening. Items such as heavy steel, rolled-uo
rugs, large tree limbs, etc., which require power inputs beyond the
capabilities of the machine, can cause jams. Thus, for these machines,
presorting of input material and separation of undesirable items is
recommended. Some mills have the capability of collecting unmillable
material so as not to damage the mill.
34-
-------
2. Hear rates: Some manufacturers of horizontal and
vertical hammermills offer reversible action for the hammer rotors.
After the hammers are well worn on one side, the rotor is operated
in the reverse direction so that the hammers wear on the other side;
purportedly reducing the frequency for manually reversina the hammers.
Most shredder operations provide routine maintenance for all
surfaces within the shredder subject to high wear rates. For instance,
some operations provide daily retipping of hammers and welding of other
wear surfaces. There are many alloys to choose from for hard surfacing,
and the decision must be made as to the correct balance between the cost
of weld material (expense increases as wear resistance increases) and
the cost of welding (labor), and downtime.
3. Scheduling of Operations: There is a time lag between
the collection of waste and its delivery to the size reduction
facility. The packer trucks start each day empty, as they do not
normally store waste overnight. It is not uncommon, therefore,
for the first packer truck to arrive at the size reduction facility
with a load of waste two to three hours after the start of working
hours. The last packer trucks may also arrive well before the
close of normal working hours to allow time for return to their
headquarters. Thus, all deliveries of waste to the size reduction
facility would be made in a five to six hour period. It is
common to schedule shredder operations beyond collection hours
to completely process all of the day's input. However, due to health
and safety hazards, unshredded waste is not usually left overnight
for processing the next morning. Common practice has been to schedule
the shredder to six to eight hours of operation a day, five days a week.
However, most of these operations have been small plants processing
150 to 500 tons/day and, consequently, have smaller capital investments.
As bigger and more expensive plants are designed and built (1,000 to
1,500 tons/day), the trend seems to be to a two-shift operation with
12 to 14 hour work periods each day.
General experience indicates that there is a practical
limit to the capacity of a single size reduction operation. A
capacity of 40 to 60 tons/hour has been the current operating limit
for reasonable conveying and feeding systems. The volume of material
represented by 40 to 60 tons/hour begins to present logistical problems
that may require subdividing the operation into two or more units if
larger capacities are desired. There have been, however, recent
specifications requiring 75 to 100 tons/hour to be processed through a
single line. Experience will determine the feasibility of material
handling of this high tonnage.
35
-------
Another consideration in the scheduling of operations concerns
the degree of redundancy or backup equipment desired to handle downtime
situations. The degree of redundancy needed should be carefully
analyzed to balance the cost of providing standby equipment versus the
cost of downtime. For some situations, the best solution might be to
have no backup processing lines, but rather to have a good inventory of
parts available for repairing the existing processing lines. It should
be remembered that for any solid waste management system, even with
resource recovery, a sanitary landfill must be available for nonprocessed
material, residuals after resource recovery and for standby when
processing facilities are down. It may be more cost effective to
occasionally use the sanitary landfill for all the waste than to have
one or more additional shredding lines. For resource recovery situa-
tions where the output must be supplied on a minimum tonnage per day
basis, extra processing equipment might be required.
4. General Maintenance Provisions: In addition to the
options heretofore mentioned concerning shredder maintenance, the
overall facility itself must be designed for ease of maintenance.
A fundamental principle to observe is to allow plenty of clearance
for any repair or replacement situation that is likely to arise. This
would include operations such as lifting out rotors, replacing motors
or pulling shafts used with conveyors. Provisions should be made for an
overhead crane, portable crane, or lifting device where necessary,
such as above the shredders.
In addition to providing adequate clearance for maintenance
and repair, the facility should be designed for good housekeeping
and sanitation. Surfaces, such as the receiving pad or storage
pit should be readily cleanable. The storage pit or conveyor pits
should have drains or sumps to remove liquids which might accumulate,
as well as water used in cleaning these areas. Routine cleanup
should be provided in areas of material spillage.
36
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CHAPTER VI
SHREDDER SELECTION EVALUATION CRITERIA
A. Introduction
This chapter explores some of the more salient factors or
criteria that should be addressed when specifying and/or selecting
shredding equipment. These factors are grouped into objective and
subjective categories depending on the degree of judgment used in
their evaluation. Objective considerations include such factors
as price, horsepower and rated throughput. Subjective factors
include criteria that do not have such distinct answers, for example,
actual or dependable capacity, and the degree of complexity of
the system. Subjective criteria should be judged in light of
actual field experience.
B. Objective Factors
Most of the data needed to evaluate objective factors can
be collected from shredder manufacturers. It will be up to the
decision-maker to determine the relative importance of each factor
for his particular situation.
1. Machine weight. This factor could affect construction
requirements (and therefore costs) with respect to
the foundation and its bearing capacity. Some believe
that machine weight is a good indicator of structural
strength and performance, although OSWMP staff has
seen no compilation of data to either support or refute
this contention.
2. Rotor weight and Rotor inertia. This information can
provide a measure of shredder's ability to handle
surge loads.
3. Machine size. This factor will have direct influence
on building structure size and cost. It could also
affect siting of the shredder and associated material
handling equipment within existing installations, such
as an incinerator, in accordance with existing clear-
ances and constraints.
4. Rate in tons/hour, a basic indicator of equipment
capacity as expressed by the manufacturer.
37
-------
5. Rate in tons/shift. This measure of capacity allows
for routine maintenance, startup, etc., and is a better
indicator of what can actually be processed over a shift.
6. Input and output locations. These can affect building
design and conveyor configuration.
7. Unique design features, as specified by manufacturer.
8. Horsepower, as specified by manufacturer. This will
affect operating and capital costs.
9. Availability of service policy.
10. Availability of field service.
11. Availability of spare parts. This factor can markedly
affect overall operating costs, effectiveness, and
dependability of operation.
12. Special installation requirements, as specified by
manufacturer.
13. Output particle size. This has direct bearing on power
requirements and possibly plant configuration where
multistage shredding is considered. Particle size
must also be considered in relation to the next pro-
cess, e.g., air classification.
14. Number of surfaces and configuration of the shredded
particles. This may affect resource recovery processes.
15. Control systems, which may have features to protect
against jams, motor overloads, etc.
16. Shipping and installation costs.
17. Total system cost, including conveyors.
18. Installation schedule.
19. Type of motor.
20. Performance bond.
21. Performance guarantee safety features.
22. Availability of fire/explosion control systems.
38
-------
23. Availability of noise, smoke, or odor control systems.
24. Availability of power assist devices.
25. Total enclosed space required, including that needed
for all support equipment and waste storage.
Much of the basis for evaluating the subjective factors
should come from actual equipment "track records", contacting
users of the equipment for data input, and site visits should be
made if possible. Since experience with certain aspects of solid
waste shredding technology is not yet extensive, unforeseen
problems may be brought to light by the users of various shredders.
In such instances, the manufacturer should be contacted to see
if any provisions have been made recently to overcome these
problems. As with the objective criteria, the subjective factors
should be ranked in importance according to local considerations.
1. Actual capacity (tons/hour, tons/shift, tons/day). This
figure would take into account storage capacities, daily
average and peak loads, input and output conveyor
capacities, and projected solid waste growth patterns.
For resource recovery systems (fuel fraction separation,
ferrous metal recovery, etc.) it is desirable, if not
necessary, to know how much material will be processed
dependably. When determining actual capacity, the nominal
particle size must accompany the data because of its
significant effect on throughput. Nominal particle
size should be specified in terms of minimum percent of
material that will pass a certain screen size, (e.g.,
90 percent passing a 3-inch square opening.)
2. Unit power (horsepower--hours/ton). This indicates
requirement for power and motor size. Once again, this
should be considered in relation to nominal particle
size, as power requirements generally increase as
particle size decreases.
3. Maximum output particle size. This can affect the next
processing step such as air classification.
4. Maximum size of input material. This factor is a
determinant of what is excluded from the shredding
process. Manual pre-shred separation v/ould be based
partly on this criterion. Before selecting a shredder,
the decision-maker should determine maximum input
particle size that he feels would be desirable to
process, and the approximate fraction of the total
waste load to be processed.
39
-------
5. Frequency and duration of breakdowns (tons/repair).
The nature of the material processed may markedly
affect this parameter.
6. Backfire (ejection from the input). If this appears
to be a problem, provisions must be made to ensure
employee safety.
7. Labor costs. Not only total labor costs but also the
separate figures for routine labor and for repairs
should be considered.
8. Types of repair required. Mechanical, electrical, and
welding skills may be required on a routine or as-needed
basis to assure maximum productivity of the system.
9. Effectiveness of power assist devices. The maintenance
needs and dependability of these devices must be con-
sidered with respect to the benefits derived.
10. Access for maintenance. Not only is easy access to
all shredder system components desirable, but adequate
clearance should also be provided for quick removal
and replacement of parts, such as a rotor shaft.
There should also be ready access to the parts of
all support equipment, such as conveyor systems, to
assure minimum downtime.
11. Effectiveness of noise, smoke, odor, and dust control.
12. Effectiveness of explosion and fire control provisions.
In addition to provisions within the system, it would
be prudent to have control over material entering the
plant in order to avoid having potentially explosive
or hazardous material going into the shredder.
Industrial waste generators might be required to
certify that they are not hazardous wastes.
13. Effectiveness of other safety features.
14. Effect of moisture in waste on power consumption,
particle size distribution, and wear rates.
15. Strength and efficiency of motor-shredder interface--
belt drive, direct coupling gears, etc.
40
-------
16. Effectiveness of mechanism for rejecting nonprocessibles
to guard against jamming. Also evaluate the method of
emptying the reject mechanism.
17. Peak and average power consumption fo shredder/conveyor
system.
18. Power cost. This depends on tonnage throughput, type of
material processed, particle size, and local unit rates.
19. Number of personnel required. Should include supportive
personnel required on a regular basis.
20. Effectiveness of lubrication systems.
21. Complexity of the system and its parts. Undue com-
plexity might mean more frequent breakdowns and
higher operating costs.
22. Operating "headaches" found by users. The manufacturer
should be asked whether there are new developments
that might correct these problems.
23. Manufacturers' reputation. Users should be asked about
the cooperativeness of the manufacturer in "debugging"
the system. Particular care should be given to defining
responsibility for the various components. If a manu-
facturer supplies only the shredder, he is not respon-
sible for overall system designs.
24. Predicted and actual life of equipment, moving parts.
25. Water requirements.
26. Adequacy of field service.
27. Wear rates (for hammers, liner plates, etc.). Cost
of alloys used for hard surfacing will have to be weighed
against increased productivity of shredder and less
frequent servicing.
28. Time required in startup to reach operating conditions.
29. Effectiveness of litter control provisions.
30. Adequacy of storage for shredded material. This factor
should be judged in relation to capacity requirements
and provisions for unloading or handling stored material.
41
-------
31. Location of control room.
32. Housekeeping requirements.
It is likely that not all installations contacted or visited
will be able to supply data for each of the above subjective
factors, and this is why several facilities should be contacted
if possible. Additionally, multiple data sources will help to
eliminate or "average out" some of the inevitable biases.
D. Use of Data Accumulated
If a thorough job has been done in gathering the
objective and subjective data listed above, plus any data deemed
desirable for the specific installation under consideration,
then some method of comparing this data in a logical fashion
is warranted.
Perhaps the easiest way to organize the data would
be to set up a form on which the characteristics of the various
shredders being considered can be noted and compared (Figure 9).
The next level of sophistication in decision-making would
be to quantify each shredder's rating with respect to each selection
criteria on a predetermined scale, such as 0 to 10 points, with
10 points being the most superior rating for any one criteria.
Points could be tallied for all criteria for each shredder with
the shredder most likely to be selected having the most points.
To go a step further, one could rank the criteria in levels
of importance for their situation, and assign a multiplier value to
this criteria. For instance, the criteria might be broken into five
levels of importance with the least important criteria receiving
multiplier values of 1 and the most important criteria receiving
multiplier values of 5. These multiplier values would then be used
to multiply the numerical rating attained in the above paragraph
for each criteria with respect to each piece of equipment. The
new ratings for each piece of equipment could then be tallied to
arrive at a score. This approach of ranking criteria assures that
relatively unimportant criteria do not carry the same weight as a
factor of great signficance.
The important point is to consider all criteria with
respect to each alternative. These decision aids do not make
decisions, but merely organize and clarify the decision-making
process.
42
-------
,
Shredder Type
Type 1
Type 2
Type 3
etc.
Selection Criteria
; Objective factors
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Figure 9. A form, such as the one shown here, can be used to
help organize the data on the shredders being evaluated.
43
-------
Appendix I
MUNICIPAL SOLID WASTE SHREDDER LOCATIONS*
STATE
California
Colorado
Connecticut
Delaware
Florida
Georgl a
Illlnoli
Iowa
Kansas
Massachusetts
Maryland
Missouri
Montana
Nebraska
New Jersey
New York
North Carol tin
Ohio
Oregon
Rhode Island
South Carolina
lexas
Washington
West Virginia
Wisconsin
Canada
LOCATION
Los Angeles
San Diego
Mountain View
San Francisco
Alamosa
Boulder
Chaffe County
Pueblo
Mil ford
New Castle Cnty
Brevard County
Gainesville
Pompano Beach
OeKalb County
Atlanta
Chicago
Ames
Cass County
START UP DATE
1975
1970
1975
1973
June 1972
1973
June 1974
Jan. 1975
April 1972
1972
1975
1966
Oct. 1972
April 1973
June 1973
1975
1975
late 1974
1975
STATUS
not In
operation
Installed
not In
operation
Installed
not In
operation
Installed
Installed
Installed
East Brldgewater 1973
Marlboro
McPherson
Baltimore
St. Louis
Great Falls
Omaha
Monmouth County
Chemung County
Onondaga County
north Hempstiad
Cull ford County
Columbus
Ullloughby
Portland
Providence
Beaufort County
Charleston
Houston
Odessa
CowlUz County
Charleston
Appleton
Madison
Edmonton ,
Alberta
Regtna,
Saskatchewan
Toronto,
Ontario
Nov. 1973
1975
early 1975
1972
Aug. 1973
Sunror 1975
Nov. 1974
1973
1973
1975
Jan. 1974
1975
Aug. 1973
1973
Aug. 1972
1974
1974
1967
Oct. 1974
early 1975
1975
June 1974
1967
1969
Sept. 1970
1974
1975
Installed
Installed
Installed
Initilled
Installed
Installed
not 1n
operation
Installed
Installed
Installed
Installed
Installed
SHREDDER TYPE
one vertical
one horizontal
one vertical
one horizontal
one vertical
one vertical
one vertical
two vertical
two vertical
four horizontal
two horizontal
two horizontal
one vertical
two vertical
three vertical
one horizontal
one horizontal
one vertical
two horizontal
one vertical
three horizontal4
one horizontal
one vertical
two horizontal
one horizontal
two vertical
one horizontal
one vertical
two horizontal
three vertical
one horizontal
one vertical
three horizontal
two vertical
one horizontal
one vertical
one vertical
three vertical
one horizontal
one horizontal
one horizontal
one vertical
two horizontal
one horizontal
one vertical
one vertical
one horizontal
one horizontal
CAPACITY
(tons per hour)
10
40
15
75
15
15
15
20,20
40,40
25,25,25,25
60,60
25.25
20
40,40
15.15.15
75
75
60
50,50
20
75,10,10
30
15
50,50
45
15,20
50
50
40,40
40,40,40
75
50
60,60.60
25,25
20
50
20
20,20,50
25
40
50
50
15
25,25
25
15
25
40
40
WASTE TYPES
municipal
municipal
municipal .commercial
municipal
municipal
municipal
municipal
municipal .commercial
municipal .commercial ,
oversized
municipal
municipal .commercial ,
oversized
municipal
niunlcl pal
municipal .commercial ,
oversized
municipal
municipal .commercial ,
oversized
municipal .oversized
already shredded waste
municipal .oversized
(wood)
municipal .commercial ,
Industrial
municipal
municipal
municipal .commercial
Industrial
municipal .Industrial ,
oversized
municipal
municipal .commercial
municipal
municipal .commercial ,
oversized
municipal Commercial .
oversized
municipal .commercial ,
oversl zed
municipal .commercial ,
oversized
municipal .commercial
oversized
municipal .commercial ,
oversized
municipal
municipal
municipal .Industrial
municipal .commercial
municipal .commercial ,
oyersized
municipal
municipal .commercial
municipal
municipal
municipal
municipal
municipal
municipal
Municipal
municipal
USE
landfill after materials
recovery
bale and landfill
landfill after materials
recovery
landfill after ferrous
recovery
landfill
composting
landfill
landfill after ferrous
separation
landfill
landfill
landfill
composting
landfill after paper and
ferrous recovery
landfill
landfill
bale and landfill
supplemental fuel
supplemental fuel
landfill after Incineration
landfill after materials
recovery
supplemental fuel
landfill after Incineration
landfill
pyrolysls
supplemental fuel
landfill after ferrous
separation
landfill after materials
recovery
landfill
landfill
landfill
bale and landfill
Undflll
landfill
landfill
landfill
landfill
landfill
landfill
originally compost;
landfill after materials
recovery, supplemental fuel
landtlll (discing with soil]
power generation
resource recovery
landfill after materials
recovery
landfill after ferrous
separation
landfill
landfill
landfill
landfill after ferrous
separation
* Source: May/June 1074 UasU.Age and the National Sol 1ft Wastes Monar|«>n
Association December TechnicalA"JJetjn.
+ One primary shredder (75 tph}, twn spcnnrlary, ihn-dtlprs {lO.lfl tnli)
44
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Appendix I con't.
INDUSTRIAL AND OVERSIZED BULKY WASTE SHREDDER LOCATIONS*
STATE
Alabama
Connecticut
District of
Columbia
Florida
Georgia
Illinois
Indiana
Kentucky
Maine
Massachusetts
Michigan
Missouri
New York
Ohio
Pennsylvania
South Carolina
Virginia
Vermont
Washington
Wisconsin
Canada
LOCATION
Decatur
Ansonla
Washington
Ft. Lauderdale
Tampa
Atlanta
DeKalb County
Chicago
East Chicago
Indianapolis
Ft. Wayne
Louisville
Romford
E. BHdgewater
Hoi listen
Marlboro
Saugas
Dearborn
Detroit
St. Louis
Berlin
Buffalo
Elmlra
New York City
Rochester
Bellevue
Colurnbus
Dayton
Newark
Harrtsburg
LeHIgh County
Georgetown Cnty.
W1ll1amsburg
County
Norfolk
Roanoke
Richmond
Hancock
Camus
Long view
Tacoma
Vancouver
Racine
Vancouver, B.C.
Windsor, Ontario
START UP DATE
November
May
June
February
January
August
February
April
February
July
October
January
November
August
June
June
August
April
July
December
September
April
September
July
June
October
May
July
July
1969
1974
1973
1973
1967
1975
1963
1970
1971
1975
1971
1971
1971
1962
1968*
1969*
1972
1973
1974
1973
1974
1970
1967
1972
1971
1969
1972
1970
1973
1973*
1968+
1968
1974
1969
1969
1972
1974
1974
1973
1974
1968
1974
1971
1965
1970
1971
1971
1972
1958+
1971
1965
SHREDDER TYPE CAPACITY
(tons per hour)
one horizontal
one horizontal
one horizontal
two horizontal
one horizontal
one horizontal
one horizontal
one horizontal
one horizontal
one horizontal
one horizontal
one horizontal
one horizontal
one horizontal
one horizontal
one horizontal
one horizontal
one horizontal
one horizontal
one horizontal
one horizontal
one horizontal
one horizontal
one horizontal
one horizontal
one horizontal
one horizontal
one horizontal
two horizontal
one horizontal
one horizontal
one horizontal
three horizontal
one horizontal
one horizontal
one horizontal
two vertical
one vertical
one vertical
one horizontal
one horizontal
one vertical
one horizontal
one horizontal
one horizontal
one horizontal
one horizontal
one vertical
one horizontal
-one vertical
one horizontal
40
30
10
50,50
6-8
75
6-8
30
30
25
50
25-35
35-50
20
32
40
40
75
40
30
20-25
40
20
50-60
10-15
30
10
240 cu.yd/hr.
40,40
7
10
5-7
60
10
10
20-25
20,20
20
20
30
40
20
25
5
20
50
40
40
24
50
30
WASTE TYPES
Industrial
oversized bulky
oversized bulky
oversized bulky
oversized bulky
oversized bulky
oversized wood
oversized bulky
oversized bulkv
oversized bulky
Industrial
oversized wood
oversized wood
oversized bulky
Industrial
Industrial
Industrial
oversized bulky
Industrial
oversized bulky
oversized bulky
Industrial
Industrial
Industrial .oversized
bulky
oversized bulky
oversized bulky
Industrial
oversized bulky
oversized bulky
oversized bulky
Industri al
Industrial (wood)
oversized bulky
bulky lumber, wood
Industrial
oversized bulky
Industrial
Industrial
industrial
oversized bulky
industrial-
Industrial
Industrial
commercial (paper,
cardboard)
industrial polyethylene
Industrial
oversized bulky
oversized bulky
oversized bulky
Industrial
oversized bulky
USE
materials recovery
incineration after materials
recovery
landfill after Incineration
landfill after Incineration
landfill after Incineration
landfill! bale, rallhaul
landfill after Incineration
landfill
landfill
landfill
landfill after Incineration
landfill after Incineration
landfill after Incineration
landfill
landfill after materials
recovery
heat recovery
materials recovery
materials recovery
landfill after Incineration
heat recovery
landfill after materials
recovery
landfill
landfill after paper
recovery
landfill after Incineration
landfill after Incineration
heat recovery
landfill after Incineration
landfill
landfill after Incineration
materials recovery
landfill
Incineration
landfill
landfill after Incineration
landfill
landfill
landfill
landfill after Incineration
landfill
landfill after ferrous-
separation
heat recovery
Incineration
Incineration
landfill
landfill
landfill
landfill
materials recovery
* Source: 'Shredder Subcommittee- of the Waste Equipment Manuf .rturers
Institute of the National Solid Waste Manufacturers Institute.
+ No longer in operation or project discontinued.
45
-------
Appendix II
POSITION ON LANDFILLING OF MILLED SOLID WASTE*
A. BACKGROUND
The landfilling of milled solid waste without daily soil cover
began in Europe with claims that it was an environmentally acceptable
and economic method of final disposal. In June of 1966, a solid
waste demonstration grant was awarded to Madison, Wisconsin to evaluate
the European experience and to determine the feasibility of landfilling
milled solid waste without daily cover in this country.
In January 1971, the Madison project personnel met with
OSWMP personnel, a consulting engineer, and entomologists from
the Bureau of Community Environmental Management (USDHEW), to
review the progress and findings to date from the Madison project.
OSWMP concluded that the policy governing soil cover for milled
solid wastes should be as stated in Sanitary Landfill Facts;
"The compacted solid wastes must be covered at
the conclusion of each day, or more frequently
if necessary, with a minimum of six inches of
compacted earth."
It was also concluded that further investigation at Madison and
in other geographic and climatic areas was needed to fully resolve
the policy issue. In a February 2, 1971 memorandum, Mr. Richard
Vaughan expressed these findings to OSWMP Senior Staff and Regional
Representatives. A copy of this memorandum is attached as Appendix 1.
Additionally, environmental evaluations of landfilling milled
solid waste made at the Madison demonstration site have been augmented
by information from site visits to other facilities. An increased
interest in the procedure is evidenced by the knowledge of six new
sites being planned, ten new sites under construction, and five
sites operational.
Some of these sites are constructed and operated with provisional
approvals, some are operated in opposition to local regulations but
in all cases the operations do not adhere to the position stated
by the OSWMP on February 2, 1971.
Recent articles, based on European experience, findings from
the Madison project, and other new sites within the United States,
have appeared in engineering and public works journals. This
information, combined with equipment promotional activities has
generated an increased interest in the process particularly where
problems exist in achieving satisfactory sanitary landfill operations
or where milling may compliment resource recovery.
* Office of Solid Waste Management Programs. Position statement
on landfilling of milled solid waste. Unpublished data, Apr. 9, 1973.
46
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B. CURRENT POSITION
Landfilling milled solid wastes can be an environmentally
acceptable method of final disposal. The same sound engineering
principles involved in sanitary landfill sites, including a
properly located, designed, financed, and operated milling facility
must be provided to insure successful operations and to minimize
adverse environmental impacts. Since environmental, economical,
and operational conditions vary from existing sites, the need
for cautious planning to meet local conditions and to determine
the feasibility of each new site must be emphasized.
It must be recognized that this position is based on detailed
investigations at the Madison site augmented by general knowledge
from a few additional sites. The ability to mill, grind, or shred
wastes such that it is environmentally acceptable to landfill them
without daily cover is dependent on the process, its operation,
and local conditions such as the environment and the waste content.
It is, therefore, recommended that conditional approvals be Riven
by regulatory agencies contingent upon verification that the
quality of operation necessary to minimize environmental hazards
is maintained. Such verification should be supported by operational
controls and monitoring.
Except as modified below, the position statement on sanitary
landfill applies to milled solid waste disposal operation. Comments
relating milled solid waste to sanitary landfill requirements are
listed below in the order presented in the pending "Guidelines for
the Land Disposal of Solid Wastes."
1. As an alternative to sanitary landfill, landfilling
•illed solid waste without daily soil cover can result in increased
surface water infiltration and accelerated decomposition which in
turn can result in earlier leachate production and temporarily
increased pollutional concentrations. Under the usual situation of
landfill construction over a period of years, peak leachate production
and concentrations occur only in a small part of the fill at any
one time. In areas where rainfall infiltration exceeds evaportrans-
piration and field capacity is reached, the total production of
leachate constituents has been shown to be equivalent to a sanitary
landfill which reaches field capacity and produces leachate. There-
fore, in accordance with the sanitary landfill position, it is
necessary to prevent leachate from entering surface or underground
sources of water supply. This can be accomplished by preventing
leachate production and/or by collecting and treating leachate
should it occur.
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2. As with sanitary landfill operations, design and operation
must conform to applicable air quality standards; specifically,
open burning of solid waste must be prohibited.
3. As with sanitary landfill cover, compacted, milled,
uncovered landfill surfaces must be left undistrubed to prevent
odor. This does not preclude vehicular traffic but precludes
excavation of a finished surface.
4. Although milling solid waste reduces the tendency for
paper to blow during placement, satisfactory control requires that
the waste be spread to a smooth contour and compacted promptly
after placement.
5. A milled, uncovered solid waste landfill is much less
obnoxious than an open dump and to many observers is no more
obnoxious than bare earth.
6. Free venting or loss of gases from milled solid waste,
experienced in test cells, indicates that milled solid waste without
cover is less likely to trap gases in pockets or cause horizontal
gas migration. However, the addition of cover or possible migration
through fissures or broken pipe lines, etc. requires the same
attention to gas control as a sanitary landfill.
7. European experience, verified by tests at Madison,
Wisconsin and Purdue University indicates that:
Rats cannot extract sufficient food to sustain life
from properly milled combined residential, commercial
solid waste (7-1/2% organics wet weight in test) nor are
they attracted more readily to an uncovered milled solid
waste landfill than to a sanitary landfill (baiting
studies); the milling process kills nearly 100% of the
maggots present in incoming solid waste virtually elim-
inating fly emergence (sampling studies); and flies are
not attracted more readily to an uncovered milled solid
waste landfill (Scudder Grill Study).
8. Undetected hazardous materials in incoming wastes have
been known to explode or ignite during the milling process.
Protection against explosions such as blow-off stacks and personnel
shields must -be provided. Equipment to extinguish fires which
may exist in incoming solid waste or which may be ignited during
the milling process, during transport or on the landfill must be
provided. No operation should be located where birds might be a
hazard to aircraft flight operations.
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9. Site selection on an engineering basis is similar to
that for a sanitary landfill operation except the availability
of daily cover material is not required. The availability of
emergency cover is required (see operational plan requirements
below). Final cover and final use criteria should be the same
as for a standard sanitary landfill.
10. Only properly milled residential and commercial solid
wastes should be accepted in an uncovered milled solid waste
landfill. Items not accepted in a conventional sanitary landfill
and volatile, flammable, explosive or sludge wastes accepted in
small quantities at a conventional sanitary landfill, should not
be accepted for milling. Final disposal of all wastes not
suitable for milling must be in accordance with pending "Guidelines
for the Land Disposal of Solid Wastes."
11. All operations and aspects including lighting, dust
control, and noise levels must meet the requirements of the
Occupational Safety and Health Act of 1970. All solid waste
storage areas must be maintained and cleaned at the end of
each day's operations, or during continuous operation, as
necessary, to prevent fly, rodent, or other vector problems.
All equipment must be maintained to control spillage and to
achieve a milled product quality necessary to prevent environ-
mental hazard.
12. All operational personnel must be specially trained
and instructed on the proper operation, maintenance, and safety
aspects of the facilities and equipment.
13. The operational plan must include provision.for removal
and proper disposal of wastes within 24 hours should the mill
facility cease to meet the above conditions because of either a
temporary equipment breakdown or a loss of quality operation.
The operational plan must include provision of a stock pile of
emergency soil cover material and provision to convert the
operation to a sanitary landfill.
Preliminary project planning must include a detailed cost
analysis including means of establishing a sound financing and
revenue system, in order to guarantee that the quality of operation
necessary for environmental acceptability can be sustained. Milling
and landfilling residential and commercial solid wastes is usually
not cost competitive with conventional sanitary landfill disposal.
Cost comparisions to justify milling as an alternative to more
extensive disposal systems including transfer stations or cover
material transport must be evaluated on a local basis. Each
community or private operator must make their own thorough economic
evaluation of the alternative disposal systems. Milling costs
including labor, amortization, utilities, maintenance, and supplies
49
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recorded at and relevant only to the Madison project were as high
as $7t07/ton for a single 9 ton/hr. Gondard mill operating 5 to 6
hours a day. Costs for a single 15 ton/hr. Tollemache mill operating
about 5 hours a day have been recorded at $5.10/ton while costs for
a similar operation with "hard to mill" wastes ran as high as
$6.44/ton. Transportation to the adjacent landfill averaged about
$0.40/ton additional. Spreading and compacting costs averaged an
additional $0.50/ton. Cost projections for the combined operation
of one Gondard mill at 9 ton/hr. and one Tollemache mill at 15 ton/hr.,
milling 280 tons/day or a two shift operation is approximately
$3.50/ton excluding transport and disposal. These costs reflect
local labor rates, union contracts, construction costs, and electrical
costs, etc.
C. REFERENCES
1. Ham, R. K., and Porter, W. K., and Reinhardt, J. J.;
Refuse Milling for Landfill Disposal. In. The Symposium
on Solid Waste Demonstration Projects, Cincinnati, Ohio,
May 4-6, 1971. 75 p.
2. Solid Waste Reduction/Salvage Plant. An Interim Report.
Demonstration Project; June 14 - December 31, 1967.
Grant No. D01-UI-00004. U. S. Public Health Service.
1968.' 25 p.
3. Sanitary Landfill Guidelines. U. S. Environmental Protection
Agency, Unpublished Report; April 1972. 21 p.
4. Brunner, D. R., and D. J. Keller. Sanitary Landfill
Design and Operation. U. S. Environmental Protection
Agency Publication (SW-65 ts). Washington, D. C.
U. S. Government Printing Office, 1972. 59 p.
5. Stirrup, F. L. Public Cleansing: Refuse disposal.
Pergamon Press, Ltd. Great Britain, 1965. 144 p.
6. Department of the Environment. Refuse Disposal. Report
of the Working Party on Refuse Disposal. London. Her
Majesty's Stationary Office, 1971. 199 p.
7. Department of the Environment. Report of the Working
Party on Refuse Disposal. Circular 26/71; April 1971. 7 p.
50
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Appendix III
EXAMPLE
SPECIFICATION
HAMMEHMILL. MOTOR AND AUXILIARY EQUIPMENT
1. SCOPE;
This Contract Includes the furnishing, for Installation by others, of a
heavy duty swing hammer horizontal type hammennlll, complete with feed and
discharge hoppers, the drive motor, coupling, and all accessories, together
with their motors and drives as specified herein. The Contractor shall
furnish all anchor bolts and other Items requiring embedment in the concrete
foundation for installation by others, for all equipment furnished under
this Contract. The Contractor also shall provide the services of a qualified
service representative, to supervise the installation of the equipment, and
to properly instruct City personnel in the operation and maintenance of the
equipment, for periods totaling not less than 10 days, at the expense of the
equipment manufacturer.
The relationship of the hammermill to other parts of the project, and
the configuration of the feed and discharge hoppers, are shown on the accom-
panying general arrangement drawing. The hammermill manufacturer will be
required to coordinate his design with the manufacturers of the mill feed and
discharge conveyors, to ensure proper clearances and function.
The manufacturer of the hammermill and its auxiliary equipment shall be
regularly engaged in the manufacture of equipment similar in design, function,
and capacity to that specified. Prior to the date set for receiving bids,
a list of Installations in which counterparts of the respective items of
equipment have been applied satisfactorily shall be supplied to the President,
who shall be the sole judge of the acceptability of the proposed equipment.
The hammermill shall be similar or equal to those manufactured by the Williams
Patent Crusher and Pulverizer Company, or the Gruendler Crusher and Pulverizer
Company.
2. FUNCTION AND CAPACITY:
The hammermill shall be designed to mill raw mixed municipal refuse,
as collected from domestic and small commercial establishments by packer-
type trucks. The mixed municipal refuse is expected to be a heterogeneous
mixture of materials of a wide variety of shapes and sizes. Although the
refuse will be collected principally from domestic sources, it is possible
that occasional heavy or oversize objects, such as discarded yard furniture,
bicycle frames, etc., may be fed to the hammermill, which shall be capable
of handling such objects without overloading the hammermill or its motor.
The hammermill shall reduce the material fed to it to particle sizes
which shall be nominally less than one and one-half inches in size. No more
than 5 per cent by weight of the particles produced by the hammermill shall
be greater than one and one-half inches, and no particles shall be greater
than 5 inches In one dimension after the hammermill has operated at at least
90 per cent of its rated capacity for 40 hours without retipping or replace-
ment of hammers. Occasional pieces of stringy, flexible materials greater
than 5 inches In one dimension may be acceptable, as long as such materials
do not interfere with the operation of rotary air-lock feeders for pneumatic
conveying.
The initial capacity of the hammennlll, operating as a single-stage mill,
shall be at least 45 tons of raw mixed municipal refuse per hour. Should the
capacity of the hammermill be less than 45 tons per hour, or should the nominal
particle sizes be greater than those specified, the manufacturer will be re-.
quired to make such modifications as necessary to provide the required capacity
and particle size. Such modifications, if required, shall be made at no
* Sample of specifications shown in Appendix III were
used in St. Louis, Missouri, in conjunction with EPA demonstration
project and should not be considered as universally applicable.
These are for illustration only.
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additional cost to the City, and shall be Initiated within five days of the
date of notification by the President to the manufacturer that such inade-
quacies exist. Correction of the inadequacies shall proceed in the most
expeditious manner. The President shall be the sole judge of such inadequacies.
The hammermlll, with minimum modification of grate bars and/or hammers,
shall be capable of future use as a primary mill in a two-stage milling
operation, with a nominal average capacity of 70 tons per hour when achieving
nominal particle sizes of A to 6 Inches for raw municipal refuse as collected
by packer-type trucks. If so modified at a later date, the hammermill shall
be capable of handling such objects as discarded refrigerators.
3. GENERAL DESIGN OF HAMMERMILL AND AUXILIARIES:
a. Housing. The hammermlll shall be of heavy duty horizontal design
of the swing-hammer type, The frame and housing shall be constructed of
heavy rolled steel plates and structural shapes, solidly welded into an
Integral unit. The main frame shall have bearing support platforms of heavy
steel plates welded integrally to the sides. The feed opening (hall be ap-
proximately 60 Inches perpendicular to the rotor, by 80 Inches parallel to
the rotor.
The hammermill shall be designed to provide quick access to the rotor,
breaker plates, grate bars and other internal parts. The design shall pro-
vide for the removal of the rotor without disturbing the feed hopper or
feeding equipment. The housing shall be opened hydraulically, as hereinafter
specified, to permit inspection, maintenance, retlpping of hammers in place,
and replacement of parts.
The hammermlll shall be fitted with manganese steel shear type breaker
plates not less than 2 Inches thick. Replaceable carbon manganese steel
liner plates shall be provided on the sides and top of the crusher chamber.
The liners and breaker plates shall be made in sections, bolted to the
housing by means of heavy bolts with locknuta. All parts subject to wear
shall be easily replaceable.
b. Rotor. The swing hammer rotor shall have a hammer circle of ap-
proximately 60 Inches and a length of approximately 80 inches inside the
housing, and shall have 4 rows of chisel-edged hammers of sufficient number,
size, and weight to provide the specified production rate and particle size.
The hammers shall be made of alloy steel having high resistance to shock
and abrasion, hard-surfaced on the working ends to 500 to 570 Brinell hard-
ness. Hammers shall be staggered so that they cover the full width of the
crusher chamber, with those In one row traveling In the spaces between the
leading and following rows. The hammer suspension shafts shall be made of
no less than 4-inch diameter high tensile alloy steel, surface-hardened to
minimize wear.
The rotor shaft shall be not less than 14 inches In diameter In the
crushing chamber, turned from a heat-treated, alloy steel forging. The dime
plates shall be of cloverleaf design, made of high tensile alloy steel,
having high resistance to shock and erosion. The discs and their spacers
shall be securely keyed to the shaft and positioned by threaded collars.
In order to prevent shock loading and excessive wear on the discs, the discs
shall not extend into the crushing area of the hammer system and there shall
be a minimum clearance of 9-1/2 Inches between the disc circle and the grate
bars. The rotor assembly shall be designed to provide an Internal balanced
flywheel system with sufficient inertia to minimize shock loadings. The
rotor shall be balanced statically and dynamically, and shall not exceed
5 mils dynamic vibration, measured peak-to-peak, at operating speed. The
WX of the rotor shall be no less than 46,500 lb-ft2.
The hammermlll rotor shall be direct-connected to no leae Chan • 1,250
horsepower, 900 rpm electric motor, as hereinafter specified, by means of a
heavy duty, flexible coupling, Falk or equal.
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c. Bearings. The rotor shall be carried In double-row, self-aligning,
spherical roller bearings having a taper bore approximately 11 inches in
diameter. The bearings shall be housed in heavy-duty steel pillow blocks,
sealed against dust and moisture, pinned and secured by high tensile steel
bolts with heavy nuts and Jam nuts, and taper wedge blocks. The shafts shall
be drilled and arranged for hydraulic seating and removal of bearings.
d. Lubrication System. The bearings shall be oil-lubricated, and the
manufacturer shall furnish an oil circulating and cooling system to supply
lubrication to the bearings, including a pump, filter, heat exchanger, valves,
temperature and pressure gauges, with appropriate safeguards and alarms to
be actuated should oil pressure fail or over-temperature occur.
e. Grate Bars. The grate bars shall be of manganese steel, consisting
either of deep section members having spacers, which may be changed In the
field to alter the size of the discharge openings, or of sectional grids
which could be replaced all or in part with grids having different openings.
The grate bars or grids shall be secured by wedges or other means to facili-
tate quick removal and replacement.
f. Hydraulic Opening System. The manufacturer shall furnish oil
hydraulic cylinders to lift and hold in an open position the top hinged
cover section of the hammermlll to facilitate inspection and maintenance.
Provisions shall be made for locking the cover securely when it is in the
closed position. The manufacturer also shall furnish the oil hydraulic
equipment components, consisting of a motor, pump and oil reservoir, together
with control valves and oil for the system. The hydraulic system shall be
designed to open the top hinged cover section of the hammermill housing in
one minute or less. When in an op-en position, the cover shall not interfere
with hammer retipplng.
g. Feed Hopper. A steel feed hopper shall be provided to mate with
the hammermill to permit the unobstructed feeding of the intended materials
and objects. The shape of the feed hopper shall be substantially as shown
on the general arrangement drawing. The feed hopper shall be supported by
the feed opening of the hammermill. It shall be fabricated of steel plate
not less than 3/A-inch thick, reinforced with structural members and welded
together to form an integral unit. Additional external reinforcing shall
be provided on the sides receiving direct impact from missiles thrown by the
rotor. The inlet of the feed hopper shall be equipped with two rows of re-
inforced rubber belting, with the strips staggered, to serve as barriers to
prevent missiles from being thrown out of the hammermill through the feed
opening. An opening in the top of the hopper shall be provided for the
installation of a dust removal duct, as shown on the Drawing. Provision
shall be made for the Installation of manually controlled water sprays into
the crusher chamber. Provisions also shall be made for the installation of
rubber skirting between the feed hopper and the mill feed conveyor as shown
on the Drawing.
h. Discharge Hopper. A steel discharge hopper shall be provided
supported from the discharge opening of the hammermill. The discharge hopper
shall be fabricated of steel plates not less than 1/2 inch in thickness,
reinforced with structural members and welded together to form an Integral
unit. The inside dimensions of the top of the discharge hopper shall b« th«
same as those of the discharge opening of the crusher. The discharge hopper
shall be shaped to conform to the configuration of the discharge conveyer
under the hammermill, and shall be fitted to prevent the escape of dust and
refuse particles. Skirting shall be provided between the discharge hopper
and the mill discharge conveyor, as shown on the Drawing.
4. HAMMERMILL DRIVE MOTOR;
a. General. The motor described herein shall conform to all applicable
standards and recommendations of ANSI, NEMA, IEEE, NBFU, UL, NEC, and th«
•lectrical and building codes of the City of St. Louis, where applicable.
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The hammermill drive motor shall be adequate to start and to drive con-
tinuously the hammermill as described herein at the production rates and condi-
tions as specified. The motor and its parts shall be designed for hammermill
duty, and shall be designed to withstand, on a continuous basis, 125 per cent
maximum pull-out torque. The heterogeneous nature of the materials fed to
the hammermill may be expected to impose occasional heavy loads in the motor.
Sharply rising stator currents can be expected, which may last on the order
of 10 seconds, and which may approach levels of 200 per cent FLA (full load
amperes). Occasional current levels of 400 to 500 per cent FLA, of approxi-
mately one second duration, must be anticipated in the motor design, to
accommodate the impact characteristics of the loads imposed on the hammermill.
b. Motor Design. The motor shall be a squirrel cage Induction motor,
with the frame size, shaft size and other details coordinated with the
requirements of the hammermill and the connecting coupling. The motor shall
be at least 1,250 horsepower, designed for 900 rpm. It shall be designed
for 3 phase, 60 cps, 4,160 vac, 3-wlre service, with a service factor of
1.15. Slip at full load shall be limited to 2.5 per cent maximum. Break-
down torque shall be at least 225 per cent of full load torque with the
rated voltage on the motor. The motor design shall correspond to NEMA
Design B (normal starting torque, low starting current).
The design temperature rise shall be 90 degrees C. above a 40-degree C.
ambient, with winding temperature measured by the resistance method at stabi-
lization, when the motor has been operated continuously at the 1.15 service
factor. The insulation system shall be Class F for 155 degrees C. service,
and shall incorporate materials and processes approved in AIEE No. 1. The
insulation materials shall consist of high temperature polyester enamel,
fiberglass, mica, polyester asbestos and aromatic polyamide (nylon) paper.
The normal starting current will be limited by a reduced voltage non-
reversing motor starter through application of 65 per cent of rated line
voltage, plus or minus 10 per cent through reactors. Starting voltage may
be varied to suit conditions by changing taps in the reactor in the motor
starter. The starting time shall not exceed 120 seconds with an unloaded
hammermill. The hammermill will not be started unless it is unloaded.
The motor shall be suitable for continuous year-around, outdoor operations
in a dirt-laden environment and the motor housing shall be equivalent to
NEMA II of the totally-enclosed, completely weather-protected type. The
housing shall be provided with replaceable glass-fibre filters contained
in protective frames and shielded by rustproof hardware cloth. The housing
shall be rustproofed, primed and painted with two coats of machine enamel,
inside and outside. Cooling air shall be drawn into the motor through the
filters by means of a cast Impeller fan secured to the rotor shaft within
the motor housing. Air shall be drawn in at one end, forced through longi-
tudinal cooling ducts In the stator, and axially along the air gap over a
smooth rotor core. Cooling air inlet and exhaust openings shall be so
placed that short-circuiting of air flow will not occur. The fan shall be
designed with inclined blades to produce low shock to the entering air, and
to deliver the air at relatively low velocity into smooth channels to mini-
mize windage losses and noise- The exhaust openings shall be equipped with
motorized sealing louvers to prevent dust from entering the motor when It
is de-energized.
The motor will be direct connected to the hammermill by a flexible
coupling, Falk or equal, suitable for the service intended.
Efficiency of the motor shall be not less than 92 per cent at full load
and rated voltage. The power factor shall be not less than 85 per cent at
full load and rated voltage.
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c. Motor Construction. Both the stator and rotor magnetic structures
shall be constructed of stacked laminations of varnished, heat-treated, high
silicon electrical grade sheet steel chosen for low loss. Stator laminations
shall be stacked and bolted, and keyed and bolted to a rolled and welded
steel frame. The rotor side of the stator shall be smooth to prevent vibra-
tion and noise due to irregular air flow. Smooth bore air ducts shall pass
through the stator for cooling. The rotor laminations shall be assembled
in the rotor shaft as single piece steel punchinga, stacked and keyed
directly to the shaft. A bolted clamping support for the rotor laminations
shall secure the rotor laminations to the shaft, with the clamping support
welded to the shaft. The rotor surface shall be smooth for noise-free
passage of cooling air.
Electrical insulation shall be constructed of a fiberglass reinforced
Class F system, which shall be vacuum impregnated after a thorough bake-out
procedure. The insulation system shall thoroughly encase coils, connections
and leads. The stator coils shall be restrained, and the coll ends shall be
braced and supported to prevent movement of the windings, even under short-
circuit conditions, and the bracing shall not impose any mechanical strain on
the winding, or permit coil vibration or distortion.
Rotor cage electrical bar conductors shall be of oxygen-free electrical
conductor grade copper, which shall be brazed or silver-soldered to the end
rings to guarantee torque characteristics. The rotor cage structural design
shall be such that thermal expansion and contraction shall be kept well within
the elastic limits of the copper. Rotor stiffness shall be ensured by welding
the rotor core support structure directly to the shaft. The rotor shall be
dynamically balanced after fabrication to ensure smooth operations.
The motor shall be run-up in speed under no-load conditions and with
rated voltage applied, to cause the rotor to assume an axial equilibrium
position relative to the rotating magnetic field produced by exciting the
stator. At equilibrium position of the rotor, while turning at full speed,
a diamond scribe shall be used to scribe a circumferential mark on the
rotating shaft at the coupling end motor bearing housing. With this refer-
ence mark, a shaft button shall be assembled into the opposite end of the
shaft. The projections of this button and the shaft shoulder shall between
them determine 1/2-inch shaft end float, and locate the scribe mark midway
between the extremes of the end float. It is intended that the scribe mark
appears exactly at the coupling and motor bearing housing when the coupled
system is rotating at rated speed. The motor shaft button and the shaft
shoulder should act as limit stops at either end of the shaft end float.
d. Bearings. Bearings shells shall be cast of an approved bearing
babbitt metal by a method designed to guarantee freedom from blowholes.
Bearings shall be of the split-sleeve type, contained in split housings
permanently aligned and doweled to the motor frame to permit bearing shell
replacement without disturbing alignment of the motor. One bearing pedestal
and its fasteners shall be electrically isolated from the motor frame to
prevent an eddy current path from encircling the rotor, the bearings and
the motor frame.
The bearings shall be oil-lubricated by slinger rings from oil pockets
in the bearing pedestals. Each oil pocket shall be equipped with a fill
plug, a drain plug and a window-type fill-level gauge. The bearings shall
be oil and dust-tight. The bearing design shall be such that the ratio of
diameter to length shall be one to one in the journal. The proportioning
of the bearing dimensions shall provide a surface velocity and a unit
seating pressure to ensure a low temperature rise when the bearing is lub-
ricated by the slinger ring. The shaft journal shall be provided with a
ground finish at the bearings of 5 to 10 microinches, rms.
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e. Frame. The motor frame shall be of sceel and shall provide high
impact strength and rigidity without excessive weight, and shall be fabricated
with smooth contours. The frame shall be fitted with heavy duty steel bat
feet, and with lifting lugs to permit handling by crane. The frame shall
be degreased, mill scale removed, rustproofed, primed and painted with two
coats of light gray machine enamel, ASA 61. All hardware and fasteners
shall be corrosion-resistant.
The motor manufacturer shall supply a suitable bed plate for embedment
in a concrete foundation. The bed plate shall provide positive means for
both lateral and longitudinal adjustment of the motor.
f. Temperature Detectors and Alarms. Two resistance temperature de-
tectors shall be wound into each phase of the stator windings during construc-
tion. Two additional temperature detectors of the spring-loaded type shall
be provided, one for each bearing housing, with the springs forcing the
detectors into good thermal contact with the bearing housing. All detectors
used with the motor shall be connected to a weathertight terminal box, with
the wires drawn through rigid conduit attached to the motor frame. The
terminal box shall allow a one point pickup of conduit for transmitting
the temperature detector signals to an Indicating and alarm unit compatible
with the detectors. The locations of the indicating and alarm unit will be
In the electrical control room, with remote indications at the control station
near the operating floor.
The Indicating and alarm unit, which shall be furnished under this
Contract, shall be of the Wheats tone bridge type in which the resistance
temperature detector Is located in one arm. The temperature trip point of
the Wheatstone bridge shall be detected by a null balance relay. The trip-
temperature value shall be adjusted by a potentiometer In the Wheatstone
bridge circuit. The assembly of eight Wheatstone bridge circuits, the
associated setting potentiometers, the array of channel Indicator pushbuttons,
switches and the test trip pushbuttons, along with the indicator, shall be
appropriately housed in the alarm circuit manufacturer's cabinet, which
shall be located in the electrical control room. The purpose of the tempera-
ture detectors is to protect the motor by tripping it from the mains when
any temperature detecting point exceeds the preset temperature for that
point. When such tripping occurs, the temperature channel initiating the
signal shall have associated with it a pilot light which remains on until
the circuit is reset.
g. Motor Heaters. Corrosion-resistant steel-sheathed magnesium oxide,
nichrome wire electric strip heaters shall be provided in the motor enclosure.
These shall be energized when the motor is de-energized. They shall have
sufficient capacity to heat the air in the motor enclosure and cause Its
circulation by convection through and about the motor electric parts to
prevent the condensation of moisture.
h. Connec11on Box. A code gauge electric connection box, made of
galvanized steel, attached to the motor, shall be provided. It shall accom-
modate conduit with high voltage service leads to power the motor, as well
as a ground cable. A three-phase surge capacitor of appropriate rating In
voltage and capacitance shall be provided in the connection box with the
common side connected to ground. Lightning arresters of adequate rating
and of a grade suitable to this service shall be provided. The capacitor
and the lightning arresters shall be connected to each phase of the incoming
line and to the motor service terminals. The common ground connections of
the capacitor and the lightning arresters shall be through their bases to
the grounded frame of the connection box in which they are mounted.
56
-------
1. Motor Testa and Data. After the motor has been assembled and in-
spected, it shall be given the following commercial tests and the te*t data
recorded. Five certified copies of the data shall be submitted to the City.
1. Locked rotor current at rated voltage and at 65 per cent of
rated voltage.
2. No-load current at rated voltage.
3. Winding resistance at ambient temperature.
4. Insulation tests, including resistance to ground measured
with 500 vdc excitation of stator, isolated bearing and
rotor, and high potential tests as prescribed by NEMA
for motors of this voltage rating and horsepower.
A thorough mechanical and electrical inspection of the motor shall be
made to ensure compliance with the Specifications.
Motor performance tests to obtain the data specified in the following
shall be conducted either on this motor, or data shall be supplied as ob-
tained from such tests of a similar motor.
1. Rotor moment of inertia.
2. Efficiency and power factor at full load, three-quarter load,
half load and one-quarter load (100 per cent voltage).
3. Full load percentage slip (100 per cent voltage).
A. Breakdown torque.
5. Starting torque.
Five sets of curves of motor current, power factor, slip, torque and
efficiency shall be provided, along with five complete sets of mechanical
drawings and details of motor construction, and five sets of recommended
Installation, operation and maintenance procedures, together with lists
of recommended spare parts.
5. SHOP PAINTING;
All external steel surfaces of the equipment furnished under this Con-
tract, except as otherwise noted, shall be thoroughly cleaned of grease, oil
and mill scale, and shall receive one shop coat of Koppers Rustinhibitlve
Primer No. 612 (phenolic), or approved equal, applied to achieve a minimum
dry thickness of 1.5 mils. Shafting and exposed machined surfaces shall b«
protected with a suitable coating of a soluble slushing compound to prevent
corrosion during transit, storage and installation. Motors and reducers
shall receive the manufacturer's standard painting system. Finish painting
will be done by others.
6. PAYMENT;
Payment for the equipment included in this Specification, together with
the associated equipment, shall be on the basis of the individual lump-sum
prices stated in the Proposal, and on the terms stated In the Instructions
for Bidders, as follows:
a. Hammermlll with Auxiliaries One Item
b. Hammermlll Feed Hopper On* Item
c. Hammermlll Discharge Hopper One Item
d. Hammermlll Drive Motor On* Item
57
-------
—-n ' /i v
S) Jd \ Mr-
REFUSE
STORAGE F/fJ
-LOQG AT ELEtf /OO-O
"~1
'-I 7^0- ££&££ HOPPER
'***&««•'• ******
NOTE
DlMfNSIOMS
AtJ*.ARE SJ&JECT TO CHANGE
AMD SHALL QE DETERMINED
EYO*
SUPPORT FRAME
far OTHERS)
SKIRTING DETAILS
ABOVE FURNISHED
HAMMERMILL MFGft
THIS DRAWING REDUCED
APPROX, 'A ORIGINAL SIZE
^^Vl
COMEYOR SJPfW
QENTfBf OTHERS},
VIBRATORY COVCfK/yVG EQUIPMENT
LOCATION PLAN AMD DETAILS
f, v C
.J L jit: jii ;N_
CITY OF ST. LOUIS
-------
SPECIFICATIONS
VIBRATORY CONVEYORS
1. SCOPE:
This Contract includes the furnishing, for installation by others, of
three vibratory conveyors, comprised of one receiving conveyor, one mill
feed conveyor and one mill discharge conveyor, complete with drives, motors,
belt guards and accessories as specified herein. The Contractor shall furnish
all anchor bolts and other items requiring embedment in concrete foundations,
for installation by others, for all equipment furnished under this Contract.
The Contractor also shall furnish the services of a qualified service rep-
resentative for a sufficient period of time to supervise the installation
of the equipment by others, and to properly instruct City personnel in the
operation and maintenance of the equipment. These services will be required
for periods to be scheduled with the Contractor installing the equipment,
totaling not less than two working days during the installation of the equip-
ment and two working days during the start-up period, at the expense of the
equipment manufacturer.
The relationship of the vibratory conveyors furnished under this Contract
to the other equipment and structures of the project is shown on the accom-
panying drawing.
The vibrating medium for each conveyor shall consist of a resonant
natural frequency spring and mass system, comprised of low stress, heavy
duty alloy steel coil springs, shot-peened and magnaflux Inspected, or of
other materials subject to approval by the City. All conveyors shall be
dynamically counter-balanced and isolated by systems of lower natural fre-
quency than those at which the conveyors operate.
All conveyors shall have positive eccentric shaft drives, with connecting
arms driven through V-belts by electric motors. The drives shall be designed
to accommodate extraordinary out-of-phase forces which may occur during
start-up and shut-down. Stability of the equipment shall be assured by
elimination of large gyrations through isolation springs and cushioned limit
stops during start-up and shut-down. The drives shall be designed to provide
acceleration and deceleration to quickly pass through the natural frequencies
of the isolation systems so as to prevent build-up of large gyrations.
All three conveyors shall be designed to accommodate nominal feed rates
of 45 tons per hour, with surges of up to 60 tons per hour, when handling
the material specified hereinafter. The conveyors shall be capable of modi-
fication for future duty to convey nominal rates of 70 tons per hour each,
with peak rates up to 100 tons per hour.
All conveyors shall be of heavy duty construction. All bearings shall
be dust-tight sealed cartridges. Provisions shall be made for lubrication
from convenient and accessible points. Parts for the three conveyors shall
be interchangeable, wherever feasible. All moving and vibrating parts shall
be easily accessible for adjustment and replacement.
The manufacturer of the vibratory conveyors shall be regularly engaged
in the manufacture of conveying equipment of similar design, function and
capacity to that specified. Prior to the date set for receiving bids, a list
of installations in which counterparts of the respective items of equipment
have been applied satisfactorily shall be supplied to the President, who
shall be sole judge of the acceptability of the proposed equipment. The
vibratory conveyors shall be similar or equal to those manufactured by the
Stephens-Adamson Company, or the Carrier Division of the Rex Chainbelt
Company.
59
-------
Minor modifications in dimensions of the equipment specified herein may
be necessary to reconcile differences with the equipment furnished by other
manufacturers. The manufacturer of the vibratory conveyors will be required
to cooperate with the City and its other Contractors in reconciling such
modifications.
The manufacturer shall provide full information relating to static and
dynamic loadings and forces, and shall guarantee the accuracy of such
information.
2. RECEIVING CONVEYOR:
Mixed municipal refuse, as collected from domestic establishments in
packer-type trucks, will be dumped from the trucks on a concrete floor.
Front-end loaders will push the raw refuse from the floor into the pan of
the receiving conveyor. The receiving conveyor, which shall have an elec-
trically controlled means of varying the conveying velocity and rate of
discharge, will be required to discharge the raw refuse at a reasonably
constant but variable rate to an inclined belt conveyor, as shown on the
accompanying drawings.
The mixed municipal refuse is expected to be a heterogeneous mixture
of materials of a wide variety of shapes and sizes, with its bulk density
ranging between 100 and 3SO pounds per cubic yard. Occasional heavy objects,
weighing on the order of 50 to 100 pounds and more, may be expected to be
included in the refuse.
The receiving conveyor will be installed by others in a concrete pit,
below the operating floor, with its isolation mountings supported by a
concrete slab and steel beams, as shown on the Drawings.
The receiving conveyor shall have a steel pan, at least 3/8 inch thick,
and 33 inches deep, 8 feet ylde at its bottom, and approximately 24 feet,
3 inches long at its centefline. The conveyor will discharge to a 60-inch
wide belt conveyor. A 1/2-inch thick replaceable liner, about 16 feet long,
shall be provided for the bottom of the pan, held in place with countersunk
flat-head bolts. There shall be no. protuberance inside the pan to interfere
with the discharge of the materials handled. The pan of the conveyor shall
be set in a horizontal plane, and shall be suitably reinforced to prevent
deformation from the impact of heavy objects.
The conveyor shall be provided with a positive eccentric shaft drive,
which shall provide a variable discharge rate, and which will permit a
stroke of at least one inch, The variable discharge characteristic shall be
such that the rate of discharge of the conveyor may be varied from about
30 tons per hour to about 60 tons per hour. The variable rate of discharge
shall be controlled by a remote control unit which will permit the desired
range of discharge. The remote control unit shall be furnished with a dial
for controlling the discharge rate. The remote control shall be accomplished
electrically, subject to approval by.the City.
The motor and drive shall be mounted on the conveyor frame, with the
motor set on an adjustable sliding base. The motor shall be at least
equivalent to a 25 horsepower, squirrel cage induction, 480 volt, 3 phase,
60 cycle, totally enclosed fan-cooled motor, NEMA Design "B". The motor
shall be designed to permit at least 10 starts per hour without overheating.
3. MILL FEED CONVEYOR:
The mill feed conveyor will receive raw mixed municipal refuse from a
belt conveyor and discharge the refuse into the feed hopper of a hammermill,
as shown on the accompanying drawing. The mixed municipal refuse is expected
to be a heterogeneous mixture of materials of a wide variety of shapes and
-------
sizes, with its bulk density ranging between 100 and 350 pounds per cubic
yard. Occasional heavy objects, weighing from 50 to 100 pounds and more,
may be included in the refuse.
The mill feed conveyor will be installed by others, on a steel supporting
framework, also provided by others.
The pan of the mill feed conveyor shall be fabricated of steel plate
no less than 3/8 inch thick, and not less than 24 inches deep, 7 feet wide
and 13 feet, 3 inches long, as shown on the Drawings. It shall be sloped
downward toward its discharge end at an angle of about 5 degrees from hori-
zontal. The discharge end shall extend inside the feed hopper of the hammer-
mill, and shall be suitably reinforced to withstand the impact of missiles
from within the hammermill. Provisions shall be made,for the installation of
heavy rubber strips along the sides of the conveyor to prevent the discharge
of missiles and debris from the mill, as shown on the Drawings.
The mill feed conveyor shall be driven by an electric motor through a
positive eccentric shaft drive, with a stroke of at least 1 inch. The motor
shall be no less than a 20 horsepower, squirrel cage induction, 480 volt,
3 phase, 60 cycle totally enclosed fan-cooled motor, NEMA Design "B," driving
the eccentric drive through V-belts. The motor shall be designed to permit
at least 10 starts per hour without overheating. The motor and drive shall
be mounted on the conveyor frame, with the motor set on an adjustable sliding
base.
4. MILL DISCHARGE CONVEYOR:
The mill discharge conveyor will receive milled municipal refuse from
the discharge of the hammermill and transfer the milled material to a belt
conveyor, as shown on the accompanying drawing. The milled refuse will con-
sist of particles nominally 1-1/2 inches in size, with essentially no particles
greater than 5 inches. The loose bulk density of the milled material is ex-
pected to be between 4 and 15 pounds per cubic foot.
The conveyor will be Installed by others in a concrete pit beneath the
hammermill, with its isolation mountings supported by a concrete structure.
The pan of the mill discharge conveyor shall be fabricated of steel
plate no less than 3/8-inch thick, and with a variable depth of 30 inches
maximum, 7 feet, 4 inches width and 15 feet, 8 inches length at its center-
line. The discharge end shall be mltered to permit uniform discharge to a
belt conveyor, as shown on the Drawings. The pan shall be sloped downward
toward its discharge end, on an angle of about 5 degrees from horizontal.
The conveyor pan shall be suitably reinforced to withstand the impact of
missiles from the hammermill.
The mill discharge conveyor shall be driven by an electric motor through
a positive eccentric shaft drive, with a stroke of at least one inch. The
motor shall be no less than a 20 horsepower, squirrel cage Induction, 480
volt, 3 phase, 60 cycle, totally enclosed fan-cooled motor, driving the
eccentric drive through V-belts, The motor and drive shall be mounted on
the conveyor frame, with the motor set on an adjustable sliding, base.
5. DIMENSIONS:
Minor dimensional changes of the conveyors may be necessary to accommo-
date equipment furnished by other manufacturers. The lump-sum bid prices
shall allow for such minor changes.
6. SHOP PAINTING:
All exposed surfaces of ferrous metal parts of the conveyors shall have
all rust, mill scale, dust, dirt, grease, oil, and all other foreign sub-
stances removed by means of wire brushes, chisels, hammers or by washing
61
-------
with water or benzine, as is necessary. Immediately after cleaning, the
surfaces shall be given one shop coat of Koppers Rustinhibitive Primer
No. 612 (Phenolic) or approved equal, applied to achieve a minimum dry thick-
ness of 1.5 mils.
7. PERFORMANCE;
Should the equipment specified herein not provide the conveying rates
of the respective quantities called for, within the limits of the bulk
densities and conditions herein described, the manufacturer will be required
to make such modifications as necessary to provide the required conveying
rates. Such modifications, if required, shall be made with the cooperation
of the Contractor installing the equipment, and shall be made at no addi-
tional cost to the City, and shall be initiated within five days of the
date of notification by the President to the manufacturer that the equipment
is not performing as specified. Correction of any such inadequacies shall
proceed in the most expeditious manner. The President shall be the sole
judge of such inadequacies.
8. PAYMENT:
Payment for the furnishing of the vibratory cpnveyors, including shop
painting, described herein shall be on the basis of the lump-sum prices
stated in the Proposal for each of the following:
Receiving Conveyor One Item
Mill Feed . , One Item
Mill Discharge Conveyor One Item
-------
LAji"a_j-—I
at ..i_t
SECTION/A
3C4LE f.'-/-0\ ]
SKIRTING DETAILS
THIS DRAWING REDUCED
APPROX. Vi ORIGINAL SIZE
CITY OF ST. LOUIS
-------
NOTE'
SIDES OF CO/WE YOff PAU
MAY BE FABRICATED JS
V OK WITH UN/FORM
SLOPE
NOTE.
SUPPORT
FRAME (8 Y OTHEK S)
ROLLED LIP FOR
SKIRTING SEE
"~ THIS SHEET
THIS DRAWING REDUCED
APPROX. 'A ORIGINAL SIZE
MILL DISCHARGE CONVEYOR
TOR Y COVIT YING EQUIPMENT
DETAIL 5
fiffUSS PROCESSING PLANT
SECTIONED
2
MILL FEED CONVEYOR
O/MEMSIOMS SHOWM WITH
AtJ • 4ff£ SUBJECT TO CHANGE
AND SHALL &E DETERMINED
5Y HAMMEHMfLL MFG*.
SKtRTING DETAIL
CITY OF ST. LOUIS
-------
SPECIFICATION
STORAGE BIN AND UNLOADER
AND
PIT UNLOADER FOR MILLED REFUSE
1. SCOPE;
This Contract includes the furnishing, for installation by others, of
a storage bin and unloader, and a pit unloader for milled municipal refuse,
complete with all motors, drives and accessories, as specified herein. The
Contractor also shall provide the services of a qualified service represen-
tative for sufficient time to supervise the installation of the equipment,
and to properly instruct City personnel in Its operation and maintenance.
These services will be required for periods to be scheduled with the Con-
tractor for the installation of the equipment, totaling not less than ten
working days, at the expense of the equipment manufacturer.
The manufacturers of the storage bin and the unloaders and their auxiliary
equipment shall be regularly engaged in the manufacture of equipment similar
in design and capacity to that specified. The storage bin and the unloaders
shall be similar to those manufactured by Miller Hofft, Inc., or approved
equal.
The manufacturer of the storage bin and the unloaders and their auxiliary
equipment shall furnish all anchor bolts and other items requiring embedment
in the concrete foundation for installation by others, for all equipment
furnished under this Contract.
2. FUNCTION:
The material to be handled by the equipment furnished under this Contract
will be milled municipal refuse, processed through a hammennlll so that the
particles to be handled will be nominally 1-1/2 inches in size and smaller,
with essentially no particles greater than 5 inches. The loose bulk density
of the milled material is expected to be between 10 and IS pounds per cubic
foot. The density of the material at the bottom of the storage bin, above
the unloaders, may be as great as 30 pounds per cubic foot.
The storage bin will be filled from the top by means of a belt conveyor
system. The bin unloaders will discharge to a belt conveyor, which, together
with the loading conveyors, will be furnished and installed by others.
The pit unloader will be installed in a pit, with a receiving hopper
furnished and Installed by others. The milled refuse will be discharged
into the receiving hopper from self-unloading truck-trailers. The pit un-
loader will discharge to a belt conveyor, to be furnished and installed by
others.
3. STORAGE BIN. UNLOADER AND DRIVES;
The storage bin shall be of the size and configuration as shown on the
accompanying drawings. The bin shall have a gross internal volume of about
33,000 cubic feat. Its Inside dimensions shall be 19 feet wide by 60 feet
long at the screw unloader level and 33 feet high from the floor of the bin.
The end walls shall be vertical, and the aide walls sloped at an angle of
about 5 degrees from vertical toward the center of the bin.
The walls of the bin shall be fabricated as flanged panels bolted to-
gether in the field. The panels shall be supported by a structural steel
system similar to that shown on the accompanying drawings. The loads Imposed
65
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by the supporting structural system shall be, carried down to reinforced con-
crete .supports, also as shown on the drawings. The concrete supports and
the bottom slab of the bin will be constructed by others.
The bin shall be designed to accommodate the loads imposed by the
distributing shuttle conveyor, the magnetic separator, the chute for magnetic
metal, and the superstructure together with the platform and walkways over
the top of the bin, and the roof shelter and walkway on the discharge side
of the bin. All of these latter items of equipment, including the super-
structure and the roof shelter will be furnished and Installed by others.
The Contractor shall design the bin and its supporting structure to
safely support the superimposed gravity and wind loads. The superimposed
loads are tabulated and shown on the drawings at the defined loading points.
The storage bin shall be designed to withstand wind loads of 20 pounds per
square foot. Allowable stresses in bin supporting members may be increased
33 per cent for cases in which wind loads are combined with gravity loads.
The bottom of the 60-foot sides of the bin shall be fitted with flexible
rubber belting extending down as far as feasible into the slot through which
the screw unloaders travel, to confine the material in the bin to the greatest
reasonable degree.
The bin unloading mechanism shall be similar or equal to Miller Hofft
Type H design. It shall consist of a twin screw traversing unloader, with
a 60-foot traverse, over the full length of the bin. The unloading screws
•hall have an 18-inch flight diameter and shall be fabricated of heavy steel
plate. The flights shall be securely welded to a heavy steel tube 8 Inches
in diameter, with a minimum wall thickness of 1-1/2 Inches. The flights
shall be designed with variable pitch and outside diameter of the flighting
carefully proportioned over their length to discharge 12,000 cubic feet of
milled refuse per hour. The flights shall be hard-surfaced on their leading
edges and shall have heavy wear-resistant digger bars welded to their outside
edges at 90-degree intervals over their entire length to provide a digging
action on the refuse in the bin. High screw efficiency and positive mate-
rial removal shall be provided over the entire length of the screws.
the drive carriage shall consist of an all steel welded frame, complete
with drive shafts, roller bearings, four 8-inch diameter roller bearing
support wheels and sweepers. The drive motor and reducer shall be mounted
on heavy steel base plates on the carriage and an oil-tight guard furnished
for the chain drive.
The thrust carriage shall be of all steel welded construction, complete
with thrust shafts, bearings, hold-down wheels, support wheels and high
capacity yoke. The hold-down beam, support beam and brackets and thrust
rail shall be furnished ready for assembly to the bin structure as shown
on the accompanying drawings.
Replaceable wear strips shall be furnished as raceways for the drive
carriage and thrust carriage along the entire length of traverse. Anchor
pads shall be provided for floor mounting on concrete surfaces.
The traversing mechanism shall consist of a separately powered chain
drive attached to the drive carriage and thrust carriage. The traversing
drive shall consist of a 1/2 horsepower, squirrel cage Induction, TEFC,
480 volt, 3 phase, 60 cycle motor, driving a differential speed reducer,
with a ratio of about 950 to 1, through a variable speed pulley with •
ratio of about 2.5 to 1. The output of the speed reducer shall be connected
to the traverse chain drive through a roller chain drive and a suitable safety
clutch.
The drive for the screws shall consist of a constant speed, squirrel
cage Induction motor and reducer combination of no lea* than 150 horsepower
and of adequate output speed to discharge the quantity of milled refuse
specified. The motor shall be TEFC for 480 volt, 3 phase, 60 cycle service.
NEMA Design "B".
-------
4. PIT UNLOADER:
The pit unloader shall be similar or equal to Miller Hofft Type H design.
It shall be designed to operate in a pit with Inside dimensions of 12 feet
width and 21 feet length, and shall be capable of discharging 8,000 cubic feet
per hour of milled municipal refuse with a loose bulk density of 10 to 15
pounds per cubic foot.
The pit unloader shall consist of twin screws, with a 21-foot traverse,
over the full length of the pit. The twin screws shall each have a 16-inch
flight diameter, and shall be fabricated of heavy steel plate. The flights
shall be securely welded to a heavy steel tube 8 inches in outside diameter
with a wall thickness of 1-1/2 inches. The flights shall be designed with
variable pitch and outside diameter of the flighting carefully proportioned
over their length to discharge 8,000 cubic feet of milled refuse per hour.
The leading edges of all flighting shall be hard-surfaced and the flights
shall have heavy wear-resisting digger bars welded to their outside edges
at 90-degree intervals over their entire length to provide a digging action
on the milled refuse in the pit. High screw efficiency and positive material
removal shall be provided over the entire length of the screws.
The drive carriage shall consist of an all-steel welded frame, complete
with drive shafts, roller bearings, four 8-inch diameter roller bearing support
wheels and sweepers. The drive motor and reducer shall be mounted on heavy
base plates on the carriage and an oil-tight guard furnished for the chain
drive.
The thrust carriage shall be of all-steel welded construction, complete
with thrust shafts, bearings, hold-down wheels, support wheels, and high
capacity yoke. The hold-down beam, support beam and thrust rail shall be
furnished, together with the supporting framework shown on the drawings, ready
for assembly to the concrete structure as shown on the accompanying drawings.
Replaceable wear strips shall be furnished as raceways for the drive
carriage and thrust carriage along the entire length of traverse. Anchor
pads shall be provided for floor mounting on concrete surfaces.
The traversing mechanism shall consist of a separately powered chain
drive attached to the drive carriage and thrust carriage. The traversing
drive shall consist of a 1/2 horsepower, squirrel cage induction, 480 volt,
3 phase, 60 cycle, TEFC motor driving a differential speed reducer, with a
ratio of about 950 to 1, through a variable speed pulley with a ratio of
about 2.5 to 1. The output of the speed reducer shall be connected to the
traverse chain drive through a roller chain drive and a suitable safety
clutch.
The drive for the screws shall consist of a constant-speed, squirrel-
cage inducation motor and reducer combination of no less than 75 horsepower
and of adequate output speed to discharge the quantity of milled material
specified. The motor shall be TEFC for 480 volt, 3 phase, 60 cycle service,
NEMA Design "B".
•5. DIMENSIONS:
Minor dimensional changes of the supporting members of the equipment
may be necessary. The lump-sum bid prices shall allow for such minor changes.
6. SHOP PAINTING!
All exposed surfaces of ferrous metal parts of the bin, structure, and
unloader*, shall have all rust, mill scale, dust, dirt, grease, oil, and all
other foreign substances removed by means of wire brushes, chisels, hammers,
or by washing with water or benzine, aa is necessary. Immediately after
cleaning, the surfaces (hall be given one shop coat of Koppers Rustinhijitive
Primer No. 612 (phenolic), or approved equal, applied to achieve a minimum
dry thickness of 1.5 nil*.
67
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7. PERFORMANCE:
Should the equipment specified herein not provide the unloading rate
of the respective quantities called for, within the limits of the bulk densities
and conditions herein described, the manufacturer will be required to make
such modifications as necessary to provide the required unloading rates.
Such modifications, if required, shall be made with the cooperation of the
Contractor installing the equipment, and shall be made at no additional cost
to the City, and shall be initiated within five days of the date of notification
by the President to the manufacturer that the equipment is not performing
as specified. Correction of any such inadequacies shall proceed in the most
expeditious manner. The President shall be the sole judge of such inadequacies.
8. PAYMEM:
Payment for the equipment included in this Specification, together with
the drives and parts specified herein shall be on the basis of the Individual
lump-sum prices stated in the Proposal, and on the terms stated in the In-
structions for Bidders, as follows:
Item No. 1 - Storage Bin, Unloader and Drives One Item
Item No. 2 - Pit Unloader and Drives One Item
68
-------
SUPPORT COL
E SHOfVAf f/v 'OLAflt AT TOP OF £
3 re • "'W '0e*< HCffT*
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PLAN OF BIN FLOOR
AQ£ S'-'f>°Off7'fO 8f S7~l
O£S/Q# 8'M TO 5Af£t- y
S££ skT SB-I roa 'LOADS
M0 W/ND LOADS
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£V{7L Or CANOPY -
NOTE 8IN AND 4-riJAME COLS SHALL fit DESlGNFl) TO
''Af£L^ SL'W't'lIT :iO f:>f POOI I L ON CANOPIC.
HALF PLAN OF BIN AT CANOPIES'
SCALE JK*I'
PLAN OF STORAGE BIN FOR
PROCESSED REFUSE
REFUSE PROCESSING PLANT
CITY OF ST. LOUIS
-------
PtNELS BY OTHERS
,— *
fr-J£
•-* \ T
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— WS'Of r*C£ Of BIN
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20'-O' OC (BY OTHERS)
Vt ,TO~*t
-------
Wf/*°/t£'Mfft"a . "'•'*-'- -I- ^J"'"*' -ff *-*•'' '
PIT UNLOADER PLAN
AND DETAILS
HORNER a >H[F1*IN, INC.
CITY OF ST. LOUIS
-------
Appendix IV
Example Specification*
1.0 Equipment Classification
1.1 Municipal Solid Waste Shredder
2.0 Number Required
2.1
3.1
4.0 Performance Requirements
4.1 Capacity - 62^ TPH daily average basis with surges
to 75 TPH.
4.2 Feed Material - Municipal solid waste with a bulk
density of approximately 280 pounds per cubic yards
as delivered by packer trucks containing occasional
bulky items including refrigerators, household furniture
and appliances such as dryers, stoves, mattresses and
washers, over the road tires and demolition debris.
For guidance the feed material may contain the following
types and quantities per 750 tons of the normal packer
waste per day:
3 refrigerators 7' x 4' x 3'
12 mattresses 7' x 6'
8 rugs 15' x 20'
3 dryers
3 stoves
3 washers
. * /ample of specifications shown in Appendix III-were used
in St Louis Missouri in conjunction with EPA demonstration
project and should not be considered as universally applicable
These are for illustration only.
72
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30 passenger car tires, 1/2 with wheels
10 tons of wood demolition items, not more
than 7 feet x 16 inches x 16 inches and
masonry not more than 500 pounds per piece.
4.3 Product Material - 99% of the shredded material
must be less than 5" in any direction.
4.4 As a guide to the design of the cage bars or grates,
the following table gives a product particle size
distribution range which is considered to be acceptable:
ish % Passing
Ranqe
4"
3"
2"
IV
1"
3/4"
1/2"
1/4"
3/16"
2M
98
92
65
55
42
35
28
18
15
5
92
84
55
45
34
28
22
14
11
3
It is desirable that cans be torn and opened out
rather than squashed.
4.5 Occupational Safety and Health Act - Manufacturer will
recomnend measures necessary to operate unit in compliance
with applicable requirements of the Occupational Safety
and Health Act.
4.6 Machine must be able to comply with all applicable local
and state regulations.
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4.7 Maintenance - Machine must be equipped with hydraulic
opening devices to provide ready accessibility to
interior parts for replacement of hammers, wear plates
and grates and also a crane with a capacity to lift
wear plates, grates and hammers, etc. All special
tools required to facilitate maintenance such as a
hydraulic pin puller shall be supplied with the shred-
der. The shredder must be able to be opened for hammer
maintenance by one man in 10 minutes. Possible quick
disconnect hold down devices should be considered.
4.8 Shredders must be operated for a one-week period pro-
ducing an average of defined capacity when operated
16 hours per day.
5.0 Electrical
5.1 Power Characteristics - 3 ph, 60 H2, 4160 and 480 V
single phase, 60 Hz, 120 V
5.2 Motor Specifications - Motors shall be T.E. or T.E.P.C.
except for the main shredder drive motor which will be
open drip proof.
5.3. General For Shredder Motor - The drive motor shall be
adequate for starting and driving the hammermill, which
will have a high inertia and wide and sudden load
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variation. The load may occasionally be great enough
to stall the motor. The motor and all motors parts
shall be adequate for the haminermill duty. The hammer-
mill drive motor and its starter shall be furnished by
one manufacturer.
The motor in all respects shall incorporate the highest
quality of modern engineering design and workmanship.
All material shall be new and of the best quality suited
for the requirements of the work. It is not the intent
to specify details of design and construction; motors
shall be constructed and equipped with accessories in
accordance with the seller's standard practices where
they do not conflict with these specifications. Design
and construction of the motors shall be coordinated
with the driven equipment requirements. The equipment
shall be the product of Allis-Chalmers, General Electric,
Westinghouse, or approved equal.
5.4. Motor Type and Rating - The motor shall be of the
following type and rating:
Type: Squirrel-cage induction,
horizontal or vertical
(Round rotor optional)
Horsepower: 1,000
Speed: 720 RPM
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Voltage: 4,160 volts, 3 phase,
60 cycle
Service Factor: 1.15
Slip: 3-5%
Breakdown Torque: 250%, with 100% rated
motor voltage
Temperature Rise: 90° C by resistance above
40° C ambient, at 1.15
service factor
Insulation: Class F
Starting: Reduced voltage at 65% of
rated line voltage ± 10%
Inertia: It is the motor manufacturers
responsibility to obtain
this information from the
shredder manufacturer.
Load: Direct connected; inertia
of hammermill motor; load
varies from 5% to 100% in a
few seconds of time, and may
stall the motor occasionally.
Enclosure: Open drip-proof.
5.5 Electrical Characteristics - Motors shall be direct
connected, induction type. Motors shall be designed
and braced to withstand the heating effect and forces of
full voltage starting and shall be on the type generally
described as normal starting current unless otherwise
specified.
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The motors shall be designed so that locked rotor
current shall not exceed 65% of rated full load
current.
Motors shall have sufficient thermal capacity in both
the rotor and stator to properly accelerate the connected
loads with no reduction in expected motor life. The
torque characteristics shall be such as to permit success-
ful operation and acceleration from rest at 5096 rated
voltage.
5.6 Stator Frame and Core - The stator frame shall be
fabricated from heavy steel plate and structural sections
to ragidly support the bearings, to provide a means of
supporting and securing the motor to the sole plate,
to provide air inlet and discharge openings, and to
support the stator core and winding. The bottom of the
frame is to have longitudinal feet with the bottom surface
finish machined and of ample cross section and with bolt
holes for securing the motor to the base. The feet shall
each have at diagonally opposite corners of the motor a
partially reamed taper dowel hole for permanently locating
the motor to the base after final alignment. Final
reaming will be by the Installing Contractor. The stator
core is to be either permanently and integrally secured
in the frame or separately supported in the frame.
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The motor frame shall have suitable means for attaching
a ground conductor in accordance with the grounding
requirements of National Electrical Code, unless other-
wise specified. The dimensions of the grounding pad, cap
screw, or other grounding means shall be adequate to
meet the requirements of Article 250 of the 1968 National
Electrical Code or the latest revision thereof. The
ground location shall be on the same side of the motor
as the main lead terminal box.
The core is to be made up from laminations punched from
precoated nonaging electrical sheet steel and is to have
air vent ducts spaced at intervals through the length
of the core. The core is to be uniformly and tightly
compressed between end heads and is to be securely
supported in the frame.
5.7 Shaft - The rotor shaft shall be horizontal, solid, of
heat-treated alloy steel.
5.8 Rotor - Ring-type motor laminations are preferred. If
segmental rotor punchings are used every lamination is
to be welded to the rotor spider. These laminations are
to be punched from the same high-quality, pre-coated steel
used for stator laminations. Heavy steel end heads which
compress and retain the core rapidly to insure uniform
tight core throughout the motor life shall be used.
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The rotor shall be pressed and keyed to the shaft.
Rotor windings shall be of high strength high tem-
perature copper bars with copper end rings. The
connection between the rotor bars and end rings is
particularly critical in shredder mtors because of
the extreme mechanical and thermal stresses encountered
in operation. For this reason, notched end connectors
are to be used to increase the contact area between
the rotor bars and the end rings.
5.9 Bearings and Bearing Brackets - The continuous pounding
encountered in shredder operation places a severe de-
mand on the bearings. For this reason, double row
spherical roller bearings shall be used exclusively.
The bearings shall be grease lubricated wherever possible.
Bearings shall be retained in a stiff one piece bearing
capsule. This construction, compared to conventional
split designs, resists fretting and vibration, and
minimizes bearing deflection to ensure long bearing life.
To further insure rigid support of the bearings, bearing
capsules shall be located and retained by machines fits
in reinforced one piece bearing brackets. The bearing
brackets are to be similarly located in the motor frame
by machined retaining fits.
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All bolts used in the motor construction which are not
normally removed during the course of normal maintenance
operation shall be tack welded to prevent them from
working loose. All other bolts shall be locked in place
with bent metal tabs to assure continued tightness from
the severe shredding duty.
The same degree of care to insure a low maintenance
rugged design applies to a vertical motor if required.
5.10 Stator Coil Construction and Insulation - The stator
winding shall be insulated with Class F or better
throughout, with mica as the fundamental component of
ground insulation. The insulation system shall be a
combination of materials and processes which provide
high resistance to moisture, and other contaminants
as experienced by a motor driving a shredder.
All windings are to be assembled using form wound coils
of the same size and shape to facilitate interchange-
ability. Coils are to be wound with rectangular copper
wire covered with strand insulation consisting of asbestos,
glass, dacron, Nomex, or other high temperature flexible
insulating film, or a combination of these. In addition.
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turn-to-turn insulation shall be adequate to ensure
that all coils wj 11 be capable of withstanding switching
or other surges well in excess of normal turn-to-turn
voltage.
Ground insulation consisting of mica and a suitable
bonding resin applied in sheets or as tapes shall be
applied to the end turn, as well as the slot portion
of the coil, to ensure all parts of all coils are fully
insulated to ground for the voltage class of the motor.
After insertion of the coils in the stator slots, all
end connections shall be either brazed or welded and
insulated with essentially the same materials as used
on the coil itself to assure that end connections will
be of the same quality and dielectric strength as the
coil. After the coils are properly wedged, end turns
braced and all moisture removed, the entire stator
assembly shall be vacuum pressure impregnated with
thermal setting epoxy resin free from voids. The complete
stator frame shall then be heat cured.
The end bracing system shall completely support each
coil, as well as the entire assembly, to essentially
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eliminate all vibration that occurs during full voltage
starting and expected operating conditions. Whenever
possible, it is desired that all binding, and blocking
materials be of the thermosetting type that, when combined
with the impregnating resin, will successfully withstand
repeat stresses such as occur during normal shredder
operation.
5.11 Conduit Box - A conduit box of ample size to permit
stress cone termination shall be provided. The conduit
box shall be capable of being rotated in 90° increments.
5.12 Special Corrosion Resistant Hardware - The motor shall
be equipped with corrosion resistant fittings and
hardware throughout.
5.13 Guard Screens - The motor shall be equipped with suitable
corrosion resistant guard screens over intake and
exhaust openings.
5.14 Stator Temperature Detectors - Resistance temperature
detectors, two 10 ohm resistance type temperature
detectors (RTD) per phase, shall be installed in the
stator winding with leads brought out to a separate
terminal box. Control equipment will be furnished by
others.
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5.15 Bearing Temperature Detectors - Each bearing shall be
equipped with a dial-type indicating thermometer. The
thermometer shall be furnished with adjustable contacts,
so that motor can be tripped slightly above maximum
normal operating temperature.
5.16 Space Heaters - Each motor shall be provided with space
heaters of sufficient capacity to keep the motor windings
and internal parts dry when the motor is not running.
Heater voltage shall be 240 volts single phase a.c.
Heater leads shall terminate in a separate terminal box.
5.17 Sole Plates - The motor shall be equipped with suitable
sole plates for imbedding in the foundation providing
a machined surface on which the motor may be mounted.
Hold down bolts between the motor and the sole plates
shall be furnished by the motor manufacturer. Foundation
bolts will be supplied by others. Shims shall be furnished
by the motor manufacturer.
5.18 Nameplates - Nameplates shall be of stainless steel
and shall show the following information as per NEMA
Standards:
Manufacturer's Type and Frame Designation-
Horsepower Output
Temperature Rise
RPM at Full Load
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Frequency
Number of Phases
Voltage
Full Load Amperes
5.19 Tests - Each motor shall be given a standard commercial
test in accordance with NEMA recommended standards to
ascertain that the motor is free from electrical and
mechanical defects and in accordance with design
specifications.
5.20 Codes - Materials and workmanship for all motors and
starters (where included) shall meet the requirements
of the following:
National Electrical Manufacturing Assoc.
National Electrical Code
A.I.E.E.
A.S.A.
6.1 Reference Drawings and Instructions - Manufacturer
will supply three copies with quotation and six copies
after receipt of the order of the following:
Spare Parts Lists
Installation Instruction Necessary to Design
Supports and Foundations and Recommendations
for Feeding and Discharging
Operating and Maintenance Instructions
Estimated Material and Labor Hours Required to
Maintain Unit is to be supplied.
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Detail drawings of shredder showing the following data:
WR2
RPM
Peed Opening
No. Hammers
Hammer Weight
Hammer Material
Hammer Pin Dia.
Grate Weight
Grate Material
Lever Material
Lever Weight
Shaft Dia @ Hammer
Shaft Dia. @> Bearing
Rotor Dia.
6-3 Construction and Start-up Assistance - Manufacturer
will furnish an engineer as required to assist in the
assembly of the machine on its foundation during the
construction phase and again to assist in operator
instruction and machine start-up.
6.4 Spare Parts - Manufacturer will supply a list with
prices of recommended spare parts to be carried to
insure against prolonged outages. Their detail drawings
and material composition will be included.
7.0 Material Supplied by Customer
7.1 Foundations and Anchor Bolts
8.0 Warranty - Minimum Requirement
8.1 Manufacturer warrants that all materials, machinery
and equipment are free from all defects in material
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and workmanship for a period of twelve (12) months
after initial start-up of the unit and agrees to
promptly replace and install without cost to the
owner any defective parts which may develop during the
period of warranty.
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REFERENCES
1. Ham, R. K., W. K. Porter, and J. J. Reinhardt. Refuse milling for
landfill disposal. In P. L. Stump, comp. Solid Waste Demonstration
Projects; Proceedings of a Symposium, Cincinnati, May 4-6, 1971.
Environmental Protection Publication SW-4p. Washington, U.S.
Government Printing Office, 1972. p.37-72.
2. Reinhardt, J. J., and G. Rohlich. Solid waste reduction/salvage
plant—an interim report; City of Madison pilot plant demonstration
project, June 14 to December 31, 1967. Cincinnati, U.S. Department
of Health, Education, and Welfare, 1968. 25 p.
3. U.S. Environmental Protection Agency. Thermal processing and land
disposal of solid waste; guidelines. Federal Register, 39(158):
29327-29338, Aug. 14, 1974.
4. Brunner, D. R., and D. J. Keller. Sanitary landfill design and
operation. Environmental Protection Publication SW-65ts.
Washington, U.S. Government Printing Office, 1972. 59 p.
5. Stirrup, F. L. Public cleansing; refuse disposal. Oxford, Pergamon
Press, 1965. 144 p.
6. Gr. Brit. Department of the Environment. Refuse disposal; report
of the Working Party on Refuse Disposal. London, Her Majesty's
Stationery Office, 1971. 199 p.
7. Gr. Brit. Department of the Environment. Report of the Working
Party on Refuse Disposal. Circular 26/71. Apr. 1971. 7 p.
(Unpublished report.)
U.S. GOVERNMENT PRINTING OFFICE: 1975— 582-420:239
86a
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